GB2512878A

GB2512878A - Gas turbine inlet anti-icing using electrical power

Info

Publication number: GB2512878A
Application number: GB1306440.7A
Authority: GB
Inventors: Philip Richard Pendrill
Original assignee: VEOTEC Ltd
Current assignee: VEOTEC Ltd
Priority date: 2013-04-09
Filing date: 2013-04-09
Publication date: 2014-10-15
Anticipated expiration: 2033-04-09
Also published as: WO2014167329A1; GB2512878B; GB201306440D0

Abstract

A vane 400 for a gas turbine air inlet filter 102 having a body that, when in position in the gas turbine air inlet filter, extends substantially in a direction of airflow. The vane has a length extending substantially perpendicular to the direction of airflow and has a plurality of channels 402, 404 each for holding an electrical trace heat element (808, figure 8). The channels are disposed towards and along an upstream edge 412 of the vane and are arranged in-line parallel to the direction of airflow. A method of heating a gas turbine air inlet is also described. Heat is provided at the gas turbine air inlet filter by means of electrical trace heating to raise the temperature at the gas turbine air inlet filter such that ice does not form, notwithstanding cooling due to acceleration of the airflow downstream of the gas turbine air inlet filter and into the gas turbine inlet.

Description

GAS TURBINE INLET ANTI-ICING USING ELECTRICAL POWER

Field of the Invention

This invention relates to apparatus and methods for heating gas turbine air inlets by electrically heating an air inlet vane separator arranged upstream of a gas turbine air inlet.

Background

Gas turbines have been used in recent times as power sources for vehicles such as ships and aircraft as well as in electrical power generation applications. The basic operating principle of a gas turbine requires the intake of atmospheric air to a compressor. If the gas turbine is being operated in an environment where the atmosphere is polluted. dusty. moist or salty. it is necessary to filter out such impurities using an air inlet filter andior vane separator I coalescer combination to maintain turbine performance and protect the turbine from damage.

The problems associated with moist air are exacerbated when operating in near-freezing conditions because moisture in the air may condense then freeze on surfaces in the filter / vane separator / coalescer, thus partially or completely blocking the air intake. Furthermore, not all moisture may be removed in the inlet filter aid so may pass through to the inlet befimouth of the gas turbine. Isentropic acceleration of the airflow as it enters the bellmouth may result in a drop in temperature to a level where ice may form on the bellmouth. Ice formation in the belimouth may reduce the surge margin of the compressor, and if pieces of ice break off and enter the compressor, the compressor may be damaged and its useful lifetime reduced.

Aspects of the present invention provide elegant, power-efficient solutions to the problem of ice formation on the inlet to a gas turbine compressor as well as to the problem of ice formation in gas turbine air inlet filters.

Other features and advantages of exemplary embodiments of the present invention will be apparent from the foflowing description taken in conjunction with the accompanying drawings.

Summary

In accordance with a preferred embodiment of the invention, a vane for a gas turbine air inlet filter is provided. The vane has a body that, when in position in the gas turbine air inlet filter, extends substantially in a direction of airflow, and has a length extending substantially perpendicular to the direction of airflow. The vane has a plurality of channels (preferably two), each for holding an electrical trace heat element. These are disposed towards and along an upstream edge of the vane and are arranged in-line parallel to the direction of airflow.

Each of the channels may further comprise: an incident channel section at its upstream edge extending across the direction of airflow and along the vane length; a channel end section extending in the direction of the airflow, defining a first lateral channel limit; and a channel joining section extending in the direction of the airflow, defining a second lateral channel limit opposite the respective channel end section.

The first lateral channel limit of a first channd is preferably in line with the second lateral channel limit of a second channel when viewed along the direction of airflow.

A downstream edge of a channel joining section of at least one channel (e.g. a downstream channel) may comprise a step extending laterally in the direction of the first lateral channel limit, partially holding the electrical trace heat element in the channel.

Some embodiments may provide that a downstream edge of a most downstream channel of the plurality of channels is joined at an angle to an incident coalescing section and a downstream edge of the incident coalescing section is joined at an angle to a downstream separating section such that the incident and downstream coalescing sections form a single corrugation when viewed along the length of the vane, and wherein a downstream edge of the downstream coalescing section is joined at an angle to a tail section, which extends substantially along the direction of airflow.

Other embodiments may further comprise drain channels for collecting water, each having a concave surface facing an upstream direction and positioned at the downstream edge of each of the incident coalescing section, the downstream coalescing section and the tail section.

