Coal-Fired Power Plant What is Coal? -is a combustible black or dark brown rock consisting mainly of carbonized plant matter, found mainly in underground deposits and widely used as fuel -is a combustible black or brownish-black sedimentary rock formed as rock strata called coal seam. -coal is mostly carbon with variable amounts of other elements; chiefly hydrogen, sulfur, oxygen and nitrogen. -the thermal efficiency of a utility-scale electrical generators is around 35%. -Power plant coals have a calorific value ranges from 9.5 MJ/kg to 27 MJ/kg. Types of Coal 1.Peat–is formed from decaying vegetation, and is considered to be the precursor of coal. Peat is an important industrial fuel in some regions, including Ireland and Finland. When dehydrated, peat becomes an effective absorbent for fuel and oil spill on both land and water. Peat appeared especially competitive in the 60-200 MW power plants which necessitated the reclamation of vast areas of peat for large scale peat extraction. The calorific value/heating value of oven-dried peat is generally 20 MJ/kg, but at the operating moisture content of 30-40% the calorific value is only about 10MJ/kg. a decayed vegetation takes 12000 years to become a peat coal. 2.Lignite–is formed from compressed peat, and refer to as brown coal. Lignite is a low ranking and highly volatile coal which is used mainly in power stations. It is sometimes found in European briquettes. Has a carbon content of 60-70%. In 2014, about 12% of Germany’s energy and specifically, 27.4% of Germany’s electricity came from lignite power plants. While in Greece the same year, lignite provided about 55% of its power needs. A total of 45% global coal reserves consists of low-rank coals (LRCs) such as lignite. The high moisture content results in higher CO2 content. The heating value of lignite ranges from
10 MJ/kg up to 17 MJ/kg. A lignite will produce after 60 million years after of the decayed vegetation. 3.Sub Bituminous Coal–is a lignite that has been subjected to an increased level of organic metamorphism. This metamorphism has driven off some of the oxygen and hydrogen in the coal. The sub bituminous coal has a carbon of 71% to 77%. Sub-bituminous coal has a heating value of 19.3 MJ/kg to 26.7 MJ/kg. Sub bituminous is most often used as fuel for steam-electric power generation. They contain 15-30% inherent moisture by weight and are non-coking. A coal takes 100 million years to become a subbituminous coal. 4.Bituminous Coal –bituminous coal is formed when a sub-bituminous coal is subjected to increase level of metamorphism. It has a carbon content of 77% to 87%. Bituminous coal has a heating value of 24 MJ/kg to 35 MJ/kg.Bituminous coal takes 100 to 300 million years to become usable. 5.Anthracite–is the highest rank of ignitable coal. It is hard, black and glossy, and as a natural smokeless fuel, is used primarily for residential and commercial space heating.