A rotary vacuum filter is a kind of filtering equipment with a high degree of automation, which takes filter cloth or screen as medium and makes full use of gravity of the slurry and vacuum suction to realize solid-liquid separation. The rotary vacuum filter is a kind of vacuum filter, which can filter the suspension with uneven suspension particle thickness. The drum of the rotary drum vacuum filter is hollow and the outer layer is the filtering medium. The pressure difference between the inner and outer sides will make the water in the slurry pass through the filtering medium, while the solid particles are intercepted and left on the filtering medium to form the filter cake, which is removed by the scraper or reverse blowing wind or folded belt or rope to achieve the purpose of filtration and dewatering.
With the continuous rotation of the drum, the drum will pass through four functional areas, in turn, namely the cake formation area, the suction and drying area, the discharge area and the resting area. Immersion into the filtrate begins through the rotation to the drop stage, completing the processes of filtration, dewatering and discharging in sequence.
The filtration power of the drum vacuum Filter mainly depends on vacuum pressure, in addition, there is a part of it by the power generated in the material settling process and the gravity of solid particles themselves. The vaccum filter is driven by the negative pressure at the outlet of the filtrate. Therefore, the vaccum filter is drivided into two types: batch operation and continuous operation.
The common rotary vacuum filter is continuously rotating. The batch rotary vaccum filter's filtration, washing, drying and discharging are carried out at different times in the same part of the equipment, so it is not common because of its long cycle time, high labor intensity of workers and unsafe disadvantages.
The filtration, washing, drying and discharging of the continuous rotary vacuum filter are carried out in different parts of the equipment. It has the advantages of high production efficiency, automation of operation process, easy adjustment and labor saving. The continuous operation vacuum filter is suitable for filtering thick suspensions containing more solid particles.
Besides drum rotary vacuum filter, there are many other types of continuous rotary vacuum filter, such as belt vacuum filter and disc vacuum filter.
According to the filtration media, rotary drum vacuum filter can be divided into internal and external filter surface drum rotary vacuum filter.
The internal surface rotary vacuum filter has a drum cylinder with a length smaller than the diameter of the cylinder and its inner surface is covered with filter media. The filter residue is discharged by a belt conveyor or a screw conveyor. This kind of filter is mostly used in the mining and metallurgical industry to handle large volume and easy to filter materials.
The external surface vacuum filter is covered with a number of plastic or other material screen panels to form the outer surface of the drum filter.
When the drum turns to the discharging area, after the air blowing back, the filter cloth will be bulged up and the filter cake will be discharged by the scraper device, and one cycle will be completed and then enter the next cycle. The structure is simple, easy to operate and maintain, cheap to build, and continuous operation.
The filter cloth is zigzagged and installed between the drum and the rollers, forming a looped belt of filter cloth that is connected at the beginning and end. With the rotation of the drum, the filter cloth runs between the drum and the folded rollers as the drum rotates. The filtrate is continuously sucked out through the filter cloth, and the filter cake on the filter cloth gradually thickens to form a filter cake. The filter cake is discharged by the sudden turning of the filter belt at the discharge roller, and sometimes there is also a scraper to discharge. An adjustable angle scraper is installed on the outside of the filter cloth washing tank to receive and remove the filter cake.
The filtration cycle consists of two operational processes, the pre-coating of the filter media and the filtration of the suspension. The drum structure is formatless and the filter chamber is not divided into chambers. Before the formal filtration, a layer of filtering aid (pre-coating) is applied to the filter cloth, and then, the filtration operation is carried out.
Pre-coating filter media: inject the stirred filter media mixture into the storage tank, turn on the tank stirring and the drum, with the rotation of the drum, under the vacuum suction, a layer of thickening filter media will be gradually sucked on the outside surface of the filter chamber until the required thickness.
The scraper device of the pre-coating type filter is more complicated, divided into manual and automatic knife feeding. The automatic knife scraper is driven by servo motor or FM motor to make the knife scraper continuously or intermittently to scrape off the filter slag together with part of the pre-coating.