FR2873306A1 - Electrical generator, useful for the combustion of a liquid and/or gaseous fuel, comprises a tangential injection of a combustive gas in a chamber of combustive-fuel - Google Patents

Abstract

Electrical generator, for the combustion of a liquid and/or gaseous fuel, comprises a tangential injection of a combustive gas in a chamber of combustive-fuel (6) traversed by a rotative flow of combustive that is excited by mobile electrical discharge of high voltage between a central electrode (3) in the form of a rod and another electrode (2) in the form of divergent tuyere. Electrical generator, for the combustion of a liquid and/or gaseous fuel, comprises a tangential injection of a combustive gas in a chamber of combustive-fuel (6) traversed by a rotative flow of combustive that is excited by mobile electrical discharge of high voltage between a central electrode (3) in the form of a rod and another electrode (2) in the form of divergent tuyere (where: the two electrodes are connected to a source of alternative current; the tuyere (2) delimiting an excitation chamber (2a) is situated upstream of the fuel combustion chamber (8); the tyere is placed at the ground potential; and the other electrode (3) is placed either symmetrically or eccentrically to the axis of (2)), and the device is intended initially to: initiate the combustion of the fuel entering separately through a tube (9) located downstream of (2a) and maintain the complete combustion or to facilitate a partial oxidation of the fuel to produce a gaseous mixture composed mainly of hydrogen and carbon monoxide. Independent claims are also included for: (1) a plasma-catalytic process of liquid or gas fuel conversion into a mixture (termed as: synthesis gas or syngas, or reformat) containing hydrogen and carbon monoxide and accompanied by methane and ethylene, comprising: partial oxidation of a fuel with elementary oxygen contained in a combustive gas added to the matter (where the conversion is characterized if the mixture (termed as reactive) of the fuel and combustive gas travels through the device; and the mixture is subjected to a plasma of mobile electric discharge, in order to first initiate a combustion of the fuel and then maintain the partial oxidation of the fuel into gas of synthesis or reformat; and the partial oxidation take place in a device (termed as reactor or reformer) composed of two sections in series for the flow of reactive and products, where the first section (or zone) is the device and the second section (or post-plasma zone) is: located downstream from the first zone, in direct contact with the first zone by means of a tube, and is filled by a catalytic refractory solid (containing nickel that is dispersed, metallic and/or oxidized) whose melting point exceeds 1250[deg]C); and (2) a plasma-catalytic device, to carry out plasma-catalytic conversion, containing two zones in series (for the flow of reactive entering separately by the tube for combustive-fuel and through the tube for fuel (where the reactive is transformed successively into products (syngas or reformat))), where the first zone has a mobile electric discharge and the second zone is filled by a catalytic refractory solid, which is permeable to the flow of reactive and/or products.

Description

The present invention relates to an electrical device for assisting the

  total or partial combustion of liquid and / or gaseous fuels. Electrical assistance is in the form of a mobile high voltage discharge. The device is intended to initiate and maintain the total combustion of a fuel or assist a partial oxidation of fuel for

produce synthesis gas.

  The idea of mixing a flame and an electric shock appeared in the 19th century when A. VOLTA and M. FARADAY were studying the electrical conductivity of flames. This idea will be applied in several patents such as that of R. SCHNABEL (1909) in Germany to overheat flames, that of GT SOUTHGATE (1926) in the USA for welding or for heating metallurgical furnaces, or that of A. RAVA ( 1926-35) in the USA to increase the temperature of the flames. To be able to inject more and more electrical energy into the flames, B. KARLOVITZ proposes a series of US patents (1961-68) which are based on an addition of alkaline salts. Thus, with a 10 kW methane flame, it allows to add 5 kW by superheating 500 C by a high voltage discharge of 2 kV. Between 1960 and 1968 Mr. DENIS proposes in France an electroburner of 1 MW but without any addition for preionization of the flame. In 1980 B.G. DJJACHKOV (USSR) proposed the use of electroburriers in the field of metallurgy to pre-crack methane or a gas oil avoiding the addition of salts. In 1982 EDF and the company STEIN-HEURTEY rediscover the old works of Mr. DENIS and then patent (FR2577304 in 1985 and FR2647186 in 1989) a 1 MW electric burner of thermal power to which we add 250 kW of electric power (to 700 Amperes); such a strong current between two electrodes of an electric arc however requires a very fragile circuit cooling water of these electrodes. In 1985 the same companies limit the power of their electric burner to 70-100 kW thermal they add 20-50 kW electric which avoids the cooling of the electrodes. In 1984 the company BERTIN filed a patent FR2564334 on a three-phase high temperature electroburrier. To avoid erosion of the electrodes and the formation of nitrogen oxides, it is proposed to generate arcing in a chamber filled with a combustible gas. The configuration of the chamber is such that a fuel acceleration is effected by a convergent and a stabilization of the flame by a divergent in which is injected air.

  In 1988 H. LESUEUR, A. CZERNICHOWSKI and J. CHAPELLE patented a device for generating plasmas by forming sliding electric arcs between two or more electrodes in the form of a knife (FR2639172). The arcs move as a result of the strong longitudinal thrust of the gas injected along the electrodes. Such a device, hereinafter called "GlidArc-1", finds multiple applications. One of these applications is to maintain the partial oxidation of light hydrocarbons to produce synthesis gas (syngas, a mixture containing mainly H2 and CO). It has been described by A. CZERNICHOWSKI and P. CZERNICHOWSKI in FR2768424 in 1997.

