The simultaneous calcination/sulfation reaction is the real reaction process of limestone in circulating fluidized bed (CFB) boiler. To obtain the true calcination process of limestone in CFB

the combined effect of H2O and SO2 on the calcination kinetics and pore structure of limestone during simultaneous calcination/sulfation reaction under CFB conditions was studied in a constant-temperature reactor. H2O (0-15%) can accelerate the calcination of CaCO3. The SO2 in flue gas decreased the calcination rate of limestone particles. This phenomenon was explained by a mechanism based on the measurement of pore structure

namely that SO2 reacted with CaO layer

and the formed CaSO4 would fill or block the pore in CaO layer

decrease the pore volume

increase the diffusion resistance of CO2

and consequently impede the calcination reaction. H2O and SO2 can work synergistically on changing the calcination rate

and an increase of the calcination rate was found under 15% H2O and 0.3% SO2 compared to that without either. This may be because intrinsic reaction played a major role in the rate controlling step of calcination

and H2O accelerated the intrinsic calcination directly. The effect of other factors like temperature and particle size on the calcination rate in the presence of H2O and SO2 were also tested. H2O also accelerated the sintering of CaO significantly

and along with SO2

the pore volume and surface area of CaO decreased further.