EP2350546A1

EP2350546A1 - Helium recovery from natural gas integrated with ngl recovery

Info

Publication number: EP2350546A1
Application number: EP09819614A
Authority: EP
Inventors: Donald Victory; Michael W. Miles; Russell H. Oelfke
Original assignee: ExxonMobil Upstream Research Co
Current assignee: ExxonMobil Upstream Research Co
Priority date: 2008-10-07
Filing date: 2009-07-28
Publication date: 2011-08-03
Also published as: US20110174017A1; CA2734853A1; WO2010042266A1

Abstract

The invention relates to a process for producing a helium-enriched vapor stream, a methane- enriched vapor stream, and a liquid stream enriched in hydrocarbons heavier than methane from a pressurized, multicomponent, multiphase stream comprising methane (C₁), helium (He) and hydrocarbons heavier than methane (C₂₊). The process includes cooling the multiphase stream to produce at least one vapor stream enriched in helium and at least one liquid stream, withdrawing at least a portion of the at least one vapor stream as a helium- enriched product stream, passing at least a portion of the at least one liquid stream to a demethanizer, withdrawing from the demethanizer a vapor enriched in methane (C₁), and withdrawing from the demethanizer a liquid enriched in hydrocarbons heavier than methane (C₂₊).

Description

HELIUM RECOVERY FROM NATURAL GAS INTEGRATED WITH NGL

RECOVERY

Cross Reference To Related Applications

[0001] This application claims the benefit of U. S. Provisional Application No. 61/103,436, filed 07 October 2008. Field of the Invention

[0002] The present invention relates to an improved process for cryogenic separation of natural gas. More particularly, the present invention relates to an improved process for cryogenically removing helium and natural gas liquids (NGLs) from natural gas to produce a product stream enriched in helium, a liquid product stream enriched in NGLs, and a gaseous product stream enriched in methane. Background

[0003] This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present invention. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.

[0004] Because of its clean burning qualities and convenience, natural gas has become widely used in recent years. The composition of natural gas can vary significantly. As used in this disclosure, a natural gas stream contains methane (Ci) as a major component. The natural gas will typically contain contaminants such as water, carbon dioxide, hydrogen sulfide, dirt, and iron sulfide; hydrocarbons such as ethane (C₂), propane (C3), and higher hydrocarbons; and diluent gases such as nitrogen and helium. [0005] In order to produce natural gas of a purity suitable for commercial use, a natural gas stream from a gas-bearing reservoir may have to be separated to enrich the methane content of the gas stream.

[0006] Natural gas is often treated to remove impurities such as carbon dioxide, water, and non-hydrocarbon acid gases. Natural gas is often further processed to separate and recover natural gas liquids (NGLs), which may include hydrocarbons such as ethane, propane, butanes, pentanes, and sometimes higher molecular weight components. NGLs are valuable as raw materials for preparing various petrochemicals. NGL is sometimes referred to as C₂₊. [0007] Various distillation methods have been considered for recovering NGL components from natural gas. The NGL is typically separated from methane and more volatile components such as nitrogen and helium in one or more distillation towers. The towers are often referred to as demethanizer or deethanizer columns. Processes employing a demethanizer column separate methane and other volatile components from ethane and heavier components. The methane fraction is typically recovered as purified gas (containing small amounts of inerts such as nitrogen, CO₂, etc.) for pipeline delivery. NGLs are recovered as much as practical from the feed gas.

[0008] One NGL recovery process is known as the Gas Subcooled Process ("GSP"), which is disclosed in U.S. patents numbers 4,140,504; 4,157,904; and 4,278,457. In the GSP process, a portion of a natural gas feed stream is condensed and subcooled, flashed down to the demethanizer operating pressure, and supplied to the demethanizer as its top feed for reflux. The remainder of the feed gas is also expanded to lower pressure (typically using a turboexpander for vapor streams) and fed to the demethanizer at one or more intermediate feed points. Another process, known as the Recycle Split-vapor Process ("RSV"), which is disclosed in U.S. patent number 5,568,737, is a residue gas recycle process in which the overhead gas (residue gas) of a demethanizer (or a deethanizer) is compressed and cooled, and is depressurized to make a low-temperature liquid, and then the liquid is supplied as a reflux to the demethanizer (or the deethanizer).

[0009] Helium is another component of natural gas in certain natural gas fields, typically present in small concentrations. The presents of helium in the natural gas reduces the heating value of the natural gas. Also, helium may have independent commercial uses if it can be economically separated from the natural gas. Consequently, the separation of helium from natural gas may have a twofold economic benefit, namely, enhancement of the natural gas heating value and production of a marketable gas such as helium.

[0010] Numerous processes are known in the art for the cryogenic separation of helium from a natural gas stream. Among these cryogenic processes are the multi-stage flash cycle process and the high pressure distillation process. The cryogenic processes typically subject the helium-bearing natural gas to successively lower temperatures to condense and thereby remove from the natural gas those components therein having boiling points higher than that of helium. These components generally include, in descending order of their boiling points, hydrocarbons heavier than methane, methane itself, and nitrogen. [0011] In the flash cycle, which is disclosed for example in U.S. Pat. No. 3,260, 058, feed gas is partially liquefied and phase separated. Dissolved helium in the liquid portion is recovered by several subsequent flash steps in which small amounts of helium-rich vapor are flashed off and eventually added to the bulk helium-rich stream. [0012] In the distillation (high pressure stripping) process, feed gas is at least partially liquefied and fed to a distillation step in which dissolved helium is stripped from the liquid at feed pressure. The high pressure distillation process has the advantage of higher helium content in the helium-enriched stream than the flash cycle. In addition, since the helium- enriched stream is produced at feed pressure, the product streams from the subsequent processing steps can be returned at higher pressure, thereby reducing energy consumption for the crude helium stream recompression.

[0013] Processes have been proposed for integrating the recovery of helium with NGL recovery. See, for example, SPE paper number 24292, entitled "Process Requirements and Enhanced Economics of Helium Recovery From Natural Gas", presented at the SPE Mid- Continent Gas Symposium in Amarillo, Texas, April 13-14, 1992, which discloses operating a NGL section of a process with a nitrogen recovery unit ("NRU") and a helium recovery unit ("HRU"). In such processes, a natural gas stream is feed to a distillation column that produces a NGL stream and one or more vapor streams that are passed to an integrated NRU/HRU unit. The NRU/HRU unit produces a vapor stream enriched in helium, a vapor stream enriched in nitrogen, and a residual gas stream enriched in methane. [0014] The prior art has long sought methods for improving efficiency and economics of processes for separating and recovering helium and natural gas liquids from natural gas. Accordingly, there has been a need for more efficient and more economical methods for performing this separation. Summary

[0015] In general, in one aspect, the invention relates to a process of producing a helium- enriched vapor stream, a methane-enriched vapor stream, and a liquid stream enriched in hydrocarbons and other compounds heavier than methane from a pressurized, multicomponent, multiphase stream comprising methane (Ci), helium (He) and hydrocarbons heavier than methane (C₂₊). The process comprises cooling the gas stream to produce at least one vapor stream enriched in helium and at least one liquid stream, withdrawing at least a portion of the at least one vapor stream as a helium-enriched product stream, passing at least a portion of the at least one liquid stream to a demethanizer, withdrawing from the demethanizer a vapor enriched in methane (Ci), and withdrawing from the demethanizer a liquid enriched in hydrocarbons heavier than methane (C₂₊).

