Regenerative burner for highly reduced NOX emissions

Abstract

The invention relates to a burner with a refractory burner body 1, 2, 3 for burning fluid or aerosolized, in particular gaseous, fuels. With the aim of reducing NOx emissions, the burner body has a gas nozzle 7, 9, 10, 11 and several air nozzles 4, 6, which are at least partially formed as integral features within the burner body and exit at a front face 16 of the burner body. The air nozzles are arranged symmetrically around the gas nozzle and diverge at an angle α to the gas nozzle. The invention also relates to a method for burning fluid or aerosolized, in particular gaseous, fuels with reduced NOx emissions.

Description

[0001] The invention relates to a burner for burning fluid or aerosolized, in particular gaseous, fuels, which can be used for heating, melting, and keeping warm in processes with high temperature requirements, such as in melting furnaces. A corresponding method is also described.

[0002] Examples of gaseous fuels include natural gas (with a major component of methane), ethane, propane, butane, ethene, pentanes and hydrogen.

[0003] One of the mechanisms by which NOx (nitrogen oxide) is formed is thermal NOx. This occurs when a mixture of nitrogen and oxygen reaches very high temperatures for a certain period of time. The influence of high temperatures is disproportionately large in this process. Regenerative burners in aluminum melting furnaces are particularly susceptible to the formation of thermal NOx. This is because the temperatures inside the furnace can reach very high levels, and the air is preheated to a very high temperature before combustion. This results in very high peak temperatures in the flame, which in turn can lead to high NOx emissions.

[0004] The following methods for reducing NOx emissions are already known from the state of the art: Oxygen burners reduce NOx emissions due to the absence of nitrogen. However, combustion must be precisely controlled. If air comes into contact with the flame due to leaks in the furnace chamber or other phenomena, NOx emissions increase sharply.

[0005] A larger distance between the air and gas nozzles promotes better internal recirculation. However, this has the disadvantage of increasing the size of the burner head, thus creating a space constraint. Furthermore, with an unfavorable charging process in a decentralized gas lance, the mixing of air and gas can be interrupted, potentially leading to CO (carbon monoxide) emissions.

[0006] External recirculation between air and gas is possible, but reduces the efficiency of the burner and is complex to implement.

[0007] Alternatively, staged combustion can be carried out, but this can only reduce emissions to a certain point or degree.

[0008] DE 41 42 401 A1 describes a method for operating a furnace heating system based on one or more burners. In this process, oxygen is used, among other things, for the combustion of the fuel to reduce nitrogen oxide formation.

[0009] US 3,418,062 A discloses a burner with a refractory burner body for burning fluid or aerosolized, in particular gaseous, fuels. The burner body has a gas nozzle and several air nozzles, which are at least partially formed as integral features within the burner body and exit at a front face of the burner body. The air nozzles are arranged symmetrically around the gas nozzle and diverge at an angle α to the gas nozzle.

[0010] US 7,175,423 B1 discloses a flat-flame burner comprising a burner body, a gas nozzle, and several air nozzles, which are at least partially formed as integral features within the burner body and exit at a front face of the burner body. The air nozzles are arranged symmetrically around the gas nozzle and diverge at an angle α to the gas nozzle.

[0011] The object of the present invention is to reduce NOx emissions while simultaneously providing an efficient and cost-effective burner.

[0012] The invention provides a burner according to claim 1 for burning fluid or aerosolized, in particular gaseous, fuels. Specifically, it is a burner with a refractory burner body. The burner body has a gas nozzle and several air nozzles, which are at least partially formed as integral features within the burner body and protrude from a front face of the burner body. The air nozzles are arranged symmetrically around the gas nozzle and diverge at an angle α to the gas nozzle.

[0013] This has the advantage that, due to the expulsion and distribution of air away from the flame, lower NOx emissions are produced. Thus, the gas is not completely combusted immediately upon exiting the gas nozzle, but is first distributed within the furnace. The angle allows the air to be expelled at a diverging angle, lengthening the flame and increasing the mixing of air and natural gas with exhaust gas, resulting in lower peak temperatures and therefore also lower NOx emissions.

[0014] The longer flame front, which results from the symmetrical distribution of the air expelled from the air nozzles, leads to a more uniform heat transfer with no or only slight temperature peaks.

[0015] As a result, but also due to the stronger temperature distribution, the refractory material, especially that of the burner, experiences less stress, thereby extending the service life of the material and the device equipped with it.

