METHOD FOR LIQUIDING A GAS

Description

[0001] The present invention relates to a method for liquefying a gas, in particular natural gas, according to the preamble of independent claim 1. State of the art

[0002] Processes and plants for the liquefaction of natural gas are known and are described, for example, in the article "Natural Gas" in Ullmann's Encyclopedia of Industrial Chemistry, online publication July 15, 2006, DOI: 10.1002 / 14356007.a17_073.pub2, in particular section 3, "Liquefaction", or in Wang and Economides, "Advanced Natural Gas Engineering", Gulf Publishing 2010, DOI: 10.1016 / C2013-0-15532-8, in particular chapter 6, "Liquefied Natural Gas (LNG)".

[0003] In particular, mixed refrigerants consisting of different hydrocarbon components and nitrogen can be used in natural gas liquefaction. For example, one, two, or even three mixed refrigerant circuits can be employed (Single Mixed Refrigerant, SMR; Dual Mixed Refrigerant, DMR; Mixed Fluid Cascade, MFC). Mixed refrigerant circuits with propane pre-cooling (C3MR) or, more generally, using a pure refrigerant (see below) are also known.

[0004] Although the present invention is described below primarily with reference to the liquefaction of natural gas, the proposed measures are also fundamentally suitable for the liquefaction of other gas mixtures. Natural gas and corresponding other gas mixtures can, in particular, contain more than 70, preferably more than 90 mol percent methane and, in the remaining fraction, (among other things) non-hydrocarbon gases such as nitrogen and sour gases. Higher hydrocarbons, especially ethane, may also be present. Higher hydrocarbons such as ethane, propane, butane, etc., are preferably present at a concentration of less than 10 mol percent. For example, such higher hydrocarbons can be removed upstream of the actual liquefaction. The natural gas or other gas mixture used for liquefaction is preferably substantially free of water and / or carbon dioxide.

[0005] Natural gas liquefaction processes are energy-intensive. Depending on the technology chosen, between 5 and 15% of the energy contained in the feed gas is consumed internally to generate the required cooling. Increased process efficiency often leads to additional investments, as more technically sophisticated systems must be used.

[0006] Large refrigeration compressors are usually driven by gas turbines, which convert only 30 to 45% of the energy of the fuel gas, i.e., its calorific value, into mechanical shaft power. The remainder, i.e., 55 to 70% of the energy, is lost if the waste heat from the turbine exhaust gas is not utilized.

[0007] Various concepts exist for utilizing the waste heat from turbine exhaust gases. Simple systems involve recovering the waste heat in the form of process heat, for example in a hot oil system that transfers the heat from the turbine exhaust gas to reboilers of regeneration columns in amine scrubbers, regeneration gas heaters for dryers, or any other heat users at a suitable temperature level.

[0008] More complex waste heat recovery systems include a closed steam cycle. The steam generated by the waste heat can be expanded in a steam turbine to perform work. A suitable steam turbine can drive any type of refrigeration compressor, including, for example, those in precooling circuits using propane, carbon dioxide, or ammonia as refrigerants. It is also possible to support a gas turbine for the main compressor. So-called waste heat recovery systems are also known, as described, for example, in US 2017 / 131027.

[0009] There is an overall desire to increase the efficiency of natural gas liquefaction and other gas liquefaction processes without the costly installation of a cycle based on an additional working fluid such as steam. Disclosure of the invention

[0010] Against this background, the present invention proposes a method with the features of the independent claim. Embodiments of the present invention are the subject of the dependent claims and the following description.

[0011] Within the scope of the present invention, a method for liquefying a gas is proposed, wherein the gas is subjected to heat exchange with a refrigerant, and at least a portion of the refrigerant, after heat exchange with the gas (during which the refrigerant can, in particular, be at least partially evaporated), is subjected to compression using a heat-generating drive and to partial or complete liquefaction. Thus, within the scope of the present invention, a refrigerant cycle is employed, comprising the known steps of heating and evaporation (against the fluid to be cooled, here the gas to be liquefied), recompression (using the heat-generating drive), and (partial) condensation within the cycle.

[0012] In general, whenever "evaporation" is mentioned below, it refers to partial or complete evaporation. Similarly, "condensation" should also be understood as partial or complete condensation, even if this is not explicitly stated. The heat exchange of the refrigerant "with the gas" can occur as an indirect heat exchange between the gas and the refrigerant without an intervening refrigerant, i.e., via a shared heat exchange surface of a heat exchanger, or via an additional refrigerant. Heat exchange "with the gas" also occurs when heat is extracted from the gas via another refrigerant and this additional refrigerant is pre-cooled with the refrigerant under consideration here.The term "heat exchange" is always used synonymously here with the more scientifically correct term "heat transfer" and the term "heat exchanger" is used synonymously with the term "heat transfer unit".

[0013] As is also known, heating and evaporation, recompression, and (partial) liquefaction can take place in the form of any (pressure or temperature) stages or in the form of several partial flows running parallel to one another, with corresponding partial flows being able to be combined at any point or formed from an initial flow. The present invention relates in particular to closed refrigerant circuits, such as those known from the prior art mentioned above for the liquefaction of natural gas.

[0014] According to the invention, after the partial or complete liquefaction of the refrigerant, a first portion of the refrigerant is subjected to heat exchange with the gas in the sense just explained, whereas a second portion of the refrigerant is successively subjected to pressurization, heating (in particular superheating) using the waste heat of the drive, and expansion to perform work. It is then returned to the refrigerant circuit at any desired point and combined with the first portion; specific positions are explained below. In other words, after its expansion to perform work, during which evaporation occurs in particular, the second portion of the refrigerant is returned to the refrigerant circuit and, in particular, combined with the first portion of the refrigerant, which was previously subjected to heat exchange with the gas and also evaporated. A partial circuit is thus created.

[0015] In other words, the present invention relates to a gas liquefaction process in which at least one compressor is used in a refrigerant circuit used for providing refrigeration. A compressor drive generates waste heat. In particular, a gas turbine is used as the drive, so that the waste heat is provided, especially with the turbine exhaust gas taken from an expansion stage of the gas turbine. In the present invention, a work-generating expansion of a partial flow of the refrigerant, the aforementioned "second portion," is carried out. Prior to this work-generating expansion, this portion is both further pressurized and heated so that the refrigerant is capable of absorbing the waste heat contained in the turbine exhaust gas of the gas turbine or another waste heat transfer medium.The heated, especially superheated, refrigerant obtained by utilizing waste heat is used as an energy source through the work-performing expansion process, thus converting the waste heat into another form of energy. The work performed during the work-performing expansion can be utilized as explained below. The work-performing expansion can also be carried out in two or more stages, with or without intermediate superheating, using the waste heat.

[0016] Within the scope of the present invention, as explained in the following embodiments, it is particularly provided that the work performed during expansion is used for the compression of the same or another refrigerant. Although in the following embodiments certain compressors are driven by the work performed during expansion, it is not excluded that other compressors can also be driven in this way. In the specific embodiments of the invention, in some cases, for example, the compressors in the refrigerant circuit that compress to the highest pressure (designated C2 in the figures) are coupled with corresponding expansion machines.Alternatively, any other compressors or compressor stages designed for compression to a lower pressure (labeled C1, C1A, or C1B in the figures) can also be driven via the work-performing expansion. It is also possible to operate compressors connected in parallel, one of which is driven by the work performed during the work-performing expansion and the other by other means, thus compressing the parallel partial flows of the refrigerant.

