AU615029B2 - Multi stage gas inlet construction for dust collectors - Google Patents

Description

P/00/011 Al&^L

AUSTRALIA

PATENTS ACT 1952-1973 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Form Class: Int. CI: S Application Number: Lodged: Complete Specification-Lodged: o f Accepted: Published: Priority: Related Art: TO BE COMPLETED BY APPLICANT NameofApplicant: HOSOKAWA MICRON INTERNATIONAL INC., a corporation organized under the laws of the State of Delaware, of 4 Addressof Applicant: 10 Chatham Road, Summit, New Jersey, 07901, United States of America.

,A 4 1 Actual Inventor: Giambattista Giusti and Robert W. Duyckinck AddressforService: Care of: LAWRIE James M. Register No. 113 RYDER Jeffrey A. Register No. 199 HOULIHAN Michael J. Register No. 227 Patent Attorneys 72 Willsmere Road, Kew, 3101, Victoria, Australia.

Complete Specification for the invention entitled: MULTI STAGE GAS INLET CONSTRUCTION FOR DUST COLLECTORS The following statement is a full description of this invention, including the best rileihod of performing it known to me:- SNote: The description is to be typed in double spacing, pica type face, in an area not exceeding 250 mm in depth and 160 mm in width, on tough white paper of good quality and it is to be inserted inside this form.

11710/76-L C. J. ToMi'soN, Commonwealth Government Printer, Canberra II II This invention relates to gas inlet system constructions for gas treating apparatus and more particularly to apparatus for effecting the controlled introduction and distribution of particulate laden gas streams into industrial fabric filter dust collectors.

BACKGROUND OF THE INVENTION It has long been recognised that a controlled pattern of equable distributions and a controlled velocity of a gas stream at the locus of introduction thereof into gas treating apparatus can materially contribute to increased efficiency of operation and extended operating life of the gas treating components thereof.

One area of preferential concern has been in the industrial gas filtration field, and particularly in the fabric filter dust collector field. One type of such fabric filter dust collector, also called a "baghouse", typically employs a large number of tubular fabric filters suspended from a tube sheet and interposed in the path of a particulate gas stream to effect the separation of the particulate matter from the gaseous carrier as the latter traverses the fabric filter media in its passage from the dirty air plenum to the clean air plenum portion of the filter housing. Another u type of fabric filter dust collector employs filter media in the form of flat panels rather than tubular filter bags. In both such types of dust collector, a particulate S laden gas stream conventionally enters the filter housing either through a breach in a portion of the lower housing wall defining a dust collecting hopper and generally changes direction and flows upwardly toward the filter or enters the housing through an opening in the upper sidewall portion of the collector housing defining at least a portion of the perimeter of the dirty air plenum. The particulate matter borne by the incoming gas stream normally accumulates on the upstream filter medium surface and, unless removed by dislodgment, results in a progressive increase in pressure drop across the filter media and in a concomitant reduction in the rate of gas flow through the filter media. In order to avoid excessive particulate accumulation on the upstream surface of the filter media, the filter media is periodically cleaned by utilisation of various known techniques, such as pulse jet and reverse flow cleaning and bag shaking. The outcome of such a cleaning operation is that a large part of the accumulated particulates are induced -2- L ~1_

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to drop off the filter media surface and fall downwardly, under the influence of gravity and generally countercurrent to normal gas flow, toward and into a collection hopper.

In most industrial fabric filter installations of the type described above, the particulate gas stream approaches the filter through a delivery or conveying conduit having a cross-sectional area sized to effect gas stream displacement at sufficiently high velocities, usually in the order of 3500-4000 feet/min., to assure maintaining the particulate matter in suspended entrained condition therein.

Antithetically thereto, it has been recognised that high efficiency low loss filter operation and increased operating life of the filter components is dependent, at least in substantial part, on an equable distribution of deposited particulates on all the available filter media surface, on minimisation, if not avoidance, of turbulence in gas flow within the dirty plenum, on minimisation of particulate re-entrainment during or after media cleaning and on minimisation of localised wear and abrasion of filter components. As is apparent, the high velocity attended operating i parameters of the conduit confined approaching particulate bearing gas stream are basically antithetical to the desired optimum parameters of gas stream displacement within the filter housing and the attempted conversion thereof, normally within localised dimensional restraints, conventionally employs transition ducting and the interposition of turning vanes, baffle plates and related gas flow direction and velocity modifiers to the end of hopefully effecting a more equable distribution of Sthe incoming particulate bearing gas stream relative to the available media surface 4 and a marked reduction in its approach velocity in a short length of gas stream travel.

The transition of the shape and velocity of the incoming particulate bearing gas stream to the desirable flow conditions within the fabric filter media housing has been a long standing problem in this art. Many expedients, such as expansion of conduit dimension and the use of baffle plates, turning vanes, flow dividers, perforated plate diffusers, gratings, grids, various types of deflector or distribution plates and the location thereof in the path of the incoming gas stream and the like have been suggested to enhance fabric filter performance in the -3separation and collection of industrial dusts. Illustrative of some of such varied expedients are U.S. Patents 4,227,903; 4,544,383; 4,655,804; 4,213,766; 3,926,L;95; 3,831,354; 3,831,350; 3,739,557; 3,425,189 and 3,155,474. While most of such expedients have resulted in some degree of improved performance, the net results have fallen far short of optimum and the problem of achieving high efficiency and economic operation of industrial fabric filter dust collectors remains a continuing one.

