RU2434190C2 - Procedure for liquefaction of hydrocarbon flow and device for its realisation - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: procedure for liquefaction of flow of natural gas in raw stock flow (10) consists in stages of circulation of flow (70) of first cooling agent in circuit (110) with first cooling agent, in cooling flow (70) of first cooling agent in circuit (110) with first cooling agent in one or more heat exchangers (14) of first stage (100) of cooling, in passing at least part of cooled flow (20) of first cooling agent through one or more expanders (12) for obtaining one or more expanded cooled flows (30) of first cooling agent, in passing one or at least one of expanded flows (30) of first cooling agent and raw stock flow (10) through first one or more heat exchangers (14) producing cooled flow (40) of hydrocarbons, in passing cooled flow (40) of hydrocarbons through second stage (200) of cooling in counter flow with flow (50) of second cooling agent and in production of liquefied flow (60) of hydrocarbons. According to the procedure generated useful power is used in circuit (110) of first cooling agent circulation for drive of one or more pumps (28a, 28b) facilitating circulation of flow of the first cooling agent to build up pressure of flow (70) of the first cooling agent. Temperature of said charged flow (70a) is reduced in one or more coolants (29) cooling it to temperature of environment before it flows through first heat exchanger (14).

EFFECT: raised efficiency.

20 cl, 1 dwg, 1 tbl

Description

The present invention relates to a method for liquefying a stream of hydrocarbons, in particular, but not necessarily, natural gas and a device for its implementation.

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

US6105389A describes a method and apparatus for liquefying natural gas using a compressed cooling mixture, the natural gas being cooled, expanded and evaporated, followed by a second cooling stage for liquefying natural gas. In the first cooling stage, the fractions of the first cooling mixture are expanded by throttling valves to cool the cooling mixture. However, the problem associated with the use of butterfly valves is that they are iso-enthalpy, so that the work that can be done by expanding a fluid such as refrigerant while reducing its pressure in the butterfly valve is largely lost.

The objective of the invention is to increase the efficiency of the liquefaction method and device for liquefaction.

One or more of these or other problems can be solved using the present invention, creating a method of liquefying a stream of hydrocarbons, such as a stream of natural gas contained in the feed stream, comprising at least the stages:

(a) circulating the flow of the first refrigerant in the circuit with the first refrigerant;

(b) cooling the first refrigerant stream in one or more heat exchangers of the first cooling stage to produce a cooled first refrigerant stream;

(c) passing at least a portion of the cooled stream of the first refrigerant through one or more expansion devices to produce one or more expanded cooled flows of the first refrigerant;

(d) passing one or at least one of the expanded streams of the first refrigerant and the feed stream through the first one or more heat exchangers to produce a cooled stream of hydrocarbons;

(e) passing a cooled stream of hydrocarbons through a second stage of cooling in countercurrent with a stream of a second refrigerant to obtain a liquefied stream of hydrocarbons;

wherein at least one expansion device is a turboexpander, the energy of which generated in stage (c) is used in the circulation circuit of the first refrigerant.

An advantage of the present invention is that by expanding at least a portion of the first refrigerant stream while passing through one or more expanders to reduce the pressure of the first refrigerant before using it to cool the feed stream in the heat exchanger (s), the expansion of the first refrigerant is close to isentropic, which increases the efficiency of the first cooling. Close to the isentropic expansion of a gas to a lower pressure leads to a decrease in the internal energy extracted from the gas during expansion, and allows you to convert at least part of this energy into useful energy. This useful energy can then be transferred and used elsewhere in the proposed liquefaction method, process and / or device to ensure the actuation of another unit or device or parts thereof, such as a compressor, pump or generator.

The hydrocarbon stream may be any suitable liquefied gas stream, but it is usually a natural gas stream obtained from natural gas or oil fields. Alternatively, the natural gas stream can also be obtained from another source, including, in addition, an artificial source, such as the Fischer-Tropsch process.

Typically, the natural gas stream contains mainly methane. Preferably, the feed stream contains at least 60 mol% of methane, more preferably at least 80 mol% of methane.