[0017] The work performed during relaxation can, in various embodiments of the present invention, also be used at least partially to drive an electric generator.

[0018] In medium-sized natural gas liquefaction plants with a capacity of, for example, approximately 0.3 to 2 megatons per year, the aforementioned SMR cycles are frequently used because they require a limited number of components and offer a reasonable thermodynamic efficiency. However, the investment costs for a steam system to utilize turbine waste heat are not necessarily economical for plants of this size if the potential energy savings do not offset the additional costs. The present invention is particularly applicable in such cases and provides an alternative and advantageous method for waste heat utilization. By using the present invention, the efficiency of an SMR process can be improved by at least 10 to 15 percentage points by correspondingly reducing the load on the gas turbine used to drive the refrigerant compressor.

[0019] On the other hand, the present invention can also be advantageously used for large-scale natural gas liquefaction, for example in plants with a capacity of approximately 2 to 10 megatons per year. In such plants, more than one refrigerant compressor is typically required to achieve the aforementioned capacity. The optimal speed of the various refrigerant compressors is not necessarily similar or identical, so gearboxes may need to be used between the individual compressors if they are to be driven by a common gas turbine. However, even when using several independent gas turbines, an imbalance in the required shaft power for each compressor can occur.In certain situations, the present invention can be advantageously used by employing the work performed during the work-providing relaxation to support the drive and thus compensating for imbalances in speed or power.

[0020] In the process according to the invention, a mixture refrigerant can in particular be used as the refrigerant in one or more mixture refrigerant circuits. The refrigerant mixture typically consists of light hydrocarbons with one to five carbon atoms and a maximum of 20 mol percent nitrogen. The invention can be used in the aforementioned SMR, but also in DMR, MFC or C3MR refrigeration circuits, as well as other refrigeration circuits in which a pure substance refrigerant is used in addition to a mixture refrigerant, as are generally known from the prior art cited above.A "pure refrigerant" is defined here as a refrigerant that contains at least 95 mol percent, and in particular at least 99 mol percent, of a single hydrocarbon, especially ethane, ethylene, propane, or propylene, or another compound with a suitable vapor pressure curve, such as ammonia or carbon dioxide, or consists essentially of such a compound. When, for example, "propane" or a "propane refrigeration cycle" is mentioned below, the explanations in question should always be understood as referring more generally to a pure refrigerant. The reference to a specific pure substance serves only for illustration. A corresponding pure refrigerant can be, in particular, one that is treated in the manner described, i.e., from which the first and second components are formed in the form of corresponding partial flows.

[0021] As mentioned several times, in the context of the present invention, natural gas or a gas mixture formed using natural gas (for example, deacidified, dried and / or natural gas freed from high-boiling hydrocarbons, in particular those with three or more carbon atoms) can be used as the gas to be liquefied and / or a gas turbine can be used as the drive generating waste heat.

[0022] Particular advantages arise in embodiments of the invention when the work performed during expansion is used in addition to the drive during compression of the same refrigerant that is also undergoing expansion, and the first and second components are formed using this refrigerant. In this way, a drive otherwise used for compression can be relieved of the work performed during expansion, resulting in corresponding energy savings directly attributable to the utilization of waste heat. The liquid pressurization of the second component of the refrigerant, which is subsequently expanded to perform work, therefore requires significantly less energy. Such embodiments are explained below.

[0023] Within the scope of the present invention, i.e., in a first group of embodiments, only mixture refrigerants, but not pure refrigerants in the sense mentioned above, are used. However, these embodiments may also include those in which pre-cooling is carried out using a mixture refrigerant. In this first group of embodiments, the compression of the refrigerant comprises, in particular, a first compression step to a first pressure level and a second compression step to a second pressure level, which is, in particular, above the first pressure level, wherein the driving force is used in the first compression step and the work performed during the work-performing expansion is used in the second compression step.In particular, the first compression step can be carried out using one or more first compressors or one or more first compressor stages, which are at least partially driven by the drive system, and the second compression step can be carried out using one or more second compressors or compressor stages, which are at least partially driven by the work performed during the work-generating expansion phase. The second compression step is driven, in particular, without using the heat-generating drive system, but advantageously only by using the work performed during the work-generating expansion phase. In this way, both compression steps can be carried out by independently operable machines, and no mechanical couplings are required.As will be explained below, the work done during work-related relaxation can also be used in any other way.

[0024] In a preferred embodiment of the present invention, which is hereinafter also referred to as the "first embodiment", the refrigerant can be subjected at least partially to the first compression step and subsequently, to obtain a first liquid fraction and a first gas fraction, to at least partial first liquefaction, wherein the first gas fraction in this first embodiment is subjected at least partially to the second compression step and subsequently, to obtain a second liquid fraction and a second gas fraction, to at least partial second liquefaction. In this first embodiment, the entire refrigerant can be subjected to the first compression step, in particular, after it has been evaporated in heat exchange with the gas to be liquefied.The process can therefore be easily implemented without significant additional effort in conjunction with known gas liquefaction processes that include corresponding steps. Reference is made to the cited prior art.

[0025] In the first embodiment, the first compression step is carried out using a single compressor, which may be multi-stage but does not compress the refrigerant to different pressures. This compressor is consistently designated with the reference numeral C1 in the relevant figures. In this and subsequent embodiments, the second compression step is carried out using a compressor that operates independently of the first compression step and is consistently designated with the reference numeral C2 in the figures.

[0026] In the first configuration, the second portion of the refrigerant, after its expansion to perform work, can be at least partially combined with the refrigerant compressed in the first compression step before the latter is cooled for the first partial condensation. In this way, the second portion of the refrigerant can be returned to the refrigerant cycle and subjected to the necessary compression and condensation steps again.

[0027] In particular, the second portion of the refrigerant used according to the invention can, in the first embodiment, be in a liquid state for subsequent expansion from a pressure level of 10 to 40 bar to a pressure level of 60 to 120 bar. Heating by means of waste heat, in particular, results in heating from a temperature level of 10 to 50 °C to a temperature level of 200 to 400 °C. For example, turbine exhaust gas from a gas turbine used as a drive or another material stream may be present at 400 to 600 °C. In the first embodiment, the work-providing expansion takes place, in particular, from the aforementioned pressure level or a higher pressure level to a pressure level of 10 to 40 bar, thereby reducing the temperature by approximately 30 to 100 °C.In the first embodiment, the first compression step can be carried out, in particular, to a pressure level of 10 to 40 bar, and the second compression step to a pressure level of 30 to 70 bar. The subsequent partial condensation steps are each carried out, in particular, to a temperature level of 10 to 50 °C. The second fraction of the refrigerant, which is ultimately subjected to expansion for work, comprises, in particular, 40 to 80% of the first liquid fraction.

