Plant control device, plant control method, and power-generating plant

Abstract

To provide a plant control device capable of appropriately controlling opening of a bypass valve for a bypass of a steam turbine.SOLUTION: According to one embodiment, a plant control device includes a heat exchanger and controls a power-generating plant, the power-generating plant including: a boiler that uses heat from the heat exchanger to generate steam; a steam turbine that is driven by the steam generated by the boiler; a pipe arrangement that sends the steam generated by the boiler to the steam turbine; a condenser that condenses the steam discharged from the steam turbine; a bypass valve that sends the steam in the pipe arrangement to the condenser bypassing the steam turbine; and a drain valve that discharges drain water generated in the heat exchanger or the pipe arrangement. The device includes a bypass valve control part that controls opening of the bypass valve, and a drain valve control part that controls an opening of the drain valve in such manner that the opening of the drain valve changes depending on the opening of the bypass valve.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] An embodiment of the present invention relates to a plant control device, a plant control method, and a power plant. [Background technology]

[0002] In general, a combined cycle power plant includes a gas turbine, a heat recovery steam generator, and a steam turbine. The gas turbine is driven by gas supplied from a combustor. The heat recovery steam generator generates main steam by utilizing heat of exhaust gas discharged from the gas turbine. The steam turbine is driven by main steam supplied from the heat recovery steam generator. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6139311 Summary of the Invention [Problem to be solved by the invention]

[0004] The combined cycle power generation system is a power generation system in which heat from the exhaust gas of a gas turbine is recovered by a heat recovery steam generator, and the steam generated by this heat drives a steam turbine. In this power generation system, before the steam turbine is started, the turbine bypass valve must be opened to bypass (detour) the steam turbine and send the main steam elsewhere. The appropriate range of opening of the turbine bypass valve is, for example, 80% or less. However, a problem occurs when the turbine bypass valve is often opened too large.

[0005] For example, a method is known in which the turbine bypass valve control pressure setting is increased to reduce the opening of the turbine bypass valve, but this method has the drawback of also increasing the steam pressure.

[0006] Therefore, an embodiment of the present invention provides a plant control device, a plant control method, and a power generation plant that are capable of suitably controlling the opening degree of a bypass valve for bypassing a steam turbine. [Means for solving the problem]

[0007] According to one embodiment, a plant control device controls a power plant including a boiler including a heat exchanger and generating steam by using heat from the heat exchanger, a steam turbine driven by the steam generated by the boiler, a pipe for sending the steam generated by the boiler to the steam turbine, a condenser for condensing the steam discharged from the steam turbine, a bypass valve for sending the steam in the pipe to the condenser while bypassing the steam turbine, a drain valve for discharging drain water generated in the heat exchanger or the pipe, and a receiving container for receiving the drain water that has passed through the drain valve. The device includes a bypass valve control unit for controlling an opening degree of the bypass valve, and a drain valve control unit for controlling an opening degree of the drain valve so that the opening degree of the drain valve changes according to the opening degree of the bypass valve. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing a configuration of a power plant according to a first embodiment. [Diagram 2] 1 is a circuit diagram showing a configuration of a plant control device according to a first embodiment. [Diagram 3] FIG. 4 is a circuit diagram showing a configuration of a plant control device according to a second embodiment. [Figure 4] FIG. 2 is a circuit diagram showing a configuration of a plant control device of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In Fig. 1 to Fig. 4, the same components are given the same reference numerals, and duplicated descriptions will be omitted.

[0010] (First embodiment) FIG. 1 is a schematic diagram showing the configuration of a power plant according to a first embodiment.

[0011] The power plant 1 of this embodiment includes a plant control device 2 that controls the power plant 1. The power plant 1 of this embodiment is a combined cycle power plant. The power plant 1 of this embodiment is, for example, a separate shaft type in which a gas turbine 12 and a steam turbine 31, which will be described later, are connected to different shafts rather than to the same shaft.

[0012] As shown in Fig. 1, the power plant 1 of this embodiment further includes a compressor 11, a gas turbine 12, a GT (gas turbine) generator 13, a combustor 14, a fuel control valve 15, a heat recovery boiler 16, a feedwater pump 21, a coal economizer 22, a drum 23, an evaporator 24, a primary superheater 25, a secondary superheater 26, a tertiary superheater 27, a main steam pipe 28, drain valves 29a, 29b, 29c, a blowdown tank 30, a steam turbine 31, a ST (steam turbine) generator 32, a control valve 33, a turbine bypass valve 34, a condenser 35, and a circulating water pump 36. The heat recovery boiler 16 is an example of a boiler. The main steam pipe 28 is an example of a piping. The blowdown tank 30 is an example of a receiving vessel. The turbine bypass valve 34 is an example of a bypass valve.

[0013] The power plant 1 of this embodiment further includes a flame detector FD that detects a flame in the gas turbine 12, a pressure sensor PS that measures the steam pressure in the main steam pipe 28, and an opening detector LVDT that detects the opening of the regulator valve 33. Signals from the flame detector FD, the pressure sensor PS, and the opening detector LVDT are input to the plant control device 2. Note that the power plant 1 of this embodiment further includes many other instrument sensors, such as a flow meter and a thermometer (not shown) that measure the flow rate and temperature of steam (main steam A5) to determine the ST ventilation permission condition described later.

[0014] The fuel control valve 15 is provided on the fuel pipe. When the fuel control valve 15 is opened, the fuel A1 is supplied from the fuel pipe to the combustor 14. Meanwhile, the compressor 11 supplies compressed air to the combustor 14. The combustor 14 burns the fuel A1 together with the compressed air to generate high-temperature, high-pressure gas. The gas turbine 12 is driven to rotate by this gas. The GT generator 13 generates electricity by utilizing this rotation. The exhaust gas A2 discharged from the gas turbine 12 is sent to the exhaust heat recovery boiler 16. The exhaust heat recovery boiler 16 recovers heat from the exhaust gas A2 to generate steam, as described below.

[0015] The feedwater pump 21 sends water to the feedwater pipe. The feedwater pipe is connected to the economizer 22, and the water heated by the economizer 22 is sent to the drum 23. The economizer 22, the evaporator 24, the primary superheater 25, the secondary superheater 26, and the tertiary superheater 27 are provided in the heat recovery boiler 16 and form a part of the heat recovery boiler 16. The economizer 22, the evaporator 24, the primary superheater 25, the secondary superheater 26, and the tertiary superheater 27 are heat exchangers that use the heat of the exhaust gas A2 to heat the water sent from the feedwater pump 21 and the steam generated from this water. Each heat exchanger heats the water or steam by exchanging heat between the exhaust gas A2 supplied to the heat exchanger and the water or steam passing through the heat exchanger.

[0016] Specifically, the water in the drum 23 is sent to the evaporator 24, where it is heated by the exhaust gas A2 to become saturated steam. The saturated steam is superheated by the exhaust gas A2 in the primary superheater 25 to become primary superheated steam A3. The primary superheated steam A3 is superheated by the exhaust gas A2 in the secondary superheater 26 to become secondary superheated steam A4. The secondary superheated steam A4 is superheated by the exhaust gas A2 in the tertiary superheater 27 to become main steam A5.

[0017] The main steam A5 generated by the heat recovery steam generator 16 is discharged to a main steam pipe 28. The main steam pipe 28 branches into a main pipe and a bypass pipe. The main pipe is connected to a steam turbine 31, and the bypass pipe is connected to a condenser 35. A regulator valve 33 is provided in the main pipe. A turbine bypass valve 34 is provided in the bypass pipe.

[0018] The drain valve 29a is provided in a branch pipe from a pipe connecting the primary superheater 25 and the secondary superheater 26. The drain valve 29b is provided in a branch pipe from a pipe connecting the secondary superheater 26 and the tertiary superheater 27. The drain valve 29c is provided in a branch pipe from the main steam pipe 28. These branch pipes are connected to a blowdown tank 30. The drain valves 29a to 29c are motor-operated valves that are installed for the purpose of completely shutting off (tightly shutting off) fluids such as water and steam. The power plant 1 of this embodiment includes, for example, about 10 drain valves, but FIG. 1 shows only three of these drain valves, 29a to 29c, as representatives for convenience of illustration. Further details of the drain valves 29a to 29c and the blowdown tank 30 will be described later.

[0019] When the control valve 33 is opened, the main steam A5 in the main piping is supplied to the steam turbine 31. When starting up the steam turbine 31, opening the control valve 33 to start supplying the main steam A5 to the steam turbine 31 is hereinafter referred to as "ST ventilation." On the other hand, when the turbine bypass valve 34 is opened, the main steam A5 in the bypass piping bypasses the steam turbine 31 and is sent to the condenser 35. The opening of the turbine bypass valve 34 will be described in further detail later.

[0020] After the ST ventilation of the steam turbine 31, the regulator valve 33 is gradually opened widely to increase the supply of main steam A5 to the steam turbine 31, and the steam turbine 31 is accelerated and paralleled while increasing the driving torque. After paralleling, the ST generator 32 is driven by the steam turbine 31 to generate electricity. After being used to drive the steam turbine 31, the main steam A5 is discharged from the steam turbine 31 to become exhaust steam A6 and is sent to the condenser 35.

