Method for liquefying and / or solidifying a gas rich in carbon dioxide

Abstract

The invention relates to a device for liquefying a gas rich in carbon dioxide, the device comprising a first heat exchanger (EI), means for sending a low-temperature methane-rich fluid (1) to the first exchanger and means for sending an intermediate fluid (5) to the first heat exchanger in order to cool the intermediate fluid, a compressor (C) connected to the first heat exchanger in order to compress the cooled intermediate fluid, means for sending the compressed intermediate fluid (7) to a second heat exchanger (E2) in order to heat it up, means for separating the reheated intermediate fluid into two parts, means for sending one portion of the intermediate fluid (11) to the first exchanger without passing through a hot end of the second heat exchanger, means for sending another portion (9) of the intermediate fluid to the first exchanger by passing through the hot end of the second heat exchanger, means for sending a flow of carbon dioxide (13) to the second heat exchanger in order to cool the flow, and means for producing a flow of liquid carbon dioxide (17) downstream of the second heat exchanger.

Description

Process of liquefaction and / or solidification of a gas rich in carbon dioxide

[0001] The present invention relates to a method for liquefying and / or solidifying a carbon dioxide-rich gas. The gas that is liquefied is a carbon dioxide-rich gas containing more than 30 mol% carbon dioxide such as a waste gas from a PSA producing a hydrogen-enriched gas or fumes.

[0002] It is known from "Integrating hydrogen liquefaction with steam methane reforming and CO2 liquefaction processes using techno-economic perspectives" by Lee et al, Energy Conversion and Management 245 (2021) to use the frigories of a vaporization of liquefied natural gas to liquefy CO2 and hydrogen.

[0003] The present invention provides a method for liquefying and / or solidifying a gas rich in carbon dioxide, i.e. containing at least 30 mol% of carbon dioxide, or even at least 50 mol% of carbon dioxide, preferably at least 90 mol% of carbon dioxide. The gas also contains at least one of the following gases: nitrogen, oxygen, hydrogen, methane, NOx, argon, carbon monoxide.

[0004] JP H06 63699, US2019151789 and FR2969404 describe the use of an intermediate cycle to transfer the cold from an LNG flow to a CO2 flow to be liquefied. JP H06 63699 published in 1990 describes an ethylene intermediate cycle in which ethylene vaporizes with the heat from the CO2 flow.

[0005] An object of the invention is to improve the exchange diagram of the process in order to avoid large temperature differences at the hot end of a heat exchanger used to liquefy a CO2-rich gas.

[0006] To make a process more energy efficient, it is necessary to avoid large temperature differences, especially when the heat exchanger is a brazed plate and fin type exchanger.

[0007] It is also planned to use an intermediate fluid cycle without phase change to transfer the cold from natural gas, liquefied or not, to the gas to be liquefied.

[0008] According to an object of the invention, there is provided a method for liquefying and / or solidifying a gas rich in carbon dioxide in which at least part of the frigories for the liquefaction and / or solidification are provided by a fluid rich in methane at low temperature characterized in that:

[0009] a) the methane-rich fluid is a methane-rich liquid, for example liquefied natural gas or methane-rich gas at a temperature below -50°C, the methane-rich fluid cools an intermediate fluid at a pressure between 5 and 40 bara to a first temperature between -30°C and -100°C

[0010] b) the intermediate fluid is compressed into gaseous form before or after cooling to the first temperature and sent to a heat exchanger at a second temperature between -30°C and -80°C, preferably between -50°C and -55°C where it heats up by indirect heat exchange with the carbon dioxide-rich gas which at least partially condenses and / or solidifies

[0011] (c) the intermediate fluid heated in the heat exchanger is divided into two, a part of the fluid leaving the heat exchanger at a temperature which differs by at most 10°C from the dew point temperature of the carbon dioxide-rich gas to be at least partially condensed and which is at least 15°C lower than the temperature at which the carbon dioxide-rich gas enters the heat exchanger at a first end thereof, this part constituting at least 50%, or even at least 70%, of the intermediate fluid entering the heat exchanger and

