EP1252417B1 - Method for operating a turbine - Google Patents

Abstract

According to the invention, the thermal load to which a turbine (4) is subjected is kept within an acceptable range by monitoring the change in temperature (T) of the medium that is supplied to the turbine (4), especially fresh steam, over time. An emergency trip for the supply of fresh steam to the turbine (4) preferably takes place if a maximum temperature gradient (dT/dt(max)) is exceeded.

Description

The invention relates to a method for operating a turbine and a turbine plant.

In industrial plants, for example in plants for power generation, a gaseous medium is supplied to drive a turbine this. The turbine is usually connected to a generator for generating electrical energy or drives, for example, a compressor or a pump. In a steam turbine, the gaseous medium is live steam. This live steam is heated in a boiler upstream of the turbine before it is fed to the turbine.

In document D1- US-A-4 655 041 (DEL VECCHIO RICHARD J ET AL) April 7, 1987 (1987-04-07) describes a method and apparatus for detecting and evaluating undesirable temperature and pressure changes. The temperature and pressure of a steam flowing into a turbine are cyclically measured and compared with predetermined values. If the specified values are exceeded, an alarm is issued. A first alarm occurs when the temperature exceeds a predetermined maximum temperature or falls below a minimum temperature or the pressure exceeds a maximum pressure or falls below a minimum pressure. Between the maximum temperature and the minimum temperature is the permissible temperature range. The permissible pressure range is between a maximum pressure and a minimum pressure.

A second alarm occurs when the temperature and pressure are outside the allowable temperature range or pressure range and the temperature change or pressure change exceeds a predetermined value.

A third alarm occurs when the temperature and pressure are outside the allowable temperature range or pressure range and the temperature change or pressure change exceeds a predetermined maximum value.

The object is achieved according to the invention by a method for operating a turbine, in particular a steam turbine, to which a gaseous medium is supplied, wherein the temporal change of the temperature of the medium is monitored.

The monitoring of the change in temperature, ie the observation of the course of the temperature gradient, is based on the consideration that too fast a temperature change - even if it is within the permitted temperature range between the absolute limits - can lead to damage to the turbine. For a too rapid change in temperature or the occurrence of temperature jumps occur under certain circumstances, material problems that have a detrimental effect in particular on the efficiency of the turbine, and possibly lead to cracks and material failure. Compared to conventional methods, which merely monitor whether the temperature exceeds a specified absolute limit, a significantly improved protective function is achieved.

The monitoring of the temperature change thus opens up the possibility of taking appropriate precautionary measures even if the temperature change is too great or too fast.

Preferably, when a maximum temperature gradient is exceeded as a measure of the temporal change in temperature, the supply of the medium to the turbine is interrupted by a quick-closing is performed. The method thus allows a certain value for the temperature change. If this value is exceeded, in particular for a longer time, the supply of live steam is prevented in order to protect the turbine from too great a thermal load.

In a preferred embodiment, the maximum allowable temperature gradient is determined as a function of the load state of the turbine, in particular such that with increasing Load the maximum permissible temperature gradient becomes smaller. This is based on the consideration that at low load conditions, the heat transfer from the live steam to the material of the turbine is low, in particular due to the lower density and the low speed of the live steam. Therefore, in the low load range higher temperature gradients are allowed without the risk of damaging the turbine.

Conveniently, in addition to monitoring the temperature change, the supply of the medium to the turbine is interrupted when an absolute threshold for the temperature is exceeded. It is therefore given a permissible absolute temperature range within which the live steam temperature may move.

In order to keep the effort necessary for monitoring low, it is advantageously provided to poll the actual value of the current temperature of the live steam cyclically. From the comparison of successive actual values, the temperature change and the temperature gradient are determined.

In a particularly advantageous embodiment, a dynamic limit value is determined as a function of the actual value, which changes with the temperature profile, but at most within the maximum temperature gradient. Defining the dynamic limit thus defines a temperature range within which temperature fluctuations are permitted. The dynamization takes into account permitted temperature changes, for example a steady rise during startup. This avoids the risk of a faulty triggering of the protective function.

Since temperature changes can occur in both directions, it is preferable to set lower and upper dynamic limits. In this case, the limit values are advantageously set such that they correspond to a defined one Temperature value are spaced from the actual value. The defined temperature value thus indicates a fixed temperature range between the actual value and the upper dynamic or the lower dynamic limit, if no extraordinary temperature changes occur. If temperature gradients exceed the maximum permissible temperature gradient, the distance from the actual value to one of the dynamic limit values decreases visibly until it finally exceeds the limit value. The actual value curve therefore intersects the curve of the dynamic limit value when the maximum temperature gradient is exceeded.

