HOME > NEWS > Company news >

Effect of the mill on the mill

Date:2019-06-25 13:33     writer:cement editor     Views:

1. Give full play to the function of powder separator.

With the increase of mill specifications and the energy saving, high yield and high quality requirements of cement grinding, closed circuit grinding is the inevitable trend of cement grinding technology. The necessary equipment for closed circuit grinding is powder separator. The function of the powder separator is to select the particles that reach a certain particle size in time. The powder separator itself does not produce fine powder, but because the fine particle material can be selected in time, the material condensation and adhesion to the grinding body and silo can be avoided, and the overgrinding of the grinding material can be reduced, and the variety of cement production can be adjusted timely and conveniently, the high fineness cement can be produced, and the grinding efficiency can be improved.
The closed circuit grinding system of the pre-grinding equipment in the grinding process, the material that enters the mill from the grinding head, is broken in a silo, passes through a warehouse quickly through the gap of the ball, and enters the second warehouse through the partition plate. The effect of the grinding body on the material in the second silo is mainly grinding, and the crushing effect is very small. Under the driving of the mill cylinder, the motion state of the small grinding body is rubbing, rolling and sliding. The grinding body grinds and peels the material particles in the process of laxation and rubbing. If the material can not be discharged outside the circulation system in time after grinding and stays in the mill for a long time, it will gather more and more, and the grinding body will continue to grind and peel these overly fine material particles. Leaving leads to overgrinding of materials. Therefore, improving the ability of powder separator to select fine powder is helpful to give full play to the grinding ability of mill. The separator is an important part of the grinding system, and the operation parameters of the separator are related to the production of the whole unit. The higher the separation efficiency of the powder separator, the more the finished product, the higher the output of the mill. In the closed circuit circulation system, the focus of cement grinding is mainly on the effect of relatively coarse grade particles.
The main functions of the powder concentrator can be summarized as: "dispersion", "classification", and "collect". The dispersion means that the material entering the powder separator is to be scattered as much as possible, and a certain space distance is formed between the material particles. Therefore, the structure, the rotating speed, the size of the material spreading space, the material moisture and the flow of the material directly influence the distribution and the dispersion effect. The grading refers to the function of sorting the dispersed material in the limited residence time of the powder-selecting chamber, and the coarse and fine particles can be separated as far as possible by means of the air flow and sent to the respective outlets. The collection is the ability to capture coarse and fine powder, which is related to the collection And the structure of the collecting member. Therefore, the influence of gas flow rate, gas flow velocity, gas flow pattern, gas-solid distribution point and flow field distribution and the number and structure of the powder selection chamber have a great influence on the classification efficiency.

Evaluation of comprehensive performance of powder separator

The influence of the separator on the working condition of the mill is mainly reflected by the powder separation efficiency, the circulating load rate and the grinding efficiency of the mill. Powder separation efficiency(E):a technical parameter indicating the ability of the separator to select fine powder. Refers to the ratio of the fine component of a certain stage in the finished product after the powder separation and the content of the particle in the feeding amount of the separator. The high powder separation efficiency indicates that the mill output of the closed-circuit grinding system is expressed by the amount of fine powder selected by the separator.
E = (100-g/100-a) × (b-a/b-g) × 100% (2)
In the formula: G, a, b, respectively, the fineness of the finished product, grinding and returning powder (excess);
The cyclic load rate (L):) refers to the ratio of the return quantity B to the finished product (feed quantity) G of the powder separator:
L ≤ B ≤ G = (a ≤ g) / (b ≤ a) × 100% (3)
The relationship between powder selection efficiency E and cyclic load rate L is as follows:
E = (g ≤ a) (1 ≤ 1 L) × 100% (4)
The circulation load of the powder separator is closely related to the comprehensive performance of the system equipment, the ventilation in the grinding machine and the gradation of the grinding body.
Excessive circulating load and excessive amount of material in the mill affect the grinding efficiency;The cyclic load rate reflects the cooperation of the mill and the separator. At the same time, the circulating load rate also shows the length of material retention time in the ball mill. The cycle load rate is too high, which indicates that the retention time of the material in the mill is short and the degree of grinding may be insufficient. The content of fine powder in the mill material is low, and the increase of the output at the mill table is limited. If the circulating load rate is too low, the material retention time in the mill is too long, the qualified fine powder cannot be polished out in time, and the grinding phenomenon is easy to occur, resulting in the reduction of grinding efficiency and affecting the output of the mill. Therefore, it must be in place.  And the production quality of the mill can be improved.
For the same milling system, the grinding effect of the mill increases with the increase of the circulation load, and increases with the increase of the powder selection efficiency. And the powder selection efficiency of the powder separator decreases with the increase of the circulation load. Therefore, in the production process, the powder selection efficiency can not be carried out on one side, and the circulation load can not be increased too much. It is necessary to improve the efficiency of the powder selection under the appropriate cyclic load, so that the grinding efficiency can be effectively improved. In general, the longer the mill, the lower the cycle load rate. The finer the fineness of the finished product, the greater the cycle load rate. The increase in the cycle load means that the amount of material passing through the mill is increased; the amount of material fed to the powder feeder is increased, separated, The more difficult it is, the easier it is to increase the load of the powder separator, and the efficiency of powder separation will inevitably decrease. It can be seen from formula (4) that the cyclic load rate is inversely proportional to the powder selection efficiency.
The comprehensive performance of the powder separator is evaluated as follows: one is the powder separation efficiency, the other is the percentage of 3 ~ 30 μ m particles in the separated finished product. Because the particles in this interval are the best part of cement strength. The efficiency of powder selection directly affects the output of mill. Too low powder separation efficiency will restrain the mill output, too high powder separation efficiency, 30 ~ 80 μ m particles account for a large proportion of the finished product, the specific surface area of cement is reduced, and the cement strength is reduced. Therefore, too high and too low powder selection efficiency is not an ideal indicator. The simplest detection method for evaluating the performance of powder separator in practical production is to measure it. The less the content of ≤ 30 μ m particles in the return material and the less the content of ≤ 30 μ m particles in the return material, the better the performance of the powder separator.
Influence of powder separator on mill