[0012] (d) the part constituting at least 50% of the intermediate fluid is not heated in the heat exchanger and

[0013] (i) is not heated outside the heat exchanger or

[0014] ii) is heated outside the heat exchanger by cooling a refrigerant and / or the carbon dioxide-rich gas

[0015] e) another part of the intermediate fluid heats up to the first end of the heat exchanger and

[0016] f) the part constituting at least 50% of the intermediate fluid and the other part are mixed and returned to be cooled by the methane-rich fluid of step a), the intermediate fluid remaining gaseous during the heat exchange with the methane-rich fluid and the intermediate fluid cycle not including a phase change.

[0017] According to other optional features: at least a portion of the intermediate fluid compressed and heated in the exchanger is expanded in a turbine to a temperature between -30°C and -80°C, preferably between -50°C and -55°C, and returned to the heat exchanger to be reheated and divided into two according to step c). intermediate fluid expanded in the turbine is reheated in the heat exchanger, then expanded in another turbine to a temperature between -30°C and -80°C, preferably between -50°C and -55°C, and returned to the heat exchanger to be reheated and divided into two according to step c). the CO2-rich gas is a waste gas from a pressure swing adsorption process producing a gas enriched in hydrogen compared to the gas feeding the adsorption process and the waste gas depleted in hydrogen compared to the gas feeding the process adsorption.the intermediate fluid contains at least 90 mol% nitrogen or methane or is a mixed refrigerant comprising at least nitrogen, methane and ethane and / or ethylene.the intermediate fluid flow rate is between 10D / L and 25D / L where D is the flow rate of carbon dioxide-rich gas sent to the heat exchanger in Nm3 / l and L is the number of intermediate fluid streams in the heat exchanger.the carbon dioxide-rich gas is compressed in a compressor upstream of the heat exchanger having at least two stages and an interstage cooler cooled either by a / the intermediate fluid portion or by water that has been cooled by the intermediate fluid portion.the inlet temperature of the intermediate fluid compressor is below 0°C.an interstage cooler cooled by a / the intermediate fluid portion to below -55°C cools a carbon dioxide-rich gas to a pressure below 5.1 bar abs.the carbon dioxide-rich gas is cooled in a cooler and then purified with water upstream of the heat exchanger and the part of the intermediate fluid is used to cool the carbon dioxide-rich gas.a flow having the same composition as the intermediate fluid is cooled to a temperature between -120°C and -160°C and provides cold to a liquefaction or separation unit operating at a temperature between -120°C and -160°C, for example an air separation device or a hydrogen liquefier.a flow having the same composition as the intermediate fluid is cooled to a temperature between -135°C and -155°C and provides cold to a liquefaction or separation unit operating at a temperature between -135°C and -155°C, to solidify a part of the liquefied carbon dioxide-rich gas.the methane-rich fluid is a methane-rich liquid that is preheated before cooling the intermediate fluid of step a) by heat exchange with at least one other intermediate fluid flow or glycolated water.the compression of step b) raises the pressure of the intermediate fluid so that the intermediate fluid that heats up in the heat exchanger exits the exchanger and is split while at a pressure substantially equal to that of the fluid upstream of the compression of step b).the intermediate fluid is a gas the heat exchanger is a brazed plate and fin heat exchanger.the heat exchanger has a first end (hot end) and a second end (cold end)the temperature difference of the heat exchanger at the first end thereof, operating at a temperature warmer than the second end, is between 2 and 10°Cthe temperature difference of the heat exchanger does not exceed 25°C.

[0018] The invention will be described in more detail with reference to the figures where:

[0019] represents a process for liquefying and / or solidifying a gas rich in carbon dioxide according to the invention.

[0020] represents a process for liquefying and / or solidifying a gas rich in carbon dioxide according to the invention.