Advantageously, exceeding the dynamic limit value is used as an indication of an impermissible temperature change, and the supply of the medium to the turbine is interrupted.

In order to prevent the protective function from being triggered too quickly, for example due to short-term electrical effects, after the dynamic or also the absolute limit value has been exceeded, the supply of the medium to the turbine is only set if the dynamic or the absolute limit value after at least one further limit Control query cycle is still exceeded. Thus, by waiting at least one further control poll cycle, a certain time buffer is inserted.

Preferably, after the dynamic or the absolute limit value has been exceeded, the interrogation cycle is shortened, ie the temperature measurement is repeated at shorter intervals. Thus, the polling frequency of the temperature is adapted to the demand in an advantageous manner, ie, in a normal course, the temperature is comparatively rare and in a critical course, the temperature is queried more frequently.

In an expedient embodiment, it is provided, when starting the turbine and / or after an error in the monitoring of the temperature profile, to use the first newly measured actual value of the live steam temperature to determine the dynamic limit value. This ensures a reliable mode of operation of the protective function set up with the monitoring of the temperature change, and it is avoided that, for example, the last measured actual value is stored before switching off the turbine and used to determine the dynamic limit values. Because this would inevitably trigger the protection function and thus switching off the live steam supply when restarting the turbine when the stored actual value of the current actual value is significantly different. As a criterion for switching on the protective function, the closing of a generator switch in a generator turbine and the exceeding of the lowest drive speed in a drive turbine are advantageously used.

In order to alert the operating personnel to a possible danger even in the event of unusual temperature changes, a warning message is advantageously issued when the actual value approaches the dynamic and / or the absolute limit value. This warning message is issued, in particular, when the actual value has approached one of the limit values up to a predetermined distance. The warning message is audible and / or visual, for example.

In order to enable the earliest possible triggering of the protective function, the temperature profile of the medium is monitored before the medium enters the turbine, in particular in the region of a boiler upstream of the turbine or already directly behind a so-called steam collector. In the case of an impermissible temperature change, therefore, the quick-closing before the too cold or too hot steam reaches the turbine.

Preferably, the protection mechanism, ie the possibility of preventing the supply of the medium to the turbine, can only be activated when the turbine is operated under a predetermined load. Thus, the protective function is not activated especially when starting the turbine. This does not compromise safety, as it and the low-load operation, the risk of damage due to temperature changes is relatively low.

The object is further achieved by an unpriced turbine system with a turbine operable with a gaseous medium, with a temperature sensor for detecting the temperature of the medium, and with a protective device for determining the temperature profile and for interrupting the supply of the medium to the turbine at a temperature gradient is exceeded ,

The advantages and expedient embodiments mentioned with regard to the method are to be transferred analogously to the turbine installation.

FIG 1

eine Turbinenanlage in einer grob vereinfachten schematischen Darstellung,

FIG 2 bis 5

unterschiedliche Temperaturverläufe der Frisch- dampftemperatur mit den Kurven der zugehörigen dynamischen Grenzwerte, und

FIG 6

die Abhängigkeit eines maximal zulässigen Tempe- raturgradientens vom Lastzustand der Turbine.

An embodiment of the invention will be explained in more detail with reference to FIGS. Show it:

FIG. 1

a turbine plant in a roughly simplified schematic representation,

FIGS. 2 to 5

different temperature curves of the fresh steam temperature with the curves of the associated dynamic limit values, and

FIG. 6

the dependence of a maximum permissible temperature gradient on the load condition of the turbine.

The turbine plant 2 according to FIG. 1 comprises a turbine 4, in particular a steam turbine, which is connected via a shaft 6 to a generator 8 for generating electrical energy. The turbine is driven by a gaseous medium, in particular live steam. The live steam is in one Boiler 10 generated and fed from there via a steam line 12 of the turbine 4. The steam line 12 can be shut off via a valve 14, in particular a quick-acting valve. The turbine system 2 further comprises a protective device 16 and a temperature sensor 18, which in the embodiment according to FIG. 1 is attached directly to the steam line 12 directly in the area of the boiler 10. The protective device 16 is connected via a data line 20 to the temperature sensor 18 and via a control line 22 to the valve 14 in connection. If necessary, the turbine protection is activated via the control line 22 by triggering a quick closing.

