Experimental and mechanistic study on chemical looping combustion of caking coal

Under high-temperature batch fluidized bed conditions and by employing Juye coal as the raw material, the present study determined the effects of the bed material, temperature, OC/C ratio, steam flow and oxygen carrier cycle on the chemical looping combustion of coal. In addition, the variations taking place in the surface functional groups of coal under different reaction times were investigated, and the variations achieved by the gas released under the pyrolysis and combustion of Juye coal were analyzed. As revealed from the results, the carbon conversion ratio and rate were elevated significantly, and the volume fraction of the outlet CO2 remained more than 92% under the oxygen carriers. The optimized reaction conditions to achieve the chemical looping combustion of Juye coal consisted of a temperature of 900 °C, an OC/C ratio of 2, as well as a steam flow rate of 0.5 g·min−1. When the coal was undergoing the chemical looping combustion, volatiles primarily originated from the pyrolysis of aliphatic CH3 and CH2, and CO and H2 were largely generated from the gasification of aromatic carbon. In the CLC process, H2O and CO2 began to separate out at 270 °C, CH4 and tar began to precipitate at 370 °C, and the amount of CO2 was continuously elevated with the rise of the temperature.