Types of the liquid filtration process

07 September 2022

The purpose of the industrial liquid filtration process is to separate liquids from solid materials. In this article, we summarise the elements of the liquid filtration process and its main types.

Liquid Filtration Process 

The filtration process is about the separation of liquids from solid materials. This is done by passing the filtering liquid through the filter medium, which retains the solids. The filtered liquid is called the filtrate, and a pressure difference occurs during the process, called filter resistance. Solids are therefore retained in the filter medium and form the filter bed.

Two types of liquid filtration processes are distinguished: static filtration and dynamic filtration. Static filtration creates a pressure difference between the media, which leads to the separation itself. It is worth noting that, depending on the design of the filtration equipment, a distinction must be made between surface, layer, spatial and depth filtration. The other variant is dynamic filtration, i.e. membrane filtration, which allows cross-flow filtration. The filtrate is therefore absorbed perpendicular to the direction of flow.

Elements of the liquid filtration process

The liquid filtration process is a complex procedure. The first step is the loading of the material, during which the material to be filtered is fed into the filtering machine. This is usually done by a pump, but in some cases, gravity is used.

The next stage is pre-pressing, which is negligible in most filtration processes. Similarly, washing is not always obligatory. 

In the post-pressing stage, high-pressure air or water is injected into the filtration sheets, causing the sheet to expand and compress the accumulated sludge slurry. In the case of post-compression, the upper limit is on average 16 bar, so that a drier sludge slurry can be produced. This step is only important for machines that have a membrane flap.

During the blow-down, high-pressure air is introduced through the loading pipe into the closed slurry stack, which removes the remaining filtrate and contributes to the drying of the slurry. Finally, during the flake discharge, the sludge flakes are removed from the filtering machine and the flake is moved.

Applications of liquid filtration

In industrial production, lubricating fluids, oils and coolants are most filtered. In addition to manufacturing, the chemical, pharmaceutical and food industries are major users of filtration equipment. In their case, the material to be filtered is typically a process fluid.

But the application of filtration technologies does not stop there. They are used for water pipe filtration, filtration of lakes, rivers, well-water, heating systems and filtration of water from heat exchangers. In an industrial environment, liquid filtration processes are used to filter open and closed cooling water. In power plants, they are used to remove solids from condensate water, while in agriculture they are used to filter thermal and irrigation water.

Choosing the right liquid filter

To choose the right liquid filter, it is important to consider the yield, temperature, pressure, viscosity, particle size and volume of the liquid to be filtered.

Particle size is a key factor in filter selection. Microfiltration is when the particle size is between 1-0.1µm, such as bacteria. Ultrafiltration, when the size ranges from 0.1-0.001µm, is used to filter out viruses and in wastewater treatment. We talk about nanofiltration when the particle size is 10-1 nm, and reverse osmosis below 1 nm, for example for conductivity reduction and desalination.

Makrofilt offers customized filtration systems for all sectors. Find out more and contact us!


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