RU2452908C2 - Method of and device for generation of cooled hydrocarbon flow - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: first (30) and second (30a) liquefied flows of hydrocarbons are produced, and they are combined to thus produce a combined liquefied flow (40) of hydrocarbons. The specified combined liquefied flow (40) of hydrocarbons is then additionally cooled in a counterflow with a coolant, and as a result, an additionally cooled liquefied flow (50) is produced, for instance, a flow of a liquefied natural gas (LNG).

EFFECT: reduced capital and operational expenses.

20 cl, 4 dwg

Description

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for producing a cooled liquefied hydrocarbon stream, for example a natural gas stream. The method and / or device according to the invention can be used in and / or for carrying out the process of liquefying a stream of hydrocarbons, for example for the production of liquefied natural gas.

State of the art

Various methods are known for liquefying natural gas, resulting in liquefied natural gas (LNG). Liquefaction of a natural gas stream is desirable for a number of reasons. For example, natural gas can be more easily stored and transported over long distances in the form of a liquid than in a gaseous state, since it takes up a smaller volume and there is no need to store it at high pressure.

Patent US 6658892 B2 relates to methods and systems for liquefying natural gas, which use a conventional separator (for example, an evaporation tank) and a steam compressor in the form of a series of repeating chains of elements. A problem with the system layout known from US 6658892 B2 is that each element chain requires equipment specifically designed for it, including a conventional separator, and operating costs. All equipment associated with the liquefaction of natural gas is expensive in terms of both capital and operating costs.

An object of the present invention is to reduce capital and / or operating costs for a liquefaction plant including a liquefaction device.

Another objective of the present invention is to provide an alternative method and device for liquefying natural gas.

Disclosure of the invention

One or more of these tasks or other tasks can be solved by the present invention. The present invention provides a method for producing a cooled liquefied hydrocarbon stream, comprising at least the following steps:

- obtaining a first liquefied hydrocarbon stream by passing the first raw hydrocarbon stream through a first liquefaction system comprising one or more cooling stages, at least one of which has a closed refrigerant circuit;

- obtaining a second liquefied hydrocarbon stream by passing the second feed stream of hydrocarbons through a second liquefaction system comprising one or more cooling stages, at least one of which has a closed refrigerant circuit;

- combining the first liquefied stream with a second liquefied stream to obtain a combined liquefied stream; and

- additional cooling of the combined liquefied stream in countercurrent with the refrigerant to obtain a cooled stream of liquefied hydrocarbons, such as a stream of liquefied natural gas (LNG).

The present invention further provides a device for producing a cooled liquefied hydrocarbon stream, for example a natural gas stream, comprising at least:

- a first liquefaction system for producing a first liquefied hydrocarbon stream, comprising at least two cooling stages, at least one of which has a closed refrigerant circuit;

- a second liquefaction system for producing a second stream of liquefied hydrocarbons, comprising at least two cooling stages, at least one of which has a closed refrigerant circuit;

- a combining element designed to combine the first liquefied stream and the second liquefied stream to obtain a combined liquefied stream; and

- an additional cooling stage adapted to cool the combined liquefied stream in countercurrent with the refrigerant and thereby obtain a liquefied stream of hydrocarbon product.

Embodiments and embodiments of the present invention will now be disclosed by way of example only and with reference to non-limiting accompanying drawings.

Figure 1 is a schematic diagram for implementing a method of producing a cooled liquefied hydrocarbon stream in accordance with one embodiment of the present invention.

Figure 2 is a schematic diagram for implementing a method in accordance with another embodiment of the present invention.

Figure 3 is a more detailed diagram of the method corresponding to figure 2.

Figure 4 is a more detailed diagram of the implementation of the method in accordance with another embodiment of the present invention.

Although the method and apparatus described herein are applicable to streams containing various hydrocarbons, they are particularly suitable for streams of natural gas that are further cooled after liquefaction.

In particular, the methods described herein include:

(a) obtaining a first liquefied hydrocarbon stream;

(b) obtaining a second liquefied hydrocarbon stream;

(c) combining the first liquefied hydrocarbon stream with a second liquefied hydrocarbon stream, thereby obtaining a combined stream of liquefied hydrocarbons;

(d) further cooling the combined liquefied hydrocarbon stream in countercurrent with the refrigerant, resulting in an additionally cooled liquefied hydrocarbon stream.

It has been unexpectedly found that by combining two or more liquefied streams and additional cooling of the combined stream in a single final stage of cooling, capital and operating costs can be reduced.

The methods described herein may be part of a method for producing a cooled liquefied hydrocarbon stream, for example, liquefied natural gas from two or more hydrocarbon streams, said streams being obtained from a single feed stream or source, or from a number of feed streams or sources.

One of skill in the art will understand how the cooling and liquefaction of a hydrocarbon stream are performed. Typically, the feed stream is supplied and passed through a liquefaction system.

In the various embodiments disclosed herein, a first liquefied hydrocarbon feed stream can be obtained by passing a first hydrocarbon feed stream through a first liquefaction system containing one or more cooling stages, at least one of which has a closed refrigerant circuit. Similarly, a second liquefied hydrocarbon feed stream can be obtained by passing a second hydrocarbon feed stream through a second liquefaction system containing one or more cooling stages, at least one of which has a closed refrigerant circuit.

