Systems and Methods for Liquefaction of a Gas by Hybrid Heat Exchange

Abstract

A liquefaction system for removing heat from a process fluid to condense the process fluid, the liquefaction system including a primary heat exchanger configured to remove heat from the process fluid via heat exchange with one or more refrigerants, a compressor configured to compress the one or more refrigerants, a first secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient air, and a second secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient water.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national stage application of PCT/IB2018/000754 filed May 25, 2018, and entitled “Systems and Methods for Liquefaction of a Gas by Hybrid Heat Exchange,” which claims priority to GB Patent Application Number 1708515.0, filed May 26, 2017 and entitled “Systems and Methods for Liquefaction of a Gas by Hybrid Heat Exchange”, the disclosures of which are hereby incorporated herein by reference as if reproduced in their entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

TECHNICAL FIELD

This disclosure relates generally to systems and methods for condensing a gas into a liquid. More particularly, this disclosure relates to systems and methods for condensing a gas via hybrid cooling comprising transferring heat from a common fluid to two different heat sinks. Still more particularly, this disclosure relates to systems and methods that employ hybrid cooling for the production of liquid natural gas (LNG) via the liquefaction of natural gas.

BACKGROUND

For reduced volume during transportation and storage, produced natural gas is often converted from a gaseous phase into a liquid phase, referred to as liquid natural gas (LNG), by a liquefaction process. The liquefaction process achieves the phase change through a series of heat exchangers, aided by a refrigerant that transfers heat from the natural gas to a “heat sink,” such as ambient air or the ocean.

Liquefaction processes employ heat exchangers to reject the heat absorbed by the refrigerant from the natural gas feed stream. Typically, these heat exchangers reject heat to a single “heat sink,” which may be, for example, a fluid such as either ambient air or locally-sourced water (i.e. one or the other, not both). LNG liquefaction performance (e.g. thermodynamic efficiency and capacity) can be strongly influenced by the temperature of the heat sink: the cooler the heat sink, the better the process efficiency and capacity. Depending on location, the temperature of the heat sink may vary considerably between different seasons of the year. In such cases, an LNG liquefaction plant may have highly variable performance from season-to-season.

SUMMARY

Herein disclosed is a liquefaction system for removing heat from a process fluid to condense the process fluid, the liquefaction system comprising: a primary heat exchanger configured to remove heat from the process fluid via heat exchange with one or more refrigerants; a compressor configured to compress the one or more refrigerants; a first secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient air; and a second secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient water.

Also disclosed herein is a method for liquefying a process fluid using a refrigerant, the method comprising: (a) transferring heat from the process fluid to the refrigerant in a primary heat exchanger; (b) flowing the refrigerant from the primary heat exchanger; (c) compressing the refrigerant stream after (b); and (d) removing heat from the process fluid via a first heat exchanger operable to effect heat exchange with ambient air and a second heat exchanger operable to effect heat exchange with ambient water

Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the disclosed exemplary embodiments, reference will now be made to the accompanying drawings, wherein:

FIG. 1 is a schematic view of an embodiment of a liquefaction system in accordance with the principles disclosed herein;

FIG. 2 is a graph illustrating the LNG production from three different liquefaction systems over the course of a year; and

FIG. 3 is a schematic view of an embodiment of a liquefaction system in accordance with the principles disclosed herein.

DETAILED DESCRIPTION

The following description is exemplary of certain embodiments of the disclosure. One of ordinary skill in the art will understand that the following description has broad application, and the discussion of any embodiment is meant to be exemplary of that embodiment, and is not intended to suggest in any way that the scope of the disclosure, including the claims, is limited to that embodiment.

The figures are not necessarily drawn to-scale. Certain features and components disclosed herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. In some of the figures, in order to improve clarity and conciseness, one or more components or aspects of a component may be omitted or may not have reference numerals identifying the features or components. In addition, within the specification, including the drawings, like or identical reference numerals may be used to identify common or similar elements.