[0021] The circulating water pump 36 supplies circulating water A7 to the condenser 35. An example of the circulating water A7 is seawater. The condenser 35 cools the exhaust steam A6 with the circulating water A7, and the exhaust steam A6 is condensed and returned to water (condensation). When the circulating water A7 is seawater, the circulating water A7 discharged from the condenser 35 is returned to the sea. The condenser 35 also cools the main steam A5 sent from the turbine bypass valve 34 with the circulating water A7, and the main steam A6 is condensed and returned to water (condensation).

[0022] The above has described the "normal operation" state of the combined power generating plant 1 in which the steam turbine 31 is started by the main steam A5 and drives the ST generator 32 to generate electricity.

[0023] Next, the "start-up operation" of the combined cycle power generating plant 1 will be described. The main steam A5 that has just been generated by the heat recovery boiler 16 is, so to speak, in an energy-deficient state, so the steam turbine 31 cannot start ST ventilation. To perform ST ventilation, the heat recovery boiler 16 needs to generate more heat and wait for the energy to be sufficient. To put it simply, the pressure, temperature, and flow rate of the main steam A5 each rise to and reach a predetermined value (ST ventilation permission condition). However, even while waiting for the energy to be sufficient, main steam A5 that is unsuitable for ST ventilation continues to be generated, so it is necessary to bypass the steam turbine 31 and recover (discard) it in the condenser 35.

[0024] Therefore, as described above, the turbine bypass valve 34 installed in the bypass piping is opened to recover the main steam A5 to the condenser 35. At that time, if the amount of recovered steam is too much or too little, the pressure in the drum 23 fluctuates and the drum water level becomes unstable. Therefore, the turbine bypass valve 34 recovers the steam while keeping the drum pressure constant so that there is neither too much nor too little steam. This control circuit will be described in detail later.

[0025] Here, the installation of the drain valves 29a to 29c and the roles they play in the start-up operation of the combined power generating plant 1 will be described.

[0026] When steam generation starts from drum 23 and primary superheated steam A3, secondary superheated steam A4, and main steam A5 are generated, the piping through which these steam A3 to A5 pass is in a cold state, and a part of the steam cooled by contacting this cold piping condenses to generate drain water. This piping includes a piping constituting primary superheater 25, a piping constituting secondary superheater 26, a piping constituting tertiary superheater 27, a main steam pipe 28, etc.

[0027] As an example, the drain valve 29c will be described. The tertiary superheater 27 and the main steam pipe 28 through which the main steam A5 passes are in a cold state, and a part of the main steam A5 that is cooled by contacting them condenses to generate drain water. This drain water is mixed with the main steam A5 and flows downstream, and accumulates at the bottom part and bent parts of the piping. In addition, a part of the drain water becomes high-speed "water droplets" and impinges and impacts the piping, and in some cases, causes damage to the piping. Therefore, the drain valve 29c is installed at a place where the drain water is likely to accumulate (typically the bottom part and bent parts), and the drain valve 29c is opened to discharge the drain water. At this time, the main steam A5 (part of it) is also discharged together with the drain water. Therefore, when the drain valve is opened, the discharge amount of the main steam A5 can be adjusted by adjusting the opening degree, and the opening degree of the turbine bypass valve 34 can also be adjusted. This embodiment focuses on this point.

[0028] Hereinafter, the drainage of drain water and steam by opening the drain valve 29c is referred to as drain blow. The drain water and main steam A5 discharged by the drain blow are discharged to the blowdown tank 30, temporarily stored in the blowdown tank 30, and then discharged from there to the outside of the power plant system by a drain pump (not shown). The blowdown tank 30 is provided to receive the drain water and main steam A5 that have passed through the drain valve 29c. The drain blow starts when steam starts to be generated from the drum 23, and ends a little after the ST ventilation. During that period, the drain blow is performed continuously. This is a measure to be fully prepared for the generation of drain water. Note that part of the drain water includes steam that remained in the power plant 1 from the previous plant shutdown to the current plant startup and was cooled and remained there. These are also discharged together during the drain blow.

[0029] The same applies to the drain valves 29a and 29b as to the drain valve 29c. Drain water is generated due to condensation in the primary superheater 25, the secondary superheater 26 and the piping connected thereto, and the drain water and steam are discharged to the blowdown tank 30 by the drain blow using the drain valves 29a and 29b. Note that, although the example in FIG. 1 shows that the blown drain water is guided to the blowdown tank 30 and discharged, it may be configured so that it is guided to the condenser 35 instead of the blowdown tank 30. In addition to the blowdown tank 30, the condenser 35 is also an example of a receiving vessel.

[0030] (1) Comparative Example (1-1) Plant control device 2b FIG. 4 is a circuit diagram showing a configuration of a plant control device 2b of the comparative example.

[0031] Before describing the details of the first embodiment, a comparative example will be described below. A plant control device 2b of this comparative example is arranged in place of the plant control device 2 in the power plant 1 shown in FIG. 1. The plant control device 2b has a function of controlling the entire power plant 1. FIG. 4 shows a control circuit included in the plant control device 2b and controlling the turbine bypass valve 34 and the drain valves 29a to 29c. Note that the numerical values ​​used in the following text are examples of specific numerical values ​​for easier understanding of the description.

[0032] The plant control device 2b of this comparative example includes a functional block for detecting gas turbine ignition 101, a comparator 102, a setter 103, an AND circuit 104, a switch 105, a setter 106, a setter 107, a setter 201, a subtractor 202, and a PI (Proportional-Integral) controller 203.

[0033] (1-2) Pressure control of turbine bypass valve 34 The setting device 201 holds 7.0 MPa as a set value (SV value) of the pressure of the main steam A5 (hereinafter referred to as the “main steam pressure”). This 7.0 MPa is selected as an appropriate value for the internal pressure of the drum 23.

[0034] The subtractor 202 acquires the measured value of the main steam pressure from the pressure sensor PS as a process value (PV value). Then, the subtractor 202 subtracts the main steam pressure set value 7.0 MPa from the process value (PV value) and outputs the deviation Δ.

[0035] The PI controller 203 obtains the deviation Δ from the subtractor 202 and performs PI control so as to make the deviation Δ zero. The output from the PI controller 203 is an opening command value MV of the turbine bypass valve 34. Therefore, the turbine bypass valve 34 performs pressure control so as to maintain the main steam pressure at 7.0 MPa. In this comparative example, the plant control device 2b outputs the opening command value MV to the turbine bypass valve 34, and the opening of the turbine bypass valve 34 is controlled according to the opening command value MV. In this comparative example, the actual opening of the turbine bypass valve 34 quickly follows the opening command value MV and becomes equal to it. Therefore, hereafter, the opening command value MV may be regarded as the opening of the turbine bypass valve 34. This is the same in the first to third embodiments.

[0036] Since the main steam pressure and the internal pressure of the drum 23 are nearly equal (with a small difference in piping pressure loss), it can be said that the turbine bypass valve 34 performs pressure control to maintain the internal pressure of the drum 34 at 7.0 MPa. By performing such pressure control, it can be said that the turbine bypass valve 34 stabilizes the pressure of the drum 23 and recovers just the right amount of main steam A5, which is unsuitable for ST venting, into the condenser 35. Due to this effect, the pressure of the drum 23 is kept constant, and the power plant 1 can continue to operate stably.

[0037] (1-3) Drain blow control of drain valves 29a to 29c As described above, the drain blow starts when steam starts to be generated from the drum 23, and ends a little after ST ventilation is performed. When the gas turbine 31 ignites and the exhaust gas A2 flows into the heat recovery steam generator 16, steam starts to be generated from the drum 23. The plant control device 2b receives a signal from the flame detector FD and detects the gas turbine ignition 101.

[0038] The comparator 102 acquires the opening signal of the regulator valve 33 from the opening detector LVDT, and takes in 15% set in a setter 103 as a set value. When the opening signal is smaller than 15%, the comparator 102 turns its output 102OUT ON. The AND circuit 104 takes in the gas turbine ignition 101 and the output 102OUT, and turns on the output 104OUT when both are established.

[0039] A switch 105 (Analog Switch, ASW) takes in an output 104OUT. In addition, the switch 105 has two input ports, and a port 1 takes in 50% set in a setter 106, and a port 2 takes in 0% set in a setter 107. Depending on the ON-OFF state of the output 104OUT, when the output 104OUT is ON, the switch 105 selects the port 1 and outputs 50% as the opening target value NORM, and when the output 104OUT is OFF, the switch 105 selects the port 2 and outputs 0% as the opening target value NORM. In this comparative example, the plant control device 2b outputs the opening target value NORM to the drain valves 29a to 29c, and the openings of the drain valves 29a to 29c are controlled depending on the opening target value NORM.

[0040] (1-4) Effects of Comparative Example When the power plant 1 starts up and the gas turbine 12 is ignited, steam begins to be generated from the drum 23. However, the main steam A5 has insufficient energy and its pressure is still far lower than 7.0 MPa, so the turbine bypass valve 34 is kept closed by pressure control.

[0041] On the other hand, the gas turbine ignition 101 signal is turned ON, and the opening of the regulator valve 33 is also below 15% (because ST ventilation has not yet started), so the output 102OUT is also turned ON. Therefore, the output 104OUT is turned ON, and the opening target value NORM is selected to be 50%. As a result, the drain valves 29a to 29c are opened to 50% and drain blow is started. That is, the steam generated from the drum 23 condenses when it comes into contact with the cold piping, and some of it becomes drain water, but this drain water is discharged to the blowdown tank 30 through the drain valves 29a to 29c. During drain blow, steam is discharged to the blowdown tank 30 together with the drain water.

