Turbo machine and method for operating such turbo machine

Abstract

A turbo machine, such as a gas turbine, includes a rotor, which rotates about a horizontal machine axis, and which is enclosed by a coaxial enclosure. The turbo machine includes a metal casing, whereby an electrical heating system is provided on the lower half of the metal casing. A safe operation is achieved by having the heating system configured as a redundant system.

Claims

1. A turbo machine configured as a gas turbine, comprising: a rotor, which rotates about a horizontal machine axis, and which is enclosed by a coaxial enclosure having a metal casing; an electrical heating system provided on the lower half of said metal casing, wherein said heating system is configured as a redundant system, wherein said heating system comprises at least one electrical heating module with two similar redundant lines running in parallel alongside each other, and wherein said heating system includes at least one heating cable and measuring means for measuring temperatures and/or electrical properties within said heating system including at least a temperature of said at least one heating cable.

2. The turbo machine as claimed in claim 1, wherein said at least one heating module is connected to a power supply unit such that either each of said redundant lines is supplied with 50% of the electrical power supplied to said heating module from the power supply unit or only one of said redundant lines is supplied with 100% of said electrical power.

3. The turbo machine as claimed in claim 1, wherein said measuring means is configured as a redundant measuring means.

4. The turbo machine as claimed in claim 3, wherein said at least one heating cable is attached to said metal casing, and said measuring means comprises at least one thermocouple box attached to said at least one heating cable to measure the temperature of said at least one heating cable.

5. The turbo machine as claimed in claim 4, wherein said at least one thermocouple box encloses a section of said at least one heating cable at a predetermined place of said at least one heating cable, that said at least one heating cable runs through said thermocouple box between an upper part and a lower part of said thermocouple box, and that at least three thermocouples for measuring the temperature of said thermocouple box are attached to said thermocouple box.

6. A method for operating a turbo machine according to claim 5, wherein said at least one thermocouple box creates an artificial hot spot at said heating cable, and that said three thermocouples attached to said thermocouple box are evaluated by a control unit with a 2-out-of-3 logic.

7. The turbo machine as claimed in claim 4, wherein said at least one thermocouple box is covered with a thermal insulation in order to increase the temperature of the thermocouple box.

8. The turbo machine as claimed in claim 1, wherein said at least one heating cable, which is attached to said metal casing by means of metal holding strips.

9. The turbo machine as claimed in claim 8, wherein said metal holding strips are placed between said metal casing and said at least one heating cable and hold said heating cable by means of hook elements.

10. The turbo machine as claimed in claim 9, wherein said at least one heating cable is provided with a bend between two distant holdings strips holding said heating cable.

11. The turbo machine as claimed in claim 1, wherein a plurality of heating modules are symmetrically arranged on said metal casing with regard to a vertical symmetry plane through the machine axis, and that said heating modules are individually and controllably supplied with electric power by means of a power supply unit.

12. A method for operating a turbo machine according to claim 11, wherein a heating module on one side of said vertical symmetry plane is turned off when its symmetric counterpart on the other side of said vertical symmetry plane fails.

13. A method for operating a turbo machine according to claim 11, wherein in case of an asymmetric cool-down with respect to said vertical symmetry plane the heating system is powered asymmetrically to counter said temperature asymmetry.

14. A method for operating a turbo machine according to claim 1, wherein a control unit within said heating system decides on the electrical power supplied to said heating system based on measurements of the temperature of the metal casing and/or the clearance of the machine and/or electric parameters of the heating system and/or operating parameters of the turbo machine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.

