Coal pollution mitigation

Coal pollution mitigation is a series of systems and technologies that seek to mitigate health and environmental impact of burning coal for energy. Burning coal releases harmful substances that contribute to air pollution, acid rain, and greenhouse gas emissions. Mitigation includes precombustion approaches, such as cleaning coal, and post combustion approaches, include flue-gas desulfurization, selective catalytic reduction, electrostatic precipitators, and fly ash reduction. These measures aim to reduce coal's impact on human health and the environment.

The combustion of coal releases diverse chemicals into the air. The main products are water and carbon dioxide, just like the combustion of petroleum. Also released are sulfur dioxide and nitrogen oxides, as well as some mercury. The residue remaining after combustion, coal ash often contains arsenic, mercury, and lead. Finally, the burning of coal, especially anthracite, can release radioactive materials.

Mitigation of coal-based pollution can be divided into several distinct approaches. Coal pollution mitigation seek to minimize negative impacts of coal combustion.

Prior to its combustion, coal can be cleaned by physical and by chemical means.

Physical cleaning of coal usually involves gravimetric processes, often in conjunction with froth flotation Such processes remove minerals and other noncombustible components of coal, exploiting their greater density vs that of coal. This technology is widely practiced.

Coal can also be cleaned in part by chemical treatments. The concept is to use chemicals to remove deleterious components of coal, leaving the combustible material behind. Typically, coal cleaning entails treatment of crushed coal with acids or bases. This technology is expensive and has rarely moved beyond the demonstration phase. During World War II, German industry removed ash from coal by treatments with hydrofluoric acid and related reagents.

The wastes produced by the combustion of coal can be classified into three categories: gases, particulates, and solids (ash). The gaseous products can be filtered and scrubbed to miminize the release of SO_x, NO_x, mercury:

Electrostatic precipitators remove particulates. Wet scrubbers can remove both gases and particulates.