Drum level control device, power plant, drum level control method, drum level control program

Abstract

This invention provides a drum level control device, a power plant, a drum level control method, and a drum level control program that can improve the controllability of the drum level. [Solution] In a power plant having a boiler and a drum for storing drum water used to cool the boiler, a drum level control device 50 for controlling the drum level, which is the water level in the drum, comprises: an acquisition unit 51 for acquiring the value of the requested generator output (MWD); a calculation unit 52 for calculating the main steam flow rate of the boiler based on the value of the requested generator output; and a correction unit 53 for deriving a lead correction signal based on the main steam flow rate and correcting the drum level control value, which is the control target value of the drum level, using the lead correction signal.

Description

Technical Field

[0001] The present disclosure relates to a drum level control device, a power generation plant, a drum level control method, and a drum level control program.

Background Art

[0002] Conventionally, an exhaust heat recovery boiler has been used in a combined cycle power generation plant configured in combination with, for example, a gas turbine or the like. In a combined cycle power generation plant, a generator is rotationally driven by a gas turbine to generate electricity, and further, steam is generated by using the exhaust heat of the combustion exhaust gas discharged from the gas turbine. By supplying this steam to a steam turbine, it can be further used for rotationally driving the generator to add power generation by the steam turbine. Therefore, a combined cycle power generation plant has attracted attention as a highly efficient and environmentally friendly power generation plant.

[0003] Such an exhaust heat recovery boiler (HRSG: Heat Recovery Steam Generator) in a combined cycle power generation plant is known as a device that generates steam by using the exhaust heat of the combustion exhaust gas discharged from a device that generates and uses heat such as a gas turbine or a combustion device. The exhaust heat recovery boiler recovers heat by heating feed water with the thermal energy of the combustion exhaust gas discharged from a gas turbine or the like.

[0004] In a drum-type boiler (drum boiler) used as an exhaust heat recovery boiler, drum level control for controlling the water level (level) of the drum is performed. For example, in Patent Document 1, in addition to control for adjusting a feed water flow rate adjustment valve according to the displacement of the drum level, control is performed to add a deviation between the drum feed water amount and the boiler evaporation amount as a lead correction to the feed water flow rate adjustment valve.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, in the invention described in Patent Document 1, the boiler evaporation rate, i.e., the main steam flow rate, is detected by a flow meter that detects the steam flow rate supplied from the steam drum to the turbine. In drum-type boilers, particularly in waste heat recovery boilers that make up combined cycle power plants, a main steam flow meter may not be installed in order to reduce equipment costs.

[0007] Furthermore, while there are methods for calculating the main steam flow rate using the first-stage afterpressure of the steam turbine or the generator output, control disturbances can occur regardless of the method used. In this case, there was a problem in that improvements in controllability could not be expected.

[0008] This disclosure has been made in view of these circumstances and aims to provide a drum level control device, a power plant, a drum level control method, and a drum level control program that can improve the controllability of the drum level. [Means for solving the problem]

[0009] To solve the above problems, the drum level control device, power plant, drum level control method, and drum level control program of this disclosure employ the following means. The drum level control device of the present disclosure is a drum level control device for controlling the drum level, which is the water level in a drum, in a power plant having a boiler and a drum for storing drum water for water cooling the boiler, and comprises: an acquisition unit that acquires a value of the required generator output (MWD, Mega Watt Demand); a calculation unit that calculates the main steam flow rate of the boiler based on the value of the required generator output; and a correction unit that derives a lead correction signal based on the main steam flow rate and corrects a drum level control value, which is the control target value of the drum level, with the lead correction signal.

[0010] The power plant of this disclosure includes a boiler, a drum for storing drum water for cooling the boiler, and the aforementioned drum level control device.

[0011] The drum level control method of the present disclosure is a drum level control method for a power plant having a boiler and a drum for storing drum water for water cooling the boiler, wherein a computer performs the following steps: an acquisition step of acquiring a value of the required generator output (MWD); a calculation step of calculating the main steam flow rate of the boiler based on the value of the required generator output; and a correction step of deriving a lead correction signal based on the main steam flow rate and correcting a drum level control value, which is a control target value of the drum level, using the lead correction signal.

