A drum screen works by mechanically separating solids from liquids using a rotating cylindrical screen. Here's a breakdown of the process:
Operating Principle
Drum screens, also known as rotary screens, use a cylindrical screen to filter solids from a liquid stream. The screen rotates, allowing liquids to pass through the screen openings while retaining solids on the screen surface. These retained solids are then removed, often by a scraper, brush, or spray system.
Key Components
- Drum: The perforated or woven mesh cylinder that performs the screening.
- Drive System: Motor and gears that rotate the drum.
- Feed System: Mechanism for introducing the liquid and solid mixture to the drum.
- Solids Removal System: Scrapers, brushes, or spray nozzles to remove captured solids.
- Collection System: System to collect filtered liquid and removed solids separately.
Types of Drum Screens
- Internally Fed: Wastewater enters the drum from the inside, flows outward through the screen, and the solids remain inside. Drumtec is an example of this type, using a deflector to evenly distribute wastewater.
- Externally Fed: Wastewater flows onto the outside of the drum screen, with the liquid passing inward and solids remaining on the exterior.
The Screening Process
- Wastewater Introduction: The liquid containing solids is fed onto or into the rotating drum screen.
- Screening: As the drum rotates, the liquid passes through the screen openings (perforations or mesh). The size of the openings determines the size of the particles that are retained.
- Solids Retention: Solids larger than the screen openings are retained on the surface of the screen.
- Solids Removal: A cleaning mechanism, such as a scraper, brush, or spray nozzles, removes the accumulated solids from the screen. These solids are then discharged for further processing or disposal.
- Effluent Collection: The filtered liquid (effluent) is collected in a separate chamber and discharged.
Applications
Drum screens are used in various applications, including:
- Wastewater Treatment: Removing solids from municipal and industrial wastewater.
- Food Processing: Separating solids from liquid streams in food production.
- Pulp and Paper Industry: Fiber recovery and wastewater treatment.
- Agriculture: Manure processing and irrigation water filtration.
Advantages
- High Solids Removal Efficiency: Effective at removing a wide range of particle sizes.
- Continuous Operation: Can operate continuously with minimal operator attention.
- Compact Design: Relatively small footprint compared to other screening technologies.
- Versatility: Can be adapted to various applications and flow rates.
In summary, a drum screen efficiently separates solids from liquids by using a rotating screen, retaining solids while allowing liquids to pass through, and employing a cleaning mechanism for continuous operation.
