Adsorbent activated carbon fiber sheet filter and method of regeneration

What is claimed is:

1. A process for regenerating an adsorbent filter which adsorbs contaminants from a fluid flow, said process comprising the steps of:

removing the filter from a filtration system, the filter being freely exposed to ambient atmosphere upon removal from the filtration system;

installing the filter in a chamber;

heating the filter to a regenerative desorption temperature by way of a heat source wherein the adsorbed contaminants are vaporized and liberated from the filter; and

removing said vaporized contaminants from said chamber.

2. The process of claim 1 wherein said chamber is a vacuum chamber being generally sealed and evacuated to create a vacuum after the filter has been installed.

3. The process of claim 1 wherein said heat source is an electric current applied to a continuous sheet of activated carbon fiber fabric of said filter.

4. The process of claim 1 wherein said heat source is an energy generator creating microwaves which are directed at and imparted upon said filter.

5. The process of claim 1 wherein said heat source is an energy generator creating microwave energy which is directed at and imparted upon a continuous sheet of activated carbon fiber fabric of said filter, said continuous sheet of activated carbon fiber fabric being serpentined between supports of said filter.

6. The process of claim 1 wherein said chamber is generally filled with an inert atmosphere.

7. A process for regenerating an adsorbent filter which adsorbs contaminants from a fluid flow, said process comprising the steps of:

removing the filter from a filtration system;

installing the filter in a chamber;

heating the filter to a regenerative desorption temperature by way of a heat source wherein the adsorbed contaminants are vaporized and liberated from the filter;

further heating the filter to a pyrolysis temperature wherein the contaminants are volatilized; and

removing said volatilized contaminants from said chamber.

8. The process of claim 7 further comprising the step of:

heating the filter to a carbonization temperature.

9. The process of claim 8 further comprising the steps of:

displacing the existing atmosphere within said chamber with an oxidizing atmosphere; and

heating the filter to an activation temperature.

10. A process for regenerating an adsorbent filter which adsorbs contaminants from a fluid flow, said process comprising the steps of:

installing the filter in a chamber;

heating the filter to a regenerative desorption temperature wherein the adsorbed contaminants are vaporized and liberated from the filter;

removing said vaporized contaminants from said chamber;

heating the filter to a pyrolysis temperature wherein the contaminants are volatilized, said pyrolysis temperature being greater than said regenerative desorption temperature;

removing said volatilized contaminants from said chamber;

heating the filter to a carbonization temperature;

displacing the existing atmosphere within said chamber with an oxidizing atmosphere;

heating the filter to an activation temperature in the presence of said oxidizing atmosphere;

removing heat from the filter; and

removing the filter from said chamber.

11. An adsorbent filter which adsorbs contaminates from a fluid stream, said filter comprising:

a frame having a first side and a second side;

a first set of supports having one or more first supports therein and being located on said first side of said frame;

a second set of supports having one or more second supports therein and being located on said second side of said frame; and

a continuous sheet of adsorbent fabric having a first surface and a second surface, said continuous sheet being located within said frame and extending between alternating first supports and second supports thereby creating two or more cross layers of said continuous sheet, said cross layers being adjacent to one another having a spacing therebetween, said spacing being achieved by applying a tension to said continuous sheet such that the fluid stream passes through said spacing and over at least one of said first surface and said second surface of said continuous sheet wherein the contaminates in the fluid stream are adsorbed by said continuous sheet.

12. The filter of claim 11 wherein said continuous sheet in made of woven fibers which are substantially all activated carbon.

13. The filter of claim 12 wherein said woven fibers are a polymeric material, said fibers being heat decomposed in an inert gas and subsequently activated in a carbon dioxide concentrated atmosphere.

14. The filter of claim 13 wherein said polymeric material is polyacrylonitrile.

15. The filter of claim 12 wherein said woven fibers are selected from a group consisting of polyacrylonitrile, rayon, pitch, phenol, lingin, and saran.

16. An adsorbent filter which adsorbs contaminates from a fluid stream, said filter comprising:

a frame;

a first continuous sheet of adsorbent fabric having a surface; and

means attached to said frame for supporting said first continuous sheet of adsorbent fabric and redirecting said first continuous sheet under a tension sufficient to create one or more flow channels, such that the fluid stream flows through said flow channels and along said surface of said sheet wherein the contaminates in the fluid stream are adsorbed by said sheet.