In accordance with a first aspect of the present invention, therefore, there is provided apparatus for treating gas being conveyed in a moving high velocity gas stream of first predetermined cross-sectional area, gas treating means perimetrically defining a gas treatment zone of predetermined height, width and depth, a gas impervious housing perimetrically surrounding said gas treatment zone, gas inlet means for equably distributing and introducing said gas stream at reduced velocity into said gas treatment zone, said gas inlet means comprising, a first velocity reducing transition section having an entry port of said first predetermined cross-sectional area for reception of said high velocity gas 4.stream moving in a first flow direction, an exit port of second and larger predetermined cross-sectional area to dellver said gas stream therefrom at a first reduced velocity and in a second flow direction substantially perpendicular to said first flow direction, a second velocity reducing transition section having an entry port of said second predetermined cross-sectional area to receive said reduced velocity gas stream moving in said second flow direction from said exit port of said first transition section, an exit port of a third and still larger cross-sectional area to deliver said gas stream therefrom at a second and further reduced velocity and in a third flow direction substantially perpendicular to both said first and second flow directions.

-p A 17- Thus in one embodiment the invention may be briefly described as an improved inlet construction for industrial fabric filter dust collectors having an -4operative particle separation zone of predetermined height, width and depth located with a gas impervious housing and which includes, in its broader aspects, the employment of a pair of velocity reducing transition sections one of which has an exit port of perimetric contour sized and shaped to substantially conform to the height and width and perimetric contour of said particle separation zone and disposed in spaced fluid communication relation thereto through a complementarycontoured opening in said gas impervious housing with said exit port being traversed by a selectively portioned gas stream turning vane means. In association therewith, the invention further includes provision of means to equably distribute gas stream over the upstream surface of said vane means and to control the angle of gas stream approach thereto. In such broad aspect, particularly adapted for utilisation in fabric filters where the particle separation zone includes a plurality of elongate tubular fabric filter bags, the invention further includes a second and functionally similar velocity reducing transition section disposed immediately upstream of the above described transition section and which also includes a selectively positioned gas stream turning vane means traversing its exit port in association with means to equably distribute the incoming gas stream over the upstream surface of the turning vane means and to control the angle of approach o thereto.

In one broad embodiment, the invention includes provision for the gas stream exiting the first velocity direction which is a transition section to exit in a second direction which is substantially perpendicular to said first velocity reducing transition section to exit in a third direction which is substantially perpendicular to both said first and second flow directions.

0 In another broad embodiment, the invention includes provision of a turbulent flow reduction zone disposed immediately downstream of the gas stream S. turning vane means to permit dissipation of localised turbulence indu~ced by :passage of the gas stream through the turning vane means.

In one preferred embodiment of the invention the gas stream turning vane means is in the form of expanded metal grid means. Among the advantages of the subject invention is the provision of substantially improved operation of gas treating apparatus, and particularly for industrial fabric Filter dust collectors of both the tubular bag and panel types, characterised by improved degrees of equable distribution of the particulate laden gas steam relative to the available filter media surface, a markedly improved uniformity of dust loading of the ifiter elements, significantly higher separation and collection efficiencies, reduced losses, and increased service life of filter components. A further advantage is reduction of particle re-entrain-ment obtained in larger part by minim-isation, if not effective elimination, of upward movement of the dirty gas stream in the vicinity of the filter media.

The primary object of this invention is the provision of an improved gas stream inlet construction for gas stream treating apparatus such as industrial fabric filter type dust collectors.

In accordance with another aspect of the invention there is provided apparatus for treating gas being conveyed in a moving high velocity gas stream of first predetermined cross-sectional area, said apparatus including: gas treating means perimetrically defining a gas treatment zone of predetermined height, width and depth, a gas impervious housing perimetrically surrounding said gas treatment zone, gas inlet means for equably distributing and introducing said gas stream at reduced velocity into said gas treatment zone, said gas inlet means including a first velocity reducing transition section having an entry port of said first predetermined cross-sectional area for reception of said high velocity gas stream, an exit port of second and larger predetermined cross-sectional area to deliver said gas stream therefrom at a first reduced velocity, and first expanded metal grid means selectively disposed in and traversing said exit port for equably distributing and diverting said gas stream through a first change of direction, means defining a first turbulent flow reduction zone located immediately downstream of said first I. expanded metal grid means to permidt dissipation of localised turbulence induced by passage of said gas stream through said first expanded metal grid means, a second velocity reducing transition section having an entry port of said second predetermined cross-sectional area to receive said reduced velocity gas stream emanating from said first turbulent flow reduction zone, an exit port of a third and -6larger cross-section perimetrically contoured to substantially conform to the shape, height and width of said gas treatment zone and disposed in spaced fluid communicating relation thereto through a complementally contoured opening in said gas impervious housing to deliver said gas stream at a second and further reduced velocity, and second expanded metal grid means selectively disposed in and traversing said exit port for equably distributing and diverting said gas stream through a second change of direction, and means defining a second tur',ulent flow reduction zone immediately downstream of said second expanded metal grid means and intermediate said grid means and said gas treatment zone to permit dissipation of localised turbulence induced by passage of said gas stream through said second expanded metal grid means.

