Steam turbine system, geothermal power generation plant, and method for operating steam turbine system

Abstract

The purpose of the present invention is to improve accuracy of estimating the clogging state of a nozzle even when steam is guided to a plurality of spaces. A steam turbine system (20) comprises: a steam pipe (7) through which steam jetted from a well flows; a steam turbine (8) having a nozzle to which the steam flowing through the steam pipe (7) is guided; a first steam pipe (21) that branches from the steam pipe (7) and guides steam to a first steam chamber (S1); a second steam pipe (22) that branches from the steam pipe (7) and guides steam to a second steam chamber (S2) having a smaller capacity than the first steam chamber (S1); a steam chamber communication valve (23) that adjusts the flow rate of the steam flowing through the second steam pipe (22); a flowmeter (18) that detects the flow rate of the steam flowing through the steam pipe (7); a pressure gauge that detects the pressure of the steam guided to the first steam chamber (S1); and a clogging state estimation unit that estimates the clogging state of the nozzle on the basis of the flow rate detected by the flowmeter (18), the pressure detected by the pressure gauge, and the opening degree of the steam chamber communication valve (23).

Description

Steam turbine system, geothermal power plant, and method of operating the steam turbine system

[0001] The present disclosure relates to a steam turbine system and a geothermal power plant, as well as a method of operating a steam turbine system.

[0002] In geothermal power plants, steam separated from geothermal fluid (mainly a mixture of steam and hot water) spouting from a well (production well) is introduced into a steam turbine to generate electricity. Some geothermal power plants have multiple steam chambers so that the inlet area of ​​the steam turbine can be adjusted depending on the amount of steam (see, for example, Patent Document 1). Patent Document 1 discloses a turbine having a main steam chamber and a sub-steam chamber.

[0003] JP 2016-75189 A

[0004] Steam separated from geothermal fluids spouting from a well contains impurities such as silica. This causes impurities to precipitate in the nozzles located upstream of the steam turbines installed in geothermal power plants. This narrows the nozzle opening area, potentially making it difficult for steam to enter the steam turbine. Furthermore, scale can cause airflow disturbances, potentially reducing turbine efficiency. Therefore, it is conceivable to determine the blockage status from the nozzle opening area.

[0005] The nozzle opening area (A1) can be calculated from the steam flow rate (G) introduced into the steam turbine, the pressure (P1) in the steam chest, and the temperature (T1) in the steam chest.

[0006] In a device having a main steam chamber and a sub-steam chamber, such as that disclosed in Patent Document 1, the sub-steam chamber may not be provided with a detection device such as a pressure gauge. In such cases, if the nozzle opening area is derived using the pressure in the main steam chamber, it may not be possible to accurately determine the nozzle blockage state.

[0007] The present disclosure has been made in consideration of the above circumstances, and aims to provide a steam turbine system, a geothermal power plant, and an operating method for a steam turbine system that can improve the accuracy of estimating the nozzle blockage status even when steam is guided to multiple spaces.

[0008] In order to solve the above problems, the present disclosure provides a steam turbine system, a geothermal power plant, and an operating method for a steam turbine system, including: a steam pipe through which steam separated from geothermal fluid blown out of a well flows; a steam turbine having a nozzle to which the steam flowing through the steam pipe is guided, the nozzle having a first nozzle portion and a second nozzle portion; a first steam pipe branching from the steam pipe and conducting the steam to the first nozzle portion; a second steam pipe branching from the steam pipe and conducting the steam to the second nozzle portion; a flow rate control valve adjusting a flow rate of steam flowing through the second steam pipe; a flow rate detection unit detecting the flow rate of steam flowing through the steam pipe; a pressure detection unit detecting the pressure of the steam guided to the first nozzle portion; and a blockage status estimation unit estimating a blockage status of the nozzle based on the flow rate detected by the flow rate detection unit, the pressure detected by the pressure detection unit, and an opening degree of the flow rate control valve.

[0009] According to one aspect of the present disclosure, there is provided a method for operating a steam turbine system, the steam turbine system comprising: a steam pipe through which steam separated from geothermal fluid spouted from a well flows; a steam turbine having a nozzle to which the steam flowing through the steam pipe is directed, the nozzle having a first nozzle portion and a second nozzle portion; a first steam pipe branching from the steam pipe and directing steam to the first nozzle portion; a second steam pipe branching from the steam pipe and directing steam to the second nozzle portion; and a flow control valve adjusting a flow rate of steam flowing through the second steam pipe, the method comprising: a flow rate detection step of detecting a flow rate of steam flowing through the steam pipe; a pressure detection step of detecting a pressure of the steam directed to the first nozzle portion or the steam directed to the first nozzle portion; and a blockage status estimation step of estimating a blockage status of the nozzle based on the flow rate detected in the flow rate detection step, the pressure detected in the pressure detection step, and an opening degree of the flow control valve.

[0010] According to the present disclosure, even when steam is guided to multiple spaces, it is possible to improve the accuracy of estimating the nozzle blockage state.

[0011] FIG. 1 is a diagram showing a schematic configuration of a geothermal power plant according to a first embodiment of the present disclosure. FIG. 2 is a longitudinal sectional view showing a main portion of a steam turbine according to a first embodiment of the present disclosure. FIG. 3 is a diagram showing a schematic configuration of a steam turbine system according to a first embodiment of the present disclosure. FIG. 4 is a diagram showing a schematic configuration of a steam turbine system according to a first embodiment of the present disclosure. FIG. 5 is a block diagram showing a control device according to a first embodiment of the present disclosure. FIG. 6 is a graph showing a relationship between an opening degree of a steam chest connecting valve and an opening area correction value in the steam turbine system according to the first embodiment of the present disclosure. FIG. 7 is a graph showing a change in the opening area of ​​a nozzle in the steam turbine system according to the first embodiment of the present disclosure. FIG. 8 is a graph explaining a method for determining a correction curve in the steam turbine system according to the first embodiment of the present disclosure using a mathematical formula. FIG. 9 is a diagram showing a schematic configuration of a steam turbine system according to a second embodiment of the present disclosure. FIG. 10 is a graph explaining a method for determining a correction curve in the steam turbine system according to the second embodiment of the present disclosure using a mathematical formula. FIG. 11 is a diagram showing a schematic configuration of a steam turbine system according to a third embodiment of the present disclosure.

