Tongli specializes in the production of various limestone grinding vertical ball mill and portland cement clinker ball mills with diameters ranging from 2m~16m.
Tongli's Portland Cement Clinker Ball Mill Grinding Plant Solution covers the main areas of cement raw material grinding, clinker grinding, slag grinding and coal powder preparation. It is one of the ball mill manufacturers with the most complete product range in the industry. The most famous is the PO42.5 cement clinker ball mill, which grinds the hardened cement clinker particles into fine powder by rotation grinding and impact, and mixes with gypsum, slag and other materials to form finished cement. The second is the ASTM C1157 cement raw material ball mill, which is mainly used to grind raw materials such as limestone to provide high-quality raw materials for the production of portland cement. We also provide slag ball mills, which are specially used to grind slag into fine powder and add it to cement to improve the performance of the finished product. In addition, our coal grinding ball mill is used to grind coal powder to provide efficient and uniform fuel for cement rotary kiln burner. With many years of R&D, Tongli has become one of the manufacturers with the strongest comprehensive production capacity in the world in the field of ball mill manufacturing.

Portland Cement Clinker Grinding Plant Equipment List:

"Efficiently grind limestone for high-quality PO42.5 cement production with our advanced cement limestone ball mill, ensuring precision, durability."

"Achieve superior performance in cement manufacturing with our ASTM C1157 cement clinker grinding ball mill, designed for high throughput and optimal energy efficiency."

"Enhance your cement properties with our granulated blast furnace slag grinding ball mill, delivering consistent, fine powder for premium-quality cement."

"Maximize combustion efficiency with our coal grinding ball mill pulverizer, engineered for reliable and efficient coal powder preparation."
CEMENT CLINKER GRINDING PLANT ADVANTAGES
High grinding efficiency: Tongli ball mill adopts advanced grinding technology and optimized design. Its grinding efficiency is significantly higher than that of others, which can greatly shorten the cement production cycle and increase the overall output of the production line.
Stable product quality: Through precise grinding control, Tongli ball mill can ensure the fineness and uniformity of the output material. The quality of the finished cement is stable and meets various high standards, further enhancing the market competitiveness.
Energy saving and green: compared with traditional ball mills, energy consumption is reduced by 15%-30%; at the same time, it adopts a sealed structure design and overall negative pressure operation, which significantly reduces dust leakage.
Low operating noise: Tongli Cement clinker ball mill grinding plant is equipped with a "zero emission negative pressure operation system" and sound insulation device, which significantly reduces the noise during the production process to 85db, making it suitable for customers with high requirements for environmental protection and factory environment.
Adjustable particle size: The equipment is equipped with automatic discharging and regrinding system, and the particle size of inlet and outlet materials is adjustable to meet different process requirements; the optimized design of lubrication structure reduces internal wear and enables the equipment to operate continuously for a long time.
Strong versatility: Tongli ball mills are suitable for grinding a variety of materials, including high-hardness metal ores, non-metallic ores, slag and sintered materials, etc., and are widely used in cement, mining, metallurgy and other industries.
Easy maintenance: With modular design and high-reliability components, Tongli ball mill is easy and quick to maintain, with low failure rate, which can effectively reduce equipment downtime and operating costs.
Strong material adaptability: The equipment can be manufactured in different specifications and sizes according to customer needs, and can flexibly adapt to various production scales to meet the diverse needs from small and medium-sized factories to large industrial projects.
Cement Clinker Grinding Plant Production Process

1. Raw material crushing
The first step of the Tongli grinding station is to crush the raw materials limestone, clay, and iron ore into particles suitable for grinding. This process is completed using jaw crushers and hammer crushers. The particle size of the discharge is controlled below 20-25 mm, depending on the requirements of the process flow. For a production line with an annual output of 1 million tons of cement, the crusher's processing capacity needs to reach 150-200 tons/hour.
2. Limestone ball mill grinding
The crushed raw materials are fed into the cement raw material ball mill for grinding. The ball mill squeezes and grinds the material through the steel balls in the cylinder to generate uniform raw material powder (the fineness is generally controlled at 80μm sieve residue <12%). In order to improve the grinding efficiency, grinding aids can be added during the grinding process. The raw material ball mill of a production line usually has a power of 1500-3000kW and an hourly output of 50-120 tons.
3. Cement clinker grinding
The fired cement clinker is sent to the clinker ball mill through a conveying device and ground with mixed materials such as gypsum and slag to produce finished cement. The clinker ball mill is usually equipped with a high-efficiency powder classifier to separate ultrafine particles and coarse particles. The fineness of the finished cement is generally controlled at 80μm sieve residue <10%, and the specific surface area is about 320-380m²/kg. The power of a clinker ball mill is usually 3000-5000kW, and the hourly production capacity is 50-150 tons.
4. Powder Classification
During the ball mill grinding process, the coarse particles that do not meet the fineness requirements are separated by the powder classifier and returned to the ball mill for re-grinding, while the fine powder that meets the requirements is sent to the next process through the airflow. This circulation system can effectively improve the grinding efficiency and product quality, and the powder selection efficiency can usually reach more than 80%.
5. Packaging
The qualified cement is transported to the storage silo by conveying equipment (such as screw conveyors or pneumatic conveying devices), and then enters the packaging system. The packaging system generally uses automated equipment to bag the cement (usually 50 kg/bag) or store and transport it in bulk. The processing capacity of the packaging machine is usually 100-200 tons/hour to meet the needs of efficient shipment.
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WHY CHOOSE US
"This clinker ball mill is so important in our production line. The grinding fineness is very uniform, the energy consumption is 15% lower than that of other equipment, and the output is higher. I am very satisfied with it!"

CFO
"The production efficiency increased by roughly 30%, the equipment runs smoothly, highly recommended"

CEO
"Slag grinding has always been a challenge for us. Their ball mill not only has good grinding effect, but also stable. The quality of cement has been significantly improved, and customer feedback has also been better."

CEO
"We tried many coal powder preparation equipment and finally chose this ball mill. The coal powder produced is fine and uniform, and the combustion efficiency is greatly improved, which helps us save a lot of fuel costs."

CEO
FAQ
Grinding systems can be divided into two main types: open-circuit systems and closed-circuit systems. Open-circuit systems have simple processes, fewer equipment requirements, lower investment costs, and are easier to operate. However, in open-circuit systems, all material must reach the desired fineness before exiting the mill. This can lead to over-grinding of finer particles, which hinders further grinding of coarse material, reduces grinding efficiency, and increases energy consumption.
In contrast, closed-circuit systems prevent over-grinding, enhance production efficiency, and ensure uniform product fineness. Due to these advantages, as well as energy savings and the need for improved product quality, modern cement plants typically adopt single-stage closed-circuit grinding systems.
In order to increase the output of the grinding mill and reduce the cost of cement production, domestic cement scholars and experts have proposed a cement grinding process of "reducing the particle size of the raw materials entering the mill, replacing grinding with crushing, increasing the output of the mill, and reducing power consumption" after years of scientific experiments and production practice. Even if the particle size of the raw materials entering the mill is reduced to less than 3 mm, the first bin work part of the ball mill is moved outside the mill to be completed by the crusher, and the crushing efficiency of the crusher reaches 25% to 40%.
1. Clinker unloading and conveying system
Clinker is transported from the nearby clinker base into the closed clinker shed in the factory by means of transportation, and then directly unloaded into the clinker unloading pit, and then transported to the clinker storage warehouse by the elevator for storage. There is a large bag dust collector in the unloading pit to collect the dust raised by the unloading and directly drop it onto the belt conveyor to reduce dust emissions.
2. Storage and warehousing of raw materials
Gypsum, stone, slag and other auxiliary materials are first stored in the pile shed. Gypsum and stone are crushed by jaw crushers and then enter the batching warehouse through elevators. Slag is dried in a drying furnace and directly enters the slag warehouse. Fly ash is directly transported to the fly ash warehouse by car, and the bag dust collector on the top of the warehouse filters the gas used to transport fly ash and then discharges it.
3. Cement batching and transportation
Depending on the type of cement produced, clinker, gypsum and mixed materials are weighed by the belt scale at the bottom of the batching warehouse and fed to the elevator by a belt conveyor. The quality control system controls the proportion and feeding amount of the raw materials and sends them to the cement mill system via the belt conveyor.