[0016] The symmetrical arrangement of the air nozzles, in particular their outlet opening(s) at the outlet or front of the burner, means, among other things, that they are arranged concentrically around the gas nozzle and have at least one axis of symmetry. In the case of multiple axes of symmetry, each axis can have the same angle to the adjacent axis of symmetry. Additionally, the air nozzles can be positioned at different distances from the gas nozzle. Preferably, the air nozzles are located on one or more, in particular concentric, circles around the gas nozzle and are evenly distributed on this or these circles, i.e., arranged at equal intervals from each other on the respective circle.In a preferred embodiment, the air nozzles on an outer circle are aligned with an angle β and the air nozzles on the inner circle(s) are aligned with an angle α, wherein the angle α is smaller than the angle β; alternatively, the angle of the air nozzles of a circle becomes linearly or exponentially smaller with each circle closer to the gas nozzle.

[0017] Similarly, the axes of symmetry can relate not only to the arrangement of the air nozzles, but also to their design, in particular their outlet opening(s). This refers to their shape and / or size or outlet area, which are designed to be point-symmetric and / or axially symmetric.

[0018] The use of air as a gas mixture also facilitates the manufacture and use of a corresponding system, in particular a furnace, with one or more burners according to the invention. In this process, ambient air is drawn in and then preferably filtered (to remove gases and / or dust), dried, pre-cooled and / or pre-heated before being directed into the air nozzles of the burner.

[0019] The gas nozzle is preferably supplied with gaseous fuel, but can also be operated with other fluid or aerosol fuels. In the case of aerosols, i.e., solid or liquid particles in a gas, these particles constitute the fuel. Furthermore, the burner, particularly the gas outlet nozzle, can have an atomizer to distribute and mix the particles in the gas.

[0020] Furthermore, it has proven advantageous if the angle α between the gas nozzle and one or more air nozzles, in particular one or more main combustion air nozzles, is in the range of 1 to 45 degrees. Preferably, the angle α is 4 degrees. The smaller the angle α, the better the expelled air can entrain the gas. The larger the angle α, the better the distribution of the expelled air in front of the burner or in the furnace. The air enters the combustion chamber via the air nozzle. Since the air nozzles are arranged diverging from each other, the air initially flows away from the gas jet. However, due to the increasing mixing with exhaust gas, the gas jet and the air jets spread out, so that after a certain time the gas jet and the air jets meet. The angle between the two air nozzles must therefore be smaller than the angle at which the jets spread out from the outlet opening (also known as the radiation angle).(Exit angle is denoted by the ). Here, the exit angle is preferably 18° and describes the directional effect of the nozzle. The directional effect of a nozzle refers in particular to the angle of the velocity vectors of the gas particles; the more proportion of the outgoing gas has a velocity parallel to the axis of a nozzle, the smaller the angle of the outgoing gas and the more effective and far-reaching the thrust of the outgoing gas.

[0021] To achieve improved air distribution with good directional action from the air nozzles, the burner body can have two to eight, preferably four, air nozzles. Furthermore, the symmetrical and directional air distribution increases with the number of air nozzles. While a small number of air nozzles allows for better mixing of the air with the exhaust gases, thus reducing gas combustion, combustion temperature, and NOx emissions, a larger number of air nozzles results in better symmetrical distribution. Four air nozzles represent an optimal configuration between NOx emissions and symmetrical distribution of the exhaust air.

[0022] Another advantageous design option lies in adjusting the size of the air nozzle outlets. The air nozzles should have outlet openings with a total area that is at most half the area of ​​a circle on the front of the burner body.

[0023] The air nozzles have outlet openings whose width increases radially from the gas nozzle. These outlet openings can form trapezoidal discharge surfaces on the front of the burner. This increases the quantity or volume of expelled air towards the outer edge of the front, ensuring that the mixing of air and gas does not occur abruptly at a single point, but rather continuously and evenly.

[0024] In a further advantageous embodiment, the gas nozzle has a pre-combustion chamber formed within the burner body. Additionally, each or at least one air nozzle has a pre-combustion air nozzle that connects the air nozzle to the pre-combustion chamber. By supplying a portion of the air from the air nozzle to the pre-combustion chamber, staged combustion by the burner occurs, which avoids or at least reduces temperature peaks. Furthermore, improved ignition of the gas-air mixture in the pre-combustion chamber is possible, particularly due to the better mixing of the fuel by a swirl nozzle and the supplied air via the pre-combustion air nozzle(s).

[0025] Furthermore, the gas nozzle preferably features a swirl nozzle for swirling the fuel, which is integrated into the burner body. This has the advantage of promoting mixing of the fuel with the air in and / or after the swirl nozzle and thus a spatially distributed combustion of the gas.

