Coupling secondary-refrigerant and heat-transfer effects in a method and a device for treating flue gases

Abstract

The invention relates to a method using a liquid transfer fluid whereof the triple point is lower than -125°C, such as isopentane, in order to recover the cold energy from the sublimation and melting of substances frozen on exchanger surfaces, and more specifically CO2. The same transfer fluid circulates in two coupled circuits; one is purely a secondary refrigerant, while the other is a heat-transfer fluid when it performs de-icing operations and a secondary refrigerant for transferring the refrigerating power recovered during de-icing operations.

Description

[0001] COUPLING OF COOLANT AND HEAT TRANSFER EFFECTS IN A PROCESS AND DEVICE FOR TREATING SMOKE

[0002] Technical field

[0003] The invention relates to the treatment of fumes containing water vapor and carbon dioxide, and possibly nitrogen oxide.

[0004] State of the art

[0005] The recovery of carbon dioxide CO2 for reuse or geological storage has become a major objective to limit the increase in CO2 concentrations in the atmosphere.

[0006] Many gas mixtures containing high concentrations of CO2 must be treated at their emission sources.

[0007] The main gas mixtures to be treated are:

[0008] - biogas, which can contain 30 to 50% CO2 by volume,

[0009] - synthesis gases from biomass gasification, which may contain 25 to 35% CO2 by volume,

[0010] - combustion fumes from energy production plants (natural gas, wood, coal, fuel oil), which may contain CO2 with volume concentrations ranging from 10 to 15%,

[0011] - fumes from industrial processes for the production of glass, lime, cement and steel, which can have CO2 volume concentrations ranging from 10 to 40%.

[0012] Note that all these gas mixtures also contain water vapor. Industrial fumes typically contain 10 to 35% CO2 and 5 to 15% water vapor.

[0013] The flow rates of the fumes to be treated typically vary from 50,000 to 1 million Nm 3 / h . Cryogenic CO2 icing processes require surfaces that number in the thousands of m 2 for such smoke flow rates.

[0014] These exchange surfaces are distributed over several dozen or even several hundred exchangers which operate according to CO2 icing and defrosting cycles.

[0015] In the energy balance, condensation and then freezing of the water represents 10 to 25% of the energy requirements, when these fumes are cooled from 50°C to -40°C.

[0016] Cooling and freezing CO2 from -90°C to -120°C represents an energy expenditure of around 45 to 55% of the total energy consumption, the 100% loop is the cooling of nitrogen.

[0017] Processes that frost and defrost CO2, as described for example in W002 / 060561 (Armines, 2002), must recover the sublimation energy of carbon dioxide, to minimize their energy consumption associated with CO2 frosting.

[0018] In the state of the art, the sublimation energy of CO2 is recovered in various processes, either in a liquid and solid mixture as described in documents WO201 2 / 061 544 (Battelle, 2012) or US2012 / 0103561 (Battelle, 2012), or by a refrigerant fluid as described in document US6082133 (Cryo Fuel Systems, 2000), or under low pressure as described in document WO2016 / 1 62643 (Cryo Pur, 201 6).

[0019] Freezing CO2 at a pressure below its triple point, which is 520 kPa and -56.5°C, requires energy ranging from 550 to 595 kJ / kg, depending on the antisublimation temperature.

[0020] Antisublimation here refers to the direct transition from the gas phase to the solid phase. The parameters influencing the capture of carbon dioxide by antisublimation are the subject of modeling attempts, see for example Tian et al. Energy Engineering 2020, 1 17(5), 267-277. https: / / d0i.0rg / l 0.32604 / EE.2020.01 1440; Ababneh et al. Processes, Vol 10, Iss 2406, p 2406 (2022) DOI: 10.3390 / pr101 12406.

[0021] The sublimation and fusion of CO2 represents an energy of the order of 200 to 220 kJ / kg. Purpose of the invention

[0022] An object of the invention is to solve the problem of high energy efficiency management of CO2 icing and defrosting cycles, but also of substances such as water H2O or nitrogen dioxide NO2, whatever the flow rates, and advantageously for high flow rates.

[0023] General presentation of the invention

[0024] The invention proposes the recovery of cold energy by a transfer fluid playing the dual role of refrigerant and heat transfer fluid, to recover energy from very low temperatures, of the order of - 150°C, and this up to ambient temperature.

[0025] Such fluids are hydrocarbons that are liquid at room temperature, such as isopentane (2-methylbutane, CAS 78-78-4) or isohexane (2-methylpentane, CAS 107-83-5), and whose triple point temperature is lower than -125°C and preferably lower than -150°C. According to Tan et al., the triple point temperature of 2-methylbutane is 117 K, or about -156°C (Journal of thermal analysis. June 1994 41 (6): 1577-1592 DOT. 10. 1007 / bf02549956). According to Douslin et al. , the triple point temperature of 2-methylpentane is 1 1 9 K, or about - 154°C (Douslin, DR; Huffman, HM, Low-Temperature Thermal Data on the Five Isomeric Hexanes, J. Am. Chem. Soc., 1946, 68, 1704, doi.org / 10. 1021 / ja01213a006).

[0026] The invention proposes the coupling of two circuits, one refrigerant and the other heat transfer and refrigerant, using the same transfer fluid, whose triple point is advantageously less than -125°C, and even more advantageously less than -150°C, such as for example isopentane whose triple point is at -156°C, to recover the cold energy from the sublimation and fusion of CO2 and the cold energy of molecules such as nitrous oxide N2O, nitrogen dioxide NO2 and water when they are present in the gas mixture to be treated by cold. The refrigerant fluid is cooled to the lowest temperature level. The heat transfer and refrigerant fluid recovers cold energy from defrosting (and then functions as a heat transfer fluid) and transmits this cold energy at a higher temperature (and then functions as a refrigerant).

[0027] It is further proposed that energy recovery be carried out by a process operating alternately on at least one pair of exchangers, one operating in icing and the other in defrosting of CO2. Depending on the size of the installation, there may be tens or even several hundred pairs of exchangers operating in parallel and alternately.

[0028] It is further proposed that the energy recovery is also carried out by a process operating alternately on at least one pair of exchangers, one operating in icing and the other in defrosting the water.

[0029] It is also proposed that the energy recovery is carried out by a process operating alternately on at least one pair of exchangers, one operating in icing and the other in defrosting of nitrogen dioxide NO2 or nitrous oxide N2O.

