Thermally equilibrated liquefied gas blends produced by indirect heat exchange with boil-off gas from liquefied gas mixtures

Abstract

Methods for forming thermally equilibrated liquefied gas mixtures may comprise: obtaining boil-off gas from a liquefied gas mixture comprising a first hydrocarbon and one or more second hydrocarbons; discharging the first hydrocarbon in liquefied form from a first reservoir and the one or more additional hydrocarbons in liquefied form from one or more second reservoirs at a mixing ratio sufficient to maintain the liquefied gas mixture at one or more specified physical parameters once blended therewith; performing indirect heat exchange between at least a portion of the boil-off gas and the one or more additional hydrocarbons discharged from the one or more second reservoirs until the one or more additional hydrocarbons are in thermal equilibrium with the boil-off gas; and combining the one or more additional hydrocarbons with the first hydrocarbon to form a thermally equilibrated liquefied hydrocarbon blend that is supplied to the liquefied gas mixture.

Description

THERMALLY EQUILIBRATED LIQUEFIED GAS BLENDS PRODUCED BY INDIRECT HEAT EXCHANGE WITH BOIL-OFF GAS FROM LIQUEFIED GAS MIXTURESFIELD

[0001] The present disclosure relates to liquefied hydrocarbon gas mixtures, such as liquefied natural gas (LNG), and more particularly, to methods for blending one or more thermally equilibrated liquefied hydrocarbons with a liquefied hydrocarbon gas mixture to maintain or attain a desired physical property profile.BACKGROUND

[0002] Natural gas is a hydrocarbon resource comprising methane and minor amounts of other light hydrocarbon gases in varying amounts. Because of its relatively low carbon emissions, 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 (e.g., 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 LNG may still have slightly differing compositions depending on the origin of the natural gas stream, the relative amounts of minority heavier hydrocarbon gases that are initially 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 theamounts of one or more C2-C4 hydrocarbons (z.e., natural gas liquids) are off-specification, the heating value of the LNG may be unsuitable for consumer or industrial use.

[0004] The composition of LNG may be modified to alter the density, heating value or other physical and chemical properties. In one approach, an inert gas may be blended with the LNG to lower the heating value, while maintaining the methane and C2-C4 hydrocarbons at the same relative ratios with respect to one another. In another approach, methane and / or C2-C4 hydrocarbons in a liquefied state may be blended with LNG to alter the relative ratios of methane and C2-C4 hydrocarbons with respect to one another in order to raise or lower the heating value. Such blending processes to alter the heating value (or another physical property) may need to be performed with care to avoid changing one or more other physical properties to an off-specification value. In addition, blending processes may alter the thermal equilibrium of the LNG, and the LNG may need to be additionally processed or stabilized before being further transported or re-gasified for consumer or industrial use. However, it may be difficult or costly to bring blending gases, such as methane and / or C2-C4 hydrocarbons, into thermal equilibrium with each other and with LNG. Excessive boil-off gas may be produced if one or more blending gases are not brought into thermal equilibrium with LNG prior to blending.SUMMARY

[0005] In various aspects, the present disclosure provides methods comprising: providing a liquefied gas mixture comprising a first hydrocarbon in liquefied form and one or more additional hydrocarbons in liquefied form, the first hydrocarbon having a higher volatility than any of the one or more additional hydrocarbons; providing a first reservoir containing the first hydrocarbon in liquefied form and one or more second reservoirs individually containing the one or more additional hydrocarbons in liquefied form, in which the first reservoir and the one or more second reservoirs are in fluid communication with the liquefied gas mixture; obtaining a boil-off gas from the liquefied gas mixture, in which the boil-off gas is in thermal equilibrium with the liquefied gas mixture and comprises 80 vol% or greater of the first hydrocarbon in gaseous form; discharging the first hydrocarbon in liquefied form from the first reservoir and the one or more additional hydrocarbons in liquefied form from the one or more second reservoirs at a mixing ratio sufficient to maintain the liquefied gas mixture at one or more specified physical parameters once blended therewith; performing indirect heat exchange between at least a portion of the boil-off gas and the one or more additional hydrocarbons in liquefied form discharged from the one or more second reservoirs until the one or more additional hydrocarbons in liquefied form are in thermal equilibrium with the boil-off gas and the liquefied gas mixture; after bringing the one or more additional hydrocarbons in liquefied form into thermal equilibrium with the boil-off gas and the liquefied gas mixture, combining the one or more additional hydrocarbons in liquefied form with the first hydrocarbon in liquefied form discharged from the first reservoir to form a thermally equilibrated liquefied hydrocarbon blend; and supplying the thermally equilibrated liquefied hydrocarbon blend to the liquefied gas mixture.

[0006] 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 DESCRIPTION OF THE DRAWINGS

[0007] 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.

[0008] FIGS. 1 -4 are diagrams of various configurations of systems and methods that may thermally equilibrate a liquefied gas mixture using boil-off gas according to one or more embodiments of the present disclosure.DETAILED DESCRIPTION

[0009] The present disclosure relates to liquefied hydrocarbon gas mixtures, such as liquefied natural gas (LNG), and more particularly, to methods for blending one or more thermally equilibrated liquefied hydrocarbons with a liquefied hydrocarbon gas mixture to maintain or attain a desired physical property profile.

[0010] It can be difficult to maintain a desired physical or chemical property profile in liquefied hydrocarbon gas mixtures, such as LNG, 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 methane and / or one or more C2-C4 hydrocarbons in liquefied form with LNG, it may be difficult to maintain thermal equilibrium of the LNG when doing so due to 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 other physical property may be further problematic in view of frequently changing target compositions for the LNG, the inconsistent compositions of raw natural gas streams being processed into LNG, inconsistent compositions of individual blending gases, and the like.

[0011] The present disclosure at least partially alleviates the foregoing concerns and provides additional advantages as well. In particular, the present disclosure utilizes boil-off gas (BOG) from a vessel containing LNG or a similar liquefied gas mixture containing multiple hydrocarbon gases in liquefied form to bring one or more external blend gases in liquefied form into thermal equilibrium with the liquefied gas mixture prior to being combined therewith. Since BOG typically constitutes the most volatile component of a liquefied gas mixture at thermal equilibrium (methane in the case of LNG) and has substantially the same temperature as the liquefied gas mixture by virtue of also being in thermal equilibrium with the liquefied gas mixture, the BOG may be utilized to cool other external blend gases in liquefied form that have a lower volatility. By using BOG to cool the less volatile external blend gases in liquefied form, the external blend gases may be brought into thermal equilibrium with each other and with the liquefied gas mixture prior to being combined therewith. The ability to bring multiple external blend gases into thermal equilibrium with the liquefied gas mixture in the foregoing manner may be particularly advantageous, since the typical storage conditions for hydrocarbon gases in liquefied form may vary considerably from one another based on differences in volatility, a function of boiling point. Active temperature control to maintain multiple external blend gases at the same temperature may be complicated and costly. The thermal equilibration procedure utilizing BOG, in contrast, is largely self-regulating and may be readily performed.

[0012] In addition to the advantages of maintaining thermal equilibrium and facilitating ready access to customized blends of liquefied gas mixtures, such as custom LNG blends, the systems and methods of the present disclosure offer various process control benefits as well. In various examples, physical properties associated with the individual blend gases in liquefied form may be measured with appropriate sensors prior to blending the individual blend gases together. Similarly, physical properties after blending the individual blend gases together may be determined as well. In either case, measurement of the physical properties may allow automated and / or manual process intervention to take place to avoid producing an off-specification liquefied gas mixture. The processing controls may be proactive or reactive in nature. For instance, if an off-specification liquefied gas mixture is being produced, the relative ratios of the blend gases may be reactively altered so as to change 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 liquefied gas mixture may be off-specification than if substantially pure propane alone was blended with other liquefied hydrocarbon gases. The systems and methods of the present disclosure may detect andaccount for such fluctuating inputs and facilitate a proactive response thereto in order to maintain an on-specification product.

