DEVICE FOR THE REMOVAL AND SEPARATION OF HELIUM ISOTOPES FROM NATURAL GAS

Abstract

This disclosure presents a new device for the removal and separation of isotopes of Helium in Compressed Natural Gas, based on a system with two cascades operating together to increase, in the first cascade, the concentration of Helium in the cascade head, and at the tail of the same cascade, Helium-depleted Compressed Natural Gas is discharged, while the second cascade, fed from the head of the first cascade, allows separation of the isotopes of Helium-3 and Helium-4, discharging Helium-3 through the head of the second cascade, while Helium-4 is discharged through the tail of the second cascade, with a configuration that is efficient from the energy consumption standpoint, while using a small number of rotating parts.

Claims

1. A device for the removal and separation of helium isotopes from natural gas, to separate isotopes from a first gas, in relation to a second majority carrier gas at pressure, with higher molecular weight than the isotopes of the first gas, with increased commercial value when the content of the first gas decreases in the second majority carrier gas, comprising two cascades with serial stages each, with the first cascade operating at a pressure that is equal or lower to the pressure of the source providing the majority carrier gas, and allows enrichment of the content of the first gas in relation to the second majority carrier gas through selective permeability of the mixture of gasses, which, when going through successive membrane stages with higher permeability to the first gas in relation to the second majority carrier gas, a flow can be extracted of the majority carrier gas as output of the first cascade, with depletion of the content in the first gas, generating a first continuous flow of a product of commercial interest, while the second output of the first stream is enriched in the content of the first gas and feeds the second cascade at some intermediate point, and where this second cascade is at a pressure lower than the pressure operating the first cascade, to produce isotope separation of its gasses through diffusion of that gas through inert porous membranes, since the mean free paths of the gas of the second cascade is similar to the pore radius of the porous membranes, generating higher permeability for molecules and isotopes with lower molecular weight, so that at the end of the second cascade towards where gasses advance with lower molecular weight, an output flow is obtained enriched with the light isotope, generating in this flow a second continuous flow of a product of commercial interest, while at the other end of the second cascade in relation to the extraction point of the output enriched with the lighter isotope and the feed point, an output flow is obtained depleted in the light isotope, which generates a third continuous flow of a product of commercial interest.

2. The device for the removal and separation of helium isotopes from natural gas of claim 1, wherein the two cascades make mixtures prior to entering a stage of the non-diffused and non-permeated recycles of the subsequent stages with flows diffused and permeated from prior stages, and the flows of the same stages when they have output flows fully or partially recirculated to form the flow entering that stages, through gas-gas injectors, where the driving flow is the flow with lower pressure that must be mixed, and receives the pressure necessary to operate as motive flow of the gas-gas injector of a specific compressor for each gas-gas injector.

3. The device for the removal and separation of helium isotopes from natural gas of claim 2, wherein the reduction of pressure necessary for the output enriched with the content of the first gas to enter with the proper pressure as feed for the second cascade, through a turbo-expander with useful power in the shaft, used to drive a turbo-compressor which increases the output pressure of the gas depleted in the light isotope produced in the second cascade.

4. The device for the removal and separation of helium isotopes from natural gas of claim 3, wherein the reduction of pressure required from the source of the majority carrier gas and the feed of the first cascade is through a turbo-expander with useful power in the shaft used to drive a turbo-compressor that increases the output pressure of the majority carrier gas depleted in the content of the first gas that is produced in the first cascade.

5. The device for the removal and separation of helium isotopes from natural gas of claim 3, wherein the output gas depleted in the light isotope produced in one of the ends of the second cascade have a substantial content of the majority carrier gas, and the output of the turbo-compressor which increases its output pressure, is connected at some intermediate stage of the first cascade as recycle flow to be aspired by the gas-gas injector with motive flow being the flow with the concentration that is more similar in content to the lightweight gas, and where extraction of the flow for depletion of the light isotope and the majority carrier gas occurs between an intermediate stage of the entering the feed flow and the end of the second cascade, which was sent by the turbo-expander as recycle to the first cascade.