[0028] In the first embodiment, the second fraction of the refrigerant can be partially or completely subjected to an indirect heat exchange with the second fraction of the refrigerant or a part thereof (i.e., at least partially "with itself") before its work-performing expansion, which has already been subjected to work-performing expansion before the latter is combined with the first gas fraction.

[0029] If the second portion of the refrigerant is only partially subjected to the aforementioned heat exchange with itself, this occurs in the form of a first partial flow of the second portion, whereas a second partial flow of the second portion is not subjected to this heat exchange with itself. The first and second partial flows can be heated separately, and in particular at different temperature levels, using waste heat, and then recombined before the expansion phase, which performs work. For example, the first partial flow of the second portion can be heated at a higher temperature level in a first waste heat exchanger with turbine exhaust gas, whereby the already partially cooled exhaust gas from the gas turbine is fed to a second waste heat exchanger, in which the second partial flow can be heated at a lower temperature level.In this way, advantageous preheating for subsequent further heating or cooling for subsequent feeding to the first gas fraction after its compression can take place.

[0030] In the process according to the invention, in the first embodiment the second liquid fraction can be at least partially expanded and combined downstream of the first compression step with the refrigerant or a part thereof after appropriate cooling, before the latter is phase-separated.

[0031] For cooling the gas in the indirect heat exchange with the refrigerant, in the first embodiment a heat exchanger with several sections or several heat exchangers can be used, in which the first portion of the refrigerant and the second gas fraction or parts thereof can be further cooled to different temperature levels and, after expansion, reheated. The heat exchanger or heat exchangers can be designed, in particular, as wound tube bundle heat exchangers or as brazed plate heat exchangers, or comprise several such heat exchangers, even heat exchangers of different types.

[0032] For example, in the first embodiment, the first fraction of the refrigerant and the second gas fraction, or parts thereof (the same applies, without explicit mention, to the other fluids mentioned below), can be fed into the heat exchanger, designed as a wound heat exchanger, at an inlet temperature level of, for example, 10 to 50 °C and cooled by separate heat exchanger tubes. The first fraction of the refrigerant can be withdrawn from the heat exchanger at a first intermediate temperature level below the inlet temperature level of, for example, -20 to -60 °C, expanded, and fed back into the heat exchanger on the jacket side. In this case, the second gas fraction can also be withdrawn from the heat exchanger at the first intermediate temperature level, where it is in a partially condensed form.After phase separation outside the heat exchanger, the liquid and gas phases are separately fed back into the heat exchanger at the first intermediate temperature level and further cooled by separate heat exchanger tubes. The liquid phase is extracted at a second intermediate temperature level below the first, for example, -70 to -100 °C, expanded, and fed back into the heat exchanger via the shell. The gas phase is extracted at a third intermediate temperature level below the second, for example, -120 to -160 °C, expanded, and also fed back into the heat exchanger via the shell. The fluids thus combined on the shell side are then fed back into the compression stage.

[0033] If a brazed plate heat exchanger is used, the first fraction of the refrigerant and the second gas fraction, or portions thereof, can be fed together into the heat exchanger at an inlet temperature within the aforementioned range and cooled in shared passages. After extraction at the cold end of the heat exchanger at an extraction temperature of, for example, -120 to -160°C, expansion can occur, and the refrigerant, cooled further to a temperature of, for example, -130 to -170°C, is returned through separate passages and, after being warmed to a temperature similar to the inlet temperature, is fed back to the compression stage.

[0034] In a further preferred embodiment of the present invention, hereinafter also referred to as the "second embodiment," the first compression step can be configured differently and carried out using two compressor stages, namely a first compressor stage and a second compressor stage, which are, however, jointly driven by the waste heat-supplying drive. The first compressor stage, which may also be structurally configured as several compressor stages of a single compressor, is consistently designated in the figures by reference numeral C1A, and the correspondingly configured second compressor stage by reference numeral C1B. The second embodiment relates in particular to a DMR process. In this process, two or three heat exchangers or heat exchanger sections are advantageously used, each of which may be configured as a wound heat exchanger or corresponding sections of a wound heat exchanger.For the sake of simplicity, the following text refers to two or three "heat exchangers," which also includes corresponding sections of a common heat exchanger. In the context of the decreasing temperature of the gas to be liquefied, these are, in the terminology used here, a first, a second, and a third heat exchanger. In configurations with three heat exchangers, the first and second heat exchangers use the same refrigerant at different evaporation pressures and can therefore, particularly in cost-effective systems, be combined, or the first heat exchanger can be omitted in such systems. The invention also relates to such processes, even though no specific reference is made to them below, and the invention is described using methods and systems with three heat exchangers.

[0035] In the second configuration, evaporated refrigerant streams from the first and second heat exchangers are fed to the first compressor stage of the first compression step at pressure levels of, for example, 5 to 20 bar and 2 to 10 bar, respectively. In the first compressor stage of the first compression step, compression occurs to, for example, 15 to 50 bar, and in the second compressor stage of the first compression step, compression occurs to, for example, 40 to 80 bar. Post-cooling takes place downstream of each compression stage. The previously mentioned first and second refrigerant fractions are formed from the fluid compressed in the first compressor stage, which may also contain additional refrigerant. The second fraction also comprises, in particular, 40 to 80% of this fluid.

[0036] The first portion is initially passed through the first heat exchanger via the pipe side and cooled there to a temperature level of, for example, 0 to -20 °C. A partial flow can be expanded downstream of the first heat exchanger and fed into the first heat exchanger via the jacket side. This partial flow represents, in particular, all of the refrigerant that has evaporated in the first heat exchanger. In the aforementioned configurations with only two heat exchangers, the measures described for the first heat exchanger are omitted. The remaining, non-expanded portion of the first refrigerant can be used to form a further partial flow, which is used in a separate, additional heat exchanger to cool the fluid compressed in the second compressor stage of the first compression step and can then be fed back into the first compressor stage of the first compression step.Any remaining portion of the first heat exchanger is initially routed through the pipe side of the second heat exchanger and cooled there to a temperature level of, for example, -30 to -70 °C. This remaining portion can then be expanded downstream of the second heat exchanger and fed into the jacket side of the second heat exchanger. This remaining portion represents, in particular, all the refrigerant that has evaporated in the second heat exchanger.

[0037] In the second embodiment, the second portion of the refrigerant can be treated essentially as described for the first embodiment and, in particular, fed to the refrigerant compressed in the first compressor stage of the first compression step before it is cooled and condensed. It is thus circulated. The refrigerant compressed in the second compressor stage of the first compression step can, in particular, be fed to the second compression step and compressed there, essentially as described for the first embodiment. Specifically, it is compressed to a pressure level of 70 to 110 bar. The correspondingly compressed refrigerant is cooled and initially passed through the first to third heat exchangers on the pipe side for further cooling. Downstream of this, this portion of the refrigerant is expanded and fed into the third heat exchanger on the jacket side.This refrigerant fraction represents, in particular, all the refrigerant that evaporated in the third heat exchanger.

