How to recycle pre-purification containers

Abstract

A system and method for regenerating a pre-purification vessel, particularly suitable for pre-purifying a feed air stream in a cryogenic air separation unit using an oxygen-rich purge gas stream, for the regeneration of a pre-purification unit, are provided. The disclosed pre-purification system and method are configured to remove substantially all water, carbon dioxide, and other impurities from a feed air stream that optionally contains hydrogen and carbon monoxide impurities. A method for regenerating a pre-purification vessel preferably comprises the steps of depressurizing the vessel, regenerating the pre-purification vessel with an oxygen-rich purge gas, and then partially repressurizing the pre-purification vessel with an auxiliary purge gas to dilute the oxygen concentration of the gas contained in the pre-purification vessel and optionally depressurizing the partially repressurized vessel.

Description

Technology Field

[0001] The present invention relates to a system and method for regenerating a pre-purification container, and more specifically, to a method and system for regenerating a pre-purification container of an air separation unit using a regenerating purge gas which is an oxygen-rich purge gas. Background Technology

[0002] Adsorption is a well-established technology for the purification of gases and the treatment of fluid waste streams. The purification and separation of atmospheric air is one of the major areas where adsorption methods are widely used. To increase their efficiency, new and improved pre-purification systems and methods are continuously being developed.

[0003] One of the areas of strong commercial and technical interest is the pre-purification of air prior to cryogenic distillation. Conventional air separation units that cryogenically separate air to produce nitrogen (N2), oxygen (O2), and argon (Ar) are basically composed of two or at least three integrated distillation columns each operating at very low temperatures. Due to these low temperatures, it is essential to remove water vapor (H2O) and carbon dioxide (CO2) from the compressed air supplied to the air separation unit. If not removed, the water and carbon dioxide present in the supply air will freeze and block the heat exchanger used to cool the supply air before distillation in the cryogenic distillation columns. Preferably, to avoid freezing, the water content in the compressed and pre-purified air supply stream must be less than 0.1 ppm (part per million), while the carbon dioxide content in the compressed and pre-purified air supply stream must be less than 1.0 ppm. Generally, to ensure the safe operation of these cryogenic distillation systems processing oxygen-rich streams, it is often necessary to remove hydrocarbons and nitrous oxide.

[0004] Current commercial methods for the pre-purification of feed air may include temperature-swing adsorption-based units using a layer of adsorbent material in conjunction with selective catalytic pre-purification technology. Typically, a pre-purification unit located upstream of a cryogenic distillation system is used, and this unit includes a pre-adsorption layer to remove water, carbon dioxide, as well as other contaminants including hydrocarbons and nitrogen oxides. Such pre-purification units may also optionally include one or more catalysts targeted for the removal of one or more contaminants, and may include a final adsorption layer downstream of the selective catalyst to remove contaminants generated in subsequent catalytic processes. For example, in some cryogenic air separation applications for the electronics industry and selected other industries, hydrogen and / or carbon monoxide must be removed from the feed air stream before processing the feed air stream in a cryogenic distillation system to produce high-purity or ultra-high-purity nitrogen products.

[0005] The thermal regeneration process applied to these temperature-fluctuation adsorption-based pre-purification units associated with air separation units serves to desorb water, carbon dioxide, hydrocarbons, and selected other contaminants, such as nitrous oxide, from various layers of the pre-purification unit. Conventional thermal regeneration is preferably performed using a multi-stage process comprising at least four general steps: (i) depressurizing the pre-purification vessel to a low pressure suitable for the regeneration process; (ii) heating the layers within the pre-purification vessel with heated purge gas to desorb water, carbon dioxide, and other contaminants from various adsorption layers and wash the catalyst layer; (iii) cooling the layers within the pre-purification vessel to a temperature suitable for the pre-purification process with cooling purge gas, often referred to as low-temperature purge gas; and (iv) repressurizing the pre-purification vessel back to a higher operating pressure required for the pre-purification process. In the thermal regeneration of conventional pre-purification vessels, the high-temperature purge gas and the low-temperature purge gas generally consist of an air stream or a waste nitrogen-rich gas stream. However, while the use of oxygen-rich streams as high-temperature and low-temperature purge gases has been used previously, special considerations regarding safety are required.

