testo-flue gas in industry 3-27-2008

8/9/2019 Testo-Flue Gas in Industry 3-27-2008

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2. Edit ion

Practical guide for

Emission and Process

MeasurementsFlue Gas Analysis in Industry


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1. Foreword 52. The combustion process 62.1 Energy a nd combus tion 62.2 C ombus tion pla nts 82.3 Fuels 92.4 C ombus tion a ir; excess a ir va lue 10

2.4.1 S toichiometric a nd exces s-air co mbustion; ma teria l ba la nce 102.4.2 Determina tion of the excess a ir va lue 122.4.3 Req uired combus tion a ir volume 14

2.4.4 G as volume; d ilution effec t; reference va lues 142.5 Flue ga s 162.6 C a lorific va lue; effic iency; flue ga s los s 192.7 Dew point; condensa te 22

3. Analysis of process gases in industry 253.1 C ombus tion optimiza tion 273.2 P rocess control 30

3.2.1 Firing pla nts 303.2.2 Indus tria l furna ces 31

3.2.3 Thermochemica l surfa ce trea tment 313.2.4 S a fety mea surements 32

3.3 Emiss ion control 333.3.1 Lega l ba s is in G erma ny 333.3.2 Lega l ins truc tions in G erma ny 353.3.3 Emiss ion Monitoring in the US A 413.3.4 Flue ga s c lea ning 44

4. Gas analysis technique 474.1 Terms of g a s a na lys is (selec tion) 47

4.1.1 C oncentra tions ; concentra tion convers ions 474.1.2 S a mple conditioning 524.1.3 C ross-sens itivity 544.1.4 C a libra tion 55

4.2 G a s a nalysis 564.2.1 Terms ; a pplica tion a rea s; a na lyzers ; sensors 564.2.2 Mea suring princ iples (used by Tes to) 61

5. Application of Testo gas analyzers 70

5.1 P ow er genera tion 715.1.1 S olid-fuel-fired furna ces 715.1.2 G a s-fired furna ces 735.1.3 G a s turbine pla nts 74

Content


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5.1.4 Oil-fired furna ces 765.1.5 C oa l-fired pow er s ta tion 775.1.6 C ombined hea ting a nd pow er s ta tions 795.1.7 G a s a nd s tea m pow er s ta tions 81

5.2 Wa s te d isposa l 825.2.1 Wa s te inc inera tion 825.2.2 Wa s te pyrolys is 855.2.3 Therma l ga s inc inera tion 86

5.3 S tone a nd c la y indus try 88

5.3.1 C ement produc tion 885.3.2 C era mic/P orcela in produc tion 905.3.3 P roduc tion of bricks 925.3.4 G la ss production 935.3.5 P roduc tion of q uicklime 96

5.4 Meta l indus try 985.4.1 P rocess ing of ores 985.4.2 Iron produc tion 995.4.3 P roduc tion of ra w s teel 101

5.4.4 C oke oven pla nt 1025.4.5 Aluminum produc tion 1045.4.6 S urfa ce trea tment 105

5.5 C hemica l/petrochemica l indus try 1075.5.1 P rocess hea ter 1075.5.2 Refineries 1085.5.3 Fla res 1105.5.4 Res idues inc inera tion 111

5.6 Others 1135.6.1 C rema toria 1135.6.2 Eng ine tes t beds 113

6. Testo gas analyzer 1156.1 The compa ny 1156.2 C ha ra c teris tic a na lyzer fea tures 1176.3 Indus tria l ga s a na lyzers (overview ) 1206.4 G a s a na lyzer a ccessories (overview ) 1236.5 Technica l description a nd da ta (S elec tion) 126

Index 134Address lis t 137

Content


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2. The combustion process

2.1 Energy and combustion

Energyis defined as the ability of a material or system to perform labor. Energy exists indifferent modifications which can be classified into six categories as follows:• Mecha nica l energy (flow ing wa ter, driving ca r)• Therma l energy (boiling wa ter, ga s fla me)• Chemica l energy (chemica l rea ction, burning proce ss , explos ion)• Electrica l energy (ca r ba ttery, electricity)• Electroma gnetic energy (light ra dia tion, microw a ve ra dia tion)• Nuclea r energy (nuclear fiss ion)

The d ifferent energy mo difica tions ca n be converted into ea ch other, w ithin a nideally closed system, with the sum remaining constant (conservation of energy).In practice, however, energy losses occur during the conversion process therebyreducing the efficiency.The natural energy carriers (coal, natural gas, crude oil, sun radiation, water

power etc.) are described as primary energies, while the term secondary energies stands for what is received from energy conversions (electricity, heat, etc.). En-ergy carriers differ in energy content. For comparison reasons the energy con-tent is described as amount of energy which could be released from a certainq uantity of a n energy c a rrier in ca se of its tota l comb ustion. The energy s ca le unitis 1 J oule [J ]. S ome energy c ontent va lues a re g iven in ta ble 1.

Table 1: Energy content of fuels

Energy ca rrier, 1 kg of... Energy co ntent [MJ ]B row n coa l 9,0Wood 14,7Ha rd coa l 29,3Natural gas (1 m3) 31,7Crude oil 42,6Fuel oil, light 42,7G a soline 43,5

For comparison: 1 kWh 3,6


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Combustion

is the conversion of primary chemical energy contained in fuels such as coal, oilor wo od into hea t (se co nda ry energy) through the proces s of oxida tion. C omb us-tion therefore is the technical term for the chemical reaction of oxygen with thecombustible components of fuels including the release of energy.Combustion processes proceed with high temperatures (up to 1000 °C anda bo ve). The o xygen req uired for the c omb ustion is supplied a s pa rt of the c om-bustion air fed to the process. From that a considerable volume of exhaust gas(flue gas, off gas) is produced together with, depending on the kind of fuel, a cer-tain amount of residues (slag, ash).

OxidationTerm for a ll chemica l rea c tions of o xyge n w ith other sub s ta nces . Oxida tionprocesses proceed with the release of energy and are of great importance inma ny technica l (comb ustion) a nd biolog ica l (brea thing) a rea s.

Greenhouse effectP rincipa lly the g reenhouse effec t is a natura l proc es s a nd one o f the reas ons forhuman life on earth. Without this effect, the global average temperature nearthe ea rth surfac e w ould b e a t -18 ° C instea d o f + 15 ° C a s it is; the ea rth wouldbe inhabita ble for huma n be ings ! The c a use for this na tura l effect is tha t thelight radiation of the sun passes through the air and is absorbed by the earth.The ea rth then re-ra dia tes this e nergy a s hea t w a ves tha t a re a bs orbed by thea ir, spec ific a lly by ca rbo n dioxide. The a ir thus b eha ves like g la ss in a g reen-house, a llow ing the pa ss a ge of light, but not of hea t.By excessive firing of fossil fuels (emission of carbon dioxide) and release ofcertain substances from chemical industry and agriculture (halogen hydrocar-bons, methane e.a.) the natural effect will be amplified causing a slow increaseof the surfac e tempera ture w ith influence to the c lima tic cond itions .

More de ta ils to the ob jec tive o f co mbus tion a re g iven in cha pter 2.4


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2.2 Combustion plants

Combustion plants are facilities that generate heat by burning solid, liquid orga seo us fuels . They a re req uired for ma ny tasks, e .g .• heating (heating pla nts, building heating)• generat ion of electrica l energy• genera tion of steam a nd hot wa ter for use in process industries• ma nufac turing certain ma teria ls (cement, gla ss , cera mics )• thermal surfac e trea tment of meta llic pa rts• incinera tion of wa ste ma teria ls a nd residues

See detailed application examples in chapter 5!

Combustion occurs in a combustion chamber; other control units are required forfuel supply and fuel distribution, combustion air supply, heat transfer, exhaust gascleaning and for discharge of exhaust gases and combustion residues (ash, slag).S olid fuels a re fired on a fixed or fluidized bed or in a flue d ust/a ir mixture. Liq uidfuels are fed to the burning chamber together with the combustion air as mist.Gaseous fuels are mixed with combustion air already in the burner.

The exha ust g a se s of c omb ustion pla nts c onta in the rea ction prod ucts of fuel a ndcombustion air and residual substances such as particulate matter (dust), sulfuroxides, nitrogen oxides and carbon monoxide. When burning coal, HCl and HFmay be present in the flue gas as well as hydrocarbons and heavy metals in caseof incineration of waste materials.In many countries, as part of a national environmental protection program, ex-haust gases must comply with strict governmental regulations regarding the limit

values of pollutants such as dust, sulfur and nitrogen oxides and carbon monox-ide. To mee t thes e limit va lues comb ustion p la nts a re eq uipped w ith flue g a scleaning systems such as gas scrubbers and dust filters.For further information on the regulations see chapter 3.


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2.3 Fuels

a re a va ila ble in d ifferent forms a nd compo sition:• Solid fuels (hard coal, bituminous coal, peat, wood, straw) contain carbon (C),

hydrogen (H2), oxygen (O2), and smaller quantities of sulfur (S), nitrogen (N2),and water (H2O). A major problem when handling such fuels is the formationof la rge q uantities of a sh, pa rticula te ma tter a nd s oot.

• Liquid fuels derive mainly from crude oil and can be classified into light,medium and heavy fuel oils. Light fuel oil (i.e. diesel fuel) is widely used in smallco mbustion pla nts.

• Gaseous fuels are a mixture of combustible (CO, H2 and hydrocarbons) andnon-co mbustible g a se s. Tod a y very o ften na tura l g a s is used , w hich c onta insmethane (CH4) a s the ma in co mponent.

The know led ge o f fuel compo s ition is important for a n optimum a nd ec ono mica lcombustion process. Increasing percentage of incombustible (inert) fuel compo-nents red uces the g ros s a nd net ca lorific value of the fuel a nd increa se s co ntami-nation of the furnace walls. Increasing water content raises the water dew pointa nd c ons umes energy to eva pora te w a ter in the flue ga s . The sulfur conta ined inthe fuel is burnt (oxidized) to SO2 and SO3, w hich, a t tempera tures below the dew point, may lead to the formation of aggressive sulfureous and sulfuric acids. Seea lso cha pter 2.7.

