Metal particle combustion system and method for application to the generation of decarbonized heat

Abstract

The invention relates to a metal particle combustion system (S4) comprising means (0) for injecting a mixture of metal particles and an oxidizing agent, these injection means (0) comprising means (2) for creating a divergent flow of all or some of the metal particles and of all or some of the oxidizing agent from a main direction of injection of the particles, means for swirling the mixture of metal particles and oxidizing agent, means for bringing the temperature of all or some of the metal particles to their ignition temperature and causing them to start combusting, defining an ignition zone, and a combustion chamber designed to accommodate all or some of the particles injected and heated so that they start or continue to combust. The divergent-flow means (2) are arranged to give all or some of the metal particles a divergent trajectory as soon as they enter the ignition zone (3).

Description

System and method for combustion of metal particles for application to the production of decarbonized heat FIELD OF THE INVENTION

[0001] The present invention relates to a metal particle combustion system for application to the production of industrial heat, domestic heating or heating of industrial buildings or installations in remote areas. It also relates to a combustion method 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 current rise in energy costs and the risk of shortages related to the energy dependency of many countries around the world are a reason to seek alternative green energy for residential and commercial heating. The use of wood for heating also poses 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 and others) 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 documents US8100095B2 for internal or external combustion automotive applications. In document WO2023080789A1, a combustion system design is claimed with an expansion towards the combustion chamber, tangential tubular inlets for air staging and flame stabilization as well as an inlet containing oxidizer and particles without aerodynamic effect.

[0005] This type of combustion system is not compact because the objective is to move the ignition zone away from the injection zone in order to avoid fouling of the latter (walls and injection outlet tube). However, there are ways to inject and ignite the particles close to the combustion system inlet without fouling and allowing very good flame stability. And this by allowing for a compact combustion system, thus making this new technology for producing energy by combustion of metal particles more easily integrated into existing installations in industrial boiler rooms, for example.

[0006] The main aim of the invention is to propose different combustion system configurations capable of stabilizing metal particle flames for applications related to the decarbonization of industry.

[0007] This objective is achieved with a metal particle combustion system comprising: means for injecting a mixture of metal particles and an oxidant, defining an injection zone, means for providing said mixture of metal particles and oxidant with a swirl effect, means for raising the temperature of all or part of said metal particles to their ignition temperature and initiating their combustion, defining an ignition zone, means for producing a divergent flow of all or part of said metal particles and all or part of the oxidant relative to a main injection direction of the particles, arranged to provide, upon entering the ignition zone, a divergent trajectory of all or part of said metal particles, and a combustion chamber, designed to accommodate all or part of the injected and heated particles so that they initiate or continue their combustion.

[0008] The diverging flow means may advantageously be arranged to provide a divergence angle greater than 10 degrees relative to the main injection axis.

[0009] A combustion system according to the invention may be provided, in which the injection zone comprises an axial injection zone of a mixture of metal particles and oxidant surrounded by a coaxial injection zone of oxidant arranged to produce a swirled coaxial flow.

[0010] In a particular configuration of the invention, the diverging flow means comprise a central injection tube having an inlet end intended to receive the mixture containing oxidant and metal particles, a closed outlet end, and a cylindrical wall in which one or more orifices are provided arranged to diverge the mixture containing oxidant and metal particles towards the ignition zone.

[0011] In another configuration of the invention, the diverging flow means comprise a central injection tube having an inlet end intended to receive the mixture containing oxidant and metal particles and an outlet end opening onto a partially obstacle-forming part arranged relative to said distal end so that a flow of metal particles and oxidant is injected in a divergent manner.

[0012] The obstacle-forming part may be a flared part having a top facing towards the inside of the central injection tube.

[0013] The means for providing a swirl effect may be arranged in the means for injecting metal particles.

[0014] In a particular embodiment, the combustion system may further comprise one or more oxidant injection stages, provided to contribute to the swirl effect on the mixture of metal particles and oxidant from the injection means and / or to a cleaning effect on a wall of the combustion chamber.

[0015] The ignition zone may advantageously comprise an enclosure made entirely or partly of a thermally refractory material.

[0016] The combustion system may further comprise means for cooling the diverging flow means.