[0012] [First embodiment] A first embodiment of a steam turbine system, a geothermal power plant, and an operating method of a steam turbine system according to the present disclosure will be described below with reference to the drawings. Note that the steam turbine system 20 can be widely applied to any geothermal power plant that generates electricity using geothermal fluid spouted from a well 2, and is not limited to application to only the geothermal power plant 1 having the configuration described below.

[0013] FIG. 1 is a diagram showing a schematic configuration of a geothermal power plant 1 equipped with a well control system according to a first embodiment of the present disclosure. In this embodiment, a case will be described in which a plurality of boreholes 2 are provided, for example, two boreholes 2 are provided. Note that the geothermal power plant 1 shown in FIG. 1 is a flash cycle type geothermal power plant. Also, in FIG. 1, for example, two boreholes 2, two steam-water separators 5, and one reinjection well 19 are provided, but the present disclosure can be applied as appropriate without being limited to the above configuration and the number of components.

[0014] 1, the geothermal power plant 1 according to this embodiment mainly comprises a geothermal fluid transport pipe 3, a steam flow control valve 4, a steam separator 5, a hot water pipe 6, a steam pipe 7, a steam turbine 8, a condenser 10, and a cooling tower 11. The steam pipe 7 and the steam turbine 8 are included in a steam turbine system, which will be described later.

[0015] The geothermal fluid transport pipe 3 is a pipe that guides geothermal fluid spouted from a borehole (geothermal well) 2 to a steam-water separator 5. A magma chamber is formed underground, and the heat from this magma heats rainwater that seeps underground and groundwater that flows in, forming a geothermal reservoir. Geothermal fluid accumulates in the geothermal reservoir and is extracted to the surface via the borehole 2. The geothermal fluid transport pipe 3 transports the geothermal fluid from the geothermal reservoir to the steam-water separator 5 via the borehole 2. Note that geothermal fluid is a two-phase mixture fluid that mainly consists of steam (gas) and hot water (liquid).

[0016] The steam flow control valve 4 is installed on the geothermal fluid transport pipe 3 and adjusts the total flow rate (the steam volume, the total flow rate of steam and hot water) of the geothermal fluid flowing from the borehole 2 into the steam-water separator 5.

[0017] In addition, an opening / closing valve 13 may be provided upstream of the geothermal fluid flow on the geothermal fluid transport pipe 3 (upstream of the steam flow control valve 4, for example, near the outlet of the borehole 2) to control the conduction state (conduction state or non-conduction state) of the geothermal fluid.

[0018] The steam-water separator 5 is a device (separator) that separates the geothermal fluid, which is a two-phase mixed fluid supplied through the geothermal fluid transport pipe 3, into steam and hot water. The hot water separated by the steam-water separator 5 is guided to a hot water pipe 6, and the steam separated by the steam separator 5 is guided to a steam pipe 7.

[0019] The hot water pipes 6 are pipes that guide the hot water separated by the steam-water separators 5 to the reinjection wells 19. Returning the hot water to the underground geothermal reservoir via the reinjection wells 19 prevents the depletion of geothermal fluid in the underground geothermal reservoir. The hot water separated by each steam-water separator 5 may be pumped to the reinjection wells 19 using a pump 14.

[0020] The steam pipe 7 is a pipe that guides the steam separated by the steam-water separators 5 to the steam turbine 8. The steam separated by each steam-water separator 5 is joined in the steam pipe 7 and supplied to the steam turbine 8. The flow rate of the steam sent to the steam turbine 8 is measured by a flow meter 18 provided on the steam pipe 7. In this embodiment, the case where the flow rate (total flow rate) of the steam separated by each steam-water separator 5 after joining is described, but the flow rate of the steam separated by each steam-water separator 5 may be measured individually. In addition, a flow control valve 15 may be provided in the steam pipe 7 for the steam separated by each steam-water separator 5 after joining, to control the flow rate of steam supplied to the steam turbine 8.

[0021] The condenser 10 is a device that condenses and condenses the steam that has completed its work of rotating the rotor blades 8d (see FIG. 3) in the steam turbine 8 by cooling it with cooling water. The condensed hot water is supplied to a cooling tower 11.

[0022] The cooling tower 11 is a device that evaporatively cools the hot water condensed in the condenser 10. Specifically, the hot water supplied to the cooling tower 11 is sprayed from a spray unit at the top of the cooling tower 11. A portion of the sprayed hot water evaporates when it comes into contact with air circulated by the cooling tower 11's fan, and the latent heat associated with this evaporation cools the remaining hot water to form water. The cooled water is stored in the cooling tower 11 as cooling tower water. The cooling tower water stored in the cooling tower 11 is supplied to the condenser 10 as cooling water via a pump 12.

[0023] Next, the steam turbine 8 will be described with reference to Figures 2 to 4. Note that, for illustrative purposes, the stator blades 8c are omitted in Figure 3. As shown in Figures 2 and 3, the steam turbine 8 has a housing 8a having an internal space, a shaft 8b penetrating the housing 8a, stator blades 8c provided inside the housing 8a and fixed to the inner circumferential surface of the housing 8a, and rotor blades 8d provided inside the housing 8a and attached to the outer circumferential surface of the shaft 8b. In the steam turbine 8, steam supplied through a steam pipe 7 is introduced via a nozzle into the space formed between the housing 8a and the shaft 8b. The energy of the steam flowing through the space drives the rotor blades 8d and the shaft 8b to rotate, which in turn drives a generator 9 (see Figure 1) connected to the shaft 8b to generate electricity.

