Vertical roller mill

When the vertical cement mill is working, the high-voltage motor drives the grinding disc to rotate through the planetary reducer, and the material falls from the feed port in the center of the grinding disc. At the same time, the waste heat flue gas from the kiln tail enters the vertical mill from the air inlet. Under the centrifugal force generated by the rotation of the grinding disc, the material will move to the edge of the grinding disc as if being "thrown". When the material passes through the annular groove on the grinding disc, it will be crushed by the grinding roller tightly pressed on the grinding disc.

The tire-type(Fl-smidth type) or conical(loesche type) grinding roller is installed on the rocker arm and can be firmly pressed on the grinding disc through the hydraulic system. If the roller sleeve is tire-type, it can be replaced on the other side after one side is worn. It is equipped with a hydraulic roller turning device to facilitate the later maintenance or replacement of the grinding roller. When the grinding disc rotates counterclockwise, the grinding roller will also roll with it to grind the material repeatedly.

The crushed material will be "rolled up" from the edge of the grinding disc by the high-speed airflow blown out from the wind ring. Among them, large particles of material will fall directly on the grinding disc because they are too heavy and will be crushed and ground by the grinding roller again. The material carried upward by the airflow passes through the classifier, which will separate the coarse powder from the fine powder. The coarse powder will fall onto the grinding disc and continue to be ground under the action of the rotating rotor; the fine powder that meets the requirements will be collected by the bag dust collector along with the airflow and become the finished product we need.

If the material contains moisture, don't worry. When the material contacts the hot gas, the moisture will be evaporated to meet the production standards.

The structure of a cement vertical roller mill are as follows but not limited to:

1. Maintenance hoist: used for lifting and replacing heavy parts such as grinding rollers, often equipped with 1~2 ton electric hoists to ensure efficient and safe maintenance.

2. Mill and separator outlet: the material and gas mixture after grinding is discharged from here, connected to the dust collection and finished product system to ensure timely separation and recovery of materials.

3. Inlet duct: raw materials and hot air enter through this duct, the hot air temperature often reaches 250°C, used to dry wet materials.

4. Rotary sluice: adjust the feed amount by rotation to prevent blockage or empty grinding, usually equipped with variable frequency motor to precisely control the feed speed.

5. Separator rotor: high-speed rotation (up to 300~900rpm), separate finished powder and coarse powder according to particle size, adjust the speed to control fineness.

6. Separator reject cone: collect coarse particles and fall back to the grinding disc to achieve closed-loop circulation and improve grinding efficiency.

7. Mill housing: seals and protects the internal structure of the mill, lined with wear-resistant plates, and pressure-resistant and temperature-resistant design to prevent hot air and dust from leaking out.

8. Grinding table: drives the material to move centrifugally on the grinding disc, with a diameter of usually 2~6 meters and equipped with a wear-resistant layer to extend its service life.

9. Grinding Roller assembly: Multiple rollers are in contact with the grinding disc, generating a pressure of up to 100~300 tons to crush the material.

10. Rocker arm: connects the hydraulic cylinder and the grinding roller to achieve the transmission of grinding pressure, and has the function of flipping the roller for easy maintenance.

11. Mill drive: The main drive device, generally a motor + reducer structure, with a power range of 800kW~5000kW, drives the grinding disc to rotate.

12. Mill foundation: provides stable support for the whole machine, needs to withstand dynamic loads and vibration, and generally adopts reinforced concrete structure.

13. Steel structure mill base(mill stand): provides a platform for installing the mill and surrounding systems, and the design takes into account load and maintenance channels.

14. Bearing block: carries the load of rotating parts, and sliding bearings or rolling bearings are used in key positions to ensure stable operation.

15. Hydraulic cylinder: controls the pressure of the grinding roller, usually works in the pressure range of 10~30MPa, and has protection and lifting functions.

16. Platforms: used for daily inspection and equipment maintenance, the design should comply with ergonomics and safety specifications, and equipped with guardrails and channels.

17. Motor: provides rotational power for the grinding disc, usually uses high-voltage motors (6.5kV or 12kV), and the starting method is mostly variable frequency or hydraulic resistance.

18. Water spray unit: sprays water into the mill to control the outlet temperature below 90℃ to prevent agglomeration and overheating.

19. Pressure device: maintains a stable working pressure of the hydraulic system, usually equipped with accumulators and pressure sensors to achieve real-time monitoring.

20. Lubrication station: supplies oil to bearings and gears, equipped with cooling and filtration systems, and the oil temperature is maintained at 40~60℃ to ensure lubrication effect.

21. Sealing: located at the bearing and rotating interface to prevent oil and gas leakage and dust from entering, and improve the sealing and life of the system.

First of all, the working principles of vertical mill and ball mill are different. In vertical mill, the material is ground by the rolling of the grinding roller on the grinding disc and the centrifugal force generated by the rotation of the grinding disc, and the qualified fine powder is taken out by wind power; in ball mill, the steel ball rises to a certain height with the drum and then falls, which has an impact and grinding effect on the material, and a powder selector is configured to achieve the powder selection effect.

From the perspective of equipment structure, vertical mill is composed of grinding disc, grinding roller, powder selector and other main components, and occupies a relatively small area; ball mill is mainly composed of drum, steel ball, feeding and discharging device, etc., the drum is longer and occupies a larger area.

In terms of grinding efficiency, vertical mill integrates grinding, drying and powder selection, and can use hot air to dry materials with high moisture content, with high grinding efficiency and relatively low energy consumption; ball mill has relatively low grinding efficiency, high energy consumption, and limited drying capacity.