[0016] In another aspect, the invention relates to a process comprising passing a natural gas feed stream containing helium and NGLs into a first phase separator to produce a first vapor phase and a first liquid phase, withdrawing the first vapor phase from the first phase separator, separating the first vapor phase into a second vapor phase and a third vapor phase, cooling the second vapor phase by indirect heat exchange in a heat exchanger, expanding the cooled second vapor phase to produce a reduced-pressure vapor phase and reduced-pressure liquid phase, and passing the reduced-pressure vapor and liquid phases to a second phase separator, withdrawing from the second phase separator a helium-enriched vapor phase, withdrawing liquid from the second phase separator and passing the withdrawn liquid to a first flow regulating device, passing liquid from the first flow regulating device to a demethanizer, expanding the third vapor phase to produce a reduced-pressure vapor phase and reduced-pressure pressure liquid phase, and passing the reduced-pressure vapor and liquid phases to the demethanizer, withdrawing liquid from the first phase separator and passing the withdrawn liquid to a second flow regulating device, passing liquid from the second flow regulating device to the demethanizer, withdrawing from the demethanizer a vapor enriched in methane (Ci), and withdrawing from the demethanizer a liquid enriched in hydrocarbons heavier than methane (C₂₊). [0017] Other aspects and advantages of the invention will be apparent from the following description and the appended claims. Brief Description of the Drawings

[0018] Further features and advantages of the present invention will become apparent from the following detailed description taken in combination with the appended drawings, in which:

[0019] Fig. 1 is a schematic diagram of one embodiment of the present invention for producing products from natural gas in which helium recovery is integrated into a GSP process for NGL recovery.

[0020] Fig. 2 is a schematic diagram of another embodiment of the present invention for producing products from natural gas in which helium recovery is integrated into a GSP process for NGL recovery.

[0021] Fig. 3 is a schematic diagram of another embodiment of the present invention for producing products from natural gas in which helium recovery is integrated into a RSV process for NGL recovery. [0022] Fig. 4 is a schematic diagram of another embodiment of the present invention for producing products from natural gas in which helium recovery is integrated into a GSP process for NGL recovery. [0023] Fig. 5 is a schematic diagram of another embodiment of the present invention for producing products from natural gas in which helium recovery is integrated into a RSV process for NGL recovery.

[0024] Fig. 6 is a schematic diagram of another embodiment of the present invention for producing products from natural gas in which helium recovery is integrated into a RSV process for NGL recovery.

[0025] Fig. 7 is a schematic diagram of another aspect of the invention which illustrates cooling by refrigeration instead of expansion devices. [0026] While the present disclosure is susceptible to various modifications and alternative forms, specific example embodiments thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific example embodiments is not intended to limit the disclosure to the particular forms disclosed herein, but on the contrary, this disclosure is to cover all modifications and equivalents as defined by the appended claims. It should also be understood that the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating principles of exemplary embodiments of the present invention. Moreover, certain dimensions may be exaggerated to help visually convey such principles. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the drawings, the same reference numerals designate like or corresponding, but not necessarily identical, elements throughout the figures. Various required subsystems such as, but not limited to, valves, pumps, motors, reboilers, flow stream mixers, control systems, and sensors have been deleted from the drawings for the purposes of simplicity and clarity of presentation. Such subsystems would be provided in accordance with standard engineering practice. Detailed Description

[0027] In the following detailed description section, the specific embodiments of the present invention are described in connection with preferred embodiments. However, to the extent that the following description is specific to a particular embodiment or a particular use of the present invention, this is intended to be for exemplary purposes only and simply provides a description of the exemplary embodiments. Accordingly, the invention is not limited to the specific embodiments described below, but rather, it includes all alternatives, modifications, and equivalents falling within the true spirit and scope of the appended claims. [0028] In the interest of clarity, not all features of an actual implementation are described in this disclosure. It will of course be appreciated by persons skilled in the art that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system- related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated by persons skilled in the art that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of the present disclosure. Definitions [0029] Various terms as used herein are defined below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent.

[0030] As used herein, "a" or "an" entity refers to one or more of that entity. As such, the terms "a" (or "an"), "one or more", and "at least one" can be used interchangeably herein unless a limit is specifically stated.

[0031] As used herein, the term "enriched" as applied to any stream withdrawn from a process means that the withdrawn stream contains a concentration of a particular component that is higher than the concentration of that component in the feed stream to the process.

[0032] As used herein, the term "expansion device" refers to one or more devices suitable for reducing the pressure of a fluid in a line (for example, a liquid stream, a vapor stream, or a multiphase stream containing both liquid and vapor). Unless a particular type of expansion device is specifically stated, the expansion device may be (1) at least partially by isenthalpic means, or (2) may be at least partially by isentropic means, or (3) may be a combination of both isentropic means and isenthalpic means. Suitable devices for isenthalpic expansion of natural gas are known in the art and generally include, but are not limited to, manually or automatically actuated throttling devices such as, for example, valves, control valves, Joule- Thomson (J-T) valves, or venturi devices. Suitable devices for isentropic expansion of natural gas are known in the art and generally include equipment such as expanders or turbo expanders that extract or derive work from such expansion. Suitable devices for isentropic expansion of liquid streams are known in the art and generally include equipment such as expanders, hydraulic expanders, liquid turbines, or turbo expanders that extract or derive work from such expansion. An example of a combination of both isentropic means and isenthalpic means may be a Joule-Thomson valve and a turbo expander in parallel, which provides the capability of using either alone or using both the J-T valve and the turbo expander simultaneously. Isenthalpic or isentropic expansion can be conducted in the all- liquid phase, all-vapor phase, or mixed phases, and can be conducted to facilitate a phase change from a vapor stream or liquid stream to a multiphase stream (a stream having both vapor and liquid phases). In the description of the drawings herein, the reference to more than one expansion device in any drawing does not necessarily mean that each expansion device is the same type or size.

[0033] As used herein, the term "demethanizer" refers broadly to any distillation column to separate methane and other volatile components from ethane and heavier components. The distillation column contains a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing. The trays and/or packing provide the necessary contact between the liquids falling downward in the column and the vapors rising upward. The column also includes one or more reboilers (not shown in the drawings) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column. These vapors strip the methane from the liquids, so that the bottom liquid product is substantially devoid of methane and comprised of the majority of the ethane, propane, and heavier hydrocarbons contained in one or more feed streams to the column.

