System and process for producing decarbonized energy by combustion of metallic particles

Abstract

A metallic particle combustion energy production system (S1) comprising a set of elementary combustion reactors (6, 6b), each comprising a metallic particle burner coupled to a combustion chamber, means (1, 2, 3, 4) for selectively feeding said elementary combustion reactors (6) with iron particles and gaseous oxidizer, means for recovering the heat from combustion in said elementary combustion reactors (6), means (9, 11, 12, 15, 16) for collecting metal oxides at the outlet of the combustion chambers, and means for controlling the selective feeding means according to at least one predetermined setpoint. See FIG. 1

Description

Title of the invention: System and method for producing decarbonized energy by combustion of metallic particles FIELD OF INVENTION

[0001] The present invention relates to a system for producing decarbonized energy by combustion of metallic particles for stationary or mobile applications. It also relates to a process for producing decarbonized energy implemented in this system. STATE OF THE ART

[0002] Most current heating systems (natural gas, propane, butane, or fuel oil boilers) use fuels that emit CO2. Furthermore, the rising cost of energy and the risk of shortages due to the energy dependencies of many countries worldwide are driving the search for green alternative energy sources for residential and commercial heating. The use of wood for heating also presents a significant risk of deforestation if responsible and sustainable forest management practices are not adopted.

[0003] In this context, the combustion of metallic particles, as detailed in the article "Direct combustion of recyclable metal fuels for zero-carbon heat and power," Applied Energy, 2015 by JF Bergthorson, is a proposed solution for producing CO2-free combustion for all types of energy production applications. Metallic fuels (magnesium, aluminum, iron) have the advantage of generating only solid metal oxides during combustion, which are easily recovered in a combustion system. These oxides can then be recycled using renewable energy via an inert anode electrolysis process or a zero-CO2 thermochemical reduction process using solar energy.

[0004] The combustion of metallic particles is historically known in aerospace propulsion applications and, as documented in US8100095B2, in internal and external combustion automotive applications. A major problem with iron combustion is the time required to burn all the particles. Some companies are developing iron combustion systems with lengths exceeding ten meters in height for only 1 MW. However, a reactor of this type is compatible with very few industrial installations or vehicles due to its great height. It is therefore important to modify the design of this system to make it compatible with a large majority of industrial installations.

[0005] The main objective of the invention is thus to propose a new concept of energy production system by metallic combustion, allowing their integration into a wide variety of industrial applications. Description of the invention

[0006] This objective is achieved with a thermal energy production system by combustion of metallic particles, comprising: - a set of elementary combustion reactors, each comprising a metallic particle burner coupled to a combustion chamber, - means for selectively supplying said elementary combustion reactors with iron particles and gaseous oxidizer, - means of recovering heat from combustion in said elementary combustion reactors, - means of collecting metal oxides exiting the combustion chambers, and - means to control the means of selective feeding according to at least one predetermined instruction.

[0007] The advantage of having several small reactors with equivalent power to a single large reactor is that it reduces the length required for each reactor to allow the particles time to burn. Having a set of metal powder combustion reactors arranged in parallel helps minimize the height of the combustion system, facilitating its integration into existing boiler buildings and thus accelerating the technology's market launch.

[0008] Selective reactor control means independent control of each reactor, but also the same control for a group of reactors, or even for all reactors.

[0009] Selective reactor control may advantageously include a screw for adjusting the dosage of metallic particles, and a device for adjusting the gaseous oxidant flow.

[0010] The predetermined control setpoint for the selective feeding means may, for example, be a power or energy setpoint. Temperature setpoints inside and / or outside an elementary reactor may also be provided, as well as fuel / oxidizer mixture setpoints (also called air-fuel ratio), and more generally, setpoints for measurable physicochemical quantities within the energy production system according to the invention.

[0011] It is also possible to use information on needs expressed by users of the energy produced, for example, steam flow rates at pressure and temperature data, to generate flow rate instructions for the injection of metallic particles and oxidizing gases.

[0012] The feeding means may advantageously include feeding means common to all or part of the elementary combustion reactors.

[0013] Heat recovery means may advantageously include recovery means common to all or part of the elementary combustion reactors.

[0014] The oxide collection means may advantageously include collection means common to all or part of the elementary combustion reactors.

[0015] Each elementary combustion reactor can be provided with a casing or enclosure having a prismatic shape.