[0030] For these purposes, there is proposed, according to a first aspect, a method for treating fumes containing water vapor and carbon dioxide and optionally a nitrogen oxide, the method comprising a first step of cooling the fumes to be treated, by icing the water and optionally nitrogen dioxide NO2, this first step producing cooled fumes, the method comprising a second step of cooling and dehumidifying the cooled fumes, by icing the water contained in these cooled fumes, this second step producing dehumidified fumes, the method comprising a third step of cooling and decarbonizing the dehumidified fumes, by icing the carbon dioxide into dry ice and optionally a nitrogen oxide contained in the dehumidified fumes, each of the three steps of treating the fumes being carried out by an exchanger of a pair of exchangers, a transfer fluid circulating in each exchanger,each exchanger of a pair of exchangers being in frosting mode for cooling the fumes while the other exchanger is in defrosting mode for the water ice or dry ice formed during a cooling step carried out previously, the transfer fluid being a coolant in the exchangers in frosting mode, the transfer fluid being a heat transfer fluid in the exchangers in defrosting mode, the transfer fluid recovering the cold energy from sublimation and fusion of the dry ice obtained in the third cooling and decarbonization step and transferring this cold energy for cooling the fumes in the first treatment step, the transfer fluid having a triple point whose temperature is lower than - 125°C.,

[0031] Advantageously, the transfer fluid comprises isopentane or isohexane.

[0032] Advantageously, the transfer fluid circulates in a refrigerant circuit and a transfer fluid (advantageously the same transfer fluid) circulates in a heat transfer / refrigerant circuit, the heat transfer / refrigerant circuit recovering the cold energy from sublimation and fusion of the dry ice obtained in the third cooling and decarbonization stage and transferring this cold energy for cooling the fumes in the first treatment stage.

[0033] In certain implementations, the method comprises a step of measuring the carbon dioxide concentration in the fumes to be treated and cooled in the first treatment step; a step of comparing the measured carbon dioxide concentration with a threshold value, a predetermined flow rate of the heat transfer / coolant circuit providing cooling power to cool the fumes to a target temperature in the first cooling step for this threshold value; a step of mixing the transfer fluid of the coolant circuit and the transfer fluid of the coolant / heat transfer circuit, when the measured carbon dioxide concentration is lower than the threshold value, the flow rate of the mixture obtained being substantially equal to the predetermined flow rate.

[0034] Advantageously, for the exchangers of the third stage of cooling and decarbonization of the fumes, the transfer fluid of the heat transfer / refrigerant circuit circulates on an exchanger alternately with the transfer fluid of the refrigerant circuit, the transfer fluid of the refrigerant circuit ensuring the cooling of the fumes and the icing of the carbon dioxide in the exchanger, the transfer fluid of the heat transfer / refrigerant circuit ensuring the defrosting of the carbon dioxide in the exchanger.

[0035] Advantageously, for the exchangers of the first stage of cooling of the fumes to be treated, the transfer fluid of the heat transfer / coolant circuit circulates on an exchanger in alternation with the transfer fluid of the coolant circuit, the transfer fluid of the coolant circuit partially or not ensuring the cooling of the fumes and the frosting of the water into water ice in the exchanger, the transfer fluid of the heat transfer / coolant circuit partially or totally ensuring the cooling of the fumes and the frosting of the water, and then being a coolant by transfer of the frigories recovered during the defrosting of the carbon dioxide during the third stage, the transfer fluid of the coolant / heat transfer circuit also being a heat transfer during the defrosting of the water ice in the exchanger.

[0036] Advantageously, for the exchangers of the second stage of cooling and dehumidification of the fumes, the transfer fluid of the heat transfer / refrigerant circuit circulates on an exchanger alternately with the transfer fluid of the refrigerant circuit, the transfer fluid of the refrigerant circuit ensuring the cooling of the fumes and the frosting of the water into water ice in the exchanger, the transfer fluid of the heat transfer / refrigerant circuit ensuring the defrosting of the water ice in the exchanger.

[0037] Advantageously, the same transfer fluid circulates in the refrigerant circuit and the heat transfer / refrigerant circuit.

[0038] According to a second aspect, there is provided a device for treating fumes containing water vapor and carbon dioxide and possibly a nitrogen oxide, the device comprising a first pair of exchangers for a first step of cooling the fumes to be treated, by icing the water, this first step producing cooled fumes, the device comprising a second pair of exchangers for a second step of cooling and dehumidification of the cooled fumes, by icing the water and possibly the nitrogen dioxide NO2 contained in these cooled fumes, this second step producing dehumidified fumes, the device comprising a third pair of exchangers, for a third step of cooling and decarbonization of the dehumidified fumes, by icing the carbon dioxide into dry ice and possibly a nitrogen oxide contained in the dehumidified fumes,a transfer fluid circulating in each exchanger, each exchanger of a pair of exchangers being in frosting mode for cooling the fumes while the other exchanger is in defrosting mode for the water ice or dry ice formed during a cooling step carried out previously, the transfer fluid being a coolant in the exchangers in frosting mode, the transfer fluid being a heat transfer fluid in the exchangers in defrosting mode, the transfer fluid recovering the cold energy from sublimation and fusion of the dry ice obtained in the third cooling and decarbonization step and transferring this cold energy for cooling the fumes in the first treatment step, the transfer fluid having a triple point whose temperature is lower than -125°C.,

[0039] Advantageously, the device comprises a refrigerant circuit in which a transfer fluid circulates, and a heat transfer / refrigerant circuit in which a transfer fluid circulates (advantageously the same transfer fluid), the heat transfer / refrigerant circuit recovering the cold energy from sublimation and fusion of the dry ice obtained in the third cooling and decarbonization stage and transferring this cold energy for cooling the fumes in the first treatment stage.

[0040] Advantageously, the device comprises means for measuring the carbon dioxide concentration in the fumes to be treated and cooled in the first pair of exchangers, at the first treatment stage; means for comparing the measured carbon dioxide concentration with a threshold value, a predetermined flow rate of the heat pump / cooler circuit providing cooling power to cool the fumes to a target temperature at the first cooling stage for this threshold value; means for mixing the transfer fluid of the refrigerant circuit and the transfer fluid of the refrigerant / heat transfer circuit, when the measured carbon dioxide concentration is lower than the threshold value, the flow rate of the mixture obtained being substantially equal to the predetermined flow rate.

[0041] Advantageously, the transfer fluid comprises isopentane or isohexane.

[0042] Advantageously, the same transfer fluid circulates in the refrigerant circuit and the heat transfer / refrigerant circuit.

