Control system, gas turbine, power generation plant, and method of controlling fuel temperature

A control system is configured to control a temperature of a fuel which is supplied to a combustor of a gas turbine via a fuel gas heater, which is configured to heat the fuel of the gas turbine, by adjusting a flow rate of heated water which is supplied to the fuel gas heater. The control system includes a water flow rate adjusting unit configured to adjust the flow rate of the heated water which is supplied to the fuel gas heater based on a difference between a target temperature of the fuel and the temperature of the fuel on an outlet side of the fuel gas heater.

CROSS-REFERENCE TO RELATED APPLICATION

Priority is claimed from Japanese Patent Application No. 2017-005030, filed Jan. 16, 2017, the content of which is incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a control system, a gas turbine, a power generation plant, and a method of controlling a fuel temperature.

BACKGROUND ART

In a gas turbine combined cycle (GTCC) plant for generation of power, a fuel gas heater (FGH) is provided in a fuel system for the purpose of control of a temperature of a fuel which is supplied to a gas turbine. In the fuel gas heater, a fuel gas is heated by exchange of heat with heated water from a heat recovery steam generator (HRSG). General control of supply of water to a fuel gas heater will be described below with reference to accompanying drawings.FIG. 14is a system diagram of a fuel gas heater according to the related art.FIG. 15is a block diagram illustrating a water supply control process in the fuel gas heater according to the related art. As illustrated inFIG. 14, a fuel gas flows in a direction of an arrow (from right to left in the drawing) and is supplied to a combustor of a gas turbine (GT). On the other hand, water HW (heated water) which is supplied from the heat recovery steam generator flows in a direction of an arrow (from left to right in the drawing), heats the fuel gas in the fuel gas heater70, and flows to the heat recovery steam generator or a steam condenser.

Opening control of a water flow rate regulator valve71according to the related art will be first described below. The water flow rate regulator valve71is provided to control a flow rate of heated water which is required for heating fuel and to recover the heated water to the HRSG side (a low-pressure water supply side) during operation of a gas turbine. Opening control of the water flow rate regulator valve71will be described below with reference toFIG. 15(a). A function element P10receives an input of a load of the gas turbine (GTMW) as an input and calculates a degree of valve opening suitable for the GTMW. The degree of opening of the water flow rate regulator valve71is controlled such that it reaches the calculated degree of valve opening. In this way, feedforward control based on a load is performed on the water flow rate regulator valve71in consideration of valve characteristics in drive modes such as starting, stopping, partial load operation, and rated operation of the gas turbine.

Opening control of a dump valve72according to the related art will be described below. The dump valve72is provided to control a flow rate of heated water to a fuel gas heater70at the time of start and stop of the gas turbine and to dump the heated water to a stem condenser. The dump valve72is controlled by feedback control for a target flow rate at the time of start and stop, and the control is switched to control using the water flow rate regulator valve71and the dump valve72is fully closed at the time of operation with a high load. When a load decreases and a flow rate of a fuel gas passing through the fuel gas heater70decreases, control for opening the dump valve by the feedback control is performed. Opening control logic of the dump valve72is illustrated inFIG. 15(b). The function element D10receives a load (GTMW) of the gas turbine as an input and converts the input load to a target flow rate F1suitable for the GTMW. A subtractor D11calculates a difference between the target flow rate F1and an actual water flow rate F2by subtracting the flow rate F2measured by a flowmeter16from the target flow rate F1. Then, a controller D12calculates a degree of valve opening for causing the difference to approach 0 by PI control and performs control such that the degree of opening of the dump valve72reaches the calculated degree of valve opening.

Japanese Unexamined Patent Application, First Publication No. 2002-256816 describes that, regarding a problem in which water is steamed due to operation with excessive fuel because adjustment of decreasing a fuel gas is insufficient with respect to a decrease in an amount of water based on a decrease in the output of a steam turbine in temperature adjustment of water for heating fuel at the time of partial load operation in a combined plant, an amount of water which is likely to be insufficient is supplemented by providing a recirculation system for recirculating water.

SUMMARY OF INVENTION

Technical Problem

As described above, the fuel gas heater70heats a fuel gas using heated water from the heat recovery steam generator, but since the heated water which is supplied to the fuel gas heater70is controlled by control for supplying a flow rate corresponding to a load of the gas turbine, there is a likelihood that the temperature of the fuel gas on the outlet side of the fuel gas heater70will not be controlled to a desired value.

The invention provides a control system, a gas turbine, a power generation plant, and a method of controlling a fuel temperature that can solve the above-mentioned problem.

Solution to Problem

According to a first aspect of the invention, there is provided a control system that controls a temperature of fuel which is supplied to a combustor of a gas turbine via a fuel gas heater, which heats the fuel of the gas turbine, by adjusting a flow rate of heated water which is supplied to the fuel gas heater, the control system including: a water flow rate adjusting unit that adjusts the flow rate of the heated water which is supplied to the fuel gas heater based on a difference between a target temperature of the fuel and the temperature of the fuel on an outlet side of the fuel gas heater.

In a second aspect of the invention, the control system may control the temperature of the fuel by controlling the flow rate of the heated water which is supplied from a supply device of heated water to the fuel gas heater by adjusting a degree of opening of a water flow rate regulator valve that regulates a flow rate of heated water which is recovered from the fuel gas heater to the supply device of heated water and a degree of opening of a dump valve that regulates a flow rate of heated water which is dumped to a steam condenser, and the water flow rate adjusting unit may include: a first valve opening calculating unit that calculates a first valve opening which is a degree of opening of the water flow rate regulator valve based on a load of the gas turbine; a third valve opening calculating unit that calculates a third valve opening by calculating a correction value based on a difference between the target temperature of the fuel which is supplied to the combustor of the gas turbine and the temperature of the fuel on the outlet side of the fuel gas heater and adding the calculated correction value to the first valve opening; a water flow rate regulator valve control unit that controls the degree of opening of the water flow rate regulator valve on the basis of the third valve opening; and a dump valve control unit that controls the degree of opening of the dump valve on the basis of a difference between a target flow rate of the heated water which is determined in advance on the basis of the load of the gas turbine and an actual flow rate.