Depending on the source of natural gas, it may contain different amounts of hydrocarbons heavier than methane, for example ethane, propane, butanes and pentanes, as well as some aromatic hydrocarbons. The natural gas stream may also contain non-hydrocarbons such as H ₂ ON ₂ , CO ₂ , H ₂ S and other sulfur compounds, and the like.

If necessary, the feed stream containing natural gas may be pretreated before use. This pretreatment may include reducing and / or recovering undesired components such as CO ₂ and H ₂ S, or other steps, such as pre-cooling, pre-compression, or the like. Since these processing steps are well known to those skilled in the art, they will not be discussed further here.

As used herein, the term "feed stream" refers to any composition including hydrocarbons, which usually contains a large amount of methane. In addition to methane, natural gas contains various amounts of ethane, propane and heavier hydrocarbons. This composition varies depending on the type and location of natural gas. As a rule, it is necessary that hydrocarbons heavier than methane should be removed from natural gas for several reasons, for example, due to differences in freezing or liquefaction temperatures, which may lead to blocking of the elements of the methane liquefaction plant by such hydrocarbons.

Thus, the term "feed stream" also refers to a composition before processing, including, for example, purification, dehydration and / or washing, as well as any composition that is partially, heavily or completely processed to reduce the content and / or complete removing one or more compounds or substances, including, but not limited to sulfur, sulfur compounds, carbon dioxide, water and C2 + hydrocarbons.

The term "expansion device" includes any unit, device, or apparatus capable of reducing flow pressure. It includes valves, as well as expanders, and, in addition, includes one or more two-phase expansion devices. In the event that at least one expansion device for heat exchangers of the first cooling stage is an expander, the valves may be other, one or more expansion devices. Preferably, all the heat exchangers of the first cooling stage are expanders.

The first stage of cooling in accordance with the present invention is intended to reduce the temperature of the cooled stream of hydrocarbons below 0 ° C, usually in the range from -20 ° C to -70 ° C. This cooling stage is also sometimes called the pre-cooling stage.

The second cooling stage is preferably separated from the first cooling stage. In this case, the second cooling stage includes one or more heat exchangers using a second refrigerant circulating in the circuit with the second refrigerant, although the refrigerant of the second refrigerant stream can also pass through at least one heat exchanger of the first cooling stage, preferably, through all heat exchangers of the first stage cooling.

Preferably, the first refrigerant circuit includes one or more apparatus cooling down to ambient temperature in front of the first heat exchanger.

In one embodiment of the present invention, the generated useful energy is used to increase the pressure flow of the first refrigerant in front of the first heat exchanger. One such example is the use of useful energy to drive one or more pumps to circulate the flow of the first refrigerant.

The use of useful energy obtained from one or more expanders in the first cooling stage (designed to reduce the temperature of the hydrocarbon stream to a temperature below 0 ° C) is particularly advantageous when the temperature of the corresponding refrigerant stream before expansion does not have to be much lower, for example, -50 ° C or -100 ° C. In this way, an increase in temperature in the refrigerant stream due to its passage through one or more pumps (at which an increase in refrigerant pressure leads to an increase in its temperature) can be more easily achieved with one or more chillers that cool to ambient temperature, for example, water and / or air coolers known in the art. The use of chillers that cool to ambient temperature in order to reduce the temperature of the refrigerant stream designed to cool the hydrocarbon stream to a much lower temperature, for example less than -100 ° C, may be clearly inadequate.

Thus, the present invention is particularly advantageous if the useful energy obtained by each expander is used in the first cooling stage or in the pre-cooling stage, since no additional energy is required in the first refrigerant circuit, which always contains before the heat exchanger ( heat exchangers) one or more chillers that cool to ambient temperature. As a result, in the entire liquefaction process, there is a maximum use of the generated useful energy or exergy, or at least minimal energy loss.

According to another embodiment of the present invention, the first cooling stage comprises two or more heat exchangers, and preferably each heat exchanger has an expander connected to it through which at least a portion of the first refrigerated refrigerant flows to provide an expanded cooled first refrigerant flow to its appropriate heat exchanger.

