Coal preparation and coal preparation process
Raw coal is mixed with various mineral impurities during the generation process, and is inevitably mixed with rocks and rocks from the roof and floor during the mining and transportation process. Other impurities (wood, metal and cement components, etc.). With the improvement of coal mining mechanization and changes in geological conditions, the quality of raw coal will become worse and worse, which is reflected in the increase in gangue mixed into raw coal, the increase in ash content, the increase in the content of final coal and pulverized coal, and the increase in moisture. In order to reduce impurities in raw coal and at the same time divide coal into various products according to quality and specifications, coal must be mechanically processed to meet the requirements of different users for coal quality, effectively and rationally utilize coal resources, and reduce the impact of coal burning. Atmospheric pollution ensures the sustainable development of the national economy. Coal preparation plant is an important department of the coal industry. 1. The main purpose of coal preparation
(1) Remove impurities in raw coal, reduce ash and sulfur content, improve coal quality, and meet the needs of users;
(2) Transform coal into Divide into products of different quality and specifications to meet user needs, so as to effectively and rationally utilize coal and save 10% to 15% of coal;
(3) After coal is washed, the gangue can be discarded on site, and Reduce ineffective transportation by 10% to 20% and create conditions for comprehensive utilization of coal gangue;
(4) Coal washing can remove most of the ash and 50% to 70% of pyrite sulfur, reducing Coal burning pollutes the atmosphere. It is the prerequisite for clean coal technology.
2. Requirements for coal quality by major coal users in my country
(1) Coal used in power plants
Types of coal burned in thermal power plants with different equipment And quality specifications are also different. Layered boilers use lump coal, and newly built power plants use pulverized coal for injection. Generally, powdered coal with a particle size less than 25mm or 13mm is used. There are also some burning coal water slurry. Generally speaking, coal slurry (anthracite, bituminous coal, lignite) as long as the volatile content is greater than 6.5% can be used as coal for power generation.
The coal quality requirements for large-scale power plants burning bituminous coal can be divided into two categories: one requires the use of "medium and high volatile coal", with a volatile content of 28% to 35%; This type uses "low-volatile lean coal", with a volatile content of 12% to 18%. The low-level calorific value is required to be above 21MJ/kg (5000kcal/kg), and some require even higher, 23 MJ/kg (5500kcal/kg). kcal/kg) or more than 25.3 MJ/kg (6000 kcal/kg)
Power plants using lignite usually require a low-level calorific value of more than 12 MJ/kg (2870 kcal/kg). Power plants using anthracite coal. The low calorific value is usually required to be above 21 MJ/kg (5000 kcal/kg)
The ash content of coal for power generation generally does not exceed 25%. From the perspective of environmental protection, selected thermal coal should be used. , to reduce the emission of slag, soot and sulfur dioxide. The total moisture of bituminous coal should generally not be higher than 12%, and the sulfur content of lignite should generally not exceed 1%. Coal-fired power plants with more than 1%. The state requires the use of desulfurization devices to reduce sulfur dioxide emissions. The melting temperature of ash should not be lower than 1150°C, preferably higher than 1350°C. The Hastelloy grindability index of coal used in power plants in my country is above 50. The average calorific value is 21.0 MJ/kg, the ash content is about 25%, and the sulfur content is about 1.0% (2) Coal for metallurgical coke
The ash content of clean coal used to produce metallurgical coke must be less than 12.5%. , the sulfur content is generally less than 1.5%. Information provided by the metallurgical department shows that for every 1% reduction in clean coal ash content, the coke ash content can be reduced by 1.35%; and if the coke ash content is reduced by 1%, the ironmaking coke ratio can be reduced by 2%. The coefficient can be increased by 3%, which can also reduce the consumption of limestone and improve the quality of pig iron. Therefore, it is required to reduce the ash content of clean coal as much as possible to improve the quality of coke and increase economic benefits. Clean coal for coking has very high requirements on sulfur content. Strictly, it makes steel brittle, and usually every 0.1% increase in sulfur content is equivalent to a 1% increase in ash content. Moisture has a negative impact on the life of the coke oven, and prolongs the coking time and consumes heat. In cold areas in winter, moisture freezes clean coal, which is harmful to the coke oven. Transportation will have an impact, so the moisture should be reduced as much as possible.
(3) Coal for industrial boilers
Industrial boilers are mostly bed combustion, including chain furnaces, reciprocating furnaces and vibration furnaces. There are fewer pulverized furnaces.
