EP1601443A2

EP1601443A2 - Method of extracting carbon dioxide and sulphur dioxide by means of anti-sublimation for the storage thereof

Info

Publication number: EP1601443A2
Application number: EP04717136A
Authority: EP
Inventors: Denis Clodic; Mourad Younes
Original assignee: Association pour la Recherche et le Developpement des Methodes et Processus Industriels
Current assignee: Association pour la Recherche et le Developpement des Methodes et Processus Industriels
Priority date: 2003-03-04
Filing date: 2004-03-04
Publication date: 2005-12-07
Also published as: FR2851936B1; JP2006519695A; WO2004080558A2; AU2004218867A1; US20060277942A1; CN1756583A; FR2851936A1; WO2004080558A3; CA2518044A1

Abstract

The invention relates to a method and a system for extracting carbon dioxide and/or sulphur dioxide from methane or fumes resulting from hydrocarbon combustion. The inventive system comprises cooling means, such as a refrigerating device with integrated cascade (18, 22, 25, 26, 28, 32, 33, 34, 39, 40) for the cooling of the methane or the fumes at a pressure which is essentially equal to atmospheric pressure and at a temperature such that the carbon dioxide and/or the sulphur dioxide pass directly from vapour state to solid state through an anti-sublimation process.

Description

PROCESS FOR THE EXTRACTION OF CARBON DIOXIDE AND SULFUR DIOXIDE BY ANTI-SUBLIMATION FOR THEIR STOCAKGE

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. Within the meaning of the present invention, 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.

Emissions of carbon dioxide or C0 ₂ linked to combustion, whether from heating systems, electric power generation or vehicle propulsion, lead to an increase in the atmospheric concentration of C0 ₂ , considered unacceptable in the long term . The Kyoto Protocol consists of commitments by signatory countries to limit these emissions. Sobriety and energy efficiency are not enough to limit the concentrations of C0 ₂ to acceptable values. 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.

For fumes from power plants operating on coal or other fuels, including hydrocarbons, containing variable concentrations of S0 ₂ of between 0.1% and a maximum of 3%, it is usual to treat these fumes. These treatments are carried out in specific units taking into account the regulations in force to limit the release of SO _x , S0 ₂ , S0 ₃ and other oxides to the atmosphere, these substances being in particular responsible for acid rain and, for urban areas , irritation and lung disease. Regulations for minimizing SO _x emissions to acceptable levels have been in place since the early 1980s in developed countries. The interest of the present process and system of the invention consists in capturing S0 ₂ , or in co-capturing C0 ₂ and S0 ₂ , or even minor species such as hydrocarbons unburnt by anti-sublimation. In fact, these minority species present at concentrations generally below one percent consequently have very low partial pressures in the fumes and can only be captured below their triple point, therefore in solid phase.

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

Preferably, 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. Preferably, to extract all or part of said water from said fumes in liquid form at a pressure substantially equal to atmospheric pressure, an air or water exchanger is used.

Preferably, 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.

Preferably, 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.

Preferably, 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.

Preferably, the mixture of refrigerants successively ensures:

• the fusion of sulfur dioxide, or carbon dioxide and sulfur dioxide, in said closed enclosure, and the anti-sublimation of sulfur dioxide, or carbon dioxide and sulfur dioxide, circulating, in circuit open, in a symmetrical enclosure from the previous one.

The melting and anti-sublimation of sulfur dioxide, or carbon dioxide and sulfur dioxide, are alternately carried out in one and the other of said enclosures: one being closed, the other being open. Preferably, 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. Preferably, 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.

Preferably, 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.

Preferably, 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

• thus contribute to the cooling of said fumes.

Preferably, 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. Preferably, to use the heat energy available in said fumes, 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. System

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.

Preferably, 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.

Preferably, 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. Preferably, to extract all the quantities of residual water in said fumes, the extraction means comprise a refrigerant exchanger and / or a dehydrator. Preferably, 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.

Preferably, 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. Preferably, 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.

Preferably, 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.

Preferably, 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. Preferably, 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. Preferably, 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.

Preferably, 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.

Preferably, 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.

General description of the method and system according to the invention.

We will now describe, in general, an alternative embodiment of the invention. Qualitative and quantitative explanations have been developed in the case of carbon dioxide. They can be transposed by the engineer in the trade to the case of sulfur dioxide, or to the case of sulfur dioxide and carbon dioxide. Whenever such a transposition must be carried out the mention (Resp. S0 ₂ ) has been introduced. Exhaust gases, also called fumes, are typically composed of carbon dioxide (C0 ₂ ), water vapor (H ₂ 0) and nitrogen (N ₂ ). There are also trace components such as CO, NOx, S0 ₂ , unburnt hydrocarbons, etc. All of the trace gases in the fumes represent contents generally less than 1 to 2%, nevertheless some of them such as S0 ₂ or unburnt hydrocarbons can be captured taking into account the cooling of the entire gas flow by the process as described.

Table 1 presents the molar and mass compositions typical of the fumes from the exhaust of a combustion engine. Table 1

Table 2 presents typical molar compositions of fumes from coal boilers.

Table 2

According to the process of the present invention, 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.

The term 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. The term 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 -

90 ° C. During this cooling, the gases produce energy from 900 ° C to about 50 ° C, then consume energy from room temperature (for example 40 ° C) to - 90 ° 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 countercurrent design of the exchanger and the very large temperature gradient along the smoke circuit makes it possible to heat and vaporize the water in the mechanical energy production circuit. In the case of the example described, 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.

At this boiling pressure, 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. Then 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.

