WO1996009887A1

WO1996009887A1 - Self-heating electrically conductive sorption system and method

Info

Publication number: WO1996009887A1
Application number: PCT/US1995/011384
Authority: WO
Inventors: Harris Gold; Richard Edwin Hicks; Andrew Cecil Harvey; John Franklin Mccoy, Iii
Original assignee: Foster-Miller Inc.
Priority date: 1994-09-26
Filing date: 1995-09-08
Publication date: 1996-04-04

Abstract

A self-heating electrically conductive sorption system (10) and method for separating species of different adsorption characteristics in a fluid includes flowing a contamined fluid through an electrically conductive sorbent bed (14) having a multiplicity of adsorption sites and providing an electrical current through the sorbent bed to self-heat the electrically conductive sorbent bed.

Description

SELF-HEATING ELECTRICALLY CONDUCTIVE SORPTION SYSTEM AND METHOD

FIELD OF INVENTION

This invention relates to an improved electrically conductive sorption system and method for separating species of different adsorption characteristics in a fluid, and more particularly to such a system in which the bed itself is electrically conductive and acts as the heater to self-heat the bed and a vacuum is used to draw off the adsorbed species.

BACKGROUND OF INVENTION Carbon bed filters containing a multiplicity of adsorption sites are used in sorption systems to filter the contaminated fluid by removing the contaminants and other adsorbates from the fluid. After a period of time, the adsorption sites of the carbon bed become sufficiently occupied by adsorbates so that regeneration of the bed to remove the contaminants and other adsorbed species from the adsorption sites becomes necessary. Regeneration requires that the bed be heated to an elevated temperature and purged with regeneration fluid such as steam or inert gas and/or placed under vacuum to remove the contaminants and other adsorbed species from the bed. Bed regeneration has been accomplished both remotely from the sorption system and more efficiently in situ. Regeneration of carbon beds in situ has been accomplished by heating the bed with an inert gas or steam to an elevated temperature and purging the bed with the inert gas or with the steam to remove contaminants and the other adsorbed species captured at the adsorption sites of the bed during fluid filtration. The contaminants and either the purge gas or the steam used to purge the bed are then typically cooled to recover the contaminants for proper disposal.

With steam systems, the steam is used to heat the carbon bed and purge the desorbed contaminants from the bed. The steam system is not energy efficient. In fact, the energy required to heat a carbon bed to the regeneration temperature with steam is approximately seven times the calculated theoretical energy needed simply to heat the same carbon bed to the given temperature. The steam containing the contaminants is then cooled to condense the steam and the contaminants and effect separation between the water and the water immiscible contaminants. In the case of water miscible contaminants, additional capital intensive equipment is required to separate the contaminants from the water. The overall energy efficiency of this process is reduced due to the indirect method of heating the carbon bed and the need for additional downstream separation.

Using an inert gas to purge the carbon bed also requires specialized equipment and is also not energy efficient. The energy required to heat the carbon bed to the

I regeneration temperature using inert gas is approximately three times the calculated theoretical energy needed simply to heat the same carbon bed to the given temperature.

With inert gas systems, the heat capacity of the inert gas, such as nitrogen, is very low, and very high gas flows are required to heat the carbon bed up in a reasonable amount of time. The inert gas is typically heated above the regeneration temperature of the carbon and then passed through the carbon bed. The gas transfers heat to the bed as the gas cools so that a temperature gradient results between the inlet and exit sides of the bed; this gradient varies with the time of hot gas circulation. The contaminants are purged from the carbon after some minimum regeneration temperature is reached or exceeded at all points in the bed. Then, both the inert gas and the contaminants are cooled and the contaminants are condensed for recovery. The gas can be recirculated if it is reheated. While the operating costs of this type of system are less than those for steam regeneration due to the elimination or reduction of the downstream separation costs, the overall energy efficiency of this system is still relatively low due to the indirect method used to heat the carbon. Moreover, similar to the forced steam system, by heating the bed with an inert gas, the bed is heated in a non-uniform manner and the heating of the bed is not easily controllable.

