Methods and systems for regenerating a temperature swing adsorption unit with pipeline hydrogen

Abstract

A method that includes withdrawing a hydrogen regeneration gas stream from a hydrogen pipeline is disclosed. The method further includes contacting the hydrogen regeneration gas stream with a rich adsorbent bed comprising one or more impurities to produce a spent regeneration gas stream enriched in the one or more impurities and a lean adsorbent bed depleted in the one or more impurities. The method also includes withdrawing a stored hydrogen stream comprising one or more impurities from the storage cavern and contacting the hydrogen stream with the lean adsorbent bed to produce a product hydrogen stream depleted in the one or more impurities and the rich adsorbent bed enriched in the one or more impurities.

Description

METHODS AND SYSTEMS FOR REGENERATING A TEMPERATURE SWING ADSORPTION UNIT WITH PIPELINE HYDROGENCROSS-REFRENCE TO RELATED APPLICATION

[0001] The present application claims priority to U.S. Provisional Application 63 / 652,311 filed May 28, 2024, which is incorporated by reference herein.BACKGROUND OF THE INVENTION

[0002] Hydrogen stored in underground formations such as salt caverns may require dehydration when withdrawn. One method of dehydration is temperature swing adsorption (TSA) in which a withdrawn hydrogen stream is passed over an adsorbent bed to remove impurities such as water vapor. Once the adsorbent bed is loaded with impurities it may be taken offline and regenerated by heating and passing a clean gas over the adsorbent bed to remove the impurities. The clean gas used to regenerate the adsorbent bed may be sourced from a nearby hydrogen pipelineSUMMARY OF THE INVENTION

[0003] A hydrogen regeneration gas stream is withdrawn from a hydrogen pipeline to regenerate a hydrogen TSA adsorbent, removing adsorbed impurities to produce a spent regeneration gas. The spent regeneration gas may be injected into a storage cavern. A stored hydrogen stream may be withdrawn from the storage cavern, or from a second storage cavern, and purified in the hydrogen TSA.BRIEF DESCRIPTION OF DRAWINGS

[0004] The figure included herein illustrates certain aspects of some of the embodiments of the present invention and should not be used to limit or define the invention.

[0005] Figure 1 is a schematic view depicting an embodiment of a hydrogen purification process according to one or more aspects of the present disclosure.DETAILED DESCRIPTION OF THE INVENTION

[0006] The ensuing detailed description provides preferred exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention, as set forth in the appended claims.

[0007] The terms “depleted” or “lean” mean having a lesser mole percent concentration of the indicated component than the original stream from which it was formed. “Depleted” and “lean” do not mean that the stream is completely lacking the indicated component.

[0008] The terms “rich” or “enriched” mean having a greater mole percent concentration of the indicated component than the original stream from which it was formed.

[0009] “Downstream” and “upstream” refer to the intended flow direction of the process fluid transferred. If the intended flow direction of the process fluid is from the first device to the second device, the second device is downstream of the first device. In case of a recycle stream, downstream and upstream refer to the first pass of the process fluid.

[0010] The present disclosure is directed to a method of purifying a stored hydrogen stream using a temperature swing adsorption (TSA) unit comprising an adsorbent and regenerating the adsorbent once it is loaded with impurities. A hydrogen storage cavern may comprise a hollowed-out portion of a solid salt formation, or a naturally occurring underground formation such as a depleted natural gas field. In the case of a cavern in a solid salt formation, the pressure of the cavern may be controlled by injecting or withdrawing a brine solution. The pressure of the cavern may be controlled by compression or withdrawal of hydrogen. The volume of the hydrogen storage cavern may be on the order of 1 billion standard cubic feet or greater to provide backup hydrogen in the case of a hydrogen production plant being taken off-line, and / or to provide hydrogen supply to customers in excess of normal demand. Hydrogen may be supplied to the hydrogen storage cavern by sources such as hydrogen production plants, hydrogen pipelines, tube trailers, or liquid ISO containers.