[0038] A further preferred embodiment of the present invention, hereinafter also referred to as the "third embodiment," comprises a first compression step being carried out using two compressors, which are now advantageously driven by two separate drives that provide waste heat. These are operated in a manner largely comparable to the corresponding compressor stages in the second embodiment and therefore bear the corresponding designations. The third embodiment also relates to a DMR process. As in the second embodiment, two or three heat exchangers or heat exchanger sections are advantageously used, so that the above explanations continue to apply.The above features and explanations regarding the second embodiment also apply to the third embodiment, except that the remaining portion of the refrigerant downstream of the first heat exchanger, which is not expanded, is optionally not used to form a further partial flow that serves to cool the fluid compressed in the second compressor of the first compression stage. The second portion of the refrigerant, which is ultimately expanded to perform work, is heated by the waste heat from both drives.

[0039] As mentioned, in the embodiments just described, the work performed during the work-providing expansion is used in addition to the drive during the compression of the same refrigerant that is also being expanded and from which the first and second components are formed, even though this refrigerant is used in different circuits within the DMR circuits. In contrast, other embodiments of the invention offer advantages if the work performed during the work-providing expansion is used during the compression of a further refrigerant, i.e., not the same refrigerant that is being expanded and from which the first and second components are formed. For better differentiation, the work-providing refrigerant expanded and used to form the first and second components is referred to as the "first" refrigerant, and the further refrigerant as the "second" refrigerant.

[0040] The first three configurations are part of the previously mentioned first group of configurations in which only mixture refrigerants are used. These are SMR and DMR circuits, including those in which a mixture refrigerant is used for pre-cooling. A second group of configurations, which will now be explained, comprises configurations in which a pure refrigerant is additionally used in a pre-cooling circuit. These include, among others, C3MR circuits.

[0041] In the second group of configurations, the compression of the pure refrigerant, which here represents a "first" refrigerant in the sense just explained, takes place in the pre-cooling circuit in a first compressor or first compressor stage. The compression of the mixed refrigerant in the mixed refrigerant circuit, which in this sense represents the "second" refrigerant, is carried out using a second compressor or second compressor stage and a third compressor or third compressor stage in the manner described below. The work performed during expansion is used to drive the third compressor or third compressor stage. For the sake of clarity, the term "compressors" will be used below, which also includes compressor stages.

[0042] In a corresponding embodiment of the invention, hereinafter also referred to as the "fourth embodiment", the first and second compressors (C1A and C1B in the figures) are driven by two separate drives, wherein only the drive of the second compressor is a drive such as a gas turbine that generates waste heat (at least to a significant and usable extent). The drive of the first compressor can, for example, be electrical, generating considerably less (and unusable) waste heat.

[0043] In contrast to the second and third embodiments, the fourth embodiment uses a brazed plate heat exchanger and a wound tube bundle heat exchanger to cool the gas to be liquefied. As mentioned, two separate refrigerant circuits are implemented: a pure refrigerant circuit for pre-cooling and a refrigerant circuit with a mixture of refrigerants. The pure refrigerant circuit, as already mentioned, comprises the first compressor, while the mixture refrigerant circuit comprises the second and third compressors.

[0044] The pure refrigerant from the pure refrigerant cycle is fed to the first compressor in several partial flows, which are heated against the mixed refrigerant from the second compression step, thus pre-cooling the mixed refrigerant. There, it is compressed. After subsequent cooling and condensation, the first and second components of the refrigerant are formed. In contrast to the previously described configurations, the first and second components are thus formed from the pure refrigerant, the "first" refrigerant, and not from the mixed refrigerant, the "second" refrigerant. The first component is initially cooled, then expanded, heated against the mixed refrigerant, and fed back to the first compressor. The second component is treated as previously mentioned and is heated using the waste heat from the drive of the second compressor.

[0045] After pre-cooling with the pure refrigerant from the pure refrigerant cycle, specifically to a temperature of -20 to -40 °C, the mixed refrigerant is further cooled on the tube side of the wound heat exchanger, specifically to a temperature of -120 to -160 °C. Downstream of this, it is expanded and fed to the jacket side of the wound heat exchanger. After being drawn from the wound heat exchanger and appropriately warmed, it undergoes further heating in the brazed plate heat exchanger and is then compressed in the second and third compressors.

[0046] One variant of the fourth embodiment just described, which is referred to as the "fifth embodiment", involves the first and second compressors being driven by a common drive that produces waste heat.

[0047] In all cases, work performed during expansion can be used in the compression of another refrigerant, with which the gas is subjected to cooling in an indirect heat exchange. This can be the case, for example, when using a pure substance or C3MR refrigerant circuit, or in variants of the first group of configurations.

[0048] In a further embodiment of the invention, referred to here as the "sixth embodiment," a mixture refrigerant is used as the first refrigerant and nitrogen as the second refrigerant. In this embodiment as well, the first and second components are components of a first refrigerant, namely the mixture refrigerant, and the work performed during expansion is used in the compression of a second refrigerant, namely the nitrogen.

[0049] In principle, in the sixth embodiment, as previously explained for the first embodiment, the refrigerant mixture can be subjected at least partially to a first compression step and subsequently, while retaining a first liquid fraction and a first gas fraction, at least partially to a first partial liquefaction. The first gas fraction can be subjected at least partially to a second compression step and subsequently, while retaining a second liquid fraction and a second gas fraction, at least partially to a second partial liquefaction. Further processing can also be identical.

[0050] In the sixth embodiment, the nitrogen is generally subjected to expansion and compression, with the compression of the nitrogen utilizing the work performed during the work-generating expansion of the second part of the refrigerant mixture. In the sixth embodiment, the expansion of the nitrogen can also be work-generating, in which case the work performed during the work-generating expansion of the nitrogen can also be used for the compression of the nitrogen.

[0051] The compressed nitrogen is successively cooled, subjected to a first indirect heat exchange (and thereby cooled), expanded, subjected to a second indirect heat exchange (and thereby heated), then subjected to the first indirect heat exchange (and thereby heated), and finally returned to compression. During the second indirect heat exchange, the gas undergoing partial or complete liquefaction is supercooled.

[0052] A further embodiment of the present invention, here referred to as the "seventh embodiment", differs from the sixth embodiment in that the compression of the nitrogen is carried out in two stages, in a first and then a second compression step, wherein the first compression step is carried out using the work performed during the work-performing expansion of the nitrogen and the second compression step is carried out using the work performed during the work-performing expansion of the second part of the refrigerant mixture.

[0053] The invention also extends to a system for liquefying a gas, wherein the system comprises means configured to subject the gas to cooling via indirect heat exchange with a refrigerant and, after heat exchange with the gas, to compression using a drive that generates waste heat, followed by partial or complete liquefaction. According to the invention, the system comprises means configured to subject a first portion of the refrigerant to heat exchange with the gas after partial or complete liquefaction, and to successively subject a second portion of the refrigerant to pressurization, heating using the waste heat from the drive, and expansion during work, and then to return it to partial or complete liquefaction.

[0054] For features and advantages of a corresponding system, which is advantageously equipped for carrying out a method according to the present invention and any previously explained embodiments, reference is expressly made to the above explanations.

