Patent Description:
A combined cycle plant includes a gas turbine driven by fuel supply, a GT generator that generates electricity by the gas turbine drive, a waste heat recovery boiler that generates steam by using heat from exhaust gas exhausted from the gas turbine, a steam turbine driven by the steam from the waste heat recovery boiler, a condenser that returns the steam exhausted from the steam turbine to water, and an ST generator that generates electricity by drive of the steam turbine.

As a method for starting up the combined cycle plant, for example, there is a method disclosed in Patent Document <NUM> below. In this method for starting up, the gas turbine is first started, and after the rotational speed of the gas turbine reaches the rated rotational speed, the GT generator connected to the gas turbine is synchronized to the power system. Subsequently, when the gas turbine output (output of the GT generator) reaches the initial output, the amount of fuel to be supplied to the gas turbine is adjusted so that the initial output is maintained for a certain period of time. Subsequently, when the temperature of steam from the waste heat recovery boiler reaches or exceeds a predetermined temperature, the steam from the waste heat recovery boiler is gradually supplied to the steam turbine. Note that the predetermined temperature here is a temperature that is set as appropriate for starting up the steam turbine. Then, after the rotational speed of the steam turbine reaches the rated rotational speed, the ST generator connected to the steam turbine is synchronized to the power system. Subsequently, the amount of fuel to be supplied to the gas turbine is gradually increased to bring the gas turbine output to the rated output. In this process, the flow rate of the steam from the waste heat recovery boiler increases and the temperature of the steam also increases, so the steam turbine output also reaches the rated output.

When the gas turbine output is rapidly increased to the rated output, high temperature steam flows into the cooled steam turbine, thereby generating high thermal stress in the steam turbine. Thus, in the method for starting up, from the viewpoint of protecting the steam turbine, the gas turbine output is once maintained at the initial output lower than the rated output, and then increased to the rated output.

Patent Document <NUM> discloses that a plant control apparatus controls a power plant including a combustor configured to burn fuel to generate a combustion gas, a gas turbine driven by the combustion gas from the combustor, a heat recovery steam generator configured to use heat of an exhaust gas from the gas turbine to generate steam, and a steam turbine driven by the steam from the heat recovery steam generator. The apparatus includes a gas turbine controller configured to control an output value of the gas turbine to a second output value that is larger than a first output value and depends on atmospheric temperature and then control the output value of the gas turbine to the first output value. The apparatus further includes a steam turbine controller configured to start up the steam turbine while the output value of the gas turbine is controlled to the first output value.

Patent Document <NUM> discloses that a control device includes a mode-recognizing unit that recognizes whether a start mode of a steam turbine is a cold mode in which a temperature of a steam contact portion of the steam turbine is lower than a predetermined temperature or a different start mode in which the temperature of the steam contact portion is equal to or higher than the predetermined temperature, a first opening generator that generates a first degree of opening greater than a second degree of opening in the different start mode as a degree of opening of an intake air regulator of a compressor in a period after generation of steam from an exhaust heat recovery boiler is started and before supplying of the steam to the steam turbine is started, and a command output unit that outputs a command corresponding to the first degree of opening to the intake air regulator.

Patent Document <NUM> discloses a method for enhanced cold (or warm) steam turbine start in a supplementary fired multi-gas turbine combined cycle plant. Boiler supplementary firing, which is normally used to increase steam flow when the plant gas turbine is at maximum load, is used to augment steam production with a partly loaded, temperature matched gas turbine. This is done to satisfy minimum required steam flow for a cold (or warm) steam turbine start. Lighting the supplementary firing burners in the heat recovery steam generator/boiler and setting them at a minimum or low heat load serves to add enough steam, at the proper temperature, to insure a successful cold or warm steam turbine start when the gas turbine load and related steam production capacity from the gas turbine exhaust flow are limited by the need to match the required steam temperature and/or maintain low gas turbine exhaust emissions.

In the power generation industry, there is a demand for shortening the time from the start-up of the gas turbine until the gas turbine output reaches the rated output as much as possible.

Accordingly, an object of the present disclosure is to provide a technique capable of increasing the gas turbine output to the rated output in a short period of time while suppressing the thermal stress generated in the steam turbine.

According to the present invention, there is provided a method for starting up a combined cycle plant, as set out in independent claim <NUM>.

An amount of steam supplied to the steam turbine per unit time has a positive correlation with a steam turbine output that is the output of the generator. In addition, the thermal stress in the steam turbine has a positive correlation with the steam turbine output for a predetermined time after the generator connected to the steam turbine is synchronized to the power system. Thus, in this aspect, the flow rate of the steam flowing into the steam turbine is controlled based on the steam turbine output so that the thermal stress generated in the steam turbine does not reach or exceed the predetermined thermal stress. Therefore, in this aspect, there is no need to maintain the gas turbine output at a low output lower than the rated output for a predetermined time to prevent the thermal stress generated in the steam turbine from becoming too high.

Thus, in this aspect, the time required for the gas turbine output to reach the rated output can be shorter than when the gas turbine output is maintained at the low output for the predetermined time, while suppressing the thermal stress generated in the steam turbine.

Furthermore, there is provided a combined cycle plant, as set out in independent claim <NUM>, and a start-up control program for a combined cycle plant, as set out in independent claim <NUM>. Advantageous developments are defined in the dependent claims.

According to one aspect of the present disclosure, the gas turbine output can be brought to the rated output in a short period of time while suppressing the thermal stress generated in the steam turbine.

Hereinafter, embodiments related to a combined cycle plant and a method for starting up the combined cycle plant according to the present invention will be described.

The present embodiment will be described with reference to <FIG>.

As illustrated in <FIG>, a combined cycle plant of the present embodiment includes a gas turbine installation G, a steam turbine installation S, and a control device <NUM>.

