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

Abstract

Abstract:The flameless oxyfuel combustion technology has been proven to be a promising new method to reduce the fuel consumption and pollutants in industrial applications. Although this technology is widely used in industrial furnaces, a lack of understanding exists about the effect of the controlling parameters on the final operational conditions is tangible. In this study, a validated computational fluid dynamics (CFD) model is used to simulate six cases of flameless oxyfuel combustion burners with different lambda values (ratio of oxygen/fuel mass flow rates). The CFD model uses the steady laminar flamelet model (SLFM) to solve the probability density function (PDF) for combustion, the discreet ordinates (DO) radiation model with the weighted sum of the gray gases model (WSGGM) to solve radiation, and the realizable k-ε to model the turbulence. It is seen that an increased oxygen injection velocity due to an increased lambda value increases the exhaust losses, but produces a larger volumetric flame. This leads to a more uniform temperature distribution. The total temperature difference in a case with a λ value of 1.02 is reported to be 272 (14.9%), while the amount for a case with a λ value of 1.2 is 67 (4.7%). This effect is further explained by introducing a new definition value for the furnace efficiency that includes both the thermal and production losses.

New weighted-sum-of-gray-gases model for typical pressurized oxy-fuel conditions

“…The temperature range of the new WSGG model was selected as 400-2500 K because most of the oxy-fuel combustion furnace flue gas temperature concentrates in this range [38][39][40] ; the path length range is 0.1-20 m, which covers the dimensions of most oxy-fuel combustion furnaces at laboratory level, [40][41][42] pilot level, 39,43 and industrial level. 44,45 The range of the molar ratio M is 0.125-2; for dry flue gas recycle of oxy-fuel combustion, the flue gas is dried prior to being recycled; thus, the molar ratio M is below 1, and the typical molar ratios are 0.125, 0.25, 0.5, and 0.75; for wet flue gas recycle of oxy-fuel combustion, the molar ratio M is not below 1 because the flue gas has not been dried before recycle, and the typical molar ratios are 1 and 2. 19,21,23…”

Experimental and Numerical Investigation of a MILD Combustion Chamber for Micro Gas Turbine Applications

“…Ghadamgahi et al [21] employed the steady laminar flamelet model (SLFM) to solve the probability density function (PDF) for combustion to model a flameless oxy-fuel burner. There are a few more studies available in the literature about the use of Transported PDF methods to simulate MILD combustion burners.…”