According to a further aspect, the present invention provides an apparatus for liquefying a hydrocarbon stream, for example, natural gas contained in a feed stream, comprising at least

a first refrigerant circuit for circulating the flow of the first refrigerant;

a first cooling stage comprising one or more heat exchangers into which a first refrigerant stream enters and in which a cooled first refrigerant stream is obtained;

one or more expansion devices designed to expand at least a portion of the cooled first refrigerant stream to produce one or more expanded first refrigerant streams, wherein at least one expansion device is an expander whose useful energy is generated by expansion, used in the circulation circuit of the first refrigerant;

one or each heat exchanger having a first input for passing a feed stream into the heat exchanger, and a second input for passing one or at least one of the expanded first refrigerant streams into the heat exchanger to cool the feed stream and thereby produce a stream of cooled hydrocarbons; and

a second cooling stage containing one or more heat exchangers adapted to supply a stream of chilled hydrocarbons from the first cooling stage and to obtain a stream of liquefied hydrocarbons.

An embodiment of the present invention will now be described by way of example and with reference to the accompanying drawing.

The drawing shows a schematic diagram of a liquefaction process in accordance with one embodiment of the present invention.

In the presentation of this description, the same reference position in the drawing is used both for the pipeline and for the flow flowing through this pipeline. Identical elements of the device are indicated in the drawing by the same reference numbers.

The drawing shows a schematic diagram of a process for liquefying a hydrocarbon stream, such as a natural gas stream. The diagram shows a feed stream containing natural gas 10. This feed stream can be pre-purified to separate at least some heavier hydrocarbons and impurities, such as carbon dioxide, nitrogen, helium, water, sulfur and sulfur compounds, including, but not necessarily, acidic gases.

The feed stream 10 passes through a first cooling stage 100 using a first refrigerant circulating in the first refrigerant circuit 110 to produce a cooled hydrocarbon stream 40b. The first refrigerant may be any suitable substance or, preferably, a mixture comprising one or more, preferably two or more substances from the group consisting of nitrogen, methane, ethane, ethylene, propane, propylene, butane, pentane, etc.

The feed stream 10 enters the first heat exchanger 14a through the inlet 32a and passes through it through the pipe 73a. At the same time, the first refrigerant enters the first heat exchanger 14a through the inlet 36a and passes through the first heat exchanger 14a through the pipe 71a. As a result, the pipe 71 a with the first refrigerant is also cooled in said first heat exchanger 14 a.

The cooled first refrigerant stream 20a exits the first heat exchanger 14a through outlet 38a. Using a suitable separator (not shown) such as a split line, the first and second fractions or parts 21a, 21b of the cooled first refrigerant stream 20a are formed, respectively.

The first part 21 a is directed to the first expander 12 a, which expands the first part of the refrigerated refrigerant in a near-isentropic thermodynamic expansion process to produce an expanded first refrigerant stream 30 a. The expanded stream 30a has an internal energy that is less than the internal energy of the stream 21a.

The specified energy difference can be used as useful energy, for example, to drive the unit or device in the circuit 110 of the circulation of the first refrigerant. In the device diagram shown in the drawing, the energy obtained by the first expander 12a is used to drive the first pump 28a, which is an element of the first refrigerant circuit 110, the functions of which are described below.

The ratio of the first and second parts 21a and 21b of the cooled first refrigerant stream 20a in the drawing may be any suitable ratio known in the art. If the first cooling stage 100 contains two heat exchangers 14a, 14b and uses mixed refrigerant, then the ratio of the two pressure levels, for example, is 35/65. An example of possible pressure levels in heat exchangers 14a, 14b is 8 bar for a high pressure heat exchanger and 3 bar for a low pressure heat exchanger.

The expanded stream 30a is returned to the first heat exchanger 14a at the top or near the top of the heat exchanger, and as the expanded stream 30a goes down through the heat exchanger 14a and evaporates, it provides cooling to the pipes of the first heat exchanger 14a through which the feed stream 10 (pipe 73a) and the first refrigerant (pipe) 71a) in a manner known in the art. Due to this, a cooled stream of hydrocarbons 40a is obtained.

In this case, the vaporized first refrigerant can be collected and discharged as the first vaporous effluent 90a through the outlet 42a from the first heat exchanger 14a located in the bottom or near the bottom of the heat exchanger and sent to the first compressor 22 for re-compression and circulation in the first circuit 110.

