AU2011257038B2

AU2011257038B2 - Reactor for the autothermal reforming of diesel

Info

Publication number: AU2011257038B2
Application number: AU2011257038A
Authority: AU
Inventors: Christophe Boyer; Jean Calvez; Fabrice Giroudiere; Willi Nastoll; Yves Pennarguear; Sylvain Rethore
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2010-05-25
Filing date: 2011-06-23
Publication date: 2016-01-21
Anticipated expiration: 2031-06-23
Also published as: AU2011257038A1; FR2960449B1; WO2011148068A8; WO2011148068A3; WO2011148068A2; EP2576435B1; ES2743725T3; FR2960449A1; EP2576435A2

Abstract

The invention relates to a method for the autothermal reforming of a hydrocarbon feed in a catalytic reforming reactor, including the steps that consist of: a) mixing the hydrocarbon feed with water vapour, and vaporising the hydrocarbon feed if not already vaporised; b) pre-distributing the vaporised mix of hydrocarbon feed and water across the section of the reforming reactor using a multipoint injector network; c) injecting a gaseous oxidising flow, preferably pure oxygen, into the pre-distributed mixture from step (b) at the injectors from step (b); d) distributing, in the presence of an autothermal reforming catalyst, the mixture obtained in step (c) homogeneously across the section of the reforming reactor; and e) reforming the mixture distributed in step (d) in the catalytic zone of the reforming reactor.

Description

1 PATENT IFP Energies nouvelles REACTOR FOR THE AUTOTHERMAL REFORMING OF GAS OIL Inventors: Christophe BOYER, Willi NASTOLL, Fabrice GIROUDIERE, Sylvain RETHORE, Jean CALVEZ, Yves PENNARGUEAR ABSTRACT The invention relates to a process for the autothermal reforming of a hydrocarbon feed in a catalytic reforming reactor comprising the steps consisting of: a) mixing the hydrocarbon feed and steam, and vaporizing the hydrocarbon feed if it is not already vaporized, b) predistributing the hydrocarbon feed/water vaporized mixture over the cross-section of the reforming reactor by means of a multipoint network of injectors, c) injecting a gaseous oxidant flow, preferably of pure oxygen, into the predistributed mixture from step (b) at the level of the injectors of step (b), d) distributing, in the presence of an autothermal reforming catalyst, the mixture obtained in step (c) homogeneously over the cross-section of the reforming reactor, e) reforming the mixture distributed in step (d) in the catalytic zone of the reforming reactor. FIGURE 2 to be published 7186345 1 (GHMatters) P92028.AU PRIYANKA 2 REACTOR FOR THE AUTOTHERMAL REFORMING OF GAS OIL TECHNICAL FIELD OF THE INVENTION The invention relates to the field of hydrogen production by reforming a hydrocarbon feed. Various reforming processes, already described in the prior art, are used for producing hydrogen from a combustible hydrocarbon: - partial oxidation (POX) is an exothermic reaction, sometimes catalysed, which produces hydrogen (H 2 ) by reaction between the hydrocarbon feed and oxygen (02): (in the case of methane for example)

CH

4 + "'/ 02 - CO + 2 H 2 - steam reforming (SMR) is an endothermic reaction, also catalytic, which produces hydrogen by reaction of the hydrocarbon feed with water (H 2 0): (in the case of methane for example)