In terms of product fineness, vertical mill product fineness adjustment is more convenient, and can be flexibly adjusted through powder selector; ball mill product fineness adjustment is relatively complex, and it is difficult to obtain finer products.

In terms of maintenance, the replacement of the grinding roller, grinding disc and other parts of the vertical mill after wear is relatively complicated, but the maintenance space is large; the replacement of the steel balls and other wearing parts of the ball mill is more frequent, but the operation is relatively simple.

Vertical roller mills in cement plants feature a horizontal grinding disc with conical rollers, reducing wear and improving material adaptability. Welded arc plate seals minimize air leakage, while automatic roller lifting enables smooth start - ups. Low - pressure hydraulics, hybrid separators, and centralized lubrication systems ensure efficient operation, reduced maintenance, and extended component life. Check the detailed explaination below:

1. Grinding parts: The design of horizontal grinding disc plus conical grinding roller is adopted. This structure has small relative speed difference, small wear and good adaptability to materials. Grinding rollers and grinding discs are usually equipped with composite wear-resistant bushings to enhance wear resistance. The bearings of grinding rollers are lubricated in circulation to ensure good lubrication effect.

2. Welded arc plate seal: adopts double-layer lap welding structure, the weld is tested by ultrasonic flaw detection, the sealing gap is controlled within ±0.3mm, the air leakage rate can be as low as 1.5% or less, and the efficiency is improved by 40% compared with the traditional labyrinth seal.

3. Automatic lifting of grinding rollers: adopts high-precision hydraulic drive system, the lifting response time is ≤15 seconds, and can realize material starting under the condition of material stacking height of 80-100mm, avoiding torque overload of reducer due to starting impact (reducing starting current by 30%-40%).

4. Mechanical limit device: adopts three-level buffer structure, the limit accuracy is ±0.5mm, when the abnormal displacement of grinding roller exceeds the set value, it can trigger braking within 0.2 seconds, avoiding the local wear of grinding disc lining plate increasing by 2-3 times due to collision.

5. Pressurization method: Each grinding roller is pressurized separately through the rocker arm, and the operation is stable. Taking the 4-roller mill as an example, it can run with 2 rollers. When some grinding rollers fail or are maintained, it can still maintain a certain production capacity, which improves the operation rate of the equipment.

6. Low-pressure hydraulic system: The working pressure is set at 8-12MPa (conventional system pressure is 15-20MPa). With the servo proportional valve control technology, the leakage in the system is less than 0.5L/min, and the vibration intensity is controlled below 4.5mm/s, which is far better than the industry standard.

7. Hydraulic roller swing out: equipped with a double-acting hydraulic cylinder, the swing out angle reaches 90°, the single roller maintenance time is shortened from the traditional 3 hours to 1.5 hours, and the roller seal can be replaced online to reduce downtime losses.

8. Powder selection device: Equipped with an efficient cage-type powder selector and a special structural seal to effectively control the fineness of the raw material. The powder selector can flexibly adjust the product fineness to concentrate the product particle size distribution and meet different production needs.

9. Hybrid separator: It integrates the principles of dynamic rotor and static powder selection, and the classification efficiency exceeds 88%. The product fineness R0.08 sieve residue can be accurately adjusted between 8-12%, and the content of coarse particles ≥45μm in fine powder is reduced to less than 5%.

10. Air ring and retaining ring: The area of ​​the air ring and the height of the retaining ring can be adjusted according to the operating conditions, which helps to optimize the air flow distribution and material layer thickness in the mill, improve the grinding efficiency and product quality.

11. Maintenance design: The grinding roller can be lifted and lowered by itself to achieve material start-up, reducing the impact load during startup. At the same time, the grinding roller can be automatically turned out of the casing through the action of the oil cylinder, which is convenient for maintenance personnel to repair and replace wearing parts, reducing the difficulty and cost of maintenance.

12. Centralized oil circulation lubrication: Equipped with intelligent temperature control and online filtration system, the oil temperature fluctuation is controlled at ±2℃, and the oil cleanliness reaches NAS level 6 standard, which extends the bearing fatigue life from the conventional 20,000 hours to more than 28,000 hours.

13. Other components: The central cloth cover, the matching patented anti-sticking feeding air locking device, the loading cylinder buffer device and other technical measures are adopted to enhance the uniformity of the cloth, enhance the air locking effect, prevent material sticking and clogging, and improve the stability and reliability of the equipment operation.

The 4 types of vertical roller mill commonly used in a 5000 tpd cement plant are: vertical raw mill, vertical slag mill, vertical cement mill, vertical coal mill. Vertical raw mill is used for limestone grinding, vertical slag mill is for additive grinding, vertical coal mill is essential for coal grinding to supply the coal powder to the rotary kiln burner, finally vertical cement mill is in charge of finished product clinker grinding.

A vertical cement mill is used for the finish-grinding of cement clinker in cement plant. The features are as follows:

1. The cement vertical mill adopts a cone roller design. Compared with the traditional cylindrical roller, the contact area between the cone roller and the grinding disc is gradually distributed, which can make the material receive a more uniform extrusion force during the grinding process. At the same time, the cone roller can effectively reduce the edge effect and reduce the overflow and splash of the material on the edge of the grinding roller. In addition, the structural design of the cone roller also enables the grinding roller to have a certain pushing effect on the material during operation, which helps the material to be evenly distributed and circulated on the grinding disc.

2. Its grinding table liners and roller sleeves are made from wear-resistant hard facing material or ceramic material. Blades of the separator use high-quality and wear-resistant plates.

