Power plants – Combustion products used as motive fluid
Reexamination Certificate
1999-02-23
2001-07-10
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039094
Reexamination Certificate
active
06256975
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of gas turbine engineering. It relates to method and apparatus for removing liquid fuel from the fuel system of a gas turbine after shutting down the turbine
BACKGROUND OF THE INVENTION
Gas turbines are increasingly being equipped with multiple burner systems. The liquid fuels are injected in this case into the burner systems by using complex atomizer nozzles. Within the scope of the attempts to optimize the combustion quality with respect to the emissions and the efficiency, it is necessary for these parameters to satisfy ever more stringent quality requirements with reference to the spray quality in the case of modern gas turbine atomizers. Stationary gas turbines are operated with a wide range of liquid fuel qualities. These fuels, for example heating oil of “extra light” quality, tend to form residues when vaporized (coking).
If a gas turbine operated with liquid fuel is shut down, the fuel injection systems heat up via the convective thermal flux of the surrounding material to such an extent that such residues can form if the fuel systems situated in the region of the thermal block have not been completely emptied of fuel. These hard residues worsen the atomizer quality to an inadmissible extent, and lead to rising through-flow resistances of the nozzles. The gas turbine can no longer be operated in the advanced stage of formation of residues.
Over and above the problem of coking, after the shutdown of a gas turbine operated with liquid fuel there is also the risk of the fuel passing from the fuel systems in an uncontrolled fashion into the combustion chamber when the rotor is stationary, or into the boiler possibly connected downstream of the gas turbine and forming an explosive mixture there with air at rest.
In order to avoid the problems described, the liquid fuel must be removed from the fuel systems in a controlled process after shutting down the gas turbine.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel method and a novel device by means of which the remaining liquid fuel can be reliably removed from the fuel systems of a shut-down gas turbine, and thus coking in the burners and the formation of explosive air/fuel mixtures in the exhaust gas section of the gas turbine can be avoided.
The object is achieved in the case of a method of the type mentioned at the beginning by virtue of the fact that the liquid fuel is flushed from the fuel system by the use of an inert auxiliary medium. The flushing out according to the invention makes it possible to remove the remaining liquid fuel in a way which is simple and can be controlled effectively. In particular, the use of an auxiliary medium provides the possibility of removing even small residues of the fuel, such as surface films, for example, rapidly and reliably from the fuel systems.
A first preferred embodiment of the method according to the invention is distinguished in that with the shutdown of the gas turbine the feed of liquid fuel via the first feeder line is interrupted at an interrupt point in the first feeder line, and in that the auxiliary medium is fed into the first feeder line via a second feeder line at a feed-in point located between the interrupt point and the burner. By virtue of feeding in at a special feed-in point on the feeder line, it is possible to start flushing very near the burner. Consequently, that liquid fuel component which must be flushed out via the burner and can lead to explosive mixtures in the exhaust gas section can be kept small.
A preferred development of this embodiment is defined in that the liquid fuel located in the fuel system between the feed-in point and fuel nozzles is flushed into the combustion chamber via the fuel nozzles in a first step by means of the auxiliary medium fed in at the feed-in point, and in that liquid fuel which is located in the first feeder line in front of the feed-in point in the direction of flow is flushed from the first feeder line via a separate outlet in a second step by means of the auxiliary medium fed in at the feed-in point. It is possible by means of the first step completely to remove the liquid fuel, which tends to cause coking, in the region of the burner in a simple way and without further structural measures on the burner/fuel system. The second step prevents liquid fuel subsequently running from the sections of the feeder line which are situated further upstream into lances or nozzles of the burner which have already been cleaned.
The first step, that is to say flushing out the fuel into the combustion chamber is preferably subdivided into two flushing operations, so that the largest portion of the liquid fuel is emptied into the combustion chamber in a first low-pressure flushing operation, the auxiliary medium displacing the liquid fuel from the relevant lines and only residual amounts of the liquid fuel remaining, in particular in the form of surface films, that the remaining residual amounts of the liquid fuel are removed in a second high-pressure flushing operation, and that a defined flow rate of the auxiliary medium is used in each case for the low-pressure flushing operation and the high-pressure flushing operation, the flow rate being greater for the high-pressure flushing operation than for the low-pressure flushing operation.
With the low-pressure flushing operation, the main portion of the fuel is emptied slowly and under controlled conditions. The duration of the low-pressure flushing operation is to be selected in this case such that the bulk of the fuel is removed from the fuel nozzles with a very low impulse. Because of the small shear forces associated with the low flow rate, only small residual amounts of fuel can remain behind in the dead water spaces of the lance or as a film on the material surfaces. The burner lances are completely cleaned with the high-pressure flushing operation. For this purpose, the working pressure, and thus the flow rate of the auxiliary or flushing medium is raised until the fuel or oil film is completely removed from the nozzle surfaces and all dead water regions are completely freed from fuel, and thus all risks of coking are eliminated.
Since in the case of the low-pressure flushing operation the main amount of the liquid fuel is emptied into the combustion chamber and has to be rendered harmless with regard to the risk of an explosion, in accordance with a preferred development of the embodiment of the invention air is sent through the combustion chamber during the low-pressure flushing operation, and the ratio of fuel to air in the combustion chamber is held below the extinction limit or the lean ignition limit. An explosion can thereby be reliably avoided. In this case, to feed the air into the combustion chamber either use is made of the coastdown phase of the gas turbine, or the gas turbine is operated with a switched-on start-up device, preferably with a defined ventilating speed.
The device according to the invention for carrying out the method, which comprises a fuel system for a gas turbine having at least one first feeder line via which the liquid fuel is directed to the burner of the gas turbine and is injected into the combustion chamber, is defined in that a second feeder line, which can be connected to the first feeder line at a feed-in point, is provided.
A first preferred embodiment of the device according to the invention is defined in that the second feeder line is the feeder line of a water injection system by means of which water can be injected into the combustion chamber, in that the second feeder line is connected via a connecting line to the feed-in point on the first feeder line, and in that means for shutting down the connecting line are arranged in the connecting line, and in that the shutdown means comprise a check valve. The existing supply system for the burner can thereby be used in a very simple way for flushing purposes.
Further embodiments follow from the dependent claims.
REFERENCES:
patent: 2015995 (1935-10-01), Egtvedt
patent: 2038998 (1936-0
Dobbeling Klaus
Engelbrecht Geoffrey
Magni Fulvio
Muller Gerhard
ABB Research Ltd.
Burns Doane Swecker & Mathis L.L.P.
Freay Charles G.
Torrente David J.
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