[0043] Other objects and advantages of the invention will appear during the following description of embodiments, a description which will be carried out with reference to the appended figures in which

[0044] - Figure 1 is a schematic representation of a flue gas cooling and water vapour icing and defrosting installation, then carbon dioxide, the installation comprising a refrigerant circuit and a heat transfer / refrigerant circuit;

[0045] - figure 2 is a schematic representation of the installation shown in figure 1, certain elements of the refrigerant circuit being omitted, for the sake of simplification, figure 2 detailing certain elements of the heat transfer / refrigerant circuit.

[0046] In the following description, the temperature values ​​correspond to an example of decarbonation of flue gases containing 30% by mass of CO2 and 70% of nitrogen, which corresponds to volume concentrations of 21.5% in carbon dioxide CO2 and therefore 78.5% in nitrogen.

[0047] The installation shown in the figures allows, on a circuit 700, the cooling of such fumes and the icing and defrosting of the water vapor, then of the carbon dioxide. In the description, the terms upstream and downstream are used in reference to the direction of circulation of the fluids, this direction of circulation being made apparent by arrows placed on the conduits of the different circuits of the installation, the conduits being represented in the form of lines.

[0048] The installation includes a refrigerant circuit 10 and a heat transfer / refrigerant circuit 20.

[0049] The use of the “ / ” sign means that the fluid circulating in the circuit 20 has a function of heat transfer fluid or refrigerant fluid, depending on the operating mode of the installation.

[0050] The circuit 700 is partially shown, so that the refrigerant circuit 10 and the heat transfer / refrigerant circuit 20 are clearly visible.

[0051] The installation shown in the attached figure 1 comprises two exchangers 1 10, 1 1 2 for cooling the fumes and icing the water.

[0052] The fumes to be cooled enter alternately via lines 701 and 702 into an enclosure 109 or 111 containing the exchangers 110, 112 respectively.

[0053] The installation includes two exchangers 1 06, 1 08 for further cooling of the fumes which have left either the exchanger 1 1 0 or the exchanger 1 12.

[0054] The fumes leaving the exchanger 110 or the exchanger 112 enter alternately via the lines 705 or 706 into an enclosure 104 or 107 containing the exchangers 106, 108 respectively.

[0055] The installation comprises two exchangers 101, 103 for cooling and decarbonizing the dehumidified fumes. Decarbonization here means the reduction of greenhouse gases contained in the fumes, in particular carbon dioxide. The fumes to be cooled and decarbonized enter alternately via lines 709 and 710 into an enclosure 100 or 102 containing the exchangers 101, 103 respectively.

[0056] The refrigerant fluid entering the exchangers 101, 103, 106, 108, 110, 112 (hereinafter referred to as evaporators 101, 103, 106, 108, 110, 112) comes from the refrigerant circuit 10.

[0057] On the circuit 10, the entry of the refrigerant into the evaporator 101 or the evaporator 103 is controlled by a solenoid valve 121 arranged on an inlet line 11 of the evaporator 101, and a solenoid valve 123 arranged on an inlet line 12 of the evaporator 103. The exit of the refrigerant from the evaporator 101 is controlled by a solenoid valve 1110. The exit of the refrigerant from the evaporator 103 is controlled by a solenoid valve 1111. The conduits carrying the outlet solenoid valves 1110, 1111 of the evaporators 101, 103 join on a common branch 13.

[0058] In the circuit 10, the circulation of the refrigerant fluid in the evaporator 106 or in the evaporator 108, from the common branch 13, is controlled by a solenoid valve 1112 arranged on an inlet line 14 of the evaporator 106, and a solenoid valve 1113 arranged on an inlet line 15 in the evaporator 108. The outlet of the refrigerant fluid from the evaporator 106 is controlled by a solenoid valve 1114 arranged on an outlet branch 16 of the evaporator 106. The outlet of the refrigerant fluid from the evaporator 108 is controlled by a solenoid valve 1115 arranged on an outlet branch 17 of the evaporator 108. The outlet branches 16 and 17 of the evaporators 106, 108 join on a common branch 19.

[0059] On the circuit 10, the circulation of the refrigerant fluid in the evaporator 110 or in the evaporator 112, from the common branch 19, is controlled by two solenoid valves, namely a solenoid valve 1118 on an inlet branch 29 in the evaporator 110, and a solenoid valve 1119 on an inlet branch 21 in the evaporator 112. The outlet of the refrigerant fluid from the evaporator 110 is controlled by a solenoid valve 1120. The outlet of the refrigerant fluid from the evaporator 112 is controlled by a solenoid valve 1121. The conduits carrying the solenoid valves 1120, 1121 join in a common branch 22.

[0060] The refrigerant circuit 10 comprises, downstream of the common branch 22, a counter-current refrigerant exchanger 30, and a pump 1 circulating the refrigerant fluid.

[0061] The refrigerant circuit 10 comprises, downstream of the refrigerant exchanger 30, a counter-current refrigerant exchanger 40.

[0062] Two probes 136, 137 allow the temperature of the refrigerant fluid to be measured at the inlet and outlet of the refrigeration exchanger 30.

[0063] Two probes 138, 120 allow the temperature of the refrigerant fluid at the inlet and outlet of the refrigeration exchanger 40 to be measured.

[0064] The installation includes a heat transfer / coolant circuit 20.

[0065] Circuit 20 includes a pump 2 circulating a transfer fluid.

[0066] The circuit 20 conveys the transfer fluid to the inlet of the evaporator 103, via a connection to the refrigerant circuit 10, on the inlet line 12 of the evaporator 103.

[0067] The entry of the transfer fluid into the evaporator 103 is controlled by a solenoid valve 204 placed on a branch 202 of the circuit 20, upstream of a connection between the circuits 10, 20.

[0068] The circuit 20 conveys the transfer fluid to the inlet of the evaporator 101, via a connection to the refrigerant circuit 10, on the inlet line 11 of the evaporator 101.

[0069] The entry of the transfer fluid into the evaporator 101 is controlled by a solenoid valve 203, placed on a branch 201 of the circuit 20, upstream of a connection between the circuits 10, 20. The circulation of the transfer fluid in the evaporators 101, 103 allows them to be defrosted, the transfer fluid is then a heat transfer fluid circulating at the outlet of the evaporators 101, 103 via outlet branches 223 and 224, a solenoid valve 221 and 222 being placed on each of these two outlet branches 223, 224.

[0070] The outlet branches 223, 224 of the evaporators 101, 103 are connected to a common line 24. A solenoid valve 225 is placed on this common line 24, between the junction point with the outlet branch 223 and the junction point with the outlet branch 224.

[0071] When the transfer fluid leaves the evaporator 101, the solenoid valves 1110 and 225 are closed, and the solenoid valve 221 is open, the transfer fluid leaving the evaporator 101 via the branch 223 and being sent to a reservoir 28 via the common branch 24.