[0021] represents a process for liquefaction and / or solidification of a gas rich in carbon dioxide according to the invention

[0022] represents a process for liquefaction and / or solidification of a gas rich in carbon dioxide and liquefaction of hydrogen according to the invention

[0023] In the, in a process for liquefaction and / or solidification of a carbon dioxide-rich gas in which at least part of the frigories for liquefaction are provided by a low-temperature methane-rich fluid. The gas contains at least 30 mol% carbon dioxide, or even at least 50 mol% carbon dioxide, preferably at least 90 mol% carbon dioxide. The gas also contains at least one of the following gases: nitrogen, oxygen, hydrogen, methane, NOx, argon, carbon monoxide.

[0024] The methane-rich fluid is a methane-rich liquid 1, for example liquefied natural gas or otherwise methane-rich gas at a temperature below -50°C. Here a liquid pressurized by a pump heats up, or even vaporizes in a heat exchanger E1 by indirect heat exchange with a single fluid which is an intermediate fluid 5 at a pressure between 5 and 40 bara up to a first temperature between -30°C and -100°C.

[0025] The intermediate fluid cooled to the first temperature, for example -70°C, is compressed in a compressor C just enough to compensate for the pressure drop in the heat exchanger E1, this pressurization being able to vary between 200 mbar and several bars, depending on the technology of the exchanger E1. The compressed fluid 7 is sent to the cold end of a heat exchanger E2 at a second temperature between -30°C and -80°C, preferably between -50°C and -55°C, for example -55°C having been heated by compression. In the exchanger E2 it heats up by indirect heat exchange with the carbon dioxide-rich gas 13 which condenses at least partially, leaving the cold end in this example in two-phase form and being separated in a separator S forming a liquid 17 and a gas 15 which heats up in the exchanger E2.

[0026] The intermediate fluid 7 heated in the heat exchanger is divided into two, a portion 11 of the fluid leaving the heat exchanger at a temperature which differs by at most 10°C from the dew point temperature of the carbon dioxide-rich gas 13 to be at least partially condensed and which is at least 15°C lower than the temperature at which the carbon dioxide-rich gas 13 enters the heat exchanger E2. The portion 11 may leave the exchanger E2 at -20°C. This portion 11 constitutes at least 50%, or even at least 70%, of the intermediate fluid 7 entering the heat exchanger E2. The portion 11 constituting at least 50% of the intermediate fluid is

[0027] i) returned in a closed circuit to be cooled by the methane-rich fluid in step a) and / or

[0028] (ii) used to cool another refrigerant

[0029] and / or

[0030] (iii) treated in another manner.

[0031] The remainder 9 of the intermediate fluid continues to heat up to the hot end of the heat exchanger E2, for example to 10°C, then passes through a valve V1 and is remixed with the flow 11 which has not been heated. Valves V1, V2 regulate the percentages of the flows 9, 11.

[0032] The intermediate fluid flow rate 7 is between 10D / L and 25D / L where D is the flow rate of carbon dioxide-rich gas 13 sent to the heat exchanger E2 in Nm3 / l and L is the number of intermediate fluid flows in the heat exchanger (here only one).

[0033] The fact that only a part 9 of the intermediate fluid (at most 50%, or even at most 30% of the flow rate 7) arrives at the hot end of the heat exchanger E2 makes it possible to reduce the temperature difference at the hot end, thus allowing the use of an exchanger such as a brazed plate and fin exchanger as exchanger E2

[0034] Obviously the cold of part 11 can be cleverly exploited as illustrated in figures 2 and 3.

[0035] Liquefaction can be replaced at least partially by solidification.

