DE3933050C2 - Method for operating a burner for rotary kilns and burners therefor - 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 for operating a burner for rotary kilns, in which concentric Fuels and primary air are supplied.

The present invention also relates to a burner for a rotary kiln with a burner nozzle essentially Supply lines for fuel arranged concentrically to one another and primary air as swirl and axial air.

Such a burner is known from DE-PS 29 05 746. At the known burner is in addition to a central fuel supply for oil a concentrically arranged fuel supply for Coal dust or the like is provided. This feeder for fixed Fuels are between for the purpose of thorough mixing two primary air streams, the inner one with a swirl, i.e. H. is provided with flow components in the circumferential direction and the outer for the purpose of stabilizing the far in the Rotary kiln furnace flame essentially axial Has flow components. Also with other known burners the inflow of primary air is relatively far inside intended.

The known burner has a feed in its center liquid fuels, generally oil. And this one liquid fuel in droplets using a nozzle stick is atomized and after leaving the central Nozzle opening mixed with the primary air coming from the radial opening for swirl air closest to the central opening exit.  

The known burners are usually with a primary air content of 8 to 25%, be pulled on the total amount of combustion air, driven.

The performance of the burner can be reduced or reduced accordingly Regulate the fuel and air supply in a certain range, the to maintain stable output adjustable minimum output at about 20 to 25% of the achievable Maximum performance is. At the beginning of the burner operation, oil must usually pass through the central nozzle opening are fed and ignited to preheat the furnace, since only when the furnace is sufficiently preheated, the combustion of the concentrically fed solid Fuel works.

Such rotary kiln are also known from: E. Steinbiß "multi-jet burner for the special requirements of coal dust firing" in cement-lime gypsum No. 5, 1982, Be ten 250 to 252, O. Hochdahl "fuels and heating industry" in cement-lime Gypsum No. 2, 1986, pages 57 to 66, G. Eckelmann "rotary kiln burner for solid fuels and fuel mixtures" in cement-lime gypsum No. 8, 1979, pages 386 to 389 and P. Schubert "More channel burner for coarse-grained, solid fuels "in cement-lime gypsum No. 5, 1982, pages 246 to 249 and in X. Heller" NO _x reduction by using a step burner with flue gas recirculation from the preheater "in cement-lime gypsum No. 2, 1987, Pages 57 to 63. Here, two fuel-dust-free primary air flow channels enclose a carrier air / coal dust ring channel concentrically between them in the radial direction, the inner primary air flow being distributed, and the outer axially or optionally with a moderate divergence angle opens at the burner outlet cross section.

Compared to this prior art, the present invention has the object de, a method for operating burners for rotary kilns and in particular also to create a burner for this purpose, which can be operated with a lower proportion of primary air are and have a larger control range and also a reduced nitrogen oxide Show part in the combustion gases.

With regard to the method, this object is achieved in that radially within a annular fuel supply and possibly directly around a central fuel around an enlarged dead core area is provided by providing inside the annular fuel supply at most a small proportion of less than 20% of the primary  air, based on the total supply of primary air, is supplied so that it is in the dead Core area comes to no significant combustion.

In the case of a burner with an additional central fuel supply, this task will work out Visibly solved the process in that directly around a central fuel supply around an enlarged dead core area is provided in that at most one ge low proportion of less than 20%, based on the total primary air supply in this area is guided, while the main part of the primary air at a radial distance from the center the fuel supply is supplied at least twice the radius of a centra len flame holder opening, so that there is no mention in the dead core area values combustion of the fuel is coming.

So in front of the center of the burner nozzle begins by providing the dead core area ches the combustion in comparison to known methods and burners only in one slightly larger distance. Seen in longitudinal section, the resulting flame has gone out going from the center of the front end of the nozzle forward and radially first core area in which there is practically no noteworthy implementation of fuel with which atmospheric oxygen takes place. Such a flame core is in principle  also available in known burners, but this is dead Deliberately sacrifice core area according to the present invention leads and increases, in particular by the fact that poss As little primary air as possible is led into this area.

