Computational investigation of oxy-combustion of pulverized coal and biomass in a swirl burner

Swirling pulverized coal and biomass flames are computationally investigated for oxy-combustion. The two-phase flow is described by a Eulerian-Eulerian approach. For radiation, the absorption coefficient is approximated by superposing particle and gas contributions, considering oxy-combustion conditions for the latter. Turbulence is modelled within a URANS framework, using the standard k-ε model and Reynolds Stress Model (RSM). It is observed that RSM captures the unsteady dynamics of the coherent structures, whereas they are not captured by k-ε model. Predicted velocities are compared with measurements. It is observed that the RSM predictions are in a better agreement with the measurements compared to the k-ε model. The discrepancy between the predictions and measurements can most clearly be quantified in terms of the peak values of the axial velocity in the forward flow region enveloping the inner recirculation zone. The calculations constantly underpredict the measurements. On the average, this is about 32% for the RSM and 52% for the k-ε model, for both flames. The biomass flame is predicted nearly twice as long compared to the coal flame. As means of verification, the coal flame is additionally calculated using a classical Eulerian-Lagrangian two-phase formulation, leading to quite similar results to the Eulerian-Eulerian formulation.