Operation method for steam turbine power generation plant, and storage medium

Abstract

Provided is a technique for stably operating a steam turbine power generation plant. The steam turbine power generation plant comprises: steam turbines 21, 22 that are connected to a generator 31; a main steam line 501 that is provided on an upstream side of the steam turbines 21, 22; bypass lines 503, 509 that are provided to allow steam supplied from the main steam line 501 to flow so as to bypass the steam turbines 21, 22, and that include bypass valves 61, 62; and an atmospheric diffusion line 505 that is provided branching from the main steam line 501 to diffuse steam to the atmosphere, and that includes an atmospheric diffusion valve 63. An operation method for the steam turbine power generation plant comprises: a step of specifying the flow rate of main steam flowing through the main steam line 501; and a step of adjusting the opening degree of the bypass valves 61, 64 and the atmospheric diffusion valve 63 in accordance with the specified flow rate of the main steam when the flow rate of the main steam supplied from the main steam line 501 exceeds the flow rate of the main steam consumed in the steam turbines 21, 22.

Description

Steam turbine power plant operation method and storage medium

[0001] The present invention relates to a technique for continuing stable operation in response to large changes in steam consumption in a steam turbine power plant.

[0002] Generally, a steam turbine power plant (hereinafter simply referred to as a "power plant") generates electricity by using steam generated in a boiler to rotate the rotor blades of a steam turbine, which then drives a generator connected to the rotor shaft of the rotor blades. During normal operation, a stable operating state is maintained by supplying steam from the boiler at a flow rate that balances the steam consumption of the steam turbine.

[0003] On the other hand, if a steam turbine undergoes an emergency shutdown or if steam consumption in the steam turbine is significantly reduced, the steam supplied from the boiler becomes surplus. However, it is difficult to immediately shut down the boiler in response to an emergency shutdown of the steam turbine. Furthermore, even if the boiler continues to operate with a reduced steam supply flow rate, it is difficult to continue operation when the boiler's steam supply flow rate is below the lower limit set due to equipment constraints, etc. Therefore, in the event of an emergency shutdown of the turbine or a significant reduction in steam consumption, it is necessary to take measures to ensure stable operation of the power plant under conditions where the steam supply flow rate from the boiler is excessive compared to the steam consumption of the equipment.

[0004] Here, Patent Document 1 describes that in a thermal power plant that generates electricity using a steam turbine, a bypass valve in a bypass line of the steam turbine is usually opened when the steam turbine is started or when steam pressure increases. Patent Document 1 also describes that in an AFC (Automatic Frequency Control) response mode that requires response to relatively fast frequency fluctuations, opening and closing the turbine bypass valve while adding a positive bias value to the boiler input command value enables load adjustment with higher responsiveness than when controlling the boiler output. However, Patent Document 1 only describes opening the bypass valve in response to an increase in steam pressure when there is an excess of steam.

[0005] Japanese Patent Application Laid-Open No. 2022-104052

[0006] The present method for operating a steam turbine power plant has been made under such circumstances, and provides a technique for stably operating a steam turbine power plant in accordance with the operating state of the steam turbine.

[0007] This method of operating a steam turbine power plant is characterized in that the steam turbine power plant comprises a steam turbine connected to a generator, a main steam line provided upstream of the steam turbine, a bypass line provided to allow steam supplied from the main steam line to bypass the steam turbine and having a bypass valve with an adjustable opening, and an atmosphere discharge line provided to discharge the steam supplied from the main steam line to the atmosphere and having an atmosphere discharge valve with an adjustable opening, and includes the steps of: specifying a flow rate of main steam flowing through the main steam line; and, when the flow rate of main steam supplied from the main steam line exceeds the flow rate of main steam consumed by the steam turbine, adjusting the opening rates of the bypass valve and the atmosphere discharge valve in accordance with the flow rate of main steam specified in the specifying step.

[0008] The method for operating a steam turbine power plant may include the following: (a) the atmosphere release valve is closed during normal operation, and in the step of adjusting the valve aperture, the bypass valve is opened prior to the atmosphere release valve, and the aperture of the atmosphere release valve is adjusted so that steam exceeding an admission constraint downstream of the bypass line is released to the atmosphere. (b) In (a), a water injection line is connected to the bypass line, the water injection line being provided for injecting cooling water to lower the temperature of the steam flowing through the bypass line, and having a water injection valve whose aperture is adjustable, and the admission constraint is determined based on a total flow rate of the steam flowing into the bypass line from the main steam line and the cooling water injected from the water injection line. Furthermore, the aperture of the water injection valve is set so that, when the bypass valve is opened in the step of adjusting the aperture of the valve, cooling water is injected at a flow rate that keeps the temperature of the steam flowing through the bypass line downstream of the cooling water injection position at or below a preset temperature constraint, based on the main steam flow rate and temperature specified in the step of specifying. (c) In (a), the downstream end of the bypass line is connected to a condenser, and the acceptance constraint is the amount that the condenser can process per unit time. (d) The downstream side of the bypass line is connected to a boiler that heats steam received via an outlet line of the steam turbine.

[0009] (e) The steam turbine is composed of a high-pressure turbine to which steam is supplied from the main steam line, and a low-pressure turbine connected to a low-pressure steam line to which low-pressure steam discharged from the high-pressure turbine is supplied and driven by the low-pressure steam, the bypass line is composed of a high-pressure bypass line provided for allowing the steam supplied from the main steam line to bypass the high-pressure turbine, and a low-pressure bypass line provided for allowing the steam supplied from the low-pressure steam line to bypass the low-pressure turbine, and the bypass valve is provided in each of the high-pressure bypass line and the low-pressure bypass line. (f) In (e), the state in which the flow rate of the main steam supplied from the main steam line exceeds the flow rate of the main steam consumed by the steam turbine is caused by a trip of the steam turbine, and in the step of adjusting the opening degree of the valve, the opening degree of the bypass valve and the atmosphere release valve are adjusted so that the entire amount of steam supplied from the main steam line flows into the bypass line or the atmosphere release line. (g) In (e), the state in which the flow rate of the main steam supplied from the main steam line exceeds the flow rate of the main steam consumed by the steam turbine is caused by a decrease in steam consumption of the steam turbine, and in the step of adjusting the valve opening, the openings of the bypass valve and the atmospheric release valve are adjusted to allow the surplus steam, obtained by subtracting the flow rate of steam supplied to the steam turbine from the flow rate of steam supplied from the main steam line, to flow into the bypass line or the atmospheric release line. In this case, the decrease in steam consumption is a state of load rejection in which a generator driven by the steam turbine is isolated, or a state of on-site isolated operation in which electricity generated by the generator is consumed only within the business premises where the steam turbine power plant is installed.

[0010] This storage medium is a storage medium that stores a computer program that operates a control device that controls the operation of the steam turbine power plant, and the computer program is characterized in that a group of steps is organized to execute any of the above-mentioned steam turbine power plant operation methods.