[0016] In a particular configuration of a system according to the invention, the set of elementary combustion reactors is structured into a plurality of subsets of elementary combustion reactors arranged radially around an axis.

[0017] In another particular configuration of the invention, the set of elementary combustion reactors is structured into a plurality of concentrically arranged subsets of elementary combustion reactors.

[0018] In another particular configuration of the invention, the set of elementary combustion reactors is structured into a plurality of subsets of elementary combustion reactors arranged in a matrix.

[0019] The elementary combustion reactors can be arranged in a common enclosure containing a heat transfer fluid. Flue pipes for transporting the effluents from the elementary combustion reactors can be arranged in the common enclosure.

[0020] According to another aspect of the invention, a process is proposed for producing energy by combustion of metallic particles, implemented in a production system according to the invention, this process comprising: - a selective supply of metallic particles and gaseous oxidizer to a set of elementary combustion reactors, each comprising a metallic particle burner coupled to a combustion chamber, - recovery of heat from the combustion of said metallic particles, in said elementary combustion reactors, - the collection of metallic oxides resulting from the combustion of metallic particles, at the outlet of the combustion chambers, and - control of the selective feeding of the elementary reactors, according to at least one predetermined setpoint.

[0021] Since, at lower power levels, with a diameter equivalent to that of a single reactor (the equivalent diameter providing the air passage cross-section which, combined with the chosen length and total air flow rate, determines the residence time necessary for the oxidation and subsequent cooling of the iron particles, and specifically chosen in the single reactor), the flow velocity is lower (air requirements generally decrease with lower power), meaning the particles need less distance to burn. Another advantage of using multiple reactors instead of increasing the diameter of the single reactor (to decrease the flow velocity and shorten the reactor) is that the heat exchange surface area will be larger, thus maximizing the compactness of the heat exchanger.Integrating heat exchangers fully immersed in the flow of the enlarged combustion chamber (to use the option with a single enlarged reactor instead of a multi-reactor) is not feasible due to the heavy fouling associated with the flow heavily laden with particles. DESCRIPTION OF THE FIGURES

[0022] Other features and advantages will become apparent from the following description of a particular, non-limiting embodiment of the invention, made with reference to the figures in which:

[0023] [Fig. 1] is a schematic representation of an example of an embodiment of an energy production system according to the invention, composed of a set of reactors within a hexagonal housing in a platform including a filtration system, a thermal recovery system and a metallic particle injector.

[0024] [Fig.2] is a schematic representation of a particular configuration of a multi-reactor module implemented in an energy production system according to the invention, with an exhaust tube distribution around the reactors and a common heat exchanger (tank with heat transfer fluid in which the reactors and exhaust tubes are immersed).

[0025] [Fig.3] illustrates a particular geometry of a combustion module in which elementary reactors are arranged in a honeycomb pattern.

[0026] [Fig.4] is a schematic representation of the combustion module with several possible geometries.

[0027] [Fig.5] illustrates a top view of a particular geometry of an energy production system according to the invention, parameterizable by adding elementary combustion reactors in a honeycomb configuration, and a section view XX' of this particular geometry.

[0028] [Fig.6] illustrates a top view of another particular geometry of an energy production system according to the invention, which can be parameterized by adding reactors combustion elements in a matrix configuration, and a section view XX' of this other particular geometry.

[0029] [Fig. 7] illustrates a particular embodiment of a modular combustion reactor implemented in a power generation system according to the invention. DETAILED DESCRIPTION

[0030] SI is a possible modular architecture for an iron powder combustion boiler, with reference to [Fig. 1]. This architecture comprises, within a casing or housing 7, a set of identical combustion reactors 6 arranged in parallel. The iron powder is stored in a silo 1 and is transferred by powder transport means 2 (screw conveyors, pneumatic, gravity, conveyors, etc.) to the reservoir of the injection system (powder metering system by screw conveyor, pneumatic, gravity, or other) 3.

[0031] The injection system allows for metering the flow rate of iron powder fuel (which allows for metering the chemical power introduced into the reactor). The transfer 4 of the powder to a combustion reactor 6 is carried out using a supply of gaseous oxidizer. The reactor 6 is the site of the iron powder combustion and therefore incorporates an iron particle burner, ignition means, and means for injecting additional oxidizer to supplement the supply provided by the powder injection.

