EP4019869A1 - Method for liquefying natural gas - Google Patents

Abstract

A method for liquefying natural gas using a coiled heat exchanger (1A, 1B), with the following steps: a) feeding (S1) the natural gas to be liquefied into a tube bundle (13) of the heat exchanger (1A, 1B), and b) extracting ( S2) heat from the natural gas with the aid of a refrigerant (K), which flushes through the tube bundle (13), the refrigerant (K) being passed through the tube bundle (13) several times within the heat exchanger (1A, 1B) in order to Heat exchanger (1A, 1B) to generate a refrigerant circulation.

Description

The invention relates to a method for liquefying natural gas using a coiled heat exchanger.

Liquefied natural gas (LNG) is natural gas that has been processed and liquefied by cooling it to -161 to -164 °C. LNG is only a fraction of the volume of gaseous natural gas. LNG therefore has great advantages, especially for transport and storage purposes. The liquefied natural gas can be transported as a liquid in suitable transport containers by road, rail or water.

According to in-house knowledge, a cascade of straight tube heat exchangers can be used to pre-cool the natural gas to be liquefied, in which a refrigerant, for example ethane, evaporates at different pressure levels and thus cools down the natural gas. Due to construction limits, several heat exchangers can be required in parallel. As an alternative, so-called coil-wound heat exchangers (CWHE) or wound heat exchangers can also be used, in which the refrigerant partially evaporates from a sump of the heat exchanger.

Evaporation from the bottom or so-called tank boiling can lead to a tube bundle of the heat exchanger being able to run dry in its upper part, which can lead to lower heat transfer. In addition, in the case of evaporation via boiling in the container, it is generally possible to achieve lower heat transfer coefficients than would be possible in connection with an additional proportion of convection. This results in a larger required heating surface. This needs to be improved.

Against this background, the object of the present invention is to provide an improved method for liquefying natural gas.

Accordingly, a method for liquefying natural gas using a coiled heat exchanger is proposed. The method comprises the following steps: a) feeding the natural gas to be liquefied into a tube bundle of the heat exchanger, and b) extracting heat from the natural gas using a refrigerant which flushes through the tube bundle, with the refrigerant being passed through the tube bundle several times within the heat exchanger is to generate a refrigerant circulation in the heat exchanger.

Implementing the refrigerant circulation in the tube bundle results in a locally higher proportion of a liquid phase of the refrigerant in the tube bundle and in a higher heat transfer coefficient on the shell side. This allows the heat transfer to be increased. Furthermore, the heating area and the costs for the coiled heat exchanger can be reduced.

The wound heat exchanger is a so-called Coil Wound Heat Exchanger (CWHE). However, the coiled heat exchanger is simply referred to below as a heat exchanger. The heat exchanger can also be used to liquefy media other than natural gas. The tube bundle is wound onto a core tube in particular in multiple layers. In addition to the tube bundle and the core tube, the heat exchanger includes a jacket that accommodates the tube bundle. A circulation or circuit of the refrigerant is created within the jacket, which is passed through the tube bundle.

The tube bundle includes a tube side and a shell side. In the present case, the “tube side” is to be understood as meaning an interior space enclosed by tubes of the tube bundle, through which the natural gas to be liquefied is conducted. The natural gas is thus fed into the tubes of the tube bundle. In the present case, “on the shell side” is to be understood as meaning an area outside the tubes of the tube bundle. On the shell side, the refrigerant flows through the tube bundle. A large number of gaps or passages through which the refrigerant is conducted lead through the tube bundle. The fact that the natural gas to be liquefied is “fed” into the tube bundle means in particular that the natural gas is introduced into tubes of the tube bundle.

The refrigerant can be ethane, for example. However, any other desired refrigerant can also be used. A refrigerant is suitable for transporting enthalpy from the goods to be cooled, in this case the natural gas to be liquefied, to the environment. The difference to the coolant is that a refrigerant can carry out this heat transport in a refrigeration circuit along a temperature gradient, so that the ambient temperature can even be higher than the temperature of the object to be cooled when the energy supplied is used, while a coolant is only able to to transport the enthalpy in a cooling circuit against the temperature gradient to a point with a lower temperature. By extracting heat from the natural gas, it is liquefied. The liquefied natural gas can be referred to as Liquefied Natural Gas (LNG).

