A filter cleaning structure, an arrangement comprising such a filter cleaning structure, and a method of using the filter cleaning structure

Field of the invention The present invention relates to a filter cleaning structure for cleaning of a stationary gas filter assembly including one or more individual filters extending in an axial direction, comprising a number of cleaning liquid nozzles. Furthermore, the invention relates to an arrangement including a filter cleaning structure and a stationary gas filter assembly including one or more filters. The present invention also relates to a method of cleaning a stationary gas filter assembly including one or more individual filters extending in an axial direction by means of a number of nozzles when operation of the filter assembly is discontinued.

Background of the invention

The use of filters in relation to process equipment such as e.g. spray dryers and fluid bed processing equipment is well known. Use of filters is, however, not limited to these types of equipment. All process equipment using filters for separating particles from a gas may use the present invention.

Such filters may be located in a separate filter unit, or may be integrated in the process equipment as seen in e.g. US 6,463,675 (Assignee: Niro A/S). US 6,676,720 describes a filter system with focus on draining the filters after CIP. US 6,149,716 describes a method of CIP of bag filters. US 6,332,902 describes a filter unit with focus on the filter gas cleaning means during operation, which further are used for filter CIP when out of operation. (Assignee of all the above-mentioned patents: Niro A/S). Filters may be of any material suitable for the purpose, and may for instance be bag filters made of felt, or may be woven of e.g. polyester or Teflon® (PTFE). A felt or polyester material may be permeable for a CIP fluid, while Teflon® is not. Alternatively, a filter bag may be constructed of a permeable material and hereafter coated with

an impermeable material, e.g. a polyester material coated with Teflon®. In general, the material used in such filters is flexible. However, filters may also be non-flexible made of e.g. steel, polymer or ceramics. Filters are typically of cylindrical shape and typically mounted vertically, but other known types of filter shape and placement may be used.

A great demand on the quality of CIP exists. In the chemical industry, e.g. for dyes, it is essential to avoid cross-contamination when shifting from one colour to another. In the dairy and food industry, the quality of the cleaning is very important for bacteriological reasons. Furthermore, the cleaning quality is essential in the pharmaceutical industry, again for bacteriological and health reasons and to meet the requirements of authority regulations.

In the pharmaceutical industry, the active components may not escape from the processing equipment and therefore impermeable filter bags may be prescribed for this area of application. In a CIP process such filter bags are being cleaned both from the outside, i.e. the product side, and from the inside, i.e. the clean gas side. In order to drain off the cleaning fluid from inside the filter, a controlled valve or drain may be provided in the bottom of the filter, in particular in the case when the bottom is impermeable. A prior art valve of this kind is e.g. disclosed in US 5,444,892 (Assignee: Niro-Aeromatic AG).

Sufficient cleaning of the filter outsides demands for a CIP- system with a great number of CIP-nozzles placed in the filter unit wall and ceiling or in the process equipment walls and ceilings in the case of integrated filters. It is vital that all external surfaces of the filter are cleaned sufficiently. Thus, the higher the number of filters in a unit or in a piece of equipment, the higher a number of nozzles is necessary to ensure that no surface of a filter is in the shadow of another filter. A large number of nozzles is costly due to the high demands that exist for nozzles of the quality used for CIP-systems, typically for nozzles positioned in the wall of the filter unit. Such nozzles may e.g. be of the retractable type, which are controlled by the pressure of the cleaning liquid. Furthermore, CIP-nozzles must be self-cleaning. Moreover, tubes or pipes carrying the cleaning fluid must be connected to every single

nozzle entailing a complex and costly system. In addition, nozzles are traditionally not placed in the bottom wall of filter chambers or process equipment, due to the fact that the bottom wall often slopes towards a centre axis and is inherently positioned at some distance to the filters to be cleaned. Placing nozzles in the bottom wall of the filter unit or process equipment would therefore not contribute significantly to the quality of the cleaning of the filters, and as a result the bottom surface of the filters are not cleaned satisfactorily.

Summary of the invention

With this background, it is an object of the invention to provide a filter cleaning structure of the kind mentioned in the introduction, which provides for a more effective cleaning.