[0013] 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 hydrocarbons), and / or one or more acid gases. As used herein, the term “natural gas liquids” refers to one or more of ethane, propane, and butane. Minor amounts of contaminants such as water, nitrogen, iron sulfide, wax, and crude oil, for example, may also be present in natural gas. Liquefied natural gas (LNG) may comprise predominantly methane after undergoing processing of a raw natural gas stream.

[0014] 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.

[0015] 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" 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, for example, valves, control valves, Joule-Thomson (J-T) valves, or Venturi devices. Suitable devices for promoting 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.

[0016] 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 acompressor-expander operatively coupled together on a single (common) shaft. Other types of turboexpanders may be coupled to a generator to promote production of electrical power.

[0017] As used herein, the term "cooling" refers to lowering and / or dropping 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 50°C, at least about 75°C, at least about 85°C, at least about 95°C, or at least about 100°C. 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 in the present disclosure may take place through indirect contact with a heat sink that is a cooling liquid. Cooling may also take place by expansion as well.

[0018] A substance that has been “cooled” means that the temperature has been lowered to an unspecified degree relative to the corresponding uncooled substance. A substance that has been “warmed” means that the temperature has been raised to an unspecified degree relative to the corresponding un-warmed substance.

[0019] 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 shell- and-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. "Heat exchangers" 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.

[0020] As used herein, the terms “liquefied gas” or “liquefied gas mixture” 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 temperature, or any combination thereof.

[0021] 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 componentsof 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.

[0022] 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 have been omitted from the drawings 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.

[0023] FIGS. 1 -4 are diagrams of various configurations of systems and methods that may thermally equilibrate a liquefied gas mixture using boil-off gas according to one or more embodiments of the present disclosure. In system and method 100 of FIG. 1, vessel 102 contains liquefied gas mixture 104 comprising a first hydrocarbon in liquefied form and one or more additional hydrocarbons in liquefied form. The first hydrocarbon in liquefied form may have a higher volatility (i.e., be more volatile) than any of the one or more additional hydrocarbons in liquefied form. Liquefied gas mixture 104 may comprise a homogeneous blend and be in thermal equilibrium, such that boil-off gas 116 from vessel 102 constitutes predominantly the most volatile component of liquefied gas mixture 104. For example, liquefied gas mixture 104 may comprise LNG of a specified composition, and boil-off gas 116 may comprise predominantly methane. In the event that liquefied gas mixture 104 comprises LNG, the LNG may comprise predominantly methane and minority amounts of one or more C2-C4 hydrocarbons in liquefied form. The type(s) of C2-C4 hydrocarbons and their relative amounts, for example, may impact the density and heating value of the LNG, as well as other physical properties.

[0024] Liquefied gas mixture 104 may be received from source 106, which may be a LNG liquefaction process according to one or more embodiments. LNG liquefaction processes are well- known and are not discussed further herein. When liquefied gas mixture 104 constitutes LNG, the LNG liquefaction process is not believed to be particularly limited.

[0025] One or more properties of liquefied gas mixture 104, such as LNG, may need to be changed due to consumer demand or application-specific needs, or if source 106 provides off-specification liquefied gas mixture 104. System and method 100 accommodates changing the composition and / or physical properties of liquefied gas mixture 104 in response to the foregoing while maintaining thermal equilibrium therein.

[0026] The composition and resulting physical properties of liquefied gas mixture 104 may be altered by introducing liquefied gases 112a-l 12d (blend gases in liquefied form) from correspondingreservoirs 11 Oa-1 lOd, which individually store liquefied gases 1 12a- 1 12d. Liquefied gas 112a is the liquefied gas having the highest volatility liquefied gas mixture 104, and liquefied gas 112a has a higher volatility than do any of liquefied gases 112b-l 12d. Liquefied gas 112a may be the predominant liquefied gas within liquefied gas mixture 104, and one or more of liquefied gases 112b- 112d may be present in liquefied gas mixture 104 as minority liquefied gas(es) therein. For example, liquefied gas 112a may comprise methane, and liquefied gases 112b-l 12d may comprise ethane, propane, and butane. Although system and method 100 shows three additional liquefied gases i.e., liquefied gases 112b-l 12d), it is to be appreciated that any number of additional liquefied gases greater than or equal to one may be present. Therefore, fewer or greater than the depicted three additional liquefied gases (i.e., liquefied gases 112b-l 12d) may be present.

[0027] Liquefied gas mixture 104 may be maintained at or near atmospheric pressure, such that the temperature of liquefied gas mixture 104 is at or near the boiling point of the component therein that has the highest volatility (lowest boiling point). A vent (not shown) may be included in vessel 102 to maintain the pressure in this range. Boil-off gas 116 released from vessel 102 may therefore comprise predominantly the component having the highest volatility and be at or near the temperature of liquefied gas mixture 104.

[0028] Liquefied gas 112a may also be maintained at + / - 50% of atmospheric pressure, or + / - 10% of atmospheric pressure, or + / - 5% of atmospheric pressure, preferably at or near atmospheric pressure and thereby also at or near the boiling point thereof. A vent (not shown) may be included in reservoir 110a to maintain the pressure in this range. Accordingly, liquefied gas 112a and liquefied gas mixture 104 may be at or near the same temperature and at or near thermal equilibrium, and liquefied gas 112a may be introduced to liquefied gas mixture 104 without disturbing the thermal equilibrium. Likewise, boil-off gas 116 and liquefied gas 112a may be at or near the same temperature and also in thermal equilibrium with one another.

[0029] Liquefied gases 112b-l 12d may also be maintained at + / -50% of atmospheric pressure, or + / -10% of atmospheric pressure, or + / -5% of atmospheric pressure, preferably at or near atmospheric pressure and similarly at or near their corresponding boiling points. A vent (not shown) may be included in reservoirs 110b-l lOd to maintain the pressure in this range. Because the boiling points of less-volatile liquefied gases 112b-l 12d are higher than that of liquefied gas 112a and also differ from one another, liquefied gases 112b- 112d are not at the same temperature as liquefied gas mixture 104 and may not be directly introduced thereto without disturbing the thermal equilibrium.

[0030] Since boil-off gas 116 is at a lower temperature than are liquefied gases 1 12b-l 12d, boil-off gas 116 may be utilized to promote cooling of liquefied gases 112b- 112d to bring them into thermal equilibrium with liquefied gas mixture 104. As shown in system and method 100, heat exchange cascade 120 may utilize at least a portion of boil-off gas 116 to promote cooling of each of liquefied gases 112b- 112d, with staged cooling being utilized for liquefied gases 112c and 112d, as explained in greater detail hereinafter.

[0031] Boil-off gas 116 may comprise predominantly the most volatile component within liquefied gas mixture 104. In non-limiting examples, boil-off gas 116 may comprise at least about 80 vol%, or at least about 85 vol%, or at least about 90 vol%, or at least about 95 vol%, or at least about 98 vol%, or at least about 99 vol% of the most volatile component, specifically liquefied gas 112a.

[0032] Liquefied gas 112a is at or near the same temperature as liquefied gas mixture 104 and boil- off gas 116. Accordingly, liquefied gas 112a need not be cooled with boil-off gas 116, and liquefied gas 112a may be supplied directly from reservoir 110a via line 130a to mixing unit 160. Mixing unit 160 may be a static mixing block, an in-line mixer, a pressure vessel, a stirred mixer, a circulating mixer, or similar equipment. Optionally, some or all of liquefied gas 112a may be provided directly to vessel 102 via a bypass line (not shown).

