FR3105818A1 - Low NOx burner - Google Patents

Abstract

Burner comprising at least one stabilizer injector (5) comprising: - at least one oxidizer channel (6) opening onto a firebox via at least one oxidizer outlet (7), - at least one fuel channel (8) opening onto the firebox by at least one fuel outlet (9), and - an ignition device (10) capable of creating a flame and leading to the hearth by a central outlet (12), burner (4) in which the outlets (7, 9 , 12) are arranged in the following order from an exterior (16) of the stabilizer injector (5) to an interior (17) of said stabilizer injector (5): - oxidant outlet (7), - fuel outlet (9) , - central output (12). Figure for abstract: Figure 2

Description

Low NOx Burner

Technical field of the invention

The invention relates to a burner intended to be integrated into an industrial furnace or an industrial boiler as well as a method for implementing the burner. The invention relates more specifically to burners with low nitrogen oxide emissions.

Technical background

Burners are used in many industries. They are a key element in many industrial installations.

In order to obtain quality combustion, i.e. as close as possible to stoichiometric conditions, manufacturers try to maximize the mixture of fuel and oxidizer. This is achieved by ejecting the fuel at high velocity from the burner.

Referring to Figure 1, there are two zones A, B located downstream of a burner 1 according to the direction of movement of an oxidizer 2 and a fuel 3.

The proximal zone A corresponds to that closest to the burner 1 while the distal zone B corresponds to a zone further from said burner 1 and adjacent to the proximal zone A.

The high-speed ejection of the fuel 3 involves an initiation of combustion, that is to say the ignition of the fuel at a point called "hearth", at a distance far from the burner 1, more particularly in zone B distal. In proximal zone A, there is no ignition of fuel 3. In this proximal zone A, fuel 3 mixes with oxidizer 2.

Combustion in the distal B zone has characteristics conducive to the production of pollutants such as nitrogen oxides for several reasons.

According to a first aspect, in this distal zone B, the stoichiometric ratios are close to 1, the combustion is therefore substantially complete. This generates high temperature peaks, producing nitrogen oxides in large quantities.

According to a second aspect, starting from the simplistic assumption that the zones A, B proximal and distal are closed volumes, the power density of the combustion is particularly high insofar as this combustion takes place only in the zone B distal .

The invention aims to remedy this drawback, by proposing a burner configured to reduce the production of nitrogen oxides.

To this end, a burner is first proposed comprising at least one stabilizer injector comprising:

- at least one oxidizer channel leading to a hearth via at least one oxidizer outlet,

- at least one fuel channel leading to the hearth via at least one fuel outlet, and

- an ignition device capable of creating a flame and leading to the hearth through a central outlet,

burner in which the outlets are arranged in the following order from an exterior of the stabilizer injector to an interior of said stabilizer injector:

- combustion outlet,

- fuel outlet,

- central outlet.

This burner advantageously makes it possible to significantly reduce the overall production of nitrogen oxides by combustion by bringing the flame closer to the burner so that the ignition occurs in the proximal zone A. This bringing together makes it possible to carry out combustion under sub-stoichiometric conditions because the mixture of fuel and oxidizer is not optimal, that is to say incomplete combustion with an excess of fuel. The flame temperature reaches lower temperature peaks which mechanically reduces the production of nitrogen oxides. Moreover, the combustion reaction being incomplete, there is production of molecules of ammonia (NH ₃ ) and molecules of hydrocyanic acid (HCN), which subsequently react with the nitrogen oxides produced by the combustion and which eliminate. On the other hand, the decrease in nitrogen oxides is also due to a lower combustion power density in this burner. In the previously established hypothesis according to which the volume of the zones A, B proximal and distal is fixed, the inflammation in the zone A proximal allows combustion in a higher volume corresponding at least to the volume of the zone B distal to which is added at least part of the volume of the proximal zone A. Since combustion takes place in a larger volume, its power density is lower and its temperature is lower. The overall production of nitrogen oxides of the burner, object of the invention, is therefore significantly reduced.

