JPH0559046B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for treating solid-liquid mixtures such as lime sludge, in which the lime sludge produced in the causticization process of a sulphate pulp mill is first It is then separated from the white liquor and then washed and dried for the subsequent process of roasting.

The causticization process (in which the green liquor obtained from cooking liquor recovery is causticized into white liquor to be reused in the cooking process) also produces lime sludge in addition to white liquor, and this lime sludge is primarily It is calcium carbonate sludge. Separate the lime sludge from the white liquor, wash it, and at least approx.
% dryness and roast it at that dryness to make quicklime to be reused in the causticization process.

Traditionally, lime sludge has been separated and processed for torrefaction, where the lime sludge is separated from the white liquor, washed by a sleeve strainer, and rotary dryer with precoat technology. It has been dried to the degree necessary for roasting. It is also known to treat lime sludge in a pressure vessel in a space bounded by a filter wire and a compressed membrane placed opposite the wire. In such a method,
The filter cake remains in the space during the separation of the white liquor and the washing and drying of the filter cake.

It is an object of the present invention to provide a new method for treating lime sludge, which separates lime sludge from white liquor, washes it, and cleans it more efficiently and economically than conventional treatments. And it dries. The present invention involves forming a filter cake of a mixture of lime sludge and white liquor on the filter surface of a filter element by suction, cleaning the cake with a cleaning liquid directed through the cake and the filter surface, and cleaning the cake and the filter surface with a cleaning liquid directed through the cake and the filter surface. It is characterized in that the lime sludge is treated in a sieve by drying the cake with compressed air led through and removing the cake from a filter element.

Hereinafter, the present invention will be explained using an example in which a drum strainer is used, but the present invention can also be carried out using, for example, a disk strainer.

Compared to known lime sludge processing in pressure vessels, the present invention uses suction directed through the drum interior instead of pressure in forming the filter cake, and this suction is provided in a safer arrangement. Provides improvements in certain respects. When using overpressure vessels, there is a risk of damaging the seals, which would result in the release of corrosive white liquor. Compared to most conventional types of lime sludge processing using sleeve filters, the present invention provides several benefits. The most important of these is that the washing and drying of the lime sludge is carried out by one and the same equipment, thereby reducing the space requirements and capital investment in that equipment. Moreover, the drum filter can pre-dry the lime sludge before the washing stage, so that when the washing starts, the solids content of the lime sludge is about 58% instead of 30-35% as in the past.
~60%. The amount of white liquor in the lime sludge is correspondingly lower, thereby reducing the amount of cleaning fluid required as well as the amount of thin white liquor produced in cleaning. The amount of cleaning chemicals required for wire cleaning is also lower and the cleaned lime sludge obtained in accordance with the present invention is cleaner.

Lime sludge processing according to the invention most preferably involves holding the drum in place during the filter cake formation stage, then rotating the drum approximately 180°, and holding the drum in place again during washing and drying. It is carried out in cycles. To form a filter cake, the bottom of the drum is placed in a vat containing a mixture of lime sludge and white liquor so that the suction inside the drum allows a filter cake to form on the filter surface of the drum. and for washing and drying the cake, the upper part of the drum is surrounded by a shell with supply ducts for supplying washing liquid and drying air to the filter cake, which further and can be forced into the interior of the drum by pressure through the filter surface of the drum. Immediately after the filter cake has been washed and dried, reapply the drum.
It is rotated 180° so that the dried filter cake can be removed from the drum, preferably by a scraper placed towards the filter surface of the drum. The removed free portion of the filter surface of the filter cake returns to the vat for the next stage of filter cake formation.

The treatment of lime sludge according to the invention is most preferably carried out as a continuous process, so that the filter cake is formed on the filter surface of the drum and at the same time the filter cake formed in the previous stage is washed and dried. It is carried out on symmetrically opposite sides of the filter surface.

The present invention also relates to a device applied to the method described above, which device includes a filter, which filter surface through which liquid and air can pass, the filter being filtered by means of a vacuum inside the filter element. means for forming a filter cake on the surface; means for washing the cake with a washing liquid directed through the cake and the filter surface; and means for drying the cake by drying air directed through the cake and the filter surface. , and means for removing the cake from the filter element. The device is characterized in that the filter element is partially placed in a vat filled with a mixture of lime sludge and white liquor, so that the filter cake is deposited on the surface of the filter in the part placed in the vat. and that the part of the filter element symmetrically opposite the part in the vat is surrounded by a shell sealed against the filter element, through which the cleaning liquid and the drying air can pass. , the filter cake can be fed to the filter cake to be further blown through the cake and the filter surface into the filter element, and between the butt and the shell of the filter element toward the filter surface, the dry filter cake can be fed to the filter surface. It is characterized by a scraper for peeling it off.

The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which: FIG. The drawing depicts a drum filter for the treatment of lime sludge according to the invention.

The drum filter shown in the drawings comprises a substantially cylindrical drum 1, the surface of which is divided into two symmetrically opposite fan-shaped areas forming the main part of the cylindrical surface of the drum. , forming a filter surface 2 through which liquid and air can pass. The filter surface 2 can be made of perforated plate or wire mesh, for example. Below the filter surface 2, a shell is formed for containing the filtered liquid and air, in which a vacuum can be created by suction through a duct 4 inside the drum.

The lower part of the drum 1, which corresponds to the sector formed by the permeable filter surface 2, is submerged in a vat 5 into which a duct is connected to the bottom of the vat. It is filled with a mixture 6 of lime sludge and white liquor produced in the oxidation process. By suction through the receiving space 3 and the duct 4, a filter cake 7 is formed with the mixture on the filter surface 2. The upper part of the drum 1 is surrounded by a shell 8 containing a free space 9 which essentially corresponds to this space and which covers the filter cake 7 on the filter surface 2. A supply duct 10 for cleaning liquid and drying air is connected thereto.