3. The separator combines highly efficient dynamic and static cages, which ensures that the specific surface area of cement can be adjusted for the finished cement product to obtain the required particle size distribution

4. The feed size of a standard cement limestone vertical roller mill is moisture ≤3%, final product moisture ≤0.5%, final product fineness R45μm=5%～20%

The vertical raw mill is used for raw material grinding mainly because of its significant advantages. The vertical mill integrates drying, powder selection and grinding functions. It can directly use 300-400℃ hot air from the kiln tail to dry raw materials with a moisture content of up to 15%, without the need for additional drying equipment. Compared with traditional equipment such as ball mills, its footprint is greatly reduced. During operation, through intelligent material layer control, dynamically adjustable air ring and other designs, the flow field in the mill is optimized, the system resistance is reduced, and energy loss is reduced. Compared with traditional grinding equipment, it can save 20-30% energy consumption. The features details are listed below:

1. The raw material mill adopts a 4-roller design, and each roller operates independently to compress and grind the material. When two rollers are worn and need to be repaired, the remaining two rollers can still reach 70% of the rated output.

2. The powder selector adopts an efficient dynamic and static cage structure, which can achieve high-precision raw material fineness control from a specific surface area of ​​3000-3800cm^2/g and sensitive cut-off point adjustment.

3. Integrated drying design: built-in efficient heat exchange channel, which can directly introduce 300-400℃ kiln tail hot air, raw materials with a moisture content of up to 15% can be dried and ground in the mill, without the need for additional drying equipment, saving investment and energy consumption.

4. Dynamically adjustable air ring: The air ring adopts a modular design, and its ventilation area can be adjusted during operation through a hydraulic drive device, accurately matching different material characteristics and production requirements, optimizing the flow field in the mill, and reducing system resistance by 10-15%.

5. Intelligent material layer control system: Equipped with a pressure sensor material layer thickness monitoring device, it monitors the grinding disc material layer in real time, automatically adjusts the roller pressure through the hydraulic system, and controls the material layer thickness fluctuation within ±5mm to ensure stable grinding efficiency.

6. Special wear-resistant material: For hard components such as quartz in raw materials, the grinding roller and grinding disc use high-chromium cast iron-ceramic composite lining, which improves wear resistance by 40%, extends service life to more than 15,000 hours, and reduces the frequency of shutdown maintenance.

Cement plants require a lot of heat to burn cement clinker during production, and coal is the main fuel source. Coal vertical roller mill(vrm) can grind lump coal into coal powder, which has a large specific surface area and can fully contact with air during combustion, achieving rapid and full combustion. Vertical coal mill can be used to grind bituminous coal, anthracite and petroleum coke required for clinker burning and power plant combustion system according to the type and amount of additives. The applicable raw coal particle size is 40-50mm, the moisture content of the furnace is ≤15%, and the moisture content of the finished product is ≤1.0%; in terms of the fineness of the finished product, bituminous coal is R80μm=10%-12%, and anthracite is R80μm=1%-3%; the applicable coal grindability index (HGI) range is 40-70. As we all know coal powder is explosive therefore the vertical coal mill has integrated the following considerations:

1. The vertical coal mill uses labyrinth seals and air seals to effectively prevent coal powder from leaking into the external environment and reduce the possibility of coal powder and air forming an explosive mixture. At the same time, it prevents external air from entering the mill to avoid the risk of explosion caused by excessive air. The coal mill is designed with an inerting system, which reduces the oxygen content in the mill to below the explosion limit of coal powder by filling the mill with inert gas (such as nitrogen). The metal parts in the mill are designed with anti-static, such as well-grounded grinding rollers and grinding discs, to prevent coal powder explosions caused by static electricity accumulation. At the same time, anti-static conveying pipes and bags are selected to reduce the risk of static electricity.

2. The VRM coal mill uses tire-shaped roller sleeves to increase the grinding area and pressure, so that the coal powder is more evenly stressed during the grinding process, improving the grinding efficiency. The coal mill is equipped with an efficient dynamic powder concentrator, which can accurately control the fineness of the coal powder. By adjusting the speed and airflow distribution of the powder concentrator, the product particle size distribution is more concentrated, the over-grinding phenomenon is reduced, and the grinding efficiency is improved. The design has a reasonable ventilation path and ventilation volume, which can promptly remove the heat and fine powder generated in the mill, ensure the good fluidity of the material in the mill, and improve the grinding efficiency.

3. The coal vertical mill adopts advanced material layer monitoring and control system. It monitors the material layer thickness on the grinding disc in real time through pressure sensors, and automatically adjusts the pressure of the grinding roller and the feed amount to keep the material layer thickness stable. A stable material layer helps to improve grinding efficiency and reduce the wear of the grinding roller and grinding disc. The grinding roller, grinding disc and other easily worn parts of the coal vertical mill are made of highly wear-resistant materials, such as high-chromium cast iron, tungsten carbide, etc., to extend the service life of the parts and reduce the reduction of grinding efficiency due to wear of the parts.

4. Efficient coal powder collection: The coal mill is equipped with an efficient explosion-proof bag dust collector to efficiently collect coal powder. The dust collection efficiency can usually reach more than 99%, ensuring that the discharged gas meets environmental protection requirements, while maximizing the recovery of coal powder and reducing coal powder loss. The coal mill is equipped with a reasonable coal powder conveying pipeline and conveying equipment, screw conveyors, air chutes, etc., which can smoothly convey the collected coal powder to the coal powder bin or other use locations. The design of the conveying system takes into account the fluidity and explosion-proof requirements of coal powder to ensure the safety and stability of coal powder during the conveying process.

