The effect of steam on simultaneous calcination and sulfation of limestone in CFBB

During simultaneous calcination and sulfation of limestone, the weight of the sample will first decrease due to calcination (the first stage) and then increase from the lowest weight point on the curve due to sulfation (the second stage). The rate of weight loss in the first stage will be accelerated by steam. However, the effect of steam on the lowest weight (%) reached by the sample is insignificant and the time needed to reach the lowest point is shorter with more steam. SO2 capture capability of Ca-based sorbent would be improved by steam (up to 15%). The effect of steam on the calcination of limestone is further enhanced with temperature increases. It seems 880 degrees C is a better desulfurization temperature at 15% steam than 850 degrees C. For smaller limestone particles the effect of 15% steam is more significant on the rate of sulfation than on the rate of calcination. The higher SO2 concentration will help to get better sulfation results. SEM-EDX analyses show that when reaction gas contains steam, there is no obvious un-reacted CaCO3/CaO zone in the core of the particles unlike what is observed without steam present. Quantitative phase analysis verifies that steam will decrease the CaCO3 quantity remaining in the sulphated samples and improve the sulfation ratio. TGA was used for accurate measurement of Ca-utilization, which was noticeably improved by steam. Based on Ca-utilization when there is steam, it seems that the size of the limestone particle is a more significant factor than SO2 concentration to determine the extent to which CaCO3 will be utilized in the sulfation reaction. The reaction tendency of two limestones, Kelly and Massieci, is very similar, which shows that the effect of steam observed is not limited to only one particular limestone. (C) 2016 Elsevier Ltd. All rights reserved.