Investigation of the oxy-fuel combustion process in the full-loop circulating fluidized bed

Abstract

Oxy-fuel combustion of fossil fuels in circulating fluidized bed (CFB) reactors has been widely implemented in various industries. However, the knowledge of complex gas thermal characteristics (e.g., gas temperature, viscosity, density, conductivity and specific heat capacity) is still in lack. Understanding the distribution of these gas thermal properties within the oxy-fuel combustion CFB reactor is crucial for predicting particle behavior, optimizing operating conditions, and performing design optimizations. In this study, the hydrodynamics and thermochemical characteristics of dense reactive flow in a 0.1 MWth pilot-scale CFB are simulated via a developed multi-phase particle-in-cell (MP-PIC) reactive model. The impacts of some key operating parameters on the gas thermal properties, gas species distribution and gas-solid flux are studied. The results show that the dynamics and thermochemical variables of gas-solid flow show non-uniform distributions in the riser due to the segregation mechanism and lateral injection of solid fuels. Combustible gases (e.g., CH4, CO, H2, and H2S) mainly concentrate in the left area of the riser. Enlarging the oxygen concentration increases gas viscosity while decreases gas density. The density of gas phase ranges from 0.35 kg/m3 to 0.50 kg/m3 while gas turbulent viscosity ranges from 4.2 × 10−5 m2/s to 4.8 × 10−5 m2/s.