EP0769655A2 - Air-blast spray nozzle - Google Patents

Abstract

The nozzle (2) consists of a liquid fuel pipe (12) around the nozzle's axle (11), with at least one fuel (4)dispenser onto an atomiser edge (19). Two concentric air ducts (13,14) are fed by an air inlet pipe (15), with concentric pilot gas duct (22). The ducts are separated by partitions (18). The air ducts (13,14) on the nozzle's atomiser cross-section (16) open into the burner's inner chamber (17). The partition between the inner (14) and outer (13) air duct forms the atomiser edge and is held by inner and outer support elements (21). The inner support elements are positioned between the partition and the fuel pipe, and the outer support elements are positioned between the partition and the outer nozzle body (23).

Description

Technical field

The invention relates to the field of combustion technology. It relates to an atomizer nozzle for atomizing liquid fuel in a burner, which works on the air-blast principle, is suitable both for operating the burner with liquid and gaseous fuels and can be used in particular in low-pollutant premix burners of the double-cone type.

State of the art

For low pollutant premix combustion, the fuel must be mixed with the combustion air as homogeneously as possible before combustion. If liquid fuel is used, it must be atomized beforehand. The liquid fuel jet is split into individual droplets so that the fuel has the largest possible evaporation surface.

So-called airblast atomizers are also used to atomize liquid fuels in combustion chambers (see AH Lefebvre, Airblast Atomization, Prog. Energy Combust. Sci. Vol. 6, pp. 233-261, 1980), which are particularly useful for operation of gas turbines are suitable. This are designed so that the relatively slow moving liquid fuel is atomized by a high speed air stream. The fuel does not have its own impulse. The liquid to be atomized is applied, for example, as a thin film with an approximately constant thickness to an atomizer edge. An air flow flows around this atomizer edge on both sides, ie an outer and an inner air flow, the atomization of the liquid fuel then taking place at the atomizer lip in the shear field of the two air flows (prefilming atomization).

As is known, the liquid fuel is applied either via central pressure atomizers or via so-called film layers, which are integrated in the lead of the atomizer edge in this component and therefore require a relatively thick component.

In order to direct the air in a targeted manner to the edge of the atomizer, the internal air flow is either swirled and / or directed outwards via a central body.

A disadvantage of this known prior art is the relatively large component diameter or the high pressure drop in the nozzle due to the narrow cross section.

In general, the twist of the internal air flow makes the nozzle diameter relatively large. To remedy this, the airblast atomizer is designed with a displacement body. The disadvantage of this displacement body is that it causes an increased susceptibility to coke and gum formation in the wake. Due to the proximity to the flame, the cooling of this part is usually a difficult problem to solve.

Presentation of the invention

The invention tries to avoid all these disadvantages. It is based on the task of developing an airblast nozzle for atomizing liquid fuel, which can also be used for gas operation and is characterized by small dimensions and is therefore, for example, well suited for use in a premixing burner of the double-cone type, the nozzle being characterized by reduced susceptibility to coking and gum formation. Furthermore, there should only be a slight loss of pressure in the nozzle. Finally, it is the object of the invention to propose a mechanism with which it is possible to throttle off the atomizing air during gas operation and to meter the required atomizing air during operation with liquid fuel.

According to the invention this is achieved in an airblast nozzle according to the preamble of claim 1 in that the intermediate wall between the inner and outer air duct is held via inner and outer support elements, the inner support elements between the intermediate wall and the fuel pipe and the outer support elements between the intermediate wall and the nozzle outer body are arranged, and that the atomizer edges are angled in the direction of the nozzle axis.

The advantages of the invention consist in the compact design of the airblast nozzle and its minimal diameter, so that they can be used particularly well in a premix burner of the double-cone type. Another advantage results from the fact that there is no longer any need to arrange components at the nozzle outlet that tend to build up or overheat. In addition, there is only a slight pressure loss in the nozzle and the design pressure drop is at the atomizer lip.

It is particularly expedient if the liquid fuel tube is axially displaceable, while the outer nozzle body is a component of the burner and is thus firmly fixed, the sliding point being provided between the inner supports on the liquid fuel pipe and the intermediate wall between the inner and the outer air duct. The thermal expansion of the lance tube is thus absorbed by moving the oil film sprayer. The position of the atomizer edge relative to the burner therefore remains unchanged. Another advantage is the saving of the problematic sealing between the pilot gas line and the atomizer, because here the outer atomizer part is part of the burner. Finally, there is a further advantage that the sensitive atomizer part can remain in the burner when the fuel lance is installed and is therefore not damaged.

As an embodiment, it is also possible to leave the atomizer in its entirety and to push it outside.

