Facility and method for liquefying carbon dioxide

Abstract

The invention relates to a method for producing liquid carbon dioxide in a facility (1), wherein the pressure and temperature of a medium containing carbon dioxide are first increased in a compressor unit (2); the medium containing carbon dioxide is separated into a first mass flow (34) and into a second mass flow (35) in a first separating device (32), said first mass flow (34) flowing through a first conversion device (36) and said second mass flow (35) flowing through a second conversion device (37); the temperature and the pressure of the medium are reduced downstream of the first and second conversion device (36, 37), the temperature of the medium downstream of the first conversion device (36) being lower than the temperature of the medium downstream of the second conversion device (37); and the medium downstream of the first conversion device (36) is conducted to a liquid heat exchanger (41) where the thermal energy of the medium from the first conversion device (36) is exchanged with the thermal energy of the medium from the second conversion device (37), as a result of which the carbon dioxide from the second conversion device (37) is liquefied downstream of the liquid heat exchanger (41).

Description

TITLE Plant and process for liquefaction of carbon dioxide TECHNICAL FIELD

[0001] The invention relates to a plant for liquefying carbon dioxide, comprising a compressor unit having an inlet opening for a medium containing carbon dioxide at a pressure pinlet and a temperature Tinlet, wherein the compressor unit is configured such that the carbon dioxide-containing medium is compressed and flows out of the compressor unit through an outlet opening at a pressure pcompressor and a temperature Tcompressor. BACKGROUND

[0002] It is known that the emission of carbon dioxide (CO2) represents a considerable problem for global climate development. Efforts are therefore being made to avoid the production of carbon dioxide or at least to capture the carbon dioxide during production and to store it safely for the future. For this purpose, the captured carbon dioxide would have to be transported.

[0003] The transport of captured carbon dioxide for storage or further use presents a challenge, especially over long distances. One possibility for transporting carbon dioxide would be to provide pipelines, although suitable pipelines are currently available only to a limited extent.

[0004] So-called amine plants are suitable for capturing carbon dioxide from flue gases and are currently regarded as a commercially successful large-scale technology. Amine systems require considerable amounts of low-pressure steam or heat to carry out the process. The carbon dioxide captured in an amine system is supplied at low pressure.

[0005] After the capture of the carbon dioxide, the carbon dioxide is generally transported to a storage reservoir or another use application. An economically viable solution would be to transport the carbon dioxide via pipelines in a supercritical state. However, there are comparatively few suitable pipelines available, and the construction of new pipelines would require considerable time and could take up to ten years. A quick way of transporting carbon dioxide would therefore be to transport liquefied carbon dioxide.

[0006] The carbon dioxide can be liquefied by cryogenic processes at low temperatures and at low pressures. The carbon dioxide thus liquefied can then be transported by truck, by rail or by ship.

[0007] Thus, a modern application consists of using a separate cryogenic refrigerant liquefaction circuit, in order to liquefy the carbon dioxide after it has been compressed to a required pressure. For this purpose, two separate compression trains are required, one being used for carbon dioxide compression and the other for the cryogenic refrigerant circuit. A frequently used refrigerant is ammonia, which, however, requires careful consideration due to its toxicity.

[0008] In the case of liquefaction of carbon dioxide, there is a loss of compression energy between the compressor stages, which has an effect on the overall efficiency of a plant.

[0009] It is desirable to provide a plant for liquefying carbon dioxide which has low capital costs and low process complexity. SUMMARY OF THE INVENTION

[0010] It is therefore an object of the present invention to provide a plant for liquefying carbon dioxide which can be constructed cost-effectively.