[0033] To promote heat exchange with liquefied gases 112b- 112d, at least a portion of boil-off gas 116 enters heat exchange cascade 120. Within heat exchange cascade 120, boil-off gas 116 is divided into exchange portion 140a and bypass portion 140b. Exchange portion 140a of boil-off gas 116 is provided to heat exchanger 141 to undergo indirect heat exchange with liquefied gas 112b received via line 130b. After undergoing heat exchange, thermally equilibrated liquefied gas 112b is conveyed via line 131b to manifold line 139 for mixing with other liquefied gases, as discussed subsequently. Manifold line 139 conveys thermally equilibrated liquefied gas 112b to mixing unit 160 for blending with liquefied gas 112a and other liquefied gases. Warmed boil-off gas stream 142 exits heat exchanger 141 after undergoing heat exchange with liquefied gas 112b.

[0034] Warmed boil-off gas stream 142 is at a higher temperature than boil-off gas 116, and therefore has diminished heat exchange capacity relative to boil-off gas 116. However, warmed boil- off gas stream 142 still has sufficient heat exchange capacity to promote initial cooling of liquefied gases 112c and 112d by virtue of their higher storage temperatures, thereby lessening the heat exchange burden for boil-off gas 116 with respect to cooling these liquefied gases.

[0035] With continued reference to FIG. 1, warmed boil-off gas stream 142 is obtained from heat exchanger 141 and conveyed to heat exchanger 143 to promote indirect heat exchange with liquefiedgas 112c received via line 130c. Warmed boil-off gas stream 144 exits heat exchanger 143 after promoting cooling of liquefied gas 112c. Warmed boil-off gas stream 144 is at a higher temperature than warmed boil-off gas stream 142, and therefore has diminished heat exchange capacity relative to warmed boil-off gas stream 142 and boil-off gas 116. However, warmed boil-off gas stream 144 still has sufficient heat exchange capacity to promote initial cooling of liquefied gas 112d by virtue of its higher storage temperature, as discussed further below.

[0036] After undergoing initial heat exchange with warmed boil-off gas stream 142 in heat exchanger 143, liquefied gas 112c is conveyed directly to heat exchanger 145 to undergo further indirect heat exchange therein. Liquefied gas 112c received by heat exchanger 145 is at a lower temperature than that housed in reservoir 110c or received in heat exchanger 143 for undergoing indirect heat exchange therein. Heat exchanger 145 receives a portion of boil-off gas 116 that has not yet promoted heat exchange within heat exchange cascade 120. As shown, bypass portion 140b of boil-off gas 116 is further subdivided into exchange portion 140c and bypass portion 140d, with exchange portion 140c being provided to heat exchanger 145 to promote indirect heat exchange therein. After undergoing heat exchange, thermally equilibrated liquefied gas 112c is conveyed via line 131c to manifold line 139 for mixing with other liquefied gases for conveyance to mixing unit 160 for blending with liquefied gas 112a and other liquefied gases. Warmed boil-off gas stream 146 exits heat exchanger 145 after undergoing heat exchange with liquefied gas 112c. Warmed boil-off gas stream 146 is at a higher temperature than boil-off gas 116, and therefore has diminished heat exchange capacity relative to boil-off gas 116 and exchange portion 140c. However, warmed boil- off gas stream 146 still has sufficient heat exchange capacity to promote intermediate cooling of liquefied gas 112d, as discussed further below.

[0037] With continued reference to FIG. 1, warmed boil-off gas stream 144 is obtained from heat exchanger 143 and conveyed to heat exchanger 147 to promote indirect heat exchange with liquefied gas 112d received via line 130d. Warmed boil-off gas stream 148 exits heat exchanger 147 after promoting cooling of liquefied gas 112d.

[0038] After undergoing initial heat exchange with warmed boil-off gas stream 144 in heat exchanger 147, liquefied gas 112d is conveyed directly to heat exchanger 149 to undergo further indirect heat exchange therein during an intermediate stage of cooling. Liquefied gas 112d received by heat exchanger 149 is at a lower temperature than that housed in reservoir 1 lOd or received in heat exchanger 147 for undergoing indirect heat exchange therein. Similar to the indirect heat exchange taking place in heat exchanger 147, warmed boil-off gas stream 146 is obtained from heat exchanger145 and conveyed to heat exchanger 149 to promote indirect heat exchange with liquefied gas 1 12d received from heat exchanger 147. The temperature of liquefied gas 112d exiting heat exchanger 147 is lower than that within reservoir 1 lOd or heat exchanger 147. Wanned boil-off gas stream 150 exits heat exchanger 149 after promoting cooling of liquefied gas 112d.

[0039] After undergoing intermediate heat exchange with warmed boil-off gas stream 146 in heat exchanger 149, liquefied gas 112d is conveyed directly to heat exchanger 151 to undergo further indirect heat exchange therein. Liquefied gas 112d received by heat exchanger 151 is at a lower temperature than that housed in reservoir HOd or received in heat exchangers 147 or 149 for undergoing indirect heat exchange therein. Heat exchanger 151 receives at least a portion of boil-off gas 116 that has not yet promoted heat exchange within heat exchange cascade 120. As shown, bypass portion 140d of boil-off gas 116 is provided to heat exchanger 151 to promote indirect heat exchange therein. After undergoing indirect heat exchange, thermally equilibrated liquefied gas 112d is conveyed via line 13 Id to manifold line 139 for mixing and transport to mixing unit 160 for mixing with other liquefied gases. Warmed boil-off gas stream 152 exits heat exchanger 151 after promoting cooling of liquefied gas 112d.

[0040] It should also be noted that although heat exchangers 141, 143, 145, 147, 149, and 151 have been depicted as single heat exchangers in FIG. 1, any of the foregoing may be multiple heat exchangers in series and / or parallel, each receiving a portion of boil-off gas 116 in a similar manner to that described above. The designs of heat exchangers 141, 143, 145, 147, 149, and 151 are not believed to be particularly limited, provided that indirect heat exchange is provided. Moreover, the designs of heat exchangers 141, 143, 145, 147, 149, and 151 may be the same or differ.

[0041] Warmed boil-off gas streams 148, 150, and 152 are all at different temperatures and may be pooled to form combined warmed boil-off gas stream 156 that may be flared or preferably undergo subsequent processing to facilitate further use thereof. As shown, combined warmed boil-off gas stream 156 is transported to gas processing unit 158, wherein the gas component obtained from liquefied gas mixture 104 ( / .< ., the most volatile component of liquefied gas mixture 104 and thus predominantly present in boil-off gas 116) may undergo processing to facilitate subsequent use thereof. For example, combined warmed boil-off gas stream 156 may be flared (without further processing) or combusted as fuel gas and / or returned to liquefied gas mixture 104 after undergoing suitable processing. In non-limiting examples, suitable processing of combined warmed boil-off gas stream 156 may include an operation of compressing combined warmed boil-off gas stream 156 to a suitable pressure. Liquefaction may or may not occur during this process. More specific detailsassociated with gas processing unit 158 and the operations taking place therein are provided in FIGS. 2-4, discussed further below.

[0042] After being processed in heat exchange cascade 120, as described above, liquefied gases 112b, 112c, and 112d may all have substantially the same temperature as liquefied gas 112a and liquefied gas mixture 104, such that liquefied gases 112b, 112c, and 112d may now be introduced to liquefied gas mixture 104 without substantially disturbing the thermal equilibrium therein. To this end, thermally equilibrated liquefied gases 112b, 112c, and 112d in manifold line 139 are combined with liquefied gas 112a and conveyed to mixing unit 160. Alternately, liquefied gases 112b, 112c, and 112d may be handled separately (e.g., without combining liquefied gases 112b, 112c, and 112d in manifold line 139) and / or liquefied gases 112b, 112c, and 112d may be introduced directly to mixing unit 160 without being combined with liquefied gas 112a (neither alternative configuration shown). After undergoing sufficient mixing in mixing unit 160, thermally equilibrated liquefied gas blend 162 is introduced to liquefied gas mixture 104 within vessel 102. The composition of thermally equilibrated liquefied gas blend 162 may be chosen to convey or modify one or more physical properties of liquefied gas mixture 104, such as density, heating value, compressibility, or relative volatility. Pre-blending thermally equilibrated liquefied gas blend 162 in mixing unit 160 may aid in ensuring homogeneity once blended with liquefied gas mixture 104 in vessel 102. However, such pre-blending is not required to take place. Pump-around loop 166 or internal circulation (not shown) within vessel 102 may further aid in maintaining homogeneity within liquefied gas mixture 104.

