EP3540182A1 - Method for controlling a clearance minimisation of a gas turbine - Google Patents

Abstract

The invention relates to a method for controlling a gap minimization of an adjustable gap between a rotor and a housing of a gas turbine. In order to ensure a high-precision gap setting during operation of the gas turbine, an actual value (P) of an operating parameter, for example the relative power (P) of the gas turbine, is continuously determined and compared with a lower and an upper threshold value (P, P) over a predetermined one Period determines a maximum value (P) of the actual value (P) and from a limit (P) determined, which is between the lower and upper threshold (P, P), wherein the limit value (P) is smaller by a difference than the maximum value (P). If the actual value (P) is below the lower threshold value (P), the gap minimization is deactivated, whereas above the upper threshold value (P) it is activated. Between the threshold values (P, P), the gap minimization is activated if the actual value (P) is above the limit value (P), but deactivated if this value is below the limit value (P).

Description

The invention relates to a method for controlling a gap minimization of an adjustable gap between a rotor and a housing of a gas turbine, wherein the gas turbine comprises means, in particular hydraulic means, for a gap adjustment. The invention further relates to a control device for carrying out the method and to a gas turbine with such a control device.

To maximize gas turbine efficiency, it is crucial to keep the gaps between the rotating and static components as small as possible during operation. In a conical turbine flow channel, one possibility for this, after transient phases in which the gaps on the blade tips are maximally narrowed, is to pass through the rotor in stationary high-load operation, e.g. to move axially with a hydraulic system. If the rotor moves against the flow direction, then the gaps are reduced.

From the WO 2014/016153 A1 For example, a method of minimizing an adjustable gap between a blade and a housing of a turbine is known. By displacement of rotor and housing against each other, the gap between the rotor and the housing is to be minimized in a simple manner. For this purpose, an output signal of the rotor and / or the housing associated structure-borne noise monitoring system is used as a measure of the size of the gap and thus to set a minimum gap.

Another method for part-load operation of a gas turbine with active hydraulic gap adjustment is for example from WO 2015/128193 A1 known.

In order to produce a marketable product, the decision about the approached position of the rotor must be automatically controlled or regulated. Since a permanent measurement of the operating column is technically difficult to implement or very expensive, a different approach is necessary. Here, in the control of the gas turbine, an HCO (Hydraulic Clearance Optimization) logic is used which, based on measurable variables, specifies how the gap optimization is to be carried out.

The invention has for its object to provide an improved HCO logic that allows optimal use of the gap setting especially during a load change during operation of the gas turbine.

• laufend wird ein Istwert eines Betriebsparameters ermittelt und mit einem unteren Schwellwert und einem oberen Schwellwert verglichen,
• über eine vorgegebene Zeitspanne wird ein Maximalwert des Istwertes bestimmt,
• ein Grenzwert, der zwischen dem unteren Schwellwert und dem oberen Schwellwert liegt, wird bestimmt, wobei der Grenzwert um eine Differenz kleiner ist als der Maximalwert,

wobei beim Vergleich des Istwerts mit dem unteren Schwellwert und dem oberen Schwellwert, wenn der Istwert:

• unterhalb des unteren Schwellwerts liegt, die Spaltminimierung deaktiviert wird,
• oberhalb des oberen Schwellwerts liegt, die Spaltminimierung aktiviert wird,
• zwischen dem unteren Schwellwert und dem oberen Schwellwert liegt, die Spaltminimierung aktiviert wird, wenn der Istwert oberhalb des Grenzwertes liegt und deaktiviert wird, wenn der Istwert unterhalb des Grenzwerts liegt.

The object is achieved by a method for controlling a gap minimization of an adjustable gap between a rotor and a housing of a gas turbine, wherein the gas turbine comprises means, in particular hydraulic means for a gap adjustment, comprising the following steps:

• an actual value of an operating parameter is continuously determined and compared with a lower threshold value and an upper threshold value,
• over a given period of time, a maximum value of the actual value is determined,
• a threshold, which is between the lower threshold and the upper threshold, is determined, the threshold being smaller by a difference than the maximum value,

comparing the actual value with the lower threshold and the upper threshold, if the actual value:

• below the lower threshold value, the gap minimization is deactivated,
• above the upper threshold, the gap minimization is activated,
• between the lower threshold and the upper threshold, the gap minimization is activated when the actual value is above the limit value and is deactivated when the actual value is below the limit value.

The object is further achieved according to the invention by a control device for carrying out the method.

The object is finally achieved according to the invention by a gas turbine with such a control device.

The advantages and preferred embodiments set out below with regard to the method can be transferred analogously to the control device and the gas turbine.

