EP2329189B1 - Fuel nozzle - Google Patents

Description

The invention relates to a fuel nozzle, comprising a nozzle tube and a nozzle outlet opening, wherein the nozzle tube is in communication with a fuel supply line for supplying a fuel into the nozzle tube, wherein the fuel from the nozzle outlet opening is injected into an air flow, which surrounds the fuel nozzle substantially annular , And a reaching to the nozzle outlet opening first nozzle tube section is formed flower-shaped in such a way that a substantially coaxial injection of the fuel in the air flow is feasible, wherein the nozzle outlet opening has a closed, conical flower scar. Such a fuel nozzle is for example from the document JP 8 145 361 A known.

The price increase of natural gas necessitates the further development of alternative fuels. This is, for example, low-calorie fuel gas hereinafter also referred to as synthesis gas. The synthesis gas can in principle be made from solid, liquid and gaseous educts. In the production of synthesis gas from solid educts, mention should be made in particular of coal gasification, biomass gasification and coke gasification.

In view of increasingly stringent requirements on the emission of nitrogen oxides, premix combustion is becoming increasingly important also in the combustion of low calorific gases.

Premix burners typically include a premix zone in which air and fuel are mixed before passing the mixture into a combustion chamber. There, the mixture burns, producing a hot gas under elevated pressure. This hot gas is forwarded to the turbine. In connection with the operation of Vormischbrennern it comes Above all, it is important to keep the nitrogen oxide emissions low and to avoid a flashback.

Synthesis gas premix burners are characterized by the fact that synthesis gases are used as fuel in them. Compared with the traditional turbine fuels natural gas and petroleum, which consist essentially of hydrocarbon compounds, the combustible components of the synthesis gas are essentially carbon monoxide and hydrogen. Depending on the gasification process and the overall plant concept, the calorific value of the synthesis gas is about 5 to 10 times smaller than that of natural gas.

Due to the low calorific value consequently high volume flows of fuel gas must be introduced into the combustion chamber. As a result, significantly larger injection cross sections are required for the combustion of low-calorie fuels, such as synthesis gases, than with conventional high-calorie combustion gases. However, to achieve low NOx levels it is necessary to burn synthesis gas in a premix operation.

In addition to the stoichiometric combustion temperature of the synthesis gas, the quality of mixing between synthesis gas and combustion air at the flame front is an important influencing variable for avoiding temperature peaks and thus for minimizing the formation of thermal nitrogen oxides. A spatially good mixture of combustion air and synthesis gas is particularly difficult due to the high volume flows of required synthesis gas and the correspondingly large spatial extent of the mixing area. On the other hand, the lowest possible production of nitrogen oxides, for reasons of environmental protection and corresponding legal guidelines for pollutant emissions, is an essential requirement for combustion, in particular for combustion in the gas turbine plant of a power plant. The formation of nitrogen oxides increases exponentially rapidly with the combustion flame temperature. In an inhomogeneous mixture of fuel and air results in a certain distribution of flame temperatures in the combustion area. The maximum temperature of such a distribution determined by the said exponential relationship of nitrogen oxide formation and flame temperature significantly the amount of undesirable nitrogen oxides formed.

In order to ensure a sufficient mixing between fuel and air, a sufficient penetration depth of the individual fuel jets in the air mass flow is necessary. In comparison to high-calorie combustion gases such as natural gas, however, correspondingly larger, free injection cross sections are required. This has the consequence that the fuel jets disturb the air flow sensitive, which ultimately leads to a local separation of the air flow in the wake region of the fuel jets. The forming Rückströmgebiete within the burner are undesirable and especially in the combustion of highly reactive synthesis gas necessarily to avoid. In extreme cases, these local Rückströmgebiete lead within the mixing zone of the burner to a flashback in the premixing zone and thus to a burner damage.

The high reactivity of synthesis gas, especially at high hydrogen content increases the risk of flashback.

Furthermore, the larger injection cross sections, which are necessary for the synthesis gas, usually lead to a poor premix of air and synthesis gas, from which just those high, undesirable NOx values are achieved.
In addition, the high volume flow often results in pressure losses during injection.