4. Raw materials limestone & portland cement clinker pre-crushing
According to relevant reports at home and abroad, the use of a crusher for pre-crushing can reduce the power consumption of cement production to 10% to 20%, and the system output of the cement mill can be increased by about 30%. After pre-crushing, due to the narrowing of the particle size distribution of the clinker entering the mill, the particle distribution of the cement leaving the mill has also improved, the average particle size and characteristic particle size of the cement have also been reduced compared to before, and the uniformity coefficient has been improved, thereby increasing the strength of the cement product.
To solve the problem of iron removal in the material using a pre-crushing system, it is necessary to add an iron remover before crushing to prevent metal iron from entering the crusher and causing damage to it. The iron remover can be an electromagnetic pulley or a suspended self-unloading electromagnetic iron remover. In addition, due to the significant reduction in the particle size of the raw materials entering the mill, during the implementation process, the grinding body grading and internal structure of each working chamber of the ball mill should be adjusted accordingly based on the particle distribution of the clinker after pre-crushing. It is best to choose steel segments for the grinding body.
5. Pre-grinding process
Cement grinding uses the pre-grinding process. In addition to being used in the new dry process clinker production line, it is also an important process in the production of slag cement. Therefore, pre-grinding has become a must-have solution for new factories and old factories to carry out technical transformation. Pre-grinding equipment mainly includes roller press, vertical mill and ball mill. From the perspective of energy utilization, roller press has a slight advantage over vertical mill and ball mill.
From the perspective of feed particle size adaptability and operation stability, vertical mill and ball mill have more advantages than roller press. From the current usage situation in my country, whether it is roller press, vertical mill or ball mill as pre-grinding equipment, it can increase production, save energy and reduce emissions, and the increase in production capacity has reached 30% to 50%.
In comparison, roller press and vertical mill are more difficult to use and maintain, while ball mill is less difficult to use and maintain. Compared with roller press and ball mill, vertical mill has higher operation rate, longer roller surface life cycle, which can reach more than 20,000 hours, and simple maintenance, but the capital investment of vertical mill is relatively high. In the production process of slag cement, when using pre-grinding process, it is best to choose ball mill as pre-grinding equipment.
6. Cement grinding
Clinker, gypsum and gravel are fed to the elevator by a belt conveyor, and are transported to the cement mill by the elevator through a chute for powdering; a small amount of dust-containing gas coming out of the cyclone passes through the circulating fan to become circulating air, and reaches the secondary air inlet of the O-Sepa powder selector, where it is collected by a high-concentration bag dust collector and becomes part of the finished product. The cement out of the mill is transported to the O-Sepa powder selector through the elevator and chute. The fine powder selected by the powder selector is collected by a high-concentration bag dust collector to become the finished product, and the coarse powder selected by the powder selector is returned to the mill for re-grinding. The cement mill is equipped with a mill load control system, which controls the technical parameters such as the feeding amount and air volume into the mill through a computer.
7. Negative pressure closed-circuit high-efficiency cement powder selection system
In order to further increase the output of cement mill and ensure the fineness of cement, we transformed the grinding system of No. 1 cement production line in 2003, from the original open-circuit grinding production process to the closed-circuit grinding production process, using cyclone powder selector as the powder selection equipment. After the transformation of the cement mill, the output increased from the original 13.5t/h. to 15.5t/h, increasing the output by about 15%.
In the closed-circuit cement grinding system, the performance and efficiency of the powder selector have a direct impact on the technical and economic indicators of the grinding system. The third-generation high-efficiency powder selectors currently being promoted are cage-type powder selectors improved under the inspiration of the working principle of the O-sepa powder selector, and their performance is basically similar.
8. Cement storage and bulk
The finished products collected by the high-concentration bag dust collector are transported by air conveying chute and elevator to 6 continuous warehouses of 20m42m
for storage, with a storage capacity of 17,800t. The cement warehouse side is equipped with a bulk loader at the bottom of the warehouse.
9. Cement packaging and platform delivery
The cement warehouse is equipped with a warehouse bottom unloading device, which is sent to the packaging workshop for packaging by a screw conveyor. The packaging workshop has 2 14-mouth rotary packaging machines with a packaging capacity of 96×2t/h. The packaged cement is transported to the cement finished product warehouse by a belt conveyor for storage and shipped out from the delivery platform.
10. Improvement of the internal structure of the ball mill
The internal structure of the ball mill also has an important impact on its grinding capacity. The modification of the closed-circuit grinding system is mainly focused on the mill lining, the compartment grate and the grinding body grading. The first bin usually uses a step lining with a relatively strong lifting capacity, and the second bin uses a grading lining.
Most of the grading linings in the second bin are a combination of two types of linings, which is conducive to the grading of the grinding body and fully demonstrates the grinding effect. The first bin of the 2×7.0m closed-circuit cement mill used a corrugated lining in the original design. Because the corrugated lining did not have an ideal lifting capacity for the steel balls, the impact crushing capacity of the first bin was insufficient. Therefore, we replaced the first bin with a step lining, which increased the hourly output of the mill by about 5%.
The grading of the grinding body in the mill has always been one of the hot spots in cement grinding technology. There are also many influencing factors. The physical properties of the grinding material, such as the particle size and grindability, should be considered comprehensively, and the matching with the powder selector, the screen curve of the material in the mill, and the strength requirements of the finished cement should be considered.
When designing and selecting, we should fully understand the characteristics of each process and the performance of the equipment, consider various factors, and determine the selection scheme based on the technical and economic comparison of multiple schemes. When selecting grinding processes and equipment, we should generally pay attention to the following factors:
1. The properties of the material to be ground
Including the particle size, grindability, abrasiveness, moisture, temperature, adhesion and drying performance of the material, so as to select the grinding process and equipment suitable for it.
2. The fineness and particle distribution of the grinding product
Choose an open circuit process or a closed circuit process, as well as the type of material grading equipment according to the fineness and particle distribution.
3. The scale of the factory
Determine the specifications, number of mills, mill process and equipment standards, and workshop investment according to the size of the factory or the hourly production requirements of the workshop.
4. Domestic equipment manufacturing and use
Try to use domestically mature equipment and processes, and consider their design and manufacturing experience and use effects when selecting.
5. Grinding energy consumption
Try to choose processes and equipment with high grinding efficiency and low energy consumption.
6. Waste heat utilization
Make full use of waste heat resources in the production process.
7. Workshop investment
Select appropriate equipment and processes according to workshop construction and financial conditions.
When choosing a suitable grinding system, the first thing to consider is the output and process route, followed by the investment budget and climate environment.
1. Open-circuit medium-long ball mill or ball mill
The dry open-circuit grinding process is simple and requires less capital investment in the workshop, but it is easy to produce over-grinding, resulting in low grinding efficiency and high power consumption.
2. First-level closed-circuit medium-ball mill or ball mill
The process of this grinding system is simpler than other closed-circuit systems, and it has the characteristics of strong grinding capacity, high efficiency, high single-machine production capacity and low power consumption. However, it is slightly more complicated than the open-circuit system, with more auxiliary facilities, and the comprehensive power consumption is equivalent to that of the open-circuit system.
3. Tail unloading lifting circulation drying ball mill
The raw materials and hot air enter from the grinding head, and the ground materials are discharged from the tail of the mill and lifted to the powder selector. Its circulation load is large, the powder selection efficiency is high, so the grinding efficiency is high, and the system has less air leakage.
4. Wind sweeping ball mill
The process is simple, the mill is short and coarse, and the inlet and outlet space is large. The mill tail has a discharging grate plate with low ventilation resistance, which can pass more hot air, so it has a strong drying capacity.
5. Vertical roller mill
Vertical mill has many advantages in drying raw materials, such as reasonable grinding method, high efficiency, low power consumption, large feed particle size, strong drying capacity, simple system, no need for additional grading equipment, good sealing, low noise and dust, and small footprint. However, it is sensitive to corrosive materials and is not suitable for grinding materials with high hardness or high flint and quartz content.
In the design of the first-level closed-circuit system of the medium and long tube ball mill, the annual output of cement is 518,720 tons, the mill specifications are 2.7×4 meters (a total of 4 units), the powder selector specifications are 5 meters in diameter (4 units), and the average production capacity is 34.2 tons/hour. The equipment utilization rate reaches 86.6%, and the total equipment weight is 518.435 tons. The plant covers an area of 904 square meters, the total equipment power is 2659.9 kilowatts, and the capital construction investment is $282,688. The unit investment is $0.566/ton of cement, the unit processing fee is $0.491/ton of cement, and the unit power consumption is 33.422 watts/ton of cement. The unit ball and liner consumption is 0.976 kg/ton of cement, the unit equipment weight is 0.999 kg/ton of cement, and the unit power is 0.0052 watts/ton of cement. The labor productivity is 28,120 tons/worker/year.
