Methods and systems for preventing lube oil leakage in gas turbines

A sump pressurization system comprising an off-board source of pressurized air is provided to supplement pressurized air to a bearing sump arrangement when the operating conditions of the gas turbine engine are such that the on-board pressurized air source, e.g. the compressor of the gas generator, are such that the air pressure generated thereby is insufficient to pressurize a sump pressurization cavity. A gas turbine engine comprising such a sump pressurization system is also provided, as is a corresponding method for operating a gas turbine engine to facilitate reducing leakage of lubrication oil.

BACKGROUND

Field of the Invention

The subject matter disclosed herein relates generally to gas turbine engines and more specifically to sump pressurization systems for gas turbine engines.

Description of the Related Art

Shaft bearings, such as for example ball bearings or roll bearings, are continuously fed with oil for lubrication and cooling purposes. Bearing assemblies are housed within sumps that are combined with a supply duct and an oil supply pump that supplies lubricating oil under pressure to the bearing assembly. A scavenge pump is further provided, that removes lubrication oil from the sump. The scavenge pump causes the return oil to pass through a heat exchanger prior to returning the oil to a tank or a reservoir. The bearing assembly sumps also include seal assemblies that facilitate minimizing oil leakage from the sumps along the rotor shaft.

U.S. Pat. No. 6,470,666 discloses methods and systems for preventing lubrication oil leakages from bearing assemblies in gas turbine engines. The systems disclosed therein include a sump oil cavity encasing a bearing assembly and in fluid communication with a lubrication oil supply for delivering pressurized oil to the bearing assembly and a scavenge pump for removing oil from this sump oil cavity. The sump oil cavity comprises sealing members for sealing a shaft passage preventing oil leakage along the rotating shaft from the interior towards the exterior of the sump oil cavity. The sump oil cavity is encased in a sump pressurization cavity surrounding the sump oil cavity and provided with further sealing arrangements preventing air from entering the sump pressurization cavity. The sump pressurization cavity is in fluid communication with a source of compressed air, arranged on board of the gas turbine engine. The pressure inside the sump pressurization cavity prevents oil leakages from the sump oil cavity towards the external sump pressurization cavity. The air pressure in the sump pressurization cavity also prevents hot external air from penetrating in the sump oil cavity. The air pressure in the sump pressurization cavity is maintained by a component driven by the gas turbine engine.

Typically, compressed air is delivered by the air compressor of the gas generator of the gas turbine itself. During engine low power and idle operations the pressure in the sump pressurization cavity may result insufficient to prevent oil leakages from the sump oil cavity. When the gas turbine operating conditions are such that the pressure in the sump pressurization cavity cannot be maintained at a sufficient level, the operating pressure in the sump oil cavity is reduced in comparison to the operating pressure of the sump pressurization cavity, using a venting system which is connected to a suction line for removing air from the sump oil cavity. This prevents oil leakages through the sealing arrangement of the sump oil cavity towards the sump pressurization chamber.

By reducing the operating pressure in the sump oil cavity, oil leakages are efficiently prevented. However, hot air present in the gas turbine engine area surrounding the bearing assembly can penetrate through the sump pressurization cavity and therefrom in the sump oil cavity leading to lubrication oil cooking due to the high temperature of such air.

There is therefore a need for improvements in bearing systems including an oil sump arrangement, specifically aimed at enhancing the operating conditions thereof when installed in hot areas of a rotating machine, such as a gas turbine.

SUMMARY OF THE INVENTION

According to the subject matter disclosed herein, a method of operating a gas turbine engine is provided, wherein an external (i.e. off board of the gas turbine engine) compressed air source is activated to provide sufficient compressed air to a sump pressurization cavity encasing a sump oil cavity housing a turbine bearing. The external compressed air source supplies sufficiently compressed air in case of insufficient pressure from the on-engine source of compressed air under certain operating conditions of the gas turbine engine. For example, the external, i.e. off-board compressed air source is activated when the gas turbine engine is running under low-power operating conditions or idle.

