WO2013091634A1

WO2013091634A1 - A method and a burner for introducing fuel into a burning zone of a kiln

Info

Publication number: WO2013091634A1
Application number: PCT/DK2012/050426
Authority: WO
Inventors: Karl Emil Andreas STRÖMBERG
Original assignee: Flsmidth A/S
Priority date: 2011-12-23
Filing date: 2012-11-20
Publication date: 2013-06-27

Abstract

A description is made of a method as well as a burner for introducing solid, liquid or gaseous fuel into a burning zone of a kiln, such as a rotary kiln for manufacturing cement clinker or similar products, by which method fuel is conducted through a number of ducts (3) to a discharge end (4) of a burner (1) having a centreline (11) and portions of primary air is conducted through ducts (5, 6; 14, 15) being arranged outside the fuel ducts (3) also to the discharge end (4) of the burner (1), and where the portions of primary air can be independently controlled. The peculiar feature of the method and burner is that the primary air is discharged from the discharge end (4) of the burner (1) in at least an inner an and outer set of air streams, where the air streams in at least one of the sets are discharged through each their nozzle (7a, 8a), where at least some of the air streams discharged from the nozzles (7a) in the outer set (9) have an axial velocity component (X₀) and a radial velocity component (Y₀) in the direction towards the centreline (11), where at least some of the air streams discharged from the nozzles (8a) in the inner set (10) have an axial velocity component (X_i) and a radial velocity component (Y _i) in the direction away from the centreline (11), and whereat least some of the air streams in a set collide with a neighbouring air stream. Hereby is obtained a method as well as a burner by means of which severe ignitable and slow burning fuels in a more effective way may be used for the firing into a kiln. This is mainly because the fuels by the method and burner according to the invention may be ignited relatively close to the burner and therefore in most cases have sufficient of the time to burn out completely before they fall into the material filling in the kiln.

Description

A method and a burner for introducing fuel into a burning zone of a kiln

The present invention relates to a method for introducing solid, liquid or gaseous fuel into a burning zone of a kiln, such as a rotary kiln for manufacturing cement clinker or similar products, by which method fuel is conducted through a number of ducts to a discharge end of a burner having a centreline and portions of primary air are conducted through ducts being arranged outside the fuel ducts also to the discharge end of the burner, and where the portions of primary air can be independently controlled. The invention also relates to a burner for carrying out the method according to the invention.

Burners for this purpose are well-known. Originally, they merely consisted of one single pipe through which a mixture of pulverized coal meal and air was injected into the burning zone of kiln. Over time, design improvements of the burners were implemented, with incorporation of features such as additional ducts for introducing other types of liquid or gaseous fuel. Furthermore, most modern burners comprise one or several separate ducts for injection of primary air, so that only a small amount of the primary air is injected together with the pulverized coal. By imparting a rotary motion to at least some of the injected primary air it has to a larger extent been possible to control the flame shape in the kiln. The fuel and primary air being injected into the kiln through the discharge end of the burner will inside the kiln mix with hot secondary air having a temperature about 1 .000 °C and normally coming from a cement clinker cooler situated next to the kiln causing ignition of the fuel. The distance from the discharge end of the burner to the point where the ignition of the fuel takes place depends on several factors, such as the kind of fuel, the mixing of fuel with secondary air, the rotary motion of the primary air and the axial velocities of the fuel and primary air.

One example of a burner of the abovementioned kind is described in EP 0 650 012 A1 . This known burner comprises one or several ducts for introduction of fuel, being surrounded by one single primary air duct which discharges into an annular nozzle. Immediately ahead of the nozzle the air is directed through a number of flexible tubes which, by means of a mechanism, can be bent sideways, thereby causing the air to rotate. The rotation of the air, and hence the flame shape, can thus be varied by changing the angle of bending of the tubes, and by changing the amount of primary air. The primary air is discharged from the discharge end of the burner through an annular nozzle, hence creating an annular jet stream of primary air surrounding the fuel being introduced.

A second example of a burner of the abovementioned kind is described in EP 0 965 019 B1 . Also this known burner comprises one or several ducts for introduction of fuel, being surrounded by two primary air ducts, where the air in one of these air ducts is made up of axial air, whereas the air in the second air duct comprises air which is made to rotate about the centre axis of the burner. The primary air ducts discharge into a joint annular collecting duct for conducting the mixed primary airstream to an annular nozzle at the discharge end of the burner. The nozzle area and thus the flame shape can be varied through an axial displacement of the two nozzle rings of the annular nozzle in relation to one another. Also, this burner configuration creates an annular jet stream of primary air surrounding the fuel being introduced.