The purpose of grinding cement clinker is to increase the hydration reaction rate, so that it can quickly and fully exert its gelling properties, improve cement fluidity and other properties, and meet the diverse needs of different projects for cement. The vertical mill is used to grind cement clinker because of its high efficiency and energy saving advantages. Compared with traditional equipment, it can save 20% - 30% energy, can accurately control the product fineness and particle size distribution to ensure quality, and can also use the exhaust gas at the kiln tail to dry the material and reduce costs.

1. Maximum clinker feed size of a cement clinker vertical roller mill is 50～80mm, final product fineness is around 3800～4300cm2/g, R80μm≤1%, R45μm≤8%. Note*Output is subject to change according to the type and quantity of additives!

2. One machine two jobs: The modular powder selection and adjustment system of the cement vertical mill is the key to achieving dual-purpose grinding of cement and slag. The system can accurately control the fineness of the finished product (R0.08 sieve residue 8-12%) when grinding cement through replaceable grading impellers and multi-channel airflow control devices; when switching to slag grinding mode, the impeller can be replaced with a large-diameter high-speed model, and the airflow distribution can be adjusted to easily achieve a specific surface area of ​​450-650m²/kg for the slag finished product. By quickly replacing a few core components, the differentiated grinding needs of the two materials can be met, and the equipment utilization rate can be increased by about 50%.

3. Flexible transmission design: The flexible transmission system can effectively buffer the impact caused by uneven feeding and hardness fluctuations of cement clinker. Through elastic couplings and high-precision reducers, the vibration amplitude of the equipment can be reduced by more than 30%, avoiding damage to the transmission components due to severe force during clinker grinding, ensuring stable operation of the equipment, and also enabling the equipment to flexibly adapt to cement grinding conditions, achieving dual-purpose use of one machine.

4. Graded adjustable air ring: The air ring structure is designed to be graded and adjustable. Through modular combination and hydraulic drive adjustment mechanism, the ventilation area and air flow speed can be flexibly adjusted according to the different grinding requirements of cement clinker or finished cement. When grinding clinker, the wind speed can be increased to quickly transport coarse particles; when grinding cement, the wind speed can be reduced to achieve finer classification, and the system resistance is reduced by 15-20%, which significantly improves the grinding efficiency of different materials.

5. Composite wear-resistant lining structure: The surface of the grinding disc and grinding roller adopts a composite wear-resistant lining, the inner layer is high-strength alloy steel to ensure structural strength, and the outer layer is inlaid with tungsten carbide or ceramic patches. In view of the high hardness and high abrasion characteristics of cement clinker, the wear resistance is improved by 40%, and the service life is extended to 18,000 hours. When grinding cement, the risk of iron mixing is reduced to ensure the stable quality of the finished product.

6. Dual-mode powder selection system: The powder selection machine is equipped with a dual-mode switching device. When grinding cement clinker, it adopts an efficient dynamic powder selection mode to quickly separate qualified coarse powder; when grinding cement products, it can be switched to fine classification mode. By adding static classification blades and optimizing the rotor speed, the product fineness R0.08 screen residue control accuracy is increased to ±1%, meeting the precise classification needs of different materials.

A slag vertical roller mill is used for grinding and drying water quenched slag that is generated by blast furnaces into an active material which is then added to the finished cement, by doing so, the performance of cement when used in cement production is improved.

The reason why steel slag and water slag are suitable for grinding with vertical roller mills is that VRM mills are efficient and energy-saving. They can exert greater grinding pressure on materials with high hardness and poor grindability such as steel slag and water slag to achieve efficient grinding, which can reduce energy consumption by 20% - 30% compared with other grinding equipment. At the same time, during the grinding process of the vertical mill, hot air can be used to dry the material, which can effectively deal with the moisture in steel slag and water slag, generally reducing the moisture to less than 1%. Moreover, the vertical mill can accurately control the particle size distribution of the product, so that the ground steel slag and water slag can achieve a higher specific surface area, meeting the requirements of material fineness in different application fields.

The vertical mill can efficiently process slag with a moisture content of < 20% and a particle size of < 10mm. During the grinding process, hot air is used to dry the material and the moisture content of the finished product is precisely controlled to ≤0.5%. At the same time, with the advanced powder selection system, it can stably produce finished products with a fineness of < 4200cm²/g to 5000cm²/g, meeting the application standards of cement admixtures and other fields. In addition, the vertical mill shows significant energy-saving advantages in this process, with a power consumption of < 33 kWh/t, which greatly reduces energy consumption compared to traditional grinding equipment.

1. The power consumption of grinding is lower than that of tube mill (ball mill): vertical mill adopts the principle of material bed grinding. The material forms a material layer between the grinding roller and the grinding disc for extrusion and grinding. Compared with the point contact impact grinding of the steel ball and the material in the tube mill, the energy efficiency conversion is higher. According to industry data, in cement grinding operations, the unit power consumption of vertical mill is generally 28-35 kWh/t, while the power consumption of traditional tube mill is about 38-45 kWh/t. Vertical mill can reduce energy consumption by about 20%-30%, significantly saving production costs.

2. The residence time of raw materials in this mill is much shorter than that of tube mill (ball mill), so the crushing process and mixing process are more coordinated, which is conducive to quality control: the residence time of materials in the vertical mill is usually only 1-2 minutes, while the residence time of materials in the tube mill is as long as 15-30 minutes. The shorter residence time enables the vertical mill to respond quickly to changes in raw material properties and process parameters and adjust the grinding process in time. For example, when the composition of the material entering the mill fluctuates, the vertical mill can complete the adjustment in a short time to stabilize the quality of the finished product; at the same time, the material passes through the mill quickly, reducing the phenomenon of over-grinding, making the particle grading more uniform, and helping to improve the strength and stability of finished products such as cement.