Various additional features may be provided singly or in combination:

- the stabilizer injector comprises a plurality of fuel channels separate from each other and a plurality of oxidizer channels separate from each other;

- the stabilizer injector comprises a deflection device capable of deflecting the flow of oxidizer in the direction of the flow of fuel towards the inside of the stabilizer injector;

- the deflection device is arranged at a distal end of said stabilizer injector, the deflection device comprising the oxidant channels, the said oxidant channels being in fluid communication with an oxidant supply line, the oxidant channels extending along an oxidant axis secant to a longitudinal axis of the burner so as to deflect the oxidant flow in the direction of the fuel flow towards the inside of the stabilizer injector;

- the combustion axis of the combustion channels defines with the longitudinal axis, a first angle between 5° and 45°;

- the combustion axis of the combustion channels defines a second angle between 5° and 60°, said second angle being measured as follows:
a first plane is drawn passing through the center of the stabilizer injector and in which the longitudinal axis is inscribed,
a second plane st traced passing through the oxidizer supply pipe on the one hand, the second plane being parallel to the first plane on the other hand,
a third plane is drawn by defining an angle equal to the first angle with the second plane,
a first straight line is drawn inscribed in the third plane,
a second straight line is drawn in the third plane, this second straight line crossing the first straight line at a point located in the second plane, the second straight line defining with the first straight line, the second angle measured in the first plane;

- the burner comprises a flame stabilizer provided with a receiving zone in which the stabilizer injector is housed;

- the stabilizer injector comprises a body defining an outer casing of said stabilizer injector and comprising a distal end located on the side of the flame stabilizer, and in which, a first distance measured along the longitudinal axis of said stabilizer injector, between the distal end and the oxidizer outlets is between D1/5 and D1, where D1 is a barrel diameter at the distal end;

- the stabilizer injector comprises a body defining an outer casing of said stabilizer injector and comprising a distal end located on the side of the flame stabilizer, and in which, a second distance measured along the longitudinal axis of said stabilizer injector, between the distal end and the fuel outlets is between D1/5 and D1/2, where D1 is a diameter of the body at the distal end;

- the stabilizer injector comprises a body defining an outer casing of said stabilizer injector and comprising a distal end located on the side of the flame stabilizer, and in which the burner comprises a main injector separate from the stabilizer injector and arranged around the flame stabilizer flame, the main injector being supplied with a fuel identical to or different from that of the stabilizer injector, burner in which the stabilizer injector and the main injector are offset from each other along the longitudinal axis ;

- the stabilizer injector and the main injector are offset by a third distance measured between ends of said injectors, said ends being located on the side of the flame stabilizer, this third distance being measured along the longitudinal axis of the stabilizer injector and between 0 and D2, where D2 is the diameter of the flame stabilizer;

- the stabilizer injector is set back from the main injector along the longitudinal axis;

- the stabilizing injector comprises a flame attachment device arranged in the ignition device, the flame attachment device comprising an attachment element, the attachment element being located at a fourth distance from the distal end of the stabilizer injector, said fourth distance being between D1 / 5 and D1;

- the fuel channels extend along a fuel axis defining with the longitudinal axis a third angle between 0° and the first angle, the third angle being measured along the first transverse axis.

Secondly, a method for implementing a burner as previously described is proposed, the method comprising the following steps:

- inject an oxidizer into the oxidizer channel of the stabilizer injector,

- inject fuel into the fuel channel of the stabilizer injector,

- inject a mixture of fuel and oxidizer into the central channel of the stabilizer injector ignition device,

- initiate a flame in the ignition device,

process in which the flow rate of oxidizer injected into the oxidizer channel of the stabilizer injector is less than or equal to 20% of the total oxidizer flow rate of the burner.

Various additional features may be provided singly or in combination:

- the flow rate of oxidizer injected is between 0.5% and 10% of the total flow rate of oxidizer of the burner;

- the flow of fuel injected into the fuel channel of the stabilizer injector is less than 10% of the total fuel flow of the burner;

- the fuel flow is between 1% and 5% of the total burner fuel flow.

