Filtration principle and filter type

1. What is the general principle of filtration? Is the filter divided into several types?

The general principle of filtration is the process by which the slurry passes through a porous filter medium (usually a filter cloth) to separate the solid material from the liquid. At this point the liquid (filtrate) flows out through the pores of the separator, while the solid particles are blocked on the surface of the filter cloth and form a dense filter cake. Filtration is generally the second stage of dehydration.

Currently used in beneficiation plant is a continuous vacuum filter, its version number, the disk is divided into park and garden cartridge filter according to the different surface shape. The cylinder type is further divided into an outer filter type and an inner filter type. In recent years, magnetic filter plants have widely used external filter magnetic filters.

2. Working principle and classification of common cartridge vacuum filter?

The tubular vacuum filter is filtered with a filter cloth (nylon cloth, canvas). A plurality of capillary pores are formed between the fibers of the filter cloth, and the slurry is pumped to a negative pressure by a vacuum pump on the filter cloth. Under this pressure, the liquid in the slurry flows through the filter tweezers to become a filtrate, and the solid particles in the slurry are retained in the slurry. The filter cake is formed on the filter cloth. As the time increases, the thickness of the filter cake also increases, and most of the moisture is removed to complete the dehydration work.

The tubular vacuum filter used in China can be basically divided into four categories: 1) tubular external filter vacuum filter; 2) cylindrical internal filter vacuum filter, 3) cylindrical external filter vacuum magnetic filter ( Referred to as magnetic filter), 4) Folding vacuum filter.

3. Why is the filtration process a very complicated and intractable process?

When filtering, the greater the degree of vacuum, the larger the particle size of the material, the smaller the viscosity of the slurry, and the thinner the filter cake, the better the filtration effect and the faster the filtration rate. However, in actual production, the filtration process is a very complicated physical process, and sometimes the degree of vacuum, particle size, and cake thickness are not ideal. The degree of vacuum, the particle size of the material, and the thickness of the filter cake are mutually constrained and do not exist in isolation. Factors affecting the speed of filtration must be analyzed in detail with specific circumstances. For example, the thinner the thickness of the filter cake, the faster the filtration speed, but if it is too thin, the air permeability of the entire filter surface will be too large, and the thickness of the filter cake will be uneven, and even there will be partial air leakage, which will cause vacuum leakage. That is, the sealing property of the filter cake is not good, so that the degree of vacuum is lowered, which in turn makes the filtration idling slow.

4. What are the indicators for the mineral processing plant to measure the filtration effect?

In the concentrator, there are two main indicators for measuring the filtration effect. One is the level of production capacity, with production per square meter per hour tons of dry coal slag fine representation of the number (t / ² when meter), called the utilization factor. The dry concentrate powder weight refers to the net weight of the concentrate powder after the filter cake is dried and completely removed.

Another indicator is the level of moisture in the filter cake, expressed as a percentage by weight of the moisture in the filter cake, known as filter cake moisture.

5. What are the production characteristics of vacuum magnetic filter?

The vacuum magnetic filter is a newly developed filter designed for the dehydration of a class of ferromagnetic concentrates such as magnetically selected iron concentrates. Its greatest feature is its high production capacity. It has a magnetic pole composed of permanent magnets, uses magnetic force to attract the strong magnetic concentrate in the slurry to form a filter cake, and then uses the vacuum negative pressure to remove the water in the filter cake.

The ability of the pole to attract concentrate is much greater than the ability to vacuum concentrate, and a filter cake that is much thicker than the inner filter can be obtained, with a factor of two or three times that of a cylindrical internal vacuum filter. However, the filter cake moisture of this filter is slightly higher than that of the internal filter vacuum filter, but it is still generally welcomed by the magnetic separation plant from the general use effect.

6. What are the production characteristics of the folding belt vacuum filter?

How to improve the dewatering effect of fine and sticky materials has always been a difficult problem in the dewatering operation. The appearance of the belt-type vacuum filter has pushed the dewatering of fine-viscous materials one step forward at the level of the cylindrical external filter vacuum filter. .

The characteristics of the belt-type vacuum filter are mainly to strengthen the washing of the filter cloth to maintain the permeability of the filter cloth, and at the same time adopt a better unloading method. Therefore, the utilization factor for filtering fine-adhesive materials is higher than that of the external filter, and the moisture is slightly lower than that of the external filter. In recent years, such filters have developed rapidly in China. Some concentrating plants have transformed the original tubular external filter vacuum filter into a folding belt filter, and the dewatering index has been improved, and good results have been achieved.

7. How to eliminate the “leakage vacuum” in the production of the cylindrical external filter vacuum filter?

When the tubular external filter type vacuum filter sucks the filter cake, sometimes the filter cake may be cracked, causing a "leakage vacuum" and a decrease in the degree of vacuum. In order to eliminate the crack, the filter cake can be pressed by a mechanical method such as a press roll, a press belt or a press to maintain the degree of vacuum. As a result of this, the filter cake is free from cracks, and the dewatering effect is also improved, and the moisture of the filter cake is lowered.

8. What are the factors that affect the filtering effect?

The main reason for the production of the concentrator is to enable the filter to have the highest possible production capacity and to obtain the filter cake with as low a moisture as possible. However, the factors that affect the dewatering effect of the filter in production are many, and the main factors affecting the filtration effect are:

1) The nature of the pulp. Mainly realized that the slime is too much, the particles are too fine and the residual agent of the pulp is too much, which makes the slurry too sticky.

2) The degree of vacuum. The degree of vacuum must be maintained at a high level, which is highly dependent on the thickness of the filter cake and the moisture level.

