Process and apparatus for cooling co2-rich flow

Abstract

To provide a process for improving a known process by reducing risks for solidifying carbon dioxide in a process for cooling and liquefying carbon dioxide.SOLUTION: In a process for cooling a carbon dioxide-rich flow 5 with an intermediate fluid to be a cooling medium and obtaining a liquid carbon dioxide flow 7 by a distillation tower K1, methane-rich fluid 1 is evaporated and vaporized in a first heat exchanger E1, so that cold heat is provided for the intermediate fluid, at least one intermediate fluid flow condensed by at least one pressure level is formed, and at least a part of the intermediate fluid evaporated by heat exchange with the carbon dioxide-rich flow in a second heat exchanger E2 is condensed again to at least one flow by at least one pressure by the first heat exchanger.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a process and an apparatus for cooling a CO₂-rich stream. At least part of the cold heat required for cooling, actually even liquefaction, is provided by heating a methane-rich fluid, for example evaporation of a methane-rich liquid containing at least 80 mol% methane, or pseudo-evaporation of a dense-phase methane-rich fluid. An example of such a liquid is liquefied natural gas (LNG). The transfer of cold heat is effected by using an intermediate fluid rich in ethane or ethylene to transfer cold heat from a liquefied gas, for example from liquefied natural gas, to liquefy the CO₂-rich stream.

[0002] The CO₂-rich stream comprises at least 70 mol% carbon dioxide, preferably at least 90 mol% carbon dioxide, and actually even at least 95 mol% carbon dioxide.

[0003] Liquefaction of the carbon dioxide-rich stream generally consumes electricity to provide the required cooling. The liquefied natural gas is evaporated against seawater or another heat provider. The two systems have complementary requirements since evaporation of the liquefied natural gas requires heat and liquefaction of the carbon dioxide requires a cold heat source. From this, it is advantageous to investigate the possibility of integrating the two systems.

Background Art

[0004] In principle, since the amount of LNG available as a refrigerant is "unlimited", compared to the liquefaction energy required by liquefaction in which CO₂ is compressed to a supercritical pressure, densified, and then depressurized to a stripping column, it should be possible to condense CO₂ at a fairly low pressure in order to minimize the liquefaction energy. On the other hand, choosing a very low liquefaction pressure may limit the CO₂ yield of the liquefaction process since the temperature profile in the stripping column is limited.

[0005] The direct use of LNG (typically available at -160°C to -145°C) as a refrigerant for heat exchange with CO2 is not feasible due to the risk of CO2 solidification. This means that an intermediate fluid must be used to transfer the cold from the LNG to the CO2. This can be done in two ways: a) To transfer cold heat from LNG exclusively in the form of sensible heat of an intermediate fluid (in this case, the latter could be gaseous nitrogen or liquid HFO), b) Transferring cold heat from LNG through the sensible and latent heat of the intermediate fluid.

[0006] The drawback of option a) is the mismatch between the enthalpy / temperature profiles of the condensing CO2 and the intermediate fluid in the heat exchanger (most of the heat is generated by CO2 at a constant temperature, while the temperature of the intermediate fluid increases at a constant rate according to its flow rate and specific heat). This obstacle can be avoided, for example, by increasing the flow rate of the intermediate fluid and / or by increasing the pressure of CO2 to approach, and in fact even exceed, the critical pressure. Both solutions require an increase in energy, and for this reason, these solutions are not very attractive.

[0007] From FR 2 869 404, JP2004069215, and JPH04148182, it is known that by using a coolant cycle, cold energy from an evaporating LNG flow can be used to condense carbon dioxide, where the coolant is ethane.

[0008] JPH04-131688 describes a closed cycle of an intermediate fluid that transfers cold energy from an LNG flow to a CO2 flow being liquefied, the cycle comprising a pump to pressurize the intermediate fluid. The fluid used is Freon®.

[0009] FR 2 869 404 describes a closed cycle of an intermediate fluid that transfers cold energy from an LNG flow to a CO2 flow being liquefied, where the intermediate fluid is ethane, which evaporates for CO2 and liquefies for LNG. The pressure of the intermediate fluid is constant.

