EP0101462B1 - Burner for pulverulent, gaseous and/or liquid fuels - Google Patents

Description

The price trend for liquid and gaseous fuels, which has risen sharply in recent years, has prompted more solid fuels to be used, which are often sufficiently cheaply available. Grate firing, which is common for solid fuels and is mainly used for steam and hot water generation, is not possible in many areas of industrial process heat, because there are usually specific requirements for the process and location of the combustion. For these areas, the solid fuels can only be used as "dust" (i.e. in fine or powdered form), which can be burned with the appropriate burners in a flame similar to the flames of liquid and gaseous fuels.

The use of fuel dust, primarily hard coal dust, has so far been limited mainly to large combustion plants with largely stationary firing conditions, especially for power plants and in the area of industrial process heat for the rotary kilns of the cement industry. However, there is an increasing need for dust firing for applications with medium firing performance, for example in annealing and melting furnaces in the metal industry, furnaces for ceramic products, melting furnaces for hollow and flat glass, steam boilers with combustion chamber or apparatus for thermal treatment (such as dryers, for example) with upstream combustion chamber). These new areas of application require extremely flexible burners, which must produce a flame with a defined ignition and burnout behavior (flame shape) even under widely varying load conditions. In addition, they must also be able to process combustible dust with different ignitability and different calorific values, because for reasons of price, besides hard coal dust, lignite dust, wood dust and sewage sludge dust as well as all other dust, if they are sufficiently combustible. This results in the need for a specific burner technology, to which the concepts and experiences from large-scale combustion powders can only be transferred to a limited extent. On the other hand, dust flames have a different ignition and burnout mechanism than flames from liquid and gaseous fuels, so that the mature burner technology for liquid and gaseous fuels cannot be used either.

Normally, the combustion dust is fed to a dust burner in a mixture with a small amount of conveying air as a relatively compact jet. This beam must first be made ignitable, i. H. it must be heated up and mixed with combustion air. During processing, the volatile constituents contained in the fuel dust are first outgassed. As soon as a sufficiently high temperature is reached, these volatile constituents ignite and burn, and then the combustible solid constituents are burned out. Such an ignition and burnout mechanism depends on the one hand on the particle size of the fuel dust (smaller particles are heated up more quickly) and on the other hand on the fuel dust material itself, because the contents of volatile components, water and ash have a wide range of different materials.

Large plants are usually operated with largely constant fuel dust, so that larger fluctuations in the type and quality of the fuel dust need not be taken into account. In general, in the case of burners intended for large systems, the fuel jet is introduced directly into the combustion chamber. The preparation and ignition of the fuel jet takes place (either only under the thermal conditions in the combustion chamber or with the support of oil or gas as support fuel) by recirculating the hot gases present in the combustion chamber to the burner mouth and penetrating the fuel jet. Additional measures can be provided that favor the penetration of the hot gases into the fuel jet and contribute to stabilizing the ignition process. For example, the fuel jet can be more or less fanned out into a cone shape by swirling or by blowing in air. A corresponding effect is obtained if the combustion air is supplied around the burner mouth and is influenced by partial obstruction or conical widening of the air pipe mouth or by swirling in such a way that a vacuum region forms near the jet root. However, as the fuel jet is fanned out, the flame becomes shorter and bulbous, and more and more dust particles and ash particles are released from the context of the flame and carried radially outwards.

These burners, which process and ignite the fuel jet in the combustion chamber, are not suitable for variable requirements because the ignition process can then no longer be kept stable. In addition, in many areas of industrial process heat, ignition stabilization, which is accompanied by a greater fanning out of the fuel jet, is also prohibited, since the radial particle discharge can cause contamination of the product and cause problems in the combustion chamber. In hot combustion chambers with temperatures above around 1100 ° C, the ash particles that are discharged become soft or even liquid and lead to caking and signs of corrosion. In less hot combustion chambers the discharged ash particles remain sufficiently solid, but the discharged dust particles no longer ignite or extinguish before they are completely burned out, something in everyone Case means a loss of fuel. Long, slim flame shapes with the least possible discharge of particles to the outside are desired.

