Filter presses are discontinuously working pressure filters for the solid-liquid separation of suspensions . There are filter presses in the designs of frame filter press, chamber filter press and membrane filter press, which differ in the design of the filter plates, but not in the filtration principle.
Filter presses as apparatus for cake filtration have a filter pack formed by filter plates in a frame, which is arranged between a fixed and a movable cover. Filter media ( fabric or pressure membranes ) are located between the individual filter plates . The solid lid on connecting and train struts connected to the bridge. The filter package is pressed on with pressures between 250 and 600 bar via a hydraulic pressure device that is integrated in the bridge and acts on the movable cover . These high pressures ensure the tightness of the filter pack. The piping for the supply lines of the suspension is integrated in the fixed cover, the passage opening for the suspension within the filter pack is in the middle of the filter plates.
In the filter chambers, the suspension is pumped against the filter cloths at 10 to 20 bar by means of a pump. The liquid passes through the filter medium and leaves the press via drainage channels; the solid parts of the suspension remain on the filter medium and form the filter cake . When the filtration cycle is complete, the press is opened and the cake is removed. If the press does not do this automatically (self-cleaning chamber filter press), the pressure is slowly released, the filter press is opened and the cake is manually removed from the filter cloths.
Membrane filter presses have the special feature that the filter cake is also pressed out mechanically. For this purpose, each filter chamber has at least one movable membrane. After the inflow of the suspension has been shut off, this membrane is set in motion in the direction of the filter cake with the aid of compressed air or pressurized water and thus additionally squeezes it out.
Chamber filter press
If a post-pressing device for increasing the content of dry matter in the filter cake is not required, the chamber filter press is a relatively simple, flexible, cost-effective, reliable and powerful design. The product to be filtered can be a suspension from mining, the food, chemical and pharmaceutical industries or process wastewater.
Chamber filter presses, with their respective options for influencing the degree of dryness of the filter cake, achieve - depending on the suspension and dewatering properties - a maximum solids content in the filter cake of 30 to over 50 percent (sometimes even higher).
Chamber filter presses are barely functional without the addition of flocculants, or only with significant performance restrictions.
Membrane filter press
In membrane filter presses, a flexible, impermeable membrane attached to the carrier body compresses the cake in the chamber after the loading process is complete. By using membrane technology in the filter plates, membrane filter presses have a major influence on the degree of dryness of the solids and achieve the lowest residual moisture values in the filter cake of the common filtration processes (except for high-temperature filter press): depending on the degree of dewatering, dry substance contents ( ie percentage by weight of the dry substance) in the filter cake of 30 to over 80 percent. This enormous performance makes the membrane filter press one of the most widely used systems.
High temperature filter press
The hot filter press combines the standard process steps of a membrane filter press (namely filtration, filter cake washing and repressing) with the additional function of thermal cake drying ( TCD ). All process steps are carried out in one system and the resulting filter cake is dewatered and dried without a downstream drying process; laborious and costly vacuum contact drying is no longer necessary at this point. In contrast to the conventional procedure, membrane filter and heat exchanger plates are installed alternately in a hot filter press . For thermal drying of the filter cake, the working space behind the membrane is exposed to hot steam or oil.
Automated filter press
In terms of architecture, working principle and process technology, automated filter presses are conventional filter presses, but with regard to the degree of automation and the corresponding continuous operation, they are based on the special requirements of fast cake release and thus a short cycle time . This is implemented using various automation options, e.g. B. automatic shifting of the filter plates, filter cake loosening aid or filter cloth washing device. The result is a fast running filter press with increased production per unit area of the filter.
The actual filter element consists of linters ( cotton fibers ) to which 1% asbestos was added for a long time . Today, fibrillated cellulose is used instead . This filter mass is pressed into several filter bowls, which - as with the filter press - are attached one behind the other and interchangeably in a frame. The liquid is pressed through the filter mass for filtering.
By washing out the filter mass, the process is very labor-intensive and causes a lot of waste water . Therefore, mass filters have now largely been replaced by other processes.
Filter presses can be used in many ways. The size of the solids to be separated ranges from the µm range (e.g. enzymes ) up to the mm range (e.g. sewage sludge ). The filter areas range from less than 1 m² for small laboratory processes to over 1000 m² for large presses. They are used in the food , chemical , ceramic and pharmaceutical industries . They can also be found in metallurgy and mining .
In the future, the market demands on the modern filter industry will demand ever finer and higher degrees of separation, especially with regard to the purpose of material recycling, energy saving and green technology. In order to meet the increasing requirements for a higher degree of dewatering from material that is difficult to filter, super high pressure filters are required. Therefore, the trend to increase the pressure for the automatic filter press will continue to develop in the future.
Enclosed filter press for the most aggressive media
In addition to standard configurations for applications such as battery cell production, this series of technologies is suitable for demanding applications that require high safety and efficiency standards with the highest level of operational reliability. In contrast to the previous standard, this novelty can treat substances with toxic and radioactive properties and hot suspensions with filtration temperatures of more than 130 ° C. In this version, an almost gas-tight and vacuum-resistant housing is used to protect the operating personnel and to ensure product quality. Sludge residues and (filter cake) dust are prevented from escaping at all times. A special sealing and wiping technology enables the holistic sealing between the individual machine housing elements. The machine casing used also prevents the environment from being contaminated with an aggressive medium.
- Klaus Luckert (Ed.): Manual of the mechanical solid-liquid separation. Vulkan-Verlag, Essen 2004, ISBN 3-8027-2196-9 .
- The membrane filter press - when time and degree of dewatering are decisive . ( mse-filterpressen.de ).
- Membrane technology for filter presses (membrane filter presses) . ( mse-filterpressen.de ).
- Peter Brustkern: High-temperature filter press saves energy and space | chemanager-online.com - chemistry and life science. Retrieved October 4, 2011 .
- Filter presses for fully automatic operation. Less staff and higher performance - process technology online . In: process technology online . ( industrie.de ).
- FILTRATION ABSOLUTELY TIGHT AND SAFE - Encapsulated filter press for aggressive media | chemietechnik.de - specialist information for decision-makers. Retrieved February 15, 2020 .