[0036] In which is a variant of the, the intermediate fluid heated in the exchanger E2 to an intermediate temperature below -20°C, is sent to expand in a turbine T to a temperature between -30°C and -80°C, preferably between -50°C and -55°C, is sent at a temperature between -30°C and -80°C, preferably between -50°C and -55°C, to the cold end of the exchanger E2 and heats up. Then it is divided into two, a part 11 of the fluid leaving the heat exchanger at a temperature which differs by at most 10°C from the dew point temperature of the carbon dioxide-rich gas 13 to be at least partially condensed and which is at least 15°C lower than the temperature at which the carbon dioxide-rich gas 13 enters the heat exchanger E2. Part 11 can exit the exchanger E2 at -20°C. This part 11 constitutes at least 50%, or even at least 70%, of the intermediate fluid 7 entering the heat exchanger E2.The portion 11 constituting at least 50% of the intermediate fluid is used to cool water 19 in the heat exchanger E3 downstream of the valve V2. The water thus cooled 19 may be a product of the process.

[0037] The liquefaction process may include or be replaced by a solidification process by solidifying the flow 13.

[0038] The remainder 9 of the intermediate fluid continues to heat up to the hot end of the heat exchanger E2, for example to 10°C, then passes through a valve V1 and is remixed with the flow 11 which has been heated in the exchanger E3.

[0039] The water 19 may be used to cool the gas 13 upstream of a purification step to remove the water it contains. Alternatively, the water 19 may cool an interstage cooler of a compressor of the gas 13 upstream of the heat exchanger E2 having at least two stages. For example, the interstage cooler may be cooled by a / the portion 11 of intermediate fluid to less than -55°C to cool a carbon dioxide-rich gas to a pressure below 5.1 bar abs.

[0040] The intermediate fluid flow rate 7 is between 10D / L and 25D / L where D is the flow rate of carbon dioxide-rich gas 13 sent to the heat exchanger E2 in Nm3 / l and L is the number of intermediate fluid flows in the heat exchanger (here two, the flow rates before and after expansion in the turbine T).

[0041] Flow 7 can be expanded in two turbines T in series so that the number of flows is three since one non-expanded flow and two expanded flows are heated in exchanger E2.

[0042] This allows operation with a reduced flow rate of liquefied natural gas 1 compared to that of the.

[0043] In this example, all the intermediate fluid is sent to the turbine. However, one could consider expanding only part of the flow in the turbine, heating it up to the hot end of exchanger E2, passing it through exchanger E1 and introducing it in the interstage into compressor C.

[0044] In which is a variant of the, we see that the exchanger E3 sends cooled water 19 to the exchanger E6 to cool the carbon dioxide-rich gas upstream of a dryer P and downstream of the compression in the compressors V1, V2. The water 19 or the intermediate gas part 11 can be sent to cool the interstage cooler E4 of the compressor V1, V2., driven by a motor M.

[0045] This figure shows a variant of the liquefaction process using a refrigeration cycle with a fluid 27 and two compressors V3, V4.

[0046] The carbon dioxide-rich gas 13 is compressed in the compression stages V1, V2, cooled by water in the exchangers E5, E6, dried in the dryer P and then cooled in the exchanger E2, compressed to cold in the compressor V5, cooled in the heat exchanger E2 where it partially condenses forming a liquid 17 and a gas 15 in the separator S, the gas 15 being compressed to cold in the compressor V6, cooled in the heat exchanger E2 where it partially condenses forming a liquid 21 and a gas 25 in the separator S1. The liquid 21 is expanded and sent to the separator S. The gas 25 heats up in the exchanger E2.

