EP2606206B1 - Method for controlling a short-term increase in power of a steam turbine - Google Patents

Description

The invention relates to a method for controlling a short-term increase in output of a steam turbine with an upstream fossil-fueled steam generator with a number of a flow path forming, flowed through by a flow medium economizer, evaporator and superheater heating, in which branched off in a pressure stage flow medium from the flow path and the flow medium side is injected before a Überhitzerheizfläche the respective pressure stage in the flow path, wherein a for the deviation of the outlet temperature of the flow medium side last superheater heating surface of the respective pressure stage of a predetermined temperature setpoint characteristic first characteristic value is used as a controlled variable for the amount of the injected flow medium.

A fossil-fueled steam generator produces superheated steam using the heat generated by burning fossil fuels. Fossil fueled steam generators are mostly used in steam power plants, which are mainly used for power generation. The generated steam is fed to a steam turbine.

Analogous to the various pressure stages of a steam turbine, the fossil-fueled steam generator also comprises a plurality of pressure stages with different thermal states of the respectively contained water-steam mixture. In the first (high) pressure stage, the flow medium first passes through economizers on its flow path, using residual heat to preheat the flow medium, and then various stages of evaporator and superheater heating surfaces. In the evaporator, the flow medium is evaporated, then separated any residual moisture in a separator and further heated the remaining steam in the superheater. After that If the superheated steam flows into the high-pressure part of the steam turbine, it is depressurized and fed to the following pressure stage of the steam generator. There it is again superheated (reheater) and fed to the next pressure part of the steam turbine.

Due to a wide variety of external influences, the heat output transferred to the superheaters can fluctuate greatly. Therefore, it is often necessary to control the superheat temperature. Usually, this is usually achieved by an injection of feed water before or after individual Überhitzerheizflächen for cooling, ie, an overflow branches off from the main flow of the flow medium and leads to there arranged injection valves. The injection is usually controlled by a characteristic of the temperature deviations from a predetermined temperature setpoint at the outlet of the superheater, such as, for example, from FR 2 401 380 A1 known.

Modern power plants not only require high levels of efficiency but also the most flexible mode of operation possible. Apart from short start-up times and high load change speeds, this also includes the possibility of compensating for frequency disturbances in the power grid. To meet these requirements, the power plant must be able to provide more power, for example, 5% and more within a few seconds.

Such power changes of a power plant block in the second range are possible only by a coordinated interaction of steam generator and steam turbine. The contribution that the fossil-fueled steam generator can make is the use of its storage, d. H. of the steam but also of the fuel storage, as well as rapid changes of the control variables feedwater, injection water, fuel and air.

This can be done, for example, by opening partially throttled turbine valves of the steam turbine or a so-called Step valve happen, whereby the vapor pressure is lowered in front of the steam turbine. As a result, steam is expelled from the steam storage of the upstream fossil-fueled steam generator and fed to the steam turbine. With this measure, an increase in performance is achieved within a few seconds.

However, a permanent throttling of the turbine valves to provide a reserve always leads to a loss of efficiency, so that for an economic driving the degree of throttling should be kept as low as absolutely necessary. In addition, some types of fossil-fueled steam generators, such. B. forced flow steam generator may have a significantly smaller storage volume than z. B. natural circulation steam generator. The difference in the size of the memory in the method described above has an influence on the behavior of power plant block power changes.

It is therefore an object of the invention to provide a method for controlling a short-term increase in output of a steam turbine with an upstream fossil-fired steam generator of the above type, in which the efficiency of the entire steam process is not excessively impaired. At the same time, the short-term increase in output should be possible without invasive structural modifications to the overall system, regardless of the design of the fossil-fueled steam generator.

This object is achieved according to the invention by reducing the temperature setpoint for the short-term increase in output of the steam turbine and temporarily increasing the characteristic value for the period of the reduction of the temperature setpoint disproportionately to the deviation.

The invention is based on the consideration that additional injection of feedwater can make a further contribution to the short-term rapid change in performance.

