Method of Cleaning Filter Elements Thereof

The present invention relates to a method and apparatus for cleaning filter elements of a filter apparatus. More particularly, it relates to a method and apparatus for cleaning filter elements provided with a filtering material upon a surface of which a cake is deposited during a filtering process, particularly in a centrifugal filter after alluvial filtration of coal in flowable state.

Alluvial filters have been used for filtration of coal in flowable state. Such a filter has a hollow shaft and a plurality of horizontal plates mounted on the shafts and spaced from one another in direction of elongation thereof. The hollow shaft and the plates are accommodated in a pressure vessel. The operation of this filter is generally satisfactory. In dependence upon the origin of the coal, as well as upon the utilized filter aids, a cake is deposited during a filtering process on the filtering elements and forms a mass which is more or less difficult to be removed. In many cases the complete removal of this mass is so difficult that in short time the filter must be opened and the filtering material of the filter elements must be mechanically or hydraulically cleaned.

It has been known to utilize spraying nozzles in a centrifugal filter apparatus for removal of a filter cake. In the Swiss patent 333,492 a filter apparatus is disclosed, in which nozzle elements supply fluid medium for cleaning the filter elements. In accordance with this patent, the filter cake is washed off by the fluid medium. In accordance with a method disclosed in the Swiss patent 402,821 a solvent in a vapor phase is pressed through the filter cake. A liquid is produced during partial condensation of the vapors in the interior of the cake and washes away the cake from inside. The solvent in the vapor phase is supplied from outside of the filter vessel or the solvent is vaporized inside the filter. An arrangement for vaporization of the solvent is not disclosed.

A disadvantage of the above-mentioned method of cleaning by means of fluid medium is that it always requires very much solvent for washing away the filter cake. Moreover, by spraying the fluid toward the cake the latter is only being eroded but not removed, and the filtering material of the filter elements is not cleaned. Generation of solvent vapors inside or outside the filter vessel requires expensive arrangements and is not suitable for removal of the filter cake and cleaning of the filter material.

Accordingly, it is an object of the present invention to provide a filtering apparatus and a method of cleaning filter elements thereof, which avoid the disadvantages of the prior art.

More particularly, it is an object of the present invention to provide a method and an arrangement in accordance with which an erosion of a filter cake, a removal of the filter cake, and cleaning of the filtering material of the filter elements can be performed with utilization of a smaller quantity of a cleaning medium, as compared with the known methods and arrangements.

In keeping with these objects, and with others which will become apparent hereinafter, one feature of the present invention resides in a method of cleaning filter elements in accordance with which a cleaning medium is supplied to nozzle elements and ejected from the latter at a pressure between substantially 5 and 100 bar toward surfaces of a filtering material of filter elements so that the cleaning medium issuing from the nozzle elements under the pressure removes the cake from these surfaces and thereupon also cleans the filtering material of the filter elements. When the filter elements are cleaned in accordance with such a method, it suffices to provide a small quantity of the cleaning medium, and at the same time the filter cake is eroded, it is removed from the filter elements, and the filtering material is cleaned by the cleaning medium.

Another feature of the present invention is that a filter apparatus includes means for cleaning filter elements, which includes a source of cleaning medium under elevated pressure and a plurality of nozzle elements communicating with the source and turnable relative to surfaces of a filtering material of the filter elements, so that the cleaning medium issuing from the nozzle elements under the elevated pressure removes the cake from these surfaces and thereupon also cleans the filtering material of the filter elements.

In accordance with a further feature of the present invention a filtrate or an inert gas may be used as the cleaning medium.

In accordance with a still further feature of the present invention a manifold, conduits communicating with the manifold, and nozzle elements mounted on the conduits may turn about an axis, and a shaft supporting the filter elements may rotate about a further axis.

The novel features which are considered as characteristic for the 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 drawing.

FIG. 1 is a view showing a partially sectioned filter apparatus in accordance with the present invention; and

FIG. 2 is a view showing a fragment of a filter element of the filter apparatus shown in FIG. 1.