[0034] As used herein the term "indirect heat exchange" means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.

[0035] As used herein the terms "turboexpansion" and "turboexpander" mean respectively method and apparatus for the flow of high pressure fluid through a turbine to reduce the pressure and the temperature of the fluid, thereby generating refrigeration and useful work. [0036] As used herein, the term "reboiler" refers to an indirect heat exchange means used to at least partially vaporize a stream withdrawn near the bottom of a demethanizer.

[0037] As used herein the term "compressor" means a machine that increases the pressure of a gas by the application of work.

[0038] As used herein the term "cryogenic pump" means a device for increasing the head of a fluid stream at cryogenic temperatures. [0039] As used herein, the term "bottoms reboiler" refers to an indirect heat exchange means used to at least partially vaporize a stream withdrawn near the bottom of a distillation column.

[0040] As used herein, the term "bottoms stream" or "bottoms product" refers to an at least partially liquid stream withdrawn from at or near the bottom port of a distillation column.

[0041] As used herein, the terms "comprising," "comprises," and "comprise" are open- ended transition terms used to transition from a subject recited before the term to one or elements recited after the term, where the element or elements listed after the transition term are not necessarily the only elements that make up of the subject. [0042] As used herein, the terms "containing," "contains," and "contain" have the same open- ended meaning as "comprising," "comprises," and "comprise." As used herein, the terms "distillation" or "fractionation" refer to the process of physically separating chemical components into a vapor phase and a liquid phase based on differences in the components' boiling points at specified temperature and pressure. [0043] As used herein, a "flow regulating device" is any device capable of regulating flow of liquid from a separator to maintain a desired liquid level in the separator, including but not limited to such devices as a liquid regulator, expansion valve, flow regulating pump, or a combination of such devices.

[0044] As used herein, the terms "having," "has," and "have" have the same open-ended meaning as "comprising," "comprises," and "comprise." As used herein, the terms

"including," "includes," and "include" have the same open-ended meaning as "comprising," "comprises," and "comprise."

[0045] As used herein, the term "indirect heat exchange" refers to a process wherein the refrigerant cools the substance to be cooled without actual physical contact between the refrigerating agent and the substance to be cooled. Core-in-kettle heat exchangers and brazed aluminum plate-fin heat exchangers are specific examples of equipment that facilitate indirect heat exchange.

[0046] As used herein, the terms "natural gas liquids" , "NGL" or "NGLs" refer to mixtures of hydrocarbons whose components are, for example, typically ethane and heavier. Some examples of hydrocarbon components of NGL streams include ethane, propane, butane, and pentane isomers, benzene, toluene, other aromatic molecules, and possibly small amounts of methane, CO₂, and other components. [0047] As used herein, the terms "overhead stream" or "overhead product" refers to an at least partially vapor stream withdrawn from at or near the top port of a fluid separation vessel such as a phase separator, demethanizer or distillation column.

[0048] As used herein, the term "reflux" refers to an at least partially liquid stream introduced into the upper portion of a distillation column in order to increase separation efficiency.

[0049] As used herein, the term "side reboiler" refers to an indirect heat exchange means used to heat and at least partially vaporize a stream withdrawn from between the upper and lower portions of a distillation column.

[0050] As used herein, the term "turboexpander" refers to any device for expanding a stream that is capable of generating useful work.

[0051] In general, the invention relates to a process for producing a helium-enriched vapor stream, a methane-enriched vapor stream, and a liquid stream enriched in hydrocarbons heavier than methane from a pressurized, multicomponent, multiphase stream comprising methane (Ci), helium (He), and NGLs, The recovery of helium can be from any stream in the NGL recovery process that is primarily liquid during the processing by passing the liquid to a phase separator and flashing out a helium-enriched vapor stream.

[0052] Fig. 1 schematically illustrates one embodiment of processing a natural gas stream to produce a vapor fraction containing substantially all the methane, a liquid fraction containing a large portion of hydrocarbons heavier than methane, and a helium-enriched fraction. Feed stream 14 is provided to the system with contaminants, if any, removed from the natural gas by pretreatment (not shown in the drawings).

[0053] Pretreatment is the first consideration in cryogenic processing of natural gas. A raw natural gas feed stock suitable for the process of this invention may comprise natural gas obtained from a crude oil well (associated gas) or from a gas well (non-associated gas). The composition of the natural gas can vary significantly. Natural gas will typically contain methane (Ci) as the major component, and will typically also contain ethane (C₂), propane (C3), and higher hydrocarbons, diluents such as nitrogen, argon, and helium, and contaminants such as water, carbon dioxide, mercury, mercaptans, hydrogen sulfide, and iron sulfide. The solubilities of these contaminants vary with temperature, pressure, and composition. At cryogenic temperatures, CO₂, water, and other contaminants can form solids, which can plug flow passages in cryogenic heat exchangers and other equipment. These potential difficulties can be avoided by removing such contaminants. In the following description, it is assumed that the natural gas stream has been suitably treated to remove unacceptable levels of mercury, sulfides, carbon dioxide, and other contaminates, and dried to remove water using conventional and well-known processes to produce a "sweet, dry" natural gas stream. Alternatively, some level of these contaminants may be left in the feed gas and become distributed into the product stream which may require additional treatment at a later stage depending on the intended use of the product.

[0054] Referring to Fig. 1, feed stream 14 preferably enters the process at a pressure above about 3,100 kPa (450 psia) and more preferably above about 4,800 kPa (700 psia) and a temperature preferably between about —40° C. and —10° C; however, different pressures and temperatures can be used, if desired, and the system can be modified accordingly. If feed stream 14 is below about 3,100 kPa (450 psia), the gas stream may be pressurized by any suitable compression means (not shown), which may comprise one or more compressors. Feed stream 14 should be sufficiently cool such that the feed stream is partly condensed, comprising a mixture of vapor and liquid. If feed stream 14 is not sufficiently cool, refrigeration may be added to chill the feed gas down by any suitable means (not shown). [0055] Feed stream 14 is passed to one or more phase separators 80 which separate the multiphase feed stream 14 into vapor stream 16 and a liquid stream 30. The separator 80 has a liquid level control means (not shown in the drawing) which operates in a known manner to control one or more flow regulating devices 72. Flow regulating device 72 can be any device capable of regulating the flow of liquid from the separator 80 to maintain a desired liquid level in separator 80, such as but not limited to a liquid regulator, expansion device, or flow regulating pump, or a combination of such equipment. Flow from the flow regulating device 72 to demethanizer 88 occurs via stream 31. If the pressure of stream 30 is higher than the pressure in the demethanizer 88, the flow regulating device 72 can be used to depressurize the liquid to a pressure at or near the pressure of the demethanizer 88. If the pressure of the stream 30 is lower than the pressure in demethanizer 88, a flow regulating pump may be used to increase the pressure of stream 30 to a pressure at or near the pressure of the demethanizer

88.

