CN113710978A

CN113710978A - Method and apparatus for liquefying gas

Info

Publication number: CN113710978A
Application number: CN202080026359.XA
Authority: CN
Inventors: B·海因茨; M·卡曼; F·卡默迈尔
Original assignee: Linde LLC
Current assignee: Linde GmbH; Messer LLC
Priority date: 2019-04-01
Filing date: 2020-03-12
Publication date: 2021-11-26
Also published as: GB201904525D0; US20220170695A1; GB2582763A; EP3948122A1; WO2020200516A1; EP3719425A1; AU2020255798A1; WO2020200516A8

Abstract

The invention relates to a method for liquefying a gas, wherein the gas is subjected to cooling in indirect heat exchange with a refrigerant, and at least a part of the refrigerant is subjected to compression using a drive (GT1) generating waste heat and partial or complete liquefaction after heat exchange with the gas. After the partial or complete liquefaction, subjecting a first portion of the refrigerant to heat exchange with the gas, and sequentially subjecting a second portion of the refrigerant to pressurization, heating and work expansion using the waste heat of the drive (GT1), and thereafter again to the partial or complete liquefaction. The invention also relates to a corresponding device.

Description

Method and apparatus for liquefying gas

The present invention relates to a method for liquefying gas, in particular natural gas, and to a corresponding device according to the respective preambles of the independent claims.

Background

Processes and plants for the liquefaction of Natural Gas are known and are for example published on-line in Ullmann's Encyclopedia of Industrial Chemistry at 2006, 7, 15, at "Natural Gas", DOI: 10.1002/14356007.a17_073.pub2, in particular section 3 "Liquefact", or "Advanced Natural Gas Engineering" by Wang and Econoids, Gult Publishing 2010, DOI: 10.1016/C2013-0-15532-8, in particular chapter 6 "Liquid Natural Gas (LNG)".

In particular, a mixed refrigerant composed of different hydrocarbon components and nitrogen may be used in the liquefaction of natural gas. For example, one, two or even three Mixed Refrigerant cycles (SMR; DMR; MFC) may be used. Mixed refrigerant cycles (see below) with propane pre-cooling (C3MR) or more generally with pure refrigerant are also known.

Although the invention is described below primarily with reference to the liquefaction of natural gas, the measures proposed are in principle also applicable to the liquefaction of other gas mixtures. The natural gas and the corresponding other gas mixture may in particular have more than 70 mole percent, preferably more than 90 mole percent, methane and in the remaining remainder (mainly) non-hydrocarbon gases, such as nitrogen and acid gases. Higher hydrocarbons, particularly ethane, may also be included. Higher hydrocarbons, such as ethane, propane, butane, etc., are preferably present in an amount less than 10 mole percent. For example, such higher hydrocarbons may 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.

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 produce the required refrigeration. The increase in process efficiency often leads to additional investments, since more technically complex systems have to be used.

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

There are different solutions to utilize the waste heat of the turbine exhaust gases. Simple systems include recovery of waste heat in the form of process heat, for example in a hot oil system that transfers heat from the turbine exhaust to, for example, the reboiler of a regeneration column in an amine scrubber, a regeneration gas heater of a dryer, or any other heat user at a corresponding temperature level.

More complex waste heat utilization systems include closed steam cycles. The steam produced from the waste heat may be work expanded in a steam turbine. Any refrigeration cycle compressor may be driven using a corresponding vapor turbine, including, for example, those compressors utilizing a pre-cooling cycle such as propane, carbon dioxide, or ammonia as the refrigerant. Support may also be provided for the gas turbine of the main compressor.

It is generally desirable to increase the efficiency of natural gas liquefaction and other gas liquefaction processes without the need for time and effort consuming installation of additional working fluid, e.g., steam, based cycles.

Disclosure of Invention

On this background, the invention proposes a method and an apparatus having the features of the independent claims. Embodiments of the invention are subject matter of the respective dependent claims and the following description.

In the context of the present invention, a method for liquefying a gas is proposed, in which the gas is subjected to a heat exchange with a refrigerant and at least a part of the refrigerant, after the heat exchange with the gas, can in particular be at least partially evaporated therein, be subjected to compression using a drive generating waste heat and be partially or completely liquefied. Thus, in the context of the present invention, a refrigerant cycle is used, which comprises the known steps of: heating and evaporation (with respect to the fluid to be cooled, in this case the gas to be liquefied), recompression (using a drive generating waste heat) and (partial) condensation in a cycle.

In general, where "evaporation" is referred to hereinafter, it is meant to be partial or complete. Correspondingly, "condensation" is also to be understood as partial or complete condensation, even if not explicitly stated in each case. Here, the heat exchange of the refrigerant "with the gas" can take place in the form of an indirect heat exchange between the gas and the refrigerant, without an intermediate connection of another refrigerant, i.e. via the common heat exchange surface of the heat exchanger, but also via an additional refrigerant. Thus, if heat is extracted from the gas via another refrigerant and the other refrigerant is pre-cooled with the refrigerant considered here, a "heat exchange with the gas" also takes place. The term "heat exchange" is always used herein synonymously with the scientifically more correct term "heat transfer", and the term "heat exchanger" is used synonymously with the term "heat transfer device".

It is also well known in this connection that the heating and evaporation, recompression and (partial) liquefaction can be carried out in any (pressure or temperature) stage or in parallel with one another in a plurality of partial streams, wherein the respective partial streams can be combined with one another at any point or formed from one output stream. The invention relates in particular to a closed refrigerant circuit, as is known from the prior art mentioned at the outset for the liquefaction of natural gas.

According to the invention, after partial or complete liquefaction of the refrigerant, a first portion of the refrigerant is subjected to heat exchange with a gas in the sense just set forth, while a second portion of the refrigerant is subjected in sequence to pressurization (liquid state), heating (in particular superheating) and work expansion using the waste heat of the drive means and is sent again to partial or complete liquefaction. In other words, the second part of the refrigerant is thus, after its work expansion, in which it is in particular evaporated, returned into the refrigerant cycle and is here in particular combined with the first part of the refrigerant, which previously has undergone heat exchange with the gas and is here also evaporated. One sub-cycle is thus generated. In principle, the second part can be returned to the refrigerant cycle again at any point and combined with the first part; the specific locations continue to be set forth below.

Thus, in other words, the invention relates to a gas liquefaction process in which at least one compressor is used in a refrigerant cycle for providing refrigeration. The drive of the compressor generates waste heat. In particular, a gas turbine is used as the drive, in order to provide waste heat, in particular using turbine exhaust gas which is extracted from an expansion stage of the gas turbine. In the present invention, work expansion is performed on one of the divided streams of refrigerant, i.e., the aforementioned "second portion". This second portion is further pressurized and heated prior to work expansion so that the refrigerant can receive waste heat contained in the turbine exhaust of the gas turbine or other waste heat carrier. By work expansion, the heated, in particular superheated, refrigerant obtained by utilizing the waste heat is used as an energy source, so that the waste heat can be converted in this way into another energy form. The work performed in work expansion may be utilized as set forth below. Work expansion can also be performed in two or more stages using waste heat with or without intermediate superheating.

