Coal-fired chemical looping combustion coupled with a high-efficiency annular carbon stripper

Abstract Coal-fired chemical looping combustion (CLC) is a promising technology with inherent CO2 separation with a low energy penalty. One of challenges for coal-fired CLC is that char particles with slow gasification kinetics can be easily transferred into the air reactor (AR) by circulated oxygen carrier (OC), thereby decreasing the carbon capture efficiency. An annular carbon stripper (CS) was proposed to efficiently separate the char particles from the mixture of OC and char. A hot system of 10 kWth CLC unit coupled with an annular CS was designed, built, and operated in order to investigate the separation performance of an annular CS at high temperature (850-950 °C). Vietnamese ilmenite was used as OC to burn Shenfu bituminous coal. The system achieved a stable solid circulation at a high temperature with steady coal feeding, and total operation reached 100 h with a thermal input of 3-5 kWth. A 90%-95% char separation efficiency was achieved by the annular CS in various tests, and the carbon capture efficiency reached 95% at 950 °C. A special particle sampling device was designed to collect solid particles from the dense phase of CLC reactor during the continuous operation stage. It was found that the char mass faction in the FR dense phase was 0.45%-5.5% and a fraction of char adhered to the ilmenite surface, which was difficult to separate by the annular CS. Additionally, the sintering and agglomeration of ilmenite was not observed during continuous operation at 850-950 °C. Furthermore, through extrapolating experimental results, it is predicted that 90% carbon capture efficiency can be achieved by using this new annular CS in a scaled-up CLC system.