Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/002—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by condensation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/20—Capture or disposal of greenhouse gases of methane

Definitions

• the present invention relates to a method and system for the extraction, or capture, of sulfur dioxide, or carbon dioxide and sulfur dioxide, by anti-sublimation at atmospheric pressure.
• sulfur dioxide denotes sulfur dioxide (S0 2 ) proper but also chemical species of the SO x type where x can in particular take the value 3. It relates more particularly to a process and a system allowing the capture of sulfur dioxide, or carbon dioxide and sulfur dioxide, present in the fumes circulating in the chimneys of installations for the production of electricity or heat or in the exhaust pipes of propulsion engines. This capture of sulfur dioxide, or carbon dioxide and sulfur dioxide, is carried out for storage.
• the present invention relates to a method for capturing sulfur dioxide, or carbon dioxide and sulfur dioxide, applicable to any combustion system.
• the method according to the invention has the characteristic of not modifying the energy efficiency of propulsion engines or propulsion or electricity production turbines implementing such combustion systems. Capture of C0 2 (Resp. S0 2 ) using the anti-sublimation pressure process atmospheric or near, is done with zero or extremely low increase in energy consumption.
• the system design for an automotive heat engine will be described by way of example. Process
• the invention relates to a method for extracting sulfur dioxide, or carbon dioxide and sulfur dioxide, from fumes from the combustion of hydrocarbons in the presence of oxygen and nitrogen from the air in an apparatus intended in particular for the production of mechanical energy.
• the method according to the invention comprises the step of cooling said fumes to a pressure substantially equal to atmospheric pressure to a temperature such that sulfur dioxide, or carbon dioxide and sulfur dioxide, pass directly from the state solid state vapor, via an anti-sublimation process
• the method according to the invention is such that the step of cooling said fumes to a pressure substantially equal to atmospheric pressure to a temperature such that sulfur dioxide, or carbon dioxide and sulfur dioxide, pass directly from the vapor state to the solid state, via an anti-sublimation process, further comprises the step of extracting said water from said fumes in liquid form at a pressure substantially equal to atmospheric pressure.
• an air or water exchanger is used to extract all or part of said water from said fumes in liquid form at a pressure substantially equal to atmospheric pressure.
• the method according to the invention further comprises the step of extracting all the quantities of residual water in said flue gases by using a refrigeration exchanger and / or a dehydrator.
• the step consisting in cooling said fumes to a pressure substantially equal to atmospheric pressure to a temperature such as sulfur dioxide, or carbon dioxide and sulfur dioxide, pass directly from the vapor state to the solid state, via an anti-sublimation process further comprises the step of cooling the mixture of nitrogen, sulfur, or carbon dioxide and sulfur dioxide, by supplying frigories by means of fractional distillation of a mixture of refrigerants.
• This fractional distillation is carried out at decreasing, staged temperatures, of the mixture of refrigerants in a cycle comprising a compression phase and successive phases of condensation and evaporation.
• the step consisting in cooling said fumes to a pressure substantially equal to atmospheric pressure to a temperature such that sulfur dioxide, or carbon dioxide and sulfur dioxide, pass directly from the vapor state to the 'solid state, via an anti-sublimation process, is followed by a step of melting sulfur dioxide, or carbon dioxide and sulfur dioxide, in a closed enclosure.
• the pressure and the temperature in said closed enclosure evolve up to the triple points of sulfur dioxide, or carbon dioxide and sulfur dioxide, as the mixture of refrigerants, while sub-cooling, provides calories in said closed enclosure.
• the mixture of refrigerants successively ensures:
• the method according to the invention further comprises the step of storing the sulfur dioxide, or the carbon dioxide and the sulfur dioxide, in liquid form in a tank, in particular removable.
• the step of storing the sulfur dioxide, or the carbon dioxide and the sulfur dioxide, in liquid form in a tank, in particular removable comprises the following steps:
• the step of sucking up the sulfur dioxide, or the carbon dioxide and the sulfur dioxide, liquid contained in said closed enclosure the step of reducing the pressure in said closed enclosure to a pressure close to atmospheric pressure, the step of transferring the sulfur dioxide, or carbon dioxide and sulfur dioxide, liquid in said tank.
• the method according to the invention further comprises the step of rejecting nitrogen into the outside air after successive extractions of water vapors, carbon dioxide, SO 2 , minor species such as hydrocarbons unburnt contained in said fumes.
• the method according to the invention further comprises the step of: transferring the frigories contained in the nitrogen discharged into the air outside the flue gases, and
• the method according to the invention further comprises the step of cooling said fumes to the anti-sublimation temperature of sulfur dioxide, or carbon dioxide and sulfur dioxide, at a substantially equal pressure. at atmospheric pressure using the heat energy available in said fumes, at least in part without additional supply of energy.
• the method according to the invention further comprises the following steps: the step of heating and then vaporizing water by means of said fumes, to produce steam d pressurized water, the step of relaxing said pressurized water vapor in a turbine producing mechanical or electrical energy.
• the invention also relates to a system for extracting sulfur dioxide, or carbon dioxide and sulfur dioxide, from the fumes from the combustion of hydrocarbons in the presence of oxygen and nitrogen from the air. in an apparatus intended in particular for the production of mechanical energy.
• the system according to the invention comprises cooling means for cooling said fumes to a pressure substantially equal to atmospheric pressure to a temperature such that sulfur dioxide, or carbon dioxide and sulfur dioxide, pass directly from the solid state vapor, via an anti-sublimation process.
• the means for cooling said fumes to a pressure substantially equal to atmospheric pressure to a temperature such as sulfur dioxide, or carbon dioxide and sulfur dioxide, pass directly from the vapor state to the state solid, via an anti-sublimation process further include extraction means, in particular exchangers, for extracting said water fumes in liquid form at a pressure substantially equal to atmospheric pressure.
• the extraction means for extracting from said smoke all or part of the water in liquid form at a pressure substantially equal to atmospheric pressure comprise an air or water exchanger.
• the extraction means comprise a refrigerant exchanger and / or a dehydrator.
• the cooling means for cooling said fumes to a pressure substantially equal to atmospheric pressure to a temperature such as sulfur dioxide, or carbon dioxide and sulfur dioxide pass directly from the vapor state to the solid state (as well as minor species) via an anti-sublimation process further includes an integrated cascade refrigeration unit for cooling the mixture of nitrogen, sulfur dioxide, or carbon dioxide and carbon dioxide sulfur, by supplying frigories by means of fractional distillation, of a mixture of refrigerants.
• the fractional distillation of the mixture of refrigerants is carried out at decreasing temperatures, stepped, according to a cycle comprising a compression phase and successive phases of condensation and evaporation.
• the refrigerating apparatus includes: a compressor, a partial condenser, a separator tank, evaporative condensers, evaporators for cooling smoke, liquid-vapor exchangers, anti-sublimation evaporators, pressure reducers.
• the system according to the invention further comprises a closed enclosure traversed by a circuit in which a mixture of refrigerants circulates.
