Liquid purification or separation – Magnetic – With additional separator
Patent
1997-04-08
1999-05-04
Reifsnyder, David A.
Liquid purification or separation
Magnetic
With additional separator
210243, 210359, 210388, 210391, 210407, 2104161, 2105001, 2105101, B01D 3506
Patent
active
059001470
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a filter medium suited to be used in the drying of finely divided material, particularly in connection with a suction drier.
The FI patent 61,739 introduces a drying method and apparatus for drying web-like, pulverous, solid or porous material, in which method the material to be dried is put, by intermediation of a fine porous liquid-saturated suction surface, into hydraulic contact with a liquid maintained at an underpressure in relation to the material to be dried. The apparatus used in the said method comprises a fine porous liquid suction surface, where the radii of the fine pores are mainly within the range 0.5-2 micrometers.
The fine porous liquid suction surface forms the filter surface for the filter medium of the suction drier, which filter surface is set into contact with the material to be dried, such as slurry. When the filter surface is for instance plane-like, and when there is created underpressure at the surface opposite to the filter surface of the filter medium, on the filter surface there is created, due to the suction, a cake filtered of the material to be dried, which cake is then scraped off the filter surface. However, the filter surface is susceptible to choking, because the pore structure of the filter surface of the filter medium, and thus also that of the filter medium itself, is gradually filled with finely divided material to be dried.
It is known in the prior art to use ultrasound in the cleaning of the filter surface of the filter medium in a suction drier, as is described in the FI patent 76,705. In the method of this FI patent 76,705, the use of ultrasound requires that for the duration of ultrasonically boosted cleaning, the filter surface is set into contact with a connecting and cleaning liquid, such as water. In that case, when the filter surface is surrounded by water, the required ultrasound power is not very high, and the risk for corrosion caused by cavitation is eliminated. However, the changing of the connecting and cleaning liquid required around the filter medium reduces the capacity available in the suction drier, and thus increases the installation and running costs of the suction drier.
From the FI patent 82,388, there is known a cleaning method for the filter medium of a suction drier, in which method the cleaning with an ultrasonic oscillator takes place essentially immediately after scraping the filter medium. In this method of the FI patent 82,388, the ultrasonic oscillator is located in the tank of the slurry to be filtered, underneath the liquid surface, in order to carry out the cleaning of the filter medium in continuous operation. With a high solid content of the surrounding slurry, the required ultrasonic power rises high, too. Likewise, the surrounding slurry corrodes the shell of the ultrasonic oscillator due to intensive cavitation. An increase in the ultrasonic power and the changing of the oscillator shells raise the running costs of the suction drier.
When applying a mechanical scraper for detaching the filter cake, part of the filter cake remains in between the scraper and the filter surface. Therefore the FI patent 87,539 introduces a method where prior to starting the removal of the filter cake, a momentous reversed pressure is caused in the suction drier, so that a thin liquid film is created in between the filter surface and the filter cake. In connection with the creation of the liquid film, gas blowing is directed to the other edge of the filter cake, so that the filter cake begins to detach from the filter surface. The gas blowing directed to the edge of the filter cake can, when necessary, be boosted by means of another gas blowing arranged at the middle part of the filter surface. The use of reversed pressure and two-step gas blowing for instance with thin filter cakes is cumbersome, because in between the blowing steps and at the end of the removal of the filter cake, there always is a serious risk that the filter cake is broken into small parts.
The object of the present invention is to eliminate so
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Outokumpu Mintec Oy
Reifsnyder David A.
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