FI61634B - REFERENCE FOUNDATION FOER AVSKILJNING AV FAST MATERIAL FRAON VAETSKA - Google Patents

Description

61 634

The present invention relates to a method for separating solids from a liquid, and in particular from a slurry obtained from a fermentor, and to an apparatus for performing the method sterile.

It is already known to thicken a fermentor slurry by circulating it through a circulating filter in which the liquid is filtered from the slurry in a sterile closed state through several overlapping planar filter surfaces which are rotated about their vertical axis to remove filter cake formed on the filter surfaces by scrapers. The slurry thus thickened is returned to the fermentor.

However, such a previously known circulating filter cannot be used for the final separation of solids after the completion of the fermentation reaction, since the cake left on the planar filter surfaces still contains so much liquid that it cannot be recovered as such.

Therefore, another filter is connected to the fermenter, the so-called pressure filter, by means of which the solid is recovered from the thickened slurry in a sufficiently dry form after the completion of the fermentation reaction.

In a known pressure filter, the slurry is introduced into the space between the cylindrical chamber and the concentric cylindrical screen cylinder inside it to filter the liquid inside the screen cylinder and remove it from inside the screen cylinder. The solid layer remaining on the surface of the screen cylinder is further compressed by a flexible membrane on the inner wall of the cylindrical chamber, which is compressed towards the screen cylinder 2,61634 by passing a pressure means between the flexible membrane and the inner surface of the cylindrical chamber. In this way, the solid on the surface of the sieve cylinder is compressed and the remaining liquid in it is separated inside the sieve cylinder. Finally, the pressure medium is discharged between the flexible membrane and the cylindrical chamber so that the screen cylinder and the solid layer thereon can be pushed out of the cylindrical chamber in the axial direction and the solids layer removed from the surface of the screen cylinder.

It is clear that it would be advantageous if the thickening of the slurry and the separation of the solid from the liquid in a sufficiently dry form could be performed in one and the same device, i.e. if the functions of the circulating filter and the pressure filter could be combined in a single device. Although the above-mentioned previously known pressure filter can thicken the slurry, it cannot be used as a circulating filter because it is not sterile sealed. Namely, in order to remove the solid layer, the cylindrical chamber must be constructed to be opened, which means that it cannot be made sufficiently airtight and sterile.

In addition, it should be noted that since the movement of the flexible film is relatively limited, the distance between the screen cylinder and the wall of the cylindrical chamber cannot be very large. This in turn means that this gap is filled relatively quickly when the sludge is thickened.

Also known is a filter with a closed chamber and a cylindrical screen cylinder rotatable about its axis, within which the filtered liquid can be removed via the shaft. In this device, the growth rate of the layer of solids 61634 3 formed on the surface of the screen cylinder can be controlled by controlling the rotation speed of the screen cylinder. Namely, the formation of a solid layer can be avoided or substantially slowed down by means of centrifugal force. In this device, filtration can also be performed with the screen cylinder in place. Upon completion of the filtration, the chamber is emptied of slurry and the screen cylinder is rotated to remove and remove the solids layer accumulated on its surface from the chamber. A filter of the above type can be used to thicken the slurry, but the solid layer on the surface of the screen cylinder still contains so much liquid that it cannot be utilized as such.

It is therefore an object of the present invention to provide a method and apparatus for separating a solid from a liquid by filtering the slurry in a sterile closed state to form a solid layer on the filter surface, and the main features of the invention appear from the appended claim 1.

Although devices are known in which the solids layer on the surface of the screen cylinder is removed by rotating the screen cylinder, i.e. by centrifugal force, it was surprising that such a separation method was sufficiently effective even in a device in narrow and roughly solid-filled. Namely, the movement of the flexible film is rather limited and in order to provide a sufficient compressive force, the filter surface must therefore not be far from it, and the solid must fill the space between the screen cylinder and the surrounding jacket practically completely. However, it has now been shown that when the pressure medium is discharged from the space between the cylindrical jacket and the membrane after compression and the membrane retracts somewhat, it at the same time slightly removes the solids layer. Ί * r 4 61634 ta from the sieve cylinder, so that when the sieve cylinder with the solids layers on it is rotated, the solids layer is easily detached from the sieve cylinder by centrifugal force. The detached solid can then be removed from the bottom of the enclosure.

