Limestone decomposition and desulfurization in a circulating fluidized bed boiler occurs simultaneously with calcination/sulfidation. A random pore model

which considered the calcination of CaCO3

the sintering of CaO and the sulfation of CaO simultaneously

was established

and the sulfation model of CaO was based on the solid state ion diffusion in the CaSO4 product layer. The results of the model are well matched with the results from the TGA test

thus the model can be used to investigate the kinetics of the simultaneous calcination sulfation (SCS) reaction. The SCS reaction contains a mass loss stage and a mass gain stage

which were divided by the minimum mass point. The minimum mass point got higher with the increase of the SO2 concentration. The calcination reaction occurred in a layer of the particle

which is different from the homogeneous reaction model or the unreacted-core shrinking model. The SO2 in the calcination atmosphere can react with the CaO layer and form CaSO4

which can fill the pore of the CaO layer and narrow the pore width

increase the CO2 diffusion resistance and slow the calcination reaction. The sulfation of the calcined CaO got slower with the reaction time. For a particle with a radius of 200 μm sulfated in 0.4% SO2 atmosphere

the decrease of the sulfation rate in the part of the inner 150 μm was mainly caused by the lower SO2 concentration here. There was a zone where the SO2 exhausted. With the sulfation reaction proceeding

more CaSO4 accumulated in the outer layer of the particle

which increased the diffusion resistance of SO2 in the outer layer of the particle

caused the exhausting zone of SO2 being larger and the sulfation rate of the total particle being slower.