The annual cement output of the first-level closed-circuit system of the medium-unloading tube ball mill is 518,720 tons. The mill specifications are 2.8×11 meters (2 units in total), the powder selector specifications are 4.2 meters in diameter (4 units), and the average production capacity is 37.86 tons/hour. The equipment utilization rate is 78.6%, and the total equipment weight is 490.07 tons. The plant covers an area of 991 square meters, the total equipment power is 2690.5 kilowatts, and the capital construction investment is $290,374. The unit investment is $0.491/ton of cement, the unit processing fee is $0.481/ton of cement, and the unit power consumption is 28.90 watts/ton of cement. The unit ball and liner consumption is 0.817 kg/ton of cement, the unit equipment weight is 0.946 kg/ton of cement, and the unit power is 0.0053 watts/ton of cement. The labor productivity is 28,820 tons/worker/year.
In the design of the ball mill secondary closed-circuit ball millsystem, the annual output of cement is 518,720 tons, the mill specifications are 3×10 meters (2 units in total), the powder selector specifications are 5 meters in diameter (2 units), and the average production capacity is 39.22 tons/hour. The equipment utilization rate is 75.9%, and the total equipment weight is 486.72 tons. The plant covers an area of 892 square meters, the total equipment power is 2788.5 kilowatts, and the capital construction investment is $278,491. The unit investment is $0.544/ton of cement, the unit processing fee is $0.567/ton of cement, and the unit power consumption is 29.03 watts/ton of cement. The unit ball and liner consumption is 0.85 kg/ton of cement, the unit equipment weight is 0.939 kg/ton of cement, and the unit power is 0.0055 watts/ton of cement. The labor productivity is 37,060 tons/worker/year.
From the data in the table, it can be seen that the medium-long ball mill system is the best in terms of overall technical and economic indicators, followed by the first-level closed-circuit middle-unloading mill, and the second-level closed-circuit end mill is the worst. The closed-circuit medium-long mill system is more suitable for grinding cement of different finenesses and meeting the needs of production of different specifications, while the first-level closed-circuit long mill has a longer retention time in the mill, which weakens the classification effect, and its technical and economic indicators are not as good as those of the first-level closed-circuit medium-long mill.
1. Ball mill selection
Closed-circuit grinding systems include mid-discharge ball mill systems and end-discharge ball mill systems. Mid-discharge systems discharge material peripherally from the middle of the mill's chamber, with drying air introduced from both the head and tail of the mill. These systems have better drying capabilities and can process higher-moisture materials. However, their mechanical design is complex and requires more maintenance.
End-discharge systems release material at the ball mill’s tail, but their drying capability is limited due to airflow constraints imposed by internal partitions. They are suitable for grinding materials with low moisture content and are preferred for their simpler maintenance requirements. Based on the need for easier maintenance, the selected design employs an end-discharge lifting grinding system.
2. Powder separator/classifier selection
The most common separators include through-flow separators, centrifugal separators, cyclone separators, and high-efficiency separators. Through-flow separators are mainly used for rough separation in air-swept mills. Centrifugal separators are simple, cost-effective, compact, and reliable, but they have a narrow range for fineness adjustments and low separation efficiency.
Cyclone separators offer stable operation, low blade wear, high efficiency, and easy fineness adjustment but require more space and have higher energy and equipment costs. High-efficiency separators, on the other hand, achieve high separation efficiency, allow for a wide range of fineness adjustments, and provide a more reasonable particle size distribution. They can handle high-dust gas and are compact, lightweight, and easy to maintain.
Considering energy savings, improved cement quality, and increased output, a high-efficiency separator is selected for this system.
3. Dedusting bag filter system
The PPC series box pulse bag filter, imported from the United States, is chosen as the dust collection system for its high efficiency. This device combines the benefits of reverse air and pulse cleaning methods. It features a compact design, simple structure, and high dust tolerance, with the ability to continuously operate during maintenance. It can directly handle the high-dust gas output from vertical mills and separators, with dust concentrations up to 1300 g/Nm³. This system is integrated with the high-efficiency separator to ensure optimal dust collection.
4. Raw material limestone/portland cement clinker batching system:
Material batching can be achieved through either head-bin batching or silo-bottom batching. Head-bin batching uses small bins near the mill to store materials for centralized control, which facilitates timely adjustments to flow rates and ratios. Silo-bottom batching involves installing metering equipment at the base of material silos, which feeds materials directly to the mill via a conveyor without the need for intermediate storage. For simplicity, the design employs a silo-bottom batching system.
5. Pre-grinding system:
Although pre-grinding systems improve grinding efficiency, reduce the size of ball mills, and enhance grinding outcomes, this design does not include them due to insufficient data, time constraints, and considerations for equipment costs.
Conclusion: The design adopts an end-discharge lifting circulation grinding system. This system features a streamlined process flow, low energy consumption, and low product temperature. Material is fed from the mill head, ground, and discharged at the mill tail. A bucket elevator transports the material to the separator for classification. Coarse powder re-enters the mill for further grinding, while fine powder is collected as the final product. This system efficiently manages airflow, eliminating the need for cyclones or specialized cement coolers, making it an ideal choice for energy conservation and improved cement quality.
1. The advantages of the cement ball mill system are: its technology is very mature and the equipment price is very cheap; it is simple to operate and easy to maintain; the particle shape is approximately spherical and the particle size distribution is reasonable, which is conducive to the hydration of cement. The disadvantages of the cement ball mill system are: relatively low efficiency of crushing and grinding, relatively high energy consumption; sensitive to the grindability of the raw materials; sensitive to the particle size of the raw materials; and sensitive to the moisture content of the raw materials.
2. The advantages of roller press + ball mill system are: in the grinding system with roller press, it can generally significantly improve the production capacity of the original ball mill system and significantly reduce the total power consumption of the system; it has a compact structure, light weight, Small size, small footprint; compared with other grinding equipment, the roller press has less dust and lower noise. The disadvantages of this system are: the main grinding mechanism of the roller press is extrusion, which is not easy to handle wet and sticky materials; the roller press requires a lot of maintenance work; also because of its compression and grinding characteristics, the roller press is not suitable for direct use Production of finished cement, etc.
3. The advantages of cement vertical mill system are: relatively high grinding efficiency and relatively low energy consumption; it covers a relatively small area, drying and grinding in a short time; product quality can be controlled by dynamic and static powder selection , which also benefits grinding efficiency; it can handle a wide variety of materials, including wet and sticky ones. The disadvantages of this system are: in order to avoid vibration, the vertical mill needs to spray water to maintain a stable material bed, which leads to reduced cement strength and the need for hot air drying, i.e. fuel consumption; the finished product fineness is too uniform, so the particle size distribution is not very reasonable; Its rolling mechanism results in the sphericity of the particles being inferior to that of cement ball milling; due to the narrow particle size distribution, the early strength is relatively low, the water requirement is large, and agglomeration and pseudo-coagulation are likely to occur.
1. Comparison of material properties
In the cement grinding process, the application of vertical mill and ball mill has its own advantages and limitations. Studies have shown that the flexural strength and compressive strength of ball-milled cement are better than those of vertical mill cement at 3 days, 7 days and 28 days when different proportions of slag are added. This difference is closely related to the effect of the grinding system on particle morphology and particle distribution. Microscopic observation shows that different grinding systems will form different particle morphologies, which in turn affect the physical properties of cement.
2. Effect of early strength and specific surface area
The early strength of cement directly affects the construction speed and is an important indicator for evaluating cement performance. In order to achieve the same early strength, vertical mill cement usually requires a higher specific surface area (based on the experimental data of vertical mill manufacturers). At the same density, the specific surface area of vertical mill cement is significantly higher than that of ball mill cement, but the water requirement is close to that of ball mill cement. This shows that vertical mill grinding can improve the fineness of cement, but there are still deficiencies in particle morphology and particle size distribution.
3. Optimizing the goal of the grinding system
Comprehensively analyzing the characteristics and shortcomings of the two grinding systems, we can derive the goal of the new grinding system:
Complementary advantages: On the basis of maintaining the respective advantages of ball mills and vertical mills, try to avoid their weaknesses.
