Pulverized coal power plants first appeared in the 1920s and serve as the backbone of the power sector in the U.S. They currently supply over half of U.S. electricity. While vastly improved over the past 80 years, pulverized coal remains a relatively simple technology, converting a little more than one-third of the fuel’s energy potential into useful electricity.
Pulverized coal power generation starts by crushing coal into a fine powder that is fed into a boiler where it is burned to create heat. The heat produces steam that is used to spin one or more turbines to generate electricity. Subcritical plants make up the bulk of the U.S. pulverized coal system, with efficiencies for new plants usually around 37 percent. Supercritical plants use higher pressure and temperatures to boost efficiency to 40 percent or more. Ultra-supercritical, using still higher pressures, achieves 42-45 percent efficiency. Europe and Asia lead in the deployment of the most advanced pulverized coal systems, although they are gaining renewed attention in North America as well. Carbon dioxide can be captured from the exhaust plume of pulverized coal plants and then sequestered in geological formations, but this process is relatively expensive, especially for retrofit applications.
Pulverized coal power plants have gained renewed interest this decade due to surging natural gas prices. The levelized cost of electricity generated at most pulverized coal plants in the U.S. is currently less than that of natural gas combined-cycle plants. While the capital costs of gas-fired combined-cycle units are only half that of pulverized coal, the fuel costs are much higher and often unstable. Utilities pay special attention to predictability of prices and currently shy away from high and unstable natural gas prices. Moreover, as domestic production of natural gas is limited, further additions to gas-fired power generation would require more imported liquefied natural gas, and exacerbate energy security concerns.
Pulverized coal units have significant environmental concerns. Emissions of oxides of sulfur and nitrogen contribute to acid rain and ozone formation, and are dangerous to human and ecosystem health. Most plants have scrubbers to remove a portion of these gases from the exhaust plume, although power plant efficiency declines as a result. Other emissions include particulates, heavy metals such as mercury and arsenic, and carbon dioxide. Coal is the most carbon intensive fuel and contributes to global warming more intensely than any other source of energy. Given the enormous number of pulverized coal plants being added in China and India each year, we will likely need to find a way to retrofit existing plants to capture CO2 emissions. This is feasible, but will be expensive unless dramatic advances in technology are achieved.
Using domestic coal offers the impression that countries can insulate themselves from global energy insecurities, but the subsequent increase of greenhouse gas emissions can create an altogether different type of security problem.