In these or other embodiments described herein, a first liquefied hydrocarbon stream may be produced in a first liquefaction system and a second liquefied hydrocarbon stream in a second liquefaction system. Each liquefaction system may include at least two cooling stages. In this case, the first and second liquefaction systems may have a common first cooling stage and at least each may have one separate second cooling stage.

In these or other embodiments, the refrigerant used in the subsequent cooling step (d) may be a refrigerant comprising a single component.

The devices described here contain:

a first liquefaction system for producing a first liquefied hydrocarbon stream;

a second liquefaction system to produce a second liquefied hydrocarbon stream;

a combining element for combining the first liquefied stream and the second liquefied stream to obtain a combined liquefied stream; and

a step for further cooling said combined liquefied fluid stream with a refrigerant to produce a cooled liquefied product stream.

In various embodiments described herein, the first and second liquefaction systems include at least two cooling stages each. At least one of the at least two cooling stages in each of these liquefaction systems may have a closed refrigerant circuit. Each liquefaction system may include a first cooling stage and a second cooling stage located downstream of the first cooling stage. The first cooling stage may be the pre-cooling stage, and the second cooling stage may be the main cryogenic cooling stage. The first and second liquefaction systems may have a common first cooling stage, which may be a common pre-cooling stage and may contain 1, 2, 3, 4 or 5, preferably 4 heat exchangers. The refrigerant for the second cooling stage may be mixed refrigerant. The refrigerant in the additional cooling stage may be a refrigerant containing a single component, for example nitrogen, mixed refrigerant or natural gas. The refrigerant for an additional cooling stage can be circulated in a closed circuit.

The hydrocarbon feed stream for the method and / or device, or from the feed stream to the liquefaction systems, may be any suitable hydrocarbon containing stream or streams to be processed and commonly referred to as “feed streams”, but they are usually streams natural gas extracted from natural deposits of natural gas or oil. Alternatively, natural gas streams can also be obtained from another source, including, in addition, an artificial source, such as the Fischer-Tropsch process.

Typically, the natural gas stream (s) contains mainly methane. Preferably, the feed stream for the method and device disclosed herein contains at least 60 mol% of methane, more preferably at least 80 mol% of methane.

Depending on the source used, natural gas may contain a different amount of hydrocarbons heavier than methane, for example ethane, propane, butanes and pentanes, as well as some aromatic hydrocarbons. Natural gas streams may also contain non-hydrocarbons, such as H ₂ O, N ₂ , CO ₂ , H ₂ S and other sulfur compounds, and the like.

If desired, a feed stream containing natural gas can be pre-treated before being fed to the liquefaction system. This pre-treatment may include the removal of any undesired components in the stream, such as CO ₂ , H ₂ S, or may include other operations, such as pre-cooling, pre-compression, or the like. Since those operations are well known to those skilled in the art, they will not be considered further here.

The advantage of the proposed scheme is to use only a single additional cooling of two liquefied streams, while these streams or liquefaction systems may or may not be the same.

At its discretion, the first cooling stage of each liquefaction system can be combined or “common”, which creates an additional advantage of an additional reduction in capital and operating costs.

As used herein, the term “natural gas” refers to any hydrocarbon-containing composition that is at least substantially methane. The term includes a composition before any treatment, including cleaning or washing, as well as any composition that has been partially, mostly or completely treated in order to reduce and / or remove one or more compounds or substances, including but not as a limitation, sulfur, carbon dioxide, water and C ₂ + hydrocarbons.

Two or more feed streams used in accordance with the method and apparatus described herein may be the same or different. Each feed stream can be obtained from the same source of feed stream, such as a well for producing natural gas. Each feed stream can be obtained by dividing the stream coming from the same source.

Any pre-processing of the stream may be the same or different. Preferably, each feed stream in terms of its parameters and composition may be completely or substantially (i.e.> 90%, more preferably> 95% and even more preferably> 99%) the same.

The liquefaction system can be implemented in various ways and typically contains one or more heat exchangers and refrigerant circuits.

The liquefaction system used in the method and apparatus described herein may include one or more cooling stages, and each of the cooling stages may contain one or more heat exchangers, strokes, levels or sections. One of the schemes includes the first stage, which is the pre-cooling stage, and the second cooling stage, which is the main cryogenic stage.

The pre-cooling stage can provide a decrease in the temperature of the feed stream below 0 ° C, for example, in the range from -10 ° C to -30 ° C.

The main cryogenic cooling stage can provide cooling of the feed stream to a temperature below -90 ° C or below -100 ° C, for example, to a temperature in the range from -100 ° C to -130 ° C, resulting in a liquefied hydrocarbon stream, for example a stream liquefied natural gas.

Each cooling stage usually includes one or more refrigerant circuits, usually one refrigerant circuit with a heat exchanger or a series of heat exchangers designed for it, and at least one compressor is included in the circuit to compress the refrigerant after it passes in countercurrent with the cooled or liquefied stream. Each refrigerant circuit may also include one or more heat exchangers, such as air and / or water chillers or other condensers, which are cooled by heat exchange with a refrigerant such as water.

Refrigerant circuits are known in the art. Although each refrigerant circuit can be separate, one or more parts of the refrigerant circuit can be connected to another refrigerant circuit (s), or can be interconnected and combined with it (with them), or at least include a relationship actions or a combination of materials and / or flow of one circuit with another circuit (s).