Finally, the fuel is advantageously applied via commercially available pressure atomizers, in particular hollow-cone atomizers. Simple bores, which are provided radially or obliquely at the closed end of the fuel line, are also suitable for applying the fuel. It is advantageous here if the fuel film is evened out by means of weirs additionally arranged in the atomizer edge.

It is also advantageous if the inner and / or outer support elements are designed as swirl blades. By swirling the air, better atomization is achieved. The swirl of the inner air flow serves to improve the flow around the atomizing lip, while the outer swirl influences the spray angle a. The fuel application can also be swirled (radially or obliquely against the nozzle axis).

Finally, it is in a method for operating the airblast nozzle according to the invention, whereby in operation with gaseous Fuel the inflow of air into the interior of the burner is at least partially throttled, which is advantageous in that the throttling takes place as a result of the different thermal expansion of the liquid fuel tube in gas or oil operation. This throttling mechanism is quite easy to implement.

Brief description of the drawing

Several exemplary embodiments of the invention are shown in the drawing.

Fig. 1

eine schematische Darstellung der Anordnung eines mit einer airblast-Düse ausgestatteten Doppelkegelbrenners;

Fig. 2

einen Teillängsschnitt der airblast-Düse bei Verwendung eines konventionellen Öldruckzerstäubers;

Fig. 3

einen Teillängsschnitt der airblast-Düse, wobei eine Flüssigbrennstoffleitung mit zur Düsenachse am geschlossenen Ende schräg angeordneten Bohrungen verwendet wird;

Fig. 4

einen Teillängsschnitt der airblast-Düse mit als Drallschaufeln ausgebildeten Stützelementen und einem Wehr;

Fig. 5

einen Teillängsschnitt der airblast-Düse mit verdrallter Flüssigbrennstoffaufbringung;

Fig. 6

einen Teilquerschnitt entlang der Linie VI-VI in Fig. 4;

Fig. 7

einen Teillängsschnitt des Brennerteiles und der Brennstoffzuführung, wobei im oberen Teilbild der Gasbetrieb und im unteren Teilbild der Ölbetrieb veranschaulicht ist.

Show it:

Fig. 1

is a schematic representation of the arrangement of a double cone burner equipped with an airblast nozzle;

Fig. 2

a partial longitudinal section of the airblast nozzle when using a conventional oil pressure atomizer;

Fig. 3

a partial longitudinal section of the airblast nozzle, wherein a liquid fuel line is used with bores arranged obliquely to the nozzle axis at the closed end;

Fig. 4

a partial longitudinal section of the airblast nozzle with support elements designed as swirl blades and a weir;

Fig. 5

a partial longitudinal section of the airblast nozzle with swirled liquid fuel application;

Fig. 6

a partial cross section along the line VI-VI in Fig. 4;

Fig. 7

a partial longitudinal section of the burner part and the fuel supply, the gas operation in the upper part and the oil operation is illustrated in the lower part.

Only the elements essential for understanding the invention are shown. The direction of flow of the work equipment is indicated by arrows.

Way of carrying out the invention

The invention is explained in more detail below on the basis of exemplary embodiments and FIGS. 1 to 7.

1 shows a schematic representation of the arrangement of a premix burner of the double-cone type equipped with an airblast nozzle.

An airblast nozzle 2 is arranged in the upstream end of the burner 1. It is supplied with liquid fuel 4 and compressed air 5, which is used to atomize the fuel 4, via a fuel lance 3 connected to the double-cone burner 1. In addition, the fuel lance 3 supplies the gaseous fuel 6 for the double-cone burner 1 while it receives its main burner air 7 from the space inside the burner hood 8. The air 5 for the airblast nozzle 2 can also be supplied from a plenum (not shown) located outside the burner hood 8. In addition, in this exemplary embodiment, additional gaseous fuel (pilot gas 9) is injected into the burner 1 in order to enrich the fuel gases near the axis of the double-cone burner 1 via the fuel lance 3. The burner 1 opens into the combustion chamber 10 downstream.

