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Combustion programs for boiler,cogeneration engineersExamples
There are two programs in this package,one for steam generators and another for HRSGs.
The first program handles boiler combustion,efficiency calculations.Up to 4 fuels(solid,liquid,gaseous)  can be fired simultaneously and the % duty for each fuel can be varied.(Of course,a single fuel can also be handled).The program computes the boiler duty based on steam parameters,performs combustion and efficiency calculations per ASME PTC 4.1 and arrives at the air flow,flue gas flows,flue gas analysis,efficiencies on HHV,LHV basis for each fuel and on overall basis.NOx,CO conversions are also computed for each fuel.Duty refers to energy absorbed by steam.The following example illustrates the type of problems that can be handled by this program.
Example:A boiler generates 100,000 lb/h of superheated steam at 600 psig,700F,using feed water at 233 F.Blow down=2%.Two fuels are fired: natural gas and #2 fuel oil. Natural gas handles 40% of the duty and fuel oil,60 %.
Natural gas has the analysis:% vol methane=90,ethane=5,propane=1,butane=1 and carbon dioxide=2 fuel temp=80F
Fuel oil has the analysis by % weight:carbon=87,hydrogen=13,deg API=32. fuel temp=80F
Excess air used=15%,ambient temperature=80F,relative humidity=60% and exit gas temperature=320F.Assume radiation and unaccounted losses each=0.5%.Combustion air is at 80F.

 Data as inputted in the program
Project-Sample 
Units-British 
steam flow=100,000 
steam temp=700 
steam pres=600 
feed water temp=233 
blow down=2 
excess air=15 
ambient temp=80 
exit gas temp=320 
rel humidity=60 
radiation loss=0.5 
unaccounted loss=0.5 
comb air temp=80
% nat gas duty=40 
% fuel oil duty=60 
fuel 1-nat gas analysis  
methane=90 
ethane=5 
propane=1 
butane=1 
carbon dioxide=2 
nitrogen=1 
fuel 2-fuel oil analysis  
carbon=87 
hydrogen=13 
deg API=32 
fuel temp=80
 Results from the program
Boiler duty-MM Btu/h=115.3 
excess air-%=15 
amb temp-F=80 
exit gas temp-F=320 
rel humidity-%=60 
Flue gas analysis-% vol (wet/dry) 
co2  10.33/12.09 
h20   14.61 
n2   72.57/84.99 
o2   2.49/2.92 
so2   -/- 
total air-lb/h=114511 
total flue gas-lb/h=121012 
efficiency-%HHV=85.8 
efficiency-%LHV=92.99 
adiab comb temp-F=3288
Note the above data are on weighted overall basis.The final flue gas analysis is computed after considering the analysis for products of combustion of each fuel and their mass flows. Combustion calculation results for each fuel are also given by the program as shown below. The ASME PTC 4.1 heat losses are printed out for each fuel as shown.
FUEL 1:gas % volume[% duty=40] 
methane=90,ethane=5,propane=1,butane=1,carb diox=2,nitrogen=2 
fuel and air input HHV-MM Btu/h=55.06 fuel fired-lb/h=2493 ad comb temp-F=3244 
air/fuel ratio=18.56 gas/fuel=19.56 eff-lhv%=92.7 eff-hhv%=83.76 
losses:dry gas-%=4.51 air moisture=.12 fuel moisture=10.61 radiation=.5 unaccounted=.5 
flue gas analysis:% vol co2=8.55 h2o=17.92 n2=71.06 o2=2.46 so2=. 
LHV-Btu/lb=19954 HHV-Btu/lb=22083 fuel temp F=80 air temp F=80 
NOx-ppmv/0.1lb per MM Btu HHV=82.7 CO-ppmv/0.1 lb per MM Btu HHV=135.9
FUEL 2: oil-% weight [% duty=60] 
carbon=87 hydrogen=13 sulfur=-nitrogen=- oxygen=- deg API=32 
fuel and air input HHV-MM Btu/h=79.31 fuel fired-lb/h=4020 ad comb temp-F=3333 
air/fuel ratio=16.97 gas/fuel=17.97 eff-lhv%=93.19 eff-hhv%=87.22 
losses:dry gas-%=4.84 air moisture=.12 fuel moisture=6.81 radiation=.5 unaccounted=.5 
flue gas analysis:% vol co2=11.57 h2o=12.29 n2=73.63 o2=2.51 so2=. 
LHV-Btu/lb=18463 HHV-Btu/lb=19727 fuel temp F=80 air temp F=80 
NOx-ppmv/0.1 lb per MM Btu HHV=77.6 CO-ppmv/0.1 lb per MM Btu HHV=127.4

The second program in this package performs combustion calculations with gas turbine or engine exhaust or simply air. Given the exhaust gas flow(or air flow),temperature and analysis in % volume,the program computes the fuel energy required to raise the temperature of the incoming stream to a desired level or the firing temperature given the fuel input. One can also add augmenting air to the exhaust gas flow. Final flue gas analysis is also given.Gas or oil fuels only.
Example:127,000 lb/h of exhaust gases at 900 F from a gas turbine having the ananlysis -% vol CO2=3,H2O=6.5,N2=76,O2=14.5 has to be raised to 1340 F using a duct burner.Determine the fuel input if natural gas having % volume methane=90,ethane=3,propane=2.5,carbon dioxide=2.5 and nitrogen=2 is used.

  Data
project-study 
units-British 
exhaust gas flow=127000 
exhaust gas temp=900 
exhaust gas analysis 
%vol co2=3 
h2o=6.5 
n2=76 
o2=14.5 
% rel humidity=. 
firing temperature=1340 
fuel input=- 
 
fuel analysis 
% vol methane=90 
ethane=3 
propane=2.5 
carb diox=2.5 
nitrogen=2 
augmenting air flow=. 
augmenting air temp=.
 Results
Project-study  units-British 
exhaust gas/air flow-lb/h=127000 exhaust temp-F=900 
tot gas flow-lb/h=127864 firing temp-F=1340 burner fuel-MM Btu/h=16.76 
% vol co2=3 h2o=6.5 n2=76 o2=14.5 so2=. (before burner) 
% vol co2=4.08 h2o=8.5 n2=75.18 o2=12.19 so2=. (after burner) 
______________________________________________ 
Fuel- gas - % volume 
methane       90 
ethane          3 
propane       2.5 
carb dioxide 2.5 
nitrogen        2 
LHV-Btu/cuft  = 931 
HHV-Btu/cuft = 1030 
LHV-Btu/lb =19396 
HHV-Btu/lb = 21523 
fuel flow-lb/h = 864
Note that fuel input is on LHV basis. Also, the fuel input on LHV basis may also be given and the program will compute the firing temperature..

V.Ganapathy

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