EP1352197B1 - Burner for the combustion of particulate fuel - Google Patents

Abstract

The burner has a secondary air tube (3) placed around the longitudinal axis (27) of the burner and closed by an end wall (38) at the end away from the burner mouth (2). The secondary air tube is enclosed by a primary mixer pipe (4) which introduces primary air or a mixture of gas and fuel and which has a flow stabilising area (49) placed upstream in the flow direction of the primary mixture. Secondary air (19) is brought in through an inlet housing (28) which encloses part of the primary mixer pipe and forms a radial channel (40) which is connected to the internal cross section of the secondary air tube through ducts (35) which cross the ring shaped cross section and feed secondary air from the channel into the secondary air pipe.

Description

The invention relates to a burner and a method for the combustion of dust-like fuel, in particular dusty and ballast rich coal.

Burners for the combustion of pulverulent fuel, in particular pulverized coal are known, for example from document "Development of low-emission dust combustion systems" from VGB Kraftwerkstechnik 76 (1996), Issue 5. A distinction is essentially between two types of burners for the combustion of dust-like fuel, the usually rectangular jet burner and the round burner, which is usually designed as a swirl or whirl burner. Jet burners usually consist of a dust nozzle, through which the dust-like fuel by means of a carrier gas, which may be primary or primary gas is entered into the combustion chamber for combustion and from a respective upper and lower air nozzle, which adjoin the dust nozzle above and below and through the Secondary air is entered into the furnace. The respective nozzles are formed with rectangular cross sections. Frequently, jet burners have multiple dust nozzles, namely two to four dust nozzles. In such a case, lying in the vertical direction between two dust nozzles upper and lower air nozzles can be combined to form an intermediate air nozzle.

When using such jet burners for the combustion of lignite brown coal is usually ground in beater mills, dried with hot, from the furnace or the combustion chamber off and sucked back flue gases and promoted by the ventilation effect of the beater wheel to the dust nozzles of the burner. From the dust nozzle, therefore, enters a mixture of fuel dust, flue gas, water vapor and primary air, which is hereinafter referred to as the primary mixture in the furnace. From the top, bottom and possibly intermediate air nozzles exits the secondary air. Within the rectangular dust nozzle core air pipes are usually integrated, through which a small part of the combustion air exits.

The ignition zone of such a jet burner is usually located at a certain distance from the burner outlet, in the area in which there is a contact between the secondary air jets and the dust jet. In this case, the dust jet is first heated to above the combustion chamber from the hot, flue gas heated to the ignition temperature and pyrolyzed. Due to the geometric arrangement of the dust and air nozzles, the recirculated, hot flue gas is sucked by the dust jet mainly on the side surfaces of the rectangular dust nozzle. A heating and pyrolization of the dust jet on the upper and lower surfaces of the jet can not take place, since these surfaces are covered by the secondary air jets.

The rectangular jet burner described above, as a design for the vast majority of the lignite varieties available worldwide, has no problem with regard to the ignition stability and is optimal in terms of the NOx emission level and the slagging behavior of the furnace. For lignite, which have an extremely high ballast content due to a very high water and / or ash content, a further increase in the ignition stability by constructive measures on the burner is desirable as an alternative or in addition to the usually used for these fuels Bridentrennung. A disadvantage of the jet burner described above, that due to the geometric arrangement not the entire circumference of the dust jet of the dust nozzle for sucking hot flue gases can be used and thus no full heating of the dust jet can be done. Also, depending on the particular constraints, the priority for the firing operation may be to increase the reaction density at the combustor, e.g. to ensure a sufficient burn-out in small fire chambers. Jet burners, however, have lower reaction densities than swirl or round burners due to the flow conditions.

In addition to the jet burners round burners are known, which have a central, round dust or primary mixture pipe and a concentric secondary air pipe, which surrounds the central dust pipe and forms an annular cross-section between the two tubes. Through the dust or primary mixture pipe is the fuel dust is introduced together with primary air or primary gas and secondary air into the combustion chamber via the annular cross-section of the secondary air pipe. In these round burners, in most cases both the secondary air and the dust jet are twisted. For this example, in the dust tube swirl blades and on the secondary air side, a spiral secondary air inlet housing with tangential secondary air supply available. As with the jet burner, core air tubes can also be integrated in round burners within the circular dust tube, through which a small part of the combustion air can escape into the combustion chamber.

However, in the known round burners with twisted dust flow is disadvantageous that a pressure loss is generated by the twisting of the dust flow, which must be additionally applied by the usually upstream beater wheel mill. This usually requires a higher beater wheel speed or other measures on the mill which increase the power requirement and wear in the mill in general and on the impact plates in particular. Another disadvantage is the wear, which adjusts to the dust-side swirl vanes. The geometric arrangement with the central dust tube and the concentric secondary air tube is also disadvantageous in that the dust flow only has contact with the hot flue gas of the combustion chamber by internal recirculation of the flue gas into the flame root of the burner flame, however, the entire outer periphery of the dust flow no direct contact to the hot flue gas of the furnace has, so that hot flue gas from the combustion chamber can be mixed only on the relatively cold secondary air on the entire circumference. This hinders early heating and pyrolysis of the dust stream.

By publication " Patent Abstracts of Japan, Publication Number 58011308 A "A coal dust burner has become known, which provides an air feed in a central air feed pipe and provides the pulverized coal feed in an annular channel formed by the inner air feed pipe and an outer, outer coal dust feed tube surrounding it or erosive Kohlenstaubstromes in The coal dust feed channel requires very expensive and high maintenance ceramic linings on the inside wall of the pulverized coal feed tube and on the outside wall of the air feed tube to maintain the useful life of the pulverized coal burner in reasonable ranges.

