A system and method for monitoring steam turbine exhaust dryness based on circulating cooling water

Abstract

The present invention discloses a system and method for monitoring the exhaust steam dryness of the last stage of a steam turbine based on circulating cooling water, comprising a low-pressure cylinder of a steam turbine, wherein the saturated wet steam discharged from the low-pressure cylinder enters a condenser through an exhaust pipe, and the saturated wet steam is completely cooled into condensed water by circulating cooling water in the condenser and then enters a water storage tank and is transported away by a condensate pump, and the circulating cooling water is transported to the condenser by the circulating cooling water pump for cooling the saturated wet steam, and an integrated orifice plate flow measurement device is arranged behind the condensate pump. The present invention utilizes the existing real-time collected measurement data of the thermal power unit, and obtains the exhaust steam dryness of the low-pressure cylinder by performing real-time heat balance calculation on the heat exchange process between the saturated wet steam of the condenser and the circulating cooling water, thereby improving the stability and long-term reliability of the measurement.

Description

Technical Field

[0001] The present invention belongs to the field of information technology of energy and power industry, and specifically relates to a system and method for monitoring exhaust steam dryness of a steam turbine based on circulating cooling water. Background Art

[0002] The last few stages of large-scale condensing steam turbines in conventional power plants and all stages of steam turbines in nuclear power plants operate under saturated wet steam (including saturated steam and saturated water). The presence of steam humidity not only reduces the operating efficiency of the turbine, but also may cause serious blade erosion, which harms the operating economy and safety of the power plant units. In addition, the low-pressure cylinder exhaust steam dryness (the content of saturated steam in the exhaust steam) is a characteristic parameter for analyzing the low-pressure cylinder blades and the efficiency of the low-pressure cylinder, and has an important impact on the safe operation and efficiency of the low-pressure cylinder blades. Measuring the dryness of flowing saturated wet steam in the turbine is of great significance to ensure the economical, efficient, safe and reliable operation of the turbine. With the adoption of high-parameter large-capacity units and saturated wet steam turbines, the research on steam dryness measurement technology has gradually received attention in recent decades, and a variety of measurement methods have emerged, such as chemical method, acoustic wave method, optical method and condensation method. These methods use measuring equipment to directly measure the saturated wet steam extracted from the low-pressure cylinder, but these measurement methods are time-consuming and require complex equipment and operation and maintenance. The installed steam extraction measurement points will have a certain impact on the equipment. For example, installing measuring equipment on the condenser will affect the maintenance of the condenser vacuum.

[0003] On the one hand, if the exhaust steam dryness can be directly calculated by thermodynamic method based on the mass flow rate of circulating cooling water, it is possible to avoid extracting steam from the condenser. The circulating cooling water is sent into the condenser by the circulating cooling water pump to cool the exhaust steam of the steam turbine to condense it and maintain a vacuum state. By monitoring the condensate flow rate and the circulating cooling water flow rate, measuring the pressure and temperature of the cold and hot media and calculating their enthalpy values, the dryness of the exhaust steam of the last stage of the steam turbine can be indirectly measured. Because the condensate entering the deaerator is heated by the wet steam extraction, its quality cannot be directly calculated by pressure and temperature, so the main condensate flow measurement device is generally located at the inlet of the deaerator and is pressurized by the condensate pump. At present, the conventional monitoring devices of the above-mentioned units have not been reasonably utilized.

[0004] On the other hand, the exhaust of condensing steam turbines requires a large amount of cooling water, so the general characteristics of circulating cooling water are large flow and low head. Due to the thicker pipeline, slower fluid flow rate and lower pressure, the differential pressure measured at the sampling point in the center of the pipe is small or even unmeasurable, and there are often problems with inaccurate measurements. On the other hand, in actual measurements, the flow cross-sectional area, flow coefficient and fluid density are all affected by operating conditions. For large-capacity and high-parameter units, high measurement accuracy can only be achieved near the rated operating conditions. Under variable operating conditions, the flow fluctuates and the measurement error is large, which may exceed the acceptable range of the project. Therefore, the measurement method of wet saturated steam dryness of steam turbine exhaust needs to be improved.

