The Efficiency of Mercury Removal in Packed Bed Wet Scrubber from Infectious Waste Incinerator

Name: Amornpon Changsuphan

Organization : King's Mongkut University of Technology Thonburi. The Joint Graduate School of Energy and Environment. Department of Environment Technology

keyword: Mercury

Abstract: The most important problem of infectious waste incinerators is the control of heavy metal especially mercury. Highly varying quantities of mercury and itscompounds occur in the combustion product during the incineration. A large number of different mercury compounds can be formed and' decomposed again due to the continuously changing composition of the flue gas as well as the increasing and decreasing temperature during the combustion process. In combustion process divalent mercury is reduced to elemental mercury on the reducing surface of a burning particles and all mercury compounds are transformed to elemental mercury since heating mercury compounds to temperatures above 700 OC. The divalent mercury is reduced to element which are easily released out of the incineration system. When the combustion gases are cooled down on heat exchangers, for example, it seems likely that a certain fraction of the mercury is oxidize. However, tlie oxidation processes are not known in a flue gas. The packed bed wet scrubber are recommended for improving removal efficiency. The feed wastes for the test experiment were composed of simulated waste include plastic, cotton, rubber gloves and 1,000 ppb pure mercury per batch(5 kg of simulated wastes per batch). Mercury was fed to incinerator every 6-10 min, at optinium temperature and combustion air during the incineration. Solutioi~ and packed bed media that used in wet scrubber must change every time of incineration. Mass balance between mercury feed rate and mercury emission to the stack was used to determined tlie mercury removal efficiency. Three oxidizing agents were selected as a capture substance for mercury removal. The three oxidizing agents were potassium permanganate, hydrochloric acid and chlorine. When adding potassium permanganate 15, 50 and 75 ppin as a capture substance. The removal efficiency was 79, 90 and 99% respectively. For l~ydrocl~loric acid as a capture substance, hydrochloric acid was added to recirculation tank to malte a pH in recirculation tank reduced to p1-I 5.0: 4.0 and 3.0. The results shown the removal efficiency around 70%. Finally cliloi-ine wasselected for mercury capture substance. Chlorine was added to recirculation pond at three concentration (50, 75 and 100 ppm) . The results showed the removal efficiency75, 80 and 87% respectively. The results of this study shown that the potassium permaganate 75 ppm was a appropikte substance for mercury I-emoval in paclcedbed wet scrubber. When increased tlie concentration of mercury and used potassium permanganate as a capture substance. The results showed when increased niercur-yconcentration in the simulated waste, the removal efficiency was decreased. These results can consider that 75 ppin potassium permanganate was not a opti~nun~concentration for removal mercury concentration higher than I mg/l