Burner, in particular for straight flame preheating section of continuous metal strip processing line
By setting up a central fuel injection pipe and an oxidizer injection pipe inside the burner, combined with an ignition electrode, the problem of unstable flame in an environment with insufficient oxidizer is solved, achieving stable combustion without an igniter, simplifying the start-up process and reducing system complexity and cost.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-07
- Publication Date
- 2026-03-27
AI Technical Summary
Existing burners are difficult to operate in the reduction mode with insufficient oxidant in the direct combustion preheating section of the steel strip processing line, resulting in metal strip oxidation and flame instability. Furthermore, an igniter is required for ignition during startup, which increases system complexity and cost.
The flameless gas burner achieves stable combustion in the internal combustion chamber by setting up a central fuel injection pipe and an oxidizer injection pipe inside the burner, combined with an ignition electrode, and uses the electrode to ignite the mixture, thus avoiding the need for an igniter.
It enables stable combustion in oxidant-deficient environments, simplifies the start-up process, reduces system complexity and cost, and improves the flexibility and durability of the burner.
Smart Images
Figure CN121752845A_ABST
Abstract
Description
[0001] Name of the relevant technical field
[0002] This invention relates to industrial burners, particularly intended for use in continuous horizontal or vertical production lines for annealing or galvanizing metal strips, and more specifically to direct combustion preheating sections of such production lines, sometimes referred to as “NOF section” (NOF being an abbreviation for “non-oxidizing furnace”) or “DFF section” (DFF being an abbreviation for “direct combustion furnace”).
[0003] This invention is an improvement on the solution disclosed in the applicant's patent FR3114375, which is used for burners with flame combustion mode and flameless combustion mode.
[0004] Technical problem solved by the present invention
[0005] In the direct combustion preheating section of the steel strip processing line, the burner must be able to operate in a reduction mode with insufficient oxidant supply in order to minimize the presence of oxygen near the metal strip and thus prevent metal strip oxidation.
[0006] When the furnace is at a low temperature, for example during startup, ignition of the burner is usually promoted by applying overstoichiometric conditions (i.e., by oversupplying the burner with oxidant).
[0007] However, in order to simplify installation and avoid different operating modes for excess air during low-temperature operation, it is advantageous to enable the burner to start in reduction mode.
[0008] In the preheating section, combustion gases flow from the outlet to the inlet of the preheating section in the opposite direction to the metal strip flow. This exposes the burners located in the inlet area of this section to combustion gases originating from burners located upstream in the direction of smoke flow. Additionally, inert gases, such as nitrogen, are present in the furnace. Therefore, the burners must be able to ignite and heat up in a highly diluted environment.
[0009] A flameless mode is achieved at high temperatures (e.g., above 850°C) by recirculating most of the combustion gases inside the furnace to obtain a reaction zone that is uniformly distributed relative to the intense combustion zone in flame mode.
[0010] During startup and at low temperatures, the burner operates in flame mode. The high recirculation rate and the presence of inert gases (such as nitrogen) inside the furnace dilute the reaction zone and disrupt the root of the flame.
[0011] Without a continuous stabilizing mechanism (such as a premixed igniter), there is a risk of flameout.
[0012] Premixing the oxidizer with the fuel downstream of the flame stabilizes the flame but creates a strong reaction zone near the burner. This leads to burner overheating and higher nitrogen oxide emissions.
[0013] Under these conditions, it is difficult to maintain a strong and stable flame, which also makes it difficult to use a UV bath to detect the flame.
[0014] Existing solutions cannot meet all these requirements without an igniter.
[0015] This invention overcomes these problems without the need for an igniter. Background Technology
[0016] Burners that meet the above requirements are usually equipped with an igniter to ensure that the burner is ignited under all conditions.
[0017] Since igniters typically operate in premixed mode and are used only to ignite the burners and help stabilize the flame during the furnace heating process, their power is limited, typically ranging from 5kW to 15kW.
[0018] The igniter is used only before the fuel reaches its auto-ignition temperature, after which it is turned off and sometimes retracted from the burner.
[0019] When the furnace is in production, the igniter, which is kept in place, typically needs to be cooled at the furnace's nominal operating temperature.
[0020] The igniter represents additional capital expenditure because, in addition to a dedicated control unit, the igniter requires a separate fuel and oxidizer circuit from the main burner circuit.
[0021] This currently limits the use of igniters to a few areas of the furnace, typically the first area in the direction of gas flow.