Process optimization: Transfer the inefficient crushing and large particle grinding links of the ball mill to the vertical mill to give full play to its high efficiency characteristics of grinding large particles.
Performance balance: Ensure that the grinding system has the adaptability of a variety of materials and achieves an ideal state in particle size distribution and particle morphology.
Avoid common problems: Try to minimize the common problems of poor particle size distribution, water injection requirements, vibration and high heat consumption in ball mills and vertical mills.
4. Solution of the combined grinding system. In order to achieve the above goals, designing a combined grinding system is the best choice. The core idea of the system is:The finished products produced by the vertical mill are directly transported to the cement depot to ensure that the efficient fine grinding characteristics are fully utilized. The semi-finished products are further ground in the ball mill after being ground by the vertical mill to optimize the particle morphology and particle size distribution. Maintain the reflux of larger particles and further grind them through the vertical mill to enhance the circulation efficiency of the system.
This combined grinding system not only combines the advantages of the two grinding equipment, but also significantly improves grinding efficiency, reduces energy consumption and improves cement performance, becoming an important development direction of modern cement grinding technology.
After nearly two years of equipment transformation and process adjustment, the system finally achieved stable operation and achieved the main goals of system design. The crushing function of the first chamber of the ball mill is completely realized by the vertical mill system, which significantly improves the grinding efficiency of the ball mill system. The system power consumption is reduced by more than 30%. The ball mill is used as the final grinding stage, and the particle size sent to the ball mill is less than 1mm.
Since the fineness of the material returned to the vertical mill is very low, the material bed is guaranteed to be stable without water spraying, and there is no need to start the hot air furnace for drying. The hot blast furnace needs to be started only when slag grinding or high moisture content materials are required. Through the following analysis of the particle distribution of the product, the system has achieved good classification control of the particles returning to the vertical grinding bed. By comprehensively comparing the particle distribution of the vertical grinding mill product, the cement mill product and the final mixed cement product, the system has achieved Particle distribution very close to that of ball-milled cement. The 45um sieve residue of the finished cement is also significantly lower than that of the vertical mill cement.
1. Limestone crushing and transportation
The limestone crushing workshop is located in the mine. It uses a single-stage hammer crusher to crush limestone with a crushing capacity of 800 t/h, feed block size ≤1500mm, and discharge particle size ≤75mm (90%). The crushed stone is sent to the limestone pre-homogenization yard in the factory area by a belt conveyor about 1000m long.
2. Limestone pre-homogenization
The limestone uses a circular pre-homogenization yard with a cover of Ø90m, with a minimum storage capacity of 47,000t. The limestone from the crushing workshop is layered by a stacker with a capacity of 2000 t/h; the reclaimer has a capacity of 500 t/h; the taken out limestone is sent to the limestone batching warehouse of the raw material batching station by a belt conveyor.
3. Crushing and transportation of auxiliary raw materials
Silica and iron ore are transported into the factory area by dump trucks, unloaded in the silica and iron ore open-air yard, fed into the unloading pit by loaders, or directly fed into the unloading pit, and then fed into an impact crusher for crushing through a plate feeder. The crusher capacity is 300t/h, the feed block size is ≤500mm, and the discharge particle size is ≤70mm (90%). The crushed silica and iron ore are sent to the auxiliary raw material pre-homogenization yard by belt conveyors. After fly ash is transported into the factory by bulk trucks, it is directly put into a fly ash warehouse for storage.
4. Pre-homogenization of auxiliary raw materials and raw coal
Silica, iron ore and raw coal share a long pre-homogenization yard with a cover. There is a stacker and two reclaimers in the homogenization yard. Auxiliary raw materials and raw coal are stacked and layered using a side cantilever stacker. Auxiliary raw materials are taken by side scraper reclaimers, and the taken auxiliary raw materials are sent to the respective batching bins of the raw material batching station by belt conveyors. Raw coal is taken by bridge scraper reclaimers, and the taken raw coal is sent to the raw coal bin of the coal mill by belt conveyors. An electromagnetic iron remover is installed on the belt conveyor entering the mill to remove possible iron pieces in the raw coal. A metal detector is installed at the head of the belt conveyor to detect whether there are residual iron pieces in the raw coal to ensure that the roller mill is not damaged.
5. Raw material batching station
The raw material batching station is equipped with three batching bins for limestone, sandstone and iron ore. Pre-feeders and quantitative feeders are installed at the bottom of each batching bin. The three raw materials are discharged by their respective quantitative feeders according to the proportion required for batching, and the batching materials are fed into the raw material mill through belt conveyors and mill inlet air lock valves. At the same time, a fly ash warehouse is set up near the raw material mill, and the measured fly ash is directly sent to the feed port of the circulating bucket elevator in the raw material grinding workshop by the chute. An electromagnetic iron remover is installed on the belt conveyor entering the mill to remove possible iron pieces in the raw materials. A metal detector is installed at the head of the belt conveyor to detect whether there are residual iron pieces in the raw materials to ensure that the roller mill is not damaged. The raw material quality is controlled by a fluorescence analyzer and an automatic adjustment system for raw material batching.
6. Raw material grinding and waste gas treatment
The raw material grinding and waste gas treatment system adopts a three-fan roller mill system with a system grinding capacity of 410 t/h. The high-temperature exhaust gas from the kiln tail of the humidification tower is used as a drying heat source. The materials are ground and dried in the mill, and the blocks falling from the roller mill wind ring are sent back to the roller mill by the unloading equipment and bucket elevator for further grinding. The gas out of the vertical mill carries qualified raw material powder. After separation by the cyclone separator, the collected raw material is sent to the raw material homogenization warehouse through the air conveying chute and bucket elevator. Part of the dusty gas returns to the mill as circulating air, and the rest is mixed with the waste gas from the kiln tail humidification tower and enters the kiln tail electric dust collector, and the purified gas is discharged into the atmosphere. When the raw material mill stops running, the waste gas is humidified and cooled by the humidification tower, and then all enters the kiln tail electric dust collector. The water spraying amount of the humidification tower will be automatically controlled to keep the waste gas temperature within the allowable range of the kiln tail electric dust collector. After purification by the dust collector, the waste gas is discharged into the atmosphere by the exhaust fan, and the dust emission concentration is ≤50mg/Nm. The kiln dust collected by the humidification tower is sent to the raw material kiln feeding system or raw material homogenization warehouse through the conveying equipment.
7. Raw material homogenization and raw material feeding into the kiln
A Φ24m continuous raw material homogenization warehouse is set up to store and homogenize raw materials, with a storage capacity of 30,000t. Since the raw material warehouse is relatively large, 17 unloading warehouses are set up below. The raw material homogenization has been completed during the unloading process. The raw materials in the warehouse are discharged to the mixing chamber through alternating partitions and aerated. The raw materials are aerated and mixed evenly in the mixing chamber. The required compressed air is supplied by the configured Roots blower. The homogenized raw material powder is metered by the metering system, and then fed into the two feed ports of the double series preheater through the air conveying chute and bucket elevator, and then through the material distribution valve and air lock valve.
8. Clinker burning system
The burning workshop consists of a five-stage double series suspension preheater, a decomposition furnace, a rotary kiln, and a grate cooler, with a daily output of 5,000t of clinker. The raw material fed into the preheater is preheated by the preheater and decomposed in the decomposition furnace before being fed into the kiln for calcination; the high-temperature clinker discharged from the kiln is cooled in the horizontal push grate cooler, and the large clinker is crushed by the crusher and combined with the small clinker that leaks under the wind chamber, and is sent to the clinker warehouse for storage by the clinker chain bucket conveyor. In addition to providing high-temperature secondary air and tertiary air to the kiln and decomposition furnace respectively, the hot air passing through the clinker bed is partly used as a drying heat source for the coal mill, and the remaining exhaust gas is purified by the electric dust collector and discharged into the atmosphere by the exhaust fan, and the dust emission concentration is ≤50mg/Nm
9. Clinker storage, transportation and bulk
The storage period of cement clinker is 5 days, and the storage capacity is 27,300t. A Φ30m circular warehouse is set up to store clinker, and its storage capacity is 48,000t. After the clinker is discharged from the bottom unloading device, it is sent to the clinker batching warehouse of the cement batching station and the train bulk station by a heat-resistant conveyor. The bulk clinker is directly loaded into the truck through the dust-free bulk head installed at the bottom of each warehouse.
