Research ArticleExperimental Study of Gas Explosions in HydrogenSulfide-Natural Gas-Air Mixtures

Andreacute Vagner Gaathaug1 Dag Bjerketvedt1 Knut Vaagsaether1 and Sandra Hennie Nilsen2

1 Telemark University College Faculty of Technology 3918 Porsgrunn Norway2 Research Development and Innovation Section for Health Safety and Water Management Statoil ASA 3905 Porsgrunn Norway

Correspondence should be addressed to Andre Vagner Gaathaug andrevgaathaughitno

Received 9 May 2014 Accepted 16 July 2014 Published 21 August 2014

Academic Editor Constantine D Rakopoulos

Copyright copy 2014 Andre Vagner Gaathaug et alThis is an open access article distributed under the Creative CommonsAttributionLicense which permits unrestricted use distribution and reproduction in anymedium provided the originalwork is properly cited

An experimental study of turbulent combustion of hydrogen sulfide (H2S) and natural gas was performed to provide reference

data for verification of CFD codes and direct comparison Hydrogen sulfide is present in most crude oil sources and the explosionbehaviour of pure H

2S andmixtures with natural gas is important to addressThe explosion behaviour was studied in a four-meter-

long square pipeThefirst twometers of the pipe had obstacles while the rest was smooth Pressure transducerswere used tomeasurethe combustion in the pipe The pure H

2S gave slightly lower explosion pressure than pure natural gas for lean-to-stoichiometric

mixturesThe rich H2S gave higher pressure than natural gas Mixtures of H

2S and natural gas were also studied and pressure spikes

were observed when 5 and 10 H2S were added to natural gas and also when 5 and 10 natural gas were added to H

2S The

addition of 5H2S to natural gas resulted in higher pressure than pure H

2S and pure natural gasThe 5mixture gave much faster

combustion than pure natural gas under fuel rich conditions

1 Introduction

Hydrogen sulfide (H2S) may be present in various concentra-

tions in crude oil natural gas and biogas an understandingof its effects is necessary since hydrogen sulfide is a toxicflammable and corrosive substanceThe industrial process ofsulfur removal will produce a lot of sulfuric biproductsThesebiproducts could be a potential hazard to factory andworkersThe mixture of natural gas and hydrogen sulfide has been asafety issue in development of new oil fields recently

Jianwen et al [1] described three major releases of hydro-gen sulfide and natural gas that caused severe accidents Toreliably calculate the hazardous consequences of a hydrogensulphide release knowledge of its properties is criticalEarlier work investigated detonations in hydrogen sulfideand its laminar properties have also been studied Howeverexperimental data fromH

2S explosions are limitedThiswork

focuses on the turbulent combustion of hydrogen sulfideand summarizes a series of experimental investigations ofexplosions with H

2S mixtures These mixtures are composed

of pure H2S artificial natural gas (NG) (10 propane and

90 methane) and NG mixed with H2S All tests are mixed

with air and are conducted at 1 atm initial pressure andambient temperature A square pipe with repeated obstaclesis used to generate turbulence and increase the flame speedin the study The experimental results provide a referencedata set for verification of CFD codes and also enable a directcomparison with natural gas for the maximum pressure Asmore unconventional oil sources are developed there will bean increasing need to accurately model the combustion ofnatural gas andhydrogen sulfidemixtures for risk assessment

2 Gas Explosions in Hydrogen Sulfide

Glassman and Yetter [2] provide a general discussion on sul-fur combustion which describes the inhibition of oxidationof hydrogen by H

2S The stoichiometric combustion of H

2S

in oxygen can be written as the overall reaction2H2S + 3O

2997888rarr 2SO

2+ 2H2O (1)

In a stoichiometric and rich mixture some of the SO2

products may also react with H2S to form solid S by the Claus

reaction [3]2H2S + SO

2997888rarr 3S + 2H

2O (2)

Hindawi Publishing CorporationJournal of CombustionVolume 2014 Article ID 905893 12 pageshttpdxdoiorg1011552014905893

2 Journal of Combustion

Alzueta et al [4] showed that SO2could either promote

or inhibit the burning of CO depending on the amountof SO

2and the stoichiometry Selim et al [3] investigated

premixed methane-air with added H2S and they showed

that combustion begins with the thermal and chemicaldecomposition of H

2S SO

2was also found to enhance the

dimerization of CH3radicals to form longer hydrocarbons

A chemical reaction mechanism of sulfur and hydrocarbonshas been proposed byWendt et al [5] and Frenklach et al [6]

Chamberlin and Clarke [7] were early investigators ofthe laminar flame speed of hydrogen sulfide Their setupwas typical of the period and consisted of a tube that was1m long and 25 cm in internal diameter The tube had aburner tip The maximum flame speed was observed at 10(120601 = 08) and had a value of 05ms Also a relatively wideflammable region in H

2S-air mixtures was observed Kurz

[8] used a Bunsen burner method to investigate the effect ofa hydrogen sulfide additive on the flame speed of propaneand he also included the flame speed measurements for pureH2S-air The flame speed decreased as H

2S was added to the

propane up to the maximum investigated concentration of6 However pure H

2S resulted in a higher flame speed than

the mix A Bunsen flame was also used by Gibbs and Calcote[9] to investigate the effect of the molecular structure on theburning velocity for different equivalence ratios These threeexperimental studies of H

2S flame speeds are summarized

in Figure 2 As seen there are relatively large discrepanciesbetween the results and it is also worth noting that none ofthe results consider the flame stretch effects This work doesnot involve any determination of the laminar flame propertiesbut states that the current knowledge of hydrogen sulfideflames is inconsistent As such it does not provide a goodbasis for evaluation of potential hazards as compared to othergases

There is need for further experimental investigations intothe laminar burning velocities and chemical kinetics for pureH2S gas and H

2S mixed with hydrocarbons These studies

could provide more consistent information regarding thelaminar flame properties of the fuel and chemical inductiondelay times Such data would be valuable as input to mod-elling tools and validation of chemical reaction mechanismsUntil new knowledge has been found one must use themethods available but beware of its limitations

Cantera software was used to calculate the constantvolume combustion pressure and the constant pressureexpansion ratio by the reaction mechanism of Wendt et al[5] These results are given in Figure 1 and are calculated forstoichiometric fuels with the H

2S content in NG ranging

from 0 (pure natural gas) to pure H2S using increasing

additions of H2S It is shown that the equilibrium pressure

and expansion ratio are inversely proportional to the hydro-gen sulfide content in the fuel The calculations suggest thatthere should be lower flame speed and pressure build-up inpropagating hydrogen sulphide deflagration than natural gasmixtures

Bozek and Rowe [10] compared fuel properties fromthe International Electrotechnical Commision (IEC) and theNational Fire Protection Association (NFPA) Both datasetsshow that the flammability region of hydrogen sulfide iswider

Equilibrium pressure left axisExpansion ratio right axis

0 5 10 20 50 80 909510004

05

06

07

08

09

1

11

12

13

14

Peq

cons

t V(M

Pa)

4

5

6

7

8

9

10

11

12

13

14

H2S in fuel (mdash)

120590=1205880120588

b(mdash

)

Figure 1 Cantera calculation Constant volume combustion equi-librium pressure for stoichiometric fuel ranging from pure NG (left)to pure H

2S (right)

0 5 10 15 200

01

02

03

04

05

06

2S

(m

s)

Chamberlin and ClarkeKurzGibbs and Calcote

H

Figure 2 Flame speed of H2S-air mixtures at different concentra-

tions

than that of methane and pentane Pahl andHoltappels [11] atthe BAM Federal Institute forMaterials Research and Testinginvestigated the explosion limits of H

2S and air in mixtures

with N2and CO

2 They found the upper and lower explosion

limits to be 498 and 39 respectively When CO2or N2

was added to themixture themeasured explosion limits werehigher than those found in an earlier work by Coward andJones [12]

Theminimum experimental safe gapMESG for hydrogensulfide is lower than that for methane and pentane whichindicates the reactivity of the fuel NFPA68Guide forVenting

Journal of Combustion 3

of Deflagrations (2002) provides data for the deflagrationindex and shows that it is higher for methane than for H

2S

Moen and coworkers [13ndash17] investigated flame accel-eration and detonations in H

2S mixtures The detonation

cell size of hydrogen sulfide detonations was 100mm whilethose of methane and propane were 280mm and 69mmrespectively This indicates that H

2S mixtures detonate easier

than methane The deflagration to detonation transition(DDT) of H

2S mixtures has not been widely investigated

Moen et al [16] investigated the flame acceleration of H2S-

air mixtures in a 18m by 18m cross-section and 155mlong square pipe with obstacles made of steel pipes withdiameters 500mm and 220mm They compared the resultsto those using acetylene-air mixtures For the hydrogensulfide experiments they recorded overpressures of only 20 to50mbar and flame speeds from 36 to 81ms In a comparisonto acetylene they suggested that the H

2S-air mixtures could

detonate if the scale was large enough the ignition was strongenough or sufficient confinement was present

Shepherd et al [17] and Vervisch et al [18] studied theactivation energy of hydrogen sulfide and compared it toother fuels The resultant value was 10967 kJmol in theShepherd study and 92 kJmol in the Vervisch study Turns[19] gave 125 kJmol activation energy for propane and 125 kJmol or 202 kJmol for methane

3 Experimental Setup

The experimental setup used in this work was made from astainless steel square pipe with inner dimensions of 84mmFour parts were bolted together and sealed to make anairtight compartment Figure 4 shows a schematic of the fourparts with their dimensions obstacle spacing and pressuretransducer positions Figure 3 shows a picture and Figure 5shows a sketch of the assembled setup The experimentalsetup was chosen to facilitate strong flame acceleration in thebeginning and enough spacing in section 2 to possibly getlocal volume explosions or DDTThe experimental setup wastested also for propane methane

The pressures were recorded with two Kistler 7001 (Ch1 and Ch 2) and four Kistler 603b (Ch 3 to Ch 6) piezo-electric transducers (Figure 2) and an oscilloscope recordingat 1MHz The ignition system was a center-mounted 10 kVspark at the end flange of section 1 At 10 cm from the end ofsection 4 one obstacle was installed not only to add strengthbut also to reflect any shock waves and achieve DDT (ifpossible) at the end obstacle DDT located at the end flange isundesirable since it would cause strain on the bolts and fillingsystem

The fuel-air mixture was made by evacuating air from thesquare pipe and filling it with fuel All tests were done with1 atm initial pressure and ambient temperature A circulationpump was used to circulate and mix the gas through thesystem The setup was placed with the obstacles in verticalalignment This prevented the fuel from being ldquotrappedrdquo inthe pockets between the obstacles at the top and bottom ofthe pipe The pump and piping was isolated from the setupbefore ignition

Figure 3 Picture of the experimental setup

Special consideration was made regarding the toxicityof hydrogen sulfide and the sulphur dioxide combustionproduct A coal filter with special coated coal was installed atthe purge of the square pipe to remove sulfuric componentsfrom the gas No H

2S was measured at the outlet of the

ventilation systemThis work was part of a larger study to compare H

2S and

natural gas mixtures to other more determined fuels Thefuels were acetylene hydrogen propane methane syntheticnatural gas and H

2S All fuels were mixed with air Four

different combustion regimes were observed in the studyTo illustrate these explosion regimes the pressure records

are plotted in a diagram showing time along the 119909-axis andpressure plus the positions of the pressure transducers alongthe 119910-axis This type of diagram gives a good display of thetrajectory of the pressure waves shock waves and detonationwaves in a gas explosion Figure 6 shows these four differentexplosion regimes in these types of diagrams

(i) slow flame propagation and no shock waves formedin front of the flame which is well known as a slowflame regime

(ii) fast flame propagation (regime) and shock waveformed but no strong local explosion due to reflectionof the shock at the end of the pipe

(iii) fast flame propagation and shock wave with localexplosion and transition to detonation due to reflec-tion of the shock wave at the end of the pipe

(iv) fast flame propagation and transition to detonation inobstructed area or close to the exit of the obstructedpart of the pipe

Only slow and fast flames were observed in the experi-ments reported in this paper but the other regimes are givento provide a qualitative justification of the assumed flamepropagation

Since there is no visual recording of the flame fronts itis only assumed that the deflagration was similar to otherreported works in a very similar setup Details of this canbe found in Lee [20] The flame fronts become stretched and

4 Journal of Combustion

100mm

100mm

200mm100mm

84mm

100mm

155mm735mm

1000mm

265mm645mm

455mm835mm

1

2

3

4

Ch 3 Ch 4

Ch 5 Ch 6

Ch 7 Ch 8

Figure 4 Schematic drawing of the experimental setup Ch = pressure recording channel number

1 2 3 4Ignition

Fillmix out Fillmix in

Figure 5 The experimental setup consisting of four stainless steeltube sections

unstable as they propagate through the obstacles and the flowthrough the obstacle openings can enhance the mixing at theflame front Shock reflections at the solid obstacles are alsowell known to cause local explosions or DDT in sensitive gasmixtures

4 Results

The fuel mixtures used in this work were pure hydrogensulfide and fuel mixtures with artificial natural gas (premade10 propane and 90 methane) The experiments with purenatural gas (NG) and pure H

2S in air are presented first to

provide a basis for comparison Next results from pure H2S

are presented and last the mixtures of H2S and NG in air are

presentedThe experimental matrix in Table 1 shows the gases

concentrations and equivalence ratios

41 Natural Gas As reference experiments tests were con-ducted using artificial natural gas The concentrations were62 83 92 and 104 corresponding to equivalenceratios of 120601 = 072 099 111 and 127

Pressure records from the stoichiometric experimentare given in Figure 7 The pressure curves are offset alongthe vertical axis an amount equal to the distance of the

Table 1 Experimental matrix

Test Gas 1 Vol Gas 2 Vol 120601

23 NG 830 09924 NG 620 07225 NG 920 11126 NG 1040 12727 H2S 1000 07928 H2S 1240 10129 H2S 900 07130 H2S 1510 12749 H2S 2500 23831 H2S 043 NG 808 10032 H2S 032 NG 599 07233 H2S 053 NG 998 12634 H2S 086 NG 774 09935 H2S 180 NG 720 10136 H2S 500 NG 500 10037 H2S 896 NG 224 10039 H2S 1053 NG 117 10040 H2S 1140 NG 060 100

transducer from the ignition end After ignition the flamefirst propagated through the obstructed part of the pipe Thiscaused the flame to increase in surface area and the flowahead of the flame became turbulent The turbulent flowcaused the flame to accelerate and increase its reaction rateThis is seen in the pressure plots as the rate of pressuregradient increases At early times a slow pressure increasewas observed on channels 1 and 2 with a faster pressurerise seen on channels 3 and 4 In the smooth section apropagating shock wave was recorded on channel 5 at 55ms

Journal of Combustion 5

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

Regime i slow flame and nostrong shock waves

Regime ii fast flamepropagation with shock wave

Regime iii fast flame propagationwith shock wave and local explosion

at the end of the tube

Regime iv fast flame propagationand transition to detonation (DDT)

Experiment 9 hydrogen conc 03 120601 = 102 Experiment 10 hydrogen conc 03 120601 = 102

Experiment 16 propane conc 006 120601 = 152 Experiment 20 methane conc 0103 120601 = 109

Figure 6 The four different explosion regimes

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 7 Pressure records from the stoichiometric NG-air mixture(test 23) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

This was generated as the flame accelerated and the displacedflow ahead was fast enough The shock wave was recordedon channel 6 at 62ms and a reflection at the end obstaclewas recorded at 65ms The reflected shock wave was alsorecorded on channel 5 at 75ms as it propagated backwardstoward the ignition end Further details on flame accelerationin obstructed pipes can be found in Ciccarelli and Dorofeev[21]

A comparison plot from the natural gas experiments withdifferent fuel concentrations is given in Figure 8The pressureis read on the left vertical axis and the equivalence ratio isshown on the right vertical axis The horizontal axis showsthe time The leanest experiment (120601 = 072) with 62fuel in air showed a pressure rise of almost 05MPa in theobstructed part of the experimental setup (channel 4) anda primary pressure wave of about 025MPa in the smoothsection The stoichiometric experiment with 83 fuel in airshowed the fastest pressure rise and the highest pressure(1MPa) A 03MPa shock wave was recorded in the smoothsection For 92 fuel in air (120601 = 111) the pressure rise in the

6 Journal of Combustion

0 5 10 15

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

099

111

127

Channel 5

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

120601

072

099

111

127

120601

Figure 8 From bottom tests 24 23 25 and 26 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richNG-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

obstructed section was lower than that in the stoichiometricexperiment while the shock wave in the smooth section wasalmost equal The richest experiment (104 fuel in air 120601 =127) resulted in a slow flame and a very slow pressure riserecorded on all pressure transducers

42Hydrogen Sulfide andAirMixtures Results fromfive testswith the pure H

2S-air mixture are presented The H

2S con-

centration ranged from 9 to 25 (see Table 1) where 124is the stoichiometric concentration The pressure recordsfrom the stoichiometric experiment are shown in Figure 9The overall phenomenon is similar to the stoichiometricnatural gas experiment The initial slow burning and thesubsequent development to a faster turbulent flame are seenin the pressure plot The pressure levels on channels 1 to 4are lower than in the NG experiment indicating that thisexperiment burned slower The shock wave in the smoothsection was roughly the same as in the NG experiment

Figure 10 shows a comparison plot of the hydrogen sulfideexperiments with the pressure shown on the left vertical axisand the equivalence ratio shown on the right vertical axisThehorizontal axis shows the time The leanest mixture was 9H2S in air (120601 = 071) and showed a pressure rise of about

03MPa It did not result in a shock in the smooth sectionof the setup The recorded pressure wave was about 02MPaand it reflected at the endwall and obstacleThe slightly richermixture of 10 (120601 = 079) showed a 03MPa shock wavepropagating in the smooth section of the experimental setupIn the obstructed part 05MPa was recorded at channel 4

