Variable pulse burner

Abstract

The invention relates to a method for controlling a burner (1) supplied with a gaseous fuel, a property (P) of which fuel has a value (PA) that varies between a minimum value (PI) and a maximum value (P2), the burner comprising a set of fuel injectors (2a, 2b, 2c, 2d) suitable for being supplied with fuel, characterised in that the method comprises a step of selecting one or more injectors (2a, 2b, 2c, 2d) to be supplied with fuel depending on the value (PA) of the property (P) of the fuel. The scale between the minimum value and the maximum value is divided into a number of value ranges, each of these value ranges being associated with one or more fuel injectors. The method comprises a step of determining the value range to which the value (PA) of the property (P) of the fuel belongs, followed by a step of supplying fuel to the one or more fuel injectors associated with this value range, the one or more other injectors not being supplied with fuel.

Description

VARIABLE PULSE BURNER Designation of the technical field concerned

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

[0002] It particularly concerns burners used to heat products present in the oven.

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

[0004] Burners in industrial furnaces are often designed for one 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 flow rate of fuel and oxidant 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 present in an oven. The characteristics of the flame, in particular its shape and in particular its length and temperature, will have an impact on the transfer of energy to the products to be 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 increased by more than three times (depending on the PCI ratio) for a slightly lower air flow rate;

[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 another. It can also be very different if the two fuels are used as a mixture.

[0012] State-of-the-art burners are therefore not suitable for maintaining the desired heat distribution in a furnace when the fuel properties change significantly, for example when changing gas.

[0013] The invention overcomes 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] 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 burner axis or not, depending on the desired flame shape, wider or longer.

[0017] According to a first aspect of the invention, there is proposed a method for controlling a burner supplied with a gaseous fuel of which a property has a variable PA value between a minimum value and a maximum value, the burner comprising a set of fuel injectors capable of being supplied with fuel, characterized in that the method comprises 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 includes several fuel injectors so that the combustion characteristics, including the flame shape, can be adjusted by selecting which injectors are supplied with fuel and which are not.

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

[0021] The invention thus makes it possible to have a variable impulse burner, making it possible to adapt the impulse of the fuel jets 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 commissioning or stopping 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 each of these ranges of values ​​is associated with one or more fuel injectors to be supplied with fuel, the method comprising a step of determining the range of values ​​to which the value PA of the property of the fuel 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 only one injector in operation for the first range, only one injector in operation for the second range, and both injectors in operation for the third range.

[0026] Advantageously, the burner comprises a plurality of fuel injectors in order to have several possible combinations. The greater the number of injectors, the greater the precision of the burner adjustment will be.

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

[0028] The number of injectors and their flow sections can be determined according to the amplitude of the variation of the considered fuel property and its nature. They can be determined by calculation with modeling of the burner operation and / or by tests on a test bench.

[0029] The injectors to be supplied and those not to be supplied are determined in advance for each of the value ranges, according to the property considered. The choice of injectors to be in service for each value range can be determined by calculation with modeling of the burner 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] Depending on 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 that 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 speed, its quality and the properties of the flame.

[0034] The fuel property 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 which most modifies the combustion speed.

[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 an 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 greatly, this variation has a significant 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, there is provided a burner comprising a set of fuel injectors suitable for use in implementing a method 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 allows combustion to be modified, in particular the length of the flame, while maintaining the principles of distribution of fuel and 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 or non-supply of fuel to said injector.

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

[0043] There can be as many isolation devices as there are injectors or a different number. One isolation device can 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 which can increase as hydrogen becomes available or according to variations in the cost of hydrogen.

[0047] Since hydrogen combustion does not emit carbon dioxide, using hydrogen as a substitute for natural gas helps reduce CO2 emissions.

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

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

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

[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 characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0053] is a schematic and partial front view of a burner according to the state of the art,

[0054] is a schematic and partial front view of a burner according to a first exemplary embodiment of the invention,

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

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

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

[0058] is a schematic side view of an installation according to an exemplary embodiment of the invention. Detailed description of the invention

[0059] The embodiments described below being in no way limiting, it will be possible in particular to consider variants of the invention comprising only a selection of the characteristics described, subsequently isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection comprises at least one characteristic, preferably functional without structural details, or with only a part of the structural details if this part only is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art.

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

[0061] Consider a fuel consisting of natural gas, hydrogen, or a mixture of natural gas and hydrogen and a reheat furnace burner having two fuel injectors.