CH

4 + H 2 0 * CO + 3 H 2 - autothermal reforming (ATR) is the combination of the reaction of partial oxidation and steam reforming: (in the case of methane for example) 2 CH 4 + ]/2 02 + H 2 0 - 2 CO + 5 H 2 As the exothermic character of the partial oxidation compensates for the endothermic character of the steam 7186345 1 (GHMatters) P92028.AU PRIYANKA 3 reforming, an autothermal reformer can be adiabatic, with the exception of heat losses. This operating procedure is therefore important for energy management. At the outlet of a reforming unit, the hydrogen-rich effluent gas has a high content of impurities, in particular carbon monoxide (CO). The latter is particularly troublesome as it poisons the catalyst of fuel cells. That is why a unit for separation and purification is generally installed for extracting the pure hydrogen. Conventionally, processes for the production of hydrogen by reforming a hydrocarbon feed are carried out at a pressure comprised between 1 and 40 bar. It will be recalled that 1 bar is equivalent to 100 kPa. In fact, the reforming reaction has a better yield at these pressures. However, in certain situations, it is necessary to operate a reforming plant at higher pressure. This is the case for example when the plant is used in a confined environment. Examples are vehicles travelling under water, but also space vehicles, or dedicated vehicles for emergency situations in dangerous environments, for example in mines. Moreover, the installations employed in a confined environment are generally without air. The hydrogen production process must therefore be anaerobic, i.e. it must be capable of operating in the absence of air. The process is therefore designed so as to operate with a source of pure oxygen. Pure oxygen is expensive to produce, so it must be used as economically as possible. 7186345 1 (GHMatters) P92028.AU PRIYANKA 4 These constraints must be taken into account in the overall design of the system for the production of hydrogen, but more particularly in the design of the reforming reactor itself. In the context of implementing the reaction of catalytic autothermal reforming of a hydrocarbon feed, the following functions have to be carried out before entering the catalytic zone of the reactor where the reaction takes place: - vaporization of the hydrocarbon feed if the latter is liquid; - efficient mixing of the reactants, i.e. hydrocarbon feed, oxidant and steam; - distribution of the flows of the mixture homogeneously over the whole cross-section of the catalytic zone of the reactor. It is generally preferable to perform these three functions in the reactor vessel so as to limit the heat losses and to achieve compactness. The operations of mixing and distributing must be carried out in a limited time so that the combustion reaction does not start too early upstream of the catalytic zone. If the feed/oxidant/steam mixture is subjected to an excessively high temperature for too long, there may be a phenomenon of self ignition and precombustion of the hydrocarbon feed upstream of the catalytic zone of the autothermal reforming reactor. The hydrocarbon feed may be decomposed or transformed, forming heavier products that can no longer be reformed to hydrogen. There is deterioration of the hydrogen yield; soot is formed, which also leads to risks of clogging of the catalyst bed. 7186345 1 (GHMatters) P92028.AU PRIYANKA 5 This phenomenon, well known to a person skilled in the art, is amplified here by the high pressure inside the reactor, i.e. comprised between 40 and 70 bar, and possibly by the fact that the oxidant flow used is pure oxygen, and not air. Self ignition is facilitated at high pressure and in the presence of pure oxygen. The problem to be solved is to mix the reactants (hydrocarbon feed, pure oxygen and steam) and distribute them in a very short residence time so as to remain below the self-ignition time, which is itself very short, i.e. less than 100 ms, or even less than 10 ms. These very short times do not allow conventional systems to be used for mixing and distributing the reactants. PRIOR ART The conventional means for mixing and distributing flows of reactants consist of using in-line mixer systems for mixing the various reactants and then using a distributor system for homogeneously distributing the mixture over the whole cross section of the reactor. The in-line mixers are generally composed of obstacles arranged in a structured or unstructured manner, in such a way that the various flows meet one another in the pipeline, and with the aim of creating turbulence and local recirculation for good mixing at local level. The distribution systems for single-phase flows are generally composed of systems that create a significant pressure drop at reactor inlet (gratings, perforated plate, etc.). In multiphase flow, systems are generally composed of tubes for passage of the gas phase, and openings or slits for passage of 7186345 1 (GHMatters) P92028.AU PRIYANKA 6 the liquid positioned on the plate supporting these tubes or arranged along the tubes. Patents US 4,865,820, US 2002/0142199 and US 4,166,834 describe means for injecting and mixing gaseous reactants and for distributing the mixture obtained at the reactor inlet without stating whether these systems are suitable for controlling very short residence times of the mixture upstream of the catalytic zone. According to these systems, it is possible to perform the operations of mixing and distributing upstream of the catalytic zone, which it is not always possible to do when the maximum residence times are very short. SUMMARY OF THE INVENTION The present invention relates to a process for autothermal reforming of a hydrocarbon feed in a catalytic reforming reactor at a pressure comprised between 40 and 70 bar, comprising the steps consisting of: a) mixing the hydrocarbon feed and steam in a mixing chamber, and vaporizing the hydrocarbon feed if it is not already vaporized, said hydrocarbon feed being injected during step (a) at the reactor inlet in the form of a jet of droplets along an axis of the reactor, using