EP0687860B1 - Self igniting combustion chamber - Google Patents

Description

Technical field

The present invention relates to a combustion chamber according to Preamble of claim 1.

State of the art

For burner configurations with a premix section and one in the outflow direction to the downstream combustion chamber the free mouth always poses the problem as on easiest way a stable flame front at extreme low NOx, CO and UHC (= unsaturated carbons / hydrogens) Emissions can be created. In this regard various proposals have already become known, that in themselves could not satisfy. One up to now The exception that has become known is that in EP-A1-0 321 809 disclosed invention, its proposals regarding flame stabilization, the efficiency and the pollutant emissions, especially with regard to NOx emissions Represent a leap in quality. However, there are combustion plants in which the above-mentioned subject matter of various reasons can not be used, with what there still forced with an outdated one Technology must be driven, be it that diffusion burner be used, be it that the premixing section in the Area of the flame front with swirl generators or Flame holders is added. In the first case, always with high NOx emissions are expected, their emissions no longer with the newer legislation most important countries in market terms; in the second case is despite installation of the proposed Precautions still a flashback from the Flame zone inside the premixing section possible, especially along the inner wall, where naturally a relatively low flow rate of the combustion air prevails. A typical furnace, at who uses the techniques mentioned against you Flashback must fail, affects one on Combustion-designed combustion chamber. Here it is usually around a largely cylindrical tube or around an annular combustion chamber, in which a working gas with a flows in relatively high temperature, there with a injected fuel comes to form a mixture, the fuel triggers a self-ignition. The caloric treatment of the working gas to hot gas takes place alone within this tube or this annular combustion chamber instead of. Is it an afterburner, which acts between a high pressure and low pressure turbine, so it is impossible for reasons of space, premix burner to be installed or aids against a flashback to provide, which is why so far attractive to them Combustion technology had to be dispensed with. Is that possible Postulate there, an annular combustion chamber as an afterburning chamber to provide a gas turbine group mounted on a shaft, this results in minimizing the length of this Combustion chamber additional problems with the Flame stabilization related.

A supersonic combustion chamber is known from WO 88/08927, in which a main amount of fuel in a premixing zone Supersonic combustion chamber is introduced into a supersonic flow. In the disclosed in WO 88/08927 Combustion chamber can be due to the high Flow rate within the combustion chamber Flashback can be avoided; however are the basic thermodynamic data within one Supersonic burners of a very special nature, and can not readily in general applications Gas turbine combustors are transmitted. Furthermore there WO 088/08927 does not indicate how one is possible uniform mixing of the fuel in the working gas can be reached beforehand, and thereby one stable combustion in a well-defined downstream Ensure pre-mixing zone located combustion zone.

Presentation of the invention

The invention seeks to remedy this. The invention, as it is characterized in the claims, the Task based on a combustion chamber of the beginning to propose measures mentioned, which a Induce flame stabilization and pollutant emissions minimize.

The combustion air for this combustion chamber is about Swirl generators (= vortex generators) are twisted in such a way that no recirculation areas in the premixing section After-run of the vortex generators mentioned occur. In this large swirl structure becomes a fuel brought in. A protruding into the channel is suitable for this Fuel lance.

A major advantage of the invention is that that the swirl flow originating from the vortex generators on the one hand for a large-scale distribution of the introduced fuel ensures, on the other hand this causes Turbulence a homogenization in the mixture formation of Combustion air with fuel.

Meanwhile, premixed fuel / air mixtures tend to general to self-ignition, therefore to one Flashback. In an advantageous embodiment of the Invention, the fuel is injected behind a narrowing point in the premix channel. This narrowing offers the advantage of being turbulent is reduced by increasing the axial speed, what the danger of a flashback from the Change in the turbulent flame speed minimized.

Furthermore, with this configuration the Stay time to prevent self-ignition decreased.

Furthermore, the large-scale distribution of the fuel continues to be guaranteed because the peripheral component of the Swirl flow is not affected.

After the narrowing point in the premixing channel, the axial component reduced again by the opening taking place there: The advantage of this is that they are now increasing turbulence for homogeneous mixing worries.