[0047] The invention also applies to a case as illustrated in patent application FR2200982 filed on February 4, 2022, in which a method is provided for cooling, or even at least partially condensing, gaseous carbon dioxide and cooling, or even at least partially liquefying, gaseous hydrogen comprising:A step of compressing a first intermediate flow and a step of compressing a second intermediate flow,A step of indirect heat exchange, preferably in a first heat exchanger, between a first flow of liquefied natural gas or with a flow of natural gas at a temperature below -50°C and at least the first and second intermediate flows compressed in step i) to cool the first intermediate flow to a temperature T1 between -30°C and -100°C,or between -30°C and -80°C, preferably between -25°C and -60°C, and to cool the second intermediate flow to a temperature below T1, preferably between -130°C and -150°C, and to form a first heated or even vaporized liquefied gas flow or a heated natural gas flow,A step of sending the first intermediate flow cooled to a temperature between -30°C and -100°C to a second indirect heat exchanger where it cools a flow rich in carbon dioxide which preferably condenses at least partially,A step of sending the second intermediate flow cooled to between -130°C and -150°C to a third indirect heat exchanger where it cools a hydrogen flow and possibly a cycle fluid, andA step of cooling, or even at least partial liquefaction of the hydrogen flow cooled in step iv).

[0048] According to the present invention, the method described above is adapted so that a portion of the first intermediate flow heats up to the hot end of the second heat exchanger and another portion of the first intermediate flow does not heat up to the hot end of the second heat exchanger.

[0049] Liquefaction can be replaced by a CO2 solidification step.

[0050] illustrates an integrated process for cooling carbon dioxide gas, cooling hydrogen gas and vaporizing liquefied natural gas. The liquefied natural gas vaporization apparatus 100 optionally comprises a pump P if the liquefied natural gas 1 is not at the required pressure. The liquefied natural gas 1 is divided into two parts, one part being sent to a plate and fin type heat exchanger E1, for example made of brazed aluminum. The liquid travels through the entire exchanger from the cold end to the hot end and vaporizes there. The remainder 5 of the liquid 1 is sent by the valve V1 to a heat exchanger E4 where it exchanges heat and is vaporized by a flow 7 of cycle gas. The two gases vaporized in the exchangers E1, E4 are mixed to form the vaporized natural gas 45. Preferably the vaporized natural gas 3 leaves the exchanger E1 at a temperature above 0°C.

[0051] Liquefied natural gas 1.3 can be replaced by natural gas at less than -50°C.

[0052] The carbon dioxide liquefier 500 comprises a compressor C3 for compressing the gaseous carbon dioxide 450. The compressed gas 13 is cooled, purified of water and possibly methanol and then compressed in a compressor C4, cooled and then compressed in a compressor C5. The gas compressed in the compressor C5 partially condenses in a plate and fin heat exchanger E2, for example made of brazed aluminum. The gas 13 is rich in carbon dioxide and contains at least 90 mol% carbon dioxide, or even at least 95% carbon dioxide. The two-phase fluid formed is sent to a phase separator S1 which produces a gas 17 which heats up in the exchanger E2 and joins the gas to be compressed in the compressor C5. The liquid from the phase separator is returned in part as liquid 21 which is vaporized in the exchanger E2 and joins the gas to be compressed in the compressor C5.The remainder 17 of the liquid from separator S1 is sent to a stripping column R, whose bottom liquid 550, purified of light impurities, constitutes the liquefied CO2. The gas from column R is heated in exchanger E2.

[0053] The gas 13 may be solidified to provide a solid product or the solid may be vaporized to form a gas or liquid.

[0054] If gas 13 is sufficiently pure, column R will not be necessary.

[0055] The frigories required for this liquefaction in the liquefier E2 are recovered at least in part by a closed cycle. The first intermediate fluid, cycle gas 11, heats up in the heat exchanger E2, is compressed in a compressor C1 and is then possibly split into two. A portion of the cycle gas arrives in the hottest part of the heat exchanger E1 and cools down to an intermediate temperature in the exchanger E2. The remainder of the cycle gas cools down in the exchanger E4 and the two cooled fluids are mixed to form the cycle gas 11.

[0056] Compressor C1 can compress cycle gas 11 just enough to overcome pressure losses or alternatively can be associated with a turbine which expands the cycle gas.

[0057] The 300 hydrogen liquefier consists of two heat exchangers, a pre-cooling heat exchanger E3 and a final heat exchanger E5.