In a first case, the condensation temperature is equal to 40 ° C and the boiling temperature is equal to 310 ° C. In the second case, the condensation temperature is always 40 ° C, but the boiling temperature is 340 ° C. On the other hand, 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 ). Before reaching the refrigeration system heat exchangers, 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. Depending on the outside temperature level and according to the contents of trace components, 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. However, taking into account the presence of trace gases in the fumes, 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. We have described below how to condense the water vapor without taking into account the trace gases in the fumes which raise the dew temperature.

Condensed water can, according to these characteristics, be either directly discharged, or stored in order to be treated beforehand before discharge. Below room temperature, 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. Between the air exchanger and the first cooling exchanger of the integrated cascade, the smoke flow M is modified since the water vapor contained therein is condensed. In the case where the mass concentrations are respectively equal to: C0 ₂ = 19.5%, H ₂ 0 = 8.6% and N ₂ = 71.9%, the flow rate of the fumes M is substantially equal to the anhydrous flow rate, in neglecting the concentrations of trace gases, namely: It is this new anhydrous flow M _{N2 + CO2} + _SO2 which continues to cool in the various exchangers of the refrigeration system before reaching the two anti-sublimation evaporators. When the S0 ₂ content is as indicated in Table 2 (0.4%), the S0 ₂ is still present in the gas phase at this temperature level, taking into account its partial pressure which is of the order of 0.004 bar. Because the surface temperature of the evaporators is lower than -90 ° C, the S0 _{2 is} deposited there simultaneously with the C0 ₂ . This co-capture of S02 takes place up to volume concentrations of 3% which are concentrations much higher than the contents of the fumes richest in S0 ₂ .

The two anti-sublimation evaporators operate alternately. The fumes and the refrigerant pass alternately on one or the other of the two evaporators.

During the anti-sublimation phase, the CO ₂ frost, respectively the SO ₂ frost, is fixed on the external walls of the exchanger circuit located in the anti-sublimation evaporator. For fumes containing S0 ₂ , 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. After a certain operating time on this evaporator, 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. In this second evaporator, the refrigerant evaporates inside the exchanger and the C0 ₂ , respectively S0 ₂ , is deposited on the external surface of the latter. During this time, the first evaporator is no longer the seat of an evaporation, the temperature rises in the first evaporator. 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. Similarly from -75.5 ° C and a lower pressure of 0.016 bar, 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.

Once 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.

It is then possible to carry out the following cycle and to carry out an anti-sublimation of the C0 ₂ (Resp. S0 ₂ ) contained in the cold fumes on the walls of the evaporator. The latter is again supplied with refrigerant. The cycle continues, so on, alternately on the two low temperature evaporators in parallel.

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). In fact, to go directly from the gaseous phase to the liquid phase, it is necessary to increase the pressure of the flue gases, at least up to 5.2 bar and lower their temperature to - 56.5 ° C. In practice, 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. This process also involves compression in pure nitrogen loss up to 5.2 bar. 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. Depending on the climatic conditions and the content of trace components, 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.

° Ternary mixtures

The ternary mixtures can be mixtures of Methane / C0 ₂ / R-152a, or, by adopting the standardized nomenclature

(ISO 817) refrigerants, R-50 / R-744 / R mixtures

152a. It is possible to replace R-152a with butane R-600 or isobutane R-600a

* The quaternary mixtures 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. The following mixtures will be cited as examples: of 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. 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, provided by way of example, relates to a refrigeration appliance with integrated cascade using a mixture of five-component refrigerants with the following mass composition: • R-50 1%

R-14 3% R-170 19% R-744 27% R-600 50%. 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, here R-600 and R-744, 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.

Preferably, the exchangers in the cascade are counter-current exchangers. They allow the use of very large temperature differences between inputs and outputs.

They also allow thermal recoveries between liquid and vapor phases at different temperatures.

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. .

Detailed description of the method and system according to the invention. Other characteristics and advantages of the invention will appear on reading the description of an alternative embodiment of the invention, given by way of indicative and non-limiting example and of FIG. 3 which 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.

We will now describe 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 thermal evolutions of the fumes and their chemical composition have been monitored as they circulate in the circuit where they are cooled.

The smoke flow M is the sum of four flows:

M = m _H20 + m _∞ 2 + m _N2 + m _tr aces where m _H2 o denotes the flow of water vapor, where ιttco2 denotes the flow of carbon dioxide, where m _N2 denotes the flow of nitrogen, where 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 energy which will be transferred by these fumes in exchanger 6 (first fume cooling exchanger) can be expressed as a function of the fume flow rate M: Q _ech = M (h _s6 - he ₆ ) where h _S6 , h _e6 designate respectively the enthalpies of the fumes at the outlet and at the inlet of the exchanger 6.

The mass compositions of the fumes at the outlet of the heat engine 1 are respectively equal to: • C0 ₂ : 19.5%,

• H ₂ 0: 8.6%,

• N ₂ : 71.9%,

In the present description, 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. It is possible to express the _yielded P _eCh power (expressed in kW) as a function of the smoke flow M expressed in kg / s: Pech = Qe _c h xM = 1000 kύ7 kg x M kg / s = 1000 M in kW. 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. Optionally, thermal energy, not counted in the energy balances described, can be recovered from the cooling circuit 3 of the heat engine 1. For this purpose, 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. In summer 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.

Tables 3 and 4 mention, in the case of each variant embodiment, the enthalpies of liquid water and and of steam water: ° at the inlet and at the outlet of the exchanger 6, ° at the outlet of the turbine 7 „and

° at the outlet of the air condenser 8.