On the outflow side of the premixing channel, there is a cross-sectional expansion instead, the size of the actual Flow cross-section of the combustion chamber or the combustion zone results. Form within this cross-sectional extension marginal zones during operation, in which by the there negative pressure vortex detachment, i.e. Vortex rings arise, which in turn become one Stabilize the flame front. This configuration is particularly advantageous where the combustion chamber is open Autoignition is designed. Such a combustion chamber has namely preferably essentially the shape of an annular one or annular combustion chamber, it is short axial Length, and it is made with a working gas of high temperature and flows through at high speed. The said peripheral Vortex detachments stabilize the flame front in such a way that no additional precautions against one Flashback is necessary.

Advantageous and expedient developments of the inventive Task solutions are dependent in the others Labeled claims.

In the following, exemplary embodiments are described with reference to the drawings the invention explained in more detail. All for the immediate Understanding the invention does not require elements are omitted. The same elements are in the different Figures with the same reference numerals. The flow direction the media is indicated by arrows.

Brief description of the drawings

Fig. 1

eine selbstzündende Brennkammer, als Ringbrennkammer konzipiert,

Fig. 2

eine perspektivische Darstellung des Wirbel-Generators,

Fig. 3

eine Ausführungsvariante des Wirbel-Generators,

Fig. 4

eine Anordnungsvariante des Wirbel-Generators nach Fig. 3,

Fig. 5

einen Wirbel-Generator im Vormischkanal,

Fig. 6-12

Varianten der Brennstoffzuführung im Zusammenhang mit Wirbel-Generatoren,

Fig. 13

eine Ausführung einer Lanze zur Eindüsung von Brennstoff und Stützluft, in Anströmungsrichtung und von vorne gesehen und

Fig. 14

ein Anfahrdiagramm der Brennkammer bezüglich der Interdependenz zwischen Brennstoff und Stützluft.

It shows:

Fig. 1

a self-igniting combustion chamber, designed as a ring combustion chamber,

Fig. 2

a perspective view of the vortex generator,

Fig. 3

a variant of the vortex generator,

Fig. 4

3 shows a variant of the arrangement of the vortex generator according to FIG. 3,

Fig. 5

a vortex generator in the premix channel,

Fig. 6-12

Variants of fuel supply in connection with vortex generators,

Fig. 13

an execution of a lance for the injection of fuel and supporting air, seen in the direction of flow and from the front and

Fig. 14

a start-up diagram of the combustion chamber with respect to the interdependence between fuel and supporting air.

