EP2718206A1

EP2718206A1 - Method and apparatus in a pneumatic material conveying system

Info

Publication number: EP2718206A1
Application number: EP12796745.3A
Authority: EP
Inventors: Göran Sundholm
Original assignee: Maricap Oy
Current assignee: Maricap Oy
Priority date: 2011-06-08
Filing date: 2012-06-07
Publication date: 2014-04-16
Also published as: EP2718206A4; FI20115555A0; FI20115555A; WO2012168560A1; CN103596857B; CN103596857A; KR20140039272A; JP2014516018A; FI123342B

Abstract

Method for improving the separating efficiency of a separating device of a pneumatic material conveying system, such as of a waste conveying system, in which the material to be conveyed, such as waste material (w), is separated from the conveying air (a), and/or for preventing blocking of the output aperture of the conveying air of the separating device. Pressure medium is sprayed into the separating device (100), into its chamber space (101), preferably in the proximity of the output aperture (7) of the conveying air.

Description

METHOD AND APPARATUS IN A PNEUMATIC MATERIAL CONVEYING SYSTEM

Background of the invention

The object of the invention is a method as defined in the preamble of claim 1 .

The object of the invention is also an apparatus as defined in the preamble of claim 12.

The invention relates generally to pneumatic material conveying systems, such as to partial-vacuum conveying systems, more particularly to the collection and conveying of wastes, such as to the conveying of household wastes. Pneumatic material conveying systems wherein wastes are conveyed in piping by means of suction, a pressure difference and/or a flow of conveying air are known in the art. Pneumatic pipe conveying systems for material are used, among other things, for the conveying of wastes in different buildings, in institutions or in more extensive areas, e.g. in blocks or city districts. It is typical to these systems that a partial-vacuum apparatus is used to achieve a pressure difference, in which apparatus a partial vacuum, a pressure difference and/or a flow of conveying air is achieved in the conveying pipe with partial-vacuum generators, such as with vacuum pumps or with an ejector apparatus or with fans. The wastes transfer from the input point along the piping together with the conveying air into a separating device, which is e.g. a cyclone separator or some other tank, in which the material to be conveyed is separated from the conveying air. The conveying air exits from the output aperture for conveying air and the waste remains in the separating device, from where it is removed, e.g. according to need. The conveying air and the waste circulate in the separating device typically near the walls, in which case the heavier waste remains in the separating device and the conveying air rises slowly upwards from the center of the cyclone separator. One problem is that papers and thin plastics that are light and have a large surface area can sometimes ascend along with the slowly ascending conveying air flow. There are therefore often waste grades, e.g. waste paper, plastic film, plastic bags, et cetera, along with the waste being conveyed, which waste grades, being unattached and lighter than the other waste, can block the output aperture of the conveying air of the separating device or other tank, either partly or completely. In addition, filtering means are often arranged in connection with the output aperture of the conveying air of the tank, or in the proximity of it, through which filtering means the conveying air exits from the separating device or tank. A problem with a separating device, such as a cyclone separator or other tank, is therefore that with waste generally e.g. paper and thin plastic try to block the output aperture of the conveying air of the separating device. Problematic waste grades, e.g. paper and plastic, typically have a large surface area and low weight. These often cause problems for a separator because problematic waste grades float very easily even with a small air flow to the output aperture of the conveying air. Efforts have been made to solve this problem by using various mechanical means, e.g. rotating brushes, to prevent blockage of the output aperture and, on the other hand, to remove rubbish that has gone into it. These have not, however, functioned satisfactorily.

The aim of the present invention is to achieve a completely new type of solution in connection with the separating devices of pneumatic material conveying systems, by means of which solution the drawbacks of prior-art solutions are avoided. Another aim of the invention is to achieve a solution applicable in connection with a pneumatic wastes conveying systems, by the aid of which blocking of the output aperture of a separating device can be prevented more easily than before and, on the other hand, blockages of the output aperture of the conveying air of the separating device can be removed. Yet another aim is to achieve a solution, by means of which the separating efficiency of a separating device can be improved. Yet another aim is to achieve a solution, with which also the action of the filtering means of a separating device can be enhanced.