[0072] When the transfer fluid leaves the evaporator 103, the solenoid valves 221 and 1111 are closed, and the solenoid valves 222 and 225 are open, the transfer fluid leaving the evaporator 103 via the branch 224 and being sent to the reservoir 28 via the common branch 24.

[0073] The tank 28 is connected by a line 23 to the common branch 19 of the circuit 10.

[0074] A solenoid valve 231 is placed on line 23.

[0075] The circuit 20 thus conveys the transfer fluid to the inlet of the evaporator 110, or of the evaporator 112.

[0076] The entry of the transfer fluid into the evaporator 1 10 is controlled by the solenoid valve 1 1 1 8 placed on the branch 29 of the circuit 10, the transfer fluid leaving the tank 28 via the branch 23, the valve 231 being open.

[0077] The entry of the transfer fluid coming from branch 23 into the evaporator 1 1 2 is controlled by the solenoid valve 1 1 1 9 placed on branch 21 of the circuit 10, the transfer fluid leaving the tank 28 via branch 23, the valve 231 being open.

[0078] The circulation of the transfer fluid in the evaporators 110, 112 allows them to be frosted, the transfer fluid then acting as a refrigerant fluid, the transfer fluid circulating at the outlet of the evaporators 110, 112 on a common line 25.

[0079] A solenoid valve 215 is arranged on an outlet branch 213 of the evaporator 112. A solenoid valve 216 is arranged on an outlet branch 214 of the evaporator 110. The two outlet branches 213, 214 of the evaporators 110, 112 are connected to the common line 25.

[0080] When the transfer fluid leaves the evaporator 110, the solenoid valve

[0081] 1120 of circuit 10 is closed, and solenoid valve 216 placed on branch 214 of circuit 20 is open.

[0082] When the transfer fluid leaves the evaporator 112, the solenoid valve

[0083] 1121 of circuit 10 is closed, and solenoid valve 215 placed on branch 213 of circuit 20 is open.

[0084] The heat transfer / refrigerant circuit 20 comprises a refrigeration system 50, and a flow meter 200.

[0085] The flue gas inlet temperatures of each exchanger 101, 103, 106, 108, 110, 112 are measured by probes 78, 79, 74, 75, 70, 71 carried by the lines or pipes 709, 710, 705, 706, 701, 702.

[0086] The flue gas outlet temperatures of each exchanger 101, 103, 106, 108, 110, 112 are measured by probes 80, 81, 76, 77, 72, 73 carried by pipes 711, 712, 707, 708, 703, 704.

[0087] The inlet temperatures of transfer fluid or refrigerant fluid in the enclosures 100, 102, 104, 107, 109, 111 of the exchangers 101, 103, 106, 108, 110, 112 are measured by probes 122 (on branch 11), 124 (on branch 12), 127 (on branch 14), 128 (on branch 15), 131 (on branch 29), 132 (on branch 21). The temperatures of the transfer fluid or refrigerant fluid leaving the enclosures 100, 102, 104, 107, 109, 111 of the exchangers 101, 103, 106, 108, 110, 112 are measured by probes 125, 126, 129 (on branch 16), 130 (on branch 17), 133, 134.

[0088] A regulating solenoid valve 1000 is arranged on the common branch 19, between the junction of the common branch 19 with the line 23 and the junction of the common branch 19 with a branch 18 connecting to the common branch 22.

[0089] A solenoid valve 1 1 17 is placed on the connecting branch 18.

[0090] The operation of the refrigerant circuit 10 on the one hand and of the heat transfer / refrigerant circuit 20 on the other hand, will be described in detail, with reference to FIG. 1, showing the circulations of the same transfer fluid in these two circuits 10, 20.

[0091] In a first operating mode of the installation, the exchanger 101 operates in CO2 frosting mode and the exchanger 103 in defrosting mode.

[0092] The icing of the CO2 is linked to the circulation of the refrigerant fluid of the circuit 10 in the exchanger 101, and the defrosting of the CO2 is linked to the circulation in the exchanger 103 of the fluid of the refrigerant / heat transfer circuit 20, this fluid acting as a heat transfer fluid. This operating mode allows the recovery of the cold energy from the defrosting of the CO2 by the heat transfer / refrigerant circuit 20 coupled to the refrigerant circuit 10.

[0093] In a second operating mode (presented later with reference to figure 2), the defrosting of the water ice by the heat transfer / refrigerant circuit 20 will be described.

[0094] The fumes are cooled by the exchanger 1 1 0 or the exchanger 1 1 2, depending on the water frosting and defrosting cycles. In cooling mode, the fumes to be treated enter the enclosure 1 1 1 which contains the cooling exchanger 1 12 via the pipe 701, and leave the enclosure 1 1 1, via the pipe 703, or the fumes to be treated enter via the pipe 702 into the enclosure 109 which contains the cooling exchanger 1 1 0 and leave the enclosure 109 via the pipe 704.

[0095] The fumes to be treated enter the enclosure 111 or the enclosure 109 advantageously at a temperature of 2°C, and leave the enclosure 111 or the enclosure 109 advantageously at a temperature of -52°C. As indicated previously, the temperature values ​​mentioned here correspond to an example of decarbonization of fumes containing 30% by mass of CO2 and 70% of nitrogen, which corresponds to volume concentrations of 21.5% in carbon dioxide CO2 and therefore 78.5% in nitrogen.

[0096] Then, the fumes leaving the enclosure 109 or 111 are cooled, advantageously from -52°C to -90°C, by the exchanger 106 contained in the enclosure 104 or by the exchanger 108 contained in the enclosure 107, according to the water frosting and defrosting cycles.

[0097] Finally, the fumes, preferably very dehumidified, advantageously around 0.1 ppm(v), leaving the exchanger 106 or the exchanger 108 are cooled, advantageously from -90°C to -120°C, by the exchanger 101 contained in the enclosure 100 or by the exchanger 103, contained in the enclosure 102 operating in CO2 frosting mode.

[0098] The fumes enter the exchanger 103 via the pipe 709, advantageously at a temperature of -90°C, and leave the exchanger 103, advantageously at a temperature of -120°C, via the pipe 711, or the fumes enter the exchanger 101 via the pipe 710 and leave the exchanger 101 via the pipe 712.

[0099] The progressive cooling of the fumes, advantageously down to a temperature of -120°C, leads to their dehumidification, and their decarbonation is carried out on the circuit 700 by the different branches 701-712. The operation of an installation as shown in figure 1 is described below, coupling a refrigerant circuit 10 and a heat transfer / refrigerant circuit 20, the two circuits 10, 20 operating advantageously with the same transfer fluid, in particular advantageously isopentane.