The layer bed combustion furnace should use 6-15mm lump coal, of which less than 3mm should not exceed 30%. The volatile content of bituminous coal is greater than 20%, the total moisture does not exceed 10%, the ash content does not exceed 30%, and the total sulfur does not exceed 1.0%. A chain furnace with a large evaporation capacity requires a high low-level calorific value of coal, which is 21 to 23 MJ/kg (5000-5500 kcal/kg). A furnace with a small evaporation capacity requires a low-level calorific value of 18.8 MJ/kg (4500 kcal/kg), that is, Can.
General industrial boilers can use anthracite, bituminous coal, lean coal and lignite. (4) Coal for synthetic ammonia gas production
Synthetic ammonia gas production is suitable for two types of coal: bituminous coal and anthracite coal, with particle sizes ranging from 13 to 100 mm, such as medium lumps, large lumps, mixed medium lumps and small lumps. It has requirements for ash, moisture, sulfur, calorific value, volatile matter, mechanical strength, thermal stability, chemical activity, adhesion, etc. The ash content of lump coal should not be higher than 24%, preferably lower than 18%; the sulfur content should not be higher than 2.0%, preferably lower than 1%; the moisture content is generally lower than 12%; the ash meltability should not be lower than 1150°C; The mechanical strength and thermal stability of lump coal should be greater than 60%; the low-level calorific value should be greater than 21 MJ/kg, and the maximum thickness of the colloid layer should be less than 12mm.
(5) Coal for steam locomotives
Steam locomotives generally require gas coal, long-flame coal or coal with a particle size of 13 to 50 mm due to their small furnaces, short chimneys and large grate pores. Weakly sticky coal has an ash content of less than 25%, a sulfur content of less than 2.5%, a volatile content of about 16%, a calorific value of more than 25.10MJ/kg, and an ash melting temperature of more than 1200°C.
(6) Coal for blast furnace injection
The use of blast furnace injection can save the amount of coke, not only protect the scarce coking coal resources, but also have good economic benefits. 1t blast furnace injection Coal blowing can replace 0.75~0.8t coke. Its usage continues to grow. In the past, anthracite pulverized coal has been used. In recent years, lean coal with lower volatile content and even gas coal have also been used. Generally, a mixture of anthracite and bituminous coal is used for injection coal, with a ratio of about 7:3 or 6. : 4.
Generally, the ash content is required to be lower than 12%, and the lower the better; the sulfur content is required to be lower than 1%, preferably below 0.5%; the total moisture content is lower, the better, and generally should be lower than 10%; the phosphorus content should be less than 0.02%; the particle size should be less than 13mm (or 25mm), the grindability of the coal should be good, the Hastelloy grindability index should generally be greater than 45, and the fixed carbon should be greater than 75%. The smaller the SiO2/CaO ratio in ash, the better.
(7) Coal for liquefaction
Coal liquefaction is divided into direct liquefaction and indirect liquefaction. The two liquefaction methods have different coal quality requirements. 1. Basic requirements for coal quality for direct liquefaction
(1) The ash content in coal should be low, generally less than 5%. (2) The grindability of coal should be better.
(3) The higher the hydrogen content in coal, the better, and the lower the oxygen content, the better. (4) The lower the content of heteroatoms such as sulfur and nitrogen in coal, the better. (5) The composition of coal rock is also a major indicator of liquefaction.
Indirect liquefaction of coal is to gasify coal to generate H2/CO raw gas, then add a catalyst under a certain pressure and temperature to synthesize liquid oil, so the requirements for coal quality are relatively low.
2. Requirements for coal quality for indirect liquefaction (1) The ash content of coal must be less than 15%.
(2) The grindability of coal should be good and the moisture content should be low.
(3) For the coal-water slurry gas production process, the coal slurrying performance is required to be better.
(4) Ash fusibility requirements of coal. Fixed bed gasification requires the ash fusion softening temperature of coal to be as high as possible, generally not less than 1250°C; fluidized bed gasification requires less than 1300°C.
(8) Coal for building materials
Coal for building materials is mainly used for cement production, brick making, glass and ceramic production. Cement rotary kilns generally require bituminous coal with slightly higher volatile content, a calorific value of 21 MJ/kg (5000 kcal/kg) or more, a sulfur content of no more than 1.5%, a particle size of -13mm, and a Hastelloy grindability index of The higher the better. The cement vertical kiln requires anthracite with a particle size between 13 and 100 mm, an ash content of less than 25%, a low calorific value of 23.0 MJ/kg, a fixed carbon of greater than 60%, and better thermal stability.