[0006] The safe operation of the air separation unit is very important. Therefore, when using oxygen-rich purge gas to regenerate the pre-purification unit associated with the air separation unit, special cleaning treatments or special materials may be required for parts such as piping, vessels, valves, and other devices to ensure safe operation when exposed to a gas stream with a high oxygen concentration. Therefore, it would be desirable to minimize the requirements for special cleaning / treatment and special materials (and associated costs) by ensuring that the oxygen content of the gas remaining in the pre-purification vessel after regeneration is diluted, thereby ensuring that the oxygen-rich air flowing to the air separation unit cryo box or the turbo machinery upstream of the cryo box is not blocked when the pre-purification vessel is circulated to the purification stage. Therefore, in order to ensure the safe operation of the air separation unit and reduce capital and operating costs associated with meeting special design and handling requirements for parts exposed to oxygen-rich gases, there is a continuous demand to improve the regeneration of the pre-purification unit using oxygen-rich purge gas so that the oxygen concentration of the gas in the repressurized pre-purification vessel is about 30% or less on a molar volume basis, more preferably about 26% or less on a molar volume basis.

[0007] The present invention can be broadly characterized as a method for regenerating a pre-purification vessel, comprising: (i) depressurizing a pre-purification vessel in which one or more adsorption layers and / or catalyst layers are disposed therein to a regeneration pressure; (ii) heating one or more adsorption material layers and / or one or more catalyst material layers disposed in the pre-purification vessel with a high-temperature oxygen-rich purge gas to desorb water and carbon dioxide from one or more layers; (iii) cooling one or more adsorption layers and / or catalyst layers in the pre-purification vessel using a low-temperature oxygen-rich purge gas; (iv) partially repressurizing the pre-purification vessel to an intermediate pressure with an auxiliary purge gas to dilute the oxygen concentration of the gas contained in the pre-purification vessel; and (v) fully repressurizing the pre-purification vessel to an operating pressure for pre-purification of the supply gas, wherein the oxygen concentration of the gas in the repressurized pre-purification vessel is about 30% or less on a molar volume basis, more preferably less than about 26% on a molar volume basis.

[0008] In some embodiments, the step of partially repressurizing the pre-purification vessel further comprises the step of partially repressurizing the pre-purification vessel with an auxiliary purge gas, then depressurizing the pre-purification vessel and releasing the auxiliary purge gas and any oxygen-rich purge gas remaining in the pre-purification vessel. In other embodiments, the step of partially repressurizing the pre-purification vessel further comprises the step of partially repressurizing the pre-purification vessel with a nitrogen-rich gas having a nitrogen concentration of about 85% or more on a molar volume basis to dilute the oxygen concentration of the gas remaining in the pre-purification vessel.

[0009] One or more adsorption layers in the pre-purification vessel comprise activated alumina, silica gel, zeolite-based molecular sieves, X-type zeolites, or a combination thereof, and one or more containing layers in the pre-purification vessel preferably comprise a noble metal catalyst such as palladium on a hopcalite catalyst or an alumina oxide catalyst. The regeneration pressure is less than about 6.0 bar, more preferably about 1.0 bar to 2.0 bar, and the operating pressure is generally preferably about 6.0 bar or higher.