By not being able to easily control the bed temperature and raise the temperature in the bed uniformly with the inert gas and steam systems, the bed may not be heated in temperature steps up to the regeneration temperature. This step heating is desirable, as after each temperature step a desorption/stripping cycle may be carried out. That is to say, if a mixture of solvents is adsorbed, some degree of solvent separation could be achieved by sequencing the regeneration process at discrete, increasing levels of uniform bed temperature. Since the bed temperature, with steam and inert gas heating, rises slowly and unevenly throughout the bed thickness, the regeneration process cannot properly be carried out in such a sequence of steps with that type of heating.

One prior art system discloses heating the bed with electric current instead of using forced steam or heated inert gas (U.S. Patent No. 5,187,131, Tigglebeck). However, this system teaches the use of iron filings located within the carbon bed in order to facilitate electrical conduction through the carbon bed. This system is ineffective and, in fact, may be inoperable in actual practice, in that the iron filings will oxidize over a period of time and will cause the resistance of the bed to increase, thereby limiting the electric current flow through the carbon bed and negatively affecting heating of the carbon bed. Moreover, the iron filings included within the carbon bed occupy valuable carbon filter space; thus, there is necessarily less filtration area. Moreover, this system teaches heating the bed and applying a vacuum in order to recover adsorbates and then using hot inert gases to heat the bed and draw off the adsorbate. The inert gas is then chilled to collect the adsorbents and reheated to maintain bed temperature.

Another prior art system (United Kingdom Patent No. 207,547) teaches self- heating a carbon bed. However, recovery of adsorbate is accomplished by liquefaction in a cooler or by compression. Also, use of a scavenging gas is taught during heating of the adsorption media.

Yet another prior art system (United Kingdom Patent No. 285,480) discloses supplying a scavenging agent such as steam, for example, to the adsorption medium prior to beginning the regeneration process.

SUMMARY OF mVENTIQN

It is therefore an object of this invention to provide an electrically conductive sorption system and method for separating species of different adsorption characteristics in a fluid in which the carbon bed is electrically self-heated by utilizing the carbon in the carbon bed as an electrical conductor.

It is a further object of this invention to provide such an electrically conductive sorption system and method which accomplishes in situ regeneration of the carbon bed without use of an inert gas or steam. It is a further object of this invention to provide such an electrically conductive sorption system and method that is energy efficient.

It is a further object of this invention to provide such an electrically conductive sorption system and method that is not capital intensive.

It is a further object of this invention to provide such an electrically conductive sorption system and method in which the carbon bed may be uniformly heated.

It is a further object of this invention to provide such an electrically conductive sorption system and method in which the heating of the carbon bed is easily controlled and may be heated in temperature steps.

The invention results from the realization that a truly simple and efficient electrically conductive sorption system for separating species of different adsorption characteristics can be achieved by using a sorbent bed which is also electrically conductive so that an electric current can be applied directly to the bed to self-heat the bed to enhance adsorption and effect regeneration as well and by the further realization that the complexity and inefficiency of using a separate purge gas or steam for heating and regeneration can be avoided by applying a vacuum instead to remove the adsorbed species.

This invention features an electrically conductive sorption system for separating species of different adsorption characteristics in a fluid. There is a containment vessel and an electrically conductive permeable sorbent bed in the vessel having a multiplicity of adsorption sites. A porting structure supplies contaminated fluid at one surface of the bed and receives the decontaminated fluid at another surface of the bed. A pair of spaced electrodes apply current through the bed to self-heat the electrically conductive 96/09887 PCJ7US95/11384

permeable sorbent bed.