The gas turbine installation G includes a gas turbine <NUM>, a GT generator <NUM> that generates electricity by the gas turbine <NUM> drive, a GT circuit breaker <NUM> that electrically connects and disconnects the GT generator <NUM> to and from a power system <NUM>, a waste heat recovery boiler <NUM> that generates steam from heat from exhaust gas EG exhausted from the gas turbine <NUM>, and a stack <NUM> that discharges the exhaust gas EG that has passed through the waste heat recovery boiler <NUM> to the atmosphere.

The gas turbine <NUM> includes a compressor <NUM> that compresses air A, a combustor <NUM> that burns fuel F in the air compressed by the compressor <NUM> to generate combustion gas, and a turbine <NUM> that is driven by the high-temperature and high-pressure combustion gas. A turbine rotor of the turbine <NUM> and a compressor rotor of the compressor <NUM> are connected to each other to form a gas turbine rotor <NUM>. A rotor of the GT generator <NUM> is connected to the gas turbine rotor <NUM>.

A fuel line <NUM> is connected to the combustor <NUM> to supply the fuel F from an external fuel supply source to the combustor <NUM>. The fuel line <NUM> is provided with a fuel control valve <NUM> that adjusts a flow rate of the fuel F to be supplied to the combustor <NUM>.

The waste heat recovery boiler <NUM> is connected to an exhaust port of the turbine <NUM> via a flue gas duct <NUM>. The stack <NUM> is provided at an exhaust port of the waste heat recovery boiler <NUM>.

The GT generator <NUM> is electrically connected to the power system <NUM> by a power line <NUM>. The power line <NUM> is provided with the GT circuit breaker <NUM>. The GT circuit breaker <NUM> electrically connects the GT generator <NUM> to the power system <NUM> in response to a command from the outside, and electrically disconnects the GT generator <NUM> from the power system <NUM> in response to a command from the outside.

The gas turbine installation G further includes a GT output gauge <NUM> capable of detecting a gas turbine output, which is the power generated by the GT generator <NUM>, and a GT rotational speed meter <NUM> capable of detecting the rotational speed of the gas turbine rotor <NUM>.

The steam turbine installation S includes the waste heat recovery boiler <NUM>, the stack <NUM>, a steam turbine <NUM> driven by the steam generated by the waste heat recovery boiler <NUM>, an ST generator <NUM> that generates electricity by the steam turbine <NUM> drive, an ST circuit breaker <NUM> that electrically connects and disconnects the ST generator <NUM> to and from the power system <NUM>, a condenser <NUM> that returns the steam exhausted from the steam turbine <NUM> to water, and a feedwater pump <NUM> that returns the water in the condenser <NUM> to the waste heat recovery boiler <NUM>. Thus, the waste heat recovery boiler <NUM> and the stack <NUM> are common devices for the gas turbine installation G and the steam turbine installation S.

A steam turbine rotor <NUM> is connected to a rotor of the ST generator <NUM>. The steam turbine rotor <NUM> is not mechanically connected to the gas turbine rotor <NUM>. Therefore, the rotation of the gas turbine rotor <NUM> is not synchronized with the rotation of the steam turbine rotor <NUM>. Thus, just because the gas turbine rotor <NUM> is rotating does not necessarily mean that the steam turbine rotor <NUM> is rotating.

The ST generator <NUM> is electrically connected to the power system <NUM> by a power line <NUM>. The power line <NUM> is provided with the ST circuit breaker <NUM>. The ST circuit breaker <NUM> electrically connects the ST generator <NUM> to the power system <NUM> in response to a command from the outside, and electrically disconnects the ST generator <NUM> from the power system <NUM> in response to a command from the outside.

A steam inlet of the steam turbine <NUM> and a steam outlet of the waste heat recovery boiler <NUM> are connected by a main steam line <NUM>. The main steam line <NUM> is provided with a steam control valve <NUM> that adjusts the flow rate of steam flowing into the steam turbine <NUM>. The steam control valve <NUM> includes a shut-off valve 22a capable of shutting off the steam flowing into the steam turbine <NUM> and a control valve 22b capable of adjusting the flow rate of the steam flowing into the steam turbine <NUM>. The control valve 22b is disposed in the main steam line <NUM> closer to the steam turbine <NUM> than the shut-off valve 22a.

A steam outlet of the steam turbine <NUM> is connected to a steam inlet of the condenser <NUM>. A bypass line <NUM> is branched from a position in the main steam line <NUM> closer to the waste heat recovery boiler <NUM> than the steam control valve <NUM>. The bypass line <NUM> is connected to the steam inlet of the condenser <NUM>. The bypass line <NUM> is provided with a bypass valve <NUM> that adjusts a flow rate of steam flowing through the bypass line <NUM>. A feedwater line <NUM> connects a condensate outlet of the condenser <NUM> and a water inlet of the waste heat recovery boiler <NUM>. The feedwater pump <NUM> is provided in the feedwater line <NUM>.

A desuperheater <NUM> capable of adjusting the temperature of the steam flowing into the steam turbine <NUM> is provided at a position in the main steam line <NUM> closer to the waste heat recovery boiler <NUM> than the branch position of the bypass line <NUM>. The desuperheater <NUM> includes a spray <NUM> capable of spraying water at a position in the main steam line <NUM> closer to the waste heat recovery boiler <NUM> than the branch position of the bypass line <NUM>, and a spray amount control valve 26v capable of adjusting an amount of water sprayed from the spray <NUM>.