The mixing of synthesis gas with air, for example, with swirling elements, such as in the EP 1 645 807 A1 , or with an injection of the gas across the air flow. However, these lead to a significant undesirable Pressure loss and can cause unwanted wake areas which lead to flashback.

Based on this problem, the object of the invention is to provide a fuel nozzle, in particular for the supply of synthesis gas, which leads to a lower nitrogen oxide formation during combustion.

This object is achieved by the disclosure of a fuel nozzle, comprising a nozzle tube and a nozzle outlet opening, wherein the nozzle tube is in communication with a fuel supply line for supplying a fuel into the nozzle tube, wherein the fuel from the nozzle outlet opening in an air flow, which the fuel nozzle substantially annular surrounds, is injected, and a reaching to the nozzle outlet opening first nozzle tube section is shaped like a flower in such a way that a substantially coaxial injection of the fuel in the air flow is feasible, wherein the nozzle outlet opening has a closed, conical flower scar.

The invention is based on the fact that, especially for large volume flows of fuel such as synthesis gas, large injection sequences must be made available, which is associated with high pressure losses. Furthermore, however, in order to achieve good NOx values, especially the premix mode with a good mixing is necessary. However, the swirling elements used in the prior art and the inflow of the fuel stream transverse to the air flow lead to a significantly undesirable pressure loss, which in turn leads to poor NOx values.

The invention is based on the recognition that an increase in the contact area between the synthesis gas stream causes a significant improvement in the mixing. This effect is particularly important if the fuel flow and the air flow have different flow velocity. Due to the flower-shaped design of first nozzle pipe section this is caused. Due to the flower-shaped configuration of the first nozzle pipe section, a second flow field, ie desired calculable turbulences, is additionally formed on the profile trailing edges, which in turn improves mixing. This is also particularly advantageous if the fuel flow and the air flow have different flow velocity. The flower-shaped embodiment according to the invention of the first nozzle tube section further enables coaxial injection of the fuel into the air flow. As a result, undesirably high pressure losses are avoided. This allows operation of the nozzle in the premix mode, even at high volume flows of fuel, such as this is the case with synthesis gas.

The nozzle outlet opening of the fuel nozzle has a closed, conical flower scar. By the flower scar, which is arranged symmetrically around the center of the designed as a flower nozzle orifice, a continuous area mixing of the fuel and the air is enforced. This is especially for the fuel, which would be passed through the central region of the nozzle exit opening, an advantage. Due to the design of the nozzle outlet opening with a flower hub quasi the contact surface between fuel and air is further increased, which has a positive effect on the mixing. However, it is still possible coaxial inflow of the fuel into the air flow, whereby only a negligible pressure loss arises despite the improved mixing.

In one embodiment, which is not part of the invention, the flower scar runs in the direction of flow sharp.

According to the invention the flower scar is double-conical. As a result, boundary layer separation can be avoided and reduce the risk of flashback by return areas.

In a preferred embodiment, the flower scar has notches. These indentations are applied to the flower scar in correspondence with the individual petals or in correspondence with the profile trailing edges. These notches essentially serve to provide a smooth passage for the fuel, i. the exit of the fuel from the fuel nozzle takes place without unwanted and unpredictable Verwirblungen. Thus, boundary layer separation can be avoided and the risk of flashback by return areas can be reduced.

Advantageously, the notches are applied in a straight line in the direction of flow and / or twisted. As a result, a swirl during the injection can be impressed on the air flow or the fuel flow.

The first nozzle pipe section preferably tapers in the flow direction. As a result, an increase in the flow rate of the fuel is achieved.

In an alternative nozzle tube with an open scar, which is not part of the invention, the flower shape of the first nozzle tube section is sawtooth-like. Predictable turbulences are formed in the flow field by the saw teeth, which causes a better mixing of the fuel with the air flow. However, since coaxial injection continues to be assured, no increase in pressure loss occurs in this embodiment of the fuel nozzle.

In this case, a second nozzle tube section may be present, to which the first nozzle tube section adjoins in the flow direction, wherein the second nozzle tube section tapers in the flow direction. Thereby, a further increase in the flow rate of the fuel can be achieved.

