Process for solid-phase extraction of substances present in gas mixtures

Abstract

Method for solid phase extraction of at least one substance such as NO2, N2O, SO2, H2S, or CO2, contained in a gas mixture (11), the method comprising: - a step of cooling (20) the gas mixture containing the substance which will at low temperatures pass directly from the gas phase to the solid phase; - a parallel step of producing hydrocarbon snow (250) in a series of ejectors (350); - a step of dispersing this hydrocarbon snow at a temperature lower than that of the triple point of the substance to be antisublimated, in a column (450) where the gas mixture containing the substance to be antisublimated circulates; - a step of sublimation of the solid particles of the hydrocarbon causing the antisublimation of the substance, contained in the gas mixture;- a step of recovering the substance (5) in solid phase, at the bottom of the column, in a double storage device (51, 52) operating alternately in recovery mode or in solid substance evacuation mode.;

Description

Title of the invention: Process for the solid phase extraction of substances present in gas mixtures

[0001] Technical field and state of the art

[0002] The invention relates to the anti-sublimation of substances such as nitrogen oxides (N2 O, NO2), SO2, H2S, or carbon dioxide (CO2), contained in a gas mixture mainly comprising gases very far from their triple points (such as CH4, N2, O2, H2), and this by the sublimation of a hydrocarbon snow projected into the circulating gas mixture.

[0003] By antisublimation is meant here the direct solidification of a substance, such as for example carbon dioxide, from its gaseous state to its solid state, at temperatures below the temperature of its triple point. Reference may be made, for example, to the document Pan et al. CO2 capture by antisublimation process and its technical économie analysis, doi.org / 10.1002 / ghg.1313. Reference may be made to documents EP2464436 (Armines, 2015), EP1979072 (GDF, 2010), WO2010 / 012658 (Alstom, 2010), WO2010076464 (Air Liquide, 2010).

[0004] In prior art carbon dioxide capture devices by antisublimation, CO2 is deposited in solid form on tube-fin heat exchangers.

[0005] Document EP1355716B1 (Armines, 2005) describes a method for extracting carbon dioxide from fumes originating from the combustion of hydrocarbons, the method comprising a step of cooling the fumes to a pressure substantially equal to atmospheric pressure at a temperature such that the carbon dioxide passes directly to the solid state by antisublimation, followed by a step of melting the carbon dioxide in a closed enclosure, the pressure and temperature in the enclosure increasing up to the triple point of carbon dioxide.

[0006] The implementation of the method described in document EP1355716B1 requires very large exchange surfaces when the flow rates of the gases to be treated are high.

[0007] WO2011 / 097043 (Exxonmobil, 2011) describes the use of a cold liquid to separate solidifiable gaseous components from process gas streams. The cold liquids may be non-oxygenated hydrocarbons, such as isopentane, isohexane, isoalkenes, mixtures thereof, alcohols and mixtures of alcohols. The cold liquid is contacted with the gas stream to be treated in a spray tower or bubble column.

[0008] The implementation of the method described in document WO2011 / 097043 requires an additional separation between the liquid and the solid.

[0009] Objects of the invention

[0010] One of the objects of the invention is to enable the denitrification, desulfurization, decarbonation of gas mixtures such as fumes or process gases, containing gases very far from their triple points (such as CH4, N2, O2, H2), in variable concentrations.

[0011] Another object of the invention is to make it possible to limit emissions of pollutants such as nitrogen oxides (NOX), sulfur oxides (SOX), or greenhouse gases such as carbon dioxide CO2.

[0012] Another object of the invention is to enable the decarbonation of atmospheric air.

[0013] Another object of the invention is to allow the solid phase extraction of any substance whose triple point temperature is higher than that of the hydrocarbons projected in the form of snow into the gas flow containing these substances.