The stoichiometric mixture resulted in a 035MPa shockin the smooth section while 075MPa was recorded in theobstructed section

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 9 Pressure records from the stoichiometric H2S-air mixture

(test 28) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

The experiment with 120601 = 127 corresponding to 151H2S in air was very similar to the stoichiometric case with

only 005MPa lower pressure in the smooth section and theobstructed section Due to the wide flammability region ofH2S 120601 = 238 was also investigated it resulted in a very slow

flame and a low pressure increase of about 01MPa

43 H2S-Natural Gas-Air Experiments Results and Discus-

sion Experiments were performed on a set of nine tests withthe first three containing 5 H

2S and 95 natural gas The

equivalence ratios were 120601 = 072 120601 = 100 and 120601 = 126

Journal of Combustion 7

0 5 10 15

0

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4 Channel 5

05

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

0

05

120601120601

071

079

101

127

238

071

079

101

127

238

Figure 10 From bottom tests 29 27 28 30 and 49 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richH2S-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

0 5 10 15

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

1

126

Channel 5

05

05

05

0

0

0

Pres

sure

(MPa

)

05

05

05

120601

072

1

126

120601

Figure 11 From bottom tests 32 31 and 33 Comparison of pressure records from channels 4 and 5 Lean stoichiometric and rich 5H2S95 NG-air mixtures Pressure is shown on the left vertical axis while the equivalence ratio is given on the right vertical axis

The following experiments were all conducted with 120601 = 1 butwith increasing hydrogen sulfide content The H

2S fractions

in natural gas were 5 10 20 50 80 90 and 95Figure 11 shows that by keeping the H

2S-to-NG ratio

constant at 5 95 and varying the equivalence ratio 120601 = 072and 120601 = 126 give quite similar pressure levels 05MPa inthe obstructed part and 03MPa in the smooth section Thestoichiometric experiment resulted in the fastest pressure riseand a peak pressure of more than 13MPa A shock wave

of 04MPa was recorded in the smooth section The richmixture (120601 = 126) resulted in strong flame acceleration05MPa recorded on channel 4 and a pressure wave in thesmooth section

With the equivalence ratio kept constant at 1 and the H2S

content in the fuel varied from 0 to 100 the pressure didnot change much except for some spikes as seen in Figure 12The pressure is shown on the left vertical axis and the H

2S

content in the fuel is shown on the right vertical axis Time is

8 Journal of Combustion

0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)

Pres

sure

(MPa

)

Channel 4

0

5

10

20

50

80

90

95

100

2S

in N

G0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)Pr

essu

re (M

Pa)

Channel 5

0

5

10

20

50

80

90

95

100

2S

in N

G

H

H

Figure 12 From bottom tests 23 31 34 35 36 37 39 40 and 28 Comparison of pressure records from channels 4 and 5The mixture variesfrom pure natural gas in the fuel (bottom) to pure H

2S in the fuel (top) All experiments are stoichiometric mixtures

shown on the horizontal axis The pressure in the obstructedpart was recorded between 08 and 1MPa and the shockpropagating in the smooth section was about 03 to 035MPaand reflected at 05MPa

5 Discussion

The experimental study for pure natural gas and air showedthat the flame propagated fast when the equivalence ratiowas lower than 127 producing strong deflagrations in theexperimental setupThe pressure results showed that the rateof energy release increased as the flame propagated throughthe square pipe The richest natural gas mixture investigatedwas 120601 = 127 and thatmixture resulted in a slow pressure risebelieved to be due to a slow burning velocity of the flame

The explosion pressures for lean H2S-air were slightly

lower than the pressures for lean NG-airThe lower explosionpressures were to some extent a result of the lower expansionratio of the H

2S-air flame compared with the other fuels The

expansion ratio (120590 = 120588119906120588119887) of H

2S is about 66 while it is 76

for NG This results in a lower flame speed less turbulenceand therefore a lower pressure rise

By comparing the H2S-air mixtures with mixtures of

natural gas and air as shown in Figure 10 and Figure 8 it wasobserved experimentally that natural gas and H

2S result in

a fast flame for 120601 = 072 On the rich side (120601 = 127) thehydrogen sulfide accelerated as a fast flame while the naturalgas was slowThis was expected due to the wider flammabilityregion of H

2S [10] compared with NG

The experiments with stoichiometric H2S-NG-air

showed that the flame in the experimental setup producedstrong deflagrations with high pressures in the obstructedpart of the experimental setup The pressures seen with

0 5 10 20 50 80 90 9510004

05

06

07

08

09

1

11

12

13

14

2S in fuel

Pm

ax(M

Pa)

Ch 2

Ch 4

Ch 5

H

Figure 13Maximumpressure from experimentsThepressure fromchannels 2 4 and 5 for various H

2S contents in the fuel

channel 4 in tests with 90 and 95 H2S in the fuel (135

and 115MPa) indicate that the compression heating of thereactants caused local ignition in a hot spot

Comparing the maximum pressure from channels 2 4and 5 a trend is observed in Figure 13 in which themaximumpressure decreases as the H

2S content in the fuel increases

however the spikes are also observed when plotting themaximum pressure for three channels when the hydrogensulfide content was varied These spikes correspond to 90

Journal of Combustion 9

Channel 4

02

Channel 5

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

02

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

Figure 14 Maximum pressure for different equivalence ratios for pure NG pure H2S and 5 H

2S in NG

and 95 H2S in the fuel as well as 5 and 10 H

2S in the

fuelCompared to the constant volume and constant pressure

calculations in Figure 1 it is clear that the pressure spikes orig-inate from different phenomena One possible explanationcould be a more sensitive mixture when small amounts ofH2S are added to natural gas or the opposite A reduction in

chemical induction delay time could lead to local explosionsin heated volumes of reactants These local explosions arevery hard to determine even with full view of the channel butother studies have shown that they are more likely to occur inthe obstructed part rather than in the unobstructed parts (Lee[20])

By comparing Figures 13 and 1 it can be seen that thepressure on channel 4 (section with obstacles) exceeds theconstant volume pressure The equilibrium pressure and theexpansion ratio do not explain the spikes seen in Figure 13

Hot spots and local ignition are closely related to defla-gration to detonation transition (DDT) which results in highpressure No DDT was recorded in these experiments butthe pressure spikes suggest that local explosions could haveoccurred

There are always uncertainties when reporting the max-imum pressure since it is measured at one position Otherspikes that may occur in other sections of the experimentalsetup may be missed by the transducer recording

By keeping the H2S content in the fuel constant and

changing the equivalence ratio differences are observed inthe combustion Figure 14 shows the maximum pressureresults from the tests with 100 NG 100 H

2S and 5 H

2S

in NG (mix) for different equivalence ratios

The addition of 5 H2S to the natural gas makes the

mixture more reactive and therefore results in a higher pres-sure than that with pure NG and pure H

2S Another notable

effect is that the mixture becomes much more insensitiveto changes in the equivalence ratio when comparing themaximumpressure from channel 5 that is it produces higherpressure on both lean and rich sides compared with purefuels

A comparison of the pressure in the obstructed sectionand the smooth section with and without 5 hydrogensulfide is shown in Figures 15 and 16 Figure 15 shows thestoichiometric case and the two pressure records fromchannel 4 and the two pressure records from channel 5 havethe same shape and orderThis indicates a similar combustionprocess

When comparing the explosion pressures with the richcases (Figure 16) it is seen that there is a major change inthe pressure recordings when comparing the same channelThe pure NG burns slowly (a) while the mixed fuel (b)burns much faster and results in a strong pressure wave inthe smooth section This is a significant change caused bythe addition of relatively small amounts of hydrogen sulfideto the fuel There is still more to investigate regarding thecombustion of hydrocarbons and sulfur compounds

These experiments are smallmedium scale and the scaleeffects of hydrogen sulfide and natural gas explosions are stillunknown however the presence of hot spots and pressurespikes suggests that DDT might occur if the scale was largerIt was suggested byMoen [15] that the use of a denser obstaclefield in experiments would increase the turbulence and flamespeed

10 Journal of Combustion

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 1 channel 4 100 NG 120601 = 1 channel 5 100 NG

(a)

5 H2S and 95 NG5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 15 Comparison of explosion pressures for 120601 = 1 in the obstructed section (channel 4) and the smooth section (channel 5) (a) 100NG and (b) NG with 5 H

2S

6 Conclusion

Only limited data are available in the open literature onH2S-air deflagrations and especially H

2S and natural gas

mixtures Data for explosions at conditions supporting strongflame acceleration are lacking In the present work we havesuccessfully performed such experiments and obtained newand unique experimental data for explosions with hydrogensulfide and natural gas mixtures A comparison to purenatural gas is also included

(i) Pure fuels hydrogen sulfide has a wide flammabilityregion compared with methane and propane asshown in the literature In this study H

2S-air mix-

tures produced lower explosion pressures at lean-to-stoichiometric compositions relative to natural gasOn the rich side the H

2S-air mixtures produced

higher explosion pressures(ii) Fuel mixtures at 120601 = 1 a decrease in the maximum

pressure was observed when increasing amounts ofhydrogen sulfide were added to the natural gasThere were however somemaximum pressure spikesobserved for 90 and 95 H

2S in NG as well as for

5 and 10H2S in NGThese spikes could be a result

of a local explosion of compressed reactants but theydid not develop into detonations

(iii) Rich fuel mixtures rich NGwith 5 hydrogen sulfideis more reactive than pure rich NG When 5 H

2S

was added to the NG at 120601 = 1 the result was similarto pure NG but with spikes When the stoichiometrywas changed to120601 = 127 the result was a fast flame anda strong pressure wave formation in the 5 mixturewhile the pure NG had a slow deflagration and a slowand low pressure riseThe 5mixed fuel also showeddecreased sensitivity to changes in the equivalenceratio when the maximum pressures from channel 5were investigated These results are important to theprocess and petroleum industry

For further work it is suggested that the experimentalresults are compared to numerical simulations using com-mercial and academic softwareThere is also a need for a thor-ough study of the laminar properties of H

2S-hydrocarbon-

air mixtures Further experimental investigations should beconducted with higher and lower blockage ratios Largerscale experiments could reveal the possibility of DDT in

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

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Chemical EngineeringInternational Journal of Antennas and

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Navigation and Observation

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DistributedSensor Networks

International Journal of

2 Journal of Combustion

Alzueta et al [4] showed that SO2could either promote

or inhibit the burning of CO depending on the amountof SO

2and the stoichiometry Selim et al [3] investigated

premixed methane-air with added H2S and they showed

that combustion begins with the thermal and chemicaldecomposition of H

2S SO

2was also found to enhance the

dimerization of CH3radicals to form longer hydrocarbons

A chemical reaction mechanism of sulfur and hydrocarbonshas been proposed byWendt et al [5] and Frenklach et al [6]

Chamberlin and Clarke [7] were early investigators ofthe laminar flame speed of hydrogen sulfide Their setupwas typical of the period and consisted of a tube that was1m long and 25 cm in internal diameter The tube had aburner tip The maximum flame speed was observed at 10(120601 = 08) and had a value of 05ms Also a relatively wideflammable region in H

2S-air mixtures was observed Kurz

[8] used a Bunsen burner method to investigate the effect ofa hydrogen sulfide additive on the flame speed of propaneand he also included the flame speed measurements for pureH2S-air The flame speed decreased as H

2S was added to the

propane up to the maximum investigated concentration of6 However pure H

2S resulted in a higher flame speed than

the mix A Bunsen flame was also used by Gibbs and Calcote[9] to investigate the effect of the molecular structure on theburning velocity for different equivalence ratios These threeexperimental studies of H

2S flame speeds are summarized

in Figure 2 As seen there are relatively large discrepanciesbetween the results and it is also worth noting that none ofthe results consider the flame stretch effects This work doesnot involve any determination of the laminar flame propertiesbut states that the current knowledge of hydrogen sulfideflames is inconsistent As such it does not provide a goodbasis for evaluation of potential hazards as compared to othergases

There is need for further experimental investigations intothe laminar burning velocities and chemical kinetics for pureH2S gas and H

2S mixed with hydrocarbons These studies

could provide more consistent information regarding thelaminar flame properties of the fuel and chemical inductiondelay times Such data would be valuable as input to mod-elling tools and validation of chemical reaction mechanismsUntil new knowledge has been found one must use themethods available but beware of its limitations

Cantera software was used to calculate the constantvolume combustion pressure and the constant pressureexpansion ratio by the reaction mechanism of Wendt et al[5] These results are given in Figure 1 and are calculated forstoichiometric fuels with the H

2S content in NG ranging

from 0 (pure natural gas) to pure H2S using increasing

additions of H2S It is shown that the equilibrium pressure

and expansion ratio are inversely proportional to the hydro-gen sulfide content in the fuel The calculations suggest thatthere should be lower flame speed and pressure build-up inpropagating hydrogen sulphide deflagration than natural gasmixtures

Bozek and Rowe [10] compared fuel properties fromthe International Electrotechnical Commision (IEC) and theNational Fire Protection Association (NFPA) Both datasetsshow that the flammability region of hydrogen sulfide iswider

Equilibrium pressure left axisExpansion ratio right axis

0 5 10 20 50 80 909510004

05

06

07

08

09

1

11

12

13

14

Peq

cons

t V(M

Pa)

4

5

6

7

8

9

10

11

12

13

14

H2S in fuel (mdash)

120590=1205880120588

b(mdash

)

Figure 1 Cantera calculation Constant volume combustion equi-librium pressure for stoichiometric fuel ranging from pure NG (left)to pure H

2S (right)

0 5 10 15 200

01

02

03

04

05

06

2S

(m

s)

Chamberlin and ClarkeKurzGibbs and Calcote

H

Figure 2 Flame speed of H2S-air mixtures at different concentra-

tions

than that of methane and pentane Pahl andHoltappels [11] atthe BAM Federal Institute forMaterials Research and Testinginvestigated the explosion limits of H

2S and air in mixtures

with N2and CO

2 They found the upper and lower explosion

limits to be 498 and 39 respectively When CO2or N2

was added to themixture themeasured explosion limits werehigher than those found in an earlier work by Coward andJones [12]

Theminimum experimental safe gapMESG for hydrogensulfide is lower than that for methane and pentane whichindicates the reactivity of the fuel NFPA68Guide forVenting

Journal of Combustion 3

of Deflagrations (2002) provides data for the deflagrationindex and shows that it is higher for methane than for H

2S

Moen and coworkers [13ndash17] investigated flame accel-eration and detonations in H

2S mixtures The detonation

cell size of hydrogen sulfide detonations was 100mm whilethose of methane and propane were 280mm and 69mmrespectively This indicates that H

2S mixtures detonate easier

than methane The deflagration to detonation transition(DDT) of H

2S mixtures has not been widely investigated

Moen et al [16] investigated the flame acceleration of H2S-

air mixtures in a 18m by 18m cross-section and 155mlong square pipe with obstacles made of steel pipes withdiameters 500mm and 220mm They compared the resultsto those using acetylene-air mixtures For the hydrogensulfide experiments they recorded overpressures of only 20 to50mbar and flame speeds from 36 to 81ms In a comparisonto acetylene they suggested that the H

2S-air mixtures could

detonate if the scale was large enough the ignition was strongenough or sufficient confinement was present

Shepherd et al [17] and Vervisch et al [18] studied theactivation energy of hydrogen sulfide and compared it toother fuels The resultant value was 10967 kJmol in theShepherd study and 92 kJmol in the Vervisch study Turns[19] gave 125 kJmol activation energy for propane and 125 kJmol or 202 kJmol for methane

3 Experimental Setup

The experimental setup used in this work was made from astainless steel square pipe with inner dimensions of 84mmFour parts were bolted together and sealed to make anairtight compartment Figure 4 shows a schematic of the fourparts with their dimensions obstacle spacing and pressuretransducer positions Figure 3 shows a picture and Figure 5shows a sketch of the assembled setup The experimentalsetup was chosen to facilitate strong flame acceleration in thebeginning and enough spacing in section 2 to possibly getlocal volume explosions or DDTThe experimental setup wastested also for propane methane

The pressures were recorded with two Kistler 7001 (Ch1 and Ch 2) and four Kistler 603b (Ch 3 to Ch 6) piezo-electric transducers (Figure 2) and an oscilloscope recordingat 1MHz The ignition system was a center-mounted 10 kVspark at the end flange of section 1 At 10 cm from the end ofsection 4 one obstacle was installed not only to add strengthbut also to reflect any shock waves and achieve DDT (ifpossible) at the end obstacle DDT located at the end flange isundesirable since it would cause strain on the bolts and fillingsystem

The fuel-air mixture was made by evacuating air from thesquare pipe and filling it with fuel All tests were done with1 atm initial pressure and ambient temperature A circulationpump was used to circulate and mix the gas through thesystem The setup was placed with the obstacles in verticalalignment This prevented the fuel from being ldquotrappedrdquo inthe pockets between the obstacles at the top and bottom ofthe pipe The pump and piping was isolated from the setupbefore ignition

Figure 3 Picture of the experimental setup

Special consideration was made regarding the toxicityof hydrogen sulfide and the sulphur dioxide combustionproduct A coal filter with special coated coal was installed atthe purge of the square pipe to remove sulfuric componentsfrom the gas No H

2S was measured at the outlet of the

ventilation systemThis work was part of a larger study to compare H

2S and

natural gas mixtures to other more determined fuels Thefuels were acetylene hydrogen propane methane syntheticnatural gas and H

2S All fuels were mixed with air Four

different combustion regimes were observed in the studyTo illustrate these explosion regimes the pressure records

are plotted in a diagram showing time along the 119909-axis andpressure plus the positions of the pressure transducers alongthe 119910-axis This type of diagram gives a good display of thetrajectory of the pressure waves shock waves and detonationwaves in a gas explosion Figure 6 shows these four differentexplosion regimes in these types of diagrams

(i) slow flame propagation and no shock waves formedin front of the flame which is well known as a slowflame regime

