Method for converting a burner of an industrial furnace to hydrogen

Abstract

Method for converting a burner (1) positioned on a wall (3) of an industrial furnace (2), said burner being supplied with carbonaceous fuel and oxidant through pipes (4, 5) inside the burner, characterized in that it comprises the addition of at least one injection lance (6) for hydrogen, or a hydrogen-rich gas, passing through the wall of the furnace and opening into the latter in the vicinity of the burner, such that the burner can use the hydrogen, or the hydrogen-rich gas, supplied by the injection lance(s) as fuel, at least partially.

Description

PROCESS FOR CONVERSING AN INDUSTRIAL FURNACE BURNER TO HYDROGEN Designation of the technical field concerned

[0001] The invention relates to industrial furnaces for heating metal products equipped with burners, in particular preheating furnaces before rolling. Technical problems that the invention addresses

[0002] Reheating furnaces play a crucial role in the steelmaking process, where steel products are heated to high temperatures for subsequent operations, e.g. rolling in hot rolling mills.

[0003] However, these ovens contribute significantly to emissions of carbon dioxide (CO2) and nitrogen oxide (NOx), which must be reduced with stricter regulations.

[0004] Today, most reheating furnace modernization projects aim to reduce the carbon footprint of the process, leading to an increasing demand for cleaner and more sustainable technologies in industrial processes.

[0005] A promising solution for reducing CO2 and NOx emissions in reheating furnaces is the adoption of alternative fuels, particularly hydrogen combustion.

[0006] Hydrogen offers several advantages over traditional fossil fuels, including clean combustion, producing essentially water, no CO2 emissions, high energy density, and compatibility with existing infrastructure.

[0007] The transition to hydrogen combustion contributes to global efforts to decarbonize the steel industry.

[0008] As the steel industry continues to evolve, there is increasing recognition of the need to adopt sustainable practices and reduce environmental impacts.

[0009] By leveraging emerging technologies, such as hydrogen combustion, and implementing strategic measures to mitigate NOx emissions, steel producers can not only meet regulatory requirements, but also achieve long-term sustainability goals while maintaining their competitiveness in the global market.

[0010] However, integrating hydrogen combustion into reheating furnaces requires modifications to existing equipment and infrastructure.

[0011] Existing conventional combustion burners tend to overheat when the usual fuel is replaced with hydrogen. This is because, with hydrogen flames, the flame is closer to the burner due to hydrogen's higher combustion rate compared to traditional fuels such as natural gas.

[0012] Furthermore, these burners typically produce high NO emissions x when they are powered by hydrogen.

[0013] A common approach is to replace existing burners with burners optimized for hydrogen combustion. These modified burners are designed to ensure efficient mixing of hydrogen and oxidizer, resulting in clean and stable combustion while minimizing NOx formation.

[0014] However, modernizing the process to current NOx standards and adapting it to hydrogen-rich fuels by changing the burners requires significant investment and extensive modifications to the furnace. Such projects are driven solely by regulations with no economic incentive, making the limitation of investment costs a priority.

[0015] Another NOx emission reduction technique described by US8075303 involves using an oxygen lance, where oxygen is injected directly into the furnace to improve combustion and heating efficiency. While effective in some applications, the oxygen lance may not be suitable for furnaces where oxygen availability is limited.

[0016] In most cases, the financial gain from reduced fuel consumption resulting from oxygen injection is offset by the increased cost of the oxygen itself. Therefore, while the idea is appealing from an environmental perspective, it offers little economic benefit in many cases, which may hinder its adoption by industry. Technical background

[0017] Steel reheating furnaces are an integral part of the steelmaking process. Typically, these furnaces use axial flame burners, which produce high-temperature zones in the product due to their intense heat concentration.

[0018] Axial injection of reagents produces long flames necessary to cover the width of the furnace. However, this approach has drawbacks, including uneven temperature distribution across the product's width and high NOx emissions.

[0019] Axial flame burners generate a concentrated flame that radiates directly onto the steel product, resulting in high, localized temperatures. While this rapid heating can be advantageous for some applications, it often causes temperature variations throughout the product, leading to inconsistent mechanical properties across its thickness and potential quality issues. Furthermore, the high combustion temperatures associated with axial burners contribute to the formation of NOx, a harmful oxidizing pollutant and a significant environmental concern.