The steam turbine installation S further includes an ST generator output gauge <NUM> capable of detecting a steam turbine output, which is the power generated by the ST generator <NUM>, an ST rotational speed meter <NUM> capable of detecting the rotational speed of the steam turbine rotor <NUM>, a thermometer <NUM> capable of detecting the temperature of the steam flowing through the main steam line <NUM>, and a pressure gauge <NUM> capable of detecting the pressure of the steam flowing through the main steam line <NUM>. The thermometer <NUM> and the pressure gauge <NUM> are provided at positions in the main steam line <NUM> closer to the steam turbine <NUM> than the branch position of the bypass line <NUM> and closer to the waste heat recovery boiler <NUM> than the steam control valve <NUM>.

The control device <NUM> is a computer. The control device <NUM> includes a central processing unit (CPU) <NUM> that executes various operations, a memory <NUM> that serves as a work area for the CPU <NUM> or the like, an auxiliary storage device <NUM> such as a hard disk drive device, a manual input device (input device) <NUM> such as a keyboard or a mouse, a display device (output device) <NUM>, an input/output interface <NUM> for the manual input device <NUM> and the display device <NUM>, a device interface (input device) <NUM> for transmitting and receiving data to and from various devices, a communication interface (input/output device) <NUM> for communicating with the outside via a network N, and a storage/playback device (input/output device) <NUM> that executes data storage processing and playback processing for a disk storage medium D. The device interface <NUM> receives detection data from the GT output gauge <NUM>, the GT rotational speed meter <NUM>, the ST generator output gauge <NUM>, the ST rotational speed meter <NUM>, the thermometer <NUM>, and the pressure gauge <NUM>. The device interface <NUM> transmits control data to the circuit breakers <NUM> and <NUM>, the fuel control valve <NUM>, the shut-off valve 22a, the control valve 22b, the bypass valve <NUM>, and the spray amount control valve 26v.

The auxiliary storage device <NUM> stores in advance a control program 58p for the combined cycle plant. A start-up control program 58pa that controls start-up of the combined cycle plant is incorporated in the control program 58p. The control program 58p is loaded into the auxiliary storage device <NUM> from the disk storage medium D via the storage/playback device <NUM>, for example. When the control program 58p is already stored in the auxiliary storage device <NUM> and the start-up control program in the control program 58p is to be updated, a new start-up control program 58pa is loaded into the auxiliary storage device <NUM> from the disk storage medium D via the storage/playback device <NUM>, for example. Note that the program may be loaded into the auxiliary storage device <NUM> from an external device via the communication interface <NUM>.

The CPU <NUM> functionally includes a start-up control unit <NUM> for the gas turbine installation G and a start-up control unit <NUM> for the steam turbine installation S. The start-up control unit <NUM> of the gas turbine installation G includes a GT start-up mode reception unit <NUM>, a GT start-up fuel control unit <NUM>, and a GT synchronization command unit <NUM>. The start-up control unit <NUM> of the steam turbine installation S includes an ST generator output control unit <NUM>, a steam pressure control unit <NUM>, an ST bypass steam pressure control unit <NUM>, an ST synchronization command unit <NUM>, a steam temperature control unit <NUM>, a steam admission command unit <NUM>, a steam supply stop command unit <NUM>, a thermal stress estimating unit <NUM>, and a thermal stress detection unit <NUM>. All of the functional units <NUM> to <NUM> and <NUM> to <NUM> function when the CPU <NUM> executes the start-up control program 58pa stored in the auxiliary storage device <NUM>. The functional contents of the functional units <NUM> to <NUM> and <NUM> to <NUM> will be described in the process of describing the operation of the control device <NUM>.

Next, the operation of the control device <NUM> described above will be described according to flowcharts shown in <FIG> and <FIG>.

In the present embodiment, there are two start-up modes of the gas turbine <NUM>: a GT rapid start-up mode and a GT normal start-up mode. The GT rapid start-up mode is a mode in which the gas turbine <NUM> is started rapidly by increasing the output of the gas turbine <NUM> to the rated output regardless of the state of the steam turbine <NUM>. The GT normal start-up mode is a mode in which the gas turbine <NUM> is not started rapidly. First, the operation of the control device <NUM> in the GT normal start-up mode will be described with reference to the flowchart shown in <FIG>.

First, the GT start-up mode reception unit <NUM> of the control device <NUM> receives the start-up mode of the gas turbine <NUM> from the outside (S10: GT start-up mode reception step). When the GT start-up mode reception unit <NUM> receives the GT normal start-up mode, the GT start-up fuel control unit <NUM> executes a GT normal start-up step (S11N). In the GT normal start-up step (S11N), until the GT generator <NUM> is synchronized to the power system <NUM>, as shown in <FIG>, the GT start-up fuel control unit <NUM> commands the fuel control valve <NUM> on a flow rate of fuel to be supplied to the gas turbine <NUM> so that the rotational speed of the gas turbine <NUM> detected by the GT rotational speed meter <NUM> changes according to a predetermined rotational speed change pattern (solid line in <FIG>). As a result, in the process in which the rotational speed of the gas turbine <NUM> indicated by the rotational speed change pattern is increasing, the flow rate of the fuel supplied to the gas turbine <NUM> increases. Thus, in this process, the temperature of steam generated from the waste heat recovery boiler <NUM> gradually increases, and the amount of the generated steam gradually increases. In the GT normal start-up step (S11N), during a period from when the GT generator <NUM> is synchronized to the power system <NUM> to when the gas turbine output reaches a rated output Pgn, the GT start-up fuel control unit <NUM> commands the fuel control valve <NUM> on the flow rate of the fuel to be supplied to the gas turbine <NUM> so that the gas turbine output detected by the GT output gauge <NUM> (long dashed line in <FIG>) changes according to a predetermined normal output change pattern, as shown in <FIG>. As a result, in the process in which the gas turbine output is increasing as indicated by the normal output change pattern, the flow rate of the fuel supplied to the gas turbine <NUM> increases. Thus, also in this process, the temperature of the steam generated from the waste heat recovery boiler <NUM> gradually increases, and the amount of the generated steam gradually increases.

