VARIABLE IMPULSE BURNER

Abstract

VARIABLE IMPULSE BURNER Method for controlling a burner (1) supplied with a gaseous fuel having a property (P) with a value (PA) that varies between a minimum value (P1) and a maximum value (P2), the burner comprising a set of fuel injectors (2a, 2b, 2c, 2d) suitable for being supplied with fuel, characterized in that the method comprises a step of selecting one or more injectors (2a, 2b, 2c, 2d) to be supplied with fuel according to the value (PA) of the property (P) of the fuel. Figure for the abstract: 2

Description

Title of the invention: VARIABLE IMPULSE BURNER Designation of the technical field concerned

[0001] The invention relates to industrial burners, for example intended for preheating furnaces before rolling, or for process furnaces especially for metallurgy.

[0002] It relates in particular to burners allowing the heating of products present in the oven.

[0003] The invention relates more particularly to burners designed to operate efficiently with different fuels, with mixtures of fuels in varying proportions or with a fuel whose properties vary. Technical problems that the invention addresses

[0004] The burners equipping industrial furnaces are often designed for a specific type of fuel. They generally tolerate, within certain limits, variations in composition, calorific value, or density.

[0005] Taking into account the Wobbe index of the fuel, for example, makes it easy to adapt the fuel and oxidizer flow rate to deliver the same amount of energy.

[0006] However, the total amount of energy delivered by combustion is not the only criterion for ensuring proper heating of the products in an oven. The characteristics of the flame, particularly its shape and especially its length and temperature, will have an impact on the transfer of energy to the products being heated and the oven walls.

[0007] In the case, for example, of a change of fuel from natural gas to hydrogen, for the same quantity of energy to be supplied, we observe that:

[0008] The fuel flow rate is multiplied by more than three (according to the ratio of the LHV). for slightly lower airflow;

[0009] . the density of hydrogen is almost eight times lower;

[0010] . the laminar combustion velocity is almost eight times higher.

[0011] The shape of the flame can therefore be very different when switching from one fuel to the other. It can also be very different if the two fuels are used as a mixture.

[0012] The burners according to the state of the art are thus not suitable for maintaining a desired thermal distribution in a furnace when the properties of the fuel change significantly, for example during a change of gas.

[0013] The invention makes it possible to overcome these problems. Technical background

[0014] The burner typically consists of a central fuel injector surrounded by several distant injections of oxidant in order to establish a preferably highly diluted combustion.

[0015] Figure 1 illustrates an example of a burner comprising a central fuel injector and four oxidizer injectors.

[0016] Alternatively, the burner may have a different number of oxidant injections, and / or lateral fuel injections. Depending on the case, the oxidant injections may be inclined towards the axis of the burner or not, depending on the desired flame shape, wider or longer. Summary of the invention

[0017] According to a first aspect of the invention, a method is proposed for controlling a burner supplied with a gaseous fuel having a property having a variable PA value between a minimum value and a maximum value, the burner comprising a set of fuel injectors suitable for being supplied with fuel, characterized in that the method includes a step of selecting one or more injectors to be supplied with fuel according to the value (PA) of the property (P) of the fuel.

[0018] The variable PA value is, for example, the calorific value of the fuel, its density, its Wobbe index or the proportion of a constituent of the fuel, for example its hydrogen content.

[0019] The burner comprises several fuel injectors so as to adjust the combustion characteristics, in particular the shape of the flame, by selecting the injectors which are supplied with fuel and those which are not.

[0020] Thus, for the same fuel flow rate, the invention makes it possible to adjust the combustion, without changing the amount of energy delivered by the burner, by varying the fuel injection speed into the combustion chamber.

[0021] The invention thus makes it possible to have a variable pulse burner, allowing the pulse of the fuel jets to be adapted according to the composition or properties of the fuel.

[0022] When the PA value of the fuel property changes beyond a predetermined threshold, the invention makes it possible to maintain a heating distribution substantially equivalent to that which preceded the change in value by modifying the fuel injectors in service.

[0023] This modification may consist of the commissioning or stopping of one or more injectors.