In this case, gap minimization means an axial offset of the rotor of the gas turbine against the flow direction, which offset is carried out with the aid of, in particular, the hydraulic means for adjusting the gap between the rotor and the housing. The term HCO is used in the following text for the term gap minimization. The gap minimization or the HCO function can be activated (the rotor is shifted towards the housing) or deactivated.

The term "activated" or "deactivated" does not only mean switching on or off of the HCO, but in the case where the gap minimization is already active, "to be activated" is to be equated with "remain activated". The same applies to an already eliminated gap minimization, in this case "disabled" means "stay disabled".

The invention is based on the consideration to provide a new HCO logic, which is mainly simple and robust, but can minimize the dangers in the operating phases with activated gap optimization. For this purpose, numerous investigations of transient maneuvers were carried out by means of computer simulation, which form the basis for the improved HCO logic.

For the optimized gap setting, an operating parameter is used, with the aid of which the operating state of the Gas turbine is detected. As an operating parameter, for example, the power of the gas turbine, a normalized relative power, temperatures or pressures along the main gas channel or temperature and pressure conditions can be used. The operating parameter is chosen so that it responds to a load change.

The actual value of the operating parameter is continuously recorded, whereby "continuous" includes both the case of a continuous, uninterrupted, direct measurement or calculation from measured data, as well as the case of a direct measurement or calculation from measured data in short time intervals. The currently detected actual value is compared with the lower and upper threshold values, the course of the actual value being subdivided into at least three operating regimes or ranges: a lower, a middle and an upper range.

In addition, a maximum value of the actual value over a period of time in the immediate past is recorded. Based on the maximum value, a limit value is determined, which is used when the actual value is in the middle range between the lower and the upper threshold value.

In the low load range, the gas turbine is usually only operated for a very short time, if at all, because of the pollutant emissions and the low efficiency. Thus, the efficiency in this load range contributes only very negligibly to the overall efficiency over the operating cycle of the machine. In this respect, there is no need to activate the HCO in this difficult environment. For this reason, the lower threshold is defined for the operating parameter. In the lower area, below the lower threshold, therefore, the gap minimization is deactivated or remains deactivated, if it was not already switched on or already switched off.

The analyzes carried out show that in the range of high loads of the gas turbine, in which range the HCO usually is switched on, a tracking or adaptation of the HCO is not required even with load fluctuations. A start from a low-load range is not critical for the use of gap minimization. For this purpose, the upper threshold value for the operating parameter is defined. In the upper area, above the upper threshold, the gap minimization is therefore activated or remains activated, if it was already switched on.

Furthermore, the analyzes show that it is in particular the large load reductions in the middle range, which lead to a transient splitting reduction and should thus be accompanied by an HCO deactivation. In order to detect such large load transients, the ratio of the actual value of the operating parameter to the maximum value of the operating parameter from the immediate past is taken into account. If the difference between the maximum value and the actual value falls below a load-dependent level, which is defined by the limit value, the gap minimization is to be deactivated. Otherwise, the HCO can be activated or remain. In other words, in the middle region between the lower and the upper threshold value for the operating parameter, the HCO function is activated or deactivated as a function of the behavior of the gas turbine in the predefined period of time. For this purpose, the limit of the operating parameter is used, which depends on the maximum value. If the actual value is above the limit, i. between the threshold and the upper threshold, the gap minimization is or remains activated. However, if the actual value is below the limit, i. between the lower threshold and the limit value, the gap optimization is or remains deactivated.

The proposed method results in a very precise activation of the HCO function, whereby several HCO activation hours are obtained during operation of the gas turbine, which has a positive effect on the efficiency of the gas turbine. The method limits the complexity of subdivision of the operating regime of the gas turbine to only three cases. where the HCO logic has to decide if the HCO is turned on or off. The HCO logic described above also provides better match with machine behavior and is independent of active gap measurement.

According to a preferred embodiment of the method is used as the operating parameter, the relative power, which is normalized to the rated power of the gas turbine. The relative power is directly coupled to the absolute power, which is well available in the control of the gas turbine and requires no additional hardware effort to be detected.

According to a further preferred embodiment, the time interval is between a few tens of minutes and a few hours, in particular between 30 minutes and 90 minutes. The time span is due to the reaction time of the turbine and is thus machine-dependent. The period of time is predetermined in particular in the control of the gas turbine.

Preferably, the lower threshold at a relative power is between 30% and 45%. This means that the gap minimization is switched on, only when at least 30% of the rated power of the gas turbine are reached. Below this relative power, it is provided that the HCO function is permanently inactive.

