LNG exergy optimization for SBCC

Abstract

The present invention is directed to a carbon capture and liquefaction system including a liquefied natural gas (LNG) exergy recovery unit. The invention is more particularly directed to such a system for liquefying carbon dioxide (CO2) gas from a CO2-containing gas, more particularly from exhaust gas from a marine vehicle. The invention is further directed to a method for recovering exergy using the exergy recovery unit, a marine vehicle including the system, and the use of such a system for liquefying carbon dioxide gas.

Description

[Technical field]

[0001] The present invention is directed to a carbon capture and liquefaction system including a liquefied natural gas exergy recovery unit. The invention is more particularly directed to such a system for liquefying carbon dioxide (CO2) gas from a CO2-containing gas, more particularly from exhaust gas from a marine vehicle. The invention is further directed to a method for recovering exergy using the exergy recovery unit, a marine vehicle including the system, and the use of such a system for liquefying carbon dioxide gas. [Background technology]

[0002] CO2 emissions have increased significantly in the past decades, due, among other things, to industrial processes that burn fossil fuels. The increase in volume is considered to be one of the main drivers of climate change. The maritime sector accounts for about 3% of CO2 emissions worldwide. Therefore, the International Maritime Organization (IMO) has set a greenhouse gas reduction target according to which emissions from the maritime sector must be minimized to at least 50% by 2050 compared to 1990. To achieve these targets, various solutions have been proposed. Such solutions include, among other things, changing fuel, speed, or using different sails to minimize headwinds.

[0003] One type of fuel seen as a promising alternative to petroleum-based or heavy fuel oil is LNG. Today, there are about 200 large ships that use LNG as a fuel source. This figure is expected to increase over the next few years. However, carbon dioxide is still a component in the exhaust gases from LNG. Typically, such exhaust gases contain 3-5% CO2, with the remaining components being water, nitrogen, oxygen, and some trace impurities.

[0004] LNG is a liquid mixture that contains primarily (i.e., greater than 90%) methane. Other constituents may include nitrogen, propane, and ethane. LNG is typically stored at atmospheric pressure (about 1 bar) and at about -162°C.

[0005] A solution to further reduce carbon dioxide emissions from ships is to use ship-based carbon capture (SBCC) to capture carbon dioxide gas from the exhaust gas, integrated with exergy recovery from LNG for liquefaction of the captured carbon dioxide gas. This is described, for example, by Ros et al. (GHGT-15, 15-18 March 2021, Abu Dhabi, UAE, and Ros et al., International Journal of Greenhouse Gas Control, Vol. 114, 2022, 103575), who further describe that SBCC could play a major role in reducing carbon dioxide emissions in the short term. SBCC entails implementing CO2 capture, liquefaction, and on-board storage of the liquefied CO2 on LNG-fueled ships. For example, the ship may include a CO2 capture system that allows for the absorption of CO2 from the exhaust gas from the ship and subsequent production of a CO2-rich gas. The carbon dioxide in the CO2-rich gas can then be liquefied and stored on board. LNG exergy can be recovered as heat by vaporization of LNG, which can then be used to liquefy CO2 gas. In other words, such a system can utilize exergy recovery from LNG in CO2 capture. As used herein, exergy is a term used to describe the amount of useful work that can be obtained from a system by the system naturally coming into thermodynamic equilibrium with its environment. Due to the very low temperature of LNG compared to atmospheric temperature (approximately -162°C vs. approximately 20°C), the potential for exergy recovery is very high.

[0006] US2010 / 0251763 describes an apparatus and method for natural gas transportation and processing. However, the apparatus does not include a CO2 capture system. CN106016968 describes a method for liquefying CO2.

[0007] A drawback of the system described in the aforementioned Ros et al. publication is that the heat obtained by vaporization of LNG can only liquefy about 60-80% of the CO2 present in the flue gas. Since CO2 capture systems are generally capable of capturing about 90% or more of the CO2 in the flue gas, the CO2 capture efficiency is therefore limited to the LNG vaporization energy availability. To further increase the capture efficiency, additional refrigeration equipment can be installed to provide additional energy, but this is generally very capital intensive and increases the operating costs of the system.

