Roller screen in coal Coarse De-media process
As most redundant energy resource in earth , coal had power human’s life for hundreds of years. With technology advancing ,the screening and crushing process became much more essential, thus the utilization of roller screen became widely.
At first , coal must be crushed and screened into ideal size to meet different needs, dense medium separation is used frequently in precise coal cleaning , to remove impurities and make sure the product is acceptable by the market, the De-Media process is the key.
What is De-media process
De-media or DEM (Dense Medium Separation) is a separation process using materials physical natures, specifically speaking , ROM coal always mixed with a suspension of finely ground dense material in water, as the density of coal slurry is limited precisely, lighter content like coal will float and heavier content like debris and dense medium sink, therefore complete the separation.
But, the clean coal still coated with dense medium, so they need to be cleaned before further handling, the integration of roller screens as an flexible part has already gained attention for specific material handling advantages.
What is a roller screen
Roller screen is a specific material screening and conveying equipment widely used in mining material handling, like lignite ,clay and coal. Through driving system powered rotating shafts with customized discs, the screening surface of a roller screen is dynamic , gap form by the shaft and disc became the screening openings allow smaller size (mostly <20mm) particle to drop through ,complete the separation sequence.
Roller screen achieve those performance by its key feature:
Staggered arranged screen shafts driven individually or by chain coupling. Wear-resistant material made disc designed to move the material effectively. Self-cleaning device to make sure large and sticky lumps will not causing clogging and blinding.
Gear motors or chain drive provides the controllable rotation speed, and heavy-duty structure with splash and abrasive-resistant protection, increasing reliability.
How roller screen work
First, rotating shaft ensured material is moving consistently thus dealing with sticky and wet material like washed coal and lignite are not a problem, relative speaking, roller screen are more suitable for rapid drainage of the slurry , it’s whole structure is designed to be durable and stable , and through simple replacement , the capacity of a roller screen can be easily adjusted. Without vibration action , lowering the noise and dust emission.
Second, roller screens’ self-cleaning device can scraping down any lump or particle adhere to the disc or shaft , so dramatically reduce the possibility to clogging and blinding.
At last, roller screen can help downstream selection equipment like vibrating screen or banana screen to work in a more efficient and safer way, because large lump or debris which will produce shock load that can damage the machine is removed.
Roller screens’ role in DEM process
Whether before or after the DEM process, the raw coal always came with lots of moisture, which makes it became sticky and adhesive, greatly increase the probability to form a large lump, affecting downstream process, slow down whole operation efficiency.
By placed a roller screen afront of the DEM process , the staggered arranged rotating shaft with customize designed screening disc create a dynamic screening surface , thus allow watery content to drop down while large debris stays on the surface ready to be discharged.
Also, a roller screen can function as feeder ahead of reject drain-and rinse screens so the loading pressure on the next level is lifted ,creating a much more evenly material spread and distribution, cut down the possibility of overloading and improve the whole DEM process efficiency.
Through roller screen’s moving screening area, sticky agglomerates of coal ,clay or magnetite slurry will be broken, thus increase the surface area exposure for spray water during rinsing, eventually improving magnetite removal efficiency and reducing product contamination.
After going through the pre-screening process, roller screen ensured after stream coal selections’ efficiency and provide a stable work flow, thus reduce the risk of system shut down and maintenance requirements.
How a roller screen helping Pre-drain and Material separation
- Draining a portion of the magnetite-rich slurry beforethe rinse stage, roller screen can reduces spray water dilution, making magnetic separators more effective , in well-tuned systems, the magnetite losses are generally reduced
- Provides even feed distribution to after stream screen deck , improving drainage efficiency.
- Remove oversize pieces before they reach the vibrating drain screens, provide protection to those equipmentaway from impact damage and reducing blinding.
- Steady feed and preventing capacity loss achieved by a single self-cleaning roller screen.
- By reducing blinding and wear on after stream equipment lowering the whole maintenance costs.
- Lesser unscheduled stops for screen cleaning or repairs.
- Through scalping off oversize or foreign objects, roller screen improves the size consistency of both clean coal and rejects. Provide aids to stockpilingand conveying ,even further processing stages.
In the De-media stage of coal preparation, roller screens could serve as feeder that can ensure size condition, can work as a pre-drain device, can protect downstream equipment form oversize lumps or particles, thus achieve lower water consumption and after stream equipment life extension , eventually improve the whole plant reliability.
Even roller screen can’t working as a substitute for drain and rinse screens like banana screen or flip-flop screen, the integration of each other into DEM circuits delivers tangible operational and economic benefits, specially in plants handling sticky or debris-contaminated material streams.