[0056] A first fraction of vapor stream 16 may optionally be withdrawn and passed as stream 25 to an expansion device 71 wherein the pressure of the vapor stream 25 is reduced, thereby effecting a reduction in temperature of this stream 25. Stream 26 exiting the expansion device 71 is passed to the demethanizer 88. A second fraction of vapor stream 16 is passed as stream 18 to one or more heat exchangers 63 wherein stream 18 is cooled by indirect heat exchange against a suitable coolant, preferably overhead vapor from demethanizer 88 (not shown in Fig. 1). This embodiment is not limited to any type of heat exchanger, but because of economics, plate-fin, spiral wound, and cold box heat exchangers are preferred. Stream 19 exiting heat exchanger 63 is passed to an expansion device 70 wherein the pressure of stream 19 is reduced, thereby effecting a flashing of liquid and expansion cooling of stream 19. Stream 20 exiting the expansion device 70 is passed to one or more phase separators 81 , which separate a vapor phase from a liquid phase, which are well known to those of ordinary skill in the art. Vapor stream 21 removed from phase separator 81 is enriched in helium. Liquid stream 22 exiting the phase separator 81 is passed to an one or more flow regulating devices 73. The separator 81 has a liquid level control means (not shown in the drawing) which operates in a known manner to control one or more flow regulating devices 73. Flow regulating device 73 can be any device capable of regulating the flow of liquid from the separator 81 to maintain a desired liquid level in separator 81 , such as but not limited to a liquid regulator, expansion device, or flow regulating pump, or a combination of such equipment. Flow from the flow regulating device 73 to demethanizer 88 occurs via stream 23. If the pressure of stream 22 is higher than the pressure in the demethanizer 88, the flow regulating device 73 can be used to depressurize the liquid to a pressure at or near the pressure of the demethanizer 88. If the pressure of the stream 22 is lower than the pressure in demethanizer 88, a flow regulating pump may be used to increase the pressure of stream 22 to a pressure at or near the pressure of the demethanizer 88. If the flow regulating device 73 is an expansion device, the pressure of the liquid stream 22 is reduced, thereby effecting some expansion cooling of this stream. Stream 35 leaves the demethanizer 88 enriched in methane and stream 36 leaves the demethanizer substantially demethanized liquid product enriched in NGLs. The demethanizer bottoms stream 36 may be passed to a conventional fractionation plant (not shown), the general operation of which is known to those skilled in the art. The fractionation plant may comprise one or more fractionation columns which separate liquid bottom stream 36 into predetermined amounts of ethane, propane, butane, pentane, and hexane.

[0057] Fig. 2 illustrates another embodiment of the disclosure. Feed stream 14, pretreated as described above with respect to Fig. 1, is passed to phase separator 80 which comprises one or more separators that separate the multiphase feed stream 14 into a gas phase discharged as vapor stream 16 and a liquid stream discharged as liquid stream 30. The liquid stream 30 is passed to an flow regulating device 72, preferably an expansion device wherein the pressure of the liquid stream 30 is reduced, thereby effecting a reduction in temperature of stream 30. Stream 31 exiting the expansion device 72 is passed to phase separator 83 which comprises one or more separators that separate the multiphase feed stream 31 into a vapor phase discharged as vapor stream 32 and a liquid phase discharged as stream 33. Vapor stream 32 removed from the phase separator 83 is enriched in helium. Liquid stream 33 exiting the phase separator 83 is passed to an flow regulating device 75. Stream 34 exiting the flow regulating device 75 is passed to the demethanizer 88.

[0058] Referring still to Fig. 2, a first fraction of vapor stream 16 is passed as stream 25 to one or more expansion devices 71 wherein the pressure of stream 25 is reduced resulting in expansion cooling. Stream 26 exiting the expansion device 71 is passed to an optional phase separator 82 which comprises one or more separators that separate the multiphase feed stream 26 into a vapor phase discharged as vapor stream 27 and a liquid stream discharged as stream 28. Vapor stream 27 removed from phase separator 82 is enriched in helium. Liquid stream

28 exiting the phase separator 82 is passed to one or more flow regulating devices 74. Stream

29 exiting the flow regulating device 74 is passed to the demethanizer 88. The use of separator 28 and expansion devise 74 to produce helium-enriched stream 27 is optional depending on the economics of helium capture.

[0059] Referring still to Fig. 2, a second fraction of vapor stream 16 is passed as stream 18 to one or more heat exchangers 63 wherein stream 18 is cooled by indirect heat exchange against a suitable coolant, preferably overhead vapor from the demethanizer 88 (not shown in Fig. 2). This embodiment is not limited to any type or number of heat exchangers, but because of economics, plate-fin, spiral wound, and cold box heat exchangers are preferred. Stream 19 exiting heat exchanger 63 is passed to an expansion device 70 wherein the pressure of the liquid stream 19 is reduced, thereby effecting a reduction in temperature of stream 19. Stream 20 exiting the expansion device 70 is passed to phase separator 81, which may comprise one or more phase separators that separate a vapor phase from a liquid phase, which are well known to those of ordinary skill in the art. Vapor stream 21 removed from phase separator 81 is enriched in helium. Liquid stream 22 exiting the phase separator 81 is passed to one or more flow regulating devices 73. Stream 23 exiting the flow regulating device 73 is passed to the demethanizer 88. Vapor stream 35 leaves the demethanizer 88 as enriched methane and liquid stream 36 leaves the demethanizer 88 as enriched NGL. [0060] Fig. 3 illustrates another embodiment of the disclosure. The process illustrated in Fig. 3 is similar to the process shown in Fig. 1 except that the vapor stream 35 from the demethanizer 88 is shown as being further processed. Vapor stream 35 is passed to heat exchanger 63a which is shown in Fig. 3 as a stand-alone heat exchanger, but preferably heat exchangers 63 a and 63 are the same heat exchanger in which vapor stream 35 cools by indirect heat exchange vapor stream 18. It should not be inferred that a heat exchange stage is equivalent to a single heat exchanger. On the contrary, a heat exchange stage should be understood to include one or more heat exchangers of various kinds which may be disposed in parallel and/or series configurations. In addition, it should be understood that other streams (not shown) may be taking part in this heat exchange, such as application of other sources of refrigeration. Stream 37 exiting the heat exchanger 63 a is passed to one or more stages of compression, preferably two stages. For the sake of simplicity, Fig. 3 shows only one compression stage 90. After each compression stage, the compressed vapor is preferably cooled by conventional air or water cooler (not shown in Fig. 3). Pressured vapor leaving compression stage 90 is separated into a methane-enriched product stream 38 and recycle vapor stream 39. Vapor stream 39 is cooled by being passed through heat exchanger 63a and stream 40 exiting the heat exchanger 63a is passed to phase separator 84 which comprises one or more separators that separate the stream 40 into a vapor phase discharged as vapor stream 41 and a liquid stream discharged as stream 42. Vapor stream 41 removed from phase separator 84 is enriched in helium. Liquid stream 42 exiting the phase separator 84 is passed to one or more flow regulating devices 76. Stream 43 exiting the flow regulating device 76 is passed to the demethanizer 88 as a reflux stream.

