HYBRID BURNER FOR INDUSTRIAL FURNACES

Abstract

The invention relates to a burner (1) for an industrial furnace, comprising a central injector extending along a longitudinal axis, at least one peripheral injector extending along a peripheral axis, a fuel injection system (4) configured to inject fuel into the central injector, an oxidant injection system (5) configured to inject oxidant into the central injector, the central injector being configured to inject a mixture of fuel and oxidant into the furnace, the oxidant injection system (5) further configured to inject oxidant into the peripheral injector, the peripheral injector comprising an electric heater configured to heat the oxidant circulating in the peripheral injector. Figure to be published with the abstract: Figure 1

Description

Title of the invention: HYBRID BURNER FOR INDUSTRIAL FURNACES TECHNICAL FIELD OF THE INVENTION

[0001] The invention is applied to the field of burners for industrial furnaces used in processes requiring heat generation. TECHNOLOGICAL BACKGROUND

[0002] In many industrial applications requiring heat production, a gas or fluid is heated by sustained combustion in a burner. Most conventional burners use carbon-based fuels, which are oxidized by an oxidant, typically air, to generate heat. Given the growing need to develop industrial solutions to reduce carbon fuel consumption, one alternative is to completely or partially replace the carbon fuel (natural gas, for example) with hydrogen. However, hydrogen production requires investment in large-scale electrolyzers, whose efficiency currently varies around 60% of the potential thermal energy of hydrogen relative to the electrical energy required.Furthermore, if the energy used to power the electrolyzer is generated by carbon-emitting power plants, the carbon emissions per unit of energy used in the final process are worse due to the efficiency of the electrolyzers.

[0003] Another solution involves installing electric radiant heaters in the furnace. Such solutions require a much larger radiant heat transfer surface than burners, making them difficult to integrate into an existing production unit or furnace due to limited available space. Furthermore, the compatibility of these elements with the combustion gases and vapors generated in the furnace could affect the lifespan of these radiant heaters.

[0004] In other known solutions, the combustion air is heated by an electric heater before being sent to the burner, but this configuration has several limitations because the air temperature must be limited to avoid a significant increase in NOx emissions due to the high flame temperature. The air temperature is also limited by the materials used for the burner components. Indeed, hot combustion air requires the supply circuits to use specific materials offering sufficient thermal and mechanical performance at high temperatures, which would drastically increase the The cost and technical complexity of the burner are also factors. Furthermore, such a solution increases the volume of the components, thus increasing the difficulty of integrating it onto the wall of a furnace.

[0005] There is a need for heating solutions for industrial applications that reduce carbon and NOx emissions, while maintaining the compactness and adaptability of conventional burners. PRESENTATION OF THE INVENTION

[0006] In order to overcome the limitations of known solutions, the invention proposes a burner for an industrial furnace, comprising: - a central injector extending along a longitudinal axis; - at least one peripheral injector extending along a peripheral axis; - a fuel injection system configured to inject fuel into the central injector, an oxidant injection system configured to inject oxidant into the central injector, the central injector being configured to inject a mixture of fuel and oxidant into the furnace; - the oxidant injection system being further configured to inject oxidant into the peripheral injector, the peripheral injector comprising an electric heater configured to heat the oxidant circulating through the peripheral injector.

[0007] Such a burner makes it possible to reduce the amount of fuel required to produce the required power, while allowing the peak power necessary for transient phases such as furnace heating, thus reducing the furnace carbon emission per unit power. It also makes it possible to reduce NOx formation during burner operation, while maintaining a stable flame shape and a low CO formation rate. The preheated oxidant injected by peripheral injectors reacts with the fuel under dilute conditions because its vapor is mixed with the furnace combustion gases, reducing the flame temperature and therefore the NOx formation.

[0008] Advantageously but optionally, the invention is complemented by the following features, taken separately or in combination.