[0010] Since most of the cold energy is available at temperatures lower than that of CO2 liquefaction, it should be possible, at least from a thermodynamic standpoint, to integrate the process with zero energy cost, and in fact even with energy generation. In practical context, a form of integration is desired that has only limited energy consumption (e.g., by using only pumps without compression driven by turbines) and is compatible with the use of small multifluid heat exchangers (e.g., plate-and-fin heat exchangers made of brazed aluminum). Ideally, the process should allow the LNG to be heated to ambient temperature for injection into the natural gas supply network or for supply to customers, without the need to heat the LNG with separate heating means.

[0011] This invention aims to improve known processes by reducing the risk of carbon dioxide solidification in processes that involve cooling, or even liquefying, carbon dioxide.

[0012] It uses an intermediate fluid to recover cold energy from LNG, which mainly consists of ethane and / or ethylene, and may also contain methane. This fluid would be designated as the C2 fluid. This fluid preferably contains at least 90 mol% ethane or ethylene.

[0013] This intermediate fluid preferably allows for the recovery of cold energy that has been reduced to a temperature below -60°C.

[0014] A dedicated heat exchanger (referred to as the "LNG heat exchanger") is used to exchange heat between an intermediate fluid and a methane-rich liquid in liquid form or in a dense phase, such as liquefied natural gas LNG. The LNG is heated or vaporized (in accordance with its pressure) with respect to the condensing C2 fluid and is cooled to a temperature below -50°C in a single pass or in multiple passes in parallel operation at different pressures (Pc1, Pc2, PcN, where N is typically 2 - 4) to limit the temperature difference between the fluids in the heat exchanger. The LNG heat exchanger will typically be a plate and fin heat exchanger, a shell and tube heat exchanger, or a printed circuit heat exchanger made of brazed aluminum or stainless steel.

[0015] When a multi-fluid heat exchanger is used, the flow of the C2 fluid is preferably subcooled to a temperature of 2 - 10 K above the inlet temperature of the LNG in the heat exchanger. At the low temperature end of the same heat exchanger, all of the subcooled C2 fluid is optionally mixed at pressure P1 using at least one pump and heated in another passage of the same heat exchanger to a temperature 2 - 5 K below the bubble point of the flow mixed at pressure P1. The subcooling of the C2 fluid close to -60°C is simply a means of limiting the temperature difference in the heat exchanger.

[0016] The resulting flow of the C2 fluid at pressure P1 is then heated and vaporized with respect to the condensing CO2, which is ideally at a single pressure of 10 - 16 bara in a separate heat exchanger for some fluids, and the C2 fluid crosses this heat exchanger either at a single pressure or in parallel at two pressures P1 and P2 < P1. When two evaporation pressures are used, P2 should typically correspond to the bubble point of the C2 fluid at approximately -55°C. In this case, the flow rate of the C2 fluid vaporized at P1 is much less (e.g., 25 - 35 times less) than the flow rate of the C2 fluid vaporized at P2, with the latter providing most of the cooling associated with the condensation of the CO2 and the former providing most of the cooling associated with the subcooling of the CO2 and the generation of reflux for the CO2 distillation column.

[0017] The CO2 fluid evaporated at P1 (or the fluid evaporated at P1 and P2), obtained at the high-temperature end of the heat exchanger where CO2 condenses, must be designed to produce the required flow rates at the condensation pressures Pc1, Pc2, and PcN selected for the LNG heat exchanger. Starting with two flows available at two different pressures, it is necessary to form N flows at pressure values ​​Pc1, Pc2, and PcN, and at specific flow rates. This assumes that at least one flow will be compressed and / or at least one flow will be depressurized. It is important to increase the pressure of the original flow (i.e., by minimizing compression, especially when it cannot be driven by depressurizing another flow in the turbine).

[0018] Ideally, only one of the condensation pressures Pc1, Pc2, and PcN is greater than P1. To this end, a portion of the gaseous C2 fluid at P1 is compressed by a centrifugal compressor to the highest of the condensation pressures. The C2 fluid at other condensation pressures is obtained by reducing the pressure of at least one valve JT and the rest of the C2 fluid in the centrifugal turbine. By selecting appropriate pressures and flow rates, the turbine can drive the compressor, and thus the only energy consumption is that of the pump.