A common drawback of the above described and similar burners is that they are not very suitable for the firing with severe ignitable and slow burning fuels because the fuels in such kind of burner are ignited relatively far away from the burner and therefore do not always have the time to burn out completely before they fall into the material filling in the kiln. The main reason for this late ignition is due to the slow mixing with hot secondary air, which is due to the primary air is injected as an annular jet stream, which forms a tubular sheath around the fuel and thereby shield the hot secondary air from coming into contact with the fuel. Even if these known burners could be adjusted to obtain ignition of the fuel closer to the burner, they would not be suitable for ignition to close to burner, because they are all relatively heat sensitive and have close tolerances which due to different thermal expansions radially through the burners complicates the setting thereof. Also, moving mechanical parts in an inaccessible area are used to regulate the burners. In addition, long-term deformations of the burners as a result of their own weight will change burner flow characteristics without the opportunity to give feedback to the operator. A further disadvantage of the known burners is that they occupy relatively much space in the kiln, whereby air velocity of secondary air from the clinker cooler is relatively high and thus able to carry inappropriate much dust up into the kiln.

The purpose of the present invention is to provide a method as well as a burner by means of which the above mentioned drawbacks may be eliminated or at least reduced. This is achieved by means of a method of the kind mentioned in the introduction and being characterized in that the primary air is discharged from the discharge end of the burner in at least an inner and an outer set of air streams, where the air streams in at least one of the sets are discharged through each their nozzle, where at least some of the air streams discharged from the nozzles in the outer set have an axial velocity component and a radial velocity component in the direction towards the centreline, where at least some of the air streams discharged from the nozzles in the inner circle have an axial velocity component and a radial velocity component in the direction away from the centreline, and where at least some of the air streams in a set collide with a neighbouring air stream.

The objective is further achieved by means of a burner for introducing solid, liquid or gaseous fuel into a burning zone of a kiln, such as a rotary kiln for manufacturing cement clinker or similar products, which burner comprises a centreline, ducts for conducting fuel to a discharge end of the burner and ducts being arranged outside the fuel ducts for conducting portions of primary air also to the discharge end of the burner, and where the portions of primary air are independently controllable, and being characterized in that it comprises at least an inner and an outer set of stationary nozzles for discharging the primary air from the discharge end of the burner into the kiln, where at least some of the nozzles in the outer set have an orientation that provide the air streams discharged there from with an axial velocity component and a radial velocity component in the direction towards the centreline, where at least some of the nozzles in the inner set have an orientation that provide the air streams discharged there from with an axial velocity component and a radial velocity component in the direction away from the centreline, and where the nozzles in a set are so arranged that at least some of the air streams from a set of nozzles collide with a neighbouring air stream.

Hereby is obtained a method as well as a burner by means of which severe ignitable and slow burning fuels in a more effective way may be used for the firing into a kiln. This is mainly because the fuels by the method and burner according to the invention may be ignited relatively close to the burner and therefore in most cases have sufficient of the time to burn out completely, before they fall into the material filling in the kiln. The reason why the ignition may take place closer to the burner is that the collision between air streams from at least two separate nozzles having opposite directed radial velocities creates turbulence and thus jet streams in this peripheral area, which jet streams draw hot secondary air from the surroundings in the direction towards the central area where it is brought into contact with the fuels, which thus ignite. Further, this collision between air streams creates a combined airstream with a combined velocity and direction, which may be controlled by extern means. In addition, a less heat sensitive burner with no critical tolerances, no mechanical parts in inaccessible area and no flow characteristics changes due to long-term deformations of the burner is obtained. Also, the burner according to the invention occupy less space in the kiln relative to known burners, whereby the velocity of secondary air from the clinker cooler is lower and thus able to carry less dust up into the kiln.