[0026] Preferably, the burner body is formed by a first burner block with the front face, a second burner block arranged coaxially to the first burner block, and a third burner block, in particular with a burner mouth, forming the outer shell of the first and second burner blocks. The split burner head or body is due to manufacturing considerations, as it facilitates casting. The burner blocks are preferably each cast in their own steel casing. Dividing the burner body into a first and second burner block simplifies the insertion of the gas outlet nozzle and the swirl nozzle. The burner mouth is funnel-shaped and can have an angle to the longitudinal or gas flame axis ranging from 15 to 75 degrees. Furthermore, in preferred embodiments, this angle is always greater than angle α to prevent the combustible gas and air from immediately compressing and mixing upon exiting the burner.Similarly, the burner mouth can be provided by the internal geometry of the furnace instead of on the third burner stone, which is why the third burner stone can be omitted in other embodiments of the burner body.

[0027] The burner stones are preferably cylindrical, but can also be cuboidal or elliptical. If the front face is rectangular, the air nozzles are arranged symmetrically around the gas nozzle, with the arrangement also being symmetrical to the rectangular front face of the burner, particularly the first and third burner stones.

[0028] Additionally or alternatively, the air nozzles, particularly their outlet opening(s), may have an outwardly tapered mouth or frame to accelerate the air and thus improve the directional effect of the expelled air. The same tapered feature may, additionally or alternatively, be incorporated into the gas nozzle, particularly its outlet opening(s). Furthermore, the aforementioned outlet openings may be shaped to expel the air and / or gas in a specific direction, thereby forming the aforementioned angle α.

[0029] The gas nozzle and / or air nozzles can be partially or completely integrally formed within the burner body through casting and / or mechanical post-processing. Additionally, components can be integrated into the burner body that at least partially form the nozzles and their paths or channels. These components can serve as connecting pieces between multi-part burner bricks, influence the direction and / or velocity of the gas or air, and / or seal the corresponding nozzle against external gases, as can be the case, for example, with a swirl nozzle. Preferably, compressed refractory wool or paper is used as a filling and / or sealing material in and / or around the burner, particularly between the burner bricks.

[0030] When using the burner, the air preferably exits at a speed of 80 to 200 m per second. The gas preferably exits at a speed of 30 to 100 m per second.

[0031] The present invention also discloses a method according to the invention for burning gaseous fuels with reduced NOx emissions according to claim 9. In this method, at least the following steps are carried out using the burner according to the invention: Providing a gaseous fuel; providing a gas mixture with oxygen and nitrogen, in particular air, suitable for oxidizing the fuel; expelling and igniting the fuel to form a gas flame; and expelling the gas mixture in at least two directions, each diverging at a certain angle α to the expelled fuel or to the gas flame.

[0032] The resulting advantages, such as lower NOx emissions, more uniform heat transfer and reduced stress on the refractory material, were explained in connection with the burner according to the invention.

[0033] Preferably, during the emission and ignition of the gaseous fuel, a partial volume of the gas mixture is supplied to the fuel in such a way that a certain percentage of the fuel pre-combustes. This pre-combustion results in a staged combustion of the gas, a more even temperature distribution, and the elimination, or at least the reduction, of temperature peaks during combustion.

[0034] Furthermore, the gaseous fuel is swirled and / or set into rotation before being discharged. This allows for better mixing with the gas mixture and thus a more spatially distributed combustion, instead of localized combustion areas.

[0035] Advantageously, the gas mixture is expelled in such a way that the at least two directions are equidistant from each other or have the same angle around the gas flame. In other words, the exit directions form imaginary intersection points on a plane perpendicular to the gas flame or its longitudinal axis, lying on a circle concentric with the flame and evenly distributed on this circle.

[0036] The figures described below refer to preferred embodiments of the burner according to the invention, and these figures serve not as a limitation but essentially to illustrate the invention. Elements from different figures, but with the same reference numerals, are identical; therefore, the description of an element from one figure is also valid for identically designated or numbered elements from other figures.

[0037] They show Figure 1 shows a cross-section through a burner according to a preferred embodiment; and Figure 2 shows a top view of the front of the burner. Figure 1 .

[0038] In Figure 1The burner 15 according to the invention is shown, comprising a burner body formed by a first burner brick 1, a second burner brick 2, and a third burner brick 3. All three burner bricks 1, 2, 3 are individual parts of the burner body and are in contact with one another. The first and second burner bricks 1, 2 are cylindrical, and the third burner brick 3 is a hollow cylinder, with the first and second burner bricks 1, 2 arranged within the third burner brick 3. This arrangement can be precisely fitted or, if inaccuracies in the dimensions exist, can be achieved or supported by insulating wool and / or refractory paper / wool between the burner bricks. For a predetermined alignment of the three burner bricks 1, 2, 3 relative to each other, they can have tongue-and-groove devices, rails, and / or projections or recesses, thereby enabling a targeted or predetermined arrangement of the burner bricks.

