Production of liquefied natural gas blends using a dual-purpose refrigeration unit

Abstract

Sub-cooled C2-C4 hydrocarbons may be combined with liquefied natural gas (LNG) with minimal boil-off gas formation to form a desired LNG blend. The C2-C4 hydrocarbons may be sub-cooled using a dual-purpose refrigeration unit that also promotes liquefaction of natural gas to produce LNG. The dual-purpose refrigeration unit may simultaneously produce LNG and sub-cooled C2-C4 hydrocarbons, or production of either LNG or sub-cooled C2-C4 hydrocarbons may occur intermittently. In the event that blending is not required at a given point in time, the dual-purpose refrigeration unit may be dedicated to LNG production.

Description

PRODUCTION OF LIQUEFIED NATURAL GAS BLENDS USING A DUAL-PURPOSEREFRIGERATION UNITFIELD

[0001] T he present disclosure relates to liquefied hydrocarbon gas blends, such as liquefied natural gas (LNG) blends, and more particularly, to methods for blending one or more thermally equilibrated liquefied hydrocarbons with LNG to form LNG blends that maintain or attain a desired physical and / or chemical property profile.BACKGROUND

[0002] Natural gas is a hydrocarbon resource comprising methane and minor amounts of other light hydrocarbon gases in varying amounts, Natural gas has become an increasingly important energy source in recent years. Natural gas is often processed into liquefied natural gas (LNG) to facilitate transport from production fields and processing facilities to a locale having a strong commercial or consumer need for natural gas. Conventional processing techniques to produce LNG may include one or more of: (a) initial treatments of natural gas to remove contaminants such as water, sulfur compounds, and carbon dioxide; (b) at least partial removal of heavier hydrocarbon gases (eg., propane, butane, pentane, and the like) from methane through various cryogenic processes; and (c) refrigeration of the natural gas to promote liquefaction thereof, such as through self-refrigeration or external refrigeration to form LNG at a temperature of about -160°C and at or near atmospheric pressure. Once transported to a desired locale, the LNG may be re-gasified for consumer or industrial use,

[0003] In spite of processing a raw natural gas stream to form LNG, the resulting LNG may still have slightly differing compositions depending on the origin of the natural gas stream, the relative amounts of minority heavier hydrocarbon gases tha t are ini tially present, and or the extent to which minority heavier hydrocarbon gases and / or impurities are removed from the natural gas stream. Differing amounts of impurities and minority heavier hydrocarbon gases may slightly alter various physical and chemical properties of the natural gas stream, such as, for example, density, heating value, compressibility, relative volatility, or any combination thereof. Even minor variations in composition may result in measurable physical and chemical property differences. Depending on consumer or industrial requirements and other application-specific needs, even such minor variations in physical and chemical properties may render the LNG unsuitable for an intended use. For example.if the amounts of one or more C2-C4 hydrocarbons (i.e., natural gas liquids, NGLs) are off- specification, the heating value of the LNG may be unsuitable tor consumer or industrial use.

[0004] In addition to the innate compositional variation of natural gas streams, improvements in natural gas liquefaction processes have further complicated the situation with respect to NGLs. Namely, natural gas liquefaction processes are increasingly producing LNG that is becoming increasingly lean in NGLs. Such LNG may be referred to herein as “lean LNG.” Lean LNG has a lower heating value per unit volume (e.g. , per standard cubic foot) than when higher amounts of NGLs are present. However, lean LNG has a high heating value per unit weight. While desirable in at least the foregoing respect, lean LNG may be unsuitable for certain applications. Moreover, the production of lean LNG is creating excess inventory of the NG Ls as a separate product stream.

[0005] The composition of LNG may be modified to alter the density, heating value, or other physical or chemical properties. In one approach, an inert gas may be blended with the LNG to lower the heating value, while maintaining methane and NGLs at the same relative ratios with respect to one another. In another approach, C2-C4 hydrocarbons in a liquefied state may be blended with LNG to alter the relative ratios of methane and NGLs with respect to one another in order to raise or lower the heating value. Such blending processes may need to be performed with care to avoid altering the thermal equilibrium of the LNG, if the C2-C4 hydrocarbons are not sufficiently cooled to or near the temperature of the LNG. The normal boiling points of C2-C4 hydrocarbons are much higher than that of LNG; hence, liquefied C2-C4 hydrocarbons are stored at much higher temperatures than is LNG. Most commonly, liquefied C2-C4 hydrocarbons are stored at or near atmospheric pressure and maintained just below their normal boiling points. If the C2-C4 hydrocarbons are not at or near the temperature of the LNG, excessive boil-off gas (BOG) may be produced when blending takes place, with consequent loss of LNG product and excessive fuel gas production. A lthough formation of boil- off gas due to a tack of thermal equilibrium is a recognized problem when forming LNG blends, it may be difficult or costly to bring sources of gases for blending, such as C2-C4 hydrocarbons, into thermal equilibrium with each other and with LNG.SUMMARY

[0006] In various aspects, the present disclosure provides methods comprising: conveying a natural gas stream through a dual-purpose refrigeration unit to form liquefied natural gas (LNG) by indirect heat exchange; conveying one or more liquefied C2-C4 hydrocarbons through the dual-purpose refrigeration unit to sub-cool the liquefied C2-C4 hydrocarbons and bring the liquefied C2-C4 hydrocarbons into thermal equilibrium with the LNG, thereby forming sub-cooled C2-C4hydrocarbons; processing the LNG to form processed LNG; wherein processing the LNG comprises at least flashing to produce end-flash gas; and blending a first portion of the sub-cooled C2-C4 hydrocarbons with the LNG before processing, with the processed LNG after processing, or any combination thereof to form a fi rst LNG blend .

[0007] In some or other various aspects, the present disclosure provides methods comprising: conveying a natural gas stream through a dual-purpose refrigeration unit to form liquefied natural gas (LNG) by indirect heat exchange; conveying one or more liquefied C2-C4 hydrocarbons through the dual-purpose refrigeration unit to sub-cool the liquefied C2-C4 hydrocarbons and bring the liquefied C2-C4 hydrocarbons into thermal equilibrium with the LNG, thereby forming sub-cooled C2-C4 hydrocarbons; processing the LNG to form processed LNG; wherein processing the LNG comprises at least flashing to produce end-flash gas: optionally, blending a first portion of the sub-cooled C2- C4 hydrocarbons with the LNG before processing, with the processed LNG after processing, or any combination thereof to form a first LNG blend; and blending a second portion of the sub-cooled C2- G4 hydrocarbons with the processed LNG or, if formed, the first LNG blend in a desired blend ratio to form a second LNG blend having a differing composition from the first LNG blend,

[0008] These and other features and attributes of the disclosed compositions and methods of the present disclosure and their advantageous applications and or uses will be apparent from the detailed description which follows.BRIEF DESCRI PTION OF THE DRAWINGS

[0009] To assist one of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings. The following figures are included to illustrate certain aspects of the disclosure, and should not be viewed as exclusive configurations. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

[0010] FIGS. 1 , 2 A and 2B are diagrams of systems and methods that may produce a LNG blend according to one or more embodiments of the present disclosure.

[0011] FIG. 3 is a diagram of a single shell-and-tube heat exchanger configured to form LNG and produce sub-cooled C2-C4 hydrocarbons according to one or more embodiments of the present disclosure.

[0012] FIG. 4 is a diagram of a split shell-and-tube heat exchanger arranged in parallel and configured to form LNG and produce sub-cooled C2-C4 hydrocarbons according to one or more embodiments of the present disclosure.

[0013] FIGS. 5 A and 5B are diagrams of two shell-and-tube heat exchangers arranged in series and configured to form LNG and produce sub-cooled C2-C4 hydrocarbons according to one or more embodiments of the present disclosure.|0014| FIG. 6 is a diagram of a system and method in which a LNG blend may be produced according to one or more embodiments of the present disclosure.DETAILED DESCRIPTION

[0015] The present disclosure relates to liquefied hydrocarbon gas blends, such as liquefied natural gas (LNG) blends, and more particularly, to methods for blending one or more thermally equilibrated liquefied hydrocarbons with LNG to form LNG blends that maintain or attain a desired physical andfor chemical property profile.

[0016] It can be difficult to achieve a desired physical or chemical property profile in liquefied hydrocarbon gas mixtures, such as LNG blends, in response to various application-specific needs, such as providing a consistent density or heating value required by a particular customer or application. Although these physical properties and others may be altered by blending liquefied C2- C4 hydrocarbons 'with LNG, it may be difficult to maintain thermal equilibrium of the LNG when doing so due to the much higher normal boiling points of the C2-C 4 hydrocarbons and the typical storage conditions of these hydrocarbons in liquefied form. In addition to the foregoing practical difficulty, blending to achieve a target heating value or physical property may be further problematic in view of frequently changing target compositions of the LNG for various customers, as well as the inconsistent compositions of both raw natural gas streams and the LNG resulting from ever-evolving natural gas liquefaction processes.

