Ball mill

Coal-water slurry is usually a mixture of 65%-70% coal with different particle size distribution, about 29%-34% water and about 1% chemical additives. It is a mixture of coal through multiple rigorous processes, sifting out impurities such as incombustible components, retaining only the carbon essence, making it as fluid as oil, with a calorific value equivalent to half of oil, and is called a liquid coal product

Power generation field: It can be used for power station boiler combustion, replacing traditional coal or fuel oil. Compared with direct coal burning, coal-water slurry has a high combustion efficiency of 95%-98%, which can effectively improve power generation efficiency, and the emissions of smoke, SO₂ and NOₓ are lower than those of coal burning, which can greatly reduce pollution to the environment and help achieve energy conservation and emission reduction in power stations.

Industrial boiler field: Many industrial production processes require a lot of steam and heat. For example, industrial boilers in the papermaking, textile, chemical and other industries use water-coal slurry as fuel, which can achieve efficient combustion and thermal efficiency of more than 83%, which is about 15% higher than traditional coal-fired boilers. It can also reduce the labor intensity of operators and improve the working environment.

Industrial kiln field: Water-coal slurry is also widely used in industrial kilns such as ceramics, glass, and refractory materials. Taking ceramic kilns as an example, water-coal slurry can accurately control the combustion temperature and atmosphere, which is conducive to improving the quality and yield of ceramic products, while reducing pollutant emissions and meeting environmental protection requirements.

Coal chemical industry field: As a gasification raw material, water-coal slurry is widely used in gasification technologies such as Texaco, and can produce synthesis gas for the production of chemical products such as synthetic ammonia and methanol. Water-coal slurry gasification technology has the characteristics of simple gasification furnace structure, wide adaptability to coal types, easy and safe feeding, and large single furnace production capacity.

Central heating field: It plays a role in centralized clean heating in large towns and centralized heat source supply in industrial parks. For example, the new water-coal slurry circulating fluidized high-efficiency and clean combustion technology uses water-coal slurry as fuel and can achieve low-temperature, low-nitrogen combustion by optimizing fluidizing wind speed and other measures. The comprehensive thermal efficiency of the boiler system reaches more than 90%, and the original emission indicators of pollutants such as sulfur dioxide and nitrogen oxides can reach ultra-low emission standards.

1) Precise particle size control ensures combustion efficiency
Particle size is a key indicator for measuring the quality of water-coal slurry and directly affects its combustion performance. The water-coal slurry ball mill performs well in particle size control and can accurately grind coal into extremely fine particles with uniform particle size distribution. Usually, the particle size of coal powder in water-coal slurry needs to be controlled within a certain range. With 74μm as the boundary, the proportion of particles smaller than this size should reach 70% - 80%. This particle size range can ensure that the water-coal slurry is fully in contact with oxygen during the combustion process and achieve efficient combustion.
The water-coal slurry ball mill can accurately control the particle size in a variety of ways. For example, grinding time is one of the important control parameters. Studies have shown that under the same other conditions, the particle size of coal powder will gradually decrease if the grinding time is appropriately extended. Taking a certain model of water-coal slurry ball mill as an example, when the grinding time is extended from 30 minutes to 60 minutes, the proportion of particles smaller than 74μm increases from 60% to 75%.
The steel ball ratio also plays a key role in particle size control. Steel balls of different diameters play different roles in the grinding process. Large-diameter steel balls are mainly used to crush larger coal blocks, while small-diameter steel balls are used to finely grind coal powder. The grinding effect can be optimized by reasonably adjusting the diameter and quantity ratio of the steel balls. Generally speaking, when the ratio of large, medium and small steel balls is 4:3:3, a more ideal particle size distribution can be obtained.
Accurate particle size control enables water-coal slurry to meet the strict requirements of different combustion equipment. For example, in industrial boilers, water-coal slurry with appropriate particle size can achieve stable and efficient combustion, and the combustion efficiency can reach more than 95%; in gas turbines, the requirements for water-coal slurry particle size are more stringent, and accurate particle size control can ensure that water-coal slurry is fully burned under high temperature and high pressure environment, thereby improving energy utilization efficiency.

2) Stable grinding quality, assisting process control
The operating stability of the water-coal slurry ball mill is an important basis for ensuring its grinding quality. During operation, the mechanical structure design and advanced control system of the ball mill enable it to maintain a relatively stable operating state, with less interference from external factors. For example, the ball mill uses high-precision bearings and advanced transmission systems, which can effectively reduce vibration and noise and ensure the stable operation of the equipment.
The stable operation state enables the water-coal slurry ball mill to continuously produce products of uniform quality. During the long-term continuous production process, the quality indicators of the water-coal slurry fluctuate very little. Taking concentration as an example, its fluctuation range can be controlled within ±1%; taking viscosity as an example, the fluctuation range can be controlled within ±5%. This high-quality stability is crucial for subsequent combustion applications and process control.
During the combustion process, the water-coal slurry with uniform quality can ensure the stability and continuity of combustion, and avoid problems such as incomplete combustion and unstable flame caused by fluctuations in the quality of the water-coal slurry. In chemical production, stable water-coal slurry quality can ensure the consistency and controllability of chemical reactions, improve product quality and production efficiency.

3)Strong adaptability to coal types, broadening the source of raw materials
The water-coal slurry ball mill has a wide range of adaptability to different types of coal, including bituminous coal, anthracite and lignite. Different types of coal have different physical and chemical properties. For example, bituminous coal has higher volatile matter and lower ash content, anthracite has higher fixed carbon content and lower volatile matter, and lignite has higher moisture content and lower calorific value.
The water-coal slurry ball mill can achieve efficient grinding by adjusting process parameters and grinding media according to the characteristics of different types of coal. For bituminous coal with higher volatile matter, the grinding time and the filling rate of steel balls can be appropriately reduced to avoid the loss of volatile matter of coal powder due to excessive grinding; for anthracite with higher hardness, the grinding time and the diameter of steel balls can be increased to improve the grinding efficiency.
Taking a water-coal slurry production plant as an example, the plant used a water-coal slurry ball mill to grind bituminous coal, anthracite and lignite respectively. The results show that after appropriately adjusting the process parameters, the three types of coal can prepare water-coal slurries that meet the quality requirements. The concentration of water-coal slurry prepared from bituminous coal can reach 65% - 70%, the concentration of water-coal slurry prepared from anthracite can reach 68% - 72%, and the concentration of water-coal slurry prepared from lignite can reach 55% - 60%.
The strong adaptability of coal types has greatly broadened the source of raw materials for water-coal slurry. Enterprises can flexibly choose different types of coal to prepare water-coal slurry according to local coal resources and market prices, reduce production costs and improve economic benefits. At the same time, this will also help alleviate the problem of uneven regional distribution of coal resources and promote the widespread application of water-coal slurry technology.

1) Leakage of the inlet chute and drum feeder:
The inlet chute of the coal mill is severely worn under the long-term scouring of coal milling water, raw coal and additives, resulting in leakage. In addition, the sealing design of the drum feeder is unreasonable, and a single-layer packing seal is used, resulting in frequent leakage and slurry running. These problems seriously affect the operation efficiency of the coal mill and the quality of coal slurry.

