Emissions from fossil fuel combustion, especially coal combustion, are major contributors to air pollution. Concentrations of suspended particles and sulfur dioxide (SO2 ) in the air of many cities in developing countries exceed World Health Organization standards. The effects of this pollution on human health can be devastating and in the most seriously affected countries the economic costs are estimated to be a significant percentage of GDP.
Supercritical steam units: Supercritical steam conditions have been applied in large power plants (typically larger than 500MW) in Europe, Japan, and the United States for the past quarter century. Early units were often unreliable especially in the case of the pressurized draft furnaces, (most of these have since been converted to balanced draft furnaces). Staff at the plants were unfamiliar with the new materials and designs. But later supercritical steam units now have a track record of more than 20 years of reliable service.
The high-efficiency electrostatic precipitator (ESP) for particulate control: Since coal typically contains 10–20 percent ash, flue gas contains particulates that must be collected before the gases are emitted. The electrostatic precipitator (ESP) is the most commonly used collection technology for electrical power utilities, but in China the wet scrubber is used with smaller units (200 MW or less). The wet scrubber has less collecting efficiency than the E S P (below 96 percent) and does not meet the guidelines set by the World Bank (50 mg/Nm3) as a primary measure of particulate control. But when the wet scrubber is installed as a measure to control SO2 and as an auxiliary to the ESP f o r particulate control, overall efficiency rises and particulate emissions fall.
Flue gas desulfurization for SO2 control: After particulates, SO2 is usually the next target in Energy Issues 3 1000 MW Supercritical plant, Matsuura, Japan (EPDC) reducing polluting emissions. Flue gas desulfurization (FGD) is a well-established method of removing SO2 from flue gas and has been widely used in electric utility plants in Europe, Japan, and the United States since the 1970s. The technology therefore has a long history and has been fine-tuned to optimize performance. New and simplified FGD technologies have been proposed and demonstrated in China and other developing countries.
Combustion modification and selective catalytic reduction to control nitrogen oxide: Coal-fired power stations also generate nitrogen oxide (NOx ). Unlike particulate and SO2 emissions, NOx emissions are affected by the combustion process as well as the quality of the coal. Modifying the combustion process by optimizing the air flow from the burner can reduce NOx emissions by 20–30 percent at a relatively low cost ($5–10/kW). This low-cost option is the first that should be applied in existing plants.
Atmospheric fluidized-bed combustion: Atmospheric fluidized-bed combustion (AFBC) has been widely applied to use low-grade coal or waste (opportunity fuel) at electric utility plants in the United States, Europe, and Japan since the 1980s. Hundreds of commercial plants are now in operation. The maximum unit size has been limited to around 200 MW, but a few 350 MW units have been built in Japan and France.
Text rights: (Takahashi, n.d.)
Text source: Takahashi, M. (n.d.). Technologies for Reducing Emissions in Coal-Fired Power Plants.
