Facility comprising an improved premixing burner

Abstract

The invention relates to a premixing burner (2) intended to be installed in a combustion chamber (3), the burner (2) being configured to be supplied with oxidant and with fuel, this burner comprising: - a central annular shroud (4); and - a peripheral annular shroud (5), the central shroud (4) being positioned inside the peripheral shroud (5) so as to form an annular space (6) between these central and peripheral shrouds (4, 5), the burner (2) comprising at least one injection of fuel and at least one injection of oxidant into the annular space (6) so as to premix the fuel and the oxidant in the annular space (6), in which burner: - the peripheral shroud (5) comprises a first inclined portion (8) defining a peripheral angle α with a longitudinal center axis (C) of the burner (2); and - the central shroud (4) comprises a second inclined portion (7) defining a central angle β with the longitudinal center axis (C), the central angle β being between 0° and α°, in which burner (2) the second inclined portion (7) and the first inclined portion (8) define a convergent zone (26) such that the fuel and the oxidant are oriented in the direction of the longitudinal center axis (C), the burner further comprising a translation mechanism functionally arranged between the central shroud and the peripheral shroud, the central shroud being movable in translation relative to the peripheral shroud along the longitudinal center axis.

Description

Installation including an improved premix burner Technical field of the invention

[0001] The invention relates to the field of burners arranged in combustion chambers with low nitrogen oxide emissions. Technical background

[0002] There are many applications in which burners are found in conjunction with small combustion chambers. This is the case, for example, with boilers, and in particular with fire-tube boilers.

[0003] In these combustion chambers where the volume is restricted, the firebox, the site of combustion, has reduced dimensions and its volumetric load is therefore particularly high.

[0004] In these difficult conditions, controlling nitrogen oxide emissions is an important challenge.

[0005] To reduce nitrogen oxide emissions, manufacturers have implemented flue gas recirculation systems. These systems recycle a portion of the flue gases to deplete the oxidizer of oxygen, thereby reducing nitrogen oxide production.

[0006] Although these systems have proven their effectiveness, they generate other disadvantages.

[0007] The flue gas recirculation function complicates the design of these systems. They require a specific ductwork network and a suitable ventilation system. Consequently, the systems are larger and more expensive to purchase.

[0008] The flue gas recirculation function leads to increased energy consumption, as the ventilation system is energy-intensive and consumes electricity. Furthermore, the combustion reaction is affected by the recirculated flue gases, thus reducing the system's efficiency.

[0009] The challenge for users is therefore to overcome these drawbacks by having installations without smoke recirculation systems, while benefiting from low nitrogen oxide emissions.

[0010] We are familiar with the applicant's document WO2023126372 which describes a particular premix burner.

[0011] The burners emit nitrogen oxides (NOx) which are sources of pollution and are all the more difficult to control when the volume and / or diameter of the combustion chamber is small and the flame temperature is high.

[0012] These burners are subject to very different environmental regulations across different regions. The most common standards for nitrogen oxides in standard gas boilers are, in parts per million in the flue gases:

[0013] - Standard NOx – Standard NOx: < 50 ppm

[0014] - Low NOx – Low NOx: < 30 ppm

[0015] - Ultra low NOx – Ultra-Low NOx: < 10 ppm

[0016] Achieving a stable flame with standard NOx emissions in these often heavily loaded combustion chambers is a major industrial challenge for the sector. Decarbonizing industry requires achieving these performance levels with hydrogen, whose combustion emits no CO2, but more NOx due to its higher flame temperature compared to natural gas.

[0017] With hydrogen, the flame temperature being higher, the current ultra-low NOx technology is not sufficient (NOx emissions are about twice as high as with hydrogen).

[0018] Premixed combustion combined with gas staging offers the best NOx performance for natural gas, but requires adaptation to control flashback when operating on hydrogen.

[0019] Indeed, the speed of flame propagation in a mixture is much greater in hydrogen (≈22 m / s) than in natural gas (≈4 m / s), which facilitates flashback.

[0020] The use of flame arresters is prohibited in this type of application due to the pressure drop available on the combustion air (use of centrifugal fans and no blowers).