In a preferred embodiment the porting structure may include means for selectively closing the ports and isolating the bed. The porting structure may also include means for reducing the total pressure in the bed and applying a current through the bed to increase its temperature to remove an adsorbed specie from the adsorption sites. The means for reducing the total pressure may include means for applying a vacuum to the bed. The sorbent bed may be carbon. The flow of fluid through the bed and the path of the electric current through the bed may be transverse or parallel to one another. There may also be included means for cooling the removed adsorbed specie to condense and collect it. There may be further included means for raising the bed temperature in a plurality of discrete temperature steps to separately remove adsorbed species from said adsorption sites. There may also be included means for sequentially cooling each removed adsorbed specie to individually condense and collect each adsorbed specie. The sorbent bed may be homogeneous.

The invention also features a method of separating species of different adsorptive characteristics, including flowing a contaminated fluid through an electrically conductive sorbent bed having a multiplicity of adsorption sites and providing an electric current through the sorbent bed to self-heat the electrically conductive sorbent bed.

In a preferred embodiment the fluid flow through the bed may be stopped and the bed isolated. The total pressure in the bed may be reduced and a current may be applied through the bed to increase its temperature to remove an adsorbed specie from the adsorption sites. The step of reducing the total pressure may include applying a vacuum to the bed or reducing the temperature in an area in proximity to the bed. The fluid flow 6/09887 PCMJS95/11384

and current path through the bed may be transverse or parallel to one another. There may also be included the step of cooling the removed adsorbed specie to condense and collect it. The total pressure in the bed may be reduced and a current may be applied through the bed to increase its temperature in a plurality of discrete temperature steps to separately remove adsorbed species from the adsorption sites. There may further be included a step of sequentially cooling each removed adsorbed specie to individually condense and collect each adsorbed specie.

DISCLOSURE OF PREFERRED EMBODIMENT

Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

Fig. 1 is a schematic flow diagram showing the operation of an electrically conductive sorption system with a self-heating electrically conductive permeable sorbent bed according to this invention;

Fig. 2A is a schematic flow diagram of the adsorbate collector system according to this invention; and

Fig. 2B is a schematic flow diagram of an alternative adsorbate collector system according to this invention.

This invention may be accomplished with an electrically conductive sorption system which separates species of different adsorption characteristics in the fluid. There is a containment vessel and inside the vessel is provided an electrically conductive permeable sorbent bed with a multiplicity of adsorption sites. The bed is typically homogeneous, e.g. carbon, and more especially activated carbon, and may be in the form of granular or pelletized particles. The flow of fluid through the bed and the path of the electric current through the bed may be transverse to one another so that the electrical characteristics and the flow characteristics can each be independently controlled: that is, the electrical resistance can be increased without increasing the flow resistance. However, the fluid flow and electric current flow may be parallel. There is a power supply which provides current flow through a pair of electrodes on either side of the bed to self-heat the conductive bed. The energy efficiency of the system is thereby significantly increased. That is, the direct heating of the very carbon bed that is the adsorption medium facilitates operation at close to theoretical efficiencies. In the past the use of conductive dopants such as iron in the carbon, while it did help conductivity until oxidation occurred, nevertheless detracted from the amount of carbon present and thereby reduced the effectiveness of the adsorption. The efficiency of this invention can be seen from the fact that a carbon bed of 210 pounds with an average power input of 55 kilowatts when operated for three minutes reaches a temperature of 150 °C and consumes 2.75 kilowatt hours. Thus the energy input to reach an average temperature of 150°C then is 1.31 kilowatt hours per 100 pounds of carbon. 1.31 kilowatt hours per 100 pounds of carbon is very efficient and close to the theoretical goal. For example, with an average temperature of 150°C and an average temperature rise of 130°C and an assumed specific heat of 0.2 BTU/lb. °R, the theoretical energy input is calculated to be 1.4 kilowatt hours per 100 pounds, slightly higher (within experimental error) than the experimentally measured value of 1.31 kilowatt hours per 100 pounds of carbon.

