Combustion calculations were performed for typical natural gas and #2 fuel oil. Table below shows the flue gas analysis,molecular weight and flue gas generated per MM Btu fired at different excess air levels.
 

Excess air,%	0	10		20		30		0	10		20		30
Fuel	<----natural gas----------->							<-----# 2 fuel oil----------->
% vol CO2	9.47		8.68		8.02		7.45	13.49		12.33		11.35		10.51
H2O	19.91		18.38		17.08		15.96	12.88		11.90		11.07		10.36
N2	70.62		71.22		71.73		72.16	73.63		74.02		74.34		74.62
O2	0		1.72		3.18		4.43	0		1.76		3.24		4.50
Mol wt	27.52		27.62		27.68		27.77	28.87		28.85		28.84		28.82
Wgm	768		841		914		986	790		864		938		1011

Natural gas analysis used:% vol # 2 fuel oil analysis methane=97,ethane=2,propane=1
(HHV=23,759 LHV=21,462 Btu/lb)
#2 fuel oil analysis used: C=87 %,H2=12.5,deg API=32(HHV=19,727,LHV=18,512)
 

CALCULATIONS FOR STEAM GENERATOR Converting mass of NOx to volumetric units we have:   Vn=106xYx (N/46)x(MW/Wgm)x(21-3)/(21-O2xY) where  MW=molecular weight of wet flue gas  N=lb of NOx per MM Btu fired(HHV basis)  O2=% volume of oxygen in wet flue gases  Vn=ppmv dry NOx  Wgm=flue gas produced per MM Btu fired  Y=100/(100-% H2O),where %H2O=volume of water vapor in wet flue gases  From Table at zero excess air:  Y=100/(100-19.91)=1.248,MW=27.53,Wgm=768,O2=0  Vn=106 x1.248xNx27.52x18/(46x768x21)=832 N  Similarly,to obtain CO conversion,use 28 instead of 46(molecular weight of CO instead of NO2)  Vc=1367 CO where CO=lb of CO per MM Btu fired  Repeat at 30 % excess air:  Wgm=986,Y=100/(100-15.96)=1.189,MW=27.77,O2=4.43  Vn=106x1.189xNx27.77/[46x986x(21-4.43x1.189)]=832N  Thus independent of excess air,we obtain 832 as the conversion factor for Nox and 1367 for CO.  Similarly for # 2 oil,it can be shown:  Vn=783 N and Vc=1286 CO  Example:If a natural gas fired boiler generates 0.1 lb/MM Btu of NOx,the equivalent is 0.1x832=83 ppmvd  If oil is the fuel,then 0.1 lb/MM Btu of CO=129 ppmvd

Calculation for Gas Turbine Exhaust  The procedure shows how to convert between lb/h of NOx or CO to ppmvd. The pollutants could be in the exhaust gas or could also be added by the burner.The main difference between steam generators and gas turbine exhaust gas is how the NOx or CO is reported. It is on 15 % dry oxygen versus 3 % in the case of steam generators. If w lb/h of NOx in a total exhaust flow of W lb/h,the following expression gives the NOx in volumetric units. V=100x(w/46)/(W/MW)/(100-% H2O) where % H2O=volume of water vapor in exhaust gas MW=molecular weight of exhaust gas Converting V to 15 % oxygen dry,we have: Vn=Vx(21-15)x106/(21-%O2dry)= Vx F %O2dry=100xO2/(100-O2) Similarly CO can be converted:  Vc=Vnx1.642 Example: 550,000 lb/h of turbine exhaust having the analysis:% vol CO2=3.5,H2O=10,N2=75,O2=11.5 contains 25 lb/h of NOx and 15 lb/h of CO. MW=.01x(3.5x44+10x18+75x28+11.5x32)=28 V=100x(25/46)/(550,000/28)/(100-10)=0.00003074 %O2dry=100x11.5/(100-10)=12.78 Vn=0.00003074x6x106/(21-12.78)=22.4 ppmvd Similarly,Vc=(15/25)x22.4x1.642=22 ppmvd In incineration systems,7 % oxygen dry is used as the basis and one can similarly use the above method to perform the conversions.

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