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Development and application of vertical mill equipment

Date:2019-07-01 17:06     writer:cement editor     Views:

1. General


At present, there are three main grinding methods of cement grinding: tube mill, vertical mill and roller press, especially in China cement industry, the combination grinding has become the mainstream cement grinding technical route by using pre-grinding synthesized by roller press and tube mill group. As far as the combined grinding of roller press is concerned, the power consumption of roller press is mostly above 30kWh/t. Although the power saving effect of this process is more obvious than that of tube mill, it is difficult to reduce the power consumption further because of its grinding principle. In addition, the semi-final grinding system composed of roller press and tube mill in recent years has the effect of saving electricity, which is restricted by the cement performance of roller press system . The completed production line has been abandoned in the semi-finished grinding production mode, and the successful case is less.

The vertical mill has the advantages of low energy consumption, stable operation, simple operation, small maintenance workload, great success in the grinding of the cement raw material and the grinding of the coal powder, I.e. a powder selector is arranged above the vertical mill. Therefore, a large amount of wind is required to be introduced in the vertical mill, because a large part of the material is blown up into the powder feeder by the high-speed injection wind of the nozzle ring, the consumption power of the internal circulating vertical mill is relatively large, and the power consumption of the product is also 28 to 34 kWh/ t, The energy-saving advantage is not It is very obvious.

This paper introduces a new type of external circulation cement vertical mill as the main equipment of combined grinding, semi-final grinding or final grinding system, which not only solves the performance problem of cement products, but also solves the problem of high power consumption of grinding system. The actual operation shows that the power consumption of the external circulation cement vertical grinding system is 25 × 29kWhat / t, which has reached the advanced level at home and abroad.

2. Introduction of cement vertical mill


According to the principle of traditional internal circulation vertical grinding, the unique energy saving concept and innovative design type external circulation vertical mill are integrated. The main working principles are as follows:

The cement clinker is fed from above the center of the disc, gradually moving to the edge of the disc with the help of centrifugal force and friction force, and bitten by the roller on the disc. Extrusion grinding between cement mixtures is carried out within the gap between the rotating disc and the roller. After high pressure rolling, the material is thrown with the rotating centrifugal force of the grinding disk, and after the scraper is collected, the material is fed into the powder selection equipment by the hoist, in which the fine powder is fed into the tube mill (or selected as the finished product), and the coarse powder continues to be returned to the mill. The external circulation vertical grinding system has the following remarkable characteristics:

The main results are as follows:

(1) the vertical mill body does not have a powder separator.

And the internal circulation vertical mill. The method has the advantages that firstly, in the traditional internal circulation vertical mill, the materials are all mechanically lifted, the conveying power consumption of the materials in the mill is reduced, and the power consumption of the system fan is reduced; secondly, the outer movement of the powder selection process can be specially designed according to different grinding processes, thus being beneficial to high-efficiency, And finally, the setting of the nozzle ring in the mill is eliminated, and the wear of the high-speed dust-containing air flow to components such as the grinding roller and the inner wall of the shell is greatly reduced.

(2)High grinding efficiency.

Making full use of the grinding principle of roller abrasive bed, the material in the grinding area outside the grinding groove is not only affected by the extrusion pressure, but also by the shear force caused by the relative speed, which makes it easier for the material to get high efficiency grinding.

The design of the special grinding roller increases the grinding area of the material, and combines with the specially designed grinding groove (grinding disk liner) to realize the uniform pressure of the grinding roller on the material layer, whether it is compression or shear grinding, all of which have excellent grinding efficiency.

In addition, by means of central feeding, the material moves towards the edge of grinding disc gradually by means of centrifugal force and friction force, which can effectively overcome the problem of uneven flow rate, bypass failure and overflow at both ends.

(3) the dispersion effect of the material after grinding is good.

Because the grinding process is the joint action of shearing and extrusion, the vertical grinding material is loose, which greatly reduces the power consumption of material dispersion and classification in the subsequent powder selection process. At the same time, the high concentration separation process (material-gas ratio ≥ 4.5) can be adopted, which does not need to set up another dispersion process, which reduces the air volume of powder selection, saves the investment of equipment and effectively reduces the power consumption of the system fan.

