EP0706007A2 - Method and burner for the combustion of pulverized fuel - Google Patents

Abstract

In the burner longitudinal axis is an oil ignition lance (1), arranged inside a core air tube (2). The core air tube at its lateral rear end is closed by a plate (2a), through which the oil lance passes, and in the vicinity of its rear end has a lateral aperture (2b). The core air tube is axially displaceably located in a guide tube (4). Joined at right-angles to the guide tube is a core air feed tube (5). The lateral aperture of the core air tube is aligned with the outlet aperture of the core air feed tube with a corresp. axial opening width so that by displacement of the core air tube the air fed via the core air feed tube can enter uninterruptedly in the core air tube.

Description

The invention relates to a method of the type mentioned in the preamble of claim 1.

When burning fuel, in particular dust-like coal, nitrogen oxides are formed primarily by oxidation of the fuel nitrogen contained in the coal. The first step is the formation of hydrogen cyanide (HCN) or ammonia (NH₃). These are then oxidized to nitrogen oxides. An at least two-stage combustion is therefore sought, in which combustion is first carried out under substoichiometric conditions (primary combustion zone) with primary and jacket air, so that remaining combustible components are burned in a subsequent secondary combustion zone. With this staged combustion, the ignition stability must remain guaranteed with a small air ratio in the primary combustion zone, i. H. it must be ensured that the fuel components to be ignited first are mixed in particularly well.

Since combustion in the primary combustion zone is substoichiometric, a relatively high proportion of tertiary or stage air must be mixed in as late as possible, but particularly well. At the same time, the possibility of Intake of flue gas into the flame from the combustion chamber surrounding the flame must be guaranteed.

It follows from this that for the operation of such a burner the greatest possible number of degrees of freedom should be available for burner optimization in order to reduce the formation of nitrogen oxides. In the process known from DE 42 17 879 A1, the tertiary air is supplied for this purpose in an annular jet surrounding the swirled jacket air, which emerges from the annular space of a tertiary air tube surrounding the jacket air pipe. The jacket air pipe and the tertiary air pipe are each connected to a spiral inlet housing and separate air inlet lines. In addition, a swirl insert which is fastened to the core air tube and which produces a rotational flow resulting in a uniform flow through the primary air tube is provided within the primary air tube. At the same time, the coal dust is enriched within the mixture flow on the outer circumference of the primary air pipe; when it emerges from the primary air pipe, the coal dust concentration in the edge region is torn open by a ring arranged there, whereby recirculation vortices are generated. These recirculation vortices ensure accelerated heating of the coal dust and sufficient mixing of the coal dust with part of the jacket air. The coal dust concentration at a defined point in the burner muffle causes the occurrence of a very severe lack of air, which is associated with the initial phase of the coal dust in terms of location and time. A rectangular intake manifold is connected upstream of the primary air pipe.

It is disadvantageous that a swirl insert arranged in the primary air flow is required for changing the coal dust distribution in the primary air pipe.

It is therefore the object of the present invention to provide a method of the generic type in which burner optimization is further improved with regard to reducing the formation of nitrogen oxides.

This object is achieved in that the flow velocity of the primary air is changed before the coal dust concentration in the edge region is torn open.

The flow rate can be changed by drawing in the cross section, as a result of which the coal dust is concentrated, accelerated and deflected in the direction of the inner recirculation area which forms in the primary combustion zone. By tearing open the coal dust concentration in the edge area, fine dust is transported out of the concentrated dust flow and mixed into the jacket air flow.

On the other hand, the flow cross section can be expanded, whereby the gas flow is slowed down. At the same time, the separation of fine dust occurs because it follows the expansion most quickly. The tearing up of the coal dust concentration in the edge area, which is primarily fine coal dust, causes turbulence, transport of the fine dust to the outside and rapid mixing of the fine dust into the jacket air. The process control with an enlarged flow cross section is preferred.

The step air can be supplied in a ring jet or in single jets. The separation of the step air into individual jets enables a greater depth of penetration to be achieved and flue gas from the combustion chamber can enter the flame between the individual jets.

The outlet area of the jacket air pipe is preferably cooled in order to avoid caking of slag.

The invention is also directed to a burner of the type mentioned in claim 6 and dependent claims 7 to 13 dependent thereon.

Furthermore, the present invention is directed to a burner according to the preamble of claim 14, the main objective of which is to simply apply the fuel / air mixture to the primary air pipe in order to reduce the formation of nitrogen oxides by evenly introducing the coal dust into the flame.