[0019] The number of C2 fluid flow rates at different pressures passing through the LNG heat exchanger is selected according to the composition of the C2 fluid and the type of heat exchanger used. Generally speaking, the more flow rates there are, the smaller the temperature difference between the fluids, and therefore heating can be carried out, for example, in a plate-and-fin type heat exchanger made of brazed aluminum.

[0020] CN105545390A and JP H04 121573A describe the process according to the premise of claim 1.

[0021] The objective of the present invention is to limit the temperature difference at one of the low-temperature ends of a heat exchanger in order to increase process efficiency. [Overview of the project]

[0022] According to the subject matter of the present invention, a process is provided for recovering cold energy from a methane-rich fluid, such as liquefied natural gas, for cooling and, optionally, liquefying, and in fact even separating a carbon dioxide-rich flow. i. The carbon dioxide-rich flow is at least partially cooled and optionally condensed in the first heat exchanger at a pressure greater than 5 bar abs, in fact even greater than 13 bar abs. ii. Cooling is provided to stage i) by evaporation of an intermediate fluid containing at least 80 mol% ethane or ethylene at at least one pressure level, preferably a single pressure level. iii. At least a portion of the intermediate fluid evaporated in stage ii) is condensed in the second heat exchanger by heat exchange with a methane-rich fluid into at least one flow at at least one pressure, preferably into a single flow at a single pressure, to form at least one flow of condensed intermediate fluid. iv. In a process, at least one condensed intermediate fluid flow is pressurized by a pump, v. At least one flow pressurized by a pump is heated in the second heat exchanger to an intermediate temperature of the heat exchanger and sent to the first heat exchanger to evaporate according to stage ii), characterized in that the intermediate temperature is higher than the temperature at the low-temperature end of the second heat exchanger and lower than the temperature at the high-temperature end of the second heat exchanger.

[0023] According to other optional embodiments of the present invention, • Methane-rich fluids are either gases or liquids. A portion of the intermediate fluid is condensed in the second heat exchanger at a first pressure, and at least another portion of the intermediate fluid is condensed in the second heat exchanger at a pressure lower than at least the first pressure. • At least another portion of the intermediate fluid condensed at a pressure lower than at least the first pressure is pressurized to the first pressure in the pump. · At least a part of the intermediate fluid heated according to stage iv) comprises a part of the intermediate fluid condensed at the first pressure and at least a part of the intermediate fluid pressurized by a pump. · The at least one condensation pressure of the intermediate fluid in the second heat exchanger is preferably at least 2 bar higher than the evaporation pressure of the intermediate fluid in the first heat exchanger, or when there are several evaporation pressures of the intermediate fluid, higher than the highest evaporation pressure of the intermediate fluid in the first heat exchanger. · The compression of the part of the vaporized intermediate fluid condensed at a pressure higher than the evaporation pressure of the intermediate fluid in the first heat exchanger, or when there are several evaporation pressures of the intermediate fluid, higher than the highest evaporation pressure of the intermediate fluid, is carried out by a compressor driven by a turbine that decompresses another part of the vaporized intermediate fluid. · The intermediate fluid cycle does not comprise a compressor or does not comprise a compressor driven by a motor. · The evaporation pressure of the intermediate fluid in the first heat exchanger is 3 bara to 25 bara, preferably 4 bara to 21 bara, and / or the condensation pressure of the intermediate fluid in the second heat exchanger is 1.05 bara to 50 bara, preferably 1.3 bara to 45 bara. · The intermediate fluid contains more than 85 vol% ethane, preferably more than 90 vol% ethane. · The intermediate fluid contains more than 85 vol% ethylene, preferably more than 90 vol% ethylene. · The ratio of at least one molar flow rate of the intermediate fluid to the molar flow rate of the carbon dioxide-rich stream sent to the first heat exchanger is 1.0 to 1.5, preferably 1 to 1.4. · The ratio of at least one molar flow rate of the intermediate fluid to the molar flow rate of the methane-rich gas, such as LNG, sent to the second heat exchanger is 0.7 to 1.0, preferably 0.75 to 0.95. · The liquefied CO2-rich gas is produced at a temperature of -40 °C or lower, preferably -50 °C or lower. · The CO₂-rich stream at the inlet of the first heat exchanger contains more than 30 vol% CO₂, preferably more than 35 vol% CO₂. · The CO₂-rich stream at the inlet of the first heat exchanger contains more than 90 vol% CO₂, preferably more than 95 vol% CO₂. · At least a part of the methane-rich gas heated or evaporated in the second heat exchanger is sent as fuel or reactant to a steam methane reforming unit, an autothermal reforming unit, or a partial oxidation unit, and the CO₂-rich stream is produced by this unit or derived from the products from this unit. · The CO₂-rich liquid produced by partial condensation or distillation of the CO₂-rich stream for liquefaction or separation is subcooled in the first heat exchanger by heat exchange with at least a part of the intermediate fluid heated in the second heat exchanger to an intermediate temperature. · The CO₂-rich liquid produced by distillation or condensation of the CO₂-rich stream for liquefaction or separation is subcooled in the first heat exchanger by heat exchange with at least a part of the intermediate fluid heated in the second heat exchanger to an intermediate temperature. · The CO₂-rich stream is separated in at least one distillation column. · A part of the CO₂-rich liquid withdrawn from the bottom of the distillation column is evaporated in the first heat exchanger at a temperature higher than the intermediate temperature and returned to the bottom of the distillation column. · A part of the intermediate fluid heated in the first heat exchanger is depressurized in a turbine to generate electricity.

