FR2937029A1 - Device for generating hydrogen by fuel reforming using electric discharge generating plasma, comprises first cylindrical element within which reactive mixture flows, second element forming electrode tip, and continuous current generator - Google Patents

Abstract

The hydrogen generating device comprises a first cylindrical element (1) within which a reactive mixture flows, a second element (2) forming an electrode tip (6) arranged along the axis of the first element, and a continuous current generator to establish a potential difference between the elements. The first cylindrical element comprises a conductive area to define with the second element, an area to establish an electrical discharge, a cylindrical electrode (4), and a first cylindrical insulating sleeve (3) closed at the side of the second element. The hydrogen generating device comprises a first cylindrical element (1) within which a reactive mixture flows, a second element (2) forming an electrode tip (6) arranged along the axis of the first element, and a continuous current generator to establish a potential difference between the elements. The first cylindrical element comprises a conductive area to define with the second element, an area to establish an electrical discharge, a cylindrical electrode (4), and a first cylindrical insulating sleeve (3) closed at the side of the second element. A unit for continuously vary the distance between the first conductive area of the first cylindrical element and the second element to vary the length of electric discharge along a flow of the reaction mixture and/or the fuel nature. The cylindrical electrode is mounted within the first insulating sleeve. The cylindrical electrode of the first cylindrical element is rotating along the axis of the first cylindrical element. A second insulating cylindrical sleeve is applied on the inner surface of the cylindrical electrode. The cylindrical electrode is motionless, and the second insulating sleeve is rotating along the axis of the first cylindrical element. A conductive area is delimited by an electrical insulation element. The electrode is stationary, and the second element forming an electrode tip is rotating along its axis. The cylindrical electrode comprises an alternating conductive element and electrically insulating elements along its axis defining a succession of coaxial conducting rings separated from one another. A switching device is able to select the active conducting part, and the other conductive parts are electrically insulated. The movable cylindrical electrode of the first cylindrical element comprises a slit provided for injection of reactive mixture. The slit cut in the cylindrical electrode of the first cylindrical element having a size equal to the flow of cylindrical electrode. The first insulating sleeve comprises a hole provided for the injection of reactive mixture and arranged opposite to the slit. The slits are each cut into the cylindrical electrode against each holes provided in the sleeve. The length of the slits has a size less than the flow of the cylindrical electrode. The holes of the first sleeve are diametrically opposite with respect to the other with respect to the axis of the first cylindrical element. The second element comprises a helical groove, dug in the element such as in insulation. Earth is coupled to the conductive area of the first cylindrical element, or to the pointed electrode of the second element. An independent claim is included for a process for generating hydrogen by fuel reforming.

Description

PATENT APPLICATION B08-0363EN AXC / EHE

Société par Actions Simplifiée known as: RENAULT s.a.s. Adapted system of hydrogen generation by fuel reforming assisted by electric discharges of variable length. Invention of: Adeline DARMON Laurent FULCHERI William PETITPAS

Adaptive system for hydrogen generation by fuel reforming assisted by electric discharges of variable length. The present invention relates to embedded reforming of liquid hydrocarbons for supplying hydrogen to a fuel cell of a motor vehicle and for other applications such as the depollution or any possible application of a reformate gas, and more particularly plasma assisted reforming. The development of fuel cells makes it possible to supply electrical energy for stationary applications as well as applications related to the aeronautics or automotive fields. Energy production in a fuel cell results from a chemical reaction between hydrogen or a gas rich in hydrogen, and oxygen. Oxygen is usually drawn from the ambient air.

Hydrogen, for its part, can be stored in compressed tanks onboard the vehicle, or produced in the vehicle itself using a reforming device that is called reformer from hydrocarbons liquid or gaseous. The reformers produce from a conventional hydrocarbon fuel such as, for example, gasoline or ethanol, a hydrogen-rich gas called reformate. Feeding an on-board reformed hydrogen fuel cell has the advantage of using the existing fuel distribution infrastructure.