[0043] Liquefied gas mixture 104 may be withdrawn via line 164 as needed to accommodate incoming thermally equilibrated liquefied gas blend 162. The withdrawn liquefied gas mixture may be, for example, gasified or transferred to a pipeline, railcar, transport vehicle, or stored in another location.

[0044] As another safeguard against altering the physical properties of liquefied gas mixture 104 in an undesired way, thermally equilibrated liquefied gas blend 162 may be further monitored with sensor 170. Sensor 170 may represent one or a plurality of sensors which may be configured to assay for composition or one or more physical 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, liquid level, 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 toprovide autonomous or manual process control if thermally equilibrated liquefied gas blend 162 is off-specification in any way. For example, if thermally equilibrated liquefied gas blend 162 is off- specification, the relative amounts of liquefied gases 112a-l 12d being fed to mixing unit 160 may be altered to change the composition in a manner to achieve a desired change in one or more physical properties.

[0045] The systems and methods of the present disclosure may utilize computer systems and other processing means to manage information received from sensor 170 and determine an appropriate response thereto. Specifically, the systems and methods may receive information from sensor 170, and a non-transitory, computer-readable medium containing instructions that, when implemented, cause one or more processors to respond to the information that is received. The instructions may be based in hardware and / or software of the computer system.

[0046] A “non-transitory, computer-readable medium,” as used herein, refers to any non-transitory 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, and EPROM, a FLASH-EPROM, 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.

[0047] 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 sensor 170. 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-processorservers 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.

[0048] FIGS. 2-4 provide further details regarding gas processing unit 158 and use of processed boil-off gas obtained therefrom. Other than the specific details noted below regarding gas processing unit 158 and additional feeds thereto, system and method 200, 300, and 400 (FIGS. 2-4) are otherwise identical to system and method 100 (FIG. 1) and may be better understood by reference thereto. Accordingly, in-common reference characters have been used in FIGS. 2-4 in regard to previously described elements. Such previously described elements are either described in brief below or not mentioned in the following description of these FIGS.

[0049] FIG. 2 is a diagram depicting one possible configuration for gas processing unit 158 in system and method 200. Other than providing details associated with gas processing unit 158, system and method 200 is identical to system and method 100 in FIG. 1. Gas processing unit 158 comprises compressor 202, which receives combined warmed boil-off gas stream 156 and raises the pressure to produce compressed warmed boil-off gas stream 204. Compressed warmed boil-off gas stream 204 is then combusted as fuel gas 210. Fuel gas 210 may be utilized to drive other processes taking place in proximity to system and method 200.

[0050] FIG. 3 is a diagram depicting another possible configuration for gas processing unit 158 in system and method 300. The configuration for gas processing unit 158 in FIG. 3 differs from that depicted in FIG. 2 in that the latter additionally incorporates functionality for recycling at least a portion of combined warmed boil-off gas stream 156 to liquefied gas mixture 104. As in system and method 200 of FIG. 2, gas processing unit 158 in system and method 300 comprises compressor 202, which receives combined warmed boil-off gas stream 156 and raises the pressure to produce compressed warmed boil-off gas stream 204. Optionally, a portion of compressed warmed boil-off gas stream 204 may be combusted as fuel gas 210. Prior to compression, combined warmed boil-off gas stream 156 may initially pass through gas-liquid separator 310 via line 311, such as a knockout drum. Alternately, all or a portion of combined warmed boil-off gas stream 156 may bypass gasliquid separator 310 and travel directly to compressor 202 via line 312. Since boil-off gas 116 is already in the gas state and undergoes further heating in the course of forming combined warmed boil-off gas stream 156, there are usually no liquids requiring separation, and conveying combined warmed boil-off gas stream 156 directly to compressor 202 may be appropriate. As such, gas-liquidseparator 310 may stand idle much of the time, but may be utilized to protect compressor 202 in the event of unexpected liquefaction, such as during start-up or shut-down of compressor 202.

[0051] Upon forming compressed warmed boil-off gas stream 204, a portion thereof may be diverted and combusted as fuel gas 210, as in system and method 200 (FIG. 2). All or a remaining portion of compressed warmed boil-off gas stream 204 may be recycled to liquefied gas mixture 104, preferably after first being provided to mixing unit 160, following indirect heat exchange and liquefaction in recycle heat exchanger 320. Cooling in recycle heat exchanger 320 may be provided by a portion of boil-off gas 116, wherein the portion of boil-off gas 116 has not provided heat exchange within heat exchange cascade 120. As shown in FIG. 3, bypass portion 330 of boil-off gas 116 is removed upstream from heat exchanger 141 within heat exchange cascade 120. Although bypass portion 330 is shown as being removed from the main stream of boil-off gas 116, it is also possible to divert bypass portion 330 from any portion of boil-off gas 116 that has not performed heat exchange in heat exchange cascade 120, such as from either of bypass portions 140b and 140d (see FIG. 1). Moreover, although recycle heat exchanger 320 is shown in FIG. 3 as being a single heat exchanger, it is to be recognized that more than one recycle heat exchanger 320 may be present in any combination of a serial or parallel arrangement, each heat exchanger being cooled by bypass portion 330 of boil-off gas 116 or a stream derived therefrom. One such configuration having multiple heat exchangers within gas processing unit 158 is shown in FIG. 4 below.

[0052] Since boil-off gas 116 is in thermal equilibrium with liquefied gas mixture 104, and bypass portion 330 of boil-off gas 116 has not yet performed heat exchange, bypass portion 330 of boil-off gas 116 may bring compressed warmed boil-off gas stream 204 into thermal equilibrium with liquefied gas mixture 104. Full or partial liquefaction of compressed warmed boil-off gas stream 204 may occur within recycle heat exchanger 320. Preferably, full liquefaction takes place to facilitate reintroduction of boil-off gas 116 to liquefied gas mixture 104. Therefore, thermally equilibrated, reliquefied boil-off gas stream 340 exits recycle heat exchanger 320 and is conveyed to mixing unit 160 for blending with one or more of thermally equilibrated liquefied gases 112a-l 12d. Optionally, all or a portion of thermally equilibrated, re-liquefied boil-off gas stream 340 may bypass mixing unit 160 via branch line 350 for being directly recombined with liquefied gas mixture 104.

[0053] After bypass portion 330 of boil-off gas 116 performs heat exchange in recycle heat exchanger 320, warmed boil-off gas stream 360 exits recycle heat exchanger 320 and is conveyed to gas-liquid separator 310. Gas-liquid separator 310 may remove any condensed liquids 370 that may form prior to recirculation to compressor 202. As warmed boil-off gas 116 is initially in a gas phaseand undergoes warming to form warmed boil-off gas stream 360, the presence of liquid is expected to be transient or minimal, and gas-liquid separator 310 may stand idle much of the time to protect compressor 202 in the event of unexpected liquefaction, such as during start-up or shut-down of compressor 202. Optionally, at least a portion of warmed boil-off gas stream 360 may bypass gasliquid separator 310 via bypass line 361 and progress directly to compressor 202.

[0054] FIG. 4 is a diagram depicting another possible configuration for gas processing unit 158 in system and method 400. System and method 400 in FIG. 4 is similar to system and method 300 in FIG. 3, except heat exchangers 320a and 320b are utilized in system and method 400. As shown in FIG. 4, warmed boil-off gas stream 204 is provided to heat exchanger 320a and subsequently passes to heat exchanger 320b. Bypass portion 330 of boil-off gas 116 is provided to heat exchanger 320b and provides final cooling to warmed boil-off gas stream 204 that has undergone initial cooling in heat exchanger 320a. Partially warmed boil-off gas stream 321 exits heat exchanger 320b after providing final cooling to warmed boil-off gas stream 204. Partially warmed boil-off gas stream 321 still retains cooling capacity for warmed boil-off gas stream 204 and is conveyed to heat exchanger 320a to provide initial cooling for warmed boil-off gas stream 204. Warmed boil-off gas stream 360 exits heat exchanger 320a and is processed in a similar manner to that discussed above for system and method 300. Other aspects relating to system and method 400 are identical to system and method 300 in FIG. 3 and may be better understood by reference thereto.