[0011] In this steam turbine power plant operation method, when the amount of main steam supplied from the main steam line exceeds the amount consumed by the steam turbine, the opening degree of the bypass valve and the atmospheric release valve are adjusted. As a result, the steam flow rate through the bypass line and the atmospheric release line can be appropriately set according to the degree of surplus main steam, so that the operation of the steam turbine power plant can be stably adjusted even when the steam supply-consumption balance changes significantly.

[0012] Fig. 1 is a configuration diagram of a power plant according to an embodiment. Fig. 2 is an explanatory diagram showing the flow of steam during normal operation. Fig. 3 is a first explanatory diagram showing the flow of steam during a turbine trip. Fig. 4 is a second explanatory diagram showing the flow of steam during a turbine trip. Fig. 5 is a first explanatory diagram showing the flow of steam when steam consumption is reduced. Fig. 6 is a second explanatory diagram showing the flow of steam when steam consumption is reduced. Fig. 7 is a configuration diagram of a power plant according to another embodiment.

[0013] 1 is a configuration diagram showing an example of a steam turbine power plant (power plant) according to this embodiment, which includes steam turbines, a high-pressure turbine 21 and a low-pressure turbine 22. The power plant includes a high-pressure boiler 11 that generates main steam (high-pressure steam), a high-pressure turbine 21 that drives a generator 31 with the main steam supplied from the high-pressure boiler 11, a low-pressure boiler 12 that reheats steam exhausted from the high-pressure turbine 21 to generate low-pressure steam, a low-pressure turbine 22 that drives the generator 31 together with the high-pressure turbine 21 with the low-pressure steam supplied from the low-pressure boiler 12, and a condenser 41 connected to the exhaust side of the low-pressure turbine 22.

[0014] The high-pressure boiler 11 generates high-pressure steam as main steam, for example, at a pressure in the range of 12.0 to 16.0 MPa (A) and a temperature in the range of 450 to 550°C, and supplies the high-pressure steam to the main steam line 501. There are no particular limitations on the configuration of the high-pressure boiler 11, but examples include a boiler with a well-known configuration that burns a liquid fuel such as heavy oil or a solid fuel such as coal or biomass pellets to generate steam.

[0015] The high-pressure turbine 21 rotates rotor blades using main steam supplied from the high-pressure boiler 11, driving a generator 31 connected to the rotor blade's rotation shaft to generate electricity. A reducer 32 is provided between the high-pressure turbine 21 and the generator 31 in this example. The inlet of the high-pressure turbine 21 is connected to the main steam line 501 via a high-pressure turbine steam line 502, and receives main steam via this high-pressure turbine steam line 502. The high-pressure turbine 21 in this example is configured as a back-pressure turbine, and discharges steam at a pressure within a range of, for example, 2.0 to 5.0 MPa (A) and 280 to 380°C toward the high-pressure turbine exhaust line 506.

[0016] The downstream end of the high-pressure turbine exhaust line 506 is connected to the low-pressure boiler 12. The low-pressure boiler 12 heats the steam discharged from the high-pressure turbine 21 and supplies the low-pressure steam to the low-pressure steam line 507 as low-pressure steam at a pressure within a range of, for example, 1.8 to 4.2 MPa (A) and 440 to 550°C. There are no particular limitations on the configuration of the low-pressure boiler 12, but an example of the low-pressure boiler is a waste heat boiler that utilizes the combustion exhaust gas discharged when fuel is combusted in the high-pressure boiler 11.

[0017] The low-pressure turbine 22 rotates rotor blades using low-pressure steam supplied from the low-pressure boiler 12, driving a generator 31 connected to the rotor blade's rotating shaft to generate electricity. In the power plant of this example, the low-pressure turbine 22 is connected to the same generator 31 as the high-pressure turbine 21, and these turbines 21, 22 jointly generate electricity. The inlet of the low-pressure turbine 22 is connected to a low-pressure steam line 507 via a low-pressure turbine row steam line 508, and receives low-pressure steam via this low-pressure turbine row steam line 508. Furthermore, the low-pressure turbine 22 of this example is configured as a condensing turbine, and a condenser 41 is provided at the downstream end of a low-pressure turbine exhaust line 511 connected to the outlet side of the low-pressure turbine 22.

[0018] The condenser 41 cools and condenses the steam discharged from the low-pressure turbine 22, and adjusts the outlet pressure of the low-pressure turbine 22 to a vacuum pressure in the range of, for example, 3.0 to 30 kPa (A). In the power plant of this example, an air-cooled condenser 41 is provided, but the method for cooling the steam discharged from the low-pressure turbine 22 is not limited to using a gas refrigerant (atmosphere in the case of an air-cooled condenser). For example, the steam may be cooled using a liquid refrigerant such as industrial water or seawater. A liquid pump 43 is connected downstream of the condenser 41 via a condensate drum 42, and the steam condensate is reused as boiler water.

[0019] A power plant having the above-described basic configuration is provided with a configuration for stably operating the power plant when the flow rate of main steam supplied from the main steam line 501 becomes unbalanced with the flow rate of main steam consumed by the high-pressure turbine 21. That is, the main steam line 501 is provided with a first bypass line 503 branching from the main steam line 501 and connected to a high-pressure turbine exhaust line 506 on the outlet side of the high-pressure turbine 21. Furthermore, the low-pressure steam line 507 is provided with a second bypass line 509 branching from the low-pressure steam line 507 and connected to a low-pressure turbine exhaust line 511 on the outlet side of the low-pressure turbine 22. The first bypass line 503 and the second bypass line 509 constitute the "bypass lines" of this power plant, which are provided to allow steam to bypass the steam turbines (high-pressure turbine 21, low-pressure turbine 22).

[0020] A first bypass valve 61 is provided in the first bypass line 503. When, for example, a pressure gauge detects that the pressure in the high-pressure turbine steam line 502 exceeds a predetermined operating pressure, the first bypass valve 61 switches from a closed state to an open state, allowing main steam to flow toward the first bypass line 503. The first bypass valve 61 controls the pressure in the high-pressure turbine steam line 502 to be equal to or lower than the operating pressure by increasing its opening degree as the detected pressure in the high-pressure turbine steam line 502 becomes higher than the operating pressure. These control operations are performed by a controller that controls the operation of the first bypass valve 61 (the pressure control controller is denoted by the letter "P" in the figure; the same applies to the control operations of various valves hereinafter). The operating pressure is set to be equal to, for example, the upper limit of the operating range of the inlet pressure of the high-pressure turbine 21.

[0021] Furthermore, a first water injection line 504 is connected to the first bypass line 503. The first water injection line 504 injects cooling water to lower the temperature of the steam flowing from the main steam line 501 toward the high-pressure turbine exhaust line 506. For example, room-temperature boiler water is supplied as cooling water from the first water injection line 504. A first water injection valve 62 is also provided in the first water injection line 504. For example, the first water injection valve 62 detects the temperature of the steam flowing through the first bypass line 503 downstream of the cooling water injection position using a thermometer. When the detected temperature exceeds a predetermined target temperature, the first water injection valve 62 switches from a closed state to an open state, thereby injecting cooling water toward the first bypass line 503. The first water injection valve 62 performs temperature control by increasing its opening degree as the detected steam temperature increases above the target temperature, thereby lowering the temperature of the steam flowing through the first bypass line 503. The target temperature is set, for example, to be equal to the temperature of the steam discharged from the high-pressure turbine 21 toward the high-pressure turbine exhaust line 506.