[0100] The refrigerant circuit 10 is circulated by pump 1.

[0101] The refrigerant, the temperature of which is measured by the probe 138, downstream of the pump 1, then enters an evaporator 4 of the refrigeration circuit 40, advantageously at a temperature of -95°C, and leaves the evaporator 4 at a temperature advantageously of -125°C, this outlet temperature being measured by the probe 120.

[0102] The refrigeration circuit 40 cools the refrigerant counter-currently with the start of evaporation, advantageously at -128°C, this temperature being measured by a probe 41, the refrigerant leaving the evaporator 4 advantageously at a temperature of -98°C, this outlet temperature being measured by a probe 42.

[0103] Depending on the CO2 frosting cycle, the refrigerant enters either the exchanger 101, contained in the enclosure 100, or the exchanger 103, contained in the enclosure 102.

[0104] When the refrigerant circulates in the exchanger 103, the solenoid valves 123 and 1111 placed at the inlet and outlet of the exchanger 103 are open, and the solenoid valves 121, 1110 and 221 placed at the inlet and outlet of the exchanger 101 are closed, the refrigerant entering the evaporator 103 via the branch 12, advantageously at -125°C, this inlet temperature being measured by the probe 124.

[0105] The refrigerant cools the fumes and frosts the CO2 in exchanger 103.

[0106] The typical duration of the frosting cycle is advantageously one hour. The refrigerant leaves the evaporator 103, advantageously at a temperature of -95°C, this outlet temperature being measured by the probe 126, and joins the common branch 13, via the solenoid valve 1111.

[0107] The refrigerant then enters the exchanger 108, advantageously at a temperature of -95°C, this inlet temperature being measured by the probe 128, the exchanger 108 being integrated into the enclosure 107 where the fumes are cooled, advantageously to a temperature of -90°C.

[0108] The duration of the water vapor frosting cycle is advantageously of the order of 48 hours, taking into account the low humidity content at the inlet of the fumes in pipe 705, a value of 30 ppm corresponding to the saturated humidity at -52°C.

[0109] The refrigerant leaves the exchanger 108, advantageously at a temperature of -57°C, this outlet temperature being measured by the probe 130.

[0110] The refrigerant joins, via branch 17, the common branch 19, the valve 1115 being open. The regulating valve 1000 is closed, the solenoid valve 1117 placed on the connecting branch 18 is open.

[0111] Advantageously, the refrigerant does not enter the common branch 19 when the volume concentration of CO2 in the fumes to be treated is greater than or equal to 21.5%, a value which allows the heat transfer fluid / refrigerant loop 20 to provide all of the refrigerating power to cool the fumes down to -52°C in the exchangers 1 1 0, 1 1 2.

[0112] Advantageously, the regulating valve 1000 opens for CO2 concentrations of less than 21.5% in the fumes to be treated, to allow mixing in the common branch 19 of the coolant coming from branch 17 with the heat transfer fluid / coolant coming from branch 23, and this to ensure temperature control, advantageously at a value of the order of -54°C, if the heat flow rate at -54°C of the heat transfer fluid / coolant in branch 23 is insufficient. When the heat flow rate of the heat transfer fluid / coolant is sufficient, as indicated, the coolant does not pass into the common branch 19 (the regulating valve 1000 being closed).The refrigerant then passes through the connecting branch 18, is sucked in by the pump 1 and cooled in the refrigerant exchanger 30, advantageously from an inlet temperature of -54°C, this temperature being measured by the probe 136, to an outlet temperature of -95°C, this outlet temperature being measured by the probe 137.

[0113] The refrigeration exchanger 30 is counter-current, with an inlet temperature, advantageously at -98°C, measured by a probe 31 and an outlet temperature, advantageously at -59°C, measured by a probe 32.

[0114] The pump 2 of the heat transfer / coolant circuit 20 advantageously circulates the same transfer fluid, advantageously isopentane, the two circuits 10, 20 circulating alternately in the same exchangers 101, 103 at each CO2 frosting and defrosting cycle.

[0115] If the heat flow of the heat transfer fluid / refrigerant must be supplemented, the control solenoid valve 1 1 20 (when the exchanger 1 1 0 is in water frosting mode) is opened or the control solenoid valve 1 1 21 (when the exchanger 1 12 is in water frosting mode) is opened, to allow the same flow rate to return to branch 1 9 of circuit 10 as the valve 1000 sent to one or other of this exchanger 1 1 0, 1 1 2 to ensure the temperature of -54°C measured by the probes 133 or 134.

[0116] By difference, the flow of the refrigerant / heat transfer fluid from circuit 20 returns to pump 2 via a branch 26.

[0117] The heat transfer / cooling circuit 20 is so named because it provides heat to defrost the CO2 from the exchangers 101 or 103 and produces cold on the exchangers 110 or 112. This gain allows the return temperature of the coolant on the branch 22 to be as low as possible, advantageously at -54°C, when the circuit 20 provides the entire cooling capacity of the exchangers 110 or 112, this is the indirect gain.

[0118] Circuit 20 is a refrigerant for cooling the fumes and icing the water in the exchangers 1 10, 1 12, this recovery of cold energy associated with the defrosting of the CO2, constitutes the direct gain.

[0119] The following description is made by following the circulation of the transfer fluid along the circuit 20, during the defrosting of the CO 2.

[0120] At the outlet of an exchanger 5 of the refrigeration circuit 50, the temperature measured by a probe 141 is advantageously -5°C, a temperature allowing the defrosting of the CO2.

[0121] The solenoid valve 203 of the branch 201 is open, as well as the solenoid valve 221 of the branch 223, the solenoid valve 204 of the branch 202 is closed as well as the solenoid valve 225 of the common branch 24, since the exchanger 103 is in frosting mode. The transfer fluid advantageously enters the exchanger 101 at -5°C, in defrosting mode, temperature measured by the probe 122, at the inlet of the exchanger 101, and the solenoid valves 121, 1110 and 204 are closed.

[0122] The exchanger 101, at the start of defrosting, is advantageously at an average temperature of -110°C, and the enclosure 100 has been placed under vacuum at the start of the CO2 defrosting cycle.

[0123] The transfer fluid cools by heating the exchanger, the CO2 sublimates, the pressure in the enclosure advantageously rises progressively to 520 kPa, which is the pressure of the triple point of CO2, then the CO2 passes from the solid phase to the gas phase at -56°C.

[0124] The transfer fluid exits through branch 223, via solenoid valve 221, and reaches reservoir 28 via common line 24.

