Coal pollution mitigation emissions of sulfur dioxide or oxides of nitrogen associated with the utilization of coal in the generation of electricity." Before being adopted in this fashion, historically "clean coal" was used to refer to clean-burning coal with low levels of impurities, though this term faded after rates of domestic coal usage dropped. The term appeared in a speech to mine workers in 1918, in context indicating coal that was "free of dirt and impurities." In the early 20th century, prior to World War II, clean coal (also called "smokeless coal") generally referred to anthracite and high-grade bituminous coal, used for cooking
Carbon capture and storage and fossil fuel-based hydrogen production plants. Extracting from air is also possible, although the far lower concentration of in air compared to combustion sources presents significant engineering challenges. Organisms that produce ethanol by fermentation generate cool, essentially pure that can be pumped underground. Fermentation produces slightly less than ethanol by weight. Flue gas from the combustion of coal in oxygen has a large concentration of , about 10-15% whereas natural gas power plant flue gas is about 5–10% . Therefore, it is more energy and cost efficient to capture from coal-fired power plants. Impurities in streams, like sulfurs and water,