Plate Filter Press (Water & Wastewater Treatment Systems, WWTS_CAMIX Vietnam)

DESCRIPTION

Filter press (sometimes called Plate-and-Frame Filter press) which describes the style of filters developed from the 19th century onwards originally for clay.^[1] The majority of today's filters are more correctly called "chamber filter press", "Membrane filter press", or "Membrane Plate Filter". Many processes in the food, chemical or pharmaceutical industries make products from liquid-solid suspensions or slurries. These mixtures are like a runny mud or milk shake. The solids in them do not dissolve in the liquid, but are carried along in it. Filter presses separate the solids from the liquids so that the useful part can be processed, packaged or delivered to the next step.

Filter presses generally work in a "batch" manner. The plates are clamped together, then a pump starts feeding the slurry into the filter press to complete a filtering cycle and produce a batch of solid filtered material, called the filter cake. The stack of plates is opened, solid is removed, and the stack of plates is re-clamped and the filtering cycle is repeated.

A filter press uses increased pump pressure to maximize the rate of filtration and produce a final filter cake with a water content under 65%. This is more efficient than regular filtration because of the increased filtration pressure applied by the pump that can reach anywhere between 50–200 pounds per square inch (3.4–14 bar).

A filter press consists of a series of filter chambers formed between square, rectangular or round filter plates supported on a metal frame. Once the filter chambers are clamped, the filter press is loaded with slurry. The plates on the filter press are clamped together with hydraulic rams that generate pressures typically in the region of 3,000 pounds per square inch (210 bar).

In addition to the filter plate filtration medium, the growing filter cake enhances removal of fine particles in the slurry. The solution coming through the filter press water bibs, called the filtrate, will be pure.

The filtrate can be drained away for safe disposal, or it can be kept in a water tank for recycled use. At the end of filtration, the solid filter cake can be removed. The whole filtration process is often controlled by electronics to make it automatic or semi-automatic.

A filter comprises a set of vertical, juxtaposed recessed plates, presses against each other by hydraulic jacks at one end of the set. The pressure applied to the joint face of each filtering plate must withstand the chamber internal pressure developed by the sludge pumping system. 
This vertical plate layout forms watertight filtration chambers allowing easy mechanisation for the discharge of cakes. Filter chlotes finely or tightly meshed are applied to the two groowed surfaces in these plates.
Orifices feed the sludge to be filtered under pressure in the filtration chamber. They are usually placed in the center of the plates allowing a proper distribution of flow, right pressure and better drainage of sludge within the chamber. Solids sludge gradually accumulates in the filtration chamber until the final compacted cake is formed. The filtrate is collected at the back of the filtration support and carried away by internal ducts.

Filtration cycle

The filter press is an intermittent dewatering process. Each press operation includes the following steps:

1- Closing of the press: as the filter is completely empty, the moving head activated by the jacks calmps the plates. Closing pressure is self regulated through filtration.

2- Filling: During this short phase chamber are filled with sludge for filtration. Filling time depends on the flow of the feed pump. For sludge having good filterability it is best to fill the filter very quickly so as to avoid the formation of a cake in the first chamber before the last ones have been filled.

3- Filtration: Once the chamber have been filled continuous arrival of sludge to be dewatered provokes a rise in pressure due to the formation of an increasingly thick layer of filter sludge on the cloths. This filtration phase can be stopped manually, by a timer or more convenientely by a filtrate flow indicator which issues a stop alarm when the end of filtration rate has been reached. When the filtration pump has stopped, the filtrate circuits and central duct, which is still filled with liquid sludge, are purged by compressed air.

3- Filter opening: The moving head is drawn back to disengage the first filtration chamber. The cake falls has a result of his own weight. A mechanised system pulles out the plates one by one. The speed of plate separation can be adjusted to account to the cake texture.

4- Washing: Whasing of clothes should be carried out every 15-30 processing oprations. For mid- or large units this take place on press using water sprayers at very high pressure (80-100 bar). Whasing is sincronized with separation of plates.

Filtration capacity

The production capacity of a filter press is somewhere between 1.5 and 10 kg of solid per m² of filtering surface. For every the filter press model the chamber volume and the filtering surface depend on the number of plates in the filer.

In practical terms pressing times are less then four hours. 
Filtration time depends on:

- cake thikness
- sludge concentration
- specific resistance
- compressibility coefficient.

One of the advantages of the filer press is that it can accept sludge with average filterability. It is always advantageous to optimally thicken sludge before filter press operations. Although sludge presenting a high filterability enables better production capacities, a filter press still accepts sludge with low conditioning precision. This tolerance means that the device offers greater owerall operational safety.

Performance

The filter press is suitable for almost all types of sludge:

REFERENCE PHOTOS