GB2147364A

GB2147364A - Anti-icing system for a gas turbine

Info

Publication number: GB2147364A
Application number: GB08423721A
Authority: GB
Inventors: Vasco Mezzedimi; Aggradi Giampiero Ferrari; Alessandro Pini
Original assignee: Nuovo Pignone SpA
Current assignee: Nuovo Pignone SpA
Priority date: 1983-10-03
Filing date: 1984-09-19
Publication date: 1985-05-09
Also published as: GB8423721D0; FR2552816A1; SE8404617L; SE8404617D0; JPS6095137A; IT8323111A0; CH660620A5; IT1166979B; DE3436273A1

Abstract

There is disclosed an anti-icing system for a gas turbine (1), in which heat is transferred from the turbine exhaust gas (2) to the inlet air (5) by an intermediate non- freezing heat-convection fluid, which circulates in a circuit (8), and by two heat exchangers (6, 11) disposed respectively at the turbine exhaust and intake. Means such as a damper (12) is provided for controlling the quantity of heat supplied to the intake air. Alternatively a further heat exchanger may be used to cool the fluid in a controlled manner. <IMAGE>

Description

SPECIFICATION Anti-icing system for a gas turbine This invention relates to an anti-icing system for use in a gas turbine.

Under certain climatic conditions, harmful ice formation is known to occur at the inlet of a gas turbine, and can sometimes cause catastrophic compressor pumping by obstructing the entry of air into the turbine. In addition, large pieces of ice can damage the turbine blades.

This phenomenon arises from the fact that expansion occurs at the intake of the axial compressor of the gas turbine due to the pressure drop through the filter/silencer system of the turbine and due to the acceieration of air upstream of the first stage. The effect of this expansion, which can be considered adiabatic, is that the air can become supersaturated, with consequent formation of liquid or ice in the first stage of the axial compressor.

Thus, ice formation occurs when the air cooling caused by the expansion is such as to cause intersection of the saturation line, and the temperature at the end of expansion falls below 0 C.

Different types of anti-icing systems are already known in the art. These systems are designed to prevent the gas turbine intake air crossing the saturation line, with the temperature at the end of expansion below 0 C. One of the known anti-icing systems uses compressed air bled from the axial compressor, this compressed air being mixed with the intake air to heat the intake air. However, as use has to be made of bleeding, such a system is obviously prejudicial to the power and efficiency of the turbine.

Another known anti-icing system consists of an arrangement for mixing part of the gas turbine exhaust gas with the intake air. This system also has various drawbacks and disadvantages such as the fact that the introduction into the intake side of the solid particles contained in the fuel and the sulphur components of the exhaust gas is extremely damaging to the filter system and to the turbine. A further drawback is that the back pressure required in the exhaust duct, in order to obtain correct operation, reduces the turbine efficiency. A further drawback is the difficulty of controlling the heat transferred to the intake air and the need for large-sized ducts.

Finally, a further drawback is the difficulty of properly distributing the withdrawn gas over the entire intake area, and, in addition, as the gas is rich in water vapour, there is the risk of the localised formation of condensate and even ice.

The object of the present invention is to obtain the aforesaid drawbacks by providing an anti-icing system for a gas turbine which does not prejudice turbine power and efficiency and does not damage its operation, and which also results in considerable operating economy and high reliability. This is attained in accordance with the invention in that the turbine intake air is heated by the heat of the turbine exhaust gas by means of an intermediate non-freezing heat-convection fluid kept moving within a closed circuit by a pump.

This heat transfer is obtained by heat exchangers at the exhaust and intake. More specifically, the anti-icing system for a gas turbine is characterised according to the present invention by being constituted by a sealed and closed circuit provided with a buffer expansion tank, within which an intermediate non-freezing heat-convection fluid is kept moving by a circulation pump, the circuit being provided with a first (preferably finnedtube) heat exchanger situated in direct contact with the heat of the exhaust gas in the gas turbine exhaust duct, of which is occupies a minimum part, and a second (preferably smooth-tube) heat exchanger situated at the air inlet to the gas turbine, means being also provided for continuously controlling the quantity of heat conveyed by the intermediate non-freezing fluid.

According to a preferred embodiment of the present invention, a mixture of water and monoethylene glycol is used as the intermediate non-freezing heat-convection fluid.

According to a preferred embodiment of the present invention, the means for continuously controlling the quantity of heat conveyed by the intermediate non-freezing fluid and supplied to the intake air consist of a damper for regulating the exhaust gas flow through the heat exchanger situated at the turbine exhaust, the damper being controlled by a double-acting pneumatic piston provided with a control positioner which is itself regulated by the signals of an ambient temperature and humidity indicator.Thus, the damper throttles the gas flow according to ambient conditions, and moreover when the anti-icing system is not required to operate, by virtue of the ambient conditions, the damper is completely closed and prevents the gas passing through the exchanger (if the gas did pass through the exchanger, this would have the effect of raising the temperature of its tubes to a high value, with consequent thermal shock on restarting the system).