Brief description of figures

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

Figure 1 is a schematic representation of a burner according to the state of the art;

FIG. 2 is a view in two dimensions and in section of a stabilizer injector according to the invention;

Figure 3 is a geometric representation of planes and axes useful for understanding the invention;

FIG. 4 is a schematic front view of a burner according to the invention;

FIG. 5 is a view in two dimensions and in section of a burner according to the invention.

Detailed description of the invention

In Figure 2 is shown a burner 4 according to the invention. The burner 4 includes a stabilizing injector 5. The stabilizer injector 5 comprises a plurality of oxidizer channels 6. The oxidant channels 6 lead to a focus F via an oxidant outlet 7.

The stabilizer injector 5 comprises a plurality of fuel channels 8. The fuel channels 8 lead to the hearth F via a fuel outlet 9.

The stabilizer injector 5 comprises an ignition device 10. The ignition device 10 is capable of creating a flame intended to sustain the focus of the stabilizer injector 5. The ignition device 10 comprises a central channel 11 leading to the hearth via a central outlet 12.

The burner 4 includes a flame stabilizer 13. The flame stabilizer 13 is in the form of a disk comprising a reception zone 14. The stabilizer injector 5 is housed in the reception zone 14.

The burner 4 comprises a main injector 15 fed by a fuel identical to or different from the stabilizer injector 5. As can be seen in Figure 4, the flame stabilizer 13 is arranged inside the main injector 15. In other words, the main injector 15 is arranged around the flame stabilizer 13 and therefore around the stabilizer injector 5. The function of the stabilizing injector 5 is to maintain and stabilize the combustion of the main injector 15.

Outputs 7, 9, 12 are advantageously arranged in a particular order. As can be seen in Figure 2, starting from the outside 16 of the stabilizer injector 5 to the inside 17 of said stabilizer injector 5, the outlets 7, 9, 12 are arranged in the following order:
- oxidizer output 7,
- output 9 fuel,
- central exit 12.

Such an arrangement advantageously makes it possible to bring the focus closer to the injector stabilizer 5 and thereby bring the focus closer to the main injector 15. This bringing together of the hearth implies an incomplete combustion reaction. This advantageously makes it possible to reduce the combustion temperature and thereby reduce the quantity of nitrogen oxides produced. In addition, the excess fuel in the stabilizer injector 5 makes it possible to produce ammonia molecules which will react with the nitrogen oxides produced on the one hand by the stabilizer injector 5 and on the other hand by the injector 15 main. In addition, since the combustion takes place in a larger volume, the power density of the combustion decreases and therefore its temperature also decreases, reducing the production of nitrogen oxides.

The stabilizer injector 5 comprises a deflection device 18. The deflection device 18 is capable of deflecting the flow of oxidizer in the direction of the flow of fuel towards the interior 17 of the stabilizer injector 5. The stabilizer injector 5 comprises a tubular body 19 defining its outer casing. The stabilizer injector 5 comprises a distal end 20 located on the side of the flame stabilizer 13. The deflection device 18 is an attached part mounted integral with the body 19 of the stabilizer injector 5. The deflection device 18 is inserted into the body 5 through the distal end 20. The deflection device 18 includes the oxidizer channels 6. The oxidizer channels 6 are in fluid communication with an oxidizer supply line 21.

It is defined, in a non-exhaustive manner and without reference to terrestrial gravity, a trihedron comprising:
- a longitudinal axis X defining a direction of extension of the stabilizer injector 5 and of the burner 4,
- a first transverse Y axis perpendicular to the X axis and defining together with the Y axis an XY plane,
- A second transverse Z axis perpendicular to the X and Y axes and respectively defining with these axes, an XZ plane and a YZ plane.

The oxidant channels 6 are substantially cylindrical and extend along an oxidant axis 22 shown in the drawings by a straight line in dotted lines. The oxidizer is thus deflected in the direction of the fuel. This promotes the mixing of the oxidizer and the fuel, and creates a movement in the form of a hyperbole as can be seen in figure 2, conducive to inflammation. This movement is represented by discontinuous lines 27.