(2) FIG. 1 shows in a perspective view an example of a turbo machine in form of a gas turbine of the applicant of type GT24, respectively GT26 (with sequential combustion);

(3) FIG. 2 shows a simplified control scheme for a turbo machine according to an embodiment of the invention;

(4) FIG. 3 shows an example of a redundant heating module used in a turbo machine according to the invention;

(5) FIG. 4 shows an exemplary symmetric arrangement of a plurality of heating modules on both sides of a vertical symmetry plane in a turbo machine according to the invention;

(6) FIG. 5 shows the fixation of the heating cables on the casing according to an embodiment of the invention;

(7) FIG. 6 shows measures for absorbing thermal expansion of the heating cables according to an embodiment of the invention; and

(8) FIGS. 7a and 7b show an example of thermocouple boxes for overheating protection of the heating cables according to an embodiment of the invention.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE INVENTION

(9) The invention described in this patent mitigates the issues caused by upwards thermal bending of a turbo machine casing which is caused by temperature differences forming during the engine's slow cool-down period. Thus it solves rubbing and rotor blocking issues both at the blades/vanes and at the bearings.

(10) The invention is a trace heating system applied on a part of the bottom of a turbo machine casing. The system consists of resistive heating cables with the associated electronics, measurement and control devices.

(11) The system can be used in two ways: preventive mode: turns on after shutdown when the bottom becomes colder than the top, to prevent casing bending during cool-down, Counteracting mode: turns on after rotor blocking is anticipated (e.g. when the rotor barring speed drops or when the roller shutter is closed).

(12) The main components of a typical embodiment of the system can be seen in FIG. 2. The system shown in FIG. 2 is associated with a gas turbine (GT) enclosure 21, which comprises an axially extending compressor housing 22 followed by a combustor and turbine housing 23. All housings have a metal casing 24. Hot parts are enclosed by a thermal insulation 25. The air passing through the housing enters at air inlet 26 and exits at air outlet 27. The thermal equalization means comprises heating cables 29 arranged at the lower part of the thermally insulated combustor and turbine housing 23. The individual heating cables 29 are supplied with electrical power by a suitable power supply unit 32, which is controlled by a control unit 33.

(13) Control unit 33 receives temperature signals from a plurality of temperature measuring points 28 distributed at the upper as well as the lower part of the thermally insulated combustor and turbine housing 23. A data storage unit 34 is connected to control unit 33 to store temperature data as well as feed control unit 33 with stored data or parameters.

(14) Application of the system shown in FIG. 2 is not limited to gas turbines but is possible to other turbo machine than gas turbines; other embodiments including more or less parts than shown in FIG. 2 are also possible.

(15) One of the main features of the system of FIG. 2 is redundancy. As shown in FIG. 3 the heating system uses on the turbo machine heating modules 35 comprising two similar redundant lines 35a and 35b, which are running in parallel along each other. During normal operation, when both lines 35a and 35b are working well, both lines shall receive half of the nominal power. If one of the lines 35a and 35b gets broken, the other line shall be operated with full power to compensate for the loss of one line.

(16) Furthermore, particular attention is paid to a symmetric operation by the control unit 33: As shown in the example of FIG. 4, heating (element) modules 36a,b and 37a,b are arranged symmetrical to a vertical plane 38 going through the centreline or machine axis 20 of the engine. In order to avoid the generation of non-desired casing temperature differences, a heating (element) module has to be shut down by the control unit 33 if its symmetric counterpart (on the other side of the symmetry plane 38) is shut down (e.g. because of cable damage).

(17) According to FIG. 5, the single heating cables 39 are fixed on the metal casing 24 by holding strips 41, which are placed between the metal casing 24 and the heating cables 39. These holding strips 41 are fixed on the metal casing 24 by bolts 40a and 40b being welded on the casing. They hold the heating cables 39 with small metal hooks, which are provided by bending small hook elements 42 of the holding strips 41 around the respective heating cable 39. This fixing scheme allows a more stable installation and easier assembly, along with improved heat transfer. In addition, the holding strips 41 could be equipped with pretension means, e.g. by springs.

(18) As shown in FIG. 6, a small bend 43 may be introduced into every cable segment between two holding strips 41a and 41b to prevent the tearing of the metal hooks by thermal expansion of the heating cables 39. The thermal expansion of the heating cables 39 is expected to be 7 mm/m. The cables can be bent in the direction normal to the surface of the casing or tangentially to the casing, i.e. along the surface of the casing.

