Removable verticle media insert system for air treatment

Abstract

A support framework for containing a granular medium that is used to remediate corrosive vaporous pollutants in an air stream. The support framework is situated within a plenum and comprises two concentric open-lattice weave cylinders made from corrosion resistant fiberglass reinforced plastic (FRP). The cylinders are of differing diameters and the granular medium is placed into and contained within the open space formed between the inside wall of the outer cylinder and the outside wall of the inner cylinder. The open-lattice weave design allows a greater radial flow through the medium per unit of time, doing so with less pressure drop and using less energy than the prior art. The use of FRP to form the cylinder walls allows creation of large units that are suitable for use in municipal and industrial settings, which was not possible previously.

Description

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to an apparatus and process for treating air streams to remove pollutants. More particularly it relates to the use of open weave fiberglass reinforced plastic (“FRP”) to create a concentric framework within a plenum containing a porous granular media which facilitates interactions which capture pollutants from an air stream being moved horizontally and radially through the media either inwardly or outwardly.

2. Description of the Relevant Prior Art

Vaporous pollutants, which are frequently toxic or corrosive or both, are created in a multiplicity of municipal, commercial and agricultural processes and become part of output airstreams. Treatment of these output airstreams to strip out the pollutants is important to human health, to prevent damage to equipment, to protect the environment and to provide odor control.

Typical treatment of airstreams is to pass the stream through a reactive media in a containment structure within a plenum which serves as a reactor. Issues include plenum size, choice of material and energy consumption. In instances where the air stream contains corrosive gases, the materials used to form the containment structure are chosen to be as non-reactive as practical. This need has traditionally placed a limitation upon the size of media containment structures. Used alone as inert structural materials, plastics do not have the structural strength for creating large structures. Metals have the strength but corrode too easily.

Over time, two differing reactor designs have emerged. The earlier reactors used vertical flow of the air stream under pressure or vacuum, thus requiring a considerable consumption of energy in their operation.

On the other hand, radial flow reactors work at ambient or just above ambient pressures, requiring no compressors or vacuum units or expensive seals for their operation and presenting less potential for escape of untreated air into the environment.

In general, radial air-flow reactors consist of a containment vessel (a plenum) within which is located a series of baffles that separate the incoming polluted air from the exiting purified air. The space between the baffles holds and supports the remediation media. Commonly, the baffles consist of a pair of cylindrically shaped elements, one having a smaller diameter than the other and being concentrically located within the former. These cylinder walls have pore spaces through which the air passes. In an inward flow reactor, the air stream moves from an inlet manifold through the outer baffle into the remediation medium, and then through the inner baffle and into an exit manifold. Or the reactor can be designed to have a reversed flow direction described as an outward flow reactor.

Past radial flow reactor designs suffered from some problems of their own. One of the main problems being that the structural weakness of non-reactive media containment materials prevented the creation of units large enough to efficiently handle large volumes of pollutants. Increasing the bulk of the solid portion of the containment cylinders to make the walls stronger reduced the amount of open air flow space within the cylinder walls, thus decreasing the efficiency of and increasing the cost of operating the unit.

Statement of the Objectives

Accordingly, it is an objective of this invention to provide a corrosion resistant media support system for use in a radial flow reactor, said support system having the structural strength allowing for its use in large commercial and municipal reactors, yet also having a flexibility of design allowing for use in small sized reactors, and at the same time providing media containment support walls with a lower solid to through space ratio that allows for the remediation of a greater volume of air per unit of time relative to other comparably sized units and doing so with a low pressure drop from the inlet side to the outlet side of the media containment structure, thus simplifying installation and conserving energy.

Another object of the invention is to provide a containment structure that is equally suitable for use with a variety of media, including porous granular substrate media such as activated carbon, or media such as foam and reticulated foam Another object of this invention is to provide a containment structure design that allows creation of supports that can be retrofitted into existing reactors.

Other objectives, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the invention and the accompanying drawings.