a single nozzle, and the steam used in step (a) being injected tangentially to a wall of the reactor, in an upper cylindrical portion of the mixing chamber, the velocity of the steam injected being in the range 5 to 20 m/s in order to induce a swirl movement inside the mixing chamber in a zone having a diameter in the range 0.5 to 0.8 times the reactor diameter, a divergent duct being 7186345 1 (GHMatters) P92028.AU PRIYANKA 7 disposed to connect the zone in which the swirl movement occurs and the rest of the reactor; a') distributing the mixture obtained at stage a)homogeneously over the cross-section of the reforming reactor by means of a packing before being predistributed in step (b), b) predistributing the hydrocarbon feed/water vaporized mixture over the cross-section of the reforming reactor by means of a multipoint network of injectors, the number of injectors per square meter of reactor section being in the range 300 to 2000 and each injector being made of a venturi tube oriented along the axis of the reactor and a concentric tube, inside the venturi tube, the lower end of which is located at the level of a neck of the venturi, the mixture obtained in step (b) circulating in the concentric tube; c) injecting a gaseous oxidant flow laterally into an annular space located between the venturi tube and the concentric tube of each injector to mix the oxidant with the mixture obtained in step (b) at the level of the neck of the venturi d) distributing, in the presence of an autothermal reforming catalyst, the mixture obtained in step (c) homogeneously over the cross-section of the reforming reactor, by mean of a packing; e) reforming the mixture distributed in step (d) in the catalytic zone of the reforming reactor, said catalytic zone consisting of catalytic monoliths. 7186345 1 (GHMatters) P92028.AU PRIYANKA 8 BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a diagram showing two preferred embodiments A and B of the injectors employed in the reforming process according to embodiments of the invention. Figure 2 is a diagram showing a preferred embodiment of the process according to the invention. Figure 3 is a graph showing the residence times, in seconds, of the droplets of gas oil at the outlet of the injection nozzle, according to the example. Figure 4 is a graph showing the concentrations of gas oil in the flow in certain parts of the reactor, according to the example. DETAILED DESCRIPTION The invention is suitable for the autothermal reforming of hydrocarbon feeds. The hydrocarbon feed according to the invention can be liquid or gaseous. It can comprise hydrocarbons, petroleum cuts or alcohol, such as methanol, ethanol or bioethanol, or finally mixtures thereof. Preferably, the hydrocarbon feed reformed in the process according to the invention is selected from petroleum cuts, more preferably from gas oil cuts, and even more preferably from light gas oils or those originating from the Fischer Tropsch process. The reforming reaction implemented in the process according to the present invention is autothermal. The reactants required for the reaction are therefore the hydrocarbon feed, an oxidant and water. 7186345 1 (GHMatters) P92028.AU PRIYANKA 9 Certain hydrocarbon feeds can contain sulphur compounds or odorous compounds added intentionally for reasons of safety or for legal reasons. These can degrade the catalysts present in the installation. It is therefore customary for a person skilled in the art to purify the hydrocarbon feed before it is used, for example using a purification unit. The process according to embodiments of the invention can therefore comprise an additional step, before step (a), which consists of purification, in particular desulphurization, of the hydrocarbon feed. Step (a) of the process according to the invention consists of mixing the hydrocarbon feed and steam, and vaporizing the hydrocarbon feed if it is not already vaporized. Step (a) is preferably carried out in a mixing chamber. The latter is located in the top part of the reforming reactor. The reforming process according to the invention takes place at a high pressure, i.e. at a pressure comprised between 40 and 70 bar, preferably between 45 and 60 bar, more preferably between 50 and 60 bar. At this pressure, the saturation temperature of water is comprised between 250 and 280'C. The process according to embodiments of the invention can comprise an additional step, before step (a), which consists of heating the hydrocarbon feed to a temperature comprised between 200 and 300'C. However, higher inlet temperatures are avoided, in order to limit the reactions of thermal cracking or pyrolysis of the hydrocarbon feed. Depending on the hydrocarbon feed selected, the latter can be in liquid form or in vapour form. 7186345 1 (GHMatters) P92028.AU PRIYANKA 10 The process according to embodiments of the invention can also comprise an additional step, before step (a) , which consists of heating the water to a temperature comprised between 400'C and 600'C, more preferably between 450'C and 550'C. At the pressure of the process, comprised between 40 and 70 bar, the water is therefore preferably in the form of superheated steam before it enters the reforming reactor. This permits complete vaporization of the hydrocarbon feed without a phenomenon of re-condensation. If the hydrocarbon feed is not completely vaporized when it enters the reforming reactor, vaporization will be performed during step (a) of the process according to the invention. According to a preferred embodiment of the present invention, the hydrocarbon feed is injected during step (a) at the reactor inlet in the form of a jet of droplets along the axis of the reactor. Preferably, the hydrocarbon feed is injected by means of a single nozzle. This type of nozzle is well known to a person skilled in the art. The energy of the liquid flow under pressure is utilized for promoting spraying thereof through a capillary channel. According to this variant of the invention, a jet of droplets is thus created and dispersed as a solid or hollow cone. The diameter of this