[0011] The object is achieved by a plant for liquefying carbon dioxide, comprising a compressor unit having an inlet opening for a carbon dioxide-containing medium at a pressure pinlet and a temperature Tinlet, wherein the compressor unit is configured such that the carbon dioxide-containing medium is compressed and flows out of the compressor unit through an outlet opening at a pressure pcompressor and a temperature Tcompressor, further comprising a first separation device which is fluidically connected on the inlet side to the compressor unit and divides the carbon dioxide containing medium coming from the compressor unit into a first mass flow MMS01 and a second mass flow MMS02, further comprising a first conversion device which is configured such that the temperature Tconv_01,in and the pressure pconv_1,in of the first mass flow MMS01 are reduced to a lower temperature Tconv_01,out and a lower pressure pconv_1,out, further comprising a second conversion device, which is configured such that the temperature Tconv_02,in and the pressure pconv_2,in of the second mass flow MMS02 are reduced to a lower temperature Tconv_02,out and a lower pressure pconv_2,out, where Tconv01,out <Tconv02,out, further comprising a liquid heat exchanger which is configured such that the thermal energy is exchanged between the medium coming from the first conversion device and the medium coming from the second conversion device such that the medium coming from the second conversion device is liquid after passing through the liquid heat exchanger.

[0012] Advantageous embodiments are the subject matter of the dependent claims.

[0013] The invention proposes dispensing with a separate refrigeration circuit for which a separate compressor is required. In the liquefaction of the carbon dioxide according to the invention, some of the carbon dioxide itself is used as the refrigerant. As a result, only one compressor unit configured as a compressor is required. Furthermore, according to the invention, a dedicated refrigerant circuit is dispensed with. In addition, the heat released during the compression process is utilized and used to generate steam. DESCRIPTION OF THE INVENTION

[0014] The invention is based on the idea of using a stream of carbon dioxide in order to liquefy previously captured carbon dioxide. This process helps to reduce capital costs. No additional refrigeration compressor or refrigerant circuit is required.

[0015] Furthermore, the invention is based on the concept of using the heat of compression generated in the compressor unit to generate low-pressure steam. As a result, the steam is reduced to the required level.

[0016] The temperature at which carbon dioxide is present in a liquid state depends on the pressure to which it is exposed. Carbon dioxide is relatively unusual in that it can be present as a gas, liquid or solid under various combinations of temperature and pressure. At atmospheric pressure, the temperature at which carbon dioxide becomes liquid is -78.5°C. If, however, pressure is applied, the carbon dioxide may be present as a liquid at higher temperatures. According to the invention, liquefaction of carbon dioxide at about 15 bar and -30° C is achieved here, which is well suited to commercial transport by road tanker or ship. Other pressure and temperature levels can be achieved according to the invention.

[0017] The plant according to the invention and the process according to the invention are described in conjunction with one another below. A carbon dioxide-containing medium is compressed at high temperature, and the heat is recovered in an aftercooling unit by supplying low-pressure saturated water, which is evaporated by the heat of compression and converted into low-pressure steam. The gaseous carbon dioxide is introduced into a separator in order to remove the condensed water before it is fed to the next stage of the compressor. After each compression stage, the heat is recovered and steam is generated. After a few compression stages, a process pressure for the carbon dioxide is reached. The carbon dioxide is then divided into two streams, and both streams are expanded to two different pressure levels by two conversion devices, preferably configured as Joule-Thomson valves. The low-pressure streams are used as refrigerant, and the high-pressure streams are then liquefied by exchanging cold energy with cold energy from the stream having a lower cryogenic temperature. At the same time, the refrigerant stream of carbon dioxide absorbs heat from the compressed stream of carbon dioxide and evaporates. The mass flow of carbon dioxide is divided such that the refrigerant stream can provide sufficient cooling to liquefy the other carbon dioxide stream. The evaporated refrigerant is then recirculated to the inlet of the compressor stages on the basis of the respective inlet pressure.

[0018] In a first advantageous development, the plant further comprises a second separation device having a first outlet line and a second outlet line, wherein the second separation device is configured such that the gaseous medium coming from the first conversion device flows into the first outlet line and the liquid medium coming from the first conversion device flows into the second outlet line, wherein the second outlet line is coupled to the liquid heat exchanger such that the thermal energy is exchanged between the medium coming from the second outlet line and the medium coming from the second conversion device.