This object is achieved by the features of the characterizing part of claim 14. These features can be used with particular advantage in a burner according to at least one of claims 6-13, since primary air with particularly uniformly distributed coal dust can be fed to the flame holder. The subclaims 15-16 relate to advantageous embodiments of the burner according to claim 14.

Various embodiments of the invention are shown in the drawings and are explained in more detail below.

Fig. 1

einen Längsschnitt durch eine erste Ausführungsform des erfindungsgemäßen Brenners, wobei am Kohlenstaubaustritt eine Einziehung vorgesehen ist,

Fig. 2

einen Teilschnitt durch den Brennerkopf gemäß Fig. 1 zur Darstellung der sich ausbildenden Kohlenstaubsträhne und der Gasströmung, wobei die Anströmung von unten erfolgt,

Fig. 3

eine Darstellung vergleichbar Fig. 2, wobei die Anströmung von oben erfolgt,

Fig. 4

eine perspektivische Teildarstellung des Brennerkopfes zur Erläuterung der Anordnung eines am Eintrittsende des Primärluftrohrs angeordneten Strähnenbrechers in "gläserner Darstellung",

Fig. 5

eine vergrößerte Teildarstellung des Flammenhalters gemäß Fig. 1,

Fig. 6

eine Teilaufsicht von rechts auf den Brenner gemäß Fig. 1

Fig. 7

eine weitere Ausführungsform des Flammenhalters,

Fig. 8

eine Abwicklung längs der Linie VIII-VIII in Fig. 1 zur Darstellung der Lage der Stufenluftdüsen und ihres Aufbaus in Form zweier Teilkanäle,

Fig. 9

eine Teildarstellung vergleichbar Fig. 6 und zur Erläuterung der Einstellagen der Einzeldüsen,

Fig.10

einen Längsschnitt durch das Austrittsende einer in einem Führungsrohr drehbar gelagerten Stufenluftdüse,

Fig.11

eine Aufsicht auf das Düsenende gemäß Fig. 10 in Blickrichtung der Pfeile XI-IX in der Fig. 10,

Fig.12

eine Aufsicht auf das Austrittsende der Düse gemäß Fig. 10,

Fig.13

ein Schaltbild zur Darstellung der Primärluftströmung, Mantelluftströmung (Sekundärluftströmung) und Stufenluftströmung (Tertiärluftströmung) und

Fig.14

zwei weitere Ausführungsformen des erfindungsgemäßen Brenners, bei denen die Stufenluft als Ringstrahl zugeführt wird und der Austrittsbereich des Stufenluftrohrs gekühlt wird.

It shows:

Fig. 1

2 shows a longitudinal section through a first embodiment of the burner according to the invention, a retraction being provided at the coal dust outlet,

Fig. 2

2 shows a partial section through the burner head according to FIG. 1 to illustrate the coal dust streak that forms and the gas flow, the inflow being effected from below,

Fig. 3

a representation comparable to FIG. 2, the flow coming from above,

Fig. 4

2 shows a perspective partial representation of the burner head to explain the arrangement of a strand breaker arranged at the inlet end of the primary air pipe in a "glass representation",

Fig. 5

2 shows an enlarged partial illustration of the flame holder according to FIG. 1,

Fig. 6

a partial view from the right of the burner according to FIG. 1

Fig. 7

another embodiment of the flame holder,

Fig. 8

a development along the line VIII-VIII in Fig. 1 to show the position of the stepped air nozzles and their structure in the form of two sub-channels,

Fig. 9

6 and to explain the setting positions of the individual nozzles,

Fig. 10

2 shows a longitudinal section through the outlet end of a stepped air nozzle rotatably mounted in a guide tube,

Fig. 11

10 in the direction of arrows XI-IX in FIG. 10,

Fig. 12

10 shows a top view of the outlet end of the nozzle according to FIG. 10,

Fig. 13

a circuit diagram to show the primary air flow, jacket air flow (secondary air flow) and step air flow (tertiary air flow) and

Fig. 14

two further embodiments of the burner according to the invention, in which the step air as a ring jet is supplied and the outlet area of the stepped air tube is cooled.