For embedded reforming, there are several different technologies such as the conventional technology of reforming the fuel by catalytic reaction. For an automotive application, catalytic reforming poses problems in terms of reaction dynamics related to the heating time of the catalysts, in terms of cost related to the use of precious metals, and in terms of lifetime of the catalysts. An alternative reforming technology consists of plasma assisted reforming. This technology consists in carrying out the reforming reaction using the energy dissipated by a plasma generated by an electric discharge between two electrodes inside a reforming reactor. The absence of use of a catalyst in the reforming also allows a gain in reaction dynamics, in production cost and in life of the reformer, but it also allows the plasma reforming system to be powered by different types of liquid fuels, a major asset for automotive applications. In order to obtain the best possible performance of the fuel cell, the operation of the hydrogen generation system must be optimized according to the operating conditions and in particular as a function of the liquid fuel flow at the inlet of the reforming reactor, the transient regimes of power during running operation of the corresponding vehicle for the reforming system to variations in the flow of liquid fuel at the inlet of the hydrogen generating system. It is also necessary to optimize the operation of the system according to the nature of the fuel used. In an electrical discharge, the voltage at its terminals depends mainly on the composition of the system input reagent gas, the pressure, the discharge current and the discharge length. While the discharge current can usually be controlled by the power source, almost all plasma systems do not allow control of the voltage. For a gas composition, a fuel pressure, a fuel flow, and a given discharge current, the voltage which is established at the terminals of the discharge depends solely on the geometry of the plasma system which imposes the discharge length and therefore voltage. International patent application WO 98/30524 discloses a process for reforming hydrocarbons with electrical discharge assisted hydrogen generating a plasma using water and / or carbon dioxide. International patent application WO 02/43438 discloses a system for igniting and reigniting unstable electrical discharges in which a secondary electrode is disposed in a set of primary electrodes. US 2003/024806 discloses a system for generating plasma within a plasma reactor.

International patent application WO 01/33056 discloses a plasma assisted hydrogen reformed hydrocarbon reforming system using high voltage and low current. The US 2005/214179 describes a system for reforming hydrocarbons in hydrogen using plasma with high voltage but low current consumption. International patent application WO 2004/094795 describes a system for reforming hydrocarbons in plasma-assisted hydrogen, the system having decoupled fluid flows. US 2002/012618 discloses a process for reforming hydrocarbons into electrical discharge assisted hydrogen generating a plasma with water and / or carbon dioxide to reduce the production of carbon monoxide. FR 2 888 835 discloses a system for producing hydrogen from a hydrocarbon product and an oxidizing product, using a non-thermal plasma generated in an enclosure by means of the coupling of a tip electrode and a cylindrical electrode. Current plasma-assisted reforming technologies as described in the aforementioned documents do not allow an adaptation of the reforming reactor according to the operating conditions varying according to the flow rate and the nature of the fuel, and the proportions of oxidant, generally involving operating regimes well below those potentially available. International patent application WO 2004/112950 describes a device comprising a mobile electrode for initiating an electric discharge in the vicinity of a fixed electrode, the mobile electrode then being able to be placed in a second position corresponding to the desired elongation of the discharge . The described system is unfortunately difficult to achieve for automotive application and high temperature, and does not allow online adaptation to the operating conditions of the vehicle. The object of the invention is to provide a system of adjustable electric discharge length for optimizing the effectiveness of the system throughout the duration of the vehicle running. According to one aspect, there is provided in one embodiment a device for generating hydrogen by fuel reforming assisted by at least one electric discharge generating a plasma comprising a first cylindrical element within which a reactive mixture can flow. a second element forming a tip electrode disposed along the axis of the first element, a DC generator capable of establishing a potential difference between said first and second elements. The first cylindrical element comprises at least one conductive zone capable of defining with the second zone element conducive to the establishment of an electric discharge, and the device comprises means for continuously varying the distance between the conductive zone of the first cylindrical element and the second element, so as to vary the length of the electric discharges depending on the flow of the reactive mixture and / or the nature of the fuel. Preferably, the first cylindrical element comprises a cylindrical electrode and a first cylindrical insulating sleeve closed on the side of the second element, the cylindrical electrode being mounted inside the first insulating sleeve.

