Seeking advice on the issue of unclear material filtration

During filtration, the filter residue adheres to the metal mesh, also playing a role in assisting with filtration. After cleaning, there is a period during which the filter residue remains in place, and the filtration efficiency is relatively low during this time. The screen can be pre-coated with a film in advance, or the mesh size of the final screen can be increased, or the filtrate can be filtered in a circulating manner.

Personally, I think it’s necessary to find the cause first, so that appropriate measures can be taken. First, it is possible to roughly analyze the particle size distribution of the turbid liquid to determine whether it consists of solid particles or other colloidal substances. If they are large solid particles, they can be filtered out using metal screens; for particles smaller than 100 microns, metal screens are generally not effective. It is necessary to switch to filters or filter elements instead. If it is a colloid, since it is soft and deformable, some form of depth filtration is needed to capture it. If the filtrate is not clean at the beginning of filtration but becomes clean after some time, it is because a filter cake has not yet formed on the surface of the filter screen. The problem can be solved by using cyclic filtration. If it remains this way, then there is a problem with the filtering method, and it needs to be adjusted. If it goes through states of dirty – clean – dirty, then there is a problem with the filtering process; it is necessary to adjust the flow rate and replace the pressure regulator.

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There is a problem with the choice of filter screen. The principle of filtration involves first forming a filter cake; just after cleaning, no filter cake has been formed yet, but it shouldn’t lead to material leakage. It is recommended to use a filter screen with a larger mesh size

The filtering precision of the filter plate in the filter is too low—the pore size is too large, which prevents small particulate impurities in the solution from being effectively trapped, resulting in an unclean filtered liquid. This is a normal and easy-to-determine question. If there is indeed a requirement for a clearer orange color in the filtered liquid, adding another precision filter with higher filtration accuracy can solve this problem.

Generally, it is due to insufficient filtration accuracy, or the filter element being damaged or falling apart, which allows large particles to enter the downstream equipment

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Check how good the pre-coating effect is, and also analyze what the impurities that prevent clear filtration are. It’s possible that there is a problem in the earlier stages of the process, which prevents the impurities present in the material from being filtered out.

When filtering using a plate and frame filter or a microfiltration unit, the material is not clear at first, and the main reason for this is the failure to form a filter cake. Filtering mainly relies on filter cake filtration; the filter screen merely serves to intercept particles. When clearing the material, start the circulation first; the pressure should not be high. Stop the circulation only after the material has been cleared.

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A denser wire mesh should be used to ensure that the pre-treated diatomite does not leak through. Before filtering, a filter layer made of pre-treated diatomite should first be formed; at the beginning of feeding, low pressure and high flow rates should be maintained to prevent leakage

There’s a problem with that diatomaceous earth; I’ve used diatomaceous earth as a filter aid before, and it doesn’t achieve clean filtration.

Metal wire mesh won’t work; you might consider other filtering media such as filter cloth or filter paper. Generally, industrial filter paper can achieve a filtration precision of 0.5um.

The operation of plate and frame filter presses is a significant issue; we have two such machines at our company, and they present many problems. We have been addressing them one by one, and now most of them have been resolved. The cross-flow type has a significant negative impact on the purity of the filtrate. Recently, we converted one of the cross-flow machines to a straight-flow type, and the results were excellent!

Before selecting a filter, it is essential to assess the material’s particle size distribution, bulk density, viscosity, etc., in order to choose the appropriate separation mechanism. There are two types of filtration methods: 1. Filtration using filter media； 2. Bed filtration ； If the material has a high added value, it is not permissible to allow leakage at the initial stage of filtration; filtering must be done in such a way that leakage is prevented from the very beginning. Otherwise, once a material layer is formed, this will lead to a decrease in flow rate and reduced efficiency ； If material layer filtration is to be used, there will definitely be leakage at the beginning of the filtration process; however, no leakage occurs once the material layer is formed. If the mother liquor can be reused, there is no need to worry too much about leakage at the initial stage. This issue of initial leakage is quite subtle, and after weighing the advantages and disadvantages of both options, the latter is more suitable for large-scale production ； The finest metal sintered mesh available is 0.25μm, so there is no need to worry about the filtering material.

For filter presses, we use filter cloths; unclear filtrate usually results from holes in the filter cloth that allow liquid to leak through. Another issue is that it’s not tightened properly