Nevertheless, a small proportion of primary air, albeit in primarily not intended for combustion in these Core area, but this small portion serves the primary air primarily for flame stabilization and Prevention of kickback of combustion gases, coals dust ash and oil coke, which otherwise contaminate the would lead central nozzle area. A little primary air electricity in this central area, but below 20% and is preferably below 10% of the total primary air such a setback of combustion products without to deliver too much oxygen, which makes the fuel free would reduce the core area.

Surprisingly, it has been shown that by providing of such an enlarged dead core area the control area of the burner can be increased considerably up to down to less than 10% of the maximum power for which the Burner is designed. This means that such a burner, provided that it is predominantly made of solid, powdered fuels should be operated, after a short preheating with oil the solid fuel can be operated.

At the same time, it has been found that with such Method and a correspondingly designed burner Proportion of primary air that is supplied for flame stabilization must be based on 2 to 10%, and preferably below 6% reduced to the total amount of combustion air supplied can be. This facilitates the manufacture of the feed device for primary air, which is designed accordingly weaker  can be.

A particular advantage of the lower primary air consumption is in the associated energy savings at otherwise same performance and in reducing the nitrogen oxide content in the combustion gases

According to the invention it is provided that separately from the A small amount of primary air is fed into the core area supplied at least two further separate primary air streams of which one is essentially axial, the other in has considerable flow components in the circumferential direction. With regard to the device mentioned at the outset, the Invention underlying problem solved in that the Supply openings for swirl and axial air radially outside the There are openings for the fuel supply and that the minimum radial distance of the outlet openings for the swirl and Axial air from the center of the burner nozzle at least twice of the radius of a central flame holder opening.

The flame holder is a flange part with a central one Opening, which is in the center of the burner nozzle and preferably at the tip of a nozzle assembly for oil is provided and Flame formation and stabilization contributes. The flame holder, which is radial over the central nozzle assembly for oil protrudes, ensures a sufficient radial distance the following radially outside the flame holder, annular supply openings for primary air and / or others Fuels. The radii of the central opening of the Flame holder and the innermost ring-shaped Opening for the main primary air flows selected so that the most farthest interior inflow of primary air from the center of the Nozzle is at least twice the distance corresponds to the central opening of the flame holder. Ent  the central opening of the flame holder essentially speaks also the nozzle opening of the central fuel supply.

In this way it is prevented that the centrally emerging Fuel too early with the oxygen in the primary primary air currents comes into contact.

It is in the preferred embodiment of the invention provided that an annular feed opening for fixed and / or gaseous fuel still radially within the Primary air supply and radially outside the flame holder hen is. The term "primary air supply" refers here generally on the majority of the primary air, which in the form of swirl and / or axial air is supplied, and should not be here include a small proportion of primary air supply (central air), which to avoid the setback of combustion products ten in the core area of the flame.

For the supply of the latter small portion of primary air are namely according to the invention outside the central opening in openings are provided for the flame holder. The influx of this Small portion of primary air is then carried out by a ring channel between the central nozzle assembly for oil and the in radial direction of the next inner wall for another Fuel supply or for one of the main streams of primary air.

It is also expedient if the feed opening for axial air is the farthest outside radially and also one has axially projecting outer edge. This outer wreath contributes to a better rectification of the axial air, so that improves combustion and stabilizes the flame is settled.

According to the invention, the annular feed channels have primary  air and / or solid or gaseous fuels conical Wall sections, these wall sections or those with them connected concentric pipes axially relative to each other are movable so that the free passage cross-section the annular openings can be regulated in this way.

However, the end sections of the respective are preferred Feeders are cylindrical to create a divergent Avoid outflow in the direction of the conical wall sections the.