More specifically, according to some embodiments, a method for operating a gas turbine engine to facilitate reducing leakage of lubrication oil and oil cooking is provided, to be used in a gas turbine engine comprising at least one bearing assembly arranged in a sump oil cavity and a sump pressurization cavity at least partly encasing the sump oil cavity and in fluid communication therewith. The method comprises the steps of: supplying sump pressurization air to the sump pressurization cavity from the gas turbine engine, for example from one of the compressors of the gas turbine or from another on-board pressurized-air source, to maintain in the sump pressurization cavity an operating pressure higher than a pressure in the sump oil cavity and higher than the pressure around the sump pressurization cavity; and when air pressure from the gas turbine engine (i.e. from the on-board pressurized-air source) is insufficient to maintain the operating pressure in the sump pressurization cavity, supplying supplemental sump pressurization air to the sump pressurization cavity from at least one auxiliary pressurized-air source, i.e. an off-board source.

Generally speaking an on board or on-engine pressurized-air source can be any source of compressed air, which delivers an air pressure, which can be dependent upon the operating conditions of the gas turbine engine. Thus, under some operating conditions of the gas turbine engine the pressure of the air delivered by the on-engine source can be insufficient to properly pressurize the sump pressurization cavity. This condition can be detected, e.g. by a pressure transducer system. A signal provided by the pressure transducer system can be used to trigger delivery of pressurized air from the off-board source. In general terms, the off-board source can provide a delivery pressure which is independent or partly independent upon the operating condition of the gas turbine engine. The off-engine or off-board source of pressurized air can include a blower, e.g. a positive displacement blower. In other embodiments a line of compressed air can be provided. Both a blower and a line of pressurized air can be provided in combination in some embodiments. The air blower, if present, can be driven by an electric motor. According to embodiments of the present invention, the rotation speed of the motor and of the blower can be controllable, to provide the correct air pressure in the sump pressurization cavity.

Further features and embodiments of the method according to the subject matter disclosed herein are set forth in the attached claims.

According to a further aspect, the subject matter disclosed herein relates to a sump pressurization system for a gas turbine engine, comprising a sump oil cavity housing a bearing assembly and a sump pressurization cavity at least partly encasing the sump oil cavity and in flow communication therewith. The system further comprises a supplemental pressurized-air delivery line for flow connection between the sump pressurization cavity and at least one auxiliary pressurized-air source, i.e. an off-board source of pressurized air. Moreover, a pressurized-air line is provided, for flow connection between the sump pressurization cavity and an on-board source of pressurized air, i.e. as source arranged on the gas turbine engine. The auxiliary pressurized-air source can be an off-engine source, capable of delivering air at a pressure which is at least partly, in an embodiment independent of the operating conditions of the gas turbine engine, while the on-board source (e.g. the compressor of the gas generator of the gas turbine engine) is at least partly dependent upon the operating conditions of the gas turbine engine. A valve arrangement is provided, for connecting the sump pressurization cavity selectively: with the pressurized-air line in fluid communication with the on-board pressurized air source, or with the supplemental pressurized-air delivery line in fluid communication with the off-board source of pressurized air.

Further embodiments and features of the system are set forth in the enclosed claims.

Features and embodiments are disclosed here below and are further set forth in the appended claims, which form an integral part of the present description. The above brief description sets forth features of the various embodiments of the present invention in order that the detailed description that follows may be better understood and in order that the present contributions to the art may be better appreciated. There are, of course, other features of the invention that will be described hereinafter and which will be set forth in the appended claims. In this respect, before explaining several embodiments of the invention in details, it is understood that the various embodiments of the invention are not limited in their application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conception, upon which the disclosure is based, may readily be utilized as a basis for designing other structures, methods, and/or systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

DETAILED DESCRIPTION

The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment(s).

Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

FIG. 1is a schematic sectional illustration of a gas turbine engine10including a low pressure compressor12, a high pressure compressor14, and a combustor16. The gas turbine engine10further includes a high pressure turbine18and a low pressure turbine20. The low pressure compressor12and the low pressure turbine20are coupled by a first shaft22. The high pressure compressor14and the high pressure turbine18are coupled by a second shaft24. The shafts22and24are coaxial, shaft24surrounding shaft22. Through shaft20the low pressure turbine20can be connected, directly or through gear box, to a load (not shown), for example a compressor or an electric generator. The hot end of the gas turbine engine is the side where the low pressure turbine20is arranged. The cold end of the gas turbine engine is the side where the low pressure compressor12is located.

