Patent Description:
As is known, operating heavy-duty gas turbine engines on different fuels is quite common and machines accepting both gas (even several types) and fuel oil. Both regulatory authorities and market are imposing increasingly strict requirements on pollutant emissions, efficiency and response, that involve nearly all operating conditions and especially aspects of operating on fuel oil. These requirements may be more easily met when gas turbine engines can be started on gas and switched to fuel oil only when higher load conditions have been reached.

More and more often, however, gas turbine engines are required to run on fuel oil at any load condition, including low load and even start-up, besides base load. Not only increase of firing temperature is sought to improve efficiency at high load, but also compliant operation at low load in therefore expected. For example, gas turbine engines running exclusively on fuel oil are frequently used as back-up systems for renewable energy market. As intervention of the back-up systems is quite rare, a relatively limited stock of fuel oil is sufficient to avoid discontinuing service and no connection to gas supply is provided, as it would be unnecessarily costly.

Fuel oil feed is accomplished through lance injector, which however are normally designed for high load and may not prove satisfactory at low load conditions. Therefore, also fuel oil injection has to be carefully designed with a twofold view of optimizing performance and avoiding coking buildup, which may reduce efficiency and even component lifetime.

Known solutions include lance injectors with concentric feed lines and nozzles dedicated to delivery of fuel oil, water and sometimes fuel gas and/or shielding air, possibly. The innermost line is normally dedicated to the supply (and return, if the case be) of fuel oil, which is delivered through injection nozzles to form a hollow cone and improve combustion. Water may be sprayed around the fuel oil cone, generally for the purpose of cutting NOx emissions. Shielding air, if present, is injected in parallel flow with the fuel oil and surrounds the water layer. Shielding air thus forms a protective cold layer that delays heating up of the fuel oil and slows down reaction kinetics. In addition, shielding air may help purge away fuel oil droplets close to the fuel oil nozzle and prevent coking build up.

Mixing of fuel oil and air within the aperture of the fuel oil cone plays an important role in combustion, which is influenced by the size of fuel oil droplets. In known lance injectors, however, there is little chance to improve mixing and reduce the average size of the droplets. The presence of a water layer immediately outside the fuel oil cone may even lead to less favorable spread of fuel oil. It would instead desirable to enhance the mixing ratio of fuel with air, thereby setting improved combustion conditions and reducing NOx emissions.

<CIT> discloses a lance injector in accordance with the preamble of claim <NUM>.

<CIT> discloses a lance injector for a gas turbine engine, comprising a supply duct arrangement, including at least a first tubular body and a second tubular body, concentrically extending along a central axis; and a terminal member coupled to downstream end of the supply duct arrangement. A fuel oil supply duct is defined inside the first tubular body and a shielding air duct is delimited by the first tubular body internally and by the second tubular body externally. The terminal member has a central fuel oil nozzle, coupled to the fuel oil supply duct, and an air outlet, coupled to the shielding air duct and surrounding the fuel oil nozzle. The fuel oil nozzle is configured to deliver a fuel oil flow in a hollow cone pattern.

Other examples of fuel oil injectors are disclosed in <CIT>, <CIT>, <CIT>,.

It is an aim of the present invention to provide a fuel oil injector that allows the above limitations to be overcome or at least reduced.

According to the present invention, there is provided a lance injector according to claim <NUM>, namely a lance injector for a gas turbine engine, the lance injector comprising:.

The first tubular body separates the fuel oil supply duct and the shielding air duct. No additional fluid layers are thus interposed between the delivered fuel oil flow and the shielding air flow, which therefore interact with each other. In turn, the interaction of the shielding air flow and of delivered fuel oil flow the has several beneficial effects on combustion. In the first place, the shielding air flow improves mixing of fuel and air and helps break the fuel oil stream into small droplets. In this manner, combustion is more efficient and oxidation is improved, thus leading to a reduction in emissions of carbon monoxide. In general, having the shielding air directed towards the centerline of the lance injector promotes interaction and gives additional degrees of freedom in shaping the resulting fuel oil cone spray angle and control of flame position. As a result, combustion dynamics and operation of the burners are remarkably improved.

Moreover, when the lance injector is not used and the burners operate on gaseous fuels, e.g. with premix burners around the lance injector, shielding air acts as a barrier and protects the fuel oil supply system from hot combustion air recirculation. Separate additional measures, such as blocking or sealing air to purge the fuel oil supply duct, are not required.

Interaction of shielding air and delivered fuel oil flow is enhanced accordingly.

