EP0421903A2 - Process for operating a burner and burners for rotary drum furnace - Google Patents

Abstract

In a corresponding process, fuels and primary combustion air are introduced concentrically and the burner comprises a burner nozzle (1) which comprises concentric supply pipes for the fuel (10') and for the primary combustion air in the form of axial air (5') and swirling air (4'). In order to provide a process and a burner which can function with a lower proportion of primary air and a wider adjustment range, a dead zone is provided at the centre of the flame directly around a central fuel pipe and inside an annular fuel supply pipe, into which a very low proportion of fuel is sent. <IMAGE>

Description

The present invention relates to a method of operating a burner for a rotary tube furnace, in which fuels and primary air are supplied concentrically.

The present invention also relates to a burner for a rotary tubular furnace equipped with a burner nozzle equipped with fuel and primary air ducts, which are arranged substantially concentric to each other, which primary air comprises air rotated and air flowing axially.

A burner of this type is known from the DE patent. PS 2,905,746.

This known burner comprises, in addition to a central fuel supply for oil, another fuel supply arranged concentrically thereto for pulverized coal or any other similar fuel.

In order to obtain a good mixture, this arrival of solid fuel is between two primary air streams, one of which is the central stream, is rotated or swirled, that is to say that 'It has a tangential or peripheral direction component and the other of which, which is external, has an essentially axial flow speed in order to stabilize the flame which penetrates far into the rotary kiln.

In other known burners, provision is also made for the primary air flow to extend relatively far inside.

The known burner has in its center an inlet for liquid fuel, generally oil. The liquid fuel is sprayed into fine droplets by means of a nozzle and mixes after it leaves the central opening of the nozzle with primary air, which leaves the swirling air outlet opening, which opening is located radially around the central opening.

Known burners are usually operated with a proportion of primary air between 8% and 25% of the amount total combustion air.

The power of the burner is adjusted, that is to say the running speed by a respective reduction or increase in the fuel and the air supply in a determined adjustment range, in which the minimum adjustable speed to obtain a stable flame is approximately 20 to 25% of the maximum possible pace.

When starting the burner, as a general rule, oil must be injected through the central orifice of the nozzle and ignited in order to preheat the oven, since combustion of the solid fuel, which is conveyed concentrically, is not possible than in a sufficiently preheated oven.

With respect to this state of the art, the object of the present invention is to provide a method of operating a burner for a rotary tubular oven and also a burner intended for the implementation of this method, which can operate with greater efficiency. low proportion of primary air and have a greater range for adjusting the operating speed.

As regards the process, this objective is achieved by providing directly around a central fuel supply duct and / or radially inside an annular fuel supply duct, a central dead zone, into which at most a reduced proportion of the primary combustion air is sent.

Thus, thanks to the presence of a central dead zone, combustion begins at a greater distance in front of the center of the burner nozzle in comparison with known methods and burners.

Thus, seen in longitudinal section, starting from the center of the front end of the nozzle, the resulting flame has a central zone which extends forward and radially, in which practically no significant combustion of the fuel takes place. with the oxygen in the air.

Such a central flame core is certainly also present in principle in known burners, however according to the present invention, this central dead zone is caused consciously and enlarged and this more particularly by the fact that the least primary air is brought in. possible in this area.

However, even if it is not primarily intended for combustion, a small proportion of primary air can be brought into this central zone, and this small proportion of primary air nevertheless serves primarily to stabilize the flame and to prevent a reversal of combustion gases, coal ash and coke, which would otherwise lead to fouling of the central part of the nozzle.

A small flow of primary air in this central area, which is however below 20% and preferably below 10% of the total primary air, prevents such a return of the products of the combustion, without providing a lot of oxygen which would decrease the central area rich in fuel.

Surprisingly, it has been found that, thanks to the presence of such an enlarged central dead zone, the adjustment range of the burner can be considerably increased and this up to less than 10% of the maximum speed, for which the burner is designed for.

