EP0544615B1 - Method of operating a once-through steam generator with low load recirculation - Google Patents

Method of operating a once-through steam generator with low load recirculation Download PDF

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Publication number
EP0544615B1
EP0544615B1 EP92810857A EP92810857A EP0544615B1 EP 0544615 B1 EP0544615 B1 EP 0544615B1 EP 92810857 A EP92810857 A EP 92810857A EP 92810857 A EP92810857 A EP 92810857A EP 0544615 B1 EP0544615 B1 EP 0544615B1
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Prior art keywords
separator
level
economizer
valve
water
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EP92810857A
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German (de)
French (fr)
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EP0544615A1 (en
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Christoph Dr. Ruchti
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ABB AG Germany
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ABB Management AG
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B35/00—Control systems for steam boilers
    • F22B35/06—Control systems for steam boilers for steam boilers of forced-flow type
    • F22B35/10—Control systems for steam boilers for steam boilers of forced-flow type of once-through type
    • F22B35/101—Control systems for steam boilers for steam boilers of forced-flow type of once-through type operating with superimposed recirculation during starting or low load periods, e.g. composite boilers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B35/00—Control systems for steam boilers

Definitions

  • the invention relates to a method for operating a once-through steam generator with low-load circulation and the following elements: feed pump, feed line, economizer, evaporator, water separator and at least one superheater, and with a circulation line connected to the water outlet of the separator and a circulation pump between the feed pump and the economizer.
  • the amount of food supplied to the steam generator is set in the upper load range as a function of the steam temperature and in the lower load range as a function of the water level in the water separator, either by changing the speed of the feed pump or by adjusting the Flow cross-section of a feed valve.
  • a switchover device was provided in the signal flow behind the steam temperature controller or the water level controller.
  • the measured superheat at the inlet of the first superheater can be used as a criterion for the switchover (CH-PS 673 697).
  • This switchover can also take place due to a race between two always active controllers (DE-B 2 149 127).
  • the level controller can only bring about a reduction and the temperature controller can only increase the feed quantity.
  • a purely load-dependent switchover criterion is often used, e.g. the feed pressure of the feed pump (CH-PS 517 266). Switching the controller is This is not always an advantage, since major changes in the supply of working fluid to the economiser can occur when switching. This is due to the fact that the signal coming from the temperature controller and the signal coming from the water level controller are not of the same size when switching and do not have to have the same sign, depending on whether the water level in the separator was rising or falling or at what height he was just now.
  • the invention has for its object to improve an operating method for a once-through steam generator with the elements listed above so that switching in the aforementioned manner is omitted.
  • the amount of food is always set so that a desired flow through the economizer results.
  • This desired flow through the economiser is formed as a function of the steam temperature, whereby a minimum flow must never be undercut, so that operation with a wet separator takes place with a fixed, minimal flow through the economiser.
  • the water level in the water separator is not - as before - influenced by changing the quantity of food, but by the valve located behind the circulation pump in the direction of flow of the working fluid. In this way, the previous switching is avoided without giving up the great advantage of the solution according to CH-PS 673 697 in comparison with even earlier methods, for example according to CH-PS 517 266.
  • An otherwise conventional valve which is arranged in the circulation line between the water separator and the circulation pump and serves the level control in the separator, does not have to be throttled because of the level control, so that no vapor bubbles can occur at the mixing point of the circulation water with the feed water. In this way, no cavitation can occur in the circulation pump.
  • the once-through steam generator with low-load circulation has an economizer 1, an evaporator 2, a water separator 3 and a superheater 4, which are connected in series in the direction of the working fluid flow.
  • a feed pump 5 is provided, which is connected via a feed line 6 to the inlet of the economizer 1.
  • a measuring device 7 for the amount of water flowing through the economizer is arranged in the line 6 near the inlet of the economizer 1.
  • the quantity measuring device 7 is connected to a comparison point 9 via a signal line 8 connected, which is also connected via a signal line 16 to the output of a feed control device 11, which is designed as a status controller with an observer and is described in the applicant's patent application No.
  • the feed control device 11 receives a temperature measurement signal which represents the actual value of the steam temperature and is taken off by means of a measuring device 13 at the outlet of the superheater 4. Further superheaters can be provided downstream of the measuring device 13 before the steam is supplied to consumers, not shown. The measuring device 13 can also be arranged between the water separator 3 and the superheater 4. Via a signal line 14, the feed control device 11 receives a target value for the steam temperature and via a signal line 15 a signal which represents the minimum amount of working fluid which has to flow through the economizer 1.
  • the minimum quantity signal becomes effective when the quantity of working fluid flowing through the economizer 1 drops to the minimum quantity, which is approximately 30% of the full load, during a load reduction.
  • the comparison point 9 belongs to a controller 17, the output of which is connected via a signal line 18 to the feed pump 5, which forms the actuator of the feed control loop.
  • the controller 17 can e.g. be designed as a PI controller.
  • a circulation line 20 is connected to the water outlet of the water separator 3 and contains a check valve 21 and a shut-off valve 22 one after the other in the flow direction.
  • the line 20 opens at 19 downstream of the feed pump 5 into the feed line 6, which contains a circulation pump 23 and a level control valve 24 below this mouth 19.
  • the the circulation pump 23 and the section 6 'of the feed line 6 containing the level control valve 24 is therefore also flowed through by water from the separator 3 during operation with a wet separator in addition to the feed water.
  • a line 25 with a non-return flap 26 is provided parallel to the line section 6 'and a portion of the quantity of feed conveyed by the feed pump flows through when the steam generator is under high load.
  • an injection water line is designated, which leads in a known, not shown manner to the superheater 4 or to some downstream superheaters.
  • a line 30 with a drain valve 31 which leads to a feed water tank (not shown) of the steam generating system.
  • the line 30 can also lead into the condenser or a special tank of the system.
  • a level control device 33 which, like the feed control device 11, is designed as a state controller with an observer.
  • the level control device 33 receives a measurement signal via a signal line 34, which represents the actual value of the water level in the separator 3.
  • the setpoint for the water level is supplied to the level control device 33 via a signal line 35.