In the context of the present invention, as is set forth below in the embodiments, it is provided in particular that the work performed in the work expansion is used to compress the same refrigerant or different refrigerants. Although in the following embodiments a particular compressor is driven by the work performed in the work expansion, it is not excluded that other compressors may also be driven in this way. In particular embodiments of the present invention, in some cases, for example, the compressors (indicated by C2 in the figure) each compressing to the highest pressure in the refrigerant cycle are coupled to the corresponding expander. Alternatively, however, any other compressor or compressor stage (designated by C1, C1A, or C1B in the figures) adapted to compress to a lower pressure may also be driven via work expansion. Likewise, it is also possible to operate parallel compressors, one driven by the work done in work expansion and the other driven by other means, and these compressors compress parallel partial flows of refrigerant.

In various embodiments of the invention, the work performed during expansion may also be used, at least in part, to drive a generator.

In medium-scale natural gas liquefaction plants with annual capacities of, for example, about 0.3 to 2 million tons, the aforementioned SMR cycle is often used because of the limited number of components required therein and reasonable thermodynamic efficiency. However, the investment costs of a steam plant utilizing turbine waste heat are not necessarily economical for such plant scale if the possible energy savings cannot compensate for the additional costs. The invention is particularly suitable for such situations and creates an alternative and advantageous possibility for waste heat utilization. By using the present invention, the efficiency of the SMR process can be improved by at least 10 to 15 percentage points by: the load on the gas turbine for driving the refrigerant compressor is correspondingly reduced.

On the other hand, the invention can also be advantageously used for larger scale natural gas liquefaction, for example in plants with annual capacities of about 2 to 10 million tons. In such plants, more than one refrigerant compressor is typically required to achieve the above-described capacity. The optimum rotational speeds of the individual refrigerant compressors need not be similar or identical, so that if the individual compressors are to be driven by means of a common gas turbine, gear transmissions must be used between the individual compressors if necessary. However, even with multiple independent gas turbines, there may be an imbalance in the shaft power required by each compressor. In some cases, the invention may be advantageously utilized herein by: the work done during work expansion is used to assist the drive and thereby compensate for speed or power imbalances.

In particular, in the method according to the invention, mixed refrigerant can be used as refrigerant in one or more mixed refrigerant cycles. The refrigerant mixture typically consists of light hydrocarbons having 1 to 5 carbon atoms and no more than 20 mole percent nitrogen. The invention can be used for the aforementioned SMR, but also for DMR, MFC or C3MR refrigeration cycles and other refrigeration cycles, wherein pure refrigerants are used in addition to mixed refrigerants, as they are basically known in the prior art cited at the outset. By "pure refrigerant" is understood here a refrigerant which has or consists essentially of at least 95 mole percent, in particular at least 99 mole percent, of a single hydrocarbon, in particular ethane, ethylene, propane or propylene, or another compound having a suitable vapor pressure profile, such as ammonia or carbon dioxide. If reference is also made below to, for example, "propane" or "propane refrigeration cycle", this statement is always to be understood as meaning that they also refer to pure substance refrigerants in general. Reference to a particular pure substance is for illustration only. The corresponding pure refrigerant can in this case be in particular those which are treated in the manner described, i.e. from which the first and second portion are formed in the form of a corresponding partial flow.

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

It is particularly advantageous in embodiments of the invention to use the work produced in work expansion in addition to the drive means in the compression of the same refrigerant, which refrigerant is likewise work expanded, and to use this refrigerant to form the first and second parts. In this way, the drive originally used for compression can be relieved of load, i.e. the work done during work expansion is subtracted, and a corresponding energy saving results, which is directly attributable to the use of waste heat. Thus, the liquid pressurization of the second portion of refrigerant, which is correspondingly work expanded later, requires relatively much less energy. Such embodiments will first be explained below.

In the context of the present invention, i.e. in the first group of embodiments, only mixed refrigerants are used, but no pure refrigerants in the sense described above are used. In this case, however, it is entirely possible to have an embodiment in which the mixed refrigerant is used for precooling. In this first group of embodiments, the compression of the refrigerant comprises in particular a first compression step at a first pressure level and a second compression step at a second pressure level, in particular higher than the first pressure level, wherein in the first compression step a drive means is used and in the second compression step the work done in work expansion is used. Thus, in particular a first compression step can be performed using one or more first compressors or one or more first compressor stages, which compressors or compressor stages are driven at least partially using a drive, and in particular a second compression step can be performed using one or more second compressors or compressor stages, which compressors or compressor stages are driven at least partially using the work done in work expansion. In this case, the second compression step is in particular not driven using a drive which generates waste heat, but advantageously only using the work which is performed during work expansion. In this way, both compression steps can be achieved by independently operable machines and no mechanical coupling is required. As will also be explained below, the work done in work expansion can also be utilized correspondingly at any other location.

In the context of the present invention, in a preferred embodiment, hereinafter also referred to as "first embodiment", the refrigerant may be at least partially subjected to a first compression step and subsequently at least partially subjected to a first partial liquefaction to obtain a first liquid fraction and a first gaseous fraction, wherein in this first embodiment the first gaseous fraction is at least partially subjected to a second compression step and subsequently at least partially subjected to a second partial liquefaction to obtain a second liquid fraction and a second gaseous fraction. In this first embodiment, in particular, the entire refrigerant may be subjected to a first compression step, after it has been evaporated in heat exchange with the gas to be liquefied. The method can therefore be used for gas liquefaction simply and without great additional effort, together with known methods, in which corresponding steps are provided. Reference is made to the cited prior art.

In this first embodiment, the first compression step is performed in particular using a single compressor, which, although possibly multistage, does not compress the refrigerant to different pressures, which is always indicated in the relative figures with the reference C1. In this and the following embodiments, the second compression step is performed in particular using a compressor operating independently of the first compression step, which compressor is designated throughout the figures with the reference C2.

In a first embodiment, the second portion of the refrigerant after its work expansion may be at least partially combined with the refrigerant compressed in the first compression step before cooling the latter to effect liquefaction of the first portion. In this way, the second part of the refrigerant can be returned to the refrigerant cycle and be subjected there again to the required compression and condensation steps.

In particular, the second portion of the refrigerant used in the first embodiment according to the invention can be brought into a liquid state in order to be subsequently expanded from a pressure level of 10 to 40bar to a pressure level of 60 to 120 bar. By heating by means of waste heat, the temperature level is in particular heated from 10 to 50 ℃ to 200 to 400 ℃. For example, the turbine exhaust or other material flow of a gas turbine used as a drive may be present at 400 to 600 ℃. In a first embodiment, work expansion is carried out, in particular starting from the aforementioned pressure level or higher, to a pressure level of 10 to 40bar, so that the temperature is in particular reduced by about 30 to 100 ℃. In the first embodiment, the first compression step may in particular be carried out at a pressure level of 10 to 40bar and the second compression step at a pressure level of 30 to 70 bar. The respective subsequent partial condensation step is in this case in particular carried out at a temperature level of 10 to 50 ℃ in each case. The second portion of the refrigerant eventually delivered to work expansion comprises in particular 40% to 80% of the first liquid fraction.

In a first embodiment, the second portion of refrigerant may be subjected, partially or completely before its work expansion, to an indirect heat exchange with the second portion of refrigerant or a portion thereof that has been subjected to work expansion (i.e. at least partially subjected to "with itself"), before the latter is combined with the first gaseous fraction.