[0011] Cryogenic liquid may be pumped into the hydrogen storage cavern using a cryogenic pump, for example to a pressure ranging from 2500 to 5000 psia (170 to 350 bar) then vaporized in a high-pressure vaporizer. Vaporizing at high pressure allows a pressure regulator downstream of the high-pressure vaporizer to further increase the pressure of the resulting gas stream because of the higher mass flow rate provided by the high-pressure vaporizer. Cryogenic pumps are more energy efficient than compressors to deliver a gas stream to the same pressure. For example, the Lawrence Livermore National Laboratory reported (LLNL-JRNL-746861) that filling a hydrogen tank to 700 bar pressure required 3 kWh / kg H2 using compressors but only 1.1 kWh / kg H2 when using cryogenic pumps. The pressure regulator may reduce the pressure required in the cryogenic pump and further improve the energy efficiency of the process. The high-pressure gas stream may range in pressure from 1000 to 3500 psia (70 to 240 bar) then be stored, for example in an underground formation. The underground formation may comprise a salt cavern formed within an impermeable solid salt layer. The pressure may be controlled in the salt cavern by injectingor withdrawing saturated brine. The pressure of the salt cavern may be controlled by compression or withdrawal of hydrogen. The underground formation may comprise a permeable rock formation sealed between impermeable layers. The pressure in the underground storage cavern may range from 800 to 2500 psia (55 to 170 bar). A low-pressure vaporizer may be used when the cryogenic liquid supply is at too low a pressure to supply the high-pressure vaporizer. The low-pressure vaporizer may also be used as a heat exchanger to bring cold light gas such as boil-off gas to near ambient temperatures before compression and storage.

[0012] The storage cavern may be maintained in between a lower pressure limit and an upper pressure limit. The lower pressure limit may be defined as a pressure sufficient to keep the storage cavern from caving in, for example ranging from 15% to 40%, or 15% to 20% of the lithostatic pressure of the surrounding formation. The lower pressure limit may be a function of the structural integrity of the salt formation. For typical formation materials this may range from 0.15 psi / ft to 0.4 psi / ft (0.034 to 0.09 bar / m), or from 0.15 psi / ft to 0.2 psi / ft (0.034 to 0.045 bar / m), of depth below the surface. The storage cavern is accessed via a well with a well casing, typically comprising one or more cemented steel sections. The upper pressure limit may be defined relative to the lithostatic pressure at the point where the bottom of the well casing meets the top of the storage cavern, for example 80% to 100%, or from 80% to 85%, of the lithostatic pressure. For typical formation materials this may range from 0.8 psi / ft to 1 psi / ft of depth (0.18 to 0.23 bar / m), or from 0.8 psi / ft to 0.85 psi / ft of depth (0.18 to 0.19 bar / m), below the surface. The upper pressure limit may be defined by regulatory agencies.

[0013] Additionally, the ability to utilize a salt cavern to assist in the supply of higher purity hydrogen without leakage through the salt cavern walls is difficult based on the properties of hydrogen. Hydrogen is the smallest and lightest element within the periodic table of elements, having an atomic radius measuring 25±5 pm. Consequently, higher purity hydrogen is typically considered one of the most difficult elements to contain within underground salt formations without measurable losses through the salt cavern walls.

[0014] While in storage, impurities such as water vapor, CO2 and H2S may contaminate the hydrogen by diffusion out of the walls and / or brine solution. CO2 and H2S may react to form COS, for example by surface-catalyzed reactions on adsorbents or cavern walls. Selecting an adsorbent such as low-sodium 5A may minimize the formation of COS within the TSA. At least a portion of the water vapor may be removed by cooling the stored hydrogen in a chiller and partially condensing a liquid water stream. The chiller may be configured to allow the liquid water stream to flow back into the storage cavern by gravity. The pressure of the stored hydrogen may be reduced in any suitable pressure reduction device or devices, such as avalve or orifice, if the storage cavern is operating at a pressure above the desired operating pressure of downstream processing units. The temperature of the stored hydrogen may be reduced after pressure reduction to further remove water by condensation. Impurities in the stored hydrogen may be removed using a lean adsorbent bed, where lean refers to a low concentration of impurities on the adsorbent, resulting in a hydrogen product stream that may be used locally, liquefied, or placed into a pipeline or tube trailer for transport. The hydrogen product stream may comprise water at a concentration less than 1 ppmv, CO2 at a concentration less than 1 ppmv, H2S at a concentration less than 1 ppmv, and COS at a concentration less than 1 ppmv. The adsorbent may be selected to have a high capacity for water vapor, CO2, and / or H2S. If the adsorbent has a low selectivity for COS, a dedicated COS removal unit may be employed downstream of the TSA. COS removal may comprise a nickel getter, hopcalite, Selexsorb® COS, and metal oxide doped zeolites. Similarly, if the adsorbent has a low selectivity for CH4, a dedicated CH4 removal unit may be employed downstream of the TSA. CH4 removal may comprise a pressure swing adsorption unit as used in purification of syngas from steam methane reforming. As the lean adsorbent bed becomes enriched in impurities, it may be taken offline and regenerated before impurities break through with the hydrogen product. A clean hydrogen regeneration gas stream may be passed over a rich adsorbent bed while one or both of the regeneration gas stream and the rich adsorbent bed is heated to drive off impurities from the rich adsorbent bed into the regeneration gas stream to produce a spent regeneration gas stream enriched in impurities and a lean adsorbent bed that may be placed back online to purify stored hydrogen. The spent regeneration gas stream may be injected into the same hydrogen storage cavern or a different nearby hydrogen storage cavern to eliminate hydrogen losses.