[0005] In summary, the thermodynamic method based on the mass flow rate of circulating cooling water is highly feasible, but it requires a simple and practical real-time calculation model, and a calibration calculation model needs to be introduced for flow measurement to improve the accuracy of the exhaust steam dryness calculation results, and the online monitoring system needs to improve economy and reliability. Summary of the invention

[0006] In order to overcome the above technical problems, the present invention provides a system and method for monitoring the exhaust steam dryness of the last stage of the steam turbine based on circulating cooling water, which utilizes the real-time collected measurement data of the thermal power unit, calculates the heat balance in real time on the heat exchange process between the saturated wet steam in the condenser and the circulating cooling water, and obtains the exhaust steam dryness of the low-pressure cylinder, thereby improving the stability and long-term reliability of the measurement. The method also calibrates the exhaust steam dryness calculation result based on the measurement of the circulating cooling water replenishment flow rate.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A system for monitoring the exhaust dryness of the last stage of a steam turbine based on circulating cooling water comprises a low-pressure cylinder 1 of a steam turbine, wherein the saturated wet steam discharged from the low-pressure cylinder 1 enters a condenser 3 through an exhaust pipe 2, wherein the saturated wet steam is completely cooled into condensed water by circulating cooling water in the condenser 3 and then enters a water storage tank 4 and is transported away by a condensate pump 5, wherein the circulating cooling water is transported to the condenser 3 by a circulating cooling water pump 6 for cooling the saturated wet steam, and an integrated orifice plate flow measurement device 7 is arranged behind the condensate pump 5.

[0009] The exhaust pipe 2 is provided with a wet saturated steam pressure measuring point.

[0010] The orifice flow meter of the integrated orifice flow measuring device 7 is installed with a pressure measuring point 11 and a temperature measuring point 12, and the integrated orifice flow measuring device 7 is connected to the pipeline through a neck butt welding flange.

[0011] The length ratio of the pipeline of the integrated orifice flow measuring device 7 upstream and downstream of the orifice is 3:2.

[0012] An integrated orifice flow measuring device 2 8 is arranged behind the circulating cooling water pump 6, and an integrated orifice flow measuring device 3 9 is arranged on the circulating cooling water replenishment pipeline. The circulating cooling water after replenishment enters the cooling tower 10 for evaporative air cooling. The integrated orifice flow measuring device 2 8 and the integrated orifice flow measuring device 3 9 have the same structure as the integrated orifice flow measuring device 1 7.

[0013] The circulating cooling water makeup water is introduced before the cooling water enters the cooling tower 10 .

[0014] A calculation method for monitoring the exhaust steam dryness of the last stage of a steam turbine based on circulating cooling water comprises the following steps;

[0015] For the circulating cooling water side of condenser 3, the circulating cooling water pressure, circulating cooling water flow rate and the water temperature of circulating cooling water entering and leaving condenser 3 are collected in real time. The heat absorption power of circulating cooling water entering and leaving condenser 3 is:

[0016] W cooling water =M cooling water (h water outlet -h water inlet )

[0017] Among them, W cooling water ——heat absorption power of circulating cooling water, kJ / s;

[0018] M cooling water ——Mass flow rate of circulating cooling water, kg / s;

[0019] h water outlet ——Enthalpy of circulating cooling water at condenser outlet, kJ / kg;

[0020] h water inlet ——Enthalpy of circulating cooling water at condenser inlet, kJ / kg.

[0021] The inlet enthalpy and outlet enthalpy of circulating cooling water can be calculated using the water temperature enthalpy table:

[0022] h water inlet =F(P cooling water ,T water inlet )

[0023] h water outlet =F(P cooling water ,T water outlet )

[0024] Among them, P cooling water ——Circulating cooling water pressure, Pa;

[0025] T water inlet ——Condenser inlet circulating cooling water temperature, °C;

[0026] Twater outlet ——Condenser outlet circulating cooling water temperature, ℃.

[0027] F() is the enthalpy calculation function of the IAPWS-IF97 (The International Association for the Properties of Water and Steam Industrial Formulation 1997) water / steam physical properties open source calculation model.