A swirl burner for oil and / or gas operation is known from AT-B-358 702, in which the entire combustion process takes place in a burner muffle. In addition to a central inlet of combustion air, which surrounds the fuel supply and is provided with swirl surfaces, a second air supply is provided, from which channels open in a ring shape into the conically widening part of the burner muffle. In this case, individual swirl generators are arranged in the individual channels, each of which produces a swirl about its own axis and thus leads to a violent swirling of the fuel in the burner muffle. In this vortex burner, there is no fuel jet in the burner muffle, so that there is no long, slim flame shape with little discharge of particles to the outside and the burner is not suitable for the use of dusty fuels.

GB-A-340 858 shows a heavy oil burner in which in a deflector which surrounds the tube for the fuel supply and which widens conically outwards, ring-shaped openings are arranged through which an undisturbed portion of combustion air flows inwards to that of one Fuel injected into the combustion chamber and is swirled intensively with it.

GB-A-893 016 describes a device for mixing fuel and combustion air. In one end of a mixing chamber which can be used as a combustion chamber, the fuel is injected centrally under pressure in such a way that an outwardly diverging main stream is formed, and in the other end of the chamber a compressed air stream is introduced in the opposite direction to the fuel stream and converges to the interior of the fuel stream , so that the two flows mix and a toroidal vortex is formed.

It has also already been proposed to ignite the fuel jet not only in the combustion chamber but rather in a special ignition chamber upstream of the burner mouth. Such a burner type is from F. Schoppe in the brochure "Calculation of burners, combustion chambers and similar flow devices", published by A. W. Gentner KG, Stuttgart (without year), pages 37ff. have been described. The ignition chamber has a conically widening wall that merges into an outlet pipe leading into the combustion chamber. The mouth of a tube for supplying the fuel jet is arranged centrally in the chamber wall, and this mouth is surrounded by an air inlet (for example an annular gap) via which the combustion air is introduced in the form of a swirl flow into the ignition chamber in order to create a negative pressure area near the jet root produce.

In operation, the swirl flow flows along the chamber wall towards the end of the chamber, where it is divided into two flow parts. The flow part near the wall reaches the combustion chamber via the outlet pipe, while the remaining part is led back to the jet root along the fuel jet in a recirculation flow, i.e. in the opposite flow direction, along the fuel jet. As a result, the hot gases resulting from the combustion processes taking place in the ignition chamber are transported to the root of the jet, so that treatment and ignition of the outer edge zone of the fuel jet begin shortly behind the mouth of the fuel pipe, which then occurs - because there is between the fuel jet and form vortices in the oppositely directed recirculation flow, continues relatively quickly into the interior of the fuel jet.

This burner has been developed for smaller outputs (e.g. for central heating boilers) and has some major disadvantages that make it unsuitable for operation at medium outputs and especially in the area of industrial process heat. Since, for various reasons, the entire combustion air has to be introduced into the ignition chamber as a swirl flow, not only does ignition occur in the ignition chamber, but also extensive combustion of the fuel dust occurs, so that only a short flame of almost burnt-out fuel leaves the burner mouth. The fuel jet is almost completely dissolved in the ignition chamber, which means that ash particles are carried to a considerable extent to the chamber wall. If the burner output is not sufficiently small, the temperatures in the ignition chamber are so high that these ash particles become liquid or viscous and can lead to caking. In addition, part of the swirl flow always reaches the combustion chamber and causes a further radial discharge of ash and fuel dust particles.

A coal dust burner is known from EP-A-6974, in which an ignition chamber with a wall that widens rotationally symmetrically in diameter in the direction toward the downstream and also has a rotationally symmetrical outlet pipe connected upstream thereof is also connected upstream of a combustion chamber that serves for the main combustion. A fuel feed opens into the center of the chamber, the mouth of which surrounds an air inlet for feeding a first stream of combustion air which runs coaxially to the fuel jet, the air inlet being provided with a swirl device which produces an internal recirculation flow in the ignition chamber through which the fuel contains hot combustion gases can be mixed and heated to ignition temperature. A further air supply, which opens directly into the combustion chamber and surrounds the outlet pipe, serves to supply the remaining combustion air. In this burner, operating difficulties such as extinguishing the flame or lowering the combustion temperature and resulting incomplete combustion are to be avoided by preheating the coal in a certain way.

With the present invention, a burner is to be created which has a stable ignition even with medium powers and variable requirements and which results in a long, slim flame shape with low radial discharge in the combustion chamber.