(ii) fast flame propagation (regime) and shock waveformed but no strong local explosion due to reflectionof the shock at the end of the pipe

(iii) fast flame propagation and shock wave with localexplosion and transition to detonation due to reflec-tion of the shock wave at the end of the pipe

(iv) fast flame propagation and transition to detonation inobstructed area or close to the exit of the obstructedpart of the pipe

Only slow and fast flames were observed in the experi-ments reported in this paper but the other regimes are givento provide a qualitative justification of the assumed flamepropagation

Since there is no visual recording of the flame fronts itis only assumed that the deflagration was similar to otherreported works in a very similar setup Details of this canbe found in Lee [20] The flame fronts become stretched and

4 Journal of Combustion

100mm

100mm

200mm100mm

84mm

100mm

155mm735mm

1000mm

265mm645mm

455mm835mm

1

2

3

4

Ch 3 Ch 4

Ch 5 Ch 6

Ch 7 Ch 8

Figure 4 Schematic drawing of the experimental setup Ch = pressure recording channel number

1 2 3 4Ignition

Fillmix out Fillmix in

Figure 5 The experimental setup consisting of four stainless steeltube sections

unstable as they propagate through the obstacles and the flowthrough the obstacle openings can enhance the mixing at theflame front Shock reflections at the solid obstacles are alsowell known to cause local explosions or DDT in sensitive gasmixtures

4 Results

The fuel mixtures used in this work were pure hydrogensulfide and fuel mixtures with artificial natural gas (premade10 propane and 90 methane) The experiments with purenatural gas (NG) and pure H

2S in air are presented first to

provide a basis for comparison Next results from pure H2S

are presented and last the mixtures of H2S and NG in air are

presentedThe experimental matrix in Table 1 shows the gases

concentrations and equivalence ratios

41 Natural Gas As reference experiments tests were con-ducted using artificial natural gas The concentrations were62 83 92 and 104 corresponding to equivalenceratios of 120601 = 072 099 111 and 127

Pressure records from the stoichiometric experimentare given in Figure 7 The pressure curves are offset alongthe vertical axis an amount equal to the distance of the

Table 1 Experimental matrix

Test Gas 1 Vol Gas 2 Vol 120601

23 NG 830 09924 NG 620 07225 NG 920 11126 NG 1040 12727 H2S 1000 07928 H2S 1240 10129 H2S 900 07130 H2S 1510 12749 H2S 2500 23831 H2S 043 NG 808 10032 H2S 032 NG 599 07233 H2S 053 NG 998 12634 H2S 086 NG 774 09935 H2S 180 NG 720 10136 H2S 500 NG 500 10037 H2S 896 NG 224 10039 H2S 1053 NG 117 10040 H2S 1140 NG 060 100

transducer from the ignition end After ignition the flamefirst propagated through the obstructed part of the pipe Thiscaused the flame to increase in surface area and the flowahead of the flame became turbulent The turbulent flowcaused the flame to accelerate and increase its reaction rateThis is seen in the pressure plots as the rate of pressuregradient increases At early times a slow pressure increasewas observed on channels 1 and 2 with a faster pressurerise seen on channels 3 and 4 In the smooth section apropagating shock wave was recorded on channel 5 at 55ms

Journal of Combustion 5

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

Regime i slow flame and nostrong shock waves

Regime ii fast flamepropagation with shock wave

Regime iii fast flame propagationwith shock wave and local explosion

at the end of the tube

Regime iv fast flame propagationand transition to detonation (DDT)

Experiment 9 hydrogen conc 03 120601 = 102 Experiment 10 hydrogen conc 03 120601 = 102

Experiment 16 propane conc 006 120601 = 152 Experiment 20 methane conc 0103 120601 = 109

Figure 6 The four different explosion regimes

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 7 Pressure records from the stoichiometric NG-air mixture(test 23) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

This was generated as the flame accelerated and the displacedflow ahead was fast enough The shock wave was recordedon channel 6 at 62ms and a reflection at the end obstaclewas recorded at 65ms The reflected shock wave was alsorecorded on channel 5 at 75ms as it propagated backwardstoward the ignition end Further details on flame accelerationin obstructed pipes can be found in Ciccarelli and Dorofeev[21]

A comparison plot from the natural gas experiments withdifferent fuel concentrations is given in Figure 8The pressureis read on the left vertical axis and the equivalence ratio isshown on the right vertical axis The horizontal axis showsthe time The leanest experiment (120601 = 072) with 62fuel in air showed a pressure rise of almost 05MPa in theobstructed part of the experimental setup (channel 4) anda primary pressure wave of about 025MPa in the smoothsection The stoichiometric experiment with 83 fuel in airshowed the fastest pressure rise and the highest pressure(1MPa) A 03MPa shock wave was recorded in the smoothsection For 92 fuel in air (120601 = 111) the pressure rise in the

6 Journal of Combustion

0 5 10 15

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

099

111

127

Channel 5

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

120601

072

099

111

127

120601

Figure 8 From bottom tests 24 23 25 and 26 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richNG-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

obstructed section was lower than that in the stoichiometricexperiment while the shock wave in the smooth section wasalmost equal The richest experiment (104 fuel in air 120601 =127) resulted in a slow flame and a very slow pressure riserecorded on all pressure transducers

42Hydrogen Sulfide andAirMixtures Results fromfive testswith the pure H

2S-air mixture are presented The H

2S con-

centration ranged from 9 to 25 (see Table 1) where 124is the stoichiometric concentration The pressure recordsfrom the stoichiometric experiment are shown in Figure 9The overall phenomenon is similar to the stoichiometricnatural gas experiment The initial slow burning and thesubsequent development to a faster turbulent flame are seenin the pressure plot The pressure levels on channels 1 to 4are lower than in the NG experiment indicating that thisexperiment burned slower The shock wave in the smoothsection was roughly the same as in the NG experiment

Figure 10 shows a comparison plot of the hydrogen sulfideexperiments with the pressure shown on the left vertical axisand the equivalence ratio shown on the right vertical axisThehorizontal axis shows the time The leanest mixture was 9H2S in air (120601 = 071) and showed a pressure rise of about

03MPa It did not result in a shock in the smooth sectionof the setup The recorded pressure wave was about 02MPaand it reflected at the endwall and obstacleThe slightly richermixture of 10 (120601 = 079) showed a 03MPa shock wavepropagating in the smooth section of the experimental setupIn the obstructed part 05MPa was recorded at channel 4

The stoichiometric mixture resulted in a 035MPa shockin the smooth section while 075MPa was recorded in theobstructed section

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 9 Pressure records from the stoichiometric H2S-air mixture

(test 28) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

The experiment with 120601 = 127 corresponding to 151H2S in air was very similar to the stoichiometric case with

only 005MPa lower pressure in the smooth section and theobstructed section Due to the wide flammability region ofH2S 120601 = 238 was also investigated it resulted in a very slow

flame and a low pressure increase of about 01MPa

43 H2S-Natural Gas-Air Experiments Results and Discus-

sion Experiments were performed on a set of nine tests withthe first three containing 5 H

2S and 95 natural gas The

equivalence ratios were 120601 = 072 120601 = 100 and 120601 = 126

Journal of Combustion 7

0 5 10 15

0

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4 Channel 5

05

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

0

05

120601120601

071

079

101

127

238

071

079

101

127

238

Figure 10 From bottom tests 29 27 28 30 and 49 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richH2S-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

0 5 10 15

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

1

126

Channel 5

05

05

05

0

0

0

Pres

sure

(MPa

)

05

05

05

120601

072

1

126

120601

Figure 11 From bottom tests 32 31 and 33 Comparison of pressure records from channels 4 and 5 Lean stoichiometric and rich 5H2S95 NG-air mixtures Pressure is shown on the left vertical axis while the equivalence ratio is given on the right vertical axis

The following experiments were all conducted with 120601 = 1 butwith increasing hydrogen sulfide content The H

2S fractions

in natural gas were 5 10 20 50 80 90 and 95Figure 11 shows that by keeping the H

2S-to-NG ratio

constant at 5 95 and varying the equivalence ratio 120601 = 072and 120601 = 126 give quite similar pressure levels 05MPa inthe obstructed part and 03MPa in the smooth section Thestoichiometric experiment resulted in the fastest pressure riseand a peak pressure of more than 13MPa A shock wave

of 04MPa was recorded in the smooth section The richmixture (120601 = 126) resulted in strong flame acceleration05MPa recorded on channel 4 and a pressure wave in thesmooth section

With the equivalence ratio kept constant at 1 and the H2S

content in the fuel varied from 0 to 100 the pressure didnot change much except for some spikes as seen in Figure 12The pressure is shown on the left vertical axis and the H

2S

content in the fuel is shown on the right vertical axis Time is

8 Journal of Combustion

0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)

Pres

sure

(MPa

)

Channel 4

0

5

10

20

50

80

90

95

100

2S

in N

G0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)Pr

essu

re (M

Pa)

Channel 5

0

5

10

20

50

80

90

95

100

2S

in N

G

H

H

Figure 12 From bottom tests 23 31 34 35 36 37 39 40 and 28 Comparison of pressure records from channels 4 and 5The mixture variesfrom pure natural gas in the fuel (bottom) to pure H

2S in the fuel (top) All experiments are stoichiometric mixtures

shown on the horizontal axis The pressure in the obstructedpart was recorded between 08 and 1MPa and the shockpropagating in the smooth section was about 03 to 035MPaand reflected at 05MPa

5 Discussion

The experimental study for pure natural gas and air showedthat the flame propagated fast when the equivalence ratiowas lower than 127 producing strong deflagrations in theexperimental setupThe pressure results showed that the rateof energy release increased as the flame propagated throughthe square pipe The richest natural gas mixture investigatedwas 120601 = 127 and thatmixture resulted in a slow pressure risebelieved to be due to a slow burning velocity of the flame

The explosion pressures for lean H2S-air were slightly

lower than the pressures for lean NG-airThe lower explosionpressures were to some extent a result of the lower expansionratio of the H

2S-air flame compared with the other fuels The

expansion ratio (120590 = 120588119906120588119887) of H

2S is about 66 while it is 76

for NG This results in a lower flame speed less turbulenceand therefore a lower pressure rise

By comparing the H2S-air mixtures with mixtures of

natural gas and air as shown in Figure 10 and Figure 8 it wasobserved experimentally that natural gas and H

2S result in

a fast flame for 120601 = 072 On the rich side (120601 = 127) thehydrogen sulfide accelerated as a fast flame while the naturalgas was slowThis was expected due to the wider flammabilityregion of H

2S [10] compared with NG

The experiments with stoichiometric H2S-NG-air

showed that the flame in the experimental setup producedstrong deflagrations with high pressures in the obstructedpart of the experimental setup The pressures seen with

0 5 10 20 50 80 90 9510004

05

06

07

08

09

1

11

12

13

14

2S in fuel

Pm

ax(M

Pa)

Ch 2

Ch 4

Ch 5

H

Figure 13Maximumpressure from experimentsThepressure fromchannels 2 4 and 5 for various H

2S contents in the fuel

channel 4 in tests with 90 and 95 H2S in the fuel (135

and 115MPa) indicate that the compression heating of thereactants caused local ignition in a hot spot

Comparing the maximum pressure from channels 2 4and 5 a trend is observed in Figure 13 in which themaximumpressure decreases as the H

2S content in the fuel increases

however the spikes are also observed when plotting themaximum pressure for three channels when the hydrogensulfide content was varied These spikes correspond to 90

Journal of Combustion 9

Channel 4

02

Channel 5

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

02

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

Figure 14 Maximum pressure for different equivalence ratios for pure NG pure H2S and 5 H

2S in NG

and 95 H2S in the fuel as well as 5 and 10 H

2S in the

fuelCompared to the constant volume and constant pressure

calculations in Figure 1 it is clear that the pressure spikes orig-inate from different phenomena One possible explanationcould be a more sensitive mixture when small amounts ofH2S are added to natural gas or the opposite A reduction in

chemical induction delay time could lead to local explosionsin heated volumes of reactants These local explosions arevery hard to determine even with full view of the channel butother studies have shown that they are more likely to occur inthe obstructed part rather than in the unobstructed parts (Lee[20])

By comparing Figures 13 and 1 it can be seen that thepressure on channel 4 (section with obstacles) exceeds theconstant volume pressure The equilibrium pressure and theexpansion ratio do not explain the spikes seen in Figure 13

Hot spots and local ignition are closely related to defla-gration to detonation transition (DDT) which results in highpressure No DDT was recorded in these experiments butthe pressure spikes suggest that local explosions could haveoccurred

There are always uncertainties when reporting the max-imum pressure since it is measured at one position Otherspikes that may occur in other sections of the experimentalsetup may be missed by the transducer recording

By keeping the H2S content in the fuel constant and

changing the equivalence ratio differences are observed inthe combustion Figure 14 shows the maximum pressureresults from the tests with 100 NG 100 H

2S and 5 H

2S

in NG (mix) for different equivalence ratios

The addition of 5 H2S to the natural gas makes the

mixture more reactive and therefore results in a higher pres-sure than that with pure NG and pure H

2S Another notable

effect is that the mixture becomes much more insensitiveto changes in the equivalence ratio when comparing themaximumpressure from channel 5 that is it produces higherpressure on both lean and rich sides compared with purefuels

A comparison of the pressure in the obstructed sectionand the smooth section with and without 5 hydrogensulfide is shown in Figures 15 and 16 Figure 15 shows thestoichiometric case and the two pressure records fromchannel 4 and the two pressure records from channel 5 havethe same shape and orderThis indicates a similar combustionprocess

When comparing the explosion pressures with the richcases (Figure 16) it is seen that there is a major change inthe pressure recordings when comparing the same channelThe pure NG burns slowly (a) while the mixed fuel (b)burns much faster and results in a strong pressure wave inthe smooth section This is a significant change caused bythe addition of relatively small amounts of hydrogen sulfideto the fuel There is still more to investigate regarding thecombustion of hydrocarbons and sulfur compounds

These experiments are smallmedium scale and the scaleeffects of hydrogen sulfide and natural gas explosions are stillunknown however the presence of hot spots and pressurespikes suggests that DDT might occur if the scale was largerIt was suggested byMoen [15] that the use of a denser obstaclefield in experiments would increase the turbulence and flamespeed

10 Journal of Combustion

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 1 channel 4 100 NG 120601 = 1 channel 5 100 NG

(a)

5 H2S and 95 NG5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 15 Comparison of explosion pressures for 120601 = 1 in the obstructed section (channel 4) and the smooth section (channel 5) (a) 100NG and (b) NG with 5 H

2S

6 Conclusion

Only limited data are available in the open literature onH2S-air deflagrations and especially H

2S and natural gas

mixtures Data for explosions at conditions supporting strongflame acceleration are lacking In the present work we havesuccessfully performed such experiments and obtained newand unique experimental data for explosions with hydrogensulfide and natural gas mixtures A comparison to purenatural gas is also included

(i) Pure fuels hydrogen sulfide has a wide flammabilityregion compared with methane and propane asshown in the literature In this study H

2S-air mix-

tures produced lower explosion pressures at lean-to-stoichiometric compositions relative to natural gasOn the rich side the H

2S-air mixtures produced

higher explosion pressures(ii) Fuel mixtures at 120601 = 1 a decrease in the maximum

pressure was observed when increasing amounts ofhydrogen sulfide were added to the natural gasThere were however somemaximum pressure spikesobserved for 90 and 95 H

2S in NG as well as for

5 and 10H2S in NGThese spikes could be a result

of a local explosion of compressed reactants but theydid not develop into detonations

(iii) Rich fuel mixtures rich NGwith 5 hydrogen sulfideis more reactive than pure rich NG When 5 H

2S

was added to the NG at 120601 = 1 the result was similarto pure NG but with spikes When the stoichiometrywas changed to120601 = 127 the result was a fast flame anda strong pressure wave formation in the 5 mixturewhile the pure NG had a slow deflagration and a slowand low pressure riseThe 5mixed fuel also showeddecreased sensitivity to changes in the equivalenceratio when the maximum pressures from channel 5were investigated These results are important to theprocess and petroleum industry

For further work it is suggested that the experimentalresults are compared to numerical simulations using com-mercial and academic softwareThere is also a need for a thor-ough study of the laminar properties of H

2S-hydrocarbon-

air mixtures Further experimental investigations should beconducted with higher and lower blockage ratios Largerscale experiments could reveal the possibility of DDT in

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

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Chemical EngineeringInternational Journal of Antennas and

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International Journal of

Journal of Combustion 3

of Deflagrations (2002) provides data for the deflagrationindex and shows that it is higher for methane than for H

2S

Moen and coworkers [13ndash17] investigated flame accel-eration and detonations in H

2S mixtures The detonation

cell size of hydrogen sulfide detonations was 100mm whilethose of methane and propane were 280mm and 69mmrespectively This indicates that H

2S mixtures detonate easier

than methane The deflagration to detonation transition(DDT) of H

2S mixtures has not been widely investigated

Moen et al [16] investigated the flame acceleration of H2S-

air mixtures in a 18m by 18m cross-section and 155mlong square pipe with obstacles made of steel pipes withdiameters 500mm and 220mm They compared the resultsto those using acetylene-air mixtures For the hydrogensulfide experiments they recorded overpressures of only 20 to50mbar and flame speeds from 36 to 81ms In a comparisonto acetylene they suggested that the H

2S-air mixtures could

detonate if the scale was large enough the ignition was strongenough or sufficient confinement was present

Shepherd et al [17] and Vervisch et al [18] studied theactivation energy of hydrogen sulfide and compared it toother fuels The resultant value was 10967 kJmol in theShepherd study and 92 kJmol in the Vervisch study Turns[19] gave 125 kJmol activation energy for propane and 125 kJmol or 202 kJmol for methane