[0017] Although it is possible to blend one or more C2-C4 hydrocarbons into LNG to achieve a desired composition and physical or chemical property profile, the vastly different temperatures of LNG (predominantly liquefied methane) and liquefied C2-C4 hydrocarbons obtained from typical storage conditions is problematic. Because liquefied C2-C4 hydrocarbons are usually maintained at a higher storage temperature than is LNG by virtue of their higher normal boiling points, direct addition of higher-temperature C2-C4 hydrocarbons into LNG may disrupt thermal equilibrium of the LNG and result in production of large quantities of boil-off gas as thermal equilibrium is reestablished. To avoid disrupting the thermal equilibrium, the C2-C4 hydrocarbons need to be cooled well below their normal boiling points ( sub-cooled) to a temperature that is at or near the temperature of the LNG. The term “sub-cooled” and grammatical variants thereof is used herein to refer to cooling of a substance below the boiling point of the substance at a given pressure. Sub-cooling of liquefiedC2-C4 hydrocarbons in preparation for blending with LNG may require a significant capital investment for suitable refrigeration equipment. This approach may not be economically feasible when one considers that blending of C2-C4 hydrocarbons with LNG may occur intermittently depending on consumer needs and product demand, given that as-produced LNG may be sufficient for many purposes.|0018] The present disclosure at least partially alleviates the foregoing difficulties and provides additional advantages as well. As mentioned previously, it can be inefficient and costly to provide refrigeration sufficient to promote sub-cooling of liquefied C2-C4 hydrocarbons to facilitate their direct blending with I NG. particularly on an intermittent basis. In the present disclosure, sub-cooling of liquefied C2-C4 hydrocarbons may be performed efficiently without a significant amount of additional capital expenditure by sub-cooling the liquefied C2-C4 hydrocarbons in a refrigeration unit that also cools natural gas to promote liquefaction thereof (z.e, to form LNG) at least part of the time (or most of the time). In particular, the present disclosure provides systems and methods in which natural gas and liquefied C2-C4 hydrocarbons (individually, as stream(s) of any one or more of the C2-C4 hydrocarbons, or as a blend of any two or more of the C2-C4 hydrocarbons) are routed separately to a refrigeration unit that may intermittently promote formation of LNG alone. The flow of liquefied C2-C4 hydrocarbons (individually or as a blend) to the refrigeration unit may occur continuously, but more typically intermittently on an on-demand basis as formation of a custom LNG blend is desired. As such, the refrigeration unit may exert its cooling duty toward promoting formation of LNG most of the time (e.g., when production of sub-cooled C2-C4 hydrocarbons for blending is not needed). When modification of the LNG is needed, flow(s) of liquefied G2-C4 hydrocarbons (individually or as a blend) to the refrigeration unit may be initiated or increased, such that the refrigeration unit splits its cooling duty between the natural gas and the liquefied C2-(. 4 hydrocarbons. The liquefied C2-C4 hydrocarbons exiting the refrigeration unit are sub-cooled and are at or near the tempera ture of the LNG produced in the refrigeration unit, such that the sub-cooled C2-C4 hydrocarbons may be combined with the LNG without disturbing the thermal equilibrium thereof. The refrigeration unit may be referred to herein as a “dual-puppose” refrigeration unit (DPRU) by virtue of its use to cool natural gas, liquefied C2-C4 hydrocarbons, or a combination thereof on-demand and in response to specified production needs. The terms “dual-purpose” and “dual-use” may be used interchangeably herein. The dual-purpose refrigeration unit may process predominantly natural gas to form LNG or predominantly liquefied C2-C4 hydrocarbons for blending with previously produced LNG at a given point in time, depending on whether production of LNG oran LNG blend is desired. In another inode of operation, the cooling duty of the dual-purpose refrigeration unit may be divided between concurrent cooling of natural gas to produce LNG and subcooling of liquefied C2-C4 hydrocarbons. When the cooling duty of the dual-purpose refrigeration unit is divided between liquefaction of LNG and sub-cooling of liquefied C2-C4 hydrocarbons, continuous production of LNG blends may take place. The extent to which the cooling duty is divided between liquefaction of LNG and sub-cooling of liquefied C2-C4 hydrocarbons may be regulated by feed rates of natural gas a nd liquefied C2-C4 hydrocarbons to the dual-purpose refrigeration unit, for example. Continuous production of LNG blends may also take place when natural gas and liquefied C2-C4 hydrocarbons are processed separately in the dual-purpose refrigeration unit and further combined with LNG from an external source, as described further herein .|0019] The dual-purpose refrigeration unit may utilize at least one refrigerant within at least one refrigerant loop. The at least one refrigerant may comprise at least nitrogen, according to some embodiments. Other refrigerants may also be suitable. The at least one refrigerant loop may comprise at least one primary refrigerant loop and. optionally, a secondary refrigerant loop. If present, the secondary refrigerant loop may be thermally coupled to the primary cooling loop, such that residual cooling duty of the primary refrigerant may cool the secondary refrigerant, or vice versa. Each refrigerant loop may contain at least one compressor, at least one expansion device (an expander or a throtling valve, such as a Joule-Thompsou valve), and at least one heat exchanger, through which the at least one refrigerant may circulate. The dual-purpose refrigeration unit may comprise a single heat exchanger or multiple heat exchangers that are used for cooling the natural gas and the liquefied C2- C4 hydrocarbons, as described and shown hereinafter. Multiple heat exchangers may be disposed in series, parallel, or any combination thereof. Furthermore, multiple dual-purpose refrigeration units may be used in parallel with one another.

[0020] In addition to the advantages of maintaining thermal equilibrium and facilitating ready access to customized LNG blends, the systems and methods of the present disclosure offer various process control benefits as well. In various examples, sensor monitoring of the liquefied C2-C4 hydrocarbons and / or the LNG may take place before and / or after cooling with the dual-purpose refrigeration unit but before blending takes place. Sensor monitoring of the LNG blend (or an intermediate blend) produced by combining the liquefied C2-C4 hydrocarbons with LNG may take place similarly as well to determine whether production specifications have been met. In either case, monitoring of various properties of the liquefied C2-C4 hydrocarbons and / or the LNG may allow automated and / or manual process intervention to take place to avoid production of an off-specification LNG blend. The processing intervention may be proactive or reactive in nature. For instance, if an off-specification LNG blend is being produced, the relative ratios of the sub-cooled C2-C4 hydrocarbons may be reactively adjusted to alter one or more physical properties in a desired way. As another example, if a liquefied propane source contains more ethane or butane than expected, the heating value of the LNG blend may be off- specification even without a process upset taking place, in which ease the systems and methods of the present disclosure may proactively detect and account for such fluctuating inputs and facilitate a proactive response thereto in order to maintain an on-specification LNG blend as a product.

[0021] As used herein, the term "natural gas" refers to a multi-component gas obtained from a crude oil well (associated gas) or from a subterranean gas-bearing formation (non-associated gas). The composition and pressure of natural gas can vary significantly. A typical natural gas stream contains methane as a significant component, often as a primary component. A natural gas stream may also contain ethane, higher molecular weight hydrocarbons (e.g., propane and butane), and / or one or more acid gases. As used herein, the term “natural gas liquids (NGLs)” refers to one or more of ethane, propane, and butane. Such NGLs may be alternately referred to herein as “C2-C4 hydrocarbons" or “liquefied C2-C4 hydrocarbons, ” and such terms may be used interchangeably herein. When using the foregoing terms, it is to be recognized that any one or more than one C2-C4 hydrocarbon may be present. Minor amounts of contaminants such as water, nitrogen, iron sulfide, wax, and crude oil, for example, may also be present in as-produced natural gas. Liquefied natural gas (LNG) may comprise predominantly methane after processing and cooling of as-produced natural gas takes place.

[0022] As used herein, the term "compressor" refers to a machine, unit, device, or apparatus that increases the pressure of a gas stream by the application of work. Compressors may feature a single compression process or step, or compressors may feature multi-stage compressions or steps, more particularly multi-stage compressors located within a single casing or shell.

[0023] As used herein, the term "expander" refers to a machine, unit, device or apparatus suitable for increasing the volume of a gas, accompanied by decreasing the gas temperature and gas pressure. Unless a particular type of expander is specifically stated herein, expanders used in the present disclosure may operate ( 1) at least partially by isenthalpic means, (2) at least partially by isentropic means, or (3) by a combination of both isentropic means and isenthalpic means. As such, the term "expander" or an equivalent term may refer to a hydraulic turbine or any alternative constructs for promoting expansion of a gas. Suitable devices for promoting isenthalpic expansion of natural gas may include, but are not limited to, manually or automatically, actuated throttling devices such as, forexample, valves, control valves, Joule-Thomson (J-T) valves, or Venturi devices. Suitable devices for promoting near-isentropic expansion of natural gas may include equipment such as expanders or compressor-expanders, including turboexpander-compressor assemblies, that extract or derive work from such expansion. An expander may comprise a hydraulic turbine effective to increase the volume of a gas from a first volume to a larger second volume. Some stages or steps of a gas cooling process may involve two or more expanders in parallel, series, or both.