Starting from a burner of the latter type, the invention achieves this goal by providing a second air inlet for a second portion of the combustion air in the transition region between the wall of the ignition chamber and its outlet pipe for a second air flow along the outer circumference of the wall of the ignition chamber that the axial length of the recirculation flow within the ignition chamber is limited by the second air flow, the fuel jet is swirled within the outlet pipe and the fuel jet leaves the outlet pipe with an essentially axial flow direction, and that the air inlets are designed such that the sum of the first and second air flow is not more than 50% of the total combustion air required for stoichiometric combustion.

Starting from the known burner with a central feed of the fuel jet and swirled combustion air that mixes with the fuel jet into an ignition chamber, the invention achieves this goal in that only a portion of the total required combustion air can be introduced into the ignition chamber via the swirl air inlet, that in Area between the chamber wall and the outlet pipe, a second air inlet is provided, via which a further portion of the combustion air that also mixes with the fuel jet can be introduced into the ignition chamber, and that the sum of the combustion air portions participating in the mixing with the fuel jet within the ignition chamber is set to no more than 50% of the total combustion air required.

The invention is based on the consequent exploitation of the knowledge that a burner equipped with an ignition chamber should, in principle, be able to be used for variable requirements even at medium outputs and in particular in the area of industrial process heat if the previous disadvantages of this type of burner can be overcome. Surprisingly, it was found that these disadvantages can actually be completely eliminated by a favorable interaction of several measures, namely - in short - that the ignition chamber is operated with substoichiometric combustion air and the introduction of the substoichiometric combustion air takes place in a certain way via two inlets.

During operation of the burner, the combustion air portion fed into the ignition chamber as swirl air forms a negative pressure area around the fuel jet, which leads to the fuel jet being fanned out somewhat and at the same time a hot recirculation flow flowing back to the jet root. This formation of a negative pressure area is supported by the further combustion air component, which is fed in via the second inlet and surrounds the fuel jet in a ring, in such a way that a small amount of swirl air is sufficient for stable ignition of the fuel jet. The additional combustion air supplied via the second inlet also has other functions. In this way, it also has the effect that the swirl flow merges better into the recirculation flow and flows less with its part near the wall through the outlet pipe. In addition, it ensures that this transition takes place within a defined and predeterminable cross-sectional zone of the ignition chamber, that is, the axial length of the recirculation area can be influenced as required. Furthermore, it completely or at least largely reduces the swirl flow of the swirl air as well as a swirl present in the fuel jet (which can be caused by a special swirl generator and / or by the action of the swirl air), so that the fuel dust particles at the burner mouth into a predominantly axial Bring flow direction. For this purpose, it may be appropriate in individual cases to provide the additional combustion air with a counter-swirl. In addition, the further combustion air cools the outlet pipe and prevents residues, in particular melted ash particles, from accumulating therein.

It is also important for the invention to set substoichiometric combustion conditions in the ignition chamber. This in turn has several functions. First, the fuel jet within the ignition chamber is only slightly dissolved, and the radial particle discharge inside the ignition chamber is correspondingly low. Furthermore, the fuel jet is only available with a sufficient amount of air for ignition and incipient combustion, but no longer for further combustion, which means that the fuel jet burns out mainly in the combustion chamber and the ignition chamber remains correspondingly cooler.

Overall, the interaction of the measures according to the invention thus results in a burner which is variable and flexible within very wide limits, which can be operated even at medium power levels free of annoying ash deposits and which emits an arbitrarily swirl-free and completely ignited fuel jet with a largely axial flow direction, which - depending on the used fuel and the required operating conditions - a tempera at the burner mouth has assumed about 700-1200 ° C. This ensures stable combustion of the fuel jet with a long, slim flame shape in every combustion chamber - whether hot or less hot. ₅

The sub-stoichiometric proportion of the combustion air required in the ignition chamber also depends on the fuel used and the required operating conditions and results from the amount of combustion air introduced into the ignition chamber in total, which mixes with the fuel jet and thereby causes ignition and incipient combustion participates. The combustion air introduced into the ignition chamber is composed of ₁₅ from the conveying air for the combustion dust (with about 2-7% of the total air), the swirl air supplied via the first inlet (with about 2-15% of the total air) and the supplied through the second inlet ₂₀ further combustion air drying. Of this, the conveying air takes part completely and the swirl air almost completely takes part in the mixing with the fuel jet, while the further combustion air can be handled differently. They can be sized to ₂₅ and guided that it is completely mixed with, in which case its amount is apparent from the requirement that the sum of the mixed combustion air no longer must not exceed 50% of the total air. On the other ₃₀ hand, but the amount may be dimensioned also higher and, if necessary. Even make up the full balance of the Gesamfluft this further combustion air, provided, for example, is ensured by suitable flow guidance for the fact that only the maximum ₃₅ allowed part mixes with the fuel jet, while the remaining part unmixed emerges around the fuel jet into the combustion chamber. With these different handling of the further combustion air, a possibility is given ₄₀ ness to influence the flow and temperature profile of the burner mouth.

