Performance of Nitrogen Oxides (NOX) Emission Controls at U.S. Power Plants
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Inquiry into health impacts of air pollution in Victoria Submission 67 - attachment 2 Performance of Nitrogen Oxides (NOX) Emission Controls at U.S. Power Plants A comparison of combustion and post-combustion control technologies for coal-fired power plants Jeremy Schreifels （石智锐） 2008380009 PhD Candidate 80050012 ʹ 能源与环境 贺克斌教授 2008 Winter Ta ble of C onte nt s Abbreviations and Acronyms ......................................................................... i Notes ......................................................................................................... i Introduction ............................................................................................... 1 Health and Environmental Impacts of Nitrogen Oxides .................................... 2 Air Quality Standards for Nitrogen Dioxide and Secondary Pollutants ................ 4 Sources of Nitrogen Oxides Emissions ........................................................... 6 Formation of Nitrogen Oxides Emissions........................................................ 9 Technologies for Reducing or Controlling Nitrogen Oxides ..............................11 Combustion Modification Technologies ....................................................12 Post-Combustion Control Technologies ....................................................18 Emerging and Advanced Control Technologies ..........................................28 Technology Performance and Costs .........................................................29 Bibliography ..............................................................................................31 Abbreviations and Acronyms BOFA boosted over-fire air NH4HSO4 ammonium bisulfate BOOS burner out of service NH3 ammonia Btu British thermal units NO nitric oxide ;ϭƚƵуϭ͘ϬϱϱŐŝŐĂũŽƵůĞƐͿ NO2 nitrogen dioxide - CAA US Clean Air Act NO3 nitrate CCOFA close-coupled over-fire air NOX nitrogen oxides CFB circulating fluidized bed NSPS New Source Performance CO carbon monoxide Standards (US Clean Air Act) EPA US Environmental Protection O3 ozone Agency OFA over-fire air ESP electrostatic precipitator OH hydroxyl radical FGD flue gas desulfurization PM2.5 fine particles (particulate GW gigawatt matter smaller than 2.5 H2SO4 sulfuric acid microns) HCN hydrogen cyanide ROFA rotating opposed fire air HNCO isocyanic acid SCR selective catalytic reduction HNO2 nitrous acid SNCR selective non-catalytic HNO3 nitric acid reduction LNB low-NOX burner SO2 sulfur dioxide - LOI loss-on-ignition SO3 sulfur trioxide MW megawatt SOFA separated over-fire air NAAQS US National Ambient Air UBC unburned carbon Quality Standards US United States NCO isocyanate WHO World Health Organization (NH4)2SO4 ammonium sulfate Notes 1. All monetary figures are in 2007 US dollars unless otherwise noted. Inflators were based on CPI available at http://oregonstate.edu/cla/polisci/faculty- research/sahr/cv2007rsx1.pdf. 2. All measurements are in metric units (i.e., metric tons) unless otherwise noted. 3. NOX emission data ranges (e.g., minimum and maximum) and quartiles for specific coal-fired electric power plants , boiler categories, and control technologies are based on the 5st and 95th percentile unless otherwise noted. This was done to eliminate outliers͕͞ƐƵďƐƚŝƚƵƚĞ͟ĞŵŝƐƐŝŽŶĚĂƚĂƚŚĂƚƉƵƌƉŽƐĞůLJŽǀĞƌĞƐƚŝŵĂƚĞƐĂĐƚƵĂůĞŵŝƐƐŝŽŶƐ͕ start-up and shutdown periods, and out-of-range data. i Introduction Nitrogen oxides (NOX) in the atmosphere contribute to a number of environmental issues that can have significant impacts on human health and the environment. As the science of atmospheric chemistry, air quality management, and epidemiology improves our understanding of the impacts of NOX and secondary pollutants related to NOX, national and local governments are implementing regulations and policies to reduce NOX emissions from key sectors and emission sources. For these regulations to be effective, policymakers must understand the extent of the problem and the potential solutions. The following questions are therefore important to ensure that the problems are resolved efficiently and effectively: x What are the human health and environmental impacts of NOX emissions and secondary pollutants? x What are the pathways by which NOX emissions and secondary pollutants are formed and transported? x What are the sources of NOX emissions that contribute to the problem? x What levels of NOX reductions are necessary to address the human health and environmental challenges? x What technologies and practices are (or will be) commercially available to reduce NOX? x What are the costs of these technologies and practices? x What are the impacts of these technologies and practices on the operations of power plants and industrial facilities? This paper briefly addresses these questions, with an emphasis on assessing the real-world effectiveness of commercially-available NOX emission control technologies in the United States (US). In particular, this paper focuses on combustion modifications and post-combustion NOX control technologies commonly installed at US coal-fired electric power plants. These facilities are the largest stationary sources of NOX emissions in the US and they have more than a decade of experience with advanced NOX controls. This paper is organized into five sections. 