As previously described, produced natural gas is commonly condensed from a gas phase into liquid natural gas (LNG) by a liquefaction process. A typical liquefaction process includes a main cryogenic heat exchanger that transfers heat from a feed stream of natural gas to a refrigerant, condensing the feed stream into LNG. The refrigerant is usually passed through a series of compressors and heat exchangers that cool or condense the refrigerant after compression. Refrigerant pressure is dropped, through a valve or expander, prior to passing through the main cryogenic heat exchanger. Many variants of the basic liquefaction process exist, including enhancements such as end flash systems and provisions to separate and extract heavier liquid components. All liquefaction processes employ heat exchangers to reject the heat absorbed by the refrigerant from the natural gas feed stream. Typically, these heat exchangers reject heat to a same, single “heat sink,” which may be, for example, a fluid such as either ambient air or locally-sourced water (i.e. one or the other, not both). As utilized herein, the term ‘ambient’ means at the surrounding environmental temperature.

Without being limited by this or any particular theory, LNG liquefaction performance (e.g. thermodynamic efficiency and capacity) is strongly influenced by the temperature of the heat sink. The cooler the heat sink, the better the process efficiency and capacity. Depending on location, the temperature of the heat sink may vary considerably between different seasons of the year. In such cases, an LNG liquefaction plant may have highly variable performance from season-to-season. For example, a plant located in a non-equatorial climate, such as a temperate or an artic region, may experience significant variations in ambient temperature throughout a year. In such cases, the LNG liquefaction plant may not achieve maximum performance in all seasons. For example, a liquefaction plant that uses sea water as a heat sink may achieve stable, consistent performance throughout the year, but may fail to achieve optimized performance in cold seasons when cooler heat sinks such as ambient air are available.

Cooling with water and cooling with air each have advantages and disadvantages. Cooling with water normally achieves colder process temperatures, which are beneficial, but can have an adverse impact on marine environments due to the large volume of water circulated. Cooling with air has a reduced environmental impact but usually requires a large physical footprint, which may be prohibitive in some situations where space is limited (e.g., on an offshore facility).

Herein disclosed are embodiments of hybrid cooling systems and methods that combine removing heat directly or indirectly from a process fluid (e.g., directly via heat exchange between the process fluid and the heat sinks or indirectly via heat exchange between a refrigerant and the heat sinks) via heat exchange with multiple heat sinks (e.g., with ambient air and with ambient water). The hybrid cooling of this disclosure may thus comprise heat exchange with a first heat sink (e.g., ambient air) that is or is not effected in series with heat exchange with a second heat sink (e.g., ambient water). As will be described in more detail below, embodiments of systems and methods described herein utilize hybrid cooling for natural gas liquefaction by employing multiple heat exchangers in series. These modifications offer the potential to achieve process improvements. As an example, various embodiments described herein include systems and methods for using multiple heat sinks concurrently with the goal of improving the rejection of heat during liquefaction of an initially gaseous process fluid. At one or more chosen points in the process, heat is transferred from the process fluid or from a refrigerant to the multiple heat sinks rather than transferring heat to a single heat sink at that point in the process. Alternately, heat is rejected from one point in the process to one heat sink, and from another point in the process to another heat sink. Although the concepts described herein are applicable to the liquefaction of a variety of fluids, in embodiments described herein, the fluid subjected to the liquefaction process is natural gas.

Referring now to FIG. 1, an embodiment of a liquefaction train or system 100 is shown. In this embodiment, system 100 includes a process fluid system 102 and a gaseous refrigerant system 104. Systems 102, 104 are joined by a heat exchanger 106, which may be considered a subcomponent of both systems 102, 104. Heat exchanger 106 may be referred to as a “primary heat exchanger” because it transfers heat directly from a process fluid to a refrigerant. In this example, the process fluid is natural gas. Thus, the primary heat exchanger 106 includes a process passage to conduct the natural gas and a refrigerant passage to conduct the refrigerant. In this embodiment, heat exchanger 106 includes one process passage 107 that flows natural gas and two refrigerant passages 108, 109 that flow refrigerant. Passage 109 is counter flow as compared to passages 107, 108. Within heat exchanger 106, fluid passages 107, 108, 109 are fluidly isolated from each other.