3 Experimental Setup

The experimental setup used in this work was made from astainless steel square pipe with inner dimensions of 84mmFour parts were bolted together and sealed to make anairtight compartment Figure 4 shows a schematic of the fourparts with their dimensions obstacle spacing and pressuretransducer positions Figure 3 shows a picture and Figure 5shows a sketch of the assembled setup The experimentalsetup was chosen to facilitate strong flame acceleration in thebeginning and enough spacing in section 2 to possibly getlocal volume explosions or DDTThe experimental setup wastested also for propane methane

The pressures were recorded with two Kistler 7001 (Ch1 and Ch 2) and four Kistler 603b (Ch 3 to Ch 6) piezo-electric transducers (Figure 2) and an oscilloscope recordingat 1MHz The ignition system was a center-mounted 10 kVspark at the end flange of section 1 At 10 cm from the end ofsection 4 one obstacle was installed not only to add strengthbut also to reflect any shock waves and achieve DDT (ifpossible) at the end obstacle DDT located at the end flange isundesirable since it would cause strain on the bolts and fillingsystem

The fuel-air mixture was made by evacuating air from thesquare pipe and filling it with fuel All tests were done with1 atm initial pressure and ambient temperature A circulationpump was used to circulate and mix the gas through thesystem The setup was placed with the obstacles in verticalalignment This prevented the fuel from being ldquotrappedrdquo inthe pockets between the obstacles at the top and bottom ofthe pipe The pump and piping was isolated from the setupbefore ignition

Figure 3 Picture of the experimental setup

Special consideration was made regarding the toxicityof hydrogen sulfide and the sulphur dioxide combustionproduct A coal filter with special coated coal was installed atthe purge of the square pipe to remove sulfuric componentsfrom the gas No H

2S was measured at the outlet of the

ventilation systemThis work was part of a larger study to compare H

2S and

natural gas mixtures to other more determined fuels Thefuels were acetylene hydrogen propane methane syntheticnatural gas and H

2S All fuels were mixed with air Four

different combustion regimes were observed in the studyTo illustrate these explosion regimes the pressure records

are plotted in a diagram showing time along the 119909-axis andpressure plus the positions of the pressure transducers alongthe 119910-axis This type of diagram gives a good display of thetrajectory of the pressure waves shock waves and detonationwaves in a gas explosion Figure 6 shows these four differentexplosion regimes in these types of diagrams

(i) slow flame propagation and no shock waves formedin front of the flame which is well known as a slowflame regime

(ii) fast flame propagation (regime) and shock waveformed but no strong local explosion due to reflectionof the shock at the end of the pipe

(iii) fast flame propagation and shock wave with localexplosion and transition to detonation due to reflec-tion of the shock wave at the end of the pipe

(iv) fast flame propagation and transition to detonation inobstructed area or close to the exit of the obstructedpart of the pipe

Only slow and fast flames were observed in the experi-ments reported in this paper but the other regimes are givento provide a qualitative justification of the assumed flamepropagation

Since there is no visual recording of the flame fronts itis only assumed that the deflagration was similar to otherreported works in a very similar setup Details of this canbe found in Lee [20] The flame fronts become stretched and

4 Journal of Combustion

100mm

100mm

200mm100mm

84mm

100mm

155mm735mm

1000mm

265mm645mm

455mm835mm

1

2

3

4

Ch 3 Ch 4

Ch 5 Ch 6

Ch 7 Ch 8

Figure 4 Schematic drawing of the experimental setup Ch = pressure recording channel number

1 2 3 4Ignition

Fillmix out Fillmix in

Figure 5 The experimental setup consisting of four stainless steeltube sections

unstable as they propagate through the obstacles and the flowthrough the obstacle openings can enhance the mixing at theflame front Shock reflections at the solid obstacles are alsowell known to cause local explosions or DDT in sensitive gasmixtures

4 Results

The fuel mixtures used in this work were pure hydrogensulfide and fuel mixtures with artificial natural gas (premade10 propane and 90 methane) The experiments with purenatural gas (NG) and pure H

2S in air are presented first to

provide a basis for comparison Next results from pure H2S

are presented and last the mixtures of H2S and NG in air are

presentedThe experimental matrix in Table 1 shows the gases

concentrations and equivalence ratios

41 Natural Gas As reference experiments tests were con-ducted using artificial natural gas The concentrations were62 83 92 and 104 corresponding to equivalenceratios of 120601 = 072 099 111 and 127

Pressure records from the stoichiometric experimentare given in Figure 7 The pressure curves are offset alongthe vertical axis an amount equal to the distance of the

Table 1 Experimental matrix

Test Gas 1 Vol Gas 2 Vol 120601

23 NG 830 09924 NG 620 07225 NG 920 11126 NG 1040 12727 H2S 1000 07928 H2S 1240 10129 H2S 900 07130 H2S 1510 12749 H2S 2500 23831 H2S 043 NG 808 10032 H2S 032 NG 599 07233 H2S 053 NG 998 12634 H2S 086 NG 774 09935 H2S 180 NG 720 10136 H2S 500 NG 500 10037 H2S 896 NG 224 10039 H2S 1053 NG 117 10040 H2S 1140 NG 060 100

transducer from the ignition end After ignition the flamefirst propagated through the obstructed part of the pipe Thiscaused the flame to increase in surface area and the flowahead of the flame became turbulent The turbulent flowcaused the flame to accelerate and increase its reaction rateThis is seen in the pressure plots as the rate of pressuregradient increases At early times a slow pressure increasewas observed on channels 1 and 2 with a faster pressurerise seen on channels 3 and 4 In the smooth section apropagating shock wave was recorded on channel 5 at 55ms

Journal of Combustion 5

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

Regime i slow flame and nostrong shock waves

Regime ii fast flamepropagation with shock wave

Regime iii fast flame propagationwith shock wave and local explosion

at the end of the tube

Regime iv fast flame propagationand transition to detonation (DDT)

Experiment 9 hydrogen conc 03 120601 = 102 Experiment 10 hydrogen conc 03 120601 = 102

Experiment 16 propane conc 006 120601 = 152 Experiment 20 methane conc 0103 120601 = 109

Figure 6 The four different explosion regimes

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 7 Pressure records from the stoichiometric NG-air mixture(test 23) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

This was generated as the flame accelerated and the displacedflow ahead was fast enough The shock wave was recordedon channel 6 at 62ms and a reflection at the end obstaclewas recorded at 65ms The reflected shock wave was alsorecorded on channel 5 at 75ms as it propagated backwardstoward the ignition end Further details on flame accelerationin obstructed pipes can be found in Ciccarelli and Dorofeev[21]

A comparison plot from the natural gas experiments withdifferent fuel concentrations is given in Figure 8The pressureis read on the left vertical axis and the equivalence ratio isshown on the right vertical axis The horizontal axis showsthe time The leanest experiment (120601 = 072) with 62fuel in air showed a pressure rise of almost 05MPa in theobstructed part of the experimental setup (channel 4) anda primary pressure wave of about 025MPa in the smoothsection The stoichiometric experiment with 83 fuel in airshowed the fastest pressure rise and the highest pressure(1MPa) A 03MPa shock wave was recorded in the smoothsection For 92 fuel in air (120601 = 111) the pressure rise in the

6 Journal of Combustion

0 5 10 15

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

099

111

127

Channel 5

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

120601

072

099

111

127

120601

Figure 8 From bottom tests 24 23 25 and 26 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richNG-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

obstructed section was lower than that in the stoichiometricexperiment while the shock wave in the smooth section wasalmost equal The richest experiment (104 fuel in air 120601 =127) resulted in a slow flame and a very slow pressure riserecorded on all pressure transducers

42Hydrogen Sulfide andAirMixtures Results fromfive testswith the pure H

2S-air mixture are presented The H

2S con-

centration ranged from 9 to 25 (see Table 1) where 124is the stoichiometric concentration The pressure recordsfrom the stoichiometric experiment are shown in Figure 9The overall phenomenon is similar to the stoichiometricnatural gas experiment The initial slow burning and thesubsequent development to a faster turbulent flame are seenin the pressure plot The pressure levels on channels 1 to 4are lower than in the NG experiment indicating that thisexperiment burned slower The shock wave in the smoothsection was roughly the same as in the NG experiment

Figure 10 shows a comparison plot of the hydrogen sulfideexperiments with the pressure shown on the left vertical axisand the equivalence ratio shown on the right vertical axisThehorizontal axis shows the time The leanest mixture was 9H2S in air (120601 = 071) and showed a pressure rise of about

03MPa It did not result in a shock in the smooth sectionof the setup The recorded pressure wave was about 02MPaand it reflected at the endwall and obstacleThe slightly richermixture of 10 (120601 = 079) showed a 03MPa shock wavepropagating in the smooth section of the experimental setupIn the obstructed part 05MPa was recorded at channel 4

The stoichiometric mixture resulted in a 035MPa shockin the smooth section while 075MPa was recorded in theobstructed section

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 9 Pressure records from the stoichiometric H2S-air mixture

(test 28) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

The experiment with 120601 = 127 corresponding to 151H2S in air was very similar to the stoichiometric case with

only 005MPa lower pressure in the smooth section and theobstructed section Due to the wide flammability region ofH2S 120601 = 238 was also investigated it resulted in a very slow

flame and a low pressure increase of about 01MPa

43 H2S-Natural Gas-Air Experiments Results and Discus-

sion Experiments were performed on a set of nine tests withthe first three containing 5 H

2S and 95 natural gas The

equivalence ratios were 120601 = 072 120601 = 100 and 120601 = 126

Journal of Combustion 7

0 5 10 15

0

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4 Channel 5

05

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

0

05

120601120601

071

079

101

127

238

071

079

101

127

238

Figure 10 From bottom tests 29 27 28 30 and 49 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richH2S-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

0 5 10 15

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

1

126

Channel 5

05

05

05

0

0

0

Pres

sure

(MPa

)

05

05

05

120601

072

1

126

120601

Figure 11 From bottom tests 32 31 and 33 Comparison of pressure records from channels 4 and 5 Lean stoichiometric and rich 5H2S95 NG-air mixtures Pressure is shown on the left vertical axis while the equivalence ratio is given on the right vertical axis

The following experiments were all conducted with 120601 = 1 butwith increasing hydrogen sulfide content The H

2S fractions

in natural gas were 5 10 20 50 80 90 and 95Figure 11 shows that by keeping the H

2S-to-NG ratio

constant at 5 95 and varying the equivalence ratio 120601 = 072and 120601 = 126 give quite similar pressure levels 05MPa inthe obstructed part and 03MPa in the smooth section Thestoichiometric experiment resulted in the fastest pressure riseand a peak pressure of more than 13MPa A shock wave

of 04MPa was recorded in the smooth section The richmixture (120601 = 126) resulted in strong flame acceleration05MPa recorded on channel 4 and a pressure wave in thesmooth section

With the equivalence ratio kept constant at 1 and the H2S

content in the fuel varied from 0 to 100 the pressure didnot change much except for some spikes as seen in Figure 12The pressure is shown on the left vertical axis and the H

2S

content in the fuel is shown on the right vertical axis Time is

8 Journal of Combustion

0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)

Pres

sure

(MPa

)

Channel 4

0

5

10

20

50

80

90

95

100

2S

in N

G0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)Pr

essu

re (M

Pa)

Channel 5

0

5

10

20

50

80

90

95

100

2S

in N

G

H

H

Figure 12 From bottom tests 23 31 34 35 36 37 39 40 and 28 Comparison of pressure records from channels 4 and 5The mixture variesfrom pure natural gas in the fuel (bottom) to pure H

2S in the fuel (top) All experiments are stoichiometric mixtures

shown on the horizontal axis The pressure in the obstructedpart was recorded between 08 and 1MPa and the shockpropagating in the smooth section was about 03 to 035MPaand reflected at 05MPa

5 Discussion

The experimental study for pure natural gas and air showedthat the flame propagated fast when the equivalence ratiowas lower than 127 producing strong deflagrations in theexperimental setupThe pressure results showed that the rateof energy release increased as the flame propagated throughthe square pipe The richest natural gas mixture investigatedwas 120601 = 127 and thatmixture resulted in a slow pressure risebelieved to be due to a slow burning velocity of the flame

The explosion pressures for lean H2S-air were slightly

lower than the pressures for lean NG-airThe lower explosionpressures were to some extent a result of the lower expansionratio of the H

2S-air flame compared with the other fuels The

expansion ratio (120590 = 120588119906120588119887) of H

2S is about 66 while it is 76

for NG This results in a lower flame speed less turbulenceand therefore a lower pressure rise

By comparing the H2S-air mixtures with mixtures of

natural gas and air as shown in Figure 10 and Figure 8 it wasobserved experimentally that natural gas and H

2S result in

a fast flame for 120601 = 072 On the rich side (120601 = 127) thehydrogen sulfide accelerated as a fast flame while the naturalgas was slowThis was expected due to the wider flammabilityregion of H

2S [10] compared with NG

The experiments with stoichiometric H2S-NG-air

showed that the flame in the experimental setup producedstrong deflagrations with high pressures in the obstructedpart of the experimental setup The pressures seen with

0 5 10 20 50 80 90 9510004

05

06

07

08

09

1

11

12

13

14

2S in fuel

Pm

ax(M

Pa)

Ch 2

Ch 4

Ch 5

H

Figure 13Maximumpressure from experimentsThepressure fromchannels 2 4 and 5 for various H

2S contents in the fuel

channel 4 in tests with 90 and 95 H2S in the fuel (135

and 115MPa) indicate that the compression heating of thereactants caused local ignition in a hot spot

Comparing the maximum pressure from channels 2 4and 5 a trend is observed in Figure 13 in which themaximumpressure decreases as the H

2S content in the fuel increases

however the spikes are also observed when plotting themaximum pressure for three channels when the hydrogensulfide content was varied These spikes correspond to 90

Journal of Combustion 9

Channel 4

02

Channel 5

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

02

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

Figure 14 Maximum pressure for different equivalence ratios for pure NG pure H2S and 5 H

2S in NG

and 95 H2S in the fuel as well as 5 and 10 H

2S in the

fuelCompared to the constant volume and constant pressure

calculations in Figure 1 it is clear that the pressure spikes orig-inate from different phenomena One possible explanationcould be a more sensitive mixture when small amounts ofH2S are added to natural gas or the opposite A reduction in

chemical induction delay time could lead to local explosionsin heated volumes of reactants These local explosions arevery hard to determine even with full view of the channel butother studies have shown that they are more likely to occur inthe obstructed part rather than in the unobstructed parts (Lee[20])

By comparing Figures 13 and 1 it can be seen that thepressure on channel 4 (section with obstacles) exceeds theconstant volume pressure The equilibrium pressure and theexpansion ratio do not explain the spikes seen in Figure 13

Hot spots and local ignition are closely related to defla-gration to detonation transition (DDT) which results in highpressure No DDT was recorded in these experiments butthe pressure spikes suggest that local explosions could haveoccurred

There are always uncertainties when reporting the max-imum pressure since it is measured at one position Otherspikes that may occur in other sections of the experimentalsetup may be missed by the transducer recording

By keeping the H2S content in the fuel constant and

changing the equivalence ratio differences are observed inthe combustion Figure 14 shows the maximum pressureresults from the tests with 100 NG 100 H

2S and 5 H

2S

in NG (mix) for different equivalence ratios

The addition of 5 H2S to the natural gas makes the

mixture more reactive and therefore results in a higher pres-sure than that with pure NG and pure H

2S Another notable

effect is that the mixture becomes much more insensitiveto changes in the equivalence ratio when comparing themaximumpressure from channel 5 that is it produces higherpressure on both lean and rich sides compared with purefuels

A comparison of the pressure in the obstructed sectionand the smooth section with and without 5 hydrogensulfide is shown in Figures 15 and 16 Figure 15 shows thestoichiometric case and the two pressure records fromchannel 4 and the two pressure records from channel 5 havethe same shape and orderThis indicates a similar combustionprocess

When comparing the explosion pressures with the richcases (Figure 16) it is seen that there is a major change inthe pressure recordings when comparing the same channelThe pure NG burns slowly (a) while the mixed fuel (b)burns much faster and results in a strong pressure wave inthe smooth section This is a significant change caused bythe addition of relatively small amounts of hydrogen sulfideto the fuel There is still more to investigate regarding thecombustion of hydrocarbons and sulfur compounds

These experiments are smallmedium scale and the scaleeffects of hydrogen sulfide and natural gas explosions are stillunknown however the presence of hot spots and pressurespikes suggests that DDT might occur if the scale was largerIt was suggested byMoen [15] that the use of a denser obstaclefield in experiments would increase the turbulence and flamespeed

10 Journal of Combustion

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 1 channel 4 100 NG 120601 = 1 channel 5 100 NG

(a)

5 H2S and 95 NG5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 15 Comparison of explosion pressures for 120601 = 1 in the obstructed section (channel 4) and the smooth section (channel 5) (a) 100NG and (b) NG with 5 H

2S

6 Conclusion

Only limited data are available in the open literature onH2S-air deflagrations and especially H

2S and natural gas

mixtures Data for explosions at conditions supporting strongflame acceleration are lacking In the present work we havesuccessfully performed such experiments and obtained newand unique experimental data for explosions with hydrogensulfide and natural gas mixtures A comparison to purenatural gas is also included

(i) Pure fuels hydrogen sulfide has a wide flammabilityregion compared with methane and propane asshown in the literature In this study H

2S-air mix-

tures produced lower explosion pressures at lean-to-stoichiometric compositions relative to natural gasOn the rich side the H

2S-air mixtures produced

higher explosion pressures(ii) Fuel mixtures at 120601 = 1 a decrease in the maximum

pressure was observed when increasing amounts ofhydrogen sulfide were added to the natural gasThere were however somemaximum pressure spikesobserved for 90 and 95 H

2S in NG as well as for

5 and 10H2S in NGThese spikes could be a result

of a local explosion of compressed reactants but theydid not develop into detonations

(iii) Rich fuel mixtures rich NGwith 5 hydrogen sulfideis more reactive than pure rich NG When 5 H