[0024] According to the invention, the scale between the minimum value and the maximum value is divided into a number of ranges of values ​​and in that at each of these ranges of values ​​is associated with one or more fuel injectors to be supplied with fuel, the process comprising a step of determining the range of values ​​to which the PA value of the fuel property belongs followed by a step of supplying fuel to the fuel injector(s) associated with this range of values, the other injector(s) not being supplied with fuel.

[0025] The number of value ranges depends on the number of fuel injectors and possible combinations. For example, if the burner has only two injectors, three value ranges are provided, with the first injector being used alone for the first range, the second injector being used alone for the second range, and both injectors being used for the third range.

[0026] Advantageously, the burner includes a plurality of fuel injectors to allow for several possible combinations. The greater the number of injectors, the finer the burner's adjustment can be.

[0027] All injectors may have the same exhaust passage cross-section in the combustion chamber. Alternatively, some injectors may share the same passage cross-section and others may have a different cross-section. All injectors may also have different passage cross-sections.

[0028] The number of injectors and their flow cross-sections can be determined according to the magnitude of the variation in the fuel property in question and its nature. They can be determined by calculation using a model of the burner's operation and / or by tests on a test bench.

[0029] The injectors to be supplied and those not to be supplied are predetermined for each range of values, according to the property considered. The selection of injectors to be in operation for each range of values ​​can be determined by calculation using a model of the burner's operation and / or by tests on a test bench. It can also be carried out during burner start-up, directly on the industrial furnace for which it is intended.

[0030] According to the value of the fuel property, the burner control and piloting system determines which range it is in and then supplies fuel only to the injectors which need to be supplied for that range of values.

[0031] Controlling the burner is therefore very simple.

[0032] According to an example of application of the invention, the gaseous fuel comprises at least two gases and its monitored property is the proportion of one of the gases.

[0033] The invention is particularly advantageous when the fuel is composed of a mixture of gases whose proportion varies over time with an impact on the combustion rate, the quality of the combustion and the properties of the flame.

[0034] The property of the fuel considered for the choice of injectors in service is for example the proportion of one of the gases in the mixture. Advantageously, the gas considered is the one that most significantly alters the combustion rate.

[0035] The fuel property considered for the choice of injectors in service can also be the sum of the proportions of at least two gases in the mixture.

[0036] According to one example of application of the invention, one of the gases constituting the fuel is hydrogen.

[0037] When the fuel contains hydrogen in a proportion that can vary significantly, this variation has a major impact on combustion and flame characteristics. It is therefore advantageous to consider the proportion of hydrogen in the fuel as a property to be taken into account for burner control.

[0038] According to a second aspect of the invention, a burner is proposed comprising a set of fuel injectors suitable for use in implementing a process according to the first aspect of the invention.

[0039] According to an exemplary embodiment of the invention, the fuel injectors form concentric rings. This simple implementation arrangement facilitates the manufacture of the burner.

[0040] It makes it possible to modify the combustion, in particular the length of the flame, while retaining the principles of distribution of the fuel and the oxidant in the flame and the conditions of their mixing.

[0041] According to the invention, at least one fuel injector is supplied via an isolation device allowing the supply of fuel to said injector or not.

[0042] The isolation device can be a component of the burner. It can also be located upstream of the burner.

[0043] There may be as many isolation devices as there are injectors, or a different number. One isolation device may act on several injectors.

[0044] Advantageously, the burner is capable of operating with an oxidant comprising a recirculation of fumes or injected water vapor.

[0045] Advantageously, the burner is capable of operating with a mixture of hydrogen and natural gas, or with a fuel composed of 100% hydrogen.

[0046] The invention allows, for example, the use of hydrogen as a substitute for natural gas with a quantity that can increase as hydrogen becomes available or according to variations in the cost of hydrogen.

[0047] Since the combustion of hydrogen does not emit carbon dioxide, the use of hydrogen as a substitute for natural gas makes it possible to reduce CO2 emissions.

