Application of the CPFD method to analyze the effects of bed material density on gas-particle hydrodynamics and wall erosion in a CFB boiler

Abstract

The effect of bed material density on gas-particle hydrodynamics and wall erosion in the world’s first 550 MWe ultra-supercritical (USC) circulating fluidized bed (CFB) boiler was investigated using computational particle fluid dynamics (CPFD). The results showed that the solid fraction in the lower region of the furnace decreased with decreasing bed material density, and the layer thickness increased significantly owing to increased volume; however, the solid fraction at the upper region of the furnace increased gradually. In addition, as the particle density increased, external circulation decreased and internal circulation increased owing to the opening of the integrated recycle heat exchangers (INTREX). An opposite flow occurred during internal circulation at a bed material density of 1400 kg·m−3. As the density increased from 2200 kg·m−3 to 3000 kg·m−3, the furnace wall erosion increased by 4.4%, 15.3%, and 14.3%, while the cyclone erosion gradually decreased by 29.5%, 44.1%, and 55.7% compared to the standard at 1400 kg·m−3. Furthermore, erosion of the loop seal and INTREX exhibited an inflection point at 2600 kg·m−3. This study proposes that 1400 kg·m−3 should be the limiting density because abnormal circulating flow occurs and attention should be paid to furnace erosion above 2600 kg·m−3 and cyclone erosion below 2600 kg·m−3. The results can help determine the optimal particle density conditions for hydrodynamics and erosion behaviors in industrial-scale boilers.