Insofar as such a burner must operate mainly with solid and pulverulent fuels, this means that after a brief preheating with oil, it can already operate with solid fuel.

At the same time, it has been found that in such a process and in a burner designed for this process, the proportion of primary air which must be used to stabilize the flame, can be reduced from 2 to 10% and, preferably , below 6% compared to the total quantity of combustion air. This facilitates the manufacture of primary air supply devices which can be designed respectively weaker.

A particular advantage of the reduced primary air consumption lies in the energy saving which is associated therewith for an equal performance in addition and also in the reduction of the proportion of nitrogen oxides in the combustion gases.

In accordance with the invention, it is intended that, apart from the introduction of a small proportion of primary air into the central zone, at least two other separate primary air streams are supplied, one of which is essentially axial and the other has a large part of the flow components in the peripheral direction.

With regard to the device mentioned above, the objective of the invention is achieved in that the inlet openings for the swirling air and the axial air are located outside the openings for the supply of fuel and that the minimum radial distance from the center of the burner nozzle of the outlet ports for swirling air and axial air is at least twice the radius of a central orifice of the flame stabilizer.

The flame stabilizer has a flange which surrounds a central opening, and which is located in the center of the burner nozzle and preferably at the end of a nozzle holder for oil. It helps to form and stabilize the flame. The flame stabilizer which overflows in the radial direction with respect to the central nozzle holder for the oil, thus provides a sufficient radial distance from the other annular openings for the primary air and / or other fuels which are located radially to the exterior of the flame stabilizer.

The radii of the central opening of the flame stabilizer and of the annular orifice for the innermost primary primary air stream are chosen so that the interior primary air stream is at a distance from the center of the nozzle which corresponds to at least twice the central opening of the flame stabilizer. Thus, the central opening of the flame stabilizer corresponds substantially to the orifice of the nozzle of the central fuel conduit.

In this way, it is avoided that the fuel leaving centrally comes into contact too early with the oxygen of the main streams of primary air.

Furthermore, in the preferred embodiment of the invention, there is further provided an annular duct for solid and / or gaseous fuel, disposed radially inside the primary air duct and radially outside. of the flame stabilizer.

The expression "primary air duct" generally refers to the major part of the primary air which is supplied axially or in swirling form and must not include the small proportion of primary air (central air) which is supplied in the central area of the flame to prevent the return of combustion products.

For the supply of this last small proportion of air primary, according to the invention, openings are provided in the flame stabilizer, outside the central opening.

The circulation of this small part of primary air takes place in an annular duct between the central support of the oil nozzle and the next internal wall in the radial direction for another fuel supply or for one of the main air streams primary.

In addition, it is advantageous that the outlet opening of the axial air stream is as far outside as possible in the radial direction and that it also has an external edge which projects axially.

This outer ring contributes to a better constancy of the axial direction of the air, so that the combustion is improved and the flame is stabilized.

According to the invention, the annular ducts for the supply of primary air and / or solid or gaseous fuel have conical walls and these walls, as well as the concentric tubes connected to them, are axially displaceable relative to one another. the other, so that one can thus adjust the free cross section of the annular passage.

However, preferably, the ends of each duct are cylindrical in order to avoid a divergent flow parallel to the direction of the conical walls.

According to the invention, in the conical part of the annular duct by the axial air, are arranged radial partitions intended for the axial orientation and for the circulation of the primary air in separate channels, which are arranged on a ring and which extend essentially in the axial direction.

These partitions contribute to an additional axial orientation of the corresponding primary air and also increase the axial outlet speed, by the fact that they reduce the free cross section of the annular duct and that they divide it into a plurality of individual channels arranged all around a ring. In addition, in a preferred embodiment of the invention, some of these channels are closed at least in part or are adjustable. For this purpose, the partitions can for example be made wide enough in the peripheral direction so that they seal a channel at least in part or that they correspond to a closed channel.