[0055] The invention is explained below with reference to the accompanying drawings, which illustrate arrangements according to embodiments of the present invention. Brief description of the drawings

[0056] Figure 1 illustrates a method according to one embodiment of the invention. Figure 2 illustrates a method according to one embodiment of the invention. Figure 3 illustrates a method according to one embodiment of the invention. Figure 4 illustrates a method according to one embodiment of the invention. Figure 5 illustrates a method according to one embodiment of the invention. Figure 6illustrates a method according to one embodiment of the invention. Figure 7 illustrates a method according to one embodiment of the invention. Figure 7A illustrates a variant of the procedure according to Figure 7 . Figure 8 illustrates a method according to one embodiment of the invention. Figure 9 illustrates a method according to one embodiment of the invention.

[0057] In the figures, corresponding elements are indicated with identical reference symbols and are not explained again for the sake of clarity. Identical elements are not labelled separately in all figures. Detailed description of the drawings

[0058] In Figure 1 A method according to an embodiment of the invention is illustrated by means of a schematic process flow diagram.

[0059] The process serves to liquefy a gas, which is fed into the process in gaseous form as mass stream 1 and provided in liquefied form as mass stream 2. A highly simplified heat exchanger or low-temperature section 10 is used for liquefaction. The heat exchanger section 10 is shown in a highly simplified form to illustrate its general applicability.

[0060] Refrigerant is discharged from heat exchanger section 10 in the form of a heated ("warm") refrigerant stream W. Any remaining condensate is separated in a separator D1. This is followed by compression of the refrigerant stream W in a first compression stage using a compressor C1, which is driven by a gas turbine GT1. In the gas turbine GT1, air from an air stream A is compressed in a compressor stage (not specifically designated) and combusted with fuel F in a combustion chamber (not shown). The hot gas is expanded in an expansion stage (also not specifically designated) and passed through a heat exchanger E4 for heat recovery. An auxiliary combustion process using additional fuel AF may also be used.

[0061] The refrigerant compressed in compressor C1 is cooled in a heat exchanger E1, partially condensing in the process, and subjected to phase separation in a separator D2. The gas and liquid phases are fed to heat exchanger section 10 in separate streams. A portion of the liquid phase, designated as the "first fraction" of the refrigerant (as previously specified), is fed to heat exchanger section 10, while another portion, designated as the "second fraction," is pressurized by a pump P1, heated in heat exchanger E3 and then in heat exchanger E4, expanded in an expansion machine X1 (where it performs work), passed through heat exchanger E3, and finally combined with the refrigerant compressed in compressor C1 before it is cooled.

[0062] The expansion machine X1 is coupled to a compressor C2 via a gearbox G. A mixed refrigerant in the form of a heated refrigerant stream W1 from the heat exchanger section 10 can be supplied to the compressor C2, thus enabling the utilization of waste heat from the gas turbine GT1. Figure 1 In addition to the refrigerant of refrigerant stream W, the refrigerant stream W1 uses a further mixture refrigerant, thus relating to a DMR cycle. The use of such a further mixture refrigerant is also possible in all embodiments of the invention described below, even if only one mixture refrigerant cycle, possibly with sub-cycles, is illustrated therein.

[0063] In Figure 2 A method according to a further embodiment of the invention is illustrated by means of a schematic process flow diagram. Figure 2The heat exchanger section 10 is illustrated in more detail. This section comprises, in particular, a wound heat exchanger 11 and a separator 12, the function of which is explained below.

[0064] The refrigerant flow W1 according to Figure 1 or a comparable material flow is not provided here, so that in the specific configuration it is an SMR cycle. The refrigerant flow W is compressed here in a first compression step using a compressor C1 and in a second compression step using a compressor C2, wherein the first compressor C1 is driven by the gas turbine GT1 and the second compressor C2 is driven by the work done during the expansion in the expansion machine X1.

[0065] The material stream W is compressed downstream of separator D1 in compressor C1 and then, after cooling in a heat exchanger E1, undergoes partial liquefaction in separator D2, yielding a first liquid fraction and a first gas fraction. The first gas fraction from separator D2, which is not specifically designated, is compressed in the second compressor C2 and then, after cooling in a heat exchanger E2, undergoes partial liquefaction in separator D3, yielding a second liquid fraction and a second gas fraction.

[0066] The first liquid fraction from separator D2 is partially treated as mass flow R, as previously explained. The remainder, along with the second gas fraction from separator D2, is fed to the coiled heat exchanger 11 as an unspecified mass flow. These refrigerant flows are routed through separate heat exchanger tubes and cooled.

[0067] The first liquid fraction from separator D2, which is not used in the form of the mass flow R, is extracted from heat exchanger 11 at a first intermediate temperature level below the corresponding inlet temperature level, expanded, and fed back into heat exchanger 11 on the jacket side. The second gas fraction can also be extracted from the heat exchanger at the first intermediate temperature level, expanded, and partially liquefied in the process, but phase separation into a liquid phase and a gas phase takes place outside of heat exchanger 11 in separator 12.

[0068] The liquid phase and the gas phase formed in the separator 12 are separately fed back into the heat exchanger 11 at the first intermediate temperature level and further cooled by separate heat exchanger tubes. The liquid phase is extracted at a second intermediate temperature level below the first, expanded, and fed back into the heat exchanger 11 via the shell. The gas phase is extracted at a third intermediate temperature level below the second, expanded, and also fed back into the heat exchanger 11 via the shell. The fluids thus combined on the shell side are fed back to the compression stage in the form of mass flow W.

[0069] The liquid stream R, after its expansion, is combined with the refrigerant that was compressed in compressor C1 before being cooled for the first partial condensation. The second liquid fraction from separator D3 is expanded via valve V1 and returned to separator D2.

[0070] In Figure 3 is illustrated a further embodiment of the invention which differs from the embodiment according to Figure 2 in particular, it differs in that a brazed plate heat exchanger 13 is provided instead of the wound tube bundle heat exchanger 11.

[0071] As illustrated here, the portion of the first liquid fraction from separator D2 not used in the form of the mass flow R and the second gas fraction from separator D3 can be fed together to heat exchanger 13 and cooled in common passages. A pump 14 transfers the portion of the first liquid fraction used in this way to the pressure of the second gas fraction, so that both fractions can be fed together to heat exchanger 13. After extraction at the cold end, pressure can be reduced via a valve 15, and the refrigerant, cooled further in this way, can be returned through separate passages and, after appropriate reheating, fed back into separator D1.

[0072] In Figure 4Figure 1 illustrates a further embodiment of the invention, in which, in particular, the first compression step previously carried out in compressor C1 is configured differently and is performed using two compressor stages (a first compressor stage C1A and a second compressor stage C1B). These are driven together by the gas turbine GT1.

[0073] Furthermore, three heat exchangers 16, 17, 18 are used, each designed as a wound heat exchanger. In the terminology used here, these are referred to as a first heat exchanger 16, a second heat exchanger 17, and a third heat exchanger 18, in the direction of decreasing temperature of the gas 1 to be liquefied. The first heat exchanger 16 can be omitted if necessary, as explained in detail above.

[0074] Evaporated refrigerant streams from the first and second heat exchangers 16, 17 are supplied to the first compressor stage C1A and compressed there. An evaporated refrigerant stream from the third heat exchanger 18 is supplied to the second compressor stage C1B and compressed there. Post-cooling takes place downstream of each compressor stage. The previously mentioned first and second refrigerant components are formed from the fluid compressed in the first compressor stage C1A, which may also contain other refrigerant in addition to the aforementioned components. This fluid is taken from the separator, also designated D2.