(19) Another advantageous design feature is related to an instrumentation to measure and monitor the maximum temperature of the heating cables 39. These temperature measurements enable the protection of the system from overheating. The measured cable segment is converted into an artificial hotspot to make sure that the hottest cable temperature is measured. However, as an alternative, validated wire resistance measurements can also be used.

(20) The maximum temperature monitoring is required for safety reasons: The maximum allowed temperature of the heating cables 39 cannot be higher than the maximum design temperature of the casing. For a gas turbine of the GT24 and GT26 type (see FIG. 1) this temperature is 450 C. This way the outer insulation needs not to be redesigned, and its surface can be touched by a person. Overheated cables can only be turned on again when they are colder than 400 C.

(21) As mentioned above, the design introduces one artificial hot spot for each heating cable 39 used. The hot spot is created by leading the heating cable 39 through a (closed) thermocouple box 44 (FIGS. 7a and b) and covering the thermocouple box 44 with a thin insulation cloth 48 (FIG. 7b). Each thermocouple box 44 has an upper part 45 and a lower part 46 and has three redundant thermocouples 47, which are evaluated by control unit 33 with a 2-out-of-3 logic.

(22) In addition, the system may be equipped with monitoring devices (not shown in FIG. 2) to measure the electric properties of the system (applied power, current, voltage, resistance, etc.). There are two main reasons to apply such electric current monitoring: identifying broken lines: to prevent current passing on them and to turn their symmetric counterparts off, power compensation: as the cables are heating up their power drops with the same voltage applied on their terminals. With current/resistance measurements the applied voltage can be compensated to get constant power on the heating cables.

(23) When certain standard heating cable modules, e.g. with a standard cable length of 25 m, will be used, it may become possible to use these electric measurements to infer the temperature of the cables. By introducing an extra safety margin to the shutdown cable temperature, this may be used to substitute the (more expensive) thermocouple boxes 44.

(24) The system shown in FIG. 2 can be controlled automatically by taking into account not only the actual measured values of the temperatures and/or electrical parameters but also adjustable parameters and/or stored data as well (data storage unit 34). Operation parameters can be for example overpower ratio or forced shutdown signal, while stored data in the data storage unit 34 can be for example the past states of the system from which trends can be calculated.

(25) In addition, inputs from clearance sensors placed in the machine (e.g. capacitive or optical) can also be used by the control logic of control unit 33.

(26) The trace heating system described so far can be assembled with or without special attention paid for improved heat transfer from the heating cables 39 to the surface of metal casing 24. Heat transfer can be improved by introducing heat bridges by thermal liquid, grooving of the casing, soldering of the cables, metal cover, embedding the cables into the casing, covering the insulation with reflective material, etc. . . . .

(27) In this application, several parts are described as upper or lower. This refers to their position when they are in use in an installed turbo machine.

LIST OF REFERENCE NUMERALS

(28) 10 gas turbine (GT, e.g. GT24 and GT26) 11 rotor 12 (inner) casing 13 air intake 14 compressor 15 combustor (e.g. a combustion chamber with an EV burner) 16 turbine (HP) 17 combustor (e.g. a combustion chamber with a SEV burner) 18 turbine (LP) 19 exhaust gas outlet 20 machine axis 21 GT enclosure 22 compressor housing 23 combustor and turbine housing 24 metal casing 25 thermal insulation 26 air inlet 27 air outlet 28 temperature measuring point 29,39 heating cable 30 power line 31 data line 32 power supply unit 33 control unit 34 data storage unit 35 heating module (redundant) 35a,b redundant line 36a,b heating module 37a,b heating module 38 vertical symmetry plane 40a,b bolt (welded) 41 holding strip 41a,b holding strip 42 hook element 43 bend 44 thermocouple box 45 upper part 46 lower part 47 thermocouple 48 thermal insulation