Characterization of chemical looping combustion of coal in a 1 kWth reactor with a nickel-based oxygen carrier

Chemical looping combustion is a novel technology that can be used to meet the demand on energy production without CO2 emission. To improve CO2 capture efficiency in the process of chemical looping combustion of coal, a prototype configuration for chemical looping combustion of coal is made in this study. It comprises a fast fluidized bed as an air reactor, a cyclone, a spout-fluid bed as a fuel reactor and a loop-seal. The loop-seal connects the spout-fluid bed with the fast fluidized bed and is fluidized by steam to prevent the contamination of the flue gas between the two reactors. The performance of chemical looping combustion of coal is experimentally investigated with a NiO/Al2O3 oxygen carrier in a 1 kWth prototype. The experimental results show that the configuration can minimize the amount of residual char entering into the air reactor from the fuel reactor with the external circulation of oxygen carrier particles giving up to 95% of CO2 capture efficiency at a fuel reactor temperature of 985 °C. The effect of the fuel reactor temperature on the release of gaseous products of sulfur species in the air and fuel reactors is carried out. The fraction of gaseous sulfur product released in the fuel reactor increases with the fuel reactor temperature, whereas the one in the air reactor decreases correspondingly. The high fuel reactor temperature results in more SO2 formation, and H2S abatement in the fuel reactor. The increase of SO2 in the fuel reactor accelerates the reaction of SO2 with CO to form COS, and COS concentration in the fuel reactor exit gas increases with the fuel reactor temperature. The SO2 in the air reactor exit gas is composed of the product of sulfur in residual char burnt with air and that of nickel sulfide oxidization with air in the air reactor. Due to the evident decrease of residual char in the fuel reactor with increasing fuel reactor temperature, it results in the decrease of residual char entering the air reactor from the fuel reactor, and the decrease of SO2 from sulfur in the residual char burnt with air in the air reactor.