3.1 relationship between grinding efficiency and cyclic load rate

(1) The production capacity of the mill increases with the increase of the cycle load rate, because the more coarse particles, the higher the grinding efficiency.
(2) The grinding efficiency is increased with the increase of the powder selection efficiency, but the powder selection efficiency is inversely proportional to the cycle load rate.
Therefore, the relationship between the grinding efficiency of the mill and the circulating load rate of the separator and the powder separation efficiency needs to be weighed. Relevant data show that for the circle flow mill composed of centrifugal separator, the circulating load rate is 200%~300%, and the powder separation efficiency is 41%~51%, the grinding efficiency is the highest;When the circulating load rate is 150%~200%and the powder separation efficiency is 55%~65%, the grinding efficiency is the highest. For the circulation mill composed of OSepa separator, the circulating load rate is 100%~200%, and the powder separation efficiency is 63%~79%.  The highest rate. With the progress of science and technology and the accumulation of production experience, the grinding process theory has been updated increasingly. At present, some enterprises adopt a new type of high-efficiency powder concentrator, the circulating load rate has been reduced to below 100%, the powder separation efficiency has been increased to more than 70%, which plays a powerful role in promoting the high output and energy saving of the mill.
As the material from the grinding tail is required for closed-circuit grinding, the material can be stored in both thickness and fine, and the grinding can not be carried out after all the products are qualified. Therefore, the circulation of the material in the mill is greatly increased;The buffer action caused by the adhesion of the fine powder to the grinding body in the mill is reduced, and the amount of material entering the grinding is increased, which greatly improves the output of the mill. Therefore, under the condition that the grinding capacity of the mill permits, the circulating load rate and the output of the mill are a direct ratio, but the relationship with the powder separation efficiency is inversely. In the same case, if the circulating load in the mill is increased, the mill output will be increased. However, large circulating load rate will decrease the efficiency of powder separation, and many qualified products cannot be selected.  Come back to the inner cycle to limit the increase in the output of the grinder. This is a state of contradiction. The main measure to solve this contradiction is to pay attention to the improvement of the performance of the powder separator.

3.2 matching of powder selection ability and grinding ability

To improve the production capacity of closed cycle cement grinding system, the first thing to solve is the matching between the powder separation ability of the separator and the grinding ability of the mill. According to the quality requirements of the product, the fineness of grinding cement should be controlled within a certain range. If the fineness of the finished product is the same: when the fineness of the feed is constant, the cyclic load rate decreases with the thicker the return material, and the powder selection efficiency increases with the thicker feed size. When the fineness of the feed is not changed, the cyclic load rate increases with the thicker feed of the powder separator, and the powder selection efficiency decreases with the thickening of the feed. The greater the difference between the fineness of the returning material and the fineness of the grinding machine, the more the powder separation ability of the powder separator will be improved, and a lower cycle load rate and a higher powder selection rate will be formed. Efficiency, the mill can increase the feed, increase the output. However, we can not only take the powder separation efficiency as the index to measure the performance of the powder separator. General high efficiency powder separator, powder separation efficiency up to 65% performance has been good. For any powder separator, the powder separation efficiency can be adjusted to more than 90%. The easiest way is to adjust the fineness of the finished product to the fineness of the finished product and go to the extreme, so that the closed circuit grinding is meaningless. It must be fully realized that the improvement of grinding efficiency is a system engineering.
In production practice, it is necessary to ensure the balance between grinding ability and powder selection ability. To realize the matching between the powder separation ability and the grinding ability of the mill, the powder separation ability of the powder separator is usually greater than that of the mill. The ability of grinding must not be affected by the lack of powder selection ability. At present, the grinding ability of cement grinding in many enterprises has not been brought into full play, one of the important reasons is that the reasonable matching between grinding ability and powder selection ability has not been realized. We should take it as a warning!

Inquiry You can get the price list and we will contact you within one business day!

Contact us

Active lime is produced from limestone dolomite chalk and other minerals with high calcium carbonate content by the calcination process under the temperature of 1000-1100 ° C. There are various processes for the active lime production mainly

Whatsapp:+86 17372753906 Skype:0086-25-82232507 Tel:0086-25-82232507 E-mail: Add:The Tiansheng Building 20 Layer,Yunlongshan Road No.98,Jianye District,Nanjing, P.R.China
WhatsApp
E-mail
WeChat
0086-25-82232507