[0012] The drum level control program of this disclosure causes a computer to execute the drum level control method described above. [Effects of the Invention]

[0013] According to this disclosure, stable drum level control can be performed without being affected by external disturbances. [Brief explanation of the drawing]

[0014] [Figure 1] This diagram shows an overview of the steam system in a conventional power plant. [Figure 2] This diagram shows the flow of drum level control using a conventional lead correction signal. [Figure 3] This figure shows the changes in each value during load increase when the main steam flow rate, calculated from the first stage afterpressure of the steam turbine, is used as a pre-correction method, which is the conventional method. [Figure 4] This figure shows the changes in each value during load increase when the main steam flow rate, calculated from the generator output, is used as a pre-correction method, which is the conventional method. [Figure 5] This figure shows the changes in each value during load reduction when using the conventional method of using the main steam flow rate, calculated from the first stage afterpressure of the steam turbine, as a pre-correction. [Figure 6] This is a diagram showing the transition of each value during load drop when the main steam flow rate calculated from the generator output, which is a conventional method, is used for prior correction. [Figure 7] This is a diagram showing an example of the hardware configuration of a control device in some embodiments of the present disclosure. [Figure 8] This is a diagram showing an example of the functions of a control device in some embodiments of the present disclosure. [Figure 9] This is a diagram showing an overview of the steam system of a power plant in some embodiments of the present disclosure. [Figure 10] This is a diagram showing the flow of drum level control using a prior correction signal in some embodiments of the present disclosure. [Figure 11] This is a diagram showing the transition of each value during load increase in some embodiments of the present disclosure. [Figure 12] This is a diagram showing the transition of each value during load drop in some embodiments of the present disclosure.

Mode for Carrying Out the Invention

[0015] Hereinafter, an embodiment of a drum level control device, a power plant, a drum level control method, and a drum level control program according to the present disclosure will be described with reference to the drawings. FIG. 1 is a diagram showing an overview of the steam system of a power plant in some embodiments of the present disclosure.

[0016] As shown in FIG. 1, a conventional power generation plant 101 includes a boiler 10 and a drum 20. The boiler 10 is, for example, a waste heat recovery boiler, and generates steam by using the waste heat of combustion exhaust gas discharged from a device that generates and uses heat, such as a gas turbine (not shown) or a combustion device (not shown). The boiler 10 is supplied with water from the drum 20, heats the water, and generates steam. The generated saturated steam and saturated water (drain) are supplied to the drum 20. The steam is supplied to a steam turbine 111 via a governor valve 150, and power generation is performed. Power generation is performed by a generator 113 connected to the steam turbine 111. A condenser 112 is connected to the steam turbine 111, and the steam that rotationally drives the steam turbine 111 is condensed by heat exchange with cooling water (for example, seawater or river water) in this condenser 112 to become condensate. By repeating this flow, the water level (level) of the drum 20 drops, but water supply including a part of the aforementioned condensate is performed to the drum 20 via a feed water flow rate adjustment valve 30. Detection of the water level of the drum 20 is performed by a drum level detector 121 (LX1'). Also, measurement of the feed water flow rate to the drum 20 is performed by a feed water flow meter 142 (FX2'). Further, as a conventional example, a case where a main steam flow meter 141 (FX1') is provided for measurement of the main steam flow rate supplied to the steam turbine 111 is shown.

[0017] Conventional drum level control is performed as follows. FIG. 2 is a diagram showing a flow of drum level control using a conventional leading correction signal.

[0018] As shown in FIG. 2, in a subtracter 62, a difference between a drum level set value 61 and a drum level detection value by the drum level detector 121 is output. The output of the subtracter 62 indicates the deviation of the actual value from the target value of the drum level (control deviation of the drum level).

[0019] The difference between the drum level set value 61 and the drum level detection value is proportionally integrated by an adjuster (PI controller) 63. The output of the adjuster 63 is a set signal of the feed water flow rate adjustment valve 30 when adjusting the feed water flow rate adjustment valve 30 according to the change in the drum level.

[0020] The output value of the regulator 63 is input to the adder 67. The adder 67 receives the difference between the main steam flow rate and the feedwater flow rate measured by the feedwater flow meter 142.

[0021] The main steam flow rate input to the adder 67 is one of the following: the measured value of the main steam flow rate from the main steam flow meter 141, the output of the function unit 64 which takes the first stage after pressure of the steam turbine 111 (steam pressure after the first stage blade row of the steam turbine 111) from the pressure gauge 43 as input, or the output of the function unit 65 which takes the generator output 44 of the generator 113 as input. In Figure 2, one of these values ​​is input to A, and then input from A to the adder 67.

[0022] The first-stage afterpressure or generator output 44 of the steam turbine 111 is positively correlated with the main steam flow rate (see the graph in the lower left of Figure 2). Therefore, it is possible to derive the main steam flow rate corresponding to the load increase or decrease by adjusting the opening of the governor valve 150 from the first-stage afterpressure or generator output 44, and it is possible to calculate the main steam flow rate as a function of the first-stage afterpressure or generator output 44.

[0023] The difference between the main steam flow rate and the feedwater flow rate measured by the feedwater flow meter 142 is the deviation between the evaporation rate of the boiler 10 and the feedwater rate to the drum 20. If this deviation is positive, the drum level decreases; if this deviation is negative, the drum level increases. This deviation is used to apply a pre-correction to the control signal of the feedwater flow control valve 30. The output of the adder 67 is the corrected control signal of the feedwater flow control valve 30.

