The Working Principle Of Vacuum Filtration
Vacuum filtration machine generally refers to drum vacuum filters. Its main body is a cylindrical filter drum, the filter drum rotates one circle, and the functions of each part in the filtration process are as shown on the right. About two-fifths of the lower half of the filter drum is immersed in the lye tank.
When the filter drum rotates, all the filter surfaces are in contact with the alkali liquid in the lye tank, the filtrate is sucked into the filter drum, and the heavy alkali crystal is attached. on the filter cloth. The function of rotating the drum one circle can be divided into the following five processes:
(1)The pumped filtrate starts at the center of the bottom of the lye tank slightly to the left (about 14°). To the liquid level, it stops and the liquid is sucked into the filter drum, and the heavy alkali crystal is attached to the felt filter cloth (or metal filter cloth). This is the real filtering effect.
(2) The first time it is sucked dry: The liquid (filtrate) in the filter cake is sucked dry from the beginning of the liquid level to about 300 to 400 mm under the alkali solution tank.
(3)Wash: from the first time the suction position to the upper washing tank, it is about 150 mm, which is the washing stage with washing. The washing water in the filtrate is about 0.2-0.25 m3/t soda ash, and the washing water remaining in the heavy alkali is about 0.36-0.4 m3/t soda.
(4)The second sucked dry starts from the washing of the water tank until the scraper. The mother liquor and washing water remaining in the heavy alkali continue to be sucked dry, that is, the real sucking dry phase, which accounts for about one-quarter of the area of the filter drum. At the same time of sucking dry, there are three pressure rollers to help squeeze out the moisture in the heavy alkali. In order to minimize the moisture content, the filter drum speed cannot be too fast.
(5) The lower part of the blowing blade (below the horizontal line) sucks the filtrate and then introduces compressed air (a part of which is carried out under the liquid level). 3 to 4 mm alkali layer remaining on the filter cloth is blown off by air to restore the performance of the filter cloth.
During the continuous rotation of the filter drum, the functions of these five stages are repeated to complete the operation of the heavy alkali filtration.