[0024] As used herein, the term "compressor-expander'' refers to a machine in which an expander provides shaft power to drive a compressor. Some types of '’turboexpanders” are representative of a compressor-expander operatively coupled together on a single (common) shaft. Other types of turboexpanders may be coupled to a generator to promote production of e lectrical power.

[0025] As used herein, the term "cooling" refers to lowering of the temperature and / or internal energy of a substance by any suitable, desired, or required amount. Cooling may include a temperature drop from a first temperature to a second temperature of at least about 1 °C, at least about 5°C, at least about 10°C, at least about 15°C, at least about 25°C, at least about 35°C, at least about 5(PC, at least about 75°C, at least about 85°C, at least about 95®C, or at least about 100fC. The cooling may be promoted by direct or indirect thermal contact with any suitable heat sink, including air or a cooling liquid, for lowering the temperature. Preferably, cooling through thermal contact with a cooling liquid may take place through indirect thermal contact with the cooling liquid. The cooling liquid may be present in a refrigerant loop, for example. Cooling may also take place by expansion as well.

[0026] A substance that has been “cooled” means that the temperature of the substance has been lowered to a specified or an unspecified degree relative to the corresponding uncooled substance. A substance that has been “warmed” means that the temperature has been raised to a specified or an unspecified degree relative to the corresponding un-warmed substance.

[0027] As used herein, the term "heat exchanger" refers to any device capable of transferring thermal energy from one medium to another medium. Heat exchangers may include "direct heat exchangers" and. "indirect heat exchangers." Thus, a heat exchanger may be of any suitable design, such as a co-current or counter-current heat exchanger, an indirect heat exchanger (e.g., a spiral wound heat exchanger, a plate-fin heat exchanger such as a brazed aluminum plate fin type, a shetland-tube heat exchanger, spiral, hairpin, core, core-and-kettle, printed-circuit, or double-pipe heat exchanger), a direct contact heat exchanger, or any other type of heat exchanger. Unless otherwise specified, heat exchange in the present disclosure takes place through indirect heat exchange. "Heatexchangers" may also refer to any column, tower, unit or other arrangement adapted to allow the passage of one or more streams for promoting direct or indirect heat exchange between one or more lines of refrigerant.

[0028] As used herein, the terms “liquefied gas” and “liquefied gas blend” (inclusive of liquefied natural gas) refer to a substance that is gas or gas mixture at standard temperature and pressure (25°C and 1 bar), but has been converted into a liquefied state by increasing the pressure, lowering the temperature, or any combination thereof. If a substance may be a gas or a liquefied gas depending on conditions, and the substance is not referred to as being “liquefied” or the presence of a liquid state is not implied (eg., by referring to a substance as being sub-cooled), it is to be presumed that the substance may be in a gaseous state or a liquefi ed state.

[0029] As used herein, the term “thermal equilibrium” refers to the condition of being in a steady state at the same temperature. In a liquefied gas mixture at a steady state, for instance, all components of the liquefied gas mixture may be in equilibrium with a vapor phase, such that there is no tendency toward flash vaporization or flash condensation of liquefied gas,

[0030] Embodiments of the present disclosure will now be described with reference to the drawings. It is to be appreciated that components such as valves, pumps, flow controllers, and the like may be omitted from the drawings in some cases in the interest of conciseness. One having ordinary skill in the art will be able to locate such components in the systems and methods of the present disclosure to achieve a particular result, such as opening or closing a specified flow pathway for delivering a liquefied gas or liquefied gas mixture to an intended location. Furthermore, elements of the drawings having similar structure and function in multiple figures are denoted with in-common reference characters unless otherwise specified below. Accordingly, in the interest of brevity, most elements of the drawings are only described in detail at the first occurrence of said elements.

[0031] FIG. 1 is a diagram of a system and method that may produce a thermally equilibrated LNG blend according to one or more embodiments of the present disclosure. System and method 100 includes source 102 containing natural gas. The natural gas in source 102 may be in a gaseous state. Source 102 may be any location from which natural gas in a gaseous state may be supplied. Preferably, the natural gas from source 102 is sufficiently purified such that the natural gas can be used for an intended application once liquefied and optionally blended with liquefied C2-C4 hydrocarbons according to the disclosure herein. The natural gas from source 102 is conveyed through line 106 to dual-purpose refrigeration unit 110, wherein cooling and liquefaction of the natural gas occurs. Optionally, the natural gas from source 102 may be pre-cooled in a secondaryheat exchanger upstream from dual-purpose refrigeration unit i 10. Dual-purpose refrigeration unit 1 10 is coupled to a refrigerant loop (not shown in FIG. 1 , but discussed further below), in which at least one refrigerant is present. The resulting liquefied natural gas (LNG) is then conveyed via line 112 to flash dram 120 and then onward to storage vessel 130 via line 122. End-flash gas formation and removal of .nitrogen from the LNG may take place in flash drum 120 (or in a separate denitrification unit, not shown in FIG. 1). The end-flash gas (and nitrogen) may be conveyed via line 124 to compressor 150 to produce compressed end-flash gas. Boil-off gas from storage vessel 130 may similarly travel by line 123 to compressor 152 to produce compressed boil-off gas. The compressed end flash gas and boil-off gas may be combined for further use or may be combusted as fuel gas. Subsequently, the LNG in storage tank 130 may be conveyed to transport vessel 140 via loading line 132 for delivery to a desired location. The LNG in storage tank 130 may all originate from source 102, or at least some and preferably a majority of the LNG in storage tank 130 may originate from an external source of LNG, which is introduced to storage tank 130 via line 160.

[0032] The foregoing may represent the normal or predominant operation mode of system and method 100, wherein “ordinary” (lean) LNG is produced with no additional liquefied C2-C4 hydrocarbons being blended therewith. When blending of liquefied C2-C4 hydrocarbons with the LNG is desired, liquefied C2-C4 hydrocarbons may undergo sub-cooling by stopping or limiting the flow of natural gas through dual-purpose refrigeration unit 1 10 and commencing flow of liquefied C2-C4 hydrocarbons through dual-purpose refrigeration unit 110, as discussed in more detail subsequently. That is, dual-purpose refrigeration unit 110 may switch from cooling substantially natural gas to cooling (sub-cooling) substantial ly liquefied C2-C4 hydrocarbons. This approach may allow blending of liquefied C2-C4 hydrocarbons with the LNG on-demand to produce a desired LN G blend downstream of storage tank 130, as described subsequently. Alternately, continuous blending of liquefied C2-C4 hydrocarbons with the LNG may take place by concurrently cooling both natural gas and liquefied C2-C4 hydrocarbons in dual-purpose refrigeration unit 110, if desired. Concurrent cooling of both natural gas and liquefied C2-C4 hydrocarbons may afford additional process flexibility, as explained further herein. Regardless of whether blending of liquefied C2-C4 hydrocarbons takes place on-demand or continuously, the liquefied C2-C4 hydrocarbons may be subcooled and combined with the LNG to afford the features and advantages described subsequently.

[0033] Referring still to FIG. 1, system and method 100 also includes vessel 104, which may be multiple vessels (see FIGS. 2A and 2B, for example), each containing liquefied C2-C4 hydrocarbons for blending with the LNG after undergoing sub-cooling according to the disclosure herein. Vessel104 may contain a blend of two or more C2--C4 hydrocarbons in liquefied form, or the liquefied C2- C4 hydrocarbons may be individually maintained in separate vessels ( / .<?., liquefied C2 hydrocarbons are maintained in a first vessel, liquefied C3 hydrocarbons are maintained in a second vessel, and liquefied C4 hydrocarbons are maintained in a third vessel). The liquefied C2-C4 hydrocarbons housed in one or more vessels 104 may be maintained under atmospheric pressure storage conditions.

[0034] The liquefied C2-C4 hydrocarbons from vessel 104 are conveyed through line 107 into dualpurpose refrigeration unit 110, wherein sub-cooling then takes place. Upon exiting dual-purpose refrigeration unit 1 10 via line 113, the liquefied C2-C4 hydrocarbons are sub-cooled and are at or near thermal equilibrium with the LNG in line 1 12. In non-limiting examples, the sub-cooled C2-C4 hydrocarbons may be within E - 5°C, or within U- 10°C, or within •* / - 20°C of the LNG.