In this case, at least one of the cooling stages may have a closed refrigerant circulation circuit, so that the circulating refrigerant is not mixed with the refrigerant of another stage, another circuit with a refrigerant or other liquefaction system. Each closed circulation circuit has its own compressor, which is not connected to other circulation circuits and / or cooling stages. Precoolers or conventional chillers, however, can be used together with one closed refrigerant circuit and another closed refrigerant circuit. In addition, it should be noted that during normal operation, the refrigerant circulating in a closed circuit, as a rule, does not mix or, at least, does not mix with another refrigerant.

In one embodiment of the method and apparatus described herein, the first and second liquefied hydrocarbon streams are provided by the first and second, preferably parallel, liquefaction systems, respectively, with each system using the mixed refrigerant mentioned above.

The method and apparatus described herein may include the use of more than two liquefied hydrocarbon streams and / or more than two feed streams and / or more than two liquefaction systems. For such streams, a combined additional cooling stage, described below, may also be provided, which is optionally used for some or all of these streams. The use of a common or combined stage of additional cooling creates an advantage in reducing capital and operating costs, especially when the cooling requirement for the additional cooling stage is less than the cooling requirement for other cooling stages (possibly relatively small compared with other stages), as a result of which the previously performed individual stages of additional cooling can be combined without any The total requirement for additional energy.

Each liquefaction system can operate with the same or different liquefaction parameters. In each stage and / or any similar stages of each liquefaction system, the same or different parameters can be used, such as flow rate, temperature, pressure, etc. Each liquefaction system and / or each stage of each liquefaction system may include recycling one or more streams or products well known in the art.

Preferably, each liquefaction system includes at least two cooling stages, preferably a first cooling stage and a second cooling stage, more preferably the first cooling stage is a pre-cooling stage and the second cooling stage is a main cryogenic cooling stage.

The first and second liquefaction systems can have a common first cooling stage, preferably a common pre-cooling stage contains 1, 2, 3, 4 or 5 heat exchangers, more preferably 4 heat exchangers.

The second cooling stage may include a closed loop. Preferably, the second cooling stages of the first and second liquefaction systems are in the form of separate closed refrigerant circuits.

The refrigerant of the after-cooling stage is preferably a specially selected refrigerant and circulates in a closed circuit.

The present invention includes a combination of any and all of the methods and devices described herein.

For the purposes of the present description, the only reference numeral in the drawing denotes a pipeline line (pipeline), as well as the flow flowing through this pipeline. The same reference numbers in the drawings refer to like elements.

Figure 1 presents a simplified flowchart for implementing a method for producing a liquefied hydrocarbon product stream from two liquefied hydrocarbon streams using two liquefaction systems.

As shown in FIG. 1, two liquefied hydrocarbon streams are obtained from two feed streams 10, 10a (for example, from previously purified natural gas streams), while reducing the content of one or more of the substances or compounds, such as sulfur, sulfur compounds, dioxide carbon and moisture or water, or they are mainly or completely removed in a manner known in the art.

The first feed stream 10 flows through a first liquefaction system 100 containing two stages, in this example, the first cooling stage 12 provides a cooled stream 20, and the second stage 14 provides a first liquefied stream 30.

The second feed stream 10a flows through a second liquefaction system 200 containing two stages, in this example, the first cooling stage 12a provides a cooled stream 20a, and the second stage 14a provides a second liquefied stream 30a.

The first and second liquefaction systems 100, 200 may differ from each other or may be the same, i.e. may have the same or different volumes, costs, process parameters, etc. The first and second cooling stages 12a, 14a of the second liquefaction system 200 may be the same or different with respect to the first and second cooling stages 12, 14 of the first liquefaction system 100. Each of the first and second cooling stages 12, 12a, 14, 14a of each liquefaction system 100, 200 may also be the same or may differ from each other.

Preferably, the first cooling stage of each of the liquefaction systems provides different cooling, i.e. a different decrease in the temperature of the flowing through it compared to the second cooling stage.

Preferably, cooling in the first cooling stage of the liquefaction system is provided by a first refrigerant circuit or circuits (not shown in FIG. 1). The refrigerant for the first refrigerant circuit may be any suitable refrigerant, preferably a refrigerant comprising a single component, for example nitrogen or propane, more preferably propane.

Preferably, cooling in the second cooling stage of the liquefaction system is provided by a second circuit or second refrigerant circuits (not shown in FIG. 1). The refrigerant for a particular at least one of the circuits or for each of the second refrigerant circuits may be any suitable refrigerant, more preferably a refrigerant selected from the group consisting of nitrogen, methane, ethane, ethylene, propane, propylene, butane and pentane.

At least one of the first and second cooling stages of the first liquefaction system and at least one of the first and second cooling stages of the second liquefaction system has a closed refrigerant circuit.

As shown in FIG. 1, the first liquefied stream 30 and the second liquefied stream 30a can be combined before further cooling to form a combined stream 40. In this case, the first and second liquefied streams 30 and 30a can be combined using a connecting element 16. The connecting element can be a suitable design, usually a coupler or pipe joint, provided at the discretion of one or more valves.

Alternatively, the first liquefied stream 30 and the second liquefied stream 30a are combined with further cooling, including the use of any device, equipment, apparatus or their element (or element for these means), which provides or contributes to further cooling. Combining the streams 30, 30a may not require complete combining or mixing for their passage upon further cooling.