[0021] Another technical problem related to combustion is thermoacoustic resonance.

[0022] The pressure waves generated by the flame can resonate with the combustion chamber and create significant vibrations in the installation, even causing mechanical damage. These thermoacoustic resonances depend on a multitude of factors, such as the burner geometry, the combustion chamber geometry (smooth, corrugated, cylindrical, rectangular boiler or furnace, etc.), the power output, and the fuels used. The combination of all these factors cannot be predicted in industry. One way to avoid or control these thermoacoustic resonance phenomena is to avoid certain distance ratios between the fuel injector in the premix channel and the bottom of the combustion chamber.

[0023] To this end, a premix burner is proposed firstly, intended to be mounted in a combustion chamber, said burner being configured to be supplied with oxidizer and fuel, this burner comprising: - an annular central shell, and - an annular peripheral shell, the central shell being arranged in the peripheral shell so as to form an annular space in a direction of flow between said central and peripheral shells, the burner comprising at least one fuel injection and at least one oxidizer injection in the annular space so as to premix the fuel and the oxidizer in said annular space, burner in which: - the peripheral shell has a first inclined portion defining a peripheral angle α with a longitudinal central axis of said burner, and - the central shell has a second inclined portion defining a central angle β with the longitudinal central axis,the central angle β being between 0° and the value of the angle α°, burner in which the second inclined portion and the first inclined portion define a convergent zone such that the fuel and the oxidizer are oriented in the direction of the central longitudinal axis,

[0024] burner further comprising a translation mechanism capable of moving the central ferrule in translation relative to the peripheral ferrule, along the longitudinal central axis.

[0025] The peripheral angle α can be between 30° and 50°.

[0026] A spacing e can be defined between the first portion and the second portion, a linear premix zone delimited transversely by the second linear portion and by the second first linear portion, the linear zone defining a linear length H measured along the longitudinal central axis, in which the linear length H is at least equal to three times the spacing e.

[0027] The length H is advantageously less than five times the spacing e.

[0028] The burner may further include injectors positioned along the longitudinal central axis at a distance I from the entrance of the annular space, the injection distance l being at least equal to half the linear length H, and preferably less than 0.8 times the linear length H.

[0029] Preferably, the central shell integrates the fuel injection system and means for supplying fuel to the injection system, the injection system further comprising one or more injectors perpendicular or nearly perpendicular to the longitudinal central axis, each defining an injection direction having a non-zero component along the longitudinal central axis in the direction of flow.

[0030] According to one possibility, the injector(s) each define an injection direction having a non-zero component forming an injection angle γ with the longitudinal central axis taken in the direction of flow, the value of the injection angle γ being between 0° and less than or equal to 20° + / -0.05°.

[0031] Fuel injection devices can be arranged in the peripheral shell.

[0032] Fuel injection devices are advantageously suited to inject fuel through an injection end located in the combustion chamber.

[0033] Burner according to the preceding claim, wherein a longitudinal end and an injection end are separated from each other by a length N of offset measured along the longitudinal central axis, and the injection end is arranged upstream of the longitudinal end in a direction of oxidant movement.

[0034] According to a second aspect of the invention, an installation is proposed comprising a burner as previously described and a combustion chamber delimited laterally by a wall, this wall comprising an opening through which the burner is able to be inserted into said combustion chamber, an installation in which a longitudinal end of the peripheral ferrule located in the combustion chamber is arranged at a first insertion length D measured from the opening and along the longitudinal central axis. Brief description of the figures

[0035] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for which reference should be made to the attached drawing in which:

[0036] laest a cross-sectional view of an installation and a burner having the central ferrule in a first position according to the invention;

[0037] This is a close-up view of the burner whose central ferrule is in the first position;

[0038] laest a cross-sectional view of an installation and a burner having the central ferrule in a second position according to the invention;

[0039] This is a close-up view of the burner with its central ferrule in the second position; and

[0040] This is a top view of an injector from the central ferrule. Detailed description of the invention

[0041] On the east is represented an installation 1 comprising a burner 2 and a combustion chamber 3.