If only the second portion of the refrigerant is partly subjected to the aforementioned heat exchange with itself, the heat exchange takes place in the form of a first partial flow of the second portion, without the second partial flow of the second portion being subjected to the heat exchange with itself. The first and second partial flows can be subjected separately from one another to heating using waste heat and in particular to different temperature levels and, after this, combined with one another again before work expansion. Thus, for example, the second partial flow of the first partial flow can be heated in a first waste heat exchanger to a higher temperature level using turbine waste heat, wherein the already partially cooled exhaust gas of the gas turbine is supplied to a second waste heat exchanger, wherein the second partial flow can be heated to a lower temperature level. In this way, it is possible to advantageously preheat the subsequent further heating or to cool the subsequent feed of the first gaseous fraction after its compression.

In the process according to the invention, in the first embodiment, the second liquid fraction may be at least partially expanded and combined downstream of the first compression step with the refrigerant or a part thereof after corresponding cooling, before phase separation of the refrigerant.

For cooling of the gas in indirect heat exchange with the refrigerant, in a first embodiment, a heat exchanger or a plurality of heat exchangers having multiple sections may be used, wherein the first and second gas fractions of the refrigerant or portions thereof may be further cooled to different temperature levels and reheated after expansion. The heat exchanger or heat exchangers may in particular be designed as a wound bundle heat exchanger or as a brazed plate heat exchanger, or comprise a plurality of such heat exchangers, also different types of heat exchangers.

For example, in a first embodiment, the first and second gaseous fractions of the refrigerant or respective portions thereof (corresponding, although not explicitly mentioned, also applies to the other fluids mentioned below) may be conveyed to a heat exchanger designed as a coil heat exchanger at an inlet temperature level of, for example, 10 to 50 ℃ and cooled by separate heat exchanger tubes. A first portion of the refrigerant may be extracted from the heat exchanger, expanded, and re-delivered to the heat exchanger on the shell side at a first intermediate temperature level, e.g., -20 to-60 ℃, that is lower than the inlet temperature level. In this case, the second gaseous fraction may also be withdrawn from the heat exchanger at a first intermediate temperature level, at which it is in a partially condensed form. After phase separation outside the heat exchanger, the liquid and gas phases are again conveyed to the heat exchanger separately from one another at a first intermediate temperature level and are further cooled by means of separate heat exchanger tubes. The liquid phase is extracted at a second intermediate temperature level, lower than the first intermediate temperature level, for example-70 to-100 ℃, expanded and re-conveyed to the heat exchanger on the shell side. The gaseous phase is extracted at a third intermediate temperature level, lower than the second intermediate temperature level, for example-120 to-160 ℃, expanded and again conveyed to the heat exchanger, likewise on the shell side. The fluid thus combined on the shell side is again conveyed to the compression.

If a brazed plate heat exchanger is used, the first and second gas fractions or respective portions thereof of the refrigerant may also be delivered together to the heat exchanger at an inlet temperature level in the above-mentioned range and cooled in a common channel. After extraction at the cold end of the heat exchanger at an extraction temperature level of, for example, -120 to-160 c, expansion can be carried out and the refrigerant which in this way has been further cooled to a temperature level of, for example, -130 to-170 c, is returned through a separate channel and, after heating to a temperature level in the range of the inlet temperature level, is again sent to compression.

In a further preferred embodiment of the invention, also referred to below as "second embodiment", the first compression step can be designed in particular differently and is carried out using two compressor stages, namely a first compressor stage and a second compressor stage, which compressor stages are, however, advantageously driven jointly by a drive which provides waste heat. The first compressor stage may also be designed structurally in the form of a plurality of compressor stages of one compressor, which are designated throughout the figures with the reference character C1A, and the correspondingly designed second compressor stage with the reference character C1B. The second embodiment relates in particular to DMR procedures. Two or three heat exchangers or heat exchanger sections, each of which may form a corresponding part of a wound heat exchanger or a wound heat exchanger, are advantageously used in the process. In the following, for the sake of simplicity, only the expression two or three "heat exchangers" is used, but the corresponding parts of one common heat exchanger should also be included therein. In the direction of the temperature drop of the gas to be liquefied here, these heat exchangers are, in the language used here, a first, a second and a third heat exchanger. In the embodiment with three heat exchangers, the first and second heat exchangers use the same refrigerant at different evaporation pressures and can therefore also be combined, in particular in a low-cost apparatus, or the first heat exchanger can be omitted in such an apparatus. The invention also relates to such a method and apparatus, even if not mentioned separately below, and is described on the basis of a method and apparatus having three heat exchangers.

In a second embodiment, the respective evaporated refrigerant streams from the first and second heat exchangers are delivered to the first compressor stage of the first compression step at pressure levels of, for example, 5 to 20bar and 2 to 10bar, respectively. In the first compressor stage of the first compression step, compression is effected to, for example, 15 to 50bar, and in the second compressor stage of the first compression step, compression is effected to, for example, 40 to 80 bar. Downstream of the compression stages, an after-cooling is carried out in each case. The first or second portion of the refrigerant previously referred to multiple times is formed by the fluid compressed in the first compressor stage, which may include additional refrigerant in addition to the refrigerant described above. The second fraction also comprises in particular from 40% to 80% thereof.

The first part is first conducted on the tube side through a first heat exchanger and cooled there to a temperature level of, for example, 0 to-20 ℃. The split stream may be expanded downstream of the first heat exchanger and fed into the first heat exchanger on the shell side. This partial flow represents in particular the entire refrigerant evaporated in the first heat exchanger. In the previously described embodiment with only two heat exchangers, the measures described for the first heat exchanger are omitted. The non-expanded remaining portion of the first portion of refrigerant may be used to form another tapped flow that may be used in a separate another heat exchanger to cool the fluid compressed in the second compressor stage of the first compression step and thereafter sent to the first compressor stage of the first compression step. The remaining part of the first part which remains thereafter is first conducted on the tube side through a second heat exchanger and cooled there to a temperature level of, for example, -30 to-70 ℃. The remaining part can now be expanded downstream of the second heat exchanger and fed into the second heat exchanger on the shell side. This remaining portion represents in particular the entire refrigerant evaporated in the second heat exchanger.

In a second embodiment, a second portion of the refrigerant may be treated substantially as set forth above with respect to the first embodiment and specifically sent to the refrigerant compressed in the first compressor stage of the first compression step before it is further cooled and condensed. In this way the second part is guided cyclically. The refrigerant compressed in the second compressor stage of the first compression step can be fed in particular to the second compression step and compressed there in principle as explained for the first embodiment. In particular, to a pressure level of 70 to 110 bar. The correspondingly compressed refrigerant is cooled and first led on the tube side through the first to third heat exchangers for further cooling. Downstream thereof, the portion of refrigerant is expanded and fed to the third heat exchanger on the shell side. The portion of refrigerant represents in particular the entire refrigerant evaporated in the third heat exchanger.

Yet another preferred embodiment of the invention, hereinafter also referred to as "third embodiment", comprises performing the first compression step using two compressors, which are now advantageously driven by two separate drives providing waste heat. They operate in substantially the same manner as the corresponding compressor stages in the second embodiment and are therefore referred to by corresponding names. The third embodiment also relates to a DMR process. It is advantageous to use two or three heat exchangers or heat exchanger sections, as in the second embodiment, so that the above explanations continue to apply. The features and explanations mentioned above in connection with the second embodiment also apply to the third embodiment, in which the remaining part of the first portion of the refrigerant which is not expanded downstream of the first heat exchanger is however optionally not used for forming a further partial flow for cooling the fluid compressed in the second compressor of the first compression step. The second portion of the refrigerant that will eventually work expand is heated using the waste heat from both drives.