[0042] Drain blow can also be performed by opening the drain valves 29a to 29c 100%. However, if the drain valves 29a to 29c are fully open, a larger amount of steam flows out to the blow-down tank 30, and the pressure rise of the main steam A5 is delayed. Therefore, drain blow is performed by opening the valves halfway, 50%. Note that 50% is an example for ease of explanation, and the signal name "NORM" is given to mean the normal opening during drain blow. The signal of the target opening value NORM is branched into three in the plant control device 2b, and is output to the drain valves 29a to 29c, respectively. The drain valves 29a to 29c open according to the target opening value NORM.

[0043] After that, the start-up of the power plant 1 continues. The fuel control valve 15 supplies a larger amount of fuel A1, and the gas turbine 12 discharges exhaust gas A2 with a higher calorific value. The heat recovery boiler 16 recovers this high calorific value from the exhaust gas A2, so that the thermal energy held by the main steam A5 increases. Then, when the "pressure" of the main steam A5 reaches 7.0 MPa, the turbine bypass valve 34 starts to open by the pressure control.

[0044] However, even though the "pressure" has increased, the "flow rate" and "temperature" of the main steam A5 are still insufficient, and the ST ventilation permission condition has not yet been met. In order for the ST ventilation permission condition to be met, the heat recovery boiler 16 needs to recover and store more heat and wait for the steam energy to be sufficient. Meanwhile, the amount of steam generated from the drum 23 continues to increase, and the turbine bypass valve 34 increases its opening by pressure control so as to maintain the pressure of the main steam A5 at 7.0 MPa.

[0045] Then, when the "flow rate" and "temperature" of the main steam A5 finally reach the predetermined ST ventilation permission conditions, ST ventilation is started. When ST ventilation starts, the control valve 33 is opened, and the steam turbine 31 starts to increase in rotation (speed up). The control valve 33 gradually increases its opening degree until it reaches 15% or more. Since the opening degree of the control valve 33 is 15% or more, the output 102OUT is turned OFF. Therefore, the output 104OUT is turned OFF, and the target opening value NORM is selected as 0%. As a result, the drain valves 29a to 29c are set to 0%, i.e., closed, and the drain blow is terminated. This is because the exhaust heat recovery boiler 16 has been sufficiently warmed up, making it unnecessary to consider the generation of drain water, and because the drain blow discharges part of the thermal energy outside the system, resulting in thermal loss, and therefore, it is terminated at an appropriate timing. Furthermore, when ST ventilation begins, the main steam A5, which had been passing through the turbine bypass valve 34 until now, begins to pass through the control valve 33, so that the turbine bypass valve 34 gradually reduces its opening degree and is finally fully closed.

[0046] (1-5) Problems with the comparative example In this comparative example, the problem of the turbine bypass valve 34 opening too large often occurs. In general, the appropriate opening of the turbine bypass valve 34 is considered to be 80% or less. If the opening of the turbine bypass valve 34 exceeds 80% and reaches, for example, 90%, there is a risk that it will be fully opened to 100% due to a minor trigger. If it is fully opened to 100%, the function of controlling the pressure inside the drum 23 is lost, and the pressure will suddenly fluctuate to 7.0 MPa or more. As a result, a so-called shrinking phenomenon occurs inside the evaporator 24, causing bubbles (voids) to collapse, the water level in the drum 23 to drop, and the heat recovery steam generator 16 to become unstable.

[0047] There are several reasons why the opening degree of the turbine bypass valve 34 becomes too large, but the process of establishing the ST ventilation permission condition itself includes the tendency and factors. That is, there is a time difference between the "flow rate" and "temperature" of the main steam A5 to reach the specified ST ventilation permission condition. Generally, the "flow rate" of the main steam A5 tends to reach the specified ST ventilation permission condition relatively early, while it takes time for the "temperature" of the main steam A5 to rise to the specified ST ventilation permission condition. In that case, the exhaust heat recovery boiler 16 continues to recover heat and tries to raise the "temperature", but at the same time, it also causes an unintended increase in the "flow rate" of the main steam A5. In other words, since the amount of steam generated from the drum 23 increases beyond the ST ventilation permission condition, the turbine bypass valve 34 increases its opening degree by pressure control to keep the pressure of the main steam A5 at 7.0 MPa, and finally the opening degree exceeds 80%.

[0048] Therefore, in this embodiment, when the opening degree of the turbine bypass valve 34 becomes 80% or more, the opening degrees of the drain valves 29a to 29c are increased. In this embodiment, the opening degree of the turbine bypass valve 34 is reduced by increasing the flow rates of the primary superheated steam A3, the secondary superheated steam A4, and the main steam A5 discharged to the blowdown tank 30 through the drain valves 29a to 29c.

[0049] (2) Details of the First Embodiment (2-1) Plant control device 2 FIG. 2 is a circuit diagram showing a configuration of the plant control device 2 of the first embodiment.

[0050] As described above, the plant control device 2 of this embodiment is disposed in the power plant 1 shown in Fig. 1. The plant control device 2 has a function of controlling the entire power plant 1. Fig. 2 shows a control circuit included in the plant control device 2, which controls the turbine bypass valve 34 and the drain valves 29a to 29c. Note that the numerical values ​​used in the following description are examples of specific numerical values ​​for easier understanding of the description.

[0051] The plant control device 2 of this embodiment includes a function block for detecting gas turbine ignition 101, a comparator 102, a setter 103, an AND circuit 104, a switch 105, a setter 106, a setter 107, a setter 201, a subtractor 202, and a PI controller 203, similar to the plant control device 2b of the comparative example. The plant control device 2 of this embodiment further includes a correction unit 301 and a multiplier 302, and the correction unit 301 includes a comparator 311, a setter 312, a switch 313, a sampling delay unit 314, a high value selector 315, and a function generator 316. The setter 201, the subtractor 202, and the PI controller 203 are examples of a bypass valve control unit. The functional block for gas turbine ignition 101, the comparator 102, the setter 103, the AND circuit 104, the switch 105, the setter 106, the setter 107, the correction unit 301, and the multiplier 302 are examples of a drain valve control unit.

[0052] (2-2) Pressure control of turbine bypass valve 34 The pressure control of the turbine bypass valve 34 in this embodiment is performed in the same manner as in the comparative example, as described below.

[0053] The setting device 201 holds 7.0 MPa as a set value (SV value) of the pressure of the main steam A5 (main steam pressure). This 7.0 MPa is selected as an appropriate value for the internal pressure of the drum 23.

[0054] The subtractor 202 acquires the measured value of the main steam pressure from the pressure sensor PS as a process value (PV value). Then, the subtractor 202 subtracts the main steam pressure set value 7.0 MPa from the process value (PV value) and outputs the deviation Δ.

[0055] The PI controller 203 acquires the deviation Δ from the subtractor 202 and performs PI control so as to make the deviation Δ zero. The PI controller 203 outputs an opening command value MV of the turbine bypass valve 34. Therefore, the turbine bypass valve 34 performs pressure control so as to maintain the main steam pressure at 7.0 MPa. In this embodiment, the plant control device 2 outputs the opening command value MV to the turbine bypass valve 34, and the opening of the turbine bypass valve 34 is controlled in accordance with the opening command value MV. The opening command value MV is an example of a first control signal.

[0056] In this embodiment, the signal of the opening degree command value MV is branched into two in the plant control device 2. One branch outputs the opening degree command value MV to the turbine bypass valve 34, and the other branch outputs the opening degree command value MV to the correction unit 301.

[0057] (2-3) Drain blow control of drain valves 29a to 29c The plant control device 2 of this embodiment, like the comparative example, receives a signal from a flame detector FD and detects gas turbine ignition 101.

[0058] The comparator 102 acquires the opening signal of the regulator valve 33 from the opening detector LVDT, and takes in 15% set in a setter 103 as a set value. When the opening signal is smaller than 15%, the comparator 102 turns its output 102OUT ON. The AND circuit 104 takes in the gas turbine ignition 101 and the output 102OUT, and turns on the output 104OUT when both are established.

[0059] Switch 105 takes in output 104OUT. In addition, switch 105 has two input ports, port 1 takes in 50% set in setter 106, and port 2 takes in 0% set in setter 107. Depending on the ON / OFF state of output 104OUT, switch 105 selects port 1 when output 104OUT is ON and outputs 50% as the target opening value NORM, and when output 104OUT is OFF, selects port 2 and outputs 0% as the target opening value NORM.

[0060] The drain blow control of this embodiment is performed in the same manner as in the comparative example. However, the plant control device 2b of the comparative example branches the opening target value NORM and outputs it to the drain valves 29a to 29c. In contrast, the plant control device 2 of this embodiment supplies the opening target value NORM to a multiplier 302. The multiplier 302 multiplies the opening target value NORM by the value GAIN supplied from the correction unit 301 to correct the opening target value NORM to an opening command CMND. In this embodiment, the plant control device 2 branches the opening command CMND and outputs it to the drain valves 29a to 29c, and the openings of the drain valves 29a to 29c are controlled according to the opening command CMND. The opening target value NORM is an example of a second control signal. The opening command CMND is an example of a third control signal.

[0061] The comparator 311 receives the opening command value MV of the turbine bypass valve 34, and also receives 80% set in the setter 312 as a set value. When MV is greater than 80%, the comparator 311 turns its output 311OUT ON. The threshold of the comparator 311 in this embodiment has a cutoff difference (Differential), and when MV is greater than 80%, the output 311OUT turns ON, and when MV is less than 40%, the output 311OUT turns OFF.