The c ompos ition o f some s olid fuels is s how n in the follow ing ta b le:

Table 2: Composition of solid fuels

For details of gross and net calorific value see chapter 2.6

Fuel

Ma ss co ntent in %Carbon in dry

material S ulfur Ash Wa ter

Ha rd coa l 80-90 1 5 3-10

B ituminous coa l 60-70 2 5 30-60

Wood (a ir-dried) 50 1 1 15

P ea t 50-60 1 5 15-30

9


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2.4 Combustion air; excess air value

The oxyg en req uired for a comb ustion proc es s is s upplied a s pa rt of the c omb us-tion air which consists of (see table 3) nitrogen (N2), oxygen (O2), a small amountof carbon dioxide and rare gases, and a variable content of water vapor. In someproc es ses pure o xyge n or a a ir/oxyg en mixture is used for the c omb ustion.The c omb ustion a ir components , exc ept o xyge n, a re a ll conta ined in the res ultingraw flue gas.

Table 3: Composition of c lean and dry air

2.4.1 Stoichiometric and excess-air combustion; material balanceThe minima l a mount o f oxyg en req uired to burn a ll co mbus tible compo nentscompletely depends on the fuel composition. 1 kg of carbon e.g. requires 2,67 kgoxygen to be burnt completely, 1 kg of hydrogen requires 8 kg oxygen, 1 kg ofsulfur however only 1 kg oxygen! Combustion occuring at these exact gasquantity ratios is called ideal combustion or stoichiometric combustion.

The releva nt eq ua tions a re

C a rbon: C + O2 C O2Hydrogen: 2H2 + O2 2H2O

S ulfur: S + O2 S O2

The idea l combustion proc ed ure is s how n sc hema tica lly in figure 1. The a mountof oxygen supplied to the combustion is just sufficient to burn all fuel combustibles

c omp letely. No oxyg en no r c omb ustibles a re left . The e xce s s a ir va lue(ex.air) is 1 in this case.

C omponent C ontent [%]Nitrogen 78,07

Oxygen 20,95

C a rbon d ioxide 0,03

Hydrogen 0,01

Argon 0,93

Neon 0,0018


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Fig. 1: Stoichiometric combustion model

In a real process this ideal oxygen volume is not sufficient for complete burningbeca use of insuffic ient mixing of fuel a nd o xyge n. The c omb ustion process ,therefore, must be supplied with more than the stoichiometric volume of oxygen.This a dditiona l a mount of comb ustion a ir is c a lled excess air and the ratio of thetotal air volume to the stoichiometric air volume is the excess air value ex.air;another expression for that is (lambda) . Fig . 2 show s this exces s a ir co mbus-tion model (ex.air>1) schematically.

Fig. 2: Excess air combustion model

Consequently the highest combustion efficiency is achieved with a (limited) ex-cess volume of oxygen, i.e. ex.air >1 (oxidizing atmosphere).The exc es s a ir va lue is of g rea t importance for a n optimum co mbus tion proc es sa nd eco nomic pla nt opera tion:• Unnecessa ry high excess a ir volumes reduce combustion temperatures a nd

increases the loss of energy released unused into the atmosphere via the hot

flue gas stream.• With too little exces s a ir some comb ustible c omponents of the fuel rema in

unburned . This mea ns reduc ed co mbustion effic ienc y a nd increa sed a ir pol-lution by emitting the unburned components to the atmosphere. 11

Resid. fuel


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C ombustion pla nt Ra nge of ex.a ir Excess O2C ombustion eng ines 0,8-1,2 8 ... 20 %

G a s burner 1,1-1,3 10 ... 30 %Oil burner 1,2-1,5 20 ... 50 %

C oa l pow der burner 1,1-1,3 10 ... 30 %

B row n coa l roa s t 1,3-1,7 30 ... 70 %

Ta ble 4 show s va rious e xcess a ir va lue ra nge s o f spec ific types o f combus tion

proc es ses . In genera l: The sma ller the rea c tive surfa ce/ma ss volume ra tio of thefuel particles is the more excess air volume is required for optimum combustion.This is a lso c orrec t co nverse ly a nd the refore solid fuels a re g round a nd liq uidfuels are sprayed to get a larger reactive surface. Only a few processes existwhich are operated definitely at deficient air (ex.air


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For calculation of the excess air value from the measured values of CO 2 or O2 the

follow ing two formula s ma y b e use d:

CO2 ma x : fuel-spec ific ma ximum CO2 value (see table 7, page 21)CO and O2: mea sured or ca lcula ted co ncentra tion values in the flue ga s

Fig. 3: Combustion d iagram

For more information regarding the combustion diagram see chapter 3.1.

13

=C O 2 ma x

CO2 = 1 +

O 2

21 – O2


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2.4.3 Required combustion air volume

The a ctua lly req uired volume of c omb ustion a ir ca n be ca lcula ted• from the a ir volume needed for the idea l combustion

(depending on the kind of fuel),• the des ired excess oxygen va lue and• the rela tive oxygen c ontent of the used a ir or the air/oxyge n mixture

The oxygen c ontent of dry a ir a t 1 ba r pres sure is 20,95%. In pra c tice, how ever, ambient air is not dry, therefore the water content must also be conside-

red for correct air volume calculation.

2.4.4 Gas volume; dilution effect; reference values

Both combustion air and humidity (water vapor) increase the absolute gas vol-ume. Fig. 4 shows this effect for the combustion of 1 kg of fuel. At stoichiometricconditions (i.e. without excess air) appr. 10 m 3 exhaust gas are generated fromtha t a t dry res p. 11,2 m3 a t humid co nditions w hils t from the s a me a mount of fuel,burnt with 25% excess air at humid conditions, 13,9 m3 exhaust gas are gener-a ted . This is a d ilution e ffec t tha t reduces the relative concentration of the par-ticular flue gas components. For instance the concentration of SO2 is relatively reduced from 0,2% (stoich., dry) to 0,18% (stoich., humid) resp. to 0,14% (25%exces s a ir, humid) a nd the c ontent o f oxygen is red uced from 4,4% to 4%.S ee tab le 5 a nd fig . 4.

Table 5: Relative exhaust gas composition in % under different gas conditions

EA = Excess air

Nitrogen C O2 S O2 Wa ter OxygenS toich./dry 82,6 16 0,20 0 0

S toich./humid 74,7 14,4 0,18 10,7 0

25% EA/dry 82,8 12,7 0,16 0 4,4

25% EA/humid 75,6 11,6 0,14 8,7 4


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Fig. 4: Dilution effect o f flue gas through hum idity and excess air

Reference valuesConcentration values are typically reported in relation to a known resp. specifiedreference value. Only then can the measured value be comparable with othervalues, e.g. specified pollution limits.In pra ctice three definitions of s etting a referenc e a re us ed :

∞ Reference to a ce rtain value of dilution through excess air. For that the

oxyge n co ncentra tion is used a s reference mea sure b y the expres sion e.g .

Reference value 8% oxygen".∞ This reference is genera lly a pplied for reg ula tory repo rting . S ometimes it is

a lso used for a specific a pplica tion s o tha t the oxyge n value is cha ra cteristicfor the standard operational conditions of the plant.

∞ Reference to a ce rtain value of dilution through the humidity content of

the ga s. Typica lly the ga s tempera ture is expres se d e.g . by " a t de w point of4 °C"; but expressions as "related to dry gas" are also used.

∞ Reference to the standard conditions of a gas. This refe rs to the influenc e

of pres sure a nd tempera ture o n the ga s volume. S ee cha pter 4.1.1.

15

3

2

2


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2.5 Exhaust (flue) gas and exhaust gas composition

Exhaust gas generated through combustion processes is called flue gas or stackgas. Its composition depends on the type of fuel and the combustion conditions,e.g. the air ratio value. Many flue gas components are air pollutants and musttherefore, due to governmental regulations (see chapter 3.3), be eliminated orminimized by special cleaning procedures before the gas is released to the at-mos phere. The exha ust ga s in its o rig ina l s ta tus is c a lled ra w ga s , a fter c lea ningit is ca lled clea n ga s.The ma in flue ga s compo nents a re d iscus sed in the follow ing.

Nitrogen (N2)Nitrogen is the ma in cons tituent (79 Vol. %) of a ir. This colorles s , odorles s a ndtasteless gas is fed to the combustion as part of the combustion air but is notinvolved directly in the combustion process. It acts as ballast material and carrierof wasted heat and is released again into the atmosphere. However, minor quan-tities of this combustion air related nitrogen are, together with the nitrogen re-leased from the fuel, responsible for the formation of the dangerous nitrogen ox-ides (see below).

Carbon Dioxide (CO2)Carbon dioxide is a colorless and odorless gas with a slightly sour taste. It is pro-duced during all combustion processes including respiration. It contributes con-siderably to the green house effect through its ability to filter heat radiation (seepa ge 7). In a mbient a ir CO2 co ncentra tion is 0,03%; a t conc entra tions of over 15%loss of consciousness will occur immediately.

Water vapor (humidity)The hyd rog en c onta ined in the fuel w ill rea c t w ith oxyg en a nd fo rm w a ter (H2O).This , tog ether w ith the w a ter content of the fuel and the c omb ustion a ir, exis tseither as flue gas humidity (at higher temperatures) or as condensate (at lowertemperatures).

Oxygen (O2)The portion of oxyg en that ha s not been co nsumed by the c omb ustion proc es srema ins a s pa rt of the flue ga s a nd is a mea sure for the efficiency of the co mbus-

tion. It is used for the determination of combustion parameters and acts also asreference value.


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Carbon Monoxide (CO)

Carbon monoxide is a colorless, odorless, toxic gas. It is formed predominantlyduring incomplete combustion of fossil fuels and other materials containing car-bon. Outdoors in ambient conditions CO is not very dangerous for human beingsbecause of its fast reaction to CO2 with oxygen. However, indoors or within en-closed spaces it must be considered as very dangerous, as at concentrations ofonly 700 ppm in the b rea thing a ir it w ill lea d to dea th w ithin a few hours! Theworking place threshold value is 50 ppm.