[0022] Similarly to the first bypass line 503, a second bypass line 509 for bypassing the low-pressure steam supplied from the low-pressure steam line 507 is also provided with a second bypass valve 64 that causes the low-pressure steam to flow toward the second bypass line 509 when the pressure in the low-pressure turbine steam line 508 detected by a pressure gauge becomes higher than a preset operating pressure. The second bypass valve 64 functions in the same manner as the first bypass valve 61, except that the operating pressure is set to be equal to, for example, the upper limit of the operating range of the inlet pressure of the low-pressure turbine 22.

[0023] Furthermore, a second water injection line 510 is connected to the second bypass line 509, through which cooling water is injected to lower the temperature of steam flowing from the low-pressure steam line 507 side toward the low-pressure turbine exhaust line 511 side. A second water injection valve 65 is also interposed in the second water injection line 510. The second water injection valve 65 detects the temperature of steam downstream of the cooling water injection position using a thermometer, and when the detected temperature becomes higher than a predetermined target temperature, the second water injection valve 65 switches from a closed state to an open state, thereby injecting cooling water. The second water injection valve 65 operates in the same manner as the first water injection valve 62, except that the target temperature is set to be equal to, for example, the temperature of steam discharged from the low-pressure turbine 22 toward the low-pressure turbine exhaust line 511.

[0024] Furthermore, in addition to the first bypass line 503 described above, the main steam line 501 is provided with an atmosphere release line 505 branching off from the main steam line 501. For example, the base end of the atmosphere release line 505 is connected downstream of the position where the first bypass line 503 branches off from the main steam line 501 and upstream of the installation position of a pressure gauge that detects pressure for controlling the operation of the first bypass valve 61. The end end of the atmosphere release line 505 is configured to be able to release steam to the atmosphere. An atmosphere release valve 63 is interposed in this atmosphere release line 505. For example, when a pressure gauge detects that the pressure in the atmosphere release line 505 upstream of the atmosphere release valve 63 has exceeded a preset operating pressure, the atmosphere release valve 63 switches from a closed state to an open state, thereby releasing the main steam to the atmosphere. The atmospheric release valve 63 performs pressure control by increasing the opening degree as the detected pressure in the atmospheric release line 505 becomes higher than the operating pressure, thereby reducing the pressure in the atmospheric release line 505 to below the operating pressure. The operating pressure is set to be higher than the upper limit of the operating range of the inlet pressure of the high-pressure turbine 21, for example, and lower than the design pressure of the piping that constitutes the atmospheric release line 505.

[0025] In the power plant having the basic configuration described above, operation control is performed via a Distributed Control System (DCS) 7, which is a control system that performs overall control of control devices provided at various locations in the power plant, including the above-mentioned control valves (first and second bypass valves 61 and 64, first and second water injection valves 62 and 65, and atmosphere release valve 63). The DCS has the function of setting control target values ​​(operating pressures and target temperatures in the case of the above-mentioned control valves 61 to 65) for the controllers of each control device, and of acquiring measurement data at predetermined time intervals from measuring devices such as thermometers, pressure gauges, and flow meters provided at various locations in the power plant, thereby monitoring the operating status of the power plant.

[0026] The DCS 7 is composed of a computer including a storage unit storing a program, a memory, and a CPU. The program contains instructions (steps) for outputting control signals such as control target values ​​to each control device in the power plant, acquiring measurement data from each measurement device, and operating the power plant. The program is stored in the computer's storage unit, such as a flexible disk, compact disk, hard disk, or non-volatile memory, and is read from this storage unit and installed in the DCS 7.

[0027] In Figure 2, the flow of steam during normal operation in the power plant described above is indicated by a bold line. In the power plants shown in Figures 2 to 7, components common to those described using Figure 1 are designated by the same reference numerals as those shown in Figure 1. During normal operation, main steam is supplied from the high-pressure boiler 11 at a flow rate F0 (unit: for example, ton / hour; hereinafter, this applies to the steam flow rate and the water injection flow rate) and temperature T1 corresponding to the output of power to be generated. The main steam is supplied in its entirety to the high-pressure turbine 21 via a main steam line 501 and a high-pressure turbine-flow steam line 502 (high-pressure turbine-flow flow rate F1 = F0). Steam discharged from the high-pressure turbine 21 is heated in the low-pressure boiler 12 and resupplied as low-pressure steam at a flow rate F3 (= F0) and temperature T2. The low-pressure steam is supplied in its entirety to the low-pressure turbine 22 via a low-pressure steam line 507 and a low-pressure turbine-flow steam line 508. Main steam and low-pressure steam are supplied to the high-pressure turbine 21 and the low-pressure turbine 22, causing rotor blades in each turbine to rotate, driving a generator 31 and generating electricity.

[0028] The steam discharged from the low-pressure turbine 22 flows into the condenser 41 via the low-pressure turbine exhaust line 511, where it is cooled and condensed to form condensed water. The processable amount C per unit time [tons / hour] of the condenser 41 (hereinafter simply referred to as the "processable amount C") is set to a value greater than the flow rate of steam exhausted from the low-pressure turbine 22 within the power output range during normal operation of the power plant. In some cases, the high-pressure turbine 21 and the low-pressure turbine 22 extract a portion of steam from an intermediate stage and supply it to other steam users. In such cases, the flow rate of steam exhausted from the low-pressure turbine 22 is less than the flow rate F0 of main steam supplied from the high-pressure boiler 11. Therefore, the processable amount C of the condenser 41 may also be set to a value smaller than the main steam flow rate F0.

[0029] Moreover, under pressure conditions during normal operation, the first bypass valve 61 and the second bypass valve 64 are closed, and steam does not flow through the first bypass line 503 and the second bypass line 509. Therefore, no cooling water is injected from the first water injection line 504 and the second water injection line 510 (f1 = f2 = 0). Moreover, under pressure conditions during normal operation, the atmosphere release valve 63 is also closed, and steam is not released from the atmosphere release line 505 to the atmosphere.

[0030] On the other hand, even during normal operation, due to a delay in control when changing the power plant's output, the pressure in the high-pressure turbine row steam line 502 and the low-pressure turbine row steam line 508 may rise and exceed the operating pressure of the first bypass valve 61 and the second bypass valve 64. In this case, the first and second bypass valves 61 and 64 are operated based on the results of detecting the pressure in the high-pressure turbine row steam line 502 and the low-pressure turbine row steam line 508, and a portion of the steam (main steam directed to the high-pressure turbine row steam line 502 and low-pressure steam directed to the low-pressure turbine row steam line 508) is caused to flow toward the first and second bypass lines 503 and 509, thereby performing the above-mentioned pressure control to restore the pressure below the operating pressure. Note that, for convenience, the operations of the first and second bypass valves 61 and 64 are described together here, but the pressure control operations of the first and second bypass valves 61 and 64 based on the results of detecting the pressure in the high-pressure and low-pressure turbine row steam lines 502 and 508 are performed independently of each other.

