EP1387986A1

EP1387986A1 - Device and method for injecting a liquid fuel in an air flow for a combustion chamber

Info

Publication number: EP1387986A1
Application number: EP02735482A
Authority: EP
Inventors: Niass Tidjani; Gérard Martin; Etienne Lebas; Guy Grienche; Gérard Schott; Hubert Verdier
Original assignee: IFP Energies Nouvelles IFPEN; Turbomeca SA
Current assignee: Safran Helicopter Engines SAS
Priority date: 2001-05-10
Filing date: 2002-04-22
Publication date: 2004-02-11
Also published as: US20040142294A1; JP4368112B2; FR2824625A1; WO2002090831A8; WO2002090831A1; AU2002310718A1; JP2004525335A; FR2824625B1; US7249721B2

Abstract

The invention relates to a device for injecting a liquid fuel in a pressurised air flow (7), in particular for a combustion chamber. The inventive device comprises: a hollow cylindrical body (10) with a longitudinal axis (YY') which defines a more or less cylindrical central space (11); air veins (12) which are more or less radial in relation to the longitudinal axis of the body (10) and which are disposed on the periphery of the body to allow the passage of said flow; and axial fuel injection pipes (5) which are disposed inside said air veins and which are connected to at least one fuel inlet (3) by means of at least one supply point (16). According to the invention, the pipes (5) are pierced with openings (9) that open into the central space (11) of said body (10) and which are oriented more or less in the direction of the flow in the air veins (12).

Description

DEVICE AND METHOD FOR INJECTING A LIQUID FUEL INTO AN AIRFLOW FOR A COMBUSTION CHAMBER

The present invention relates to a device and a method for injecting a liquid fuel into an air flow making it possible to produce a homogeneous fuel / air mixture in a combustion chamber.

The invention finds a use in particular in the field of terrestrial gas turbines, by promoting, during the operation of said turbine, obtaining a high energy yield associated with a low production of pollutants.

In conventional combustion chambers for gas turbines, the main concern is, as a priority, obtaining stable combustion over a wide range of operating conditions. To achieve this objective in the most efficient manner, conventionally, firstly, combustion is carried out in the vicinity of stoichiometry with part of the air coming from the compressor and the fumes obtained are gradually diluted, in a second step. with another part of the air from this compressor to lower their temperature to the thermal level admissible by the expansion turbine. However, this approach has the drawback of generating large quantities of nitrogen oxides (also called thermal NO _x ), because of the very high temperatures reached in the combustion zone (flame temperatures typically between 2000 and 2400 ° C. ).

To meet new environmental regulations, gas turbine manufacturers are now seeking to develop units capable of operating at full capacity, that is to say under heavy loads without producing large quantities of air pollutants.

The pollutants generally produced by gas turbines during the combustion of hydrocarbons are, as previously mentioned, nitrogen oxides but also carbon monoxide and unburnt hydrocarbons. It is also well known that the oxidation of molecular nitrogen to thermal NO _x within the combustion chambers of turbines strongly depends on the maximum temperature of the hot gases in the reactive zone.

The formation of nitrogen oxides can thus be represented by an increasing exponential function of the temperature. It therefore follows from the above that it is possible to limit the formation of nitrogen oxides by avoiding the temperature peaks of the gases within the combustion chamber.

Several methods have been proposed for this purpose: According to a first operating mode, it has been proposed to inject water or water vapor into the combustion chamber to reduce the temperature peaks, which has an effect beneficial for limiting the formation of nitrogen oxide of thermal origin.

This solution is however cumbersome to implement in view of the results obtained because it requires sophisticated water treatment to remove all impurities as well as a steam generator in the case of a steam injection, and can only be reasonably envisaged for very large machines. In addition, the lowering of the temperature causes a significant slowing down of the oxidation reaction of the hydrocarbons sometimes leading to the joint increase in the emission level of carbon monoxide and unburnt hydrocarbons.

Another solution consists in practicing staged combustion, with a rich stage and a lean stage, the transition from one to the other taking place very quickly. Here too, the temperature peaks, which generate nitrogen oxides NOx, are reduced, and the rich zone is also used to limit their formation, but this solution leads to a significant production of unburnt hydrocarbons.

