Process simulation on oxy-fuel combustion of coal and biomass in a circulating fluidized bed

Abstract

Appropriately evaluating the gas–solid hydrodynamics and reaction kinetics of reactors within process simulation approach can provide more accurate and comprehensive techno-economic and environmental assessments, as well as more effective design and optimization for new processes and technologies. In this study, a one-dimensional process simulation of biomass and coal oxy-co-firing in a 100 kW_th circulating fluidized bed was developed, with the models for gas–solid hydrodynamics and synergistic reactions of two fuels being established in Aspen Plus software. The effects of fuel properties, gas atmosphere, and operating parameters on the combustion process, flue gas products, and heat distributions in the bed were studied. Results show that the proposed process models can successfully describe the oxy-co-firing of coal and biomass in the furnace including the pyrolysis and the combustions of gaseous volatile and char. Increasing the oxygen concentration and biomass blending ratio will improve the combustions in dense phase region and obviously increase the heat release in this region. More heating surfaces should be arranged in the dense phase region when retrofitting an existing circulating fluidized bed (CFB) boiler with air combustion to be the oxy-fuel one. Additionally, the increase of oxygen concentration could reduce the emissions of pollutants such as CO and NO_X, while the addition of biomass may bring a slight increase in NO_X emission.