[0017] The combustion system according to the invention may also comprise, coaxially with the injection means, means for providing a mixture of fuel and oxidant to generate a pilot flame at the ignition zone.

[0018] It may also include, downstream of the injection zone, an inlet designed to supply a mixture of fuel and oxidant to generate a pilot flame, this inlet being arranged to direct this flame towards the flow of metal particles.

[0019] The combustion system according to the invention may be arranged to receive a mixture of metal particles, oxidant and gaseous fuel to produce a pilot flame within the flow of metal particles.

[0020] According to another aspect of the invention, there is provided a method for burning metal particles, implemented in a combustion system according to the invention, comprising the following steps: injecting a mixture of metal particles and an oxidant, defining an injection zone, raising the temperature of all or part of said metal particles to their ignition temperature and initiating their combustion, defining an ignition zone, producing a divergent flow of all or part of said metal particles and all or part of the oxidant relative to a main injection direction of the particles, this divergent flow being produced upon entering the ignition zone, providing said mixture of metal particles and oxidant with a swirl effect, leading said metal particles thus swirled into a combustion chamber, so that they initiate or continue their combustion. DESCRIPTION OF FIGURES

[0021] 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

[0022] is a schematic representation of an embodiment of a combustion system according to the invention comprising the three zones contributing to the stabilization of the metal powder flame, integrating in the first zone a swirled injection of oxidant coaxial with the injection of an aerosol of metal powder, itself composed of a nozzle pierced laterally (and blocked axially) so as to inject the powder in a divergent manner into the ignition zone.

[0023] is a schematic representation of an embodiment of a combustion system according to the invention comprising the three zones contributing to the stabilization of the metal powder flame, integrating in the first zone a swirled oxidizer injection coaxial with the metal powder aerosol injection, itself composed of a central tube partially blocked at its end by a pointed obstacle (with the point oriented in the direction of the aerosol injection inlet) and open (in a ring or with holes) laterally and close to the base of the obstacle to inject the powder in a divergent manner into the ignition zone.

[0024] is a schematic representation of an embodiment of a combustion system according to the invention comprising the three zones contributing to the stabilization of the metal powder flame, integrating in the first zone an injection of oxidant coaxial with the injection of metal powder aerosol, this injection zone comprising means making it possible to swirl said metal particles so as to inject the powder in a divergent and swirled manner into the ignition zone.

[0025] is a schematic representation of an embodiment of a combustion system according to the invention comprising the three zones contributing to the stabilization of the metal powder flame, integrating in the first zone a swirled oxidizer injection coaxial with a fuel and oxidizer injection making it possible to generate a pilot flame at the level of the metal powder aerosol injection emerging close to the center of the combustion system.

[0026] is a schematic representation of an embodiment of a combustion system according to the invention comprising the three zones contributing to the stabilization of the metal powder flame, integrating in the first zone a swirled oxidizer injection coaxial with the metal powder aerosol injection. A pilot flame offset downstream of the injection zone is arranged and generated to ignite the particles at the outlet of the aerosol injection.

[0027] is a schematic representation of an embodiment of a combustion system according to the invention comprising the three zones contributing to the stabilization of the metal powder flame, further comprising one or more oxidant injection stages, provided to contribute to the swirl effect on the mixture of metal particles and oxidant coming from the central injection tube and / or to a cleaning effect of the wall of the combustion chamber.

[0028] is a schematic representation of an embodiment of a combustion system according to the invention comprising the three zones contributing to the stabilization of the metal powder flame, in which the ignition zone comprises an enclosure made in whole or in part of a thermally refractory material. DETAILED DESCRIPTION

[0029] We will now describe, with reference to the aforementioned figures, several embodiments of a metal particle combustion system according to the invention.

[0030] In a first embodiment illustrated by the, a metal particle combustion system S1 comprises three main zones: an injection zone 0 for the powder and the oxidant, an ignition zone 3 and a combustion zone 4 for heat recovery. In the first zone, a suspension comprising metal powder and an oxidant mixture containing oxygen 0 is injected. This injection may be accompanied by a swirled coaxial flow 1 in order to provide additional oxygen to allow the combustion of the particles to begin and / or continue.