Process fluid system 102 includes a gas feed line 111, an air-cooled heat exchanger 112, a water-cooled heat exchanger 114 connected in series with heat exchanger 112, and a process fluid feed line 113 extending from heat exchanger 114 to the inlet of process passage 107. The terms ‘air-cooled heat exchanger’ and ‘air cooler’ are used interchangeably herein; the terms ‘water-cooled heat exchanger’ and ‘water cooler’ are used interchangeably herein. A process fluid discharge line 115 extends from the outlet of process passage 107. Discharge line 115 receives process fluid (e.g., liquefied natural gas) from process passage 107, includes a valve 116, and delivers the process fluid to a storage location or to a vehicle loading location. The components of system 102 are configured to remove heat from the natural gas while the natural gas flows from feed line 111 to discharge line 115.

Similar to heat exchanger 106, heat exchangers 112, 114 are primary heat exchangers because they remove heat directly from the process fluid (e.g. the natural gas) prior to the liquefaction process. Heat exchangers 112, 114 may be described as forming a first hybrid heat exchanger group because (a) they transfer heat from a common fluid (natural gas) to two different heat sinks (air and water, respectively); and (b) the common fluid flows directly between heat exchangers 112, 114. Heat exchanger 112 transfers heat to a first heat sink, which in this embodiment is ambient air, while heat exchanger 114 transfers heat to a second heat sink, which in this embodiment is a locally-sourced supply of water.

Referring still to FIG. 1, refrigerant system 104 circulates a gaseous phase refrigerant. In this embodiment, the refrigerant is gaseous nitrogen. Refrigerant system 104 includes a refrigerant supply line 121 extending to the inlet of refrigerant passage 108 in heat exchanger 106, a refrigerant line 123 extending from an outlet at an intermediate location along passage 108 to the high pressure inlet of a higher temperature or ‘warm’ expander 124, and a refrigerant line 125 extending from the low pressure outlet of expander 124 to an inlet at an intermediate location along refrigerant passage 109. In addition, system 104 further includes a refrigerant line 127 extending from the outlet of passage 108 to a relatively lower (relative to warm expander 124) temperature or ‘cold’ expander 128 and a refrigerant line 129 extending from the outlet of lower temperature expander to the inlet of passage 109.

Expander 124 is coupled to a compressor 132 with a shaft 126, which transfers mechanical energy to compressor 132. Expander 128 is coupled to a compressor 134 with a shaft 130, which transfers mechanical energy to compressor 134. Thus, shafts 126, 130 drive the operation of compressors 132, 134, respectively. As needed, additional power may be supplied to either of the compressors 132, 134 by a motor or another external source.

Referring still to FIG. 1, a refrigerant line 131 extends from the outlet of passage 109 to the low pressure inlet of compressor 132, and a refrigerant discharge line 135 is in fluid communication with the high pressure outlets of both compressors 132, 134 and extends to an air-cooled heat exchanger 136. A water-cooled heat exchanger 138 is serially connected to and downstream of air-cooled heat exchanger 136, and a refrigerant line 139 extends from the outlet of water-cooled heat exchanger 138 to the low pressure inlet of a compressor 140. The high pressure outlet of compressor 140 is coupled to an air-cooled heat exchanger 142 with a refrigerant line 141. A water-cooled heat exchanger 144 is serially connected to and downstream of air-cooled heat exchanger 142. Line 121 previously described extends from the outlet of water-cooled heat exchanger 144 to the inlet of passage 108.

Heat exchangers 136, 138 are examples of secondary heat exchangers because they transfer heat to or from the refrigerant, in this instance removing heat from the refrigerant. These and other secondary heat exchangers in system 104 transfer heat to or from the process fluid indirectly, through the refrigerant via heat exchanger 106. Heat exchangers 136, 138 may be described as forming another hybrid heat exchanger group because (1) they transfer heat between a common fluid (refrigerant) and two different heat sinks (air and water, respectively); and (2) the common fluid flows directly between heat exchangers 136, 138. Air-cooled heat exchanger 136 transfers heat to the first heat sink, which is ambient air in this embodiment, while water-cooled heat exchanger 138 transfers heat to the second heat sink, which is locally-sourced supply of water. Similar to heat exchangers 136, 138, heat exchangers 142, 144 are secondary heat exchangers and form another hybrid heat exchanger group, positioned in sequence to transfer heat between the refrigerant and two different heat sinks. Air-cooled heat exchanger 142 transfers heat to the first heat sink, and water-cooled heat exchanger 144 transfers heat to the second heat sink.

