GB2460644A

GB2460644A - Vane separator for an air intake of a gas turbine

Info

Publication number: GB2460644A
Application number: GB0810025A
Authority: GB
Inventors: Simon Larcombe
Original assignee: Altair Filter Technology Ltd
Current assignee: Altair Filter Technology Ltd
Priority date: 2008-06-02
Filing date: 2008-06-02
Publication date: 2009-12-09
Anticipated expiration: 2028-06-02
Also published as: GB2460644B; CN101619676A; CA2667122A1; DE102009025880A1; FR2931883A1; AU2009202061A1; GB0810025D0

Abstract

A vane 61 for an inlet of a gas turbine engine comprises a surface having a surface roughness of at least 0.5 microns to attract liquid in airflow arranged to pass over it. The surface roughness of the vane 61 may be 2.5 micrometers. Ideally several vanes are arranged at the air intake so as to form a baffle / vane separator 60. The vanes may we wetted so as to improve water attraction. The air may also be heated upstream of the water separator baffle so as to further improve water elimination. The surface of the vane may be roughened by sandblasting. The vane separator may serve as a marine vane separator, removing seawater and moisture from the airflow, and may be located at the air intake of a gas turbine engine of a ship.

Description

VANE FOR AIR INLET OF A TURBINE

This invention relates generally to a vane for removing water from air supplied to a turbine, such as a gas turbine.

Gas turbine engines generally include a compressor for compressing an incoming air stream. The compressed air stream is mixed with fuel and ignited in a combustor for generating hot combustion gases. The combustion gases in turn flow to a turbine. The turbine extracts energy from the combustion gases, typically for driving a turbine shaft. The turbine shaft powers the compressor and generally an external load such as an electrical generator.

The presence of water droplets in the air flow into the compressor can lead to rapid and significant erosion and corrosion issues on the compressor blades, especially if the water droplets contain contamination or salt for example.

Consequently, this can lead to a rapid decrease in the performance of the turbine or even catastrophic blade failures. In many gas turbine operating environments such as offshore oil and gas plafforms, marine applications and coastal sites, high levels of water can be present in the air in the form of contaminated rain water or sea spray. Current technologies utilise Vane Separators (VS) or Marine Vane Separators (MVS) to remove this contaminated water. These products typically utilise aerodynamically shaped metal vanes to separate the contaminated water from the airflow by inertial separation. These separators are designed to remove large amounts of bulk water from the inlet of a gas turbine with minimal pressure loss.

These separator vanes are typically made either in stainless steel or aluminium sheet material to avoid issues of corrosion by the salt present in the water droplets. The use of coating technology for increasing the ability of a surface to attract water droplets has been considered. However, the risk of he coatings breaking down over time is high, especially with the Marine Vane Separator which typically operates in harsh conditions. The breaking down of the coatings over time may also cause compressor blade damage or failure due to debris from the broken down coatings entering the compressor.

Consequently, it would be desirable to be able to provide a vane for an air inlet of a turbine for removing water from the airflow which does not suffer from the problems associated with breakdown of the coatings discussed above.

According to a first aspect of the present invention, there is provided a vane for removing water from an air inlet of a turbine, the vane having a surface roughness of at least 0.5 microns (Ra) to attract liquid from airflow passing thereover.

It has been found that the provision of a vane with a roughened surface considerably increases the vanes ability to attract liquid droplets and retain them without the risks associated with the breakdown of prior art coatings.

According to a second aspect of the present invention there is provided a method of forming a vane for a vane separator arranged to be provided at an air inlet of a gas turbine wherein the surface of the vane is roughened. The surface is preferably roughened to at least 0.5 microns (Ra). The roughening may be produced by a blasting process, such as bead blasting or sand blasting for example.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a typical gas turbine engine with a vane separator; Figure 2 is a perspective view of a portion of the vane separator provided on the gas turbine; Figure 3 is a magnified view of a surface finish of a typical conventional stainless steel vane; Figure 4 is a view of a surface finish of a vane with a roughened surface in accordance with an embodiment of the present invention; and Figure 5 is a graph illustrating liquid breakthrough efficiency for various different surface finishes.

Figure 1 shows a typical turbine engine 10. The turbine engine 10 generally includes a compressor 20 disposed in serial flow communication with a combustor 30 and a turbine 40. The turbine 40 may be coupled to the compressor 20 via a drive shaft 50 which in this example also extends from the turbine 40 for powering an electrical generator (not shown) or any other type of desired external load. Airflow into the compressor 20 passes through a vane separator 60.

During operation, inlet airflow passes through vane separator 60 with much of the liquid or water contained in the airflow impacting against vanes in the vane separator 60 such that the water remains in contact with the vanes producing an airflow with a substantially reduced water content that is passed to the compressor 20. The compressor 20 discharges a compressed airflow 70 into the combustor 30. Fuel flow 80 is also delivered to the combustor 30 for mixing therein with the compressed airflow 70. The compressed airflow 70 and the fuel flow 80 are combusted in the combustor 30 to create a combustion gas stream 90. The energy from the combustion gas stream 90 is extracted by the turbine 40 for rotating the turbine shaft 50 to power the compressor 20 as well as for driving a generator or other type of external load.