These four enthalpy values are representative of the energy efficiency of the energy recovery circuit. The exchanger 6, the turbine 7, the condenser 8 and the pump 9 are connected by pipes and constitute the circuit for recovering thermal energy from the flue gases. The thermal energy thus recovered is transformed into mechanical energy.

An alternator 10 coupled to the turbine 7 transforms mechanical energy into electrical energy.

Table 3

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. In the case of the first variant, the vaporization takes place at 310 ° C, under a pressure of 99 bar. In the second case, 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. In the case of the first variant, when the temperature at the outlet of the exchanger 6 is equal to 400 ° C., when the pressure at the inlet of the exchanger 6 is equal to 99 bar and when the condensation temperature is equal at 40 ° C, table n ° 3 makes it possible to determine the mechanical energy, expressed by unit mass flow of water in the circuit of the exchanger 6. For a mechanical efficiency of the turbine 7 of 0.85, l mechanical energy is equal to:

(3098.2 - 1935.9) x 0.85 = 988 kJ / kg

In the case of the second variant, when the temperature at the outlet of the exchanger 6 is equal to 500 ° C., when the pressure at the inlet of the exchanger 6 is equal to 145 bar and when the condensation temperature is equal at 40 ° C, table n ° 4 makes it possible to determine the mechanical energy, expressed by unit mass flow of water in the circuit of the exchanger 6. For a mechanical efficiency of the turbine 7 of 0.85, l mechanical energy is equal to:

(3314.8 - 1982.1) x 0.85 = 1132.8 kJ / kg. In the case of the first variant, the energy supplied by the smoke circuit to the exchanger 6 is equal to: Q _ech = 3098.2 - 177.4 = 2920.8 kJ / kg.

In the case of the second variant, the energy supplied by the smoke circuit to the exchanger 6 is equal to: Qech = 3314.8 - 182 = 3132.8 kJ / kg It was previously stated that the thermal power P _{eC given off} by the fumes in the exchanger 6, as a function of the flow rate of the fumes, is equal to:

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 mechanical energy extracted, referred to this flow M, amounts to expressing the efficiency of the turbine cycle as a function of this smoke flow, that is: in case 1: P _mecha = (988 / 2920.8) x 1000 x M =

338.3 M in kW in case 2: P _méC a = (1132.8 / 3132.8) x 1000 x M = 361.6 M in kW

In the case of the first and second variant embodiments, the alternator 10 has an efficiency of 0.9. The electrical power P _é iec obtained thanks to the circuit for recovering thermal energy from the fumes, is: in the case of the first alternative embodiment equal to: P _é ι _ec = 304.5 M in kW in the case of the second variant of construction equal to: Péi _ec = 325.4 M in kW.

It is therefore possible to recover between 30.5 and 32.5% of electrical energy from the fumes, as soon as their temperature is above 400 ° C. We will now describe the successive cooling phases of the fumes in the various exchangers. 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

(Resp. S0 ₂ solid), then liquid, it is necessary to follow both the variations of the mass flow rates of these three components and the variations of energy along the smoke cooling circuit, that is to say along of the piping 13. The energy variations are expressed for each of the components in kJ / kg and are additive quantities, as are mass fractions. The enthalpies of nitrogen are reported in Table 6., the enthalpies of C0 ₂ (Resp. S0 ₂ ) are reported in Table 5 and in Figure 2 which represents, in a manner known per se, a temperature-entropy diagram C0 ₂ (Resp. S0 ₂ ). On this diagram, the temperatures are expressed in Kelvin ^Θ the entropies are expressed in kJ / kg.K. 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.

S0 ₂ ) at the inlet of the anti-sublimation evaporator (n ° 1) 39, before the gas / solid phase change. The pressure is

0.85 bar and the temperature is - 72 ° C (201 K), the enthalpy is 349 kJ / kg (see table 5).

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 5

The energy balances using the values in Table 5 are described below.

We will now continue the description of the evolution of the smoke flow at the inlet of the smoke cooling exchanger 11 and explain the mechanism for capturing water vapor as well as the energy consumption associated therewith.

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. For other temperature conditions or due to the presence of trace compounds which modify the dew temperature of water, the condensation of water can start in the exchanger 6. In fact, 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.

Let us specify the mode of exchange between the 2 pipes 13 and 55, they are in thermally efficient contact, for each connecting section that constitutes the pipe 13 between the exchangers 11, 25, 33 and 39 or 40. These 3 sections constitute real exchangers where the coldness of the nitrogen flow in the piping 55 cools the flow of fumes flowing against the current in the piping 13. Table 6 shows the variation in enthalpy of the nitrogen flow in the piping 55 for each of the 3 sections between heat exchangers 39 or 40 and heat exchanger 33, then between heat exchanger 33 and heat exchanger 25 and finally between heat exchanger 25 and heat exchanger 11. 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.

At the outlet 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. In fact, 8.6% of the mass flow rate was captured in the form of liquid water in the smoke cooling exchanger 11, in the exchanger constituted by the sections of the pipes 13 and 55 in contact, in the first (no. 1) evaporator cooler 25 and in the dehydrator 56.

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.

In the second (n ° 2) evaporator-cooler 33, a cooling capacity of 5.4 M is supplied and the residual flow M _{N2 + C} o2 ₊ so2 of nitrogen and C0 ₂ (Resp. S0 ₂ ) is cooled to 'at a temperature of -20 ° C.

