Gas turbine control system and method for single-shaft combined cycle plant

An object is to maintain a constant gas turbine output without requiring a complicated procedure on site and without being affected by variations in the output of a steam turbine during a reverse-washing/normal-washing switching period of a condenser. A gas turbine control system for a single-shaft combined cycle plant generates a gas turbine output command using a parameter reflecting a gas turbine output during a reverse-washing/normal-washing switching period of a condenser and generates the gas turbine output command on the basis of a generator output command and a steam turbine output during a period other than the reverse-washing/normal-washing switching period of the condenser.

RELATED APPLICATIONS

The present application is based on International Application Number PCT/JP2009/058281, filed Apr. 27, 2009, and claims priority from Japanese Application Number 2008-117428, filed Apr. 28, 2008, the disclosures of which are hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a single-shaft combined cycle plant in which rotating shafts of a gas turbine, a steam turbine, and a generator are coupled together, and particularly to a gas turbine control system and method for output control of the gas turbine.

BACKGROUND ART

In a single-shaft combined cycle plant, when a condenser is switched between normal washing and reverse washing, the flow of sea water stops momentarily, with the result that the degree of vacuum of the condenser decreases suddenly. The decreased degree of vacuum of the condenser decreases the output of a steam turbine, thus causing a situation where the output of a generator decreases.

The steam turbine output is conventionally calculated with correction based on the degree of vacuum of the condenser, but if the degree of vacuum of the condenser changes suddenly, an instrument cannot follow the change in degree of vacuum, and the steam turbine output may be erroneously recognized to remain unchanged by calculation despite the fact that the steam turbine output has actually decreased.

In general, the generator output is calculated as the sum of the steam turbine output and the gas turbine output; as described above, so when the generator output decreases while the steam turbine output apparently remains unchanged as described above, the gas turbine output is erroneously recognized to have decreased. This prevents proper control of the gas turbine and poses the risk of malfunctions of various equipment in the power plant.

To eliminate this problem, therefore, Patent Literature 1, for example, discloses a gas turbine control system capable of more accurately calculating the steam turbine output and more precisely setting the gas turbine output by adding correction of the degree of opening of a condenser reverse washing valve to the calculation of the steam turbine output to compensate for a delay in response from an instrument measuring the degree of vacuum of a condenser by using the degree of opening of the condenser reverse washing valve.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

For the invention in Patent Literature 1 above, however, it is difficult to determine the setting for correction of the degree of opening of the condenser reverse washing valve used for correcting the steam turbine output, and repeated tests are needed on site to adapt the setting to the actual equipment, thus requiring a complicated procedure on site.

An object of the present invention is to provide a gas turbine control system and method, for a single-shaft combined cycle plant, that can maintain a constant gas turbine output without requiring a complicated procedure on site and without being affected by variations in the output of a steam turbine during a reverse-washing/normal-washing switching period of a condenser.

Solution to Problem

To solve the above problem, the present invention employs the following solutions.

A first aspect of the present invention provides a gas turbine control system for a single-shaft combined cycle plant including a gas turbine, a steam turbine, a generator, and a condenser for condensing exhaust steam from the steam turbine, the gas turbine, the steam turbine, and the generator have rotating shafts thereof coupled together, and the control system generates a gas turbine output command using a parameter reflecting the gas turbine output during a reverse-washing/normal-washing switching period of the condenser.

With this configuration, the output command for the gas turbine is determined using the parameter reflecting the output of the gas turbine without taking the output of the steam turbine into account during the reverse-washing/normal-washing switching period of the condenser, so that a constant gas turbine output can be maintained without requiring a complicated procedure on site and without being affected by variations in the output of the steam turbine during the reverse-washing/normal-washing switching period of the condenser.

The gas turbine control system for the single-shaft combined cycle plant, as described above, may include a first command-generating section for generating the gas turbine output command on the basis of a generator output and a steam turbine output, a second command-generating section for generating the gas turbine output command using the parameter reflecting the gas turbine output, and a selection section for selecting the second command-generating section during the reverse-washing/normal-washing switching period of the condenser and selecting the first command-generating section during a period other than the reverse-washing/normal-washing switching period of the condenser.

