Coal-fired plants

The high temperatures in the MHD combustion system mean that no complex organic compounds should be present in the combustion products. Gas chromatograph/mass spectrometer analysis of radiant furnace slag and ESP/baghouse composite, down to the part per biUion level, confirms this behef (53). With respect to inorganic priority pollutants, except for mercury, concentrations in MHD-derived fly-ash are expected to be lower than from conventional coal-fired plants. More complete discussion of this topic can be found in References 53 and 63. 

Conceptual designs of two repowered existing coal-fired plants in the United States, the Montana Power Company s Corette plant in Billings, Montana, and Gulf Power s Schofi plant, in Sneads, Florida are described in References 150 and 151. 

Lower power ratings of reactors provide greater dexibiUty for a utihty to add power generation to a system (19). The AP600 uses prefabricated modules to shorten the constmction time. Thus constmction and operating costs are expected to be competitive with coal-fired plants. 

The product gas after cleanup consists of primarily CO and H2. Combustion of coal gas in high firing-temperature gas turbines converts virtually all of the CO to CO2, and gas turbine exhaust is expected to contain no more than 10 ppm CO when operating at design conditions. Carbon monoxide emissions from a CGCC plant are thus expected to be around one-tenth those of a modem coal-fired plant equipped with low NO burners. 

From an economic standpoint, electricity production from a new natural gas plant versus a newly built coal-fired plant heavily favors natural gas, because natural gas-fired plants are cheaper to build. However, older coal-fired plants built 20 to 30 years ago are often more profitable than newly built gas plants, because — among other reasons — coal is cheaper than natural gas, and the older plants have long since paid for their capital investments through depreciation. 

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. 

There are several problems with these standards for older coal-fired plants that limit a sensible NO,-reduction policy. First, they are relatively lenient. Because they require only that low-NO, burners be used at coal-fired plants, relatively inexpensive NO,-reduction technologies are not being used, because the plants already meet the minimum standards. Second, standards are established on a technology-by-technology basis, and have resulted in more lenient requirements for dirtier technologies. This has created little or no incentive to switch to cleaner processes in the past decade. Thirdly, these standards are input-based, which means they provide no incentive for efficiency within any technology category. 

Soud, et al., 1993. Hermine N. Soud, Ivlitsuru Takeshita, and Irene M. Smith, "FGC Systems and Installations for Coal-Fired Plants" from "Desulfurization 3," Institution of Chemical Engineers, Warwickshire, UK, 1993. 

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. 

Nuclear reactors, however, do generate highly radioactive waste. This waste, which consists primarily of the fission fragments and their radioactive-decay products, must be stored for many years before its radioactivity decays to a reasonable level, and the safe long-term storage of this waste is a matter of great concern and debate. Fortunately, the volume of waste that is created is only about 20 cubic meters annually from a reactor, compared with 200,000 cubic meters of waste ash from a coal-fired plant. When nuclear weapions were tested in the atmosphere, the radioactive products from the nuclear explosions were released into the air and fell to Earth as radioactive fallout. 

Few coal gasification plants have yet reached commercial development, and they still have to compete with cheaper technologies such as conventional pulverized coal-fired plants and natural gas for the production of electricity. 

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. 

By 2025 the world is sequestering 1 billion metric tons of CC>2 per year while simultaneously producing hydrogen and shipping it hundreds of miles for use in cars. This is equivalent to sequestering the C02 produced by more than 700 medium-sized generation units, about two-thirds of all coal-fired plants in the United States today. 

Many of these plants may be built before CCS is ready and we will need to use our electricity more efficiently to slow the demand for such power plants, while building as many cleaner power plants as possible. Natural gas is far more cleaner for this power than coal. Generating hydrogen with renewables may be needed in order to avoid building coal-fired plants. More electricity from renewable power would reduce the pressure on the natural gas supply and reduce prices. The United States could have essentially carbon-free electricity before 2050 with hydrogen fuel playing a key role. 

Tadmor J. 1986. Atmospheric release of volatilized species of radioelements from coal fired plants. Health Phys 50 270-273. 

Coal-fired power plants release very large amounts of particulate material. The question Is, however, what fractions of the various elements In ambient air can be accounted for by particles from coal-fired plants A major fraction of an element can be contributed by coal combustion only If (1) coal accounts for an appreciable fraction of the A1 In the local atmosphere and (2) the EF value of the element on particles from coal combustion Is as great as for ambient particles. Only for those elements In Figure 1 for which there Is considerable overlap between the ranges for cities and for coal-fired plants can coal possibly be a major contributor. Even If there Is overlap, coal Is not necessarily a major source, as condition 1 above may not be met. On this basis, coal combustion could be a major source of many llthophlles plus Cr, N1, As, Se and, In cities where little residual oil Is used (Charleston and St. Louis), V. The very high EF values for As and Se and low values for V and Nl In Charleston, where little oil and a great deal of coal are burned, lends credence to this Interpretation. 

The enormous enrichments of Se on ambient particles relative to particles from coal-fired plants are surely due to the same problems as noted for As, but especially the well established fact that a major fraction of Se Is In the vapor phase at stack temperatures (47, 48). The very large Se enrichments for ambient particles Indicate that much of the vapor-phase Se condenses on particles after release. In some areas there may be additional Important sources of As and Se, e.g., non-ferrous smelters. 

In summary, coal-fired power plants appear not to be the major source of most enriched elements on particles In urban areas, despite the great attention devoted to mechanisms by which those elements become preferentially attached to fine particles (e.g.. Refs. 18, 34). However, the detailed studies of processes In coal-fired plants are of considerable value, as the fundamentals should be applicable to other kinds of combustion sources. Furthermore, It may be necessary to use this fundamental approach to develop methods for predicting the source compositions for coal-fired power plants that have not been measured. Selenium Is much... 

Smith, R. D. 1980. The trace element chemistry of coal during combustion and the emissions from coal-fired plants. Progress in Energy and Combustion Science, 6, 53-119. 

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