[0024] The shaft portion 8b extends linearly in a predetermined direction and rotates around a central axis that also extends in the predetermined direction.

[0025] A plurality of stator vanes 8c are provided. The plurality of stator vanes 8c are arranged side by side at predetermined intervals along a predetermined direction. For example, the plurality of stator vanes 8c are fixed to the inner peripheral surface of the housing 8a. The plurality of stator vanes 8c are arranged side by side at predetermined intervals along the circumferential direction. A nozzle refers to a flow path (opening) formed between two adjacent stator vanes 8c belonging to the stator vanes 8c on the most upstream side in the steam flow direction, for example, and a plurality of nozzles are provided. The plurality of nozzles are arranged side by side at predetermined intervals along the circumferential direction.

[0026] A plurality of rotor blades 8d are provided. The rotor blades 8d are arranged in a row at predetermined intervals along a predetermined direction. Each rotor blade 8d has a plurality of blades arranged in a row in the circumferential direction on the outer circumferential surface of the shaft portion 8b. The stator blades 8c and the rotor blades 8d are arranged alternately in a row in the predetermined direction.

[0027] A plurality of steam chambers (two in this embodiment, for example) are formed upstream of the plurality of nozzles.

[0028] As shown in Fig. 4, the multiple steam chambers include a first steam chamber S1 and a second steam chamber S2 that are arranged circumferentially around the central axis of the shaft portion 8b of the steam turbine 8. The first steam chamber S1 and the second steam chamber S2 are separated by two partition walls 8e that are spaced apart in the circumferential direction. The first steam chamber S1 and the second steam chamber S2 are formed upstream of the nozzles. The multiple nozzles include a first nozzle portion that is connected to the first steam chamber S1 and through which steam is guided from the first steam chamber S1, and a second nozzle portion that is connected to the second steam chamber S2 and through which steam is guided from the second steam chamber S2.

[0029] The opening area of ​​the nozzle (first nozzle portion) connected to the first steam chamber S1 (if there are multiple first nozzle portions, the sum of the opening areas of the multiple first nozzle portions) is larger than the opening area of ​​the nozzle (second nozzle portion) connected to the second steam chamber S2 (if there are multiple second nozzle portions, the sum of the opening areas of the multiple second nozzle portions). If the sum of the nozzle opening areas is 100%, for example, the opening area of ​​the first nozzle portion is approximately 70% to 80% of the total, and the opening area of ​​the second nozzle portion is approximately 20% to 30% of the total. Note that the proportion of the opening area of ​​each nozzle portion is not limited to this and may be set to any proportion.

[0030] Next, a detailed description will be given of the steam turbine system 20 according to this embodiment. As shown in Figures 3 and 4, the steam turbine system 20 includes a steam pipe 7 through which steam separated from geothermal fluid spouted from the well 2 (see Figure 1) flows, and a steam turbine 8 having a nozzle through which the steam flowing through the steam pipe 7 is guided. The steam turbine system 20 also includes a first steam pipe 21 that branches off from the downstream end of the steam pipe 7 and guides steam to a first steam chamber S1, and a second steam pipe 22 that branches off from the downstream end of the steam pipe 7 and guides steam to a second steam chamber S2. The steam turbine system 20 also includes a steam chest connecting valve (flow rate control valve) 23 that adjusts the flow rate of steam flowing through the second steam pipe 22, a flow meter (flow rate detection unit) 18 that detects the flow rate of steam flowing through the steam pipe 7, a pressure gauge (pressure detection unit) 25 that detects the pressure of the steam led to the first steam chest S1 (in other words, the steam in the first steam chest S1), and a thermometer 26 that detects the temperature of the steam led to the first steam chest S1 (in other words, the steam in the first steam chest S1). The steam turbine system 20 also includes a control device 30 that receives measurement results from the flow meter 18 and the pressure gauge 25 and adjusts the opening degree of the steam chest connecting valve 23.

[0031] In the geothermal power plant 1 of this embodiment, when the steam flow rate supplied to the steam turbine 8 decreases due to, for example, attenuation of geothermal fluid, additional drilling of wells, maintenance, or the like, or when the steam flow rate flowing into the steam turbine 8 decreases due to a reduction in the nozzle opening area caused by scale, the output of the steam turbine 8 (i.e., the amount of power generated by the generator 9) decreases and falls below a specified threshold, the steam chest connection valve 23 is opened (with an opening corresponding to the amount of decrease in output) and the second steam chest S2 is partially used. By operating in this manner, the geothermal power plant 1 can maintain a stable output.

[0032] As shown in Fig. 5, the control device 30 has a blockage situation estimation unit 31 and a cleaning necessity determination unit 32. The control device 30 receives information measured by various devices from the flow meter 18, the pressure gauge 25, and the thermometer 26. The control device 30 also transmits and receives signals related to the opening degree to and from the steam chest connection valve 23, and controls the opening degree of the steam chest connection valve 23. The opening degree of the steam chest connection valve 23 may also be manually operated by an operator. In this case, the information measured by the various devices from the flow meter 18, the pressure gauge 25, and the thermometer 26 is output to a display or the like, and the operator checks the output information and operates the opening degree of the steam chest connection valve 23.