A plasma reactor is thus defined by the assembly formed of the cylindrical electrode and the tip electrode. The first cylindrical insulating sleeve makes it possible to close the reactor on the side of the second element and at the same time, on the injection side of the reactive mixture. The cylindrical electrode of the first cylindrical element can advantageously be mobile in translation along the axis of the first cylindrical element. The displacement of the cylindrical electrode makes it possible to modify the length of the electric discharge generated between the two electrodes, and therefore the voltage of the plasma. The displacement of this cylindrical electrode can be achieved using a worm system for example. The cylindrical electrode of the first cylindrical element can also be immobile, while a second cylindrical insulator applied to the inner surface of said cylindrical electrode can move in translation along the axis of the first cylindrical element. The first cylindrical element may also comprise a second cylindrical insulating sleeve applied to the inner surface of said cylindrical electrode, said cylindrical electrode being stationary and said second insulating sleeve being movable in translation along the axis of the first cylindrical element. In this way, the electric discharge is always generated at the same location of the cylindrical electrode, but the propagation length varies according to the position of the second insulating sleeve at the moment when the electric discharge occurs. This changes the length of the electric discharge, and therefore the voltage of the plasma. The cylindrical electrode of the first cylindrical element may advantageously comprise a conductive zone delimited by an electrical insulating element, said electrode being immobile and the second element forming a tip electrode being movable in translation along its axis. The cylindrical electrode may also comprise an alternation of conductive elements and electrically insulating elements along its axis defining a succession of coaxial conductive rings separated from each other, the device comprising a switching device capable of selecting the active conductive part. the other conductive parts being electrically insulated. Thus, the length of the electric discharge depends directly on the conductive area defined on the cylindrical electrode, and can be modified by modifying the conductive area by means of a switching device, thus controlling the plasma voltage. Reactive mixing can be achieved through the first cylindrical member at the tip electrode to lengthen the electrical discharge just after it is created.

The movable cylindrical electrode of the first cylindrical element may advantageously comprise a slit provided for the injection of reactive mixture, the slit dug in the cylindrical electrode of the first cylindrical element having a dimension at least equal to the stroke of said cylindrical electrode, and the first insulating sleeve comprising a hole provided for the injection of reactive mixture and disposed opposite the slot. The slot cut in the movable element of the first cylindrical element, namely the cylindrical electrode or the second insulator, must be of a dimension at least equal to the stroke of said movable element when it is movable so that the beam of reactive mixture is permanently facing a hole for supplying the plasma reactor with a reactive mixture. The first sleeve may advantageously have two holes opposite the second element and diametrically opposite one another with respect to the axis of the first cylindrical element, provided for the injection of reactive mixture. In the case where the cylindrical electrode of the first cylindrical element is movable, the first sleeve may also comprise two holes opposite the second element and diametrically opposed relative to the axis of the first cylindrical element, provided for the injection of reactive mixture , and the cylindrical electrode then comprises two slots provided for the injection of reactive mixture, the slots being each hollowed out in the cylindrical electrode opposite each hole provided in the sleeve, the length of the slots having a dimension at least equal to the stroke of said cylindrical electrode. The injection of reactive mixture through two holes in the first element tangentially to the inner wall of the reactor allows to introduce the reaction mixture in the form of a vortex promoting the formation of the electric discharge under the effect of an elongation of the discharge, due to the entrainment of the electric discharge by the kinetic mixing fluid of the reactive mixture, and a stabilization of the electric discharge by the wall effect. Indeed, the mixture forming a vortex just lick the reactor walls and is not blown as in the case of a purely axial injection into the cylinder. The feed of the reactive plasma reactor can also be carried out by the closed side of the first cylindrical element, that is to say on the side of the second element. Preferably, the second element comprises in this case a helical groove dug in it, in particular in the insulator 7, provided for the injection of reactive mixture. In this way, the reaction mixture is also introduced in the form of a vortex promoting the formation of the electric discharge under the effect of elongation and stabilization by wall effect. The earth may preferentially be coupled to either the conductive zone of the first cylindrical element or the tip electrode of the second element.