17. The filter of claim 16 wherein said means for supporting includes a first set of supports and a second set of supports, said first set of supports and said second set of supports being generally opposite one another and extend at least partially from an upstream plane of said frame to a downstream plane of said frame with said continuous sheet extending alternatingly between said first set of supports and said second set of supports.

18. An adsorbent filter which adsorbs contaminates from a fluid stream, said filter comprising:

a frame;

a first continuous sheet of adsorbent fabric having a surface;

means attached to said frame for supporting said first continuous sheet of adsorbent fabric such that the fluid stream flows along said surface of said sheet such that the contaminates in the fluid stream are adsorbed by said sheet;

a second continuous sheet of adsorbent fabric having a surface; and

means attached to said frame for supporting said second continuous sheet of adsorbent fabric such that the fluid stream flows along said surface of said first sheet prior to flowing along said surface of said second sheet.

19. The filter of claim 18 wherein said means for supporting includes a first set of supports and a second set of supports for supporting said first continuous sheet, and a third set of supports and a fourth set of supports for supporting said second continuous sheet, said first set of supports and said second set of supports being generally opposite one another and extending at least partially from an upstream plane of said frame to a downstream plane of said frame with said first continuous sheet extending alternatingly between said first set of supports and said second set of supports, and said third set of supports and said fourth set of supports being generally opposite one another and extending substantially the remainder of the distance from said upstream plane to said downstream plane with said second continuous sheet extending alternatingly between said third set of supports and said fourth set of supports.

20. The filter of claim 18 wherein said frame includes an upstream plane and a downstream plane and said surface of said first continuous sheet and said surface of said second continuous sheet are positioned at an angle to one another relative to said upstream plane and said downstream plane of said frame.

21. An adsorbent filter which adsorbs contaminates from a fluid stream, said filter comprising:

a frame;

a plurality of supports generally parallel to the direction of flow of the fluid stream; and

a continuous sheet of adsorbent fabric having a first surface and a second surface, said sheet being located within said frame and serpentined between said supports to form two or more cross layers of said sheet, said sheet being under a tension sufficient to maintain said cross layers in a substantially planar condition, and forming flow channels between said cross layers in which the fluid stream flows along said surfaces of said sheet such that the contaminates in the fluid stream are adsorbed by said sheet.

22. The filter of claim 21 wherein a first dimension of said flow channels is determined by one dimension of said plurality of supports, and a second dimension of said flow channel is determined by a distance between said supports as said sheet is serpentined therebetween.

23. The filter of claim 22 wherein said supports are two or more sets of elongated rods.

24. The filter of claim 23 wherein said elongated rods are substantially circular in cross section, said one dimension of said supports being the diameter of said rod.

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BACKGROUND OF THE INVENTION

1. Technical Field

This invention generally relates to a process and apparatus for adsorbing and later desorbing contaminants from a fluid stream and, more particularly, to a filter utilizing a continuous sheet of activated carbon fabric which adsorbs contaminants from a contaminant-laden fluid stream, and which later desorbs the contaminants under controlled conditions. The filter is capable of periodic removal from use and is regenerable in a controlled environment at regeneration temperatures in excess of the in-use desorbtion temperatures.

2. Discussion

The use of activated carbon to adsorb contaminants, particularly hydrocarbons and other volatile organic compounds, is known in the art of filtration. One typical approach to filtration of hydrocarbons from a fluid stream is shown in FIG. 1 and involves forcing the contaminated fluid through a sacrificial bed of granulated activated carbon or particulate filters, referred to as pre-filters, and subsequently directing the fluid through a filter having a structure, typically either a stacked corrugated structure or a monolithic structure, made of a nonconductive inorganic substrate which is coated or an organic substrate containing activated carbon surfaces.

