600 mw boiler
TRANSCRIPT
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Experimental investigation on a 600 MWe
supercritical boiler with the technology of less-oil
ignition
Gonggang SunCollege of metrology and measurement engineering
China Jiliang UniversityHangzhou China
Lin ZhuCollege of metrology and measurement engineering
China Jiliang UniversityHangzhou China
Zuohe ChiCollege of metrology and measurement engineering
China Jiliang UniversityHangzhou China
Yihong WangCollege of metrology and measurement engineering
China Jiliang UniversityHangzhou China
AbstractExperimental studies were carried out on a 600
MWe supercritical boiler that was ignited by the technology
of less-oil ignition. The variation of steam temperature and
pressure, wall temperature of heat exchange surfaces and
combustion status were investigated. Test results
demonstrated that the pulverized coal is able to be
combusted fully and stably in the less-oil ignition combustor,
and the wall temperature of the combustor remains less than
300oC. It was also shown that the wall temperature of heat
exchange surfaces is also not overheated, which expands
uniformly, and the rising rate of the steam temperature and
pressure satisfies the requirement of operation rules. In
addition, compared to the cases using conventional ignition
techniques, the economical benefit by employing thetechnology of less-oil ignition is pronounced.
Keywords-supercritical boiler; cold starting; less-oil
ignition; economical analysis
I. INTRODUCTION
Oil-saving ignition technology has been extensivelystudied due to the large consumption of oil during boilerstart-up and pulverized coal combustion stabilization withthe conventional coal burning method. In a conventionalpulverized coal combustion boiler, oil which is deliveredby the oil-gun (OG) is primarily used to pre-heat thefurnace. When the radiation from the flame and heatexchange surfaces can give the coal particle sufficientenergy, then coal is fed by primary air and burned withsecondary air, so stable combustion is sustained in theboiler. Meanwhile, during burning of low-quality coal orat the reduction of boilers capacity, it is also necessary tointroduce additional thermal energy such as oil into thesystem to support stable combustion. Therefore, many ofthe liquid fuel are consumed in these above processes.
In order to achieve certain savings of liquid fuel, agreat number of efforts have been made to investigate anddevelop the technology of oil-saving ignition, i.e.,
plasma-aided ignition technology[1-2], high-temperatureair ignition technology[3-4], laser-heated ignitiontechnology[5] and induction-heating ignition technology[6-7]. For the plasma-aided ignition technology, methodsof both numerical simulation
[8-9]and the full-scaled trials
[10-11]had been employed to study the plasma supportedcoal combustion. Chen et al. [12] and Nie et al. [13]investigated the high-temperature air ignition technologyused the CFD simulations and experiments, respectively.Note that all the four above-mentioned technologies arefree of utilization of oil in assisting the ignition. However,some shortcomings for oil-free technologies, when facing
the engineering applications, are found, such as too highoperating costs, frequent maintenance during operationand lack of system stability et al. Recently, a less-oilignition technology (LOIT) has been proposed, whichhave the advantages of low operating costs, highoil-saving rates, maintenance-free and good performancein stability. Chi et al. [14] and Fu et al. [15] had asimulation to study the characteristics of coal combustionin the burner of LOIT. However, the authors are unawareof any published work on an engineering application of theLOIT in utility boilers, especially in supercritical boilers.Hence, to study the performance of combustion andstabilization in a supercritical boilers retrofitted by LOIT,the variation of steam temperature and pressure, wall
temperature of heat exchange surfaces and combustionstatus are investigated in this paper during the process ofthe 600 MWe supercritical boiler cold start-up.
II. EXPERIMENTAL FACILITIES
The rest of this paper is consisted of three sections.The retrofitting program of the boiler and test programsare described in the next section, which are followed by adetailed presentation and discussion of the experimentalresults. Some concluding remarks are finally drawn basedon the foregoing analysis.
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Figure 1. Schematic layout of the utility boiler.
A.. The Less-oil burnerFor oil-saving during the boiler start-up and
combustion stabilization, the boiler was retrofitted withthe LOIT and four primary air nozzles at Level B were
replaced by the Less-oil burner (LOB) that was sketchedin Fig.2.In the duct of the LOB, pulverized coal with the
primary air, which flows through the concentrator installednear the wall of the burner and be concentrated centrally,ignites and combusts intensively in the first-stage firingchamber with the high-intensity oil flame of the less-oilgun (LOG) in which the oil for igniting the pulverized coalis atomized and combusted in an adiabatic chamber firstly.
