System and process for the combustion of metallic particles for application in the production of decarbonized heat

Abstract

Metallic particle combustion system (S4) comprising means (0) for injecting a mixture of metallic particles and an oxidizer, these injection means (0) comprising means (2) for achieving a divergent flow of all or part of the metallic particles and all or part of the oxidizer with respect to a principal direction of particle injection, means for providing the mixture of metallic particles and oxidizer with a swirl effect, means for raising the temperature of all or part of said metallic particles to their ignition temperature and initiating their combustion, defining an ignition zone, a combustion chamber, provided to accommodate all or part of the injected and heated particles so that they initiate or continue their combustion.The diverging flow means (2) are arranged to provide, from the entrance of the ignition zone (3), a diverging trajectory for all or part of the metallic particles. See Figure 4.

Description

Title of the invention: System and method for the combustion of metallic particles for application in the production of decarbonized heat. FIELD OF THE INVENTION

[0001] The present invention relates to a metallic particle combustion system for application in industrial heat production, domestic heating, or heating of industrial buildings or installations in remote areas. It also relates to a combustion process 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, and others) 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 also in 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, and an inlet containing oxidizer and particles without aerodynamic effect.

[0005] This type of combustion system is not compact because the objective is to keep the ignition zone away from the injection zone to prevent fouling of the latter (walls and injection outlet tube). Nevertheless, there are ways to inject and to ignite particles near the combustion system inlet without fouling and to ensure excellent flame stability. This is achieved by allowing for a compact combustion system, making this new technology for producing energy by burning metallic particles more easily integrated into existing industrial boiler installations, for example.

[0006] The main purpose of the invention is to propose different combustion system configurations that can stabilize flames of metallic particles for applications related to the decarbonization of industry. Description of the invention

[0007] This objective is achieved with a metallic particle combustion system comprising: - means for injecting a mixture of metallic particles and an oxidizer, defining an injection zone, - means of providing said mixture of metallic particles and oxidizer with a swirl effect, - means for raising the temperature of all or part of said metallic particles to their ignition temperature and initiating their combustion, defining an ignition zone, - means for achieving a divergent flow of all or part of said metallic particles and all or part of the oxidizer with respect to a principal direction of particle injection, arranged to provide, from the entrance of the ignition zone, a divergent trajectory of all or part of said metallic particles, and - a combustion chamber, designed to accommodate all or part of the injected particles and heated so that they initiate or continue their combustion.

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

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

[0010] In a particular configuration of the invention, the diverging flow means comprise a central injection tube having an inlet end provided for receiving the mixture containing oxidizer and metallic particles, a sealed outlet end, and a cylindrical wall in which are formed one or several orifices arranged to divert the mixture containing oxidizer and metallic particles towards the ignition zone.

[0011] In another configuration of the invention, the divergent flow means comprise a central injection tube having an inlet end provided for receiving the mixture containing oxidizer and metallic particles and an outlet end opening onto a partially obstructing part disposed with respect to said distal end so that a flow of metallic particles and oxidizer is injected in a divergent manner.

[0012] The part forming the obstacle can be a flared part having a vertex turned towards the inside of the central injection tube.

[0013] The means for providing a swirl effect can be disposed in the metallic particle injection means.

[0014] In a particular embodiment, the combustion system may further include one or more oxidant injection stages, intended to contribute to the swirl effect on the mixture of metallic 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 include means for cooling the divergent flow means.

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

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

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

[0020] According to another aspect of the invention, a method for burning metallic particles is proposed, implemented in a combustion system according to the invention, comprising the following steps: - inject a mixture of metallic particles and an oxidizer, defining an injection zone, - raising the temperature of all or part of said metallic particles to their ignition temperature and initiating their combustion, defining an ignition zone, - to achieve a divergent flow of all or part of said metallic particles and all or part of the oxidizer with respect to a main direction of particle injection, this divergent flow being achieved from the entrance of the ignition zone, - to provide said mixture of metallic particles and oxidizer with a swirling effect, - to conduct the said swirled metallic particles into a combustion chamber, so that they initiate or continue their combustion. DESCRIPTION OF THE FIGURES

[0021] 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

[0022] [Fig. 1] 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 to the injection of a metal powder aerosol, 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] [Fig.2] 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 closed at its end by a pointed obstacle (with the point oriented towards the inlet of the aerosol injection) and open (in a ring or with holes) laterally and near the base of the obstacle to inject the powder in a divergent manner into the ignition zone.