2) Broken and leaking problem of cylinder bolts: During the operation of the coal mill, the steel bars in the cylinder constantly collide and fall, exerting a large impact force on the cylinder bolts. After long-term operation, the bolts loosen and the seal is not tight, resulting in leakage. Aging and corrosion of the rubber lining are also one of the reasons for leakage.

3) Defects of drum screen and coarse particle drop pipe: In the process of screening coal slurry, the drum screen has poor screening effect and unqualified coal slurry particle size due to the enlargement of the screen hole and the desoldering of the screen bar. In addition, the coarse particle drop pipe is improperly designed, and wet coarse particles are easy to adhere to the pipe wall, resulting in poor drop, affecting the stable operation of the entire coal slurry system.

4) Problems with the pneumatic clutch and glycerol air supply system: The pneumatic clutch is one of the core components of the coal mill, but due to the presence of moisture in the air compressor's air supply system, the pneumatic clutch cannot operate normally, affecting the stability of the coal mill. Moisture enters the air bag and lubrication system, causing corrosion and equipment failure.

Two key technical improvements were made to solve the slurry leakage problem of the mill barrel bolts.

1) First, the design of the bolt head was changed from the original prism to a semi-arc shape to enhance the contact sealing with the liner.

2) Secondly, a short tube was welded to the outer wall of the barrel, and a double-layer rubber sealing gasket was installed to prevent the outside air from affecting the sealing effect. Through these improvements, the sealing performance of the bolts was significantly improved and the slurry leakage phenomenon was reduced. In addition, the material of the liner was also changed from the original rubber liner to a steel liner, avoiding the corrosion and damage of the rubber liner after long-term use.

3) Modification of the inlet chute pipeline and drum feeder: The design of the inlet chute pipeline was changed from the original circle to a triangle, which can increase the contact area with the coal slurry, thereby reducing abrasion and slurry leakage. For the drum feeder, a double-layer packing interference seal was used instead, and wear-resistant packing filler was used. By adjusting the raw coal feeding pipeline and increasing the sealing of the feeding end, the leakage phenomenon was effectively reduced.

4) Cylinder bolt modification: In order to solve the leakage problem of the cylinder bolt, the bolt head design was first changed, and the prism shape was changed to a semi-arc shape to enhance the sealing effect. At the same time, a short pipe was welded on the outer wall of the cylinder and a double-layer rubber sealing gasket was added to reduce the erosion of the rubber sealing gasket by the outside air and prevent the occurrence of leakage. In addition, the lining material was replaced, and the steel lining was used instead of the rubber lining, thereby avoiding the problems caused by rubber aging and damage.

In order to solve the problems of enlarged screen holes and wear of screen bars in the drum screen and coarse particle drop pipe, the following improvements were made:

1) Thickening of the drum screen bars: The screen bars of the drum screen were thickened, and the welding quality was strengthened to extend the service life of the screen bars, thereby ensuring the screening effect.

2) Improvement of the design of the coarse particle drop pipe: The original design of the coarse particle drop pipe was unreasonable in shape, which caused the wet coarse particles to easily adhere to the pipe wall, resulting in poor discharge. The modified drop pipe adopts a triangular design to increase the flow area, and flushing water pipelines are added on both sides of the pipe, which effectively reduces the particle adhesion phenomenon.

How to solve the problem of pneumatic clutch and glycerin gas supply system of coal mill?

In order to solve the moisture problem in the pneumatic clutch and glycerin gas supply system, the modification plan includes introducing factory compressed air to prevent moisture in the system from corroding equipment and valves. At the same time, two sets of gas check valves are installed in the new air compression system, which can avoid moisture in the gas supply system and ensure the stable operation of the equipment. In addition, the air compressor, as a backup equipment, can be started when the factory compressed air pressure drops, so as to ensure that the coal mill can continue to operate until the air pressure returns to normal.

The water-coal slurry grinding process is the key technical link in converting coal into water-coal slurry. It aims to grind coal blocks into fine particles and evenly mix them with water and additives through a series of physical operations to form a water-coal slurry product with good fluidity and stability.

Main process flow
1) Coal crushing: First, the original coal is preliminarily crushed, and the larger coal blocks are crushed into smaller particles by jaw crushers, cone crushers and other equipment. The particle size is generally below 50mm for subsequent grinding operations.

2) Grinding and classification
Grinding: The crushed coal particles enter the mill, such as ball mills, rod mills, etc., and an appropriate amount of water and grinding media (such as steel balls and steel rods) are added to the mill. When the mill rotates, the grinding media impacts and grinds the coal particles to further refine the coal particles.

3) Classification: The ground coal slurry passes through classification equipment, such as spiral classifiers, hydrocyclones, etc., to separate the coal slurry according to particle size. Coal slurry with qualified particle size enters the next process, and coarse particles return to the mill for further grinding.

4) Additive addition: In order to improve the performance of water-coal slurry, such as fluidity and stability, it is necessary to add an appropriate amount of additives to the coal slurry. Common additives include dispersants, stabilizers, etc., which are generally added during or after grinding and fully mixed with the coal slurry by stirring.

5) Mixing and homogenizing: After grinding, grading and adding additives, the coal slurry enters the stirring tank for mixing and homogenization, so that the coal particles, water and additives are more evenly mixed to form a water-coal slurry product with stable performance.

Process characteristics
1) High concentration grinding: The water-coal slurry grinding process is usually carried out at a higher coal slurry concentration. The mass fraction of coal is generally around 60% - 70%, which is conducive to improving the grinding efficiency and reducing the load of subsequent dehydration processes.

2) Wet grinding: Compared with dry grinding, wet grinding has the advantages of less dust, low noise, high grinding efficiency, and relatively low energy consumption. It is also conducive to the wetting of the coal particle surface and the uniform dispersion of additives.

3) Adjustable particle size: By adjusting the operating parameters of the mill, the type and quantity of grinding media, the parameters of the grading equipment, etc., the particle size distribution of the water-coal slurry can be flexibly controlled to meet the needs of different users.

Influencing factors
1) Coal quality characteristics: The hardness, grindability, moisture content, etc. of coal have an important influence on the grinding process. Coal with high hardness and poor grindability requires more grinding energy and time; excessive moisture will affect the fluidity and grinding efficiency of the coal slurry.

2) Grinding equipment: Different types of grinding equipment have different grinding effects and energy consumption. The speed, filling rate, shape and size of the grinding media of the mill will affect the grinding efficiency and product quality.

3) Additives: The type and amount of additives are directly related to the performance of the water-coal slurry. Suitable additives can reduce the surface energy of the coal particles, improve the fluidity and stability of the coal slurry, and reduce the agglomeration phenomenon during the grinding process.

4) Operating parameters: including grinding concentration, grinding time, overflow concentration and underflow concentration of the grading equipment, etc. Reasonable operating parameters can make the grinding process achieve the best effect and improve product quality and production efficiency.

Ball mill
Working principle: The ball mill crushes the material by the impact and grinding effect of the grinding body (steel balls, etc.) in the cylinder when it rotates with the cylinder. When the cylinder rotates, the steel balls are lifted to a certain height and then fall down, impacting the coal blocks. At the same time, the friction between the steel balls and between the steel balls and the inner wall of the cylinder will also grind the coal particles.