[0032] Reactor 6 can also incorporate a heat exchanger that recovers heat directly from iron combustion. The heat exchanger can be, for example, a cylindrical coil located on the periphery of the combustion chamber to limit fouling. The fluid in the exchanger can then transport useful heat (generated by combustion) for an industrial process or to contribute to electricity generation (using a thermodynamic converter composed of turbine(s) or, more generally, an external combustion engine), or both.

[0033] Several reactors are arranged in parallel and supplied by a single injection system 3 or by several independent injection systems. The reactors generate heat independently and distribute the total thermal power required by the user through a control system (not shown) that strategically distributes the power. Several power distribution configurations between the reactors are possible, ranging, for example, from equal power distribution to a distribution where some reactors can be switched off while the others share all the power.

[0034] Once the gas and particle flow has partially cooled along the reactors 6 by means of a main exchanger (not shown) within them, it enters a sedimentation chamber 9 where it is forced to make a half-turn 8, which improves the filtration efficiency of metal oxides by sedimentation. Once the stream has been freed of a large portion of its metal oxides, it passes through one or more secondary heat exchangers 10 to transfer some of the remaining heat to the heat transfer fluid. Several types of fluids can be used in the heat exchanger circuits (e.g., oil, water, steam, air, etc.) to meet different user requirements. The heat transfer fluid circuits of the secondary heat exchangers can be connected to the fluid circuits of the primary heat exchangers to extend the heating of the fluid in a second heat exchange stage, or they can be independent to address different operating temperatures for the user.In cases where the number of secondary heat exchangers differs from the number of primary heat exchangers, the designer has free choice in the design of the fluid circuits and the possible combinations of connections or disconnections between the heat exchangers.

[0035] The distinctive feature of these heat exchangers is that they have a larger exchange surface area per unit volume than the main heat exchangers located in the combustion chambers 6. This is made possible by the fact that fouling will be significantly reduced by the upstream filtration stage 9. The flow exiting the secondary heat exchange zone then passes through a cyclone 11 to filter some of the oxide particles remaining in the flow. The secondary heat exchange zone 10 can also be located downstream of the cyclone 11 in order to further reduce fouling of the heat exchangers (at the expense of the heat recovery rate).

[0036] This modular architecture concept does not limit the number of heat exchange or filtration stages, nor their relative positioning. The oxide particles are deposited in the tank 12, which can be connected via 13 to the sedimentation tank, so that the oxides can be transferred to the silo 16 by a powder transfer system 15. The gas stream, having been freed of some of its iron oxide particles, escapes via 14 to other filtration or heat recovery means, or to the outside of the system.

[0037] The preliminary sizing of each combustion chamber (also called reactor 6) is based on the desired residence time of the gas within it and the available height for such a reactor at the installation site (the number of reactors will also depend on the available surface area in the boiler room and their relative positioning – aligned in a single row, in several rows, circularly, or otherwise, depending on the available space configuration). The law allowing for the rough preliminary sizing of each reactor based solely on the gas flow rate is:

[0038] tj- „ c — D-total xf res - H is the equivalent height of each reactor - S is the area of ​​the equivalent air passage cross-section in each reactor - D_total is the total volumetric flow rate of oxidant under normal conditions required to oxidize iron particles while maintaining a specific air-fuel ratio (iron-oxygen ratio relative to stoichiometry) ranging, for example, from 0.2 to 1. An additional flow rate can be used to regulate the temperature of the hot gases or the oxygen concentration (for example, by recirculating the exhaust gases). The total volumetric flow rate must be adjusted for the average temperature of the exhaust gases (gas expansion factor). - t_res is the residence time of the gas in each of the 6 reactors to reach an oxidation level targeted by the designer. This residence time can also be determined by the heat exchange time required to sufficiently cool the flow. The purpose of this formula is to provide an indication that gives an idea of ​​the sizing of each reactor. In the case of a vertical reactor with top-down particle injection, and particles of sufficiently high density and size, the effect of gravity on the particles reduces this residence time because the sedimentation rate must be added to the gas flow velocity. - N_r is the number of reactors, therefore strictly greater than 1.

[0039] This formula makes it possible to understand the importance of this new degree of freedom, which is the number of reactors (and therefore of modularity or the notion of multi-reactors), on the geometric dimensioning of the latter.

