Changes in coal use

The use of coal is closely related to the type of coal. Different kinds of coal have different uses. The types and uses of coal can be roughly summarized as follows.

(1) types of coal

The classification of coal is different due to different main standards, and the classification methods are also varied. Here I mainly introduce classification by reason and practical classification.

Genetic classification: genetic classification is based on various comprehensive factors of coal-forming plants in coal-accumulating period, mainly based on the types of coal-forming substances-higher plants or lower plants; The environment and conditions of plant remains-the depth of marsh water, water activity, oxygen supply and microbial activities. It is also determined by the decomposition and transformation process of coal-forming substances.

According to the types of coal-forming substances, it can be divided into three categories: humus coal formed by higher plants; Sapropelic coal formed by lower plants; Humus-sapropelic coal formed by higher plants and lower plants. According to the environmental conditions of plant accumulation and the transformation process of coal-forming substances, the genetic types of coal can be divided into humic coal and residual coal. Humus coal and residual coal are all transformed from higher plants. The original substances of humus coal are mainly composed of wood and cellulose of higher plants, and the original substances of residual coal are mainly biochemical stable tissues of plants, such as cuticle, spores, resin substances and cork tissues of bark. The material composition of sapropelic coal is mainly the product of algae material change. Humus sapropelic coal is a transitional type between humus coal and sapropelic coal. Most of the coal in nature is humic coal, and there are relatively few residual coal, humic-sapropelic coal and sapropelic coal. They usually form interlayers and lenses in humus coal, and in rare cases, they can form coal seams alone.

Classification by practicality: This classification method requires a comprehensive understanding of the material composition of coal. Coal is mainly composed of carbon, hydrogen, oxygen, nitrogen and some inorganic substances such as mineral impurities and water. The quality of coal is determined by the main composition index and metamorphic degree of coal. The main indexes that determine coal quality are moisture, ash, volatile matter, coke residue, cuticle thickness, calorific value, phosphorus, sulfur, ash, ash fusibility, washability and so on.

Moisture: The moisture in coal can be divided into external moisture and internal moisture. External moisture is the moisture left on the surface and cracks during the process of coal mining, transportation, storage and washing. This moisture can be removed by natural air drying. The other is internal moisture, which is absorbed and condensed in some tiny pores inside coal molecules. This kind of water cannot be removed by natural air drying, and it can only be dried and evaporated when the temperature reaches 100 or above. Internal moisture is related to the degree of metamorphism and weathering of coal. Generally speaking, the degree of metamorphism of coal is extremely high, and the internal moisture is less. After coal weathering, it will loosely absorb water, and the internal water will increase. In geological exploration, inherent moisture is often used as data to evaluate coal quality. The sum of internal moisture and external moisture is called total moisture, which is the total moisture content of coal directly produced by mine mining or agriculture, and is usually used as one of the basis for evaluating coal quality by both coal supply and demand sides. The commonly used moisture index is total moisture, which is expressed by "mt" and also commonly expressed by "Mar". Air-dried moisture is usually used, which can also be considered as inherent moisture (Mad).

Ash: Ash is the residue left after coal is completely burned. According to the causes, it can be divided into memory gray and external gray. The external ash comes from rock fragments and gangue in the roof and floor of coal seam, which has a great relationship with the rationality of coal mining methods. Most of the external ash can be removed by washing. Memory ash is an inorganic substance contained in the original coal-forming material itself, and it also includes mineral impurities carried by wind and water in the deposition process. Inherent ash is difficult to be removed by washing, and it is very difficult to select coal containing a lot of inherent ash. Commonly used indicators are air-dried base ash (Aad), dry base ash (ad) and partially received base ash (Aar). The ash content of coal has a great influence on the practical value of coal and is one of the main indexes to evaluate coal quality. If the ash content of metallurgical coal is increased by 65438 0%, the ironmaking furnace will consume 2% ~ 2.5% more coke on average, and the production efficiency of the ironmaking furnace will be reduced by about 2%. Ash also increases the transportation burden and transportation cost. Different countries have different requirements for coal ash index. Our country stipulates that the ash content of coking coal should not exceed 10%, and the index of thermal coal can be appropriately higher, as long as the calorific value meets the requirements. When the ash content is more than 40%, it is not coal.