Both the second fraction or part 21b of the cooled first first refrigerant stream 20a and the cooled hydrocarbon stream 40a then enter the second heat exchanger 14b through its bottom or near the bottom through the inlets 36b and 32b, respectively, and pass through the heat exchanger from the bottom up. The first refrigerant stream flows through the outlet 38b at the top or near the top of the heat exchanger 14b as another cooled first refrigerant stream 20b and expands as it passes through the second turboexpander 12b to produce a second expanded first refrigerant stream 30b, which can then be directed back to the second heat exchanger 14b through the inlet 44b for passing from top to bottom through this heat exchanger. As the second expanded stream 30b flows downward through the second heat exchanger 14b, it is known in the prior art to cool pipes with a hydrocarbon stream (pipe 73b) and a first refrigerant (pipe 71b) flowing upstream of the second heat exchanger 14b. The expanded second refrigerant stream 30b evaporates as it flows from top to bottom through the second heat exchanger 14b and can be diverted through outlet 42b as a second vapor stream 90b that flows to the first compressor 22 for re-compression and circulation in the first refrigerant circuit 110.

The second expanded stream 30b is obtained in the second expander 12b in a thermodynamic expansion process close to isentropic, and the difference in the energy of the stream 20b before expansion and the energy of the stream 30b after expansion can also be used as useful energy in the first refrigerant circuit 110.

As shown in the drawing, the first refrigerant discharged from the first and second heat exchangers 14a, 14b is compressed in the compressor 22 to produce a compressed stream 95 and cooled by means of a water and / or air cooler 26 to produce a re-condensed stream 70 for re-introduction into the heat exchangers 14a, 14b. To circulate the re-condensed refrigerant stream 70, it is sequentially passed through the first and second pumps 28b, 28a to produce an injection stream 70a in front of the final cooler 29, cooling to ambient temperature, which may include one or more such chillers, such as water and / or an air cooler designed to produce a cooled compressed stream 70b that can be reused in heat exchangers 14a, 14b.

Pumps are common for cooling circuits and again require a drive, i.e. energy supply. In addition, they also increase the temperature of the stream passing through them, since the stream is compressed. In the present invention, it is particularly advantageous to provide a drive or energy for the pumps 28a, 28b using the useful energy generated by the closely located expanders 12a, 12b. The useful energy obtained in the expanders 12a, 12b can be transferred to the respective pumps 28a, 28b using any mechanical connection that ensures their interconnection, for example, by means of a common shaft.

In hot or warm climates in which a liquefaction plant operates, the temperature of the re-condensed stream 70 is typically 40 to 60 ° C, for example 50 ° C. Each pump in the first refrigerant circuit can increase the temperature of the re-condensed stream by several degrees Celsius, so that for the circuit shown in FIG. 1 and designed for hot climates, a typical temperature for the discharge stream 70a can be, for example, from 53 to 56 ° FROM. One or more ambient temperature chillers, such as cooler 29 shown in FIG. 1, can then lower the temperature of the cooled charge stream 70b by 10 to 20 ° C., so that a typical temperature of the cooled charge stream 70b is 40 ° C. In colder or colder climates, the temperatures of these flows can be lower - in the range from 10 to 20 ° C, but the temperature increase from the action of the pumps is the same as in hot or warm climates.

The drive for one or both pumps 28a, 28b can be partially, mainly or completely provided with useful energy obtained by expansion in expanders 12a, 12b. In this way, the need for external energy of the first refrigerant circuit 110 is reduced, thereby making it more efficient.

If additional sequential heat exchangers are used in the first cooling stage 100, the additionally cooled first refrigerant stream 20b can be divided to provide an additional line for the first refrigerant to pass through it, and so on for any additional heat exchangers, to the very last heat exchanger from which the entire first refrigerant is returned back as shown in the drawing for stream 20b.

The hydrocarbon stream exits the second heat exchanger 14b through the outlet 34b in the form of a cooled hydrocarbon stream 40b.

