METHOD FOR MONITORING A COMBUSTOR

Abstract

A method for monitoring a combustor comprising: measuring several times a distance between a first wall of the combustor and either a second wall of the combustor or a sensor of the combustor by the sensor, and concluding from a variation in the distances a formation of deposit on the first and/or second wall and/or sensor, and/or a temperature change within the combustor, and/or a pressure change within the combustor.

Claims

1. A method for monitoring a combustor, comprising: measuring several times a distance between a first wall of the combustor and either a second wall of the combustor or a sensor of the combustor by means of the sensor, and concluding from a variation in the distances a formation of deposit on the first and/or second wall and/or sensor, and/or a temperature change within the combustor, and/or a pressure change within the combustor.

2. The method according to claim 1, wherein an ultrasonic sensor is used.

3. The method according to claim 1, wherein a relatively slow decline in the distances is regarded as related to a formation of deposit, a relatively fast variation in the distances is regarded as related to a pressure change, and a variation in the distances at a medium speed level is regarded as related to a temperature change.

4. The method according to claim 1, wherein a number of running cycles of the combustor is derived from concluded temperature changes.

5. The method according to claim 1, wherein specific combustion dynamics are derived from concluded pressure changes.

6. The method according to claim 1, wherein a maintenance status is derived from the conclusion(s) regarding the formation of deposit, the pressure change and/or the temperature change.

7. The method according to claim 6, wherein a maintenance value (US) is derived from the conclusion(s) regarding the formation of deposit, the pressure change and/or the temperature change, wherein the combustor is set for a stop of operation if the maintenance value (US) exceeds a threshold value (A.sub.Lim).

8. The method according to claim 6, wherein a maintenance value (US) is derived from the conclusion(s) regarding the formation of deposit, the pressure change and/or the temperature change, wherein the combustor is scheduled for a maintenance, if the maintenance value (US) exceeds a threshold value (B.sub.Lim).

9. The method according to claim 7, wherein said threshold (A.sub.Lim) for a stop of operation is higher than said threshold (B.sub.Lim) for scheduling a maintenance.

10. A combustor comprising a sensor being adapted to measure several times a distance between a first wall of the combustor and either a second wall of the combustor or the sensor, and an evaluation unit, the evaluation unit being connected to the sensor to receive measuring signals therefrom and being adapted to process a method according to claim 1.

11. The combustor according to claim 10, further comprising: a cavity for guiding liquid fuel, and/or a cavity for guiding gaseous fuel, and/or a cavity for guiding combustion gas, wherein a sensor is provided in one, several or all of said cavities for measuring a distance between a first wall of the respective cavity and either a second wall of the respective cavity or the sensor.

12. A gas turbine engine comprising a combustor according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] A specific embodiment of a gas turbine engine according to the invention is explained in more detail with reference to the accompanying drawings. The drawings show schematically in

[0026] FIG. 1 the gas turbine in a longitudinal sectional view;

[0027] FIG. 2 the general structure of a combustor of a gas turbine engine;

[0028] FIG. 3 a section of the combustor of the gas turbine according to FIG. 1 in a longitudinal sectional view; and

[0029] FIG. 4 a block diagram illustrating a process for monitoring the combustor according to FIG. 3.

DETAILED DESCRIPTION OF INVENTION

[0030] The terms upstream and downstream refer to the flow direction of the airflow and/or working gas flow through the engine unless otherwise stated. The terms forward and rearward refer to the general flow of gas through the engine. The terms axial, radial and circumferential are made with reference to a rotational axis 20 of the gas turbine engine.

[0031] FIG. 1 shows an example of a gas turbine engine 10 according to the invention in a sectional view. The gas turbine engine 10 comprises, in flow series, an air inlet 12, a compressor section 14, a combustor section 16 and a turbine section 18 which are generally arranged in flow series and generally in the direction of the rotational axis 20 (which is thus also the longitudinal axis of the gas turbine engine 10). The gas turbine engine 10 further comprises a shaft 22 which is rotatable about the rotational axis 20 and which extends longitudinally through the gas turbine engine 10. The shaft 22 drivingly connects the turbine section 18 to the compressor section 14.

