FR2891951A1 - Plasma reformer for e.g. electricity generator of motor vehicle, has catalytic burner heating reactants in sealed duct before introducing reactants in plasma reactor and extending around plasma reactor - Google Patents

Abstract

The reformer has a plasma reactor (61) for producing a reformat from a set of reactants comprising a primary fuel, air and water. A catalytic burner (72) heats the reactants in a sealed duct (215) before introducing the reactants in the plasma reactor and extends around the plasma reactor. A double wall (210) of the reactor extends between an external wall (212`) of the reactor and the catalytic burner. A conduit (216) connects an outlet (217) of the duct and an inlet (218) of the double wall.

Description

The invention relates to a reforming device for a motor vehicle

  and an electricity generator implementing this device. An electricity generator, or "power module" (MP), is used in particular in a motor vehicle to power the vehicle's electrical consumers, in particular an electric traction motor. It allows the transformation of a fuel embedded in the vehicle into electrical power. The fuel may be hydrogen, directly consumable by the fuel cell. For increased autonomy, it is more generally used a primary fuel easier to store such as gasoline, diesel, naphtha, alcohol, an ester, or a hydrocarbon. The generator then comprises a reforming device, that is to say of transformation of the primary fuel into hydrogen. Figure 1 shows a typical simplified architecture of an electricity generator 10 according to the prior art.

  The generator shown comprises a fuel cell 20, for example of the PEMFC type, supplied with hydrogen and oxygen, via pipes 22 and 24, respectively. The fuel cell 20 comprises anode compartments 26 and cathode 28 cooled by means of a cell cooling circuit 30 having a radiator 32 able to evacuate to the outside the recovered heat energy. The oxygen is supplied by outside air, successively compressed by a low-pressure compressor (LP) 36 and a high-pressure compressor (HP) 38 separated by an exchanger 40, called the radiator of the low-pressure supercharging air or exchanger. RAS BP.

  The compressor BP 36, capable of compressing the air at a pressure typically between 2 and 3 bars, is driven by a motor 42. The compressor HP 38 is able to compress the air exiting the exchanger RAS BP at a pressure typically between 4 and 5 bars. The HP compressor 38 is coupled to a turbine 44 recovering mechanical energy by expansion of the hot exhaust gas from the fuel cell 20, transported by a pipe 46. Another exchanger 50, said HP RAS, is provided downstream of the HP compressor 38 for cooling the compressed air to the operating temperature of the fuel cell 20. The RAS HP 50 and RAS LP 40 exchangers are integrated in an air cooling circuit 52, having a radiator 54 fit to evacuate to the outside the recovered heat energy. The generator 10 further comprises a reforming device, or "FPS" (English, "Fuel Processing System"), comprising a reformer 60 able to transform, in the presence of air and water vapor, the primary fuel in a reformate rich in hydrogen. For this purpose, the reformer 60 may comprise a plasma reactor 61, shown schematically in FIG. 2, capable of generating a plasma from a mixture M of reactants introduced therein via a nozzle 62. The reformer then comprises first and second electrodes 63 and 63 'respectively, for example in the form of a tip disposed near the inlet 64 of the reactants in the reactor 61 and a metal side wall, of revolution about an axis X, delimiting the internal volume of the reactor 61. An electric generator 65 is also provided to establish a high electrical voltage between these electrodes so as to create an electric arc 66. The electric arc 66 makes it possible to create a plasma, hot or cold, at the reactor interior for decomposing the introduced hydrocarbons into hydrogen and carbon monoxide. The electric arc 66 may be rotating or, as in the example of Figure 2, sliding. Such sliding arches are still called Glid Arcs.

  Preferably, cold plasmas, also called out of equilibrium, are used in which the temperature of the electrons is greater than that of the heavy particles (ions, radicals, neutrons, molecules). The means for generating a cold plasma are well known. They can also use, for example, microwave discharges or crowns.

