Patent Description:
As known, a gas turbine assembly for power plants comprises a compressor assembly, a combustor assembly and a turbine assembly. The compressor assembly is configured for compressing incoming air supplied at a compressor inlet. The compressed air leaving the compressor assembly flows into a closed volume (called "plenum") and from there into the combustor assembly. This combustor assembly comprises usually a plurality of burners configured for injecting fuel (at least one type of fuel) into the compressed air flow. The mixture of fuel and compressed air enters a combustion chamber where this mixture ignites. The resulting hot gas flow leaves the combustion chamber and flowing by the turbine assembly performs a rotating work on a rotor connected to a generator. Usually the same rotor supports also the compressor assembly. As known, the turbine assembly comprises a plurality of stages, or rows, of rotating blades that are interposed by a plurality of stages, or rows, of stator vanes. The rotating blades are supported by the rotor whereas the stator vanes are supported by a casing (called "vane carrier") that is concentric and surrounding the turbine assembly.

In order to achieve a high efficiency, the hot gas flow has to have a very high turbine inlet temperature. However, in general this high temperature involves an undesired high NOx emission level. In order to reduce this emission and to increase operational flexibility without decreasing the efficiency, a so called "sequential" gas turbine is particularly suitable. In general, a sequential gas turbine performs two combustion stages in series. Today at least two different kinds of sequential gas turbines are known.

According to a first embodiment, the gas turbine comprises a first combustor and the second combustor that are annular shaped and are physically separated by a turbine, called high pressure turbine. Downstream the second combustor a second turbine unit is present (called low pressure turbine).

A gas turbine of this type is produced by the Applicant and is available on the market as "GT26".

According to a second embodiment of a sequential gas turbine, the gas turbine is not provided with the highpressure turbine and the combustor assembly is realized in form of a plurality of can-combustors wherein each can-combustor comprises a first combustor and a second combustor arranged directly one downstream the other inside a common casing can-shaped. Also a gas turbine of this type is produced by the Applicant and is available on the market as "GT36". These two examples of gas turbine assemblies (GT26 and GT36) have been cited only as non-limiting examples wherein the present invention can be applied.

In these gas turbine assemblies, for cooling reasons it is known to spill part of the compressed air from the compressor or from the plenum and to guide this air inside the rotor and the turbine, i.e. the parts to be cooled in contact with to the hot gas flow. For lowering the temperature of the spilled compressed air it is known to provide the gas turbine with a first heat exchanger, in particular a cooler or cooling device (for instance a so called Once Through Cooler or "OTC") configured for cooling the spilled compressed air and for feeding this cooled air to the turbine and the rotor for cooling purposes. This cooling device is usually a component arranged outside the gas turbine casing and therefore ducts are present for feeding the spilled compressed air to the cooling device (at least a spilled air inlet duct) and for guiding the cooled air to the turbine and the rotor (at least a cooled air outlet duct). In detail, this cooling device is a counter-flow heat exchanger using a cooling medium for lowering the temperature of the spilled compressed air. For this scope, the plant is also provided with ducts for feeding the cooling medium to the cooling device (at least a cooling medium inlet duct) and for guiding the "heated" cooling medium away from the cooling device (at least a cooling medium outlet duct).

Moreover, a gas turbine assembly may also be provided with a second heat exchanger, in particular a heater or heating device, configured for heating the fuel, the gas fuel, before the feeding to the combustor assembly (a so called pre-heated fuel gas). Indeed it is known that a pre-heated gas fuel up to <NUM> improves the assembly performance in terms of an improved combustion efficiency.

The gas turbine assembly may cooperate with a steam turbine assembly for forming a so called combined cycle power plant. In particular, in a combined cycle the steam configured for driving the steam turbine is generated by using the heat of the exhaust gas leaving the gas turbine assembly. In this plant, it is known to use the water or steam spilled from the steam turbine as cooling medium in the above mentioned cooling device (OTC). The heated cooling medium in form of high pressure steam can be fed in turn to the steam turbine assembly. Under particular circumstances, the high pressure steam leaving the cooling device is not directed to the steam turbine but is directly guided to the exhaust stack of the gas turbine. This configuration is called "open loop" and the plant requires a continuous supply of purified water in order to replace the loss released through the stack. Under different circumstances, the high pressure steam leaving the cooling device is guided to a condenser. In this configuration, called "closed loop", water is circulated for preventing loss.

The dumping of the high pressure steam into the exhaust stack or collecting it in the condenser involves an inefficient use of the heat.

<CIT> discloses a power plant comprising a gas turbine, a steam turbine, a cooler for cooling air, a first heater for heating fuel or water to be injected in the gas turbine and a second heater for heating water to be injected in the steam turbine. A fluid medium is provided flowing in a closed loop by a pump through the cooler for cooling the air, through the first heater for heating the fuel/water to be injected in the gas turbine or through the second heater for heating the water to be injected in the steam turbine.

Accordingly, a primary object of the present invention is to provide a new and inventive power plant suitable for overcoming the above problem, i.e. to improve the performance and the energy efficiency.