The object of the invention is therefore to provide a burner which is more efficient and cost-effective than the state of the art and which is suitable in particular for burning pulverulent coal which has a high dust content, and to provide a method for operating such a burner.

The above object is achieved in terms of the burner by the features of claim 1 and in terms of the method for operating a burner by the features of claim 23.

Advantageous embodiments of the invention can be found in the dependent claims.

• Durch den Aufbau des erfindungsgemäßen Brenners mit einem zentralen Sekundärluffrohr und einem dieses konzentrisch umgebendes und einen Kreisringquerschnitt zwischen den beiden Rohren bildendes Primärgemischrohr hat der aus dem Primärgemisch- bzw. Staubrohr in den Feuerraum austretende Primärgemisch- bzw. Staubstrahl über seinen gesamten Umfang unmittelbaren Kontakt zu den heißen Rauchgasen des Feuerraumes, die somit ungehindert angesaugt werden können und den Staubstrahl aufheizen können. Gegenüber Rundbrennern, bei denen üblicherweise der Primärgemischstrom durch den Sekundärluftstrom ummantelt wird und somit keine Kontaktflächen zwischen dem Primärgemisch- bzw. Staubstrahl und dem heißen Rauchgas des Feuerraumes besitzen, wird nunmehr eine solche Kontaktfläche in vollem Umfang geschaffen und gegenüber den bekannten Strahlbrennern mit rechteckig ausgebildeten Primärgemisch- und Sekundärluffdüsen ist die Kontaktfläche zwischen Primärgemisch- bzw. Staubstrahl und heißen Rauchgasen wesentlich vergrößert worden. Damit wird beim erfindungsgemäßen Brenner die frühzeitige Aufheizung der Brennstoffpartikel des Primärgemisch- bzw. Staubstrahls auf die Zündtemperatur und die Pyrolyse derselben wesentlich verbessert und dadurch die Zündstabilität in erheblichem Maße erhöht.
• Durch den primärgemischströmungsseitig stromaufwärts des Sekundärluftrohres gelegenen Strömungsstabilitätsbereich wird eine axiale Einleitung des Primärgemischstromes in den Brenner bewirkt und dadurch eine gleichförmige Aufteilung des Feststoffes über den Querschnitt und ein geringerer Druckverlust im System erzielt. Durch die axiale Einleitung des Primärgemischstromes in den Brenner können in besonders vorteilhafter Weise Erosionen an der Primärgemisch- und Sekundärluftleitung weitgehendst vermieden werden, so dass der Einsatz von kostenintensiven Verschleißteilen und Wartungen diesbezüglich vermieden werden kann. Die axiale Einleitung des Primärgemischstromes in den Brenner wird letztendlich auch durch die erfindungsgemäße Heranführung der Sekundärluft mittels eines auf dem Umfang des Primärgemischrohres angeordneten Sekundarlufteintrittsgehäuses und der davon abgehenden und in die Sekundärluftleitung führenden Durchtrittskanäle ermöglicht.
• Durch den oben genannten geringeren Druckverlust im System wird gleichzeitig die vorgeschaltete Schlagradmühle entlastet, d.h. sie benötigt eine geringere Leistung.

The inventive solution provides a burner and a method for operating a burner, which has the following advantages:

• Due to the structure of the burner according to the invention with a central Sekundärluffrohr and this concentrically surrounding and a circular ring cross-section between the two tubes forming primary mixture tube exiting the Primärgemisch- or dust tube in the firebox primary mixture or dust jet over its entire circumference has direct contact with the hot flue gases of the combustion chamber, which can thus be sucked in unhindered and can heat the dust jet. Compared to round burners, in which usually the primary mixed stream is covered by the secondary air flow and thus have no contact surfaces between the Primärgemisch- or dust jet and the hot flue gas of the furnace, now such a contact surface is created in full and compared to the known jet burners with rectangular primary mixture and secondary air nozzles is the contact area between primary mixture or dust jet and hot flue gases have been substantially increased. Thus, in the burner according to the invention, the early heating of the fuel particles of the primary mixture or dust jet to the ignition temperature and the pyrolysis of the same is substantially improved, thereby increasing the ignition stability to a considerable extent.
• By the Primärströmströmungsseitig upstream of the secondary air tube flow stability region axial introduction of the primary mixture flow is effected in the burner, thereby achieving a uniform distribution of the solid over the cross section and a lower pressure drop in the system. Due to the axial introduction of the primary mixture stream into the burner, erosions on the primary mixture line and secondary air line can be largely avoided in a particularly advantageous manner, so that the use of expensive wearing parts and maintenance can be avoided in this regard. The axial introduction of the primary mixture stream into the burner is ultimately also made possible by the pre-introduction of the secondary air according to the invention by means of a secondary air inlet housing arranged on the circumference of the primary mixture pipe and the passage channels leading away from it and leading into the secondary air line.
• Due to the lower pressure drop in the system mentioned above, the upstream beater wheel mill is relieved at the same time, ie it requires less power.

In an advantageous embodiment of the invention, the passage channel is designed such that the secondary air flow tangentially, radially and an intermediate angle range can be introduced into the secondary air tube. By this design measure, it is possible, the secondary air flow by means of an aid, e.g. a swirl control device, with a strong, a weakened or no swirl supplied to the secondary air tube.