In the present case, the fact that the refrigerant “flushes” or “flows around” the tube bundle means in particular that the refrigerant is passed through the tube bundle on the shell side. For this purpose, passages or gaps are provided in the tube bundle. The refrigerant does not come into direct contact with the natural gas. The refrigerant preferably comprises a gaseous phase and a liquid phase which can be transformed into one another. The refrigerant is preferably conducted in two phases through the tube bundle.

According to one embodiment, the refrigerant is conducted through the tube bundle counter to a direction of gravity from an inlet side of the tube bundle to an outlet side of the tube bundle.

The tube bundle preferably has a cylindrical geometry in its entirety. Viewed with respect to the direction of gravity, a lower end face of the cylindrical geometry forms the entry side. An upper end face of the cylindrical geometry then forms the exit side of the tube bundle. The refrigerant rises from the inlet side against the direction of gravity upwards to the outlet side, the refrigerant being at least partially evaporated in the tube bundle. Circulation evaporation thus takes place.

According to a further embodiment, the refrigerant is conducted outside of the tube bundle along the direction of gravity from the outlet side to the inlet side.

In the present case, "outside" means in particular that the refrigerant is not passed through the tube bundle from the outlet side to the inlet side. This means in particular that an additional component, for example the aforementioned core tube, is present in order to conduct the refrigerant from the outlet side to the inlet side. In particular, the refrigerant is conducted within the heat exchanger or within the jacket along the direction of gravity from the outlet side to the inlet side.

According to a further embodiment, the refrigerant at least partially evaporates as it is conducted through the tube bundle, with only a liquid phase of the refrigerant being conducted from the outlet side to the inlet side.

When the refrigerant partially evaporates, it absorbs heat from the natural gas in order to cool it down. The refrigerant thus has the liquid phase and a gaseous phase when passing through the tube bundle. The gaseous phase is preferably conducted away from the tube bundle and is therefore not fed back to the inlet side of the tube bundle.

According to a further embodiment, the liquid phase inside the heat exchanger is mixed with coolant supplied from outside the heat exchanger.

In this way, refrigerant that has evaporated in the tube bundle can be replaced. For example, the refrigerant supplied from the outside of the heat exchanger mixes with the refrigerant supplied from the exit side to the entrance side in the core tube.

According to a further embodiment, the refrigerant supplied from outside the heat exchanger is fed into the heat exchanger via an inlet connection.

The inlet connector can be provided, for example, on the side of a cylindrical base section of the jacket. A pipe can be mounted on the inlet port, which leads the refrigerant supplied from the outside into the core tube feeds. However, the refrigerant can also be introduced into the heat exchanger at any other point. This means that the inlet port is optional.

According to a further embodiment, the liquid phase is at least partially drawn off from the heat exchanger.

A discharge nozzle is provided on the shell of the heat exchanger for drawing off the liquid phase. Viewed in relation to the direction of gravity, the discharge connection is preferably arranged below the tube bundle. The vent may be attached to a cover portion of the shell.

According to a further embodiment, a gaseous phase of the refrigerant formed during the at least partial evaporation of the refrigerant is at least partially drawn off from the heat exchanger.

To extract the gaseous phase of the refrigerant, the shell of the heat exchanger includes a further discharge port. With regard to the direction of gravity, this discharge connection is preferably placed above the tube bundle.

According to a further embodiment, the refrigerant is conducted from the outlet side to the inlet side with the aid of a core tube onto which the tube bundle is wound.

The core tube is preferably cylindrical. The core tube is preferably placed centrally in the tube bundle. The tube bundle can be wound onto the core tube in multiple layers. The core tube is open at the front so that the refrigerant can flow through the core tube.

According to a further embodiment, the refrigerant is conducted from the outlet side into the core tube via an upper edge of the core tube.

The refrigerant or the liquid phase of the refrigerant builds up on the outlet side up to the upper edge of the core tube. The liquid phase then flows over the top edge into the core tube. The gaseous phase of the refrigerant escapes upwards from the core tube against the direction of gravity.

