This application claims priority to European application 13154714.3 filed Feb. 8, 2013, the contents of which are hereby incorporated in its entirety.
The present invention relates to the generation of electric power by means of a gas turbine and generator. It refers to a power generating unit according to the preamble of claim 1. It further refers to a method for operating such a power generating unit.
A generators capability (i.e. its maximum possible output) usually is reduced at hot ambient temperatures, since temperatures of the cold water entering the generator cooler increase with increasing ambient temperatures, particularly when cooling water is re-cooled in a cooling water cooler against ambient air (as opposed to water).
Usually, the reduced capability matches the reduced power output of a gas turbine, which drives the generator in a power generating unit, at higher ambient temperatures. However, when gas turbine power output is augmented with evaporative cooling or fogging, and possibly further augmented by additional water injection, the generator may not be able to convert this augmented power within its specification limits (typically isolation class E).
On the other hand, gas turbines operating at cold ambient temperatures usually need a mechanism to prevent icing of the compressor inlet and front stages.
To solve the problem related to the gas turbine power augmentation a generator with higher capability could be used: Usually this means a bigger and more expensive generator for this specific operation window. The cost increases disproportionally, if a technology change from air cooled generators to hydrogen cooled generators becomes necessary.
Alternatively, re-cooling could be provided with evaporative re-coolers outside the air intake system.
Alternatively, a mechanical chilling device (heat pump) could be used to re-cool the generator cold water.
However, above described solutions are complex and/or costly and require significant additional space.
To solve the problem related to icing of the gas turbine, bleed air from the compressor could be used with the following disadvantages: It reduces gas turbine efficiency, and requires high temperature and pressure class piping.
Alternatively, a heat exchanger may be used. Typically, low temperature steam from a water steam cycle is used for the purpose. Hence, this would be limited to combined cycle power plants (CCPP) and hence would not be feasible for simple cycle plants.
Document U.S. Pat. No. 6,112,544 discloses a method for optimizing the cooling efficiency of a generator cooling system for a generator used for electric power generation in a power station. The generator has a generator cooler which is arranged, together with further coolers, in a closed intermediate cooling circuit which transfers heat to a main cooling water system via at least one intermediate cooler. The method includes providing means for increasing the mean driving temperature difference between the media flowing through the generator cooler in the intermediate cooling circuit to improve the transmission of heat from the generator cooler to the main cooling water system. The cooling system is not related to a gas turbine.
Document US 2012/0216546 A1 discloses a method and apparatus for the operation of a gas turbine unit with an evaporative intake air cooling system in the intake air pathway, wherein the return water flow of the evaporative intake air cooling system is used for the cooling of components of the gas turbine unit and/or of a generator coupled to the gas turbine unit and/or of another element coupled to the gas turbine unit, and a gas turbine unit adapted to be operated using this method. A connection between gas turbine and generator cooling is established only via the use of the return water flow.
Document WO 03/048545 A1 discloses a gas turbine unit as well as a method for operating a gas turbine with high-pressure turbine and a low-pressure turbine unit. In this unit a very quick and at the same time easily controllable augmentation or reduction of the shaft power of the gas turbine unit can be achieved by providing at least one liquid droplet injection device on the upstream side of said compressor for injecting liquid into the stream of intake air in order to increase the shaft power generated by the gas turbine unit. The amount of water mass flow corresponding to the desired increase or decrease of shaft power output of the gas turbine unit is added or reduced in the form of liquid droplets in a substantially stepless manner and immediately within a time interval that is determined by the design characteristics of the liquid droplet injection device. A relation to a generator is not disclosed.
It is an object of the present invention to provide a power generating unit according to the preamble of claim 1, which synchronizes the power and cooling requirements of gas turbine and generator in a simple and most effective way.
It is another object of the present invention to disclose a method for operating such a power generating unit.
These and other objects are obtained by a power generating unit according to claim 1 and a method according to claim 14.
The power generating unit according to the present invention comprises a gas turbine with an air intake section, a compressor, at least one combustor and at least one turbine, and further comprises a gas-cooled generator, being driven by said gas turbine and having a generator cooling system comprising at least one cooler, through which cooling water flows during operation, and which removes heat from said generator during operation. The at least one cooler is suitable for having cooling water flowing through it.
The unit is characterized in that said generator cooling system is connected to an air intake heat exchanger arranged within said air intake section of said gas turbine in order to transfer heat from said cooling water flowing through said generator cooling system, to the air flowing through said air intake section.
According to an embodiment of the invention said air intake section of said gas turbine comprises a filter at the entrance of said air intake section, and said air intake heat exchanger is arranged downstream of said filter.