In accordance with the method described here, the combined liquefied stream 40 is subjected to further cooling to obtain a cooled liquefied stream of hydrocarbons. Additional cooling may be the same or may differ in principle, design, used equipment or layout for its first and second stages 12, 12a, 14, 14a of the first and second systems 100, 200 and can be performed with the same, similar or different process parameters, implemented in the first and second stages 12, 12a, 14, 14a of the first and second liquefaction systems 100, 200.

In one example, the post-cooling stage 18 is a sub-cooling stage adapted to lower the temperature of the combined liquefied stream 40 to a temperature in the range of −150 ° C. to

-160 ° C to obtain a cooled liquefied stream of 50 hydrocarbons.

Stage 18 additional cooling may also include one or more strokes, levels or sections. The cooling for the additional cooling stage 18 may be provided by at least one (third) refrigerant (s), which is preferably circulated in the refrigerant circuit (not shown in FIG. 1). The third refrigerant in this circuit may be a single component refrigerant, such as nitrogen, or other refrigerants, such as natural gas or mixed refrigerant.

Any refrigerant circuit for the additional cooling stage 18 may be a “stand-alone” circuit, or it may partially or completely pass through one or more elements or apparatuses of the first and / or second liquefaction systems 100, 200. Alternatively or additionally, at least some cooling of the refrigerant of the additional cooling stage can be independently provided using one element or apparatus of the first and / or second liquefaction systems 100, 200. Many such systems or schemes for refrigerant refrigeration are known in the art.

Optionally, the cooled liquefied hydrocarbon stream 50 may be directed to a final separator where steam can be recovered for use as a fuel in the installation, for example, to operate gas turbines driving compressors used in the refrigerant circuits, and the liquefied hydrocarbon product , for example, liquefied natural gas, may be transported to a storage tank or other storage and transportation equipment.

As an example, the final separator 22 may be an evaporation tank 22, shown in figure 1. In general, the final evaporation tank 22 can be used at the downstream end of the subcooling stage to optimize the production of liquefied natural gas. It typically provides a stream 60 of a final product, such as LNG, and a separate gaseous stream (not shown).

Figure 2 presents a diagram of a device similar to that shown in figure 1, but in this scheme, the first and second liquefaction systems 300 have a common first cooling stage.

Thus, FIG. 2 shows a single feed stream 10b similar to the feed streams 10, 10a of FIG. 1, which can be similarly pretreated by passing through a common first cooling stage, preferably representing a preliminary cooling stage 12b and intended to provide initial cooling the feed stream 10b to a temperature below 0 ° C. The cooled stream 10c from the pre-cooling stage 12b is then divided into a number of parts — partial flows. Figure 2 illustrates the division into two partial streams 20b, 20c only as an example. The division of the cooled stream 10c may be based on any ratio of mass and / or volume and / or flow. This ratio may be based on the size or performance of the sequentially located elements or apparatuses of the liquefaction stages or liquefaction systems, or for other reasons. One example may be equal division of the cooled mass of the stream.

In FIG. 2, partial streams 20b, 20c are liquefied using separate or specially designed second cooling stages 14b, 14c, respectively, and liquefied hydrocarbon streams 30b, 30c are obtained, respectively.

The scheme shown in figure 2, provides for the first stage of cooling two, preferably the main cryogenic stages of liquefaction, preferably units. An example of using a system with a single pre-cooling stage, with two stages of heat exchangers and two refrigerant circuits is disclosed in patent document US63 89844 B1.

The two liquefied hydrocarbon streams 30b, 30c shown in FIG. 2 can then be combined in a similar manner as described for the circuit shown in FIG. 1 to obtain a combined liquefied stream 40, which can then be further cooled in stage 18 of an additional cooling or hypothermia, usually in countercurrent with a (third) refrigerant, to produce a cooled liquefied stream of 50 hydrocarbons, and at the discretion of this stage is followed by stage 22 of the final processing.

The diagram of the first and second stages in FIG. 2 includes two liquefaction systems having a common first cooling stage, which provides two liquefied hydrocarbon streams 30b, 30c for use in accordance with the method described herein.

Figure 3 presents a more detailed diagram in comparison with that presented in figure 2. In particular, FIG. 3 illustrates the use of four heat exchangers 32a, 32b, 32c and 32d arranged in series in the first common cooling stage 12b. The aforementioned feed stream 10b passes through said heat exchangers 32a, 32b, 32c and 32d before it is divided into two partial streams 20b, 20c, which enter the second stages 14b, 14c.

In the first cooling stage 12b, four heat exchangers 32a, 32b, 32c and 32d can operate at different pressures achieved by expansion valves 31a, b, c, d, in particular if refrigerant containing a single component, such as propane, is used. Propane can be used at different pressure levels, and after evaporation in each of the heat exchangers it can be sent to two compressors 34a, 34b driven by a drive D, which provides a repeated increase in vapor pressure of the refrigerant within the first refrigerant circuit 101 before condensation and reuse with passage through four heat exchangers 32a, 32b, 32c and 32d. One of skill in the art will recognize the use of four heat exchangers and the mode of operation of the first refrigerant circuit 101 for the first cooling stage 12b.