[0020] This applies not only to axial burners, but also to most conventional burners. The conventional view of combustion is that flame stability is linked to the fact that it is attached to the burner and that it is intense.

[0021] Generally, in most conventional burners, gas is injected in the center at a moderate or low speed, surrounded by a dominant amount of oxidant injected at a higher speed to create the long flame.

[0022] The available pressure is not always sufficient for recycled gas from steel production, such as mixed gas and coke oven gas for example.

[0023] Another reason for the lower speed is to facilitate burner ignition in cold conditions, at furnace start-up. A lower gas speed improves the mixing of reactants near the burner.

[0024] All these conditions create an intense flame attached to the burner which, in most cases, is unsuitable for hydrogen combustion. This is why conventional burners tend to overheat and produce a shorter flame with high NOx levels when fueled by hydrogen.

[0025] One solution is to limit the concentration of hydrogen in the gas to a certain level that the burner can handle.

[0026] Another solution is to change the burner material in contact with the flame. This is not an option for burners in reheating furnaces because they are generally already made of high-temperature refractory concrete. Furthermore, this does not solve the problem of the shorter flame structure and higher NOx emissions.

[0027] To address these challenges, the focus has shifted to adopting burners with more diffuse combustion and a wide flame in steel reheating furnaces, as taught in WO2015078862 by the applicant. These burners produce a wider flame profile with a high injection velocity, which facilitates more uniform heating of the product, improving temperature homogeneity and reducing thermal gradients.

[0028] By distributing heat more evenly across the entire product, wide flame burners help mitigate problems such as overheating and underheating, thereby improving the quality and uniformity of the product's mechanical characteristics.

[0029] Furthermore, the use of wide-flame burners also offers environmental benefits by reducing NOx emissions. By operating at lower maximum temperatures and distributing heat more evenly, these burners promote more complete combustion and lower NOx formation rates. This emission reduction aligns with increasingly stringent environmental regulations and the sustainability goals of the steel industry.

[0030] Because of the greater distance between the oxidant injection and the gas injection, and the wider injection angle, these new burners are generally larger than conventional burners and require a modification of the furnace to be installed.

[0031] While newer furnaces are designed with greater heights to accommodate larger burners, most existing furnaces have limitations on the size of burners that can be fitted.

[0032] These large burners increase the risk of introducing more oxygen to the product surface due to the proximity of the oxidizing jets to the product. Furthermore, large burners are not suitable for front-facing installation.

[0033] Furthermore, although wide flame burners represent a significant improvement over conventional burners in terms of temperature uniformity and emission reduction, there is still room for optimization.

[0034] Most burners have a fixed flame structure that does not adapt to the product's heating requirements. Some burners solve this problem by incorporating multiple oxidizer injection configurations to modulate the flame shape, but this comes at the cost of even larger burners requiring increased furnace volumes, thus impacting furnace heat losses.

[0035] Burners increasingly require greater operational flexibility regarding fuel type, flame shape, and oxidant-to-fuel ratio. Conventional burners, and even most new burners, lack this flexibility due to their fixed flame shape.

[0036] New burners are being developed to address these technical challenges. These new burners are compact, high-recirculation burners that often use dilute combustion or flameless combustion to reduce NOx emissions.

[0037] One solution available today for adapting hydrogen to existing furnaces is to adopt these burners. Such modernization projects are costly and not suitable for all furnaces. The modifications are not limited to structural work and burner replacement.

[0038] The new burners operate with different heating curves and flame structures, impacting the product's heating curve. The furnace's control programs and mathematical models must also be adapted to these changes.

[0039] The invention provides a novel solution to these problems. It allows for the easy modernization of existing furnaces as well as the construction of new ones.

[0040] According to a first aspect of the invention, a method is proposed for converting a burner positioned on the wall of an industrial furnace, said burner being supplied with carbon fuel and oxidizer through internal conduits in the burner, characterized in that it includes the addition of at least one hydrogen injection lance, or of a hydrogen-rich gas, passing through the wall of the furnace and opening into it in the vicinity of the burner, so that the burner is able to use as fuel, at least partially, the hydrogen, or the hydrogen-rich gas, supplied by the injection lance(s).

