(NOx, a mix of NO and NO2) control technology development during the 1980s. The acid deposition provisions of the 1990 Clean Air Act amendments (CAAAs) established for the first time an absolute cap on total U.S. SO2 emissions, with provisions for emissions trading to achieve the required overall reduction in utility emissions most cost-effective ly. A reduction in NOx emissions was also mandated, although no cap on total emissions was established.

Significant progress has been made over the past decade in the capability of commercial systems to reduce SO2, NOx, and particulate emissions from pulverized coal-fired power plants. Emissions trends for a new pulverized coal power plant burning medium-sulfur coal are shown in Figure 3-2. Air pollution control devices today achieve emission levels well below federal NSPS. The most effi-

FIGURE 3-2 Trend in emission rates of criteria air pollutants from a new pulverized coal power plant. Percentage reductions are relative to an uncontrolled power plant based on a dry-bottom tangentially fired boiler firing bituminous coal of 10,000 Btu/lb heating value and containing 2.5 percent sulfur, 12 percent ash, and 10,000 Btu/lb. Percentages on the bars are percent reductions relative to uncontrolled emissions of that component. NSPS = New Source Performance Standards. FGD = flue gas desulfurization (wet magnesium-enhanced lime). FF = fabric filter (baghouse). ESP = electrostatic precipitator. LNB = low NOx burner. SCR = selective catalytic reduction.

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