[0031] The swirl effect is also useful for extending the distance traveled by particles in the ignition zone and maximizing their ignition by increasing their residence time in this zone. The means for obtaining such a swirl can be varied, ranging from simple static turbines to tubular tangential inlets and a simple flow guide arranged to generate this swirling effect.

[0032] An obstacle 2, located at the outlet end of the powder injection (near the injection outlet), comprises orifices small enough to give the particles sufficient speed to avoid agglomeration on the injection nozzle, these orifices being configured to give the particles a divergent trajectory at the entrance to the ignition zone, in order to mix with the coaxial flow composed of oxidant and promote efficient ignition and combustion.

[0033] The orifices can be positioned laterally and / or axially and arranged so as to obtain this divergence effect from the entrance to the ignition zone. One or more annular orifices can also be provided, the central injection tube then being equipped with suitable fixing devices.

[0034] In a second embodiment illustrated by the, a metal particle combustion system S2 comprises a central cylindrical tube incorporating a flared obstacle 2a, for example a cone, located at the outlet end of the powder injection, leaving an annular passage small enough to give the particles sufficient speed to avoid agglomeration on the injection nozzle.

[0035] This flared obstacle is configured to give the particles a divergent trajectory at the inlet of the ignition zone to mix with the coaxial flow composed of oxidant in order to promote efficient ignition and combustion. The passage can also be achieved by one or more orifices located laterally and / or axially and arranged so as to provide a divergent trajectory for the particles. The obstacle can be held fixed using either an axial fixing rod passing through the injection tube, or using radial fixing lugs attached to any element of the structure of the combustion system.

[0036] In a third embodiment illustrated by the, a metal particle combustion system S3 comprises divergent flow means which comprise, in the central injection zone, a central injection tube comprising internal means 2b for providing the mixture of metal particles and oxidant with a swirl effect. These swirl means can be arranged upstream of the divergent flow means or be combined with the divergent flow means explained with reference to the aforementioned figures, in order to combine swirl and divergence of the aerosol flow.

[0037] In a fourth embodiment illustrated by the, a metal particle combustion system S4 comprises divergent flow means which comprise, in the central injection zone, a central injection tube comprising internal means for providing the mixture of metal particles and oxidant with a divergent trajectory.

[0038] An additional coaxial inlet consisting of oxidant and gaseous fuel 5, located between the particle injection and the swirled coaxial inlet of an oxidant mixture, makes it possible to generate a pilot flame at the outlet of the particle injection, participating in the ignition of the latter.

[0039] In a fifth embodiment illustrated by the, a combustion system S5 further comprises, downstream of the injection zone, an inlet 5a provided to supply a mixture of fuel and oxidant configured to generate a pilot flame at the outlet end of said central injection tube, this inlet being arranged to direct this flame towards the flow of metal particles, thus participating in the ignition of the latter.

[0040] In a sixth embodiment illustrated by 1a, a combustion system S6 further comprises one or more stages 1, 5c, 6a for injecting oxidant, provided to contribute to the swirl effect on the mixture of metal particles and oxidant coming from the central injection tube and / or to a cleaning effect on the wall of the combustion chamber 4.

[0041] In a seventh embodiment illustrated by the, a metal particle combustion system S7 comprises a central tube transporting, in part, an aerosol of metal particles and opening onto an ignition zone and this with a divergent trajectory thanks to divergent flow means 2a.

[0042] In ignition zone 3, the idea is to preheat the particles to their self-ignition temperature (by initiating the first exothermic reactions between oxygen and the metal particle) so that they reach the combustion chamber (4) in a quasi-self-sustained combustion regime and release most of the reaction heat in this zone.

[0043] To this end, in this zone 3, a refractory insulating material 6a makes it possible to limit heat losses to the outside in order to concentrate the heat on the preheating of the particles in order to quickly raise their temperature and promote their self-ignition (reducing the need for additional combustible gas).

[0044] In addition, a reflective coating on the refractory inner wall helps concentrate the radiation on the particles to accelerate their temperature rise. Indeed, a particularity of solid combustion is the high thermal radiation losses of the fuel, which can be exploited to promote ignition.

[0045] In addition, within the ignition zone 3, placing a second stage 5c (potentially with several inlets) consisting of a gas including oxygen (injected tangentially) makes it possible to stage the richness in the ignition zone, gradually creating a mixture close to sub-stoichiometric (or even much leaner, depending on the targeted richness) along this zone in order to maximize the reaction temperature and promote the stabilization of the flame which will take root there.