In accordance with yet a further aspect of the present invention there is provided a fabric filter dust collector for separating and collecting entrained particulate matter being conveyed in a moving high velocity gas stream of first predetermined cross-sectional area, including: a multiplicity of fabric filter particle separating means arranged in spaced parallel relation to each other and perimetrically defining a particle separation zone of predetermined height, width It and depth, a gas impervious housing surrounding said particle separation zone and dependently terminating in a particle collection hopper disposed beneath said filter bags, gas inlet means for equably distributing and introducing said gas stream and entrained particulate matter at reduced velocity into said particle separation zone, said gas inlet means, including a first velocity reducing transition section having an entry port of said first predetermined cross-sectional area for reception of said high velocity gas stream, an exit port of second and larger A' °25 predetermined cross-sectional area to deliver said gas stream therefrom at a first reduced velocity, and first expanded metal grid means selectively disposed in and traversing said exit port for equably distribution and diverting said gas stream p..O through a first change of direction, and a second velocity reducing transition section having an entry port of said second predetermined cross-sectional area to receive said reduced velocity gas stream emanating from said first velocity reducing transition section, an exit port of a third and larger cross-section perimetrically -7-

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contoured to substantially conform to the shape, height and width of said particle separation zone and disposed in spaced fluid communicatintg relation thereto through a complementallyy contoured opening in said gas impervious housing to deliver said gas stream therefrom at a second and further reduced velocity, and second expanded metal grid means selectively disposed in and traversing said exit port for equably distributing and diverting said gas stream through a second change of direction.

In accordance with yet another aspect of the present invention there is provided a fabric filter dust collector for separating and collecting entrained particulate matter being conveyed in a moving high velocity gas stream of first predetermined cross-sectional area, includintg a multiplicity of vertically oriented elongate tubular filter bags perimetrically defining a gas treatment zone of predetermined height, width and depth, a gas impervious housing perimetrically surrounding said particle separation zone and dependently terminating in a particle collection hopper disposed below said filter bags, gas inlet means for equably distributing and introducing said gas stream at reduced velocity into said particle separation zone, said gas inlet means including, a fkrst velocity reducing transition section having an entry port of said first predetermined cross-sectional area for reception of said high velocity gas stream, an exit port of second and larger predetermined cross-sectional. area to deliver said gas stream therefrom at a first reduced velocity, first expanded metal grid means selectively disposed in and traversing said exit port for equably distributing and diverting said gas stream through at least a 90 *change of direction and means for directing said gas stream *to approach said expanded metal grid means at an angle of from 5 *to 30 *from the plane thereof, means defining a first turbulent flow reduction zone located ixmmediately downstream of said first expanded metal grid means to permit dissipation of localised turbulence induced by passage of said gas stream through said first expanded metal grid means, I econd velocity reducing transition section having an entry port of said second predetermined cross-sectional area to receive said reduced velocity gas stream emanating from said first turbulent flow reduction zone, an exit port of a third and larger cross-section perimetrically contoured to -8substantially conform to the shape, height and width of said particle separation zone and disposed in spaced fluid communicating relation thereto through a complementally contoured opening in a side wall of said gas impervious housing to deliver said gas stream at a second and further reduced velocity toward said particle separation zone in a direction substantially perpendicular to the longitudinal center line of said filter bags, and second expanded metal grid means selectively disposed in and traversing said exit port for equably distributing and diverting said gas stream through at least a 90 change of direction, and means for directing said gas stream to approach said second expanded metal grid means at an angle of from 5 to 30 from the plane thereof, and means defining a second turbulent flow reduction zone immediately downstream of said second expanded metal grid means and intermediate said grid means and said particle separation zone to permit dissipation of localised turbulence induced by passage of said gas stream through said second expanded metal grid means.

In order that the invention may be more clearly understood and put into practical effect there shall now be described in detail preferred constructions of an apparatus for treating gas being conveyed in a moving high velocity gas stream of first predetermined cross-sectional area, in accordance with the invention. The description is given by way of non-limitative example only and 270" is with reference to the accompanying drawings, wherein: Figure 1 is a schematic oblique view of components of a conventional fabric filter type of dust collector employing elongate tubular filter bags in association with an exploded view of an improved gas stream inlet assembly embodying the principles of this invention; P' I Figure 2 is a second schematic oblique view of the assemblage of Figure 1 as viewed from a different direction; Figure 3 is an expanded side elevation, partially in section, of a preferred construction for the first velocity reducing transition section incorporated in the assemblage shown in Figures 1 and 2; Figure 4 is an enlarged scale plan view of suitable expanded metal grid Smaterial employable in the practice of this invention; -9-

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Figure 5 is a section as taken on the line 5-5 of Figure 4; Figure 6 is a side elevation, partially in section, of a preferred construction for the second velocity reducing transition section incorporated in the assembly shown in Figures 1 and 2; Figure 7 is a schematic representation of controlled gas stream approach to a selectively expanded metal grid and effective diversion thereof; Figure 8 is a plot of observed data illustrating drop in gas velocity and reduction in turbulence on the downstream side of an expanded metal grid; Figures 9A and 9B are schematic representations of a dust collector having a top entry gas inlet construction incorporating the principles of this invention; and Figures 1OA and 10B are schematic representations of a dust collector having a side entry gas inle~t construction incorporating the principles of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings and initially to Figures 1 aind 2 there is schematically depicted, by way of illustrative example, certnin components of a conventional industrial fabric filter dust collector, such as a MikroPulsaire collector as manufactured by the MikroPul Corporation of Summit, New Jersey. As there depicted, such a device conventionally includes a rectangular gas impervious housing, generally designated 8, made up of side panels 10, 12, 14 and 16 and dependently terminating in a pyramidal dust collecting hopper 18. Positioned within the housing 8 are a plurality of elongated vertically disposed fabric filter bags 20 conventionally suspended from a tube sheet 22 in uniform spaced relation from each other. Conventionally, the contained volume disposed beneath the tube sheet 22 and externally 6f the filter tubes 20 is broadly delineated as a "dirty gas plenum". Similarly, the contained volume located above the tube sheet 22 is broadly delineated as a "filtered" or "clean gas plenum", and such is normally vented through a clean gas delivery conduit 24.

