The Effect of Chlorine and Sulfur on the Composition of Ash Deposits in a Fluidized Bed Combustion System

Abstract

The major advantage of fluidized bed combustion (FBC) of fuels is the ability to absorb SO2 and HCl when limestone is used in the combustor. The combustion of high chlorine coal does generate some concerns about the possibility of chlorine-related corrosion of boiler components at high temperatures. It is believed that molten alkali salts may cause severe corrosion when they deposit on the surfaces of heat exchange tubes in a boiler. A better understanding of the effect of temperature on the deposition of alkali chloride will help find a way to convert them to harmless salts before they condense on the components of an FBC system. Furthermore, the knowledge of the distribution of sulfur and chlorine in ash under different conditions is necessary not only to understand the principle and efficiency of desulfurization by limestone, but also to evaluate the role of limestone in the capture of HCl. In this study three different fuels with different chlorine, sulfur, and alkali contents were burned in a 0.1 MWth bench scale FBC system. The effects of coal types, temperature, position, and exposure time on the composition of ash deposits were investigated by ICP-AES and XRD spectroscopy. The major compound in the ash deposits is CaSO4. The experimental results show that the operating temperature has a major effect on the condensation of alkali chloride. The absorption of HCl is favored at the lower temperatures.