FI87995C - Method and apparatus for treating mesa - Google Patents

Description

1 87995

METHOD AND APPARATUS FOR HANDLING HONEY - FORM FOR THE HANDLING OF HONEY

The present invention relates to a process for the treatment of lime, in which the lime produced in the causticisation process of a sulphate cellulose mill is separated from the hard liquor by filtration, washed and dried in the process for subsequent calcination.

In the causticization process, in which the green liquor obtained in the recovery of the cooking liquor is causticized into white liquor for reuse in cooking, besides the white liquor, lime is formed, which is mainly a calcium carbonate precipitate. The honey is separated from the white liquor, washed and dried to a dry matter content of at least about 80%, where it is calcined into quicklime for reuse in causticization.

The usual procedure for the separation and treatment of lime for calcination has been to separate the lime from the protein and the washing is carried out using a so-called sock filter and. drying to the dry matter content required for calcination. tuu rumpukui vai me 11 a ns. precoat technique i ka 11 a. In addition, a method has become known in which the treatment of lime takes place in a pressure filter in a space delimited by a filter wire and an opposing compression channel. Ko. in the method, the mesa cake remains in place in said state throughout the process of separating, washing and drying the white liquor.

. It is an object of the present invention to provide a novel method for treating mesa by which mesa can be separated from white liquor, washed and dried more efficiently and more preferably. The invention is characterized in that the treatment is carried out with a filter rotating about its axis, forming a lime cake on the filter surface of the mixture of lime and white liquor, washing the cake with a washing liquid passed through it and the filter surface, drying the cake with compressed air and passing through the filter surface. The honey cake is preferably formed by suction.

Compared to the known treatment of lime with a pressure filter, the invention provides an improvement in that the formation of the lime cake preferably uses suction conducted through the inside of the filter instead of the increased pressure, which is a safer solution. When a pressure filter is used, there is a risk of the seal breaking and the resulting corrosive white liquor being spilled into the environment. Compared to the most commonly used treatment of lime, the invention still provides numerous advantages. The most important of these is that the washing and drying of the lime takes place with the same equipment, which reduces the need for space and equipment investment. In addition, the mesh can be pre-dried as a rotating filter before the washing step, so that at the start of the washing the solids content of the mesh is about 58-60% instead of the previous 30-35%. The amount of white liquor present in the honey is thus correspondingly even smaller, whereby an even smaller amount of washing liquid is determined and the amount of lean white liquor generated in the washing is reduced. The amount of washing chemicals required for washing the wire is also reduced, and the washed lime obtained according to the invention is even cleaner.

The lime treatment according to the invention is preferably carried out intermittently by holding the filter in place during the lime cake formation step, then rotating it by about 180 ° and holding it in place again during the washing and drying steps of the cake. To form a honey cake, the lower part of the filter may be located in a ‘containing a mixture of lime and white liquor’. in the basin so that the cake can be formed on the filter surface by suction inside the filter, and for washing and drying the cake the top of the filter can be surrounded by a shell with supply lines to supply washing liquid and drying air to the lime cake so that they can be forced under pressure on the cake and filter surface. through the inside of the filter. After the lime cake has been washed and dried, the filter can be rotated again by about 3 87995 180 °, whereby the dried lime cake can be removed from the filter by means of a scraper suitably placed for the filter surface. The released filter surface returns to the basin for the next lime cake formation step.

The lime treatment process according to the invention is most preferably carried out in a substantially continuous manner, so that while part of the filter surface of the filter is formed with lime cake, washing and drying of the lime cake formed in the previous step with the symmetrically opposite part of the filter surface is performed.

The rotary filter used in the invention is preferably a drum filter, but it is also possible to use a disc filter which operates in a substantially similar manner.

The invention also relates to an apparatus for applying the method described above, comprising a drum filter comprising a liquid and air permeable filter surface and means for forming a lime cake on the filter surface by suction inside the drum, washing the cake with a washing liquid passed through the cake and the filter surface. to dry the cake with a drying air guide passed through the cake and filter surface and to remove the dried cake from the drum. The device is characterized in that the drum is located in a basin partially filled with a mixture of lime and white liquor, whereby a lime cake can be formed on the basin part of the drum filter surface, that the part symmetrically opposite to the drum basin is surrounded by a drum are imported for lime cake for further derivation its ··· -; and through the filter surface inside the drum, and that a scraper is installed between the basin and the shell ____ against the filter surface of the drum to remove the dried lime cake from the filter surface.

The invention will be described in more detail below by way of example with reference to the accompanying drawing, which shows a drum filter according to the invention for the treatment of lime.

The drum filter according to the drawing comprises a substantially cylindrical drum 1, the surface of which is formed in the area of two symmetrically opposite sectors forming the main cylindrical surface of the drum as a liquid and air permeable filter surface 2. The filter surfaces 2 may be e.g. perforated plate or wire cloth. Under the filter surfaces 2, jacket-like collector spaces 3 for filtered liquid and air are formed, which can be subjected to a vacuum by suction through the channels 4 inside the drum.