Oxides of nitrogen (NO and NO2, sum formula NOx)

In combustion processes nitrogen of the fuel and, at high temperatures, also ofthe combustion air reacts to a certain amount with oxygen of the combustion aira nd forms firs t nitric oxide (fuel-NO a nd thermal-NO). This NO will rea c t w ith o xy-gen a lrea dy in the sta ck a nd/or la ter on in the a tmos phere a nd form the da nge rousnitrogen dioxide (NO2). Both oxides are toxic! Specifically NO2 is a da ngerous lungpoison and contributes, in connection with sun light, to the formation ofozone. Extensive technologies are used to clean flue gases from NOx, e.g theSelective Catalytic Reaction (SCR) process. In addition to that, special measures(e.g. staged air supply) have been developed to reduce the formation of nitrogen

oxide s a lrea dy during c omb ustion proc es s. S ee c hapter 3.3.4.

Sulfur dioxide (SO2)Sulfur dioxide is a colorless, toxic gas with a pungent smell. It is formed throughoxidation of sulfur that is present in the fuel.The w orking pla ce threshold limit va lue is 5 ppm. Tog ether with w a ter or co nden-sate sulfurous acid (H2S O3 ) and sulfuric acid (H2S O4) are formed, both of whichare responsible for various damages to e.g. nature and buildings (acid rain).S crubb ing technolog ies a re used to c lea n flue g a ses from sulfur oxides.

Hydrogen sulfide (H2S)Hydrog en s ulfide is a toxic a nd , even a t very low conc entra tions (a ppr. 2,5 µg/m3),very odorous gas. It is a component of crude oil and natural gas and is thereforepresent in refineries and Natural Gas plants but also generated during some otherindustrial processes and, as product of an incomplete combustion, in catalysts ofmoto r vehic les . H2S is removed from exhaust gases by conversion to SO2 throughcertain absorption processes or, for larger quantities, through reaction to ele-

mental sulfur (Claus process).


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2.6 Calorific value; combustion efficiency; flue gas loss

Gross and net calorific valueThe gross calorific value is a characteristic parameter of a fuel that describes thea mount of energy relea sed from the fuel during complete combustion in relation tothe a mount of fuel involved . The net ca lorific va lue is the energy relea sed les s thehea t of evapo ra tion of the w a ter vapo r a t a tempera ture of 25 ° C genera ted duringthe combustion, again related to the amount of fuel involved.The g ros s ca lorific va lue is princ ipa lly higher than the net va lue.

Condensing value boilersCondensing boilers are boilers that make use of the condensation heat of the fluegas added to the combustion heat by means of heat exchangers. Related to thenet calorific value these boilers can reach an efficiency of 107%. Condensate isformed, however; this process may transfer pollutants from the gas to the waterw hich ma y need spevia l disc ha rge co nside ra tions .

Combustion efficiencyCombustion efficiency is a value determined from input and output data of a com-bus tion proces s a t c ons ta nt opera tiona l co nditions . Tota l effic ienc y (it is a lw a ysbelow 100%) is the ratio between the total energy fed into the firing chamber andthe amount of energy available for the actual process (heating, melting, sinteringetc .). The to ta l efficiency va lue is compo sed a s follow s:• The term combustion efficiency describes the portion of the total energy (fed

to the combustion chamber) that is available in the combustion chamber afterthe c omb ustion.

• The term furnace efficiency depends on the furnac e d esign a nd operation a nd

describes the portion of the combustion energy which can finally be applied tothe process of interest.The to ta l effic ienc y is the c omb ina tion of c omb ustion a nd furna ce effic ienc y.


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Energy balance of a combustion process; flue gas heat loss

At constant operation the sum of all energies fed into a combustion process isequal to the sum of all energies delivered by the process, see table 6.

Table 6: Contribut ions to energy balance of a combust ion plant

The mos t important a nd mo st neg a tive ba la nce contribution is the flue gas loss

(or efficiency). It depends (a) on the temperature difference between flue gasand combustion air, (b) the concentrations of O2 or CO2 in the flue gas and (c) onfuel-specific parameters, see table 7. Using condensing value boilers the flue gasloss is reduced considerably by utilizing the condensation heat and thus loweringthe flue ga s tempera ture a t the sa me time.

The flue ga s hea t los s ca n be ca lcula ted using the follow ing formula s (G erman):

FT: Flue ga s tempera ture

AT: Amb ient a ir tempera tureA2, B : Fue l-spec ific fa c to rs

(see table 7)21: Oxygen level in a irO2: Mea sured oxygen level

For solid fuels the factors A2 and B are zero. With that and using the factor f andthe value of CO2 (see table 7) the above formula will be simplified to the so calledSiegert Formula

Energ ies fes into the proces s Energ ies delivered by the proces s

Net calorific value of fuel andenergy of fuel

Sensible heat and chemical energy offlue ga s co mponents (flue ga s los s)

Hea t of combus tion a ir Hea t a nd ca lorific va lues of res iduesin sla g a nd a sh.

Heat equivalent of mechanical energyproduced in the plant Energy los se s through therma lconduction

Hea t c ontent o f work fuel fed to the fur-nance

Heat content of fuel released from thefurnance

Heat losses through furnance leaks

q A = (FT-AT) x + BA2

(21-O2)

q A = f xFT - AT

C O2

[ ]


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Fuel-specific factors used in the formula (German calculation) are listed in the

following table:

Table 7: Fuel-spec ific facto rs (German calculation)

Calculation formulae (British)

Flue gas loss (efficiency)

FT Flue ga s tempera tureAT Ambient tempera tureKgr, Kne t, K1 Fuel-spec ific fac tors , see table 7aX M + 9 x HM, H Fuel-spec ific fa c tors , see ta ble 7aQgr, Qne t Fuel-sp ec ific fac tors, s ee ta ble 7a

EffG = 100 - + +Kne t x (FT-AT) X x (210 + 2.1 x FT - 4.2 x AT) K1 x Qgr x CO

C O2 Qg r x 1000 Qne t x CO2 + CO[[ ] [ ] [ ]]

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Fuel A2 B f CO2 max

Fuel oil 0,68 0,007 - 15,4Na tura l ga s 0,65 0,009 - 11,9Liq uid ga s 0,63 0,008 - 13,9C oke, w ood 0 0 0,74 20,0

B riq uet 0 0 0,75 19,3

B row n coa l 0 0 0,90 19,2Ha rd coa l 0 0 0,60 18,5

C oke oven ga s 0,60 0,011 - -

Tow n ga s 0,63 0,011 - 11,6

Tes t g a s 0 0 - 13,0

EffG = 100 - + +Kgr x (FT-AT) X x (2488 + 2.1 x FT - 4.2 x AT) K1 x CO

CO2 Qgr x 1000 CO2 + C O[[ ] [ ] [ ]]


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FuelK

gr

Knet

CO2max

K1

K2 H M

Qgr

Qnet

O2 ref F Br

Na tura l g a s 0.350 0.390 11.9 40 44.3 24.4 0 53.42 48.16 3 0.2304

Fuel oilClas s D

0.480 0.510 15.4 53 56.4 13.0 0 45.60 42.80 3 0.2434

Fuel oilClass E,F,G

0.510 0.540 15.8 54 57.2 11.5 0.2 42.90 40.50 3 0.2545

Coa l 0.620 0.650 18.4 63 66.0 4.0 13.0 26.75 25.50 6 0.2561

Anthra c ite 0.670 0.690 19.1 65 66.5 3.0 12.0 29.65 28.95 6 0.2551

Coke LP G 0.750 0.760 20.6 70 71.1 0.4 10.0 27.9 27.45 6 0.2919

P ropa ne LP G 0.420 0.450 13.8 48 51.8 18.2 0 50.0 46.30 3 0.2341

B uta ne 0.430 0.460 14.1 48 51.6 17.2 0 49.30 45.80 3 0.2301

Fuel 1 0.350 0.390 11.9 40 44.3 24.4 0 53.42 48.16 3 0.2304

Fuel 2 0.480 0.510 15.4 53 56.4 13.0 0 45.60 42.80 3 0.2434

H: Hydrogen content of fuelM: Mois ture content of fuel

F B r: C o nve rs io n fa c to r mg /m

3

in g /G J

Factors of fuel 1 and fuel 2 set by the factory can be freely selected

Table 7a: Fuel-specific factors (British calculation)

2.7 Dew point; condensate

Dew point

The dew po int or dew point temperature of a gas is the temperature at which thew a ter va por co nta ined in the ga s is tra nsformed into the liq uid s ta te. This tra nsi-tion is ca lled co ndens a tion, the formed liq uid is ca lled co ndens a te. B elow the dew point temperature humidity (moisture) exists as liquid, above the dew point asgaseous component of the gas. An example for that is the formation and decom-position of fog or dew as a function of the temperature.The d ew point tempera ture is a function o f the mois ture c ontent o f the g a s: Thedew point of a ir w ith 30% moisture c ontent is a t a ppr. 70 ° C , w hile d ry a ir w ithonly 5% moisture c ontent ha s a dew point at a ppr. 35 ° C , see fig . 5.

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Fig. 5: Moisture content of air as function of dew point tmperature (1013 mbar)

For a n a na lyzer operated without samp le gas conditioning the dew point tempera-ture of the sample gas corresponds approximately with the ambient temperature,e.g, 25 °C. Comparison of measured values obtained from that with those of ana nalyzer with sa mple g a s co nditioning a t e.g. 5 ° C de w point tempera ture w ill show

a d ifferenc e o f appr. 3% due to this mois ture c ontent effect. S ee a lso cha pter 4.1.2

Heated sample lines; gas coolerFlue ga se s w ith e.g. 8% moisture c ontent ha ve a d ew point at a ppr. 40 ° C . Be low this temperature moisture will exist as liquid condensate resulting in two importantco nseq uences for the comb ustion pla nt as w ell a s the mea suring eq uipment:

• In ca se of sulfur oxides existing in the flue ga s, c orros ive sulfurous a nd/or

sulfuric acid will be formed at temperatures below 40 °C (e.g. in unheatedsample lines or analyzer parts) therefore damaging components coming intocontact with the condensate. For this reason, all components of the combus-tion proc es s upstrea m the ga s clea ning s crubb er should be kept a t tempera tu-res above the dew point.The s a me is true for components of the mea suring device including s a mpleprobe and sample lines that are in contact with the flue gas: All these partsshould be kept at temperatures above the dew point. Consequently heatedsample probes and sampling lines are used upstream the gas cooler. Other-w ise the eq uipment w ill be da ma ged a nd the mea sured values w ill be incorrec t.