During execution of the GT normal start-up step (S11N), as shown in <FIG>, when the rotational speed of the gas turbine <NUM> (solid line in <FIG>) reaches a rated rotational speed Nn, the GT synchronization command unit <NUM> of the control device <NUM> commands the GT circuit breaker <NUM> to electrically connect the GT generator <NUM> to the power system <NUM> (S12: GT synchronization step). As a result, the GT generator <NUM> is synchronized to the power system <NUM>, and the gas turbine output can be detected by the GT output gauge <NUM>.

When the GT generator <NUM> is synchronized to the power system <NUM>, as described above, as part of the GT normal start-up step (S11N), the GT start-up fuel control unit <NUM> commands the fuel control valve <NUM> on the flow rate of the fuel to be supplied to the gas turbine <NUM> so that the gas turbine output detected by the GT output gauge <NUM> changes according to the predetermined normal output change pattern. As shown in <FIG>, the normal output change pattern is set so that when the gas turbine output reaches a low output Pga lower than the rated output Pgn, the low output Pga is maintained for a predetermined time. Thus, as part of the GT normal start-up step (S11N), when the gas turbine output (long dashed line in <FIG>) reaches the low output Pga, the GT start-up fuel control unit <NUM> commands the fuel control valve <NUM> on the flow rate of the fuel to be supplied to the gas turbine <NUM> so that the low output Pga is maintained (S11Na).

As shown in <FIG>, the normal output change pattern is set so that after the low output Pga is maintained for the predetermined time, the gas turbine output gradually increases from the low output Pga to the rated output Pgn. Thus, as part of the GT normal start-up step (S11N), after causing the fuel control valve <NUM> to maintain the low output Pga for the predetermined time, the GT start-up fuel control unit <NUM> commands the fuel control valve <NUM> on the flow rate of the fuel to be supplied to the gas turbine <NUM> so that the gas turbine output (long dashed line in <FIG>) is gradually increased to the rated output Pgn. The operation of the GT start-up fuel control unit <NUM> causes the gas turbine output to reach the rated output Pgn (S13).

When the thermal stress generated in the steam turbine <NUM> reaches or exceeds a predetermined thermal stress while maintaining the gas turbine output at the low output Pga or while increasing the gas turbine output from the low output Pga to the rated output Pgn, the GT start-up fuel control unit <NUM> adjusts the gas turbine output (S11Nb), regardless of the normal output change pattern, as part of the GT normal start-up step (S11N). Specifically, when the thermal stress generated in the steam turbine <NUM> reaches or exceeds the predetermined thermal stress, the GT start-up fuel control unit <NUM> commands the fuel control valve <NUM> to temporarily reduce the flow rate of the fuel to be supplied to the gas turbine <NUM>. As a result, the gas turbine output falls below the gas turbine output indicated by the normal output change pattern. Thus, any one of the temperature, the pressure, and the flow rate of the steam flowing into the steam turbine <NUM> becomes smaller, and the thermal stress generated in the steam turbine <NUM> falls below the predetermined thermal stress. When the thermal stress generated in the steam turbine <NUM> falls below the predetermined thermal stress, the GT start-up fuel control unit <NUM> again commands the fuel control valve <NUM> on the flow rate of the fuel to be supplied to the gas turbine <NUM> so that the gas turbine output changes according to the normal output change pattern.

As described above, when the fuel is supplied to the gas turbine <NUM>, the steam is generated from the waste heat recovery boiler <NUM>. The steam temperature control unit <NUM> of the control device <NUM> commands the desuperheater <NUM> so that the temperature of the steam detected by the thermometer <NUM> does not exceed a predetermined temperature at least until the steam turbine output reaches a rated output (S20: steam temperature control step). When the spray amount control valve 26v of the desuperheater <NUM> receives the command, the amount of water sprayed from the spray <NUM> to the main steam line <NUM> becomes an amount of water sprayed corresponding to the command. As a result, the temperature of the steam at a position in the main steam line <NUM> closer to the steam turbine <NUM> than a position where the desuperheater <NUM> is provided does not exceed the predetermined temperature.

The ST bypass steam pressure control unit <NUM> of the control device <NUM> commands the bypass valve <NUM> to open (S21: ST bypass steam pressure control step) when the steam pressure detected by the pressure gauge <NUM> reaches or exceeds a predetermined value (which may not be a fixed value) at least until the steam turbine output reaches the rated output. Thus, when the pressure of the steam detected by the pressure gauge <NUM> reaches or exceeds the predetermined value during a period from when the steam starts to be generated from the waste heat recovery boiler <NUM> until at least the steam turbine output reaches the rated output, the bypass valve <NUM> opens, and some of the steam from the waste heat recovery boiler <NUM> is sent to the condenser <NUM> via the bypass line <NUM>.

When the temperature of the steam detected by the thermometer <NUM> reaches or exceeds the predetermined temperature, the steam admission command unit <NUM> of the control device <NUM> commands the steam control valve <NUM> to open so that the steam supply to the steam turbine <NUM> is started (S22: steam admission step). As a result, the steam generated in the waste heat recovery boiler <NUM> flows into the steam turbine <NUM> via the main steam line <NUM> and the steam control valve <NUM>. The steam turbine <NUM> begins to be driven by the steam. The steam admission step (S22) is basically executed after the GT synchronization step (S12).