Ways of carrying out the invention, commercial usability

1 shows, as can be seen from the shaft axis 16, a Annular combustion chamber 1, which is essentially in the form of a coherent has annular or quasi-annular cylinder. In addition, such a combustion chamber can also be used a number of axially, quasi-axially or helically arranged and individually exist in self-contained combustion chambers. Such ring combustion chambers are excellent as self-igniting combustion chambers to be operated, which in Flow direction between two bearings on a shaft Turbines are placed. If such an annular combustion chamber 1 operated on self-ignition, so is the upstream Turbine 2 designed only for a partial relaxation of the hot gases 3, with which the exhaust gases 4 are downstream with this turbine 2 a fairly high temperature in the inflow zone 5 of the annular combustion chamber 1 stream. This inflow zone 5 is on the inside and in the circumferential direction of the channel wall 6 with a series of vortex-generating elements 100, hereinafter only vortex generators called, populated, on which below is discussed in more detail. The exhaust gases 4 are caused by the Vortex generators 100 are twisted in such a way that subsequent pre-mixing section 7 no recirculation areas occur in the wake of the vortex generators 100 mentioned. In the circumferential direction of this premixing section designed as a Venturi channel 7, several fuel lances 8 are planned, which is the supply of fuel 9 and supporting air 10 take over. These fuel lances 8 will be described below discussed in more detail. The feeding of these media to the individual Fuel lances 8, for example, cannot shown ring line can be made. The one from the vortex generators 100 triggered swirl flow ensures a large-scale distribution of the introduced fuel 9, if necessary also the admixed supporting air 10. Furthermore the swirl flow ensures homogenization of the mixture from combustion air and fuel. The one through the Fuel lance 8 fuel 9 injected into the exhaust gases 4 triggers a self-ignition, insofar as these exhaust gases 4 have that specific one Have temperature which is the fuel-dependent Auto ignition can trigger. If the annular combustion chamber 1 operated with a gaseous fuel must for the Initiation of auto-ignition a temperature of the exhaust gases 4 are greater than 850 ° C. With such a combustion as already mentioned above, there is in itself the risk of Flashback. This problem is solved by on the one hand, the premix zone 7 is designed as a venturi channel is, on the other hand by the injection of the fuel 9 in Area of largest constriction in premix zone 7 is scheduled. Due to the restriction in the premix zone 7 becomes turbulence by increasing the axial speed diminishes what the risk of kickback due to the diminution the turbulent flame speed is minimized. On the other hand, the large-scale distribution of the fuel 9 continues to be guaranteed, since the circumferential component of the swirl flow originating from the vortex generators 100 is affected. Behind the relatively short premix zone 7 is followed by a combustion zone 11. The Transition between the two zones is marked by a radial one Cross-sectional jump 12 formed, the flow cross section first the combustion zone 11 induced. In the plane the cross-sectional jump 12 also presents a flame front on. To reignite the flame inside the premix zone 7 To avoid the flame front must be kept stable become. For this purpose, the vortex generators 100 designed so that there is no recirculation in the premixing zone 7 takes place; only after the sudden cross-sectional expansion the swirl flow is desired to burst. The Swirl flow supports the quick reinstallation of the Flow behind the cross-sectional jump 12, so that through the full use of the volume of the combustion zone 11 high burnout achieved with a short overall length can be. Forms within this cross-sectional jump 12 there is a flow boundary zone during operation, in which due to the negative pressure prevailing there arise, which then stabilize the Lead flame front. The processed in the combustion zone 11 Exhaust gases 4 to hot gases 14 then act another downstream turbine 14. The exhaust gases 15 can then used to operate a steam cycle in the latter case, the system then is a combination system.

The actual inflow zone 5 is not shown in FIGS. 2, 3 and 4. By contrast, the flow of the exhaust gases 4 is shown by an arrow, which also specifies the direction of flow. According to these figures, a vortex generator 100, 101, 102 essentially consists of three freely flowing triangular surfaces. These are a roof surface 110 and two side surfaces 111 and 113. In their longitudinal extent, these surfaces run at certain angles in the direction of flow. The side walls of the vortex generators 100, 101, 102, which preferably consist of right-angled triangles, are fixed with their long sides on the channel wall 6 already mentioned, preferably gas-tight. They are oriented so that they form a joint on their narrow sides, including an arrow angle α. The joint is designed as a sharp connecting edge 116 and is perpendicular to each channel wall 6 with which the side surfaces are flush. The two side surfaces 111, 113 including the arrow angle α are symmetrical in shape, size and orientation in FIG. 4, they are arranged on both sides of an axis of symmetry 117 which is aligned in the same direction as the channel axis.
The roof surface 110 lies against the same channel wall 6 as the side surfaces 111, 113 with a very narrow edge 115 running transversely to the flow channel. Its longitudinal edges 112, 114 are flush with the longitudinal edges of the side surfaces 111 protruding into the flow channel , 113. The roof surface 110 extends at an angle of inclination Θ to the channel wall 6, the longitudinal edges 112, 114 of which, together with the connecting edge 116, form a point 118. Of course, the vortex generator 100, 101, 102 can also be provided with a bottom surface with which it is attached to the channel wall 6 in a suitable manner. Such a floor area is, however, unrelated to the mode of operation of the element.

