“Geometries of iron particle burners for application to the production of decarbonized heat”

Abstract

The present invention relates to a system for producing thermal energy by combustion of iron for application to domestic heating or industrial buildings or installations in remote areas. It also relates to a method for producing thermal energy implemented in this system.

Description

Title of the invention: “Geometries of iron particle burners for application to the production of decarbonized heat” FIELD OF THE INVENTION

[0001] The present invention relates to a system for producing thermal energy by combustion of iron for application to domestic heating or industrial buildings or installations in remote areas. 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 around the world are a reason for the search for a green alternative energy for residential and professional heating. 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 automotive applications with internal or external combustion. In document WO2023080789A1, a burner design is claimed with an expansion towards the combustion chamber, tangential tubular inlets for air staging and flame stabilization as well as an air and particle inlet without aerodynamic effect. There are nevertheless designs which allow more flexibility in operation on the intensity of the swirl, but also to allow the particles to increase their residence time, which in the case of iron is particularly important given the very high combustion times compared to gas or other metal particles (aluminum or magnesium).

[0005] The main aim of the invention is to propose different burner configurations which can make it possible to stabilize iron particle flames for applications linked to the decarbonization of industry. Statement of the invention

[0006] The burner geometries of said invention comprise 3 zones essential to the establishment of a self-sustaining iron flame. The objective being to accelerate the self-ignition of the iron particles in the second zone, by limiting the use of an additional combustible gas to maintain the iron particle flame. DESCRIPTION OF THE FIGURES

[0007] 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

[0008] [Fig. 1] is a schematic representation of the burner comprising the 3 zones necessary for the stabilization of the iron flame.

[0009] [Fig.2] is a schematic representation of the burner with a central inlet swirled air and particles, and two swirled coaxial inlets (static turbines represented by crosses).

[0010] [Fig.3] is a schematic representation of the burner with a central air and particle inlet distributed at the end of the tube by a set of holes placed in the circumference in order to inject the particles radially, and two coaxial swirled inlets (static turbines represented by crosses).

[0011] [Fig.4] is a schematic representation of the burner with an air inlet and particles with at the end of the tube a conical obstacle which allows the aerosol to be deflected radially towards the coaxial swirl, and two coaxial swirled inlets.

[0012] [Fig.5] is a schematic representation of the burner with an air and particle inlet, and three swirled coaxial inlets.

[0013] [Fig.6] is a schematic representation of the burner with an air and particle inlet, and two swirled coaxial inlets, and additional coaxial inlets perpendicular to the combustion chamber walls.

[0014] [Fig.7] is a schematic representation of the burner with an air inlet and particles, and two swirled coaxial inlets, and additional coaxial inlets close to the combustion chamber walls. DETAILED DESCRIPTION

[0015] SI is an iron particle burner composed of 3 main zones: an injection zone for the powder 0 and the oxidant, an ignition zone 1 and a combustion zone 2 for heat recovery. In the first zone, the suspension comprising metal powder and oxygen 0b can be accompanied by a swirled coaxial flow Oa in order to initiate the rotation of the particles to maximize their residence time. In this same zone, a combustible mixture consisting of a flammable gas can be injected into a third coaxial inlet between the central injection of particles and the swirled inlet Oa (in the form of an annular inlet), accompanied by an oxidizer, or, optionally, into the central injection with the suspension of particles Ob. Close to the transition with the second zone (1), ignition electrodes can be arranged in order to ignite the fuel assembly and initiate the preheating of the iron particles entering the ignition zone. The following figures present alternative geometries to this injection zone.In the ignition zone (1), the idea is to preheat the particles to their self-ignition temperature (by initiating the first exothermic surface reactions between oxygen and iron) so that they reach the third zone (2) in quasi-self-sustained heterogeneous combustion and release the heat of reaction in this zone where tubes are arranged on the periphery (or any other means of heat exchange) transporting the heat transfer fluid heading towards user equipment. To this end, in this zone (1), a refractory insulating material allows 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). In addition, a reflective coating on the refractory wall allows to concentrate the radiation on the particles in order to accelerate their rise in temperature.Indeed, a particularity of solid combustion is the high losses by thermal radiation of the fuel which can be exploited to promote ignition. In addition, within the second zone (1), placing a second stage 1a and 1b (potentially with several inlets) consisting of a gas including oxygen (injected tangentially) makes it possible to stage the richness in the ignition zone, by progressively 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.