[0014] General presentation of the invention

[0015] For these purposes, there is proposed, according to a first aspect, a method for solid phase extraction of at least one substance such as NO2, N2O, SO2, H2S, or CO2, contained in a gas mixture, the method comprising:

[0016] - a step of cooling the gas mixture containing the substance which goes to low temperatures pass directly from the gas phase to the solid phase;

[0017] - a parallel step of hydrocarbon snow production in a series of ejectors;

[0018] - a step of dispersing this hydrocarbon snow at a lower temperature to that of the triple point of the substance to be antisublimated, in a column where the gas mixture containing the substance to be antisublimated circulates;

[0019] - a step of sublimation of the solid particles of the hydrocarbon resulting in antisublimation of the substance contained in the gas mixture;

[0020] - a step of recovering the substance in solid phase, at the bottom of the column, in a dual storage device operating alternately in recovery mode or in solid substance evacuation mode.

[0021] Advantageously, the step of producing hydrocarbon snow comprises a step of mixing the liquid hydrocarbon with a propellant gas at a temperature below the triple point of the hydrocarbon.

[0022] Advantageously, a treated gas mixture, devoid of at least one substance such as NO2, N2O, SO2, H2S, or CO2 is obtained, this treated gas mixture being used to form at least part of the propellant gas.

[0023] Advantageously, the step of dispersing the hydrocarbon snow is carried out in a cyclonic column.

[0024] Advantageously, the method comprises a step of recovering the coldness of the treated gas mixture, freed from the substance having been extracted in solid phase.

[0025] Advantageously, the method comprises a step of condensation of the hydrocarbon vapor advantageously followed by passage through an activated carbon filter.

[0026] Advantageously, the method comprises a step of rejecting the treated gas mixture, freed from most of the substances extracted in the solid phase, such as NO2, N2O, SO2, H2S, or CO2.

[0027] In some implementations, the triple point of the hydrocarbon is less than -95°C.

[0028] In certain implementations, the hydrocarbon is selected from the group including pentane (CAS 109-66-0), hexane (CAS 110-54-3), isopentane (2-methylbutane CAS 78-78-4), isohexane (2-methylpentane CAS 107-83-5), 2,3-dimethylbutane (CAS 79-29-8), 2,2-dimethylbutane (CAS 75-83-2), 3-methylpentane (CAS 96-14-0).

[0029] Advantageously, the substance to be extracted from the gas mixture is carbon dioxide CO2.

[0030] In some implementations, the gas mixture to be treated is a flue gas, or a process gas.

[0031] Advantageously, several cyclone-shaped separation columns are arranged in series to carry out progressive decarbonization.

[0032] In some implementations, the substance(s) extracted from the gas mixture are recovered and transported in the solid phase.

[0033] In other implementations, the extracted substance(s) are recovered in solid phase, then liquefied with recovery of cold energy due to sublimation, and fusion.

[0034] In other implementations, the extracted substance(s) are recovered in solid phase, then liquefied and vaporized with recovery of cold energy.

[0035] The process thus makes it possible to recover solid CO2 in large quantities with high energy efficiency and alternately in two storage volumes, the CO2 then being able to be recovered and transported in the solid phase, or in the liquid phase with pressurization and recovery of cold energy, or even in the gaseous phase with thermal recovery.

[0036] Other objects and advantages of the invention will appear in light of the description of embodiments, given below with reference to the appended figures.

[0037] List of figures

[0038] [Fig-1] is a diagram of the stages of solid condensation of substances for temperatures below their triple points and particularly carbon dioxide by sublimation of hydrocarbon snow;

[0039] [Fig.2] is a schematic representation of a type of ejector mixing a flow of decarbonized fumes at a temperature below the triple point of the hydrocarbon and the liquid hydrocarbon at a temperature close to its triple point;

[0040] [Fig.3] is a diagram of a cyclonic column for antisublimation of CO2 by injection of hydrocarbon snow.

[0041] Description of embodiments

[0042] The following table gives the temperatures and pressures of the triple points of certain substances capable of being extracted in solid phase from a mixture of gases whose other components are CH4, N2, O2, H2 Substance Triple point temperature (°C) Triple point pressure (kPa) so2 -76.8 1.466 h2s -85.5 22.700 no2 -11.2 1.860 n2o -90.8 87.800 co2 -56.6 520.000

[0043] In the remainder of this description, the substance to be extracted is carbon dioxide.