[0041] The invention allows existing furnaces to be adapted to new fuels such as hydrogen by adding fuel lances at a certain radial distance from the burner axis. The idea is to add one or more hydrogen injection lances next to any burner in the furnace and to link them to the furnace's fuel flow control.

[0042] The invention thus makes it possible to convert existing furnace burners to hydrogen, or a hydrogen-rich gas, or the entire furnace, with little modification of the existing equipment and at a limited cost.

[0043] It is simply a matter of creating channels in the wall of the oven by drilling with drill bits, from the external metal wall of the oven on which the burner is fixed until they reach the oven by passing through the refractory, and then sliding the lances into these.

[0044] The lance opens in the vicinity of the burner, for example at a distance of approximately 10 to 100 cm from the burner.

[0045] The burner conversion is carried out without any modification to the existing burners, which reduces the cost.

[0046] The method applies to furnaces with burners installed in any burner configuration, including side, front and vault heating, and regardless of burner type.

[0047] Without needing to change the burners, the furnace can switch to hydrogen and hydrogen-rich fuels.

[0048] Replacing at least part of a carbon fuel with hydrogen allows for at least partial decarbonization of the furnace's operation.

[0049] The invention relates to reheating furnaces with a method for injecting fuel through lances placed near the burners and converting the furnace to a diluted combustion compatible with hydrogen and low NOx emissions with limited modifications.

[0050] The injection method creates a very dilute combustion and can be adapted to any burner by introducing a number of lances at a specific distance from the burners. The lances are connected to the furnace's fuel flow control and can be linked to the fuel control of the burners near which they are positioned. The lances operate independently or in parallel with the existing burner's fuel injection to provide the total required heat input. The existing burner's fuel flow can be reduced or shut off.

[0051] The invention generates homogeneous temperature profiles on the product surface by creating a uniform flame. Temperature variation along the longitudinal and transverse axes is reduced. Furthermore, the lateral fuel jets encompass the central oxidizer jet, thus reducing oxygen availability at the product surface. This leads to less scale formation on the metal load being heated.

[0052] The invention allows existing furnaces to be adapted to hydrogen and hydrogen-rich fuels without damaging the burner due to the high flame temperature. The flame will be volumetric, occupying a larger space within the furnace, and will not be fixed to the burners since the fuel is injected away from it.

[0053] Advantageously according to the invention, the hydrogen-rich gas is ammonia or a mixture of ammonia and hydrogen.

[0054] Hydrogen is a good candidate to replace fossil fuels, but it is expensive to transport and store. When its production is not close to the point of consumption, it is more cost-effective to transport hydrogen in the form of ammonia. In this case, it is advantageous to burn it directly rather than converting it to hydrogen, which is a very expensive process.

[0055] Ammonia has a very slow maximum combustion speed (0.07 m / s) compared to natural gas (0.37 m / s) or hydrogen (2.91 m / s). Flame stabilization can sometimes be difficult. Advantageously, according to one embodiment of the invention, the gas injected by the nozzles is a mixture comprising mainly ammonia and a small amount of hydrogen, for example 10%, to facilitate flame ignition.

[0056] According to a second aspect of the invention, an industrial furnace is proposed comprising a wall on which a burner is positioned, characterized in that it comprises at least one hydrogen injection lance, or of a hydrogen-rich gas, passing through the wall of the furnace and opening into it in the vicinity of the burner, the end of the injection lance being formed by a converging nozzle capable of creating a coherent jet, the burner being capable of operating, at least partially, with hydrogen, or hydrogen-rich gas, supplied by the injection lance(s) as fuel.

[0057] According to the invention, the burner is thus able to operate with hydrogen, or a hydrogen-rich gas, as fuel, supplied by the injection lance(s) in addition to the carbon fuel supplied by an internal conduit to the burner, or as a replacement for it.

[0058] The position of the lance tip in the furnace and the angle of the lance relative to the burner axis and the burner's oxidizer and fuel ducts are chosen so that the burner operates correctly with fuel supplied through the lance.

[0059] Using a converging nozzle capable of creating a consistent jet offers several advantages, including:

[0060] - Increased hydrogen injection speed: The convergent nozzle design accelerates the flow of injected gas by progressively decreasing the cross-section. This generates a higher velocity at the nozzle outlet.

