The present invention relates to a device for producing hydrogen from electron cyclotron resonance plasma.
Today hydrogen (H2) appears to be an energy vector of great interest, which is called to take on more and more importance and which may, eventually, advantageously be substituted for petroleum and fossil fuels, whose reserves will significantly decrease in the decades to come. In this perspective, it is necessary to develop effective methods to produce hydrogen.
Admittedly, many methods for producing hydrogen from various sources have been described, but a number of these methods have turned out to be unsuitable with regard to the limitation of greenhouse gases.
A first technique consists of using water vapor reforming. This is a technique for transforming light hydrocarbons such as methane into synthesis gas by reaction with water vapor on a catalyst. The two main chemical reactions of this method are the production of synthesis gas and the conversion of CO:
CH4+H2O→CO+3H2
CO+H2O→CO2+H2
the overall result being
CH4+2H2O→CO2+4H2
One of the main problems with this synthesis route is that it produces, as by-products, significant quantities of CO2-type greenhouse gases.
A second method consists of using a partial oxidation technique: This is an exothermal technique, generally without oxidation catalyst, for products such as natural gas, heavy oil residues and coal. The production of synthesis gas is given by the reaction:
CnHm+(n/2)O2→nCO+(m/2)H2
The conversion of carbon monoxide is given by the reaction:
nCO+nH2O→nCO2+nH2
As with reforming, this technique produces a significant quantity of carbon dioxide.
Mention may also be made of a third technique using the direct thermal decomposition of water; such a technique would necessitate extremely high temperatures on the order of 3000 to 4000 K (the use of a catalyst enables this temperature to be reduced, which would, however, remain very high, approaching 1400 K). This production technique is considered by utilizing high-temperature nuclear reactors cooled by a gaseous coolant such as helium (the case of HTR “High Temperature Reactor” type, fourth generation reactors). By virtue of its principle, this technique is connected to uranium production. The other disadvantage is that using this method for producing small amounts of hydrogen is unthinkable.
A fourth pathway consists of carrying out water electrolysis: this is a technique of dissociating water by the passage of an electric current according to the reaction:
This reaction, in which the enthalpy is ΔH=285 kJ.mol-1 (at 298K and 1 bar) is carried out according to the following method: An electrolyte cell is constituted of two electrodes, an anode and a cathode, connected to a direct current generator. The electrodes are immersed in an electrolyte used as a electrical conductor. In general, this electrolyte is an acid or basic aqueous solution, a polymeric proton exchange membrane (H+) or an oxygen ion conductive membrane (O2−).
However, this technique poses certain difficulties; thus the electrodes corrode over time. In addition, such a method necessitates the ongoing adjustment of concentrations and the use of membranes that are either fragile for organic membranes, or have a low yield for mineral membranes.
A fifth solution consists of water decomposition by thermochemical cycle (TCC): This method uses a series of chemical reactions. One example is the use of the iodine-sulfur cycle based on the decomposition of two acids at high temperature: sulfuric acid produces oxygen and sulfur dioxide, and hydroiodic acid produces hydrogen and iodine.
The disadvantage of this technique is the implementation of rather complex chemical reactions producing, in addition to hydrogen, many other elements, such as sulfur in the case of the iodine-sulfur cycle or Fe304 and HBr in the case of the UT-3 cycle.
A sixth pathway considered is the biomass: Obtained by the photosynthesis of carbon dioxide and water, it uses solar energy to produce C6H9O4 molecules. Then there is a thermochemical treatment according to the reaction:
C6H9O4+2H2O+880kJ→6CO+13/2H2
Gasification to water vapor around 900° C. then produces synthesis gas (CO+H2O). A hydrogen supplement is then obtained by the “gas shift” reaction.
6CO+6H2O→6CO2+6H2
Again, the main disadvantage of this technique resides in its production of carbon dioxide.
A seventh technique consists of carrying out photoelectrolysis of water: This is a process that uses the dissociation of the water molecule by an electric current produced by illuminating a semiconductor photocatalyst (Ti02, AsGa).
This process does not produce greenhouse gas but has a relatively low conversion efficiency.