Raw coal crushing and transportation
Raw coal is transported into the factory area by train, unloaded in the raw coal open-air yard for storage, unloaded into the raw coal unloading pit by a bucket truck, sent to the vibrating screen for sorting by a belt conveyor, and then unloaded into the hammer crusher for crushing. The crushed coal is sent to the covered auxiliary raw materials and raw coal pre-homogenization yard by a belt conveyor.
10. Coal powder preparation and metering transportation
A set of roller mill system is used for coal powder preparation. The medium-temperature exhaust gas discharged from the cooler is used as the drying heat source. The raw coal is fed into the coal mill by the quantitative feeder under the raw coal bunker for drying and grinding. The coal powder discharged from the mill enters the bag dust collector with the air flow. The qualified coal powder is collected and sent to the coal powder bunker with a load sensor by a screw conveyor. After being measured, the pulverized coal is sent to the kiln head burner and the kiln tail decomposition furnace for combustion. The dusty gas is purified and discharged into the atmosphere by the exhaust fan, and the dust emission concentration is ≤50mg/Nm.
The pulverized coal bin and bag dust collector are equipped with CO detectors and a set of CO automatic fire extinguishing devices. Explosion-proof valves are installed in the pulverized coal bin and dust collector.
11. Drying and transportation of mixed materials (slag, steel slag)
Wet slag and steel slag are transported into the factory area by dump trucks and unloaded into the pile shed. They can also be unloaded into the open-air yard for storage, and are sent to the receiving hopper by the loader and then to the wet bin of the drying workshop via a belt conveyor.
The coal for drying slag and steel slag is taken from the raw coal pre-homogenization yard near the pile shed by the loader and sent to the receiving hopper. It is then sent to the coal crusher in the slag and steel slag drying workshop via a bucket elevator. The crushed coal is stored in the coal crushing bin in the slag and steel slag drying workshop. Wet slag and steel slag are dried in a rotary dryer and then sent to the dry slag and steel slag warehouses of the cement batching station by a belt conveyor and a bucket elevator. The slag and steel slag drying system is equipped with a hot air furnace to provide heat source for the dryer. The waste gas after material drying is collected and treated by a bag dust collector and then discharged into the atmosphere. Dust emission concentration ≤50mg/Nm
12. Gypsum crushing and cement batching
Gypsum is transported into the factory area by dump trucks, unloaded into an open-air yard, and transferred by loaders to the receiving hopper in front of the crusher. It is fed into a jaw crusher for crushing. The crushed gypsum is sent to the gypsum batching bin of the cement batching station by a belt conveyor and a bucket elevator. The cement batching station is equipped with four batching warehouses for clinker, gypsum, slag, and steel slag. Electronic belt scales are installed at the bottom of each batching warehouse. According to the type of cement produced, the four materials are mixed according to the predetermined ratio and sent to two sets of closed-circuit grinding systems composed of 4.2×13m ball mills and high-efficiency powder concentrators through belt conveyors. The production capacity of a single set is 180t/h. The cement discharged from the mill is sent to the O-SEPA powder concentrator through bucket elevators and air conveying chutes. The coarse powder is returned to the mill through the air conveying chute for re-grinding. The finished cement is collected by the high-efficiency bag dust collector and sent to the cement warehouse through the air conveying chute. The exhaust gas discharged from the mill and the dust exhaust gas from various places are used as primary air for powder selection. The purified exhaust gas is discharged into the atmosphere by the system fan. The dust emission concentration is ≤30mg/Nm.
13. Cement storage, cement packaging and bulk
Considering the diversity of production varieties, six Φ20m circular warehouses are used to store cement, with a minimum storage capacity of 60,000t. The cement leaving the warehouse is sent to the cement truck bulk station and finished product packaging workshop respectively through the electric flow control valve, air conveying chute and bucket elevator. The cement truck bulk workshop is equipped with four sets of cement truck bulk loaders, which can simultaneously load four bulk trucks. The finished product packaging workshop is equipped with two eight-mouth rotary packaging machines. The packaged bagged cement can be directly loaded onto the truck or stored in the finished product warehouse for shipment. The ratio of bagged cement to bulk cement is considered to be 30%:70%, which can be adjusted at any time according to market demand.
A central laboratory is set up to be responsible for the inspection of raw materials, semi-finished products and finished products throughout the plant; an air compressor station is set up to supply compressed air for production throughout the plant.
Roller press grinding system is a general term that is different from roller press final grinding system. It can be divided into pre-grinding system, combined grinding system, semi-final grinding system and mixed grinding system. Among them, pre-grinding system and combined grinding system are the most common. The pre-grinding unit of the front roller press and the fine grinding unit of the rear ball mill can be arranged separately, so these two schemes are more suitable for the transformation of old lines.
In the semi-final grinding system, some cement products have not passed through the ball mill, and the qualified fine powder squeezed by the roller press is directly selected by the powder selector. The finished products of the other three grinding systems are all produced by the mill. The pre-grinding system uses the side material of the roller press as the circulating material; the combined grinding and semi-final grinding use the coarse material selected by the powder selector of the roller press as the circulating material; and the mixed grinding uses the coarse material selected by the powder selector of the roller press and the coarse powder selected by the powder selector of the ball mill as the circulating material. In this process system, the coarse powder returned by the powder selector of the mill is easy to change the operating parameters of the roller press. At present, this process system is basically not used in China and is not introduced in this article. The pre-grinding system, combined grinding system, and semi-final grinding system are described as follows.
1. The pre-grinding system is an early grinding solution. After being squeezed by the roller press, the material is divided into two parts: the middle cake part with better extrusion effect is sent to the ball mill for grinding, and the side material part with poor extrusion effect is returned to the roller press for re-extrusion. This solution has the following characteristics:
(I) The process flow is simple. The pre-grinding unit and the ball mill unit can be arranged separately, which is suitable for the transformation of old lines that need to increase production.
(II) The use of roller press pre-grinding can increase the output of the ball mill by more than 25%, and reduce the power consumption of cement grinding by about 3~5kWh/t, that is, saving about 20% of electricity.
(III) In the pre-grinding system, the ratio of roller press throughput to finished product volume is generally considered to be 2~2.5, and the main equipment configuration is a small roller press with a large ball mill.
2. Combined grinding is an extrusion combined grinding process that aims to give full play to the excellent crushing and coarse grinding functions of the roller press and the fine grinding function of the ball mill. The material cake extruded by the roller press is dispersed and sorted by the powder selector. The coarse material is used as the circulating material of the roller press, and the fine material enters the ball mill for further grinding. All cement products are produced by the cement mill. The division of labor between the grinding equipment in this process is clear, which greatly reduces the comprehensive power consumption of the grinding system and greatly increases the system output. The characteristics of this solution are as follows:
(I) The system process is relatively complex. The roller press and the ball mill run synchronously, so the operation rate of the roller press is required to be high. Since the material out of the roller press is in the form of cake, the powder selector that matches it must have a breaking function.
(II) The adverse effects caused by the edge effect of the grinding roller and the wear of the side baffle of the feeding device are basically eliminated. All finished products are completely re-grinded by the ball mill. The product has a wide particle distribution and a high content of micropowder, so it is suitable for the grinding of cement products.
(III) Adopt a large roller press and a small ball mill configuration scheme, and use a low-pressure large-circulation operation mode. The ratio of roller press throughput to finished product volume is generally between 3 and 5.5.
(IV) The increase in ball mill output is generally more than 50%. Compared with ordinary ball mills, the reduction in cement grinding power consumption can exceed 30% (8-10kWh/t).
3. There are two main types of grading equipment for combined grinding according to the roller press system: one is a dispersing classifier and the other is a V-type powder selector. The ball mill part is divided into two types: open-flow system and circle flow system. Therefore, the combined grinding system mainly has the following four process schemes: roller press + dispersing classifier + open-flow mill, roller press + dispersing classifier + circle flow mill, roller press + V-type powder selector + open-flow mill, roller press + V-type powder selector + circle flow mill system. Each scheme has advantages and disadvantages, and the differences are as follows:
(I) Classification principle and classification accuracy: The V-type powder selector relies entirely on wind power to lift the classification, and the classification accuracy is relatively high. It is suitable for sorting materials below 0.5mm; the dispersing classifier is a combination of machinery and wind power, with low classification accuracy, and the sorting particle size can reach 3.0mm.
(II) Requirements for roller press process parameters: The V-type powder selector system must adopt a low-pressure large-circulation operation mode, otherwise the material cake cannot be dispersed, and the fine powder squeezed from the material cake cannot be selected. The dispersing classifier can adopt a high-pressure small-circulation operation mode.