The system uses a porting structure which can be selectively closed so that the 96/09887 PCMJS95/11384

bed is isolated. For regeneration, once the bed is isolated, the total pressure in the bed is reduced to draw off the adsorbed specie or species. Reducing the total pressure also minimizes oxidation of the bed when it is self-heated. A current is applied through the bed to increase its temperature and enhance the removal of the adsorbed species from the adsorption sites. The technique for reducing the total pressure may employ applying a vacuum to the bed or providing a cold surface in the porting structure which causes a drop in the pressure of the adsorbate by condensing it on said surface.

Heating the carbon bed reduces the thermodynamic adsorption capacity of the carbon, and thus the contaminants adsorbed onto the carbon desorb into the vapor phase. In order to maintain this thermodynamic driving force for desorption, the desorbed contaminants must be removed from the carbon bed. This is accomplished by applying the vacuum which allows the contaminants to escape. Thus the partial pressure of the contaminants is reduced (which maintains the thermodynamic driving force at a given temperature) primarily through removing them from the carbon bed. It is the combined effect of reducing the total pressure and removing the contaminants and other fluids from the vapor space in the bed which reduces the contaminant partial pressure and maintains the thermodynamic driving force.

Even if some small quantity of inert purge gas is required, one of the advantages of a resistively heated system is that the purge gas requirement can be reduced by over an order of magnitude relative to conventionally heated inert gas systems. In the resistively heated system, the inert gas is used only to help sweep out the desorbed adsorbates, for example, volatile organic compounds (VOCs), that is, assisting pure diffusion, while in conventional systems the gas is also used to heat the carbon bed. Because the heat capacity of inert gas is generally low, high gas flows are required to heat the carbon in a reasonable amount of time.

The adsorbed species removed from the bed may then be cooled to condense and collect the adsorbed species together or separately.

The electrically conductive sorption system according to this invention may be used in any sorption system application regardless of size, from large scale industrial applications to personal size (e.g., respirators) portable units.

There is shown in Fig. 1 an electrically conductive sorption system 10 including a container 12 which holds electrically conductive permeable sorbent bed 14 typically made of carbon granules. Container 12 includes input plenum 16 and screen or grid 18 at the input port 20 controlled by input valve 22. There is also an output plenum 24 and output screen or grid 26 which communicates with the output port 28 controlled by output valve 30. Power supply 32 provides a current from electrode 34 through bed 14 to electrode 36 in a path as indicated by arrows 38 which is transverse to the flow of the fluid from input port 20 to output port 28. Alternatively, electrodes 34a and 36a, shown in phantom, may provide current through the bed which is parallel to the fluid flow. Electrodes 34 and 36 are suitably insulated from the surrounding environment such as container 12 and screens or grids 18 and 26. Also, insulators 35 and 37 are provided to insulate electrodes 34 and 36 from the environment outside of sorption system 10. A control 33 may be used to manually or automatically adjust the electric power flow from the power supply 32 to bed 14 to raise the temperature in steps for separation of a number of different adsorbed species. The bed may be homogeneous or at least may contain only filter materials, which are electrically conductive, but not contain additives or dopants added solely to affect electrical conductivity.

When the adsorption sites in bed 14 become sufficiently occupied by the adsorbate so that the system is no longer effective, the valves 22 and 30 may be closed to isolate bed 14. The total pressure in bed 14 is then decreased and the adsorbates are allowed to escape to reduce the total pressure of the adsorbates in the bed. The total pressure may be reduced by applying a vacuum from vacuum source 40 through valve 42 which is directional and can selectively apply the vacuum either to the input end through valve 22 or the output end through valve 30, or both. The reduction in total pressure can also be effected by using a cold surface 46 which can be installed in the area of input port 20 and kept cool either by a cryogenic or conventional refrigeration source 48. In addition, a small amount of an inert gas may be supplied, for example nitrogen from nitrogen source 50 applied through directional valve 52 to either the input end at valve 22 or the output end at valve 30, preferably only after the maximum temperature is reached. This gas is only used to accelerate the transport of contaminant from the bed and vessel by bulk convection, that is, displacement, which is faster than pure diffusion, especially when the total pressure is low.

