EP0057747B1 - Burner for the combustion of dust-like fuels - Google Patents

Description

The invention relates to a burner for the combustion of dusty fuels with a central channel for the supply of a core air jet with an essentially annular primary air outlet, with a jacket channel for the supply of secondary air with an annular secondary air outlet surrounding the primary air outlet and with a fuel channel for the supply of the fuel an annular fuel outlet arranged between the primary and secondary air outlet, at least one of the two circumferential walls of the fuel outlet being rotatable and driven, and furthermore the core air jet being directed at least partially outward against the fuel and the fuel being acted on by secondary air.

GB-A-528 018 shows a burner which is primarily intended for the combustion of oil fuels. However, it is also considered suitable for the use of other fuels, for example dust-like fuels.

The burner has a central duct for the supply of core air with an annular primary air outlet which is directed slightly outwards. The central channel is surrounded by a fuel channel through which the respective fuel is supplied. The fuel outlet is also ring-shaped, the inner wall of the fuel outlet simultaneously forming the outer wall of the central channel. The outer wall of the fuel outlet is cup-shaped and protrudes beyond the primary air outlet. The primary air outlet and fuel outlet are practically parallel.

The fuel channel and fuel outlet are surrounded by a jacket channel for the supply of secondary air. In the area of fuel outlet and primary air outlet, the jacket channel is divided into two ring channels, the inner ring channel being formed on the inside by the rotatable outer wall of the fuel channel and on the outside by a conically widening ring wall. This in turn forms the inner wall of the outer ring channel, the outlet for the outer ring channel opening far before the primary air outlet or fuel outlet. The inner ring channel is so narrow that the vast majority of the secondary air escapes through the outer ring channel.

There are openings in the outer and inner walls of the fuel channel in front of the fuel outlet, which make the connection on the one hand to the central channel and on the other hand to the inner ring channel of the jacket channel. Through these openings, primary air and secondary air get into the fuel before it leaves the fuel.

Due to the design of this burner, the escaping fuel - apart from the air that has entered through the aforementioned openings - initially only comes into contact with the core air jet, i.e. the primary air. With liquid fuels, this is sufficient to burn the low-boiling components. The heat generated ignites the high-boiling components. It is then not important that the secondary air required for this combustion hits the oil only a good distance behind the outlet of the primary air. The outer wall of the fuel channel prevents the oil from being forced into the portion of the secondary air, because this outer wall is pulled a good way beyond the primary air outlet. Primary air, oil and secondary air meet only tangentially. The much larger part of the secondary air comes into contact with the fuel mixture much later, although here, too, the contact is only tangential.

With this structural design of the burner, the use of coal dust as fuel should not lead to satisfactory results. A stable flame can hardly be created because the primary air with which the coal dust would initially come into contact would be sufficient to burn the volatile components in the carbon. The outgassed coal particles would then only hit the then still cold secondary air at the end of the burner and can then no longer ignite. The flame would go out again.

The invention is therefore based on the object of designing a burner of the type mentioned in such a way that it is also suitable for small power ranges, has a large control range and is insensitive to a wide coal dust band.

According to the invention, this object is achieved in that the core air jet at the primary air outlet is directed essentially radially to the mouth of the fuel outlet and onto the secondary air outlet.

Due to this design of the burner, the fuel is immediately deflected outwards by the core air jet after it has emerged and thus reaches the area of the secondary air outlet in the shortest possible way. This creates an intensive mixing of the fuel with the primary air and then with the secondary air. This provides enough oxygen to maintain the combustion of the outgassed coal particles. The path is so short that the flame, once started, does not go out. It has been shown that the burner is also suitable for small output ranges well below 5 Gcal / h, especially for the output range of 0.3 to 3.5 Gcal / h and has a large control range. So that with this burner opened up a new performance range for dusty fuels.

Since, in contrast to large burners, the flame volume in burners working in the aforementioned performance range is correspondingly low, the coal dust must escape at a low speed, which is expediently between 3 and 8 m / s. At partial load in particular, this corresponds to the flame reignition rate. A reignition is avoided by the rotating part of the ring nozzle, since this causes such a high heat transfer to the coal dust that it acts like a flame filter. Circumferential speeds of 12 to 30 m / s have proven to be sufficient and expedient for the rotating part or parts.

Another advantage of the burner according to the invention is the enlargement of the control range, which is now approximately 25% to 100%. Again, the burner is much less sensitive to a wide range of fuel dust so that mixed bed dust can also be used. The fine and ultra-fine dust content is carried out of the ring nozzle with the carrier air, while the larger particles slide to the outlet due to the rotating movement of the part of the ring nozzle in question.