[0010] It is preferable that the high-temperature oxygen-rich purge gas be heated to a temperature of 150°C or higher using a heater, and the low-temperature oxygen-rich purge gas be at a temperature of about 50°C or lower, and it is preferable that both be supplied from an oxygen-rich stream in the condenser of a distillation column system or an air separation unit. It is preferable that the auxiliary purge gas be air such as a dry air stream taken downstream of the pre-purifier unit, a diverted portion of the feed air taken upstream of the pre-purifier unit, or even a synthetic air stream taken from the air separation unit. Alternatively, the auxiliary purge gas may be a nitrogen-rich gas taken from the air separation unit or a nearby nitrogen storage tank. Brief explanation of the drawing

[0011] Although this specification concludes with one or more claims specifically describing the gist of the invention that the applicant considers to be the present invention, the system and method of the present invention for the pre-purification of a feed gas stream are believed to be more clearly understood when interpreted in conjunction with the accompanying drawings. FIG. 1 is a schematic diagram showing a pre-purification vessel having one or more adsorption layers and / or catalyst layers associated with an air separation unit. FIG. 2 is a schematic diagram showing a 2-bed pre-purification unit configured to be used with the current method for regenerating a pre-purification vessel, and various flow circuits and valves within the pre-purification unit. Specific details for implementing the invention

[0012] The present system and method for regenerating a pre-purification vessel are intended for applications such as regenerating a pre-purification unit associated with a cryogenic air separation unit, preferably regenerating the pre-purification unit using an oxygen-rich purge gas stream.

[0013] Now, referring to FIG. 1, an embodiment of a pre-purification bed (20) suitable for use with the present system and method for pre-purifying a feed gas stream, such as air, is illustrated. When associated with an air separation unit, the present system and method for pre-purifying a feed gas stream preferably comprises at least two pre-purification beds configured to purify a feed air stream received at the inlet (22) of a cylindrical vessel (21) housing a plurality of adsorption layers and / or catalyst layers, and to deliver a purified air stream at the outlet (23). Additionally, each of the at least two pre-purification vessels is configured to regenerate the adsorption layers and catalyst layers contained within the pre-purification vessel using one or more oxygen-rich purge gas streams. As is well known in the art, using two or more pre-purification vessels in a cryogenic air separation unit allows for the continuous production of purified air that is subsequently separated into a distillation column within the cryogenic box of the air separation unit. When one or more pre-purification vessels are used to purify incoming supply air, one or more other pre-purification vessels are regenerated, and it is preferable to use a process widely known as thermal regeneration. Each pre-purification vessel comprises a plurality of layers, including one or more layers of adsorbent material such as activated alumina and / or zeolite-based molecular sieves and one or more layers of catalytic material such as hopcalite and / or precious metal catalysts.

[0014] The pre-purification layer (20) illustrated in FIG. 1 comprises a first layer of alumina (24) and a second layer of zeolite-based molecular sieve (25) disposed within a cylindrical container (21), both configured to purify the feed gas stream by adsorbing impurities such as water vapor, carbon dioxide hydrocarbons, and nitrous oxide. A third layer (26) comprising hopcalite, a catalytic material that oxidizes carbon monoxide to carbon dioxide and adsorbs and / or converts hydrogen into water, is disposed downstream of the initial adsorption layers (24, 25). Downstream of the hopcalite-containing layer (26), there is a selective zeolite-based molecular sieve (not shown) configured to remove water and carbon dioxide from the gas stream exiting the hopcalite-containing layer, and a selective noble metal catalyst-containing layer (not shown) such as palladium of an aluminum oxide catalyst (e.g., 0.5 wt% Pd / Al2O3) configured to oxidize most of the remaining hydrogen into water. A final capping layer (28) of a zeolite-based molecular sieve configured to adsorb water vapor and carbon dioxide generated in a layer containing a catalytic material is also shown. Multiple separation screens (27), such as Monel separation screens, may also be installed between various catalyst layers (26) and any adjacent adsorption layers (25) and adsorption layers (28).