[0024] The output of the adder 67 is proportionally and integrally processed by the regulator (PI controller) 68 to become an opening command for the water supply flow control valve 30. The opening of the water supply flow control valve 30 is adjusted according to the opening command, and drum level control is performed.

[0025] Thus, in conventional drum level control, the measured or calculated value of the main steam flow rate is used as a lead correction to reduce the response delay to the drum level setpoint (default value) SG61. When the main steam flow rate measured by the main steam flow meter 141 is used for pre-correction, the main steam flow meter 141 needs to be installed in the main steam pipe. However, since the main steam pipe is generally high temperature and pressure and has a large diameter, this leads to increased costs.

[0026] On the other hand, if the main steam flow rate is estimated using the first-stage afterpressure of the steam turbine 111 (pressure gauge 43) or the generator output 44 without installing the main steam flow meter 141 in order to suppress cost increases, the first-stage afterpressure of the steam turbine 111 is affected by pressure changes in the drum 20, as well as by changes in the main steam pressure at the inlet of the steam turbine 111 due to the operation of the steam turbine 111's governor. In other words, the main steam flow rate calculated from the first-stage afterpressure of the steam turbine 111 is susceptible to disturbances. Because the generator output 44 has a delayed response to governor operation due to the heat recovery delay in the HRSG, the main steam flow rate calculated from the generator output 44 is also susceptible to disturbances. Therefore, in drum level control, using the main steam flow rate calculated from the first stage after pressure (pressure gauge 43) of the steam turbine 111 or the generator output 44 as a pre-correction would result in an overly sensitive change in the opening command of the feedwater flow control valve 30.

[0027] Figure 3 shows the changes in each value during load increase when the main steam flow rate, calculated from the first stage afterpressure of the steam turbine, is used as a pre-correction method, which is a conventional method. The horizontal axis in Figure 3 represents time, with the load increase starting at time t1 and completing at time t2. MWD represents the requested generator output, governor opening is the opening of governor valve 150, turbine first stage after pressure is the first stage after pressure of steam turbine 111, main steam flow rate is the main steam flow rate calculated based on the first stage after pressure of steam turbine 111, feedwater flow control valve command value is the command value of feedwater flow control valve 30, and drum level is the measured value of the water level of drum 20. The solid line for governor opening represents the process value of governor opening, and the dashed line for governor opening represents the static characteristic value of governor opening. The solid line for turbine first stage after pressure represents the measured value of turbine first stage after pressure, and the dashed line for turbine first stage after pressure represents the static characteristic value of turbine first stage after pressure. The solid line for main steam flow rate shows the estimated main steam flow rate calculated from the turbine first stage after pressure, while the dashed line for main steam flow rate shows the target control value calculated from the MWD. ​​The solid line for feedwater flow control valve command value shows the actual opening of the feedwater flow control valve, while the dashed line for feedwater flow control valve command value shows the static characteristic value (target control value) of the feedwater flow control valve opening. The solid line for drum level shows the measured value of the drum level, while the dashed line for drum level shows the target control value of the drum level.

[0028] As shown in Figure 3, when the MWD starts to rise at time t1, the governor opening is increased to increase the generator output. When the governor opening is increased, the amount of main steam supplied to the steam turbine 111 increases, so the pressure at the inlet of the steam turbine 111 decreases, and consequently the pressure after the first stage of the turbine also decreases.

[0029] The main steam flow rate (estimated value) calculated from the turbine's first-stage afterpressure will be lower than the control target value as the turbine's first-stage afterpressure decreases.

[0030] The feedwater flow rate control valve command value is subject to a pre-correction based on the main steam flow rate, so it will become lower than the control target value as the main steam flow rate (estimated value) decreases.

[0031] As the command value for the water supply flow control valve decreases, the water flow rate to drum 20 is also reduced, resulting in a drum level lower than the control target value.

[0032] When the MWD rise stops at time t2, the increase in governor opening also stops (converges to a predetermined opening), and accordingly, the turbine first stage pressure tends to increase. As a result, the main steam flow rate (estimated value) increases, and the feedwater flow control valve command value also tends to increase.

[0033] When the main steam flow rate (estimated value) calculated from the first-stage afterpressure of the steam turbine 111 is used as a lead correction, the main steam flow rate (estimated value) will fluctuate due to changes in the pressure inside the drum 20 and changes in the main steam pressure at the inlet of the steam turbine 111 due to changes in the governor opening, thus disturbing the drum level control.

