GB2403272A

GB2403272A - A gas turbine engine having regulated combustion and steam cooled guide vanes

Info

Publication number: GB2403272A
Application number: GB0315189A
Authority: GB
Inventors: Paul Fletcher; Philip David Butler
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2003-06-28
Filing date: 2003-06-28
Publication date: 2004-12-29
Also published as: GB0315189D0

Abstract

A gas turbine engine 10, in use, has an airflow though it to provide propulsion and power, a portion of which acts as an engine coolant, also to regulate combustor 20 temperature, and has guide vanes 30 cooled by a separate supply of steam, which may be supplied about vanes 30. The coolant air flow may be presented to combustor 20 at its intake and may also be received by vanes 30, the vane surfaces having apertures 30 for film cooling using the steam. The respective amounts of, and the ratio between, coolant airflow and steam received by the vanes, may be variable dependent upon combustion temperature. The combustion temperature is preferably regulated for relatively acceptable levels of carbon monoxide and oxides of nitrogen, and engine power and efficiency may be improved by the airflow's density, which is enhanced by the steam. This may also be a method of operating a gas turbine engine.

Description

A Gas Turbine Engine and Method of Operation thereof The present invention

relates to a gas turbine engine and method of operation thereof and in particular to such gas turbine engines in stationary installations or surface propulsion situations.

Operation of gas turbine engines is well known. In short, banks of turbines and compressors are utilised in association with a combustor in order to create propulsion.

Of particular concern with regard to the present invention are the emissions from the combustion process and the gas turbine engine. It will be understood it is desirable to reduce the level of noxious emissions from gas turbine engines. Typically, below a certain temperature carbon monoxide emissions occur due to incomplete combustion whilst at higher temperatures there is dissociation of atmospheric nitrogen which leads to unacceptable nitrogen oxide emissions. In such circumstances, care is taken with regard to the operating temperature of a gas turbine engine in order to reduce both carbon monoxide and nitrogen oxides as emissions due to operation of the engine.

In the above circumstances, in order to achieve low emissions it is typical to provide pre-mixed fuel combustors with several combustion zones in series. It will also be understood that the combustion process produces increased temperatures so that the discharge nozzle and turbine nozzle guide vanes of a gas turbine engine require substantial cooling to remain operational.

In such circumstances, the combustor gas exit temperature is normally substantially higher than the high pressure turbine rotor inlet temperature. Generally cooling air is supplied from the combustor inlet air flow and therefore it is commonly necessary for the combustor to operate at zone temperatures which are higher than those desirable to achieve nitrogen oxides emissions levels which are acceptable. Ideally, air for cooling of the nozzle guide vanes should not be drawn from the combustor inlet so that the combustor can then operate at reduced temperatures as a result of that cooling air.

In accordance with the present invention there is provided a gas turbine engine having a combustor and guide vanes whereby in use an air flow is presented through the engine and combustion occurs in the combustor, a proportion of that air flow acting as a coolant air flow within the engine and some of that coolant air flow being presented to the combustor to regulate combustion temperature whilst the guide vanes are separately supplied with steam released to act as a coolant for the guide vanes.

Normally, the coolant air flow presented to the combustor is presented at an intake for that combustor.

Preferably, the steam separately supplied to the guide vanes acts as a surface film coolant released from surface apertures upon the guide vanes.

Possibly, the guide vanes also receive some coolant air flow. Generally, the ratio of separately supplied steam to coolant air flow is variable dependent upon combustion temperature.

Possibly, the combustion temperature is regulated for acceptable relative levels of carbon monoxide and oxides of nitrogen as emissions from the gas turbine engine.

Normally, the separately supplied steam released to act as a coolant for the guide vanes also enhances air flow density for improved turbine power and efficiency of the gas turbine engine.

Also in accordance with the present invention there is provided a method of operating a gas turbine engine in which a proportion of the air flow through the engine is collected to act as a coolant air flow, some of that coolant air flow is presented to a combustor within the gas turbine engine in order to regulate combustion temperature whilst steam is separately supplied to guide vanes within the gas turbine engine in order to act when released about those guide vanes as a coolant for those guide vanes.

Possibly, some of the coolant air flow is presented with the separately supplied steam to act as a combined coolant for the guide vanes.

Advantageously, the method includes varying the amount of separately supplied steam and/or coolant air flow presented to the guide vanes dependent upon combustion temperature.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Fig. 1 is a schematic cross section of a gas turbine engine; and Fig. 2 is a perspective view illustrating a guide nozzle construction and cooling regime.

