CCSEM ANALYSIS OF ASH FROM COMBUSTION OF COAL ADDED WITH LIMESTONE

摘要

Combustion of three Chinese coals, mixed with limestone physically, is carried out in the drop tube furnace (DTF). The SOx removal of ca. 89% and 76% were obtained in the combustion of Yanzhou with high and low sulfur, respectively. While for Datong coal, it is only 50% even at the Ca/S molar ratio of 2.0. The ashes are characterized by several techniques. A novel calcium-based phase definition, based on CCSEM data, was developed to investigate the modes of occurrence of added Calcium. The governing mechanisms for sulfur capture and interaction between calcium and internal minerals were correspondingly revealed. It was found that under the given high temperature (1300℃), the Calcium distribution in the ash varies with coal type and residence time. Increasing time leads to more calcium located in mixed Ca Al-Silicates with and without sulfur. The fine dispersion of mineral in raw coal facilitates Al-silicates scavenging calcium, which reacts more quickly than sulfation of limestone, leading to a lower utilization efficiency of limestone.