Note that the regeneration of the bed 14 can be accomplished with and without the use of a purge gas. This is one of the reasons why the system of this invention is so efficient: the conductive bed itself is heated directly, not through a gas. During the early period of the regeneration cycle, the contaminant evolves from the bed rapidly, massively, and is easily purged from the vessel using moderate vacuum. In the case where a purge gas is used, it serves only to sweep the residual desorbed contaminants from the bed approaching the end of the heating and regeneration cycle, which allows purge gas rates to be reduced by over an order of magnitude relative to prior art inert gas systems. When a strong vacuum is applied, the purge gas can be eliminated which further increases the system efficiency but may increase cycle time. In this case, there is no need to heat a gas, apply it to the bed, then cool the gas to remove the contaminants and reheat the gas once again in order to recycle the gas back to the bed. Rather, with this invention the bed is heated constantly and uniformly by applying current directly to the substance of the bed and during the cleaning of the bed no purge gas is used, the total pressure is simply reduced using a vacuum pump or one of the other approaches explained, and the adsorbates are removed from the bed by the vacuum source.

Also, because the temperature of the bed rises uniformly and the temperature level is easily controllable, the bed temperature may be raised in a series of discrete steps up to the regeneration temperature. At each temperature step with the total pressure reduced, different adsorbed species may be individually removed from the carbon bed. This is useful when a mixture of materials is adsorbed.

A system 60 for accomplishing collection of different adsorbed species separately or together is shown in Fig. 2A. When the adsorption sites in bed 14, Fig. 1, become sufficiently occupied by the adsorbate, valves 22 and 30 may be closed to isolate bed 14. However, although the bed is isolated, either one or both of valves 22, 30 allow connection between either or both ports 20, 28 and vacuum source 49a through tubing 62. Vacuum source 49a is used to decrease the total pressure in the carbon bed while the carbon bed is heated which allows adsorbates to escape through tubing 62. These adsorbates are cooled by cooler 64 and further cooled and condensed by cooler 66 and chiller 68. The cooled and condensed adsorbates then pass through valve 70 and are collected in initial adsorbate collector 72. As discussed above, the bed temperature may be raised in uniform steps so that separate species are separately drawn from the carbon bed. If the evacuation is accomplished in this manner then the initial adsorbate collector 72 may be used to collect the first specie drawn off the carbon bed and additional adsorbate collector 74 may be used to collect a second adsorbate specie. Further collectors, depending on the number of separate species, may also be used. The flow of adsorbates to these various collectors may be controlled by valves 76 and 78. Also, there may be additional valves if there are more than two species of adsorbates to be collected.

After the majority of the adsorbate is collected, the bed temperature may be raised quickly to a higher level in order to drive out residual adsorbate and reach a low equilibrium partial pressure. If desired, small quantities of purge gas may be used to transport the low-partial pressure adsorbate out of the bed because pure diffusion by adsorbate at low pressure (strong vacuum) would require more time. After the low- partial pressure adsorbate is removed from the bed, a high mass flow rate but minimal total mass of recirculated gases to cool the bed to below the air oxidation temperature may be performed. Then, the bed may be cooled down to the operating temperature using, for example, an inert gas.

If an inert gas is used, it may be recirculated through the carbon bed by valve 70 through valves 81, and 22 and 30, after adsorbate has been condensed and the gas re-heated by heater 80, if desired. Valve 81 also controls the flow of water mist which may be supplied to the bed if desired for cooling the bed. Another configuration of this same system is shown in Fig. 2B. The major difference between this system and the system of Fig. 2 A is that a recuperative heat exchanger 82 is utilized to perform both the cooling function of cooler 64 and the heating function of heater 80.

Although specific features of this invention are shown in some drawings and not others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention.