Another method to produce hydrogen gas by microwave plasma is proposed in document WO2006/123883. This method uses the dissociation of gaseous molecules by electron impact. The method disclosed consists of injecting microwave frequencies into a dielectric tube containing an H20 or CH4 type gas or vapor under reduced pressure, on the order of 50-300 torr. This microwave power causes the ionization and/or dissociation of gas by thus releasing hydrogen (initiating microwave plasma). At the end of the tube, a separator, type palladium, separates the hydrogen by gaseous diffusion.
Another method to produce hydrogen from water molecules is described in document WO2005/005009. The method disclosed consists of placing water molecules in an electromagnetic field to excite the molecules by thermal agitation until their excitation energy exceeds the bond energy of the H and O atoms composing the water molecule.
Another method of producing hydrogen by injecting water vapor in plasma is described in document US2004/0265137. This patent describes a method of obtaining hydrogen from vapor dissociated in plasma. The document notably mentions the use of electron cyclotron resonance (ECR) to produce said plasma. With relation to the hydrogen production methods previously cited, the use of an ECR plasma machine presents many advantages:
However, despite the advantages mentioned above, a major problem with a plasma machine that breaks, by electron impact, water molecule bonds is the separation of the products formed.
Inserting a dielectric is a possible solution. However, this method presents the disadvantage of using rare and costly compounds.
In this context, the object of the present invention is to provide a device for producing hydrogen from water with electron cyclotron resonance plasma not necessarily requiring significant magnetic fields and enabling effective dissociation of the water molecules and simple separation of the products formed.
For this purpose, the invention proposes a device for producing hydrogen with electron cyclotron resonance plasma comprising:
Sealed vacuum chamber is understood to refer to a chamber in which a working pressure of less than or equal to 5.10−3 mbar exists, said working pressure substantially corresponding to the partial pressure of water vapor injected into the chamber.
Magnetic field substantially equal to the magnetic field corresponding to the electron cyclotron resonance is understood to refer to a magnetic field equal to about ±10% of the magnetic field corresponding to the electron cyclotron resonance.
Magnetic field substantially constant to the magnetic resonance field is understood to refer to a magnetic field not deviating by more than 10% from the magnetic resonance field.
Thanks to the invention, effective production of hydrogen from water vapor is obtained. The device according to the invention is based on the combined use of electron cyclotron resonance plasma and at least one selective cryogenic condenser. This non-C02 emitting device does not use electrodes, ohmic heating, membranes or high temperatures.
Thanks to the principle of electron cyclotron resonance plasma, at every passage near the resonance zone, the electrons will acquire energy. They will then be able to dissociate the water molecules and then ionize the products of dissociation. Thanks to the electroneutrality of plasma, these ions will follow the electrons along the magnetic field lines.
According to the invention, the mirror configuration of the magnetic field forms a profile of the magnetic field comprising a nonpoint-shaped minimum, called a “flat field” minimum, in which the value of the module of the magnetic field is equal to the value of the magnetic resonance field at about ±10%. This value of the magnetic field minimum module, equal to or very close to the electron cyclotron resonance, at least partially extends along the sealed chamber of the device, typically over a length greater than 10 cm, between the two maxima of the magnetic field, thus allowing an extensive surface of hot plasma to be obtained. The value of the module inside the chamber is constant over the entire height of said chamber for a given z on the axis of the chamber. In this way, the electrons will acquire a large quantity of energy in order to effectively dissociate the water molecules and ionize the dissociation products. In addition, the oxygen coming from the dissociation of water molecules will be effectively trapped along the entire sealed chamber and over a great length.
By observing the phase diagrams of the hydrogen and oxygen elements for the low temperatures represented in
In fact, if the oxygen cryocondensation device is placed in the magnetic field lines, hydrogen cryocondensation devices may then advantageously be placed outside the magnetic field lines.
It will be noted that, although an electromagnetic field is used, the device according to the invention does not use the water molecule thermal agitation method, but on the other hand breaks the atomic bonds by collisions with plasma electrons.
According to a particularly advantageous method of the invention, said chamber comprises water vapor injection means, injecting the water vapor along the longitudinal axis AA′ of the chamber directly into the hot plasma.
