The characteristics of simultaneous calcination and sulfation of limestone in circulating fluidized bed boiler (CFBB) conditions were studied. The calcination and sulfation reaction of the limestone was tested in a TGA. The lowest weight(%) reached by samples underwent calcination and sulfation simultaneously was higher than that of samples calcined in N-2 then sulfated, and it took more time for the former to reach the lowest weight(%) point. The lowest weight(%) point was a point at which the rate of weight loss due to calcination equaled the rate of weight gain due to sulfation. It was not a point that signified the end of calcination of limestone and nor the point of beginning of the sulfation reaction. The effects of some factors, including SO2 concentration, temperature, particle size, etc., were tested. The effect of SO2 on the calcination of limestone is a function of SO2 concentration. The differences in the lowest weight point reached at different SO2 concentrations (2250 and 3800 ppm) decrease at higher temperatures, for example 7.3% at 850 degrees C but only 3.6% at 880 degrees C. The effect of particle size is the most significant among all the variables tested. SEM-EDX showed there are some un-reacted calcium zones in the particles, especially in the core of the particles. Quantitative XRD phase analysis verified that for the limestone samples underwent calcination and sulfation simultaneously, there were indeed some CaCO3 remaining in the sorbent, even after 90 min of reaction. The sulfated limestone samples were crushed and heated in TGA to determine if and how much CaCO3 still remain. The limestone that calcined in N-2 then sulfated has higher utilization than that underwent calcination and sulfation simultaneously. (C) 2015 Elsevier Ltd. All rights reserved.