Figure 2 is a perspective view of a portion of the vane separator 60. As can be seen, the vane separator 60 includes a plurality of vanes 61 arranged for the water containing inlet air to impact against. The vanes 61 may have any appropriate cross sectional shape, such as flat plates or suitable aerodynamically shaped curved cross sections. However, curved cross sections are preferred since they provide a larger surface area against which the inlet air is passed and they typically provide lower aerodynamic resistance. The rear ends of the vanes may also include vertical channels to direct liquids collected on the vanes 61 to the bottom of the separator 60 where it may be suitably drained and to reduce the likelihood of liquid on the vanes 61 from being blown by the incoming air into the compressor 20.

Figure 2 also illustrates a top wall 62, a bottom wall 63 and one side wall 64 for mounting the vanes 61 within the vane separator 60.

The vane separator 60 may be provided with any suitable number, density spacing and number of layers of vanes 61 depending upon the degree of water separation required. The vane separator 60 may also be any suitable size from a few centimetres to several meters depending upon the size of the inlet of the compressor 20 of the turbine engine 10 with which it is to be used.

Figure 3 is a scanning electron microscope image of the surface of a typical conventional vane made from stainless steel. External analysis of such a typical stainless steel vane has shown that it typically has a surface finish roughness of 0.28 microns Ra.

Another vane, made from aluminium was also analysed and found to have a surface finish roughness or rogosity of 0.36 microns Ra (not shown).

A number of the stainless steel vanes illustrated in Figure 3 were treated to obtain a modified surface finish. The new finish was attained by blasting, in this case sand blasting the surface of the stainless steel using synthetic sand.

The vane appearance was modified from a polished shiny look to a dull matt look. Sample sections of this modified surface finish were analysed and found to have a significantly increased surface roughness or rogosity of 2.0 microns Ra. Other samples were also treated by bead blasting to obtain ranges of roughened surfaces from 0.50 microns to 2.50 microns. Figure 4 is a scanning electron microscope image of a sand blasted surface of a vane with a surface roughness of 2.50 microns Ra.

Testing of the vane sections with roughened surfaces showed that when water came into contact with the roughened surfaces it became much more diluted across a wider area of the metal surface than when water came into contact with the more polished stainless steel surface of the standard vane, It was found that by increasing the roughness of the surface, water was increasingly attracted to the surface of a vane to a much greater extent than the non modified, smoother surface finish.

Figure 5 illustrates the results of tests measuring the amount of liquid breakthrough of a number of different types of vanes. As can be seen, the conventional stainless steel vane with a surface roughness of 0.36 microns Ra removes the vast majority of water from an input airflow. However, vanes with increased roughness from 0.50 microns Ra show significantly reduced levels of liquid breakthrough for an equivalent fluid flow. As can be seen from Figure 5, further increasing the roughness of the surface, for example up to 250 microns Ra, further reduces the proportion of liquid that is passed through the vane separator. These significantly enhanced levels of liquid/water removal potentially extend the working life of the compressor components, especially the blades, enhance servicing intervals and reduce down time for the turbine.

Tests on the sample vanes found that the vanes had reduced liquid breakthrough upon initial use if the vanes are pre-wetted. Consequently, when a turbine 10 is first started, it may be desirable to pre-wet the vane separator 60 in order to obtain suitable liquid removal from the passing air stream from first use.

Further tests were carried out to determine whether liquid breakthrough efficiency was affected by temperature. It was found that with increasing temperature, the hotter water adhering to a vane was found to spread out in a flatter form than that of cooler water such that the hotter water adhered to the vane surfaces better than the cooler water and a lower liquid breakthrough was achieved for hotter inlet fluid flow. Consequently, in some circumstances it may be desirable to pre-heat airflow to be passed through a vane separator 60.

Although the invention has been described in detail in the examples described above, many variations may be made to those examples while still falling within the scope of the invention. For example, any material surface having a roughness of 0.5 microns Ra or more may be used regardless of how the roughness is obtained. Howver, blasting a metal surface with particles such as sand or beads with a suitably selected size is a convenient method of obtaining a desired level of roughness.

Claims

CLAIMS: 1. A vane for an air inlet of a gas turbine, the vane having a surface with a roughness of at least 0.5 microns Ra to attract liquid in airflow arranged to pass thereover.
2. A vane according to claim 1, wherein the vane surface has a roughness of at least 1.0 microns Ra.
3. A vane according to claim 2, wherein the vane surface has a roughness of at least 1.5 microns Ra.
4. A vane according to claim 3, wherein the vane surface has a roughness of at least 2.0 microns Ra.
5. A vane according to claim 4, wherein the vane surface has a roughness of at least 2.5 microns Ra.
6. A vane separator including a plurality of vanes according to any one of the preceding claims.
7. A turbine engine including a vane separator in accordance with claim 6 provided at an airflow inlet to the turbine engine.
8. A method of preparing a vane for an air inlet passage of a gas turbine, the method comprising treating the surface of the vane to provide a roughness of at least 0.5 microns Ra.
9. The method according to claim 8, wherein the surface of the vane is roughened by blasting with particles.
10. The method according to claim 8 or claim 9, wherein, prior to use, the surfaces of the vanes are wetted.
11. The method according to any one of claims 8 to 10, wherein, in use, an inlet airflow is heated.
12. A vane substantially as hereinbefore described with reference to the accompanying drawings.
13. A vane separator substantially as hereinbefore described with reference to the accompanying drawings.
14. A turbine substantially as hereinbefore described with reference to the accompanying drawings.
15. A method substantially as hereinbefore described with reference to the accompanying drawings.