[0042] Burner 2 is a premix type. This means that the oxidizer and fuel are mixed inside burner 2. Burner 2 is therefore configured to be supplied with both oxidizer and fuel. Burner 2 is suitable for insertion into combustion chamber 3.

[0043] Burner 2 includes: - a central annular ferrule 4, and - a peripheral annular ferrule 5.

[0044] The central ferrule 4 is arranged within the peripheral ferrule 5 to form an annular space 6 between them. The burner 2 includes at least one fuel injection and at least one oxidizer injection into the annular space 6. Thus, premixing of the fuel and oxidizer is carried out in the annular space 6.

[0045] The central ferrule 4 has a second inclined portion 7. This second inclined portion 7 defines a central angle β with a central longitudinal axis C. The central angle β has a value between 0° and α°.

[0046] The peripheral ferrule 5 has a first inclined portion 8. The first inclined portion 8 defines a peripheral angle α with the central longitudinal axis C of the burner 2.

[0047] As can be seen in the figure, the second inclined portion 7 and the first inclined portion 8 together define a convergent zone 26. This convergent zone 26 allows the fuel-oxidizer mixture to be oriented towards the central longitudinal axis C.

[0048] This burner 2, particularly due to the peripheral α and central β angles defining the convergent zone 26, makes it possible to reduce the production of nitrogen oxides.

[0049] These angles reduce the cross-section at the premix circuit outlet, and this restriction accelerates the flow, thus generating a localized pressure drop around the annular circuit, which in turn creates an internal recirculation effect for the flue gases. This drawing of the gases back into the flame reduces nitrogen oxide production.

[0050] Advantageously, the peripheral angle α and the central angle β are measured in the counterclockwise or trigonometric direction. Thus, it is possible to obtain the convergent zone 26.

[0051] Advantageously, the peripheral angle α is between 30° and 50°. The applicant has determined that a peripheral angle α within this range makes it possible to reduce nitrogen oxide emissions without the use of a recirculation system.

[0052] Advantageously, the central ferrule 4 has a second linear portion 9. The second linear portion 9 is substantially parallel to the central longitudinal axis C and is located upstream of the second portion 7 inclined in the direction of oxidizer flow.

[0053] The direction of movement of the oxidizer is represented by an arrow F on the.

[0054] The peripheral ferrule 5 is provided with a first linear portion 10. This first linear portion 10 is substantially parallel to the central longitudinal axis C and is located upstream of the first portion 8 inclined in the direction of oxidizer flow. The first linear portion 10 of the peripheral ferrule 5 is located opposite the second linear portion 9 of the central ferrule 4.

[0055] The annular space 6 thus includes a linear premixing zone 11. The linear premixing zone 11 is delimited transversely, that is to say in a direction perpendicular to the central longitudinal axis C, by the second linear portion 9 on one side, and by the first linear portion 10 on the other.

[0056] The linear premixing zone 11 is defined by a linear length H measured along the central longitudinal axis C and by a spacing e measured between the second linear portion 9 and the first linear portion 10 in a transverse direction perpendicular to the central longitudinal axis C. The spacing e is therefore measured between the peripheral ferrule 5 and the central ferrule 4. In the linear premixing zone 11, the spacing e is constant along the linear length H.

[0057] Thus, the linear premix zone 11 is delimited longitudinally, that is, along the central longitudinal axis C, by a proximal end 12 and a distal end 13. The proximal end 12 is located on the side of the convergent zone 26; that is, the proximal end 12 is the one closest to the convergent zone 26. The distal end 13 is opposite the proximal end 12 and is therefore further from the convergent zone 26.

[0058] The linear premixing zone 11, arranged in this way, allows for a high-quality premix. This reduces the production of nitrogen oxides.

[0059] Advantageously, the linear length H is defined so that it is at least equal to three times the spacing e, and preferably less than five times the spacing e. The applicant has thus determined that such a linear length H makes it possible to obtain a sufficiently homogeneous premix, thereby reducing the production of nitrogen oxides by burner 2.