Figure 3 shows four heat exchangers 32a, 32b, 32c and 32d for the first combined cooling stage 12b. In an alternative embodiment (not shown), each heat exchanger 32a, 32b, 32c and 32d can be replaced by a separate heat exchanger for primary cooling of the feed stream 10b and for cooling each of the two refrigerant streams of the second parallel cooling stage 14b, 14c. Thus, the heat exchanger 32a can be replaced by three heat exchangers, wherein the first heat exchanger cools the feed stream 10b, the second heat exchanger cools the refrigerant stream of the second cooling stage 14b, and the third heat exchanger cools the refrigerant stream of the second cooling stage 14c.

Similarly, heat exchangers 32b, 32c and 32d can each be divided into three separate heat exchangers, respectively, to produce a total of twelve heat exchangers for the first combined cooling stage of this alternative embodiment. Each group of three heat exchangers corresponding to heat exchangers 32a, 32b, 32c and 32d can operate at different refrigerant pressures, similar to their operation in the circuit shown in FIG. 3.

In each second stage 14b, 14c of FIG. 3, there is a cryogenic heat exchanger, preferably in the form of a spiral tube heat exchanger or coil coil 36b, 36c, respectively. Such heat exchangers are also well known in the art. For the example shown in FIG. 3, each chilled stream 20b, 20c is fed into the bottom of a corresponding heat exchanger 36b, 36c and then passed through it from the bottom up to obtain a liquefied hydrocarbon stream 30b, 30c, respectively. Each of the second cooling stages 14b, 14c includes a second refrigerant circuit 201, 202, respectively.

The second refrigerant circuits 201, 202 may be different, but they are preferably the same or similar, and typically include piping for a second refrigerant, the second refrigerant for each second refrigerant circuit 201, 202 may be the same or different. Preferably, each second refrigerant is the same and is a mixed refrigerant, preferably a mixed refrigerant containing two or more components, preferably two or more components selected from the group consisting of nitrogen, methane, ethane, ethylene, propane, propylene, butane and pentane.

For the example shown in FIG. 3, each second circuit 201, 202 circulates its second refrigerant, which flows through the heat exchangers 32a, 32b, 32c and 32d of the pre-cooling stage 12b, and is separated into flows of light and heavy refrigerants in the separators 210, 210a, passes through heat exchangers 36b, 36c, as through separate lines, is used for cooling, and then it is collected and sent for recycling, as is known in the prior art.

In the embodiment illustrated in FIG. 3, the heavy refrigerant stream exiting the separator 210, 210a is passed through the heat exchanger 36b, 36c before being expanded into the expander 211, 211a and directed into the annular space of the heat exchanger 36b, 36c. The flow of light refrigerant leaving the separator 210, 210a, before expanding in the expansion valve 212, 212a is passed through the heat exchanger 36b, 36c and also sent to the annular space of the heat exchanger 36b, 36c.

The first and second liquefied refrigerant streams 30b, 30c are then combined in a combining element 16, as noted above, to obtain a combined liquefied stream 40, which can then be further cooled in the additional cooling or subcooling stage 18 shown in FIG. in the form of a heat exchanger 38. Cooling in the heat exchanger 38 is provided by a third refrigerant circulating in the third circulation circuit 301, the circuit of which may be any suitable circuit, the performance of which is known at level t hniki. In the circuit shown in FIG. 3, the third refrigerant is compressed in a compressor 303, then cooled in a cooler 304 and passed through a heat exchanger 302. Then, the third refrigerant, before being cooled by a refrigerant stream 40 of liquefied hydrocarbons in the heat exchanger 38, is expanded in expansion valve 305, passed through a heat exchanger 302, after which it is returned to the compressor 303.

In one example, the third refrigerant may be nitrogen, the use of which in the subcooling stage 18 is known in the art. Typically, the nitrogen-containing refrigerant can further cool the combined stream of liquefied hydrocarbons 40 to obtain an additionally cooled stream 50 of liquefied hydrocarbons having a temperature below at least -140 ° C, preferably less than -150 ° C.

Thus, FIG. 3 illustrates a three-stage cooling unit and a method for liquefying a hydrocarbon feed stream 10b, preferably a natural gas stream, using a) a general pre-cooling stage 12b, in which propane is preferably used as the first refrigerant, b) parallel liquefaction stages in the form two elements 14b, 14c, wherein each of these elements uses a second refrigerant, preferably mixed refrigerant, and c) an additional, usually third or subcooling stage 18, using boiling in a third refrigerant nitrogen.

Figure 4 presents a detailed diagram of an implementation of a method of manufacturing a liquefied stream of hydrocarbon product in accordance with the third embodiment described here.

4 shows a liquefaction system including a pre-cooling stage 12c and two separate liquefaction stages 14d, 14e, respectively. The pre-cooling stage 12c is similar to that shown in FIG. 3 and includes four successive heat exchangers 32a, 32b, 32c, 32d through which the feed stream 10b flows to produce a cooled feed stream 10c with a temperature below 0 ° C. In contrast to that shown in FIG. 3, vapor refrigerant streams 42a, 42b, 42c and 42d discharged from each heat exchanger 32a, 32b, 32c and 32d, respectively, are sent to a single compressor 34c before being cooled in cooler 44, resulting in a stream 102 refrigerant prepared for flow through heat exchangers 32a, 32b, 32c and 32d. According to the above, in an alternative embodiment (not shown), the heat exchanger 32a can be replaced by a separate heat exchanger for the initial cooling of the feed stream 10b through which each of the two refrigerant flows 204, 204a, 14d, 14e of the second parallel cooling stage and the third stream 65 refrigerant from the additional cooling stage described above. Similarly, heat exchangers 32b, 32c and 32d can each be replaced by three heat exchangers, with the first heat exchanger cooling the feed stream 10b, the second heat exchanger cooling the refrigerant stream 204 of the second cooling stage 14b, and the third heat exchanger cooling the refrigerant stream 204a of the second cooling stage 14e.