[0044] The detailed example below for CO2 applies to other substances whose triple point temperature is higher than that of the hydrocarbons injected as snow into the gas flow, in particular the substances mentioned in the table above (NO2, N2O, SO2, H2S).

[0045] As recalled, antisublimation is the direct passage from the gas phase to the solid phase.

[0046] Carbon dioxide CO2 has a triple point at a pressure of 520 kPa and a temperature of -56.6°C, which means that any cooling of carbon dioxide to pressures below 520 kPa causes its antisublimation, at temperatures which depend on its partial pressure.

[0047] For the capture of CO2 contained in fumes or in gaseous effluents from industrial processes (for example cement works, steelworks) or means of transport (for example ships), or even directly in the air, the partial pressure of CO2 is equivalent to the molar concentration in the gas mixtures, and this concentration defines the antisublimation start temperature.

[0048] Examples of temperatures are given in the following table, using the equations of solid-vapor equilibria as defined by the NIST -National Institute of Science and Technology- Refprop 10 software, software recognized worldwide by the thermodynamic research community. Molar concentration of CO2 (%) Antisublimation temperature (°C) 40 -89 30 -92 20 -96.5 15 -99 10 -103 5 -109 1 -122 0.5 -126.5 0.04 -141 0.01 -148

[0049] The CO2 concentrations of a biogas vary from 25% to 50%, in cement works and steel industry these concentrations vary from 5% to 35%, in the combustion fumes of gas turbines these concentrations vary from 3% to 10%, in the fumes of large ships these concentrations vary from 4 to 5%, and the concentration of carbon dioxide in the air is generally 400 ppm, or 0.04%.

[0050] For each inlet concentration, an outlet concentration is defined, generally ensuring a CO2 capture efficiency of 90%, i.e. if the inlet concentration is 15% the outlet concentration is 1.5%.

[0051] For this example, the antisublimation start temperature is -99°C and the exit temperature is -119°C.

[0052] In the process, the sublimation at atmospheric pressure of a hydrocarbon snow makes it possible to antisublimate substances whose triple point is higher than the triple point of this hydrocarbon.

[0053] The CO2 present in the gas mixture to be treated comprising variable concentrations of CO2, the carbon dioxide will antisublimate at variable temperatures, between -90°C and -150°C, the other gases in the gas mixture being for example nitrogen, oxygen, argon, hydrogen, or methane.

[0054] The flow rates to be treated in cement or steelworks, but also for gas-fired electricity production plants, vary from 100,000 to 3 million Nm3 / h. The solid CO2 flow rates can vary for these large flow rates from 10 to 100 tonnes / hour. The NOx and SOx flow rates are a few tonnes.

[0055] To handle such flow rates, the CO2 capture device must be robust, equipped with simple regulation, energy efficient and the floor space of the installation must be relatively small.

[0056] The method operates advantageously around atmospheric pressure, for limit energy consumption.

[0057] In the process, the flow of the gas mixture containing carbon dioxide (or any substance capable of antisubliming such as SO2, H2S, NO2, N2O) advantageously circulates in a separation column in which a cryogenic solid of hydrocarbon type circulates in the form of snow.

[0058] The sublimation of the hydrocarbon snow at the given temperature results in antisublimation of the substance to be extracted from the gas mixture, particularly CO2

[0059] This CO2 anti-sublimation column advantageously has the shape of a cyclone, to promote the separation of the CO2 snow and the mixture of gas to be decarbonized enriched with the sublimed hydrocarbon.

[0060] The substances which can become cryogenic snow and which sublime between -90°C and -160°C are advantageously hydrocarbons whose triple point is lower than the antisublimation temperatures of CO2 or other substances to be extracted from the gas mixture.

[0061] It is advantageous to be able to condense these molecules once they are in the gas phase and this at temperatures of the order of 20°C at atmospheric pressure.

