OCR Text |
Show emissions decrease with thermal input from the afterburning fuel and can also be easily reduced to 50 ppmv or lower, as in the previous case of propane afterburning with the burner, shown in Fig. 2(a). Propane afterburning by direct fuel injection also resulted in small increases in N O / N O x emissions, as shown in Fig. 4(b). At a high initial oxygen level (5.7%) in the exhaust, N O and N O x emissions increased with thermal input from propane injection, while at a low initial oxygen level (4.4%), they increased initially and then decreased after the thermal input from propane injection reached about 11 k W . The effects of propane afterburning by direct fuel injection on S 0 2 and C O emissions are very similar to those observed for propane afterburning with the burner, as demonstrated by Fig. 2(c) and Fig. 4(c). 180 £ 150 a. 5 120 £ 90 60 30 E Q. a. 120 w 100 E _ Q 80 60 Q. 80 a. | 600 | 400 c\j O Cfl 200I oO o a •-.._ ^NNB**' - - - Ik. • T • T -t. O -_- •* O ..£ ^rf_H*^""_ •cr • 1 • 1- . ) 1 - i - • • - Initial 02 = 4 4 % J Initial 02 = 5.7% J (a) "** G (b) Closed symbol: NO Open symbol: NOx (c) Closed symbol: CO Open symb0l:SO2 , ., . . T __. 5 10 15 20 Thermal input by propane injection, k W 25 Figure 4 The effect of thermal input from propane injection on: (a) N 2 0 emission, (b) N O and N O x emissions, (c) S 0 2 and C O emissions Comparative performance - burner versus direct fuel injection: In terms of plant operation, a burner would be preferred to direct fuel injection as it can be independently ignited and controlled and is inherently safer. However, Fig. 5 shows that afterburning by direct fuel injection is more effective than by the burner for the same initial conditions and thermal input of the afterburning fuel. Effect of secondary fuel: T o investigate the effect of secondary fuel on N 2 0 reduction, methane or ethane was also injected into the riser through the fuel injector following the same experimental procedures as propane injection. Figure 6 summarises the relationship between the N 2 0 reduction, related to the amount of N 2 0 emitted before fuel injection, and the thermal |