[0015] The present system and method are a modification or improvement of a conventional process for thermally regenerating a prepurification vessel in a cryogenic air separation unit, and are particularly suitable for prepurification applications in which the prepurification unit is regenerated using an oxygen-rich purge gas. The present method adds one or more additional steps to the conventional thermal regeneration process and is broadly characterized as follows: (i) a step of depressurizing the prepurification vessel to a lower pressure suitable for prepurification regeneration; (ii) a step of heating the adsorption layer and catalyst layer within the prepurification vessel with an oxygen-rich heated purge gas to desorb water and carbon dioxide from the various layers and regenerate the catalyst layer; (iii) a step of cooling the adsorption layer and catalyst layer within the prepurification vessel to a temperature suitable for the prepurification process with an oxygen-rich low-temperature purge gas; (iv) a step of partially repressurizing the prepurification vessel with an auxiliary purge gas to dilute the oxygen concentration of the gas remaining in the prepurification vessel after the cooling step and optionally depressurizing the partially repressurized vessel; and (v) a step of completely repressurizing the pre-purification vessel to a higher operating pressure required for the pre-purification process, wherein the oxygen concentration of the gas in the completely repressurized pre-purification vessel is about 30% or less based on molar volume, more preferably about 26% or less based on molar volume.

[0016] Specifically, in a preferred embodiment, step (iv) of the identified process further comprises: (a) partially repressurizing the pre-purification vessel to a predetermined suitable pressure with an auxiliary purge gas having an oxygen concentration of about 23%, preferably a clean dry air stream taken downstream of the pre-purification unit or alternatively a diverted portion of a feed air stream taken upstream of the pre-purification unit or even a synthetic air stream (e.g., a mixture of oxygen and nitrogen streams taken from an air separation unit); and (b) depressurizing the pre-purification vessel by releasing most of the auxiliary purge gas and any remaining oxygen-rich purge gas from within the pre-purification vessel. Alternatively, step (iv) may further comprise a single step of partially repressurizing the pre-purification vessel to a predetermined suitable pressure with a nitrogen-rich gas having a nitrogen concentration of preferably greater than 85% until the oxygen concentration in the pre-purification vessel becomes less than 30% by molar volume, more preferably about 26% or less by molar volume.

[0017] Thermal regeneration of the pre-purification vessel is preferably performed at a low pressure, such as 1.0 bar to 2.0 bar, compared to the higher pressure maintained during the purification process, and must be performed at a temperature of 150°C or higher in accordance with appropriate safety requirements. The heating step in the thermal regeneration process is generally performed by heating the purge gas to create a high-temperature purge gas stream supplied to the vessel through the outlet, and passing it through the layers of the pre-purification vessel in reverse order relative to the pre-purification process. In many applications of this method, the purge gas may be a portion of the oxygen-generating gas taken from the distillation column of a cryogenic air separation unit or from an oxygen-rich boiling-off, or waste gas taken from an argon condenser. As the oxygen-rich high-temperature purge gas passes through the various layers of the pre-purification vessel, the catalyst layer and the adsorption layer are regenerated. The oxygen-rich effluent purge gas exiting the pre-purification vessel through the inlet is generally discharged. After the catalyst layer and the adsorption layer are heated and regenerated, the adsorption layer and the catalyst layer of the pre-purification vessel are cooled using a low-temperature oxygen-rich purge gas that flows through the pre-purification vessel in the same direction as the high-temperature purge gas at a temperature generally of about 10°C to a maximum of 50°C. After cooling, the oxygen concentration of the residual gas in the pre-purification vessel is diluted with an auxiliary purge gas, and the pre-purification vessel is repressurized to a higher operating pressure required for the pre-purification process.

[0018] The regeneration phase is performed for a predetermined period as described above and is generally referred to as a cycle time during which the service or function of the pre-purification unit is switched so that the vessel previously being regenerated becomes "online" to begin the purification process, while the vessel previously purifying the supply air becomes "offline" to begin the regeneration process. A typical pre-purification cycle time for an air separation plant producing high-purity or ultra-high-purity nitrogen is approximately 360 to 1200 minutes (i.e., the total cycle time including blending, purification service, and regeneration service). Each pre-purification unit alternates between purification and regeneration services to continuously produce purified air that is substantially free of carbon dioxide, water, carbon monoxide, hydrogen, and other impurities.

