Numerical simulation on co-firing ultra-low volatile carbon-based fuels with bituminous coal under oxy-fuel condition

Abstract

The oxy-fuel combustion allows the large-scale CO2 capture from coal-fired power plant, which is an effective approach to reduce CO2 emission and achieve carbon neutrality. The ultra-low volatile carbon-based fuels (LVFs, mainly including gasification residual carbon and pyrolyzed semi-coke) generated from the coal chemical industry cannot be directly disposed effectively, but co-firing with other fuels (bituminous coal for example) is a potential option. However, many nitrogen oxides (NOx) are possibly generated with the absence of combustion stability. Here, the present study aimed at co-combusting LVFs with bituminous coal under oxy-fuel condition to take advantages of oxy-fuel technology to deeply reduce NOx and realize large-scale CO2 capture. The effects of atmosphere and fuel property on co-combustion performances were numerically investigated. The simulation results of co-combustion demonstrate that the NOx emission increases as the mass fraction of bituminous coal falls. The effects of oxidizing gas distribution method on the co-combustion characteristics are highly related to the properties of co-firing fuels. The premixed combustion for bituminous coal/semi-coke co-combustion and in-furnace blending (residual carbon injected from the E layer) for bituminous coal/residual carbon co-combustion could yield less NOx. It is recommended that the oxy-fuel O2 concentration could be kept between 27% and 30% considering the balance between NOx generation and combustion behavior. The 50% bituminous coal/50% semi-coke co-combustion is applicable to co-fire using premixed combustion and appropriate reduction of secondary oxidizing gas flow in the semi-coke layers. The present research will contribute to a further understanding of the efficient and environmentally-friendly utilization of LVFs, as well as better knowledge of CO2 capture and carbon neutrality during electricity generation.