Fig. 1 shows a longitudinal section through an embodiment of the burner according to the invention. An oil ignition lance 1 is provided in the longitudinal axis of the burner and is arranged within a core air tube 2. The flame cone 3 of the oil pilot flame is indicated schematically in the figure. The core air tube is closed at its rear end by a plate 2a, which is penetrated by the oil lance, and has a side opening 2b near its rear end. Furthermore, the core air tube is axially displaceable — as indicated by the arrow P — in a guide tube 4. At right angles to the guide tube 4, a core air supply tube 5 is connected to it. The outlet opening of the core air supply pipe 5 is assigned to the lateral opening 2b of the core air pipe 2 and provided with a corresponding axial opening width such that when the core air pipe is displaced, the air brought in via the core air supply pipe can enter the core air pipe unhindered.

The front section of the core air tube is surrounded by a primary air tube 6 to form a cylindrical ring channel, the outlet opening of which is set back relative to the outlet opening of the core air tube.

The core air tube is charged with a coal dust-gas mixture in the following way. The coal dust-gas mixture brought up from a coal grinding plant or coal dust source, not shown, is fed to a deflection manifold 7 upstream of the burner, in which a concentration of the coal dust K is forced on the side of the manifold facing the combustion chamber. The deflection manifold 7 is preferably a continuously curved manifold. As FIGS. 2 and 3 show, this forced concentration takes place independently whether the flow is from below (Fig. 2) or from above (Fig. 3). The manifold 7 is followed by a channel extension 8 serving as a delay channel, which in the embodiment shown is a channel with a rectangular cross section, ie there is an expanding transition from a line with a round cross section to a line with a rectangular cross section. In the delay channel, the flow rate of the gas from z. B. reduced 23 m / s to 12 m / s, which also reduces the coal dust speed. In addition to slowing the flow, at least partial segregation of the coal dust-gas mixture is achieved in the delay channel 8, as is shown schematically in FIGS. 2 and 3 by the coal dust K and the gas flow G. In the case of a vertical flow from below or above, the formation of the dust streak K can be determined by a corresponding geometric design of the entry of the coal dust line into the delay channel.

The already slowed down coal dust strand K meets a strand breaker 9 at the end of the delay channel 8. The strand breaker 9 consists of a multiplicity of rod-shaped crushing elements 10 which are connected upstream of a predetermined circular sector of the inlet opening 11a of a venturi-like inlet assembly 11 and extend essentially parallel to the burner axis . In the embodiment shown in FIG. 4, the crusher elements consist of cuboids arranged at a distance. The crushing elements can be easily replaced when worn.

The inlet assembly 11 surrounds the end of the guide tube 4 facing the combustion chamber, forming an annular channel. The gas flow applied to the rear wall of the delay channel is introduced into the through a closing plate 12, preferably extending at an angle of 45 ° and penetrated by the guide tube 4 deflected annular entry opening of the inlet assembly 11 and strikes the delayed dust flow which is broken up by the strand breaker at an angle of almost 90 °. This ensures that the coal dust is evenly distributed over the ring cross-section. The venturi-like design of the inlet assembly 11 accelerates the gas flow parallel to the burner axis. As a result of the vortex formation that occurs at the outlet of the venturi assembly, any local strands of coal dust that may be present on the circumference are dissolved, whereby coal dust and gas are mixed. The constriction of the free cross-section in the entry assembly can be between 10 - 70%. At the same time, the gas flow is blocked, which results in a further equalization.

As can be seen in particular from FIGS. 1-4, the closing plate 12 together with the associated side walls 13 and 14, and the end wall 15 carrying the crushing elements 10 together with the inlet assembly 11 constitute a structural unit which is one with the side wall 16a facing away from the combustion chamber Air box 16 is connected by a screw 17. Components 12, 13, 14 and 15 form an intake manifold. After the connection has been established, the inlet assembly 11 projects into the primary air pipe 6, which is welded to the side wall 16a.

For the primary flame, a hot, strongly substoichiometric, compact primary combustion zone with the most complete pyrolysis of the fuel and internal fuel grading is sought. An air ratio of 0.4 - 0.6 should be realized in the primary flame. For this purpose, such a design is sought at the dust outlet end of the primary air pipe 6 that, on the one hand, a gradation of the fuel input into the primary flame is achieved and, on the other hand, a stable and fast ignition of the coal dust is supported. For this purpose, the aim is Concentrate and slow down fine dust on the outer circumference of the dust outlet in order to ensure rapid mixing with the jacket air, which is supplied via a jacket air pipe which concentrically surrounds the primary air pipe 6 to form a cylindrical ring channel. For the coarser fraction, it is necessary to transport it into the inner recirculation zone of the primary flame that is being formed at higher speeds. It should therefore be aimed for, when the dust flow enters the inner recirculation zone of the flame, a cross-flow screening of the coal dust takes place, so that the finer particles are deflected relatively quickly into the combustion zone and the coarsest particles penetrate the furthest into the recirculation area. In this way it can be ensured that with increasing particle size there is a longer period of time for heating and pyrolysis and that there is a delayed continuous introduction of fuel into the primary flame.