An advantage of the invention is, moreover, that the burner pulverized fuels is not limited to use, but can be operated without additional ₄₅ in the same manner with liquid or gaseous fuels. In the case of fuel dust as the main fuel and gas or oil as the support fuel, it is sufficient, for example, to switch off the main fuel and run the support fuel to full capacity without interrupting the burner operation if this should be necessary in the event of bottlenecks in the supply of the fuel dust. Also, from the outset gas and / or oil in particular the poor ₅₅ ignitable heavy oil, can be provided as the main fuel.

• Fig. 1 im Längsschnitt einen Brenner für Brenn-- staub als Hauptbrennstoff und mit Gas als Stützbrennstoff;
• Fig. 2 einen Querschnitt durch den Brenner in ₅ der Ebene II-II der Fig. 1;
• Fig. 3 im Längsschnitt einen Brenner mit einer anderen Ausgestaltung des Einlasses zur Einleitung der weiteren Verbrennungsluft in die Zündkammer;
• 10 Fig. 4 im Längsschnitt einen Brenner mit einer anderen Ausgestaltung des Einlasses zur Einleitung von Dralluft in die Zündkammer;
• Fig. 5 im Längsschnitt eine gegenüber Fig. 4 abgewandelte Ausführungsform des Brenners;
• ₁₅ Fig. 6 einen Querschnitt durch den Brenner in der Ebene V-V der Fig. 5;
• Fig. 7 im Längsschnitt eine weitere Ausführungsform eines Brenners für Brennstaub als Hauptbrennstoff mit Gas als Stützbrennstoff;
• ₂₀ Fig. 8 einen Querschnitt durch den Brenner in der Ebene VIII-VIII der Fig. 7;
• Fig. 9 im Längsschnitt einen Brenner für Brennstaub mit abgewandelter Zuführung des Stützgases;
• ₂₅ Fig. 10 im Längsschnitt eine Zündkammer mit einer gegenüber Fig. 1 abgewandelten Ausbildung des Einlasses für die weitere Verbrennungsluft;
• Fig. 11 im Längsschnitt einen Brenner für ₃₀ Brennstaub als Hauptbrennstoff und Öl als Stützbrennstoff;
• Fig. 12 einen Querschnitt durch den Brenner in der Ebene XII-XII der Fig. 11;
• Fig. 13 im Längsschnitt einen Brenner für flüssi- ₃₅ gen Brennstoff mit Drallzerstäubung;
• Fig. 14 im Längsschnitt eine Abwandlung des Brenners gemäß Fig. 13; und
• Fig. 15 im Längsschnitt eine Abwandlung des Brenners gemäß Fig. 14.

Numerous refinements and developments of the burner according to the invention are defined in the subclaims and are explained in more detail in the following description of individual embodiments with reference to the drawings. The same or functionally identical parts are designated with the same reference numerals. The figures show: ₆₅

• 1 shows a longitudinal section of a burner for fuel dust as the main fuel and with gas as the auxiliary fuel;
• Figure 2 shows a cross section through the burner in _{5 of} the plane II-II of Fig. 1.
• 3 shows in longitudinal section a burner with a different embodiment of the inlet for introducing the further combustion air into the ignition chamber;
• 10 shows a longitudinal section of a burner with a different embodiment of the inlet for introducing swirl air into the ignition chamber;
• 5 shows in longitudinal section an embodiment of the burner which is modified compared to FIG. 4;
• 6 is a cross section through the burner on the plane VV of Fig ₁₅ Fig. 5.
• 7 shows in longitudinal section a further embodiment of a burner for fuel dust as the main fuel with gas as the supporting fuel;
• 8 is a cross section through the burner in the plane VIII-VIII of Fig ₂₀ Fig. 7.
• 9 shows in longitudinal section a burner for fuel dust with a modified supply of the support gas;
• ₂₅ Figure 10 in longitudinal section of an ignition chamber with a comparison with FIG 1 modified embodiment of the inlet for the combustion air more..;
• 11 is a longitudinal section of a burner for ₃₀ fuel dust as the main fuel and oil as the auxiliary fuel;
• FIG. 12 shows a cross section through the burner in the plane XII-XII of FIG. 11;
• Fig. 13 in longitudinal section a burner for flüssi- ₃₅ gen fuel with Drallzerstäubung;
• FIG. 14 in longitudinal section a modification of the burner according to FIG. 13; and
• 15 shows a modification of the burner according to FIG. 14 in longitudinal section.