• the pressure and the temperature in said closed enclosure evolve up to the triple points of carbon dioxide, or sulfur dioxide and sulfur dioxide, as: • the mixture of refrigerants, by sub-cooling , brings calories into said closed enclosure, the sulfur dioxide, or the carbon dioxide and the sulfur dioxide, pass from the solid state to the liquid state.
• the mixture of refrigerants successively ensures the fusion of the sulfur dioxide, or of the carbon dioxide and sulfur dioxide, in said closed enclosure and the anti-sublimation of sulfur dioxide, or carbon dioxide and sulfur dioxide, circulating in an open circuit in a symmetrical enclosure of the previous one.
• the fusion and the anti-sublimation of sulfur dioxide, or of carbon dioxide and sulfur dioxide are alternately carried out in one and the other of said enclosures: one being closed, the other being open.
• the system according to the invention further comprises storage means, in particular a fixed and / or removable reservoir for storing sulfur dioxide, or carbon dioxide and sulfur dioxide, in liquid form.
• storage means in particular a fixed and / or removable reservoir for storing sulfur dioxide, or carbon dioxide and sulfur dioxide, in liquid form.
• the means for storing sulfur dioxide, or carbon dioxide and sulfur dioxide, in liquid form in a fixed and / or removable tank also comprise suction means, in particular a pneumatic pump.
• the suction means suck the sulfur dioxide, or carbon dioxide and sulfur dioxide, liquid contained in said closed enclosure, reduce the pressure in said closed enclosure to a pressure close to atmospheric pressure, transfer the dioxide of sulfur, or carbon dioxide and sulfur dioxide, liquid in said tank.
• the system according to the invention further comprises compression and / or suction means for discharging the nitrogen to the outside air after successive extractions of the water vapors, sulfur dioxide, or carbon dioxide. carbon and sulfur dioxide, contained in said fumes.
• the system according to the invention further comprises transfer means for transferring the frigories contained in the nitrogen discharged to the air outside the flue gases and thus contributing to the cooling of said flue gases.
• the system according to the invention further comprises means for recovering heat energy available in said fumes to cool, at least in part without additional supply of energy, said fumes to the anti-sublimation temperature of sulfur dioxide, or carbon dioxide and sulfur dioxide, to a pressure substantially equal to atmospheric pressure.
• the means for recovering the heat energy available in said fumes comprise:
• Heating means in particular an exchanger, for heating and vaporizing water by means of said fumes and for producing pressurized steam
• expansion means in particular a turbine, for relaxing said pressurized water vapor and producing mechanical or electrical energy.
• Table 1 presents the molar and mass compositions typical of the fumes from the exhaust of a combustion engine.
• Table 2 presents typical molar compositions of fumes from coal boilers.
• these fumes are cooled both to recover mechanical energy and to lower their temperatures a little above ambient temperature. They are then cooled by a refrigerating cycle at a gradually low temperature to allow the anti-sublimation of C0 2 (Resp. S0 2 ) at a temperature which is around - 80 ° C and at a pressure which is of the order of atmospheric pressure.
• anti-sublimation here designates a direct gas / solid phase change which occurs when the temperature of the gas concerned is below that of the triple point.
• Figure 1 recalls the coexistence diagram of the solid, liquid and vapor phases in the pressure temperature diagram. This diagram applies to any pure body. Below the triple point, the changes take place directly between the solid phase and the vapor phase. The transition from solid to vapor is called sublimation. There is no commonly used term for the reverse passage.
• anti-sublimation has been used, in the present description, to designate the direct passage from the vapor phase to the solid phase.
• the thermodynamic data on the fumes show that the energy available from 900 ° C to 50 ° C is a little more than 1000 kJ / kg. The example described shows that it is possible to convert 34 to 36% of this thermal energy into mechanical energy by a simple steam turbine cycle which, by taking an alternator efficiency of 0.9, makes it possible to recover from 30.5 to 32.5% of electrical energy.
• the system according to the invention consists on the one hand of an energy producing device allowing the transformation of thermal energy into mechanical and / or electrical energy and of an energy consuming device constituted by a refrigerating appliance designed in integrated waterfall.
• the exhaust gases change thermally from around + 900 ° C to -
• the gases produce energy from 900 ° C to about 50 ° C, then consume energy from room temperature (for example 40 ° C) to - 90 ° C.
• room temperature for example 40 ° C
• the example described shows that the available energy is significantly higher than the energy consumed and thus makes it possible, successively, to extract fumes from the water vapor, then the C0 2 (Resp. S0 2 ), by rejecting at l simply nitrogen and trace gases with dew temperatures below -90 ° C.
• the size of the steam turbine depends on the flow of smoke to be treated. For an automobile heat engine, it is a small turbine producing electrical energy of the order of 3 to 30 kW, depending on the power and the operating speed of the heat engine itself.
• the vaporization of the water from the mechanical energy producing circuit is carried out by exchange between a closed water circuit under pressure and the exhaust piping. Indeed, the extraction of thermal energy from the exhaust gases by a water circuit makes it possible to limit the mechanical disturbance on the exhaust gases that would cause, for example, a gas turbine operating directly on the flue gases. It is known that the operating parameters of diesel or petrol engines are strongly disturbed by changes in exhaust pressure. If these changes in the exhaust pressure are changed significantly, they have the effect of reducing the fuel efficiency of the engines.
• the condensation temperature is equal to 40 ° C. This temperature of 40 ° C corresponds to the typical summer conditions of an air condenser.
• This water is reheated to a saturation temperature varying between 310 and 340 ° C, at these temperatures corresponds a saturation pressure in the boiler varying between 99 bar and 145 bar approximately.
• the pressure level is adjusted according to the operating conditions of the engine. To best adjust the pressure level, the water flow is modified from the measurement of the temperature of the exhaust gases at the inlet and / or outlet of the exchanger. The smoke flow is very variable but is known by the knowledge of the engine speed and the fuel flow. This data is available both from the engine tachometer and the fuel injection control electronics. These data make it possible to predict the range of water flow to be circulated in the energy recovery circuit, the pressure in the water circuit being adjusted as a function of the temperature of the exhaust gases at the inlet and / or at the exit of the exchanger.
• the liquid is therefore transformed into vapor.
• the vapor is then itself superheated to typical temperatures of 400 ° C to 550 ° C depending on the available temperature level of the exhaust gases.
• the steam is expanded in the body of the turbine. It is thus possible to extract mechanical energy from the fumes.
• the turbine can drive an electric alternator, a flywheel or even directly the compressor of the refrigeration system.
• the drive version of an electric alternator gives more flexibility according to the different mission profiles of a vehicle thermal engine. The data below assess the quantities of mechanical energy available in the case of two cycle operations.
• the condensation temperature is equal to 40 ° C and the boiling temperature is equal to 310 ° C.
• the condensation temperature is always 40 ° C, but the boiling temperature is 340 ° C.
• the steam is superheated in the first case to 400 ° C, in the second case to 500 ° C.