[0009] According to one embodiment, the electric heating includes an electrical resistive wire, for example a bare electrical resistive wire; such an element makes it possible to heat the oxidant flow up to temperatures approaching 800°C, thus making it possible to produce a hot oxidant flow, facilitating the reaction with the fuel even under dilute conditions;

[0010] According to another embodiment, the peripheral axis can be inclined at a first angle of less than 20° towards the central axis; such a structure ensures that the fuel flow and the oxidant flow will mix with each other. in a stable location, while ensuring that the mixing takes place under diluted conditions; this helps to limit the risk of uncontrolled combustion in the oven, and to limit the formation of NOx;

[0011] According to another embodiment, the central injector has a central outlet centered on the central axis, and the peripheral injector has a peripheral outlet centered on the peripheral axis, the center of the central outlet being positioned at a first distance from the center of the peripheral outlet, the first distance being between 0.7 and 1.7 times a parametric index, the parametric index being defined by the output power P expressed in megawatts of the burner and the first angle 0 according to the equation d = PA0.33 / 4cos 0; such a characteristic allows the burner to operate in different combustion modes, such as flameless combustion, or conventional combustion, thus reducing the formation of NOx;

[0012] According to another embodiment, the oxidant injection system comprises several peripheral injectors, and the central injector has a central outlet cross section of a first area, the peripheral injectors each have a peripheral outlet cross section, the sum of all the areas of the peripheral outlet cross sections being between 0.4 and 0.6 times the first area, such a characteristic makes it possible to obtain a sufficient oxidant velocity on the peripheral orifices to ensure good mixing in the flame and the low NOx effect expected.

[0013] According to another embodiment, the oxidant injection system comprises, from upstream to downstream: - a blower unit configured to force the circulation of the oxidant, - a main regulating valve configured to control the airflow of the oxidant circulating in the system, - a common manifold supplying air to the peripheral injectors and the central injector, - at least one peripheral channel connecting the peripheral injector to the common manifold, and at least one central channel connecting the central injector to the common manifold. The fuel injection system comprises, from upstream to downstream: - a gas regulating valve configured to regulate the flow of fuel injected into the fuel injection system, the opening of the gas regulating valve being coupled to the main control valve mechanically, pneumatically or electronically, a fuel channel connecting the gas regulating valve to the central injector;

[0014] According to another embodiment, the central channel includes a central control valve configured to alternatively allow the oxidant to flow through the central channel or at least partially obstruct the central channel;

[0015] According to another embodiment, the fuel injection system includes a power balance unit configured to adapt the quantity of fuel per unit of oxidant injected into the furnace by the central injector, the power balance unit comprising a central valve mounted on the fuel channel, or a distributor mounted on the air flow sensing, or a controller adapted to modify the opening control of the gas regulating valve, or a combination of these means.

[0016] According to another embodiment, the burner comprises a number N of peripheral injectors, the number N being a function of the output power of the burner expressed in megawatts, the number N being between 1.5*(P(MW) / 100)A0.5 < N < 3*(P(MW) / 100)a0.5.

[0017] According to Another aspect of the invention, a method of operation of a burner corresponding to the invention is described, in which the main injector is actuated in two modes: - a sub-stoichiometric condition mode during which the air-fuel mixture is injected with a core lambda Le less than 0.7, for example between 0.30 and 0.5; - a flameless combustion mode during which only the fuel is injected.

[0018] Optionally, but advantageously, the operating mode can be supplemented by the following features, taken separately or in combination:

[0019] - the flow rate of oxidant circulating through the peripheral injector is set to allow a total lambda ratio Lt of the burner between 1.05 and 1.15;

[0020] - the fuel flow and the electric heating of the combustion air are regulated based on a lambda of the heart The preset, the air flow being increased or decreased according to a temperature command, the fuel flow being adapted to match the lambda of the heart The preset according to the modified air flow, the electric heater being adapted to the air flow to ensure a required temperature of the injected air. DESCRIPTION OF THE DRAWINGS

[0021] The following figures are drawn for illustrative purposes, but are not exhaustive.

[0022] [Fig. 1] is a schematic representation of a burner corresponding to the invention.

