System and method for producing thermal energy using metal powder as fuel

Abstract

System (S1) for producing thermal energy from the combustion of metallic particles, comprising a metallic particle burner in a combustion chamber (4), means (100) for injecting metallic particles into said burner means, means (5,6) for air intake so as to constitute a premix of air and metallic particles, means for capturing oxidized particles in the exhaust gases, downstream or combined with first means for heat exchange, a heat exchanger (7) between a transfer fluid and the combustion chamber (4), for transferring part of the thermal energy of combustion into a user equipment (13).This system further includes a recirculation loop (20) for a first fraction (22) of the exhaust gases from the combustion chamber (4), having a gas intake inlet downstream of the combustion chamber (4) and a gas injection outlet upstream of the burner means (3). See Figure 1.

Description

Title of the invention: System and method for producing thermal energy using metal powder as fuel FIELD OF THE INVENTION

[0001] The present invention relates to a system for producing thermal energy by combustion of metals, in particular for application to domestic heating or industrial buildings or installations in remote areas, as well as for industrial heat production applications. It also relates to a method for producing thermal 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. In addition, the current increase in the cost of energy and the risk of shortages linked to the energy dependencies of many countries in the world are a reason for the search for a green alternative energy for residential and professional heating as well as for equipment requiring industrial heat. The use of wood for heating also presents a significant risk of deforestation if responsible and sustainable forest management is not adopted.

[0003] In this context, the combustion of metal 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 solution discussed to produce combustion without CO2 emissions, for all types of energy production applications. Metallic fuels (magnesium, aluminum, iron) have the advantage of generating, during their combustion, only solid metal oxides that are easily recoverable in a combustion system. These can then be recycled using renewable energy through an inert anode electrolysis process or zero CO2 thermochemical reduction by solar energy.

[0004] The combustion of metal particles is historically known in aerospace propulsion applications or even documents US8100095B2 for internal or external combustion automotive applications. In document WO2023028697A1, the proposed solution does not make it possible to reduce the emissions of nanometric iron oxides because the oxygen concentration is not adjustable, yet this concentration is critical to minimize these emissions and optimize the overall energy or material efficiency of the metal cycle [Stereoscopic high-speed imaging of iron microexplosions and nanoparticle-release, Li et al., Vol. 29, Optics Express, 2021}. Indeed, the mass of nanoparticles produced means that it is necessary to spend energy to reform the micron particles afterwards in order to reproduce the initial fuel.

[0005] In addition, the mass losses in the exhaust linked to these nanoparticle emissions influence the number of cycles possible with the same quantity of material. Recovering 99% of the mass of oxides instead of 99.9% reduces by a factor of 10 the number of times that the same mass of iron can be burned and recycled.

[0006] The main aim of the invention is to propose a solution for reducing emissions of oxide nanoparticles. Another aim of the invention is to facilitate the ignition of the flame compared to the state of the art set out in the aforementioned document which discloses ignition of the flame using a gas / particle premix in air. Statement of the invention

[0007] This objective is achieved with a system for producing thermal energy from a combustion of metal particles, comprising: - means for burning metal particles in a combustion chamber, comprising an ignition system designed to generate a pilot flame, - means for injecting metal particles into said burner means, - means for admitting air to be injected into the burner means so as to constitute a premixture of air and metal particles, comprising fan means, - means for capturing oxidized particles in the exhaust gases, downstream or combined with first heat exchange means, - first means of heat exchange between a transfer fluid and the combustion chamber, said transfer fluid being intended to be injected into said heat exchange means via pump means and to transfer part of the thermal combustion energy into user equipment,

[0008] characterized in that it further comprises a recirculation loop for a first fraction of the exhaust gases from the combustion chamber, having a gas sampling inlet downstream of the combustion chamber and a gas injection outlet upstream of the burner means.

[0009] In a first embodiment, the reinjection outlet of the recirculation loop is arranged downstream of the air intake means, and more particularly between the metal particle injection means and the burner means.

[0010] In a second embodiment, the reinjection output of the recirculation loop- culation is arranged upstream of the air intake means.

[0011] The air intake means may further advantageously comprise additional means for adjusting the air intake flow rate.

[0012] The production system according to the invention may further comprise fan means for extracting the exhaust gases downstream of the capture means.

[0013] The recirculation loop may advantageously comprise means for adjusting the recirculation flow rate, as well as fan means.

[0014] In a particular version of the invention, the production system according to the invention may further comprise means for preheating the intake air upstream of its injection into the burner means, these preheating means comprising second means for heat exchange between a second fraction of the exhaust gases from the combustion chamber and the intake air.