[0016] S2 is a metal particle burner composed of a central cylindrical tube composed of a static turbine close to its outlet, and transporting, in part, an aerosol of metal particles and opening onto a combustion chamber. Co-axially to this tube, two annular inlets having static turbines make it possible to open two “swirled” air flows into the combustion chamber in order to create recirculation and shear zones in order to stabilize the metal flame (the aim being to obtain zones of low flow velocity in order to correspond to the flame velocity and keep it almost stationary). Configurations with one or three swirled annular inlets are also possible. The interest to add a static turbine in the central tube carrying the flow of metal particles and to allow the particles to have a helical trajectory at the outlet of the burner and to extend their residence time in the flame zone in order to maximize the combustion efficiency by minimizing the chamber length. It is possible to have a system which electromechanically allows the turbines to rotate each around their axis of symmetry, and potentially cooling around the fins by a double wall in the central tube. These two elements respectively allow the intensity of the swirl to be varied (by increasing the tangential deflection angle of the flow), and to limit the heating of the turbines to minimize the risk of particle deposits by melting or sintering.

[0017] S3 is a metal particle burner composed of a central cylindrical tube composed of a nozzle which does not open axially but opens radially using a set of perforations at the circumference of the tube, and which carries, in part, an aerosol of metal particles and opens into a combustion chamber. Coaxially with this tube, two annular inlets having static turbines allow two “swirled” air flows to open into the combustion chamber in order to create recirculation and shear zones in order to stabilize the metal flame (the aim being to obtain zones of low flow velocity in order to correspond to the flame velocity and keep it almost stationary). Configurations with one or three swirled annular inlets are also possible.The advantage of adding a radially opening nozzle at the end of the central tube carrying the flow of metal particles is to allow the particles to be directed towards the swirled coaxial flow and thus have a helical trajectory at the outlet of the burner and to extend their residence time in the flame zone in order to maximize combustion efficiency by minimizing the chamber length. It is possible to have cooling around the holes at the end of the tube by a double wall where water circulates. This element makes it possible to minimize the risks of particle deposits by fusion or sintering which could block the outlet and affect efficiency.

[0018] S4 is a metal particle burner composed of a central cylindrical tube composed at its outlet of a pointed obstacle (point oriented towards the outlet of the tube) connected by bars to the central tube. The objective is to radially deflect the particles in order to direct them towards the swirled coaxial flow and thus allow them to have a helical trajectory at the outlet of the burner and to extend their residence time in the flame zone in order to maximize the combustion efficiency by minimizing the chamber length. Coaxially to this tube, two annular inlets having static turbines make it possible to open two “swirled” air flows into the combustion chamber in order to create recirculation and shear zones in order to stabilize the metal flame (the aim being to obtain areas of low flow velocity in order to match the flame velocity and keep it almost stationary). Configurations with one or three swirled annular inlets are also possible. It is possible to have cooling at the sharp obstacle by a water circuit in the double wall which passes through the obstacle fixings and cools it. This element makes it possible to minimize the risks of particle deposits by fusion or sintering which could block the outlet and affect the efficiency.

[0019] S5 is a metal particle burner composed of a central cylindrical tube carrying, in part, an aerosol of metal particles and opening onto a combustion chamber. Coaxially with this tube, three annular inlets having static turbines allow two “swirled” air flows to open into the combustion chamber in order to create recirculation and shear zones in order to stabilize the metal flame (the aim being to obtain zones of low flow velocity in order to correspond to the flame velocity and keep it almost stationary).

[0020] S6 is a metal particle burner composed of a central cylindrical tube carrying, in part, an aerosol of metal particles and opening onto a combustion chamber. Coaxially to this tube, two annular inlets having static turbines allow two “swirled” air flows to open into the combustion chamber in order to create recirculation and shear zones in order to stabilize the metal flame (the aim being to obtain zones of low flow velocity in order to correspond to the flame velocity and keep it almost stationary). Additional air inlets perpendicular to the axis of the burner and close to the wall of the combustion chamber make it possible to prevent powder deposits. This addition is optional.

[0021] S7 is a metal particle burner composed of a central cylindrical tube carrying, in part, an aerosol of metal particles and opening onto a combustion chamber. Coaxially to this tube, two annular inlets having static turbines allow two “swirled” air flows to open into the combustion chamber in order to create recirculation and shear zones in order to stabilize the metal flame (the aim being to obtain zones of low flow velocity in order to correspond to the flame velocity and keep it almost stationary). Additional air inlets parallel to the axis of the burner and close to the wall of the combustion chamber make it possible to prevent powder deposits. This addition is optional.

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