Brief description of the invention

The invention is based on a concept wherein pressure medium nozzles are arranged in connection with the separating device of a pneumatic material conveying system, preferably in the output aperture of the conveying air, or in the proximity of it, which pressure medium nozzles are, when activated, arranged to spray/blow pressure medium such that the spraying reduces or prevents the traveling of waste particles, such as paper or plastic films or bags, into the output aperture of the conveying air and/or reduces or prevents the blocking of the output aperture. The method according to the invention is mainly characterized in that pressure medium is sprayed into the separating device, into its chamber space, preferably in the proximity of the output aperture of the conveying air. The method according to the invention is also characterized by what is stated in claims 2 - 1 1 .

The apparatus according to the invention is mainly characterized in that at least one spraying nozzle of the pressure medium is arranged in the separating device, for spraying pressure medium into the chamber space of the separating device, preferably in the proximity of the output aperture of the conveying air.

The apparatus according to the invention is also characterized by what is stated in claims 13 - 22.

The solution according to the invention has a number of important advantages. By arranging pressure medium nozzles in connection with a separating device, preferably in the output aperture, or in the proximity of it, which pressure medium nozzles are, when activated, arranged to spray/blow pressure medium such that waste particles, such as papers or plastic films or bags, do not go into the output aperture and/or block the output aperture, a separating device for a pneumatic wastes conveying system is achieved that is more operationally reliable than before. The pressure medium nozzles blow papers/plastics that are floating upwards away from the output aperture. The total quantity of pressure medium, such as of compressed air, is small, so it has no essential significance on the actual quantity of conveying air. In addition to, or instead of, gas, such as compressed air, as a pressure medium, nozzles that when activated spray a liquid, preferably nozzles that blow a water mist, can be used. Pressure medium nozzles spraying a liquid also irrigate the waste particles drifting into the coverage area of the nozzles of the output aperture and make the particles, such as paper or plastic, typically heavier, in which case they descend downwards in the separating device. The pressure medium nozzles can also be a combination of nozzles spraying a gas and nozzles spraying a liquid. The water evaporates quickly in the large amount of conveying air, so it is not a detriment in the wastes conveying process. In addition, with a pressure medium spray the action of the filtering means of a separating device can also be enhanced. Brief description of the figures

In the following, the invention will be described in more detail by the aid of an embodiment with reference to the attached drawings, wherein

Fig. 1 presents a simplified and sectioned view of one device according to an embodiment of the invention, in connection with a separating device,

Fig. 2 presents the device of the embodiment of Fig. 1 from the direction of the arrow A,

Fig. 3 presents a device according to an embodiment of the invention, sectioned along the line III - III of Fig. 1 , Fig. 4 presents a simplified and sectioned view of a device according to an embodiment of the invention,

Fig. 5 presents a device according to an embodiment of the invention, sectioned along the line V - V of Fig. 4,

Fig. 6 presents a simplified and sectioned view of a device according to an embodiment of the invention, and

Fig. 7 presents a device according to an embodiment of the invention, sectioned along the line VII - VII of Fig. 6.