According to another aspect, it is proposed in one embodiment a hydrogen generation process by fuel reforming assisted by at least one electric discharge generating a plasma. According to this aspect, the distance between the conductive zone of the first cylindrical element and the second element is continuously varied so as to vary the length of the electric discharges as a function of the flow rate of the reactive mixture and / or the nature of the fuel. Other advantages and characteristics of the invention will appear on examining the detailed description of an embodiment of the invention which is in no way limitative, and the attached drawings, in which: FIG. 1 schematically illustrates an axial section through an example of a device according to a first embodiment; FIG. 2 schematically illustrates an axial section of another example of a device according to a second embodiment; - Figure 3 schematically illustrates an axial section of another exemplary device according to a third embodiment; - Figure 4 schematically illustrates an axial section of another exemplary device according to a fourth embodiment. - Figure 5 schematically illustrates an axial section of another exemplary device according to a fifth embodiment; - Figure 6 schematically illustrates an axial section of another exemplary device according to a sixth embodiment.

FIG. 1 very schematically shows an axial section of an example of a device for generating hydrogen by fuel reforming assisted by at least one electric discharge generating a plasma. This hydrogen generation device is in the form of a first cylindrical element 1 comprising a cylindrical insulating sleeve 3 closed at one end by a bottom wall 3a, and a cylindrical electrode 4 mounted inside the cylindrical insulating sleeve 3. The cylindrical electrode 4 is coupled to a translation means 5 such as a worm capable of translating the electrode 4 along the axis of the cylindrical element 1 inside the sleeve 3 in the two translation directions, and up to the wall 3a. The translation means 5 is controlled by a not shown electronic control unit coupled to the translation means 5 by a connection 50. The control can thus take into account the flow rate of the fuel or the reactive mixture injected into the device, or the nature or fuel composition. The hydrogen generation device also comprises a second element 2 disposed along the axis of the first element 1. This element 2 comprises a conductive rod 6 having a tip 6a at one of its two ends thus forming an electrode. The electrode 6 is covered with an insulating envelope 7 over its entire surface except for the tip end 6a.

The two electrodes 4 and 6 are coupled to a generator 8 of direct current through the respective connections 9 and 10. The cylindrical electrode 4 can be connected to the ground by a connection 11. The injection of a fuel or a Reactive mixture in the device can be achieved in different ways. In FIG. 1, it has been chosen to represent an example of injection by means of two injectors 12 and 12 'through the cylindrical electrode 4. It is of course possible to perform the injection only at the help from an injector; injection with two injectors promoting the formation of a vortex for the reaction mixture. Two holes 13 and 13 'are each drilled in the sleeve 3 on a part facing the cylindrical electrode 4, the holes being diametrically opposite with respect to the axis of the first cylindrical element 1. The two holes 13 and 13' are pierced so as to be disposed in the transverse plane defined by the tip of the electrode 6a 6. A first slot 14 facing the hole 13 and a second slot 14 'opposite the hole 13' are hollowed in the electrode cylindrical 4 mobile. These slots 14 and 14 'have a dimension along the axis of the first element 1 at least equal to the maximum displacement of the cylindrical electrode 4. In this way, the injectors 12 and 12' are always respectively opposite the holes 13 and 13 'passing through the sleeve 3 and the cylindrical electrode 4. A stop 3c may be provided on the edge of the hole 13 on the side of the wall 3a, and respectively a stop 3d on the edge of the hole 13', in order to stop the displacement of the cylindrical electrode 4 on the opposite side to the wall 3a. The generated electric discharges are initially formed at a location of the cylindrical electrode 4 closest to the tip 6a of the electrode 6, the pointed form of the electrode 6 to promote the generation of discharges directly on the tip 6a . Thus, when the cylindrical electrode 4 will abut the wall 3a, the initial electrical discharge of length d; will be formed between the tip of the electrode 6 and the closest point of the cylindrical electrode 4. Once initiated, the electric discharge propagates along the electrode to reach its final length df.

