抄録
In fluidized bed combustors (FBCs), in-situ SO_2 capture is conducted by feeding limestone (CaCO_3) to the reactor to form harmless CaSO_4. Pure CaSO_4 is known to be very stable under oxidizing conditions at FBC bed temperatures (800-900℃). However, the temperature of burning fuel particles or the temperature near fuel feed points where volatile matter combustion occurs are considered to be higher than the average bed temperature. In addition, there exist coal ash particles around the sulfated limestone particles (or fine sulfated limestone powders around coal particles), and the temperature of CaSO_4 decomposition may be affected by the coexistence. The objective of this work is to evaluate the decomposition rate of CaSO_4 mixed with coal ash. The mixture was heated up to 1350℃ in oxidizing atmosphere, measuring SO_2 release and weight change of the mixture. Pure CaSO_4 was found to be very stable and decomposition occurred only at higher temperatures than 1250℃. When coal ash was mixed with CaSO_4, the decomposition and SO_2 release occurred at relatively lower temperatures, for example, 1000℃. Mechanism of the decrease in CaSO_4 decomposition temperature is discussed based on equilibrium calculation using FactSage.