[0008] Exergy recovery systems for LNG have also been described in CN103075250, WO2020180015, and by Dorosz et al. (Entropy, 2018, 20, 59). In these systems, additional electricity is generated, which is the main operating principle behind these systems. However, the heat required to vaporize the LNG is added to the system in the form of steam cooling water. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US2010 / 0251763 [Patent Document 2] CN106016968 [Patent Document 3] CN103075250 [Patent Document 4] WO2020180015 [Patent Document 5] US1783901 [Non-patent literature]

[0010] [Non-Patent Document 1] Ros et al., GHGT-15, pages 15–18, March 2021, Abu Dhabi, UAE [Non-Patent Document 2] Ros et al., International Journal of Greenhouse Gas Control, Volume 114, 2022, 103575 [Non-Patent Document 3] Dorosz et al., Entropy, 2018, 20, 59 Summary of the Invention [Problem to be solved by the invention]

[0011] It is the inventors' objective to provide a system, preferably an offshore system, based on exergy recovery from LNG that allows for increased overall CO2 capture efficiency. [Means for solving the problem]

[0012] The inventors have discovered that this objective can be surprisingly achieved by improving exergy recovery from LNG. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 illustrates a preferred embodiment of a system according to the present invention. [Diagram 2] FIG. 1 shows a preferred embodiment of a system according to the present invention including a heat exchange section. [Diagram 3] FIG. 1 shows the results of a theoretical proof of principle experiment carried out in Aspen Plus® software. [Figure 4] FIG. 13 is a diagram showing theoretically calculated net power generation. [Diagram 5] FIG. 1 shows theoretically calculated net heat demand. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In a first aspect, the present invention provides a method for producing a composition comprising the steps of: (a) a CO2 capture system (100) adapted to provide a CO2-rich gas stream (101) during use; (b) a CO2 liquefaction section (200) adapted to liquefy at least a portion of the CO2-rich gas stream (101) during use to provide a liquefied CO2 stream (201); (c) a liquefied natural gas (LNG) exergy recovery section (300) for recovering exergy from liquefied natural gas (LNG); The present invention relates to a carbon capture and liquefaction system (1) comprising:

[0015] The LNG exergy recovery system includes an LNG tank (2) adapted to contain the LNG during use. The fuel tank includes an LNG outlet (21) for the LNG stream (301) so that the LNG stream can be fluidly connected with subsequent portions of the LNG exergy recovery system. Suitable fuel tanks are commercially available and are typically adapted to store LNG at atmospheric pressure (about 1 bar) or at higher pressures, such as about 2 or 3 bar, and at temperatures between -170°C and -155°C, such as -162°C.

[0016] The exergy recovery section further comprises a pressurizer section (3) adapted to pressurize, during use, the LNG stream (301) to obtain a pressurized LNG stream (302). The pressurizer section comprises an LNG inlet (31) and a pressurized LNG outlet (32). In an exemplary embodiment, the pressurizer section (3) is adapted to pressurize, during use, the LNG stream to a pressure between 5 bar and 40 bar, preferably between 6 bar and 30 bar, more preferably between 7 bar and 20 bar. The pressurizer is typically a fluid pump.

[0017] Furthermore, the exergy recovery section includes a vaporizer section (4) adapted to vaporize the pressurized LNG stream (302) during use to obtain a pressurized natural gas (NG) stream (401), the vaporizer section including a pressurized LNG inlet (41) and a pressurized NG outlet (42). The vaporizer section may include one or more vaporization devices to recover at least a portion of the exergy from the LNG. The type of vaporizer device used in the vaporizer section is not particularly limited. A suitable vaporizer device may, for example, use the ambient environment as a heat source. Particular types of suitable vaporizer devices may include plate heat exchangers as well as shell-and-tube heat exchangers. Desirably, the vaporizer section (4) is adapted to condition the pressurized natural gas stream to a temperature during use between -70°C and -10°C, desirably between -65°C and -15°C, more desirably between -60°C and -20°C. This temperature generally depends on the pressure of the CO2-rich gas stream. This is because the pressurized LNG stream, in use, exchanges heat with a CO2-rich gas stream to obtain a pressurized NG stream, and because liquefying CO2 at a higher pressure does not get colder than liquefying CO2 at a lower pressure (see below).

[0018] The exergy recovery section further comprises a turbine section (5) adapted to reduce the pressure during use of the pressurized NG stream (401) to obtain a reduced pressure NG stream (501). It has been found that reducing the pressure of the NG stream can have the desirable result of, for example, generating electricity that can be utilized in other parts of the system. Moreover, the inventors have found that advantageously reducing the pressure of the NG stream allows additional exergy recovery in a further part of the system (i.e. the heat exchange section) that is desirably present. This further part can be connected to the turbine section via a reduced pressure NG outlet (52) of the turbine section.