(III) Installed power ratio: In the V-type powder concentrator system, the roller press must be large enough to ensure that a sufficient amount of fine powder below 0.5 mm is produced for the V-type powder concentrator to be classified. Therefore, the installed power ratio of the roller press to the ball mill should be: 1:1.0~2.5 (open flow); 1:1.0~2.0 (closed flow). In the dispersing and classifying machine system, the installed power ratio of the roller press to the ball mill is 1:2.5~3.5. If the ratio is further increased, as the role of the roller press in the grinding system decreases, the system power consumption will increase accordingly. For the open-flow mill system and the circle-flow mill system, the installed power of the equipment in the open-flow mill system is lower and the investment is less, while the installed power of the equipment in the circle-flow mill system is higher and the investment is higher.
(IV) Requirements for material moisture: In the V-type powder concentrator system, the comprehensive moisture of the material should be ≤1%, and in the dispersing and classifying machine system, the comprehensive moisture of the material should be ≤1.5%.
(V) When the system output is ≤150t/h, the power consumption of the dispersing and classifying machine system is lower; when the system is ≥150t/h, the power consumption of the V-type powder selector system is lower. Compared with the open-flow mill system of the same specification, the output of the circle flow mill system is about 10% to 20% higher; and the finished product of the open-flow mill system contains coarse particles, and the temperature of the finished cement product is higher, while there are no coarse particles in the circle flow mill system, and the temperature of the finished cement product is lower.
(VI) Process comparison: The open-flow mill system has fewer equipment, simple process layout, simple and convenient operation and management, and lower technical requirements for operators; while the circle flow mill has more equipment, more complex process layout, longer start-up and shutdown time, more complex operation and management, and relatively higher technical requirements for operators.
4. The semi-final grinding system is to send the materials selected after roller press and the subsequent ball mill materials into the powder selector to select the finished cement. The coarse powder of the powder selector enters the ball mill for further grinding. That is, some of the finished cement particles that meet the cement fineness requirements after roller press are directly selected by the powder selector without passing through the ball mill. Its main features are as follows:
(I) The finished fine powder produced after roller press is directly selected to avoid being sent to the ball mill for further grinding, which reduces the over-grinding phenomenon in the cement mill and effectively increases the system output, thereby reducing the unit power consumption of finished cement.
(II) In this system, due to the increase in the processing capacity of the powder selector, the specifications of the powder selector will inevitably increase, and the specifications of the subsequent dust collector and fan will also need to be increased simultaneously. That is, while the system output is increased and the unit power consumption is reduced, the system equipment investment cost and operating cost will increase.
(III) The particle distribution of the products produced by this process system is relatively concentrated, which is slightly insufficient for cement products with certain particle grading requirements.
(IV) The pre-grinding system and the combined grinding system are more suitable for cement plant production and energy saving transformation plans, among which the combined grinding system has the most significant effect.
(V) In the combined grinding system plan, the power ratio of the mill and the roller press should be determined, and the appropriate grading equipment should be selected; in addition, the open flow or circle flow grinding system should be selected according to the factory's cement variety requirements and other actual conditions.
The particle size of the material after being crushed by the crushing equipment is mostly around 20mm. If the fineness required by the production process is to be achieved, it must be ground by the grinding equipment. Grinding is an important process in many industrial productions. Among them, the ball mill is a grinding machine with a wide range of uses and a large volume. In cement production, it is used to grind raw materials, fuels and cement. Ceramics and refractory factories also use ball mills to crush raw materials.
The main body of the ball mill is a rotating cylinder made of rolled steel plates. Grinding heads with hollow shafts are installed at both ends of the cylinder, lining plates are installed on the inner wall of the cylinder, and grinding bodies of different specifications are installed in the mill. When the mill rotates, the grinding body adheres to the surface of the cylinder lining due to the centrifugal force, and rotates with the cylinder. When it is brought to a certain height, it falls like a projectile due to its own gravity and impacts the material in the cylinder. During the rotation of the mill, the grinding body also grinds the material between the grinding body and the lining and between adjacent grinding bodies by sliding and rolling. During the rotation of the mill, the grinding head constantly forces the material to be fed, and the material rotates with the cylinder, forming the material being squeezed forward. With the height difference of the material surface between the feed end and the discharge end, and the continuous exhaust of the mill tail, even though the mill body is placed horizontally, the material can continue to move to the discharge end until it is discharged from the mill.
When the mill rotates at different speeds, the grinding body in the cylinder may have three basic situations: the speed is too fast, the grinding body and the material are attached to the cylinder and rotate together, which is called the "turnover state", and the grinding body has no impact and grinding effect on the material; the speed is too slow, which is not enough to bring the grinding body to a certain height, and the energy of the grinding body falling is not large, which is called the "dumping state"; the speed is relatively moderate, and the grinding body is lifted to a certain height and then thrown down, which is called the "throwing state", and the grinding body has a greater impact and grinding effect on the material, and the grinding effect is better. In fact, the movement state of the grinding body is very complicated, including movement attached to the wall of the mill cylinder; sliding down along the cylinder wall and the grinding body layer; and similar to the throwing and rolling of the projectile.
1. Advantage
A significant advantage of ball mill in the grinding process is its strong adaptability to fluctuations in the physical properties of materials. It is capable of continuous production and has a large production capacity, which enables the ball mill to meet the needs of large-scale production in modern enterprises. In addition, the ball mill has a large crushing ratio, which can usually reach 300 or even exceed 1000, which makes it more adaptable in the grinding process and can handle relatively coarse materials. Moreover, the product fineness and particle size distribution of the ball mill can be adjusted, and the particle shape is close to round, which is conducive to the hydration, hardening and raw material calcination of cement.
The ball mill has a flexible working mode. It can perform dry operation or wet operation, and can even perform drying and grinding at the same time, which enables it to work efficiently under a variety of materials and process requirements. In addition, the ball mill can also mix, stir and homogenize the materials during the grinding process, thus ensuring the quality of the finished product. The ball mill has a simple and sturdy structure, can be operated under negative pressure, and has good sealing performance, which also makes it easier to maintain and manage, and its operation is more reliable.
2. Disadvantages:
Although ball mills have many advantages, their disadvantages cannot be ignored. First, the working efficiency of the ball mill is low, and the effective utilization rate of electricity is only 2%-3%. Therefore, its electricity consumption is relatively high. The comprehensive electricity consumption for grinding one ton of cement is about 90-110 kWh, accounting for about one-third to two-thirds of the total electricity consumption of the whole plant. In addition, the ball mill also has significant consumption of grinding media and liner, which increases the operating cost of production.
The ball mill is relatively large in size, and the total weight of the equipment can reach several hundred tons, which means a large one-time investment and high difficulty in installation and maintenance. At the same time, the ball mill will generate large noise and vibration during operation, which may have adverse effects on the production environment and workers' health, so measures need to be taken to reduce the impact of noise and vibration. The speed of the ball mill is generally low, usually between 15 and 30 r/min, so it needs to be equipped with a deceleration device, which also increases the complexity of the equipment.
Advantages and disadvantages of ball mill for grinding clinker or limestone and material properties
1. Advantages and disadvantages of ball mill grinding clinker
One advantage of grinding clinker with a ball mill is that it can grind the clinker into relatively uniform particles, and the fineness and particle size distribution can be adjusted, which helps to increase the hydration reaction rate of cement and thus improve the strength of cement. In addition, the ball mill can adapt to a variety of different clinker types. Whether it is clinker with high water content or clinker with other special physical properties, the ball mill can effectively grind it. However, the high energy consumption of ball mill for grinding clinker is its significant disadvantage. Due to its inefficient grinding process, ball mills consume a lot of electricity when grinding clinker, which makes the overall production cost higher. In addition, when the ball mill grinds clinker, the fineness and particle shape of the ground material sometimes cannot meet the fine requirements of equipment such as vertical mills, resulting in a decrease in the early and final strength of cement. This is a major disadvantage of ball mills when grinding clinker.