In normal filtering operations, a particulate laden gas stream is most .comonl introduced inothe drair~ plenum through a breach in the wall of the %0 cmlo~ nt i -4 I

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10 yl Illl~lyl II^ dust collection hopper 18. Such gas is induced to flow upwardly toward and through the filter tubes 20 and into the clean gas plenum, usually by action of a fan or other prime mover located downstream of the delivery conduit 24. As previously noted and depicted in the above listed patents, turning vanes, baffle plates and other gas flow modifiers are often placed on the path of the incoming gas stream in the hopper 18 in an effort to change the direction of flow upwardly toward the filter media and to equably distribute the gas flow over the available fabric filter media surface. As the gas passes through the filter tubes 20 the particulates entrained therein are se-arated and accumulate on the upstream (here the external) surfaces of such tubes. As also previously pointed out, such accumulated particulates are removed by a cleaning operation such as pulse jet cleaning, reverse flow cleaning or by shaking. The particulates dislodged by the cleaning operation fall, under the influence of gravity and countercurrent to the direction of gas flow with undesirable amounts of re-entrainment thereof, into the dust collection hopper 18.

In order to provide a markedly improved equable distribution, nonturbulent and reduced velocity gas flow to the totality of available filter media surface, there is herein provided an improved gas inlet system. Such improved gas inlet system includes a first velocity reducing transition section, generally o designated 30, having an entry port 32 sized and shaped to receive a high particulate laden gas stream of a first predetermined cross-sectional area as determined by the dimensions and shape of a conveying duct 34. Conventionally such incoming "dirty" gas stream is conveyed at velocities of about 3500 to 4000 feet per minute to assure maintenance of particulate entrainment and to thereby 2 effectively preclude particle separation in the conveying system. Disposed at right angles to the entry port 32 is an exit port 36 of a second and appreciably larger cross-sectional area. In the illustrated embodiment, the width of the entry port 32 and exit port 36 are the same and the increase in exit port area is obtained by markedly increasing the length thereof. As shown in Figures 4 and 5, the expanded metal grid is a commercially available fabricated product that results from the selective deformation, as effected by either punching or by slitting and 'I A N

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11 drawing, of a flat sheet of metal to form a series of elongated but regular diamond, or preferably hexagonal, shaped openings 50 therein. The metal displaced by the deformation process forms a three-dimensional border surrounding each opening and this bordering metal is in the form of double-width angled strands 52 which are disposed at an angle to the base sheet's original planar dimension and determine the effective overall thickness of the deformed product and adjacent angularly skewed single width strands 4.

As indicated above, the expanded metal gild is a commercially available fabricated product, conventionally used as flooring for runways, Latwaiks, platforms, stair treads and like purposes. Suitable expanded metal grid material can be obtained as RYEX Expanded Metal Grating from the Ryerson Division of Inland Steel Corporation and from McNichols Co. of Tampa, Florida. As identified i the literature of the above fabricators, the type of expanded metal grid that is of utility in the performance of this invention is identified as the "standard" version of expanded metal grid material wherein the strands are angularly offset.

S While such "standard" version of expanded metal grid material is available with 4., 4: 0. either diamond-shaped or hexagonal-shaped openings 50, the hexagonal-shaped opening material has proven more effective in the diversion of gas flow and is preferred. Available evidence to date indicates that the diamond shape is only 2- about 70% as effective as the hexagonal shape for diverting gas flow.

Carbon steel grades of domestically available expanded metal grid material are apparently produced as 1.2, 2.5, 3.0, 3.14, 4.0, 4.25, 5, 6.26 and 7 ao pounds per square foot grades. Of these, hexagonal opening material of the 4.0, 5.0, 6.25 and 7.0 pound per square foot grades are the most useful. As will 2 5. be apparent, it is the geometrical configuration of the expanded metal grid material that is the controlling operating parameter and, as such, other material of metallic or non-metallic character and formed into a similar configuration could also be employed.

4 00 Efforts to date have indicated~ that the mere use of expanded metal will not, in and of itself, provide for improved fiter performance. Other factors that must be observed include the selective posiiiioning of the metal grid material, the 12 p.

-7 control of the angle of approach of the gas stream to the face of the expanded metal grid, the equable distribution of the approaching gas stream over the full surface of the selectively positioned expanded metal grid and reducing the gas stream velocity to a degree desirable to decrease or minimise turbulence.