[0015] The first heat exchange means may advantageously comprise an enclosure surrounding the combustion chamber and arranged to circulate the transfer fluid therein. This heat exchange enclosure may also surround the filtering means.

[0016] In a first family of applications of the production system according to the invention, the transfer fluid is water injected into the first heat exchange means by means of a water pump. This system can be implemented in a central heating installation for a room or for heating domestic water.

[0017] In a second family of applications of the production system according to the invention, the transfer fluid is air injected into the second heat exchange means by means of fan means. This system can be implemented in an installation for heating the air of a room or in an installation for drying a wet product, this installation comprising a drying drum provided (i) to receive at the inlet on the one hand hot air coming from the second heat exchange means and on the other hand wet product coming from a wet product storage unit and (ii) to deliver at the outlet dried product in a recovery unit and cooled drying air.

[0018] In a third family of application of the production system according to the invention, the transfer fluid is water vapor injected into the second heat exchange means by means of a steam pump, and the production system further comprises an air recirculation loop designed to receive cooled steam from the user equipment at the inlet and inject it at the inlet of said steam pump. The production system according to the invention may further comprise surplus steam in the steam recirculation loop and be implemented in a facility for drying a wet product or in an industrial system consuming heat transported by water vapor.

[0019] In a fourth family of applications of the invention, the fluid is two-phase (i) in a liquid form upstream of the first heat exchange means and (ii) in a vapor form downstream of the first heat exchange means and at the inlet of the user equipment, and the production system according to the invention further comprises means for condensing the cooled vapor from the user equipment and injecting it in liquid form into the pump means.

[0020] The condensation means cooperate with means for recovering thermal energy during condensation for the purpose of recovering the fatal heat resulting from the energy conversion. The user equipment may comprise a high-pressure steam turbine driving an electricity generator.

[0021] According to another aspect of the invention, there is provided a method for producing thermal energy from a combustion of metal particles, implemented in the production system according to the invention, this method comprising the following steps: - mixing air from an air intake and metal particles from a metal particle injection, - inject the mixture of air and metal particles into a burner, - burn this mixture in a combustion chamber, leading to a heat and exhaust gas production, - exchange the heat thus produced, via a transfer fluid, in user equipment, - capture, from the exhaust gases, oxidized particles downstream of the burner,

[0022] characterized in that it further comprises a recirculation of a first fraction of the exhaust gases, said recirculation comprising a sampling downstream of the combustion chamber and an injection of said first fraction of exhaust gas upstream of the burner means.

[0023] The injection of exhaust gas can be carried out downstream of an injection of the metal particles, or upstream of the air intake. DESCRIPTION OF FIGURES

[0024] Other features and advantages will appear on reading the following description of a particular, non-limiting embodiment of the invention, given with reference to the figures in which

[0025] [Fig.l] is a schematic representation of the water heating system of a home (sanitary and / or heating).

[0026] [Fig.2] is a schematic representation of the water heating system of a dwelling (sanitary and / or heating) with a large gas recirculation loop exhaust.

[0027] [Fig.3] is a schematic representation of the air heating system of a dwelling.

[0028] [Fig.4] is a schematic representation of the indirect hot air drying system of wet products in chemistry, construction etc.

[0029] [Fig.5] is a schematic representation of the indirect closed-loop drying system with heated steam of wet products in chemistry, construction etc.

[0030] [Fig.6] is a schematic representation of the steam generation system for industry (brewery etc.).

[0031] [Fig.7] is a schematic representation of the electricity generation system by a Rankine cycle (with water vapor or organic liquid called ORC).

[0032] [Fig.8] is a schematic representation of the heat and electricity cogeneration system using a Rankine cycle and a heat recovery unit placed at the condenser to recover the waste heat and maximize the total efficiency. DETAILED DESCRIPTION

[0033] Several examples of embodiments of energy production systems according to the invention will now be described with reference to the aforementioned figures. It should be noted that the components and modules common to the different examples illustrated have common references.

[0034] With reference to [Fig.l], a thermal energy production system of the boiler / boiler room type SI comprises an injector 100 of metal particles, a burner 3 of metal particles to be burned in a combustion chamber 4 with fixed volume, the combustion chamber 4 being connected to a duct 20 for sucking a fraction 22 of exhaust gas, which is a component of a recirculation loop 20 whose reinjection outlet is arranged downstream of the particle injector 100 and upstream of the inlet of the burner 3. The other fraction 23 of the exhaust gas passes through a heat exchanger 1 to heat the intake air and is extracted by the action of an extraction fan 11.