[0075] The first portion is initially passed through the first heat exchanger 16 via the pipe side and cooled there. A partial flow can be expanded downstream of the first heat exchanger 16 and fed into the first heat exchanger 16 via the jacket side. The remaining, non-expanded portion of the first refrigerant can be used to form another partial flow, which is used in a separate heat exchanger E5 to cool the fluid compressed in the second compressor stage C1B of the first compression stage and can then be fed to the first compressor stage C1A of the first compression stage. Any remaining portion of the first flow is initially passed through the second heat exchanger 17 via the pipe side and cooled there. This remaining portion can then be expanded downstream of the second heat exchanger 17 and fed into the second heat exchanger 17 via the jacket side.

[0076] The second portion of the refrigerant can essentially be treated as previously explained in the form of the mass flow R and, in particular, fed to the refrigerant compressed in the first compressor stage C1A of the first compression step before it is further cooled and condensed. It is thus circulated.

[0077] The refrigerant compressed in the second compressor stage C1B of the first compression step can be fed to the second compression step with compressor C2 and compressed there in principle as described for the first embodiment. The compressed refrigerant is cooled in a further heat exchanger E6 and initially passed through the first to third heat exchangers 16, 17, 18 for further cooling. Downstream of the third heat exchanger, this portion of the refrigerant is expanded and fed into the jacket side of the third heat exchanger 18.

[0078] A further preferred embodiment of the present invention is described in Figure 5 This illustrates that the first compression step is carried out using two compressors, which, for the sake of comparability, are still designated C1A and C1B, but are now driven by two separate, waste-heat-generating drives (gas turbines) GT1A and GT1B. Accordingly, the previously single heat exchangers E3 and E4 are now duplicated as heat exchangers E3A, E3B and E4A, E4B. The second portion of the refrigerant, which is ultimately expanded in the form of the mass flow R, is preheated in this configuration using the waste heat from both drives GT1A and GT1B.

[0079] A further embodiment of the present invention is described in Figure 6 illustrated and implemented in the form of a mixed cycle (e.g. C3MR) process pre-cooled with a pure substance refrigerant.

[0080] The compression of a pure refrigerant (illustrated here as propane C3H8) in a precooling circuit is performed in a first compressor C1A, while the compression of a mixed refrigerant in a mixed refrigerant circuit is carried out using a second compressor C1B and a third compressor C2. The work performed during expansion is used to drive the third compressor C2. The first and second compressors C1A and C1B are driven by two separate drives, but only the drive for the second compressor C1B is a heat-generating drive (at least to a significant and usable extent), such as a gas turbine GT1. The drive for the first compressor C1A can, for example, be achieved by a motor M, generating considerably less (and unusable) waste heat.

[0081] In contrast to the previously described configurations, a brazed plate heat exchanger 19 is used in addition to a wound heat exchanger 11 to cool the gas 1 to be liquefied. The refrigerant from the pure refrigerant cycle is fed to the first compressor C1A in several partial flows, which are heated and evaporated, particularly against the mixed refrigerant from the second compression step, thus pre-cooling the mixed refrigerant. There, it is compressed. After subsequent cooling and condensation, the first and second fractions of the refrigerant are formed. The first fraction is initially subcooled, then heated and evaporated against the mixed refrigerant from the second compressor, and fed back to the first compressor C1A. The second fraction R is treated as previously mentioned and is heated by the waste heat from the drive of the second compressor.

[0082] After pre-cooling with the refrigerant from the pure refrigerant circuit, the mixed refrigerant is further cooled on the tube side of the wound heat exchanger 11. Downstream of this, it is expanded and fed to the jacket side of the wound heat exchanger 11. After being drawn from the wound heat exchanger 11 and heated accordingly, it undergoes further heating in the brazed plate heat exchanger 19, followed by compression in the second and third compressors C1B and C2.

[0083] One variant of the design just described is in Figure 7 This illustrates that the first and second compressors C1A, C1B are driven by a common, waste heat-producing drive GT1.

[0084] Yet another variant of the in Figure 7 illustrated design, which can easily also be considered a variant of, for example, the one in Figure 6The invention can be realized in the illustrated embodiment or in another embodiment of the invention, is in Figure 7A As shown, a partial flow R' of the refrigerant flow R is not routed through heat exchanger E3, but through a heat exchanger E4', which is located downstream of heat exchanger E4 in the turbine exhaust stream of gas turbine GT1. As illustrated by dashed, but not separately labeled, material flows and heat exchangers, the pre-cooling of the refrigerant can also be configured differently and, in particular, may include fewer heat exchanger stages than previously shown.

[0085] In all cases, work performed during expansion can be used in the compression of another refrigerant with which the gas is subjected to cooling in an indirect heat exchange. This can be the case, for example, when using a mixed refrigerant circuit pre-cooled with a pure refrigerant, or in further embodiments of the invention, which are described in the Figures 8 and 9 These are illustrated. In these, further brazed plate heat exchangers 19A and 19B are used, which are operated using a nitrogen circuit.

[0086] The treatment of the mixed refrigerant results directly from the Figures 8 and 9 and the preceding explanations, and is essentially analogous to, for example, in Figure 3 , however, compressors C1 and C2 are operated using the gas turbine GT1.

[0087] The nitrogen of the nitrogen cycle is designed according to Figure 8 The nitrogen is subjected to expansion in an expansion machine X2 and compression in a compressor C3, wherein the compression of the nitrogen is carried out using the work performed during the work-generating expansion of the second part of the refrigerant mixture in the expansion machine X1. The expansion of the nitrogen is carried out work-generating in an expansion machine X2, wherein work performed during the work-generating expansion of the nitrogen is also used in the compression of the nitrogen. The expansion machines X1 and X2 and the compressor C3 are mechanically coupled.

[0088] The compressed nitrogen is successively cooled, subjected to a first indirect heat exchange in heat exchanger 19B (and thereby cooled), subjected to expansion, subjected to a second indirect heat exchange in heat exchanger 19A (and thereby heated), then again subjected to the first indirect heat exchange in heat exchanger 19B (and thereby heated), and finally returned to compression. In the second indirect heat exchange in heat exchanger 19A, the gas, which was previously subjected to partial or complete liquefaction, is subcooled. A heat exchanger E7 is provided for post-cooling the nitrogen in the nitrogen circuit downstream of compressor C3.

[0089] In the design according to Figure 9 , which otherwise essentially determine the design of the Figure 8In this configuration, the nitrogen is compressed in two stages: a first compression step followed by a second compression step in compressors C3 and C4. The first compression step utilizes the work performed during the expansion of the nitrogen in an expansion machine X1, and the second compression step utilizes the work performed during the expansion of the second portion of the refrigerant mixture in an expansion machine X2. In this configuration, expansion machine X1 and compressor C4 are coupled, while expansion machine X2 and compressor C3 are coupled.