According to a further embodiment, the refrigerant is conducted from the outlet side into the core tube via at least one radial slot provided in the core tube.

The number of slots is arbitrary. For example, three such slots can be provided. In the event that the radial slots are provided, it is possible to close the end tube on the top side, that is to say at its upper edge.

According to a further embodiment, the refrigerant is conducted from the outlet side to the inlet side with the aid of an annular gap, which is provided between a shirt enveloping the tube bundle and a jacket of the heat exchanger.

The shirt may be a tubular member that encases or encases the tube bundle. Between the shirt and the jacket, the annular gap that runs completely around the tube bundle is provided. The refrigerant supplied from the outside can also be introduced into the annular gap.

According to a further embodiment, the refrigerant is conducted from the outlet side into the annular gap via an upper edge of the skirt.

This means in particular that the liquid phase of the refrigerant accumulates on the outlet side up to the upper edge of the shirt. The liquid phase of the refrigerant then flows over the upper edge into the annular gap.

According to a further embodiment, the tube bundle is completely immersed in the refrigerant.

As previously mentioned, the refrigerant within the tube bundle is two-phase. This means that both the liquid phase and the gaseous phase of the refrigerant are present within the tube bundle. The gaseous phase can form bubbles in the liquid phase.

According to a further embodiment, the refrigerant is fed to the heat exchanger in two phases.

The refrigerant is preferably ethane. However, any other suitable refrigerant can also be used. The refrigerant can also be fed to the heat exchanger as a single phase, in particular as a liquid phase.

As used herein, "a" is not necessarily meant to be limited to just one element. Rather, a plurality of elements, such as two, three or more, can also be provided. Any other counting word used here should also not be understood to mean that an exact restriction to exactly the corresponding number of elements must be implemented. Rather, numerical deviations upwards and downwards are possible.

Further possible implementations of the method also include combinations of features or embodiments described above or below with regard to the exemplary embodiments that are not explicitly mentioned. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the method.

• Fig. 1 zeigt eine schematische Schnittansicht einer Ausführungsform eines gewickelten Wärmetauschers;
• Fig. 2 zeigt eine schematische Ansicht einer Ausführungsform eines Kernrohrs für den gewickelten Wärmetauscher gemäß Fig. 1;
• Fig. 3 zeigt eine schematische Schnittansicht einer weiteren Ausführungsform eines gewickelten Wärmetauschers; und
• Fig. 4 zeigt ein schematisches Blockdiagramm einer Ausführungsform eines Verfahrens zum Verflüssigen von Erdgas.

Further advantageous refinements of the method are the subject of the dependent claims and the exemplary embodiments of the method described below. The method is explained in more detail below on the basis of preferred embodiments with reference to the enclosed figures.

• 1 Figure 12 shows a schematic sectional view of one embodiment of a coiled heat exchanger;
• 2 12 shows a schematic view of an embodiment of a core tube for the coil-wound heat exchanger according to FIG 1 ;
• 3 Figure 12 shows a schematic sectional view of another embodiment of a coiled heat exchanger; and
• 4 Figure 12 shows a schematic block diagram of one embodiment of a process for liquefying natural gas.

Elements that are the same or have the same function have been provided with the same reference symbols in the figures, unless otherwise stated.

the 1 shows a schematic sectional view of an embodiment of a coil wound heat exchanger (CWHE) 1A. Such a coiled heat exchanger 1A can be used to liquefy natural gas (Liquefied Natural Gas, LNG). However, other gases can also be liquefied. The wound heat exchanger 1A is hereinafter simply referred to as a heat exchanger.

The heat exchanger 1A comprises a jacket 2. The jacket 2 is made up of a cylindrical base section 3 and two cover sections 4, 5 curved in the shape of a dome. For example, the base section 3 and the cover sections 4, 5 are soldered, welded, screwed or riveted to one another. The jacket 2 is fluid-tight. The jacket 2 can be made of an aluminum alloy or a steel alloy. The shell 2 is constructed essentially rotationally symmetrically to a central axis or axis of symmetry 6 . The lid portion 4 is placed above the lid portion 5 when viewed in a gravity direction g.

