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Underground coal gasification (UCG) is an industrial gasification process, which is carried out in non-mined coal seams. It involves injection of a gaseous oxidizing agent , usually oxygen or air, and bringing the resulting product gas to the surface through production wells drilled from the surface.
Secunda CTL is a synthetic fuel plant owned by Sasol at Secunda, Mpumalanga in South Africa. It uses coal liquefaction to produce petroleum-like synthetic crude oil from coal. The process used by Sasol is based on the Fischer–Tropsch process. It is the largest coal liquefaction plant and the largest single emitter of greenhouse gas in the world.
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.
Typically coal liquefaction processes are associated with significant CO 2 emissions from the gasification process or as well as from generation of necessary process heat and electricity inputs to the liquefaction reactors, [10] thus releasing greenhouse gases that can contribute to anthropogenic global warming.
Air pollution emission factors are usually expressed as the weight of the pollutant divided by a unit weight, volume, distance, or duration of the activity emitting the pollutant (e.g., kilograms of particulate matter emitted per megagram of coal burned). The factors help to estimate emissions from various sources of air pollution.
The chemical composition of syngas varies based on the raw materials and the processes. Syngas produced by coal gasification generally is a mixture of 30 to 60% carbon monoxide, 25 to 30% hydrogen, 5 to 15% carbon dioxide, and 0 to 5% methane. It also contains lesser amount of other gases. [10]
Coal liquefaction emits more carbon dioxide than liquid fuel production from crude oil. Mixing in biomass and using carbon capture and storage (CCS) would emit slightly less than the oil process but at a high cost. [101] State owned China Energy Investment runs a coal liquefaction plant and plans to build 2 more. [102]
Air pollution in Africa is coming to the forefront and must not be ignored. For example, in South Africa the mercury levels are severe due to coal combustion and gold mining. Mercury is absorbed from the air into the soil and water. [19] The soil allows the crops to absorb the mercury, which humans ingest.