[0035] Depending on whether multiple sources of liquefied C2-C4 hydrocarbons or mixtures thereof undergo sub-cooling in dual-purpose refrigeration unit 1 10, line 1 13 may represent a single line or multiple lines for conveying the liquefied C2-C4 hydrocarbons to downstream components of system and method 100. For example, multiple C2-C4 hydrocarbons may be provided from multiple vessels 104 and blended upstream of dual-purpose refrigeration unit 1 10 before being sub-cooled therein. Blending may take place in-line within line 107, such as within an inline mixer, or in a separate mixing vessel (not shown). By blending the liquefied C2-C4 hydrocarbons upstream from dual-purpose refrigeration unit 110, the need for multiple transport lines traversing dual-purpose refrigeration unit 1 10 may be averted, which may be more cost effective and operationally simpler than when multiple transport lines are used. Further, by blending multiple liquefied C2-C4 hydrocarbons together prior to sub-cooling in dual-purpose refrigeration unit 110, downstream handling of the sub-cooled C2-C-4 hydrocarbons may be made operationally simpler. For example, by having the sub-cooled C2-C4 hydrocarbons blended together, a single feed line may be utilized at the various downstream locations where the sub-cooled C2-C4 hydrocarbons may be combined with LNG.

[0036] The sub-cooled C2-C4 hydrocarbons may be blended with LNG at one or more locations within system and method 100, In some examples, at least a portion of the sub-cooled C2-C4 hydrocarbons produced in dual-purpose refrigeration unit 110 may be combined with the LNG in line 112 and / or the processed LNG in line 122, and the resulting LNG blend (first LNG blend) may be optionally blended with additional LNG from an external source before subsequently being transported. The first LNG blend and the LNG from the external source may have a substantially similar composition (4 / - W% on a mass basis of the amounts of LNG and the C2-C4 hydrocarbonspresent within the LNG from the external source), such that the LNG from the external source simply supplements the amount of the first LNG blend that is present for subsequent storage and transport. In this mode of operation, natural gas and liquefied C2-C4 hydrocarbons may be concurrently processed in dual-purpose refrigeration unit 1 10. In some or other examples, at least a portion of the sub-cooled C2-C4 hydrocarbons may be further combined with the I .NG produced in dual-purpose refrigeration unit 1 10 and or the first LNG blend to form a second LNG blend having a composition different than the first LNG blend or the initially produced LNG. The LNG and or the first LNG blend may be stored in storage vessel 130, and the second LNG blend may be formed in loading line 132 leading to transport vessel 140. Additional description regarding the foregoing follows hereinafter.

[0037] In some embodiments, al l or a majority of the sub-cooled C2-C4 hydrocarbons in line 113 may bypass flash drum 120 and storage vessel 130 via line 1 15, whereupon the liquefied C2-C4 hydrocarbons in line 115 are subsequently blended on-the-fly at high feed rates in loading line 132 with LNG that is discharged from storage vessel 130. The resulting LNG blend (second LNG blend, corresponding to the second LNG blend described above) may then be conveyed to transport vessel 140.[0038| In some embodiments, a first portion of the sub-cooled C2-C4 hydrocarbons may be blended with the LN'G in line 1 .12 and or with the processed LNG in line 122, which may afford a first LNG blend that may be stored in storage vessel 130 and subsequently transferred to transport vessel 140 via loading line 132. Addition of the first portion of the sub-cooled C2-C4 hydrocarbons may take place via line 115a into the LNG upstream from flash drum 120 (or directly into flash drum 120) and / or via line 1 15b downstream from flash drum 120, either of which may produce a first LNG blend having a composition matching that in storage vessel 130. Optionally, LNG from an external source may be introduced to line 122 via line 161 and / or to storage vessel 130 via line 160 to supplement production of the first LNG blend or modify the composition of the fi rst LNG blend. Preferably, the LNG from the external source has substantially the same composition as the first LNG blend produced by combining the first portion of sub-cooled C2-C4 hydrocarbons with the LNG each produced in dual-purpose refrigeration unit l it). The first LNG blend may be subsequently conveyed to transport vessel 140 via loading line 132, or the first LNG blend may be further modified by combining a second portion of sub-cooled C2-C4 hydrocarbons with the first LNG blend in loading line 132 to form a second LNG blend that is conveyed to transport vessel 140.

[0039] In the foregoing description, LNG and sub-cooled C2-C4 hydrocarbons may be produced in dual-purpose refrigeration unit 1 10 at the same time. This type of operation reflects one aspect of the duality of dual-purpose refrigeration unit 110. In such aspects, the cooling duty of dual-purpose refrigeration unit 110 is shared between sub-cooling C2-C4 hydrocarbons and liquefying natural gas to produce LNG. The extent to which the cooling duty is divided between sub-cooling C2-C4 hydrocarbons and producing LNG may be determined, at least in part, by the flow rates at which natural gas and liquefied C2-C4 hydrocarbons are delivered to dual-purpose refrigeration unit 110.

[0040] In another aspect of the duality of dual-purpose refrigeration unit 1 10, at least a portion of the LNG being blended with the sub-cooled C2-C4 hydrocarbons may have been previously produced using dual-purpose refrigeration unit 1 10, such that dual-purpose refrigeration unit 1 10 alternately provides cooling duty to forming sub-cooled C2-C4 hydrocarbons and LNG ( / .£., not at the same time). In the instance where the cooling duty alternates, a majority of the cooling duty of dual-purpose refrigeration unit 110 may be devoted to forming LNG, with the remaining cooling duty being devoted to forming sub-cooled C2-C4 hydrocarbons on an as-needed basis. That is, dual-purpose refrigeration unit 110 may be utilized predominantly or exclusively for forming lean LNG, and subcooled C2-C4 hydrocarbons may be produced when formation of a LNG blend is desired. The LNG produced when sub-cooled C2-C4 hydrocarbons are not being produced or blended with the LNG may be conveyed to storage vessel 130 and / or onward to transport vessel 140. LNG housed in storage vessel 130 may be subsequently blended with sub-cooled C2-C4 hydrocarbons in loading line 132 in the manner described above when formation of such a LNG blend is desired.

[0041] As discussed above, vessel 104 in FIG. 1 may represent multiple vessels that may provide C2-C4 hydrocarbons to dual-purpose refrigeration unit 1 10 individually or as separate blends of C2- G4 hydrocarbons. System and method 400A in FIG. 2A and system and method 400B in FIO. 2B show plural vessels 104a, 104b, and 104c that individually provide C2-C4 hydrocarbons to dualpurpose refrigeration unit 1 10 via lines 107a* 107b, and 107c, respectively. For example, in FIG. 2A vessel 104a may supply C2 hydrocarbons (e.g., ethane), vessel 104b may supply C3 hydrocarbons (e.g., propane), and vessel 104c may supply C4 hydrocarbons (e.g.sbutane). Alternately, each of plural vessels 104a, 104b, and 104c may' supply mixtures containing two or more liquefied C2-C4 hydrocarbons that differ in composition from one another. Upon exiting dual-purpose refrigeration unit 110 via lines 1 13a, 1 13b, and 113c, respectively, the liquefied C2-C4 hydrocarbons may be introduced to line 115 individual ly, as depicted, or be blended together in a mixing device (not shown)prior to being introduced to line 115. System and method 400A corresponds to system and method 100 in PIG. I and will not be described in further detail in the interest of brevity.

[0042] FIG. 2B shows another configuration in which plural vessels 104a, 104b, and 104c may individually provide C2-C4 hydrocarbons to dual-purpose refrigeration unit 1.10. As in system and method 400 A (FIG. 1 ), C2 C4 hydrocarbons are provided by lines 107a, 107b, and 107c. Instead of being conveyed directly to dual-purpose refrigeration unit 110, the C2-C4 hydrocarbons are combined in mixing device 415 and then introduced to dual-purpose refrigeration unit 110 via line 107d. Because system and method 400B only introduces one stream to dual-purpose refrigeration unit 110, there is only one line 1 13 exiting dual-purpose refrigeration unit 110 and conveying sub-cooled C2- C4 hydrocarbons for blending. Like system and method 400 A, system and method 400B is otherwise similar to system and method 100 in FIG. 1 and will not be described in further detail herein in the interest of brevity.

[0043] Various configurations are possible for dual-purpose refrigeration unit 1 10, specifically at least the number and disposition of heat exchangers, refrigerant loops, and the like that are present therein. Dual-purpose refrigeration unit 1 10 may comprise any structure that allows indirect heat exchange to take place between a refrigerant and both natural gas and liquefied C2-C4 hydrocarbons that are maintained in separate streams as they pass through the structure. Suitable structures for facilitating indirect heat exchange may include heat exchangers such as, for example, spiral wound heat exchangers, plate-fin heat exchangers, shell -and-tube heat exchangers, spiral heat exchangers, hairpin heat exchangers, core heat exchangers, core-and-kettle heat exchangers, printed-circuit heat exchangers, double-pipe heat exchangers, or any combination thereof. Non-limiting examples of suitable refrigerants are discussed further below.