[0022] The area equipped with an igniter is used for ignition and reheating, while other areas are subsequently ignited one after another as their temperatures reach the auto-ignition temperature of the fuel due to the energy supplied by the adjacent areas during operation.
[0023] Because most areas depend on temperature during operation, the operating system is not very flexible.
[0024] In a non-oxidizing furnace, combustion occurs in an environment lacking oxidant to prevent oxidation of the metal strip. This reaction produces unoxidized or partially oxidized substances such as carbon monoxide and hydrocarbons. These substances must then be oxidized in the recovery zone of the preheating section or in a dedicated section commonly referred to as the afterburner.
[0025] It is preferable that the last zone in the gas flow direction is in operation under low load and low furnace temperature, so that the flue gas leaves at a relatively high temperature, thereby promoting the oxidation of unburned materials in the recovery zone.
[0026] Operating in several zones equipped with igniters that are typically located far from the flue gas outlet requires a large afterburner to heat the fuel gas to a higher temperature suitable for oxidizing unburned materials. Summary of the Invention
[0027] According to a first aspect of the invention, a gaseous fuel burner capable of operating in a so-called "flameless" mode is provided, the gaseous fuel burner having a longitudinal axis at the intersection of two vertical planes and including a diffuser, through which a fuel injection conduit and an oxidizer injection conduit operating in flameless mode pass, the oxidizer injection conduit opening from the diffuser closer to the burner axis than the fuel injection conduit operating in flameless mode, the burner also including a central fuel injection conduit operating in flame mode, the central fuel injection conduit extending axially in the burner, characterized in that the burner includes a combustion chamber located inside the burner and at least one passage for supplying oxidizer, the central fuel injection conduit opening at least partially into the combustion chamber, the internal combustion chamber also including an ignition electrode capable of initiating combustion in the internal combustion chamber of at least a portion of a fuel / oxidizer mixture supplied to the internal combustion chamber by the central fuel injection conduit and the at least one passage for supplying oxidizer.
[0028] The internal combustion chamber is a volume in which combustion can take place under stable and controlled conditions, independent of the furnace temperature and atmosphere.
[0029] The use of electrodes allows the combustion to be ignited using a simple and inexpensive device. The electrodes can also be used to verify the presence of a flame through ionization.
[0030] The internal combustion chamber is designed to supply fuel to the chamber via a central fuel injection pipe.
[0031] According to the present invention, the internal combustion chamber forms a channel according to the fluid flow direction, and the inlet diameter of the channel is larger than the outlet diameter of the channel.
[0032] The internal combustion chamber is a converging channel whose size gradually decreases to a diameter smaller than that of the oxidizer disc.
[0033] This reduction in diameter increases the force of the gas leaving the internal combustion chamber. The result is a longer and more intense flame, which better sustains the main combustion in the burner.
[0034] The average diameter of the internal combustion chamber depends on its desired power. A larger combustion chamber means greater power. However, the internal combustion chamber must not interfere with the flow of oxidizer into the oxidizer injection channels of the diffuser.
[0035] The size of the combustion chamber is also limited by its pressure drop. This pressure drop must be high enough to limit the amount of oxidizer entering the combustion chamber, ensuring sufficient oxidizer passes through the oxidizer injection channels of the diffuser. This, in turn, maintains the aerodynamic characteristics of the burner in flameless operation mode.
[0036] Advantageously, according to the invention, the downstream end of the internal combustion chamber in the fluid flow direction is located in an axial conduit of the diffuser that opens into the flame passage.
[0037] An axial conduit leading to the burner mechanically retains the downstream end of the combustion chamber. This axial conduit also allows for the substantial maintenance of the combustion chamber's outlet diameter over an additional length, which is the length of the axial conduit extending beyond the inner combustion chamber. This additional length helps maintain the flame from the inner combustion chamber.
[0038] According to the present invention, the central fuel injection conduit includes fuel injection passages arranged at two levels along the conduit.
[0039] The first stage of radial fuel injection is designed to mix with the oxidizer to form the root of the flame in the internal combustion chamber.
[0040] The second stage of fuel, injected later, is primarily intended to mix with the oxidizer supplied to the exterior of the internal combustion chamber via oxidizer injection pipes through the diffuser. Its purpose is to provide the flame with adequate propulsion and protect it from the effects of a diluting environment.
[0041] According to the present invention, the central fuel injection conduit includes a fuel injection passage that opens into a combustion chamber inside the burner.
[0042] This arrangement makes it easy to supply the fuel needed to achieve combustion in the internal combustion chamber.
[0043] Advantageously, according to the invention, the fuel injection passage may be axial and / or radial, and / or inclined at an angle between 0% and 90% relative to the burner axis.