[0058] The hydrogen to be liquefied 250 is first cooled in exchanger E3, then in exchanger E6 and finally in exchanger E5 to form liquefied hydrogen 350.

[0059] Another closed cycle consisting of a second intermediate fluid transfers frigories from the liquefied natural gas to the heat exchanger E3. The cycle gas 39 is compressed in a compressor C2 then passes through the exchanger E1 from the hot end to the cold end before being divided into two. A portion 41 of the gas 39 is expanded in a turbine T1. The remainder 43 is sent to the cold end of the exchanger E3 where it partially condenses, then is sent to a phase separator 37. The gas from the separator mixed with the turbine flow 41 becomes the gas 39 which heats up in the exchanger E3 by passing through it from the cold end to the hot end.

[0060] The liquid 35 from the separator is vaporized in an exchanger E6 and joins the separator 37.

[0061] The molar flow rate D of the second intermediate fluid 39 and the molar flow rate D1 of the fraction 3 of the first intermediate fluid exchanging heat with the first flow rate of liquefied natural gas are chosen so that 0.9D <D1<1,3D.

[0062] The first and / or second intermediate fluid 9, 39 contains at least 50 mol% nitrogen, or even at least 90 mol% nitrogen, or even 99 mol% nitrogen.

[0063] The first and / or second intermediate fluid 9, 39 remains in the gaseous state during any cooling of the process.

[0064] A flow 41, 43 having the same composition as the intermediate fluid 9, 11 is cooled to a temperature between -120°C and -160°C and provides cold to a liquefaction or separation unit operating at a temperature between -120°C and -160°C, for example an air separation apparatus or a hydrogen liquefier E3 27. a flow having the same composition as the intermediate fluid is cooled to a temperature between -135°C and -155°C and provides cold to a liquefaction or separation unit operating at a temperature between -135°C and -155°C, to solidify a portion of gas rich in liquefied carbon dioxide.

[0065] The methane-rich fluid 1 is a methane-rich liquid which may be preheated before cooling the intermediate fluid 5 of step a) by heat exchange with at least one other flow of intermediate fluid or glycolated water.

[0066] For all figures, the temperature difference of the heat exchanger E2 at the hot end is between 2 and 10°C and the temperature difference of the heat exchanger E2 preferably does not exceed 25°C.

[0067] The intermediate fluid cycle does not include a phase change to transfer the cold from the natural gas, liquefied or not, to the gas to be liquefied. Thus, the intermediate fluid remains gaseous throughout the cycle and in particular the intermediate fluid remains gaseous during the heat exchange with the methane-rich fluid and does not condense.