By forming the passage channel with a swirl control device or flap, the introduction or the inflow direction of the secondary air flow into the Secondary air tube can be controlled advantageous. With this measure, it is possible that the secondary air flow radially, ie introduced without any tangle or tangential, ie with swirl in the secondary air pipe or introduced without having to provide special facilities within the secondary air tube. The introduction with a weakened twist is also possible if the direction of introduction generated by the swirl control flap lies in a range between radial and tangential introduction. Due to the twisting of the secondary air flow, a negative pressure zone is formed at the burner outlet in the direction of the burner axis, which additionally transports hot flue gases out of the flame in the direction of the flame root and thus increases the ignition stability and the reaction density in the flame. In the defined ignition zone close to the burner, an area is created in which, due to the mixing between the dust jet and secondary air, both an ignitable dust / air concentration and the mixing of hot flue gases from the combustion chamber and hot flue gases from the flame itself reaches the ignition temperature. If, on the firing side or due to the fuel, no twisted secondary air is required, then this can be introduced radially into the secondary air tube.

In an advantageous embodiment of the invention, the channel of the inlet housing a with increasing circumferential angle to a substantially reduced depth in order to achieve a uniform flow velocity within the inlet housing and in the branching off therefrom passageways. This can most conveniently be achieved by a spiral entry housing.

In order to be able to optimize the position of the ignition zone on the burner, the secondary air tube or at least one outlet-side part of the secondary air tube can advantageously be displaced axially within the primary mixture tube.

The plane of the Sekundärluftrohraustrittes is advantageously flow medium side and with respect to the longitudinal axis of the secondary and primary mixture pipe seen downstream or upstream or at the same level of Primärgemischrohraustrittes. By this arrangement, an optimal alignment of the two Air pipes are created with respect to the ignition zone and the ignition stability.

It is advantageous to form the end face of the secondary air tube or of the passage channel facing away from the burner mouth on the upstream side of the primary mixture with a wear-resistant or flow-repellent agent in order to prevent vortices and wear on the end wall.

In an advantageous embodiment of the invention, the burner mouth facing the end wall of the passage channel is formed on the downstream side of the primary gas mixture with a displacement body to also prevent turbulence and deposits.

In an advantageous embodiment of the invention, the secondary air tube is formed on its outer periphery of the outlet end with a stagnation ring or it is flared to exit into the combustion chamber out. By both measures, the ignition stability can be additionally increased.

Due to the arrangement of a plurality of accumulation segments at the burner outlet, wherein each accumulation segment extends radially between secondary air tube and primary mixture tube and angularly over a partial area of the burner outlet circumference or over a partial area of the annular outlet between the secondary air tube and the primary mixture tube and the stowage segments are angularly spaced from one another uniformly Advantageously, the contact surface between primary mixture and hot flue gases further increased and achieved an improved mixing of primary mixture, secondary air and flue gases. An increased ignition stability is the result.

It is advantageous to arrange a swirl device and / or fluid side immediately upstream of the primary mixture tube, ie upstream, a spiral-shaped primary mixture housing within the primary mixture tube. With one of these measures can a twisted dust flow are generated and an additional ignition stability of the mixture flow can be achieved.

In an expedient embodiment of the invention, the distance L between the burner port and the burner port facing end wall of the secondary air inlet housing is 1.0 to 10 times the diameter d _{SL of} the secondary air tube to have a sufficient or effective rotational spin of the secondary air at the burner port.

In a further advantageous embodiment of the invention, the primary mixture pipe at its outlet end on a conical widening in order to influence the ignition stability.

An expedient embodiment of the invention has at the side opposite the primary mixture tube inlet side of the inner surface of the primary mixture tube at least one fluid side downstream of the Primärgemischrohreintrittes equalization body for equalization of the primary mixture stream. By this measure, mixture strands can be dissolved in the primary mixture pipe, which form predominantly on the opposite side of the mixture inlet, and the mixture flow can be made uniform.

It is also advantageous to design the longitudinal axis of the secondary air tube and primary mixture tube inclined in the exit direction by 0 to 20 ° to the horizontal in order to push the combustion zone deeper into the combustion chamber and thus to achieve a larger Ausbrandweg of the fuel.

In a further advantageous embodiment of the invention, an annular guide body is arranged on the inner circumference or the inner surface of the primary mixture pipe in the region of the secondary air tube or in the region of the Sekundärluftrohraustritt, which occupies part of the annular cross-section between the primary mixture tube and secondary air tube. This can be a local enrichment of the primary mixture be achieved on the inner periphery of the annular cross-section and consequently a more efficient mixing of the primary mixture with the secondary air.

It is also advantageous to arrange each of the passageways at the same angular distance from one another and to make them equally wide, i. that they angularly occupy an equal portion of the annular cross-section in order to achieve equal passage cross-sections for the primary mixture flow.

The burner according to the invention is advantageously sub-stoichiometric, ie operated with an oxygen supply, in order to achieve the lowest possible NO _x combustion of the fuel and thus to create the most environmentally friendly firing possible.

Embodiments of the invention with reference to the drawings and the description are explained in more detail.