Experiments have indicated that, as the bordering strands 52 and 54 defining the hexagonal openings in the expanded metal grid become wider and thicker, in accordance with the weight of the product in pounds per square foot, and the openings 50 become smaller and the total free area of such openings decreases, the greater is the magnitude of the deflection of the gas stream. Thus it appears that, for a given gas stream approach angle, the heavier grades of expanded metal will deflect the gas stream flow more than the lighter grades. Figure 7 depicts the desired orientation of the expanded metal grid material relative to the approaching gas stream. It has been noted that the angle of gas stream deflection not only varies for the different grades of expanded metal but also with each grade as the approach angle is changed. In general an approach angle a of from 5" to 30' is preferred. Stated otherwise, correct orientation of the expanded metal grid is present when the angle of approach of the incoming gas stream is at least normal to or forms an obtuse angle f9 with the double width strand surface 52.

Referring back to Figures 1 and 2 it will now be apparent that the converging character of the transition section bottom wall 44 relative to the grid 42 and the resultant progressively decreasing cross-sectional area of the section in the direction of gas flow, together with the vanes 40, are directed to providing an equable distribution of gas flow as it approaches the expanded metal grid 42 disposed in the exit port 36. In association therewith, the markedly increased area of the exit port 36 as compared with the cross-sectional area of the entry port 32 functions to provide a marked reduction in gas velocity as it is diverted and passes upwardly through the exit port 36.

The passage of the gas stream through, and diversion by, the expanded metal grid 42 will inherently produce some degree of localised turbulence in the form of eddy currents and vortices. In order to dissipate and effectively eliminate 'ia such localised turbulence, a turbulent flow reduction zone 60, defined by the t c:1~ i r" r 13 upstream surface of the grid 42 and gas-impervious side walls 62 and end walls 64, is located immediately downstream of the grid 42. Such zone 60 is in the general nature of a dclose-walled conduit of limited length and of a cross-sectional extent equal to that of the exit port 36. Such zone 60 functions to permit dissipation of localised turbulence induced by the passage of the gas stream through the first expanded mecal grid 42 and further reduction in velocity thereof.

Referring now to Figures 1, 2, 3 and 6, the exit port of the turbulent flow reduction zone 60 serves as the entry port 70 of a second velocity reducing transition section, generally designated 72. The entry port 70 is suitably of a crosssectional area generally equal to that of the exit port 36 of the first transition section 30. Disposed at right angles to such entry port 70 is an exit port 74 of markedly greater cross-sectional area. Desirably, the exit port 74 of this second transition section 72 is of a perimetric contour, here rectangular, sized to substantially conform to the height and width of the particle separation zone as the latter is defined by the overall height and width of the assemblage of filter bags within the dirty gas plenum. As was the case with the first transition section the exit port 74 is traversed by a second expanded metal grid 76.

In order to effect an equable distribution of the particulate gas stream over the available area of the exit port 74 and at a proper angle of approach, as above described, to the expanded metal grid 76, the second transition section 72 is also of tapering character and of progressively decreasing cross-sectional area in the direction of gas flow. If desired, flow splitting channel members or vanes of the type shown and described in conjunction with the first transition section may also be included in the second transition section 72. The turbulence reduced and reduced velocity gas stream emanating from the first turbulent flow reduction zone 60 will be markedly further reduced in velocity and diverted at right angles as it passes through the expanded metal grid 76 to a direction effectively perpendicular to the surface of the filter bags 20 and equably distributed over an area substantially conforming both in shape and dimension to that of the particle separation zone. As will be apparent to those skilled in this art local conditions, such as the presence of obstructions, catwalks and thb like may function to limit -14- 2 the area of the exit port 74. Desirably, however, such port should be as large as possible with respect to the height and width of the particle separation zone.

Since the passage of the gas stream, albeit at reduced velocity, through the second expanded metal grid 76 will be attended by localised turbulence adjacent the downstream surface thereof, a second turbulence reduction zone again in the general form of a short length dosed conduit of a cross-section conforming generally in size and shape to the exit port and formed by walls 82, 84, 86 and 88, is disposed immediately downstream of the grid 76 and intermediate said grid and the particle separation zone within the filter housing. The downstream end of the second turbulence reduction zone 80 is in fluid communication with an opening 90 in the wall of the perimetric housing 8, again sized to substantially conform both in shape and dimension with the particle separation zone.

Figure 8 illustrates the marked drop in localised gas stream velocity within the turbulence reduction zones and immediately downstream of the expanded metal grids.

foSince the passage of particulates through the expanded metal grids will, for at least some types of particulates, result in a separation and accumulation of S particulate matter on the surface of the grids, it will be desirable in such instances to provide some means for dislodging such accumulated particulates. To the above end, a rapping device, as for example in the form of a solenoid operated hammer member 100, may be positioned on the turbulence reduction zones to impact and jar the grids.