3. Smaller installation space and lower noise: The vertical mill integrates grinding, drying, and powder selection functions in one, and the system is compact. Its footprint is only 50% - 60% of the tube mill system with the same output, and its height is relatively low, which has more flexible requirements for plant space and can greatly save infrastructure investment. In terms of noise control, the vertical mill adopts a sealed structure and shock-absorbing design. The noise value during operation is generally 85-90 decibels, while the noise of the tube mill is usually 100-110 decibels due to steel ball impact and other reasons. The vertical mill can effectively improve the working environment and reduce noise pollution.

4. This type of mill can crush materials that are too large to be fed into a tube mill (ball mill): the feed size of a vertical mill is usually 50-100mm, and some large vertical mills can even accept 150mm materials; while a tube mill generally requires the particle size of the material entering the mill to be less than 25mm, and materials exceeding this particle size must first undergo multiple stages of crushing. The powerful crushing capacity of the vertical mill reduces the configuration of the front-end crushing equipment, simplifies the process flow, reduces equipment investment and operating costs, and can also adapt to working conditions with large fluctuations in raw material particle size.

5. The ground materials are dried using kiln flue gas: the vertical mill system is closely integrated with the kiln, and can directly introduce kiln tail gas with a temperature of 300-400℃ as a drying medium. By rationally designing the ventilation and heat exchange devices in the mill, the exhaust gas is fully in contact with the material, and the moisture content of the material can be quickly reduced from 8%-10% to below 1%, meeting the requirements of grinding and finished product quality. This waste heat utilization method not only reduces the additional drying energy consumption and lowers production costs, but also realizes the secondary utilization of industrial waste gas, reduces waste gas emissions, and complies with the concept of energy conservation and environmental protection.

In the traditional vertical mill system, the raw materials are crushed and ground after entering the grinding disc, and the drying, transportation and separation are achieved by the gas introduced from the kiln tail. If there is no external circulation system, the uncrushed or semi-crushed large pieces of raw materials produced after the grinding disc rotates and grinds, need to rely on the airflow above the grinding disc or keep them inside the grinding disc until they reach the required particle size through the sintering process. The energy consumed in this internal material holding and separation process accounts for about 60% of the total energy consumption of raw material grinding.

Around 1980, the external material circulation system came into being. When the vertical mill adopts this system, the uncrushed materials thrown off the grinding disc will fall into the mechanical transportation equipment such as chain conveyors and bucket elevators under the mill through the air intake box, and will be collected and transported to the new material feeding device and re-sent to the mill. In this process, the uncrushed raw materials no longer rely on gas transportation, which greatly reduces the gas transportation energy consumption of the mill fan and significantly improves the energy utilization efficiency of vertical mill grinding.

In recent years, many existing cement plants are still using tube mills. Due to their high power consumption, the grinding performance is reduced by about 25~30%. Therefore, the optimization and upgrading of the tube mill grinding system has become an urgent need in the industry.

Tube mills mainly rely on the impact and friction between the grinding balls and the raw materials, as well as the collision and friction between the grinding balls and the mill liner to crush the raw materials. Most tube mills are equipped with two grinding chambers, which are responsible for coarse grinding and fine grinding respectively.

The size specifications and distribution of the grinding balls need to be carefully designed and flexibly adjusted according to factors such as raw material characteristics and mill specifications. However, in reality, the energy utilization efficiency of the coarse grinding chamber is extremely low, and it is difficult to achieve significant improvement in coarse grinding and fine grinding performance on the same tube mill by simply adjusting the size of the balls.

In order to break through this dilemma, the industry has proposed and developed a new system: the main difference between the pre-powder vertical mill and the ordinary vertical mill is the different functional focus. The pre-grinding vertical mill is mainly used for pre-grinding of materials. It prepares for the subsequent grinding process by quickly crushing the block materials and preliminarily grinding them into smaller particles, which reduces the load on the subsequent grinding equipment. Simply put, the difference from the ordinary vertical mill is that the pre-grinding vertical mill does not have a powder selector and the fineness of the finished product does not need to be controlled. After the successful development of this system, it not only greatly reduced the unit energy consumption, but also significantly improved the production capacity. At present, this system has been implemented in more than 200 factories in China. After adopting the roller mill pre-grinding machine, the factory output has increased by 30~50%

1. Tongli Heavy Machinery has built an advanced vertical mill test platform based on its self-built professional test research center. The platform can simulate a variety of complex working conditions and conduct a full range of grinding tests and performance tests for materials of different hardness, humidity, and particle size, such as cement raw materials, slag, coal gangue, etc., so as to accurately match the most suitable vertical mill model and configuration scheme, ensuring that the most suitable solution is provided to customers.

2. Tongli Heavy Machinery's professional R&D team uses advanced finite element analysis (FEA) software, combined with 65+ years of practical experience, to conduct in-depth analysis, precise calculation and optimization design of core components such as grinding roller shafts, rocker arms, and grinding discs. Through the careful selection of component materials (such as high-strength alloy steel, etc.) and innovative improvements in structure (such as optimizing the transition design of stress concentration parts), not only the structural strength and wear resistance of each component are significantly improved, but also the overall service life of the equipment is extended, ensuring that the equipment remains stable and reliable under long-term and high-load operation.