  Another device, called "GlidArc-II", has been proposed by rotating a central electrode in the form of a disk in the middle of several flat immobile electrodes. Sliding arcs are thus obtained in an almost stagnant gas. Such a device was proposed in 1998 by A. CZERNICHOWSKI and P. CZERNICHOWSKI to convert a carbonaceous material, see FR2786409.

  In recent years, there has been a high demand for Hydrogen or synthesis gas for various applications, for example to feed Fuel Cells (PAC). These batteries are more and more in demand for various applications such as cars, trucks, boats, aircraft, homes, etc. The entire system for preparing a gaseous fuel to feed these batteries from an easily accessible fuel (propane, butane, gasoline, diesel, etc.) must then follow a miniaturization, be robust and be able to operate thousands hours.

  In our work on the reforming of various carbonaceous materials, we have discovered some difficulties in using GlidArc-1 and II devices to convert carbonaceous materials. Two points were of particular concern to us: GlidArc-I and / or Il can not be reduced in size, especially in the diameter of the plasma zone where the electrodes are housed, which limits the miniaturization of these devices; During prolonged operation in the presence of a carbonaceous material, a slow deposition of soot or graphite is observed on the dielectric connectors bringing a high voltage to the electrodes, which leads to troublesome electrical short circuits. To overcome these problems, we have developed a new mobile discharge generator, the object of the present invention.

DEVICE

  The device is shown schematically (and in a simplified manner) in FIG. 1. This diagram illustrates the invention but is obviously only a non-limiting example of the realization of a future industrial device. The body / 1 / metal of the device has axial symmetry. It is grounded (earthed) and at the same time connected to one of the two electrical poles of a high-voltage AC power supply (5 Hz kHz, 3 - 15 kV, <5 A). This body / 1 / is in electrical contact with a convergent-divergent conical metal insert / 2 /, also of axial symmetry. The insert thus constitutes an electrode with zero potential. A stick (a rod) metal / 3 / located on the axis of symmetry of the device is the other electrode, the high voltage. This electrode / 3 / is electrically insulated from the rest of the device / 1 / with a dielectric part 14 / also called "candle". The body / 1 /, the electrode / 3 / and the candle / 4 / are assembled in a sealed manner. A tube / 5 / is placed tangentially with respect to the upper part of the device / 1 /. The tube opens into the chamber / 6 / oxidant which is reserved for a gas flow called "A" of oxidizing nature, for example air, air enriched in oxygen, pure oxygen or technical quality, all these gases can be mixed with water vapor. The main property of the gas entering the chamber / 6 / is that it must not carry any electrically conductive body or body that can decompose thermally or under the influence of an electric shock by giving, as a product, a conductive substance (non-dielectric). Are excluded in the flow of gas A, for example, all metal vapors or dust, soot, carbon dust or graphite, mists, vapors or dust of mineral salts, organic compounds, metallurgical organic, etc. The tangentially incoming oxidant flow can only exit the chamber / 6 / through a groove / 7 / traversed symmetrically (relative to the axis of the device) by the electrode / 3 /. As a result of its tangential introduction, the fluid A is rapidly rotated about the axis of the chamber / 6 / and at the same time the fluid advances along this chamber. This type of movement of the "tornado" (vortex) type is also preserved in the groove / 7 / where the distance between the electrodes / 2 / and / 3 / is minimal. It is therefore in this groove / 7 / that burst an electric discharge caused by an alternating electric field greater than that of the dielectric breakdown in the medium such that a flow A tornado. It should be added that the evoked high voltage supply just delivers an alternating voltage higher than the maximum voltage characterizing the break. An electric discharge therefore bursts between the electrodes / 2 / and / 3 / in the flow of the oxidant A in rotation and the filament of the discharge is consequently also rotated. This filament is traversed by the alternating current thus having the multiple zero crossings followed by the reappearance of the current, all this at the frequency of the power supply. The filament is also pushed by the fluid A along the diverging portion of the insert / 2 / (thus having a nozzle) and along the electrode / 3 /. Thus, the mobile and pulsed electric discharge excites the fluid A during its course in the groove / 7 / and in the nozzle. The oxidizer thus excited in such an excitation chamber / 2a / then enters the chamber / 8 / combustion fed continuously by another fluid called "B" entering another tube / 9 /. The chamber / 8 / combustion is located downstream of the excitation chamber / 2a /. The fluid B (a liquid and / or a gas and / or a vapor and / or a mist) has no constraints such as for the fluid A and may then contain, for example, carbon compounds of fossil origin. This fluid B which we call "fuel" or "fuel" has in this case a reducing character and can then react with an oxidant carried by the fluid A. The tube / 9 / can be placed tangentially with respect to the axis of symmetry of the device or perpendicularly with respect to this axis. Two tangential directions of such placement of the tube / 9 / with respect to the tube / 5 / can be exploited: that which causes a rotation of the fluid B corresponding to the vortex generated by the fluid A (this case is designated in FIG. ) or a counter-direction causing the rotation of the fluid B against the current. The fluids A and B thus mix in the chamber / 8 / where we can observe, for example, a beginning of reaction between A and B giving products C: A + B = C. (1) This process (1) is mainly generated and activated by the presence of the mobile electric discharge which, carried by the tornado (vortex) of the fluid A, enters the chamber / 8 /. The discharge then continues its course in the tornado (vortex) now composed of A, B, and products C of the reaction (1). The resulting fluid can only come out through the tube / 10 /.