The electrical trace heat element is preferably an electrical trace heating tape capable of providing at least 80Wm' of power per unit length.

In accordance with another aspect of the invention, a gas turbine air inlet filter is provided that comprises a plurality of vanes as described above. When connected to a gas turbine air inlet, the separator may be capable of providing sufficient heat to raise the temperature of air entering the gas turbine inlet system such that, without further heat input from a compressor bleed system. cooling due to acceleration of air flow downstream of the inlet filter and into the gas turbine inlet (e.g. a belimouth gas turbine air inlet) does not lower the temperature at the gas turbine inlet to a temperature at which ice may form.

In yet another preferred embodiment, a method of heating a gas turbine air inlet having a gas turbine air inlet filter is provided. The method comprises: providing sufficient heat at the gas turbine air inlet filter by means of dectrical trace heating to raise the temperature at the gas turbine air inlet filter such that, without heat input from a compressor bleed system, cooling due to acceleration of the airflow downstream of the gas turbine air inlet filter and into the gas turbine ifflet does not lower the temperature at the gas turbine air inlet to a temperature at which ice may form. Some embodiments may provide that the temperature at the gas turbine air inlet filter is raised by approximately 2.0°C -4.0°C and more preferably 2.5°C to 3.5°C.

The power for the electrical trace heating is preferably provided by a generator powered by the gas turbine.

In accordance with another aspect of the invention, a vane is provided with plural trace elements, and means are provided for independently switching off one or some of the trace elements, e.g. when the gas turbine is running at a reduced flow rate.

In accordance with another aspect of the invention, a control system is provided such that the humidity of air at a gas turbine inlet is measured and a trace heat element is modulated (or one or some of plural trace heat elements is or are modulated) in response to measured humidity to maintain a desired heat input level or to maintain a desired temperature at the gas turbine inlet.

These and other embodiments are now described by way of example only, with reference to the accompanying drawings.

Brief Description of the Drawings

Figurc 1 is a schematic view of a prior art gas turbine air inlet heating system.

Figure 2 is an alternative prior art gas turbine air inlet heating system.

Figure 3 is an exemplary prior art vane for a turbine inlet filter in cross-section from a view perpendicular to the airflow.

Figure 4 shows a revised design of air inlet filter vane in accordance with the present invention.

Figure 5 shows a sectional view of the same vane as Figure 4.

Figure 6 shows a sectional view of a vane in accordance with the present invention in which the heat tape channels have been crimped.

Figure 7 shows a cutaway view of a length of heat tape.

Figure 8 shows an exemplary gas turbine air inlet filter.

Figure 9 shows a gas turbine air inlet heating system employing the air intake filter of Figure 8.

Detailed Description

IS Figure 1 shows a prior art gas turbine inlet heating system 100 in which air entering the system is heated by a compressor bleed system. Air enters inlet filter 102 where moisture and/or dust particles are substantially removed. The air then flows through duct 104 and enters gas turbine inlet 106. From here it enters the gas turbine 108 and may be used in a large variety of engine or power generation applications. Although only one inlet filter 102 and duct 104 are shown, one skilled in the art will appreciate that multiple inlet filters 102 and ducts 104 may feed into a single gas turbine 108.

As previously described, a problem occurs when using gas turbines in cold conditions; ice may form on the gas turbine inlet 106 and subsequently break off, falling into the gas turbine 108. It will be appreciated that this can cause substantial damage to the turbine 108 and seriously reduce usable lifetime. In order to counteract this problem, the heating system of Figure 1 uses compressor bleed inlet heating. As a result of the compressive forces that air discharged from the compressor of a gas turbine has been subjected to, this air has a substantially higher temperature than that of the air entenng the turbine 108. In a compressor bleed heating system, a portion 110 of the compressor discharge air is fed back to the inlet filter 102 where it mixes with the ambient air. The temperature of the mixed air entering the air inlet filter 102 should be sufficient that ice can no longer form on the gas turbine inlet filter 102 and may even be sufficient to prevent ice forming at the gas turbine inlet 106.

A system such as that of Figure 1 however has a major disadvantage in that, by extracting air on which work has been done, the extracted air is no longer used in the application for which the turbine 108 was designed (e.g. in dectrical power generation or to power a vehicle). Efficiency of the gas turbine 108 is therefore reduced. Furthermore, while the system of Figure 1 is effective in preventing ice formation on the air inlet filter 102, the air must be heated considerably at the filter 102 to prevent ice formation at the gas turbine inlet 106 and therefore requires a substantial amount of discharge air to be extracted from the compressor.