The drum 1 is immersed in a basin 5 from an area corresponding to the sector formed by the filter surface 2 passing through its bottom, which is filled with a spherical mixture 6 of mesa and white liquor 1 obtained in the causticization process through a bottom-connected channel. e 2. The upper part of the drum 1 is surrounded by a substantially corresponding area by a shell 8 comprising a free space covering the lime cake 7 on the filter surface 2, to which the washing liquid and drying air supply channels 10 are connected. a compression groove 11 for smoothing the current; . ·. by closing the cracks in the cake during the suction phase, to which the washing water would otherwise be channeled, and space 9 \. a variable pressure seal 12 is placed on each side against the drum 1. A scraper 13 is mounted on the other side of the shell 8 against the drum 1 to remove the washed and dried lime cake 7 from the filter surface 2.

The drawing shows a situation where the lime cake 7 is ____; currently being formed on the filter surface of the part of the drum 1 in the basin 5 by the suction inside the drum through the collecting space 3 and the channels 4. White liquor. leaches from the basin through the lime and filter surface 2 into the inner collecting space 3 while the lime particles are retained in the growing lime layer. In the opposite sector of the drum 1, surrounded by the shell 8, the washing and drying of the lime cake 7 formed in the previous step is carried out at the same time. The washing takes place as a displacement wash through the supply channels 10 with washing water introduced into the jacket-like space 9 covering the lime cake, which is forced by pressure through the cake and the underlying filter 2 into the collector space 3 inside the drum and further into the channels 4 '. When the strong white liquor remaining in the honey cake 7 is rinsed into the wash water, a lean white liquor is obtained. The drying after washing takes place in a similar manner by passing pressurized drying air from the supply ducts 10 to the jacket-like space 9 and from there through the cake and the filter surface to the collector 3 and the ducts 4 '.

When the lime mud cake 7 is formed on the drum 1 in the pool to a filter 5 on the surface 2 and the lime mud cake formed in the preceding step in 7 has been washed and dried, the drum is rotated 180 ° to the drawing direction of the arrow 14. The variable pressure seals 12 against the drum 1 are loosened during the cycle by reducing the pressure. As drum 1 rotates. . the scraper 13 removes the washed and dried lime cake 7 from the drum and the released filter surface 2 continues to the basin 5 for the next lime cake formation step. At the same time, the last formed lime cake 7 in the basin 5 moves to the area of the shell 8 for the subsequent washing and drying steps. The internal suction of the drum is maintained during the transfer so as to cause the lime cake to pre-dry to a dry matter content of about 60% before the start of the washing step. After the drum 1 has stopped, the seals 12 are again sealed against the drum by increasing the pressure, after which the operation continues in the same way as described above.

It will be apparent to those skilled in the art that the various embodiments of the invention are not limited to the example described above but may vary within the scope of the appended claims. you. Thus, for example, it is possible that the process described is accompanied by a countercurrent washing of the filter surface with white liquor after the washed and dried lime cake has been removed therefrom. It is also possible that not constantly in the same direction according to the arrow 14, the drum circumvented by a reciprocating 6 87 995 sequence of about 180 °, wherein the cake removal takes place alternately from opposite sides of the drum for those positioned scrapers. Also, the filter does not necessarily have to be a drum filter, but a disk filter operating in a substantially similar manner may also be considered.

Claims (4)

A method of treating mesa, in which the process of mixing mesa and white liquor arising in the causticization process at a sulfate cellulose plant, a mesaka cake is formed on the portion of a shaft rotating filter's filtering surface which is in the basin which cake is washed. with a washing solution passed through it and the filtering surface and dried with a drying air passing through it and the filtering surface and which cake is removed from the filter in the process for subsequent calcination, characterized in that the treatment is carried out periodically, whereby the filter (1) is poured into its place. at the formation stage of the cake (7), after which it is rotated about 180 ° and poured back into its place as the cake is washed and dried, and again rotated about 180 ° and the dried cake is removed during rotation. Method according to claim 1, characterized in that the direction of rotation of the filter (1) is still the same. Method according to claim 1 or 2, characterized in that when the filter surface (7) is formed on a part of the filtering surface of the filter (1), the mesaka cake which is formed at the preceding stage on the symmetrically opposite part of the filtering surface is washed and dried. 4. Drum filter for applying the method according to any of the preceding claims, consisting of a drum (1) fitted with liquid and air-permeable filtration surface (1), which is partially located in a filler and white liquor blend (6) pool (5), wherein the mesaka cake (7) can be formed on the portion of the drum's J. drying surface (2) which is in the basin, and means for washing the cake with a washing solution guided by the cake and the filtering surface, for drying the med through it. and the filtering surface guided drying air and for removing the cake 37995 from the drum, characterized in that the part of the drum (1) which is symmetrically opposite with respect to the part in the bass meadow is surrounded by a compressible belt (8) consisting of a filter surface (2) pressed against the meek cake (7) of the drum (1) of the drum (1) and a space (9) located over the free space (9), to which the washing solution and the drying air under pressure can be directed so that they expand. where they reach the entire surface of the mesakak.