[0033] The control device 30 (Controller) includes, for example, a CPU (Central Processing Unit: Processor), a main memory, and a secondary storage. The control device 30 may also include a communication unit for transmitting and receiving information to and from other devices. The main memory is composed of, for example, a writable memory such as a cache memory or a RAM (Random Access Memory), and is used as a working area for reading the CPU's execution program and writing data processed by the execution program. The secondary storage is a non-transitory computer-readable storage medium. The secondary storage is, for example, a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, etc. For example, a series of processes for realizing various functions is stored in the form of a program in a secondary storage device, and the CPU reads this program into the main storage device and executes information processing and arithmetic operations to realize various functions. Note that the program may be pre-installed in the secondary storage device, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Examples of computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

[0034] The clogging condition estimation unit 31 estimates the clogging condition of the nozzle based on the flow rate detected by the flow meter 18, the pressure detected by the pressure gauge 25, and the opening degree of the steam chest connection valve 23. Specifically, the clogging condition estimation unit 31 estimates the clogging condition of the nozzle by correcting data obtained based on the flow rate detected by the flow meter 18 and the pressure detected by the pressure gauge 25 based on the opening degree of the steam chest connection valve 23. The clogging condition estimation unit 31 estimates the clogging condition of the nozzle when steam is being guided to the second steam chest S2 via the second steam pipe 22. Note that the clogging condition of the nozzle may be derived based on, for example, a change in the nozzle opening area (hereinafter referred to as the "nozzle opening ratio"). The nozzle opening ratio may be the ratio of the current nozzle opening area to the nozzle opening area in a predetermined state (e.g., a state before the steam turbine system 20 starts operating or a state immediately after cleaning) set to 100%.

[0035] The cleaning necessity determining unit 32 determines whether or not to clean the nozzle based on the clogged state of the nozzle estimated by the clogged state estimating unit 31. The cleaning necessity determining unit 32 may determine to clean the nozzle when the nozzle opening rate estimated by the clogged state estimating unit 31 is equal to or less than a predetermined threshold. Note that the final decision on whether or not to clean the nozzle may be made by an operator. In this case, the cleaning necessity determining unit 32 outputs the decision on whether or not to clean on a display or the like, and the operator confirms the output decision and makes the final decision on whether or not to clean the nozzle.

[0036] Next, a method for estimating the nozzle clogging state by the clogging state estimation unit 31 will be described. The steam separated from the geothermal fluid spouting from the well 2 contains impurities such as silica. As a result, the impurities precipitate in the nozzle provided upstream of the steam turbine 8 provided in the geothermal power plant 1. This narrows the opening area of ​​the nozzle (i.e., the nozzle becomes clogged).

[0037] The nozzle clogging status can be estimated by estimating the nozzle opening area based on the current operating state of the steam turbine 8. The nozzle opening area (A1) can be derived from the steam flow rate (G) guided to the steam turbine 8, the pressure (P1) of the first steam chamber S1, and the temperature (T1) of the first steam chamber S1. In the case of a geothermal power plant 1, the temperature of the first steam chamber S1 changes little, so the nozzle opening area (A1) can be simply calculated from the ratio (P1) of the steam flow rate (G) to the pressure of the first steam chamber S1 (hereinafter referred to as the "G / P ratio") without considering the temperature of the first steam chamber S1. In this simplified calculation, the nozzle opening area (A1) can be calculated using the following equation (1). In equation (1), c(T) is a proportionality constant that can be derived from the measured temperature. In the case of a geothermal power plant, the steam chamber temperature changes little and the proportionality constant c(T) has little temperature dependency, so the proportionality constant c(T) may be a fixed value.

[0038] A1=c(T)×G / P1 (1)

[0039] In the case of a structure in which the second steam chamber S2 is not provided with a pressure gauge and steam is supplied to both the first steam chamber S1 and the second steam chamber S2, as in this embodiment, if the opening area is estimated solely based on the G / P ratio based on the first steam chamber S1, it will be affected by the opening area of ​​the second steam chamber S2, which could result in a loss of consistency in the estimation standard (based on the first steam chamber S1) and a decrease in accuracy. Specifically, as shown by the dashed line in Figure 7, a value larger than the actual opening area is calculated depending on the opening degree of the steam chamber connection valve 23.

[0040] Generally, the apparent opening area increases as the opening degree of the steam chest connection valve 23 increases, but the degree of this increase is uniquely determined by the opening degree of the steam chest connection valve 23. For this reason, the control device 30 of this embodiment corrects the calculated value of the opening area obtained based on the flow rate detected by the flow meter 18 (i.e., the steam flow rate (G)) and the pressure detected by the pressure gauge 25 (i.e., the pressure (P1) of the first steam chest S1) in accordance with the opening degree of the steam chest connection valve 23, thereby eliminating the influence of the opening area of ​​the second steam chest S2, and maintaining consistency in the estimation criteria, making it possible to more accurately estimate the nozzle clogging state.

[0041] The memory unit of the control device 30 stores a correction curve (see FIG. 6 ) that defines the relationship between the opening of the steam chest connection valve 23 and the correction value for the opening area, and determines a correction value corresponding to the opening of the steam chest connection valve 23 based on the correction curve. The calculated nozzle opening area is corrected using the determined correction value. In this embodiment, the correction value increases as the opening of the steam chest connection valve 23 increases.

[0042] Specifically, when the opening degree of the steam chest connection valve 23 is 50%, it is derived from the correction curve that the correction value is C1, as shown in Fig. 6. In this case, the nozzle opening area (i.e., the blocked state) is estimated by subtracting C1 from the calculated nozzle opening area, as shown in Fig. 7. Similarly, when the opening degree of the steam chest connection valve 23 is 100%, it is derived from the correction curve that the correction value is C2, as shown in Fig. 6. In this case, the nozzle opening area (i.e., the blocked state) is estimated by subtracting C2 from the calculated nozzle opening area, as shown in Fig. 7.

