Pilot plant testing of elemental mercury reemission from a wet scrubber

This paper is to discuss the recent observations of elemental mercury (Hg-0) reemissions from a pilot-scale limestone wet scrubber. Simulated flue gas was generated by burning natural gas in a down-tired furnace and doped with 2000 ppm of sulfur dioxide (SO2). Mercuric chloride (HgCl2) solution was delivered to the scrubber at a controlled rate to simulate the absorption of ionized mercury (Hg2+). Testing results have shown that, after Hg2+ was injected, elevated He concentrations were soon detected both in the scrubber effluent flue gas and the hold tank air, which reflected the occurrence of Hg-0 reemissions in both places. When the HgCl2 feed was stopped, the Hg-0 reemission continued for more than 2 h. In addition, a significant Hg-0 reemission was also detected outside the scrubber loop. In an attempt to understand the Hg-0 reemission increase across the wet scrubber system under transient and steady states and to understand the underlying relationship with the mercury complexes retained in the wet scrubber system, a mercury reemission model was developed. With this model, it was found that the Hg-0 reemission rate under the current testing conditions can be simulated by a first-order reaction, and only a portion of Hg center dot S(IV) complexes retained in the slurry were participating in the reemission reaction.