[0024] According to another subject of the present invention, an apparatus is provided for recovering cold energy from a methane-rich fluid, such as liquefied natural gas, to cool and optionally liquefy, in fact even separate, a carbon dioxide-rich flow, the apparatus comprising a first heat exchanger, a second heat exchanger, means for feeding a carbon dioxide-rich flow into the first heat exchanger to be cooled and optionally condensed, a closed intermediate fluid cycle, the closed intermediate fluid cycle means for feeding an intermediate fluid containing at least 80 mol% ethane or ethylene so that it evaporates in the first heat exchanger at at least one pressure level, preferably a single pressure level, by heat exchange with the methane-rich fluid in the second heat exchanger at at least one pressure An apparatus comprising means for transporting evaporated fluid so that it is condensed into a single flow, preferably at a single pressure, to form a flow of at least one condensed intermediate fluid, and a pump for pressurizing the flow of at least one condensed intermediate fluid, wherein the apparatus comprises means for transporting the flow from the pump to a second heat exchanger so that it is heated to an intermediate temperature of the first heat exchanger, and means for extracting the flow heated from the second heat exchanger at an intermediate temperature, connected to means for transporting an intermediate fluid containing at least 80 mol% ethane or ethylene so that it is evaporated into the first heat exchanger, wherein the intermediate temperature is higher than the temperature at the low-temperature end of the second heat exchanger and lower than the temperature at the high-temperature end of the second heat exchanger.

[0025] The present invention will be described in more detail with reference to the figures. [Brief explanation of the drawing]

[0026] [Figure 1] This refers to a process that uses a cycle to condense CO2 through heat exchange with a methane-rich liquid, such as LNG, where the fluid is 100% ethane. [Figure 2] This refers to a process that uses a cycle to condense CO2 through heat exchange with a methane-rich liquid, such as LNG, where the fluid is 100% ethylene. [Figure 3]This represents a process for condensing CO2 by heat exchange with a methane-rich liquid, such as LNG, using a cycle, where the fluid is 93.5 mol% ethane and 6.5 mol% methane. [Figure 4] This refers to a process for condensing CO2 by heat exchange with a methane-rich liquid, such as LNG, using a cycle, where the fluid is ethylene containing 6-7% methane. [Modes for carrying out the invention]

[0027] Figure 1 illustrates a process for condensing CO2 by heat exchange with a methane-rich liquid, such as LNG, using a cycle, where the fluid is 100% ethane, and two fluid flow rates condense in the heat exchanger at two different condensation pressures. The flow of liquefied natural gas (LNG) 1 is sent to the low-temperature end of heat exchanger E2, which may be a plate-and-fin heat exchanger or a printed circuit heat exchanger. The liquefied natural gas is evaporated and heated in heat exchanger E2 to produce natural gas 3 exiting from the high-temperature end, preferably at a temperature above 0°C, e.g., ambient temperature. Fluid 1 may be a gas or a liquid.