[0028] For the saturated wet steam side of condenser 3, the heat release power of saturated wet steam being cooled into condensed water by circulating cooling water is:

[0029] W condensate =M condensate (h wet steam -h condensate )

[0030] Among them, W condensate ——heat release power of saturated wet steam condensation, kJ / s;

[0031] M condensate ——Condensate mass flow rate, kg / s;

[0032] h wet steam ——Saturated wet steam enthalpy, kJ / kg;

[0033] h condensate ——Enthalpy of condensation water, kJ / kg.

[0034] The enthalpy of condensation water can be calculated using the water temperature enthalpy table:

[0035] h condensate =F(P condensate ,T condensate )

[0036] Among them, P condensate ——Condensation water pressure, Pa;

[0037] T condensate ——Condensation water temperature, ℃.

[0038] Condensate flow, condensate pressure and condensate temperature can be collected in real time;

[0039] The relationship between the heat absorption power of circulating cooling water and the heat release power of saturated wet steam is:

[0040] W cooling water =ηW condensate

[0041] Among them, η is the heat exchange efficiency of the condenser. Because the temperatures of the cold and hot working fluids in the condenser are close to the atmospheric parameters, and the flow rate is slow and the heat exchange is sufficient, the heat exchange loss of the condenser can be ignored, and η is approximately equal to 1;

[0042] The relationship between saturated wet steam enthalpy and saturated steam dryness is as follows:

[0043] h wet steam =xh saturate steam +(1-x)h saturate water

[0044] Among them, x is the dryness of saturated steam;

[0045] h saturate steam ——Saturated steam enthalpy, kJ / kg;

[0046] h saturate water ——Saturated water enthalpy, kJ / kg.

[0047] Through the real-time acquisition of saturated wet steam pressure, the saturated steam enthalpy and saturated water enthalpy of saturated wet steam can be calculated through the water vapor temperature enthalpy table:

[0048] h saturate steam =F(P wet steam )

[0049] h saturate water =F(P wet steam )

[0050] Among them, P wet steam ——Saturated wet steam pressure, Pa.

[0051] Therefore, based on the measurement of circulating cooling water flow, pressure and temperature, the reference formula for calculating exhaust steam dryness is:

[0052] x0=[m(h water outlet -h water inlet )+(h condensate -h saturate water )] / (h saturate steam -h saturate water )

[0053] m=M cooling water / M condensate

[0054] Where x0 is the reference value of exhaust steam dryness calculated based on the measurement of circulating cooling water flow, pressure and temperature.

[0055] m——Cooling ratio, the number of kilograms of cooling water required to condense one kilogram of wet saturated steam;

[0056] For safety reasons, the safety margin of the cooling ratio can be very large in actual operation. In addition, during the normal operation of the unit, the circulating cooling water evaporates in large quantities in the cooling tower, resulting in water flow consumption. Therefore, a large amount of circulating cooling water must be replenished during the unit operation stage. The present invention utilizes the heat balance of the confluence of circulating cooling water and circulating cooling water replenishment. While measuring the circulating cooling water flow at the outlet of the condenser 3, the circulating cooling water replenishment flow is measured and monitored, and the exhaust steam dryness calibration value is iteratively calculated based on this, and the exhaust steam dryness reference value x0 is calibrated. The influence of the operating conditions and atmospheric parameter changes during the iteration process on the circulating cooling water flow can be ignored; the derivation formula is as follows:

[0057] M cooling water +M compensate =M compensated water

[0058] M cooling water h water outlet +M compensate h compensate =M compensated water h compensated water

[0059] M cooling water =M compensate (h compensated water -h compensate ) / (h water outlet -h compensated water )

[0060] Among them, M compensate ——Mass flow rate of circulating cooling water make-up water;

[0061] M compensated ——Mass flow rate of circulating cooling water after water replenishment;

[0062] h compensate——Circulating cooling water make-up water enthalpy;

[0063] h compensated ——Enthalpy of circulating cooling water after water replenishment.

