Mercury emissions monitoring in a coal-fired power plant by using the EPA method 30B based on a calcium-based sorbent trap

A novel calcium-based sorbent was synthesized from calcium acetate and mesoporous silica through chemical impregnation method. The Brunauer-Emmett-Teller (BET) and scanning electron microscope (SEM) analysis revealed that the sorbent possessed a good surface structure as the calcium salt decomposed to calcium oxide (CaO) through multiple calcination steps. The mercury adsorption performance of the sorbent was investigated in a fixed bed system, the results showed that the sorbent has an obvious penetration behavior for gaseous element mercury (Hg0(g)) while completely adsorbed reactive gaseous mercury (Hg2+(g)) under the pure nitrogen and simulated flue gas atmosphere. On-site sampling test of the calcium-based sorbent traps was ultimately conducted on a 600 MW coal-fired power plant. The Ontario Hydra Method (OHM) was chosen as the reference method to evaluate the accuracy of the sorbent traps sampling results. The measured data obtained by sorbent traps was well consistent with OHM under the selected operational load and all the sorbent traps passed the QA/QC criteria, show that the sorbent traps performed with almost the same accuracy as OHM. The mercury emission and removal characteristics across the existing air pollution control devices (APCDs) were reported based on the sorbent traps sampling results. With the help of SCR for the Hg0 oxidation, ESP for the removal of Hg2+ and Hgp, and the good water solubility of Hg2+ in WFGD, the combination of SCR + ESP + WFGD achieved an excellent mercury removal efficiency with the value of 88.54%. The final mercury emissions from the exhaust were 3.75 μg/m3 and meet the emission requirements of China.