In order to achieve these goals, a flame holder 19 is assigned to the outlet end of the primary air pipe 6 in the embodiment according to FIG. 1, the end of the flame facing the combustion chamber is shown on an enlarged scale in FIG. 5. This flame holder consists of a tubular channel 20 with a straight cylindrical section 20a, a conically tapering section 20b and a conically widening section 20c. The channel overlaps with its straight cylindrical end 20a the free edge of the primary air pipe and is supported on the end of the core air pipe 2 by means of radially extending webs 21, so that when the core air pipe 2 is displaced, the flame holder 19 moves in a corresponding manner (see FIG. 1 and 6). In the area of the indentation of the channel 20 given by the sections 20b and 20c, blocking teeth 22 are provided which protrude into the primary flow and are arranged in a uniform circumferential distribution. Instead of individual locking teeth, one can toothed locking ring may be provided. By drawing in the cross section of the channel 20, the coal dust in the coal dust-gas mixture is concentrated, accelerated and deflected in the direction of the inner recirculation area of the flame forming at the burner mouth. The blocking teeth in the area of the narrowest cross-section cause a swirling of the flow in the outer area, as a result of which fine dust in particular is discharged from the concentrated flow and transported away to the outside. The turbulence of the flow also favors the mixing of the fine dust into the jacket air flow. The accelerated and inwardly deflected coarse dust reaches the inner recirculation zone, where the coal dust is cross-viewed by the recirculation flow. The fuel input into the primary flame is thus classified several times.

By changing the position of the flame holder 19 by moving the core air pipe 2 relative to the coal dust pipe 6, an optimization between the deflection inwards and acceleration of the coal dust can take place.

Another possibility for the design of the channel of a flame holder is shown in FIG. 7. The channel 23 there has a straight cylindrical section 23a and an adjoining conically widening section 23b. Blocking teeth 24, comparable to blocking teeth 22, are formed near the outlet end of the widening section 23b. It should be pointed out that separate locking teeth may not be required, but that a continuous locking ring may be sufficient.

In the embodiment according to FIG. 7, the expansion of the dust cross section in the channel section 23b slows down the gas flow and results in a Speed profile with an outside slower and an inside faster flow. At the same time, a separation of fine dust occurs, since this follows the expansion most quickly, ie the coal concentration will be higher in the area adjacent to the core air pipe than in the outer, slower flow, since the coarser coal particles will keep their direction of flow. The blocking teeth 24 cause a further slowdown of the dust in the outer region of the coal dust cross section and a swirling of the flow, which favors the transport of the fine dust to the outside and thus its rapid mixing into the jacket air. The coarser dust is only slowed down comparatively little by the delayed flow. It reaches the inner recirculation area at a relatively high speed, where cross-flow screening of the coarser dust takes place. Overall, a multiple gradation of the fuel in the primary flame is also achieved in this embodiment. The widening of the coal dust cross section also causes a dynamic separation of the jacket air from the main flow of the coal dust, which also favors a stepped fuel input into the primary flame.

A device for influencing the swirl in the form of rotatably mounted axial swirl flaps 25 is arranged in a section of the jacket air pipe 18 that widens toward the inflow end and can be adjusted from the outside via a linkage 26 and an actuator. These axial swirl flaps impose a swirl of adjustable size on the jacket air.