In particular, the present invention refers to a power plant comprising a gas turbine assembly and a steam turbine assembly according to claim <NUM> for forming an improved combined cycle.

The above listed components forming a gas turbine assembly are well known by the skill person in the art and therefore no additional details are due for understanding the field of the present invention. Moreover, the present invention does not affect the shape or kind of the above components that therefore may be realized in many different forms. For instance, the combustor assembly may be a single annular combustor or a plurality of can combustors.

The gas turbine assembly according the present invention comprises moreover a heater or heating assembly comprising:.

According to the invention the term "duct" does not mean necessary a single duct but also a distribution line comprising more than a duct.

The heating device is a counter-flow heat exchanger and therefore the heating assembly moreover comprises:.

The heating assembly, in particular the heating medium, is configured for heating the fuel between <NUM> and <NUM>, preferably at <NUM>, before feeding the combustor assembly.

The gas turbine assembly according the present invention comprises moreover a cooling assembly comprising:.

The cooling device is a counter-flow heat exchanger and therefore the cooling assembly moreover comprises:.

The cooling assembly, in particular the cooling medium, is configured for cooling the compressed air before the feeding to the turbine or rotor.

In this configuration, according to the main feature of the present invention the inlet heating medium duct is connected to the outlet cooling medium duct, i.e. for forming a common duct, so that the cooling medium delivered by the cooling device and heated by the compressed air is used as heating medium in the heating device for pre-heating the fuel.

The cooling medium fed to the cooling device is steam and therefore the cooling medium leaving the cooler device is high pressure steam. The inlet cooling medium duct is therefore connected to a steam source.

Preferably, the power plant comprises a stack for the exhaust hot gas. In this case, the outlet heating medium duct is provided with a valve for selectively feeding the steam leaving the heating device to the stack or to a condenser.

As foregoing mentioned, the steam fed to the cooling device is coming from a steam source. According to the invention, this source is a steam turbine assembly that in cooperation with the gas turbine assembly forms a combined cycle. In this sense, the power plant of the present invention comprises also a steam turbine assembly wherein the exhaust hot gas leaving the gas turbine is used as heating medium for heating the water/steam circulating in the steam turbine assembly. The cooling medium duct is therefore connected to the steam turbine assembly for feeding to the cooling device steam spilled from the steam turbine assembly as cooling medium. The inlet cooling medium duct may also be provided with a valve for selectively connecting the cooling device to the steam turbine assembly or to a different water or steam source.

Preferably, the outlet cooling medium duct comprises a valve for selectively feeding the high pressure steam leaving the cooling device to the heating device or to the steam turbine assembly depending on the operating conditions of the plant.

A method for operating a power plant according to the present invention is defined in claim <NUM> and comprises the steps of:.

wherein the method comprises also the step of:
d) feeding the cooling medium leaving the cooling device to the heating device in order to use the heated cooling medium leaving the cooler device as heating medium in the heating device.

Advantageously, in this case and in particular during open cycle operations, the heat of the heated cooling medium leaving the cooling device is not lost but it is used in the heating device for pre-heating the fuel.

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Other advantages and features of the invention will be apparent from the following description, drawings and claims.

The features of the invention are set forth in the appended claims.

The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which:.

In cooperation with the attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to preferred embodiments, being not used to limit its executing scope.

Reference will now be made to the drawing figures to describe the present invention in detail.

Reference is now made to <FIG>, that is a schematic view of an embodiment of a power plant comprising a gas turbine assembly suitable for being improved according to the present invention. <FIG> discloses a gas turbine assembly <NUM> having a rotor <NUM> defining an axis A and comprising in series along the main flow M:.

According to <FIG>, the combustor assembly <NUM> comprises a plurality of can combustors <NUM> arranged as a ring around the axis A. In each can combustor <NUM>, a single combustion stage or two combustion stages in series may be realized. In <FIG> reference <NUM> refers to a cooling device connected via ducts <NUM><NUM> to the gas turbine assembly. In particular reference <NUM> refers to duct configured for connecting the plenum <NUM> to the cooling device <NUM> so that part of the compressed air may be spilled, cooled and forwarded via ducts <NUM> inside the turbine <NUM> (inside the blades and or vanes) and/or inside the rotor <NUM> for cooling reason.

Reference is made now to <FIG> that is a schematic view of a power plant comprising the gas turbine assembly of <FIG> and a steam turbine assembly <NUM> forming a combined cycle power plant. As known, in this plant the exhaust hot gas leaving the gas turbine is used in the steam turbine assembly as heating medium for heating the steam driving the steam turbines <NUM><NUM><NUM>. In <FIG> reference <NUM> refers to a fuel source, in particular a gas fuel source, configured for feeding fuel via ducts <NUM> to the combustor assembly <NUM>. <FIG> discloses that the cooling device <NUM> is a counter-flow heat exchanger (called OTC) wherein water or steam spilled from the steam turbine assembly <NUM> is used as cooling medium for cooling the compressed air fed to the cooling device <NUM>. For this reason, the plant comprises at least a duct <NUM> for feeding water or steam spilled from the steam turbine assembly <NUM> to the cooling device <NUM> and at least a duct <NUM> for guiding the pressurized steam leaving the cooling device <NUM>. In this example the duct <NUM> is configured for guiding the pressurized steam from the cooling device <NUM> in the steam turbine assembly <NUM> for driving the steam turbines <NUM><NUM><NUM>.