With this configuration, the gas turbine output command generated using the parameter reflecting the gas turbine output without taking the steam turbine output into account is selected during the reverse-washing/normal-washing switching period of the condenser, whereas the gas turbine output command generated on the basis of the generation output and the steam turbine output is selected during a period other than the reverse-washing/normal-washing switching period of the condenser. This enables control of the gas turbine with an optimum gas turbine output command depending on the washing status of the condenser.

The gas turbine control system for the single-shaft combined cycle plant, as described above, may employ a command value related to control of the amount of fuel supplied to a combustor or the inlet temperature of the gas turbine as the parameter reflecting the output of the gas turbine.

The present invention provides a gas turbine control method for a single-shaft combined cycle plant including a gas turbine, a steam turbine, a generator, and a condenser for condensing exhaust steam from the steam turbine, the gas turbine, the steam turbine, and the generator have rotating shafts thereof coupled together, and the control method includes generating a gas turbine output command using a parameter reflecting a gas turbine output during a reverse-washing/normal-washing switching period of the condenser.

Advantageous Effects of Invention

The present invention provides the advantage of maintaining a constant gas turbine output without requiring a complicated procedure on site and without being affected by variations in the output of the steam turbine during switching between reverse washing and normal washing.

DESCRIPTION OF EMBODIMENTS

An embodiment of a gas turbine control system and method for a single-shaft combined cycle plant according to the present invention will be described below with reference to the drawings.

FIG. 1is a schematic configuration diagram of a single-shaft combined cycle power plant according to an embodiment of the present invention. The single-shaft combined cycle power plant includes a compressor1, a gas turbine3, a generator5, a steam turbine6, a condenser7, a condensate pump8, a waste heat recovery boiler9, a combustor11, a main steam regulating valve12, and a steam regulating valve13. The gas turbine3, the steam turbine6, and the generator5have rotating shafts thereof coupled together and are configured such that the gas turbine3and the steam turbine6are directly connected to the single generator5. In addition, a pipe for supplying, for example, air to the compressor1is equipped with a compressor inlet guide vane control valve (IGV control valve)2for controlling the angle of a compressor inlet guide vane for adjusting the flow rate of a working fluid such as air. In addition, a fuel pipe of the combustor11is equipped with a fuel flow rate control valve10for adjusting the fuel flow rate.

In this configuration, the combustor11is supplied with compressed air compressed by the compressor1and fuel whose flow rate has been adjusted by the fuel flow rate control valve10, and they are mixed and burned to generate combustion gas. This combustion gas flows into the gas turbine3to provide force for rotating the gas turbine3. Thus, the torque of the gas turbine3is transferred to the generator5so that the generator5generates electricity.

The combustion gas that has done work through the gas turbine3is guided, in the form of exhaust gas4, to the waste heat recovery boiler9downstream of the gas turbine4and is released to the atmosphere through a flue15. The waste heat recovery boiler9recovers heat from the exhaust gas4to generate steam with feedwater from the condensate pump8, high-pressure steam being guided into the steam turbine6through the main steam regulating valve12and low-pressure steam being guided into the steam turbine6through the steam regulating valve13. The steam guided into the steam turbine6rotates the steam turbine6. The torque of the steam turbine is transferred to the generator5so that the generator5generates electricity.

The steam that has done work through the steam turbine6is cooled and condensed by the downstream condenser7, is guided, in the form of condensate, into the condensate pump8, and is recirculated to the waste heat recovery boiler9. The steam turbine6, called a reheat turbine, has an intercept valve14for controlling reheat steam at a turbine inlet for reheat steam.

In normal operation, all steam generated by the waste heat recovery boiler9with the exhaust gas4from the gas turbine3is guided into the steam turbine6, with the main steam regulating valve12and the steam regulating valve13for adjusting the amount of steam being fully open. In this state, load control is mainly performed by adjusting the amount of fuel supplied to the gas turbine3through the fuel flow rate control valve10. The degree of opening of the fuel flow rate control valve10is adjusted on the basis of a fuel command value (CSO) appropriate for the deviation from the output of the generator5with respect to the output requested.

