EP1741977B1 - Pulverized coal burner for low NOx emissions - Google Patents

Abstract

A coal-dust burner with low NOx emissions has a concentric general arrangement with primary a primary air pipe (1) within a secondary (2) air pipe. The primary air pipe inlet has an external array of deflection grooves (3) and an inner stabilization ring (4) formed as a one-piece component.

Description

The invention is directed to a burner for burning pulverulent fuel, such as hard coal or lignite, preferably with a concentric structure comprising a primary air tube and a secondary air tube surrounding the primary air tube, wherein the mouth region of the primary air tube on the outside a Luftabweiskhle and inside a stabilizing ring has, which are formed as a one-piece component, wherein the stabilizing ring projects radially inwardly in the form of an internal toothing in the primary air tube, wherein the Luftabweiskehle, the stabilizing ring and a part of the primary air tube are integrally formed.

In burners, which are used for the combustion of dust-like carbon, the reduction of NO _x emissions is still a current and problem to be solved. The distribution of the combustion air into several sub-streams allows the adjustment of the individual air flows in terms of air flow, air distribution and swirl intensity and is known as a measure to reduce nitrogen oxides in coal combustion. The structure of such a burner with stepped air supply is in the EP-B-571 704 described. With this type of air guidance, the stepped air supply already contributes to a reduction in NO _x emissions during combustion.

The burner technology for the combustion of dusty carbon pursues the goal at the present time of producing an intensive separation between oxygen and pyrolysis gas during the initial reaction or ignition in order subsequently to allow the combustion air to take part in the further oxidation of the solids and thereby to achieve an even more effective reduction of NO _x emissions.

From the EP 0 260 382 A1 For example, there is known a NOx-arm burner comprising a pulverized coal nozzle for injecting a stream of a mixture of pulverized coal with primary air, a secondary air nozzle disposed outside and coaxial with the pulverized coal nozzle, a tertiary-air nozzle outside Secondary air nozzle and disposed coaxially with the pulverized coal nozzle, and eddy current generating means for injecting secondary air and tertiary air as eddy current. Between the secondary air nozzle and the tertiary air nozzle is disposed a spacer having a thickness such that the mixing of the secondary air with the tertiary air is delayed and an eddy current is formed between the secondary air and the tertiary air.

In addition to the distribution of the combustion air into partial flows, a further reduction of the NO _x emissions can be achieved by a clear temporal and spatial definition of the ignition conditions and the separation between fuel-rich flame core and oxygen-rich edge flow.

Such a definition can be made by the interaction of the components of a swirl generator in the primary air tube, a stabilizing ring at the mouth of the primary air tube and a Luftabweiskehle the secondary air tube, as it EP-B-670 454 describes. This patent discloses a generic burner, in which at the end of a burner tube, which is surrounded by a secondary air tube, arranged inside the mouth of the burner tube, a stabilizing ring and on the outside of the burner tube Luftabweiskhle is arranged.

In this area, on the one hand the burner tube and the stabilizing ring and on the other hand the burner tube and the Luftabweiskhle must be connected to each other. This is usually done by welding, so that in this area on each side of the burner tube, a weld or a welding surface is formed. For this purpose, it is necessary that the materials are matched accordingly. The choice of materials and the formation of the weld in this area leads to increased design effort. In addition, an increased repair and susceptibility due to the presence of welds and an impaired by these conditions durability is thus expected in the temperature-moderately high and flowed through by aggressive media mouth region of the primary or burner tube.

The invention is based on the object to provide a solution that makes it possible to form the mouth region of a generic burner durable and / or structurally simpler.

In a burner of the type described, this object is achieved in that form the Luftabweiskehle, the stabilizing ring and a portion of the primary air tube the mouth region of the primary air tube, the Luftabweiskehle and the stabilizing ring flush with the mouth of the primary air tube and wherein the Luftabweiskehle on the Outside of the outlet-side end of the primary air tube is formed as a conically expanding radially outward portion.