[0023] [Fig.2] is a schematic representation of a furnace comprising a burner corresponding to the invention. DETAILED DESCRIPTION

[0024] The invention relates to a burner 1 for an industrial oven, comprising a central injector extending along a longitudinal axis; - at least one peripheral injector extending along a peripheral axis; - a fuel injection system 4 configured to inject fuel into the central injector, an oxidant injection system 5 configured to inject oxidant into the central injector, the central injector being configured to inject a mixture of fuel and oxidant into the furnace; - the oxidant injection system 5 being further configured to inject oxidant into the peripheral injector, the peripheral injector comprising an electric heater configured to heat the oxidant circulating in the peripheral injector.

[0025] Such a burner 1 would make it possible to reduce the fuel required to increase the temperature of the gas stream entering the furnace, or to avoid having to use fuel to maintain the temperature of the furnace if the desired temperature allows it, or to reduce the time required to heat the furnace for a certain amount of fuel used, thus reducing the carbon emissions of the furnace per unit of power.

[0026] Furthermore, such a structure reduces NOx formation during burner operation, while maintaining a stable flame shape and a low CO formation rate. Injecting combustion air through peripheral injectors, instead of premixing all reactants in the main burner, reduces both thermal NOx and fuel NOx by minimizing the free oxygen content at the flame root, thereby reducing nitrogen oxidation in NOx kinetics. It is well known that NOx from combustion is primarily created from thermal NOx, which is sensitive to temperature and flame oxygen content, and from fuel NOx when the fuel contains nitrogen bound to hydrocarbons.The combustion air injected by the peripheral injectors reacts with the fuel under dilute conditions because its vapor is mixed with the combustion gases from the furnace and / or the combustion gases from the root of the flame, reducing the flame temperature and therefore the formation of NOx. Preheating the air with electric heaters allows for the rapid achievement of reaction conditions between the air and the fuel, a sufficient temperature being necessary to trigger the reaction, particularly under the dilute conditions caused by the injection of air through peripheral injectors.

[0027] Furthermore, such an arrangement facilitates the operation of the burner under flameless oxidation conditions. The injection of oxidant through the lateral injectors 3, preheated to a temperature level enabling the reaction of the oxidant with the fuel injected by the central injector in a dilute state, produces a flameless oxidation reaction, thus reducing NOx emissions from the burner.

[0028] The peripheral axis is either parallel to the central axis or inclined towards the central axis at a first angle θ, preferably less than 20°. The central injector consists of The system consists of a central outlet centered on the longitudinal axis X, and a peripheral injector with a peripheral outlet centered on the peripheral axis. Advantageously, the center of the central outlet is positioned at a distance from the center of the peripheral outlet, this distance being between 0.7 and 1.7 times a parametric index d. The parametric index d is defined by the burner output power P expressed in Megawatts and the first angle θ according to the equation d = P(MW)A0.33 / 4cosθ. Such a structure promotes late mixing of the heated oxidant injected by the peripheral injectors and the fuel injected by the central injector, thus allowing the reactants to react under more dilute conditions.It helps to avoid local temperature spikes and NOx formation, while ensuring that the reactants mix in a stable area to guarantee proper combustion and prevent the risk of reactant accumulation in the furnace, which could lead to an explosion.

[0029] Advantageously, a distance between 0.7 and 1.3 times the parametric index d makes it possible to increase the stability of the combustion and to ensure a better reaction of the reactants.

[0030] Advantageously, a distance of between 1.2 and 1.7 times the parametric index d is particularly suitable for operating burner 1 in flameless combustion mode. The oxidant injected by the peripheral injectors mixes with the combustion gases circulating in the furnace, diluting the oxygen in a gaseous mixture before mixing with the fuel injected by the central injector. The low volumetric concentration of the reactants and the high temperature of the furnace and the heated oxidant from the peripheral injectors create conditions that favor flameless combustion of the reactants rather than conventional combustion, thus contributing to a significant reduction in NOx formation. Advantageously, burner 1 includes a control unit configured to operate burner 1.

[0031] Advantageously, there is one electric heating element per peripheral injector. These electric heaters are all powered in parallel. The air is balanced so that all peripheral injectors have the same outlet temperature. Preferably, the electric heaters consist of an electrical resistive wire (bare wire or other technology) configured to heat an airflow up to 1100°C, depending on their technology and the process requirements.