FIG. 2is a circulating water system diagram of the condenser7, where sea water is used as circulating water. First, sea water is pumped by a circulating water pump21and is introduced into an inlet water box of the condenser7through a circulating water pump discharge valve22, a condenser reverse washing valve23, etc. The sea water that has been used for cooling and condensing steam in the condenser7flows from an outlet water box of the condenser7through the condenser reverse washing valve23and then through a ball catcher24, a condenser outlet valve25, etc. and is released into a drain26. The ball catcher24collects balls for cleaning tubes of the condenser7, and the balls collected by the ball catcher24are sent to a ball-circulating pump27and are collected by a ball collector28. The balls collected by the ball collector28are injected into the circulating water system upstream of the condenser reverse washing valve23.

The condenser reverse washing valve23switches the circulating water system to switch the operation of the condenser7between reverse washing and normal washing. In reverse washing, the condenser reverse washing valve23is fully closed and operates so as to send the sea water pumped by the circulating water pump21to the output water box of the condenser7. Thus, the sea water pumped by the circulating water pump21is introduced into the output water box of the condenser7through the circulating water pump discharge valve22, the condenser reverse washing valve23, etc. The sea water reversed through the condenser7flows from the inlet water box of the condenser7through the condenser reverse washing valve23and then through the ball catcher24, the condenser outlet valve25, etc. and is released into the drain26.

Next, a gas turbine control system and method for the single-shaft combined cycle power plant will be described with reference toFIG. 3.

FIG. 3is a control system diagram of the gas turbine control system according to this embodiment. As shown inFIG. 3, a gas turbine control system30includes a first command-generating section31for generating a gas turbine output command by subtracting the steam turbine output from a requested output command for the generator5, a second command-generating section32for generating a gas turbine output command using a parameter reflecting the gas turbine output, a selection section33for selecting the second command-generating section32during a reverse-washing/normal-washing switching period of the condenser7and selecting the first command-generating section during a period other than the reverse-washing/normal-washing switching period of the condenser7, and a status-determining section34for determining whether or not the condenser7is currently in the reverse-washing/normal-washing switching period and outputting a signal corresponding to the determination result.

The first command-generating section31includes function generators41and42, a multiplier43, and a subtractor44as major components.

The inlet steam pressure of the steam turbine6is input to the function generator41. The inlet steam pressure used is, for example, a steam pressure measured by a pressure sensor provided downstream of the intercept valve14disposed in the steam turbine6. The function generator41possesses a characteristic diagram, shown inFIG. 4, that associates the inlet steam pressure with the steam turbine output, and by referring to the characteristic diagram, calculates the steam turbine output from the inlet steam pressure and outputs the steam turbine output to the multiplier43.

The degree of vacuum of the condenser7is input to the function generator42. The function generator42possesses a characteristic diagram, shown inFIG. 5, that associates the degree of vacuum of the condenser with a vacuum correction coefficient, and by referring to the characteristic diagram, calculates the vacuum correction coefficient from the degree of vacuum of the condenser and outputs the calculated vacuum correction coefficient to the multiplier43.

The multiplier43corrects the steam turbine output, which has been input from the function generator41, by multiplying the steam turbine output by the vacuum correction coefficient input from the function generator42and outputs the corrected steam turbine output to the subtractor44.

The subtractor44calculates the gas turbine output command by subtracting the corrected steam turbine output, which has been input from the multiplier43, from a generator output command generated by another system and outputs the gas turbine output command to the selection section33.

The second command-generating section32generates the gas turbine output command using a parameter reflecting the gas turbine output. Specifically, the second command-generating section32includes a function generator51as a major component. A fuel command value CSO related to the control of the amount of fuel supplied to the combustor11is input to the function generator51. The function generator51possesses a characteristic diagram, shown inFIG. 6, that associates the fuel command value CSO with the gas turbine output command, and by referring to the characteristic diagram, calculates the gas turbine output command from the fuel command value CSO and outputs the calculated gas turbine output command to the selection section33.

