. Oxy-fuel combustion is a modern carbon capture and storage (CCS) technique that improves the combustion process and reduces the environmental penalty of many combustion systems.Evidently, the accurate radiative calculation of oxy-fuel combustion is very important to arrive at more improved combustion system designs with less environmental drawbacks. In the present study, a small scale unconfined turbulent bluff-body flame is numerically simulated to calculate the gas radiative properties using three different approaches of ignoring radiation, applying a modified version of the weighted sum of gray gases (WSGG) model, and employing the spectral line based weighted sum of gray gases (SLW) model. First, the selected bluff-body flame is validated against experimental data.The early outcome is that the simulation results of three chosen approaches are very close if there is no oxygen enrichment. Next, the effect of oxygen enrichment is carefully investigated imposing the aforementioned spectral radiation approaches. The achieved results indicate that the predicted gas temperature becomes more sensitive to the implemented radiative approach as the oxygen concentration in the oxidizer increases. In very high oxygen enrichment case, the gas temperature predicted by SLW model shows up to 155 K differences with that of ignoring radiation approach. The simulation results also show that the oxygen enrichment would raise the CO2 and H2O volume fractions in the flame zone. Therefore, the non-grayness of gases becomes more significant in such cases and the accurate radiative calculation becomes more essential. This is investigated carefully in this study.
Combustion emission is one of the most important issues in the design of industries. Todays’ strict environmental standards have limited the productions of CO, NOx, SOx, and other hazardous pollutants from the related industries. In this work, we study a typical oil refinery incinerator, which is used to burn waste gases residue produced during bitumen production process. The waste gas mainly includes a mixture including N2, H2O-vapor, and O2 species. Additionally, there are significant amounts of CO species and CxHy droplets in the waste gas composition. The measurements show that the CO emission becomes so crucial in high flow rate of feeding waste gas to the incinerator. Here, we numerically simulate the combustion process in this incinerator by solving the full turbulent reacting flow equations. In this regard, we use the finite-volume method to solve the RANS equations. For turbulence modeling purposes, we use the two-equation k-ε model along with standard wall functions. The non-premixed combustion is simulated by solving the mixture fraction equations for both fuel and waste gas streams. The interaction between turbulence and combustion is properly considered in the current modeling. We use the P1 method to solve the radiation transfer equation in emitting and absorbing medium of combustion gasses. The WSGG model is used to consider the absorption coefficient variation. The set of governing equations are solved using a SIMPLE-based algorithm. The current solutions provide good knowledge about the mixing pattern of flue gas and air-fuel streams in the incinerator. The improper mixing in the incinerator suggests we present a new design to re-design the waste gas inlet to the incinerator. Our simulation shows that the new design would result in substantial improvement in mixing process of these two streams. We find that this new design would effectively reduce the CO ppm at the exit of incinerator’s stack.
In this paper, the radiation heat transfer is calculated numerically in a three dimensional enclosure containing non-gray gases. The radiation heat transfer equation is solved using the finite-volume formulation of discrete ordinate method and the SLW model is employed to calculate the radiation absorption coefficients. Three cases are simulated here including the isothermal/homogeneous, isothermal/nonhomogeneous, and the non-isothermal/homogeneous media. The calculated radiation source terms and the wall heat fluxes are compared with the results of SNB method. It is shown that the SLW results are in very good agreement with the SNB in case of isothermal/homogeneous. In the two other cases, the SLW results show more deviations than this one. It is because the SLW formulation employs more additional assumptions to calculate the radiation in media with non-uniform distribution of temperature or mixture composition and multicomponent gas mixture. However, comparing the results of SLW with those of the WSGG model, it indicates that the former case would be more accurate. This is because the parameters of SLW model are calculated directly from the high resolution spectroscopic database of gas molecules.
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