I. purpose and significance of the research

As is known to all, the crushing of materials by ball mill mainly depends on the impact and grinding effect of the grinding body on the materials. Such impact and grinding effect is transmitted through the surface of the grinding body to the materials in contact with it, which belongs to single particle grinding. Because of the accident of single particle grinding, a large amount of energy is consumed between the grinding body and the collision and wear between the grinding body and the liner of the grinding machine, so its efficiency is very low. Based on the Answlm crushing power theory, the pure mechanical loss of bearings and gears will account for 12.3%. Cooling with product accounted for 47.6%; Radiation from mill barrel accounted for 6.4%. Heat removal from air accounted for 31.4%; The theoretical energy consumption for pulverized materials is only a small fraction, about 2.3%.

At present, generally in the following two aspects to improve the ball mill grinding efficiency. One is to change the internal device. The development of energy-saving lining board and adjustable compartment board reduces energy consumption for the grinding system. The second aspect is to change the pulverizing system from open-circuit pulverizing system to closed-circuit pulverizing system. Accordingly, in order to improve the efficiency of powder selection and reduce the energy consumption of the system, the traditional first generation centrifugal separator and the second generation whirlwind separator have developed to the third generation of highly efficient separator due to the need of technological development.

The open-circuit grinding system is characterized by simple flow, less equipment, less investment and convenient operation. But because the material must meet all finished product fineness of material to the ground, therefore, when the fineness requirement is higher, has been fine grinding in meeting the requirements of the fineness of part of the material is not discharged in time and grinding occurred, reducing the grinding efficiency of grinding system, increase energy consumption (when grinding sexual difference between high quality cement and easy large mixed powder, grinding phenomenon more serious). The closed-circuit pulverizing system is equipped with a powder separator, which can separate qualified materials after pulverizing in a timely manner, thus effectively reducing the phenomenon of over-pulverizing, improving the system's pulverizing efficiency and output, and reducing energy consumption. At the same time, the fineness of the product is even and can be flexibly controlled by adjusting the operating parameters of powder selecting equipment to meet the production requirements. The disadvantage is that the system flow is complex and the investment is large.

The choice between the two grinding systems depends on the fineness of the product. According to the literature, when the product specific surface area of the grinding system is less than 3100cm2/g, the unit power consumption of the two systems (including auxiliary machines) is equivalent. But when the fineness is high, the unit power consumption of open circuit system is obviously higher than that of closed circuit system. Due to the development of the construction industry, the requirements for the strength of cement are higher and higher, and the corresponding requirements for product fineness are also improved. At the same time, the closed-circuit system is easier to control the product fineness, change the product variety, the adaptability to the market is stronger. Therefore, the closed circuit system has been widely used.

As an important auxiliary equipment of closed-circuit pulverizing system -- powder separator, although it does not have the function of crushing materials, its performance directly affects the running state of the system, that is, the pulverizing efficiency, output and energy consumption of the system. Therefore, the study of high-efficiency separator technology is of great significance, mainly reflected in the following aspects:

1. Requirements for increasing production and reducing consumption of the grinding system. The grinding system matched with the high-efficiency separator has higher grinding efficiency, higher output and lower energy consumption. The closed-circuit pulverizing system equipped with traditional pulverizer can produce cement of general fineness with no lower energy consumption per unit than open-circuit system. In the production of high fineness cement, although compared with the open circuit, the power consumption is reduced and the output is increased, but compared with the production of general fineness cement, the output is significantly reduced. And if the use of efficient separator, although there is a similar phenomenon, but its reduction significantly reduced.

