Hybrid Bead Layered Arrangement for Thermal Swing Adsorption Applications

Abstract

An adsorption vessel for removing contaminants from a feed gas upstream of a cryogenic distillation process using pressure swing adsorption, temperature swing adsorption or thermal swing pressure adsorption. The adsorption vessel has an adsorption bed composed of multiple layers of adsorption material, including two layers of adsorption material that selectively adsorbs carbon dioxide. Each of the two layers is formed of an adsorption material having a different ability to adsorb carbon dioxide.

Description

Technical Field

[0001] The present invention generally relates to a method and apparatus for removing impurities from a feed gas stream by adsorption, particularly by thermal swing adsorption (TSA). In particular, it relates to the use of a layered combination of adsorbent materials having different adsorption capacities for the adsorbate to minimize capital costs and pressure drops in the adsorbent beds and to improve the efficiency of the adsorption process. Background Art

[0002] TSA is often used in conjunction with technologies such as pressure swing adsorption (PSA) and thermal pressure swing adsorption (TPSA) for air pre-purification in cryogenic distillation processes. Its function is to remove components with relatively high freezing points, such as ambient moisture and carbon dioxide. If not removed, these components will freeze in downstream processes, causing operability problems such as plugging. Air pre-purification adsorption systems also remove impurities such as nitrous oxide and hydrocarbons, which may cause safety issues if allowed to accumulate in downstream processes.

[0003] Current practice for TSA air prepurification is to pass the feed gas through an adsorbent bed with a moisture removal layer followed by a carbon dioxide removal layer. The carbon dioxide removal layer is typically a carbon dioxide selective molecular sieve. The loading arrangement of the molecular sieve layer is a uniform layer of material with uniform capacity for carbon dioxide. Silica gel or activated alumina are typically used to remove moisture, and type X zeolites (e.g., 13X) are typically used to remove carbon dioxide, nitrous oxide, and some hydrocarbons.

[0004] The TSA purification process operates in a cyclic manner, wherein one or more adsorption vessels containing adsorption beds are in operation and one or more vessels are undergoing regeneration. During the operation step, a compressed process fluid is passed through the bed via the vessel inlet. As the process fluid flows through the vessel, the target undesirable components (adsorbates) are subsequently stripped off by different types of adsorbents, producing a process fluid depleted in adsorbates. The process fluid depleted in adsorbates enters the downstream process through the vessel outlet. After a period of operation, the adsorbent is saturated with the adsorbate, at which point the adsorption load is switched to the regeneration bed, and the saturated bed is regenerated. Regeneration is typically performed by passing a heated fluid stream that is substantially free of adsorbates through the adsorption bed in the opposite direction to the process fluid.

[0005] When the process fluid flows through the adsorbent bed, an equilibrium zone and a mass transfer zone are formed in the bed. In the equilibrium zone, the adsorbate in the process fluid is in equilibrium with the adsorbate on the adsorbent, and no additional adsorption occurs. In the mass transfer zone, the adsorbent is not yet saturated with the adsorbate, and adsorption and mass transfer occur.

[0006] US5728198 teaches an adsorbent arrangement for a vessel that uses a downward adsorption process flow and an upward regeneration process flow in a TSA process to remove carbon dioxide from air. The CO2 selective layer in this arrangement consists of two layers, wherein the particle size of the first layer material is larger than the particle size of the second layer material.

[0007] US4964888 teaches a PSA with product separation applications, where separation occurs in two adsorption zones. The type of adsorbent used in the two adsorption zones varies depending on the desired product. The present invention also teaches that the particle size of adsorption zone 1 should be smaller than the particle size of adsorption zone 2.

[0008] US6027548 teaches an adsorbent arrangement for PSA applications for removing hydrocarbons and carbon dioxide from a nitrogen stream, wherein the equilibrium zone is a mixture of a strong adsorbent and a weak adsorbent. The strong adsorbent may be LiX, NaX, NaY, and the weak adsorbent may be alumina and NaX.

[0009] The pressure drop generated by the adsorption bed is closely related to the particle size of the adsorbent material and the thickness of the adsorption layer. When any size other than a large particle size is used in the equilibrium zone, additional pressure drop will also be added to the unit operation because the particle size of the material has less effect in the equilibrium zone than in the mass transfer zone.

[0010] The cost of molecular sieve materials increases at a much greater rate than their capacity for adsorbate.Therefore, there is an unmet need for an adsorption arrangement that can maximize purification capacity and efficiency while minimizing capital cost and pressure drop. Summary of the invention

[0011] Aspect 1: An apparatus for removing at least one pollutant from a gaseous feed stream, the at least one pollutant comprising carbon dioxide, the apparatus comprising:

[0012] at least one adsorption vessel including an adsorption bed, an inlet, and an outlet, the adsorption bed including a plurality of layers, the plurality of layers including a first layer formed of a first adsorption material capable of selectively adsorbing the at least one pollutant at a first temperature and selectively desorbing the at least one pollutant at a second temperature, and a second layer formed of a second adsorption material capable of selectively adsorbing the at least one pollutant at the first temperature and selectively desorbing the at least one pollutant at a third temperature;

[0013] wherein the second temperature and the third temperature are both higher than the first temperature;

[0014] wherein an arrangement of the plurality of layers from the inlet to the outlet comprises the first layer followed by the second layer;

[0015] wherein the first adsorbent material has a greater adsorption capacity for the at least one pollutant than the second adsorbent material; and

[0016] The adsorption bed has an equilibrium zone and a mass transfer zone, wherein the first layer is located in the equilibrium zone, and the second layer is located in the mass transfer zone.