Fig. 1

schematisch dargestellt die Frontansicht eines Strahlbrenners gemäß einem Stand der Technik,

Fig. 2

einen Längsschnitt durch den Strahlbrenner gemäß Schnitt A-A der Figur 1,

Fig. 3

schematisch dargestellt die Frontansicht eines Rundbrenners gemäß einem Stand der Technik,

Fig. 4

einen Längsschnitt durch den Rundbrenner gemäß Schnitt B-B der Figur 3,

Fig. 5

schematisch dargestellt den Querschnitt eines erfindungsgemäßen Brenners im Bereich der tangentialen bzw. radialen Zuführung der Sekundärluft (Schnitt E-E der Figur 6),

Fig. 6

einen Längsschnitt durch den Brenner gemäß Schnitt D-D der Figur 5,

Fig. 7

einen Längsschnitt gemäß Schnitt F-F der Figur 6,

Fig. 8

einen Teillängsschnitt durch den Brenner gemäß Schnitt D-D der Figur 5 im Bereich zwischen tangentialer bzw. radialer Sekundärluftzuführung und Brennermündung,

Fig. 9

schematisch dargestellt die Frontansicht eines erfindungsgemäßen Brenners, alternative Ausführung,

Fig. 10

einen Teillängsschnitt durch den Brenner gemäß Schnitt D-D der Figur 5 im Bereich zwischen tangentialer bzw. radialer Sekundärluftzuführung und Brennermündung, alternative Ausführung,

Fig. 11

einen Längsschnitt durch den Brenner gemäß Schnitt D-D der Figur 5, alternative Ausführung.

Fig. 12

wie Figur 5, jedoch alternative Ausführung

It shows:

Fig. 1

schematically shows the front view of a jet burner according to a prior art,

Fig. 2

3 a longitudinal section through the jet burner according to section AA of FIG. 1,

Fig. 3

schematically shows the front view of a round burner according to a prior art,

Fig. 4

a longitudinal section through the round burner according to section BB of Figure 3,

Fig. 5

schematically shows the cross section of a burner according to the invention in the region of the tangential or radial supply of secondary air (section EE of Figure 6),

Fig. 6

a longitudinal section through the burner according to section DD of Figure 5,

Fig. 7

a longitudinal section along section FF of Figure 6,

Fig. 8

a partial longitudinal section through the burner according to section DD of Figure 5 in the region between the tangential and radial secondary air supply and burner port,

Fig. 9

schematically shows the front view of a burner according to the invention, alternative embodiment,

Fig. 10

a partial longitudinal section through the burner according to section DD of Figure 5 in the region between the tangential and radial secondary air supply and burner port, alternative embodiment,

Fig. 11

a longitudinal section through the burner according to section DD of Figure 5, alternative embodiment.

Fig. 12

as Figure 5, but alternative design

Figures 1 and 2 comprises a jet burner according to a prior art. These burners consist of a dust nozzle 24, an under-air nozzle 25 and an upper-air nozzle 26, their cross-sections being rectangular. The entire burner consists in most cases of several dust nozzles 24, usually 2 or 3 pieces. In this case, lying in the vertical direction between two dust nozzles 24 upper and lower air cross-sections can be combined to form an intermediate air cross section.

Brown coal is mainly ground in beater mills, dried with hot, sucked back from the combustion chamber or the combustion chamber 10 flue gases and by the ventilation effect of the beater wheel mill, not shown to the Dust nozzles 24 of the burner promoted. Therefore, a mixture of combustible dust, flue gas, water vapor and primary air exits from the dust nozzle 24 into the combustion chamber 10, which is referred to below as the primary mixture. From the top, bottom and intermediate air nozzles 25, 26 exits the secondary air. Inside the rectangular dust nozzle 24, core air pipes (not shown) are generally integrated, through which a small part of the combustion air emerges.

FIG. 2 shows the longitudinal section of a jet burner with the exit of the jets into the combustion chamber 10. The ignition zone 18 of such a burner is generally located at a certain distance from the burner outlet, namely in the region in which it makes contact between the secondary air streams or . rays 19 and the dust stream or jet 20 comes. In this case, the dust jet 20 is first heated to above the combustion chamber 10 sucked, hot flue gas 21 to the ignition temperature and pyrolyzed. Due to the geometrical arrangement of the dust 24 and air nozzles 25, 26, the recirculated, hot flue gas 21 is sucked by the dust jet 20 mainly on the side surfaces of the rectangular dust nozzle 24 (FIG. 1).

FIGS. 3 and 4 show a round or swirl burner according to a prior art, which has a central, round dust or primary mixture pipe 4 and a secondary air pipe 3 concentric therewith. In these round burners, usually both the secondary air flow 19 and the dust flow 20 are twisted. For this purpose, in the dust tube 4, the swirl blades 12 and on the secondary air side, a spiral secondary air inlet housing 28 with tangential secondary air supply available.

FIGS. 5 to 12 show possible embodiments of a burner 1 according to the invention, with FIGS. 5 and 12 showing a cross-section in the area of pre-insertion and introduction of the secondary air into the secondary air tube, and FIGS. 6, 8, 10 and 11 each show a longitudinal section or partial longitudinal section of the burner 1 show, from which the structure of this burner will be apparent. According to FIGS. 5 and 6, the burner 1 is essentially formed from a central and round secondary air tube 3, the center of which is the longitudinal axis 27, and a round primary mixture tube or dust tube 4, which concentrically surrounds the secondary air tube 3 to form an annular cross-section 9. The inlet-side end 6 of the primary mixture pipe 4 is connected to a supply line 17 arranged substantially perpendicular to the primary mixture pipe 4 and the inlet-side end 5 of the secondary air pipe 3 is connected via passageways 35 and via the channel 40 of the secondary air inlet housing 28 to a supply line 16. The outlet-side ends 7, 8 of the primary mixture 4 and secondary air pipe 3 open into the burner opening or burner opening 2 of the combustion chamber wall 11. The secondary air outlet pipe 7 extends over the entire cross-section of the secondary air pipe 3 and optionally via the conical expansion 30, which in the, Figure 8 is shown as a preferred embodiment of the invention. The Primärgemischrohraustritt 8 extends over the entire cross-section of the annular cross section 9 between the two tubes 3 and 4 reduced by - if applied - by the conical expansion 30 of the secondary air tube 3 caused narrowing or extended - if applied - to the conical expansion 48 of Primary mixture pipe 4.