6. The device for the removal and separation of helium isotopes from natural gas of claim 4, wherein an output of gas depleted in the light isotope produced in one of the ends of the second cascade with a substantial content of the majority carrier gas, and the output of the turbo-compressor which increases its output pressure connected at some intermediate stage of the first stream as flow of the recycle to be aspired by the gas-gas injector with drive flow being the concentration that is more similar in content to the lightweight gas, and where extraction of the depleted flow of the light isotope and the majority carrier gas occurs between an intermediate stage of the entering the feed flow and the end of the second cascade, which was sent by the turbo-expander as recycle to the first cascade.

7. The device for the removal and separation of helium isotopes from natural gas of claim 5, wherein the membranes of the first cascade are polymeric membranes.

8. The device for the removal and separation of helium isotopes from natural gas of claim 6, wherein the membranes of the first cascade are polymeric membranes.

9. The device for the removal and separation of helium isotopes from natural gas of claim 7, wherein the light gas is Helium and the majority carrier gas is Methane.

10. The device for the removal and separation of helium isotopes from natural gas of claim 8, wherein the light gas is Helium and the majority carrier gas is Methane.

11. The device for the removal and separation of helium isotopes from natural gas of claim 7, wherein the light gas is Helium, and the majority carrier gas is Methane mixed with other gases which can also be extracted from various stages of both from the first and the second cascade of the device.

12. The device for the removal and separation of helium isotopes from natural gas of claim 8, wherein the light gas is Helium, and the majority carrier gas is Methane mixed with other gases which can also be extracted from various stages of both from the first and the second cascade of the device.

13. The device for the removal and separation of helium isotopes from natural gas of claim 2, wherein the device only has the first cascade, and does not separate the isotopes of the first gas.

14. The device for the removal and separation of helium isotopes from natural gas of claim 13, wherein the reduction of pressure necessary for the output enriched with the content of the first gas to enter with the proper pressure as feed for the second cascade, through a turbo-expander with useful power in the shaft, used to drive a turbo-compressor which increases the output pressure of the gas deployed in the light isotope produced in the second cascade.

15. The device for the removal and separation of helium isotopes from natural gas of claim 14, wherein the membranes of the cascade are polymeric membranes.

16. The device for the removal and separation of helium isotopes from natural gas of claim 15, wherein the light gas is Helium and the majority carrier gas is Methane.

17. The device for the removal and separation of helium isotopes from natural gas of claim 14, wherein the light gas is Helium and the majority carrier gas is Methane mixed with other gases that can be extracted at different stages of the cascade.

18. The device for the removal and separation of helium isotopes from natural gas of claim 2, wherein the device only has the second cascade, and the feed is from a pressure source of the first gas.

19. The device for the removal and separation of helium isotopes from natural gas of claim 3, wherein the device only has the second cascade, and the feed is from a pressure source of the first gas.

20. The device for the removal and separation of helium isotopes from natural gas of claim 19, wherein the light gas is Helium and the majority carrier gas is Methane.

21. The device for the removal and separation of helium isotopes from natural gas of claim 19, wherein the light gas is Helium and the majority carrier gas is Methane mixed with other gases that can be extracted at different stages of the cascade.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] In order to have a better understanding of this disclosure, hereinafter there is a detailed description, based on the accompanying drawings, included for the sole purpose of illustrating the preferred way to implement this disclosure, without limiting the disclosure:

[0071] FIG. 1 shows a diagram of the embodiment of the disclosure, including the two cascades for the separation of Helium-3, Helium-4, and Natural Gas.

[0072] FIG. 2 shows a diagram of the first cascade of permeable membranes to separate the Helium of Compressed Natural Gas, which illustrates the recycle gas-gas injectors, and the feed turbo-expander and turbo-compressor and return to the Natural Gas source.

[0073] FIG. 3 shows a diagram of the second cascade of porous membranes to separate Helium isotopes, which illustrates the recycle gas-gas injectors, and the feed turbo-expander and turbo-compressor and return to the Natural Gas source.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0074] Before going into a detailed description, it is noted that the implementation described is not to limited to the separation of Helium isotopes from Compressed Natural Gas alone, and therefore, although this implementation is shown and described for explanation purposes as applied to the separation of Helium-3 and Helium-4 present in Compressed Natural Gas, it can be implemented to separate other isotopes of other minority lightweight gasses contained in a heavier carrier gas present in larger proportions, and, if not needed to separate the isotopes of some light gas, the device can be limited to the first cascade of separation of the light minority gas from the heavy majority gas, using the recycles and feeds and withdrawals proposed for this device, or, if the minority light gas is already separated from the heavier carrier gas, the device may be limited to separating the isotopes of the light gas, using the recycles and feeds and withdrawals proposed for this device.