The present invention is primarily applicable to ground based / stationary gas turbine engines. Referring to the drawings, in Fig. 1 there is shown an industrial gas turbine power plant 10 comprising a gas generator 12 and a power turbine 14 arranged to drive a load 16 which may be for example an electricity generator or a pump. The gas generator 12 comprises, in axial flow series, a compressor 18, a combustor 20 and a turbine 22 mounted on a common shaft with the compressor 18. High temperature, high velocity gas produced in the gas generator 12 by combustion of fuel and compressed air in the combustor 20, drives turbine 22, which drives the compressor 18 through the common shaft. The excess power in the turbine gases after passage through the turbine 22 is used to drive the power turbine 14. The invention may also be applicable to moving gas turbine engines arranged to drive a propeller, generator etc. The present invention in particular relates to obtaining lower carbon monoxide and NOX emissions from a gas turbine engine. As indicated above too low a combustion temperature results in inadequate combustion and therefore unacceptably high carbon monoxide levels whilst too high a combustion temperature causes nitrogen disassociation and therefore unacceptable levels of nitrogen oxides in the engine exhaust flow. In such circumstances, control of combustion is essential and as described previously multi- stage combustion in various combustion zones is typically provided in order to achieve best emissions performance.

As can be seen from above with regard to the engine air flows are presented through the engine in order to provide propulsion and power. The present invention in particular relates to gas turbine engines used in static locations or as prime movers with regard to surface vehicles. The engine depicted in Fig. 1 is utilised merely to show positional relationships. The present invention in particular relates to the combustor 20 and high pressure turbine 22. The combustor 20 incorporates guide vanes which guide the combusted air flow towards the high pressure turbine 22. It will be appreciated that these guide vanes are subjected to high temperatures as a result of the combustion gases immediately presented to them prior to the high pressure turbine 22. In such circumstances the guide vanes must be cooled.

Previously, guide vanes were cooled by air flows taken from the combustor 22 inlet in the flow path through the engine 10. It will be understood that a number of components within the engine 10 require cooling and so a proportion of the general air flow through the engine 10 from the inlet to the exhaust is bled off that principal air flow in order to provide a coolant air flow for those parts of the engine 10. Diverting coolant air flow from the combustor 22 inlet may result in higher temperatures due to the reduced cooling effect of such air presented through the combustor 22 inlet. Such increased temperatures will result in a higher proportion of nitrogen oxides emissions in the exhaust gases presented through the exhaust nozzle.

In accordance with the present invention coolant air flow is not necessarily taken from the intake for the combustor 22 and so this diverted cooling air flow passes through the combustor 22 reducing combustion zone temperatures. Such reduced combustion temperatures create a reciprocal cooler inlet temperature presented to the guide vanes for better NOx performance. Nevertheless, the guide vanes still require cooling and this is provided by separate provision of steam released through apertures in the respective guide vanes in order to provide film cooling of those guide vanes. It will be appreciated that steam has significantly greater heat capacity than dry air and so greater cooling potential. Furthermore, steam has a greater specific heat capacity ("Cp") than dry air such that there will be improved turbine efficiency and power production on a like for like basis in comparison with dry downstream air flows allowing a further reduction in emissions.

Clearly, in order to provide a separate steam cooling regime for the guide vanes it is necessary to supply existing cooling networks within the respective guide vanes with steam. This steam will be separately generated in appropriate steam generating plant and so as described above the present invention has particular application with regard to stationary and land propulsion uses of gas turbine engines where such separate steam generating capacity is available.

Although it is known to provide closed circuit steam cooling regimes the present invention releases the steam in order to create surface film cooling of the guide vanes.

In such circumstances, the steam is released from apertures about the guide vane surface in order to cool those guide vanes in an open cooling regime. In such circumstances, with the present invention the steam is lost with regard to the cooling system but, as indicated above, provides significant enhancement in turbine power and efficiency upon its transit through the turbine 22 of the engine 10 along with better control of exhaust gas emissions.

Fig. 2 is a perspective illustration of a guide vane construction and cooling regime utilised in accordance with the present invention. This guide vane construction and cooling regime is adapted from previous systems where diverted air flow as described is utilised as a coolant air flow for cooling of the guide vanes. However, according to the present invention, as described, instead of coolant air flow steam is presented through apertures in the guide vanes in order to provide cooling. In Fig. 2 steam is presented in the direction of arrow heads 31 to hollow cavities within the respective guide vanes 30. This steam flow as with previous coolant air flows passes through apertures in the respective guide vane 30 surfaces and flows upon those surfaces in the direction of arrow heads 32. Due to the nature of such flows they ride as a film upon that surface of the guide vanes 30 and so provide cooling. It should also be understood within the guide vanes 30 various structures 33 are normally provided in order to achieve further cooling through impingement of the steam flows. Once the steam has passed beyond the guide vanes 30 and so reacts with turbine 22 (Fig. 1) this steam is lost. In such circumstances, previous practice would suggest that loss of steam through such an open steam cooling system will be inefficient due to the energy input required for steam raising but, as indicated above, the principal object with regard to the present invention is achieving appropriate nitrogen oxides emissions and it will be appreciated that there may be excess steam raising capacity within other plant associated with the gas turbine engine. In any event, steam content within the air flow presented to the turbine will improve power and efficiency for the gas turbine engine. In such circumstances, the present invention provides improved emissions performance with greater power and efficiency so that overall better gas turbine engine performance is achieved. In any event, the improved power and efficiency response of the gas turbine engine operated in accordance with the present invention allows a stator outlet temperature ("SOT") reduction which may more than offset any steam generation losses.

