Plate and frame filter press - Pharmaceutical Engineering B. Pharm Third Semester PDF Notes

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

• The filter press is used for slurries containing less about 5 % solids

• In view of the high labour costs, it is most suitable for expensive materials e.g. the removal of precipitated proteins from insulin liquors.

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