Figure 2 shows an alternative design for a prior art gas turbine inlet heating system 200, which may offer some efficiency savings over the system of Figure 1. This system 200 differs from that of Figure 1 in that the inlet filter 102 is heated by its own electrical heater system 202. A compressor bleed irfiet heating system 210 is still used but it is fed into the duct 104 downstream of the inlet filter 102 at point 204. The electrical heater system 202 uses less compressor power (from an electric generator coupled to the turbine) than compressor bleed heating I 10 to produce a comparable temperature rise. However, because compressor bleed heating is still used, considerable compressor power is wasted.

Figure 3 shows a vane 300 viewed in cross-section along a length of the vane perpendicular to the airflow, a plurality of which may be used in a gas turbine inlet filter like filter 102 of Figure 2. In operation, air flows from heat tape channel 302 towards water separating drain channels 303, 304 and 305 and then through to a gas turbine (not shown). The upstream limit of heat tape channel 302 is defined by incident channel section 312. The lateral extent of heat tape channel 302 is defined between lateral end section 314 and lateral joining section 316. To prevent ice formation on the surfaces of an air inlet separator, electrical trace heat tape may be placed in heat tape channel 302 and kept in contact with all three sections 312, 314 and 316. Typical trace heat tape produces a power per unit length ranging from 5Wm to 60Wm'. For applications where one merely requires the heating of the gas turbine inlet filter, this is entirely sufficient.

At its downstream edge, lateral joining section 316 is joined at an angle to incident section 306. Tn turn, incident section 306 is joined at its downstream edge to downstream section 308 at an angle such that sections 306 and 308 form a single corrugation. Downstream section 308 is connected at an angle to tail section 310, which is substantially parallel to the airflow. Drain channel 303 is formed at the intersection between sections 306 and 308; drain channel 304 is formed at the intersection between sections 303 and 310; and drain channel 305 is formed at the downstream edge of section 310.

With a plurality of such corrugated vanes 300 arranged side-by-side across the airflow, moist air is directed to the surface of the vanes where it may be separated.

Due to the direction of the airflow, water is particularly collected in drain channels 303 -305. From here, it may drain down under gravity and be removed from the airflow, thus substantially decreasing the moisture content of the air.

As airflow enters the gas turbine inlet bellmouth, it may undergo isentropic acceleration, resulting in a temperature drop at the bellmouth such that ice may form.

Some values for properties of the airflow at a gas turbine inlet filter are shown in

Table 1.

Table 1

Heat Input Calculation Warming intake air Z (Density) 1.224 kg.m3 Q.A (Volume Flow) 2.5 C Specific Heat Capacity.006 iwg'k1 T1 (Environment) 0 °C (Target) 2.5 mA (Air Mass Flow) 3.06 kg.s' q.warm=(m.air)(Cp)(T2-T1) 9.36 kW The inventors have recognized that these values may be used in calculating a heating power required at the air inlet filter to counteract the temperature drop at the bellrnouth. Ofparticuar note is the 2.5°C value of temperature, T2. This represents a target temperature for the airflow at the air inlet filter. This phenomenon is largely independent of ambient conditions. Warmer conditions (above freezing) are not problematic. Sub-zero conditions imply dryer air. It has been found that raising the temperature at the air inlet filter from 0°C to 2.5°C independent of other conditions is sufficient to raise the temperature at the belirnouth to a temperature at which ice can no longer form.

To raise the temperature at the air inlet, higher power trace heat would be required.

Example values are shown in Table 2.

Table 2

trace Heater Power Tape powei pci unit length 4OWm 6OWrn l6OWm Power input from trace heat (wm-2) 2360 3540 9400 At present, trace heat tape cannot deliver more than 60Wm'. Higher power would lead to degradation of the tape insulation (in a stand-alone tape).

The power output of the trace heat tape can be varied to account for changes in operational conditions. For example, when a gas turbine is operated at a reduced flow rate, the power required by the trace heat tape is conespondingly reduced. By supplying only the power necessary to raise the temperature of the gas turbine inlet to a temperature at which ice cannot form, efficiency savings can be made compared to operating the heat tape at a power output in normal operation. Other scenarios affecting the required temperature change at an air inlet separator will be apparent to one skilled in the art; for instance, the temperature at the gas turbine air inlet may be affected by radiation and/or conduction from hot parts of the gas turbine.

