| Description |
Gasification of coal provides society with electricity, commodity chemicals, substitute natural gas, and consumer products. With the continued use of coal in the United States and abroad, the utilization of this fuel must be optimized with the aid of continued research on laboratory, pilot, and industrial scales in addition to responsible government regulation and legislation. This study aims to forge a relationship between laboratory measurements and gas-phase data collected from a pressurized entrained-flow gasifier. Experiments utilizing a wire-mesh reactor and thermogravimetric analyzer lay the groundwork for extracting hot, pressurized gases from an entrained-flow gasifier by using a novel sampling system developed as part of the work presented here. Models for entrained-flow gasification of coal complement the experimental endeavors and aid in data analysis. A novel pressurized wire-mesh reactor was used to determine the extent to which temperature, pressure, hold time, and heating rate influence coal devolatilization and associated char yields. Pressurized thermogravimetric studies were performed to determine the influence of pressure and gas composition on char conversion rates under a range of partial pressures of carbon monoxide and carbon dioxide. The resulting yields and devolatilization rates measured in the pressurized wire mesh heater and char conversion rates from the thermogravimetric analyzer were used to create a model for the entrained-flow gasifier and predict useful synthesis gas and gasification metrics. To sample the reaction zone of the gasifier, a sample system was fabricated, allowing for radial measurements of gas composition at variable operating conditions. Key laboratory-scale results indicate that volatiles yields increase with temperature and hold time (residence time), and decrease with pressure, but to a lesser degree. During char gasification, high pressures were concluded to decrease the gasification rate, which was further inhibited by higher carbon monoxide partial pressures. Pilot-scale data show that syngas compositions change with temperature and carbon monoxide and hydrogen yields decrease as temperature increases. Conversely, higher temperatures increase carbon dioxide yields. A significant conclusion is that gas concentrations do not change radially in the pilot-scale entrained-flow gasifier. Correlations of laboratory-scale data provide a context for data acquired during the pilot-scale gasifier operation in addition to modeling endeavors. A developed additive reaction model characterizes char burnout characteristics and extends to devolatilization behavior and drying. This model yields residence times that corresponds within an order of magnitude to a one-dimensional model that tracks syngas composition, residence time, and coal conversion as a function of gasifier length. These results agree within 50% of the experimental data acquired from the entrained-flow gasifier at temperatures above 2650 ℉ (1438 ℃) and is recommended as a tool to predict gasifier behavior and metrics. |
