The majority of components in the circulating material of a Circulating Fluidized Bed (CFB) boiler are desulfurization products. Under different working conditions, the reducing components are enriched at the bottom of the furnace, which affects the decomposition of the desulfurization products. The reaction processes between the desulfurization products, CaSO4, bituminous coal and CO was experimentally investigated under different mass ratios or concentrations with a TGA-FTIR and quartz tube furnace heating system. The results were analyzed with an XRF. Where the temperature was higher than 700 degrees C, the bituminous coal had been pyrolyzed. The CaSO4 that blended with the bituminous coal decomposed, releasing SO2. Less SO2 was released when the mass fraction of the bituminous coal in the mixture was reduced. The CaSO4 struggled to decompose when the CO concentration was less than 0.1%. The decomposition rate of the CaSO4 and the fraction of S released increased when the CO concentration was more than 0.1%. Under 1%, more than 44.07% of SO2 was released, approximately double when under 0.25% CO. Reducing the components had a negative effect on SO2 emission control. Here, a higher reduction of components resulted in a greater fraction of S released. (C) 2016 Elsevier Ltd. All rights reserved.