  The discharge between the central electrode / 3 / and the insert / 2 / stretches more and more in the space / 2a / following the displacement of its attachment feet to the electrodes more and more distant one the other. The length of the filament of the discharge also becomes larger because of the curvature of the filament caused by the rotation of the fluid which occurs firstly in the divergent zone / 2a / of the insert / 2 / and then in the convergent part which is formed by the inner walls of the chamber / 8 /. The discharge attachment legs move differently and almost independently of each other because their stability at a given point on each electrode depends mainly on local conditions, such as temperature, surface quality and roughness, speed of fluid, etc., from the point of attachment to the electrode in question. The foot of the discharge which rotates, which slides and which jumps on the central electrode / 3 / finally arrives at the extreme point / 11 / where it fixes itself provisionally. It is then that the other foot can leave the surface of the insert / 2 / to then move on the metal surface of the chamber / 8 / at zero potential. Finally, there is a moment when the filament of the discharge becomes so long that the supply (limited in voltage and current) can no longer maintain the discharge. It is then that the discharge disappears. A new discharge is then immediately reinstalled in the groove / 7 / and perpetuates the fate of the previous discharge. The life time between the appearance and the disappearance of a singular discharge depends on a large number of parameters such as fluid flow, temperature, geometry, etc. Such a cycle can last between 1 ms and 1s, to give an order of magnitude by way of example. Pulsations (5 Hz to 50 kHz) causing zero crossings of the discharge current prevent any establishment of electrical and thermal equilibrium within the filament of the discharge and then lead to a thermodynamic out of equilibrium state of the plasma of the discharge. discharge. In addition, the curved or meandering shape of the discharge, its disordered displacement, its pulsation at the rate of the power supply frequency, its sudden appearance and disappearance, etc. - All this gives us a great reaction medium very active to prime and then to assist a process (1) of partial oxidation of a fuel to produce the syngas.

  If the tornadoes produced by fluids A and B are in a direction opposite to each other or if the entry of fluid B is perpendicular - then we increase the turbulence and reinforce the mixing of these fluids in the room / 8 /. The lifetime of an individual discharge is shortened but this does not change the very advantageous properties of the plasma-chemical zone that forms in the chamber / 8 / and propagates to the output / 10 / device.

  These successive discharges form a purely electric "flame" in the presence of the single fluid A. This "flame" can be observed by opening / 10 / looking in the axial direction. In the presence of an oxidant mixture A + fuel B, this flame becomes a true electro-reinforced thermal flame. It is lit and maintained continuously by the device.

  We have experimented several mixtures A + B which ignite in the presence of the electric discharge while the cut of electric supply of such assistance with the combustion causes the immediate extinction of the flames. These ignition and assistance effects are especially appreciated in the case of flow rates that are too high compared to the geometry of the device or in the case of mixtures "poor" in fuel B with respect to the oxidizer. code. Our device is therefore first of all an igniter and then a continuous and very effective assistance of the flames.

  We underline the fact of the absence in the chamber / 6 /, in which is installed the candle / 4 /, any electrically conductive material that can be deposited on the candle and thus compromise the dielectric separation between the electrode central / 3 / and the body / 1 / of the device set to zero potential. This contributes decisively to a prolonged longevity of the device compared to previous models - 1 and / or II.

  As for the dimensions of the groove / 7 / which is traversed by the electrode / 3 / - we choose its inner diameter D7 and that D3 of the central electrode so that the spacing e = (D7-D3) / 2 between these two electrodes / 2 / and / 3 / at the groove / 7 / is adequate. It is a question of adapting it at the same time to the type of high voltage supply and the type of physicochemical medium of gas A in tornado (vortex), this to organize a dielectric rupture in this throat there. We are not looking for a great precision to place the electrode exactly in the axis of the groove. On the contrary, a slight eccentricity will always give a real distance e 'between these electrodes slightly less than e somewhere in the throat and then the discharge will tend to burst at this point without hindering the course of the sequence of events. Also, we sometimes observe a slight curvature of the central electrode / 3 / which is manifested somewhere between the groove / 7 / and the end / 11 /, witnessing an irregular heating of the part of the electrode which is embedded in the medium at high temperature prevailing in the chamber / 8 /. This is not a problem either because the function of the electrode / 3 / is always ensured and the exact axial symmetry of the point / 11 / with respect to the electrode / 2 / or with respect to the inner wall of the chamber / 8 / is not crucial.

  The device can be considered as a stand-alone unit, for example as a flare igniter, as a mini-electroburner, and for other applications. The tube / 10 / can be used to connect the device with, for example, a post-plasma chamber (zone) where the continuation of the process (1) and its eventual termination take place.

  DEVICE ASSOCIATED WITH A CATALYTIC REACTOR

  One of several applications of the device is to assist a catalytic reaction that can take place in a chamber (zone) called "post-plasma" which is located directly downstream of the output / 10 / as schematically shown in FIG. 2. This diagram illustrates the invention but is obviously only a non-limiting example of the realization of a future industrial reactor.