[0031] Furthermore, when the temperature of the steam detected downstream of the water injection position becomes higher than the target temperature due to the flow of steam through the first and second bypass lines 503 and 509, the first and second water injection valves 62 and 65 are activated to start injecting cooling water. Then, the amount of water injected is increased or decreased according to the temperature detection results of each bypass line 503 and 509, thereby executing the above-mentioned temperature control to maintain the temperature of the bypass lines 503 and 509 at the target temperature.

[0032] Here, during normal operation, the processing capacity C of the condenser 41 is set to be greater than the value obtained by adding the flow rate of low-pressure steam flowing into the second bypass line 509 and the flow rate f2 of cooling water injected from the second water injection line 510 to the flow rate of steam exhausted from the low-pressure turbine 22 when a pressure control operation is performed to flow steam into each bypass line 503, 509.

[0033] Furthermore, during normal operation, even if the first bypass valve 61 is operated to control the pressure, if the pressure continues to rise and it is detected that the pressure in the atmospheric release line 505 is greater than the operating pressure described above, the atmospheric release valve 63 opens and releases steam into the atmosphere.

[0034] As described above, during normal operation, unless the pressures in the high-pressure and low-pressure turbine steam lines 502 and 508 reach or exceed the operating pressures of the first and second bypass valves 61 and 64, operation is performed without steam flowing into the first and second bypass lines 503 and 509. Then, once the pressures in the high-pressure and low-pressure turbine steam lines 502 and 508 reach or exceed the operating pressures, the first and second bypass valves 61 and 64 are opened as described above to allow steam to flow into the first and second bypass lines 503 and 509, and water is injected through the first and second water injection lines 504 and 510. Furthermore, once the pressure on the inlet side of the high-pressure turbine 21 rises and the pressure in the atmospheric release line 505 reaches or exceed the operating pressure, the atmospheric release valve 63 is opened to release a portion of the steam into the atmosphere.

[0035] In this way, for the first bypass line 503, the second bypass line 509 and the atmospheric release line 505, the opening of each valve 61, 64, 63 is adjusted to allow steam to flow depending on the pressure on the inlet side of the high-pressure turbine 21 (high-pressure turbine steam line 502 or atmospheric release line 505) or the inlet side of the low-pressure turbine 22 (low-pressure turbine steam line 508).

[0036] Meanwhile, in a power plant, an emergency shutdown operation (hereinafter also referred to as a "turbine trip") of the high-pressure turbine 21 or the low-pressure turbine 22 may be performed. During a turbine trip, the steam consumption in the high-pressure turbine 21 and the low-pressure turbine 22 becomes zero in an extremely short time of less than a few seconds, usually less than one second. On the other hand, it is preferable to continue operation of the high-pressure boiler 11 (including the low-pressure boiler 12, which is a waste heat boiler) as long as possible, because it is difficult to significantly reduce the steam supply flow rate in a short time in response to a turbine trip and restarting the boiler once it has stopped is difficult. Therefore, there will be a prolonged period in which the flow rate F0 of the main steam supplied from the high-pressure boiler 11 via the main steam line 501 significantly exceeds the flow rate of steam consumed by the high-pressure turbine 21 and the low-pressure turbine 22 (F1 = F3 = 0 during a turbine trip).

[0037] If no action is taken at this time, the pressure in the high-pressure and low-pressure turbine steam lines 502 and 508 will rise because the main steam flow rate F0 exceeds the consumption flow rates (F1 and F3) in the high-pressure turbine 21 and the low-pressure turbine 22. This pressure rise will open the first and second bypass valves 61 and 64, allowing steam to flow toward the first and second bypass lines 503 and 509. Furthermore, even after these pressure adjustment operations have been performed, there will still be excess steam, and if this causes the pressure in the atmospheric release line 505 to rise, the atmospheric release valve 63 will operate and the steam will be released into the atmosphere.

[0038] However, if the main steam flow rate F0 significantly exceeds the consumption flow rates (F1, F3) of the high-pressure turbine 21 and the low-pressure turbine 22, opening and closing the valves 61, 64, and 63 in response to the pressure detection results of the lines 502, 508, and 505 as described above will cause severe pressure fluctuations during the transient response period until the pressure is stabilized, resulting in an unstable power plant. In particular, if the flow rate of steam flowing into the bypass lines 503 and 509 increases suddenly, the water injection control from the water injection lines 504 and 510 may be unable to keep up, resulting in an over-temperature condition, an emergency shutdown of each component, and ultimately a trip of the entire power plant, including the high-pressure boiler 11. Furthermore, if a turbine trip occurs, a large amount of excess steam may be generated in an extremely short time, causing the pressure control by the valves 61, 64, and 63 to be unable to keep up, which may trigger the activation of a safety valve (not shown) installed in the system, resulting in a loss of a large amount of steam being released to the outside.

[0039] To avoid such an unstable state, the power plant of this embodiment is configured to directly adjust the openings of the first bypass valve 61, the second bypass valve 64, the atmospheric release valve 63, etc., instead of the pressure control described above, when the main steam flow rate F0 greatly exceeds the consumption flow rates (F1, F3) of the high-pressure turbine 21 and the low-pressure turbine 22, as occurs during a turbine trip.

[0040] However, if the only measure to be taken is to prevent the power plant from becoming unstable, operation with a margin can be achieved by maximizing the aperture of the atmospheric release valve 63, fixing the amount of atmospheric release, and then flowing the remaining steam through the first bypass line 503 and the second bypass line 509. However, because variable costs and other expenses are required to produce pure water for generating steam, there are cases where it is desirable to avoid aperture adjustment that prioritizes atmospheric release. Therefore, in the power plant of this embodiment, aperture adjustment of the first and second bypass valves 61 and 64, the atmospheric release valve 63, and the like is performed to enable stable operation while suppressing an increase in loss due to prioritizing atmospheric release. Specific details of aperture adjustment will be described below.

[0041] 2 and other figures, in response to a turbine trip, DCS 7 uses information on the main steam flow rate F0, the main steam temperature T1, and the low-pressure steam temperature T2. By identifying the flow rate of the main steam flowing through main steam line 501, it is possible to determine the steam flow rate that needs to be directed toward first and second bypass lines 503 and 509 or atmospheric release line 505 in the event of a turbine trip (step of identifying the flow rate of the main steam flowing through main steam line 501).

[0042] Furthermore, once the main steam temperature T1 is specified, the water injection flow rate f1 from the first water injection line 504 can be calculated according to the flow rate of the main steam flowing into the first bypass line 503 and the target temperature of the steam after water injection. Similarly, once the low-pressure steam temperature T2 is specified, the water injection flow rate f2 from the second water injection line 510 can be calculated according to the flow rate of the low-pressure steam flowing into the second bypass line 509 and the target temperature of the steam after water injection. Then, the openings of the first and second water injection valves 62, 65 are determined based on these water injection flows f1, f2.

