Simultaneous reduction of emissions of SO₂, NOX, and N₂O from fluidized bed combustors

The effects of staged air feed and limestone feed into a bubbling fluidized bed combustor on emissions of SO₂, NOx and N₂O were investigated. The staged air feed reduced both NOx and N₂O emissions, but it inhibited SO₂ removal. NOx emission increased with increasing sulfur removal. To solve the interference problem among reduction of NOx, N₂O, and SO₂, a two-staged fluidized bed combustor was proposed, in which combustion of coal was conducted in the lower bed and SO₂ capture in the upper bed. To simulate two-staged FBC, flue gas from a circulating fluidized bed combustor was fed in to a fluidized bed reactor of limestone. NOx emission did not increase with SO₂ capture and more effective decrease in N₂O emission was achieved for the two-staged fluidized bed combustion in comparison to the conventional in-situ SO₂ capture. The results of SO₂ capture and N₂O reduction for two-staged fluidized bed were analyzed using the Kunii-Levenspiel model. A fixed bed reactor was employed to obtain kinetic data. The results of the calculations agreed fairly well with the experimental results.