[0024] [Fig.3] 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 oxidizer coaxial with the injection of metal powder aerosol, this injection zone comprising means for swirling said metal particles so as to inject the powder in a divergent and swirled manner into the ignition zone.

[0025] [Fig. 4] 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 to a fuel and oxidizer injection allowing to generate a pilot flame at the level of the metal powder aerosol injection opening near the center of the combustion system.

[0026] [Fig.5] is a schematic representation of one embodiment of a system of Combustion according to the invention comprises three zones contributing to the stabilization of the metal powder flame, incorporating in the first zone a swirled oxidizer injection coaxial with the metal powder aerosol injection. A pilot flame located downstream of the injection zone is arranged and generated to ignite the particles exiting the aerosol injection.

[0027] [Fig.6] is a schematic representation of one embodiment of a system of combustion according to the invention comprising the three zones contributing to the stabilization of the metal powder flame, further comprising one or more stages of oxidant injection, provided to contribute to the swirl effect on the mixture of metal particles and oxidant from the central injection tube and / or to a cleaning effect on the wall of the combustion chamber.

[0028] [Fig.7] is a schematic representation of one embodiment of a system of Combustion according to the invention comprising three zones contributing to the stabilization of the metal powder flame, wherein the ignition zone comprises an enclosure made entirely or partially of a thermally refractory material. DETAILED DESCRIPTION

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

[0030] In a first embodiment illustrated by [Fig. 1], a metallic particle combustion system SI comprises three main zones: a powder and oxidizer injection zone 0, an ignition zone 3, and a combustion zone 4 for heat recovery. A suspension comprising metallic powder and an oxidizer mixture containing oxygen O is injected into the first zone. This injection may be accompanied by a coaxial swirling flow 1 to supply additional oxygen to initiate and / or continue particle combustion.

[0031] The swirl effect is also advantageous 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 of obtaining such a swirl can be varied, ranging from simple static turbines to tubular tangential inlets, or even a simple flow guide arranged to generate this swirling effect.

[0032] An obstacle 2, located at the outlet end of the powder injection (close to the injection outlet), includes orifices small enough to give the particles sufficient velocity 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 oxidizer and promote efficient ignition and combustion.

[0033] The orifices can be positioned laterally and / or axially and arranged to obtain this divergence effect from the moment they enter 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 [Fig.2], a metallic 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 a speed sufficient to avoid agglomeration on the injection nozzle.

[0035] This flared obstacle is configured to give the particles a divergent trajectory upon entering the ignition zone, allowing them to mix with the coaxial flow of oxidizer to promote efficient ignition and combustion. The passage can also be achieved through one or more orifices located laterally and / or axially and arranged to provide a divergent trajectory for the particles. The obstacle can be held in place either by means of an axial fixing rod passing through the injection tube, or by means of radial fixing tabs attached to any element of the combustion system structure.

[0036] In a third embodiment illustrated by [Fig. 3], a metallic particle combustion system S3 comprises diverging flow means which include, in the central injection zone, a central injection tube having internal means 2b for imparting a swirl effect to the mixture of metallic particles and oxidizer. These swirl means may be arranged upstream of the diverging flow means or be combined with the diverging flow means shown with reference to the aforementioned figures, in order to combine swirl and divergence of the aerosol flow.

[0037] In a fourth embodiment illustrated by [Fig.4], a metallic particle combustion system S4 includes divergent flow means which include, in the central injection zone, a central injection tube having internal means for providing the mixture of metallic particles and oxidizer with a divergent trajectory.

[0038] An additional coaxial inlet consisting of oxidizer and gaseous fuel 5, located between the particle injection and the swirled coaxial inlet of a the oxidizing mixture allows a pilot flame to be generated at the point where the particles are injected, contributing to the ignition of the latter.

[0039] In a fifth embodiment illustrated by [Fig.5], a combustion system S5 further includes, downstream of the injection zone, an inlet 5a provided to supply a mixture of fuel and oxidizer 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 metallic particles, thus participating in the ignition of the latter.

