Multiscale modeling of electrostatic precipitations of fly ash and mercury sorbents: Discontinuous current density effects

Abstract

Injection of mercury sorbents such as powdered activated carbon (PAC) introduces a second particle phase into the flue gas at coal-fired power plants. Full-scale testing results of PAC injection upstream of electrostatic precipitators (ESPs) have shown darkening filters from in-stack particulate sampling. Previous experimental studies on the electrostatic precipitation of PAC-fly ash admixtures showed an increase in the mass of uncollected particles as the PAC concentration is increased in the admixtures. To explore variables that lead to an increase in the mass of uncollected particles and its relation to darkening filters, a multiscale model was developed in COMSOL Multiphysics®based on a 2D Euler–Lagrange numerical scheme to study the particle collection behaviors of two separated particle phases: fly ash and PAC. The results showed that submicron particles (i.e. dp≤1μm) of both fly ash and PAC can enhance the induced vortical flows due to discontinuous current density. The present study provides a new understanding of the darkening PM filters due to PAC injection and for optimizing PAC injection when burning different coals.