[0125] Given that the sublimation of CO2 from -120°C to -56°C represents a third of the fusion energy, the average temperature of the transfer fluid in the reservoir 28 is of the order of -62°C, measured by two probes 2210 and 231 1, these two probes 2210, 231 1 being respectively placed at the inlet and outlet of the reservoir 28.

[0126] The storage of the transfer fluid in the tank 28 ensures a stable flow of the heat transfer fluid / coolant for the frosting operations of the exchangers 1 1 0 or 1 12.

[0127] With the solenoid valve 231 open, the transfer fluid leaving the tank 28 via the branch 23 then becomes a refrigerant.

[0128] This fluid joins branch 19 and will cool exchanger 1 1 0 because solenoid valve 1 1 1 8 of branch 29 is open and solenoid valve 1 1 1 9 of branch 21 is closed.

[0129] The exchanger 1 1 0 is advantageously a tube-fin exchanger, where the fumes circulating on the fins cool by 2°C, temperature measured by the probe 71, to advantageously -52°C, temperature measured by the probe 73.

[0130] The refrigerant, circulating in the tubes, advantageously enters at -64°C, temperature measured by probe 131, and advantageously leaves at -5°C, temperature measured by probe 133, and joins branch 25 via the regulating valve 21 6 which is open, the regulating valve 21 5 being closed.

[0131] The heat transfer fluid / refrigerant reaches pump 2 via line 26 and in this operating case, exchanger 5 does not need to cool the heat transfer fluid / refrigerant.

[0132] The refrigerant / heat transfer circuit 20 recovers the cold energy from defrosting the CO2 and transfers this energy to cool the fumes from 2°C to -52°C.

[0133] Advantageously, as soon as the volume concentration of CO2 is equal to or greater than 21.5% in the gas mixture to be treated, the heat flow rate of the heat transfer fluid / coolant from the cold energy recovered from the defrosting of the CO2 is sufficient to meet all the refrigeration requirements.

[0134] To give another example, if the volume concentration of CO2 is 14% in a mixture of gases to be treated, the heat transfer / refrigerant circuit 20 provides 60% of the refrigeration requirement from 2°C to -54°C; the additional 40% is provided by the refrigerant circuit 10.

[0135] In this case, the regulating valve 1000 is opened by a control system 800, so that the temperature measured by the probes 133 or 134 is controlled at -5°C.

[0136] The flow rate of pump 1 is regulated so as to ensure the cooling requirements of exchangers 101 or 102 and 106 or 108, in frosting mode.

[0137] The energy gains are significant, since the cooling power linked to the defrosting of the CO2 is recovered by the heat transfer fluid / refrigerant of circuit 20 at the level of cooling the gas mixture in the exchangers 1 1 0 or 1 12.

[0138] The operation of the refrigerant / heat transfer circuit 20 for, on the one hand, defrosting the exchangers 110, 112 for cooling the fumes and for icing the water in the exchangers 106, 108 on the other hand will be described with reference to Figure 2.

[0139] In Figure 2, the elements of the circuits 10, 20 in connection with the exchangers 101, 103 are not shown, for the sake of simplification.

[0140] In this figure 2 the circuit 20 represented in figure 1 is completed by three branches 27, 36 and 37.

[0141] Branch 27 of circuit 20 comprises a branch 209 for connection to branch 21 of circuit 10. A solenoid valve 1001 is arranged on the connection branch 209. Branch 27 of circuit 20 comprises a branch 210 for connection to branch 29 of circuit 10. A solenoid valve 1002 is arranged on the connection branch 210.

[0142] Upstream of the connection with branch 21 0, branch 27 of circuit 20 is connected to branch 26 and successively comprises a regulating solenoid valve 1003, an exchanger 8, and a pump 33.

[0143] Two probes 321, 322 make it possible to measure the temperature of the fluid at the inlet and outlet of the exchanger 8.

[0144] Pump 33 of branch 27 takes part of the return flow from line 26, this flow is regulated by the regulating solenoid valve 1003, the refrigerant / heat transfer fluid is reheated in the exchanger 8, advantageously up to 15°C, to alternately defrost the exchangers 110, 112.

[0145] The heat transfer flow is controlled by solenoid valve 1002 on branch 210 or by solenoid valve 1001 on branch 209 at the inlet of exchangers 110, 112, and is controlled at the outlet of exchangers 110, 112 by valve 216 on branch 214 or valve 215 on branch 213.

[0146] Branch 37 of circuit 20 comprises a branch 207 for connection to branch 15 of circuit 10. A solenoid valve 1006 is arranged on this connection branch 207.

[0147] Branch 37 of circuit 20 comprises a branch 208 for connection to branch 14 of circuit 10. A solenoid valve 1005 is arranged on this connection branch 208.

[0148] Upstream of the connection with branch 208, branch 37 of circuit 20 is connected to branch 26 and successively comprises a regulating solenoid valve 1004, an exchanger 7, and a pump 35.

[0149] Two probes 143, 144 make it possible to measure the temperature of the fluid at the inlet and outlet of the exchanger 7. The branch 36 of the circuit 20 comprises a branch 226 for connection to the circuit 10, at the outlet of the exchanger 108. A solenoid valve 212 is arranged on this branch 226.

[0150] Branch 36 of circuit 20 includes a branch 227 for connection to circuit 10, at the outlet of exchanger 106. A solenoid valve 211 is arranged on this branch 227.

[0151] Upstream of the connection with branch 227, branch 36 of circuit 20 is connected to branch 26.

[0152] Pump 35 of branch 37 takes part of the return flow from line 26, this flow is regulated by the regulating solenoid valve 1004, the refrigerant / heat transfer fluid is heated in the exchanger 7, advantageously up to 15°C, to alternately defrost the exchangers 106, 108.

[0153] The heat transfer flow is controlled by solenoid valve 1005 on branch 208 or by solenoid valve 1006 on branch 207 at the inlet of exchangers 106, 108 and is controlled at the outlet of exchangers 106, 108 by valve 211 on branch 227 and valve 212 on branch 226.

[0154] Branch 36 is the return branch of the heat transfer fluid to branch 26. This branch 36 is supplied by branch 227 when solenoid valve 21 1 is open during defrosting of exchanger 106, or by branch 226 when solenoid valve 21 2 is open during defrosting of exchanger 108.

[0155] Exchangers 7 and 8 are heated by a circuit 60, advantageously coming from an air cooler,

[0156] An exchanger 6 takes the heat from circuit 60 to a circuit 39 where a heat transfer fluid / coolant is circulated by a pump 34.