[0034] Figure 4 shows the changes in each value during load increase when the main steam flow rate calculated from the generator output is used as a pre-correction, which is a conventional method. The horizontal axis of Figure 4 represents time, with the load increase starting at time t1 and completing at time t2. MWD represents the requested generator output, governor opening represents the opening of governor valve 150, generator output represents the output of generator 113, main steam flow rate represents the main steam flow rate (estimated value) calculated from the generator output, feedwater flow control valve command value represents the command value of feedwater flow control valve 30, and drum level represents the measured water level (level) of drum 20. The solid line for governor opening represents the process value of governor opening, and the dashed line for governor opening represents the static characteristic value of governor opening. The solid line for generator output represents the measured value of generator output, and the dashed line for generator output represents MWD. ​​The solid line for main steam flow rate represents the main steam flow rate (estimated value) calculated from the generator output, and the dashed line for main steam flow rate represents the main steam flow rate (control target value) calculated from MWD. The solid line for the water supply flow control valve command value represents the actual opening of the water supply flow control valve, while the dashed line for the water supply flow control valve command value represents the static characteristic value (control target value) of the water supply flow control valve opening. The solid line for the drum level represents the measured value of the drum level, while the dashed line for the drum level represents the control target value of the drum level.

[0035] As shown in Figure 4, when MWD increases at time t1, the governor opening is operated in the open direction to increase the generator output. In response to the increase in MWD, the generator output begins to increase later than the control target value due to the response delay of heat absorption in the HRSG.

[0036] The main steam flow rate (estimated value) calculated from the generator output will show a delayed upward trend compared to the control target value, depending on the response delay of the generator output.

[0037] Since the feedwater flow rate control valve command value is corrected in advance by the main steam flow rate, the upward trend lags behind the control target value in accordance with the delay in the increase of the main steam flow rate.

[0038] Because the upward trend of the water supply flow rate control valve command value is delayed, the water supply flow rate to drum 20 is also delayed, and the drum level remains lower than the control target value.

[0039] At time t2, when the MWD reaches its target value and stops rising, the governor opening is operated in the closing direction. The generator output stops increasing when it reaches its target value, which is later than the MWD. ​​Therefore, the main steam flow rate (estimated value) calculated from the generator output also stops increasing when it reaches the control target value.

[0040] When the main steam flow rate calculated from the generator output is used as a lead correction, the response delay of heat recovery in the HRSG causes a delay in the operation of the governor corresponding to the MWD, thus disturbing the drum level control.

[0041] Figure 5 shows the changes in each value during load reduction when the main steam flow rate, calculated from the first stage afterpressure of the steam turbine, is used as a pre-correction method, which is a conventional method. The horizontal axis in Figure 5 represents time, with the load reduction starting at time t3 and completing at time t4. MWD is the requested generator output, governor opening is the opening of governor valve 150, turbine first stage after pressure is the first stage after pressure of steam turbine 111, main steam flow rate is the main steam flow rate (estimated value) calculated from the first stage after pressure of steam turbine 111, feedwater flow control valve command value is the command value of feedwater flow control valve 30, and drum level is the measured value of the water level of drum 20. The solid line for governor opening represents the process value of governor opening, and the dashed line for governor opening represents the static characteristic value of governor opening. The solid line for turbine first stage after pressure represents the measured value of turbine first stage after pressure, and the dashed line for turbine first stage after pressure represents the static characteristic value of turbine first stage after pressure. The solid line for main steam flow rate shows the estimated main steam flow rate calculated from the turbine first stage after pressure, while the dashed line for main steam flow rate shows the target control value calculated from the MWD. ​​The solid line for feedwater flow control valve command value shows the actual opening of the feedwater flow control valve, while the dashed line for feedwater flow control valve command value shows the static characteristic value (target control value) of the feedwater flow control valve opening. The solid line for drum level shows the measured value of the drum level, while the dashed line for drum level shows the target control value of the drum level.

[0042] As shown in Figure 5, when the MWD starts to decline at time t3, the governor opening is operated in the closing direction to reduce the generator output. When the governor valve 150 is operated in the closing direction, the amount of main steam supplied to the steam turbine 111 decreases, causing the pressure at the inlet of the steam turbine 111 to rise, and consequently the pressure after the first stage of the turbine to rise temporarily. After that, the pressure after the first stage of the turbine tends to decline.

[0043] The main steam flow rate, calculated from the pressure behind the first stage of the turbine, temporarily increases in response to changes in the pressure behind the first stage of the turbine, and then tends to decrease while remaining above the control target value.

[0044] The feedwater flow rate control valve command value is subject to a pre-correction based on the main steam flow rate, and therefore tends to decrease while remaining above the control target value in accordance with changes in the main steam flow rate (estimated value).

[0045] Since the water supply flow rate control valve command value remains above the control target value, the water supply flow rate to drum 20 increases, resulting in a drum level higher than the control target value.

