Valve control device, gas turbine, and valve control method

A valve control device is provided in a gas turbine having a combustor for generating combustion gas, a turbine driven by the combustion gas generated by the combustor, a flow rate regulating valve for regulating the flow rate of the fuel to be supplied to the combustor, and a pressure regulating valve disposed upstream of the flow rate regulating valve, for regulating the fuel pressure. The valve control device controls the opening degree of the valve. The valve control device includes a load decrease detection part which detects a load decrease of the gas turbine, and a pressure control part which controls the opening degree of the valve in accordance with the output of the gas turbine. The valve control device suppresses instability of the gas turbine output even when the load rapidly decreases.

TECHNICAL FIELD

The present invention relates to a valve control device, a gas turbine, and a valve control method.

BACKGROUND ART

A decrease in gas turbine load during operation of the gas turbine can cause a rapid increase in the rotational speed of the gas turbine.

For example, in a plant including a power generating facility which is grid-connected with a commercial power system and drives a generator by a gas turbine, and a load facility which consumes power, the rotational speed of the gas turbine increases when the power generating facility is isolated from the commercial power system and the power generating facility shifts to isolated operation of transmitting power only to the load facility in the plant. In this case, the demand for gas turbine output rapidly decreases (load decrease) by an amount corresponding to the loss of load under which the power generating facility would otherwise transmit power to the commercial power system. This makes it necessary to rapidly throttle the fuel to be supplied to a combustor of the gas turbine.

In actual operation, however, reduction in the mechanical output of the gas turbine can be delayed due to the following reasons: a delay in detection of the load decrease; supply of the fuel remaining in a fuel passage to the combustor; a delay in action of a flow rate regulating valve for regulating the fuel flow rate or a pressure regulating valve for regulating the fuel pressure; or other causes, which can result in an increase in frequency of the power system in the plant.

Therefore, when a shift to isolated operation occurs, it is necessary to suppress an increase in frequency as well as to secure stability of combustion.

In view of this, PTL 1 describes a gas turbine fuel control device, which, upon occurrence of isolation from a load or isolation from a power transmission system, sets a fuel flow rate in a predetermined premixed combustion fuel system of multiple premixed combustion fuel systems to a predetermined first minimum fuel flow rate required for flame retention, for a first effective time, and sets a fuel flow rate in a diffusion combustion fuel system to a predetermined second minimum fuel flow rate required for flame retention, for a second effective time.

CITATION LIST

Patent Literature

The Publication of Japanese Patent No. 3828738

SUMMARY OF INVENTION

Technical Problem

Setting the fuel flow rate to a predetermined value upon occurrence of isolation from the load or isolation from the power transmission system, as described in PTL 1, is effective only if the demanded gas turbine output after isolated operation is always at a fixed value.

However, when the demanded gas turbine output before and after the isolated operation is not at a fixed value, the required fuel amount changes accordingly. In this case, unless an appropriate opening degree of the fuel control valve is set in accordance with the demanded output after isolated operation, frequency variations or combustion instability can be caused.

The present invention has been made in consideration of this situation, and an object thereof is to provide a valve control device, a gas turbine, and a valve control method, which can suppress instability of the gas turbine output even when the load rapidly decreases.

Solution to Problem

In order to make an improvement in the above situation, a valve control device, a gas turbine, and a valve control method of the present invention have adopted the following solutions.

According to a first aspect of the present invention, there is provided a valve control device disposed in a gas turbine, the gas turbine comprising: a combustor for generating combustion gas by combusting fuel; a turbine driven by the combustion gas generated by the combustor; a flow rate regulating valve for regulating a flow rate of the fuel to be supplied to the combustor; and a pressure regulating valve disposed upstream of the flow rate regulating valve in a fuel passage for supplying the fuel to the combustor, for regulating the fuel pressure, wherein the valve control device controls at least opening degree of the pressure regulating valve, the valve control device comprising: a detection section for detecting a load decrease of the gas turbine; and a pressure control section for controlling the opening degree of the pressure regulating valve on the basis of an output value of the gas turbine after the load decreases when the detection section detects the load decrease.

