Brown coal: methods of mining
Low cost and extensive reserves - the main factors causing an increase in the number of applications of brown coal. This type of fossil solid fuel, the earliest type of coal, has been mined by man for more than one hundred years. Brown coal is a product of peat metamorphism, in the stage between lignite and coal. Compared with the latter, this type of fuel is less popular, however, due to its low cost, it is widely used for the production of electricity, heating and other types of fuel.
Brown coal - a dense, earthy or fibrous carbonaceous mass of brown or tar-black color with a high content of volatile bituminous substances. As a rule, the plant structure, shell-like fractures, and wood pulp are well preserved in it. It burns easily, the flame is smoky, and a peculiar unpleasant burning smell is emitted. Reacting with potassium hydroxide, it forms a dark brown liquid. When dry distilled, brown coal forms ammonia with acetic acid.Chemical composition (on average), less ash: carbon - 63%, oxygen - 32%, hydrogen 3-5%, nitrogen 0-2%.
Brown coal is formed by layers of sedimentary rock deposits — flots, often of great thickness and length. The material for the formation of brown coal are various kinds of pyalpy, conifer, trees and peat plants. The deposits of these substances gradually decompose without air access, under water, under the cap of a mixture of clay and sand. The process of smoldering is accompanied by a constant release of volatile substances and gradually leads to the enrichment of plant residues with carbon. Brown coal is one of the first stages of the metamorphism of such plant sediments, after peat. Further stages - coal, anthracite, graphite. The longer the process, the closer the condition to pure carbon-graphite. So, graphite belongs to the Azoic group, coal - to the Paleozoic, brown coal - mainly to the Mesozoic and Cenozoic.
Brown and brown coal: differences
As you can see from the name itself, lignite is different from stone in color (lighter or darker). There are also black varieties, but in powder form the shade of such coal is still brown. The color of stone and anthracite always remains black.The characteristic properties of brown coal are in a higher carbon content compared to hard coal and a lower content of bituminous substances. This explains why lignite burns more easily and produces a large amount of smoke. The high carbon content also explains the above reaction with potassium hydroxide and a peculiar unpleasant odor during combustion. The nitrogen content, as compared to black coal, is also significantly lower. With a long stay in the air, brown coal rapidly loses moisture, crumbling to powder.
There are a lot of varieties and varieties of brown coal, among which there are several main ones:
- Normal brown coal, consistence dense, opaque brown color.
- Brown coal earthy fracture, easily washable.
- Tarry, very dense, dark brown, sometimes even blue-black. In a kink like resin.
- Lignite, or the tar tree. Coal with a well-preserved plant structure. Sometimes found even in the form of whole tree trunks with roots.
- Disodil - brown paper coal in the form of decayed thin-layered plant mass.Easily divided into thin sheets.
- Brown peat coal. Reminding peat, with a large number of impurities, sometimes reminiscent of the earth.
The percentage ratio of ash and combustible elements in different types of brown coal varies widely, which determines the advantages of combustible material of a particular variety.
The methods for brown coal mining are similar for all fossil coal. There are open (career) and closed. The oldest method of closed mining is tunnels, inclined wells to a coal seam of small thickness and shallow bed. It is used in case of financial inefficiency of the quarry device.
The shaft is a vertical or inclined well in the rock from the surface to the coal seam. This method is used for deep-seated coal-bearing formations. It is characterized by high cost of extracted resources and high accident rate.
Production by open pit is carried out at a relatively small (up to 100 m) depth of the coal seam. Open-cast or open-pit mining is the most economical; today, about 65% of all coal is mined in this way.The main disadvantage of the mine is a great damage to the environment. Mining of brown coal is mainly carried out by the open method due to the small depth. Initially, overburden is removed (the rock layer above the coal seam). After that, the coal is crushed by the drilling and blasting method and transported by specialized (quarry) vehicles from the production site. Stripping work, depending on the size and composition of the layer, can be done by bulldozers (with a loose layer of negligible thickness) or with rotary excavators and draglines (with a thicker and more dense layer of rock).
As a fuel, brown coal is used much less frequently than stone. It is used for heating private houses and small power plants. By so-called. dry distillation from brown coal is obtained from mountain wax for the woodworking, paper and textile industries, creosote, carbolic acid and other similar products. It is also processed into liquid hydrocarbon fuel. Humic acids in the composition of brown coal can be used in agriculture as a fertilizer.
Modern technologies allow to produce synthetic gas from brown coal, which acts as an analogue of natural gas. To do this, the coal is heated to 1000 degrees Celsius, as a result of which gas formation occurs. In practice, a fairly efficient method is used: a high temperature is supplied through a pipe through a drilled well to a brown coal deposit, and another gas is already producing finished gas, an underground processing product.