Detailed description of the invention Fig. 1 presents a simplified view of one device according to an embodiment of the invention connected to a separating device 100 of a pneumatic material conveying system, more particularly of a wastes conveying system. In the embodiment of the figure, the separating device 100 is a so-called cyclone separator comprising a chamber space 101 that is bounded by walls 1 , 15. An input branch coupling 2 is connected to the chamber space of the separating device, via which branch coupling the material to be conveyed, such as waste material, is conducted together with the conveying air into the separating device from the input aperture 3. In the material conveying system, the material fed into the conveying piping is transported along the conveying piping to the separating device, in which the material being transported separates, e.g. due to the dropping of speed and due to centrifugal force, from the conveying air. In the embodiment of the figure, the separated material, such as waste material, drifts to the bottom of the separating device. In Fig. 1 , the drifting of the separated material to the bottom part of the chamber space 101 of the separating device 100 is described with the arrow w. The separated material is removed, e.g. according to need, from the separating device, e.g. via a material output aperture 5 arranged in the bottom part of the separating device 100. The conveying air is conducted from the separating device with an output branch coupling 4 for the conveying air. The conveying air is typically deflected in the separating device, in which case the heavier material accompanying the conveying air separates from the conveying air more easily. In the embodiment of the figure, a wall part 6 is arranged in the top part of the separating device, which wall part extends into the separating means. In the embodiment of the figure, the wall part 6 is cylindrical. A space 9 is formed on the inside of the rim of the wall part 6, into which space the aperture of the bottom part of the wall 6, i.e. the output aperture, leads. There is a connection from the top part of the space to the output branch coupling 4 for conveying air. In the embodiment of the figure, there is an output aperture 7 in the bottom part of the wall part 6. In the embodiment of the figure, the bottom end of the cylindrical wall part 6 is open. The top part of the wall 6 comprises an output branch coupling 4 for conveying air. In the embodiment of the figure, the cylindrical wall part 6 and the space 9 extend through the top end, such as through the top wall 15, of the separating device, e.g. from an aperture formed in the top wall 15. At the top end of the wall part 6 is an end plate 8. An output branch coupling 4 for the conveying air is arranged in the top part of the wall part 6. The movement of the conveying air in the separating means is roughly illustrated with the arrow a. In the embodiment of the figure, the input aperture 3 is arranged in the wall 1 of the separating device in the area between the top wall 15 of it and the aperture 7 in the bottom part of the wall 6 extending into the inside part of the separating device. The separating device thus comprises a ring-like section in an area in which the wall 6 forms the inner rim of the ring-like section and the wall 1 of the separating device the outer in of the ring-like section. At least one spraying nozzle 10 is arranged in the separating device, which spraying nozzle, when activated, is arranged to spray pressure medium in the separating device in the proximity of the output aperture for the conveying air or of a duct leading to it, such as the output aperture 7 leading to the space 9 and to the output branch coupling 4. The pressure medium is sprayed in essentially the opposite direction with respect to the flow direction of the conveying air. The pressure medium is sprayed with a spraying nozzle 10 such that the waste substances that have traveled into the output aperture 7, or into the proximity of it, travel out of the output aperture or away from its proximity. There can be a number of spraying nozzles 10. According to the embodiment of Figs. 1 - 3, the spraying nozzles 10 are arranged in the target area in a divided manner. According to one embodiment the pressure medium sprays 13 cover essentially the whole area of the output aperture 7. The sprays prevent the passage of waste particles, more particularly papers or plastic films or bags, into the output aperture 7. In the embodiment of Fig. 1 , a plurality of spraying nozzles 10 is arranged in the bottom part of the cylindrical wall 6, or in the proximity of it, preferably in the aperture 7. In the embodiment of the figures the pipe means 1 1 are arranged to bring pressure medium from a trunk pipe 12 to the nozzles 10, in the figure the pipe means 1 1 are led through the space 9. Bringing the pressure medium to the trunk pipe 12 is assumed to be per se known to a person skilled in the art and it is not described in more detail in the drawing. The pressure medium can be brought from a medium source with a pump means connected to the trunk pipe 12. If the pressure medium is gaseous, e.g. compressed air, an air compressor that is per se known in the art can be used for bringing the pressure medium. If a liquid pressure medium is used, e.g. water, a liquid source can be used, from which the liquid is pumped with a medium pump with the necessary pressure into the trunk pipe 12 and onwards to the pipe 1 1 taking it to the nozzles 10.

By arranging pressure medium nozzles 10 in connection with a separating device, preferably in the output aperture 7, or in the proximity of it, which pressure medium nozzles are, when activated, arranged to spray/blow pressure medium such that waste particles, such as papers or plastic films or bags, do not go into the output aperture and/or block the output aperture, a separating device for a pneumatic wastes conveying system is achieved that is more operationally reliable than before. The pressure medium nozzles blow papers/plastics accompanying the conveying air that are floating towards the output aperture 7 away from the output aperture. The total quantity of pressure medium, such as of compressed air, to be sprayed from the nozzles 10 is small, so it has no essential significance on the actual quantity of conveying air and therefore it does not detrimentally affect the operation of the material conveying system itself. In addition to, or instead of, gas, such as compressed air, a liquid, preferably a water mist, can be used as the pressure medium to be sprayed. Pressure medium nozzles spraying a liquid also irrigate the waste particles drifting into the coverage area of the nozzles, such as into the proximity of the output aperture, and therefore make the particles, such as paper or plastic, typically heavier, in which case the waste particles descend downwards in the separating device. The pressure medium nozzles 10 can also be a combination of nozzles spraying a gas and nozzles spraying a liquid. It can be conceived that, if necessary, a different pressure medium can be sprayed from the same nozzle, such as e.g. alternately a gas and a liquid. When spraying a liquid, such as water, the water evaporates quickly in the large amount of conveying air, so it is not detrimental to the wastes conveying process.