[0048] According to another aspect of the invention, a heating system for an industrial furnace is proposed, characterized in that it comprises a burner according to the invention and computer control means configured to receive a PA value of the fuel property and to determine the injector(s) to be supplied with fuel. fuel depending on the PA value.

[0049] The installation may include one or more burners according to the invention.

[0050] The computer control means is for example embedded in the control and command system of the installation.

[0051] The determination of the injectors to be supplied with fuel is advantageously carried out by taking into account the desired temperature distribution in the installation. Brief description of the figures

[0052] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the accompanying drawings in which:

[0053] [Fig. 1] is a schematic and partial front view of a burner according to the state of the technical,

[0054] [Fig.2] is a schematic and partial front view of a burner according to a first example of an implementation of the invention,

[0055] [Fig.3] is a diagram illustrating the implementation of a step of the method according to a example of an application of the invention,

[0056] [Fig.4] is a schematic and partial side view of the burner of [Fig.2], with a enlargement at the level of the fuel injectors,

[0057] [Fig.5] is a schematic and partial front view of a burner according to a second exemplary embodiment of the invention, and

[0058] [Fig.6] is a schematic side view of an installation according to an example of a lization of the invention. Detailed description of the invention

[0059] The embodiments described below are not in any way limiting; variants of the invention may, in particular, be considered comprising only a selection of the features described, hereinafter isolated from the other features described, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one feature, preferably a functional one without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0060] In the following description, elements having an identical structure or analogous functions will be designated by the same references.

[0061] Consider a fuel composed of natural gas, hydrogen, or a mixture of natural gas and hydrogen, and a burner for a reheating furnace having two in- fuel injectors.

[0062] For the same amount of energy delivered by the burner, with 100% hydrogen, the required volume of fuel is three times higher.

[0063] If we want to maintain the same fuel injection speed at the burner, we need an injector surface three times larger for hydrogen than for natural gas.

[0064] But this is not the only factor to be taken into account, the combustion rate being almost ten times faster, it is then necessary to increase the flow rate of hydrogen relative to natural gas, according to the behavior of the burner, in order to prevent the flame from getting too close to the burner and damaging its metal or refractory parts.

[0065] In this example, using the parameters of Table 1 below, depending on the proportion of hydrogen mixed with the natural gas, using either the first injector or both injectors simultaneously, it is possible to adapt the fuel speed, in order to best control the flame length and therefore the heating quality, as can be seen in Table 2.

[0066] Table 1: Parameters of the natural gas / hydrogen example Parameter Value Unit Power PCI 5 MW Lambda 1.2 - PCI GN 39 MJ / Nm3 VaOGN 10.6 NmVNm3 pcih2 10.8 MJ / Nm3 VaOH2 2.4 Nm3 / Nm3 Surface 1st injector 2000 mm2 Surface 2nd injector 1000 mm2

[0067] Table 2: Example of flow rates and velocities according to the percentage of hydrogen Natural Gas % vol. 100 70 50 30 0 H2 % vol. 0 30 50 70 100 Natural Gas Flow Rate Nm3 / h 462 323 231 138 0 H2 Flow Rate Nm3 / h 0 500 833 1167 1667 Fuel Flow Rate Nm3 / h 462 823 1064 1305 1667 Air flow rate Nm3 / h 5871 5550 5335 5121 4800 Speed ​​1st injector m / s 64 114 148 181 231 Speed ​​2nd injector m / s 43 76 99 121 154

[0068] Indeed, it can be seen that the use of a single injector in this example leads to 231 m / s for hydrogen alone, a very high speed for this type of application and burner, which can lead to a stall of the flame, and possibly an extinction of the burner.

[0069] In this case, using both injections together allows for a return to more reasonable speeds, 145 m / s in this example. Depending on the desired flame lengths and speeds, the injector surfaces will be adjusted. Additional injectors can also be added.

[0070] Furthermore, if we look at Table 2 for the quantity of air required for combustion with the same excess air and the same power, we notice a decrease of nearly 20% in the volume of air, which can impact the length of the flame.

