Computational Modeling of Mercury Control by Sorbent Injection

Impending regulations of mercury emission from coal-fired utilities are driving current efforts to develop efficient control technologies. This includes a comprehensive field test program that considers full-scale use of mercury control by injection of activated carbon upstream of a particulate collection device (baghouse or ESP). The present effort aims at numerical modeling of the in-flight mercury capture by adsorption using Computational Fluid Dynamics (CFD). Such a modeling capability enables optimization of sorbent injection strategies in order to better overcome mass transfer limitations. CFD provides detailed duct-scale information on the flow of flue gases as well as the dispersion of injected sorbent. Sorbent particle trajectories are determined using Lagrangian tracking, while a convective-diffusive transport equation describes the gas-phase mercury distribution. Mercury sink terms are defined based on a particle model for mass transfer and surface adsorption on an entrained sorbent particle. We present simulation results for the sorbent dispersion of large-scale field tests carried out at the Brayton Point power station in Massachusetts.