A third solution for jointly controlling the temperature and the emission of pollutants consists, before combustion, of mixing the air and the fuel in the form of a lean mixture, in order to obtain a fuel / air richness of between 0.3 and 1, preferably between 0.5 and 0.8. The mass of air present in excess in the reaction zone thus absorbs part of the heat generated by the oxidation reaction of the fuel and reduces the temperature to which the products of the reaction are subjected. In addition, the need for cooling air to adjust the temperature at the inlet of the expansion turbine is much less. This process thus effectively limits the production of nitrogen oxides without significantly increasing the emission level of other pollutants (hydrocarbons, carbon monoxide, etc.). The main problem posed by a lean mixture operation is that the premix must be sufficiently homogeneous and uniform to achieve the low levels of pollutant emissions sought. Thus, it is possible, for a non-uniform distribution of the fuel in the air in the combustion zone, that the presence of an excess of fuel in certain regions leads to the existence of hot spots with as a corollary the uncontrolled formation of nitrogen oxides. Similarly, in other regions of very low wealth, local cooling is to prevent combustion and ultimately lead to unburnt gaseous and solid. In addition, if the mixing of a gaseous fuel with air takes place thanks to the effects of molecular diffusion and especially of the kinetic energy ratio between the fuel and the air as well as of the spatial distribution of the points of Injection, the mixing of a liquid fuel with air also requires prior spraying which conditions the quality of the mixture and therefore of the combustion.

Indeed, the combustion always taking place in the gas phase, it is necessary to transform the fuel into a cloud of droplets whose diameter must be as small as possible, the evaporation of said fuel being all the more rapid as the diameter of the droplets liquids is small. This fuel evaporation is often carried out in two stages by systems provided, on the one hand, with a vaporization chamber and, on the other hand, with liquid fuel injectors. The quality of the vaporization is generally dependent on the geometry of the vaporization chamber.

US patent 6,094,916 proposes for example a device in which the air / fuel mixture is carried out under pressure thanks to the presence of a fixed device with radial blades generating a rotational movement of the flow of fluids. Between each blade of the device is axially disposed a fuel injection tube. Fuel injection is performed through orifices made in the tubes with an opening angle of 60 ° relative to a radial direction of said device.

Such an arrangement cannot be suitable for injection in liquid form of the fuel, since it would in this case have the effect of sending said fuel directly onto the vanes of the device with the inevitable consequence of the formation of coke on the walls thereof. leading to significant nuisances on the performance, the lifespan of the materials of the device and the pollutant emission levels of the turbine. In addition, it has been found by the applicant that such an injection does not allow optimum spraying and a homogeneous mixture with the air in the case of the injection of a liquid fuel.

Thus, the subject of the present invention is a device making it possible to obtain a homogeneous lean mixture of fuel and air before combustion.

According to the present invention it is possible to obtain a stable flame over the entire range of operating conditions of a gas turbine operating in a lean mixture.

To this end, a device for injecting a liquid fuel into a pressurized air flow, in particular for a combustion chamber, comprising a hollow cylindrical body of longitudinal axis delimiting a central volume of substantially cylindrical shape, veins substantially radial with respect to the longitudinal axis of the body and arranged at the periphery of said body for the passage of said flow, and axial fuel injection tubes, disposed inside said veins and connected to at least one fuel inlet by at least one feed point, is characterized in that said tubes are pierced with openings open on the central volume of said body and oriented substantially in the direction of flow flow in the fluid veins. According to another characteristic, the median axis of the veins can form an angle between 20 ° and 60 ° with the radius of the cylindrical body.

Advantageously, the fluid streams can have a three-dimensional shape calculated to minimize the pressure losses caused during the crossing of the fluid streams by the flow of air under pressure.

The orifices can be distributed linearly in the axial direction of the fuel injection tubes.

The fuel injection tubes can have a variable internal cross section as a function of the distance from the fuel supply point of said tube.

Alternatively, the device may further comprise axial tubes for injecting a gaseous fuel, said tubes being pierced with openings open on said central cylindrical volume and oriented substantially perpendicular to the direction of flow flow in the veins fluids.