Embodiments of system 100, and hybrid cooling in general, may offer particular advantages in geographic regions in which (a) the temperature of the ambient air (e.g. the first heat sink) has a wide seasonal variation between winter and summer; and (b) the temperature of the local water (e.g., the second heat sink) is colder than the ambient air during part of the year (e.g., summer). To optimize system 100 and the potential benefits of hybrid cooling in such geographic regions, air-coolers 112, 136, 142 are used to reject heat throughout the year, and these same air-coolers 112, 136, 142 are supplemented by water-coolers 114, 138, 144 when the temperature of the ambient air (e.g. the first heat sink) is above the temperature of the local water (e.g., the second heat sink). As will be described in more detail below, operating in this manner offers the potential to increase the efficiency and/or production capacity of liquefaction system 100 as compared to a conventional system that uses only air or only water cooling as the single heat sink. The increased efficiency may be realized as increased capacity for a given power consumption of system 100. Increased capacity includes increased output of liquefied gas through line 115 (FIG. 1). Furthermore, in embodiments, removing a proportion of the heat in water-cooled heat exchangers reduces the amount of air-cooling required, and hence reduces the space taken by the air-coolers.

Water cooling is often beneficial, but often carries a high cost and environmental impact due to the high water circulation rates required. Hybrid cooling (e.g., cooling with water and/or air) offers the potential to achieve the same or similar beneficial performance as water cooling alone but with a smaller cooling water system and less environmental footprint because air-cooling is also provided to perform a proportion of the heat rejection. For example, in at least some embodiments of system 100, a water-cooled heat exchanger 114, 138, 144 is smaller than would be required by a water-cooled heat exchanger of a conventional liquefaction system because heat exchangers 114, 138, 144 are closely coupled in hybrid groups with air-cooled heat exchangers 112, 136, 142, respectively.

In some instances, system 100 may achieve reduced variation in capacity between winter and summer operation, as compared to a conventional liquefaction system, so the facility that utilizes system 100 makes maximum use of the installed capacity of the entire gas supply chain (e.g. equipment coupled to lines 111, 115) throughout the year.

As previously described, a liquefaction system that includes a hybrid heat exchanger group may achieve increased efficiency or production capacity through multiple or all seasons of the year, as compared to a conventional system that uses only air cooling or only water cooling as the single heat sink. For example, referring now to FIG. 2, representative plots of LNG production for three different systems during multiple seasons are shown. At reference numeral 145, a first plot is LNG production for a system using only air cooling, having highly variable performance, from season to season. At reference numeral 146, a second plot is LNG production for a system using only water cooling, having more stable, consistent performance that is better than plot 145 in the summer but is worse than plot 145 in winter. At reference numeral 147, a third plot is LNG production for a system using both air cooling and water cooling by implementation of a hybrid heat exchanger group. As compared to the first two systems, plot 147 achieves optimized or maximum performance through all seasons. By enabling cooling via heat exchange with multiple heat sinks, heat exchange may be effected via heat exchange with one or both heat sinks, depending on ambient conditions. For example, when the ambient water has a temperature below a minimum operating temperature, heat exchange may be effected solely via heat exchange with ambient air.

Although process fluid system 102 and refrigerant system 104 each include a hybrid heat exchanger group in the embodiment shown in FIG. 1, in other embodiments, only the process fluid system or only the refrigerant system includes a hybrid heat exchanger group. Further, in some embodiments, refrigerant system 104 include just one hybrid heat exchanger group and may include a single heat exchanger in place of the second group (e.g. in place of heat exchanger group 136, 138 or in place of heat exchanger group 142, 144). Some other refrigerant system embodiments include two (as described above), three, four, or any practical number of hybrid heat exchanger groups. Likewise, some embodiments of process fluid system 102 include two, three, four, or any practical number of hybrid heat exchanger groups.