[0044] The arrangement of the fuel injection path is selected based on the properties of the gaseous fuel, especially its calorific value, so that the fuel flow in the internal combustion chamber generates a stable flame of sufficient intensity.
[0045] Advantageously, according to the invention, the central fuel injection conduit includes at least one fuel injection passage that opens downstream of the combustion chamber inside the burner in the direction of fluid flow.
[0046] Adding fuel downstream of this chamber limits the power released within it. This has the effect of limiting the temperature of the internal combustion chamber walls and thus improving their durability over time.
[0047] Advantageously, according to the invention, the burner includes an oxidizer disc connected to a central fuel injection duct, the disc forming an annular passage with the internal combustion chamber in which the oxidizer can circulate.
[0048] The oxidizer is injected into the combustion chamber in a manner that confines the flame away from the walls of the internal combustion chamber. The peripheral oxidizer flow cools the internal combustion chamber and limits the reaction zone.
[0049] Advantageously, according to the invention, the oxidant disc includes a passage through which the oxidant can flow.
[0050] These pathways ensure optimal distribution of the oxidizer within the internal combustion chamber. These pathways are arranged in an axisymmetric manner around the central fuel injection pipe.
[0051] Advantageously, according to the invention, the passage in the oxidant disk forms a groove having radial and tangential components to generate an oxidant vortex downstream of the oxidant disk.
[0052] The swirling flow created by the grooves promotes the mixing of the oxidant and fuel.
[0053] Advantageously, according to the invention, the oxidizer disc includes a circular opening adjacent to the end of a groove near the burner axis.
[0054] Advantageously, according to the invention, the oxidizer disc includes a cylindrical passage that converges toward the burner axis in the oxidizer flow direction.
[0055] Determine the spray angle to form a stable flame root.
[0056] Advantageously, according to the invention, the combustion chamber inside the burner has silicon carbide walls.
[0057] The use of silicon carbide ensures that the internal combustion chamber can operate continuously for extended periods. Because silicon carbide can withstand higher temperatures compared to high-temperature steel, it also allows for more intense combustion within the combustion chamber.
[0058] Other materials with good heat resistance, such as high-temperature steel, can also be used. Attached Figure Description
[0059] Other features and advantages of the invention will become apparent during the reading of the following detailed description. To understand these features and advantages, reference will be made to the accompanying drawings, in which:
[0060] [ Figure 1[This is a schematic front view of the diffuser plate of a burner according to the prior art.]
[0061] [ Figure 2 ] is based on [ Figure 1 A schematic three-dimensional cross-sectional view of half of the diffuser sheet.
[0062] [ Figure 3 [Illustration] is a schematic enlarged cross-sectional view of the internal portion of a burner according to a first exemplary embodiment of the present invention.
[0063] [ Figure 4 ] is with [ Figure 3 The view is similar to the view used in the second exemplary embodiment of the present invention.
[0064] [ Figure 5 ] is with [ Figure 3 The view is similar to the view used in the third exemplary embodiment of the present invention.
[0065] [ Figure 6 ] is with [ Figure 3 The view is similar to the view used in the fourth exemplary embodiment of the present invention, and
[0066] [ Figure 7 [Illustrated front view of the injector and oxidizer disc of the central fuel injection pipe in a fifth exemplary embodiment of the present invention.] Detailed Implementation
[0067] Since the embodiments described below are not intended to be limiting in any way, variations of the invention that specifically include only the series of features described below, isolated from the other features described, can be considered if such series of features is sufficient to provide a technical advantage or to distinguish the invention from the prior art. This series includes at least one feature, preferably functional, without structural details, or only a portion thereof, if this portion alone is sufficient to provide a technical advantage or to distinguish the invention from the prior art.
[0068] In the remainder of the specification, elements with the same structure or similar function will be indicated by the same reference numerals.
[0069] Refer to the attached diagram [ Figure 1 The figure in question partially and schematically illustrates a burner 1 according to the prior art, as described in the applicant's patent FR3114375, as viewed from the front, and the burner is oriented along a vertical plane P1 and a horizontal plane P2. The figure shows the orientation of the burner when it is positioned in a vertical preheating section of a continuous production line, with the band extending vertically.
[0070] Fuel passes through two converging pipes 3 arranged on plane P1. Oxidant passes through four pipes 4 and 5, where pipe 4 on plane P1 diverges and pipe 5 on plane P2 converges.
[0071] When the furnace is at a sufficient temperature, oxidizer and fuel are injected through pipes 3, 4, and 5 to enable combustion in a flameless mode.
