Patent Description:
The invention further relates to a method for operating a combustor assembly.

As is known, a gas turbine assembly for power plants comprises a compressor, a combustor unit and a turbine.

In particular, the compressor comprises an inlet, supplied with air, and a plurality of blades compressing the passing air. The compressed air leaving the compressor flows into a plenum, i.e. a closed volume, and from there into the combustor unit, where the compressed air is mixed with at least one fuel and combusted. The resulting hot gas leaves the combustor unit and is expanded in the turbine, producing mechanical work.

Traditionally the fuel supplied to the combustor unit of a gas turbine assembly is natural gas or oil.

The market requires the gas turbine assemblies to operate in the future with fuels different from natural gas or oil; in particular, gas turbine assemblies should be able to correctly operate with hydrogen (pure hydrogen) or mixtures containing hydrogen. The hydrogen amount in the mixtures can be small or large, e.g. a mixture can contain about <NUM>% or <NUM>% or <NUM>% or <NUM>% or <NUM>% or <NUM>% or <NUM>% or more hydrogen and the balance can be natural gas.

Combustor units operating with increased proportions of hydrogen fuel poses risks for flame flashback and overheating of fuel injectors due to the higher reactivity of hydrogen fuel.

Furthermore, the higher hydrogen reactivity increases the NOx emissions.

In order to reduce NOx emissions and to increase operational flexibility, gas turbine assemblies comprising a combustor unit performing a sequential combustion cycle have been developed.

In general, a sequential combustor unit comprises two combustors in series, wherein each combustor is provided with a respective burner and combustion chamber. Following the main gas flow direction, the upstream combustor is called "premix" combustor and is fed by the compressed air. The downstream combustor is called "sequential" or "reheat" combustor and is fed by the hot gas leaving the first combustion chamber.

According to a first known configuration, the two combustors are physically separated by a high pressure turbine. Following the main gas flow, this first configuration includes the compressor, the premix combustor, the high-pressure turbine, the reheat combustor and a low-pressure turbine.

According to a second known configuration, the premix and the reheat combustor are arranged directly one downstream the other inside a common casing, in particular a can-shaped casing, and no high-pressure turbine is used. According to this kind of sequential gas turbine assemblies, a plurality of can combustors are provided, which are distributed around the turbine axis.

Each reheat combustor is preferably provided with a reheat burner and a reheat combustion chamber into which the hot flow coming from the premix is discharged. A transition duct is arranged downstream the reheat combustion chamber and guides the hot gas leaving the reheat combustor toward the turbine.

The reheat burner may include a plurality of identical injection units, which are circumferentially arranged about the reheat combustion chamber and are designed to uniformly inject fuel into the reheat combustion chamber.

However, operating problems associated with increased proportions of hydrogen fuel become particularly serious in combustor units with sequential combustion cycle comprising premixed combustion or at least partly premixed combustion.

The much higher reactivity makes the hydrogen or mixture containing hydrogen to combust faster once it has been supplied into the combustor unit than natural gas or oil; the consequence is that the flame generated by hydrogen or mixture containing hydrogen anchors more upstream than flames generated by natural gas or oil. Therefore, the hot gas generated during the combustion has a longer post-flame residence time in the combustor and NOx have more time to generate.

A solution is disclosed in document <CIT>.

A combustor assembly according to the preamble of claim <NUM> is disclosed by <CIT>.

Therefore, it is primary object of the present invention to provide a combustor unit with a sequential combustion cycle wherein hydrogen fuel can be used without affecting the reliability of the combustor unit and guaranteeing NOx emissions under law limits.

This object is attained, according to the present invention, by a combustor assembly for a gas turbine assembly as claimed in claim <NUM>.

It is also another object of the present invention to provide a gas turbine assembly wherein hydrogen fuel can be used guaranteeing the reliability of the gas turbine assembly and, at the same time, without affecting NOx emissions.

According to these objects the present invention relates to a gas turbine assembly as claimed in claim <NUM>.

It is also another object of the present invention to provide a method for operating a combustor assembly, which allows the use of hydrogen fuel in a reliable and cost effective way and, at the same time, without affecting NOx emissions.

According to these objects the present invention relates to a method for operating a combustor assembly as claimed in claim <NUM>.

For a better comprehension of the present invention and its advantages, an exemplary embodiment of the invention is described below in conjunction with the accompanying drawings, in which:.