  The reformer 60 is fed with compressed air A, from the outlet of the HP compressor 38, via a pipe 67, supplied with primary fuel P, from a tank, not shown, via a pipe 68, and supplied with water E, in the form of steam, via a pipe 69.

  During the start-up phase and prior to their introduction into the reformer 60, the reactants, that is to say the primary fuel, water and air, are heated via an exchanger 70 by means of a burner. flame 72, as described for example in US 6,245,309. In the case of a gas phase plasma, of Glid Arc type for example, the reagents must be brought to a temperature above the vaporization temperature (about 120 ° C.) in order to initiate the reaction, which may take place between 700 ° C. and 1000 C. In the reforming device described in WO 98/30524, the reactants are thus preheated by passing through a double wall surrounding the reactor and by electrical resistors.

  The burner 72 is supplied with compressed air by the compressor HP 38 via a pipe 74, and residual hydrogen, that is to say not consumed by the fuel cell 20, via a pipe 76. After passing through the exchanger 70, the exhaust gas from the burner 72 are sent through a pipe 78 to the inlet of the turbine 44, and then discharged to the outside. The reformate produced by the reformer 60, conveyed by a pipe 80, passes successively in the direction of the reformate flow, an exchanger 82, a reactor HTS 84 (in English High Temperature Shift), an exchanger 86, an LTS 88 reactor, (English Low Temperature Shift), a heat exchanger 90, a preferential oxidation reactor PrOx 92 (English preferential oxidation), and a pre-anodic condenser 94, before joining the anode compartment 26 of the fuel cell 20. The preferential oxidation reactor PrOx 92 is also supplied with compressed air leaving the compressor HP 38 via a pipe 95. The HTS and LTS reactors can for example be directly supplied with water. The gas-to-water (Shift) reactions and the preferential oxidation make it possible to convert a large part of the CO present in the reformate into CO2. The exchangers 82, 86 and 90 are intended to cool the reformate between each treatment stage. They are cooled by a circulation of the water intended for the reformer 60, the heat energy recovered by the water being able to be used in the exchanger 70 for the vaporization and the heating of the reagents of the reformer 60, as represented, or to be taken supported by an external cooling circuit. In FIG. 1, the water outlets of the exchangers 82, 88 and 90 thus meet in the common pipe 69 connected to the inlet of the exchanger 70 of the reformer.

  In fuel cell 20, the hydrogen contained in the reformate is partially converted by an electrochemical reaction to provide electricity. The exhaust gas G, containing hydrogen not consumed by the fuel cell 20, leaving the anode compartment 26 via a pipe 96 passes through an anode condenser 100, before feeding, via the pipe 76, the burner 72. The hot air leaving the cathode compartment 28 through a pipe 102 passes through a cathode condenser 104, before being sent via line 46 to the turbine 44 and discharged to the outside via the pipe 106. The anodic condensers 100, cathode 104 and pre-anodic 94 are cooled by means of a condenser cooling circuit, referenced 110, comprising a radiator 112 able to evacuate to the outside the recovered heat energy. The water recovered by these condensers is sent, via pipes not shown, to a tank not shown, then, if necessary, pumped to the entries 114, 116 and 118 of the exchangers HTS 82, LTS 86 and PrOx 90. The cooling circuits 30, 52 and 110 of the fuel cell 20, the compressed air by the compressors 36 and 38 and the condensers 94, 100 and 104, respectively, have been shown separated from each other for the clarity of the drawing. In fact, these three circuits are merged into a single cooling circuit. The operation of the hydrogen processor 10 of Figure 1 is as follows. The compressors BP 36 and HP 38, separated by the RAS exchanger BP 40, produce compressed air at about 190 ° C. and at a pressure of about 4.5 bars.