In the annular channel for axial air are in the cone rich according to the present invention aperture for the axial Alignment and the supply of primary air in separate, arranged in a ring and essentially axially first Kenden channels provided. These panels contribute to one additional axial alignment of the corresponding primary air stream and thereby also increase the axial outflow speed that the free cross section of the ring-shaped Reduce the channel and arrange it in a series of rings divide individual channels. Here are in the preferred Embodiment of the invention at least some of these channels partially closed or lockable. You can do this for example, the diaphragms are so wide in the circumferential direction leads that they ver at least partially a channel close or essentially a closed channel correspond.

In this way it can be ensured that the sum of the free channel cross sections is significantly smaller than the cross cut the annular feed for the axially flowing primary air. As already mentioned, this makes the flow rate Axial clearance increases, which in turn for stabilization contributes to the flame.  

Furthermore, it is provided according to the invention that the flames holder relative to the outlet openings for the main part of the Primary air and for solid or gaseous fuels in axial Direction is set back. This can e.g. B. by attaching the Flame holder on the axially movable jacket tube for the Nozzle stick happen, which is set back axially accordingly becomes.

Further advantages, features and possible applications of the present invention result from the following description Practice preferred embodiments in connection with the Characters. Show it:

Fig. 1 is a general view of a burner with a part of the supply means,

Fig. 2a shows a longitudinal section through a first embodiment of a burner nozzle,

FIG. 2b shows the detail of a view on Fig. 2a from the left,

Fig. 3 is a longitudinal section through another embodiment of a burner with means for feeding solid powdery fuels

Fig. 4 shows a longitudinal section through a burner nozzle with additional supply option for gaseous fuel and

Fig. 5 shows a longitudinal section through a burner nozzle with additional supply option for solid and gaseous fuel.

In Fig. 1 can be seen at the tip of an outer burner tube 5 '', which is also the outer boundary of a feed channel 5 'for predominantly axially flowing primary air, a burner nozzle 1st At the other end of the outer tube 5 '' various supply devices are connected or flanged. The supply of axial air takes place through a pipe 25 , the supply of swirl air through a pipe 24 , these two primary air components being adjustable separately via valves 45 and 44 and being connected to the same primary air main line. A branch line 22 branches off from this primary air main line at the rear end of the burner shown in FIG. 1 into a tube which concentrically surrounds the casing tube for the nozzle assembly 10 ′, the supply of which can be adjusted via a valve 42 .

As a result, a small part of primary air flows through the channel 11 'and the openings 13 into the core area of the flame. Oil is fed centrally to the burner nozzle 1 through line 21 . A tube 23 is provided for the supply of solid, powdery fuel, generally coal dust, the tube 23 being connected to the annular channel 15 'shown in FIGS. 3 and 5.

The concentrically nested pipes 10 '', 11 '', 4 '', 5 '', 15 '' and 19 '' have different lengths, with the pipes lying further inside projecting beyond what was initially outside, so that, as in Fig. 1 recognizable, Verstelleinrich lines 33 , 34 and 35 can be provided, which allow a relative axial displacement of the tubes to each other. For this purpose, the individual pipes are connected to each other via corrugated hoses.

A control unit 30 is used to monitor and control the primary air flows.

Fig. 2 shows a burner nozzle in longitudinal section and in plan view from the front, which is used exclusively for operation with centrally supplied fuel, for. B. oil is provided.

By the flame holder 3 provided on the tip of the casing tube 10 'for the nozzle stock' for oil, which protrudes considerably in the radial direction beyond the nozzle opening 10 , it is ensured that the next annular feed channel 4 'or its opening 4 only in considerable radial Distance to the central opening 2 of the flame holder 3 opens. In the example shown, the radial distance D of the annular opening 4 from the axis of the burner is more than three times the diameter d of the opening 2 . The corresponding distances are illustrated in FIG. 4, where the size ratio D / d is even more pronounced.