Advantages
1) High grinding efficiency: There are many steel balls in the ball mill, which are evenly distributed. A large number of impact points and grinding surfaces can be generated on the coal particles in the high-speed rotating cylinder. For coals with higher hardness, the high-intensity impact and grinding effect of many steel balls can effectively crush the coal blocks into fine particles. It is suitable for large-scale water-coal slurry production and can process a large amount of coal raw materials per unit time.
2) Fine product particle size: The coal slurry particle size after ball mill grinding can reach a very fine degree, which can generally meet the strict requirements of water-coal slurry for particle size, such as being able to grind coal particles to 200 mesh or even finer, which is conducive to improving the stability and combustion performance of water-coal slurry.

3) Strong adaptability: It has good adaptability to coal types with different hardness and grindability. Whether it is hard coal or soft coal, it can achieve better grinding effect by adjusting the operating parameters of the ball mill (such as speed, steel ball ratio, etc.).

4) Limitations: During the grinding process of the ball mill, the impact of the steel ball on the coal particles is random, which is prone to over-crushing, that is, some coal particles are over-ground into extremely fine particles, which not only increases energy consumption, but also may affect the rheological properties of water-coal slurry.

Rod mill
Working principle: The rod mill uses steel rods as grinding media. The steel rods are lifted to a certain height in the cylinder as the cylinder rotates and then fall down to impact and grind the material. Unlike the ball mill, the steel bars in the rod mill are in line contact, which has a certain selectivity during grinding.

Advantages
1) Uniform product particle size: Since the steel bars are in line contact, the force on the coal particles during the grinding process is relatively uniform, and it is not easy to have local over-grinding. Therefore, the ground coal slurry has good particle size uniformity, which can effectively control the particle size distribution of the coal slurry and reduce the content of coarse particles and fine particles.

2) Reduce over-crushing: Compared with the ball mill, the grinding method of the rod mill is more gentle, which can significantly reduce the phenomenon of over-crushing, reduce energy consumption, and improve grinding efficiency. Especially for some water-coal slurry production scenarios with high requirements for particle size uniformity, such as water-coal slurry used in certain specific industrial furnaces, the advantages of the rod mill are more obvious.

3) Good adaptability to coal quality changes: When the coal quality fluctuates, the rod mill can relatively stably produce water-coal slurry with qualified particle size, and will not cause large fluctuations in product particle size due to small changes in coal quality.
Limitations: The grinding efficiency of rod mill is lower than that of ball mill. When processing coal with higher hardness, it may take longer grinding time or larger equipment scale to achieve the same output.

Overall Comparison
1) From the perspective of coal characteristics
Ball mill: If the processed coal is of high hardness and poor grindability, the ball mill is more suitable. For example, for coal with high hardness such as anthracite, the strong impact of a large number of steel balls in the ball mill can effectively crush the coal blocks into fine particles, making it easier to meet the particle size requirements required for water-coal slurry production.

Rod mill: For coal with low hardness and good grindability, such as lignite, the rod mill can play a good role. The relatively gentle grinding method of the rod mill can not only grind the coal to the appropriate particle size, but also reduce the phenomenon of over-crushing, improve the grinding efficiency and product quality.

2) From the perspective of product quality requirements
Ball mill: When the particle size of water-coal slurry is required to be extremely fine, such as for some advanced combustion equipment with extremely high combustion efficiency requirements, the ball mill has more advantages. It can grind coal particles to 200 mesh or even finer, meeting the needs of water-coal slurry in these special application scenarios.

Rod mill: If the particle size uniformity of water-coal slurry is required to be very high, and the particle size distribution is expected to be concentrated in a narrow range, rod mill is a better choice. Its line contact grinding method makes the ground coal slurry particle size uniform, which can effectively reduce the content of coarse particles and fine particles, and ensure the stability and rheology of water-coal slurry.

3) From the perspective of production scale
Ball mill: In large-scale water-coal slurry production, the high processing capacity of ball mill makes it the first choice. For example, large-scale water-coal slurry gasification plants need to produce a large amount of water-coal slurry per unit time. Ball mills can meet the needs of such large-scale production. By running multiple ball mills in parallel, high output can be achieved.

Rod mill: For small and medium-scale water-coal slurry production, the flexibility and relatively low energy consumption of rod mills are more advantageous. Some small industrial boilers or water-coal slurry preparation systems for enterprise use can reduce equipment investment and operating costs while meeting production needs by using rod mills.

4) From the perspective of investment and operating costs
Ball mill: The equipment investment of ball mill is relatively high, and due to its high energy consumption, it needs to consume more electricity during operation. At the same time, the steel balls wear quickly and need to be replaced regularly, which increases the operating cost.

Rod mill: The equipment investment of rod mill is relatively low, the energy consumption during operation is relatively small, the steel rods wear relatively slowly, the replacement frequency is low, and the operating cost is relatively low.

In summary, if the output of water-coal slurry is required to be high, the adaptability of coal hardness is required to be wide, and a certain degree of over-crushing can be accepted, the ball mill is more suitable; if more attention is paid to the uniformity of the particle size of water-coal slurry products, over-crushing is expected to be reduced to reduce energy consumption, and the output requirement is not extremely high, or the coal quality is relatively soft, the rod mill may be a better choice. In practical applications, ball mills and rod mills can also be used together according to specific circumstances to achieve better grinding effects and production benefits.

The energy consumption of rod mill and ball mill in water-coal slurry production is affected by many factors. Generally speaking, the energy consumption of rod mill is relatively lower than that of ball mill. The following compares the energy consumption of the two from the aspects of grinding media, working principle, processing capacity and product particle size:

1) Influence of grinding media
Ball mill: The ball mill uses steel balls as grinding media. When the steel balls move in the cylinder, the collisions between each other and between the cylinder and the material are relatively complex, and there are more invalid collisions and energy losses. In addition, in order to achieve a better grinding effect, a larger number of steel balls are required, which makes the ball mill consume more energy to drive these steel balls to move during operation.

Rod mill: The rod mill uses steel rods as grinding media. There is line contact between the steel rods. During the grinding process, the energy transfer is relatively more direct and more effective. The movement of the steel rods is relatively orderly, and there are fewer invalid collisions and frictions. Therefore, the energy utilization efficiency in terms of grinding media is relatively high and the energy consumption is relatively low.

2) Influence of working principle
Ball mill: The ball mill mainly relies on the impact energy of the steel balls when they fall and the grinding energy between the steel balls and the materials to crush the materials. In order to make the steel balls obtain enough impact energy, the cylinder speed needs to be increased to a certain extent, which causes the motor to output a larger power, thereby consuming more electricity. At the same time, the impact force and grinding force of the materials in the ball mill are uneven during the grinding process, which is prone to over-crushing. The energy consumed by this part of over-crushing belongs to ineffective energy consumption, which further increases the overall energy consumption.

Rod mill: The rod mill mainly uses the linear contact grinding effect of the steel rod to grind the materials more gently and evenly. Its working speed is lower than that of the ball mill, and the output power required by the motor is relatively small. Moreover, because the grinding method of the rod mill is more uniform, it is not easy to produce over-crushing. The energy is mainly used to grind the material to the appropriate particle size, the energy utilization is more sufficient, and the energy consumption is relatively low.