It is a further object of the invention to provide a filter cleaning structure of a more cost-effective design.

These and further objects are met by a filter cleaning structure for cleaning of a stationary gas filter assembly including one or more individual filters extending in an axial direction, comprising a number of cleaning liquid nozzles, characterized in that said filter cleaning structure is moveable in relation to said filters.

By making the filter cleaning structure moveable, it becomes possible to clean filters much more effectively as fewer nozzles are required. Nozzles, e.g. mounted in the wall of the processing equipment, are in themselves expensive components, and reducing the number of nozzles will thus reduce the cost of the entire structure. Furthermore, a less complex construction is provided, in that the amount of piping or the like for the cleaning liquid to each nozzle is also reduced, due to the reduced number of nozzles. Thus, a more simple and cost effective structure is provided. In a preferred embodiment, said filter cleaning structure comprises a longitudinal main element extending in a direction substantially parallel to the axial direction of said filter or filters, said main element being provided with one or more nozzles. This configuration permits provision of a number of moveable nozzles in a simple manner.

In order to make it possible to clean also the underside of the individual filters more efficiently, said filter cleaning structure may comprise one or more arm elements protruding from said main element in a direction substantially perpendicular to said main element, said arm element or elements being provided with one or more nozzles.

In a further development of this embodiment, said filter cleaning structure comprises one or more branch elements protruding from said arm elements, said branch element or elements each being provided with one or more nozzles. This arrangement enables the structure to reach more positions within the filter unit or process equipment, thus eliminating or reducing the areas being shaded for by other filters. Reducing the risk of one filter shading for another, also renders it possible to reduce the amount of cleaning fluid used for the cleaning of a filter assembly as the cleaning becomes more effective. In an embodiment, in which an increased simplicity of the structure is obtained, each of the elements of the filter cleaning structure is tubular and adapted to supply cleaning liquid to said plurality of nozzles. Hereby, no concurrently piping or tubing is necessary.

The filter cleaning structure may be moved in any suitable man- ner. To this end driving means for rotating said cleaning structure about an axis parallel to the longitudinal axis of the filters may be provided. The driving means may comprise a motor, preferably a hydraulic motor, which may utilize said cleaning liquid for actuation. In order to provide appropriate transmission of the driving torque, said driving means may include a planet type gear.

Preferably, the number of said arm elements is larger than one, and said arm elements are evenly distributed on the circumference of the longitudinal main element. Thus, an outbalancing of weight in the overall structure is obtained, providing advantages e.g. in the form of less wear and tear on bearings.

In another aspect of the invention, an arrangement including a filter cleaning structure and a stationary gas filter assembly including one or more filters, wherein said one or more filters is/are cylindrical is provided.

In a further aspect of the invention, a method of cleaning a stationary gas filter assembly including one or more individual filters extending in an axial direction by means of a number of nozzles, is provided. The method comprises the steps of: providing a cleaning structure having a plurality of nozzles, discontinuing the operation of said gas filter assembly, supplying cleaning liquid to said nozzles, spraying said cleaning liquid through said plurality of nozzles, moving said cleaning structure a sufficient number of times to clean substantially all surfaces of all filters, drying filters, and continuing the operation of said gas filter assembly.

Further embodiments and advantages will appear from the following description.

Brief description of the drawings

Fig. 1 is an isometric view seen of an embodiment of the arrangement according to the invention;

Fig. 2 is a side view of the arrangement of Fig. 1; Fig. 3 shows the arrangement of Figs 1 and 2 seen from below;

Fig. 4 is an isometric view of another embodiment of the arrangement according to the invention;

Fig. 5 is a side view of the arrangement of Fig. 4;

Fig. 6 shows the arrangement of Figs 4 and 5 seen from below; Fig. 7 is an isometric view of a plurality of filter cleaning structures in a further embodiment in connection with a filter assembly comprising a number of bag filters arranged in clusters;

Fig. 8 is a side view of the filter cleaning structures and filter assembly shown in Fig. 7; Fig. 9 is a bottom view of the filter cleaning structures and filter assembly shown in Fig. 7.