The gaseous fuel injection tubes can be placed, relative to the direction of movement of the pressurized air flow in the fluid streams, upstream of the liquid fuel injection tubes.

According to the invention, a method of injecting a liquid fuel into a pressurized air flow is characterized in that the following steps are carried out: - pressurized air is brought into a volume upstream d '' at least one combustion zone, a swirling movement of air is generated in said volume by passing the pressurized air flow through a plurality of passages arranged at the periphery of said volume,

- The liquid fuel is injected into said passages substantially in the direction of flow of the pressurized air flow.

Advantageously, air can be injected into said volume so that its speed varies from approximately 10 m / s to approximately 200 m / s.

A gaseous fuel can be injected, as a substitute, substantially perpendicularly to the direction of flow of the pressurized air flow.

Water can be injected in liquid form or in vapor form to replace the fuel.

Other characteristics and advantages of the device and / or of the method according to the invention will appear better on reading the description below of nonlimiting exemplary embodiments which follow, with reference to FIGS. 1 • to 6 in which:

- Figure 1 shows a partial sectional view of an injection device according to the invention;

- Figure 2 is a cross-sectional view along line 2-2 of Figure 1;

- Figure 3A is a local view on a larger scale showing a detail of the device according to the invention;

- Figure 3B is a sectional view along line 3-3 of Figure 3A; - Figure 4 shows a longitudinal sectional view of a possible embodiment of the liquid fuel injection tubes

- Figures 5A and 5B show schematically, in two views identical to those of Figures 3A and 3B, an alternative embodiment of the invention;

- Figure 6 illustrates another embodiment of the invention.

The terms “upstream” and “downstream” must be associated with the reading of this description in the sense of air circulation in the present device.

FIG. 1 shows a cross section of a fuel injection and air introduction device 1 and leading to a combustion chamber 2 of a pilot stage or of a main stage of a gas turbine, for example.

This device 1, with a longitudinal axis YY ′, comprises a liquid fuel inlet tube 3 bringing said fuel to a distribution pipe or manifold 4 of substantially annular shape. A multitude of channels or tubes 5, in communication with the pipe 4 via the injection points 16, extend substantially axially in the space between two blades 6 of a hollow body 10 of substantially cylindrical shape, this space forming a vein 12 for the passage of fluids, as is better visible in FIG. 2. The hollow body 10 delimits a central zone 11 whose cross section is illustrated in FIG. 2. A swirling movement of the air caused by its passage between the vanes 6 allows better stabilization of the combustion by promoting the recirculation of the combustion gases in the space 11 and in the combustion chamber 2. The tubes 5 have, over their entire length, orifices 9 open substantially in the direction of air flow in veins 12 and allowing the injection of the liquid fuel in a substantially radial manner between the said blades as well as the mixing of this fuel with the air 7 which arrives, for example, under pressure from the compressor of the turbine (not shown). The hollow body 10 is made integral with a fixed part 8 of the device by a known technique.

Figure 2 shows schematically a cross section of the cylindrical body 10 shown in Figure 1. The pressurized air passes through the hollow cylindrical body 10 by the fluid veins 12 delimited by the blades 6. The median axis XX 'of the veins 12 forms a angle θ with the radius R between the center of the body 10 and the center of the tube 5. The angle θ will be chosen by a person skilled in the art so that the vortex movement in the central zone 11 optimizes the recirculation of the gases of combustion. The angle θ will thus generally be between 20 and 60 °.

A liquid fuel injection tube 5 is placed in each vein 12. In the illustration illustrated in FIG. 2, there are thus, regularly distributed along the circumference of the body 10, twelve fluid veins 12 for the passage of air under pressure 7 delimited by twelve blades 6 between which are inserted twelve fuel injection tubes 5.

Of course, the embodiment thus presented is illustrative and the number of blades, their shape and that of the fluid streams allowing the passage of air will be optimized according to the technical characteristics of the entire device by the man of art according to any known technique.