[0157] The outlet of the exchanger 7 is connected by a branch 38 to the inlet of the exchanger 8. Three solenoid valves 351, 352, 353 are arranged on the branch 38. The outlet of the exchanger 8 is connected by a branch 43 to the inlet of the exchanger 7. A solenoid valve 354 is arranged on the branch 43.

[0158] The circuit 60 is connected to the line 43 by a first branch, on which the pump 34 and a solenoid valve 341 are placed. The circuit 60 is connected to the line 43 by a second branch, on which a solenoid valve 342 is placed.

[0159] The set of valves 341, 342, 351, 352, 353, 354 makes it possible to supply exchanger 7 or exchanger 8 alternately.

[0160] Exchanger 1 1 2 is in defrost mode and exchanger 1 1 0 is in frost mode, as described previously.

[0161] The total flow rate of the heat transfer fluid / coolant must be doubled, since the circuit of branch 21 requires this additional flow rate by operating pump 33 of branch 27 for defrosting exchanger 1 12.

[0162] The exchanger 1 12 in defrost mode is advantageously initially at an average temperature of -27°C and the heat transfer fluid will gradually heat it and melt the water ice deposited on the fins of this exchanger.

[0163] When the defrost cycle of the exchanger 1 1 2 is initialized, triggered by exceeding the pressure drop threshold on the flue gas circuit measured by a differential pressure sensor (not shown), the control system 800 opens the regulating valve 1003 on the branch 27, and opens the valve 1 001 located on the branch 209, as well as the solenoid valve 21 5 located on the branch 213, the valve 1 002 being closed.

[0164] The control system 800 increases the flow rate of pump 2 by a factor of 2, which is verified by the flow meter 200. The branches 209 and 210 are then supplied by a similar flow rate, one refrigerant for branch 210, the other heat transfer fluid for branch 209.

[0165] A circuit 60 operating on an air cooler will provide the heat necessary for defrosting, by providing the necessary flow rate at 20°C, temperature measured by a temperature probe 61, and thus heat the heat transfer fluid, advantageously isopentane, from a variable temperature, advantageously -30°C, to a temperature advantageously of +15°C, measured by a probe 331.

[0166] The pump 34 circulates a suitable heat transfer medium, for example potassium acetate, at 20°C, on the exchanger 8, the two solenoid valves 352, 342 being open, the four solenoid valves 341, 351, 353 and 354 being closed.

[0167] Pump 33 of branch 27 is put into operation to suck the flow of heat transfer fluid, also regulated by the regulating valve 1003 set so as to pass half of the return flow to the exchanger 8.

[0168] The return to branch 25 is made via solenoid valve 21 5 of branch 213.

[0169] In defrosting mode of an exchanger 1 10, 1 12, the flow rate measured by the flow meter 200 of branch 26 is therefore double the flow rate without defrosting of these exchangers.

[0170] The cooling flow rate of the refrigeration circuit 50 is itself increased, to provide the refrigerating power at -10°C measured by a temperature probe 51, and advantageously comes out at +3°C, temperature measured by a probe 52, this probe serving as an indicator for the control system 800 to regulate the flow rate of the refrigeration system 50. The defrosting time of the exchangers 110 or 112 is advantageously short, of the order of half an hour, while the frosting time is of the order of 4 hours.

[0171] When the temperature of 15°C is reached, indicated by the probe 134, the control system 800 stops the pump 33, closes the control valves 1001 and 1003, closes the solenoid valve 215 and the flow rate of the pump 2 is reduced by a factor of 2.

[0172] The defrosting of exchangers 106 or 108 is carried out according to the same principle, but the defrosting advantageously takes place once every 48 hours and the control system 800 gives priority to the defrosting of exchangers 110 or 112, because exchangers 106 and 108 can wait, to avoid having two exchangers defrosting simultaneously on branch 26.

[0173] Advantageously, the exchanger 106 is in frosting mode, the exchanger 108 is in defrosting mode, its initial average temperature is approximately -70°C.

[0174] The heat transfer fluid, preferably isopentane, will heat this exchanger and melt the water ice deposited on the fins of this exchanger.

[0175] When the defrost cycle of the exchanger 108 is initialized, triggered by exceeding the pressure drop threshold on the flue gas circuit, measured by a differential pressure sensor (not shown), the control system 800 opens the regulating valve 1004 and the valve 1006 on the branch 207 as well as the solenoid valve 212 located on the branch 226, and increases the flow rate of the pump 2 by a factor of 2.

[0176] The circuit 60 will provide the heat necessary for defrosting, by providing the necessary flow rate at 20°C, measured by the temperature probe 61, and thus heat the heat transfer fluid, advantageously isopentane, in the exchanger 7 advantageously from a temperature of -60°C to a temperature of +15°C, measured by the probe 144. The pump 34 circulates the heat transfer fluid, advantageously potassium acetate, at 20°C on the exchanger 7, the solenoid valves 351, 352 and 342 being closed and the solenoid valves 341, 353 and 354 being open.

[0177] The pump 35 of the branch 37 is put into operation, to suck the flow of heat transfer fluid, regulated by the regulating valve 1004 adjusted so as to pass half of the return flow from the branch 26 to the exchanger 7.

[0178] The return to branch 36 which joins branch 26 is carried out via solenoid valve 21 2 of branch 226, solenoid valves 1 1 15 and 21 1 being closed.

[0179] The cooling flow rate of the refrigeration circuit 50 is increased, to provide the refrigerating power, advantageously at -10°C, temperature measured by the temperature probe 51, and advantageously comes out at its warmest at +3°C, temperature measured by the probe 52, this probe serving as an indicator for the control system 800 to regulate the flow rate of the refrigeration system 50.

[0180] The defrosting time is advantageously significantly shorter, of the order of half an hour, while the icing time is of the order of 48 hours, and therefore when the temperature of 15°C is reached on the probe 130, the control system 800 stops the pump 35, closes the regulating valves 1004 and 1006, closes the solenoid valve 21 2 and the flow rate of the pump 2 is reduced by a factor of 2.

[0181] Pump 34 is also stopped.

[0182] The return branch of circuit 20 transfers the cooling power due to the defrosting of the water on the exchangers 106 and 108 on the one hand and 110 and 112 on the other hand to the heat transfer / refrigerant circuit, this cooling power contributing to the cooling of the gas mixture or to that of the refrigeration systems, which shows how the coldness of the defrosting of the exchangers 106, 108, 110, 112 is recovered by the refrigerant / heat transfer circuit.