[0043] In this embodiment, the correction is described using the estimation standard (i.e., first steam chamber S1 standard) when the steam chamber connection valve 23 is at 0% opening (i.e., fully closed), but the estimation standard may also be when the steam chamber connection valve 23 is at 100% opening (i.e., fully open) (i.e., first steam chamber S1 + second steam chamber S2 standard), or a predetermined intermediate opening may be used as the estimation standard. Which opening is used as the estimation standard is arbitrary and is determined depending on the geothermal power plant 1.

[0044] The correction curve may be determined, for example, by learning from operational data. For example, calculated values ​​of the opening degree and opening area of ​​the steam chest connection valve 23 are recorded during actual operation, and the correction curve can be determined from changes in the calculated value of the opening area according to the opening degree of the steam chest connection valve 23. If this method is performed over a period that is sufficiently short compared to the rate of scale growth (for example, acquired within one hour), the correction curve can be determined without being affected by changes in the opening area due to scale.

[0045] Also, the change in the calculated value of the opening area when the steam chest connection valve 23 is operated to an open position (for example, the change in the calculated value of the opening area when the valve is operated from 50% to 100%) may be recorded, and the correction curve may be determined by learning from this data set. With this method, the correction curve can be determined more accurately because it can be determined from data over a relatively long period of time, such as when scale grows.

[0046] Depending on the operating history up to that point, the degree of scale deposition in the nozzles of the first steam chamber S1 and the second steam chamber S2 may differ (for example, when the steam chamber connecting valve 23 is operated in an open state after having been operated in a fully closed state for a long period of time, etc.).

[0047] Next, a method for cleaning the nozzle of the steam turbine 8 will be described. The cleaning necessity determining unit 32 determines whether or not the nozzle needs to be cleaned based on the blockage state estimated by the blockage state estimating unit 31. If the cleaning necessity determining unit 32 determines that the nozzle needs to be cleaned, the nozzle is cleaned. The nozzle cleaning method is not particularly limited, and examples of the nozzle cleaning method include online cleaning and open cleaning.

[0048] Online cleaning is a method in which cleaning is performed automatically by issuing a command to the geothermal power plant 1, and scale adhering to the nozzles, etc. is dissolved and removed by supplying a cleaning liquid (for example, water or an aqueous sodium hydroxide solution) to the steam turbine 8 from a water supply line (not shown) connected to the steam pipes 7, etc., upstream of the steam turbine 8. Open cleaning is a method in which the steam turbine 8 is opened and scale adhering to the nozzles, etc. is removed manually.

[0049] This embodiment has the following advantageous effects: In this embodiment, the blockage condition estimation unit 31 estimates the blockage condition of the nozzle based on the flow rate detected by the flow meter 18, the pressure detected by the pressure gauge 25, and the opening degree of the steam chest connection valve 23. By estimating the blockage condition based on the opening degree of the steam chest connection valve 23 in this way, it is possible to improve the accuracy of estimating the blockage condition of the nozzle even when steam is guided to the second steam chest S2 via the steam chest connection valve 23.

[0050] Furthermore, in this embodiment, even when steam is guided to the second steam chamber S2, it is possible to estimate the nozzle blockage state without detecting the pressure of the steam flowing through the second steam pipe 22. Therefore, there is no need to provide a device for detecting the pressure of the steam flowing through the second steam pipe 22, and the number of parts can be reduced. This makes installation easier and reduces costs.

[0051] In this embodiment, the blockage condition estimation unit 31 performs correction based on the opening degree of the steam chest communication valve 23. This makes it possible to more accurately estimate the blockage condition of the nozzle even when steam is guided to the second steam chest S2 via the steam chest communication valve 23.

[0052] Furthermore, in this embodiment, even when steam is guided to the first steam chamber S1 and the second steam chamber S2, it is possible to estimate the nozzle blockage state. Also, the number of parts can be reduced.

[0053] In this embodiment, the blockage state estimation unit 31 estimates the blockage state of the nozzle when the second steam pipe 22 leads to the second steam chamber S2. This makes it possible to accurately estimate the blockage state of the nozzle even when steam is led to the second steam chamber S2 via the steam chamber connection valve 23.

[0054] In addition, this embodiment includes a cleaning necessity determining unit 32 that determines whether or not to clean the nozzle, thereby making it possible to determine whether or not to clean the nozzle depending on the clogging state.

[0055] [Modification] In the first embodiment, an example has been described in which the correction curve is determined by learning from driving data, but the correction curve may also be determined by a mathematical formula. A method of determining the correction curve by a mathematical formula will be described below (see also FIG. 8).

[0056] As described above, the following equations (2) and (3) hold when the proportionality constant is c.

[0057] A1 = c × G1 / P1 (2) A2 = c × G2 / P2 (3) A1 is the opening area of ​​the nozzle corresponding to the first steam chamber S1 A2 is the opening area of ​​the nozzle corresponding to the second steam chamber S2 P1 is the pressure of the first steam chamber S1 P2 is the pressure of the second steam chamber S2 G1 is the steam flow rate led to the first steam chamber S1 G2 is the steam flow rate led to the second steam chamber S2

[0058] Furthermore, the steam chest connection valve 23 has a Cv value, which is the capacity coefficient of the valve, determined according to the opening degree (X), and based on this, the following equation (4) is established: Note that a in equation (4) is an arbitrary coefficient.

[0059]

[0060] When P2 is eliminated from equation (5), the following equation (5) is established.

[0061]

[0062] On the other hand, the flow rate actually measured by the flow meter 18 is G0 = G1 + G2, and the apparent opening area (A0) calculated from this can be found by the following formula (6): G0 is the flow rate of steam flowing through the steam pipe 7.

[0063]

[0064] That is, the corrected area (the difference between the apparent opening area A0 and the nozzle opening area A1 of the first steam chamber S1) is calculated by the following equation (7).

