Ash Deposition Behavior during Char-Slag Transition under Simulated Gasification Conditions

Ash deposition experiments at various conversions of a bituminous coal were performed under gasification conditions using a laminar entrained-flow reactor and a deposition probe. Results showed that the particle capture efficiency (a measure of ash deposition propensity) was a function of coal conversion. In particular, the capture efficiency increased dramatically at a critical conversion, which is ascribed to the increase in particle stickiness. To clarify this phenomenon, ash formation experiments were conducted to collect char and ash particles under experimental conditions identical to those in the ash deposition experiments. Collected particles were presumed to have the same properties as the particles approaching the deposition probe in ash deposition experiments. Properties of the particles including internal surface area and morphology were determined by isothermal gas adsorption and scanning electron microscopy, respectively. The internal surface area of the particles dropped sharply at the critical conversion, which indicates a char-slag transition. This suggests that the char-slag transition is associated with a drastic increase in particle stickiness. Examination of the particle morphology revealed that physical transformation of mineral-carbon association in the particle has a major impact on particle stickiness during char-slag transition.