Detailed description of the invention and of preferred embodiments

In Figs 1, 2 and 3 a filter assembly generally designated 1 is

shown (a filter unit). The filter assembly 1 comprises a horizontal and circular filter support plate 2 supporting a number of vertical individual cylindrical filters 3 in one open end 3a of each filter 3. The other end of each filter 3b is closed and free. The filters 3 are arranged in two circular concentric rows having a centre axis indicated by the letter A, as most clearly seen from Fig. 3. Although not shown in the drawings, the support plate 2 is in turn supported by an enclosure wall or other process equipment confining the filter assembly 1.

A filter cleaning structure 4 emerges from the vertical centre axis A of the concentric rows of filters 3. As is seen from Figs 1 to 3, this particular embodiment of the filter cleaning structure 4 has one vertical main element 5 and one horizontal arm element 6 protruding from the main element 5. From the arm element 6 two branch elements 7, 8 protrude substantially perpendicular to the arm element 6 and substantially parallel to said main element 5, i.e. vertically, in a way so that the branches 7 are positioned among the filters 3 in a manner to be described in detail further on. In the embodiment shown, each branch element has a longitudinal extension, but other configurations are conceivable as well. One branch element 7 projects from the arm element 5 at the radially outer end of the arm element 5 so as to describe a circle with a diameter slightly larger than the outer perimeter of the outermost filter row when the entire filter cleaning structure is rotated around its axis of rotation A coinciding with the centre axis of the filters 3. The other branch element 8 projects from the arm element 5 at such a distance from the main element 5 so as to describe a circle with a diameter slightly larger than the outer perimeter of the innermost filter row when the entire filter cleaning structure is rotated around its axis of rotation A. Evidently, the other branch element 8 should be positioned at a smaller distance from the main element 5 than the outermost row of filters 3.

As is most clearly seen from Fig. 2, a drive 9 for moving the entire filter cleaning structure 4 is supported by the filter support plate 2. In the embodiment shown, the drive 9 is arranged for rotating the filter cleaning structure 4 about the axis of rotation A and is supported

substantially on its own vertical centre. The driving means may comprise a motor, e.g. a hydraulic motor utilizing cleaning liquid for actuation, and a planet type gear for ensuring adequate transmission of the driving torque in order to be able to control the rotational speed. Even though not depicted in any of the figures, in some embodiments, the drive 9 may be positioned outside the enclosure wall or whatever other process equipment that may confine the filter assembly 1.

Eventually, a plurality of nozzles is provided on each of the elements of the cleaning structure 4 in the embodiment shown. On the main element 5, said plurality is constituted by a single nozzle 10 near the upper end or the main element 5. The arm element 6 is provided with two nozzles 11 and 12 immediately beneath each row of filters 3. Each branch element 7 and 8 is provided with a respective nozzle 13 and 14 positioned at such a distance from their connection to the arm element 6 that nozzles 10, 13 and 14 are at substantially the same level. Thus, with nozzles 10-14 located at the shown positions on said elements 5, 6, 7 and 8 (most clearly seen from Fig. 2), cleaning of a large part of the surface of each individual filter is feasible. Other configurations of the nozzles are of course conceivable. For instance, there may be more than one nozzle on the main element 5 and the branch elements 7 and 8, e.g. depending on the length of the filters 3. The nozzles 10-14 may be of any conceivable kind suitable for the purpose. In its simplest form each nozzle is an aperture in the corresponding element. Alternatively, each nozzle may include a nozzle head, for instance comprises a rotating ball. The nozzle head may be retractable or stationary.

In the embodiment shown, the main element 5, the arm element 6 and each of the branch elements 7, 8 are tubular such that cleaning liquid may be supplied to the pluralities of nozzles through these elements. Other arrangements are conceivable as well; the elements may comprise conduits for carrying the cleaning liquid.