[0046] Of course, the present invention is not limited to the embodiments which have just been described and many other configurations of the combustion system can be envisaged without departing from the scope of the invention.

[0047] The metal particles injected into a combustion system according to the invention may be particles of iron, magnesium, aluminum, or other metals, or a mixture of these metals.

Claims

A system for combustion of metal particles (S1-S7) comprising: means for injecting a mixture (0) of metal particles and an oxidant, defining an injection zone, means (1) for providing said mixture of metal particles and oxidant with a swirl effect, means for raising the temperature of all or part of said metal particles to their ignition temperature and initiating their combustion, defining an ignition zone (3), means for producing a divergent flow of all or part of said metal particles and all or part of the oxidant relative to a main direction of injection of the particles, arranged to provide, upon entering the ignition zone (3), a divergent trajectory of all or part of said metal particles, a combustion chamber (4), designed to accommodate all or part of the injected and heated particles so that they initiate or continue their combustion. Combustion system (S1-S7) according to the preceding claim, characterized in that the diverging flow means (2) are arranged to provide a divergence angle greater than 10 degrees relative to the main injection axis. Combustion system (S1-S7) according to one of claims 1 or 2, in which the injection zone comprises an axial injection zone of a mixture of metal particles and oxidant surrounded by a coaxial injection zone of oxidant arranged to produce a swirled coaxial flow. Combustion system (S1, S4, S5, S6) according to any one of the preceding claims, characterized in that the diverging flow means comprise a central injection tube (2) having an inlet end intended to receive the mixture containing oxidant and metal particles, a closed outlet end, and a cylindrical wall in which one or more orifices are provided arranged to diverge the mixture containing oxidant and metal particles towards the ignition zone (3). Combustion system (S2, S7) according to any one of the preceding claims, characterized in that the diverging flow means comprise a central injection tube having an inlet end intended to receive the mixture containing oxidant and metal particles and an outlet end opening onto a part (2) forming a partial obstacle arranged relative to said distal end so that a flow of metal particles and oxidant is injected in a divergent manner. Combustion system (S2, S7) according to the preceding claim, characterized in that the obstacle-forming part is a flared part (2a) having a top facing towards the inside of the central injection tube. Combustion system (S3) according to any one of the preceding claims, characterized in that the means (2b) for providing a swirl effect are arranged in the means for injecting metal particles. Combustion system (S6) according to any one of the preceding claims, characterized in that it further comprises one or more stages (1, 5b, 6) for injecting oxidant, provided to contribute to the swirl effect on the mixture of metal particles and oxidant coming from the injection means and / or to a cleaning effect on a wall of the combustion chamber (4). Combustion system (S7) according to any one of the preceding claims, characterized in that the ignition zone comprises an enclosure (6a) made entirely or partly of a thermally refractory material. Combustion system according to any one of the preceding claims, characterized in that it further comprises means for cooling the diverging flow means. Combustion system (S1-S7) according to any one of the preceding claims, characterized in that it further comprises, coaxially with the injection means, means for supplying a mixture of fuel and oxidant to generate a pilot flame at the ignition zone. Combustion system (S5) according to any one of the preceding claims, characterized in that it further comprises downstream of the injection zone an inlet (5a) provided to supply a mixture of fuel and oxidant to generate a pilot flame, this inlet being arranged to direct this flame towards the flow of metal particles. Combustion system (S1-S7) according to any one of the preceding claims, characterized in that it is arranged to receive a mixture of metal particles, oxidant and gaseous fuel to produce a pilot flame within the flow of metal particles. A method for burning metal particles, implemented in a combustion system according to any one of the preceding claims, comprising the following steps: injecting a mixture of metal particles and an oxidant into an injection zone, raising the temperature of all or part of said metal particles to their ignition temperature and initiating their combustion, defining an ignition zone, producing a divergent flow of all or part of said metal particles and all or part of the oxidant relative to a main injection direction of the particles, this divergent flow being produced upon entering the ignition zone, providing said mixture of metal particles and oxidant with a swirl effect, leading said metal particles thus swirled into a combustion chamber, so that they initiate or continue their combustion.