[0017] Aspect 2: The apparatus of claim 1, wherein the at least one pollutant further comprises nitrous oxide and hydrocarbons.

[0018] Aspect 3: The device according to any one of claims 1 to 2, wherein the first adsorbent material has a greater adsorption capacity for carbon dioxide than the second adsorbent material.

[0019] Aspect 4: The apparatus according to any one of claims 1 to 3, wherein the first adsorbent material has a first average particle size, and the second adsorbent material has a second average particle size, the first average particle size being larger than the second average particle size.

[0020] Aspect 5: The apparatus according to claim 4, wherein the first adsorbent material has an average particle size of at least 3.5 mm, and the second adsorbent material has an average particle size of less than 2.5 mm.

[0021] Aspect 6: The apparatus according to any one of claims 1 to 5, wherein the Si / Al ratio of the first adsorbent material is in the range of 1.0 to 1.2, and the Si / Al ratio of the second adsorbent material is in the range of 1.2 to 1.5, and the Si / Al ratio of the first adsorbent material is lower than the Si / Al ratio of the second adsorbent material.

[0022] Aspect 7: The apparatus according to any one of claims 1-6, wherein the first adsorbent material is a cation exchange 13X having a Si / Al ratio in the range of 1.0 to 1.2, and the second adsorbent material is a cation exchange 13X having a Si / Al ratio in the range of 1.2 to 1.5.

[0023] Aspect 8: The apparatus of any one of claims 1-7, wherein the first adsorbent material comprises an adsorption capacity of 1.1 to 1.6, and the second adsorbent material comprises an adsorption capacity of 1.0 to 1.2.

[0024] Aspect 9: An apparatus according to any one of claims 1-8, wherein the multiple layers further include a third layer formed of a third adsorbent material, the third adsorbent material being capable of selectively adsorbing moisture at the first temperature and selectively desorbing moisture at a fourth temperature, the fourth temperature being higher than the first temperature, wherein the arrangement of the multiple layers from the inlet to the outlet includes the third layer, the first layer and then the second layer.

[0025] Aspect 10: The apparatus of any one of claims 1-9, wherein the first layer has a first layer length and the second layer has a second layer length, wherein the second layer length is in the range of 10% to 50% of the sum of the second layer length and the first layer length.

[0026] Aspect 11: A system comprising:

[0027] a feed conduit in fluid flow communication with air, the feed conduit being adapted to supply the air to at least one adsorption vessel at a feed temperature;

[0028] at least one adsorption vessel having an inlet, an adsorption bed, and an outlet, the inlet being in fluid flow communication with the feed conduit, the adsorption bed comprising a plurality of layers, the plurality of layers comprising a first layer formed of a first adsorbent material capable of selectively adsorbing at least one contaminant at a first temperature and selectively desorbing the at least one contaminant at a second temperature, and a second layer formed of a second adsorbent material capable of selectively adsorbing the at least one contaminant at the first temperature and selectively desorbing the at least one contaminant at a third temperature;

[0029] a cryogenic distillation subsystem in fluid flow communication with said outlet of said at least one adsorption vessel;

[0030] a regeneration conduit in fluid flow communication with the outlet of the at least one adsorption vessel, the regeneration conduit being adapted to supply a regeneration gas at a regeneration temperature, the regeneration temperature being higher than the feed temperature;

[0031] wherein the arrangement of the plurality of layers between the inlet and the outlet consists of the first layer and the second layer;

[0032] wherein the second temperature and the third temperature are both higher than the first temperature;

[0033] wherein an arrangement of the plurality of layers from the inlet to the outlet comprises the first layer followed by the second layer;

[0034] wherein the first adsorbent material has a greater adsorption capacity for at least one pollutant than the second adsorbent material; and

[0035] The adsorption bed has an equilibrium zone and a mass transfer zone, wherein the first layer is located in the equilibrium zone, and the second layer is located in the mass transfer zone.

[0036] Aspect 12: The system of claim 11, wherein the at least one pollutant further comprises nitrous oxide and hydrocarbons.

[0037] Aspect 13: The system according to any one of claims 11-12, wherein the first adsorbent material has a greater adsorption capacity for carbon dioxide than the second adsorbent material.

[0038] Aspect 14: The system of any one of claims 11-13, wherein the first adsorbent material has a first average particle size and the second adsorbent material has a second average particle size, the first average particle size being larger than the second average particle size.