The sliding of the dust grains towards the fuel outlet is promoted by the conically widening design of the diameter of the ring nozzle. This conical widening should be the same, preferably smaller than the angle of repose of the fuel in question, in order to avoid erosions and agglomerations.

The fuel channel should have an S-shaped cross section in the area of the ring nozzle. The overall cross-section should initially widen in the area of the S-shaped course and narrow again towards the ring nozzle. This measure brings about a comparison of the fuel flow over the circumference.

According to a further feature of the invention it is provided that the central channel runs out against a shielding plate to form an annular gap which opens before the exit of the ring nozzle. Since this shielding plate is very hot due to the temperatures prevailing in the combustion chamber, the core air can heat up there, which favors the initial ignition of the fuel. In addition, a deflection in the radial direction to the exit of the fuel at the ring nozzle is thereby easily achieved. The core air should expediently emerge from the annular gap at approximately 20 to 100 m / s in order to achieve intensive mixing with the escaping fuel and a deflection into the secondary air flow, which likewise contributes to the mixing. The mixing power achieved in this way from the three mixing pulses acting at an angle to one another is essentially load-independent. The core air jet also forms a load-independent backfire shield to protect against cup fire.

In order to avoid slagging of the shielding plate, a large number of small bores are provided in it, from which a small part of the core air can escape. These holes can be arranged at an angle in the edge area in order to compensate for the falling air pressure in the area of the exit from the annular gap.

In addition, gap nozzles can emanate from the central channel, in particular in the area of the annular gap, which open into the fuel channel, possibly into the middle of its S-shaped course. As a result, the fuel dust flow is evened out before entering the ring nozzle.

If the temperature of the core air jet is not sufficient for the initial ignition of the fuel, appropriate preheating should be provided. This can consist, for example, of an electrical heat exchanger, the electrical connection power of which does not exceed a value of 2% of the burner output even with low-volatile coal as fuel. This corresponds to the relatively small proportion of core air here, which expediently represents 10% to 15% of the total amount of combustion air. Additional ignition stabilization can also be achieved by mixing the core air with steam. This steam accelerates the fuel gasification in such a way that lower temperatures are sufficient for preheating, so the heating power required for this can be reduced.

In order to improve the ignition stability of the fuel-air mixture, vibration generators can be provided in the central channel and / or in the jacket channel, which set the core air and / or the secondary air into gas dynamic vibrations before they exit. These vibration generators can be designed as annular spaces surrounding the respective channel, which are connected to the respective channel via a coordinated annular gap. Other embodiments for impressing a gas dynamic vibration are also possible.

At the outlet of the jacket channel, guide vanes can also be arranged to impart a swirl. Such a swirl contributes to the intensification of the external and internal hot gas recirculation and thereby increases the supply of ignition energy. This in turn reduces the need for preheating the core air.

In order to reduce the heat effect of the core air, which is preheated to a relatively high degree, particularly when using fuel with small amounts of volatile constituents, the invention provides that an intermediate channel is provided between the fuel channel and the jacket channel. This can be supplied with cooling air during normal burner operation and with ignition gas during start-up, with a throughput that is adequate for the burner heat output for the fuel used.

• Figur 1 einen Längsschnitt durch den oberen Teil eines Kohlenstaubbrenners in schematischer Darstellung und
• Figur 2 einen Längsschnitt durch den oberen Teil einer anderen Ausführungsform eines Kohlenstaubbrenners in schematischer Darstellung.

In the drawing, the invention is based on two embodiments illustrated. Show it :

• 1 shows a longitudinal section through the upper part of a coal dust burner in a schematic representation and
• Figure 2 shows a longitudinal section through the upper part of another embodiment of a coal dust burner in a schematic representation.

The coal dust burner 1 shown in FIG. 1 is inserted as a whole into a conically expanding burner sleeve 2. It has an outer jacket 3, in which a jacket tube 4 is arranged at a distance from this.

As a result, two jacket channels 5, 6 are formed, via which secondary air 7, 8 can flow into the combustion chamber which adjoins this illustration at the top.

A central tube 10 surrounding a central channel 9 and a fuel tube 11, which surrounds the central tube 10 to form an annular fuel channel 12, are arranged coaxially with the outer jacket 3 and the jacket tube 4. If necessary, heated core air 13 is conveyed via the central duct 9 and a coal dust / air mixture 14 is conveyed via the fuel duct 12.