The device according to the invention may also present one or more of the characteristics below, considered individually or according to all technically possible combinations:
Other characteristics and advantages of the invention will clearly emerge from the description given below, for indicative and in no way limiting purposes, with reference to the attached figures, among which:
In all figures, common elements bear the same reference numbers.
The device 1 comprises:
Chamber 2 is put under vacuum, the vacuum being achieved by pumping means. In order to have the fewest impurities in chamber 2, a residual vacuum of 10−4 mbar minimum is necessary. During operation of device 1, the working pressure of chamber 2 is typically less than or equal to 5.10−3 mbar, this pressure being connected to the partial pressure of water vapor injected into chamber 2.
The magnetic structure, formed by the eight permanent bar magnets 3, 4, 5, 6, 7, 8, 9, 10 surrounding chamber 2, produces inside chamber 2 an axial magnetic field in which the configuration of the module corresponds to a magnetic mirror type configuration in which profile 5 presents at least two maxima (Bmax) at abscissae located respectively in the injection and extraction zones and one nonpoint-shaped minimum (Bmin) at least partially extending along chamber 2 and located between the two maxima (Bmax). The two maxima (Bmax) have a value greater than the value of the magnetic field (Bres) for which the electron cyclotron resonance is obtained. The minimum (Bmin) is a minimum known as flat field, whose value is equal to or slightly less than the value for which the electron cyclotron resonance is obtained over a long abscissa length.
The magnetic mirror configuration is a configuration known as minimum-B: The plasma electrons are confined in magnetic well. The longer the length of the minimum-B less than or equal to the resonance field, the more the plasma will comprise fast electrons, leading to a better dissociation of water vapor into oxygen and hydrogen.
Thanks to the principle of electron cyclotron resonance, at every passage in the resonance zone, the electrons will acquire energy. They will then be able to dissociate the water molecules and then partially ionize the products of dissociation. The electrons follow the magnetic field lines thanks to Laplace's law; And, thanks to the electroneutrality of plasma, these ions will follow the electrons along the magnetic field lines.
Microwaves injected into the plasma tend to propagate through the plasma up to the resonance zone. In fact, the energy transfer of the injected microwave power to the plasma electrons is produced at a magnetic field location (Bres) such that the electron cyclotron resonance condition is established, i.e., when there is equality between the high frequency wave HFW pulse and the cyclotron pulse of the electron:
ti ωHF=ωce=qeBres/me
where qe is the electron charge (Cb); Bres is the magnetic field corresponding to the resonance (T);
me is the electron mass.
A microwave generator, not represented, is placed outside chamber 2; this generator injects high-frequency waves inside chamber 2 via propagation means 15. The microwave frequency range may go from the GHz to a hundred GHz, the most common generator being the magnetron at 2.45 GHz commonly used for domestic microwave ovens. For a frequency of 2.45 GHz, there is a magnetic field resonance Bres=0.0875 T. However, for miniature hydrogen production devices (for embedded systems, for example), power transistors may also be used. In fact, field effect transistors capable of delivering approximately 60 W at 14.5 GHz now exist.
Advantageously, the high-frequency wave entrance window is placed in a strong magnetic field zone, in the region, for example, of the first maxima (Bmax) of profile 20 of the axial magnetic field module, such that the plasma diffuses in the direction of plasma chamber 2 and not towards the entrance window, so as to avoid any bombardment of this window by the plasma, thus guaranteeing an unlimited lifetime. Using “overdense” plasmas, where the plasma frequency is greater than the microwave frequency, is also possible. The use of “overdense” plasmas enables the electronic density to be advantageously increased and thus the system efficiency to be increased.
The means 14 for injecting water vapor into chamber 2 are preferentially placed near the microwave propagation means (however, another location may also be chosen for reasons of convenience). Water is introduced in plasma chamber 2 in the form of a supersonic jet of vapor with the intention of obtaining high directivity of the water vapor in order to direct the water vapor directly in the hot plasma towards the resonance zone of chamber 2. This jet comes from a nozzle 24, itself used as an opening to an enclosure where the water vapor is located. divertors 25 are placed at the output of nozzle 24 so as to define the angular opening of the jet. These divertors 25 are constituted of pipes in which a liquid whose temperature is close to 5° C. (a lower temperature would lead to solidification of the water on the divertors) circulates. The water vapor that comes in contact with the divertors is immediately condensed and flows along divertors 25.