The filter is structured such that the substrate provides a honeycomb form, or a series of tubes which are closely spaced, to provide as much surface area as possible to contact the fluid as it flows through the filter. Since the activated carbon is carried on a substrate, the surface perpendicular to the fluid flow direction must be large, or the length of the filter in the flow direction must be long, in order to provide sufficient contact surface area with the activated carbon. The contact surface area is important because the contaminants in the fluid must contact the surface of the activated carbon in order to be adsorbed and removed from the fluid stream. If sufficient contact area is not provided, the contaminants will not be adsorbed and will therefore remain in the fluid stream. Once the fluid flows through the monolithic structure of the filter, the fluid is exhausted as presumably clean fluid.

In advanced systems the monolithic filter is positioned on a rotary device which provides in-use desorption of the filter. Other systems have been utilized where there are two or more parallel filter sets. In such a system, the fluid stream is switched from the first filter set to the second filter set when the first set is saturated. As the second set adsorbs the contaminants from the fluid stream the contaminants held in the first set are desorbed. The fluid stream is switched back to the first filter set when the second filter set is saturated. This type of parallel system is less effective than the rotary systems in many or most industrial applications and has fallen into disfavor.

In the rotary type system shown in FIG. 1, the filters are positioned around the rotary device such that a channel is created in a central portion of the filters. This channel acts as a clean exhaust channel through the center of the device. A portion of the rotary device, typically positioned opposite the fluid flow entry, is shielded from the incoming fluid flow and acts as a desorption area. The desorption area is intended to drive the adsorbed contaminants from the activated carbon surfaces of the filter.

Typically, hot air is forced through the honeycomb or tube passages of the monolithic structure when the filter is rotated to the desorption area. The hot air raises the temperature of the filter structure to between about 100.degree. C. and 180.degree. C. The raised temperature causes some of the adsorbed contaminants to become vaporized and desorbed from the activated carbon surfaces. The vapor phase contaminants enter the flow of the hot air stream which carries the contaminants as solvent laden desorption air to a secondary operation.

The secondary operation for the filter system of FIG. 1 is typically a thermal oxidizer or a condensation system. The thermal oxidizer heats the contaminants to a point where the molecular chain of the contaminants are broken apart and form non-hazardous molecules which can be safely discharged into the environment. The condensation system is used to cool the hot solvent laden air and collect the contaminants in liquid form as they condense from the air stream. The contaminants can then be processed for commercial use, can be further filtered and treated, or can be properly disposed.

One disadvantage of utilizing a hot air stream to desorb the contaminants from the filters is that the heat transfer properties of air are relatively inefficient. Another process for desorbing the contaminants from the filters has been the suggested use of electrical heating of the filter structure itself. This advantageously allows for a lower volume of air flow to carry the desorbed contaminants to the secondary operation.

Even though heating the filter structures to a temperature in the range of 100.degree. C. to 180.degree. C. liberates many of the contaminants from the filter, there is an ongoing problem with high boiling point contaminants which are not desorbed at these temperatures. High temperature boiling point contaminants are considered to include contaminants which have a boiling point above the in use heating temperature used in the present systems. As a result of leaving the high boiling point contaminants in the filter, the efficiency of the filter decreases over time. By leaving the high boiling point contaminants in the filter the effective surface area available to adsorb the contaminants as they flow through the filter is reduced and more contaminants will exit the filter and be exhausted into the environment.

A portion of this problem can be attributed to the materials used to form the structure of the filter. This problem is particularly prevalent in monolithic and corrugated structures which require the use of resins or binders. If the in use temperature of desorption were raised to a level which would desorb or pyrollize the high boiling point contaminants (i.e. 600.degree. C. or more), the binders used to form the structure of the filter would experience structural decomposition and would fail to properly support the honeycomb or tube formation required to allow fluid flow through the filter. It is further recognized that no heat source or method is presently used which can heat the filter to a temperature high enough, and in a short enough time period, to drive off all of the high boiling point contaminants during the in use desorption phase of the filtration system without structural decomposition.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, there is provided an adsorbent filter for adsorbing contaminants from a fluid stream. The filter provides a continuous sheet of adsorbent fabric which is located within a frame and extends between alternating first and second supports located generally opposite one another. The supports suspend each crossing layer of the fabric sheet in proximity to an adjacent crossing layer such that flow channels are formed therebetween. The contaminated fluid flows within the flow channels and over the surface or surfaces of the fabric sheet. The contaminants are adsorbed by the activated carbon fibers from which the fabric sheet is made.

