EP0057747A2 - Burner for the combustion of dust-like fuels - Google Patents

Abstract

A burner (1, 29) for the combustion of dusty fuels, in particular coal dust, has a central channel (9, 37) for the supply of a core air jet (13, 41), a fuel channel (12, 40) for the supply of the fuel and one Jacket channel (5, 6; 31) for the supply of secondary air (7, 8; 36). So that such a burner (1, 29) is also suitable for small power ranges, has a larger control range and is less sensitive to a wide coal dust band, the outlet of the fuel channel (12, 40) is designed as an annular nozzle (23, 53), of which two Circumferential walls at least one (19, 47) is rotatable and driven, and the outlet of the central channel (9, 37) is designed such that the core air jet (13, 41) at least partially outwards against the escaping fuel for the purpose of deflecting into the area of Secondary air (7, 8; 36) is directed.

Description

Burners for the combustion of dusty fuels

The invention relates to a burner for the combustion of dust-like fuels, in particular coal dust, with a central channel for the supply of a core air jet, with a fuel channel for the supply of fuel = and with a jacket channel for the supply of secondary air.

So-called coal dust burners are used for the combustion of coal dust, particularly in steam boiler and hot water systems, in which the coal dust is supplied to the burners by means of carrier air or carrier gas. The combustion air partly flows into the combustion chamber through a central core air duct as a core air jet and through a jacket duct as secondary air. A separate pilot burner is generally used for the ignition.

The known coal dust burners have different parts. So they are only capable of large output units above approx. 5 Gcal / h heat output per burner insert. The coal dust grit spec be kept within limits to prevent the flame from moving back or out of the burner root. Otherwise there would be a danger of the burner slipping or of flame or combustion chamber vibrations. In addition, the control range is also small due to the reignition and distribution problems of the known coal dust burners and is between 50% and 100%. Only in large systems with multiple burner operation can the control range be increased by switching off individual burners.

The invention has for its object to design a burner of the type mentioned in such a way that it is also suitable for small power ranges, has an enlarged control range and is less sensitive to a wide coal dust band and can accordingly also be operated with mixed bed dust from large central grinding plants.

This object is achieved in that the outlet of the fuel channel is designed as an annular nozzle, at least one of the two circumferential walls of which is rotatable and driven, and in that the outlet of the central channel is designed such that the core air jet is at least partially towards the escaping fuel is directed into the area of the secondary air for the purpose of distraction.

The burner according to the invention is particularly suitable for a performance range significantly below 5 Gcal / h, especially for the performance range 0.3 to 3.5 Gcal / h. This burner opens up a new performance range for dusty fuels, especially coal dust. 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 around 25% to 100%. The burner is also much more 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 latter is particularly the case when the outer circumferential wall of the ring nozzle is rotatably mounted, since the larger grains are then distributed outwards as a result of the centrifugal forces acting on them. The sliding to the 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 an equalization of the fuel flow over the scope.

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. In addition, the core air jet forms a load-independent backfire screen for the see. 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. In the edge region, these holes can be arranged at an angle to the falling air pressure in the region of the exit _'from the annular gap to compensate.

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 lo% 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.

To improve the ignition stability of the fuel-air mixture, 5 vibration generators can be provided in the central duct and / or in the jacket duct, 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, it is provided according to the invention 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.

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

In the drawing, the invention is illustrated in more detail using two exemplary embodiments. Show it:

• Fig. 1 shows a longitudinal section through the upper part of a coal dust burner in a schematic representation
• Fig. 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 recurculation 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 in detail here - is rotatably mounted 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 2o of the central tube 10, which has a U-shaped cross section and is bent downward, projects into the intermediate space thereby formed. A conical body 21 is arranged around this collar 20, the conical surface 22 of which forms an annular nozzle 23 with the conically widening region of the cup 19. 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 cone 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 fact that the coal dust can 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 area of the secondary air 7, 8, which flows out via the jacket channels 5, 6. The secondary air portion 8 emerging from the jacket duct 6 is a swirl supporting the inner and outer hot gas recirculation is impressed 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 an electric heating up to 35 ₀ ° 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.