3. In terms of fluid dynamics optimization, Tongli Heavy Machinery introduced the world's leading fluid flow simulation software, and combined with self-developed simulation technology, carried out refined simulation analysis of the air flow field and material flow inside the vertical grinding mill. By repeatedly optimizing the internal air duct structure of the mill, the angle of the guide vane of the powder selector and other key parts, the internal resistance was effectively reduced, the dispersion and classification efficiency of the material were improved, and the optimal configuration of fluid dynamics in the grinding process was achieved, further improving the grinding efficiency and energy saving effect of the equipment.

4. With its deep technical accumulation and innovation capabilities, Tongli Heavy Machinery and NGC jointly developed a high-performance large vertical planetary gear reducer. The reducer adopts a unique one-stage bevel gear and two-stage planetary gear transmission structure, combined with high-precision gear processing technology (such as gear grinding technology to ensure tooth surface accuracy) and advanced heat treatment technology (to improve the hardness and toughness of the gear), so that the transmission accuracy reaches the industry-leading level, the stress distribution is more uniform, and it has super bearing capacity. Its gearbox service factor is as high as 2.8 (far exceeding the AGMA standard requirements), which can easily cope with various harsh working conditions and heavy loads, providing solid and reliable power transmission guarantee for the stable operation of the vertical mill.

5. The new generation of O-sepa and T-sepax vertical mill dynamic classifiers independently developed by Tongli Heavy Machinery adopt innovative aerodynamic design and intelligent control technology, and are integrated into the vertical mill. The classifier optimizes the blade shape, number and speed of the classifying rotor, combined with a high-precision variable frequency speed regulation system, to achieve precise control of the product particle size, with a classification accuracy of more than 95%. At the same time, it has high classification efficiency, extremely low pressure loss and energy consumption levels, which can meet the diverse and strict requirements of different industries for finished product particle size.

6. The DCS intelligent control system equipped by Tongli Heavy Machinery is equipped with advanced Omron speed sensors and automation control modules, which can monitor and analyze the operating parameters of the equipment (such as mill temperature, pressure, speed, material layer thickness, etc.) in real time and accurately. The system uses an intuitive and easy-to-use touch screen operation interface, supports multiple control modes (manual, automatic, semi-automatic), and has fault warning, intelligent diagnosis and adaptive adjustment functions.

7. Tongli Heavy Machinery provides customers with a one-stop solution covering the entire process, from early process consultation, equipment selection and design, to mid-term project planning and design, equipment customization configuration, to later on-site installation and commissioning, operator training, until the final turnkey project acceptance and delivery, follow up throughout the process to ensure the smooth implementation and efficient operation of the project.

Multiple aspects must be focused on during operation to ensure normal operation.

First, a stable material layer with appropriate thickness must be maintained. Too thick or too thin a layer will reduce grinding efficiency and damage the equipment. Secondly, the vibration of the mill must be controlled, as it is affected by many factors such as grinding pressure and material layer thickness.

Furthermore, the grinding pressure should be adjusted according to the characteristics of the material. Too high or too low a pressure will affect output, quality, and equipment stability. At the same time, the gas temperature at the outlet must be moderate to avoid damage to the equipment and production caused by excessively high or low temperatures.

In addition, the air volume in the mill must match the feed rate, and the hot air discharged from the rotary kiln should also be reasonably regulated to maintain the system pressure balance.

To stabilize the material layer in vertical mill operation, control feeding amount (fluctuation ≤±20t/h, moisture 2%-5%), adjust grinding pressure (8-14MPa), set powder selector speed (60-100r/min), control ventilation volume, monitor layer thickness (40-50mm) and maintain equipment. Please check the following aspects:

1. Feeding amount control: The feeding amount should be precisely controlled according to the production capacity of the vertical mill. For example, when the design output of a certain model of vertical mill is 500t/h, the feeding amount should be stable between 480-520t/h, and the fluctuation range should be controlled within ±20t/h as much as possible to avoid fluctuations in the material layer due to large changes in feeding. At the same time, it is necessary to ensure that the comprehensive moisture content of the material entering the mill is between 2% and 5%. If the material is too dry and too fine, it will be difficult to form a stable material layer; if it is too wet, it will affect the grinding efficiency and equipment operation.

2. Grinding pressure adjustment: The grinding pressure needs to be adjusted according to the thickness of the material layer and the properties of the material. Generally speaking, for materials with good grindability, the grinding pressure can be controlled at 8-10MPa; for materials that are difficult to grind, the pressure can be appropriately increased to 10-12MPa. When the material layer thickness exceeds the set value, such as reaching 60-70mm (normal material layer thickness is generally controlled at 40-50mm), the grinding pressure can be increased by 1-2MPa to make the material layer thinner; if the material layer thickness is less than 30mm, the grinding pressure can be reduced by 1-2MPa to prevent excessive grinding and equipment vibration.

3. Adjustment of powder selector speed: The speed of the powder selector affects the fineness of the finished product and the thickness of the material layer. When the product quality requirements are high and finer finished products are required, the speed of the powder selector can be set at 80-100r/min; if the requirements for the fineness of the finished product are low, the speed can be appropriately reduced to 60-80r/min. When it is found that the material layer is gradually thickening, the speed of the powder selector can be appropriately increased by 1-2r/min to speed up the discharge of fine powder and make the material layer thinner; conversely, the speed is reduced when the material layer becomes thinner.