In each expander 12a, 12b, the expansion process of the first refrigerant is provided by a process close to the isentropic process, which increases the efficiency of the circulation circuit 110 of the first refrigerant. In this case, the internal energy of the streams 30a, 30b decreases, which is advantageous from the point of view of the efficiency of this expansion process. In addition, lower internal energy, for example, lower entropy of the first refrigerant circulation stream, causes lower temperatures of the refrigerant, so that the recirculating flows of the refrigerant provide a greater degree of cooling in the heat exchangers and / or lower compressor (s) power required to re-compress the refrigerant.

Preferably, the first cooling stage 100 cools the feed stream 10 to a temperature below 0 ° C, for example, in the range from -20 ° C to -70 ° C, preferably either from -20 ° C to -35 ° C or from -40 ° C to -70 ° C, usually - depending on the nature of the process implemented in the first cooling stage.

In one embodiment of the present invention, each heat exchanger of the first cooling stage 100 including several stages is characterized by a different pressure of the first refrigerant. Expanded refrigerant leaving each stage with different pressures can be compressed in one or more compressors using, for example, different compressors for different refrigerant inlet pressures.

In another embodiment of the present invention, the feed stream does not pass through all the heat exchangers of the first cooling stage, but can only pass through one or more of the heat exchangers. For example, in the diagram shown in the drawing, the feed stream 10 can pass through the second heat exchanger 14b only to achieve the necessary cooling in the first cooling stage 100.

The final cooled hydrocarbon stream 40b from the second heat exchanger 14b is then sent to a second cooling stage 200 using a second refrigerant, preferably the mixed refrigerant described above, circulating in the second refrigerant circuit 80.

For a chilled hydrocarbon stream 40b and a second circuit 80 with refrigerant circulating in the second stage and through the second cooling stage 200, various schemes may exist. Such schemes are known in the art. These circuits may include one or more stages, not necessarily functioning at different pressure levels, and not necessarily within the same tank, such as a cryogenic heat exchanger.

The second cooling stage 200 may lower the temperature of the cooled hydrocarbon stream 40b to produce a liquefied hydrocarbon stream 60 at a temperature of approximately equal to or less than -130 ° C.

The second refrigerant circuit 80, shown in a simplified form in the drawing, allows the vaporized second refrigerant effluent 50a to pass through two second circuit compressors 52 driven by the actuator 54 and through a water and / or air cooler 56. After the cooler 56, a second condensing refrigerant can pass through heat exchangers 14a, 14b of the first cooling stage 100, namely, through lines 75a, 75b to obtain a cooler liquefied stream 50 of the second refrigerant with its subsequent use in a second cooling stage 200.

Thus, the second refrigerant is at least partially cooled in the first cooling stage 100. This scheme simplifies the process of liquefying a hydrocarbon feed stream, for example a natural gas stream, by combining the implementation of a portion of the first stage duty cycle for cooling the feed stream with equivalent cooling of the second refrigerant. In this case, the same equipment is used instead of the second refrigerant circuit 200, requiring other heat exchangers to cool the second refrigerant, sufficient for its use in the second cooling stage 200. This solution, therefore, allows to reduce the level of necessary apparatus and equipment and to reduce capital and operating costs for the process illustrated in the drawing.

Additional cooling of the feed stream, the cooled and / or liquefied stream of hydrocarbons and / or refrigerant (s) can be achieved using one or more other refrigerant circuits, in addition to cooling in the first and second cooling stages, optionally connected to another stage of the method and / or element of a device for liquefying the flow of hydrocarbons disclosed in this description.

For example, the liquefied stream 60 may then pass through a third cooling stage (not shown), preferably a subcooling stage. Subcooling can be accomplished by passing a liquefied stream through one or more stages using one or more subcooling heat exchangers. One or each subcooling heat exchanger can be provided with cooling using a mixed (third) refrigerant. Additional cooling of the liquefied stream and / or supercooling refrigerant can be achieved using one or more other refrigerants or refrigerant circuits, optionally connected to another process step and / or element of the hydrocarbon stream liquefying device disclosed herein.

In addition, one of ordinary skill in the art will understand that after liquefaction, liquefied natural gas may, if necessary, be further processed. For example, the pressure of the produced LNG can be reduced using a Joule-Thompson valve or a cryogenic turbo expander.