When the steam admission step (S22) is executed, the thermal stress estimating unit <NUM> of the control device <NUM> estimates the thermal stress generated in the steam turbine <NUM> at least until the steam turbine output reaches the rated output (S23: thermal stress estimation step). When steam starts to flow into the steam turbine <NUM>, a high thermal stress is generated in a portion in the vicinity of an inlet in the steam turbine rotor <NUM> in the vicinity of the steam inlet. The thermal stress estimating unit <NUM> estimates the thermal stress of the portion in the vicinity of the inlet. Specifically, the thermal stress estimating unit <NUM> first estimates the temperature in the portion in the vicinity of the inlet at the present time from the temperature of the steam detected by the thermometer <NUM>, and obtains the temperature differential between this temperature and the temperature in the portion of the vicinity of the inlet estimated a predetermined time ago. Then, the thermal stress estimating unit <NUM> obtains the thermal stress of the portion in the vicinity of the inlet based on the temperature differential, the shape of the portion in the vicinity of the inlet, the Young's modulus and the expansion coefficient of the material forming the portion in the vicinity of the inlet, and the like. The thermal stress estimated by the thermal stress estimating unit <NUM> is used when adjusting the gas turbine output described above (S11Nb).

When the steam admission step (S22) is executed, the steam pressure control unit <NUM> of the control device <NUM> commands the control valve 22b of the steam control valve <NUM> on the degree of opening so that the flow rate of steam flowing into the steam turbine <NUM> gradually increases, and commands the bypass valve <NUM> on the degree of opening so that the steam pressure detected by the pressure gauge <NUM> increases according to a predetermined pressure change pattern (S24: steam pressure control step).

During execution of the steam pressure control step (S24), when the rotational speed of the steam turbine <NUM> (alternate long and short dash line in <FIG>) reaches a rated rotational speed Nn, the ST synchronization command unit <NUM> of the control device <NUM> commands the ST circuit breaker <NUM> to electrically connect the ST generator <NUM> to the power system <NUM> (S26: ST synchronization step). As a result, the ST generator <NUM> is synchronized to the power system <NUM>, and the steam turbine output can be detected by the ST generator output gauge <NUM>.

After the execution of the ST synchronization step (S26), the steam pressure control step (S24) is still executed, and as shown in <FIG>, the steam turbine output (two-dot chain line in <FIG>) reaches a rated output Psn.

Thus, the start-up of the gas turbine <NUM> and the start-up of the steam turbine <NUM> in the GT normal start-up mode are completed.

Next, the operation of the control device <NUM> in the GT rapid start-up mode will be described with reference to the flowchart shown in <FIG>.

First, the GT start-up mode reception unit <NUM> of the control device <NUM> receives the start-up mode of the gas turbine <NUM> from the outside (S10: GT start-up mode reception step). When the GT start-up mode reception unit <NUM> receives the GT rapid start-up mode, the GT start-up fuel control unit <NUM> executes a GT rapid start-up step (S11Q). Also in the GT rapid start-up step (S11Q), as in the GT normal start-up step (S11N), until the GT generator <NUM> is synchronized to the power system <NUM>, as shown in <FIG>, the GT start-up fuel control unit <NUM> commands the fuel control valve <NUM> on the flow rate of the fuel to be supplied to the gas turbine <NUM> so that the rotational speed of the gas turbine <NUM> detected by the GT rotational speed meter <NUM> (solid line in <FIG>) changes according to the predetermined rotational speed change pattern. As a result, in the process in which the rotational speed of the gas turbine <NUM> indicated by the rotational speed change pattern is increasing, the flow rate of the fuel supplied to the gas turbine <NUM> increases. Thus, in this process, the temperature of the steam generated from the waste heat recovery boiler <NUM> gradually increases, and the amount of the generated steam gradually increases. In the GT rapid start-up step (S11Q), during the period from when the GT generator <NUM> is synchronized to the power system <NUM> to when the gas turbine output reaches the rated output, the GT start-up fuel control unit <NUM> commands the fuel control valve <NUM> on the flow rate of the fuel to be supplied to the gas turbine <NUM> so that the gas turbine output detected by the GT output gauge <NUM> (short dashed line in <FIG>) changes according to a predetermined rapid output change pattern, as shown in <FIG>. In the present embodiment, the rapid output change pattern is set so that the gas turbine output changes linearly over time. As a result, the flow rate of the fuel supplied to the gas turbine <NUM> gradually increases over time. Thus, also in this process, the temperature of the steam generated from the waste heat recovery boiler <NUM> gradually increases, and the amount of the generated steam gradually increases.

During execution of the GT rapid start-up step (S11Q), as shown in <FIG>, when the rotational speed of the gas turbine <NUM> reaches the rated rotational speed Nn, the GT synchronization command unit <NUM> of the control device <NUM> commands the GT circuit breaker <NUM> to electrically connect the GT generator <NUM> to the power system <NUM> (S12: GT synchronization step). As a result, the GT generator <NUM> is synchronized to the power system <NUM>, and the gas turbine output can be detected by the GT output gauge <NUM>.

After the execution of the GT synchronization step (S12), the GT rapid start-up step (S11Q) is still executed, and as shown in <FIG>, the gas turbine output (short dashed line in <FIG>) reaches the rated output Pgn.

As described above, when the fuel is supplied to the gas turbine <NUM>, the steam is generated from the waste heat recovery boiler <NUM>. When the GT start-up mode reception unit <NUM> receives the GT rapid start-up mode, as when the GT start-up mode reception unit <NUM> receives the GT normal start-up mode, the steam temperature control unit <NUM> of the control device <NUM> commands the desuperheater <NUM> so that the temperature of the steam detected by the thermometer <NUM> does not exceed the predetermined temperature at least until the steam turbine output reaches the rated output (S20: steam temperature control step). When the spray amount control valve 26v of the desuperheater <NUM> receives the command, the spray <NUM> sprays the amount of water corresponding to the command to the main steam line <NUM>. As a result, the temperature of the steam at the position in the main steam line <NUM> closer to the steam turbine <NUM> than the position where the desuperheater <NUM> is provided does not exceed the predetermined temperature.

