EFFECT OF PORE DIFFUSION ON THE GASIFICATION CHARACTERISTICS OF COAL CHAR UNDER CO2 ATMOSPHERE

Abstract

The effect of pore diffusion on kinetic parameters is of particular interest to the current study using coal char under CO2 gasification conditions. A high-temperature entrained-flow gasifier was used for the preparation of char through the rapid pyrolysis process. The kinetic study with the char was then carried at temperatures of 973-1473 K under atmospheric pressure. A prediction of carbon conversion for large particle size (100 μm) is reported from the carbon conversion of small particle size (25 μm) considering the diffusion effect. The effect of diffusion caused by temperatures and particle size was reported through activation energy. The apparent activation energy in the chemically controlled region (973-1173 K) was calculated to be 178 kJ/mol, whereas it was 69 kJ/mol in the pore diffusion zone (1373-1473 K) using smaller particle size. The apparent activation energy using large particle size was found to be 186 and 99 kJ/mol in chemically controlled and pore diffusion zone, respectively. The intrinsic activation energy for both particle sizes was almost similar. A variation between apparent and intrinsic reaction rates was depicted mostly at higher temperatures of over 1273 K. The change in the surface area of char particle was crucial in terms of decreasing reaction rates, which was decreased with the progression of the conversion. The predicted carbon conversion for large particle size was in good agreement with the experimentally measured conversion except for little discrepancies at higher temperatures.