The supply of the entire secondary air flow 19 or all beyond the primary air in the air burner 1 takes place in the flow direction (shown by arrows in the figures) through the supply line 16, which is preferably perpendicular to the burner longitudinal axis 27, through the one radial After deflection of the flow 19 in the secondary air tube 3 - the end face of the inlet-side end of the secondary air tube 3 is closed according to the invention with an end wall 38 - this flows parallel to the longitudinal axis 27 and exits at the open cross-section of the Sekundärluftrohraustrittes 7 from the secondary air pipe 3 into the combustion chamber 10. In this case, the passage channels 35 are formed such that the secondary air flow 19 can be introduced into the secondary air tube 3 tangentially, radially and in any desired intermediate direction.

In order to allow the entry of the brought by the supply line 16 and the inlet housing 28 Sekundärluffstromes 19 in the centrally located secondary air duct 3 according to the invention at least two passageways 35 - in the example according to Figures 5 to 12, there are three passageways 35 - provided the channel 40 of the Ingress housing 28 connect to the inner cross section of the secondary air tube 3. In the region of the passageways 35, both the primary mixture pipe 4 and the secondary air pipe 3 openings 42, 43 in the size of the cross section of the passage channel 35 for the passage of the secondary air stream 19. Each passageway 35 assumes an angular part of the annular cross-section 9 between the primary mixture pipe 4 and the secondary air pipe 3, wherein in a preferred embodiment, each passage channel 35 angular occupies the same part of the annular cross-section 9.

The cross section of the passageways 35 is generally rectangular - with a width b and a height h - formed. In the flow direction, the passageway 35 is formed such that, as already stated above, the secondary air flow 19 can be introduced into the secondary air tube 3 either radially, tangentially or in an angular range therebetween. This specification can be achieved for example by a passageway 35 according to FIG 12, in which the side walls 46, 47 are formed accordingly. To control the desired secondary air inflow direction, a swirl control device 34, in particular a swirl control flap, which is arranged within the passage channel 35 or at the secondary air tube inlet 5 or at the opening 42, can be provided. The passageway 35 is formed by means of the end walls 39 and 45 and the side walls 46 and 47.

In a preferred mode of operation of the burner 1, the secondary air flow 19 is tangentially introduced into the secondary air tube 3 by means of the swirl control device 34 and the current 19 is thus given a rotational twist which is maintained until exit into the combustion chamber 10 and is achieved without separate devices in the secondary air tube 3 , By means of the swirl control device 34, the swirl of the secondary air flow 19 can be influenced or weakened up to the swirl-free feeding with radial introduction of the secondary air flow 19 into the secondary air pipe 3.

The swirl control device 34 of all passageways 35 can be operated, for example, by a central, not shown Spindelverstelleinrichtung, so that at each passageway 35 exactly the same control position and thus the same secondary air quantity setting is achieved.

The passageways 35 are preferably uniformly spaced from each other within the annular cross-section 9, so that the passages 44 for the primary mixed stream 20 at the same transverse dimensions of the passageways 35 have the same cross-sections and a uniform distribution of the primary mixture stream 20 is achieved.

The inlet housing 28, which is arranged radially outside the primary mixture tube 4 and in the region of the passage channels 35, extends over at least part of the circumference of the tube 4 in such a way that secondary air can be applied to all existing passage channels 35. The inlet housing 28 may simply be a box-shaped housing, thus forming the aforementioned channel 40 between the tube 4 and the outer wall of the housing 28 (see Figure 12). In this case, the channel 40 formed by the inlet housing 28 on the outer circumference of the tube 4 preferably has a substantially reduced depth with a larger circumferential angle to a largely uniform over the circumference speed and allocation of the secondary air flow 19 to each passageway 35 and 35 in further to achieve the secondary air tube 3. This requirement can be achieved, inter alia, by a preferred spiral formation of the inlet housing 28.

Since the swirl generated by the tangential introduction into the secondary air pipe 3 may decrease with the length of the pipe 3, it makes sense that the tangential introduction of the secondary air is not arranged too far away from the burner orifice 2. The distance L between the burner orifice 2 and the end wall of the inlet housing 28 facing the burner mouth 2 (corresponds essentially also to the opening of the combustion opening 2 towards the opening 5) preferably formed with 0.5 to 10 times the diameter d _{SL of} the secondary air tube 3.

In order to change or optimize the position of the ignition zone 18 at the burner outlet 2, it is provided that the secondary air pipe 3 and a part 13 on the outlet side of the secondary air pipe 3 can be displaced axially within the primary mixture pipe 4. Thus, the exit plane of the exit-side end 7 of the secondary air pipe 3 or the outlet-side part 13 can be brought into different positions in relation to the exit plane of the outlet-side end 8 of the primary mixture pipe 4. In FIG. 6, the outlet plane of the outlet-side end 7 of the secondary air tube 3 or of the outlet-side part 13 is located upstream of the outlet plane of the outlet-side end 8 of the primary mixture tube 4, as seen on the flow medium side. Depending on the fuel and burner size, the dimension k can be up to 0.5 times the diameter d _{SL of} the secondary air tube 3, ie the two outlet-side ends 7, 8 can also be flush with one another. A supernatant of the secondary air tube 3, ie the exit plane of the outlet end 7 of the secondary air tube 3 is seen flow medium side by the dimension k downstream of the exit plane of the outlet end 8 of the primary mixture pipe 4, is possible. Here, the dimension k can also be up to 0.5 times the diameter d _{SL of} the secondary air tube 3.