3) The life and water permeability of the filter cloth. In recent years, after the emergence of nylon canvas, a part of cotton woven canvas has been replaced, which has improved the service life. However, the production practice proves that the weave of the filter cloth has a great influence on the filtration effect, and different filter cloths are required for materials of different natures. For example, the magnetic filter uses canvas, and the filter cloth is very clogged. The main reason is that the water permeability is not good. Therefore, a special weaving “nylon blanket” must be used, which not only solves the problem of clogging of the filter cloth, but also improves the filtration. Machine utilization factor. This nylon carpet is also very effective for use in an internal filter.

4) The level of pulp concentration. The higher the concentration of the slurry, the better the filtration effect.

9. What effect does the slurry concentration have on the filtration effect?

The concentration of pulp is one of the most important factors affecting the filtration effect. The concentration of the slurry has a great influence on the output of the filter cake, and also affects the water content of the filter cake. When the slurry concentration is too low, the filter cake is formed at a slow rate, the yield is low, and the filter cake has a high moisture content. In the production of the concentrator, the filter cake is required to have a high feed concentration. Generally required to reach more than 60%. The filter for filtering the magnetic separation concentrate can be directly fed by the magnetic separator, but the accuracy of the discharge of the magnetic separator should be controlled. The filter for filtering the flotation concentrate cannot be directly fed by the flotation machine. Since the flotation concentrate is too low, it must be concentrated by a thickener and then fed into the filter.

However, increasing the concentration of the slurry is limited. The high concentration of the filter will affect the formation of the filter cake, but will reduce the production of the concentrate. The main performance is the phenomenon of “rolling” in the filtration zone. material.

10. What effect does the speed of the filter have on production?

The number of revolutions of the filter has a great influence on the production effect. The vacuum filter currently used has a high number of revolutions of 2 rpm or more and a low of 0.11 rpm. For different materials, the most suitable number of revolutions should be selected in order to achieve a higher utilization factor while maintaining a lower filter cake moisture.

When the number of revolutions is too low, the production capacity will decrease and the moisture will decrease little; when the number of revolutions is too high, the yield will increase little and the moisture may increase more. The most suitable number of revolutions is different depending on the nature of the material being filtered. Different, it needs to be determined according to the experiment. Under normal circumstances, the finer and more viscous materials should use lower speed; the coarser and looser materials should use higher speed.

11. How does the filter produce “back water” and how to control it?

For filters that use blast discharge, control the return water. When the filter chamber of the filter is in a vacuum state, the water permeable filter cloth enters the filter chamber, and is taken out of the machine through the pipe, the throat, and the distribution head. When the filter chamber is separated from the vacuum zone and enters the discharge zone, the air from the blower is used. After being sent through the same pipe, the filter cake is blown off. The water remaining in this channel must be blown out together with the air into the filter cake, so that the water content of the dewatered filter cake is increased. This part of the water is the return water. Or called "back to blowing water." The return water generally accounts for about one tenth of the moisture of the filter cake, and the control will be less, otherwise it will be more.

How to control it? The method is mainly to adjust the dispensing head and adjust the blast pressure of the unloading. The position of the dispensing head can be adjusted a small amount by the adjusting rod, so that most of the filter cake removed from one filter chamber falls into the feeding funnel during the rotation of the cylinder, so that the water is blown out later than the filter cake. Most of them fall outside the funnel of the mining and are no longer mixed into the filter cake. At the same time, it is necessary to pay attention to controlling the blast pressure of the unloading, and it is required to blow the filter cake down. Under this premise, the lower the blast pressure, the better.

12. How many filter system configurations are there?

The filtering system is configured in three ways.

The vacuum filter must be combined with a gas water separator, a centrifugal pump, an automatic drain device, a blower, a vacuum pump, a pipeline, etc. to form a system to operate.

The first filtrate and air are first pumped to the gas water separator by vacuum pumping, the air is pumped away from the upper part, and the filtrate is automatically discharged from the lower part. Because the gas-water separator is under negative pressure, the filtrate must be discharged from the separator, and the separator bottom and the trench should maintain a height difference of 9 meters. A water seal is installed at the mouth of the filtrate to prevent air from entering the gas water separator. The gas water separator inlet is below the filter filtrate outlet. The biggest disadvantage of this configuration method is that the filter must be installed in a very high position, the advantage is that the filtrate can be automatically discharged without consuming power. New configurations are generally not used in new concentrators.

The second filtrate entering the gas-water separator was forcibly withdrawn by a centrifugal pump. The filter can be installed in a lower position. The disadvantage is that a centrifugal pump needs to be specially configured to consume power.

The third feature makes it possible to automatically discharge the filtrate without setting the filter in a high position. This configuration is an innovation in the dewatering operation of our concentrator in recent years, replacing the original gas water separator and centrifugal pump with an automatic drain device. In the new concentrator, the filtration system generally adopts this configuration.

282. What equipment does the filter discharge and filter cloth use for blasting?

In the filtration system, the 3# Ye's blower or the Roots blower is generally used to supply the unloading and cleaning filter cloth. However, in recent years, some concentrators have used the air discharged from the water ring vacuum pump as a discharge and cleaning filter cloth, which is very effective, saving the blast equipment and power consumption. To supply compressed air in this way, a gas-water separator is required in the vacuum pump exhaust line to reduce the moisture that the blast brings into the filter chamber. Because the blast pressure required by the filter is very small, only 0.1-0.3 kg/cm2 is enough, so it is completely sufficient to use the exhaust of the vacuum pump as the blast, which is worth promoting.

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