The dead core area 20 is essentially the area in front of the flame holder which lies outside the central fuel flow and clearly inside the main primary air supply from the annular openings 4 and 5 . This area can extend in the axial direction by a multiple of the diameter of the flame holder. Adequate mixing of primary air and fuel for flame formation only occurs outside this core area. The flame holder 3 has diaphragms 12 on its outer flange part, which guide the small proportion of primary air emerging from the openings 13 .

The outer feed channel 5 ′ has wall sections 6 that diverge conically outwards at its end section. In the area of these wall sections 6 , adjacent, longitudinally approximately triangular diaphragms 6 'are provided, the side parts of which lie against one another and have the same radial distance from the axis of the burner as the outer wall of the channel 5 '. In this way, the pipe 4 ″ can be moved relative to the pipe 5 ″ without the function of the diaphragms 6 ′ being impaired thereby. The diaphragms 6 'can be seen in FIG. 2b in a top view of their front edges. The diaphragms 6 ', however, can also be made so wide in the circumferential direction that they correspond to the parts lying between the channels 5 shown in FIG. 2b. These parts can also be regarded as closed channels 5 .

In the feed channel 4 ', a swirl device 14 is provided in front of the conical end section, which consists essentially of guide plates which are inclined to the axis of the burner.

The distance between the conical wall sections 7 of the channel 4 'can be varied by axially displacing the tube 11 ''relative to the tube 4 ', so that the cross section of the channel 4 'can be changed. The end section of the channel 4 'in the region of the opening 4 is again cylindrical, however, in order to avoid a divergent flow of the swirl air emerging.

In an analogous manner, the edge 8 projecting in the axial direction ensures the alignment of the axial air flow, which in connection with the alignment and acceleration of the axial air in the channels 5 thus ensures a stable, uniform and far-reaching axial air flow.

The embodiment of the burner nozzle according to FIG. 3 differs from the embodiment shown in FIG. 2 essentially by the channel 15 ′ additionally provided between flame holder and primary swirl air flow for solid, powdery fuels. This is generally coal dust from a carrier gas, e.g. B. air is transported into the burner. Because of the abrasive properties of such solid fuels, the end region of the channel 15 'is only weakly conical in order to allow the solid fuel to pass through the annular opening 15 as freely as possible.

In the embodiment according to FIG. 4, instead of this channel 15 'for solid fuel, a further channel 19 ' is provided for a gaseous fuel, the end section of which can be made conical in a similar manner to channel 4 'and which can also have a device, to give the gas a twist. Again, the end portion of the channel 19 'in the area of the opening 19 is designed cylin drisch to avoid divergence of the outflowing, gaseous fuel.

Finally, FIG. 5 shows an embodiment which has both a feed channel 15 'for solid fuels and a channel 19 ' for gaseous fuels. Again, the channels 4 'and 5 ' for the main primary air portion in the form of swirl and axial air are provided only radially outside of these two fuel channels. The radially inner edge of the opening 15 , through which a considerable part of the primary air can flow into the burner in the form of carrier gas for solid fuels, is still more than twice the distance D 'from the axis of the burner of the radius d of the opening 2 of the flame holder 3 , so that a sufficiently large dead core area of the flame of the burner is guaranteed in any case, which brings the advantageous properties of the present invention with it.

Through this invention, a burner and generally a Process for operating a burner for rotary kilns which have a reduced proportion of primary air and a allow greater burner control range, resulting in a leads to lower energy consumption and thus also education environmentally harmful nitrogen oxides is reduced.

Claims (17)