This makes it possible, the mouth region by a one-piece, the outside of the shape of Luftabweiskehle exhibiting and inside the shape and contour of the Form stabilization ring having component. This component can then be welded, for example, by means of a circumferential weld on the end face of a burner tube or primary air tube, so that only one weld is present in the region of the mouth. Since only one weld is required, the burner can be made faster than a burner of the prior art, in which two welds are necessary. In addition, it is thereby possible to arrange the weld further upstream, ie offset from the burner outlet opening, with respect to the air flow in the burner or primary or secondary air pipe, so that the weld seam is arranged upstream of the mouth end of a core air pipe optionally arranged in the primary pipe. The inventively embodied burner area is characterized more durable, ie less susceptible to interference and repair and structurally simpler designed.

In order to be able to place the connection point between the primary air tube and the mouth region and the stabilizing ring of the one-piece component upstream of the burner very far in particular temperature moderately low-loaded areas, the one-piece component advantageously also has a part which forms an extension of the primary air tube, so to speak, as part of the primary air tube is to be regarded. The Luftabweiskhle, the stabilizing ring and at least a portion of the primary air tube are therefore integrally formed and form the mouth region of the primary air tube, wherein the stabilizing ring with the mouth of the primary air tube terminates and / or the Luftabweiskehle flush with the mouth of the primary air tube.

For the production of the one-piece component is in particular the centrifugal casting process, so that the Invention provides in an embodiment that the one-piece component is made by centrifugal casting.

Since a connection between the one-piece component and the burner tube or primary air tube must be made, the invention provides in an embodiment that the one-piece component to the primary air tube, preferably by welding, is fixed.

In an advantageous embodiment, the invention is characterized by a arranged in the annular gap between the primary air tube and the secondary air duct air guide body which is adjustable in and against the flow direction between a retracted position in the annular gap and a flush with the mouth of the primary air pipe final position.

In this case, it is furthermore advantageous if the burner has a core air tube arranged in the primary air tube, in which a pilot burner which is disposed between a burner ignition position and a burner operating position in and against the burner Flow direction is displaceable, is arranged, which the invention also provides.

In an embodiment of the invention, it is then also advantageous if the mouth of the core air tube is arranged upstream of the mouth of the primary air tube.

In order to achieve optimum air guidance, the invention also provides that a swirl body is arranged on the ignition-flame-side end of the pilot burner.

Here, a particularly advantageous embodiment of the swirl body according to the invention is characterized in that on the swirl body, a pipe section is arranged around the Zündbrennerlängsachse, wherein the preferably conically formed ignition flame end of the pipe section in the burner ignition position of the burner via the outlet end (mouth) of the primary air pipe protrudes.

Finally, the invention provides that a primary swirl body is arranged in the annular gap between the core air tube and the primary air tube.

The invention is based on the known from the prior art burner technology for the combustion of pulverized hard coal and pulverized lignite.

The burner according to the invention, which can be used both for the combustion of hard coal and for the combustion of lignite, preferably has a concentric structure with a primary air tube and a secondary air tube. The surrounded by the cylindrical secondary air tube primary air tube forms this with a combustion air leading annular channel (secondary air channel).

In addition, an air deflector throat is arranged on the outside at the outlet end (mouth) of the primary air tube, which narrows the cross section of the annular channel between the primary air tube and the secondary air tube at the outlet ends and preferably terminates flush with the mouth.

On the inside at the outlet end (mouth) of the primary air tube, a stabilizing ring is arranged, which is formed by an inner edge to the burner longitudinal edge, which preferably terminates flush with the mouth and protrudes into the flow of primary air and coal dust.

On the outside at the outlet end of the primary air tube, a secondary air guide is arranged, which is adjustable in the flow direction of a retracted position in the annular channel and a flush with the mouth of the primary air tube final position.

The burner according to the invention additionally has a core air tube which is surrounded by the cylindrical primary air tube and forms a primary air and pulverized coal-carrying annular channel (primary air nozzle or dust tube nozzle). Due to the concentric arrangement of the core air tube, primary air tube and secondary air tube an individual single air supply is possible.

A pilot burner is disposed within the core air tube in the burner longitudinal axis. At this pilot burner, a swirler is attached in the form of a blade ring, which is covered in the radial direction at its outer end by a pipe extension extending in Direction of flow widens conically and extends beyond the mouth of the pilot out. The pilot burner, the swirl body of the pilot burner and the conical tube extension are preferably designed as a one-piece component, which is displaceable in the flow direction from a retracted position in the core air tube to a position at the mouth of the core air tube.

