Evidence of powdered activated carbon preferential collection and enrichment on electrostatic precipitator discharge electrodes during sorbent injection for mercury emissions control

Removal of mercury from coal-derived flue gas by injecting powdered sorbents often involves a substantial portion removed within an electrostatic precipitator (ESP). The present investigation uses a lab-scale ESP to assess the potential for injected sorbents to collect preferentially on discharge electrode wires. Such preferential collection would increase the adsorption capacity of the accumulated dust cake on the discharge electrodes, increasing their potential contribution to the total mercury removal performance of the ESP. The lab-scale results involving various fly ashes and both carbon-based and non-carbon mercury sorbents confirm that powdered activated carbon is enriched in the discharge electrode dust cake relative to its concentration in suspension in the gas flow. Other results explore the effects of applied ESP polarity, voltage, and power, percent PAC added to the fly ash, and total particulate matter loading entering the ESP on the collection behavior.