  • the shut-off valve 22 is subject to a control signal which comes from the level control device 33 via a signal line 20 and whose function is described below.
  • the drain valve 31 is subordinate to a level measurement signal, which is taken from the signal line 34 and passed over a signal line 32 and whose function is also explained further below.
  • the water level 7.7 m is the target water level for the level control device 33 during normal circulation operation of the steam generator system.
  • the water levels of 1 m and 3 m play a role in the transition from operation with a wet separator to operation with a dry separator and vice versa, while the water levels of 10.7 m and 14.2 m play a role in the first start-up phase of the steam generator.
  • the drain valve 31 opens under the influence of the level measurement signal in the line 32 until it is 100% open at the mark 14.2 m , as shown in Fig.2a in the middle by the line B.
  • the shut-off valve 22 goes from the opening cross-section 100% to the closed position 0% and when the water level mark 3 m is reached, it opens from 0% to 100%, as indicated by the two horizontal lines C in FIG. 2a.
  • the valve movements of the level control valve 24 at the water levels 1 m and 3 m are shown on the right in FIG. 2a by the two horizontal lines D, the dashed line showing the influence of the fully automatic control when operating with a wet separator.
  • the system described is operated as follows. In normal operation, ie above the minimum flow rate for the economizer 1, ie above approximately 30% of the full load, the feed quantity supplied to the forced-flow steam generator is conveyed by the feed pump 5 as a function of the steam temperature, which is measured by means of the measuring device 13. In the feed control device 11, this actual value of the temperature is compared with the setpoint value of the temperature supplied via the signal line 14 compared and processed to an output signal, which is fed as a setpoint for the flow rate in the economizer 1 via the signal line 16 to the comparison point 9. The measurement point for the flow rate is fed as an actual value to the comparison point 9 via the signal line 8.
  • a control signal is then generated in the controller 17 subordinate to the device 11, which adjusts the speed of the feed pump 5 via the signal line 18, namely with increasing steam temperature in the direction of a larger quantity of food and with decreasing steam temperature in the direction of a reduced one Amount of food.
  • superheated steam reaches the separator 3, so that no saturated water is returned to the economizer 1 via the circulation line 20.
  • the separator 3 is in dry operation, ie the water level in the separator is very low and the level control device 33 should actually keep the level control valve 24 in the fully closed position.
  • the circulation pump 23 is always to be flowed through in order to avoid that after a longer standstill of this pump temperature shocks occur in it when it resumes circulation operation.
  • the level control valve 24 remains fully open in the operating phase described and the circulating pump 23, which is switched off above 50% load, is flowed through by part of the feed quantity conveyed by the feed pump 5, while the remaining feed quantity is fed via line 25 to the economizer 1 flows.
  • An empty running of the separator 3 is prevented by the shut-off valve 22, which is then in the fully closed position, as is the drain valve 31.
  • the transition from dry to wet operation of the separator takes place as follows:
  • the level control valve 24 and the shut-off valve 22 have the position just described, i.e. they are in the ready position (area E in Fig. 2b) and the water level in the separator 3 is below 3 m.
  • the water level in separator 3 increases (see curve H in Fig. 2b).
  • the opening cross section of the level control valve 24 is reduced to 31% by a first sequence of control commands programmed into the level control device 33 (compare area F in FIG. 2b).
  • shut-off valve 22 is moved to the full opening area by the control commands (end of area F), whereupon they switch the level control device 33 into automatic control mode (area G in FIG. 2b), ie it adjusts the level control valve 24 so that the setpoint for the water level, which is 7.7 m, is maintained.
  • the level control device 33 reduces the opening cross section of the level control valve 24, so that the circulating quantity decreases in step with the inflow of saturated water into the separator 3 and the level in the separator remains constant .
  • the circulation volume is therefore automatically reduced to zero.
  • safe forced operation e.g. with a load of 50% of the At full load
  • the operating team switches off the circulation pump 23.
  • the control logic of the control device 33 then closes the shut-off valve 22 and opens the level control valve 24 completely, so that the circulation pump 23 passively receives a small flow that is sufficient for keeping it warm.
  • Fig. 2c forms a safety circuit that guarantees that steam is never circulated. If violent transients occur, it could happen that the level control device 33 reacts too slowly and that the level in the separator 3 temporarily drops below the mark of 1 m.
  • a second sequence of control commands is programmed into the control device 33.
  • the shut-off valve 22 closes immediately by these control commands (area I in FIG. 2c).
  • the level control device 33 leaves the automatic control mode and the control commands open the level control valve 24 to the maximum permitted value (area K in FIG. 2c). The system is thus ready to automatically take over the automatic control operation if the level in the separator 3 rises again.
  • the level control device 33 can then not regulate satisfactorily.
  • the level control device 33 according to FIG. 3 is modified in that it additionally receives an input signal PE and a pilot signal FF are applied.
  • the lines 25 and 30 and the check valve 21, the shut-off valve 22 and the drain valve 31 with the signal line 29 have been omitted for clarity.
  • the input signal PE is formed from the difference between the pressure PA in the separator 3 and the pressure PS on the delivery side of the feed pump 5.
  • An increase in the delivery pressure PS causes a change in the signal PE in the pre-circuit of the level control device 33, which immediately causes a corresponding increase in the opening cross section of the level control valve 24, even before the level in the separator 3 begins to rise.
  • the pilot signal FF is formed in a function generator 38 and a downstream multiplier 39. As the diagram in the function generator 38 shows, the signal is proportional to the minimum flow rate in the economizer 1 and is weighted in a multiplier 39 with the multiplier L.
  • the multiplier L is selected such that when the minimum flow rate through the economiser 1 increases, the level control valve 24 opens in a controlled manner as far as is necessary for the steady state with a constant level in the separator 3.
  • the feed control device 11 is also possible to design the feed control device 11 as a classic PID controller with limitation of its output signal and with a PI controller connected in cascade. Analogously, the same for the level control device 33.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Control Of Steam Boilers And Waste-Gas Boilers (AREA)

Description

Die Erfindung betrifft ein Verfahren zum Betrieb eines Zwangdurchlaufdampferzeugers mit Schwachlastumwälzung und folgenden Elementen: Speisepumpe, Speiseleitung, Economiser, Verdampfer, Wasserabscheider und mindestens ein Ueberhitzer, sowie mit einer am Wasseraustritt des Abscheiders angeschlossenen Umwälzleitung und einer Umwälzpumpe zwischen der Speisepumpe und dem Economiser.The invention relates to a method for operating a once-through steam generator with low-load circulation and the following elements: feed pump, feed line, economizer, evaporator, water separator and at least one superheater, and with a circulation line connected to the water outlet of the separator and a circulation pump between the feed pump and the economizer.