[0060] Advantageously, the burner 2 includes a fuel injection system 14. The fuel injection system 14 is arranged to inject fuel into the linear premix zone 11. These injectors are positioned along the axis of the boiler at a distance I from the inlet of the annular space.

[0061] Advantageously, the injection distance l is defined so that it is at least equal to half the linear length H, and preferably less than 0.8 times the linear length H.

[0062] By positioning the fuel injection system 14, away from the distal end 13 in the linear premix zone 11, the oxidant flow between the distal end 13 and the fuel injection system 14 has time to stabilize, allowing the mixing of fuel gas molecules and combustion air molecules, which subsequently improves the homogeneity of the premix and reduces the production of nitrogen oxides.

[0063] The central shell 4 integrates the fuel injection system 14 and means for supplying fuel to the injection system 14.

[0064] The injection system 14 further includes one or more injectors 141 perpendicular or almost perpendicular to the longitudinal central axis C, each defining an injection direction having a non-zero component along the longitudinal central axis C in the flow direction F.

[0065] Each injector 141 defines an injection direction with a non-zero component forming an injection angle γ with the longitudinal central axis C taken in the flow direction F. The value of the injection angle γ is between 0° and less than or equal to 20° + / - 0.05°. This is more clearly visible where the angle γ is represented. This injection angle prevents any fuel return in the opposite direction to the flow direction in all configurations of the central ferrule 4, which is moving in translation.

[0066] In practice, the central shell 4 is movable in translation along axis C and integrates the fuel injection system 14 and its fuel supply means

[0067] In addition, the injection system 14 includes one or more injectors oriented perpendicularly or almost perpendicularly to the longitudinal central axis C, and configured to inject the fuel radially from the center outwards from the linear premix zone 11.

[0068] Advantageously, this orientation of the injection system 14 allows for injection points to be mobile in translation during the movement of the central ferrule 4, and an injection distance l adjustable with the entry of the annular space to limit thermo-acoustic resonances.

[0069] Advantageously, the linear premixing zone 11 is fluidically connected to an oxidant supply sleeve 27. The annular space 6 is thus supplied with oxidant, in this case air, which can be mixed with a fuel, in this case hydrogen.

[0070] Advantageously, the central ferrule 4 includes a second annular end portion. This second end portion 15 is arranged downstream of the second inclined portion 7, in the direction of oxidizer flow. This second end portion 15 defines a first end diameter D1.

[0071] The peripheral ferrule 5 has an annular end 16. The annular end 16 defines a second end diameter D2.

[0072] It should be noted that the first end diameter D1 is measured from an external face of the central ferrule 4 and that the second end diameter D2 is measured from an internal face of the peripheral ferrule 5.

[0073] The duct 26 thus allows a portion of the fuel-oxidizer mixture to be ejected from the burner 2 in a direction substantially parallel to the central longitudinal axis C. This results in a stable flame while reducing the production of nitrogen oxides.

[0074] Advantageously, the central shell 4 includes fuel supply tubes 24 opening onto a central end 25 and capable of injecting fuel through this central end 25.

[0075] As previously mentioned, installation 1 includes a combustion chamber 3.

[0076] The combustion chamber 3 is laterally delimited by a wall 18. The wall 18 includes an opening 19 through which the burner 2 is suitable to be inserted into the combustion chamber 3.

[0077] A longitudinal end 20 of the peripheral ferrule 5 is located in the combustion chamber 3. The longitudinal end 20 is arranged at a first insertion length D measured from the opening 19 and along the central longitudinal axis C.

[0078] Advantageously, the burner 2 includes fuel injection devices 21. The fuel injection devices 21 are arranged in the peripheral ferrule 5. The fuel injection devices 21 are capable of injecting fuel through an injection end 22, also located in the combustion chamber 3.

[0079] The longitudinal end 20 and the injection end 22 are separated by a distance N offset. This offset length N is measured along the central longitudinal axis C, and the injection end 22 is positioned upstream of the longitudinal end 20 in the direction of oxidizer flow. This delays fuel ignition and thus allows for flue gas recirculation, reducing nitrogen oxide production.

[0080] The distance N is adjustable.

