GB2292098A - Cleaning of filters - Google Patents

Abstract

A method and apparatus by which small and larger types of filters may be cleaned comprises heating the filters, immersing the filters in a liquid bath and vibrating filter contaminants by means of an ultrasonic source so as to dislodge the contaminants from the filters, so that the contaminants fall harmlessly into the bath.

Description

CLEANING OF FILTERS The invention relates to the cleaning of filters and is particularly, although not exclusively, directed towards the cleaning of metallic filters for use in polymer production in industry such as the plastics industry, CD and video industries, and film and paper industries.

Metallic filters of the aforementioned type, are composed of a number of layers of wire mesh which may, for instance, be of stainless steel, mild steel or aluminium. During the production of pellets of polymer, the mesh of these filters becomes clogged with polymer material and the filters performance is progressively de-graded, until the filters need to be replaced.

Typically, in the plastics industry, two hundred small filters of the above type may be used each day, leading to an annual cost of replacements of around 50,000.

In the CD and video industry. very large filters are used which may, for instance, be around 1 m2 and inlaid in a stainless steel frame and, in these cases, each filter may cost between 5.000-10,000.

Up until now, onlv the very large filters such as those used in the CD industry are cleaned and re-used. Tbis is because the chemical cleaning, which it was thought was necessary to effectively clean the filters, has a number of disadvantages. Firstly, the material costs in providing a suitable tank and the correct chemicals and disposal methods are relatively high. The chemicals used have a quite short life span and there are considerable environmental hazards involved in disposing of such chemicals.

In view of the above, it has up until now not been considered economical to clean the smaller type of filters and they are simply replaced, whilst the larger filters are cleaned but at considerable cost and with potentially adverse environmental consequences.

In accordance with a first aspect of the invention, there is provided a method of cleaning a filter. the method comprising the steps of: heating a contaminated filter; immersing the heated filter into a bath of liquid; and dislodging contaminants from the filter by means of vibration.

Preferably, the vibration is achieved by bombarding the filter with ultrasonic energy once the filter is immersed in the liquid, so that the contaminants are dislodged and fall into the bath.

The filter is preferably heated by a heater, prior to its immersion. The heater may be an induction heater or other suitable heating means such as an electric or gas infra-red heater.

Preferably, a temperature to x hich the filter is heated is controlled by an optical pyrometer.

Preferably the filter is heated to a temperature of approximately 200 250"C.

Preferably, the liquid is heated.

Preferably, the liquid is water which is heated to a temperature close to 1000C.

Preferably, the filters are mesh filters.

Preferably, the mesh is a metallic mesh.

In accordance with a second aspect of the invention, there is provided apparatus for cleaning filters, the apparatus comprising: a heater; a liquid bath; and means associated with the liquid bath for dislodging contaminants from the filters by means of vibration.

Preferably, the means associated with the bath comprise an ultrasonic source.

Preferably, the heater is an induction heater.

Preferably. heater temperature is regulated by an optical pyrometer.

Preferably the temperature of the heater is regulated so as to heat contaminated filters to a temperature of 200-250 C.

Preferably, filters to be cleaned are attached to a conveyor system which is closely associated with the heater and is at least partially immersed in the liquid.

Preferably, the conveyor system comprises a continuous conveyor belt, which may be driven by a variable speed motor.

Preferably, the motor is arranged to allow a variation in conveyor belt speed from 0-5 metres per minute.

Preferably, a heating means is provided associated with the liquid bath.

Preferably, the liquid is water.

Preferably, the water is heated to a temperature close to 100"C.

In a particular arrangement. the heater may be provided in close association with one or more filters and may be arranged to be brought into such close association by control means.

The control means may comprise hydraulic, pneumatic, or electrical arrangements.

In such an arrallgement, the bath may also be provided in close association with said one or more filters and the position of the bath in relation to said one or more filters is variable. The position may be controlled by said control means.

By way of example, embodiments of the present invention will now be described, with reference to the accompanying figure which shows apparatus for use in the cleaning of filters.