[0044] Dual-purpose refrigeration unit 1 10 may utilize a single heat exchanger or two or more heat exchangers in series and / or parallel to facilitate formation of LNG and sub-cooling of C2-C4 hydrocarbons to bring these components into thermal equilibrium with one another. When multiple heat exchangers are used, the refrigerant within the refrigerant loop that provides cooling to each heat exchanger may be the same or different, Shell-and-tube heat exchangers in which the natural gas and the liquefied C2-C4 hydrocarbons pass through one or more tubes housed within a shell in which the refrigerant circulates may be particularly desirable. Configurations for dual-purpose refrigeration unit 110 utilizing one or more shell -and-tube heat exchangers are described hereinafter. Although the following description is directed to shell -and-tube heat exchangers, it is to be appreciated that alternative heat exchanger types also may be suitably used.

[0045] FIG. 3 is a diagram of a single shell-and-tube heat exchanger configured to form LNG and produce sub-cooled C2-C4 hydrocarbons according to one or more embodiments of the present disclosure. As shown, natural gas is provided from source 102 and conveyed via line 106 to dualpurpose refrigeration unit 110, and liquefied C2-C4 hydrocarbons are provided from source 104 and conveyed via Line 107 to dual-purpose refrigeration unit 1 10. As above, it is to be appreciated that although only one source 104 and one line 107 are shown, more than one stream of liquefied C2-C4 hydrocarbons may be provided to dual-purpose refrigeration unit 110.

[0046] Dual-purpose refrigeration unit I 10 comprises a she11-and-tube heat exchanger having shell 510 and tubes 512 and 514 (each shown in phantom) present within internal space 520 therein. Tube 512 conveys natural gas through internal space 520, and tube 514 conveys liquefied C2-C4 hydrocarbons through internal space 520. Dual-purpose refrigeration unit 110 also includes refrigerant loop 500, which supplies a refrigerant to internal space 520 in a countercurrent fashion relative to the direction in which natural gas and liquefied C2-C4 hydrocarbons flow. It is to be appreciated that refrigerant loop 500 is depicted in simplified form, and conventional components such as compressors, expanders or like expansion devices, heat exchangers, pumps, and the like may be present to provide a refrigerant that is suitably chilled upon entering internal space 520.

[0047] Upon exiting shell 510 via lines 112 and 113, respectively, the LNG and NGLs may be further manipulated as described above in reference to any of FIGS. 1 , 2A, or 2B.(0048] F 1G. 4 is a diagram of a split shell -and- tube heat exchanger configured to form LNG and produce sub-cooled C2-C4 hydrocarbons according to one or more embodiments of the present disclosure. In a split shell-and-tube heat exchanger, the LNG and liquefied C2-C4 hydrocarbons are cooled in separate shells disposed in parallel and that are individually provided with refrigerant from a suitable refrigerant loop. As shown, natural gas is provided from source 102 and conveyed via line 106 to dual-purpose refrigeration unit 1 10, and liquefied C2-C4 hydrocarbons are provided from source 104 and conveyed via line 107 to dual-purpose refrigeration unit 1 10. Again, it is to be appreciated that although only one source 104 and one line 107 are shown, more than one stream of liquefied C2-C4 hydrocarbons may be provided to dual-purpose refrigeration unit 1 10.

[0049] In FIG. 4, dual-purpose refrigeration unit 110 comprises parallel heat exchangers A and B, each having a shell-and-tube configuration. Heat exchanger A comprises shell 510a and tube 512a (shown in phantom) present within internal space 520a therein. Heat exchanger B comprises shell 510b and tube 512b (shown in phantom) present within internal space 520b therein. Tube 512a conveys natural gas, and tube 512b conveys liquefied C2-C4 hydrocarbons. Dual-purposerefrigeration unit 1 10 also includes refrigerant loop 500, which supplies separate streams of a refrigerant to internal spaces 520a and 520b in a countercurrent fashion relative to the direction in which natural gas and liquefied C2-C4 hydrocarbons flow. The separate streams of refrigerant exiting heat exchangers A and B may be recombined and undergo reconditioning within refrigerant loop 500. The cooling duty of heat exchangers A and B may be regulated using valves or other flow-control means to regulate the amounts of natural gas and C2-C4 hydrocarbons flowing to heat exchangers A and B, respectively. Similar flow-control means may be utilized in refrigeration loop 500 to regulate the flow rate of refrigerant through heat exchangers A and B. Although a single refrigerant loop 500 supplies refrigerant to both of heat exchangers A and B in FIG, 4, it is to be appreciated that separate refrigerant loops, each containing the same or different refrigerants, may supply heat exchangers A and B with chilled refrigerant.

[0050] Upon exiting shells 510a and 510b via lines 112 and 1 13, respectively, the LNG and subcooled C2-C4 hydrocarbons may be further manipulated as described above in reference to any of FIGS. 1, 2A, or 2B.

[0051] FIGS. 5A and 5B are diagrams of two shell-and-tube heat exchangers arranged in series to form LNG and produce sub-cooled C2-C4 hydrocarbons according to one or more embodiments of the present disclosure. In such a series arrangement of shell -and-tubc heat exchangers, different refrigerants may be provided to the two shell-and-tube heat exchangers (FIG. 5 A), or the same refrigerant in two different cooling states may be provided to the two shell-and tube heat exchangers in reverse sequence (e.g., from a downstream heat exchanger to an upstream heat exchanger, FIG. 5B). The refrigerant provided to the upstream exchanger may have a higher temperature than the refrigerant provided to a downstream heat exchanger. When different refrigerants are provided to the two heat exchangers, the different refrigerants may be provided from separate refrigerant loops servicing each heat exchanger. Optionally, there may be thermal communication between the two refrigerant loops. When the same refrigerant in different cooling states is provided to the heat exchangers in reverse sequence, a single refrigeration loop servicing both heat exchangers may be used or separate refrigerant loops maintaining the refrigerant in different cooling states may be used as an alternative.

[0052] As shown, natural gas is provided from source 102 and conveyed via line 106 to an upstream portion of dual-purpose refrigeration unit 110, and liquefied C2-C4 hydrocarbons are provided from source 104 and conveyed via line 107 to the upstream portion of dual-purpose refrigeration unit 1 10.Again, it is to be appreciated that although only one source 104 and one line 107 are shown, multiple streams of liquefied C2-C4 hydrocarbons may be provided to dual-purpose refrigeration unit 1 10.

[0053] In both FIGS. 5 A and 5B, dual-purpose refrigeration unit 110 comprises heat exchangers arranged in series, each having a shell-and-tube configuration. Heat exchanger A comprises shell 710a and tubes 712a and 714a (both shown in phantom) present within internal space 720a therein. Tube 712a conveys natural gas, and tube 714a conveys liquefied C2-C4 hydrocarbons. Heat exchanger A comprises an upstream portion of dual-purpose refrigeration unit 110. Natural gas exits shell 710a via line 706 and is conveyed to heat exchanger B, and liquefied C2-C4 hydrocarbons exit shell 710a via line 707 and are conveyed to heat exchanger B. The natural gas exiting heat exchanger A may not yet be hilly liquefied and or the liquefied C2-C4 hydrocarbons exiting heat exchanger A may not yet be fully or sufficiently sub-cooled. Liquefaction of natural gas and complete sub-cooling of the C2-C-4 hydrocarbons may take place in heat exchanger B, as heat exchanger B may utilize a lower-temperature refrigerant than does heat exchanger A, as discussed subsequently. Heat exchanger B comprises shell 710b and tubes 712b and 714b ( both shown in phantom ) present within internal space 720b therein. Tube 712b receives natural gas from line 706, and tube 714b receives liquefied C2-C4 hydrocarbons from line 707, Heat exchanger B comprises a downstream portion of dual-purpose refrigeration unit 1 10.

[0054] In FIG, 5A, two refrigerant loops 700a and 700b are utilized to supply separate refrigerants to heat exchangers A and B. Refrigerant loop 700a supplies a first refrigerant to internal space 720a of heat exchanger A in a countercurrent fashion. The natural gas exiting shell 710a need not necessarily be liquefied but is at a lower temperature than the entering natural gas. Similarly, the liquefied C2-C4 hydrocarbons exiting shell 710a need not necessarily be fully or sufficiently subcooled but are at a lower temperature than the entering liquefied C2-C4 hydrocarbons. Refrigerant loop 700b supplies a second refrigerant to internal space 720b of heat exchanger B, also in a countercurrent fashion. The natural gas exiting shell 710b is now liquefied (r.e., LNG), and the liquefied C2-C4 hydrocarbons exiting shell 710b are fully sub-cooled and in thermal equilibrium with the LNG for subsequent combining therewith.