According to this configuration, the valve control device is disposed in the gas turbine, and the gas turbine comprises the following elements: the combustor for generating the combustion gas by combusting the fuel; the turbine driven by the combustion gas generated by the combustor; the flow rate regulating valve for regulating the flow rate of the fuel to be supplied to the combustor; and the pressure regulating valve for regulating the fuel pressure, disposed upstream of the flow rate regulating valve in the fuel passage for supplying the fuel to the combustor, and the valve control device controls at least the opening degree of the pressure regulating valve.

Then, the detection section detects a load decrease of the gas turbine. When the gas turbine load decreases and the fuel amount fails to be reduced in a desired time period in accordance with the load, the gas turbine output can become unstable.

Here, the fuel flow rate is regulated by feedback control of the opening degree of the flow rate regulating valve, for example, on the basis of the gas turbine output. However, even when the feedback control is performed on the flow rate regulating valve on the basis of the gas value after the load decrease, an increase in the frequency or combustion instability cannot be suppressed unless the pressure regulating valve disposed upstream of the flow rate regulating valve is at an appropriate opening degree.

Therefore, upon detection of a load decrease by the detection section, the opening degree of the pressure regulating valve is controlled by the pressure control section in accordance with the gas turbine output after the load decrease. The control in accordance with the gas turbine output after the load decrease refers namely to feedforward control. In this way, when the gas turbine load decreases, control is performed such that the pressure regulating valve regulates the fuel pressure to an appropriate value corresponding to the load. This makes it possible to control such that the flow rate regulating valve disposed downstream of the pressure regulating valve regulates the fuel flow rate to an appropriate value corresponding to the load.

Thus, this configuration can suppress instability of the gas turbine output even when the load rapidly decreases.

In the first aspect, it is preferable that the pressure control section obtains a fuel demand value indicating an amount of the fuel to be supplied to the combustor on the basis of an output demand value for the gas turbine after the load decrease, and determines the opening degree of the pressure regulating valve on the basis of the fuel demand value.

According to this configuration, since the fuel demand value indicating the amount of fuel to be supplied to the combustor is obtained in accordance with the output demand value of the gas turbine after the load decrease, and the opening degree of the pressure regulating valve is determined on the basis of the fuel demand value, the opening degree of the pressure regulating valve after the load decrease can be precisely determined.

In the first aspect, it is preferable that the valve control device further includes an air flow rate calculation section for calculating a flow rate of air to be fed to a compressor on the basis of the output demand value, the compressor introducing compressed air into the combustor, wherein the pressure control section derives the fuel demand value corresponding to the air flow rate calculated by the air flow rate calculation section, atmospheric temperature, and the output demand value, by using heat balance data indicating at least one of state values at inlets and outlets of components constituting the gas turbine.

According to this configuration, the flow rate of the air to be fed to the compressor, which introduces the compressed air into the combustor, is calculated by the air flow rate calculation section on the basis of the output demand value of the gas turbine. Then, the fuel demand value is derived, as a value corresponding to the air flow rate calculated by the air flow rate calculation section, the atmospheric temperature, and the output demand value of the gas turbine, from the heat balance data indicating at least one of the state values at the inlets and outlets of the components constituting the gas turbine.

Thus, in this configuration, since the fuel demand value corresponding to the output demand value of the gas turbine after the load decrease is obtained from the heat balance of the gas turbine, and the opening degree of the pressure regulating valve is determined accordingly, the opening degree of the pressure regulating valve after the load decrease can be precisely determined.

In the first aspect, it is preferable that the pressure control section derives the fuel demand value corresponding to the output demand value by using first information indicating a relation between the output demand value and the fuel demand value.

