EP0421903B1 - 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 component in tangential or peripheral direction 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 total amount of 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 fed 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 implementing this method, which can operate with greater efficiency. low proportion of primary air and have a greater range for adjusting the operating speed.

• - on dispose lesdits conduits de courants d'air primaire, présentant respectivement des composantes périphériques et axiales, radialement à l'extérieur de tout conduit de combustible ;
• - on envoie dans la zone centrale soit directement tout autour du conduit central d'alimentation en combustible et/ou radialement à l'intérieur du conduit annulaire d'alimentation en combustible, tout au plus une petite quantité d'air primaire d'au plus 20% de la totalité de l'air primaire, de telle façon que dans ladite zone centrale ne se produise aucune combustion notable du combustible, qualifiant ladite zone centrale de morte.

As regards the method, this objective is achieved for rotary tube ovens according to the first claim, in which fuels and primary combustion air are supplied concentrically in at least two ducts, said primary air itself being introduced. by at least two annular ducts respectively, by one in the form of a swirling air stream comprising peripheral flow components, and by the other in the form of an axial air stream comprising substantially flow components axial; according to the invention:

• - Said primary air ducts are arranged, having respectively peripheral and axial components, radially outside any fuel duct;
• - at most a small amount of primary air is sent to the central zone either directly around the central fuel supply duct and / or radially inside the annular fuel supply duct 20% of the total primary air, so that in said central zone no significant combustion of the fuel takes place, qualifying said central zone as dead.

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, the central zone is sent either directly around the central fuel supply duct and / or radially inside the annular fuel supply duct, qualifying the said central zone as dead.

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 burners known, 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 possible primary air is brought into this zone.

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 backward flow 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 rate, 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 provided 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 above-mentioned device, 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 the combustible and that the minimum radial distance from the center of the burner nozzle of the outlets of the swirling air and the 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 a radial direction with respect to the central nozzle holder for oil, thus provides a sufficient radial distance from the other annular openings for 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 the annular opening 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.

In addition, in the preferred embodiment of the invention, there is further provided an annular duct for solid and / or gaseous fuel, arranged 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 latter small proportion of primary air, in accordance with 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 comprised between the central support of the oil nozzle and the following internal wall in the radial direction for another supply of fuel 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 outward as possible in the radial direction and that it has, in addition, an external edge which projects beyond 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 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 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 may for example be made wide enough in the peripheral direction so that they close off 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 offset 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.
• La figure 1 représente une buse de brûleur 1 placée à l'extrémité d'un tube externe de brûleur 5", qui est en même temps la paroi externe d'un conduit 5'd'air primaire qui s'écoule en direction axiale.

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 shows 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 5 "external tube, various supply devices are fixed or connected by flanges.

The inlet of the axial air takes place via 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 line 22 derives from this main primary air line and this branch ends in 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 by line 21.

A tube 23, which is intended for supplying pulverized solid fuels, generally pulverized coal, is connected to the annular conduit 5 ′ 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 protrude axially towards the rear of the tubes situated more outside, so that, as can be seen in FIG. 1, adjustment devices 33, 34, 35 can be put in place. 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 projects clearly in the radial direction relative to the opening of the nozzle guarantees that the opening 4 of the following annular supply duct 4 ′ opens at a considerable radial distance from the central opening 2 of the flame stabilizer.

In the example shown, the radial distance D of the annular opening 4 relative to the axis of the burner is more than three times the radius d of the opening 2. The corresponding distances are indicated in FIG. 4, in which the D / d ratio 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 for 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 flange-shaped hub surrounding a central orifice 2. This hub has small openings 13. The outer face of the hub, that is to say the front face, carries fins 12 which guide the low 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 axially move the tube 4 "relative to the tube 5" without the function of the partitions 6 'being influenced thereby.

FIG. 2b shows 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 'relative 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 diverging flow of the swirling air leaving this opening.

Likewise, the edge 8, which projects forward in the axial direction, provides an axial outlet direction for 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 represents an embodiment of the burner nozzle which differs from the embodiment represented in FIG. 2 essentially by the presence of an additional duct 15 ′, for solid pulverulent 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 conduit 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 duct 15 ′ for solid fuels and a duct 19 ′ for gaseous fuels.