_40. The embodiment shown in Figs. 1 and 2 illustrates the principle of the inventive burner-βen the example of pulverized fuel as principal fuel, in conjunction with gas as a support fuel. Within an air tube 16, three ₄₅ concentric tubes 1, 2 and 3 are provided, which open together into an ignition chamber 20. Of these three pipes, the central pipe 1 is used to supply the fuel jet, the central tube 2 for supplying the supporting gas and the _50-making equipped at its Munich with a swirl generator 21 outer pipe 3 for supplying Dralluft into the chamber 20. In the illustrated embodiment, this swirl generator consists of a tube 3 final use, a space ₅₅ Drallring- 4 is in the standing over tangential holes 5 to the interior of the tube 3 and via an inlet 50 to the chamber 20 in connection. A constricting threshold 22 is expediently arranged at the inlet 50, which prevents ₆₀ backflow from the chamber 20 into the swirl annulus 4.

The chamber 20 is delimited by a curved wall 8, which extends outward from the swirl air inlet 50, and an outlet pipe 17, which is arranged downstream ₆₅ thereof, the cylinder can be formed drily, but can also expand or decrease in diameter. In Fig. 1 is shown in full that the outlet pipe 17 is reduced to the diameter of a cylindrical mouth part 11, and at the same time 17 'is indicated by a dashed cylindrical design of this outlet pipe. Between the wall 8 and the outlet pipe 17, the chamber 20 has a second annular inlet 60, which is formed in that the outlet pipe 17 has a somewhat larger diameter than the wall 8 at this point. The opening cross section of this inlet is expediently adjustable. For this purpose, for example, the outlet pipe 17 can be arranged displaceably in the axial direction of the air pipe 16, or a throttle body which is displaceable in the axial direction of the air pipe 16 and is not shown in FIG. 1 can be provided on the outside of the chamber wall 8.

1 and 2, the supporting gas is first fed into the chamber 20 together with the swirl air and caused to burn. Then the fuel dust jet consisting of a fuel dust / conveying air mixture is fed to the chamber 20. A swirl generator 24 can also be arranged in the tube 1 in order to fan out the fuel jet in the chamber 20 in a conical manner, as indicated by the arrows A. The swirl air emerging from the inlet 50 flows outward along the chamber wall 8 and then, as shown by the arrows B, transitions into an internal recirculation. As a result, the hot gases, which result from the combustion processes taking place in the chamber 20, are transported to the root of the fuel jet, so that there is stable ignition of the fuel jet and the jet at the burner mouth 49 is completely ignited.

The majority of the total required combustion air is supplied in the embodiment according to FIGS. 1 and 2 via the air pipe 16 and partly flows past the chamber 20 directly into the combustion chamber, as illustrated by the arrows D, but also partly via the Inlet 60 into the chamber 20 and flows there according to the arrows C along the outlet pipe 17 to the burner orifice 49. This partial air flow C which has entered the chamber 20 can make up about 5-45% of the total air and forms the further combustion air fraction which is inside the chamber 20 in addition to the swirl air and the conveying air is at least partially used for the ignition and incineration of the fuel dust. The combustion air available in the combustion chamber for the complete burnout of the fuel jet thus results from the outer partial air flow D and, if appropriate, an unburned remainder of the partial air flow C.

If the partial air flow C is to be provided with a counter-swirl to support its swirl-reducing effect, the simplest way of doing this is to arrange corresponding swirl generators in the area of the inlet 60, which are no longer shown in FIG. 1.

In addition, it is expedient to supply the swirl air to the burner with an upstream pressure that is higher than that of the main air, so that sufficient swirl energy can be generated even with a small amount of air. The typical range for the admission pressure of the combustion air in the main pipe 16 is about 0.01 to 0.06 bar overpressure, while the admission pressure of the swirl air in the pipe 2 can be about 0.08 to 0.4 bar overpressure.

