Characteristics of a biomass-based sorbent trap and its application to coal-fired flue gas mercury emission monitoring

A novel sorbent trap based on rice husk char (RHC) was developed. Scanning electron microscopy and Brunauer–Emmett–Teller analysis revealed that the raw RHC possesses a developed pore structure and has potential for mercury adsorption after brominated impregnation (RHC-HBr). The performance of both the raw and impregnated sorbents for Hg capture was investigated in a fixed bed system and compared with the performance of commercial activated carbon (AC). RHC-HBr showed a remarkable Hg adsorption capacity (57.84 μg/g) comparable with commercial AC. The RHC-HBr sorbent passed the analytical bias test for mercury detection when spiked by Hg0 and HgCl2 under both the lower and upper concentration levels. Field verification test of the biomass-based sorbent traps was performed in a 6 kWth fluidized-bed combustion (FBC) system. The Ontario Hydra Method (OHM) was applied as the reference method for evaluating HgT(g) measured by the sorbent traps. The field verification test showed that RHC-HBr sorbent traps perform with almost the same accuracy as AC-based sorbent traps, with 97.5 ± 2.9% field recovery rate, 3.2% breakthrough rate, and 0.6% relative deviation. HgT(g) field sampling based on the biomass-based traps was performed in a utility 660 MW coal-fired unit in parallel with the OHM under two different operational loads (100% and 75%). Mercury migration and the removal characteristics of the existing air pollution control devices (APCDs) were evaluated using the biomass-based sorbent traps. The final Hg emissions from the stack were determined to be 0.65 and 1.54 μg/Nm3 for 100% and 75% operational loads, respectively, indicating that a high load operation condition could be beneficial for mercury control by existing APCDs.