Computational study of staged pressurized oxy-fuel combustion of methane and pulverized coal in a lab-scale reactor

Staged pressurized oxy-coal combustion (SPOC) is a promising technology for advanced low-cost, low-emission, high-efficiency power generation. This technology is being developed at Washington University at St. Louis (WUSTL) using a 100 kW lab-scale reactor to investigate the process experimentally. In the present study, computational simulations performed at West Virginia University (WVU) compliment the WUSTL experimental research to understand the impacts of the fluid flow, particle dynamics, turbulence, flame dynamics, and heat transfer. The simulations employ the species transport model with the finite rate/eddy-dissipation turbulent-chemistry interaction sub-model for coal combustion as well as the non-premixed combustion model for methane burning. The discrete ordinates radiation model is used to account for the effects of radiation. The simulations are performed for the power of 90 kW resulted from coal combustion, with varying amounts of methane addition. A small amount of carbon dioxide (CO2) is injected as a coal carrier. Steady and unsteady Reynolds-Averaged Navier-Stokes (RANS) simulations have been performed showing an asymmetric shape of the fame front. In this respect, three causes of such a flame asymmetry are hypothesized, namely: (i) influence of coal injection, (ii) onset of the shear-layer instability due to various densities and velocities of the streams in a shear layer where mixing occurs and (iii) presence of the vortex shedding due to the flow past a bluff body, which is used to stabilize the flame. As a result, the impact of the presence of coal on flame symmetry is demonstrated, and a critical condition at which further increase of coal result in flame asymmetry has been found. The RANS are followed by the large-eddy simulations (LES) to be compared to the WUSTL experimental results. It is anticipated that the results of this computational study will guide the scale-up when the experimental and computational observations from the lab-scale reactor are extrapolated to a large pilot-scale reactor and, eventually, to a full-scale one.