Seeking advice on automated filtering devices
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One of our company’s production units also requires a filtering device; it uses diatomaceous earth coating on filter rods equipped with filter fabric, and the entire process is automated. The medium used for filtration is the reaction mixture (HDI+ adducts + catalyst + terminator); what needs to be filtered out are the fine particulate forms of catalyst and terminator. Previously, filtering one batch of material (about 20 tons) took around 2 hours. The filtration rate was determined based on changes in pressure difference. However, now the pressure difference increases more rapidly when filtering a batch, which prevents an increase in the flow rate and results in longer filtration times. As designed, one diatomite coating can filter two batches, after which it is removed, purged, and then recoated. The state of the reaction mixture has not changed; in other words, the state of the small solid particles has been confirmed. The reason for the increased filtering time at present might be related to the filter, but the actual cause has not been identified yet; therefore, I hope fellow sailors can provide some guidance.
The poster should specify what kind of filtering device is being used; generally, if filter rods are used, there’s no need for filter cloth, so maybe the filter cloth needs to be replaced!
It uses a filter cloth; what I call a filter rod is only similar in shape. The filter cloth has been replaced, and the initial pressure is normal.
First, please have the instrumentation staff confirm that the differential pressure gauge and flow meter are showing correct readings! If there’s nothing wrong with your filter cloth, could it be a difference in the medium or the design? :handshake
Using diatomaceous earth for pre-film filtration aims to form a filter cake for the purpose of filtration; the function of the filter cloth is to form the filter cake rather than to carry out filtration. After replacing the filter cloth, if the initial pressure is normal, it indicates that the problem lies with the filter cloth. Therefore, I estimate that it is possible the pore size of the filter cloth has increased to be comparable to the size of the catalyst particles, or the catalyst has become smaller than the pore size of the filter cloth. During the pre-coating process, the catalyst blocks the pores in the filter cloth. Another possibility is that the quality of the products you produce has changed, with polymers appearing that clog the pores in the filter fabric. You need to observe carefully whether there are any changes in diatomite. Or, depending on the catalyst you are using, could you not simply use a different type of filter to achieve filtration?
This is likely a problem with the filtering medium you are using; factors such as the mechanical strength and flow rate of that medium play a role in this. Perhaps it isn’t suitable for your processing requirements. As some of the experts mentioned, polymers appear in your process, and the medium you are using is not designed to filter substances containing polymers. A similar issue arises in acrylic fiber production as well. We have encountered such problems before. My suggestion is that, for the long-term success of your process, it would be better to use a different filtering medium. Otherwise, if you continue to use the same type of medium, the same problems will persist. That’s what we used to do – we had to replace the medium after each batch of processing, which increased our investment costs significantly.
You can contact Wang Hao from Nanjing Beichiller Machinery Co., Ltd. They specialize in filters; their filters have a rational design and are easy to operate. You can discuss this matter with him. Phone numbers: 025-85757887, 13814093921； He can help you solve the problem. This post was last edited by Zhongyuanren on 2009-2-9 07:37.]
Based on your description, it seems to be a type of bundled automatic filtration system. However, in our company, metal filters are generally used in such backwashing systems, with wedge-shaped nets being the most common option (as they make backwashing easier). I’m not sure why you chose to use filter fabric in the first place Filter cloth generally belongs to deep filtration media; how can impurities trapped within the pores be blown out? It can only blow away impurities on the surface. If your liquid is viscous. Then filter cloth should not be chosen at all. I represent Feichao Filtration at www.feature-tec.com; feel free to contact me at marketing@feature-tec.com if you have any questions
I agree with the first opinion from the 5th floor; actually, the function of the filter cloth here is not just for filtering. We also suspected that the pore size of the filter cloth had increased, but the problem persisted even after replacing the filter cloth. Therefore, we tried using diatomaceous earth with a slightly larger particle size; as a result, the filtration time was reduced without any impact on the quality requirements (the length of the filtration time plays a key role in our production volume). The problem seemed to be solved on the surface, but it remains unclear why diatomaceous earth used before resulted in a shorter filtration time while it does not have the same effect now – the issue has not been fully resolved yet. Thank you to all colleagues for joining us in this discussion!
I don’t fully understand this process. After a filter cake is formed, the filtration pressure difference will definitely increase due to the resistance of the filter cake. During design, there should be an appropriate filter cake thickness; that is, the filtration area is determined based on the amount of material to be filtered.
The filter rod inside should not only serve a supporting function but also be designed with grooves.