Kinetic transformation of mercury in coal combustion flue gas in a bench-scale entrained-flow reactor

A bench-scale entrained-flow reactor was used to extract flue gas produced by burning a subbituminous Belle Ayr coal in a 580-MJ/h combustion system. The reactor was operated at 400, 275, and 150 °C and a flow rate corresponding to residence times of 0–7 s. Elemental mercury (Hg0) and total gas mercury (Hggas) concentrations in the reactor were measured using an on-line Hg analyzer. At 400 and 275 °C, approximately 30% of the Hg0 released from the Belle Ayr coal was converted to Hg2+ in the 580-MJ/h combustion system. This conversion occurred rapidly at >400 °C as evidenced by similar Hg0 concentrations at 275 and 400 °C and the lack of Hg0 to Hg2+ conversion measured in the reactor at residence times of 0.5–7 s. Conversions of Hggas to particle-associated mercury Hg(p), and Hg0 to Hg2+ and/or Hg(p) were detected in the reactor at 150 °C. The reaction order and rate constant for Hggas and Hg0 conversions at 150 °C were 4.62 and 1.73 and 9.8×10−5 μg−3.62/(m−10.86 s) and 5.1×10−2 μg−0.73/(m−2.19 s), respectively.