As previously mentioned, in the embodiment just described, the work performed in the work expansion is used in addition to the driving device in the compression of the same refrigerant, which is also work expanded, and the first and second portions are formed using this refrigerant, although this refrigerant is used in different cycles in the DMR cycle. In contrast, in other embodiments of the invention it may be advantageous to use the work done in work expansion to compress another refrigerant, i.e. the same refrigerant that is not compressed in work expansion and used to form the first and second portions. To better differentiate, the refrigerant that is work expanded and used to form the first and second portions is referred to as the "first" refrigerant, while the other refrigerant is referred to as the "second" refrigerant.

The first to third embodiments are part of the first group of embodiments previously mentioned, in which only mixed refrigerants are used. SMR and DMR cycles are contemplated herein, i.e., cycles that also include those that use mixed refrigerants for pre-cooling. A second set of embodiments, now to be described, includes embodiments that additionally use a pure substance refrigerant in the pre-cooling cycle. And thus primarily involves the C3MR cycle.

In a second group of embodiments, compression of a pure substance refrigerant, which here represents the "first" refrigerant in the sense just set forth, is carried out in the first compressor or first compressor stage in a pre-cooling cycle, while compression of a mixed refrigerant, which here represents the "second" refrigerant, in the sense set forth below, in a mixed refrigerant cycle is carried out using the second compressor or second compressor stage and the third compressor or third compressor stage. The work done during work expansion is used to drive the third compressor or third compressor stage. For the sake of clarity only, the expression compressor will be used hereinafter, which is also understood to mean a compressor stage.

In a corresponding embodiment of the invention, hereinafter also referred to as "fourth embodiment", the first and second compressors (C1A and C1B in the drawings) are driven by two separate drives, of which only the drive of the second compressor is the drive providing waste heat (at least to an appreciable and usable extent), such as a gas turbine. For example, the first compressor may be electrically driven, generating significantly less waste heat (and not being usable).

Unlike the second and third embodiments, the brazed plate heat exchanger and the wound tube bundle heat exchanger are used to cool the gas to be liquefied in the fourth embodiment. As mentioned before, two separate refrigerant cycles are realized, i.e. one pure substance cycle with pure substance refrigerant for pre-cooling and one refrigerant cycle with mixed refrigerant. As already mentioned, the pure substance refrigerant cycle comprises a first compressor, while the mixed refrigerant cycle comprises a second and a third compressor.

The pure-substance refrigerant of the pure-substance circuit is fed to the first compressor and compressed there in the form of a plurality of partial flows which are heated in particular with respect to the mixed refrigerant from the second compression step and thus precool the mixed refrigerant. After subsequent cooling and liquefaction, the first and second portions of refrigerant are also formed therein. Unlike the previously set forth embodiments, the first and second portions are thus formed from pure substance refrigerant, i.e., "first" refrigerant, rather than a mixed refrigerant, i.e., "second" refrigerant. The first portion is first cooled, then expanded, heated against the mixed refrigerant, and sent again to the first compressor. The second part is treated as already explained above and is heated here by the waste heat of the drive of the second compressor.

The mixed refrigerant is cooled, after pre-cooling with a pure substance refrigerant of a pure substance cycle, in particular to a temperature level of-20 to-40 ℃, and further cooled in a coil heat exchanger on the tube side, in particular to a temperature level of-120 to-160 ℃. Downstream thereof, the mixed refrigerant is expanded and delivered to the wrap heat exchanger on the shell side. After extraction from the wound heat exchanger and corresponding heating, further heating is performed in the brazed plate heat exchanger and subsequently compression is performed in the second and third compressors.

A variation of the fourth embodiment just described, referred to as the "fifth embodiment", includes the first and second compressors being driven by a common waste heat generating drive.

In all cases, the work done in work expansion can be used in the compression of another refrigerant with which the gas is subjected to cooling in indirect heat exchange. This may be the case, for example, when a pure substance refrigerant or C3MR refrigerant cycle is used, or in variations of the first set of embodiments.

In another embodiment of the present invention, referred to herein as the "sixth embodiment", the first refrigerant is a mixed refrigerant and the second refrigerant is nitrogen. Also in this embodiment, the first and second portions are portions of the first refrigerant, i.e., the mixed refrigerant, and the work performed in the work expansion is used in the compression of the second refrigerant, i.e., nitrogen.

In principle, in a sixth embodiment, the mixed refrigerant may be at least partially subjected to a first compression step, and subsequently at least partially subjected to a first partial liquefaction to obtain a first liquid fraction and a first gaseous fraction, as previously explained for the first embodiment. The first gaseous fraction may be at least partially subjected to a second compression step and subsequently at least partially subjected to a second partial liquefaction to obtain a second liquid fraction and a second gaseous fraction. The further processing may also be the same.

In a fifth embodiment, nitrogen is generally subjected to expansion and compression, where the compression of the nitrogen is performed using work done in work expanding the second portion of the mixed refrigerant. In a fifth embodiment, the nitrogen may be work expanded, wherein the work performed on the nitrogen in the work expansion may also be used in the compression of the nitrogen.

The compressed nitrogen is successively cooled, subjected to a first indirect heat exchange and cooled there, subjected to expansion, subjected to a second indirect heat exchange and heated there, subjected to a first indirect heat exchange thereafter and heated there and conveyed again to compression. In the second indirect heat exchange, the gas which is partially or completely subjected to liquefaction is subcooled here.

Another embodiment of the present invention, referred to herein as the "seventh embodiment," differs from the sixth embodiment in that the compression of nitrogen is performed in two stages, a first compression step using work done in work expanding the nitrogen and a second compression step thereafter using work done in work expanding a second portion of the mixed refrigerant.

The invention also relates to a device for liquefying gas, wherein the device has means adapted to subject the gas to cooling in indirect heat exchange with a refrigerant and to subject at least a part of the refrigerant, after heat exchange with the gas, to compression using a drive producing waste heat and subsequent partial or total liquefaction. According to the invention, the device has means adapted to subject a first part of the refrigerant, after partial or total liquefaction, to heat exchange with a gas and to subject a second part of the refrigerant in turn to pressurization, heating using the waste heat of the drive means and work expansion, and after this is sent again to the partial or total liquefaction.

The features and advantages of the corresponding apparatus advantageously adapted for carrying out the invention and any of the previously described embodiments are expressly referred to the above description.

The invention is elucidated below with reference to the accompanying drawings, which show an arrangement according to embodiments of the invention.

Drawings

Fig. 1 shows a method according to an embodiment of the invention.

Fig. 2 shows a method according to an embodiment of the invention.

Fig. 3 shows a method according to an embodiment of the invention.

Fig. 4 shows a method according to an embodiment of the invention.

Fig. 5 shows a method according to an embodiment of the invention.

Fig. 6 shows a method according to an embodiment of the invention.

Fig. 7 shows a method according to an embodiment of the invention.

Fig. 7A shows a variant of the method according to fig. 7.

Fig. 8 illustrates a method according to an embodiment of the invention.

Fig. 9 shows a method according to an embodiment of the invention.

In the drawings, parts corresponding to each other are given the same reference numerals and are not repeated for clarity. Corresponding parts are not to be considered as individually labeled in all figures.