[0028] In heat exchanger E2, two C2 flows, ethane 19 and 21 in this example, are cooled, with flow 21 at a lower pressure than flow 19. Flow 21 passes through heat exchanger E1 from the high-temperature end to the low-temperature end, completely condensing as it goes. The condensed flow is sent to drum S. Liquid 23 from drum S is pressurized by pump P and mixed with flow 19, which has been condensed and depressurized in the valve. The resulting flow 11 is de-subcooled in heat exchanger E1 and thus heated to an intermediate temperature in the heat exchanger, i.e., a temperature between the temperature of the low-temperature end and the temperature of the high-temperature end of the heat exchanger.

[0029] Flow 11 is sent to the CO2 liquefier either through an insulated pipe or by passing through an insulated cold box common to the heat exchanger E2 and the CO2 liquefier. Flow 11 is divided into two parts, and the two parts 13 and 15 are depressurized in their respective valves and heated in the heat exchanger E1 as they pass from the cold end to the hot end. After heating, flow 15 is divided into two parts to form flows 19 and 17. Flow 19 is compressed in the compressor C, cooled in a cooler (not shown), and sent to the heat exchanger E2 at the cooler outlet pressure. Flow 17 is depressurized from pressure P1 in the turbine T driving the compressor C, mixed with flow 13 to form flow 21, which enters the heat exchanger E2.

[0030] A carbon dioxide-rich flow 5 at 10-16 bara is divided into two parts 51 and 53. Flow 53 passes entirely through heat exchanger E1 and is sent as top reflux to distillation column K1, where it condenses. The other part 51 is cooled in heat exchanger E1 at the same pressure as part 53, but exits heat exchanger E1 at a temperature intermediate between the high-temperature and low-temperature ends. Part 51 is then sent to column K1.

[0031] Re-boiling of column K1 is provided by taking a portion 57 of the carbon dioxide-enriched bottom liquid 55 from column K1. The bottom liquid 55 is sent to an intermediate level in heat exchanger E1, which is hotter than the outlet point of the flow 51. A portion 57 is evaporated, heated, and returned to the bottom of column K1 as a gas. The remaining portion 7 of the liquid 55 is subcooled in heat exchanger E1 by heat exchange with the intermediate fluid 11, forming liquid carbon dioxide, the product of the process. The top gas 9 from column K1 is heated in heat exchanger E1 from the low-temperature end to the high-temperature end and exits the system. This gas 9 is enriched with light impurities such as nitrogen, hydrogen, and carbon monoxide.

[0032] The condensation pressure of the intermediate fluid flow 19 in the second heat exchanger E2 is preferably at least 2 bar higher than the highest evaporation pressure of the intermediate fluid in the first heat exchanger E1.

[0033] Figure 2 illustrates a process for condensing CO2 by heat exchange with a methane-rich liquid, such as LNG, using a cycle, where the CO2 fluid is 100% ethylene. Details of the CO2 liquefaction apparatus are not given, but the same or similar process as that in Figure 1 can be used for liquefaction.

[0034] In this example, the C2 fluid is evaporated at two different pressures in a heat exchanger E2 to condense a gas rich in carbon dioxide. The gas 15 taken out at the high-temperature end of heat exchanger E1 is split into two parts. Part 45 is compressed in a compressor, cooled in a heat exchanger E3, and then condensed against LNG in heat exchanger E2. The remaining part 25 of gas 15 is split into three parts, one part 29 is mixed with gas 13 to form gas 43, which is depressurized in a turbine driving the compressor and then sent to heat exchanger E2 to be completely condensed and form a liquid flow 47 sent to drum S.

[0035] Another portion 27 of the gas 25 is depressurized and then sent to a heat exchanger E2, where it is condensed, subcooled, and then mixed with the subcooled liquid 47.

[0036] Another portion 41 of the gas 25 is depressurized and then sent to the heat exchanger E2, where it is condensed, subcooled, and then mixed with the liquid 47.

[0037] From this, we can see that the fluid C2, ethylene in this case, condenses in the heat exchanger E2 at four different pressures.

[0038] Heat exchanger E2, having a cooler downstream of the compression of flow 45, could be a plate-and-fin type heat exchanger, for example, made of brazed aluminum. The turbine is supplied with a flow of fluid C2 at pressure P2, in this case ethylene.

[0039] Heat exchanger E3 is cooled by the flow 1A of evaporated LNG taken out at the high-temperature outlet of heat exchanger E2.

