Patent Application
20110027732
This application claims priority under 35 U.S.C. §119 to European Patent Application No. 09166907.7 filed in Europe on Jul. 30, 2009, the entire content of which is hereby incorporated by reference in its entirety.
The present disclosure relates to a burner of a gas turbine.
The air generates in the centre of the cone shaped chamber 1 (i.e. along the axis 5 of the cone shaped chamber 1) a zone of larger vortices 6 (the vortex core).
A lance 8 is provided along the axis 5 to inject a thin liquid fuel jet 15 into the cone shaped chamber 1. In particular the liquid fuel jet 15 can be injected into the vortex core 6 to mix with the air and form a combustible mixture.
Nevertheless, when the liquid fuel jet cross-section is too small, it withstands large asymmetrical centrifugal forces because the liquid fuel jet can not reliably stay within the equally small vortex core and misses the centre, with large gradients of circumferential velocity, which then can prevent it from staying at the vortex core. In practice, during operation the liquid fuel jet 15 fluctuates radially around the vortex core.
These fluctuations can lead to combustion instabilities that are amplified in the burner and combustion chamber downstream of the burner.
U.S. Pat. No. 6,270,338 describes a burner of a gas turbine having these features.
Combustion instabilities can influence both the lifetime and noise emissions. In particular, low frequency instabilities with a frequency less than 30 Hz can be difficult to deal with.
In fact, it can be difficult to suppress these instabilities with operation changes, and damping of these low frequency's instabilities using, for example, Helmholtz dampers can be difficult, because of the huge resonator volumes that would be required.
These problems can also be increased by the fact that low frequency pulsations couple the exhaust system, amplify the noise and propagate it into the neighbouring areas of the power plant.
Burners having a lance with a divergent outlet are also known.
In this respect, WO 03/054447 discloses a lance having a tip with a diverging portion and a diverter facing it. The diffuser angle is very large and also thanks to the diverter, the fuel jet can be diverted laterally generating a conical fuel flow.
U.S. Patent Application No. 2003/150217 discloses a lance with a large conical tip arranged to fan out the fuel after injection.
DE 19537636 discloses a lance with a very short diverging portion with a wide diverging angle. This diverging portion can be arranged to generate a conical fuel flow.
EP 692675 and DE 4446609 disclose a lance having a cylindrical end that feeds the fuel in a conical atomisation chamber wherein atomisation air is injected. The mixture formed in the atomisation chamber can then be fed to a conical burner chamber. In these burners the lance does not inject a liquid jet (in the form of a liquid cylinder) into the vortex core.
A burner of a gas turbine is disclosed including at least two part cone shells arranged offset with respect to one another and defining a cone shaped chamber with longitudinal tangential slots for feeding air therein, and a lance carrying at least a liquid fuel nozzle arranged centrally in the cone shaped chamber. A portion of the nozzle facing the cone shaped chamber is divergent in shape. A diffuser angle (α) between a wall of the nozzle and a longitudinal axis of the cone shaped chamber is less than 5°, and the diverging portion of the nozzle has a diffuser length to nozzle diameter ratio between 2-6, and the nozzle diameter is a smaller diameter of the diverging portion.
Further characteristics and advantages of the disclosure will be more apparent from the description of an exemplary but non-exclusive embodiments of the burner according to the disclosure, illustrated by way of non-limiting example in the accompanying drawings, in which:
An aspect of the disclosure provides a burner with which combustion instabilities are limited and thus noise, in particular low frequency noise, can be reduced.
A further aspect of the disclosure provides a burner in which a liquid fuel jet can be injected into the vortex core.
Another aspect of the disclosure provides a burner that can have a longer lifetime with respect to traditional burners.
The burner in exemplary embodiments of the disclosure has a lance with a small angle with defined proportions that can allow a liquid jet to be generated that has a cross-section larger than the cross-section of the passage defined by the lance, but does not open forming a fuel cone. This allows a lance having small-cross-section to be manufactured, increasing ease of assembly and reducing lance complexity.
The disclosure relates to a burner of a gas turbine. The structure of the burner has two part cone shells 2 arranged offset with respect to one another and defining a cone shaped chamber 1. The cone shaped chamber 1 has two longitudinal tangential slots 4 for feeding air 3, and a lance 8 arranged along the axis 5 for feeding a liquid fuel. The lance 8 faces the cone shaped chamber 1 directly, i.e. without any component in between and can be arranged to inject a liquid jet (i.e. in the form of a liquid cylinder).