In order to vary the power output of the air inlet separator. one or more of the lengths of heat tape of each vane may be independently switched off Other more sophisticated control systems may also be employed to alter the power output of one or more lengths of heat tape. For example, the power input to each length of heat tape may be adjusted manually by an operator or, more preferably, properties of the airflow or the environment may be measured by a system of sensors, and the power output of one or more lengths of heat tape modulated accordingly. In one embodiment, the property of the airflow may be the humidity and the system of sensors maybe a humidity sensor.

Turning to Figure 4. this shows a gas turbine ifflet separator vane 400 in accordance with an embodiment of the present invention viewed along the length of the vane. It shares all of the features of vane 300 in Figure 3 but there are several additional features that deserve closer attention. Firstly, there are now two heat tape channels: upstream heat tape channel 402 and downstream heat tape channel 404. While only two heat tape channels are shown, one skilled in the art will appreciate that any number (in particular three or four) of heat tape channels can be included depending on design requirements.

The upstream limit of upstream heat tape channel 402 is defined by upstream incident channel section 412. The lateral extent of upstream heat tape channel 402 is defined between upstream lateral end section 414 and upstream lateral joining section 416.

Similarly, the upstream limit of downstream heat tape channel 404 is defined by downstream incident channel section 417 and the lateral extent of heat tape channel 302 is defined between downstream lateral end section 415 and downstream lateral joining section 419. Electrical trace heat tape may be placed in each of heat tape channels 402 and 404 where it may be kept in contact with all three of its channel sections 412, 414, 415, 416. 417 and 419. Upstream lateral joining section 416, downstream incident channel section 417 and downstream lateral end section 415 meet at trifurcation point 410 such that downstream heat tape channel 404 lies substantially behind upstream heat tape channel 402 when viewed from the upstream direction. This presents the channels 402 and 404 in an in-line configuration, one behind the other, thereby minimising airflow resistance.

To assemble a filter comprising a plurality of vanes Uke that of Figure 4, the heat tape lengths are inserted into channels 402 and 404, which are subsequently crimped by applying pressure to their respective lateral end sections thereby tightly securing each length of heat tape. The act of crimping may cause the vane to bend laterally.

By arranging upstream lateral end section 414 and downstream lateral end section 415 on opposite sides of their respective heat tape channels, crimping both end sections enables the bending of one end section to be substantially cancelled out by the bending due to the crimping of the other end section. This benefit also applies where there are three tape channels. For vanes including more than two heat tape channels, it will be recognised that by having approximately equal numbers of heat tape channels with their respective free lengths on either side of the vane, bending (and corresponding performance losses) can be reduced.

There may also be difficulties in keeping lengths of heat tape in place in their respective channels before cnmping. Upstream heat tape channel 402 does not present any particular problem in this regard, as it is generally easily accessible at the front of the vane assembly. However, the person assembling an inlet filter system may have difficulty accessing downstream heat tape channel 404. The inclusion of step section 408 of downstream lateral joining section 419 extending laterally towards heat tape channel 404 presents an elegant solution to this potential problem. A length of heat tape may easily be guided in from opening 418 at the downstream edge, but step section 408 provides sufficient resistance to stop the tape moving back out. The person assembling may then crimp the downstream channel, substantially permanently securing the heat tape.

The inclusion of two heat tape channels enables twice the length of heat tape to be used. If the same or greater power is supplied to each section of heat tape. the heating of the airflow can be doubled. However, using twice the length of 60Wm1 tape in an environment with an ambient temperature of around 0°C may not be enough to counteract the cooling due to the acceleration of the airflow once it has left the air inlet filter. In is&ation, tape which outputs power per unit length greater than 60Wm' (i.e. tape with a larger number of turns per unit length of resistance wire) may degrade due to excess heating. However, when in contact with an air inlet vane the material of the vane acts as a heat sink. Thus, tape with a greater power per unit length than 60Wm' may be used without degrading the insirlation. In a preferred embodiment, two parallel lengths of 8OWnf1 tape may be used per vane.