[0035] The exhaust gases are composed of metal oxides and nitrogen (magnesium, iron or aluminum oxides depending on which of the three fuels is used), and pass through a filtration system 8 then a heat recovery block 1.

[0036] It should be noted that this filtration system and this heat recovery block 1 can be nested or in cascade.

[0037] The metal particle injector 100 may be in the form of a fluidization aerosol generator which injects the particles into an air flow with the aid of a venturi system. It is also possible to use gravity injection of the particles using a vibrating (or non-vibrating) funnel on an air line, adding a slight fluidizing flow at the inlet of the funnel to prevent the outlet from clogging. Another possibility is to use a worm screw, the diameter and rotation speed of which allow the precision and flow rate of powder injection to be controlled into an air line receiving the latter.

[0038] The metal burner 4 can be made using a "swirler" (air swirler) which makes it possible to increase the air injection flow rate without worrying about the risk of blowing out the pilot flame generated by an ignition system 2. The principle is to have a part of the air flow injected axially, and another part injected tangentially using tangential tubes or static turbines, in order to create shear and recirculation zones towards the interior of the burner 3 (depression effect within the swirl generated by the centrifugal flow) and to facilitate the stabilization of the flame. Indeed, this aerodynamic stabilization mechanism makes it possible to create zones in the flow where the speeds are low enough to be close to those of the metal flames, thus ensuring that the flame attaches to the burner.This mechanism is all the more important as the air load increases and the fuel concerned has relatively low flame speeds. Adjusting the intensity of the "swirl" makes it possible to manage the size of the flame and its overall morphology.

[0039] In order to achieve continuous stabilization of the metal flame, when using iron powder only, it is possible to preheat the combustion air entering the system. In order to reduce the use of natural gas from a pilot flame which makes it possible to supplement the heat released per unit volume during the combustion of iron and facilitate its ignition, it may be advantageous to add a preheating block 1 of the intake air by recovering the fatal heat from the exhaust of the system. The iron flame is in fact more difficult to stabilize than those of magnesium or aluminum, due to its low reaction rate linked to its combustion in heterogeneous mode and to the layer of oxides around the particles which greatly reduce the rate of heat release and therefore the reaction temperature.

[0040] This penalizes the stabilization of the flame which is thus disturbed by losses by convection and radiation. The contribution of heat via that contained in the exhaust gases thus makes it possible to increase the overall energy efficiency, and to reduce the quantity of gas in the pilot gas flame and therefore CO2 emissions.

[0041] The intake preheating system consists of a gas-gas exchanger 1 which recovers, in the main exhaust circuit, the fatal calories to transfer them into a secondary circuit (serpentine tube, or any geometry allowing the exchange surface to be maximized such as plate exchangers) to the air intake drawn in by a ventilation and which goes towards the burner for the supply of oxidant.

[0042] The pilot flame may be in the form of a methane injector 2 (or propane or butane) placed in the direction of the axial flow of iron and air, which generates a diffusion flame, or in the form of a hybrid methane / iron / air flame premixed by adding methane to the axial conduit transporting the particles in the air. A spark activated by a remote actuator may be used to ignite the pilot flame and thus allow the iron flame to stabilize. In the case of aluminum or magnesium, this pilot flame may be extinguished as soon as stabilization has been achieved thanks to their high-temperature homogeneous phase combustion which facilitates self-maintenance of the flame.

[0043] The combustion system is also optimized by the addition of a recirculation of the exhaust gases 20, consisting largely of nitrogen, by a secondary circuit to regulate the percentage of oxygen in the mixture around the iron particles.

[0044] This secondary recirculation circuit 20 comprises a device 9 for ventilation of exhaust gas extraction and a controlled throttle valve 10 for adjusting the recirculation flow rate.

[0045] A high oxygen concentration, of the order of that of ambient air, can locally increase the reaction rate and therefore the temperature of the particles, bringing them locally above the boiling point of iron (3134 K), increasing the risk of micro-explosions of the particles (depending on the temperature and the speed of expansion of the gases formed within the particle), ultimately generating oxide nanoparticles that are very difficult to filter and regenerate into pure iron with micron particle size [Stereoscopic high-speed imaging of iron microexplosions and nanoparticle-release, Li et al., Vol. 29, Optics Express, 2021].