[0040] The condensation pressure of the intermediate fluid flow 45 in the second heat exchanger is preferably at least 2 bar higher than the highest evaporation pressure of the intermediate fluid in the first heat exchanger.

[0041] Figure 3 illustrates the process for condensing CO2 by heat exchange with LNG using a cycle, where the CO2 fluid is 93.5 mol% ethane and 6.5 mol% methane. Details of the CO2 liquefaction equipment are not given, but the same or similar process as that in Figure 1 can be used for liquefaction.

[0042] In this example, the C2 fluid is evaporated at two different pressures in a heat exchanger E1 to condense a gas rich in carbon dioxide. The gas 15 taken out at the high-temperature end of heat exchanger E1 is split into two parts. Part 33 is compressed in compressor C, cooled in heat exchanger E3, and then condensed against LNG in heat exchanger E2. The remaining part 25 of gas 15 is split into two parts, one part 29 which is mixed with gas 13 to form gas 43, which is depressurized in turbine T driving compressor C, and then sent to heat exchanger E2 to be completely condensed and form a liquid flow 35 which is sent to drum S.

[0043] The other portion 27 of the gas 25 is depressurized in the valve and then sent to the heat exchanger E2, where it is condensed and then mixed with the subcooled flow 35 upstream of the drum S.

[0044] Heat exchanger E3 is cooled by the flow 1A of evaporated LNG taken out at the high-temperature outlet of heat exchanger E2.

[0045] The heat exchanger E2 may be a plate-and-fin type heat exchanger made of, for example, brazed aluminum, as there is a cooler E3 downstream of the compression of the flow 33. The turbine is supplied with a flow of fluid C2 at pressure P2.

[0046] The condensation pressure of the intermediate fluid flow 33 in the second heat exchanger is preferably at least 2 bar higher than the highest evaporation pressure of the intermediate fluid in the first heat exchanger.

[0047] Figure 4 illustrates a process for condensing CO2 by heat exchange with a methane-rich liquid, such as LNG, using a cycle, where the fluid is 93 mol% ethylene and 7 mol% methane, and a single flow of the fluid condenses in the heat exchanger E2. The flow of liquefied natural gas (LNG) 1 is sent to the low-temperature end of the heat exchanger E2, which may be a plate-and-fin heat exchanger or a printed circuit heat exchanger. The liquefied natural gas is evaporated and heated in the heat exchanger E2 to produce natural gas 3 exiting from the high-temperature end, preferably at a temperature above 0°C, e.g., ambient temperature.

[0048] Flow 21 C2 is cooled in heat exchanger E2. Flow 21 passes through heat exchanger E1 from the high-temperature end to the low-temperature end, completely condensed and subcooled. The subcooled flow is separated in drum S. Gas 25 from drum S rejoins flow 21 at the inlet of heat exchanger E2. Liquid 23 from drum is pressurized by pump P. The pumped flow 11 is desubcooled in heat exchanger E2 to an intermediate temperature and is therefore heated.

[0049] Flow 11 is sent to the CO2 liquefier either through an insulated pipe or by passing through an insulated cold box common to the heat exchanger E2 and the CO2 liquefier. Flow 11 becomes flow 13 and is heated in the heat exchanger E1 as it passes from the low-temperature end to the high-temperature end. After heating, flow 13 is heated again, for example to 60°C, and sent to the heat exchanger E2 at the outlet pressure of the heater R. The flow enters the heat exchanger E2.

[0050] First, flow 12 short-circuits heat exchanger E1 to allow the intermediate fluid to be heated by the heater.

[0051] A carbon dioxide-rich flow 5 at 10-16 bara is divided into two parts 51 and 53. Flow 53 passes entirely through heat exchanger E1 and is sent as top reflux to distillation column K1, where it condenses. The other part 51 is cooled in heat exchanger E1 at the same pressure as part 53, but exits heat exchanger E1 at a temperature intermediate between the high-temperature and low-temperature ends. Part 51 is then sent to column K1.

