Modeling of mercuric chloride removal in ductwork and fabric filter by raw activated carbon injection

Based on previous experimental adsorption kinetic and equilibrium data for mercuric chloride (HgCl2) adsorption onto raw activated carbon (AC), a comprehensive model was formulated for its removal in the ductwork and fabric filter by raw AC injection in coal combustion flue gas. Various factors that can impact the performance and sorbent utilization were investigated, including inlet HgCl2 concentration, sorbent loading, particle size, external and internal mass-transfer considerations, residence time, filtration time, injection mode, and pressure drop. Despite these considerations, in-flight removal of HgCl2 in the ductwork was found to be almost negligible. For the removal in fabric filter, the effect of particle size was found to be significant, particularly for continuous sorbent injection. On the other hand, a discontinuous injection mode delivering the same amount of sorbent in 10% of a cleaning cycle resulted in higher removal performance and sorbent utilization. However, at the end of the cleaning cycle, most of the sorbent capacity was not used (<0.2%). The pressure drop across the filter cake built by fly ash and sorbent was found to be manageable within typical operating limits.