  The BP 40 RAS exchanger cools the air heated by the BP 36 compressor, which increases the compression ratio and reduces the mechanical work required for each compressor. The compressed air supplies the burner 72, the reformer 60 if it is a reforming PDX or ATR through the exchanger 70, the PrOX and the cathode compartment 28 of the fuel cell 20 by the The exchanger 70 of the reformer 60, heated by the exhaust gas of the burner 72, heats all the reagents for the reformer 60 to a temperature suitable for reforming the fuel. The reformate leaving reformer 60, at a temperature of between 800 and 1000 ° C., for example, is then cooled to about 400 ° C. by exchanger 82, then to about 200 ° C. through exchanger 86, then finally to about 120 ° C. the exchanger 90. The reformate can thus be purified efficiently in the HTS 84 and LTS 88 reactors, then oxidized preferentially in the PrOx oxidation reactor 92. It then passes through the pre-anodic condenser 94 which cools it to a temperature of approximately 80 to 110 C adapted for its injection into the anode compartment 26 of the fuel cell 20. In the fuel cell 20, the hydrogen of the injected reformate is partially converted by an electrochemical reaction to provide electricity. The residual hydrogen leaving the anode compartment at a pressure of about 3 bars is used by the burner 72, after recovery of the water vapor in the anode condenser 100. The exhaust gases of the cathode compartment 28, at a pressure about 3 bar, after recovery of water vapor in the cathode condenser 104, are used by the turbine 44, and then discharged to the outside. In an electricity generator such as that described above, the reforming device, that is to say all the means used to reform the fuel, has several disadvantages.

  Firstly, the burner 72 generates very high temperatures that can rapidly damage its environment, and in particular the reactor 61, unless highly heat-resistant but expensive materials are used. Then, the burner 72 does not allow a perfectly controlled combustion and therefore generates pollutant gases that must be treated before discharge.

  The object of the present invention is to provide a reforming device, which can be implemented in the context of a generator of the type described in the preamble, but does not have the disadvantages mentioned above. According to the invention, this object is achieved by means of a plasma reforming device, in particular for an electricity generator intended for a motor vehicle, comprising a plasma reactor capable of producing a reformate from a set reagents comprising a fuel, air and water, and a burner adapted to heat at least one of the reagents prior to introduction into the plasma reactor.

  This device is remarkable in that the burner is a catalytic burner. The use of catalytic burners for heating reagents (fuel, air and water) for a catalytic reformer is known. These burners conventionally comprise a support of alumina coated with a catalyst such as palladium or platinum. The operation of a catalytic reformer, however, is very different from that of a plasma reformer. In particular, the temperatures reached with a plasma reformer, and therefore the thermomechanical stresses within the reformer, are incommensurate with those reached with a catalytic reformer. In addition, the use of arcing creates a highly disturbed electromagnetic environment, which can influence the cracking of fuel. The inventors have found, however, that a catalytic burner makes it possible to obtain efficient heating of the reactants and a rate of unburnt advantageously reduced. In addition, the use of a catalytic burner allows a slower combustion, at a much lower temperature than that resulting from a combustion flame. Advantageously, the materials surrounding the burner thus undergo reduced thermomechanical stresses. In addition, the reactants for the reactor 61 are advantageously not excessively heated. Preferably, the reforming device according to the invention also has one or more of the following optional features. Unlike a flame burner, a catalytic burner can be shaped to optimize heat exchange with the reactor. Thus, preferably, the catalytic burner extends, at least in part, around the reformer reactor, preferably in contact with it, so as to allow heat exchange with said reactor. Preferably, the catalytic burner substantially covers the entire reactor.