[0040] Problem of reducing the height of the iron-burning single-reactor boiler

[0041] In the case of a multi-reactor, if one wishes to divide by 5 the height taken by the If a single reactor is required, and the total power and gas residence time must be maintained, five parallel reactors of height H / 5 will be needed to share the total air flow rate. It might be preferable to also reduce S and increase the number of reactors to maximize the surface area for heat exchange with the heat transfer fluid circulating between the reactors (double-walled or immersed heat exchange circuit).

[0042] However, in the case of a single-reactor, the equation above shows that, without the possibility of having multiple reactors, the only degree of freedom to compensate for the reduction in height (without changing the power and residence time) is the air passage area. But dividing the height by 5 implies multiplying the cross-section by 5, at the expense of a smaller heat exchange surface area or fouling of the heat exchangers if they are immersed in the hot flow in direct contact with the particles (to compensate for the reduction in heat exchange surface area due to the reactor geometry).

[0043] The advantage of the multi-reactor lies at this level. It is even possible to imagine reactors of slightly different dimensions, as long as the concepts of modularity and compactness are respected. The main idea is to give engineers more freedom in their design of an iron combustion system which has characteristics that otherwise make it poorly suited to integration into existing boiler rooms (which are in most cases 3 to 5 meters high for a power output between 200 kWth and 5 MWth).

[0044] Particle residence time for vertical top-down injection reactors

[0045] One particular case, common to iron combustion systems, concerns the two-phase flow from top to bottom in the vertical reactor. The sedimentation velocity of the particles must be taken into account in the constraint related to the minimum residence time of the particles in order to maximize their oxidation rate and cooling. Indeed, in the case of iron, this velocity for particles with a diameter d50 between 20 and 60 pm is not negligible, even quite high (on the order of 20 to 60 cm / s). And the minimum residence time of the particles is dictated by the oxidation time and, above all, by the cooling time of the oxides to avoid sintering and agglomeration at the end of the reactor (during deposition by sedimentation).

[0046] Explanation of the trade-off between residence time and heat recovery rate in the case of the single-reactor

[0047] In addition to ensuring that a minimum residence time is respected, it is necessary to ensure that the dimensions (diameter and height) of the reactor allow for optimal heat exchange in the first peripheral heat exchanger. To maximize the heat recovered by the heat exchanger by convection, one can use the following formula: Q = h*A*AT (where A is the total surface area of ​​the heat exchanger, h is the convection coefficient, and AT is the temperature difference between the inlet and outlet).

[0048] Reducing the height, without changing the reactor diameter, necessarily reduces the amount of heat recovered in the primary heat exchanger. Reducing the diameter accordingly is beneficial for increasing the convection coefficient h, which depends on the Reynolds number (h proportional to the Nusselt constant) of the flow and is inversely proportional to the diameter (h = Nu*k / D). This is true despite the reduction in the heat exchange surface area caused by the decrease in diameter. Theoretically, the height (to reach the desired 3-4 meters) and the diameter of the multi-reactor can therefore be further reduced until the minimum particle residence time threshold is reached while maintaining equivalent heat exchange (even if it means increasing the number of reactors).

[0049] The constraint for a single reactor is that the combined reduction in diameter and height significantly reduces the residence time of the particles, which can Representing a few hundred milliseconds is insufficient to preheat, burn, and cool the iron particles adequately (for example, below 800 degrees Celsius). Hence the advantage of being able to distribute the flow rate across different reactors (with smaller diameters) in order to achieve a sufficient residence time and, in the process, increase the exchange surface area.

[0050] Proof of the interest of the multi-reactor concept by thermal and fluidic simulation for several multi-reactor configurations compared with the single-reactor

[0051] A comparative simulation of a single 1 MW reactor was conducted in comparison with a multi-reactor configuration (taking into account only the heat recovery from the main heat exchanger located in reactors numbered 6). The aim was to maintain the residence time of particles between 1.5 and 3 seconds and to ensure the same heat recovery rate while reducing the height from 9 to 4 meters. The degrees of freedom are therefore the diameter and the number of reactors. The following simulation results were obtained: Parameter Reactor Single (9 meters) 5 reactors (4 meters) 10 reactors (4 meters) 20 reactors (4 meters) 20 reactors (4 meters) Number of reactors 1 5 10 20 20 Reactor diameter (mm) 1100 600 700 500 300 Height (mm) 9000 4000 4000 4000 4000 Gas velocity, m / s 3.3 2.2 0.77 0.75 2 Particle residence time, s 3 1.46 3.5 3.52 1.7 Heat transfer surface area, m2 79 95 225 312 172 Heat transfer coefficient W / m2K 3.9 3.1 1.3 1.6 6 Overall heat transfer coefficient (W / m²-K) 3.8 3.1 1.29 1.6 5.8 Heat transfer rate (kW) 503.4 475 490 680 920

