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Influence of powder separator on mill

Date:2019-05-07 17:27     writer:admin     Views:

  Influence of powder separator on mill

  With the increase of mill size and the requirement of energy saving, high yield and high quality for cement grinding, the closed circuit grinding is the inevitable trend of cement grinding technology.

  The necessary equipment for closed circuit grinding is a powder separator.

  The function of the separator is to select the particles of certain size in time.

  The separator itself does not produce fine powder, but because of the ability to select the fine particle material in time, avoid the occurrence of material condensation, adhesion to the grinding body and sticky warehouse, can reduce the grinding of the materials in the grinding;

  Can promptly and conveniently adjust the varieties of cement production, production of high fineness cement, improve grinding efficiency.

  The closed circuit grinding system of the pre-grinding equipment in the grinding process, the material from the grinding head into the mill, is broken in the first warehouse, from the gap in the ball quickly through the first warehouse, through the compartment board into the second warehouse.

  The grinding body in the second storehouse plays a major role in the grinding of materials, and the crushing effect is very small. The small grinding body is driven by the cylinder of the mill, and its movement state presents as rubbing, rolling and sliding.

  The abrasive body grinds and strips the material particles in the process of shedding and rubbing.

  If the material is not discharged out of the circulation system in time after grinding, it will stay in the grinding for a long time and will accumulate more and more. The grinding body will continue to grind and peel these ultra-fine material particles, which will lead to excessive grinding.

  Therefore, improving the ability of selecting fine powder is helpful to give full play to the grinding ability of the mill.

  Powder separator is an important part of the grinding system. The operating parameters of the separator are related to the production of the whole unit.

  The higher the sorting efficiency, the more finished products, the higher the output of the mill.

  In the closed circulation system, cement grinding is mainly focused on the role of relatively coarse particles.

  The main functions of the separator can be summarized as: "dispersion", "classification", "collection".

  Dispersion refers to the material into the separator to scatter as far as possible, material particles to form a certain distance between the space.

  Therefore, the structure, rotating speed, size of spreader space, material moisture and material flow directly affect the cloth and dispersion effect.

  Classification refers to the separation of dispersed materials in the powder room within a limited time, the use of various forms of air separation function, to make full use of the air to separate coarse and fine particles as far as possible, and sent to their respective export.

  Collection is the ability to capture both coarse and fine powder, depending on the method of collection and the structural form of the collected parts.

  Therefore, gas flow rate, airflow velocity, airflow mode, gas-solid junction and flow field distribution, as well as the number and structure of powder separation chamber have a great impact on the grading efficiency.

  Comprehensive performance evaluation of the separator

  The influence of the separator on the working condition of the mill is mainly reflected by the efficiency of powder selection, the rate of cycle load and the grinding efficiency of the mill.

  Powder selection efficiency (E) : it is a technical parameter to show the ability of selecting fine powder.

  Refers to the ratio of the fine weight of a certain grain grade in the finished product after powder preparation to the content of the grain grade in the feed amount of the powder separator.

  The high efficiency of powder selection indicates that the separator can select more fine powder from the grinding materials, and the output of the mill in the closed circuit grinding system is expressed by the amount of fine powder selected by the separator. Therefore, the high efficiency of powder selection is conducive to improving the output of the mill.

  E = (100 - g / 100 - a) * (b - a/b - g) x 100% (2)

  Where: g, a and b -- fineness (passing amount) of finished product, outgoing grinding and return powder, respectively;

  Cycle load rate (L) : refers to the ratio of the feed quantity B of the separator to the finished product quantity (feed quantity)G:

  L = B/G = (a - G)/(B - a) x 100% (3)

  There is the following relationship between powder selection efficiency E and cycle load rate L:

  E = (g/a) 100% (1/1) + L x (4)

  The circulating load of the separator is closely related to the comprehensive performance of the system equipment, the ventilation in the mill and the gradation of the grinding body.

  Too much circulating load, too much material in the grinding, affecting the grinding efficiency;

  The cycle load rate reflects the coordination between the mill and the separator.

  At the same time, the cycle load rate also shows the length of time the material stays in the ball mill.

  The high cycle load rate indicates that the material has a short residence time in the mill and the degree of being ground may be insufficient.

  If the content of fine powder is low, the increase of output will be limited.

  If the cycle load rate is too low, the material stays in the mill for too long, qualified fine powder can not be timely out of the mill, the phenomenon of excessive grinding, resulting in the reduction of grinding efficiency, affect the mill output.

  Therefore, it is necessary to operate under proper cycle load rate to improve the production quality of the mill.

  For the same grinding system, the grinding effect of the mill increases with the increase of circulating load, and increases with the increase of selecting efficiency.

  The efficiency of powder selecting machine decreases with the increase of circulating load.

  Therefore, in the production process, neither one-sided pursuit of powder selection efficiency, nor too much to improve the cycle load.