[0055] Accordingly, methods of the present disclosure may comprise: providing a liquefied gas mixture comprising a first hydrocarbon in liquefied form and one or more additional hydrocarbons in liquefied form, the first hydrocarbon having a higher volatility than any of the one or more additional hydrocarbons; wherein the liquefied gas mixture is in thermal equilibrium; providing a first reservoir containing the first hydrocarbon in liquefied form and one or more second reservoirs individually containing the one or more additional hydrocarbons in liquefied form; wherein the first reservoir and the one or more second reservoirs are in fluid communication with the liquefied gas mixture; obtaining a boil-off gas from the liquefied gas mixture, the boil-off gas being in thermal equilibrium with the liquefied gas mixture; wherein the boil-off gas comprises 80 vol% or greater of the first hydrocarbon in gaseous form; discharging the first hydrocarbon in liquefied form from the first reservoir and the one or more additional hydrocarbons in liquefied form from the one or more second reservoirs at a mixing ratio sufficient to maintain the liquefied gas mixture at one or more specified physical parameters once blended therewith; performing indirect heat exchange between at least a portion of the boil-off gas and the one or more additional hydrocarbons in liquefied form dischargedfrom the one or more second reservoirs until the one or more additional hydrocarbons in liquefied form are in thermal equilibrium with the boil-off gas and the liquefied gas mixture; after bringing the one or more additional hydrocarbons in liquefied form into thermal equilibrium with the boil-off gas and the liquefied gas mixture, combining the one or more additional hydrocarbons in liquefied form with the first hydrocarbon in liquefied form discharged from the first reservoir to form a thermally equilibrated liquefied hydrocarbon blend; and supplying the thermally equilibrated liquefied hydrocarbon blend to the liquefied gas mixture.

[0056] Preferably, the first hydrocarbon in liquefied form and the one or more additional hydrocarbons in liquefied form, after being thermally equilibrated, are blended in a mixing unit to form the thermally equilibrated liquefied hydrocarbon blend that is supplied to the liquefied gas mixture. The mixing unit may comprise an inline mixer, a static mixer, a pressure vessel, a stirred mixer, a circulating mixer, or any combination thereof.

[0057] Warmed boil-off gas may be formed after performing the heat exchange. The warmed boil- off gas may be a) flared, or b) compressed to form compressed warmed boil-off gas. The compressed warmed boil-off gas may be withdrawn as a product, combusted as fuel gas, returned to the liquefied gas mixture, or any combination thereof.

[0058] The methods may further comprise assaying the thermally equilibrated liquefied hydrocarbon blend in-line before supplying the thermally equilibrated liquefied hydrocarbon blend to the liquefied gas mixture; and optionally, altering the mixing ratio if the one or more specified physical parameters are off-specifi cation.

[0059] Preferably, the one or more additional hydrocarbons in liquefied form may comprise at least a second hydrocarbon in liquefied form and a third hydrocarbon in liquefied form, the second hydrocarbon being more volatile than the third hydrocarbon. More preferably, a fourth additional hydrocarbon in liquefied form may be present. The second hydrocarbon in liquefied gas may undergo indirect heat exchange in a first heat exchanger interceding between the second reservoir and the liquefied gas mixture, and the third hydrocarbon in liquefied form may undergo indirect heat exchange sequentially in a second heat exchanger and a third heat exchanger interceding between the third reservoir and the liquefied gas mixture; wherein a first portion of the boil-off gas is supplied to the first heat exchanger and a first bypass portion of the boil-off gas bypasses the first heat exchanger and is supplied to the third heat exchanger; and wherein a first warmed boil-off gas stream is obtained from the first heat exchanger and is conveyed to the second heat exchanger, a second warmed boil-off gas stream is obtained from the second heat exchanger, and a third warmed boil-off gas stream is obtained from the third heat exchanger.

[0060] The methods of the present disclosure may comprise combining at least the second warmed boil-off gas stream and the third warmed boil-off gas stream to form a combined warmed boil-off gas stream; and processing the combined warmed boil-off gas stream. Processing the combined warmed boil-off gas stream may comprise compressing the combined warmed boil-off gas stream to form a compressed warmed boil-off gas stream; and optionally, combusting at least a portion of the compressed warmed boil-off gas stream as fuel gas. Preferably, the methods may comprise performing indirect heat exchange between all or a remaining portion of the compressed warmed boil- off gas stream and an additional bypass portion of the boil-off gas in a recycle heat exchanger, thereby forming compressed, thermally equilibrated boil-off gas that is in thermal equilibrium with the boil- off gas and the liquefied gas mixture; wherein the additional bypass portion of the boil-off gas has not performed indirect heat exchange with any of the one or more additional hydrocarbon gases in liquefied form.

[0061] Embodiments disclosed herein include:

[0062] A. Methods for thermally equilibrating liquefied gases. The methods comprise: providing a liquefied gas mixture comprising a first hydrocarbon in liquefied form and one or more additional hydrocarbons in liquefied form, the first hydrocarbon having a higher volatility than any of the one or more additional hydrocarbons; providing a first reservoir containing the first hydrocarbon in liquefied form and one or more second reservoirs individually containing the one or more additional hydrocarbons in liquefied form; wherein the first reservoir and the one or more second reservoirs are in fluid communication with the liquefied gas mixture; obtaining a boil-off gas from the liquefied gas mixture, the boil-off gas being in thermal equilibrium with the liquefied gas mixture; wherein the boil-off gas comprises 80 vol% or greater of the first hydrocarbon in gaseous form; discharging the first hydrocarbon in liquefied form from the first reservoir and the one or more additional hydrocarbons in liquefied form from the one or more second reservoirs at a mixing ratio sufficient to maintain the liquefied gas mixture at one or more specified physical parameters once blended therewith; performing indirect heat exchange between at least a portion of the boil-off gas and the one or more additional hydrocarbons in liquefied form discharged from the one or more second reservoirs until the one or more additional hydrocarbons in liquefied form are in thermal equilibrium with the boil-off gas and the liquefied gas mixture; after bringing the one or more additional hydrocarbons in liquefied form into thermal equilibrium with the boil-off gas and the liquefied gasmixture, combining the one or more additional hydrocarbons in liquefied form with the first hydrocarbon in liquefied form discharged from the first reservoir to form a thermally equilibrated liquefied hydrocarbon blend; and supplying the thermally equilibrated liquefied hydrocarbon blend to the liquefied gas mixture.

[0063] Embodiment A may have one or more of the following additional elements in any combination:

[0064] Element 1 : wherein the one or more additional hydrocarbons in liquefied form in the one or more second reservoirs are not in thermal equilibrium with the boil-off gas and the liquefied gas mixture.

[0065] Element 2: wherein the first reservoir and the one or more second reservoirs are maintained + / -50% of atmospheric pressure.

[0066] Element 3 : wherein performing indirect heat exchange between at least a portion of the boil- off gas and the one or more additional hydrocarbons in liquefied form comprises cooling the one or more additional hydrocarbons in liquefied form and heating the at least a portion of the boil-off gas to form a warmed boil-off gas.

[0067] Element 4: wherein the warmed boil-off gas is a) flared, or b) compressed to form compressed warmed boil-off gas; wherein the compressed warmed boil-off gas is withdrawn as a product, combusted as fuel gas, returned to the liquefied gas mixture, or any combination thereof.