[0046] This is problematic in the context of using iron as a circular fuel. Carrying out recirculation of the exhaust gases allowing the oxygen concentration to be lowered to 14% makes it possible to significantly reduce the appearance of clouds of oxide nanoparticles by reducing the reaction temperature and therefore that of the particles. The latter leads to a strong reduction in the saturated vapor pressure of the metal, thus significantly reducing its evaporation [Critical temperature for nanoparticle cloud formation during combustion of single micron-sized iron particle, Ning et al., Combustion and Flame 244, 2022].

[0047] Since oxygen concentration plays a predominant role in overall richness for fuel-lean mixtures, richness gains importance in oxygen transport and therefore in reaction temperature for richnesses closer to stoichiometry. In order to avoid deposits of unburned metal particles, an overall richness below stoichiometry is necessary. Losses thermal radiation are also more important with the strong increase in the temperature of these particles, which also disadvantages stabilization and causes a strong increase in NOx emissions.

[0048] A more common effect in the context of exhaust gas recirculation applied to combustion is the reduction of thermal nitrogen oxide emissions by lowering the combustion temperature (Zeldovich mechanism).

[0049] The exhaust gas recirculation system consists of a pipe connected to the exhaust pipe, preferably downstream of the filtration, which takes the gas consisting essentially of nitrogen (and excess oxygen in the case of combustion close to stoichiometry) using suction ventilation followed by a recirculation flow control butterfly, in order to reinject this gas upstream of the burner or directly into the intake pipe upstream of the main ventilation (in this case, thanks to the main ventilation, the suction ventilation is no longer necessary).

[0050] The recirculation rate can vary from 0 to more than 50% of the total injected flow rate (the reduction in NOx emissions reaches a plateau after 50% recirculation rate) and an oxygen concentration of around 14% already makes it possible to greatly reduce the phenomena of formation of oxide nanoparticles (but with this system the oxygen concentration in the intake can drop to 10%). Thus, in the context of a circular energy application, where the aim is to regenerate the initial iron particles from the oxides, minimizing the effects producing nanoparticle emissions makes it possible to maintain the integrity of the particles throughout the cycle to avoid intermediate processes of reforming the micrometric iron particles.

[0051] The means 8 for capturing the oxides may consist of a set of cyclones sized to allow the filtration of oxide particles ranging from one micron to several hundred microns. This is a common process in the dust removal of industrial fumes. It would also be possible to implement a sedimentation chamber which uses the inertia of large particles with a diameter of between a few microns and a few hundred microns, which, subjected to gravity, will settle at the bottom of the chamber.

[0052] It is possible to filter the remaining nanoparticles using a bag filter or HEPA (“High Efficiency Particulate Air” for “very high density air particle filter”), or an electrostatic or electromagnetic filter accompanied by downstream suction ventilation to overcome the pressure losses generated by all the filtration elements.

[0053] The energy production system S2 according to the invention can be used to heat the air of a dwelling, the water of a dwelling (sanitary and heating water) (SI), generate steam for industry (S5), dry aggregates or any product wet (S3,S4), generate electricity in a steam or organic liquid Rankine cycle (S6), or co-generate heat and electricity if the heat is recovered in the condenser (S7).

[0054] The SI System for producing thermal energy from a combustion of metal particles, comprises means 3 for burning metal particles in a combustion chamber 4, comprising an ignition system 2 provided for generating a pilot flame, means 100 for injecting metal particles into said burner means, means 5, 6 for admitting air to be injected into the burner means 3 so as to constitute a premixture of air and metal particles, comprising fan means 5 (of the blower ventilation type) and means 6 for adjusting the air intake flow rate, means for capturing the oxidized particles in the exhaust gases, downstream of the first heat exchange means, means 11 for extracting the exhaust gases downstream of the capture means, a heat exchanger 7 between a transfer fluid and the combustion chamber 4,this transfer fluid being intended to be injected into the heat exchange means 7 via pump means 12 and to transfer part of the thermal combustion energy into user equipment 13.,

[0055] The heat exchanger 7 may be composed of a set of tubes through which the heat transfer fluid circulates, transporting the heat to the user equipment. These tubes may be located in the hot volume of the combustion chamber and the filtration or arranged around the latter but in contact with their walls. The heat transfer fluid is either distributed in several tubes arranged in parallel, or in a coil, with the aim of maximizing the heat exchange surface with the hot flow from the combustion chamber.

[0056] The production system SI further comprises a recirculation loop for a fraction of the exhaust gases from the combustion chamber 4, having a gas sampling inlet downstream of the combustion chamber 4 and a gas injection outlet upstream of the burner means 3.