[0090] The invention described above and its embodiments, as explained and particularly illustrated in the figures, are described again below in different words. The terms used below may be synonymous with those used above for the respective process steps, equipment, and media they denote. The following explanations describe the same inventive concept with corresponding advantageous developments as the explanations above, albeit in at least partially different wording.

[0091] The present invention presents a method for capturing or recovering waste heat generated in a gas liquefaction process, comprising liquefying a gas by a heat exchange process using a refrigerant fluid, compressing the spent refrigerant fluid from the liquefaction process by a method that generates excess heat, liquefying at least a portion of the compressed refrigerant fluid, pumping a portion of the liquefied compressed refrigerant fluid to a higher pressure, heating the portion of the liquefied compressed refrigerant fluid at the higher pressure by absorbing the excess heat generated by the compression of the spent refrigerant fluid, thereby superheating the portion of the compressed refrigerant fluid at the higher pressure, and using the superheated compressed refrigerant fluid in a work-performing expansion.

[0092] One embodiment of the present invention applies to a natural gas liquefaction process with at least one compressor used in the refrigerant circuit for the cryogenic process of natural gas liquefaction. The present invention uses a compressor in the refrigerant circuit, wherein the compressor is driven by a gas turbine or a similar energy source that generates waste heat while producing power to operate the compressor. The present invention uses a working expander, wherein the fluid circuit for the working expander is used to absorb the waste heat from the gas turbine or similar power source that drives the compressor in the refrigerant circuit.According to the invention, the fluid circuit for the working expander is both pressurized and heated so that it can absorb the waste heat present in the exhaust gas stream of the gas turbine or other waste heat from the power source driving the compressor in the refrigeration circuit. The resulting superheated fluid, generated from the waste heat energy recovery process, is then used as an energy source to drive the working expander.

[0093] According to the present invention, the fluid used in the fluid circuit for the working expander is also used for the refrigerant circuit. In this embodiment of the invention, a second compressor is additionally used in the refrigerant circuit, the second compressor being driven by the working expander. Accordingly, according to the invention, the refrigerant fluid, which is used in the cryogenic process for the liquefaction of natural gas, is also used to absorb waste heat generated to drive the first compressor, in order to provide power to drive the working expander, which in turn drives the second compressor to further compress the refrigerant fluid. Accordingly, this embodiment of the present invention offers advantages over other systems for capturing waste heat energy. For example, the present invention does not require the introduction of additional working fluids, such as...Water, nor the addition of other liquids (e.g. steam, ammonia, propane, etc.) in closed circuits.

[0094] In a prior art natural gas liquefaction process (not illustrated) using a single mixed refrigerant (SMR) with a two-stage SMR compression process, two compressors, C1 and C2, can be driven by a single gas turbine, GT1. A cryogenic portion of the process liquefies the natural gas through a heat exchange process with the mixed refrigerant. In the natural gas liquefaction process, the mixed refrigerant is compressed, cooled, and partially liquefied before being recycled in the cryogenic process. Mixed refrigerant discharged by the cryogenic portion can be collected in a container, D1, and then fed into the first compressor, C1, and the heat exchanger, E1.In a corresponding two-stage compression process, the liquid fraction from the first compressor C1 and heat exchanger E1 is collected in a storage vessel D2, while the vapor fraction from the first compressor C1 is fed into the second stage of the process via the second compressor C2 and heat exchanger E2. The resulting fraction from the second compressor C2 and heat exchanger E2 is combined and collected in a vessel D3. The two fractions collected in vessels D2 and D3 can be fed into the cryogenic section to carry out the liquefaction of natural gas via a heat exchange process.

[0095] Figure 2 This represents an embodiment of the present invention in a natural gas liquefaction process in which a single mixed refrigerant (SMR) is used with a two-stage SMR compression process. Figure 2The second compressor C2 is driven by a work expander X1 instead of a gas turbine. The work expander X1 is driven by superheated fluid supplied by a heat exchanger E4. The fluid discharged by the work expander X1 is cooled by an economizer or waste heat exchanger E3 and then combined with the refrigerant generated by the first compressor C1. The combined fluids are then further cooled by a heat exchanger E1 or similar device and collected in a tank D2. A portion of the combined fluids collected in tank D2 is then pumped by P1 to heat exchanger E3. The cooled fluid pumped into waste heat exchanger E3 is heated and then directed to heat exchanger E4. Heat exchanger E4 is in fluid contact with the warm exhaust gas from gas turbine GT1, which drives the first compressor C1.The heat exchanger E4 uses the heat from the exhaust gas of gas turbine GT1 to superheat the heated fluid from waste heat exchanger E3 that is fed into heat exchanger E4. The superheated fluid from heat exchanger E4 is then directed to the working expander X1 to drive the second compressor C2.

[0096] In one embodiment of the present invention, the cryogenic part can be designed with coiled heat exchangers (CWHEs), brazed plate heat exchangers (PFHEs) or a combination thereof. Figure 3 For example, an illustration of an embodiment of the present invention using a single-mix refrigerant (SMR) configuration using brazed plate heat exchangers (PFHEs) in the cryogenic part.

[0097] In one embodiment of the invention, which is in Figure 1As shown, a partial flow of 30 to 90 vol.% from the outgoing liquid reservoir D2 is pumped by pump P1 to at least three times the pressure in the reservoir D2. The high-pressure flow from pump P1 is then heated by a waste heat exchanger E3 and fed to the superheater E4. The superheater E4 recovers waste heat from the exhaust gas stream of the gas turbine GT1 and heats the high-pressure flow from the waste heat exchanger E3 to at least 180 °C, preferably at least 200 °C. The hot gas from the superheater E4 is then fed into the working expander X1 and reduced to a pressure slightly above the operating pressure of the reservoir D2. In one embodiment of the invention, the pressure of the flow leaving the working expander X1 is high enough to overcome the pressure drop in the heat exchangers E3 and E1, which still encounter the pressure in D2.The current exiting the work expander X1 is then cooled and at least partially condensed by the economizer E3 and the heat exchanger E1, and subsequently returned to the storage tank D2. The shaft power generated by the work expander X1 is used to drive the compressor C2 to compress the refrigerant, which is then fed into the cryogenic part of the process.

[0098] How to the in Figure 1As explained in the illustrated embodiment of the invention, the pressure ratio of at least three times the suction pressure in the reservoir D2, generated by the pump P1, results in a similar, only slightly lower, pressure ratio in the working expander X1, which is a preferred operating range for a working expander. Furthermore, the inlet pressure of the working expander X1 can be maintained below 100 bar, enabling a cost-effective mechanical design. Moreover, the increased pressure generated by the pump P1 ensures that the working expander X1 receives an inlet pressure significantly higher than the critical pressure of the fluid, thus preventing two-phase effects within the fluid.In embodiments of the invention illustrated in Figures 1 to 9, the refrigerant is used in the process for two processes: the natural gas liquefaction process in the cryogenic zone and the process of recovering waste heat generated by the gas turbine to drive the refrigerant compression process. Further improvements can be made to the present invention to enhance its performance. For example, the performance of the working expander X1 could be increased by additionally firing an additional heat source into the flue gas ducts of the gas turbine GT1. The working expansion performed by the working expander X1 can be divided into successive steps, with or without the need to reheat the working fluid as desired.