[0052] If the height were to be reduced from 9 to 4 meters on a single reactor while maintaining the same particle residence time and heat recovery rate, the only degree of freedom would be the diameter, and the equation would therefore have no optimal solution. However, as shown in the table above, if five 4-meter reactors (5 x 200 kW) are connected in parallel, it is possible to achieve a sufficient particle residence time and a heat recovery rate equivalent to that of a 9-meter reactor. (IxlMW). Increasing the number of reactors naturally improves both the heat recovery rate and the particle residence time.

[0053] For accurate preliminary sizing of the multi-reactor, a minimum particle residence time (taking into account the sedimentation rate in the case of a vertical multi-reactor system with top-down powder injection) and the maximum desired height for a compact system must be established as constraints. The diameter of each reactor will then depend on the desired number of reactors (a large number of reactors increases the risk of partial failures, although without complete boiler shutdown) and the desired level of heat recovery in the main peripheral heat exchanger (the convective heat transfer coefficient is strongly dependent on the diameter). The thermal power / reactor diameter ratio must also be considered, because if it is too high, the system may become excessively fouled with particles.

[0054] With reference to [Fig. 2], we will now describe an S2 architecture for an iron combustion power generation system that shares the main heat exchanger between all the reactors. The combustion reactors 6b and the fire tubes 10b, whose flow from 6b (after a half-turn 8b) is partially discharged as particles into a base 9b, are immersed in a water tank 9a to transfer the heat from combustion in order to generate steam. This architecture provides an example of sharing the heat recovery component at the combustion chamber level.

[0055] This reactor will necessarily have a greater thermal inertia than SI, but it is a configuration which simplifies the realization of the thermal recovery part.

[0056] With reference to [Fig.3], an S3 mode of assembling the 6c honeycomb reactors can be foreseen thanks to a housing 7b which allows the whole of the modules to be joined together by interlocking shape.

[0057] Other reactor casing geometries 7c, 7d, and 7e can be considered, as illustrated in [Fig. 4]. Casing 7e corresponds to the simple cylindrical reactor shown in the S2 configuration described above. Reactor casings of type 7c and 7d, with triangular and parallelepiped cross-sections respectively, allow for matrix assembly.

[0058] The energy production system according to the invention is intrinsically modular and configurable according to the energy needs of the users, as illustrated in Figures 5 and 6.

[0059] Thus, with reference to [Fig. 5], a modular honeycomb-shaped energy production system S4 can be foreseen, constructed around a first inner ring of six elementary combustion reactors 36 installed in hexagonal enclosures 37, around which other reactors of the same shape 30 can be arranged.

[0060] All elementary combustion reactors installed in system 3 receive 34, in the upper part, oxidizing gas and metallic particles from a common feed device 33 (connected to a powder storage not shown) the selective control of which can be carried out by 35 upstream of the injection into the burner (not shown) itself located in the reactor 36.

[0061] The reactors deliver 38 in their lower part combustion fumes comprising iron oxides collected in a collection device 39. A heat recovery device (not shown) is installed within the system S4 to recover the combustion heat 3a. This heat recovery device may be of the heat exchanger type and may be located within each reactor or shared across all reactors.

[0062] The modular geometry can be of the matrix type with the implementation of elementary combustion reactors arranged in housings or casings of triangular cross-section, as illustrated in [Fig. 6]. An energy production system S5 according to the invention can thus comprise a set of elementary combustion reactors arranged in a matrix, this set of reactors being fed at the top by a common metallic particle feeding device 43 receiving a particle stream 44, at the top, of the combustion gas and metallic particles from a common feeding device 43 (connected to a powder storage unit not shown) the selective control of which can be carried out by 45 upstream of the injection into the burner (not shown) itself located in the reactor 46.

[0063] The reactors deliver 48 in the lower part of combustion fumes charged with metal oxides into a collection device 49.

