The Significance of Air-Staging on Sulphur Capture in a Fluidised Bed Combustor

Staged combustion is an established technique for reducing NO emissions, and limestone addition has been shown to be an effect i ve method of sul phur capture in fluidised bed combustors operating conventionally. This paper has investigated the effect of air-staging on sulphur capture by limestone in a pilot scale 0.3m square fluidised bed combustor. The results showed that wi thout air stagi ng, up to 70% of the sul phur can be retained, and staged operation has little effect on sulphur emissions without limestone addition. However, during staged operation, with limestone addition, sulphur retention decreases by up to 75% as the level of air staging is raised. At high staging levels (at a primary air factor 1 ess than 0.95) sul phur capture is always poor, being less than 10%, irrespective of bed temperature, whilst at lower staging levels, sulphur capture is very temperature sensitive and decreases significantly at bed temperature greater than 850°C.