[0064] The circulating cooling water replenishment enthalpy and the circulating cooling water enthalpy after replenishment are obtained through the water temperature enthalpy table:

[0065] h compensate =F(P compensate ,T compensate )

[0066] h compensated =F(P compensated ,T compensated )

[0067] The above calibration method requires that the make-up water flow rate accounts for more than 5% of the circulating cooling water flow rate. However, since the make-up water volume of the circulating cooling water will fluctuate, the make-up water flow rate will be insufficient. Therefore, according to the actual situation, it is only necessary to use the circulating cooling water make-up water heat balance every 1 minute to calibrate the reference value x0.

[0068] If the water replenishment at each 1-minute monitoring time point is still insufficient, the replenishment amount can be increased to improve the safety margin of the cooling water and ensure that the calculation results are corrected in time.

[0069] The exhaust steam dryness formula calculated by calibration using circulating cooling water make-up water heat balance is:

[0070] x'=[m'(h water outlet -h water inlet )+(h condensate -h saturate water )] / (h saturate steam -h saturate water )

[0071] m'=(M compensate / M condensate )(h compensated -h compensate ) / (h water outlet -h compensated )

[0072] Where, x' is the exhaust steam dryness of the last stage of the steam turbine after calibration, which is at the same time point as x0 calculated once per minute;

[0073] m'——cooling ratio after calibration; obviously, the calibrated exhaust steam dryness x' has nothing to do with the circulating cooling water flow rate, and the measurement accuracy of the calibration value x' is greater than the reference value x0;

[0074] That is to say, the accurate exhaust steam dryness is calculated once every 1 minute;

[0075] During the one-minute interval without calibration, because the data collection unit time of the pressure and temperature measuring points 11 and 12 can generally be achieved in seconds, the real-time reference value x0 is calculated using the conventional directly measured circulating cooling water flow, and the exhaust steam dryness reference value with insufficient accuracy calculated in real time is stored in the database. Then, the calibration difference calculated by accurately measuring the circulating cooling water replenishment water heat balance is used to automatically correct the reference value in the database to obtain the moving correction value of the exhaust steam dryness:

[0076] x t =x 0t +(x'-x0)

[0077] Among them, x t ——The moving correction value of exhaust steam dryness at a certain moment during a one-minute interval without calibration;

[0078] x 0t ——During the one-minute interval without calibration, the circulating cooling water heat balance is measured and calculated in real time to obtain the exhaust steam dryness reference value.

[0079] Beneficial effects of the present invention:

[0080] The present invention can utilize the existing pressure, temperature, flow measurement points and data acquisition system of the circulating cooling water system of the thermal power unit, and can simply and quickly realize the real-time calculation of the wet saturated steam dryness of the final exhaust steam of the steam turbine, and realize the online monitoring of the operating parameters of the low-pressure cylinder without adding additional professional measuring equipment. The calculation model can ignore the heat dissipation and heat exchange loss of the pipeline transporting the working fluid. The integrated orifice flow measurement device is connected to the pipeline through a neck butt welding flange to reduce the impact on the flow field. The length ratio of the measuring device pipeline to the upstream and downstream of the orifice is 3:2.

[0081] The present invention also proposes to arrange the circulating cooling water replenishment device on the pipeline before the cooling water enters the cooling tower, and utilize the large temperature difference between the circulating cooling water and the replenishment water at the outlet of the condenser to accurately calculate the heat balance of the circulating cooling water replenishment, and obtain the cooling ratio that is independent of the measured value of the circulating cooling water flow rate, and thereby introduce the calibration model to obtain the low-pressure cylinder exhaust steam dryness that meets the engineering accuracy requirements. The present invention avoids the engineering problem of large errors in direct measurement of large-flow circulating cooling water flow, and utilizes the characteristics of fast and adjustable circulating cooling water replenishment flow rate to make its flow measurement accurate and reliable, and establishes a calculation model for the exhaust steam dryness calibration value with a large time interval and high accuracy, which is used to time-shift and correct the exhaust steam dryness reference value that can be measured in real time but has low accuracy.