[0064] This modular geometry allows for the addition of one or more additional reactors 40, depending on evolving user needs. The S5 power generation system is also equipped with one or more heat recovery devices (not shown) for the heat produced 4a by the combustion reactors. Preferably, each reactor has its own primary heat exchanger. This does not preclude sharing a secondary heat exchanger further downstream, as illustrated in SL.

[0065] Thus, [Fig. 7] illustrates an embodiment of a modular reactor 6d which may include the metallic particle burner 60, fed by one or more oxidizer and particle inlets 41, and a coil or cylindrical heat exchanger 63 (or any other conventional exchanger sized to minimize fouling) recovering heat produced by the combustion 64. The flow of metallic particles, largely oxidized 42, can move towards a first filtration block (not shown).

[0066] The heat transfer fluid enters counter-currently 61 and exits from the top of reactor 62. This fluid at 61 originates either from a secondary heat exchanger (which preheats the fluid) positioned downstream of the hot gas flow (or of reactor 6) as illustrated in SI, or independently from the secondary heat exchanger circuit. The heated outgoing heat transfer fluid 62 can either join a collection device (not shown) for all the fluids heated by the other elementary reactors placed in parallel (illustrated in SI, S3, S4, S5) or exit independently to supply heat to the industrial process or the user equipment (not shown) in general.

[0067] The energy production systems according to the invention are generally equipped with computers programmed to process information on energy needs expressed by the users of these systems and to generate commands for the power control devices of the combustion reactors.

[0068] Of course, the present invention is not limited to the examples just described. Other geometries of combustion reactors and multi-reactor modules can be considered without departing from the scope of the present invention. Furthermore, in addition to iron, the energy production system according to the invention can be applied to magnesium, aluminum, or other metals.

Claims

Demands

1. Thermal energy production system (S1-S5) by combustion of metallic particles, comprising: - a set of elementary combustion reactors (6,6b,36,46,6d) each comprising a metallic particle burner coupled to a combustion chamber, - means (1,2,3,4) for selectively feeding said elementary combustion reactors (6,6b,36,46,6d) with iron particles and gaseous oxidant, - means (63) for recovering the heat from combustion in said elementary combustion reactors (6,6b,36,46,6d), - means (9,11,12,15,16,9b,39,49) for collecting the metallic oxides at the outlet of the combustion chambers, and - means for controlling the selective feeding means according to at least one predetermined setpoint.

2. Production system (SI) according to the preceding claim, characterized in that the feeding means comprise feeding means (1,2,3) common to all or part of the elementary combustion reactors (6).

3. Production system (SI) according to any one of the preceding claims, characterized in that the heat recovery means include recovery means common to all or part of the elementary combustion reactors (6).

4. Production system (SI) according to any one of the preceding claims, characterized in that the oxide collection means include collection means (11,12,15,16) common to all or part of the elementary combustion reactors (6).

5. Production system (SI) according to any one of the preceding claims, characterized in that each elementary combustion reactor (6) is provided with a casing or enclosure (9a) having a prismatic shape.

6. Production system (S4) according to any one of the preceding claims, characterized in that the set of elementary combustion reactors is structured into a plurality of subsets of elementary combustion reactors arranged radially or concentrically around an axis.

7. Production system (S5) according to any one of claims 1 to 5, characterized in that the set of elementary combustion reactors is structured into a plurality of subsets of elementary combustion reactors arranged in a matrix.

8. Production system (S2) according to any one of the preceding claims, characterized in that the elementary combustion reactors (6b) are arranged in a common enclosure (9a) containing a heat transfer fluid.

9. Production system (S2) according to the preceding claim, characterized in that smoke tubes (10b) intended to transport the effluents from the elementary combustion reactors (6b) are arranged in the common enclosure.

10. A method for producing thermal energy by combustion of metallic particles, implemented in a production system (S1,S5) according to any one of the preceding claims, said method comprising: - a selective feeding of metallic particles and gaseous oxidant, of a set of elementary combustion reactors (6,6b,36,46,6d) each comprising a metallic particle burner coupled to a combustion chamber, - a recovery of the heat from the combustion of said metallic particles, in said elementary combustion reactors (6,6b,36,46,6d), - a collection of the metallic oxides from the combustion of metallic particles, at the outlet of the combustion chambers, and - a control of the selective feeding of the elementary combustion reactors (6,6b,36,46,6d) according to at least one predetermined setpoint.

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