New Weighted Sum of Gray Gases Model Applicable to Computational Fluid Dynamics (CFD) Modeling of Oxy−Fuel Combustion: Derivation, Validation, and Implementation

Abstract

Radiation is the principal mode of heat transfer in furnaces. Models for gaseous radiative properties have been well-established for air combustion. However, there is uncertainty regarding their applicability to oxy−fuel conditions. In this paper, a new and complete set of weighted sum of gray gases model (WSGGM) is derived, which is applicable to computational fluid dynamics (CFD) modeling of both air−fuel and oxy−fuel combustion. First, a computer code is developed to evaluate the emissivity of any gas mixture at any condition using the exponential wide band model (EWBM), and the calculated results are validated in detail against data in the literature. Then, the validated code is used to generate emissivity databases for representative air- and oxy-firing conditions, for each of which a refined WSGGM with new parameters is derived. The practical way to implement the model to CFD simulations of combustion systems is given. Finally, as a demonstration, the new model is implemented to CFD modeling of two furnaces of very different beam lengths. The CFD results are compared to those based on the widely used WSGGM in the literature, from which some useful guidelines on oxy−fuel modeling are recommended.

Biomass co-firing under oxy-fuel conditions: A computational fluid dynamics modelling study and experimental validation

“…In the oxy-fuel combustion modelling, non-gray calculation of the oxy-fuel WSGGM [16] was performed to evaluate the gaseous radiative properties. Compared to the conventional gray calculation of the Smith et al…”

“…In recent years, on the basis of the accumulated knowledge of the fundamental differences between airfuel and oxy-fuel combustion, much effort has been devoted to developing and validating sub-models for the new combustion environment. For instance, new approaches have been developed for heat transfer modelling in environments with high concentrations of CO 2 and H 2 O vapor, e.g., the Weighted-Sum-of-Gray-Gases-Model (WSGGM) refined for oxy-fuel combustion modelling [16,17]. Specific models for volatile combustion in CO 2 -rich environments [18] and for char combustion under oxyfuel conditions [19] have also been developed.…”

Nongray EWB and WSGG Radiation Modeling in Oxy-Fuel Environments

“…We also notice that the relative deviations between the various WSGG models and the box/EWB predictions for the radiative flux differ from the deviations reported for the centerline radiative source. In particular, the 5-gas/cubic WSGGM (27) that showed noticeable error in the radiative source, has excellent agreement (-0.70%) with the box/EWB solution in the wet-recycle oxy-fuel environment and good agreement (-2.67%) in the dry-recycle environment. The radiative flux at the center point (Z=20 m) of the profiles in Figure 6 and their relative errors with respect to the box/EWB are compared in Tables 5 and 6 for the wet-recycle and dry-recycle oxy-fuel environments, respectively.…”

“…The box/EWB solution exhibits a smaller decrease of the radiative source near the walls than the WSGG solutions. For both environments, the air-fuel WSGGM (28) and the 5-gas/cubic WSGGM (27) show noticeable overprediction of the radiative source, which indicates a weaker influence of radiation on the thermal field.…”

Study of coupled double diffusive convection–radiation in a tilted cavity via a hybrid multi-relaxation time-lattice Boltzmann-finite difference and discrete ordinate methods

“…Therefore, improvements of the numerical methods in reason to minimize the computational effort have motivated the interest of the scientific community. Some main references related to these methods may be found in [3][4][5][6][7][8][9][10][11][12], for instance. The spectral line weighted-sum-of-gray-gases (SLW) method introduced by Denison and Webb [4] remains one of the most efficient methods of modelling radiative transfer in high-temperature gaseous media because of its simple formulation, accuracy of the method and implementation.…”