[0075] This disclosure presents a new device to separate the isotopes of Helium in Compressed Natural Gas, while returning Compressed Natural Gas with concentration reduced in Helium, based on a continuous and coupled operation of two cascades operating jointly to increase, in the first cascade, the concentration of Helium in Natural Gas, and, from the depletion section of the first cascade, Compressed Natural Gas is discharged and recovered with concentration reduced in Helium, while the second cascade, fed by the flow with higher Helium-enrichment from the first cascade, separates the isotopes of Helium-3 and Helium-4, discharging the Helium-3 from the section with greater Helium-3 enrichment in the second cascade, while Helium-4 is discharged from the section with less Helium-3 content from the second cascade.

[0076] FIG. 1 illustrates a schematic view of the proposed device, which processes a source of Natural Gas at pressure with a certain content of Helium that wants to be removed, outlined as a feed line (10), which can be a downstream pipeline, a downstream Natural Gas well, or a Natural Gas processing plant, down-streamed as schematically shown in (12), where the return of the Helium-depleted Compressed Natural Gas is produced by the connection section (14), where a restriction is shown (16), placed for illustration purposes as a closed valve, to shows that when connecting the proposed device to the source of Natural Gas, caution shall be taken to avoid mixing the Helium-depleted current of connection (14) with the Helium current of connection (12). The line feeding (17) of the device drives the flow towards the turbo-expander (20), which moves a turbo-compressor (22) through a shaft (23) that transfer the mechanical power produced in the turbo-expander (20) to the turbo-compressor (22), which drives the return line of Natural Gas (24), with the Helium-depleted Natural Gas produced by the proposed device.

[0077] The downstream from the turbo-expander (20) is driven through the feed line (26) to the first cascade of permeable membranes (30), which shall preferable be polymeric membranes, given the current technologies available.

[0078] The turbo-expander (20) is necessary when, as usual, the pressure from the Natural Gas source (10) is higher than the pressure required for optimum operation of the first stream (30).

[0079] The output of the return, Helium-depleted, Natural Gas (24), after going through the output turbo-compressor (22) may have a pressure lower than the pressure required to inject it again into the source of Natural Gas (10). In this case, exit (32) of the turbo-compressor (22) has a second compressor (33), which is driven by the motor (34), and discharges through the connection (14) in the Natural Gas line (10), and therefore becomes a line with its Helium-depleted Natural Gas.

[0080] Because the line of Helium-enriched gas (35) produced by the first cascade (30) has a pressure higher than the optimal pressure at which a cascade must operate to separate helium isotopes, it reduces pressure through a turbo-expander (36), that moves a turbo-compressor (37) through the shaft (38) that transmits the mechanical power produced by the turbo-expander (36) to the turbo-compressor (37). The downstream from the turbo-expander (36) is driven towards the second cascade through the line (39) connecting the Helium-enriched gas with the flow that is circulating through the second cascade, in the feed point (40).

[0081] Since the second source has membranes suitable for isotope separation, and given the attainable separation factors to separate Helium isotopes, it has both a part of the cascade generating Helium-3 enrichment, also called section of enrichment of the cascade, shown in the figure schematically as block (42), and a part of the cascade for the depletion of Helium-3, also called section of depletion, shown in the figure schematically as block (44).

[0082] With the technologies currently available, it is convenient for membranes of the second cascade to be porous membranes.

[0083] The profile and operation of the second cascade, consisting of the enrichment section (42) and the depletion section (44), is designed so that the feed point (40) has a minimum difference in enrichment between the currents that are mixed in the feed point (40).