[0043] If the flow rate of main steam flowing into first bypass line 503 and the flow rates f1 and f2 of water injection from first and second water injection lines 504 and 510 can be determined from the results of these calculations, it is possible to determine the flow rate of steam to be treated in condenser 41. DCS 7 determines opening degrees Q1 to Q5 of first and second bypass valves 61 and 64, first and second water injection valves 62 and 65, and atmospheric release valve 63 so as to flow all of the excess steam due to a turbine trip toward first and second bypass lines 503 and 509 or atmospheric release line 505, while avoiding atmospheric release of steam from atmospheric release line 505 as much as possible (a process of adjusting the opening degrees of first bypass valve 61, second bypass valve 64, and atmospheric release valve 63).

[0044] In order to avoid venting steam to the atmosphere as much as possible, the DCS 7 determines the opening degrees Q1, Q3, and Q2 so as to open the first and second bypass valves 61, 64 prior to the atmospheric vent valve 63. Meanwhile, as a criterion for determining whether venting steam to the atmosphere is necessary, the DCS 7 determines whether the total flow rate of the main steam flow rate F0 and the water injection flow rates f1, f2 exceeds the downstream acceptance constraint of the first and second bypass lines 503, 509. In this embodiment, a case is illustrated in which the acceptance constraint is the processable amount C of the condenser 41 connected to the downstream end of the bypass line (the entirety of the first bypass line 503 and the second bypass line 509). However, the acceptance constraint is not limited to the processable amount C of the condenser 41. For example, the acceptance constraint may be an upper limit of the liquid feed flow rate of the liquid feed pump 43, a constraint on the piping flow rate, or a flow rate constraint of equipment or meters installed in the flow path.

[0045] 3, the thick line shows the steam flow when the total flow rate of the main steam flow rate F0 and the injected water flow rates f1 and f2 does not exceed the processable amount C of the condenser 41 (F0 + f1 + f2 < C) during a turbine trip. Upon receiving a turbine trip signal, the DCS 7 calculates the injected water flow rates f1 and f2 based on the measurement results of the main steam flow rate F0, the main steam temperature T1, and the low-pressure steam temperature T2.

[0046] As a result, if the total flow rate of F0, f1, and f2 does not exceed the processable amount C of the condenser 41, the DCS 7 sets the aperture Q1 of the first bypass valve 61 so that the entire amount F0 of main steam flows into the first bypass line 503. Then, the aperture Q4 of the first water injection valve 62 is set so that cooling water is injected at an injection flow rate f1 corresponding to the main steam flow rate F0 and temperature T1. As a result, the flow rate of steam downstream of the cooling water injection position in the first bypass line 503 (high-pressure bypass line flow rate) becomes F2 (= F0 + f1).

[0047] Since this steam flow rate F2 corresponds to the flow rate of low-pressure steam supplied from the low-pressure boiler 12, the DCS 7 sets the aperture Q3 of the second bypass valve 64 so that the entire amount of low-pressure steam flows into the second bypass line 509. Furthermore, the DCS 7 sets the aperture Q5 of the second water injection valve 65 so that cooling water is injected at an injection flow rate f2 corresponding to the low-pressure steam flow rate F2 and the temperature T2. Meanwhile, as described above, the entire amount of main steam flowing through the main steam line 501 can flow into the first bypass line 503, so the DCS 7 leaves the atmosphere release valve 63 closed (aperture Q2 = 0).

[0048] Here, when determining whether the total flow rate of F0, f1, and f2 exceeds the processable capacity C of the condenser 41, it is not essential to perform a calculation to determine the total value of these flow rates. The water injection flow rates f1 and f2 can be determined in advance by assuming the main steam and low-pressure steam temperatures T1 and T2. Therefore, an upper limit value of the main steam flow rate F0 that is allowable from the processable capacity C may be determined in advance based on the results of determining these water injection flow rates f1 and f2 in advance. In this case, it is only necessary to determine whether the main steam flow rate F0 exceeds the upper limit value at the time of turbine trip, allowing for more rapid control.

[0049] Here, the injection water flow rates f1 and f2 are small compared to the flow rates of steam flowing through the bypass lines 503 and 509. Therefore, when the above-described method is adopted, even if the actual steam temperatures T1 and T2 deviate from the assumed values, the rate of increase or decrease in the injection water flow rates f1 and f2 is small. Furthermore, taking the injection water flow rates f1 and f2 into consideration, the upper limit value of the main steam flow rate F0 can be set so that the flow rate of steam flowing through the bypass lines 503 and 509 has a margin relative to the processable amount C. Therefore, even when the openings Q1 to Q5 of the valves 61, 64, 62, 65, and 63 are set using the upper limit value of the main steam flow rate F0, which is set by determining the injection water flow rates f1 and f2 in advance, as a criterion, operation control during a turbine trip can be stably executed.

[0050] By setting the valve openings Q1 to Q5 as described above, when a turbine trip occurs, all of the excess main steam flows into the first bypass line 503, passes through the first bypass line 503, then the low-pressure boiler 12, and then the second bypass line 509, and is recovered as condensate in the condenser 41, as shown by the bold lines in Figure 3. At this time, the valve openings Q1 to Q5 are set based on the main steam flow rate F0 and the injection water flow rates f1 and f2, which are determined in advance. This reduces fluctuations in pressure and flow rate, and enables stable disposal of the excess main steam, compared to when control is performed in which the openings Q1 to Q5 are changed in accordance with the results of detecting the pressures in the high-pressure turbine steam line 502, the low-pressure turbine steam line 508, and the atmospheric release line 505.

[0051] 4 shows, with a bold line, the flow of steam when the total flow rate of the main steam flow rate F0 and the injection water flow rates f1 and f2 exceeds the processing capacity C of the condenser 41 (F0+f1+f2≧C) during a turbine trip. In this case, the condenser 41 cannot process the entire amount of main steam supplied to the main steam line 501, so the steam must be released into the atmosphere.

[0052] Therefore, upon receiving the turbine trip signal, the DCS 7 calculates the injection water flow rates f1 and f2 based on the measurement results of the main steam flow rate F0, the main steam temperature T1, and the low-pressure steam temperature T2. As a result, if the total flow rate of F0, f1, and f2 exceeds the processing capacity C of the condenser 41, the DCS 7 executes the following operation. Note that, as already explained, the above determination is not limited to the case of performing a calculation to determine the total value of the flow rates of F0, f1, and f2, and it is also possible to only determine whether the main steam flow rate F0 exceeds a preset upper limit value.

[0053] For example, the DCS 7 calculates, by back-calculating from the processable amount C, which is the acceptance constraint, for example, the low-pressure steam flow rate (i.e., the steam flow rate flowing in from the first bypass line 503 side) F2 (=F0+f1) and the water injection flow rate f2 from the second water injection line 510 so that F0+f1+f2≦C holds. In the following example, in order to minimize the atmospheric release flow rate F4, the maximum steam flow rate F2 is calculated so that F0+f1+f2=C holds. ＭＡＸ , water injection flow rate f1 ＭＡＸ , f2 ＭＡＸ However, the flow rates F2, f1, and f2 may be calculated so that a margin is provided for the processable amount C of the condenser 41 and F2+f2=αC (for example, α=0.6 to 0.9).

