OCR Text |
Show WHO d = z (l-M)YH WH z W=W-W- eX. eoz ,lll.T alT z = (l-M)kyc 7 [5] [6] [7] where M is the fuel moisture content, wet basis, the Wi are the molecular weights, the Yi are the mass fractions of elements (carbon, C, and hydrogen, H) or ash in the dry fuel, the Xi are the mole fractions (dry basis) of carbonaceous species in the gas or inlet air, and rna is the mass flow rate (measured) of combustion air. When preheat was used, the carbon balance was corrected for the contribution from natural gas combustion. The balance assumes only carbon and ash remain in the condensed phase. The fraction, k, was determined by calibrating the estimated cumulative fuel consumption against measured fuel consumption obtained gravimetrically, with values generally close to unity. The emission factors are reported only for periods of stable operation. Results Results from the wood and rice straw experiments are illustrated in Figures 2 through 6. The trends in emission factors are typical of the results from the other three fuels as well. Figure 2 compares the equivalence ratios derived by carbon balance with the measured values obtained gravimetrically. Each of the values shown for the carbon balance is an average taken over the period during which each measured value was obtained. The carbon balance technique appears to yield an adequate measure of the instantaneous fuel consumption, which was not measured directly. NOx emission factors are shown in Figure 3. The values are given as percent of dry fuel mass. The NOx profiles show a quite typical decline as the equivalence ratio increases toward unity from fuel lean conditions. Under extremely lean conditions, the emission factor also appears to fall off, but this is less certain as the values shown come from portions of the steady periods near start-up and shut-down transients. Steady operation at t/> < 0.2 was not normally attempted. |