Combined non-catalytic reduction of NO(x) and SO₂ by ammonia liquor during staged fluidized-bed combustion

Emissions of NO(x) and SO₂ were monitored in the presence of ammonia liquor in a 0.09 m² and 2 m high stainless-steel fluidized-bed combustor. Experiments were carried out at 2 m/s fluidizing velocity, 40% excess air, and 870°C bed temperature. Ammonia liquor with 7% ammonia by weight was injected into the freeboard of the combustor 52 cm above the distributor through a water-cooled injector. A 65:34 primary/secondary air ratio was maintained throughout the investigation. Approximately 70% of NO and 20% of SO₂ was reduced at an NH₃/NO molar ratio of 2:1, respectively. However, a higher reduction in SO₂ emissions (62%) was achieved at a very high NH₃/NO molar ratio of 7:1. These experiments showed that ammonia addition did have a significant effect in SO₂ reduction if injected in an excess amount. The injection of ammonia liquor combined with staged combustion was found to be very effective in reducing NO(x) emissions. A reduction of about 50% was achieved at an NH₃/NO molar ratio of 0.6:1 which is also coupled with a very low level of ammonia in the flue.