[0065] In this case, an error occurs by the nozzle opening area A2 of the second steam chamber S2, but since the ratio of the nozzle opening area A2 of the second steam chamber S2 to the nozzle opening area A1 of the first steam chamber S1 is small, and furthermore, the steam introduced into the second steam chamber S2 is depressurized by the steam chamber connecting valve 23, the effect on the output of the steam turbine 8 is sufficiently small and does not have a significant practical effect on estimating the nozzle blockage status.

[0066] Second Embodiment Next, a second embodiment of the present disclosure will be described with reference to Figures 9 and 10. This embodiment differs from the first embodiment in that the steam chamber is divided into three steam chambers. Accordingly, this embodiment also differs from the first embodiment in that a third steam pipe 43 is provided to guide steam to the third steam chamber S3. Since the other points are the same as those of the first embodiment, in the following description, the same components are designated by the same reference numerals and detailed description thereof will be omitted.

[0067] 9 , a steam turbine system 120 of this embodiment includes a first steam pipe 21 that branches off from the downstream end of the steam pipe 7 and leads steam to a first steam chamber S1, a second steam pipe 22 that branches off from the downstream end of the steam pipe 7 and leads steam to a second steam chamber S2, and a third steam pipe 43 that branches off from the downstream end of the steam pipe 7 and leads steam to a third steam chamber S3. The steam turbine system 120 also includes a steam chamber connection valve 23 that adjusts the flow rate of steam flowing through the second steam pipe 22, and a steam chamber connection valve 44 that adjusts the flow rate of steam flowing through the third steam pipe 43.

[0068] The multiple steam chambers include a first steam chamber S1, a second steam chamber S2, and a third steam chamber S3, which are arranged circumferentially around the central axis of the shaft 8b of the steam turbine 8. The capacity of the first steam chamber S1 is larger than the capacity of the second steam chamber S2. The capacity of the second steam chamber S2 is larger than the capacity of the third steam chamber S3. For example, if the capacity of the entire steam chamber is 100%, the capacity of the first steam chamber S1 is approximately 70%, the capacity of the second steam chamber S2 is approximately 20%, and the capacity of the third steam chamber S3 is approximately 10%. The ratio of the capacities of the steam chambers is not limited to this and may be set to any ratio.

[0069] In this embodiment, a method for determining the correction curve by a mathematical formula will be described (see also FIG. 10).

[0070] As described above, when the proportionality constant is c, the following equations (8), (9), and (10) hold.

[0071] A1 = c × G1 / P1 (8) A2 = c × G2 / P2 (9) A3 = c × G3 / P3 (10) A1 is the opening area of ​​the nozzle corresponding to the first steam chamber S1 A2 is the opening area of ​​the nozzle corresponding to the second steam chamber S2 A3 is the opening area of ​​the nozzle corresponding to the third steam chamber S3 P1 is the pressure of the first steam chamber S1 P2 is the pressure of the second steam chamber S2 P3 is the pressure of the third steam chamber S3 G1 is the steam flow rate led to the first steam chamber S1 G2 is the steam flow rate led to the second steam chamber S2 G3 is the steam flow rate led to the third steam chamber S3

[0072] Furthermore, if the Cv value of the steam chest connection valve 23 is Cv2 and the Cv value of the steam chest connection valve 44 is Cv3, the following equations (11) and (12) hold: Note that a in equations (11) and (12) is an arbitrary coefficient.

[0073]

[0074]

[0075] On the other hand, the actually measured flow rate is G0 = G1 + G2 + G3, and the apparent opening area (A0) calculated from this is found by the following formula (13): G0 is the flow rate of steam flowing through the steam pipe 7.

[0076] That is, the corrected area is calculated by the following formula (14): The corrected area is a linear sum of the correction terms for the second steam chamber S2 and the third steam chamber S3.

[0077]

[0078] Similarly, when the steam chamber is divided into three or more sections, the correction factor is a linear sum of the correction terms for the valves provided in the pipes that lead steam to chambers other than the first steam chamber S1.

[0079] In this way, even when the steam chamber is divided into three or more sections, the same effect as in the first embodiment can be achieved by making corrections based on the opening degrees of the steam chamber communication valves.

[0080] Third Embodiment Next, a third embodiment of the present disclosure will be described with reference to Fig. 11. This embodiment differs from the first embodiment in that the steam chamber is not divided in the circumferential direction and the position at which the second steam pipe 52 is connected is different. Since the other points are the same as those of the first embodiment, in the following description, the same components are denoted by the same reference numerals and detailed description thereof will be omitted.

[0081] In the steam turbine system 220 of this embodiment, the steam chest is not divided in the circumferential direction. The first steam pipe 21 is connected to the undivided steam chest. As shown in FIG. 11 , the second steam pipe 52 is connected to a second nozzle section (i.e., an opening formed between the stator vanes 8 c located downstream of the first nozzle section), which is a nozzle located most upstream (i.e., an opening formed between the stator vanes 8 c located downstream of the first nozzle section). The second steam pipe 52 is provided with a steam chest connection valve 54 that adjusts the flow rate of steam flowing through the second steam pipe 52. The steam turbine system 220 also includes a pressure gauge (pressure detection section) 55 that detects the pressure of steam flowing through the second steam pipe 52 and a thermometer 56 that detects the temperature of steam flowing through the second steam pipe 52.

[0082] In this embodiment, a method for determining the correction curve using a mathematical formula will be described.

[0083] As described above, the following equations (15) and (16) hold when the proportionality constant is c.

[0084] A1=c×G1 / P1 (15) A1 is the opening area of ​​the nozzle (first nozzle portion) corresponding to the first steam chamber S1.

[0085]

[0086] On the other hand, the flow rate actually measured by the flow meter 18 is G0 = G1 + G2, and the apparent opening area (A0) calculated from this is found by the following formula (17). Note that G0 is the flow rate of steam flowing through the steam pipe 7.