(4) simple control and convenient operation

Because the roller press belongs to the short grinding track, the working principle of pure extrusion, the stress area is narrow, which causes the local pressure to be too large. Under long-term, continuous and high-pressure working conditions, the wear-resistant layer of the roller surface is easily damaged by fatigue, resulting in mechanical failure, and the roller shall be stopped repeatedly for repair welding. Vertical grinding effectively avoids such mechanical failures. In terms of operation control, the control of roller press is complicated, which needs to be adjusted with the steady flow chamber, roll speed and roller pressure. However, the external circulation vertical mill and general pipe mill control mode are the same, and the flow rate is controlled by the circulating elevator current, which is simple and easy.

(5) High spherical degree of material particles after grinding

The morphology of material particles after extrusion by roller press and vertical mill is high due to the combined action of extrusion and shear of external circulation vertical mill . However, the grinding track of roller press is short, and the pure extrusion effect makes most of its material particles appear as plate, column and so on. This makes the application of external circulation vertical grinding in cement semi-final grinding and cement final grinding system has obvious advantages, and the water requirement of finished cement is comparable to that of pipe mill products .

3. Cement vertical grinding process system


At present, the external circulation vertical mill is used for the cement grinding mainly including three kinds of process systems, such as the combined grinding system, the semi-final grinding system and the final powder grinding system.

(1) combined grinding system of vertical mill

In this system, the external circulation vertical mill is used as the pre-grinding equipment. After the material is separated by the external V-type powder separator with high material / gas ratio, the coarse powder is returned to the vertical mill to continue grinding, and the fine powder is sent to the pipe mill to form the final product after grinding by the tube mill.

In the combined grinding system of external circulation vertical mill, the V type separator used in the vertical grinding pregrinding system is the V type separator with horizontal dynamic rotating cage. This separator has the advantages of both V type separator and the third generation separator. Compared with the system of ordinary V type separator, it can effectively reduce and control the grinding particle size of the post sequence tube mill, and thus greatly improve the grinding condition of the mill. After grinding and sorting by external circulation vertical grinding, the particle size of the material is greatly reduced, the characteristic particle size is 0.057mm, and the 0.08mm screen residue of the grinding material is less than 30%. The vertical mill with high grinding efficiency bears the breaking of most materials. Crushing function:the pipe mill completes the final processing process of materials.

Semi-final grinding system of cement vertical grinding


On the basis of the combined grinding system, the system adds the fine powder separation system. Through the high-efficiency powder separation system, the qualified finished products rolled by vertical mill are selected in advance and no longer entering the pipe mill. On the one hand, it can benefit the stability of the external circulation vertical abrasive machine and improve the grinding efficiency. On the other hand, the qualified fine powder is selected in advance, which greatly reduces the phenomenon of``over-grinding'' in the pipe mill, avoids the formation of material mat in the pipe mill, improves the crushing and grinding efficiency of the ball tube mill, and achieves the purpose of increasing the production and reducing the consumption.

The recently rising semi-final grinding system of roller press, as mentioned earlier, because of its low spherical degree of material particles after grinding, taking out qualified fine powder will lead to an increase in the water requirement of cement marking consistency, so the proportion of this part of the finished product should not be too high, generally less than 15% ≤ 20% of the total amount of cement. However, if the semi-final grinding system is used, the proportion of this part of the finished product has little effect on the water demand of cement, so it can be equipped with an efficient powder separation system to select all the qualified fine powder in advance as far as possible, the output of the system is higher and the power consumption is lower.

Cement vertical grinding final grinding system


The system completely cancels the pipe mill with low grinding efficiency, and is completely made of cement by high efficiency material bed grinding, and realizes the non-nodulization of cement grinding. On the one hand, it is beneficial to reduce the power consumption of the system (compared with the tube grinding system without pre-grinding equipment, the power consumption of the product process is reduced by more than 35%), on the other hand, it can also greatly reduce the metal consumption.

