Emissions of particles and trace elements from coal gasification

Abstract

Some of the trace elements in coal are easily emitted with the syngas obtained from coal gasification in the gaseous phase and condensed as fine particles. Such impurities in syngas could result in corrosion and/or degradation of electrode materials in fuel cells if the coal gasification process is applied to Integrated Gasification Fuel Cell (IGFC). Thus, to realize the coal gasification process combined with fuel cells, it is extremely important to control the emission behavior of hazardous trace elements in coal gasification. In this study, particles in the coal gasification gas were sampled and analyzed in detail to determine their particle size distributions and elemental compositions. A drop tube type furnace was utilized for the coal gasification experiment. Pb and Se were evaluated in terms of their distribution behavior to particles. Pb is one of the most typical volatile heavy metals, and Se is known as a corrosive substance for Solid Oxide Fuel Cells (SOFC). Thermal equilibrium calculations were also conducted to derive the chemical forms of Pb and Se during their emissions. As a result, particles entrained in syngas from the coal gasification process were confirmed to have bimodal peaks in their particle size distributions. The peak larger than 7.8μm in the super-micron size range consists of ash with unburnt carbon, while the smaller peak at 0.5μm in the sub-micron range consists of soot with mineral deposits. Se and Pb were found to react together during coal gasification process. In addition, almost all of them were vaporized in the reactor and deposited on soot particles in the sub-micron range during the gas cooling process.