FIGS. 3A and 3B respectively show a transverse and longitudinal section of a fluid stream 12 and of the tube 5 present within it. The pressurized air 7 passes through the fluid streams 12 along the arrows 17 and is mixed within them with the fuel arriving from an injection point 16 and leaving the orifices 9 in a direction illustrated by the arrows 18. The arrows 17 and 18 are collinear in FIGS. 3A and 3B, that is to say that said tubes 5 are pierced with openings open on the central volume of the hollow cylindrical body substantially in the direction of flow of the in the fluid veins. This configuration has the advantage in the context of a liquid injection of limiting the formation of coke on the walls 19 of the blades and improving in the fluid streams 12, on the one hand, the mixture between the air and the fuel. and, on the other hand, spraying said fuel downstream of the tubes 5 according to the principles previously described. Thus, it has been found by the applicant that the turbulence zone in the wake of the tube 5 generated by the flow of air 7 at high speed strongly promotes the atomization of the liquid fuel and contributes to improving the homogeneity of the air mixture. / fuel in said area. The work carried out in the context of the present invention has also shown that the air flow speed should be of the order of a few tens of m / s, preferably of the order of about 100 m / s while the speed of the fuel had to be as low as possible (of the order of 0.1 m / s to 10 m / s and preferably between about 0.5 m / s and 2 m / s) to promote said spraying and said mixture.

As shown in these figures, the cross section of the fluid veins, illustrated by the arrows 14 and 15, has a significant narrowing from upstream to downstream so as to increase the speed of the air in it and therefore the turbulence of the 'flow. This arrangement advantageously makes it possible to further improve the air / fuel mixture and the atomization of the fuel in the fluid streams 12. However, the cross section of the streams 12 may be rectangular or of another form known to those skilled in the art. so as to optimize the pressure drop caused by crossing the device. In addition, it can be fitted with a shutter system to adjust the air flow of the floor combustion depending on the load of the turbine, which facilitates operations in reduced steps.

Thus, at the outlet of the fluid veins, according to the device illustrated in FIGS. 1, 2 and 3A, 3B, a very homogeneous lean air / fuel mixture is obtained, generating stable combustion whatever the regime considered.

In addition, the swirling movement of the fluids in the central space 11 generated by the passage of the veins 12 of the body 10 also allows recirculation of the hot combustion products also favorable to stabilization of said combustion whatever the operating speed of the combustion chamber.

FIG. 4 illustrates a possible embodiment of a tube 5 for injecting liquid fuel according to the invention.

This tube has an evolving section 401 which is a function of the distance to the injection point 16 of the fuel in said tube.

The tube thus comprises two separate parts: a hollow part 403 ensuring the passage of the fuel to the injection orifices 9 and a solid part 404 produced according to any technique known to those skilled in the art so that it limits gradually the fuel passage section in said tube from the vicinity of its injection point 16 to its free end. This arrangement makes it possible to maintain, in a simple and economical manner, a substantially identical flow of fuel for each of the orifices 9.

The studies carried out by the applicant show that, for such a tube, the average diameter of the droplets at the outlet of the fluid streams is substantially independent of the air / fuel mass flow ratio and that said mean diameter is substantially constant over the entire outlet section. fluid veins. This property allows you to keep the same spray performance for different operating conditions of the combustion chamber.

A particular embodiment of the invention is illustrated by FIGS. 5A and 5B, which respectively represent a cross section and a longitudinal section of a fluid stream 12 and of an injection tube 505 of gaseous fuel present within it.

Unlike the liquid injection system described in relation to FIGS. 3A and 3B, the injection orifices 509 are oriented perpendicular to the mean direction of the flow of air in the fluid veins. The speed of the mixing will be, in this embodiment, all the more effective the higher the ratio between the speeds of the gaseous fuel and the air.

Without departing from the scope of the invention, the embodiments described in relation to FIGS. 3A, 3B and 5A, 5B can be combined to allow a supply and a mode of operation in liquid-gas dual-fueling of the combustion chamber. The supply of gaseous fuel to the gaseous fuel injection tubes may be carried out by a second distribution pipe of substantially annular shape substantially identical to that shown in relation to FIG. 1.

