Determination of the Effect of Carbon Dioxide/Water on Physical and Chemical Properties of Coal: Final Report

摘要

A process for the simultaneous cleaning and fracturing of a variety of coals using a pressurized carbon-dioxide and water solvent system has been explored by Brookhaven National Laboratory. This technique was implemented in batch-wise reactions to characterize its effect on test coals provided by Florida Power and Light to achieve coal ash reduction and improved grinding behavior. Pressure, temperature, and reaction times were key parameters studied for suitable integration with coal slurry transport applications. Coal particles sized between 0.6 to 1.12 mm were utilized for initial tests. Key results demonstrate that: (1) breakage rates were increased for treated coal, resulting in improved grinding performance, (2) reductions in total ash content for treated coals were observed, although no selectivity in mineral matter removal was noted, and (3) contact times of one-half hour were sufficient in effecting coal changes; mild temperatures, and high CO sub 2 pressure combinations were favored reaction conditions. Slurry pipeline effects, such as the role of the inherent mechanical mixing and comminution of the coal, were tested in an agitated reactor system pressurized with CO sub 2 /water. Mixing did not appear to greatly influence coal reactivity, suggesting that mass transport effects are not important for the type and size of coal used. Coal comminution resulted from mechanical agitation of the slurry, and increased comminution was observed under a CO sub 2 /water atmosphere. The feasibility of directly preparing a coal-water slurry with the CO sub 2 /water treatment combined with a comminution step was tested. Experiments on an integrated reactor/grinder suggest an increased breakage rate for coal exposed to pressurized CO sub 2 . The possibility of using CO sub 2 /water treatments to achieve coal beneficiation, while preparing coal for slurry pipeline transportation may offer potential advantages. 5 refs., 15 tabs. (ERA citation 12:019890)