The mode of operation of the vortex generator 100, 101, 102 is the following: When flowing around edges 112 and 114, the Main flow converted into a pair of counter-rotating vortices, as schematically sketched in the figures. The swirl axes lie in the axis of the main flow. The swirl number and the location of the vortex breakdown (vortex breakdown), if the latter is sought, be replaced by appropriate Choice of the angle of attack  and the arrow angle α determined. With increasing angles, the vortex strength or the swirl number becomes increased, and the location of the vortex burst shifts upstream into the area of the vortex generator 100, 101, 102 itself. Depending on the application, these are two Angle  and α through constructional conditions and through predefined the process itself. These have to be adjusted Vortex generators only in terms of length and height, like this below in detail in FIG. 5 for execution will arrive.

2 forms the connecting edge 116 of the two side surfaces 111, 113 the downstream edge of the vortex generator 100. The one running across the channel Edge 115 of roof surface 110 is thus that of the channel flow edge applied first.

In Fig. 3 is a so-called half "vortex generator" the basis of a vertebrae geneartor shown in FIG. 2. At the Vortex generator 101 shown here is only one of the two Provide side surfaces with the arrow angle α / 2. The other Side surface is straight and aligned in the direction of flow. In contrast to the symmetrical vortex generator only a vortex on the swept side is created here, like this is symbolized in the figure. Accordingly, it is downstream this vortex generator does not have a vortex-neutral field, but instead a swirl is imposed on the current.

Fig. 4 differs from Fig. 2 insofar as here the sharp connecting edge 116 of the vortex generator 102 is the point which is affected first by the channel flow becomes. The element is therefore rotated by 180 °. How it can be seen from the illustration that the two have opposite directions Vortex changed their sense of rotation.

Fig. 5 shows the basic geometry of one in one Channel 5 built-in vortex generator 100. Usually will the height h of the connecting edge 116 with the channel height H, or the height of the channel part, which the vortex generator is assigned so that the generated vortex is immediate such a downstream of the vortex generator 100 Size reached such that the full channel height H is filled out. This leads to an even speed distribution in the loaded cross section. On Another criterion, the influence on the ratio to be chosen of the two heights h / H is the pressure drop, that occurs when the vortex generator 100 flows around. It it goes without saying that with a larger ratio h / H the Pressure loss coefficient increases.

The vortex generators 100, 101, 102 are mainly used when it comes to two currents with each other to mix. The main flow 4 in the form of combustion air attacks the transverse edge 115 in the direction of the arrow respectively the connecting edge 116. The secondary flow in Form of a gaseous and / or liquid fuel, the possibly enriched with a proportion of supporting air (cf. Fig. 13), has a substantially smaller mass flow than the mainstream. This secondary flow is in the present Fall downstream of the vortex generator into the main flow initiated, as can be seen particularly well from FIG. 1.

In the example shown in FIG. 1 there are four vortex generators 100 distributed at a distance over the circumference of the channel 5. Of course, the vortex generators can be in Circumferential direction are also lined up so that none Spaces on the channel wall 6 are left blank. For the Choice of the number and arrangement of the vortex generators is ultimately the vortices to be generated are decisive.

Figures 6-12 show other possible forms of introduction of fuel in combustion air 4. These variants can interact with one another in a variety of ways central fuel injection, such as from 1 emerges can be combined.

In Fig. 6, the fuel is added to channel wall bores 120, which are located downstream of the vortex generators, also injected via wall holes 121, which are immediate next to the side surfaces 111, 113 and in their longitudinal extent are in the same channel wall 6 on which the Vortex generators are arranged. The introduction of fuel through the wall holes 121 gives the generated Whirling an extra impulse, extending the life of the Vortex generator extended.

7 and 8, the fuel is passed through a slot 122 or injected via wall holes 123, both precautions immediately in front of the cross-canal extending edge 115 of the roof surface 110 and in the Longitudinal extension in the same channel wall 6 are located on the the vortex generators are arranged. The geometry of the Wall bores 123 or the slot 122 is selected so that the fuel at a certain injection angle into the Main flow 4 is entered and the re-placed vortex generator as a protective film against the hot main flow 4 largely shielded by flow.

In the examples described below, the secondary flow (See above) first of all via guides not shown through the channel wall 6 into the hollow interior of the vortex generators initiated. In this way, an internal cooling facility for the vortex generators created.