2. Advantages and Disadvantages of Ball Mill Grinding Limestone
One advantage of grinding limestone with a ball mill is its adaptability to cope with limestone grinding requirements. The ball mill can adjust the grinding process according to the characteristics of the material, especially when processing limestone with moderate hardness, the grinding effect is more ideal. Another advantage of ball mills is their flexibility, as they can perform both dry and wet operations, which provides more options for processing limestone. However, ball mills also have some disadvantages when grinding limestone. The energy consumption for grinding limestone is high due to the low working efficiency of ball mill. In order to achieve the ideal fineness, the ball mill consumes a lot of electricity, and its grinding efficiency is slightly inferior to other advanced grinding equipment, such as vertical mill. In addition, when the ball mill is grinding limestone, its particle distribution may not be as ideal as that of equipment such as the vertical mill, and the particle shape is relatively uneven, which has a greater impact on the properties of cement, especially the compressive strength and early strength.
3. Comparison with other grinding equipment
Compared with vertical mill, roller mill and other grinding equipment, the advantage of ball mill lies in its strong adaptability and ability to process various materials, especially when processing materials with high moisture content or low hardness. However, vertical mills and roller mills have more advantages in energy efficiency and production efficiency, and can effectively reduce electricity consumption and improve production efficiency. Although the ball mill has low energy efficiency, it can better adjust the fineness and particle size distribution and has strong adaptability to materials. Therefore, the ball mill still has a place in some specific applications.
The classification of ball mills can be divided in detail from many aspects, including the ratio of the length to the diameter of the cylinder, the shape and material of the grinding media loaded in the mill, the unloading method, the transmission method, the production method, and whether the production process is continuous.
1. According to the ratio of the length to the diameter of the cylinder, ball mills can be divided into short mills, medium-long mills and long mills. Short mills, also known as ball mills, have an aspect ratio of less than 2 and are generally single-bin. Medium-long mills have an aspect ratio of between 23.5 and are generally 2 bins. Long mills have an aspect ratio of more than 3.5 and are generally 24 bins. The mills used in cement plants are mostly medium-long mills and long mills. These mills are collectively called tube mills, also commonly known as ball mills.
2. According to the shape and material of the grinding media loaded in the mill, ball mills can be divided into ball mills, baseball mills, small grinding media mills and gravel mills. The grinding media in the ball mill are steel balls and steel segments. Baseball mills are equipped with steel bars in the first chamber and steel balls in other chambers (some tail chambers are equipped with steel segments). Small grinding media mills are mills with small grinding bodies inside, such as the Compidan mill, which is equipped with steel segments of φ4~φ14. The high-fine mill developed by a design institute in my country also belongs to this type of mill. Gravel mills use gravel, pebbles, porcelain balls, etc. as grinding media, and granite, porcelain, and rubber as linings inside the mill. They are mainly used for grinding white cement, colored cement, and ceramic raw materials.
3. According to the unloading method, ball mills can be divided into two types. The first type is tail unloading mills and middle unloading mills. The materials of tail unloading mills are fed from the head end and discharged from the tail end; the materials of middle unloading mills are fed from both ends and discharged from the middle. The second type is center unloading mills and peripheral unloading mills. The materials of center unloading mills are discharged from the center of the mill body, while those of peripheral unloading mills are discharged from the periphery of the mill body.
4. According to the transmission method, ball mills can be divided into center drive mills and edge drive mills. The center drive mill drives the hollow shaft at the discharge end of the mill through the motor (through the reducer) to make the mill body rotate; the edge drive mill drives the large gear fixed to the discharge end of the cylinder through the motor through the reducer to drive the cylinder to rotate.
5. According to the production method, ball mills can be divided into dry mills, wet mills and drying mills. Dry mills are mills that feed dry materials and produce dry powder; wet mills are mills that add an appropriate amount of water when feeding and produce slurry; drying mills are mills that feed wet materials and use external hot air to dry the materials during the grinding process. This type of mill includes tail discharge drying mills, middle discharge drying mills, wind sweeping mills and vertical mills.
6. According to whether the production process is continuous, ball mills can be divided into intermittent mills and continuous mills. Intermittent mills are mills that pour out the abrasives after each grinding, and then grind the second batch of materials. This type of mill is often used in ceramic factories and refractory factories, and some factories also use intermittent mills as test mills. Continuous mills are mills that continuously feed and discharge materials, and are suitable for large-scale production.
Through these different classification methods, ball mills can be selected and configured according to actual production needs, so as to maximize their efficiency in cement production.
The grinding system is also called the grinding process. Its selection should be based on the performance of the material entering the mill, the type of product, the fineness of the product, the output, the power consumption, the investment, and whether it is easy to operate and maintain. The grinding operation of the cement plant consists of three parts: raw material, cement and coal powder. This section does not introduce the coal grinding process, but focuses on the raw material and cement grinding system.
1. Open and closed circuits and their characteristics
(I)Open circuit In the grinding process, the material only passes through the mill once, and the process of unloading as the finished product is open circuit grinding, as shown in Figure 2.3. Its advantages are: simple process, less equipment, less investment, and easy operation. Its disadvantages are: since all materials can only be discharged from the mill after reaching the fineness requirements, the ground materials will be over-grinded in the mill and form a buffer layer, which prevents the coarse materials from being further ground, thereby reducing the grinding efficiency and increasing power consumption.
(II)B Closed circuit After the material is discharged from the mill, it is sorted by the grading equipment. The qualified fine powder is the finished product, and the coarse material is returned to the mill for re-grinding. The process is closed-circuit grinding, as shown in Figure 2.4. Its advantages are: the qualified fine powder is selected in time, the over-grinding phenomenon is reduced, the output is 15%~25% higher than the open-circuit mill of the same specification, the product particle size is more uniform, the particle composition is more ideal, and when grinding cement, there are more particles of 3~30μm and higher strength. When grinding raw materials, there are fewer large particles and less free lime content. The product fineness is easy to adjust. It is suitable for producing cement with various fineness requirements. The heat dissipation area is large and the temperature inside the mill is low. Its disadvantages are: complex process, many equipment, large investment, high plant, troublesome operation, and large maintenance workload.
2. Dry Raw Material Grinding System
In the past, drying raw materials and grinding raw materials were carried out separately, and there were open circuit and closed circuit grinding of raw materials. With the development of new dry technology, drying and grinding are basically carried out simultaneously in one unit, which is called drying and grinding. Most of its heat flow also comes from the kiln tail. In this drying and grinding system, the material is crushed on one side and dried on the other side. Because the material is highly dispersed and directly exposed and suspended in the air flow, the heat exchange is very rapid and the water evaporates quickly. With the development of dry production in the cement industry, the drying and grinding system has been continuously improved and developed, and there are many types. According to the drying method, there are drying inside the mill, drying outside the mill, and simultaneous drying inside and outside the mill. Now several typical methods are explained as follows:
(I)Ordinary air-sweeping mill system (Figure 2.5) The material and the hot air flow enter the mill together, grinding on one side and drying on the other side. The material ground to a certain fineness is swept out of the mill by the hot air flow and lifted to the coarse powder separator by air force. The selected coarse powder is returned to the mill for re-grinding, and the fine powder is recovered by the fine powder separator as a finished product. If the moisture content of the raw material is low, the air volume for drying is less than the air volume required for air sweeping or lifting, so part of the return air is returned to the mill or the lifting pipe at the end of the mill for recirculation.
The air-swept ball mill has a small aspect ratio, a large hollow shaft for feeding, and no discharge grate at the end of the mill, so the ventilation resistance is small, the wind speed in the mill is high (up to 5m/s), a large amount of hot air can enter, and the drying capacity is strong. Using the exhaust gas at the end of the kiln, materials with a moisture content of 8% can be dried. If another heat source is set, the moisture content of the material entering the mill can reach 15%. The grinding efficiency of this system is relatively low, and the output per unit theoretical work is 15%~20% lower than that of the lifting circulation mill. Modern large-scale wind-sweep mills have large drying capacity, simple systems, small maintenance workload, easy operation, and can make full use of waste heat at the kiln tail. In recent years, they have been redeveloped: large-scale wind-sweep mills with a size of φ5.8m×14.75m and an output of about 350t/h have appeared.
(II)Tail unloading and lifting circulation mill system (Figure 2.6) The basic difference between it and the wind-sweep mill is that the material entering the mill is discharged mechanically through the drying bin to the tail end of the grinding bin, and then sent to the powder selector by a hoist. The hot air is drawn out through the discharge hood at the tail end of the mill and discharged through the dust collection equipment.