Application of cement Vertical Mill in cement Mill


3.1 Application of combined grinding system of external circulation vertical grinding

3.1.1 Application of cement Mill system in Plant A

The original cement grinding system of Plant A is a cement closed circuit system of 3.2 × 13m. The output is low and the power consumption is as high as 38 × 40kWht. Nanjing Kaisheng International Engineering Co., Ltd. adopts the combined grinding system composed of "22.3 outer circulation vertical mill + V type separator with rotor cage + dust collector + 3.2x13m tube mill (open circuit)".

The vertical grinding efficiency of the pre-grinding equipment in the cement grinding system is high. The content of fine powder in the vertical grinding material is as follows: 17 ≤ 22% of 0.045mm particles and 24 ≤ 28% of 0.08mm particles. In addition, the V-type powder separator with rotor cage can effectively prevent the particles above 0.5mm from entering the pipe mill, which ensures that the materials entering the pipe mill are basically below 0.5mm. The internal structure of the pipe mill is designed for such fine materials, and the high efficiency grinding function of the pipe mill is brought into full play, so that the output and power consumption index of the system are superior.

3.1.2 Application of cement Mill system in Plant B

B. There are a plurality of sets of cement pipe mills in the range of 3.2 to 13m. Because of the large water content of the cement raw materials, the comprehensive moisture content in the grinding of the PC32. 5R cement is about 3.5%, up to 4.3%, and even when the PO42.5 cement is ground, the comprehensive moisture content of the raw materials reaches 2.5%, and the yield at the stage is 35-40t/ h, and the power consumption of the system is between 45 and 50 kWh/ t. In order to improve the production capacity, the factory uses the "22.3-P external circulation vertical mill + V type powder separator + horizontal fine powder separator" pre-powder grinding system, which is developed by Nanjing Kaisheng, to carry out technical transformation on the pipe mill system, which is made up of a pipe mill. Combined grinding system of road

The features of the production line are as follows:

The main results are as follows:

(1) because of the large moisture content of cement raw material, the kiln head waste gas feeding and powder separation system which is introduced into the kiln system of the plant is designed.

The material is dried in the middle, and the new high moisture material first enters the powder separation system to dry initially and then into the vertical mill for grinding, but it will increase the power consumption of cement process.

(2) in order to realize the effective drying of materials in the powder separation system, the system adopts V selection and horizontal selection.

On the other hand, this type of powder selection system increases the power consumption of cement grinding.

(3)The production line is higher than the same specification due to the pipe mill itself(the mill is old and the transmission efficiency is low).

The running power consumption of the tube mill with the installed power is high, which is lower than the rated load, and the actual power consumption exceeds the rated power. The successful operation of the production line is a great breakthrough in the high moisture raw material cement grinding production line by the external circulation cement vertical grinding system. Through reasonable equipment and process design, the external circulation cement vertical grinding system has good adaptability to the higher moisture raw materials.

3.2 Application of semi-final grinding system in external circulation vertical grinding

The cement mill in Plant C is a new cement grinding system, which is composed of "26.3 outer circulation + 3.8 × 14.5m tube mill V fine separator", which shares a set of double loop flow semi-final grinding system of fine separator.

The characteristics of the process system are that the external circulation vertical mill and the tube mill share a fine powder separator, the fine powder of the vertical grinding system after V separation and sorting is brought into the fine powder separator from the inlet of the fine powder separator, and the material of the pipe mill enters the fine powder separator through the upper material distribution device. The system reduces a set of powder separation system and reduces the investment of equipment and civil construction. at the same time, the finished product of vertical mill and pipe mill can be fully mixed in the separator, which avoids the problem of cement quality fluctuation caused by the large composition difference between the two parts in the semi-final grinding system. However, a fine powder separator is shared. The design of the system, the performance of the fine powder separator and the operation control are required. Ask for higher.

3.3 Application of the final grinding system of external circulation vertical grinding

As mentioned before, the spherical degree of the fine powder particles milled by the external circulation vertical mill is superior to that of the roller press, and the vertical mill can be used as the final powder mill to grind the cement.

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