9, the fuel is injected via wall bores 124, which is located directly within the roof area 110 behind and along the one running across the channel Edge 115. The vortex generator is cooled here more external than internal. The emerging secondary flow forms a flow against the roof surface 110 against this hot main flow 4 shielding protective layer.

10 the fuel is injected via wall bores 125, which within the roof surface 110 along the line of symmetry 117 are staggered. With this variant the channel walls 6 are particularly good before the hot main flow 4 protected because the fuel is initially on the outer circumference the vertebra is introduced.

11 the fuel is injected via wall bores 126, which are located in the longitudinal edges 112, 114 of the Roof area 110 are. This solution ensures a good one Cooling of the vortex generators because of the fuel on it Extremities emerge and thus the inner walls of the element fully washed. The secondary flow is here directly put the resulting vortex into what to define Flow conditions leads.

12, the injection takes place via wall bores 127, which are in the side surfaces 111 and 113, on the one hand in the area of the longitudinal edges 112 and 114, on the other hand in Area of the connecting edge 116. This variant has a similar effect like those from FIG. 6 (bores 121) and from FIG. 11 (holes 126).

13 shows an embodiment of a fuel lance 8 in Flow direction 4 and from the front. This lance is for one central fuel injection designed. It is for about 10% of the total volume flow through the channel, where the fuel 9 is injected transversely to the direction of flow. It goes without saying that the fuel can also be injected lengthways be provided in the direction of flow. In this In this case, the injection pulse corresponds approximately to that of the main flow. The injected fuel 9 is in connection with a portion of supporting air 10 over several radial openings 17 entrained by the upstream injected vertebrae and with the main flow 4 is mixed. The injected fuel 9 follows the helical course of the vertebrae (see Fig. 2-4) and becomes uniform downstream of the vortex in the chamber finely divided. This reduces the risk of impact rays on the opposite channel wall as well as the formation from so-called "hot spots", as is the case with a non-vortexed Current is the case. Because the main mixing process occurs in the vertebrae and he is largely insensitive is against the injection pulse of the secondary flow, the fuel injection can be kept flexible and be adapted to other boundary conditions. So on the whole The same injection pulse is maintained in the load range itself be, here for the sake of completeness to the Reference is made to Fig. 14. Accordingly, since the Mix quality largely depends on the geometry of the vortex generators is only determined in the transient Area on the fuel injection. By adjusting the combustion process by adjusting the ignition delay time of the fuel 9 optimized at the mixing time of the vortex is a general minimization of pollutant emissions guaranteed. It should also be emphasized that this is Relation to the description of the vortex generators 2-4 that the intensive mixing has a good temperature profile over the entire cross-section flowed through gives what causes the occurrence of thermoacoustic Instabilities is reduced. So the vortex generators work, viewed alone, as a damping measure against thermoacoustic vibrations. The fuel lance 8 also shows the already tapped feed of Support air 10 on. Below is this type of debt collection entered closer.

Fig. 14 shows a diagram regarding supply of fuel 9 and supporting air 10, and after which the described combustion chamber is approached. This is about starting to create those conditions that are optimal Mixing of the injected fuel with the main flow ensure optimal ignition behavior and optimal combustion in the transient range up to Full load of the combustion chamber. The ordinate Y carries the set of injected media to each other, the abscissa X the load the plant. Now you can see that at the start the amount Support air 10 is maximum; it increases with increasing load Combustion chamber successively decreases while fuel 9 is being injected gradually increases. At full load, the fuel 9 always points still a portion Z of supporting air 10. The advantage of this The procedure can be seen in the fact that the supporting air 10 works well, flexions of the fuel pulse, which interfering with the deterioration of the mixture. Furthermore, sudden changes in the fuel pulse lead to thermoacoustic instabilities within the Combustion chamber. This is achieved through the constant supply of a minimal portion Z of supporting air 10 prevented.

