AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Numerical Simulations of Inhomogeneous Current Density Effects on ESP Performance for Fly Ash and Mercury Sorbent Mixtures
ERIC MONSU LEE, Herek Clack, Illinois Institute of Technology
Abstract Number: 60 Working Group: Control and Mitigation Technology
Abstract Injection of powdered activated carbon (PAC) upstream of electrostatic precipitators (ESPs) has been the most commonly used strategy for post-combustion mercury emissions control at coal-fired power plants. However, as PAC injection rate increases upstream of ESPs, the darkening filters with particulate matter (PM) samples collected downstream of ESPs indicates an unidentified performance anomaly. It has been hypothesized that injection of PAC can introduce unexpected heterogeneity to the PM collection process in ESPs as PAC differs greatly from fly ash in both physical and electrical properties and can potentially pose challenges to ESPs that were originally designed and operated for coal fly ash removal. A previous experimental study centering on the differential collection of PAC-fly ash admixtures shows increasing trends of unaccounted-for particles based on mass balances as PAC concentration increases in the PAC-fly ash admixtures. Furthermore, measurement of powder resistivity of the ESP-collected powder samples infers that the unaccountable particles becomes more PAC-concentrated as PAC concentration increases. The objective of the present study is to develop a numerical model using COMSOL MultiphysicsTM and explore additional variables leading to the increasing mass of unaccountable particles as PAC concentration increases. A Euler-Lagrange numerical scheme enables the modeling of the cylindrical ESP used during the experimental study and allows for solving the interrelated physics, including Maxwell’s electric field coupled with charge conservation, electro-hydro-dynamics (EHD) induced flow field, and particle tracing affected by transient electric force, aerodynamic drag and gravitational forces. The model shows that PAC is more susceptible to the vortex flows induced by the inhomogeneous current density on the collection electrode. In addition, when considering mutual couplings between the EHD flow and the dispersed phase, PAC can induce higher rates of momentum transfer and lead to intensified vortex flows. The findings provide new evidence for explaining the increasing mass of PAC-concentrated unaccountable particles and thus the darkening PM filters as PAC concentration increases.