Taking into account the cooling between pipes 13 and 55, the residual flow M _{N2 + œ2 +} 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 ) is thus captured by anti-sublimation at a temperature of the order of - 80 ° C at the pressure of 0.85 bar absolute or - 78.6 ° C at the pressure of a bar in the anti-sublimation evaporator 39 or 40 while the residual nitrogen flow denoted M _N2 is cooled down to -90 ° C., then is conveyed to the atmosphere through the pipe 55 which exchanges in against current with piping 13. We detail the energy evolution of C0 ₂ (Resp. S0 ₂ ) in the anti-sublimation evaporator (n ° 1) 39 where it returns at a temperature of around - 72 ° C and an enthalpy of 349 kJ / kg

(point C table 5 and figure 2). The change of vapor phase - complete solid (anti-sublimation) takes place on the tube of the anti-sublimation evaporator (n ° 1) 39, the C0 ₂ (Resp. S0 ₂ ) progresses to point D (Table 5 and Figure 2), its enthalpy is - 228 kJ / kg.

The cooling capacity, expressed in kW, as a function of the smoke flow rate, is (349 - (-228)) x 0.195 M = 112.5 M

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. In the case of the variant embodiment described, the transfer efficiency of the exchangers is 90%. Consequently, the energy recovered is equal to 205 kJ / kg. The cooling capacity recovered as a function of the total flow M of smoke is 40 M, expressed in kW: 205 x 0.195 M = 40 M. Taking into account the energy recovery from defrosting C0 ₂ (Resp. S0 ₂ ) by the liquid refrigerant, 1 anti-sublimation of C0 ₂ (Resp. S0 ₂ ) at an evaporation temperature of - 90 ° C (it takes a difference of about 10 ° C between the refrigerant and the C0 ₂ vapor or solid to frost the CO ₂ ) (Resp. SO ₂ ) requires only a cooling capacity of: (112.5-40) M = 72.5 M (expressed in kW)

We have seen that 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.

This energy balance can be validated by making a theoretical estimate of the electrical compression power that the compressor must provide to produce the cooling power. To make this estimate, it is necessary to recall beforehand what is meant by coefficient of performance of a refrigerating machine. The coefficient of performance is the ratio of the cooling power P _fr ι _g to the electric power supplied by the motor-compressor

-telec._Comp - • OJr - frig / Pelec._Comp-

Taking into account that cooling capacities will be exchanged at different temperature levels: -

5 ° C, - 30 ° C, - 90 ° C, it is essential to use a typical law of variation of the coefficient of performance according to the temperature.

The simplest way to express this law is to express it in terms of Carnot's coefficient of performance. The Carnot coefficient of performance represents the ideal performance of refrigeration machines and is calculated simply according to the condensation (T cond) and evaporation (Tevap) temperatures according to the formula: COP camot = Tevap / (T cond - T evap) temperatures being expressed in Kelvin.

A law based on the analysis of real machines can be expressed by:

COP = (2.15 x 10 ^"3 T + 0.025) Carnot COP

Table 7 below gives the COPs according to the evaporation temperatures.

Table 7

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. As the cooling power to be supplied is equal to 138 M (Table 6) and as the coefficient of performance is 3.57 (Table 7), the electric power consumed by the compressor is equal to: 138 M / 3.57 = 38 , 6 M in kW.

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

(table 7) the electric power consumed by the compressor is equal to: 5.4 / 1.9 = 2.8 M in kW. The cooling capacity supplied to the anti-sublimation evaporators (n ° l) 39 or (n ° 2) 40 is supplied at - 90 ° C. As the cooling capacity is (125.9M - 40M) = 85.9 M and since the coefficient of performance is 0.59 (Table 7), the electrical power consumed by the compressor is equal to: 85.9 M / 0.59 = 145.6 M in kW.

The cooling capacity necessary for cooling the nitrogen from 50 to - 90 ° C was taken into account in the calculations of each exchanger. The total electrical compression power (P _CO mp) is therefore to be supplied only for evaporators 25, 33 and 39 or 40 and is therefore equal to: _com p = 38.6 + 2.8 + 145.6 = 187 M in kW, as previously mentioned. 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.

We will now specify, referring again to Figure 3, the operation of the refrigeration apparatus operating in integrated cascade. 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%)

- R-14 (3%) ° R-170 (19%) ° R-744 (27%) ° R-600 (50%). 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 condensation, in the second (n ° 2) evapo-condenser 32, of the flow in gas phase (Mtête2) leaving the separating tank 28 was carried out by the partial evaporation of the liquid flow (Mpied2) leaving at the bottom of the separating tank 28 and after this liquid flow (Mpied2) has expanded in the expansion valve 31. The liquid flow (Mpied2) completes its evaporation in the smoke cooler evaporator 33. The fully vaporized liquid flow (Mpied2) gives up its coldness in the second ( n ° 2) vapor liquid exchanger 34 then joins the suction manifold of the compressor 17 via the piping 35.

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 flow of refrigerant vapors (Mtête2) leaving the first anti-sublimation evaporator (n ° 1) 39 passes through the second (n ° 2) three-way valve 46 and reintegrates the refrigerating compressor 17 via the gas return pipe 45. This flow (Mtête2) represents around 20% of the total refrigerant flow (Mf) drawn in by the refrigeration compressor 17.

When the operation of the first evaporator (no.

1) of anti-sublimation 39 is alternated with that of the second evaporator (n ° 2) of anti-sublimation 40, the first (n ° 1) three-way valve 37 switches, via the piping 44, the circulation of the refrigerant liquid to the first anti-sublimation evaporator (n ° 1) 39 where it is sub-cooled. The refrigerant then expands in the expansion valve (n ° 2) 42. It then evaporates in the second anti-sublimation evaporator (n ° 2) 40 then reintegrates, via the second (n ° 2) three-way valve 46 and the piping 45 the refrigeration compressor 17.