By this additional injection in the superheater namely the steam mass flow can be temporarily increased. If, however, an injection is initiated, bypassing the vapor control system normally controlling it, in this case an inadmissibly high drop in the steam temperature upstream of the turbine can not always be avoided. In addition, in the subsequently required reactivation of the complete steam temperature control with more or less severe disturbances of the normal operation of the steam temperature must be expected. For these reasons, it is therefore better to use the active in load mode steam temperature control to provide the short-term power reserve. The injection should therefore be triggered by reducing the temperature setpoint. A jump in the temperature setpoint is linked to a jump in the controller deviation via a corresponding characteristic value, which causes the controller to change the opening degree of the injection control valve. Thus, a power increase of the steam turbine exactly by such a measure, d. H. a sudden reduction of the temperature setpoint, be realized.

However, this power increase and thus also the injection mass flow should be provided as quickly as possible. But damping properties of the control system can be a hindrance that prevent excessively rapid changes in the injection mass flow, which is also desirable for reasons of stability of the scheme in ordinary load operation, but not in a rapidly increasing power to be provided. Therefore, the scheme should be adjusted accordingly in the event of a short-term increase in capacity. This is possible in a particularly simple manner, in which the control signal for the injection mass flow is correspondingly increased, specifically for the period of the desired short-term power increase. For this purpose, the characteristic value for the period of the reduction characteristic of the deviation of the outlet temperature of the last superheater heating surface from the flow medium side from a predetermined temperature setpoint value is obtained of the temperature setpoint increases temporarily disproportionately to the deviation.

In the method described above, a desired-actual comparison between desired and measured steam temperature is made in a corresponding control system via a subtractor. Depending on the control concept used, this signal can be further modified by additional information from the process before it is subsequently connected as an input signal (control deviation), for example, to a PI controller. Advantageously, in addition, the temperature immediately after the injection of the flow medium, d. H. At the entrance of the last superheater heating surfaces, be used as a controlled variable. In such a so-called two-circuit control abrupt changes in the injection mass flow, which are carried out by a controller intervention, damped. Under these circumstances, the fast-intervention-optimized control can be stabilized by preventing overshoot.

For the provision of an immediate reserve on the injection system, however, this damping effect of the dual-circuit control is more of a hindrance. Therefore, it is particularly in the two-circuit control of particular advantage to make the described amplifying adjustment of the characteristic. The regular artificial increase in the deviation of the actual temperature from the predetermined desired value thus produced achieves namely that the subsequent correction by the temperature at the entry of the last superheater heating surfaces, ie immediately after the injection location, is relatively less in the two-circuit control. As a result, a larger control deviation remains, which directly results in a stronger regulator response, ie a greater increase in the injection mass flow, which is desirable in this case. Due to the fact that the characteristic value is temporarily increased disproportionately only for the period of the reduction of the temperature setpoint, the influence of this overshoot disappears again, so that the value set above the setpoint value Steam temperature can really be achieved. Thus, the advantage of the dual circuit control to avoid inadmissible steam temperature drops remains.

In a particularly simple manner, the temporary increase of the characteristic value can be generated by advantageously forming the parameter characteristic for the deviation of the temperature from the desired value from the sum of this deviation and a second characteristic value characteristic of the temporal change of the temperature nominal value. In this case, in a particularly advantageous embodiment, the second characteristic value is essentially the temporal change of the temperature setpoint multiplied by a gain factor. Control technology this is realized by the predetermined steam temperature setpoint is used as the input signal of a differentiating first order and the output of this element is subtracted after appropriate amplification of the difference between the measured and predetermined temperature at the Heizflächenaustritt. As a result, the desired artificial increase in the deviation is realized in a particularly simple manner, and the injection mass flow and thus the additionally released power via the steam turbine are increased much more quickly via the additional differentiating element of the first order.