[0071] To maintain a heating profile similar to the initial case, i.e. corresponding to the fuel for which the furnace was sized, it may be interesting to recirculate part of the fumes in the combustion air to find the same flame length.

[0072] It is also possible to inject water vapor, as described in patent EP0425363, to obtain the same effect on the flame length, while reducing the flame temperature, thereby reducing NOx emissions.

[0073] The injection of water vapor also makes it possible to increase the radiation of the flame towards the walls of the furnace and the product by the increased quantity of water in the combustion products.

[0074] By referring to the diagram in [Fig.1] of the attached drawings, a burner 10 can be seen partially and schematically represented according to the prior art.

[0075] It comprises a central fuel injector 20 and four air injectors 60 arranged so as to generate highly diluted combustion.

[0076] The air injections can be inclined towards the axis of the burner or not, depending on the desired flame shape, wider or longer.

[0077] By referring to the diagram in [Fig.2] of the attached drawings, a burner 1 can be seen partially and schematically represented according to a first embodiment of the invention.

[0078] It comprises a set of four concentric and axial fuel injectors 2a, 2b, 2c, 2d. It also comprises four air injectors 6 arranged similarly to those in [Fig. 1], in order to generate diffuse combustion.

[0079] The fuel injector 2a has an exhaust surface of Sa mm2, the fuel injector 2b has an exhaust surface of Sb mm2, the fuel injector 2c has an exhaust surface of Sc mm2 and the fuel injector 2d has an exhaust surface of Sd mm2.

[0080] For example, the surface area of ​​Sb is twice as large as that of Sa, that of Sc is twice as large as that of Sb, and that of Sd is twice as large as that of Sc.

[0081] According to another embodiment of the invention, the surface area of ​​Sb is 20% larger than that of Sa, that of Sc is 20% larger than the combined areas of Sa and Sb and that of Sd is 20% larger than the combined areas of Sa, Sb and Sc.

[0082] Other relationships between the surfaces Sa, Sb, Sc and Sd are possible, depending on the nature of the fuel property P taken into account for the control of the fuel injection and depending on the evolution of this property, for example according to the concentration of hydrogen in the fuel.

[0083] According to one example of application of the invention, the fuel is composed of a mixture of natural gas and hydrogen and the property P taken into account for the control of the fuel injection is the volume percentage of hydrogen in the fuel.

[0084] Fig. 3 is a diagram illustrating the implementation of the step of the process according to the invention where the value pages of the fuel property P taken into account for the burner control are determined.

[0085] In this example, it is the volume percentage of hydrogen in the fuel that is considered. It can vary between 0%, corresponding to the value PI, and 100%, corresponding to the value P2.

[0086] The scale between PI and P2 is split into four ranges of values, the RI range going from 0% to 24% hydrogen in the fuel, the R2 range going from 25% to 49% hydrogen, the R3 range going from 50% to 74% hydrogen and the R4 range going from 75% to 100% hydrogen.

[0087] In this example, when the volume percentage of hydrogen in the fuel is in the range RI, only injector 2a is supplied with fuel, injectors 2b, 2c and 2d are not supplied. When the volume percentage of hydrogen in the fuel is in the range R2, injectors 2a and 2b are supplied with fuel and injectors 2c and 2d are not. When the volume percentage of hydrogen in the fuel is in the range R3, injectors 2a, 2b and 2c are supplied with fuel and injector 2d is not. And when the volume percentage of hydrogen in the fuel is in the range R4, all injectors 2a, 2b, 2c and 2d are supplied with fuel.

[0088] For example, if the PA value of the volume percentage of hydrogen in the com When the fuel level is 60%, the installation's control and command system determines that this PA value is within the R3 range. For burner operation, it opens isolation devices 3a, 3b, and 3c to allow fuel to be supplied to injectors 2a, 2b, and 2c, and it keeps isolation device 3d closed to prevent fuel from being supplied to injector 3d.

[0089] Depending on the injector surface area, other combinations of injectors in operation are possible. More value ranges can also be considered, up to ten with four injectors.

