Effect of water vapor on the pore structure and sulfation of CaO

Limestone is widely used for controlling sulfur emissions from fluidized bed combustion. Flue gases generated by coal combustion mainly consist of N2, O2, CO2, SOx, NOx, and about 5-15% water vapor. However, few investigations were carried out to study the effect of H2O on the sulfation behavior of limestone. In this study, the effects of H2O on pore structure of CaO and its sulfation behavior were studied. The temperature range was 800-950 °C and water vapor concentration was from 0% to 20%. It was found that the presence of H2O could reduce the calcination time of the limestone and both BET surface area and pore volume of the resulting CaO decreased with the increase of water vapor concentrations in the temperature range of 850-950 °C. The results showed that water vapor promoted sintering of CaO during the calcination period of the limestone and led to the deteriorated pore structure. The BET surface area and the pore volume of CaO continue to decrease with the increase of sintering duration, regardless of whether water vapor is present or not. The test results showed also that the presence of water vapor during the calcination stage was detrimental to the following sulfation of CaO. However, regardless of the initial calcination environment (with or without water vapor), the sulfation of the resulting CaO improves by the presence of water vapor.