Due to the differential character, ie the consideration of only the temporal change of the setpoint, the influence of such a control on the overall system decreases over time (disappearance pulse). This means that the differentiator has no further influence on the control deviation and the actual temperature set above the setpoint is also reached. Even in the event that the set point of the steam temperature does not change (the standard case in the usual load operation), such a design has no influence on the rest of the control structure. Thus, in normal load operation, there are no differences in the control behavior of the steam temperature control between the control structure with or without this additional differentiator.

In an advantageous embodiment, a parameter of one of the parameters is determined system-specific. That is, the amount of amplification, the parameters of the differentiating element, etc. should be determined specifically based on the individual equipment concerned. This can be done in advance, for example, with the help of simulation calculations or during the commissioning of the control.

The advantages achieved by the invention are in particular that the targeted reduction of the steam temperature setpoint using the injection control method, the stored in the downstream of the injection metal masses stored thermal energy for a temporary increase in power of the steam turbine can be used. If the adjusted control methods described are used, significantly faster power increases can be achieved with the aid of the injection system in the event of a sudden reduction in the steam temperature setpoint. The method is applicable in each pressure stage either individually or in combination, d. H. both in the live steam (high pressure stage) and in the reheat (medium or low pressure stage).

Due to the integration into the existing steam temperature control system, the lowered temperature setpoint, with good control quality, does not fall significantly below the temperature control after opening the injection fittings. Thus, one becomes inadmissible high temperature drop of the steam at the turbine entry effectively counteracted. Start-up and shut-down processes of control and coordination are also eliminated as the control system can remain permanently active.

In addition, the method for providing a temporary increase in power of the steam turbine is independent of other measures, so that, for example, throttled turbine valves can be additionally opened in order to increase the power increase of the steam turbine yet. The effectiveness of the procedure remains largely unaffected by these parallel measures.

It should be emphasized that with a fixed requirement for additional power, the degree of throttling of the turbine valves can be reduced, the use of the injection system should be used for the power increase. The desired performance release can then be achieved under these circumstances with less, in the best case even completely without additional throttling. Thus, the plant can be operated in the usual load operation, where it must be available for an immediate reserve, with a relatively greater efficiency, which also reduces the operating costs.

Ultimately, the method can also be implemented without invasive structural measures, but merely by additional components are to be provided or implemented in the control system. As a result, higher system flexibility and benefits are achieved at no extra cost.

FIG 1

strömungsmediumsseitig schematisch den Mitteldruckteil eines fossil befeuerten Dampferzeugers mit datenseitiger Verschaltung des Einspritzregelsystems mit Zweikreisregelung zur Nutzung für eine Sofortleistungsentbindung,

FIG 2

ein Diagramm mit Simulationsergebnissen zur Verbesserung der Sofortreserve eines fossil befeuerten Dampferzeugers durch Erhöhung der Einspritzung von Hochdruck-Dampf, Zwischenüberhitzungs-Dampf und jeweils in beiden Drucksystemen in einem oberen Lastbereich, und

FIG 3

ein Diagramm mit Simulationsergebnissen zur Verbesserung der Sofortreserve eines fossil befeuerten Dampferzeugers durch Erhöhung der Einspritzung von Hochdruck-Dampf, Zwischenüberhitzungs-Dampf und jeweils beiden Drucksystemen für einen unteren Lastbereich.

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

FIG. 1

flow medium side schematically the medium-pressure part of a fossil-fired steam generator with data-side interconnection of the injection control system Dual circuit control for use for immediate delivery,

FIG. 2

a graph of simulation results to improve the immediate reserve of a fossil-fired steam generator by increasing the injection of high-pressure steam, reheat steam and in each case in an upper load range in both pressure systems, and

FIG. 3

a graph of simulation results to improve the instantaneous reserve of a fossil fired steam generator by increasing the injection of high pressure steam, reheat steam, and both lower pressure range pressure systems.

Identical parts are provided with the same reference numerals in all figures.