SUMMARY OF THE INVENTION

The invention involves the creation of two corrosion resistant fiberglass-reinforced plastic (FRP) cylinders of differing diameters that have been extruded in a woven pattern with approximately a 68% through space ratio; the walls of each of which cylinders comprise a three layered construction that is fused into a unit, the layers being: an external FRP wall, a central corrosion resistant screen material and finally an internal FRP wall that matches the configuration of and is arranged colinear with the open weave pattern of the outer FRP segment of the wall. The cylinders are concentrically situated one within the other within a vertically standing plenum, the space between the two cylinders being designed to hold a medium capable of remediating toxic, corrosive vapors that are carried to it in an air stream that moves through the purification system in a radial flow direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objectives and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings illustrating a preferred embodiment pf the invention. The drawings are:

FIG. 1 a. Presents a cross sectional view looking down onto the top of a media support cylinder.

FIG. 1 b. Presents a diagrammatic side view of a section of a media support cylinder wall.

FIG. 2. Presents a perspective view as a vertical cross section at the vertical axis center of a radial-flow air remediation system plenum.

FIG. 3. Presents a sectional perspective view at the top of the body section of a remediation system plenum with the removable split-cover section removed over one half of the unit.

FIG. 4. Presents a lateral view of the inter-connected attachment of the removable split-cover sections of the plenum's top cover as well as the relationship of the removable split-cover section to the base section of the plenum.

FIG. 5. Presents a view of a portion of the media containment section of a large radial flow vaporous pollutant remediation plenum depicting a laborer retrofitting a probe for an air quality monitoring device through to the inside of the external FRP lattice wall of the media support system and into the media containment space.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The invention involves the creation of two open weave walled cylinders of different diameters that are made of corrosion resistant fiberglass-reinforced plastic (FRP) or other corrosion resistant material and that are situated one within the other within a vertically standing plenum serving as a radial flow air purification reactor.

Viewed from above in FIG. 1a, the cylinder walls consist of a sandwich of three layers that are fused into a singular element during their fabrication: an external layer of corrosion resistant FRP 1FIG. 1a, a central screen material layer 2FIG. 1a, and an internal layer of corrosion resistant FRP 3FIG. 1a.

Seen in a sectional side view, each continuous basket weave FRP cylinder displays an outer layer of FRP created in a diamond shape pattern 1FIG. 1b with the middle layer screen material of the cylinder wall 2FIG. 1b filling the open spaces left within the diamond shaped open spaces of the outer cylinder wall layer 1; said screen material 2 having a pore size slightly smaller than the size of the units of the purification media that is to be contained. The central most FRP layer of the wall is not visible, being of the same design and created to lie in alignment with the outer FRP layer 1FIG. 1b but being situated internal to the screen layer 2.

The wall elements, when viewed from the side as in FIG. 1b, present as a fused panel in which the central-core section 2 is a corrosion resistant screen having an approximate pore space to solid material ratio of 50%; the superimposed internal and external support frame layers 1 are solid and present no pore space within their lattice work walls, and represent approximately 32 percent of the total cylindrical wall area; the total configuration creating an excellent pore space to solid support ratio of approximately 30-34% of the support cylinder's wall area while creating an exceptional structural strength of the cylinder walls.

When viewing a perspective view as a vertical cross section at the longitudinal center of an air remediation plenum FIG. 2; the media containment space 4FIG. 2, is bounded externally by the lateral FRP cylinder wall 3 and centrally by the inner FRP cylinder wall 5; space 4 being designed to contain media capable of remediating toxic, corrosive vapors that are carried to it in an air stream that moves through the purification system in a radial flow direction. The cylindrical support walls 3 & 5FIG. 2 are aligned coaxially with the vertically standing external wall of the plenum 7a, and provide for a uniform thickness of remediation medium in a radial direction between the inlet-manifold side 2 and the outlet-manifold side 6 of the plenum over the entire length of the cylindrical media bed 4.

The granular porous substrate material held within the cylinders 3 & 5FIG. 2, commonly activated charcoal, but not limited to being activated charcoal, is commonly 3-4 mm in diameter, but could be larger or smaller dependent upon the needs of the particular application.

By presenting a perspective view as a vertical cross section at the vertical axis center of a radial-flow air remediation system plenum as a preferred embodiment of a complete radial flow air purification unit, FIG. 2 presents an example from which can be learned one method of aligning and supporting the FRP media support walls that are the foundation of this invention. This example is not intended to represent nor should it be taken to be the sole manner of appropriately aligning and supporting the FRP cylinders, rather, it is presented to educate people familiar with the art as to a method of fabricating a plenum such that there is ease of introduction and removal of the FRP cylinders into the plenum as needed, and such that control of the air stream pathway throughout the plenum presents minimal possibility of the escape of unremediated air into the environment while providing maximal flow of the airstream from the inlet to the outlet side of the plenum with a minimal pressure drop between the inlet and the outlet sides of the unit.