cone, at the level of the maximum path of the droplets prior to their vaporization, is preferably less than the minimum diameter of the mixing chamber of the reactor where said cone forms. Moreover, the size of the droplets is preferably comprised between 10 pm (micrometre) and 1 mm and preferably between 10 and 200 pm (micrometre). A person skilled in the art knows how to use this type of nozzle in order to obtain the desired cone diameter and droplet size. 7186345 1 (GHMatters) P92028.AU PRIYANKA 11 In a preferred variant of the process according to the invention, the steam used in step (a) is injected tangentially to the reactor wall. The velocities at the level of steam injection are preferably comprised between 5 and 50 m/s, and even more preferably between 5 and 20 m/s. This embodiment of the process according to the invention makes it possible to create, within the mixing chamber, a longitudinal swirling motion of the flow of steam. This motion helps to promote contact and heat exchange between the steam and the hydrocarbon feed, which preferably enters in the form of a cone of droplets along the axis of the reactor, and also contributes to mixing between the steam and the vaporized hydrocarbon feed in the reactor cross-section. Preferably, this swirling flow is created, within the mixing chamber, in a zone with a diameter less than the diameter of the reactor, preferably between 0.5 and 0.8 times the diameter of the reactor, so as to accelerate the flow. According to this preferred arrangement, a divergent duct is arranged to connect the cylindrical zone where the swirling flow is produced and the rest of the reactor. Preferably, the mixture obtained in step (a) of the process according to the present invention is distributed homogeneously over the cross-section of the reforming reactor before being predistributed following step (b) . A person skilled in the art can utilize any suitable known equipment for carrying out this step of homogeneous distribution. Preferably, this homogeneous distribution of the mixture obtained in step (a) is ensured by passage through packing of the structured or bulk type. Said packing is for example arranged at the outlet of the mixing chamber. It allows the water / hydrocarbon feed mixture to be distributed over the 7186345 1 (GHMatters) P92028.AU PRIYANKA 12 whole cross-section of the reactor. Moreover, if a swirling flow has been used, packing makes it possible to break the vortex created by the flow and to orient the flow velocities predominantly along the reactor axis. Finally, the packing makes it possible to increase the contact between the water and the unvaporized hydrocarbon feed, which will flow in the form of liquid films, and thus complete their vaporization if necessary. Step (b) of the reforming process according to the present invention consists of predistributing the hydrocarbon feed/water vaporized mixture over the cross-section of the reforming reactor by means of a multipoint network of injectors. Preferably, the density of the injectors of the multipoint network in step (b) is comprised between 100 and 5000 injectors per square metre, preferably between 300 and 2000 injectors per square metre. Preferably, the injectors have a spherical section, and their inside diameter is preferably comprised between 2 and 50 mm, more preferably between 2 and 20 mm, even more preferably between 2 and 10 mm. Considering the reactor cross-section located at the upper end of the injectors, the ratio of the surface area of the interior of the injectors to the total surface area of the reactor is preferably less than 50%, more preferably between 1% and 30%, even more preferably between 1% and 20%. Step (c) of the process according to the present invention consists of injecting a gaseous oxidant flow into the 7186345 1 (GHMatters) P92028.AU PRIYANKA 13 predistributed mixture from step (b) at the level of the injectors of step (b). The oxidant according to embodiments of the present invention can be pure oxygen, air, or oxygen-enriched air. In the sense of the present invention, by "flow of pure oxygen" is meant a flow containing at least 95% by volume of oxygen, preferably a percentage by volume of oxygen comprised between 98 and 100%, preferably between 99 and 100%. Preferably, the oxidant used in the present invention is pure oxygen. The process according to embodiments of the invention can comprise an additional step, before step (c) , which consists of heating the oxidant to a temperature comprised between 250 and 300'C. The injectors according to embodiments of the present invention fulfil two functions: On the one hand, they serve for point-wise predistribution of the water/hydrocarbon feed mixture, and on the other hand they permit very rapid injection of the oxidant into said mixture. Preferably, the oxidant flow is injected laterally into an injection chamber, through which the injectors pass. According to a first variant, the injectors can each consist of a venturi tube oriented along the axis of the reactor and a concentric tube, inside the venturi tube, the lower end of which is located at the level of the neck of the venturi, the predistributed mixture obtained in step (b) circulating in the concentric tube and the oxidant flow being injected laterally into an annular space located between a venturi tube and the concentric tube and with the flows mixing at the neck of the 7186345 1 (GHMatters) P92028.AU PRIYANKA 14 venturi. This variant of the injectors is shown in Figure 1 (A). In Figure 1(A), the injector consists of a venturi tube 1 and a straight concentric tube 2, which is located inside the venturi tube 1. The lower end 3 of the concentric tube 2 is at the level of the neck of the venturi 4. It is at the level of the neck of the venturi 4 that the flow velocity of the flows is highest. The upper end 5 of the concentric tube 2 is located in the mixing chamber. Thus, the water/hydrocarbon feed mixture is predistributed in as many points as there are injectors. The mixture thus predistributed enters the concentric tube 2 via its upper end 5, and circulates