Stainless Steel Filter Element Used For Water Treatment

ZHEHAN is a manufacturer of the stainless steel filter element for water treatment. 

Stainless steel filter element often used in water treatment

- Wedge wire filter

- Sintered filter

- Pleated filter

Today, we will not introduce the metal filters commonly used in water treatment. This paper mainly introduces the filtration principle and operation mode of water treatment.

The water quality of raw water is very complex, and it needs a series of filtration steps to get the required water quality, so the filtration process of water treatment is necessary.

Filtration is the separation of suspension by using a porous medium.

When working, under the action of external force, the liquid in the suspension flows out through the channel of the medium, and the solid particles are intercepted, thus realizing separation.

In general, the suspension to be filtered is called filter slurry; the porous medium used is called filter medium; the liquid passing through the channel of the medium is called filter fluid.

The solid being intercepted is called filter cake or filter residue.

The driving force of the filtration operation is the pressure difference between the upstream and downstream sides of the filter medium. There are several ways to produce the pressure difference as follows:

(1) Pressure head of filter slurry

(2) Pressure on the surface of filter pulp

(3) Vacuum pumping on the downstream side of the filter medium

(4) Utilizing Inertial Centrifugal Force

The filtration operation can be divided into two categories according to the principle of action:

(1) The number of holes in the sieving filter medium is less than the diameter of solid particles, and solid particles are removed from suspension by sieving(The stainless steel filter element is the best choice). 

In the initial stage of filtration, fine particles flow out and the filtrate is turbid. With the formation and thickening of the cake layer, the filtrate becomes clear gradually.

As the sieve hole is gradually blocked, the filtration rate tends to decrease. When the cake layer is formed in the filtration process, the sieving effect is produced by the cake layer. The filter medium loses the sieving effect and only plays the role of supporting the cake layer, which is called cake layer filtration.

It is necessary to select the filter element according to the actual use. If the metal filter element is used, the wedge wire filter element is the best choice.

(2) Adsorption filtration (deep bed filtration): The number of mesh holes in the filter medium is larger than the diameter of solid particles, and the solid particles are absorbed by the surface of the medium after entering the channel of the filter medium.

In actual production, sieving and adsorption act simultaneously, the adsorption filter medium intercepts larger particles, and the cake layer of sieving filter medium can adsorb smaller particles.

Filtration media and filter aids

The commonly used filter media are the following types:

(1) Fabric media, such as industrial filter cloth, stainless steel wire mesh, etc.

It should be noted that both stainless steel sintered filter element, pleated filter element and wedge wire filter element play the role of coarse filtration.

(2) Granular media, such as perlite powder, cellulose, diatomite, etc.

(3) Solid cardboard, such as decolorized wood cardboard, synthetic fiberboard, etc.

(4) The filter membrane consists of cellulose and other polymers. Granular media are used as filter aids to pre-coat the surface of fabric media for coarse filtration. Solid paperboard media are mostly used for semi-fine filtration and fine filtration, while filter membrane media are used for fine filtration and ultra-fine filtration.

The filter aids pre-coat some hard granules on the surface of the filter media or add them to the filtered pulp to form a harder and looser filter cake so that the filtrate can pass smoothly. The granules are called filter aids.

Requirements for filter aid: filter aid is a hard, loose structure of powdery or fibrous solid, energy-shaped filter aid should be able to better suspend in the media, particle size is appropriate, does not contain substances soluble in the filtrate.

The commonly used filter aids are diatomite, cellulose and so on.

The purpose of using filter aids is to prevent the blockage of filter media channels or to reduce the filtration resistance of filter cakes.

The methods of adding filter aids include pre-coating and pre-mixing.

Diatomite and cellulose are the main filter aids used in wine filtration. Diatomite is the fossil of diatom of aquatic plant, which is composed of the remains of a diatom from sedimentary rocks of paleontology. Its main component is SiO 2 (85-90%) which is gray-white powder. Its particle size is generally 30-40 micron, the minimum is 2 micron, the maximum is 300-400 micron, and the specific gravity is 0.31-0.7.

Comparison of ion exchange and reverse osmosis technology

We are the manufacturer of the stainless steel filter element. This part is a brief introduction.

Ion exchange has the advantage of low investment cost compared with reverse osmosis.

Ion exchange equipment occupies less space than general reverse osmosis equipment.

The way of a filtering operation

Constant pressure filtration

The filtration operation is carried out under constant pressure difference, which is called constant pressure filtration.

Constant pressure filtration is the most commonly used method of filtration. In the process of filtration, with the increasing of the cake layer, the resistance increases. Because the pressure difference remains unchanged, the filtration speed will gradually decrease.

Constant speed filtration

The filtering operation is carried out at a constant speed, which is called constant speed filtration.

With the continuous filtration time, the cake layer thickness increases, the resistance increases, and the filtration pressure difference increase linearly with the continuous time. The pressure resistance of filter equipment is limited and the pressure cannot be too high.

For compressible filter cake, excessive pressure does not increase the speed, on the contrary, it will cause the termination of filtration.

Firstly constant speed and then constant pressure filtration

In order to avoid the blockage of the flow passage caused by the premature increase of pressure, constant pressure filtration is adopted after the pressure is raised to a given value.

The constant speed is maintained in the initial stage of filtration by using a quantitative pump, and the pressure at the outlet of the pump increases with time. If the pressure rises to a set value that can automatically open the branch valve, the branch opens, and part of the filtered slurry returns to the inlet of the pump. The slurry entering the filter press decreases, and the pressure at the inlet of the filter press keeps constant, so constant pressure filtering begins.

Factors Influencing Filtration Speed(stainless steel filter element)

The following applies to Wedge Wire Filter, Pleated Filter, Sintered Filter.

(1) The bigger the viscosity of the filtered slurry, the bigger the filtration resistance and the smaller the filtration speed.

(2) The bigger the cake thickness is, the bigger the resistance is and the smaller the filtration speed is. When the thickness reaches a certain level, the filtration will be terminated.

(3) The particles of the incompressible cake are hard. The channel through which the filtrate passes will not decrease with the increase of pressure. The resistance will remain basically unchanged, or it will increase slowly with the continuous resistance of filtration time. The filtration speed will increase proportionally with the increase of pressure. Small particles will block the channel under larger pressure, so the initial pressure should not be too high to avoid premature blockage of the channel.

Installation of oil filters (stainless steel filter element) in hydraulic systems usually has the following locations:

(1) To be installed at the suction port of the pump:

Surface oil filters are usually installed on the suction path of pumps in order to filter out large impurity particles to protect the hydraulic pump. In addition, the filtering capacity of the oil filters should be more than twice the flow rate of the pump and the pressure loss should be less than 0.02 MPa.

(2) Installed on the outlet oil road of the pump:

The purpose of installing oil filters here is to filter out contaminants that may invade components such as valves. Its filtering accuracy should be 10-15 micron, and it can withstand the working pressure and impact pressure on the oil pipeline, and the pressure drop should be less than 0.35 MPa. At the same time, the safety valve should be installed to prevent blockage of the oil filter.

(3) Installed on the return line of the system: This installation plays an indirect filtering role. Generally, a back pressure valve is installed in parallel with the filter. When the blockage of the filter reaches a certain pressure value, the back pressure valve opens.

(4) Separate filtering system: A hydraulic pump and oil filter are specially designed for the large hydraulic system to form an independent filtering circuit.