[0039] Aspect 15: The system of claim 14, wherein the first adsorbent material has an average particle size of at least 3.5 mm and the second adsorbent material has an average particle size of less than 2.5 mm.

[0040] Aspect 16: The system according to any one of claims 11-15, wherein the Si / Al ratio of the first adsorbent material is in the range of 1.0 to 1.2, and the Si / Al ratio of the second adsorbent material is in the range of 1.2 to 1.5, and the Si / Al ratio of the first adsorbent material is lower than the Si / Al ratio of the second adsorbent material.

[0041] Aspect 17: The system of any one of claims 11-16, wherein the first adsorbent material is a cation exchange 13X having a Si / Al ratio in the range of 1.0 to 1.2, and the second adsorbent material is a cation exchange 13X having a Si / Al ratio in the range of 1.2 to 1.5.

[0042] Aspect 18: The system of any one of claims 11-17, wherein the first adsorbent material comprises an adsorption capacity of 1.1 to 1.6, and the second adsorbent material comprises an adsorption capacity of 1.0 to 1.2.

[0043] Aspect 19: The system of any one of claims 11-18, wherein the plurality of layers further comprises a third layer formed of a third adsorbent material, the third adsorbent material being capable of selectively adsorbing moisture at the first temperature and selectively desorbing moisture at a fourth temperature, the fourth temperature being higher than the first temperature, wherein the arrangement of the plurality of layers from the inlet to the outlet comprises the third layer, the first layer and then the second layer.

[0044] Aspect 20: The system of any one of claims 11-19, wherein the first layer has a first layer length and the second layer has a second layer length, wherein the second layer length is in the range of 10% to 50% of the sum of the second layer length and the first layer length.

[0045] Aspect 21: The system of any one of claims 11-20, further comprising a cooling system operably configured to cool the air before the air enters the at least one adsorption vessel.

[0046] Aspect 22: The system of claim 21, wherein the cooling system comprises a direct contact aftercooler.

[0047] Aspect 23: The system of claim 21, wherein the cooling system comprises a mechanical refrigerator.

[0048] Aspect 24: A method comprising:

[0049] (a) forming a plurality of layers of adsorbent material in an adsorption bed of each of at least one adsorption vessel, the at least one adsorption vessel having an inlet and an outlet, the plurality of layers of adsorbent material comprising a first layer formed of a first adsorbent material capable of selectively adsorbing at least one pollutant at a first temperature and selectively desorbing the at least one pollutant at a second temperature, and a second layer formed of a second adsorbent material capable of selectively adsorbing the at least one pollutant at the first temperature and selectively desorbing the at least one pollutant at a third temperature, wherein the first layer is located in an equilibrium zone of the adsorption bed and the second layer is located in a mass transfer zone of the adsorption bed, wherein the second temperature and the third temperature are both higher than the first temperature, wherein the arrangement of the plurality of layers from the inlet to the outlet comprises the first layer followed by the second layer, wherein the first adsorbent material has a greater adsorption capacity for the at least one pollutant than the second adsorbent material, and wherein the at least one pollutant comprises carbon dioxide.

[0050] Aspect 25: The method according to claim 24, further comprising:

[0051] (b) selectively adsorbing the at least one contaminant from the gaseous feed stream by passing the gaseous feed stream through at least one adsorption vessel at a feed temperature to form a purified stream; and

[0052] (c) regenerating the adsorption bed by flowing a regeneration stream through the at least one adsorption vessel in a direction opposite to the direction of the gaseous feed stream of step (b) at a regeneration temperature greater than the feed temperature, causing the at least one contaminant to be desorbed from the adsorption bed into the regeneration stream.

[0053] Aspect 26: The method according to any one of claims 24-25, further comprising:

[0054] (d) supplying the purified stream to a cryogenic distillation subsystem in fluid flow communication with the outlet of the at least one adsorption vessel.

[0055] Aspect 27: The method according to any one of claims 24-26, wherein the first adsorbent material has a greater adsorption capacity for carbon dioxide than the second adsorbent material.

[0056] Embodiments of the present invention present an adsorbent layered arrangement to optimize adsorbent utilization in an adsorption system for providing pre-purification in cryogenic distillation of air. The layered arrangement involves a carbon dioxide removal layer of a bed, wherein the adsorbent in this layer is composed of a molecular sieve. The carbon dioxide removal layer is divided into at least two layers, at least one layer is equipped with a strong molecular sieve, and at least another layer is equipped with a weak molecular sieve. Strong molecular sieves have a higher carbon dioxide adsorption capacity than weak molecular sieves. The adsorption bed is arranged so that the process fluid flows through the high capacity adsorbent layer before the lower capacity adsorbent layer. An equilibrium zone is formed in the high capacity layer, and a mass transfer zone is formed in the lower capacity layer. The amount of strong adsorbent required is determined by the length of the equilibrium zone, while the amount of weak adsorbent required is determined by the length of the mass transfer zone. The adsorbent particle size of the stronger material is larger than that of the weaker material.