• the examples described are chosen to illustrate different operating conditions of the exhaust gas temperatures and to provide typical figures of available powers, expressed as a function of the flow rate M of smoke, itself expressed in kg / s. They make it possible to generalize the process according to the invention to any high temperature smoke rejection pipe containing C0 2 (Resp. S0 2 ). Energy recovery from the fumes therefore brought them from typical temperatures varying between 750 ° C and 900 ° C up to temperatures of the order of 50 ° C to 80 ° C.
• the data below set the orders of magnitude of the quantities of mechanical energy necessary to cool the fumes, through a refrigeration cycle, up to the anti-sublimation temperature of C0 2 (Resp. S0 2 ).
• the flue gases are cooled from 50 ° C to room temperature.
• the heat exchange to cool the flue gases from 50 ° C to room temperature takes place in an air or water exchanger.
• the water contained in the smoke flow is partially condensed in this exchanger since the dew temperature for concentrations of the order of 86 grams of water per kg of dry smoke is around 50 ° C.
• the water can be acidic and have specific dew points, higher than those of pure water.
• the dew points are in this case typically between 50 ° C and 100 ° C.
• Condensed water can, according to these characteristics, be either directly discharged, or stored in order to be treated beforehand before discharge.
• the flue gases are cooled in a circuit comprising several exchange segments. They are thus brought to a temperature lower than the anti-sublimation temperature of C0 2 (Resp. S0 2 ) at atmospheric pressure or close to atmospheric pressure.
• the smoke flow M is modified since the water vapor contained therein is condensed.
• the two anti-sublimation evaporators operate alternately.
• the fumes and the refrigerant pass alternately on one or the other of the two evaporators.
• the CO 2 frost is fixed on the external walls of the exchanger circuit located in the anti-sublimation evaporator.
• S0 2 also passes directly from the gaseous phase to the solid phase taking into account its partial pressure. This deposit gradually creates an obstacle to the circulation of cold smoke.
• the smoke flow rates on the external part of the exchanger and the refrigerant flow rates inside the exchanger are respectively switched to the symmetrical evaporator.
• the refrigerant evaporates inside the exchanger and the C0 2 , respectively S0 2 , is deposited on the external surface of the latter.
• This temperature rise is accelerated by circulating the liquid refrigerant before expansion, in the exchanger of the first evaporator.
• the solid C0 2 heats up from - 78.5 ° C, which is the equilibrium temperature of the solid and gaseous phase at atmospheric pressure, to - 56.5 ° C and 5.2 bar which are the pressure / temperature of the triple point where the three solid, liquid and gaseous phases therefore coexist.
• the solid CO 2 melts, that is to say passes from the solid phase to the liquid phase.
• the S0 2 melts before therefore the C0 2 and can be, if necessary, recovered in a privileged manner in the first moments of defrosting, by extraction ad hoc by partial vacuum.
• the pressure in this exchanger continues to rise with the rise in temperature.
• the C0 2 (Resp. S0 2 ) is fully in the liquid phase, it is transferred by pump to a thermally insulated tank.
• the pump is also capable of sucking up residual gas, in particular C0 2 (Resp. S0 2 ). It is thus possible to reduce the pressure inside the anti-sublimation evaporator of 5.2 bar to a pressure close to atmospheric pressure, so that the fumes can again penetrate there.
• the process according to the invention which uses anti-sublimation, is advantageous compared to the process which consists in passing from the gas phase to the liquid C0 2 phase (Resp. S0 2 liquid).
• the process which consists in passing from the gas phase to the liquid C0 2 phase (Resp. S0 2 liquid).
• this process involves lowering the temperature of the fumes to 0 ° C to remove the water and then compressing the mixture of nitrogen and C0 2 to at least 6 bar. During this compression, the mixture of nitrogen and C0 2 will heat up to 120 "C. It will have to be cooled again from 120 ° C to - 56.5 ° C.
• the refrigeration device implements a cooling principle, known per se, known as integrated cascade.
• the refrigeration device according to the invention however has specific technical features which will be described below. Indeed to cool the flue gases, over a significant temperature difference ranging from ambient temperature to ⁇ 90 ° C., by means of of a refrigeration device which is simple to produce, comprising only one compressor, the method according to the invention uses a mixture of refrigerants.
• the refrigeration apparatus according to the invention comprises a single compressor, two intermediate evapo-condensers and the two low temperature anti-sublimation evaporators in parallel previously described. Intermediate evapo-condensers allow both the distillation of the refrigerant mixture and the gradual cooling of the smoke flow.
• the residual water vapor contained in the flue gases is condensed either totally or partially in one air or water cooling exchanger described above. If this is not the case, the water is condensed in a complementary manner in the first heat exchanger of the refrigeration unit where the temperature is slightly higher at 0 ° C and where the residence time is sufficient to permit this condensation.
• the refrigerant mixtures used to carry out a cycle can be ternary, quaternary or five-component mixtures.
• the mixtures described integrate the constraints of the Montreal Protocol which prohibits the production and, ultimately, the use of refrigerant gases containing chlorine. This implies that no CFC (Chloro-fluorocarbon), nor H-CFC (Hydro-Chloro-Fluoro-carbide) is retained in the usable components, although several of these fluids are functionally quite interesting to be used as working fluids in an integrated cascade.
• the Kyoto Protocol also imposes constraints on gases with high Global Warming Potential (GWP). Even if they are not prohibited at present, preferably, according to the invention, fluids are used whose GWP is as low as possible.
• the mixtures which can be used in the integrated cascade according to the invention, for capture C0 2 (Resp. S0 2 ) in the flue gases, are indicated below.
• the ternary mixtures can be mixtures of Methane / C0 2 / R-152a, or, by adopting the standardized nomenclature
• the quaternary mixtures can be mixtures: of R-50 / R-170 / R-744 / R-152a, or of R-50 / R-170 / R-744 / R-600, or of R -50 / R-170 / R-744 / R-600a.
• the R-50 can also be replaced by the R-14 but its GWP is very high (6500 kg C0 2 equivalent).
• Mixtures with 5 components can be made by choosing 5 of these components from the list of the following 8 fluids: R-740, R-50, R-14, R-170, R-744, R-600, R-600a, R-152a in adequate proportions with gradually staged critical temperatures, these critical temperatures being presented in Table 2.
• the two intermediate evapo-condensers and the anti-sublimation evaporators make up the three temperature stages of the integrated cascade. These three stages all operate at the same pressure since they are all connected to the compressor suction, but the average temperatures in these three stages are typically of the order of - 5 ° C, - 30 ° C and - 90 ° C since there is a temperature difference between the flow of refrigerants circulating in the other piping of each of the exchangers.
• the flow rates of the refrigerant mixture in the three "stages" of the integrated cascade depend on the proportion of the components in the refrigerant mixtures. There is therefore a link between composition and temperature levels of the waterfall.
• the data below relates to a refrigeration appliance with integrated cascade using a mixture of five-component refrigerants with the following mass composition: • R-50 1%
• the proportion between flammable and non-flammable components is such that the mixture is a non-flammable safety mixture.
• the critical temperature of this mixture is 74.2 ° C and its critical pressure 50 bar.