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24

Another alternative to reduce or suppress the formation of condensate is the

use of a very high gas flow velocity in the sample lines, as developed andpatented by Testo. This princ iple utilize s turbulent flow a nd minima l res idenc etime a s the mec ha nism to keep the mo isture entra ined in the flue g a s . Thismethod replaces the heated sample line which is a very important benefit forporta ble a nalyzers beca use of the reduced pow er input req uirements.

• Depending on the g as cooler tempera ture, a certain amount of wa ter vapor iscondensed and removed in the cooled flue gas which results in the other gas

species (e.g. CO) showing (without any change in their absolute quantity) ahigher rela tive c onc entra tion va lue. Therefore, in order to c ompa re the res ultsof two different measurement methods the sample gases must have the sametemperature and humidity.

Consequently a sample gas cooler or a sample gas dryer are used to get thesa mple g a s to a defined a nd c ons ta nt temperature a nd level of humidity. Thisprocedure is called sample conditioning.

Note:• To cool a g as means to dry the ga s

a nd• In dry ga s the mea sured (rela tive) co ncentra tion va lues a re

higher tha n in the s a me g a s w ith a higher level of humidity

Tes to a na lyzers a re eq uipped w ith sa mple g a s co oler ac co rding to thePeltier principle:The joint surfa ce b etw een tw o d ifferent meta ls , w ith a n electric current flow ingthrough, is heated up or cooled down depending on the flow direction of the cur-rent. The coo ler of the tes to 350 a nd tes to 360 is d es igned to c oo l the sa mple g a sdo w n to + 3 ° C a nd to keep this tempera ture c ons tant. Therefore the temperatureand moisture extracted is constant.

Another w a ter remova l method operates a cc ording to thePermeation principle:These c oo lers, how ever, show so me disa dva ntag es :

a They cannot keep a specified d ew point a t a c onstant level a ndb they ma y be blocked through dust pa rticles a nd orga nics resulting in higherma intenance a nd spa re pa rt cos ts.


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3. Combustion analysis of process gases in industry

Combustion analysis (i.e. measuring technology for analyzing combustion gascompositions) is an indispensable tool for reliable and economical process controlin almost all industries. All combustion processes are concerned with productiona nd ma teria l trea tment proc es se s. Fig. 6 show s the various s eg ments of a c omb us-tion process from feed of fuel and combustion air to the furnace, the combustionitself w ith the variety o f co nnected proc es se s, up to flue g a s clea ning a nd e miss ioncontrol.

Fig. 6: Segments and variety of combust ion processes


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In all segments of a combustion process combustion analysis provides impor-

tant information about combustion details and composition of the flue gases.Thus c omb ustion a na lyzers a re indispens a ble proc es s d evices for relia ble a ndeconomical plant operation, to guarantee product quality and to comply withemiss ion reg ula tions .

Gas analyzers are offered in great variety by many manufacturers. Analyzers arebased on different measuring principles, mostly optimized for the analysis of cer-tain components. More details are available in chapter 4.

Testo gas analyzers are extensively utilized in industry for the analysis of com-bustion gases with the area of emission control being just one field of application.The follow ing a pplica tions a re w ell es ta blished :

1. Adjustment and service measurements for general plant upgrade pur-poses, for localization of process instabilities, for checks after repair work ora s prepa ra tion in a dva nce of reg ula tory mea surements.

2. Process measurements for combustion optimization analyzing fuel, com-

bustion air and combustion gases in order e.g. to reduce fuel costs, to im-prove pla nt effic ienc y or to extend the lifetime o f the pla nt. Thes e a pplica tionsare also related to emission control (see below) because optimized plant op-eration normally will cause a reduction of emission levels.

3. Process measurements for control of a defined gas atmosphere in spe-cial furnaces or kilns for processes such as burning (e.g. cement), sintering orsurfac e trea tment.

4. Process and emission measurements for function control of flue gascleaning installations.

5. Emission measurements at the stack to monitor the emission values of pol-lutants a nd to ensure complia nce w ith the offic ia l reg ula tions .


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3.1 Gas analysis for combustion optimization

Major contributions to combustion optimization are made by• Composit ion of fuel and combustion air• Ignit ion proced ure a nd combustion tempera ture• Details of burner and combustion chamber design• The fuel/a ir ra t io

For a g iven plant a nd a g iven fuel the optimum fuel/combustion a ir ra tio (ex.a irvalue) can be determined from gas analysis results using the combustion dia-

g ra m, see fig . 7. In this d ia gram the co ncentra tion of the ga s c omponents CO, C O2and O2 a re displa yed in function o f the exc es s exces s a ir va lue. The linerepres enting idea l co mbus tion w ithout a ny exc es s a ir (ex.a ir= 1) is in the c enter ofthe diagram; to the right the excess air value increases; air deficiency (ex.air


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The optimum ra nge of excess a ir for a pa rticula r comb ustion pla nt ca n be deter-

mined from the concentration values of CO2 and CO (CO2 alone is not definitedue to the curve maximum). Currently the O2-method is more often used.Sampling point locations may differ from plant to plant depending on the plantdesign a nd pla nt opera tor.

The functions sho w n in the comb ustion d ia g ra m a re subs ta ntia ted fo r the co m-bustion of hard coal in table 8:

Table 8: Air value, excess air and oxygen content

for the combustion process of hard coal

Economic relevanceOptimization of a combustion process through plant operation at the most

effec tive exc es s a ir level ha s , bes ides red uction o f emiss ion levels , the objec tive o fsaving fuel costs. B a sed on experience a nd d oc umented in the litera ture is the fac t,that reduction of oxygen excess of 1%-point, e.g. from 4,5% to 3,5%, will impro-ve the efficiency of the combustion plant by 1%. With fuel costs of $ 15 Mio. permonth for a middle sized power station this results in monthly cost savings of$ 30.000 if, by means of reliable gas analysis, the plant can be operated at only0,2%-point closer to the optimal excess air value than before! Similar savings arepos s ible if short time de via tions from optimum operation co nditions a re rec og nizedand eliminated early by using gas analysis continuously.

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Air va lue Excess air [%] Oxygen content [%]( dry flue gas)

0,9 Air defic iency Oxygen defic iency

1,0 0 0

1,1 10% 2

1,2 20% 3,5

1,3 30% 4,8

1,4 40% 6,2


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3.2 Combustion analysis for process control

3.2.1 Combustion plant for firing processesA process firing plant, in contrast to the well known boiler plants, is characterizedby a direct contact between the flame and the hot firing gases and a material orw ork piec es tha t sha ll be trea ted therma lly. The hea t a s w ell a s the spec ific a t-mosphere to which the material is exposed causes certain steps in their produc-tion proc es s.Produc tion of cement clinker is a good exa mple for such a firing proces s (se e a lsothe application examples in chapter 5.3):

• The moist ra w materia l is c rushed a nd dried using hot off gas esThe prec ipitated ra w mea l is hea ted up to 800 ° C by hot g a se s incounter-current

• C O2 is driven off the ra w mea l a t a ppr. 950 ° C in the c a lc ina tor througha multi-stage firing process (de-acidification)

• The ra w mea l together w ith ad ditives is finally s intered in the kiln a t a ppr.1400 °C.

Combustion analysis at these locations provides critical information with regard toexcess air values, to detect and calculate false air flows and to perform balancesfor ea ch s tep s epa ra tely. It is c ritic a l for the c a lc ina tor performa nce (mea surementof CO2 and O2) because a deficient level of calcination can cause considerablemalfunctions in kiln operation

During firing processes substances from the treated material may be released intothe "firing" gas and thus increase the emission rate of the flue gas. In some

ca se s, how ever, c omponents including polluta nts ma y b e tra nsferred from the g a sinto either the production material or into substances (e.g. slag) especially pro-vided for this purpos e. An exa mple is the c eme nt or lime industry whe re the sul-fur of the fuel is tra nsferred a s S O2 to the prod uct instea d of being relea sed to theatmosphere. Inversely during glass or brick production SO 2 will escape from thematerial and increase the level of emission considerably. Another example is anincreased CO content in processes where material and hot gases are in contact incounter-current, e.g. in rotating kilns. Heavy metals may be either integrated intothe burnt material (cement, lime) or released from the material into the flue gas

(g la s s or meta l industry).


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By measuring combustion parameters furnace design, flame guidance, furnace

tempera ture a nd c omb ustion a ir supply, the emiss ions ca used by the proc es s ca nbe red uced . For that po rta ble g a s a nalyzers provide the necess a ry informa tion.

3.2.2 Industrial furnacesIndustrial furnaces are used to produce steam and hot water or to heat up otherheat carrier materials. Industrial furnaces also include those that are used formaterial conversion e.g. in refineries or coke oven plants. Heat output of industrialfurnaces normally is in the MW range.

Comb ustion a na lys is in this a pplica tion a re fo r comb ustion optimiza tion, co ntrol offlue g a s c lea ning insta lla tion a nd monitoring of the pollutant e miss ions .