[0054] When the target temperature of the second bypass line 509 after the cooling water injection is constant, the flow rate ratio (f2 / F2) between the low-pressure steam flow rate F2 and the injection water flow rate f2 can be determined according to the low-pressure steam temperature T2. From this flow rate ratio and the relationship F0+f1+f2=F2+f2=C, the maximum value of each flow rate (F2 ＭＡＸ , f2 ＭＡＸ Next, the DCS 7 calculates the maximum values ​​of the main steam flow rate F5 and the water injection flow rate f1 that can be received in the first bypass line 503 (F5 ＭＡＸ , f1 ＭＡＸ In this calculation, the maximum value of each flow rate can also be calculated from the relationship of F2=F5+f1 and the flow rate ratio (f1 / F5) between the main steam flow rate F5 and the water injection flow rate f1 that can be received by the first bypass line 503.

[0055] Then, the value obtained by subtracting the maximum value of the main steam flow rate that can be accepted into the first bypass line 503 from the actual main steam flow rate F0 specified at the time of turbine trip (F0-F5) is calculated. ＭＡＸ ) can be identified as corresponding to the atmospheric release flow rate F4 that must be released into the atmosphere from the atmospheric release line 505.

[0056] After specifying the atmospheric release flow rate F4, the DCS 7 determines the maximum value F5 of the steam flow rate flowing into the first bypass line 503 and the second bypass line 509. ＭＡＸ , F2 ＭＡＸ , and the water injection flow rate f1 corresponding to these steam flow rates ＭＡＸ , f2 ＭＡＸ and setting the valve openings Q1 to Q5 to realize the atmospheric emission flow rate F4.

[0057] By setting the valve openings Q1 to Q5 as described above, when a turbine trip occurs, excess main steam flows into the first bypass line 503 at a flow rate that corresponds to the processable amount C (acceptance constraint) of the condenser 41, flows through the first bypass line 503 → low-pressure boiler 12 → second bypass line 509, and is recovered as condensate in the condenser 41, as shown by the bold line in Fig. 4. At this time, in the balance of flow rates also shown in Fig. 4, the steam flow rate (high-pressure bypass line flow rate) in the first bypass line 503 downstream of the water injection position is "F2≦C−f2" (in the case of the maximum value described above, F2=C−f2), and the atmospheric release flow rate is "F4=F0−(F2−f1)>0".

[0058] At this time, the flow rate of main steam released into the atmosphere (atmospheric release flow rate F4) can be limited to only the amount in excess of the processable amount C of the condenser 41, thereby reducing losses associated with release into the atmosphere. In these operations, the valve openings Q1 to Q5 are set based on the main steam flow rate F0 and the water injection flow rates f1 and f2, which are determined in advance, so fluctuations in pressure and flow rate are small, and the excess main steam can be processed stably.

[0059] According to the power plant operation method of this embodiment, when the flow rate of main steam supplied from main steam line 501 exceeds the flow rate consumed by high-pressure turbine 21 and low-pressure turbine 22 (F1 → 0, F3 → 0 during turbine trip), the openings of first bypass valve 61, second bypass valve 64, and atmosphere release valve 63 are adjusted. Therefore, the flow rates of steam flowing through first bypass line 503, second bypass line 509, and atmosphere release line 505 can be appropriately set according to the degree of surplus main steam, so that stable operation adjustment of the power plant can be performed even when the steam supply-consumption balance changes significantly.

[0060] In the above-described embodiment, when a turbine trip occurs and the valve openings Q1 to Q5 are set, the water injection flow rates f1 and f2, the steam flow rates F5 and F2 flowing into the bypass lines 503 and 509, and the atmospheric diffusion flow rate F4 are calculated in real time by the DCS 7, and the valve openings Q1 to Q5 are set. However, as described above, when a turbine trip occurs, the balance of steam consumption changes suddenly in an extremely short time, from less than one second to several seconds, and therefore, it is also required to set the valve openings Q1 to Q5 even more quickly.

[0061] Therefore, the water injection flow rates f1 and f2, the steam flow rates F5 and F2 flowing into the bypass lines 503 and 509, and the atmospheric diffusion flow rate F4 may be calculated in advance according to the estimated values ​​of the main steam flow rate F0, the main steam temperature T1, and the low-pressure steam temperature T2, and a table may be created in which the valve openings Q1 to Q5 correspond to these flow rates. In this case, after receiving a turbine trip signal and detecting the main steam flow rate F0, the steam temperature T1, and the steam temperature T2, the valve openings Q1 to Q5 that match these conditions are searched for in the table, and the openings can be immediately set based on the search results.

[0062] 5 and 6 show examples of how to deal with an excess of main steam under conditions different from those during a turbine trip. That is, in these figures, the high-pressure turbine 21 and the low-pressure turbine 22 continue to operate, but because the steam consumption rate has decreased, the flow rate of main steam supplied from the main steam line 501 exceeds the flow rate of main steam consumed by the high-pressure turbine 21 and the low-pressure turbine 22.

[0063] For example, a power plant may enter a load rejection state during a test operation, in which the high-pressure turbine 21 and the low-pressure turbine 22 are operated with the generator 31 disconnected, or an on-site isolated operation state in which electricity generated by the generator 31 is consumed only within the facility where the power plant is installed, without selling the electricity. In these states, the steam consumption in the high-pressure turbine 21 and the low-pressure turbine 22 is significantly reduced. Meanwhile, the high-pressure boiler 11 may have a lower limit on the steam supply flow rate due to, for example, equipment limitations, and may not be able to adjust the supply flow rate below this lower limit. As a result, the main steam flow rate supplied from the main steam line 501 may not balance with the flow rate consumed by the high-pressure turbine 21 and the low-pressure turbine 22, resulting in a surplus.

[0064] 5, the thick line shows the steam flow when the total flow rate of the main steam flow rate F0 and the injected water flow rates f1 and f2 does not exceed the processing capacity C of the condenser 41 (F0 + f1 + f2 < C) during a decrease in steam consumption. When the steam flow rates of the high-pressure turbine 21 and low-pressure turbine 22 decrease from F1 to F1' (F1 > F1') and from F3 to F3' (F3 > F3'), respectively, the excess main steam is the main steam flow rate F0 minus the high-pressure turbine steam flow rate F1'. Using this excess and the main steam temperature T1, the DCS 7 calculates the injected water flow rate f1 that would be obtained if the entire excess were to flow into the first bypass line 503, and determines the high-pressure bypass line flow rate F2 (= F0 - F1' + f1).

[0065] The steam flowing through the first bypass line 503 is combined with steam exhausted from the high-pressure turbine 21 at a flow rate F1' and then heated in the low-pressure boiler 12. As a result, low-pressure steam at a flow rate F0+f1 is supplied from the low-pressure boiler 12. The flow rate obtained by subtracting the low-pressure turbine steam flow rate F3' from the supplied low-pressure steam is the surplus. Furthermore, the DCS 7 calculates the injection water flow rate f2 that would be achieved if the entire surplus amount were to flow into the second bypass line 509, based on this surplus low-pressure steam and the temperature T2.