The annular convergent shape of the air outlet allows to achieve the desired direction and exit angle of the shielding air and to optimize interaction with the resulting fuel oil cone spray.

According to an aspect of the invention, the terminal member comprises a hollow second convergent body, connected to the second tubular body, and wherein the shielding air duct has a convergent section delimited by the body internally and by the second convergent body externally.

In order to favor interaction, the shielding air is kept separated from the fuel oil flow only by the first convergent body, without any other fluid layers in between.

According to an aspect of the invention, the first convergent body has a frustoconical end portion and an injection end of the second convergent body has a convergent frustoconical opening and wherein the air outlet is defined by the frustoconical end portion internally and by the frustoconical opening externally.

The geometry of the frustoconical end portion and of the frustoconical opening precisely determines the features of the air outlet and the action of the shielding air flow on the cone of the delivered fuel oil flow.

According to an aspect of the invention, the first convergent body has a frustoconical intermediate portion between the first tubular body and the frustoconical end portion and wherein an annular step is defined between the frustoconical intermediate portion and the frustoconical end portion in a plane perpendicular to the central axis.

According to an aspect of the invention, the injection end of the second convergent body has a cylindrical shape and defines an air plenum around the frustoconical end portion of the first convergent body, between the convergent section of the shielding air duct and the air outlet.

The air plenum around the around the frustoconical end portion of the first convergent body allows to equalize the shielding air flow before ejection, so that the effect on the delivered fuel oil flow may be accurately determined.

According to an aspect of the invention, the supply duct arrangement comprises an outer tubular body extending coaxially around the first tubular body and the second tubular body, wherein a water supply duct is delimited by the second tubular body internally and by the outer tubular body externally, wherein the terminal member has a water outlet coupled to the water supply duct and configured to deliver a water flow around the delivered fuel oil flow.

According to an aspect of the invention, the terminal member comprises an outer convergent body extending around the second convergent body and coupled to the water supply duct.

The water flow may be used to improve control of temperature combustion and pollutant emissions, in particular NOx. As the water duct is arranged around the shielding air duct, however, spraying the water layer does not affect interaction of shielding air and fuel oil. In addition, the combined action with the shielding air flow reduces the requirements in terms of water supply.

According to an aspect of the invention, the supply duct arrangement comprises an inner tubular body, extending concentrically inside the first tubular body, wherein a fuel oil return duct is defined inside the inner tubular body and is coupled to the fuel delivery chamber and wherein the terminal member has passages coupling the fuel oil supply duct and the fuel oil return duct upstream of the fuel delivery chamber.

The use of a return line for excess fuel oil allows to optimize pressure and flow condition for delivery of fuel oil through the fuel oil nozzle.

According the present invention, there is also provided a gas turbine engine, comprising at least one fuel oil injector as defined above, a fuel oil supply system coupled to the fuel oil supply duct and an air source coupled to the shielding air duct.

According to an aspect of the invention, the gas turbine engine comprises an air control valve for each of the at least one fuel oil injector, the air control valve being configured to set air supply to the shielding air duct of the respective fuel oil injector.

The air supply to the shielding air duct and therefore the shielding air flow of the lance injectors may be thus adjusted in accordance to circumstances, e.g. to optimize or possibly restore combustion conditions, if changes intervenes during the lifetime of the gas turbine engine.

According to an aspect of the invention, the gas turbine engine comprises a first group of lance injectors, having the respective air control valves set to allow a first shielding air flow to the respective shielding air ducts, and a second group of lance injectors, having the respective air control valves set to allow a second shielding air flow to the respective shielding air ducts, the second shielding air flow being different from the first shielding air flow.

Different settings of the lance injectors in the first group and in the second group allow to establish asymmetries in combustion conditions of different burners. Such asymmetries are effective in mitigating pulsations with rotational modes.

According to an aspect of the invention, the gas turbine engine comprises a controller and a sensors configured to detect operating quantities of the gas turbine engine, wherein at least one air control valve is an adjustable control valve and the controller is configured to adjust the at least one air control valve based on a response of the sensors.

Accordingly, the shielding air flow may be dynamically adjusted during operation of the gas turbine engine by a feedback action in response to changing operating condition, for example because of ageing or varying pulsation regimes.

The present invention will now be described with reference to the accompanying drawings, which show a number of non-limitative embodiments thereof, in which:.

With reference to <FIG>, number <NUM> defines a gas-turbine plant as a whole comprising a gas turbine engine <NUM> and a controller <NUM>.

