A Comparative CFD Study on Simulating Flameless Oxy-Fuel Combustion in a Pilot-Scale Furnace

Abstract

The current study presents a method to model the flameless oxy-fuel system, with a comparative approach, as well as validation of the predictions. The validation has been done by comparing the predicted results with previously published experimental results from a 200 kW pilot furnace. A suction pyrometer has been used to measure the local temperature and concentrations of CO, CO 2 , and O 2 at 24 different locations. A three-dimensional CFD model was developed and the validity of using different submodels describing turbulence and chemical reactions was evaluated. The standard -model was compared with the realizable -model for turbulence, while Probability Density Function (PDF) with either chemical equilibrium or the Steady Laminar Flamelet Model (SLFM) was evaluated for combustion. Radiation was described using a Discrete Ordinates Model (DOM) with weighted-sumof-grey-gases model (WSGGM). The smallest deviation between predictions and experiments for temperature (1.2%) was found using the realizable -model and the SLFM. This improvement affects the prediction of gaseous species as well since the deviation between predictions and experiments for CO 2 volume percentages decreased from 6% to 1.5%. This provides a recommendation for model selections in further studies on flameless oxy-fuel combustion.

Numerical Study on the Effect of Lambda Value (Oxygen/Fuel Ratio) on Temperature Distribution and Efficiency of a Flameless Oxyfuel Combustion System

“…The comparisons show many advantages of using the flameless oxyfuel burners in comparison to traditional burners, such as a lower NO x formation and a better temperature uniformity [25]. Later in 2016, Ghadamgahi et al [12] used the experimental data from Krishnamurthy et al [25] to compare three different CFD models and to validate the predictions for simulations of a flameless oxyfuel combustion [12]. These models were later used to simulate a full-scale soaking pit furnace and the predicted results were compared with experimental results presented by Ghadamgahi et al [26].…”

“…In this study, the validated models from the work by Ghadamgahi et al [12,26] are used to simulate a full-size soaking pit furnace containing ingots, since the differences in the geometries is negligible. Simulations have been performed for six cases, using different magnitudes of the lambda value (inlet oxygen values).…”

“…The realizable k-ε turbulence model was used to solve the Navier-Stokes equations and to model the turbulence. The validity of this sub-model for such problems is intensely argued in the work by Ghadamgahi et al [12]. The turbulent kinetic energy (k) and the turbulent dissipation rate (ε) were solved as shown in Equations (5) and (6):…”

“…This model considers the non-equilibrium effects of the combustion. This selection of a sub-model for reaching an accurate prediction for combustion is explained and argued in the work by Ghadamgahi et al [12]. In this approach, the thermochemistry parameters are a function of the mixture fraction and the strain rate or Dissipation rate (χ):…”

“…where Φ represents the species mass fractions and temperature while χ st represents the stoichiometric dissipation rate [12]. For modeling the radiation, the DO radiation model with the WSGGM is used to solve the general radiative transfer equation (RTE).…”