4. Ventilation volume control: Reasonable ventilation volume is the key to stabilizing the material layer. Usually, the ventilation volume of the vertical mill needs to be determined according to the specifications and production capacity of the mill. For example, for a vertical mill with a diameter of 5m, the ventilation volume is generally controlled at 180,000-220,000 m³/h. If the ventilation volume is too large, the material will stay in the mill for a short time and the material layer will become thinner; if the ventilation volume is too small, the material cannot be discharged in time and the material layer will become thicker. The ventilation volume can be controlled by adjusting the fan valve to keep the parameters of the mill pressure drop, mill inlet negative pressure, mill outlet negative pressure stable. Generally speaking, the pressure drop of the mill is stable at 4000-5000Pa, the mill inlet negative pressure is -2000--3000Pa, and the mill outlet negative pressure is -500--1000Pa, which can ensure the stability of the material layer.

5. Material layer thickness monitoring: The material layer thickness is monitored in real time by a material layer thickness monitoring device installed in the mill, such as a radar level meter, an ultrasonic level meter, etc. The set value of the material layer thickness is controlled at 40-50mm. When the monitoring data shows that the material layer thickness exceeds this range, the relevant operating parameters are adjusted in time.

6. Equipment maintenance: Regularly check the wear of the grinding roller and grinding disc. It is recommended that when the roller skin wear reaches 30mm from the highest point to the lowest point, it should be used after flanging to increase the life of the roller skin; the roller skin needs to be replaced when the sum of the wear of the roller skin and the grinding disc liner reaches 120-150mm. At the same time, ensure the normal operation of the hydraulic system, lubrication system, etc. to provide guarantee for the stable operation of the vertical mill.

In order toreduce the vibration, the operator can check the following methods: Adjust feed rate, adjust grinding pressure, adjust powder separator spindle speed, reset the ventilation volume. Details are as follows:

1. Maintaining a stable feed rate is the basis for controlling the stability of the material layer. According to the production capacity and material characteristics of the vertical mill, set the appropriate feed rate and accurately control it through the feeding equipment. At the same time, pay attention to the particle size distribution and moisture content of the material.

2. Grinding pressure adjustment: When the material layer thickens, increase the grinding pressure appropriately to enhance the grinding effect and make the material layer thinner; when the material layer thins, reduce the grinding pressure appropriately to prevent excessive grinding and equipment vibration.

3. Powder selector speed adjustment: The speed of the powder selector affects the fineness of the finished product and the thickness of the material layer. If the speed is too fast, the finished product will be too fine, and a large amount of fine powder will return to the grinding disc, resulting in a thickening of the material layer; if the speed is too slow, the finished product will be coarse and the material layer will gradually become thinner.

4. Ventilation volume control: If the ventilation volume is too large, the material will stay in the mill for a short time and the material layer will become thinner; if the ventilation volume is too small, the material cannot be discharged in time, which will make the material layer thicker.

5. Material layer thickness monitoring: The material layer thickness is monitored in real time through the material layer thickness monitoring device installed in the mill, such as radar level meter, ultrasonic level meter, etc. The operator adjusts the relevant operating parameters in time according to the monitoring data to keep the material layer thickness within the set range.

When determining the correct grinding roller pressure, we can adjust roller pressure in vertical mill operation based on multiple factors. Consider grindability (8 - 14MPa), particle size, humidity. Adjust according to material layer thickness (±0.5 - 1.1MPa), main motor current (85% - 90% of rated), and vibration value (≤7.2mm/s).

1. Grindability: For materials with good grindability, the roller pressure can be appropriately reduced, generally at 8-10MPa; for materials that are difficult to grind, the pressure needs to be increased and can be controlled at 10-14MPa. For example, for easy-to-grind materials such as limestone, a lower pressure can achieve a better grinding effect; while for difficult-to-grind materials such as iron ore, a higher pressure is required.

2. Particle size and humidity: When the material particle size is large or the humidity is high, a larger roller pressure is required for crushing and grinding. When the material particle size is 20-30mm, the roller pressure can be set at 10-12MPa; if the material humidity increases to 5%-8%, the pressure can be increased by 1-2MPa accordingly.

3. Thickening of the material layer: When the material layer thickness exceeds the set value, such as reaching 60-70mm (normal material layer thickness is generally 40-50mm), the roller pressure should be gradually increased by 0.5-1.1MPa each time to make the material layer thinner and improve the grinding efficiency.

4. Thinning of the material layer: If the material layer thickness is less than 30mm, it means that the roller pressure may be too large, and it is necessary to reduce the pressure appropriately, by 0.5-1MPa each time, to prevent excessive grinding and equipment vibration, and to avoid the material layer being too thin, causing the roller to directly contact the grinding disc and damage the equipment.

5. motor current: When the main motor current increases, it means that the mill load increases, which may be due to excessive roller pressure or excessive material volume. At this time, the roller pressure or the feed amount should be appropriately reduced according to the actual situation; if the main motor current is too low, it may be due to insufficient roller pressure, and the pressure can be appropriately increased. Generally, the main motor current should be controlled between 85%-90% of the rated current.

6. Mill vibration value: mill vibration value is also an important reference indicator for adjusting roller pressure. When the vibration value exceeds the normal range (generally the vibration intensity does not exceed 7.2mm/s), it may be that the roller pressure is too high or the material properties have changed, and the roller pressure needs to be reduced; if the vibration value is small and the grinding effect is not good, the pressure can be appropriately increased.

Air volume is very import in terms of controling the output of the vertical roller mill, The air volume of the vertical mill should be adjusted according to the actual production situation. You can refer to the thickness of the material layer. If it is thick, increase the air volume; if it is thin, reduce the air volume; according to the pressure difference of the mill, increase the air volume if it increases, and reduce the air volume if it decreases; according to the main motor current, increase the air volume if it increases, and reduce the air volume if it decreases; combined with the vibration of the mill, if it is violent and the wind is strong, reduce the air volume; if the vibration is small and the grinding is poor, increase the air volume; according to the product fineness requirements, increase the air volume if it is high, and reduce the air volume if it is low.