The conveying air of the separating device can, in addition, be cleaned with filtering means 17, through which the conveying air flows as it travels from the separating device towards the output branch coupling 4 for conveying air. According to Figs. 4 and 5, the spraying nozzles 10 according to the invention are arranged before the filtering means 17 in the flow direction of the conveying air.

The filtering means 17 are arranged according to Figs. 4 and 5 in the chamber space 9 bounded by the wall 6. In the embodiment of the figures the filtering surface area of the filtering means has been made to be rather large by using filter cartridges comprising filtering means of conical shape or of cylindrical shape. A filtering element of a filtering means 17 is arranged to taper conically from the top part 19 of the filtering means towards the bottom part 18 of the filtering means. The top part 19 of the filtering means comprises an aperture 20, from which the conveying air that has traveled through the filter is conducted towards the outlet coupling branch 4 for the conveying air. According to the figure, some of the pipe means 1 1 leading to the spraying nozzles 10 are arranged through the aperture 20 of the top part 19 of the filtering means and a second aperture formed of the bottom part 18 of said filtering means. According to one embodiment (Fig. 4), the filtering means 17 are arranged with fixing means from the flange 16 to adjoin the top wall 15 of the separating device in the edge area of the aperture or in the proximity of it. Figs. 6 and 7 further present a second embodiment, in which at least one of the spraying nozzles 10, 10' is arranged to spray, when activated, a pressure medium spray 13' onto the filter surface of the filtering means 17, in which case the pressure medium spray 13' in question on the one hand prevents waste particles, more particularly paper particles or plastic particles, from drifting onto the surface of the filter of the filtering means 17 and, on the other hand, removes particles that have adhered to the surface of the filtering means 17 from the surface of the filter and directs them to the bottom of the separating device towards the output aperture 5 (as in Fig. 1 ). According to Figs. 6 and 7, the spraying nozzles 10' in question of the pressure medium spray 13' that are at least partly directed to spray onto the surface of a filtering means are arranged side-by-side in the spaces between the filtering means 17 in the manner of Fig. 7. Fig. 7 presents the locations of the pipe means 1 1 ' leading to the nozzles in relation to the filtering means 17, in which case the locations of the nozzles arranged in the pipe means are essentially corresponding. Fig. 6 shows the position of a spraying nozzle 10' in the height direction when the separating device is in a vertical attitude. In this case it is seen that with the sprays 13' pressure medium can be advantageously sprayed rather extensively onto the surfaces of the filtering means. The second nozzles 10' are in the height direction preferably at a distance in the flow direction of the conveying air from the lower end 18 of a filtering means near the top end 19 of the filtering means. At least some of the nozzles 10, 10' can conduct a second medium, either liquid or gas. Figs. 6 and 7 present an embodiment wherein a pressure medium (pressure medium) is conducted to first nozzles with first pipelines 1 1 from a first trunk pipe 12 and the pressure medium or a second pressure medium (pressure medium') to second nozzles 10' with second pipelines 1 1 ' from a second trunk pipe 12'. The first and the second pressure medium can be the same pressure medium or different pressure mediums to each other. According to one embodiment the first pressure medium is a gas, such as compressed air, and the second pressure medium a liquid, e.g. water mist. According to a second embodiment the second medium is a gas and the first medium a liquid, such as water mist.

Cleaning of the filtering means 17 can be further enhanced by bringing about a so- called "back blow" from the aperture 20 into the filtering means, in which case the air flow travels through the filtering means in the opposite direction with respect to the normal situation. The pressure medium spraying contributes to the traveling of waste particles that have detached from the filter to the bottom part of the chamber space 101 of the separating device 100.

The invention also relates to a method for improving the separating efficiency of a separating device of a pneumatic material conveying system, such as of a waste conveying system, in which the material to be conveyed, such as waste material w, is separated from the conveying air a, and/or for preventing blocking of the output aperture of the conveying air of the separating device. Pressure medium is sprayed into the separating device 100, into its chamber space 101 , preferably in the proximity of the output aperture 7 of the conveying air.