[0061] Fig. 4 illustrates another embodiment of the disclosure. Referring to Fig. 4, feed gas 110 is passed through cooler 160. A first fraction of the cooled stream 111 leaving cooler 160 is passed to cooler 161. A second fraction of stream 111 is passed as stream 112 to heat exchanger 162 in which stream 112 is cooled by indirect heat exchange against a portion of vapor stream 135 removed from demethanizer 188. The coolers 160 and 161 may comprise one or more conventional heat exchangers that cool the natural gas stream to cryogenic temperatures, preferably down to about —10° C to —40° C. The coolers 160 and 161 may comprise one or more heat exchange systems cooled by conventional refrigeration systems, one or more expansion means such as Joule-Thomson valves or turboexpanders, one or more heat exchangers which use liquid from the lower section of the demethanizer 188 as coolant, one or more heat exchangers that use the bottoms product stream 136 of demethanizer 188 as coolant, or any other suitable source of cooling. The preferred cooling system will depend on the availability of refrigeration cooling, space limitation, if any, and environmental and safety considerations. Those skilled in the art can select a suitable cooling system taking into account the operating circumstance of the liquefaction process. Stream 113 exiting heat exchanger 162 and the stream exiting cooler 161 are combined as stream 114 which enters phase separator 180 which produces vapor stream 116 and a liquid stream 130. The liquid stream 130 is passed to a flow regulating device 168, preferably is preferably an expansion device, more preferably a Joule-Thomson valve, wherein the pressure of the liquid stream 130 is reduced, thereby effecting a reduction in temperature of stream 130. Stream 131 exiting the flow regulating device 168 is passed to the demethanizer 188. A first fraction of vapor stream 116 is passed as stream 125 to an expansion device 167, preferably a turboexpander, wherein the pressure of the vapor stream 125 is reduced, thereby effecting a reduction in temperature of this stream. Stream 126 exiting the expansion device 167 is passed to the demethanizer 188. A second fraction of vapor stream 116 is passed as stream 118 to a heater exchanger 163 wherein stream 118 is cooled by indirect heat exchange by overhead vapor stream 135 from demethanizer 188. This embodiment is not limited to any type of heat exchanger 163, but because of economics, plate-fin, spiral wound, and cold box heat exchangers are preferred. Stream 119 exiting heat exchanger 163 is passed to an expansion device 164 wherein the pressure of stream 119 is reduced, thereby effecting a reduction in temperature of this stream. Stream 120 exiting the expansion device 164 is passed to one or more phase separators 165, which separate a vapor phase from a liquid phase, which are well known to those of ordinary skill in the art. Vapor stream 145 removed from phase separator 165, which is enriched in helium, is passed through heat exchanger 171 and is then passed as cooled stream 146 to expansion device 172, preferably a J-T valve, wherein the pressure of stream 146 is reduced, thereby effecting a reduction in temperature of stream 146. Stream 147 exiting the expansion device 172 is passed to phase separator 173 which comprises one or more separators that separate feed stream 147 into a gas phase discharged as vapor stream 148 and a liquid stream discharged as stream 149. Vapor stream 148 is more enriched in helium than stream 145. Vapor stream 148 is passed through heat exchanger 171 to provide refrigeration duty for vapor stream 145 entering heat exchanger 171. Vapor stream 148 exits heat exchanger 171 as crude helium stream 151 which may be upgraded to a higher helium concentration by one or more low temperature processing steps (not shown in the drawings) or other helium enrichment processes (also not shown in the drawings), which are known to those skilled in the art to produce helium. [0062] Liquid stream 149 exiting the phase separator 173 is passed to a flow regulating device 174, preferably a J-T valve, wherein the pressure of the liquid stream 149 is reduced, thereby effecting a reduction in temperature of this stream. Stream 150 exiting the flow regulating device 174 is passed through heat exchanger 171 to provide additional refrigeration duty for vapor stream 145. Stream 152 exiting heat exchanger 171 is passed through heat exchanger 163 to provide cooling for vapor stream 118. Vapor stream 153 exits heat exchanger 163 as low pressure (LP) fuel which may supply a portion of the power needed to drive compressors and pumps in the separation process or may be further compressed to join stream 144 as methane-enriched product.

[0063] Liquid stream 122 exiting phase separator 165 is passed to one or more flow regulating devices 166, preferably an expansion device wherein the pressure of the liquid stream 122 is reduced, thereby effecting a reduction in temperature of this stream. Stream 123 exiting the flow regulating device 166 is passed to the demethanizer 188. Stream 135 leaves the demethanizer 188 as enriched methane and stream 136 leaves the demethanizer substantially demethanized liquid product enriched in NGL. The demethanizer bottoms stream 136 may be passed to a conventional fractionation plant (not shown), the general operation of which is known to those skilled in the art. The fractionation plant may comprise one or more fractionation columns which separate liquid bottom stream 136 into predetermined amounts of ethane, propane, butane, pentane, and hexane. [0064] Vapor stream 135 removed from the demethanizer 188 provides refrigeration duty for heat exchanger 163. Warmed stream 135 exits heat exchanger 163 as stream 138, a portion of which is passed as stream 139 through heat exchanger 162 to cool part stream 112. Stream 140 exits heat exchanger 162 and is recombined with stream 138. A part of the vapor stream 138 may be withdrawn from the system as fuel gas (stream 141). The remaining portion of vapor stream 138 is compressed by one or more compressors. Two compressors 169 and 170 are shown in Fig. 4. Optionally, high pressure (HP) fuel (stream 143) may be withdrawn after any one of the compression stages. Residual gas stream 144 is enriched in methane.