Detailed Description

A method according to an embodiment of the invention is shown in fig. 1 in the form of a schematic process flow diagram.

The process is used for the liquefaction of a gas which is supplied to the process in gaseous state as stream 1 and is provided in liquefied form as stream 2. Here liquefaction is carried out using a heat exchanger or cryogenic section 10 which is greatly simplified as a whole. To illustrate general applicability, the heat exchanger portion 10 is shown in greatly simplified form.

The refrigerant is output from the heat exchanger portion 10 in the form of a heated ("hot") refrigerant stream W. The remaining condensed water is separated in separator D1. In the first compression step, the refrigerant of stream W is compressed using compressor C1 driven by gas turbine GT 1. In the gas turbine GT1, air of the air flow a is compressed in a compressor stage, not separately indicated, and combusted with fuel F in a combustion chamber (not shown). The hot gas is expanded in an expansion stage, which is likewise not separately indicated, and is output via a heat exchanger E4 for heat recovery. Additional fuel AF may also be used for spark assist.

The refrigerant compressed in compressor C1 was cooled in heat exchanger E1, partially condensed there, and subjected to phase separation in separator D2. The gas phase and the liquid phase are conveyed to the heat exchanger section 10 in the form of separate streams, wherein one part of the liquid phase is conveyed to the heat exchanger section 10 as a "first part" of the refrigerant which has been mentioned correspondingly a number of times before, and the other part is pressurized as a "second part" correspondingly in the form of stream R by means of a pump P1, heated in heat exchanger E3 and thereafter in heat exchanger E4, then work-expanded in an expander X1, conducted through heat exchanger E3, and subsequently combined with the refrigerant compressed in compressor C1 before cooling.

Compressor C2 is coupled with expander X1 via gear assembly G. The mixed refrigerant from the heat exchanger section 10 may be delivered to the compressor C2 in the form of a heated refrigerant flow W1, so that the waste heat of the gas turbine GT1 can be utilized in this way. For refrigerant flow W1, fig. 1 uses another mixed refrigerant in addition to the refrigerant of refrigerant flow W, and thus involves a DMR cycle. In all the embodiments of the invention described below, it is likewise possible to use such a further mixed refrigerant, even if only one mixed refrigerant cycle, if necessary with sub-cycles, is shown in each case there.

In fig. 2, a method according to a further embodiment of the invention is shown by means of a schematic process flow diagram. In fig. 2, the heat exchanger section 10 is shown here in particular in detail. The heat exchanger section comprises in particular a wound heat exchanger 11 and a separator 12, the function of which will be further elucidated below.

Refrigerant stream W1 or a similar stream according to fig. 1 is not provided here, and therefore in a practical embodiment it is an SMR cycle. Here, a refrigerant flow W is compressed 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 a gas turbine GT1 and the second compressor C2 is driven by the work produced in the work-producing expansion in the expander X1.

Stream W is compressed downstream of separator D1 in compressor C1 and is subsequently subjected to partial liquefaction in separator D2 after cooling in heat exchanger E1 to obtain a first liquid fraction and a first gaseous fraction. The first gaseous fraction, not separately indicated, coming from separator D2 is compressed in a second compressor C2 and subsequently, after cooling in heat exchanger E2, is subjected to partial liquefaction in separator D3 to obtain a second liquid fraction and a second gaseous fraction.

The first liquid fraction from separator D2 is partially treated in stream R as already explained previously. The remainder is sent to the coiled heat exchanger 11 as a stream not separately labeled, as is the second gas fraction from separator D2. The refrigerant flow is directed through individual heat exchanger tubes and cooled.

The first liquid fraction from separator D2, which is not used in the form of stream R, is extracted from heat exchanger 11 at a first intermediate temperature level below the corresponding inlet temperature level, expanded and sent again to heat exchanger 11 on the shell side. The second gaseous fraction can likewise be extracted from the heat exchanger at a first intermediate temperature level, expanded and partially liquefied there, wherein, however, a phase separation takes place outside the heat exchanger 11, into a liquid phase and a gaseous phase in a separator 12.

The liquid and gaseous phases formed in the separator 12 are conveyed again to the heat exchanger 11 separately from one another at a first intermediate temperature level and are further cooled by means of separate heat exchanger tubes. The liquid phase is extracted at a second intermediate temperature level lower than the first intermediate temperature level, expanded and again conveyed to the heat exchanger 11 on the shell side. The gaseous phase is extracted at a third intermediate temperature level, which is lower than the second intermediate temperature level, expanded and again fed to the heat exchanger 11, likewise on the shell side. The fluid combined in this way on the shell side is again conveyed to the compression in the form of a material flow W.

Stream R, after its work expansion, is combined with the refrigerant compressed in compressor C1 before cooling the refrigerant for the first partial condensation. The second liquid fraction from separator D3 was expanded via valve V1 and returned to separator D2.

In fig. 3 is shown another embodiment of the invention, which differs from the embodiment according to fig. 2 in particular in that a brazed plate heat exchanger 13 is provided instead of the wound tube bundle heat exchanger 11.

As shown here, the portion of the first liquid fraction from separator D2 that is not used in stream R may be sent to heat exchanger 13 along with the second gas fraction from separator D3 and cooled in a common channel. The pump 14 here pumps part of the first liquid fraction used in this way up to the pressure of the second gaseous fraction, whereby both fractions can be sent together to the heat exchanger 13. After withdrawal at the cold end, expansion can take place via valve 15, and the refrigerant which has been further cooled in this way can be returned through a separate channel and, after corresponding heating, again fed into separator D1.

In fig. 4, a further embodiment of the invention is shown, in which in particular the first compression step previously carried out in the compressor C1 is designed differently and is carried out using two compressor stages (first compressor stage C1A and second compressor stage C1B). The compressor stages are here jointly driven by a gas turbine GT 1.

In addition, three

heat exchangers

16, 17, 18 are used, each of which is designed as a coil heat exchanger. In the direction of the temperature drop of the gas 1 to be liquefied here, these are, in the language used here, a first heat exchanger 16, a second heat exchanger 17 and a third heat exchanger 18. The first heat exchanger 16 may be omitted if desired, as set forth in detail above.

The respective evaporated refrigerant streams from the first and

second heat exchangers

16, 17 are delivered to the first compressor stage C1A and compressed therein. The evaporated refrigerant stream from third heat exchanger 18 is delivered to and compressed at second compressor stage C1B. Downstream of the compressor stages, an after-cooling is carried out in each case. The fluid compressed by the first compressor stage C1A, which fluid may include additional refrigerant in addition to the refrigerant described above, extracted from the separator designated herein as D2, forms the first and second portions of the refrigerant previously mentioned multiple times.

The first part is first conducted on the tube side through the first heat exchanger 16 and cooled there. The split stream may be expanded downstream of the first heat exchanger 16 and fed into the first heat exchanger 16 on the shell side. The non-expanded remaining portion of the first portion of refrigerant may be used to form another tap that may be used in a separate heat exchanger E5 to cool the fluid compressed in the second compressor stage C1B of the first compression step and thereafter sent to the first compressor stage C1A of the first compression step. The remaining part of the first part which remains after this is first conducted on the tube side through the second heat exchanger 17 and cooled there. This remaining portion can now be expanded downstream of the second heat exchanger 17 and fed into the second heat exchanger 17 on the shell side.