The temperature sensor 18 serves to detect an actual value I of the temperature T of the live steam. The measured actual value I is transmitted to the protective device 16 where it is stored and evaluated. The actual value I is cyclically interrogated by the protective device 16, the period of the interrogation cycle being, for example, 6 seconds. The temporal profile of the temperature T of the live steam thus detected by the protective device 16 is preferably visually displayed via a display 24, in particular a screen or a digital measuring device. Depending on the change in the measured actual value I over time, that is, as a function of the temperature gradient dT / dt determined from the measured actual values I, the protective device 16 decides whether the valve 14 is actuated. Preferably, a quick-closing is triggered in the actuation case, so that the turbine 4 is cut off from the live steam supply. The quick closure of the valve 14 serves to protect the turbine from thermal damage, for example in the form of cracks due to excessive temperature changes. The quick-closing is also activated when the measured actual value I exceeds or falls below an absolute limit. With such a monitoring of the temperature T, a high protection function for the turbine 4 is provided.

So that the measured actual value I corresponds as far as possible to the actual temperature T of the live steam, the temperature sensor 18 is designed as a fast thermocouple, which is characterized in that it is mounted with its metal contact directly on a so-called dip tube of the steam line 12. Differences caused by systematic measurement errors between the measured actual value I and the actual temperature T are preferably automatically corrected by the protective device 16. In the following it will be assumed for the sake of simplicity that the measured actual value I corresponds to the actual temperature T.

The internal decision process within the protection device 16 will be described below with reference to FIG FIGS. 2 to 5 explained in more detail. In the figures, the temperature T is plotted against the time t in each case. A total of three temperature profiles are plotted in the illustration, namely the temperature curve 28 of the temperature T of the live steam and an upper dynamic limit curve 30 and a lower dynamic limit curve 32. The temperature curve 28 is formed from a number of discrete actual values I detected by the control device 16 , and one of which is exemplified. Each measured actual value I is assigned an upper dynamic limit value OG and a lower dynamic limit value UG. The individual discrete dynamic limit values OG, UG form the two dynamic limit value curves 30, 32.

• Fall A: Der Istwert I ist kleiner als der obere Grenzwert OG bzw. größer als der untere Grenzwert UG. Es erfolgt eine Neufestlegung der dynamischen Grenzwerte OG,UG.

To monitor the temperature T of the live steam, the following procedure is used for each polling cycle: the measured actual value I is compared with the dynamic limit values OG, UG:

• Case A: The actual value I is smaller than the upper limit value OG or greater than the lower limit value UG. A redefinition of the dynamic limit values OG, UG takes place.

In the case of the upper limit value OG, this occurs in that, on the one hand, the newly measured actual value I is added to a defined temperature value X. On the other hand, the previous upper limit OG is increased by a change value Y.

In order to determine the new upper limit value OG, the sum (I + X) of the actual value I and the temperature value X is compared with the sum (OG + Y) from the previous upper limit value OG and the change value Y with one another. The lower sum value is defined as the new upper limit OG.

Similarly, the lower limit value UG is determined with the proviso that the temperature value X is subtracted from the actual value I and the change value Y is subtracted from the lower limit value UG, and that the larger sum value is set as the new lower limit value UG.

The change value Y is based on the maximum permissible temperature gradient dT / dt (max) of the temperature T of the live steam. Namely, the change dY / dt of the change value Y corresponds to the maximum temperature gradient dT / dt. The maximum temperature gradient dT / dt (max), for example, a value of 3K / min is used. For a polling cycle of preferably 6 sec, this corresponds to 0.3K / polling cycle. In this case, the change value Y is 0.3K.

The limit value curves 30, 32 determined according to this specification form a permitted temperature band 34, within which the temperature curve 28 can vary, without triggering a quick closing. This temperature band 34 is dynamic and follows the course of the temperature curve 28. Only in the case of very rapid and permanent temperature changes does the temperature curve 28 run out of the permitted temperature band 34. This leads to case B, in which the actual value I is above the upper limit value OG or below the lower limit value UG. It is preferably carried out after a control phase automatic activation of the quick closing of the valve 14. This is in detail to FIG. 3 explained in more detail.

According to the FIG. 2 the temperature curve 28 has two points of discontinuity with an otherwise horizontal course. The temperature T jumps once abruptly and drops once abruptly. After the increase, the temperature curve 28 first moves close to the upper dynamic limit curve 30, which according to the algorithm described above gradually shifts to higher temperature values, until it is finally again spaced by the temperature value X from the temperature curve 28. The rise of the upper limit curve 30 is determined by the time course of the change value dY / dt. In contrast to the upper limit curve 30, the lower limit curve 32 immediately follows the jump of the temperature curve 28, ie the lower limit curve 32 also has a jump. This results from the fact that the actual value I minus the temperature value X is decisive for the calculation of the new lower limit value UG. In a jump with the opposite sign, ie with a sudden drop in the temperature curve 28 for the limit curves 30,32 the same applies, with the proviso that now the lower limit curve 32 is gradually shifted to lower temperature values and the upper limit curve 30 is abruptly pulled down ,