[0055] Refrigerant loops 700a and 700b may be thermally coupled to one another or thermally noncoupled. When thermally coupled, a wanned second refrigerant produced in refrigerant loop 700b after promoting formation of LNG and sub-cooled C2-C4 hydrocarbons may still retain sufficient cooling capacity for cooling a first refrigerant within refrigerant loop 700a, For example, as shown in FIG. 5A, warmed second refrigerant may be withdrawn from refrigerant loop 700b through line740 and conveyed to heat exchanger 750. The wanned second refrigerant may cool a first refrigerant passing through heat exchanger 750. After promoting cooling of the first refrigerant, the second refrigerant may be returned to refrigerant loop 700b by line 760. Each refrigerant may then undergo further manipulations, including at least one compression operation and at least one expansion operation (not shown) to return each refrigerant to its original condition within refrigerant loops 700a and 700b before being recirculated to corresponding heat exchangers A and B.

[0056] In FIG. 5B, single refrigerant loop 701) supplies the same refrigerant to both heat exchangers A and B, wherein the refrigerant is in different conditions when provided to heat exchangers A and B. For example, the refrigerant being provided to heat exchanger B may have a lower temperature than does the same refrigerant provided to heat exchanger A, such as may occur when the refrigerant is at a lower pressure when provided to heal exchanger B than to heat exchanger A, As a non-limiting example, low-pressure nitrogen may be supplied as the refrigerant to heat exchanger B. After promoting cooling in heat exchanger B, the nitrogen undergoes warming but sti ll retains at least some cooling capacity. As such, the wanned nitrogen may be provided as the refrigerant to heat exchanger A. After promoting cooling in heat exchanger A, the refrigerant (e.g., nitrogen) may be reconditioned in refrigerant loop 700 and returned to heat exchanger B.

[0057] Upon exiting shell 710b via lines 112 and 1 13, respectively, the LNG and NGLs may be further processed as described above in reference to any of FIGS. 1, 2A, or 2B.

[0058] .Although not shown in FIGS. 5A or 5B, it is to be appreciated that heat exchanger A and / or B may also be separated as split-tube heat exchangers operated in parallel, in a similar configuration to that depicted in FIG. 4.

[0059] As shown in FIGS. 3, 4, 5A, and 5B, dual-purpose refrigeration unit 110 may comprise at. least one refrigerant loop to promote sub-cooli ng of C2-C4 hydrocarbons and liquefaction of natural gas. Any combination of refrigerants and refrigerant loops may be utilized, provided that the refrigerant may be cooled sufficiently to promote liquefaction of the natural gas. Suitable refrigerants may include, but are not limited to, nitrogen, ammonia, natural gas or methane, ethane, propane, isopentane, carbon dioxide, or any mixture thereof. Preferably, if a single refrigerant is used, the single refrigerant comprises nitrogen. Preferably, if first and second refrigerants are utilized for chilling two or more heat exchangers in series, at least the refrigerant provided to the downstream heat exchanger comprises nitrogen. Optionally, the refrigerant provided to the upstream heat exchanger may also comprise nitrogen, preferably with the nitrogen being at a higher pressure than when provided to the downstream heat exchanger.

[0060] In some embodiments, a first refrigerant loop may promote cooling of a natural gas stream to a temperature above a liquefaction temperature, and a second refrigerant loop may promote formation of LNG and sub-cooling of C2-C4 hydrocarbons in the manner described herein. Such a configuration is shown in FIG. 5A. Another such configuration is shown in FIG. 6, which is discussed further below. The first refrigerant loop may utilize a first refrigerant, and the second refrigerant loop may utilize a second refrigerant that is different than the first refrigerant.

[0061] FIG. 6 is a diagram of a system and method that may produce LNG, NGLs, and a thermally equil ibrated liquefied gas mixture according to one or more embodiments of the present disclosure. The configuration for dual-parpose refrigeration unit 1 10 in F IG. 6 bears substantial similarity to that in FIG. 5 and may be better understood by reference thereto. Additional context for FIG. 6 may also be obtained through reference to FIG. 1 . As shown in system and method 800 in FIG. 6, natural gas is conveyed from vessel 102 to heat exchanger A via line 106. C2-C4 hydrocarbons are conveyed from vessel 104 to heat exchanger A via line 107, wherein line 107 may optionally bypass heat exchanger A (bypass not shown). Again, although only one vessel 104 and line 107 are depicted, multiple lines may be present (e.g., one line 107 for each individual C2-C4 hydrocarbon or a blend thereof), and C2-C4 hydrocarbons from multiple lines 107 may be mixed together upstream from heat exchanger A. The refrigerant in refrigerant loop 700a lowers the temperature of the natural gas to form chilled natural gas, but the temperature of the chilled natural gas remains above the temperature at which LNG forms. The chilled natural gas is then conveyed to heat exchanger B via line 706. Optionally, a portion of the chilled natural gas is conveyed directly to flash drum 120 via line 810, after first passing through heat exchanger 820, which is cooled by end flash gas from flash drum 120, The end flash gas is transferred from flash drum 120 to heat exchanger 820 via line 830, and after promoting cooling, the end flash gas may be compressed in compressor 150 and burned as fuel gas. LNG is formed in heat exchanger B, exits via line 112, and is conveyed to flash drum 120.

[0062] Liquefied C2-C4 hydrocarbons exit heat exchanger A and are conveyed by line 807 to heat exchanger B. Sub-cooled C2-C4 hydrocarbons then exit heat exchanger B via line 113. The blending of the sub-cooled C2-C4 hydrocarbons downstream from heat exchanger B may occur continuously or intermitently as LNG is being produced. For example, blending of one or more portions of subcooled C2-C4 hydrocarbons may take place via line 115a or line 115b to produce a first LNG blend in storage vessel 130, Additionally or alternately, sub-cooled C2-C4 hydrocarbons in line 1.15 may be conveyed to loading line 132 to form a second LNG blend therein.

[0063] Optionally, a portion of the sub-cooled C2-C4 hydrocarbons are combined with the LNG in flash drum 120 or downstream from flash drum 120 before storage, but a majority of the sub-cooled C2-C4 hydrocarbons are conveyed downstream for combining with the LNG after further processing and storage thereof. LNG is conveyed from denitrification unit 840 to storage vessel 130. External LNG may also be provided to storage vessel 130 via line 161 or immediately upstream from storage vessel 130 via line 161 . As production of a second LNG blend having a different composition than the LNG or fust LNG blend in storage vessel 130 is desired, LNG or the first LNG blend may be released from storage vessel 130 through loading line 132 and undergo blending therein with the sub- cooled C2-C4 hydrocarbons received from line 1 15.

[0064] Optionally, the properties of the LNG blend may be monitored after formation thereof in loading line 132. Sensor 170 may represent one or a plurality of sensors which may be configured io assay for composition or one or more physical or chemical properties, such as density, heating value, compressibility, relative volatility', or the like. Optionally, the one or more physical properties may be inferred from composition and other directly measured physical parameters, In non-limiting examples, sensor 170 may be one or more sensors that measure quantities such as, for instance, pressure, temperature, flow rate, or the like. Composition may be measured with an in-line gas chromatograph containing sensor 170. The output from sensor 170 (or a result derived therefrom) may be utilized to provide autonomous or manual process control if the LNG blend is off-specification in any way. In FIG. 6, sensor 170 is configured to assay the second LNG blend formed within loading fine 132,

[0065] Other locations for sensor 170 are also possible for monitoring any of the liquefied gases or blends thereof produced according to the disclosure herein. Plural sensors 170 may also be present at multiple locations as well.

[0066] The systems and methods of the present disclosure may utilize computer systems and other processing means to manage information received from a sensor and determine an appropriate response thereto. Specifically, the systems and methods may receive information from a sensor, and a non-transitoiy, computer-readable medium containing instructions that, when implemented, cause one or more processors to generate a response to the information that is received. The instructions may be based in hardware and / or software of the computer system,

[0067] A Aion-transitory, computer-readable medium,” as used herein, refers io any non-transitoiy'' storage and or transmission medium that participates in providing instructions to a processor for execution. Such media may include non-volatile media, volatile media, or combinations thereof.Non-volatile media include, for example, NVRAM, or magnetic or optical disks. Volatile media include dynamic memory, such as a main memory. Common forms of computer- readable media include, for example, a floppy disk, a flexible disk, a hard disk, an array of hard disks, a magnetic tape, or any other magnetic medium, magneto-optical medium, a CD-ROM, a holographic medium, any other optical medium, a RAM, a PROM, an EPROM, a FL, A SI I -EPRO M, a solid state medium like a memory card, any other memory chip or cartridge, or any other tangible medium from which a computer can read data or instructions. The computer-readable media may be at least partially configured as a database, which may be any type of database, such as relational, hierarchical, object- oriented, and / or the like. Accordingly, a tangible storage medium or tangible distribution medium and art-recognized equivalents and successor media thereof may be utilized in software implementations related to the present disclosure.