[0062] The switch 313 takes in the output 311OUT. In addition, the switch 313 has two input ports. Port 1 takes in the value MV-MAX' from one cycle ago from a sampling delay unit 314, which will be described later, and port 2 takes in the opening command value MV of the turbine bypass valve 34. Depending on the ON / OFF state of the output 311OUT, the switch 313 selects port 1 when the output 311OUT is ON and outputs the value MV-MAX' as the output 313OUT, and when the output 311OUT is OFF, the switch 313 selects port 2 and outputs MV as the output 313OUT.

[0063] The high value selector 315 takes in the output 313OUT from the switch 313 and the opening command value MV. The high value selector 315 selects the larger of the output 313OUT and the MV (the high value), and outputs the selected value as the value MV-MAX. The value MV-MAX is the maximum value of the opening (opening command value MV) of the turbine bypass valve 34 from the past to the present.

[0064] The sampling delay unit 314 is denoted by the symbol “Z -1 ". Sampling delay unit 314 takes in value MV-MAX output from high value selector 315 and stores the taken-in value MV-MAX. In the next calculation cycle, sampling delay unit 314 outputs the stored value MV-MAX as value MV-MAX' from one cycle before.

[0065] The function generator 316 takes in the value MV-MAX output from the high value selector 315, converts the taken-in value MV-MAX to a value GAIN, and outputs it. For this reason, the function generator 316 has a built-in graph that converts the x-axis value MV-MAX to the y-axis value GAIN, as shown in FIG. 2. The graph is a function that connects the coordinates of four points, the first point (0%, 1.0), the second point (80%, 1.0), the third point (90%, 2.0), and the fourth point (100%, 2.0), with straight lines. This allows the function generator 316 to make the value GAIN greater than 1.0 when the value MV-MAX is greater than 80%. When the function generator 316 determines that the value MV-MAX is less than 80%, it outputs 1 as the value GAIN, and when it determines that the value MV-MAX is greater than 80%, it outputs a value greater than 1 as the value GAIN. This value of 80% is an example of the first opening.

[0066] The output side of the correction unit 301 is connected to a multiplier 302 provided on the output side of the switch 105. The multiplier 302 takes in a value GAIN which is an output of a function generator 316 and a target opening value NORM which is an output of the switch 105. The multiplier 302 multiplies the target opening value NORM by the value GAIN, and outputs an opening command CMND to the drain valves 29a to 29c. The signal of the opening command CMND is branched into three in the plant control device 2, and is output to the drain valves 29a to 29c, respectively. The drain valves 29a to 29c open in response to the opening command CMND.

[0067] In this embodiment, during a period when drain blow is required (when the drain valves 29a to 29c need to be opened), the target opening value NORM is set to 50% set in the setter 106. In this case, when the value MV-MAX is smaller than 80%, that is, when the value GAIN is 1, the opening command CMND is also 50%. While the value GAIN is 1, the opening command CMND is maintained at 50% even if the opening command value MV changes and the value MV-MAX changes. On the other hand, when the value MV-MAX is larger than 80%, that is, when the value GAIN is larger than 1, the opening command CMND becomes larger than 50%. While the value GAIN is larger than 1, the opening command CMND changes within the range of 50 to 100% when the opening command value MV changes and the value MV-MAX changes. For example, when the value MV-MAX increases from 80% to 85%, the value GAIN increases from 1 to 1.5, and the opening command CMND increases from 50% to 75%. This value of 50% is an example of the second opening.

[0068] In this way, the opening command CMND in this embodiment changes according to the opening command value MV (value MV-MAX). In other words, the opening of the drain valves 29a to 29c in this embodiment changes according to the opening of the turbine bypass valve 34. This is because, as described above, the opening of the turbine bypass valve 34 quickly follows and becomes equal to the opening command value MV, and the opening command value MV can be regarded as the opening. Further details of such an operation in this embodiment will be described later.

[0069] (2-4) Functions and Effects of the First Embodiment Next, the actions and effects of this embodiment will be described below.

[0070] In this embodiment, a DCS (Distributed Control System) that performs calculations at each sampling period is used as a model model of the plant control device 2. Although an actual sampling period of a DCS is, for example, 200 ms, for convenience of explanation, the sampling period is set to 1 second in this specification. In the following explanation, the sampling time t is set to t=0 second, t=1 second, t=2 seconds, and so on, in 1 second increments.

[0071] In reality, the behavior and responsiveness of the turbine bypass 34 is slower, and the opening does not change significantly in a short period of time such as one second. However, for the sake of convenience, such a fast change in MV (opening) is assumed. For the same reason, the behavior of the actual drain valves 29a to 29c is also slow, but in the following explanation, a response according to the opening command CMND that changes quickly is assumed.

[0072] [t=0 seconds] At time t=0 seconds, the power plant 1 is in the process of starting up. In the startup section at this time, the "flow rate" of the main steam A5 has reached the specified ST ventilation permission condition, but the "temperature" of the main steam A5 has not yet reached the specified ST ventilation permission condition, that is, the situation is one in which the "temperature" is waiting to rise. At t=0 seconds, the turbine bypass 34 is open at 79%. Also, the drain valves 29a to 29c are in the process of drain blowing, and are open at 50%. This will be explained on the control circuit of FIG. 2.

[0073] a) MV=79% is output from the PI controller 203.

[0074] b) This MV is input to comparator 311. The threshold of comparator 311 is ON at 80% or more, so when MV=79%, output 311OUT of comparator 311 is OFF and is taken in by switch 313. Since output 311OUT of switch 313 is OFF, it selects the MV of port 2 as output 313OUT and outputs this. Therefore, output 313OUT is 79%.

[0075] c) The high value selector 315 selects the larger of the MV and the output 313OUT and outputs it as the value MV-MAX. Here, MV=79% and the output 313OUT=79%, and since the two are the same value, the value MV-MAX is 79%. In this case, the value MV-MAX is the value of MV at time t=0 seconds, that is, the current value of MV.

[0076] d) Function generator 316 converts the x-axis value MV-MAX to the y-axis value GAIN. The x-axis value MV-MAX is 79%. Since the y-axis at x-axis=79% is 1.0, function generator 316 outputs 1.0 as the value GAIN. Multiplier 302 multiplies NORM=50% by GAIN=1.0 to calculate CMND=50%. As a result, drain valves 29a-29c open at 50%.

[0077] e) At time t=0 seconds, drain valves 29a to 29c are maintained at 50% opening, which is the normal opening during drain blow, as in the comparative example.

[0078] [t=1 second] a) Here, a large amount of main steam A5 is generated, and the turbine bypass 34 opens more widely, becoming 83%. That is, the MV output from the PI controller 203 becomes 83%.

[0079] b) This MV=83% is input to comparator 311. The threshold of comparator 311 is ON when MV=83%, so output 311OUT turns ON and is taken in by switch 313. Since output 311OUT is ON, switch 313 selects value MV-MAX' of port 1 as output 313OUT. Since value MV-MAX' is the value MV-MAX at t=0 seconds one cycle ago, output 313OUT is 79%. In this case, the value of MV at time t=1 second, i.e., the current value of MV, is greater than value MV-MAX' stored in sampling delay unit 314.

[0080] c) The high value selector 315 selects the larger of MV and the output 313OUT and outputs it as the value MV-MAX. Since MV=83% and the output 313OUT=79%, the value MV-MAX is 83%. In this case, the value MV-MAX is the value of MV at time t=1 second, i.e., the current value of MV.

[0081] d) Function generator 316 converts the x-axis value MV-MAX to the y-axis value GAIN. The x-axis value MV-MAX is 83%. Since the y-axis at x-axis=83% is 1.30, function generator 316 outputs 1.30 as the value GAIN. Multiplier 302 multiplies NORM=50% by GAIN=1.30 to calculate CMND=65%. As a result, drain valves 29a-29c open at 65%.

[0082] e) In this case, the valves open from 50% at t=0 seconds to 65%, which is 15% larger, so the amount of steam discharged from drain valves 29a-29c increases. Thus, at t=1 second, since the current MV value (>80%) is greater than the value MV-MAX', the value MV-MAX increases from the value MV-MAX' to the current MV value, and the opening command CMND increases. The MV range of 80% or less is an example of a predetermined range.

[0083] [t=2 seconds] a) However, the 65% opening of the drain valves 29a to 29c is an insufficient opening, and the MV output from the PI controller 203 increases to 85%.

[0084] b) This MV=85% is input to comparator 311. Since the threshold of comparator 311 is ON when MV=85%, output 311OUT of comparator 311 remains ON and is taken in by switch 313. Since output 311OUT of switch 313 is ON, it selects value MV-MAX' of port 1 as output 313OUT. Since value MV-MAX' is the value MV-MAX at t=1 second one cycle ago, output 313OUT is 83%. In this case, the value of MV at time t=2 seconds, i.e., the current value of MV, is greater than value MV-MAX' stored in sampling delay unit 314.

[0085] c) The high value selector 315 selects the larger of MV and the output 313OUT and outputs it as the value MV-MAX. Since MV=85% and the output 313OUT=83%, the value MV-MAX is 85%. In this case, the value MV-MAX is the value of MV at time t=2 seconds, i.e., the current value of MV.