[0087]

[0088] That is, the corrected area is calculated by the following equation (18). If the pressure gauge 55 is not provided, the pressure ratio before and after the most upstream moving blade 8d in the steam flow direction, which is preset at the time of construction, may be used for P2 / P1.

[0089] In this embodiment, too, the same effects as in the first embodiment can be achieved by making corrections based on the opening degree of the steam chamber communication valve.

[0090] The present disclosure is not limited to the above-described embodiments and may be modified as appropriate without departing from the spirit and scope of the present disclosure. For example, in the above-described embodiments, the pressure gauge 25 and the thermometer 26 are provided in the first steam chamber S1, but the present disclosure is not limited thereto. For example, the pressure gauge 25 and the thermometer 26 may be provided in the first steam pipe 21.

[0091] The steam turbine system, the geothermal power plant, and the method of operating the steam turbine system described in the above-described embodiments can be understood, for example, as follows: A steam turbine system according to a first aspect of the present disclosure includes a steam pipe (7) through which steam separated from geothermal fluid spouted from a borehole (2) flows, a steam turbine (8) having a nozzle to which the steam flowing through the steam pipe (7) is guided and which has a first nozzle portion and a second nozzle portion, a first steam pipe (21) branching from the steam pipe (7) and guiding the steam to the first nozzle portion (8c), and a second steam pipe (22) branching from the steam pipe (7) and guiding the steam to the second nozzle portion (8c), The system includes a flow rate control valve (23) that controls the flow rate of steam flowing through the second steam pipe (22), a flow rate detection unit (18) that detects the flow rate of steam flowing through the steam pipe (7), a pressure detection unit (25) that detects the pressure of steam guided to the first nozzle unit, and a blockage situation estimation unit (31) that estimates the blockage situation of the nozzle (8 c) based on the flow rate detected by the flow rate detection unit (18), the pressure detected by the pressure detection unit (25), and the opening degree of the flow rate control valve (23).

[0092] In the above configuration, the blockage state estimation unit estimates the blockage state of the nozzle based on the flow rate detected by the flow rate detection unit, the pressure detected by the pressure detection unit, and the aperture of the flow rate control valve. In this way, by estimating the blockage state based on the aperture of the flow rate control valve, it is possible to improve the accuracy of estimating the blockage state of the nozzle even when steam is guided to the second turbine section via the flow rate control valve.

[0093] Furthermore, with the above configuration, even when steam is guided to the second turbine section, it is possible to estimate the nozzle blockage state without detecting the pressure of the steam flowing through the second steam pipe. Therefore, since there is no need to provide a device for detecting the pressure of the steam flowing through the second steam pipe, the number of parts can be reduced, and therefore costs can be reduced.

[0094] In addition, for example, when the nozzle has a plurality of blades arranged side by side at a predetermined interval in the circumferential direction, the nozzle clogging state may be derived based on the aperture ratio of the gaps formed between the plurality of blades (hereinafter referred to as the "nozzle aperture ratio"). The nozzle aperture ratio may be the ratio of the current nozzle aperture area to the nozzle aperture area in a predetermined state (e.g., a state before the steam turbine system starts operating or a state immediately after cleaning) set to 100%.

[0095] In addition, in a steam turbine system according to a second aspect of the present disclosure, in the first aspect, the blockage situation estimation unit (31) estimates the blockage situation of the nozzle (8 c) by correcting data obtained based on the flow rate detected by the flow rate detection unit (18) and the pressure detected by the pressure detection unit (25) based on the opening degree of the flow rate control valve (23).

[0096] In the above configuration, the clogging state estimation unit performs correction based on the opening degree of the flow rate adjustment valve, thereby making it possible to more accurately estimate the clogging state of the nozzle even when steam is guided to the second space via the flow rate adjustment valve.

[0097] In addition, a steam turbine system according to a third aspect of the present disclosure is the first or second aspect, wherein the steam turbine (8) has a first steam chamber (S1) that guides steam to the first nozzle section (8c) and a second steam chamber (S2) that guides steam to the second nozzle section, and the first steam chamber (S1) and the second steam chamber (S2) are arranged side by side in a circumferential direction around a central axis of the steam turbine (8).

[0098] With the above configuration, even when steam is guided to the first steam chamber and the second steam chamber, it is possible to estimate the clogging state of the nozzle, and the number of parts can be reduced.

[0099] In addition, in a steam turbine system according to a fourth aspect of the present disclosure, in any of the first to third aspects, the blockage situation estimation unit (31) estimates a blockage situation of the nozzle (8 c) when the second steam pipe (22) is guiding steam to the second nozzle section.

[0100] In the above configuration, the blockage state estimation unit estimates the blockage state of the nozzle when the second steam pipe leads to the second turbine section, thereby making it possible to accurately estimate the blockage state of the nozzle even when steam is led to the second turbine section via a flow control valve.

[0101] Furthermore, a steam turbine system according to a fifth aspect of the present disclosure is any one of the first to fourth aspects, and further includes a cleaning necessity determination unit (32) that determines whether or not to clean the nozzle (8c) based on the blockage state estimated by the blockage state estimation unit (31).

[0102] The above-described configuration includes a cleaning necessity determining unit that determines whether or not to clean the nozzle, thereby making it possible to determine whether or not to clean the nozzle depending on the clogging state.

[0103] In addition, in a steam turbine system according to a sixth aspect of the present disclosure, in the fifth aspect, the blockage situation estimation unit (31) estimates an opening rate of the nozzle (8 c) and estimates a blockage situation based on the opening rate, and the cleaning necessity determination unit (32) determines to clean the nozzle (8 c) when the opening rate of the nozzle (8 c) estimated by the blockage situation estimation unit (31) is equal to or lower than a predetermined threshold value.