The device according to the invention can also be used in a manner known per se as a slurry thickener by rotating the filter surface at such a speed during the thickening step that the solids layer does not substantially increase during the thickening. In this case, the filter surface is not rotated to prevent the holes in the screen cylinder from filling but primarily to limit the layer thickness of the solids layer so that it does not completely fill the space between the screen cylinder and the surrounding cylindrical shell and thus prevent sludge recirculation.

The invention will be described in more detail below with reference to the accompanying drawing, which shows a cross-sectional vertical view of a preferred embodiment of the invention.

In the device according to the invention, the filtering and pressing operations can be performed sterile.

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The main structural parts of the cylindrical device shown in the figure are the outer jacket 1 and its cover 2 and base 3, flexible pressing membrane 4, filter cloth or wire 6, perforated inner cylinder 5, shaft 7, and therein an axial fluid outlet 9, screw 8, actuator 10, filterable liquid inlet pipe 14, liquid drain pipes 15 and 17, solid outlet pipe 18, sterile air inlet pipes 13 and 16, compression fluid inlet pipe 11 and outlet pipe 12.

The operating steps of the device are as follows:. r * 5 616 34

In the filtration step, the solid-containing liquid is pumped into the device through a pipe 14. The liquid flows through the filter cloth or wire 6 and the inner cylinder 5, leaving the channel 9 in the middle of its shaft 7 out of the device.

As the filtration continues, a solid layer is formed against the fabric or wire 6. When the solid layer has filled the space 19 between the fabric 6 and the flexible membrane 4, the pumping of the liquid is stopped and the liquid at the top and bottom of the device is removed through the pipes 15 and 17.

In connection with the liquid removal, purified, sterile air is blown from the tubes 13 and 16. If necessary, the inner cylinder 5 can be rotated during the filtration step so that the solid layer does not fill the space 19 too quickly.

Simultaneously with the removal of the excess liquid, the compression is started by pumping the liquid from the tube 11 into the space 20 between the flexible membrane 4 and the outer jacket 1.

The membrane 4 is pressed against the solid layer, removing some of the liquid remaining in it after the filtration step.

The solids are removed from the filter cloth 6 by rotating the shaft 7 by means of the drive mechanism 10 after the liquid compressing the membrane 4 has been removed from the tube 12. The solids removed by centrifugal and shear forces fall to the

Claims (6)

A method for separating solids from liquid, wherein the sludge obtained from a fermentor is filtered in a sterile closed space (1, 2, 3) to form a layer of solid material on a filter surface (6), liquid is pressed (4) from the layer of solid material on the filter surface, liquid (15, 17) is removed from the enclosed space (1, 2, 3) and finally the layer of the solid material from the filter surface (6) is removed (18) from the enclosed space, characterized in that the filter surface (6) is rotated (10) to release the solid from the filter surface by centrifugal force, 2. A method according to claim 1, wherein the sludge obtained from the fermenter is thickened by filtering from there liquid in said sterile closed space (1, 2, 3) and feeding (17) a similarly thickened sludge to the fermenter, characterized in that the filter surface (6). ) is rotated at such a rate that the solid layer does not substantially grow during the thickening. Apparatus for separating solids from liquid comprising a sterile closed chamber (1, 2, 3), means (14) for feeding fermentor mud into this chamber, including a filter surface (6), means (4) for compressing the layer of solid material separated from the filter surface (6), means for removal from the chamber (1, 2, 3) of liquid separated through the filter surface (6) and pressed out of the layer of the solid material and means (7, 10, 18 ) for detaching the layer of the solid material from the filter surface and removing it from the sterile closed chamber (1, 2, 3), characterized in that the means for releasing the layer of the solid material from the filter surface is made up of the filter surface rotating means (7, 10). Device according to claim 3, characterized in