Mineral processing and processing technology and comprehensive development and utilization of coal

(A) coal processing and utilization through a series of processing technology, improve product quality, to produce varieties adapted to the different needs of the use of coal sectors, coal resources to be efficient and clean to create conditions.
1. Coal preparation
Includes screening and coal preparation. The raw coal is first sieved, graded according to particle size, and large blocks of vermiculite and debris are excluded. Then, coal is used to screen coal with different properties such as density, sedimentation speed and surface tension of coal, and low-ash clean coal and other products of various specifications are sorted. According to the different sorting medium, the coal is divided into wet coal preparation and dry coal preparation. The former is the main one. The operations included in the operation include crushing, screening, jigging, heavy selection, flotation, special selection, slime water treatment, dewatering, dust removal, and drying. These process steps work together to form a variety of different processes.
2. Coal preparation products have different requirements for coal preparation products according to different uses.
(1) metallurgical coal coking coal grades are used in gas coal, fat coal, coking coal, lean coal, 1/3 coking, 1/2-caking coal, gas coal, lean coal and the like. The main indicators of the product are ash content less than 5.5% to 12.5%, sulfur content less than 0.5% to 2.5%, and moisture less than 12%. Synthetic ammonia coal, using anthracite lump coal as raw material, the main index is less than 10% volatile matter, fixed carbon 56% ~ 75% and more than 75%, sulfur content less than 0.5% ~ 2.0%, ash melting point greater than 1250 ~ 1350 °C. Generally, the medium-sized fertilizer plant supplies anthracite lump coal of more than 25mm grade, and the small fertilizer plant supplies 13-25mm of smokeless lump coal.
(2) Coal for power generation requires coal with a particle size of less than 13 mm. The coal type is not limited, and bituminous coal, anthracite, and lignite may be used. The main indicators are volatiles greater than 6.5, calorific value greater than 11.7 ~ 20.9MJ / kg, sulfur less than 1% ~ 3%, ash melting point greater than 1350 ° C and so on.
(3) The coal used for steam locomotives is long-burn coal, weak-viscous coal and non-coking coal. The middle block with a particle size of 25 to 50 mm, the mixed medium block of 13 to 50 mm, and the 6 to 50 mm mixed block including the granular coal have a calorific value of more than 21 MJ/kg and an ash melting point of more than 1200 °C.
(4) Civil coal should not burn loose coal and popularize burning coal.
3. Briquette
The pulverized coal is the main body, and the binder is added, and the pressure-formed block fuel has the dual functions of environmental protection and energy saving. According to the preparation process, it is divided into cold pressing and hot pressing. The former is mainly used, and only the wear resistance of mechanical equipment is required. In terms of binders, organic and inorganic types, organic binders, hydrophobic binders, such as tar pitch , petroleum asphalt, etc., and hydrophilic binders, such as starch, sulfite pulp waste, brewing waste Liquid and the like; inorganic binders include water-soluble water glass and water-insoluble lime, cement and clay . Industrial briquette requires a certain amount of heat, less ash and sulfur, higher ash melting point, less environmental pollution when burning. In addition, the coal is required to be smoothed, crack-free, and has high mechanical strength. The compressive strength of the briquette should be greater than 600-800N. The ratio of the amount of briquette greater than 13 mm after three times of free fall from 1.85 m is called the drop strength of the briquette. Up to 95%. At present, China's civil coal accounts for 80% of civilian coal in 1995 and 100% in 2000. Industrial briquette developed late, reaching only about 40% in 2000. [next]
4. Coal water slurry
The coal-water mixture prepared by grinding low-ash clean coal into fine coal powder, 70% coal, 30% water, and a small amount of chemical additives. Easy to store and transport, can be atomized and burned, high in combustion efficiency, and clean fuel for low pollution. The quality of coal water slurry depends on three factors: coal type, grinding grade combination and additives. The preparation process is to achieve the optimal particle size distribution by grinding the fine-grained coal material, so that the coal can have the highest stacking efficiency between the large and small particles. The commonly used methods are wet grinding, high concentration grinding and medium Grinding concentration. The chemical additives used are anionic surfactants, nonionic surfactants, and polymer compounds and inorganic salts. At present, two additive factories in Anhui Huainan and Beijing Yanqing have been built, with an annual production of 3000t. The application benefit of coal water slurry is significant. The first is oil generation benefit. 1.8~2.1t coal water slurry can replace 1t fuel oil. Secondly, it is energy-saving, its combustion efficiency is 5% to 10% higher than that of pulverized coal, and SO2 and NOX emissions are reduced by 20% to 30%, which has environmental benefits. In addition, the coal slurry and flotation tail coal can be used to produce medium-high ash, medium-low concentration coal slurry water coal slurry for heating and burning in the waste-stone power boiler, turning waste into treasure.
(2) Coal conversion technology
Gasification
Under certain temperature and pressure conditions, the coal is thermally processed with a gasifying agent to convert the coal into a combustible gas. At present, there are four types of industrialized gasification: fixed bed gasification (including atmospheric pressure, pressurization, solid-state ash discharge and liquid ash discharge), fluidized bed gasification (normal pressure and pressure), and entrained flow gasification ( Atmospheric pressure and pressure) and molten bed gasification (normal pressure). Classification according to different gasification media, including the following:
(1) Air gas The gas produced by a fixed-bed coal gasifier with air as the gasification medium has a low calorific value. Water gas: A technique in which water vapor is added to an air blast to produce a mixed producer gas to supply a raw material gas for producing ammonia and methanol.