2S

was added to the NG at 120601 = 1 the result was similarto pure NG but with spikes When the stoichiometrywas changed to120601 = 127 the result was a fast flame anda strong pressure wave formation in the 5 mixturewhile the pure NG had a slow deflagration and a slowand low pressure riseThe 5mixed fuel also showeddecreased sensitivity to changes in the equivalenceratio when the maximum pressures from channel 5were investigated These results are important to theprocess and petroleum industry

For further work it is suggested that the experimentalresults are compared to numerical simulations using com-mercial and academic softwareThere is also a need for a thor-ough study of the laminar properties of H

2S-hydrocarbon-

air mixtures Further experimental investigations should beconducted with higher and lower blockage ratios Largerscale experiments could reveal the possibility of DDT in

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

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RotatingMachinery

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Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

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Shock and Vibration

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Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

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Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

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Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

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Navigation and Observation

International Journal of

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DistributedSensor Networks

International Journal of

4 Journal of Combustion

100mm

100mm

200mm100mm

84mm

100mm

155mm735mm

1000mm

265mm645mm

455mm835mm

1

2

3

4

Ch 3 Ch 4

Ch 5 Ch 6

Ch 7 Ch 8

Figure 4 Schematic drawing of the experimental setup Ch = pressure recording channel number

1 2 3 4Ignition

Fillmix out Fillmix in

Figure 5 The experimental setup consisting of four stainless steeltube sections

unstable as they propagate through the obstacles and the flowthrough the obstacle openings can enhance the mixing at theflame front Shock reflections at the solid obstacles are alsowell known to cause local explosions or DDT in sensitive gasmixtures

4 Results

The fuel mixtures used in this work were pure hydrogensulfide and fuel mixtures with artificial natural gas (premade10 propane and 90 methane) The experiments with purenatural gas (NG) and pure H

2S in air are presented first to

provide a basis for comparison Next results from pure H2S

are presented and last the mixtures of H2S and NG in air are

presentedThe experimental matrix in Table 1 shows the gases

concentrations and equivalence ratios

41 Natural Gas As reference experiments tests were con-ducted using artificial natural gas The concentrations were62 83 92 and 104 corresponding to equivalenceratios of 120601 = 072 099 111 and 127

Pressure records from the stoichiometric experimentare given in Figure 7 The pressure curves are offset alongthe vertical axis an amount equal to the distance of the

Table 1 Experimental matrix

Test Gas 1 Vol Gas 2 Vol 120601

23 NG 830 09924 NG 620 07225 NG 920 11126 NG 1040 12727 H2S 1000 07928 H2S 1240 10129 H2S 900 07130 H2S 1510 12749 H2S 2500 23831 H2S 043 NG 808 10032 H2S 032 NG 599 07233 H2S 053 NG 998 12634 H2S 086 NG 774 09935 H2S 180 NG 720 10136 H2S 500 NG 500 10037 H2S 896 NG 224 10039 H2S 1053 NG 117 10040 H2S 1140 NG 060 100

transducer from the ignition end After ignition the flamefirst propagated through the obstructed part of the pipe Thiscaused the flame to increase in surface area and the flowahead of the flame became turbulent The turbulent flowcaused the flame to accelerate and increase its reaction rateThis is seen in the pressure plots as the rate of pressuregradient increases At early times a slow pressure increasewas observed on channels 1 and 2 with a faster pressurerise seen on channels 3 and 4 In the smooth section apropagating shock wave was recorded on channel 5 at 55ms

Journal of Combustion 5

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

Regime i slow flame and nostrong shock waves

Regime ii fast flamepropagation with shock wave

Regime iii fast flame propagationwith shock wave and local explosion

at the end of the tube

Regime iv fast flame propagationand transition to detonation (DDT)

Experiment 9 hydrogen conc 03 120601 = 102 Experiment 10 hydrogen conc 03 120601 = 102

Experiment 16 propane conc 006 120601 = 152 Experiment 20 methane conc 0103 120601 = 109

Figure 6 The four different explosion regimes

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 7 Pressure records from the stoichiometric NG-air mixture(test 23) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

This was generated as the flame accelerated and the displacedflow ahead was fast enough The shock wave was recordedon channel 6 at 62ms and a reflection at the end obstaclewas recorded at 65ms The reflected shock wave was alsorecorded on channel 5 at 75ms as it propagated backwardstoward the ignition end Further details on flame accelerationin obstructed pipes can be found in Ciccarelli and Dorofeev[21]

A comparison plot from the natural gas experiments withdifferent fuel concentrations is given in Figure 8The pressureis read on the left vertical axis and the equivalence ratio isshown on the right vertical axis The horizontal axis showsthe time The leanest experiment (120601 = 072) with 62fuel in air showed a pressure rise of almost 05MPa in theobstructed part of the experimental setup (channel 4) anda primary pressure wave of about 025MPa in the smoothsection The stoichiometric experiment with 83 fuel in airshowed the fastest pressure rise and the highest pressure(1MPa) A 03MPa shock wave was recorded in the smoothsection For 92 fuel in air (120601 = 111) the pressure rise in the

6 Journal of Combustion

0 5 10 15

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

099

111

127

Channel 5

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

120601

072

099

111

127

120601

Figure 8 From bottom tests 24 23 25 and 26 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richNG-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

obstructed section was lower than that in the stoichiometricexperiment while the shock wave in the smooth section wasalmost equal The richest experiment (104 fuel in air 120601 =127) resulted in a slow flame and a very slow pressure riserecorded on all pressure transducers

42Hydrogen Sulfide andAirMixtures Results fromfive testswith the pure H

2S-air mixture are presented The H

2S con-

centration ranged from 9 to 25 (see Table 1) where 124is the stoichiometric concentration The pressure recordsfrom the stoichiometric experiment are shown in Figure 9The overall phenomenon is similar to the stoichiometricnatural gas experiment The initial slow burning and thesubsequent development to a faster turbulent flame are seenin the pressure plot The pressure levels on channels 1 to 4are lower than in the NG experiment indicating that thisexperiment burned slower The shock wave in the smoothsection was roughly the same as in the NG experiment

Figure 10 shows a comparison plot of the hydrogen sulfideexperiments with the pressure shown on the left vertical axisand the equivalence ratio shown on the right vertical axisThehorizontal axis shows the time The leanest mixture was 9H2S in air (120601 = 071) and showed a pressure rise of about

03MPa It did not result in a shock in the smooth sectionof the setup The recorded pressure wave was about 02MPaand it reflected at the endwall and obstacleThe slightly richermixture of 10 (120601 = 079) showed a 03MPa shock wavepropagating in the smooth section of the experimental setupIn the obstructed part 05MPa was recorded at channel 4

The stoichiometric mixture resulted in a 035MPa shockin the smooth section while 075MPa was recorded in theobstructed section

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 9 Pressure records from the stoichiometric H2S-air mixture

(test 28) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

The experiment with 120601 = 127 corresponding to 151H2S in air was very similar to the stoichiometric case with

only 005MPa lower pressure in the smooth section and theobstructed section Due to the wide flammability region ofH2S 120601 = 238 was also investigated it resulted in a very slow

flame and a low pressure increase of about 01MPa

43 H2S-Natural Gas-Air Experiments Results and Discus-

sion Experiments were performed on a set of nine tests withthe first three containing 5 H

2S and 95 natural gas The

equivalence ratios were 120601 = 072 120601 = 100 and 120601 = 126

Journal of Combustion 7

0 5 10 15

0

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4 Channel 5

05

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

0

05

120601120601

071

079

101

127

238

071

079

101

127

238

Figure 10 From bottom tests 29 27 28 30 and 49 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richH2S-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

0 5 10 15

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

1

126

Channel 5

05

05

05

0

0

0

Pres

sure

(MPa

)

05

05

05

120601

072

1

126

120601

Figure 11 From bottom tests 32 31 and 33 Comparison of pressure records from channels 4 and 5 Lean stoichiometric and rich 5H2S95 NG-air mixtures Pressure is shown on the left vertical axis while the equivalence ratio is given on the right vertical axis

The following experiments were all conducted with 120601 = 1 butwith increasing hydrogen sulfide content The H

2S fractions

in natural gas were 5 10 20 50 80 90 and 95Figure 11 shows that by keeping the H

2S-to-NG ratio

constant at 5 95 and varying the equivalence ratio 120601 = 072and 120601 = 126 give quite similar pressure levels 05MPa inthe obstructed part and 03MPa in the smooth section Thestoichiometric experiment resulted in the fastest pressure riseand a peak pressure of more than 13MPa A shock wave

of 04MPa was recorded in the smooth section The richmixture (120601 = 126) resulted in strong flame acceleration05MPa recorded on channel 4 and a pressure wave in thesmooth section

With the equivalence ratio kept constant at 1 and the H2S

content in the fuel varied from 0 to 100 the pressure didnot change much except for some spikes as seen in Figure 12The pressure is shown on the left vertical axis and the H

2S

content in the fuel is shown on the right vertical axis Time is

8 Journal of Combustion

0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)

Pres

sure

(MPa

)

Channel 4

0

5

10

20

50

80

90

95

100

2S

in N

G0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)Pr

essu

re (M

Pa)

Channel 5

0

5

10

20

50

80

90

95

100

2S

in N

G

H

H

Figure 12 From bottom tests 23 31 34 35 36 37 39 40 and 28 Comparison of pressure records from channels 4 and 5The mixture variesfrom pure natural gas in the fuel (bottom) to pure H

2S in the fuel (top) All experiments are stoichiometric mixtures

shown on the horizontal axis The pressure in the obstructedpart was recorded between 08 and 1MPa and the shockpropagating in the smooth section was about 03 to 035MPaand reflected at 05MPa

5 Discussion

The experimental study for pure natural gas and air showedthat the flame propagated fast when the equivalence ratiowas lower than 127 producing strong deflagrations in theexperimental setupThe pressure results showed that the rateof energy release increased as the flame propagated throughthe square pipe The richest natural gas mixture investigatedwas 120601 = 127 and thatmixture resulted in a slow pressure risebelieved to be due to a slow burning velocity of the flame

The explosion pressures for lean H2S-air were slightly

lower than the pressures for lean NG-airThe lower explosionpressures were to some extent a result of the lower expansionratio of the H

2S-air flame compared with the other fuels The

expansion ratio (120590 = 120588119906120588119887) of H

2S is about 66 while it is 76

for NG This results in a lower flame speed less turbulenceand therefore a lower pressure rise

By comparing the H2S-air mixtures with mixtures of

natural gas and air as shown in Figure 10 and Figure 8 it wasobserved experimentally that natural gas and H

2S result in

a fast flame for 120601 = 072 On the rich side (120601 = 127) thehydrogen sulfide accelerated as a fast flame while the naturalgas was slowThis was expected due to the wider flammabilityregion of H

2S [10] compared with NG

The experiments with stoichiometric H2S-NG-air

showed that the flame in the experimental setup producedstrong deflagrations with high pressures in the obstructedpart of the experimental setup The pressures seen with

0 5 10 20 50 80 90 9510004

05

06

07

08

09

1

11

12

13

14

2S in fuel

Pm

ax(M

Pa)

Ch 2

Ch 4

Ch 5

H

Figure 13Maximumpressure from experimentsThepressure fromchannels 2 4 and 5 for various H

2S contents in the fuel

channel 4 in tests with 90 and 95 H2S in the fuel (135

and 115MPa) indicate that the compression heating of thereactants caused local ignition in a hot spot

Comparing the maximum pressure from channels 2 4and 5 a trend is observed in Figure 13 in which themaximumpressure decreases as the H

2S content in the fuel increases

however the spikes are also observed when plotting themaximum pressure for three channels when the hydrogensulfide content was varied These spikes correspond to 90

Journal of Combustion 9

Channel 4

02

Channel 5

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

02

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

Figure 14 Maximum pressure for different equivalence ratios for pure NG pure H2S and 5 H

2S in NG

and 95 H2S in the fuel as well as 5 and 10 H

2S in the

fuelCompared to the constant volume and constant pressure

calculations in Figure 1 it is clear that the pressure spikes orig-inate from different phenomena One possible explanationcould be a more sensitive mixture when small amounts ofH2S are added to natural gas or the opposite A reduction in

chemical induction delay time could lead to local explosionsin heated volumes of reactants These local explosions arevery hard to determine even with full view of the channel butother studies have shown that they are more likely to occur inthe obstructed part rather than in the unobstructed parts (Lee[20])

By comparing Figures 13 and 1 it can be seen that thepressure on channel 4 (section with obstacles) exceeds theconstant volume pressure The equilibrium pressure and theexpansion ratio do not explain the spikes seen in Figure 13

Hot spots and local ignition are closely related to defla-gration to detonation transition (DDT) which results in highpressure No DDT was recorded in these experiments butthe pressure spikes suggest that local explosions could haveoccurred

There are always uncertainties when reporting the max-imum pressure since it is measured at one position Otherspikes that may occur in other sections of the experimentalsetup may be missed by the transducer recording

By keeping the H2S content in the fuel constant and

changing the equivalence ratio differences are observed inthe combustion Figure 14 shows the maximum pressureresults from the tests with 100 NG 100 H

2S and 5 H

2S

in NG (mix) for different equivalence ratios

The addition of 5 H2S to the natural gas makes the

mixture more reactive and therefore results in a higher pres-sure than that with pure NG and pure H

2S Another notable

effect is that the mixture becomes much more insensitiveto changes in the equivalence ratio when comparing themaximumpressure from channel 5 that is it produces higherpressure on both lean and rich sides compared with purefuels

A comparison of the pressure in the obstructed sectionand the smooth section with and without 5 hydrogensulfide is shown in Figures 15 and 16 Figure 15 shows thestoichiometric case and the two pressure records fromchannel 4 and the two pressure records from channel 5 havethe same shape and orderThis indicates a similar combustionprocess

When comparing the explosion pressures with the richcases (Figure 16) it is seen that there is a major change inthe pressure recordings when comparing the same channelThe pure NG burns slowly (a) while the mixed fuel (b)burns much faster and results in a strong pressure wave inthe smooth section This is a significant change caused bythe addition of relatively small amounts of hydrogen sulfideto the fuel There is still more to investigate regarding thecombustion of hydrocarbons and sulfur compounds

These experiments are smallmedium scale and the scaleeffects of hydrogen sulfide and natural gas explosions are stillunknown however the presence of hot spots and pressurespikes suggests that DDT might occur if the scale was largerIt was suggested byMoen [15] that the use of a denser obstaclefield in experiments would increase the turbulence and flamespeed

10 Journal of Combustion

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 1 channel 4 100 NG 120601 = 1 channel 5 100 NG

(a)

5 H2S and 95 NG5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 15 Comparison of explosion pressures for 120601 = 1 in the obstructed section (channel 4) and the smooth section (channel 5) (a) 100NG and (b) NG with 5 H

2S

6 Conclusion

Only limited data are available in the open literature onH2S-air deflagrations and especially H

2S and natural gas

mixtures Data for explosions at conditions supporting strongflame acceleration are lacking In the present work we havesuccessfully performed such experiments and obtained newand unique experimental data for explosions with hydrogensulfide and natural gas mixtures A comparison to purenatural gas is also included

(i) Pure fuels hydrogen sulfide has a wide flammabilityregion compared with methane and propane asshown in the literature In this study H

2S-air mix-

tures produced lower explosion pressures at lean-to-stoichiometric compositions relative to natural gasOn the rich side the H

2S-air mixtures produced

higher explosion pressures(ii) Fuel mixtures at 120601 = 1 a decrease in the maximum

pressure was observed when increasing amounts ofhydrogen sulfide were added to the natural gasThere were however somemaximum pressure spikesobserved for 90 and 95 H

2S in NG as well as for

5 and 10H2S in NGThese spikes could be a result

of a local explosion of compressed reactants but theydid not develop into detonations

(iii) Rich fuel mixtures rich NGwith 5 hydrogen sulfideis more reactive than pure rich NG When 5 H

2S

was added to the NG at 120601 = 1 the result was similarto pure NG but with spikes When the stoichiometrywas changed to120601 = 127 the result was a fast flame anda strong pressure wave formation in the 5 mixturewhile the pure NG had a slow deflagration and a slowand low pressure riseThe 5mixed fuel also showeddecreased sensitivity to changes in the equivalenceratio when the maximum pressures from channel 5were investigated These results are important to theprocess and petroleum industry

For further work it is suggested that the experimentalresults are compared to numerical simulations using com-mercial and academic softwareThere is also a need for a thor-ough study of the laminar properties of H

2S-hydrocarbon-

air mixtures Further experimental investigations should beconducted with higher and lower blockage ratios Largerscale experiments could reveal the possibility of DDT in

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

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Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

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Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

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Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

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Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Journal of Combustion 5

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

0 5 10 150

2

4

6

8

Time (ms)

Pres

sure

(MPa

)+di

stan

ce (m

)

Regime i slow flame and nostrong shock waves

Regime ii fast flamepropagation with shock wave

Regime iii fast flame propagationwith shock wave and local explosion

at the end of the tube

Regime iv fast flame propagationand transition to detonation (DDT)

Experiment 9 hydrogen conc 03 120601 = 102 Experiment 10 hydrogen conc 03 120601 = 102

Experiment 16 propane conc 006 120601 = 152 Experiment 20 methane conc 0103 120601 = 109

Figure 6 The four different explosion regimes

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 7 Pressure records from the stoichiometric NG-air mixture(test 23) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

This was generated as the flame accelerated and the displacedflow ahead was fast enough The shock wave was recordedon channel 6 at 62ms and a reflection at the end obstaclewas recorded at 65ms The reflected shock wave was alsorecorded on channel 5 at 75ms as it propagated backwardstoward the ignition end Further details on flame accelerationin obstructed pipes can be found in Ciccarelli and Dorofeev[21]

