Multiphase flow and reactor optimization of a 1MWth pilot-scale circulating fluidized bed for coal staged conversion

Abstract

Coal-based cogeneration technology can realize the graded utilization of energy through the graded conversion of coal. In this work, the coal staged conversion in a 1MWth pilot-scale system was numerically studied using the multiphase particle-in-cell method which features gas–solid flow hydrodynamics, heat and mass transfer, homogeneous reactions, and heterogeneous reactions. The model was verified to be reliable and accurate in modeling coal staged conversion in fluidized bed reactors. Then the operating mechanism and particle behavior during the coal staged conversion process were comprehensively discussed. Additionally, the effects of operating and structural parameters on gas–solid mixing and chemical reactions in the reactor are explored for reactor optimization. The findings indicate that as the operating temperature increases, the CH4 concentration at the outlet of the gasifier’s cyclone initially rises before declining, whereas the trend for H2 concentration is inverse. As the particle size distribution (PSD) width becomes broader, the “core-annulus” structure of the expansion section in the dense-phase zone gradually disappears. Increasing the diameter of the expansion section in the dense-phase zone hinders the gas generation in the rare-phase zone. Increasing the diameter of the rare-phase zone significantly reduces the number of fine particles at the exit of the gasifier, and the height of the rare-phase zone can be appropriately lowered without leading to the overflow of fine particles. The change in structure size has little effect on the product gas yields at the outlet of the cyclone separator.