[0019] The pre-purification vessel illustrated in the drawing is preferably densely loaded. Dense loading provides the most consistent and uniform packing of the adsorbent and catalyst with minimal leveling of the required layers. Additionally, dense packing minimizes adsorbent sedimentation. Such dense packing for a pre-purifier designed for carbon monoxide and hydrogen removal is optional and can be used in all layers within the bed to ensure completeness and uniform depth. Due to the relatively thin layers within the second purification section for carbon monoxide and hydrogen removal, which include multiple layers of hopcalite and adsorbent layers as well as any precious metal-based catalyst that may be used, it is important to minimize layer movement and / or sedimentation to maintain a uniform depth of the layers over the life of the pre-purifier unit.

[0020] Now, referring to FIG. 2, two bed temperature changing adsorption pre-purifier units (10) are schematically illustrated. The two bed temperature changing adsorption pre-purifier units (10) include two parallel pre-purifier beds (20) and pre-purifier beds (40). The pre-purifier beds (20) and pre-purifier beds (40) each include a packing bed comprising a cylindrical container (21, 41) and a plurality of adsorption layers and / or catalyst layers.

[0021] The compressed air stream (15) may be directed toward one of the pre-purifier bed (20) and the pre-purifier bed (40) in parallel by conduits through stream (31) and stream (51), respectively. Valves (32) and (52) control the flow of supply air entering the pre-purifier bed (20) and the pre-purifier bed (40), and pre-purified air is discharged from the pre-purifier bed (20) and the pre-purifier bed (40) through conduits (33) and (53) including valves (34) and (54), thereby controlling the flow of the pre-purified air stream through conduits (33) and (53). Conduits (33) and (53) are both connected to discharge the compressed and pre-purified air stream (60) directed toward the low-temperature box of the air separation unit.

[0022] As described in more detail below, the oxygen-rich purge stream (65) is heated by optionally passing through a heat exchanger or an electric heater (66) and enters the pre-purifier bed (20) and pre-purifier bed (40) through conduit (35) and conduit (55). The oxygen-rich purge stream regenerates the adsorbent contained in the pre-purifier bed (20) and pre-purifier bed (40). The oxygen-rich purge flow within conduit (35) and conduit (55) is controlled by valve (36) and valve (56), respectively. A somewhat continuous effluent stream containing previously adsorbed water vapor, carbon dioxide, and other impurities within the pre-purifier bed (20) and pre-purifier bed (40) passes through conduit (37) and conduit (57) and is discharged as a waste stream (67) that can be discharged into the atmosphere. The flow of the outflow stream within the conduit (37) and conduit (57) is controlled by the valve (38) and valve (58), respectively.

[0023] For a temperature-changing adsorption process performed within a two-bed temperature-changing adsorption pre-purifier, it is desirable to have a continuous flow of dry pre-purified feed air entering the low-temperature box of the associated air separation unit. This is performed using at least two pre-purifier beds (20) and pre-purifier beds (40), with at least one pre-purifier bed online, at least one other pre-purifier bed offline while adsorbing or catalyzing impurities in the air, and regenerating. The online pre-purifier bed may remain online only until it reaches a capacity to adsorb impurities, at which point an impurity breakthrough will occur. The breakthrough point is generally defined as the time required for contaminants, such as water vapor and carbon dioxide, to reach an unacceptable level at the outlet, which indicates that the pre-purifier bed is saturated with contaminants. Once the breakthrough point is reached, the online pre-purifier bed is switched offline, and the previously regenerated bed is switched back online to adsorb and / or catalyze impurities.

