Power plants – Combustion products used as motive fluid – With safety device
Reexamination Certificate
2001-02-26
2003-03-04
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
With safety device
C060S039550, C060S739000
Reexamination Certificate
active
06526742
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an oil supply system for a gas turbine having a number of combustion chambers being able alternatively to be fired with gas or with oil, and equipped with primary and secondary nozzles. The system comprises an oil feeding device, a water feeding device and a blow-off device. The oil feeding device is provided with an oil supply line with a fuel distributor and a number of primary oil-conducting conduits leading from the fuel distributor to the combustion chamber to deliver oil to the primary nozzles and of secondary oil-conducting conduits running parallel to the primary oil-conducting conduits leading to the secondary nozzles. The water feeding device is provided with a water supply line and a number of primary water-conducting conduits and secondary water-conducting conduits corresponding to the number of combustion chambers and connected to the water supply line via a distributor, to deliver water to the primary and secondary nozzles. The blow-off device is provided with an air supply line split into two supply branch lines and with two closed circular pipes connected to the supply branch linen via connection valves. A number of primary air-conducting conduits and secondary air-conducting conduits corresponding to the number of gas turbine combustion chambers deliver blow-off air to the primary and secondary nozzles.
DESCRIPTION OF THE PRIOR ART
To be able to comply with the often very restrictive emission standards in case of gas turbines that can alternatively be fired with gas or oil, these gas turbines are operated according to the Dual-Fuel-Dry-Low-Nox (DLN) process, in which thermal Nox is already reduced in the combustion chamber by a better mixing of gas and air. This presupposes a multi-nozzle system of primary nozzles and secondary nozzles for each combustion chamber. In case of oil firing, the NOx reduction is achieved by the injection of water for flame cooling, with water and oil being mixed immediately upstream of the gas turbine combustion chambers or injected separately into the combustion chambers. If turbine operation is changed from oil to gas firing, each oil and water duct of each combustion chamber nozzle, air must be blown through each nozzle to remove oil residues and to provide for a continuous duct cooling. Therefore, the gas turbine requires an oil supply system for oil firing that comprises an oil feeding device, a water feeding device and a blow-off device and that, compared with gas firing, presents considerable difficulties as far as control and the distribution of fuel are concerned.
For oil supply, the burning oil delivered via an oil pump has heretofore been pumped through a fuel distributor to individual primary oil-conducting conduits leading to the gas turbine combustion chambers for the oil delivery to the primary nozzles. The primary oil-conducting conduits have been branched off the secondary oil-conducting conduits for the delivery of oil to the secondary nozzles. Secondary valves have permitted connection and disconnection of the secondary oil-conducting conduits, as the secondary nozzles are fired only after a certain firing temperature is reached. Till then, the whole fuel quantity is delivered to the primary nozzles. Afterwards, however, the fuel quantity must be distributed to the primary and secondary nozzles at a certain ratio. Due to branching the secondary oil conduits off the primary oil conduits, however, fuel distribution depends on the resistances in the supply lines and fuel dosing is uncontrolled, which time and again leads to thermal overloads and/or irregular loads of the individual gas turbine combustion chambers and/or the combustion chamber nozzles, the flame tubes, cross ignition tubes and the like, and may even cause a total wreckage of the turbine.
To reduce the NOx emissions the in oil firing operation, water must be injected at a certain quantitative proportion to oil for flame cooling, whereby thermal NOx can be reduced. To this end, deionized water is delivered to the primary and secondary nozzles by means of an appropriate jetting pump via multiple connection valves. The water injection starts only after firing temperature is reached, when the secondary nozzles are connected to the primary nozzles. Water injection is controlled via a flap valve that first reduces the pump pressure to the desired injection pressure, whereupon a control valve controlled by a water meter determines the quantity of water as a function of the oil quantity, to comply with the maximum admissible quantity ratio water/oil of, for instance, 0.85. In this case, too, there are high load variations due to the flap valve, mainly during the beginning of water injection. Because of the use of single connection valves, due to the different line resistances, there is an irregular distribution of the overall water quantity to the individual gas turbine combustion chambers with irregular loads of the combustion chambers and/or their parts.
When changing the operating mode from oil to gas firing, the oil and water ducts of the combustion nozzles must be cooled with air. Additionally, the residual oil remaining in the combustion nozzles must be blown off for cleaning and to prevent coking. Therefore, there is a blow-off device with corresponding primary and secondary air-conducting conduits. The blow-off air is tapped from the gas turbine compressor and then, by means of a separate mechanically driven air compressor, its pressure is increased, for instance, to 1.4 times the compressor pressure for blowing against the combustion chamber pressure. When changing to gas firing takes place at a firing temperature, where primary and secondary nozzles are operated, both the primary and the secondary air conducting conduits are all of a sudden connected via mere on/off valves, whereby the residual oil quantities are blown into the combustion chamber all of a sudden too. This creates a sudden increase of power, which, in turn, entails load variations affecting the service life of the turbine, endangers availability due to a turbine failure and even may lead to a shut-down of the turbine due to the over temperature in the combustion chambers.
SUMMARY OF THE INVENTION
The invention has therefore the object to provide an oil supply system of the above mentioned kind that ensures a sound oil firing operation of the gas turbine, complying with the emission standards even when the operating mode is changed, and furthermore ensures that firing of the turbine is easy on the combustion chambers and their parts.
The object of the invention is achieved according to one aspect thereof in that the oil feeding device comprises a secondary fuel distributor for the secondary oil-conducting conduits in addition to the primary fuel distributor for the primary oil-conducting conduits. The secondary fuel distributor is also connected to the oil supply line and the fuel distributors deliver quantities of oil in an adjustable distribution ratio through the oil-conducting conduits to the combustion chambers. According to another aspect, water distributors, such as variable-speed distribution pumps, with an adjustable distribution ratio are provided in the water feeding device as distributors for the primary and secondary water-conducting conduits. According to still another aspect, the blow-off device is equipped with proportional minimum pressure valves for the supply branch lines.
Due to the primary fuel distributor and the secondary fuel distributor distributing the delivered oil quantity exactly to the primary oil-conducting conduit and the secondary oil-conducting conduit according to a certain adjustable distribution ratio such as 60:40, an exact dosing of the oil quantity is ensured both for the primary nozzles and for the secondary nozzles of the combustion chambers. The fuel distributor is a positive fuel distributor such as a gear-type fuel distributor or a piston-type fuel distributor. Therefore, the fuel quantity combusted by the primary and/or secondary nozzles is exactly predetermined for each power range, thus av
Ausserwoger Gottfried
Hess Alexander
Casaregola Louis J.
Collard & Roe P.C.
Linzer Elektriztäts-, Fernwärme- und Verkehrsbetriebe Aktiengese
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