The combustion axis 22 defines with the longitudinal axis X a first angle α. The first angle α is between 5° and 45°. According to a preferred embodiment shown in the drawings, the first angle α is 40°. Such an arrangement contributes to bringing the focus of the stabilizer injector closer together and promotes mixing. The first angle α is measured as follows:

- a first plane P1 is drawn passing through the center of the stabilizer injector 5 and in which is inscribed the longitudinal X axis,

- a second plane P2 is drawn passing through the oxidizer supply pipe 21 on the one hand, the second plane P2 being drawn parallel to the first plane P1 on the other hand,

- a third plane P3 is drawn by defining an angle equal to the first angle α with the second plane P2, this geometrically implying that the third plane P3 also defines with the first plane P1, an angle equal to the first angle α,

- a first straight line D1 is drawn inscribed in the third plane P3, this straight line D1 therefore geometrically intersects the longitudinal X axis with an angle equal to the first angle α.

Combustion axis 22 defines a second angle β. The second angle β is between 5° and 60°. According to a preferred embodiment shown in the drawings, the second angle β is 27°. Such an arrangement helps to achieve a hyperbolic shape of the gas-fuel mixture, which is conducive to ignition. The second angle β is measured as follows:

- a first plane P1 is drawn passing through the center of the stabilizer injector 5 and in which is inscribed the longitudinal X axis,

- a second plane P2 is drawn passing through the oxidizer supply pipe 21 on the one hand, the second plane P2 being drawn parallel to the first plane P1 on the other hand,

- a third plane P3 is drawn by defining an angle equal to the first angle α with the second plane P2, this geometrically implying that the third plane P3 also defines with the first plane P1, an angle equal to the first angle α,

- a first straight line D1 is drawn inscribed in the third plane P3, this straight line D1 therefore geometrically intersects the longitudinal X axis with an angle equal to the first angle α,

- a second straight line D2 is drawn in the third plane P3, this second straight line D2 crossing the first straight line D1 at a point H situated in the second plane P2, the second straight line D2 defines with the first straight line D1 the second angle β measured in the foreground P1.

Ultimately , the line D2 corresponds to the oxidant axis 22.

The fuel channels 8 extend along a fuel axis 23. The fuel axis 23 defines with the longitudinal axis X, a third angle θ. According to a preferred embodiment shown in the drawings, the third angle θ defines an angle of 0° with the longitudinal axis X. Thus the fuel flow is ejected from the stabilizer injector 5 in a direction substantially parallel to the longitudinal axis X. The fuel flow crosses the oxidizer flow. The third angle θ can be between 0° and the value of the first angle α. The third angle θ is measured along the first transverse axis Y. Such an arrangement contributes to bringing the focal point of the stabilizer injector 5 closer together and promotes mixing.

Advantageously, a first distance L1 measured along the longitudinal axis X of the stabilizer injector 5 between the distal end 20 and the oxidant outlets 7 is between 1/5. D1 and D1, where D1 is a diameter of the body 19 at the distal end 20. According to a preferred embodiment shown in the drawings, the first distance L1 is 30 millimeters and D1 is 130.7 millimeters. Such an arrangement contributes to the bringing together of the focus of the injector 5 stabilizer.

Advantageously, a second distance L2 measured along the longitudinal axis X of the stabilizer injector 5 between the distal end 20 and the fuel outlets 9 is between 1/5. D1 and D1/2. According to a preferred embodiment shown in the drawings, the second distance L2 is 39 millimeters. Such an arrangement contributes to the bringing together of the focus of the injector 5 stabilizer.

Advantageously, a third distance L3 measured along the longitudinal axis X of the stabilizer injector 5 between the distal end 20 of said stabilizer injector 5 and an end 24 of the main injector is between 0 and D2, where D2 is a diameter of the 13 flame stabilizer. The offset is such that the stabilizer injector 5 is set back from the main injector 15 along the longitudinal axis X. According to a preferred embodiment shown in the drawings, the third distance L3 is 10 millimeters and D2 is 271 millimeters. Such an arrangement contributes to the bringing together of the focus of the injector 5 stabilizer.

