JPS63215511A - Treatment of lime sludge and apparatus therefor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Regarding the treatment method, in this treatment method, the lime sludge produced in the causticization process of a sulfate bulk plant is first separated from the white liquor by filtration, and then the subsequent process Wash and dry for roasting.

The causticization process (in which the green liquor obtained from the recovery of cooking liquor is causticized into white liquor to be reused in the cooking process) produces lime sludge in addition to white liquor, and this lime sludge is primarily It is calcium carbonate sludge. The lime sludge is separated from the white liquor, washed and dried to at least about 80% dryness, at which point it is roasted into 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 filter, and roasted by a rotary dryer in the bricoat technique. It has dried to the level required for baking. It is also known to treat lime sludge in a pressure vessel in a space bounded by a filter wire and a compression membrane placed opposite the wire. In such a process, the filter cake remains in the space while the white liquor separation and filter cake washing and drying are carried out.

It is an object of the present invention to provide a new process for treating lime sludge, which separates lime sludge from white liquor, washes it and dries it more efficiently and economically than traditional processes. It is something to do. The present invention forms a filter cake of a mixture of lime sludge and white liquor on the filter surface of a filter element by suction, washes the cake with a cleaning liquid directed through the cake and the filter surface, and cleans the cake with a cleaning fluid directed through the cake and filter surface. characterized in that the lime sludge is treated by a filter by drying the cake with compressed air and removing the cake from the filter element. shall be.

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

Compared to lime sludge treatment in known pressure I filters, the present invention uses suction directed through the drum interior instead of pressure in forming the filter cake, and this suction is a safer arrangement. Provides an improvement in that. When using a pressure filter, there is a risk of damaging the seal, and if the seal 1F is damaged, the result will be spillage of corrosive white liquor. Compared to the most conventional type of lime sludge treatment 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. in addition,
The drum filter can pre-dry the lime sludge before the washing step, so that when washing begins the solids content of the lime sludge is about 58-60% instead of 30-35% as in the past. . 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 during cleaning.

There are also fewer cleaning chemicals required for wire cleaning, and the cleaned lime sludge obtained in accordance with the present invention is cleaner. Most preferably, the lime sludge treatment in accordance with the present invention is performed during the filter cake formation stage. A cycle is carried out in which the drum is held in position t, then the drum is rotated approximately 180@, and the drum is held in position again during washing and drying. To form a filter cake, the bottom of the drum is placed in a vat containing a mixture of lime sludge and white liquor such that 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 in turn are connected to the drum and to the drying of the filter cake. It can be forced by pressure through the filter surface of the cake into the interior of the drum. Immediately after the filter cake has been washed and dried, the drum should be replaced again for approx.
800 revolutions, whereby the dried filter cake can be removed from the drum by means of a scraper, preferably placed towards the filter surface of the cake. The removed free portion of the filter surface of the filter cake is returned 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 tram, 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 comprises a filter, which filter surface through which liquid and air can pass, a vacuum inside the filter element. means for forming a filter cake on the filter surface, means for cleaning the cake with a cleaning liquid directed through the cake and the filter surface, means for drying the cake with drying air directed through the cake and the filter surface, and the cake. and means for removing the filter element from the filter element. The device is partially disposed in a vat filled with a filter element or mixture of lime sludge and white liquor, such that lime sludge cake is deposited on the filter surface in the portion disposed 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 drying air can pass through the cake. and between the vat and the shell towards the filter surface of the filter element there is a filter for peeling the dry filter cake from the filter surface. It is characterized by the fact that a scraper is distributed.

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

The drum filter shown in the drawings is a substantially cylindrical drum.
, the surface of which forms a filter surface 2 through which liquid and air can pass, in two symmetrically opposite fan-shaped areas forming the main part of the cylindrical surface of the drum. ing. The filter surface 2 can be made of, for example, a perforated plate or a full screen. Below the filter surface 2 there is a receiving cavity f! for filtered liquid and air. f3 is formed into a shell, in which space a vacuum can be generated by suction through a duct 4 inside the drum.

The lower part of the tram l, the area corresponding to the sector formed by the permeable filter surface 2, is submerged in a vat 5, into which the causticization process is carried out through a tact connected to its bottom. It is filled with a mixture 6 of lime sludge and white liquor produced in . 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. One part of the drum l has an area essentially corresponding to said space, and has a filter cake 7 on the filter surface 2.
It is surrounded by a shell 8 containing a free chamber rIM9 covering the wafer, to which a supply duct 10 for cleaning liquid and drying air is connected.

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

The figure shows how, due to the vacuum exerted through the receiving space 3 and the duct 4, a filter cake 7 is formed on the filter surface of the part of the tram l arranged 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;
The lime sludge particles, on the other hand, are retained in the growing layer of lime sludge. At the same time, in the fan-shaped area surrounded by it 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 lO into the shell-formed space 9 covering the two-filter cake, which water is forced under pressure into the cake 7 and below. 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 1 by conducting drying compressed air from the supply duct IC+ into the shell-formed space 9 and further through the cake and filter surface into the receiving space 3 and the duct 4. Implemented.