3) Influence of processing capacity and product particle size
Ball mill: The ball mill has a large processing capacity and can process a large amount of material per unit time. However, in order to achieve the particle size requirements required for water-coal slurry production, it often requires a longer grinding time or a higher speed, which will lead to increased energy consumption. Especially for coal with higher hardness, the ball mill needs to consume more energy to crush and grind.

Rod mill: The processing capacity of rod mill is relatively small, but the particle size of the product it produces is uniform. When the same coal-water slurry particle size requirement is achieved, the rod mill does not need to be over-grinded like a ball mill. Therefore, when processing the same quality of coal, the energy consumption of the rod mill may be relatively low. However, if the output requirement is higher, the number or specifications of the rod mill needs to be increased, and the energy consumption will increase accordingly. However, under the same output conditions, its energy consumption is generally still lower than that of a ball mill.

There are three major elements in the preparation of water-coal slurry: coal quality, coal powder particle size distribution, and additives.
The production process of water-coal slurry usually includes coal selection, crushing, grinding (adding additives), stirring and shearing, slurry filtering and other links. The role of each link is:

(1) Coal selection is the basis of slurry making, which includes two aspects: one is to select suitable coal or blending coal for slurry making, that is, coal with good slurry performance and good combustion characteristics; the other is to deash and desulfurize the raw coal to ensure the quality of raw coal for slurry making.

(2) Crushing and grinding are the most critical links in the slurry making process. In order to reduce the power consumption of grinding, the raw coal must be crushed before grinding (according to the principle of more crushing and less grinding, the finer the crushing particle size, the better), and then ground until the fineness required by the water-coal slurry product is reached, and its particle size distribution reaches a higher stacking efficiency.

(3) Kneading is only used in dry grinding and medium-concentration wet pulping. Its function is to make the coal powder produced by dry grinding or the filter cake obtained by dehydrating the medium-concentration grinding product through the filter to be evenly mixed with water and dispersant, and form a slurry with a certain fluidity, so as to facilitate further mixing in the next stirring process.

(4) The function of stirring is to fully mix the coal particles, water and additives, improve the stability of the water-coal slurry, and in the stirring process, the coal slurry is subjected to strong shear force, which strengthens the interaction between the additives and the surface of the coal particles and improves the fluidity of the slurry.

(5) The function of the slurry filtering process is to remove the coarse particles and certain impurities mixed into the slurry during the slurrying process to prevent the water-coal slurry from clogging the pipeline and nozzle during storage, transportation and combustion.

(6) In the slurrying process, online detection and control devices such as coal quantity, water quantity, additive dosage, coal slurry flow, material level, and liquid level must also be configured. The reasonable selection of pulping raw coal and additives and the determination of pulping process are the three major elements of pulping technology, and are also the basic conditions for achieving the production of high-quality water-coal slurry products with lower pulping costs.

The pulping process (wet pulping with high concentration) is generally divided into four parts: raw coal link, reagent preparation link, grinding link and slurry storage and transportation link. The raw coal link is to send the raw coal to the crusher through a belt conveyor for crushing. The crushed coal is then sent to the pulverized coal bin by the conveyor for grinding; the reagent preparation link is to respectively prepare the dispersant stock solution, stabilizer dry powder and a certain amount of water into dispersant solution and stabilizer solution and pump them to the dispersant buffer tank and stabilizer buffer tank; the grinding link is to send water, coal and dispersant into the mill for grinding. The water-coal slurry coming out of the mill is the original water-coal slurry. The original water-coal slurry is removed by the vibrating screen and flows into the buffer stirring tank for stirring. Then it is pumped to the filter for processing. The treated slurry and a certain amount of stabilizer solution are added to the stability stirring tank for stirring again. The stirred slurry is sent to the enhanced pump for high shear treatment. Then it is sent to the homogenizing stirring tank for stirring and maturation. In this way, the finished slurry is obtained; the slurry storage and transportation link is to send the finished slurry to the slurry storage tank for storage or to transport it outward: the entire water-coal slurry preparation process ends here.

Wet pulping: According to the different grinding concentrations, the wet pulping process is divided into high-concentration grinding pulping process, medium-concentration grinding pulping process and medium-high concentration combined grinding pulping process.

1) The high-concentration grinding pulping process is to add coal, water and dispersant into the mill for grinding. After the grinding product is stirred and treated with a stabilizer, it is the finished water-coal slurry. Most water-coal slurry plants in my country and abroad (such as Atlantic Company in the United States, Hitachi Company and COM Company in Japan) adopt this process. Its advantages: low investment, simple process, and easy production management; at high concentrations, more coal slurry can adhere to the surface of the grinding medium, which is conducive to producing more fine particles during grinding, improving particle size distribution, and improving stacking efficiency. When running well, the particle size distribution of the product of this process can reach 72% stacking efficiency. It is also conducive to the timely contact of the dispersant with the surface of the coal particles, thereby improving the pulping effect. Its disadvantages: the unit production capacity is generally lower than that of the medium concentration, and the grinding power consumption is relatively high; at the same time. There are certain limitations in adjusting the particle size distribution of the grinding product, and it is necessary to master the mill operating parameters well because the viscosity of the coal slurry is high.

2) The medium-concentration grinding pulping process refers to the pulping process using about 50% grinding concentration. The process is: add the raw coal, water and some additives to the mill together, grind at medium concentration, and then the grinding product enters the next process for grinding (the stacking efficiency of the particle size distribution of the medium-concentration grinding product is low, and generally more than two stages of grinding processes are required), and then the grinding product is filtered and dehydrated, and the dehydrated product is added with a dispersant for kneading, mixing, slurry filtering, stability treatment and homogenization and maturation to obtain the finished water-coal slurry. Its advantages: grinding is easier to carry out, and the capacity of the grinding machine is greater than that of the high-concentration grinding machine. Its disadvantages: grinding must be matched through different stages, and the grinding product needs to be dehydrated, which requires large investment, complex process flow, and inconvenient operation, management and maintenance.

3) The medium-high concentration grinding pulping process is a combination of the above two processes. In principle, high-concentration and medium-concentration two-stage grinding is adopted. The medium-concentration grinding product then enters the high-concentration mill and is mixed with the feed of the high-concentration mill for high-concentration grinding. The product of high-concentration grinding is the primary product of water-coal slurry after stirring and filtering; or the medium-concentration grinding product is filtered and dehydrated, and then kneaded with the high-concentration grinding product, and the kneaded product is the primary product of water-coal slurry. The primary product of water-coal slurry is then subjected to several processes such as stirring and slurry adjustment, slurry filtration, stability treatment, high shear treatment and homogenization and maturation to obtain the finished water-coal slurry. The advantage of this process is that it can obtain grinding products with high stacking efficiency. (For example, the stacking efficiency of grinding products of Chongri water-coal slurry plant is about 74%). Its disadvantage is that the grinding link only plays a role in improving grading. It has little effect on improving processing capacity and the energy consumption is relatively high. For example, the Yanri water-coal slurry plant has a pulping power consumption of up to 143 kWh/(t coal). Therefore, it has advantages only when dealing with difficult-to-pulp coal and requiring the production of high-quality water-coal slurry. In terms of plant construction investment, it is between the other two processes, and the production operation and management are relatively complex.
The flotation clean coal pulping process is a wet pulping process invented in my country. The feature of this process is to use the newly generated fine coal slime in the coal washing process. The water-coal slurry is made after flotation-filtration-adjustment of particle size. The biggest advantage of this process is that it saves the grinding of coal and greatly reduces the pulping cost.