in the concentric tube 2 as far as its lower end 3, located at the level of the neck of the venturi 4. The oxidant flow is injected laterally into the injection chamber 6, via pipeline 7, which passes through the reactor wall. The upper end 9 of the venturi tube 1 communicates with the injection chamber 6. The oxidant flow is therefore in an annular space 8 located between the venturi tube 1 and the concentric tube 2. The oxidant flow and the predistributed water/hydrocarbon feed mixture mix together at the level of the neck of the venturi 4. At the outlet of the neck of the venturi 4, a divergent nozzle 10 makes it possible to improve the mixing and increase its distribution surface area. According to a second variant, the injectors can each consist of a straight tube oriented along the axis of the reactor possessing openings, and preferably a convergent section, the predistributed mixture obtained in step (b) circulating in said tube and the oxidant flow being injected laterally via said openings. This variant of the injectors is shown in Figure 1 (B). 7186345 1 (GHMatters) P92028.AU PRIYANKA 15 In Figure 1(B), the injector consists of a straight tube 11, oriented along the axis of the reactor, which has a convergent section 12, and one or more openings 13. The upper end 14 of the straight tube 11 is located in the mixing chamber. Thus, the water/hydrocarbon feed mixture is predistributed in as many points as there are injectors. The mixture thus predistributed enters the straight tube 11 via its upper end 14, and circulates in the straight tube 11 to the section where the opening or openings 13 are located, then to its lower end 15. The oxidant flow is injected laterally into the injection chamber 15, via pipeline 17 which passes through the reactor wall. Mixing of the oxidant flow with the predistributed water/hydrocarbon feed mixture takes place by shearing between the axial flow of the water/hydrocarbon feed mixture and the lateral flow of the oxidant flow from the opening or openings 13. To maximize the turbulent energy in the shearing zone, the opening or openings are located at the level of the neck of the convergent nozzle 12. Between the opening or openings 13 and the lower end 15 of the straight tube 11, the tube is preferably cylindrical and of the same cross-section as the neck of the convergent nozzle, so as to minimize the residence time, as well as the distances of radial diffusion of the flow to promote mixing. It can optionally be equipped with a divergent section with a maximum angle of 15' when allowed by the residence time (variant not shown). If it is present, the divergent nozzle makes it possible to improve mixing and increase its distribution surface area. When the straight tube is cylindrical between the opening or openings 13 and the lower end 15, the diameter and the length of said cylinder are determined by a person skilled in the art so as to find a compromise between good efficiency of mixing and a short residence time. 7186345 1 (GHMatters) P92028.AU PRIYANKA 16 Moreover, according to one or other variants of the injectors, a device creating a pressure drop can be employed on the injectors, in order to prevent rising of the mixture into the oxidant flow. This device can be, for example, a diaphragm or a porous material compatible with the fluids in use. Regardless of the type of injector selected, it is possible for the lower end of the injectors to comprise a divergent nozzle. However, considering the reactor cross-section at the level of the lower end of the divergent nozzle, the ratio of the internal surface area of the divergent nozzles to the total surface area of the reactor is preferably less than 50%, more preferably comprised between 5% and 50%, even more preferably comprised between 10% and 50%. Step (d) of the process according to the present invention consists of distributing, in the presence of an autothermal reforming catalyst, the mixture obtained in step (c) homogeneously over the cross-section of the reforming reactor. In fact, the constraints imposed on the residence time of the reactants after they are mixed in step (c) does not allow the injectors to be very close together and covering a large fraction of the reactor cross-section. To guarantee good distribution of the reaction mixture over the whole surface of the reactor, it is necessary for the jet leaving the injectors to be diffused radially. This distribution step (d) is applied in a distribution zone. The distribution step (d) is carried out in the presence of an autothermal reforming catalyst, which allows the reforming reaction to start. In this way, the risks of self-ignition of the mixture are limited, and if ignition does occur, the flame front is limited in its spread owing to the presence of a 7186345 1 (GHMatters) P92028.AU PRIYANKA 17 distributing device in which the hydraulic diameter of the fluid passages is very small, preferably less than 2 mm, even more preferably less than 1 mm. Moreover, the presence of an autothermal reforming catalyst in the distribution zone employed in step (d) makes it possible to avoid development of the oxidation reaction only, which would lead to the formation of soot. Diffusion of the mixture obtained in step (c) during step (d) can be carried out by any device known to a person skilled in the art that is suitable for the fluids in use. According to a first variant of the process according to the invention, homogeneous distribution during step (d) of the mixture obtained at the end of step (c) is ensured by passage through packing of the structured or bulk type that can contain at least one reforming catalyst. According to a second variant of the process according to the invention, homogeneous distribution during step (d) of the mixture obtained at the end of step (c) is ensured by passage through successive beds of catalytic monoliths spaced apart with free heights. By "free height" is meant a zone not containing packing and with a height preferably comprised between 2 and 10 mm, and more preferably comprised between 2 and 5 mm. According to a third variant of