[0019] It is thus achieved that the carbon dioxide coming from the first conversion device, which comprises a mixture of gaseous and liquid carbon dioxide, is separated in the second separation device. The liquid carbon dioxide passes to the liquid heat exchanger, where it becomes gaseous again by exchange of thermal energy, since it interacts with the warmer gaseous carbon dioxide from the second conversion device. As a result of this interaction, the gaseous carbon dioxide from the second conversion device ultimately becomes liquid carbon dioxide having physical parameters suitable for transport.

[0020] In a further advantageous development, the first conversion device and / or the second conversion device are configured as a Joule-Thomson valve.

[0021] In a Joule-Thomson valve, the temperature of the carbon dioxide is reduced during expansion, provided that the temperature is below the inversion temperature of carbon dioxide. A Joule-Thomson valve is a comparatively inexpensive way of reducing the temperature of the carbon dioxide in a suitable manner.

[0022] In an alternative embodiment, the first conversion device and / or the second conversion device is configured as an expansion turbine.

[0023] As an alternative to a Joule-Thomson valve, the temperature and pressure may also be reduced with a suitable expansion turbine. The rotational energy produced in the process can be further utilized.

[0024] In a further advantageous development, the compressor unit has different compressor stages. It should be noted here that the compressor unit is a compressor having a single drive. In this case, the compressor has a plurality of compressor stages. In the case of a geared compressor as an embodiment of the compressor, a bull gear is driven by a drive unit. A plurality of pinions is arranged on the bull gear, wherein an impeller for a compressor stage is arranged on each pinion.

[0025] One advantage of the invention is that only one compressor is required for the plant according to the invention. This may, for example, be a geared compressor. This leads to a significant cost saving.

[0026] In a further advantageous development, the compressor unit has a first compressor stage with the inlet opening, wherein the first compressor stage has a first compressor stage outlet, wherein the compressor unit further has a second compressor stage with a second flow inlet, wherein the first compressor stage outlet is fluidically connected to the second flow inlet, wherein a first heat exchanger is arranged between the first compressor stage outlet and the second flow inlet, said first heat exchanger being configured such that the thermal energy is exchanged between the medium flowing in the compressor unit and an exchange medium flowing through the first heat exchanger.

[0027] As a result, the medium containing carbon dioxide can be cooled after each compressor stage before it reaches a next compressor stage. The thermal energy converted in the first heat exchanger can be used to heat the exchange medium. Ideally, when water is used as the exchange medium, it is evaporated, and the steam formed as a result can be used.

[0028] In a further advantageous development, a third compressor stage is arranged downstream of the second compressor stage, wherein the third compressor stage is fluidically connected to the second compressor stage, wherein a second heat exchanger is arranged between the second compressor stage and the third compressor stage, wherein the second heat exchanger is configured such that the temperature of the exchange medium is increased.

[0029] In an advantageous development, a third heat exchanger is arranged between the compressor unit and the first separation device, wherein the third heat exchanger is configured such that the temperature of the exchange medium is increased.

[0030] In a further advantageous development, the plant has a cooling feed line which is configured such that the gaseous medium present downstream of the second separation device and downstream of the liquid heat exchanger is fed to the compressor unit.

[0031] The carbon dioxide required in the liquid heat exchanger for liquefaction of carbon dioxide is thus fed in at a suitable point in the compressor unit, in order to further reduce the temperature of the carbon dioxide-containing medium.

[0032] Advantageously, the cooling feed line supplies the gaseous medium present downstream of the second separation device and downstream of the liquid heat exchanger to the second compressor stage.