A comparison plot from the natural gas experiments withdifferent fuel concentrations is given in Figure 8The pressureis read on the left vertical axis and the equivalence ratio isshown on the right vertical axis The horizontal axis showsthe time The leanest experiment (120601 = 072) with 62fuel in air showed a pressure rise of almost 05MPa in theobstructed part of the experimental setup (channel 4) anda primary pressure wave of about 025MPa in the smoothsection The stoichiometric experiment with 83 fuel in airshowed the fastest pressure rise and the highest pressure(1MPa) A 03MPa shock wave was recorded in the smoothsection For 92 fuel in air (120601 = 111) the pressure rise in the

6 Journal of Combustion

0 5 10 15

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

099

111

127

Channel 5

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

120601

072

099

111

127

120601

Figure 8 From bottom tests 24 23 25 and 26 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richNG-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

obstructed section was lower than that in the stoichiometricexperiment while the shock wave in the smooth section wasalmost equal The richest experiment (104 fuel in air 120601 =127) resulted in a slow flame and a very slow pressure riserecorded on all pressure transducers

42Hydrogen Sulfide andAirMixtures Results fromfive testswith the pure H

2S-air mixture are presented The H

2S con-

centration ranged from 9 to 25 (see Table 1) where 124is the stoichiometric concentration The pressure recordsfrom the stoichiometric experiment are shown in Figure 9The overall phenomenon is similar to the stoichiometricnatural gas experiment The initial slow burning and thesubsequent development to a faster turbulent flame are seenin the pressure plot The pressure levels on channels 1 to 4are lower than in the NG experiment indicating that thisexperiment burned slower The shock wave in the smoothsection was roughly the same as in the NG experiment

Figure 10 shows a comparison plot of the hydrogen sulfideexperiments with the pressure shown on the left vertical axisand the equivalence ratio shown on the right vertical axisThehorizontal axis shows the time The leanest mixture was 9H2S in air (120601 = 071) and showed a pressure rise of about

03MPa It did not result in a shock in the smooth sectionof the setup The recorded pressure wave was about 02MPaand it reflected at the endwall and obstacleThe slightly richermixture of 10 (120601 = 079) showed a 03MPa shock wavepropagating in the smooth section of the experimental setupIn the obstructed part 05MPa was recorded at channel 4

The stoichiometric mixture resulted in a 035MPa shockin the smooth section while 075MPa was recorded in theobstructed section

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 9 Pressure records from the stoichiometric H2S-air mixture

(test 28) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

The experiment with 120601 = 127 corresponding to 151H2S in air was very similar to the stoichiometric case with

only 005MPa lower pressure in the smooth section and theobstructed section Due to the wide flammability region ofH2S 120601 = 238 was also investigated it resulted in a very slow

flame and a low pressure increase of about 01MPa

43 H2S-Natural Gas-Air Experiments Results and Discus-

sion Experiments were performed on a set of nine tests withthe first three containing 5 H

2S and 95 natural gas The

equivalence ratios were 120601 = 072 120601 = 100 and 120601 = 126

Journal of Combustion 7

0 5 10 15

0

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4 Channel 5

05

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

0

05

120601120601

071

079

101

127

238

071

079

101

127

238

Figure 10 From bottom tests 29 27 28 30 and 49 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richH2S-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

0 5 10 15

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

1

126

Channel 5

05

05

05

0

0

0

Pres

sure

(MPa

)

05

05

05

120601

072

1

126

120601

Figure 11 From bottom tests 32 31 and 33 Comparison of pressure records from channels 4 and 5 Lean stoichiometric and rich 5H2S95 NG-air mixtures Pressure is shown on the left vertical axis while the equivalence ratio is given on the right vertical axis

The following experiments were all conducted with 120601 = 1 butwith increasing hydrogen sulfide content The H

2S fractions

in natural gas were 5 10 20 50 80 90 and 95Figure 11 shows that by keeping the H

2S-to-NG ratio

constant at 5 95 and varying the equivalence ratio 120601 = 072and 120601 = 126 give quite similar pressure levels 05MPa inthe obstructed part and 03MPa in the smooth section Thestoichiometric experiment resulted in the fastest pressure riseand a peak pressure of more than 13MPa A shock wave

of 04MPa was recorded in the smooth section The richmixture (120601 = 126) resulted in strong flame acceleration05MPa recorded on channel 4 and a pressure wave in thesmooth section

With the equivalence ratio kept constant at 1 and the H2S

content in the fuel varied from 0 to 100 the pressure didnot change much except for some spikes as seen in Figure 12The pressure is shown on the left vertical axis and the H

2S

content in the fuel is shown on the right vertical axis Time is

8 Journal of Combustion

0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)

Pres

sure

(MPa

)

Channel 4

0

5

10

20

50

80

90

95

100

2S

in N

G0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)Pr

essu

re (M

Pa)

Channel 5

0

5

10

20

50

80

90

95

100

2S

in N

G

H

H

Figure 12 From bottom tests 23 31 34 35 36 37 39 40 and 28 Comparison of pressure records from channels 4 and 5The mixture variesfrom pure natural gas in the fuel (bottom) to pure H

2S in the fuel (top) All experiments are stoichiometric mixtures

shown on the horizontal axis The pressure in the obstructedpart was recorded between 08 and 1MPa and the shockpropagating in the smooth section was about 03 to 035MPaand reflected at 05MPa

5 Discussion

The experimental study for pure natural gas and air showedthat the flame propagated fast when the equivalence ratiowas lower than 127 producing strong deflagrations in theexperimental setupThe pressure results showed that the rateof energy release increased as the flame propagated throughthe square pipe The richest natural gas mixture investigatedwas 120601 = 127 and thatmixture resulted in a slow pressure risebelieved to be due to a slow burning velocity of the flame

The explosion pressures for lean H2S-air were slightly

lower than the pressures for lean NG-airThe lower explosionpressures were to some extent a result of the lower expansionratio of the H

2S-air flame compared with the other fuels The

expansion ratio (120590 = 120588119906120588119887) of H

2S is about 66 while it is 76

for NG This results in a lower flame speed less turbulenceand therefore a lower pressure rise

By comparing the H2S-air mixtures with mixtures of

natural gas and air as shown in Figure 10 and Figure 8 it wasobserved experimentally that natural gas and H

2S result in

a fast flame for 120601 = 072 On the rich side (120601 = 127) thehydrogen sulfide accelerated as a fast flame while the naturalgas was slowThis was expected due to the wider flammabilityregion of H

2S [10] compared with NG

The experiments with stoichiometric H2S-NG-air

showed that the flame in the experimental setup producedstrong deflagrations with high pressures in the obstructedpart of the experimental setup The pressures seen with

0 5 10 20 50 80 90 9510004

05

06

07

08

09

1

11

12

13

14

2S in fuel

Pm

ax(M

Pa)

Ch 2

Ch 4

Ch 5

H

Figure 13Maximumpressure from experimentsThepressure fromchannels 2 4 and 5 for various H

2S contents in the fuel

channel 4 in tests with 90 and 95 H2S in the fuel (135

and 115MPa) indicate that the compression heating of thereactants caused local ignition in a hot spot

Comparing the maximum pressure from channels 2 4and 5 a trend is observed in Figure 13 in which themaximumpressure decreases as the H

2S content in the fuel increases

however the spikes are also observed when plotting themaximum pressure for three channels when the hydrogensulfide content was varied These spikes correspond to 90

Journal of Combustion 9

Channel 4

02

Channel 5

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

02

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

Figure 14 Maximum pressure for different equivalence ratios for pure NG pure H2S and 5 H

2S in NG

and 95 H2S in the fuel as well as 5 and 10 H

2S in the

fuelCompared to the constant volume and constant pressure

calculations in Figure 1 it is clear that the pressure spikes orig-inate from different phenomena One possible explanationcould be a more sensitive mixture when small amounts ofH2S are added to natural gas or the opposite A reduction in

chemical induction delay time could lead to local explosionsin heated volumes of reactants These local explosions arevery hard to determine even with full view of the channel butother studies have shown that they are more likely to occur inthe obstructed part rather than in the unobstructed parts (Lee[20])

By comparing Figures 13 and 1 it can be seen that thepressure on channel 4 (section with obstacles) exceeds theconstant volume pressure The equilibrium pressure and theexpansion ratio do not explain the spikes seen in Figure 13

Hot spots and local ignition are closely related to defla-gration to detonation transition (DDT) which results in highpressure No DDT was recorded in these experiments butthe pressure spikes suggest that local explosions could haveoccurred

There are always uncertainties when reporting the max-imum pressure since it is measured at one position Otherspikes that may occur in other sections of the experimentalsetup may be missed by the transducer recording

By keeping the H2S content in the fuel constant and

changing the equivalence ratio differences are observed inthe combustion Figure 14 shows the maximum pressureresults from the tests with 100 NG 100 H

2S and 5 H

2S

in NG (mix) for different equivalence ratios

The addition of 5 H2S to the natural gas makes the

mixture more reactive and therefore results in a higher pres-sure than that with pure NG and pure H

2S Another notable

effect is that the mixture becomes much more insensitiveto changes in the equivalence ratio when comparing themaximumpressure from channel 5 that is it produces higherpressure on both lean and rich sides compared with purefuels

A comparison of the pressure in the obstructed sectionand the smooth section with and without 5 hydrogensulfide is shown in Figures 15 and 16 Figure 15 shows thestoichiometric case and the two pressure records fromchannel 4 and the two pressure records from channel 5 havethe same shape and orderThis indicates a similar combustionprocess

When comparing the explosion pressures with the richcases (Figure 16) it is seen that there is a major change inthe pressure recordings when comparing the same channelThe pure NG burns slowly (a) while the mixed fuel (b)burns much faster and results in a strong pressure wave inthe smooth section This is a significant change caused bythe addition of relatively small amounts of hydrogen sulfideto the fuel There is still more to investigate regarding thecombustion of hydrocarbons and sulfur compounds

These experiments are smallmedium scale and the scaleeffects of hydrogen sulfide and natural gas explosions are stillunknown however the presence of hot spots and pressurespikes suggests that DDT might occur if the scale was largerIt was suggested byMoen [15] that the use of a denser obstaclefield in experiments would increase the turbulence and flamespeed

10 Journal of Combustion

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 1 channel 4 100 NG 120601 = 1 channel 5 100 NG

(a)

5 H2S and 95 NG5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 15 Comparison of explosion pressures for 120601 = 1 in the obstructed section (channel 4) and the smooth section (channel 5) (a) 100NG and (b) NG with 5 H

2S

6 Conclusion

Only limited data are available in the open literature onH2S-air deflagrations and especially H

2S and natural gas

mixtures Data for explosions at conditions supporting strongflame acceleration are lacking In the present work we havesuccessfully performed such experiments and obtained newand unique experimental data for explosions with hydrogensulfide and natural gas mixtures A comparison to purenatural gas is also included

(i) Pure fuels hydrogen sulfide has a wide flammabilityregion compared with methane and propane asshown in the literature In this study H

2S-air mix-

tures produced lower explosion pressures at lean-to-stoichiometric compositions relative to natural gasOn the rich side the H

2S-air mixtures produced

higher explosion pressures(ii) Fuel mixtures at 120601 = 1 a decrease in the maximum

pressure was observed when increasing amounts ofhydrogen sulfide were added to the natural gasThere were however somemaximum pressure spikesobserved for 90 and 95 H

2S in NG as well as for

5 and 10H2S in NGThese spikes could be a result

of a local explosion of compressed reactants but theydid not develop into detonations

(iii) Rich fuel mixtures rich NGwith 5 hydrogen sulfideis more reactive than pure rich NG When 5 H

2S

was added to the NG at 120601 = 1 the result was similarto pure NG but with spikes When the stoichiometrywas changed to120601 = 127 the result was a fast flame anda strong pressure wave formation in the 5 mixturewhile the pure NG had a slow deflagration and a slowand low pressure riseThe 5mixed fuel also showeddecreased sensitivity to changes in the equivalenceratio when the maximum pressures from channel 5were investigated These results are important to theprocess and petroleum industry

For further work it is suggested that the experimentalresults are compared to numerical simulations using com-mercial and academic softwareThere is also a need for a thor-ough study of the laminar properties of H

2S-hydrocarbon-

air mixtures Further experimental investigations should beconducted with higher and lower blockage ratios Largerscale experiments could reveal the possibility of DDT in

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

6 Journal of Combustion

0 5 10 15

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

099

111

127

Channel 5

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

120601

072

099

111

127

120601

Figure 8 From bottom tests 24 23 25 and 26 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richNG-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

obstructed section was lower than that in the stoichiometricexperiment while the shock wave in the smooth section wasalmost equal The richest experiment (104 fuel in air 120601 =127) resulted in a slow flame and a very slow pressure riserecorded on all pressure transducers

42Hydrogen Sulfide andAirMixtures Results fromfive testswith the pure H

2S-air mixture are presented The H

2S con-

centration ranged from 9 to 25 (see Table 1) where 124is the stoichiometric concentration The pressure recordsfrom the stoichiometric experiment are shown in Figure 9The overall phenomenon is similar to the stoichiometricnatural gas experiment The initial slow burning and thesubsequent development to a faster turbulent flame are seenin the pressure plot The pressure levels on channels 1 to 4are lower than in the NG experiment indicating that thisexperiment burned slower The shock wave in the smoothsection was roughly the same as in the NG experiment

Figure 10 shows a comparison plot of the hydrogen sulfideexperiments with the pressure shown on the left vertical axisand the equivalence ratio shown on the right vertical axisThehorizontal axis shows the time The leanest mixture was 9H2S in air (120601 = 071) and showed a pressure rise of about

03MPa It did not result in a shock in the smooth sectionof the setup The recorded pressure wave was about 02MPaand it reflected at the endwall and obstacleThe slightly richermixture of 10 (120601 = 079) showed a 03MPa shock wavepropagating in the smooth section of the experimental setupIn the obstructed part 05MPa was recorded at channel 4

The stoichiometric mixture resulted in a 035MPa shockin the smooth section while 075MPa was recorded in theobstructed section

0 5 10 15Time (ms)

0

05

1

15

2

25

3

35

4

45

5

Pres

sure

(MPa

)+di

stan

ce (m

)

Figure 9 Pressure records from the stoichiometric H2S-air mixture

(test 28) Channels 1ndash6 are shown from bottom to top The pressurelevels are offset an amount equal to the distance (m) from theignition end

The experiment with 120601 = 127 corresponding to 151H2S in air was very similar to the stoichiometric case with

only 005MPa lower pressure in the smooth section and theobstructed section Due to the wide flammability region ofH2S 120601 = 238 was also investigated it resulted in a very slow

flame and a low pressure increase of about 01MPa

43 H2S-Natural Gas-Air Experiments Results and Discus-

sion Experiments were performed on a set of nine tests withthe first three containing 5 H

2S and 95 natural gas The

equivalence ratios were 120601 = 072 120601 = 100 and 120601 = 126

Journal of Combustion 7

0 5 10 15

0

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4 Channel 5

05

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

0

05

120601120601

071

079

101

127

238

071

079

101

127

238

Figure 10 From bottom tests 29 27 28 30 and 49 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richH2S-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

0 5 10 15

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

1

126

Channel 5

05

05

05

0

0

0

Pres

sure

(MPa

)

05

05

05

120601

072

1

126

120601

Figure 11 From bottom tests 32 31 and 33 Comparison of pressure records from channels 4 and 5 Lean stoichiometric and rich 5H2S95 NG-air mixtures Pressure is shown on the left vertical axis while the equivalence ratio is given on the right vertical axis

The following experiments were all conducted with 120601 = 1 butwith increasing hydrogen sulfide content The H

2S fractions

in natural gas were 5 10 20 50 80 90 and 95Figure 11 shows that by keeping the H

2S-to-NG ratio

constant at 5 95 and varying the equivalence ratio 120601 = 072and 120601 = 126 give quite similar pressure levels 05MPa inthe obstructed part and 03MPa in the smooth section Thestoichiometric experiment resulted in the fastest pressure riseand a peak pressure of more than 13MPa A shock wave

of 04MPa was recorded in the smooth section The richmixture (120601 = 126) resulted in strong flame acceleration05MPa recorded on channel 4 and a pressure wave in thesmooth section

With the equivalence ratio kept constant at 1 and the H2S

content in the fuel varied from 0 to 100 the pressure didnot change much except for some spikes as seen in Figure 12The pressure is shown on the left vertical axis and the H

2S

content in the fuel is shown on the right vertical axis Time is

8 Journal of Combustion

0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)

Pres

sure

(MPa

)

Channel 4

0

5

10

20

50

80

90

95

100

2S

in N

G0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)Pr

essu

re (M

Pa)

Channel 5

0

5

10

20

50

80

90

95

100

2S

in N

G

H

H

Figure 12 From bottom tests 23 31 34 35 36 37 39 40 and 28 Comparison of pressure records from channels 4 and 5The mixture variesfrom pure natural gas in the fuel (bottom) to pure H

2S in the fuel (top) All experiments are stoichiometric mixtures

shown on the horizontal axis The pressure in the obstructedpart was recorded between 08 and 1MPa and the shockpropagating in the smooth section was about 03 to 035MPaand reflected at 05MPa

5 Discussion

The experimental study for pure natural gas and air showedthat the flame propagated fast when the equivalence ratiowas lower than 127 producing strong deflagrations in theexperimental setupThe pressure results showed that the rateof energy release increased as the flame propagated throughthe square pipe The richest natural gas mixture investigatedwas 120601 = 127 and thatmixture resulted in a slow pressure risebelieved to be due to a slow burning velocity of the flame

The explosion pressures for lean H2S-air were slightly

lower than the pressures for lean NG-airThe lower explosionpressures were to some extent a result of the lower expansionratio of the H

2S-air flame compared with the other fuels The

expansion ratio (120590 = 120588119906120588119887) of H

2S is about 66 while it is 76

for NG This results in a lower flame speed less turbulenceand therefore a lower pressure rise

By comparing the H2S-air mixtures with mixtures of

natural gas and air as shown in Figure 10 and Figure 8 it wasobserved experimentally that natural gas and H