We will now describe the circulation of the refrigerant in the two anti-sublimation evaporators 39 and 40. These anti-sublimation evaporators operate alternately. When one is effectively an evaporator, the other is a sub-cooling exchanger and vice versa. In the case where evaporation takes place in the first anti-sublimation evaporator (n ° 1) 39, the first (n ° 1) three-way valve 37 is open, the mixture of refrigerant can circulate in the piping 38 but cannot flow through piping 44.

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.

In the case studied, 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.

2) anti-sublimation 40. These fumes cool from their inlet temperature which is approximately - 72 ° C to the anti-sublimation temperature of C0 ₂ which is either equal to - 78.6 ° C, or equal to - 80 ° C, depending on whether the pressure in the first anti-sublimation evaporator (n ° 1) 39 is 1 bar abs., Or 0.85 bar abs. Once this temperature has been reached, the C0 ₂ is frosted, inside the first anti-sublimation evaporator (n ° 1) 39, on the external wall of the piping in which the refrigerant mixture circulates. 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 ). During defrosting, liquid C0 ₂ accumulates in the lower part of the second anti-sublimation evaporator (n ° 2) 40. Before switching the operation of the second anti-sublimation evaporator (n ° 2) 40 by evaporation mode and at the end of the liquefaction of C0 ₂ (Resp. S0 ₂ ), 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. S0 ₂ ) mixed with nitrogen until the gaseous atmosphere is restored. 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. For practical reasons, in particular for vehicles, 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.

We will now describe the circulation of nitrogen leaving the first (n ° 1) anti-sublimation evaporator 39. 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.

During defrosting, the pressure rises by sublimation of C0 ₂ (Resp. S0 ₂ ) in the anti-sublimation evaporators 39 and 40 which are then in closed circuit. At the equilibrium temperature of the triple point, the pressure is equal to 5.2 bar. At this pressure the C0 ₂ (Resp. S0 ₂ ) changes from the solid state to the liquid state.

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.

The elimination of the water in the smoke cooling exchanger 11, in the first smoke cooling evaporator 25 and in the dehydrator 56, would cause a reduction in the pressure in the pipes. 2, 13, 55, if this was not compensated for: atmospheric air would enter the refrigerating appliance through the pipe 55 for bringing nitrogen into the air. Likewise, the anti-sublimation of C0 ₂ (Resp. S0 ₂ ) in the anti-sublimation evaporators 39 and 40 would cause a further reduction in pressure. This pressure drop must be compensated for so that nitrogen can be released to the atmosphere. The solution represented in 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.

If the contents of the trace components and in particular those of carbon monoxide CO and certain light hydrocarbons are not negligible, 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. Indeed, when the temperature of - 55 ° C is reached during the defrosting of C0 ₂ (Resp. S0 ₂ ), we can consider that the CO ₂ (Resp. SO ₂ ) has passed entirely into the liquid phase. We can then switch on the liquid C0 ₂ suction pump 48

(Resp. S0 ₂ liquid) for transfer to storage tank 49. It is then possible, by measuring the pressures in the interior volume of the evaporator when defrosting C0 ₂

(Resp. S0 ₂ ) to stop the emptying process, then restart the cycle by evaporating the refrigerant in this anti-sublimation evaporator previously emptied of its liquid CO ₂ (Resp. S0 ₂ liquid). Note that at the start of the cycle, when no evaporator is iced, the integrated cascade compression system consumes more energy. Indeed, the mixture which expands in the anti-sublimation evaporator is not sub-cooled. Energy optimization takes into account the most likely operating times of the engine, the energy production process, etc. to set the rhythm of the alternations between the two 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.

This capture of C0 ₂ and / or S0 ₂ is carried out with a view to its storage, its reinjection, further processing or use.

Emissions of carbon dioxide or C0 ₂ lead to an increase in the atmospheric concentration of C0 ₂ , considered unacceptable in the long term. 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) are already regulated both to avoid acid rain and to limit respiratory accidents in urban areas. For various reasons, 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.

For example, 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. Advantageously, 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.

Preferably, 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. Preferably, 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. , via an anti-sublimation process, is followed by 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. Preferably, 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 one.

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. Preferably, 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.

Preferably, 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 step of reducing the pressure in said closed enclosure to a pressure close to atmospheric pressure, - the step of transferring C0 ₂ and / or S0 ₂ , in liquid form in said reservoir.

Preferably, 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.

Preferably, 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. Preferably, 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. Preferably, 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.

Preferably, 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.

Preferably, 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. Preferably, 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.

Preferably, 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.

We will now describe, in general, an alternative embodiment of the invention. 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%, According to the process of the present invention, 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.

The term 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. The term 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. It is thus brought to a temperature lower than the anti-sublimation temperature of C0 ₂ and / or S0 ₂ at atmospheric pressure or close to atmospheric pressure. The total flow is cooled in the various exchangers of the refrigeration system before reaching the two anti-sublimation evaporators.

The two anti-sublimation evaporators operate alternately. The total flow passes alternately on one or the other of the two evaporators.

During the anti-sublimation phase, 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. During this time, the first evaporator is no longer the seat of an evaporation, 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. Initially 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 ). When these pressures are respectively reached, the melting of the frost then takes place from the solid phase to the liquid phase.

Once 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. Depending on the separation needs of S0 ₂ and C0 ₂ when they are frosted together, transfers can be carried out at successive pressures corresponding to the preferential presence of one of these bodies. At the end of the transfer, 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.

