This invention relates to the field of decontaminating fluids and gases.

In particular, this invention relates to adsorbing contaminants from a stream onto an adsorption material and then desorbing the adsorbed contaminants into another stream.

2. Description of the Related Art.

The prior art discloses systems that selectively adsorb organic contaminants from a polluant gas stream of typically nitrogen or air. After adsorption, the gas stream is discharged to the atmosphere, if clean enough, while the polluants are retained in an adsorbing material. The adsorbing material is typically resin or carbon, such as activated charcoal. Next, the contaminants are desorbed from the adsorbing material for further treatment.

Some prior art systems use an inefficient, stationary, adsorbent packed bed batch process that adsorbs and desorbs in the same vessel. The adsorption material is normally below 40 C to adsorb the contaminants and above the desorption temperature of the adsorbed contaminants to desorb them.

Therefore, a stationary packed bed adsorbs the contaminants, is heated, desorbs the contaminant, is cooled, and then can adsorb again. For continuously flowing

polluant streams, the prior art systems have multiple packed beds with some of the packed beds adsorbing contaminants while the other beds are heating, desorbing, and cooling. The duplication of packed beds in continuous systems increases the capital cost of the system.

Having the adsorbing and desorbing process occur in the same process vessel results in increased vessel design and operating costs. The thermal cycling of the adsorbing and desorbing process is very hard on the components of the vessel, requiring robust vessels and/or shortened equipment life cycles with increased maintenance costs. The presence of halogenated compounds in the streams means that the vessels must be protected from both aqueous phase- halogen attack and high-temperature halogen attack.

U. S. Pat. No. 4,385,993 (Hedrick) discloses a complex apparatus and method for treating a continuously flowing feed stream with a recirculating resin exchange system. A regenerated resin stream is pulsed out of a load pulse chamber and up through a loading column in a series of resin bands (each pulse forms a band). The feed stream passes counter-currently through the loading column and is removed at the column base. The resin stream leaves the top of the loading column, moves through a treatment chamber, and into a regeneration pulse chamber. Next, the resin stream is pulsed out of the regeneration pulse chamber and up through a regeneration column. A regenerate stream flows down through the regeneration column and exits at the column bottom. The regenerated resin exits the top of the regeneration column, moves through a second treatment chamber, and into the load pulse chamber, thus completing the resin recirculation.

U. S. Pat. No. 5,126,056 (Carlson) discloses a complex resin cycling contactor assembly for treating an aqueous stream. The aqueous stream and the resin co-currently flow through an exceptionally elongated and relatively narrow contactor for enabling rapid and turbulent flow. Simultaneously, quantities of spent resin are regenerated in a separate assembly. The resin recirculates through the contactor and the regenerator. Pumps are used to move the resin through the system, especially the narrow contactor.

The continuous adsorption systems in the prior art utilize costly and complex mechanical means to move adsorptive material through the stream to be

decontaminanted and a regeneration stream. Thus, there is a need for a simple, continuous adsorbing/desorbing packed bed system and process that does not require mechanical means to move the bed through the streams, thermally cycle, nor require aqueous-phase and high-temperature halogen attack prevention design in the same areas.

SUMMARY OF THE INVENTION The present invention provides methods and systems for removing contaminants from a contaminated stream by continuously descending, via gravity, a packed bed through the stream and adsorbing the contaminants thereon. The packed bed is formed from recirculated adsorption material. The contaminant- adsorbed portion of the packed bed is then desorbed of the contaminants by being descended, via gravity, through a desorbing stream. The adsorption material of the desorbed packed bed portion is thereafter recirculated to the top of the system.

The methods and systems of the present invention provide an economic alternative to the batch process method of decontaminating streams.

Because the present invention is a continuously recirculating process, multiple packed beds are not needed for treating a continuously flowing, contaminated stream. Further, the invention provides a relatively simple and inexpensive alternative--gravity--to using a mechanical force for moving the packed bed through the streams.

The packed bed descends, via gravity, through adsorption and desorption channels in the systems of the invention. Each channel is defined by two vertical walls. The streams pass through their respective channels without carrying away the packed bed's adsorption material. An aspect of the invention accomplishes this by having portions of the vertical walls being perforated and feeding the streams through those portions. Another aspect of the invention accomplishes this by feeding the streams into a set of slotted pipes extending into the channel and removing the stream with another set of slotted pipes.