A filter apparatus in accordance with the present invention and a method of cleaning filter elements thereof are illustrated in the drawing. The filter apparatus has a central shaft which is identified by reference numeral 2 and includes a hollow portion 2' and a driving portion 3. The shaft 2 is accommodated in a pressure vessel identified in toto by a reference numeral 1. Drive means 4 are provided outside the pressure vessel 1. The shaft 2 is mounted in a cover 1' of the pressure vessel 1 by means of a bushing 5 in known manner.

A plurality of filter elements 6 are mounted on the shaft 2 and spaced from one another in direction of elongation thereof by means of spacer rings 7. The shaft 2 and the filter elements 6 together form a filter pack.

A manifold 11 is rotatably mounted in a space between the filter pack and a wall 1" of the pressure vessel 1. A plurality of conduits or arms 8 extend from the manifold 11 toward and above the filter elements 6. As shown in FIG. 2, each of the filter elements 6 is dish-shaped and has a hollow body portion 6' which is filled with spacer members 6". A filtering material is arranged above the spacer members 6".

A spraying nozzle 9 is mounted on an end portion of each of the arms 8. The manifold 11 is turnable in both directions and operatively connected with drive means 12. The manifold 11 together with the arms 8 and the nozzles 9 can be moved either by hand or by motor-operated drive means 12.

The drive means 4 is operative for rotation of the shaft 2 about an axis which may be substantially parallel to an axis about which the drive means 12 rotates the manifold 11 together with the arms 8 and the nozzles 9. The manifold 11 communicates with a supply conduit 13 provided with a valve. Means 15 is also provided for imparting a pressure to a cleaning medium supplied through the supply conduit 13. Any known means can be used for this purpose, for example a pump.

During a filtering process, a filter cake 10 is deposited on the filtering material 6'" of the filter elements 6. In order to clean the filter elements 6, the shaft 2 is slowly rotated by the drive means 4. Simultaneously, the valve 14 is opened and a cleaning medium is supplied through the supply conduit 13 to the manifold 11 under pressure. The pressure corresponds to between substantially 5 and 100 bar and can be adjusted by the high pressure pump 15. Any suitable cleaning medium can be used for cleaning the filter elements 6. For instance, a filtrate may also be used as a cleaning medium. On the other hand, an inert gas may be used as a cleaning medium for cleaning the filter elements 6. The filtrate atomized by high speed is supplied through the arms 8 and ejected through the nozzles 9 onto the filter cake 10 which is deposited on the filtering material 6'" of the filter elements 6. First, the filter cake 10 is eroded by the cleaning medium. Thereupon under the action of the pressure of the cleaning medium the filter cake 10 is removed from the filtering material 6'" of the filter element 6 and the filtering material 6'" is cleaned from the filter cake 10. It is also possible to supply the cleaning medium under a relatively low pressure so as to erode the filter cake 10 in the initial period of the cleaning process, and to thereupon increase the pressure of the cleaning medium so as to remove the filter cake 10 from the filter elements 6 and to clean the filtering material 6'" of the filtering element 6. The uniformity of the cleaning process is attained not only by rotation of the filter elements 6, but also by forward and reverse turning movements of the manifold 11 together with the arms 8 and the nozzles 9. Thereby the nozzles 9 during its turning movements overlap the entire upper surface of the filtering material 6'" of the filter elements 6 and fully clean the same. In order to guarantee the full removal of the filter cake 10, the speed of the shaft rotation is so increased that the remainder portions of the filter cake 10 are flung under the action of the centrifugal force against the wall 1" of the pressure vessel 1 and thereupon fall into a not-shown bottom from which they are removed.

The method and the arrangement in accordance with the present invention are preferably used for cleaning the filter elements of a filter apparatus for filtering a coal in flowable state wherein extreme requirements to temperatures and contamination are made.

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 method of and arrangement for cleaning filter elements of a filter apparatus, 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 this invention.