Thus it is possible to obtain that the sum of the free sections of the channels is less than the cross section of the annular duct for the primary air flowing in the axial direction.

As already explained, the axial flow speed of the air is thus increased, which further contributes to stabilizing the flame.

In addition, according to the invention, it is provided that the flame stabilizer is shifted rearward in an axial direction relative to the outlet openings of the main part of the primary air and solid or gaseous fuels. This can be achieved, for example, by attaching the flame stabilizer to the shell tube of the burner rod, which is axially displaceable, which tube is axially offset accordingly.

• Figure 1 : une vue d'ensemble d'un brûleur avec une partie des installations d'alimentation.
• Figure 2a : une section longitudinale d'un premier mode de réalisation d'une buse de brûleur.
• Figure 2b : une vue de gauche partielle de la figure 2a.
• Figure 3 : une coupe longitudinale d'un autre mode de réalisation d'une buse de brûleur avec possibilité d'amenée de combustibles solides pulvérisés.
• Figure 4 : une coupe longitudinale d'une buse de brûleur avec possibilité supplémentaire d'amenée d'un combustible gazeux.
• Figure 5 : une coupe longitudinale d'une buse de brûleur avec possibilité supplémentaire d'amenée d'un combustible solide et d'un combustible gazeux.

Other advantages, characteristics and possibilities of use of the present invention follow from the following description of preferred embodiments in relation to the drawings which represent:

• Figure 1: an overview of a burner with part of the supply installations.
• Figure 2a: a longitudinal section of a first embodiment of a burner nozzle.
• Figure 2b: a partial left view of Figure 2a.
• Figure 3: a longitudinal section of another embodiment of a burner nozzle with the possibility of supplying pulverized solid fuels.
• Figure 4: a longitudinal section of a burner nozzle with the additional possibility of supplying a gaseous fuel.
• Figure 5: a longitudinal section of a burner nozzle with the additional possibility of supplying a solid fuel and a gaseous fuel.

FIG. 1 represents a burner nozzle 1 placed at the end of an external burner tube 5˝, which is at the same time the external wall of a primary air duct 5 ′ which flows in the axial direction.

At the other end of the external tube 5˝, various supply devices are fixed or connected by flanges.

The inlet of the axial air takes place through a tube 25, the inlet of the swirling air takes place through a tube 24, and these two parts of primary air are adjustable separately by respective valves 45 and 44 and are connected on the same main primary air line. At the rear end of the burner shown in FIG. 1, a pipe 22 derives from this main primary air pipe and this branch leads into a tube which concentrically surrounds the envelope tube of the burner rod 10 ′.

Thus, a small part of the primary air coming from the bypass 22 flows through an annular duct 11 ′ and exits through openings 13 (cf. FIG. 2b) in the central zone of the flame. Liquid fuel, such as oil, is brought centrally to the burner nozzle via line 21.

A tube 23, which is intended for supplying pulverized solid fuels, generally pulverized coal, is connected to the annular duct 15 ′ visible in FIGS. 3 and 5.

The concentric tubes 10˝, 11˝, 4˝, 5˝, 15˝ and 19˝, which are engaged one in the other, have different lengths. The tubes placed more inside extend axially towards the rear of the tubes situated more outside, so that, as can be seen in FIG. 1, it is possible to install adjustment devices 33, 34, which allow relative axial displacement of the tubes relative to each other. For this purpose, the individual tubes are connected to each other by means of deformable bellows.

A control unit 30 is used for monitoring and controlling the primary air flows.

FIG. 2a represents a longitudinal section and FIG. 2b a partial front view of a burner nozzle which is designed to operate exclusively with a fuel, for example oil, arriving in the center.

The flame stabilizer 3, which is located at the end of the tube 10 ′, which envelops the nozzle holder rod of the oil burner and which protrudes clearly in the radial direction relative to the opening of the nozzle guarantees that the opening 4 of the annular supply duct along 4 ′ opens at a significant radial distance from the central opening 2 of the flame stabilizer.

