Coal combustion and gasification in a compartmented, fluidized-bed coal gasifier

A conceptual compartmented fluidized-bed coal gasifier (CFBCG) which separates coal combustion from gasification for synthesis gas production was investigated in a small pilot plant in two major stages: combustion-only experiments and combustion-gasificatian experiments. The combustion-only experiments showed that volatiles were released and burned in the compartment where coal is fed. Volatiles and char combustion were sufficient to maintain the operating temperature of the CFBCG. Solid circulation induced by two sets of v-valve/riser arrangements was crucial, and determined heat-transfer between the two beds and, thus, controlled the reaction rates. The rate of solid circulation, carbon burning rate, and carbon inventory in a bed were indirectly estimated by measuring pressure drop over a bed compartment. Since there was no ash withdrawal facility in the pilot plant, ash accumulated during prolonged operation and caused ash agglomeration at high temperatures, which further resulted in fluidization and solid circulation difficulties. Based on information and experience obtained in the combustion-only experiments, the combustion-gasification experiments were performed to study energy transfer from combustor to gasifier, and quality of the synthesis gas produced. It was found that circulation of hot solids from the combustor was sufficient to support endothermic reactions in the gasifier. High-quality synthesis gas with an H-2/CO ratio of 4 was achieved. Nn contamination of the synthesis gas (12-22%) occurred due to air leakage from the riser and in the plenum to the gasifier. While the CFBCG concept has proved to be sound, further development is needed to improve the operatibility before practical application.