In a third aspect of the invention, the third valve opening calculating unit may perform calculation of the correction value based on the difference between the target temperature of the fuel and the temperature of the fuel on the outlet side of the fuel gas heater by feedback control.

In a fourth aspect of the invention, the control system may further include a second valve opening calculating unit that calculates a second valve opening by multiplying the first valve opening by a coefficient based on a temperature of the fuel on an inlet side of the fuel gas heater, and the third valve opening calculating unit may calculate the third valve opening by adding the correction value to the second valve opening instead of the first valve opening.

In a fifth aspect of the invention, the dump valve control unit may control the degree of opening of the dump valve using a flow rate which is less than the flow rate of the heated water passing through the water flow rate regulator valve as a target flow rate.

In a sixth aspect of the invention, the dump valve control unit may set a flow rate which is less than the flow rate of the heated water passing through the water flow rate regulator valve as the target flow rate when the load of the gas turbine is equal to or greater than a predetermined value.

In a seventh aspect of the invention, the control system may control the temperature of the fuel by controlling the flow rate of the heated water which is supplied from a supply device of heated water to the fuel gas heater by adjusting a degree of opening of a three-way valve, which is provided upstream in a path of the heated water in the fuel gas heater and switches a proportion of the heated water sent out to the fuel gas heater and a proportion of the heated water sent out to a path bypassing the fuel gas heater, a degree of opening of a water flow rate regulator valve that regulates a flow rate of heated water which is recovered from the fuel gas heater to the supply device of heated water, and a degree of opening of a dump valve that regulates a flow rate of heated water which is dumped to a steam condenser. The water flow rate adjusting unit may include: a first valve opening calculating unit that calculates a first valve opening which is a degree of opening of the water flow rate regulator valve based on a load of the gas turbine; a water flow rate regulator valve control unit that controls the degree of opening of the water flow rate regulator valve on the basis of the first valve opening; a dump valve control unit that controls the degree of opening of the dump valve on the basis of a difference between a target flow rate of the heated water which is determined in advance on the basis of the load of the gas turbine and an actual flow rate; and a three-way valve control unit that controls the degree of opening of the three-way valve on the basis of a difference between a target temperature of the fuel and the temperature of the fuel on the outlet side of the fuel gas heater.

According to an eighth aspect of the invention, there is provided a control system that controls a temperature of fuel by controlling a flow rate of heated water which is supplied from a supply device of heated water to a fuel gas heater that heats fuel of a gas turbine by adjusting a degree of opening of a water flow rate regulator valve that regulates a flow rate of heated water which is recovered to the supply device of heated water and a degree of opening of a dump valve that regulates a flow rate of heated water which is dumped to a steam condenser, the control system including: a first valve opening calculating unit that calculates a first valve opening which is a degree of opening of the water flow rate regulator valve based on a load of the gas turbine; a second valve opening calculating unit that calculates a second valve opening by multiplying a coefficient based on the temperature of the fuel on an inlet side of the fuel gas heater by the first valve opening; and a water flow rate regulator valve control unit that controls the degree of opening of the water flow rate regulator valve on the basis of the second valve opening.

According to a ninth aspect of the invention, there is provided a gas turbine including a compressor, a combustor, a turbine, and the control system according to any one of the above-mentioned aspects.

According to a tenth aspect of the invention, there is provided a power generation plant including: the gas turbine according to the ninth aspect, a steam turbine, and a power generator.

According to an eleventh aspect of the invention, there is provided a method of controlling a fuel temperature, comprising causing a control system that controls a temperature of fuel which is supplied to a combustor of a gas turbine via a fuel gas heater, which heats the fuel of the gas turbine, by adjusting a flow rate of heated water which is supplied to the fuel gas heater to perform adjusting the flow rate of the heated water which is supplied to the fuel gas heater on the basis of a difference between a target temperature of the fuel and the temperature of the fuel on an outlet side of the fuel gas heater.

Advantageous Effects of Invention

With the control system, the gas turbine, the power generation plant, and the method of controlling a fuel temperature, it is possible to control a temperature of fuel in a desired temperature by controlling a flow rate of water which is supplied to the fuel gas heater while monitoring the temperature of the fuel on the outlet side of the fuel gas heater.

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, a method of controlling a flow rate of water to a fuel gas heater in a first embodiment of the invention will be described with reference toFIGS. 1 to 5.

FIG. 1is a system diagram illustrating a gas turbine combined cycle plant according to first and second embodiments of the invention.

As illustrated inFIG. 1, the gas turbine combined cycle (GTCC) plant according to this embodiment includes a gas turbine10, a heat recovery steam generator20that generates steam using heat of exhaust gas which is discharged from the gas turbine10, a steam turbine30(a high-pressure steam turbine31, an intermediate-pressure steam turbine32, and a low-pressure steam turbine33) that is driven using steam from the heat recovery steam generator20, a power generator34that generates electric power by driving the turbines10,31,32, and33, a steam condenser35that restores steam discharged from the low-pressure steam turbine33to water, and a control device100that controls the devices.

The gas turbine10includes a compressor11that compresses outside air to generate compressed air, a combustor12that mixes the compressed air with a fuel gas and combusts the mixed gas to generate a combustion gas of a high temperature, and a turbine13that is driven with the combustion gas. A fuel line R1for supplying fuel from a fuel supply device which is not illustrated to the combustor12is connected to the combustor12. A fuel gas heater70is provided in the fuel line. An exhaust port of the turbine13is connected to the heat recovery steam generator20.