3.2.3 Thermochemical surface treatmentThermoc hemica l surfac e trea tment is a hea ting proc ed ure w ith the objec tive tomodify the property of the surface of parts or work pieces etc. by means of diffu-sion proc es se s. The pa rts a re expos ed to a hot ga s a tmosphere w ith certa in ele-ments d iffusing from the ga s into o r out of the ma teria l. This include s s tee l ha rd-

ening or the process of s toving co lors o r la cq uer in the ce ra mic indus try. Thermo-chemical processes are characterized by species and concentration of the usedelements (e.g . nitrog en fo r nitra ting, chrome for chrome pla ting) a nd proc es s tem-pera tures (400 up to 1400 ° C ). Furna ces a re a va ila ble in very different de s ign forcontinuous flow or batch operation.Gas analysis is used to achieve optimum plant operation (cost reduction, safety)a nd for controlling the proc es s-spec ific ga s a tmos phere (prod uct q uality includingdoc umenta tion a cc ording to IS O 9000 ff.). The mos t co mmon mea suring c ompo -nents a re O

2, CO, CO

2and SO

2. S ee a lso the a pplica tion exa mple in cha pter 5.4.6.


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3.2.4 Safety measurements

Process applications of gas analysis also include measuring tasks which are per-formed to protec t perso ns a nd pla nts from c omb ustible, explos ive or toxic g a ses.Monitoring CO is the main concern in plant atmospheres, in coal mills or coalpowder silos (to detect smouldering fire in time) or, in connection with the use ofelectrostatic filters, to avoid the formation of explosive gas mixtures in the filter.Similar applications are monitoring of plants for dangerous concentrations ofmethane or other explos ive ga se s.

Explosion limitsMixtures of combustible substances and air or oxygen are ignitable in certainconcentration ranges. For each mixture low and high ignition limit values a respecified that depend on temperature and pressure of the gas. Both limitvalues d es cribe the co ncentra tion va lues o f the c omb ustible s ubsta nce for ag iven tempera ture a nd pressure (normally 20° C a nd 1 ba r) in Vol. % or g/m3.The rang e be tween the tw o limit va lues is the ignition range , see ta ble 19.

Table 9: Ignition limits of combustible gases

A spec ia l mea suring s ens or is typica lly use d in ga s a na lys is to de termine com-bustibles in gas mixtures (see chapter 4.2.2.). However, this sensor only detectsthe s um of a ll co mbus tible c ompo nents. Therefore, w hen monitoring a ga s mix-

ture for its lower ignition limit, the measuring range of the analyzer should be ad-justed a cc ording to the c omb ustible c omponent w ith the lowest ignition limit.

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Combustiblesubstances

Formel Ignition limits in a ir (Vol. %)T= 20 ° C a nd p= 1 ba rlow high

Ammonia NH3 15,0 28,0

Ca rbon monoxide C O 12,5 74

Hydrogen H2 4,0 75,6

Metha ne C H4 5,0 15,0

P ropa ne C 3H8 2,1 9,5B uta ne C 4H10 1,5 8,5

Acetylene C 2H2 1,5 82,5


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3.3 Gas analysis for emission monitoring

In most countries many types of plants ranging from power stations, steel works,cement plants, chemical plants etc. down to smaller production units or municipalfacilities are liable to comply with legal regulations regarding emission of pollut-ants into the atmosphere. It must be ensured that the emission of specified pollut-a nts d oes not exceed specified limit values. Many c ountries ha ve iss ued la w s a ndordinances containing instructions for emission control measures including limitva lues for the emiss ion o f pollutants . In G ermany this is the " B undes immiss ions -Schutzgesetz" (BImSchG) or Federal Immission Control Act, in the United States

it is the Environmental Protection Agency (EPA) Clean Air Act. For larger regionssuch as Europe or Asia a uniform legal regulation does not yet exist. Many coun-tries therefore use the German BImSchG or the US Clean Air Act as basis fortheir ow n s pec ific a tions .

Gas analysis plays a key role in achieving effective pollution control and compli-ance with the regulations.

EmissionMaterial released into the atmosphere either by a discrete source(prima ry emiss ion from smokesta cks, other vents, moto r vehic le etc .) or a s theresult of a photochemical reactionImmissionThe tra nsfer of co ntamina nts (chemica l subs ta nces, no ise, ...) from the a tmos -phere into receptors such as human beings, animals, plants, soil, buildings etc.

3.3.1 Legal fundamentals of Emission and Immission regulations in Germany

Legal basis of the entire prevention of harmful effect in the environmentin G ermany includes• the Bundesimm isionsschutzgesetz (BImSchG), Federal Immission Control Act,

a la w a mended a s of 1990 and 1994• numerous Rechtsverordnungen (BImSchV ), ordinances resp. regulations for the

implementation of the law and• the TA Luft, Technisc he Anleitung Luft, Tec hnica l Ins truction Air (TI Air), a spe-

cific regulation to support the authorities with definite instructions for approval

a nd monitoring of insta lla tions a cco rd ing to the 4. B lmS chV.

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1. Ord ina nc e S ma ll-s ca le firing ins ta lla tions

3. Ord ina nc e S ulfur c ontent of lig ht fuel oil

4. Ord ina nc e Ins ta lla tio ns s ub jec t to lic ens ing

9. Ord ina nc e B a sic s of lic ens ing of ins ta lla tions

11. Ordina nce Emiss ion dec la ra tion13. Ord ina nc e La rg e-s ca le firing ins ta lla tions

17. Ord ina nc e Wa s te inc inera tio n ins ta lla tions

27. Ordina nce Crema toria

The BImSchG is categorized as follows:

• Genera l provis ions (§ § 1ff)• Establishment a nd Opera tion of Installa tions (§ § 4 for 31)• Na ture of Insta llat ions, Substances, P roducts, .. .. (§ § 32 to 37)• Na ture a nd Opera tion of Vehicles . . . .. (§ § 38 to 43)• Monitoring o f Air P ollution, . . . (§ § 44 to 47a)• J o int P rovis ions (§ § 48 to 62)• Final P rovis ions (§ § 66 to 74)

27 ordinances (regulations) have been released for implementation of the law, a

selec tion o f which is sho w n in ta ble 10. Thos e w ith releva nce to c omb ustionpla nts a re ma rked . The rela tion b etw een ord ina nces a nd definite types of insta lla -tions (fuel and pow er output as pa ra meter) is sho w n in fig . 8.

Table 10: Ordinances of the German Federal Immission Control Ac t (Selection)

Fig. 8: Relation o f type of installations and valid ordinances


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Emission values and emission limit values

• Emission values a re s ta nda rds w ith a lia bility rang ing be low emission limitvalues. Emiss ion va lues a re d efined a s values, w hich, a cc ording to the sta teof the a rt, ma y not be exceed ed . Emiss ion va lues for air pollution c ontrol arespecified in the TI Air.

• Emission limit values are legal standards with a high range of liability. Suchlimit va lues a re s pec ified e.g . in the 1., 4., 13., 17., and 27. o rd ina nce a nd theTI Air.

3.3.2 Specifications of the BImSchG for Germany (Selection)

1. Ordinance on small-scale firing installationsThis ordina nce c onc erns a ll firing ins ta lla tions w hich mus t not be licensed up to1,5 resp. 10 MW power output depending on the type of fuel used, see fig. 8.Official monitoring of these installations is in the responsibility of the chimneysweep. Once a year the firing installation must be tested whether it complies withthe specified limit values: Dust and sometimes CO must be monitored in the fluegas of solid-fuel-fired installations, while for gas and oil fired installations the fluega s hea t los s must be c a lcula ted from mea sured va lues of O2 or C O2 concentrationa nd the d ifference betw een flue ga s a nd a mbient a ir temperature.

More informa tion a bo ut flue g a s mea surements on sma ll-sca le firing insta lla -tions is a va ila ble in the Tes to ha ndb oo k " Flue G a s Ana lys is for P ra ctica lUsers" .

4. Ordinance on installations subject to licensingThis ordina nce c omprises in groups (see ta b le 11) a lis t of a bout 150 types ofinstallations with a power output of some MW which require a license for opera-tion. The instruc tions for implementa tion of the 4. ordina nce a re c omprised in theTI Air, see the fo llow ing sec tion.


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G ro up Type of ins ta lla tio n

1 Hea t genera tion, mining , energy2 S tone a nd c la y, g la ss , cera mic s, building ma teria l

3 S teel, iron, other meta ls

4 C hemic al prod uc ts , c rude oil (refinery a nd proces -s ing), pha rma ceutica ls

5 P rocess ing of pla s tic s

6 Wood, pulp

7 Food s tuff e.a .

9 S toring , loa ding a nd unloa ding of ma teria lsTable 11: Grouping o f installations accord ing to the 4. ordinance

TI Air (Technical Instruction Air)The TI Air is a n a dminis tra tive d oc ument o n the control a c t (B lmS chG ). It c om-prises all regulations required for an installation, from first application on con-s truction up to monitoring the routine operation. The TI a ir reg ula tes a ll ins ta lla -tions subjec t to lice nsing w hich a re lis ted in the 4. o rdina nce .

The TI a ir is g rouped in four pa rts :

• P a rt 1: Regula tions o n applica tion a rea s• P a rt 2: G enera l provis ions on a ir pollution c ontrol• P a rt 3: Req uirements on limitation a nd de tection o f emiss ions• P a rt 4: Reco nstruction o f old insta lla tions

Part 3 of the TI a ir is o f pa rticula r interest for ga s a na lys is , be ca use it inc ludes thespecification of limit emission values of pollutants of definite installations.

Section 3.1 contains general regulations with a classification of pollutants into4 cla ss es : The limit value of cla ss I subs tanc es (the mos t da ngerous subs ta nces ,e.g phos gene) a mounts to only 1 mg/m3 while the class IV limit value (e.g. sulfura nd nitrogen o xides ) is 500 mg/m3.

These general spec ifications, however, are replaced in

definite cases (section 3.3) by more strict requirements!


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Section 3.2 handles in detail the procedures of monitoring and controlling emis-

sions. S ection 3.2 dema nds:• tha t s uita ble sampling point locations have to be defined during licensingwhich allow representative and correct emission measurements;

• tha t through firs t and repeated single measurements the emission valuesare determined of those substances that have been listed including limit val-ues in the lice nse doc uments of the insta lla tion;

• tha t , in ca se o f pa rt icula r high ma ss flow of limited substances, these sub-sta nces have to be monitored by continuous measurements; a nd

• tha t for pa rticula r da ngerous substanc es w hose continuous determination is

des ira ble b ut either not po ss ible o r too expens ive, a reg ula rly single measure-ment is obligatory.