[0084] If the cascade zone with lower Helium-3 enrichment of the depletion section is referred to as a tail, and the cascade zone of higher enrichment in Helium-3 from the enrichment section is referred to as a head, then the tail of the second cascade (44) comes from the extraction line of minimum enrichment in Helium-3 (46), the corresponding higher enrichment in Helium-4, which corresponds due to its properties with the Helium that is currently on the market, so that the outflow (48) may be marketed as compressed Helium after increasing its pressure with the turbo-compressor (37).

[0085] Because the discharge pressure required to fill normalized cylinders to store and transport Helium is much higher than the usual pressure of Natural Gas sources, the output pressure of Helium exiting the turbo-compressor (37), available at the point of extraction (48) it is not enough to fill normalized cylinders, and a second compressor not shown in FIG. 1 must be added, which is not included because it is a commercial product with no special features and connections, and not part of the proposed device.

[0086] The head of the second cascade (42) produces in its extraction line with higher Helium-3 enrichment (50), which is discharged through the connection (52). The purification equipment and increase in concentration that may be required to market the gas with maximum Helium-3 enrichment of the output (52), is not shown in FIG. 1, and since their flows and sizes are extremely low, they do not strictly require continuous production, are not shown in FIG. 1, and are not part of the proposed device.

[0087] Other gases, such as Nitrogen, CO.sub.2 and Hydrogen, among others, which can also be found in the source of Natural Gas, depending on the separation factors of the two cascades for each of these gases, may also be extracted at points close to the heads and tails of each stream depending on the gases and membranes, as shown generically as extractions (70) (72) and (74), of which only extraction is shown for each section of the streams (30) (42) and (44) for simplicity purposes, but each stream can have more than one intermediate point of gases extraction, so as to improve the purity of the three main productions of the device, Helium-depleted Natural Gas (14), Helium-4-enriched Natural Gas (48) and Helium-3-enriched Natural Gas (52).

[0088] If the extraction form the head of the first cascade (35), due to its design and optimization still has a substantial Methane content that needs to be recovered, the extraction from the tail of the second cascade, since it has membranes that separate gases due to the difference in molecular weights, also causes these more methane-enriched concentrations to exit through the tail (46), and therefore it may be convenient for the extraction from the tail of the second cascade to be recycled into the first cascade at some intermediate point of the first cascade, instead of feeding the helium charging system (48), generically shown as the dotted line (80), to minimize the energy consumption of the stream and, in that case, the extraction of Helium-4 and subsequent re-compression shall be through some intermediate extractions of the depletion section (44) of the second cascade, for instance, the intermediate extraction (72).

[0089] Line (90) outlines the limit that defines the proposed device in accordance with this disclosure.

[0090] FIG. 2 contains a schematic view of the first cascade that makes up the proposed device, processing a source of Natural Gas with a certain content of the Helium that is intended to be removed, schematized as a feed line (10), with the turbo-expander (20) and the turbo-compressor (22) system, with an output compressor (33) already explained in FIG. 1.

[0091] The first cascade is displayed in this figure as composed of five stages for illustration purposes, but more or less stages can be used, depending on the Helium separation factor sought at this cascade, and the general economy of the device, but always maintaining the design explained below. After the turbo-expander (20), the Natural Gas source feed is through line (26), entering through feed line (100) to the first stage (101), with the membranes outlined as the barrier (102), and where the feed (26) is combined with the non-permeated recycle of the subsequent stage (103), through a gas-gas injector (104), with the flow as driving fluid (105) coming from the non-permeated flow of the same stage (102) that is extracted with the compressor (106), that is driven by the engine (107) that gets its flow from derivation (108) that separates the recycled flow that is not sent as recovered Helium-depleted Natural Gas (24) to the Natural Gas source, where the drive flow (105) aspires when the non-permeated recycle flow of the subsequent stage accelerates (103) and the feed flow from the first cascade (26) to then increase the pressure at the gas-gas injector outlet diffuser (104), shown for illustration purposes only as composed by a convergent piece and a divergent piece.

[0092] The compressor (109), driven by a motor (110), extracts the diffused material of stage (101) through the membranes (102) and injects it through the feed line (111) to the second stage (112), composed of membranes (113), after passing through a second gas-gas injector, outlined as (114) for illustration purposes, which is discharged into the input line (115) to stage (112), after combining with the non-permeated recycle (116) of the subsequent stage, where the engine fluid is flow (111) from the compressor (109).