In summary, in the depicted unit the first transition section 30 will operate to direct the incoming high velocity gas stream through a right-angled turn. As the gas flow enters the initial expanded metal grid 42, the latter functions to both divert essentially at right angles and, in association with the turbulent flow reduction zone 60, to uniformly reduce the gas stream velocity prior to its entry into the second transition section 72. Desirably, the first expanded metal grid 42 has the same width as the inlet conduit 34 and a length that matches the width of the second expanded metal grid 76. If equably distributed, the gas flow -t encountering the first expanded metal grid 42 will be expanded with a consequent velocity reduction and directed to properly approach the second expanded grid 76 in equably distributed character. The reduced velocity gas stream will again be turned at right angles and further reduced in average velocity as it passes through the second expa.aded metal grid 76 and zone 80. The gas stream emanating from the second grid 76 and adjacent turbulence reduction zone 80 will be of a perimetric contour, both as to shape and dimension, desirably substantially matching that of the opening 90 in the housing 8 and of the particle separation zone therewithin and will be moving in a direction effectively perpendicular to the centerline of the filter media assembly. With the herein disclosed two stage transition sections and expanded metal grids disposed in the exit ports thereof the velocity of the gas stream can readily be reduced by a factor of 10 or more and converted in form for a markedly improved equable distribution relative to the ,available filter media surfaces and in a path devoid of upward components with consequent reduction of particle re-entrainment. With the flexibility afforded by use of selective approach angles to the expanded metal grids of from 5 to degrees, depending upon the grade of expanded metal employed in each of the two stages, any number of specific stage arrangements can be designed to accommodate various inlet gas velocities, various dust loadings and other 2-Q' characteristics of the particulate-laden gas stream being conveyed to the filter.

As will now be apparent the foregoing depicted an described construction functions to effect entry of the gas stream into the housing substantially perpendicular to the longitudinal axis of the housing 8 and to the longitudinal centerline of the filter media disposed therewithin. Such direction of 25 entry effectively eliminates the generation of any upwardly moving components

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of the gas stream within the housing with the heretofor described diminution of re-entrainment.

The above described nature of direction of reduced velocity gas stream entry also results in a progressive diminution of gas stream velocity as the gas steam traverses the depth of the particle separation zone.

The above described side entry of the gas steam into the housing -16i

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7 4* L __A initially brought the incoming gas stream to the filter in the vicinity of the lower portion of the housing. Depending upon the local geometry of the filter at the locus of use thereof, gas stream entry into the first transition section 30 can be effected at the top of the housing 8, as shown in Figs. 9A and 9B, or from the side housing 8, as shown in Figs. 10A and It will also be apparent to those skilled in the art that the transition sections could be effected by having the solid base thereof disposed parallel to the direction of gas flow and by having the expanded metal grids disposed at an angle thereto and at rights angles to the plane of the entry aperture.

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Claims (38)

1. Apparatus for treating gas being conveyed in a moving high velocity gas stream of first predetermined cross-sectional area, said apparatus including: gas treating means perimetrically defining a gas treatment zone of predetermined height, width and depth; a gas-impervious housing perimetrically surrounding said gas treatment zone; gas inlet means for equably distributing and introducing said gas stream at reduced velocity into said gas treatment zone, said gas inlet means including a first velocity reducing transition section having an entry port of said first predetermined cross-sectional area for reception of said high velocity gas stream moving in a first flow direction, an exit port of second and larger predetermined cross-sectional area to deliver said gas stream therefrom at a first reduced velocity and in a second flow direction substantially perpendicular to said first flow direction, a second velocity reducing transition section having an entry port of said second predetermined cross-sectional area to receive said reduced velocity gas stream moving in said second flow direction from said exit port of said first transition section, an exit port of a third and still larger cross-sectional area to deliver said gas stream therefrom at a second and further reduced velocity and in a third flow direction substantially perpendicular to both said first and second flow directions.

2. Apparatus as claimed in claim 1, further including an array of selectively positioned gas stream turning vane means disposed in and traversing the exit ports in said first and second transition sections.

3. Apparatus as claimed in claim 1 or claim 2, wherein said turning vane means includes expanded metal grid means.

4. Apparatus as claimed in any one of claims 1 to 3, further including means defining a turbulent flow reduction zone located immediately downstream of the exit port of said first transition section to permit dissipation of localised turbulence induced by diversion of said gas stream from said first flow direction to said second flow direction.

5. Apparatus as claimed in any one of the preceding claims, further including means defining a turbulent flow reduction zone located immediately S -18- '2- downstream of the exit port of said second transition section to permit dissipation of localised turbulence induced by diversion of said gas stream from said second flow direction to said third flow direction.

6. Apparatus as claimed in claim 5, wherein said turbulent flow reduction zone includes an inclined bottom wall to prevent accumulation of particulate matter being carried by said gas stream thereon.

7. Apparatus as claimed in any one of the preceding claims, wherein said second flow direction is disposed at an angle between 75' and 120 relative to said first flow direction.

8. Apparatus as claimed in any one of the preceding claims, wherein said third flow direction is disposed at an angle between 75 and 120 relative to said second flow direction.

9. Apparatus as claimed in any one of claim. 2 to 8, wherein said gas streams approach said turning vane means at an angle between 5 and 30' from the longitudinal axis thereof. Apparatus as claimed in any one of claims 3 to 9, wherein said expanded metal grid means are of overall planar character for equally distributing and changing the direction of flow of said gas stream.

11. Apparatus as claimed in any one of the preceding claims, wherein said exit port of said second transition section is perimetrically contoured to conform to the shape, height and width of said gas treatment zone and is disposed in spaced fluid communicating relation thereto through a complementally contoured ,0 y opening in said gas impervious housing.

12. Apparatus as claimed in any one of the preceding claims, wherein the gas treatment means includes particle separating means.

13. Apparatus as claimed in any one of the preceding claims, wherein said gas treatment zone includes a multiplicity of fabric filter particle separating means arranged in spaced parallel relation to each other.

14. Apparatus as claimed in any one of the preceding claims, wherein said first velocity reducing transition section includes flow directing vanes means for Seffecting an equable distribution of the approaching gas stream on the upstream -19 d IY side of the exit port thereof. Apparatus as claimed in any one of the preceding crlaims, wherein said gas treatment means includes elongate tubular fabric filter bags.