The first common pre-cooling stage 12c, shown in the diagram of FIG. 4, provides a chilled feed stream 10c that is combined with the feed stream 70 to create a common chilled feed stream 10d. Like the example in FIG. 2 and FIG. 3, this feed stream 10d is divided into two partial streams 20b, 20c. The cooled partial streams 20b, 20c are directed to the second cooling stages 14d, 14e, which may be the same, similar or different from the second cooling stages 14b, 14c shown in FIG. 2 and FIG. 3, and also provide liquefied flows 30b, 30c hydrocarbons, which are combined to form a liquefied stream of 40 hydrocarbons.

Each second cooling stage 14d, 14e has its own separate circulation circuit for the second refrigerant, the circuits may be the same and may differ, but preferably they are similar in design and use of the refrigerant. As an example, the second refrigerant circuit 201 for the upper (shown) second cooling stage 14d shown in FIG. 4 includes a vapor refrigerant stream 203 compressed in a compressor 207 (corresponding to the compressor 207a in parallel to the second cooling stage 14e) and then cooled in a water or air cooler 208 (which corresponds to a cooler 208a in parallel to the second cooling stage 14e) to produce a cooled second refrigerant stream 204, which then passes through four heat exchangers 32a, 32b, 32c and 32d c Upenu 12c precooling and condensed, thereby obtaining a second condensed liquid refrigerant stream 205, which can then be used in a heat exchanger of the second cooling stage 14d. Such use typically involves the first passage of refrigerant through an additional cooling heat exchanger, followed by leakage and expansion of the refrigerant as it passes through expansion valve 209 (corresponding to valve 209a in parallel to the second cooling stage 14e) to produce an expanded refrigerant stream 206, which can then be reused in the heat exchanger of the second cooling stage 14d in order to cool and liquefy the hydrocarbon stream passing through it, resulting in compression adjoint hydrocarbon stream 30b.

Suitable components, flows, flows and temperatures for the second refrigerant circuit 201 are well known in the art, especially if the second refrigerant for the second refrigerant circuit 201 is mixed refrigerant, as discussed above.

In accordance with another embodiment disclosed herein, the combined liquefied stream 40, as shown in FIG. 4, is then further cooled. In contrast to figure 3, the specified additional cooling is provided through an expanded system of final evaporation. Many types of post-evaporation systems are known in the art which are capable of providing additional cooling and, optionally, further promoting the production of liquefied hydrocarbon streams or products, for example, liquefied natural gas. Such systems are described, for example, in patent documents US 5893274 and WO 2006/005746 A1.

Another example is the final evaporation system described in US Pat. No. 5,611,216, incorporated herein by reference. As shown in US 5611216, a liquefied hydrocarbon stream can be passed through a methane economizer and then further cooled through a series of expansions, each using either Joule-Thompson expansion valves or expanders, followed by separation of the gas-liquid product using a separator. Additional cooling may be achieved by rapidly evaporating at least a portion of the liquefied hydrocarbon stream as it passes through one or more expanders, and / or a heat exchanger using vapor generated during each rapid evaporation or separation.

As shown in figure 4, the combined liquefied stream 40 enters the first tertiary heat exchanger 71, in which it is further cooled, as described below, leaves the specified heat exchanger through a pipe 72, passes through an expansion valve 73 and enters the first separator, which is a cylindrical evaporation tank 74, in which the stream is separated into the vapor phase of natural gas, i.e. a phase consisting mainly of methane, usually with a certain nitrogen content, which flows upstream of the pipe 51 and returns to the first tertiary heat exchanger. The liquid phase obtained in tank 74 flows through conduit 75 and enters a second tertiary heat exchanger 76, smaller than the first tertiary heat exchanger 71.

Tertiary heat exchangers may include one or more heat exchangers arranged in series or in parallel, while various schemes for conducting heat exchange in an additional cooling stage are known and possible, implemented in the examples and embodiments described herein.

From the second tertiary heat exchanger 76, an additionally cooled stream enters through an expansion valve 77 into a second separator, which is a second cylindrical evaporation tank 78, in which the stream is separated into a vapor phase of natural gas flowing through a pipeline 52 and a liquid phase that flows through a valve 82 additional expansion and enters the third separator 79, where the stream is again separated into the vapor phase 53 of natural gas and the stream 50 of the final hydrocarbon product, which before By storage (in tank 81) and / or transport, it can pass through an expansion valve 83.