[0093] All intermediate stages follows the same design of the previous stage; in the case of the third stage, the compressor (119), driven by a motor (120) extracts the diffused material of stage (112) through the membranes (113) and injects it through the feed line (121) to the third stage (122), composed of membranes (123), after passing through a gas-gas injector, outlined as (124) for illustration purposes, which is discharged into the input line (125) to stage (122), after combining with the non-permeated recycle (126) of the subsequent stage, and where the engine fluid is flow (121) from the compressor (119).

[0094] The same for the fourth state, the compressor (129), driven by a motor (130), extracts the diffused material of stage (122) through the membranes (123) and injects it through the feed line (131) to the fourth stage (132), composed of membranes (133), after passing through a third gas-gas injector, outlined as (134) for illustration purposes, which unloads into the input line (135) to stage (132), after combining with the non-permeated recycle (136) of the subsequent stage, and where the motive fluid is the flow (131) from the compressor (129).

[0095] Since the explanation is carried out on a cascade with five stages, the last stage does not follow the scheme explained for stages 1 through 4, but is fed directly through the compressor (139) driven by a motor (140) that feeds the last stage (142), composed of membranes (143) directly through the line of injection (144).

[0096] The output flow of the last stage is extracted by the compressor (149), driven by a motor (150), and injects the output gas (151) to the point of connection of the output withdrawal (160) Helium-enriched and Methane-depleted.

[0097] As shown in FIG. 2, the proposed device carries out all non-permeated recycles of subsequent stages without using a turbo-compressor, but using gas-gas injectors (106) (114) (124) and (134) it manages to feed all recycles of subsequent stages (105) (116) (126) and (136) without using mobile parts, modified turbo-machines and additional seals.

[0098] In this scheme heat exchangers have been omitted, necessary at each stage of compression for the purposes of removing the compression work of the engines, so as to simplify the explanation of FIG. 2.

[0099] In another alternative configurations of this device, when it is not convenient to send all the Helium-enriched flow to the second cascade, the fraction of the flow not sent to the second cascade can be recycled, adding a gas-gas injector between the compressor (139) and the last stage (142), and where the driving flow is the flow from the compressor (139), so that the last stage would have the same components as the preceding stage, which is why it is not shown in FIG. 2, and thus simplify the explanation of the first cascade.

[0100] For the purposes of being clear as to how to implement this alternative in the proposed device, the extraction of most Heilum-3-enriched material through the end of the second cascade shall be made including the option of extracting only a fraction of the flow that goes through the membranes in the last stage, so as to detail both extraction alternatives of the flow more enriched at the ends of any of the two cascades for the proposed device.

[0101] FIG. 3 illustrates a schematic view of the second cascade that makes up the proposed device, processing Helium-enriched gas from the first cascade, with its Helium isotopes separated on this second cascade, and feeding outlined as injection point (160), with its pressure reduced by the turbo-expander (36), which drives the turbo-compressor (37), already explained in FIG. 1.

[0102] The second stream is displayed in this figure as composed by eight stages for illustration purposes, in which 6 stages are displayed, making the section of Helium-3 enrichment, while the two remaining are displayed making the section of Helium-3-depletion or Helium-4 enrichment, with the option to use more or less stages depending on the factor of separation of Helium of each stage, the separation gain expected in the second cascade, and the general economy of the device, and only this number of stages have been placed for illustration purposes, so that the device used in the practice will use more or less stages depending on the specific design, but always keeping the concept of connections and design detailed below. The discharge of the turbo-expander (36) is driven to the second stream through line (39) which connects Helium-enriched gas that is obtained at the first cascade with the flow that is circulating through the second cascade, at the feed point (40), forming the feed flow (200) entering the first stage (202) of the enrichment section of the cascade, after mixing with the flow (203) from the mix of non-diffused recycle of the subsequent stage (204) of the enrichment section of the cascade, along with forwarding from the previous stage (205) in the depletion section of the cascade.

[0103] The mixing of flows (204) and (205) is carried out through the gas-gas injector (206), similar to the one described for gas-gas injectors in the first cascade in FIG. 2, and where the motive flow is the forwarding flow of the previous stage (205).