[0057] With reference to [Fig. 2], the production system S2 is a variant of the system SI, comprising a large recirculation loop 30 for a fraction of the exhaust gases from the combustion chamber 4, this large recirculation loop having a gas sampling inlet downstream of the combustion chamber 4, a gas injection outlet 32 ​​upstream of the inlet of the ventilation means 5 for air intake, and optionally provided with a regulation unit 10.

[0058] With reference to [Fig. 3], the production system S3 is a variant of the system SI for heating air by combustion of metal particles. It comprises, in place of the exchanger 13, a gas-air exchanger 13b.

[0059] With reference to [Fig.4], the production system S4 is a variant of the modes of embodiment S1-3 implemented in an installation for drying a wet product, this installation 13c comprising a drying drum 14 provided (i) to receive at the inlet on the one hand hot air coming from the second heat exchange means 7 and on the other hand wet product coming from a wet product storage unit 13c and (ii) to deliver at the outlet dried product in a recovery unit 15 and cooled drying air.

[0060] With reference to [Fig. 5], the production system S5 is a variant of the production system S4, in which the transfer fluid is water vapor injected into the heat exchange exchanger 7 by means of a steam pump 12, this system further comprising an air recirculation loop 50 provided to receive at the inlet cooled steam from the user equipment 13c and inject it at the inlet of the steam pump 12.

[0061] With reference to [Fig.6], the production system S6 is a variant of the embodiments of production systems S1-S4, which makes it possible to transfer the combustion heat to an industrial system 13d consuming heat transported by water vapor consisting of the elements of a steam generator.

[0062] With reference to [Fig. 7], the production system S7 is a variant of the embodiment S6, in which the transfer fluid is two-phase (i), in a liquid form upstream of the heat exchanger 7 and (ii) in a vapor form downstream of the heat exchanger 7 and at the inlet of the user equipment 17. This production system 7 further comprises a loop 70 for recovering the cooled vapor at the outlet of the user equipment 17, conducting it to the inlet of a condensation unit 18 and injecting it in liquid form into the pump means 15. The user equipment 17 includes a high-pressure steam turbine driving an electricity generator 13.The S7 system can use a Rankine cycle but also a Stirling type thermodynamic converter or even a gas turbine type converter by external combustion, the combustion gas being heated by an exchanger the expansion gas which passes into the turbine, even if for applications of several MW we more often find Rankine cycle type converters (organic liquid or water vapor) for their economic profitability.

[0063] With reference to [Fig.8], the production system S8 is a variant of the embodiment S7, in which the condensation means 14 cooperate with equipment 19, inserted in the recovery loop 70, provided for recovering thermal energy during condensation for the purpose of recovering the fatal heat resulting from the energy conversion.

[0064] Of course, the present invention is not limited to the examples which have just been described and many other embodiments can be envisaged without departing from the scope of the present invention. In particular, the system of on-board energy production for the propulsion of mobility systems and vehicles such as ships, railway systems, spacecraft, aircraft and in particular airships.

[0065] Furthermore, it is possible to envisage implementing thermal energy production systems according to the invention on the moon, by exploiting metallic particles and oxygen resulting from a process of reducing the regolith covering its soil.

Claims

Claims

1. System (S1-S8) for producing thermal energy from a combustion of metal particles, comprising: - means (3) for burning metal particles in a combustion chamber (4), comprising an ignition system (2) provided for generating a pilot flame, - means (100) for injecting metal particles into said burner means, - means (5, 6) for admitting air to be injected into the burner means (3) so as to constitute a premixture of air and metal particles, comprising fan means (5), - means (8) for capturing the oxidized particles in the exhaust gases, downstream or combined with first heat exchange means, - first means (7) for heat exchange between a transfer fluid and the combustion chamber (4),said transfer fluid being intended to be injected into said heat exchange means (7) via pump means (12) and to transfer part of the thermal combustion energy into user equipment (13, 13b, 13c, 13d, 17), characterized in that it further comprises a loop (20) for recirculating a first fraction (22) of the exhaust gases from the combustion chamber (4), having a gas sampling inlet downstream of the combustion chamber (4) and a gas injection outlet upstream of the burner means (3).,

2. Production system (SI) according to the preceding claim, characterized in that the reinjection outlet of the recirculation loop is arranged downstream of the air intake means.

3. Production system (SI) according to the preceding claim, characterized in that the recirculation loop (20) further comprises fan means (9).