2S result in

a fast flame for 120601 = 072 On the rich side (120601 = 127) thehydrogen sulfide accelerated as a fast flame while the naturalgas was slowThis was expected due to the wider flammabilityregion of H

2S [10] compared with NG

The experiments with stoichiometric H2S-NG-air

showed that the flame in the experimental setup producedstrong deflagrations with high pressures in the obstructedpart of the experimental setup The pressures seen with

0 5 10 20 50 80 90 9510004

05

06

07

08

09

1

11

12

13

14

2S in fuel

Pm

ax(M

Pa)

Ch 2

Ch 4

Ch 5

H

Figure 13Maximumpressure from experimentsThepressure fromchannels 2 4 and 5 for various H

2S contents in the fuel

channel 4 in tests with 90 and 95 H2S in the fuel (135

and 115MPa) indicate that the compression heating of thereactants caused local ignition in a hot spot

Comparing the maximum pressure from channels 2 4and 5 a trend is observed in Figure 13 in which themaximumpressure decreases as the H

2S content in the fuel increases

however the spikes are also observed when plotting themaximum pressure for three channels when the hydrogensulfide content was varied These spikes correspond to 90

Journal of Combustion 9

Channel 4

02

Channel 5

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

02

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

Figure 14 Maximum pressure for different equivalence ratios for pure NG pure H2S and 5 H

2S in NG

and 95 H2S in the fuel as well as 5 and 10 H

2S in the

fuelCompared to the constant volume and constant pressure

calculations in Figure 1 it is clear that the pressure spikes orig-inate from different phenomena One possible explanationcould be a more sensitive mixture when small amounts ofH2S are added to natural gas or the opposite A reduction in

chemical induction delay time could lead to local explosionsin heated volumes of reactants These local explosions arevery hard to determine even with full view of the channel butother studies have shown that they are more likely to occur inthe obstructed part rather than in the unobstructed parts (Lee[20])

By comparing Figures 13 and 1 it can be seen that thepressure on channel 4 (section with obstacles) exceeds theconstant volume pressure The equilibrium pressure and theexpansion ratio do not explain the spikes seen in Figure 13

Hot spots and local ignition are closely related to defla-gration to detonation transition (DDT) which results in highpressure No DDT was recorded in these experiments butthe pressure spikes suggest that local explosions could haveoccurred

There are always uncertainties when reporting the max-imum pressure since it is measured at one position Otherspikes that may occur in other sections of the experimentalsetup may be missed by the transducer recording

By keeping the H2S content in the fuel constant and

changing the equivalence ratio differences are observed inthe combustion Figure 14 shows the maximum pressureresults from the tests with 100 NG 100 H

2S and 5 H

2S

in NG (mix) for different equivalence ratios

The addition of 5 H2S to the natural gas makes the

mixture more reactive and therefore results in a higher pres-sure than that with pure NG and pure H

2S Another notable

effect is that the mixture becomes much more insensitiveto changes in the equivalence ratio when comparing themaximumpressure from channel 5 that is it produces higherpressure on both lean and rich sides compared with purefuels

A comparison of the pressure in the obstructed sectionand the smooth section with and without 5 hydrogensulfide is shown in Figures 15 and 16 Figure 15 shows thestoichiometric case and the two pressure records fromchannel 4 and the two pressure records from channel 5 havethe same shape and orderThis indicates a similar combustionprocess

When comparing the explosion pressures with the richcases (Figure 16) it is seen that there is a major change inthe pressure recordings when comparing the same channelThe pure NG burns slowly (a) while the mixed fuel (b)burns much faster and results in a strong pressure wave inthe smooth section This is a significant change caused bythe addition of relatively small amounts of hydrogen sulfideto the fuel There is still more to investigate regarding thecombustion of hydrocarbons and sulfur compounds

These experiments are smallmedium scale and the scaleeffects of hydrogen sulfide and natural gas explosions are stillunknown however the presence of hot spots and pressurespikes suggests that DDT might occur if the scale was largerIt was suggested byMoen [15] that the use of a denser obstaclefield in experiments would increase the turbulence and flamespeed

10 Journal of Combustion

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 1 channel 4 100 NG 120601 = 1 channel 5 100 NG

(a)

5 H2S and 95 NG5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 15 Comparison of explosion pressures for 120601 = 1 in the obstructed section (channel 4) and the smooth section (channel 5) (a) 100NG and (b) NG with 5 H

2S

6 Conclusion

Only limited data are available in the open literature onH2S-air deflagrations and especially H

2S and natural gas

mixtures Data for explosions at conditions supporting strongflame acceleration are lacking In the present work we havesuccessfully performed such experiments and obtained newand unique experimental data for explosions with hydrogensulfide and natural gas mixtures A comparison to purenatural gas is also included

(i) Pure fuels hydrogen sulfide has a wide flammabilityregion compared with methane and propane asshown in the literature In this study H

2S-air mix-

tures produced lower explosion pressures at lean-to-stoichiometric compositions relative to natural gasOn the rich side the H

2S-air mixtures produced

higher explosion pressures(ii) Fuel mixtures at 120601 = 1 a decrease in the maximum

pressure was observed when increasing amounts ofhydrogen sulfide were added to the natural gasThere were however somemaximum pressure spikesobserved for 90 and 95 H

2S in NG as well as for

5 and 10H2S in NGThese spikes could be a result

of a local explosion of compressed reactants but theydid not develop into detonations

(iii) Rich fuel mixtures rich NGwith 5 hydrogen sulfideis more reactive than pure rich NG When 5 H

2S

was added to the NG at 120601 = 1 the result was similarto pure NG but with spikes When the stoichiometrywas changed to120601 = 127 the result was a fast flame anda strong pressure wave formation in the 5 mixturewhile the pure NG had a slow deflagration and a slowand low pressure riseThe 5mixed fuel also showeddecreased sensitivity to changes in the equivalenceratio when the maximum pressures from channel 5were investigated These results are important to theprocess and petroleum industry

For further work it is suggested that the experimentalresults are compared to numerical simulations using com-mercial and academic softwareThere is also a need for a thor-ough study of the laminar properties of H

2S-hydrocarbon-

air mixtures Further experimental investigations should beconducted with higher and lower blockage ratios Largerscale experiments could reveal the possibility of DDT in

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Journal of Combustion 7

0 5 10 15

0

0

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4 Channel 5

05

05

05

05

05

0

0

0

0

Pres

sure

(MPa

)

05

05

05

05

0

05

120601120601

071

079

101

127

238

071

079

101

127

238

Figure 10 From bottom tests 29 27 28 30 and 49 Comparison of pressure records from channels 4 and 5 for lean stoichiometric and richH2S-air mixtures Pressure is shown on left vertical axis while the equivalence ratio is given on the right vertical axis

0 5 10 15

0

0

0

Time (ms)0 5 10 15

Time (ms)

Pres

sure

(MPa

)

Channel 4

072

1

126

Channel 5

05

05

05

0

0

0

Pres

sure

(MPa

)

05

05

05

120601

072

1

126

120601

Figure 11 From bottom tests 32 31 and 33 Comparison of pressure records from channels 4 and 5 Lean stoichiometric and rich 5H2S95 NG-air mixtures Pressure is shown on the left vertical axis while the equivalence ratio is given on the right vertical axis

The following experiments were all conducted with 120601 = 1 butwith increasing hydrogen sulfide content The H

2S fractions

in natural gas were 5 10 20 50 80 90 and 95Figure 11 shows that by keeping the H

2S-to-NG ratio

constant at 5 95 and varying the equivalence ratio 120601 = 072and 120601 = 126 give quite similar pressure levels 05MPa inthe obstructed part and 03MPa in the smooth section Thestoichiometric experiment resulted in the fastest pressure riseand a peak pressure of more than 13MPa A shock wave

of 04MPa was recorded in the smooth section The richmixture (120601 = 126) resulted in strong flame acceleration05MPa recorded on channel 4 and a pressure wave in thesmooth section

With the equivalence ratio kept constant at 1 and the H2S

content in the fuel varied from 0 to 100 the pressure didnot change much except for some spikes as seen in Figure 12The pressure is shown on the left vertical axis and the H

2S

content in the fuel is shown on the right vertical axis Time is

8 Journal of Combustion

0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)

Pres

sure

(MPa

)

Channel 4

0

5

10

20

50

80

90

95

100

2S

in N

G0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)Pr

essu

re (M

Pa)

Channel 5

0

5

10

20

50

80

90

95

100

2S

in N

G

H

H

Figure 12 From bottom tests 23 31 34 35 36 37 39 40 and 28 Comparison of pressure records from channels 4 and 5The mixture variesfrom pure natural gas in the fuel (bottom) to pure H

2S in the fuel (top) All experiments are stoichiometric mixtures

shown on the horizontal axis The pressure in the obstructedpart was recorded between 08 and 1MPa and the shockpropagating in the smooth section was about 03 to 035MPaand reflected at 05MPa

5 Discussion

The experimental study for pure natural gas and air showedthat the flame propagated fast when the equivalence ratiowas lower than 127 producing strong deflagrations in theexperimental setupThe pressure results showed that the rateof energy release increased as the flame propagated throughthe square pipe The richest natural gas mixture investigatedwas 120601 = 127 and thatmixture resulted in a slow pressure risebelieved to be due to a slow burning velocity of the flame

The explosion pressures for lean H2S-air were slightly

lower than the pressures for lean NG-airThe lower explosionpressures were to some extent a result of the lower expansionratio of the H

2S-air flame compared with the other fuels The

expansion ratio (120590 = 120588119906120588119887) of H

2S is about 66 while it is 76

for NG This results in a lower flame speed less turbulenceand therefore a lower pressure rise

By comparing the H2S-air mixtures with mixtures of

natural gas and air as shown in Figure 10 and Figure 8 it wasobserved experimentally that natural gas and H

2S result in

a fast flame for 120601 = 072 On the rich side (120601 = 127) thehydrogen sulfide accelerated as a fast flame while the naturalgas was slowThis was expected due to the wider flammabilityregion of H

2S [10] compared with NG

The experiments with stoichiometric H2S-NG-air

showed that the flame in the experimental setup producedstrong deflagrations with high pressures in the obstructedpart of the experimental setup The pressures seen with

0 5 10 20 50 80 90 9510004

05

06

07

08

09

1

11

12

13

14

2S in fuel

Pm

ax(M

Pa)

Ch 2

Ch 4

Ch 5

H

Figure 13Maximumpressure from experimentsThepressure fromchannels 2 4 and 5 for various H

2S contents in the fuel

channel 4 in tests with 90 and 95 H2S in the fuel (135

and 115MPa) indicate that the compression heating of thereactants caused local ignition in a hot spot

Comparing the maximum pressure from channels 2 4and 5 a trend is observed in Figure 13 in which themaximumpressure decreases as the H

2S content in the fuel increases

however the spikes are also observed when plotting themaximum pressure for three channels when the hydrogensulfide content was varied These spikes correspond to 90

Journal of Combustion 9

Channel 4

02

Channel 5

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

02

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

Figure 14 Maximum pressure for different equivalence ratios for pure NG pure H2S and 5 H

2S in NG

and 95 H2S in the fuel as well as 5 and 10 H

2S in the

fuelCompared to the constant volume and constant pressure

calculations in Figure 1 it is clear that the pressure spikes orig-inate from different phenomena One possible explanationcould be a more sensitive mixture when small amounts ofH2S are added to natural gas or the opposite A reduction in

chemical induction delay time could lead to local explosionsin heated volumes of reactants These local explosions arevery hard to determine even with full view of the channel butother studies have shown that they are more likely to occur inthe obstructed part rather than in the unobstructed parts (Lee[20])

By comparing Figures 13 and 1 it can be seen that thepressure on channel 4 (section with obstacles) exceeds theconstant volume pressure The equilibrium pressure and theexpansion ratio do not explain the spikes seen in Figure 13

Hot spots and local ignition are closely related to defla-gration to detonation transition (DDT) which results in highpressure No DDT was recorded in these experiments butthe pressure spikes suggest that local explosions could haveoccurred

There are always uncertainties when reporting the max-imum pressure since it is measured at one position Otherspikes that may occur in other sections of the experimentalsetup may be missed by the transducer recording

By keeping the H2S content in the fuel constant and

changing the equivalence ratio differences are observed inthe combustion Figure 14 shows the maximum pressureresults from the tests with 100 NG 100 H

2S and 5 H

2S

in NG (mix) for different equivalence ratios

The addition of 5 H2S to the natural gas makes the

mixture more reactive and therefore results in a higher pres-sure than that with pure NG and pure H

2S Another notable

effect is that the mixture becomes much more insensitiveto changes in the equivalence ratio when comparing themaximumpressure from channel 5 that is it produces higherpressure on both lean and rich sides compared with purefuels

A comparison of the pressure in the obstructed sectionand the smooth section with and without 5 hydrogensulfide is shown in Figures 15 and 16 Figure 15 shows thestoichiometric case and the two pressure records fromchannel 4 and the two pressure records from channel 5 havethe same shape and orderThis indicates a similar combustionprocess

When comparing the explosion pressures with the richcases (Figure 16) it is seen that there is a major change inthe pressure recordings when comparing the same channelThe pure NG burns slowly (a) while the mixed fuel (b)burns much faster and results in a strong pressure wave inthe smooth section This is a significant change caused bythe addition of relatively small amounts of hydrogen sulfideto the fuel There is still more to investigate regarding thecombustion of hydrocarbons and sulfur compounds

These experiments are smallmedium scale and the scaleeffects of hydrogen sulfide and natural gas explosions are stillunknown however the presence of hot spots and pressurespikes suggests that DDT might occur if the scale was largerIt was suggested byMoen [15] that the use of a denser obstaclefield in experiments would increase the turbulence and flamespeed

10 Journal of Combustion

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 1 channel 4 100 NG 120601 = 1 channel 5 100 NG

(a)

5 H2S and 95 NG5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 15 Comparison of explosion pressures for 120601 = 1 in the obstructed section (channel 4) and the smooth section (channel 5) (a) 100NG and (b) NG with 5 H

2S

6 Conclusion

Only limited data are available in the open literature onH2S-air deflagrations and especially H

2S and natural gas

mixtures Data for explosions at conditions supporting strongflame acceleration are lacking In the present work we havesuccessfully performed such experiments and obtained newand unique experimental data for explosions with hydrogensulfide and natural gas mixtures A comparison to purenatural gas is also included

(i) Pure fuels hydrogen sulfide has a wide flammabilityregion compared with methane and propane asshown in the literature In this study H

2S-air mix-

tures produced lower explosion pressures at lean-to-stoichiometric compositions relative to natural gasOn the rich side the H

2S-air mixtures produced

higher explosion pressures(ii) Fuel mixtures at 120601 = 1 a decrease in the maximum

pressure was observed when increasing amounts ofhydrogen sulfide were added to the natural gasThere were however somemaximum pressure spikesobserved for 90 and 95 H

2S in NG as well as for

5 and 10H2S in NGThese spikes could be a result

of a local explosion of compressed reactants but theydid not develop into detonations

(iii) Rich fuel mixtures rich NGwith 5 hydrogen sulfideis more reactive than pure rich NG When 5 H

2S

was added to the NG at 120601 = 1 the result was similarto pure NG but with spikes When the stoichiometrywas changed to120601 = 127 the result was a fast flame anda strong pressure wave formation in the 5 mixturewhile the pure NG had a slow deflagration and a slowand low pressure riseThe 5mixed fuel also showeddecreased sensitivity to changes in the equivalenceratio when the maximum pressures from channel 5were investigated These results are important to theprocess and petroleum industry

For further work it is suggested that the experimentalresults are compared to numerical simulations using com-mercial and academic softwareThere is also a need for a thor-ough study of the laminar properties of H

2S-hydrocarbon-

air mixtures Further experimental investigations should beconducted with higher and lower blockage ratios Largerscale experiments could reveal the possibility of DDT in

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

8 Journal of Combustion

0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)

Pres

sure

(MPa

)

Channel 4

0

5

10

20

50

80

90

95

100

2S

in N

G0 2 4 6 8 10

005

005

005

005

005

005

005

005

005

Time (ms)Pr

essu

re (M

Pa)

Channel 5

0

5

10

20

50

80

90

95

100

2S

in N

G

H

H

Figure 12 From bottom tests 23 31 34 35 36 37 39 40 and 28 Comparison of pressure records from channels 4 and 5The mixture variesfrom pure natural gas in the fuel (bottom) to pure H

2S in the fuel (top) All experiments are stoichiometric mixtures

shown on the horizontal axis The pressure in the obstructedpart was recorded between 08 and 1MPa and the shockpropagating in the smooth section was about 03 to 035MPaand reflected at 05MPa

5 Discussion

The experimental study for pure natural gas and air showedthat the flame propagated fast when the equivalence ratiowas lower than 127 producing strong deflagrations in theexperimental setupThe pressure results showed that the rateof energy release increased as the flame propagated throughthe square pipe The richest natural gas mixture investigatedwas 120601 = 127 and thatmixture resulted in a slow pressure risebelieved to be due to a slow burning velocity of the flame

The explosion pressures for lean H2S-air were slightly

lower than the pressures for lean NG-airThe lower explosionpressures were to some extent a result of the lower expansionratio of the H

2S-air flame compared with the other fuels The

expansion ratio (120590 = 120588119906120588119887) of H

2S is about 66 while it is 76

for NG This results in a lower flame speed less turbulenceand therefore a lower pressure rise

By comparing the H2S-air mixtures with mixtures of

natural gas and air as shown in Figure 10 and Figure 8 it wasobserved experimentally that natural gas and H

2S result in

a fast flame for 120601 = 072 On the rich side (120601 = 127) thehydrogen sulfide accelerated as a fast flame while the naturalgas was slowThis was expected due to the wider flammabilityregion of H

2S [10] compared with NG

The experiments with stoichiometric H2S-NG-air

showed that the flame in the experimental setup producedstrong deflagrations with high pressures in the obstructedpart of the experimental setup The pressures seen with