Bei den bisher bekannten Betriebsverfahren für Dampferzeuger mit den eingangs aufgezählten Elementen wird die dem Dampferzeuger zugeführte Speisemenge im oberen Lastbereich in Abhängigkeit der Dampftemperatur und im unteren Lastbereich in Abhängigkeit vom Wasserstand im Wasserabscheider eingestellt, und zwar entweder durch Verändern der Drehzahl der Speisepumpe oder durch Verstellen des Durchflussquerschnitts eines Speiseventils. Um den Wechsel in der Abhängigkeit von der Dampftemperatur zum Wasserstand und umgekehrt zu bewerkstelligen, wurde im Signalfluss hinter dem Dampftemperaturregler bzw. dem Wasserstandsregler ein Umschaltorgan vorgesehen. Als Kriterium für das Umschalten kann die gemessene Ueberhitzung am Eintritt des ersten Ueberhitzers verwendet werden (CH-PS 673 697). Diese Umschaltung kann auch aufgrund eines Wettlaufes zwischen zwei immer aktiven Reglern geschehen (DE-B 2 149 127). Bezogen auf einen passend gewählten lastabhängigen Referenzpunkt kann der Niveauregler dabei nur eine Reduktion und der Temperaturregler nur eine Erhöhung der Speisemenge bewirken.In the previously known operating methods for steam generators with the elements listed at the outset, the amount of food supplied to the steam generator is set in the upper load range as a function of the steam temperature and in the lower load range as a function of the water level in the water separator, either by changing the speed of the feed pump or by adjusting the Flow cross-section of a feed valve. In order to make the change depending on the steam temperature to the water level and vice versa, a switchover device was provided in the signal flow behind the steam temperature controller or the water level controller. The measured superheat at the inlet of the first superheater can be used as a criterion for the switchover (CH-PS 673 697). This switchover can also take place due to a race between two always active controllers (DE-B 2 149 127). In relation to a suitably chosen load-dependent reference point, the level controller can only bring about a reduction and the temperature controller can only increase the feed quantity.

Oft wird auch ein rein lastabhängiges Umschaltkriterium verwendet, z.B. der Förderdruck der Speisepumpe (CH-PS 517 266). Das Umschalten der Regler ist nicht immer von Vorteil, da beim Umschalten grössere Aenderungen in die Arbeitsmittelzufuhr zum Economiser auftreten können. Dies ist dadurch bedingt, dass das vom Temperaturregler kommende Signal und das vom Wasserstandsregler kommende Signal beim Umschalten nicht gleich gross sind und nicht gleiches Vorzeichen haben müssen, je nachdem, ob beim Umschalten der Wasserstand im Abscheider im Steigen oder im Fallen war oder auf welcher Höhe er sich gerade befand.A purely load-dependent switchover criterion is often used, e.g. the feed pressure of the feed pump (CH-PS 517 266). Switching the controller is This is not always an advantage, since major changes in the supply of working fluid to the economiser can occur when switching. This is due to the fact that the signal coming from the temperature controller and the signal coming from the water level controller are not of the same size when switching and do not have to have the same sign, depending on whether the water level in the separator was rising or falling or at what height he was just now.

Der Erfindung liegt die Aufgabe zugrunde, ein Betriebsverfahren für einen Zwangdurchlaufdampferzeuger mit den eingangs aufgezählten Elementen so zu verbessern, dass ein Umschalten in der zuvor erwähnten Art entfällt.The invention has for its object to improve an operating method for a once-through steam generator with the elements listed above so that switching in the aforementioned manner is omitted.

Diese Aufgabe wird mit den Merkmalen des-Anspruchs 1 gelöst. Gemäss diesem Verfahren wird die Speisemenge grundsätzlich und immer so eingestellt, dass ein gewünschter Durchfluss durch den Economiser resultiert. Dieser gewünschte Durchfluss durch den Economiser wird in Abhängigkeit von der Dampftemperatur gebildet, wobei ein minimaler Durchfluss nie unterschritten werden darf, so dass der Betrieb mit nassem Abscheider mit festen, minimalen Durchfluss durch den Economiser erfolgt. Der Wasserstand im Wasserabscheider wird nicht - wie bisher - durch Verändern der Speisemenge beeinflusst, sondern durch das in Fliessrichtung des Arbeitsmittels hinter der Umwälzpumpe angeordnete Ventil. Auf diese Weise wird das bisherige Umschalten vermieden, ohne den grossen Vorteil der Lösung gemäss der CH-PS 673 697 im Vergleich mit noch früheren Verfahren z.B. gemäss CH-PS 517 266 aufzugeben. Ein sonst übliches, in der Umwälzleitung zwischen dem Wasserabscheider und der Umwälzpumpe angeordnetes und der Niveauregelung im Abscheider dienendes Ventil muss wegen der Niveauregelung nicht angedrosselt werden, so dass an der Mischstelle des Umwälzwassers mit dem Speisewasser keine Dampfblasen entstehen können. Auf diese Weise kann in der Umwälzpumpe sicher keine Kavitation auftreten.This object is achieved with the features of claim 1. According to this method, the amount of food is always set so that a desired flow through the economizer results. This desired flow through the economiser is formed as a function of the steam temperature, whereby a minimum flow must never be undercut, so that operation with a wet separator takes place with a fixed, minimal flow through the economiser. The water level in the water separator is not - as before - influenced by changing the quantity of food, but by the valve located behind the circulation pump in the direction of flow of the working fluid. In this way, the previous switching is avoided without giving up the great advantage of the solution according to CH-PS 673 697 in comparison with even earlier methods, for example according to CH-PS 517 266. An otherwise conventional valve, which is arranged in the circulation line between the water separator and the circulation pump and serves the level control in the separator, does not have to be throttled because of the level control, so that no vapor bubbles can occur at the mixing point of the circulation water with the feed water. In this way, no cavitation can occur in the circulation pump.