[0062] Managing the process at atmospheric pressure thus avoids the compression of large flow rates of gas mixture to be treated and results in a significant energy saving, compared to any process which requires compressing the gas mixture to be decarbonized.

[0063] The table below gives the values of the temperatures and pressures in Pa of the triple points as well as the condensation pressures in kPa at 20°C of hydrocarbons capable of producing cryogenic snow. Substance Triple point temperature (°C) Triple point pressure (Pa) Saturation pressure at 20°C (kPa) pentane -129.7 0.08 56 hexane -95.3 12 16 isopentane -160.5 0.0001 76.6 isohexane -153.5 0.00001 22.8 2,3-Dimethylbutane -128 0.015 25.3 2,2Dimethylbutane -98.9 5.2 35 3-Methylpentane -162.9 0.0002 0.205

[0064] The interests of the properties of these fluid hydrocarbons are as follows.

[0065] Firstly, their latent heat of sublimation is of the same order of magnitude as that of CO2, i.e. of the order of 570 kJ / kg.

[0066] Secondly, once sublimated, these hydrocarbon vapors are condensed at atmospheric pressure to be recycled.

[0067] It is possible to successively use these hydrocarbons to antisublimate the substances found in the fumes: NO2, N2O, SO2, H2S, CO2 at temperatures depending on their partial pressures in the gas mixture additionally containing gases far from their triple points such as CH4, N2, O2, Ar, H2.

[0068] The solid condensation or antisublimation of these substances and mainly CO2 will occur by direct contact between the hydrocarbon snow, advantageously pentane or isopentane, for the antisublimation of CO2 at the desired residual concentrations for decarbonization of the fumes, advantageously of the order of 0.5% to 1% corresponding respectively to final CO2 antisublimation temperatures of -126.5°C to -122°C.

[0069] To decarbonize the air up to 100 ppm, the anti-sublimation temperature of CO2 will advantageously be -148°C, it will then be necessary to use, for example, isopentane snow.

[0070] Several solid condensation columns can advantageously be placed in series, depending on the CO2 content of the fumes and the fume flow rate.

[0071] For example, for a flow rate of 100,000 NmVh at a volume concentration of 15%, the mass of CO2 captured when the concentration drops from 15% to 1.5% is approximately 26 tonnes / hour, it is then advisable to divide this capture into thirds, i.e. to put three columns of solid condensation of progressively colder CO2 for example -105°C, -115°C and -125°C.

[0072] We first refer to [Fig.l].

[0073] During step 10 the flow of gas mixture 11 to be decarbonized is sent, for example by a booster 100.

[0074] During step 20, the flow of gas mixture 11 is cooled around atmospheric pressure to a temperature just above the anti-sublimation temperature of CO2 according to its concentration in the gas mixture 11, and this in exchangers 200.

[0075] During step 30, the liquid hydrocarbon 25 recovered from step 70 is cooled, to a temperature very close to the triple point of this hydrocarbon 25, in an exchanger 300.

[0076] The liquid hydrocarbon 25 is injected by a pump 325 towards the ejectors 350.

[0077] Step 35 comprises mixing in a series of ejectors 350 of the propellant gas, advantageously a fraction of the flow rate of the mixture of decarbonized gas 155 with the liquid hydrocarbon 25.

[0078] Due to the fact that the temperature of the propellant gas 155 is lower than that of the triple point of the hydrocarbon 25 and the depressogenic effect of the injection of the propellant gas 155 into the ejector 350, the hydrocarbon 25 passes from the liquid phase to the solid phase, and this hydrocarbon snow 250 is ejected by the ejectors 350 towards the flow rate of the gas mixture 11 to be decarbonized.

[0079] Step 40 comprises the lateral injection by the ejectors 350 of the hydrocarbon snow 250 into the mixture of gas to be decarbonized 11, and this in one or more columns 450 in series, advantageously in the form of cyclones.

[0080] Step 45 comprises the sublimation of the hydrocarbon snow 250 at a temperature lower than that of the triple point of CO2 at its lowest concentration, for example -126.5°C for 0.5%, causing the antisublimation of the CO2 in one or more columns 450, advantageously in the form of a cyclone, forming at the outlet a mixture 12 of decarbonized gas and CO2 snow separated by the cyclonic form of the separation column 450.