[0057] Embodiments of the present invention present an adsorbent layered arrangement to optimize adsorbent utilization in an adsorption system for providing pre-purification in cryogenic distillation of air. The layered arrangement involves a carbon dioxide removal layer of a bed, wherein the adsorbent in this layer is composed of a molecular sieve. The carbon dioxide removal layer is divided into at least two layers, at least one layer is equipped with a strong molecular sieve, and at least another layer is equipped with a weak molecular sieve. Strong molecular sieves have a higher carbon dioxide adsorption capacity than weak molecular sieves. The adsorption bed is arranged so that the process fluid flows through the high capacity adsorbent layer before the lower capacity adsorbent layer. An equilibrium zone is formed in the high capacity layer, and a mass transfer zone is formed in the lower capacity layer. The amount of strong adsorbent required is determined by the length of the equilibrium zone, while the amount of weak adsorbent required is determined by the length of the mass transfer zone. The adsorbent particle size of the stronger material is larger than that of the weaker material. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention will be described below with reference to the accompanying drawings, wherein like numerals represent like components.

[0059] FIG. 1 is a schematic diagram of a prior art thermal swing adsorption process for cryogenic air distillation.

[0060] Figure 2 is an embodiment of an adsorption system according to the claimed invention having two or more adsorption vessels connected in parallel.

[0061] Figure 3 yes Figure 2 Detailed view of an adsorption vessel of an embodiment. DETAILED DESCRIPTION

[0062] The following detailed description only provides preferred exemplary embodiments and is not intended to limit the scope, applicability or configuration of the present invention. On the contrary, the following detailed description of the preferred exemplary embodiments will provide a feasible description for implementing the preferred exemplary embodiments of the present invention to those skilled in the art. It should be understood that various changes may be made to the functions and arrangements of the components without departing from the spirit and scope of the present invention as described in the appended claims.

[0063] To aid in describing the present invention, directional terms are used in the specification and claims to describe parts of the present invention (e.g., upper, lower, left, right, etc.). These directional definitions are merely to aid in describing and claiming the present invention and are not intended to limit the present invention in any way. In addition, reference numerals introduced in the specification in conjunction with the drawings may be repeated in one or more subsequent drawings without additional description in the specification in order to provide context for other features.

[0064] Reference numerals introduced in the specification in connection with a drawing may be repeated in one or more subsequent drawings without additional description in the specification, in order to provide context for other features.

[0065] In the claims, letters are used to identify claimed steps (e.g., (a), (b), and (c). These letters are used to aid in referring to method steps and are not intended to indicate the order in which the claimed steps may be performed, unless and only to the extent such an order is specifically recited in the claims.

[0066] Directional terms may be used in the specification and claims to describe parts of the invention (e.g., upper, lower, left, right, etc.). These directional terms are merely to aid in describing exemplary embodiments and are not intended to limit the scope of the claimed invention. As used herein, the term "upstream" is intended to mean a direction opposite to the direction of flow of a fluid in a conduit from a reference point. Similarly, the term "downstream" is intended to mean the same direction as the direction of flow of a fluid in a conduit from a reference point.

[0067] Unless otherwise specified herein, any and all percentages identified in the specification, drawings and claims should be understood to be based on weight percentages. Unless otherwise specified herein, any and all pressures identified in the specification, drawings and claims should be understood to mean gauge pressures.

[0068] The term "fluid flow communication" as used in the specification and claims refers to the property of a connection between two or more components that enables liquid, vapor and / or a two-phase mixture to be transmitted directly or indirectly between these components in a controlled manner (i.e., without leakage). Coupling two or more components so that they are in fluid flow communication with each other may involve any suitable method known in the art, such as using welds, flanged conduits, gaskets and bolts. Two or more components may also be coupled together via other components of the system that can separate them (e.g., valves, doors, or other devices that can selectively limit or direct fluid flow).

[0069] The term "equilibrium zone" as used in the specification and claims means the portion of the length of the adsorbent bed where the adsorbate concentration is equal to the adsorbate concentration in the fluid to be purified.

[0070] The term "mass transfer zone" as used in the specification and claims means the portion of the length of the adsorbent bed in which the adsorbate concentration profile decreases from the adsorbate concentration in the fluid to be purified to the adsorbate concentration required in the process. The adsorbate concentration profile within the adsorbent bed can be determined by measuring the adsorbent concentration versus time as the adsorbent leaves the bed (commonly referred to in the art as a breakthrough test).

[0071] The term "adsorption capacity" as used in this specification and claims refers to the ratio of adsorbate captured or removed to adsorbent under process conditions. Unless otherwise stated, the ratio is based on mass.

[0072] The term "conduit" as used in the specification and claims refers to one or more structures through which a fluid can be transmitted between two or more components of a system. For example, a conduit may include pipes, ducts, passages, and combinations thereof that transmit liquids, vapors, and / or gases.

