As the temperature of the reactor is insufficient to generate thermal NO, the source of NO is fuel nitrogen. Thus most NO comes from oxidation of fuel N. Correcting the NO emissions of 3% O2 is a common industry practice to prevent utilities from artificially diluting NOx emissions with O2. In the very lean regime, correcting caused the NOx emissions to increase. However, for

all other equivalence ratios, correcting caused the NOX emissions to decrease because there is less than 3% O2 in the exhaust prior to correcting. Figure 3.29 and Figure 3.30 present the NOX emissions forTXL andTXL:DB blended fuels in ppm and corrected to 3% O2. With the exception of 95-5 TXL:HA-PC-DB-SoilS, all of the blended fuels produced more NOX in the lean region than the pure TXL even though DB contains more N. There are three possible reasons: (i) higher amount of fuel-bound nitrogen present in the biomass binding with the excess oxygen to form NOX, (ii) release of more N in the form of NH3 due to high urea in DB, and (iii) depletion of oxygen due to oxidation of higher amount of VM released at lower temperatures from biomass thus preventing the oxygen from bonding with fuel nitrogen.

Instead of reporting NO at 3% O2, another method employed to prevent emission dilution is to report NOX levels on a heat basis. Annamalai and Puri (2007) presented the conversion formula from ppm of pollutant species k to k in kg/GJ, given that the fuel fired is CcHfcO0N„Ss. For pollutant species k:

on an atom basis, where c is the carbon atoms in the fuel, Xk mole fraction of species k and MF is the molecular weight of the empirical formula for the fuel. With k = NO:

where the molecular weight for NO is expressed in terms of the molecular weight of NO2, as required by the EPA. Figure 3.31 presents the NOX emissions in kg/GJ of heat input.

Note that in the lean region, the blended fuels produce more NOX than the pure WYO. In the slightly rich region, the blended fuels produce less NOX than the pure WYO due to more release ofN in the form ofNH3 from DB.

Figure 3.29. Effect of fuel onNOj forTXL andTXL:DB blended fuels. Note that blended fuels have lower NOx values at stoichiometric and in rich combustion (adopted from Lawrence, 2007).

Effect of Fuel on NO„ for TXL and TXL:DB Blended Fuels eTXL И95-5 TXL LA-PC-DB-SepS A 90-10 TXL LA-PC-DB-SepS Є 80-20 TXL LA-PC-DB-SepS

Figure 3.30. Effect of fuel onNOx forTXL andTXL:DB blended fuels corrected to 3% O2 (adopted from Lawrence, 2007).

The same explanation for TXL applies to the WYO fuels. Figure 3.32 and Figure 3.33 present the NOX emissions from WYO and WYO:DB blended fuels in ppm and corrected to 3% O2. Figure 3.34 presents the NOX emissions from WYO and WYO:DB blended fuels in kg/GJ of heat input.