Liquid filtration is a unit operation that achieves liquid-solid separation via porous media. Its core function is to efficiently remove impurities such as suspended solids, colloidal particles, grease and microorganisms from liquids. Relying on the microporous structure of filter media, the liquid flows through the channels of the media under the driving force of pressure difference. Solid particles larger than the pore size are trapped and accumulated on or inside the media, so as to purify the liquid.

Main Methods and Technologies of Liquid Filtration

Primary Liquid Filtration Methods

1. Sieving Filtration Based on mechanical sieving principle, filter media with pores smaller than solid particle diameters physically intercept and separate particles larger than the pore openings from suspensions.

2. Adsorption Filtration The filter media have pores larger than target solid particles. As liquid passes through, particles are captured on the media surface via surface adsorption forces (e.g., van der Waals forces) or chemical affinity, forming a deep adsorption layer to complete separation.

3. Depth Filtration Matching media pore size with particle size, particles are three-dimensionally trapped deep inside the media through physical and chemical effects including inertial collision, diffusive deposition and electrostatic adsorption within the complex internal pore structure.

4. Membrane Filtration Utilizing the selective permeability of semipermeable membranes, driven by pressure or concentration gradient, precise separation of different liquid components is realized based on differences in molecular size, electrical charge and hydrophilic/hydrophobic properties.

Criteria for Selecting Liquid Filter Media

The following factors shall be taken into account when selecting liquid filter media:

1. Matching between filter media pore size and feed slurry particle size, to guarantee effective interception of target particles to be removed;

2. Mechanical strength and corrosion resistance of filter media, to maintain stability and durability during operation;

3. Chemical inertness of filter media, to avoid chemical reactions with substances contained in the liquid;

4. Cost efficiency of filter media: select cost-effective materials on the premise of meeting all technical requirements.

Sintered Metal Powder Filter Cartridges

Sintered metal powder filter cartridges are porous metal filter materials manufactured by cold isostatic pressing followed by vacuum sintering. Their porosity ranges from 30% to 40% with wall thickness of 1.0~4.0 mm. The pore size and porosity of cartridges can be adjusted by powder particle size, molding and sintering processes, making them an ideal option for micron-scale filtration.

Coated Sintered Metal Powder Filter Cartridges

As asymmetric membrane elements, coated sintered metal powder filter cartridges are produced by sintering a fine layer of metal or oxide powder onto the surface of conventional sintered metal powder substrates. The newly sintered coating acts as either a precision control layer or performance improvement layer, delivering higher filtration precision without sacrificing flux.

Coated Sintered Wire Mesh Filter Cartridges

Also categorized as asymmetric membrane elements, coated sintered wire mesh filter cartridges feature a fine metal or oxide powder layer sintered onto multi-layer sintered wire mesh base. The additional coating elevates filtration precision while retaining the original high gas permeability of sintered wire mesh.