To recirculate the adsorption material from below the desorption channel to the top of the system, one embodiment of the invention provides an eductor and a conveyance stream. The eductor's suction inlet educts the

adsorption material into the conveyance stream. A duct then directs the conveyance stream to the top of the system. The invention may be practiced with the contaminated stream, the desorbing stream, and the conveyance stream being liquid or gas. Further, the adsorption material may be resin, carbon, zeolite, desiccant, or any other suitable material.

In a preferred embodiment of the invention, the systems and methods adsorb organic contaminants from a contaminated air stream onto resin. To adsorb the contaminants, the packed bed temperature is adjusted to an appropriate temperature range. The temperature may be adjusted by providing a cool conveyance air stream, cooling the duct, or cooling a hopper into which the duct deposits the resin before it is formed into the packed bed and descends through the channels. To desorb the contaminants, the packed bed is heated to an appropriate temperature range, which is above the desorption temperature of the specific contaminants being treated. In an embodiment, the packed bed is heated by electric heaters at the vertical walls of the desorption channel.

To further assist in removing the organic contaminants, the packed bed is maintained at a negative pressure while descending through the desorbing air stream. This is accomplished by a vacuum blower system that draws the desorbing stream through the packed bed. Further, rotary air lock valves are positioned above and below where the desorbing air stream moves through the packed bed to help maintain the negative pressure. The lower rotary air lock valve also controls the flow of the adsorption material into the eductor.

The present invention also provides for the contaminant-laden desorption stream to be further processed using known techniques. The processing may involve further condensing or oxidizing of the contaminants.

Accordingly, it is an object of the present invention to provide a continuous adsorbing/desorbing system and process that does not thermally cycle or require aqueous-phase and high-temperature halogen attack prevention design in the same areas. Other and further objects and advantages will appear hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a schematic diagram of a recirculating bed adsorption/desorption system for removing contaminants from a contaminated air stream according to the invention.

Figure 2 shows an isometric view of the recirculating bed adsorption/desorption system of Figure 1.

Figure 3 shows an isometric view of an alternative arrangement for flowing a desorption stream through a descending, contaminant-adsorbed packed bed according to an embodiment of the invention.

Figure 4 shows a schematic diagram of an alternative configuration of an air lock for use in maintaining a pressure difference between the adsorption and desorption sections of the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT (S) Referring to the drawings, wherein like reference numerals referto like elements, there is shown in Figures 1 and 2 a recirculating bed adsorption/desorption system 10 that enables a desorbed packed bed 12B and a contaminant-adsorbed packed bed 13B to flow through portions of the system under the power of gravitational force 14. By using gravitational force 14, the system 10 has a simple design with reduced capital and operational costs compared to systems that transport the packed beds entirely through mechanical means.

The recirculating bed adsorption/desorption system 10 continuously recirculates adsorption material 44 through an adsorption section 16, a desorption section 18 and a transfer section 20 (shown in Figure 1 only) in a loop. The phrase "continuously recirculates"is understood to mean that the material moves through the system 10 over a period of time, and is not restricted to mean that the material is constantly moving. The adsorption material 44 forms the desorbed packed beds 12A and 12B and the contaminant-adsorbed packed beds 13A and 13B, as discussed below. In a preferred embodiment of the invention, the adsorption section 16 removes organic contaminants from a high volume-low concentration contaminated air stream 22 to produce a clean air stream 24, while the desorption

section 18 produces a high concentration-low volume contaminated desorption air stream 26 from a desorption air stream 28. Other embodiments of the system 10 may process contaminated liquid streams, use liquid desorption streams, and remove other types of species.

The adsorption section 16 has first and second vertical walls 30 and 32, each having a screened section 34 and 36, respectively. The walls 30 and 32 define an adsorption channel 38 through which the packed bed 12B flows, via gravity, in a direction 40. Adsorption material 44 enters the top end of the channel 38 through an adsorption material inlet 46 and forms the packed bed 12B in the channel. The screened sections 34 and 36 permit the contaminated air stream 22 to pass through the packed bed 12B without carrying away the packed bed 12B.

Any equivalent to screening, such as a perforated sheet, may be used in the screened sections. In a preferred embodiment of the invention, the adsorption material 44 is a resin. Other embodiments of the invention may use other equivalent materials for adsorbing contaminants, such as carbon in the form of activated charcoal, zeolite, desiccant, or any other suitable material.

In the adsorption section 16, the packed bed 12B cleans the contaminated air stream 22 by adsorbing its contaminants. The stream 22 flows through a contaminated stream inlet 42 at the first vertical wall screened portion 34.