[0104] Once the output flow (203) of the injector (206) and the feed flow (39) enter the first stage (202), to spread the gas through the porous membranes (207), the gas spread, enriched in Helium-3 is driven by the compressor (208) towards the subsequent stage, with the motor's driving power (209).

[0105] This Helium-3 enriched flow (210), after joining the non-diffused recycle current of the subsequent stage (212), in the gas-gas injector (214), form the input flow (215) to stage (216), so that the flow diffusing through membranes (217) increases its Helium-3 enrichment and circulates to the subsequent stage driven by the compressor (218) due to the engine's driving force (219).

[0106] As schematically shown with the dotted line (220), the set described by stage (216), membranes (217), gas-gas injector (217), compressor (218) and motor (219), are part of a set that is repeated functionally towards the higher enrichment flows to form the enrichment section of the cascade, and also repeated towards lower enrichment units to form the depletion section of the cascade, except the last stage (230) or head of the stage, since it lacks recycle from a subsequent phase, the feed gas-gas injector (231), is driven by the driving flow from the previous stage (232), and recycles the flow (233) coming from the flow that circulates through the membranes (234), but not derived as extraction flow of highest Helium-3-enrichment (235), which is generated by the extraction made by the compressor (236), that is driven by the motor (237), to extract the Helium-3-enriched flow by pressure through the extraction point (50) of the second cascade of the proposed device.

[0107] The stage of less Helium-3 enrichment is also different to the repetition of the various functional units, in the last stage or tail of the cascade, since it lacks a prior stage providing the driving flow for the gas-gas injector. This is the reason why the stage of less Helium-3 enrichment (240), enters the flow (242) that comes from the gas-gas injector (243) which mixes the non-diffused flow (244) of stage (240) which has not been derived to the discharge system through line (46) which feeds the output compressor (37), forming the flow (245) which is driven by the compressor (246) through the motor's driving power (247), to act as the motive flow (247) of the injector (243) and suck the non-diffused recycle (248) of the subsequent stage (249).

[0108] The volume extracted by the turbo-compressor (37) feeds the point of extraction of cascade (48) corresponding to the lowest Helium-3 content or Helium-4-enriched content, which can be loaded as Helium by pressure in standardized transport and storage cylinders, not shown in FIG. 3, but with loading pressure schematically achieved with compressor (250), which is driven by the driving force of the motor (252) so that the pressure Helium cylinders can be connected to the schematic load point (254) for storage and transportation.

[0109] Heat exchangers are omitted in this scheme, necessary at each stage of compression for the purposes of removing the compression effort of the engines, so as to simplify the explanation of FIG. 3.

[0110] Another option for the design of this device, when it is not convenient that only fraction (235) of the flow diffused at stage (230) is sent to the extraction point (50), since the device sends the other part of the diffused flow of stage (230) as flow (233) of recycle to the same stage (230), but it is convenient to send to the point of extraction (50) all of the flow diffused towards the point of extraction (50), so the recirculation line (233) has a null flow, and in this case, for the proposed device, the gas-gas injector is not necessary (232) and the line of the flow (232) can be discharged directly at stage (230).

[0111] Just like the proposed device has the option of sending all of the higher Helium-3 enrichment diffused flow from stage (230) of the cascade head or not, towards the point of extraction, as explained, the proposed device has a similar alternative for the non-diffused recycle with less Helium-3 enrichment from stage (240) of the tail of the cascade.

[0112] In another design alternative for this device, when it is not convenient to send only the flow (46) towards the point of extraction (48) because the non-diffused flow (244) of the last stage (240) of the tail of the second cascade, the fraction of flow (245) is extracted to recycle on the same stage (240), gas-gas injector (243) is not necessary, because there is no need to mix two recycles, (247) and (248), before entering phase (240). For that design alternative of the proposed device, the bypass (245) of the flow (244) is not required, and all the flow (244) is directed through the line (46) to the compressor (37) and then the compressor is not necessary (246), nor is its motor (247), or the gas-gas injector (243), and the recycle of the non-diffused material (248) of the subsequent stage (249) enters stage (240) through an additional compressor not shown in the figure.