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Energy Futures and Urban Air Pollution: Challenges for China and the United States
throughout the world. Supercritical plants are widely used in the United States, Europe, Russia, and Japan, with a limited number in operation in South Africa and China. Europe and Japan have also constructed ultra-supercritical plants, which demonstrate even higher efficiencies than do their supercritical counterparts. However, without successful commercial application in the United States, the ultra-supercritical technology is still considered to be unproven and a potential technical and economic risk (EPA, 2006). Supercritical power generation technologies have been considered to be the standard in the electric power industry. Though larger demonstration plants are under development, the average capacity of supercritical plants is between 300 and 600 MW.
Increasing thermal efficiency has been a goal of many PC-fired plants, although low energy prices often serve as a disincentive to implement more efficient methods. Nevertheless, this represents a potentially cost-effective way to reduce CO2 and other emissions and to decrease fuel consumption. Methods such as reducing the excess air ratio, reducing stack gas exit temperature (while recovering the heat), and increasing steam pressure and temperature have all been utilized at various times over the past several decades. Fuel type has an impact on efficiency, as does the type of plant. Older subcritical plants using poor-quality coal can have thermal efficiencies as low as 30 percent, while modern subcritical plants tend to operate between 35 and 36 percent. Meanwhile, modern supercritical plants typically operate in the 43-45 percent range (IEA, 2006a). As a reference, a 1 percent increase in efficiency can reduce specific emissions such as CO2, NOx, and SO2 by 2 percent (World Bank, 2006b). Moreover, installation costs are only 2 percent more for supercritical plants as opposed to subcritical, while operation costs are comparable and fuel costs, due to higher efficiency, are lower for supercritical systems.
China has recently been focused on adapting supercritical technologies from abroad. The Henan Qinbei power plant, a 600 MW demonstration plant, is a supercritical coal-fired plant utilizing domestically designed technologies, and has been online since late 2004. Another domestic supercritical demonstration plant with a capacity of 1,000 MW—Zhejiang Yuhuan—is under construction. Table 6-1 illustrates the growth of China’s power generation industry since 2000, and highlights the dominant role of thermal power, 98.7 percent of which comes from coal combustion.
Fluidized Bed Combustion
Fluidized bed combustion (FBC) is considered to be a clean coal technology and can be particularly useful for high-ash coals. It evolved as a result of efforts to develop a combustion process able to control pollutant emissions without implementing external controls, such as scrubbers. Coal particles are fed into a combustion chamber, suspended on jets of forced air, and combusted at 800-900°C, yielding less NOx formation in comparison to PC combustion. In the process, the