Characterization of unburned carbon present in coarse gasification ash

Depending on the mode of operation and quality of the feed material, discrete unburned carbon particles are evident in coarse gasification ash emanating from a commercial gasifier. Black, partially reacted carbon particles in the size range −13 + 4 mm were randomly hand picked from grab sample following a gasifier shutdown. These particles were classified into three major categories namely: unburned carbon, carbonaceous shale, and “shrinking core” particles. The unburned carbon particles were further macroscopically subdivided into remnant “coal” particles, solid carbon, layered carbon, and porous carbon. The unburned carbon particles were characterized using a petrographic analysis, reflectance analysis, chemical analysis, TGA mass loss curves, pore volume and surface area, and mineral characterization. The carbon particles were compared to the feed coal. The petrographic-based characterization technique as developed for the characterization of coarse unburned carbon particles indicated that remnant coal, devolatilised coal, highly porous isotropic carbon, dense anisotropic carbon, and variations in-between occurred in the coarse gasification ash sample.