Enhancement of sorbent utilization in fluidized-bed combustion

A new, simple and non-corrosive method is described which can substantially reduce the lime requirement in fluidized-bed combustion of coal. The method entails spraying the limestone particles before they are fed to the combustor with an aqueous solution of iron (ferric and/or ferrous) sulphate and/or sulphite. These compounds rapidly decompose in the environment of the combustor and Fe₂O₃ is deposited on the lime surface. Small amounts of Fe₂O₃ deposited in this manner substantially catalyse the rate of SO₂ uptake. For example, 1.4% Fe₂O₃ on Greer limestone nearly doubles the rate. The catalysis would translate into a calculated reduction of the lime requirement by over 40%, although direct translation would require large-scale testing. The basis of the catalysis is that Fe₂O₃ catalyses the oxidation of SO₂ to form SO₃. The SO₂ capacity of the limestone is also enhanced. This simple technique may also be applied to various hot-gas desulphurization processes, such as those with the dry scrubbers, and to other SO₂ sorbents.