In one embodiment of the invention the air streams in at least two of the sets are discharged through each their nozzle. However, it is also conceivable that for some uses sufficient turbulence may be created if only the air streams in one set are discharged through each their nozzle. In this latter embodiment the air streams in the other set may be discharged through an annular air nozzle, where the air streams being discharged through each their nozzle preferably include the outer set of air streams. To further increase the creation of turbulence and thus jet streams in the peripheral area for drawing hot secondary air from the surroundings in the direction towards the central area and thus into contact with the fuels, it is preferred that least some of the air streams discharged from the nozzles in at least one of the sets of nozzles also have a tangential velocity component. The tangential velocity component of the air streams discharged from nozzles in the same set may in one embodiment be directed in the same direction. However, in another embodiment they may alternately be directed in opposite directions. Further, if air streams discharged from the nozzles in at least two sets have a tangential velocity component it is preferred that the tangential velocity component of at least some of the air streams in one set is directed in the opposite direction to the tangential velocity component of at least some of the air streams in the other set. Even it may be possible as intimated above that at least some of the air streams in one set collide with a neighbouring air stream in the same set, it is preferred that at least some of the air streams in one set collide with a neighbouring air stream in at least one of the other sets of air streams. The primary air may be conducted to the nozzles at the discharge end of the burner via at least two concentric annular ducts, where the outer duct is used for conducting primary air to the nozzles in the outer set and the inner duct is used for conducting primary air to the nozzle(s) in the inner outer set. In this way the amount of primary air to the sets of air streams may be regulated independently by extern means, i.e. means arranged outside the burner. However, in another embodiment it may be preferred that each nozzle is supplied with the primary air trough each their duct, whereby the amount of primary air being conducted to each nozzle may be regulated independently by extern means. In this way, e.g. the primary air to an optional number of nozzles may be shut off or brought down to idle mode for a period which may be advantageous during for example startup. Further, in some situations it might be advantageously that a third stream of primary air is discharged from the discharge end of the burner through an intermediate third set of nozzles, where at least some of the air streams discharged from said third set of nozzles only have an axial velocity component and a tangential velocity component. In a particular embodiment, a number, preferably half, of the air streams discharged from said third set of nozzles may have a tangential velocity component in one direction and the remaining air streams in the opposite direction. In such an embodiment the primary air conducted to each nozzle in this third set is preferably conducted trough each their duct, so the amount of primary air being conducted to each nozzle may be regulated independently by extern means.

The burner according to the invention may comprise at least two concentric annular ducts being arranged radially outside the fuel ducts for conducting primary air to nozzles at the discharge end of the burner, where the outer duct is used for conducting primary air to the nozzles in the outer set and the inner duct is used for conducting primary air to the nozzles in the inner set. In this embodiment the burner may further comprise means for independently regulating the amount of primary air being conducted to each set of air streams.

In another embodiment the burner may comprise one duct for each nozzle for conducting the primary air separately trough each duct to the respective nozzle. In this embodiment the burner may further comprise means for independently regulating the amount of primary air being conducted to each nozzle.

The sets of stationary nozzles for discharging the primary air from the discharge end of the burner into the kiln may be provided in any appropriate manner. Thus, in one embodiment they may simply be provided as the end sections of the ducts for conducting the primary air to the nozzles. In another embodiment, the burner may comprise at least one nozzle plate being arranged at the discharge end of the burner and comprising at least some of the nozzles. In such an embodiment, the nozzles may simply be constituted of cylindrical holes made in the nozzles plate with the required directions for obtaining the desired velocity components. The burner may in a particular embodiment comprise two or more annular concentric nozzle plates, the angular position of which may be adjusted to obtain different collision patterns. Further, the sets of nozzles, preferably the inner set, may be constituted by an annular air nozzle(s).

The invention will now be described in further details with reference to the drawing, being diagrammatical, and where

Fig. 1 shows a perspective view with parts cut away of a first embodiment of a burner according to the invention,

Fig. 2 shows a sectional view of an alternative embodiment of the burner according to the invention, and

Fig. 3 and 3A show details of the burner according to the invention.

In Fig. 1 is shown a burner 1 according to the invention comprising a centreline 1 1 , a number of ducts 3 for conducting fuel to a discharge end 4 of the burner 1 and ducts 5, 6 being arranged radially outside the fuel ducts 3 for conducting portions of primary air also to the discharge end 4 of the burner. The burner may further comprise additional annular ducts, not shown, being arranged radially outside the fuel ducts 3 for conducting e.g. coal powder to the discharge end 4 of the burner. The portions of primary air being conducted through each primary air duct 5, 6 are independently controllable by means of extern means, such as valves, not shown.