[0019] The turbine may be supplied with pressurized NG via the pressurized NG inlet (51). As described herein above, the turbine section is most desirably adapted to generate electricity during its use. Advantageously, the electricity that may be obtained from the turbine during use is greater than the electricity consumed in the compressor section during use. The generated electricity may be used in other parts of the system, for example, in the CO2 capture system (100), the CO2 liquefaction section (200), and / or the compressor section (3). As a result, the turbine section may be electrically connected to the CO2 capture system (100), the CO2 liquefaction section (200), and / or the compressor section (3). It will be appreciated that these electrical connections may in practice be accomplished by connecting the various sections to a power grid.

[0020] Thus, from the above, the LNG outlet (21) is fluidly connected to the LNG inlet (31), the pressurized LNG outlet (32) is fluidly connected to the pressurized LNG inlet (41), and the pressurized NG outlet (42) is fluidly connected to the pressurized NG inlet (51).

[0021] In the system of the present invention, the CO2 liquefaction section (200) is thermally connected to the vaporization section (4) such that, in use, heat (i.e., negative heat, also referred to as cold) can be transferred from the pressurized LNG stream (302) to the CO2-rich gas stream (101). This heat transfer can facilitate lowering the temperature of the CO2-rich gas stream and generally facilitate further liquefaction of at least a portion of the CO2-rich gas stream to obtain a cooled or even liquefied CO2 stream (201).

[0022] The CO2 capture system (100) is not particularly limited. The system may be based on a conventional carbon dioxide capture system that is generally commercially available. The principles behind such commercially available CO2 capture systems are described, among others, in US1783901. US1783901 generally involves feeding a gas containing carbon dioxide to an absorber that contains an alkaline solvent, such as an amine-based solvent. The CO2 can be absorbed by the solvent, leaving a CO2-lean gas that can exit the absorber. The CO2-rich liquid stream (i.e., the solvent with absorbed CO2) is then generally fed to a regenerator, where the solvent is regenerated and gaseous CO2 is released by desorbing carbon dioxide from the solvent. This thus provides a CO2-rich gas stream. The CO2-rich gas stream may be provided at a high (i.e., higher than ambient pressure) pressure, such as a pressure of at least 2 bar. As a result, the CO2 capture system (100) generally includes an absorber section that absorbs CO2 from a CO2-containing gas during use to provide a CO2-rich liquid fraction. Furthermore, the CO2 capture system typically includes a regenerator section which, in use, provides a CO2-rich gas stream (101) from the CO2-rich fraction. The CO2-rich gas stream may be further processed, inter alia, in a CO2 liquefaction section.

[0023] The inventors have realized that the carbon dioxide-containing gas that can be fed to the CO2 capture system can be obtained from a vehicle. Desirably, the carbon dioxide-containing gas is exhaust gas from a marine vehicle. Any marine vehicle will suffice as long as its main fuel is LNG. Examples of these include cruise ships, lifting ships, dredgers, and cargo ships. These are generally large enough to support the system according to the invention on board. Therefore, the invention is also directed to marine vehicles including a system for carbon capture and liquefaction. It will be appreciated that the carbon capture and liquefaction system can be provided on a floating device. The components of the carbon capture and liquefaction system can be efficiently combined and integrated to take advantage of the limited space available at sea. As a result, the carbon capture and liquefaction system according to the invention is desirably a marine system, and advantageously for marine applications.

[0024] The amount of negative heat (i.e., low temperature) required to liquefy the CO2 gas depends on the pressure to which the gas is pressurized. For example, to liquefy CO2 at 20 bar requires substantially less low temperature than to liquefy CO2 at 7 bar. Therefore, the amount of exergy required to be recovered from the LNG to liquefy all the CO2 in the CO2-rich gas stream depends on the desired final pressure of the liquefied CO2. In typical embodiments of the invention, CO2 is liquefied at a pressure where exergy recovery by the vaporization section alone is not sufficient. In those embodiments, additional exergy is desirably recovered from the reduced pressure NG stream obtained from the turbine section. Advantageously, reducing the pressure of the NG stream in the turbine leads to a reduction in the temperature of the NG stream, for example to a temperature between -140°C and -50°C, as described in more detail below. This reduction in temperature allows additional exergy recoverable from the NG in the form of negative heat (i.e., low temperature). Thus, transferring this low temperature to the CO2-rich gas stream may further facilitate the liquefaction of this stream. As a result, the exergy recovery section desirably also includes a heat exchange section (7) as shown in FIG. 2 to provide a heated NG stream (701) during use. The heat exchange section includes a reduced pressure NG inlet (71) and a heated NG outlet (72). The reduced pressure NG inlet is fluidly connected to the reduced pressure NG outlet (52). The type of heat exchanger is not particularly limited. Suitable heat exchangers include shell-and-tube heat exchangers and plate-frame heat exchangers.