When the stationary gas filter assembly is to be cleaned by spraying cleaning liquid onto the external surface of the filters, the following operational steps are carried out:

a) the operation of the gas filter assembly is discontinued, b) cleaning liquid is supplied to said nozzles from a suitable supply means, c) the cleaning liquid is sprayed through said plurality of nozzles, d) the cleaning structure is moved a sufficient number of times, i.e. in the embodiment shown rotated a number of rotations which may be predetermined according to the field of application of the filter assembly, and finally, after drying, e) continuing the operation of said gas filter assembly

In the following reference will be made to Figs 4, 5 and 6, which all illustrate another embodiment of the present invention integrated in a process equipment. Elements having the same or analogous function as corresponding elements in the first embodiment shown in Figs 1 to 3 carry the same reference numerals to which 100 has been added. Only differences relative to the first embodiment will be described in detail. Also in this embodiment, the filter assembly 101 comprises a horizontal and circular filter support plate 102 supporting a number of vertical individual cylindrical filters 103. In this embodiment, however, only one circular row of filters exists having a centre axis indicated by the letter A, as most clearly seen from Fig. 6. Here too, the filter cleaning structure 104 emerges from said vertical centre axis A of said circular row of filters 103. As is seen from Figs 4 to 6 the filter cleaning structure 104 has one vertical main element 105 and one horizontal arm element 106 protruding from said main element 105. This particular embodiment, however, has only one branch element 107 protruding from said arm element 106. Said branch element 107 is substantially perpendicular to the arm element 106 and substantially parallel to the main element 105, i.e. it extends vertically. Nozzle 110 is provided on the main element 105, nozzle 111 on arm element 106 and nozzle 113 on branch element 107. Operation of the

cleaning structure 104 is carried out as described in the above by activating the driving means 109. Atomizing nozzles 120 for processing purposes are placed in the support plate 102 which in this case is the roof of a processing chamber also. In the following reference will be made to Figs 7 to 9, which all illustrate a third embodiment of the present invention. Elements having the same or analogous function as corresponding elements in the second embodiment shown in Figs 4 to 7 carry the same reference numerals to which 100 has been added. Only differences relative to the first embodiment will be described in detail.

The embodiment of the actual cleaning structure 204 depicted in Figs 7 to 9 is substantially identical to the embodiment of the actual cleaning structure 104 depicted in Figs 4 to 7. Also the relative positioning of the individual filter cleaning structures 204 with regard to the individual circular rows of filters 203 in Figs 7 to 9 is substantially identical to the relative positioning of the same in Figs 4 to 7. Also in this embodiment, an atomizing nozzle 220 for processing purpose is placed in the support plate 202 which in this case is the roof of a processing chamber also. This embodiment, however, differs in that it comprises an arrangement of three individual cleaning structures 204 as well as three individual groups of filters 203, 203' and 203", each group being arranged in a circular row. In the embodiment shown, each set of circular, concentric rows is provided with a filter cleaning structure. The operation of for instance cleaning structure 204 in relation to the group of filters 203 corresponds to the operation described in the above. Correspondingly, the group of filters 203' and 203" may operate in substantially the same manner as the group of filters 203. However, mutually different configurations between the groups are of course possible.

Other configurations than the embodiments shown and described in the above are conceivable. For instance, more than one arm element may protrude from each main element of the filter cleaning structure. Two arm elements could for instance be arranged with 180°

between them in order to create a structure in gravitational balance. Similarly, three arms could be arranged with 120° between them and so on.

All depicted embodiments rotate, but embodiments of the filter cleaning structure are conceivable, in which the main element is pulled up and down between the filter rows in a translational movement along the filters in addition to, or instead of, rotating between them is possible.

Furthermore, all shown filters are individual cylindrical oblong filters. One annular filter could be envisaged in some embodiments of the invention.

Although not described in the above, cleaning of the inside of the filters is of course conceivable as well.

The described cleaning method takes place when the operation of the filter assembly is discontinued. When the filter is actively used, the cleaning structure may be purged with air or gas to secure that product does not enter into the cleaning structure.

The invention is not limited to the embodiments shown and/or described in the above, but various modifications and combinations may be carried out without departing from the scope of the appended claims.