Any vapor, for example, steam released from the tank 81, can be compressed in the compressor 56 to obtain a compressed stream 54, which can be combined with the vapor stream 53, removed from the third separator 79, to obtain a combined vapor stream 55. Combined stream 55 and the vapor stream 52 from the second evaporative cylindrical tank 78 flows through the second tertiary heat exchanger 76, cooling the liquefied hydrocarbon stream 75 flowing through the heat exchanger in countercurrent mode. The vapor flows leaving the second tertiary heat exchanger 76, together with the vapor stream 51 from the first cylindrical evaporation tank 74, then provide cooling (combined liquefied stream) in the first tertiary heat exchanger 71.

The additional cooling scheme illustrated in FIG. 4 allows the use of natural gas as a refrigerant for additional cooling. This natural gas refrigerant typically contains> 90% methane, possibly> 95% methane, or even> 98% methane, usually also with some nitrogen content.

Three flows of cooling steam 61, 62, 63, leaving the first tertiary heat exchanger 71, are then sent to the individual inputs of one or more compressors (figure 4 shows three compressors 92, 94, 96, each of which, in addition, compresses the compressed the stream leaving the previous compressor) to obtain the combined compressed (and cooled) refrigerant stream 64. After passing through each of the compressors 92, 94, 96, the compressed stream can be cooled in a cooler 93, 95, 97.

Some portion of the combined refrigerant stream 64 may be diverted or separated as a stream 64a for use as a fuel, typically high pressure fuel, for example, in a liquefaction plant or elsewhere.

The combined refrigerant stream 64 or the remainder thereof is then compressed in a compressor 98 and cooled in a cooler 99 to obtain a third refrigerant stream 65. Said third refrigerant stream 65 is further cooled in the first heat exchanger 32a of the pre-cooling stage 12c to obtain a cooled refrigerant stream 66, which is sent to the first tertiary heat exchanger 71. Part of the cooled third refrigerant stream 66 after passing this part through the first tertiary heat exchanger 71 may exit the first tertiary heat exchanger 71 as a raw feed stream 70 for subsequent combination with a cooled feed stream 10c (produced using stage 1 2c pre-cooling) to obtain a combined chilled feed stream 10d.

The scheme of additional cooling of the combined liquefied stream 40 for producing an additionally cooled liquefied stream of hydrocarbons 50 shown in FIG. 4 has significant benefits, including some efficiency achieved by using various circulation loops and cycles. It should be noted that the third refrigerant used in the additional cooling in FIG. 4 is the same (or has a similar composition) as the combined liquefied stream 40 and / or the additionally cooled liquefied hydrocarbon stream 50. In the event that the additionally cooled liquefied hydrocarbon stream 50 is liquefied natural gas, the third refrigerant contains mainly methane, and the additional cooling circuit shown in FIG. 4 is called “methane cooling” in the prior art.

Thus, FIG. 4 shows a general pre-cooling stage in which propane is used as the first refrigerant, a second stage with liquefaction of two parallel flows, preferably using mixed refrigerant in each second refrigerant circuit as a second refrigerant, and a combined or general supercooling stage using methane or natural gas as a third refrigerant and a third refrigerant circuit, the operation of which is partially combined with the production of liquefied coal odorodov or which it is common for the production of liquefied hydrocarbon.

Table 1 shows a typical demo example of temperatures, pressures and flow rates for various elements of a circuit that implements an example implementation of the method described here with reference to figure 4.

Table 1 The flow position number in FIG. 4 Temperature (° C) Pressure (bar) Mass flow (kg / s) Phase state 10b 46.0 72.7 391.5 steam 10s -17.0 71.3 391.5 steam 10d -17.1 71.3 454.8 steam 20b -17.1 71.3 227.4 steam 30b -116.0 66.8 227.4 liquid 40 -116.0 66.8 454.8 liquid 51 -129.9 9,4 54.9 steam 52 -142.3 4,5 48.9 steam 53 -152.4 2.2 33.9 steam 54 -134.1 2.2 25.3 steam 55 -144.4 2.2 59.2 steam 61 6.4 1.4 59.2 steam 62 6.4 3,5 48.9 steam 63 6.4 8.6 54.9 steam 65 43.0 71.8 116.1 steam 203 -20.3 3.0 630.8 steam 204 43.0 49.0 630.8 steam 205 -17.0 47.6 630.8 liquid 206 -122.3 3,5 630.8 mixture 102 43.0 20,0 1155.0 liquid 42d -20.3 2,3 272.4 steam 42s -0.3 4.6 262.6 steam 42b 13.7 7.0 292.0 steam 42a 24.7 9,4 327.9 steam

Table 2 provides general information regarding the individual and total required power for an example of the method described above with reference to figure 4.

table 2 Parameter unit of measurement C3-MR-C1, Figure 4, three stages with refrigerants C3-C2-C1, analogue, three stages with refrigerants Methane Compressor Power MW 94.2 174 CX / ethylene compressor power MW 192.4 128 Propane Compressor Power MW 97.2 138 PG expander MW 5,0 7.3 Expander for CX MW 3.3 general power MW 375.5 432.5 LNG production tons / day 29760 29436 Power density MW / ton / day 12.6 14.7 Propane Mass Flow kg / s 1401 1155 Mass ethylene flow rate kg / s 655 631 Mass flow in methane circuit kg / s 329 145

An example for an analogue relates to the method described in US 5611216, in which propane (C3), ethylene (C2) and methane (C1) are used as the first, second and third refrigerants, respectively. The comparative example corresponds to FIG. 4, with propane (C3), mixed refrigerant (CX) and methane (C1) used in the comparative example.