The mixing intensity of fuel and combustion air may be adjusted by a primary swirler disposed in the annular channel between the core air tube and the primary air tube, and a secondary swirler disposed in the annular channel between the primary air tube and the secondary air tube.

The burner according to the invention makes possible, beyond the burner technology for pulverized coal known from the prior art, burner operation in which the reduction reactions of an oxygen-poor (substoichiometric) combustion chamber are shifted into the burner-near zone between primary flame and secondary air flow. With the aid of the burner according to the invention, an oxygen-poor flue gas recirculation zone is established in this region near the burner, in which NO compounds which inevitably form during the primary reaction are split and reduced to molecular nitrogen. As a result, a more effective reduction of NO _x emissions is possible with the burner according to the invention in comparison to burners of the prior art.

Fig. 1

den Längsschnitt durch einen erfindungsgemäßen Steinkohlebrenner, wobei der Zündbrenner in das Kernluftrohr zurückgezogen ist und der axial verschiebbare Sekundärluftleitkörper in der Mündung der Primärluftdüse angeordnet ist,

Fig. 2

den Längsschnitt durch einen erfindungsgemäßen Steinkohlebrenner, wobei der Zündbrenner in der Position entsprechend Figur 1 angeordnet ist und der axial verschiebbare Sekundärluftleitkörper auf der Außenseite des Primärluftrohres in den betreffenden Ringkanal zurückgezogen ist,

Fig. 3

den Längsschnitt durch einen erfindungsgemäßen Steinkohlebrenner, wobei der Zündbrenner in der-Mündung des Kernluftrohres angeordnet ist und der axial verschiebbare Sekundärluftleitkörper die in Fig. 1 beschrieben Position aufweist, und

Fig. 4

den Längsschnitt durch einen erfindungsgemäßen Braunkohlebrenner, wobei der Zündbrenner in der Mündung des Kernluftrohres angeordnet ist und der axial verschiebbare Sekundärluftleitkörper eine gemäß Fig. 3 beschrieben Position einnimmt.

The burner according to the invention is illustrated in embodiments for both a hard coal burner and a lignite burner in the accompanying figures. The in the FIGS. 1 to 3 shown burner shows Embodiments of a hard coal burner, while in FIG. 4 shown burner represents an embodiment of a lignite burner. The burner according to the invention for burning pulverulent fuel such as hard coal or lignite is explained in more detail below. Show it:

Fig. 1

the longitudinal section through a hard coal burner according to the invention, wherein the pilot burner is retracted into the core air tube and the axially displaceable Sekundärluftleitkörper is arranged in the mouth of the primary air nozzle,

Fig. 2

the longitudinal section through a hard coal burner according to the invention, wherein the pilot burner in the position corresponding FIG. 1 is arranged and the axially displaceable Sekundärluftleitkörper is withdrawn on the outside of the primary air tube in the respective annular channel,

Fig. 3

the longitudinal section through a hard coal burner according to the invention, wherein the pilot burner is arranged in the mouth of the core air tube and the axially displaceable Sekundärluftleitkörper the in Fig. 1 has described position, and

Fig. 4

the longitudinal section through a lignite burner according to the invention, wherein the pilot burner is arranged in the mouth of the core air tube and the axially displaceable secondary air guide according to Fig. 3 described position occupies.

Due to the invention characterizing common features between coal burners and lignite burners, the description of the FIGS. 1 to 4 initially in a generally valid form.

The burner according to the invention, which in the FIGS. 1 to 4 is shown, has a displaceable in the flow direction pilot burner 7, which is arranged in the burner longitudinal axis within a core air tube 6. The cylindrical core air tube 6 is surrounded by a cylindrical primary air tube 1, whereby an annular channel is formed. This annular channel is in turn surrounded by a cylindrical secondary air tube 2 and thereby divides the combustion air sector in at least one or two annular channels.