[0061] - Improved mixing of reactants: A higher injection speed helps create a more homogeneous mixture of reactants in the combustion zone. A homogeneous mixture is essential for more efficient and complete combustion, thus reducing the formation of hot spots and the resulting NOx emissions and unburned combustion products.

[0062] - Precise flame control: The converging nozzle shape allows for better control of the flame's shape and direction. This is particularly important in industrial applications where the flame's position and stability must be precisely controlled for specific processes.

[0063] In summary, the use of a convergent nozzle for the injection of hydrogen, or hydrogen-rich gas, optimizes combustion conditions, thereby improving energy efficiency, reducing pollutant emissions, and contributing to the safety and control of the combustion process.

[0064] The nozzle can be made of durable metallic or ceramic material that can withstand high temperatures.

[0065] The tip of the lance can be positioned slightly recessed from the inner wall of the furnace to protect the nozzle from radiation, especially when the nozzle is not gas-cooled. The recess in the inner wall can be small with a ceramic nozzle, due to its high temperature resistance, and larger with a metal nozzle, which has lower temperature resistance.

[0066] Under extreme conditions, the lance can be cooled by an external fluid circulating through a jacket that is part of the lance or external to the lance.

[0067] According to one embodiment of the invention, the longitudinal axis of the injection lance converges towards the axis of the burner, in the direction of flow of the hydrogen, or of the hydrogen-rich gas.

[0068] The angle of inclination of the lance is chosen so that the position of the convergence point is close to or far from the hot face of the burner in order to obtain the desired quality of mixing of hydrogen, or hydrogen-rich gas, with the fuel and / or oxidizer from the burner.

[0069] According to another embodiment of the invention, the longitudinal axis of the injection lance is parallel to the axis of an internal oxidizer duct in the burner.

[0070] Injecting hydrogen alongside the oxidizer jets delays the interaction between the hydrogen and oxidizer jets, thus maximizing flame dilution. This effect can also be achieved by placing the nozzles further from the burner.

[0071] The ability to delay the interaction between the hydrogen and oxidant jets is limited by the fact that the oxidant must be present in small quantities on the product surface. Therefore, careful attention must be paid to the injection angle and position.

[0072] By maintaining the same momentum as the gas jet initially injected into the burner, the flame structure can be largely preserved, as the oxidation moment is dominant and the flame aerodynamics are not significantly affected. The advantage of this configuration is the minimal impact on the product's heating curve.

[0073] The injection speed and the angle of the lances can vary depending on the aerodynamics of the burner.

[0074] Simulations and experiments show that a low injection velocity from the nozzles does not achieve the dilute flame behavior, especially if the nozzles are close to the existing burner. The fuel is drawn directly by the oxidant injected by the burner and reacts rapidly, just as if the fuel were injected directly into the burner. However, some advantages are gained, such as reducing oxygen on the product surface.

[0075] Because the fuel is injected outside the oxidizer, it surrounds the oxidizer, reducing the oxygen content in the atmosphere near the product. Furthermore, flame takeoff is increased, protecting the burner from overheating.

[0076] On the other hand, injection at a high speed close to or greater than the speed of the oxidant creates a reaction zone in the oxidant recirculation zone, favorably maximizing the dilution effect.

[0077] Tests conducted in a test furnace on various types of burners show that this method produces a more homogeneous flame. In all cases, hydrogen combustion is achieved with a highly dilute flame. The burner temperature remains within acceptable limits, and NOx emissions are improved in most cases, becoming less dependent on the oxidizing fuel ratio.

[0078] According to one embodiment of the invention, the furnace comprises two hydrogen injection lances, or lances of a hydrogen-rich gas, arranged on either side of the burner and symmetrically with respect to the axis of the burner, the two lances being able to be arranged on the vertical or horizontal axis of the burner.

[0079] The lances can be positioned on a horizontal plane including the axis of the burner, symmetrically on either side of it.

[0080] The lances can also be positioned on a vertical plane encompassing the burner axis, on either side of a metal product being heated in the furnace. This configuration can create a fuel-rich layer near the product's surface, thereby reducing scale formation.

[0081] The positioning may vary depending on the oven configuration.

[0082] The use of two lances arranged in this way is advantageous because it promotes the development of a symmetrical flame along the axis of the burner, without protrusion on the side where the lance is located when only one lance is used.