[0024] In the current temperature change adsorption process, there are generally up to 8 stages in the entire cycle, and each pre-purifier bed undergoes a continuously repeated process. The 8 stages are, namely, 'blending'; 'purification'; 'depressurization'; 'high-temperature purging'; 'low-temperature purging'; 'partial repressurization'; 'partial depressurization'; and 'full repressurization'. Table 1 below, together with FIG. 2, shows the correlation of performance between the various stages within the pre-purification cycle using two pre-purifier beds (20) and a pre-purifier bed (40) and an air auxiliary purging gas, which will be explained in more detail in the following paragraph.

[0025] [Table 1]

[0026]

[0027] In the 'blended' stage, both pre-purification beds (20, 40) are 'online', valves (32, 34, 52 and 54) are open, and valves (36, 38, 56 and 58) are closed. The supply air stream (15) is evenly divided between the two beds in this stage, with no regeneration gas (65) in the system. In the online state, pre-purification bed (20) and pre-purification bed (40) have any catalyst present to adsorb water vapor, carbon dioxide and other contaminants, while oxidizing impurities such as carbon monoxide and hydrogen. The purpose of this 'blended' stage is to dilute the amount of residual heat remaining in the pre-purification beds during regeneration and further dilute the oxygen content of the resulting blending stream to prevent the heated stream or oxygen-rich stream from being fed back into the low-temperature box of the air separation unit.

[0028] After a ‘blended’ stage of about 30 minutes, one of the pre-purifier beds (20) is switched to an offline state through a depressurization or ‘depressurization’ stage, and the other pre-purifier bed (40) undergoes a ‘purification’ stage in which water vapor, carbon dioxide and nitrous oxide, hydrocarbons, carbon monoxide, hydrogen, and other impurities are removed by receiving a full supply flow. The “offline” pre-purifier bed (20) is known to often undergo regeneration. This regeneration is completed through 5 to 6 individual stages, including, in order: (i) ‘depressurization’; (ii) ‘high temperature purging’; (iii) ‘low temperature purging’; (iv) ‘partial repressurization’ with auxiliary purging gas; (v) ‘partial depressurization’ (optional); and (vi) ‘full repressurization’ with air. During ‘depressurization,’ the pre-purifier bed (20) is depressurized from the operating pressure to a low pressure, typically referred to as the regeneration pressure just above atmospheric pressure, which is about 6.0 bar, more preferably 2.0 bar. This is achieved by closing valves (32, 34 and 36) and opening valve (38). ‘Depressurization’ is typically maintained for about 15 minutes, but the duration of the ‘depressurization’ phase may vary depending on device constraints or process limitations. Once depressurized, the ‘high-temperature purging’ phase begins by using a heater (66) to heat the oxygen-rich purge gas stream (65) to a temperature higher than the supply temperature, preferably above 150°C depending on the pre-purification process and material constraints, and is typically heated to about 190°C or lower because the oxygen concentration of the purge gas stream is high. During this 'high temperature purge' stage, the valve (36) is opened and a stream of heated oxygen-rich purge gas can pass through the pre-purifier bed (20) via the conduit (35) and conduit (37).

[0029] After a certain period of time, in this embodiment, after 163 minutes, the oxygen-rich purge gas stream bypasses the heater (66) or the heater (66) is shut off, lowering the temperature of the oxygen-rich purge gas stream to near ambient conditions, generally to about 50°C or lower. Then, a 'low-temperature purge' step begins, continuing the purge with the oxygen-rich stream (65) but without applying heat. This 'low-temperature purge' step not only lowers the temperature of the pre-purification bed (20) but also advances the heat wire through the pre-purification bed. In this embodiment, the 'low-temperature purge' step proceeds for about 272 minutes.