In an existing axially displaceable outlet-side part 13, the secondary air tube 3 may consist of two parts, a stationary part and an axially displaceable part 13, wherein both parts are formed overlapping (Figure 10).

The ignition stability can also be influenced by design measures at the outlet 7 of the secondary air tube 3, by the end of the tube 3 undergoes a conical widening 30 or according to Figure 6 on the outer periphery of the secondary air tube 3, a jam ring 15 is provided according to Figure 10, which is the annular Reduced cross-section 9 at the Primärgemischrohraustritt 8.

According to FIG. 6, the burner 1 is supplied with primary air or primary gas, which essentially consists of primary air, flue gas and water vapor, together with particulate or pulverulent fuel through the feed line 17 arranged perpendicular to the primary mixture pipe 4 in most cases, and this mixture ( Downstream of the inlet 6 and upstream of the secondary air tube 3, the primary mixture tube 4 includes a flow stabilization region 49 in which the diverted primary mixture stream 20 is stabilized according to the invention, ie is aligned in the axial flow direction. Seen in the direction of flow, the primary mixture pipe 4 downstream of the flow stabilization region 49 or upstream of the secondary air pipe 3 experience a widening of the outer diameter to possibly substantially the same flow rates in the circular cross section 9 as in the flow stabilization region 49 to achieve. After flowing through the located in the region of or between the secondary air passageways 35 passages 44 and the primary mixture pipe 4 in a direction parallel to the longitudinal axis 27 of the primary mixed stream 20 emerges at the outlet 8 in the combustion chamber 10. In the passage 44 occurs compared to the free circular ring cross-section 9, an increased flow velocity, which proves to prevent deposits on this narrowed cross section to be advantageous.

For equalization of the primary mixture flow 20 within the flow stabilization region 49, at least one homogenizing body 31 can be provided within the primary mixture pipe 4, since strands, ie fuel dust accumulations, can form on entry of the primary mixture stream 20 into the primary mixture pipe 4. This occurs in particular on the side of the primary mixture pipe 4, which is located opposite the primary mixture pipe inlet 6. Conveniently, the or the homogenization body 31 is arranged on this side of the inner surface of the primary mixture tube 4, and that downstream of the flow path of the Primärgemischrohreintritt 6. The homogenization body 31 1 may be, for example, a sheet metal body.

FIG. 6 furthermore has an annular guide body 32 which can be arranged on the inner circumference or on the inner surface of the primary mixture pipe 4 in the region of the secondary air pipe 3 or preferably in the region of the secondary air pipe outlet 7 and which forms a radial part of the annular cross section 9 between the primary mixture pipe 4 and the secondary air pipe 3 occupies. Thus, a local enrichment of the primary mixture 20 to the inner periphery of the annular cross-section 9 can be achieved.

The inventive supply of the primary mixed stream 20 into the burner 1, the pressure loss is reduced in this system in an advantageous manner. Furthermore, a more uniform distribution of the dusty fuel over the cross section is achieved.

If the firing conditions require it, a swirl device can also be provided directly upstream of the primary mixture pipe 4 or the latter for the dust stream 20. This can be achieved in the form of a not shown spiral primary mixture inlet housing 29, which is arranged on the outer circumference of the primary mixture pipe 4 and is connected to the feed line 17. By the twisting of the dust stream 20, an increase in the ignition stability is again achieved. Instead of the spiral-shaped primary mixture inlet housing 29, a swirl device 14 can be provided within the primary mixture pipe 4 or its annular cross-section 9 for swirling the dust stream 20 (FIG. 8). Furthermore, in order to increase the ignition stability instead of a jam ring 15 according to FIG. 10, the outlet-side end 7 of the secondary air tube 3 is alternatively designed with a conical widening 30.

In order to prevent the primary mixed stream 20, which is brought up by the primary mixture pipe 4 and distributed in the area of the secondary air pipe 3 against the annular cross section 9, from striking against the end wall 38 of the secondary air pipe 3 or against the end wall 39 of the throughflow channels 35, strong turbulences are formed and on the other strong erosion on the end walls occur in an advantageous embodiment of the invention, the end wall 38 and / or the end walls 39 upstream of the same with wear-resistant or current-repellent means 36 and 37, respectively. These means 36, 37 may be solid or hollow body and may be formed of known wear protection materials and in the form known for Abweiskörper, for example, flat, semicircular, streamlined, triangular, etc. (Figures 6 and 7).

After the primary mixed stream 20 has passed through the passages 44 between the passageways 35, downstream of the end wall 45 of the respective passageways 35, turbulences and solid accumulations of the primary mixture stream 20 can occur, resulting in pressure losses and non-uniform supply of the combustible dust in the burner 1. In order to prevent this, preferably the end wall 45 according to FIG. 7 is formed downstream with a displacement body or spoiler 41. This can be the same as the means 36, 37 procured or trained.

In order to maintain a uniform velocity of the primary mixed stream 20 within the cross section 9, with conical expansion 30 of the secondary air pipe 3, the outlet of the primary mixture pipe 4 can also be formed with a conical widening 48 (FIG. 8).

