Around Micronics, we always say that proper filter cloth selection is one of the key ingredients – if not the key ingredient – to achieving excellent filter press performance.
Having said that, even the best filter cloth needs regular cleaning to maintain excellent filtration performance and ensure that the filter press is working optimally. Cloth, plates, and press work together as a system to give you the excellent dewatering performance you need in your industrial operation. If your filter cakes are wetter, sloppier and stickier than they were or if cycle times are longer, it is likely that your filter cloth needs cleaning or changing.
The easiest and most effective way to clean filter cloth is while the filter cloth is still installed on the filter press plates. This method, referred to as “recirculation cleaning,” – or Clean-In-Place (CIP) – requires a system to handle the in-situ cleaning procedure including a holding tank, pumps, recirculating piping, valves and the like. Micronics’ filtration experts are pleased to discuss whether this is right for your operation. In this method of cleaning, a chemical cleaning solution such as a 5% solution of muriatic acid (aka hydrochloric acid or HCl) is a good starting point for circulating through a closed filter press. A lower or higher concentration may be appropriate for your particular conditions.
CIP acid washing helps to breakup solids that have built up in the hard-to-reach areas such as the filtration ports and filtration drainage ports on the filter plates. Regular pressure washing will help to clean the faces/exposed areas of the cloth but might be less effective in flushing out those spots that aren’t exposed. CIP acid washing will get “back there” to those hard-to-reach spots and flush out those ports so as to achieve better flow rates and better filtration performance.
With acid washing – as with all aspects of filter press operation – safety should be a top priority. Extreme care and precautions should be taken when handling acid. Great care should be taken to ensure that, during the cleaning cycle, the cleaning solution does not squirt from between the filter plates. Recessed plates should use splash curtains and the filter press should be equipped with CGR plates, the benefits of which were discussed in a recent blog post.
How to Acid Wash
On filtration systems discharging from 4 corner ports, close the bottom two ports and recirculate the chemical cleaning solution through the top filter ports until the cloths are thoroughly clean. Effective closure of the filter press is critical as circulating liquor without solids will create edge leaks or wicking. Drip trays should be utilized and, as noted previously, splash curtains should be used in conjunction with recessed plates. Micronics can help you with both drip trays and splash curtains.
Nitric acid is not to be used as it is an oxidizing agent and is destructive to the filter cloth.
Sulfuric acid should never be used for cleaning the filter cloths, particularly if calcium is present in the slurry. Use of sulfuric acid in the presence of calcium would produce calcium sulfate (gypsum) as a byproduct of the reaction and this would likely permanently blind the filter cloths.
What If I Am Not Set-up for A “Clean-In-Place” Chemical Wash?
While it is preferable to clean the filter cloths without having to remove them from the filter plates or remove the filter plates from the press, if your installation is not set-up for an in-situ or Clean-In-Place chemical wash, the cloths may be removed and simply placed in a container to soak in the cleaning solution.
Polypropylene filter cloths can be safely cleaned in muriatic acid; in fact, the fibers have a high tolerance for both acidic and alkali cleaning solutions. With nylon and polyester filter cloths, the fibers require much more careful selection of the cleaning medium. Micronics’ experts can assist in cleaning protocols for ensuring that your filter cloths are helping you achieve optimal filtration for your set of operating conditions.
Cloths made with man-made, synthetic fibers such as a polypropylene weave, need only be neutralized before being reinstalled on the plates and press. It is not recommended that the cloths be dried in industrial dryers because this will cause shrinkage, resulting in misalignment of the cloths on the filter plates which, in turn, will affect press performance. If the filter cloths are left draped in a wet state, the cloths will dry without detrimental effects to the fibers. This is because most synthetic fibers have little or no regain (a measure of the moisture content of the fiber).
Every filter press operation and set of operating conditions is different so there is no single recipe for cleaning filter cloth. We encourage you to talk to our filtration experts to put our decades of experience to work for you. As with anything else, cleaning and regular maintenance are key to maximizing your filtration equipment investment.
Contact us to ensure that your filter cloth is performing at its best.