Table 1 provides general information regarding power consumption for three examples.

Table 1 Parameter unit of measurement Example 1 Example 2 Example 3 Power mW 251.4 250.6 249.8 Power density kW / ton per day 10.39 10.36 10.32

Specific power for the liquefaction process is defined as the compressor power for the refrigerant (kW) required for the process divided by the amount (in tons per day) of the flow of liquefied hydrocarbons (for example, LNG) obtained.

Example 1 relates to the power required to drive a compressor in a refrigerant circuit for a first stage or a pre-cooling stage of a natural gas liquefaction plant that uses two heat exchangers and throttle valves, as described in US Pat. No. 6,105,389A.

Example 2 shows the power required to drive the compressor 22 in the liquefaction process described above, illustrated in the drawing, but without the use of pumps 28a, 28b.

Example 3 shows the power required to drive the compressor 22 in the drawing, where, as shown, the first refrigerant circuit 110 comprises pumps 28a, 28b.

As you can see, the power consumption in example 2 is less than in example 1, so that the use of expanders reduces the power required to re-compress the first refrigerant in the first circuit 110 of the circulation of the first refrigerant. Less compression pressure is needed since the expanded first refrigerant (after passing through the expanders) has less energy and therefore is cooler than when using throttle valves.

In Example 3, pumps 28a, 28b are used, driven by the useful energy generated by the expanders 12a, 12b. Example 3 shows that in this case the power required to drive the compressor 22 is even lower than in example 2, since the first refrigerant circulation circuit 110 provides additional efficiency through the use of pumps 28a, 28b, and thereby reduces the total discharge power, created by compressor 2 to maintain the circulation of the first refrigerant in circuit 110 with the first refrigerant.

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

Claims (20)