Further preferably, the upper threshold is at a relative power between 50% and 65%. At the latest when 65% of the rated output of the gas turbine is reached, depending on the case, this can also be done at 50% of the nominal power of the gas turbine, the HCO is activated and remains permanently active above the upper threshold.

After a decrease in relative power followed by an increase in relative power, the gap minimization is preferably delayed activated when the actual value exceeds the limit. A time-delayed activation of the HCO prevents a considerable load difference from being bypassed by rapid maneuvers. For this reason, another block of HCO is defined which blocks HCO activation for a period of a few minutes to a maximum of 30 minutes.

In view of a particularly simple machine control, a plurality of steps for the maximum value are defined between the lower threshold value and the upper threshold value, with only consideration being given for the activation or deactivation of the gap minimization, which is the highest stage which was exceeded by the maximum value in the time interval. In this way, no continuous storage of the maximum value is required each time the maximum value is changed. Only when, for example, increases the gas turbine in a higher power level, it is noted that the gas turbine has been operated above this level. Such a procedure represents a further simplification in the determination of the limit value, since thereby the maximum value remains constant over a longer time.

The difference between the limit value and the maximum value is preferably predefined. For practical reasons, the relationship between the maximum value and the limit value is specified in particular in the form of a table. This is perfectly adequate for the application, and very reliable and controllable. It is therefore only necessary to know the maximum value of the operating parameter in order to determine the limit value quickly and without great computational effort. In the case that the middle area is divided into several stages, a difference between the limit value and the maximum value is preferably predefined for each stage. The respective differences are recorded in the table.

According to an alternative embodiment, the difference between the limit value and the maximum value is determined by calculation. This is done in particular according to a formula stored in the control.

In order to achieve maximum efficiency in the operation of the gas turbine with active gap minimization by a maximum temporal utilization of the gap minimization, the method is advantageously carried out continuously during operation of the gas turbine, as soon as the gas turbine is put into operation.

FIG 1

die Aufteilung der relativen Leistung einer Gasturbine in drei Bereiche bezüglich der HCO-Aktivierung, und

FIG 2

einen Ausschnitt vom Verlauf der relativen Leistung der Gasturbine über die Zeit.

An embodiment of the invention will be explained in more detail with reference to a drawing. Herein show:

FIG. 1

the distribution of the relative power of a gas turbine in three areas with respect to the HCO activation, and

FIG. 2

a section of the course of the relative performance of the gas turbine over time.

Like reference numerals have the same meaning in the figures.

In FIG. 1 3 is a graphical representation of the three power ranges into which the power of a gas turbine not shown in detail is subdivided according to the new HCO logic and which is characterized by different operating regimes. On the X-axis, the relative power P _{REL is} plotted, which is formed by a current power, which is normalized by the rated power of the gas turbine. The maximum value of the relative power P _{MAX of} the gas turbine is plotted on the Y axis. The three regions U, M and O on the X-axis are separated by a lower threshold P _U and an upper threshold P _O. Between zero and the lower threshold P _U , the power range is marked with U. Above the upper threshold P _O the power range is marked with O. Between the lower threshold P _U and the upper threshold P _O is the middle region M, in which a limit value P _G is located. The threshold values P _U and P _O are machine-specific and are in the control of the gas turbine, which is included in a control device, not shown, deposited. For example, P _U = 40% and P _O = 60%. These numbers can also be changed if necessary.

The line F, which extends over the middle region M, shows the dependence of the limit value P _G on the maximum value P _MAX . This dependency is stored in the illustrated embodiment in a table, which can be accessed by the controller.

The decision as to whether the HCO is activated or deactivated, or remains active or inactive, is based on the development of an actual value P _{I of} the relative power P _REL . For this purpose, for a period of time which, for example, always corresponds to the last hour, the maximum value P _{MAX of} the actual value P _I (see FIG. 2 ) detected. The time span is also stored in the controller and is machine-specific. The time span can also be shorter than 1 hour (eg the measurements of the relative power P _REL from the last 45 min are used) or even longer (eg 90 min).

If the actual value P _I lies below the lower threshold value P _U in the lower range U, the control switches off the gap minimization or, if the gap minimization is already inactive, it remains switched off.

If the actual value P _{I is} in the upper range O above the upper threshold value P _O , the controller activates the gap minimization or, if the gap minimization is already active, it remains switched on.

In the middle region M, the gap minimization is switched on or off depending on whether the actual value in the range M 'is below the limit value P _G or in the range M "above the limit value P _G. The limit value P _G , as already explained, depends doing so after the maximum value P _{MAX of} the maximum power P _MAX in the last hour.