The fuel gas heater70is provided to increase the temperature of a fuel gas to improve heat efficiency in the combustor12. The fuel gas heater70is supplied with a fuel gas of a desired flow rate corresponding to a load from a fuel supply device which is not illustrated. A thermometer14is provided on an inlet side of the fuel gas heater70in the fuel line R1, and a thermometer15is provided on an outlet side thereof. The thermometer14measures the temperature of the fuel gas on the inlet side. The thermometer15measures the temperature of the fuel gas on the outlet side.

The fuel gas heater70is connected to the heat recovery steam generator (HRSG)20via a heated water supply line L1. Heated water is supplied to the fuel gas heater70from the heat recovery steam generator20via the heated water supply line L1. In the fuel gas heater70, the heated water and the fuel gas supplied from the fuel line R1exchange heat with each other. At this time, heat moves from the heated water to the fuel gas and the temperature of the fuel gas increases. The fuel gas which has been controlled to a desired high temperature is supplied to the combustor12. In the related art, the temperature of the fuel gas passing through the fuel gas heater70(the temperature of the fuel gas on the outlet side of the fuel gas heater70) may deviate from a desired temperature. In this embodiment, the temperature of the fuel gas on the outlet side of the fuel gas heater70is controlled to a desired temperature using a control method which will be described below. A flowmeter16is provided in the heated water supply line L1. The flowmeter16measures a flow rate of the heated water which is supplied to the fuel gas heater70.

One end of a heated water return line L2is connected to the outlet side of the fuel gas heater70. The other end of the heated water return line L2is connected to the heat recovery steam generator20. The heated water that has exchanged heat in the fuel gas heater70is returned to the heat recovery steam generator20via the heated water return line L2. A water flow rate regulator valve71is provided in the heated water return line L2. The heated water return line L2branches into a condensed water line L3at a branch point DC. The condensed water line L3is connected to the steam condenser35. A dump valve72is provided in the condensed water line L3. Some of the heated water which is returned from the fuel gas heater70to the heat recovery steam generator20is dumped to the steam condenser35via the condensed water line L3according to a degree of opening of the dump valve72. The degree of opening of the water flow rate regulator valve71or the dump valve72is controlled by the control device100.

The heat recovery steam generator (HRSG)20includes a high-pressure steam generating unit21that generates high-pressure steam which is supplied to the high-pressure steam turbine31, an intermediate-pressure steam generating unit22that generates intermediate-pressure steam which is supplied to the intermediate-pressure steam turbine32, a low-pressure steam generating unit24that generates low-pressure steam which is supplied to the low-pressure steam turbine33, and a reheating unit23that heats steam discharged from the high-pressure steam turbine31.

The high-pressure steam generating unit21of the heat recovery steam generator20and a steam inlet of the high-pressure steam turbine31are connected to each other by a high-pressure main steam line41that guides high-pressure steam to the high-pressure steam turbine31, a steam outlet of the high-pressure steam turbine31and a steam inlet of the intermediate-pressure steam turbine32are connected to each other by an intermediate steam line44that guides steam discharged from the high-pressure steam turbine31to the steam inlet of the intermediate-pressure steam turbine32via the reheating unit23of the heat recovery steam generator20, and the low-pressure steam generating unit24of the heat recovery steam generator20and a steam inlet of the low-pressure steam turbine33are connected to each other by a low-pressure main steam line51that guides low-pressure steam to the low-pressure steam turbine33.

The steam outlet of the intermediate-pressure steam turbine32and the steam inlet of the low-pressure steam turbine33are connected to each other by an intermediate-pressure turbine exhaust line54. The steam condenser35is connected to the steam outlet of the low-pressure steam turbine33. A water supply line55that guides condensed water to the heat recovery steam generator20is connected to the steam condenser35.

The intermediate-pressure steam generating unit22of the heat recovery steam generator20and a part of the intermediate steam line44upstream from the reheating unit23are connected to each other by an intermediate-pressure main steam line61.

A high-pressure steam stop valve42and a high-pressure main steam governor valve43that adjusts an amount of steam flowing into the high-pressure steam turbine31are provided in the high-pressure main steam line41. An intermediate-pressure steam stop valve45and an intermediate-pressure steam governor valve46that adjusts an amount of steam flowing into the intermediate-pressure steam turbine32are provided in the intermediate steam line44. A low-pressure steam stop valve52and a low-pressure main steam governor valve53that adjusts an amount of steam flowing into the low-pressure steam turbine33are provided in the low-pressure main steam line51.

The control device100adjusts the degree of opening of the water flow rate regulator valve71or the dump valve72and controls a flow rate of heated water which performs heat exchange with a fuel gas in the fuel gas heater70. Accordingly, the control device100controls the temperature of the fuel gas on the outlet side of the fuel gas heater70to a desired temperature. In addition, the control device100receives various types of operation data or instruction data and the like and generates electric power using the power generator34by performing control of the output of the gas turbine10, control of the output of the steam turbine30, and the like.

FIG. 2is a block diagram of the control device according to the first embodiment of the invention.

The control device100controls a flow rate of heated water which is supplied from the heat recovery steam generator20to the fuel gas heater70by adjusting the degree of opening of the water flow rate regulator valve71and the degree of opening of the dump valve72. The control device100controls the temperature of the fuel gas which is supplied to the combustor12of the gas turbine10via the fuel gas heater70by controlling the flow rate of the heated water. The control device100is constituted by a computer. As illustrated in the drawing, the control device100includes an operation data acquiring unit101, a first valve opening calculating unit102, a second valve opening calculating unit103, a third valve opening calculating unit104, a water flow rate regulator valve control unit105, a dump valve control unit106, and a storage unit107.