Dry pulping:
The typical process of dry pulping is shown in Figure 1. The raw coal is crushed and dried, and the dry moisture is not more than 5%. After drying, it is kneaded to make the coal powder, water and dispersant mix evenly, and initially form a slurry with a certain fluidity, so that it can be further mixed and slurried in the next stirring process. If it is necessary to further improve the stability of the slurry, it is necessary to add an appropriate amount of stabilizer, and then stir, mix and shear to further mature the slurry. Before entering the storage tank, the slurry must be filtered to remove impurities to obtain the product.

Its existing problems:
(1) The energy consumption of dry grinding is higher than that of wet grinding. Under the condition of the same product fineness, the energy consumption of dry ball mill is about 30% higher than that of wet ball mill.
(2) In general, the effect of dry grinding is not as good as that of wet grinding. This is because, according to the particle size distribution data of dry-milled coal powder, its stacking efficiency is far lower than that of wet products, and the new surface area is quickly oxidized during dry grinding, thereby reducing its slurryability.
(3) The safety and environmental conditions of dry grinding are worse than those of wet grinding.

The water-coal slurry mill is connected to the pinion through an asynchronous motor and a reducer, and then directly drives the surrounding large gear reduction transmission to drive the rotating part to rotate. Inside the cylinder, an appropriate amount of steel balls are installed as grinding media. Under the action of centrifugal force and friction, these grinding media are lifted to a certain height and then fall in a throwing state. The water-coal slurry raw materials to be ground continuously enter the cylinder from the feeding pipe, are crushed by the moving grinding media, and then the products are discharged from the machine with the help of overflow and continuous feeding for subsequent processing.

The structure of the water-coal slurry mill is relatively complex, mainly covering the main motor, reducer, transmission part, cylinder part, main bearing part, slow transmission device, feeder, feeding part, discharging part, high and low pressure lubrication station, foundation part, lifting device, etc. Its specific structure can be referred to tongli pdf 1.

From the perspective of the transmission device, the main motor of the water-coal slurry mill is a high-power asynchronous motor specially designed for the mill. The transmission shaft bearings use double-row radial spherical roller bearings, and the peripheral large gears use large modulus cast steel gears, which makes the rotation process smooth, less noisy and long service life. The large gears are equipped with radial sealing gear covers to achieve effective sealing. Their lubrication relies on a spray device to spray a certain amount of lubricating oil onto the working surface of the gears at a certain period.

The main bearing of the water-coal slurry mill adopts a completely enclosed self-aligning 120° "rocker" type structure. The bearing is made of low-hardness Babbitt alloy, and a serpentine cooling pipe is buried in its lower part to reduce the bearing temperature by passing cooling water. The bearing has a static pressure structure and is lubricated by a high- and low-pressure thin oil station. During the startup and shutdown stages, the high-pressure system will float the rotating part and interlock it with the main engine. It will start after floating for 30 seconds, which can reduce the starting torque and bearing wear. During normal operation, the oil flow is continuously input at low pressure to achieve good dynamic pressure lubrication. The main bearing is sealed with a fully enclosed piston ring, and a good sealing effect is achieved with the help of rubber strips and grease to prevent dust from entering, ensure the cleanliness of the bearing joint surface, and reduce the possibility of burning.

In addition, a platinum thermal temperature measuring resistor is installed inside the bearing and interlocked with the main motor. The shutdown temperature can be set according to the needs and can also be adjusted according to the actual situation on site. The inner wall of the cylinder of the water-coal slurry mill is equipped with a wavy liner, which is connected to the inlet and outlet end cover through an external flange. An external cover-type grinding door is provided on the cylinder to facilitate the staff to inspect and replace various vulnerable parts in the cylinder, as well as to load and unload grinding media.

The inlet and outlet end covers of the water-coal slurry mill are equipped with liner plates, and their cross-sectional shapes are carefully designed according to the wear conditions. The feeding method adopts a self-slip mill with a simple structure and low resistance. When discharging, the material first passes through the reverse spiral tube in the discharge end cover, and then enters the cylindrical screen to complete the unloading and screening operations. The cylindrical screen is split, which is convenient for later maintenance and replacement.

The slow transmission device equipped with the water-coal slurry mill can make the main engine obtain a speed of 0.15~0.2 rpm through the cooperation of the motor and the reducer. It is mainly used for turning, maintenance and loosening loads. When the downtime exceeds four hours, the material in the cylinder may be agglomerated. Before starting the main motor, use the slow drive device to turn the car first, which can achieve the purpose of loosening the material. In addition, the tooth clutch in the slow drive device is unidirectional, which can effectively protect the safety of maintenance personnel.

The lifting device of the water-coal slurry mill consists of a jack, a square box and a bracket. When the machine is shut down for maintenance, the lifting device can be placed under the cylinder to lift the cylinder, so as to facilitate the inspection and maintenance of the main bearing bushing.
The foundation of the water-coal slurry mill clearly gives the relative position and base elevation of the anchor bolts of each part, as well as the anchor bolts and related embedded parts.
It is worth noting that the water-coal slurry mill has two rotation directions of "left-hand" and "right-hand" for users to choose. When ordering, the user must clearly specify the required rotation direction. If no clear specification is given, the supply will be based on "right rotation".

When installing a mill, safety and standardized operation are crucial. Personal and equipment safety must be ensured during the installation process. When installing the liner, the cylinder must be prevented from rotating due to eccentricity. Before assembly, the main bearing and the journal should be carefully checked and cleaned of scratches and dirt to ensure that the lubricating oil is clean and prevent grinding.

When installing gears, the gear runout and meshing requirements must be met to ensure transmission quality. All mating surfaces and friction surfaces must be carefully cleaned, thin oil must be injected into the mating surfaces, and dry oil must be applied to the friction surfaces. When the installation is completed and the power is turned on, be sure to strictly follow the operating procedures and do not start the mill at will. No-load and full-load test runs should be carried out continuously and the time should be extended as much as possible. In addition to referring to this manual, the installation technical requirements should also refer to the "Mechanical Equipment Installation and Construction Specifications" and the technical requirements of various departments.

The installation order of the mill is: foundation bolts and base plate, main bearing, rotary part (including cylinder, inlet and outlet parts, and the manhole cover on the cylinder is installed later), transmission part, large and small gears, couplings and slow transmission devices, motors and couplings, feeding parts, gear covers and injection devices, high and low pressure lubricating oil stations, oil and water pipelines, safety covers, handrails, railings, etc.

The mill needs to be installed on a reinforced concrete foundation that can support the weight of the equipment and the operating load. The foundation map of the random drawing only provides the relative elevation of the foundation and the location and size of the anchor bolts. The details such as the size and strength of the foundation need to be determined by the user according to the natural geographical structure design on site. The foundation map is for reference only.

