Study on scale-up characteristics in supercritical CO2 circulating fluidized bed boiler by 3D CFD simulation

Abstract

For the wide industrial applications of supercritical CO2 (S-CO2) circulating fluidized bed (CFB) technology, the simulation on scale-up characteristics would be a crucial and reliable means to investigate specific combustion process before establishing costly and complex boilers in industry. This study conducted 3D CFD simulations in lab-scale, pilot-scale, and industry-scale S-CO2 CFB boilers (0.1 MW to 600 MW) based on the Eulerian-Lagrangian method. The scale-up characteristics were comprehensively discussed from the angles of furnace structure, gas-solid flow dynamic, combustion characteristics, heat transfer characteristics, gas emission characteristics, and boiler efficiency with the fitting formulas of the scaled-up regularities derived. Results show that with the power capacity increased, the heating surface area in the furnace and flue system enlarged, in which the furnace heating surface accounted for a larger proportion. The particle flow rates and the circulating ratio increased, and the voidage distribution was less affected by disturbance with more complicated core-annulus structures appeared. With the thermal input increased, furnace temperature decreased accompanied by better thermal inertia, and the heat transfer of cold walls enhanced although its transverse distribution became uneven. The emissions of CO, NOx, and SO2 from the industry-scale CFB were lower than the other two scales. The carbon conversion ratio and the combustion efficiency increased with the thermal input increased, and the growth slowed for industry-scale boiler.