<FIG> is a schematic view of a gas turbine assembly <NUM> for power plants according to the present invention.

Gas turbine assembly <NUM> comprises a compressor <NUM>, a combustor assembly <NUM> and a turbine <NUM>. Compressor <NUM> and turbine <NUM> have a common axis A and form respective sections of a rotor <NUM> rotatable about axis A.

As is known, ambient air <NUM> enters in the compressor <NUM> and is compressed. Compressed air <NUM> leaves the compressor <NUM> and enters a plenum <NUM>, i.e. a volume defined by a main casing <NUM>. From plenum <NUM>, compressed air <NUM> enters combustor assembly <NUM> that comprises a plurality of combustor units <NUM> annularly arranged around axis A. Combustor units <NUM> are often defined "can combustors". In combustor units <NUM> at least one fuel is injected, and the air/fuel mixture is ignited, producing hot gas <NUM> that is conveyed to turbine <NUM>.

As is better shown in <FIG>, each combustor unit <NUM> is housed in a respective portal hole of the main casing <NUM> and has an axis B.

Combustor unit <NUM> comprises, in series along gas flow M, a first or premix combustor <NUM>, a mixer <NUM>, a second or reheat combustor <NUM> and a transition duct <NUM>, which guides the hot gas leaving the reheat combustor <NUM> toward the turbine <NUM> (not shown in <FIG>).

In particular, premix combustor <NUM> comprises at least one premix burner <NUM> and a first combustion chamber <NUM>.

In the non-limiting example here disclosed and illustrated, the premix combustor <NUM> comprises a plurality of premix burners <NUM> (only two visible in <FIG>).

Reheat combustor <NUM> comprises a reheat combustion chamber <NUM> and at least one reheat burner <NUM>.

In the non-limiting example here disclosed and illustrated, the reheat combustor <NUM> comprises one reheat burner <NUM>. According to a variant not shown the reheat combustor <NUM> a plurality of reheat burners.

Mixer <NUM> comprises a mixing chamber <NUM>.

Transition duct <NUM> comprises a transition chamber <NUM>.

In use, hot gas flows from the first combustion chamber <NUM> into the mixing chamber <NUM>, then into the reheat combustion chamber <NUM> and the transition chamber <NUM>.

First combustion chamber <NUM> is defined by a double wall premix liner <NUM> wherein a cooling interspace <NUM> is formed.

Mixing chamber <NUM> is defined by a double wall mixing liner <NUM> wherein a cooling interspace <NUM> is formed.

Reheat combustion chamber <NUM> is defined by a double wall reheat liner <NUM> wherein a cooling interspace <NUM> is formed.

Transition chamber <NUM> is defined by a double wall transition liner <NUM> wherein a cooling interspace <NUM> is formed.

In the non-limiting example here disclosed and illustrated, the double wall mixing liner <NUM> and double wall reheat liner <NUM> are connected so as the cooling interspace <NUM> and cooling interspace <NUM> create a common interspace.

The first combustor <NUM> and the mixer <NUM> are arranged in an outer casing <NUM> comprising a tubular portion <NUM> and a hood <NUM>.

The tubular portion <NUM> surrounds the double wall premix liner <NUM> and double wall mixing liner <NUM> leaving a gap defining an annular chamber <NUM>.

The hood <NUM> is fixed at one end of the tubular portion <NUM> to close it. The hood <NUM> substantially houses the two premix burners <NUM> of the first combustor <NUM>.

The hood <NUM> comprises a hood annular chamber <NUM>, which is in fluid communication with the annular chamber <NUM> of the tubular portion <NUM>. In the non-limiting example here disclosed and illustrated, the hood annular chamber <NUM> is directly connected to the annular chamber <NUM>.

Preferably, the annular chamber <NUM> is in fluid communication with the cooling interspace <NUM> of the double wall premix liner <NUM>.

Air in the plenum <NUM> is fed, through respective openings, to the annular chamber <NUM>, to the cooling interspace <NUM> of the double wall transition liner <NUM> and the cooling interspace <NUM> of the double wall reheat liner <NUM> (see arrows indicating the air flows in <FIG>).

Air flowing in the annular chamber <NUM> reaches the hood annular chamber <NUM> and the cooling interspace <NUM> of the double wall premix liner <NUM>.

Air flowing in the cooling interspace <NUM> of the double wall reheat liner <NUM> reaches the cooling interspace <NUM> of double wall reheat liner <NUM>.