Specifically, said air intake section of said gas turbine comprises a silencer downstream of said filter, and said air intake heat exchanger is arranged downstream of said silencer.
More specifically, said air intake section of said gas turbine comprises means for cooling intake air flowing through said air intake section, and said cooling means is arranged between said filter and said silencer.
Even more specifically, said cooling means comprises a droplet injection device for fogging.
Alternatively, said cooling means comprises an evaporative cooler, preferably with a droplet catcher arranged downstream said evaporative cooler.
According to another embodiment of the invention said air intake section of said gas turbine comprises a silencer downstream of said filter, said air intake section of said gas turbine further comprises means for cooling intake air flowing through said air intake section, which cooling means is arranged between said filter and said silencer, and said air intake heat exchanger is arranged downstream of said cooling means. In particular the said air intake heat exchanger can be arranged between said cooling means and said silencer.
Specifically, said cooling means comprises a droplet injection device for fogging.
Alternatively, said cooling means comprises an evaporative cooler, preferably with a droplet catcher arranged downstream said evaporative cooler.
According to a further embodiment of the invention said generator cooling system comprises a generator cooler and a lube oil cooler, which are connected to a cooling water cooler, and connecting means are provided for selectively connecting said air intake heat exchanger in series with said generator cooler such that cold water flowing to the generator cooler is further cooled by routing it through said intake heat exchanger, or in parallel to said cooling water cooler in order to prevent icing of the compressor inlet and/or front stages of said gas turbine.
Specifically, a first valve is arranged in a feed line of said generator cooler, said air intake heat exchanger is connected with a first feed line to said feed line of said generator cooler upstream of said first valve, and with a first return line to said feed line of said generator cooler downstream of said first valve, and a second and third valve are arranged in said first feed line and first return line.
More specifically, said air intake heat exchanger is connected with a second feed line to a common return line of said generator cooler and said lube oil cooler, and with a second return line to a common feed line of said generator cooler and said lube oil cooler, and a fourth and fifth valve are arranged in said second feed line and second return line.
Even more specifically, a sixth valve is arranged in said common return line or common feed line between said air intake heat exchanger and said cooling water cooler.
The method for operating an inventive power generating unit according to the invention is characterized in that heat is transferred from said generator cooling system to intake air flowing through said air intake section of said gas turbine by means of said air intake heat exchanger.
According to an embodiment of the inventive method said at least one cooler is a generator cooler, and cold water flowing to said generator cooler is further cooled by routing it through said air intake heat exchanger arranged within said air intake section of said gas turbine to inherently synchronize an additional cooling demand with a higher output of said gas turbine when air inlet cooling is activated.
According to another embodiment of the inventive method said air intake heat exchanger is used at low ambient temperature to act as an efficient anti-icing means.
According to a further embodiment of the inventive method said air intake heat exchanger is used for intake air pre-heating in order to control NOx emission of said gas turbine.
The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.
The power generating unit 10 of
An exemplary configuration of generator cooling system 19 is shown in
Both coolers 21 and 23 are operated with cooling water CW, which is pumped by water pump 24 through feed lines 25a, and 26a and flows back through return lines 26a and 26b. Coolers 21 and 23 are connected in parallel with their cooling water sides and may be both connected to a cooling water cooler 22. In addition, a bypass line 27 may be provided upstream of water pump 24.
Now, according to the invention, generator cooling system 19 of
Two cases are possible for the use of air intake heat exchanger 30 in this configuration:
In order to be able to select one of these two operating modes, several valves V1-V6 are arranged in lines 25b, 31-34 and the return line to cooling water cooler 22, as shown in
On the other hand, air intake heat exchanger 30 is connected with feed line 33 to a common return line 26 of generator cooler 21 and lube oil cooler 23, and with a return line 34 to a common feed 25 line of generator cooler 21 and lube oil cooler 23. A fourth and fifth valve V4, V5 are arranged in feed line 33 and return line 34, respectively.
When the ambient temperature is low enough to cause an icing problem, valves V1 and V2 are closed, and valves V4 and V5 are opened (
When additional generator cooling is needed in view of a higher gas turbine output caused by augmentation procedures at air intake section 12, valves V3, V4 and V5 are closed, and valves V1 and V2 are opened (
Air intake heat exchanger 30 can be arranged in air intake section 12 at different places, depending on the configuration of air intake section 12.
In general, the power generating unit according to the invention has the following features and advantages:
Number | Date | Country | Kind |
---|---|---|---|
13154714.3 | Feb 2013 | EP | regional |