the process according to the invention, homogeneous distribution during step (d) of the mixture obtained at the end of step (c) is ensured by passage through packing composed of metallic or ceramic foams that can contain at least one reforming catalyst. The diameter of the pores of these foams is generally less than 1 mm, preferably 7186345 1 (GHMatters) P92028.AU PRIYANKA 18 less than 0.5 mm. In this case, radial diffusion is carried out directly within the foam through the pores and there is no need to provide a succession of packings spaced apart with free heights. Step (e) of the process according to the present invention consists of reforming the mixture distributed in step (d) in the catalytic zone of the reforming reactor. The catalytic zone of the autothermal reforming reactor contains one or more catalysts suitably selected by a person skilled in the art. For example, autothermal reforming catalysts are marketed by the company SAdChemie (FCR-14 monolith) or the company Engelhard (Selectra ATR catalyst). According to a preferred embodiment, the catalytic zone of the reforming reactor consists of catalytic monoliths. The latter offer the advantage of generating a small pressure drop. Optionally, several segments of catalytic monoliths are superposed on one other, the spaces between the segments having a larger dimension preferably comprised between 2 and 10 mm. Said spaces can be filled with packing of the bulk granular bed of catalyst type or with metallic or ceramic foam coated with catalyst. They can thus promote radial diffusion of the flow between the segments of monoliths, to maintain good homogeneity of the flows. The reformate obtained after passage over the catalytic zone can be led onto a particle filter, for recovering the soot generated by the reforming reaction. Preferably, the process according to the invention comprises an additional step wherein the reformed gas originating from step (e) is cooled downstream of the catalytic zone in the 7186345 1 (GHMatters) P92028.AU PRIYANKA 19 reactor vessel. One embodiment of this step consists of arranging a system for cooling the reformed gas originating from step (e) downstream of the catalytic zone in the reactor vessel. This cooling system makes it possible to evacuate the reformed gas originating from step (e) at a temperature below 500'C. In this way the problems of mechanical strength of the vessel and pipework arranged downstream of the catalytic zone are avoided. Advantageously, the energy recovered in the cooling of the reformed gas is used for generating and/or superheating the water required for the process, which is mixed with the hydrocarbon feed during step (a) of the process according to embodiments of the present invention. The system for cooling the reformed gas from step (e) can consist of a coil in contact with said reformed gas, and said coil can be arranged both downstream of and/or at the periphery of the catalytic zone of the reactor. Finally, the process according to the invention is preferably characterized in that all the steps mentioned above are carried out within the vessel of the reforming reactor. For this, in a preferred variant of the process according to the invention, the vessel of the reforming reactor, within which all the steps mentioned above are carried out, comprises: - an outer wall that can withstand the high pressure differences comprised between 40 and 70 bar, and - an inner wall that can withstand temperatures comprised between 700 and 1000'C, 7186345 1 (GHMatters) P92028.AU PRIYANKA 20 the space between the two walls thus defining, around the catalytic zone of the reactor, an envelope of inert gas at a pressure comprised between 40 and 70 bar and at a temperature below 500'C, preferably comprised between 100 and 300'C. This type of double-walled vessel was described in patent application FR 2924358 Al. It makes it possible to uncouple the temperature stresses and the pressure stresses that are exerted on the reactor. Owing to this uncoupling of the stresses, the outer wall can be made of a material that is resistant to the high pressure differences, but not to the high temperatures, and the inner wall can be made of a material that is resistant to the high temperatures of the process, but can only withstand a small pressure difference. The space between the two walls can be utilized for performing the role of a thermal barrier, in particular by being filled with an inert gas. PREFERRED EMBODIMENT OF THE INVENTION Figure 2 shows a preferred embodiment of the present invention. The autothermal reforming reactor 100 is used for implementing the reforming process according to embodiments of the present invention. This reactor comprises a vessel formed of an outer wall 101 and of inner walls 102 and 102'. The space between the two walls (101 and 102') 103 is filled with steam, which is at a pressure comprised between 40 and 70 bar and at a temperature below 500 0 C, preferably comprised between 100 and 300 0 C. The outer wall 101 consists of a material that can withstand high pressure differences. The inner wall 102 consists of a material that is resistant to high temperatures, 7186345 1 (GHMatters) P92028.AU PRIYANKA 21 between 700 and 1000'C, and the inner wall 102' consists of a material that is resistant to intermediate temperatures, preferably comprised between 300 and 700'C. The hydrocarbon feed enters the reforming reactor via pipe 104. A nozzle 105 provides atomization of said feed in the form of a jet of droplets. The atomized hydrocarbon feed, in the form of a cone, enters the mixing chamber 106. This chamber has a cylindrical upper portion 107 with diameter less than the diameter of the reactor. A divergent duct 108 connects the cylindrical upper portion 107 to the rest of the reactor. Water, in the form of superheated steam at a temperature between 450 and 500 0 C, enters the reactor via pipe 109. The water is injected tangentially to the reactor wall in the cylindrical upper portion 107 of the mixing chamber 106 via pipe 110. The velocities during steam injection are preferably between 5 and 