1. Health and environmental impacts of NOX explores the human health and environmental effects of nitrogen dioxide (NO2) and secondary pollutants formed from NOX. 2. Air quality standards highlights US national ambient air quality standards for nitrogen dioxide (NO2), fine particles (PM2.5), and ozone (O3) and air quality levels across the US. 3. Source of NOX emissions provides details on NOX emissions from different source categories including coal-fired electric power plants and the policies implemented to control those emissions. 4. Formation of NOX emissions describes the formation of NOX during coal combustion and opportunities for reducing its formation. 5. Technologies for controlling NOX describes primary (i.e., combustion) controls for reducing NOX formation and secondary (i.e., post-combustion) controls for removing NOX from flue gas. Each of these technologies has distinct advantages and disadvantages that are discussed in this paper. The final section also includes case studies demonstrating how three coal-fired electric power plants reduced emissions. The first case study is for a 126 megawatt (MW) plant in New York that installed combustion modifications (low-NOX burners with boosted over-fire air technology) to reduce NOX emissions by 60 percent. The second case study is for a 1,300 MW plant in Florida that upgraded combustion technologies (advanced low-NOX burners with over-fire air technology) to reduce NOX emissions by an additional 35 percent. The final case study is for a 2,600 MW plant in Ohio that installed combustion modifications (low-NOX burners) in combination with post-combustion controls (selective catalytic reduction) to reduce NOX by approximately 90 percent. However, the Ohio plant experienced a number of problems related to the SCR. These problems, and the attempted solutions, are reviewed in the case study. 1 Health and Environmental Impacts of Nitrogen Oxides NOX is a generic term for a group of gases that contain nitrogen and varying amounts of oxygen. While there are a number of different gases that meet this definition1, we are most concerned with nitric oxide (NO) and NO2 ʹ two gases that are emitted in large quantities from fuel combustion. NOX emissions and - secondary pollutants formed from NOX (e.g., O3, nitrate (NO3 ), and acid aerosols) are often transported over long distances, creating regional problems beyond the geographic and political boundaries of the areas where the NOX is emitted. These regional impacts can include the direct health effects of NO2 [1; 2; 3; 4] pollution ʹ NO2 can be a severe respiratory irritant and can lead to premature death ʹ as well as acid deposition, tropospheric ozone, fine particles, eutrophication of waterways, and regional haze. Acid Deposition Acid deposition is the general term for both wet (e.g., rain, snow) and dry deposition of acid particles. In the atmosphere, NOX can oxidize into a variety of compounds that dissolve in water and decompose to 2 form nitric acid (HNO3) or nitrous acid (HNO2). These acid gases and neutralized salts contribute to acid rain. The primary acidic compound ʹ HNO3 ʹ is produced when NO2 reacts with hydroxyl radicals (OH), water, or O3 (see Equations 1, 2, and 3). During daytime conditions, OH and NO2 (Equation 1) are the dominant source of air-phase HNO3. During nighttime conditions, Equation 3 is the dominant source of aqueous- [5 ] phase HNO3. Equation 1: NO2 + OH → HNO3 Equation 2: 3NO2 + H2O → 2HNO3 + NO Equation 3: O3 + NO2 → NO3 + O2 ⇄ N2O5 N2O5 + H2O → 2HNO3 Because it is extremely water soluble, HNO3 rapidly deposits on particles and water droplets in the atmosphere. [5] When these acidic particles or moisture fall to earth they: x Impair waterways; x Damage aquatic ecosystems; x Reduce forest and agricultural productivity; and x Damage paint finishes, buildings, infrastructure, and historical monuments. [5; 6; 7; 8; 9] Tropospheric Ozone Tropospheric ozone, often referred to as ground-level ozone or smog, is a photo-oxidant that is formed when NO2 dissociates in the presence of sunlight (wavelengths shorter than 420 nanometers) and the resulting atomic oxygen reacts with molecular oxygen (see equation 4). [3; 5] Equation 4: NO2 + hv → NO + O O + O2 → O3 O3 can have serious health impacts