[0086] d) Function generator 316 converts the x-axis value MV-MAX to the y-axis value GAIN. The x-axis value MV-MAX is 85%. Since the y-axis at x-axis=85% is 1.5, function generator 316 outputs 1.5 as the value GAIN. Multiplier 302 multiplies NORM=50% by GAIN=1.5 to calculate CMND=75%. As a result, drain valves 29a-29c open at 75%.

[0087] e) In this case, the valves open from 65% at t = 1 second to 75%, which is 10% larger, so the amount of steam discharged from the drain valves 29a to 29c increases further, and the pressure of the main steam A5 decreases accordingly.In this way, at t = 2 seconds, since the current MV value (>80%) is greater than the value MV-MAX', the value MV-MAX increases from the value MV-MAX' to the current MV value, and the opening command CMND increases.

[0088] [t=3 seconds] a) 75% opening of the drain valves 29a to 29c is an appropriate opening, the pressure of the main steam A5 drops, the pressure sensor PS detects this, and the MV output from the PI controller 203 drops to 81%. In other words, this phenomenon means that sufficient steam has been discharged from the 75% of the drain valves 29a to 29c, and the amount of main steam A5 passing through the turbine bypass 34 has decreased accordingly.

[0089] b) This MV=81% is input to comparator 311. Since the threshold of comparator 311 is ON when MV=81%, output 311OUT of comparator 311 remains ON and is taken into switch 313. Since output 311OUT of switch 313 is ON, it selects value MV-MAX' of port 1 as output 313OUT. Since value MV-MAX' is the value MV-MAX at t=2 seconds one cycle ago, output 313OUT is 85%. In this case, the value of MV at time t=3 seconds, i.e., the current MV value, is smaller than value MV-MAX' stored in sampling delay unit 314.

[0090] c) High value selector 315 selects the larger of MV and output 313OUT and outputs it as value MV-MAX. Since MV=81% and output 313OUT=85%, value MV-MAX is 85%. That is, correction unit 301 including high value selector 315 and sampling delay unit 314 operates to select the largest value of MV up to that point as value MV-MAX. In this case, value MV-MAX is the value of MV at time t=2 seconds, that is, the past MV value.

[0091] d) Function generator 316 converts the x-axis value MV-MAX to the y-axis value GAIN. The x-axis value MV-MAX is 85%. Since the y-axis at x-axis=85% is 1.5, function generator 316 outputs 1.5 as the value GAIN. Multiplier 302 multiplies NORM=50% by GAIN=1.5 to calculate CMND=75%. As a result, drain valves 29a-29c are kept open 75%.

[0092] e) As a result, the amount of steam discharged from the drain valves 29a to 29c is also maintained. That is, even though the MV of the turbine bypass 34 has decreased from 85% to 81%, the drain valves 29a to 29c are maintained open (75%) when the MV is 85%. This shows the effect that "the value MV-MAX selects the largest value among the MV values ​​up to now, stores it as the value MV-MAX', and uses it in the next calculation cycle." In this way, at t=3 seconds, since the current MV value (>80%) is smaller than the value MV-MAX', the value MV-MAX is maintained as the value MV-MAX', and the opening command CMND is also maintained. The condition that the current MV value is smaller than the value MV-MAX' is an example of a predetermined condition.

[0093] f) In a primitive control method that does not use the value MV-MAX other than that of this embodiment, when the MV of the turbine bypass 34 is reduced from 85% to 81%, the current MV of 81% is input to the x-axis of the function generator 316, the value GAIN on the y-axis becomes 1.10, and the opening of the drain valves 29a to 29c is reduced to 55%. As a result, the amount of steam discharged from the drain valves 29a to 29c decreases, and the opening of the turbine bypass 34 opens to 81% or more again. As a result, the value GAIN becomes 1.10 or more, and the drain valves 29a to 29c try to open to 55% or more. From then on, the opening of both (valves) continues to increase and decrease infinitely.

[0094] That is, fluctuations in the drain valve opening (CMND) affect the opening (MV) of the turbine bypass valve 34, and conversely, when the opening (MV) of the turbine bypass valve 34 fluctuates, the drain valve opening (CMND) is affected. This mutual link between cause and effect is the reason for repeated increases and decreases. Therefore, the correction unit 301 acts to break the chain of cause and effect by generating and storing a value MV-MAX, which is the maximum value of MV up to now.

[0095] [t=4 seconds] a) The pressure of the main steam A5 further decreases, the pressure sensor PS detects this, and the MV output from the PI controller 203 decreases to 77%.

[0096] b) This MV=77% is input to comparator 311. As mentioned above, the threshold of comparator 311 has a cutoff differential. In other words, once the MV is turned on when it is 80% or more and enters the ON state, it turns off when MV subsequently falls to 40% or less. Therefore, even if MV is reduced to 77%, output 311OUT of comparator 311 remains in the ON state and is taken in by switch 313. Since output 311OUT is ON, switch 313 selects value MV-MAX' of port 1 as output 313OUT. Since value MV-MAX' is the value MV-MAX at t=3 seconds one cycle ago, output 313OUT is 85%.

[0097] c) High value selector 315 selects the larger of MV and output 313OUT and outputs it as value MV-MAX. Since MV=77% and output 313OUT=85%, value MV-MAX is 85%. As mentioned above, value MV-MAX selects the largest value of MV so far.

[0098] d) The function generator 316 converts the x-axis value MV-MAX to the y-axis value GAIN. The x-axis value MV-MAX is 85%. Since the y-axis at x-axis=85% is 1.5, the function generator 316 outputs 1.5 as the value GAIN. The multiplier 302 multiplies NORM=50% by GAIN=1.5 to calculate CMND=75%. As a result, the drain valves 29a-29c are kept 75% open. In this way, if the drain valves 29a-29c are kept at an appropriate opening of 75% and the drain blow is continued, the MV of the turbine bypass 34 can be kept at a stable 77%, which is a sufficient margin for 100% full opening.

[0099] e) If a primitive control method were used as in this embodiment, in which no cut-off difference is set for the threshold of comparator 311, that is, if the threshold is set to turn ON when MV is 80% or higher and then turn OFF when MV falls below 80%, the output 311OUT of comparator 311 would turn OFF the moment MV reduced to 77% and be taken in by switch 313.

[0100] Since the output 311OUT is OFF, the switch 313 selects the MV of port 2 as the output 313OUT and outputs it. Therefore, the output 313OUT is 77%. The high value selector 315 selects the larger of the MV and the output 313OUT and outputs it as the value MV-MAX. Since MV=77% and the output 313OUT=77%, both are the same value, and the value MV-MAX is 77%. The function generator 316 converts the x-axis value MV-MAX to the y-axis value GAIN. The x-axis value MV-MAX is 77%. Since the y-axis at x-axis=77% is 1.0, the function generator 316 outputs 1.0 as the value GAIN. The multiplier 302 multiplies NORM=50% by GAIN=1.0 to calculate CMND=50%. As a result, the drain valves 29a to 29c close from 75% to 50%. As a result, the MV of the turbine bypass 34 increases and rises to 80% or more again, the value GAIN becomes 1.0 or more, and the drain valves 29a to 29c attempt to become 50% or more again.

[0101] This is a problem caused by the mutual chain of cause and effect described above in "t=3 seconds." The cutoff difference of comparator 311 acts to break this chain of cause and effect.

[0102] [t=5 seconds and thereafter] a) The state at t=4 seconds is continued. That is, since the value MV-MAX is maintained at 85%, the drain valves 29a-29c continue drain blowing with 75% opening, and the MV of the turbine bypass 34 increases and decreases at 77% or a value close to that, while maintaining the pressure of the main steam A5 at 7.0 MPa. This embodiment aims to realize an operating state in which the opening degree (MV) of the turbine bypass valve is opened between approximately 40% and 80%, and intends to control the drain valve opening degree to an appropriate degree that maintains and continues such a stable operating state. The intention of this embodiment is to maintain this stable state until the ST ventilation starts at the next "t=n seconds".

[0103] b) However, if, contrary to expectations, the MV of the turbine bypass 34 exceeds 85%, the following will be explained. This situation corresponds to a case where the opening of the drain valves 29a to 29c at 75% is judged to be insufficient. For the sake of convenience, the following will explain a case where the MV of the turbine bypass 34 becomes 90%.

[0104] In this case, the same action as when "t = 2 seconds" described above occurs, and the value MV-MAX rises from 85% to 90%, and the value GAIN becomes 2.0, so that the drain valves 29a to 29c are fully opened 100%, and a large amount of steam is discharged to the blowdown tank 30. As a result, the main steam A5 passing through the turbine bypass 34 decreases, and the MV of the turbine bypass 34 decreases from 90%, preventing the turbine bypass 34 from being fully opened 100%.

[0105] The specific percentage of MV of the turbine bypass 34 is determined by the heat balance between the total amount of main steam A5 and the amount of steam discharged to the blowdown tank 30.

[0106] c) A case where the MV of the turbine bypass 34 becomes 40% or less will be explained below. This situation corresponds to a case where the opening degree of the drain valves 29a to 29c is determined to be 75% excessively large. For the sake of convenience, a case where the MV of the turbine bypass 34 becomes 38% will be explained.

[0107] In this case, MV=38% is input to comparator 311. The threshold of comparator 311 has a cutoff difference, and output 311OUT turns OFF when MV becomes 80% or more and then becomes ON, and then becomes OFF when MV becomes 40% or less. Therefore, when MV=38%, output 311OUT turns OFF and is taken in by switch 313.