Ein Ausführungsbeispiel der Erfindung ist in der folgenden Beschreibung anhand der Zeichnung näher erläutert. Es zeigen:

Fig.1
ein Schaltschema eines Zwangdurchlaufdampferzeugers zur Ausführung des erfindungsgemässen Verfahrens,
Fig.2a
schematisch den Wasserabscheider mit mehreren Wasserständen und den zugehörigen Ventilstellungen, wobei die %-Angaben sich auf den Oeffnungsquerschnitt der Ventile beziehen,
Fig.2b
ein Diagramm für den Uebergang von trockenem zu nassem Abscheiderbetrieb,
Fig.2c
ein Diagramm für den Uebergang von nassem zu trockenem Abscheiderbetrieb in einer speziellen Situation und
Fig.3
ein gegenüber Fig.1 abgewandeltes Regelschema für die Niveauregeleinrichtung.
An embodiment of the invention is explained in more detail in the following description with reference to the drawing. Show it:
Fig. 1
1 shows a circuit diagram of a once-through steam generator for carrying out the method according to the invention,
Fig.2a
schematic of the water separator with several water levels and the associated valve positions, the% data relating to the opening cross section of the valves,
Fig.2b
a diagram for the transition from dry to wet separator operation,
Fig.2c
a diagram for the transition from wet to dry separator operation in a special situation and
Fig. 3
a modified compared to Fig.1 control scheme for the level control device.

Gemäss Fig.1 weist der Zwangdurchlaufdampferzeuger mit Schwachlastumwälzung einen Economiser 1, einen Verdampfer 2, einen Wasserabscheider 3 und einen Ueberhitzer 4 auf, die in Richtung des Arbeitsmittelstroms in Reihe geschaltet sind. Zum Speisen des Dampferzeugers ist eine Speisepumpe 5 vorgesehen, die über eine Speiseleitung 6 mit dem Eintritt des Economisers 1 verbunden ist. Nahe dem Eintritt des Economisers 1 ist in der Leitung 6 eine Messvorrichtung 7 für die den Economiser durchströmende Wassermenge angeordnet. Die Mengenmesseinrichtung 7 ist über eine Signalleitung 8 mit einem Vergleichspunkt 9 verbunden, der ausserdem über eine Signalleitung 16 mit dem Ausgang einer Speiseregeleinrichtung 11 verbunden ist, die als Zustandsregler mit Beobachter ausgebildet und in der Patentanmeldung Nr.0 507 730 A1 der Anmelderin beschrieben ist. Die Speiseregeleinrichtung 11 erhält über eine Signalleitung 12 ein Temperaturmessignal, das den Istwert der Dampftemperatur repräsentiert und mittels einer Messvorrichtung 13 am Austritt des Ueberhitzers 4 abgenommen wird. Stromunterhalb der Messvorrichtung 13 können weitere Ueberhitzer vorgesehen sein, bevor der Dampf nichtgezeigten Verbrauchern zugeführt wird. Die Messvorrichtung 13 kann auch zwischen dem Wasserabscheider 3 und dem Ueberhitzer 4 angeordnet sein. Ueber eine Signalleitung 14 erhält die Speiseregeleinrichtung 11 einen Sollwert für die Dampftemperatur und über eine Signalleitung 15 ein Signal, das die Mindestarbeitsmittelmenge repräsentiert, die den Economiser 1 durchströmen muss.According to FIG. 1, the once-through steam generator with low-load circulation has an economizer 1, an evaporator 2, a water separator 3 and a superheater 4, which are connected in series in the direction of the working fluid flow. To feed the steam generator, a feed pump 5 is provided, which is connected via a feed line 6 to the inlet of the economizer 1. A measuring device 7 for the amount of water flowing through the economizer is arranged in the line 6 near the inlet of the economizer 1. The quantity measuring device 7 is connected to a comparison point 9 via a signal line 8 connected, which is also connected via a signal line 16 to the output of a feed control device 11, which is designed as a status controller with an observer and is described in the applicant's patent application No. 0 507 730 A1. Via a signal line 12, the feed control device 11 receives a temperature measurement signal which represents the actual value of the steam temperature and is taken off by means of a measuring device 13 at the outlet of the superheater 4. Further superheaters can be provided downstream of the measuring device 13 before the steam is supplied to consumers, not shown. The measuring device 13 can also be arranged between the water separator 3 and the superheater 4. Via a signal line 14, the feed control device 11 receives a target value for the steam temperature and via a signal line 15 a signal which represents the minimum amount of working fluid which has to flow through the economizer 1.

Das Mindestmengensignal wird wirksam, wenn bei einer Lastabsenkung die den Economiser 1 durchströmende Arbeitsmittelmenge auf die Mindestmenge absinkt, die bei ungefähr 30% der Vollast liegt. Der Vergleichspunkt 9 gehört zu einem Regler 17, dessen Ausgang über eine Signalleitung 18 mit der Speisepumpe 5 verbunden ist, die das Stellorgan des Speiseregelkreises bildet. Der Regler 17 kann z.B. als PI-Regler ausgebildet sein.The minimum quantity signal becomes effective when the quantity of working fluid flowing through the economizer 1 drops to the minimum quantity, which is approximately 30% of the full load, during a load reduction. The comparison point 9 belongs to a controller 17, the output of which is connected via a signal line 18 to the feed pump 5, which forms the actuator of the feed control loop. The controller 17 can e.g. be designed as a PI controller.

Am Wasseraustritt des Wasserabscheiders 3 ist eine Umwälzleitung 20 angeschlossen, die in Strömungsrichtung hintereinander eine Rückschlagklappe 21 und ein Absperrventil 22 enthält. Die Leitung 20 mündet bei 19 stromunterhalb der Speisepumpe 5 in die Speiseleitung 6, die stromunterhalb dieser Mündungsstelle 19 eine Umwälzpumpe 23 und ein Niveauregelventil 24 enthält. Der die Umwälzpumpe 23 und das Niveauregelventil 24 enthaltende Abschnitt 6' der Speiseleitung 6 wird also während des Betriebes mit nassem Abscheider ausser vom Speisewasser auch von Wasser aus dem Abscheider 3 durchströmt. Parallel zum Leitungsabschnitt 6' ist eine Leitung 25 mit Rückschlagklappe 26 vorgesehen, die bei hoher Last des Dampferzeugers von einem Teil der von der Speisepumpe geförderten Speisemenge durchströmt wird. Mit 27 ist eine Einspritzwasserleitung bezeichnet, die in bekannter, nicht gezeigter Weise zum Ueberhitzer 4 bzw. zu etwa nachgeschalteten Ueberhitzern führt.A circulation line 20 is connected to the water outlet of the water separator 3 and contains a check valve 21 and a shut-off valve 22 one after the other in the flow direction. The line 20 opens at 19 downstream of the feed pump 5 into the feed line 6, which contains a circulation pump 23 and a level control valve 24 below this mouth 19. The the circulation pump 23 and the section 6 'of the feed line 6 containing the level control valve 24 is therefore also flowed through by water from the separator 3 during operation with a wet separator in addition to the feed water. A line 25 with a non-return flap 26 is provided parallel to the line section 6 'and a portion of the quantity of feed conveyed by the feed pump flows through when the steam generator is under high load. With 27 an injection water line is designated, which leads in a known, not shown manner to the superheater 4 or to some downstream superheaters.

