The Use of Pre-Coating in Filter Presses

The Use of Pre-Coating in Filter Presses

As a solid-liquid separation equipment, the filtration efficiency of the filter press is very important. If you want a very precise filtration effect, you must choose a filter cloth with smaller gaps, but at the same time, the flow rate will be reduced, and the filtration time will be increased. Adding pre-coat in the filter press will achieve the best filtration effect without affecting the flow rate. This article will introduce you to the relevant knowledge about pre-coating.

plate and frame filter press
Plate and Frame Filter Press

Introduction to Plate and Frame Filter Press: The plate and frame filter press is widely used for solid-liquid separation in various industries. It is known for its versatility ...

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What is Pre-Coating Filtration?

The pre-coating filtration is to add a certain amount of filter aid during the filtration process. After a short period of circulation, a stable filtration pre-coating is formed on the filter element. It turns simple medium surface filtration into deep filtration, resulting in Strong purification and filtration effect.

Commonly used filter aids include perlite, cellulose, diatomaceous earth, carbon black, and asbestos. Diatomite filter aid has been widely used due to its comprehensive advantages in performance, price, source, and other aspects.

Diatomite filter aid

Characteristics of Diatomite Filter Aid

Diatomite filter aid products are available in a variety of colors. Its basic component is a siliceous shell wall with a porous structure. Its main performance indicators include particle size, bulk density, surface area, and ingredient content. Among them, particle size distribution is one of the most important performance indicators. It directly determines the size of the filter pores and the size distribution of the micropores. Coarse-grained particles have better water permeability but lower filtration accuracy, so they should be based on the required flow rate and filtration accuracy, choose diatomaceous earth with appropriate thickness.

Domestic products are divided into two types: thick and fine, which can be used alone or in combination with different particle sizes to achieve extremely high filtration accuracy. The bulk density of diatomite also has a great influence on the filtration effect. The smaller the bulk density, the larger the pore volume of the filter aid particles, and the better its permeability and adsorption. Therefore, diatomite with a lower bulk density is generally selected. of diatomaceous earth.

Filtration Principle

Use a filter pump to pass the suspension-containing filter aids into the filter tank. After a period of circulation, the filter aids bridge the surface of the filter medium to form a layer of filter pre-coating with complex micro-pores. Due to the existence of the pre-coating, a higher filtration accuracy is obtained in the initial stage of filtration in the next step, and it can also prevent dirt particles from clogging the pores of the filter element. During the filtration process, the solid particles in the suspension are mixed with diatomite particles that are continuously added quantitatively and then accumulate on the filter element to form a loose filter cake, which keeps the filtration rate basically stable.

Pre-coat filtration principle

Benefits of Using Pre-Coat

Improve filtrate clarity: It helps improve the clarity of the filtrate by trapping finer particles that might otherwise pass through the filter media.

Protect the Filter Media: Pre-coating protects the filter media from being clogged by impurities or damaged by abrasive particles present in the slurry. This extends the life of the filter cloth and reduces maintenance costs.

Aid in Cake Release: It can facilitate easier cake discharge. By creating a layer between the filter media and the filtered material, the pre-coat can prevent the filter cake from sticking to the media, making it easier to remove the cake after the filtration is complete.

Enhance Filtration Efficiency: It can increase filtration efficiency by preventing the initial blinding of the filter media. This is particularly useful when filtering materials that contain a high amount of fine particles.

Filter cake with pre-coating


In summary, in applications where filtrate clarity is critical or when dealing with particularly challenging or abrasive slurries, pre-coating is an important step that can significantly improve performance and protect the filtration system.

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