50 m/s, and even more preferably between 5 and 20 m/s. This tangential injection makes it possible to create a longitudinal swirling motion of the flow of steam within the cylindrical upper portion 107 of the mixing chamber 106. The combination of swirling flow of the steam and cone-shaped flow of the hydrocarbon feed promotes good mixing of the reactants in the mixing chamber 106. The steam/hydrocarbon feed mixture is distributed homogeneously over the whole surface of the reactor due to the packing 111. The steam/hydrocarbon feed mixture is then predistributed in a plurality of points by means of the multipoint network of injectors 112. Each injector complies with the second 7186345 1 (GHMatters) P92028.AU PRIYANKA 22 embodiment of the injectors as described above and as shown in Figure 1(B) . Each injector consists of a straight tube passing through the injection chamber 113. The oxidant flow enters the reforming reactor via pipe 114. It is injected laterally into the injection chamber 113 via pipe 115. Mixing of the oxidant flow and the predistributed water/hydrocarbon feed mixture takes place by shearing between the axial flow of the predistributed water/hydrocarbon feed mixture and the lateral flow of the oxidant flow at the level of the openings 116. The mixture of reactants water/hydrocarbon feed/pure oxygen is led over packing 117 for distributing the mixture of reactants over the whole reactor cross-section. The packing 117 can optionally comprise an autothermal reforming catalyst, which allows the reaction of autothermal reforming to begin once the mixture of reactants arrives on the packing 117. In other words, the zone in which self-ignition of the reactants could occur is reduced to a minimum: it is located in the tubes of the injectors 112 between the opening 116 for injection of the oxidant flow and the lower end of the tubes 118. The mixture distributed by the packing 117 arrives in the catalytic zone of the reforming reactor, which comprises several segments of catalytic monoliths 119, which are separated from one another by several spaces 120. Each space 120 can be filled with packing, which can contain an autothermal reforming catalyst, promoting good radial diffusion of the gas flow. 7186345 1 (GHMatters) P92028.AU PRIYANKA 23 The reformate obtained after passage over the catalytic zone is led onto a particle filter 121, for recovery of the soot generated by the reforming reaction. The reformate leaving particle filter 121 is cooled inside the vessel of the reactor 100 in a cooling zone 122. A coil 123 is wound around said cooling zone 122. Cold water arriving from outside the reactor 100 via pipe 124, and leaving the reactor 100 in pipe 125, circulates in the coil 123, and recovers the heat from the reformate. The coil is also arranged around the catalytic zone of the reactor, so as to recover more thermal energy. The reformate leaving the reactor 100 via pipe 126 is at a temperature preferably between 350 and 500 0 C. The reformate leaving the exchanger 123 can also be used for generating or superheating steam in an additional exchanger inside the equipment before leaving the vessel under pressure. EXAMPLES A reactor for autothermal reforming of a gas oil, the latter originating from a column for atmospheric distillation of a crude oil, was dimensioned according to the criteria of this invention, and according to the preferred embodiment of the process according to the invention, as shown in Figure 2. The oxidizing gas used is pure oxygen at 100%, which is injected without dilution at the level of the chamber 108. The operating conditions are described in Table 1. 7186345 1 (GHMatters) P92028.AU PRIYANKA 24 Mass flow of gas oil kg/h 7.75 Temperature of gas C 200 oil Mass flow of 02 kg/h 6 Temperature of 02 0 C 250 Mass flow of H 2 0 kg/h 35 Temperature of H 2 0 0 C 460 Table 1: Operating conditions A single injection nozzle for the gas oil 105 is arranged at the top of the reactor and produces a spray with droplets about 100 pm (micrometre) in diameter in a cone with angle of 900. The diameter of the upper portion 107 of the mixing chamber, where the swirling motion of the steam is created, is 80 mm and the diameter of the reactor is 120 mm. The height of the mixing chamber 106 and that of the packing 111 are 70 mm. The number of injectors in the injection chamber 113 is 19. The geometry of the injectors is as described in Figure 2(B) with a divergent nozzle in the lower portion of the tubes. Each injector has an inside diameter of 10 mm at its upper end, a diameter of 3 mm at the level of the opening for the injection of oxygen, and a diameter of 3 mm at the level of the lower end of the divergent nozzle. The average residence time between the opening 116 for the injection of oxygen and entry into the packing 117 is 7 ms, which is less than the theoretical self-ignition time of 20 ms. The packing 117 is composed of a metallic foam with a pore density of 27 to 33 pores per inch, or about 10 to 12 pores per centimetre, and 7186345 1 (GHMatters) P92028.AU PRIYANKA 25 can be coated with catalyst. The height of the packing 117 is 100 mm. Figure 3 shows the residence times, in seconds, of the droplets of gas oil at the outlet of the injection nozzle 105, which are subjected to tangential injection of the flow of steam at 460 0 C. The residence times are represented by grey levels: black corresponds to 0 second and light grey to 0.13 second. When the droplets are vaporized, they disappear from Figure 3. These calculations were carried out with the Fluent software version 6.3.26 marketed by the company Ansys. As can be seen from Figure 3, the mixing chamber 106 (referring to Figure 2) provides effective vaporization of the gas oil, since the droplets disappear before leaving the upper portion 107 of the mixing chamber. Figure 4 shows the concentrations of gas oil in the flow in the mixing chamber 106, in the packing 111 (referring to Figure 2), in the multipoint network of injectors 112 and in the packing 117. The gas oil is simulated by an imaginary molecule with the empirical formula C 1 6