To simplify the detection of the maximum value P _MAX , several steps can be defined on the Y-axis for the maximum value P _MAX , taking into account for activating or deactivating the gap minimization, which is the highest level that is the maximum value P _MAX in the last hour was exceeded. For example, between 3 and 10 such stages can be defined, which can also be of different sizes. In particular, the line F looks somewhat different for each stage, ie the predefined or calculated difference between the threshold P _G and the maximum value P _MAX can vary from stage to stage.

In addition, a further barrier of HCO can be incorporated which inhibits HCO activation for e.g. Blocked for 15 minutes. The lock engages in particular after a considerable load or. Power increase in the middle range M or in the upper range O, which follows a significant load or power drop in the lower region U.

This case is in FIG. 2 in which the relative power P _REL is plotted against time t. Until the time t ₁ , the actual value P _I is substantially constant and is in the upper power range O, in which the HCO is active. Between t ₁ and t ₃ P _I drops rapidly until a value below the lower threshold P _{U is} reached. When falling below the limit value P _G in the middle region M at the time t ₂ while the gap minimization is turned off. Between t ₃ and t ₄ , the actual value P _I remains in the lower region U and thus the HCO remains inactive. Between t ₄ and t ₇ , the P _I rises steadily, wherein at time t _5, the limit value P _{G is} exceeded again. However, this still does not trigger activation of the HCO in t _5, but the gap minimization takes place only after, for example, a further 15 min, t ₆ at the time, although the actual value of P is _I all the time in the range M ". At the time t ₇ is of the Actual value P _I again at the level of the initial state of the gas turbine according to FIG. 2 ,

If, after activating the HCO, the actual value P ₁ drops again, for example, after t ₄ , this would possibly influence P _MAX from the last hour, which in turn could lead to a new limit value P _G.

Claims (13)

Method for controlling a gap minimization of an adjustable gap between a rotor and a housing of a gas turbine, wherein the gas turbine comprises means, in particular hydraulic means, for a gap adjustment, characterized by
following steps: an actual value (P _I ) of an operating parameter is continuously determined and compared with a lower threshold value (P _U ) and an upper threshold value (P _O ), over a predetermined period of time, a maximum value (P _MAX ) of the actual value (P _I ) is determined, a limit value (P _G ) lying between the lower threshold value (P _U ) and the upper threshold value (P _O ) is determined, the limit value (P _G ) being smaller by a difference than the maximum value (P _MAX ), comparing the actual value (P _I ) with the lower threshold value (P _U ) and the upper threshold value (P _O ), if the actual value (P _I ): is below the lower threshold value (P _U ), the gap minimization is deactivated, - above the upper threshold (P _O ), the gap minimization is activated, - Between the lower threshold (P _U ) and the upper threshold (P _O ) is, the gap minimization is activated when the actual value (P _I ) is above the limit value (P _G ) and is deactivated when the actual value (P _I ) below the limit (P _G ). Method according to one of the preceding claims, wherein as an operating parameter, the relative power (P _REL ) is used, which is normalized to the rated power of the gas turbine. Method according to one of the preceding claims,
wherein the time period in which the maximum value (P _MAX ) is determined, between a few tens of minutes and a few Hours, in particular between 30 min and 90 min. Method according to one of claims 2 or 3,
wherein the lower threshold (P _U ) at a relative power (P _REL ) is between 30% and 45%. Method according to one of claims 2 to 4,
wherein the upper threshold (P _O ) at a relative power (P _REL ) is between 50% and 65%. Method according to one of claims 2 to 5,
wherein after a drop of the relative power (P _REL), which is followed by an increase of the relative power (P _REL), the gap minimization is activated delayed if the actual value exceeds (P _I) to the limit value (P _G). Method according to one of the preceding claims,
wherein a plurality of levels for the maximum value (P _MAX ) are defined between the lower threshold value (P _U ) and the upper threshold value (P _O ), taking into account only the highest level, that of the maximum value, for the activation or deactivation of the gap minimization (P _MAX ) was exceeded in the time span. Method according to one of claims 1 to 7,
wherein the difference between the limit value (P _G ) and the maximum value (P _MAX ) is predefined. Method according to claim 7 and claim 8,
wherein a difference between the limit value (P _G ) and the maximum value (P _MAX ) is predefined for each stage. Method according to one of the preceding claims,
wherein the difference between the limit value (P _G ) and the maximum value (P _MAX ) is determined by calculation. Method according to one of the preceding claims,
wherein during operation of the gas turbine, the process is carried out continuously. Control device for carrying out the method according to one of the preceding claims. Gas turbine with a control device according to claim 12.

Images