A muffle 27 constructed of a ceramic mass adjoins the end of the jacket air tube 18 facing the combustion chamber and extends towards the combustion chamber with an S-shaped configuration of its inner surface. This muffle shape combines with the corresponding design of the Coal dust discharge and a strong swirl of the jacket air with the help of the swirl flaps 25 guarantees a fast, intensive ignition. Due to the high peripheral speed of the jacket air and an appropriate design of the dust outlet cross-section, a rapid mixing of fine dust into the jacket air is realized. The S-shape of the muffle, which can be seen in particular in FIG. 1, prevents the primary flame from tearing open even with a high swirl intensity of the jacket air. The S-shape runs out to the combustion chamber in such a way that an outflow of the jacket air can take place with a flow component almost parallel to the burner axis. This results in a compact primary flame, a smaller but more intensive (higher backflow speed) internal recirculation zone and a stronger external recirculation of the flue gas through the lanes between the step air nozzles 28 to be explained below. As already mentioned, the core air tube 6 and the flame holder 19, and thus the dust outlet cross section, are axially displaceable to control the course of the combustion in the primary flame. With a corresponding design of the coal dust outlet cross section, the exit speed of the jacket air and the location and speed of the mixing of the coal dust into the jacket air can be influenced by shifting the inner outlet cross section. The location and intensity of the ignition and the grading of the fuel within the primary flame can thus be set. In addition to the possibility of controlling a certain combustion process in the primary flame, the shift in the coal dust outlet cross-section can react very well to a wide variety of coal qualities with regard to ignition and combustion behavior.

The secondary combustion will now be described with reference to FIGS. 1, 6 and 8-12.

In the secondary combustion area, an air ratio of 0.9 - 1.05 should be achieved with a combustion with burnout air and an air ratio of 1.1 - 1.3 with a combustion without burnout air.

In order to achieve secondary combustion, a ring comprising a plurality of stepped air nozzles 28 is provided around the burner muffle 27, the stepped air nozzles being embedded in the ceramic compound KM forming the muffle 27. Eight spaced stage air nozzles 28 are preferably provided. The arrangement of the stepped air nozzles 28 is intended, on the one hand, to enable adequate external recirculation to the primary flame and to keep the oxygen away from the primary flame for a sufficiently long time, and on the other hand to securely enclose the primary flame in an oxygen-rich cas flow. By using individual nozzles in comparison to an annular nozzle surrounding the muffle, a high penetration depth of the oxygen-rich gas flow is to be achieved. As can be derived from the figures, in particular FIG. 9, the nozzles 28 are initially arranged with an angle of incidence directed outward from the burner axis in order to avoid direct rapid mixing of the step air into the primary flame which is formed. In the figures, the air nozzles 28 are all shown with the same outward angle of attack. However, it is also possible to assign differentiated axial angles of attack to the nozzles and thus to achieve a multiple air gradation within the flame.

As can be seen in particular from FIG. 9 in conjunction with FIGS. 1 and 8, the stepped air nozzles 28 not only have a radially outward angle of attack, but also a tangential angle at the same time, ie they extend so that the nozzle axis Torch axis does not cut. A swirl is thus imparted to the step air flow so that it concentrically forms a muffle 27 "pneumatic muffle" is coming. A swirl is preferably applied to the step air flow which is in the same direction as the swirl imparted to the jacket air flow by the swirl flaps 25. This stabilizes the flow and prevents the step air flow from mixing too quickly with the flow of the primary flame.

The jets emerging from the stepped air nozzles 28 draw flue gas RG out of the flame environment as they flow out, as a result of which the oxygen partial pressure in the secondary combustion zone drops and the NO _x formation in this area is reduced.

Although the nozzles with a constant discharge angle can be used as stepped air nozzles, it is advantageous if nozzles with a variable discharge angle are used. To achieve this, two-channel nozzles are used, the design of which can be read in particular from FIGS. 10-12.

The two-channel nozzle 28 has a straight cylindrical section 28a, in which a partition 29 is arranged. According to the desired flow distribution, the partition does not have to be arranged in the center, but can be arranged offset from a radial plane. The partition 29 ends at a distance from an outlet opening 30 which is inclined with respect to the nozzle axis A. By means of suitable cutouts from a tube, the outlet opening 30 is covered by remaining tube sections 28b and 28c and also by a cover plate 31 which is inclined at a first angle with respect to the axis A and by an opposite one another predetermined angle with respect to the axis A inclined cover plate 32 limited.

The angles of the cover plates 31 and 32 determine the possible exit angles with which a gas flow can exit the exit opening 30.

A different exit angle with respect to the axis A can be achieved by volumetrically different action of the channels 33 or 34 determined by the partition 29 with step air. It can e.g. B. be possible that when the channels 33 and 34 are loaded with 50% of the step air, the step air jet emerges parallel to the cover plate 31 or that when the channel 33 is loaded with 10% of the step air and the channel 34 with 90% of the step air of the nozzle 28 the beam emerges parallel to the cover plate 32.

