Coal is a fossil fuel produced by previously dead plants preserved in ecosystems of water and sediment. Dead plants in this environment can avoid oxidation and biodegradation, so The carbon in it can be fixed. Coal is a black or dark brown rock that burns easily. It is a sedimentary rock but is not too hard. Lignite, for example, can be considered a metamorphic rock because it has been subjected to high temperatures and pressures since it was formed. The main components of coal are carbon and hydrogen, with small amounts of other elements, most notably sulfur. Coal is the most used fuel in the global power generation industry and the largest source of carbon dioxide emissions. Of course, it is also an important culprit of climate change and global warming. In terms of carbon dioxide emissions, coal emits slightly more than oil and about twice as much as natural gas. Coal is mined from underground coal mines, either deep underground or in open pits (surface mining).
Coal-fired power station
Coal is mainly used as a solid fuel for power generation and generates heat through combustion. Source of global annual coal consumption: WER, 2006; Wikipedia, 2007. About 6.2 billion tons, about 75% of which is used for power generation. In 2007, China's coal output was 2.85 billion tons, and India's coal output was approximately 536.7 million tons. 68.7% of China's electricity came from coal power generation. The United States consumes 1.053 billion tons of coal every year, 90% of which is used for power generation. In 2007, total global coal production was 6.81 billion tons. When using coal to generate electricity, the coal must first be crushed into powder and then burned in the boiler. The heat generated in the furnace heats the water in the boiler into steam, which is then used to drive a turbine generator to generate electricity. The thermodynamic efficiency of this process has been greatly improved over the past few years. Standard steam turbine technology is far from satisfactory. In the above process, the thermodynamic efficiency only reaches 35%, which means that 65% of the heat of the burned coal is emitted to the surrounding environment - wasted. Older coal-fired power stations are less thermally efficient and waste more heat energy.
Theoretically, increases in temperature and pressure may lead to higher thermodynamic efficiency, so the emergence of the supercritical turbine concept demonstrates an extremely high temperature boiler with a thermodynamic efficiency of up to 46%. . Another efficient way to utilize coal is a combined cycle generator, known as combined heat and power, and an MHD top cycle generator. About 40% of the world's electricity is generated by burning coal. The total amount of this sedimentary rock (coal) that can be mined with existing technology can be used for more than 300 years at current consumption levels, including coal types with high pollution and low energy intensity (such as lignite and bituminous coal). Within a few decades, global coal production will reach its maximum.
A more energy-efficient way to generate electricity from coal is to use monoxide fuel cells or molten carbonate fuel cells (or any oxygen ion conversion-based cells, which, when they burn oxygen, There is no difference between the fuel of the battery). Using these methods, the thermodynamic efficiency can reach 60% to 85% (direct power generation + waste heat steam turbine). Currently, this fuel cell technology can only use gaseous fuels, and they are very sensitive to sulfur poisoning. Until there is large-scale commercial success with coal, this technology alone will not be enough. As gaseous fuel research and development progressed, there was a view that coal powder could be transported using nitrogen as a carrier. Another view is to gasify the coal with water, in which introducing oxygen into the fuel side of the electrolyte may reduce the voltage on the fuel side, but may also greatly simplify carbon recovery.