Numerical investigation of effects of CO2 recirculation in an oxy-fuel IGCC on gasification characteristics of a two-stage entrained flow coal gasifier

Effects of CO2 recirculation within an oxy-fuel IGCC plant on a gasification characteristics of a two-stage entrained flow coal gasifier was numerically investigated by means of a three-dimensional unsteady Reynolds-averaged Navier-Stokes(RANS) simulation. The RNG k−ε model and the Eulerian-Lagrangian manner were used to consider the effect of turbulence and the particles' motions, respectively. A char gasification model in which the Langmuir-Hinshelwood formulation was coupled with the random pore model was employed to estimate gasification reaction rate. Results showed that the gasification performance such as the per pass carbon conversion efficiency for the oxy-fuel condition in which CO2 replaced N2 in the primary and secondary gas flows was in the same level for the air-blown condition in which O2 flowed into the gasifier with N2, while the gaseous temperature drastically decreased for the former case. It was also found that the gaseous temperature was recovered to the same level for the air-blown condition with at least more than 35% of oxygen concentration in the gasifying agent and simultaneously the highly gasification performance was observed. It is essential to control O2 and CO2 concentrations in the gasifying agent to turn the CO2 recirculation to advantage in utilization of the O2-CO2 blown gasifier in the oxy-fuel IGCC system.