[0052] Re-boiling of column K1 is provided by taking a portion 57 of the carbon dioxide-enriched bottom liquid 55 from column K1. The bottom liquid 55 is sent to an intermediate level in heat exchanger E1, which is hotter than the outlet point of the flow 51. A portion 57 is evaporated, heated, and returned to the bottom of column K1 as a gas. The remaining portion 7 of the liquid 55 is subcooled in heat exchanger E1 by heat exchange with the intermediate fluid 11, forming liquid carbon dioxide, the product of the process. The top gas 9 from column K1 is heated in heat exchanger E1 from the low-temperature end to the high-temperature end and exits the system. This gas 9 is enriched with light impurities such as nitrogen, hydrogen, and carbon monoxide.

[0053] The condensation pressure of the intermediate fluid flow 19 in the second heat exchanger differs from the highest evaporation pressure among the intermediate fluid evaporation pressures in the first heat exchanger, by only head loss. The intermediate fluid cycle does not involve compression (apart from pump pressurization) or depressurization in the turbine. Pump P is used solely to compensate for the pressure drop.

[0054] Figures 1, 2, 3, and 4 each show a pipe that can be provided upstream of the heat exchanger E2 for transporting the gas generated in the drum S. This gas is generated as heat enters the drum, and the gas evaporates a small portion of the liquid it contains. The formed gas 25 is sent from the drum S and rejoins with gas 21.

Claims

1. A process for cooling a carbon dioxide-rich flow (5) and recovering cold energy from a methane-rich fluid, such as liquefied natural gas, for optional liquefaction, and even separation, i. The carbon dioxide-rich flow is at least partially cooled and optionally condensed in the first heat exchanger (E1) at a pressure greater than 5 bar abs, in fact even greater than 13 bar abs. ii. Cooling is provided to stage i) by evaporation of an intermediate fluid containing at least 80 mol% ethane or ethylene at at least one pressure level, preferably a single pressure level. iii. At least a portion of the intermediate fluid evaporated in stage ii) is condensed in the second heat exchanger (E2) by heat exchange with the methane-rich fluid (1) into at least one flow at at least one pressure, preferably into a single flow at a single pressure, to form at least one flow of condensed intermediate fluid. iv. The flow of at least one condensed intermediate fluid is pressurized by a pump (P) in the process, v. A process characterized in that the at least one flow (37) pressurized by the pump is heated in the second heat exchanger to an intermediate temperature of the second heat exchanger and sent to the first heat exchanger to evaporate according to stage ii), wherein the intermediate temperature is higher than the temperature at the low-temperature end of the second heat exchanger and lower than the temperature at the high-temperature end of the second heat exchanger.

2. The process according to claim 1, wherein a portion of the intermediate fluid is condensed in the second heat exchanger (E2) at a first pressure, and at least another portion of the intermediate fluid is condensed in the second heat exchanger at a pressure at least lower than the first pressure.

3. The process according to claim 2, wherein at least another portion of the intermediate fluid condensed at a pressure lower than the first pressure is pressurized in the pump (P) to the first pressure.

4. The process according to claim 3, wherein the at least portion of the intermediate fluid heated according to stage iv) comprises the portion of the intermediate fluid condensed at the first pressure and the at least portion of the intermediate fluid pressurized by the pump.

5. The process according to any one of claims 1 to 4, wherein at least one condensation pressure of the intermediate fluid in the second heat exchanger (E2) is preferably at least 2 bar higher than the evaporation pressure of the intermediate fluid in the first heat exchanger, or, if there are several evaporation pressures of the intermediate fluid, is higher than the highest of the evaporation pressures of the intermediate fluid in the first heat exchanger.

6. The process according to claim 5, wherein the compression of the portion of the evaporated intermediate fluid, which is condensed at a pressure higher than the evaporation pressure of the intermediate fluid in the first heat exchanger, or, if there are several evaporation pressures of the intermediate fluid, at the highest of the evaporation pressures, is carried out by a compressor (C) driven by a turbine (T) that reduces the pressure of another portion of the evaporated intermediate fluid.

7. The process according to any one of claims 1 to 4, wherein the intermediate fluid cycle is not equipped with a compressor or is not equipped with a motor-driven compressor.

8. The process according to any one of claims 1 to 4, wherein the evaporation pressure of the intermediate fluid in the first heat exchanger (E1) is 3 bar to 25 bar, preferably 4 bar to 21 bar, and / or the condensation pressure of the intermediate fluid in the second heat exchanger (E2) is 1.05 bar to 50 bar, preferably 1.3 bar to 45 bar.

