(9d) Investigation of Coal Char-Slag Transition at High Temperature
Performance of high temperature slagging entrained-flow coal gasifiers is in large part dictated by coal burnout behavior. In particular, the transition from porous, relatively low density char to liquid slag affects overall carbon conversion and relative residence times of material on the wall and in the gas phase. A high temperature drop tube furnace (HTDTF) was set up to study coal char gasification by O2 under atmospheric pressure. In this study, char is generated by pyrolyzing coal particles in nitrogen in the HTDTF. Prepared char is collected using a receiving probe and re-fed into the HTDTF with a premixed air-nitrogen flow. Char is partially oxidized to specific carbon conversions by varying the feeding rate, oxidation temperature and gas oxygen content. Post-oxidized char /ash particles are collected by the receiving probe for further analysis. The carbon content and corresponding degree of carbon conversion is determined by the loss and ignition (LOI) test. The physical properties of the resulting particles are determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and BET surface area analysis. The stickiness of the ash/slag as a function of carbon burnout and temperature is also studied using a heated impaction probe. These investigations provide information concerning the influence of gasification conditions on the physical characteristics of coal char and ash.