The pulverized coal ignites in the first-stage firingchamber and high-temperature gas flue is then directedinto the second-stage firing chamber to ignite pulverizedcoal in it. Finally, as the principle of energy amplification,pulverized coal in the duct of the LOB is ignited all and
the purpose of oil-saving is achieved. The cross sectional area of the LOB should be
equal to the one of the original burner so that themomentum of the flow at the exit of the burnercan keep equivalent before and after the retrofit.
For a given quality of coal, the ignition ofpulverized coal stream is obviously related withthe concentration of it. Therefore, to increase theconcentration of the pulverized coal has greatinfluence on the reduction of energy for heatingthe coal particles and good at raising the burnoutof the pulverized coal.
The concentrators should have good effect on
concentrating but little effect on increasing theresistance of the burner. In general, theconcentration of the pulverized coal in the
first-stage firing chamber could be double than theaverage of the pulverized coal concentration in theprimary air-coal mixture ducting.
Measurements such as cooling film should betaken to make sure that the wall of the LOB is safe
during the LOB in operation.Tab.1 lists the specific operating parameters during the
operation of the supercritical boiler with the LOIT.According to the basements mentioned above, the exit
of the LOB is similar to the original burner before theretrofit in area. Output of each LOG equipped in the LOBat Level B is 60kg/h and resistance of the LOB is 600Paon the condition that the primary air-coal mixture flowvelocity is 25m/s according to the calculation. The type ofoil atomization employed a mechanical method that has agood adaptability and stable atomization performance atvariation of oil pressure over a wide range from 0.5MPa to2.0MPa.
B.. Fuel qualitiesThe coal used in the experiments is a Chinese
bituminous coal, of which the proximate and ultimate
analysis data are given in Tab.2.
III. METHODS
During the boiler start up with the LOIT, theparameters of operation were recorded at intervals of 30minutes such as temperature and pressure of primarysteam, wall temperature of heat exchange surfaces andLOBs. To detect the combustion status, fly-ash was taken
every 60 minutes before electrostatic precipitator byisokinetic sampling system. The rectangular flue gas duct
was divided into 36 uniform sections and the samplingpoint was located at the center of each uniform section.
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Figure 2. Schematic diagram of the LOB.
TABLE I. BOILEROPERATING CONDITIONS
Boiler Operating Conditions Oil Type 0 # Light Diesel Oil
Oil pressure ( MPa ) 1.20
Oil-flow rate of the less-oil gun ( kg/h ) 60.0
Resistance of the less-oil burner ( Pa ) 600.0
Primary air temperature ( oC ) 76.0
Primary air velocity ( m/s ) 25.0
Primary air ratio ( % ) 19.8
Secondary air temperature ( oC ) 345.0
Secondary air velocity ( m/s ) 57.0
TABLE II. SPECIFICATION OF COAL USED IN THE EXPERIMENTS
Proximate Analysis ( As Received )
Moisture ( % ) 13.00
Ash ( % ) 14.00
Volatile ( % ) 25.55
Fixed carbon ( % )coal 47.45
Ultimate analysis ( as received )
Carbon ( % ) 58.04
Hydrogen ( % ) 3.62
Oxygen ( % ) 9.94
Nitrogen ( % ) 0.70
Sulfur ( % ) 0.70
Heating Value ( as received )
Gross calorific value ( kcal/kg ) 5330
Particle size distribution
R90 ( % ) 20
IV. RESULTS AND DISCUSSION
A.. The rising procedure of steam temperatureAt the beginning of the boiler cold startup, it was
taken some minutes to start blowers, introduce theauxiliary steam for heating the air and regulate theventilation of the pulverizer which grinds the coal for the
LOB of Level B. At the same time, four LOGs wereignited and a high-temperature fire-core was formed inthe first-stage firing chamber. When the pulverized coalwas delivered by the primary air to pass through the LOB,they were ignited rapidly in the way as described above.The whole boiler startup procedure continued about 6
hours. Fig.3 illustrates the heating-rate of primary steamwhich is required by the operation rules and obtainedduring the actual operation of the boiler startup after theretrofit. For the operation rules, the heating-rate ofprimary steam was 1.6667
oC/min at the beginning of the
boiler cold startup and dropped to 0.8333oC/min before
the steam turbine running. When the speed increase of thesteam turbine finished, the heating-rate of primary steamthen increased from 0oC/min to 0.6667oC/min for the sake
of grid connected operation.After that operation, although it dropped to 0oC/min in
a short period of time, the heating-rate of primary steamjumped to 1.6667
oC/min and maintained this status until
the end of the boiler cold startup.By comparing, it is found that the heating-rate of
primary steam obtained during the actual operationexhibits nearly similar trend with that required by the
operation rules. The maximum value of the heating rate ofprimary steam obtained during the actual operation was1.5333
oC/min, which was less than the one required by
the operation rules.