9. The process according to any one of claims 1 to 4, wherein the intermediate fluid (11) contains more than 85 vol% of ethane, preferably more than 90 vol% of ethane.

10. The process according to any one of claims 1 to 4, wherein the intermediate fluid (11) contains more than 85 vol% of ethylene, preferably more than 90 vol% of ethylene.

11. The process according to any one of claims 1 to 4, wherein the ratio of the molar flow rate of at least one intermediate fluid to the molar flow rate of the carbon dioxide-rich flow sent to the first heat exchanger (E1) is 1.0 to 1.5, preferably 1 to 1.

4.

12. The process according to any one of claims 1 to 4, wherein the ratio of at least one molar flow rate of the intermediate fluid to the molar flow rate of the methane-rich gas (1), for example LNG, sent to the second heat exchanger is 0.7 to 1.0, preferably 0.75 to 0.

95.

13. Liquefied CO 2 The process according to any one of claims 1 to 4, wherein the gas rich in is produced at a temperature of -40°C or lower, preferably -50°C or lower.

14. The carbon dioxide-rich flow (5) at the inlet of the first heat exchanger (E1) contains more than 30 vol% CO 2 Preferably, more than 35 vol% of CO 2 The process according to any one of claims 1 to 4, comprising:

15. The carbon dioxide-rich flow at the inlet of the first heat exchanger (E1) is greater than 90 vol% CO 2 Preferably, more than 95 vol% of CO 2 The process according to claim 14, comprising:

16. At least a portion of the methane-rich gas heated or evaporated in the second heat exchanger (E2) is sent as fuel or reactant to a steam methane reforming unit, a self-heat reforming unit, or a partial oxidation unit, and CO 2 The process according to any one of claims 1 to 4, wherein the rich flow (5) is generated by or derived from the products of this unit.

17. CO2 produced by partial condensation, distillation, liquefaction, or separation of the aforementioned carbon dioxide-rich flow 2 The process according to any one of claims 1 to 4, wherein the liquid (55) rich in is subcooled in the first heat exchanger (E1) by heat exchange with at least a portion of the intermediate fluid heated in the second heat exchanger to the intermediate temperature.

18. CO 2 The process according to any one of claims 1 to 4, wherein the rich flow (55) is separated in at least one distillation column (K1).

19. CO withdrawn from the bottom of the distillation column (K1) 2 A part (57) of the liquid rich in 2 is evaporated in the first heat exchanger at a temperature higher than the intermediate temperature and returned to the bottom of the distillation column, according to the process of claim 18.

20. The process according to any one of claims 1 to 4, wherein a portion (17) of the intermediate fluid heated in the first heat exchanger (E1) is depressurized in a turbine (T) to generate electricity.

21. A device for cooling a carbon dioxide-rich flow (5) and recovering cold energy from a methane-rich fluid (1), such as liquefied natural gas, for which liquefaction, and in fact even separation, is also performed. The apparatus comprises a first heat exchanger (E1), a second heat exchanger (E2), means for delivering the carbon dioxide-rich flow into the first heat exchanger (E1) to be cooled and optionally condensed, and a closed intermediate fluid cycle. In an apparatus comprising: means for supplying an intermediate fluid containing at least 80 mol% ethane or ethylene so that the closed intermediate fluid cycle evaporates in the first heat exchanger at at least one pressure level, preferably a single pressure level; means for supplying the evaporated intermediate fluid so that, by heat exchange with the methane-rich fluid (1), it condenses in the second heat exchanger (E2) into at least one flow at at least one pressure, preferably a single flow at a single pressure, to form at least one condensed intermediate fluid flow; and a pump for pressurizing the at least one condensed intermediate fluid flow, The system comprises means for supplying the flow from the pump to the second heat exchanger so as to be heated to an intermediate temperature of the second heat exchanger, and means connected to means for supplying the intermediate fluid containing at least 80 mol% ethane or ethylene so as to be evaporated into the first heat exchanger, and means for extracting the flow heated from the second heat exchanger at the intermediate temperature, An apparatus for recovering cold energy, characterized in that the intermediate temperature is higher than the temperature at the low-temperature end of the second heat exchanger and lower than the temperature at the high-temperature end of the second heat exchanger.

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