According to this configuration, the fuel demand value is derived from the first information indicating the relation between the output demand value and the fuel demand value of the gas turbine after the load decrease, and the opening degree of the pressure regulating valve is determined accordingly. Since the amount of calculations performed to determine the opening degree of the pressure regulating valve can be reduced, the opening degree of the pressure regulating valve after the load decrease can be determined in a simple configuration.

In the first aspect, it is preferable that the pressure control section derives the opening degree corresponding to the output demand value by using second information indicating a relation between the output demand value of the gas turbine and the opening degree of the pressure regulating valve.

According to this configuration, the opening degree of the pressure regulating valve is derived from the second information indicating the relation between the output demand value of the gas turbine and the opening degree of the pressure regulating valve. Since the amount of calculations performed to determine the opening degree of the pressure regulating valve is reduced, the opening degree of the pressure regulating valve after the load decrease can be determined in a simple configuration.

In the first aspect, it is preferable that the pressure control section corrects the derived opening degree on the basis of parameters influencing a combustion state in the combustor.

According to this configuration, since the opening degree of the pressure regulating valve derived by using the second information is corrected on the basis of the parameters influencing the combustion state in the combustor, the opening degree of the pressure regulating valve after the load decrease can be precisely determined. The above-mentioned parameters include atmospheric temperature, a fuel calorific value, fuel temperature, and fuel supply pressure.

In the first aspect, it is preferable that the pressure control section determines the opening degree of the pressure regulating valve by using a command value and on the basis of the fuel demand value derived from third information indicating a relation between the command value and the fuel demand value indicating an amount of the fuel to be supplied to the combustor, the command value indicating the fuel flow rate calculated on the basis of rotational speed of the gas turbine after the load decrease.

According to this configuration, since the fuel demand value is calculated by using the command value indicating the fuel flow rate calculated on the basis of the rotational speed of the gas turbine after the load decrease, the opening degree of the pressure regulating valve after the load decrease can be more precisely determined. As the opening degree of the flow rate regulating valve corresponds to the fuel flow rate, the above-mentioned command value also includes the opening degree of the flow rate regulating valve.

In the first aspect, it is preferable that the pressure control section controls the opening degree of the pressure regulating valve on the basis of the gas turbine output value after the load decrease when the amount of the load decrease exceeds a predetermined threshold value.

Since the pressure regulating valve is not controlled in accordance with the load decrease if the amount of the load decrease is small, this configuration can suppress the risk of flame-out, etc. caused by controlling the pressure regulating valve in accordance with the load decrease.

According to a second aspect of the present invention, there is provided a gas turbine including: a combustor for generating combustion gas by combusting fuel; a turbine driven by the combustion gas generated by the combustor; a flow rate regulating valve for regulating flow rate of the fuel to be supplied to the combustor; a pressure regulating valve disposed upstream of the flow rate regulating valve, for regulating fuel pressure; and the valve control device configured in accordance with any one of claims1to8, for controlling the opening degree of the pressure regulating valve.

According to a third aspect of the present invention, there is provided a valve control method disposed in a gas turbine including the following elements: a combustor for generating combustion gas by combusting fuel; a turbine driven by the combustion gas generated by the combustor; a flow rate regulating valve for regulating the flow rate of the fuel to be supplied to the combustor; and a pressure regulating valve for regulating the fuel pressure, disposed upstream of the flow rate regulating valve in a fuel passage for supplying the fuel to the combustor, the valve control method controlling at least the opening degree of the pressure regulating valve, wherein the valve control method includes the following: a first step of detecting a load decrease of the gas turbine; and a second step of, upon detection of the load decrease, controlling the opening degree of the pressure regulating valve in accordance with the gas turbine output after the load decrease.

Advantageous Effects of Invention

According to the present invention, an advantage of suppressing instability of gas turbine output even when the load rapidly decreases is obtained.

DESCRIPTION OF EMBODIMENTS

An embodiment of a valve control device, a gas turbine, and a valve control method according to the present invention will be described below with reference to the drawings.

FIG. 1is a configuration diagram of an entire plant10according to a first embodiment. The plant10includes the following elements: a power generating facility16constituted of a gas turbine12and a generator14; and load facilities18consuming power.

