The vacuum filter constitutes negative pressure at the outlet of the filtrate as the propulsion force for filtration. The filter is divided into two types: intermittent operation and continuous operation. Intermittent operation of the vacuum filter can filter various concentrations of suspension. The continuous operation of the vacuum filter is suitable for filtering thick suspensions containing more solid particles.
Intermittently operated filters have been developed for automated operation, and the filtration area is increasing. In order to get filter residue with low moisture content, a mechanical press was developed. The filter is used to separate the container into the upper and the lower cavity, which forms a simple filter. The suspension takes part in the upper chamber, and the filter medium enters the lower cavity under the action of pressure to become the filtrate, and the solid particles are intercepted on the surface of the filter medium to form filter residue (or filter cake). During the filtration process, the slag layer accumulated on the surface of the filter media is gradually thickened, and the resistance of the liquid through the filtration layer increases, and the filtration speed decreases. When the filter chamber is filled with filter residue or filtration rate is too small, stop filtration, purge filter residue, and filter medium regeneration, so as to complete a filtration cycle.
The liquid must be restrained through the filtration layer and filtration medium. Therefore, there must be pressure difference on both sides of the filter medium, which is the propulsion for filtering. Increasing the pressure difference can accelerate filtration, but the particles deformed after compression are easy to filter the pore of the filter medium when the pressure difference is large, but the filtration slows down. Suspension filtration consists of three ways: filtration, filtration and filtration. The filtration of the filter layer means that the initial filtration layer is formed after the initial filtration. Then, the filter slag layer plays a major role in the filtration, and the large and small particles are intercepted, and the deep filtration means that the filter media is thicker, the solid particles in the suspension are less, and the particles are less than the filter medium, when the particles are filtered, after the particles enter into the filter, the particles enter after the filtration. Filtration is adsorbed in the channel; sieve filtration is the pore of the filtered solid particles larger than the filter medium, and the filtration mode of the solid particles is not adsorbed inside the filter medium, for example, the coarse grained impurities in the sewage are filtered through the cylinder filter screen.
In the process of practice, the three ways often appear at the same time or in succession. The disposal of the filter depends on the speed of the filter. When the solid particles in the suspension are large and the granularity is average, the pores of the filtered slag layer are relatively smooth, and the filtrate passes through the slag layer. The application of coagulant to the aggregation of fine particles is conducive to the improvement of filtration speed. A filter with fast settling velocity of solid particles, which is applied to the filter in the upper part of the filter medium, diverts the direction of the filter from the direction of gravity, and the coarse particles are first settled, which can reduce the infarct of the filter media and the filter slag layer, and mixed with the coarser solid particles, such as diatomite and contractile perlite, in the filtrated suspension (such as colloids). Particles can make the filter layer loose. When the viscosity of the filtrate is large, the suspension can be heated to reduce the viscosity. These measures can speed up the filtering speed.