[0072] The burner also includes a central fuel injection conduit 6 that enables the burner to operate in flame mode at a lower temperature. An annular passage surrounding the conduit 6 provides the supply of oxidizer.
[0073] [ Figure 2 [Seen in perspective and along a cross-section of plane P1] Figure 1 The diagram shows a partial view of the burner. This makes it easier to see the inclination of the fuel injection pipe 3 and the diverging oxidizer pipe 4 in the diffuser plate 2.
[0074] Oxidizer pipes 4 and 5 open into combustion channel 13 to improve flame retention.
[0075] Refer to the attached diagram [ Figure 3 The diagram in [ ] shows an enlarged view of the internal portion of the burner 1, which schematically illustrates the combustion chamber 7 inside the burner according to a first exemplary embodiment of the present invention.
[0076] The combustion chamber is basically cylindrical, and its longitudinal axis coincides with the burner axis A.
[0077] The internal combustion chamber includes a first section 15 with a larger diameter, which is connected to a third section 17 with a smaller diameter via a second conical section 16.
[0078] The third section 17 is located in the axial pipe 12 connected to the flame channel 13.
[0079] The chamber is held in place by connecting pipe 12 and support and guide components (not shown).
[0080] The fluid flows primarily from left to right, as indicated by arrow 14.
[0081] The upstream surface 18 of the internal combustion chamber 7 includes a passage 8 that allows oxidant to enter the chamber.
[0082] These passages can be distributed at different distances from the burner axis A on the upstream face 18. The gap between the upstream face 18 and the central fuel injection pipe 6 can form passages.
[0083] The central fuel injection conduit 6 includes radial passages 19 for injecting fuel into the internal combustion chamber, such as the four cylindrical orifices described herein.
[0084] The oxidant entering the internal chamber 7 through passage 8 mixes with the fuel entering the chamber through passage 19 in the internal combustion chamber 7.
[0085] When energized, the ignition electrode 9 generates an electric arc to initiate combustion in the chamber 7.
[0086] The flow rates of the oxidizer and fuel entering the combustion chamber, as well as the fluid velocity within the combustion chamber, cause incomplete combustion within the inner chamber. This combustion extends outside the inner chamber as the fluid escapes through the downstream opening 21.
[0087] Therefore, the flame originating from the inner chamber extends to the outside of the inner chamber, through pipe 12, into channel 13, and then into the furnace.
[0088] In this example, the downstream end of the central fuel injection conduit 6 also includes an axial passage 20, which is substantially located at the inlet of the flame passage 13. Fuel supply via the axial passage 20 ensures that the flame is stabilized at sufficient power to prevent the main flame from extinguishing.
[0089] For example, 60% of the fuel flow supplied by the central fuel injection pipe 6 passes through the radial passage 19 and 40% passes through the axial passage 20, and the oxidant flow passing through the passage 8 enables the production of a mixture of the fuel flow having a 5% excess air relative to stoichiometric combustion.
[0090] exist[ Figure 4 In the second example embodiment schematically shown in the diagram, the central fuel injection conduit 6 extends into the flame channel 13. Additionally, the axial passage is replaced by a new radial passage 22 arranged at the downstream end of the conduit.
[0091] This arrangement of passage 22 allows the fuel arriving from passage 22 to mix more intensely with the oxidant arriving via pipes 4 and 5.
[0092] Therefore, in accordance with the use of [ Figure 3 Compared to the flame obtained by the arrangement of the first example implementation, the main flame present in channel 13 is brighter, resulting in a shorter and more intense flame.
[0093] exist[ Figure 5 The third example embodiment is schematically shown in the figure. In this case, the internal combustion chamber 7 is opened at its upstream end 23 in the direction of oxidant flow.
[0094] The central fuel injection conduit 6 includes an injector 33, which includes a set of eight passages 24 with radial components and an axial passage 25, all of which open into the internal combustion chamber 7.
[0095] Passage 24 is inclined at an angle of 75° relative to the burner axis A, and the cross section of axial passage 25 is 10% of the total cross section of passage 24 in this document.
[0096] The injector 33 carries an oxidizer disc 26 arranged in the internal combustion chamber 7. The oxidizer disc and the internal combustion chamber form an annular passage 27 through which the oxidizer can flow.
[0097] The mixture of oxidant and fuel supplied through passages 24, 25, and 27 in the internal combustion chamber allows the fuel to be ignited by electrode 9. The inclination of fuel passage 24 promotes rapid mixing with the oxidant in the internal combustion chamber, which is beneficial for reliable ignition and maintenance of internal combustion. Axial passage 25 allows for flame extension, which is beneficial for main combustion in both passage 13 and the furnace.