[0083] According to another embodiment of the invention, more than two lances are positioned around a burner.

[0084] According to a third aspect of the invention, a method for controlling a furnace according to the invention is proposed, characterized in that the proportion of fuel supplied by the injection lance(s) is between 1% and 100% of the total fuel in the burner.

[0085] Thus, depending on the availability of hydrogen and / or the cost of hydrogen, or hydrogen-rich gas, the process allows for adjusting the proportion of hydrogen consumed. This proportion will be high if hydrogen availability is high and its cost low, and it will be low if hydrogen availability is low and its cost high.

[0086] Varying the proportion of fuel delivered by the injection nozzles can alter the flame structure. When all the fuel is injected through the nozzles, the flame is most diluted, creating a flameless mode.

[0087] The nozzles of a burner can be coupled to each other, and to those of adjacent burners, or operate separately.

[0088] The amount of fuel injected through the lances is monitored and controlled by a program integrated into or operating with the furnace's fuel supply system.

[0089] With proportional control, flow regulating valves are required. For different fuels, the nozzles are connected to a different gas supply.

[0090] When the furnace is cold, the burners start in conventional mode, but some of the fuel can also be injected through the nozzles. As the furnace temperature rises and reaches the auto-ignition temperature, more fuel can be injected through the nozzles, up to 100% under high-temperature conditions and in production mode.

[0091] Advantageously according to the invention, the proportion of fuel supplied to the burner by the injection lance(s) is adjusted according to the temperature of the furnace.

[0092] It is therefore possible to control the furnace temperature, and / or the furnace temperature profile, by adjusting the proportion of hydrogen or hydrogen-rich gas. This proportion is reduced when it is advantageous to lower the furnace temperature and, conversely, it is increased when it is advantageous to raise the furnace temperature.

[0093] Hydrogen, or hydrogen-rich gas, can be injected into the furnace at a speed substantially lower or higher than the speed at which the burner oxidizer is injected into the furnace, for example between 50% and 200% of the oxidizer injection speed.

[0094] Advantageously according to the invention, hydrogen, or hydrogen-rich gas, supplied by an injection lance is injected into the furnace at a speed between 80% and 150% of the injection speed of the burner oxidant into the furnace.

[0095] Existing burners are connected to the oxidizer circuit for oxidizer injection and to the fuel circuit for fuel injection. Fuel and oxidizer are delivered to the furnace in a specific proportion to achieve combustion. The generated flame heats the product. The burners operate using digital control (also known as pulse ignition), proportional control, or a hybrid of both.

[0096] Advantageously according to the invention, the fuel is injected totally or mainly via the lances, without modification on the injection of oxidant which continues to be delivered by the burner. Brief description of the figures

[0097] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for understanding which reference should be made to the attached drawings in which:

[0098] is a schematically and partially represented front view of a furnace wall on which a burner is mounted according to the prior art.

[0099] is a schematic and partially represented vertical cross-sectional view of the wall of the lasagna on which the burner is mounted according to the prior art.

[0100] is a view similar to that after the addition of two injection lances according to an exemplary embodiment of the invention,

[0101] is a view similar to that after the addition of the two injection lances according to the embodiment shown in the invention,

[0102] is a schematically and partially represented longitudinal cross-sectional view of a pre-rolling reheating furnace according to an exemplary embodiment of the invention,

[0103] is a partial and schematic view of a lance according to an exemplary embodiment of the invention, comprising a metallic nozzle 61, and,

[0104] is a partial and schematic view of a lance according to an example of an embodiment of the invention, comprising a nozzle 61 made of ceramic material. Detailed description of the invention

[0105] A partially represented front view from inside the furnace shows a wall 3 of a preheating furnace 200 comprising a burner 100 according to the prior art. The burner includes an opening 13 made of refractory material with a central gas pipe 4, and four air injectors 5 arranged around the central gas pipe at equal intervals. Two air injectors are positioned on a vertical plane 10 passing through the axis of the burner, and two air injectors are positioned on a horizontal plane 11 also passing through the axis of the burner.

[0106] The wall 3 of the furnace 200 is partially shown in vertical section along plane 10 passing through the axis of the burner. The burner 100 further comprises a metal casing 12 and a combustion air inlet 14.