Von der Umwälzleitung 20 zweigt zwischen der Rückschlagklappe 21 und dem Absperrventil 22 eine Leitung 30 mit Ablaufventil 31 ab, die zu einem nichtgezeigten Speisewasserbehälter der Dampferzeugungsanlage führt. Die Leitung 30 kann auch in den Kondensator oder einen speziellen Tank der Anlage führen.From the circulation line 20 branches off between the check valve 21 and the shut-off valve 22, a line 30 with a drain valve 31, which leads to a feed water tank (not shown) of the steam generating system. The line 30 can also lead into the condenser or a special tank of the system.

Zum Betätigen des Niveauregelventils 24 ist eine Niveauregeleinrichtung 33 vorgesehen, die - wie die Speiseregeleinrichtung 11 - als Zustandsreqler mit Beobachter ausgebildet ist. Die Niveauregeleinrichtung 33 erhält über eine Signalleitung 34 ein Messignal, das den Istwert des Wasserstandes im Abscheider 3 repräsentiert. Der Sollwert für den Wasserstand wird über eine Signalleitung 35 der Niveauregeleinrichtung 33 zugeführt. Das Absperrventil 22 untersteht einem Steuersignal, das über eine Signalleitung 20 von der Niveauregelvorrichtung 33 kommt und dessen Funktion weiter unten beschrieben wird. Das Ablaufventil 31 untersteht einem Niveaumessignal, das von der Signalleitung 34 abgenommen und über eine Signalleitung 32 geführt wird und dessen Funktion ebenfalls weiter unten erläutert wird.To operate the level control valve 24, a level control device 33 is provided which, like the feed control device 11, is designed as a state controller with an observer. The level control device 33 receives a measurement signal via a signal line 34, which represents the actual value of the water level in the separator 3. The setpoint for the water level is supplied to the level control device 33 via a signal line 35. The shut-off valve 22 is subject to a control signal which comes from the level control device 33 via a signal line 20 and whose function is described below. The drain valve 31 is subordinate to a level measurement signal, which is taken from the signal line 34 and passed over a signal line 32 and whose function is also explained further below.

Gemäss Fig.2a sind in dem Wasserabscheider 3 fünf verschiedene Wasserstände angedeutet, und zwar bei 1 m, 3 m, 7,7 m, 10,7 m und 14,2 m. Der Wasserstand 7,7 m ist der Sollwasserstand für die Niveauregeleinrichtung 33 bei normalem Umwälzbetrieb der Dampferzeugeranlage. Die Wasserstände von 1 m und 3 m spielen eine Rolle beim Uebergang von Betrieb mit nassem Abscheider zum Betrieb mit trockenem Abscheider und umgekehrt, während die Wasserstände von 10,7 m und 14,2 m in der ersten Anfahrphase des Dampferzeugers eine Rolle spielen. In dieser Phase fällt sehr viel Wasser im Abscheider 3 an, so dass bei Ueberschreiten der Marke von 10,7 m das Ablaufventil 31 unter dem Einfluss des Niveaumessignals in der Leitung 32 öffnet, bis es bei der Marke 14,2 m 100% offen ist, wie dies in Fig.2a in der Mitte durch den Linienzug B dargestellt ist. Bei der Wasserstandsmarke 1 m geht das Absperrventil 22 vom Oeffnungsquerschnitt 100% in die Schliessstellung 0% und bei Erreichen der Wasserstandsmarke 3 m öffnet es von 0% auf 100%, wie dies durch die beiden horizontalen Linien C in Fig.2a angedeutet ist. Die Ventilbewegungen des Niveauregelventils 24 bei den Wasserständen 1 m und 3 m sind in Fig.2a rechts durch die beiden horizontalen Linien D dargestellt, wobei der gestrichelte Linienzug den Einfluss der vollautomatischen Regelung bei Betrieb mit nassem Abscheider zeigt.According to FIG. 2a, five different water levels are indicated in the water separator 3, specifically at 1 m, 3 m, 7.7 m, 10.7 m and 14.2 m. The water level 7.7 m is the target water level for the level control device 33 during normal circulation operation of the steam generator system. The water levels of 1 m and 3 m play a role in the transition from operation with a wet separator to operation with a dry separator and vice versa, while the water levels of 10.7 m and 14.2 m play a role in the first start-up phase of the steam generator. In this phase, a lot of water accumulates in the separator 3, so that when the mark exceeds 10.7 m, the drain valve 31 opens under the influence of the level measurement signal in the line 32 until it is 100% open at the mark 14.2 m , as shown in Fig.2a in the middle by the line B. At the water level mark 1 m, the shut-off valve 22 goes from the opening cross-section 100% to the closed position 0% and when the water level mark 3 m is reached, it opens from 0% to 100%, as indicated by the two horizontal lines C in FIG. 2a. The valve movements of the level control valve 24 at the water levels 1 m and 3 m are shown on the right in FIG. 2a by the two horizontal lines D, the dashed line showing the influence of the fully automatic control when operating with a wet separator.