[0081] The solid CO2 whose density at this temperature is of the order of 1550 kg / m3 is sent by the swirling movement towards the walls of the cyclone-shaped column, thus separating from the gas mixture whose density at this temperature is typically of the order of 2.5 kg / m3

[0082] Step 50 comprises the recovery of solid CO2 5 at the base of the column, advantageously in the form of a cyclone.

[0083] The steps 51 and 52 of storing the solid CO2 5 are carried out alternately. When the level of the storage 510 is at the maximum threshold, a flap 511 closes and a flap 521 of the storage 520 opens (these flaps are visible in [Fig.3]). Each of the storages 510 and 520 empties CO2 either in solid form or in liquid form with energy recovery.

[0084] Step 60 comprises the transfer of cold energy from the flow of the decarbonized mixture 15 to the mixture to be decarbonized 11 during step 20, by exchangers 200, with a view to limiting energy consumption.

[0085] Step 70 comprises the condensation around 20°C of the hydrocarbon 25 contained in the decarbonized gas mixture 15 in a gas-liquid exchanger-separator 700, in order to recycle the hydrocarbon 25.

[0086] To limit the hydrocarbon content 25 of the decarbonized gas mixture 15 to less than 1 ppm, regenerable activated carbon filters can advantageously be installed downstream of the hydrocarbon condenser 700.

[0087] Step 80 comprises the return of the fraction 150 of the decarbonized flow 15 and after condensation of the hydrocarbon 25 to the next use or to the atmosphere.

[0088] Step 90 comprises the compression of a fraction 155 of the decarbonized and hydrocarbon-free flow 25 by the compression system 900, to make it advantageously- carefully the propellant flow 155 of the ejectors.

[0089] Step 65 comprises cooling the flow 155 to a temperature below the triple point of the hydrocarbon in the exchanger 650, which completes the recycling of this flow 155.

[0090] The result of all these steps is the decarbonization of a flow of gas mixture, with recovery of the CO2 in solid phase.

[0091] The result can also be the denitrification or desulfurization of gas mixture with solid phase recovery of SO2, H2S or NO2 and N2O.

[0092] Referring to [Fig.2] which is a section of a type of ejector whose operation to produce hydrocarbon ice is as follows.

[0093] The propellant gas, advantageously the mixture of decarbonized and hydrocarbon-free gas 155, is injected into the ejector 350 via an injection nozzle 355.

[0094] The speed of this gas close to the sonic speed at the outlet of the injection nozzle 355 creates a depressogenic effect and sucks the hydrocarbon 25 via the feed pipe 345.

[0095] The depression thus generated associated with the temperature of the propellant gas 155 lower than the triple point of the hydrocarbon 25 leads to the formation of the hydrocarbon snow 250 in a mixing chamber 360.

[0096] A restriction 365 at the outlet of the ejector 350 advantageously increases the speed of ejection of the snow 250 as well as its dispersion.

[0097] Refer to [Fig.3], which is a volumetric representation of a column 450 in the form of a cyclone.

[0098] The mixture to be decarbonized 11 enters laterally through a pipe 451 into the column 450 with an angle which generates a swirling movement, which rotates in [Fig.3] in a clockwise direction.

[0099] Along the wall of the column 450 are placed rings of ejectors 350 which project the hydrocarbon ice 25 at a temperature lower than the triple point temperature corresponding to the final concentration targeted for the decarbonation of the gas mixture 11.

[0100] The CO2 contained in the mixture 11 passes from the gas phase to the solid phase, an antisublimation evolution due to the sublimation of the hydrocarbon snow 25.

[0101] The solid CO2 5 falls towards the bottom of the column 450, where it is recovered in a storage 510 or 520 depending on whether the flap 511 or 521 is open.