• the proportions of the components with the highest critical temperature are predominant in the mixture because their evaporation in the two intermediate stages makes it possible to distill the components at low critical temperature.
• the components at low critical temperature can then evaporate at low temperature in the anti-sublimation evaporator which is a double evaporator, operating alternately on one or the other of its parallel pipes.
• the exchangers in the cascade are counter-current exchangers. They allow the use of very large temperature differences between inputs and outputs.
• the anhydrous smoke flow rate, MN 2 + CO2 + SO 2 after passing over the anti-sublimation evaporator is reduced to the nitrogen flow rate, N2 , which represents 0.719 of the initial flow rate M.
• This nitrogen flow rate whose temperature is at - 90 "C, circulates against the current of the smoke tube to participate in the cooling of the anhydrous smoke flow M N2 + co 2+ so2 / then of the total smoke flow M.
• the participation of the nitrogen flow leaving the anti-sublimation evaporator on cooling the fumes occurs until the temperature of nitrogen has returned to ambient temperature.
• the pressure of the nitrogen flow M N2 is equal to 73% of the initial pressure of the flow M, taking into account the successive captures of the water vapor and the vapors of C0 2 (Resp. S0 2 ).
• the overpressure necessary for circulation is achieved for example by an air compressor whose flow injected into a venturi allows extraction of the nitrogen flow.
• Another design consists in compressing the total flow rate at the outlet of the air cooling exchanger in order to allow a slight overpressure with respect to atmospheric pressure all along the smoke circulation circuit and until it is vented. .
• FIG. 3 represents a schematic view of an alternative embodiment of a system for capturing carbon dioxide by antisublimation.
• the numerical values indicated correspond to carbon dioxide, they are transposable by the engineer of the trade in the case of sulfur dioxide, or in the case of sulfur dioxide and carbon dioxide. Whenever it is necessary to carry out such a transposition, the entry (Resp. S0 2 ) has been inserted.
• FIG. 3 The numerical references are those of FIG. 3.
• the table below specifies the reference system used. It explains the meaning of identical technical terms bearing different reference numbers.
• the smoke flow M is the sum of four flows:
• M m H20 + m ⁇ 2 + m N2 + m tr aces
• m H2 o denotes the flow of water vapor
• ⁇ ttco2 denotes the flow of carbon dioxide
• m N2 denotes the flow of nitrogen
• m t races means the flow of trace gases including S0 2 or unburnt hydrocarbons.
• the fumes come out of the heat engine 1 (of the internal combustion engine) through the pipe 2 (outlet pipe of the heat engine). Their temperature is 900 ° C.
• the mass compositions of the fumes at the outlet of the heat engine 1 are respectively equal to: • C0 2 : 19.5%,
• trace gases such as S0 2 have been neglected given their negligible impact from an energy point of view.
• the energy Q eCh given off by the fumes in the exchanger 6 is approximately equal to 1000 kJ / kg.
• the temperature of the fumes at the outlet of the exchanger 6 is 50 ° C.
• the thermal energy given off by the fumes in the exchanger 6 is transformed in a manner known per se into mechanical energy, then into electrical energy.
• the fumes yield their energy to the water circulating in the exchanger 6.
• This water is successively reheated in the liquid phase from 42 ° C to 310 ° C, then brought to the boil at saturation pressure at 310 ° C, ie at 99 bar, or 340 ° C and 145 bar, second variant of the exchanger 6, and finally this water is superheated to 400 ° C, or 500 ° C, second variant of the exchanger 6.
• the superheated steam is expanded in a turbine 7 which, in the variant described, drives an alternator 10.
• the expanded vapors, partially two-phase after this expansion, are condensed in a condenser 8, air condenser.
• the liquid thus formed is compressed by a pump 9 at a pressure of 99 bar, 145 bar, in the case of the second variant.
• thermal energy can be recovered from the cooling circuit 3 of the heat engine 1.
• the heat exchanger 5 recovering the energy from the cooling circuit 3 of the heat engine 1 comprises a recovery circuit 4.
• the connections between the recovery circuit 4 and the cooling circuit 3 of the heat engine 1 are not shown.
• the condensing temperature is 40 ° C in the air condenser 8.
• the condensing temperature can typically vary from 10 ° C to 65 ° C, between winter and summer in the hottest countries.
• the energy recoverable in the case of a condensation temperature of the steam equal to 10 ° C is higher than that recovered in the case of a condensation temperature equal to 65 ° C.
• An alternator 10 coupled to the turbine 7 transforms mechanical energy into electrical energy.
• the fumes circulate in the exchanger 6 against the flow of water.
• the temperature of the fumes varies from 900 ° C to 50 ° C while the water temperature varies from 40 C C to 400 ° C in the first variant and up to 500 ° C in the second variant.
• the vaporization takes place at 310 ° C, under a pressure of 99 bar.
• the vaporization takes place at 340 ° C, under a pressure of 145 bar.
• the exchanger 6 is therefore both a water heater and a boiler.
• Pec h 1000 M, expressed in kW.
• the mechanical power extracted is expressed as a function of the smoke flow from the efficiency of the turbine cycle:
• the alternator 10 has an efficiency of 0.9.
• Cooling is pure cooling for nitrogen, cooling and condensation for water, cooling and anti-sublimation for C0 2 (Resp. S0 2 ). To understand where liquid water and solid C0 2 are extracted
• Point A is a representative point of C0 2 at the inlet of the first (n ° 1) cooler evaporator 25.
• the pressure is 1 bar
• the temperature is 50 ° C (323 K)
• the enthalpy of C0 2 (Resp. S0 2 ) is 450.8 kJ / kg (see table 5).
• Point B is a point representative of the state of C0 2 (Resp. S0 2 ) at the outlet of the exchanger 11, the temperature is 40 ° C, the enthalpy is shown in Table 5.
• Point C is a representative point of C0 2 (Resp.
• Point D is a representative point of C0 2 (Resp. S0 2 ) on the complete solidification curve of C0 2 (Resp. S0 2 ) at - 80 ° C. Solidification takes place on the wall of the anti-sublimation 39 evaporator tube (no. 1). The complete gas / solid phase change required a cooling energy of 568 kJ / kg.
• Point E is a representative point of C0 2 (Resp. S0 2 ), during the defrosting operation by sublimation of solid C0 2 (Resp. S0 2 solid) in the evaporator enclosure (n ° 2) anti-sublimation 40. This operation causes the pressure to rise by partial sublimation of solid C0 2 (Resp. S0 2 solid), which increases the vapor pressure up to 5.2 bar.
• Point F is a representative point of C0 2 (Resp. S0 2 solid, at the end of fusion of C0 2 (Resp. S0 2 solid), at pressure constant 5.2 bar.
• the C0 2 (Resp. S0 2 liquid) is therefore entirely liquid at point F.
• Table 6 gives the variations in temperature, enthalpy and mass fractions at the inputs and outputs of the exchangers and the sections of piping connecting them. As well as the variation of the flow according to the successive captures of the water vapors, then of C0 2 (Resp. S0 2 ), by indicating the quantity of energy extracted from each exchanger.