[0108] Since the output 311OUT is OFF, the switch 313 selects the MV of port 2 as the output 313OUT and outputs it. Therefore, the output 313OUT is 38%. The high value selector 315 selects the larger of the MV and the output 313OUT and outputs it as the value MV-MAX, but since MV=38% and the output 313OUT=38%, both values ​​are the same, and the value MV-MAX is 38%. The function generator 316 converts the x-axis value MV-MAX to the y-axis value GAIN. The x-axis value MV-MAX is 38%. Since the y-axis at x-axis=38% is 1.0, the function generator 316 outputs 1.0 as the value GAIN. The multiplier 302 multiplies NORM=50% and GAIN=1.0 to calculate CMND=50%. As a result, the opening degree of the drain valves 29a to 29c is reduced from 75% to 50%. As a result, the amount of steam discharged to the blowdown tank 30 is reduced, and the amount of main steam A5 passing through the turbine bypass 34 is increased, so that its MV rises to a value of 40% or more.

[0109] The specific percentage of MV of the turbine bypass 34 is determined by the heat balance between the total amount of main steam A5 and the amount discharged to the blowdown tank 30, but in most cases the MV value is 80% or less. Incidentally, a situation in which the MV of the turbine bypass 34 becomes 40% or less inevitably occurs after ST ventilation, but this will be described again later in "t = m seconds".

[0110] [t=n seconds] a) ST ventilation begins at t=n seconds. That is, t=n seconds is the point in time when about 30 minutes have passed since t=5 seconds, and is the point in time when the "temperature" of main steam A5 reaches the specified ST ventilation permission condition. When ST ventilation begins at t=n seconds and regulating valve 33 opens, main steam A5 flows into regulating valve 33. Regulating valve 33 gradually increases its opening, and in response, PI controller 203 gradually reduces MV to maintain the pressure of main steam A5 at 7.0 MPa. This reduction in MV continues until the next "t=m seconds."

[0111] [t=m seconds] a) At t=m seconds, MV is reduced to 39%. t=m seconds is the time point when about 3 minutes have passed since t=n seconds. ST ventilation continues, and the MV output from the PI controller 203 is reduced to 39%.

[0112] b) This MV = 39% is input to comparator 311. The threshold of comparator 311 has a cut-off difference, and when MV is above 80% and turns ON once, and then falls to below 40%, output 311OUT turns OFF. Therefore, when MV is reduced to 39%, output 311OUT turns OFF and is taken into switch 313. Since output 311OUT is OFF, switch 313 selects the MV of port 2 as output 313OUT and outputs this. Therefore, output 313OUT is 39%.

[0113] c) The high value selector 315 selects the larger of MV and the output 313OUT and outputs it as the value MV-MAX. MV=39% and the output 313OUT=39%, which are the same value, so the value MV-MAX is 39%.

[0114] d) Function generator 316 converts the x-axis value MV-MAX to the y-axis value GAIN. The x-axis value MV-MAX is 39%. Since the y-axis at x-axis=39% is 1.0, function generator 316 outputs 1.0 as the value GAIN. Multiplier 302 multiplies NORM=50% by GAIN=1.0 to calculate CMND=50%. As a result, the opening of drain valves 29a-29c is reduced from 75% to 50%.

[0115] e) As a result, the amount of steam discharged from the drain valves 29a to 29c is reduced, but since the main steam A5 flows into the control valve 33, the MV of the turbine bypass 34 does not rise again as in “c)” above at “t=5 seconds and thereafter.”

[0116] [t=p seconds and thereafter] a) At t=p seconds, the opening of regulating valve 33 rises to 15%. t=p seconds is the point in time when about 30 seconds have passed since t=m seconds. Because the opening of regulating valve 33 is 15% or more, output 102OUT, which is the output of comparator 102, turns OFF. Therefore, output 104OUT, which is the output of AND circuit 104, turns OFF, and 0% is selected as the target opening value NORM, which is the output of switch 105. As a result, drain valves 29a to 29c are 0%, i.e. fully closed, and drain blow ends.

[0117] b) After p seconds, the opening of the control valve 33 continues to increase. When the control valve 33 reaches a certain opening, the entire amount of main steam A5 that had been passing through the turbine bypass valve 34 passes through the control valve 33. At that point, the MV is zero, i.e., the turbine bypass valve 34 is fully closed. After this, the control valve 33 performs IPC control (Inlet Pressure Control) to maintain the pressure of the main steam A5 at 7.0 MPa. The plant startup reaches a turning point when IPC control is entered, and the phase of increasing the fuel A1 of the gas turbine 12 begins. In this phase, the flow rate of the main steam A5 increases, and the IPC control acts to open the control valve 33 100%. When the fuel A1 of the gas turbine 12 increases further and the power generation of the GT generator 13 and the ST generator 32 reaches the rated output, the plant startup of the power plant 1 ends.

[0118] (2-5) Effects of the First Embodiment In this embodiment, when the opening degree (MV) of the turbine bypass valve 34 exceeds 80%, the opening degree of the drain valves 29a to 29c is increased to discharge a larger amount of steam to the blowdown tank 30. As a result, the flow rate of the main steam A5 passing through the turbine bypass valve 34 is reduced, and the opening degree (MV) of the turbine bypass valve 34 can be reduced to 80% or less. At this time, if there is an excess or deficiency in the drain valve opening, the opening degree (MV) of the turbine bypass valve 34 is judged to be large or small, and the excess or deficiency is adjusted by further increasing or decreasing the opening degree. That is, in this embodiment, the drain valve opening degree is controlled to an appropriate opening degree according to the opening degree (MV) of the turbine bypass valve 34. As a result, it is possible to set the opening degree (MV) of the turbine bypass valve 34 to an appropriate range of 40% to 80%, which contributes to stable operation of the power plant.

[0119] In addition, when the total amount of main steam A5 is extremely large, applying this embodiment may cause the opening degree (MV) of the turbine bypass 34 to exceed 80%. If this reaches a large opening degree (MV) of approximately 90%, it is effective to use the means disclosed in Japanese Patent No. 6139311 (Patent Document 1) in addition to this embodiment.

[0120] In the above-mentioned action and mechanism, fluctuations in the drain valve opening affect the opening (MV) of the turbine bypass valve 34. On the other hand, when the opening (MV) of the turbine bypass valve 34 fluctuates, the drain valve opening is affected. In other words, cause and effect are linked to each other, and this point must be taken into consideration. Therefore, the correction unit 301 stores the value MV-MAX as the maximum value from the past to the present, determines the value GAIN based on the value MV-MAX, and provides a cutoff difference in the threshold of the comparator 311. This breaks the chain of cause and effect, and solves the problem of the turbine bypass 34 and the drain valves 29a to 29c repeatedly increasing and decreasing.

[0121] As described above, according to this embodiment, it is possible to suitably control the opening degree of the turbine bypass valve 34.

[0122] Second embodiment (1) Plant control device 2a FIG. 3 is a circuit diagram showing a configuration of a plant control device 2a according to the second embodiment.

[0123] The plant control device 2a of this embodiment is disposed in place of the plant control device 2 in the power plant 1 shown in Fig. 1. The plant control device 2a has a function of controlling the entire power plant 1. Fig. 3 shows a control circuit included in the plant control device 2a and controlling the turbine bypass valve 34 and the drain valves 29a to 29c. Note that the numerical values ​​used in the following description are examples of specific numerical values ​​for easier understanding of the description.

[0124] The plant control device 2a of this embodiment includes a function block for detecting gas turbine ignition 101, a comparator 102, a setter 103, an AND circuit 104, a switch 105, a setter 106, a setter 107, a setter 201, a subtracter 202, and a PI controller 203, similar to the plant control device 2b of the comparative example and the plant control device 2 of the first embodiment. The plant control device 2a of this embodiment further includes a correction unit 401 and a multiplier 402, and the correction unit 401 includes a comparator 411, a setter 412, a switch 413, a sampling delay unit 414, a high value selector 415, and a function generator 416. The setter 201, the subtracter 202, and the PI controller 203 are examples of a bypass valve control unit. The functional block for gas turbine ignition 101, the comparator 102, the setter 103, the AND circuit 104, the switch 105, the setter 106, the setter 107, the correction unit 401, and the multiplier 402 are examples of a drain valve control unit.

[0125] The second embodiment is a counterpart of the first embodiment. That is, the first embodiment relates to a drain valve opening increase control that operates when the opening (MV) of the turbine bypass valve 34 becomes too large, and the second embodiment relates to a drain valve opening decrease control that operates when the opening (MV) of the turbine bypass valve 34 becomes too small.

[0126] The background to this is that when the opening degree (MV) of the turbine bypass valve 34 falls below 30%, this state is an insufficient opening degree, and there is an increased risk that the turbine bypass valve 34 will be fully closed. If the turbine bypass valve 34 is fully closed, the function of pressure control inside the drum 23 is lost, and the pressure will suddenly fluctuate to 7.0 MPa or less. As a result, a so-called swelling phenomenon occurs inside the evaporator 24, causing bubbles (voids) to expand, the water level in the drum 23 to rise, and the heat recovery steam generator 16 to become unstable.

[0127] (2) Pressure control of the turbine bypass valve 34 The pressure control of the turbine bypass valve 34 in the second embodiment is the same as that in the first embodiment, and a description thereof will be omitted.