Different embodiments of the disclosure are possible and, in this respect, the burner may also have more than two part cone shells.
The cone shells can also be provided with nozzles 10 arranged on each of the cone shell, close to the tangential slots 4, to inject gaseous fuel into the cone shaped chamber 1.
In addition, the cone shells 2 can be housed in a plenum (not shown) wherein compressed air coming from the compressor of the gas turbine (not shown) can be fed. This air enters through the tangential slots 4 into the cone shaped chamber 1. Downstream of the cone shaped chamber 1 a combustion chamber (not shown) can be provided.
The lance 8 carries a liquid fuel nozzle 12 arranged centrally in the cone shaped chamber 1, i.e. a longitudinal axis of the nozzle 12 overlaps the axis 5.
The axis of the lance 8 can be the same as the axis of the nozzle 12 and it can also be the same as the axis 5 of the cone shaped chamber 1.
The nozzle 12 has a first portion 13 with a constant diameter D and, downstream of it, a second portion 14, facing the cone shaped chamber 1, that is divergent in shape.
The diverging portion 14 of the nozzle 12 has a diffuser angle α (i.e. an angle between the wall of the nozzle and the axis 5) of less than 5° and greater than 0°. The diffuser angle α can be between 1.5-2.2° and in other exemplary embodiments the diffuser angle α can be between 2-4°.
In addition, the diverging portion 14 of the nozzle 12 can have a diffuser length L to nozzle diameter D ratio between 2-6, between 3-5 or about 4. The diffuser length L is the length of the diverging portion 14 of the nozzle 12 and the nozzle diameter D is the smaller diameter of the diverging portion 14 (i.e. the diameter D of the first portion 13 of the nozzle 12).
The operation of the burner of the disclosure is now described below.
The burner can operate with gaseous fuel and liquid fuel.
During operation with gaseous fuel, air can be injected through the tangential slots 4 and gaseous fuel through the nozzles 10. This operation occurs in a known way.
During operation with liquid fuel, air can be introduced into the cone shaped chamber 1 through the slots 4 and liquid fuel can be injected through the nozzle 12 at the tip of the lance 8.
Because of the diverging portion 14, when the liquid fuel goes out from the nozzle 12 it can form a liquid jet 15 having a thickness (i.e. a diameter) larger than the smaller diameter of the diverging portion 14 and also larger than the greater diameter of the diverging portion 14 (i.e. the diameter of the terminal portion of the diverging portion 14) but it does not open forming a conical surface. For example, the liquid fuel forms a liquid jet that is substantially cylindrical with a cross-section larger than the largest inner cross-section of the nozzle.
Since the diameter of the liquid jet 15 can be large (in particular larger than in traditional burners), when the liquid fuel jet 15 enters the vortex core 6, it can be subjected to substantially symmetrical centrifugal forces that do not urge it outside of the vortex core 6.
Consequently the liquid jet 15 can stay within the vortex core 6 without radial fluctuations, limiting in particular low frequency combustion instabilities and low frequency noise.
In addition, thanks to the diverging portion 14, immediately outside of the nozzle 12 a number of liquid fuel drops can start to separate from the liquid fuel jet 15, generating a large zone 17 made of liquid fuel drops and vapour fuel (the vapour being the liquid already evaporated). This zone can improve mixing of the fuel with air and limits combustion instabilities (and in particular low frequency instabilities) and noise (in particular low frequency noise).
Advantageously, thanks to the mixing improvement of the liquid fuel and air, the burner of the disclosure also has sensibly reduced NOx emissions and smoke emissions.
Moreover, the improved combustion stability can allow an extended lifetime to be achieved.
Tests were performed to ascertain the operation of a combustion chamber having a lance in embodiments of the disclosure.
In particular the lance used during the tests has these features:
L/D=4
D=3.2 millimeters
α=2
The results of those tests are shown in
Naturally the features described may be independently provided from one another.
In practice the materials used and the dimensions can be chosen according to requirements.
It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09166907.7 | Jul 2009 | EP | regional |
