OCR Text |
Show Operating experience and design will likely improve the concepts. It should be noted that while normal kiln coal burners receive their primary combustion air directly with the fuel, Low-NOx burners would require an independent air supply (indirect firing) largely fed from the clinker cooler. O n an existing kiln, this represents a significant cost compared to that of the new burner. Staged Air Combustion By breaking the heat input into two locations, short precalciner kilns avoid the need to transfer heat a great distance in a long kiln, thereby reducing emissions and fuel consumption. There is however some thermal and fuel N O x formed by the fuel-rich precalciner burner. Studies are underway to mitigate this effect by firing s o m e of the precalciner fuel in the initial kiln exhaust to create a reducing condition (NOx -• N2), with the remainder fired in the upper calcining section for complete burnout. Staged Air Combustion has the potential for about 20-30% emission reduction in n e w precalciner kilns, but these levels are more difficult to achieve on existing plants. Clinker quality in the upstream portion of the kiln would not be affected. SAC: Reduction of N O x emusiofu by selective fud supply to the kiln inlet (Knjpp Polysius) (Scarce: Ref. 9) Selective Non-Catalytic Reduction SNCR using injection of ammonia compounds is also being investigated in Europe as a feasible post-combustion technology. Solid urea or liquid ammonia injection into a high temperature exhaust stream (900 -1000 °C) has been done on a trial basis, with a reported 30-60 percent N O x reduction on precalciner kilns. Issues to be resolved include possible effects on E SP performance, sensitivity to injection location and gas temperature, increased N20, C O emissions and N H 3 slip, and the costs and effort in handling ammonia. 16 |