[0033] The object is likewise achieved by a process for liquefying carbon dioxide, wherein, in a compressor unit, the pressure and temperature of a carbon dioxide-containing medium are first increased, wherein, in a first separation device, the carbon dioxide-containing medium is divided into a first mass flow and a second mass flow, wherein the first mass flow flows through a first conversion device and the second mass flow flows through a second conversion device, wherein the temperature and the pressure of the medium downstream of the first and second conversion devices are reduced, wherein the temperature of the medium downstream of the first conversion device is lower than the temperature of the medium downstream of the second conversion device, wherein the medium downstream of the first conversion device is guided to a liquid heat exchanger, where the thermal energy of the medium from the first conversion device is exchanged with the thermal energy of the medium from the second conversion device, as a result of which liquefaction of the carbon dioxide from the second conversion device takes place downstream of the liquid heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] An exemplary embodiment of the invention will be explained in greater detail below with reference to the figures that follow.

[0035] The above-described properties, features and advantages of this invention and the way in which they are achieved will become clearer and more distinctly understood in connection with the following description of the exemplary embodiments, which will be explained in greater detail in connection with the drawings.

[0036] In this context, identical components or components with the same function are identified by the same reference signs.

[0037] Exemplary embodiments of the invention will be described below with reference to the drawings. These drawings are not intended to illustrate the exemplary embodiments to scale; instead, the drawings are presented in a schematic and / or slightly distorted form where this aids understanding. With regard to additions to the teachings which are directly apparent in the drawings, reference is made to the relevant prior art.

[0038] In the drawings:

[0039] FIG 1 shows a schematic illustration of the plant according to the invention DESCRIPTION OF THE EMBODIMENTS

[0040] Figure 1 shows a schematic illustration of the plant 1 for liquefying carbon dioxide. The plant 1 comprises a compressor unit 2. In this case, the compressor unit 2 comprises a geared compressor which has a plurality of compressor stages 3, 4, 5. In this case, a compressor stage 3, 4, 5 is arranged as a radial turbine on a bull gear of the geared compressor. In this case, the geared compressor is driven only via a drive unit (not illustrated). The compressor stages 3, 4, 5 have impellers. The construction of a geared compressor is sufficiently well known. Therefore, a detailed description of a geared compressor is omitted here. The number of compressor stages may vary here. The plant according to the invention can therefore also be configured with fewer than three or with more than three compressor stages.

[0041] A carbon dioxide-containing medium 7 passes via an inlet opening 6 into the compressor unit 2, more precisely into the first compressor stage 3. In this exemplary embodiment, the medium 7 is assumed to consist of gaseous carbon dioxide contaminated with water. It should be noted that the plant 1 according to the invention can also be operated with gaseous carbon dioxide without impurities. The medium 7 is usually present at atmospheric pressure.

[0042] In the first compressor stage 3, the temperature and the pressure of the medium 7 are increased, and the medium passes via a line 8 to a first heat exchanger 9. An exchange medium such as water is fed to the first heat exchanger 9 via an inletside line 10. By exchanging the thermal energy between the medium coming from the first compressor stage 3 and of the water, the temperature of the water is increased and the temperature of the medium is reduced, such that steam flows out via an outlet-side line 11.

[0043] The medium cooled in the first heat exchanger 9 is fed via a line 12 to a separator 13, where a portion of the water is separated from the medium and discharged via a line 14.

[0044] Via a further line 15, the medium reaches a second compressor stage 4, where the temperature and the pressure of the medium are increased. After the second compressor stage 4, the medium passes via an outlet-side line 16 to a second heat exchanger 17. Water is also supplied to the second heat exchanger 17 via a line 18. Through heat exchange between the medium coming from the second compressor stage 4 and the water, the temperature of the water is increased and the temperature of the medium is reduced, so that steam flows out via an outlet-side line 19.

[0045] After the second heat exchanger 17, the medium passes via a line 20 to a further separator 21, where in turn a portion of the water is separated from the medium and discharged via a line 22. After the separator 21, the cooled medium reaches a third compressor stage 5, where the temperature and the pressure are increased. After the third compressor stage 5, the medium passes via an outlet-side line 24 to a third heat exchanger 25. Water is also supplied to the third heat exchanger 25 via a line 26. Through heat exchange between the medium coming from the third compressor stage 5 and the water, the temperature of the water is increased and the temperature of the medium is reduced, so that steam flows out via an outlet-side line 27.