Conduits 4 'and 5' for the main proportion of primary air in the form of swirling air and air having an axial direction are arranged outside these two fuel conduits in the radial direction. The internal edge of the opening 15, by which a significant part of the primary combustion air can enter the burner in the form of solid fuel transport gas is at a distance D 'from the axis of the burner, which is more than twice the radius d of l 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 of operating a burner intended for equipping a rotary tube furnace have been created, which allow a reduced proportion of primary air and a greater adjustment range of the burner, which leads to lower energy consumption and a reduction in the formation of nitrogen oxides harmful to the environment.

Claims (14)

1. Process for operating a burner for rotary tube furnaces, in which fuels and primary combustion air are supplied concentrically, in at least two conduits, said primary air being itself introduced through at least two annular conduits (4', 5') respectively, through one in the form of a stream of eddying air comprising peripheral flow components, and through the other in the form of axial air current comprising substantially axial flow components, characterized in that:

- said conduits (4', 5') of primary air streams respectively having peripheral and axial components, are disposed radially outside any conduit for the fuel;

- only a small quantity of primary air being at the most 20% of the totality of the primary air is sent into the central zone (20) either directly all around the central fuel supply conduit (2) and/or radially inside the annular fuel supply conduit (15, 19), such that in said central zone there is no noticeable combustion of the fuel occurring, said central zone (2) being termed dead zone.

2. Process according to claim 1, characterized in that the percentage of primary combustion air sent into said central dead zone (20) is less than 10% of the total quantity of primary air including any vector gas for a solid fuel.

3. Process according to any one of claims 1 or 2, characterized in that the proportion of primary combustion air is comprised between 2% and 10% of the total combustion air and, preferably, less than 6%.

4. Burner for a rotary tube furnace, of the type comprising a burner nozzle, equipped with substantially concentric fuel supply conduits and primary combustion air conduits comprising axial air and eddying air, characterized in that the outlet orifices (4, 5) for the eddying air and for the axial air are disposed radially outside the outlet openings for the fuels (10, 15, 19), and in that the minimum radial distance of said outlet openings (4, 5) for the major part of the primary air with respect to the centre of the nozzle of the burner (1), is at least twice the radius of the central opening (2) of a flame stabilizer (3).

5. Burner according to claim 4, 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) for the eddying primary air and the axial air and outside the flame stabilizer (3).

6. Burner according to any one of claims 4 or 5, characterized in that the flame stabilizer (3) is disposed at the front end of a central oil nozzle-holder.

7. Burner according to any one of claims 4 to 6, characterized in that the flame stabilizer (3) comprises openings (13) for the passage of a small part of the primary combustion air, which are located outside the central opening (2).

8. Burner according to any one of claims 4 to 7, characterized in that the outlet opening (5) for axial air is located radially as far to the outside as possible and comprises an outer edge (8) which projects axially towards the front.

9. Burner according to any one of claims 4 to 8, characterized in that the annular supply conduits present, upstream of their outlet opening (4, 5, 15, 19) conical wall portions (6, 7, 16, 17) which are axially displaceable with respect to one another.

10. Burner according to claim 9, characterized in that at least certain of the annular supply conduits comprise a cylindrical terminal portion (9) of at least one wall (6, 7, 16, 17) of each of said supply conduits, which is located between the conical wall portion and the annular outlet opening.

11. Burner according to any one of claims 8 to 10, 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, disposed in a ring and extending axially.

12. Burner according to claim 11, characterized in that the section of the annular passage (5) for the axial air or the corresponding channels disposed in a ring are at least in part closed or adapted to be obturated.

13. Burner according to any one of claims 11 or 12, characterized in that the sum of the sections of free passage of the axial channels is substantially smaller than the section of the annular conduit (5') for the primary air flowing in axial direction.

14. Burner according to any one of claims 4 to 13, characterized in that the flame stabilizer (4) is offset axially to the rear with respect to the outlet openings (4, 5, 15, 19) for the eddying air, the axial air and/or for the solid or gaseous fuels.

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