2 shows the airblast nozzle 2 in an enlarged partial longitudinal section. It has a fuel pipe 12 for the liquid fuel 4 arranged around the nozzle axis 11 and in each case an inner 13 and an outer air duct 14 arranged concentrically therewith. The two air channels 13, 14 are upstream with an air supply line 15 in which the Atomizing air 5 is led to the nozzle, connected and opening at the atomizing cross section 16 into the burner interior 17. The channels 13, 14 are through an intermediate wall 18, which according to the invention is angled at its downstream end in the direction of the nozzle axis 11 and there the atomizing edge 19 with the atomizing lip 20 forms, separated from each other, so that the atomizing air 5 is divided into an outer 5a and an inner airflow 5b. The intermediate wall 18, including the atomizer edge 19, is held between the fuel tube 12 and the outer nozzle body 23 with the aid of inner and outer support elements 21, which are preferably arranged at uniform intervals over the circumference. The inner support elements 21 are arranged between the fuel pipe 12 and the intermediate wall 18, while the outer support elements 21 are arranged between the intermediate wall 18 and the nozzle outer body 23. In the present exemplary embodiment, a pilot gas channel 22 is provided in the burner 1, which provides pilot gas 9, which serves to enrich the gaseous fuel 6 in the interior of the burner, thereby expanding the stability range of the burner. According to FIG. 2, the pilot gas channel 22 is delimited by the outer nozzle body 23 and by the wall of the burner 1. The connection of the nozzle 2 to the burner 1 and the feed of the pilot gas channel 22 are not shown in FIG. 2. The latter can be implemented, for example, by a feed bore for the pilot gas which is arranged in the burner wall and is not shown here. The nozzle 2 can be connected, for example, via a cover, not shown, which is welded over the entire circumference at the upstream end of the pilot gas channel 22 to the outer nozzle body 23 and on the wall of the burner 1 and closes off the pilot gas channel 22. Of course, the arrangement of a pilot gas channel can also be dispensed with in other exemplary embodiments.

The liquid fuel 4, preferably oil, is made thinner by means of an exchangeable, commercially available pressure atomizer 24 Film applied to the atomizer edge 19. Hollow-cone atomizers are optimal, but full-cone atomizers with a well atomized fuel core can also be used. According to the invention, the atomizer edges 19 are narrowed inward in order to obtain a maximum air velocity in the atomization cross section 16 or at the atomizer lip 20. The outer air flow 5a brought up in the outer air duct 14 is likewise brought to the atomizer lip 20 via a narrowing at the atomizer edge 19, where the fuel film is atomized finely by the shear forces of the two air streams 5a, 5b. The high air speed has a positive effect on improved atomization quality.

The spray angle α can be influenced by the division of the two air mass flows 5a, 5b and by the geometry of the outlet cross section.

In the embodiment shown in FIG. 2, the inner support elements 21 are not firmly connected to the intermediate wall 18 in the upper part of the figure, so that a sliding point 28 is present at this point. This enables the liquid fuel tube 12 including the oil pressure atomizer 24 to be displaced, so that the thermal expansion of the fuel lance 3 can be absorbed and the position of the atomizer edge 19 relative to the double-cone burner 1 does not change, which is a great advantage. This arrangement only requires a somewhat longer atomizer sleeve (= partition 18). In addition, this version also saves a problematic seal between the pilot gas channel 22 and the atomizer in the burner 1, since the outer atomizer part would become part of the burner 1. Another advantage is that the sensitive atomizer part remains in the double-cone burner 1 during assembly of the fuel lance 3 and is therefore not damaged.

As a further embodiment, which is illustrated in the lower part of Fig. 2, it is also possible to leave the atomizer as a whole, i.e. both the inner and the outer support elements 21 are firmly connected to the intermediate wall 18 and the liquid fuel tube 12 or the nozzle outer body 23. Then the nozzle 2 as a whole can only be moved from the outside (sliding point 29).

3 shows an embodiment variant in which the liquid fuel 4 is applied to the atomizer edge 19 via simple bores 25. These are arranged radially or obliquely at the closed end of the liquid fuel line 12. For the purpose of uniformizing the fuel film and thereby improving the atomization quality, weirs 26 can be arranged in the atomization edge.

Another embodiment variant is shown in FIG. 4. In contrast to FIG. 3, the support elements 21 are designed as swirl blades 27. It is possible to arrange only the inner support elements 21 as swirl blades, so that only the inner air flow 5b is swirled in order to achieve a better flow around the atomizer lip 20. If only the outer air flow 5a is swirled, the spray angle α can be influenced. Of course, as can be seen from FIG. 4, both air streams 5a, 5b can also be swirled by designing both the inner and the outer support elements 21 as swirl generators.

Since the gas operation of the double-cone burner 1 is disturbed as a result of the atomizing air 5 flowing through the airblast nozzle 2, a mechanism is proposed to solve this problem according to FIG. 7, which uses the different thermal expansion of the fuel line 12 in oil and gas operation. The upper part of Fig. 7 relates to gas operation, the lower part, however, to oil operation. 7, the airblast nozzle 2 is at the downstream end of the oil line 12 not shown. In gas operation, the atomizing air 5 is throttled, since the oil line 12 is heated by the air coming from the compressor and accordingly the entry area of the atomizing air 5 into the burner part is reduced or completely closed by the thermal expansion of the oil line. In contrast to this, the required atomizing air 5 is metered during oil operation or when water is added due to the lower thermal expansion of the colder oil line 12 under these operating conditions (see open entry area of air 5 in the lower part of FIG. 7). The prerequisite for this is that the liquid fuel line 12 is fixedly attached to the housing and the burner 1 is arranged firmly on the combustion chamber 10, which is not shown in FIG. 7.