The fuel and air conducting primary air ring passage formed by the core air tube 6 and the primary air tube 1 is connected to a mill, not shown, in which the coal is ground and dried during grinding with a hot, gaseous medium. At a certain distance from the outlet end of this annular channel, a primary swirl body 10 is arranged on the outside of the core air tube 6, which imparts a rotation of the primary air and pulverized coal flow. As a result, the flow is made uniform and the pulverized coal preferably enriched on the inside of the primary air tube 1.

Furthermore, a stabilizing ring 4 is arranged on the inside at the outlet end of the primary air tube 1, which has a radially inwardly directed edge. This edge, which projects into the stream of primary air and pulverized coal, ensures that the coal particles encounter resistance before they leave the primary air tube 1, are thereby delayed and are accelerated again by the gas flow in the direction of the center of the burner tube.

At a certain distance in front of the dust nozzle mouth or the stabilizing ring 4 having the mouth of the adjustable outer core primary body 10 is arranged on the core air tube 6, which sets the primary air coal dust flow in a rotational flow. As a result, a homogenization of the flow within the primary tube or primary air tube 1 is effected with simultaneous enrichment of the coal dust on the outer circumference of the dust tube.

This ring 4 has the shape of an internal toothing and protrudes into the flow region of the pulverized coal, so that the coal particles collide against a resistance before leaving the primary tube or primary air tube 1. Due to the impact on the ring 4, the carbon particles are braked sharply.

Their flow rate drops briefly below the fuel-characteristic Rückzündgeschwindigkeit. This process defines the ignition point of outgassing fuel products. In response to the impact, the coal dust is reflected, re-accelerated by the deflection into the primary gas stream, and discharged into the furnace. Schematically, the above sequence is shown by the arrow 12 in the figures.

The outer side of the exit-side end of the primary air tube 1 has a conically radially outwardly widening section, which represents a Luftabweiskhle 3 for the outside guided past flow of secondary air, the actual throat is provided with the reference numeral 11, the Luftabweiskehle 3 total but extends on both sides of the throat 11. The by the Secondary air tube 2 guided secondary air flows along or over the Luftabweiskhle 3 to the outside, away from the fuel-rich flame kernel and is sufficiently delayed supplied to the fuel products. The Luftabweiskhle 3 ensures an ignition that runs without affecting the secondary air and is not disturbed by air fluctuations or turbulence.

Through the stabilizing ring 4 and the Luftabweiskhle 3 takes place in the manner described above, a controlled ignition of the pulverized coal in almost all operating situations. In this case, a rotationally symmetrical Rezirkulationsgebiet hot, low-oxygen fumes downstream of the mouth of the primary air tube 1 between the primary flame and the secondary air flow is formed by the stabilizing ring 4 and the Luftabweiskhle 3.

In order to shift the particle flow of pulverized coal from the annular channel, which is formed by the core air tube 6 and the primary air tube 1, further in the direction of the burner axis and thus increase the extent of the recirculation region, the core air tube 6, viewed in the flow direction, preferably clearly before the stabilizing ring 4 of the dust tube nozzle end. However, with such an assignment of the tubes of the burner according to the invention a safe operation of the adjustable pilot burner 7, especially in combined operation with oil and coal, not possible because the inwardly directed to the burner axis flow of coal dust affects the flame of the pilot burner 7 and additionally the Ignition flame monitoring is obstructed due to the darkening of the coal dust.

In order nevertheless to ensure safe burner operation for all operating conditions, the spin burner 7 attached to the swirl body 8 is in its outer region by a Pipe extension 9 covered. This pipe extension 9, which surrounds the blade ring of the swirl body 8, is extended downstream conically and serves as a deflector for the coal dust, which is deflected by the stabilizing ring 4 in the direction of the burner center. Together with the pilot burner 7, the local position of the conical tube extension 9 is adjustable in the flow direction. This ensures reliable ignition and monitorability of the pilot burner flame in all operating situations.

The importance of the recirculation area formed by the stabilizing ring 4 and the air deflecting throat 3, which is an oxygen-poor area, is known in view of the prior art NO _x reduction. Much of the reaction product resulting from the primary combustion passes into the oxygen-free recirculation zone, where the decomposition of nitrogen oxides occurs through reactive fuel components. Therefore, it is an effort to set the size of the recirculation area to optimum with respect to low NO _x emissions.