[0068] Suitable computer systems, processor- based devices, and other processing means may include a processor; a memory coupled to the processor; and instructions provided to the memory, wherein the instructions are executable by the processor to perform one or more actions related to information received from a sensor. The instructions can be a portion of code on a non -transitory computer readable medium. Any suitable processor-based device may be utilized for implementing various aspects of the present disclosure, including without limitation personal computers, networks of personal computers, laptop computers, computer workstations, mobile devices, multi -processor servers or workstations with (or without) shared memory, high-performance computers, and the like. Moreover, embodiments may be implemented on application specific integrated circuits (ASICs) or very large scale integrated (VLSI) circuits.

[0069] Accordingly, methods of the present disclosure may form a first LNG blend by blending sub-cooled C2-C4 hydrocarbons with LNG produced in a dual-purpose refrigeration unit, optionally, wherein the first LNG blend is further blended with LNG obtained from an external source. Such methods may comprise: conveying a natural gas stream through a dual-purpose refrigeration unit to form liquefied natural gas (LNG) by indirect heat exchange; conveying one or more liquefied C2-C4 hydrocarbons through the dual-purpose refrigeration unit io sub-cool the liquefied C2-C4 hydrocarbons and bring the liquefied C2-C4 hydrocarbons into thermal equilibrium with the LNG, thereby forming sub-cooled C2-C4 hydrocarbons; processing the LNG to form processed LNG. processing comprising at least flashing to produce end-flash gas; and blending a first portion of the sub-cooled C2-C4 hydrocarbons with the LNG before processing, with the processed LNG after processing, or any combination thereof to form a first LNG blend. Optionally, a second portion ofthe sub-cooled C2-C4 hydrocarbons may be blended with the first LNG blend to form a second LNG blend having a composition differing from the first LNG blend, preferably wherein the second LNG blend is formed in a loading line leading to a transport vessel.

[0070] In some configurations, a LNG blend may be formed in a loading line without first forming the first LNG blend. Such methods may comprise: conveying a natural gas stream through a dualpurpose refrigeration unit to form liquefied natural gas (LNG) by indirect heat exchange; conveying one or more liquefied (.'2-C4 hydrocarbons through the dual-purpose refrigeration unit to sub-cool the liquefied C2-C4 hydrocarbons and bring the liquefied C2-C4 hydrocarbons into thermal equilibrium with the LNG, thereby forming sub-cooled C2-C4 hydrocarbons: processing the LNG to form processed LNG , the processing comprising at least flashing to produce end-flash gas; optionally, blending a first portion of the sub-cooled C2-C4 hydrocarbons with the LNG before processing, with the processed LNG after processing, or any combination thereof to form a first LNG blend; and blending a second portion of the sub-cooled C2-C4 hydrocarbons with the processed LNG or, if formed, the first LNG blend in a desired blend ratio to form a second LNG blend having a differing composition from the first LNG blend or the processed LNG.

[0071] The present disclosure is further directed to the following non-limiting embodiments.

[0072] Embodiment I . A method comprising: conveying a natural gas stream through a dual-purpose refrigeration unit to form liquefied natural gas (LNG) by indirect heat exchange; conveying one or more liquefied C2-C4 hydrocarbons through the dual-purpose refrigeration unit to sub-cool the liquefied C2-C4 hydrocarbons and bring the liquefied C2-C4 hydrocarbons into thermal equilibrium with the LNG, thereby forming sub-cooled C2-C4 hydrocarbons; processing the LNG to form processed LNG; wherein processing the LNG comprises at least, flashing to produce end-flash gas; and blending a first portion of the sub-cooled C2-C4 hydrocarbons with the LNG before processing, with the processed LNG after processing, or any combination thereof io form a first LNG blend.

[0073] Embodiment 2. The method of Embodiment 1, further comprising: combining LNG from an extent al source with first LNG blend.

[0074] Embodiment 3. The method of Embodiment 2, wherein the LNG from the external source has substantially the same composition as the first LNG blend.

[0075] Embodiment 4. The method of any one of Embodiments 1 -3, wherein processing the LNG further comprises performing de-n.itrification of the LNG after flashing the LNG.

[0076] Embodiment 5. The method of any one of Embodiments 1-4, further comprising: loading the first LNG blend into a transport vessel via a loading line.

[0077] Embodiment 6. The method of Embodiment 5, further comprising: storing the first LNG blend in a storage vessel before loading the first LNG blend into the transport vessel via the loading line.

[0078] Embodiment 7. The method of any one of Embodiments 1-4, further comprising: blending a second portion of the sub-cooled C2-C4 hydrocarbons with the first LNG blend to form a second LNG blend having a composition differing from the first LNG blend.

[0079] Embodiment 8, The method of Embodiment 7, further comprising: loading the second LNG blend into a transport vessel via a loading line.

[0080] Embodiment 9. The method of Embodiment 8, further comprising: storing the first LNG blend in a storage vessel before forming the second LNG blertd; wherein the loading line establishes fluid communication between the storage vessel and the transport vessel, the second portion of the sub-cooled C2-C4 hydrocarbons is introduced io the loading line, and the second LNG blend is formed within the loading line.

[0081] Embodiment 10. The method of Embodiment 9, wherein the second portion of the subcooled C2-C4 hydrocarbons is greater than the first portion of the sub-cooled C2-C4 hydrocarbons.

[0082] Embodiment 1 1. The method of any one of Embodiments I -10, wherein the natural gas and the liquefied C2-C4 hydrocarbons are conveyed through the dual-purpose refrigeration unit concurrently.

[0083] Embodiment 12. The method of any one of Embodiments 1-11, wherein the dualpurpose refrigeration unit comprises one or more heat exchangers through which the natural gas and the liquefied C2-C4 hydrocarbons are conveyed.

[0084] Embodiment 13. The method of Embodiment 12, wherein at least some of the one or more heat exchangers utilize nitrogen as a refrigerant.

[0085] Embodiment 14. The method of any one of Embodiments 1-13, wherein the dualpurpose refrigeration unit comprises at least two heat exchangers in parallel, the natural gas being conveyed through a first of the al least two heal exchangers and the liquefied C2-C4 hydrocarbons being conveyed through a second of the at least two heat exchangers.

[0086] Embodiment 15. The method of any one of Embodiments 1-14, wherein the dual- purpose refrigeration unit comprises at least two heat exchangers in series, an upstream heat exchanger of the at least two heat exchangers operating at a higher temperature than a downstream heat exchanger of the at least two heat exchangers.

[0087] Embodiment 16. The method of Embodiment 15, wherein the upstream heat exchanger and the downstream heat exchanger utilize first and second refrigerants that are different from one another.

[0088] Embodiment 17. The method of Embodiment 15 or Embodiment 16, wherein the downstream heat exchanger utilizes nitrogen as a refrigerant.

[0089] Embodiment 18. The method of Embodiment 15 or Embodiment 17, wherein the downstream heat exchanger utilizes a second refrigerant and after promoting heat exchange a wanned second refrigerant is produced; wherein the warmed second refrigerant is provided to the upstream heat exchanger as a first refrigerant for promoting heat exchange therein.

[0090] Embodiment 19. The method of any one of Embodiments 15-18, wherein the upstream heat exchanger does not liquefy the natural gas or fully sub-cool the one or more liquefied C2-C4 hydrocarbons.

[0091] Embodiment 20. The method of any one of Embodiments 1-19, wherein the natural gas is pre-cooled in a secondary heat exchanger upstream from the dual-purpose refrigeration unit.

[0092] Embodiment 21. A method comprising: conveying a natural gas stream through a dual-purpose refrigeration unit to form liquefied natural gas (LNG) by indirect heat exchange; conveying one or more liquefied C2-C4 hydrocarbons through the dual-purpose refrigeration unit to sub-cool the liquefied C2-C4 hydrocarbons and bring the liquefied C2-C4 hydrocarbons into thermal equilibrium with the LNG, thereby forming sub-cooled C2-C4 hydrocarbons; processing the LNG to form processed LNG; wherein processing the LNG comprises at least flashing to produce end-flash gas; optionally, blending a first portion of the sub-cooled C2-C4 hydrocarbons with the LNG before processing, with the processed LNG after processing, or any combination thereof to form a first LNG blend; andblending a second portion of the sub-cooled C2-C4 hydrocarbons with the processed LNG or, if formed, the first LNG blend in a desired blend ratio to form a second LNG blend having a differing composition from the first LNG blend or the processed LNG.

[0093] Embodiment 22. The method of Embodiment 21 , wherein the first LNG blend is formed, the method further comprising: combining LNG from an external source with first LNG blend; wherein the second portion of the sub-cooled C2-C4 hydrocarbons is blended with the first LNG blend in the desired blend ratio to form the second LNG blend.

[0094] Embodiment 23. The method of Embodiment 21 or Embodiment 22, wherein processing the LNG further comprises performing de-nitrification of the LNG after flashing the LNG.

[0095] Embodiment 24. The method of any one of Embodiments 21-23, further comprising: loading the second LNG blend into a transport vessel via a loading line.