[0073] The term "particle size" used in the specification and claims to describe the adsorbent material is intended to mean the average particle size of the adsorbent material. In the art, the average particle size is usually measured by passing the adsorbent particles through a series of wire mesh sieves with different known mesh sizes. The calculated weighted average is determined by the fraction of adsorbent retained on each mesh size.

[0074] FIG. 1 shows an embodiment of a conventional TSA pre-purification system 100 for cryogenic air distillation. It should be noted that the inventive concepts disclosed herein can be used with any suitable type of adsorption system, including TSA, PSA, and TPSA. It should also be noted that the improved adsorption systems and methods disclosed herein can be beneficially applied to other applications, such as [Example]. The improved adsorption systems and methods disclosed herein are not limited to air pre-purification alone, and can also be used for other gas purification by adsorption applications, such as CO2 capture and purification of other gases such as hydrogen, nitrogen, oxygen, etc.

[0075] A gaseous feed stream 102 (in this case ambient air) is compressed by a compressor 104 to form a compressed feed stream 106. To improve the adsorption process and / or reduce moisture content, the compressed feed stream 106 is optionally cooled by a cooling unit 108, such as a direct contact aftercooler or a mechanical chiller, to form a cooled feed stream 110. The temperature to which the cooled feed stream 110 is cooled will depend on the specific application, but it is generally desirable to cool to between 5°C and 20°C. The cooled feed stream 110 enters the inlet 112, 116 of each adsorption vessel 114, 118. In this example, two adsorption vessels 114, 118 are operated in parallel. As is known in the art, several other configurations are also possible, such as a single adsorption vessel, any number of adsorption vessels operated in parallel, and multiple adsorption vessels operated in parallel, but with staggered operating stages for continuous operation (e.g., operating the adsorption vessel 114 in an adsorption step while the adsorption vessel 118 is flushed and regenerated).

[0076] exist Figure 2 , the adsorption vessels 114, 118 are shown as being oriented vertically, and the cooled feed stream 110 enters the adsorption vessels 114, 118 at the bottom. In other embodiments, other vessel configurations may be used, such as horizontal or radial orientation of the adsorption vessels and top feeding of the adsorption vessels in a vertical orientation. As the cooled feed stream 110 passes through the adsorption beds 120, 120', adsorbates such as ambient moisture, carbon dioxide, nitrous oxide, and other hydrocarbon components are adsorbed by the adsorbent and removed from the cooled feed stream 110. In the following description

[0077] In this embodiment, the adsorbent beds 120, 120' include a moisture removal layer 122, 122', which includes an adsorbent that selectively removes ambient moisture; and a carbon dioxide removal layer 124, 124', which includes an adsorbent that selectively removes carbon dioxide as well as nitrous oxide and hydrocarbons from the air feed. The adsorbent material used for the moisture removal layer 122, 122' can be the same or different material as the carbon dioxide removal layer 124, 124'. Silica gel or activated alumina are commonly used to remove moisture, and type X zeolites (e.g., 13X) are commonly used to remove carbon dioxide, nitrous oxide, and some hydrocarbons. At the container outlets 126, 128, the purified feed 130 depleted in adsorbate leaves the TSA purification system 100 and is fed into a downstream cryogenic distillation process 132. An example of a cryogenic distillation process 132 is disclosed in US6651460, which is incorporated herein by reference.

[0078] When the adsorption bed 120 becomes "exhausted" (approaching the limit of its ability to adsorb the adsorbate), it is taken offline and regenerated. The regeneration process can be initiated by reducing the pressure in the adsorption vessel 114. The waste stream 136 from the cryogenic distillation process 134 is heated to at least 150 degrees Celsius by a heater 138 to produce a heated regeneration stream 140, which is substantially free (typically less than 0.1 weight percent adsorbate) of the adsorbate removed during the adsorption step (ambient moisture, carbon dioxide, nitrous oxide, and hydrocarbons). The heater 138 can be a heat exchange device, such as an electric heater, a steam heater, or a gas heater. The heated regeneration stream 140 enters the adsorption vessel 114 via outlets 126, 128 in the opposite flow direction during adsorption. The heated regeneration stream 140 desorbs the adsorbate from the adsorbent material and carries them out of the adsorption vessel (see regeneration outlet 144). When the adsorbent bed 120 has been regenerated, the heater 138 is deactivated and the unheated regeneration stream 140 is allowed to flow through the adsorbent bed 120 until it cools to a predetermined temperature (typically in the range of 5 to 25° C. above the cooled feed temperature). The adsorption vessel 114 is then repressurized and adsorption is restarted by resuming the flow of the cooled feed stream 110 through the adsorbent bed 120. Optionally, the purification duty can be shared for a period of time between an adsorbent bed 120 that is returned online from regeneration and another adsorbent bed 120′ that is spent, after which the spent adsorbent bed 120′ is transitioned to the regeneration process.