The apparatus of the figure comprises a DC motor 1 having a variable drive speed which is connected to a belt drive 2. The belt drive 2 connects with a further pulley 3 which acts as a main drive pulley for continuous conveyor belt 4. At a position above the conveyor 4, there is provided a temperature controlled induction heater 5, which receives signals from and is regulated by optical pyrometer 6. A continuous conveyor belt 4 is then passed over guide pulleys 7, 8 before being lead into a tank 9. The tank is at least partially filled with a liquid. such as water 10 and the belt 4 passes into the water 10 and around return pulley 11. An ultrasonic source (not shown) is provided within the tank for bombarding articles conveyed by the belt 4 with ultrasonic energy. The water in the bath 10 is heated by a water heater 12.The belt 4 is returned to the drive pulley 3 via guide pulleys 13, 14.

A description of the method of cleaning filters utilising the apparatus shown in the figure will now be given. For the purposes of this example, a cleaning of the smaller type of filters will be described.

Filters which are removed from their associated filtering apparatus are attached to conveyor belt 4 by means of pins or other suitable attachment means, at a position adjacent to the main drive pulley 3.

Induction heater 5 is set so as to heat filters passing underneath it to a given temperature. which in this example may be around 240"C. This temperature is set at a level so that the contaminants clogging the metallic filters are heated up significantly, but do not burn.

DC drive motor 1 drives belt 2, drive pulley 3 and conveyor belt 4 and is controllable so as to give a conveyor belt speed of between 0 to 5 metres per minute. Typically, during a first cleaning operation the drive motor 1 is set so as to drive conveyor belt 4 at a speed of around 0.5 metres per minute.

Filters attached to the conveyor belt 4 pass beneath induction heater 5 (which is typically around 4 metres long) and the temperature of the filters as they emerge from underneath induction heater 5 are monitored by optical pyrometer 6. Advantageously, the optical pyrometer 6 will regulate the output of induction heater 5 to a temperature which is just less than a burning temperature of the contaminants. Typically, the output of induction heater 5 is regulated so as to heat the filters to between 200 and 250"C, and preferably to 240"C.

Conveyor belt 4 thereafter passes over guide roller 7 and under guide roller 8 and into the tank 9. Water held within the tank 9 is heated close to 100"C and as the clogged filters, whose contaminants have already now been heated so as to make them more easily dislodged, are bombarded by ultrasonic energy from the ultrasonic source (not shown) located within the tank 9.

The ultrasonic energy hits the filters and vibrates the contaminants so as to dislodge them from the filters. these contaminants are as a result shaken free from the filters and move down to a bottom region of the tank 9.

The cleaned filters, thereafter emerge from the tank 9, and are guided back to their beginning position via pulleys 11,13 and 14. If the filters require further cleaning, then a second or third pass around the apparatus may be performed. The subsequent passes may be performed at different conveyor belt speeds.

Although the liquid in the tank 9 is described as being water, of course other liquids could be utilised and, in particular, liquids having a boiling point of greater than 100"C might be effectively employed so as to enhance the operation of the apparatus. However. one big advantage of utilising water is that the apparatus is very environmentally friendly. Contaminants dislodged from the filters do not contaminate the water. but remain in their solid form and collect at the bottom of the tank 9. These contaminants are therefore very easily separable from the water and in fact the dislodged materials may actually be re-used or re-cycled Filters cleaned by the apparatus may be re-used a number of times before being replaced.Typically, a small filter of the type described could be re-used up to ten times. meaning a great saving in material costs.

Although the heater described in the foregoing embodiment has an induction heater 5 provided above conveyor belt 4, the heater may be in the form of a tunnel heater through which the conveyor belt 4 passes. Alternative types of heater other than induction heaters may also be utilised such as electric or gas infra-red heaters.