B.. The rising procedure of steam pressureFig.4 illustrates the pressure-rate of primary steam
which is required by the operation rules and obtainedduring the actual operation of the boiler startup after the
retrofit. For the operation rules, the pressure-rate ofprimary steam was 0.0847MPa/min at the beginning of
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the boiler cold startup and then jumped from 0MPa/min to0.2963MPa/min at the end of the boiler cold startup.
50 100 150 200 250 300 350 400
0.0
0.5
1.0
1.5
2.0
Rules required
Actual operation
Time interval (min)
Heating-rateofprimarysteam
(OC/min)
Figure 3. Heating-rate of primary steam required by the operation
rules and obtained during the actual operation.
In contrast, the pressure-rate of primary steamobtained during the actual operation changed smoothly
and the maximum value of the pressure-rate of primarysteam was 0.06013MPa/min which is far less than the onerequired by the operation rules.
50 100 150 200 250 300 350 400-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
Rules required
Actual operation
Time interval (min)
Pressure-rateo
fprimarysteam(MPa/min)
Figure 4. Pressure-rate of primary steam required by the operation
rules and obtained during the actual operation.
C.. Wall temperatures of the LOB and the utility boilerDuring the LOB in operation, due to combustion of
pulverized coal, a large number of heat released in theburner. Thus, it is necessary to investigate the safety of
the LOB when it is put into use. The variation of walltemperature of the LOB during the operation is displayedin Fig.5.
Obviously, until the end of the boiler startup, the wall
temperature of all LOBs was no more than 300oC. It is
evident that the cooling film has a good effect on cooling
the wall during the LOB in operation and the LOB canoperate steady and safe.
For the purpose of the safety of the utility, it is alsoimportant to investigate the expansion feature of theboiler during the LOB in operation; especially the water
wall employs spiral tubes. The variation of walltemperature of the spiral tubes outlet as the boilerstart-up is presented in Fig.6. It is seen that the heat
exchange surfaces absorb heat and expand uniformly;wall temperature of the spiral tubes outlet of the frontwall, rear wall and side wall has little difference between
them and the maximum value of it is less than 10oC.
0 50 100 150 200 250 300 350 40050
100
150
200
250
Walltemperature(OC)
Time interval (min)
No.1
No.2
No.3
No.4
Figure 5. Variation of wall temperature of the LOB.
0 50 100 150 200 250 300 350 400100
120
140
160
180
200
220
240
260
280
300
Walltemperature(OC)
Time interval (min)
front wall
rear wall
side wall
Figure 6. Variation of wall temperature at the exit of the spiral tubes
of the water wall
50 100 150 200 250 300 350 4000
15
30
45
60
75
Unburned carbon in ash
Burnout
Time interval (min)
Unburnedcarboninfly
-ash(wt%)
93
94
95
96
97
98
99
100
Burnout(wt%)
Figure 7. Variation of the coal burnout rate.
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D..Burnout rate of coalThe burnout of coal is defined as
%100)100/(
CV
FAACV
WW
WWWW (1)
where is the coal burnout rate, WV, WC, WA and WFArepresents the weight fraction of volatile, char, ash, and
fly-ash, respectively. is a constant which is fixed at =0.9.Fig.7 depicts the variation of the unburned carbon in ash andthe coal burnout rate in the process of the boiler cold startup.At the beginning, because the furnace was totally cold, theunburned char in fly-ash is higher than 70% and the coalburnout is lower than 94% correspondingly. However, as the
heat absorbed from the furnace increased, the coal burnoutrate increased from less than 94% to more than 98% and wasup to 99.5% at the end of the boiler startup. It is clearly shownthat the pulverized coal is able to be combusted fully andstably in the LOIT combustor.
E.. Analysis of the economical benefitThe oil-saving efficiency is calculated as:
100%OG LOG
OG
C C
C
(2)
Where is the oil-saving efficiency, COG and CLOGrepresents the oil consumption for boiler cold startup using
the conventional ignition method and the less-oil ignitionmethod, respectively.Tab.3lists the output of the OG and the LOG, the number ofthe gun put into use and its run time. Obviously, bycalculation, the oil-saving efficiency obtained after the retrofitis 98.3%.
