Power plants, coal-fired emissions

Emissions control systems play an important role at most coal-fired power plants. For example, PC-fired plants sited in the United States require some type of sulfur dioxide control system to meet the regulations set forth in the Clean Air Act Amendments of 1990, unless the boiler bums low sulfur coal or benefits from offsets from other highly controlled boilers within a given utiUty system. Flue-gas desulfurization (FGD) is most commonly accomphshed by the appHcation of either dry- or wet-limestone systems. Wet FGD systems, also referred to as wet scmbbers, are the most effective solution for large faciUties. Modem scmbbers can typically produce a saleable waUboard-quaUty gypsum as a by-product of the SO2 control process (see SULFURREMOVAL AND RECOVERY). 

Also, wood fuel is low in sulfur, ash, and trace toxic metals. Wood-fired power plants emit about 45% less nitrogen oxides, NO, than coal-fired units. Legislation intended to reduce sulfur oxides, SO, and NO emissions may therefore result in the encouragement of wood-burning or cofiring wood with coal. 

Another reason why we can question whether such a technology investment really makes sense is the fact that emissions-control requirements tend to be less stringent when it comes to older coal-fired plants. In the United States the great majority of NOj emissions from the power sector come from existing coal-fired plants, many of which were built between 1950 and 1980. 

Major sources for emissions of SO, and NO, m the United States are presented in Figures 3 and 4 respectively. Approximately two-thirds of the SO, emissions are from electric utilities. Efforts to reduce SO, emissions both nationally and regionally have focused on electric utilities. The CAAA of 1990 have stipulated a reduction of 9.1 million metric tons (10 million short tons) of SO, below 1980 levels, with most of this reduction coming from coal-fired power plants. Implementation of Phase I reductions (199.5-2000) has been successful and has resulted in an 18 percent decline in SO, emissions from electric utilities, compared with 1990 SO, emissions. There has been a 16 percent decline in SO, for this time period when all sources are considered. Phase 2 of the CAAA, which is designed to reduce SO, emissions from electric utilities by another 20 percent... 

In the future, if the criterion for selecting new generating capacity was solely fuel cost, coal will be the number one choice. But the much greater costs of coal-fired plants (primarily to meet local and federal emission standards), as well as the potential of tighter standards, will make gas more attractive in many cases. And although natural gas prices may rise, the fuel costs per kilowatt-hour for gas-fired power plants should remain unchanged as efficiency gains offset the rise in fuel prices. 

Although the petrochemical and metals industries were the primai y focus of the toxic air pollutants legislation, approximately forty of these substances have been detected in fossil power plant flue gas. Mercury, which is found in trace amounts in fossil fuels such as coal and oil, is liberated during the combustion process and these emissions may be regulated in the future. EPA issued an Information Collection Request (ICR) that required all coal-fired plants to analyze their feed coal for mercury and chlorine. Since these data will be used in making a regulatory decision on mercury near the end ot the year 2000, it is critical that the power industry provide the most accurate data possible. 

Emissions in excess of allotted levels are taxed. As an incentive to clean up emissions, companies that emit less than their allotted amounts are allowed to sell their unsued portions (so-called emission credits) to other companies. Several years ago, the Tennessee Valley Authority (TVA), which operates 11 coal-fired electricity plants, purchased emission credits from Wisconsin Power and Light. The TVA bought pollution rights for the emission of 1.00 X 10 tons of sulfur dioxide per year at a price of 275 per ton. How much will it cost to emit 1 mol of SO2 How many molecules can be emitted for 1.00 ... 

Reductions in U.S. mercuiy emissions from medical and municipal waste incinerators and other industrial sectors have already occurred. Additional emission reductions from some coal-fired power plants have also already begun as co-benefits from technologies used to control SO2 and NO emissions. These mercury emissions from power plants are, however, expected to be reduced further over the next few decades. Meanwhile, changes in mercuiy emissions in other parts of the world may also affect some U.S. ecosystems. 

Table 4. Cost estimates of alternative mitigation technologies in the power generation sector compared to baseline pulverized coal-fired power plant and natural gas Combined Cycle with Gas Turbine (CCGT) power stations and the potential reductions in C02 emissions to 2020 [14]...

In the energy sector, coal-fired power plants contribute 54% of C02 emissions, and gas-fired power plants contribute 40%. In 2009, C02 emission from fossil fuels is estimated to increase by 113% compared to the year 2000. Each kWh of electricity of Vietnam contributes 0.52 kg C02 emission. The contribution of each sector to the total emissions in Vietnam through the years is shown in Fig. 9. 

Emissions of silver from coal-fired power plants may lead to accumulations in nearby soils (Fowler and Nordberg 1986). Silver in soils is largely immobilized by precipitation to insoluble salts and by complexation or adsorption by organic matter, clays, and manganese and iron oxides (Smith and Carson 1972). 

Exposure of humans and wildlife to arsenic may occur through air (emissions from smelters, coal-fired power plants, herbicide sprays), water (mine tailings runoff, smelter wastes, natural mineralization), and food (especially seafoods). 

Meeting the Kyoto goals could have a major impact on the electric power and auto industries and many believed the economy would suffer greatly. Developing countries like China and India would be exempt from the reduction of carbon dioxide emissions. China and India have plans to build over 600 coal-fired plants. The emissions of these plants would be 5 times the total saving of Kyoto. 

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