It is an object of the present invention to provide a more compact and/or more efficient adsorbent filter than the present monolithic or corrugated paper type adsorbent filters. This object is believed to be achieved by utilizing a sheet of fabric which is constructed of substantially all activated carbon fibers. The elimination of a substrate should allow for a filter which provides an equivalent amount of adsorption in an equal or smaller volume.

It is a further object of the present invention to provide an adsorbent filter which can be subjected to higher temperatures than presently produced filters without experiencing structural degradation which would hinder the filters continued usefulness. The higher temperatures allow desorption of the high boiling point contaminants which have been adsorbed. This is achieved by providing a filter having a filter sheet made of substantially all activated carbon fibers which do not require binders or resins to form the channels through which the contaminated fluid flows.

It is a further object of the present invention to provide a means of heating the adsorbent filter to a desorption temperature sufficiently high to force substantially all of the high boiling point contaminants into a gas phase during the normal in use desorption stage of the filtration system.

A further object of the present invention is to provide a method and apparatus for regenerating filters which have been used to adsorb contaminates from a fluid stream. The regeneration is achieved under controlled conditions which remove substantially all of the adsorbed contaminates and provide a filter having adsorption capacities which are substantially equal to a filter which has not been exposed to a contaminated fluid stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The various advantages of the present invention will become apparent to one skilled in the art upon reading the following specification and by reference to the drawings in which:

FIG. 1 is a prior art filtration system used to adsorb, and later desorb, contaminants from a fluid stream;

FIG. 2 is a perspective view of a filter having a continuous fabric sheet made of substantially all activated carbon fibers and being made in accordance with the teachings of the present invention;

FIG. 3 is a detailed view of a portion of the filter of FIG. 2;

FIG. 4 is a detailed plan view of a portion of the filter shown in FIG. 2;

FIG. 5 is a detailed view of an alternate retention means for securing the continuous fabric sheet to the frame of a filter made in accordance with the present invention;

FIG. 6 is an alternate embodiment of a filter made in accordance with the teachings of the present invention;

FIG. 7 is a flow chart of a regeneration process taught in the present invention and used to regenerate filters used to adsorb contaminates from a contaminated fluid flow;

FIG. 8 is a plan view of a desorption portion of a filtration system incorporating an energy generator as a heat source made in accordance with the teachings of the present invention;

FIG. 9 is an exploded view of a further preferred embodiment of the filter frame of the present invention; and

FIG. 10 is a plan view of the filter frame of FIG. 9 including the positioning of the supports of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention or its application or uses.

Referring to FIG. 2, there is shown an adsorbent filter, generally at 20. Filter 20 includes a frame 22, a continuous adsorbent fabric sheet 24, and supports 26. Frame 22 is preferably made of a stainless steel material which provides a durable, chemically resistant structure. Alternate materials such as coated metals, chemically resistant plastics or resins, ceramic composite materials, or similar durable, chemically resistant materials able to withstand temperatures of 600.degree. C. or more without structural or dimensional degradation can also be used with equal results. These temperatures may be reached in a conventional or an inert atmosphere depending upon the application of the present invention.

Frame 22 of the preferred embodiment is a generally rectangular shaped cube having an upstream right side member 30, an upstream left side member 32, a downstream right side member 34, a downstream left side member 36, an upstream top member 38, a downstream top member 40, a right side top member 42, a left side top member 44, an upstream bottom member 46, a downstream bottom member 48, a right side bottom member 50, and a left side bottom member 52. During use of the filter the contaminated fluid flow enters filter 20 through an upstream plane 54 (defined by members 30, 32, 38, and 46), flows over the surfaces of sheet 24 which adsorbs the contaminants, and the cleaned fluid exits through a downstream plane 56 (defined by members 34, 36, 40, and 48).

