WO1996036418A1

WO1996036418A1 - A filter bag and production of such a filter bag

Info

Publication number: WO1996036418A1
Application number: PCT/SE1996/000637
Authority: WO
Inventors: Evald Johansson
Original assignee: ABB Flaekt AB; Flaekt AB
Current assignee: ABB Technology FLB AB
Priority date: 1995-05-15
Filing date: 1996-05-14
Publication date: 1996-11-21
Anticipated expiration: 1997-11-15
Also published as: SE9501793L; AU5785896A; SE9501793D0; SE504540C2

Abstract

The invention relates to a filter element (2) comprising an elongated, essentially cylindrical body (4) of filter material with an open end and a closed end. The closed end comprises an end part (6) of solid shape overlapping the cylindrical body (4), and its outer diameter is larger than that of the cylindrical body (4). The invention also relates to a method for producing said filter element.

Description

SHOCK WAVE GENERATOR

The present invention relates to combustion and explosion processes in general, more particularly, to the use of combustion or explosion processes for industrial application, such as cleaning of industrial equipment and machinery by devices employing these processes.

Proper maintenance of industrial machinery generally includes frequent removal of undesired accumulations of particles on different elements of the machinery. Parti¬ cles accumulation on the machinery parts can be minimized by cleaning the environment surrounding the machinery. Various air cleaning devices have been used for that purpose.

Although a clean working environment reduces parti¬ cle accumulation on the machinery parts, it cannot pre¬ vent such accumulation completely. Thus, more direct methods for cleaning the machinery parts are often re¬ quired.

It is known that efficient cleaning of various machinery parts may be achieved by generating shock waves in the vicinity of the parts thereby "shaking off" dust particles and other accumulations from the parts. Alter¬ natively, the shock waves may be induced onto a machinery part, causing the part to vibrate and "shake off" the accumulations. Shock wave cleaning is particularly useful for elements which are not readily removed for cleaning and/or elements which are particularly susceptible to the use of other cleaning methods and/or cleaning materials.

Gas dynamic generators which induce shock wave vibrations in their vicinity are known in the art. When a gas dynamic generator is placed near a machinery element to be cleaned, the shock waves induced in the vicinity of the element can be utilized to clean the element, as described above. Gas dynamic generators are useful aids in the production of construction materials and appara¬ tus, metallurgy, mining, the chemical industry, oil processing and the food industry.

Gas dynamic generators have been used in the past, for example, for cleaning dust accumulation and other deposits in a centrifugal compressor. The centrifugal compressor includes a pumping wheel with pumping blades mounted in a pumping chamber. Nozzles, which are connect¬ ed to a source of pressured gas via a gas channel, are mounted in the pumping chamber at a preselected distance from the pumping blades. The source generates high pres¬ sure gas pulses which impinge on the pumping blades thereby removing undesired accumulations from the blades. For optimal results, the distance between the nozzles and the pumping blades is selected to be between 1 and 1.5 times the diameter of the gas channel.

Gas dynamic generators have also been used for cleaning contaminated electrodes, particularly for puri¬ fying electrodes of electrofilters. An ignited air-fuel mixture is transported through an elongated detonation chamber, in which the burning mixture develops a high velocity, and is released onto a shock receiving plate which is associated with a shock transporting block. The block carries shock waves produced in the plate to the electrodes, thereby causing high acceleration vibrations in the electrodes to "shake off" the deposits.

Although existing gas dynamic pulse generators are useful for some applications, such as for cleaning com¬ pressor blades and removing deposits from electrodes, these systems generally suffer from high energy consump¬ tion and low operating efficiency. The output pressures obtained by devices as described above generally does not exceed 10 - 12 bars and, even then, most of the gas dynamic energy is not utilized since only a fraction of the pulsed gas dynamic energy is converted into shock waves in the part to be cleaned. Additionally, since the burning rate of the air-fuel mixture is relatively low (typically 400-500 meters per second) compared to the expansion rate of the mixture, only part of the mixture (typically not more than 30%) is utilized to produce the gas dynamic pulses. This difference between the burning rate and the expansion rate may also result in undesira¬ ble release of a flammable air-fuel mixture, thereby reducing the efficiency of the system and endangering the persons operating the system.