Finally, according to another preferred embodiment of the invention, the means for continuously controlling the quantity of heat conveyed by the intermediate non-freezing fluid and supplied to the intake air, instead of consisting of a means for controlling the heat exchanger at the exhaust by throttling the gas flow, consist of a means for varying the throughput of non-freezing fluid to the heat exchanger on the intake side by deviating part of the flow, by means of a three-way regulator valve which is electrically regulated and pneu matically actuated, to an auxiliary cooling circuit comprising an additional heat exchanger positioned on the forced-air lubricating oil cooler of the turbo unit, downstream of the oil cooler itself.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of an antiicing system according to the invention; and Figure 2 is a diagrammatic view of another anti-icing system according to the invention.

In each Figure, there is shown a gas turbine 1 the exhaust gas 2 which flows through a turbine exhaust duct 3. Air 5 for the turbine enters through an intake chamber 5.

A finned-tube heat exchanger 6 is situated in a branch 7 of the exhaust duct 3, so that the gas 2 comes into direct contact with the heat exchanger 6. The heat exchanger 6 is connected into a sealed and closed circuit 8 provided with a buffer expansion tank 9, within which circuit 8 an intermediate nonfreezing heat convection fluid generally constituted by a mixture of water and monoethylene glycol is kept moving by a circulation pump 10. A smooth-tube heat exchanger 11, arranged to transfer heat to the intake air 5, is connected into the circuit 8 in a position corresponding to the intake chamber 4.

The degree of opening of the branch 7 can be varied, in order to regulate the flow of gas 2 through it, by means of a damper 1 2 (see Fig. 1) which is pivoted at point 13 and is caused to pivot by a double-acting pneumatic piston 1 4 provided with a control positioner (not shown) sensitive to ambient temperature and humidity.

According to a modified embodiment of the invention (see Fig. 2), into the closed circuit 8 there is connected a three-way regulator valve 1 5 which is electrically regulated and pneumatically actuated. This valve 1 5 causes part of the non-freezing fluid to flow to an additional heat exchanger 1 6 positioned on a forced-air lubricating oil cooler 1 7 of the turbo unit, downstream of the oil cooler itself.

Claims

1. An anti-icing system for a gas turbine, comprising a sealed and closed circuit containing a non-freezing heat-convection fluid, the circuit being provided with (a) an expansion tank, (b) a circulation pump for keeping the fluid in motion during use of the system, (c) a first heat exchanger which in use is disposed in the exhaust gas of the gas turbine, and (d) a second heat exchanger which in use is disposed in the air entering the gas turbine; the system further comprising means for controlling in use of the system the amount of heat conveyed by the fluid.

2. A system as claimed in claim 1, wherein the first heat exchanger is a finnedtube heat exchanger, and the second heat exchanger is a smooth-tube heat exchanger.

3. A system as claimed in claim 1 or 2, wherein the fluid is a mixture comprising water and monoethylene glycol.

4. A system as claimed in any of claims 1 to 3, wherein the means for controlling the amount of heat conveyed by the fluid comprises a damper for regulating the flow of exhaust gas through the first heat exchanger, and means for controlling the damper in dependence upon the ambient temperature and humidity.

5. A system as claimed in claim 4, wherein the means for controlling the damper comprises a double-acting pneumatic piston provided with a control positioner which in turn is adapted to be regulated by signals from an ambient temperature and humidity indicator.

6. A system as claimed in any one of claims 1 to 3, wherein the means for controlling the amount of heat conveyed by the fluid comprises a bypass line adapted to allow a part of the circulating fluid to bypass the first heat exchanger.

7. A system as claimed in claim 6, including an electrically-controlled pneumatically-ac- tuated three-way regulator valve for controlling the amount of circulating fluid bypassing the first heat exchanger.

8. A system as claimed in claim 6 or 7, wherein the bypass line includes an additional heat exchanger positioned in the vicinity of a forced-air lubricating cooler of the gas turbine.

9. A gas turbine provided with an antiicing system as claimed in any of claims 1 to 8.

1 0. An anti-icing system as claimed in claim 1, substantially as hereinbefore described with reference to, and as shown in, Fig. 1 or Fig. 2 of the drawings.

11. A gas turbine as claimed in claim 9, substantially as hereinbefore described with reference to, and as shown in, Fig. 1 or Fig. 2 of the drawings.