It is then possible to carry out the following cycle and to carry out an anti-sublimation of the C0 ₂ and / or of the S0 ₂ contained in the methane extracted from a borehole on the walls of the evaporator. The latter is again supplied with refrigerant. The cycle continues, so on, alternately on the two low temperature evaporators in parallel.

The refrigeration device implements a cooling principle, known per se, known as integrated cascade. However, the refrigeration device according to the invention has specific technical features which will be described below. In fact, to cool the fumes, over a significant temperature difference ranging from ambient temperature to -90 ° C and even up to -20 ° C, by means of a refrigeration device which is simple to make, comprising only one compressor , 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

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-

152a. It is possible to replace R-152a with butane R-600 or isobutane R-600a

• The quaternary mixtures

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. The following mixtures will be cited as examples: of 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.

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. For a system operating up to -120 ° C, 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.

They also allow thermal recoveries between liquid and vapor phase at different temperatures.

If 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.

There has been described above in detail a variant embodiment of an installation intended for the concomitant extraction of CO 2 and SO 2 from the fumes, in particular those circulating in the chimneys of electricity production plants. This description is applicable, subject to technical transposition within the reach of those skilled in the art, to an installation intended for the extraction of C02 and / or S02 contained in methane (CH4) coming from deposits.

HQ MCIA UKE

Claims

1. A method of 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; said method comprising the following steps: 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, said step of cooling said fumes comprising:

- the step of cooling the mixture of nitrogen, sulfur dioxide, or carbon dioxide and sulfur dioxide by supplying frigories by means of fractional distillation, at decreasing, staged temperatures, of a mixture refrigerants according to a cycle comprising a compression phase and successive condensation and evaporation phases.

2. Method according to claim 1; said method being 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 includes:

the step of extracting said water from said fumes in liquid form at a pressure substantially equal to atmospheric pressure.

3. Method according to claim 2; such that to extract from said smoke all or part of the water in liquid form at a pressure substantially equal to atmospheric pressure, an air or water exchanger is used.

4. Method according to claim 3; said method further comprising: the step of extracting all the quantities of residual water in said flue gases by using a refrigeration exchanger and / or a dehydrator.

5. Method according to any one of claims 1 to 4; 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 a anti-sublimation process being 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 enclosure closed during said melting, evolving up to the triple points of sulfur dioxide or carbon dioxide and sulfur dioxide, as the mixture of refrigerants, under cooling, brings calories into said enclosure.

6. Method according to claim 5; such that the mixture of refrigerants successively ensures the fusion of sulfur dioxide or carbon dioxide and said sulfur dioxide in a closed enclosure and the anti-sublimation of sulfur dioxide or carbon dioxide and sulfur dioxide circulating in open circuit in a symmetrical enclosure of the previous one; the fusion and anti-sublimation of sulfur dioxide or carbon dioxide and sulfur dioxide being alternately carried out in one and the other of said enclosures, one closed, the other open.

7. Method according to any one of claims 5 or 6; said method further comprising: the step of storing sulfur dioxide or carbon dioxide and sulfur dioxide in liquid form in a tank, in particular removable.

8. The method of claim 7; such as the step of storing sulfur dioxide or carbon dioxide and the sulfur dioxide in liquid form in a tank, in particular removable, comprises the following steps: the step of sucking the sulfur dioxide or carbon dioxide and the liquid sulfur dioxide contained in said closed enclosure, the step of bringing the pressure in said closed enclosure at a pressure close to atmospheric pressure, the step of transferring the sulfur dioxide or carbon dioxide and the liquid sulfur dioxide in said tank.

9. Method according to any one of claims 1 to 8; said method further comprising: the step of discharging nitrogen into the outside air after successive extractions of water vapors, sulfur dioxide, or carbon dioxide and sulfur dioxide, contained in said fumes.

10. The method of claim 9; said method further comprising:

the step of transferring the frigories contained in the nitrogen discharged into the air outside the flue gases and thus contributing to the cooling of said flue gases.

11. Method according to any one of claims 1 to 10; said method further comprising: the step of cooling said fumes to the anti-sublimation temperature of sulfur dioxide, or to the anti-sublimation temperatures of carbon dioxide and sulfur dioxide, to a pressure substantially equal to atmospheric pressure using the heat energy available in said smoke without additional supply of energy.

12. The method of claim 11; such that to use the heat energy available in said fumes, said process further comprises the following steps: the step of heating and then vaporizing water by means of said fumes, to produce pressurized steam, the step of expanding said pressurized steam in a turbine producing mechanical energy or electric.

13. 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; said system comprising: 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 vapor state to the solid state via an anti-sublimation process, said cooling means comprise: a refrigeration apparatus with integrated cascade (18, 22, 25, 26, 28, 32, 33, 34, 39, 40) for cooling the mixture of nitrogen, sulfur dioxide, or carbon dioxide and sulfur dioxide, by providing frigories by means of fractional distillation, at decreasing, staged temperatures, of a mixture of refrigerants according to a cycle comprising compression phase (17) and successive condensation and evaporation phases; said refrigerating apparatus comprising: a compressor (17), a partial condenser (18), - a separator tank (28), evapo-condensers (22, 32), smoke cooling evaporators (25, 33), exchangers liquid-vapor (26,34) - anti-sublimation evaporators (39, 40), regulators (24, 31, 41, 42).

14. The system of claim 13; said 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 via a anti-sublimation processes further comprise: extraction means, in particular exchangers (11, 25), for extracting said water fumes in liquid form at a pressure substantially equal to atmospheric pressure.