To produce sufficiently powerful shock waves, existing shock-wave generators often employ straight, elongated, combustion chambers, typically having a length of 4 meters or longer. This results in systems which are highly space-consuming and, therefore, imprac¬ tical for various application.

It is well known that the life-span of filters, such as the air filters used by heavy-duty diesel en¬ gines, can be somewhat extended by periodic cleaning of the filters. Normally, such filters are cleaned either superficially, by manually shaking the filters, or by applying pressured air in a reverse direction, i.e. in a direction opposite that of the air flow during normal operation. However, since air-pressure cleaning is local in nature, the use of air-pressure cleaning devices is often tedious and damaging to the filters being cleaned and is generally not thorough. It is an object of the present invention to provide a more efficient and more powerful method and apparatus for generating gas dynamic pulses, e.g. shock waves. A shock wave generator constructed and operative in accord¬ ance with the present invention may be utilized to remove various deposits from industrial machinery parts, for example to clear clogged pipes or to ensure free flow of dry materials.

It is a further object of the present invention to provide a folded gas dynamic pulse generator wherein the long dimension of the generator is folded, in accordance with a predetermined folding scheme, to provide a rela¬ tively compact shock wave generator having a relatively long effective length.

It is yet a further object of the present invention to provide improved apparatus for cleaning filters, particularly air filters, using gas dynamic pulses.

In accordance with a preferred embodiment of the present invention there is thus provided a two-phase shock wave generator including a combustion chamber including a first, combustion, portion having an input port and a second, detonation, portion downstream of the first portion and having an output aperture, an air-fuel supply line, operative to feed the input port with an air-fuel mixture, an igniter, associated with the air- fuel supply line, which ignites the air-fuel mixture in the supply line and initiates a burning front which propagates towards the input port and a turbulence stimu¬ lator, fixedly mounted in the combustion chamber, which enhances and controls burning of the air-fuel mixture and includes a first section, situated within the combustion portion of the combustion chamber and having a predeter¬ mined first gas dynamic resistance and a second section, situated within the detonation portion of the combustion chamber and having a predetermined second gas dynamic resistance, wherein the first resistance is such that burning of the air-fuel mixture in the combustion portion yields a predetermined pressure level suitable for initi¬ ating detonation of the remaining air-fuel mixture, in the detonation portion, and wherein the second resistance supports continued detonation of the remaining air-fuel mixture in the detonation portion.

Preferably, according to the present invention, the second gas dynamic resistance is lower than the first gas dynamic resistance.

In a preferred embodiment of the present invention, the air-fuel supply line is associated with the input port via a perforated nozzle which scatters the burning front substantially upon entry of the burning front into the combustion chamber.

Additionally, in a preferred embodiment of the invention, the turbulence generator includes a plurality of gas dynamic obstructers positioned at fixed locations along the combustion chamber to yield the preselected first and second gas dynamic resistances along the com¬ bustion and detonation portions, respectively.

Preferably, each obstructer includes a plurality of rods, generally perpendicular to the direction of propa¬ gation of the burning front in the combustion chamber.

In a preferred embodiment of the invention, the plurality of rods are arranged along a generally helical path, having a predetermined pitch.

In one preferred embodiment of the present inven¬ tion, the combustion chamber of the shock wave generator includes at least one bent portion. The at least one bent portion may be include at least one bend in the combus¬ tion portion of the combustion chamber and/or at least one bend in the detonation portion of the combustion chamber. The locations of the bent portions are prefera¬ bly selected in accordance with a predetermined folding scheme. Alternatively, in accordance with a preferred embod¬ iment of the invention, there is provided a shock wave generator including a combustion chamber having an input port and an output aperture, an air-fuel supply line operative to feed the input port with an air-fuel mix¬ ture, an igniter, associated with the air-fuel supply line, which ignites the air-fuel mixture in the supply line and initiates a burning front which propagates towards the input port, a turbulence stimulator, fixedly mounted in the combustion chamber, which enhances and controls burning of the air-fuel mixture and a perforated nozzle, associated with the input port, which scatters the burning front substantially upon entry of the burning front into the combustion chamber.

