Clean Technology (청정기술)

The Korean Society of Clean Technology (한국청정기술학회)
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A Review of Pilot Plant Studies on Elemental Mercury Oxidation Using Catalytic DeNOxing Systems in MW-Scale Coal Combustion Flue Gases

MW급 석탄연소 배가스에서 탈질촉매시스템을 이용한 원소수은 산화 실증사례

  • Received : 2021.07.03
  • Accepted : 2021.07.30
  • Published : 2021.09.30
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Abstract

Major anthropogenic emissions of elemental mercury (Hg0) occur from coal-fired power plants, and the emissions can be controlled successfully using NH3-SCR (selective catalytic reduction) systems with catalysts. Although the catalysts can easily convert the gaseous mercury into Hg2+ species, the reactions are greatly dependent on the flue gas constituents and SCR conditions. Numerous deNOxing catalysts have been proposed for considerable reduction in power plant mercury emissions; however, there are few studies to date of elemental mercury oxidation using SCR processes with MW- and full-scale coal-fired boilers. In these flue gas streams, the chemistry of the mercury oxidation is very complicated. Coal types, deNOxing catalytic systems, and operating conditions are critical in determining the extent of the oxidation. Of these parameters, halogen element levels in coals may become a key vehicle for obtaining better Hg0 oxidation efficiency. Such halogens are Cl, Br, and F and the former one is predominant in coals. The chlorine exists in the form of salts and is transformed to gaseous HCl with a trace amount of Cl2 during the course of coal combustion. The HCl acts as a very powerful promoter for high catalytic Hg0 oxidation; however, this can be strongly dependent on the type of coal because of a wide variation in the chlorine contents of coal.

석탄화력발전소로부터 배출되는 질소산화물(NO + NO2 = NOx)은 NH3를 환원제로 사용하여 선택적으로 환원시키는 SCR(selective catalytic reduction) 탈질촉매시스템에서 효과적으로 제거될 수 있다. 이 SCR 촉매공정에서 원소수은을 산화시켜 후속공정에서 제거하기 위하여 수많은 산화촉매들이 제안되었으나 MW급 석탄연소시설이나 상업운전 중인 석탄발전소 탈질시스템에서 원소수은 산화성능을 실증한 사례들은 매우 드물다. 실배가스에서 수행한 실증연구들을 심층적으로 조사·분석한 바는 기존 SCR 탈질촉매뿐 아니라 수은산화능을 향상시킨 신촉매의 원소수은 산화활성은 석탄연소, 실배가스 등의 특성에 따라 매우 복잡한 양상을 띤다는 점이다. 그럼에도 불구하고 석탄연소시설에 사용하는 원료탄, 탈질시스템과 실증조건이 원소수은 산화능에 가장 큰 영향을 미치는 핵심 요소이다. 특히, 원료탄에 함유된 할로겐 함량은 탈질촉매공정의 중요성을 넘어서는 것으로 보여진다. 석탄에 존재하는 대표적인 할로겐 성분은 Cl, Br과 F이고 이들 중에서 Cl이 지배적이며 다른 할로겐계처럼 염으로 존재하지만 석탄연소 과정에서 미량의 Cl2와 함께 HCl로 전환된다. 이러한 HCl은 원소수은 산화에 있어서 강력한 산화제로 작용하지만 석탄마다 Cl 함량이 다르기 때문에 HCl 농도 또한 강하게 의존한다.

Keywords

Acknowledgement

본 연구는 산업통상자원부의 재원으로 한국에너지기술평가원의 지원(20193410100050)을 받아 수행되었다.

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