In order to obtain that severe ignitable and slow burning fuels in a more effective way may be used for the firing into a kiln the shown burner according to the invention comprises two sets 7, 8 of stationary nozzles 7a, 8a for discharging the primary air from the discharge end 4 of the burner 1 into the kiln, where the centres of the nozzles 7a, 8a in the two sets lie on a circle 9, 10, respectively, being concentric in relation to the centreline 1 1 of the burner and having different diameters. Without being clearly shown in the figure, it should be understood that the nozzles 7a lying on the outer circle 9 have an orientation that provide the air streams discharged there from with an axial velocity component X₀, a radial velocity component Y₀ in the direction towards the centreline 1 1 and a tangential velocity component Z₀ in relation to the circles in one circumference direction, whereas the nozzles 8a lying on the inner circle 10 have an orientation that provide the air streams discharged there from with an axial velocity component Xi, a radial velocity component Y, in the direction away from the centreline and a tangential velocity component Z, in relation to the circles in the other circumference direction. Further the nozzles 7a, 8a in the two sets are so arranged in relation another that each air stream from one set of nozzles collides with a neighbouring air stream discharged from the other set of nozzles, thus creating a combined airstream with a combined velocity and direction, which may be controlled by extern means.

The collision between air streams from the two separate sets of nozzles 7a, 8a having opposite directed radial and tangential velocities creates turbulence and thus jet streams in this peripheral area, which jet streams draw hot secondary air, indicated by arrows 12, e.g. coming from a cement clinker cooler, not shown, in the direction toward the centreline 1 1 of the burner and thus the central area where it is brought into contact with the fuels, which thus ignite. Hereby the ignition of the fuels will take place close to the burner 1 , hence giving the fuels more time to burn out completely before falling down into the material filling in the kiln.

In the embodiment shown in Fig. 1 the burner 1 comprises one duct 5, 6 for each nozzle 7a, 8a for conducting the primary air separately trough each duct to the respective nozzle. In this embodiment the burner 1 may further comprise means, not shown, for independently regulating the amount of primary air being conducted to each nozzle 7a, 8a. In an alternative embodiment as shown in Fig. 2 the burner 1 according to the invention comprises two concentric annular ducts 14, 15 being arranged radially outside the fuel ducts, not shown in Fig. 2, for conducting primary air to nozzles 7a, 8a at the discharge end 4 of the burner 1 , where the outer duct 14 is used for conducting primary air to the nozzles 7a lying on the outer circle 7 and the inner duct 15 is used for conducting primary air to the nozzles 8a lying on inner outer circle 8. In this embodiment the burner 1 may further comprise means, not shown, for independently regulating the amount of primary air being conducted through each annular duct 14, 15.

The burner shown in Fig. 2 comprises an annular nozzle plate 16 being arranged at the discharge end 4 of the burner 1 and comprising the nozzles 7a, 8a. Also, the embodiment shown in Fig. 1 may comprise such an annular nozzle plate 16 instead of having nozzles 7a, 8a simply provided as the end sections of the ducts 5, 6, as shown, for conducting the primary air to the nozzles 7a, 8a.

Fig. 3 and 3A show in greater details the design of such an annular nozzle plate 16. In such a design, the nozzles 7a, 8a are simply constituted of cylindrical holes 7a, 8a made in the nozzles plate 16 with the required directions for obtaining the desired velocity components. The burner may in a particular embodiment comprise two or more annular concentric nozzle plates 16, not shown, the angular position of which may be adjusted to obtain different collision patterns.

Claims

1 . A method for introducing solid, liquid or gaseous fuel into a burning zone of a kiln, such as a rotary kiln for manufacturing cement clinker or similar products, by which method fuel is conducted through a number of ducts (3) to a discharge end (4) of a burner (1 ) having a centreline (1 1 ) and portions of primary air is conducted through ducts (5, 6; 14, 15) being arranged outside the fuel ducts (3) also to the discharge end (4) of the burner (1 ), and where the portions of primary air can be independently controlled, characterized in that the primary air is discharged from the discharge end (4) of the burner (1 ) in at least an inner and an outer set (10, 9) of air streams, where the air streams in at least one of the sets are discharged through each their nozzle (7a, 8a), where at least some of the air streams discharged from the nozzles (7a) in the outer set (9) have an axial velocity component (X₀) and a radial velocity component (Y₀) in the direction towards the centreline (1 1 ), where at least some of the air streams discharged from the nozzles (8a) in the inner set (10) have an axial velocity component (X,) and a radial velocity component (Y,) in the direction away from the centreline (1 1 ), and where at least some of the air streams in a set collide with a neighbouring air stream.