  This chamber / 12 /, typically cylindrical, is filled with a refractory solid 13 / in the form of granules or any other form (for example a porous or multi-channel monolithic insert) leaving this zone easily penetrable (permeable) by a stream of products C accompanied by residual reagents A and B leaving the device through the sealed aperture / 101 to the top cover / 14 / of the chamber. The refractory chosen is characterized by its porous structure and by its melting point exceeding 1250 C. The zones / 8 / and / 12 / thus communicate directly (no separation) so that the end of the flame is close (or even in contact) with the top layer of refractory granules (or other catalytic refractory filler). To facilitate the penetration of the fluid leaving the zone / 8 / by the tube / 10 / in the filling / 13 /, we leave a hollow / 15 / in the upper part of the filling. If the body of the post-plasma / 12 / area is metallic, we put it at ground potential for safety reasons. The post-plasma zone is closed by a bottom cover 16 / where the outlet 17 / of the products of the reaction (1) is housed. Several thermocouples / 18 / can be inserted into the filling of the post-plasma area to measure the temperatures in different points of this area. This reactor zone is thermally insulated / 19 / with respect to the environment. For weakly exothermic reactions (1) we also add a thermal insulation / 20 / around the device to maximize the thermal power released by such a process (1). Such a reduction in heat losses may, in some cases, be beneficial to the processes involved in the post-plasma zone. Finally, no part of the reactor is forcedly cooled.

DEVICE

  ASSOCIATED WITH A PARTIAL FUEL OXIDATION REACTOR The combination of the device with a partial oxidation reactor is particularly advantageous as a plasma-catalytic device for carrying out a process for converting various liquid or gaseous fuels in the presence of oxygen O2, added to these matters. According to this method, the fuels are converted into a gaseous mixture composed mainly of hydrogen H 2, carbon monoxide CO, carbon dioxide CO 2 and water vapor H 2 O, accompanied by light gaseous hydrocarbons. Such a "synthesis gas" (syngas) mixture is called when the hydrocarbon content is limited. Otherwise we can call it "reformat". These gases can be diluted in N2 nitrogen if the air is used as an oxygen source.

  The production of syngas is a very important step in the development of natural gas or associated with oil wells. In addition, there has been a growing interest in recent years for the production of syngas or reformate from liquid fuels to fuel Combustion Piles. For low temperature heat pumps, syngas is considered a source of pure hydrogen. High temperature batteries, such as the Solid Oxide Fuel Cell (SOFC) or the Molten Carbonate Fuel Cell (MCFC), directly accept syngas (or even reformat!) As fuel, which greatly simplifies the entire fuel chain. conversion of fuel into electrical energy in PAC-based systems.

  The process described here is illustrated firstly by the conversion of a hydrocarbon mixture such as commercial gas oil. This liquid models a wide range of liquid fuels from fossil sources such as gasoline, kerosene or heavy oil for heating or that used for the propulsion of boats.

  Another illustration given is the conversion of commercial C3H3 propane (otherwise called "LPG") used for heating or fuel. This gas models other fossil or industrial gases such as methane (natural gas), gas associated with oil wells, gas flares, pyrolysis gases of a fossil material (such a gas sometimes containing water vapor), firedamp mines, etc. Our "device + post-plasma reactor" assembly is presented in FIG. 2. The two compartments / 8 / and / 12 / are arranged in series with respect to the flow of reactants A and B incoming. In the device at the zone / 8 /, these reagents A and B are accompanied by products C in formation. The first phase of the partial oxidative conversion of a carbonaceous material having a chemical formula averaged CpHgOr (r = 0 for hydrocarbons), begins in the zone / 8 / very active and ends in the post-plasma zone at the level of the first top layer of filling / 13 /, somewhere near hollow / 15 /. The filling used is, for example, a granular material passing the flow of reagents and / or products through it. Moreover, regardless of the form or the technique of the filling, it must always be permeable, allowing the flow of reagents and products to pass and thus guaranteeing contact with the entire filling.

  The progression of this conversion phase which takes place mainly in the zone / 8 / of the discharge of the device can be described in a simplified way as the total combustion of a fraction f of the carbonaceous charge: f CpHqOr + [f (p + q / 4) -r / 2] 02 = f * p CO2 + f * q / 2 H2O. (1 a) This reaction is highly exothermic and the heat dissipated in the zone / 8 / causes the rapid warming of this zone as well as the heating of the upper layer of the filling (granules). The temperature can then reach 1200 C. Under these conditions, the non-consumed portion of the carbonaceous material pyrolyzes mainly producing H2, CO, methane CH4, ethylene C2H4, acetylene C2H2 and elemental carbon C (for example in the form of soot).

  The gas stream containing the pyrolysis products mixed with the products of the reaction (1 a) then passes through the successive layers of the filling / 13 / where mainly endothermic reactions take place which successively transform reactants into syngas (or reformate): CO2 + CH4 = 2 CO + 2 H2, (2) 2 CO2 + C2H4 = 4 CO + 2 H2, (3) 2 CO2 + C2H2 = 2 CO + H2, (4) CO2 + C = 2CO3 (5) H2O + CH4 = CO + 3H2, (6) 2H2O + C2H4 = 2CO + 4H2, (7) 2H20 + C2H2 = 2CO + 3H2, H2O + C = H2 + CO.

  These endothermic reactions (heat-consuming) cause a gradual lowering of the fluid temperature (and that of the successive layers of the fluid-filled filling), slowing down the progression of the reactions (2) to (9). It is the heterogeneous reactions (5) and (9) that are particularly slow. In the case of liquid fuels, their pyrolysis results in a particularly strong and intolerable soot formation for certain uses, such as, for example, to feed SOFC or MCFC type PACs.

