Views: 168 Author: Site Editor Publish Time: 2020-02-19 Origin: Site
Filter Press Basics
The Filter Press is one of the oldest filtration technologies still in use today. It was first developed in the mid 1800’s. Unlike vacuum filters, which operate continually, the Filter Press and many other pressure filters run in batches. After a batch of slurry has run through the filter, and the filtrate drained out, it must shut down, open the filter pack, and discharge the solid cake.
The components of a filter press include the frame or skeleton and the filter pack. The filter pack consists of plates, sometimes frames, and filter media.
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.
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.
TYPES OF FILTER PLATES
There are three basic categories of filter press plates: recessed chamber, membrane squeeze (diaphragm squeeze) and plate and frame. Continue reading to learn the differences between each type of design.
Recessed Chamber Filter Press Plates
Gasketed (CGR) Filter Plates
These filter plates are utilized in various brands of recessed chamber filter presses, and represent the most commonly used plate.
The filter plates are stronger and have a higher fill pressure than plates and frame
Gasketed, virtually leak free (CGR)
Allows for mechanical plate shifting
Non-gasketed available (NG)
“CGR” is an acronym for “Caulked, Gasketed, Recessed chamber.” CGR filter plates should provide a virtually leak-proof filter press. Filter cloths for these plates are octagon shaped, with a caulking rope or cord sewn into the edge of the cloth.
“NG” means “Non-Gasketed.” The NG cloth is faster and simpler to install, though the tradeoff is that occasionally some dripping can happen when using NG cloths.
Caulked, Gasketed, Recessed Chamber (CGR) Filter Plate in Press
Non-Gasketed (NG) Filter Plate in Press
These filter plates are utilized in a membrane squeeze filter press and are designed for unique applications. This type of plate is also more costly than recessed chamber plates. Using diaphragm/membrane squeeze filter press plates may result in significant additional fluid removal and/or cycle time reduction if the filter cake is compressible.
These are considerations that our Sales and Service Team keeps in mind when recommending membrane squeeze plates:
The filter cake is compressible
Slurry has higher than average solids
Time is money – the time saved by the squeeze justifies more expensive equipment
The slurry has variable volume
Membrane Squeeze Plate with Welded Diaphragm
In a typical filter press application, approximately 80% of the solids are pumped into the press in the first half of the cycle, with the remaining half considered the consolidation stage. With membrane squeeze, the cycle is shortened and the cake moisture content is reduced (see chart).
The result is increased throughput and better liquid recovery. Adding membrane squeeze to a filter press requires a specialized plate stack, a squeeze water manifold, and a filter plate pressurization system. Typically, membrane plates are alternated with standard chamber plates in a “mixed pack” as shown in the photo below.
Plate and frame is the oldest of the filter plate designs, but is still useful in certain applications.
Used for fine filtration where filter paper may be required
Allows for different filter cake thicknesses by adding a thicker or thinner frame
Filter cloth drapes over plate
You should expect some leakage
Operated at lower pressures
Applications:
Polishing
Specialty chemicals
Plate and Frame Filter Press
Check out this article if your recessed plate filter press has some chambers that either have wet cakes or chambers that won’t fill or dewater. This has been a problem in industries ranging from wine to antifreeze reclamation. This is likelier to occur if precoat and bodyfeed are used to aid in cake formation.
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.