[0015] TSA operation may occur in a continuous process in which adsorbent beds rotate from online service to regeneration. In a continuous process there is a constant flow (barring plant shutdown) of a clean product stream, a small fraction of which may be divided to form a regeneration gas stream. However, operation of a hydrogen storage cavern may occur in an intermittent process since there may be extended periods of time when hydrogen may be injected into the storage cavern and no hydrogen may be produced. This may result in times when a rich adsorbent bed must be regenerated while there is no stored hydrogen flowing through a lean adsorbent bed to produce a hydrogen product stream. Therefore, in the context of TSA operation we define an intermittent process as a process in which there are periods when a rich adsorbent bed is being regenerated when no lean adsorbent beds are producing hydrogen and / or periods when a lean adsorbent bed is producing hydrogen when no rich adsorbent beds are being regenerated.

[0016] Additionally, the stored hydrogen may have a relatively low concentration of impurities, so a lean adsorbent bed may spend significantly longer time online than in the regeneration phase. For example, the lean adsorbent bed may be online for a period ranging from 7 to 14 days, or from 2 to 30 days, or from 2 to 60 days, but only require regeneration for a period ranging from 1 to 12 hours or from 1 to 24 hours.

[0017] Prior to injection, the spent regeneration gas may be purified to reduce or eliminate buildup of impurities. Water vapor may be removed during compression after intercoolers and / or aftercoolers. Acid gases such as CO2, H2S, and COS may accumulate in the storage cavern if the spent regeneration gas is reinjected without treatment, which may over time cause degradation of the TSA performance and / or early breakthrough of acid gas into the product hydrogen. Acid gases may be removed from the spent regeneration gas using an absorption or adsorption system, such as an acid gas scrubber. Acid gas removal may be installed after operation for several years if acid gases are accumulating at a slow rate. Acid gas removal may not be operated on every regeneration cycle to reduce operating costs.

[0018] Figure 1 is a schematic view depicting an embodiment of a hydrogen purification process according to one or more aspects of the present disclosure. Hydrogen pipeline 1 may supply hydrogen 101 to salt cavern 4, first being compressed in compressor 2 if needed to reach the pressure of salt cavern 4. First flowmeter 3a in a metering station may be used to calculate the amount of hydrogen stored in the salt cavern 4. When stored hydrogen is withdrawn from storage cavern 4, it may first be cooled in wellhead chiller 5. Water condensate 103 may be separated from the stored hydrogen and returned to the salt cavern. In at least some embodiments, the water condensate 103 may flow back into the salt cavern 4 by gravity. The flowrate of stored hydrogen leaving wellhead chiller 5 may be calculated using a second flowmeter 3b which may be in the same metering station as first flowmeter 3a. Stored hydrogen 105 may be reduced in pressure across pressure reducer 6 and may be reduced in temperature in second chiller 7 to remove a second water condensate stream 107. The partially treated stored hydrogen stream 109 may then be passed over lean adsorbent bed 8a to remove impurities such as water vapor and acid gases to form a hydrogen product stream 111. If COS levels exiting the lean adsorbent bed 8a are higher than desired, a COS removal unit 9 may be placed downstream of the lean adsorbent bed 8a. The product hydrogen may be transported by hydrogen pipeline 1 , liquefied on-site for export, and / or used onsite.