The operation data acquiring unit101acquires operation data (such as state quantities and target control values) of the devices (such as the gas turbine10and the heat recovery steam generator20) of the GTCC. For example, the operation data acquiring unit101acquires a load (GTMW) of the gas turbine, the measured values of the thermometers14and15, the measured value of the flowmeter16, and a target temperature of the fuel gas.

The first valve opening calculating unit102calculates a valve opening (a first valve opening) of the water flow rate regulator valve71according to the load (GTMW) of the gas turbine10.

The second valve opening calculating unit103calculates a second valve opening by multiplying the first valve opening by a coefficient corresponding to the temperature of the fuel on the inlet side of the fuel gas heater70measured by the thermometer14.

The third valve opening calculating unit104calculates a third valve opening by adding a correction value based on a difference between a predetermined target temperature of the fuel gas and the temperature of the fuel gas on the outlet side of the fuel gas heater70to the second valve opening.

The water flow rate regulator valve control unit105controls the degree of opening of the water flow rate regulator valve71on the basis of the third valve opening.

The dump valve control unit106controls the degree of opening of the dump valve72by feedback control according to a difference between a target heated water flow rate corresponding to the load (GTMW) of the gas turbine10and an actual heated water flow rate.

The storage unit107stores various types of information on the opening control of the water flow rate regulator valve71and the dump valve72.

The control device100has various other functions associated with control of the GTCC and description of functions not associated with this embodiment will be omitted.

FIG. 3is a system diagram of the fuel gas heater according to the first embodiment of the invention.

As illustrated inFIG. 3, the fuel gas heater70is supplied with a fuel gas via the fuel line R1and is supplied with heated water via the heated water supply line L1. Heated water flow rate control of this embodiment is characterized in that the flow rate of heated water which is supplied to the fuel gas heater70is adjusted by performing control according to the difference between the target temperature of the fuel gas (a target fuel temperature) on the outlet side of the fuel gas heater70and an actual measured value of the fuel gas such that the difference approaches 0. In the drawing, the characterized configuration of this embodiment is illustrated in a part surrounded by a dotted line. Control of the dump valve72is the same as described with reference toFIG. 15. That is, a function element D10of the dump valve control unit106calculates a target flow rate for control of the dump valve72. The function element D10calculates a small target flow rate for a high load and calculates a large target flow rate for a low load. A subtractor D11of the dump valve control unit106calculates a difference between the target flow rate from the function element D10and the measured flow rate of the heated water from the flowmeter16. A controller D12of the dump valve control unit106controls the degree of opening of the dump valve72by feedback control such that the difference approaches 0. Through this control, the dump valve72is controlled such that it is fully closed (0%) when the load of the gas turbine10is a high load. For example, at the time of starting, at the time of stopping, and at the time of partial load operation in which the load of the gas turbine10is low, the dump valve is adjusted to the degree of opening based on the control in order to secure diversion of the heated water.

Control logic of the dotted part inFIG. 3will be described below in detail with reference toFIG. 4.

FIG. 4is a diagram illustrating a method of controlling a flow rate of water to the fuel gas heater in the first embodiment of the invention.

The first valve opening calculating unit102includes a function element P10that converts the load of the gas turbine into a valve opening. The function element P10is prepared in consideration of valve characteristics of the water flow rate regulator valve71. The first valve opening calculating unit102acquires the load (GTMW) of the gas turbine10from the operation data acquiring unit101. The function element P10receives an input of the load of the gas turbine10and calculates the degree of opening of the water flow rate regulator valve71according to the input load. The function element P10calculates a valve opening having a large value for a high load and calculates a valve opening having a small value for a low load. The function element P10calculates a valve opening (a first valve opening) corresponding to the valve characteristics of the water flow rate regulator valve71.

The second valve opening calculating unit103includes a function element P11and a multiplier P12. The second valve opening calculating unit103acquires the temperature of the fuel gas on the inlet side of the fuel gas heater70measured by the thermometer14from the operation data acquiring unit101. The function element P11receives an input of the temperature of the fuel gas on the inlet side and calculates a coefficient according to the input temperature. The multiplier P12receives an input of the coefficient calculated by the function element P11and the valve opening calculated by the function element P10and multiplies the two values. That is, the multiplier P12calculates a valve opening (a second valve opening) of the water flow rate regulator valve71corresponding to the load of the gas turbine10or the temperature of the fuel gas by multiplying the coefficient (which has a larger value as the temperature of the fuel gas becomes lower) corresponding to the temperature of the fuel gas on the inlet side calculated by the function element P11by the valve opening corresponding to the load of the gas turbine10.

The third valve opening calculating unit104includes a subtractor P13and an adder P14. The third valve opening calculating unit104acquires the temperature of the fuel gas on the outlet side of the fuel gas heater70which is measured by the thermometer15from the operation data acquiring unit101. The third valve opening calculating unit104acquires a target temperature of the fuel gas from the operation data acquiring unit101. The target temperature of the fuel gas may be stored in the storage unit107or may be calculated on the basis of, for example, the load of the gas turbine10by the control device100. The subtractor P13receives an input of the temperature of the fuel gas on the outlet side of the fuel gas heater70and a target fuel temperature and calculates a difference therebetween by subtracting the temperature of the fuel gas on the outlet side of the fuel gas heater70from the target fuel temperature. The third valve opening calculating unit104calculates a correction value of the valve opening based on the difference such that the difference approaches 0. For example, a function for converting the difference into the correction value of the valve opening is stored in the storage unit107, and the third valve opening calculating unit104calculates the correction value of the valve opening using the function. Then, the adder P14receives an input of the second valve opening calculated by the multiplier P12and the correction value of the valve opening calculated by the third valve opening calculating unit104and adds the two values. That is, the valve opening of the water flow rate regulator valve71corresponding to the load of the gas turbine10or the temperature of the fuel gas is corrected using the correction value based on the difference between the target temperature of the fuel gas and the actual temperature of the fuel gas (a third valve opening).