This is done by an adjustable in the flow direction Sekundärluftleitkörper 5, which is arranged on the outside of the primary air tube 1 and in the flow direction between a retracted position in the secondary air channel and a position with the mouth of the primary pipe 1 flush position adjustable.

Furthermore, the mouth of the primary air tube 1 and the burner nozzle from Luftabweiskehle 3 and stabilizing ring 4 is formed as a component and permanently connected to the dust pipe or primary air tube 1 of the burner permanently. For this purpose, a one-piece production of the Luftabweiskhle 3 and the stabilizing ring 4 is preferred.

This one-piece component from the Luftabweiskhle 3 and the stabilizing ring 4 is primarily, but not exclusively produced by centrifugal casting. But even the primary air tube 1 may be part of the one-piece component with a part having the Luftabweiskhle 3 and the stabilizing ring 4.

The operation of the adjustable secondary Luftleitkörpers 5 in connection with the Luftabweiskhle 3 with respect to the Rezirkulationsgebiet and taking into account the operating condition will be explained with reference to the accompanying drawings below.

FIG. 1 shows a hard coal burner, in which the pilot burner 7 is retracted into the core air tube 6 and the adjustable secondary air guide 5 is disposed in the mouth of the primary air tube 1. In this position of the Sekundärluftleitkörpers 5 this is not further downstream and closes flush with the Luftabweiskhle 3, whereby the operation of the Luftabweiskehle 3 is amplified. The secondary air flowing through the annular channel formed by the primary air tube 1 and the secondary air tube 2 is deflected outwardly and moves away from the flame core of the primary combustion zone in the radial direction. By adjusting the Sekundärluftleitkörpers 5 on the in FIG. 1 As shown, an adjustable maximum separation layer is created downstream of the mouth of the primary air tube 1 between primary combustion and secondary air flow. This maximum in its extent recirculation area provides for the in FIG. 1 Underlying operating condition is an optimum in terms of NO _x reduction.

FIG. 2 shows the longitudinal section through a hard coal burner according to the invention, in which the pilot burner 7 at the in figure 1 is shown and the displaceable Sekundärluftleitkörper 5 is retracted on the outside of the primary air tube 1 in the secondary air duct. Here, the components are arranged for an operating state of the hard coal burner, in which a less large separation layer between primary combustion and secondary air flow and thus a less large in the radial direction Rezirkulationsgebiet downstream of the mouth of the primary air tube 1 is required. The adjustable pilot burner 7 is in turn withdrawn into the core air tube 6 for this operating state. The Sekundärluftleitkörper 5, which influences the size of the Rezirkulationsgebietes by its adjustable position is retracted according to the position of the pilot burner 7 in the respective annular channel. In this position, the Sekundärluftleitkörper 5 divides the air flow of the secondary air pipe 2 into two different partial flows and makes them even. As a result, the Sekundärluftleitkörper 5 ensures that the ignition process at the burner outlet is not disturbed by air fluctuations or turbulence of the secondary air and the secondary air is sufficiently delayed fed to the fuel products.

FIG. 3 shows the longitudinal section through a hard coal burner according to the invention, wherein the pilot burner 7 is disposed in the mouth of the core air tube 6 and the movable secondary air guide 5, the in FIG. 1 has shown position. The components of the burner according to the invention are arranged according to an operating state in the ignition mode or combined operation of the hard coal burner. For this operating state, the conical tube extension 9 protrudes beyond the mouth of the core air tube 6 as well as downstream beyond the stabilizing ring 4 of the primary air tube 1 in the flow direction, in order to ensure reliable ignition and monitorability of the pilot burner 7. Of the Secondary air guide 5 is, as in FIG. 1 , disposed in the mouth of the primary air tube 1 and is not further downstream displaceable. The arrangement of the air guide 5, the operation of the Luftabweiskehle 3 is amplified and it forms a maximum large separation layer downstream of the mouth of the primary air tube 1, in which the NO compounds of the primary reaction can be split and reduced to molecular nitrogen and an optimum in terms the NO _x reduction is set for the illustrated operating state.

FIG. 4 shows an embodiment of a lignite burner having the same inventive features as the hard coal burner described above. Differences to a hard coal burner exist in the proportions of the diameter of the burner pipes.

