Retention of trace elements in coal-fired flue gas by a novel heterogeneous agglomeration technology.

Heterogeneous agglomeration (HA) is a very potential technology for coal-fired flue gas treatment. In this paper, the distribution and migration mechanisms of trace elements (TEs) such as Se, As and Pb in CFPPs were studied on a 30,000 m3/hr pilot-scale experimental platform. The influences of HA on the removal efficiency of gaseous and particulate TEs were well analyzed. The results showed that Se, As and Pb were enriched in fly ash, and their sensitivity to particle size is quite different. The content of Se was the highest in PM1, reaching 193.04 mg/kg at the electrostatic precipitator (ESP) outlet. The average particle size of the total dust before ESP increased significantly from 21.686 to 62.612 µm after injecting the heterogeneous agglomeration adsorbent, conducive to its further removal by ESP. In addition, the concentrations of gaseous Se, As and Pb in the flue gas decreased after adsorbent spray, and accordingly, their contents in the hierarchical particles increased, indicating that the adsorbent could effectively promote the adsorption of gaseous trace elements in fly ash and reduce the possibility of their escape to the atmosphere. Total concentrations of Se, As and Pb emitted by wet flue gas desulfurization (WFGD) are 0.223, 0.668 and 0.076 µg/m3, which decreased by 59.98%, 47.69% and 90.71%, respectively. Finally, a possible HA mechanism model was proposed, where chemical adsorption, physical condensation and collision agglomeration of gaseous TEs and fine particles with adsorbent droplets occurred to form larger agglomerates.

Mercury species and potential leaching in sludge from coal-fired power plants.

Wet flue gas desulfurization (WFGD) sludge, generated from the WFGD effluent treatment process, is suitable for multiple uses in various industries. However, risk assessments of its utilization are limited. Systematic study of Hg species occurrences, partitioning and risks of leaching is required, and these concerns were addressed in the present study. Hg temperature-programmed decomposition (Hg-TPD) and an improved European Community Bureau of Reference (BCR) method indicated residual Hg in WFGD sludge was related to HgS, and the content of this fraction was from 2 to 3%. HgCl2, HgO and HgSO4 were assigned to the water/acid-soluble fractions, and reducible Hg was related to Fe species in the sludge. Leachate evaluation of the WFGD sludge indicated potentially high Hg leaching risk. WFGD sludge with higher Hg concentrations and smaller particulate diameters exhibited greater leaching potential. Leaching of Hg from WFGD sludge in China into the environment was estimated at 7.46 t/yr.