An example of such a gas turbine engine is commercially available from by General Electric Company of Evendale, Ohio under the designation LM6000. A further gas turbine engine wherein the subject matter disclosed herein can be incorporated is an LM2500 or LM2500+ gas turbine engine, both commercially available from General Electric Company, Cincinnati Ohio, USA.

The gas turbine engine comprises a plurality of bearing assemblies some of which are schematically illustrated inFIG. 1. More specifically, bearing assemblies are shown at25,26,27,28and29. In particular, the bearing assembly28is located in a hot area of the gas turbine engine, i.e. at or near the combustor of the gas turbine. In this area of the gas turbine engine the air surrounding the bearing assembly is particularly hot due to the high temperature of the combustion gases generated in the combustor.

FIG. 2schematically illustrates one embodiment of the bearing assembly28and relevant bearing sump. The bearing sump is globally labeled32. In some embodiments the bearing assembly28is comprised of three bearings28A,28B,28C arranged in the bearing sump32. A sump oil pressurization cavity45surrounds the bearing assembly, as will be described in greater detail later on.

FIG. 2schematically illustrates also a portion of shaft24supported by the bearing assembly28and a portion of the inner shaft22extending through shaft24. In other embodiments, as known to those skilled in the art, the gas turbine engine10can be comprised of a single shaft or may be provided with more than one shaft but in a non-concentric arrangement. The bearing assembly ofFIG. 2can be utilized also in those different gas turbine configurations.

According to some embodiments, the bearing assembly28is housed within a sump oil cavity33. The interior of the sump oil cavity33can be in fluid communication through oil supply ducts35with a lubrication oil tank, schematically shown at36. Pressurized oil is delivered to the bearing assembly28through the oil supply ducts35, for example by means of a pump34in fluid communication with the lubrication oil tank36. In some embodiments an oil removal duct37ending in the interior of the sump oil cavity33is in fluid communication with a scavenge pump schematically shown at39. The oil removed from the sump oil cavity33through the scavenge pump39can be delivered through a filter40and for example also through a heat exchanger42and returned to the lubrication oil tank36.

Lubrication oil supplied through the oil supply ducts35lubricates the bearings28A,28B,28C of the bearing assembly28, removes heat therefrom, and is then returned through the oil removal duct37and the scavenge pump39to the lubrication oil tank36after having been filtered in filter40and cooled in heat exchanger42.

In the exemplary embodiment ofFIG. 2, the sump oil cavity33is provided with first sealing members41,43, defining shaft passageways31A,31B through the sump oil cavity33. The sump oil cavity33is encased in a sump pressurization cavity45. The sealing members41and43prevent or reduce oil leakage from the sump oil cavity33towards the sump pressurization cavity45along the shaft24which extends through the shaft passageways31A,31B.

The sump pressurization cavity45comprises further sealing members47,49through which the shaft24extends and which prevent or reduce air leakage from the sump pressurization cavity45towards the exterior. Second shaft passageways48,50are surrounded by the sealing members47,49, the shaft24extending through the second shaft passageways. The air pressure in the sump pressurization cavity45prevents or limit lubrication oil leakages through the sealing members41and43. The air pressure further prevents hot air penetration through the sealing members47and49into the sump pressurization cavity45and consequently into the sump oil cavity33.

During normal engine operation, air is ingested by the low pressure compressor12, compressed at a first pressure by the compressor, delivered to the high pressure compressor14and further compressed at a final pressure. The compressed air flows in the combustor16, where the compressed air flow is mixed with fuel and the mixture is ignited to generate combustion gas at high temperature and high pressure. The combustion gas is sequentially expanded in the high pressure turbine18and in the low pressure turbine20respectively. Power generated by the high pressure turbine18is used to drive the high pressure compressor14. Power generated by the low pressure turbine20is partly used to drive the low pressure compressor12and partly available on the shaft20for driving the load (not shown).