The results show that with an increase in the load in the second cooling stage described here, the decrease in power for the pre-cooling and additional cooling stages is so significant that it prevails over the increase in load in the second cooling stage. The requirements in terms of the total specific power for the example according to figure 4 correspond to 12.6 kW / tons / day, which is 2.1 kW / tons / day (or 8.8%) less than the total power required to implement the method according to the analogue . Such a reduction is significant in terms of the required dimensions and capacity of the natural gas liquefaction plant.

In addition, using the method described here, an increase in LNG production is achieved.

In each of the examples described above or illustrated here, a liquefaction system for producing a liquefied hydrocarbon stream is shown comprising first and second cooling stages. Other liquefaction systems are known in the art that may include more or less cooling stages, or one liquefaction stage in which the feed stream is pre-treated before liquefaction, for example by pre-cooling, elsewhere, for example, using one or more heat exchangers located in a separate part of the liquefaction plant, using a cooling pipe line or a cooling stream, for example, exhaust gas or fuel gas. It should be noted that the term “liquefaction system” as used herein is not limited to a system with two separate cooling stages.

One skilled in the art will appreciate that the present invention can be practiced in many different ways without departing from the scope of the appended claims.

Claims (20)

1. A method of obtaining a cooled liquefied stream of hydrocarbons, characterized in that it includes at least the stages:
(a) providing a first liquefied hydrocarbon stream by passing a first hydrocarbon feed stream through a first liquefaction system having at least two cooling stages, at least one of which has a closed refrigerant circuit;
(b) providing a second liquefied hydrocarbon stream by passing a second feed stream of hydrocarbons through a second liquefaction system having at least two cooling stages, at least one of which has a closed refrigerant circuit;
(c) combining the first liquefied hydrocarbon stream with a second liquefied hydrocarbon stream to obtain a combined liquefied hydrocarbon stream;
(d) further cooling the combined liquefied hydrocarbon stream in countercurrent with the refrigerant in a common supercooling step to produce a cooled liquefied hydrocarbon stream, such as a liquefied natural gas (LNG) stream; and
(e) passing a cooled liquefied hydrocarbon stream through a final processing step comprising one or more separation stages;
moreover, each liquefaction system contains at least a first cooling stage, behind which a second cooling stage is located, and the second cooling stage of each liquefaction system includes a closed refrigerant circuit, with each second cooling stage having its own separate refrigerant circuit. 2. The method according to claim 1, characterized in that every first cooling stage is a pre-cooling stage, and every second cooling stage is a main cryogenic cooling stage. 3. The method according to claim 1, characterized in that the refrigerant of each first cooling stage is a refrigerant containing a single component. 4. The method according to claim 3, characterized in that the refrigerant containing a single component is propane. 5. The method according to claim 4, characterized in that the refrigerant of the second cooling stage is a mixed refrigerant. 6. The method according to claim 3, characterized in that the refrigerant of the second cooling stage is a mixed refrigerant. 7. The method according to claim 1, characterized in that the refrigerant of the second cooling stage is a mixed refrigerant. 8. The method according to any one of claims 1 to 7, characterized in that the first and second liquefaction systems have a common first cooling stage. 9. The method according to claim 8, characterized in that the first common cooling stage is a pre-cooling stage. 10. The method according to claim 8, characterized in that the refrigerant of the common first cooling stage is a refrigerant containing a single component. 11. The method according to claim 10, characterized in that the refrigerant containing a single component is propane. 12. The method according to claim 8, characterized in that the refrigerant in step (d) is a refrigerant containing a single component. 13. The method according to p. 12, characterized in that the only component is nitrogen. 14. The method according to claim 8, characterized in that the refrigerant in step (d) is a mixed refrigerant. 15. The method according to claim 8, characterized in that the refrigerant in step (d) is natural gas. 16. The method according to any one of claims 1 to 7, characterized in that the refrigerant in step (d) is a refrigerant containing a single component. 17. The method according to clause 16, wherein the only component is nitrogen. 18. The method according to any one of claims 1 to 7, characterized in that the refrigerant in step (d) is a mixed refrigerant. 19. The method according to any one of claims 1 to 7, characterized in that the refrigerant in step (d) is natural gas. 20. A device for producing a cooled liquefied hydrocarbon stream, which is a natural gas stream, from two or more liquefied hydrocarbon streams, at least containing:
a first liquefaction system for producing a first liquefied hydrocarbon stream comprising at least two cooling stages, at least one of which has a closed refrigerant circuit;
a second liquefaction system for producing a second liquefied hydrocarbon stream comprising at least two cooling stages, at least one of which has a closed refrigerant circuit;
a combining element for combining a first liquefied hydrocarbon stream and a second liquefied hydrocarbon stream to form a combined liquefied hydrocarbon stream;
a general supercooling stage adapted to cool the combined liquefied hydrocarbon stream with a refrigerant to produce a cooled liquefied hydrocarbon stream; and
a final processing step comprising a final evaporation tank into which a cooled liquefied hydrocarbon stream is supplied;
moreover, each liquefaction system contains at least a first cooling stage, behind which a second cooling stage is located, and the second cooling stage of each liquefaction system includes a closed refrigerant circuit, with each second cooling stage having its own separate refrigerant circuit.

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