  A reactor feed pipe, preferably in the form of a double wall, extends, at least in part, between an outer wall of the reactor and the catalytic burner. Preferably, this double wall is constituted by an outer side wall of the reactor and by an inner wall of the burner, as will be seen in more detail in the light of the description of FIG. 3. Preferably, the device according to the invention further comprises a line connecting an outlet of the catalytic burner and an inlet of this supply line of the reactor. Advantageously, the gas flowing in this duct can thus be heated both by the heat released by the catalytic burner and by that released by the reactor. Preferably, this gas is a mixture of water vapor or water and primary fuel. More preferably, this gas is, prior to its introduction into said reactor feed pipe, heated by the catalytic burner. The reforming device further comprises a mixer receiving at least one reagent having passed through the catalytic burner and / or by a reactor feed pipe extending at least partly between an outer wall of the reactor and the catalytic burner. The plasma reactor is in the form of a coil. Advantageously, this form increases the contact surface with the surrounding medium, in particular with the liquid or gaseous reactants, and therefore increases the heat exchange with the latter. The invention also relates to an electricity generator for a motor vehicle, comprising a plasma reforming device capable of producing a reformate from a fuel, air and water, and a fuel cell capable of producing electrical energy from said reformate and air. The generator according to the invention is remarkable in that the plasma reforming device is in accordance with the invention. Preferably, the generator according to the invention still has one or more of the following optional features. At least one reactant heated by the catalytic burner is steam and / or fuel. The plasma reactor of the reformer is preferably in heat exchange relationship with this reagent (s) before it (s) reaches (s) to said reactor, preferably via a double wall delimiting the internal volume of the plasma reactor. The electricity generator comprises a heat exchanger able to put in heat exchange relationship on the one hand at least one reagent for the plasma reactor and, on the other hand, reformate leaving said reactor and / or combustion gases generated by the catalytic burner.

  The generator comprises a flame burner adapted to preheat the catalytic burner until the latter reaches its activation temperature. Advantageously, the activation temperature of a catalytic burner is about 100 to 200 C. This preheating is therefore short-lived.

  The invention also relates to a motor vehicle comprising a reforming device according to the invention. The invention finally relates to the use of a reforming device according to the invention for reducing nitrogen oxides and / or particles emitted by an internal combustion engine, in particular by an internal combustion engine of a vehicle. automobile. Other features and advantages of the present invention will appear on reading the following description and on examining the appended drawing in which: FIGS. 1 and 2, described in the introduction, schematically represent an electricity generator and a plasma reformer according to the prior art, respectively; FIG. 3 schematically represents a reforming device according to the invention.

  In the various figures, identical references have been used to describe identical or similar members. In Figure 1, the air supply circuits of the fuel cell, the burner, the preferred oxidation reactor and the reformer have been shown in broken lines. The reformat feed circuit of the fuel cell has been shown in thick lines. The water supply circuit of the reformer has been shown in dashed line. The pipes in which the gases escaping from the fuel cell circulate have been shown in dotted lines. FIGS. 1 and 2 having been described in the introduction, reference is now made to FIG.

  In the preferred embodiment of the invention, the reactor 61 has a double wall 210 which makes it possible to put the gases circulating therein in heat exchange relation with the reaction volume 211. This double wall 210 preferably has internal side walls. 212 and outer 212 'of the reactor 61. Preferably, the inner side wall 212 is of revolution about the axis X of the reactor 61, the injection and evacuation of the gas flows being along the axis X. The outer wall 212' It is covered, for example, in the form of a mass 213 coated with a catalyst, for example platinum or palladium. The mass 213 may especially be a monolith of cordierite type or a metal foam. Preferably, the pipe 215 is thermally insulated by covering its outer surface by means of a layer 214 made of a refractory ceramic material. The porosity of the mass 213 allows a circulation of gaseous compositions able to react chemically when placed in contact with the catalyst. As will be seen in more detail in the following description, in this case, the gaseous composition is a mixture of compressed air A and primary fuel P during the start-up phase of the electricity generator, then, in stationary phase, a mixture of compressed air A and an exhaust gas G of the fuel cell (anode), this exhaust gas comprising secondary fuel S, in particular in the form of hydrogen. For greater clarity of the drawing, this circulation is not represented.

  The outer wall 219 of the burner forms a sealed pipe 215 with the inner wall 220 of the insulating layer 214, so as to put in heat exchange relation the burner 72, in which the combustion of the injected primary or secondary fuel, and one or more reagents to be heated, in this case a mixture of water vapor E and primary fuel P, intended to be injected into the reactor 61 in the stationary phase. A pipe 216, represented symbolically by an arrow (P * + E *), connects an outlet 217 of the pipe 215 and an inlet 218 of the double wall 210. The pipe 215, the pipe 216 and the double wall 210 may thus constitute the same supply line of reagents.