Coaxial to the outer jacket 32 and jacket tube 33 is a 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 4o. The core air 41 passes through 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 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 is likewise rotatably mounted here and is 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 5o, formed onto the central tube 38 and bent downward in a U-shape, projects into the annular groove 49 from above. 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 4o receives a deflection with an S-shaped cross section through the collar 5o and the annular groove 48.

There is a between the cone body 51 and the collar 5o slot-shaped passage 54 kept clear 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 in low-frequency vibrations. In this way the mixing pulse effect on the emerging Koh _- lens deaf intensified, thus improving 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 6o 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 6 ₀ - is the same as that of the coal dust burner 1 according to FIG. 1.

Claims (12)

l. Burner (1, 29) atomized for combustion fuels, particularly coal dust, with a central channel (9, 37) for supplying a _K ernluftstrahls- (13, 41) with a fuel channel (12, 4 ₀₎ for the supply of the Fuel and with a jacket channel (5, 6; 31.) for the supply of secondary air (7, 8; 36), characterized in that the outlet of the fuel channel (12, 4 ₀ ) is designed as an annular nozzle (23, 53), ' at least one (19, 47) of the two peripheral walls of which is rotatable and driven, and that the outlet of the central channel (9, 37) is designed such that the core air jet (13, 41) at least partially outwards against the escaping fuel for the purpose of Deflection in the area of the secondary air (7, 8; 36) is directed. 2. Burner according to claim 1, characterized in that the fuel at speeds between 3 to 8 m / s emerges. 3. Burner according to claim 1 or 2, characterized in that the outer peripheral wall (19, 47) of the ring nozzle (23, 53) is rotatably mounted and driven. 4. Burner according to one of claims 1 to 3, characterized in that the ring nozzle (23, 53) has a conically increasing diameter. 5. Burner according to one of claims 1 to 4, characterized in that the fuel channel (12, 4 ₀ ) in the region of the ring nozzle has an S-shaped profile in cross-section, the overall cross-section preferably initially expanding in the area of the S-shaped profile and reduced towards the ring nozzle (23, 53) again. Burner according to one of claims 1 to 5, characterized in that the central channel runs out against a shielding plate (15, 43) to form an annular gap (16, 44) opening before the exit of the ring nozzle (23, 53). 7. Burner according to claim 6, characterized in that the shielding plate (15, 43) has small bores (17, 45) for the escape of a small part of the core air (13, 41). 8. Burner according to one of claims 1 to 7, characterized in that from the central channel: (9, 37) gap nozzles (26, 54) into the fuel channel (12, 4 ₀ ), optionally in the middle of its S-shaped course. 9. Burner according to one of claims 1 to 8, characterized in that the core air jet (13, 41) is appropriately preheated to effect an initial ignition of the fuel, optionally by an electrical heat exchanger with an electrical connection power, which is also a fuel with low volatility coal Do not exceed a value of 2% of the burner output. lo. Burner according to one of claims 1 to 9, characterized in that the central channel (9, 37) and / or the jacket channel (5, 6; 31) is each provided with a vibration generator. which is preferably designed as an annular space (55, 57) surrounding the respective channel (12, 40; 5, 6, 31), which with the respective channel (12, 40; 5, 6, 31) via a coordinated annular gap ( 56, 58) is connected. 11. Burner according to one of claims 1 to lo, characterized in that between the fuel channel (12, 4 ₀ ) and jacket channel (5, 6; 31), an intermediate channel (6 ₀ ) for the supply of cooling air (61) and / or heating gas is provided. 12. Burner according to one of claims 1 to 11, characterized in that at the outlet of the casing channel (5, 6; 31) guide vanes (27, 28; 34, 35) are arranged to impress a swirl.

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