15. The system of claim 14; said system being such that said 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 (11).

16. The system of claim 15; said system being such that said extraction means for extracting all the quantities of residual water in said flue gases comprise a refrigeration exchanger (25) and / or a dehydrator (56).

17. System according to any one of claims 13 to 16; said system further comprising: a closed enclosure (39, 40) traversed by a circuit in which a mixture of refrigerants circulates; the pressure and the temperature in said closed enclosure evolving up to the triple points of sulfur dioxide, or of carbon dioxide and sulfur dioxide, as and when:

• the mixture of refrigerants, while sub-cooling, brings calories into said enclosure,

° said sulfur dioxide, or said carbon dioxide and sulfur dioxide, pass from the solid state to the liquid state.

18. The system of claim 17; such that the mixture of refrigerants successively ensures the fusion sulfur dioxide, or carbon dioxide and sulfur dioxide, in a closed enclosure and anti-sublimation of sulfur dioxide, or carbon dioxide and sulfur dioxide, circulating in open circuit in a symmetrical enclosure from the previous one; the fusion and anti-sublimation of sulfur dioxide, or of carbon dioxide and sulfur dioxide, being alternately carried out in one and the other of said enclosures (39, 40), one closed, the other open.

19. System according to any one of claims 17 or 18; said system further comprising:

- Storage means, in particular a fixed tank (49) and / or removable (51) for storing sulfur dioxide, or carbon dioxide and sulfur dioxide, in liquid form.

20. The system of claim 19; such that said means for storing sulfur dioxide, or carbon dioxide and sulfur dioxide, in liquid form in a fixed (49) and / or removable (51) tank further comprises suction means, in particular a pneumatic pump (48) for: sucking sulfur dioxide, or carbon dioxide and sulfur dioxide, liquid contained in said enclosure

(39, 40), bringing the pressure in said enclosure (39, 40) to a pressure close to atmospheric pressure, transferring the sulfur dioxide, or carbon dioxide and sulfur dioxide, liquid in said tank (49) .

21. System according to any one of claims 13 to 20; said system further comprising: compression and / or suction means (57, 59) for discharging nitrogen into the outside air after successive extractions of water vapors, sulfur dioxide, or carbon dioxide and sulfur dioxide, contained in said fumes.

22. The system of claim 21; said system further comprising: transfer means (55, 13) 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.

23. System according to any one of claims

13 to 22; said system further comprising:

means of recovery (6, 7, 8, 9, 10) of the heat energy available in said fumes to cool, at least in part, said fumes to the anti-sublimation temperature of sulfur dioxide, or carbon dioxide and sulfur dioxide, at a pressure substantially equal to atmospheric pressure.

24. The system of claim 23; such that said means for recovering (6, 7, 8, 9, 10) the heat energy available in said fumes comprises: reheating means, in particular an exchanger (6), for reheating and vaporizing the water by means of said smoke and for producing pressurized water vapor, expansion means, in particular a turbine (7), for expanding said pressurized water vapor and producing mechanical or electrical energy (10).

25. Process for extracting carbon dioxide and / or sulfur dioxide contained in methane originating in particular from deposits; said method comprising the following steps: the step of cooling said methane to a pressure substantially equal to atmospheric pressure to a temperature such that carbon dioxide and / or sulfur dioxide pass directly from the vapor state to the state solid via an anti-sublimation process, the step of cooling said methane comprising: the step of cooling the mixture of methane, carbon dioxide and / or sulfur dioxide by providing frigories by means of a fractional distillation, at decreasing temperatures, stepped, of a mixture of fluids refrigerants according to a cycle comprising a compression phase and successive condensation and evaporation phases.

26. The method of claim 25; said methane containing water in a vapor state; said method being such that the step of cooling said methane to a pressure substantially equal to atmospheric pressure to a temperature such that carbon dioxide and / or sulfur dioxide pass directly from the vapor state to the solid state via an anti-sublimation process further comprises: the step of extracting said methane from water in liquid form at a pressure substantially equal to atmospheric pressure.

27. The method of claim 26; such that to extract from said methane all or part of the water in liquid form at a pressure substantially equal to atmospheric pressure, an air or water exchanger is used.

28. The method of claim 27; said method further comprising: the step of extracting all the quantities of residual water in said methane by using a refrigerant exchanger and / or a dehydrator.

29. Method according to any one of claims 25 to 28; the step consisting in cooling said methane to a pressure substantially equal to atmospheric pressure to a temperature such that carbon dioxide and / or sulfur dioxide pass directly from the vapor state to the solid state via a process of anti-sublimation being followed: by a step of melting carbon dioxide and / or sulfur dioxide in a closed enclosure; the pressure and the temperature in said enclosure closed during said melting, evolving up to the triple points of carbon dioxide and / or sulfur dioxide, as the mixture of refrigerants, by sub-cooling, provides in said calorie enclosure.

30. The method of claim 29; such that the mixture of refrigerants successively ensures the fusion of carbon dioxide and / or sulfur dioxide in a closed enclosure and the anti-sublimation of carbon dioxide and / or sulfur dioxide circulating in an open circuit in an enclosure symmetrical to the previous one; the fusion and antisublimation of carbon dioxide and / or sulfur dioxide being alternately carried out in one and the other of said enclosures, one closed, the other open.

31. Method according to any one of the claims

29 or 30; said method further comprising:

- The step of storing carbon dioxide and / or sulfur dioxide in liquid form in a tank, in particular removable.