Die beschriebene Anlage wird wie folgt betrieben. Im Normalbetrieb, d.h. oberhalb der Mindestdurchflussmenge für den Economiser 1, d.h. oberhalb ungefähr 30% der Vollast, wird die dem Zwanglaufdampferzeuger zugeführte Speisemenge von der Speisepumpe 5 gefördert, und zwar in Abhängigkeit von der Dampftemperatur, die mittels der Messvorrichtung 13 gemessen wird. In der Speiseregeleinrichtung 11 wird dieser Istwert der Temperatur mit dem über die Signalleitung 14 zugeführten Sollwert der Temperatur verglichen und zu einem Ausgangssignal verarbeitet, das als Sollwert für die Durchflussmenge im Economiser 1 über die Signalleitung 16 dem Vergleichspunkt 9 zugeführt wird. Dem Vergleichspunkt 9 wird über die Signalleitung 8 der Messwert für die Durchflussmenge als Istwert zugeführt. Abhängig vom Vergleich dieser beiden Signale wird dann in dem der Einrichtung 11 unterlagerten Regler 17 ein Stellsignal erzeugt, das über die Signalleitung 18 die Drehzahl der Speisepumpe 5 verstellt, und zwar bei steigender Dampftemperatur in Richtung einer grösseren Speisemenge und bei sinkender Dampftemperatur in Richtung einer verringerten Speisemenge. Während dieses Normalbetriebes, in dem also reiner Zwangdurchlauf des Arbeitsmittels im Dampferzeuger herrscht, gelangt überhitzter Dampf in den Abscheider 3, so dass kein Sattwasser über die Umwälzleitung 20 zum Economiser 1 zurückgeführt wird. Wegen des überhitzten Zustandes des Dampfes befindet sich der Abscheider 3 im trockenen Betrieb, d.h. der Wasserstand im Abscheider ist sehr tief und die Niveauregeleinrichtung 33 müsste eigentlich das Niveauregelventil 24 in voll geschlossener Stellung halten. Nach der Erfindung soll jedoch die Umwälzpumpe 23 immer durchströmt sein, um zu vermeiden, dass nach einem längeren Stillstand dieser Pumpe Temperaturschocks in ihr auftreten, wenn sie wieder den Umwälzbetrieb aufnimmt. Aus diesem Grunde bleibt das Niveauregelventil 24 in der geschilderten Betriebsphase voll offen und die Umwälzpumpe 23, die oberhalb 50% Last abgeschaltet ist, wird von einem Teil der von der Speisepumpe 5 geförderten Speisemenge durchströmt, während die restliche Speisemenge über die Leitung 25 zum Economiser 1 strömt. Ein Leerlaufen des Abscheiders 3 wird dabei durch das Absperrventil 22 verhindert, das dann in voll geschlossener Stellung ist, ebenso wie das Ablaufventil 31.The system described is operated as follows. In normal operation, ie above the minimum flow rate for the economizer 1, ie above approximately 30% of the full load, the feed quantity supplied to the forced-flow steam generator is conveyed by the feed pump 5 as a function of the steam temperature, which is measured by means of the measuring device 13. In the feed control device 11, this actual value of the temperature is compared with the setpoint value of the temperature supplied via the signal line 14 compared and processed to an output signal, which is fed as a setpoint for the flow rate in the economizer 1 via the signal line 16 to the comparison point 9. The measurement point for the flow rate is fed as an actual value to the comparison point 9 via the signal line 8. Depending on the comparison of these two signals, a control signal is then generated in the controller 17 subordinate to the device 11, which adjusts the speed of the feed pump 5 via the signal line 18, namely with increasing steam temperature in the direction of a larger quantity of food and with decreasing steam temperature in the direction of a reduced one Amount of food. During this normal operation, in which there is therefore a pure forced passage of the working medium in the steam generator, superheated steam reaches the separator 3, so that no saturated water is returned to the economizer 1 via the circulation line 20. Because of the overheated condition of the steam, the separator 3 is in dry operation, ie the water level in the separator is very low and the level control device 33 should actually keep the level control valve 24 in the fully closed position. According to the invention, however, the circulation pump 23 is always to be flowed through in order to avoid that after a longer standstill of this pump temperature shocks occur in it when it resumes circulation operation. For this reason, the level control valve 24 remains fully open in the operating phase described and the circulating pump 23, which is switched off above 50% load, is flowed through by part of the feed quantity conveyed by the feed pump 5, while the remaining feed quantity is fed via line 25 to the economizer 1 flows. An empty running of the separator 3 is prevented by the shut-off valve 22, which is then in the fully closed position, as is the drain valve 31.

Der Uebergang von trockenem zu nassem Betrieb des Abscheiders, der in Fig.2b dargestellt ist, geht folgendermassen vor sich: Das Niveauregelventil 24 und das Absperrventil 22 haben die eben zuletzt beschriebene Stellung inne, d.h. sie befinden sich in Bereitschaftsstellung (Gebiet E in Fig.2b) und der Wasserstand im Abscheider 3 befindet sich unterhalb von 3 m. Mit dem Absinken der Last des Dampferzeugers tritt Sattdampf in den Abscheider 3 ein. Als Folge davon steigt der Wasserstand im Abscheider 3 (vergleiche Kurve H in Fig.2b). Wenn der Wasserstand die Höhe von 3 m erreicht hat, wird der Oeffnungsquerschnitt des Niveauregelventils 24 durch eine erste Sequenz von in der Niveauregeleinrichtung 33 einprogrammierten Steuerbefehlen auf 31% verringert (vergleiche Gebiet F in Fig.2b). In dem Moment, in dem der Oeffnungsquerschnitt 31% erreicht ist, wird das Absperrventil 22 durch die Steuerbefehle auf vollen Oeffnungsquerschnitt gefahren (Ende des Gebiets F), woraufhin sie die Niveauregeleinrichtung 33 in den automatischen Regelbetrieb schalten (Gebiet G in Fig.2b), d.h. sie verstellt das Niveauregelventil 24 so, dass der bei 7,7 m liegende Sollwert für den Wasserstand eingehalten wird.The transition from dry to wet operation of the separator, which is shown in Fig. 2b, takes place as follows: The level control valve 24 and the shut-off valve 22 have the position just described, i.e. they are in the ready position (area E in Fig. 2b) and the water level in the separator 3 is below 3 m. As the load of the steam generator drops, saturated steam enters the separator 3. As a result, the water level in separator 3 increases (see curve H in Fig. 2b). When the water level has reached the height of 3 m, the opening cross section of the level control valve 24 is reduced to 31% by a first sequence of control commands programmed into the level control device 33 (compare area F in FIG. 2b). At the moment when the opening area reaches 31%, the shut-off valve 22 is moved to the full opening area by the control commands (end of area F), whereupon they switch the level control device 33 into automatic control mode (area G in FIG. 2b), ie it adjusts the level control valve 24 so that the setpoint for the water level, which is 7.7 m, is maintained.