The plenum FIG. 2 that contains cylinders 3 & 5FIG. 2 comprises a base section 7abcdefg, and a removable top section 9-14. Unremediated air enters the plenum through the air intake pipe 1FIG. 2, and enters an inlet manifold 2, the lateral wall of which inlet manifold 2 is formed by the inner aspect of the side wall 7a of the plenum. The unremediated air then flows horizontally through the lateral FRP support cylinder wall 3FIG. 2, then continues radially through the media bed section 4, next passing through the internal most FRP support cylinder wall 5, and into the outlet manifold 6 after which it exits as remediated air.

For use within a radial flow remediation plenum designed to allow removal of the media support as a unitary segment for purposes of media replacement, the bases of the FRP cylinders are joined, forming a basket shape, however, in the present embodiment, the FRP cylinders 3 & 5FIG. 2 are not removed during the process of replacing spent remediation media and so are not conjoined at the base. In the present embodiment, two concentric, circular positioning sections 7c & 7d FIG. 2 are formed by projections upwards from the floor 7b of the plenum. Projection 7c FIG. 2 has an internal diameter slightly larger than that of the external diameter of the lateral FRP support cylinder wall 3, and serves to position the base of that cylinder and to prevent lateral spread of the base of that cylinder under the weight of the media particles in the media bed section 4. Projection 7d FIG. 2 has an external diameter that is slightly smaller than the internal diameter of the central most FRP support tube wall 5, and serves to position the base of that cylinder and to prevent displacement of the base of that cylinder in towards the outlet manifold 6 under the weight of the media particles located in the media bed section 4.

The circular floor section 7b FIG. 2 that forms the bottom seal section of the plenum, is appropriately anchored by one of several means to an appropriate foundation section, and at its periphery is joined to the side wall 7a of the plenum, which side wall forms the lateral boundary of the inlet manifold 2. Above, said side wall 7a FIG. 2 is continuous with the vertical collar 7efg portion of the plenum's base section 7abcdefg. Said collar 7efg FIG. 2 forms a constriction at the top of said side wall 7a section in which section 7e of said collar 7efg is seen as an inward projection at 90° to the side wall 7a, and then turns 90° upwards as the vertical section seen at 7f; said vertical section 7f then reflects laterally at 90° to form the laterally projecting flange 7g that serves as the top plate of the base section 7abcdefg of the plenum.

The configuration of collar 7efg FIG. 2 specifically provides: a horizontal projection 7e FIG. 2 that forms the top sealing element covering the intake manifold 2; a vertical portion 7f that serves as the top guide/support for positioning the external FRP cylinder 3; and a laterally projecting horizontal flange 7g that is perforated by holes (not visible) designed to receive bolts/nuts 10 that serve to attach the plenum's base section 7abcdefg to the removable split cover section 9. It will be noted that a gasket 8FIG. 2 is interposed between flange 7g and the removable split-cover 9 section of the plenum and serves to seal the junction of the two parts. A circular, central cutout in removable split-cover section 9FIG. 2 represented by line cl serves as the top guide/support for positioning the internal FRP cylinder 5 and keeps the top of said cylinder properly aligned such that it forms the peripheral boundary of the exit manifold 6 within the base section 7abcdefg of the plenum. Removable split-cover section 9FIG. 2, has 2 sets of holes, a peripheral set designed to receive bolts/nuts 10, and a series surrounding the central cutout that receive bolts/nuts 12 which bolts/nuts affix said split-cover section to a surmounting cover section collar 13abc.

As will be seen in FIGS. 3 and 4, removable split-cover section 9 is actually formed by the combination of two mirror image sections, the details of which configuration is not presented here for sake of clarity. A series of transverse braces (not shown but described as internal cross braces 15a & 15b in FIG. 3, affix the top portion of the central most FRP support cylinder wall 5FIG. 2 to the vertical section 7f of the base section vertical collar 7efg and prevent distortion of said support cylinder wall in towards the outlet manifold 6 under the weight of the media in the media bed section 4.