The ST bypass steam pressure control unit <NUM> of the control device <NUM> commands the bypass valve <NUM> to open (S21: ST bypass steam pressure control step) when the steam pressure detected by the pressure gauge <NUM> reaches or exceeds the predetermined value (which may not be a fixed value), at least until the steam turbine output reaches the rated output. Thus, when the pressure of the steam detected by the pressure gauge <NUM> reaches or exceeds the predetermined value during the period from when the steam starts to be generated from the waste heat recovery boiler <NUM> until at least the steam turbine output reaches the rated output, the bypass valve <NUM> opens, and some of the steam from the waste heat recovery boiler <NUM> is sent to the condenser <NUM> via the bypass line <NUM>.

When the temperature of the steam detected by the thermometer <NUM> reaches or exceeds the predetermined temperature, the steam admission command unit <NUM> of the control device <NUM> commands the steam control valve <NUM> to open so that the steam supply to the steam turbine <NUM> is started (S22: steam admission step). As a result, the steam generated in the waste heat recovery boiler <NUM> flows into the steam turbine <NUM> via the main steam line <NUM> and the steam control valve <NUM>. The steam turbine <NUM> begins to be driven by the steam. The steam admission step (S22) is executed after the GT synchronization step (S12) described above is executed and the gas turbine output reaches the rated output Pgn (S13), that is, after the GT rapid start-up step (S11Q) is completed.

When the steam admission step (S22) is executed, as when the GT start-up mode reception unit <NUM> receives the GT normal start-up mode, the thermal stress estimating unit <NUM> of the control device <NUM> estimates the thermal stress generated in the steam turbine <NUM> at least until the steam turbine output reaches the rated output (S23: thermal stress estimation step).

The steam supply stop command unit <NUM> of the control device <NUM> executes a steam supply stop step (S25) during a period from the start of steam supply to the steam turbine <NUM> to the execution of the ST synchronization step (S26) described later. In the steam supply stop step (S25), the steam supply stop command unit <NUM> first detects whether the thermal stress estimated in the thermal stress estimation step (S23) has reached or exceeded a predetermined second thermal stress (S25a). Then, when the steam supply stop command unit <NUM> detects that the thermal stress estimated in the thermal stress estimation step (S23) has reached or exceeded the predetermined second thermal stress, the steam supply stop command unit <NUM> commands the steam control valve <NUM> to close the valve (S25b) so that the steam supply to the steam turbine <NUM> is stopped.

Thus, in the present embodiment, even when a thermal stress that reaches or exceeds the second thermal stress occurs in the steam turbine <NUM> during the period from the start of the steam supply to the steam turbine <NUM> to the execution of the synchronization step, the time during which the thermal stress occurs can be minimized, thereby minimizing deterioration of the steam turbine <NUM> due to the thermal stress.

After the steam supply stop step (S25) is executed, the steam admission step (S22) described above is executed again.

After the steam admission step (S22) is executed, when the thermal stress estimated in the thermal stress estimation step (S23) falls below the predetermined second thermal stress and the rotational speed of the steam turbine <NUM> (alternate long and short dash line in <FIG>) reaches the rated rotational speed Nn, the ST synchronization command unit <NUM> of the control device <NUM> commands the ST circuit breaker <NUM> to electrically connect the ST generator <NUM> to the power system <NUM> (S26: ST synchronization step). As a result, the ST generator <NUM> is synchronized to the power system <NUM>, and the steam turbine output can be detected by the ST generator output gauge <NUM>.

After the ST synchronization step (S26) is executed, the ST generator output control unit <NUM> of the control device <NUM> executes an ST generator output control step (S27). As part of the ST generator output control step (S27), the ST generator output control unit <NUM> commands the control valve 22b on the degree of opening to control the flow rate of the steam flowing into the steam turbine <NUM> so that the output of the ST generator <NUM>, that is, the steam turbine output, increases according to the target output change pattern (S27a). The target output change pattern is set so that the thermal stress generated in the steam turbine <NUM> does not reach the predetermined first thermal stress. The first thermal stress may have the same value as the second thermal stress described above, or may have a different value from the second thermal stress described above. Even when the steam turbine output is controlled to increase according to the target output change pattern as described above, the thermal stress generated in the steam turbine <NUM> may reach or exceed the first thermal stress. Thus, as part of the ST generator output control step (S27), the ST generator output control unit <NUM> detects whether the thermal stress estimated in the thermal stress estimation step (S23) has reached or exceeded the predetermined first thermal stress (S27b). Then, when the ST generator output control unit <NUM> detects that the thermal stress estimated in the thermal stress estimation step (S23) has reached or exceeded the predetermined first thermal stress, as part of the ST generator output control step (S27), the ST generator output control unit <NUM> commands the control valve 22b on the degree of opening to adjust the flow rate of the steam flowing into the steam turbine <NUM> so that the change in the steam turbine output is smaller than the change indicated by the target output change pattern (S27c). At this time, the ST generator output control unit <NUM> controls the flow rate of the steam flowing into the steam turbine <NUM> so that the steam turbine output is temporarily maintained.

During the execution of the ST generator output control step (S27), the thermal stress detection unit <NUM> of the control device <NUM> executes a thermal stress detection step (S28). In the thermal stress detection step (S28), the thermal stress detection unit <NUM> detects whether the thermal stress has reached a stable thermal stress state in which an amount of change per unit time of the thermal stress estimated in the thermal stress estimation step (S23) is smaller than a predetermined amount of change and the thermal stress at the present time is smaller than the first thermal stress.