2, cement quality requirements, but also put forward higher requirements for the separator. On the one hand is the use of manufacturers to improve the quality of cement requirements, to high fineness, high grade cement development trend, and for the production of high fineness cement, open-circuit grinding or with traditional powder separator closed circuit grinding system is difficult to competent. On the other hand, people's further understanding of cement quality has changed some opinions on the evaluation of cement quality. At first, cement fineness as one of the main indicators of cement quality is controlled by sieve residue, with sieve residue control can only reflect the number of coarse particles in the finished product, can not reflect the size of all the particles; Then it developed to specific surface area control, the finer the cement, the larger the specific surface area. Now it is found that even the cement products with the same surface have different strength due to different grinding process and powder selection. Closed circuit grinding with high efficiency separator can be lower, the reason is the different particle size. The results show that the hydration properties of cement vary with the size of cement particles. Particles larger than 60 m have little effect on the strength of cement and only act as filler. The hydration process of particles less than 3 m is completed in the early hardening stage, which is only beneficial to the early strength of cement. Particles of 3-30 m are the main active part of the cement, bearing the main diameter of strength growth. In this regard, some cement varieties have put forward specific requirements for the content of 3-30 m particles:

Portland cement: 40-50%

High strength fast setting cement: 50-60%

Ultra high strength fast cement: > 70%

It can be seen that the quality of cement is closely related to the content of 3-30 m particles in the finished cement products. However, in the cement grinding operation, in order to get a cement product with a high particle size range and a relatively narrow distribution, it is difficult to achieve it unless it is regulated and controlled by an efficient powder separator.

3. Research results of high-efficiency separator technology can be extended to separation technology in non-metallic mineral, chemical, food and other industries; The classification of ultrafine powder is a key technology in the field of mechanical preparation of ultrafine powder.

Second, the development and status of the powder separator

Cement industrial separator was invented by the British Munfond and Moadie in 1885, after the German acquired the manufacturing right, began to sell in 1888. Traditionally known as Sturtevant, the so-called "Sturtevant" concentrator, because the American producer Sturtovant is the best known for its production, it is called the "first generation" concentrator. With the progress and development of industrial technology in the world, humbold-vidag company of Germany developed humbold-vidag type powder separator in the early 1960s, namely the so-called cyclone type powder separator, namely the second generation of powder separator. Because of the limitation of the structure and working principle of the first generation separator, the efficiency of powder selection is not high, and the efficiency and output of the grinding system are limited. Because the core structure of the second generation of powder separator does not deviate from the category of the first generation of powder separator, there is no fundamental change in the working principle, so the performance improvement is limited. In nearly a decade, has been a breakthrough classifier research development, the foreign companies have developed a new type of high efficiency of the third generation classifier, such as Japan onoda company pioneered O - Sepa classifier, by using a new hierarchical structure and principle, significantly improve the efficiency of the classifier of powder and output, cement quality and energy consumption system is also improved.

Iii. Performance characteristics and classification mechanism of various classifiers

3.1 centrifugal separator

Centrifugal separator due to its own structural defects, the existence of powder selection efficiency is low, fineness adjustment is not convenient and other shortcomings, when the demand for high yield, fineness and more varieties of cement, performance is more prominent. Generally speaking, the air separator powder selection process is mainly divided into the following three links: material dispersion, classification and fine powder collection. It is in these three links that centrifugal separator has problems to varying degrees. The analysis is as follows:

The force of particles in the centrifugal separator is as follows:

Gravity Fg, the direction downward, the size is proportional to the particle mass;

The direction of centrifugal force Fe is horizontal, radial and outward.

The direction and magnitude of the gas resistance Fd vary with the position.

The sum of the three is R. Due to the large change in the shape of the section in the grading area, the size and direction of the airflow velocity in each section change greatly, and the graded airflow cannot form a stable and uniform grading force field. Therefore, particles of the same size in the grading zone will be subject to different resultant forces in size and direction due to their different positions. A local eddy current is formed in the dead Angle due to the sudden change of the top-to-bottom grading air flow at the upper cover of the grading area, which interferes with the flow field in the grading area. At the same time, the presence of wall effect, but also affect the separation of fine powder, so that part of the fine powder and coarse powder together with the inner wall and settlement. These two factors result in the classifier has no clear grading interface and stable grading field, and the grading accuracy is low.