Notwithstanding the foregoing, in some embodiments, the gaseous phase refrigerant system may include more or fewer expanders, compressors, or heat exchangers, or flow paths within a heat exchanger. In some embodiments of system 100, an alternate to system 104 is designed to use a condensing refrigerant with a hybrid heat exchanger group installed to extract heat from the refrigerant at chosen points in the process. As examples, a hybrid heat exchanger group may be used with an air cooler deployed as a condenser, and water cooler deployed as a sub-cooler. Multiple hybrid heat exchanger groups may be installed at different points in the process. For various embodiments, hybrid cooling can be applied to pre-cool the process feed gas (e.g. natural gas) in line 111 to maximize efficiency throughout the year.

In some embodiments of system 100, an alternate to refrigerant system 104 is designed to use a condensing refrigerant with hybrid heat exchangers installed to extract heat from the refrigerant at chosen points in the process. As examples, with a condensing refrigerant, air-cooling can be used to remove superheat at the compressor discharge and water cooling used to condense the refrigerant, or air-cooling used to condense the refrigerant, and water cooling used to sub-cool the refrigerant. In the simplified example illustrated in FIG. 3, a system 200 using two condensing refrigerants is shown. The liquefaction cycle of system 3 of FIG. 3 includes two refrigerant cycles: a “cold cycle” that removes heat from the process gas (e.g., natural gas) at lower temperatures, and a “warm cycle” that removes heat from the process gas (e.g., natural gas) at higher temperatures and also removes heat from the warm cycle refrigerant. In such embodiments, a warm cycle refrigerant in one or more refrigerant lines 223 can be de-superheated at the discharge of a warm cycle compressor 232 using an air cooler 236A (into which the refrigerant is introduced via refrigerant line 235), and condensed and sub-cooled using one or more water-coolers 238A, 238B connected via accumulator 250. The sub-cooled refrigerant from water-coolers 238A, 238B is then be reintroduced into primary heat exchanger 206 via refrigerant line 239. Cold cycle refrigerant can be removed from primary heat exchanger 206 via refrigerant line 227, compressed in one or more cold cycle compressors 234A, 234B, and then sub-cooled in one or more air coolers 236B, 236C. The sub-cooled refrigerant from air coolers 236B, 236C is then reintroduced into primary heat exchanger 206 via refrigerant line 221. A system of this disclosure can comprise one or a plurality of condensing refrigerants, and can include, for example, one, two, three or four different refrigerant cycles. Without being limited by this or any particular theory, in general, it is beneficial to use air cooling for higher temperature heat rejection (e.g., warm cycle refrigerant) and water cooling for lower temperature heat rejection (cold cycle refrigerant). Multiple hybrid heat exchangers may be installed at different points in the process. For various embodiments, hybrid cooling can be applied to pre-cool the process feed gas in line 111 to maximize efficiency throughout the year.

Although embodiments described herein are directed to the liquefaction of natural gas, in general, the concepts presented herein are applicable to liquefaction processes for a variety of gases.

While exemplary embodiments have been shown and described, modifications thereof can be made by one of ordinary skill in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations, combinations, and modifications of the systems, apparatuses, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. The inclusion of any particular method step or operation within the written description or a figure does not necessarily mean that the particular step or operation is necessary to the method. The steps or operations of a method listed in the specification or the claims may be performed in any feasible order, except for those particular steps or operations, if any, for which a sequence is expressly stated. In some implementations two or more of the method steps or operations may be performed in parallel, rather than serially. The recitation of identifiers such as (a), (b), (c); (1), (2), (3); etc. before operations in a method claim are not intended to and do not specify a particular order to the operations, but rather are used to simplify subsequent reference to such operations.

The particular embodiments disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art 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 or modified and all such variations are considered within the scope and spirit of the present disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. While compositions and methods are described in broader terms of “having”, “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim.

Numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range are 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. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents, the definitions that are consistent with this specification should be adopted.