The ventilation resistance of this system is relatively large, and the wind speed at the feed end is generally allowed to be 3~4m/s. The waste gas at the kiln tail can be used to dry materials with a moisture content of 4%~5%. If another heat source is set up, materials with a moisture content of 8% can be dried; the unit power consumption of the entire system is lower than that of ordinary wind-sweep mill systems. The largest mill of this system abroad has a specification of φ5.6m×10.75m+2.4m, with an installed power of 2×3000kw.
(III)Middle discharge lifting circulation mill system (Figure 2.7) The material is fed from the mill head, and the return material of the powder selector is returned to the coarse grinding bin and fine grinding bin from the mill head and mill tail respectively. The material is discharged from the mill and lifted to the powder selector for sorting by the elevator. Most of the return material (generally 2/3) is returned to the fine grinding bin, and the rest is returned to the coarse grinding bin. The purpose is to improve the fluidity of the cold material and also to facilitate the material balance in the mill. The separation of coarse and fine grinding is conducive to the best ball distribution, less over-grinding, and high grinding efficiency.
Most of the hot air (generally 80%~90%) enters from the mill head, and a small part of the hot air enters from the mill tail. For example, the exhaust gas from the kiln tail can be used to dry materials with a moisture content of 6%~7%. If another heat source is set up, materials with a moisture content of 14% can be dried.
This system is a combination of wind sweeping mill and tail discharge lifting circulation mill in terms of drying effect; in terms of grinding effect, it is actually equivalent to a two-stage closed circuit. Suitable for large-scale.
(IV)Simplified lifting circulation mill system
It is a process that combines the gas purification system and the powder selection system, combining the coarse powder separation and powder selection tasks together. It not only accepts the feed of the elevator, but also accepts the dust lifted by the gas from the mill by the pneumatic force, thus greatly simplifying the entire system. This process can be applied to both tail discharge and middle discharge mills. The tail discharge is shown in Figure 2.8 as an example.
(V)Vertical roller mill system It is a machine that grinds materials based on the principle of material bed grinding through the relative motion of the grinding roller and grinding disc grinding device. Its main features are: large inlet particle size (generally 40~100mm, even up to 120mm); strong drying capacity (can dry 8%~10%, even 20% of the raw materials); low power consumption (15%~30% lower than tube mill); high grinding efficiency, high output, low noise, easy control, high operation rate, etc., so it is currently widely used in the cement industry, especially raw material grinding. For detailed introduction, please refer to 3.3.
3. Powder selection and drying system
It is an external drying system. The drying medium passes into the powder selector instead of the mill. However, in order to improve the effect of the drying and grinding system, powder selection and drying are also carried out simultaneously on the basis of ventilation in the mill. This system is essentially a system that dries both inside and outside the mill at the same time. The dry raw material drying and grinding system also includes: grinding system with vertical drying tower and drying and grinding system with pre-crushing.
4. Types of cement grinding system:
Cement grinding system Cement grinding system usually includes open circuit long mill and medium long ball mill, closed circuit ball mill and medium long ball mill, closed circuit medium unloading ball mill, as well as high pressure roller press system and roller vertical mill system. As far as tube ball mills are concerned, open circuit and closed circuit have always been complementary and developed alternately.
When the grinding specific surface area does not exceed 310m2/kg, the unit power consumption of open circuit and closed circuit is basically the same. When this value is exceeded, the unit power consumption of open circuit grinding is significantly higher than that of closed circuit grinding. A typical closed-circuit cement grinding system is shown in Figure 2.10. It is generally believed that if the grinding specific surface area does not exceed 300m2/kg, or the mill output is less than 30t/h, it is appropriate to use open circuit.
Vertical Roller mills have been successful in raw material grinding systems, but due to problems such as particle grading, particle morphology, and abrasion of cement products, their use in cement grinding is subject to certain limitations. In recent years, people have conducted in-depth research on its use in cement grinding. Through the test, the process parameters such as disc speed, pressure, material bed thickness, air-to-material ratio, powder selection method, etc. were adjusted; the material of wear-resistant parts was improved, and the conclusion was drawn that the roller mill can successfully produce different strength grades. Portland cement and slag cement. The system processes include: pre-grinding, mixed grinding, combined grinding, final grinding, etc.
LIMESTONE CEMENT CLINKER GRINDING PLANT TECHNICAL PARAMETERS
Equipment Name | Model/Specification | Parameters | Quantity |
Steady Flow Weighing Silo | 3300×3300mm | Silo Capacity: 30t | 2 |
RP170-120 Roller Press | Diameter: 1500mm, Width: 1200mm | Capacity: 610-710t/h, Input Temperature: ≤100℃ | 2 |
Bucket Elevator | NSE1000×42300mm | Capacity: Normal 750t/h, Max 1100t/h, Lift Height: 80m | 2 |
RCYL Pipe Permanent Magnet Iron Remover | RCYL-100I | Inner Diameter: 1500×600×1500mm, Material Density: 1.45t/m³, Angle with Ground: 46° | 2 |
VRP1000 Separator | VRP1000 | Max Feed: 1000t/h, Load Capacity: 180-210t/h, Resistance: 1.5-2.0kPa | 2 |
Double Cyclone Separator | 2-Φ3700mm | Airflow: 240000m³/h, Efficiency: 85%-90%, Temperature: Normal 95°C, Max 150°C | 2 |
Double Flap Valve | SYSV--II, DN600mm | Ash Discharge: ~100m³/h, Temperature: Normal 25°C, Max 50°C | 4 |
Cement Mill Circulation Fan | SL4-73 No.21F | Flow Rate: 270000m³/h, Pressure: 4200Pa, Temperature: 80°C (Max 100°C) | 2 |
Cement Mill | Φ4.2×13m | Capacity: 180t/h, Feed Size: ≤2mm, Center Drive, Double Sliding Support, Speed: 15.6r/min | 2 |
Air Slide Conveyor | XC500 | Material: Cement, Capacity: 600t/h, Slope: 12° | 2 |
Centrifugal Fan | XQINo.5.4A | Flow Rate: 595m³/h, Pressure: 6862Pa | 2 |
Bucket Elevator | NSE700 | Capacity: Normal 700t/h, Max 750t/h, Bucket Speed: 66m/min | 2 |
Air Slide Conveyor | XC500 | Capacity: 600t/h, Slope: 12° | 2 |
Centrifugal Fan | 9-19No.4.5A | Flow Rate: 1616m³/h, Pressure: 4672Pa, Speed: 2900r/min | 2 |
O-Sepa N4000 Separator | N4000 | Cement Output: 110-190t/h, Airflow: 240000m³/h, Rotor Speed: 75-165r/min, Max Cycle: 720t/h | 2 |
Pulse Jet Bag Filter | PPW128-2×13 | Filter Area: 4030m², Airflow: 240000m³/h, Dust Concentration: ≤1000g/m³ | 2 |
Cement Mill System Fan | 2150 DI BB50 | Airflow: 270000m³/h, Pressure: 5500-5700Pa, Inlet Pressure: -5000Pa | 2 |
Centrifugal Fan | 9-19No.4A | Airflow: 1264m³/h, Pressure: 3597Pa, Speed: 2900r/min | 2 |
Air Slide Conveyor | XC500 | Material: Separator Dust, Capacity: 400t/h, Slope: 10°, Pressure: 4-5.5kPa, Flow Rate: 1.5-2m³/min | 2 |
Centrifugal Fan | 9-19No.4A | Airflow: 1558m³/h, Pressure: 3384Pa, Speed: 2900r/min | 2 |
Pulse Jet Bag Filter | PPW96—8 | Airflow: 53000m³/h, Total Filter Area: 929m², Net Area: 813m², Dust Concentration: ≤1000g/m³ | 2 |
Cement Mill Exhaust Fan | Y5-48No.12D | Airflow: 55000m³/h, Pressure: 3400Pa, Speed: 1450r/min, Temperature: 90°C | 2 |
High-Pressure Centrifugal Fan | 6-27-13No.6.5A | Airflow: 574m³/h, Pressure: 6800Pa, Speed: 2900r/min | 2 |
Air Slide Conveyor | XC315×7374mm | Material: Mill Dust, Capacity: 70t/h, Slope: 5° | 2 |
Centrifugal Fan | 6-27-13No.6.5.A | Airflow: 574m³/h, Pressure: 6800Pa, Speed: 2900r/min | 2 |
Air Slide Conveyor | XC500×44074mm | Material: Cement, Capacity: 250t/h, Slope: 5° | 2 |
Slope Fan | 9-19No.5A | Airflow: 2254m³/h, Pressure: 5740kPa, Speed: 2900r/min | 4 |