[0098] [ Figure 6 The diagram illustrates the relationship between [[]. Figure 5 The fourth example implementation is similar to the implementation of []. Figure 5 The difference in the implementation scheme lies in the larger diameter oxidizer disk 26, which means there is no significant flow outside the oxidizer disk. The outline of the internal combustion chamber 7 is also slightly different.
[0099] The oxidizer disc includes passages 28 for allowing oxidizer to enter the internal combustion chamber, which contribute to good ignition and good flame maintenance.
[0100] exist[ Figure 7 The fifth example embodiment is shown in the figure. Only the central fuel injection conduit 6 and the oxidizer disc 26 are shown in the front view and cross-section at the radial fuel passage 19. The oxidizer disc 26 includes four circular passages 32 for supplying oxidizer into the combustion chamber 7 inside the burner. These passages are inclined and converge toward the burner axis A. These passages are arranged opposite to the passage 19 for injecting fuel into the internal combustion chamber 7. Passage 34 is intended to receive the ignition electrode 9.
[0101] Therefore, the present invention is that the burner is ignited and preheated by means of a central fuel injector ignited by an electrode that replaces the igniter.
[0102] The gas injector is designed as a coaxial burner, and its power can account for more than half of the total power of the main burner. The design of the fuel injector is not limited to a coaxial structure.
[0103] Of course, the present invention is not limited to the examples just described, and many modifications can be made to these examples without departing from the scope of the invention. Furthermore, various features, forms, variations, and embodiments of the invention can be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive.
Claims
1. A gaseous fuel burner (1) capable of operating in a so-called "flameless" mode, the gaseous fuel burner having a longitudinal axis (A) at the intersection of two vertical planes (P1, P2) and including a diffuser (2), a fuel injection conduit (3) operating in flameless mode and an oxidizer injection conduit (4, 5) passing through the diffuser, the oxidizer injection conduit (4, 5) opening from the diffuser closer to the burner axis than the fuel injection conduit (3) operating in flameless mode, the burner further including a central fuel injection conduit (6) operating in flame mode, the central fuel injection conduit extending in the axial direction (A) of the burner, characterized in that, The burner includes a combustion chamber (7) located inside the burner and at least one passage (8, 27, 28) for supplying oxidant. The central fuel injection pipe (6) is at least partially open to the combustion chamber. The internal combustion chamber also includes an ignition electrode (9) that enables at least a portion of the fuel / oxidant mixture supplied to the internal combustion chamber by the central fuel injection pipe (6) and the at least one passage (8, 27, 28) for supplying oxidant to begin combustion in the internal combustion chamber (7).
2. The burner according to claim 1, characterized in that, The internal combustion chamber (7) forms a channel (10) according to the fluid flow direction, and the inlet diameter of the channel is larger than the outlet diameter.
3. The burner according to any one of the preceding claims, characterized in that, The downstream end (17) of the internal combustion chamber (7) in the fluid flow direction is located in the axial diffuser duct (12), which opens into the flame channel (13).
4. The burner according to claim 1, characterized in that, The central fuel injection conduit (6) includes fuel injection passages (19) arranged at two levels along the conduit.
5. The burner according to claim 4, characterized in that, The central fuel injection pipe (6) includes a fuel injection passage (19) that opens into the combustion chamber (7) inside the burner.
6. The burner according to the preceding claim, characterized in that, The fuel injection passage (19) can be axial and / or radial, and / or inclined at an angle between 0° and 90° relative to the burner axis (A).
7. The burner according to claim 5 or 6, characterized in that, The central fuel injection pipe (6) includes at least one fuel injection passage (20, 21) which opens downstream of the combustion chamber (7) inside the burner in the direction of fluid flow.
8. The burner according to any one of the preceding claims, characterized in that, The burner includes an oxidizer disc (26) connected to the central fuel injection pipe (6), the disc forming an annular passage (27) with the internal combustion chamber through which the oxidizer can flow.
9. The burner according to the preceding claim, characterized in that, The oxidant disk (26) includes a passage (28) through which the oxidant can flow.
10. The burner according to claim 9, characterized in that, The oxidizer disk (26) includes a cylindrical passage (32) that converges toward the burner axis (A) in the direction of oxidizer flow.
11. The burner according to any one of the preceding claims, characterized in that, The combustion chamber (7) inside the burner has a silicon carbide wall (31).