[0128] (3) Drain blow control of drain valves 29a to 29c In the second embodiment, the drain blow control of the drain valves 29a to 29c is performed by a correction unit 401 and a multiplier 402 instead of the correction unit 301 and the multiplier 302 in the first embodiment. The drain blow control other than the correction unit 401 and the multiplier 402 is the same as that in the first embodiment, and the description will be omitted.

[0129] While the plant control device 2 in the first embodiment supplies the opening target value NORM to the multiplier 302, the plant control device 2a in this embodiment supplies the opening target value NORM to a multiplier 402. The multiplier 402 multiplies the opening target value NORM by a value DISCNT supplied from the correction unit 401 to correct the opening target value NORM to an opening command DMND. In this embodiment, the plant control device 2a branches the opening command DMND and outputs it to the drain valves 29a to 29c, and the openings of the drain valves 29a to 29c are controlled according to the opening command DMND. The opening command DMND is an example of a third control signal, similar to the opening command CMND.

[0130] The comparator 411 receives the opening command value MV of the turbine bypass valve 34, and also receives 30% set in the setter 412 as a set value. When MV is smaller than 30%, the comparator 411 turns its output 411OUT ON. The threshold of the comparator 411 in this embodiment has a cutoff difference (Differential), and when MV is smaller than 30%, the output 411OUT turns ON, and when MV is greater than 60%, the output 411OUT turns OFF.

[0131] The switch 413 takes in the output 411OUT. In addition, the switch 413 has two input ports. Port 1 takes in the value MV-MIN' from one cycle ago from a sampling delay unit 414, which will be described later, and port 2 takes in the opening command value MV of the turbine bypass valve 34. Depending on the ON / OFF state of the output 411OUT, the switch 413 selects port 1 when the output 411OUT is ON and outputs the value MV-MIN' as the output 413OUT, and when the output 411OUT is OFF, it selects port 2 and outputs MV as the output 413OUT.

[0132] The low value selector 415 takes in the output 413OUT from the switch 413 and the opening command value MV. The low value selector 415 selects the smaller of the output 413OUT and the MV (lower value), and outputs the selected value as the value MV-MIN. The value MV-MIN is the minimum value of the opening (opening command value MV) of the turbine bypass valve 34 from the past to the present.

[0133] The sampling delay unit 414 is denoted by the symbol “Z -1 ". Sampling delay unit 414 takes in value MV-MIN output from low value selector 415 and stores the taken-in value MV-MIN. In the next calculation cycle, sampling delay unit 414 outputs the stored value MV-MIN as value MV-MIN' from one cycle before.

[0134] The function generator 416 takes in the value MV-MIN output from the low value selector 415, converts the taken-in value MV-MIN to a value DISCNT, and outputs it. For this reason, the function generator 416 incorporates a graph that converts the x-axis value MV-MIN to a y-axis value DISCNT, as shown in FIG. 3. The graph is a function that connects the coordinates of four points, the first point (0%, 0.6), the second point (20%, 0.6), the third point (30%, 1.0), and the fourth point (100%, 1.0), with straight lines. This allows the function generator 416 to make the value DISCNT smaller than 1.0 when the value MV-MIN is smaller than 30%. When the function generator 416 determines that the value MV-MIN is larger than 30%, it outputs 1 as the value DISCNT, and when it determines that the value MV-MIN is smaller than 30%, it outputs a value smaller than 1 as the value DISCNT. This value of 30% is an example of the third opening.

[0135] The value GAIN generated by the function generator 316 in the first embodiment is named "GAIN" because it is greater than 1.0. On the other hand, the value DISCNT generated by the function generator 416 in this embodiment is named "DISCNT" because it is less than 1.0. DISCNT means discount.

[0136] The output side of the correction unit 401 is connected to a multiplier 402 provided on the output side of the switch 105. The multiplier 402 takes in a value DISCNT which is an output of a function generator 416 and an opening command value NORM which is an output of the switch 105. The multiplier 402 multiplies the opening command value NORM by the value DISCNT, and outputs DMND which is an opening command (Demand) to the drain valves 29a to 29c. The signal of the opening command DMND is branched into three in the plant control device 2a and output to the drain valves 29a to 29c, respectively. The drain valves 29a to 29c open in response to the opening command DMND.

[0137] In this embodiment, during a period when drain blow is required (when the drain valves 29a to 29c need to be opened), the target opening value NORM is set to 50% set in the setter 106. In this case, when the value MV-MIN is greater than 30%, that is, when the value DISCNT is 1, the opening command DMND is also 50%. While the value DISCNT is 1, the opening command DMND is maintained at 50% even if the opening command value MV changes and the value MV-MIN changes. On the other hand, when the value MV-MIN is smaller than 30%, that is, when the value DISCNT is smaller than 1, the opening command DMND is smaller than 50%. While the value DISCNT is smaller than 1, the opening command DMND changes within the range of 30 to 50% when the opening command value MV changes and the value MV-MIN changes. For example, when the value MV-MIN decreases from 30% to 25%, the value DISCNT decreases from 1 to 0.8, and the opening command DMND decreases from 50% to 40%. This value of 50% is an example of the fourth opening.

[0138] In this manner, the opening command DMND in this embodiment changes according to the opening command value MV (value MV-MIN). That is, the openings of the drain valves 29a to 29c in this embodiment change according to the opening of the turbine bypass valve 34, similarly to the first embodiment. Further details of such an operation in this embodiment will be described later.

[0139] In the first embodiment, the maximum value of the value GAIN generated by the function generator 316 is 2.0, and the opening command CMND at this time is 100%, and the maximum opening of the drain valves 29a to 29c is allowed to be 100% fully open. In contrast, the minimum value of the value DISCNT generated by the function generator 416 in this embodiment is a modest value of 0.6, and the opening command DMND at this time is 30%. That is, the minimum opening of the drain valves 29a to 29c allowed in this embodiment is 30%. This is because there is a risk that an extremely small opening of 30% or less may cause a problem in discharging the drain water.

[0140] (4) Functions and Effects of the Second Embodiment Next, the actions and effects of this embodiment will be briefly described below.

[0141] a) Explain the effect when, at a certain point (current cycle), the opening command value MV, which was 31% one cycle ago, drops to 26%.

[0142] b) This MV=26% is input to comparator 411. Since the threshold of comparator 311 is ON when MV=26%, output 411OUT turns ON and is taken in by switch 413. Since output 411OUT is ON, switch 413 selects value MV-MIN' of port 1 as output 413OUT. Value MV-MIN' is the value MV-MIN from one cycle ago, and output 413OUT is 31%. In this case, the current MV value is smaller than value MV-MIN' stored in sampling delay unit 414.

[0143] c) The low value selector 415 selects the smaller of MV and output 413OUT and outputs it as the value MV-MIN. Since MV=26% and output 413OUT=31%, the value MV-MIN is 26%. In this case, the value MV-MIN becomes the current value of MV.

[0144] d) Function generator 416 converts the x-axis value MV-MIN to the y-axis value DISCNT. The x-axis value MV-MIN is 26%. Since the y-axis at x-axis=26% is 0.84, function generator 416 outputs 0.84 as the value DISCNT. Multiplier 402 multiplies NORM=50% by DISCNT=0.84 to calculate DMND=42%. As a result, drain valves 29a-29c are closed from 50% to 42%.

[0145] e) As a result, the amount of steam discharged from the drain valves 29a to 29c decreases, so the pressure of the main steam A5 rises, which is detected by the pressure sensor PS, and the MV output from the PI controller 203 increases to 30% or more. In other words, the amount of steam discharged from the drain valves 29a to 29c is reduced by 42%, so the amount of main steam A5 passing through the turbine bypass 34 increases accordingly. Thus, at this point in time, the current MV value (<30%) is smaller than the value MV-MIN', so the value MV-MIN decreases from the value MV-MIN' to the current MV value, and the opening command DMND decreases. The MV range of 30% or more is an example of a predetermined range.

[0146] Thereafter, when the opening command value MV starts to increase, the current MV value becomes larger than the value MV-MIN'. In this case, as in the first embodiment, the value MV-MIN is maintained at the value MV-MIN', and the opening command DMND is also maintained. The condition that the current MV value is larger than the value MV-MIN' is an example of the predetermined condition.

[0147] (5) Effects of the Second Embodiment In this embodiment, when the opening degree (MV) of the turbine bypass valve 34 falls below 30%, the opening degrees of the drain valves 29a to 29c are reduced to discharge a small amount of steam to the blowdown tank 30. As a result, the flow rate of the main steam A5 passing through the turbine bypass valve 34 increases, and the opening degree (MV) of the turbine bypass valve 34 can be increased to 30% or more. That is, in this embodiment, the drain valve opening degree is controlled to an appropriate opening degree according to the opening degree (MV) of the turbine bypass valve 34.

[0148] In the above-mentioned action and mechanism, the fluctuation of the drain valve opening affects the opening (MV) of the turbine bypass valve 34. On the other hand, when the opening (MV) of the turbine bypass valve 34 fluctuates, the drain valve opening is affected. That is, as in the first embodiment, in this embodiment, cause and effect are linked to each other. Therefore, the correction unit 401 stores the value MV-MIN as the minimum value from the past to the present, determines the value DISCNT based on the value MV-MIN, and provides a cutoff difference in the threshold of the comparator 411. This breaks the chain of cause and effect, and solves the problem of the turbine bypass 34 and the drain valves 29a to 29c repeatedly increasing and decreasing.

[0149] As described above, according to this embodiment, it is possible to suitably control the opening degree of the turbine bypass valve 34.