The water flow rate regulator valve control unit105performs control for matching the degree of opening of the water flow rate regulator valve71with the third valve opening.

A flow of a water flow rate control process will be described below in consideration of the process details described above with reference toFIG. 4.

FIG. 5is a flowchart illustrating an example of the water flow rate control process according to the first embodiment of the invention.

First, the operation data acquiring unit101acquires operation data during operation of the GTCC (Step S11). Specifically, the operation data acquiring unit101acquires the magnitude of the load of the gas turbine10, the measured value of the thermometer14, the measured value of the thermometer15, the measured value of the flowmeter16, and the target fuel temperature.

Then, the first valve opening calculating unit102calculates the first valve opening corresponding to the magnitude of the load of the gas turbine10using the function element P10(Step S12). The first valve opening calculating unit102outputs the first valve opening to the second valve opening calculating unit103. Then, the second valve opening calculating unit103calculates the second valve opening using the function element P11and the multiplier P12(Step S13). The second valve opening calculating unit103outputs the first valve opening to the third valve opening calculating unit104. Then, the third valve opening calculating unit104calculates the third valve opening using the subtractor P13and the adder P14(Step S14). The third valve opening calculating unit104outputs the third valve opening to the water flow rate regulator valve control unit105. The water flow rate regulator valve control unit105outputs the third valve opening as a command value to the water flow rate regulator valve71and controls the degree of opening of the water flow rate regulator valve71(Step S15).

The dump valve control unit106performs the following processes in parallel with Steps S12to S15. First, the dump valve control unit106calculates a target flow rate using the function element D10and calculates a difference between the target flow rate and the actual flow rate measured by the flowmeter16(Step S16). Then, the dump valve control unit106calculates a valve opening of the dump valve72such that the calculated difference becomes 0, and controls the degree of opening of the dump valve72to the calculated valve opening (Step S17). The dump valve control unit106continuously performs the processes of Steps S16to S17by feedback control (for example, PI control).

According to this embodiment, the temperature of the fuel gas on the outlet side of the fuel gas heater70is monitored and the flow rate of heated water which is supplied from the heat recovery steam generator20to the fuel gas heater70is controlled such that the temperature of the fuel gas on the outlet side approaches the target fuel temperature. That is, when the temperature of the fuel gas on the outlet side is high, the degree of opening of the water flow rate regulator valve71is decreased to decrease the flow rate. On the other hand, when the temperature of the fuel gas on the outlet side is low, the water flow rate regulator valve71is opened to increase the flow rate of heated water and to heat the fuel gas. Accordingly, the temperature of the fuel gas can be made into a desired temperature.

The second valve opening calculating unit103can control the water flow rate regulator valve71to a degree of opening more suitable for the current circumstances by multiplying the valve opening thereof by a coefficient based on the fuel temperature on the inlet side of the fuel gas heater70.

This embodiment is not limited to the above-mentioned configuration. For example, the following embodiments are conceivable.

Modified Example 1

For example, the third valve opening calculating unit104may calculate a correction value of the valve opening based on the difference between the measured value of the temperature of the fuel gas and the target fuel temperature, adjust the correction value by feedback control such as PI control, and cause the temperature of the fuel gas on the outlet side of the fuel gas heater70to approach the target fuel temperature.

Modified Example 2

For example, the second valve opening calculating unit103may not be provided. That is, the first valve opening calculating unit102calculates the degree of opening (the first valve opening) of the water flow rate regulator valve71based on the load of the gas turbine10. Then, the third valve opening calculating unit104calculates the correction value of the valve opening based on the difference between the temperature of the fuel gas and the target fuel gas and adds the correction value to the first valve opening to calculate the third valve opening. The water flow rate regulator valve control unit105performs control for causing the degree of opening of the water flow rate regulator valve71to approach the third valve opening.

Modified Example 3

For example, the third valve opening calculating unit104may not be provided. That is, the first valve opening calculating unit102calculates the degree of opening (the first valve opening) of the water flow rate regulator valve71based on the load of the gas turbine10. Then, the second valve opening calculating unit103calculates the second valve opening by multiplying the first valve opening by a coefficient based on the temperature of the fuel gas on the inlet side of the fuel gas heater70. The water flow rate regulator valve control unit105performs control for causing the degree of opening of the water flow rate regulator valve71to the second valve opening.

Second Embodiment

Hereinafter, a method of controlling a water flow rate to a fuel gas heater according to a second embodiment of the invention will be described with reference toFIGS. 6 to 8.

A control device100A according to the second embodiment will be described below. The control device100A controls the dump valve72using a method other than that used in the first embodiment. In the first embodiment, the dump valve control unit106calculates the target flow rate using the function element D10. In the second embodiment, a dump valve control unit106A switches a target flow rate for controlling the dump vale72on the basis of the load of the gas turbine10.

FIG. 6is a block diagram illustrating the control device according to the second embodiment of the invention.

Among elements in the second embodiment of the invention, the same elements as the functional units constituting the control device100according to the first embodiment will be referred to by the same reference signs and description thereof will not be repeated. As illustrated in the drawing, the control device100A includes an operation data acquiring unit101, a first valve opening calculating unit102, a second valve opening calculating unit103, a third valve opening calculating unit104, a water flow rate regulator valve control unit105, a dump valve control unit106A, and a storage unit107.

