Plate and frame filter press:
Principle:
Mechanism is surface filtration.
The slurry enters the frame by pressure and flows through the filter medium.
The filtrate is collected on the plates and sent to the 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:
It consists of plates and frames.
The frame is open and is used as an inlet for the material to be filtered.
Plate has a grooved surface which gives support to the filter cloth.
The plate and frame may be made of various metals which provide resistance to corrosion or prevent metallic contamination of the filtrate.
Filter cloth is fitted on each side of the plate.
The plates and frames are placed alternatively and fitted in the outer frame of the press.
Each plate acts as a single filtration unit.
The outlet of each plate is connected to a common outlet pipe.
Working:
As shown in the following diagram the filtering liquid enters the frame under pressure from the feed channel.
The filtrate passes through the filter medium onto the surface of the plate.
The filtrate is collected in the plates from where it is collected through a common outlet pipe.
The cake is deposited in the frames.
The process of filtration is continued until the frame is filled with filter cake.
When the process is stopped, the frame is emptied and the cycle is restarted.
The thickness of the cake can be varied by using frames of different thickness.
The thickness of filter cake depends mainly on the solid content present in the filtering liquid and the resistance of filter cake.
Advantages of filter press:
The filtering media can be used repeatedly.
Operation and maintenance is simple.
It requires less space.
It provides a large surface area for filtration.
Efficient washing of cake is possible.
Disadvantages of filter press:
It is not a continuous process.
It is used where the proportion of solid in the liquid to be filtered is about 5% or less.
The process becomes costlier because a lot of labor cost is required for washing and replacement of the filter cloth.
Leakage between the plates may take place through faulty assembly.