[0104] In the above configuration, the cleaning necessity determining unit determines to clean the nozzle when the nozzle opening rate estimated by the blockage state estimating unit is equal to or less than a predetermined threshold, thereby enabling a more accurate determination of whether to clean the nozzle.

[0105] In addition, a geothermal power plant according to a first aspect of the present disclosure includes a steam turbine system (20) described in any one of the first to sixth aspects, a well from which steam is ejected and led to the steam turbine system (20), and a generator that generates electricity using the driving force of the steam turbine system (20).

[0106] A method for operating a steam turbine system according to a first aspect of the present disclosure is a method for operating a steam turbine system (20), the steam turbine system (20) including: a steam pipe (7) through which steam separated from geothermal fluid spouted from a well (2) flows; a steam turbine (8) having a nozzle to which the steam flowing through the steam pipe (7) is guided, the nozzle having a first nozzle portion and a second nozzle portion; a first steam pipe (21) branching off from the steam pipe (7) and guiding steam to the first nozzle portion (8c); a second steam pipe (22) that guides steam to the first nozzle section (8c), and a flow rate control valve (23) that adjusts the flow rate of steam flowing through the second steam pipe (22), and the system includes a flow rate detection step that detects the flow rate of steam flowing through the steam pipe (7), a pressure detection step that detects the pressure of the steam guided to the first nozzle section or the steam guided to the first nozzle section, and a blockage status estimation step that estimates the blockage status of the nozzle (8c) based on the flow rate detected in the flow rate detection step, the pressure detected in the pressure detection step, and the opening of the flow rate control valve (23).

[0107] REFERENCE SIGNS LIST 1: Geothermal power plant 2: Well 3: Geothermal fluid transport pipe 4: Steam flow control valve 5: Steam-water separator 6: Hot water pipe 7: Steam pipe 8: Steam turbine 8a: Housing 8b: Shaft 8c: Stationary blade 8d: Rotating blade 8e: Bulkhead 9: Generator 10: Condenser 11: Cooling tower 12: Pump 13: On-off valve 14: Pump 15: Flow control valve 18: Flow meter 19: Reinjection well 20: Steam turbine system 21: First steam pipe 22: Second steam pipe 23: Steam chest connecting valve (flow control valve) 25: Pressure gauge (pressure detection unit) 26: Thermometer 30: Control device 31: Blockage status estimation unit 32: Cleaning necessity determination unit 43 : Third steam pipe 44 : Steam chest connecting valve 52 : Second steam pipe 54 : Steam chest connecting valve 55 : Pressure gauge (pressure detection unit) 56 : Thermometer 120 : Steam turbine system 220 : Steam turbine system S1 : First steam chest S2 : Second steam chest S3 : Third steam chest

Claims

1. A steam turbine system comprising: a steam pipe through which steam separated from geothermal fluid sprayed from a borehole flows; a steam turbine having a nozzle to which the steam flowing through the steam pipe is guided, the nozzle having a first nozzle section and a second nozzle section; a first steam pipe branching off from the steam pipe and directing steam to the first nozzle section; a second steam pipe branching off from the steam pipe and directing steam to the second nozzle section; a flow control valve adjusting the flow rate of steam flowing through the second steam pipe; a flow detection unit detecting the flow rate of steam flowing through the steam pipe; a pressure detection unit detecting the pressure of steam guided to the first nozzle section; and a blockage condition estimation unit estimating a blockage condition of the nozzle based on the flow rate detected by the flow detection unit, the pressure detected by the pressure detection unit, and the opening degree of the flow control valve.

2. A steam turbine system as described in claim 1, wherein the blockage condition estimation unit estimates the blockage condition of the nozzle by correcting data obtained based on the flow rate detected by the flow rate detection unit and the pressure detected by the pressure detection unit based on the opening degree of the flow control valve.

3. A steam turbine system as described in claim 1, wherein the steam turbine has a first steam chamber that guides steam to the first nozzle section and a second steam chamber that guides steam to the second nozzle section, and the first steam chamber and the second steam chamber are arranged side by side in a circumferential direction about a central axis of the steam turbine.

4. A steam turbine system according to claim 1, wherein the blockage state estimation unit estimates a blockage state of the nozzle when the second steam pipe is conducting steam to the second nozzle portion.

5. A steam turbine system according to claim 1, further comprising a cleaning necessity determining section which determines whether or not to clean said nozzle based on the clogging condition estimated by said clogging condition estimating section.

6. A steam turbine system as described in claim 5, wherein the clogging condition estimation unit estimates an opening rate of the nozzle and estimates a clogging condition based on the opening rate, and the cleaning necessity determination unit decides to clean the nozzle when the opening rate of the nozzle estimated by the clogging condition estimation unit falls below a predetermined threshold value.

7. A geothermal power plant comprising: a steam turbine system according to any one of claims 1 to 6; a well from which steam directed to said steam turbine system is ejected; and a generator which generates electric power using the driving force of said steam turbine system.

8. A method for operating a steam turbine system, the steam turbine system comprising: a steam pipe through which steam separated from geothermal fluid spouted from a well flows; a steam turbine having a nozzle to which the steam flowing through the steam pipe is guided, the nozzle having a first nozzle section and a second nozzle section; a first steam pipe branching off from the steam pipe and directing steam to the first nozzle section; a second steam pipe branching off from the steam pipe and directing steam to the second nozzle section; and a flow control valve adjusting the flow rate of steam flowing through the second steam pipe, the method comprising: a flow rate detection step for detecting the flow rate of steam flowing through the steam pipe; a pressure detection step for detecting the pressure of the steam guided to the first nozzle section or the steam guided to the first nozzle section; and a blockage condition estimation step for estimating a blockage condition of the nozzle based on the flow rate detected in the flow rate detection step, the pressure detected in the pressure detection step, and an opening degree of the flow control valve.

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