3 shows a burner in which the partial air flow C is introduced into the chamber 20 with a tube 10 which is arranged concentrically with the central tube 1 and is connected to the chamber 20 via a number of oblique bores 29. In this embodiment, the chamber wall 8 is flat and the outlet pipe 61 adjoining the bores 29 is cylindrical, but this does not change the basic mode of operation of the burner. For the rest, as in FIG. 1, the swirl-reducing effect of the partial air flow C can also be supported by providing means for generating a counter-swirl in the tube 10 or by arranging the holes 29 obliquely in the tangential direction. The supply of the partial air flow D into the combustion chamber can take place analogously to FIG. 1 via an air pipe 16, but is expediently effected via separate air inlets, which can each be preceded by air preheaters. Neither is shown any further.

In the embodiment according to FIG. 1, it is possible to influence the length of the recirculation area of the swirl air during burner operation by appropriately adjusting the amount and, if necessary, the flow rate of the partial air flow C, so that the recirculation area either extends to the mouth 49 (arrows B ') or is pushed back to the holes 29 (arrows B). This allows the swirl flow to be reduced only after it has fulfilled its function, which is e.g. is important when using fuel dust with changing properties. If necessary, the partial air flow C can also be set so that it makes up the total amount of combustion air required, that is to say no further combustion air needs to be introduced separately into the combustion chamber.

The embodiment according to FIG. 4 largely corresponds to the embodiment according to FIG. 3, but provides for the introduction of two swirl air flows into the chamber 20. The wall of the chamber 20 is divided into an inner wall part 8 and an outer wall part 9. The first swirl air flow is fed to the swirl annulus 4 analogously to FIG. 1 via a tube 27 and the bore 5, so that it enters the chamber 20 in a swirled manner from the inlet 50. For the second swirl air flow, an additional annular inlet is provided between the wall parts 8 and 9, via an inlet concentrically surrounding the tube 27 28 and a second swirl annulus 7 connected to it by tangential bores 6 is fed. The partial air flow C is in turn fed through the tube 10 and introduced via an annular inlet 60 into the chamber 20, the outlet tube 62 of which is slightly conically widened. In this embodiment, there is the additional advantage that the swirl flow has a higher angular momentum due to the greater distance of the additional annular inlet 51 from the chamber axis.

In the embodiment according to FIGS. 5 and 6, as in FIG. 4, the wall of the chamber 20 is divided into the inner wall part 8 and the outer wall part 9. However, the entire swirl air is supplied through the pipe 3 and introduced via the bores 5 and 6 both into the inner swirl ring space 4 and into the outer swirl ring space 7. The swirl air then flows out of the swirl ring spaces 4 and 7 via the inlets 50 and 51 onto the wall parts 8 and 9, which are conical in this case. The outlet pipe 17 of the chamber is attached to the outer pipe 10, through which the partial air flow C on the outside of the wall part 8 is introduced into the chamber 20. 5 also shows swirl-generating means 18 in the tube 10.

In the embodiments according to FIGS. 1 to 6, the swirl of the swirl air emerging from the inlets 50 and 51 is generated through bores 5 and 6 which are introduced tangentially into the swirl ring spaces 4 and 7. Instead, as shown in FIG. 18, guide vane grids can also be used for swirl generation. Such an arrangement is shown in FIGS. 7 and 8. The inlets 50 and 51 are each assigned their own pipes 14 and 15, in which guide vane grids 12 and 13 are arranged for swirl generation. In addition, leading edges 23 are also provided in the mouth part 11 of the outlet pipe for swirl reduction. In addition, desired turbulence can also be generated by a radial blocking surface 19 arranged on the outside of the mouth part 11 in the path of the combustion air conducted past the chamber 20 on the outside.

FIG. 9 shows a modification of the previously described embodiments of the burner according to the invention in that the support fuel is introduced into the chamber 20 through an inner pipe 25 arranged in the fuel pipe 26. The fuel is thus supplied via the annular space which is formed between the tubes 25 and 26.

A modified embodiment of the inlet for the partial air flow C is shown in the embodiment according to FIG. 10. The chamber wall 9 is connected in the area of its largest diameter to the outlet pipe 17, the inlet for the partial air flow C being formed by bores 29 or slots 58.