[0066] The steam flowing through the second bypass line 509 is then merged with steam at a flow rate F3' exhausted from the low-pressure turbine 22, and is then cooled and condensed in the condenser 41. Therefore, in the condenser 41, steam at a flow rate F0+f1+f2 is processed, and if the condition F0+f1+f2<C is satisfied as described above, excess main steam can be made to flow through the first bypass line 503 and the second bypass line 509 and processed in the condenser 41 without steam being released from the atmosphere release valve 63. The DCS 7 sets the valve openings Q1 to Q5 so as to achieve the above-mentioned flow rate balance.

[0067] 5 , when the steam consumption rate decreases, all of the excess main steam flows into the first bypass line 503. The steam then flows through the high-pressure turbine 21 and the first bypass line 503, the low-pressure boiler 12, the low-pressure turbine 22, and the second bypass line 509, and is recovered as condensate in the condenser 41. In this case, by setting the valve openings Q1 to Q5 based on the main steam flow rate F0 and the injection water flow rates f1 and f2 that are determined in advance, fluctuations in pressure and flow rate are reduced, and the excess main steam can be stably treated, just like in the case of a turbine trip.

[0068] 6 shows, with a bold line, the flow of steam when the total flow rate of the main steam flow rate F0 and the water injection flow rates f1 and f2 exceeds the processable amount C of the condenser 41 (F0+f1+f2≧C) during a decrease in steam consumption. In this case, the condenser 41 cannot process all of the excess main steam, so it is necessary to release it to the atmosphere through the atmospheric release line 505.

[0069] Therefore, when the steam consumption rates of the high-pressure turbine 21 and the low-pressure turbine 22 decrease to the above-mentioned F1' and F3', respectively, the DCS 7 calculates the injection water flow rates f1 and f2 based on the measurement results of the main steam flow rate F0, the main steam temperature T1, and the low-pressure steam temperature T2. As a result, when the total flow rate of F0, f1, and f2 exceeds the processing capacity C of the condenser 41, the DCS 7 performs the following operation.

[0070] 4, the DCS 7 calculates, for example, the steam flow rate F0+f1-F3' (hereinafter, this flow rate will be referred to as F6) flowing into the second bypass line 509 and the water injection flow rate f2 from the second water injection line 510 by back-calculating from the processable amount C, which is the acceptance constraint, so that F0+f1+f2≦C holds. In this example, too, in order to minimize the atmospheric release flow rate F4, the maximum steam flow rate F5 that can be accepted by each of the first and second bypass lines 503 and 509 is calculated so that F0+f1+f2=C holds. ＭＡＸ , F6 ＭＡＸ , water injection flow rate f1 ＭＡＸ , f2 ＭＡＸ The calculation of

[0071] As described above, when the target temperature of the second bypass line 509 after the cooling water injection is constant, the flow rate ratio (f2 / F6) of the steam flow rate F0+f1-F3'=F6 flowing into the second bypass line 509 to the water injection flow rate f2 can be determined according to the low-pressure steam temperature T2. From this flow rate ratio, the low-pressure turbine steam flow rate F3', and the relationship of F0+f1+f2=F3'+F6+f2=C, the maximum value of each flow rate (F6 ＭＡＸ , f2 ＭＡＸ ) can be obtained.

[0072] Next, the DCS 7 calculates the maximum values ​​of the main steam flow rate F and the injection water flow rate f1 that can be accepted by the first bypass line 503 (F5 ＭＡＸ , f1 ＭＡＸ ) Taking into consideration the constraint of F5+f1+F1′+f2=C, in this calculation as well, the maximum value of each flow rate can be calculated from the flow rate ratio (f1 / F) between the main steam flow rate F and the injected water flow rate f1 that can be accepted by the first bypass line 503.

[0073] Therefore, the DCS 7 calculates the maximum values ​​of the main steam flow rate and the injection water flow rate f1 that can be accepted by the first bypass line 503 (F5 ＭＡＸ , f1 ＭＡＸ Then, the actual main steam flow rate F0 determined when the steam consumption rate is reduced is subtracted from the maximum value of the main steam flow rate that can be received by the first bypass line 503 and the high-pressure turbine steam flow rate F1' (F0-F5). ＭＡＸ −F1′) can be identified as corresponding to the atmospheric release flow rate F4 that must be released into the atmosphere from the atmospheric release line 505.

[0074] After specifying the atmospheric release flow rate F4, the DCS 7 determines the maximum value F5 of the steam flow rate flowing into the first and second bypass lines 503 and 509. ＭＡＸ , F6 ＭＡＸ , and the water injection flow rate f1 corresponding to these steam flow rates ＭＡＸ , f2 ＭＡＸ and setting the valve openings Q1 to Q5 to realize the atmospheric emission flow rate F4.

[0075] By setting the valve openings Q1 to Q5 as described above, when the steam consumption rate decreases, excess main steam flows into the first bypass line 503 at a flow rate that corresponds to the processable amount C (acceptance constraint) of the condenser 41, as shown by the bold line in Fig. 6 , flows through the high-pressure turbine 21 and the first bypass line 503 → low-pressure boiler 12 → low-pressure turbine 22 and the second bypass line 509, and is recovered as condensate in the condenser 41. At this time, in the balance of the flow rates also shown in Fig. 6 , the steam flow rate (high-pressure bypass line flow rate) in the first bypass line 503 downstream of the water injection position is "F2≦C−(F1′+f2)", and the atmospheric release flow rate is "F4=F0−(F1′+F2−f1)>0".

[0076] Even in this case, the flow rate of main steam released into the atmosphere (atmospheric release flow rate F4) can be limited to only the amount in excess of the processable amount C of the condenser 41, thereby minimizing losses associated with release into the atmosphere. Also in these operations, the valve openings Q1 to Q5 are set based on the main steam flow rate F0 and the water injection flow rates f1 and f2, which are determined in advance, so fluctuations in pressure and flow rate are small, and the excess main steam can be processed stably.

[0077] 5 and 6, real-time calculation of the steam balance by the DCS 7 is not essential. As described above, in the case of a turbine trip, the valve openings Q1 to Q5 may be set based solely on the determination of whether the assumed main steam flow rate F0 exceeds a preset upper limit. Alternatively, a table may be created in which the valve openings Q1 to Q5 correspond to the steam consumptions F1', F2', main steam temperature T1, and low-pressure steam temperature T2 in the turbines 21 and 22. The valve openings Q1 to Q5 may be searched for in the table based on the values ​​of F0, F1', F2', T1, and T2 when the steam consumption is reduced, and the valve openings may be set accordingly.

[0078] The above-described method of adjusting the first bypass valve 61, the second bypass valve 64, and the atmospheric release valve 63 when a turbine trips or when steam consumption is reduced is not limited to application to a power plant in which multiple steam turbines (high-pressure turbine 21, low-pressure turbine 22) are connected via a low-pressure boiler 12, as exemplified in Figures 1 to 6. For example, a similar method can also be applied to a power plant equipped with a single steam turbine 21a, as shown in Figure 7.

