Mercury emissions control in coal combustion systems using potassium iodide: Bench-scale and pilot-scale studies

Ying Li, Michael Daukoru, Achariya Suriyawong, Pratim Biswas

Research output: Contribution to journalArticlepeer-review

31 Scopus citations

Abstract

Addition of halogens or halides has been reported to promote mercury removal in coal-fired power plants. In this study, bench- and pilot-scale experiments were conducted using potassium iodide (KI) for capture and removal of Hg in air and coal combustion exhaust. Two bench-scale reactor systems were used: (1) a packedbed reactor (PBR) packed with granular or powder KI and (2) an aerosol flow reactor (AFR) with injection of KI particles. It was found that a higher temperature, a higher concentration of KI, and a longer gas residence time resulted in a higher Hg removal efficiency. A 100% Hg removal was achieved in the PBR above 300 °C using 0.5 g of powder KI and in the AFR above 500 °C with a KI/Hg molar ratio of 600 at a 5.8 s residence time. The low KI injection ratio relative to Hg indicated that KI is highly effective for Hg removal in air. Formation of I 2 vapor by the oxidation of KI by O 2 at high temperatures, which then reacts with Hg to produce HgI 2, was identified as the pathway for removal. The pilot-scale experiments were conducted in a 160 kW pulverized coal combustor. KI was introduced in two ways: as a powder mixed with coal and by spraying KI solution droplets into the flue gas. In both cases the Hg removal efficiency increased with an increase in the feed rate of KI. Mixing KI powder with coal was found to be more effective than spraying KI into the flue gas, very likely due to the higher temperature, longer residence time of KI, and the formation of a secondary reactive sorbent. The Hg removal by KI was less efficient in the pilot-scale tests than in the bench-scale tests probably due to certain flue gas components reacting with KI or I 2. Hg speciation measurements in both benchand pilot-scale experiments indicated no oxidized mercury in the gas phase upon introduction of KI, indicating that the oxidation product HgI 2 was captured in the particulate phase. This is very beneficial in coal-fired power plants equipped with electrostatic precipitators where particulate-bound Hg can be efficiently removed.

Original languageEnglish (US)
Pages (from-to)236-243
Number of pages8
JournalEnergy and Fuels
Volume23
Issue number1
DOIs
StatePublished - Jan 22 2009
Externally publishedYes

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology

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