TABLE III. COMPARISON OF THE ECONOMICAL BENEFIT
Less-oil
IgnitionTraditional Ignition
Output of the oil-gun ( kg/h ) 60 3575
Number of the oil-gun 4 4
Time in operation ( h ) 6.5 6.5
Oil-saving efficiency ( % ) 98.3
V. CONCLUSIONS
An experimental investigation on a 600MWe supercritical
boiler that was ignited by the LOIT was presented. Based onthe foregoing analysis of the experimental results, someconcluding remarks can be drawn as follows:
For the utility boiler firing a bituminous coal, therising rate of primary steam temperature and pressurecan satisfy the demand of the operation rules after theretrofit of the LOIT. The heat exchange surfacesabsorb heat and expand uniformly, and the safety ofthe utility boiler can be well guaranteed.
The pulverized coal is able to be combusted fully andstably in the less-oil ignition combustor and the wall
temperature of the LOB remains less than 300oC in the
whole process of the boiler startup.
The burnout rate of coal was relative low at thebeginning of the boiler startup because the furnace wasin a full cold state. As the heat absorbed from thefurnace increased and the combustion conditionimproved, the coal burnout rate increased significantlyand rapidly.
The technology of the less-oil ignition represents asignificant economical benefit and more than 95%oil-saving efficiency can be achieved during the boilerstart-up for the utility boiler firing a bituminous coal.
ACKNOWLEDGMENTProject is supported by the Science and Technology
Research Program of Zhejiang Province, China. (No.2008C11034)
REFERENCES
[1] M. Sugimoto, K. Maruta, K Takeda, et al. Stabilization of pulverizedcoal combustion by plasma assist, Thin Solid Film, 2002,407,pp.186-191.
[2] E. I. Karpenko, V. E. Messerle, and V. S. Pcregudov, Plasmathermochemical treatment of coals for reducing the consumption of fueloil at coal-fired thermal power stations, Thermal engineering, 2002,49(1), pp.25-28.
[3] S.Tashiyuki, T. Makoto, H. Tetsuya, et al. A study of combustionbehavior of pulverized coal in high-temperature air, Proceedings ofCombustion Institute, 2002, 29, pp.503-509.
[4] W. J. Feng, D. Li, L. H. Zhao, et al. Experimental study onhigh-temperature air ignition of pulverized coals, Journal of China CoalSociety, 2004, 29(5), pp.611-613.
[5] D. K. Zhang, Laser-induced ignition of pulverized fuel particles,Combustion and Flame, 1992, 90, pp.134-142.
[6] W. J. Li, K. F. Cen, C. G. Zheng, et al. Induction-heating ignition ofpulverized coal, Fuel, 2004, 83, pp.2103-7.
[7] J. H. Zhou, X. Nie, Z. J. Zhou, et al. Numerical simulation of oil-free
ignition combustor. Proceedings of the CSEE, 2004, 24(9),pp.243-247.
[8] S. Belosevic, M. Sijercic, and P. Stefanovic, A numerical study ofpulverized coal ignition by means of plasma torches in air-coal dustmixture ducts of utility boiler furnaces, International Journal of Heatand Mass Transfer, 2008, 51, pp:1970-1978.
[9] X. Y. Zhang, Y. P. Wang, Y. H. Guo, et al. Numerical simulation ofcombustion characteristics of burners with plasma ignition, Journal ofPower Engineering, 2005, 25(6), pp.834-839.
[10] E. I. Karpenko, V. E. Messerle, and A. B. Ustimenko, Plasma-aidedsolid fuel combustion., Proceedings of Combustion Institute, 2007, 31,pp.3353-3360.
[11] P. M. Kanilo, V. I. Kazanesev, N. I. Rasyuk, et al. Microwave plasmacombustion of coal, Fuel, 2003, 82, pp.187-93.
[12] Y. Chen, H. Wang, L. H. Zhao, et al. Ignition of pulverized coal with
hot air burners, Journal of Power Engineering, 2007, 27(1), pp.38-41.[13] X.Nie, Z. J. Zhou, M. Lu, et al. Experimental study on pulverized coal
flow ignition and flameout in high temperature air, Proceedings of theCSEE, 2008, 28(14), pp.67-72.
[14] Z. H. Chi, and G. G. Sun, Study on numerical simulation of first-stagefiring chamber structure in oil-saving ignition burner, Thermal PowerGeneration, 2007, 11, pp.20-23.
[15] Z. G. Fu, Z. P. Wang, and L. L. Shi, Numerical simulation of thetiny-oil ignition burner in the coal fired boiler, Journal of EngineeringThermophysics, 2008, 29(4), pp.609-612