[0019] When the lean adsorbent bed 8a is loaded with impurities, it must be taken offline as rich adsorbent bed 8b and regenerated. Regeneration gas 113 may be withdrawn from hydrogen pipeline 1 , heated in heater 10, and passed over the rich adsorbent bed 8b totransfer impurities from the adsorbent to the regeneration gas 113, producing a spent regeneration gas 115 enriched in impurities and a regenerated, lean adsorbent bed 8a that may be put back online. The spent regeneration gas 115 may be compressed in compressor 2 and returned to the salt cavern 4. If required, acid gases may be removed from the spent regeneration gas 115 in acid gas scrubber 11 prior to compression.

[0020] Aspect 1 : A method comprising withdrawing a hydrogen regeneration gas stream from a hydrogen pipeline; contacting the hydrogen regeneration gas stream with a rich adsorbent bed comprising one or more impurities to produce a spent regeneration gas stream enriched in the one or more impurities and a lean adsorbent bed depleted in the one or more impurities; withdrawing a stored hydrogen stream comprising one or more impurities from the storage cavern; and contacting the stored hydrogen stream with the lean adsorbent bed to produce a product hydrogen stream depleted in the one or more impurities and the rich adsorbent bed enriched in the one or more impurities.

[0021] Aspect 2: A method according to Aspect 1 , further comprising delivering the spent regeneration gas stream to the storage cavern.

[0022] Aspect 3: A method according to Aspect 1 or Aspect 2, further comprising delivering the product hydrogen stream to the hydrogen pipeline.

[0023] Aspect 4: A method according to any of Aspects 1 to 3, further comprising cooling the hydrogen stream prior to contacting with the lean adsorbent bed to produce a liquid water stream.

[0024] Aspect 5: A method according to Aspect 4, further comprising delivering the liquid water stream to the storage cavern.

[0025] Aspect 6: A method according to Aspect 5, wherein the liquid water stream is delivered to the storage cavern by gravity.

[0026] Aspect 7: A method according to any of Aspects 1 to 6, further comprising removing at least one of CO2, H2S, and COS from the spent regeneration gas stream prior to delivering the spent regeneration gas to the storage cavern.

[0027] Aspect 8: A method according to any of Aspects 1 to 7, wherein the hydrogen regeneration gas stream is withdrawn from the hydrogen pipeline during periods in which the hydrogen stream is not being withdrawn from the storage cavern in an intermittent process.

[0028] Aspect 9: A method according to any of Aspects 1 to 8, further comprising reducing the pressure of the hydrogen stream prior to contacting with the lean adsorbent bed to produce a liquid water stream.

[0029] Aspect 10: A method according to any of Aspects 1 to 9, further comprising removing COS from the hydrogen product stream.

[0030] Aspect 11 : A method according to any of Aspects 1 to 10, further comprising removing CH4 from the hydrogen product stream.

[0031] Aspect 12: A system comprising a storage cavern configured to receive and deliver hydrogen gas at an elevated pressure; a lean adsorbent bed in fluid flow communication with the storage cavern configured to receive a stored hydrogen stream from the storage cavern and remove impurities from the stored hydrogen stream to produce a product hydrogen stream and a rich adsorbent bed; a hydrogen pipeline in fluid flow communication with the rich adsorbent bed configured to deliver a hydrogen regeneration gas stream to remove impurities from the rich adsorbent bed to product a spent regeneration gas stream and the lean adsorbent bed; wherein the rich adsorbent bed is in fluid flow communication with the storage cavern and configured to deliver the spent regeneration gas stream to the storage cavern.

[0032] Aspect 13: A system according to Aspect 12, wherein the lean adsorbent bed is in fluid flow communication with the hydrogen pipeline.

[0033] Aspect 14: A system according to Aspect 12 or Aspect 13, further comprising a heat exchanger in fluid flow communication with the storage cavern and the lean adsorbent bed, configured to cool and partially condense a liquid water stream from the stored hydrogen stream.

[0034] Aspect 15: A system according to Aspect 14, wherein the heat exchanger is configured to deliver the liquid water stream to the storage cavern.