In order to further improve this directivity by the size reduction of the vapor jet, a cryogenic condenser 16, formed for example by a cryogenic ring, is placed in the region of the first maxima (Bmax) of the magnetic field, whose profile 20 represents the magnetic field module along chamber 2. The cryogenic condenser 16, whose temperature is close to 200 K, is used as a diaphragm with the intention of trapping by cryocondensation the water vapor located in the external part of the vapor jet. Condenser 16 also prevents the saturation in non-dissociated water of main cryogenic condensers 11 and 12 necessary for the dissociation of ionized elements. When cryogenic condenser 16 is water saturated, a device, not represented, enables condenser 16 to be insulated with the intention of regenerating the condenser. To do this, the device heats the cold walls of the condenser in order to recover, from the cold walls, the water in liquid or gaseous form to be reinjected in device 1 by recycling pump 17.
The cryogenic condenser 16 may be replaced by a liquid condenser comprising vertical tubing in which a pressure gradient (from 10−3 mbar to 102 mbar or 1 bar) is established. Thus, the water, that passes from vapor form to liquid form, flows along the vertical tubing by gravity and is advantageously recycled via recycling pump 17. However, if the recycling tubing is short, the pressure gradient in the tubing may remain low and the water may be reinjected into device 1 directly in vapor phase.
The magnetic structure is formed by permanent magnets 3, 4, 5, 6, 7, 8, 9 and 10 in bar form having the same magnetization direction for all the magnets. The orientation of permanent magnets 3, 4, 5, 6, 7, 8, 9 and 10 is such that the magnetic profile 20 has a magnetic mirror configuration formed by a nonpoint-shaped minimum-B, known as “flat field minimum” extending over a large part of the length of the device along the AA′ axis and situated between two maximum values (Bmax) of the magnetic field. The maximum values of the field are rather high, on the order from 0.15 T to 0.3 T, so as to limit axial leaks of plasma; the maximum values may also reach several tesla.
The minimum-B value is a value equal to or less than the value of the magnetic resonance field (Bres) on the order of 90% Bres, i.e., approximately 0.08T. This magnetic field value equal to or slightly less than the electron cyclotron resonance is extended over a large part of the length of the device, on the order of 25 cm. Thus, the electrons may acquire a large quantity of energy in order to effectively dissociate the water molecules over the entire length of device 1.
Using a multi-frequency microwave injection source in which the combination of bandwidths of each frequency forms a large frequency band leading to the formation of a large resonance zone is also possible; the width of the resonance zone substantially corresponding to the bandwidth of the microwave source.
Thanks to the flat minimum-B magnetic configuration, the plasma has the form of a long column extending over a large part of the chamber, with a significant density in output of the vapor jet and a pressure gradient along chamber 2. Device 1 does not provide radial confinement of the plasma by virtue of the radial inhomogeneity of the magnetic field. In this case, the ionized particles forming the plasma tend to undergo radial drift, according to a phenomenon known in plasma physics.
Cryogenic condensers 11 and 12 are cold-wall condensers, called cryopanels or cryogenic panels. Condenser 11 is advantageously placed on the inner surface of chamber 2 so as to condense the desired ionized particles. The cold walls of condenser 11 have a temperature close to, for example, 20-30K so as to condense all the elements present in chamber 2, except the hydrogen which remains in gaseous form at this temperature under the working pressure of 0.1 Pa.
In fact, according to the phase diagrams from
It will be noted that the various components coming from the dissociation of water are essentially: H2, 02, OH, H, O, 0+, H+, H2+, 02+, OH−. All the ionized elements cancel each other out before touching a wall (either a cold wall of a cryopanel or another wall), while the neutral elements recombine to give stable elements: H2, 02, H20.
The cryogenic condenser 12 is advantageously placed in the axis of the vapor jet 14 outside of the plasma before a hydrogen pumping system, so as to condense the ionized oxygen particles as well as the non-dissociated water vapor. As the oxygen coming from the water dissociation is trapped on the entire length of device 1, the hydrogen only has to be pumped axially to the other end of device 1 and then sent to a compressor (not represented).