[0082] The calculation model results show that the exhaust steam dryness calibration value is only related to the circulating cooling water replenishment flow, the discharged condensed water flow, and the pressure and temperature measurement values. The accuracy of the pressure and temperature measurement points is guaranteed, and the unit operating status parameters can be continuously and effectively collected. Therefore, the flow online monitoring system has the ability to collect and process data in real time and with high accuracy. At the same time, the entire iteration of the calculation model is a linear process with an extremely fast convergence speed, which can meet the requirements of online monitoring. The present invention can reduce the workload of personnel involved and can provide a basis for the design of real-time economic analysis, online load optimization distribution, fault diagnosis and control systems of power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 It is a system schematic diagram of the present invention.

[0084] Figure 2 It is a schematic diagram of the specific structure of the present invention. DETAILED DESCRIPTION

[0085] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0086] like Figure 1 , Figure 2 As shown: A measurement method for real-time calculation of the exhaust dryness of the low-pressure cylinder of a steam turbine. For a steam turbine, the saturated wet steam discharged from the low-pressure cylinder 1 enters the condenser 3 through the exhaust pipe 2. In the condenser 3, the saturated wet steam is completely cooled by the circulating cooling water into condensed water and then enters the water storage tank 4 and is transported away by the condensate pump 5. The circulating cooling water is transported to the condenser 3 by the circulating cooling water pump 6 for cooling the saturated wet steam. A wet saturated steam pressure measuring point is arranged on the exhaust pipe 2, and an integrated orifice plate flow measurement device 7 (such as the one designed by the present invention) is arranged behind the condensate pump 5. Figure 2As shown in the figure, the orifice flowmeter is equipped with pressure and temperature measuring points 11 and 12. The integrated orifice flow measuring device 7 is connected to the pipeline through a neck welding flange to reduce the impact on the flow field. The length ratio of the integrated orifice flow measuring device 7 pipeline upstream and downstream of the orifice is 3:2. The integrated orifice flow measuring device 8 is also arranged after the circulating cooling water pump 6 (as shown in the figure). Figure 2 The integrated orifice plate flow measurement device 9 is also arranged on the circulating cooling water supply pipeline (as shown in FIG. Figure 2 As shown), the circulating cooling water after replenishment enters the cooling tower 10 for evaporative air cooling. The circulating cooling water replenishment water is collected in the pipeline before the cooling water enters the cooling tower.

[0087] The measuring method of the present invention:

[0088] Step 1

[0089] The saturated wet steam pressure P discharged from the low-pressure cylinder 1 is collected in real time by using the integrated orifice flow measurement devices 7, 8, 9 and the unit pressure and temperature measurement points. wet steam , the condensate flow rate M discharged from condenser 3 condensate , condensation water pressure P condensate and condensing water temperature T condensate , the circulating cooling water pressure P delivered by the circulating cooling water pump 6 to the condenser 3 cooling water , circulating cooling water flow M cooling water , circulating cooling water inlet and outlet condenser 3 water temperature T water inlet , T water outlet , and circulating cooling water replenishment volume M compensate , water supply pressure temperature P compensate ,T compensate , circulating cooling water pressure temperature P after water replenishment compensated ,T compensated ;

[0090] Step 2

[0091] Through the water and water vapor temperature enthalpy table, the circulating cooling water inlet h is obtained water inlet and outlet enthalpy h water outlet , condensation water enthalpy h cooling water , saturated steam enthalpy of saturated wet steam h saturate steam and saturated water enthalpy h saturate water , and water replenishment enthalpy h compensateand the circulating cooling water enthalpy after replenishment h compensated ;

[0092] Step 3

[0093] The circulating cooling water is used to make up the water every 1 minute to calibrate and calculate the accurate dryness of the wet saturated steam, and the calibration difference is obtained.

[0094] Step 4

[0095] The accurate calculated calibration difference is added to the turbine exhaust steam dryness reference value which is calculated in real time at the second level but is not accurate enough to obtain the moving correction value.