The material in the separator is mainly scattered by the centrifugal force of the spreader, which cannot be evenly distributed on the whole section. At the same time, the instability of the flow field in the classification area aggravates the uneven dispersion of materials, and the sufficient and even dispersion of materials is the precondition to achieve high efficiency classification.

The fine powder of the centrifugal separator is collected by the external cylinder. Due to the larger diameter of the external cylinder and the lower efficiency of fine powder collection, a large amount of fine powder circulates with the air flow. On the one hand, it increases the powder concentration in the grading area and intensifies the mutual interference between particles. On the other hand, with the increase of powder concentration, the fine powder is easier to agglomerate or settle to the wall together with the coarse powder, so that the fine powder content in the coarse powder increases.

As a result of the above factors, resulting in the reduction of powder separation efficiency.

3.2 cyclone separator

Because the cyclone separator set up an independent air circulation fan outside, instead of centrifugal separator in the wind blade; 6-8 cyclone dust collectors are arranged around the body to collect fine powder. The internal circulation mode of the centrifugal separator is changed to the external circulation mode. The two processes of material classification and fine powder collection of the separator are separated.

• the rotor speed and the circulating air volume of the system can be adjusted separately, which is easy to adjust the product fineness, but also expand the fineness adjustment range. The specific surface area of cement products can be adjusted from 2500 to 7000cm2/g.

The adoption of small diameter cyclone dust collector to collect fine powder, can improve the collection efficiency of fine powder (its collection efficiency can reach 90%, and the centrifugal separator collection efficiency is only 50%), reduce the circulation of fine powder, is conducive to improve the efficiency of powder selection.

Powder selection efficiency is improved, the treatment of increased air volume. Under the same powder separation capacity, the body diameter of the cyclone separator is smaller than that of the centrifugal separator, and the amount of material processed per unit sectional area of the grading room is 2-2.5 times higher than that of the centrifugal separator.

However, because the classification structure of the cyclone separator is similar to that of the centrifugal separator, the main defects of the centrifugal separator (such as the instability of the classification field, the existence of local eddy in the wall effect, etc.) have not been eliminated. Therefore, the improvement of its grading performance is limited.

3.3 the third generation of high-efficiency separator (taking 0-sepa separator as an example)

The material to be added to the separator is passed from top to bottom through a higher classification opportunity consisting of a vertical arrangement of eddy current regulating blades and guide blades on the separator rotor. In the classifying zone, there is no local eddy current caused by the wall effect and dead Angle, and the pressure difference between inside and outside is always the same at any height of the same radius, and the airflow velocity is the same, so as to ensure the stability and invariability of the equilibrium relationship between the forces exerted on the particles. The impact of buffer plate and the scouring of horizontal eddy current make the material fully dispersed and evenly distributed in the grading area. This makes the classifier have the following performance characteristics:

1, powder selection efficiency is high, generally more than 85%.

2, high precision, that is, the Tromp curve is relatively steep.

3. The fineness adjustment is simple, sensitive and accurate.

According to the literature, the separation rate of centrifugal separator is generally in 40-60%, classification accuracy is less than 0.3; The separation efficiency of the cyclone type powder separator is generally about 60%, the classification accuracy is 0.3-0.45; The separation efficiency of the third generation of high efficiency separator represented by 0-sepa is generally above 80%, and the grading accuracy can reach about 0.5.

At present, the domestic research on the powder concentrator is mainly focused on the research and development of high-efficiency powder concentrator, or on the transformation of existing equipment, in the digestion and absorption of foreign similar products advanced technology, at the same time, strive to have a breakthrough, the development of high-performance powder concentrator.

Development and performance of high efficiency double rotor type separator

Efficient of the classifier performance superiority is obvious, however, the subjects classifier without powder collection device, need to be equipped with and match the parameters of the large size of bag type dust collector or electrostatic precipitator is used to collect the finished product, it is greatly increase the investment system, also make the complex process arrangement, operating control is difficult, to a certain extent, limits the application of highly efficient classifier.