According to FIG. 9, four stowage segments 33 can be arranged at the burner outlet 2, wherein each stowage segment 33 extends radially between secondary air tube 3 and primary mixture tube 4 and angularly over a partial area of the annular outlet between the two tubes 3, 4 and the stowage segments 33 are uniformly spaced from each other , As a result, the contact area between the exiting primary mixed stream 20 and the sucked hot flue gases is further increased and an improved mixing of primary mixture 20, secondary air 19 and flue gases 21 is achieved. An increased ignition stability is the result. The storage segment 33 may be, for example, a correspondingly manufactured sheet metal segment.

By the measure that the primary mixture or dust stream 20 at the outlet into the combustion chamber 10 is not enveloped by a shell air (secondary, tertiary air), hot flue gases from the combustion chamber 10 can immediately after the exit over the entire circumference of the dust stream exit jet be sucked so that they can act on the fuel particles and heat them. Thus, the dust jet receives its ignition temperature early, the dust-like fuel pyrolyzed much better, i. it releases the gaseous components of the fuel, and as a result the ignition stability is improved.

By injecting a twisted central secondary air flow 19 into the combustion chamber 10 is formed at the burner outlet 2 in the immediate vicinity of the longitudinal axis 27, a negative pressure zone 23, the additional hot flue gases 22 transported from the flame towards the flame root and thus increases the ignition stability and the reaction density in the flame. Thus arises in the burner outlet near ignition zone 18, an area in which by mixing between the dust jet 20 and secondary air 19 both an ignitable dust / air concentration and the interference of hot flue gases 21 from the furnace 10 and hot flue gases 22 from the flame Ignition temperature is reached.

It is advantageous to combine two or more burners 1 according to FIG. 11. The respective secondary air and primary mixture pipes 3, 4 are usually arranged spaced apart in the vertical direction. By this measure, the reaction density in the ignition zone 18 and thus the ignition stability is increased. The summary of several burners 1 but can also have constructive reasons, for example, to make the firebox 10 no larger than necessary.

The longitudinal axis 27 of the burner 1 may be formed horizontally or, as shown in Figure 11, by an angle which is preferably 0 to 20 °, be inclined in the discharge or to the burner outlet 2 towards the horizontal. Due to the slightly inclined downward direction of the secondary air and primary mixture pipes 3, 4, the residence time of the fuel in the combustion chamber 10 can be increased and thus the burnout can be improved.

The burner 1 according to the invention, for example, in direct (ie the fuel comes directly from the mill) lignite dust with upstream coal mills, especially Schlagrad- or bowl mills (not shown) and indirect (ie the fuel is already ground and is for example from a fuel silo by means of pneumatic Conveyors) dry brown coal dust furnaces (not shown). The differences are only in the amount and in the composition of the gas mixture present in the dust jet 20 in addition to the fuel dust.

The burner 1 according to the invention is operated in a preferred mode of operation substoichiometric, ie with an oxygen supply to achieve the lowest possible NO _x combustion of the fuel used and thus to create the most environmentally friendly firing. The air required for further combustion of the fuel is added to the furnace, for example in the form of upper air in the course of the combustion within the combustion chamber 10.

LIST OF REFERENCE NUMBERS

1

burner

2

Burner mouth or outlet

3

Secondary air pipe

4

Primary mixture tube

5

Secondary air pipe inlet

6

Primary mixture tube inlet

7

Secondary air tube outlet

8th

Primärgemischrohraustrüt

9

Annular cross section between secondary air and primary mixture pipe

10

firebox

11

Furnace wall

12

swirl device

13

Outlet-side part of the secondary air tube

14

swirl device

15

storage ring

16

Supply line for secondary air

17

Supply line for primary air or gas and fuel (primary mixture)

18

ignition zone

19

Secondary air flow

20

Primary mixture or dust stream

21

Recirculated hot flue gas stream

22

Recirculated hot flue gas stream

23

Under pressure zone

24

Dust or primary mixture nozzle

25

Unterluftdüse

26

overfire

27

longitudinal axis

28

Secondary air inlet housing

29

Spiral primary mixture inlet housing

30

Conical expansion of the secondary air tube

31

Homogenization body

32

conducting body

33

accumulation segment

34

Swirl control valve

35

Passageway

36

Stromabweisendens means or guide

37

Stromabweisendens means or guide

38

Front wall secondary air tube

39

Front wall passage channel

40

channel

41

Outflow body or spoiler

42

opening

43

opening

44

passage

45

Front wall passage channel

46

Sidewall passageway

47

Sidewall passageway

48

Conical expansion of the primary mixture pipe

49

Flow stabilization region

Claims (28)