Claims

Claims 1. A method for treating fumes containing water vapor and carbon dioxide and optionally a nitrogen oxide, the method comprising a first step of cooling the fumes to be treated, by icing the water and optionally nitrogen dioxide NO2, this first step producing cooled fumes, the method comprising a second step of cooling and dehumidifying the cooled fumes, by icing the water contained in these cooled fumes, this second step producing dehumidified fumes, the method comprising a third step of cooling and decarbonizing the dehumidified fumes, by icing the carbon dioxide into dry ice and optionally a nitrogen oxide contained in the dehumidified fumes, each of the three steps of treating the fumes being carried out by an exchanger of a pair of exchangers, a transfer fluid circulating in each exchanger,each exchanger of a pair of exchangers being in frosting mode for cooling the fumes while the other exchanger is in defrosting mode for the water ice or dry ice formed during a cooling step carried out previously, the transfer fluid being a coolant in the exchangers in frosting mode, the transfer fluid being a heat transfer fluid in the exchangers in defrosting mode, the transfer fluid recovering the cold energy from sublimation and fusion of the dry ice obtained in the third cooling and decarbonization step and transferring this cold energy for cooling the fumes in the first treatment step, the transfer fluid having a triple point whose temperature is lower than - 125°C., 2. Method according to claim 1, characterized in that the transfer fluid comprises isopentane or isohexane.

3. Method according to claim 1 or 2, characterized in that a transfer fluid circulates in a refrigerant circuit and a transfer fluid circulates in a heat transfer / refrigerant circuit, the heat transfer / refrigerant circuit recovering the cold energy from sublimation and fusion of the dry ice obtained in the third step of cooling and decarbonization and transferring this cold energy for cooling the flue gases in the first treatment stage.

4. Method according to claim 3, characterized in that it comprises a step of measuring the carbon dioxide concentration in the fumes to be treated and cooled in the first treatment step; a step of comparing the measured carbon dioxide concentration with a threshold value, a predetermined flow rate of the heat transfer / coolant circuit providing cooling power to cool the fumes to a target temperature in the first cooling step for this threshold value; a step of mixing transfer fluid from the coolant circuit and transfer fluid from the coolant / heat transfer circuit, when the measured carbon dioxide concentration is lower than the threshold value, the flow rate of the mixture obtained being substantially equal to the predetermined flow rate.

5. Method according to any one of claims 3 to 4, characterized in that, for the exchangers of the third stage of cooling and decarbonization of the fumes, the transfer fluid of the heat transfer / refrigerant circuit circulates on an exchanger alternately with the transfer fluid of the refrigerant circuit, the transfer fluid of the refrigerant circuit ensuring the cooling of the fumes and the icing of the carbon dioxide in the exchanger, the transfer fluid of the heat transfer / refrigerant circuit ensuring the defrosting of the carbon dioxide in the exchanger.

6. Method according to any one of claims 3 to 5, characterized in that, for the exchangers of the first stage of cooling the fumes to be treated, the transfer fluid of the heat transfer / coolant circuit circulates on an exchanger in alternation with the transfer fluid of the coolant circuit, the transfer fluid of the coolant circuit partially or not ensuring the cooling of the fumes and the frosting of the water into water ice in the exchanger, the transfer fluid of the heat transfer / coolant circuit partially or totally ensuring the cooling of the fumes and the frosting of the water, and then being a coolant by transfer of the frigories recovered during the defrosting of the carbon dioxide during the third stage, the transfer fluid of the heat transfer / refrigerant circuit also being heat transfer during defrosting of the water ice in the exchanger.

7. Method according to any one of claims 3 to 6, characterized in that, for the exchangers of the second stage of cooling and dehumidification of the fumes, the transfer fluid of the heat transfer / refrigerant circuit circulates on an exchanger alternately with the transfer fluid of the refrigerant circuit, the transfer fluid of the refrigerant circuit ensuring the cooling of the fumes and the frosting of the water into water ice in the exchanger, the transfer fluid of the heat transfer / refrigerant circuit ensuring the defrosting of the water ice in the exchanger.

8. Method according to any one of claims 3 to 7, characterized in that the same transfer fluid circulates in the refrigerant circuit and the heat transfer / refrigerant circuit.

9. Device for treating fumes containing water vapor and carbon dioxide and possibly a nitrogen oxide, the device comprising a first pair of exchangers (1 10, 1 1 2) for a first step of cooling the fumes to be treated, by icing the water, this first step producing cooled fumes, the device comprising a second pair of exchangers (1 06, 108) for a second step of cooling and dehumidification of the cooled fumes, by icing the water contained in these cooled fumes, this second step producing dehumidified fumes, the device comprising a third pair of exchangers (1 01 , 1 03), for a third step of cooling and decarbonization of the dehumidified fumes, by icing the carbon dioxide into dry ice and possibly a nitrogen oxide contained in the dehumidified fumes, a transfer fluid circulating in each exchanger (1 10, 1 1 2, 106, 1 08, 1 01 ,103), each exchanger of a pair of exchangers being in frosting mode for cooling the fumes while the other exchanger is in defrosting mode for the water ice or dry ice formed during a cooling step carried out previously, the transfer fluid being a coolant in the exchangers in frosting mode, the transfer fluid being a heat transfer fluid in the exchangers in defrosting mode, the transfer fluid recovering, the cold energy of sublimation and fusion of the dry ice obtained in the third cooling and decarbonization stage and transferring this cold energy for cooling the fumes in the first treatment stage, the transfer fluid having a triple point whose temperature is lower than - 125°C.

10. Device according to claim 9, the device being characterized in that it comprises a refrigerant circuit (10) in which a transfer fluid circulates, and a heat transfer / refrigerant circuit (20) in which a transfer fluid circulates, the heat transfer / refrigerant circuit (20) recovering the cold energy from sublimation and fusion of the dry ice obtained in the third cooling and decarbonization stage and transferring this cold energy for cooling the fumes in the first treatment stage. 1 1 . Device according to claim 9 or 10, characterized in that it comprises means for measuring the carbon dioxide concentration in the fumes to be treated and cooled in the first pair of exchangers (1 10, 1 12), at the first treatment stage; means for comparing the measured carbon dioxide concentration with a threshold value, a predetermined flow rate of the heat transfer / coolant circuit providing cooling power to cool the fumes to a target temperature at the first cooling stage for this threshold value; means for mixing the transfer fluid of the coolant circuit (1 0) and the transfer fluid of the coolant / heat transfer circuit (20), when the measured carbon dioxide concentration is lower than the threshold value, the flow rate of the mixture obtained being substantially equal to the predetermined flow rate.

12. Device according to any one of claims 9 to 11, characterized in that the transfer fluid comprises isopentane or isohexane.

13. Device according to any one of claims 10 to 12, characterized in that the same transfer fluid circulates in the refrigerant circuit (10) and the heat transfer / refrigerant circuit (20).

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