Study of the effect of coal type and particle size on char-CO₂ gasification via gas analysis

Char gasification is affected by operating conditions such as reaction temperature, reactant gas partial pressure, total system pressure, and particle size, in addition to the chemical composition and the physical structure of the coal. We characterized the effects of coal type and particle size on the CO ₂ gasification of chars prepared from 12 bituminous coals at different reaction temperatures (1050-1400 °C). Each coal sample was devolatilized at 950 °C in a nitrogen atmosphere to become coal char, and it was further heated to reach the desired temperature for gasification with CO₂ under isothermal conditions. Temporal variations of CO and CO₂ concentrations were measured using a real time gas analyzer with a nondispersive infrared (NDIR) CO/CO₂ sensor. The reactivity increased as the volatile matter content and alkali index of the coal increased. In addition, the reactivity increased as the particle size decreased for a given temperature. The shrinking core model (SCM) was better for higher particle sizes, whereas the volume reaction model (VRM) was better for smaller particle sizes.