For the different loading of the two channels 33 and 34, as can be seen from FIG. 1, provision is made for two inner walls 36 and 37 to be provided in the air box 16 in addition to the side wall 16a and the side wall 35 shown on the right in the air box 16. The inner wall 36 separates the step air from the jacket air and the inner wall 37 separates the step air into two partial flows. The space between the partition walls 36 and 37 is connected via the space between the partition walls 37 and 35 through passage sections 38 to the subchannels 34 of the stepped air nozzles 28, while the subchannels 33 are connected directly to the space between the side wall 35 and the partition wall 37. The action of the channels 33 and 34 with different air flows is made possible by adjusting the air entering the spaces between the partition 36 and 37 or 37 and 35 by means of control flaps 39 and 40. With regard to FIG. 8, it should be noted that this represents a development along the line VIII-VIII in FIG. 1, while FIG. 1 shows a section along the line I-I in FIG. 8.

The above-described loading of the subchannels 34 takes place via channels 38 rigidly connected to them.

Another connection configuration is required if the stepped air nozzles 28 each individually at least via one Sub-area are rotatably arranged. For this purpose, the individual nozzle is rotatably supported in a guide tube 39. With such an arrangement, both the tangential and the radial inflow angle would be adjustable and thus a particularly good optimization of the air gradation on the burner could be achieved. The application of subchannels 33 and 34 would, however, be more complicated.

It is also provided that individual step air nozzles can be shut off in order to be able to implement the required exit speeds of the step air even in part-load operation.

It goes without saying that the amount of primary air, core air and jacket air can also be regulated. In FIG. 13, control flaps 41, 42 and 43 are shown, which shows a diagram of the air flows supplied to the burner by a blower 44 and the fuel supplied by a coal mill 45. The control flap 41 regulates the jacket air and the step air upstream of the control flaps 39 and 40 simultaneously. The control flap 42 regulates the primary air supplied via a pressure-increasing blower 42a and the control flap 43 regulates the core air insofar as the core air pipe has to be acted on.

As can be seen from FIG. 1, the muffle 27 is formed in a pipe basket 46 which is integrated into the steam circuit of a steam generator and which is connected to the wall bore 47 of the combustion chamber and burns into the burner. Insulation 48 is also provided in the area of the muffle.

14 shows two further embodiments of the burner according to the invention. As far as possible, the reference numerals have been taken from FIG. 1.

In contrast to Fig. 1, the core air tube 2 is not axially displaceable. Rather, the oil ignition lance is 1 with a guide cylinder 1a and swirl ring 1b arranged at its front end, axially displaceable, as indicated by the double arrow. Furthermore, the inlet assembly 11 is not designed in a venturi-like manner, but is instead formed by a straight tube 11 ′ with a fastening flange. The diameter of the straight tube 11 'corresponds essentially to the diameter of the primary air tube 6 and thus represents an extension of the primary air tube.

14, a flame holder 19 is used, the channel 23 of which is designed according to FIG. 7. The straight cylindrical section 23a overlaps the outlet end of the primary air tube 6, but is not connected to the core air tube 2 via webs as in the embodiment according to FIG. 1, but is axially displaceable in the direction of the double arrow via at least one schematically illustrated actuating rod 23c.

With regard to the design of the jacket air tube 18, different embodiments are shown in the lower and upper half of FIG. 14. An embodiment is shown in the upper half of FIG. 14, in which the jacket air tube 18 is designed as a double-walled air tube with walls 18a and 18b. The annular space delimited by the walls is acted upon with air via a duct 49 arranged in the air box 16, regulated by a regulating flap 50, which can escape into the combustion chamber from the annular gap at the front end of the double-walled jacket air pipe. In the exit area, the double jacket is formed in the longitudinal direction with an essentially S-shaped cross section.

In the embodiment shown in the lower half of FIG. 14, the jacket air pipe is provided in its outlet area with a cooling winding 51 through which a cooling medium 52 flows. Here, too, the cross section of the outlet area in the longitudinal direction is in essentially S-shaped. Contamination in the outlet flow area of the jacket air pipe is largely avoided by cooling by means of air or the cooling medium flowing into the combustion chamber.