[0096] Embodiment 25. The method of Embodiment 24, wherein the second portion of subcooled C2-C4 hydrocarbons is introduced to the loading line, and the second LNG blend is formed within the loading line.

[0097] Embodiment 26. The method of Embodiment 24, further comprising: storing the processed LNG or, if formed, the first LNG blend in a storage vessel before forming the second LNG blend: wherein the loading line establishes fluid communication between the storage vessel and the transport vessel, and the second LNG blend is formed within the loading line.

[0098] Embodiment 27. The method of Embodiment 26, wherein the natural gas is conveyed through the dual-purpose refrigeration unit before the liquefied C2-C4 hydrocarbons and the processed LNG or. if formed, the first LNG blend is then stored in the storage vessel, and the liquefied C2-C4 hydrocarbons are conveyed through the dual-purpose refrigeration unit after a desired amount of processed LNG or, if formed, the first LNG blend has been stored in the storage vessel for blending with the second portion of the sub-cooled C2-C4 hydrocarbons.

[0099] Embodiment 28. The method of any one of Embodiments 21-26, wherein the natural gas and the liquefied C2-C4 hydrocarbons are conveyed through the dual-purpose refrigeration unit concurrently.

[0100] Embodiment 29. The method of any one of Embodiments 21-28. wherein the dual- purpose refrigeration unit comprises one or more heat exchangers through which the natural gas and the liquefied C2-C4 hydrocarbons are conveyed.

[0101] Embodiment 30. The method of Embodiment 29, wherein at least some of the one or more heat exchangers utilize nitrogen as a refrigerant.

[0102] Embodiment 31. The method of any one of Embodiments 21.-30, wherein the dual- purpose refrigeration unit comprises at least two heat exchangers in parallel, the natural gas being conveyed through a first of the at least two heat exchangers and the liquefied C2-C4 hydrocarbons being conveyed through a second of the at least two heat exchangers.

[0103] Embodiment .32. The method of any one of Embodiments 21 -31. wherein the dualpurpose refrigeration unit comprises at least two heat exchangers in series, an upstream heat exchanger of the at least two heat exchangers operating at a higher temperature than a downstream heat exchanger of the at least two heat exchangers.

[0104] Embodiment 33. The method of Embodiment 32, wherein the upstream heat exchanger and the downstream heat exchanger utilize first and second refrigerants that are different from one another.

[0105] Embodiment 34. The method of Embodiment 32 or Embodiment 33, wherein the downstream heat exchanger utilizes nitrogen as a refrigerant.

[0106] Embodiment 35. The method of Embodiment 32 or Embodiment 34, wherein the downstream heat exchanger utilizes a second refrigerant and after promoting heat exchange a warmed second refrigerant is produced; wherein the warmed second refrigerant is provided to the upstream heat exchanger as a first refrigerant for promoting heat exchange therein.

[0107] Embodiment 36. The method of any one of Embodiments 32-35, wherein the upstream heat exchanger does not liquefy the natural gas or fully sub-cool the one or more liquefied C2-C4 hydrocarbons.

[0108] Embodiment 37. The method of any one of Embodiments 21-36, wherein the one or more liquefied C2-C4 hydrocarbons are stored in one or more storage vessels and are conveyed through the dual-purpose refrigeration unit on-demand when blending is desired.

[0109] Embodiment 38. The method, of Embodiment 37, wherein the one or more storage vessels are maintained at + / - 10% of atmospheric pressure.

[0110] Embodiment 39. The method of any one of Embodiments 21 -38. wherein the natural gas is pre-cooled in a secondary heat exchanger upstream from the dual-purpose refrigeration unit.

[0111] Embodiment 40. The method of any one of Embodiments 21-39, further comprising: combining ENG from an external I.NG source with the processed LNG;wherein the second portion of the sub-cooled C2-C4 hydrocarbons are concurrently combined with the processed LNG and the LNG from the external source.

[0112] All documents described herein are incorporated by reference herein for purposes of ail jurisdictions where such practice is allowed, including any priority documents and / or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific embodiments, while forms of the disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited thereby. For example, the compositions described herein may be free of any component, or composition not expressly recited or disclosed herein. Any method may lack any step not recited or disclosed herein. Likewise, the term “comprising” is considered synonymous with the term “including.” Whenever a method, composition, element or group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “is” preced i ng the recitation of the composition, element, or elements and vice versa.

[0113] Unless otherwise indicated , all numbers expressing quanti ties of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by one or more embodiments described herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0114] Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces.

[0115] One or more illustrative embodiments are presented herein. Not al! features of a physical implementation are described or shown in this application tor the sake of clarity. It is understood that in the development of a physical embodiment of the present disclosure, numerous implementationspecific decisions must be made to achieve the developer’s goals, such as compliance with system- related, business-related, government-related and other constraints, which vary by implementation and from time to time. While a developer's efforts might be time-consuming, such efforts would be, nevertheless, a routine undertaking for one of ordinary skill in the art and having benefit of this disclosure.

[0116] I herefore, the present disclosure is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to one having ordinary skill in the art and having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present disclosure. The embodiments illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and / or any optional element disclosed herein.

Claims

CLAIMSWhat is claimed is the following:

1. A method comprising: conveying a natural gas stream through a dual-purpose refrigeration unit to form liquefied natural gas (LNG) by indirect heat exchange; optionally, wherein the natural gas stream is pre-cooled in a secondary heat exchanger upstream from the dual-purpose refrigeration unit; conveying one or more liquefied C2-C4 hydrocarbons through the dual-purpose refrigeration unit to sub-cool the liquefied C2-C4 hydrocarbons and bring the liquefied C2- C4 hydrocarbons into thermal equilibrium with the LNG, thereby forming sub-cooled C2- C4 hydrocarbons; processing the LNG to form processed LNG; wherein processing the LNG comprises at least flashing to produce end- flash gas; and blending a first portion of the sub-cooled C2-C4 hydrocarbons with the LNG before processing, with the processed LNG after processing, or any combination thereof to form a first LNG blend.

2. The method of claim I , further comprising: combining LNG from an external source with first LNG blend; optionally, wherein the LNG from the external source has substantially the same composition as the first LNG blend.

3. The method of claim 1 or claim 2, wherein processing the L NG further comprises performing de-nitrification of the LNG after flashing the LNG.

4. The method of any one of claims 1-3, further com prising: loading the first LNG blend into a transport vessel via a loading line; and optionally, storing the first LNG blend in a storage vessel before loading the first LNG blend into the transport vessel via the loading line.

5. The method of any one of claims 1-4, further comprising: blending a second portion of the sub-cooled C2-C4 hydrocarbons with the first LNG blend to form a second LNG blend having a composition differing from the first LNG blend.

6. The method of claim 5, further comprising: loading the second LNG blend into a transport vessel via a loading line; and optionally, storing the first LNG blend in a storage vessel before forming the secondLNG blend: wherein the loading line establishes fluid communication between the storage vessel and the transport vessel, the second portion of the sub-cooled C2-C4 hydrocarbons is introduced to the loading line, and the second LNG blend is formed within the loading line.

7. The method of claim 5 or claim 6, wherein the second portion of the sub-cooled C2-C4 hydrocarbons is greater than the first portion of the sub-cooled C2-C4 hydrocarbons.

8. The method of any one of claims 1-7, wherein the natural gas stream and the liquefied C2- C4 hydrocarbons are conveyed through the dual -purpose refrigeration unit concurrently.

9. The method of any one of claims 1-8, wherein the dual-purpose refrigeration unit comprises one or more heat exchangers through which the natural gas stream and the liquefied C2-C4 hydrocarbons are conveyed.

10. The method of claim 9, wherein at least some of the one or more heat exchangers utilize nitrogen as a refrigerant.

11. The method of any one of claims 1-10, wherein the dual-purpose refrigeration unit comprises at least two heat exchangers in parallel, the natural gas stream being conveyed through a first of the at least two heat exchangers in parallel and the liquefied C2-C4 hydrocarbons being conveyed through a second of the at least two heat exchangers in parallel,12. The method of any one of claims 1-11, wherein the dual-purpose refrigeration unit comprises at least two heat exchangers in series, an upstream heat exchanger of the at least two heat exchangers in series operating at a higher temperature than a downstream heat exchanger of the at least two heat exchangers in series.

13. The method of claim 12, wherein the upstream heat exchanger and the downstream heat exchanger utilize first and second refrigerants that are different from one another; optionally, wherein the downstream heat exchanger utilizes nitrogen as a refrigerant.

14. The method of claim 12, wherein the downstream heat exchanger utilizes a second refrigerant and after promoting heat exchange, a wanned second refrigerant is produced; wherein the warmed second refrigerant is provided to the upstream heat exchanger as a first refrigerant for promoting heat exchange therein.

15. The method of any one of claims 12-14, wherein the upstream heat exchanger does not liquefy the natural gas or fully sub-cool the one or more liquefied C2-C4 hydrocarbons.

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