[0032] In operation of the gas turbine engine 10, air 24, which is taken in through the air inlet 12, is compressed by the compressor section 14 and delivered to the combustor section 16.

[0033] The compressor section 14 comprises an axial series of guide vane stages 46 and rotor blade stages 48.

[0034] The combustor section 16 comprises a burner plenum 26, one or more combustion chambers 28 defined by a double wall can 27 and at least one combustor 30 fixed to each combustion chamber 28. The combustion chambers 28 and the combustors 30 are located inside the burner plenum 26. The compressed air passing through the compressor section 14 enters a diffuser 32 and is discharged from the diffuser 32 into the burner plenum 26 from where a portion of the air enters the combustors 30 and is mixed with a gaseous or liquid fuel. The fuel/air mixture is then burned and the working gas 34 from the combustion is guided via a transition duct to the turbine section 18.

[0035] The turbine section 18 comprises a number of turbine blades 38 attached to the shaft 22. In addition, guiding vanes 40, which are fixed to a stator 42 of the gas turbine 10, are disposed between the turbine blades 38.

[0036] The combustion gas from the combustion chamber 28 enters the turbine section 18 and drives the turbine blades 38, which in turn rotate the shaft 22. The guiding vanes 40 serve to optimize the angle of the combustion or working gas on to the turbine blades 38.

[0037] As shown schematically in FIG. 2, the combustor 30 of the gas turbine engine 10 may comprise three parts: a burner 50, a swirler 52, and a transition piece 54, which is connected to the combustion chamber 28. Main fuel is introduced into the swirler 52 by way of the burner 50 through a main fuel supply line 56, while pilot fuel enters the swirler 52 through a pilot fuel supply line 58 comprising a pilot fuel nozzle 60.

[0038] The flows of main and pilot fuel are derived from a fuel-split valve 62, which is connected to a common fuel supply 64. The flow of main fuel enters the swirler 52 through a set of main fuel nozzles 66, from where it is guided along swirler vanes while being mixed with incoming compressed air. The resulting fuel/air mixture is burned within the transition piece 54 with the resulting combustion air entering the combustion chamber 28.

[0039] FIG. 3 shows a section of the combustor 30 of the gas turbine engine 10 in more detail. The combustor 30 is designed to be operated with liquid or gaseous fuel. Its burner 50 comprises a main liquid burner 68, a main gas burner 70, and a pilot burner 72. The main liquid burner 68 and the main gas burner 70 each comprise a gallery 74, 76, which is an annular cavity used to distribute the respective fuel to several nozzles for introduction into the swirler 52.

[0040] At least one ultrasonic sensor 78 is allocated to all of the parts of the burner 50, i.e. the main liquid burner 68, the main gas burner 70, and the pilot burner 72. The ultrasonic sensors 78 are located in blind holes 80, each of which reaching from the outside of a respective burner casing to almost the galleries 74, 76 respectively the fuel gallery 82 located proximate the pilot burner 72.

[0041] Ultrasonic waves transmitted from the sensors 78 travel through the air within the blind holes 80 and through the narrow sections of massive material being situated between the blind holes 80 and the galleries 74, 76 respectively the fuel gallery 82. At least a portion of the ultrasonic waves will then travel through the fluid situated with the galleries 74, 76 and the fuel gallery 82 and will then be reflected at least partly from the walls onto which they impinge. Taking the same route back, a portion of the transmitted ultrasonic waves can be received by the ultrasonic sensors 78 and transformed into electric signals. Evaluating the received signals, in particular with respect to the travel time, allows to determine the distances between the sensors and the respective (sections of the) walls used to reflect the ultrasonic waves. Those distances vary if deposit (indicated schematically at 84) is forming upon the walls.

[0042] In an alternative embodiment (not shown) of the combustor 30 through holes (reaching into the galleries 74, 76 and the fuel gallery 82) may be provided for the ultrasonic sensors 78 instead of the blind holes 80. This may be advantageous for transmitting ultrasonic waves into the cavities but disadvantageous with respect to contamination of the ultrasonic sensors 78, as those would be exposed directly to the fluids being present within the cavities.

