Reduction of SO2 emissions by ammonia gas during staged combustion

To reduce SO2 emissions, ammonia gas was injected into a coal-fired fluidiz ed-bed combustor under staged commbustion condition. The combustor was 2 m high with a 30 cm static bed height and a freeboard height of 170 cm. The a mmonia gas was injected at 52 cm and 65 cm above the distributor, which had a temperature of ca. 700 degrees C, by an uncooled stainless-steel tube in jector. The experiments investigated the effects of ammonia gas injection o n sulphur dioxide emissions at staged conditions, varying the: (i) excess a ir level, (ii) secondary air ratio, (iii) fluidizing velocity, (iv) ammonia injection position, and (v) the ammonia : sulphur dioxide molar ratio. A maximum reduction of 66% in SO2 emissions was found at 40% excess air, 65 : 35 staging, 1.5 m/s fluidizing velocity, 65 cm injection height, and an NH3 : SO2 molar ratio of 1.2. The onset of SO2 reduction occurred at an NH3 : SO2 ratio of 0.5. The fluidizing velocity, excess air, level of staging, and ammonia injection height all have a significant influence on SO2 reduc tion. It is difficult to determine how the SO2 reduction varies with the operatin g conditions when ammonia is injected in the high temperature zone of the c ombustor. As sulphur oxides-ammonia reactions are low temperature reactions , the findings confirm the occurrence of reactions above the freeboard or n ear the exit to the cyclone.