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What is a Membrane Filter Press?

When time is a concern with regard to filter press cycle time, you might want to consider a membrane filter press.

Generally speaking, a filter press takes 4 hours to fill.  (Actual time depends upon solids loading capacity and the type of slurry being fed through the press).  However, a membrane press can reduce cycle time by approximately, 50% on average and, in some cases, even as much as by 75% depending upon the application. 

How this works…

A standard filter press application for metal hydroxide sludge, for example, with plates that provide a 32mm cake thickness generally takes about 4 hours to fill.  The unit is usually 80% full at about the 2 hour mark.  Due to the high pressure (100 psi from the diaphragm pump being counteracted by the 4,000 psi of hydraulic pressure), resistance builds and the diaphragm pump begins to slow down considerably. 

If you need a quicker turnaround time to get your press back up and running, it might be wise to consider a membrane press.  A membrane press is identical to a standard filter press except that the chambers (area between the plates) have membranes to squeeze out excess water from the slurry.  A press with all membrane plates can be costly, however, the mixed pack is a more cost effective alternative.  In a mixed pack each chamber has one side with a membrane that will inflate, thereby causing the squeezing action against a solid recessed plate.  When the press is filled to about 80% capacity (this is determined by historical information and/or by the timing of the diaphragm pump), this is the ideal time to inflate the membrane diaphragms to provide the extra squeeze.

How are the membranes inflated?

The safest way to inflate the membranes is to use water instead of air.  If you are using air to inflate the membrane and you experience a tear, you run the risk of plastic breaking which can be extremely hazardous.  However, if you use water and experience a rupture, you may end up with a water leak, which is much safer and easier to contain.  A tank and pump are used to fill the membranes with water via the manifold piping which would be stainless, PVC or steel (depending on the application) and flexible tubing to connect the manifold to the plates.  The water pumps into the membranes during the squeeze process and once that is complete, it is drawn back to the water tank for reuse. 

Types of membrane plates:

There are two types of membrane filter plates:  Polypropylene membrane plate with a welded membrane or a polypropylene plate with a removable rubber diaphragm.  In both instances, the plates are polypropylene.  The welded membrane plates are a more expensive option.  If the membrane should break, the entire plate would need to be replaced.  The second option, polypro plate with removable rubber diaphragm is more cost effective.  In the event that one of these diaphragms should break, it is not necessary to replace the entire plate.  If there is a rupture in plates with the removable rubber diaphragm, only the diaphragm needs to be replaced.  Not only is this a cheaper but it’s a quicker fix than waiting to order new plates since these diaphragms are usually in stock or have minimal lead times compared to weeks or in many cases, months for the welded plates.

Membrane plates are also either center feed, gasketed or corner feed, non-gasketed.  The corner feed, non-gasketed is the most popular membrane option because it allows the whole area of the plate/cloth to be used for the membrane squeeze whereas the center feed design puts more pressure on the center hole and can cause tears in the cloth or in the membrane itself.

Membrane plates have proven successful in a number of applications.  Including but not limited to:

  • Breweries – Mash is filtered to get recover wort for brewing.  The mash is pumped into the press and then it is compressed until the last bit of wort is squeezed out of the mash.  This provides quick turnaround and more batches of beer brewed per day.
  • Chemical Plants – The product is pumped into the filter press and then the membranes are inflated and squeezed to allow for a quick turnaround of the press to increase productivity.
  • Gold Mining - The faster the solids can be pumped into the membrane press, the quicker the press can be turned around for more batches to dewater the solids and reclaim gold. 

In some instances where the solids are waste and the press is under no strain to operate quickly, the standard non-membrane filter press plates are sufficient; but when time and turnaround are critical, the membrane plate is the solution.

Phases of Membrane Filter Press Cycle

Filter Press

Filling: Mash enters the chambers through a feed pump in the upper right corner. Mash will fill each chamber sequentially.

Filter Press

Filtration: Once the chambers are full, the mash that is being pushed by the feed pump will force the liquid out from the chambers.

Filter Press

Compression: Once the Feed Pressure has cycled out, the system will be closed and the membrane squeeze will begin.

Filter Press

Draining: As the Squeezing is happening, the liquid will be forced out of the chambers and into one of the 3 return pipes.

Filter Press

Grain Discharge: The hydraulic closure of press is opened. Each chamber is opened up for cleaning and grain discharge.