By moving the cylindrical electrode 4, it is possible to adapt the discharge lengths d; and df to obtain the desired plasma voltage. FIG. 2 shows an axial section of another example of a device for generating hydrogen. The elements identical to those of Figure 1 bear the same references. In this embodiment, the cylindrical electrode 4 is stationary and occupies the entire interior of the sleeve 3 to a shoulder 3b. The translation means 5 is coupled to a second cylindrical insulating sleeve 15 which slides on the inner surface of the cylindrical electrode 4. Thus, in this example, the initial length d; electrical discharges remain constant while the propagation distance defining the final length df of the electric discharges is modified according to the displacement of the second sleeve 15.

The injection of the reactive mixture can be carried out through the sleeve 3 of the first cylindrical element 1. Holes 13a and 13b are drilled in the sleeve 3 so as to be diametrically opposed with respect to the axis of the first cylindrical element 1. In this way, injectors 12a and 12b respectively opposite the holes 13a and 13b introduce the reactive mixture to form a vortex promoting the formation of the electric discharge and its stabilization. In FIG. 3 is illustrated an axial section of a third example of a device for generating hydrogen. The elements identical to those of the preceding figures bear the same references. In this embodiment, the cylindrical electrode 4 is stationary and occupies the entire interior of the sleeve 3 to the shoulder 3b. The electrode 4 consists of two juxtaposed zones, a conductive zone 17 and an insulating zone 18. The insulating zone 18 forms a cylindrical portion located axially between the conductive zone 17 and the electrode 6. The conductive zone 17 of the electrode 4 and the pointed electrode 6 are coupled to the DC generator 8 by the respective connections 9 and 10. The conductive zone 17 of the electrode 4 can be connected to the ground by a connection 11.

In this example, the translational means 5 is coupled to the second element 2 thus making it possible to move the electrode 6 along its axis and to modify the initial length d; and the final length df of the electric discharges that extend between the electrode 6 and the conductive zone 17. The injection of the reactive mixture can be carried out as previously using the two injectors 12a and 12b through the sleeve 3. In FIG. 4 is illustrated an axial section of a fourth example of a device for generating hydrogen. The elements identical to those of the preceding figures bear the same references. In this embodiment, the cylindrical electrode 4 is stationary and arranged as in the examples of FIGS. 2 and 3. The electrode 4 comprises an alternation of conducting annular elements 19, 20, 21, 22, 23, and of annular elements 24 electrically insulating along its axis, thus defining a succession of coaxial conductive rings isolated from each other. The active conductive part, for example the conductive area 21, can be selected using a switch 25, the other conductive parts then being isolated. The conductive zones 19, 20, 21, 22, 23 are coupled to the switch 25 via the respective connections 26, 27, 28, 29, 30. The second element 2 is also stationary in this embodiment. The switch 25 and the electrode 6 are coupled to a generator 8 of direct current through the respective connections 9 and 10. The switch 25 can be connected to the ground by a connection 11. The injection of the reaction mixture is carried out in this example using an injector 12c supplying the plasma reactor through the wall 3a via a duct 42 coupled to the second element 2. The second element 2 has a helical groove 16 hollowed in particular in the insulating casing 7 thus making it possible to inject the reagent mixture in a vortex form promoting the formation of plasma. In FIG. 5 is illustrated an axial section of a fifth example of a device for generating hydrogen.

The elements identical to those of the preceding figures bear the same references. In this embodiment, the injection has been modified so that the slots 14 and 14 ', the holes 13 and 13', the stops 3c and 3d, and the injectors 12 and 12 'used in FIG. reactive mixture were replaced by injectors 12a and 12b supplying the reactor through the sleeve 3 as in Figures 2 and 3. In Figure 6, is shown an axial section of a sixth example of a hydrogen generating device.

The elements identical to those of Figure 2 bear the same references. This embodiment differs from that of FIG. 2 in that the injection has been modified so that the holes 13a and 13b, and the injectors 12a and 12b used in FIG. 2 to introduce the reaction mixture, have been replaced by an injector 12c feeding the plasma reactor through the wall 3a via a duct 42 coupled to the second element 2. The second element 2 has a helicoidal groove 16 hollowed in particular in the insulating casing 7 thus making it possible to inject the reagent mixture according to a vortex shape favoring the formation of the electric shock.