Before installing the equipment, check the location and size of the anchor bolts and the size of the relevant equipment to ensure that the actual object is consistent with the drawings. The elevation of each base plate must meet the requirements and can be adjusted with self-made pads and adjustment pads, but the pads must be in full contact with the bottom surface of the base plate so that they can be firmly fixed after grouting. The top surface of the secondary layer should be lower than the top surface of the base plate, and no more than half of the thickness of the base plate at most. In order to make the secondary pouring closely combined with the original foundation, the foundation surface needs to be shoveled into a rough surface, and pits with a diameter of about 30-50mm are shoveled out with a steel flat shovel. The pit spacing is about 150mm, and gaps are shoveled out at the corners of the foundation.

Before laying the anchor bolts, rust and oil stains must be removed, the threaded part must be greased to prevent rust, and the bolts and nuts must be checked for fit. The axial distance deviation between the two bearing base plates is no more than 0.5mm, the relative elevation difference is no more than 0.5mm, and the discharge end is no higher than the feed end. Before the secondary pouring, the anchor bolts can be tightened only when the concrete strength reaches more than 75%. At the same time, the oil stains, paint, rust and dust on the bearing seat, shim and foundation must be cleaned to ensure that the lower part of the bearing seat is filled with cement slurry and compacted. The final level of the installed and fixed base plate is no more than 0.1mm per meter in any direction. After the secondary pouring layer is dried and the anchor bolts are tightened, the distance, elevation and levelness should remain unchanged.

The main bearing installation should be carried out after the foundation strength reaches more than 75% and the inspection is qualified. Before installation, clean the bearing base plate, draw the vertical and horizontal center lines on its upper surface as the alignment reference line, install the anchor bolts and the base plate together on the foundation and adjust the position. The gasket is made of 25X100 steel plate, the length is not greater than the width of the base plate, the main bearing base plate is not less than 8 pieces, and the remaining base plates are reduced as appropriate.

The adjustment plate is made of thin steel plates of different thicknesses, and there are no more than 2 pieces on each gasket. The center distance between the two bearing base plates should comply with the requirements of the design or equipment documents. At the same time, measure the actual size of the cylinder and the end cover after assembly and adjust it appropriately. Use a liquid communicating device or theodolite to measure the relative elevation of the two main bearing base plates, with a tolerance of 0.5mm. The feed end is higher than the discharge end, and the elevation and levelness are measured at the same time, and the level is found while measuring. Place the bearing seat on the bearing base plate so that the center lines coincide.

The two should be in uniform contact, with a local gap of no more than 0.1mm, a continuous length of no more than 1/4 of the side length, and a depth of no more than 100mm, otherwise scrape and grind. Clean the saddle seat surface and the bearing liner, apply lubricant and drop the bearing liner into the saddle seat, scrape the working surface of the bearing liner and the surface of the journal, with a contact angle of 70º - 90º, and no less than 4 contact spots on an area of ​​25x25 square millimeters. After the bearing is installed, perform a pressure test, with a pressure not lower than the rated working pressure of the high-pressure oil pump, and a test time of no less than 30 minutes. If there is leakage, it should be completely eliminated.

Before installing the cover, connect the main bearing cooling water pipe and perform a water pressure test, with a test pressure of 0.4 - 0.6Mpa, a test time of 30 minutes, and no leakage. After the bearing seat is installed, check whether the internal cooling water hose touches the shaft diameter, whether the bearing bush pressure plate and the bearing bush meet the requirements of the drawing, clean the foreign matter inside the bearing base, plug the useless holes of the shell with bolts, fill the sealing ring groove lubricating oil at the contact point between the main bearing housing and the shaft diameter, and test the smooth filling of the oil.

Before installing the cylinder, check the end cover, repair the surface damage, remove the burrs, flash and anti-rust paint on the mating surface. If it is not assembled immediately, apply anti-rust grease on the machined surface and pack it. Before installing the cylinder, first install the gear lower cover of the transmission part in place, thoroughly clean the inside of the main bearing and the journal. It is forbidden to tie a wire rope on the journal during installation to prevent dust and debris from falling on the bearing bush surface and avoid impact damage to the bearing.

A lifting device can be used. Place the slewing unit on the top frame of the lifting device 20-30mm higher than the final horizontal position, and then slowly drop into the bearing, or first tie the bearing liner tightly against the predetermined position of the hollow shaft and drop it on the bearing base together. The axial clearance between the feed end bearing and the journal is at least 5mm on the outside of the cylinder. The end face runout of the main bearing liner caused by the different axiality of the two hollow shafts after assembly shall not exceed 0.8mm. The feed end is higher than the discharge end, and the generatrix horizontality shall not exceed 0.8mm. It is strictly forbidden to use the lifting lug on the end cover to lift the entire rotating part. The lifting lug can only lift the end cover itself.

Before installing the large gear on the cylinder, confirm that the gear lower cover has been installed and check for leakage, and remove it in time. The two halves of the gear should be firmly joined and all bolts should be tightened. When the large gear and the cylinder flange are combined, use the adjustment bolts to repeatedly align them. After the radial runout and axial runout of the large gear meet the requirements of the drawing, tighten the bolts to fix them. If necessary, the user can prepare the pin hole on site to fix them. Pay attention to safety when lifting the liner in and out of the mill to prevent the mill from rotating unbalanced. Install the manhole liner first, then install other liners. The bolts of the liner should be tightened and not loose.

Clean the annular seal according to the requirements of the drawing, use oilstone and fine file to blunt the sharp corners, burrs and protrusions, and also clean the bearing base and hollow shaft sealing surface, and then apply lubricant respectively. First, put the sealing rubber strip into the lower half ring groove, so that it protrudes from the ring groove by at least 2mm, and stick the introduction end with tape, and gently introduce the half ring and rubber strip from the side without the fixed pin plate. Install the upper half ring, apply adhesive to the ring joint, correct the sealing rubber strip joint and stick it with adhesive, install other parts, plug the unused holes, connect the oil pipe and fill it with grease.

Before assembling the transmission part, thoroughly clean the rolling bearing, bearing seat, transmission shaft, pinion, etc. Strictly check the transmission bearing bottom plate, bearing seat and transmission shaft position to ensure good gear meshing performance. When installing the coupling, check the size of the matching part in advance, and use oil bath or iron box to heat to the specified temperature for hot installation. It is strictly forbidden to grill with open fire. The coaxiality error of each transmission shaft shall not exceed 0.2mm, and the clearance between the two halves of the coupling shall be as specified. After assembly, the tooth side clearance of large and small gears should meet the requirements of the drawings (1.4 - 2.18mm), and the meshing contact spot should be no less than 45% along the tooth height and no less than 60% along the tooth length. Install the gear seal ring and gear cover, strictly check and correct, and ensure tight sealing without motion interference.

After installing the slow transmission device, the motor and planetary gear reducer are in place, the transmission clutch should be able to flexibly clutch, and there should be no phenomenon of being unable to disengage or close, and the guide sleeve sliding surface and the slider (groove) should be coated with grease.

