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The development of a dynamic thickened flame (TF) turbulence-chemistry interaction model is presented based on a novel approach to determine the subfilter flame wrinkling efficiency. The basic premise of the TF model is to artificially decrease the reaction rates and increase the species and thermal diffusivities by the same amount, which thickens the flame to a scale that can be resolved on the large eddy simulation (LES) grid while still recovering the laminar flame speed. The TF modeling approach adopted here uses local reaction rates and gradients of product species to thicken the flame to a scale large enough to be resolved by the LES grid. The thickening factor, which is a function of the local grid size and laminar flame thickness, is only applied in the flame region and is commonly referred to as dynamic thickening. Spatial filtering of the velocity field is used to determine the efficiency function by accounting for turbulent kinetic energy between the grid-scale and the thickened flame scale. The TF model was implemented into the commercial computational fluid dynamics code FLUENT. Validation in the approach is conducted by comparing model results to experimental data collected in a laboratory-scale burner. The burner is based on an enclosed scaled-down version of the low swirl injector developed at Lawrence Berkeley National Laboratory. A perfectly premixed lean methane-air flame was studied, as well as the cold-flow characteristics of the combustor. Planar laser induced fluorescence of the hydroxyl molecule was collected for the combusting condition, as well as the velocity field data using particle image velocimetry. Thermal imaging of the quartz liner surface temperature was also conducted to validate the thermal wall boundary conditions applied in the LES calculations.

Activated carbon injection (ACI) is an effective mercury control technology demonstrated in both short-term and long-term full-scale tests. The effectiveness of mercury capture by activated carbon depends on the mercury speciation, total mercury concentration, flue gas composition, method of capture, and activated carbon properties, such as pore size, type of carbon impregnation, and surface area, etc. It is also desired that an ACI system be designed to produce good mixing between the activated carbon and the flue gas. In recent years, General Electric Energy has conducted both short-term and long-term tests in large-scale coal-fired boilers for ACI mercury capture demonstration. The programs consisted of (1) combustion optimization to improve natural mercury capture by fly ash, (2) computational fluid dynamics (CFD) modeling of activated carbon injection to design ACI lances, (3) a short-term test to select the activated carbon type, and (4) a long-term test to evaluate the mercury capture performance. This paper presents the CFD modeling for an ACI demonstration in Sundance Station Unit 5. The CFD model developed describes the film mass transport, pore diffusion, and carbon surface adsorption and desorption phenomena for the prediction of the mercury capture rate. The model was applied to evaluate the lance design and to calculate the mercury capture rate. The test data were also presented for comparison with the model results.