[0040] In a sixth embodiment illustrated by [Fig.6], a combustion system S6 further includes one or more stages 1,5c,6a of oxidant injection, intended to contribute to the swirl effect on the mixture of metallic particles and oxidant 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 [Fig.7], a metallic particle combustion system S7 comprises a central tube carrying, in part, an aerosol of metallic particles and opening onto an ignition zone with a divergent trajectory thanks to divergent flow means 2a.

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

[0043] For this purpose, 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 raise their temperature rapidly and to promote their self-ignition (reducing the need for additional fuel gas).

[0044] In addition, a reflective coating on the inner refractory wall concentrates the radiation onto the particles to accelerate their temperature rise. Indeed, a characteristic of solid combustion is the high heat loss through radiation from the fuel, which can be exploited to promote ignition.

[0045] In addition, within the ignition zone 3, a second stage 5c (potentially with several inlets) consisting of a gas including oxygen (injected tangentially) allows the richness to be staged in the ignition zone, by progressively creating a near sub-stoichiometric mixture (or even much leaner, depending on the target 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 just described and many other configurations of the combustion system can be envisaged without going out of the scope of the invention.

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

Claims

Demands

1. A metallic particle combustion system (S1-S7) comprising: - means for injecting a mixture (0) of metallic particles and an oxidizer, defining an injection zone, - means (1) for providing said mixture of metallic particles and oxidizer with a swirl effect, - means for raising the temperature of all or part of said metallic particles to their ignition temperature and initiating their combustion, defining an ignition zone (3), - means for achieving a divergent flow of all or part of said metallic particles and all or part of the oxidizer with respect to a principal direction of particle injection, arranged to provide, from the entrance of the ignition zone (3), a divergent trajectory of all or part of said metallic 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.

2. 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 with respect to the main injection axis.

3. Combustion system (S1-S7) according to any one of claims 1 or 2, wherein the injection zone comprises an axial injection zone of a mixture of metallic particles and oxidizer surrounded by a coaxial oxidizer injection zone arranged to produce a swirling coaxial flow.

4. 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 provided for receiving the mixture containing oxidizer and metallic particles, a sealed outlet end, and a cylindrical wall in which are formed one or more orifices arranged to divert the mixture containing oxidizer and metallic particles towards the ignition zone (3).

5. Combustion system (S2,S7) according to any one of the preceding claims, characterized in that the divergent flow means comprise a central injection tube having an inlet end provided for receiving the mixture containing oxidizer and metallic particles and an outlet end opening onto a part (2) forming a partial obstruction disposed with respect to said distal end so that a flow of metallic particles and oxidizer is injected in a divergent manner.

6. Combustion system (S2,S7) according to the preceding claim, characterized in that the part forming the obstacle is a flared part (2a) having a vertex turned towards the inside of the central injection tube.

7. 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 metallic particle injection means.

8. Combustion system (S6) according to any one of the preceding claims, characterized in that it further comprises one or more stages (1,5b,6) of oxidizer injection, provided(s) to contribute to the swirl effect on the mixture of metallic particles and oxidizer from the injection means and / or to a cleaning effect on a wall of the combustion chamber (4).

9. Combustion system (S7) according to any one of the preceding claims, characterized in that the ignition zone comprises an enclosure (6a) made in whole or in part of a thermally refractory material.

10. Combustion system according to any one of the preceding claims, characterized in that it further comprises means for cooling the divergent flow means.

11. 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 oxidizer to generate a pilot flame at the ignition zone.

12. 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 oxidizer to generate a pilot flame, this inlet being arranged to direct this flame towards the flow of metallic particles.

13. Combustion system (S1-S7) according to any one of the preceding claims, characterized in that it is arranged to receive a mixture of metallic particles, oxidizer and gaseous fuel to produce a pilot flame within the flow of metallic particles.

14. A method for burning metallic particles, implemented in a combustion system according to any one of the preceding claims, comprising the following steps: - injecting a mixture of metallic particles and an oxidizer into an injection zone, - raising the temperature of all or part of said metallic particles to their ignition temperature and initiating their combustion, defining an ignition zone, - creating a divergent flow of all or part of said metallic particles and all or part of the oxidizer with respect to a principal direction of particle injection, this divergent flow being created from the inlet of the ignition zone, - providing said mixture of metallic particles and oxidizer with a swirl effect, - conducting said swirled metallic particles into a combustion chamber, so that they initiate or continue their combustion.

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