The gas turbine12includes a compressor20, a combustor22, and a turbine24.

The compressor20is driven by a rotating shaft26and thereby compresses air suctioned from an air intake port and generates compressed air. The combustor22injects fuel to the compressed air which is introduced from the compressor20into a casing28, and generates high-temperature, high-pressure combustion gas. The turbine24is driven to rotate by the combustion gas generated in the combustor22. The amount of air suctioned into the compressor20is regulated by opening and closing of an inlet guide vane (hereinafter referred to as “IGV”) provided at an inlet of the compressor20.

A bypass pipe30is provided between the casing28and the combustor22, and when the air inside the combustor22becomes insufficient due to load variations of the turbine24, the bypass pipe30serves as a passage for introducing the air in the casing28into the combustor22upon opening of a combustor bypass valve32. A bleed pipe34is provided between the compressor20and the turbine24for introducing cooling air from the compressor20into the turbine24.

The turbine24, the compressor20, and the generator14are coupled together by the rotating shaft26, and rotary drive force generated in the turbine24is transmitted by the rotating shaft26to the compressor20and the generator14. Then, the generator14generates power by the rotary drive force of the turbine24. The generator14is connected with the load facilities18and supplies generated power to the load facilities18in the plant10. The generator14is also grid-connected with a commercial power system, and supplies generated power to the commercial power system which is a power grid outside the plant10.

A breaker36A is provided in a power transmission line between the power generating facility16and the load facilities18, while a breaker36B is provided in a power transmission line between the power generating facility16and the commercial power system.

The combustor22has a nozzle38and combusts the fuel supplied through the nozzle38by using the compressed air.

A fuel passage40for supplying the fuel to the combustor22is provided with a flow rate regulating valve42for regulating the flow rate of the fuel to be supplied to the combustor22, and a pressure regulating valve44which is for regulating the fuel pressure and disposed upstream of the flow rate regulating valve42in the fuel passage40. The amount of fuel to be supplied to the combustor22is controlled as the opening degrees of the flow rate regulating valve42and the pressure regulating valve44are controlled.

A valve control device50includes a load decrease detection part52, a flow rate control part54, and a pressure control part56.

The load decrease detection part52detects a decrease in the load (hereinafter referred to as “load decrease”) of the gas turbine12.

The flow rate control part54controls the opening degree of the flow rate regulating valve42and thereby controls the flow rate of the fuel to be supplied to the combustor22. More specifically, the flow rate control part54controls the fuel flow rate by performing feedback control of the opening degree of the flow rate regulating valve42on the basis of the output of the gas turbine12.

The pressure control part56controls the opening degree of the pressure regulating valve44and thereby controls the pressure of the fuel to be supplied to the combustor22. More specifically, the pressure control part56controls the opening degree of the pressure regulating valve44such that the pressure of the fuel flowing through the fuel passage40is at a predetermined value.

The cases where the load of the gas turbine12decreases include, for example, a case where power supply from the power generating facility16to the commercial power system is cut off, due to a break in the power transmission line between the power generating facility16and the commercial power system, opening of the breaker36B, or other causes. In such cases, the load of the gas turbine12rapidly decreases.

Referring toFIG. 2, a change in the output of the gas turbine12upon occurrence of a load decrease will now be described, by taking the case for example where power supply to the commercial power system is cut off.

When the power supply to the commercial power system is cut off, the power generating facility16shifts to isolated operation of transmitting power only to the load facilities18in the plant10. As shown inFIG. 2, this causes a rapid decrease in the output of the gas turbine12by an amount corresponding to the loss of load (lost load) under which the power would otherwise be transmitted to the commercial power system. In other words, the output demand for the gas turbine12becomes an amount corresponding to the load possessed by the load facilities18(load within the system).