1. A burner to combust particulate fuel, in particular inert-rich coal dust, involving
   a secondary air tube (3), located about a burner longitudinal axis (27) and closed off at the end facing away from the burner opening (2) with an end wall (38), to introduce the entirety of the secondary air,
   a primary mixture tube (4) that surrounds the secondary air tube (3), forming an annular cross-section (9), to introduce primary air or primary gas and fuel, wherein the primary mixture tube (4) has a flow stabilization zone (49) placed upstream of the secondary air tube (3) as seen in the flow direction of the primary mixture (20),
   an inlet housing (28) that surrounds at least a portion of the primary mixture tube (4) as seen along the perimeter and that forms a radial channel (40) to feed the secondary air (19),
   and at least two penetration channels (35) that connect the channel (40) to the inner cross-section of the secondary air tube (3) and that pass across the annular cross-section (9) to introduce the secondary air stream (19) from the channel (40) into the secondary air tube (3).
2. A burner according to claim 1, characterized in that the penetration channel (35) is designed such that the secondary air stream (19) can be introduced to the secondary air tube (3) tangentially, radially and at an angle in between.
3. A burner according to claim 1 or 2, characterized in that the penetration channel (35) is designed with a vortex control device (34) to introduce the secondary air stream (19) into the secondary air tube (3) in a tangential or radial direction, or in a direction eccentric to the longitudinal axis (27) of the secondary air tube (3).
4. A burner according to one of claims 1 through 3, characterized in that the channel (40) of the inlet housing (28) has a depth that essentially decreases along the perimeter with increased angle.
5. A burner according to claim 4, characterized in that the inlet housing (28) is spiral in design.
6. A burner according to one of claims 1 through 5, characterized in that the secondary air tube (3) or at least an outlet section (13) of the secondary air tube (3) can shift inside the primary mixture tube (4).
7. A burner according to one of claims 1 through 6, characterized in that the plane of the secondary air tube outlet (7) lies upstream or downstream or in the same plane as the primary mixture tube outlet (8) in the direction of flow and with respect to the longitudinal axis (27).
8. A burner according to one of claims 1 through 7, characterized in that the end wall (38) of the secondary air tube (3) upstream of the primary mixture (20) and facing away from the burner opening (2) is designed with a wear-resistant and flow deviating means (36).
9. A burner according to one of claims 1 through 8, characterized in that the end wall (39) of the penetration channel (35) upstream of the primary mixture (20) facing away from the burner opening (2) is designed with a wear-resistant and flow deviating means (37).
10. A burner according to one of claims 1 through 9, characterized in that the end wall (45) of the penetration channel (35) on the downstream side of the primary mixture (20) facing toward the burner opening (2) is designed with a deviating element (41).
11. A burner according to one of claims 1 through 10, characterized in that the secondary air tube (3) is designed with a baffle ring (15) on the outer perimeter of the outlet end (7).
12. A burner according to one of claims 1 through 11, characterized in that the secondary air tube (3) is designed with a conical widening (30) at its outlet end (7).
13. A burner according to one of claims 1 through 12, characterized in that the burner outlet (2) is designed with multiple baffle segments (33), wherein each baffle segment (33) extends radially between the secondary air tube (3) and the primary mixture tube (4) and angularly across a portion of the annular outlet between the secondary air tube (3) and the primary mixture tube (4) and wherein the baffle segments (33) are at an even angular distance from one another.
14. A burner according to one of claims 1 through 13, characterized in that there is a vortex device (14) located inside the primary mixture tube (4) or is attached directly upstream to it.
15. A burner according to one of claims 1 through 14, characterized in that the distance L between the burner opening (2) and the end wall of the inlet housing (28) facing toward the burner opening (2) is 0.5 to 10 times the diameter d_SL of the secondary air tube (3).
16. A burner according to one of claims 1 through 15, characterized in that the primary mixture tube (4) is designed at its outlet end (8) with a conical widening (48).
17. A burner according to one of claims 1 through 16, characterized in that at least one smoothing element (31) is placed downstream of the primary mixture tube inlet (6) at the section of the inner surface of the primary mixture tube (4) that sits opposite the primary mixture tube inlet (6), said smoothing means intended to smooth out the primary mixture stream.
18. A burner according to one of claims 1 through 17, characterized in that the longitudinal axis (27) of the secondary air and primary mixture tubes (3, 4) is tilted by 0 to 20° to horizontal in the discharge direction.
19. A burner according to one of claims 1 through 18, characterized in that an annular guide (32) is placed at the inner circumference or the inner surface of the primary mixture tube (4) in the area of the secondary air tube (3) or in the area of the secondary air tube outlet (7) that takes up a radial section of the annular cross-section (9).
20. A burner according to one of claims 1 through 19, characterized in that the primary mixture feed line (17) is designed as a spiral primary mixture housing (29) directly upstream of the primary mixture tube inlet (6) to produce a vortexed dust stream or primary mixture stream (20).
21. A burner according to one of claims 1 through 20, characterized in that the penetration channels (35) are placed at the same angular separation from one another.
22. A burner according to one of claims 1 through 21, characterized in that the penetration channels (35) each take up the same size section of the annular cross-section (9).
23. A process to combust particulate fuel, in particular inert-rich coal dust, by means of a burner that involves a central secondary air tube and a primary mixture tube that surrounds the secondary air tube concentrically and that forms an annular cross-section, wherein all secondary air fed to the burner, or air not included in the primary air, is fed to the burner via the secondary air tube, and wherein a primary mixture consisting of primary air or gas and fuel is fed through the primary mixture tube, and wherein the secondary air is fed to the secondary air tube through at least two penetration channels that penetrate the annular cross-section between the secondary air tube and the primary mixture tube.
24. A process according to claim 23, characterized in that the secondary air stream is introduced radially into the secondary air tube by means of a vortex device placed in the penetration channel.
25. A process according to claim 23, characterized in that the secondary air stream is introduced into the secondary air tube by means of a vortex device placed in the penetration channel, forming a rotating vortex flow tangentially or eccentric to the centre axis of the secondary air tube.
26. A process according to one of claims 23 through 25, characterized in that a vortex is imparted to the primary mixture stream by a vortex device.
27. A process according to one of claims 23 through 26, characterized in that the ignition zone can be shifted within the burner opening by axially shifting the secondary air tube or an outlet section of the secondary air tube.
28. A process according to one of claims 23 through 27, characterized in that the burner is operated sub-stoichiometrically.

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