[0090] Depending on the property P of the fuel, its evolution between its minimum value PI and its maximum value P2 may not be linear. For example, it may increase slightly up to a first value before increasing more and more rapidly.

[0091] Thus, the ratio between the exhaust surfaces of the fuel injectors may not be linear in order to keep pace with the evolution of the fuel property P.

[0092] According to one embodiment of the invention, the fuel injection pressure is the same for all injectors. The burner adjustment is only carried out by opening or closing certain fuel injectors.

[0093] According to another embodiment of the invention, the fuel injection pressure is adjusted according to the injectors to benefit from an additional burner adjustment possibility.

[0094] According to one embodiment of the invention, the fuel has the same composition for all fuel injectors. According to another embodiment of the invention, the fuel has a different composition depending on the fuel injector.

[0095] For example, injectors 2a and 2b can be supplied with a mixture comprising 75% natural gas and 25% hydrogen and injectors 2c and 2d can be supplied with a mixture comprising 60% natural gas and 40% hydrogen.

[0096] In [Fig.4], a schematic and partial side view of burner 1 of [Fig.2] is shown, with a magnification at the level of the fuel injectors 2a, 2b, 2c, 2d.

[0097] Each injector includes an isolation device 3a, 3b, 3c, 3d, for example a solenoid valve. In this example, the isolation devices are part of the burner.

[0098] In [Fig.5], a schematic and partial front view of a burner is shown according to a second embodiment of the invention.

[0099] This burner includes four fuel injectors arranged in two pairs of coaxial injectors 2a, 2b and 2c, 2d.

[0100] Other arrangements and combinations of injectors are possible.

[0101] In [Fig. 6], a schematic side view of an installation 4 is shown according to a An example of an embodiment of the invention. This includes a burner 1 according to an example of the invention comprising four fuel injectors 5a, 5b, 5c, 5d. In this example, the isolation devices are arranged upstream of the burner, on the burner's fuel supply circuits.

[0102] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention. In addition, the various characteristics, forms, variants and embodiments of the invention can be associated with each other in various combinations to the extent that they are not incompatible or mutually exclusive.

Claims

Claims

1. Method for controlling a burner (1) supplied with a gaseous fuel of which a property (P) has a value (PA) variable between a minimum value (PI) and a maximum value (P2), the burner comprising a set of fuel injectors (2a, 2b, 2c, 2d) capable of being supplied with fuel, characterized in that the method comprises a step of selecting one or more injectors (2a, 2b, 2c, 2d) to be supplied with fuel according to the value (PA) of the property (P) of the fuel.

2. Method according to the preceding claim, characterized in that the scale between the minimum value (PI) and the maximum value (P2) is divided into a number of ranges of values ​​and in that each of these ranges of values ​​is associated with one or more fuel injectors (2a, 2b, 2c, 2d) to be supplied with fuel, the method comprising a step of determining the range of values ​​to which the value (PA) of the property (P) of the fuel belongs followed by a step of supplying fuel to the fuel injector(s) (2a, 2b, 2c, 2d) associated with this range of values, the other injector(s) (2a, 2b, 2c, 2d) not being supplied with fuel.

3. A method according to any preceding claim wherein the gaseous fuel comprises at least two gases and wherein said property is the proportion of one of the gases.

4. A method according to the preceding claim wherein said gas is hydrogen.

5. Burner comprising a set of fuel injectors (2a, 2b, 2c, 2d) suitable for use in implementing a method according to one of the preceding claims.

6. Burner according to the preceding claim, characterized in that the fuel injectors (2a, 2b, 2c, 2d) form concentric rings.

7. Burner according to claim 5 or 6, characterized in that at least one fuel injector (2a, 2b, 2c, 2d) is supplied via an isolation device (3a, 3b, 3c, 3d) allowing the supply or not of fuel to said injector.

8. Installation (4) for heating an industrial furnace, characterized in that it comprises a burner (1) according to one of claims 5 to 7 and computer control means configured to receive a value (PA) of the property (P) of the fuel and to determine the injector(s) to be supplied with fuel according to the value (PA).

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