Patent Application
20070107391
1. Field of the Invention
The present invention relates to a filtration device having at least one filter bag between a crude gas side and a clean gas side. Each filter bag has a bag body with a longitudinal axis and a first end with a bag opening, as well as a cleaning device for cleaning the filter bag. The cleaning device has a nozzle head with a plurality of nozzles, the operation of which causes the cleaning device to rotate, and wherein the cleaning device can be moved in the longitudinal direction of each filter bag during operation of the nozzles.
2. Description of the Related Art
U.K. Patent Application No. GB 1,184,784 describes a cleaning device for cleaning a filter screen, i.e., a “hard” filter element. The cleaning is accomplished by rinsing off the inner surface of the filter screen by means of a rotating nozzle assembly. The nozzle assembly delivers a jet of water for cleaning the filter screen.
German Patent Application No. DE 39 20 097 describes a similar filtration device for cleaning filter canisters. Filter canisters of this type are produced from a pleated filter material, i.e., they are stiffened and folded. The cleaning gas strikes the inside of the filter material and mechanically dislodges contaminants.
In both cases, successful cleaning depends exclusively on a singular event at the point of impact of the cleaning agent on the “hard” filter material of the filter canister or filter screen.
In contrast to filter canisters and filter screens, filter bags are composed of a much more flexible material, which can elude mechanical impact much more readily than the material of a filter canister or filter screen. Therefore, cleaning with cleaning devices of the cited prior art is much less successful in this case.
Filter bags cannot be mechanically cleaned very well by the means described above. However, the contaminants, i.e., the filter cake, retained on the body or wall of the bag must be removed from the body of the bag from time to time to maintain the cleaning effect of the filter bag.
Cleaning methods for cleaning of this type are already known. In one method, a nozzle is arranged above the filter bag and directs a so-called “jet pulse” into the filter bag obliquely to a longitudinal axis, so that the body of the bag is caused to undulate or vibrate. This is designed to shake the filter cake from the body of the bag. This type of jet pulse occurs in an uncontrolled way, with the result that satisfactory cleaning is not obtained in all parts of the bag.
Alternatively, a nozzle lance into the body of the bag. However, a nozzle lance frequently damages the body of the bag, e.g., by cutting it open so that time-consuming operations become necessary to replace the damaged filter bag with a new one. The same problem is encountered with the use of the nozzle head, which is mounted on one end of a flexible hose as described in U.S. Pat. No. 5,182,832. This device can easily damage the sensitive filter material as it moves.
A third variant for cleaning a filter bag of this type is to remove the filter bag and have it cleaned in either a dry or wet cleaning operation.
All of the above methods for cleaning filter bags are unsatisfactory because they either do not work carefully enough, are cost-intensive, or are technically complex.
An object of the present invention is to develop a filtration device of the aforesaid type that ensures satisfactory cleaning of the coating that is deposited on a filter bag.
This object is achieved by means of a pressure wave generated in the body of the bag by the cleaning device during the operation of the nozzles and propagating from the opening of the bag to a free end of the body of the bag.
The filtration device of the present invention guarantees reliable cleaning of a filter bag. The cleaning device can have a nozzle head which is moved in a filter bag or along a filter bag, parallel to it. The delivery of a pressurized fluid at a certain position in the longitudinal direction ensures that every region of the body of the bag is reliably reached, and damage to the body of the bag is avoided. Finally, the detachable mounting possibility allows variable mounting and arrangement of nozzles, depending on the material and the degree of contamination.
The cleaning device of the invention does not blow against the filter bags or blow off the filter dust, but rather filter media made of relatively soft material (e.g., filter bags) are excited to natural-frequency vibration by high rotational speeds, e.g., greater than 10,000 rpm, which causes them to shake and causes the filter dust to fall off.
The cleaning effect is better than what can be achieved by removing and washing the filter medium, since during washing, the finish and the felt composite are subjected to considerable stress and partially detached and lost.
Another advantage is that each nozzle has one nozzle orifice, and at least two nozzles differ with respect to their orifice cross section.
Filter bags can be coated with different dusts and thus have different natural frequencies. For this reason, a frequency band including the natural frequency of the dust-covered filter bag can be obtained by nozzles with orifices of different orifice widths and/or angles.
In the case of sensitive composite materials, e.g., membrane filters, there is the danger that the membrane will become detached from the felt or delaminated from the composite material. For this reason, it is advantages in these cases to arrange a grid construction that consists of a perforated plate, grating bars or the like in front of the rotating part of the nozzle head. In this way, the jet of pressurized fluid directed at the filter bag is broken and diffusely directed at the material of the filter bag. This amplitude of the natural-frequency vibration can be significantly reduced by this measure.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.
A specific embodiment of the present invention is described in greater detail below with reference to the drawings in which:
a shows a schematic side view of a first version of a variable nozzle.
b shows a schematic top view of the variable nozzle in
a shows a schematic side view of a second version of a variable nozzle.
b shows a schematic top view of the variable nozzle in
a shows a schematic side view of a third version of a variable nozzle.
b shows a schematic top view of the variable nozzle in
A cleaning device 13 (shown in detail in
The nozzles 13.3 are tightly but detachably inserted in receptacles 13.4 formed in the periphery or the lateral surface 13.5 of the nozzle head 13.2. In the present embodiment, the receptacles 13.4 have an internal thread 13.6, and the nozzles have an external thread 13.7 that matches the internal thread 13.6. The individual nozzles 13.3 can thus be optionally screwed into or out of the nozzle head. In other embodiments, however, other connecting or fastening techniques can be used. For example, it is possible to use plug connectors.
In other embodiments, the nozzle head 13.2 is divided into nozzle rings (not shown), and the tangential orientation of the nozzles 13.3 with respect to adjacent nozzle rings is in the opposite or same direction. When a pressurized fluid is ejected from the nozzles 13.3, the individual nozzle rings are thus caused to rotate in opposite directions.
In the embodiment shown in
Depending on the speed of rotation (approximately greater than 10,000 rpm) of the nozzle head 13.2 or the nozzle rings (not shown), and depending on the number of nozzles 13.3, the undulatory motion becomes a controlled vibration, with which filtered material adhering to the outside of the bag body 3.1 can be shaken off. For membrane composite filters, a grid construction or screen 13.9 (as shown in
Referring to
a and 4b show a nozzle 13.3 with a circular nozzle orifice 13.5,
Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