A filter cake 7 is formed on the filter surface 2 of the drum 1 in the vat 5 and rotated 180° when the filter cake 7 is washed and dried. The sealing 12, which is under alternating pressure and is located towards the tram l, is released by reducing the pressure during the rotation. While the drum l is rotating, the scraper 13
removes its washed and dried filter cake 7 from the drum and leaves its free filter surface 2
continues to the vat for the formation of its next filter cake, while at the same time the filter cake 7 just formed in the vat 5 is transferred to the shell 8 for the next washing and drying stage.
Move to the area. The vacuum in the drum is maintained during its movement so as to pre-dry the filter cake to approximately 60% dryness before beginning the washing phase. As soon as drum I has stopped, its seal is pressed against the drum again 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, it is common practice to add countercurrent washing of the filter surface with white liquor to the process described above after removing the washed and dried filter cake from the filter surface. It is also possible to not rotate the drum continuously in the direction of arrow 14, but to rotate it back and forth about 180'', whereby the cake is removed alternately from both sides of the drum by 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, l is the drum, 2 is the filter surface, 5 is the bat,
6 is a mixture of lime sludge and white liquor, 7 is a filter cake, 8 is a shell, 11 is a wire, and 13 is a scraper. Drawing side/text (no change in content) Procedural amendment 1986 2 B 9 B Director General of the Patent Office Kunio Ogawa, Incident indication 1988 Patent Application No. 301389 2, Title of invention Lime sludge treatment Law and processing equipment Name of person making the amendment Name: Nie, Ahlstrom Corporation 4
, Representative 1u Story (213) 1561 (Representative) 5. Subject of Supplementary iE As shown in the appendix "Details 1", we will submit one printable copy of the full statement. Procedure person 13 ff1E dF (Method) % formula % 2, Name of the invention Lime sludge treatment method and treatment device 3, Name of person making the amendment Nie, Aalst 0m Corporation 4
, Agent Name (6444) Patent Attorney Tadashi Okabe
Husband: ,'□゛1゛□ ", 14' (2) ``Drawings'' (1) I received a directive for the specification dated February 3, 1988, but as of February 98, 1988, It has already been submitted. (2) As shown in the attached sheet, we will submit one official drawing. Procedural amendments February 9, 1988 [1]

Claims (1)

[Claims] 1. A process for producing lime sludge, which involves first separating the lime sludge produced in the causticization process of a sulfate pulp mill from white liquor, then washing and drying it for torrefaction. In the processing method, the processing is performed using a filter element (
forming a filter cake (7) of a mixture (6) of lime sludge and white liquor on the filter surface (2) of 1); by displacing the white liquor by a washing liquid directed through the cake and the filter surface under pressure; carrying out in a filter by washing the cake; drying the cake by displacing the washing liquid by air directed through the cake and filter surface under pressure; and removing the cake from the filter element. The above lime sludge treatment method. 2. Hold the filter element (1) in place while forming the filter cake (7), then rotate the filter element approximately 180°, and wash the cake, while the filter is drying. Process according to claim 1, characterized in that the process is carried out in cycles in which the elements are held in place again. 3. Claim characterized in that after washing and drying the filter cake (7) the filter element (1) is rotated by approximately 180° and that the dried cake is removed while the filter element is being rotated. The treatment method described in item 2 of the scope. 4. The processing method according to claim 2 or 3, characterized in that the rotation direction of the filter element (1) is constant. 5. The filter cake (7) is the filter element (
forming on a part of the filter surface (2) of 1), while at the same time washing and drying the other filter cake formed in the previous stage on a symmetrically opposite part of the filter surface; Claim 2, characterized in that
The treatment method according to any one of Items 1 to 4. 6. A filter surface (2) through which liquid and air can pass, means for forming a filter cake (7) on said surface, for cleaning the cake by means of a cleaning liquid directed through said filter cake and filter surface. a filter element (1) comprising means for drying the filter cake by means of drying air directed through the filter cake and the filter surface; and means for removing the dried filter cake from the filter element (1); 1) is a vat filled with a mixture (6) of a solid substance and a liquid (
5) partially submerged in the vat, whereby a filter cake (7) can be formed on the filter surface (2) of the part of the filter element placed in the vat by suction within the filter element. and that the part of the filter element symmetrically opposite to the part arranged in the butt is surrounded by a shell (8) which is sealed against the filter element and through which The cleaning liquid and gas can be conducted under pressure into the filter cake and further through the filter cake and the filter surface into the filter element, and between the vat and the shell there is a scraper for stripping the filter cake from the filter element. (13) A filter characterized by having the following. 7. the shell (8) comprises a wire (11) and a free space (9) above the wire arranged to compress the filter cake (7) towards the filter surface (2) of the filter element; , characterized in that in its free space it is possible to conduct a cleaning liquid and a drying gas and spread it over the entire surface of the filter cake,
A filter according to claim 6.