The oil station is installed according to the installation and use instructions of the lubricating oil station. During installation, the oil tank drain hole should extend beyond the oil tank foundation and be no less than 300mm from the ground for easy draining. The lubrication pipeline and accessories are provided by the user. There should be no leakage after connection, and they should be thoroughly cleaned. There should be no residue in the lubrication equipment pipeline or bearing box. The lubrication system is tested after assembly, and the test pressure of the cooling water channel at each location should meet the system requirements.

The lifting device is movable and should be removed when not in use. When it is used and installed, the bottom should be flat and firm, and should not be tilted. The load on both sides should be basically equal. Assemble the remaining parts according to the requirements of the drawings, and install walkways, handrails, railings, shields, etc. The oil station pipeline should be installed so that the connection distance between the oil station and the main bearing is the shortest. The return oil pipeline has a slope of not less than 2.5/100, and the valves and joints designed for the mill oil circuit should be installed in place. The lubricating oil model should be consistent with the oil station manual and the injection device manual. It is recommended that the oil station use ISO VG150 or ISO VG220 oil, and the injection device use ISO VG460 oil. If the temperature of the oil station is lower than 30° before starting, it should be heated to 40° before starting to ensure the service life of the equipment.

The equipment can only be tested after it is installed and inspected. Before the mill is operated, strictly check that there is no residue in the equipment, all sealing points are in good condition, and the connection points are firm. Check whether the oil level of each lubrication station has reached the specified elevation. In winter, heat the lubricating oil to 20 - 25ºC, and check the flow and pressure of oil, gas, and water. Before the no-load test run, carefully check the high and low pressure combined oil station, dry oil automatic spray device, and bearing water cooling system to ensure that they are in good working condition. The rotation direction of the motor must meet the requirements of the drawings and be checked by the motor's self-rotation. Clean up the site and remove obstacles that affect the operation of the mill. It is strictly forbidden to stand on both sides when the mill is turned on.

Start the high-pressure system, float the rotating part, and generate an oil film of sufficient strength so that there is enough lubricating oil in the bearing box. Open the cooling circulation water, use an oil gun to fill a sufficient amount of grease into the annular sealing cavity, manually apply a proper amount of grease to the gear meshing, and also apply grease between the gear wheel rim sealing felt. Start the slow transmission device to make the main engine rotate, and at the same time start the automatic dry oil atomizer to spray oil continuously for 10 minutes (make the main engine rotate slowly for one circle), check whether there is any motion interference, collision, or loose bolts in each part of the mill, and stop the machine immediately to eliminate any problems.

The no-load test run is formally carried out, and the high and low pressure oil stations are restarted. The oil stations interlocked with the main motor are allowed to run for 3 minutes, and the main motor is automatically started after receiving the feedback signal that the oil film has been generated. After the mill is running, the following requirements should be met: the lubrication of each lubrication point is normal, and there is no leakage; the temperature of the mill main bearing does not exceed 60ºC; the mill runs smoothly, the gear transmission has no abnormal noise, and the tooth surface has good contact; the liner and the rotating parts are not loose.

After the no-load operation is qualified, steel balls can be added, but be careful to avoid the mill running without material after the steel balls are loaded to damage the liner. The filling rate load given in the mill specification is the maximum value, and overload operation is not allowed. The added medium and material should be balanced with the consumed medium and product. During the load test, first add 20-30% steel balls, 50% of the total weight of the material, into the mill, start according to the prescribed procedure, and after running without abnormality, add 10% of the total amount of the medium every 30 minutes, and continuously feed the appropriate amount of material until the mill reaches full load, and run continuously for 24 hours. The following requirements should be met: stable operation, no sharp periodic vibration; the current value of the main motor is within the allowable range; all components operate normally; there is no powder leakage at the bolts of each lining plate, and if there is leakage, tighten the bolts in time; check whether the bolts at each part are loose, broken or falling off, the main bearing temperature is lower than 60ºC, and the return oil temperature is lower than 50ºC.

The start-up of the mill needs to follow a strict sequence. Start the low-pressure oil pump first to prepare for the subsequent lubrication work. Then start the high-pressure oil pump, which can provide the necessary pressure support for the equipment during the startup phase. Then start the main motor to get the core of the mill running. Finally, start the feed motor to ensure that the material can enter the mill smoothly. Under normal circumstances, it is necessary to avoid starting the mill twice in a row within an hour, because frequent starts may cause additional impact and wear to the various components of the mill, affecting the service life and performance of the equipment.

When shutting down, there is also a clear operating process. First, stop the feeder and stop the input of materials. Then stop the main motor to stop the mill. After the main motor stops, the high-pressure oil pump will start automatically. This is to continue to provide lubrication and protection for related components during the process of stopping the mill. After the mill stops completely, stop the low-pressure oil pump. Then stop the high-pressure oil pump according to the bearing temperature. After the mill stops running, it is necessary to manually open the high-pressure oil pump for 2 minutes every 30 minutes to ensure that the journal and the bearing shell are always in good lubrication during the cooling of the barrel until the barrel cools to room temperature. In addition, the jet lubrication device system is linked with the main motor. It works automatically when the main motor is working, and it also stops automatically when the main motor stops. At the same time, there is an interlocking mechanism between the main motor and the slow transmission device. When the main motor is working, the slow transmission device cannot be started; when the slow transmission device is working, the main motor cannot be started, so as to ensure the safe operation of the equipment.

During the operation of the mill, if there is a special situation, emergency stop measures must be taken to ensure the safety of the equipment. When the large and small gears do not mesh properly, and a sudden large vibration or abnormal sound occurs, this indicates that there is a serious problem with the gear transmission, which may cause equipment damage and requires immediate shutdown for inspection; when the lubrication system fails and cannot supply oil normally, the various moving parts of the equipment cannot be well lubricated, which will aggravate wear and even cause failures, so emergency shutdown is required; loose or broken liner bolts may cause the liner to shift, affecting the normal operation of the mill, which also requires emergency treatment; continuous idling without material in the cylinder will damage the liner and consume the medium, so it should be stopped in time; the temperature rise of the main bearing and main motor exceeds the specified value, or the current of the main motor exceeds the specified value, which indicates that the equipment is operating abnormally, which may cause serious consequences and must be stopped urgently; if the conveying equipment fails and loses its conveying capacity, it will affect the entire production process and also require emergency shutdown; loose anchor bolts of the main bearing, transmission device and main motor will make the equipment unstable, which also requires emergency treatment; in addition, if other situations requiring emergency shutdown occur, measures should be taken immediately. When the mill stops suddenly due to an accident, the feeding should be stopped immediately to prevent the material from continuing to enter the mill, and then the power supply of the motor and other units should be cut off, and then the accident should be handled to ensure safe operation.

There are some special precautions when the mill is stopped for a long time. When the mill is stopped for a long time, the cylinder gradually cools and shrinks, and the journal will slip on the bearing. In order to reduce friction and reduce the axial tension caused by the shrinkage of the cylinder, the high-pressure oil pump should automatically supply oil for 3 minutes every 30 minutes within 24 hours of stopping the mill, so that a certain oil film thickness can be maintained between the journal and the bearing to protect the journal and the bearing. When the mill is stopped in winter, all the cooling water in the relevant water cooling part should be drained. In order to ensure that the water is completely discharged, compressed air can be used to blow to prevent the cooling water from expanding in volume after freezing and cracking the relevant pipes. Under normal circumstances, the feeding should be stopped before stopping the mill, and then the mill should be stopped as soon as possible. If the mill is stopped for a long time, the steel balls should be poured out, because the long-term placement of the steel balls may cause uneven force on the cylinder, which will cause deformation.