Lubrication oil is circulated in the bearing assemblies25-29. Pressurized air taken from an on-engine source of compressed air is delivered to the sump pressurization cavity45of at least one of the bearing assemblies, to prevent oil leakages and penetration of air towards the sump oil cavity. In some exemplary embodiments, the on-engine source of compressed air can comprise the low pressure compressor12or the high pressure compressor14. More generally, an on-engine source of compressed air is any source of compressed air which is part of the gas engine motor and which is driven thereby, so that the delivery pressure of the on-engine source of compressed air is dependent upon the operating conditions of the gas turbine engine10.

In some operating conditions, for example during engine low power and idle operations, the pressure of the air delivered to the sump pressurization cavity45through a duct51(FIG. 2) can be insufficient to prevent leakage of lubrication oil from the sump oil cavity33and penetration of hot air through the sealing members47,49from the exterior of the sump pressurization cavity45towards the interior thereof and therefrom towards the sump oil cavity33. If this happens, oil is “cooked” due to the high temperature of the air in the hot area of the gas turbine engine10.

To prevent this situation for occurring, in some embodiments a sump pressurization system is provided, in combination with the on-engine source of compressed air.

FIGS. 3, 4 and 5schematically illustrate a diagram of an exemplary embodiment of a sump pressurization system in three different operating conditions. InFIGS. 3, 4 and 5the gas turbine engine10along with the on-engine source of compressed air, labeled14, and the bearing sumps, labeled32.

According to some embodiments, the sump pressurization system, globally labeled60, comprises a fluid connection61,63between the on-engine source14of compressed air and the bearing sumps32. The fluid connection61,63extends outside the gas turbine engine10for the purposes which will become apparent from the following description.

Along the fluid connection61an engine side automatic isolation valve65is provided, in combination with a first check valve67. Reference numbers65A and65B schematically designate a first position sensor and a second position sensor detecting the fully-opened and fully-closed position of the automatic isolation valve65. In further embodiments, not shown, only one or the other of the valves65,67can be provided. A position transducer instead of two position sensors can also be used.

A pressure detection system69detects the air pressure delivered to the sump pressurization cavity45. In some embodiments the pressure detection system69can be comprised of a first pressure transducer69A and a second pressure transducer69B in parallel, forming a redundant configuration. In other embodiments more than two pressure transducers can be provided. In simpler embodiments, where less stringent safety conditions apply, a single pressure transducer can suffice.

In the exemplary embodiment ofFIGS. 3, 4 and 5the sump pressurization system60comprises a blower71. In some embodiments the blower71can be a positive displacement blower. In other embodiments, a turbo-blower, for example a centrifugal compressor or a fan can be provided instead of a positive displacement blower. In the exemplary embodiment shown, the blower71is driven into rotation by an electric motor73, for example an AC electric motor. The electric motor73can be controlled by a speed controller75. The speed controller75can comprise a variable frequency driver, so that the speed of the blower71can be controlled. The speed controller allows the delivery pressure of the blower71to be controlled. In other embodiments the blower can be operated at a fixed rotation speed and can be provided with a bleed valve or a similar arrangement, for adjusting the delivery pressure.

A pressurized air delivery duct77connects the blower71to the fluid connection63. Along the pressurized delivery line77a blower side automatic isolation valve78can be provided. A check valve79can be arranged in series with the automatic isolation valve78. In other embodiments, not shown, only one or the other of the valves78,79can be provided. A manual valve80can further be arranged in series with valves79and78. In some embodiments a first position sensor78A and a second position sensor78B can be associated with the automatic isolation valve78, to detect a fully-closed position and a fully-opened position of the valve78, respectively. The two position sensors can be replaced by a position transducer.

According to some embodiments, a further manual valve81can be provided upstream of the blower71and a pressure safety valve83can be provided downstream of the blower71.

A further compressed air supply, globally shown at85, can be connected through a line86to fluid connection63between the pressure source14and the bearing sumps32. The compressed air supply85can be for example a compressed air service line of a plant where the gas turbine engine10is installed.

