Which is more commonly used, the heavy-alkali crystal paddle filter drum vacuum filter or the belt filter?

This post was last edited by mkp369 on 2018-4-18 at 10:39. As far as the soda ash manufacturing enterprises in our country are concerned, vacuum drum filters are more commonly used in the production process, while vacuum belt filters are used less frequently. The vacuum drum filter features a drum with an external filtering surface and a scraper for unloading material. The parts of the filter that come into contact with the suspension can be made of stainless steel, carbon steel, or materials with anti-corrosion properties such as PP, ensuring good corrosion resistance. The vacuum drum filter is more compact and occupies less space than the vacuum belt filter. It operates continuously and automatically, features variable speed control, and is easy to maintain; it is therefore a filter with excellent performance, reliability, and practicality. Vacuum filters mainly include external-filter surface drums, internal-filter surface drums, disks, and other types of vacuum filters. During filtration in a vacuum filter, a part of the drum is immersed in the filtrate, and it rotates driven by a prime mover through a reduction gear. The entire drum can be roughly divided into four working areas. 1. Filtration area: The filtration chamber in this area is connected to Chamber I on the distribution head, and Chamber I is linked to the vacuum system. Under vacuum, the filtrate passes through the filter cloth into the filtration chamber and is discharged outside the machine via the filter’s distribution head. The solid phase in the filtrate is retained on the surface of the filter cloth, forming a filter cake layer. To prevent solid phase sedimentation, an oscillating stirrer is installed in the slurry filtration tank. 2. Washing and dewatering zone: The washing liquid is evenly sprayed onto the filter cloth through nozzles; under vacuum, it expels and carries away the filtrate remaining in the filter cake as well as other impurities dissolved in the washing liquid, which are then discharged through chamber II of the distribution head. To improve the liquid removal efficiency of the filter and prevent a large amount of air from entering the filter and causing a drop in vacuum level, devices for flattening the filter cake can be installed in that area, such as rollers or pressing belts. 3. Discharge area: Compressed air enters each filter chamber in this area through chamber III of the distribution head, thereby separating the filter cake from the filter cloth; subsequently, a scraper is used to remove the material. 4. Regeneration zone: To remove particles trapped in the pores of the filter fabric and reduce filtration resistance, compressed air or steam is introduced from chamber VI of the distribution head into each filter chamber in this zone, thereby blowing away the particles on the filter fabric and enabling its regeneration. The vacuum rubber belt filter is an efficient separation device for the rapid filtration and dewatering of suspended solids with high density and large volume. Its main features are as follows: 1. High extraction efficiency: Thanks to the horizontal filtering surface and feeding from above, under the action of gravity, larger solid particles settle at the bottom first, forming a filter aid layer that reduces clogging of the filter cloth, resulting in low filtering resistance and high extraction efficiency. 2. Rational structural composition: All components are made of anti-corrosion materials and undergo anti-corrosion treatment; the main drive system uses belt transmission, and the vacuum chamber is constructed from corrosion-resistant materials, ensuring a long service life. 3. The filter cake thickness is adjustable, it has a low moisture content, and it is easy to remove: The thickness of the filter cake can be adjusted as needed based on the properties of the material. 4. The filter cloth can be cleaned on both sides simultaneously: Spraying devices for cleaning are available on both sides of the filter cloth, which prevents clogging and extends its service life.

Personally, I think the filtration loss with a filter unit is lower, especially when crystal formation is poor – for instance, at the beginning of production when operations are not yet stable and the crystals are of varying sizes; in such cases, using a filter might yield better results.

Looking at future development trends, filters will likely be used more and more, as they have many advantages: the heavy alkali content is low, the need for centrifugal separation of heavy alkali is eliminated, and they offer significant energy savings.

The cost of filters-equipped machines is higher than that of drum types, and they require more space; if conditions permit, companies will choose machines equipped with filters. The newly built alkali plants these days tend to use those equipped with filter machines. It should become common in the future.

Obviously, the future trend is to use filters; with traditional alkali filtration machines, it’s not possible to reduce salt content and moisture levels

The belt-type alkali removal machine has clear advantages: it results in low salt content and low moisture levels, enables an increase in the capacity of the calcination furnace, reduces consumption, and lowers emissions.