The Effect of Kaolin As Bed Material in an Oxy-CFB Combustor

Kaolin (Al2Si2O5(OH)4) has been considered as an effective addition for bed material in a circulating fluidized bed combustion (CFBC) system due to its advantages to reduce agglomeration, fouling and deposit problems. In the present paper, the impact of kaolin addition as bed material during the oxy-combustion in a 0.1 MWth oxy-CFB system with sub-bituminous coal and wood pellet were investigated through the combustion characteristics. The above aspects are operating temperature and pressure profile, flue gas composition including CO2, O2, SO2, NO, CO and the sampled ash properties by analyzing XRF, SEM-EDS, unburned carbon (combustion efficiency) and their particle size distribution. The results revealed that kaolin in steady of silica sand has contributed to smooth fluidization and could keep the oxy-fuel combustion stable with the exit gas of having a high concentration of CO2 (above 90 vol.% on dry basis) and low emission of CO, SO2, and NOx. The attrition index (AI) value of raw silica sand and fly ash sampled with experimentally added kaolin were 0.46 and 0.58%, respectively. No agglomeration was found in the bed for the most operating period. Consequently, it can be said that the feasibility of a kaolin material as substitutive silica sand is reasonable.