[0102] The opening or closing of the flap 511 or 521 is generated by the level sensor 512 for the storage 510 respectively 522 for the storage 520, when the level 512 indicates that the tank 510 is full of solid CO2 5, it generates a signal which will cause the opening of the flap 521 and the closing of the flap 511 and vice versa for the sensor 522.

[0103] The decarbonized gas mixture 12 leaves the column 450 through the pipe 452 by a swirling movement whose direction is opposite to the swirl of the carbonized gas mixture 11 in the process of decarbonizing in contact with the hydrocarbon snow 25.

[0104] Various solid CO2 management options are possible.

[0105] In some implementations, the CO2 is transferred in solid phase out of the storages 510 and 520 into a mobile storage for transport in solid phase.

[0106] In some implementations, the CO2 is transferred into enclosures where the sublimation and fusion coldness will be recovered; the CO2 may be transferred into tanks or pipelines to be transported at pressures ranging from 600 KPa to 2 MPa and temperatures ranging from -50°C to -20°C.

[0107] In some implementations, the liquid CO2 may also be vaporized for use in a process near the CO2 capture facility.

Claims

Claims

1. Method for solid phase extraction of at least one substance such as NO2, N2O, SO2, H2S, or CO2, contained in a gas mixture (11), the method comprising: - a step of cooling (20) the gas mixture (11) containing the substance which will at low temperatures pass directly from the gas phase to the solid phase; - a parallel step of producing hydrocarbon snow (250) in a series of ejectors (350); - a step of dispersing this hydrocarbon snow (250) at a temperature lower than that of the triple point of the substance to be antisublimated, in a column (450) where the gas mixture (11) containing the substance to be antisublimated circulates; - a step of sublimation of the solid particles of the hydrocarbon causing the antisublimation of the substance, contained in the gas mixture (11);- a step of recovering the substance (5) in solid phase, at the bottom of the column (450), in a double storage device (51, 52) operating alternately in recovery mode or in evacuation mode of the solid substance (5).;

2. Method according to claim 1, characterized in that the step of producing hydrocarbon snow (250) comprises a step of mixing (35) the liquid hydrocarbon (25) with a propellant gas at a temperature lower than the triple point of the hydrocarbon (25).

3. Method according to any one of claims 1 to 2, characterized in that the step of dispersing the hydrocarbon snow (250) is carried out in a cyclonic column (450).

4. Method according to any one of claims 1 to 3, characterized in that it comprises a step of recovering the coldness of the treated gas mixture (12), freed from the substance having been extracted in solid phase (5).

5. Method according to any one of claims 1 to 4, characterized in that it comprises a step of condensation (70) of the hydrocarbon vapor advantageously followed by passage through an activated carbon filter.

6. Method according to any one of claims 1 to 5, characterized in that it comprises a step of rejecting the treated gas mixture (12), freed from the majority of the substances extracted in solid phase, such as NO2, N2O, SO2, H2S, or CO2.

7. A method according to any one of claims 2 to 6, characterized in that the triple point of the hydrocarbon (25) is less than -95°C.

8. Method according to any one of claims 2 to 6, characterized in that the hydrocarbon (25) is chosen from the group comprising pentane, hexane, isopentane, isohexane, 2,3-dimethylbutane, 2,2-dimethylbutane, 3-methylpentane.

9. Method according to any one of claims 1 to 8, characterized in that the substance to be extracted from the gas mixture (11) is carbon dioxide CO2.

10. A method according to any one of claims 1 to 9, characterized in that the gas mixture (11) is a flue gas or a process gas.

11. A method according to any one of claims 1 to 10, characterized in that several cyclone-shaped separation columns are arranged in series to carry out progressive decarbonization.

12. Method according to any one of claims 1 to 11, characterized in that the substances extracted from the gas mixture (11) are recovered and transported in solid phase.

13. Method according to any one of claims 1 to 11, characterized in that the extracted substances are recovered in solid phase, then liquefied with recovery of cold energy due to sublimation, and fusion.

14. Method according to any one of claims 1 to 11, characterized in that the extracted substances are recovered in solid phase, then liquefied and vaporized with recovery of cold energy.

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