Volatile matter: Volatile matter is the volatile matter discharged by coal under the condition of high temperature isolated from air, and its main components are hydrocarbons such as biogas, hydrogen and carbon dioxide. The volatile content is related to the metamorphic degree of coal. The higher the metamorphic degree, the less volatile. Volatiles can be used as various fuels with high calorific value, and can also be used to make dyes, plastics, explosives and other chemical products. Volatile is one of the main indexes to evaluate coal quality and classify coal types. Because volatile is a part of organic combustible in coal, in actual production, the percentage of volatile in organic combustible is usually used as an index. Commonly used are air-dried volatile matter (Vad), dry volatile matter (Vd), dry ashless volatile matter (Vdaf) and received volatile matter (Var), among which Vdaf is one of the important indexes of coal classification.

Coke residue: the solid matter left in the crucible after the volatile matter of coal is removed is coke residue. It consists of ash and fixed carbon, which is nonvolatile organic matter in coal. The content of fixed carbon is usually expressed by its percentage of organic combustible materials, and its content increases with the increase of metamorphic degree. The characteristics of coke slag formed by different coal types are different. Some cinders are powdery, and some cinders are fused and bonded into blocks with high strength. Therefore, according to the characteristics of coke residue, the caking property of coal can be preliminarily judged, which is of great significance to judge whether coal is coking.

Thickness of stratum corneum: The thickness of stratum corneum is measured by instruments in the laboratory according to the coking process. When the caking coal is crushed into fine particles and heated to a certain temperature under sealed conditions, the organic matter in the coal is decomposed by heating, softened into cuticle and finally formed massive coke. When the coal with good caking property is heated, the thickness of the stratum corneum formed is appropriate, and the formed coke is melted and bonded into blocks. Unbonded coal can't produce cuticle when heated, so it can't form coke and is in powder form. Generally speaking, the cuticle thickness of coal changes regularly with the increase of coal metamorphism. The cuticle thickness of coal with very low or high metamorphic degree is very small or equal to zero, that is, the cohesiveness is not good or there is no cohesiveness. The thickness of cuticle can reflect the caking property of coal, so it becomes one of the important indexes to evaluate coal quality and coal industry classification. Usually represented by y or B.

Calorific value: The calorific value of coal refers to the heat released when the coal per unit weight is completely burned. It is of great significance to evaluate the combustion value of coal. In the evaluation of coal quality, the low calorific value of coal is usually used to evaluate the combustion value of coal, that is, the actual heat that can be selected per kilogram of coal after burning in the crucible. The calorific value of coal is related to the content of combustible elements such as carbon and hydrogen in coal, so it is also related to the metamorphic degree of coal. Generally speaking, the higher the degree of deterioration, the greater the calorific value. However, during the transition from bituminous coal to anthracite, the storage of hydrogen is obviously reduced. Because the heat generated by hydrogen during combustion is about 4.2 times that of carbon, the calorific value of some bituminous coals is slightly higher than that of anthracite. In addition, the increase of moisture and ash will reduce the calorific value of coal. Different kinds of calorific value of coal are different, so the calorific value of coal is expressed in different grades.

(1) low calorific value coal, expressed as LQ8.50 ~ 12.50 MJ/kg.

(2) Medium and low calorific value coal, expressed as mlq12.51~17.00 mj/kg.

(3) medium calorific value coal, expressed as MQ17.01~ 21.00 mj/kg.

(4) medium and high calorific value coal, expressed as mhq21.01~ 24.00 mj/kg.

(5) high calorific value coal, expressed as hq24.0 1 ~ 27.00 mj/kg.

(6) Ultra-high calorific value coal, expressed by shq >; 27.00 mj/kg

Note:1cal15 (15℃ card) = 4. 1855j.

Sulfur and phosphorus: Coal usually contains sulfur and phosphorus. Sulfur is a harmful impurity in coal. When coal is burned, sulfur will become sulfur dioxide, which will corrode boilers and pipelines, pollute the atmosphere and increase the greenhouse effect. If there is too much sulfur in the air, acid rain will form. During coking, some sulfur will be transferred to coke, and ironmaking with coke with high sulfur content will reduce the quality of steel. When the sulfur content in steel exceeds a certain limit, it will make steel brittle and reduce its strength. The inorganic sulfur in coal is mainly pyrite sulfur, which is often filled in the cracks of coal in the form of veinlets or sandwiched in the coal seam in the form of nodules. This part of sulfur can be removed by mechanical washing. It is difficult to remove organic sulfur uniformly dispersed in coal. Sulfur content in coal is an extremely important index to evaluate coal quality. In actual production, the total sulfur content of absolutely dry coal samples is usually used to evaluate the quality of coal. China stipulates that all industrial coal must be washed first to reduce the sulfur content as much as possible; Coal with sulfur content greater than 3% cannot be mined. Commonly used indicators are air-dried total sulfur (St, ad), dry total sulfur (St, D) and received total sulfur (ST, ar).