If the thermal stress is detected to be not stable in the thermal stress detection step (S28), the ST generator output control step (S27) is continued. On the other hand, if the thermal stress is detected to be stable in the thermal stress detection step (S28), the ST generator output control step (S27) is completed, and the steam pressure control unit <NUM> of the control device <NUM> executes a steam pressure control step (S29). In the steam pressure control step (S29), as in the steam pressure control step (S24) described with reference to <FIG>, the steam pressure control unit <NUM> commands the control valve 22b of the steam control valve <NUM> on the degree of opening so that the flow rate of the steam flowing into the steam turbine <NUM> gradually increases, and commands the bypass valve <NUM> on the degree of opening so that the steam pressure detected by the pressure gauge <NUM> increases according to the predetermined pressure change pattern.

By executing the steam pressure control step (S29), as shown in <FIG>, the steam turbine output (two-dot chain line in <FIG>) reaches the rated output Psn.

Thus, the start-up of the gas turbine <NUM> and the start-up of the steam turbine <NUM> in the GT rapid start-up mode are completed.

In the present embodiment, when the GT start-up mode reception unit <NUM> receives the GT normal start-up mode, as described with reference to <FIG>, the gas turbine output (long dashed line in <FIG>) is maintained at the low output Pga lower than the rated output Pgn for the predetermined time so that the thermal stress generated in the steam turbine <NUM> is not high.

The amount of steam supplied to the steam turbine <NUM> per unit time has a positive correlation with the steam turbine output. In addition, in the initial stage of the start-up process of the steam turbine <NUM> (for a predetermined time after ST synchronization), the thermal stress in the steam turbine <NUM> has a positive correlation with the steam turbine output. Thus, in the present embodiment, when the GT start-up mode reception unit <NUM> receives the GT rapid start-up mode, the flow rate of the steam flowing into the steam turbine <NUM> is controlled based on the steam turbine output detected by the ST generator output gauge <NUM>, so that the thermal stress generated in the steam turbine <NUM> does not reach or exceed the predetermined thermal stress. Therefore, in the present embodiment, when the GT start-up mode reception unit <NUM> receives the GT rapid start-up mode, unlike when the GT start-up mode reception unit <NUM> receives the GT normal start-up mode, there is no need to maintain the gas turbine output at the low output Pga for the predetermined time.

Thus, in the present embodiment, as shown in <FIG>, when the GT start-up mode reception unit <NUM> receives the GT rapid start-up mode, the time required for the gas turbine output to reach the rated output Pgn (short dashed line in <FIG>) can be shorter than when the GT start-up mode reception unit <NUM> receives the GT normal start-up mode, while suppressing the thermal stress generated in the steam turbine <NUM>. In other words, in the present embodiment, when the GT start-up mode reception unit <NUM> receives the GT rapid start-up mode, the time required for the gas turbine output to reach the rated output Pgn can be shorter than when the gas turbine output is maintained at the low output for the predetermined time, while suppressing the thermal stress generated in the steam turbine <NUM>.

As illustrated in <FIG>, a combined cycle plant of the present embodiment includes a first gas turbine installation Ga, a second gas turbine installation Gb, a steam turbine installation Sa, and a control device 50a.

Both the first gas turbine installation Ga and the second gas turbine installation Gb are the same as the gas turbine installation G in the first embodiment. Accordingly, the first gas turbine installation Ga includes a first gas turbine 10a, a first GT generator 17a, a first GT circuit breaker 18a, a first waste heat recovery boiler 20a, and a first stack 29a. The second gas turbine installation Gb includes a second gas turbine 10b, a second GT generator 17b, a second GT circuit breaker 18b, a second waste heat recovery boiler 20b, and a second stack 29b.

The steam turbine installation Sa in the present embodiment, similarly to the steam turbine installation S in the first embodiment, for the first gas turbine installation Ga, includes the first waste heat recovery boiler 20a, which is a common device with the first gas turbine installation Ga, a steam turbine <NUM>, an ST generator <NUM>, an ST circuit breaker <NUM>, a condenser <NUM>, a feedwater pump <NUM>, a first main steam line 21a, a steam control valve <NUM>, a bypass line <NUM>, a bypass valve <NUM>, a feedwater line <NUM>, a first desuperheater 26a, an ST generator output gauge <NUM>, an ST rotational speed meter <NUM>, a thermometer <NUM>, and a pressure gauge <NUM>. The first main steam line 21a connects a steam outlet of the first waste heat recovery boiler 20a and a steam inlet of the steam turbine <NUM>.

The steam turbine installation Sa of the present embodiment further includes the second waste heat recovery boiler 20b, which is a common device with the second gas turbine installation Gb, a second main steam line 21b, a second desuperheater 26b, a first switching valve 28a, and a second switching valve 28b. The second main steam line 21b connects a steam outlet of the second waste heat recovery boiler 20b and the steam inlet of the steam turbine <NUM>. Accordingly, the second main steam line 21b and the first main steam line 21a share a portion on the steam turbine <NUM> side. Here, the portion shared by the second main steam line 21b and the first main steam line 21a is referred to as a shared main steam line 21c. A portion of the second main steam line 21b excluding the shared main steam line 21c is referred to as a second main steam dedicated line 21bd, and a portion of the first main steam line 21a excluding the shared main steam line 21c is referred to as a first main steam dedicated line 21ad.

The steam control valve <NUM> is provided in the shared main steam line 21c. A second switching valve 28b is provided in the second main steam dedicated line 21bd. A first switching valve 28a is provided at a position in the first main steam dedicated line 21ad closer to the first waste heat recovery boiler 20a than a branch position of the bypass line <NUM>.

When the first gas turbine 10a is started and the second gas turbine 10b is not started, the first switching valve 28a is open and the second switching valve 28b is closed. Thus, the steam generated in the first waste heat recovery boiler 20a by starting up the first gas turbine 10a flows into the steam turbine <NUM> via the first main steam line 21a. When the steam pressure detected by the pressure gauge <NUM> increases, the bypass valve <NUM> opens, and some of the steam generated in the first waste heat recovery boiler 20a is sent to the condenser <NUM> via the bypass line <NUM>.