[0025] The heat exchange section (7) may be thermally connected to the CO2 liquefaction section (200). This thermal connection allows heat to be transferred from the CO2 rich gas stream to the reduced pressure NG stream (501). In this way, at least a portion of the CO2 rich gas stream may be cooled and, preferably, liquefied to obtain a liquid CO2 stream (201).

[0026] The system may further include an engine section (6) adapted to consume, during use, NG that is directed to the engine section via a NG inlet (61), as shown in Figures 1 and 2 .

[0027] It will be appreciated that each of the systems and parts described herein may include one or more units, devices, components, etc., which together may realize the functions of the respective system and part. Moreover, each of the systems and parts may include one or more units, devices, components, such as valves, fluid pumps, pipes, vessels, etc., to assist in accomplishing said tasks. In particular, the liquefaction part may include one or more separate units to operate the liquefaction of CO2. In addition, the part may include one or more compressor units that allow for increasing the pressure of the CO2-rich gas stream, which is generally required for the liquefaction of CO2. Since the CO2-rich gas may be obtained from the CO2 capture system at high pressure in some embodiments, the need for one or more compressor units may be limited. The vaporization part and / or the heat exchange part may each be individually thermally connected to one or more units of the CO2 liquefaction part. The heat exchange of the LNG and / or NG streams with the CO2 gas stream may be accomplished with or without the assistance of a heat transfer fluid (HTF). Desirably, the thermal connection is at least partially provided by the HTF. Suitable HTFs include ammonia (NH3) or a water / glycol mixture. Preferably, the HTF is ammonia, since ammonia generally allows for optimal heat transfer and ammonia can be liquid (and not solid) at the low temperatures of the LNG and / or NG streams. As shown in FIG. 2, the system thus preferably includes one or more heat transfer fluid circuits (8, 9) adapted to direct the HTF in use. The HTF circuit preferably provides at least a portion of the thermal connection between the vaporizer section (4) and the CO2 liquefaction section, and / or between the heat exchange section (7) and the CO2 liquefaction section. Thus, the HTF can serve as an intermediate heat carrier capable of transferring heat from the CO2-rich gas stream to the pressurized LNG and / or reduced pressure NG streams.

[0028] A further aspect of the invention is directed to a method for recovering LNG exergy using an exergy recovery section (300). This exergy recovery system can be part of the carbon capture and liquefaction system (1) described herein, or the exergy recovery system can be provided independently to provide useful heat for liquefying a CO2 gas stream obtained at another site. For example, one or more carbon capture facilities and one or more LNG combustion engines can be operated or installed independently within a (land-based) area, such as a large (land-based) industrial site. In such a case, it is possible to provide an exergy recovery section before the LNG combustion engine to recover LNG exergy independently and use the recovered exergy to liquefy CO2 at a different site, or to direct CO2 gas from a different site to an exergy recovery section coupled to a CO2 liquefaction section.

[0029] As a result, the method of the present invention comprises the steps of providing an exergy recovery system (300); - supplying LNG to the LNG tank (2); - directing the LNG stream (301) into a pressurizer section (3) to obtain a pressurized LNG stream (302); - directing the pressurized LNG stream (302) into a vaporizer section (4) to obtain a pressurized NG stream (401); - directing the pressurized NG flow (401) to a turbine section (5) to obtain a reduced pressure NG flow (501); - optionally directing the reduced pressure NG stream (501) to a heat exchanger (7) to obtain a heated NG stream (701); The method further comprises exchanging heat of the CO2 rich gas stream (101) with a pressurized LNG stream (302).