According to FIG. 3 , on the basis of which the case B, ie the triggering of the protective function is explained, the temperature curve 28 is divided into four subregions. Within these subregions, the temperature gradient dT / dt becomes increasingly greater and in the fourth subregion exceeds the maximum temperature gradient dT / dt of 3K / min. It can be seen that the limit curves 30, 32 follow the temperature curve 28 initially, while maintaining the distance around the temperature value X, until the temperature gradient dT / dt in the fourth partial region becomes too great. The temperature curve 28 then runs out of the temperature band 34 and cuts the lower limit curve 32 a time t1. Once this is done, advantageously the polling cycles are shortened, for example, from 6sec to 2sec. If, after three further short cycles, the actual value I is still below the limit value curve 32, a rapid closure takes place at the time t2. Waiting for further control cycles with a smaller polling cycle ensures that no single event, such as a measurement error or other electrical impact, will trigger the trip.

According to the FIGS. 4 and 5 Further typical temperature curves 28 with the corresponding curves of the limit curves 30 and 32 are shown. How out FIG. 5 can be seen, has a sudden alternating change in the temperature curve 28 with the result that the temperature band 34 is visibly narrowing. Only when the temperature curve 28 again assumes a continuous course, the temperature band 34 expands, so that the threshold curves 30,32 are spaced from the temperature curve 28 by the temperature value X.

In FIG. 5 In addition to the dynamic limit curves 30, 32, an upper absolute limit value OA and a lower absolute limit value UA are shown as bold lines. Again FIG. 5 Furthermore, the temperature curve 28 intersects the horizontal line representing the upper limit value OA at a time t3, which leads to the triggering of the quick closing. In addition to monitoring the temperature gradient dT / dt, the protective device 16 therefore also monitors whether the temperature T of the live steam exceeds or falls below the absolute limit values OA and UA.

According to FIG. 6 the maximum temperature gradient dT / dt (max) decreases with increasing load state L. Preferably, the maximum temperature gradient dT / dt (max) at very low load state L is about 10k / min and drops linearly to about 3K / min in full load operation. The load state L is in FIG. 6 specified as relative size between 0 and 1. This dependence the maximum temperature gradient dT / dt (max) is possible without loss of security, since during low load operation, the heat transfer from the live steam to the turbine 4 is lower than in full load operation. Preferably, in a simplified embodiment, the maximum temperature gradient dT / dt (max) is set to the minimum value independent of the load state L.

Claims (10)

1. Method for operating a turbine (4), in particular a steam turbine, to which a gaseous medium is supplied, the change with time of the temperature (T) of the medium being monitored and in which the supply of the medium to the turbine is interrupted when a maximum temperature gradient dT/dt(max) is exceeded, characterized in that the maximum permissible temperature gradient dT/dt(max) is specified as a function of the load condition (L) of the turbine (4) and, in fact, in such a way that the maximum permissible temperature gradient (dT/dt(max)) becomes smaller with increasing load condition (L).
2. Method according to Claim 1, in which a dynamic limiting value (UG, OG) is specified as a function of an actual value (I) of the current temperature (T), which dynamic limiting value (UG, OG) changes with the variation of the temperature but, as a maximum, within the compass of the maximum temperature gradient (dT/dt(max)).
3. Method according to Claim 2, in which a lower dynamic limiting value (UG) and an upper dynamic limiting value (OG) are specified.
4. Method according to Claim 2 or 3, in which the dynamic limiting value (UG, OG) is specified as differing from the actual value (I) by a defined temperature value (X).
5. Method according to one of Claims 2 to 4, in which the supply of the medium to the turbine (4) is interrupted when the dynamic limiting value (UG, OG) is exceeded.
6. Method according to Claim 5, in which, after the dynamic limiting value (UG, OG) or the absolute limiting value (UA, OA) has been exceeded, the supply of the medium to the turbine (4) is only interrupted when the dynamic limiting value (UG, OG) or the absolute limiting (UA, OA) value continues to be exceeded after at least one further control scanning cycle.
7. Method according to Claim 6, in which the scanning cycle is shortened after the dynamic limiting value (UG, OG) or the absolute limiting value (UA, OA) has been exceeded.
8. Method according to one of Claims 2 to 7, in which the first newly measured actual value (I) is used to determine the dynamic limiting value (UG, OG) in the case of a starting procedure of the turbine (4) and/or after a fault in the monitoring of the temperature variation.
9. Method according to one of Claims 2 to 8, in which an alarm occurs when the actual value (I) approaches the dynamic limiting value (UG, OG) and/or the absolute limiting value (UA, OA).
10. Method according to one of Claims 2 to 9, in which the supply of the medium to the turbine (4) can only be shut off when the turbine (4) is operated above a specified load condition (2).

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