A high-frequency (HF) screen 21 is placed before cryopanels 11 so as to protect the cryopanels and prevent them from being heated by microwaves, the mesh of the HF screen (21) being determined according to the microwave wavelength.
It will be noted that, according to the grid represented in
The best water dissociation rates being obtained for pressures of less than 5.10−3 mbar, this value is considered to be a maximum pressure in enclosure 2, all the more so as the electrons would not be magnetically guided if this pressure is increased beyond 5.10−3 mbar.
A metal cylinder 35, that is mobile along the AA′ axis, is inserted between condensers 31, 32, 33, 34 and the plasma. Metal cylinder 35 is used as a protection screen for condensers 31, 32, 33, 34. Cylinder 35 comprises solid parts and parts 37 pierced by a mesh, said mesh corresponding to the wavelength of the microwaves utilized.
When all the pierced parts are placed before condensers 31, 32, 33, 34, the oxygen dissociated by the plasma is trapped by the cold walls of condensers 31, 32, 33, 34. The cold walls of condensers 31, 32, 33, 34 have a temperature close to, for example, 20-30K so as to condense all the elements present in chamber 2 except for the hydrogen, that remains in gaseous form. In a second position of this mobile cylinder 35, the solid parts are placed before the cold walls of condensers 31, 32, 33, 34. In this position, the device is stopped, enabling oxygen to be recovered by regeneration of cold walls of condensers 31, 32, 33, 34 by heating the walls.
The arrangement of these solid parts 36 and pierced parts 37 is such that in a first position of cylinder 41, three cryogenic condensers, for example 31, 32 and 34 are in operation, i.e., they are trapping the hydrogen elements, and a cryogenic condenser, for example 33, is in a regeneration process. In this way, device 40 may operate without interruption. As soon as a condenser 31, 32, 33, or 34 wall is saturated, the mobile cylinder 41 only has to be displaced along different positions so as to conceal the oxygen-saturated wall from the plasma with the intention of regenerating it during operation of the device.
According to a particular embodiment of the invention, it is possible to have different condensers 31, 32, 33, 34 at different distances from the center of chamber 2 where the hot plasma is housed. For example, condenser 34 placed close to the vapor jet will be farther from the center of chamber 2 so as to protect it from projections of water from the vapor jet that would excessively freeze on the cold wall. Condenser 31 located close to the system for recovering hydrogen in gaseous form may be placed closer to the plasma or the center of chamber 2 so as to be able to pump the last oxygen atoms remaining in this zone.
The additional part is a part substantially in elongated form in iron or ferro-cobalt, for example, including means for propagating high-frequency waves 15 and surrounding the water vapor jet 14.
In this way, the arrangement and material of nozzle 51 enable the first maxima (Bmax) of profile 53 to be increased without modifying the minimum-B, remaining identical to the embodiments detailed previously, profile 53 representing the intensity of the axial magnetic field present in chamber 2.
In this way, the maximum value Bmax of profile 53 may be three times greater than the maximum value Bmax of profile 20 detailed in the previous embodiments of the invention illustrated with reference to
The minimum-B value is equal to or slightly less than the value of the magnetic resonance field (Bres) on the order of 90% Bres, i.e., approximately 0.08T. This magnetic field value equal to or slightly less than the electron cyclotron resonance is extended over a large part of the length of the device, on the order of 25 cm.
Thus according to this fifth embodiment, profile 56 representing the intensity of the magnetic field presents two maxima whose intensity is higher than the maxima from the previous embodiments, thus ensuring better plasma confinement.
The device 70 comprises:
Chamber 72 is put under vacuum, the vacuum being achieved by pumping means. In order to have the fewest impurities in chamber 2, a residual vacuum of 10−4 mbar minimum is necessary. During operation of device 70, the working pressure of chamber 72 is typically less than or equal to 5.10−3 mbar, this pressure being connected to the partial pressure of water vapor injected into chamber 2.
The magnetic structure is formed by eight permanent bar magnets 73, 74, 75, 76, 77, 78, 79, 80 surrounding chamber 2.