Other embodiments will occur to those skilled in the art and are within the following claims:

Claims

1. An electrically conductive sorption system for separating species of different adsorption characteristics in a fluid, comprising: a containment vessel; an electrically conductive permeable sorbent bed having a multiplicity of adsorption sites in said vessel; a porting structure for supplying contaminated fluid at one surface of said bed and for receiving the decontaminated fluid at another surface of said bed; and

a pair of spaced electrodes for applying current through said bed to self-heat said electrically conductive permeable sorbent bed.

2. The sorption system of claim 1 in which said porting structure includes means for selectively closing said ports and isolating said bed.

3. The sorption system of claim 2 in which said porting structure includes means for reducing the total pressure in said bed and applying a current through said bed to increase its temperature to remove an adsorbed specie from said adsorption sites.

4. The sorption system of claim 2 in which said porting structure includes means for applying a vacuum to said bed.

5. The sorption system of claim 1 in which said sorbent bed is carbon.

6. The sorption system of claim 1 in which the flow of fluid through said bed and the path of electric current through said bed are transverse to one another.

7. The sorption system of claim 1 in which the flow of fluid through said bed and the path of electric current through said bed are parallel to one another.

8. The sorption system of claim 3 further including means for cooling said removed adsorbed specie to condense and collect it.

9. The sorption system of claim 1 further including means for raising the bed temperature in a plurality of discrete temperature steps to separately remove adsorbed species from said collection sites.

10. The sorption system of claim 9 further including means for sequentially cooling each said removed adsorbed specie to individually condense and collect each said adsorbed specie.

11. The sorption system of claim 1 in which said sorbent bed is homogeneous.

12. A method of separating species of different adsorptive characteristics, comprising: flowing a contaminated fluid through an electrically conductive sorbent bed having a multiplicity of adsorption sites; and providing an electrical current through said sorbent bed to self-heat said electrically conductive sorbent bed.

13. The method of separating species of different adsorptive characteristics of claim 12 which includes stopping fluid flow through said bed and isolating said bed.

14. The method of separating species of different adsorptive characteristics of claim 13 further including reducing the total pressure in said bed and applying a current through said bed to increase its temperature to remove an adsorbed specie from said collection sites.

15. The method of separating species of different adsorptive characteristics of claim 14 in which reducing the total pressure includes applying a vacuum to said bed.

16. The method of separating species of different adsorptive characteristics of claim 14 in which reducing the total pressure includes reducing the temperature in an area in proximity of said bed.

17. The method of separating species of different adsorptive characteristics of claim 12 in which the fluid flow and current path through said bed are transverse to one another.

18. The method of separating species of different adsorptive characteristics of claim 12 in which the fluid flow and current path through said bed are parallel to one another.

19. The method of separating species of different adsorptive characteristics of claim 14 further including cooling said removed adsorbed specie to condense and collect it.

20. The method of separating species of different adsorptive characteristics of claim 12 further including reducing the total pressure in said bed and applying a current through said bed to increase its temperature in a plurality of discrete temperature steps to separately remove adsorbed species from said adsorption sites.

21. The method of separating species of different adsorptive characteristics of claim 20 further including sequentially cooling each said removed adsorbed specie to individually condense and collect each said adsorbed specie. AMENDED CLAIMS

[received by the International Bureau on 29 January 1996 (29.01.96); original claims 1-21 replaced by amended clains 1-20 (4 pages)].

1. An electrically conductive sorption system for removing adsorbed species from a sorbent bed, comprising: a containment vessel; an electrically conductive permeable sorbent bed in said vessel having a multiplicity of adsorption sites and having a bed pressure and bed temperature; a porting structure for supplying a contaminated fluid flow to a first port at one surface of said bed and for receiving a decontaminated fluid flow from a second port at another surface of said bed; the adsorption sites of said bed adsorbing the adsorbed species from the fluid; means for selectively closing said first and second ports to isolate said bed; means, responsive to said means for selectively closing, for reducing the total pressure in said bed after the bed is isolated; and a pair of spaced electrodes for applying a current flow over a current flow path through said bed to self-heat said bed while the total pressure in said bed is reduced to remove from the adsorption sites the adsorbed species.