Rotor type classifier is aimed at the situation and development of a new type of high efficient classifier, in order to achieve the efficient classifier in performance, in the complexity of system layout, investment and technology, etc and is superior to the efficient classifier, it certainly, grinding system for the development of the cement production technology of energy saving is very meaningful to increase production. On this basis, aiming at the new requirement of fineness of cement in cement factory, we have developed a new type of double-rotor separator together with tsinghua unisplendour gillida company.

The structural characteristics of the high-efficiency double-rotor separator are as follows:

1. Centrifugal force field is adopted as the grading force field, and double-cage rotor is adopted in the structure. Considering the characteristics of air flow movement and distribution in the classifier, the rotor is of inverted cone structure to ensure the stability of classifying field in the classifier.

2. The cage rotor is mounted on the spindle together with the feeding pan. The spindle is driven by a speed-regulating motor, which ensures that the strength of the grading force field can be flexibly adjusted by changing the motor speed, so as to change the force of particles in the grading force field, control the cutting size of the grading, and adjust the fineness and granularity of the product.

3, the use of high throwing force of the propeller type spreader, so that the material can be more evenly distributed in the grading area, the use of cone constraints, in order to stabilize the flow field of the powder room, and with the ring into the air drip device to form a secondary separation structure, in order to enhance the secondary separation effect, reduce the amount of fine powder mixed in the coarse powder.

4, the collection of fine powder using a number of small specifications of efficient cyclone parallel, arranged around the main body of the separator to form a whole, on the one hand to improve the separation efficiency of fine powder, on the other hand compared with other efficient separator, simplify the system process, save the system investment, regulation, control is more convenient.

5, classifier processing using external circulation fan supply air flow and lower part of the classifier tangential import classifier, and the drip tube formed by the diversion of a rotating flow field into the selected powder chamber of rising with the sa are scattered in the area of material mixing, forming a hierarchical classification of material flow field is relatively stable, fine powder by the air flow to carry out after the classification classifier, imported cyclone cylinder gas-solid separation. In this way, the treated air volume in the separator can be controlled by the regulating valve in the fan pipe, and together with the cage rotor with adjustable speed, the grading force field in the grading room can be adjusted to control the fineness and particle size composition of the product.

In addition, considering the first generation of the cement industry, the application of the second generation of classifier is relatively common, especially the application of the second generation of classifier is more common, in production applications, such as to take effective measures to reform and improve the performance of the classifier, and improve the efficiency of the grinding system, output, the effective ways to reduce energy consumption. Therefore, in the structural design of the high-efficiency double-rotor type powder separator, the possibility of applying the technology to the transformation of the original powder separator is fully taken into account, so as to achieve the development of the technology as a new high-efficiency powder separator and the transformation of the existing powder separator.

Based on the above structural characteristics, the experimental study and production application show that the high-efficiency double-rotor separator has the following performance characteristics:

1. Materials in the grading room have good dispersion, high strength and high grading efficiency under the action of strong swirling and radial shear force.

2, the separation of materials through the grading interface clear powder selection area, the powder selection conditions of each part is stable, so the classifier classification accuracy is high.

3. The fineness adjustment is convenient and reliable, and the adjustment range is wide, which can be flexibly controlled by adjusting the spindle speed and air volume.

4. The open-flow mill can increase production by 40-60% and the efficiency of powder selection can reach over 85%. If the existing wind separator or centrifugal separator for transformation, without changing the main structure and motor load, to ensure that the efficiency of more than 85%, 20-30% increase.

5, in the same output, compared with the high efficiency of the eddy current separator, but can reduce the system investment of 20-30%, compared with the cyclone and high efficiency of the centrifugal separator, not only can reduce the equipment specifications, and can improve the efficiency of 20-40%.