[0068] Element 5: wherein the one or more additional hydrocarbons in liquefied form comprise at least a second hydrocarbon in liquefied form and a third hydrocarbon in liquefied form, the second hydrocarbon being more volatile than the third hydrocarbon.

[0069] Element 6: wherein the second hydrocarbon in liquefied form undergoes indirect heat exchange in a first heat exchanger interceding between the second reservoir and the liquefied gas mixture, and the third hydrocarbon in liquefied form undergoes indirect heat exchange sequentially in a second heat exchanger and a third heat exchanger interceding between the third reservoir and the liquefied gas mixture; wherein a first portion of the boil-off gas is supplied to the first heat exchanger and a first bypass portion of the boil-off gas bypasses the first heat exchanger and is supplied to the third heat exchanger; and wherein a first warmed boil-off gas stream is obtained from the first heat exchanger and is conveyed to the second heat exchanger, a second warmed boil-off gas stream is obtained from the second heat exchanger, and a third warmed boil-off gas stream is obtained from the third heat exchanger.

[0070] Element 7: wherein the one or more additional hydrocarbons in liquefied form further comprise a fourth hydrocarbon in liquefied form, the third hydrocarbon being more volatile than the fourth hydrocarbon, and the fourth hydrocarbon in liquefied form undergoes indirect heat exchange sequentially in a fourth heat exchanger, fifth heat exchanger, and a sixth heat exchanger interceding between the fourth reservoir and the liquefied gas mixture; wherein the second warmed boil-off gas stream is obtained from the second heat exchanger and is conveyed to the fourth heat exchanger, the third warmed boil-off gas stream is obtained from the third heat exchanger and is conveyed to the fifth heat exchanger, and a second bypass portion of the boil-off gas bypasses the third heat exchanger and is supplied to the sixth heat exchanger; and wherein a fourth warmed boil-off gas stream is obtained from the fourth heat exchanger, a fifth warmed boil-off gas stream is obtained from the fifth heat exchanger, and a sixth warmed boil-off gas stream is obtained from the sixth heat exchanger.

[0071] Element 8: wherein the method further comprises combining the fourth warmed boil-off gas stream, the fifth warmed boil-off gas stream, and the sixth warmed boil-off gas stream to form a combined warmed boil-off gas stream; and processing the combined warmed boil-off gas stream.

[0072] Element 9: wherein the method further comprises combining the second warmed boil-off gas stream and the third warmed boil-off gas stream to form a combined warmed boil-off gas stream; and processing the combined warmed boil-off gas stream.

[0073] Element 10: wherein processing the combined warmed boil-off gas stream comprises: compressing the combined warmed boil-off gas stream to form a compressed warmed boil-off gas stream; and optionally, combusting at least a portion of the compressed warmed boil-off gas stream as fuel gas.

[0074] Element 11 : wherein the method further comprises performing indirect heat exchange between all or a remaining portion of the compressed warmed boil-off gas stream and an additional bypass portion of the boil-off gas in a recycle heat exchanger, thereby forming compressed, thermally equilibrated boil-off gas that is in thermal equilibrium with the boil-off gas and the liquefied gas mixture; wherein the additional bypass portion of the boil-off gas has not performed indirect heat exchange with any of the one or more additional hydrocarbon gases in liquefied form.

[0075] Element 12: wherein the compressed, thermally equilibrated boil-off gas is in at least partially liquefied form.

[0076] Element 13: wherein the method further comprises returning the compressed, thermally equilibrated boil-off gas to the liquefied gas mixture.

[0077] Element 14: wherein the compressed, thermally equilibrated boil-off gas is combined with the thermally equilibrated liquefied hydrocarbon blend before being returned to the liquefied gas mixture.

[0078] Element 15: wherein the first hydrocarbon in liquefied form and the one or more additional hydrocarbons in liquefied form, after being thermally equilibrated, are blended in a mixing unit to form the thermally equilibrated liquefied hydrocarbon blend that is supplied to the liquefied gas mixture.

[0079] Element 16: wherein the mixing unit comprises one or more of an inline mixer, a static mixer, a pressure vessel, a stirred mixer, a circulating mixer, or any combination thereof.

[0080] Element 17: wherein the one or more specified physical parameters comprise one or more of density, heating value, compressibility, relative volatility, temperature, pressure, liquid level, flow rate, and any combination thereof.

[0081] Element 18: wherein the method further comprises assaying the thermally equilibrated liquefied hydrocarbon blend in-line before supplying the thermally equilibrated liquefied hydrocarbon blend to the liquefied gas mixture; and optionally, altering the mixing ratio if the one or more specified physical parameters are off-specification.

[0082] Element 19: wherein the liquefied gas mixture comprises natural gas.

[0083] Element 20A: wherein the first hydrocarbon in liquefied form comprises methane and the one or more additional hydrocarbons in liquefied form comprise one or more of ethane, propane, and butane.

[0084] Element 20B: wherein the first hydrocarbon in liquefied form comprises methane and the one or more additional hydrocarbons in liquefied form comprise ethane, propane, and butane.

[0085] Element 21 : wherein the liquefied gas mixture is in thermal equilibrium.

[0086] By way of non-limiting example, exemplary combinations applicable to A include, but are not limited to: 1 and 2; 1 and 3; 1, 3, and 4; 1 and 5; 1, 5, and 6; 1, and 5-7; 1, and 5-8; 1, 5-7, and 9;1, 5-8, and 10; 1, 5-8, 10, and 11; 1, 5-7, 10, and 11; 1, 5-8, 10, 11, 13, and optionally 14; 1, 5-7, 10, 11, 13, and optionally 14; 1 and 15; 1, 15, and 16; 1 and 17; 1, 17, and 18; 1 and 19; 1, and 20A or 20B; 1 and 21; 2 and 3; 2-4; 2 and 5; 2, 5, and 6; 2, and 5-7; 2, and 5-8; 2, 5-7, and 9; 2, 5-8, and 10;2, 5-8, 10, and 11; 2, 5-7, 10, and 11; 2, 5-8, 10, 11, 13, and optionally 14; 2, 5-7, 10, 11, 13, and optionally 14; 2 and 15; 2, 15, and 16; 2 and 17; 2, 17, and 18; 2 and 19; 2, and 20A or 20B; 2 and 21; 3 and 4; 3 and 5; 3, 15, and 16; 3 and 17; 3, 17, and 18; 3 and 19; 3, and 20A or 20B; 3 and 21; 4 and 5; 4, 15, and 16; 4 and 17; 4, 17, and 18; 4 and 19; 4, and 20A or 20B; 4 and 21; 5 and 6; 5-7; 5-8; 5-7, and 10; 5-8, and 10; 5-7, 10, and 1 1 ; 5-8, 10, and 1 1 ; 5-7, 10, 1 1, 13, and optionally 14; 5-8, 10, 11, 13, and optionally 14; 5 and 15; 5, 15, and 16; 5 and 17; 5, 17, and 18; 5 and 19; 5, and 20A or 20B; 5 and 21; 15 and 16; 15 and 17; 15, 17, and 18; 15 and 19; 15, and 20A or 20B; 15 and 21; 17 and 18; 17 and 19; 17-19; 17, and 20A or 20B; 17 and 21; 18 and 19; 18, and 20A or 20B; 18 and 21; 19, and 20A or 20B; and 19 and 21. Any of 5 and 6; 5-7; 5-8; 5-7, and 10; 5-8, and 10; 5-7, 10, and 11; 5-8, 10, and 11; 5-7, 10, 11, 13, and optionally 14; 5-8, 10, 11, 13, and optionally 14 may be optionally further combined with 15; 15 and 16; 17; 17 and 18; 19; 20A or 20B, or 21.