Figure 5 shows a sectional view of the vane of Figure 4. Incident section 306 and drain channel 303 are shown with microgrooves 504. These microgrooves 504 increase the surface area of the vane sections on which they are formed, thereby increasing the Ukefihood of water coalescing on said sections. Furthermore, water coalescing on the grooves may drain down and be removed from the airflow in much the same way as for drain channels 304. As incident section 306 and drain channel 303 are the first surfaces the airflow may be incident upon. it is of most use to include microgrooves 504 on these sections. However, one skilled in the art will recognise that microgrooves 504 may be present on any of the vane surface sections.

Figure 6 shows the same vane as Figure 5 but now the vane is shown in a cnmped state. The trailing edges of lateral end sections 414 and 415 display a slight inward curvature 614 and 615 towards their respective heat tape channels. With heat tape in place, the act of crimping allows the heat tape to be secured substantially and permanently within the heat tape channel. Because lateral end sections 414 arid 415 are on opposing sides of the vane, crimping each lateral end section can lead to downstream heat tape channel 404 remaining substantially behind upstream heat tape channel 402 when viewed from the upstream direction, giving the advantage that integnty of share is maintained and filter performance losses are mitigated.

Figure 7 shows a cutaway view of a length of electrical trace heat tape 700. Electrical bus wires 702 are contained within and extend down the length of a piece of insulating material 708. Resistance wire 704 is wrapped around the insulating material and is contacted to the electrical bus wires at contacts 706 alTanged periodically along the length of the tape. In operation, a voltage is applied to the bus wires, which in turn causes a current to flow within the resistance wire. It is this current flow in the resistance wire that causes resistive heating to occur and thereby heat the surrounding environment. Jr the case of the present invention, the vane and surrounding airflow would be heated. By increasing or decreasing the frequency of turns along the length of the heat tape, the power output per unit length can be increased or decreased respectively.

The resistance wire 704 and insulating material 708 are insulated from grounding braid layer 712 by inner insulation layer 710. Grounding braid layer 712 is insulated in turn by outer insulation layer 714. When dectrical trace heat tape is placed in contact with the material of a vane in accordance with the present invention, a heat output power per unit length of 80Wm1 can be supported. This is because the material of the vane acts as a heat sink and prevents over heating and degradation of the heat tape. This is true even of the vane design of Figure 4 wherein two lengths of heat tape are placed in close proximity.

A preferred embodiment of the present invention would therefore have a heat power output per unit length of l6OWnf' per vane. For a large assembly of vanes in a gas turbine inlet filter, for example, one with 60 vanes of length im. a heating power of nearly 10kW per m2 can be applied to the gas flow. This may be sufficient to overcome the cooling associated with an accelerated airflow in conditions with near-freezing ambient temperatures. Ice formafion on the gas turbine inlet downstream of the vane assembly gas turbine inlet filter can be prevented without extracting any

II

energy from a compressor bleed inlet system. This provides a huge efficiency

advantage over the prior art systems.

It is estimated that at temperatures near 0°C, in a typical power generation gas turbine, 3% of compressor power is lost in a compressor bleed heating system compared to a 0.5% loss in compressor power in the present invention. As previously explained, compressor power loss in the present invention is due to the fact that energy for the electrical trace heating may be derived from an electrical generator powered by the gas turbine.

Figure 8 shows an assembled gas turbine air inlet filter including an expanded view of its internal structure. A plurality of vanes 802 and filter element 804 is provided in filter housing 806. Plurality of vanes 802 may comprise vanes in accordance with that of Figure 4. Electncal trace heat tape 808 extends down channels at the leading edge of the vanes and may be controlled by heating control console 810. In cold conditions, heat tape 808 prevents ice formation on the vanes. In warmer conditions, heating control console 810 may turn off heating of the heat tape 808. Moisture from an incident airflow will coalesce on the surface of the vanes particularly in drain channels 812. From here, the water will drain down due to gravity and flow out through drain 814. After moisture has been removed from the airflow by the plurality of vanes 802, the air passes through filter element 804, where dust particles and other impurities not removed by the vane section 802 are extracted.

Figure 9 shows a gas turbine air inlet heating system employing the air intake filter of Figure 8. At the inlet 106 of the gas turbine 108, there is a humidity sensor 901 that gives a humidity measurement to a control circuit 902. This provides control signals 904 to a driver 906 that drives the element or elements of an electrical heater system 908. For example, the heater system may have two heater elements, an upstream element and a downstream element. Each of these is a continuous circuit extending in a serpentine manner across multiple vanes 802 of the intake filter. The driver 906 can drive each of these independently. (There may be three or four such elements.) In normal operation in a cold, humid environment, both (or all) heating elements are driven by the driver circuit 906 to heat the incoming air. When the sensor 901 senses a significant drop in humidity, the control circuit 902 provides a signal to the driver 906 to shut down lpartially or completely) one (or more) of the heater element(s).