[0081] For example, it is adjusted by means of a translation mechanism functionally arranged between the central ferrule 4 and the peripheral ferrule 5, the central ferrule 4 being movable in translation relative to the peripheral ferrule 5, along the central longitudinal axis C.

[0082] As a non-limiting example, the translation mechanism is of the worm gear type.

[0083] This setting allows you to adjust the outlet section and thus maintain a sufficient speed to avoid backfire.

[0084] The ability to adjust this distance N also allows the position of the injector to be varied in the mixture stream, thus eliminating the phenomenon of resonances.

[0085] The fuel injection devices 21 are arranged in an annular manner in the peripheral ferrule 5.

Claims

Premix burner (2), intended to be mounted in a combustion chamber (3), said burner (2) being configured to be supplied with oxidizer and fuel, this burner comprising: - a central annular shell (4), and - a peripheral annular shell (5), the central shell (4) being arranged in the peripheral shell (5) so as to form an annular space (6) between said central and peripheral shells (4, 5), the burner (2) comprising at least one fuel injection and at least one oxidizer injection into the annular space (6) in a flow direction (F) so as to premix the fuel and the oxidizer in said annular space (6), burner (2) in which: - the peripheral shell (5) has a first inclined portion (8) defining a peripheral angle α with a central longitudinal axis (C) of said burner (2),and- the central ferrule (4) comprises a second inclined portion (7) defining a central angle β with the central longitudinal axis (C), the central angle β being between 0° and the value of the angle α, burner (2) in which the second inclined portion (7) and the first inclined portion (8) define a convergent zone (26) such that the fuel and the oxidizer are oriented in the direction of the central longitudinal axis (C), the burner further comprising a translation mechanism capable of moving the central ferrule in translation relative to the peripheral ferrule, along the central longitudinal axis. Burner according to the preceding claim, wherein the peripheral angle α is between 30° and 50°. Burner according to claim 1 or 2, wherein a spacing e is defined between the first portion (10) and the second portion (9), a linear premix zone (11) delimited transversely by the second linear portion (9) and by the first linear portion (10), the linear zone (11) defining a linear length H measured along the central longitudinal axis (C), wherein the linear length H is at least equal to three times the spacing e. Burner according to the preceding claim, wherein the length H is less than five times the spacing e. Burner according to any one of the preceding claims, further comprising injectors (14) positioned along the central longitudinal axis (C) at a distance I from the inlet of the annular space (6), the injection distance l being at least equal to half the linear length H, and preferably less than 0.8 times the linear length H. Burner according to the preceding claim, in which the central shell (4) integrates the fuel injection system (14) and means for supplying fuel to the injection system (14), the injection system (14) further comprising one or more injectors (141) perpendicular or quasi-perpendicular to the longitudinal central axis (C), each defining an injection direction having a non-zero component along the longitudinal central axis (C) in the flow direction (F). Burner according to claim 5, wherein the injector(s) (141) each define an injection direction having a non-zero component forming an injection angle γ with the longitudinal central axis (C) taken in the direction of flow (F), the value of the injection angle γ being between 0° and less than or equal to 20° + / -0.05°. Burner according to any one of the preceding claims, comprising fuel injection devices 21, said fuel injection devices (21) being arranged in the peripheral shell (5). Burner according to the preceding claim, wherein the fuel injection devices (21) are capable of injecting fuel through an injection end (22) located in the combustion chamber (3). Burner according to the preceding claim, wherein a longitudinal end (20) and an injection end (22) are separated from each other by a length N of offset measured along the central longitudinal axis ©, and the injection end (22) is arranged upstream of the longitudinal end (20) in a direction of movement of the oxidant (F). Installation (1) comprising a burner (2) according to one of the preceding claims and a combustion chamber (3) laterally delimited by a wall (18), this wall (18) comprising an opening (19) through which the burner (2) is able to be inserted into said combustion chamber (3), installation (1) in which a longitudinal end (20) of the peripheral shell (5) located in the combustion chamber (3) is arranged at a first insertion length D measured from the opening (19) and along the central longitudinal axis (C).

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