The dump valve control unit106A sets a flow rate less than a flow rate of water passing through the water flow rate regulator valve71as a target flow rate when the load of the gas turbine10is greater than a predetermined value, and sets a flow rate which is calculated using the function element D10as the target flow rate when the load of the gas turbine10is equal to or less than the predetermined value similarly to the first embodiment. When the target flow rate is determined, the dump valve control unit106A calculates the degree of opening of the dump valve72by feedback control on the basis of a difference between the target flow rate and an actual flow rate of water (a measured value from the flowmeter16).

Control logic of a dotted part inFIG. 7will be described below in detail with reference toFIG. 7.

FIG. 7is a diagram illustrating a method of controlling a flow rate of water to the fuel gas heater in the second embodiment of the invention.

The dump valve control unit106A includes a function element D10, a subtractor D11, a controller D12, a function element D13, a controller D14, a multiplier D15, and a switch D16. The function element D10receives an input of the load of the gas turbine10and calculates a target flow rate based on the load. The subtractor D11calculates a difference between the target flow rate and an actual flow rate of water by subtracting the actual flow rate from the target flow rate. The controller D12calculates a vale opening of the dump valve72such that the difference calculated by the subtractor D11approaches 0 by PI control. The function element D13receives an input of a valve opening command value to the water flow rate regulator valve71and calculates a CV value of the water flow rate regulator valve71. The controller D14receives an input of the CV value calculated by the function element D13and the pressure difference of the water flow rate regulator valve71and calculates a flow rate of heated water flowing through the water flow rate regulator valve71. The calculated flow rate is referred to as a flow rate command value. The controller D14acquires the measured value from the pressure meter17provided upstream from the water flow rate regulator valve71and the measured vale from the pressure meter18provided downstream therefrom and calculates a pressure difference of the water flow rate regulator valve71(the measured value from the pressure meter17—the measured value from the pressure meter18). The multiplier D15receives an input of the flow rate command value of the water flow rate regulator valve71calculated by the controller D14and calculates a target flow rate for a high load by multiplying the flow rate command value by 0.95 (95%). The switch D16switches the target flow rate between the target flow rate calculated by the function element D10and the target flow rate (for a high load) calculated by the multiplier D15on the basis of the magnitude of the load of the gas turbine10.

A method of calculating a target flow rate for the dump valve72will be described below. First, similarly to the first embodiment, the function element D10receives an input of the load of the gas turbine and calculates a target flow rate. The function element D10outputs the calculated target flow rate to the switch D16. The target flow rate is a target flow rate for an intermediate or low load.

On the other hand, the target flow rate for a high load is calculated as follows. First, the function element D13calculates the CV value of the water flow rate regulator valve71at the current degree of opening. Then, the controller D14calculates a flow rate command value flowing through the water flow rate regulator valve71on the basis of the CV value and the pressure difference before and after the water flow rate regulator valve71. The controller D14outputs the calculated flow rate to the multiplier D15. The multiplier D15calculates the target flow rate for a high load corresponding to 95% of the flow rate. The multiplier D15outputs the target flow rate to the switch D16.

The switch D16receives an input of the load (GTMW) of the gas turbine10and outputs the target flow rate for a high load to the subtractor D11, for example, when the load is greater than 80% of a rated load. When the load is equal to or less than 80%, the switch D16outputs the target flow rate for an intermediate or low load to the subtractor D11.

In the first embodiment, since the water flow rate regulator valve71is controlled on the basis of the temperature of the fuel gas and the dump valve72is controlled on the basis of the water flow rate, there is a likelihood that both controls will interfere with each other and the water flow rate or the fuel temperature will not be settled in a target value. In this regard, in the second embodiment, the target flow rate in a high-load operation (for example, with a load equal to or greater than 80%) is switched from the valve opening command for the water flow rate regulator valve71to the calculated flow rate command value. By setting 95% of the calculated flow rate command value as the target flow rate of the dump valve72, the flow rate will not become greater than the target flow rate of the water flow rate regulator valve71. Accordingly, it is possible to appropriately control the fuel temperature without interfering with the water flow rate control. At the time of starting, stopping, or the like in which the load is low, feedback control is performed using the function element D10that calculates the target flow rate based on the load of the gas turbine10similarly to the related art.

In the operation when the target flow rate for a high load which characterizes this embodiment is applied, normally, the value calculated by the subtractor D11is negative and the dump valve72is controlled such that it is fully closed (a degree of opening of 0%), for example, in order to set 95% of the flow command value of the water flow rate regulator valve71as the target flow rate. On the other hand, when the water flow rate regulator valve71does not operate as commanded due to fixing of the water flow rate regulator valve71or the like (when the flow rate flowing through the water flow rate regulator valve71is less than the command value), there is a likelihood that an actual flow rate will be less than the target flow rate which is 95% of the flow rate command value. In this case, the dump valve72is controlled to a degree of opening (>0%) which can supplement the lack of the flow rate. In this way, in the high-load operation of the gas turbine10, a backup function of the water flow rate regulator valve71is achieved.

A flow of a method of controlling the dump valve72according to the second embodiment will be described below.

FIG. 8is a flowchart illustrating an example of a water supply control process in the second embodiment of the invention.

First, during operation of the GTCC, the operation data acquiring unit101acquires operation data (Step S21). Specifically, the operation data acquiring unit101acquires the magnitude of the load of the gas turbine10, a measured value from the flowmeter16, and an opening command value of the water flow rate regulator valve71.

Then, the dump valve control unit106A determines whether the load is greater than 80% of the rated load on the basis of the magnitude of the load of the gas turbine10(Step S22). Specifically, the switch D16receives an input of the value of the gas turbine load and performs the determination. When the load is equal to or less than 80% (NO in Step S22), the dump valve control unit106A calculates a target flow rate based on the load (Step S24). Specifically, the function element D10of the dump valve control unit106A calculates the target flow rate corresponding to the magnitude of the load with the value of the load as an input. The function element D10outputs the calculated target flow rate to the switch D16. The switch D16outputs the input target flow rate to the subtractor D11.