Preferably the downstream heater element(s) is (are) switched off. The upstream heater element provides sufficient heat in these circumstances to heat the incoming air to a temperature at which ice will not form even after undergoing isentropic acceleration in the belimouth at the gas turbine inlet 106.

As many apparently different embodiments of the present invention can be made without departing from the scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof.

Claims

CLAIMS1. A vane for a gas turbine air inlet filter, the vane having a body that, when in position in the gas turbine air inlet filter, extends substantially in a direction of airflow, and having a length extending substantially perpendicular to the direction of airflow, the vane being characterised by a plurality of channels each for holding an electrical trace heat element, wherein, the plurality of channels are disposed towards and along an upstream edge of the vane and are alTanged in-line parallel to the direction of airflow.
2. The vane of claim I. wherein there are only two channels.
3. The vane of claim 2, wherein each of the plurality of channels further comprises: an incident channel section at its upstream edge extending across the direction of airflow and along the vane length; a channel end section extending in the direction of the airflow, defining a first lateral channel limit; a channel joining section extending in the direction of the airflow, defining a second aterai channel limit opposite the respective channel end section; wherein the first lateral channel limit of a first channel is in line with the second lateral channel limit of a second channel when viewed along the direction of airflow.
4. The vane of claim 3, wherein a downstream edge of a channel joining section of at least one channel comprises a step extending laterally in the direction of the first lateral channel limit, partially holding the electrical trace heat element in the channel.
5. The vane of claim 4, wherein the at least one channel is a downstream channel.
6-A vane in accordance with any one of daims I to 5. wherein a downstream edge of a most downstream channel of the plurality of channels is joined at an angle to an incident coalescing section and a downstream edge of the incident coalescing section is joined at an angle to a downstream coalescing section such that the incident and downstream coalescing sections form a single corrugation when viewed along the length of the vane, and wherein a downstream edge of the downstream coalescing section is joined at an angle to a tail section, which extends substantially along the direction of airflow.
7. The vane of claim 6, further comprising drain channels for collecting water, each having a concave surface facing an upstream direction and positioned at the downstream edge of each of the incident coalescing section, the downstream coalescing section and the tail section.
A vane in accordance with any one of daims I to 7, wherein the electrical trace heat element is electrical trace heating tape capable of providing 80Wm' of power per unit length.
9 A gas turbine air inlet filter comprising a plurality of vanes in accordance with any one of claims I to 8.
10. The gas turbine air inlet filter of claim 9. which, when connected to a gas turbine air inlet, is capable of providing sufficient heat to raise the temperature of air entering the gas turbine inlet filter such that, without further heat input from a compressor bleed system, cooling due to acceleration of air flow downstream of the inlet filter and into the gas turbine inlet does not lower the temperature at the gas turbine inlet to a temperature at which ice may form.
11. The gas turbine air inlet filter of claim 10, wherein the gas turbine air inlet is a bellrnouth gas turbine air inlet.
12. The gas turbine air inlet filter of claim 10, wherein each of the plurality of vanes further comprises a plurality of trace heat elements, each disposed in a different channel of the plurality of channels, wherein at least one of the plurality of trace heat elements is adapted to be independently switched off.
13. The gas turbine air inlet filter of claim 10, further comprising a control system configured to measure humidity of air at the gas turbine intake and to modulate one or more of the heat elements in response to measured humidity.
14. A method of heating a gas turbine air inlet having a gas turbine air inlet filter comprising: providing sufficient heat at the gas turbine air inlet filter by means of electrical trace heating to raise the temperature at the gas turbine air inlet filter such that.without heat input from a compressor bleed system, cooling due to acceleration of the airflow downstream of the gas turbine air inlet filter and into the gas turbine inlet does not lower the temperature at the gas turbine air inlet to a temperature at which ice may form.
15. The method of claim 14, wherein the temperature at the gas turbine air inlet filter is raised by approximately 2.0 to 4.0°C.
16. The method of claim 15, wherein the power for the electrical trace heating is provided by a generator powered by a gas turbine or another electrical supply.
17. A vane for a gas turbine air inlet filter substantially as described herein with reference to Figures 4 to 6.