Washability: As mentioned above, ash, sulfur and phosphorus in coal are harmful impurities for coal processing and utilization. In order to reduce harmful impurities in coal and improve the quality of coal, especially for coking, it is necessary to wash raw coal. For impurities such as gangue and pyrite with a diameter greater than 50 mm, it can be selected manually, and for pulverized coal with a particle size less than 1 mm, flotation can be used for coal preparation. The granularity and distribution of minerals in coal directly affect the difficulty of coal washing, that is, the washability of coal. Coal washability is one of the important indexes to evaluate coal quality, especially coking coal quality.

Ash composition and ash fusibility: Ash composition is a mineral component in coal ash, and ash fusibility refers to the deformation, softening and melting state of coal ash at different temperatures. They are also one of the important indicators that affect the use of coal.

In addition, the harmful and toxic elements in coal also have great influence on the quality and use of coal, such as arsenic, mercury and radioactive uranium. If the content exceeds the standard, it will have a great impact on human health.

According to the above coal quality indexes, combined with the metamorphic degree and use of coal, coal can be classified practically. The classification of coal in China is based on the degree of coalification of coal, and all coals in China are divided into three categories: lignite, bituminous coal and anthracite. According to the degree of coalification, the composition of coal and the characteristics of industrial utilization, lignite is divided into two small categories, and anthracite is divided into three small categories. Bituminous coal is complex, which can be divided into four grades according to volatile matter and five or six grades according to caking property. The main types are lignite, long flame coal, non-caking coal, weakly caking coal, 1/2 medium caking coal, gas coal, gas-fat coal, fat coal, 1/3 coking coal, coking coal, lean coal, lean coal and anthracite. Among them, lignite has the lowest metamorphic degree, while anthracite has the highest metamorphic degree. Long bituminous coal to gas coal is low metamorphic bituminous coal, fat coal to coking coal is medium metamorphic bituminous coal, and lean coal, lean coal and anthracite coal are high metamorphic coal.

Lignite is characterized by dull luster, undeveloped endogenous cracks, many shrinkage cracks, high humic acid content and low calorific value. It is a low calorific value fuel and a raw material for making chemical fertilizer.

Long-flame coal, non-caking coal, weak-caking coal and medium-caking coal have the common characteristics of high toughness, weak luster, few endogenous cracks, long combustion flame and no coking, and are the best coal for combustion boilers, chemical industry and oil recovery. In addition to the above properties and uses, gas coal also has the phenomena of expansion, melting and slagging, and sometimes gas is ejected. Gas coal has certain coking performance and can also be used as coking coal blending.

What fat coal and coking coal have in common is that they have glass luster, developed endogenous cracks and are fragile and easily broken. It has good expansion and melting adhesion, and the coke residue is shiny, so it is the best raw material for coking.

Lean coal has strong luster, slightly expands and melts, and is not easy to catch fire when burning, so it can be used as coking coal blending.

Lean coal has diamond luster, does not expand and melt, and is not easy to catch fire when burning. It is suitable for burning boilers and chemical coal.

Anthracite has a diamond-like luster, is dense and hard, has a large specific gravity, is not easy to catch fire when burning, is smokeless and almost flameless, and can be used as chemical coal and civil coal.

(B) the main uses of coal

As early as thousands of years ago, working people discovered that coal can be burned, which can be used for heating, cooking and ironmaking. After the invention of the steam engine, coal became the main fuel of machine power. Later, coal was used for coking, power generation, making calcium carbide, gas and so on. Now, coal is still the main energy source. Coal accounts for about 70% of China's disposable energy structure. Some experts predict that this energy structure will not change much in the near future. At present, the main uses of coal are power generation, coking, heating and civil combustion, but the comprehensive utilization of coal such as coal gasification, coal liquefaction and coal chemical industry is also developing rapidly.

Power coal: Power coal is the main use of coal, as a fuel-fired boiler for heating and power generation, and as the power of steam locomotives. Because it mainly burns thermal coal, any brand of coal can be used as fuel to obtain heat source.