The central tube 10 ends at a distance from a shielding plate 15, which on the one hand serves as protection against the heat caused by the flame and the recirculation and on the other hand redirects the core air jet 13 radially outward. The core air 13 then emerges laterally from an annular gap 16.

The shielding plate 15 has a multiplicity of small bores 17, from which a small part of the core air 13 can flow out. In this way, the slag particles arriving there during the recirculation are cooled down to such an extent that they cannot get stuck on the shielding plate 15.

The fuel pipe 11 is surrounded by a drive shaft 18, which - which is not shown here - is rotatably supported and driven by an electric motor. In the area of the upper end of the drive shaft 18 a cup 19 is fastened, which is cylindrical in the lower area and widens conically in the upper area.

The drive shaft 18 continues through the attachment of the cup 19 upwards. A collar 20 of central tube 10 with a U-shaped cross section and bent downward protrudes from above into the intermediate space formed thereby. A conical body 21 is arranged around this collar 20, the conical surface 22 of which, together with the conically widening region of the cup 19, forms an annular nozzle 23. At the same time, the fuel channel 12 receives a deflection which is S-shaped in cross section through the collar 20 or cone body 21 and the extension of the fuel tube 11 or the drive shaft 18. Coal dust settles in the pockets 24, 25 of the deflection, so that the deflection is evened out and the pockets 24, 25 are protected against erosion.

Between the conical body 21 and the collar 20, a slot-shaped passage 26 is kept open for a small part of the core air 13. This part of the core air 13 contributes to the coal dust being able to emerge from the ring nozzle 23 in a uniform density.

When operating the coal dust burner 1, coal dust is introduced into the combustion chamber via the fuel channel 12, its S-shaped deflection and the ring nozzle 23. Since this coal dust burner 1 is intended in particular for low heating outputs, the outflow speed must be relatively low, for example 3 to 8 m / s, since otherwise the flame would detach from the burner and be carried away. The emerging coal dust is immediately detected by the core air 13 emerging from the annular gap 16 at speeds between 20 to 100 m / s and pressed into the region of the secondary air 7, 8 which flows out via the jacket channels 5, 6. A swirl supporting the inner and outer hot gas recirculation is impressed on the secondary air portion 8 emerging from the jacket channel 6 via guide vanes 27, 28, the burner sleeve 2 stabilizing the flame.

Depending on the proportion of volatile constituents of the coal dust, the core air 13 is heated in such a way that it initiates the initial ignition, together with the radiant heat from the flame and the hot gas recirculation. The heating can be done by electric heating up to 350 ° C. The core air 13 is additionally heated on the shielding plate 15.

The rotating cup 19 reliably prevents blockages in the S-shaped deflection and the ring nozzle 23 due to the shear forces in the circumferential direction. Furthermore, it ensures sufficient heat transfer into the coal dust to prevent reignition despite the low exit speed of the coal dust.

FIG. 2 shows another embodiment of a coal dust burner 29. In the illustration shown, it is also inserted into a burner muffle 30, the conical design of which serves to stabilize the flame.

In this embodiment, only one jacket channel 31 is provided, which is formed by an outer jacket 32 and by a jacket tube 33. At the outlet of the jacket channel 31, guide vanes 34, 35 are provided in order to impart a swirl to the secondary air 36 flowing out there in order to support the recirculation.

A central tube 38 surrounding a central channel 37 and a fuel tube 39, which surrounds the central tube 38 to form an annular fuel channel 40, are arranged coaxially with the outer jacket 32 and jacket tube 33. The core air 41 enters the central duct 37 and a carbon-air mixture 42 enters the combustion chamber via the fuel duct 40.

The central tube 38 ends - as in the exemplary embodiment according to FIG. 1 - at a distance from a shielding plate 43. The core air 41 becomes is diverted radially outward through this shielding plate 43 and then emerges laterally from an annular gap 44.

The shielding plate 43 also has a large number of small bores 45 from which a small part of the core air 41 can flow out for the purpose of avoiding slag deposits.

The fuel pipe 39 is surrounded by a drive shaft 46, which here is rotatably supported and driven by an electric motor. The upper end of the drive shaft 46 is formed into a cup 47 which widens conically towards the outside and has an annular web 48 on the inside, as a result of which an annular groove 49 is formed.

A collar 50, formed onto the central tube 38 and bent downward in a U-shape, projects into the annular groove 49. A hollow conical body 51 is arranged around this collar 50, the conical surface 52 of which, together with the cup 47, form an annular nozzle 53. At the same time, the fuel channel 40 receives a deflection which is S-shaped in cross section through the collar 50 and the annular groove 49.