When the first gas turbine 10a is not started and the second gas turbine 10b is started, the first switching valve 28a is closed and the second switching valve 28b is open. Thus, the steam generated in the second waste heat recovery boiler 20b by starting up the second gas turbine 10b flows into the steam turbine <NUM> via the second main steam line 21b. When the steam pressure detected by the pressure gauge <NUM> increases, the bypass valve <NUM> opens, and some of the steam generated in the second waste heat recovery boiler 20b is sent to the condenser <NUM> via the bypass line <NUM>.

When the first gas turbine 10a and the second gas turbine 10b are started, the first switching valve 28a and the second switching valve 28b are both open. Thus, the steam generated in the first waste heat recovery boiler 20a by starting up the first gas turbine 10a flows into the steam turbine <NUM> via the first main steam line 21a, and the steam generated in the second waste heat recovery boiler 20b flows into the steam turbine <NUM> via the second main steam line 21b. When the steam pressure detected by the pressure gauge <NUM> increases, the bypass valve <NUM> opens, and some of the steam generated in the first waste heat recovery boiler 20a or some of the steam generated in the second waste heat recovery boiler 20b is sent to the condenser <NUM> via the bypass line <NUM>.

The control device 50a is a computer like the control device <NUM> of the first embodiment. The control device 50a functionally includes a start-up control unit for the first gas turbine installation Ga, a start-up control unit for the second gas turbine installation Gb, and a start-up control unit for the steam turbine installation S. Both the start-up control unit for the first gas turbine installation Ga and the start-up control unit for the second gas turbine installation Gb have the same configuration as the start-up control unit <NUM> in the control device <NUM> of the first embodiment. The start-up control unit for the steam turbine installation S has basically the same configuration as the start-up control unit <NUM> in the control device <NUM> of the first embodiment. However, the start-up control unit for the steam turbine installation S in the present embodiment further includes a switching control unit that controls opening and closing of the first switching valve 28a and the second switching valve 28b.

Also in the present embodiment, as in the first embodiment, when the GT start-up mode reception unit <NUM> receives the GT rapid start-up mode, the time required for the gas turbine output to reach the rated output Pgn can be shorter than when the GT start-up mode reception unit <NUM> receives the GT normal start-up mode, while suppressing the thermal stress generated in the steam turbine <NUM>.

The combined cycle plant of the present embodiment is a plant including two gas turbine installations Ga and Gb for one steam turbine installation S. However, the combined cycle plant may be a plant including three or more gas turbine installations G for one steam turbine installation S.

Each of the control devices <NUM> and 50a in the above embodiments includes the GT start-up mode reception unit <NUM>. When the GT start-up mode reception unit <NUM> receives the GT rapid start-up mode, the GT rapid start-up step (S11Q) is executed, and when the GT start-up mode reception unit <NUM> receives the GT normal start-up mode, the GT normal start-up step (S11N) is executed. However, the control device that does not include the GT start-up mode reception unit <NUM> may be used. In this case, the control device executes a GT start-up step similar to the GT rapid start-up step (S11Q) in each of the embodiments.

Each of the control devices <NUM> and 50a in the embodiments is configured by one computer. However, the control device may be configured by a computer for the gas turbine installation and a computer for the steam turbine installation. In this case, the two computers need to be able to communicate with each other via a local network or the like. Alternatively, the control device may be functionally configured by a controller having only the function of the ST bypass steam pressure control unit <NUM> and a controller having only the function of the steam temperature control unit <NUM> in addition to the computer including the GT start-up fuel control unit <NUM>, the ST generator output control unit <NUM>, the steam pressure control unit <NUM>, and the like.

The preferred embodiments of the present invention and the modification examples thereof have been described above.

Claim 1:
A method for starting up a combined cycle plant including a gas turbine (<NUM>) configured to be driven by fuel supply, a waste heat recovery boiler (<NUM>) configured to generate steam by using heat from exhaust gas exhausted from the gas turbine (<NUM>), a steam turbine (<NUM>) configured to be driven by the steam from the waste heat recovery boiler (<NUM>), a condenser (<NUM>) configured to return the steam exhausted from the steam turbine (<NUM>) to water, and a generator (<NUM>) configured to generate electricity by drive of the steam turbine (<NUM>), the method comprising:
a gas turbine start-up step (S11Q) of increasing an output of the gas turbine (<NUM>) to a rated output by supplying fuel to the gas turbine (<NUM>);
a steam admission step (S22) of, when a temperature of the steam from the waste heat recovery boiler (<NUM>) reaches or exceeds a predetermined temperature, starting steam supply to the steam turbine (<NUM>);
a synchronization step (S26) of, after the steam admission step (S22), when a rotational speed of the steam turbine (<NUM>) reaches a rated rotational speed, synchronizing the generator (<NUM>) to a power system (<NUM>);
an ST generator output control step (S27) of, after the generator (<NUM>) is synchronized, controlling a flow rate of the steam flowing into the steam turbine (<NUM>) so that an output of the generator (<NUM>) increases according to a target output change pattern; and
a thermal stress estimation step (S23) of estimating a thermal stress generated in the steam turbine (<NUM>) based on a temperature of the steam flowing into the steam turbine (<NUM>), wherein
in the ST generator output control step (S27), when the thermal stress estimated in the thermal stress estimation step (S23) reaches or exceeds a predetermined first thermal stress, the flow rate of the steam flowing into the steam turbine (<NUM>) is controlled so that a change in the output of the generator (<NUM>) is smaller than a change indicated by the target output change pattern.