When cleaning the larger type of filters. such as those in use in the CD and video industry for instance. a modified form of apparatus may advantageously be utilised. The apparatus operates in accordance with the same principles as that illustrated in the figure, but is adapted so that the larger filters may be cleaned at a position close to their normally operating procedure or may actually be left insitu. In this case, an induction heater 5, or similar, may be provided at a position remote from the filter and be brought into proximity with it by means of a suitable hydraulic, pneumatic or electrical control arrangement. Similarly, an ultrasonic source and liquid tank may be provided associated with each of the filters so that after a predetermined period of use, a cleaning cycle may be carried out with minimal disruption to the filter installation.

It will be evident from the above described arrangements, that important advantages are provided which overcome the problems with the prior art. In particular, an effective means is provided of cleaning filters, both large and small. without there being an associated environmental hazard and without high costs.

The very simple nature of the apparatus required for cleaning of small to medium sized filters means that for the first time it is more economical to clean those filters than to replace them.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination. of the features disclosed in this specification (including any accompanying claims, abstract and drawings). or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (28)

1. A method of cleaning a filter. the method comprising the steps of: heating a contaminated filter; immersing the heated filter into a bath of liquid; and dislodging contaminants from the filter by means of vibration.

2. A method according to Claim 1, wherein the vibration is achieved by bombarding the filter with ultrasonic energy once the filter is immersed in the liquid, so that the contaminants are dislodged and fall into the bath.

3. A method according to Claim 1 or 2, wherein the filter is heated by a heater, prior to its immersion.

4. A method according to any of the preceding Claims, wherein a temperature to which the filter is heated is controlled by an optical pyrometer.

5. A method according to any of the preceding Claims, wherein the filter is heated to a temperature of approximately 200 to 250"C.

6. A method according to any of the preceding Claims, wherein the liquid is heated.

7. A method according to Claim 6. wherein the liquid is water which is heated to a temperature close to 100or.

8. A method according to any of the preceding Claims, wherein the filters are mesh filters.

9. A method according to Claim 8, wherein the mesh is a metallic mesh.

10. A method according to any of Claims 3 to 9, wherein the heater is an induction heater.

11. A method substantially as herein described with reference to the accompanying Figure.

12. Apparatus for cleaning filters. the apparatus comprising: a heater; a liquid bath; and means associated with the liquid bath for dislodging contaminants from the filter by means of vibration.

13. Apparatus according to Claim 12, wherein the means associated with the bath comprise an ultrasonic source.

14. Apparatus according to Claim 12 or 13, wherein the heater is an induction heater.

15. Apparatus according to any of Claims 12 to 14, wherein the heater is arranged to heat contaminated filters to a temperature of 200 - 250"C.

16. Apparatus according to any of Claims 12 to 15, wherein heater temperature is regulated by an optical pyrometer.

17. Apparatus according to any of Claims 12 to 16, wherein filters to be cleaned are attached to a conveyor system which is closely associated with the heater and is at least partially immersed in the liquid.

18. Apparatus according to Claim 17, wherein the conveyor system comprises a continuous conveyor belt.

19. Apparatus according to Claim 18, wherein the conveyor belt is driven by variable speed motor.

20. Apparatus according to Claim 19, wherein the motor is arranged to allow variation in conveyor belt speed from 0-5 metres per minute.

21. Apparatus according to any Claims 12 to 20, wherein heating means is provided associated with the liquid bath.

22. Apparatus according to any of Claims 12 to 21, wherein the liquid is water.

23. Apparatus according to Claim 22, as appendant to Claim 20, wherein the water is heated to a tenlperature close to 100"C.

24. Apparatus according to any of Claims 12 to 23, wherein the heater is provided in close association with one or more filters and may be arranged to be brought into such close association by control means.

25. Apparatus according to Claim 24, wherein the control means may comprise hydraulic, pneumatic or electrical arrangements.

26. Apparatus according to Claim 24 or 25, wherein the bath is provided in close association with said one or more filters and the position of the bath in relation to said one or more filters is variable.

27. Apparatus according to Claim 26, wherein the position of the bath is controlled by said control means.

28. Apparatus for cleaning filters substantially as herein described, with reference to the accompanying figure.