Air coming from the plenum <NUM> is supplied to the first combustion chamber <NUM> through holes <NUM> facing the annular chamber <NUM>.

Air coming from the plenum <NUM> is supplied to the premix burners <NUM> of the premix combustor <NUM> through the hood annular chamber <NUM>.

Air coming from the plenum <NUM> is supplied to the mixing chamber <NUM> through holes <NUM> facing the cooling interspace <NUM> of the double wall mixing liner <NUM>.

The combustor assembly <NUM> comprises also a water/steam injection assembly <NUM> comprising a water/steam source <NUM> and a water/steam circuit <NUM> configured to supply water steam to the combustor units <NUM> of the combustor assembly <NUM>.

The expression water/steam should be intended in the following as water and/or steam. In other words, the water/steam injection assembly <NUM> can supply water or steam or a mixture comprising water and steam.

The water/steam circuit <NUM> comprises, for each combustor unit <NUM>, at least one injecting layout <NUM>.

The at least one injecting layout <NUM> is arranged in at least one air channel of the combustor unit <NUM> supplying air to the combustor unit <NUM>. Preferably, water/steam is injected in the air flows destined to the first combustor <NUM> and/or to the mixer <NUM> (or to the reheat combustor <NUM> if the mixer is not present).

In particular, the injecting layout <NUM> can be arranged in the annular chamber <NUM> or in the hood annular chamber <NUM> for supplying steam/water to the first combustor <NUM> and/or in the cooling interspace <NUM> of the double wall mixing liner <NUM> for supplying steam/water to the reheat combustor <NUM>.

According to a variant, the injecting layout <NUM> can be arranged in the annular chamber <NUM> and in the hood annular chamber <NUM>.

In <FIG>, two injecting layouts <NUM> are arranged respectively in the hood annular chamber <NUM> and in the cooling interspace <NUM>.

Preferably, the injecting layout <NUM> is arranged in the cooling interspace <NUM> upstream of the holes <NUM> along the gas flow direction D.

In the annular chamber <NUM> the injecting layout <NUM> is represented with dotted lines being optional.

According to variant not shown, the water/steam injection assembly <NUM> can comprise only one or two injecting layout <NUM>.

According to another variant not shown, the water/steam injection assembly <NUM> can comprise at least one further injecting layout <NUM> arranged in other air channels of the combustor <NUM>, for example in the cooling interspace <NUM> of the double wall reheat liner <NUM>, in the cooling interspace <NUM> of the double wall premix liner <NUM> and/or in the cooling interspace <NUM> of the double wall transition liner <NUM>.

With reference to <FIG>, the injecting layout <NUM> comprises an annular manifold <NUM> provided with a plurality of nozzles <NUM>.

Preferably, the nozzles <NUM> are evenly distributed along the annular manifold <NUM>.

If the injecting layout <NUM> is arranged in the annular chamber <NUM> supplying air to the first combustion chamber <NUM>, the plurality of nozzles <NUM> are distributed around the first combustion chamber <NUM>.

If the injecting layout <NUM> is arranged in the hood annular chamber <NUM>, the plurality of nozzles <NUM> are distributed around the first burners <NUM>.

If the injecting layout <NUM> is arranged in the cooling interspace <NUM> of the double wall mixing liner <NUM>, the plurality of nozzles <NUM> are distributed around the mixing chamber <NUM>. Air coming from the plenum <NUM> is supplied to the first combustion chamber <NUM> through holes <NUM> facing the annular chamber <NUM>.

In <FIG> a variant of the injecting layout <NUM> is shown. According to this variant, the nozzles <NUM> are not evenly distributed around the mixing chamber <NUM>.

Preferably, the nozzles <NUM> are arranged in groups <NUM> of nozzles <NUM> (in the non-limiting example each group <NUM> is composed by three nozzles <NUM>). The groups <NUM> are preferably evenly distributed. In other words, the groups <NUM> are equally spaced.

In <FIG> a further variant of the injecting layout <NUM> is shown. According to this variant, the manifold <NUM> is annularly arranged, but it does not define a common annular channel. The manifold <NUM> comprises two branches <NUM>, which are curved and extend along an annular path. Each branch <NUM> is provided with a plurality of nozzles <NUM>.

In this way, the nozzles <NUM> can be concentrated in zones wherein a bigger amount of steam/water is needed.