2. The sorption system of claim 1 in which said means for reducing the total pressure in said bed includes means for applying a vacuum to said bed.

3. The sorption system of claim 1 in which said means for reducing the total pressure in said bed includes means for reducing the temperature in an area in proximity of said bed.

4. The sorption system of claim 1 in which said sorbent bed is carbon.

5. The sorption system of claim 1 in which the flow of fluid through said bed and the path of electric current through said bed are transverse to one another. 6. The sorption system of claim 1 in which the flow of fluid through said bed and the path of electric current through said bed are parallel to one another.

7. The sorption system of claim 1 further including means for raising the bed temperature in a plurality of discrete temperature steps to separately remove adsorbed species from said adsorption sites.

8. The sorption system of claim 7 further including means for sequentially cooling each said removed adsorbed species to individually condense and collect each said adsorbed species.

9. The sorption system of claim 1 in which said sorbent bed is homogeneous.

10. The sorption system of claim 1 further including means for cooling said bed after the plurality of species have been removed from said adsorption sites.

11. A method of removing adsorbed species from a sorbent bed, comprising: flowing a contaminated fluid containing the species through an electrically conductive sorbent bed having a multiplicity of adsorption sites and having a bed pressure and bed temperature; said sites adsorbing the species from the contaminated fluid flow; stopping the fluid flow through and isolating said bed; reducing the total pressure in said bed; and applying an electric current flow over a current flow path through the bed to self-heat said bed while the total pressure in said bed is reduced to remove from the adsorption sites the adsorbed species. 12. The method of claim 11 in which reducing the total pressure includes applying a vacuum to said bed.

13. The method of claim 11 in which reducing the total pressure includes reducing the temperature in an area in proximity of said bed.

14. The method of claim 11 in which the fluid flow and current path through said bed are transverse to one another.

15. The method of claim 11 in which the fluid flow and current path through said bed are parallel to one another.

16. The method of claim 11 further including increasing the bed temperature in a plurality of discrete temperature steps to separately remove adsorbed species from said adsorption sites.

17. The method of claim 16 further including sequentially cooling each said removed adsorbed species to individually condense and collect each adsorbed species.

18. The method of claim 11 further including cooling said bed after the plurality of adsorbed species have been removed from said adsorption sites.

19. An electrically conductive sorption system for separately removing a plurality of species having different adsorption characteristics from a sorbent bed, comprising: a containment vessel; an electrically conductive permeable sorbent bed in said vessel having a multiplicity of adsorption sites and having a bed pressure and bed temperature; a porting structure for supplying a contaminated fluid flow to a first port at one surface of said bed and for receiving a decontaminated fluid flow from a second port at another surface 21

of said bed; the adsorption sites of said bed adsorbing the plurality of species from the fluid; a pair of spaced electrodes for applying a current flow over a current flow path through said bed to self-heat said bed;

means for selectively closing said first and second ports to isolate said bed; means, responsive to said means for selectively closing, for reducing the total pressure in said bed after the bed is isolated; and means for adjusting the current flow from said electrodes while the total pressure in the bed is reduced to uniformly raise the bed temperature in a plurality of discrete temperature steps to separately remove each adsorbed species from said adsorption sites.

20. A method of separately removing a plurality of species having different adsorption characteristics from a sorbent bed, comprising: flowing a contaminated fluid containing the plurality of species through an electrically conductive sorbent bed having a multiplicity of adsorption sites and having a bed temperature and bed pressure; said sites adsorbing the plurality of species from the contaminated fluid flow; stopping the fluid flow through said bed and isolating said bed; reducing the total pressure in said bed; applying a variable electrical current flow over a current flow path through said bed while the total pressure in the bed is reduced to uniformly self-heat said bed in a plurality of discrete temperature steps to separately remove each adsorbed species from said adsorption sites.