Formation of Calcium Chloride and Its Interaction With the Sand Particles During Fluidised Bed Combustion

Fluidised bed boilers are well suited to burning fuels that have diverse characteristics such as refuse-derived fuels and biofuels. These fuels often contain various amounts of chlorine. In many countries, the emissions of HCl from waste material combustion are regulated by stringent laws. In the fluidised bed combustion of sulphur-containing fuels, the addition of a Ca-based sorbent into the bed is a widely used method for controlling SO₂ emission. In this work, the absorption of HCl with limestone was studied in the laboratory at high temperatures, 650–850°C, by using a special thermogravimetric apparatus (TGA). In addition to the absorption rates, special emphasis was placed on studying the effects of molten phase formation during chlorination. We have recently reported our first results on the interactions between the calcium chloride being formed and the quartz sand. We proposed a chemical mechanism for the formation of the calcium silicate coatings frequently found on the sand particles in fluidised beds. Here, the proposed mechanism in which calcium chloride acts as a crucial intermediate is more thoroughly discussed.