Design of large scale oxy-fuel fluidized bed boilers: Constant thermal power and constant furnace size scenarios

Abstract

This work investigates the design of large scale oxy-fuel circulating fluidized bed (CFB) boilers in two industrial pathways of constant thermal power scenario and constant furnace size scenario using a new version of a model validated with 100 kWth and 4 MWth oxy-fuel CFB boilers. This work suggests that the major approach for elevating the circulating solids flux is to utilize more efficient cyclones with better efficiency which leads to higher share of fines and nanoparticles in the CFB loop while the amount of aerosols is reduced. Maximum heat flux from furnace walls is 2.4 times and CO peak is 2.2 times in constant furnace size scenario compared to constant thermal power scenario respectively, showing more intense combustion in the prior scenario. Based on the results found in this work, if the industry is to aim to operate the large-scale oxy-fuel CFB boilers at high O2 concentrations, the utilization of the constant thermal power scenario is much safer for the industry compared to constant furnace size scenario. This work shows that the aspect ratio of future large-scale oxy-fuel CFB furnaces are larger than the current air-fired ones leading the oxy-CFB furnace geometry to approach the fluid catalytic cracking fluidized beds.