[0046] The steam flowing off is discharged via a collection line 28 and further utilized (not shown). The supplied water is fed to the respective heat exchangers 9, 17, 25 via a collection line 29.

[0047] It should once again be noted that the first compressor stage 3, the second compressor stage 4 and the third compressor stage 5 are part of a single geared compressor, which leads to a great cost saving.

[0048] The compressor unit 2 is thus configured such that the carbon dioxide-containing medium 7 is compressed and flows out of the compressor unit 2 through an outlet opening 31 at a pressure pcompressor and a temperature Tcompressor. The medium passes into a separator 30, which can also be called a dryer. Water is again separated from the medium in the separator 30. Downstream of the separator, the medium ideally comprises pure gaseous carbon dioxide.

[0049] In a first separation device 32, which is also referred to as a divider, the inlet 33 of the first separation device 32 is fluidically connected to the compressor unit 2. The carbon dioxide-containing medium coming from the compressor unit 2 is divided in the first separation device 32 into a first mass flow (MMS01) 34 and into a second mass flow (MMS02) 35. The first mass flow (MMS01) 34 flows through a first conversion device 36. In this first conversion device 36, the temperature Tconv_01,in and the pressure pconv_01,in of the first mass flow (MMS01) 34 are reduced to a lower temperature Tconv_01,out and a lower pressure pconv_01,out. For this purpose, the first conversion device 36 is configured as a Joule-Thomson valve. The mode of operation of a Joule-Thomson valve is known. A detailed illustration of a Joule-Thomson valve is therefore dispensed with at this point. Other embodiments are possible for the first conversion device. Thus, in an alternative embodiment, the first conversion device 36 can be configured as an expansion turbine.

[0050] The second mass flow (MMS02) 35 flows through a second conversion device 37. In this second conversion device 37, the temperature Tconv_02,in and the pressure pconv_02,inof the second mass flow (MMS02) 35 are reduced to a lower temperature Tconv_02,out and a lower pressure pconv_02,out. For this purpose, the second conversion device 37 is configured as a Joule-Thomson valve. The mode of operation of a Joule-Thomson valve is known. A detailed illustration of a Joule-Thomson valve is therefore dispensed with at this point. Other embodiments are possible for the second conversion device. Thus, in an alternative embodiment, the second conversion device 37 can be configured as an expansion turbine.

[0051] In this case, the first conversion device 36 and the second conversion device 37 are configured such that the following applies:   Tconv01,out < Tconv02,out. This means that the medium coming from the first conversion device 36 is cooler than the medium coming from the second conversion device 37.

[0052] The medium coming from the first conversion device 36 is fed to a second separation device 38. In this second separation device 38, the medium coming from the first conversion device 36 is divided into a line having a gaseous portion 39 and into a line having a liquid portion 40.

[0053] The plant 1 further comprises a liquid heat exchanger 41. The medium from the line with the liquid portion 40 flows through the liquid heat exchanger 41. The cooler medium coming from the second conversion device 37 likewise flows through the liquid heat exchanger 41, wherein the medium coming from the second conversion device 37 is further cooled in the liquid heat exchanger 41 in such a way that the medium becomes liquid at an outlet 42 of the liquid heat exchanger 41. The medium, which is now pure carbon dioxide at this point after the various dewatering devices (separator 30, separator 21, separator 13), is now in liquefied form and can be transported in a transport container 43. The liquefied carbon dioxide is present at a temperature of T= approximately -30° C and a pressure of about 14 bar. Other temperatures and pressures can be achieved by the plant according to the invention.

[0054] The gaseous portion 39 of the medium in the line is collected in a collecting device 44 and fed to the plant 1 at a suitable point via a cooling feed line 45. The medium situated in the cooling feed line 45 has physical parameters such as pressure and temperature, which are suitable for use in the compressor unit 2 for cooling purposes. Thus, a suitable point would be to connect the cooling feed line 45 to the further line 15 so that the medium can flow in upstream of the second compressor stage 4. A different arrangement would be possible.