[0032] In the embodiment shown in [Fig. 1], the oxidant injection system 5 comprises, upstream and downstream, a blower unit 51, configured to deliver an oxidant flow at the required pressure and velocity for a selected burner 1 of required power, a main control valve configured to adjust the oxidant flow rate blown by the blower unit 51, a manifold configured to transfer the flow from the main control valve to a central channel configured to supply oxidant to the central injector, and a peripheral channel configured to supply oxidant to the peripheral injector. In the embodiment shown, the burner 1 comprises at least two peripheral injectors. In such an embodiment, a plurality of peripheral channels are connected respectively to each of the peripheral injectors and to the manifold.

[0033] Advantageously, the central channel is equipped with a central control valve configured to adjust the flow rate of oxidant injected by the central injector to the required need. Alternatively, or optionally, the peripheral channel is equipped with a peripheral control valve configured to adjust the flow rate of oxidant injected by the peripheral injector to the required need. Such a structure makes it possible to control the proportion of oxidant injected by the central injector and the peripheral injectors and to adjust the balance between the heating power supplied by the electric heater and the air lambda of the central injector. In particular, when the burner 1 is operated in flameless combustion mode, the control unit is adapted to stop the injection of oxidant by the central injector. In the illustrated embodiment, the control unit is adapted to close the central control valve.

[0034] The lambda of Air is defined as the ratio between the oxidant flow rate and the stoichiometric oxidant flow rate.

[0035] In the embodiment shown in [Fig. 1], the fuel injection system 4 comprises, upstream or downstream, a fuel supply connected to a central fuel channel, the central fuel channel being connected to the central injector. A gas regulating valve is mounted on the central fuel channel to regulate the fuel flow circulating in the fuel injection system 4. Preferably, the opening of the gas regulating valve is coupled to the main regulating valve, mechanically, pneumatically, or electronically. Such a structure makes it possible to maintain a total lambda Lt of the burner 1, which is the air / fuel molar ratio of the burner 1, when a change in the output power of the burner 1 is commanded, with a single control signal.More precisely, the total lambda Lt represents a ratio between the actual volume of air supplied to burner 1 per unit mass of fuel and the volume of air required to achieve stoichiometric combustion for the same unit mass of fuel.

[0036] Advantageously, the fuel injection system 4 includes a power balance unit configured to adapt the quantity of fuel per oxidant unit injected into the furnace by the central injector, in order to adapt the ratio of electrical power to gas power in the total power of the burner 1.

[0037] In a first embodiment, the power balancing unit includes a central valve mounted on the central fuel channel. The central valve is configured to reduce the gas flow from the central injector independently of the flow total air of burner 1. This embodiment allows control of a core lambda Le of the central injector even when the gas regulating valve is coupled to the main regulating valve, pneumatically or mechanically.

[0038] In a second embodiment, the power balancing unit includes a controller configured to directly control the gas regulating valve in order to adapt the gas flow of the central injector independently of the total air flow of the burner 1. This embodiment is preferred when the gas regulating valve is electronically controlled.

[0039] In a third embodiment, the gas regulating valve is pneumatically coupled to the main regulating valve. The power balancing unit comprises a distributor that allows the pressure sent to the gas regulating valve to be modified, thereby changing the coupling between the gas regulating valve and the main regulating valve.

[0040] Optionally, the power balancing unit is configured to control the central control valve.

[0041] Operating modes

[0042] In a preferred embodiment, the burner 1 is configured to operate with a total lambda ratio Lt between 1.05 and 1.2 for maximum power. The air injected into the burner 1 is distributed between the central injector and the peripheral injectors, such that the central injector is configured to operate with a core lambda Le less than 0.7, for example between 0.3 and 0.5, the core lambda Le being the air / fuel ratio of the air / gas mixture injected by the central injector. The air injected into the peripheral injectors is supplied in such a way as to maintain the total lambda ratio Lt of the burner 1.

[0043] Staggered mode in the air

[0044] The control unit is configured to provide a staged operating mode for the air of burner 1, in which burner 1 operates under nominal conditions. The central injector operates under substoichiometric conditions in which the air-fuel mixture is injected through the central injector with the core lambda Le less than 0.7.