[0046] When the MWD reaches the target value at time t4 and its descent stops, the governor opening is operated in the open direction, and the turbine first-stage pressure, after falling below the control target value, begins to increase. Correspondingly, the main steam flow rate and feedwater flow control valve command values ​​also begin to increase.

[0047] When the main steam flow rate calculated from the first stage pressure of the turbine is used as a lead correction, the calculated main steam flow rate will fluctuate due to changes in the pressure inside the drum 20 and changes in the main steam pressure at the inlet of the steam turbine 111 due to changes in the governor opening, thus disturbing the drum level control.

[0048] Figure 6 shows the changes in each value during load reduction when the main steam flow rate calculated from the generator output is used as a pre-correction, which is a conventional method. The horizontal axis of Figure 6 represents time, with the load reduction starting at time t3 and completing at time t4. MWD represents the requested generator output, governor opening is the opening of governor valve 150, generator output is the output of generator 113, main steam flow rate is the main steam flow rate (estimated value) calculated from the generator output, feedwater flow control valve command value is the command value of feedwater flow control valve 30, and drum level is the water level (level) of drum 20. The solid line for governor opening represents the process value of governor opening, and the dashed line for governor opening represents the static characteristic value of governor opening. The solid line for generator output represents the measured value of generator output, and the dashed line for generator output represents the static characteristic value of generator output. The solid line for main steam flow rate represents the main steam flow rate (estimated value) calculated from the generator output, and the dashed line for main steam flow rate represents the main steam flow rate (control target value) calculated from MWD. The solid line for the water supply flow control valve command value represents the actual opening of the water supply flow control valve, while the dashed line for the water supply flow control valve command value represents the static characteristic value (control target value) of the water supply flow control valve opening. The solid line for the drum level represents the measured value of the drum level, while the dashed line for the drum level represents the control target value of the drum level.

[0049] As shown in Figure 6, when the MWD decreases at time t3, the governor opening is operated in the closing direction to reduce the generator output. Due to the response delay of heat absorption in the HRSG in response to the decrease in MWD, the generator output responds late and begins to decrease later than the control target value.

[0050] The main steam flow rate (estimated value) calculated from the generator output begins to decline later than the control target value in response to changes in the generator output.

[0051] Since the feedwater flow rate control valve command value is corrected in advance by the main steam flow rate, it begins to decrease later than the control target value in response to changes in the main steam flow rate.

[0052] Because the decrease in the water supply flow rate control valve command value is delayed, the water supply flow rate to drum 20 remains high, and the drum level remains higher than the control target value.

[0053] When the MWD reaches its target value at time t4 and its descent stops, the governor opening is operated in the open direction. The generator output reaches its target value later than the MWD due to the heat recovery response delay in the HRSG, then continues to decrease, and then settles. Correspondingly, the main steam flow rate (estimated value) also continues to decrease after reaching the control target value, undershoots briefly, and then settles near the control target value.

[0054] When the main steam flow rate calculated from the generator output is used as a lead correction, the response delay of heat recovery in the HRSG causes a delay in the response to the governor operation corresponding to the MWD, thus disturbing the drum level control.

[0055] Conventionally, when the main steam flow rate calculated from the first-stage afterpressure of the steam turbine 111 or the generator output is used for lead correction, it tends to be susceptible to disturbances, and drum level control is unstable. Therefore, in this disclosure, drum level control is performed using a main steam flow rate setpoint based on the MWD.

[0056] Figure 7 is a diagram showing an example of the hardware configuration of a control device in some embodiments of the present disclosure. As shown in Figure 7, the drum level control device (Controller) 50 is a computer system, and for example, it includes a CPU (Central Processing Unit: processor) 1100, secondary storage (ROM, Secondary storage: memory) 1300, main memory (RAM, Main Memory) 1200, a hard disk drive (HDD) 1500 as a mass storage device, and a communication unit 1400 for connecting to a network, etc. A solid-state drive (SSD) may be used as the mass storage device. These parts are connected via a bus 1800.

[0057] The CPU 1100 controls the entire drum level control device 50 using an OS (Operating System) stored in a secondary storage device 1300 connected via the bus 1800, and also performs various processes by executing various programs stored in the secondary storage device 1300. One or more CPUs 1100 may be provided and may cooperate with each other to achieve processing.

[0058] The main memory 1200 consists of writable memory such as cache memory and RAM (Random Access Memory), and is used as a work area for reading the CPU 1100's executable program and writing processing data by the executable program.