Claims

A method for liquefying and / or solidifying a carbon dioxide-rich gas (13) in which at least part of the frigories for liquefaction and / or solidification are provided by a low-temperature methane-rich fluid (1) in which:a) the methane-rich fluid is a methane-rich liquid, for example liquefied natural gas or methane-rich gas at a temperature below -50°C, the methane-rich fluid cools an intermediate fluid (5) at a pressure between 5 and 40 bara to a first temperature between -30°C and -100°Cb) the intermediate fluid is compressed (C, C1) in gaseous form before or after cooling to the first temperature and sent to a heat exchanger (E2) at a second temperature between -30°C and -80°C,preferably between -50°C and -55°C where it heats up by indirect heat exchange with the carbon dioxide-rich gas which at least partially condenses and / or solidifiesc) the intermediate fluid heated in the heat exchanger is divided into two, a part (11) of the fluid leaving the heat exchanger at a temperature which differs by at most 10°C from the dew point temperature of the carbon dioxide-rich gas to be at least partially condensed and which is at least 15°C lower than the temperature at which the carbon dioxide-rich gas enters the heat exchanger at a first end thereof, this part constituting at least 50%, or even at least 70%,of the intermediate fluid entering the heat exchanger andthe portion constituting at least 50% of the intermediate fluid is not reheated in the heat exchanger andi) is not reheated outside the heat exchanger orii) is reheated outside the heat exchanger by cooling a refrigerant (19) and / or the carbon dioxide-rich gase) another portion of the intermediate fluid (9) is reheated up to the first end of the heat exchanger andf) the portion constituting at least 50% of the intermediate fluid and the other portion are mixed and returned to be cooled by the methane-rich fluid of step a), the intermediate fluid remaining gaseous during the heat exchange with the methane-rich fluid and the intermediate fluid cycle not including a phase change., Method according to claim 1 in which at least part of the intermediate fluid compressed and heated in the exchanger is expanded in a turbine (T) to a temperature between -30°C and -80°C, preferably between -50°C and -55°C, and returned to the heat exchanger (E2) to be heated and divided into two according to step c). Method according to claim 2 in which intermediate fluid expanded in the turbine (T) is reheated in the heat exchanger (E2), then expanded in another turbine to a temperature between -30°C and -80°C, preferably between -50°C and -55°C, and returned to the heat exchanger to be reheated and divided into two according to step c). A method according to any preceding claim wherein the CO2-rich gas (13) is a waste gas from a pressure swing adsorption process producing a gas enriched in hydrogen relative to the gas feeding the adsorption process and the waste gas depleted in hydrogen relative to the gas feeding the adsorption process. Method according to one of the preceding claims in which the intermediate fluid (9, 11) contains at least 90 mol% of nitrogen or methane or is a mixed refrigerant comprising at least nitrogen, methane and ethane and / or ethylene. Method according to one of the preceding claims in which the flow rate of intermediate fluid (5) is between 10D / L and 25D / L where D is the flow rate of carbon dioxide-rich gas (13) sent to the heat exchanger (E2) in Nm3 / h and L is the number of intermediate fluid flows in the heat exchanger. Method according to one of the preceding claims in which the carbon dioxide-rich gas is compressed in a compressor (V1, V2, C3, C4, C5) upstream of the heat exchanger having at least two stages and an interstage cooler (E5) cooled either by a / the intermediate fluid portion or by the water (19) which has been cooled by the intermediate fluid portion (11). A method according to claim 7 wherein an interstage cooler (E5) cooled by a / the intermediate fluid portion (11) to less than -55°C cools a carbon dioxide rich gas to a pressure below 5.1 bar abs. Method according to one of the preceding claims in which the carbon dioxide-rich gas (13) is cooled in a cooler (E6) then purified of water (P) upstream of the heat exchanger (E2) and the part of the intermediate fluid (11) is used to cool the carbon dioxide-rich gas. Method according to one of the preceding claims in which a flow having the same composition (41, 43) as the intermediate fluid is cooled to a temperature between -120°C and -160°C and provides cold to a liquefaction or separation unit (300) operating at a temperature between -120°C and -160°C, for example an air separation apparatus or a hydrogen liquefier (27). Method according to one of the preceding claims in which a flow having the same composition (41, 43) as the intermediate fluid is cooled to a temperature between -135°C and -155°C and provides cold to a liquefaction or separation unit operating at a temperature between -135°C and -155°C, to solidify a portion of gas (27) rich in liquefied carbon dioxide. Method according to one of the preceding claims in which the methane-rich fluid is a methane-rich liquid (1) which is preheated before cooling the intermediate fluid (5) of step a) by heat exchange with at least one other flow of intermediate fluid or glycolated water. Method according to one of the preceding claims in which the compression (C, C1) of step b) raises the pressure of the intermediate fluid so that the intermediate fluid which heats up in the heat exchanger (E2) leaves the exchanger and is divided while it is at a pressure substantially equal to that of the fluid upstream of the compression of step b). Method according to one of the preceding claims in which the intermediate fluid (5) is a gas and is not condensed by heat exchange with the methane-rich fluid (1). Method according to one of the preceding claims in which the heat exchanger (E2) is a brazed plate and fin exchanger.

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