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

[0063] If we want to maintain the same fuel injection speed in 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 take into account, the combustion speed being almost ten times faster, it is then necessary to increase the flow speed of hydrogen compared to natural gas, depending on 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 in Table 1 below, depending on the proportion of hydrogen mixed with 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 for the natural gas / hydrogen exampleParameterValueUnitPower PCI5MWLambda1.2-PCI GN39MJ / Nm³Va0 GN10.6Nm³ / Nm³PCI H₂10.8MJ / Nm³Va0 H₂2.4Nm³ / Nm³Surface 1st injector2000mm²Surface 2nd injector1000mm²

[0067] Table 2: Example of flow rates and speeds according to the percentage of hydrogenNatural Gas% vol.1007050300H₂% vol.0305070100Natural Gas Flow RateNm 3 / h4623232311380Flow H2Nm 3 / h050083311671667Fuel flowNm 3 / h462823106413051667Air flowNm 3 / h587155505335512148001st injector speedm / s641141481812312nd injector speedm / s437699121154

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

[0069] In this case, using the two combined injections allows us to 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. Other 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 reduction of almost 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 achieve the same effect on flame length, while reducing flame temperature, thereby reducing NOx emissions.

[0073] The injection of water vapor also increases 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] Referring to the diagram of the attached drawings, a burner 10 according to the state of the art can be seen partially and schematically represented.

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

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

[0077] Referring to the diagram of the attached drawings, a burner 1 according to a first exemplary embodiment of the invention can be seen partially and schematically represented.

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

[0079] Fuel injector 2a has an exhaust area of ​​Sa mm², fuel injector 2b has an exhaust area of ​​Sb mm², fuel injector 2c has an exhaust area of ​​Sc mm² and fuel injector 2d has an exhaust area of ​​Sd mm².

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

[0081] According to another exemplary embodiment of the invention, the surface area of ​​Sb is 20% larger than that of Sa, that of Sc is 20% larger than the cumulative areas of Sa and Sb, and that of Sd is 20% larger than the cumulative 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 property P of the fuel taken into account for controlling the fuel injection and depending on its evolution, for example depending on the hydrogen concentration in the fuel.

[0083] According to an 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 controlling the injection of the fuel is the volume percentage of hydrogen in the fuel.

[0084] This is a diagram illustrating the implementation of the step of the method according to the invention where the pages of values ​​of the property P of the fuel taken into account for the control of the burner are determined.

[0085] In this example, the volume percentage of hydrogen in the fuel is considered. It can vary between 0%, corresponding to the value P1, and 100%, corresponding to the value P2.

[0086] The scale between P1 and P2 is split into four ranges of values, the R1 range from 0% to 24% hydrogen in the fuel, the R2 range from 25% to 49% hydrogen, the R3 range from 50% to 74% hydrogen and the R4 range from 75% to 100% hydrogen.

[0087] In this example, when the volume percentage of hydrogen in the fuel is in the R1 range, only injector 2a is supplied with fuel, while injectors 2b, 2c, and 2d are not supplied. When the volume percentage of hydrogen in the fuel is in the R2 range, 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 R3 range, 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 R4 range, 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 fuel is 60%, the control and command system of the installation determines that this PA value is in the R3 range. For burner operation, it opens the isolation devices 3a, 3b and 3c to allow fuel to be supplied to the injectors 2a, 2b and 2c and it keeps the isolation device 3d closed so as not to supply fuel to the 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 fuel's property P, its evolution between its minimum value P1 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 follow the rate of evolution of the fuel property P.

[0092] According to an exemplary embodiment of the invention, the fuel injection pressure is the same for all injectors. The burner is adjusted only 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 adjustment possibility of the burner.

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

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

[0096] In, a schematic and partial side view of the burner 1 of the is shown, with an enlargement 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, there is shown a schematic and partial front view of a burner according to a second exemplary embodiment of the invention.

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

[0100] Other injector arrangements and combinations are possible.

[0101] In, a schematic side view of an installation 4 according to an exemplary embodiment of the invention is shown. This comprises a burner 1 according to an exemplary embodiment 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 fuel supply circuits of the burner.

[0102] Of course, the invention is not limited to the examples just described and many adjustments can be made to these examples without departing from the scope of the invention. In addition, the various features, forms, variants 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

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 (P1) and a maximum value (P2), the burner comprising a set of fuel injectors (2a, 2b, 2c, 2d) capable of being supplied with fuel, in which 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, characterized in that the scale between the minimum value (P1) 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 injectors (2a, 2b, 2c, 2d) of fuel 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 followed belongs of a step of supplying fuel to the injector(s) (2a, 2b,2c, 2d) of fuel associated with this range of values, the other injector(s) (2a, 2b, 2c, 2d) not being supplied with fuel., A method according to the preceding claim, wherein the gaseous fuel comprises at least two gases and wherein said property is the proportion of one of the gases. Method according to the preceding claim, wherein said gas is hydrogen. 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, in which at least one fuel injector (2a, 2b, 2c, 2d) is supplied via an isolation device (3a, 3b, 3c, 3d) enabling the supply or non-supply of fuel to said injector. Burner according to the preceding claim, in which the fuel injectors (2a, 2b, 2c, 2d) form concentric rings. Installation (4) for heating an industrial furnace, characterized in that it comprises a burner (1) according to one of claims 4 or 5 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 as a function of the value (PA).

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