[0035] Aspect 16: A system according to Aspect 15, wherein the heat exchanger is configured to deliver the liquid water stream to the storage cavern by gravity.

[0036] Aspect 17: A system according to any of Aspects 12 to 16, further comprising an acid gas removal unit in fluid flow communication with the rich adsorbent bed and the storage cavern, configured to remove at least one of CO2, H2S, and COS from the spent regeneration gas stream prior to delivering the spent regeneration gas to the storage cavern.

[0037] Aspect 18: A system according to any of Aspects 12 to 17, further comprising a pressure reducer in fluid flow communication with the storage cavern and the lean adsorbent bed, configured to reduce the pressure of the stored hydrogen stream prior to contacting with the lean adsorbent bed.

[0038] Aspect 19: A system according to any of Aspects 12 to 18, further comprising a COS removal unit in fluid flow communication with the lean adsorbent bed, configured to remove COS from the hydrogen product stream.

[0039] Aspect 20: A system comprising a compressor in fluid flow communication with a storage cavern, the storage cavern configured to receive and deliver hydrogen gas at an elevated pressure; a heat exchanger in fluid flow communication with the storage cavern configured to receive a hydrogen stream from the storage cavern, cool and partially condense the hydrogen stream to produce a liquid water stream that is delivered to the storage cavern; a lean adsorbent bed in fluid flow communication with the heat exchanger configured to remove impurities from the hydrogen stream to produce a product hydrogen stream and a rich adsorbent bed; a hydrogen pipeline in fluid flow communication with the rich adsorbent bed configured to deliver a hydrogen regeneration gas stream to remove impurities from the rich adsorbent bed to product a spent regeneration gas stream and the lean adsorbent bed; wherein the rich adsorbent bed is in fluid flow communication with the storage cavern and configured to deliver the spent regeneration gas stream to the storage cavern.

[0040] Aspect 21 : A method comprising withdrawing a hydrogen regeneration gas stream from a hydrogen pipeline; contacting the hydrogen regeneration gas stream with a rich adsorbent bed comprising one or more impurities to produce a spent regeneration gas stream enriched in the one or more impurities and a lean adsorbent bed depleted in the one or more impurities; withdrawing a stored hydrogen stream comprising one or more impurities from the storage cavern; partially condensing the stored hydrogen stream to produce a partially treated hydrogen stream and a liquid water stream; delivering the liquid water stream to the storage cavern by gravity; contacting the partially treated hydrogen stream with the lean adsorbent bed to produce a product hydrogen stream depleted in the one or more impurities and the rich adsorbent bed enriched in the one or more impurities.

[0041] Aspect 22: A method according to Aspect 21 , further comprising delivering the spent regeneration gas stream to the storage cavern.

[0042] Aspect 23: A method according to Aspect 21 or Aspect 22, further comprising delivering the product hydrogen stream to the hydrogen pipeline.

[0043] Aspect 24: A method according to any of Aspects 21 to 23, further comprising removing at least one of CO2, H2S, and COS from the spent regeneration gas stream prior to delivering the spent regeneration gas to the storage cavern.

[0044] Aspect 25: A method according to any of Aspects 21 to 24, wherein the hydrogen regeneration gas stream is withdrawn from the hydrogen pipeline during periods in which thestored hydrogen stream is not being withdrawn from the storage cavern in an intermittent process.

[0045] Aspect 26: A method according to any of Aspects 21 to 25, further comprising removing COS from the hydrogen product stream.EXAMPLE

[0046] The performance of a TSA was simulated for a number of regeneration gas cases using proprietary software that solves the heat, mass, and momentum balances in an adsorption bed. The TSA was modeled at a pressure of 900 psia (bar) during the adsorption phase and 20 psia (bar) during the regeneration phase. Case 1 regenerated the rich adsorbent bed using pipeline hydrogen and returned the hydrogen to a storage cavern as described in the present disclosure. Case 2 regenerated the rich adsorbent bed using pipeline hydrogen in an open loop process in which the spent regeneration gas is vented or flared. Case 3 regenerated the rich adsorbent bed using nitrogen in an open loop process. Compared with Case 1 , Case 2 increased the losses by about 12%. Compared with Case 1 , Case 3 introduced a nitrogen impurity in the product hydrogen equal to about 270 ppm which would be an unacceptable level in most high purity applications.