• the pipe 13 of the flue gases and the pipe 55 for the release of nitrogen to the air are arranged in close contact and are thermally insulated from the outside.
• the sections of the pipes 13 and 55 located between the elements 11, 25, 33, 39 and 40 constitute successive exchangers.
• the cooling of the fumes in the exchanger 11 from 50 to 40 ° C with partial condensation of the water requires a power of 109 M (kW), in the example treated the water begins to condense in this exchanger for cooling the fumes 11.
• the condensation of water can start in the exchanger 6.
• the point temperature dew of water is around 50 ° C for a mass concentration of water in the smoke of 8.6%.
• the smoke flow rate at the outlet of the exchanger 11 is equal to 0.964 M.
• the mass fraction of water increased from 8.6% to 5%.
• the exchanger 11 is designed to allow evacuation water condensate through the pipe 14.
• the pipe 14 connects the exchanger 11 to the water collection tank 16.
• the fumes in the pipe 13 are cooled by the pipe 55 from the outlet of the exchanger 11 to the inlet of the exchanger 25.
• These pipe sections are also thermally insulated from the outside.
• the change in enthalpy of the nitrogen flow of 0.719 M (kg / s) is transmitted with an exchange efficiency of 90% at the flow rate of the fumes flowing in the pipe 13 on each of the 3 sections of the above-mentioned exchangers.
• the energy transferred by the nitrogen flow between the exchangers 11 and 25 is 26.3 M (kW). It is used both to condense part of the water vapor which is reduced to 4.2% and to cool the flow of flue gases to 36.5 ° C at the inlet of the exchanger 25.
• the smoke flow is at a temperature of 1 ° C. which requires a cooling power of 138 M (kW) in the exchanger 25 to allow such a lowering of the temperature of the fumes and the condensation of the remaining water vapor.
• the temperature of the fumes is regulated at 1 ° C to avoid frosting of the water contained in the fumes.
• the section and the design of the first (n ° 1) evaporator cooler 25 ensure a thorough dehumidification of the smoke flow. Typically, less than 0.05% water by mass remains in the fumes at the outlet of the first (n ° 1) cooler evaporator 25.
• the smoke pipe 13 is in communication with the internal chamber of the first (n ° 1) cooler evaporator 25.
• the water extracted from the fumes during its passage in the first (n ° 1) cooler evaporator 25 is recovered in the internal room . It is then transferred to the water collecting tank 16 via the water evacuation pipe 15 from the first (n ° 1) cooler evaporator 25.
• the fumes leaving the first (n ° 1) cooler evaporator 25 pass through a dehydrator 56 which ensures the complete drying of the fumes.
• the anhydrous mass flow rate of the fumes, denoted M N 2 + co2 + so2f is equal to 0.914 of the flow rate M leaving the heat engine 1.
• the nitrogen flow circulating in the pipe 55 provides a cooling power of 14 M (kW) to the pipe section 13 which connects the exchanger 25 to 33 and cools the residual smoke flow M N2 + C o 2+ so 2 d 'nitrogen and C0 2 (Resp. S0 2 ) down to a temperature of -14 ° C at the inlet of exchanger 33.
• the residual flow M N2 + ⁇ 2 + so 2 enters one of the two anti-sublimation evaporators (n ° l) 39 or (n ° 2) 40 at a temperature of - 72 ° C because the piping 55 provided a cooling power of 47 M (kW).
• the shape and design of the two anti-sublimation evaporators (n ° l) 39 or (n ° 2) 40 allow a long residence time of the gases.
• the residual smoke flow M N2 + co2 + so2 is cooled to anti-sublimation of C0 2 (Resp. S0 2 ) which requires a cooling capacity of 125.9 M (in kW).
• the C0 2 (Resp. S0 2 ) which requires a cooling capacity of 125.9 M (in kW).
• the refrigerant Before expansion in the expansion valve (n ° 1) 41, the refrigerant passes through the anti-sublimation evaporator (n ° 2) 40 which is in the defrosting phase.
• the refrigerant thus recovers the fusion energy of C0 2 .
• the recoverable energy corresponds, on the diagram in Figure 2, to the passage from point D (solid C0 2 at 0.85 bar) (Resp. S0 2 ) to point F (liquid C0 2 at 5.2 bar) (Resp S0 2 ).
• the change in gross enthalpy is 228 kJ / kg.
• the transfer efficiency of the exchangers is 90%. Consequently, the energy recovered is equal to 205 kJ / kg.
• the electrical powers (expressed in kW) that can be recovered in the case of the two embodiments described above are respectively equal to 304.5 M and 325.4 M. They are greater than the electrical power of compression that the compressor must provide to produce the cooling capacity. Indeed, expressed in kW as a function of the smoke flow M, the electrical compression power is of the order of 187 M.
• Table 7 gives the COPs according to the evaporation temperatures.
• This table is used to calculate the electrical power consumed by the compressor according to the temperature level at which the cooling power is supplied.
• the performance coefficients are used to calculate the power consumed by the compressor to supply the cooling power to the different exchangers.
• the cooling capacity supplied to the exchanger 25, to cool the flue gases to 0 ° C, is supplied at - 5 ° C.
• the cooling power supplied to the second smoke cooler evaporator 33 is supplied at -30 ° C.
• As the cooling capacity to be supplied is equal to 5.4 M (Table 6) and as the coefficient of performance is 1.9
• the cooling capacity necessary for cooling the nitrogen from 50 to - 90 ° C was taken into account in the calculations of each exchanger.
• the electric power consumed by the refrigeration compressor as a function of the smoke flow M is therefore 187 M in kW.
• This power is to be compared to the electric power recovered on the smoke flow which is variable between 304.5 M and 325.4 M.
• the electric power of the compressor therefore represents around 60% of the electric energy recoverable by the steam recovery cycle described above.
• the refrigeration compressor 17 draws in the mass flow in the vapor phase of one of the above-defined multi-component refrigerant mixtures. More particularly, in the case of the variant embodiment which will be described below, the mixture is composed of five components whose mass percentages are as follows: • R-50 (1%)
• the suction pressure is 1.7 bar.
• the condensing pressure, for a condensate outlet temperature of 40 ° C, is 22 bar.
• the partial refrigerating condenser 18 is cooled by a cooling circuit 19, the cooling circuit of the partial refrigerating condenser. Water or air circulates in the cooling circuit 19.
• the partial refrigeration condenser 18 is a liquid and gaseous phase separator of the total flow of incoming refrigerant, hereinafter designated Mf.
• the flow in the gas phase hereinafter designated Mtêtel, leaves at the top, at the top, from the partial refrigerating condenser 18 by the piping 20.
• the liquid flow hereinafter designated Mpiedl, exits at the bottom, at the bottom, by the piping 21
• the liquids are drained at the bottom of the partial refrigerating condenser 18 due to gravity.