Claims

1. A method for measuring the exhaust steam dryness of the last stage of a steam turbine based on circulating cooling water, characterized in that: The method is implemented by a system for monitoring the exhaust dryness of the last stage of a steam turbine based on circulating cooling water, the system comprising a low-pressure cylinder (1) of a steam turbine, the saturated wet steam discharged from the low-pressure cylinder (1) entering a condenser (3) through an exhaust pipe (2), the saturated wet steam in the condenser (3) being completely cooled by circulating cooling water into condensed water and then entering a water storage tank (4) and being transported away by a condensate pump (5), the circulating cooling water being transported by a circulating cooling water pump (6) into the condenser (3) for cooling the saturated wet steam, and an integrated orifice plate flow measurement device (7) being arranged behind the condensate pump (5); The method comprises the following steps: For the circulating cooling water side of the condenser (3), the circulating cooling water pressure, circulating cooling water flow rate and the water temperature of the circulating cooling water entering and leaving the condenser (3) are collected in real time. The heat absorption power of the circulating cooling water entering and leaving the condenser (3) is: W coolingwater =M coolingwater (h wateroutlet -h waterinlet ) Among them, W coolingwater ——heat absorption power of circulating cooling water, kJ / s; M coolingwater ——Mass flow rate of circulating cooling water, kg / s; h wateroutlet ——Enthalpy of circulating cooling water at condenser outlet, kJ / kg; h waterinlet ——Enthalpy of circulating cooling water at the condenser inlet, kJ / kg; The inlet enthalpy and outlet enthalpy of circulating cooling water are calculated by the water temperature enthalpy table: h waterinlet =F(P coolingwater ,T waterinlet ) h wateroutlet =F(P coolingwater ,T wateroutlet ) Among them, P coolingwater ——Circulating cooling water pressure, Pa; T waterinlet ——Condenser inlet circulating cooling water temperature, °C; T wateroutlet ——Condenser outlet circulating cooling water temperature, °C; F() is the enthalpy calculation function of the water / steam physical property open source calculation model; On the saturated wet steam side of the condenser (3), the heat release power of the saturated wet steam being cooled by the circulating cooling water into condensed water is: W condensate =M condensate (h wetsteam -h condensate ) Among them, W condensate ——heat release power of saturated wet steam condensation, kJ / s; M condensate ——Condensate mass flow rate, kg / s; h wetsteam ——Saturated wet steam enthalpy, kJ / kg; h condensate ——condensation enthalpy, kJ / kg; The enthalpy of condensed water is calculated using the water temperature enthalpy table: h condensate =F(P condensate ,T condensate ) Among them, P condensate ——Condensation water pressure, Pa; T condensate ——Condensate temperature, °C; Real-time collection of condensate flow, condensate pressure and condensate temperature; The relationship between the heat absorption power of circulating cooling water and the heat release power of saturated wet steam is: IN coolingwater =ηW condensate Among them, η is the heat transfer efficiency of the condenser, and η is approximately equal to 1; The relationship between saturated wet steam enthalpy and saturated steam dryness is as follows: h wetsteam =xh saturatesteam +(1-x)h saturatewater Among them, x is the dryness of saturated steam; h saturatesteam ——Saturated steam enthalpy, kJ / kg; h saturatewater ——Saturated water enthalpy, kJ / kg; The saturated wet steam pressure collected in real time is used to calculate the saturated steam enthalpy and saturated water enthalpy of the saturated wet steam using the water vapor temperature enthalpy table: h saturatesteam =F(P wetsteam ) h saturatewater =F(P wetsteam ) Among them, P wetsteam ——saturated wet steam pressure, Pa; Based on the measurement of circulating cooling water flow, pressure and temperature, the reference formula for calculating exhaust steam dryness is: x0=[m(h wateroutlet -h waterinlet )+(h condensate -h saturatewater )] / (h saturatesteam -h saturatewater ) m=M coolingwater / M condensate Where, x0 is the reference value of exhaust steam dryness calculated based on the measured circulating cooling water flow, pressure and temperature; m——Cooling ratio, the number of kilograms of cooling water required to condense one kilogram of wet saturated steam; By utilizing the heat balance of the confluence of circulating cooling water and circulating cooling water make-up water, the circulating cooling water make-up water flow rate is measured and monitored while measuring the circulating cooling water flow rate at the outlet of the condenser (3), and the exhaust steam dryness calibration value is iteratively calculated based on this, and the exhaust steam dryness reference value x0 is calibrated. The influence of the operating conditions and atmospheric parameter changes on the circulating cooling water flow rate during the iteration process is ignored; the formula is as follows: M coolingwater +M compensate =M compensatedwater M coolingwater h wateroutlet +M compensate h compensate =M compensatedwater h compensatedwater M coolingwater =M compensate (h compensatedwater -h compensate ) / (h wateroutlet -h compensatedwater ) Among them, M compensate ——Mass flow rate of circulating cooling water make-up water; M compensated ——Mass flow rate of circulating cooling water after water replenishment; h compensate ——Circulating cooling water make-up water enthalpy; h compensated ——Enthalpy of circulating cooling water after water replenishment; The circulating cooling water replenishment enthalpy and the circulating cooling water enthalpy after replenishment are obtained through the water temperature enthalpy table: h compensate =F(P compensate ,T compensate ) h compensated =F(P compensated ,T compensated ) The reference value x0 is calibrated and calculated every 1 minute using circulating cooling water to make up the heat balance; If the water replenishment at each 1-minute monitoring time point is still insufficient, increase the water replenishment to increase the safety margin of cooling water and ensure that the calculation results are corrected in time; The exhaust steam dryness formula for calibration calculation using circulating cooling water make-up water heat balance is: x’=[m’(h wateroutlet -h waterinlet )+(h condensate -h saturatewater )] / (h saturatesteam -h saturatewater ) m’=(M compensate / M condensate )(h compensated -h compensate ) / (h wateroutlet -h compensated ) Where, x' is the exhaust steam dryness of the last stage of the steam turbine after calibration, which is at the same time point as x0 calculated once per minute; m'——cooling ratio after calibration; the measurement accuracy of the calibration value x' is greater than the reference value x0; During the one-minute interval without calibration, the real-time reference value x0 is calculated using the conventional directly measured circulating cooling water flow rate, and the exhaust steam dryness reference value obtained in real time and with insufficient accuracy is stored in the database. Then, the reference value is automatically corrected in the database using the calibration difference calculated by accurately measuring the circulating cooling water make-up water heat balance to obtain the moving correction value of the exhaust steam dryness: x t =x 0t +(x'-x0) Among them, x t ——The moving correction value of exhaust steam dryness at a certain moment during a one-minute interval without calibration; x 0t ——During the one-minute interval without calibration, the circulating cooling water heat balance is measured and calculated in real time to obtain the exhaust steam dryness reference value.