The opening degrees of the flow rate regulating valve42and the pressure regulating valve44are throttled in accordance with the load decrease to reduce the fuel to be supplied to the combustor22. In an actual operation, however, reduction of the mechanical output of the gas turbine12can be delayed due to a delay in detection of the load decrease, supply of the fuel remaining in the fuel passage40to the combustor22, a delay in action of the flow rate regulating valve42or the pressure regulating valve44, or other causes, which can result in an increase in frequency of the power system in the plant10.

Even when the opening degree of the flow rate regulating valve42is throttled, if throttling of the pressure regulating valve44disposed upstream of the flow rate regulating valve42is delayed, the amount of fuel supplied to the combustor22becomes larger than expected due to the increased fuel pressure, causing a further increase in the frequency. On the other hand, excessively throttling the fuel deteriorates the combustion stability and can result in flame-out.

FIG. 3is a graph showing an example of a change in the frequency of the power system in the plant10upon occurrence of a load decrease, in a case where a determined throttled opening degree of the pressure regulating valve44is small. As shown inFIG. 3, if the opening degree of the pressure regulating valve44after the load decrease is small, the pressure of the fuel supplied to the combustor22decreases, and accordingly, the amount of fuel becomes too small relative to the load, and therefore the frequency can significantly decrease after increasing with the load decrease.

FIG. 4is a graph showing an example of a change in the frequency of the power system in the plant10upon occurrence of a load decrease, in a case where the determined throttled opening degree of the pressure regulating valve44is large. As shown inFIG. 4, when the opening degree of the pressure regulating valve44after the load decrease is large, the pressure of the fuel supplied to the combustor22decreases insufficiently, and accordingly, the fuel amount becomes too large relative to the load, and therefore the frequency can significantly increase with the load decrease.

As shown inFIG. 3andFIG. 4, even when feedback control is performed on the flow rate regulating valve42on the basis of the output of the gas turbine12after the load decrease, an increase in the frequency or combustion instability cannot be suppressed unless the pressure regulating valve44disposed upstream of the flow rate regulating valve42is at an appropriate opening degree.

Therefore, upon detection of a load decrease of the gas turbine12by the load decrease detection part52, the pressure control part56according to the first embodiment of the present invention performs load-decrease opening degree control for controlling the opening degree of the pressure regulating valve44in accordance with the output of the gas turbine12after the load decrease. The load-decrease opening degree control according to the first embodiment obtains a fuel demand value indicating an amount of fuel to be supplied to the combustor22in accordance with an output demand value of the gas turbine12(hereinafter referred to as “GT output demand value”) after the load decrease, and determines the opening degree of the pressure regulating valve44on the basis of the fuel demand value.

FIG. 5is a function block diagram showing a function of the pressure control part56for performing the load-decrease opening degree control according to the first embodiment.

The pressure control part56includes an IGV opening degree calculation part60, a fuel demand value deriving part62, a valve flow rate calculation part64, and an opening degree determining part66.

The GT output demand value and a measured atmospheric temperature value, which is a measurement result of the atmospheric temperature, are inputted into the IGV opening degree calculation part60. Then, the IGV opening degree calculation part60calculates the flow rate of the air to be fed to the compressor20on the basis of the GT output demand value and the measured atmospheric temperature value, and calculates the opening degree of the IGV corresponding to the calculated air flow rate.

The fuel demand value deriving part62derives the fuel demand value corresponding to the air flow rate calculated by the IGV opening degree calculation part60, the measured atmospheric temperature value, and the GT output demand value, by using GT heat balance data indicating state values (temperature, pressure, enthalpy, flow rate, etc.) at inlets and outlets of components constituting the gas turbine12. The GT heat balance data is created in advance as design values of the gas turbine12and stored in the fuel demand value deriving part62.

To determine the opening degree of the pressure regulating valve44corresponding to the fuel demand value, the pressure control part56calculates a Cv value in the valve flow rate calculation part64.