A second portion of the refrigerant may be treated in the form of a stream R substantially as set forth previously and in particular sent to the refrigerant compressed in the first compressor stage C1A of the first compression step before it is further cooled and condensed. In this way the second part is guided cyclically.

In particular, the refrigerant compressed in the second compressor stage C1B of the first compression step can be fed to the second compression step with the compressor C2 and compressed there in principle as explained for the first embodiment. The correspondingly compressed refrigerant is cooled in the further heat exchanger E6 and is first led on the tube side through the first to

third heat exchangers

16, 17, 18 for further cooling. Downstream of the latter, the portion of refrigerant is expanded and sent to the third heat exchanger 18 on the shell side.

Yet another preferred embodiment of the present invention is shown in fig. 5. This involves performing the first compression step using two compressors, here designated as C1A and C1B as before for better comparison, but now driven by two separate drives (gas turbines) GT1A and GT1B providing waste heat. Correspondingly, the previously single-existing heat exchangers E3 and E4 now exist in a double form of heat exchangers E3A, E3B and E4A, E4B. In this embodiment, the second portion of the refrigerant, which is ultimately expanded in stream R, is preheated using the waste heat from the two drives GT1A and GT 1B.

Another embodiment of the invention is shown in fig. 6 and is implemented as a hybrid cycle (e.g., C3MR) process with pure refrigerant pre-cooling.

In the pre-cooling cycle, compression of the pure substance refrigerant (here shown illustratively as propane C3H 8) is here performed in the first compressor C1A, and compression of the mixed refrigerant in the mixed refrigerant cycle is performed using the second compressor C1B and the third compressor C2. The work done in the work expansion is used to drive the third compressor C2. The first and second compressors C1A, C1B are driven by two separate drives, of which only the drive of the second compressor C1B is the drive providing waste heat (at least to an appreciable and usable extent), such as the gas turbine GT 1. For example, the first compressor C1A may be driven by the motor M, generating significantly less waste heat (and not being usable).

The difference with the previously illustrated embodiment is that in addition to the wound heat exchanger 11, a brazed plate heat exchanger 19 is used to cool the gas 1 to be liquefied. The pure substance circulated refrigerant is delivered to the first compressor C1A and compressed there in the form of a plurality of partial flows which are heated in particular with respect to the mixed refrigerant from the second compression step and thus precool the mixed refrigerant. After subsequent cooling and liquefaction, the first and second portions of refrigerant are also formed therein. The first portion is first subcooled, then heated and evaporated against the mixed refrigerant from the second compressor, and again delivered to the first compressor C1A. The second part R is treated as already explained above and is heated here by the waste heat of the drive of the second compressor.

The mixed refrigerant is further cooled on the tube side in the coiled heat exchanger 11 after pre-cooling with a refrigerant of pure substance refrigerant cycle. Downstream thereof, the mixed refrigerant is expanded and delivered to the wound heat exchanger 11 on the shell side. After extraction from the wound heat exchanger 11 and corresponding heating, further heating is performed in the brazed plate heat exchanger 19 and subsequent compression in the second and third compressors C1B and C2.

A variation of the embodiment just set forth is shown in fig. 7. The variant comprises the first and second compressors C1A, C1B being driven by a common waste heat generating drive GT 1.

While a variant of the embodiment shown in fig. 7 is shown in fig. 7A, this embodiment can, however, also be implemented unconditionally as a variant of the embodiment shown in fig. 6 or of other embodiments of the invention, for example. Here, the partial flow R 'of the refrigerant flow R is not conducted through the heat exchanger E3, but through a heat exchanger E4', which is arranged downstream of the heat exchanger E4 in the turbine exhaust gas flow of the gas turbine GT 1. As indicated by the streams and heat exchangers shown in dashed lines, but not separately labeled, the pre-cooling of the refrigerant may also be implemented differently, and in particular include fewer heat exchanger stages than previously shown.

In all cases, the work done in work expansion can be used in the compression of another refrigerant with which the gas is subjected to cooling in indirect heat exchange. This may be the case, for example, when a mixed refrigerant cycle with pre-cooling with a pure substance refrigerant is used, or in other variations of the invention as shown in fig. 8 and 9. In these variants, additional brazed

plate heat exchangers

19A and 19B are used, which are operated using nitrogen circulation.

The processing of the mixed refrigerant is directly from fig. 8 and 9 and the previous explanation and is performed substantially similar to, for example, fig. 3, where here compressors C1 and C2 are operated but using gas turbine GT 1.

In the embodiment according to fig. 8, the nitrogen of the nitrogen cycle is subjected to compression in expander X2 and in compressor C3, wherein the compression of the nitrogen is performed using the work done in work expansion of the second portion of the mixed refrigerant in expander X1. The nitrogen is work expanded in expander X2, wherein the work done in work expanding the nitrogen is also used in the compression of the nitrogen. The expanders X1 and X2 and compressor C3 are mechanically coupled here.

The compressed nitrogen is successively cooled, subjected to a first indirect heat exchange in the heat exchanger 19B and cooled there, subjected to expansion, subjected to a second indirect heat exchange in the heat exchanger 19A and heated there, after which it is subjected to a first indirect heat exchange again in the heat exchanger 19B and heated there and sent again to compression. In a second indirect heat exchange in heat exchanger 19A, the gas that was previously partially or fully liquefied is subcooled here. To aftercool the nitrogen in the nitrogen cycle downstream of compressor C3, a heat exchanger E7 is provided.

In the embodiment according to fig. 9, which corresponds substantially to the embodiment of fig. 8, the compression of nitrogen is performed in two stages, i.e. a first and thereafter a second compression step, in compressors C3 and C4, wherein the first compression step is performed using the work done in the work expansion of nitrogen in expander X1 and the second compression step is performed using the work done in the work expansion of the second part of the mixed refrigerant in expander X2. In this embodiment, the expander X1 and the compressor C4 are coupled on the one hand and the expander X2 and the compressor C3 are coupled on the other hand.

The invention described above and the embodiments thereof which are set forth and are shown in particular in the drawings will be described again below in further text. The terms used below may be synonymous with the terms used above for the method steps, apparatus and medium each identified thereby. The following description describes the same inventive idea as the above description in an at least partially different representation with corresponding advantageous refinements.

The present invention provides a method of collecting or recovering waste heat generated in a gas liquefaction process, the method comprising: liquefying the gas with a refrigerant fluid by a heat exchange process; compressing the spent refrigerant fluid from the liquefaction process by generating excess heat; liquefying at least a portion of the compressed refrigerant fluid; pumping the liquefied compressed refrigerant fluid to a higher pressure; heating a portion of the liquefied compressed refrigerant fluid having a high pressure by receiving excess heat generated by compressing the used refrigerant fluid, thereby superheating the portion of the compressed refrigerant fluid having a high pressure; and powering the mechanical process using the superheated compressed refrigerant fluid.

One embodiment of the invention is applicable to a natural gas liquefaction process having at least one compressor for use in a cryogenic process for natural gas liquefaction in a refrigerant cycle. The present invention uses a compressor in the refrigerant cycle, wherein the compressor is driven by a gas turbine or similar energy source that generates waste heat when generating power to operate the compressor. The present invention uses a work expander wherein the fluid cycle of the work expander is used to receive waste heat from a gas turbine or similar power source that drives a compressor in a refrigerant cycle. In one embodiment of the invention, the fluid cycle of the work expander is both pressurized and heated to enable the fluid cycle to receive waste heat present in the exhaust gas stream of a gas turbine or other waste heat of a power source that drives a compressor in a refrigeration cycle. The superheated fluid produced therein, which is produced from the waste heat energy recovery process, is then used as an energy source to drive the work expansion machine.