According to one embodiment the pressure medium is sprayed with a spraying nozzle 10, which is arranged in the output aperture 7 or in the proximity of it. According to one embodiment the pressure medium is sprayed in essentially the opposite direction with respect to the flow direction of the conveying air.

According to one embodiment the pressure medium is sprayed with a number of nozzles 10, 10'.

According to one embodiment the pressure medium is sprayed such that a waste grade is acted upon, which waste grade tries to move along with the conveying air towards the output aperture 7, such that the waste grade is guided, at least partly owing to the pressure medium spray 13, towards the bottom part of the separating device.

According to one embodiment the pressure medium is a gas, such as compressed air. According to one embodiment the pressure medium is a liquid, in which case preferably liquid mist is sprayed.

According to one embodiment the conveying air is filtered with filtering means 17, in which case the pressure medium spray 13, 13' is directed at least partly onto the filter surface of the filtering means 17. According to one embodiment an air flow is brought about through the filtering means 17 in the opposite direction, in which case removal or cleaning of a blockage of the filtering means is enhanced. According to one embodiment when the pressure medium is a liquid, a part of a waste grade is moistened with a spray 13, 13', which waste grade when moistened settles towards the bottom part of the separating device.

According to one embodiment the separating device 100 is a cyclone separator.

According to one embodiment the separating device 100 is a waste tank.

The invention also relates to an apparatus for improving the separating efficiency of a separating device of a pneumatic material conveying system, in which the material to be conveyed, such as waste material w, is separated from the conveying air a, and/or for preventing blocking of the output aperture of the conveying air of the separating device, which separating device comprises a chamber space 101 , an input aperture 3 for the material to be conveyed as well as for the conveying air, an output aperture 7 for the conveying air, and also an output aperture 5 for the separated material. At least one spraying nozzle 10, 10' of the pressure medium is arranged in the separating device 100, for spraying pressure medium into the chamber space 101 of the separating device, preferably in the proximity of the output aperture 7 of the conveying air, such that the pressure medium spray is adapted to act upon a waste grade, which waste grade tries to move along with the conveying air towards the output aperture 7, such that the waste grade is guided, at least partly owing to the pressure medium spray 13, towards the bottom part of the separating device 100.

According to one embodiment the spraying nozzle 10, 10' of the pressure medium is arranged in the output aperture 7 of the conveying air, or in the proximity of it.

According to one embodiment the spraying nozzle 10, 10' of the pressure medium is arranged in the output duct 9 of the conveying air. According to one embodiment a spraying nozzle 10, 10' of the pressure medium is directed, when activated, to spray in essentially the opposite direction with respect to the flow direction of the conveying air. According to one embodiment there are a number of spraying nozzles 10, 10' of the pressure medium. According to one embodiment the spraying nozzles 10, 10' of the pressure medium are arranged at a distance from each other.

According to one embodiment a number of spraying nozzles 10, 10' of the pressure medium are arranged a number side-by-side.

According to one embodiment the spraying nozzles 10, 10' of the pressure medium are arranged at a distance from each other in the flow direction of the conveying air. According to one embodiment a spraying nozzle 10, 10' is, when activated, configured to spray gas and/or a liquid.

According to one embodiment the apparatus comprises at least one filtering means 17 of the conveying air, the filter surface of which a spraying nozzle 10' of the pressure medium is, when activated, directed to spray.

According to one embodiment, with the apparatus an air flow is brought about through the filtering means 17 in the opposite direction, in which case removal or cleaning of a blockage of the filtering means is further enhanced.

It is obvious to the person skilled in the art that the invention is not limited to the embodiments presented above, but that it can be varied within the scope of the claims presented below. The characteristic features possibly presented in the description in conjunction with other characteristic features can also, if necessary, be used separately to each other.

Claims

1. Method for improving the separating efficiency of a separating device of a pneumatic waste conveying system, in which the waste material (w), is separated from the conveying air (a), and/or for preventing blocking of the output aperture of the conveying air of the separating device, characterized in that pressure medium is sprayed into the separating device (100), into its chamber space (101), preferably in the proximity of the output aperture (7) of the conveying air, such that a waste grade is acted upon, which waste grade tries to move along with the conveying air towards the output aperture (7), such that the waste grade is guided, at least partly owing to the pressure medium spray (13), towards the bottom part of the separating device (100).