(2) Coal hydrogenation In order to increase the methane content in the gas, hydrogen gas is used as a gasification medium under pressurized conditions, which strengthens the gasification furnace production capacity and simplifies the gas purification step.
2. Liquefaction
Coal conversion technology for producing clean liquid fuels and chemical raw materials from solid coal. Can be divided into direct liquefaction, indirect liquefaction two categories. Several methods have been developed for direct liquefaction. The well-known processes include solvent refined oil method (SRC-1, SRC-2), hydrogen supply solvent method (EOS), and hydrogen coal method. Indirect liquefaction includes the Mobil process, which converts methanol to high-quality gasoline, and the one- and two-stage process technologies for synthesizing gasoline from syngas. Liquefaction technology is still in the research and experimental stage in China. [next]
3. Coking
Using coal as raw material, coke is produced by high-temperature dry distillation, coal gas and coal tar are obtained at the same time, and coal conversion technology of other chemical products is recovered. The main products of coking coke for blast furnace ironmaking, can also be used for casting non-ferrous metal smelting, preparation of calcium carbide, carbon disulfide, elemental phosphorus. The second product is coal tar, which is a raw material for the pharmaceutical, dye and explosive industries after separation and purification by the industrial sector. Coke oven gas and chemical products such as ammonia, refined benzene, sulfur and thiocyanate are products in the gas purification process. The purified gas is a medium heat value gas with a calorific value of about 17500 MJ/m3, and the coking gas can be produced per ton of coal. 300 to 400 m3, which is a gaseous fuel for the steel industry. It can also produce hydrogen and methane after separation.
(3) Clean coal technology
It refers to a variety of coal technologies that can reduce sulfur dioxide (SO2), nitrogen oxides (NOX) and dust pollution than traditional coal-fired processes. It also refers to advanced coal-fired technologies that are cleaner and more efficient in coal-fired power plants. It includes four aspects, namely pre-combustion, combustion, post-combustion and conversion technology.
1. Clean technology before combustion
Mainly refers to the selection of coal. It is an important measure to improve coal quality, rational use of coal resources, reduce inefficient transportation, and reduce pollution. Physical coal preparation separates objects that are different from the physical properties of coal by the difference in density and surface properties, such as vermiculite and iron sulfide. Usually 30% to 50% of sulfur compounds and 60% of ash can be removed, but organic sulfur and nitride cannot be separated. Chemical coal preparation removes organic sulfur from coal by chemical methods, and generally obtains low-ash, low-sulfur clean coal by molten alkali leaching. Biological coal preparation is a technology that removes sulfur from coal by bacteria, enzymes and microorganisms, and can remove 90% to 100% of sulfur. It is still in the experimental stage.
2. Clean technology in combustion
Fluidized bed boilers with reduced combustion temperatures and slagging boilers with increased combustion temperatures are used to reduce SO2 and NOx emissions or increase heat exchange rates. In a fluidized bed boiler, pulverized coal and lime powder are suspended together in a gas stream to form a bed, and sulfur and lime released during combustion are chemically reacted or adsorbed to form sulfur-containing lime powder as a dry waste. The slag-type boiler is produced by a swirling burner to burn coal in a combustion chamber outside the boiler, and then introduced into a boiler for heat exchange to prevent ash from accumulating in the boiler pipe, thereby increasing the heat exchange rate.
3. Clean technology after combustion
The focus is on the removal of SO2 and NOX produced after combustion. The use of selective catalyst nitrogen removal technology (SCR) to remove NOx from flue gas can reduce nitrogen emissions by 50% to 80%. Another technique, known as natural gas reburning, injects a small amount of natural gas over the combustion zone, creating an anoxic zone that prevents it from forming NOx. The limestone is sprayed into the center of the flue pipe, and the sulfur-containing particles are generated by the linear jet adsorption method, and collected at the downwind port to remove 50% to 70% of the SO2. [next]
4. Conversion clean technology is the gasification, liquefaction and coking of coal.
(iv) Comprehensive utilization of coal 1. Coalbed methane
It is a natural gas mainly composed of methane in the coal seam and surrounding rock in the state of adsorption and free state. On the one hand, it is a serious threat to the safety of coal mines when it is poured into the mine. At the same time, it is discharged into the atmosphere and becomes a strong greenhouse gas, which can destroy the ozone layer. However, coalbed methane is a high-quality, high-efficiency, clean energy source that emits no sulphur dioxide gas and soot when burned. According to the calorific value, 1000m3 methane can be equivalent to 1t standard coal. Due to the high thermal efficiency of the former, the actual 250m ³ methane can replace 1t standard coal. China's coalbed methane resources are abundant, and the amount of gas emitted by coal mining is only 6 billion m ³ per year.
2. Coal gangue
The output of coal gangue accounts for about 20% of the original coal, which not only occupies the land, but also seriously pollutes the environment. However, coal gangue can be used for the benefit of pollution, in which the calorific value is higher than 6MJ/kg for boiling furnace fuel; the low calorific value can be used to build roads or produce building materials; the higher Al2O3 can produce polymerized aluminum and chlorine. Aluminum; high sulfur-containing recoverable sulfide; low carbon content can be used for backfilling or covering soil in underground mining areas.
3. Associated minerals including kaolin , refractory clay , bentonite , diatomaceous earth , graphite , pyrite, etc., can be comprehensively developed and utilized.
Humic acid
The extraction of humic acid from low rank coal can be widely used in agriculture, animal husbandry and many industrial sectors. In addition, montan wax can be extracted from lignite, and coal can be used as a raw material to produce non-fuel-utilized industrial products.

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