Reduction of SO₂ emissions from a fluidized bed under staged combustion by fine limestone

This paper considers the effects of operating variables on SO₂ emission in staged combustion with a stainless steel combustor 2 m high with a 0.3 x 0.3 m cross section. Fluidizing air was supplied through a multihole distributor. The experiments were carried out for fluidizing velocities of 1- 2 m/s, bed temperature of 830-880°C, 20-40% excess air, and bed particle sizes of 0.313 and 0.655 mm. The bed temperature, fluidizing velocity, and excess air level had a significant effect on SO₂ emissions reduction during staged combustion. A maximum reduction of 64% was obtained at 70:30 stage, 830°C bed temperature and 1.0 m/s fluidizing velocity. The zero or negative emissions reduction resulted from the balance between the SO₂ pick-up by limestone in the region where oxidizing conditions prevail (due to a higher stage level, i.e. 60:40) and the release of SO₂, already captured elsewhere in the combustor, from CaSO₄ in reducing regions (due to higher stage and low excess air.