Single measurements according to TI AirAfter construction of a new plant (or after reconstruction) a first measurement isperformed within 3-12 months after start-up by a certified testing organization.This firs t mea surement is co nsidered a s a ccepta nce tes t. After the initia l tes t,single measurements are performed every 3 years in such a way, that the meas-

uring values of the limited components are averaged over a period of 30 minutesand compared with the specified limit values. 3 measurements are required onins ta lla tions w ith co ntinuous o pera tion, o therwise 6 mea sureme nts . The firingplant shall be optimized by the operator before the measurements start.

Continuous measurements according to TI AirThe a vera ge va lue of 30 minutes mea suring time is ca lcula ted every ha lf a n hourduring normal opera tion o f the pla nt. From this va lues a n average value of the day is generated, stored and processed statistically; this value must not exceed thespecified limit value.


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• Officia l single mea surements a cc ording to TI Air must be performed by

using de vices that ha ve be en c ertified for that b y pa ss ing succ es sfully adedicated suitability test. This is a s w ell ob liga tory for s ta tiona ry eq uipment toperform continuous measurements.

• Testo-ga s a nalyzers a re s uita ble, tes ted a nd c ertified for single a s w ell a s forco ntinuous mea surements.

Section 3.3 handles regulations concerning definite sorts of installations, seeta ble 12.

Tab. 12: Grouping of TI Air, section 3.3, for definite sorts of installations

Please note:Limit values specified for definite sorts of installations are included in most of theapplication examples given in chapter 5 of this handbook.

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Sectionof TI Air Sort of installation

3.3.1 Hea t genera tion, mining , energy

3.3.2 S tone a nd c la y

3.3.3 S teel, iron, a nd other meta ls3.3.4 C hemica l prod ucts , pha rma ceutic als , refineries

3.3.5 S urfa c e trea tment, foil prod uc tio n, pro ces sing of pla s tic s

3.3.6 Wood, pulp

3.3.7 Food stuff, agriculture products

3.3.8 Wa s te inc inera tio n (me a nw hile re pla c ed by the 17. Ord ina nc e)

3.3.9 S toring , loa ding a nd unloa ding of ma teria ls

3.3.10 Other

S pecia l ca se P ow er sta tions >50 MW (g a s -fired : >100 MW) a re ha nd ledse pa ra tely b y the 13. ordinanc e!


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13. Ordinance on large-scale firing installations

The 13. o rd ina nce is for firing ins ta lla tions w ith po w er output >50 MW (solid fuels )and >100 MW (liquid and gaseous fuels). Emission limit values are specified forparticulate matter, sulfur dioxide, nitrogen oxides, carbon monoxide and gaseouscompounds of chlorine and fluorine depending on heat power output and planttype. Some values are subject to a dynamic regulation that allows to reduce thelimit values according to progress in the state of the art of the measurement orcontrol tec hnolog y.

Table 13: Limit values of po llutants accord ing to the 13. ordinance (select ion)

17. Ordinance on waste incineration installationsWaste incineration installations are used for thermal treatment of solid, liquid andpasty waste materials from households or hospitals as well as from industry, in-cluding used tires, solvents, sewage sludge etc. with the objective to reduce vol-ume a nd pollution potentia l of the w a s te ma teria l. The flue g a ses prod uced duringthe w a s te incinera tion mus t, reg a rd ing their content o f pollutants , c omply w ith theregulations and specifications of the 17. ordinance as of 1990, see table 14.

Pollutant Limit va lues [mg /m3] according to the 13. ordinance

FuelS olid Liq uid G a seous

P a rticula te ma tter 50 50 510 (bla st furna ce ga s)100 (industrial gas)

C O 250 175 100

S O2 (pla nts > 300 MW) 400 400 355 (LG)100 (coke oven ga s )200-800 (compo site ga s )

S O2 (pla nts > 50 MW) 2000 1700 -

NOx (pla nts > 300 MW) 200 150 100

NOx (pla nts > 50 MW) 400 300 200

O2-reference va lue 5-7%dependingon firing

3% 3%


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40

Table 14: Limit values of po llutants accord ing to the 17. ord inance (select ion)

27. Ordinance on cremation installationsThe 27. ord ina nce c onta ins reg ula tions inc luding limit va lues conc erning c rema -tion installations. (See also chapter 5.6.1).

Analyzers for use in emission controlAna lyzers fo r use in emiss ion c ontrol are of ide ntica l des ign to those us ed in othera rea s of proc es s a na lys is. They mus t, how ever, meet pa rticula r req uirementsa nd, in many countries, pa ss a ded ica ted suitability test to get the certification foruse in emission monitoring applications.

The high numbe r of co mponents w hich may be pres ent in the exhaus t ga ses re-quires selective analyzers whose cross sensitivity is either very low or well knownand thus can be taken into account by calculations. Furthermore, the analyzersmust be easy to calibrate and deliver correct and reproducible results. High avail-ability and low maintenance requirements are also part of the certification condi-tions.Emission monitoring measurements require also well designed sample gas ex-tracting and conditioning systems because of the high temperatures as well asdust and water content of the flue gases. Gas sampling must deliver a represen-

tative proportion of the flue gas stream which sometimes requires more than onesa mpling point.

P olluta nt Limit va lue [mg/m3]

a cc ording to the 17. ordina nceP a rticula te ma tter 10

Ca rbon monoxide C O 50

S ulfur oxides (a s S O2) 50

Nitrogen oxides (as NO2) 200

Orga nic co mpounds (a s C total) 10

Compounds of chlorine (HCL) 10

Compounds of fluorine (HF) 1


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Suitability test of emission analyzers

Analyzers for use in official emission monitoring and control must pass success-fully a certific a tion tes t in ma ny countries . Thus high q ua lity a nd compa ra bility o fthe measurement results are ensured and uniform conditions can be realized inmonitoring different pla nts . The c ertific a tion tes t proced ure is spec ified in d eta ila nd includes la bo ra tory a nd field mea surements by a lice nsed orga niza tion o ver atime period of several weeks. Finally the certified analyzers are listed and the listpublished by the a uthorities .

The tes to 360 ana lyzer ha s be en c ertified in G ermany for mea suring O2, CO, NO,NO2 and SO2 for use a ccording to the 13. and 17. ord ina nce a nd TI Air.For ce rtific a tions of other tes to a na lyzers a nd in other countries se e ta ble 47 onpa ge 121 of this ha ndb ook.

3.3.3 Emission Monitoring in the USA

The leg a l ba s is of emission monitoring in the United S ta tes is through the fed erala uthority, the US Environmenta l P rotec tion Agenc y (EPA). The a dminis tration a ndenforcement of air quality regulations can also be found at other agencies includ-ing State Departments of Environmental Protection (DEP’s), county or local cities,or reg iona l a ir d is tric ts . EPA reg ula tions dic ta te the minimum req uireme nts fo r a irq ua lity. In a ddition the othe r a uthorities ma y req uire d ifferent or more s tringent s ta n-dards.

The EPA d evelope d reg ula tory sta nda rd s w ith the p urpos e of id entifying

the sources of a ir pollutants , de velop tes t method s to mea sure the a ir pollution, a ndmandate controls on equipment to reduce the pollution for the protection of hu-ma n hea lth a nd the environment. The C lea n Air Ac t (C AA), first e s ta b lished in1963, set the initial frame work of how to develop air quality standards, who orw ha t a ir pollution s ource s w ould be effec ted, a nd how the la w w ould be enforce d.

CAAIn 1970 the C AA w a s a pproved a s la w. The la w ta rgeted la rger sing le-point a irpollution sources, such as utilities, power plants, and large industrial smoke

s ta cks a nd a rea so urce s s uch a s c a rs a nd trucks. The CAA is g enera lly dividedinto 7 Titles.

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• Title 1 - National Ambient Air Quality Standards (NAAQS ) – Lists the

criteria Air P ollutants a nd the ma ximum a llow a ble leve ls in a mb ient a ir. Thepollutants a re:- Sulfur Oxides (SOx)- Nitric Oxides (NOx)- Ca rbo n Monoxide (CO)- Ozone (O3)- Particulate Matter (PM)- Lead (Pb)

• Title 2 - Mobile Sources - Regulations regarding the emission from cars,

truck, ships , etc .• Title 3 - Hazardous Air Pollutants (HAPS)– Regulations regarding more than

188 different compounds that are hazardous to life.• Title 4 - Acid Rain Deposition Program – Requires emission monitoring of

S O2, NOx, C O, a nd o pa city a t utilities & la rger sources to a dd res s a cid ra ina nd intersta te tra nsport.

• Title 5 - National Operating Permits Program - An administrative programdesigned to identify large polluters (in a given air district) and requires a fa-c ility (source) to ha ve a s ing le Title V permit tha t incorpora tes a ll the other a ir

regulations.• Title 6 - Stratospheric Ozone Protection – Regulates sources associated

with Ozone depletion or degradation• Title 7 - Enforcement – Provides the method for government to implement

c rimina l a nd/or c ivil pena lties & fines for so urces not in c omplia nce w ith a irregulations.

• Title 8 - Miscellaneous – Other items not a dd res s a bo ve

In 1990 the CAA Amendments (CAAA) lowered the allowable emission limits to

be implemented throug h yea r 2010. The C AA a lso es ta blished othe r reg ula tions .The mos t nota ble ones a re the:

New S ource P erformance S tanda rds (NS P S )• S ets emiss ion limits for a ll new sources of a ir pollution.

S tate Implementa tion Pla n (S IP )• Requires ea ch s tate to come up with a pla n to reac h the federa l a ir

q uality s tanda rds .

S tate Req uirementsEach State in the United States is responsible for implementing the federal lawsthrough the SIP. In addition they are also responsible for many other state-

42.1


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• Non-Attainment Area = 25 tons pe r yea r (t/y)

• S evere Non-Attainment Area = 10 tons per yea r (t/y)As s uch, a fac ility must loo k a t ALL of their a ir pollution s ources , combine the tota land if it exceeds the limits stated above, they are NOW considered a largesource. With this large source designation comes extensive data gathering andreporting and it also triggers other federal and state regulations.