[0079] Figure 2 1 shows an exemplary embodiment of a TSA system 200 for cryogenic air distillation according to the present invention. In this embodiment, components shared with the first embodiment (FIG. 1) are represented by reference numerals increased by a factor of 100. For example, the gaseous feed stream 102 of FIG. 1 corresponds to Figure 2 To avoid duplication of description, some features of this embodiment shared with the first embodiment are described in Figure 2 but not repeated in the instructions.

[0080] In this embodiment, each adsorbent bed 220, 220' includes a moisture removal layer 222, 222', a first carbon dioxide removal layer 223, 223', and a second carbon dioxide removal layer 225, 225'. As in the first embodiment, the moisture removal layer 222, 222' includes an adsorbent that selectively removes ambient moisture from the cooled feed stream 210. The first carbon dioxide removal layer 223, 223' and the second carbon dioxide removal layer 225, 225' each include an adsorbent that selectively removes CO2, N2O, and other heavy hydrocarbons from the cooled feed stream 210. The cooled feed stream 210 flows sequentially first through the moisture removal layer, then through the first carbon dioxide removal layer, and then through the second carbon dioxide removal layer.

[0081] Combination Figure 2 The hierarchical arrangement of the system 200 described in Figure 3 The adsorption vessel 214 is shown in more detail in FIG. Figure 3 . In this embodiment, the adsorption vessel 216 has the same configuration. As the cooled feed stream 210 flows through the adsorption vessel 214, an equilibrium zone E and a mass transfer zone M are formed in the adsorption bed 220. It should be noted that the following description of the equilibrium zone E and the mass transfer zone M is at a given point in time. As is understood in the art, the characteristics of these zones (e.g., relative lengths, transition locations, etc.) change over time as long as fluid continues to flow through the absorbent.

[0082] Preferably, the length of the first carbon dioxide removal layer 223 is equal to the length of the equilibrium zone, and the length of the second carbon dioxide removal layer 225 is equal to the length of the mass transfer zone M. It should be understood that in the context of the adsorbent bed 220, the length dimension is parallel to the general flow direction of the cooled feed stream 210 through the adsorbent bed 220. Figure 3 In many applications, the length of the mass transfer zone M will be in the range of 10% to 50% of the sum of the lengths of the mass transfer zone M and the equilibrium zone E.

[0083] The location and length of the mass transfer zone 24 depend on several factors, including pressure, temperature, mass flow rate, adsorbate concentration in the fluid being purified, adsorbent type, adsorbent particle size, and adsorbent CO2 adsorption capacity. Generally, adsorbents with smaller particle sizes provide smaller (shorter) mass transfer zones, thereby more efficiently utilizing the adsorbent bed 220. Unfortunately, the use of smaller particle sizes results in a greater pressure drop and may also cause premature fluidization problems. Therefore, it is not advisable to use smaller particles for the entire molecular sieve layer.

[0084] In the equilibrium zone E (usually between half and two-thirds of the total length of the molecular sieve bed), the capacity of the adsorbent material used for the adsorbate has a great influence on the purification process. In contrast, in the mass transfer zone M, its length is less affected by the adsorbent capacity than the equilibrium zone E, but is still affected by the adsorbent particle size. Higher capacity adsorbents will generally allow a shorter equilibrium zone E, which is more efficient and allows the use of less adsorbent. Using adsorbent materials with smaller particle sizes in the mass transfer zone M is expected to shorten the total bed length due to improved kinetics and reduced size of the mass transfer zone M. The inventors unexpectedly found that when using lower capacity adsorbents, the mass transfer zone M does not have a negative impact on the overall mass transfer of the bed.

[0085] In this embodiment, the adsorbent material in the first carbon dioxide removal layer 223 has a higher CO2 adsorption capacity than the adsorbent in the second carbon dioxide removal layer 225. The CO2 adsorption capacity of the first carbon dioxide removal layer 223 is preferably greater than the CO2 adsorption capacity of the adsorbent in the second carbon dioxide removal layer 225, more preferably greater than at least 10%, and most preferably greater than at least 20%. In most embodiments, the first carbon dioxide removal layer 223 has a CO2 adsorption capacity that is 10% to 30% greater than the adsorbent in the second carbon dioxide removal layer 225.

[0086] The adsorption capacity of the adsorbent for CO2 is also related to the silicon-to-aluminum ratio ("Si / Al ratio") in the adsorbent. Therefore, preferably, the Si / Al ratio of the first carbon dioxide removal layer 223 is in the range of 1.0 to 1.2, and the Si / Al ratio of the adsorbent in the second carbon dioxide removal layer 225 is in the range of 1.2 to 1.5. It is also preferred that the Si / Al ratio in the first carbon dioxide removal layer 223 is at least 10% lower than the Si / Al ratio of the second carbon dioxide removal layer 225.

[0087] In addition, the first carbon dioxide removal layer 223 preferably has a larger average particle size than the adsorbent in the second carbon dioxide removal layer 225. Preferably, the average particle size of the first carbon dioxide removal layer 223 is at least 3.5 mm, and more preferably, between 3.5 and 5 mm. Preferably, the average particle size of the second carbon dioxide removal layer 225 is no greater than 2.5 mm, and more preferably, between 1.0 and 2.5 mm.