[0059] The secondary storage device 1300 is a non-transitory computer-readable storage medium. Examples of secondary storage devices 1300 include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memory. Examples of secondary storage devices 1300 include ROM (Read Only Memory), HDD (Hard Disk Drive), SSD (Solid State Drive), and flash memory. The secondary storage device 1300 stores, for example, an OS for controlling the entire information processing device such as Windows®, iOS®, and Android®, a BIOS (Basic Input / Output System), various device drivers for hardware operation of peripheral devices, various application software, and various data and files. Furthermore, the secondary storage device 1300 stores programs for implementing various processes and various data required to implement those processes. Multiple secondary storage devices 1300 may be provided, and the aforementioned programs and data may be divided and stored in each secondary storage device 1300.

[0060] Furthermore, the drum level control device 50 may include an input unit consisting of a keyboard or mouse, and a display unit consisting of a liquid crystal display device or the like for displaying data. It may also include a notification unit that includes a display unit and outputs lights, sounds, and especially alarm sounds, such as a speaker.

[0061] Figure 8 is a diagram illustrating an example of the functions of a control device in some embodiments of the present disclosure. As shown in Figure 8, the drum level control device 50 includes an acquisition unit 51, a calculation unit 52, and a correction unit 53.

[0062] The series of processes required to realize the functions of the drum level control device 50 are stored in the form of a program in the secondary storage device 1300 (see Figure 7), and the CPU (processor) 1100 (see Figure 7) reads this program into the main memory 1200 (see Figure 7) and performs information processing and calculations to realize various functions. The program may be pre-installed in the secondary storage device 1300, provided stored in other non-temporary computer-readable storage media, or distributed via wired or wireless communication. Examples of non-temporary computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memory.

[0063] The acquisition unit 51 shown in Figure 8 acquires the value of the requested generator output (MWD). The acquisition unit 51 may also acquire the drum level detection value from the drum level detector 21 (described later) and the water supply flow rate from the water supply flow meter 42 (described later).

[0064] The calculation unit 52 calculates the main steam flow rate of the boiler 10 based on the value of the requested generator output. In this case, the calculated main steam flow rate is the planned value (design value) of the main steam flow rate required to generate the amount of power corresponding to the requested generator output.

[0065] The correction unit 53 derives a lead correction signal based on the main steam flow rate calculated from the requested generator output, and corrects the drum level control value (feedwater flow rate control valve control value), which is the control target value for the drum level, using the lead correction signal.

[0066] Figure 9 shows an overview of the steam systems in a power plant in some embodiments of the present disclosure. In Figure 9, the same components as those in the conventional power plant 101 shown in Figure 1 are given the same reference numerals. As shown in Figure 9, the power plant 1 of this disclosure comprises a boiler 10 and a drum 20. The boiler 10 is, for example, a waste heat recovery boiler, and generates steam by utilizing the waste heat of combustion exhaust gas discharged from a heat-generating and utilizing device, such as a gas turbine (not shown) or a combustion device (not shown). The boiler 10 is supplied with water from the drum 20, and the water is heated to generate steam. The generated saturated steam and saturated water (drain) are supplied to the drum 20, and the steam is supplied to the steam turbine 111 via a governor valve 150 to generate electricity. The power generation is performed by a generator 113 connected to the steam turbine 111. A condenser 112 is connected to the steam turbine 111, and the steam that rotated the steam turbine 111 is condensed in this condenser 112 by heat exchange with cooling water (for example, seawater or river water) to become condensate. As this process repeats, the water level in drum 20 decreases, but water, including a portion of the condensate mentioned above, is supplied to drum 20 via the water supply flow control valve 30. The water level in drum 20 is detected by the drum level detector 21 (LX1). The water supply flow rate to drum 20 is measured by the water supply flow meter 42 (FX2). The drum level control device 50 controls the drum level by controlling the water supply flow control valve 30 and other components.

[0067] Figure 10 shows the flow of drum level control using a pre-correction signal in some embodiments of the present disclosure.

[0068] As shown in Figure 10, the subtractor 62 outputs the difference between the drum level set value 61 and the drum level detected by the drum level detector 21. The output of the subtractor 62 shows the deviation (control deviation) of the actual value from the target value of the drum level.

[0069] The difference between the drum level setting value 61 and the drum level detection value is proportionally and integrally calculated by the controller (PI controller) 63. The output of the controller 63 is a control signal for the water supply flow rate control valve 30 when the water supply flow rate control valve 30 is adjusted in response to changes in the drum level.

[0070] The output value of the regulator 63 is input to the adder 73. The adder 73 receives the difference between the output of the function unit 72 and the water flow rate measured by the water flow meter 42.

[0071] The function unit 72 takes the generator output command value (requested generator output, MWD) 71 as input and outputs the main steam flow rate.

