Study on gas-solid flow characteristics of loop seal surge in circulating fluidized bed boiler

During the operation of a 350 MWe supercritical circulating fluidized bed (CFB) boiler, a low-frequency surge in the loop seal can lead to cracks in the castable material of the internal insulation layer, thereby impacting normal and safe boiler operation. Using the computational particle fluid dynamics (CPFD) method, the effect of a low-frequency loop seal surge on the gas-solid flow of a 350 MWe supercritical CFB boiler was studied in this paper. The causes, parameters and elimination conditions of the loop seal surge were analysed. The results show that when the loop seal is under a surge condition, the pressure drop gradient is greater than the critical material sealing value of 3526 Pa/m, and the material flow in the downcomer is not smooth. The volume fraction of material particles in the loop seal is low, which cannot effectively seal the material. When the primary fluidized air, supply air, and recycle air are controlled within a reasonable range, the loop seal surge can be effectively prevented. The acceptable range for primary fluidized air is 14.5 m/s to 16.0 m/s; for supply air, it is 0.05 m/s to 0.10 m/s; and for recycle air, it is 1.0 m/s to 1.5 m/s.