Embodiments disclosed herein include:

A: A liquefaction system for removing heat from a process fluid to condense the process fluid, the liquefaction system comprising: a primary heat exchanger configured to remove heat from the process fluid via heat exchange with one or more refrigerants; a compressor configured to compress the one or more refrigerants; a first secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient air; and a second secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient water.

B: A method for liquefying a process fluid using a refrigerant, the method comprising: (a) transferring heat from the process fluid to the refrigerant in a primary heat exchanger; (b) flowing the refrigerant from the primary heat exchanger; (c) compressing the refrigerant stream after (b); and (d) removing heat from the process fluid via a first heat exchanger operable to effect heat exchange with ambient air and a second heat exchanger operable to effect heat exchange with ambient water.

C: A liquefaction system for removing heat from a process fluid to condense it, the system comprising: a primary heat exchanger having a process passage and a refrigerant passage; a process fluid system including a process fluid feed line and a process fluid discharge line, wherein the process fluid feed line and the process fluid discharge line are coupled to the process passage; a refrigerant system including a plurality of refrigerant lines coupled to the refrigerant passage; a hybrid cooling system including an air-cooled heat exchanger connected in series with a liquid-cooled heat exchanger; wherein the hybrid cooling system is coupled to one or more of the following: the process fluid feed line; and one or more of the plurality of refrigerant lines; wherein the air-cooled heat exchanger is configured to reject heat to air; and wherein the liquid-cooled heat exchanger is configured to reject heat to water.

D: A liquefaction system for removing heat from a process fluid to condense the process fluid, the system comprising: a refrigerant system comprising: a refrigerant compressor; a first hybrid heat exchanger group including a first air-cooled heat exchanger connected in series with a first liquid-cooled heat exchanger; and a primary heat exchanger having a process passage and a refrigerant passage; wherein the refrigerant compressor, the first hybrid heat exchanger pair, and the refrigerant passage of the primary heat exchanger are coupled together to circulate the refrigerant.

E: A method for liquefying a process fluid using a refrigerant, the method comprising: (a) compressing the refrigerant; (b) transferring heat from the process fluid directly or indirectly to a first heat sink with a first air-cooled heat exchanger; (c) transferring heat from the process fluid directly or indirectly to a second heat sink with a first liquid-cooled heat exchanger, wherein the first air-cooled heat exchanger and the first liquid-cooled heat exchanger are connected in series; and (d) transferring heat from at least a portion of the process fluid to the refrigerant.