16. Apparatus as claimed in any one of claims 2 to 15, further including means for dislodging particulate matter accumulated on said turning vane means.

17. Apparatus as claimed in any one of the preceding claims, wherein the gas stream exiting from the exit part of the second transition section enters said gas impervious housing through a side wall thereof.

18. Apparatus as claimed in any one of the preceding claims, wherein the gas stream exiting from the exit port of said second transition section enters said gas impervious housing through a dependent particle collecting nozzle portion thereof.

19. Apparatus for treating gas being conveyed in a moving high velocity gas stream of first predetermined cross-sectional area, said apparatus including: gas treating means perimetrically defining a gas treatment zone of predetermined height, width and depth, a gas impervious housing perimetrically surrounding said gas treatment zone, gas inlet means for equably distributing and introducing said gas stream at reduced velocity into said gas treatment zone, said gas inlet means including a first velocity reducing transition section having an entry port of said first predetermined cross-sectional area for reception of said high velocity gas stream, an exit port of second and larger predetermined cross-sectional area to deliver said gas stream therefrom at a first reduced velocity, and first expanded S metal grid means selectively disposed in and traversing said exit port for equably distributing and diverting said gas stream through a first change of direction, 25 means defining a first turbulent flow reduction zone located immediately downstream of said first expanded metal grid means to permit dissipation of localised turbulence induced by passage of said gas stream through said first expanded metal grid means, a second velocity reducing transition section having an entry port of said second predetermined cross-sectional area to receive said reduced velocity gas stream emanating from said first turbulent flow reduction zone, an exit port of a third and larger cross-section perimetrically contoured to 1 y J I c 1, h. i~ substantially conform to the shape, height and width of said gas treatment zone and disposed in spaced fluid communicating relation thereto through a complementally contoured opening in said gas impervious housing to deliver said gas stream at a second and further reduced velocity, and second expanded metal grid means selectively disposed in and traversing said exit port for equably distributing and diverting said gas stream through a second change of direction, and means defining a second turbulent flow reduction zone immediately downstream of said second expanded metal grid means and intermediate said grid means and said gas treatment zone to permit dissipation of localised turbulence induced by passage of said gas stream through said second expanded metal grid means. Apparatus as claimed in claim 19, wherein said gas stream approaches said expanded metal grid means at an angle of from 5 to 30' from the plane thereof.

21. Apparatus as claimed in claim 19 or claim 20, wherein said gas treatment means includes particle separation means.

22. Apparatus as claimed in any one of claims 19 to 21, wherein said first velocity reducing transition section includes means for effecting a equable distribution of the approaching gas stream on the upstream side of said expanded metal grid means.

23. Apparatus as claimed in any one of claims 19 to 22, wherein said entry and exit ports in said first velocity reducing transition section are at right angles to each other.

24. Apparatus as claimed in any one of claims 19 to 23, wherein said entry and exit ports in said second velocity reducing transition sections are at right angles to each other. The apparatus as claimed in any one of claims 19 to 24, wherein said means defining said second turbulent flow reduction zone is perimetrically contoured to substantially conform to the height and width of said particle separation zone.

26. Apparatus as claimed in any one of claims 19 to 25, wherein said first f .11 V.; 21 change of direction is at least

27. Apparatwls as claimed in any one of claims 19 to 26, wherein said second change of direction is at least 90

28. A fabric filter dust collector for separating and collecting entrained particulate matter being conveyed in a moving high velocity gas stream of first predetermined cross-sectional area, including: a multiplicity of fabric filter particle separating means arranged in spaced parallel relation to each other and perimetrically defining a particle separation zone of predetermined height, width and depth, a gas impervious housing surrounding said particle separation zone and dependently terminating in a particle collection hopper disposed beneath said filter bags, gas inlet means for equably distributing and introducing said gas stream and entrained particulate matter at reduced velocity into said particle separation zone, said gas inlet means, including a first velocity reducing transition section having an entry port of said first predetermined cross-sectional area for reception of said high velocity gas stream, an exit port of second and larger N predetermined cross-sectional area to deliver said gas stream therefrom at a first ri reduced velocity, and first expanded metal grid means selectively disposed in and traversing said exit port for equably distrib-don and diverting said gas stream r through a first change of direction, and a second velocity reducing transition 20.4 section having an entry port of said second predetermined cross-sectional area to receive said reduced velocity gas stream emanating from said first velocity reducing transition section, an exit port of a third and larger cross-section perimetrically 4 contoured to substantially conform to the shape, height and width of said particle 4 separation zone and disposed in spaced fluid communicating relation thereto through a complementally-y contoured opening in said gas impervious housing to deliver said gas stream therefrom at a second and further reduced velocity, and second expanded metal grid means selectively disposed in and traversing said exit port for equably distributing and diverting said gas stream through a second change of direction.

29. The fabric filter dust collector apparatus as claimed in claim 28, further 1 l 1 including means defining at least one turbulent flow reduction zone located ±i immediately downstream of one of said expanded metal grid means to permit dissipation of localised turbulence induced by passage of said gas stream through said expanded metal grid means. The fabric filter dust collector apparatus as claimed in claim 28 or claim 29, further including means defining a first turbulent flow reduction zone imwediately downstream of said first expanded metal grid means to permit dissipation of localised turbulence induced by passage of said gas stream through said first expanded metal grid means, and means defining a second turbulent flow reduction zone immediately downstream of said second expanded metal grid means and intermediate said grid means and said particle separation zone to permit dissipation of localised turbulence induced by passage of said gas stream through said second expanded metal grid means.