The space is bounded by a press wire 11 which compresses towards the filter cake 7, the role of which is to remove the cracks that have formed during the suction stage and, if they are not closed, The aim is to make the flow uniform by closing the cracks in which the cleaning water flows. At both ends of the space there are arranged sealings 12 which are under variable pressure and facing the drum 1. On one side of the shell 8, facing the drum 1, a scraper is arranged for removing the washed and dried filter cake 7 from the filter surface 2.

The figure shows that, due to the vacuum exerted through the receiving space 3 and the duct 4, a filter cake 7 has formed on the filter surface of the part of the drum 1 located in the vat 5. White liquor is passed from the vat through the lime sludge and the filter surface 2 into the internal receiving space 3, while the lime sludge particles are retained in the growing layer of lime sludge. At the same time, in the fan-shaped area located on the opposite side of the drum 1 and surrounded by the shell 8, the filter cake 7 formed in the previous stage is being washed and dried. The cleaning is carried out as a displacement cleaning with cleaning water led through the supply duct 10 into the shell-formed space 9 covering the filter cake, which water is forced under pressure to the cake 7 and below. It is passed through the filter surface 2 into the receiving space 3 inside the drum and further into the duct 4'. The thick white liquor residue is rinsed out of the filter cake 7 into the wash water, so that a dilute white liquor is obtained. Drying after washing is carried out in a corresponding manner by conducting drying compressed air from the supply duct 10 into the shell-formed space 9 and further through the cake and filter surface into the receiving space 3 and the duct 4'. It will be carried out in

When the filter cake 7 has been formed on the filter surface 2 of the drum 1 in the vat 5 and the filter cake 7 has been washed and dried, the drum is rotated 180 DEG in the direction of the arrow 14 shown in the drawing. The sealing 12, which is under variable pressure and is located facing the drum 1, is released by reducing the pressure during rotation. drum 1
While rotating, the scraper 13 removes the washed and dried filter cake 7 from the drum and frees the free filter surface 2.
followed by the butt for the formation of its next filter cake. At the same time, the filter cake 7 formed just before in the vat 5 moves to the area of the shell 8 for the next washing and drying stage. The vacuum in the drum is maintained during its movement so as to pre-dry the filter cake to approximately 60% dryness before the start of the washing phase. As soon as the drum 1 has stopped, its seal is pressed again against the drum by increasing pressure. Thereafter, the system continues to function as described above.

It is clear to those skilled in the art that the various applications of the invention are not limited to the examples described above, but can vary within the scope of the claims. Thus, for example, countercurrent washing of the filter surface with white liquor can be added to the process described above after the washed and dried filter cake has been removed from the filter surface. Drum arrow 14
Do not rotate continuously in the direction of
It is also possible to rotate it back and forth through 180°, whereby the cake can be removed alternately from both sides of the drum by means of scrapers placed on both sides of the drum.

[Brief explanation of the drawing]

The drawing shows a drum filter for the treatment of lime sludge according to the invention. In the figure, 1 is the drum, 2 is the filter surface, 5 is the butt, 6 is the mixture of lime sludge and white liquor, and 7
is a filter cake, 8 is a shell, 11 is a wire, and 13 is a scraper.

Claims (1)

Claims: 1. A method for treating lime sludge produced in the causticization process of a sulfate pulp mill, comprising first separating the lime sludge from the white liquor, then washing and drying it for torrefaction. , the filter element 1 is held in place and the filter element 1 is
a filter cake 7 of a mixture of lime sludge and white liquor 6 is formed on the filter surface 2 of the filter; the element is rotated approximately 180° and held in place by a cleaning liquid directed under pressure through the cake and the filter surface. wash the cake by displacing the white liquor; dry the cake by displacing the wash liquor by air directed through the cake and filter surface under pressure; and dry the cake by displacing the white liquor; by rotating 180° and removing the cake from the filter element during the rotation.
The method for treating lime sludge as described above, characterized in that the treatment of lime sludge is carried out in a rotation and holding cycle between two fixed positions using a filter. 2. The processing method according to claim 1, wherein the rotation direction of the filter element 1 is constant. 3. At the same time that the filter cake 7 is formed on a part of the filter surface 2 of the filter element 1, the other filter cake formed in the previous stage is washed on a symmetrically opposite part of the filter surface. characterized by drying and drying,
A treatment method according to any one of claims 1 to 2. 4. A filter surface 2 through which liquid and air can pass, means for forming a filter cake 7 on said surface, means for cleaning said filter cake and said cake by a cleaning liquid directed through said filter surface, said filter. A filter comprising means for drying the filter cake by drying air directed through the cake and filter surfaces, and means for removing the dried filter cake from the filter element 1, wherein the filter element 1 is free from solid matter. The filter cake 7 is partially submerged in the vat 5 filled with the mixture 6 with liquid, so that the filter cake 7 is partially submerged in the vat 5 by the suction in the filter element. , and that the part of the filter element symmetrically opposite to the part disposed in the vat is surrounded by a shell 8, which shell is oriented relative to the filter element. and that the cleaning liquid and gas can be conducted under pressure into the filter cake through the shell and into the filter element through the filter cake and the filter surface, and that there is a filter between the vat and the shell. A filter, characterized in that there is a scraper 13 for peeling the cake from the filter element. 5 The shell 8 comprises a wire 11 arranged to compress the filter cake 7 towards the filter surface 2 of the filter element and a free space 9 above the wire, in which the cleaning liquid and the drying gas 5. A filter according to claim 4, characterized in that it is capable of guiding and spreading it over the entire surface of the filter cake.