In the example shown, the radial distance D from the opening annular 4 relative to the axis of the burner is more than three times the radius d of the opening 2. The corresponding distances are shown in Figure 4, in which the ratio D / d is even greater.

The zone situated essentially in front of the flame stabilizer constitutes a central dead zone 20, which is outside the central fuel stream and clearly inside the main inlet of primary air leaving the annular openings 4 and 5.

This dead zone can extend in the axial direction up to a multiple of the diameter of the flame stabilizer. A mixture of primary combustion air and sufficient fuel for flame formation occurs only outside of this central dead zone. The flame stabilizer 3 has a hub in the form of a flange surrounding a central orifice 2. This hub has small openings 13. The external face of the hub, that is to say the front face, carries fins 12 which guide the weak proportion of primary air leaving the openings 13.

The external supply duct 5 ′ has at its end conical walls 6, which diverge outwards. In the area of these walls 6 are juxtaposed partitions 6 ′, which have a longitudinal section of triangular shape. These triangular walls are juxtaposed along a common side which is parallel to the axis of the burner and which is placed at the same radial distance from this axis as the external wall of the duct 5 ′.

Thus, it is possible to move the tube 4˝ axially with respect to the tube 5˝ without the function of the partitions 6 ′ being influenced thereby.

We see in Figure 2b a front view of the front edges of the partitions 6 ′.

However, the partitions 6 ′ may also have in the peripheral direction a width sufficient to correspond to the parts situated between the channels 5 shown in FIG. 2. These parts can also be considered as closed channels 5.

The supply duct 4 ′ comprises, in front of the conical end, a device 14 for swirling the air, that is to say for rotating around the axis of the burner. This device consists essentially of air guide fins which are oriented obliquely to the axis of the burner.

Thanks to an axial displacement of the tube 11 ′ with respect to the tube 4 ′, the distance between the conical walls 7 of the conduit 4 ′ can be varied, so that the cross section of the conduit 4 ′ can thus be modified. The end part of the duct 4 ′ in the region of the opening 4 is however again cylindrical in order to avoid a divergent flow of the swirling air leaving this opening.

Likewise, the edge 8, which projects forward in the axial direction, provides an axial direction of exit of the axial air stream.

In connection with the direction of exit and the acceleration of the axial air in the duct 5, this guarantees a stable, uniform and long-range axial air flow.

FIG. 3 shows an embodiment of the burner nozzle which differs from the embodiment shown in FIG. 2 essentially by the presence of an additional duct 15 ′, for pulverulent solid fuels, which is located between the stabilizer of flame 3 and the swirling primary air duct 4 ′.

It is generally pulverized coal which is transported in the burner by a carrier gas, for example air. Due to the abrasive properties of such a solid fuel, the end region of the duct 15 ′ is only slightly conical in order to allow the fuel to pass as easily as possible.

FIG. 4 represents an embodiment comprising, in place of the conduit 15 ′ for solid fuel, another conduit 19 ′ for a gaseous fuel, the end section of which can be conical, as for the conduit 4 ′, and which may also include a device for swirling the gas leaving this pipe. In this case also, the end section of the duct 19 ′ has a cylindrical shape in the region of the opening 19, in order to avoid a divergence of the gaseous fuel which leaves it.

FIG. 5 represents an embodiment which comprises both a supply pipe 15 ′ for solid fuels and a pipe 19 ′ for gaseous fuels.

Ducts 4 ′ and 5 ′ for the main proportion of primary air in the form of swirling air and air having a direction axial are arranged outside these two fuel conduits in the radial direction. The internal edge of the opening 15, through which a significant part of the primary combustion air can enter the burner in the form of gas for transporting the solid fuel is at a distance D ′ from the axis of the burner, which is more than twice the radius d of the opening 2 of the flame stabilizer, so that in all cases, the center of the flame is guaranteed to have a sufficiently large dead zone, which provides the advantageous properties of the present invention.

