Mercury Migration Behavior from Flue Gas to Fly Ashes in a Commercial Coal-Fired CFB Power Plant

Xiaohang Li, Yang Teng, Kai Zhang, Hao Peng, Fangqin Cheng and Kunio Yoshikawa
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Xiaohang Li: Beijing Key Laboratory of Emission Surveillance and Control for Thermal Power Generation, North China Electric Power University, Beijing 102206, China
Yang Teng: Beijing Key Laboratory of Emission Surveillance and Control for Thermal Power Generation, North China Electric Power University, Beijing 102206, China
Kai Zhang: Beijing Key Laboratory of Emission Surveillance and Control for Thermal Power Generation, North China Electric Power University, Beijing 102206, China
Hao Peng: State Environmental Protection Key Laboratory of Efficient Utilization Technology of Coal Waste Resources, Shanxi University, Taiyuan 030006, China
Fangqin Cheng: State Environmental Protection Key Laboratory of Efficient Utilization Technology of Coal Waste Resources, Shanxi University, Taiyuan 030006, China
Kunio Yoshikawa: School of Environment and Society, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan

Energies, 2020, vol. 13, issue 5, 1-15

Abstract: Mercury (Hg) emissions from coal-fired power plants are of increasing concern around the world. In this study, field tests were carried out to understand the Hg emission characteristics and its migration behaviors in a commercial CFB boiler unit with the electricity generation capacity of 25 MW. This boiler is equipped with one electrostatic precipitator (ESP) and two fabric filters (FFs) in series for removing particulates from the flue gas. The EPA 30B method was used for simultaneous flue gas Hg sampling at the inlet of the ESP and the outlet of the second FF. The Hg mass balance in the range of 104.07% to 112.87% was obtained throughout the CFB unit by measuring the Hg contents in the feed fuel, the fly ash and the bottom ash, as well as in the flue gas at the outlet of the particulate control device (PCD) system. More than 99% of Hg contained in the feed fuel was captured by the fly ash, whilst less than 1% of Hg was remained in the bottom ash or the flue gas after passing the PCD system. The gaseous Hg obviously migrated from the flue gas to the fly ash in the air pre-heater, where the flue gas temperature decreased from 250 °C at the inlet to 120 °C at the outlet. Other gaseous Hg migrated from the flue gas to the fly ash in the PCD system, as the Hg concentrations in the flue gas ranged from 3.14 to 4.14 μg/m 3 at the inlet of the ESP and ranged from 0.30 to 0.36 μg/m 3 at the outlet of the second FF. The average Hg contents in the fly ash samples collected from the ESP, the first FF and the second FF were 912.3, 1313.6 and 1464.9 ng/g, respectively, while the mean particle diameters of these fly ash samples tend to decrease along the flow pass in the PCD system. Compared to large fly ash particles, smaller fly ash particles exhibit higher Hg capture performance due to their high unburned carbon (UBC) content and large specific surface area. The migration of gaseous Hg from the flue gas to the fly ash downstream of the CFB boiler unit was easier than that downstream of the PC boiler unit due to high UBC content and specific surface area.

Keywords: Hg emission; circulating fluidized bed boiler; air pre-heater; particulates control device system; fly ash (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (4)

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