An inlet connector 7 is provided on the base section 3 and is oriented perpendicularly to the axis of symmetry 6 . A refrigerant K, for example ethane, can be supplied to the heat exchanger 1A via the inlet connector 7 . The refrigerant K can be in two phases, so that it has a liquid phase KL and a gaseous phase KG.

The refrigerant K is in the 1 represented by block arrows. Block arrows with oblique hatching stand for a two-phase state of the refrigerant K. Horizontally hatched block arrows stand for the gaseous phase KG of the refrigerant K. Unhatched block arrows stand for the liquid phase KL of the refrigerant K.

On the cover portion 4, which in the orientation of 1 is attached to the top of the base portion 3, a vent 8 is provided. The gaseous phase KG of the refrigerant K can be drawn off at least partially via the draw-off connection piece 8 . On the cover section 5 is accordingly a Deduction nozzle 9 attached, through which the liquid phase KL of the refrigerant K can be at least partially deducted.

A cylindrical core tube 10 is accommodated in the jacket 2 . The core tube 10 runs along the direction of gravity g and is rotationally symmetrical to the axis of symmetry 6 . The core tube 10 comprises an upper edge 11 and a lower edge 12 placed below the upper edge 11 viewed in the direction of gravity g. The core tube 10 is open at the front. This means that neither the upper edge 11 nor the lower edge 12 is provided with a cover closing the core tube 10 . The coolant K can thus flow through the core tube 10 .

A tube bundle 13 is wound onto the core tube 10 . The tube bundle 13 is multi-layered and at least partially fills an annular gap 14 placed between the core tube 10 and the base section 3 of the shell 2 . In the 1 only individual tubes of the tube bundle 13 are shown. However, viewed along the axis of symmetry 6, the tube bundle 13 extends from the upper edge 11 to the lower edge 12 of the core tube 10. A medium to be liquefied, for example natural gas, flows through the tube bundle 13. The tube bundle 13 comprises a large number of gaps or passages through which the refrigerant K can flow. The tube bundle 13 comprises an entry side 15 and an exit side 16.

A line 17 leads from the inlet connection 7 to the core tube 10. The line 17 ends above or below the upper edge 11 of the core tube 10. The coolant K can be supplied to the core tube 10 with the aid of the line 17.

The functionality of the heat exchanger 1A is explained below. As previously mentioned, the refrigerant K is fed into the core tube 10 via the inlet connection 7 and the line 17 . The refrigerant K here has two phases, namely the liquid phase KL and the gaseous phase KG. The liquid phase KL accumulates in the core tube 10 so that a liquid level 18 is set there which is arranged below the upper edge 11 of the core tube 10 viewed along the direction of gravity g. The liquid level 18 is illustrated with the help of a triangle.

The gaseous phase KG rises out of the core tube 10 in the opposite direction to the direction of gravity g and can be at least partially drawn off via the discharge nozzle 8 . Due to density differences of the refrigerant K in the core tube 10 and on the side of the tube bundle 13, the refrigerant K or the liquid phase KL flows downwards against the direction of gravity g and is distributed over the tube bundle 13.

Only the liquid phase KL is present in the core tube 10 below the liquid level 18 . The jacket 2 is filled with the liquid phase KL in a region 19 below the core tube 10 and the tube bundle 13 . At least part of the liquid phase KL can be drawn off via the discharge nozzle 9 . The refrigerant K rises as a two-phase mixture against the direction of gravity g from the inlet side 15 to the outlet side 16 through the tube bundle 13 , the refrigerant K absorbing heat from the medium to be liquefied contained in the tube bundle 13 .

The refrigerant K at least partially evaporates as it rises in the tube bundle 13, so that the refrigerant K is in two phases. A partial evaporation of the refrigerant K thus takes place in the tube bundle 13 in the upward direction. The gaseous phase KG rises and can be drawn off at least partially via the discharge nozzle 8 . The liquid phase KL accumulates up to a liquid level 20 which is at the same height as the upper edge 11 with respect to the direction of gravity g. The liquid level 20 is illustrated with the aid of a triangle. The liquid phase KL flows over the upper edge 11 into the core tube 10 and mixes there with the liquid phase KL of the refrigerant K supplied via the line 17. The refrigerant K can therefore circulate in the heat exchanger 1A.