Advantageously, the ignition device 10 comprises a hooking device 25 . The attachment device 25 comprises an attachment element 26. The attachment element 26 is in the form of a plate arranged at the distal end 20 of the stabilizer injector 5. The attachment element 26 is located at a fourth distance L4 from the distal end of the stabilizer injector 5. This distance is measured along the longitudinal axis. According to a preferred embodiment shown in the drawings, the fourth distance L4 is 5 millimeters. Such an arrangement contributes to the bringing together of the focus of the injector 5 stabilizer.

In what follows, there will be described a method of implementing the burner 4 previously described.

The process includes the following steps:
- injecting an oxidizer into the oxidizer supply pipe 21 in order to supply the oxidizer channels 6,
- inject fuel into the fuel channels 8 of the stabilizer injector 5,
- injecting a mixture of fuel and oxidizer into the central channel 11 of the ignition device 10,
- Initiate a flame in the ignition device 10.

In this process, the flow rate of oxidant injected into all of the oxidant channels 6 is less than or equal to 20% of the total flow rate of oxidant passing through the burner 4. This advantageously makes it possible to reduce the production of nitrogen oxide.

According to a preferred embodiment, optimal results have been obtained with a flow rate of oxidizer injected into the oxidizer channels 6 of the stabilizer injector 5 of between 0.5% and 10% of the total oxidizer flow rate of the burner 4.

The oxidizer used is air and the fuel used is gas.

Advantageously, the fuel flow injected into the fuel channels 8 of the stabilizer injector 5 is less than 10% of the total fuel flow passing through the burner 4.

According to a preferred embodiment, optimal results have been obtained with a fuel flow rate injected into the fuel channels 8 of between 1% and 5% of the total fuel flow rate of the burner 4.

Claims (18)