Referring to FIGS. 9 and 10, there is shown a further preferred embodiment of the frame 322 of filter 20. Frame 322 includes an upper cap portion 302, a lower cap portion 304, a left side member 306, and a right side member 308. Cap portions 302 and 304 may be symmetrically opposite, identical, or dissimilar from one another depending upon the system the filter 20 is to be used. Preferably cap portions 302 and 304 are identical and therefor require only one set of tools to produce. Further, the caps may be made of a nonconductive material and act as an insulator if electrical current will be utilized in the regeneration process as discussed later.

Side members 306 and 308 may also be symmetrically opposite, identical, or dissimilar from one another. Each side member includes a bracket structure 310 which is attached to or formed as part of the side member. The purpose of the bracket structure is to create a channel 312 for receiving a support means as will become apparent from further review of the first preferred embodiment.

Referring again to FIG. 2, adsorbent fabric sheet 24 of the preferred embodiment is made of woven fibers of polyacrylonitrile (PAN) which are then heat treated in the process of carbonization and activation. This method of producing the fabric sheet provides significantly more activated carbon adsorption area than is provided by a cloth which is impregnated with or coated by granular activated carbon. Other materials which can be used to produce the woven fibers used to form fabric sheet 24 include, but are not limited to: Rayon; Pitch, Phenol; Lignin; Saran; or any other naturally occurring or man made fiber which can be carbonized and activated. Further, while the preferred embodiment utilizes a fabric sheet which is woven the filter of the present invention can use a sheet material which is produced by other methods provided the tensile requirements (discussed later) can be achieved. In general, the manufacture of activated carbon fibers requires heat decomposing the polymer material, such as PAN, in an inert gas and then activating the fibers in a carbon dioxide concentrated or steam atmosphere at a high temperature.

The tensile strength of the activated carbon fiber fabric sheet 24 along a length of the fabric, or in the direction of the warp fibers, is sufficiently high that as sheet 24 is extended across frame 22 a tensile force of approximately 0.75 kg/cm.sup.2 (10.67 psi) can be applied which prevents sagging of sheet 24 while not damaging the fibers of sheet 24. The tension which is applied to sheet 24 keeps sheet 24 in a substantially planar condition as the sheet 24 extends across frame 22. The dimensional stability of sheet 24 along a width of the fabric, or in the direction of the weft fibers, is preferably controlled such that little or no sagging is allowed in the direction of flow when the sheet 24 is tensilely loaded at approximately 0.25 kg/cm.sup.2 (3.56 psi) in the direction of the weft fibers. As will be detailed below, the spacing between successive layers of sheet 24 as it extends across frame 22 is generally between 1 and 4 millimeters. The preferred embodiment will be described as providing a spacing of 2 mm although applications where spacings of less than 1 mm, or greater than 4 mm are envisioned by the inventor and are within the scope of this disclosure and claimed invention.

The spacing between each crossing layer 76 of sheet 24 is designed to encourage, either alone or jointly with non-laminar flow enhancement devices, substantially all of the fluid flowing through filter 20 to come in contact with a surface of sheet 24. By contacting the surface of sheet 24 the contaminants in the fluid, particularly hydrocarbon's in the preferred embodiment, are adsorbed by the activated carbon fibers of sheet 24. The term `hydrocarbon` within the text of this specification includes, but is not limited to, VOCs, halogenated hydrocarbons, hydrocarbons and other pollutants and/or products whose absorption is common to those skilled in the art.

If design constraints or other reasons require or make it desirable to provide a large spacing between each crossing layer 76 of sheet 24, non-laminar or turbulent flow of the fluid through the flow channels 68, created between each pair of transverse crossing layers 76, can be enhanced by controlling the orientation of a series of sheets 24, by varying the surface texture or weave of sheet 24, or by adding physical mixers either within flow channels 68 or to the upstream plane 54 or downstream plane 56 of filter 20. These alternatives will be further detailed below.

In the preferred embodiment, shown in FIGS. 2, 3, and 4, supports 26 are shown as extending from the upstream right side member 30 to the downstream right side member 34 and from the upstream left side member 32 to the downstream left side member 36. The supports extending between member 30 and member 34 will be referred to as right side supports 26R, while the supports extending between member 32 and member 36 will be referred to as left side supports 26L. In the present embodiment the supports 26 are shown as a series of elongated generally circular rods 58 having each end restrained in a channel 60, 62,