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The prospect and development trend of diatomite filter
- 2020-01-14-

Diatomite filter is a device that uses porous filter medium to intercept solid particles in the mixture of liquid and solid particles, and realizes solid and liquid separation. Diatomite filter is widely used in chemical industry, petroleum, pharmaceutical, light industry, food , mineral processing, coal and water treatment departments.

In ancient China, filtration technology has been applied to production, and paper made of plant fibers has been made in the 2nd century BC. In 105 AD, Cai Lun improved the papermaking method. The water is filtered through the gap of the bamboo curtain, and a thin layer of wet pulp is left on the surface of the bamboo curtain, which becomes paper after drying.

Most of the early filtration was gravity filtration. Later, pressure filtration was used to increase the filtration speed, and then vacuum filtration appeared. The drum vacuum diatomite filter invented in the early 20th century realized the continuous filtration operation. Since then, various Types of continuous diatomite filters have appeared one after another. The intermittent operation of diatomite filters has been developed because of the ability to automate operations, and the filtration area has become larger and larger. In order to obtain filter residues with low moisture content, mechanically pressed diatomite Filters have been developed.

The container is divided into upper and lower chambers by a filter medium, which constitutes a simple filter. The suspension is added to the upper chamber, and enters the lower chamber through the filter medium under pressure to become filtrate, and the solid particles are trapped on the surface of the filter medium to form filter residue (or called filter cake).

During the filtration process, the filter residue layer on the surface of the filter medium gradually thickens, the resistance of the liquid passing through the filter residue layer increases, and the filtration speed decreases. When the filter chamber is full of filter residue or the filtration speed is too low, the filtration is stopped, the filter residue is removed, and the filter medium is regenerated. , to complete a filter cycle.

The liquid must overcome the resistance when it passes through the filter residue layer and the filter medium, so there must be a pressure difference between the two sides of the filter medium, which is the driving force to achieve filtration. Increasing the pressure difference can speed up the filtration, but the deformed particles after being pressed will have a large pressure difference. It is easy to block the pores of the filter medium, and the filtration is slowed down.

Suspension filtration has three methods: filter residue layer filtration, deep filtration and sieve filtration. Filter residue layer filtration refers to the formation of an initial filter residue layer after the initial stage of filtration. After that, the filter residue layer plays a major role in filtration. At this time, large and small particles are retained; deep filtration refers to the filtration in which the filter medium is thicker, the suspension contains less solid particles, and the particles are smaller than the pores of the filter medium. During filtration, the particles are adsorbed in the pores after entering; The solid particles are larger than the pores of the filter medium, and the filter medium does not adsorb solid particles in the filter medium, such as the rotary drum filter screen to filter out the coarse impurities in the sewage.

In the actual filtration process, the three methods often appear at the same time or one after another. The processing capacity of the diatomite filter depends on the filtration speed. When the solid particles in the suspension are large and the particle size is uniform, the pores of the filtered residue layer are relatively smooth. The speed of the filtrate passing through the filter residue layer is relatively large. The use of a coagulant to aggregate the fine particles into larger agglomerates is beneficial to improve the filtration speed.

For the suspension with fast settling speed of solid particles, a diatomite filter is applied to the upper part of the filter medium, so that the filtration direction is consistent with the direction of gravity, and the coarse particles settle first, which can reduce the blockage of the filter medium and the filter residue layer; Mixing coarser solid particles such as diatomaceous earth and expanded perlite into the suspension (such as colloid) can make the filter residue layer loose; when the viscosity of the filtrate is high, the suspension can be heated to reduce the viscosity. These measures can speed up filter speed.

  Diatomaceous earth filterAccording to the method of obtaining the filtration driving force, it is divided into three categories: gravity filter, vacuum diatomite filter and pressurized diatomite filter. Gravity filter is formed on the filter medium by means of the gravity and potential difference of the suspension. The pressure of the filter is used as the driving force for filtration, and it is generally operated intermittently.