| OCR Text |
Show These calculations have assumed, that conversion of total fuel nitrogen to N02 was 100%. The experimental results obtained with these six fuels with SRO=l burnt under unstaged conditions show that the rate of NO formation is an order of magnitude less than theoretically calculated curves ~~heor and Exp SRO=l in Figure 11). This shows that not all fuel nitrogen was converted to NO. Figure 11 shows also the minimum NO (staged) emissions from the six liquid fuels as a function of fuel nitrogen (curve exp SR1=0.7). NO emissions is an order of magnitude less than the results without staged combustion. Fuel NO emissions generally increased with increasing fuel nitrogen content for both staged and unstaged combustion. Under optimum conditions, NO emissions correlate well with total fuel nitrogen content but the slope is signi-ficantly less under excess air conditions (Figure 11)The results show that the source of liquid fuel had little impact upon fuel NO production. The highest nitrogen fuel tested was nitrotoluene (9.5% fuel N) which also gave the highest NO emissions. The toluene with 4% oil contained less than 0.05% nitrogen and gave very low emissions. Again all other fuels tested (with 0.99, 2.8, 5.1% nitrogen) correlate very well with total fuel nitrogen content, and overall NO emissions depended on factors other than total nitrogen. Predicted exhaust NO emissions Solomon and co-workers (5) determined the reactive volatile nitrogen content of the 19 most diverse coals by pyrolyzing them in vacuum of 1370K and measuring the HCN yield by FTIR. From these results a multi-variable regression algorithm yielded the following equation: where NO = 318+702[N]+0.188[HCN]-0.347[non-volatile N] (Eq.1) [N] = [HCN] = [non-volatile wt % nitrogen in original coal (daf) inert pyrolysis HCN yield, ppm equivalent N] = modified ASTM solid nitrogen; ppm equivalent. The above equation has been used to predict the NO emissions from three liquid fuels (oil, 30NT and lOON) for combustion under unstaged conditions. For [N] and [HCN] in equation I, the wt % fuel nitrogen and the maximum HCN yield at stoichiometry SR1=0.5 have been- used. Figure 11 shows the results of the empirical correlation with the experimental measurements (Exp SRO=l). These data correlate very well with experimental measurements and show that conversion of fuel nitrogen to NO does not depend on how nitrogen is bounded in fuels which evolved as volatile matter. The same results have been obtained for oil and gas (C02 and H~) doped with 3000 ppm HCN and burned in a commercial 7.2 MW b01ler (6). However, the form of the above correlation is consistent with the physical understanding. Staged combustion predicts secondary NO concentration from NH3 , HCN and NO concentrations emitted from the primary stage. An empirical correlation is used, originally developed to predict NO concentration emitted from the secondary stage of rich primary staged coal combustion (7). The formula is as follows: 8 |