[0087] Additional embodiments disclosed herein include those defined by the following nonlimiting clauses:

[0088] Clause 1. A method comprising: providing a liquefied gas mixture comprising a first hydrocarbon in liquefied form and one or more additional hydrocarbons in liquefied form, the first hydrocarbon having a higher volatility than any of the one or more additional hydrocarbons; providing a first reservoir containing the first hydrocarbon in liquefied form and one or more second reservoirs individually containing the one or more additional hydrocarbons in liquefied form; wherein the first reservoir and the one or more second reservoirs are in fluid communication with the liquefied gas mixture; obtaining a boil-off gas from the liquefied gas mixture, the boil-off gas being in thermal equilibrium with the liquefied gas mixture; wherein the boil-off gas comprises 80 vol% or greater of the first hydrocarbon in gaseous form; discharging the first hydrocarbon in liquefied form from the first reservoir and the one or more additional hydrocarbons in liquefied form from the one or more second reservoirs at a mixing ratio sufficient to maintain the liquefied gas mixture at one or more specified physical parameters once blended therewith; performing indirect heat exchange between at least a portion of the boil-off gas and the one or more additional hydrocarbons in liquefied form discharged from the one or more second reservoirs until the one or more additional hydrocarbons in liquefied form are in thermal equilibrium with the boil-off gas and the liquefied gas mixture; after bringing the one or more additional hydrocarbons in liquefied form into thermal equilibrium with the boil-off gas and the liquefied gas mixture, combining the one or more additionalhydrocarbons in liquefied form with the first hydrocarbon in liquefied form discharged from the first reservoir to form a thermally equilibrated liquefied hydrocarbon blend; and supplying the thermally equilibrated liquefied hydrocarbon blend to the liquefied gas mixture.

[0089] Clause 2. The method of clause 1, wherein the one or more additional hydrocarbons in liquefied form in the one or more second reservoirs are not in thermal equilibrium with the boil-off gas and the liquefied gas mixture.

[0090] Clause 3. The method of clause 1 or clause 2, wherein the first reservoir and the one or more second reservoirs are maintained + / -50% of atmospheric pressure.

[0091] Clause d. The method of any one of clauses 1-3, wherein performing indirect heat exchange between at least a portion of the boil-off gas and the one or more additional hydrocarbons in liquefied form comprises cooling the one or more additional hydrocarbons in liquefied form and heating the at least a portion of the boil-off gas to form a warmed boil-off gas.

[0092] Clause 5. The method of clause 4, wherein the warmed boil-off gas is a) flared, or b) compressed to form compressed warmed boil-off gas; wherein the compressed warmed boil-off gas is withdrawn as a product, combusted as fuel gas, returned to the liquefied gas mixture, or any combination thereof.

[0093] Clause 6. The method of any one of clauses 1-5, wherein the one or more additional hydrocarbons in liquefied form comprise at least a second hydrocarbon in liquefied form and a third hydrocarbon in liquefied form, the second hydrocarbon being more volatile than the third hydrocarbon.

[0094] Clause 7. The method of clause 6, wherein the second hydrocarbon in liquefied form undergoes indirect heat exchange in a first heat exchanger interceding between the second reservoir and the liquefied gas mixture, and the third hydrocarbon in liquefied form undergoes indirect heat exchange sequentially in a second heat exchanger and a third heat exchanger interceding between the third reservoir and the liquefied gas mixture; wherein a first portion of the boil-off gas is supplied to the first heat exchanger and a first bypass portion of the boil-off gas bypasses the first heat exchanger and is supplied to the third heat exchanger; and wherein a first warmed boil-off gas stream is obtained from the first heat exchanger and is conveyed to the second heat exchanger, a second warmed boil-off gas stream is obtained from thesecond heat exchanger, and a third warmed boil-off gas stream is obtained from the third heat exchanger.

[0095] Clause 8. The method of clause 7, wherein the one or more additional hydrocarbons in liquefied form further comprise a fourth hydrocarbon in liquefied form, the third hydrocarbon being more volatile than the fourth hydrocarbon, and the fourth hydrocarbon in liquefied form undergoes indirect heat exchange sequentially in a fourth heat exchanger, fifth heat exchanger, and a sixth heat exchanger interceding between the fourth reservoir and the liquefied gas mixture; wherein the second warmed boil-off gas stream is obtained from the second heat exchanger and is conveyed to the fourth heat exchanger, the third warmed boil-off gas stream is obtained from the third heat exchanger and is conveyed to the fifth heat exchanger, and a second bypass portion of the boil-off gas bypasses the third heat exchanger and is supplied to the sixth heat exchanger; and wherein a fourth warmed boil-off gas stream is obtained from the fourth heat exchanger, a fifth warmed boil-off gas stream is obtained from the fifth heat exchanger, and a sixth warmed boil- off gas stream is obtained from the sixth heat exchanger.

[0096] Clause 9. The method of clause 8, further comprising: combining the fourth warmed boil-off gas stream, the fifth warmed boil-off gas stream, and the sixth warmed boil-off gas stream to form a combined warmed boil-off gas stream; and processing the combined warmed boil-off gas stream.

[0097] Clause 10. The method of clause 7, further comprising: combining the second warmed boil-off gas stream and the third warmed boil-off gas stream to form a combined warmed boil-off gas stream; and processing the combined warmed boil-off gas stream.

[0098] Clause 11. The method of clause 9 or clause 10, wherein processing the combined warmed boil-off gas stream comprises: compressing the combined warmed boil-off gas stream to form a compressed warmed boil- off gas stream; and optionally, combusting at least a portion of the compressed warmed boil-off gas stream as fuel gas.

[0099] Clause 12. The method of clause 10 or clause 11, further comprising: performing indirect heat exchange between all or a remaining portion of the compressed warmed boil-off gas stream and an additional bypass portion of the boil-off gas in a recycle heatexchanger, thereby forming compressed, thermally equilibrated boil-off gas that is in thermal equilibrium with the boil-off gas and the liquefied gas mixture; wherein the additional bypass portion of the boil-off gas has not performed indirect heat exchange with any of the one or more additional hydrocarbon gases in liquefied form.

[0100] Clause 13. The method of clause 12, wherein the compressed, thermally equilibrated boil- off gas is in at least partially liquefied form.

[0101] Clause 14. The method of clause 12 or clause 13, further comprising: returning the compressed, thermally equilibrated boil-off gas to the liquefied gas mixture.

[0102] Clause 15. The method of clause 14, wherein the compressed, thermally equilibrated boil- off gas is combined with the thermally equilibrated liquefied hydrocarbon blend before being returned to the liquefied gas mixture.

[0103] Clause 16. The method of any one of clauses 1-15, wherein the first hydrocarbon in liquefied form and the one or more additional hydrocarbons in liquefied form, after being thermally equilibrated, are blended in a mixing unit to form the thermally equilibrated liquefied hydrocarbon blend that is supplied to the liquefied gas mixture.

[0104] Clause 17. The method of clause 16, wherein the mixing unit comprises one or more of an inline mixer, a static mixer, a pressure vessel, a stirred mixer, a circulating mixer, or any combination thereof.

[0105] Clause 18. The method of any one of clauses 1-17, wherein the one or more specified physical parameters comprise one or more of density, heating value, compressibility, relative volatility, temperature, pressure, liquid level, flow rate, and any combination thereof.

[0106] Clause 19. The method of any one of clauses 1-18, further comprising: assaying the thermally equilibrated liquefied hydrocarbon blend in-line before supplying the thermally equilibrated liquefied hydrocarbon blend to the liquefied gas mixture; and optionally, altering the mixing ratio if the one or more specified physical parameters are off- specification.

[0107] Clause 20. The method of any one of clauses 1-19, wherein the liquefied gas mixture comprises natural gas.

[0108] Clause 21. The method of any one of clauses 1-20, wherein the first hydrocarbon in liquefied form comprises methane and the one or more additional hydrocarbons in liquefied form comprise one or more of ethane, propane, and butane.

[0109] Clause 22. The method of any one of clauses 1-21, wherein the first hydrocarbon in liquefied form comprises methane and the one or more additional hydrocarbons in liquefied form comprise ethane, propane, and butane.