By implementing the previously explained circulation evaporation in the tube bundle 13, there is a locally higher proportion of the liquid phase KL and a higher heat transfer coefficient on the shell side. As a result, the heat transfer can be increased and the heating surface and the costs for the heat exchanger 1A can be reduced. "Surface side" here means on the outside of tubes of the tube bundle 13 or in gaps or passages of the tube bundle 13.

The supply of the refrigerant K is not absolutely necessary via the inlet socket 7 and the line 17 . The feed can also take place in any other desired area of the jacket 2 . The refrigerant K can also include several components. In this case, the refrigerant is not a mixed refrigerant. Circulation evaporation can also be used to separate components.

the 2 shows a schematic view of another embodiment of a core tube 10 for the heat exchanger 1A. The core tube 10 according to the 2 comprises radial slots 21 to 23 through which the liquid phase KL coming from the tube bundle 13 can enter the core tube 10 . The number of slots 21 to 23 is arbitrary. The top edge 11 can be closed. However, the upper edge 11 can also be open, so that the coolant K can be fed to the core tube 10 via the inlet connector 7 and the line 17 .

the 3 1B shows a schematic sectional view of another embodiment of a coiled heat exchanger. The structure of the heat exchanger 1B essentially corresponds to that of the heat exchanger 1A. Only the differences between the heat exchangers 1A, 1B will be discussed below. In contrast to the heat exchanger 1A, the refrigerant K does not circulate in the heat exchanger 1B with the help of the core tube 10, but with the help of an annular gap 25 provided between a shirt 24 and the jacket 2. The shirt 24 can be a tubular component enveloping the tube bundle 13. The core tube 10 can be sealed fluid-tight at its upper edge 11 and/or at its lower edge 12 .

The two-phase refrigerant K is fed to the annular gap 25 via the inlet connector 7 and the line 17 which opens into the annular gap 25 . In the annular gap 25 there is a liquid level 26 which is illustrated with the aid of triangles. The gaseous phase KG rises out of the annular gap 25 against the direction of gravity g, where it can be at least partially drawn off via the discharge nozzle 8 .

The liquid phase KL flows downwards in the direction of gravity g in order to then rise through the tube bundle 13 counter to the direction of gravity g. In the process, the liquid phase KL is at least partially evaporated. The gaseous phase KG rises upwards and can be at least partially drawn off via the discharge nozzle 8. The liquid phase KL flows over an upper edge 27 of the skirt 24 into the annular gap 25 where it mixes with the refrigerant K supplied via the inlet connector 7 and the line 17 . A circulation of the refrigerant K and thus a circulation evaporation also takes place in the heat exchanger 1B.

the 4 shows a schematic block diagram of an embodiment of a method for liquefying natural gas using the heat exchanger 1A, 1B. In the method, the natural gas to be liquefied is fed into the tube bundle 13 of the heat exchanger 1A, 1B in a step S1. This means that the natural gas flows through the tube bundle 13 . In a step S2, heat is extracted from the natural gas using the refrigerant K in order to cool or liquefy the natural gas. The refrigerant K flows around or through the tube bundle 13, the refrigerant K being passed through the tube bundle 13 several times within the heat exchanger 1A, 1B in order to generate a refrigerant circulation or refrigerant circuit in the heat exchanger 1A, 1B.

The refrigerant K is conducted through the tube bundle 13 counter to the direction of gravity g from the inlet side 15 of the tube bundle 13 to the outlet side 16 of the tube bundle 13 . The refrigerant K is conducted outside of the tube bundle 13 along the direction of gravity g from the outlet side 16 to the inlet side 15 . This means in particular that the refrigerant K is not passed through the tube bundle 13 from the outlet side 16 to the inlet side 15 .