Coking of coal: Coking of coal means coking with coal. It heats coal in a closed coking furnace isolated from the air to obtain three raw materials: coke, coal tar and coke oven gas. These three raw materials can be further processed to obtain a series of coal chemical products. About 78% coke, 4% tar and 18% coke oven gas can be obtained by high temperature coking. The main use of coke is ironmaking, followed by fertilizer industry. After further processing, coke can be made into synthetic ammonia and calcium carbide. Calcium carbide can also be made into plastics, synthetic fibers, synthetic rubber and synthetic chemical products. Coal tar is a by-product of coal coking, a black viscous liquid, and its main component is aromatic compounds. Widely used, it can be made into light oil, phenol oil, naphthalene oil, washing oil, anthracene oil, asphalt and so on. These products can also be made into benzene, pesticides, explosives, dyes, paints, dioxins, polyethylene stabilizers, synthetic materials and so on. Coke oven gas is a good gas fuel and valuable chemical raw material, which can be used as metallurgical industrial fuel and civil gas, as well as ammonia, crude benzene, hydrogen, methane, ethylene, hydrogen sulfide and various chemical products. If a coking plant can produce 15000 cubic meters of coke oven gas as chemical raw materials per hour, it can produce 55000 tons of urea or 70000 tons of ammonium nitrate, 16000 tons of methanol and 2500 tons of ethylene a year. Therefore, the comprehensive utilization of coke oven gas in coking plant is of great significance to the development of agriculture, metallurgical industry and chemical industry.

Coal gasification: Coal gasification is the process of transforming organic matter in coal into gases containing carbon monoxide, biogas, hydrogen and so on under the conditions of high temperature and oxygen. Gas is an excellent industrial and civil fuel. Using natural gas as fuel is more than twice as efficient as burning coal directly. Gas fuel also has a series of advantages such as complete combustion, convenient use and transportation. Therefore, gas has been widely used in metallurgical industry, machinery industry, chemical industry, building materials industry and urban civil fuel. Carbon monoxide and hydrogen in coal gas can be synthesized into methanol, aldehyde, ketone, acid, saturated hydrocarbon, olefin, aromatic hydrocarbon and synthetic ammonia. Therefore, gas is also an important raw material for organic chemical industry.

Coal gasification includes surface gasification and underground gasification. Ground gasification is to change coal into gas with a gas producer. Underground gasification is to directly burn and gasify the coal seam underground, and then transport the gas from underground to the ground for use.

There are many methods to produce gas from solid raw materials such as coal and coke on the ground, which can be roughly divided into two categories. One is the gasification of solid raw materials, which converts coal or coke into gas under the conditions of high temperature and gasification agent. According to the different types of solid raw materials used in gasification and the different states of solid raw materials in gasifier, gasification methods can be divided into fixed bed gasification and fluidized bed gasification. The other is dry distillation of solid raw materials, which is a method of pyrolyzing organic matter in coal into gas and a common method of producing city gas.

The fixed bed gasification method is that the gasified solids are basically fixed in the gas producer. The gasification process of producer gas is carried out in a fixed bed gas producer. Air and a small amount of steam are introduced from the bottom of the gas producer, and coal or coking coal is added from the top of the gas producer, so that gas and coal react violently at a high temperature above 700℃ ~ 800℃ to generate gas. Producer gas is used to heat steelmaking furnaces, glass kilns, coking furnaces, etc. It can also be mixed with water gas as feed gas for synthetic ammonia and methanol. Water gas is the product of the interaction between steam and industrial coking coal of hot anthracite. Water gas is the main feed gas for making synthetic ammonia.

The fluidized bed gasification method is called fluidized bed gasification method because the gasification agent is introduced from the bottom of the furnace at a high speed, which makes the pulverized coal in the gasifier in a floating state, much like the boiling of liquid. Boiling bed gasification is a method of directly and continuously gasifying coal particles smaller than10 mm.

Coal liquefaction: Coal liquefaction is the process of changing coal from solid to liquid. Coal liquefaction can be direct liquefaction or indirect liquefaction.

Direct liquefaction of coal can be achieved by low-temperature dry distillation and hydro-liquefaction. Hydroliquefaction of coal is to mix coal, catalyst and heavy oil together, and at the high temperature of 380℃ ~ 550℃ and high pressure hydrogen of 200 ~ 700 atmospheres, almost all the organic matter in coal is converted into liquid and gas products, and further processed to obtain liquid fuels such as gasoline and diesel. Low-temperature dry distillation is to turn coal into tar products through an internal heating generator, and further process them into liquid fuels and chemical products.

Indirect liquefaction of coal is the process of gasification and further processing into liquid fuel.

Coal chemical industry: Coal chemical industry is a method of making coal into chemical products. There are many ways to make chemical products from coal. Coal is usually gasified or liquefied first and then further processed into chemical products. It is also possible to process coal into calcium carbide first and then convert it into chemical products.