By this invention, a burner and a method for operating a burner intended for equipping a rotary tube furnace have been created, which allow a reduced proportion of primary air and a greater range of adjustment of the burner, which leads to lower energy consumption and a reduction in the formation of nitrogen oxides harmful to the environment.

Claims (15)

1. Method for operating a burner for rotary tube ovens, in which fuels and primary combustion air are supplied concentrically, characterized in that, directly around a central duct (2) d ' fuel supply and / or radially inside an annular fuel supply duct (15, 19), a central dead zone (20) is provided, into which at most a reduced proportion of the primary combustion air. 2. Method according to claim 1, characterized in that the percentage of primary combustion air sent to said central dead zone (20) is less than 20% and, preferably, 10% of the total air of primary combustion, possibly including air used as carrier gas for solid fuels. 3. Method according to any one of claims 1 and 2, characterized in that at least two other streams of primary combustion air (4 ′, 5,) are sent into the burner, one of which has a essentially axial direction and the other of which has, for the most part, flow components in the peripheral direction, which streams are separated from the primary air supply sent to said central dead zone (20). 4. Method according to any one of claims 1 to 3, characterized in that the proportion of primary combustion air is between 2% and 10% of the total combustion air and, preferably, less than 6% . 5. Burner for a rotary tubular oven of the type comprising a burner nozzle (1), equipped with substantially concentric fuel supply ducts (10 ′, 15 ′, 19 ′) and primary combustion air ducts comprising the axial air and the rotated air, characterized in that the outlet orifices (4, 5) for the rotated air and for the axial air, are arranged radially outside the openings of fuel outlet (10, 15, 19) and in that the minimum radial distance of said outlet openings (4, 5) of most of the primary air from the center of the burner nozzle (1), s 'raises the radius of the central opening (2) of a flame stabilizer (3) to at least twice. 6. Burner according to claim 5, characterized in that it comprises an annular outlet opening (15. 19) for solid and / or gaseous fuels, which is located radially inside the outlet openings (4, 5 ) primary air rotated and axial air and outside the flame stabilizer (3). 7. Burner according to any one of claims 5 and 6, characterized in that the flame stabilizer (3) is arranged at the front end of a central oil nozzle holder. 8. Burner according to any one of claims 5 to 7, characterized in that the flame stabilizer (3) has openings (13) for the passage of a small part of the primary combustion air, which are located outside the central opening (2). 9. Burner according to any one of claims 5 to 8, characterized in that the outlet opening (5) of axial air is located radially as far outside as possible and has an external edge (8) which projects beyond axially forward. 10. Burner according to any one of claims 5 to 9, characterized in that the annular supply conduits have, upstream of their outlet opening (4, 5, 15, 19), portions of conical walls (6 , 7, 16, 17) which are axially movable relative to each other. 11. Burner according to claim 10, characterized in that at least some of the annular supply conduits comprise a cylindrical end portion (9) of at least one wall (6, 7, 16, 17) of each of said conduits d feed, which is located between the conical wall portion and the annular outlet opening. 12. Burner according to any one of claims 9 to 11, characterized in that the annular channel (5 ′) for the axial air comprises, in the conical zone (6). partitions (6 ′) for the supply and axial orientation of the primary air in separate channels, arranged on a ring and extending axially. 13. Burner according to claim 12, characterized in that the section of the annular passage (5) for the axial air or the corresponding channels arranged in a ring are partly at least closed or closable. 14. Burner according to any one of claims 12 to 13, characterized in that the sum of the free passage sections of the axial channels is substantially smaller than the section of the annular duct (5 ′) for the primary air flowing in axial direction. 15. Burner according to any one of claims 5 to 14, characterized in that the flame stabilizer (4) is offset axially backwards with respect to the outlet openings (4, 5, 15. 19) of the air in rotation, axial air and / or for solid or gaseous fuels.

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