The gas turbine engine <NUM>, in turn, comprises a compressor <NUM>, a combustor assembly <NUM> and an expansion section or turbine <NUM>. Moreover, sensors <NUM> are arranged and configured to sense operating quantities of the gas turbine engine <NUM> and to send measurement signals SM to the controller <NUM>.

The compressor <NUM> feeds the combustor assembly <NUM> with a flow of air drawn from outside.

The combustor assembly <NUM> comprises a plurality of burner assemblies <NUM>, which cause the combustion inside the combustor assembly <NUM>, of a mixture of air and fuel. An air plenum <NUM>, coupled to the burners <NUM>, is supplied with compressed air by the compressor <NUM> and defines a compressed air source for the burners <NUM>.

The turbine <NUM> receives and expands a flow of burnt hot gas from the combustor assembly <NUM> to extract mechanical work, which is transferred to an external user, typically an electric generator, which is not shown here.

The fuel may be of several types and includes at least fuel oil. In addition to fuel oil, the gas turbine engine <NUM> may be structured to work also on other types of fuel, both gaseous and liquid. Fuel oil is supplied to the burners <NUM> by a fuel supply system <NUM>, that comprises a fuel oil supply line 10a and a return line 10b. At least a fuel oil control valve 11a and a return control valve 11b are provided along the fuel oil supply line 10a and the return line 10b, respectively.

The gas turbine engine <NUM> also comprises a water supply system <NUM>, configured to supply a controlled flow of water to the burner assemblies <NUM> for the purpose of reducing NOx emissions. The water supply system <NUM> includes at least one water supply line <NUM> and a water control valve <NUM>, operable to adjust water supply to the burner assemblies <NUM>.

The controller <NUM> is configured to determine set-points of the gas turbine engine <NUM> for desired operating conditions and to use actuators of the gas turbine engine <NUM>, including the fuel oil control valve 11a and the return control valve 11b, so that set-points may be achieved.

The burner <NUM> comprise respective fuel oil lance injectors <NUM>, one of which is schematically shown in <FIG> and <FIG>.

The lance injector <NUM> extends along a central axis A and comprises a supply duct arrangement <NUM> and a terminal member <NUM> coupled to downstream end of the supply duct arrangement <NUM>.

The supply duct arrangement <NUM> comprises a first tubular body <NUM>, a second tubular body <NUM>, an inner tubular body <NUM> and an outer tubular body <NUM>. In some embodiments not shown, however, one or both of the inner tubular body <NUM> and the outer tubular body <NUM> may not be present and the supply duct arrangement may include only the first tubular body and the second tubular body.

All the first tubular body <NUM>, second tubular body <NUM>, inner tubular body <NUM> and outer tubular body <NUM> extend concentrically along the central axis A.

A fuel oil supply duct <NUM> is defined inside the first tubular body <NUM>. More precisely, the inner tubular body <NUM> extends concentrically inside the first tubular body <NUM>, whereby the fuel oil supply duct <NUM> is delimited by the first tubular body <NUM> externally and by the inner tubular body <NUM> internally. A return duct <NUM> is defined inside the inner tubular body <NUM> and is coupled to the fuel oil supply duct <NUM> through the terminal member <NUM>, as explained in detail later on. The return duct may not be present in embodiments not including the inner tubular body. The fuel oil supply duct <NUM> is furthermore coupled to the fuel oil supply line 10a through the fuel oil control valve 11a to receive a flow of fuel oil to be supplied into the combustor assembly <NUM>. The return duct <NUM> is coupled to the return line 10b through the return control valve 11b to return an excess fuel oil to a reservoir (not shown). The fuel oil control valve 11a and the return control valve 11b are operated by the controller <NUM> to adjust a pressure and an amount of fuel oil actually delivered to support combustion.

A shielding air duct <NUM> is delimited by the first tubular body <NUM> internally and by the second tubular body <NUM> externally. The shielding air duct <NUM> is coupled to the air plenum <NUM> through an air control valve <NUM> and receives an airflow to be used as shielding air. In one embodiment, the control valve <NUM> may be an orifice. Moreover, each lance injector <NUM> has a respective air control valve <NUM>, thus meaning that either there is a dedicated air control valve <NUM> separately for each lance injector <NUM> (as in the example of <FIG>, see also <FIG>) or that each lance injector <NUM> is coupled to an air control valve <NUM>, but air control valves <NUM> may be shared by several each lance injectors <NUM>.