The valve flow rate calculation part64calculates a Cv value of the pressure regulating valve44on the basis of the fuel demand value derived in the fuel demand value deriving part62, inlet pressure of the pressure regulating valve44(supply pressure of the fuel to the pressure regulating valve44), a set value of outlet pressure of the pressure regulating valve44, and a measured value of the fuel temperature.

The Cv value is calculated, for example, using a general formula as shown in Formula 1, where the fuel demand value is W, a difference between the inlet pressure and the outlet pressure in the pressure regulating valve44is AP, and the fuel temperature is T:

Table information A (table function) indicating a relation between the Cv value and the opening degree of the pressure regulating valve44is stored in advance in the opening degree determining part66. Then, the opening degree determining part66determines the opening degree corresponding to the Cv value, calculated in the valve flow rate calculation part64, as the opening degree of the pressure regulating valve44and sends a valve opening degree setting value indicating the determined opening degree to the pressure regulating valve44.

The load decrease detection part52sends an instruction for execution of the load-decrease opening degree control to the pressure control part56, if the load decrease amount exceeds a predetermined threshold value. In this way, when the load decrease amount is small, the valve control device50according to the first embodiment does not perform the load-decrease opening degree control on the pressure regulating valve44. Accordingly, the risk of flame-out, etc. caused by controlling the pressure regulating valve44in accordance with the load decrease can be suppressed.

FIG. 6is a flowchart showing a flow of processing by the load decrease detection part52according to the first embodiment.

First, in step100, the load of the gas turbine12is measured. The load is measured, for example, by detecting the output of the generator14(hereinafter referred to as “generator output”), and the detected value of the generator output is sequentially stored.

In the next step102, a difference between the detected current generator output and a generator output detected a predetermined time (e.g., one second) earlier is calculated as the load decrease amount.

In the next step104, it is determined whether the calculated load decrease amount is on or higher than the threshold value. If the determination results in the affirmative, the flow proceeds to step106, while if it results in the negative, the flow returns to step100. The threshold value is, for example, an expected loss of the load when the power generating facility16is isolated from the commercial power system.

In step106, the instruction for execution of the load-decrease opening degree control is sent to the pressure control part56.

Upon receipt of the instruction for execution of the load-decrease opening degree control, the pressure control part56controls the opening degree of the pressure regulating valve44in accordance with the output of the gas turbine12after the load decrease.

As mentioned above, the pressure control part56according to the first embodiment calculates the flow rate of the air to be fed to the compressor20on the basis of the GT output demand value and the measured atmospheric temperature value, and derives the fuel demand value, by using the GT heat balance data, as a value corresponding to the calculated air flow rate, the measured atmospheric temperature value, and the GT output demand value. Then, the pressure control part56determines the opening degree of the pressure regulating valve44corresponding to the fuel demand value, and sends the valve opening degree setting value indicating the determined opening degree to the pressure regulating valve44.

Upon receipt of the valve opening degree setting value, the pressure regulating valve44is regulated to the opening degree as indicated by the valve opening degree setting value.

The load-decrease opening degree control refers namely to feedforward control on the pressure regulating valve44. In this way, when the load of the gas turbine12decreases, the fuel pressure is controlled to an appropriate value, which corresponds to the load, by the pressure regulating valve44. This makes it possible to control such that the flow rate regulating valve42disposed downstream of the pressure regulating valve44controls the fuel flow rate to an appropriate value corresponding to the load.

FIG. 7is a graph showing a change over time in the opening degree of the pressure regulating valve44and a change over time in the frequency of the power system in the plant10, in a case where the load-decrease opening degree control according to the first embodiment is performed.

As shown inFIG. 7, the opening degree of the pressure regulating valve44varies near the opening degree in a stabilized state (stabilized opening degree), and as this opening degree reaches an appropriate value, the fuel flow rate also becomes appropriate, so that variations in the frequency become smaller.

As described above, upon detection of a load decrease by the load decrease detection part52, the valve control device50according to the first embodiment controls the opening degree of the pressure regulating valve44by the pressure control part56in accordance with the output of the gas turbine12after the load decrease.