[0039] The burner 15 shown is equipped with a gas nozzle and four air nozzles. The gas nozzle preferably comprises the following components, arranged sequentially and coaxially or along a longitudinal axis 14: a hollow cylindrical outlet nozzle 11 made of metal, which is supplied with gas via a supply line 12; a swirl nozzle 9 for swirling the gas, which is inserted in the second burner block 2; a tubular mixing path 10, through which the swirled gas is conveyed; and a pre-combustion chamber 7, into which the mixing path 10 and four pre-combustion air nozzles or channels 5 of the air nozzles open. In this pre-combustion chamber 7, the swirled gas is mixed with the air from the pre-combustion air nozzles 5 and preferably ignited initially. The mixing path 10 and the pre-combustion chamber 7 are integrally formed in the first burner block 1. The swirl nozzle 9 is located at the transition from the second burner stone 2 to the first burner stone 1.The swirl nozzle 9 can be designed such that no gases from the boundary layer between the first and second burner blocks 1, 2 can enter the gas nozzle; i.e., the outer surface of the swirl nozzle 9 preferably seals the gas nozzle against unwanted gases or gas leaks. The outlet nozzle 11 is arranged in a cavity in the second burner block 2, with the gas supply line 12 being arranged in a cooling line 13, which preferably supplies cooled air to cool the supply line 12 and the outlet nozzle 11. This prevents premature ignition of the gas due to elevated temperatures, particularly before the gas enters the swirl nozzle 9. Furthermore, the air in the cooling line 13 protects the metallic components of the burner. In other embodiments, a burner can have multiple gas supply and cooling air lines.Each air nozzle preferably comprises the following components: an air channel 4 formed in the second burner block 2; a main combustion air nozzle or channel 6 formed in the first burner block 1 and connected to the air channel 4; and a pre-combustion air nozzle or channel 5, also formed in the first burner block 1 and branching off from the main burner air nozzle 6 into the pre-combustion chamber 7. Thus, with the exception of the outlet nozzle 11, the supply line 12, and the swirl nozzle 9, all other components of the burner 15, particularly those mentioned above, are formed by cavities in the burner blocks 1, 2, and 3.

[0040] In the Figure 1The angle α between the longitudinal axis 14 (or the gas nozzle) and an air nozzle is shown, indicating the airflow diverging towards the exiting gas or gas flame. In this case, the air duct 4 and the main combustion nozzle 6 are identical and form a channel with constant shape, thickness, and width from the rear of the burner 15 to the front 16 of the burner 15. The angle α is formed, in particular, between the longitudinal axis 14 and the inner side or edge of the air duct 4 or the main combustion nozzle 6. In other embodiments, the duct 4 and the nozzle 6 may differ; in these cases, other components, such as the outlet opening of the air nozzle, especially the main combustion air nozzle 6 at the front, may be designed such that the air is expelled at an angle α to the longitudinal axis 14.

[0041] Preferably, the burner body or at least one or all of the burner blocks 1, 2, 3 is refractory. The first burner block 1 has a circular front surface 16, and the third burner block 3 has a funnel-shaped, widening burner mouth 8. In particular, these components 16, 8, as well as the pre-combustion chamber 7, are at least refractory; or alternatively, the components that face the combustion or gas flame and / or are exposed to its heat / radiation. The four main combustion air nozzles 6 and the pre-combustion chamber 7 protrude from the front surface 16. These components form openings or exit surfaces that are arranged symmetrically around the longitudinal axis 14.

[0042] The in Figure 1The cross-section shown through the burner 15 according to the invention is taken at a specific angle, less than 180 degrees, along the longitudinal or symmetry axis 14. This makes both the gas supply channel for the gas nozzle and the air supply channel 4 for the air nozzle visible; finally, the four air nozzles are symmetrically designed and, with a straight cross-sectional area, would not show the cooling air line 13 with the supply line 12, unlike the angled surfaces shown. The air nozzle and gas nozzle, or rather their channels, are separated from each other in the second and third burner blocks 2, 3.