[0043] Formation of deposit 84 on the walls of the gas gallery 76 may in particular be due to a high sulphur content of the gaseous fuel, which may lead to blockage of passages due to formation of silver sulphide. This is particularly the case, if gaseous fuel is supplied, which does not correspond to specific standards for use in such a combustor 30. Such gaseous fuel may also comprise liquids (e.g. from gas compressor), which may be carried over with the gas, leading to burnout of components of the combustor 30. Both, the formation of silver sulphide as well as carried over liquids may cause the gas turbine engine 10 to shut down.

[0044] Liquid fuel of poor quality may also have a negative impact on the turbine operation. It may in particular lead to the formation of deposit 84 on those cavities, which are used to guide the liquid fuel within the combustor (in particular the liquid gallery 74). It may further lead to a formation of carbon deposit 84 on other key components of the combustor (including the walls of the fuel gallery 82), as a result of burning the liquid fuel.

[0045] By evaluating a variation and in particular a decline in the distances measured by means of the ultrasonic sensors 78, the thickness of the deposit 84 formed on the monitored walls can be determined. Based on those results a maintenance status for the combustor 30 can be created. For example, if a general maintenance schedule for the combustor 30 is based on fixed intervals, monitoring the formation of deposit 84 may be used to alter the intervals when necessary.

[0046] FIG. 4 shows such a process of altering a maintenance schedule when necessary. This process is running automatically based on software in an evaluation unit 86 of the combustor 30. After starting the process, in step 1, the readings from the ultrasonic sensors 78 are transformed into maintenance values (US). With respect to the formation of deposit 84 on the respective walls, the maintenance values (or a combined maintenance value) may be inversely proportional to the measured distances. The maintenance value (s) may then be compared to a first threshold value (A.sub.Lim); step 2. If at least one of the maintenance values is larger than the first threshold value (and thus the comparison requirement is true (T)), the operation of the combustor 30 is stopped (automatically) in order to avoid damage due to formation of deposit 84 and/or carry-over of liquid with the gaseous fuel; step 3a.

[0047] Otherwise, i.e. if the comparison requirement is false (F) and thus the maintenance values are all smaller than the first threshold value, a further comparison is conducted, determining whether at least one of the maintenance values is larger than a second threshold value (B.sub.Lim), which is smaller than the first threshold value (A.sub.Lim); step 3b. If this is true (T), a detailed inspection and/or a change out of one or several components of the combustor 30 is planned for a next scheduled maintenance and/or the time until the next maintenance will be conducted is set shorter; step 4a. An additional process step 5 may include giving out a warning sign to maintenance staff, indicating that specific maintenance requirements are oncoming. Otherwise, i.e. if the comparison of the maintenance values with the second threshold value delivers a false (F) result, then the combustor is kept in operation without changing the maintenance status; step 4b. In both cases, measuring the distances by means of the ultrasonic sensors and comparing the readings with the first and second threshold values are continued (i.e. starting with step 1 again).

[0048] Variations of the measured distances are influenced not only by formations of deposit 84 on the walls, but also by changing temperatures and pressures within the combustor 30. Those changing temperatures and pressures may therefore also have an influence on the maintenance values, whereas a differentiation between the different reasons for the variations in the distances can be made based on the speed with which those occur. Formations of deposit 84 on the walls progress relatively slowly compared to (relevant) variations in the temperature, which may be due in particular to the operation of the combustor 30 in cycles (i.e. heating the combustor 30 up when beginning operation and cooling it down when terminating operation). Changes in pressure, in particular due to combustion dynamics, are occurring even faster than the temperature changes. Therefore, the speed with which variations in the distances occur may be divided into at least three ranges. A first range with relatively slow variations, representing a formation of deposit 84. A second range defined by a medium speed level of the variations, representing temperature changes, and a third range with relatively fast variations, representing pressure changes. Each of the ranges may be represented by a (different) range of maintenance values. Thus, comparing the maintenance value (s) with the threshold values may comprise comparing a specific maintenance value for each of the ranges with the same or specific (and thus different) first and second threshold values.