Of course, other, known throttling mechanisms, such as throttling the air 5 by displacement by means of pilot gas 9, can also be used to throttle the atomizing air 5 of the airblast nozzle according to the invention in gas operation.

• kompakte Bauweise mit minimalem Durchmesser
• geringer Druckverlust in der Düse
• Auslegungsdruckabfall an der Zerstäuberlippe
• keine Bauteile am Düsenaustritt, die zu Ablagerung bzw. Überhitzung neigen
• enger Sprühwinkel α
• einfache Kalibrierbarkeit und Auswechselbarkeit der kritischen Ölquerschnitte.

In summary, it can be stated that the airblast nozzle according to the invention is characterized by the following properties:

• compact design with minimal diameter
• low pressure loss in the nozzle
• Design pressure drop at the atomizer lip
• no components at the nozzle outlet that tend to deposit or overheat
• narrow spray angle α
• easy calibration and exchangeability of the critical oil cross-sections.

Reference list

1

burner

2nd

airblast nozzle

3rd

Fuel lance

4th

Liquid fuel

5

Air for the airblast nozzle

5a

external airflow

5b

internal airflow

6

gaseous fuel

7

Main burner air

8th

Burner hood

9

Pilot gas

10th

Combustion chamber

11

Nozzle axis

12th

Fuel pipe

13

outer air duct

14

inner air duct

15

Air supply line

16

Atomizing cross section

17th

Burner interior

18th

Partition

19th

Atomizer edge

20th

Atomizer lip

21

Support elements

22

Pilot gas duct

23

Nozzle outer body

24th

Oil pressure atomizer

25th

Holes

26

Weir

27

Swirl generator

28.29

Sliding point

α

Spray angle

Claims (11)

Airblast atomizer nozzle (2) for operating a burner (1) operated with liquid and gaseous fuels (4, 6), the nozzle (2) consisting essentially of a liquid fuel pipe (12) arranged centrally around the nozzle axis (11) with at least an end-to-end means for applying the liquid fuel (4) to an atomizing edge (19), as well as two concentric air channels (13, 14) fed by an air supply line (15) and optionally a pilot gas channel (22) arranged concentrically therewith , wherein the channels (13, 14, 22) are separated from each other by partitions (18), and from an outer nozzle body (23), the air channels (13, 14) at the atomizing cross section (16) of the nozzle (2) into the interior of the burner (17) open, the outer air duct (13) narrows before the atomizing cross section (16) and the partition (18) between the inner (14) and outer air duct (13) at the downstream end Atomizer edge (19), characterized in that the intermediate wall (18) between the inner (14) and outer air duct (13) via inner and outer support elements (21), the inner support elements between the intermediate wall (18) and the fuel pipe (12 ) and the outer support elements (21) are arranged between the intermediate wall (18) and the nozzle outer body (23), is held and that the atomizer edges (19) are angled in the direction of the nozzle axis (11). Airblast atomizing nozzle according to claim 1, characterized in that the liquid fuel tube (12) is axially displaceable, while the outer nozzle body (23) is part of the burner (1) and thus fixed. Airblast atomizing nozzle according to claim 1, characterized in that its individual components are firmly fixed and the nozzle (2) is axially displaceable only as a whole. Airblast atomizer nozzle according to claim 2, characterized in that a sliding point (28) is provided between the inner support elements (21) on the liquid fuel pipe (12) and the intermediate wall (18) between the inner (14) and the outer air duct (13). Airblast atomizer nozzle according to claim 1, characterized in that the means for applying the liquid fuel (4) is an oil pressure atomizer (24). Airblast atomizer nozzle according to claim 5, characterized in that the oil pressure atomizer (24) is a hollow cone atomizer. Airblast atomizer nozzle according to claim 5, characterized in that the oil pressure atomizer (24) is a full cone atomizer. Airblast atomizing nozzle according to claim 1, characterized in that the means for applying the liquid fuel (4) are radially or obliquely arranged bores (25) at the closed end of the fuel tube (12). Airblast atomizer nozzle according to claim 8, characterized in that weirs (26) are arranged on the atomizer edge (19). Airblast atomizing nozzle according to claim 1, characterized in that the outer and / or inner support elements (21) are designed as swirl generators (27), in particular as swirl blades. Method for operating a burner (1) with an airblast nozzle according to one of Claims 1 to 10, in which the liquid fuel line (12) is fixed to the housing and the burner (1) is fixed to the combustion chamber (10), during operation the flow of air (5) into the burner interior (17) is at least partially throttled with gaseous fuel (9), characterized in that the throttling takes place as a result of the different thermal expansion of the liquid fuel tube (12) in gas or oil operation.

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