The pressure control part56according to the first embodiment obtains the fuel demand value in accordance with the GT output demand value and determines the opening degree of the pressure regulating valve44on the basis of the fuel demand value. For this purpose, the pressure control part56calculates the flow rate of the air to be fed to the compressor20on the basis of the GT output demand value, and by using the GT heat balance data, derives the fuel demand value corresponding to the calculated air flow rate, the atmospheric temperature, and the GT output demand value.

Thus, the valve control device50according to the first embodiment can precisely determine the opening degree of the pressure regulating valve44after the load decrease, and can suppress instability of the output of the gas turbine12even when the load rapidly decreases.

In the valve control device50according to the first embodiment, it is not essential to use the atmospheric temperature in deriving the fuel demand value by using the GT heat balance data. More specifically, the fuel demand value corresponding to the air flow rate and the output demand value is derived by using the GT heat balance data, with the atmospheric temperature taken as a fixed value. The atmospheric temperature taken as a fixed value may be varied according to the season.

Description of the configuration of the plant10according to the second embodiment will be omitted, as it is similar to or the same as the configuration of the plant10according to the first embodiment shown inFIG. 1.

FIG. 8is a function block diagram showing a function of the pressure control part56for performing load-decrease opening degree control according to the second embodiment. Components inFIG. 8that are the same as those inFIG. 5will be denoted by the same reference signs as inFIG. 5and description thereof will be omitted.

Table information B (table function) indicating a relation between the GT output demand value and the fuel demand value is stored in a fuel demand value deriving part70according to the second embodiment. This table information B is created in advance. When the instruction for execution of the load-decrease opening degree control is received by the pressure control part56and the GT output demand value after the load decrease is inputted, the fuel demand value deriving part70derives the fuel demand value corresponding to the inputted GT output demand value by using the table information B, and outputs the fuel demand value to the valve flow rate calculation part64.

Then, the pressure control part56according to the second embodiment determines the opening degree of the pressure regulating valve44by the valve flow rate calculation part64and the opening degree determining part66, on the basis of the fuel demand value derived by the fuel demand value deriving part70.

As described above, the pressure control part56according to the second embodiment derives the fuel demand value corresponding to the GT output demand value after the load decrease by using the table information B indicating the relation between the GT output demand value and the fuel demand value. Thus, since the amount of calculations performed to determine the opening degree of the pressure regulating valve44is reduced, the pressure control part56according to the second embodiment can determine the opening degree of the pressure regulating valve44after the load decrease in a simple configuration.

A third embodiment of the present invention will be described below.

Description of the configuration of the plant10according to the third embodiment will be omitted, as it is similar to or the same as the configuration of the plant10according to the first embodiment shown inFIG. 1.

FIG. 9is a function block diagram showing a function of the pressure control part56for performing load-decrease opening degree control according to the third embodiment.

The pressure control part56according to the third embodiment includes an opening degree determining part80and a correction part82.

Table information C (table function) indicating a relation between the GT output demand value and the opening degree of the pressure regulating valve44is stored in the opening degree determining part80. This table information C is created in advance. When the instruction for execution of the load-decrease opening degree control is received by the pressure control part56and the GT output demand value after the load decrease is inputted, the opening degree determining part80derives the opening degree of the pressure regulating valve44corresponding to the inputted GT output demand value by using the table information C, and outputs the valve opening degree setting value indicating the opening degree to the correction part82.

The correction part82corrects the inputted valve opening degree setting value on the basis of parameters influencing the combustion state in the combustor22. The above-mentioned parameters include atmospheric temperature, a fuel calorific value, fuel temperature, fuel supply pressure, or etc., each value of which is inputted into the correction part82as a correction signal.

For example, a higher atmospheric temperature means a lower air density, hence the output of the gas turbine12decreases. Therefore, at high atmospheric temperatures, the correction part82corrects the valve opening degree setting value such that the amount of fuel to be supplied to the combustor22becomes larger.

