Pilot scale studies of simultaneous control of SO/sub x//NO/sub x/ emissions derived from the combustion of low-rank coal

Simultaneous control of SO/sub x//NO/sub x/ emissions, derived from the combustion of low-rank coal, is being investigated at the University of North Dakota Energy Research Center (UNDERC). Process development work has been performed on both bench-scale and pilot-scale systems. Direct furnace injection of calcium-based SO/sub 2/ sorbent materials with subsequent collection on ceramic bags in a high-temperature baghouse is the SO/sub 2/ control technique being evaluated. Control of NO/sub x/ emissions is accomplished in conjunction with the high-temperature baghouse by catalytic reduction methods. Furnace injection tests have focused on the direct injection of pressure hydrated lime at flue gas temperature regimes ranging from 1500 to 3000/sup 0/F (815 to 1650/sup 0/C) followed by collection in a baghouse operated at temperatures up to 1000/sup 0/F (540/sup 0/C). Sorbent utilization values of approximately 40% at Ca/S mole ratios of 1.0 to 2.0 have been observed. Residence time and the temperature regime of the sorbent injection location appear to be the critical parameters controlling SO/sub 2/ retention and sorbent utilization. Catalytic reduction of NO/sub x/ using throwaway catalysts collected in the high-temperature baghouse is being investigated. Materials containing various forms of iron and a synthetic mordenite have been evaluated. Reductions of up tomore » 29% were achieved with a lignite fly ash containing about 8% Fe/sub 2/O/sub 3/, and up to 65% reduction using a synthetic mordenite have been observed. Control of NO/sub x/ emissions with an ammonia/selective catalytic reduction (NH/sub 3//SCR) reactor, located downstream of the high-temperature baghouse, has been successfully demonstrated. Simultaneous SO/sub x//NO/sub x/ control was demonstrated using direct furnace injection of pressure hydrated lime and the NH/sub 3//SCR system. Eighty percent SO/sub 2/ and NO/sub x/ reduction were achieved at a Ca/S ratio of 2.0 and a NH/sub 3//NO ratio of 1.0, respectively.« less