Der Uebergang von nassem Betrieb oder Umwälzbetrieb zu trockenem Betrieb oder Zwangdurchlaufbetrieb erfordert keine speziellen Eingriffe. In dem Masse, wie sich der Zustrom von Sattwasser in den Abscheider 3 verringert, verkleinert die Niveauregeleinrichtung 33 den Oeffnungsquerschnitt des Niveauregelventils 24, so dass sich die Umwälzmenge im Gleichschritt mit dem Zustrom von Sattwasser in den Abscheider 3 verringert und das Niveau im Abscheider konstant bleibt. Die Umwälzmenge reduziert sich also ganz automatisch auf Null. Wenn sicherer Zwangdurchlaufbetrieb erreicht ist, z.B. bei einer Last von 50% der Vollast, schaltet die Bedienmannschaft die Umwälzpumpe 23 aus. Die Steuerlogik der Regeleinrichtung 33 schliesst dann das Absperrventil 22 und öffnet das Niveauregelventil 24 vollständig, so dass die Umwälzpumpe 23 passiv einen kleinen Durchfluss erhält, der für ihr Warmhalten ausreicht.The transition from wet operation or circulation operation to dry operation or forced operation does not require any special intervention. To the extent that the inflow of saturated water into the separator 3 is reduced, the level control device 33 reduces the opening cross section of the level control valve 24, so that the circulating quantity decreases in step with the inflow of saturated water into the separator 3 and the level in the separator remains constant . The circulation volume is therefore automatically reduced to zero. When safe forced operation is achieved, e.g. with a load of 50% of the At full load, the operating team switches off the circulation pump 23. The control logic of the control device 33 then closes the shut-off valve 22 and opens the level control valve 24 completely, so that the circulation pump 23 passively receives a small flow that is sufficient for keeping it warm.

Der in Fig.2c dargestellte Ablauf bildet eine Sicherheitsschaltung, die garantiert, dass nie Dampf umgewälzt wird. Bei einem Auftreten von heftigen Transienten könnte es passieren, dass die Niveauregeleinrichtung 33 zu langsam reagiert und dass das Niveau im Abscheider 3 vorübergehend unter die Marke von 1 m absinkt. Für diesen Fall ist in die Regeleinrichtung 33 eine zweite Sequenz von Steuerbefehlen einprogrammiert. Durch diese Steuerbefehle schliesst das Absperrventil 22 sofort (Gebiet I in Fig.2c). Wenn es geschlossen ist, verlässt die Niveauregeleinrichtung 33 den automatischen Regelbetrieb, und die Steuerbefehle öffnen das Niveauregelventil 24 auf den maximal zugelassenen Wert (Gebiet K in Fig.2c). So ist die Anlage bereit, um bei einem allfälligen Wiederansteigen des Niveaus im Abscheider 3 den automatischen Regelbetrieb selbsttätig wieder zu übernehmen.The sequence shown in Fig. 2c forms a safety circuit that guarantees that steam is never circulated. If violent transients occur, it could happen that the level control device 33 reacts too slowly and that the level in the separator 3 temporarily drops below the mark of 1 m. In this case, a second sequence of control commands is programmed into the control device 33. The shut-off valve 22 closes immediately by these control commands (area I in FIG. 2c). When it is closed, the level control device 33 leaves the automatic control mode and the control commands open the level control valve 24 to the maximum permitted value (area K in FIG. 2c). The system is thus ready to automatically take over the automatic control operation if the level in the separator 3 rises again.

Während des Betriebes mit nassem Wasserabscheider, d.h. während des Umwälzbetriebes, können Speisewasserdruckerhöhungen die Wasserumwälzung verhindern, indem starke Druckerhöhungen zum Schliessen der Rückschlagklappe 21 führen. Dieser Fall kann eintreten, wenn bei kleiner Last, z.B. bei etwa 15% der Vollast die geforderte Mindestdurchflussmenge durch den Economiser 1 aus Sicherheitsgründen erhöht wird. Die Niveauregeleinrichtung 33 kann dann nicht zufriedenstellend regeln. Um dies zu vermeiden, ist die Niveauregeleinrichtung 33 gemäss Fig.3 abgewandelt, indem ihr zusätzlich ein Eingangssignal PE und ein Vorsteuersignal FF aufgeschaltet werden. In Fig.3 sind der Uebersichtlichkeit wegen die Leitungen 25 und 30 sowie die Rückschlagklappe 21, das Absperrventil 22 und das Ablaufventil 31 mit der Signalleitung 29 weggelassen worden. Das Eingangssignal PE wird aus der Differenz zwischen dem Druck PA im Abscheider 3 und dem Druck PS auf der Förderseite der Speisepumpe 5 gebildet. Eine Erhöhung des Förderdrucks PS bewirkt eine Aenderung des Signals PE im Vorkreis der Niveauregeleinrichtung 33, die sofort eine entsprechende Vergrösserung des Oeffnungsquerschnitts des Niveauregelventils 24 veranlasst, schon bevor das Niveau im Abscheider 3 zu steigen beginnt. Das Vorsteuersignal FF wird in einem Funktionsgenerator 38 und einem nachgeschalteten Multiplikationsorgan 39 gebildet. Wie das Diagramm im Funktionsgenerator 38 zeigt, ist das Signal proportional zum Mindestmengendurchfluss im Economiser 1 und wird in einem Multiplikationsorgan 39 mit dem Multiplikator L gewichtet. Der Multiplikator L ist so gewählt, dass bei einer Erhöhung der Mindestdurchflussmenge durch den Economiser 1 das Niveauregelventil 24 gesteuert sich soweit öffnet, wie das für den stationären Zustand mit konstantem Niveau im Abscheider 3 erforderlich ist.During operation with a wet water separator, that is to say during the circulation operation, feed water pressure increases can prevent the water circulation by causing strong pressure increases to close the check valve 21. This can occur if the required minimum flow rate is increased by the economiser 1 for safety reasons at a low load, for example at about 15% of the full load. The level control device 33 can then not regulate satisfactorily. In order to avoid this, the level control device 33 according to FIG. 3 is modified in that it additionally receives an input signal PE and a pilot signal FF are applied. In Figure 3 the lines 25 and 30 and the check valve 21, the shut-off valve 22 and the drain valve 31 with the signal line 29 have been omitted for clarity. The input signal PE is formed from the difference between the pressure PA in the separator 3 and the pressure PS on the delivery side of the feed pump 5. An increase in the delivery pressure PS causes a change in the signal PE in the pre-circuit of the level control device 33, which immediately causes a corresponding increase in the opening cross section of the level control valve 24, even before the level in the separator 3 begins to rise. The pilot signal FF is formed in a function generator 38 and a downstream multiplier 39. As the diagram in the function generator 38 shows, the signal is proportional to the minimum flow rate in the economizer 1 and is weighted in a multiplier 39 with the multiplier L. The multiplier L is selected such that when the minimum flow rate through the economiser 1 increases, the level control valve 24 opens in a controlled manner as far as is necessary for the steady state with a constant level in the separator 3.