[0055] The gaseous medium heated from the liquid heat exchanger 41 is likewise conducted to the collecting device 44 via a line 46.

Claims

1. A plant (1) for liquefying carbon dioxide, comprising a compressor unit (2) having an inlet opening (6) for a carbon dioxide-containing medium at a pressure pinlet and a temperature Tinlet, wherein the compressor unit (2) is configured such that the carbon dioxide-containing medium is compressed and flows out of the compressor unit (2) through an outlet opening (31) at a pressure pcompressor and a temperature Tcompressor, further comprising a first separation device (32), which is fluidically connected on the inlet side to the compressor unit (2) and divides the carbon dioxide-containing medium coming from the compressor unit (2) into a first mass flow MMS01 (34) and a second mass flowMMS02 (35), further comprising a first conversion device (36)which is configured such that the temperature Tconv_01,in and the pressure pconv_1,in of the first mass flow MMS01 (34) arereduced to a lower temperature Tconv_01,out and a lower pressure pconv_1,out, further comprising a second conversion device (37), which is configured such that the temperature Tconv_02,in and the pressure pconv_2,in of the second mass flow MMS02 (35)are reduced to a lower temperature Tconv_02,out and a lower pressure pconv_2,out, wherein Tconv01,out < Tconv02,out, further comprising a liquid heat exchanger (41) which is configured such that the thermal energy is exchanged between the medium coming from the first conversion device (36) and the medium coming from the second conversion device (37) in such a way that the medium coming from the second conversion device (37) is liquid after passing through the liquid heat exchanger (41).

2. The plant (1) as claimed in claim 1,wherein the plant (1) further comprises a second separationdevice (38) having a first outlet line (39) and a second outlet line (40), wherein the second separation device (38)is configured such that the gaseous medium coming from the first conversion device (36) flows into the first outlet line (39) and the liquid medium coming from the first conversion device (36) flows into the second outlet line (40), wherein the second outlet line (40) is coupled to theliquid heat exchanger (41) such that the thermal energy is exchanged between the medium coming from the second outletline (40) and the medium coming from the second conversion device (37).

3. The plant   (1) as claimed in claim 1 or 2,wherein the first conversion device (36) and / or the second conversion device (37) is configured as a Joule-Thomson valve.

4. The plant   (1) as claimed in claim 1 or 2,wherein the first conversion device (36) and / or the second conversion device (37) is configured as an expansion turbine.

5. The plant (1) as claimed in any one of the preceding claims, wherein the compressor unit (2) has different compressor stages (3, 4, 5).

6. The plant (1) as claimed in claim 5,wherein the compressor unit (2) has a first compressor stage(3) with the inlet opening (6), wherein the first compressorstage (3) has a first compressor stage outlet, wherein the compressor unit (2) further has a second compressor stage (4) with a second flow inlet, wherein the first compressor stage outlet is fluidically connected to the second flow inlet, wherein a first heat exchanger (9) is arranged between the first compressor stage outlet and the second flow inlet, said first heat exchanger being configured such that the thermal energy is exchanged between the medium flowing in the compressor unit (2) and an exchange medium flowing through the first heat exchanger (9).

7. The plant (1) as claimed in claim 6, wherein the first heat exchanger (9) is configured such thatthe temperature of the exchange medium is increased.

8. The plant    (1) as claimed in claim 6 or 7,wherein a third compressor stage (5) is arranged downstream of the second compressor stage (4), wherein the third compressor stage (5) is fluidically connected to the secondcompressor stage (4), wherein a second heat exchanger (17) is arranged between the second compressor stage (4) and thethird compressor stage (5), wherein the second heat exchanger (17) is configured such that the temperature of the exchange medium is increased.

9. The plant (1) as claimed in any one of the preceding claims, wherein a third heat exchanger (25) is arranged between the compressor unit (2) and the first separation device (32), wherein the third heat exchanger (25) is configured such that the temperature of the exchange medium is increased.