2. A method according to claim 1 characterized in that the air streams in at least two of the sets (10, 9) are discharged through each their nozzle.

3. A method according to claim 1 characterized in that the air streams in one set are discharged through an annular air nozzle.

4. A method according to claim 3 characterized in that the air streams being discharged through each their nozzle preferably include the outer set (9) of air streams.

5. A method according to claim 1 characterized in that least some of the air streams discharged from the nozzles in at least one of the sets of nozzles also have a tangential velocity component (Z).

6. A method according to claim 5 characterized in that the tangential velocity component (Z) of the air streams discharged from nozzles in the same set (10, 9) is directed in the same direction.

7. A method according to claim 5 characterized in that the tangential velocity component (Z) of the air streams discharged from nozzles in the same set (10, 9) is directed in opposite directions.

8. A method according to claim 5 characterized in that at least some of air streams discharged from the nozzles in at least two sets (10, 9) have a tangential velocity component (Z,, Z₀), and that the tangential velocity component (Z,) of at least some of the air streams in one set (10) is directed in the opposite direction to the tangential velocity component (Z₀) of at least some of the air streams in the other set (9).

9. A method according to claim 1 characterized in that at least some of the air streams in one set (10) collide with a neighbouring air stream in at least one of the other sets (9) of air streams.

10. A method according to claim 1 characterized in that the primary air is conducted to the nozzles (7a, 8a) at the discharge end (4) of the burner (1 ) via at least two concentric annular ducts (14, 15), where the outer duct (14) is used for conducting primary air to the nozzles (7a) in the outer set (9) and the inner duct (15) is used for conducting primary air to the nozzles (8a) in the inner set (10).

1 1 . A method according to claim 1 characterized in that each nozzle (7a, 8a) is supplied with the primary air trough each their duct (5, 6).

12. A burner (1 ) for introducing solid, liquid or gaseous fuel into a burning zone of a kiln, such as a rotary kiln for manufacturing cement clinker or similar products, which burner (1 ) comprises a centreline (1 1 ), ducts (3) for conducting fuel to a discharge end (4) of the burner (1 ) and ducts 5, 6; 14, 15) being arranged outside the fuel ducts (3) for conducting portions of primary air also to the discharge end (4) of the burner (1 ), and where the portions of primary air are independently controllable, characterized in that it comprises at least an inner and an outer set (10, 9) of stationary nozzles (7a, 8a) for discharging the primary air from the discharge end (4) of the burner (1 ) into the kiln, where at least some of the nozzles (7a) in the outer set (9) have an orientation that provide at least some of the air streams discharged there from with an axial velocity component X₀ and a radial velocity component Y₀ in the direction towards the centreline (1 1 ), where the nozzles (8a) in the inner set (10) have an orientation that provide at least some of the air streams discharged there from with an axial velocity component Xj and a radial velocity component Y, in the direction away from the centreline (1 1 ), and where the nozzles (7a, 8a) in a set are so arranged that at least some of the air streams from a set of nozzles collide with a neighbouring air stream.

13. A burner according to claim 12 characterized in that at least some of the nozzles (7a, 8a) in at least one of the sets (10, 9) have an orientation that provide at least some of the air streams discharged there from with a tangential velocity component (Z).

14. A burner according to claim 12 characterized in that it comprises at least two concentric annular ducts (14, 15) being arranged radially outside the fuel ducts (3) for conducting primary air to nozzles (7a, 8a) at the discharge end (4) of the burner (1 ), where the outer duct (14) is used for conducting primary air to the nozzles (7a) in the outer set (9) and the inner duct (15) is used for conducting primary air to the nozzles (8a) in inner set (10).

15. A burner according to claim 12 characterized in that it comprises one duct (5, 6) for each nozzle (7a, 8a) for conducting the primary air separately trough each duct to the respective nozzle.

16. A burner according to claim 12 characterized in that it comprises at least one nozzle plate (16) being arranged at the discharge end (4) of the burner (1 ) and comprising at least some of the nozzles (7a, 8a), where the nozzles (7a, 8a) are constituted of cylindrical holes made in the nozzles plate (16) with the required directions for obtaining the desired velocity components.