0 5 10 20 50 80 90 9510004

05

06

07

08

09

1

11

12

13

14

2S in fuel

Pm

ax(M

Pa)

Ch 2

Ch 4

Ch 5

H

Figure 13Maximumpressure from experimentsThepressure fromchannels 2 4 and 5 for various H

2S contents in the fuel

channel 4 in tests with 90 and 95 H2S in the fuel (135

and 115MPa) indicate that the compression heating of thereactants caused local ignition in a hot spot

Comparing the maximum pressure from channels 2 4and 5 a trend is observed in Figure 13 in which themaximumpressure decreases as the H

2S content in the fuel increases

however the spikes are also observed when plotting themaximum pressure for three channels when the hydrogensulfide content was varied These spikes correspond to 90

Journal of Combustion 9

Channel 4

02

Channel 5

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

02

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

Figure 14 Maximum pressure for different equivalence ratios for pure NG pure H2S and 5 H

2S in NG

and 95 H2S in the fuel as well as 5 and 10 H

2S in the

fuelCompared to the constant volume and constant pressure

calculations in Figure 1 it is clear that the pressure spikes orig-inate from different phenomena One possible explanationcould be a more sensitive mixture when small amounts ofH2S are added to natural gas or the opposite A reduction in

chemical induction delay time could lead to local explosionsin heated volumes of reactants These local explosions arevery hard to determine even with full view of the channel butother studies have shown that they are more likely to occur inthe obstructed part rather than in the unobstructed parts (Lee[20])

By comparing Figures 13 and 1 it can be seen that thepressure on channel 4 (section with obstacles) exceeds theconstant volume pressure The equilibrium pressure and theexpansion ratio do not explain the spikes seen in Figure 13

Hot spots and local ignition are closely related to defla-gration to detonation transition (DDT) which results in highpressure No DDT was recorded in these experiments butthe pressure spikes suggest that local explosions could haveoccurred

There are always uncertainties when reporting the max-imum pressure since it is measured at one position Otherspikes that may occur in other sections of the experimentalsetup may be missed by the transducer recording

By keeping the H2S content in the fuel constant and

changing the equivalence ratio differences are observed inthe combustion Figure 14 shows the maximum pressureresults from the tests with 100 NG 100 H

2S and 5 H

2S

in NG (mix) for different equivalence ratios

The addition of 5 H2S to the natural gas makes the

mixture more reactive and therefore results in a higher pres-sure than that with pure NG and pure H

2S Another notable

effect is that the mixture becomes much more insensitiveto changes in the equivalence ratio when comparing themaximumpressure from channel 5 that is it produces higherpressure on both lean and rich sides compared with purefuels

A comparison of the pressure in the obstructed sectionand the smooth section with and without 5 hydrogensulfide is shown in Figures 15 and 16 Figure 15 shows thestoichiometric case and the two pressure records fromchannel 4 and the two pressure records from channel 5 havethe same shape and orderThis indicates a similar combustionprocess

When comparing the explosion pressures with the richcases (Figure 16) it is seen that there is a major change inthe pressure recordings when comparing the same channelThe pure NG burns slowly (a) while the mixed fuel (b)burns much faster and results in a strong pressure wave inthe smooth section This is a significant change caused bythe addition of relatively small amounts of hydrogen sulfideto the fuel There is still more to investigate regarding thecombustion of hydrocarbons and sulfur compounds

These experiments are smallmedium scale and the scaleeffects of hydrogen sulfide and natural gas explosions are stillunknown however the presence of hot spots and pressurespikes suggests that DDT might occur if the scale was largerIt was suggested byMoen [15] that the use of a denser obstaclefield in experiments would increase the turbulence and flamespeed

10 Journal of Combustion

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 1 channel 4 100 NG 120601 = 1 channel 5 100 NG

(a)

5 H2S and 95 NG5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 15 Comparison of explosion pressures for 120601 = 1 in the obstructed section (channel 4) and the smooth section (channel 5) (a) 100NG and (b) NG with 5 H

2S

6 Conclusion

Only limited data are available in the open literature onH2S-air deflagrations and especially H

2S and natural gas

mixtures Data for explosions at conditions supporting strongflame acceleration are lacking In the present work we havesuccessfully performed such experiments and obtained newand unique experimental data for explosions with hydrogensulfide and natural gas mixtures A comparison to purenatural gas is also included

(i) Pure fuels hydrogen sulfide has a wide flammabilityregion compared with methane and propane asshown in the literature In this study H

2S-air mix-

tures produced lower explosion pressures at lean-to-stoichiometric compositions relative to natural gasOn the rich side the H

2S-air mixtures produced

higher explosion pressures(ii) Fuel mixtures at 120601 = 1 a decrease in the maximum

pressure was observed when increasing amounts ofhydrogen sulfide were added to the natural gasThere were however somemaximum pressure spikesobserved for 90 and 95 H

2S in NG as well as for

5 and 10H2S in NGThese spikes could be a result

of a local explosion of compressed reactants but theydid not develop into detonations

(iii) Rich fuel mixtures rich NGwith 5 hydrogen sulfideis more reactive than pure rich NG When 5 H

2S

was added to the NG at 120601 = 1 the result was similarto pure NG but with spikes When the stoichiometrywas changed to120601 = 127 the result was a fast flame anda strong pressure wave formation in the 5 mixturewhile the pure NG had a slow deflagration and a slowand low pressure riseThe 5mixed fuel also showeddecreased sensitivity to changes in the equivalenceratio when the maximum pressures from channel 5were investigated These results are important to theprocess and petroleum industry

For further work it is suggested that the experimentalresults are compared to numerical simulations using com-mercial and academic softwareThere is also a need for a thor-ough study of the laminar properties of H

2S-hydrocarbon-

air mixtures Further experimental investigations should beconducted with higher and lower blockage ratios Largerscale experiments could reveal the possibility of DDT in

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Journal of Combustion 9

Channel 4

02

Channel 5

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

02

04

06

08

1

12

14

Pm

ax(M

Pa)

05 1 15

5 mix

120601

H2SNG

Figure 14 Maximum pressure for different equivalence ratios for pure NG pure H2S and 5 H

2S in NG

and 95 H2S in the fuel as well as 5 and 10 H

2S in the

fuelCompared to the constant volume and constant pressure

calculations in Figure 1 it is clear that the pressure spikes orig-inate from different phenomena One possible explanationcould be a more sensitive mixture when small amounts ofH2S are added to natural gas or the opposite A reduction in

chemical induction delay time could lead to local explosionsin heated volumes of reactants These local explosions arevery hard to determine even with full view of the channel butother studies have shown that they are more likely to occur inthe obstructed part rather than in the unobstructed parts (Lee[20])

By comparing Figures 13 and 1 it can be seen that thepressure on channel 4 (section with obstacles) exceeds theconstant volume pressure The equilibrium pressure and theexpansion ratio do not explain the spikes seen in Figure 13

Hot spots and local ignition are closely related to defla-gration to detonation transition (DDT) which results in highpressure No DDT was recorded in these experiments butthe pressure spikes suggest that local explosions could haveoccurred

There are always uncertainties when reporting the max-imum pressure since it is measured at one position Otherspikes that may occur in other sections of the experimentalsetup may be missed by the transducer recording

By keeping the H2S content in the fuel constant and

changing the equivalence ratio differences are observed inthe combustion Figure 14 shows the maximum pressureresults from the tests with 100 NG 100 H

2S and 5 H

2S

in NG (mix) for different equivalence ratios

The addition of 5 H2S to the natural gas makes the

mixture more reactive and therefore results in a higher pres-sure than that with pure NG and pure H

2S Another notable

effect is that the mixture becomes much more insensitiveto changes in the equivalence ratio when comparing themaximumpressure from channel 5 that is it produces higherpressure on both lean and rich sides compared with purefuels

A comparison of the pressure in the obstructed sectionand the smooth section with and without 5 hydrogensulfide is shown in Figures 15 and 16 Figure 15 shows thestoichiometric case and the two pressure records fromchannel 4 and the two pressure records from channel 5 havethe same shape and orderThis indicates a similar combustionprocess

When comparing the explosion pressures with the richcases (Figure 16) it is seen that there is a major change inthe pressure recordings when comparing the same channelThe pure NG burns slowly (a) while the mixed fuel (b)burns much faster and results in a strong pressure wave inthe smooth section This is a significant change caused bythe addition of relatively small amounts of hydrogen sulfideto the fuel There is still more to investigate regarding thecombustion of hydrocarbons and sulfur compounds

These experiments are smallmedium scale and the scaleeffects of hydrogen sulfide and natural gas explosions are stillunknown however the presence of hot spots and pressurespikes suggests that DDT might occur if the scale was largerIt was suggested byMoen [15] that the use of a denser obstaclefield in experiments would increase the turbulence and flamespeed

10 Journal of Combustion

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 1 channel 4 100 NG 120601 = 1 channel 5 100 NG

(a)

5 H2S and 95 NG5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 15 Comparison of explosion pressures for 120601 = 1 in the obstructed section (channel 4) and the smooth section (channel 5) (a) 100NG and (b) NG with 5 H

2S

6 Conclusion

Only limited data are available in the open literature onH2S-air deflagrations and especially H

2S and natural gas

mixtures Data for explosions at conditions supporting strongflame acceleration are lacking In the present work we havesuccessfully performed such experiments and obtained newand unique experimental data for explosions with hydrogensulfide and natural gas mixtures A comparison to purenatural gas is also included

(i) Pure fuels hydrogen sulfide has a wide flammabilityregion compared with methane and propane asshown in the literature In this study H

2S-air mix-

tures produced lower explosion pressures at lean-to-stoichiometric compositions relative to natural gasOn the rich side the H

2S-air mixtures produced

higher explosion pressures(ii) Fuel mixtures at 120601 = 1 a decrease in the maximum

pressure was observed when increasing amounts ofhydrogen sulfide were added to the natural gasThere were however somemaximum pressure spikesobserved for 90 and 95 H

2S in NG as well as for

5 and 10H2S in NGThese spikes could be a result

of a local explosion of compressed reactants but theydid not develop into detonations

(iii) Rich fuel mixtures rich NGwith 5 hydrogen sulfideis more reactive than pure rich NG When 5 H

2S

was added to the NG at 120601 = 1 the result was similarto pure NG but with spikes When the stoichiometrywas changed to120601 = 127 the result was a fast flame anda strong pressure wave formation in the 5 mixturewhile the pure NG had a slow deflagration and a slowand low pressure riseThe 5mixed fuel also showeddecreased sensitivity to changes in the equivalenceratio when the maximum pressures from channel 5were investigated These results are important to theprocess and petroleum industry

For further work it is suggested that the experimentalresults are compared to numerical simulations using com-mercial and academic softwareThere is also a need for a thor-ough study of the laminar properties of H

2S-hydrocarbon-

air mixtures Further experimental investigations should beconducted with higher and lower blockage ratios Largerscale experiments could reveal the possibility of DDT in

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

10 Journal of Combustion

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 1 channel 4 100 NG 120601 = 1 channel 5 100 NG

(a)

5 H2S and 95 NG5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 15 Comparison of explosion pressures for 120601 = 1 in the obstructed section (channel 4) and the smooth section (channel 5) (a) 100NG and (b) NG with 5 H

2S

6 Conclusion

Only limited data are available in the open literature onH2S-air deflagrations and especially H

2S and natural gas

mixtures Data for explosions at conditions supporting strongflame acceleration are lacking In the present work we havesuccessfully performed such experiments and obtained newand unique experimental data for explosions with hydrogensulfide and natural gas mixtures A comparison to purenatural gas is also included

(i) Pure fuels hydrogen sulfide has a wide flammabilityregion compared with methane and propane asshown in the literature In this study H

2S-air mix-

tures produced lower explosion pressures at lean-to-stoichiometric compositions relative to natural gasOn the rich side the H

2S-air mixtures produced

higher explosion pressures(ii) Fuel mixtures at 120601 = 1 a decrease in the maximum

pressure was observed when increasing amounts ofhydrogen sulfide were added to the natural gasThere were however somemaximum pressure spikesobserved for 90 and 95 H

2S in NG as well as for

5 and 10H2S in NGThese spikes could be a result

of a local explosion of compressed reactants but theydid not develop into detonations

(iii) Rich fuel mixtures rich NGwith 5 hydrogen sulfideis more reactive than pure rich NG When 5 H

2S

was added to the NG at 120601 = 1 the result was similarto pure NG but with spikes When the stoichiometrywas changed to120601 = 127 the result was a fast flame anda strong pressure wave formation in the 5 mixturewhile the pure NG had a slow deflagration and a slowand low pressure riseThe 5mixed fuel also showeddecreased sensitivity to changes in the equivalenceratio when the maximum pressures from channel 5were investigated These results are important to theprocess and petroleum industry

For further work it is suggested that the experimentalresults are compared to numerical simulations using com-mercial and academic softwareThere is also a need for a thor-ough study of the laminar properties of H

2S-hydrocarbon-

air mixtures Further experimental investigations should beconducted with higher and lower blockage ratios Largerscale experiments could reveal the possibility of DDT in

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Journal of Combustion 11

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15120601 = 127 channel 4 100 NG 120601 = 127 channel 5 100 NG

(a)

5 H2S and 95 NG 5 H2S and 95 NG

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

0 5 10 15Time (ms)

Pres

sure

(MPa

)

minus05

0

05

1

15

(b)

Figure 16 Comparison of explosion pressures for 120601 = 127 in the obstructed section (channel 4) and the smooth section (channel 5) (a)100 NG and (b) NG with 5 H

2S

H2S mixtures and investigations of rich mixtures should be

conducted to better understand the effects of added hydrogensulfide to natural gas

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors gratefully acknowledge the financial support byStatoil ASA

References

[1] Z Jianwen L Da and F Wenxing ldquoAnalysis of chemicaldisasters caused by release of hydrogen sulfide-bearing naturalgasrdquo Procedia Engineering vol 26 pp 1878ndash1890 2011

[2] I Glassman and R Yetter Combustion Academic Press 4thedition 2008

[3] H Selim A Al Shoaibi and A K Gupta ldquoEffect of H2S in

methaneair flames on sulfur chemistry and products specia-tionrdquo Applied Energy vol 88 no 8 pp 2593ndash2600 2011

[4] M U Alzueta R Bilbao and P Glarborg ldquoInhibition andsensitization of fuel oxidation by SO

2rdquo Combustion and Flame

vol 127 no 4 pp 2234ndash2251 2001[5] J O L Wendt E C Wootan and T L Corley ldquoPostflame

behavior of nitrogenous species in the presence of fuel sulfurI Rich moist COArO

2flamesrdquo Combustion and Flame vol

49 no 1ndash3 pp 261ndash274 1983[6] M Frenklach J H Lee J N White and W C Gardiner Jr

ldquoOxidation of hydrogen sulfiderdquoCombustion and Flame vol 41pp 1ndash16 1981

[7] D S Chamberlin and D R Clarke ldquoFlame speed of hydrogensulfiderdquo Proceedings of the Symposium on Combustion vol 1-2no C pp 33ndash35 1948

[8] P F Kurz ldquoInfluence of hydrogen sulfide on flame speed ofpropane-air mixturesrdquo Industrial amp Engineering Chemistry vol45 no 10 pp 2361ndash2366 1953

[9] G J Gibbs and H F Calcote ldquoEffect of molecular structure onburning velocityrdquo Journal of Chemical and Engineering Datavol 4 no 3 pp 226ndash237 1959

[10] A P Bozek and V Rowe ldquoFlammable mixture analysis forhazardous area classificationrdquo in Proceedings of the 55th IEEE

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

12 Journal of Combustion

Petroleum and Chemical Industry Technical Conference (PCICrsquo08) pp 1ndash10 September 2008

[11] R Pahl and K Holtappels ldquoExplosions limits of H2SCO

2air

and H2SN2airrdquo Chemical Engineering amp Technology vol 28

no 7 pp 746ndash749 2005[12] H Coward and G Jones Limits of Flammability of Gases and

Vapors Bulletin 503 US Bureau of Mines Juneau Alaska USA1952

[13] A Sulmistras I O Moen and A J Saber ldquoDetonations inhydrogen sulphide-air cloudsrdquo Suffield Memorandum 1140Defence Research Establishment Suffield Alberta Canada1985

[14] A J Saber A Sulmistras I O Moen and P A ThibaultldquoInvestigation of the explosion hazard of hydrogen sulphide(Phase I)rdquo Research Report Defence Research EstablishmentSuffield Alberta Canada 1985

[15] I O Moen ldquoInvestigation of the explosion hazard of hydrogensulphide (phase II)rdquo Research Report Defence Research Estab-lishment Suffield Alberta Canada 1986

[16] I OMoen A Sulmistras B H Hjertager and J R Bakke ldquoTur-bulent flame propagation and transition to detonation in largefuel-air cloudsrdquo Symposium (International) on Combustion vol21 no 1 pp 1617ndash1627 1988

[17] J E Shepherd A Sulmistras A J Saber and I O MoenldquoChemical kinetics and cellular structure of detonations inhydrogen sulfide and airrdquo inProceedings of the 10th InternationalCommittee on the Dynamics of Explosions and Reactive Systems(ICDERS rsquo85) p 294 Berkeley Calif USA 1985

[18] L Vervisch B Labegorre and J Reveillon ldquoHydrogen-sulphuroxy-flame analysis and single-step flame tabulated chemistryrdquoFuel vol 83 no 4-5 pp 605ndash614 2004

[19] S R Turns An Introduction to Combustion McGraw-Hill NewYork NY USA 2nd edition 2000

[20] J H S LeeThe Detonation Phenomena Cambridge UniversityPress New York NY USA 1st edition 2008

[21] G Ciccarelli and S Dorofeev ldquoFlame acceleration and transi-tion to detonation in ductsrdquo Progress in Energy and CombustionScience vol 34 no 4 pp 499ndash550 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of