  However, we have found the solution to this problem: it consists in using nickel dispersed on the surface and inside a porous granular material bearing high temperatures. As support we have privileged here the "chamotte" (a natural aluminosilicate cooked at high temperature). Other aggregates (or other forms, for example refractory monoliths) may also be used. As an example will be described herein the firecracker granules and the process for initiating its catalytic character.

  To impregnate (pre-activate) these granules with nickel, the granules of size between 5 and 10 mm are soaked for 10 to 30 minutes in a boiling concentrated solution of nickel nitrate (we do not add any precious metal!). The granules thus impregnated are dried and then calcined in an oxidizing atmosphere (for example in air). Green in color, these granules then become completely black (the color of some nickel oxides), a sign of the complete decomposition of nickel nitrate and its conversion into nickel oxides. Other soluble nickel compounds (chloride, sulfate, acetate, etc.) have also been successfully tested to impregnate the granules for calcination. The granules thus prepared (pre-activated) are then stored in the post-plasma zone / 12 / of the reformer. From the first use, these granules will become chemically active by the mechanism described below. When starting the cold reactor, filled with the pre-activated granules, we heat the inside of the reactor (especially the first layer of the zone / 13 /) at a temperature between 700 and 1200 C (depending on the carbonaceous material to convert). This heating is provided by the use of the device first for ignition and then for the maintenance of the complete combustion flame (la) of a fuel in the presence of an excess of oxidant. The post-plasma compartment filled with the pre-activated granules / 13 / is then in a stream of combustion products still containing an excess of oxygen. Under these conditions, any nickel (whatever its initial chemical form) on the surface and inside of the granules becomes totally oxidized. Nickel oxides NiO, Ni 2 O 3 and Ni 3 O 4 (otherwise known as NiO * Ni 2 O 3) are mainly known. These oxides are transformed towards each other as a function of the temperature and the oxidation-reduction medium. It is precisely this property that we use judiciously for our plasma-catalytic process of partial oxidation of fuels, the object of the present innovative application.

  During operation of the reactor, when the temperature of the upper layer of granules (measured for example using one of the thermocouples concerned / 18 /) reaches between 700 and 1200 C, we increase the flow rate of the fuel B to be converted and / or we decrease the flow of the oxidizing gas A (oxidant), for example air. During the start-up phase of the process, the outgoing gas is not flammable. We observe this by observing a small burner fed by the gas product leaving / 17 /. Following the tilting of the flows, a small diffusion flame (in the air) is born. The flame is then characterized by one of the following cases depending on the atomic ratio ra = O / C (this ratio being directly related to the oxidant / fuel mass ratio): É A flame difficult to maintain when ra> 1.7 or when flammable products are highly diluted in a neutral gas matrix such as nitrogen, water vapor and / or carbon dioxide.

  É A flame that is barely visible in the eye but stable when it rises from 1.2 to 1.7. This is the ideal case for our process presented here, indicating that the outgoing gas is composed mainly of H2 and CO with only a few traces of other flammable components (this is called a "syngas" mixture). É A stable blue flame with a slight upper end slightly

  yellowish when ra 1.0 - 1.2. This is an acceptable case for our process, where the outgoing gas is composed mainly of H2 and CO and also contains larger amounts of other flammable components such as CH4 or C2H4; remember that we call such a mixture the "reformat".

  É A stable flame of yellow color when ra 1.0. It indicates the presence of soot in the post-plasma zone. The outgoing gas also contains acetylene. To "save" the conversion, we increase the value of ra until the control flame

become acceptable.

  We carry out the processes of total conversion (100%) of the carbon load (and thus without any trace of this load at the exit of the reformer) towards the syngas or the reformate. We explain this performance as follows: nickel oxides NiO (global formula) initially present on (and inside) the porous granules housed in the post-plasma zone react with certain oxidation and pyrolysis products. We can distinguish two cases: E these oxides increase their oxidation state, for example: 2 NiO + H2O = Ni2O3 + H2, (10) 2 NiO + CO2 = Ni2O3 + CO, (11) E where these oxides reduce their state oxidation, for example: 2 Ni2O3 + C2H4 = 4 NiO + 2 CO + 2 H2, (12) 2 NiO + C2H2 = 2 Ni + 2 CO + H2. (13) The oxidation or reduction reactions depend on where the nickel oxides are present in the post-plasma zone / 12 /. Indeed, the thermocouples / 18 / inserted in the filling / 13 / indicate a strong negative gradient of the temperatures along the fluid passing through this filling. This temperature drop as the gas passes through the filling 113 / does not come from a deficiency of the thermal insulation 1191 of the zone but it is well related to the endothermic reactions (2) to (9) and those of type (10) to (13). The temperature distribution stabilizes after a certain time necessary to warm the entire post-plasma zone to a thermal equilibrium. To obtain this stabilization we keep the device still in operation because otherwise, we observe a gradual displacement of the "good" temperature distribution zone to the outlet 117 / of the reactor. This causes cooling of the first layers of the filling and finally their thermal and catalytic deactivation. Finally, this inevitably leads to a deposit of soot on the layers upstream of the displaced zone and finally the cessation of the process.

  For the proper functioning of the reactor, we must therefore maintain the filling at a sufficiently high temperature to achieve the very important process of carbon consumption: s C + NiOX -> E CO (or s CO2) + NiOx_E (or NiO) ( 14) where e takes a value> 0 and <_ x. This highly efficient process takes place on the contact surface between soot and nickel oxides, thanks to the migration property of O 2 ions in the structure of oxides carried at high temperature. A NiOXe sub-oxide thus formed then immediately undergoes a reverse oxidation process of the type: thus giving the desired products H2 and CO. This is indeed the new catalytic processes of a heterogeneous conversion of soot into syngas. This process is in addition to the soot removal reactions (5) and (9).