The packed bed 12B then adsorbs the contaminants in the stream to produce the clean air stream 24 and a contaminant-adsorbed packed bed 13A. The stream 24 exits the adsorption section 16 through a clean air stream outlet 43 at the second vertical wall screened portion 36. In a preferred embodiment of the invention, the packed bed flow 40 is perpendicular to the contaminated air stream 22 flow. Other embodiments of the invention may have the screened portions aligned such that the packed bed flow 40 is more co-current or counter-current with the contaminated air stream 22 flow, so long as the bed does not become substantially fluidized.

The contaminant-adsorbed packed bed 13A then descends, via gravity, out of the channel adsorption channel bottom end 47 and into the desorption section 18 to form the contaminant-adsorbed packed bed 13B. The desorption section 18 has third and fourth vertical walls 48 and 50, each having a screened section 52 and 54, respectively. The walls 48 and 50 define a desorption

channel 56 through which the contaminant-adsorbed packed bed 13B flows, via gravity, in the direction 40. The packed bed 13A enters the top end of the channel 56 through a packed bed inlet 58. In a preferred embodiment of the invention, the packed bed 13 passes through a rotary air lock valve 60 before entering the channel 56. The purpose of the air lock is discussed below. Other embodiments of the invention may not have an air lock.

The contaminant-adsorbed packed bed 13B is desorbed of contaminants by descending, via gravity, through the desorption air stream 28. In the embodiment of the invention of Figures 1 and 2, the stream 28 flows through a desorption stream inlet 70 at the third vertical wall screened portion 52. The packed bed 13B then desorbs the contaminants, forming the contaminated desorption stream 26 and a desorbed packed bed 12A. The contaminated desorption stream 26 exits the desorption section 18 through desorption stream outlet 72 at the fourth vertical wall screened portion 54. The screened sections 52 and 54 permit stream 28 to flow through the packed bed without carrying the adsorption material away. The stream inlet and outlet of the desorption section are typically smaller than the stream inlet and outlet of the adsorption section because of the higher volume of the stream passing through the adsorption section. The packed bed 12A exits the desorption channel 56 at the adsorption material outlet 90.

The adsorption material 44 of the packed bed 12A is transferred to the adsorption channel 38 and repacked to form the packed bed 12B. The transfer section 20 moves the adsorption material 44 up to the adsorption material inlet 46 at the top of the adsorption channel 38. The adsorption material is then repacked, thus completing bed recirculation of this continuous process. Equivalents to the transfer section 20 may move the packed bed 12A without unpacking it.

In an embodiment of the invention, the transfer section 20 may have a rotary air lock valve 74, an eductor 76, and a duct 78. The rotary air lock valve 74 controls the flow of the desorbed packed bed 12A out of the desorption channel 56. The valve 74 also loosens the packed bed 12A into the adsorption material 44 that is directed into a suction inlet 80 of the eductor 76. Other embodiments of the invention may use other equivalent valves, i. e., a pinch valve. A conveyance air

stream 82 is directed into an air stream inlet 84 of the eductor 76. The adsorption material 44 is educted into the air stream 82 to form a laden conveyance air stream 86. The stream 86 passes through though the eductor's air stream outlet 88 and into the duct 78. The duct 78 directs the laden conveyance air stream 86 to the adsorption material inlet 46 of the adsorption section 16. The adsorption material 44 collects to form the packed bed 12B while the air stream 82 exits the adsorption channel 38 with the clean air stream 24. Other embodiments of the invention may use other equivalent transfer sections, e. g., a screw conveyor, bucket conveyor, and the like. Other embodiments of the invention may also use a conveyance liquid stream.

In an embodiment of the invention, the desorbed packed bed 12B may need to be in a first temperature range to adsorb contaminants while the contaminant-adsorbed packed bed 13B needs to be at a second temperature range to desorb the contaminants. The first temperature range is typically below 40 C and the second temperature range is typically above the desorption temperature of the contaminants being desorbed.

A cooling system may chill the absorbent material, either in the adsorption material 44 or the packed bed 12A or 12B, in a number of ways. The cooling system may provide the conveyance air stream 82 at a lower temperature than the adsorption material 44 at the adsorption material outlet 90, thus cooling the adsorption material. The cooling system may be a duct cooler 92 that cools adsorption material as it moves to the adsorption section 16. The cooling system may be a hopper cooler 96 incorporated in a hopper 94 that connects the duct 78 to the adsorption material inlet 46. The cooling system may be any other equivalent means that cools the adsorption material after it descends through the desorption air stream 28 and before it descends through the contaminated air stream 22.