When the mill is operating normally, the operator must strictly abide by and pay attention to a series of matters. The mill cannot run for a long time without feeding, otherwise the liner will be damaged and the medium will be consumed; uniform feeding is one of the important conditions for the mill to achieve the best working efficiency. The operator should always pay attention to the feeding situation to ensure the uniformity of the feeding material; the wear of the liner and the medium inside the mill cylinder should be checked regularly. Once the liner is found to be worn through or broken, it should be replaced in time. The loose or broken bolts should also be tightened or replaced in time to prevent the cylinder from being worn through; frequently check and ensure that each lubrication point, including the main bearing sealing ring, has sufficient and clean lubricating oil or grease, clean the return oil filter of the thin oil station at least once a month, check the quality of the lubricating oil every six months, and replace it with new oil if necessary; regularly check and ensure that each lubrication point, including the main bearing sealing ring, has sufficient and clean lubricating oil or grease, clean the return oil filter of the thin oil station at least once a month, and check the quality of the lubricating oil every six months. If the quality of the lubricating oil is found to have declined, replace it with new oil if necessary; Check the meshing of the large and small gears of the mill and whether the bolts are loose. At the same time, pay attention to the fact that the reducer is not allowed to have abnormal vibration and sound during operation; according to the requirements of the material entering the mill and the particle size of the product, reasonably adjust the amount and gradation of steel balls, and add steel balls to the mill in time to keep the steel balls in the mill in the best condition. The additional steel balls are generally the largest diameter specifications in the first ball addition, but if the balls have not been added for a long time, smaller diameter balls should also be added to ensure the grinding effect; the protective cover of the mill coupling and clutch and other safety protection devices should be intact and reliable, and warning signs should be hung in dangerous areas to remind operators to pay attention to safety; during the operation of the mill, it is strictly forbidden to engage in any disassembly and maintenance of the machine body. If you need to enter the internal work of the cylinder, you must communicate and coordinate with the relevant personnel in advance and take monitoring measures. If you observe the internal situation of the main bearing when the mill is running, be particularly careful to prevent it from being scratched by the bolts on the end cover; when inspecting, maintaining and repairing the auxiliary machine of the mill, low-voltage lighting equipment should be used to ensure safe operation. When welding parts on the mill, attention should be paid to grounding protection to prevent the current from burning the tooth surface and the bearing surface; the temperature and amount of cooling water for the main bearing and each oil station should be based on the liner temperature not exceeding the allowable temperature, which can be adjusted appropriately according to the actual situation; a regular inspection system should be formulated during use, and the machine should be repaired according to the system to promptly discover and solve potential problems; the equipment must be carefully maintained, and the environment must be cleaned frequently to ensure that there is no water leakage, no slurry leakage, no oil stains, no loose bolts, and no debris around the equipment, so as to maintain a good operating environment for the equipment.

In addition to daily inspection and maintenance, the maintenance of the mill should also implement a regular maintenance system. According to the specific situation of the equipment, a detailed maintenance plan should be formulated, and then regular maintenance should be carried out according to the plan. Maintenance is divided into minor repairs, medium repairs and major repairs according to the degree of damage to the equipment. Minor repairs are generally carried out once every 1-2 months, and can be carried out at any time if special circumstances occur. The overhaul items of minor repair mainly include: check the oil pump, oil filter and lubrication pipeline. If there is any blockage or contamination, clean and replace the lubricating oil if necessary; check the connection bolts at various places, replace the defective fasteners in time to ensure the equipment is firmly connected; clean and check whether the pinion has cracks and other defects, check the meshing condition and record its wear depth, and check whether the bolts of the large gear are loose; check the coupling and clutch and replace the wearing parts; check and repair the easily worn parts of the feeding and discharging device; replace some mill barrel liners; check the thickness of the main bearing bearing lining; check the cooling water system to see if the pipeline is blocked or leaking. If there is an aging oil-resistant rubber tube, especially in the main bearing box, it should be replaced in time. The medium repair cycle is generally 12 months. In addition to the minor repair items, the overhaul items also need to replace the liner; check, repair or replace the pinion; check and adjust the horizontal position of the barrel, check the coaxiality of the drive shaft and the motor to ensure the smooth operation of the equipment; clean the oil stains in the large gear cover; check and calibrate various instruments to ensure their accuracy; and other items that need to be repaired. The overhaul cycle is generally 5-10 years, depending on the damage to the equipment. The overhaul includes minor and medium repairs, and in addition, the main bearing and gears need to be replaced; the feed and discharge end covers of the mill need to be repaired or replaced; the foundation needs to be checked, realigned and cast again to restore the equipment to a good operating state.

This series of mills uses high and low pressure oil stations for lubrication, mainly for lubricating the main bearings of the mill. During the startup and shutdown stages, high pressure and low flow lubrication is used to provide sufficient pressure and lubrication guarantee for the equipment; during normal operation, low pressure and high flow lubrication is used to meet the lubrication needs of normal operation of the equipment. For detailed information on the specific structure, commissioning, operation, maintenance and electronic control of the oil station, please refer to the "High and Low Pressure Oil Station Manual". In addition, there is a spray lubrication device specially designed for lubricating large and small gears, which is linked with the main motor and can automatically spray oil periodically. For details on its structure, commissioning, operation, maintenance and electronic control, please refer to the "Spray Device Manual".

The lifting device is a special lifting accessory for the mill, and the hydraulic jack in it can also be used alone. When the cylinder is lowered after the maintenance work is completed, special attention should be paid to not unload the pressure quickly. It should be shut down slowly to allow the shaft neck to fall slowly to avoid impact on the equipment. The technical characteristics and use requirements of the hydraulic jack can be found in its specific instruction manual. In order to facilitate the understanding of the actual load situation, the jack can be installed with a pressure gauge. The lifting device should be fully inspected before entering the cylinder. First, the hydraulic system should be checked to ensure that there is no dirt or blockage in each part to ensure the normal operation of the system. For the two jacks, both their respective working conditions should be checked and synchronized, and the asynchronous rate should be less than 3%. The center line of the lifting device should be aligned with the axis of the cylinder so that the combined load force passes through the center line of the jack piston to ensure uniform force. The lifting device can only work after it is padded and firmly to prevent tilting or movement during the work process. During use, the lifting device should avoid vibration and impact to avoid damage to the equipment. The working oil should always be kept clean. It is recommended to filter the working oil once every season or before each use to ensure good oil quality. The oil pump and pipe joints should be kept clean and free of dirt to prevent impurities from entering the system. The jack and oil pump should be regularly inspected and maintained according to the usage. Once the parts are worn, they should be replaced in time to ensure the reliability of the equipment. The oil pump, pipes and jacks should be stored in a well-ventilated place with rain and sun protection facilities to extend the service life of the equipment.