Glass and ceramics require the use of low-sulfur, low-ash bituminous coal.
(9) Civilian coal
Generally, anthracite lump coal is used, or briquettes and briquettes formed from anthracite coal powder. From an environmental and safety perspective, its sulfur content should be as low as possible. 3. Coal Preparation Methods
There are many types of coal preparation methods, which can be broadly divided into two categories: dry coal preparation and wet coal preparation. The coal preparation process is carried out in the air and is called dry coal preparation. The coal preparation process is carried out in water, heavy liquid or suspension, which is called wet coal preparation.
Coal preparation methods can also be divided into gravity coal preparation, floating coal preparation and special coal preparation.
Gravity coal separation is mainly a method of separating coal and gangue based on the density difference between coal and gangue. The density of coal is usually between 1.2 and 1.8g/cm3, while the density of gangue is above 1.8g/cm3. Coal with different densities and gangue are separated by gravity in the coal preparation machine. Gravity coal preparation can be divided into jigs, heavy media, chute, chute and shaker.
Flotation coal preparation, referred to as flotation, is a coal preparation method that separates fine-grained (less than 0.5mm) coal based on the difference in surface wettability of coal and gangue.
Special coal preparation mainly uses the differences in electrical conductivity, magnetic permeability, friction factors, and radiation penetration capabilities of coal and gangue to separate coal and gangue. Including electrostatic separation, magnetic separation, friction separation, radioactive isotopic separation and X-ray separation, etc.
In addition, there is also manual selection, that is, manual sorting of gangue, which is manually sorted based on the differences in color, luster and appearance of coal lumps and gangue. For lump coal with a large difference in hardness between coal and gangue, a drum crusher can be used for selective crushing to separate coal and gangue.
The most widely used coal preparation method in my country's coal preparation plants is jigging, followed by heavy medium separation and flotation, and other methods are rarely used.
The main product of coal preparation is clean coal, and by-products include medium coal, mixed coal, coal slime, etc. The gangue and coal tailings after selection are wastes. Since they contain some combustible materials such as gangue coal, they can also be used as raw materials for making bricks and burning cement for comprehensive utilization.
Coal preparation plant is a processing plant that sorts coal and produces products of different qualities and specifications. According to the different purposes of using clean coal, coal preparation plants can be divided into coking coal preparation plants and thermal coal preparation plants. The process of the coking coal preparation plant is relatively complex, and the clean coal produced has low ash content and high quality, and is mainly supplied to the coking plant for the production of coke. The technological process of thermal coal preparation plants is generally relatively simple. The clean coal produced is mainly used as power fuel. Most thermal coal preparation plants only select lump coal, and do not select fine coal and pulverized coal. 4. Types of coal preparation plants
Coal preparation plants are processing plants that sort coal and produce products of different qualities and specifications. According to the location of the coal preparation plant and its relationship with the coal mine, the coal preparation plant can be divided into 5 types:
(1) Mine coal preparation plant
The mine coal preparation plant is the site of the plant A coal preparation plant located in a coal mine industrial site that only selects crude coal or raw coal produced by the mine. The raw coal mentioned here refers to coal produced in coal mines without any processing; raw coal refers to the coal after selecting gangue of specified particle size (including pyrite and other impurities) from the raw coal.
(2) Qun Mine Coal Preparation Plant
The Qun Mine Coal Preparation Plant is located in the industrial site of a certain coal mine and can simultaneously select the raw materials produced by the mine and nearby coal mines ( Formerly) coal preparation plant.
(3) Coal Preparation Plant in Mining Area
Coal Preparation Plant in Mining Area refers to a coal preparation plant located on a separate industrial site within the scope of coal mining area to select foreign coal.
(4) Central Coal Preparation Plant
The central coal preparation plant refers to a coal preparation plant located on an independent industrial site outside the mining area that selects imported coal.
(5) User coal preparation plant
User coal preparation plant refers to a coal preparation plant located on the industrial site of the user (such as a coking plant, etc.). Most of the existing coal preparation plants in my country are mine coal preparation plants.
The production process of a modern coal preparation plant is a continuous mechanical processing process composed of many operations.