Each of embodiments A, B, C, D, and E may have one or more of the following additional elements: Element 1: wherein the first secondary heat exchanger and the second secondary heat exchanger are arranged in series. Element 2: further comprising: a third secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient air; and a fourth secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient water. Element 3: wherein the compressor is located upstream of the first secondary heat exchanger and the second secondary heat exchanger. Element 4: wherein the first secondary heat exchanger is configured to remove heat from a first portion of the one or more refrigerants and the second secondary heat exchanger is configured to remove heat from a second portion of the one or more refrigerants. Element 5: wherein the primary heat exchanger comprises a first fluid passage fluidly connected with the first secondary heat exchanger configured to reject heat to ambient air, and a second fluid passage fluidly connected with the second secondary heat exchanger configured to reject heat to ambient water. Element 6: further comprising: a first heat exchanger upstream of the primary heat exchanger and configured to remove heat from the process fluid via heat exchange with ambient air; and a second heat exchanger upstream of the primary heat exchanger and configured to remove heat from the process fluid via heat exchange with the ambient water. Element 7: wherein the first heat exchanger and the second heat exchanger are arranged in series. Element 8: wherein the first heat exchanger configured to remove heat from the process fluid via heat exchange with ambient air is upstream of the second heat exchanger configured to remove heat from the process fluid via heat exchange with ambient water. Element 9: wherein the first heat exchanger and the second heat exchanger are in series. Element 10: wherein (d) comprises: removing heat directly from the process fluid via heat exchange between the process fluid and ambient air with the first heat exchanger; and removing heat directly from the process fluid via heat exchange between the process fluid and ambient water with the secondary heat exchanger. Element 11: further comprising a third heat exchanger that is not in series with the first heat exchanger and the second heat exchanger. Element 12: wherein (d) comprises: removing heat indirectly from the process fluid via heat exchange between the refrigerant and ambient air with the first heat exchanger; and removing heat indirectly from the process fluid via heat exchange between the refrigerant and ambient water with the second heat exchanger. Element 13: further comprising: removing heat indirectly from the process fluid via heat exchange between the refrigerant and ambient air with a third heat exchanger; and removing heat directly from the process fluid via heat exchange between the refrigerant and ambient water with a fourth heat exchanger. Element 14: wherein the third heat exchanger and the fourth heat exchanger are arranged in series. Element 15: wherein the third heat exchanger and the fourth heat exchanger are not in series with the first heat exchanger and the second heat exchanger, and remove heat from a portion of the one or more refrigerants that has a different temperature from that of another portion of the one or more refrigerants from which the first heat exchanger and the second heat exchanger remove heat. Element 16: wherein the first heat exchanger and the second heat exchanger are not operated in series. Element 17: further comprising operating the hybrid cooling system to effect heat exchange with the ambient water and not with the ambient air, operating the hybrid cooling system to effect heat exchange with the ambient water and not with the ambient air, or operating the hybrid cooling system to effect heat exchange with the ambient air and heat exchange with the ambient water. Element 18: further comprising operating the hybrid cooling system to effect heat exchange with the ambient water and heat exchange with the ambient air when the temperature of the ambient air is above the temperature of the ambient water, and operating the hybrid cooling system to effect heat exchange with the ambient air and not with the ambient water when the temperature of the ambient air is not above the temperature of the ambient water and/or when the temperature of the water is below a minimum operating temperature. Element 19: wherein the system further comprises a process fluid system that includes a second hybrid heat exchanger pair coupled for fluid communication with the process passage and having an second air-cooled heat exchanger connected in series with a second liquid-cooled heat exchanger. Element 20: wherein the first and second air-cooled heat exchangers are coupled to a first environmental heat sink for heat rejection; and wherein the first and second water-cooled heat exchangers are coupled to a second environmental heat sink for heat rejection, wherein the first environmental heat sink is different from the second environmental heat sink. Element 21: wherein (b) includes pre-cooling the process fluid using the first air-cooled heat exchanger and the first liquid-cooled heat exchanger. Element 22: wherein (b) includes removing heat from the refrigerant using the first air-cooled heat exchanger and the first liquid-cooled heat exchanger. Element 23: wherein (b) occurs after (a). Element 24: wherein (b) includes transferring heat from the process fluid directly or indirectly to the first h heat sink with a second air-cooled heat exchanger and transferring heat from the process fluid directly or indirectly to the second heat sink with a second liquid-cooled heat exchanger, wherein the second air-cooled heat exchanger and the second liquid-cooled heat exchanger are connected in series; wherein (b) occurs before (a) using the first air-cooled heat exchanger and the first liquid-cooled heat exchanger and occurs after (a) using the second air-cooled heat exchanger and the second liquid-cooled heat exchanger. Element 25: further comprising: (d) removing heat from the process fluid using a second air-cooled heat exchanger and a second liquid-cooled heat exchanger connected in series, wherein the second air-cooled heat exchanger and the second liquid-cooled heat exchanger are configured to transfer heat to the environment. Element 26: wherein (d) occurs before (c).

While preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the teachings of this disclosure. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention.

Numerous other modifications, equivalents, and alternatives, will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such modifications, equivalents, and alternatives where applicable. Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the detailed description of the present invention. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference. Unless expressly stated otherwise, the steps in a method claim may be performed in any order and with any suitable combination of materials and processing conditions.

Claims

1. A liquefaction system for removing heat from a process fluid to condense the process fluid, the liquefaction system comprising:

a primary heat exchanger configured to remove heat from the process fluid via heat exchange with one or more refrigerants;

a compressor configured to compress the one or more refrigerants;

a first secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient air; and

a second secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient water.

2. The liquefaction system of claim 1, wherein the first secondary heat exchanger and the second secondary heat exchanger are arranged in series.