In the embodiment according to FIGS. 11 and 12, in contrast to the previous exemplary embodiments, oil is used as the auxiliary fuel. This support oil is supplied via a tube 30 which coaxially surrounds the central fuel tube 1 and which is closed at the end and connected to a further coaxial tube 33 via radial bores 31, into which atomizing air is introduced. The support oil then emerges together with the atomizing air from the mouth 32 of a channel 54 into the chamber 20. The bores 31 can optionally be arranged obliquely in order to impart a swirl to the support oil.

But it is also possible to use oil (especially heavy oil) as the main fuel. Embodiments suitable for this are shown in FIGS. 13-15. These embodiments have in common that only the fuel supply needs to be adapted to the oil use, while the formation of the ignition chamber and its operation with swirl air or the further combustion air (partial air flow C) remains unchanged.

In the embodiment according to FIG. 13, a swirl atomization of the main oil with additional swirl oil is provided. The main oil is introduced through a central tube 35 into the chamber 20 via a swirl device 40, an outlet nozzle 41 connecting to the tube 35. Oil is also supplied through a tube 36 surrounding the central tube 35, which is introduced tangentially into a swirl chamber 38 via bores 37, from there it passes into a fuel nozzle 39 arranged in front of the outlet region of the outlet nozzle 41 and from there together with the main oil into the chamber 20 exit. The outlet nozzle 41 is preferably axially displaceable with respect to the fuel nozzle 39. In addition, the tube 36 for supplying the swirl oil is expediently surrounded by a tube 42, which forms an annular jacket closed on the end face, into which a heating medium for preheating the fuel can be introduced.

In the burner shown in FIG. 14, of which only the inner part is shown, the main oil is swirled with swirl oil. In this case, the main oil is introduced through a central tube 45, which is provided at the front end with an outlet nozzle 53, in front of the mouth 46 of which the fuel nozzle 39 is located. Together with the main oil emerging from the mouth 46, swirl oil gets into the fuel nozzle. The swirl oil is fed through the pipe 36 as in FIG. 13, undergoes a swirl through the bores 37 and enters the nozzle 39 via the swirl chamber 38. In this embodiment, the position of the tube 45 with respect to the fuel nozzle 39 cannot be changed. Instead, a central nozzle needle 55 is arranged axially displaceably in the tube 35, through whose conical tip 59 the amount of oil emerging can be adjusted. Otherwise, the main oil can also be introduced into the fuel nozzle 39 with a swirl by arranging a swirl device 48 in the space between the nozzle needle 55 and the tube 45.

The burner shown in FIG. 15 differs from the burner according to FIG. 14 only in that instead of the central nozzle needle 55 there is a central tube 43 which is axially displaceably mounted in the tube 45. That before the end 47 of this tube 43 is conical for adjusting the fuel supply through the nozzle 53 and also contains a passage 44 through which air can be blown into the fuel nozzle 39 to assist the atomization of the main oil by the swirl oil. Here too, as in FIG. 14, a heating jacket can be provided, which is not shown further.

Claims (20)

1. Burner for pulverized, gaseous and/or liquid fuels, comprising an ignition chamber (20) preceding a combustion space which serves for the main combustion, said ignition chamber being provided with a wall (8; 9) diverging rotationally symmetrically in diameter in a downstream direction and with an outlet pipe (17, 11; 17', 61, 62) adjoining thereto, a tubular fuel feed (1; 26; 35; 45) opening centrally into the ignition chamber, an air inlet (50) annularly surrounding the mouth of said feed for feeding a first combustion airstream extending coaxially with the fuel jet, said air inlet being provided with a twisting device (5) which produces inside the ignition chamber an internal recirculation flow (B) by which the fuel is thoroughly mixed with the hot combustion gases and heated up to ignition temperature, and a further air-feed opening directly into the combustion chamber and surrounding said outlet pipe for feeding the remaining combustion air, characterized in that in the transition zone between the wall (8; 9) of the ignition chamber and its outlet pipe (17, 11; 17'; 61, 62) a second air inlet (60) for a second portion (C) of the combustion air is provided along the outer circumference of the wall (8; 9) of the ignition chamber such that by the second airstream the axial length of the recirculation flow (B) within the ignition chamber is limited, the fuel jet (A) is de- twisted within the outlet pipe and the fuel jet leaves the outlet pipe with substantially axial flow direction, and that the air inlets are designed such that the sum of said first and said second airstream is not more than 50% of the combustion air totally required for stoichiometric combustion.