As indicated above combustion temperature control is a principal element with regard to nitrogen oxides emission levels. In such circumstances, it will be appreciated that some coolant air flow may be mixed with steam presented and released through the guide vanes to adjust combustion temperature. As indicated above a balance must be struck between low combustion temperature creating unacceptable carbon monoxide levels whilst too high a combustion temperature causes nitrogen oxide levels which are unacceptable. In such circumstances by varying the bleed of coolant air taken from the combustor inlet and so allowing adjustment upwards of combustion temperature, that combustion temperature can be raised so that carbon monoxide emissions are controlled whilst if it is necessary to reduce combustion temperature such diversion of coolant air flow from the combustor inlet can be reduced or eliminated. The separately presented steam to the guide vanes maintains a constant coolant effect with regard to those guide vanes without any or less coolant burden upon the coolant air flow presented to the combustor inlet. In such circumstances, by varying the proportion of coolant air flow drawn from the combustor inlet it may be possible to alter combustion temperature as required by current operational conditions. In order to provide this facility it would be appreciated that either direct combustion temperature sensing is required or indirect sensing through carbon monoxide or NOX levels can be utilised by a controller in order to vary the proportion of coolant air diversion taken from the combustor inlet.

With the present invention coolant air flow is presented to the combustor in order to reduce combustion zone temperatures. As indicated previously this coolant air flow was previously necessarily supplied to the guide vanes for appropriate cooling due to the high combustion temperatures. By introducing the coolant air flow to the inlet of the combustor it will be appreciated that this creates a reduced combustion temperature which in turn necessitates less cooling of the guide vanes to remain within operational parameters. Furthermore, the enhanced heat capacity of steam also reduces the necessary steam coolant flow rate for appropriate cooling of those guide vanes to remain within operational parameters. Although the steam used to cool the guide vanes is lost, that steam necessarily discharged by the guide vanes provides work in the subsequent turbine 22 (Fig. 1) increasing power and efficiency for a given stator outlet temperature ("SOT").

Although it is known, as described above, from our Patent No. 3729930 and U.S. Patent No. 5758487 to provide closed steam cooling systems. These systems are closed in view of the inherent combustion damping nature of steam.

In such circumstances, steam may not be utilised with regard to cooling guide vanes by through flow to the combustor. It is by preferentially providing coolant air flow to the combustor inlet in order to regulate combustion temperature which achieves the principal benefits of the present invention.

The present invention also incorporates a method of operating a gas turbine engine whereby coolant air flow is preferentially presented to the intake of a combustor in order to regulate and reduce the combustion temperature within that combustor whilst guide vanes are separately cooled by release of steam about those guide vanes. The steam flow may be mixed with some coolant air flow in order to provide a combined coolant flow for further control of both combustion temperature and guide vane temperature.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

Claims 1. A gas turbine engine for an industrial, marine or aerospace

power plant having a combustor and guide vanes whereby in use an air flow is presented through the engine and combustion occurs in the combustor, a proportion of that air flow acting as a coolant air flow within the engine and some of that coolant air flow being presented to the combustor to regulate combustion temperature whilst the guide vanes are separately supplied with steam released to act as a coolant for the guide vanes.
2. A gas turbine engine as claimed in claim 1 wherein the coolant air flow presented to the combustor is presented at an intake for that combustor.
3. A gas turbine engine as claimed in claim 1 or claim 2 wherein the steam separately supplied to the guide vanes acts as a surface film coolant released from surface apertures upon the guide vanes.
4. A gas turbine engine as claimed in any of claims 1 to 3 wherein the guide vanes also receive some coolant air flow.
5. A gas turbine engine as claimed in claim 4 wherein the ratio of separately supplied steam to coolant air flow is variable dependent upon combustion temperature.
6. A gas turbine engine as claimed in any preceding claim wherein the combustion temperature is regulated for acceptable relative levels of carbon monoxide and oxides of nitrogen as emissions from the gas turbine engine.
7. A gas turbine engine as claimed in any preceding claim wherein the separately supplied steam released to act as a coolant for the guide vanes also enhances air flow density for improved turbine power and efficiency of the gas turbine engine.
8. A gas turbine engine substantially as hereinbefore described with reference to any accompanying drawing.
9. A guide vane for a gas turbine engine in which the guide vane incorporates apertures to release separately supplied steam to act as a coolant about that guide vane.
10. A method of operating a gas turbine engine in which a proportion of the air flow through the engine is collected to act as a coolant air flow, some of that coolant air flow is presented to a combustor within the gas turbine engine in order to regulate combustion temperature whilst steam is separately supplied to guide vanes within the gas turbine engine in order to act when released about those guide vanes as a coolant for those guide vanes.
11. A method as claimed in claim 10 wherein some of the coolant air flow is presented with the separately supplied steam to act as a combined coolant for the guide vanes.
12. A method as claimed in claim 10 or claim 11 wherein the method includes varying the amount of separately supplied steam and/or coolant air flow presented to the guide vanes dependent upon combustion temperature within the combustor.
13. A method of operating a gas turbine engine substantially as hereinbefore described with reference to the accompanying drawings.
14. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.