[0065] Fig. 5 illustrates another embodiment of the disclosure. Referring to Fig. 5, pretreated feed gas 210 is passed through cooler 260. A first fraction of the cooled stream 211 leaving cooler 260 is passed to cooler 261. A second fraction of stream 211 is passed as stream 212 to heat exchanger 262 in which stream 212 is cooled by indirect heat exchange against a portion of vapor stream 235 removed from demethanizer 288. The coolers 260 and 261 may comprise one or more conventional heat exchangers that cool the natural gas stream to cryogenic temperatures, preferably down to about —10° C to —40° C. The coolers 260 and 261 may comprise one or more heat exchange systems cooled by conventional refrigeration systems, one or more expansion means such as Joule-Thomson valves or turbo expanders, one or more heat exchangers which use liquid from the lower section of the demethanizer 288 as coolant, one or more heat exchangers that use the bottoms product stream 236 of demethanizer 288 as coolant, or any other suitable source of cooling. The preferred cooling system will depend on the availability of refrigeration cooling, space limitation, if any, and environmental and safety considerations. Those skilled in the art can select a suitable cooling system taking into account the operating circumstance of the liquefaction process. Stream 213 exiting heat exchanger 262 and the stream exiting cooler 261 are combined as stream 214 which enters phase separator 280 which produces vapor stream 216 and a liquid stream 230. The liquid stream 230 is passed to a flow regulating device 268, preferably a Joule-Thomson valve, wherein the pressure of the liquid stream 230 is reduced, thereby effecting a reduction in temperature of this stream. Stream 231 exiting the flow regulating device 268 is passed to the demethanizer 288. A first fraction of vapor stream 216 is passed as stream 225 to an expansion device 267, preferably a turboexpander, wherein the pressure of the vapor stream 225 is reduced, thereby effecting a reduction in temperature of this stream. Stream 226 exiting the expansion device 267 is passed to the demethanizer 288. A second fraction of vapor stream 216 is passed as stream 218 to a heat exchanger 263 wherein stream 218 is cooled by indirect heat exchange by overhead vapor stream 235 from demethanizer 288. This embodiment is not limited to any type of heat exchanger 263, but because of economics, plate-fin, spiral wound, and cold box heat exchangers are preferred. Stream 219 exiting heat exchanger 263 is passed to an expansion device 264, preferably a J-T valve, wherein the pressure of stream 219 is reduced, thereby effecting a reduction in temperature of this stream. Stream 220 exiting the expansion device 264 is passed to one or more phase separators 265, which separate a vapor phase from a liquid phase, which are well known to those of ordinary skill in the art. Vapor stream 221 removed from phase separator 265, which is enriched in helium, is combined with vapor stream 283, and the combined stream 223 is passed to heat exchanger 271. Cooled stream 246 exits heat exchanger 271 and is passed to an expansion device 272 wherein the pressure of stream 246 is reduced, thereby effecting a reduction in temperature of stream 246. Stream 247 exiting the expansion device 272 is passed to phase separator 273 which comprises one or more separators that separate feed stream 247 into a gas phase discharged as vapor stream 248 and a liquid stream discharged as liquid stream 249. Vapor stream 248 removed from phase separator 273 is more enriched in helium than stream 221. Vapor stream 248 is passed through heat exchanger 271 to provide refrigeration duty for vapor stream 223. Stream 248 exits heat exchanger 271 as crude helium stream 251 , which may be upgraded to a higher helium concentration by one or more processing steps (not shown) to produce helium.

[0066] Liquid stream 249 exiting the phase separator 273 is passed to flow regulating device 274, preferably a Joule-Thomson valve, wherein the pressure of the liquid stream 249 is reduced, thereby effecting a reduction in temperature of this stream. Stream 250 exiting the expansion device 274 is passed through heat exchanger 271 to provide refrigeration assistance for stream 223 entering heat exchanger 271. Stream 252 exiting heat exchanger 271 is passed through heat exchanger 263 to provide refrigeration duty for cooling vapor stream 218. Vapor stream 253 exits heat exchanger 263 as a gas which, for example, can be used as low pressure (LP) fuel, which may supply a portion of the power needed to drive compressors and pumps in the separation process.

[0067] Vapor stream 235 removed from the demethanizer 288 provides refrigeration duty for heat exchanger 263. Warmed stream 235 exits heat exchanger 263 as stream 238, a first portion of which is passed as stream 239 through heat exchanger 262 to cool part of the feed stream 212. Stream 240 exits heat exchanger 262 and is recombined with stream 238. A second portion of stream 238 is passed through heat exchanger 276 and recombined with stream 240. A portion of the vapor stream 238 may be withdrawn from the system as fuel gas (stream 241). The remaining portion of vapor stream 238 is compressed by one or more compressors. Two compressors 269 and 270 are shown in Fig. 5. Optionally, high pressure (HP) fuel (stream 243), enriched in methane, may be withdrawn after any one of the compression stages 269 and 270. Optionally, enriched methane in stream 243 may also be drawn as a product stream. One portion of stream 244 exits the process as residual gas enriched in methane and a second portion of stream 244 is passed as stream 275 to heat exchanger 276. Stream 277 exiting heat exchanger 276 is passed through heat exchanger 263 for further cooling. Stream 278 exiting heat exchanger 263 is passed to expansion device 279, preferably a Joule-Thomson valve, wherein the pressure of the stream 278 is reduced, thereby effecting a reduction in temperature of this stream. Stream 281 exiting the expansion device 279 is passed to phase separator 282 which produces vapor stream 283 and a liquid stream 284. Vapor stream 283 is merged with vapor stream 221. Liquid stream 284 is passed to flow regulating device 285, preferably a pressure reduction means, and more preferably a Joule-Thomson valve, wherein the pressure of the stream 284 is reduced, thereby effecting a reduction in temperature of this stream. Stream 286 exiting the flow regulating device 285 is passed to demethanizer 288. [0068] Liquid stream 222 from phase separator 265 is passed to flow regulating device 266, preferably a pressure reduction means, and more preferably a Joule-Thomson valve, wherein the pressure of the stream 222 is reduced, thereby effecting a reduction in temperature of this stream. Stream 224 exiting the flow regulating device 266 is passed to demethanizer 288. [0069] Liquid stream 236 leaves the demethanizer 288 as substantially demethanized liquid product enriched in NGL. The demethanizer bottoms stream 236 may be passed to a conventional fractionation plant (not shown), the general operation of which is known to those skilled in the art. The fractionation plant may comprise one or more fractionation columns which separate liquid bottom stream 236 into predetermined amounts of ethane, propane, butane, pentane, and hexane.

[0070] Fig. 6 illustrates still another embodiment of the disclosure which is similar to the process illustrated in Fig. 5 except that recycle vapor stream 278 is passed to phase separator 265 instead of being passed to phase separator 282 as shown in Fig. 5. In Fig. 6, the phase separator 282 shown in Fig. 5 is omitted.

[0071] Fig. 7 illustrates another embodiment of the disclosure which is similar to the embodiment shown in Fig. 1 except that refrigeration systems are used to cool vapor streams in place of expansion devices as shown in Fig. 1. Feed stream 300, pretreated as described above with respect to Fig. 1, is passed to phase separator 301 which comprises one or more separators that separate the multiphase feed stream 300 into a gas phase discharged as vapor stream 302 and a liquid stream discharged as liquid stream 303. The liquid stream 303 is passed to an flow regulating device 304, preferably an expansion device wherein the pressure of the liquid stream 303 is reduced, thereby effecting a reduction in temperature of stream 303. Stream 305 exiting the flow regulating device 304 is passed to the demethanizer 388. [0072] Referring still to Fig. 7, vapor stream 302 is passed to one or more heat exchangers 306 wherein stream 302 is cooled by indirect heat exchange against a suitable coolant, preferably overhead vapor (not shown in Fig. 7) from demethanizer 388. Stream 307 exiting the heat exchanger 306 is passed to phase separator 308 which comprises one or more separators that separate the multiphase stream 307 into a vapor phase discharged as vapor stream 309 and a liquid stream discharged as stream 310. Vapor stream 309 is passed to one or more heat exchangers 311 wherein stream 309 is cooled by indirect heat exchange. Stream 312 exiting heat exchanger 311 is passed to phase separator 313 which comprises one or more separators that separate the multiphase stream 312 into a vapor stream 314 which is enriched in helium and a liquid bottoms stream 315. Liquid stream 315 exiting the phase separator 313 is passed to one or more flow regulating devices 316. Stream 317 exiting the flow regulating device 316 is passed to the demethanizer 388. Liquid stream 310 from phase separator 308 is passed to a flow regulating device 320. Stream 321 exiting the flow regulating device 320 is passed to the demethanizer 388. Vapor stream 318 leaves the demethanizer 388 as enriched methane and liquid stream 319 leaves the demethanizer 388 as enriched NGL.