[0079] 7 , when a turbine trips or steam consumption rate decreases, the need for atmospheric release is determined based on whether the main steam flow rate F0 supplied from the main steam line 501 exceeds a steam acceptance constraint downstream of the bypass line 503a (for example, the processable amount C of the condenser 41).Then, the flow rates of the main steam to be flowed toward the bypass line 503a and the atmospheric release line 505 and the flow rate of cooling water to be injected from the water injection line 504a are determined, and the openings of the bypass valve 61a, the water injection valve 62a, and the atmospheric release valve 63 are directly controlled. Note that, for convenience of illustration, a single-stage steam turbine 21a is shown as an example in FIG. 7 , but a multi-stage steam turbine may also be used.

[0080] Furthermore, when the main steam flow rate F0 supplied from the main steam line 501 exceeds the flow rate consumed by the steam turbines 21, 22, and 21a, it is not essential to adjust the opening of the bypass valves 61, 64, and 61a to avoid atmospheric release. During a turbine trip or when steam consumption is low, a minimum release flow rate F4' to be released into the atmosphere may be determined in advance, prioritizing stable operation of the power plant. Then, the valve openings Q1 to Q5 may be determined by calculating the steam balance for the main steam at a flow rate F0-F4', obtained by subtracting the minimum release flow rate F4' from the main steam flow rate F0, using the method described with reference to FIGS. 3 to 7. According to this method, for example, in the case shown in FIG. 3, the atmospheric release flow rate is F4' > 0, and in the case shown in FIG. 4, the atmospheric release flow rate is F4 + F4'.

[0081] 1 to 7 show the configuration of the power plant in a very simplified manner. In reality, steam may be extracted from intermediate stages of the steam turbines 21, 22, and 21a or from the bypass lines 503, 509, and 503a and consumed within the power plant. In such cases, the steam balance described with reference to FIGS. 3 to 7 (the consumption flow rate of each steam turbine 21, 22, and 21a, the steam flow rate flowing into each bypass line 503, 509, and 503a, the water injection flow rate, comparison with the intake constraint, etc.) may be calculated taking into account the flow rate of steam extracted to the outside. In this case, the flow rate of steam extracted to the outside may be measured by a flow meter, or a predetermined fixed value may be used.

[0082] 11 High-pressure boiler 12 Low-pressure boiler 21 High-pressure turbine 21a Steam turbine 22 Low-pressure turbine 31 Generator 32 Reducer 41 Condenser 42 Condensate drum 43 Liquid feed pump 501 Main steam line 502 High-pressure turbine steam line 503 First bypass line 503a Bypass line 504 First water injection line 504a Water injection line 505 Atmospheric release line 506 High-pressure turbine exhaust line 507 Low-pressure steam line 508 Low-pressure turbine steam line 509 Second bypass line 510 Second water injection line 511 Low-pressure turbine exhaust line 512 Pure liquid feed line 61 First bypass valve 61a Bypass valve 62 First water injection valve 62 Water injection valve 63 Atmospheric release valve 64 Second bypass valve 65 Second water injection valve 7 DCS

Claims

1. A method for operating a steam turbine power plant comprising: a steam turbine connected to a generator; a main steam line provided upstream of the steam turbine; a bypass line provided for allowing steam supplied from the main steam line to bypass the steam turbine and having a bypass valve with an adjustable opening; and an atmosphere release line provided for releasing the steam supplied from the main steam line to the atmosphere and having an atmosphere release valve with an adjustable opening; the method for operating a steam turbine power plant comprising: a step of specifying a flow rate of main steam flowing through the main steam line; and a step of adjusting the opening rates of the bypass valve and the atmosphere release valve in accordance with the flow rate of main steam specified in the step of specifying, when the flow rate of main steam supplied from the main steam line exceeds the flow rate of main steam consumed by the steam turbine.

2. A method for operating a steam turbine power plant as described in claim 1, characterized in that the atmospheric release valve is closed during normal operation, and in the process of adjusting the valve opening, the bypass valve is opened in preference to the atmospheric release valve, and the opening of the atmospheric release valve is adjusted so that steam exceeding the acceptance constraint downstream of the bypass line is released into the atmosphere.

3. A method for operating a steam turbine power plant as described in claim 2, characterized in that a water injection line having an adjustable water injection valve is connected to the bypass line to inject cooling water to lower the temperature of the steam flowing through the bypass line, and the acceptance constraint is determined based on the total flow rate of the steam flowing from the main steam line into the bypass line and the cooling water injected from the water injection line.

4. A method for operating a steam turbine power plant as described in claim 3, characterized in that when the bypass valve is opened in the step of adjusting the valve opening, the opening of the water injection valve is set so that cooling water is injected at a flow rate that keeps the temperature of the steam flowing through the bypass line downstream of the cooling water injection position below a preset temperature constraint, based on the main steam flow rate and temperature identified in the step of identifying the main steam.

5. A method for operating a steam turbine power plant according to claim 2, characterized in that the downstream end of the bypass line is connected to a condenser, and the acceptance constraint is the amount of steam that can be processed per unit time by the condenser.

6. A method for operating a steam turbine power plant according to claim 1, wherein the downstream side of the bypass line is connected to a boiler that heats steam received through the outlet line of the steam turbine.

7. A method for operating a steam turbine power plant as described in claim 1, characterized in that the steam turbine is composed of a high-pressure turbine to which steam is supplied from the main steam line, and a low-pressure turbine connected to a low-pressure steam line to which low-pressure steam discharged from the high-pressure turbine is supplied and driven by the low-pressure steam, the bypass lines are composed of a high-pressure bypass line provided to allow the steam supplied from the main steam line to bypass the high-pressure turbine, and a low-pressure bypass line provided to allow the steam supplied from the low-pressure steam line to bypass the low-pressure turbine, and the bypass valve is provided in each of the high-pressure bypass line and the low-pressure bypass line.

8. A method for operating a steam turbine power plant as described in claim 1, characterized in that the state in which the flow rate of main steam supplied from the main steam line exceeds the flow rate of main steam consumed by the steam turbine is caused by a trip of the steam turbine, and in the step of adjusting the valve opening, the opening rates of the bypass valve and the atmospheric release valve are adjusted so that the entire amount of steam supplied from the main steam line flows into the bypass line or the atmospheric release line.

9. A method for operating a steam turbine power plant as described in claim 1, characterized in that the state in which the flow rate of main steam supplied from the main steam line exceeds the flow rate of main steam consumed by the steam turbine is caused by a decrease in steam consumption by the steam turbine, and in the step of adjusting the valve opening, the opening rates of the bypass valve and the atmospheric release valve are adjusted so that the surplus steam obtained by subtracting the flow rate of steam supplied to the steam turbine from the flow rate of steam supplied from the main steam line flows into the bypass line or the atmospheric release line.

10. A method for operating a steam turbine power plant as described in claim 9, characterized in that the reduction in steam consumption is a load shedding state in which the generator driven by the steam turbine is disconnected, or a state of on-site isolated operation in which the electricity generated by the generator is consumed only within the business premises where the steam turbine power plant is installed.

11. A storage medium storing a computer program for operating a control device that controls the operation of the steam turbine power plant, wherein the computer program is configured to include a group of steps that executes the steam turbine power plant operation method described in any one of claims 1 to 10.

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