Comprehensive utilization of coal: There are many kinds of beneficial elements in coal. Germanium, gallium, uranium, vanadium and other important rare dispersed elements and radioactive elements can be extracted from coal ash, which is the raw material of national defense industry. Coalbed methane with great development value is also associated with coal. Coal ash can also be used to make cement and improve soil. Comprehensive utilization of fly ash is an important aspect of comprehensive utilization of coal.

Utilization of germanium and gallium in coal: germanium is one of the important raw materials in semiconductor and electronic industries. Germanium rarely occurs as a single mineral in the earth's crust, but mainly exists as an associated component in lead-zinc mines and coal seams. The extraction process of germanium is simple, and it is mainly extracted from coal ash and smoke. The grade of germanium in coal is generally low, but it is widely distributed, which is the main metallogenic type of germanium deposits. The germanium content in coal can be recovered when it reaches 20 grams per ton of coal. The coal seams of Yili and Qinghe coal mines in Xinjiang contain germanium and gallium.

Utilization of uranium in coal: uranium mainly exists in coal in the form of uranium-containing organic compounds, which is one of the important industrial types of uranium deposits. Generally, the industrial grade of associated uranium in coal is required to be 0.02%. The enrichment of uranium in coal is caused by the strong adsorption of humic acid after the aqueous solution containing uranium is injected into peat swamp during the peat accumulation stage. Second, the leaching of groundwater brings uranium to the coal seam. The enrichment of uranium in coal is mainly due to humic acid adsorbing uranium ions into metal-organic complexes, or as a reducing agent, transforming uranium ions into insoluble state and fixing them in organic components. Uranium usually occurs in sandstone on the roof and floor of coal seam and can be enriched locally. Uranium-rich areas often appear in Jurassic coal-bearing strata in Xinjiang, and the uranium content in coal-bearing strata in southern Yili and Turpan has reached industrial grade. At present, the in-situ leaching method has achieved good results in mining low-grade uranium in coal measures strata.

Utilization of vanadium in coal: Vanadium is mainly used for refining high-quality alloy in iron and steel industry. Vanadium is widely distributed in nature and often associated with other elements to form vanadium-bearing deposits. The enrichment of vanadium in coal measures strata is closely related to the organic matter caused by marine plankton and benthos, so the vanadium content in sapropelic coal formed by algae aggregation in shallow sea is high. Vanadium mainly exists in coal seams in the form of organometallic complexes. Generally speaking, the higher the organic matter content, the richer the vanadium content. Vanadium-bearing sandstone sometimes exists in coal measures strata, and vanadium and uranium often coexist to form vanadium-potassium uranium deposits.

In recent years, the development and utilization of coalbed methane at home and abroad have developed rapidly. It can be said that a new industry is emerging and will occupy a very important position in the energy structure. I only mention it here, and I will introduce the situation of coal in detail when I finish.

(C) coal mining should pay attention to the protection of resources and the environment

Coal is a non-renewable resource, and it will be gone when it is used up, so we should cherish it very much. Coal mining should be planned rationally and arranged as a whole; Choose advanced and reasonable coal mining methods to improve the recovery rate of coal resources and make full use of thin coal seams; Under the guidance of Scientific Outlook on Development, we should establish a circular economy industrial chain, make full use of various utilization efficiencies of coal resources, and improve the utilization efficiency of coal.

The development and utilization of coal will have a certain impact on the environment, so special attention should be paid to environmental protection when developing and utilizing coal resources. In coal mining, due to underground hollowing and collapse, geological disasters such as cracks, collapse pits, rock slides and landslides often form on the ground, which do harm to forests, grasslands and farmland, and even cause serious damage; Gas, carbon dioxide and carbon monoxide emitted by coal mining will pollute the atmosphere and increase the greenhouse effect; The discharged hydrogen sulfide gas will also form acid rain, which will cause serious harm to people, organisms and crops. The discharged wastewater will pollute the environment and groundwater; The discharged dust and gangue will pollute the atmosphere and surrounding environment. Smoke and dust produced by coking, industrial boilers and civil boilers will pollute the atmosphere; Coal liquefaction and coal chemical industry will also form a lot of waste gas and wastewater, polluting the environment. However, in the above-mentioned coal mining and utilization process, there are various adverse effects and harms to the environment. As long as effective measures are taken, the degree of influence can be greatly reduced, and even the harm can be completely avoided. The key is to firmly establish environmental awareness when mining and utilizing coal mines, to protect the environment throughout the whole process of mining and utilizing, and to take practical and effective measures to prevent the impact and harm to the environment, so as to make the best use of everything, make the best use of everything, have a good environment and live in harmony with nature.