Once d es igna ted a s a Title V fac ility, ea ch so urce must propo se w ha t methods itw ill do to c ontrol and monitor emiss ions. The a cc epta nce of ea ch propos a ldepends upon the loc a l a nd/or sta te req uirements. The s ources ha ve a variety o f

w a ys to mo nitor their emiss ions . They ma y use f-fac tors a nd fuel ca lcula tion; totemperature or other parametric monitoring; to measuring flue gas with eitherportab le a na lyzers, s ta ck testing tra ilers, o r CEMS . The a uthorities w ish is tohave real flue gas measurements and portable analyzers provide a very goodmea ns to c ollect true, ac cura te a nd less cos tly da ta.

Title V reg ula tions , including the Complia nce Assura nce Monitoring (C AM) a ndPeriodic Monitoring (PM) are the driving force in targeting these smaller sources.CAM and PM were developed to address all the sources not previously identified

through the other programs.

Funda mental Cha nge in Co mplia nceA fundamental regulatory change has recently taken place. Historically, sourcesonly needed to be in compliance during their stack test (generally tested onceevery 1 or 5 years). Now, sources are required to be in compliance 100% of thetime. The proof o f co mplia nce is now the res pons ibility o f the s ource a nd not theone-time emission (stack) test.A company officer is now legally responsible for his facility’s air quality

complia nce . The reg ula tory enforcement a genc ies ha ve the a uthority to iss uec ivil fines a nd/or ta ke c rimina l a c tion if complia nce is no t met. Thes e tw o newconcepts of continuous compliance and enforcement authority provide theincentive to co mply w ith the reg ula tions . This opens a w hole new ma rket forporta ble a nalyzers.

Trend s fo r P orta b le a na lyze rsThe s tep to tes ting s ma ller so urces provide d a goo d reason to utilize a nother a na -lyzer technology, name ly elec troc hemica l sens ors. They provide a cc ura te da ta , a re

more cost effective, and are widely available. Portable electrochemical analyzersa re now a cc epted a t the federal, s ta te, a nd loc a l levels for monitoring emiss ions.

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Tes t Methods utilizing P orta b le Elec troc hemica l Ana lyze rs

The US EPA does not a pprove or certify a n ins trument o r a na lyze r for emiss ionmonitoring. Instead, EPA uses approved test methods. The US EPA a nd theAmerica n S oc iety for Tes ting a nd Ma teria ls (AS TM) ha ve iss ued tes t method sspecifying the use of porta ble a nalyzers the test method a re:

• C TM-030• C TM-034• AS TM Method D6522-00

Thes e methods a re performance-ba se d , mea ning the a na lyzer must perform withina tight specification and the testing data must meet special quality control stan-da rds . The s pec ific a tions w ere d eveloped spec ific a lly for elec troc hemica l tec hno-log y. The me thods req uire the use of c a libra tion ga s for the verific a tion o f a na lyzeraccuracy. For example, calibration checks are performed before and after eachtes t, for s ta bility tes ting , for linea rity tes ting , etc . The s a me o r s imila r tes ting is use din a ll US EPA tes t method s .

CTM-030 contains the highest specification or in other words the highest qualitya ssura nce a nd q ua lity c ontrol (QA/QC) proc ed ures . It is used for tes ting NO, NO2,CO, and O2 emiss ion from na tura l g a s fired source s . It is a more co mplex a nd time-cons uming tes t method . It req uires numerous pre- a nd po s t-tes t runs w ith ca libra-tion ga s , linea rity tes ting, interferenc e tes ting , s ta bility tes ting , e tc.

ASTM Method D6522-00 is ba sed upon C TM-030. It is a lso used for testingNO, NO2, CO, and O2 emission from natural gas fired sources in the US andInterna tiona lly. This method is expec ted to b e a pproved by EPA a s the next a lter-

native reference method.

CTM-034 is for tes ting sources on a period ic ba s is (i.e. Title V P eriod ic Monitoring ,CAM, &state specific regulations). It can be used for testing NO, NO2, CO, and O2emiss ion from na tura l g a s a nd fuel-oil fired sources . The method is les s cos tlyin terms c a libra tion g a s a nd time expended therefore provid ing a n ea s ier a nd mo repractical methodology for more frequent testing.

The testo 350 and 360 meet the requirements of these testing methods

(Cond itiona l Tes t Method CTM-030, &CTM-034, a nd the AS TM Metho d D6522-00)In addition the testo 360 ga s a na lyzer meets the req uirements o f EPA’s te s tmethod found in 40 CFR, P a rt 60, Append ix A &B pa rt 75 subpa rt C .

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3.3.4 Flue gas purification/Cleaning

The a mount of a ir pollutants ca rried in flue ga ses a nd their emiss ion into theatmosphere can be reduced by installation of dedicated purification units in theflue gas path between boiler and stack:• Emission of particulate matter

is red uced or a lmos t elimina ted by insta lla tion o f dus t prec ipita tors o f numere-ous designs and operating principles

• Emission of gaseous pollutantscan be reduced to a certain extent by using low-emission fuels; a more effecti-

ve reduction is achieved by combustion optimization (fluidized bed combus-tion, staged air supply) and even more by flue gas purification processes sucha s a ds orption, therma l trea tment, etc.

G a s a na lysis is a n importa nt too l to monitor a nd c ontrol suc h proc es ses.

Particulate matter control

• Centrifugal separators (cyclones)C yclones a re d evice s in which pa rticles a re c a used by mea ns o f centrifuga lforces to b e propelled to loc a tions outside the ga s strea m from w here theyma y be removed a nd d isc harge d. Reverse flow cyc lones a re the most c om-mon ones with tangential inlet and axial gas and particle outlet.

• Electrostatic precipitatorsElectrostatic precipitators are devices in which an electrical field is maintainedto c a use pa rtic les to a cq uire a n elec trica l cha rge. The cha rged pa rtic les a reforced to travel to a collector electrode where from they are removed and

discharged from the process. Electrostatic precipitators are preferably used tofilter high volume gas streams in power stations, cement plants, metallurgicalplants etc.

Elec tros ta tic filters ma y b e d a ma ge d in c a se of a n explos ive g a s mixture entersthe filter cha mbe r and pa sses through the e lec tric field . Effective protec tionfrom tha t ma y b e rea lized by mea suring the C O co ntent of the flue ga s upstre-am the filter.


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• Fabric filters

Fabric filters remove particulate matter from gas streams by retention of theparticles in or on a porous structure (bags, beds) where the gas flowsthrough. The po rous s tructure is mos t commo nly a w oven o r felted fab ric , butcan also include materials such as coke, sand, ceramics, etc.

• SrubbersScrubbers are primarily employed to remove gases and vapor phase con-taminants from the flue gas, but are sometimes used to remove particulatema tter. The pa rtic les a re b roug ht into c onta c t with a liq uid (introd uce d e .g . bysprayers) resulting in a reaction that collects the particles in the liquid.

Flue gas denitrificationPrimary and secondary measures are available to reduce NOx (NO+ NO2) contentof flue gases:• Primary measures include staged combustion by staged air supply, fluidized

bed combustion and the use of specifically designed burners. All of thesemeasures will considerably reduce the formation of nitrogen oxides. Moredetails see below.

• A secondary (postcombustion) measure is the Selective Catalytic Reduc tion (SLC) process, which is by far the most accepted one. Ammonia is injectedinto the flue ga s to rea ct w ith NOx forming nitrog en a nd w a ter. The use of a ca ta -lyst improves this reaction and reduces the quantity of ammonia required.Sometimes the term DENOX plant is used to describe such a denitrificationplant.

Fluidized bed combustion (FBC)Fluidized bed technology is based on the physical principle that particles can be

fluidized in a reactor (e.g. pulverized coal in a combustion chamber) by blowinghot a ir ag a inst them from be low. This principle a llow s for more complete c onta c tbetween fuel particles and oxygen resulting in an almost complete combustionwith low emission levels. Combustion temperature is as high as 900 °C whichprevents the formation of thermal nitrogen oxides almost completely. Addition oflimestone to a FBC process will reduce also the sulfur oxide formation at thesame time.


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Staged air supply

Staged air supply is a very effective primary measure to suppress nitrogen oxideformation by reducing fuel - NO as well as thermal NO. Combustion air supply isreduced at the burner (first stage, primary air), the air value is


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4. Gas analysis technique

4.1 Terms of gas analysis technique (selected)

4.1.1 Concentration

The term concentration describes the amount of a substance, expressed asmass, volume, or number of particles in a unit volume of a solid, liquid, orga se ous s ubsta nce e.g . a lco hol in beer or oxyge n in a ir.

Different units are in use to describe concentration in gases:

• Mass concentrationConcentration expressed in terms of mass of substance per unit volume[g subs ta nce/m3 gas volume]

• Volume concentrationConcentration expressed in terms of gaseous volume of substance per unitvolume [cm3 subs ta nce/m3 ga s volume]

• Part concentrationConcentration expressed as number of particles of substance per a certain

number of pa rtic les

In flue gas analysis both the terms mass concentration and part concentration arecommon and us ed in pa ra llel. The mass unit is gram (and mg, g, see table 15)and the most popular expression for part concentration is ppm (parts per million)."ppm" means "x number of parts in a million parts". ppm is usually used for low conc entra tions ; la rger conc entra tions a re expres se d in " percent" (%), see ta ble 16.

Consequently the concentration of a gaseous pollutant is expressed

• either us in g (or mg or g etc.) with reference to a definite gas volume, usuallycubic metres (m3), e .g . 200 mg/m3

• or us ing ppm w ithout a ny reference , e.g. 140 ppm

Table 15: Mass unit gram with subd ivisions 47

Express ion S pellingG ra m gMillig ra m mg 10-3 gMikrogram g 10

-6 g

Na nogra m ng 10-9 g

P icogra m pg 10-12

gFemtogra m fg 10-15 g


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Express ion S pelling

P a rts per b illion 0,001 ppm 0,0000001%P a rts per million 1 ppm 0,0001%

10 ppm 0,001%

100 ppm 0,01%

1000 ppm 0,1%

10000 ppm 1%

Table 16: Particle concentration in ppm and % with subdivisions

Please noteBecause of the variation of a gas volume with temperature and pressure changesit is necessary to use one of the following alternatives for describing a concentra-tion va lue:• a dd it ional specifica tion of ga s temperature a nd pressure values

existing during mea surementor

• co nversion of the meas ured c oncentra tion value into the corresponding valuea t standard zero cond itions, see the follow ing cha pter.After conversion, the volume is expressed as standard volume(s ta nda rd cubic meter, Nm3 or m3N).