[0072] The difference between the main steam flow rate, which is the output of the function unit 72, and the feedwater flow rate measured by the feedwater flow meter 42, is the deviation between the boiler evaporation rate and the drum feedwater rate. This deviation is used to apply a pre-correction to the setting signal of the feedwater flow control valve 30. The output of the adder 73 is the corrected setting signal of the feedwater flow control valve 30.

[0073] The output of the adder 73 is proportionally integrated by the regulator (PI controller) 74 to become an opening command for the feedwater flow control valve 30. The feedwater flow control valve 30 is opened according to the opening command, which has been pre-corrected by the main steam flow rate based on the MWD, and drum level control is performed.

[0074] Figure 11 shows the changes in each value as the load increases in some embodiments of the present disclosure. The horizontal axis of Figure 11 represents time, with the load increase starting at time t1 and completing at time t2. MWD represents the requested generator output, governor opening represents the opening of governor valve 150, generator output represents the output of generator 113, main steam flow rate represents the main steam flow rate calculated from MWD (i.e., the planned value of the main steam flow rate supplied to steam turbine 111), feedwater flow control valve command value represents the command value of feedwater flow control valve 30, and drum level represents the water level of drum 20. The solid line for governor opening represents the process value of governor opening, and the dashed line for governor opening represents the static characteristic value of governor opening. The solid line for generator output represents the measured value of generator output, and the dashed line for generator output represents MWD. ​​The solid line for main steam flow rate represents the main steam flow rate (estimated value) calculated from the generator output command value (MWD), and the dashed line for main steam flow rate represents the main steam flow rate (control target value) calculated from MWD. The solid line for the water supply flow control valve command value represents the actual opening of the water supply flow control valve, while the dashed line for the water supply flow control valve command value represents the static characteristic value (control target value) of the water supply flow control valve opening. The solid line for the drum level represents the measured value of the drum level, while the dashed line for the drum level represents the control target value of the drum level.

[0075] As shown in Figure 11, when the MWD increases at time t1, the governor opening is manipulated to increase the generator output. The generator output starts to increase later than the control target value because it lags behind the MWD in response.

[0076] In this disclosure, since the main steam flow rate is calculated from the MWD, the main steam flow rate changes in accordance with the MWD and becomes the same value as the control target value.

[0077] The feedwater flow rate control valve command value is pre-corrected based on the main steam flow rate calculated from the MWD, so it becomes approximately the same as the control target value in response to changes in the main steam flow rate.

[0078] Since the water supply flow rate control valve command value is approximately the same as the control target value, water is supplied to drum 20 at an appropriate flow rate, and the drum level is approximately the same as the control target value.

[0079] At time t2, when the MWD reaches the target value and its rise stops, the governor opening is operated in the closing direction. The generator output reaches the MWD value with a delay and then settles near the target value.

[0080] When the main steam flow rate calculated from the MWD is used as a lead correction in this way, the stability of drum level control is improved because it is not affected by disturbances such as pressure changes in the drum 20 or changes in the main steam pressure at the inlet of the steam turbine 111 due to changes in the governor opening of the steam turbine 111.

[0081] Figure 12 shows the changes in each value during load reduction in some embodiments of the present disclosure. The horizontal axis of Figure 12 represents time, with the load reduction starting at time t3 and completing at time t4. MWD represents the requested generator output, governor opening represents the opening of governor valve 150, generator output represents the output of generator 113, main steam flow rate represents the main steam flow rate calculated from MWD (i.e., the planned value of the main steam flow rate supplied to steam turbine 111), feedwater flow control valve command value represents the command value of feedwater flow control valve 30, and drum level represents the water level of drum 20. The solid line for governor opening represents the process value of governor opening, and the dashed line for governor opening represents the static characteristic value of governor opening. The solid line for generator output represents the measured value of generator output, and the dashed line for generator output represents MWD. ​​The solid line for main steam flow rate represents the main steam flow rate (estimated value) calculated from the generator output command value (MWD), and the dashed line for main steam flow rate represents the main steam flow rate (control target value) calculated from MWD. The solid line for the water supply flow control valve command value represents the actual opening of the water supply flow control valve, while the dashed line for the water supply flow control valve command value represents the static characteristic value (control target value) of the water supply flow control valve opening. The solid line for the drum level represents the measured value of the drum level, while the dashed line for the drum level represents the control target value of the drum level.

[0082] As shown in Figure 12, when the MWD decreases at time t3, the governor opening is operated in the closing direction to reduce the generator output. The generator output begins to decrease later than the control target value because it lags behind the MWD in response.

[0083] In this disclosure, since the main steam flow rate is calculated from the MWD, the main steam flow rate changes in accordance with the MWD and becomes the same value as the control target value.

[0084] The feedwater flow rate control valve command value is pre-corrected based on the main steam flow rate calculated from the MWD, so it becomes approximately the same as the control target value in response to changes in the main steam flow rate.