• the liquid flow (Mpiedl) cools down in the liquid-vapor exchanger (n ° 1) 26. This flow (Mpiedl) is approximately equal to 50% of the total refrigerant flow (Mf).
• the liquid flow (Mpiedl) is rich in the heaviest components, that is to say here the R-600 and the R-744, and expands in the regulator 24 at the evaporation pressure of 1.7 bar.
• the expanded liquid flow (Mpiedl) evaporates successively in the first (n ° 1) evaporator-condenser 22 then in the first (n ° 1) evaporator cooler of fumes 25 where the evaporation is completed.
• the fluid flow (Mpiedl) thus completely vaporized will give up its coldness in the heat exchanger (n ° 1) of the liquid vapor 26 and then join the suction manifold of the compressor 17 by the piping 27.
• the gas flow (Mtêtel), leaving the partial condenser 18, represents the other 50% of the total refrigerant flow (Mf).
• the gas flow (Mtêtel) will partially condense in the first (n ° 1) evapo-condenser 22.
• This flow (Mtêtel) become two-phase (liquid-vapor) at the outlet of the first (n ° 1) evapo-condenser 22 will separate into independent liquid and vapor phases in the separator tank 28.
• the vapor phase flow rate (Mtête2) comes out at the top of the tank separator 28 by the piping 29.
• the liquid flow (Mpied2) leaves at the bottom of the separator tank 28.
• the gas flow (Mtêtel) leaving at the head of the partial condenser 18, has thus been separated into two flows: a gas flow (Mtête2) representing 40% of the incoming flow (Mtêtel) and a liquid flow (Mpied2) representing 60% of the incoming flow (Mtêtel).
• the gas phase flow (Mtête2) leaving the separator tank 28 through the piping 29 will fully condense in the second (n ° 2) evaporator-condenser 32.
• the entirely liquid flow (Mtête2) alternately evaporates in the evaporators (n ° l) or (n ° 2) of anti-sublimation 39 or 40.
• the liquid flow (Mtête2) passes through the first (n ° 1) three-way valve 37. This valve is open on the piping 38 and therefore closed on the piping 44.
• the liquid flow (Mtête2) is sub-cooled in the second evaporator (n ° 2) of anti-sublimation 40 which then serves as a sub-cooling exchanger during its defrosting phase of C0 2 .
• the sub-cooled liquid flow (Mtête2) is then expanded in the first (n ° 1) expansion valve 41. Then, it evaporates in the first (n ° 1) anti-sublimation evaporator 39.
• the liquid refrigerant mixture (Mtête2) after expansion in the pressure reducer (n ° l) 41 evaporates in the first anti-sublimation evaporator (n ° 1) 39 at a starting temperature of approximately - 100 ° C up to at a temperature of the order of - 70 ° C at the outlet.
• the fumes from the second (n ° 2) smoke cooler evaporator 33 pass through the fourth (n ° 4) three-way valve 53 to go to the first anti-vaporizer (n ° 1) sublimation 39. In this case, the fumes do not go into the second evaporator (no.
• the refrigerant Before entering the first anti-sublimation evaporator (n ° 1) 39, the refrigerant enters around - 45 ° C in the second anti-sublimation evaporator (n ° 2) 40, which operates as a sub-exchanger - cooling.
• the refrigerant sub-cools from - 45 ° C to - 78 ° C at the start of the C0 2 defrosting cycle (Resp. S0 2 ) and only from - 45 ° C to - 55 ° C at the end defrost cycle C0 2 (Resp. S0 2 ).
• liquid C0 2 accumulates in the lower part of the second anti-sublimation evaporator (n ° 2) 40.
• the third (n ° 3) three-way valve 47 is open. It is thus possible to aspirate the liquid C0 2 (Resp. S0 2 liquid) by means of pump 48, the liquid CO2 suction pump (Resp. S0 2 liquid).
• the pump 48 is for example an electric pneumatic pump making it possible to aspirate both liquid and gas.
• the pump 48 transfers the liquid C0 2 (Resp. S0 2 liquid) to the storage tank 49, then sucks the vapors of C0 2 (Resp.
• second anti-sublimation evaporator (n ° 2) 40 at operating pressure, either 0.85 bar abs., or 1 bar abs., depending on the technical option chosen for the circulation of smoke.
• a removable tank 51 is connected to the storage tank 49.
• the pump 50 the pump filling of the removable tank, allows filling of the removable tank 51 from the storage tank 49.
• the valve 52 allows pressure balancing between the two tanks 49 and 51 if necessary.
• the removable tank 51 allows the transport of captured C0 2 (Resp. S0 2 captured). A new removable vacuum tank replaces the one that has been filled.
• the nitrogen vapors pass through the fifth (n ° 5) three-way valve 54, then join the piping of nitrogen 55 air vent.
• the fifth (n ° 5) three-way valve 54 puts in communication, as the case may be, the nitrogen 55 air piping either with the first (n ° 1) anti-sublimation evaporator 39, ie with the second (n ° 2) anti-sublimation evaporator 40.
• the nitrogen flow M N2 in the nitrogen 55 venting pipe, now only represents 71.9% of the initial mass flow of the fumes.
• the pressure of nitrogen alone is equal to 0.736 bar, without taking into account either pressure drops or trace gases.
• the pipe 2 for the outlet of the heat engine 1, the smoke pipe 13 and the nitrogen vent pipe 55 are in communication, they constitute the same circuit.
• FIG. 3 is that of an air compressor 57 injecting an air flow through the piping 58, the venturi injection piping, at the neck of a venturi 59 allowing the suction of the flow of nitrogen at a pressure of the order of 0.65 bar and preventing the entry of air into the system.
• This solution also has the advantage of recreating a mixture of nitrogen and oxygen at the outlet of the venturi.
• Another solution, not shown in FIG. 3, is to install a compressor with a small pressure difference, of the blower type, at the outlet of the flue gas heat exchanger 11, in the flue pipe 13 to create the overpressure which allows the nitrogen flow or the nitrogen flow with trace components to be returned to the atmosphere at the outlet of the nitrogen venting pipe 55.
• the flows of nitrogen and trace components can be reintegrated in a mixer with an additional flow of air suitable for create a so-called lean fuel mixture.
• the combustion of this combustible mixture is favorable for reducing pollutants and increasing the energy efficiency of a heat engine designed for this purpose. Note that during the defrosting of C0 2 (Resp. S0 2 ) on the anti-sublimation exchanger in operation, the temperature varies between - 80 ° C and - 55 ° C. This significant variation in temperature can be used to regulate the alternation of the two anti-sublimation evaporators.
• the present invention also relates to a method and a system allowing the extraction (capture) of C0 2 and / or S0 2 by anti-sublimation (icing) at atmospheric or almost atmospheric pressure at + or - 0.3bar of C0 2 , in methane (CH 4 ) extracted from deposits.
• the capture of S0 2 alone also applies to gaseous effluents or fumes, when this S0 2 is at concentrations varying between 0.1% and 3%. It relates more particularly to a process and a system allowing the capture by solidification of C0 2 and / or S0 2 in the gas phase, contained in a methane gas flow, in particular for methane (CH 4 )) extracted from deposits.