  A mixer 220 is finally provided for mixing the preheated reagents exiting the line 210, for example primary fuel and water vapor or warmed water (E * and P *, respectively), and other reagents. , For example compressed air A. To implement the reforming device according to the invention, one can for example implement the following method. In a start-up phase, the catalytic burner 72 is preheated by means of a flame burner, not shown, at least until the mass 213 of the catalytic burner 72 reaches the activation temperature of the catalyst. The flame burner is then stopped and a mixture of compressed air A and primary fuel P is injected into the mass 213 of the catalytic burner 72. The mixture then reacts with the catalyst. The combustion is total, which avoids any emission of unburnt and soot. If the reagent mixture is poor (in fuel), then the flame burner and the catalytic burner can be operated in series so as not to extinguish the combustion flame and to obtain a clean combustion. The heat produced by the catalytic burner 72 is used to heat one or more of the reagents for the reformer, in this case water vapor or water E and the primary fuel P injected into the pipe 215.

  The tightness of the pipe 215 prevents any leakage of these reagents through the mass 213. The water or water vapor E * and the primary fuel P * heated by the catalytic burner 72 then circulate in the pipe 216, then in the envelope formed by the double wall 210, and then are injected into the mixer 220. They are mixed with air A, compressed and heated by the compressor 38, which reaches the mixer 220 at a temperature typically between 150 and 180 ° C. to form a mixture M. The temperature of the catalytic burner is about 900 ° C., that is, about 300 ° C. lower than the temperature of a gas-consuming flame burner. The heat exchange with the mass 213 makes it possible to heat the reagents circulating in the pipe 215 to a temperature which, after mixing with the air heated by the compressor 38, transforms the mixture M into a reformate in the plasma reactor. The heated and mixed reactants are injected into the reactor 61 through the nozzle 62 and a plasma arc 66 is initiated by means of a spark plug, formed by the central electrode 63. Under the effect of the plasma arc 66, the fuel mixture M decomposes into a reformate R rich in hydrogen and still including, in particular, CO, CO2, H2O, CH4 N2, C2H2 and C2H4. This decomposition is generally called plasma catalysis The reformate thus produced is purified and used by the fuel cell 20 to generate electrical energy and exhaust gas G still containing hydrogen not consumed by the battery.

  With an exothermic plasma reactor, of the so-called autothermal or partial oxidation type, the temperature of the inner wall 212 of the reactor 61 is of the order of 1000 C. As soon as the plasma reactor is in operation, it can thus advantageously heat the reagents circulating in the double wall 210 of the reactor 61. The heat exchange is even more effective if the circulation in the double wall 210 is countercurrent with respect to the flow direction of the reagents in the reactor. We then enter a stationary phase. In the stationary phase, the catalytic burner 72 preferably operates by means of secondary fuel S, in this case residual hydrogen which the exhaust gas G of the fuel cell 20 supplies it with. Advantageously, the catalytic burner 72 there is therefore no need to be fed with primary fuel to heat the reagents and the secondary fuel S replaces the primary fuel P.

  Whatever the operating phase, the combustion gases of the catalytic burner 72 are directed towards the exhaust of the vehicle. Preferably, their residual thermal energy is recovered in a turbine. More preferably, before being evacuated, the combustion gases of the catalytic burner 72 pass through a heat exchanger, not shown, putting them in heat exchange relationship with one or more of the reactants for the reformer 60. Still preferably, the Electricity generator comprises a heat exchanger, not shown, able to put in heat exchange relationship the reformate leaving the reformer 60, with at least one of the reagents for this reformer.

  As is clear now, the invention provides a plasma reforming device whose burner advantageously generates lower temperatures than those generated by prior art burners. The durability of the reactor is thus improved. The burner also allows a well controlled combustion and thus limits the generation of unwanted gases.

