A review of chlorine-induced corrosion in underground mines and coal preparation plants

Abstract

Chlorine is a harmful constituent in coals because, above a concentration of 0.1 or 0.2 weight percent, it causes rather costly corrosive attack on metals used in boilers, combustion devices, piping, and other hardware. In coal preparation plants, due to recycling of the water, very high concentrations of chloride, an extremely corrosive agent, are observed. The process water corrosivity has a deleterious effect on the equipment thus necessitating expenditures on replacement and costly repairs. Due to agitation of solids and enhanced dissolved oxygen concentration, materials degradation occurs via an erosion-corrosion mechanism in many parts of the plants. It is observed that process water is almost as corrosive as seawater because of the high concentration of chloride and other ions. Analyses of a number of degraded metal samples from coal mines and preparation plants indicate the presence of chloride ions in the corrosion products. A number of recommendations for the control of materials degradations and strategies for materials selection are proposed.