Prospects and issues of integration of co-combustion of solid fuels (coal and biomass) in chemical looping technology

The utilization of fossil fuels leads to the emission of greenhouse gases into the environment. As a consequence, ozone layer depletion, global warming, acid rain, etc. are caused. Thus, alternate ways have to be planned to eradicate the detrimental effects of the usage of fossil fuels. As biomass is a renewable energy source, co-utilization of coal with biomass could significantly reduce carbon emission. In addition, chemical looping combustion (CLC) is a promising technology for the inherent capture of CO2 without any post-treatment of flue gas. Hence, the integration of co-combustion of solid fuel with CLC technology can produce clean energy in the context of carbon negative system. The present study addresses the issues and prospects of the co-CLC process of solid fuels such as coal and biomass. Low-cost oxygen carriers, which are suitable for the solid-CLC process, are elucidated. The effect of solid fuel based inherent constituents such as ash, volatile matter and tar on the performance of the CLC process is discussed. Furthermore, the beneficial and inhibitory effects of the co-combustion of solid fuels are elaborated. The formation and reduction mechanism of NOx and SOx pollutants during the CLC process are investigated. In addition, the effect of gasifying medium (CO2 and steam) during the co-CLC technology is also discussed. The performance of the CLC based thermal power plants is analyzed, and the results show a gain of 5-6% in net thermal efficiency, compared to a power system operating under conventional technology. The effect of the process parameters on gas conversion, char conversion, overall solid fuel conversion, combustion efficiency and CO2 yield is investigated. The investigation shows that the co-combustion based CLC is a potential technology for the implementation of carbon capture and storage (CCS) with a low energy penalty.