2. Method according to claim 1, characterized in that the pressure medium is sprayed with a spraying nozzle (10), which is arranged in the output aperture (7) or in the proximity of it.

3. Method according to claim 1 or 2, c h a ra cte ri ze d in that the pressure medium is sprayed in essentially the opposite direction with respect to the flow direction of the conveying air.

4. Method according to any of claims 1 - 3, c h a r a c t e r i z e d in that the pressure medium is sprayed with a number of nozzles (10, 10').

5. Method according to any of claims 1 -4, c h a r a c t e r i z e d in that the pressure medium is a gas, such as compressed air.

6. Method according to any of claims 1 - 5, c h a r a c t e r i z e d in that the pressure medium is a liquid, in which case preferably liquid mist is sprayed.

7. Method according to any of claims 1 - 6, c h a r a c t e r i z e d in that the conveying air is filtered with filtering means (17), in which case the pressure medium spray (13, 13') is directed at least partly onto the filter surface of the filtering means (17).

8. Method according to claim 7, characterized in that an air flow is brought about through the filtering means (17) in the opposite direction, in which case removal or cleaning of a blockage of the filtering means is enhanced.

9. Method according to any of claims 1 -8, characterized in that when the pressure medium is a liquid, a part of a waste grade is moistened with a pressure medium spray (13, 13'), which waste grade when moistened settles towards the bottom part of the separating device (100).

10. Method according to any of claims 1 -9, c h a ra ct e r i z e d in that the separating device (100) is a cyclone separator.

11. Method according to any of claims 1 - 10, c h a ra cte r i zed in that the separating device (100) is a waste tank.

12. Apparatus for improving the separating efficiency of a separating device of a pneumatic waste material conveying system, in which the waste material (w) to be conveyed is separated from the conveying air (a), and/or for preventing blocking of the output aperture of the conveying air of the separating device, which separating device (100) comprises a chamber space (101), an input aperture (3) for the material to be conveyed as well as for the conveying air, an output aperture (7) for the conveying air, and also an output aperture (5) for the separated material, c h a r a c t e r i z e d in that at least one spraying nozzle (10, 10') of the pressure medium is arranged in the separating device (100), for spraying pressure medium into the chamber space (101) of the separating device, preferably in the proximity of the output aperture (7) of the conveying air such that the pressure medium spray is adapted to act upon a waste grade, which waste grade tries to move along with the conveying air towards the output aperture (7), such that the waste grade is guided, at least partly owing to the pressure medium spray (13), towards the bottom part of the separating device (100).

13. Apparatus according to claim 12, c h a ra ct e ri ze d in that the spraying nozzle (10, 10') of the pressure medium is arranged in the output aperture (7) of the conveying air, or in the proximity of it.

14. Apparatus according to claim 12 or 13, c h a r a c t e r i z e d in that the spraying nozzle (10, 10') of the pressure medium is arranged in the output duct (9) of the conveying air.

15. Apparatus according to any of claims 12- 14, ch a racterized in that a spraying nozzle (10, 10') of the pressure medium is directed, when activated, to spray in essentially the opposite direction with respect to the flow direction of the conveying air.

16. Apparatus according to any of claims 12 - 15, c h a ra ct e r i z ed in that there are a number of spraying nozzles of the pressure medium.

17. Apparatus according to any of claims 12- 16, characterized in that the spraying nozzles (10, 10') of the pressure medium are arranged are arranged at a distance from each other.

18. Apparatus according to any of claims 12- 17, ch a racterized in that a number of spraying nozzles (10, 10') of the pressure medium are arranged a number side-by-side.

19. Apparatus according to any of claims 12- 18, characterized in that the spraying nozzles (10, 10') of the pressure medium are arranged at a distance from each other in the flow direction of the conveying air.

20. Apparatus according to any of claims 12- 19, ch a racterized in that a spraying nozzle (10, 10') is, when activated, configured to spray gas and/or a liquid.

21. Apparatus according to any of claims 12 - 20, characterized in that the apparatus comprises at least one filtering means (17) of the conveying air, the filter surface of which a spraying nozzle (10') of the pressure medium is, when activated, directed to spray.

22. Apparatus according to claim 21, c h a r a c t e r i z e d in that with the apparatus an air flow is brought about through the filtering means (17) in the opposite direction, in which case removal or cleaning of a blockage of the filtering means is further enhanced.