H

2 9 with physical properties (density, viscosity, boiling point) representative of gas oil. The concentration values are represented on a grey scale. They range from light grey for a concentration greater than or equal to 23% to black for concentrations less than or equal to 21%. These concentration fields were also calculated with the Fluent software version 6.3.26. It can be seen from Figure 4 that the efficiency of mixing is very good in the mixing chamber 106 since the concentrations of gas oil are homogenous at the outlet from this chamber. 7186345 1 (GHMatters) P92028.AU PRIYANKA 26 Moreover, calculations have shown that the efficiency of distribution of the system is very good since the gas flow velocities are homogenous over the whole cross-section, as well as the concentrations of oxygen. Finally, the yield at the reactor outlet is good, since conversion rates of the gas oil above 98% are achieved. It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 7186345 1 (GHMatters) P92028.AU PRIYANKA

Claims

1. Process for autothermal reforming of a hydrocarbon feed in a catalytic reforming reactor at a pressure comprised between 40 and 70 bar, comprising the steps consisting of: a) mixing the hydrocarbon feed and steam in a mixing chamber, and vaporizing the hydrocarbon feed if it is not already vaporized, said hydrocarbon feed being injected during step (a) at the reactor inlet in the form of a jet of droplets along an axis of the reactor, using a single nozzle, and the steam used in step (a) being injected tangentially to a wall of the reactor, in an upper cylindrical portion of the mixing chamber, the velocity of the steam injected being in the range 5 to 20 m/s in order to induce a swirl movement inside the mixing chamber in a zone having a diameter in the range 0.5 to 0.8 times the reactor diameter, a divergent duct being disposed to connect the zone in which the swirl movement occurs and the rest of the reactor; a') distributing the mixture obtained at stage a)homogeneously over the cross-section of the reforming reactor by means of a packing before being predistributed in step (b),b) predistributing the hydrocarbon feed/water vaporized mixture over the cross-section of the reforming reactor by means of a multipoint network of injectors, the number of injectors per square meter of reactor section being in the range 300 to 2000 and each injector being made of a venturi tube oriented along the axis of the reactor and a concentric tube, inside the venturi tube, the lower end of which is located at the level of a neck of the venturi, the mixture obtained in step (b) circulating in the concentric tube; 7186345 1 (GHMatters) P92028.AU PRIYANKA 28 c) injecting a gaseous oxidant flow laterally into an annular space located between the venturi tube and the concentric tube of each injector to mix the oxidant with the mixture obtained in step (b) at the level of the neck of the venturi d) distributing, in the presence of an autothermal reforming catalyst, the mixture obtained in step (c) homogeneously over the cross-section of the reforming reactor, by mean of a packing; e) reforming the mixture distributed in step (d) in the catalytic zone of the reforming reactor, said catalytic zone consisting of catalytic monoliths.

2. The process according to claim 1, wherein the reactor comprises a vessel and the steps of the process are carried out in the vessel, the vessel comprising: - an outer wall resistant to high pressure differences of between 40 and 70 bar, and - an inner wall resistant to temperatures of between 700 and

1000-C, a space between the two walls defining, around the catalytic zone of the reactor, an envelope of inert gas at a pressure of between 40 and 70 bar and at a temperature below 500'C.

3. The process of claim 2, wherein the inert gas in the space between the two walls is at a temperature of between 100 and 300 0 C.

4. The process according to any one of claims 1 to 3, wherein homogeneous distribution during step (d) of the mixture obtained at the end of step (c) is provided by passage through 7186345 1 (GHMatters) P92028.AU PRIYANKA 29 packing of the structured or bulk type comprising at least one reforming catalyst.

5. The process according to any one of claims 1 to 3, wherein homogeneous distribution during step (d) of the mixture obtained at the end of step (c) is provided by passage through packing composed of metallic or ceramic foams that can be coated with a reforming catalyst.

6. The process according to any one of claims 1 to 5 wherein the process comprises an additional step wherein the reformed gas from step (e) is cooled downstream of the catalytic zone.

7. The process according to any one of claims 1 to 6, wherein the homogeneous distribution of the mixture obtained in step (a') is provided by passage through packing of the structured or bulk type.

8. The process according to any one of claims 1 to 7, wherein the oxidant is pure oxygen.

9. The process according to any one of claims 1 to 8, wherein the catalytic zone comprises several segments of catalytic monoliths superposed on one another.

10. The process according to claim 9, wherein the segments are spaced apart by between 2 and 10mm. 7186345 1 (GHMatters) P92028.AU PRIYANKA