10. The plant (1) as claimed in any one of claims 6 to 9, comprising a cooling feed line (45) which is configured such that the gaseous medium present downstream of the second separation device (32) and downstream of the liquid heat exchanger (41) is fed to the compressor unit (2).

11. The plant (1) as claimed in claim 10,wherein the cooling feed line (45) feeds the gaseous medium present downstream of the second separation device (32) and downstream of the liquid heat exchanger (41) to the second compressor stage (4).

12. The plant (1) as claimed in any one of claims 6 to 11, wherein the exchange medium is water.

13. The plant (1) as claimed in one of claims 1 to 12, wherein the compressor unit (2) is configured as a geared compressor.

14. A process for producing liquid carbon dioxide, wherein a pressure and temperature of a carbon dioxidecontaining medium are first increased in a compressor unit (2), wherein, in a first separation device (32), the carbondioxide-containing medium is divided into a first mass flow (34) and a second mass flow (35), wherein the first mass flow (34) flows through a first conversion device (36) and the second mass flow (35) flows through a second conversion device (37), wherein the temperature and the pressure of the medium downstream of the first conversion device (36) and the second conversion device (37) are reduced, wherein the temperature of the medium downstream of the first conversion device (36) is lower than the temperature of the medium downstream of the second conversion device (37), wherein the medium downstream of the first conversion device (36) is guided to a liquid heat exchanger (41), where the thermal energy is exchanged between the medium from the first conversion device (36) and the medium from the second conversion device (37), as a result of which the carbon dioxide from the second conversion device (37) is liquefied downstream of the liquid heat exchanger (41).

15. The process for producing liquid carbon dioxide as claimed in claim 14, wherein the first conversion device (36) and / or the second conversion device (37) is configured as a Joule-Thomson valve.

16. The process for producing liquid carbon dioxide as claimed in claim 14, wherein the first conversion device (36) and / or the second conversion device (37) is configured as an expansion turbine.

17. The process for producing liquid carbon dioxide as claimed in any one of claims 14 to 16, wherein the compressor unit (2) has a first compressor stage (3) through which the carbon dioxide-containing medium flows, wherein a first heat exchanger (9) is arranged downstream of the compressor stage (3), in which thermal energy is exchanged between the medium and an exchange medium.

18. The process for producing liquid carbon dioxide as claimed in claim 17, wherein the exchange medium is water.

19. The process for producing liquid carbon dioxide as claimed in any one of claims 14 to 18, wherein the compressor unit (2) has a second compressor stage (4) which is arranged downstream of the first compressor stage (3), wherein the temperature and the pressure in the second compressor stage (4) are increased further, wherein a second heat exchanger (17) is arranged downstream of the second compressor stage (4), where the thermal energy is exchanged between the medium and the exchange medium.

20. The process for producing liquid carbon dioxide as claimed in any one of claims 14 to 19, wherein the compressor unit (2) has a third compressor stage (5) which is arranged downstream of the second compressor stage (4), wherein the temperature and the pressure in the third compressor stage (5) are increased further, wherein a third heat exchanger (25) is arranged downstream of the third compressor stage (5), where the thermal energy is exchanged between the medium and the exchange medium.

21. The process for producing liquid carbon dioxide as claimed in any one of claims 14 to 20, wherein the compressor unit (2) is configured as a geared compressor.

22. The process for producing liquid carbon dioxide as claimed in any one of claims 14 to 20, wherein the cooled carbon dioxide present in gaseous form downstream of the first conversion device (36) and the carbon dioxide present in gaseous form downstream of the liquid heat exchanger (41) are fed to the compressor unit (2).

23. The process for producing liquid carbon dioxide as claimed in claim 22, wherein the cooled carbon dioxide present in gaseous form downstream of the first conversion device (36) and the carbon dioxide present in gaseous form downstream of the liquid heat exchanger (41) are fed to the second compressor stage (4) of the compressor unit (2).

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