In contrast to the embodiment according to FIG. 1, the step air does not emerge into the combustion chamber in individual jets but in an annular jet surrounding the jacket air. For this purpose, the jacket air tube 18 is surrounded by a stepped air tube 53, to which the burner muffle 27 made of ceramic material is connected. An adjustable swirl device 54 is provided in the inlet area of the stepped air pipe 53, which swirls the air supplied by a duct 55 arranged in the air box 16 with a control flap 56.

It should be noted that in the embodiment according to FIG. 1, the venturi-like configuration of the inlet assembly 11 can be dispensed with. In the embodiment according to FIG. 1, the displaceability of the core air tube 2 can also be dispensed with if the flame holder 19 is arranged to be displaceable alone, as in the embodiment according to FIG. 14.

Claims (16)

Method for the combustion of dusty fuel, in particular coal, by means of a burner with a primary air pipe carrying a mixture of air and fuel (primary air) and a jacket air pipe guiding and surrounding the primary air pipe, in which the primary air and swirled jacket air into a burner muffle to form a primary combustion zone exit with an internal recirculation area, in which when the primary air emerges, the coal dust concentration in the edge area of the primary air pipe is broken up with the production of eddies and in which swirled step air is fed to the primary flame,
characterized,
that the flow velocity of the primary air is changed before the coal dust concentration in the edge region is torn open. Method according to claim 1,
characterized,
that the change in the flow velocity takes place by drawing in the flow cross section or by expanding the flow cross section. The method of claim 1 or 2,
characterized,
that the step air is supplied in a ring of individual jets surrounding the primary combustion zone in such a way that a swirl is imparted to the total step air. The method of claim 1 or 2,
characterized by
that the step air is supplied in a ring jet surrounding the primary combustion zone. Method according to one of claims 1-4,
characterized by
that the outlet area of the jacket air pipe is cooled. Burner for the combustion of dusty fuel, in particular coal, with a primary air pipe carrying a mixture of air and fuel (primary air), a jacket air pipe carrying jacket air and surrounding the primary air pipe, and a device for supplying swirled step air, the outlet end of the primary air pipe being a flame holder with a is assigned to a block protruding into the primary air,
characterized by
that the blocking (22; 24) of the flame holder (19) is preceded by a change (20b, 20c, 23b) in the cross section for the primary air flow. Burner according to claim 6,
characterized by
that for the supply of the step air, a ring of step air nozzles (28) is provided which surrounds the burner muffle and which are arranged tangentially at least with respect to the burner axis in such a way that a twist is imparted to the step air. Burner according to claim 6,
characterized by
that an annular gap is provided for the supply of step air. Burner according to one of claims 6-8,
characterized by
that a core air tube (2) accommodating an oil ignition lance (1) is arranged within the primary air tube (6). Burner according to one of claims 6-9,
characterized by
that the flame holder (19) is arranged displaceably relative to the primary air pipe (6). Burner according to at least one of claims 6-10,
characterized by
that the cross-sectional change is a cross-sectional expansion (FIG. 7) or a cross-sectional narrowing (FIG. 5). Burner according to at least one of claims 6-11,
characterized by
that the jacket air outlet (27; 18a, 18b; 51) has an essentially S-shaped cross section in the direction of the burner axis such that jacket air flows into the outlet or flows out of the outlet into the combustion chamber essentially parallel to the burner axis. Burner according to at least one of Claims 6-12,
characterized by
that the jacket air outlet (18a, 18b; 51) is cooled. Burner for burning dusty fuel with at least one primary air pipe carrying a mixture of air and fuel (primary air) and with an inlet manifold upstream of the primary air pipe, in particular burner according to one of the Claims 6-13,
characterized by
that in addition a deflection bend (7) is provided and that between the deflection bend (7) and the inlet bend (12, 13, 14, 15) there is a delay channel (8) which is enlarged in its cross section compared to the cross section of the deflection bend and at the end of the delay channel (8) a strand breaker (9; 10) is arranged in the area of the fuel dust lock (K) forming in the deflection manifold and guided through the delay duct and the gas flow (G) passing through the delay duct is deflected in the inlet manifold so that the gas flow (G) is below a predetermined angle strikes the fuel dust strand (K) broken at least in partial strands and air and coal dust enter the primary air pipe (6) in a uniform distribution. Burner according to claim 14,
characterized by
that the entry into the primary air pipe (6) is preceded by a venturi-like blockage (11). Burner according to claim 14 or 15,
characterized by
that the strand breaker (9) consists of a plurality of rod-shaped breaking elements (10) arranged at a distance and preferably on a circular sector.

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