| OCR Text |
Show (1) Flue gas recirculation alone reduced NOx by 30% to 40%, but CO and Tptal Hydrocarbon(THC) remained high. (2) Natural gas, equivalent to 7% to 15% in heat value of MSW was injected through the secondary air nozzle at the near wal I. NOx was reduced by 50% to 70%. (3) NOx reduction rate was high when stoichiometric ratio was kept at 0.9 within the reburning zone, and the residence time at 1.5 seconds. (4) By injecting natural gas, stoichiometric ratio was reduced from 1.7 to 1.4 without increasing CO or THC. (5) Natural gas injection did not show significant effect on flue gas temperature at furnace exit. (6) Natural gas injection of 7% to 15% of MSW heat value stabi I ized combustion, which in turn stabi I ized O2 and CO levels at the furance exit. (Figure 4) 3.0 2.5 2.0 .r. w" 1.5 -l: t- 1.0 0.5 0 0 \.lITH NATURAL GAS \.IJTHOUT NAT~ GAS 25 0 \.11TH NATURAL GAS \·HTHOUT NATURAL GAS CO" ppm 500 Figure 4 THE EFFECT OF REBURNING ON STABILITY OF OPERATION 1. 3 Fie I d TEst With the successful result of the pi lot-scale test, a field test was conducted using natural gas reburn technology at the 100 TPD Olmsted furnace where basel ine data was collected earl ier. The furnace has a stoker as illustrated in Figure 5. MSW fed from the hopper onto the grates is heat-disintegrated and partially incinerated by the primary combustion air suppl ied from underneath the stoker, and completes its combustion by the secondary air injected into the furnace. Figure 6 shows the residence times and temperatures at each area of stoker, furnace and boi ler. With stoker-type incineration, flue gas recirculation creates reducing atmosphere inside furnace, reduces excess air ratio and reduces NOx most effectively, whi Ie an increase in CO is unavoidable. 5 |