[0088] The preferred high capacity adsorbent material for the first carbon dioxide removal layer is sodium exchanged medium or low silicon 13X. The preferred adsorbent material for the second carbon dioxide removal layer is zeolite 13X, which differs from the first layer in that it contains a higher silicon content and / or is non-sodium exchanged. The cost of high capacity adsorbents is higher than low cost adsorbents, but it may reduce the amount of adsorbent required. In the prior art methods, the entire molecular sieve layer contains the high capacity adsorbent, which results in a higher capital cost for the system.

[0089] The inventors have discovered that this combination of CO 2 adsorbent layers allows for a significant reduction in capital expenditures associated with the adsorption bed 220 by reducing the amount of high capacity molecular sieve material without sacrificing adsorption performance.

[0090] Example

[0091] The table below shows data for three different sets of equipment conditions, each with a configuration of a single layer of CO2 adsorbent (labeled "default") and a configuration of two layers of CO2 adsorbent (labeled "mixed layered"). In each example, the high capacity CO2 adsorbent in the "default" configuration has a Si / Al ratio of 1.0 to 1.2 and an average particle size of 2.5 to 3.5. In the mixed layer configuration, the high capacity CO2 adsorbent has a Si / Al ratio of 1.0 to 1.2 and an average particle size of 3.5 mm to 5.0 mm, while the conventional capacity CO2 adsorbent has a Si / Al ratio of 1.2 to 1.5 and an average particle size of 1.0 mm to 2.5 mm.

[0092] Table 1

[0093]

[0094]

[0095] Table 2

[0096]

[0097] Table 3

[0098]

[0099] As shown in each of these examples, the hybrid layered structure enables the system to operate with a significant reduction in the amount of high capacity adsorbent and a reduced pressure drop across the adsorption vessel without reducing purification capacity. In the examples shown above, a 5% reduction in adsorbent cost and a 10% to 20% power savings (due to reduced pressure drop) were achieved.

[0100] The application of this layering technique can also be applied to operating equipment under upset conditions. Such upset conditions include, but are not limited to, adsorbent leaks resulting in reduced adsorbent levels within the vessel or adsorbate breakthrough into downstream processes. In this case, alkaline 13X material can be added on top of the existing layer, even though the existing layer is composed of higher capacity material (meeting fluidization standards). The lower cost and greater availability of alkaline 13X results in reduced costs associated with implementing temporary remedial measures, as well as reduced costs associated with on-site storage of adsorbent required to implement such measures. Another benefit of using a low CO2 capacity adsorbent as the surface layer (MTZ) is that if the adsorbent material in the product end of the vessel becomes contaminated with moisture (i.e., due to a steam heater leak, etc.), the CO2 adsorption capacity can be regenerated and restored at a lower temperature than with a high CO2 adsorption capacity material.

[0101] Although the principles of the present invention have been described above in conjunction with the preferred embodiments, it should be clearly understood that this description is intended only as an example and not as a limitation on the scope of the present invention.

Claims

1. An apparatus for removing at least one pollutant from a gaseous feed stream, the at least one pollutant comprising carbon dioxide, the apparatus comprising: at least one adsorption vessel comprising an adsorption bed, an inlet, and an outlet, the adsorption bed comprising a plurality of layers, the plurality of layers comprising a first layer formed of a first adsorption material capable of selectively adsorbing the at least one pollutant at a first temperature and selectively desorbing the at least one pollutant at a second temperature and a second layer formed of a second adsorption material capable of selectively adsorbing the at least one pollutant at the first temperature and selectively desorbing the at least one pollutant at a third temperature; wherein the second temperature and the third temperature are both higher than the first temperature; wherein an arrangement of the plurality of layers from the inlet to the outlet comprises the first layer followed by the second layer; wherein the first adsorbent material has a greater adsorption capacity for carbon dioxide than the second adsorbent material; wherein the first adsorbent material has a first average particle size, and the second adsorbent material has a second average particle size, and the first average particle size is greater than the second average particle size; and The adsorption bed has an equilibrium zone and a mass transfer zone when in use.

2. The apparatus of claim 1, wherein the at least one pollutant further comprises nitrous oxide and hydrocarbons.

3. The apparatus according to claim 1, wherein the first adsorbent material has a Si / Al ratio in the range of 1.0 to 1.2, and the second adsorbent material has a Si / Al ratio of 1.2 to 1.5, the Si / Al ratio of the first adsorbent material being lower than the Si / Al ratio of the second adsorbent material.

4. The apparatus of claim 1 , wherein the plurality of layers further comprises a third layer formed of a third adsorbent material capable of selectively adsorbing moisture at the first temperature and selectively desorbing moisture at a fourth temperature, the fourth temperature being higher than the first temperature, wherein the arrangement of the plurality of layers from the inlet to the outlet comprises the third layer, the first layer, and then the second layer.