  Of course, the present invention is not limited to the embodiment described and shown provided by way of illustrative and non-limiting example.

  In particular, the invention is not limited to a type of fuel cell or reformer. Even if it is preferable to use an exothermic reformer, the invention is not limited to this type of reformer. In addition, the double wall 210 may extend over all or part of the reactor 61. Similarly, the catalytic burner 72 may extend over all or part of the double wall 210 or all or part of the reactor 61. The The air intended for the reactor 61 may also be heated by a passage in the double wall 210 of the reactor 61 and / or in the line 215 of the catalytic burner 72.

  The invention is also not limited to a plasma reforming device feeding a fuel cell. Another particularly advantageous application relates to the depollution of catalytic converters. A heat engine generates nitrogen oxides which, conventionally, are trapped by means of a catalytic converter NOx trap and then reduced by means of a mixture charged with the same fuel as that used by the heat engine. For this reduction to be effective, it is however necessary that the temperature of the catalytic converter is high. During a cold start of the vehicle, that is to say precisely when the engine generates the largest amount of nitrogen oxides, the available heat energy does not sufficiently heat DeNOx catalyst to make it operational. The use of a reforming device according to the invention makes it possible to generate hydrogen very quickly during a cold start. This hydrogen advantageously allows a reduction of nitrogen oxides, even without the use of a catalyst. In addition, this reduction is effective even at low temperatures. Finally, the use of a catalytic burner advantageously allows controlled combustion, without generating additional undesirable gases. The use of a reforming device according to the invention is therefore particularly well suited to the reduction of nitrogen oxides emitted by an internal combustion engine, in particular by an internal combustion engine of a motor vehicle.

Claims (10)

  Plasma reforming device, in particular for an electricity generator for a motor vehicle (V), comprising a plasma reactor (61) capable of producing a reformate from a set of reagents comprising a primary fuel , and possibly air and water, and a burner (72) able to heat at least one of the reagents in a line (215) before it is introduced into the plasma reactor (61), characterized in that the burner (72) is a catalytic burner.   2. Plasma reforming device according to claim 1, characterized in that the catalytic burner (72) extends, at least in part, around the plasma reactor (61).   3. Plasma reforming device according to any one of claims 1 and 2, characterized in that a supply line (210) of the reactor (61) extends, at least in part, between an outer wall (212 ') of the reactor (61) and the catalytic burner (72).   4. plasma reforming device according to claim 3, characterized in that it comprises a pipe (216) connecting an outlet (217) of the pipe (215) 20 and an inlet (218) of said supply pipe ( 210) of the reactor (61).   5. Plasma reforming device according to any one of the preceding claims, characterized in that it further comprises a mixer (220) receiving at least one reagent having passed through a supply line (210) of the reactor s' extending at least partially between an outer wall (212 ') of the reactor (61) and the catalytic burner (72) and / or air (A).   6. Plasma reforming device according to any one of the preceding claims, characterized in that the plasma reactor (61) has the shape of a coil circulating in a chamber partially filled with gaseous or liquid reagents. 30   7.Electricity generator for a motor vehicle, comprisinga plasma reforming device adapted to produce a reformate from a fuel, air and water, and a fuel cell (20) adapted to produce the electrical energy from said reformate and air, characterized in that the plasma reforming device is according to any one of claims 1 to 6.   8. Electricity generator according to claim 7, wherein said at least one reactant heated by the catalytic burner (72) is steam or water and / or fuel.   9. Electricity generator according to any one of claims 7 and 8, comprising a heat exchanger adapted to put in heat exchange relationship on the one hand said at least one reagent (72) and on the other hand, the reformate exiting said reactor (61) and / or combustion gases from the catalytic burner (72).   10.Utilization of a reforming device according to any one of claims 1 to 6 for reducing nitrogen oxides and / or particles emitted by an internal combustion engine, in particular by an internal combustion engine of a motor vehicle.