[0110] Clause 23. The method of any one of clauses 1-22, wherein the liquefied gas mixture is in thermal equilibrium.

[0111] All documents described herein are incorporated by reference herein for purposes of all 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” preceding the recitation of the composition, element, or elements and vice versa.

[0112] Unless otherwise indicated, all numbers expressing quantities 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.

[0113] 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 theirplain, 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.

[0114] One or more illustrative embodiments are presented herein. Not all features of a physical implementation are described or shown in this application for 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.

[0115] Therefore, 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:

1. A method comprising: providing a liquefied gas mixture comprising a first hydrocarbon in liquefied form and one or more additional hydrocarbons in liquefied form, the first hydrocarbon having a higher volatility than any of the one or more additional hydrocarbons; providing a first reservoir containing the first hydrocarbon in liquefied form and one or more second reservoirs individually containing the one or more additional hydrocarbons in liquefied form; wherein the first reservoir and the one or more second reservoirs are in fluid communication with the liquefied gas mixture; obtaining a boil-off gas from the liquefied gas mixture, the boil-off gas being in thermal equilibrium with the liquefied gas mixture; wherein the boil-off gas comprises 80 vol% or greater of the first hydrocarbon in gaseous form; discharging the first hydrocarbon in liquefied form from the first reservoir and the one or more additional hydrocarbons in liquefied form from the one or more second reservoirs at a mixing ratio sufficient to maintain the liquefied gas mixture at one or more specified physical parameters once blended therewith; performing indirect heat exchange between at least a portion of the boil-off gas and the one or more additional hydrocarbons in liquefied form discharged from the one or more second reservoirs until the one or more additional hydrocarbons in liquefied form are in thermal equilibrium with the boil-off gas and the liquefied gas mixture; after bringing the one or more additional hydrocarbons in liquefied form into thermal equilibrium with the boil-off gas and the liquefied gas mixture, combining the one or more additional hydrocarbons in liquefied form with the first hydrocarbon in liquefied form discharged from the first reservoir to form a thermally equilibrated liquefied hydrocarbon blend; and supplying the thermally equilibrated liquefied hydrocarbon blend to the liquefied gas mixture.

2. The method of claim 1, wherein the one or more additional hydrocarbons in liquefied form in the one or more second reservoirs are not in thermal equilibrium with the boil-off gas and the liquefied gas mixture.

3. The method of claim 1 or claim 2, wherein the first reservoir and the one or more second reservoirs are maintained + / -50% of atmospheric pressure.

4. The method of any one of claims 1-3, wherein performing indirect heat exchange between at least a portion of the boil-off gas and the one or more additional hydrocarbons in liquefied form comprises cooling the one or more additional hydrocarbons in liquefied form and heating the at least a portion of the boil-off gas to form a warmed boil-off gas.

5. The method of claim 4, wherein the warmed boil-off gas is a) flared, or b) compressed to form compressed warmed boil-off gas; wherein the compressed warmed boil-off gas is withdrawn as a product, combusted as fuel gas, returned to the liquefied gas mixture, or any combination thereof.

6. The method of any one of claims 1-5, wherein the one or more additional hydrocarbons in liquefied form comprise at least a second hydrocarbon in liquefied form and a third hydrocarbon in liquefied form, the second hydrocarbon being more volatile than the third hydrocarbon.

7. The method of claim 6, wherein the second hydrocarbon in liquefied form undergoes indirect heat exchange in a first heat exchanger interceding between the second reservoir and the liquefied gas mixture, and the third hydrocarbon in liquefied form undergoes indirect heat exchange sequentially in a second heat exchanger and a third heat exchanger interceding between the third reservoir and the liquefied gas mixture; wherein a first portion of the boil-off gas is supplied to the first heat exchanger and a first bypass portion of the boil-off gas bypasses the first heat exchanger and is supplied to the third heat exchanger; and wherein a first warmed boil-off gas stream is obtained from the first heat exchanger and is conveyed to the second heat exchanger, a second warmed boil-off gas stream isobtained from the second heat exchanger, and a third warmed boil-off gas stream is obtained from the third heat exchanger.

8. The method of claim 7, wherein the one or more additional hydrocarbons in liquefied form further comprise a fourth hydrocarbon in liquefied form, the third hydrocarbon being more volatile than the fourth hydrocarbon, and the fourth hydrocarbon in liquefied form undergoes indirect heat exchange sequentially in a fourth heat exchanger, fifth heat exchanger, and a sixth heat exchanger interceding between the fourth reservoir and the liquefied gas mixture; wherein the second warmed boil-off gas stream is obtained from the second heat exchanger and is conveyed to the fourth heat exchanger, the third warmed boil-off gas stream is obtained from the third heat exchanger and is conveyed to the fifth heat exchanger, and a second bypass portion of the boil-off gas bypasses the third heat exchanger and is supplied to the sixth heat exchanger; and wherein a fourth warmed boil-off gas stream is obtained from the fourth heat exchanger, a fifth warmed boil-off gas stream is obtained from the fifth heat exchanger, and a sixth warmed boil-off gas stream is obtained from the sixth heat exchanger.

9. The method of claim 8, further comprising: combining the fourth warmed boil-off gas stream, the fifth warmed boil-off gas stream, and the sixth warmed boil-off gas stream to form a combined warmed boil-off gas stream; and processing the combined warmed boil-off gas stream.

10. The method of claim 7, further comprising: combining the second warmed boil-off gas stream and the third warmed boil-off gas stream to form a combined warmed boil-off gas stream; and processing the combined warmed boil-off gas stream.

11. The method of claim 9 or claim 10, wherein processing the combined warmed boil-off gas stream comprises: compressing the combined warmed boil-off gas stream to form a compressedwarmed boil-off gas stream; and optionally, combusting at least a portion of the compressed warmed boil-off gas stream as fuel gas.

12. The method of claim 10 or claim 11, further comprising: performing indirect heat exchange between all or a remaining portion of the compressed warmed boil -off gas stream and an additional bypass portion of the boil-off gas in a recycle heat exchanger, thereby forming compressed, thermally equilibrated boil -off gas that is in thermal equilibrium with the boil-off gas and the liquefied gas mixture; wherein the additional bypass portion of the boil-off gas has not performed indirect heat exchange with any of the one or more additional hydrocarbon gases in liquefied form.

13. The method of claim 12, further comprising: returning the compressed, thermally equilibrated boil-off gas to the liquefied gas mixture.

14. The method of any one of claims 1-13, wherein the first hydrocarbon in liquefied form and the one or more additional hydrocarbons in liquefied form, after being thermally equilibrated, are blended in a mixing unit to form the thermally equilibrated liquefied hydrocarbon blend that is supplied to the liquefied gas mixture.

15. The method of claim 14, wherein the mixing unit comprises one or more of an inline mixer, a static mixer, a pressure vessel, a stirred mixer, a circulating mixer, or any combination thereof.

16. The method of any one of claims 1-15, wherein the one or more specified physical parameters comprise one or more of density, heating value, compressibility, relative volatility, temperature, pressure, liquid level, flow rate, and any combination thereof.

17. The method of any one of claims 1-16, further comprising: assaying the thermally equilibrated liquefied hydrocarbon blend in-line beforesupplying the thermally equilibrated liquefied hydrocarbon blend to the liquefied gas mixture; and optionally, altering the mixing ratio if the one or more specified physical parameters are off-specification.

18. The method of any one of claims 1-17, wherein the liquefied gas mixture comprises natural gas.

19. The method of any one of claims 1-18, wherein the first hydrocarbon in liquefied form comprises methane and the one or more additional hydrocarbons in liquefied form comprise one or more of ethane, propane, and butane.

20. The method of any one of claims 1-19, wherein the first hydrocarbon in liquefied form comprises methane and the one or more additional hydrocarbons in liquefied form comprise ethane, propane, and butane.

21. The method of any one of claims 1-20, wherein the liquefied gas mixture is in thermal equilibrium.

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