[0030] The LNG supplied to the LNG tank typically has a pressure below 5 bar, such as about 2 bar, and a temperature between -165°C and -160°C, such as about -162°C. In the pressurization section, the pressure of the LNG stream is desirably increased to a pressure between 5 bar and 40 bar. High pressure is generally desirable, since it may contribute to a higher efficiency of the turbine section. In addition, a higher pressure generally results in a lower temperature of the reduced pressure NG gas stream obtained after the turbine section, which may subsequently result in a higher exergy recovery, since the temperature difference between the reduced pressure NG stream and the environment is larger relative to the lower temperature of the reduced pressure NG stream. This exergy may be used, for example, for CO2 liquefaction by using an optional heat exchange section. As a result, the pressure is desirably adjusted to a pressure of 7 bar or more, such as between 6 bar and 30 bar, more desirably between 7 bar and 20 bar. It has been found that a pressure of at least 8 bar provides sufficient exergy recovery from a CO2 liquefaction perspective to capture and liquefy up to 100% of the CO2 from LNG exhaust gases, such as those from marine vehicles. The method is therefore particularly suitable for maritime applications.

[0031] Additionally, the high pressure flow allows more electricity to be generated in the turbine. For example, flowing a pressurized NG stream with a pressure of about 8 bar through the turbine section can provide about 25% of the electricity required for a CO2 capture and liquefaction system, if one is present. Therefore, advantageously, the present invention can be used to not only minimize the emission of carbon dioxide to the environment, but also to provide additional electricity. It is noted that the desired pressure can be determined by balancing several factors, such as the electricity required to achieve the pressure and the end benefit from the efficiency of the turbine section. For example, the electricity required to provide the pressurized LNG stream in the pressurizer section may be sufficient for the high pressure, while the efficiency of the turbine section is not sufficient to balance this required electricity.

[0032] The pressurized LNG stream is directed from the pressurizer section to the vaporizer section (4) to increase the temperature so that a pressurized NG stream (401) is obtained. The pressurized LNG stream may have a temperature between -165°C and -160°C, such as about -162°C. The temperature of the pressurized NG stream may be between -70°C and -10°C, preferably between -65°C and -15°C, and most preferably between -60°C and -20°C. As detailed above, the temperature generally depends on the pressure of the CO2-rich gas stream and thus the liquefaction temperature. The temperature, together with the high pressure of the pressurized NG stream, allows for optimization of turbine efficiency.

[0033] The pressurized NG stream (401) is directed to the turbine section (5) to reduce the pressure and obtain a reduced pressure NG stream (501). Reducing the pressure of the gas in a given volume results in the expansion of the gas and a concomitant reduction in temperature of the gas. Depending on the temperature of the reduced pressure NG stream, it may be used directly in the engine or combustion reactor, or it may first be directed to an optional heat exchange section (7). For example, if the temperature is around 0° C., the reduced pressure NG gas stream may be directly directed to the engine section.

[0034] If the temperature of the reduced pressure NG stream (501) is low enough, additional exergy can be recovered in the heat exchange section (7) by exchanging the heat of this stream with the CO2 rich gas stream (101) in the heat exchange section (7). For example, exergy can still be efficiently recovered if the temperature of the reduced pressure NG stream is between -140°C and -50°C, preferably between -140°C and -70°C, most preferably between -140°C and -100°C. The heat exchange results in a heated NG stream (701) with a temperature suitable for the desired application (e.g. engine section).

[0035] Preferably, exchanging heat of the CO2-rich gas stream with the pressurized LNG stream and / or the reduced pressure NG stream is accomplished using a HTF, preferably including ammonia. Using ammonia as the HTF may result in a heated NG stream (701) having a temperature that may be too low for direct use in an application. The temperature may be between -23°C and -18°C, such as about -20°C. As a result, one or more additional heat exchange units may be present in the heat exchange section.

[0036] When the reduced pressure or heated NG stream is directed to the engine section, exhaust gas is produced. The exhaust gas generally has a temperature higher than 100°C, such as at least 200°C or at least 350°C. Heat from the exhaust gas can also be extracted by a heat exchanger. The energy from the exhaust gas can be used, for example, in a CO2 capture system. After the heat exchanger, the exhaust gas can have a temperature of about 135°C.