The status-determining section34determines whether or not the condenser7is currently switching between reverse washing and normal washing and outputs a signal corresponding to the determination result to the selection section33. Specifically, the reverse-washing-status determining section34determines whether or not switching between reverse washing and normal washing is underway on the basis of the degree of opening of the condenser reverse washing valve23. Specifically, as shown inFIG. 7, switching between reverse washing and normal washing is determined to be underway during a period when the condenser reverse washing valve23is shifting from a fully open state to a fully closed state and during a period when the condenser reverse washing valve23is shifting from a fully closed state to a fully open state.

More specifically, if the degree of valve opening of the condenser revere washing valve23falls within the range of 2% to 98%, the status-determining section34recognizes as switching between reverse washing and normal washing is underway and outputs a signal indicating that switching between reverse washing and normal washing is underway to the selection section33.

The selection section33selects and outputs the gas turbine output command input from the second command-generating section32while the signal being input from the status-determining section34, indicates that switching between reverse washing and normal washing is underway, and selects and outputs the gas turbine output command input from the first command-generating section31while the signal indicating that switching between reverse washing and normal washing is underway is not being input.

The gas turbine output command output from the selection section33is output to a controller35for controlling the angle of the compressor inlet guide vane (IGV control valve)2provided in the air pipe for supplying air to the compressor1and a controller36for controlling the degree of opening of the fuel flow rate control valve10for adjusting the flow rate of fuel to the combustor11.

The controller35possesses, for example, a characteristic diagram that associates the gas turbine output command with the angle of the compressor inlet guide vane, and by referring to the characteristic diagram, calculates the angle of the compressor inlet guide vane from the gas turbine output command and controls the compressor inlet guide vane control valve2to tilt the compressor inlet guide vane to the calculated angle.

In addition, the controller36possesses, for example, a characteristic diagram that associates the gas turbine output command with the fuel command value CSO, and by referring to the characteristic diagram, calculates the fuel command value CSO and controls the degree of opening of the fuel flow rate control valve10on the basis of the fuel command value CSO.

As described above, with the gas turbine control system and method for the single-shaft combined cycle plant according to this embodiment, the gas turbine output command is generated on the basis of a parameter reflecting the output of the gas turbine, such as the fuel command value CSO related to the control of the amount of fuel supplied to the combustor11, without taking the steam turbine output into account during the switching of the condenser7between reverse washing and normal washing. This allows an appropriate gas turbine output command to be generated without being affected by a decrease in steam turbine output due to a decrease in the degree of vacuum of the condenser7occurring during the switching of the condenser7between reverse washing and normal washing (seeFIG. 7). As a result, it is possible to achieve a stable generator output during the switching between reverse washing and normal washing and to prevent malfunctions of various equipment due to miscalculation of the gas turbine output command.

In addition, because the angle of the compressor inlet guide vane2and the degree of opening of the fuel flow rate control valve10are adjusted on the basis of the gas turbine output command determined as above, the angle of the compressor inlet guide vane2can be optimally controlled to improve the partial load efficiency of the single-shaft combined cycle power plant, and the degree of opening of the fuel flow rate control valve10can be optimally controlled to prevent an accidental fire and therefore to improve the reliability of the gas turbine3.

Furthermore, in the control of the gas turbine according to this embodiment, governor-free control is performed so that the degree of valve opening of the fuel flow rate control valve10becomes fully closed when, as shown inFIG. 8, the frequency of the power system reaches or exceeds a certain value (in this case, 52.5 Hz). Since the gas turbine output command is generated on the basis of the fuel command value CSO related to the control of the amount of fuel, the gas turbine control system and method according to this embodiment has the advantage that, even if the above governor-free control changes the fuel command value CSO related to the control of the amount of fuel during the switching of the condenser7between reverse washing and normal washing, the gas turbine output command can be generated so as to follow that change.

Although the case where the second command-generating section32generates the gas turbine output command on the basis of the fuel command value CSO has been described in the above embodiment, this is not limited thereto; for example, the gas turbine output command may be generated on the basis of the gas turbine inlet temperature.

REFERENCE SIGNS LIST