Enhancement of Coal Quality by Microbial Demetalization and Desulfurization

摘要

The removal of metals from coal improves quality by reducing the ash content and possibly altering the ash fusion temperature, which reduces fouling of combustion equipment. This study characterized the demetallization and desulfurization of coal catalyzed by the bacterium Thiobacillus ferrooxidans, and estimated the economic feasibility of a commercial-scale microbial coal-benefication process. The effects of slurry concentration, coal type, particle size, temperature, degree of agitation, nutrient concentration, and CO sub 2 concentration on the rate and extent of metal and sulfur solubilization by Thiobacillus ferrooxidans were investigated in lab-scale batch experiments. Thiobacillus ferrooxidans greatly enhanced the extent of sulfur and iron leaching from the three coals tested, slightly enhanced aluminum leaching, but did not improve the leaching of Mg, Na, or Ca. The fractional amount of each metal removed increased with decreasing slurry concentration, perhaps due to insufficient mixing by the mechanical shakers. After 16 days, the maximum amount of inorganic sulfur removed was 79% while the maximum amount of iron removed was 45%. Ash content was reduced significantly for all three coals tested. Pittsburgh coal displayed a 27% reduction in ash content with bacteria present. The hemispherical ash fusion temperature increased between 150 F and 450F due to bacterial leaching for two types of coal. The proposed coal benefication process, to be located at a new 500-MW utility in Ohio, incorporates a 20% slurry and achieves 90% inorganic sulfur removal. An estimated total capital cost of $27 million and an estimated operating cost of $26 million per year yield a total cost of $9.58ton of coal treated. This total cost is highly sensitive to the annual operating cost and compares favorably with other proposed coal desulfurization processes. 26 refs., 21 figs., 36 tabs. (ERA citation 13:035555)