[0043] In Figure 2 The burner will be 15 off Figure 1The diagram shows a top view. In particular, the circular front surface 16 of the first burner block 1 and the annular burner mouth 8 of the third burner block 3 are shown. At the center of the front surface 16, through which the longitudinal axis of the burner 15 runs, is the partially blind opening of the pre-combustion chamber 7 with the subsequent mixing path 10 and the swirl nozzle 9. The pre-combustion chamber 7 is a partially blind opening because it is not completely sealed except for an annular base. The four openings to the pre-combustion air nozzles 5 are arranged at 90-degree angles to each other around the center point or longitudinal axis of this base.

[0044] The four openings of the main combustion air nozzles 6 are radiated from the longitudinal axis of the burner 15, in particular in a cross shape, and are identical to the four pre-combustion air nozzles 5. It should be noted that the area of ​​an outlet opening of the main combustion air nozzle 6 is the same size and / or shape as the cross-section of the main combustion air nozzle 6 within the first burner block 1. In other embodiments, the outlet openings and their connected channels, such as those of the main combustion air nozzles 6, the pre-combustion air nozzle 5, and the air channels 4, may differ in their shape and / or size. The openings shown each form a trapezoidal area that tapers towards the longitudinal axis and widens towards the outer circumference of the burner 15. Other shapes instead of the trapezoidal shape are possible in other embodiments. Reference symbol list

[0045] 1. First burner block, front of the burner 2. Second burner block, back of the burner 3. Third burner block, outer casing of the burner 4. Air duct 5. Pre-combustion air nozzle / duct 6. Main combustion air nozzle / duct 7. Pre-combustion chamber 8. Burner mouth 9. Swirl nozzle 10. Mixing path 11. Outlet nozzle 12. Gas nozzle supply line 13. Cooling air line 14. (Symmetry) axis 15. Burner 16. Front side / surface of the burner, especially of the first burner block

Claims

1. A burner (15) with a refractory burner body (1, 2, 3) for burning liquid or aerosol fuels, in particular, gaseous fuels, wherein the burner body comprises a gas nozzle (7, 9, 10, 11) and a plurality of air nozzles (6) which are at least partially formed as integral mouldings in the burner body and flow out on a front side (16) side of the burner body, wherein the air nozzles (6) are arranged symmetrically around the gas nozzle and diverge at an angle α to the gas nozzle, characterized in that the air nozzles (6) comprise outlet openings, the widths of which grow radially from the gas nozzle.

2. The burner according to claim 1, characterized in that the angle α is between 1 and 45 degrees.

3. The burner according to claims 1 or 2, characterized in that the burner body comprises two to eight, preferably four, air nozzles.

4. The burner according to any of claims 1 to 3, characterized in that the air nozzles comprise outlet openings with a total area that is not more than half of a circular surface of the front side (16) of the burner body.

5. The burner according to any of claims 1 to 4, characterized in that the gas nozzle comprises a pre-combustion chamber (7) which is formed in the burner body, and at least one air nozzle comprises a pre-combustion air nozzle (5), which connects the air nozzle to the pre-combustion chamber (7).

6. The burner according to any of claims 1 to 5, characterized in that the gas nozzle comprises a swirl nozzle (9) for swirling the fuel, which is used in the burner body.

7. The burner according to any of claims 1 to 6, characterized in that the burner body is formed by a first quarl (1) with the front side, a second quarl (2), which is arranged coaxially to the first quarl (1), and a third quarl (3) with a burner orifice (8) and is designed as an outer shell of the first and second quarl.

8. A method for burning gaseous fuels with reduced NOx emissions, wherein the following steps are performed: - providing a gaseous fuel; - providing a gas mixture with oxygen and nitrogen, which is suitable for oxidation of the fuel, wherein the gas mixture is air; - emitting and igniting the gaseous fuel into a gas flame; and - emitting air in at least two directions, each of which diverges at a certain angle α to the gas flame. characterized in that the air is emitted through outlet openings of air nozzles (6) of a burner (15) according to any one of the Claims 1-7, the width of which increases radially from a gas nozzle (7, 9, 10, 11) of a burner body (1, 2, 3) in such a way that the amount of emitted air increases towards an outer edge of a front side (16) of the burner body (1, 2, 3) so that the air is mixed with the gaseous fuel in a continuous and spatially distributed manner.

9. The method according to claim 8, characterized in that when emitting and igniting the gaseous fuel, such a partial volume of the gas mixture is provided to the fuel to burn a certain percentage of the fuel.

10. The method according to claims 8 or 9, characterized in that the gaseous fuel is swirled and / or rotated before being emitted.

11. Method according to any of claims 8 to 10, characterized in that the at least two directions are equally spaced from each other and have the same angle around the gas flame.

Images