31. The fabric filter dust collector apparatus as claimed in any one of claims 28 to 30, wherein said entry and exit ports in each of said velocity reducing transition sections are at right angles to each other and each said transition section is of progressively diminishing cross-sectional area to effect a substantially equable distribution of the approaching gas stream on the upstream side of each of the expanded metal grid means.

32. The fabric filter dust collector apparatus as claimed in any one of claims 28 6o 31, further including flow directing vanes in at least one of said velocity reducing transition sections.

33. The fabric filter dust collector apparatus as claimed in any one of claims to 32, wherein said means defining said second turbulent flow reduction zrine is perimetrically contoured to substantially conform to the shape, height and width of said particle separation zone.

34. The fabric filter dust collector apparatus as claimed in any one of claims 28 to 33, wherein said gas stream approaches said expanded metal grid means at an angle of from 5' to 30" from the plane thereof. The fabric filter dust collection apparatus as claimed in any one of claims 28 to 34, wherein said first change of direction is at least

36. The fabric filter dust collection apparatus as claimed in any one of claims -23- r 28 to 35, wherein said second change of direction is at least

37. The fabric filter dust collecting apparatus as claimed in any one of claims 28 to 36, wherein said fabric filter particle separating means includes elongate tubular filter bags.

38. The fabric filter dust collecting apparatus as claimed in any one of claims 28 to 36, wherein said fabric filter particle separating means includes elongate filter panels.

39. The fabric filter dust collection apparatus as claimed in any one of claims 28 to 38, further including means for dislodging particulate matter that accumulates on said expanded metal grid means. The fabric filter dust collection apparatus as claimed in any one of claims 28 to 39, wherein said gas passing through the opening in the housing is moving in a direction substantially perpendicular to the center line of said particle separation means.

41. A fabric filter dust collector for separating and collecting entrained particulate matter being conveyed in a moving high velocity gas stream of first predetermined cross-sectional area, incuding a multiplicity of vertically oriented elongate tubular filter bags perimetrically defining a gas treatment zone of S predetermined height, width and depth, a gas impervious housing perimetrically surrounding said particle separation zone and dependently terminating in a particle collection hopper disposed below said filter bags, gas inlet means for equably distributing and introducing said gas stream at reduced velocity into said S: particle separation zone, said gas inlet means including, a first velocity reducing transition section having an entry port of said first predetermined cross-sectional area for reception of said high velocity gas stream, an exit port of second and larger predetermined cross-sectional area to deliver said gas stream therefrom at a first reduced velocity, first expanded metal grid means selectively disposed in and traversing said exit port for equably distributing and diverting said gas stream through at least a 90" change of direction and means for directing said gas stream to approach said expanded metal grid means at an angle of from 5 to 30 from the plane thereof, means defining a first turbulent flow reduction zone located .I I, o I 4~ 'i s r- r r r I~ I" -12' -24- ppI- immediately downstream of said first expanded metal grid means to permit dissipation of localised turbulence induced by passage of said gas stream through said first expanded metal grid means, a second velocity reducing transition section having an entry port of said second predetermined cross-sectional area to receive said reduced velocity gas stream emanating from said first turbulent flow reduction zone, an exit port of a third and larger cross-section perimetrically contoured to substantially conform to the shape, height and width of said particle separation zone and disposed in spaced fluid communicating relation thereto through a complementally contoured opening in a side wall of said gas impervious housing to deliver said gas stream at a second and further reduced velocity toward said particle separation zone in a direction substantially perpendicular to the longitudinal center line of said filter bags, and second expanded metal grid means selectively disposed in and traversing said exit port for equably distributing and diverting said gas stream through at least a 90 *change of direction, and means for directing said gas stream to approach said second expanded metal grid means at an angle of from 5" to 30" fiom the plane thereof, and means defining a second turbulent flow reduction zone immediately downstream of said second expanded metal grid means and intermediate said grid means and said particle separation zone to permit dissipation of localised lurbulence induced by passage of said gas stream through said second expanded metal grid means.

42. The fabric filter dust collector apparatus as claimed in claim 41, wherein S said first and second expanded metal grid means have a plurality of polygonal openings therein bounded by a three-dimensional border of angularly offset strands, at least one strand of which is of a double width disposed in generally '25 facing relation to the approaching gas stream.

43. The fabric filter dust collector apparatus as claimed in claim 41 or claim 42, further including means for dislodging particulate matter accumulating on said expanded metal grid means.

44. The fabric filter dust collector apparatus as claimed in any one of claims 41 to 43, wherein said polygonal openings in said first and second grid means are hexagonal. 4: r i ~t ct:::f 25 Apparatus for treating gas being conveyed in a moving high velocity gas stream of first predetermined cross-sectional area, substantially as described herein with reference to the accompanying drawings.

46. A fabric filter dust collector, substantially as described herein with reference to the accompanying drawings. DATED the 11th day of June, 1991 HUSOKAWA MICRON INTERNATIONAL INC. by their Patent Attorneys CALLINAN LAWRIE 0 4 0 4, 0S 0- l 0 -j S0K o n *BS :7- -26-