[0047] While the principles of the invention have been described above in connection with preferred embodiments, it is to be clearly understood that this description is made only by way of example and not as a limitation of the scope of the invention.

Claims

CLAIMS1. A method comprising: withdrawing a hydrogen regeneration gas stream from a hydrogen pipeline; contacting the hydrogen regeneration gas stream with a rich adsorbent bed comprising one or more impurities to produce a spent regeneration gas stream enriched in the one or more impurities and a lean adsorbent bed depleted in the one or more impurities; withdrawing a stored hydrogen stream comprising one or more impurities from the storage cavern; and contacting the stored hydrogen stream with the lean adsorbent bed to produce a product hydrogen stream depleted in the one or more impurities and the rich adsorbent bed enriched in the one or more impurities.

2. The method of claim 1 , further comprising delivering the spent regeneration gas stream to the storage cavern.

3. The method of claim 1 , further comprising delivering the product hydrogen stream to the hydrogen pipeline.

4. The method of claim 1 , further comprising cooling the hydrogen stream prior to contacting with the lean adsorbent bed to produce a liquid water stream.

5. The method of claim 4, further comprising delivering the liquid water stream to the storage cavern by gravity.

6. The method of claim 1 , further comprising removing at least one of CO2, H2S, and COS from the spent regeneration gas stream prior to delivering the spent regeneration gas to the storage cavern.

7. The method of claim 1 , wherein the hydrogen regeneration gas stream is withdrawn from the hydrogen pipeline and the hydrogen stream is not being withdrawn from the storage cavern in an intermittent process.

8. The method of claim 1 , further comprising reducing the pressure of the hydrogen stream prior to contacting with the lean adsorbent bed to produce a liquid water stream.

9. The method of claim 1 , further comprising removing at least one of COS and CH4 from the hydrogen product stream.

10. A method comprising: withdrawing a hydrogen regeneration gas stream from a hydrogen pipeline; contacting the hydrogen regeneration gas stream with a rich adsorbent bed comprising one or more impurities to produce a spent regeneration gas stream enriched in the one or more impurities and a lean adsorbent bed depleted in the one or more impurities; withdrawing a stored hydrogen stream comprising one or more impurities from the storage cavern; partially condensing the stored hydrogen stream to produce a partially treated hydrogen stream and a liquid water stream; delivering the liquid water stream to the storage cavern by gravity; contacting the partially treated hydrogen stream with the lean adsorbent bed to produce a product hydrogen stream depleted in the one or more impurities and the rich adsorbent bed enriched in the one or more impurities.

11. The method of claim 10, further comprising delivering the spent regeneration gas stream to the storage cavern; and delivering the product hydrogen stream to the hydrogen pipeline.

12. The method of claim 10, further comprising removing at least one of CO2, H2S, and COS from the spent regeneration gas stream prior to delivering the spent regeneration gas to the storage cavern or removing COS from the hydrogen product stream.

13. The method of claim 10, wherein the hydrogen regeneration gas stream is withdrawn from the hydrogen pipeline and the hydrogen stream is not being withdrawn from the storage cavern in an intermittent process.

14. A system comprising: a storage cavern configured to receive and deliver hydrogen gas at an elevated pressure;a lean adsorbent bed in fluid flow communication with the storage cavern configured to receive a hydrogen stream from the storage cavern and remove impurities from the hydrogen stream to produce a product hydrogen stream and a rich adsorbent bed; a hydrogen pipeline in fluid flow communication with the rich adsorbent bed configured to deliver a hydrogen regeneration gas stream to remove impurities from the rich adsorbent bed to product a spent regeneration gas stream and the lean adsorbent bed; wherein the rich adsorbent bed is in fluid flow communication with the storage cavern and configured to deliver the spent regeneration gas stream to the storage cavern.

15. The system of claim 14, further comprising a heat exchanger in fluid flow communication with the storage cavern and the lean adsorbent bed, configured to cool and partially condense a liquid water stream from the hydrogen stream; and an acid gas removal unit in fluid flow communication with the rich adsorbent bed and the storage cavern, configured to remove at least one of CO2, H2S, and COS from the spent regeneration gas stream prior to delivering the spent regeneration gas to the storage cavern.

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