Plate and frame filter press

Principle

• Mechanism is surface filtration

• The slurry enters the frame by pressure and flows through filter medium

• The filtrate is collected on the plates and send to outlet

• A number of frames and plates are used so that surface area increases and consequently large volumes of slurry can be processed simultaneously with or without washing

Construction

• The Filter press is made of two types of units, plate and frames.

• Usually made of aluminium alloy.

• Sometimes, these are also lacquered for protection against corrosive chemicals and made suitable for steam sterilization.

Frame

It contains an open space inside wherein the slurry reservoir is maintained for filtration and an inlet to receive the slurry.

It is indicated by two dots in description.

• Frames of different thickness are available.

• It is selected based on the thickness of cake formed during filtration.

• Optimum thickness of frame should be chosen.

Plate

The plate has a studded or grooved surface to support the filter cloth and an outlet.

It is indicated by one dot in description.

• Plate supports the filter medium, receiving the filtrate and outlet

• The filter medium usually cloth is interposed between plate and frame

• Plate, filter medium, frame, filter medium and plate are arranged in sequence and clamed to a supporting structure

• It is normally described by dots as 1.2.1.2.1 so on

• A number of plates and frames are employed so that the filtration area is as large as necessary.

• Number of filtration units are operated in parallel

• Channels for slurry inlet and filtrate outlet can be arranged by fitting eyes to the plates and frames, these join together to form a channel

• In some types only one inlet channel is formed, while each plate is having individual outlets controlled by valves

Assembly of plate and frame filter

Working

• Working can be divided into two steps-

1. Filtration operation

2. Washing of cake (if desirable)

• Filtration operation

Advantages

• Provide large filtration area in relatively small floor space. The capacity being variable according to thickness of frames and number used

• Sturdy construction permits the use of considerable pressure difference. (2000 Kilopascals normally used)

• Efficient washing of cake is possible

• Operation and maintenance is easy

• It produce dry cake in form of slab

Disadvantages

• It is a batch filter, so it is a time consuming

• The filter press is an expensive filter; the emptying time, the labour involved, and the wear and tear on the cloths resulting in high costs

• Operation is critical, as the frames should be full, otherwise washing is inefficient and the cake is on the cloths resulting in high costs difficult to remove