The characteristics of the various examples illustrated can be interchanged according to the complementarity of the injection systems with the elements defining the plasma reactor. Instead of connecting the electrode 4 to the earth, it would also be possible to connect the electrode 6 to the earth.

Claims (12)

REVENDICATIONS1. Fuel reforming hydrogen generating device assisted by at least one electric discharge generating a plasma, comprising a first cylindrical element (1) inside which a reactive mixture can flow, a second element (2) forming a tip electrode (6) arranged along the axis of the first element (1), a DC generator (8) capable of establishing a potential difference between said first and second elements, characterized in that the first cylindrical element ( 1) comprises at least one conductive zone capable of defining with the second element (2) an area favorable to the establishment of an electric discharge, in that the device comprises means for continuously varying the distance between the conductive zone of the first cylindrical element (1) and the second element (2), so as to vary the length of the electric discharges as a function of the flow of the reaction mixture if and / or the nature of the fuel. 2. Device according to claim 1, characterized in that the first cylindrical element (1) comprises a cylindrical electrode (4) and a first cylindrical insulating sleeve (3) closed on the side of the second element, the cylindrical electrode (4) being mounted within the first insulating sleeve (3). 3. Device according to claim 2, characterized in that the cylindrical electrode (4) of the first cylindrical member (1) is movable in translation along the axis of the first cylindrical member (1). 4. Device according to claim 2, characterized in that the first cylindrical element (1) also comprises a second cylindrical insulating sleeve (15) applied on the inner surface of said cylindrical electrode (4), said cylindrical electrode (4) being immobile and said second insulating sleeve (15) being movable in translation along the axis of the first cylindrical member (1). 5. Device according to claim 2, characterized in that the cylindrical electrode (4) of the first cylindrical element (1) comprises a conductive zone (17) delimited by an electrical insulating element (18), said electrode (4) being immobile and the second element (2) forming a tip electrode (6) being movable in translation along its axis. 6. Device according to claim 2, characterized in that the cylindrical electrode (4) comprises an alternation of conductive elements (19), (20), (21), (22), (23) and electrically elements. insulators (24) along its axis defining a succession of coaxial conductive rings separated from each other, and comprising a switching device (25) adapted to select the active conductive part, the other conductive parts being electrically insulated. 7. Device according to claim 3, characterized in that the movable cylindrical electrode (4) of the first cylindrical element (1) comprises a slot (14) provided for the injection of reactive mixture, the slot (14) hollowed in the cylindrical electrode (4) of the first cylindrical element (1) having a dimension at least equal to the stroke of said cylindrical electrode (4), and the first insulating sleeve (3) comprising a hole (13) provided for the injection of reactive mixture and disposed opposite the slot (14). 8. Device according to claim 3, characterized in that the first sleeve (3) comprises two holes (13 and 13 ') facing the second member (2) and diametrically opposite to the axis of the first cylindrical member (1). ) provided for the injection of reactive mixture, and the cylindrical electrode (4) comprises two slots (14 and 14 ') provided for the injection of reactive mixture, the slots (14 and 14') being each hollowed out in the cylindrical electrode (4) facing each hole (13 and 13 ') provided in the sleeve (3), the length of the slots (14 and 14') having a dimension at least equal to the stroke of said cylindrical electrode (4) . 9. Device according to one of claims 1 to 6, characterized in that the first sleeve (3) has two holes (13a and 13b) opposite the second element (2) and diametrically opposite one with respect to the other relative to the axis of the first cylindrical member (1), provided for the injection of reactive mixture. 10. Device according to one of claims 1 to 5, characterized in that the second element (2) comprises a helical groove (16) hollowed therein, in particular in the insulator (7), provided for the injection of reactive mixture. 11. Device according to one of claims 1 to 9, characterized in that the earth is coupled to either the conductive zone of the first cylindrical element (1) or the tip-shaped electrode (6) of the second element ( 2). 12. Process for generating hydrogen by fuel reforming assisted by at least one electric discharge generating a plasma, characterized in that the distance between the conductive zone of the first cylindrical element (1) and the second element (2) varies continuously. ), so as to vary the length of the electric discharges according to the flow rate of the reactive mixture and / or the nature of the fuel.