2. Burner according to claim 1, characterized in that the second air inlet (60, 29, 58) is so arranged inside an airpipe (16) for feeding combustion air, that the second portion of the combustion air enters the ignition chamber (20) and the remaining portion (D) flows past the ignition chamber into the combustion space.

3. Burner according to claim 1, characterized in that the second air inlet (60, 29, 58) for the second portion (C) of the combustion air is connected with a separate feedpipe (10).

4. Burner according to claims 2 or 3, characterized in that the second air inlet (60) is formed as an annular gap between the wall (8; 9) of the ignition chamber and the outlet pipe.

5. Burner according to claims 2 or 3, characterized in that the second air inlet consists of a number of bores (29) or openings (58), which are disposed in the region of the transition from the chamber wall into the outlet pipe.

6. Burner according to one of the preceding claims, characterized in that a twist generator (e.g. 18) for generating a twist oriented in the opposite direction to the recirculation flow (B) is associated with the second air inlet (60, 29, 58).

7. Burner according to one of the preceding claims, characterized in that the aperture cross section of the second air inlet (60, 29, 58) is arranged adjustably.

8. Burner according to one of the preceding claims, characterized in that the wall (8) of the ignition chamber adjoins in conically or domed diverging form the air inlet (50) for the first combustion airstream, said air inlet being connected with a separate air-feedpipe (3, 27, 14) containing in its outlet zone a twist generator (21, 13).

9. Burner according to claim 8, characterized in that the wall of the ignition chamber (20) is subdivided into an inner wall part (8) and an outer wall part (9), that the inner wall part adjoins the air inlet (50) for the first combustion airstream and that, between the two wall parts, an additional twisting air inlet (51) is disposed, wherein a partial stream of the total combustion air provided can be introduced into the chamber through each of the two inlets.

10. Burner according to claim 9, characterized in that each of the two air inlets (50, 51) is connected with a separate air-feedpipe (27, 28), each possessing, in its outlet zone, a twist device (4, 5).

11. Burner according to claim 9, characterized in that both the air inlets (50, 51) are connected with a common air-feedpipe (3) which possesses two twist devices (4, 5, 6, 7).

12. Burner according to one of claims 8 to 11, characterized in that the air intended for twisting can be introduced into at least one of the air-feed- pipes (3, 27, 28, 14) with a prepressure raised above that of the second portion of the combustion air.

13. Burner according to one of claims 8 to 11, characterized in that one or both of the air inlets (50, 51) is formed as an annular gap.

14. Burner according to one of the preceding claims with pulverized fuel as principal fuel, characterized in that inside the first air inlet (50) for the first combustion airstream the outlets of a central pipe (1) and of a pipe (2) surrounding this concentrically, are disposed, one of the pipe outlets serving for supplying the principal fuel and the other serving for supplying a twisted or non-twisted support gas.

15. Burner according to one of claims 1 to 13 with pulverized fuel as principal fuel, characterized in that, inside the first air inlet (50) for the first combustion airstream, the outlet of a central pipe (1) for supplying the principal fuel and the common outlet (32) of a pair of pipes (30, 33) concentrically surrounding the central pipe for supplying supporting oil charged in twisting or non-twisting manner with atomizing air, are disposed.

16. Burner according to claims 1 to 13, with oil as principal fuel, characterized in that inside the first air inlet (50) for the first combustion airstream the outlets of a central pipe (35, 45) having an outlet nozzle (41) for the principal fuel and of a pipe (36) surrounding this concentrically and equipped with twist generating means (37), for supplying liquid twisting fuel, are disposed, a fuel nozzle (39) being disposed in the direction of flow after the outlet nozzle (41), through which the principal fuel and the twisting fuel flow jointly.

17. Burner according to claim 16, characterized in that the outlet nozzle (41) and the fuel nozzle (39) are mounted displaceably relative to each other.

18. Burner according to claim 16, characterized in that, in the central pipe (45), a nozzle needle (55) adjustable in the axial direction is disposed.

19. Burner according to claim 18, characterized in that the nozzle needle is formed as a pipe (43) adjustable in the axial direction, through which atomizing air can be introduced into the fuel nozzle (39).

20. Burner according to one of claims 16 to 19, characterized in that the pipe (36) for supplying liquid twisting fuel is surrounded by a heating jacket (42).

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