Figure 6 shows schematically a cross section of a cylindrical body 600, identical to that described in connection with Figure 2 and associated with an injection device allowing operation in liquid-gas bicarburation. This dual-fueling is carried out by combining, in the same device, tubes for injecting liquid fuel and tubes for injecting gaseous fuel as described above in relation to FIGS. 3A, 3B and 5A, 5B. Between the vanes 6 of the hollow cylindrical body, tubes 5 are dedicated to the injection of liquid fuel and tubes 505 allow the injection of a gaseous fuel. The tubes 505 are placed in the fluid veins upstream from the tubes 5.

The use of two distribution ramps leading to separate injection tubes in a gas turbine combustion chamber offers significant flexibility due to the possibility of using alternatively or in the same cycle a gaseous fuel or a liquid fuel , without modifying the fuel supply system and without stopping the turbine. In addition, the injection system remains compact and advantageously offers the possibility of switching from one to the other in the event of damage to a ramp (gas or liquid) or a problem with the supply of fuel ( gas or liquid).

Without departing from the scope of the invention, it is possible to use, during the operation of this device, one of the two tubes 5 or 505 as previously described for injecting either water in liquid form or steam of water in the combustion chamber. This procedure has the advantage, in accordance with the prior art described above, of reducing the emissions of nitrogen oxides.

The present device and / or the present method, although it has an obvious application therein, is not limited to the sole domain of gas turbines but may also be envisaged in any combustion device or method requiring the introduction a fuel in liquid form and a homogeneous mixture between said liquid fuel and the air prior to said combustion.

Claims

1. Device for injecting a liquid fuel into a pressurized air flow (7), in particular for a combustion chamber, comprising a hollow cylindrical body (10) with a longitudinal axis (YY ') delimiting a central volume (11) of substantially cylindrical shape, veins (12) substantially radial with respect to the longitudinal axis of the body (10) and arranged at the periphery of said body for the passage of said flow, and fuel injection tubes (5 ), arranged inside said fluid streams and connected to at least one fuel inlet (3) by at least one supply point (16), characterized in that said tubes are pierced with orifices (9) open on the central volume (11) of said body (10) and oriented substantially in the direction of flow flow in the fluid veins (12).

2. An injection device according to claim 1 in which the median axis (XX ') of the veins (1) forms an angle (θ) between 20 ° and 60 ° with the radius (R) of the cylindrical body (10) .

3. An injection device according to claim 1 or 2 wherein the fluid streams (12) have a three-dimensional shape calculated to minimize the pressure losses caused during the crossing of the fluid streams (12) by the pressurized air flow (7).

4. Injection device according to one of the preceding claims wherein the orifices (9) are distributed linearly in the axial direction of the fuel injection tubes (5).

5. Injection device according to one of the preceding claims wherein the fuel injection tubes (5) have a section internal variable according to the distance to the fuel supply point (16) of said tube.

6. An injection device according to one of the preceding claims further comprising axial tubes for injecting a gaseous fuel (505), said tubes being pierced with openings in said central cylindrical volume and oriented substantially perpendicular to the direction of flow flow in the fluid veins (12).

7. An injection device according to claim 6 in which the gaseous fuel injection tubes (505) are placed, relative to the direction of movement of the pressurized air flow in the fluid streams (12), upstream of the liquid fuel inlet tubes (5).

8. Method for injecting and mixing a liquid fuel into a pressurized air flow, characterized in that the following steps are carried out:

- pressurized air is brought into a volume upstream of at least one combustion zone,

- a swirling movement of air is generated in said volume by passing the pressurized air flow through a plurality of passages (12) arranged at the periphery of said volume,

9. An injection method according to claim 8 wherein air is injected into said volume so that its speed varies from about 10 m / s to about 200 m / s.

10. An injection method according to one of claims 8 or 9 in which is injected, in a substitute manner, into said passages a gaseous fuel substantially perpendicular to the direction of flow of the pressurized air flow.

11. Injection method according to one of claims 8 to 10 wherein water is injected in liquid form or in vapor form in substitution for liquid fuel or gaseous fuel

12. Application of the injection device according to one of claims 1 to 7 and / or of the injection method according to one of claims 8 to 11 to the main combustion stage of a gas turbine comprising at least a combustion stage.

13. Application of the injection device according to one of claims 1 to 7 and / or of the injection method according to one of claims 8 to 11 to the pilot combustion stage of a gas turbine comprising several stages combustion.