From the fossil-fired steam generator 1 is in the FIG. 1 exemplified the medium-pressure part. Of course, the invention can also be used in other pressure stages. The FIG. 1 schematically represents a part of the flow path 2 of the flow medium M, in particular the superheater 4. The spatial arrangement of the individual superheater 4 in the hot gas duct is not shown and may vary. The illustrated superheater heating surfaces 4 may each represent a plurality of serially connected heating surfaces, which are not shown differentiated due to the clarity.

The flow medium M is before entering the in the FIG. 1 shown relaxed part in the high pressure part of a steam turbine. The flow medium M can then optionally enter a first, not shown superheater heating surface before it reaches the part shown. First, an injection valve 6 is arranged on the flow medium side. Here can cooler and unevaporated flow medium M for control the outlet temperature at the outlet 8 of the medium-pressure part of the fossil-fired steam generator 1 are injected. The introduced into the injection valve 6 amount of flow medium M is controlled by an injection control valve 10. The flow medium M is supplied via a previously branched off in the flow path 2 overflow 12. In the flow path 2, a plurality of measuring devices are further provided for controlling the injection, namely a temperature measuring device 14 and a pressure measuring device 16 after the injection valve 6 and before the superheater heating surfaces 4, and a temperature measuring device 18 after the superheater 4. In FIG.

The remaining parts of the FIG. 1 show the control system 20 for injection. First, a temperature setpoint is set at a setpoint generator 22. This temperature setpoint is connected together with the output of the temperature measuring device 18 after the superheater 4 to a subtractor 24, where thus the deviation of the temperature at the outlet of the superheater 4 is formed by the desired value. This deviation is corrected in an adder 26, the correction modeling the time delay of a temperature change as it passes through the superheater heating surfaces 4. For this purpose, the temperature at the entrance of the superheater heating surfaces 4 from the temperature measuring device 14 is switched to a time-delaying PTn element 28 which is fed to the adder 26 on the input side. The output of the adder 26 is switched to a maximum member 30 and in the further course together with the signal of the temperature measuring device 14 to a subtractor 32nd

In the maximum member 30 on the input side, another parameter is taken into account, namely that the temperature should have a certain distance to the pressure-dependent boiling temperature. For this purpose, the pressure measured at the pressure measuring device 16 is switched into a functional element 34 that outputs the boiling temperature of the flow medium M corresponding to this pressure. In an adder 36, a preset constant is output a transmitter 38 added, which may be for example 10 ° C and ensures a safe distance to the boiling line. The thus determined minimum temperature is given to the maximum member 30. The signal detected in the maximum element 30 is applied via the subtractor 32 to a PI control element 40 for controlling the injection control valve 10.

In order to be able to use the injection system not only to regulate the outlet temperature but also to provide an immediate power reserve, it comprises corresponding means for carrying out the method for regulating a short-term power increase of a steam turbine. First of all, the temperature setpoint at the setpoint generator 22 is reduced, which results in an increase in the injection quantity. However, in order for it to lead directly to an increase in power, a fast controller response of the PI control element 40 should be ensured. However, the caused deviation of the actual temperature from the temperature target value is alleviated by the PTn member 28 shortly after the change.

In order to prevent this in the case of a desired rapid power increase, the signal of the desired temperature setpoint generator 22 is switched to a first-order differentiator (DT1). For this purpose, a PT1 element 42 is acted on the input side with the signal of the setpoint generator 22 and the output side connected together with the original signal of the setpoint generator 22 to a subtractor 44 whose output is connected to a multiplier 46, the signal by a factor, for. B. 10 amplified from a transmitter 48. This signal is given via the adder 50 in the signal of the temperature deviation from the subtractor 24. In the case of a change in the setpoint, the interconnection via the PT1 element 42 generates a signal which is different from zero and which is amplified by the multiplier 46 and artificially disproportionately amplifies the characteristic value characteristic of the deviation. The signal via the interconnection of the PTn element 28 is then relatively smaller and a faster controller response of the PI controller element 40 is forced. Thus, an increase in steam quantity is achieved quickly and the power of the downstream steam turbine is increased.