In this way, the water/steam flow is splitted in the two branches <NUM> and injected through the nozzles <NUM>.

Advantageously, this configuration could improve flow distribution and manufacturability. Moreover, thanks to the separation of the manifold <NUM> in two branches <NUM>, thermal expansion are better tolerated.

According to a variant not shown, the nozzles <NUM> can be oriented and positioned in different ways so as to differentiate the injection of steam/water in the air channel. For example some (or all) nozzles can inject the steam/water towards a direction counter-current to the gas flow direction D, or towards a direction concurrent with gas flow direction D.

For example, injections in counter current flow can help the atomization and evaporation of the steam/water injected.

According to another variant not shown, the nozzles can inject the steam/water towards a direction which is transversal to the gas flow direction D for best mixing, distribution, atomization and, ultimately, for facing in the best way flashbacks and NOx emissions.

For example, the nozzles can be arranged perpendicular to the gas flow direction D or can be properly inclined with respect to the gas flow direction D.

Other variants of the injecting layout <NUM> relates to a different geometrical layout of the manifold (depending on the shape of the channels wherein the layout is arranged), or to a different distribution of the nozzles <NUM> along the manifold so that the water/steam is distributed locally to mix with air in the regions where it most beneficially mitigates flashback and NOx formation. For example, the injecting layout <NUM> can comprise a manifold having a different shape to distribute the water/steam locally where it's needed. Moreover, depending on the fuel distribution to the burners, the circumferential distribution of the water/steam nozzles could be varied, for example one sector of the manifold could be without nozzles.

According to another variant not shown, more than one inlet in the manifold can be provided.

Advantageously, water/steam injection into the air path of premix combustor <NUM> or reheat combustor <NUM> increases the inert mass of the air and fuel mixture. The inert mass causes the peak flame temperatures to drop. One of the main drivers for flashback on premix combustor <NUM> or reheat combustor <NUM> is the peak flame temperature. Therefore, the injection of water/steam can be used as flashback mitigation.

In the sequential combustion assembly <NUM>, water/steam injection may be more beneficial for either the premix combustor <NUM> or reheat combustor <NUM>. Therefore, the injecting layouts <NUM> as above described are advantageously arranged in locations so as to distribute the water/steam to the premix combustor <NUM> and/or the reheat combustor <NUM>.

Advantageously, the injection layouts <NUM> above can be arranged in specific locations and can be configured so as to perform a desired injection distribution. In this way, water/steam is injected where it best mitigates the risk of flame flashback.

Claim 1:
A combustor assembly (<NUM>) for a gas turbine assembly (<NUM>) wherein hydrogen can be used, comprising:
• at least one combustor unit (<NUM>) provided with a premix combustor (<NUM>)and with a reheat combustor (<NUM>), which is arranged downstream the premix combustor (<NUM>) along the gas flow direction (D); wherein the combustor unit comprises a mixer (<NUM>) arranged between the premix combustor (<NUM>) and the reheat combustor (<NUM>);
• a water/steam injection assembly (<NUM>) comprising a water/steam source (<NUM>) and a water/steam circuit (<NUM>) configured to supply water/steam to the at least one combustor unit (<NUM>) of the combustor assembly (<NUM>); the water/steam circuit (<NUM>) comprising, for each combustor unit (<NUM>), at least two injecting layouts (<NUM>); wherein the premix combustor (<NUM>) comprises at least one premix burner (<NUM>)and a first combustion chamber (<NUM>);
characterized in that the injecting layouts (<NUM>) are arranged in at least one air channel (<NUM>; <NUM>; <NUM>) of the combustor unit (<NUM>); a first injecting layout (<NUM>) being arranged in an air chamber (<NUM>; <NUM>) supplying air to the at least one premix burner (<NUM>); wherein the mixer (<NUM>) comprises a mixing chamber (<NUM>) defined by a double wall mixing liner (<NUM>) wherein a cooling interspace (<NUM>) is formed; the cooling interspace (<NUM>) supplying air to the mixer (<NUM>); a second injecting layout (<NUM>) being arranged in the cooling interspace (<NUM>); wherein the double wall mixing liner (<NUM>) comprises holes (<NUM>) connecting the cooling interspace (<NUM>) and the mixing chamber (<NUM>); the second injecting layout (<NUM>) being arranged in the cooling interspace (<NUM>) upstream of the holes (<NUM>) along the gas flow direction (D).