[0030] Subsequently, the ‘partial repressurization’ step is accomplished by closing valves (36) and (38) and opening valve (72) to introduce auxiliary purge gas (70) into the pre-purification vessel (20) through conduit (73) for a specified period (e.g., 6 to 15 minutes) or so that the pre-purification vessel (20) reaches an intermediate pressure between the regeneration pressure and the operating pressure. It is preferable to introduce the auxiliary purge gas into the pre-purification vessel at a location adjacent to the clean end of the purge valve and the pre-purification vessel (e.g., a location adjacent to the vale (36, 56) and outlet (23)), and to remove the auxiliary purge gas and any remaining oxygen-rich purge gas at a location adjacent to the dirty end of the pre-purification vessel (e.g., a location adjacent to the inlet (23). This preferred arrangement ensures that there is no blockage of the oxygen-rich gas at or near the clean end of the purge valve or the pre-purification vessel after the full repressurization step.

[0031] In an embodiment in which clean dry air or synthetic air is used as the auxiliary purge gas (70), partial repressurization is sustained for about 6 minutes, and the pre-purification bed (20) is partially depressurized by opening valve (38) and closing valve (72), and valves (36, 34 and 32) are kept closed for an additional 9 minutes. The partial depressurization step is terminated when the oxygen concentration in the pre-purification bed is reduced to about 30% or less in molar volume, more preferably about 26% or less in molar volume.

[0032] In an embodiment using a nitrogen stream as an auxiliary purge gas (70), the nitrogen stream preferably has a nitrogen concentration greater than 85% by molar volume, and the partial repressurization step may last for up to 15 minutes. The partial repressurization step ends when the oxygen concentration in the pre-purifier bed decreases to about 30% or less by molar volume, more preferably about 26% or less by molar volume.

[0033] Subsequently, the regeneration process continues the 'complete repressurization' step by keeping valves (34) and (38) closed and opening either valve (72) or valve (32). When valve (32) is opened, a portion of the compressed purification air stream (15) can pressurize the pre-purification bed (20) to maximum operating pressure. Alternatively, if the auxiliary purge gas is an air stream or a synthetic air stream, valve (72) is opened to repressurize the pre-purification bed (20) to maximum operating pressure. Once pressurized to operating pressure, both the pre-purification bed (20) and the pre-purification bed (40) enter the 'blend' step, and thus valves (32, 34, 52 and 54) are fully opened so that the supply air stream (15) can be evenly divided and purified between the pre-purification bed (20) and the pre-purification bed (40). After a certain amount of time has passed in the ‘blended’ stage, the pre-purification bed is switched, and while the pre-purification bed (20) is online in the ‘purification’ stage, the pre-purification bed (40) undergoes a series of regeneration stages as described above with reference to Table 1.

[0034] Although the system and method of the present invention have been described with reference to preferred embodiments or embodiments, it should be understood that numerous additions, modifications, and omissions may be made without departing from the spirit and scope of the invention as set forth in the appended claims. For example, the system and method disclosed herein are intended for applications using thermal regeneration and thermal change adsorption-based pre-purification technologies and are considered to be adaptable or further modified for use with pressure change adsorption-based pre-purification units and / or hybrid pre-purification units using both pressure change adsorption-based pre-purification and thermal change adsorption-based pre-purification technologies.