[0150] Third embodiment The above-described first embodiment is a control for increasing the drain valve opening degree by the opening command CMND when the opening degree (MV) of the turbine bypass valve 34 becomes too large. The above-described second embodiment is a control for decreasing the drain valve opening degree by the opening command DMND when the opening degree (MV) of the turbine bypass valve 34 becomes too small.

[0151] In contrast, the plant control device (not shown) of this embodiment incorporates both a control circuit (FIG. 2) that generates an opening command CMND and a control circuit (FIG. 3) that generates an opening command DMND. Therefore, the plant control device of this embodiment increases the drain valve opening by the opening command CMND when the opening of the turbine bypass valve 34 becomes too large, and decreases the drain valve opening by the opening command DMND when the opening of the turbine bypass valve 34 becomes too small. This makes it possible to enjoy both the advantages of the first embodiment and the second embodiment.

[0152] Several embodiments have been described above. The power plant 1 shown in Fig. 1 is a separate-shaft type in which one gas turbine 12 and one steam turbine 31 are not directly connected on the same shaft, but other types may be used. For example, the power plant 1 may be a single-shaft type in which one gas turbine and one steam turbine are directly connected on the same shaft, or a multi-shaft type including a plurality of gas turbines and one steam turbine. The power plant 1 may be a combined cycle power plant of a different type from the combined cycle power plant shown in Fig. 1.

[0153] The power plant 1 may be a power plant other than a combined cycle power plant. For example, the power plant 1 may be a steam power plant that does not have a gas turbine and uses coal or the like as a heat source. The steam power plant includes a steam boiler, a steam turbine, a turbine bypass valve, a drain valve, etc.

[0154] The heat recovery steam generator 16 shown in FIG. 1 generates main steam in three superheater groups (26, 27, 28), and drives a steam turbine 31 with this main steam. The heat recovery steam generator 16 may further include a built-in reheater. In this case, the high-pressure turbine of the steam turbine 31 is driven by the main steam generated by the superheater groups, and the intermediate-pressure turbine and low-pressure turbine of the steam turbine 31 are driven by reheated steam generated by the reheater. In this case, the first to third embodiments are also applicable to the turbine bypass valves and drain valves associated with the reheater and the reheated steam.

[0155] Although several embodiments have been described above, these embodiments are presented only as examples and are not intended to limit the scope of the invention. The novel apparatus, method, and plant described in this specification can be embodied in various other forms. In addition, various omissions, substitutions, and modifications can be made to the forms of the apparatus, method, and plant described in this specification without departing from the spirit of the invention. The appended claims and their equivalents are intended to include such forms and modifications that fall within the scope and spirit of the invention. [Explanation of symbols]

[0156] 1: Power plant, 2: Plant control device, 2a: plant control device, 2b: plant control device, 11: compressor, 12: gas turbine, 13: GT generator, 14: combustor, 15: fuel control valve, 16: exhaust heat recovery boiler, 21: water supply pump, 22: economizer, 23: drum, 24: evaporator, 25: Primary superheater, 26: Secondary superheater, 27: Tertiary superheater, 28: Main steam pipe, 29a: drain valve, 29b: drain valve, 29c: drain valve, 30: blowdown tank, 31: steam turbine, 32: ST generator, 33: control valve, 34: turbine bypass valve, 35: condenser, 36: circulating water pump, 101: gas turbine ignition, 102: comparator, 103: setting device, 104: AND circuit, 105: switch, 106: setting device, 107: setting device, 201: Setter, 202: Subtractor, 203: PI controller, 301: correction unit, 302: multiplier, 311: comparator, 312: setting device, 313: switch, 314: sampling delay unit, 315: high value selector, 316: function generator, 401: correction unit, 402: multiplier, 411: comparator, 412: setting device, 413: switch, 414: sampling delay unit, 415: low value selector, 416: function generator, FD: Flame detector, PS: Pressure sensor, LVDT: Opening detector

Claims

1. a boiler including a heat exchanger and using heat from the heat exchanger to generate steam; a steam turbine driven by the steam generated by the boiler; A pipe that delivers the steam generated by the boiler to the steam turbine; a condenser that condenses the steam discharged from the steam turbine; a bypass valve that causes the steam in the piping to bypass the steam turbine and to be sent to the condenser; A drain valve for discharging drain water generated in the heat exchanger or the piping; a receiving vessel for receiving the drain water that has passed through the drain valve; A plant control device for controlling a power generation plant comprising: A bypass valve control unit that controls an opening degree of the bypass valve; a drain valve control unit that controls an opening degree of the drain valve so that the opening degree of the drain valve changes in accordance with an opening degree of the bypass valve; A plant control device comprising:

2. The bypass valve control unit outputs a first control signal that controls an opening degree of the bypass valve, The drain valve control unit generates a second control signal for controlling an opening degree of the drain valve, corrects the second control signal to the third control signal in response to the first control signal, and outputs the third control signal. The plant control device according to claim 1 .

3. The power plant further comprises a gas turbine driven by gas; 2. The plant control device according to claim 1, wherein the boiler is a heat recovery boiler that supplies exhaust gas discharged from the gas turbine to the heat exchanger and generates the steam by using heat from the heat exchanger.

4. 2 . The plant control device according to claim 1 , wherein the drain valve control unit changes the opening degree of the drain valve in accordance with the opening degree of the bypass valve when it determines that the opening degree of the bypass valve is larger than a first opening degree.

5. The drain valve control unit is When it is determined that the opening degree of the bypass valve is smaller than the first opening degree, the opening degree of the drain valve is set to a second opening degree; when it is determined that the opening degree of the bypass valve is larger than the first opening degree, the opening degree of the drain valve is set to be larger than the second opening degree. The plant control device according to claim 4.

6. The drain valve control unit is storing the maximum values ​​of the opening degree of the bypass valve from the past to the present; When it is determined that the opening degree of the bypass valve is greater than the first opening degree and then the current opening degree of the bypass valve is greater than the maximum value, the opening degree of the drain valve is increased; maintain the opening degree of the drain valve when it is determined that the current opening degree of the bypass valve is smaller than the maximum value after it is determined that the opening degree of the bypass valve is larger than the first opening degree; The plant control device according to claim 4.

7. 2 . The plant control device according to claim 1 , wherein the drain valve control unit changes the opening degree of the drain valve in accordance with the opening degree of the bypass valve when it determines that the opening degree of the bypass valve is smaller than a third opening degree.

8. The drain valve control unit is When it is determined that the opening degree of the bypass valve is larger than the third opening degree, the opening degree of the drain valve is set to a fourth opening degree; when it is determined that the opening degree of the bypass valve is smaller than the third opening degree, the opening degree of the drain valve is set to be smaller than the fourth opening degree. The plant control device according to claim 7.

9. The drain valve control unit is storing a minimum value of the opening degree of the bypass valve from the past to the present; When it is determined that the opening degree of the bypass valve is smaller than the third opening degree and then the current opening degree of the bypass valve is smaller than the minimum value, the opening degree of the drain valve is reduced; maintain the opening degree of the drain valve when it is determined that the current opening degree of the bypass valve is greater than the minimum value after it is determined that the opening degree of the bypass valve is smaller than the third opening degree; The plant control device according to claim 7.

10. The drain valve control unit is when it is determined that the opening degree of the bypass valve is outside a predetermined range, changing the opening degree of the drain valve according to the opening degree of the bypass valve; when the opening degree of the bypass valve satisfies a predetermined condition after it is determined that the opening degree of the bypass valve is outside the predetermined range, the opening degree of the drain valve is maintained even if the opening degree of the bypass valve changes. The plant control device according to claim 1 .

11. The drain valve control unit is storing a maximum or minimum value of the opening degree of the bypass valve from the past to the present; when it is determined that the opening degree of the bypass valve is outside the predetermined range and then the current opening degree of the bypass valve is smaller than the maximum value or larger than the minimum value, the opening degree of the drain valve is maintained even if the opening degree of the bypass valve changes. The plant control device according to claim 10.

12. a boiler including a heat exchanger and using heat from the heat exchanger to generate steam; a steam turbine driven by the steam generated by the boiler; A pipe that delivers the steam generated by the boiler to the steam turbine; a condenser that condenses the steam discharged from the steam turbine; a bypass valve that causes the steam in the piping to bypass the steam turbine and to be sent to the condenser; A drain valve for discharging drain water generated in the heat exchanger or the piping; a receiving vessel for receiving the drain water that has passed through the drain valve; A plant control method for controlling a power plant comprising: The opening degree of the bypass valve is controlled by a bypass valve control unit, an opening degree of the drain valve is controlled by a drain valve control unit so that the opening degree of the drain valve changes depending on the opening degree of the bypass valve; A plant control method comprising:

13. a boiler including a heat exchanger and using heat from the heat exchanger to generate steam; a steam turbine driven by the steam generated by the boiler; A pipe that delivers the steam generated by the boiler to the steam turbine; a condenser that condenses the steam discharged from the steam turbine; a bypass valve that causes the steam in the piping to bypass the steam turbine and to be sent to the condenser; A drain valve for discharging drain water generated in the heat exchanger or the piping; a receiving vessel for receiving the drain water that has passed through the drain valve; A bypass valve control unit that controls an opening degree of the bypass valve; a drain valve control unit that controls an opening degree of the drain valve so that the opening degree of the drain valve changes in accordance with an opening degree of the bypass valve; A power plant comprising:

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