1. A method of liquefying a hydrocarbon stream, such as a natural gas stream contained in a feed stream (10), comprising at least the steps of:
(a) circulating a stream (70) of a first refrigerant in a circuit (110) with a first refrigerant;
(b) cooling the first refrigerant stream (70) in one or more heat exchangers (14) of the first cooling stage (100) to produce a cooled first refrigerant stream (20);
(c) passing at least a portion of the cooled stream (20) of the first refrigerant through one or more expansion devices to produce one or more expanded cooled streams (30) of the first refrigerant;
(d) passing one or at least one of the expanded streams (30) of the first refrigerant and the feed stream (10) through the first one or more heat exchangers (14) to produce a cooled stream (40) of hydrocarbons;
(e) passing the cooled stream (40) of hydrocarbons through the second stage (200) of cooling in countercurrent with the stream (50) of the second refrigerant to obtain a liquefied stream (60) of hydrocarbons;
in which at least one expansion device is an expander (12), the useful energy generated by which in step (c) is used in the circulation circuit (110) of the first refrigerant, and the generated useful energy is used to drive one or more pumps (28a, 28b) circulating the first refrigerant stream in order to increase the pressure of the first refrigerant stream (70), thereby providing a charge stream (70a), and the temperature of said charge stream (70a) is reduced in one or more refrigerants firs (29), cooling to ambient temperature before passing through the first heat exchanger (14). 2. The method according to claim 1, in which the temperature of the cooled stream (40) of hydrocarbons after the first stage (100) of cooling is in the range from -20 ° C to -70 ° C, while the second stage (200) of cooling is separated from the first stage (100) cooling. 3. The method according to claim 1, wherein the first refrigerant stream is a re-condensable stream obtained by compressing the vaporized refrigerant collected and removed from one or more heat exchangers (14) of the first cooling stage (100) and subsequent cooling using water and / or an air cooler (26). 4. The method according to claim 1, in which the second cooling stage (200) is separated from the first cooling stage (100), the second cooling stage (200) comprising one or more separate heat exchangers using a second refrigerant circulating in the circuit (80) circulation of the second refrigerant. 5. The method according to claim 1, in which the refrigerant of the second stage (50) passes, in addition, through at least one heat exchanger (14a, 14b) of the first stage (100) of cooling, preferably through all heat exchangers (14) of the first stage (100) cooling. 6. The method according to claim 1, wherein each expansion device in step (c) is an expander (12). 7. The method according to claim 1, wherein the first cooling stage (100) comprises two or three heat exchangers (14a, 14b). 8. The method according to claim 7, in which each heat exchanger (11a, 14b) is equipped with an expander (12a, 12b) connected to it through which at least a portion of the cooled first refrigerant stream (20a, 20b) passes to produce expanded cooled the stream (30a, 30b) of the first refrigerant directed to the corresponding heat exchanger (14a, 14b). 9. The method according to claim 7, in which for each heat exchanger (14a, 14b) of the first cooling stage (100) in stage (c), a different pressure of the first refrigerant is provided. 10. The method according to claim 1, in which the refrigerant stream (70) of the first refrigerant is a mixed refrigerant comprising a mixture of gases, while these gases are preferably selected from the group of gases including nitrogen, methane, ethane, ethylene, propane, propylene, butane and pentane. 11. The method according to claim 1, in which the refrigerant stream (50) of the second refrigerant flows through at least one heat exchanger (14) of the first cooling stage (100), preferably through all heat exchangers of the first cooling stage (100). 12. The method according to one or more of the preceding paragraphs, in which the temperature of the discharge stream (70a) is reduced by 10-20 ° C. 13. A device for liquefying a hydrocarbon stream, for example, a natural gas stream contained in a feed stream (10), containing at least
a first refrigerant circuit (110) for circulating a first refrigerant stream (70);
a first cooling stage (100) containing one or more heat exchangers (14) into which a first refrigerant stream (70) enters and in which a cooled first refrigerant stream (20) is obtained;
one or more expansion devices designed to expand at least a portion of the cooled stream (20) of the first refrigerant to produce one or more expanded flows (30) of the first refrigerant, wherein at least one expansion device is an expander ( 12), whose useful energy generated during expansion is used in the circulation circuit (110) of the first refrigerant;
one or more pumps (28a, 28b) to circulate the first refrigerant stream (70), while the useful energy generated during the expansion process is used to drive one or more pumps (28a, 28b);
one or more coolers (29) cooling to ambient temperature, placed after one or more pumps and before the first one or more heat exchanger (14);
one or each heat exchanger (14) having a first inlet for the passage of the feed stream (10) to the heat exchanger, and a second inlet for the passage of one or at least one of the expanded flows (30) of the first refrigerant to cool the feed stream (10) ) and thus providing a cooled stream (40) of hydrocarbons; and
a second cooling stage (200) containing one or more heat exchangers adapted to supply a cooled hydrocarbon stream (40) from the first cooling stage (100) and to obtain a liquefied hydrocarbon stream (60). 14. The device according to item 13, in which the first cooling stage (100) comprises two or more heat exchangers (14a, 14b), each of which is connected to a corresponding expander (12a, 12b). 15. The device according to item 13, further comprising a compressor (22) and a water and / or air cooler (26) located up to one or more pumps (28a, 28b). 16. The device according to one of paragraphs.13-15, in which the first stage (100) of cooling provides a cooled stream (20) of the first refrigerant having a temperature in the range from -20 ° C to -70 ° C, while the second stage ( 200) cooling is separated from the first cooling stage (100). 17. The device according to clause 16, in which the second cooling stage (200) is separated from the first cooling stage (100), the second cooling stage comprising one or more separate heat exchangers using a second refrigerant circulating in the second refrigerant circuit (80) . 18. The device according to 17, in which the refrigerant stream (50) of the second refrigerant also passes through at least one heat exchanger (14a, 14b) of the first stage (100) cooling, preferably through all heat exchangers (14) of the first stage (100) ) cooling. 19. The device according to one of paragraphs.13-15, in which the second cooling stage (200) is separated from the first cooling stage (100), the second cooling stage comprising one or more separate heat exchangers using a second refrigerant circulating in the second circuit ( 80) refrigerant circulation. 20. The device according to claim 19, in which the refrigerant of the stream (50) of the second refrigerant also passes through at least one heat exchanger (14a, 14b) of the first cooling stage (100), preferably through all heat exchangers (14) of the first stage (100) ) cooling.