1. Adjust according to the thickness of the material layer: The thickness of the material layer is generally controlled at 40-50mm. If the material layer becomes thicker, such as exceeding 60-70mm, the air volume can be appropriately increased to speed up the circulation of the material in the mill by increasing the air flow speed, thereby thinning the material layer; if the thickness of the material layer is less than 30mm, the air volume can be appropriately reduced to reduce the circulation speed of the material and restore the thickness of the material layer to normal.

2. Adjust according to the pressure difference of the mill: When the mill is operating normally, the pressure difference is generally stable at 4000-5000Pa. When the pressure difference increases, it means that the ventilation resistance in the mill increases, which may be insufficient air volume. At this time, the air volume should be increased, which can be achieved by increasing the power of the circulating fan or increasing the opening of the kiln tail exhaust fan; if the pressure difference decreases, it may be that the air volume is too large, and the air volume needs to be appropriately reduced.

3. Refer to the main motor current adjustment: The main motor current is generally controlled at 85%-90% of the rated current. If the current increases, it may be caused by too much material in the mill or insufficient air volume. If it is determined that the air volume is a problem, the air volume should be increased; if the current decreases, it may be that the air volume is too large, causing the material to stay in the mill for too short a time. At this time, the air volume needs to be reduced.

4. Adjust according to the vibration of the mill: Under normal circumstances, the vibration intensity of the mill does not exceed 7.2mm/s. When the mill vibrates violently, if it is accompanied by other manifestations of excessive air volume, such as reduced pressure difference, thinning of the material layer, etc., the air volume should be reduced; if the mill vibrates less but the grinding effect is not good, the air volume can be appropriately increased.

5. Adjust according to the product fineness requirements: If the product fineness requirements are high, the air volume needs to be appropriately increased so that the fine powder can be taken out of the mill in time by the air flow to avoid over-grinding; if the product fineness requirements are low, the air volume can be appropriately reduced to allow the material to have more grinding time in the mill and increase production.

The outlet gas temperature will not affect the residence time and movement state of the material in the mill, on the other hand it is a indication of the operation status of the vertical roller mill. When the temperature is too low, the material will stay in the mill for a long time, which may lead to over-grinding and increase the content of fine particles in the product; when the temperature is too high, the material flow rate is too fast, which may increase the content of coarse particles in the product and affect the particle size distribution and specific surface area of ​​the product.

If the gas temperature at the discharge port is too low, it means that the moisture in the material cannot be fully evaporated, which will lead to too high moisture content in the finished product, affecting product quality, and may also cause problems such as agglomeration and pipe clogging during transportation; while if the temperature is too high, although the material drying effect is good, it may cause excessive drying of the material, increase dust, and waste energy.

Appropriate gas temperature at the discharge port helps maintain a good grinding environment in the mill. If the temperature is too low, the material is easily affected by moisture and the fluidity becomes poor, which will slow down the flow rate of the material during the grinding process and reduce the grinding efficiency; if the temperature is too high, the gas in the mill will expand too violently, increase the ventilation resistance of the system, and damage the components such as the mill lining due to thermal stress.

Large fluctuations in the gas temperature at the discharge port will cause thermal shock to the equipment, which will accelerate the wear of the equipment in the long term. Excessive temperature may cause deformation of components such as grinding rollers and grinding discs, affecting their contact with the material and the grinding effect; if the temperature is too low, some components may be damaged due to low-temperature embrittlement. In addition, abnormal temperature may also affect the normal operation of subsequent equipment such as dust collectors. For example, if the temperature is too high, the dust collection bag may burn, and if the temperature is too low, condensation may occur inside the dust collector, affecting the dust collection effect.

The gas temperature will affect the residence time and movement state of the material in the mill. When the temperature is too low, the material stays in the mill for a long time, which may lead to over-grinding and increase the content of fine particles in the product; when the temperature is too high and the material flow rate is too fast, the content of coarse particles in the product may increase, affecting the particle grading and specific surface area of ​​the product, and thus affecting the performance of the product.

A lot of factory owner wants to have better quality product to win the market, the surface area of the cement powder is the key to that, in order to increase the specific surface area of the cement powder, the following actions could be helpful:

Generally, when the pressure is increased by 10%-15%, the material can be ground more fully and the specific surface area of ​​the finished product can be increased by 50-100㎡/kg. However, excessive pressure will accelerate equipment wear.

Reduce the wind speed in the mill from 45m/s to 40m/s, and the residence time of the material in the mill will be extended by about 10%-15%. The specific surface area is expected to increase by 80-120㎡/kg. However, too low a wind speed will affect the output. Increase the speed of the powder concentrator. For every 10r/min increase in speed, the proportion of fine particles in the finished product increases by 5%-8%, and the specific surface area increases by 60-100㎡/kg.

In terms of material properties, reducing the particle size of the material entering the mill from 50mm to 30mm can improve the grindability by 15%-20%, and the specific surface area of ​​the finished product can be increased by 70-100㎡/kg; controlling the moisture content of the material entering the mill at 1%-2%, the specific surface area can be increased by about 100-150㎡/kg compared to 3%-4% moisture.

In terms of equipment maintenance, regularly replace the grinding rollers and grinding discs that are worn beyond the standard to ensure the grinding effect and keep the specific surface area at a stable level; ensure that the equipment is well sealed to avoid a decrease of 100-150㎡/kg in the specific surface area due to air leakage.