FIG. 4 shows the longitudinal section through a lignite burner according to the invention, wherein the pilot burner 7 is arranged in the mouth of the core air tube 6 and the displaceable secondary air guide 5 according to FIG. 3 described position occupies. The components of the burner are arranged according to an operating state in the ignition operation or combined operation of the lignite burner. For this operating state of the burner according to the invention, the pilot burner 7 assumes a position in the mouth of the core air tube 6 and is not further displaced downstream. The conical tube extension 9 protrudes beyond the mouth of the core air tube 6 and the stabilizing ring 4, to ensure a reliable ignition of the pilot burner 7. The movable secondary air guide 5 has the in FIG. 1 and 3 described position from which he is not further downstream. As a result of this positioning of the secondary air guide body 5, a maximally large recirculation area is formed downstream of the mouth of the primary air tube 1, in which the reduction of the NO compounds to molecular nitrogen, according to the operating state with regard to an optimum NO _x reduction, can take place.

By the burner 5 according to the invention for the combustion of pulverized fuel such as hard coal or brown coal, a device is provided which allows a higher reduction of NO _x emissions in terms of load condition and quality of the pulverized coal compared to the prior art.

LIST OF REFERENCE NUMBERS

1

Primary air pipe

2

Secondary air pipe

3

Luftabweiskehle

4

stabilizing ring

5

Sekundärluftleitkörper

6

Core air pipe

7

Adjustable igniter

8th

swirler

9

Conical tube extension

10

Primary swirler

11

throat

Claims (10)

1. Burner for burning pulverised fuel such as hard coal or lignite, which burner comprises a primary air pipe (1) and a secondary air pipe (2) which surrounds the primary air pipe (1), the mouth region of the primary air pipe (1) comprising on the outside thereof an air deflection groove (3) and on the inside thereof a stabilisation ring (4), which air deflection groove and stabilisation ring are formed as a one-piece component, the stabilisation ring (4) projecting radially inwards in the form of inner toothing into the primary air pipe (1), the air deflection groove (3), the stabilisation ring (4) and part of the primary air pipe (1) being formed in one piece, characterised in that the one-piece formation of the air deflection groove (3), the stabilisation ring (4) and part of the primary air pipe (1) forms the mouth region of the primary air pipe (1), the air deflection groove (3) and the stabilisation ring (4) ending flush with the mouth of the primary air pipe (1) and the air deflection groove (3) being formed on the outer face of the outlet end of the primary air pipe (1) as a portion which extends radially outwards in a conical manner.
2. Burner according to claim 1, characterised in that the burner has a concentric construction.
3. Burner according to either claim 1 or claim 2, characterised in that the one-piece component is a centrifugally cast component.
4. Burner according to any one of claims 1 to 3, characterised in that the one-piece component is fixed to the primary air pipe (1) by welding.
5. Burner according to any one of the preceding claims, characterised by an air guide member (5) which is arranged between the primary air pipe (1) and the secondary air pipe (2) and can be adjusted in and counter to the flow direction between a position in which it is retracted into the annular gap and a position in which it ends flush with the mouth of the primary air pipe (1).
6. Burner according to any one of the preceding claims, characterised in that the burner comprises a core air pipe (6) which is arranged in the primary air pipe (1) and in which a pilot burner (7) is arranged, which pilot burner can be displaced in and counter to the flow direction between a burner ignition position and a burner operating position.
7. Burner according to claim 6, characterised in that the mouth of the core air pipe (6) is arranged upstream of the mouth of the primary air pipe (1).
8. Burner according to either claim 6 or claim 7, characterised in that a swirler (8) is arranged at the pilot flame end of the pilot burner (7).
9. Burner according to claim 8, characterised in that a pipe portion is arranged on the swirler (8) about the longitudinal axis of the pilot burner, the preferably conical pilot flame end of the pipe portion projecting beyond the outlet end (mouth) of the primary air pipe (1) when the pilot burner (7) is in the burner ignition position.
10. Burner according to any one of claims 6-9, characterised in that a primary swirler (10) is arranged in the annular gap between the core air pipe (6) and the primary air pipe (1).

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