In another embodiment of the invention, the fluid used in the fluid cycle for the work expansion machine is also used in the refrigerant cycle. In this embodiment of the invention, a second compressor is additionally used in the refrigerant cycle, wherein the second compressor is driven by a work expander. Thus, in this embodiment of the invention, the refrigerant fluid used for natural gas liquefaction in the cryogenic process is also used to absorb waste heat generated to drive the first compressor to provide power for driving the work expander, which in turn drives the second compressor to further compress the refrigerant fluid. This embodiment of the invention therefore has advantages over other systems for harvesting waste heat energy sources. Thus, this embodiment of the invention does not require the introduction of additional working liquid, such as water, nor the addition of other liquids (such as steam, ammonia, propane, etc.) in the closed loop.

In a natural gas hydraulic process, not shown, according to the prior art, in which a Single Mixed Refrigerant (SMR) is used with a two-stage SMR compression process, it may be provided that the two compressors C1 and C2 are driven by only one gas turbine GT 1. Here, the low temperature part of the process performs liquefaction of natural gas by a heat exchange process with the mixed refrigerant. In a natural gas liquefaction process, a mixed refrigerant is compressed, cooled, and partially liquefied before being recovered in a cryogenic process. The mixed refrigerant discharged from the low temperature part may be collected in the container D1 and then introduced into the first compressor C1 and the heat exchanger E1. In a corresponding two-stage compression process, the liquid portion of the first compressor C1 and heat exchanger E1 was collected in storage vessel D2, with the vapor portion of the first compressor C1 being fed to the second stage of the process via the second compressor C2 and heat exchanger E2. The fractions resulting from second compressor C2 and heat exchanger E2 were combined and collected in vessel D3. Both fractions collected in vessels D2 and D3 may be fed into the cryogenic section to perform the liquefaction process of natural gas by a heat exchange process.

Figure 2 shows an embodiment of the present invention in a natural gas liquefaction process in which a Single Mixed Refrigerant (SMR) is used using a two-stage SMR compression process. In fig. 2, the second compressor C2 is driven by the work expander X1, rather than a gas turbine. The work expander X1 is driven by a superheated fluid delivered by heat exchanger E4. The liquid exiting the work expander X1 is cooled by a preheater or waste heat exchanger E3 and then combined with the refrigerant produced by the first compressor C1. The combined liquids are then further cooled by heat exchanger E1 or similar means and collected in vessel D2. A portion of the combined liquid collected in vessel D2 was then pumped by pump P1 to heat exchanger E3. The cooled fluid pumped into the waste heat exchanger E3 is heated and subsequently introduced into the heat exchanger E4. The heat exchanger E4 is in fluid connection with the hot exhaust gas of the gas turbine GT1, which drives the first compressor C1. Here, the heat exchanger E4 utilises heat from exhaust gas from the gas turbine GT1 to superheat the heated liquid delivered to the heat exchanger E4 from the waste heat exchanger E3. The superheated fluid from heat exchanger E4 is then directed to work expander X1 to drive second compressor C2.

In one embodiment of the invention, the low temperature part may be designed as a wound heat exchanger (CWHE), a brazed plate heat exchanger (PFHE) or a combination thereof. For example, FIG. 3 is a schematic diagram of an embodiment of the present invention using a Single Mixed Refrigerant (SMR) configuration and a brazed plate heat exchanger (PFHE) in the low temperature section.

In one embodiment of the invention, as shown in FIG. 1, a 30 to 90 volume percent split of discharged liquid container D2 is pumped by pump P1 to at least three times the pressure in container D2. The high pressure stream of pump P1 is then heated by waste heat exchanger E3 and sent to superheater E4. The superheater E4 recovers waste heat from the exhaust gas flow of the gas turbine GT1 and heats the high pressure stream from the waste heat exchanger E3 to at least 180 ℃, preferably at least 200 ℃. The high temperature gas from superheater E4 is then fed into work expander X1 and reduced to a pressure slightly above the operating pressure of vessel D2. In one embodiment of the invention, the pressure of the stream exiting work expander X1 is high enough to overcome the pressure drop in heat exchangers E3 and E1, which still reach the pressure in D2. The stream exiting work expander X1 is then cooled and at least partially condensed by preheater E3 and heat exchanger E1 and then returned to vessel D2. The shaft power produced by work expander X1 is used to drive compressor C2 to compress refrigerant, which is then stored in vessel D3 and then sent to the low temperature portion of the process.

As explained for the embodiment of the invention shown in fig. 1, a pressure ratio of at least three times the suction pressure in vessel D2 produced by pump P1 results in a similar, but slightly lower, pressure ratio in the work expander X1, which is the preferred operating range of the work expander. Furthermore, the inlet pressure of the work expander X1 can be kept below 100bar, which makes a cost-effective mechanical design possible. Furthermore, the increased pressure generated by pump P1 ensures that work expander X1 obtains an inlet pressure that is well above the critical pressure of the fluid, and thus avoids two-phase effects within the fluid. In the embodiment of the present invention shown in fig. 1 to 9, the refrigerant in the process is used in two processes, i.e., a natural gas liquefaction process in a low temperature region and a waste heat recovery process, which is generated by a gas turbine for driving a refrigerant compression process. The present invention can be further modified to enhance the performance of the present invention. For example, the power of the work expander X1 may be increased by auxiliary ignition to an additional heat source in the flue of the gas turbine GT 1. The work expansion performed by the work expander X1 may be divided into successive steps, whether necessary to reheat the working fluid as needed or not.

In other embodiments of the invention, the shaft power produced by the work expander X1 may be used to drive other processes, such as a generator, feed gas compression, end flash gas compression, any type of refrigerant compression, or other service requiring flow.

The entire refrigeration system has at least one refrigerant which consists of pure components or mixed 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 allowable refrigerant components may include nitrogen and light paraffins or olefins from C1 to C5 (e.g., CH4, C2H4, C2H6, C2H6, C3H6, C3H8, iC4H10, nC4H10, nC4H10, iC5H12, nC5H12, and nC5H12, etc.). The refrigeration system may also comprise more than one cycle, wherein the additional cycles are pure refrigerant cycles and/or mixed refrigerant cycles and/or gas expansion cycles.

Fig. 4 is an embodiment of the invention using a dual mixed refrigerant configuration (DMR) with three coiled heat exchangers (CWHE) in the low temperature region and only one gas turbine GT1 for two mixed refrigerant cycles. As shown in fig. 6, this configuration decouples the high pressure compressor C2 from the low pressure compressors C1A, C1B, which are driven by a common shaft driven by the gas turbine GT 1. This embodiment of the present invention also eliminates the need for a gear assembly that would otherwise be required to operate the compressor C2 at higher pressures and higher operating speeds when the compressor C2 has a capacity similar to that of the compressor C1A or C1B.

Fig. 5 is an embodiment of the invention using a dual mixed refrigerant configuration (DMR) with three wrap around heat exchangers (CWHE) in the cold section where compressors C1A and C1B are driven by separate gas turbines GT1A and GT1B where the waste heat of two gas turbines GT1A and GT1B are used in heat exchangers E4A and E4B to superheat the liquid fed to work expander X1. An advantage of the embodiment of the invention shown in fig. 5 is that a higher power of the work expander X1 can be achieved to drive the compressor C2.