Further, in accordance with a preferred embodiment of the invention, there is provided a method of generat¬ ing a shock wave using a two-phase burning process, including the steps of supplying an air fuel mixture from an air-fuel supply line to a combustion chamber, igniting the air-fuel mixture in the supply line when the combus¬ tion chamber is filled with a preselected amount of air- fuel mixture, thereby initiating a burning front propa¬ gating towards the combustion chamber and enhancing and controlling the burning process by stimulating turbulence in the combustion chamber, wherein turbulence is stimu¬ lated by the steps of imposing a first, predetermined, gas dynamic resistance in the combustion portion during a first, combustion, phase of the burning process and imposing a second, predetermined, gas dynamic resistance during a second, detonation, phase of the burning proc¬ ess, and wherein the first resistance is such that burn¬ ing of the air-fuel mixture during the combustion phase yields a predetermined pressure level suitable for initi¬ ating detonation of the remaining air-fuel mixture, during the detonation phase, and wherein the second resistance supports continued detonation of the remaining air-fuel mixture.

In a preferred embodiment of the invention, the second gas dynamic resistance is lower than the first gas dynamic resistance.

Preferably, the method further includes the step of scattering the burning front substantially upon entry of the burning front into the combustion chamber.

Alternatively, in accordance with a preferred embod¬ iment of the invention, there is provided a method of generating a shock wave including the steps of supplying an air fuel mixture from an air-fuel supply line to a combustion chamber, igniting the air-fuel mixture in the supply line when the combustion chamber is filled with a preselected amount of air-fuel mixture, thereby initiat¬ ing a burning front propagating towards the combustion chamber, enhancing and controlling the burning process by stimulating turbulence in the combustion chamber, scat¬ tering the burning front substantially upon entry of the burning front into the combustion chamber and detonating the air fuel mixture in the combustion chamber.

In a preferred embodiment of the invention, the method further includes the step of removing the detonat¬ ed mixture at an output aperture to form a gas dynamic pulse thereat.

Further, in accordance with a preferred embodi¬ ment of the invention, there is provided apparatus for cleaning a filter including a shock wave generator which generates at least one gas dynamic pulse in a given direction and a reflector which reflects the at least one gas dynamic pulse onto at least a portion of the filter.

Preferably, the shock wave generator used by the cleaning apparatus includes a two-phase shock wave gener¬ ator as described above.

The apparatus preferably further includes an enclo¬ sure for accommodating the filter. The filter is prefera- bly an air filter.

In a preferred embodiment of the invention, the cleaning apparatus further including a positioning mechanism which controls the position of the reflector relative to the filter. The apparatus preferably fur¬ ther includes a controller which controls the operation of the positioning mechanism and the activation of the shock wave generator. The controller preferably operates the positioning mechanism and activates the shock wave generator in accordance with a predetermined cleaning sequence.

The cleaning sequence preferably includes a prede¬ termined number of activations of the shock wave genera¬ tor at each of a predetermined number of positions of the reflector relative to the filter. Preferably, the prede¬ termined number of activations of the shock wave genera¬ tor includes between 1 and 20 activations at each posi¬ tion of the reflector. In a preferred embodiment of the invention, the filter is a cylindrical filter and the predetermined number of positions are spaced along the height of the cylindrical filter. Preferably, the prede¬ termined number of positions are spaced by a spacing of between 5 and 10 centimeters.

The present invention will be better understood from the following detailed description of preferred embodi¬ ments of the invention, taken in conjunction with the accompanying drawings in which:

Fig. 1 is a schematic, cross-sectional, illustration of a gas dynamic pulse generator, constructed and opera¬ tive in accordance with a preferred embodiment of the present invention;

Fig. 2 is a pictorial, side view, illustration of a two-phase turbulence stimulator useful for the operation of the gas dynamic generator of Fig. 1 according to a preferred embodiment of the present invention;

Fig. 3 is a schematic, cross-sectional, illustration of a portion of a folded gas dynamic pulse generator, constructed and operative in accordance with another preferred embodiment of the present invention; and

Fig. 4 is a schematic, cross-sectional illustration of apparatus for cleaning a filter using pulse dynamic pulse generation, constructed and operative in accordance with yet another preferred embodiment of the present invention.