32. The method of claim 31; such that the step of storing carbon dioxide and / or sulfur dioxide in liquid form in a tank, in particular removable, comprises the following steps:

the step of sucking up the carbon dioxide and / or the liquid sulfur dioxide 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 carbon dioxide and / or liquid sulfur dioxide in said tank.

33. Method according to any one of claims

25 to 32; said method further comprising: the step of recovering methane after extractions of carbon dioxide and / or sulfur dioxide contained in said methane.

34. The method of claim 33; said process further comprising: the step of transferring the frigories contained in the methane recovered to methane coming from a deposit and thus contributing to the cooling of said methane.

35. Method according to any one of claims 25 to 34; said methane being at a temperature above ambient temperature; said method further comprising: the step of cooling said methane to the anti-sublimation temperature of carbon dioxide and / or sulfur dioxide to a pressure substantially equal to atmospheric pressure using the available heat energy in said methane without additional supply of energy.

36. The method of claim 35; such as to use the heat energy available in said methane, said method further comprises the following steps: the step of heating and then vaporizing water using said methane, to produce pressurized steam,

- The step of relaxing said pressurized water vapor in a turbine producing mechanical or electrical energy.

37. System for extracting carbon dioxide and / or sulfur dioxide contained in methane originating in particular from deposits; said system comprising: cooling means for cooling said methane to a pressure substantially equal to atmospheric pressure to a temperature such that carbon dioxide and / or sulfur dioxide pass directly from the vapor state to the solid state via an anti-sublimation process, said cooling means comprise: a refrigeration appliance with integrated cascade (18, 22, 25, 26, 28, 32, 33, 34, 39, 40) for cooling the mixture of methane and dioxide of carbon and / or sulfur dioxide by supplying frigories by means of fractional distillation, at decreasing, staged temperatures, of a mixture of refrigerants in a cycle comprising a compression phase (17) and successive condensation and evaporation phases; said refrigerating apparatus comprising:

- a compressor (17), - a partial condenser (18), a separator tank (28), evapo-condensers (22, 32), evaporators for cooling flue gases (25, 33), - liquid-vapor exchangers (26,34) anti-sublimation evaporators (39, 40),

- regulators (24, 31, 41, 42).

38. The system of claim 37; said methane containing water in a vapor state; said means for cooling said methane to a pressure substantially equal to atmospheric pressure to a temperature such that carbon dioxide and / or sulfur dioxide pass directly from the vapor state to the solid state via an anti-aging process. sublimation further include: - extraction means, in particular exchangers

(11, 25), to extract from said methane water in liquid form at a pressure substantially equal to atmospheric pressure.

39. The system of claim 38; said system being such that said extraction means for extracting from said methane all or part of the water in liquid form at a pressure substantially equal to atmospheric pressure comprise an air or water exchanger (11).

40. The system of claim 39; said system being such that said extraction means for extracting all the quantities of residual water in said methane comprise a refrigerant exchanger (25) and / or a dehydrator (56).

41. System according to any one of claims 37 to 40; said system further comprising: a closed enclosure (39, 40) traversed by a circuit in which a mixture of refrigerants circulates; the pressure and the temperature in said closed enclosure evolving up to the triple points of carbon dioxide and / or sulfur dioxide, as and when:

° the mixture of refrigerants, while sub-cooling, brings calories into said enclosure,

° the carbon dioxide and / or sulfur dioxide pass from the solid state to the liquid state.

42. The system of claim 41; such that the mixture of refrigerants successively ensures the fusion of carbon dioxide and / or sulfur dioxide in a closed enclosure and the anti-sublimation of carbon dioxide and / or sulfur dioxide circulating in an open circuit in an enclosure symmetrical to the previous one; the fusion and antisublimation of carbon dioxide and / or sulfur dioxide being alternately carried out in one and the other of said enclosures (39, 40), one closed, the other open.

43. System according to any one of claims 41 or 42; said system further comprising: storage means, in particular a fixed tank (49) and / or removable (51) for storing carbon dioxide and / or sulfur dioxide in liquid form.

44. The system of claim 43; such that said means for storing carbon dioxide and / or sulfur dioxide in liquid form in a fixed (49) and / or removable tank (51) further comprises suction means, in particular a pneumatic pump (48) for: sucking up the carbon dioxide and / or the liquid sulfur dioxide contained in said enclosure (39, 40), reducing the pressure in said enclosure (39, 40) to a pressure close to atmospheric pressure, transferring the carbon dioxide and / or the liquid sulfur dioxide in said tank (49).

45. System according to any one of claims 37 to 44; said system further comprising: compression and / or suction means (57, 59) for recovering the methane after extraction of the carbon dioxide and / or sulfur dioxide contained in said methane.

46. The system of claim 45; said system further comprising: transfer means (55, 13) for transferring the frigories contained in said recovered methane to methane coming from a deposit and thereby contributing to the cooling of said methane.

47. System according to any one of claims 37 to 46; said methane being at a temperature above ambient temperature; said system further comprising: - means for recovering (6, 7, 8, 9, 10) of the heat energy available in said methane to cool, at least in part, said methane to the temperature of anti sublimation of carbon dioxide and / or sulfur dioxide at a pressure substantially equal to atmospheric pressure.

48. The system of claim 47; such that said means for recovering (6, 7, 8, 9, 10) of the heat energy available in said methane comprises: reheating means, in particular an exchanger (6), for reheating and vaporizing the water by means of said smoke and for producing pressurized water vapor, expansion means, in particular a turbine (7), for expanding said pressurized water vapor and producing mechanical or electrical energy (10).