A water supply duct <NUM> is delimited by the second tubular body <NUM> internally and by the outer tubular body <NUM> externally and is coupled to the water supply system <NUM> via the water control valve <NUM>.

The terminal member <NUM> has a central fuel oil nozzle <NUM>, coupled to the fuel oil supply duct <NUM>, and an air outlet <NUM>, coupled to the shielding air duct <NUM> and surrounding the fuel oil nozzle <NUM>. The fuel oil nozzle <NUM> is configured to deliver a fuel oil flow F in a hollow cone pattern with aperture angle β and the air outlet <NUM> is configured to direct a shielding air flow AF from the shielding air duct <NUM> such that the shielding air flow AF crosses the delivered fuel oil flow F. Specifically, direction of an airflow velocity at the air outlet intersects the hollow cone pattern of the fuel oil flow F and, in one embodiment, also intersects the central axis. To this end, the air outlet <NUM> has an annular convergent shape. Here and in what follows, "convergent" is to be understood with reference to a direction from a supply end 15a to an injection end 15b of the lance injector <NUM>. This direction is also the direction of flow of fuel oil supplied trough the fuel oil supply duct <NUM> and a of shielding air supplied through the shielding air duct <NUM> (as well as of water supplied through the water supply duct <NUM>, if present), whereas the return fuel oil flows through the return duct <NUM> (if present) in an opposite direction. Therefore, "convergent" here means that a radial dimension perpendicularly to or a distance from the central axis A decreases in the direction from the supply end 15a to the injection end 15b of the lance injector <NUM>. On account of the annular convergent shape of the air outlet <NUM>, a velocity of the shielding air flow AF at the air outlet <NUM> has a non-zero axial component, parallel to the central axis A, a non-zero radial component, perpendicular to the central axis A, and a zero tangential component, or at least the tangential component is lower than a velocity threshold that allows intersection with the delivered fuel oil flow F.

An exit angle α of the velocity of the shielding air flow AF at the air outlet <NUM>, i.e. the angle formed by the velocity of the shielding air flow AF and the central axis A, is for example comprised between <NUM>° and <NUM>° and, preferably, between <NUM>° and <NUM>°. In this range, the shielding air flow AF protects from hot gas recirculation and effectively promotes mixing of air and fuel oil.

The terminal member <NUM> comprises a hollow first convergent body <NUM>, a hollow second convergent body <NUM> and an outer convergent body <NUM>. The first convergent body <NUM> is connected to the first tubular body <NUM> and to the inner tubular body <NUM> and forms a fuel delivery chamber <NUM> fluidly coupled to the fuel oil supply duct <NUM> and to the fuel oil nozzle <NUM>. The fuel oil nozzle <NUM> is formed in the first convergent body <NUM> at the injection end 15b of the lance injector <NUM>. The fuel delivery chamber <NUM> is also coupled to the fuel oil return duct <NUM>. Passages <NUM> provided in the first convergent body <NUM> of the terminal member <NUM> upstream of the fuel delivery chamber <NUM> allow fluid coupling of the fuel oil supply duct <NUM> with the delivery chamber <NUM> and the return duct <NUM>. Therefore, part of the fuel oil conveyed by the fuel oil supply duct <NUM> is delivered through the nozzle <NUM> and part is returned through the fuel oil return duct <NUM>.

The second convergent body <NUM> is connected to the second tubular body <NUM>. Thus, a convergent section of the shielding air duct <NUM> is delimited by the first convergent body <NUM> internally and by the second convergent body <NUM> externally. In one embodiment, the configuration of the air outlet <NUM> is defined by the first convergent body <NUM> and by the second convergent body <NUM>. As shown in greater detail in <FIG>, the first convergent body <NUM> has a frustoconical end portion 33a and an injection end 34a of the second convergent body <NUM> has a convergent frustoconical opening 34b surrounding the frustoconical end portion 33a of the first convergent body <NUM>. The air outlet <NUM> is therefore defined by the frustoconical end portion 33a internally and by the frustoconical opening 34b externally.

The first convergent body <NUM> has also a frustoconical intermediate portion 33b between the first tubular body <NUM> and the frustoconical end portion 33a. An annular step 33c is defined between the frustoconical intermediate portion 33b and the frustoconical end portion 33a in a plane perpendicular to the central axis A. The injection end 34a of the second convergent body <NUM> has a cylindrical shape and defines an air plenum <NUM> around the frustoconical end portion 33a of the first convergent body <NUM>, between the convergent section of the shielding air duct <NUM> and the air outlet <NUM>.

