LES modelling of air and oxy-fuel pulverised coal combustion-Impact on flame properties

Large eddy simulations (LES) are used in a CFD model to simulate air-and oxy-fired pulverised coal combustion in a 0.5 MWth combustion test facility. Simulations are carried out using two different burners, namely, a triple-staged low-NOx wall fired burner and an IFRF Aerodynamically Air-Staged Burner (AASB). Non-gray radiation is considered in order to deal with the spectral nature of absorption and emission by high levels of combustion products in oxy-fuel combustion. Predictions using LES are compared with Reynolds averaged Navier Stokes (RANS) calculations using variants of the k-ε model for turbulence and against available experimental measurements. The results suggest that LES can offer improvements over RANS in predicting recirculation zones and flame properties of the pulverised combustion systems investigated. Flame flickering frequencies from the LES simulations are calculated and validated against available measurements. The work presented demonstrates the potential importance of using LES turbulence models for coal combustion.