The sawtooth-like first nozzle tube section connects in the horizontal direction to the second nozzle tube section. In this case, the sawtooth-like first nozzle tube section adjoins the second nozzle tube section inclined relative to the horizon. This increases the flow rate of the fuel.

In one embodiment, which is not part of the invention, the flower scar is connected to a tube extending substantially coaxially to the nozzle tube for the supply of high-calorie fuel and has at least one tangential and / or axial inlet opening.

Depending on the configuration of the burner, the arrangement, the number, and the diameter of the inlet openings can vary. Since the high calorie fuel feed within the synthesis gas feed (high calorie fuel feed is annularly surrounded by the synthesis gas feed), these are preferably tangential and axial inlet ports, i. Holes.

It should be noted that both the inlet openings for high-calorie fuel and the feed itself only require a small diameter, since the volume flow of the high-calorie fuel is substantially lower than that of the synthesis gas. This fact contributes to the supply of high calorific fuel causing little or no disturbance in the air stream during synthesis gas operation.

In one embodiment, which is not part of the invention, the at least one tangential inlet opening is arranged on the flower web between two petals of the flower-shaped synthesis gas injection. Thus, it is ensured that the Eindüserichtung of eg natural gas takes place substantially transverse to the air flow. This corresponds to the preferred blowing direction of a conventional premixed natural gas burner. This ensures a good mixing of the natural gas with the air flow, so that low NOx values can be achieved. These low NOx levels must also comply with the regulations in one Synthesis gas burner to be guaranteed if it is operated with high-calorie fuel such as natural gas, even if this natural gas is merely a "backup" function.

In a preferred embodiment, the fuel nozzle is present in a burner. This is in particular a synthesis gas burner operated in a premix mode. The burner can be designed as a two- or multi-fuel burner, which can also be operated with, for example, natural gas in Vormischmodus. Advantageously, the burner is present in a gas turbine.

Further features, advantages and details of the invention will now be described with reference to the drawings.

Fig. 1

eine Brennstoffdüse,

Fig. 2

einen Querschnitt durch die Brennstoffdüse,

Fig. 3

ein Diagramm für den Vermischungsgrad,

Fig. 4

eine Brennstoffdüse nach der Erfindung mit Blütennarbe,

Fig. 5

eine alternative Brennstoffdüse mit horizontalen Sägezähnen, die nicht Teil der Erfindung ist,

Fig. 6

eine alternative Brennstoffdüse mit geneigten Sägezähnen, die nicht Teil der Erfindung ist,

Fig. 7

eine vergrößerte Darstellung der Brennstoffzufuhr mit einer Zweitbrennstoffzufuhr die nicht Teil der Erfindung ist, und

Fig. 8

schematisch eine Zweitbrennstoffzufuhr (Erdgaszufuhr).

It shows in a simplified and not to scale representation:

Fig. 1

a fuel nozzle,

Fig. 2

a cross section through the fuel nozzle,

Fig. 3

a diagram for the degree of mixing,

Fig. 4

a fuel nozzle according to the invention with flower scar,

Fig. 5

an alternative fuel nozzle with horizontal saw teeth, which is not part of the invention,

Fig. 6

an alternative fuel nozzle with inclined saw teeth, which is not part of the invention,

Fig. 7

an enlarged view of the fuel supply with a second fuel supply which is not part of the invention, and

Fig. 8

schematically a second fuel supply (natural gas supply).

Identical parts are provided with the same reference numerals in all figures.

Due to the high price of natural gas, the current development of gas turbines in the direction of alternative fuels such for example, syngas promoted. The synthesis gas can in principle be made from solid, liquid and gaseous educts. In the production of synthesis gas from solid educts, especially the coal gasification should be mentioned. Coal is converted in a mixture of partial oxidation and gasification with water vapor to a mixture of CO and hydrogen. In addition to coal, the use of other solids such as biomass and coke should be mentioned in principle. Different crude oil distillates can be used as the liquid reactants for synthesis gas. The most important gaseous educt is natural gas. However, it should be noted that the low calorific value of synthesis gas has the consequence that much higher volume flows of the combustion chamber must be supplied for combustion, as is the case for example with natural gas. This has the consequence that large Eindüsequerschnitte must be provided for the flow of the synthesis gas. However, these lead to a poor premix of air and synthesis gas, which are just high, undesirable NOx levels are achieved. In addition, the high volume flow often results in pressure losses during injection.

