Simultaneous Carbonation and Sulfation of CaO in Oxy-Fuel Circulating Fluidized Bed Combustion

For anthracites and petroleum cokes, the typical combustion temperature in a circulating fluidized bed (CFB) is > 900 degrees C. At CO2 concentrations of 80-85% (typical of oxy-fuel CFBC conditions), limestone still calcines. When the ash which includes unreacted CaO cools to the calcination temperature, carbonation of fly ash deposited on cool surfaces may occur. At the same time, indirect and direct sulfation of limestone also will occur, possibly leading to more deposition. In this study, CaO was carbonated and sulfated simultaneously in a thermogravimetric analyzer (TGA) under conditions expected in an oxy-fuel CFBC. It was found that temperature, and concentrations of CO2, SO2, and especially H2O are important factors in determining the carbonation/sulfation reactions of CaO.