  The efficiency of powder selection must be improved under proper cycle load in order to effectively improve the grinding efficiency.

  Generally, the longer the mill, the lower the cycle load rate.

  The finer the fineness of the finished product, the higher the cycle load rate.

  The increase of cycle load rate means the increase of material through the mill;

  The more the material is fed into the separator, the more difficult the separation will be.

  If the load of powder separator increases, the efficiency of powder separator will inevitably decrease.

  It can be seen from equation (4) that the cyclic load rate is inversely proportional to the efficiency of powder selection.

  Evaluation of the comprehensive performance of the separator: one is the efficiency of powder separation;

  The second is the percentage of 3 ~ 30 m particles in the separated product.

  Because the particles in this section are the best part of the strength of the cement.

  The efficiency of powder selection directly affects the output of the mill.

  Too low powder selection efficiency will choke mill output;

  High powder selection efficiency, 30 ~ 80 m of particles in the finished product occupies a large proportion, cement specific surface area decreased, reduced cement strength.

  Therefore, too high and too low powder selection efficiency is not an ideal index.

  In practical production to evaluate the performance of the separator, the simplest test method is to determine the content of 30 m particles in the feed, the less the content of 30 m in the feed, the better the performance of the separator.

  Effect of powder separator on mill

  3.1 relationship between grinding efficiency and cycle load rate

  (1) the production capacity of the mill increases with the increase of cycle load rate, because the more coarse particles, the higher grinding efficiency.

  (2) the grinding efficiency increases with the increase of the milling efficiency, but the milling efficiency is inversely proportional to the cycle load rate.

  Therefore, the relationship between the grinding efficiency of the mill and the cycle load rate and the milling efficiency of the separator needs to be weighed.

  The relevant data show that: for the coil flow mill composed of centrifugal separator, the cycle load rate is 200%~300%, powder selection efficiency is 41%~51%, the grinding efficiency is the highest;

  For the cyclone mill, the cycle load rate of 150%~200%, powder selection efficiency of 55%~65%, grinding efficiency is the highest;

  For the o-sepa mill, the efficiency is the highest when the cycle load rate is 100%~200% and the efficiency is 63%~79%.

  With the progress of science and technology and the accumulation of production experience, the theory of grinding technology is being updated day by day.

  At present, some enterprises use the new high-efficiency separator, cycle load rate has been reduced to less than 100%, powder selection efficiency increased to more than 70%, to the mill high yield, energy-saving play a powerful role in promoting.

  Because the closed-circuit grinding requirements of the end of the material can be thick and thin coexist, do not need all qualified before grinding.

  Therefore, the material circulation in the mill is greatly increased.

  The buffering effect of fine powder adhered to the grinding body in the mill is reduced, and the amount of grinding materials is increased, so that the output of the mill is greatly increased.

  Thus it can be seen that, when the grinding capacity of the mill is allowed, the cycle load rate is proportional to the output of the mill, but inversely proportional to the efficiency of powder selection.

  In the same case, if increase the mill cycle load, the mill output will increase.

  But the larger cycle load rate will make the efficiency of powder selection decline, a lot of qualified products can not be selected, back to the mill cycle, limit the mill when the output increase.

  It's an oxymoron.

  The main measure to solve this contradiction is to pay attention to the improvement of the performance of the separator.

  3.2 matching of powder selecting ability and grinding ability

  To improve the capacity of closed cycle cement grinding system, the first thing to be solved is the matching of the powder selecting ability of the separator and the grinding ability of the grinder.

  According to the requirement of product quality, the fineness of grinding cement should be controlled within a certain range.

  If fineness of finished product remains unchanged: when fineness of feed remains unchanged, cycle load rate decreases with thickening of feed, while powder selection efficiency increases with thickening of feed.

  When the fineness of the feed remains unchanged, the cyclic load rate increases with the thickening of the feed, and the powder selection efficiency decreases with the thickening of the feed.

  The greater the difference between the fineness of the feed and the fineness of the mill, the higher the power of the mill, the lower the cycle load rate and the higher the efficiency of the mill.

  However, it is not only the efficiency of the powder as a measure of the performance of the powder separator.

  General efficient separator, powder selection efficiency reached 65% performance is good.

  For any one set of concentrator, can be selected powder efficiency to more than 90%, the simplest way is to put the grinding fineness of the finished product to the fineness, go to the extreme, so closed grinding is meaningless.

  It must be realized that the improvement of grinding efficiency is a systematic engineering.

  In the production practice, the balance between milling capacity and milling capacity should be ensured.

  In general, the powder selecting capacity of the equipped powder separator is greater than that of the mill.

  It must not affect the performance of grinding ability due to the insufficient ability of powder selection.

  At present, the grinding ability of many cement mills has not been well played, one of the important reasons is that there is no reasonable matching between grinding ability and powder selection ability.

  Take warning!

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