[0037] Preferably, the method is performed at sea, preferably on a floating device or on a marine vehicle. As a result, the CO2-rich gas stream (101) is obtained from LNG exhaust gas from the marine vehicle, preferably at least partially purified. For example, the LNG exhaust gas may be at least partially purified in a CO2 capture system of the carbon capture and liquefaction system (1) as described herein above. Typically, at least 70%, preferably at least 80%, more preferably at least 90%, and most preferably at least 99% of the total amount of exhaust gas is at least partially purified. Preferably, substantially all of the exhaust gas is directed to the CO2 capture system to minimize emissions to the environment.

[0038] Using the systems and / or methods according to the present invention, CO2 emissions into the environment can be reduced by significant amounts, and as an added bonus, additional electricity is also provided that can be used for various applications, such as CO2 capture systems.

[0039] For clarity and brevity, features are described herein as part of the same or separate embodiments, but it will be appreciated that the scope of the invention may include embodiments having all or a partial combination of the described features.

[0040] The invention may be further illustrated by the following non-limiting examples. EXAMPLES

[0041] Proof of concept A proof of principle in silico experiment was carried out in Aspen Plus® software, the results of which are shown in FIG.

[0042] The triangles represent comparative examples, where the turbine and heat exchange sections are not present. As shown, the lower triangle, representing electricity provided by LNG for CO2 capture and liquefaction, is 0%. The upper triangle, representing heat provided by LNG for CO2 liquefaction, is approximately 80%.

[0043] The results further show that for a system according to the invention, at pressures above 8 bar, 100% of the CO2 present in the gas can be liquefied using the available (negative) heat in the LNG. About 25% of the electricity required for the CO2 capture system is also provided. EXAMPLES

[0044] Net power generation In silico experiments were performed with an LNG flow of 1 kg / s. Herein, the net power generation (i.e., the electricity required for the pressurizer section minus the electricity generated by the turbine section) was determined based on the pump outlet pressure (i.e., the pressure of the pressurized LNG flow). The results are shown in FIG. 4 for pressures up to 20 bar. As shown, the net power generation increases with increasing pump outlet pressure. EXAMPLES

[0045] pure heat demand In silico experiments were performed with an LNG flow of 1 kg / s. The net heat demand (i.e., the heat demand for the vaporizer section plus the heat demand for the heat exchange section) was determined based on the pump outlet pressure. Herein, the heat demand is used to account for the negative heat released from the LNG. The results are shown in FIG. 5 for pressures up to 20 bar. Increasing the pump outlet pressure results in a higher net heat demand. [Explanation of symbols]

[0046] 1 Carbon Capture and Liquefaction System 2 LNG tanks 3. Pressurizer section 4. Carburetor section 5. Turbine section 6 Engine section 7 Heat exchange section 8 Heat Transfer Fluid Circuit 9 Heat Transfer Fluid Circuit 21 LNG outlet 31 LNG inlet 32 Pressurized LNG outlet 41 Pressurized LNG inlet 42 Pressurized NG outlet 51 Pressurized NG inlet 52 Pressure reduction NG outlet 61 NG inlet 71 Decompression NG Inlet 72 Heating NG outlet 100 CO2 Capture System 101 CO2 dense gas stream 200 CO2 liquefaction section 201 Liquefied CO2 stream 300 Liquefied Natural Gas (LNG) Exergy Recovery Section 301 LNG flow 302 Pressurized LNG flow 401 Pressurized Natural Gas (NG) Flow 501 Reduced pressure NG flow 501a Decompression NG flow 701 Heating NG flow

Claims

1. (a) CO ２ A CO2 gas supply adapted to supply a rich gas stream (101) during use. ２ A capture system (100); (b) Liquefied CO ２ to provide a CO ２ A CO2 extractor adapted to liquefy at least a portion of the rich gas stream (101) during use. ２ A liquefaction section (200); (c) an LNG exergy recovery unit (300) for recovering exergy from liquefied natural gas (LNG), the LNG exergy recovery unit comprising: an LNG tank (2) adapted to contain LNG during use, the LNG tank (2) including an LNG outlet (21) for an LNG stream (301); a pressurizer section (3) adapted to pressurize, during use, said LNG stream (301) to obtain a pressurized LNG stream (302), the pressurizer section (3) including an LNG inlet (31) and a pressurized LNG outlet (32); a vaporizer section (4) adapted for vaporizing, in use, said pressurized LNG stream (302) to obtain a pressurized natural gas (NG) stream (401), the vaporizer section (4) including a pressurized LNG inlet (41) and a pressurized NG outlet (42); a turbine section (5) adapted to reduce the pressure during use of the pressurized NG flow (401) to obtain a reduced pressure NG flow (501), the turbine section (5) including a pressurized NG inlet (51) and a reduced pressure NG outlet (52); the LNG outlet (21) is fluidly connected to the LNG inlet (31), the pressurized LNG outlet (32) is fluidly connected to the pressurized LNG inlet (41), and the pressurized NG outlet (42) is fluidly connected to the pressurized NG inlet (51); The CO ２ The liquefaction section (200) is configured to, in use, convert heat from the pressurized LNG stream (302) into the CO ２ A carbon capture and liquefaction system (1) thermally connected to said vaporizer section (4) so ​​as to be capable of being transferred to the rich gas stream.