FIG. 2 now shows a diagram with simulation results using the described control method. Plotted is the percent additional power versus full load 52 vs. time 54 in seconds after a 20 ° C sudden drop in the setpoint temperature set point 22 for the respective stage of a fossil fired steam generator with high pressure and intermediate superheat or medium pressure stage at 95% load. As already mentioned, the circuit described above can be used with the PT1 element 42 for the disproportionate amplification of the characteristic value characteristic of the deviation in both stages. The curves 56 and 58 show the results for a modification of the high-pressure part, the curves 60 and 62, the results for a modification of reheat and the curves 64 and 66, the results for a modification of both stages. In this case, the curves 56, 60 and 64 each show the results without PT1 element 42, ie according to the usual control system, the curves 58, 62 and 66 respectively the results with PT1 element 42 connected as described above.

In FIG. 2 It can be seen that the maxima of the curves 58, 62 and 66 are arranged on the one hand higher and farther left than their respective corresponding curves 56, 60 and 64. The additional unbound power is therefore higher, on the other hand, it is available faster. The acceleration is less pronounced in the curves 60, 62 of the reheat, but a significant relative increase in performance is recognizable, albeit at a completely lower level than in the high-pressure part.

FIG. 3 is opposite FIG. 2 only slightly modified and shows the simulated curves 56, 58, 60, 62, 64, 66 for 40% load, all other parameters coincide FIG. 2 the same applies to the curves 56, 58, 60, 62, 64, 66.

Here, in particular, the unmodified curves 56, 60, 62 show a much flatter course than in FIG. 2 That is, an even slower controller response of the PI controller 40 can be seen. Due to the described interconnection of the PT1 member 42 in the high pressure part, the maximum of the curve 58 is further left and higher than curve 56, so it is a faster and higher performance increase achieved. However, the curve 58 remains relatively flat.

The modification of the reheat, shown in trace 62, shows a similar behavior, but in addition shows a comparatively high power increase about 60 seconds after changing the setpoint, which then drops rapidly thereafter, to go to the maximum of the flat course. This increase in performance is also evident in a modification of both pressure levels after curve 66 in comparison to curve 64.

A steam power plant equipped with such a fossil-fueled steam generator 1 is capable of rapidly increasing the output via an instant power output of the steam turbine, which serves to support the frequency of the composite power network. The fact that this power reserve is achieved by a double use of injection fittings in addition to the usual temperature control, a permanent throttling of the steam turbine valves to provide a reserve can be reduced or eliminated, whereby a particularly high efficiency is achieved during normal operation.

Claims (5)

1. Method for controlling a short-term increase in power in a steam turbine comprising a fossil-fired steam generator (1) arranged upstream having a plurality of economiser, evaporator and super heater heating surfaces (4), which form a flow path (2) and through which a flow medium (M) flows, in which flow medium (M) is tapped off from the flow path (2) in a pressure stage and is injected into the flow path on the flow-medium side upstream of a super heater heating surface (4) of the respective pressure stage, a first characteristic value, which is characteristic of the deviation between the outlet temperature of the final super heater heating surface of the respective pressure stage on the flow medium side and a predetermined nominal temperature value, being used as a controlled variable for the amount of injected flow medium (M),
   wherein, in order to achieve a short-term increase in power of the steam turbine, the nominal temperature value is reduced and, for the duration of the reduction in the nominal temperature value, the characteristic value is temporarily increased over-proportionately to the deviation.
2. Method according to claim 1, wherein, in addition, the temperature directly downstream from the point of injection of the flow medium M is used as a controlled variable for the amount of injected flow medium M.
3. Method according to one of the preceding claims, wherein the first characteristic value is made up of the sum of the deviation and a second characteristic value that is characteristic of the change over time in the nominal temperature value.
4. Method according to claim 3, wherein the second characteristic value is essentially the change over time in the nominal temperature value multiplied by an amplification factor.
5. Method according to one of the preceding claims, wherein a parameter for one of the characteristic values is determined in a plant-specific manner.

Images