[0107] A furnace 2 is shown, comprising a burner 1 similar to that of the [missing image]. Two lances 6 have been added, according to an embodiment of the invention, for the injection of hydrogen or a hydrogen-rich gas. They are arranged on the plane 10 of the [missing image], on either side of the burner and symmetrically along the axis of the burner.

[0108] As shown in the image, the lances pass through the wall of the oven, which has been previously pierced to receive them.

[0109] In this example, the lances have a nozzle 61 at their end, the tip of which 62 is slightly recessed from the hot face of the furnace wall 3 in order to limit its temperature. This is particularly advantageous when the nozzle 61 is metallic.

[0110] The angle of the nozzles is chosen so that their longitudinal axes converge at a point on the axis of the gas pipe 4, at a predetermined distance from the burner opening. This distance from the convergence point is chosen according to the type of burner, particularly the arrangement of the oxidizer and fuel lines, the type of primary fuel used by the burner, and the desired flame shape.

[0111] The number, position and mode of operation of the combustion ducts, some of which may or may not be supplied depending on the operating regime of the burner, are taken into account in particular when deciding on the position and inclination of the lances.

[0112] In another example of an embodiment not shown, the lances can be horizontal, without inclination, parallel to the fuel conduits 4 and the oxidizer conduits 5.

[0113] The position and inclination of the lances can be determined in particular by numerical simulation or by tests.

[0114] Figure 1 schematically illustrates another application of the invention for a preheating oven 2 prior to rolling. The oven is shown in longitudinal section, with the products to be reheated, not shown, circulating from left to right. In this example, two lances 6 are arranged on either side of each burner 1 on a horizontal plane. This arrangement is advantageous in this type of oven where a flat flame is desired to distribute heat over the products.

[0115] The illustration partially and schematically shows a lance 6 according to an example of an embodiment of the invention, comprising a metallic nozzle 61.

[0116] Laillustrate partially and schematically a lance 6 according to another embodiment of the invention, comprising a nozzle 61 made of ceramic material.

Claims

Method of converting a burner (1) positioned on a wall (3) of an industrial furnace (2), said burner being supplied with carbon fuel and oxidizer by conduits (4, 5) internal to the burner, characterized in that it comprises the addition of at least one hydrogen injection lance (6), or of a hydrogen-rich gas, passing through the wall of the furnace and opening into it in the vicinity of the burner, so that the burner is able to use as fuel, at least partially, the hydrogen, or the hydrogen-rich gas, supplied by the injection lance(s). A process according to claim 1, characterized in that the hydrogen-rich gas is ammonia or a mixture of ammonia and hydrogen. industrial furnace (2) comprising a wall (3) on which is positioned a burner (1), characterized in that it comprises at least one hydrogen injection lance (6), or of a hydrogen-rich gas, passing through the wall of the furnace and opening into it in the vicinity of the burner, the end of the injection lance being formed by a converging nozzle capable of creating a coherent jet, the burner being capable of operating, at least partially, with hydrogen, or hydrogen-rich gas, supplied by the injection lance(s) as fuel. Oven according to claim 3, characterized in that the longitudinal axis of the injection lance (6) converges towards the axis of the burner, in the direction of flow of the hydrogen, or of the hydrogen-rich gas. Oven according to one of claims 3 or 4, characterized in that the longitudinal axis of the injection lance(s) (6) is parallel to the axis of the internal oxidizer conduit(s) (4) of the burner. Oven according to any one of claims 3 to 5, characterized in that it comprises two hydrogen injection lances (6), or lances of a hydrogen-rich gas, arranged on either side of the burner and symmetrically with respect to the axis of the burner. Method of controlling an industrial furnace (2) according to any one of claims 3 to 6, characterized in that the proportion of fuel supplied by the injection lance(s) (6) to a burner (1) is between 1% and 100% of the total fuel of the burner. Method according to claim 7, characterized in that the proportion of fuel to the burner (1) supplied by the injection lance(s) (6) is adjusted according to the temperature of the furnace. A method according to any one of claims 7 or 8, characterized in that the hydrogen, or hydrogen-rich gas, supplied by an injection lance (6) is injected into the furnace (2) at a speed between 80% and 150% of the injection speed of the oxidant from the burner (1) into the furnace.

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