The refrigerant K at least partially evaporates as it is conducted through the tube bundle 13 , only the liquid phase KL of the refrigerant K being conducted from the outlet side 16 to the inlet side 15 . The gaseous phase KG can be drawn off. In particular, the liquid phase KL is mixed inside the heat exchanger 1A, 1B with refrigerant K supplied from outside the heat exchanger 1A, 1B. The mixing can be carried out in the core barrel 10, for example. The tube bundle 13 is preferably always completely immersed in the refrigerant K.

Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

Reference signs used

1A

heat exchanger

1B

heat exchanger

2

a coat

3

base section

4

cover section

5

cover section

6

axis of symmetry

7

inlet port

8th

trigger nozzle

9

trigger nozzle

10

core barrel

11

top edge

12

bottom edge

13

tube bundle

14

annular gap

15

entry side

16

exit side

17

Management

18

liquid level

19

area

20

liquid level

21

slot

22

slot

23

slot

24

shirt

25

annular gap

26

liquid level

27

top edge

G

direction of gravity

K

refrigerant

KG

gaseous phase of the refrigerant

cl

liquid phase of the refrigerant

S1

Step

S2

Step

Claims (15)

Process for liquefying natural gas using a coil-wound heat exchanger (1A, 1B), comprising the following steps: a) feeding (S1) the natural gas to be liquefied into a tube bundle (13) of the heat exchanger (1A, 1B), and b) Extraction (S2) of heat from the natural gas using a refrigerant (K) which flushes through the tube bundle (13), the refrigerant (K) being passed through the tube bundle (13) several times within the heat exchanger (1A, 1B). to generate a refrigerant circulation in the heat exchanger (1A, 1B). Method according to claim 1, wherein the refrigerant (K) is passed through the tube bundle (13) against a direction of gravity (g) from an inlet side (15) of the tube bundle (13) to an outlet side (16) of the tube bundle (13). Method according to Claim 2, in which the refrigerant (K) is routed outside the tube bundle (13) along the direction of gravity (g) from the outlet side (16) to the inlet side (15). Method according to Claim 3, in which the refrigerant (K) at least partially evaporates as it is passed through the tube bundle (13), and in which only a liquid phase (KL) of the refrigerant (K) flows from the outlet side (16) to the inlet side (15 ) is routed. Method according to Claim 4, in which the liquid phase (KL) is mixed within the heat exchanger (1A, 1B) with refrigerant (K) supplied from outside the heat exchanger (1A, 1B). Method according to Claim 5, in which the refrigerant (K) supplied from outside the heat exchanger (1A, 1B) is fed into the heat exchanger (1A, 1B) via an inlet connection (7). Method according to one of Claims 4 - 6, in which the liquid phase (KL) is at least partially drawn off from the heat exchanger (1A, 1B). Method according to one of Claims 4 - 7, in which a gaseous phase (KG) of the refrigerant (K) formed during the at least partial evaporation of the refrigerant (K) is at least partly drawn off from the heat exchanger (1A, 1B). Method according to one of Claims 3 - 8, in which the refrigerant (K) is conducted from the outlet side (16) to the inlet side (15) with the aid of a core tube (10) onto which the tube bundle (13) is wound. Method according to Claim 9, in which the refrigerant (K) is conducted from the outlet side (16) over an upper edge (11) of the core tube (10) into the core tube (10). Method according to Claim 9, in which the refrigerant (K) is conducted from the outlet side (16) into the core tube (10) via at least one radial slot (21 - 23) provided in the core tube (10). Method according to one of claims 3 - 8, wherein the refrigerant (K) is provided with the aid of an annular gap (25) which is provided between a sleeve (24) enveloping the tube bundle (13) and a jacket (2) of the heat exchanger (1B), from the exit side (16) to the entry side (15). Method according to Claim 12, in which the refrigerant (K) is conducted from the outlet side (16) over an upper edge (27) of the skirt (24) into the annular gap (25). Method according to one of claims 1 - 13, wherein the tube bundle (13) is completely immersed in the refrigerant (K). Method according to one of Claims 1 - 14, in which the refrigerant (K) is fed to the heat exchanger (1A, 1B) in two phases.

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