Abweichend von den beschriebenen Ausführungsformen ist es auch möglich, die Speiseregeleinrichtung 11 als klassischen PID-Regler mit Begrenzung seines Ausgangssignals auszubilden und mit in Kaskade geschaltetem PI-Regler. Sinngemäss das gleiche für die Niveauregeleinrichtung 33.Deviating from the described embodiments, it is also possible to design the feed control device 11 as a classic PID controller with limitation of its output signal and with a PI controller connected in cascade. Analogously, the same for the level control device 33.

Claims (5)

  1. Method of operating a once-through steam generator with low load recirculation and having the following elements: feed pump (5), feed line (6), economizer (1), evaporator (2), water separator (3) and at least one superheater (4), having a recirculation line (20) which is connected to the water outlet of the water separator (3) and opens into the feed line (6) between the feed pump (5) and the economizer (1), and having a recirculation pump (23) which is arranged in the feed line (6) between the opening (19) of the recirculation line (20) into the feed line and the economizer (1), and having a valve (24) for controlling the level of liquid in the water separator (3), said valve (24) being arranged between the recirculation pump (23) and the economizer (1), the temperature of the steam being measured downstream of the water separator (3) and the level of liquid being measured in the water separator (3), the feed quantity above a minimum flow rate of the economizer (= operation with dry separator) being adjusted by means of a control device (11) as a function of the steam temperature measured, and otherwise (= operation with wet separator) the water level in the water separator (3) being controlled by means of a level-control device (33) by actuating the valve (24) arranged between the recirculation pump (23) and the economizer (1), and the feed quantity being adjusted such that a constant minimum flow through the economizer (1) is guaranteed.
  2. Method according to Claim 1, with the arrangement of a shutoff valve (22) in the recirculation line (20) upstream of the opening (19) into the feed line (6), characterized in that, in operation above the minimum flow rate (= operation with dry separator, recirculation pump (23) switched off), the shutoff valve (22) is moved into the closed position and the valve (24) arranged between the recirculation pump (23) and the economizer (1) is moved to a full opening cross-section so that a small flow flows through the recirculation pump (23).
  3. Method according to Claim 2, characterized in that, in the course of a load reduction during which the water level in the separator (3) rises above a predetermined mark, a first sequence of control commands brings about the transition to operation with level control in the separator (3), in that the control commands firstly adjust the valve (24) arranged between the recirculation pump (23) and the economizer (1) to an opening cross-section which is favourable for this operation, then fully open the shutoff valve (22) and subsequently switch the level-control device smoothly into automatic control operation.
  4. Method according to Claim 3, characterized in that, in the case of the water level rapidly dropping below a predetermined mark, a second sequence of control commands is triggered, which firstly close the shutoff valve (22), then switch the level-control device (33) over to manual operation, and automatically fully open the valve (24) arranged between the recirculation pump (23) and the economizer (1).
  5. Method according to Claim 1, characterized in that the difference between the pressure in the water separator (3) and the conveying pressure in the feed line (6) is applied in an advance circuit to the level-control device (33) constructed as a cascade.
EP92810857A 1991-11-28 1992-11-05 Method of operating a once-through steam generator with low load recirculation Revoked EP0544615B1 (en)

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CH348891 1991-11-28
CH3488/91 1991-11-28

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Publication number Priority date Publication date Assignee Title
CN110476014A (en) * 2017-03-30 2019-11-19 西门子股份公司 Water in vertical forced-circulation steam generator is cooling

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DE19619836B4 (en) * 1996-05-17 2005-05-12 Alstom Device for feeding water pilot control of a cooling air temperature controller for a cooling air cooler
EP2065641A3 (en) * 2007-11-28 2010-06-09 Siemens Aktiengesellschaft Method for operating a continuous flow steam generator and once-through steam generator
US20100251976A1 (en) * 2009-04-02 2010-10-07 Alstom Technology Ltd. Ejector driven steam generator start up system
DE102011006390A1 (en) 2011-03-30 2012-10-04 Siemens Aktiengesellschaft Method for operating a continuous steam generator and for carrying out the method designed steam generator

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US3194020A (en) * 1963-03-25 1965-07-13 Combustion Eng Method and apparatus relating to vapor generation
BE788957A (en) * 1971-09-24 1973-03-19 Sulzer Ag PROCESS FOR ADJUSTING THE POWER SUPPLY OF A FORCED CIRCULATION STEAM GENERATOR
CH552173A (en) * 1972-05-16 1974-07-31 Sulzer Ag DEVICE FOR REGULATING THE FEED WATER SUPPLY OF A FORCED STEAM GENERATOR OPERATING WITH SLIDING PRESSURE.
CH552771A (en) * 1972-06-12 1974-08-15 Sulzer Ag FORCED FLOW STEAM GENERATOR.

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110476014A (en) * 2017-03-30 2019-11-19 西门子股份公司 Water in vertical forced-circulation steam generator is cooling
CN110476014B (en) * 2017-03-30 2021-08-03 西门子股份公司 Water cooling in vertical forced circulation steam generator

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KR930010432A (en) 1993-06-22
DE59206231D1 (en) 1996-06-13
EP0544615A1 (en) 1993-06-02

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