5. The apparatus of claim 1, wherein the first layer has a first layer length and the second layer has a second layer length, wherein the second layer length is in a range of 10% to 50% of the sum of the second layer length and the first layer length.

6. A system for removing at least one contaminant from a gaseous feed stream, the at least one contaminant comprising carbon dioxide, the system comprising: a feed conduit in fluid flow communication with air, the feed conduit being adapted to supply the air to at least one adsorption vessel at a feed temperature; at least one adsorption vessel having an inlet in fluid flow communication with the feed conduit, an adsorption bed, and an outlet, the inlet being in fluid flow communication with the feed conduit, the adsorption bed comprising a plurality of layers, the plurality of layers comprising a first layer formed of a first adsorbent material capable of selectively adsorbing the at least one contaminant at a first temperature and selectively desorbing the at least one contaminant at a second temperature, and a second layer formed of a second adsorbent material capable of selectively adsorbing the at least one contaminant at the first temperature and selectively desorbing the at least one contaminant at a third temperature; a cryogenic distillation subsystem in fluid flow communication with said outlet of said at least one adsorption vessel; a regeneration conduit in fluid flow communication with the outlet of the at least one adsorption vessel, the regeneration conduit being adapted to supply a regeneration gas at a regeneration temperature, the regeneration temperature being higher than the feed temperature; wherein the arrangement of the plurality of layers between the inlet and the outlet consists of the first layer and the second layer; wherein the second temperature and the third temperature are both higher than the first temperature; wherein said arrangement of said plurality of layers from said inlet to said outlet comprises said first layer followed by said second layer; wherein the first adsorbent material has a greater adsorption capacity for carbon dioxide than the second adsorbent material; wherein the first adsorbent material has a first average particle size, and the second adsorbent material has a second average particle size, and the first average particle size is greater than the second average particle size; and The adsorption bed has an equilibrium zone and a mass transfer zone when in use.

7. The system of claim 6, wherein the at least one pollutant further comprises nitrous oxide and hydrocarbons.

8. The system of claim 6, wherein the first adsorbent material has a Si / Al ratio in the range of 1.0 to 1.2, and the second adsorbent material has a Si / Al ratio of 1.2 to 1.5, the Si / Al ratio of the first adsorbent material being lower than the Si / Al ratio of the second adsorbent material.

9. The system of claim 6, wherein the first adsorbent material comprises an adsorption capacity of 1.1 to 1.6, and the second adsorbent material comprises an adsorption capacity of 1.0 to 1.

2.

10. The system of claim 6, wherein the plurality of layers further comprises a third layer formed of a third adsorbent material capable of selectively adsorbing moisture at the first temperature and selectively desorbing moisture at a fourth temperature, the fourth temperature being higher than the first temperature, wherein the arrangement of the plurality of layers from the inlet to the outlet comprises the third layer, the first layer, and then the second layer.

11. The system of claim 6, wherein the first layer has a first layer length and the second layer has a second layer length, wherein the second layer length is in a range of 10% to 50% of the sum of the second layer length and the first layer length.

12. The system of claim 6, further comprising a cooling system operably configured to cool the air before the air enters the at least one adsorption vessel.

13. A method for removing at least one contaminant from a gaseous feed stream, the at least one contaminant comprising carbon dioxide, the method comprising: (a) forming a plurality of layers of adsorbent material in an adsorption bed of each of at least one adsorption vessel, the at least one adsorption vessel having an inlet and an outlet, the plurality of layers of adsorbent material comprising a first layer formed of a first adsorbent material capable of selectively adsorbing the at least one pollutant at a first temperature and selectively desorbing the at least one pollutant at a second temperature, and a second layer formed of a second adsorbent material capable of selectively adsorbing the at least one pollutant at the first temperature and selectively desorbing the at least one pollutant at a third temperature, wherein the second temperature and the third temperature are both higher than the first temperature, wherein an arrangement of the plurality of layers from the inlet to the outlet comprises the first layer followed by the second layer, wherein the first adsorbent material has a greater adsorption capacity for carbon dioxide than the second adsorbent material, wherein the first adsorbent material has a first average particle size and the second adsorbent material has a second average particle size, the first average particle size being larger than the second average particle size, and wherein the adsorbent bed has an equilibrium zone and a mass transfer zone when in use.

14. The method according to claim 13, further comprising: (b) selectively adsorbing the at least one contaminant from the gaseous feed stream by passing the gaseous feed stream through at least one adsorption vessel at a feed temperature to form a purified stream; and (c) regenerating the adsorption bed by flowing a regeneration stream through the at least one adsorption vessel in a direction opposite to the direction of the gaseous feed stream of step (b) at a regeneration temperature greater than the feed temperature, causing the at least one contaminant to be desorbed from the adsorption bed into the regeneration stream.

15. The method according to claim 13, further comprising: (d) supplying a purified stream to a cryogenic distillation subsystem in fluid flow communication with the outlet of the at least one adsorption vessel.

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