• the Kyoto Protocol consists of commitments by signatory countries to limit these emissions.
• the capture of carbon dioxide and its sequestration are essential objectives for economic development and the maintenance of atmospheric concentrations at levels limiting climate change.
• SOx emissions S0 2 , S0 3 and other oxides
• SOx emissions are already regulated both to avoid acid rain and to limit respiratory accidents in urban areas.
• the capture of CO2 and S0 2 constitute existing or emerging markets for depollution systems.
• the present invention relates to a process for capturing carbon dioxide and minority species at low partial pressure by anti-sublimation.
• Methane (CH 4 ) liquefies at atmospheric pressure at -161.5 ° C while C0 2 , S0 2 , according to their partial pressures in the gas mixture, will pass from the gas phase to the solid phase under atmospheric pressure at variable temperatures between -80 and -120 ° C.
• S0 2 will be frosted on any cold wall whose temperature is typically lower than -75 ° C for a volume concentration of the order of 0.5%.
• These bodies can then be recovered in the liquid phase by an alternating icing / defrosting process where pressure and temperature rise above the respective triple points of C0 2 and S0 2 in a closed and sealed enclosure during this defrosting.
• this alternating defrosting process can be designed so as to recover the defrosting energy.
• the invention relates to a method for extracting C0 2 and / or S0 2 .
• the method according to the invention comprises the step of cooling methane extracted from a borehole, to a pressure substantially equal to atmospheric pressure at a temperature such that C0 2 and / or S0 2 pass directly from the state solid state vapor, via an anti-sublimation process.
• the step consisting in cooling the methane extracted from a borehole to a pressure substantially equal to atmospheric pressure to a temperature such that carbon dioxide and / or SO 2 pass directly from the vapor state to the solid state, via an anti-sublimation process further comprises the step of cooling the methane extracted from a borehole on the one hand, and the C0 2 , the S0 2 , on the other hand, by supplying frigories by means of a fractional distillation of a mixture of refrigerants. This fractional distillation is carried out at decreasing, staged temperatures, of the mixture of refrigerants in a cycle comprising a compression phase and successive phases of condensation and evaporation.
• the step consisting in cooling the methane extracted from a borehole to a pressure substantially equal to atmospheric pressure to a temperature such that the CO 2 and / or the SO 2 pass directly from the vapor state to the solid state.
• a step of melting C0 2 , and / or S0 2 in a closed enclosure.
• the pressure and the temperature in said closed enclosure evolve up to the triple points of C0 2 , and / or of S0 2 , as the mixture of refrigerants, while sub-cooling, brings calories into said enclosure closed.
• the mixture of refrigerants successively ensures:
• the method according to the invention further comprises the step of storing C0 2 and / or S0 2 , in liquid form in a tank, in particular removable.
• the step of storing the CO2 and / or the SO 2 , in liquid form in a tank, in particular removable comprises the following steps: the step of aspirating the C0 2 , and / or the S0 2 , in liquid form contained in said closed enclosure,
• the method according to the invention further comprises the step of cooling the methane extracted from a borehole to the anti-sublimation temperature of C0 2 and / or S0 2 , at a pressure substantially equal to atmospheric pressure using the cooling energy available in said flue gases without additional supply of energy.
• the system according to the invention comprises cooling means for cooling the methane extracted from a borehole to a pressure substantially equal to atmospheric pressure at a temperature such that C0 2 and / or S0 2 pass directly from the state solid state vapor, via an anti-sublimation process.
• the cooling means for cooling the methane extracted from a borehole to a pressure substantially equal to atmospheric pressure at a temperature such as C0 2 and / or S0 2 pass directly from the vapor state to the solid state, via an anti-sublimation process further include an integrated cascade refrigeration unit for cooling the methane flow and C0 2 and / or S0 2 by supplying frigories by means of fractional distillation, a mixture of refrigerants.
• the fractional distillation of the mixture of refrigerants is carried out at decreasing temperatures, stepped, according to a cycle comprising a compression phase and successive phases of condensation and evaporation.
• the refrigeration unit includes: a compressor, a partial condenser, a separator tank, evapo-condensers, smoke cooling evaporators, liquid-vapor exchangers, anti-sublimation evaporators, pressure reducers.
• the system according to the invention further comprises a closed enclosure traversed by a circuit in which a mixture of refrigerants circulates. The pressure and the temperature in said closed enclosure evolve up to the triple points of C0 2 , and / or SO 2 as and when:
• the mixture of refrigerant fluids by sub-cooling, provides calories in said closed enclosure, said s C0 2 and / or SO 2 pass from the solid state to the liquid state.
• the mixture of refrigerants successively ensures the fusion of C0 2 and / or S0 2 , in said closed enclosure and the anti-sublimation of C0 2 and / or S0 2 circulating in open circuit in a symmetrical enclosure of the previous.
• the fusion and anti-sublimation of C0 2 and / or S0 2 are alternately carried out in one and the other of said enclosures: one being closed, the other being open.
• the system according to the invention further comprises storage means, in particular a fixed and / or removable reservoir for storing the C0 2 and / or the S0 2 in liquid form.
• storage means in particular a fixed and / or removable reservoir for storing the C0 2 and / or the S0 2 in liquid form.
• the means for storing C0 2 and / or S0 2 in liquid form in a fixed and / or removable tank also comprises suction means, in particular a pneumatic pump.
• the suction means make it possible to selectively recover S0 2 and C0 2 when they are captured together: S0 2 returns to the liquid state at a temperature of -75.5 ° C and at a pressure from 0.016664 bar the C0 2 returns to the liquid state at a temperature of -56.5 ° C and a pressure of 5.2 bar.
• the suction means also make it possible: to reduce the pressure in said closed enclosure to a pressure close to atmospheric pressure, to transfer the C0 2 and / or the liquid SO2 in said tank.
• the system according to the invention further comprises compression and / or suction means for transferring the methane extracted from a borehole into devices corresponding to storage, or to subsequent treatments, after extraction of the C0 2 and / or SO 2 contained in methane.
• the system according to the invention further comprises transfer means for transferring the frigories contained in the methane after separation of the C0 2 , the S0 2 from the total flow (methane + C0 2 + S0 2 ) entering the pipes of the refrigeration system and thus contribute to the cooling of said total flow.
• the gases to be treated are composed: - on the one hand of methane (CH 4 ) whose typical concentration can be 90 to 99%, on the other hand of minority species: C0 2 whose volume concentration can vary from 1 at 10%, and / or S0 2 , the concentration of which can vary from 0.1% to 3%,
• the total flow rate comprising methane extracted from a borehole and C0 2 and / or S0 2 is cooled by a refrigeration cycle at a gradually low temperature to allow anti-sublimation of C0 2 and / or S0 2 at a temperature between - 80 ° C and -120 ° C and at a pressure which is of the order of atmospheric pressure at + or - 0.3 bar.
• anti-sublimation here designates a direct gas / solid phase change which occurs when the temperature of the gas concerned is below that of the triple point.
