An Explanation Of The Vacuum Filtration
An overview of the Vacuum filtration is the most widely used and most mature filtration method in theory and practice.Like other filter cake filtration methods, vacuum filtration technology USES porous filter media to support the filter cake.The difference is that vacuum filtration USES less thrust, so it is suitable for some special applications.
Vacuum filtration is a continuous filtration operation of sludge waterproofing, usually done in a cylindrical rotary drum filter.The filter media covered on the drum can be natural fabric, synthetic fiber products or wire mesh. The drum is arranged horizontally on top of the sludge tank and partially immersed in the tank. When the rotary drum rotates slowly, part of the circumference of the rotary drum bears the internal vacuum and sucks the sludge to the media of the filter. The water in the sludge is sucked out in the rotation and the cement cake is scraped off. The wet sludge is usually conditioned in order for the vacuum filter to achieve good handling capacity.
The principle of vacuum filtration, is due to the role of the vacuum machine, in the filter drum of the filter into negative pressure, forming the pressure difference between the two sides of the filter media layer (press cloth). With the rotation of the filter, the mother liquor in the lye is removed, and the heavy alkali is absorbed on the press cloth, which is finally scraped off by the scraper.
Rotary vacuum filter
Its main body is a rotating horizontal cylinder, called a rotating drum, with a diameter of 0.3~4.5m and a length of 3~ 6m. The outer surface of the cylinder is composed of a porous plate or a special drainage member covered with a press cloth. The inside of the cylinder is divided into a number of fan-shaped compartments, each of which has a straw connected with a hole in the hollow shaft, and the hole in the hollow shaft leads axially to a rotating disk located at the end of the shaft and rotating with the shaft. The rotating disc and the fixing disc are closely matched to form a special rotary valve called the distribution head. The fixed disk of the distribution head is divided into several arc-shaped voids, which are connected with the pressure relief tube, the washing liquid storage tank, and the compressed air pipeline respectively.
When the drum rotates, the fan can obtain vacuum and pressure respectively by using the function of the distribution head, so that the filtration, washing and other operations can be controlled step by step.
Advantages of a rotary vacuum filter:
(1)Continuous production, the higher degree of mechanization;
(2)According to the nature of the material, process requirements, using different materials to manufacture various types, in order to meet different filtration requirements (usually, for the suspension of medium particle size, viscosity is not too big material, rotary drum vacuum filter is applicable);
(3)Filter cake thickness and washing effect can be controlled by adjusting rotating drum speed;
(4)The loss of press cloth is smaller than that of other types of filters.
Disadvantages of rotary drum vacuum filter:
(1)Filter force is small, it is only the use of vacuum as the driving force. Due to the pipeline resistance loss, the maximum is no more than 80kPa, generally 26.7-66.7kpa, so it is not easy to drain, the final humidity of the filter cake is generally more than 20%;
(2)Equipment processing and manufacturing complex, the main equipment and auxiliary vacuum equipment investment is expensive, high energy consumption in the vacuum, at the same time, the larger the filter area manufacturing more difficult. The maximum filtration area of domestic production is about 50, generally 5 ~ 40.
Rotary vacuum filter
As shown in the figure on the right is the schematic diagram of the rotary table vacuum filter. It consists of a set of filter plates (or turntables) mounted on a horizontal rotating shaft and rotating along the shaft. The structure and operating principle of the rotary disk vacuum filter are similar to that of a rotary drum vacuum filter.
Each sector of the disk has its own outlet pipe leading to the central axis, and when a number of disks are joined together, the outlet of the sector of a rotary disk forms a continuous channel with the corresponding outlet of the other rotary plates in the same phase Angle. Similar to a rotary drum vacuum filter, these continuous channels are connected to a shaft end rotary valve (distribution head). The operation of the rotary disk vacuum filter is very similar to that of a rotary drum vacuum filter. Each turntable is equivalent to a drum, and the operating cycle is also controlled by a rotary valve. Each rotary table has its own filter cake unloading device, but unloading is more difficult.
Rotary vacuum filter machine has a very large filtration area, can be as large as 85, its unit filtration area covers less land, a press cloth is easy to replace, less consumption, energy consumption is low. Its disadvantage is poor washing of filter cake, washing water and suspension are easy to mix in the filter tank.