EXPERIMENTAL RESULTS

  Example A. Reforming a diesel fuel (also called "diesel fuel") is a very difficult or impossible process. Indeed, we do not have the knowledge of a competitive process of conversion of a commercial diesel into syngas. The fuel used in our experiments is brand "Total". According to chemical analysis, it contains mainly C7 to C27 hydrocarbons (C156 as a weighted average and CH1.83 as the simplified chemical formula) of paraffin type, olefins and aromatics. Its relative density is 0.826 and its sulfur content is 310 ppm by weight. The reactor used is the one whose diagram is drawn in FIG. 2. The body of the post-plasma zone / 12 / is made of stainless steel, its interior volume is 0.6 L (a 6 cm diameter tube) and it is completely filled with nickel-activated fireclay granules and obtained by employing the activation described above.

  The device in its function of activator is constructed using ordinary plumbing commercial pieces in standard outer diameter 27, 21 and 17 40 mm. All this structure is easily assembled by standard threads of these parts NiOx_E + 8 H2O = s H2 + NiOx or (10a) NiOX _, + 8CO2 = eCO + NiOx (11a) and is therefore removable. The central electrode / 3 / also made of ordinary steel has the shape of a rod with a diameter of 5 mm. The ceramic connector / 4 / with a standard car candle thread (M14 x 125) is screwed axially to the top of the body / 1 / of the device. A tangential entry of air is through the metal tube / 5 / diameter 13.5 mm. This tube is welded to the upper body / 1 /. The fuel enters the lower body / 11 through the tube / 9 / welded perpendicular to the axis of the device. The electrical discharge is powered by a transformer 50 Hz 220V / 5kV limited to 25 mA. The power dissipated in the discharge of the device is measured by a wattmeter; it is equal to 40 W. A single thermocouple / 18 / is inserted near the outlet / 17 / products where the temperature can reach 900 C. All tests were carried out at atmospheric pressure.

  Atmospheric air is used as an oxidant at a constant flow rate of 30 L (n) / min controlled by a mass flow meter. Before entering the zone 16 / by the tube / 5 /, the air is preheated in an exchanger. The diesel fuel is sent by a metering pump to the tube / 9 / through a rotameter to control the stability of the flow. The absolute flow rate (in g / min) is frequently measured from the difference in mass of the liquid sucked by the pump. The explored range of flow rates is 0.4 0.7 kg per hour. The fuel is preheated in a metal tube through which an electric current of adjustable intensity is passed; we then maintain the fuel inlet temperature in the chamber / 8 / at about 200 C.

  Chemical analyzes of the outgoing gas (syngas or reformate) are performed using gas chromatography (GC). We use a single two-way micro-GC dedicated to CO2, C2H4, C2H6, C2H2, C3H6 + C3H8 and H2O (moisture) molecules for the first pathway and H2, 02, N2, CH4 and CO molecules for the second pathway. The complete analysis of the gas takes place in 255 s only.

  We tested our process for 12 continuous hours without any difficulty. We have not observed any progressive increase in pressure inside the reactor / 12 /. The test was completed voluntarily.

  At the outlet of the reactor, there was no complete soot on the filter composed of a cotton wool exposed to the outgoing gas flow. The syngas had the following composition (in% of the dry gas volume): H2 = 14, CO = 19, CO2 = 4.2, CH4 = 2.0, C2H4 = 0.3, C2H6 = 0.003, C2H2, C3 and 02 absent, the rest being N2 and Ar. Methane is present in the reformate from carbonaceous liquids because it is the hardest molecule to crack or reform. It appears during the pyrolysis of a complex carbonaceous charge and / or is synthesized in the lower part of the active filling by an anaerobic digestion process: C0 + 3H2 = CH4 + H20. (15) After cooling (under nitrogen) and dismantling the reactor, we did not find soot marks on the granules or other parts of the reactor.

  The gas leaving the device has a lower heating capacity (PCI) of 5.3 kW. The electric power of the electric discharge used is equal to 40 W. The electric power of assistance is then equivalent to less than 1% of the PCI of the syngas (or reformate) produced.

  An important note concerns the fate of sulfur initially present at the relatively high level of 310 ppm (wt) in this commercial fuel. The presence of H2S in the outgoing gas indicates that the sulfur is not retained in the post-plasma zone, thus not risking the deactivation of our nickel-based catalyst. This is an important fact that will facilitate the use of polluted sulfur fuels by avoiding their prior purification. It is indeed very difficult to desulphurize a carbonaceous material containing hundreds of sulphide molecules while it is much simpler to extract a single H2S molecule from reformate or syngas.