4. Production system (S2) according to claim 1, characterized in that the reinjection outlet of the recirculation loop is arranged in upstream of the air intake means (5,6).

5. Production system according to any one of the preceding claims, characterized in that the air intake means further comprise additional means (6) for adjusting the air intake flow rate.

6. Production system according to any one of the preceding claims, characterized in that it further comprises fan means (11) for extracting the exhaust gases downstream of the capture means.

7. Production system according to any one of the preceding claims, characterized in that the recirculation loop (20, 30) comprises means (10) for adjusting the recirculation flow rate.

8. Production system (S1-S8) according to any one of the preceding claims, characterized in that it further comprises means for preheating the intake air upstream of its injection into the burner means, said preheating means comprising second means for heat exchange (21) between a second fraction (23) of the exhaust gases from the combustion chamber and the intake air (1),

9. Production system (S1-S8) according to one of the preceding claims, characterized in that the first heat exchange means (7) comprise an enclosure surrounding the combustion chamber (4) and arranged to circulate the transfer fluid therein.

10. Production system (S1-S8) according to the preceding claim, characterized in that the heat exchange enclosure (7) also surrounds the oxide capture means (8).

11. Production system (SI) according to any one of the preceding claims, characterized in that the transfer fluid is water injected into the first heat exchange means (7) by means of a water pump (12).

12. Production system (SI) according to the preceding claim, implemented in a central heating installation of a room (13).

13. Production system (SI) according to one of the two preceding claims, implemented in a domestic water heating installation (13).

14. Production system (S3) according to any one of claims 1 to 10, characterized in that the transfer fluid is air injected into the second heat exchange means (7) by means of ventilating means tilators (12).

15. Production system (S3) according to the preceding claim, implemented in an installation (13b) for heating the air of a room.

16. Production system (S4) according to claim 14, implemented in a drying installation for a wet product, said installation (13c) comprising a drying drum (14) provided (i) to receive at the inlet on the one hand hot air coming from the second heat exchange means (7) and on the other hand wet product coming from a wet product storage unit (13c) and (ii) to deliver at the outlet dried product in a recovery unit (15) and cooled drying air.

17. Production system (S5) according to any one of claims 1 to 10, characterized in that the transfer fluid is water vapor injected into the second heat exchange means (7) by means of a steam pump (12), and in that it further comprises a recirculation loop provided to receive at the inlet cooled steam from the user equipment (13c) and inject it at the inlet of said steam pump (12).

18. Production system (S5) according to the preceding claim, characterized in that it further comprises means for evacuating excess steam in the steam recirculation loop.

19. Production system (S5) according to one of the two preceding claims, implemented in a drying installation for a wet product.

20. Production system (S6) according to one of claims 17 or 18, implemented in an industrial system (13d) consuming heat transported by water vapor.

21. Production system (S7, S8) according to any one of claims 1 to 10, characterized in that the fluid is two-phase (i) in a liquid form upstream of the first heat exchange means (7) and (ii) in a vapor form downstream of the first heat exchange means (7) and at the inlet of the user equipment (17), and in that it further comprises means (18, 19) for condensing the cooled vapor from the user equipment (17) and injecting it in liquid form into the pump means (15).

22. Production system (S8) according to the preceding claim, characterized in that the condensation means (19) cooperate with means for recovering thermal energy during condensation at for the purpose of recovering the waste heat from energy conversion.

23. Production system (S7,S8) according to one of the two preceding claims, characterized in that the user equipment comprises a high-pressure steam turbine (17) driving an electricity generator (13e).

24. Method for producing thermal energy from a combustion of metal particles, implemented in the production system (S1-S7) according to any one of the preceding claims, this method comprising the following steps: • mixing air from an air intake and metal particles from an injection of metal particles, • injecting the mixture of air and metal particles into a burner (3), • burning this mixture in a combustion chamber (4), leading to a production of heat and exhaust gases, • exchanging the heat thus produced, via a transfer fluid, in a user equipment (13, 13b, 13c, 13d, 12), • capturing, from the exhaust gases, oxidized particles downstream of the burner (3), characterized in that it further comprises a recirculation of a first fraction (22) of the exhaust gases,said recirculation comprising a sampling downstream of the combustion chamber (4) and an injection of said first fraction of exhaust gas upstream of the burner means (3).,

25. Production method (SI) according to the preceding claim, characterized in that the injection of exhaust gas is carried out downstream of the air intake.

26. Production method (S2) according to claim 24, characterized in that the injection of exhaust gas is carried out upstream of the air intake.