The outer convergent body <NUM> extends around the second convergent body <NUM> and is coupled to the water supply duct <NUM>. The injection end 34a of the second convergent body <NUM> axially projects from the outer convergent body <NUM> and a water outlet <NUM>, which is coupled to the water supply duct <NUM>, is defined therebetween. The water outlet <NUM> is thus configured to deliver a water flow W around the delivered fuel oil flow F. The water outlet <NUM> may be defined by a single annular opening around the injection end 34a of the second convergent body <NUM> or by a plurality of openings or holes arranged circumferentially, in accordance with design preferences.

<FIG> shows the effect of velocity of the shielding air flow AF on the cone aperture angle β of the delivered fuel oil flow with different nozzle geometries (e.g. different exit angles α or return flow).

With reference to <FIG>, in the gas turbine engine <NUM> the burners <NUM> may be divided into groups. In a first group of lance injectors <NUM>, the respective air control valves <NUM> are set to allow a first shielding air flow AF1 to the respective shielding air ducts <NUM>. In a second group of lance injectors <NUM>, the respective air control valves <NUM> are set to allow a second shielding air flow AF2, different from the first shielding air flow AF1, to the respective shielding air ducts <NUM>. Lance injectors <NUM> of the first group and of the second group may be alternated. The first group and the second group need not contain the same number of lance injectors. Asymmetries in combustion conditions (e.g. cone aperture angle β of the delivered fuel oil flow) help reduce pulsations with rotational modes. In the embodiment of <FIG>, each lance injector is provided with a respective dedicated air control valve <NUM>. In other embodiments, however, a single air control valve may serve several lance injectors. For example, a single air control valve may serve all the lance injectors of the first group and another single air control valve may serve all the lance injectors of the second group.

With reference to <FIG>, a gas turbine engine <NUM>, having substantially the structure of the gas turbine engine <NUM> of <FIG>, comprises air control valves <NUM> of an adjustable type for supply of shielding air to the lance injectors <NUM>. In this case, the controller <NUM> is configured to adjust the air control valves <NUM> based on a response of the sensors <NUM>. Thus, the supply of shielding air to the lance injectors <NUM> and the effect thereof on the shape and mixing rate of delivered fuel oil flow F may be changed during operation of the gas turbine engine <NUM> in accordance with design preferences.

Claim 1:
A lance injector for a gas turbine engine, the lance injector comprising:
a supply duct arrangement (<NUM>), including at least a first tubular body (<NUM>) and a second tubular body (<NUM>), concentrically extending along a central axis (A); and
a terminal member (<NUM>) coupled to downstream end of the supply duct arrangement (<NUM>);
wherein a fuel oil supply duct (<NUM>) is defined inside the first tubular body (<NUM>) and a shielding air duct (<NUM>) is delimited by the first tubular body (<NUM>) internally and by the second tubular body (<NUM>) externally;
wherein the terminal member (<NUM>) has a central fuel oil nozzle (<NUM>), coupled to the fuel oil supply duct (<NUM>), and an air outlet (<NUM>), coupled to the shielding air duct (<NUM>) and surrounding the fuel oil nozzle (<NUM>);
wherein the fuel oil nozzle (<NUM>) is configured to deliver a fuel oil flow (F) in a hollow cone pattern; and
wherein the air outlet (<NUM>) is configured to direct a shielding air flow from the shielding air duct (<NUM>) such that the shielding air flow crosses the delivered fuel oil flow (F), wherein a direction of an airflow velocity (V) at the air outlet (<NUM>) intersects the delivered fuel oil flow (F) and intersects the central axis (A);
characterized in that the terminal member (<NUM>) comprises a hollow first convergent body (<NUM>), connected to the first tubular body (<NUM>) and forming a fuel delivery chamber (<NUM>) fluidly coupled to the fuel oil supply duct (<NUM>) and to the fuel oil nozzle (<NUM>) and wherein the fuel oil nozzle (<NUM>) is formed in the first convergent body (<NUM>) of the terminal member (<NUM>);
wherein the terminal member (<NUM>) comprises a hollow second convergent body (<NUM>), connected to the second tubular body (<NUM>), and wherein the shielding air duct (<NUM>) has a convergent section delimited by the first convergent body (<NUM>) internally and by the second convergent body (<NUM>) externally;
and wherein the air outlet (<NUM>) has an annular convergent shape.