  Another important remark concerns the voluntary stopping of the device at the end of its use. To prepare it for a restart, we recommend the following procedure: sudden stop of the device by blocking the arrival of the fuel then cutting off the power supply of the device, followed immediately after by the drastic reduction of the flow of air (or other oxidant ) to a certain level, which depends on the size of the reactor. It will be about 2 L (n) / min for 1 L of volume of the post-plasma / 12 / reformer zone. By this means we organize the oxidation of all nickel sub-oxides up to NiO and then up to Ni203, retained in the filling. Indeed, when the temperature decreases and becomes lower than 600 C we observe an exothermic re-oxidation: NiO, + 02> NiO -> Ni2O3. (16) In order to prevent a sudden rise in the temperatures of the successive layers of the filling during such stratified oxidation, we limit the flow of oxidant (02). The temperatures observed during such an operation can reach 1200 C without however affecting our filling. The high temperature zone moves slowly in the direction of the oxidant flow leaving the successive layers of oxidized nickel to the maximum. Once the nickel has regained its maximum oxidation, the reaction (16) stops and the device begins to cool until it reaches room temperature. The restart of such a device, become cold, takes between 10 and 20 min. In this period we already get a syngas whose quality is such that it is able, for example, to supply a SOFC or MCFC. About 20 to 40 minutes of operation of the device will still be needed to achieve the conditions for optimal reforming and thermal equilibrium of the device.

  Reforming can also be stopped in another way if you want to restart it quickly. In these cases, the fuel flow rate is drastically reduced, then the power supply to the device is immediately cut off and finally the flow rate of the oxidizer is greatly reduced to organize the total combustion of the residual carbonaceous charge. The heat provided by this combustion thus compensates for the thermal losses of the device and makes it possible to maintain a sufficiently high temperature of the filling / 13 / of the post-plasma zone in anticipation of restarting the reforming. On the occasion of such a "standby", we also observe the reactions (16) that prepare well the filling massive contact with the fuel during restart. Such a restart then takes only between 1 and 3 minutes.

  On the occasion of a shutdown of the process, whether definitive or of the "standby" type, we also oxidize the possible traces of carbon or soot (if present, deposited in the device) in CO and / or CO2. We also transform the nickel sulphides possibly deposited in the NiO (and / or Ni2O3) and S02 filling. This short operation of reactivation of the catalytic refractory can also be conducted, if necessary, periodically.

  Example B. This example shows how the new process can be applied to the reforming, at atmospheric pressure, of a commercial LPG. This fuel is composed of> 95% propane C3H8, the rest being butanes. Sulfur is present at a concentration of 100 ppm. Our tests are carried out in the same post-plasma reactor (that of Example A) activated by the same electrical power device 40 W. Several series of tests were carried out under different operating conditions. These tests of a total duration of 10 hours did not require any specific intervention to change any part of the device or the post-plasma portion of the reforming device. The process was still very stable. Even when soot began to appear during some "failed" experiments with insufficient air / propane ratio, we could restore good reforming conditions by adding more air or reducing LPG flow (measured with 'a mass flow meter).

  A typical reforming series was performed for a constant air flow rate of 32 L (n) / min by changing the LPG flow rate within a range of 5.8 to 7.0 g / min. Starting cold it takes us less than 8 min to preheat the entire device (by the total combustion of a low LPG flow). We then get the first flow of syngas while increasing the rate of incoming LPG quite sharply. A minimal adjustment of the air / LPG ratio is then necessary for the entire reforming device to reach thermal equilibrium, which manifests itself in a constant composition of the outgoing syngas. The outgoing gas analyzes indicate that LPG is completely reformed and the absence of soot or other heavy products is confirmed. At the exit we total between 38 and 46% vol. H2 + CO diluted in nitrogen (dry gas analysis). This corresponds to 17 and 20 L (n) / min of a pure syngas, or 3.3 and 4.0 kW of lower heat output (PCI) output. The energy efficiency of the process reaches up to 76%, the rest being converted into heat. In this calculation of efficiency we do not take into consideration the heat contained in the gas produced by reforming at a temperature> 650 C. The other secondary products of reforming are: water vapor, CO2 and CH4 (respectively 3 - 4% and 0.5 - 2% in the dry gas). The concentration of methane can be limited to <1% in optimal O / C ranges from 1.3 to 1.4. The presence of CH4 in these proportions is not a problem for SOFC or MCFC batteries that easily "burn" this molecule.

  Based on gas analyzes and inflow and outflow rates, we can write our partial LPG reforming process by the reaction: C3H3 + 1.85 02 = 2.7 CO + 3.6 H2 + 0 , 3 CO2 + 0.4 H2O (17) which presents a compromise between the ideal partial oxidation (OIC = 1.00) and the total combustion (O / C = 3.33).

Claims (10)