<FIG> discloses the plant of <FIG> with additional details. Under particular circumstances, the pressurized steam leaving the cooling device <NUM> in the duct <NUM> is not guided to the steam turbine assembly <NUM> but to a stack <NUM> or a condenser <NUM> for forming so called open cycle or closed cycle. For this scope, the duct <NUM> is provided with a valve <NUM> for selectively guiding the pressurized steam to the steam turbine assembly <NUM> or to the stack <NUM> (or to the condenser <NUM> via an additional valve <NUM>). Reference <NUM> in <FIG> refers to a heating device configured for heating the gas fuel before the feeding to the combustor assembly <NUM>. For this scope, the plant <NUM> of <FIG> comprises at least a duct <NUM> connecting the fuel source <NUM> to the heating device <NUM> and at least a duct <NUM> connecting the heating device <NUM> to the combustor assembly <NUM>. As for the cooling device <NUM>, also the heating device <NUM> is a counter-flow heat exchanger and the references <NUM> and <NUM> refer to at least a duct for feeding a heating medium to the heating device <NUM> and to at least a duct for guiding the cooled heating medium <NUM> away from the heating device <NUM>. Starting from this configuration currently used in the prior art practice, <FIG> discloses how the plant of <FIG> may be modified and improved according to the present invention.

As foregoing described, and as supported by <FIG>, during the so called open cycle the pressurized steam leaving the cooling device <NUM> is directly guided to the stack <NUM>. On the contrary, the present invention offers an inventive solution for using the heat of this pressurized steam in this open cycle application before the delivery to the stack <NUM> (or to the condenser <NUM>). In particular, as disclosed in <FIG>, the inlet heating medium duct configured for feeding the heating device <NUM> is connected to the outlet cooling medium duct <NUM> starting from the cooling device <NUM>. Thus, by the valve <NUM> the pressurized air leaving the cooling device may be directed to the steam turbine assembly or to the heating device <NUM> for being used as heating medium for pre-heating the fuel. After the heating step, the steam leaving the heating device <NUM> is guided to the stack <NUM> or (via the valve <NUM>) to the condenser <NUM>. Finally, reference <NUM> refers to an independent or separate water source <NUM> for selectively feeding (via valve <NUM>) the cooling device <NUM> with fresh water instead of water or steam coming from the steam turbine assembly.

Although the invention has been explained in relation to its preferred embodiment(s) as mentioned above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the present invention. For instance the teaching of the current disclosure can be applied not necessary in a combined cycle power plant but also in a single gas turbine assembly having the claimed cooling device and heating, whereby this application is not covered by the claims.

Claim 1:
Power plant comprising a gas turbine assembly (<NUM>);
the gas turbine (<NUM>) comprises:
- a compressor (<NUM>) configured for compressing incoming air and feeding compressed air to a plenum (<NUM>);
- a combustor assembly (<NUM>) configured for feeding at least a fuel coming from a fuel source (<NUM>) in the compressed air and for generating by combustion a hot gas flow;
- a turbine (<NUM>) configured for being driven by the hot gas for performing work on a rotor (<NUM>) connected to a generator (<NUM>) ;
- a heating assembly comprising a heating device (<NUM>) configured for pre-heating the fuel, an inlet fuel duct (<NUM>) connecting the fuel source (<NUM>) to the heating device (<NUM>), an outer fuel duct (<NUM>) connecting the heating device (<NUM>) to the combustor assembly (<NUM>), an inlet heating medium duct (<NUM>) for feeding a heating medium to the heating device (<NUM>) and a outlet heating medium duct (<NUM>) for delivery the heating medium from the heating device (<NUM>);
- a cooling assembly comprising a cooling device (<NUM>) configured for cooling spilled high pressure air, an inlet air duct (<NUM>) connecting the plenum (<NUM>) to the cooling device (<NUM>), an outlet air duct (<NUM>) connecting the cooling device (<NUM>) to the turbine (<NUM>) and/or the rotor (<NUM>) for cooling reason, an inlet cooling medium duct (<NUM>) for feeding a cooling medium to the cooling device (<NUM>) and an outlet cooling medium duct (<NUM>) for delivering the cooling medium from the cooling device (<NUM>);
wherein
the inlet heating medium duct (<NUM>) is connected to the outlet cooling medium duct (<NUM>) so that the cooling medium delivered by the cooling device (<NUM>) is used as heating medium in the heating device (<NUM>) for pre-heating the fuel;
wherein the power plant (<NUM>) comprises a steam turbine assembly (<NUM>) wherein the exhaust hot gas leaving the gas turbine is used as heating medium for heating the water/steam circulating in the steam turbine assembly (<NUM>); characterized in that the inlet cooling medium duct (<NUM>) is connected to the steam turbine assembly (<NUM>) for feeding to the cooling device (<NUM>) steam spilled from the steam turbine assembly (<NUM>).