In order to achieve a good mixing swirling elements are used or the synthesis gas flows across the air flow. However, this results in a significant undesirable pressure loss. Furthermore, trailing areas can be formed, which lead to a flashback. This will now be avoided by means of the invention.

Fig. 1 shows a fuel nozzle. This has a nozzle tube 2 and a nozzle outlet opening 10. The nozzle tube 2 is in communication with a fuel supply line (not shown) which supplies fuel to the nozzle tube 2. The fuel is injected from the nozzle outlet opening 10 into an air stream 8, which surrounds the fuel nozzle in an annular manner. The reaching up to the nozzle outlet opening 10 first nozzle pipe section 4 is shaped like a flower 6 in such a way that a substantially coaxial injection of the fuel in the air stream 4 is feasible. The synthesis gas is guided inside the nozzle tube 2.

Fig. 2 shows a cross section of such a nozzle outlet opening 10 with six individual flowers. The number of flowers is mainly dependent on the individual burner types or gas turbine types and may vary. The nozzle tube section 4 and the nozzle outlet opening 10 provide by their flower-shaped configuration 6 a larger contact area between the synthesis gas stream and air stream 8 ago. As a result, an improved mixing between synthesis gas and air stream 8 is achieved without increased pressure loss. This embodiment is particularly advantageous if the air stream 8 and the synthesis gas stream have different flow velocities. Furthermore, this flower-shaped embodiment 6 has the significant advantage that a second flow field is formed, in particular at the profile trailing edges of the individual flowers. Here vortex structures are formed. This also contributes significantly to improving the mixing, especially when there is a significant difference in the flow rates of the synthesis gas and the air stream 8.

Fig. 3 shows by way of example as a diagram, the improved interference of a flower-shaped fuel nozzle, here in the FIG. 3 indicated at b, as compared to a fuel nozzle, here for example an annular, tapered nozzle tube according to the prior art (in FIG. 3 indicated with a). The non-mixing degree is indicated on the y-axis. The flower-shaped fuel nozzle has a higher mixing, but due to the coaxial injection with lower pressure loss.

Fig. 4 shows an embodiment of a fuel nozzle according to the invention. This has at the flower-shaped nozzle outlet opening 10 centrally a conical flower scar 14. According to the invention the flower scar 14 is formed doppelkonisch. This has the advantage of being a smooth transition of the two streams is ensured. Furthermore, this embodiment prevents a boundary layer separation or the formation of return flow areas, which can cause a flashback.

Advantageously, 14 notches 16 may be mounted in the conical flower scar. These are advantageously on the one hand in their radial extension and attachment in accordance with the individual flowers attached, that is, the notch 16 and the flowers face each other. This achieves a smooth exit surface for the synthesis gas. On the other hand, further indentations 16 are provided, which lie opposite the profile trailing edges 20 and in their radial width essentially coincide with them. These achieve a smooth exit surface for the air flow 8. The notches 16 may be rectilinear in the flow direction or wound so as to achieve a turbulence of the air or the fuel.

With the configuration of a flower scar 14, therefore, the mixing in the middle of the flower-shaped 6 fuel nozzle (ie around the injection axes) is improved. By means of the flower scar 14, a mixing of the synthesis gas stream with the air stream 8 is thus also achieved in the center of the flower, in which the contact area between the synthesis gas stream and the air stream 8 is once again increased. As a result, a continuous surface mixing is possible. Due to the coaxial injection, the pressure loss is low despite the extensive and therefore very good mixing.

Fig. 5 shows an alternative fuel nozzle which is not part of the invention, in which the flower form has 8 tapered flowers, that is formed substantially sawtooth-like. In this case, these saw teeth 22 are attached to a first pipe section 4. This first pipe section 4 may have a constant pipe diameter in the flow direction (ie, the saw teeth 22 are substantially horizontal) or may be tapered in the flow direction (ie, the saw teeth 22 are inclined to the horizon line 26, Fig. 6 ). A second pipe section 24, to which the first pipe section 4 adjoins in the flow direction, can be tapered in the direction of flow for better injection. The design of the fuel nozzle with saw teeth 22 desired turbulence in the flow field to be generated, which in turn improves the mixing between synthesis gas and air stream 8.