2. 2. The system of claim 1, wherein the LNG exergy recovery section further comprises a heat exchange section (7) for providing a heated NG stream (701) during use, the heat exchange section comprising a reduced pressure NG inlet (71) and a heated NG outlet (72), the reduced pressure NG inlet (71) being fluidly connected to the reduced pressure NG outlet (52).

3. The heat exchange section (7) is adapted to transfer heat from the reduced pressure NG stream (501) to the CO ２ The CO may be delivered to a rich gas stream (101). ２ The system of claim 2 , wherein the system is thermally connected to the liquefaction section (200).

4. The system further includes one or more heat transfer fluid (HTF) circuits (8, 9) adapted to direct a heat transfer fluid (HTF) during use, the HTF circuits connecting the evaporator section (4) and the CO ２ Between the liquefaction section (200) and / or the heat exchange section (7) and the CO ２ The system of claim 1 , wherein at least a portion of the thermal connection is with a liquefier (200).

5. 5. A system as claimed in any one of claims 1 to 4, wherein the pressurizer section (3) is adapted to pressurise, in use, the LNG stream to a pressure of between 5 bar and 40 bar, preferably between 6 bar and 30 bar, more preferably between 7 bar and 20 bar.

6. 6. A system as claimed in any one of claims 1 to 5, wherein the vaporizer section (4) is adapted to condition, in use, the pressurized natural gas stream to a temperature between -70°C and -10°C, preferably between -65°C and -15°C, most preferably between -60°C and -20°C.

7. The turbine section is adapted to generate electricity during use, the turbine section being coupled to the compressor section and / or the CO ２ A system according to claim 1 , electrically connected to a capture system.

8. A method for recovering exergy from LNG in an exergy recovery section (300) according to any one of claims 1 to 7, comprising the steps of: supplying LNG to the LNG tank (2); directing a LNG stream (301) into said pressurizer section (3) to obtain a pressurized LNG stream (302); directing said pressurized LNG stream (302) to said vaporizer section (4) to obtain a pressurized NG stream (401); directing said pressurized NG flow (401) to said turbine section (5) to obtain a reduced pressure NG flow (501); Optionally, directing said reduced pressure NG stream (501) to a heat exchange section (7) to obtain a heated NG stream (701), CO ２ The method further comprising exchanging heat between a rich gas stream (101) and said pressurized LNG stream (302).

9. The method further comprises: ２ The method further comprises exchanging heat of a rich gas stream (101) with said reduced pressure NG stream (501), preferably by ２ 9. The method of claim 8, wherein the step of exchanging heat of a rich gas stream with the pressurized LNG stream (302) and / or the reduced pressure NG stream (501) is accomplished using a HTF, preferably the HTF is ammonia.

10. The method according to claim 8 or 9, wherein the temperature of the reduced pressure NG stream (501) is between -140°C and -50°C, preferably between -140°C and -70°C, most preferably between -140°C and -100°C.

11. 11. The method of any one of claims 8 to 10, wherein the pressure of the pressurized LNG stream (302) is between 5 bar and 40 bar, preferably between 6 bar and 30 bar, more preferably between 7 bar and 20 bar.

12. The CO ２ 12. The method according to any one of claims 8 to 11, wherein the rich gas stream (101) is obtained from an at least partially purified LNG exhaust gas from a marine vehicle, and wherein at least 70%, preferably at least 80%, more preferably at least 90%, most preferably at least 99% of the total amount of said exhaust gas is at least partially purified.

13. A marine vehicle comprising a system (1) according to any one of claims 1 to 7.

14. CO ２ CO from contained gas ２ CO to obtain liquid ２ 8. Use of a system (1) according to any one of claims 1 to 7 for liquefying a gas.

Images