Reference is now made to Fig. 1, which schematically illustrates a preferred embodiment of the gas dynamic pulse generator of the present invention. As shown in Fig. 1, the gas dynamic pulse generator preferably in¬ cludes a fuel supply line 10, an air supply line 12, a mixer 14, an air-fuel mixture carrier line 15, an igniter 16 associated with a preselected portion of carrier line 15, a perforated nozzle 18 mounted to the end of carrier line 15, a combustion chamber 20 and a two-phase turbu¬ lence stimulator 22 mounted in combustion chamber 22.

Fuel, preferably a combustible gas such as Methane

Claims

(CH₄), and air are compressed through lines 10 and 12, respectively, into mixer 14 at suitable pressures so as to provide, at the output of mixer 14, an air-fuel mix¬ ture having a preselected fuel to air ratio. Preferably, the fuel to air ratio provided by mixer 14 is higher than the ratio required for a normal chemical reaction between the fuel and the air. The air-fuel mixture is carried via carrier line 15 and released via perforated nozzle 18 into combustion chamber 20. Igniter 16, preferably a spark plug sealingly mounted into carrier line 15, is activated only after combustion chamber 20 has been filled with a predetermined amount of fuel-air mixture suitable for proper combustion.

Activation of igniter 16 initiates burning of the air-fuel mixture in carrier line 15, creating a burning front which propagates towards perforated nozzle 18. When the burning front reaches perforated nozzle 18, the front is broken and a scattered flame front is released into combustion chamber 20. Scattering of the burning front by nozzle 18 is preferred because it provides a considerably larger area of contact between the propagating burning front and the air-fuel mixture in combustion chamber 20. It should be appreciated that the increased contact area between the burning front and the air-fuel mixture pro¬ vides more rapid combustion of the air-fuel mixture in combustion chamber 20. This initiates a first phase of the burning process, hereinafter referred to as the combustion phase.

Within combustion chamber 20, the burning front confronts two-phase turbulence stimulator 22 which en¬ hances and expedites combustion of the air-fuel mixture in a controlled manner, as will now be described.

Fig. 2 pictorially illustrates turbulence stimulator 22 in greater detail. As shown in Fig. 2, turbulence stimulator 22 is preferably composed of a longitudinal axis 23 and a plurality of radially extending rods 28 which are generally perpendicular to a longitudinal axis 23, i.e. generally perpendicular to the propagation direction of the burning front. In accordance with a preferred embodiment of the present invention, turbulence stimulator 22 includes a first section 24, associated with a first, combustion, portion 25 of combustion cham¬ ber 20 (Fig. 1), and a second section 26, associated with a second, detonation, portion 27 of combustion chamber 20 (Fig. 1) . The spaces between neighboring rods 28 in first section 24 are preferably smaller than the spaces between neighboring rods 28 in second section 26. Additionally or alternatively, rods 28 in section 24 may be thicker than rods 28 in detonation section 26.

In a preferred embodiment of the invention, rods 28 of sections 24 and 26 of stimulator 22 are arranged in equiplanar groups, hereinafter referred to as obstructers 30 and 32, respectively. The number of rods in each obstructer may vary but, preferably, each obstructer 30 includes more rods 28 than each obstructer 32. For exam¬ ple, each of obstructers 30 may include four rods 28, arranged in the form of a cross, and each of obstructers 32 may include two radially aligned rods 28. The rods of successive obstructers, 30 or 32, are preferably angular¬ ly shifted such that the outward ends of rods 28 define a helical path having a preselected pitch. The pitch of the helical path defined by the ends of rods 28 is preferably selected, empirically, so as to produce optimal turbu¬ lence of the burning air-fuel mixture in combustion chamber 20.

In a preferred embodiment of the present invention, the radially outward ends of rods 28 do not touch the internal surface of combustion chamber 20. Preferably, there is a preselected distance, typically at least 2 - 3 millimeters, between the ends of rods 28 and the internal surface of chamber 20. This provides improved, turbulat- ed, flow of the burning air-fuel mixture in combustion