Between the cone body 51 and the collar 50, a slot-shaped passage 54 is kept free for a small part of the core air 41. It has the same task as the passage 26 in the embodiment according to FIG. 1.

The hollow interior 55 of the cone body 51 is connected to the annular gap 44 via slot nozzles 56. According to the principle of the flute, this creates a gas dynamic vibration generator which sets the core air 41 flowing through the annular gap 44 into low-frequency vibrations. This intensifies the effect of the mixed impulses on the emerging coal dust and thus improves the ignition stability. The same goal is served by a vibration generator for the secondary air 36, which consists of an annular channel 57 placed around the outer jacket 32, which is connected to the jacket channel 31 by a circumferential slot nozzle 58. In this way, the secondary air 36 is set in low-frequency vibrations.

An intermediate tube 59 is arranged between the drive shaft 46 and the jacket tube 33, which includes a cooling channel 60 with the jacket tube 33. Cooling air 61 can be passed through it in order to cool the bearings of the drive shaft 46, which are not shown here. In the starting phase, instead of the cooling air 61, pilot gas is passed through, which emerges via the ring opening 62 and is ignited there.

The function of the coal dust burner 29 shown in FIG. 2 - apart from the effect of the vibration generators and the cooling duct 60 - is the same as that of the coal dust burner 1 according to FIG. 1.

Claims (11)

1. Burner (1, 29) for the combustion of pulverised fuels, with a central duct (9, 37) for supplying a core air jet (13, 41), with a substantially annular primary air outlet, with an envelope duct (5, 6 ; 31 ) for supplying secondary air (7, 8, 36), with an annular secondary air outlet surrounding the primary air outlet, and with a fuel duct (12, 40) for supplying the fuel and with an annular fuel outlet (23, 53) arranged between the primary and secondary air outlets, at least one of the two peripheral walls (19, 47) of the fuel outlet (23, 53) being rotatable and driven, and the core air jet (13, 41) being also directed at least partly outwardly towards the fuel, and the fuel being acted upon by secondary air (7, 8, 36), characterised in that at the primary air outlet the core air jet (13, 41) is directed substantially radially to the mouth of the fuel outlet (23, 53) and to the secondary air outlet.

2. Burner according to claim 1, characterised in that the fuel issues at speeds between 3 to 8 m/s.

3. Burner according to claim 1 or 2, characterised in that the annular nozzle (23, 53) has a conically increasing diameter.

4. Burner according to one of claims 1 to 3, characterised in that the fuel duct (12, 40) in the region of the annular nozzle has an S shape in cross-section, and preferably the overall cross-section in the region of the S-shaped course first of all widens and reduces again towards the annular nozzle (23, 53).

5. Burner according to one of claims 1 to 4, characterised in that the end of the central duct faces towards a shield plate (15, 43) for forming an annular gap (16, 44) debouching in front of the outlet of the annular nozzle (23, 53).

6. Burner according to claim 5, characterised in that the shield plate (15, 43) comprises small holes (17, 45) for the outflow of a slight proportion of the core air (13, 41).

7. Burner according to one of claims 1 to 6, characterised in that from the central duct.(9, 37) slit nozzles (26, 54) extend into the fuel duct (12, 40), into the middle of the S-shaped region of said fuel duct if appropriate.

8. Burner according to one of claims 1 to 7, characterised in that the core air jet (13, 41) is suitably pre-heated to effect initial ignigion of the fuel, possibly by an electrical heat exchanger with a connected electrical power which even when using low-volatile coal as fuel does not exceed a value of 2 % of the burner power.

9. Burner according to one of claims 1 to 8, characterised in that the central duct (9, 37) and/or the envelope duct (5, 6 ; 31) is/are provided each with an oscillation generator, constructed preferably as an annular chamber (55, 57) which surrounds the respective duct (12, 40 ; 5, 6, 31) and which communicates with the respective duct (12, 40 ; 5, 6, 31) by way of a tuned annular gap (56, 58).

10. Burner according to one of claims 1 to 9, characterised in that an intermediate duct (60) for introducing cooling air (61) and/or heating gas is provided between the fuel duct (12, 40) and the envelope duct (5, 6 ; 31).

11. Burner according to one of claims 1 to 10, characterised in that guide vanes (27, 28 ; 34. 35) are arranged at the outlet of the envelope duct (5, 6, 31) for imparting a spinning motion.

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