Industrial Filtration Equipment: Operation and Design
1. Plate and Frame Filter Press
The plate and frame filter press is one of the most common batch filtration devices used in chemical and pharmaceutical processing.
Principle
It works on the principle of surface filtration under pressure.
Construction
- It consists of a series of alternating plates (with grooved surfaces for drainage) and frames (hollow chambers where the cake accumulates).
- These components are supported on rails and squeezed together by a hydraulic or manual screw mechanism.
Working Process
- Slurry is pumped into the hollow frames under pressure.
- The solids are trapped in the frame, forming a filter cake.
- The filtrate passes through the filter cloth, flows down the grooved plate surfaces, and exits through an outlet channel.
- Once the frames are full of cake, the press is opened, and the cake is removed manually.
Uses
Used for clarifying liquids like fruit juices, chemicals, and pharmaceuticals, and for wastewater sludge dewatering.
2. Filter Leaf
Principle
Similar to the filter press, it uses surface filtration but often utilizes vacuum or pressure to pull/push the liquid through a flat leaf (frame).
Construction
A leaf consists of a metal frame enclosing a drainage screen, which is covered with a filter cloth. Multiple leaves can be grouped together in a vessel.
Working
- The leaf is immersed in a tank of slurry.
- A vacuum is applied to the inside of the leaf, drawing the filtrate through the cloth while the cake builds up on the outside.
- To remove the cake, the leaf is removed from the tank, and a reverse blast of air is often used to “blow” the cake off.
Uses
Ideal for filtering slurries with a low solid content (<5%) and for materials that are flammable or toxic since the process can be fully enclosed.
3. Rotary Drum Filter
Principle
This is a continuous vacuum filter that separates solids from liquids by sucking the liquid through a rotating porous drum.
Construction
A large horizontal drum with a perforated surface covered in filter cloth. The drum is divided into internal sectors and partially submerged in a trough of slurry.
Working
- As the drum rotates, a vacuum is applied to the submerged sectors, drawing slurry onto the cloth.
- The filtrate is sucked through the drum to the center and discharged.
- The solids form a cake on the outside. As the drum rotates out of the slurry, the cake is washed and dried by the air.
- A doctor knife scrapes the dry cake off before the drum rotates back into the slurry.
Uses
Large-scale industrial processes like mining, sugar refining, and primary wastewater treatment.
4. Perforated Basket Centrifuge
Principle
It works on the principle of centrifugal filtration. Centrifugal force pushes the liquid through a porous barrier while solids are retained.
Construction
It consists of a stainless steel basket with perforated walls lined with a filter cloth. The basket is mounted on a vertical shaft and enclosed in a stationary casing.
Working
- Slurry is added to the basket while it is stationary or spinning slowly.
- The basket is spun at high speeds (1000+ rpm).
- Centrifugal force drives the liquid through the perforations into the outer casing, where it is collected.
- The solids form a hard cake against the inner wall, which is then scraped off manually or by a blade.
Uses
Separating drug crystals (like aspirin) from mother liquor.
5. Non-Perforated Basket Centrifuge
Principle
This is a sedimentation-type centrifuge. It uses centrifugal force to separate particles based on their density rather than size or porosity.
Construction
The basket has solid walls (no holes). It includes an inlet tube and a skimming tube to remove the clarified liquid.
Working
- Slurry is fed into the spinning basket.
- Because the walls are solid, the denser solids are forced against the wall.
- The lighter liquid forms an inner layer (the “supernatant”).
- The skimming tube is lowered into the liquid layer to draw the filtrate out while the machine is still spinning.
Uses
Used for separating very fine solids that would clog a filter cloth or for separating two immiscible liquids (like oil and water).