When the load is greater than 80% (YES in Step S22), the dump valve control unit106A calculates the flow rate command value of the water flow rate regulator valve71and sets a flow rate (for example, 95%) less than the flow rate command value as a target flow rate (Step S23). Specifically, as described above with reference toFIG. 7, the function element D13calculates the CV value from the opening command value of the water flow rate regulator valve71, the controller D14calculates the flow rate command value of the water flow rate regulator valve71from the CV value and the pressure difference, and the multiplier D15calculates the target flow rate of the dump valve72corresponding to 95% of the flow rate command value. The multiplier D15outputs the calculated target flow rate to the switch D16. The switch D16outputs the input target flow rate to the subtractor D11.

Then, the dump valve control unit106A performs feedback control on the basis of the difference between the target flow rate and the actual flow rate (Step S25). Specifically, the subtractor D11acquires the measured value of the flowmeter16from the operation data acquiring unit101and calculates a difference by subtracting the measured value from the target flow rate. The controller D12calculates the degree of opening of the dump valve72such that the difference between the target flow rate and the measured value approaches 0. The controller D12repeatedly performs the process of Step S25by PI control.

According to this embodiment, in addition to the advantageous effects of the first embodiment, it is possible to prevent interference between fuel temperature control and water flow rate control by setting the target flow rate for a high load to be lower than that in the related art. The dump valve72can perform a function of securing a water flow rate at the time of starting, stopping, and partial load operation of the gas turbine10as in the related art, and can perform a backup function at the time of operation with a high load of the gas turbine10. The numerical values of 80% and 95% are only examples and can be changed depending on operation conditions or the like.

Third Embodiment

Hereinafter, a method of controlling a water flow rate to a fuel gas heater according to a third embodiment of the invention will be described with reference toFIGS. 9 to 13.

A control device100B according to the third embodiment will be described below. The control device100B performs flow rate control for heated water which is supplied to the fuel gas heater70using a method different those in the first and second embodiments. In the third embodiment, a three-way valve is provided upstream from the fuel gas heater70, and a bypass passage that connects the three-way valve to a part downstream from the fuel gas heater70without passing through the fuel gas heater70is provided. The control device100B adjusts a degree of the three-way valve on the fuel gas heater70side on the basis of a difference between a target temperature of a fuel gas and a measured value of a fuel gas temperature on the outlet side of the fuel gas heater70, and controls the flow rate of heated water which passes through the fuel gas heater70.

FIG. 9is a block diagram illustrating the control device according to the third embodiment of the invention.

Among elements in the third embodiment of the invention, the same elements as the functional units constituting the control device100according to the first embodiment will be referred to by the same reference signs and description thereof will not be repeated. As illustrated in the drawing, the control device100B includes an operation data acquiring unit101, a first valve opening calculating unit102, a water flow rate regulator valve control unit105, a dump valve control unit106, a storage unit107, and a three-way valve control unit108.

The three-way valve control unit108controls the degree of opening of a three-way valve73on the basis of the difference between the target temperature of the fuel gas and the fuel gas temperature on the outlet side of the fuel gas heater70.

A water supply system of the fuel gas heater70according to the third embodiment will be described below.

FIG. 10is a system diagram of the fuel gas heater according to the third embodiment of the invention.

As illustrated inFIG. 10, the three-way valve73is provided in the heated water supply line L1which is upstream from the water supply system of the fuel gas heater70, and the water flow rate regulator valve71is provided in the heated water return line L2which is downstream therefrom. The dump valve72is provided in the condensed water line L3which branches from the heated water return line L2. The three-way valve73includes an inlet into which heated water supplied from the heat recovery steam generator20flows, an outlet from which the heated water is discharged to the fuel gas heater70, and an outlet from which the heated water is discharged to a bypass line L4connected to a part downstream from the fuel gas heater70by bypassing the fuel gas heater70. The three-way valve control unit108adjusts a valve opening of the outlet on the fuel gas heater70side and adjusts a proportion of heated water discharged to the fuel gas heater70side and a proportion of heated water discharged to the bypass line L4side. That is, in the third embodiment, the flow rate of heated water flowing through the fuel gas heater70is adjusted such that the temperature of fuel gas is adjusted to a desired temperature by controlling the valve opening of the fuel gas heater70side.

The thermometer15is provided on the outlet side of the fuel gas heater70in the fuel line R1. The flowmeter16is provided in the heated water supply line L1. The other elements are the same as illustrated inFIG. 1.

Control logic of a dotted part inFIG. 10will be described below in detail with reference toFIG. 11.

FIG. 11is a diagram illustrating a method of controlling a flow rate of water to the fuel gas heater in the third embodiment of the invention.

The three-way valve control unit108includes a subtractor H10and a controller H11. The three-way valve control unit108acquires the temperature of the fuel gas on the outlet side of the fuel gas heater70which is measured by the thermometer15from the operation data acquiring unit101. The three-way valve control unit108acquires a target fuel temperature from the operation data acquiring unit101. The subtractor H10receives an input of the temperature of the fuel gas on the outlet side of the fuel gas heater70and the target fuel temperature and subtracts the temperature of the fuel gas on the outlet side of the fuel gas heater70from the target fuel temperature. The controller H11calculates the valve opening on the fuel gas heater70side of the three-way valve73such that the difference between the target fuel temperature and the temperature of the fuel gas on the outlet side of the fuel gas heater70approaches 0. The three-way valve control unit108controls a degree of opening on the fuel gas heater70side of the three-way valve73such that the degree of opening reaches the valve opening calculated by the controller H11.

A water flow rate control process according to the third embodiment will be described below with reference toFIGS. 12 and 13.