In an embodiment of the invention, electric heaters 98 may be placed outside the third and fourth vertical walls 48 and 50 to heat the contaminate- adsorbed packed bed 13B prior to it descending through the desorption air stream 28. Other embodiments of the invention may use other equivalent types of heaters, i. e., steam or hot oil jackets and recuperative systems, such as those recuperating

heat from a flameless thermal oxidizer. Other embodiments of the invention may have the packed bed 13A heated prior to entering the rotary air lock valve 60.

By having the higher temperatures in one area of the system 10 and the lower temperatures in another area, the components of the system do not thermally cycle (except for the adsorption material), thus increasing their life and lowering operational costs. An embodiment of the invention may have only the higher temperature portions of the system designed to resist high temperature halogen attack, while the lower temperature portions of the system may only be designed to resist aqueous phase halogen attack, resulting in lower capital costs.

In an embodiment of the invention shown in Figure 1, the contaminant-adsorbed packed bed 13B is maintained at a negative pressure to aid in desorbing the contaminates. The negative pressure is maintained by a vacuum blower system 100. The contaminated, desorption air stream 26 is directed into the inlet 102 of the blower system 100, thus generating and maintaining a negative pressure in the packed bed 13B.

Now referring to Figure 3, a preferred embodiment of the invention may transfer the desorption air stream 28 through the packed bed 13B (not shown) via slotted pipes. The desorption air stream 28 enters the packed bed 13B through a slotted inlet pipe 150 that extends into the channel 56. The desorption air stream 28 flows through the packed bed and exits the channel through slotted outlet pipes 152 also extending through the channel. The contaminated, desorption air stream 26 is then directed into the inlet of the blower system, thus generating and maintaining a negative pressure to draw the air stream through the bed. Preferably, the outlet pipes 152 are upstream of the bed flow 40 so that the desorption air stream 28 flows in a countercurrent direction to maximize desorption.

Referring now to Figures 1 and 2, the rotary air lock valves 60 and 74 isolate the desorption channel 56 to assist in maintaining the negative pressure therein. Other embodiments of the invention may use other air locking means.

Now referring to Figure 4, an embodiment of the invention may use a valve- chamber-valve system 200 as an air lock. The system 200 has a first valve 202 between the adsorption channel 38 and an isolation chamber 204. A second valve 206 is located between the isolation chamber 204 and the desorption channel 56.

The packed bed 13A is transferred by opening the first valve 202 and the bed falling into the isolation chamber 204, as is shown in Figure 4. The first valve is then closed and the second valve 206 is opened, enabling the adsorption material 44 of packed bed 13A to fall into the desorption channel 56 to form packed bed 13B.

Other embodiments of the invention may have a sufficient pressure drop in the packed bed 13B to essentially act as an air lock.

The contaminated, desorbed air stream 26 may be further processed in a treatment system 104 (as shown in Figure 1). In an embodiment of the invention, the treatment system 104 may further condense the contaminants of the stream, such as is disclosed in U. S. Patent No. 5,281,257 to Harris entitled"System for Increasing Efficiency of Vapor Phase Polluant Removal with On-site Regeneration and Polluant Recovery,"which is incorporated herein by reference in its entirety. In another embodiment of the invention, the treatment system may process the stream by oxidizing the contaminants, such as is disclosed in U. S.

Patents Nos. 4,688,495 to Galloway entitled"Hazardous Waste Removal System" ; 4,823,711 to Kroneberger et al. entitled"Thermal Decomposition Processor and System" ; 5,165,884 to Martin et al. entitled"Method and Apparatus for Controlled Reaction in a Reaction Matrix" ; 5,320,518 to Stilger et al. entitled"Method and Apparatus for Recuperative Heating of Reactants in a Reaction Matrix" ; and 5,601,790 to Stilger et al. entitled"Method and Afterburner Apparatus for Control of Highly Variable Flows,"which are all incorporated herein by reference in their entireties.

While the Figures depict the adsorption and desorption channels as being aligned and vertically oriented, other embodiments of the invention may have channels that are tilted, skewed, curved, or not aligned. Additionally, the invention may be used to in other removal processes that adsorb a species onto adsorbent material and then regenerate the material, such as decontaminating nitrogen, desalinization, water softening, ion extraction, and air drying, such as for compressed air, control air, or landfill-produced methane prior to combustion.

Consequently, the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.