[0099] In other embodiments of the invention, the shaft power generated by the working expander X1 could be used to drive other processes, such as a power generator, a feed gas compression, a terminal flash gas compression, any type of refrigerant compression, or any other service that requires electricity.

[0100] The entire cooling system will comprise at least one refrigerant, consisting either of a single component or a mixture of components, wherein, in one embodiment of the invention, the refrigerant can be at least partially condensed at ambient temperature. In one embodiment of the invention, the permissible refrigerant components could include nitrogen and light paraffinic or olefinic hydrocarbons from C1 to C5 (such as CH4, C2H4, C2H6, C2H6, C3H6, C3H8, iC4H10, nC4H10, nC4H10, iC5H12, nC5H12, nC5H12, etc.). The cooling system may also comprise more than one circuit, wherein the additional circuits are pure refrigerant circuits and / or mixed refrigerant circuits and / or gas expansion circuits.

[0101] Figure 4This is an embodiment of the present invention using a dual mixed refrigerant configuration (DMR) with three wound heat exchangers (CWHEs) in the cryogenic zone and a single gas turbine GT1 used for both mixed refrigerant circuits. As shown in Figure 6 As shown, the configuration decouples a high-pressure compressor C2 from the low-pressure compressors C1A and C1B, which are driven by a common shaft driven by the gas turbine GT1. This embodiment of the present invention also eliminates the need for a gearbox that would be required to operate compressor C2 at a higher pressure and a higher operating speed when compressor C2 has a similar capacity to compressors C1A or C1B.

[0102] Figure 5is an embodiment of the present invention using a dual refrigerant mixture (DMR) configuration with three wound-wind heat exchangers (CWHEs) in the cryogenic section, wherein the compressors C1A and C1B are driven by independent gas turbines GT1A and GT1B, and wherein the waste heat from the two gas turbines GT1A and GT1B is used in the heat exchangers E4A and E4B to superheat the liquid fed into the working machines X1. An advantage of the embodiment described in Figure 5 The invention described is the ability to achieve a higher performance of the work expander X1 for driving the compressor C2.

[0103] Figure 6 This is an embodiment of the present invention using a C3MR configuration (propane-precooled mixed refrigerant) with a single wound heat exchanger (CWHE) in the cryogenic section. Figure 8Compressors C1A and C1B are driven by independent power mechanisms, with the waste heat from gas turbine GT1, which drives compressor C1B, being used to superheat the fluid supplied to the working expander X1. The in Figure 8 The illustrated embodiment would use a suitable fluid, such as propane, propylene, or other hydrocarbons, for the pre-cooling process. Alternatively, as shown in Figure 7 As shown, compressors C1A and C1B can be driven by a common gas turbine GT1.

[0104] In other embodiments of the invention, in which the cooling system includes more than one circuit, the additional circuits can be pure refrigerant circuits, mixed refrigerant circuits, and / or gas expansion circuits. Furthermore, in other configurations, one or more gas turbines can be operated in parallel or in series. Figures 8 and 9 illustrate, for example, an alternative application of the present invention for a gas liquefaction process using a two-stage cryogenic method. In the figures shown in the Figures 8 and 9 In the illustrated embodiments, a mixed refrigerant cycle is used for pre-cooling and liquefaction, and a gas expansion process is used for subcooling the natural gas in separate stages of the cryogenic process.

Claims

1. Method for liquefying a gas (1), wherein the gas is subjected to cooling and liquefaction in indirect heat exchange (11, 13, 16-18) with a refrigerant of a refrigerant circuit, and, after heat exchange with the gas, at least a part of the refrigerant is subjected to compression (C1, C1A, C1B) using a drive (GT1, GT1A, GT1B) that generates waste heat, and to partial or complete liquefaction (E1), and after partial or complete liquefaction, a first portion of the refrigerant is subjected to heat exchange with the gas, characterized in that a second portion of the refrigerant (R) is successively subjected to pressurization (P1), heating (E4, E4A, E4B) using the waste heat from the drive (GT1, GT1A, GT1B), and work-performing expansion (X1), and is then returned to the refrigerant circuit.

2. Method according to claim 1, wherein a mixed refrigerant is used as the refrigerant in one or more mixed refrigerant circuits and / or wherein natural gas or a gas mixture formed using natural gas is used as the gas (1) and / or wherein a gas turbine is used as the drive (GT1, GT1A, GT1B) that generates the waste heat.

3. Method according to any of the preceding claims, wherein work performed during the work-performing expansion (X1) is used in addition to the drive (GT1, GT1A, GT1B) in the compression of the same refrigerant.

4. Method according to claim 3, wherein compression of the refrigerant comprises a first compression step to a first pressure level (C1, C1A, C1B) and a second compression step to a second pressure level (C2) above the first pressure level, wherein the drive (GT1, GT1A, GT1B) is used in the first compression step and work performed during the work-performing expansion (X1) is used in the second compression step.

5. Method according to claim 1, wherein the first and the second portion are in each case portions of a first refrigerant, and wherein work performed during the work-performing expansion (X1) is used in the compression of a second refrigerant, wherein the first refrigerant is a pure refrigerant and the second refrigerant is a mixed refrigerant, or the first refrigerant is a mixed refrigerant and the second refrigerant is nitrogen.

6. Method according to claim 4, wherein the refrigerant is at least partially subjected to the first compression step (C1, C1A, C1B) and subsequently is at least partially subjected to a first partial liquefaction (E1) to obtain a first liquid fraction and a first gas fraction, wherein the first gas fraction is at least partially subjected to the second compression step (C2) and subsequently is at least partially subjected to a second partial liquefaction (E2) to obtain a second liquid fraction and a second gas fraction.

7. Method according to claim 6, wherein the second portion of the refrigerant (R), after the work-performing expansion (X1) thereof, is at least partially combined with the refrigerant or a part thereof before the refrigerant or the part thereof is subjected to cooling (E1) for the first partial liquefaction.

8. Method according to claim 6 or claim 7, wherein the second portion of the refrigerant (R), before the work-performing expansion thereof, is at least partially subjected to indirect heat exchange (E3) with the second portion of the refrigerant or a part thereof, after the second portion of the refrigerant or the part thereof was subjected to the work-performing expansion and before the second portion of the refrigerant or the part thereof is combined with the first gas fraction.

9. Method according to any of claims 6 to 8, wherein the second liquid fraction is at least partially expanded (V1) and combined with the refrigerant compressed in the first compression step (C1, C1A, C1B).

10. Method according to any of claims 6 to 9, wherein a heat exchanger having a plurality of sections or a plurality of heat exchangers is / are used to cool and liquefy the gas (1) in indirect heat exchange (11, 13, 16-18) with the refrigerant, the first portion of the refrigerant and the second gas fraction or parts thereof being further cooled to different temperature levels and reheated after expansion.

11. Method according to any of claims 1 to 4, wherein work performed during the work-performing expansion (X1) is used in addition to the drive (GT1, GT1A, GT1B) in the compression of a further refrigerant, with which the gas (1) is subjected to cooling and liquefaction in indirect heat exchange (11, 13, 16-18).