3. The liquefaction system of claim 2, further comprising:

a third secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient air; and

a fourth secondary heat exchanger configured to remove heat from the one or more refrigerants via heat exchange with ambient water.

4. The liquefaction system of claim 2, wherein the compressor is located upstream of the first secondary heat exchanger and the second secondary heat exchanger.

5. The liquefaction system of claim 1 wherein the first secondary heat exchanger is configured to remove heat from a first portion of the one or more refrigerants and the second secondary heat exchanger is configured to remove heat from a second portion of the one or more refrigerants.

6. The liquefaction system of claim 1, wherein the primary heat exchanger comprises a first fluid passage fluidly connected with the first secondary heat exchanger configured to reject heat to ambient air, and a second fluid passage fluidly connected with the second secondary heat exchanger configured to reject heat to ambient water.

7. The liquefaction system of claim 1, further comprising:

a first heat exchanger upstream of the primary heat exchanger and configured to remove heat from the process fluid via heat exchange with ambient air; and

a second heat exchanger upstream of the primary heat exchanger and configured to remove heat from the process fluid via heat exchange with the ambient water.

8. The liquefaction system of claim 7, wherein the first heat exchanger and the second heat exchanger are arranged in series.

9. The liquefaction system of claim 8, wherein the first heat exchanger configured to remove heat from the process fluid via heat exchange with ambient air is upstream of the second heat exchanger configured to remove heat from the process fluid via heat exchange with ambient water.

10. A method for liquefying a process fluid using a refrigerant, the method comprising:

(a) transferring heat from the process fluid to the refrigerant in a primary heat exchanger;

(b) flowing the refrigerant from the primary heat exchanger;

(c) compressing the refrigerant stream after (b); and

(d) removing heat from the process fluid via a first heat exchanger operable to effect heat exchange with ambient air and a second heat exchanger operable to effect heat exchange with ambient water.

11. The method of claim 10, wherein the first heat exchanger and the second heat exchanger are in series.

12. The method of claim 11, wherein (d) comprises:

removing heat directly from the process fluid via heat exchange between the process fluid and ambient air with the first heat exchanger; and

removing heat directly from the process fluid via heat exchange between the process fluid and ambient water with the secondary heat exchanger.

13. The method of claim 11 further comprising a third heat exchanger that is not in series with the first heat exchanger and the second heat exchanger.

14. The method of claim 11, wherein (d) comprises:

removing heat indirectly from the process fluid via heat exchange between the refrigerant and ambient air with the first heat exchanger; and

removing heat indirectly from the process fluid via heat exchange between the refrigerant and ambient water with the second heat exchanger.

15. The method of claim 14, further comprising:

removing heat indirectly from the process fluid via heat exchange between the refrigerant and ambient air with a third heat exchanger; and

removing heat directly from the process fluid via heat exchange between the refrigerant and ambient water with a fourth heat exchanger.

16. The method of claim 15, wherein the third heat exchanger and the fourth heat exchanger are arranged in series.

17. The method of claim 16, wherein the third heat exchanger and the fourth heat exchanger are not in series with the first heat exchanger and the second heat exchanger, and remove heat from a portion of the one or more refrigerants that has a different temperature from that of another portion of the one or more refrigerants from which the first heat exchanger and the second heat exchanger remove heat.

18. The method of claim 10, wherein the first heat exchanger and the second heat exchanger are not operated in series.

19. The method of claim 10, further comprising operating the hybrid cooling system to effect heat exchange with the ambient water and not with the ambient air, operating the hybrid cooling system to effect heat exchange with the ambient water and not with the ambient air, or operating the hybrid cooling system to effect heat exchange with the ambient air and heat exchange with the ambient water.

20. The method of claim 10, further comprising operating the hybrid cooling system to effect heat exchange with the ambient water and heat exchange with the ambient air when the temperature of the ambient air is above the temperature of the ambient water, and operating the hybrid cooling system to effect heat exchange with the ambient air and not with the ambient water when the temperature of the ambient air is not above the temperature of the ambient water and/or when the temperature of the water is below a minimum operating temperature.