Process Simulations of Chemical Looping Combustion for Mixtures of Coal and Biomass Using an Iron Based Oxygen Carrier—Part I

Abstract

Chemical-looping combustion (CLC) is a recent carbon capture technology that has shown great promise for almost pure CO₂ separation and capture in combustion of fossil fuels in power generation plants. In this paper, several process simulations of chemical-looping combustion are conducted using ASPEN Plus. The entire CLC process is modeled and validated against the experimental data using a mixture of biomass and coal and pure biomass as fuels. The effect of fuel reactor temperature on gas concentrations (namely CO₂, CO, CH₄ and O₂) in the fuel and air reactors, the conversion efficiency of carbonaceous gases, the char conversion efficiency, the carbon capture efficiency, and the energy output are investigated. It is found that increasing the fuel reactor temperature increases the CO₂ concentration in the fuel reactor for the biomass/coal mixture and decreases the CO₂ concentration for pure biomass in agreement with the experimental data. However, for the coal/biomass mixture and pure biomass, there is an increase in CO concentration in the fuel reactor. Poor oxygen transport capacity of the iron ore (Fe₂O₃) used as an oxygen carrier results in decrease in conversion efficiency for both types of fuels. However, both types of fuel showed an increase in carbon conversion efficiency since lesser amount of residual char made it past the fuel reactor as temperatures increased. Energy output for both fuels grew steadily with increase in fuel reactor temperature, but for pure biomass it stagnated between 760 and 800 °C and it peaked for biomass/coal mixture at 960 °C. Variations of gas concentrations in fuel and air reactors as well as energy output as a function of different mass fractions of coal and biomass are also obtained. The concentrations of CO₂, CO, and CH₄, and energy output all decrease with decreasing fraction of coal in the coal/biomass mixture.