The bar magnets 75, 76, 79, 80 have the same magnetization direction along the longitudinal axis of chamber 72, corresponding to the magnetization direction of bars 3, 4, 5, 6, 7, 8, 9 and 10 such as represented in the previous figures.
Similarly to the description done previously, the magnetic profile 90 has a magnetic mirror type configuration formed by a nonpoint-shaped minimum B, known as “flat field minimum” extending at least partially along chamber 2 and situated between two maximum values (Bmax) of the magnetic field. The maximum values of the field (Bmax) are rather high, on the order from 0.15 T to 0.3 T, so as to limit axial leaks of plasma.
Bar magnets 73, 74, 77, 78 are placed at the ends of enclosure 2 and their magnetization direction is perpendicular to the magnetization direction of magnets 75, 76, 79, 80, the field lines created by these magnets 73, 77 and 74, 78 being in opposition. The placement of magnets with a magnetization direction perpendicular to the direction of longitudinal axis AA′ of the enclosure enables the size of magnets 75, 76, 79, 80 to be reduced, which enables a magnetic mirror configuration with a flat field minimum-B slightly less than or equal to the magnetic resonance field to be obtained.
In this way, the magnets located around chamber 2 occupy less space than the previous representations, which enables the placement of means to regenerate the cold walls of cryogenic condensers present inside chamber 2 to be simplified.
According to a variation of
The invention has been mainly described with means enabling the extraction of hydrogen in gaseous form located at the end of chamber 2 and pumping the hydrogen axially; However, it is also possible to equip the device according to the invention with means to extract hydrogen pumping the hydrogen from the chamber radially in the region of the end of the device chamber. In fact, in the case of the utilization of a simple magnetic mirror configuration such as represented in
The invention has mainly been described, in the embodiments illustrated with reference to
The invention has mainly been described with a magnetic configuration comprising a minimum-B equal to or less than the value corresponding to the magnetic resonance field in which the minimum-B value is a constant value over a certain length of the device chamber corresponding to the distance between the two maxima (Bmax); However, in another representation of the invention, the minimum-B of the magnetic configuration may be around a minimum value, while remaining very close to this minimum value over a long distance of the device chamber corresponding to the distance between the two maxima Bmax.
The invention has mainly been described with a parallelepiped chamber surrounded by a magnetic structure formed by bar magnets and comprising cryogenic condensers in plate form; However, the invention is also attainable with a cylindrical sealed plasma chamber surrounded by a magnetic structure formed by circular magnets and comprising cryogenic condensers in ring form placed over the length of the plasma chamber.
The invention has mainly been described with a parallelepiped chamber surrounded by a magnetic structure formed of bar magnets; However, a part of the magnetic structure surrounding the plasma chamber such as, for example, the upper bar magnets may also be used as lower bar magnets for a magnetic structure surrounding a second sealed plasma chamber.
Lastly, the invention has mainly been described with an axial magnetic field, however, it is also possible to add a radial component to the axial magnetic field, for the dissociation for example of other elements necessitating the use of a radial magnetic field and/or to prevent radial leaks of plasma due to particle drift and to thus ensure better plasma confinement.
Of course, the invention is not limited to the embodiment that has just been described.
Thus, if one wishes to process a greater quantity of water, it is possible to increase the dimensions of the equipment while ensuring resonance zones in the plasma chamber. Thus, the length of the minimum-B equal to or slightly less than the resonance may be increased as needed up to several meters. It will be noted that the longer the plate of the minimum-B, the more effective the device according to the invention.
In addition, it is possible to use magnetic field coils (superconducting or not) to create more intense fields.
Even if the invention was more particularly described for low-frequency microwave frequencies on the order of 2.45 GHz, one may of course use higher microwave frequencies, as well as two injections of microwaves with similar frequencies so as to obtain a minimum-B value of between the two resonance values, as well as several injections of microwaves in which the bandwidth of each (some MHz) leads to a very wide frequency bandwidth and thus to a larger resonance zone.
Number | Date | Country | Kind |
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0856613 | Sep 2008 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR09/51841 | 9/29/2009 | WO | 00 | 7/15/2011 |