  1) Electrical assistance device for the combustion of a liquid and / or gaseous fuel, characterized by a tangential injection of an oxidizing gas into an oxidizer chamber / 6 / traversed by a flow of oxidizer in rotation, this oxidant being then excited by high voltage mobile electrical discharges between a central / rod-shaped electrode and another divergent nozzle-shaped electrode /, the two electrodes being connected to an alternating current source, the nozzle / 2 thus delimiting an excitation chamber / 2a / situated upstream of the combustion chamber / 8 / of the fuel, the nozzle / 2 / being put at the potential of the earth, and the other electrode / 3 / placed either symmetrically or eccentrically relative to the axis of the nozzle / 2 /, all this device being intended to first initiate the combustion of the fuel entering separately by a tube / 9 / located downstream of the chamber / 2a /, and then either to maintain this Complete combustion is to assist partial oxidation of the fuel to produce a gaseous mixture composed mainly of hydrogen H2 and carbon monoxide CO.   2) Plasma-catalytic process for converting liquid or gaseous fuels into a mixture containing hydrogen H 2 and carbon monoxide CO, this mixture (called "synthesis gas" or "syngas") which can be accompanied by methane CH 4 and ethylene C2H4 (such a mixture is then called "reformate"), said conversion being carried out by a partial oxidation of a fuel with elemental oxygen O 2 contained in an oxidizing gas added to said material, this conversion being characterized in that the mixture (also called "reagents") of said fuel with the oxidant gas passes through the device according to claim 1, where this mixture is subjected to the plasma of the mobile electric discharge, this to first initiate a combustion of the fuel and to then maintain said partial oxidation of the fuel in synthesis gas or reformate, while knowing further that this combustion and this partial oxidation proceed from in a device (also called "reactor" or "reformer") composed of two parts in series with respect to the flow of reactants and products, the first part (or "zone") / 1 / being the device itself and the second part (also called "post-plasma zone") / 12 / being situated downstream of the first zone / 1 / and necessarily in direct contact with this zone / 1 / via a tube / 10 /, knowing finally, the second post-plasma zone / 12 / is filled with a catalytic refractory solid / 13 / whose melting point exceeds 1250 ° C. and that said solid contains dispersed nickel metal and / or oxidized.   3) A plasma-catalytic device for carrying out the plasmacatalytic conversion according to claim 2, characterized in that this device contains two zones in series with respect to the flow of the incoming reactants separately by the tube / 5 / for the oxidant and by the tube / 9 for the fuel, these reactants successively transforming into products (syngaz or reformate), the first zone / 1 / harboring a mobile electric discharge and the second zone / 12 / being filled by a catalytic refractory solid / 13 / whose point of melting exceeds 1250 C, this refractory containing dispersed nickel metal and / or oxidized and filling / 13 / being permeable to the flow of reagents and / or products.   4) Process according to claim 2, characterized in that the fuel subjected to partial plasma-catalytic oxidation is of fossil origin and that it is liquid or gaseous.   5) Process according to claim 2, characterized in that the oxidizing gas (oxidant) for performing the partial oxidation plasmacatalytique fuels contains elemental oxygen O 2, this oxidant can be air, air enriched by oxygen or oxygen of technical quality, knowing that the oxidizing gas may also contain water vapor.   6) Process according to claim 2, characterized in that the postplasma / 12 / area is filled by a granular or monolithic porous refractory solid / 13 / whose melting point exceeds 1250 C, knowing that this refractory contains dispersed nickel oxides these nickel oxides being previously deposited on the surface of the refractory and in its interior by impregnation of said refractory in a concentrated solution of a nickel compound followed by calcination in air, which transforms this initial nickel compound in nickel oxide, again knowing that such filling of the post-plasma zone / 13 / is in close contact with the flow of reagents and / or products while at the same time allowing said flow to flow freely through the filling / 13 / .   7) Process according to claim 2, characterized in that a plasma-catalytic partial oxidation starts at a minimum temperature between 600 and 1000 C, and in that to reach such a temperature, at least in the first layer of the catalytic filling / 13 / of the post-plasma zone / 12 / which is the layer in contact with the plasma zone / 1 / (this contact being necessary to start the partial oxidation of a fuel), it is first of all initiated a total combustion of said fuel using the device / 1 / which is upstream of the post-plasma zone / 12 /, which consequently carries this first layer of the catalytic refractory / 13 /, that in direct contact with the flame electrorenforced combustion in the zone / 8 /, at such a temperature (between 600 and 1000 C), after which the oxidizer / fuel mass ratio is reduced to achieve said partial oxidation of the fuel in syngas or reformate maintaining the function of the device, so that the temperature distribution in the post-plasma zone is stable and knowing that such electrical maintenance consumes less than 1% of the electrical power of the device, this compared to the lower heat output carried by the flow outbound products / 17 /.   8) Process according to claim 2, characterized in that the procedure for complete shutdown of the plasma-catalytic conversion of a fuel is as follows: the complete shutdown of the fuel flow, followed immediately by that of the power supply of the fuel. device, then by a sharp decrease in the oxidant flow rate, this last step causing the progressive oxidation of all the nickel compounds contained in the post-plasma / 12 / nickel oxide zone NiO and Ni203, because this exothermic oxidation progressively occurs in the post-plasma zone / 12 / by the successive layers of the catalytic filling / 13 / which heat up to a temperature of up to 1200 C because of said oxidation, again knowing that the flow of oxidant passing through said zone / 12 / corresponds to approximately 2 L (n) / min of air for each liter of the post-plasma filled zone / 12 /.   9) Process according to claim 2, characterized in that the procedure of standby plasma-catalytic conversion of a fuel is as follows: a sharp decrease in fuel flow, followed immediately by the total power failure electrical device, then by a sharp decrease in the oxidizer flow to a level sufficient to maintain a total combustion of the fuel, said combustion providing a heat output equal to the thermal losses suffered by the entire device "standby", knowing that during such a standby all the nickel compounds contained in the post-plasma zone / 12 / are oxidized progressively to NiO and Ni 2 O 3 oxides, this to accelerate a future restart of the plasma-catalytic conversion of a fuel into syngas or in reformat.   10) Process according to claim 8 or 9, characterized in that the operations of total shutdown or standby of the plasma conversion of a fuel, these two short operations requiring a reduced flow of oxidant passing through the post-combustion zone. plasma / 12 / filled with a catalytic refractory based on nickel / 13 /, are accompanied by a combustion of carbon and / or soot possibly present in said zone / 12 / and / or by a transformation of the nickel sulphides possibly present in said zone / 12 / in oxides of nickel and SO 2, which reactivates the catalytic properties of the filling / 13 /, such reactivation can be made periodically in order to recover the initial catalytic properties of the filling / 13 / of the zone post- plasma / 12 / reforming device.