[0045] Low carbon mode

[0046] The control unit is configured to provide a low-carbon operating mode for burner 1, in which burner 1 is used at reduced load. In this case, the power balancing unit is driven by the control unit to reduce the amount of fuel injected by the central injector and optionally adjust the airflow through the central injector, while the main control valve is configured to balance the oxidant flow circulating in the peripheral injector.

[0047] Flameless mode

[0048] Advantageously, the control unit is configured to provide a flameless oxidation operating mode for burner 1, during which only fuel is injected through the central injector. This mode is applied when the temperature in the furnace exceeds the fuel's auto-ignition temperature. In this case, the control unit significantly reduces or stops the airflow through the central injector via the central control valve. For example, the airflow from the central injector can be reduced to less than 10% of the total airflow from burner 1.

[0049] In a non-continuous operating furnace, such as heat treatment furnaces or melting furnaces, where the furnace has production cycles with preheating, a long standby phase during which the temperature is reasonably stable, and a cooling phase, burner 1 can be used in air-staged mode during the heating phase, which generally requires the burner to operate at maximum capacity. Advantageously, burner 1 is configured to meet the needs of the standby phase with its low-carbon mode. In this case, the low-carbon mode is used to achieve a higher decarbonation rate throughout its cycle.

[0050] In other embodiments, when the burner 1 is used in a process requiring lower temperatures and a large convective heat exchange, for example a drying process, the air injected through the peripheral injectors can be increased, so that the total lambda Lt can exceed 1.15 and / or the core lambda Le exceeds 0.7.

[0051] Advantageously, the furnace is delimited by a wall. The wall consists of a layer of refractory and insulating material. Preferably, the peripheral injectors are partially integrated into the wall, extending at least partially through the layer of refractory and insulating material, thus reducing the volume required for the implementation of the system compared to an external electric heat exchanger.

[0052] This compact solution allows for easy application on existing ovens, applicable both for new ovens and for the renovation of existing ovens.

[0053] This is why the number of air nozzles is greater for large capacity burners than that generally applied on pneumatically staged burners.

[0054] The number of air nozzles varies depending on several parameters such as the burner power, the furnace temperature for controlling CO emissions, the electrical power relative to the total burner power ratio, and whether a significant excess air or a flameless mode is planned. For example, a burner Operating with a slight excess air, the burner includes 2 to 4 peripheral injectors for a burner output of approximately 200 kW. This promotes combustion through better air distribution, reduces space constraints thanks to a controlled number of peripheral injectors, and achieves a decarbonation rate between 30 and 50%. Preferably, the number N of peripheral injectors in the burner is defined by the following inequality: 1.5*(P(MW) / 100)A0.5 < N < 3*(P(MW) / 100)A0.5. Such values ​​improve burner performance with regard to combustion quality and decarbonation ratio.

[0055] Advantageously, as can be seen in [Fig.2], the furnace includes an exhaust system 9 comprising a recirculation loop 10 configured to redirect the hot gases exiting the furnace to the oxidant injection system 5. In [Fig.2], for example, the recirculation loop 10 is supplied by a recirculation fan 57. Such a structure makes it possible to reduce the amount of energy required to maintain a furnace temperature if the furnace operates with only peripheral injectors and electric heating.

[0056] Advantageously, as seen in [Fig.2], the exhaust system 9 includes a heat exchanger 11 connected to the oxidant injection system 5, configured to transfer energy from the furnace fumes to the combustion oxidant in order to supply the peripheral injectors and the central injector with hot air undiluted with combustion gases, thus avoiding exposure of the electric heaters 6 to the combustion gases while maximizing the efficiency of the system and the decarbonation rate.

Claims

Demands

1. Burner (1) for an industrial furnace, comprising: - a central injector extending along a central axis; - at least one peripheral injector extending along a peripheral axis; - a fuel injection system (4) configured to inject fuel into the central injector, an oxidant injection system (5) configured to inject oxidant into the central injector, the central injector being configured to inject a mixture of fuel and oxidant into the furnace; - the oxidant injection system (5) being further configured to inject oxidant into the peripheral injector, the peripheral injector comprising an electric heater configured to heat the oxidant circulating through the peripheral injector.

