Three gray models for the radiative properties of gases were examined for their usage in oxy-combustion simulations of a full scale boiler with flue gas recycle. Fully coupled computational fluid dynamic (CFD) simulations of a full scale boiler were carried out employing the weighted-sum-of-gray-gases model (WSGGM) at air burn, dry-recycle and wet-recycle conditions. The resulting thermal and composition fields were then frozen and the radiative properties of the gaseous media recomputed employing the Exponential Wide Band Model (EWBM) and correlations for total emissivities of gas mixtures. It is shown that when high CO2/H2O ratios were encountered within the boiler such as in dry-recycle scenarios, employing emissivity correlations developed for purely CO2 media within the models can result in incorrect gas properties. The errors associated with this can be significant when there are large pockets within the furnace where the gas radiation dominates the particle radiation.

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