• FIG. 1 recalls the diagram of coexistence of the solid, liquid and vapor phases in the pressure-temperature diagram of C0 2 . This diagram is valid for any pure body and in particular for S0 2 . Below the triple point, the changes take place directly between the solid phase and the vapor phase. The transition from solid to vapor is called sublimation. He does not exist commonly used to designate the reverse passage.
• anti-sublimation has been used, in the present description, to designate the direct passage from the vapor phase to the solid phase. Below room temperature, the total flow is cooled in a circuit comprising several exchange segments.
• the two anti-sublimation evaporators operate alternately.
• the total flow passes alternately on one or the other of the two evaporators.
• the frost of C0 2 and / or S0 2 is fixed on the external walls of the exchanger circuit located in the anti-sublimation evaporator. This deposit gradually creates an obstacle to the circulation of methane extracted from a borehole. After a certain operating time on this evaporator, the total flow rate as well as the flow rate of the mixture of refrigerants are respectively switched over to the symmetrical evaporator. In this second evaporator, the mixture of refrigerants evaporates inside the exchanger and the CO 2 and / or S0 2 is deposited on the external surface of the latter.
• the temperature therefore rises in this first evaporator.
• This temperature rise is accelerated by circulating the liquid refrigerant before expansion, in the exchanger of the first evaporator.
• S0 2 and / or C0 2 solids heat up from temperatures which can be between -80 and -120 ° C up to the respective melting temperatures.
• the sublimation of frosted species on the walls of the exchanger produces vapors which increase the pressure in the enclosure from the evaporator during defrosting until the respective pressures corresponding to the triple points of the different substances are reached (0.016 bar for S0 2 , 5.2 bar for CO 2 ).
• the melting of the frost then takes place from the solid phase to the liquid phase.
• the SO 2 , the minority species and the C0 2 are fully in the liquid phase, they are transferred by relative depression into one or more thermally insulated tanks.
• transfers can be carried out at successive pressures corresponding to the preferential presence of one of these bodies.
• the pump is also able to suck up the residual gas (es). It is thus possible to reduce the pressure inside the enclosure of the anti-sublimation evaporator of the final pressure corresponding to the end of defrosting to the initial pressure close to atmospheric pressure, so that the total flow can enter it again and the C0 2 and / or S0 2 can be separated from the methane there.
• the refrigeration device implements a cooling principle, known per se, known as integrated cascade.
• the refrigeration device according to the invention has specific technical features which will be described below.
• the process according to the invention uses a mixture of refrigerants.
• the refrigeration apparatus according to the invention comprises a single compressor, two intermediate evapo-condensers and the two low temperature anti-sublimation evaporators in parallel previously described. Intermediate evapo-condensers allow both the distillation of the refrigerant mixture and the gradual cooling of the smoke flow.
• the refrigerant mixtures used to carry out a cycle can be ternary, quaternary or five-component mixtures.
• the mixtures described integrate the constraints of the Montreal Protocol which prohibits the production and, ultimately, the use of refrigerant gases containing chlorine. This implies that no CFC (Chloro-fluorocarbon), nor H-CFC (Hydro-Chloro-Fluoro-carbide) is retained in the usable components, although several of these fluids are functionally quite interesting to be used as working fluids in an integrated cascade.
• the Kyoto Protocol also imposes constraints on gases with high Global Warming Potential (GWP). Even if they are not prohibited at present, preferably, according to the invention, fluids are used whose GWP is as low as possible.
• the mixtures which can be used in the integrated cascade according to the invention, for carrying out the capture of C0 2 in the flue gases, are indicated below.
• Ternary mixtures can be mixtures of
• Methane / C0 2 / R-152a i.e., by adopting the standard nomenclature (ISO 817) of refrigerants, mixtures R-50 / R-744 / R-
• the quaternary mixtures can be mixtures: of R-50 / R-170 / R-744 / R-152a, or of R-50 / R-170 / R-744 / R-600, or of R-50 / R-170 / R-744 / R-600a.
• the R-50 can also be replaced by the R-14 but its GWP is very high (6500 kg C0 2 equivalent). ° Five-component mixtures
• Mixtures with 5 components can be made by choosing 5 of these components from the list of the following 8 fluids: R-740, R-50, R-14, R-170, R-744, R-600, R-600a, R-152a in adequate proportions with gradually staged critical temperatures, these critical temperatures being presented in Table 2.
• R-50 / R-14 / R-170 / R-744 / R-600 or R-740 / R-14 / R-170 / R-744 / R-600 or R-740 / R-14 / R-170 / R-744 / R-600a or R -740 / R-14 / R-170 / R-744 / R-152a or of R-740 / R-50 / R-170 / R-744 / R-152a, R-740 being argon.
• Table 2 gives the main thermochemical characteristics and the names of these fluids.
• the two intermediate evapo-condensers and the anti-sublimation evaporators make up the three temperature stages of the integrated cascade. These three stages all operate at the same pressure since they are all connected to the compressor suction, but the average temperatures in these three stages are typically of the order of - 5 ° C, - 30 ° C and - 90 ° C since there is a temperature difference between the flow of refrigerants circulating in the other piping of each of the exchangers.
• the cascade can have 4 stages at respective average temperatures of the order of - 5 ° C, -40 ° C, -85 ° C and - 120 ° C.
• the flow rates of the refrigerant mixture in the three or four stages of the integrated cascade depend on the proportion of the components in the refrigerant mixtures. There is therefore a link between composition and temperature levels of the waterfall.
• the data below relates to a refrigeration appliance with integrated cascade using a mixture of five-component refrigerants with the following mass composition: • R-50 1%
• the proportion between flammable and non-flammable components is such that the mixture is a non-flammable safety mixture.
• the critical temperature of this mixture is 74.2 ° C and its critical pressure 50 bar.
• the proportions of the components with the highest critical temperature are predominant in the mixture because their evaporation in the two intermediate stages makes it possible to distill the components at low critical temperature.
• the components at low critical temperature can then evaporate at low temperature in the anti-sublimation evaporator which is a double evaporator, operating alternately on one or the other of its parallel pipes.
• the exchangers in the cascade are counter-current exchangers. They allow the use of very large temperature differences between inputs and outputs.
• the methane is subsequently liquefied, then cooling continues according to the usual methane liquefaction process. However, if it is not, then the “Coldness” of the methane leaving the anti-sublimation evaporator of C02 and / or S02 can be used to cool the total flow. The participation of the cold methane flow leaving the anti-sublimation evaporator in the cooling of the total flow occurs until the temperature of the methane has returned to ambient temperature. The methane pressure is then equal to values between 90% and 99% of the initial pressure of the total flow, taking into account the capture of C0 2 and / or S0 2 . The overpressure necessary for circulation is achieved for example by an air compressor whose flow injected into a venturi allows the extraction of the methane flow after extraction of C0 2 , and / or S0 2 .
• Another design consists in compressing the total flow upstream of the refrigeration system so as to create a slight overpressure relative to atmospheric pressure all along the methane circuit extracted from a borehole.

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