In some embodiments, an automatic isolation/pressure control valve87is arranged between the compressed air supply85and the fluid connection61,63. A check valve88and/or a manual valve89can further be arranged in series with the automatic isolation valve87. A position sensor87can be provided to detect the fully-closed position of the automatic isolation/pressure control valve87. In some embodiments a position transducer sensor can be associated with the automatic isolation/pressure control valve78, to detect the actual position. Finally, a pressure safety valve90can be connected to the line86. In some embodiments one of the valves88and87can be omitted.

The operation of the sump pressurization system60described so far will now be explained in greater detail, reference being made toFIGS. 3, 4 and 5.

InFIG. 3the gas turbine engine10is operating for example at full power, and the on-engine source of compressed air, for example the high pressure compressor14, provides sufficient pressure to the sump pressurization cavity45of the bearing sumps32. This is represented by arrows f1, showing air circulating from the on-engine pressure source14towards the bearing sumps32along the fluid connection61,63. The engine side automatic isolation valve65is opened, while the blower side automatic isolation valve78and the automatic isolation/pressure control valve87are closed. The blower71is non-operating or the valve83is opened.

If the pressure of the air delivered through the fluid connection61,63by the on-engine pressure source14of the gas turbine engine10become insufficient to properly pressurize the sump pressurization cavity45of the bearing sumps, either one or the other of the compressed air auxiliary sources71,85will become operative. Drop in the air pressure delivered to the sump pressurization cavity45is detected by the pressure transducer system69.

If the pressure transducer system69detects a drop of the air pressure below a threshold, the following operations are performed. The engine side automatic isolation valve65is closed and the blower side automatic isolation valve78is opened. The blower71is started and the automatic isolation/pressure control valve87remains closed. Pressurized air will thus be delivered by the blower71to the bearing sumps32through fluid connection63as show by arrows f2inFIG. 4. The speed of the blower71can be controlled through the blower speed control system75until the proper pressure value is detected by the pressure transducer system69. The controller75maintains the blower rotation speed at the proper value to provide the correct pressure in the sump pressurization cavities.

Closing the valve65prevents pressurized air from the blower71to enter the gas turbine engine10. In this operating condition, shown inFIG. 4, the sump pressurization cavities45are maintained under sufficient pressure condition on the one side to prevent oil leakage from the sump oil cavity33towards the sump pressurization cavity45and on the other side to prevent penetration of high-temperature air into the sump pressurization cavity45and therefrom into the sump oil cavity33with consequent damages to the lubrication oil due to the high temperature of the air surrounding the sump pressurization cavity45especially in the hot area of the gas turbine engine10.

The pressure transducer system69continuously detects the pressure of the air delivered towards the sump pressurization cavity45. If such pressure drops beyond a threshold value, which is required to achieve the effect of preventing oil leakage and hot air penetration, for example due to malfunctioning of the blower71, the sump pressurization system60is switched to the mode of operation shown inFIG. 5. The blower side automatic isolation valve78is closed, the engine side automatic isolation valve65remains closed and the automatic isolation/pressure control valve87is 5 opened. Compressed air from the compressed air supply85is thus delivered (see arrow f3inFIG. 5) along the line86towards the fluid connection63and to the bearing sumps32.

In this embodiment therefore the compressed air supply85provides a safety auxiliary source to be used in case of failure of the blower71.

According to a further embodiment, schematically shown inFIG. 6, the compressed air supply85can be the only compressed air supply or source of the sump pressurization system60, arranged outside the gas turbine engine10. The same reference numbers are used inFIG. 6to designate the same or corresponding components, parts or elements as in the embodiment ofFIGS. 3, 4 and 5.

When the pressure transducer system69detects a drop in the pressure of the air delivered to the bearing sumps, the engine automatic isolation valve65is closed and the automatic isolation valve87is opened to allow compressed air from the compressed air supply85to flow (arrow f4) towards the bearing sumps through line63.

While the disclosed embodiments of the subject matter described herein have been shown in the drawings and fully described above with particularity and detail in connection with several exemplary embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without materially departing from the novel teachings, the principles and concepts set forth herein, and advantages of the subject matter recited in the appended claims. Hence, the proper scope of the disclosed innovations should be determined only by the broadest interpretation of the appended claims so as to encompass all such modifications, changes, and omissions. In addition, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.