Cover section collar 13abc FIG. 2 is formed of an inferior, horizontally aligned flange 13a through which the bolts 12 pass in order to attach said collar to top section 9. At its central termination, flange 13a FIG. 2 then turns upwards at 90° as section 13b which then is continuous with the 90° laterally projecting flange section 13c. Said flange section 13c FIG. 2 being pierced by holes 14 to receive bolts (not shown) for attachment to an exit duct that carries the remediated air into the environment.

Lines a¹ and a² FIG. 2 represent the internally projecting curvature of the internal aspect of the side wall 7a of the plenum. Lines b¹ and b² FIG. 2 represent the internally curved projections of the internal aspect of the lateral FRP support cylinder wall 3. Lines c¹ and c² FIG. 2 represent the top cross section of the central most FRP support cylinder 5.

Greater detail of the connection of and sealing of the base section 7abcdefg FIG. 2 to the top section 9-14FIG. 2 of the plenum is presented as a sectional perspective view looking down at the top of the unit in FIG. 3. In FIG. 3 it is seen that a portion of the split-cover section 9FIG. 3 has been removed over the forward half of the plenum. The topmost portion 7fg FIGS. 2 & 3 of the base section vertical collar 7efg FIGS. 2 & 3 is shown in the lower left corner of the diagram. The top flange 7g FIG. 3 of that section of the plenum is covered by a gasket 8 with holes 8a to receive bolts 10 (not shown) that affix the removable split-cover section 9 to the top flange 7g of the base section of the plenum 7abcdefg FIG. 2.

An internal cross brace 15a FIG. 3 joins the top portion of the central most FRP support cylinder wall 5FIG. 2 to the vertical section 7f FIG. 3 of the base section vertical collar 7efg. A portion of another of the four such internal cross braces is seen as 15b FIG. 3 around at the left rear of the drawing. Said cross braces prevent distortion of the central most support cylinder wall in towards the outlet manifold 6FIG. 2 under the weight of the media in the media bed section 4; the lateral attachment of Internal supports 15a & 15b FIG. 3 to base section vertical collar section 7f FIG. 3 are via T shaped projections that attach to the walls of the base section of the plenum with bolts 15c FIG. 3, only two of which are seen, the others not being visible in this drawing.

Gasket 11FIG. 3 with holes 1 la is seen near the center of the plenum. This gasket serves to separate and form the airtight seal between the removable split-cover section 9FIG. 3 and the cover section collar 13abc (not shown here but depicted in FIG. 2). It should be noted that the portion of the outlet manifold 6FIG. 3 that is found above removable split-cover section 9FIG. 3 is actually formed by the internal aspect of the cover section collar 13abc FIG. 2 which cover section collar has been deleted in FIG. 3 in order to allow visualization of gasket 11 and internal cross braces 15a, 15b. Thus, the area demarcated as the outlet manifold 6 in FIG. 3 represents the potential space that exists only when said cover section collar is actually affixed to the base section of the plenum (as shown prior in FIG. 2). Numbers 9a¹ and 9a² FIG. 3, seen as the topmost elements and located at the left of outlet manifold 6, are the vertical connecting elements that hold the two sections of the removable split-cover section 9 together with bolts (not shown) that are placed through holes shown as 9a & 9b; said vertical connecting elements being continuous with and projecting upward at a 90° angle across the intersecting widths of the two halves of the removable split-cover section 9. A gasket that forms the sealing element between these two vertical connecting elements is not shown, but a representation of same is found in FIG. 4.

FIG. 4 presents a diagrammatic lateral view representation of the vertical interconnecting elements 9a¹ and 9b¹ FIG. 4 of the removable split-cover sections 9a and 9b. The bases of said vertical connecting elements are welded to the removable top split-cover sections 9a and 9b FIG. 4 across their widths, and where vertical interconnecting elements 9a¹ and 9b¹ come together they are interconnected by bolts 9c (only one of which is visible). The line 9d FIG. 4 represents a vertically situated gasket that seals the junction between the attachment flanges 9a¹ and 9a².