2. The measuring method of a system for monitoring the final stage exhaust steam dryness of a steam turbine based on circulating cooling water according to claim 1 is characterized in that: A wet saturated steam pressure measuring point is arranged on the exhaust pipe (2).

3. The measuring method of a system for monitoring the final stage exhaust steam dryness of a steam turbine based on circulating cooling water according to claim 1 is characterized in that: The orifice flow meter of the integrated orifice flow measuring device (7) is installed with a pressure measuring point (11) and a temperature measuring point (12). The integrated orifice flow measuring device (7) is connected to the pipeline through a neck butt welding flange.

4. The measuring method of a system for monitoring the final stage exhaust steam dryness of a steam turbine based on circulating cooling water according to claim 1 is characterized in that: The ratio of the length of the pipeline upstream and downstream of the orifice plate of the integrated orifice plate flow measurement device (7) is 3:

2.

5. The measuring method of a system for monitoring the final stage exhaust steam dryness of a steam turbine based on circulating cooling water according to claim 1 is characterized in that: An integrated orifice flow measuring device 2 (8) is arranged behind the circulating cooling water pump (6), and an integrated orifice flow measuring device 3 (9) is arranged on the circulating cooling water replenishment pipeline. The circulating cooling water after replenishment enters the cooling tower (10) for evaporative air cooling. The integrated orifice flow measuring device 2 (8) and the integrated orifice flow measuring device 3 (9) have the same structure as the integrated orifice flow measuring device 1 (7), and the circulating cooling water replenishment is introduced before the cooling water enters the cooling tower (10).

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