First, control of the three-way valve73will be described.

FIG. 12is a first flowchart illustrating an example of the water supply control process according to the third embodiment of the invention.

First, during operation of the GTCC, the operation data acquiring unit101acquires operation data (Step S31). Specifically, the operation data acquiring unit101acquires a temperature of a fuel gas on the outlet side of the fuel gas heater70and a target fuel temperature. The operation data acquiring unit101outputs the acquired values to the three-way valve control unit108. Then, the three-way valve control unit108calculates a difference between the target fuel temperature and the actual temperature (Step S32). Specifically, as described above with reference toFIG. 11, the subtractor H10calculates the difference between the target fuel temperature and the measured value from the thermometer15. Then, the three-way valve control unit108controls the degree of opening on the fuel gas heater70side of the three-way valve73(Step S33). Specifically, the controller H11calculates the valve opening for causing the difference between the target fuel temperature and the measured value to approach 0. The three-way valve control unit108performs control such that the degree of opening on the fuel gas heater70side of the three-way valve73reaches the valve opening calculated by the controller H11. The three-way valve control unit108repeatedly performs the process of Step S33by PI control.

An example in which the valve opening on the fuel gas heater70side of the three-way valve73is controlled in Step S33has been described, but the valve opening on the bypass line L4side.

Control of the water flow rate regulator valve71and the dump valve72will be described below.

FIG. 13is a flowchart illustrating a second example of the water supply control process according to the third embodiment of the invention.

First, during operation of the GTCC, the operation data acquiring unit101acquires operation data (Step S41). Specifically, the operation data acquiring unit101acquires the magnitude of the load of the gas turbine10and the measured value from the flowmeter16.

Then, the first valve opening calculating unit102calculates the first valve opening based on the magnitude of the load of the gas turbine10using a function element P10(Step S42). The first valve opening calculating unit102outputs the first valve opening to the water flow rate regulator valve control unit105. Then, the water flow rate regulator valve control unit105controls the water flow rate regulator valve71such that the degree of opening of the water flow rate regulator valve71reaches the first valve opening (Step S43).

The dump valve control unit106performs the following processes in parallel with Steps S42and S43. First, the dump valve control unit106calculates a target flow rate using the function element D10and calculates a difference between the target flow rate and the actual flow rate measured by the flowmeter16(Step S44). Then, the dump valve control unit106calculates a valve opening of the dump valve72such that the calculated difference becomes 0, and controls the degree of opening of the dump valve72to the calculated valve opening (Step S45). The dump valve control unit106repeatedly performs the processes of Steps S44and S45by feedback control (for example, PI control).

In this embodiment, the temperature of the fuel gas on the outlet side of the fuel gas heater70is monitored and the flow rate of heated water which is supplied from the heat recovery steam generator20to the fuel gas heater70is controlled such that the temperature of the fuel gas on the outlet side approaches the target fuel temperature by the valve opening control of the three-way valve73. That is, when the temperature of the fuel gas on the outlet side is high, the valve opening on the fuel gas heater70side of the three-way valve73is decreased to decrease the flow rate of heated water which flows into the fuel gas heater70. On the other hand, when the temperature of the fuel gas on the outlet side is low, the valve opening on the fuel gas heater70side of the three-way valve73is increased to increase the flow rate of heated water which flows into the fuel gas heater70and to further heat the fuel gas. Accordingly, the temperature of the fuel gas can be made into a desired temperature.

According to this embodiment, by only newly providing the three-way valve73and adding the control logic described above with reference toFIG. 11, the temperature of the fuel gas can be controlled with the control logic of the water flow rate regulator valve71or the dump valve72maintained as in the related art.

The control devices100,100A, and100B are an example of a control system. At least some of the operation data acquiring unit101, the first valve opening calculating unit102, the second valve opening calculating unit103, the third valve opening calculating unit104, the water flow rate regulator valve control unit105, the dump valve control units106and106A, and the three-way valve control unit108are functions which are embodied by causing a processor of the control device100or the like to read and execute a program from the storage unit107. Some or all of the operation data acquiring unit101, the first valve opening calculating unit102, the second valve opening calculating unit103, the third valve opening calculating unit104, the water flow rate regulator valve control unit105, the dump valve control units106and106A, and the three-way valve control unit108may be embodied using hardware such as a microcomputer, a large scale integration (LSI) circuit, an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field-programmable gate array (FPGA).

Without departing from the gist of the invention, the elements in the above-mentioned embodiments can be appropriately replaced with known elements. The technical scope of the invention is not limited to the above-mentioned embodiments and can be modified in various forms without departing from the gist of the invention.

The operation data acquiring unit101, the first valve opening calculating unit102, the second valve opening calculating unit103, the third valve opening calculating unit104, the water flow rate regulator valve control unit105, the dump valve control unit106, and the storage unit107which are included in the control device100are an example of a water flow rate adjusting unit. The operation data acquiring unit101, the first valve opening calculating unit102, the second valve opening calculating unit103, the third valve opening calculating unit104, the water flow rate regulator valve control unit105, the dump valve control unit106A, and the storage unit107which are included in the control device100A are an example of a water flow rate adjusting unit. The operation data acquiring unit101, the first valve opening calculating unit102, the water flow rate regulator valve control unit105, the dump valve control unit106, the storage unit107, and the three-way valve control unit108which are included in the control device100B are an example of a water flow rate adjusting unit. The GTCC is an example of a power generation plant.

INDUSTRIAL APPLICABILITY

With the control system, the gas turbine, the power generation plant, and the method of controlling a fuel temperature, it is possible to control a temperature of a fuel in a desired temperature by controlling a flow rate of water which is supplied to the fuel gas heater while monitoring the temperature of the fuel on the outlet side of the fuel gas heater.

REFERENCE SIGNS LIST