A higher fuel calorific value means an increased output of the gas turbine12. Therefore, at high fuel calorific values, the correction part82corrects the valve opening degree setting value such that the amount of fuel to be supplied to the combustor22becomes smaller.

A higher fuel temperature means a lower fuel density, hence the output of the gas turbine12decreases. Therefore, at high fuel temperatures, the correction part82corrects the valve opening degree setting value such that the amount of fuel to be supplied to the combustor22becomes larger.

A higher fuel supply pressure means a higher fuel density, hence the output of the gas turbine12increases. Therefore, at high fuel temperatures, the correction part82corrects the valve opening degree setting value such that the amount of fuel to be supplied to the combustor22becomes smaller.

Then, the valve opening degree setting value corrected by the correction part82is sent to the pressure regulating valve44.

As described above, the pressure control part56according to the third embodiment derives the opening degree of the pressure regulating valve44corresponding to the GT output demand value after the load decrease by using the table information C indicating the relation between the GT output demand value and the opening degree of the pressure regulating valve44. Thus, since the amount of calculations performed to determine the opening degree of the pressure regulating valve44is reduced, the pressure control part56according to the third embodiment can determine the opening degree of the pressure regulating valve44after the load decrease in a simple configuration.

In addition, since the pressure control part56according to the third embodiment corrects the opening degree of the pressure regulating valve44, derived by using the table information C, on the basis of the parameters which influences the combustion state in the combustor22, the opening degree of the pressure regulating valve44after the load decrease can be precisely determined.

A fourth embodiment of the present invention will be described below.

Description of the configuration of the plant10according to the fourth embodiment will be omitted, as it is similar to or the same as the configuration of the plant10according to the first embodiment shown inFIG. 1.

A fuel flow rate command value, which is a command value indicating the fuel flow rate, immediately after a shift to isolated operation is under rotational speed control as control based on the rotational speed of the gas turbine12. For this reason, due to the rotational speed control, the fuel flow rate command value immediately after the shift to isolated operation is a value different from the flow rate for a case of the gas turbine12in a stabilized state. Especially when the loss of the load is large, the fuel flow rate command value is suppressed to a flow rate lower than the flow rate in the stabilized state.

Therefore, the pressure control part56according to the fourth embodiment derives the fuel demand value by using the fuel flow rate command value as a value corresponding to the output of the gas turbine12after the load decrease.

FIG. 10is a function block diagram showing a function of the pressure control part56for performing load-decrease opening degree control according to the fourth embodiment. Components inFIG. 10that are the same as those inFIG. 5will be denoted by the same reference signs as inFIG. 5and description thereof will be omitted.

Table information D (table function) indicating a relation between the fuel flow rate command value and the fuel demand value is stored in a fuel demand value deriving part90according to the fourth embodiment. This table information D is created in advance. When the instruction for execution of the load-decrease opening degree control is received by the pressure control part56and the fuel flow rate command value after the load decrease is inputted, the fuel demand value deriving part90derives the fuel demand value corresponding to the inputted fuel flow rate command value by using the table information D, and outputs the fuel demand value to the valve flow rate calculation part64.

Then, the pressure control part56according to the fourth embodiment determines the opening degree of the pressure regulating valve44by the valve flow rate calculation part64and the opening degree determining part66, on the basis of the fuel demand value derived by the fuel demand value deriving part90.

As described above, since the pressure control part56according to the fourth embodiment derives the fuel demand value corresponding to the fuel flow rate command value after the load decrease, by using the fuel flow rate command value, the opening degree of the pressure regulating valve44after the load decrease can be precisely determined. Since the opening degree of the flow rate regulating valve42corresponds to the fuel flow rate, the pressure control part56according to the fourth embodiment may use a opening degree command value of the flow rate regulating valve42instead of the fuel flow rate command value.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. Various modifications or improvements can be made to each of the embodiments within the scope of the present invention, and such modified or improved forms are also included in the technical scope of the present invention.

REFERENCE SIGNS LIST