Bolts 10FIG. 4 serve as the connection of the removable split-cover sections 9a and 9b to the top flange section 7g of the base section vertical collar 7efg. The gasket situated between the removable split-cover sections 9a/9b FIG. 4 and top flange section 7g of base section vertical collar 7efg, is represented by the dark line at 11. The relative position of the above described elements to the walls of the base section of the plenum is indicated by lines 7aefg FIG. 4. The bracketed section 13abc FIG. 4 has been included in order to spatially indicate the relationship of the removable split-cover sections 9a & 9b to the cover section collar 13abc that forms the continuation of the outlet manifold above the level of the removable split-cover sections 9^a and 9^b.

The great strength and design flexibility created by this invention allow of creation of FRP cylinders for plenums ranging from very small to large to commercial/industrial size radial flow units. Current production has created units ranging from small units in which the FRP support cylinders were 4 feet tall, having an inner FRP tube internal diameter of 6 inches with the external tube diameter being 3 feet; up to a very large unit, 20 feet tall with an internal FRP tube diameter of 7 feet and an external FRP tube diameter of 11 feet. With respect to the larger construction mentioned above, it is the specific combination of materials and design elements created in this invention that allows of the creation of systems suitable for service in large scale industrial and commercial purification projects, such as were not possible utilizing the prior art. As an illustration of the actual size of such a construction, FIG. 5 presents a perspective drawing showing a man 1FIG. 5 braced in a horizontal position between the central most FRP support cylinder wall 5 and the lateral FRP support cylinder wall 3. Significantly, the strength of the two FRP cylinder walls 3 & 5FIG. 5 is such that the man is able to support his weight by applying pressure against said walls while he is preparing a hole for the placement of an accessory entry port for placement of a test probe through the lateral FRP support tube wall 3 into media bed section 4. The drawing is not intended to display any new feature of the invention, rather, it is intended to show the large scale of remediation units that can be fabricated using this invention, the size of which was not possible prior to this invention.

Claims

1. A media support wall framework comprising three layers of material that are fused into a single sheet; 1. an external layer of corrosion resistant Fiberglass Reinforced Plastic (FRP) that is created in the form of an open-weave diamond shaped lattice having a 65% to 75% ratio of through space between the bands of FRP material, 2. a central layer of corrosion resistant plastic screening material having a pore size comprising between 40% and 60% of said screen's total surface with said pores being slightly smaller than the granule size of the medium it is to be used to contain, and, 3. an internal layer designed and made of the same material and in the same pattern as the external layer and placed so as to be in alignment with the external latticework as closely as possible throughout the full vertical length of the cylinder wall, said framework being formed into an appropriate shape and a variety of sizes for the containment of granular organic porous remediation media suitable for treating contaminated air, including but not necessarily being limited to air containing corrosive vapors.

2. The media support wall of claim 1 in which the combined open pore space of the screen material and the FRP framework ranges from 25% to 35% of the total surface area of the support wall area.

3. The media support wall framework of claim 1 in which said framework is situated within a plenum having an air inlet, an air outlet, bottom, top and either multifaceted or cylindrical sidewall(s), and which plenum is formed having an appropriately anchored base section, and a removable split-top section, and within which are situated two separate, concentrically arranged media support cylinders of different diameters; said cylinders being aligned vertically coaxial with and extending from the top to the bottom of the solid, outer wall of the base section of the plenum, thus forming, between themselves, a space allowing of a uniform thickness of remediation media in a radial direction between the inlet manifold and outlet manifold of the plenum over the entire vertical length of the cylinders; the walls of said cylinders being of a proportionate size and thickness for use within plenums of greater or lesser size as the need may vary; and in which the cylindrical media support walls have an overall through space to solid surface ratio of between 28% and 34% for allowing passage of contaminated air from the inlet manifold, through the lateral support cylinder wall, into and through the remediation media, then through the central most support cylinder wall, and finally into an outlet manifold for discharge from the unit; said cylinder's walls being held at their proportionate distance from each other throughout their vertical lengths by their situation into prepared receptacles in the bottom plate of the base section of the plenum as well as by their situation within support collars at the top of the base section of said plenum, with optional cross braces serving as further support at the top of the cylinders in larger units; thus forming a media support system that is designed such that the support cylinders are not commonly removed during the process of removing and replacing spent remediation media particles.