Reference list

1

Annular combustion chamber

2nd

turbine

3rd

Hot gases

4th

Exhaust gases

5

Inflow zone, channel of the inflow zone

6

Canal wall of the inflow zone

7

Premixing zone

8th

Fuel lance

9

fuel

10th

Support air

11

Combustion zone

12th

Cross-sectional jump

13

Hot gases

14

turbine

15

Exhaust gases

16

Shaft axis

17th

Openings for fuel / supporting air injection

100, 101, 102

Vortex generators

110

Roof area

111, 113

Side faces

112, 114

Longitudinal edges

115

Transverse edge

116

Connecting edge

117

Axis of symmetry

120-127

Drilling holes for fuel injection

L, h,

Dimensions of the vortex generator

H

Height of the channel

α

Arrow angle



Angle of attack

Y

Ordinate scheme Fig. 14

X

Abscissa diagram Fig. 14

Z.

Proportion of supporting air at full load

Claims (10)

1. Combustion chamber having self-ignition, which essentially consists of an inflow zone designed as a duct (5) and a combustion zone, the two zones being arranged in succession and having the same direction of flow, and in which combustion chamber a premixing zone (7) is arranged downstream of the inflow zone (5), into which premixing zone a gaseous and/or liquid fuel (9) can be injected as secondary flow into a gaseous main flow (4), characterized in that the inflow zone (5) has vortex generators (100, 101, 102), of which a plurality are arranged next to one another over the periphery of the duct through which flow passes, and in that there is a jump (12) in cross-section between the premixing zone (7) and the combustion zone (11), which jump in cross-section induces the initial cross-section of flow of the combustion zone (11).
2. Combustion chamber according to Claim 1, characterized in that the fuel (9) is provided with a portion of assisting air (10).
3. Combustion chamber according to either of Claims 1 or 2, characterized in that the premixing zone (7) is a venturi-shaped duct, and characterized in that the fuel (9) can be injected via a fuel nozzle (8) along or transversely to the main flow (4) in the region of the greatest reduction in area of the venturi-shaped duct.
4. Combustion chamber according to Claim 1, characterized in that the combustion chamber is an annular combustion chamber (1).
5. Combustion chamber according to Claim 1, characterized in that a vortex generator (100) has three surfaces around which flow occurs freely and which extend in the direction of flow and of which one forms the top surface (110) and the other two form the side surfaces (111, 113), in that the side surfaces (111, 113) are flush with an identical wall segment of the duct (5) and enclose the angle () of sweepback with one another, in that the top surface (110), with an edge (115) running transversely to the duct (5) through which the flow passes, bears against the same wall segment of the duct (6) [sic] as the side surfaces (111, 113), and in that longitudinally directed edges (112, 114) of the top surface (110) are flush with the longitudinally directed edges of the side surfaces (111, 113) projecting into the duct (5) and run at an angle () of incidence to the wall segment of the duct (5).
6. Combustion chamber according to Claim 5, characterized in that the two side surfaces (11 [sic], 113), enclosing the angle () of sweepback, of the vortex generator (100) are arranged symmetrically around an axis (117) of symmetry.
7. Combustion chamber according to Claim 5, characterized in that the two side surfaces (111, 113) enclosing the angle (, /2) of sweepback enclose a connecting edge (116) with one another which together with the longitudinally directed edges (112, 114) of the top surface (110) form a point (118), and in that the connecting edge (116) lies in the radial line of the circular duct (5).
8. Combustion chamber according to Claim 7, characterized in that the connecting edge (116) and/or the longitudinally directed edges (112, 114) of the top surface (110) are designed to be at least more or less sharp.
9. Combustion chamber according to Claims 5, 6, 7, characterized in that the axis (117) of symmetry of the vortex generator (100) runs parallel to the duct axis, in that the connecting edge (116) of the two side surfaces (111, 113) forms the downstream edge of the vortex generator (100), and in that the edge (115) of the top surface (10) [sic] running transversely to the duct (5) through which flow passes is the edge acted upon first by the main flow (4).
10. Combustion chamber according to Claim 1, characterized in that the ratio of height (h) of the vortex generator to height (H) of the duct (5) is selected in such a way that the vortex produced fills the full height (H) of the duct (5) and the full height (h) of the duct part allocated to the vortex generator (100) directly downstream of the vortex generator (100).

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