Backwash Multiple Alluvial Filter and Method of Filtering Therewith

The present invention relates to a backwash alluvial filter with a plurality of filter elements, as well as to its utilization for washing out solid matter.

Filters for fluids are known, comprising filtering elements which are composed of suspended candles and removable in rows. One of such filters are disclosed, for example, in the German Offenlegungsschrift No. 2,741,639. This filter has a filter container with a collecting pipe located in the interior of the container and mounting a plurality of suspended filter elements arranged one behind the other. The collecting pipes are located adjacent to one another on supporting bodies and can be removed from the filter container by rows.

The Austrian Pat. No. 211,329 shows a device for backwashing of filter candles arranged in rows and mounted on the collecting conduit in standing position. The collecting conduits extend at both sides horizontally through the container wall. The arrangement at both sides is very expensive. In addition, each collecting conduit is provided with two locking elements for the plurality of tank openings and require a plurality of valves and armatures.

In all methods and arrangements the outlet valves for the clarified filtrate must be switched to backwash mode during the backwashing. This means that a clarified filtrate cannot be recovered during the entire backwashing operation.

Accordingly, it is an object of the present invention to provide a backwash alluvial filter and a method of filtering which avoid the disadvantages of the prior art.

More particularly, it is an object of the present invention to provide a backwash alluvial filter and a method of filtering which allows washing off of solid matter with washing fluid without interruption of withdrawal of a clarified filtrate.

In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a backwash alluvial filter with a plurality of filter elements, and a method of filtering, in accordance with which a filter container is subdivided into at least two chambers which communicate with one another by vertical overflow shafts. It is another advantageous feature of the present invention that a washing fluid is supplied via pipes directly under the overflow shaft.

In accordance with still another feature of the present invention, the overflow shafts are formed by separating walls. One of the separating walls which faces toward a pulp inlet is spaced by a predetermined distance from a container bottom and extends with its outer part above a fluid level in a gas chamber.

The other separating wall is mounted on the bottom of the container and forms with its upper part an overflow weir. The washing fluid together with solid matter removed from the filter elements is supplied via a guiding shaft into the shafts from below upwardly, it is washed and supplied via the overflow weir into a further filter chamber. This process can be repeated many times.

Still a further feature of the present invention is that the fluid level above the filter elements is adjusted by the gas pressure in a head part of the filter container with the aid of a lever controlling element. An outlet valve is controlled automatically, whereas the backwashing of the filter candles is peformed separately in rows.

The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

FIG. 1 is a view showing a vertical section of a filter in accordance with the present invention;

FIG. 2 is a view showing a horizontal section of the filter of FIG. 1; and

FIG. 3 is a view showing a part of a backwashing device.

A backwashing alluvial filter with a plurality of filter elements has a filter container which includes a cylinder 1 with a conical bottom 2 and a cover 3.

The cover 3 is connected by a pair of flanges 4 with an intermediate cylindrical part 5. The intermediate cylindrical part 5 is connected, in turn, with the cylinder 1 by a pair of flanges 6. The cylinder 1 has a supply pipe 7 for a material to be filtered such as a pulp, and a outlet pipe 8 provided with an outlet valve 8' for a filtered material, such as cleaned solid matter suspension. Pipes 9 and 9' are provided for washing fluid and/or gas supply.

A pipe 10 for gas supply or withdrawal is provided in the cover 3 of the filter container. A control valve 11 is controlled via a level controlling element 12.

A circular ring 13 is arranged inside the filter container. A plurality of collecting pipes, for example collecting pipes 14, 14', 14", 14'", 14.sup.IV, 14.sup.V are mounted on the circular ring 13. The number of the collecting pipes depends upon the available space in the container and the desirable filter surface. Filter elements 15, 15', 15", 15'", 15.sup.IV and 15.sup.V are mounted on pipes 16, 16', 16", 16'", 16.sup.IV and 16.sup.V.

Separating walls are further provided in the interior of the filter container. A separating wall 17 is open in a lower part of the conical bottom 2 toward the pulp side. A second separating wall 18 is connected with the bottom 2 and forms in upper part an overflow weir. Further separating walls form washing chambers. One of the washing chambers is provided between the separating walls 18 and 17', whereas the other washing chamber is formed between the separating wall 18' and the wall of the container. Collecting pipes 14.sup.IV and 14.sup.V are mounted on intermediate elements 16.sup.IV and 16.sup.V in the washing chambers, respectively. Several rows of the connecting pipes may be provided in each washing chamber.

FIG. 2 is a horizontal section of the inventive filter at the height of the filter elements 15. Conduits 24, 24', 24", 24'", 24.sup.'V, 24.sup.V open in branching conduits 20, 20', 20", 20'", 20.sup.'V, 20.sup.V and are provided with valves 21. Check valves 25, 25', 25", 25'", 25.sup.IV, 25.sup.V are arranged at the end of the branching conduits 20 and lead to a collecting conduit 19 for withdrawing a clarified filtrate. The collecting pipe 14.sup.'V in the first washing chamber leads to the conduit 20.sup.'V, valve 21.sup.'V and the washing conduit 24.sup.'V, the check valve 25.sup.'V and a conduit 23. Similarly, the conduit 20.sup.V leads from the second washing chamber from the collecting pipe 14.sup.V via the valve 25.sup.V and the washing conduit 24.sup.V with the valve 21.sup.V to the conduit 23.

The backwash alluvial filter with a plurality of filter elements in accordance with the present invention operate in the following manner: A pulp is supplied via the inlet pipe 7 into the filter container. The solid matter deposits on the fabric of the filter elements 15 where it forms a solid cake. The liquid removed from the solid matter flows via the pipe 16 and the collecting pipe 14 as filtrate out of the filter container. As soon as the filter cake reaches a predetermined thickness, a process of removing the filter cake takes place. The individual rows of the filter elements mounted on the collecting pipe 14 are successively released from filter cake with gas or liquid countercurrent fluid by closing one of the clarifate check valves 25 and opening one of the valves 21 in the washing fluid conduit 24. The removed filter cake falls into the conical bottom 2 of the filter container. The row 16 of the filter elements 15 released from cake is free for further filtration, and a further row, for example the row 16' can be released from the filter cake in the same manner. The sunk solid matter can be displaced via the pipe 9' with washing fluid under pressure and thereby supplied into the first washing chamber in which it deposits on the filter elements 15.sup.IV. Then it is again removed by closing of the valve 25.sup.IV and opening of the valve 21 in the conduit 24.sup.IV and supplied into a second washing chamber in the above-described manner. The washing step can be repeated as often as possible, depending upon the number of the washing chambers. The washed solid matter is withdrawn via the pipe 8.

The above-described method and arrangement is particularly suitable for washing of solid matter. As an example it can be used for releasing red pulp from caustic soda. It also can be utilized for salt water purification before and after the electrolysis. It can be utilized for spinning baths in the process of manufacturing of viscous and separation of condensate, PVC waste water and filtration of thin juice during production of sugar.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a backwashing alluvial filter with multiple filter elements, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of the present invention.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.