[0073] The embodiments disclosed herein can be used for new plant designs or can be used to retrofit existing NGL recovery plants to recover helium. For example, any of the embodiments of Figs. 1 , 2 and 4 may be installed as a retrofit to a pre-existing Gas Subcooled Process ("GSP") of the type disclosed in U.S. patents numbers 4,140,504; 4,157,904; and 4,278,457 and the embodiments of Figs. 3, 5, and 6 may be installed as a retrofit to a preexisting Recycle Split-vapor Process ("RSV") of the type disclosed in U.S. patent number 5,568,737. The additional equipment added to an existing NGL plant would not significantly affect the recovery of NGL from the natural gas. The amount of helium recovered, as well as the purity of the helium-enriched product streams (stream 21 in Fig. 1; streams 21, 27, and 32 in Fig. 2; streams 41 and 21 in Fig. 3; and streams 151 in Figs. 4, 5, and 6) can be regulated by persons skilled in the art to meet desired product compositions and flow rates by adjusting the pressure drop through the various expansion devices. Moreover, the retrofitted helium recovery unit disclosed herein can flexibly adapt to variations in the rate and composition of the natural gas feed stream, and can readily be adjusted to change the composition of the helium-enriched product streams.

[0074] One benefit of using the invention over methods used in the past is the ability to integrate helium recovery with existing units or processes in a natural gas plant. Helium recovery schemes in the past typically have separate unit operations from NGL recovery units or processes. Integration of helium recovery and NGL recovery minimizes the capital cost associated with the entire facility, which afford more helium recovery in gas plants. Examples [0075] A simulated mass and energy balance was carried out to illustrate the embodiments illustrated in the Figs. 4 and 5, and the results are set forth in Tables 1 and 2 below. The data presented in the Tables below are offered to provide a better understanding of the embodiments shown in Figs. 4 and 5, but the invention is not to be construed as unnecessarily limited thereto. The temperatures, pressures, and flow rates presented in the Tables are not to be considered as limitations upon the invention which can have many variations in operating conditions in view of the teachings herein. The Table 1 corresponds to the process illustrated in Fig. 4 and Table 2 corresponds to the process illustrated in Fig. 5. [0076] The data were obtained using a commercially available process simulation program called HYSYS™, version 2004.1 (13.2.0.6510), available from Hyprotech Ltd.; however, other commercially available process simulation programs can be used to develop similar data, including for example HYSIM™, PROII™, and ASPEN PLUS™, all of which are familiar to those of ordinary skill in the art.

Table 1

[0077] It should be understood that the preceding is merely a detailed description of specific embodiments of this invention and that numerous changes, modifications, and alternatives to the disclosed embodiments can be made in accordance with the disclosure here without departing from the scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined only by the appended claims and their equivalents.

Claims

What is claimed is:

1. A process for producing a helium-enriched vapor stream, a methane-enriched vapor stream, and a liquid stream enriched in hydrocarbons heavier than methane from a pressurized, multicomponent, multiphase stream comprising methane (Ci), helium (He) and hydrocarbons heavier than methane (C₂₊), the process comprising the steps of:

(a) cooling the multiphase stream to produce at least one vapor stream enriched in helium and at least one liquid stream;

(b) withdrawing at least a portion of the at least one vapor stream as a helium- enriched product stream;

(c) passing at least a portion of the at least one liquid stream to a demethanizer;

(d) withdrawing from the demethanizer a vapor enriched in methane (Ci); and

(e) withdrawing from the demethanizer a liquid enriched in hydrocarbons heavier than methane (C₂+).

2. The process of claim 1 wherein the step of cooling the feed stream is carried out using one or more heat exchangers.

3. The process of claim 1 further comprising, after cooling the multiphase stream, passing the cooled multiphase stream to a phase separator which separates the cooled feed stream into the at least one vapor stream and the at least one liquid stream.

4. The method of claim 3 further comprising withdrawing the at least one liquid stream from the phase separator and passing the at least one liquid stream to a flow regulating device and thereafter passing at least a portion of the at least one liquid stream to the demethanizer.

5. A process for producing a helium-enriched vapor stream, a methane-enriched vapor stream, and a liquid stream enriched in hydrocarbons heavier than methane (C₂₊) from a pressurized, multicomponent, multiphase feed stream comprising methane (Ci), helium (He) and hydrocarbons heavier than methane (C₂₊), the process comprising the steps of:

(a) passing the feed stream into a first phase separator to produce a first vapor phase and a first liquid phase;

(b) withdrawing the first vapor phase from the first phase separator;

(c) separating the first vapor phase into a second vapor phase and a third vapor phase; (d) cooling the second vapor phase by indirect heat exchange in a heat exchanger;

(e) expanding the cooled second vapor phase to produce a reduced-pressure vapor phase and reduced-pressure liquid phase, and passing the reduced-pressure vapor and liquid phases to a second phase separator; (f) withdrawing from the second phase separator a helium-enriched vapor phase;

(g) withdrawing liquid from the second phase separator and passing the withdrawn liquid to a first flow regulating device;

(h) passing the liquid from the flow regulating device to a demethanizer;

(i) expanding the third vapor phase of step (c) to produce a reduced-pressure vapor phase and reduced-pressure pressure liquid phase, and passing the reduced- pressure vapor and liquid phases to the demethanizer;

(j) withdrawing liquid from the first phase separator and passing the withdrawn liquid to a second flow regulating device;

(k) passing the liquid from the second flow regulating device to the demethanizer; (1) withdrawing from the demethanizer a vapor enriched in methane (Ci); and

(m) withdrawing from the demethanizer a liquid enriched in hydrocarbons heavier than methane (C₂₊).

6. The process of claim 5 wherein the first flow regulating device is an expansion device.

7. The process of claim 6 wherein the expansion device is a J-T valve.

8. The process of claim 6 wherein the expansion device is a turboexpander.

9. The process of claim 5 wherein at least one of the first flow regulating device or the second flow regulating devices is a flow regulating pump.