Fig. 6 is an embodiment of the present invention using a C3MR configuration (propane pre-cooled mixed refrigerant) with only one coiled heat exchanger (CWHE) in the low temperature section. In fig. 8, the compressors C1A and C1B are driven by independent power mechanisms, where the waste heat of the gas turbine GT1 driving the compressor C1B is used to superheat the fluid delivered to the work expander X1. The embodiment shown in fig. 8 will use a suitable fluid, such as propane, propylene, or other hydrocarbon, for the pre-cooling process. Alternatively, as shown in fig. 7, the compressors C1A and C1B may be driven by a common gas turbine GT 1.

In other embodiments of the invention in which the cooling system comprises more than one cycle, the additional cycles may be pure refrigerant cycles, mixed refrigerant cycles and/or gas expansion cycles. Further, in other configurations, one or more gas turbines may be operated in parallel or in series. Fig. 8 and 9, for example, illustrate an alternative application of the present invention for a gas liquefaction process using a two-stage cryogenic process. In the embodiments shown in fig. 8 and 9, a mixed refrigerant cycle is used for pre-cooling and liquefaction, and a gas expansion process is used to subcool the natural gas in a separate stage of the cryogenic process.

According to a1 st aspect, the invention comprises a method for separating waste heat generated in a gas liquefaction process, the method comprising: liquefying the gas with a refrigerant fluid by a heat exchange process; compressing the spent refrigerant fluid from the liquefaction process by generating excess heat; liquefying at least a portion of the compressed refrigerant fluid; pumping the liquefied compressed refrigerant fluid to a higher pressure; heating a portion of the liquefied compressed refrigerant fluid having a high pressure by capturing excess heat generated by compressing the used refrigerant fluid, thereby superheating the portion of the compressed refrigerant fluid having a high pressure; and using the superheated compressed refrigerant fluid to perform a mechanical process.

According to the 2 nd aspect, according to the 1 st aspect, a method for recovering waste heat generated in a gas hydraulic method is provided, the method additionally comprising that the mechanical process represents a further compression of the compressed refrigerant fluid.

According to aspect 3, according to aspect 1, a method for recovering waste heat is provided, which is generated in a gas hydraulic method, wherein the mechanical process is furthermore the operation of a work expander.

According to aspect 4, according to aspect 3 there is provided a method for recovering waste heat generated in a gas hydraulic method, the method additionally comprising heating a portion of liquefied compressed refrigerant fluid having a high pressure by heat exchange with fluid discharged by a work expander.

According to the 5 th aspect, according to the 4 th aspect, a method for recovering waste heat generated in a gas hydraulic method is provided, wherein additionally a fluid from a work expander used in heat exchange is combined with a liquefied compressed refrigerant fluid.

According to aspect 6, according to aspect 3 there is provided a method for recovering waste heat generated in a gas hydraulic method, the method additionally comprising that the mechanical process represents a further compression of the compressed refrigerant fluid.

According to aspect 7, there is provided according to aspect 6 a method for recovering waste heat generated in a gas hydraulic method, the method additionally comprising that the further compressed refrigerant fluid is the refrigerant fluid in the liquefaction step.

According to aspect 8, according to aspect 1 there is provided a method for recovering waste heat generated in a gas hydraulic method, the method additionally comprising mechanically generating electrical energy.

According to aspect 9, there is provided according to aspect 1a method for recovering waste heat generated in a gas hydraulic method, the method additionally comprising heating a portion of liquefied compressed refrigerant fluid having a high pressure involving assisted ignition to an additional heat source of captured excess heat generated by compressing used refrigerant fluid.

Claims

1. A method for liquefying a gas, wherein the gas is subjected to cooling in indirect heat exchange with a refrigerant, and at least a part of the refrigerant is subjected to compression using a drive (GT1) generating waste heat and partial or complete liquefaction after heat exchange with the gas, characterized in that after the partial or complete liquefaction a first part of the refrigerant is subjected to heat exchange with the gas, and a second part of the refrigerant is sequentially subjected to pressurization, heating and work expansion using the waste heat of the drive (GT1), and after this is again conveyed to the partial or complete liquefaction.

2. A method according to claim 1, wherein a mixed refrigerant is used as said refrigerant in one or several mixed refrigerant cycles, and/or wherein natural gas or a mixed gas formed using natural gas is used as said gas, and/or wherein a gas turbine is used as said waste heat generating drive (GT 1).

3. A method according to one of the preceding claims, in which at the compression of the same refrigerant, the work done at work expansion is used in addition to the drive (GT 1).

4. A method according to claim 3, in which the compression of the refrigerant comprises a first compression step at a first pressure level and a second compression step at a second pressure level higher than the first pressure level, wherein the work done in the work expansion is used in the first compression step and in the second compression step the drive (GT 1).

5. The method of one of claims 1 or 2, in which the first and second portions are each portions of a first refrigerant, and in which work performed in the expansion using the work is used in the compression of a second refrigerant, wherein the first refrigerant is a pure substance refrigerant and the second refrigerant is a mixed refrigerant, or wherein the first refrigerant is a mixed refrigerant and the second refrigerant is nitrogen.

6. The process according to claim 4, wherein the refrigerant is at least partially subjected to the first compression step and subsequently at least partially subjected to a first partial liquefaction to obtain a first liquid fraction and a first gaseous fraction, wherein the first gaseous fraction is at least partially subjected to the second compression step and subsequently at least partially subjected to a second partial liquefaction to obtain a second liquid fraction and a second gaseous fraction.

7. The method of claim 6, in which the second portion of the refrigerant is at least partially combined with the refrigerant or a portion thereof after work expansion thereof, prior to subjecting the refrigerant or the portion to cooling for the first partial liquefaction.

8. A process according to claim 6 or 7, in which the second portion of the refrigerant is at least partially subjected to indirect heat exchange with the second portion of the refrigerant or a part thereof before it is work expanded, after it is subjected to work expansion and before it is combined with the first gas fraction.

9. The process according to one of claims 6 to 8, wherein the second liquid fraction is at least partially expanded and combined with the refrigerant compressed in the first compression step.

10. The process according to one of claims 6 to 9, in which the gas which is indirectly heat exchanged with the refrigerant is cooled using a heat exchanger or heat exchangers having a plurality of sections, wherein the first and second gas fractions of the refrigerant or parts thereof are further cooled to different temperature levels and reheated after expansion.

11. A method according to one of claims 1 to 4, in which at the compression of a further refrigerant with which the gas is subjected to cooling in indirect heat exchange, the work done at work expansion is used in addition to the drive (GT 1).

12. A device for liquefying gas, wherein the device has means adapted to subject the gas to cooling in indirect heat exchange with a refrigerant and to subject at least a part of the refrigerant after heat exchange with the gas to compression using a driving means (GT1) generating waste heat and to partial or complete liquefaction, characterized in that means are adapted to, after the partial or complete liquefaction, subject a first part of the refrigerant to heat exchange with the gas and to subject a second part of the refrigerant in turn to pressurization, heating and work expansion using the waste heat of the driving means (GT1) and after that to re-delivery to the partial or complete liquefaction.

13. The device according to claim 12, adapted to perform the method of one of claims 1 to 11.