Burner (4) comprising at least one stabilizer injector (5) comprising:
- at least one oxidizer channel (6) leading to a hearth via at least one oxidizer outlet (7),
- at least one fuel channel (8) opening onto the hearth via at least one fuel outlet (9), and
- an ignition device (10) capable of creating a flame and leading to the hearth via a central outlet (12),
burner (4) in which the outlets (7, 9, 12) are arranged in the following order from an exterior (16) of the stabilizer injector (5) to an interior (17) of said stabilizer injector (5):
- oxidizer outlet (7),
- fuel outlet (9),
- central outlet (12). Burner (4) according to Claim 1, in which the stabilizer injector (5) comprises a plurality of fuel channels (8) distinct from each other and a plurality of oxidizer channels (6) distinct from each other. Burner (4) according to Claim 2, in which the stabilizer injector (5) comprises a deflection device (18) capable of deflecting the flow of oxidant in the direction of the flow of fuel towards the interior (17) of the injector (5) stabilizer. Burner (1) according to Claim 3, in which the deflection device (18) is arranged at a distal end (20) of the said stabilizer injector (5), the deflection device (18) comprising the oxidant channels (6), said oxidant channels (6) being in fluid communication with an oxidant supply line (21), the oxidant channels (6) extending along an oxidant axis (22) secant to a longitudinal axis (X) of the burner (4) so as to deflect the flow of oxidizer in the direction of the flow of fuel towards the inside (17) of the stabilizer injector (5). Burner (4) according to Claim 4, in which the combustion axis (22) of the combustion channels (6) defines, with the longitudinal axis (X), a first angle (α) of between 5° and 45°. Burner (4) according to Claim 5, in which the combustion axis (22) of the combustion channels (6) defines a second angle (β) comprised between 5° and 60°, the said second angle (β) being measured from the following way:
- a first plane (P1) is drawn passing through the center of the stabilizer injector (5) and in which is inscribed the longitudinal axis (X),
- a second plane (P2) st traced passing through the oxidizer supply pipe (21) on the one hand, the second plane (P2) being parallel to the first plane (P1) on the other hand,
- a third plane (P3) is drawn by defining an angle equal to the first angle (α) with the second plane (P2),
- a first straight line (D1) is drawn inscribed in the third plane (P3),
- a second straight line (D2) is drawn in the third plane (P3) this second straight line (D2) crossing the first straight line (D1) at a point (H) located in the second plane (P2), the second straight line (D2) defining with the first line (D1), the second angle (β) measured in the first plane (P1). Burner (4) according to any one of Claims 1 to 6, in which the latter comprises a flame stabilizer (13) provided with a receiving zone (14) in which the stabilizer injector (5) is housed. Burner (4) according to Claim 7, in which the stabilizer injector (5) comprises a body (19) defining an outer casing of the said stabilizer injector (5) and comprising a distal end (20) situated on the side of the stabilizer (13) of flame, and in which, a first distance (L1) measured along the longitudinal axis (X) of said stabilizer injector (5), between the distal end (20) and the oxidant outlets (7) is between D1 / 5 and D1, where D1 is a diameter of the body (19) at the distal end (20). Burner (4) according to any one of Claims 7 or 8, in which the stabilizer injector (5) comprises a body (19) defining an outer casing of the said stabilizer injector (5) and comprising a distal end (20) located on the side of the flame stabilizer (13), and in which a second distance (L2) measured along the longitudinal axis (X) of said stabilizer injector (5), between the distal end (20) and the fuel outlets (9) is between D1/5 and D1/2, where D1 is a diameter of the body (19) at the distal end (20). Burner (4) according to any one of Claims 7 to 9, in which the stabilizer injector (5) comprises a body (19) defining an outer casing of the said stabilizer injector (5) and comprising a distal end (20) located side of the flame stabilizer (13), and in which the burner (4) comprises a main injector (15) separate from the stabilizer injector (5) and arranged around the flame stabilizer (14), the injector (15 ) main being supplied with a fuel identical to or different from that of the stabilizer injector (5), burner (4) in which the stabilizer injector (5) and the main injector (15) are offset from one another the other along the longitudinal axis (X). Burner (4) according to Claim 10, in which the stabilizer injector (5) and the main injector (15) are offset by a third distance (L3) measured between ends (20, 24) of the said injectors (5, 15 ), said ends (20, 24) being located on the flame stabilizer (13) side, this third distance (L3) being measured along the longitudinal axis (X) of the stabilizer injector (5) and between 0 and D2, where D2 is the diameter of the flame stabilizer (13). Burner (4) according to Claim 11, in which the stabilizer injector (5) is recessed with respect to the main injector (15) along the longitudinal axis (X). Burner (4) according to any one of Claims 9 to 12, in which the stabilizer injector (5) comprises a flame retention device (25) arranged in the ignition device (10), the device (10 ) flame attachment comprising an attachment element (26), the attachment element (26) being located at a fourth distance (L4) from the distal end (20) of the stabilizer injector (5) , said fourth distance (L4) being between D1 / 5 and D1. Burner (4) according to any one of Claims 5 to 13, in which the fuel channels (8) extend along a fuel axis (23) defining with the longitudinal axis (X) a third angle (θ) comprised between 0° and the first angle (α), the third angle (θ) being measured along the first transverse axis (Y). A method of operating a burner (4) according to any preceding claim, the method comprising the following steps:
- inject an oxidizer into the oxidizer channel of the stabilizer injector,
- inject fuel into the fuel channel of the stabilizer injector,
- inject a mixture of fuel and oxidizer into the central channel of the stabilizer injector ignition device,
- initiate a flame in the ignition device,
process in which the flow rate of oxidizer injected into the oxidizer channel of the stabilizer injector is less than or equal to 20% of the total oxidizer flow rate of the burner. Process according to Claim 15, in which the flow rate of oxidant injected is between 0.5% and 10% of the total flow rate of oxidant of the burner. Process according to any one of Claims 15 or 16, in which the fuel flow rate injected into the fuel channel of the stabilizer injector is less than 10% of the total fuel flow rate of the burner. Process according to Claim 17, in which the fuel flow rate is between 1% and 5% of the total fuel flow rate of the burner.