10. The process of claim 5 wherein the second flow regulating device is an expansion device.

11. The process of claim 10 wherein the expansion device is a J-T valve.

12. The process of claim 10 wherein the expansion device is a turboexpander.

13. The process of claim 10 wherein the second flow regulating device is liquid regulator.

14. A process for separating a feed stream comprising methane (Ci), and hydrocarbons heavier than methane, and helium into a gas fraction containing substantially all the methane, a liquid fraction containing a large portion of the hydrocarbons heavier than methane, and a helium-enriched fraction, the process comprising the steps of:

(a) providing the feed stream at a temperature sufficiently low for feed stream to be multiphase; (b) passing the multiphase feed stream of step (a) to a phase separator produce a first vapor stream and a first liquid stream;

(c) passing the first liquid stream to a first flow regulating device;

(d) passing the liquid from the first flow regulating device to a demethanizer;

(e) passing a first fraction of the first vapor stream to an expander device to lower the pressure of the first fraction, thereby cooling the first fraction of the vapor stream to produce a second multiphase stream;

(f) passing the second multiphase stream to the demethanizer;

(g) passing a second fraction of the first vapor stream to a heat exchanger to cool the second fraction of the first vapor stream to a lower temperature, thereby producing a cooled stream and passing the cooled stream to an expander device thereby producing a third multiphase stream;

(h) passing the third multiphase stream of step (g) to a separator to produce a helium-enriched vapor stream and a second liquid stream;

(i) passing the second liquid to a second flow regulating device; (j) passing the second liquid from the second flow regulating device to the demethanizer;

(k) withdrawing a vapor stream from the demethanizer enriched in methane; and

(1) withdrawing a liquid stream from the demethanizer enriched in hydrocarbons heavier than methane.

15. The process of claim 14 wherein the first flow regulating device is an expansion device.

16. The process of claim 15 wherein the expansion device is a J-T valve.

17. The process of claim 15 wherein the expansion device is a turboexpander.

18. The process of claim 14 wherein the first flow regulating device is a cryogenic pump.

19. The process of claim 14 wherein the second flow regulating device is an expansion device.

20. The process of claim 19 wherein the expansion device is a J-T valve.

21. The process of claim 19 wherein the expansion device is a turboexpander.

22. The process of claim 14 wherein the second flow regulating device is a cryogenic pump.

23. A process for separating a feed stream comprising methane, hydrocarbons heavier than methane, and helium into a gas fraction rich in methane, a liquid fraction rich in hydrocarbons heavier than methane, and vapor fraction rich in helium, the process comprising the steps of:

(a) providing the feed stream at a temperature sufficiently low for the feed stream to be multiphase;

(b) passing the multiphase stream of step (a) to a first separator produce a first vapor stream and a first liquid stream; (c) passing the first liquid stream to a first flow regulating device;

(d) passing the liquid stream from the first flow regulating device to a second separator to produce a first helium-enriched vapor stream and a second liquid stream;

(e) passing the second liquid stream to a second flow regulating device; (f) passing the second liquid stream from the second flow regulating device to a demethanizer;

(g) passing a first fraction of the first vapor stream to an expansion device, thereby cooling the first fraction to produce a cooled stream;

(h) passing the cooled stream of step (g) to a third separator to produce a vapor stream and a third liquid stream;

(i) passing the third liquid stream to a third flow regulating device;

(j) passing the third liquid stream from the third flow regulating device to the demethanizer; (k) passing a second fraction of the first vapor stream to a heat exchanger to cool the second fraction a lower temperature, and thereafter passing the cooled second fraction to an expander device to further cool the second fraction;

(1) passing the cooled second fraction from the expander device of step (k) to a fourth separator to produce a helium-enriched vapor stream and a fourth liquid stream;

(m) passing the fourth liquid stream to a fourth flow regulating device;

(n) passing fourth liquid stream to the demethanizer;

(o) withdrawing a vapor stream from the demethanizer enriched in methane; (p) withdrawing a liquid stream from the demethanizer enriched in hydrocarbons heavier than methane.

24. The process of claim 23 wherein at least one of the first, second, third and fourth flow regulating devices is an expansion device.

25. The process of claim 24 wherein the expansion device is selected from a J-T valve or turboexpander.

26. The process of claim 23 wherein at least one of the first, second, third, and fourth flow regulating devices is a cryogenic pump.

27. A process for separation of hydrocarbons to separate a feed stream containing at least methane, a hydrocarbon less volatile than methane, and helium, into a residue gas enriched with methane and lean in the hydrocarbon less volatile than methane, a heavier fraction lean in methane and enriched with the hydrocarbon less volatile than methane, and a fraction enriched in helium, the process comprising the steps of:

(a) providing a feed stream that is partly condensed;

(b) separating the feed stream into a vapor and a first liquid; (c) passing the liquid separated in step (b) to a first flow regulating device;

(d) passing the liquid from the flow regulating device to a distillation column;

(e) dividing the vapor obtained in step (b) into a first portion and a second portion;

(f) expanding a first portion of the vapor separated in step (b), thereby producing a second reduced pressure stream, and passing the second reduced pressure stream to the distillation column; (g) cooling the second portion of the vapor separated in step (b) in a heat exchanger and expanding the cooled second vapor portion, thereby partly condensing the cooled second vapor portion;

(h) separating partly condensed, cooled second vapor portion of step (g) into a helium-enriched stream and a second liquid;

(i) passing the second liquid separated in step (h) to a second flow regulating device; (j) passing second liquid from the second flow regulating device to the distillation column; and (k) recovering from the distillation column a vapor stream enriched in methane and a liquid enriched in hydrocarbons less volatile than methane.

28. A process for separating a natural gas stream comprising methane, hydrocarbons heavier than methane, and helium into a gas fraction rich in methane, a liquid fraction rich in hydrocarbons heavier than methane, and vapor fraction rich in helium, the process comprising the steps of:

(a) providing the natural gas stream at a temperature sufficiently low for the natural gas stream to be multiphase;

(b) passing the natural gas stream of step (a) to a first phase separator to produce a first vapor stream and a first liquid stream; (c) passing the first liquid stream to a first flow regulating device;

(d) passing the liquid stream from the first flow regulating device to a demethanizer;

(e) passing the first vapor stream to an a first heat exchanger, thereby cooling the first vapor fraction to produce second multiphase stream; (f) passing the second multiphase stream of step (e) to a second phase separator to produce a second vapor stream and second liquid stream;

(g) passing the second liquid stream to a second flow regulating device;

(h) passing the second liquid from the second flow regulating device to the demethanizer; (i) passing the second vapor stream to a second heat exchanger, thereby cooling the second vapor fraction to produce third multiphase stream; (j) passing the third multiphase stream of step (i) to a third phase separator to produce a third vapor stream that is enriched in helium and a third liquid stream;

(k) passing the third liquid stream to a third flow regulating device;

(1) passing the third liquid from the third flow regulating device to the demethanizer;

(m) withdrawing a vapor stream from the demethanizer enriched in methane; and

(n) withdrawing a liquid stream from the demethanizer enriched in hydrocarbons heavier than methane.