[0085] Since the water supply flow rate control valve command value is approximately the same as the control target value, water is supplied to drum 20 at an appropriate flow rate, and the drum level is approximately the same as the control target value.

[0086] At time t4, when the MWD reaches the target value and its descent stops, the governor opening is operated in the open direction. The generator output reaches the MWD value with a delay, and then settles near the target value.

[0087] When the main steam flow rate calculated from the MWD is used as a pre-correction, the stability of the drum level control is improved because it is not affected by disturbances such as pressure changes in the drum 20 or changes in the main steam pressure at the inlet of the steam turbine 111 due to changes in the governor opening of the steam turbine 111.

[0088] <Note> The drum level control device, power plant, drum level control method, and drum level control program described in the embodiments above can be understood, for example, as follows.

[0089] A drum level control device (50) according to a first aspect of the present disclosure is a drum level control device that controls the drum level, which is the water level in the drum, in a power plant (1) having a boiler (10) and a drum (20) for storing drum water for water cooling the boiler, and comprises: an acquisition unit (51) for acquiring a value of the requested generator output (MWD); a calculation unit (52) for calculating the main steam flow rate of the boiler based on the value of the requested generator output; and a correction unit (53) for deriving a lead correction signal based on the main steam flow rate and correcting a drum level control value, which is the control target value of the drum level, with respect to the lead correction signal.

[0090] Since drum level control is performed using the main steam flow rate, and the main steam flow rate is calculated based on the MWD, stable drum level control can be performed without being affected by disturbances such as pressure changes inside the drum or changes in the main steam pressure at the steam turbine inlet due to changes in the governor opening of the steam turbine (111).

[0091] In a second aspect of the present disclosure, the drum level control device, in the first aspect, may derive the advance correction signal based on the difference between the main steam flow rate and the feedwater flow rate supplied to the drum.

[0092] By deriving a lead correction signal based on the difference between the feedwater flow rate (the amount of water supplied to the drum) and the main steam flow rate (the amount of evaporation in the boiler), and correcting the drum level control value, the drum level control can be corrected in advance, thereby improving the control's responsiveness.

[0093] A power plant according to a third aspect of the present disclosure includes a boiler, a drum for storing drum water for cooling the boiler, and a drum level control device according to the first or second aspect.

[0094] A fourth aspect of the present disclosure is a drum level control method for a power plant having a boiler and a drum for storing drum water for water cooling the boiler, the method for controlling the drum level, which is the water level in the drum, comprising: an acquisition step of acquiring a value of the required generator output (MWD); a calculation step of calculating the main steam flow rate of the boiler based on the value of the required generator output; and a correction step of deriving a lead correction signal based on the main steam flow rate and correcting a drum level control value, which is a control target value of the drum level, using the lead correction signal, all of which are performed by a computer.

[0095] The drum level control program of the fifth aspect of this disclosure causes a computer to execute the drum level control method described in the fourth aspect. [Explanation of Symbols]

[0096] 1. 101 Power Plants 10 Boilers 20 drums 21, 121 Drum Level Detector 30 Water supply flow rate control valve 42, 142 Water supply flow meter 50 Drum Level Control Device 51 Acquisition Department 52 Calculation Section 53 Correction section 111 Steam Turbine 112 Condenser 113 Generator 141 Main steam flow meter 150 Governor valve 1100 CPU 1200 Main storage 1300 Secondary storage 1400 Communications Department 1800 Bus

Claims

1. In a power plant having a boiler and a drum for storing drum water used to cool the boiler, a drum level control device controls the drum level, which is the water level in the drum, An acquisition unit that acquires the value of the requested generator output (MWD), A calculation unit that calculates the main steam flow rate of the boiler based on the value of the requested generator output, A drum level control device comprising: a correction unit that derives a lead correction signal based on the main steam flow rate and corrects the drum level control value, which is the control target value of the drum level, using the lead correction signal.

2. The drum level control device according to claim 1, wherein the correction unit derives the preceding correction signal based on the difference between the main steam flow rate and the feedwater flow rate supplied to the drum.

3. Boiler and, A drum for storing drum water used to cool the boiler, A power plant comprising the drum level control device described in claim 1.

4. A drum level control method for controlling the drum level, which is the water level in the drum, in a power plant having a boiler and a drum for storing drum water used to cool the boiler, The acquisition process involves obtaining the value of the requested generator output (MWD), A calculation step for calculating the main steam flow rate of the boiler based on the value of the requested generator output, A drum level control method, wherein a computer performs a correction step of deriving a lead correction signal based on the main steam flow rate and correcting the drum level control value, which is the control target value for the drum level, using the lead correction signal.

5. A drum level control program for causing a computer to execute the drum level control method of claim 4.

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