2. Burner (1) according to claim 1, wherein the electric heating comprises a bare electrical resistive wire.

3. Burner according to claims 1 or 2, wherein the peripheral axis can be inclined at a first angle 0 with respect to the central axis, the first angle 0 being less than 20° and the peripheral axis being inclined towards the central axis.

4. Burner according to claim 3, wherein the central injector has a central outlet centered on the central axis, and the peripheral injector has a peripheral outlet centered on the peripheral axis, the center of the central outlet being positioned at a first distance from the center of the peripheral outlet, the first distance being between 0.7 and 1.7 times a parametric index, the parametric index being defined by the output power P of the burner and the first angle 0 according to the equation d = P(MW)A0.33 / 4cos0.

5. Burner according to any one of the preceding claims, wherein the oxidant injection system (5) comprises several peripheral injectors, and wherein the central injector has a central outlet with a first zone cross section (SI), the peripheral injectors each have a peripheral outlet having a peripheral outlet cross section, the sum of all the areas of the peripheral outlet cross sections being between 0.4 and 0.6 times the first zone cross section (SI).

6. A burner according to any one of the preceding claims, wherein the oxidant injection system (5) comprises, from upstream to downstream: - a blower unit (51) configured to force the circulation of the oxidant, - a main control valve configured to control the flow rate of the oxidant circulating in the system, - a common manifold supplying air to the peripheral injectors and the central injector, - at least one peripheral channel connecting the peripheral injector to the common manifold, and at least one central channel connecting the central injector to the common manifold, and wherein the fuel injection system (4) comprises, from upstream to downstream: - a gas control valve configured to regulate the flow rate of fuel injected into the fuel injection system (4), the opening of the gas control valve being coupled to the main control valve mechanically, pneumatically, or electronically,a fuel channel connecting the gas regulating valve to the central injector.

7. Burner according to claim 6 combined with claim 4, wherein the central channel includes a central control valve configured to alternatively permit the oxidant to flow through the central channel or at least partially obstruct the central channel.

8. Burner according to claim 6, wherein the fuel injection system (4) comprises a power balancing unit configured to adapt the quantity of fuel per oxidant unit injected into the furnace by the central injector, the power balancing unit comprising a central valve mounted on the fuel channel, or a distributor mounted on an air flow sensing device, or a controller adapted to modify the opening control of the gas regulating valve, or a combination of these means.

9. A burner according to any one of claims 1 to 6, wherein the burner comprises a number N of peripheral injectors, the number N being a function of the output power P of the burner expressed in megawatt, the number N being between 1.5*(P / 100)A0.5 < N < 3*(P / 100)A0.

5.

10. Burner according to any one of claims 1 to 7, wherein the oxidizer injection system (5) of the burner is connected to an exhaust system (9) comprising a recirculation loop (10) configured to redirect the hot gases exiting the furnace to the oxidizer injection system (5) with a recirculation fan (57).

11. Burner according to claim 10, wherein the exhaust system (9) comprises a heat exchanger (11) connected to the oxidant injection system (5), configured to transfer energy from the furnace combustion gases to the combustion oxidant in order to supply the peripheral injectors and the central injector with hot air undiluted with combustion gases.

12. A method of operating a burner according to any one of claims 1 to 9, wherein the central injector is actuated in two modes: - a sub-stoichiometric condition mode during which an air-fuel mixture is injected with a core lambda (Le) less than 0.7, for example between 0.3 and 0.5; or - a flameless combustion mode during which only fuel is injected.

13. A method of operation according to claim 12, wherein the air flow through the peripheral injector (1) is configured to permit a total lambda ratio (Lt) of the burner between 1.05 and 1.

15.

14. A method of operation according to any one of claims 12 or 13, wherein the fuel flow and the electric heating of the combustion air are regulated according to a preset core lambda (Le), the air flow being increased or decreased according to a temperature control, the fuel flow being adapted to match the preset core lambda (Le) according to the modified air flow, the electric heating being adapted to the air flow to ensure a required temperature of the injected air.

Images