Desulfurization extent in the 71MWe PFBC demonstration plant was analyzed in terms of operational parameters and morphology of the desulfurizing bed material. High removal level of SO2 achieved in PFBC in spite of high CO2 partial pressure was correlated not with the temperature of the bed but with the temperature of the exhaust gas (Tg), suggesting that the emission of SO2 is governed by the decomposition of CaSO4 flying out from the boiler. The residence time in the fluidized bed did not influence the level of SO2 emission, indicating the saturation of desulfurization reaction in the bed within rather short time . The sorbent particles in the bed had CaSO4 layer of 30-40μm thickness on the surface . Since the calcium minerals produced are porous in the core as well as in the skin, such observation suggests the formation of CaO at the bottom of the furnace where the CO2 partial pressure was sufficiently low for the decomposition of CaCO3. The skin of material was eroded to expose the active surface for further desulfurization. Such CaO of sufficient amount in the bed adsorbs SO2 very rapidly to complete the desulfurization in the bed . Hense the concentration of SO2 in the flue gas is determined by the reaction CaSO4+CO→CaCO3+SO2 in the freeboard. This reaction appears in equilibrium since a fair linear correlation was observed between ln (PSO2/PCO) and 1/Tg.