1. A method of operating a burner for rotary kilns, in which fuels and primary air are supplied concentrically, characterized in that radially in an annular fuel supply ( 15 , 19 ) and optionally directly around a central fuel supply ( 2 ) around an enlarged dead core area ( 20 ) is provided in that within the annular fuel supply ( 15 , 19 ) at most a small proportion of less than 20% of the primary air, based on the total supply of primary air, is supplied so that there is none in the dead core area ( 20 ) significant combustion comes. 2. A method of operating a burner for rotary kilns in which concentric fuels and primary air are supplied, characterized in that an enlarged dead core area ( 20 ) is provided around a central fuel supply ( 2 ) in that at most a small proportion of less than 20%, based on the total primary air supply is supplied in this area, while the main part of the primary air is supplied at a radial distance from the center of the fuel supply which is at least twice the radius of a central flame holder opening, so that it is in the dead Core area ( 20 ) comes to no significant combustion of the fuel. 3. The method according to claim 1, characterized in that the portion of the primary air guided into the core region ( 20 ) is below 10% of the total primary air. 4. The method according to any one of claims 1 to 3, characterized in that separated from a primary air supply in the core region ( 20 ) at least two further primary air streams ( 4 ', 5 ') are supplied, one of which is essentially axial, and the other has significant flow components in the circumferential direction. 5. The method according to any one of claims 1 to 4, characterized in that the The proportion of primary air in the total combustion air is 2 to 10%. 6. The method according to claim 5, characterized in that the proportion of primary air of the total combustion air is below 6%. 7. Burner for a rotary kiln with a burner nozzle ( 1 ) with essentially concentrically arranged fuel feeds ( 10 ', 15 ', 19 ') and primary air feeds as axial air supply ( 5 ') and as swirl air supply ( 4 '), characterized in that the outlet openings ( 4 , 5 ) for swirl and axial air are arranged substantially radially outside the fuel outlet openings ( 10 , 15 , 19 ) and that the minimum radial distance of the innermost outlet opening ( 4 , 5 ) for the main part of the Swirl and axial air supplied primary air from the center of the burner nozzle ( 1 ) is at least twice the radius of a central opening ( 2 ) of a flame holder ( 3 ). 8. Burner according to claim 7, characterized in that radially inside the outlet openings ( 4 , 5 ) for swirl and axial air and outside of the flame holder ( 3 ) an outlet opening ( 15 , 19 ) with a cross section is provided for solid and / or gaseous fuel is. 9. Burner according to claim 7 or 8, characterized in that the flame holder ( 3 ) is provided at the front end of a central nozzle assembly for oil. 10. Burner according to one of claims 7 to 9, characterized in that outside the central opening ( 2 ) in the flame holder ( 3 ) openings ( 13 ) are provided for the inflow of a small part of the primary air into a dead core area. 11. Burner according to one of claims 7 to 10, characterized in that the outlet opening ( 5 ) for axial air lies radially outermost and has an axially projecting outer edge ( 8 ). 12. Burner according to one of claims 7 to 11, characterized in that the annular feed channels ( 4 ', 5 ', 15 ', 19 ') in front of their outlet openings ( 4 , 5 , 15 , 19 ) conical wall sections ( 6 , 7 , 16 , 17 ), the wall sections being axially displaceable relative to one another. 13. Burner according to claim 12, characterized in that between the conical wall sections ( 6 , 7 , 16 , 17 ) and the annular outlet openings ( 4 , 5 , 15 , 19 ) cut a cylindrical Endab at least for part of the annular feed channels ( 9 ) is seen on at least one wall ( 6 , 7 , 16 , 17 ) of the respective feed channel. 14. Burner according to one of claims 12 or 13, characterized in that the annular channel ( 5 ') for axial air in the conical wall section ( 6 ) orifices ( 6 ') for the supply and axial alignment of primary air in separate, ring-shaped angeord Neten and has substantially axially extending channels. 15. Burner according to claim 14, characterized in that the cross section of the annular opening ( 5 ) for axial air or the corresponding annularly arranged channel is at least partially closed or closable. 16. Burner according to claim 14 or 15, characterized in that the sum of the free cross sections of the axial air channels is substantially smaller than the cross section of the annular feed ( 5 ') for the predominantly axially flowing primary air. 17. Burner according to one of claims 7 to 16, characterized in that the flame holder ( 3 ) is set back in the axial direction relative to the outlet openings ( 4 , 5 , 15 , 19 ) for swirl air, axial air and / or solid or gaseous fuels .