A rotary vacuum filter works by using a rotating drum partially submerged in a slurry to continuously separate solids from liquids through vacuum suction and mechanical action.
Here's a breakdown of the process:
1. Slurry Immersion:
- A cylindrical drum, covered with a filter medium (cloth or mesh), is partially submerged in a tank containing the slurry (a mixture of solid particles and liquid).
2. Vacuum Application:
- A vacuum is applied to the internal sections of the drum as it rotates through the slurry. This vacuum sucks liquid through the filter medium, leaving the solid particles on the drum's surface.
3. Cake Formation:
- As the drum rotates, the vacuum continues to draw liquid through the filter medium, building up a layer of solid material called the filter cake. The thickness of the cake can be controlled by factors like drum speed, vacuum pressure, and slurry concentration.
4. Cake Washing (Optional):
- In some applications, a wash liquid is sprayed onto the filter cake as the drum rotates. This washes away any remaining impurities or soluble components from the solids.
5. Cake Drying:
- As the drum continues to rotate, it enters a drying zone where the vacuum pulls air through the filter cake, further reducing its moisture content.
6. Cake Discharge:
- Once the drum reaches the discharge point, the vacuum is released from that section of the drum. A scraper or other mechanical device then removes the filter cake from the filter medium. Common methods include:
- Scraper Blade: A fixed blade scrapes the cake off the drum.
- Air Blowback: Compressed air is blown from inside the drum to dislodge the cake.
- Belt Discharge: A belt lifts the cake off the drum.
7. Filtrate Removal:
- The liquid that passes through the filter medium (the filtrate) is drawn into the internal sections of the drum and then discharged through a pipe connected to the drum's center.
Key Components & their functions:
| Component | Function |
|---|---|
| Rotating Drum | Provides the surface for filtration and carries the filter cake. |
| Filter Medium | Separates the solids from the liquid. |
| Vacuum System | Creates the pressure differential for liquid extraction. |
| Slurry Tank | Holds the slurry to be filtered. |
| Discharge Mechanism | Removes the filter cake from the drum. |
| Filtrate System | Collects and removes the filtered liquid. |
Advantages of Rotary Vacuum Filters:
- Continuous Operation: Can operate continuously with minimal operator attention.
- Relatively High Throughput: Can process large volumes of slurry.
- Versatile: Can be used with a wide range of materials.
Disadvantages of Rotary Vacuum Filters:
- Relatively High Capital Cost: More expensive than some other filtration methods.
- Cake Cracking: Can occur if the cake dries too quickly.
- Filter Cloth Blinding: The filter medium can become clogged over time, reducing efficiency.
Applications:
Rotary vacuum filters are used in various industries, including:
- Wastewater Treatment: Dewatering sludge.
- Mining: Recovering valuable minerals.
- Chemical Processing: Separating solids from liquids in chemical reactions.
- Food Processing: Recovering solids from liquid food streams.
In summary, a rotary vacuum filter is a continuous filtration device that uses a rotating drum, vacuum pressure, and a filter medium to efficiently separate solids from liquids in a slurry. This process is particularly well-suited for high-volume applications.
