Vaillant, one of the largest manufacturers of hot water equipment in Germany, used a neutralization and detoxification plant with static thickening for treating the effluent from the electroplating facilities up to a few years ago. The suspensions produced were concentrated to a water content of 98% and the resulting thin sludges transported by tankers to storage faculties.
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After investigating various systems of dewatering, it was decided to employ Rittershaus & Blecher filter presses (R & B Filter Press). The volume of sludge was reduced to 1/15 of the previous figure, and in contrast to the thin sludge previously produced, it was possible to dump the filter cake (moisture content 67%) without risk of contamination ground water. There was also a considerable cost saving due to the smaller volume of material to be transported.
At the Jacobi Pit of the aforementioned concern four (4) chamber filter presses supplied by Rittershaus & Blecher (R&B) with a total filter area of 600m² are installed. They dewater 8 tons of dry matter from flotation effluent per hour; this effluent being produced by concentration at the rate of 300g/liter.
These suspensions, which used to be transported to settling ponds, can be dewatered to a residual water content of some 20% by means of filter presses using a working pressure of 12 to 15 bar-without any filtration aids being needed.
In , Rittershaus & Blecher (R&B) was asked to conduct a number of tests relating to the dehydration of raw cement slurries.
The customer&#;s intention was to reduce as far as possible energy consumption and expenditures incurred during the thermal dehydration of the raw material. They wanted this, as well as the ability to produce high-quality cement by means of bigger and more economical kilns. This required an efficient pretreatment involving mechanical dehydration.
To meet the requirements, Rittershaus & Blecher developed filter presses which operated at pressures of up to thirty (30) bars (425psi), produced an output of forty-five (45) tons of filter cake per hour and required only a minimum of operator attention. By means of the Rittershaus & Blecher filter presses the water content of the cement slurry was reduced from 42% to 19%. There remained only a minor proportion of 19% residual water to be dehydrated thermally, which meant considerable savings in energy and costs.
In addition, the quality of the cement produced was greatly improved since the soluble alkalis could be removed with the filtrate.
At present sixteen (16) R&B filter presses Type A4 S are installed at the Lagerdorf Plant with a filter area of 400m² (4,300 sq. ft.) each.
Stationary Head- The side of the frame without the closure system has a head that aligns with the filter pack. It is also known as the fixed head. It has a feed hole for the slurry to enter and drain hole for filtrate to exit.
Follower Head- The hydraulic ram pushes the follower head, or thrust head against the filter pack. There are no feed or drain holes on this head.
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Closure System- A hydraulic ram is used to press the plates together and hold the filter together during operation. It creates a positive seal and prevents leaks.
Sidebars- The filter press plates rest on sidebars to keep alignment and bear weight.
Pump- Necessary to create the pressure which drives the process, it is usually a positive displacement pump or a centrifugal feed pump.
Extra Features- Newer models can include additional components like plate shifters, spray bars, and automatic cake dischargers.
Plate and Frame Filters- Plate and Frame was the original design, and is still used in some applications. The plate has a series of channels or pips creating high and low points. A cloth or paper filter media sits on top of the plate and filtrate passes through in the drainage area around the low points. The frame creates the empty space necessary for two plates to have a chamber between them. Cake accumulates within the chamber.
Recessed Filter Plates- Recessed filter plates eliminate the need for frames. The plate&#;s border is thicker than the high points of the drainage area, creating half of the chamber. The plate it touches creates the other half.
CGR: Caulked Gasketed Recessed Filter Plates- CGR plates are a recessed plate that has filter media caulked into place, normally in an octagonal configuration. It seal feed and drain holes with o-rings.
Diaphragm Filter Plates- A recessed filter plate with a diaphragm. When solid cake has bridged its chamber, touching both plates, water is pumped into the diaphragm which swells. This swelling decreases the amount of space available, further dewatering the cake. Diaphragm plates are sometimes staggered with recessed filter plates, so that only one side of any given chamber will swell.
While cotton was the main filter media, in the s synthetic fibers created better-performing and longer-lasting press cloths. The Micronics Engineered Filtration Group has a wide variety of fibers, and weave types. Please contact us if you would like to ensure that the cloth your filter uses is the best one for your application.
Drape Over cloth- Twice the length of a plate, a Drape Over Cloth sits on top of the plate and lays down each side. It can be held in place by small nubs, or &#;dog ears&#;.
Drape Over Paper- If the cake has a tendency to blind the filter media after one batch, a filter paper can be draped on top of the cloth. When the Filter Press opens to discharge, the paper is thrown out with the cake.
Duplex Cloth- Two separate cloths, each the size of a plate&#;s single face, are sewn to a gusset that covers the feed hole that runs through a plate. The top and side edges of the cloth either have grommets or Velcro to secure both sides of the cloth to the plate.
CGR Cloth- This Duplex Cloth is shaped to fit in the grooves of a CGR Plate. There is a rope sewn into the cloth&#;s border that gets caulked into each side of the plate.
As filtrate passes through the filter cloth it collects on the plate panel and drains into outlet holes on the corner(s) of the panel. The outlet holes have a channel that goes into the adjacent corner eye. The channel runs between the packing surfaces. Another function of the system is to allow the cake to be dried &#;blown down&#; by compressed air. The manifold piping at the end of the press can be valved to let air into the even-numbered plates pushing the liquid thru the cloth/cake/cloth out the odd-numbered plates. Sometimes particles of precoat and bodyfeed pass through the filter cloth and become trapped within the drainage channels plugging or partially blocking them. It can be easy to overlook, since you can&#;t see into the channels unaided.
The plug likely occurs after a filter cloth tear or if the filter media is too permeable for the precoat and body feed used. The best time to check is when you notice a chamber has not formed a dry, firm cake as it usually does. If some chambers in the filter pack form great cakes and others form wet partial cakes, this could indicate which plates are plugged.
Why is this bypass occurring? Contact us and we&#;ll dig into the specifics of your process to ensure that both your body feed selection and the filter media are the best choice.
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