Again, however, due to the coaxial injection of the pressure loss despite the flat and thus very good mixing but low.

In Fig. 7 is an embodiment of the fuel nozzle with a second fuel supply shown, which is not part of the invention. Since the synthesis gas inlet openings must ensure a large volume flow, the fuel nozzle is formed in the shape of a flower 6 in relation to the synthesis gas.

Tangential natural gas inlet openings 16 are placed between two petals 18. The point of contact or the line of contact of two petals 18 with each other is referred to below as flower spike 19. This means that the natural gas stream 33 can be injected directly into the air stream 8 without a petal 18 being therebetween. This ensures that the natural gas is injected substantially transversely to the air stream 8. Fig. 7 has six tangential natural gas inlet openings 16 and an axial natural gas inlet openings 17. Depending on the burner and gas turbine, both the number and the arrangement may vary. The natural gas inlet openings 16, 17 are essentially round, and can be produced by means of bores.

The syngas feed and its flower-shaped syngas inlet opening 6 as well as the natural gas supply 30 with the natural gas inlet 16,17 are designed so that a pressure drop below 25 dp / p is achieved with the same heat input with respect to synthesis and natural gas.

Fig. 8 schematically shows the natural gas supply 30. Since the volume flow of natural gas is much lower than that for synthesis gas, the diameter of the natural gas supply 30 is substantially lower than the synthesis gas supply. In order to switch from synthesis gas to natural gas operation or vice versa, it is only necessary to interrupt the synthesis gas or natural gas supply 30. This can be achieved without hardware changes.

Instead of natural gas, any other high-calorie burner material can be used, for example fuel oil. Similarly, the flower shape 6 of the synthesis gas inlet port is merely an example, other forms for syngas inlet port are also conceivable.

With the fuel nozzle according to the invention a good mixing between high-volume synthesis gas and air is possible. Due to the coaxial injection, however, the pressure loss is low. Resulting pressure losses, which are caused for example by the sole attachment of Verwirbelungselementen, thereby avoided. This promotes pre-mix mode operation, which in turn has a positive effect on NOx levels.

With the fuel nozzle according to the invention, it is also possible to integrate a so-called backup fuel line, since synthesis gas burners should be operable not only with a fuel, but possibly with different fuels, such as oil, natural gas and / or coal gas optional or even in combination to increase security of supply and flexibility in operation. By means of this invention it is possible to use the same nozzle for natural gas (or diluted natural gas) or synthesis gas. This simplifies the design of the burner and significantly reduces component components.

However, the fuel nozzle presented here is not limited only to the operation with synthesis gas, but it can be operated advantageously with any fuel. This To emphasize the advantage especially with volume-rich fuel flow. The fuel nozzle according to the invention is particularly suitable in premix operation.

Claims (6)

1. Fuel nozzle for an essentially coaxial injection of a fuel into an air flow (8) essentially enclosing the nozzle tube in an annular manner, said fuel nozzle comprising a nozzle tube (2) and a nozzle outlet opening (10) for injecting the fuel into the air flow (8), wherein the nozzle tube (2) is connected to a fuel feed line for the purpose of feeding a fuel into the nozzle tube (2), wherein a first nozzle tube section (4) extending as far as the nozzle outlet opening (10) is embodied in a flower shape (6) and
   the nozzle outlet opening (10) has a closed stigma (14) embodied in a cone shape,
   characterised in that the stigma (14) is embodied in a double-cone shape.
2. Fuel nozzle according to claim 1,
   characterised in that the stigma (14) has grooves (16).
3. Fuel nozzle according to claim 2,
   characterised in that the grooves (16) are aligned in a straight line in the flow direction and/or wound.
4. Fuel nozzle according to one of the preceding claims,
   characterised in that the first nozzle tube section (4) tapers in the flow direction.
5. Burner having a fuel nozzle according to one of the preceding claims.
6. Gas turbine having a burner according to claim 5.

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