Standard zero conditions of a gas

The volume of a g a s de pends on its a ctua l tempera ture a nd pres sure.To a chieve compa ra ble res ults a standard zero volume has been d efined:A ga s ha s its sta nda rd zero volume a t a pres sure o f 1013 mba r (hP a )and a temperature of 273 K (corresponding to 0 °C).


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Conversion of concentration values

Conversion of a measured value to standard conditionsThe c onversion o f a n a ctua l mea suring va lue (s ta tus 1) to s ta nda rd co nditions(status 2) is performed using the formula

w ith the follow ing expres s ions :

ExampleThe va lue " 200mg /m3" a t conditions of 35 ° C a nd 920 hP ares ults , a fter convers ion into s ta nda rd c ond itions , in the va lue " 248,4 mg/Nm3" .

Conversion of ppm to mass concentration [mg/m3]ppm (parts per million ) is a very common concentration unit as expression for arelation of particles in a gas volume. Simultaneously the unit mass concentration

is us ed .A concentration value in [ppm] can be converted to the corresponding value ex-pres sed a s ma ss conc entra tion [mg/Nm3] using the s ta nda rd d ensity of the g a s a sa factor. For that the dilution of the gas by air (excess air, specially added air orfalse air from leaks) must be considered by using the oxygen concentration asreference. All measured values must be in reference to a certain oxygen content(" referenc e O2" ). Only c onc entra tion va lues w ith ide ntica l oxyg en referenc e va luesa re c ompa ra ble to ea ch other! Therefore, in offic ia l reg ula tions , limit co ncentra tionvalues of pollutants are always specified together with a certain oxygen reference

value.The a ctua l oxyg en c onc entra tion va lue is a lso req uired for the c onversion c a lcula -tion as measure for the actually existing gas dilution level.

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S tatus 1Conditions duringmeasurement

T1 : G a s tempera ture during mea surement(273 + a ctua l tempera ture in ° C )

p1 : G a s pres sure d uring me a surement in hP a c 1 :ge mes se ne Konzentra tion

c 1 : mea sured co ncentra tion va lue

S tatus 2S tanda rd co nditions

T2 : S ta nda rd zero tempera ture (= 273 K)p2 : S ta nda rd zero pres sure (= 1013 hP a )c 2 : Co ncentra tion co nverted to sta nda rd

conditions

c 2 = c 1 ·T1 · p2

T2 · p1


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Conversion formulas for CO, NOx, and SO2

The fa c tor (1,25 etc.) a pplied in the a bo ve formula s corres pond s to the s ta nda rddens ity in mg/m3 of the gas concerned. For that please note the following com-ments:• for S O2 standard density values are reported in the literature between 2,86

and 2,93; the difference is caused by the difference between calculateda nd mea sured values;

• for NOx the sta nda rd density value of NO2 (2,05) is used, because only NO2 is astabile compound and NO will react very fast with oxygen to NO 2 a nd

• for H2S (formula not shown) the factor is 1,52.

For conversion calculations without reference to the oxygen concentration theabove formulas are simplified to (shown only for CO)

This is a lso true for the other ga se s .

NOx ( mg /m3 ) = x (NO (ppm ) + NO2 (ppm)) x 2,05

CO ( mg /m3 ) = x C O (ppm ) x 1,25

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21- O2- refer.

( 21-O2 )[ ]

S O2 ( mg /m3 ) = x S O2 (ppm ) x 2,86

21- O2- refer.

( 21-O2 )[ ]

21- O2- refer.

( 21-O2 )[ ]

C O in [mg /m3] = CO in [ppm] x 1,25


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4.1.2 Sample gas extraction and conditioning

Extractive samplingMost of gas analysis measurements are performed using the extract ive gas sampling method. A representative portion of the process gas is extracted from theprocess stream (in contrast to the in-situ principle) via a sampling probe and, afterpassing a conditioning unit, fed to the analyzer. Sample conditioning (sometimesalso called sample preparation) means to clean the gas of particles and to coolthe ga s dow n to a de fined tempera ture level be low the de w point. This c oo lingresults in drying the gas. A gas extraction and conditioning installation is shownschematically in figure 9.

Adva ntag es of extra ctive s a mpling a re:• the a nalyzer itself is s epara ted a nd protected from the process stream a nd its

ha rsh a nd often a gg res sive environment,• the sa mple ga s, through the conditioning proc edure, is tra nsformed into a

status that is defined and thus comparable, and

• more tha n one a nalyzer may be operated w ith one sa mpling unit or one ana-lyzer may be connected to several sampling points using a sample lineswitching unit.

Fig. 9: Samp le gas extraction and cond itioning (schematic)

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Sampling probewith coarse filter,occ. heated

Flue ga s orprocess gas

Ga s coolerwith fine filter

Analyzer withinput filter

S a mple lines,occ. heated

Condensatedischarge


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• Ga s extrac t ion is done by means of sampling probes that are positioned in

the flue ga s or proc es s ga s strea m. They a re a va ila ble in different des ign,ma teria ls a nd for different tempe ra ture ranges up to 1200 ° C (3200 ° F) a ndabove. A coarse ceramic filter is built in the head of the probe and, in certainprob es (e.g . the Tes to multiple function probe ), sensors for determining pres-sure a nd temperature o f the sa mple g a s a re a lso b uilt in the prob e hea d . Thega s e xtra ction is pe rformed by mea ns o f a s a mple g a s pump in the ana lyzer.

• The sample gas cooler is located between the sample probe and the ana-lyzer. Flue and process gases always carry a certain amount of humidity thatat high temperatures of the gas (above the dew point) exists as water vapor

and at low temperatures (below the dew point) as liquid. In both cases themeasuring result is influenced by the humidity itself and by chemical reactionsof other gas components with the water. Furthermore, the measuring equip-ment may be damaged by aggressive compounds (acids) formed through re-a ctions of S O2 or S O3 w ith wa ter. S ee a lso cha pter 2.7.Sample gas cooler are used to cool the sample gas and thus to dry it to adefinite a nd c ons ta nt level, e.g . 4 ° C . The rema ining leve l of humidity is low a tthat temperatures (see fig. 5, page 23). It is kept constant and is thus compa-ra ble with tha t of other mea sureme nts . The c oo ling proc ed ure res ults in

forming a liquid (condensate) that is discharged from the cooler by a pump.• The sample lines (made from metal or plastics) are either unheated (in case

of uncritical gases or very high ambient temperatures) or heated to keep thegas above the dew point and thus to avoid the formation of condensate in thesa mple lines .

• The analyzer, depending on the design, may as well contain gas filter, gascooler and heated internal sample lines.

The content of humidity in a sample gas is critical for gas analysis twice:• As vapor it dilutes the sample gas and, with varying levels of humidity,

the d ilution levels a nd thus the mea sured co ncentra tions va lues w ill va ry.• As water it will react with components of the gas and thus reduce the con-

centration of the components and consequently their measured concentra-tions va lues.

Remedial measures:• The humidity level should be mea sured together w ith the ga s co mponents.• The humidity should be d ropped to a low level a nd kept consta nt by using a

sample gas cooler.• The forma tion of condensa te in the a nalyzer eq uipment should b e a voidedby a ppropria te hea ting o f the a nalyzer ga s pa th.

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4.1.3 Cross-sensitivity

C ros s-sens itivity of a de tector (sensor) sys tem is ca used by the fa ct, tha t the spe-cies-specific resolution of the system is not unlimited. With that the detector is notonly sens itive for the c omponent o f interes t but a lso, mo re or les s , for othe r (" in-terfering") components present in the gas. Changes in concentration of thosecomponents will therefore also influence the measured value of the component ofinteres t. This effec t must b e c ompe nsa ted in order to ob ta in correc t a nd relia blemeasuring values. For that also the concentration of the interfering gases must beknown for use as correction values.Cross-sensitivity is expressed by the influence (increase or decrease of themeasured value, in concentration units) that is affected by the interfering compo-

nent. The extent of c ros s-sens itivity de pend s o n the cha ra cte ristic s o f the d etec -tion system (i.e it is analyzer-specific!) and on the concentration of the interferingcompo nents. The res ults for the tes to 360 ga s a na lyzer a re s how n in tab le 18.Thes e va lues a re typica lly low er than w ith other a na lyzers.

Table 18: Cross-sensitivities of the testo 360 gas analyzer

• Express ion 0 means " no influence"• Express ion 0 (sha ded ) mea ns " no influence b eca use of a utoma tic c orrection in

the a na lyzer" (the sens ors for the interfering c ompo nents must be a va ila ble inthe analyzer)

• No a lgeb ra ic sign mea ns pos itive influence (increa se of the mea sured value)• S ign " -" means nega tive influence (dec rea se of the meas ured value)

• Oxygen as measuring component is not shown as , except for CO2 (internallycompensated, no cross-sensitivity exist.• C O2 a nd NH3 as well as saturated hydrocarbons do not produce cross-sensiti-

vities.

Measuring components resp. type of sensor (testo 360)with cross-sensitivity values, expressed in % of the measured value ofthe interfering component

CO with H2 -compensation

CO without H2-compensation

NO NO2 S O2

I n

t e r f e r i n g g a s

c o m p o n e n t s

CO 100 100 0 0 0

H2S 0 0 0 a pprox. -25 a pprox. 200

S O2 0 0 0 a pprox. -3 100

NO


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Further information about influencing components:

• Unsa tura ted hydroca rbons a t higher concentra tion levels c an ca use zeropoint drifts and reduce sensor sensitivity, particularly for the CO and NO cell.

• High conc entra tion levels of ag gress ive ga ses such as HCN, HCl or Fluoridesmay attack sample lines and sensor housings.

4.1.4 Calibration

CalibrationCalibration is the process of adjusting the instrument read-out so that it corre-sponds to the actual concentration value or a reference standard. Calibrationinvolves checking the instrument with a known concentration of a gas or vapor tosee that the instrument gives the proper respon

testo-flue gas in industry 3-27-2008

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