Claims

Claim 1 A method for regenerating a pre-purification vessel comprising: (i) depressurizing the pre-purification vessel, in which one or more adsorption layers and / or catalyst layers are disposed therein, to a regeneration pressure; (ii) heating the one or more adsorption material layers and / or one or more catalyst material layers disposed within the pre-purification vessel with a high-temperature oxygen-rich purge gas to desorb water and carbon dioxide from the one or more layers; (iii) cooling the one or more adsorption layers and / or catalyst layers within the pre-purification vessel using a low-temperature oxygen-rich purge gas; (iv) partially repressurizing the pre-purification vessel with an auxiliary purge gas to dilute the oxygen concentration of the gas contained within the pre-purification vessel after the cooling step; (v) completely repressurizing the pre-purification vessel to an operating pressure for the pre-purification of the supply gas, wherein the oxygen concentration of the gas within the repressurized pre-purification vessel is 30% or less based on molar volume, wherein the regeneration pressure is less than 6.0 bar and the operating pressure is 6.0 bar or more. Claim 2 A method according to claim 1, wherein the oxygen concentration of the gas in the repressurized pre-purification vessel is 26% or less based on molar volume. Claim 3 The method of claim 1, wherein the step of partially repressurizing the pre-purification vessel with the auxiliary purge gas further comprises: the step of partially repressurizing the pre-purification vessel to an intermediate pressure with the auxiliary purge gas; and subsequently depressurizing the pre-purification vessel and releasing the auxiliary purge gas and the oxygen-rich purge gas remaining in the pre-purification vessel, wherein the intermediate pressure is between the regeneration pressure and the operating pressure. Claim 4 The method according to claim 1, wherein the step of partially repressurizing the pre-purification vessel with the auxiliary purge gas further comprises the step of diluting the oxygen concentration of the gas remaining in the pre-purification vessel by partially repressurizing the pre-purification vessel to an intermediate pressure with a nitrogen-rich gas having a nitrogen concentration of more than 85% on a molar volume basis, wherein the intermediate pressure is between the regeneration pressure and the operating pressure. Claim 5 In claim 1, the method wherein the high-temperature oxygen-rich purge gas has a temperature of 150°C or higher. Claim 6 In claim 1, the method wherein the low-temperature oxygen-rich purge gas has a temperature of 50°C or lower. Claim 7 A method according to claim 1, wherein the pre-purification vessel is coupled to an air separation unit, the supply gas is air, and one or more adsorption layers within the pre-purification vessel comprise activated alumina, silica gel, zeolite-based molecular sieve, X-type zeolite, or a combination thereof, and are configured to remove impurities including water, carbon dioxide, and other contaminants in the supply gas. Claim 8 A method according to claim 7, wherein one or more catalyst layers in the pre-purification vessel comprise a hopcalite or precious metal catalyst and are configured to remove impurities including hydrogen and carbon monoxide. Claim 9 A method according to claim 1, wherein the pre-purification vessel is coupled to an air separation unit, and the high-temperature oxygen-rich purge gas and the low-temperature oxygen-rich purge gas are taken from an oxygen-rich stream from a distillation column system of the air separation unit. Claim 10 A method according to claim 9, wherein the step of heating the one or more adsorbent material layers and / or one or more catalyst material layers with the oxygen-rich purge gas further comprises the step of heating the oxygen-rich stream using an electric, gas combustion, or steam heater. Claim 11 A method according to claim 1, wherein the pre-purification vessel is coupled to an air separation unit that generates argon, and the high-temperature oxygen-rich purge gas and the low-temperature oxygen-rich purge gas are oxygen-rich streams taken from an argon condenser associated with the air separation unit that generates argon. Claim 12 delete Claim 13 A method according to paragraph 3, wherein the pre-purification vessel is coupled to an air separation unit, and the auxiliary purge gas further comprises a dry air stream taken from a downstream location of the pre-purification vessel associated with the air separation unit, a bypassed portion of supply air taken from an upstream location of the pre-purification vessel associated with the air separation unit, or a synthetic air stream taken from the air separation unit. Claim 14 A method according to paragraph 3, wherein the auxiliary purge gas is introduced into the pre-purification vessel through an auxiliary purge control valve, and during depressurization, the release of the auxiliary purge gas and the residual oxygen-rich gas from the pre-purification vessel occurs through a partial depressurization control valve or a depressurization control valve. Claim 15 A method according to paragraph 4, wherein the pre-purification vessel is coupled to an air separation unit, and the nitrogen-rich stream is taken from the air separation unit or a nitrogen storage tank. Claim 16 A method according to paragraph 4, wherein a nitrogen-rich gas is introduced into the pre-purification vessel through an auxiliary purge gas control valve. Claim 17 delete

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