4. The media support wall framework of claim 3 in which the bases of the two cylinders are conjoined by a solid FRP floor section, said cylinders being held at their proportionate distance from each other throughout their vertical lengths by said floor section in conjunction with their situation within support collars at the top of the base section of said plenum, with optional cross braces serving as further support at the top of the cylinders in larger units; thus forming a media support system in which the support cylinders are designed to be removed as a unit for purposes of removing and replacing spent remediation media particles.

5. The media support cylinders of claim 1 wherein the configuration of the FRP cylinders is designed to support a remediation medium other than a porous organic granular substrate media, the basket weave walls of the support cylinders being designed to support inorganic media such as conventional foam, reticulated foam, etc., or organic media such as lava rock, wood chips, etc.

6. The media support cylinders of claim 5 wherein the screen sections of the FRP cylinders have a pore space sized slightly smaller than the diameter of the specific organic media being used, such as lava rock or wood chips.

7. The media support cylinders of claim 5 wherein the FRP cylinders are not formed with a central screen membrane, comprising only basket weave walls made of FRP, said cylinders being designed specifically for the support of non-granular, inorganic media such as conventional foam or reticulated foam.

8. The media support cylinders of claim 1 wherein the basket weave walls of the support cylinders are formed of non-FRP plastic or other such materials that are corrosion resistant.

9. The media support cylinders of claim 8 wherein the basket weave walls of the support cylinders are designed to support remediation media other than a porous organic granular substrate medium, such cylinder wall configurations being designed to support inorganic media such as conventional foam or reticulated foam, or, organic media such as lava rock or wood chips.

10. The media support cylinders of claim 9 wherein the screen sections of the support cylinder wall have a pore space sized slightly smaller than the diameter of the specific organic media, such as lava rock or wood chips.

11. The media support cylinders of claim 9 wherein the support cylinder walls are not lined with screen material, said cylinder walls being designed specifically for the support of non-granular, inorganic media such as conventional foam or reticulated foam.

12. The media support cylinders of claim 8 in which the two support cylinders are joined together at the base for use in remediation reactor containment vessels that allow removal of the medium support system as a unit for purposes of recharging the unit with fresh remediation media.

13. The media support cylinders of claim 3 in which the two support cylinders are joined by cross braces at the lowest and topmost levels, said cross braces serving to maintain the desired separation between the internal aspect of the external cylinder and the external aspect of the internal cylinder, and, which cylinders also bear external, horizontally extending braces sized to situate and stabilize the cylinders against the internal aspect of the side walls of plenums that were not originally designed to receive said support cylinders.

14. The media support cylinders of claim 8 in which the two support cylinders are joined by cross braces at the lowest and topmost levels, said cross braces serving to maintain the desired separation between the internal aspect of the external cylinder and the external aspect of the internal cylinder, and, which cylinders also bear external, horizontally extending braces sized to situate and stabilize the cylinders against the internal aspect of the side walls of plenums that were not originally designed to receive said support cylinders.

15. A process for treating contaminated air: a. by moving the contaminated air, at ambient or slightly above ambient air pressure, into the inlet manifold of a plenum then radially through a medium comprising a granular porous substrate media such as activated charcoal, or other organic media such as wood chips or lava rock;b. contacting the air with media contained within two concentrically arranged support cylinders of differing diameters, said cylinders having porous walls, and said walls comprising a fused sandwich formed from a single layer of corrosion resistant plastic screening situated between two layers of woven bands of Fiberglass Reinforced Plastic (FRP), the lattice weave FRP wall segment of said walls being formed in a diamond shaped basket weave arrangement, the total through space of such combined screen and FRP wall materials comprising between 25% and 45% of the total wall area of said cylinders;c. after passing through which media and cylinders the now purified air is moved into an outlet manifold;d. and thence exits from the plenum.

16. A process for treating contaminated air: a. by moving the air, at ambient or slightly above ambient air pressure into the inlet manifold of a plenum then radially through an inorganic medium such as, foam or reticulated foam;b. containing said medium between two concentrically arranged support cylinders of differing diameters, said cylinders being formed of a corrosion resistant material such as plastic or other like materials, and having porous walls by virtue of being formed in a diamond shaped basket weave arrangement, the total through space of which support wall material comprises between 65% and 75% of the total wall area of said cylindersc after passing through which media and cylinders, the now purified air is moved into an outlet manifold;d. and thence exits from the plenum.