Method for measuring extraction flow rate of condensing steam turbine

Abstract

A kind of condensing steam turbine extraction flow measurement method, pipeline heating device, vortex flowmeter are arranged in turn along the direction of medium flow on pipeline between condenser extraction port and extraction equipment inlet, temperature and pressure sensors are respectively arranged on inlet and outlet pipes of pipeline heating device;Adopt pipeline electromagnetic pipeline heating device, all steam-water two-phase mixture of negative pressure and entrained condensate liquid water is heated, vaporized into single-phase slightly superheated dry steam above 5℃ higher than local steam pressure saturation temperature, according to outlet temperature and pressure signals, judge the state of medium in pipeline and automatically adjust and control heating power in closed loop, after meeting the superheat requirement, use vortex flowmeter to accurately measure extraction flow.The present application has full-diameter pipeline without throttling, the additional pressure loss is very low, which will not increase the power consumption of extraction equipment and destroy the vacuum of unit;Solve the industry pain point that condensing steam turbine condenser steam-water two-phase extraction flow cannot be accurately measured.

Description

Technical Field

[0001] This invention relates to the field of condensing steam turbine testing technology, and in particular to a method for measuring the extraction flow rate of a condensing steam turbine. Background Technology

[0002] A condensing steam turbine is a type of steam turbine in which steam expands and does work inside the turbine, and then, except for a small amount of steam leaking from the shaft seals, all of it enters the condenser and condenses into water.

[0003] During the operation of a condensing steam turbine unit, the gas extracted from the condenser by the extraction equipment (such as vacuum pumps, water jet ejectors, and steam jet ejectors) is a two-phase mixture of saturated steam and condensed liquid water. Conventional vortex flowmeters and orifice plate flowmeters are only suitable for measuring the flow rate of single-phase dry gases. In two-phase flows, liquid water interferes with the flow detection element and cannot be measured simultaneously, resulting in distorted and highly erroneous extraction flow measurement data. If throttling flowmeters (such as orifice plates and venturi tubes) with high resistance losses are directly installed, additional pressure losses will occur, increasing the power consumption of extraction equipment such as vacuum pumps, reducing the operating efficiency of the extraction system, and in severe cases, even disrupting the unit's vacuum and affecting the safe and stable operation of the steam turbine.

[0004] In existing technologies, there are wet steam flow measurement schemes that indirectly measure the total wet steam flow by heating a portion of the total wet steam flow and measuring the heating power of this portion of the wet steam flow and the changes in steam state parameters before and after heating. For example, CN106768118A is such a scheme. However, it does not directly measure the total wet steam flow, nor does it convert all the wet steam into slightly superheated dry steam for direct measurement. It adopts a sampling branch heating method, which requires drawing steam from the main pipeline for heating and then sending it back. The system is complex and subject to sampling disturbances. It uses a nozzle flow meter, which does not fully consider the extreme sensitivity of the condenser extraction pipeline of the condensing steam turbine to the additional pressure loss. It also does not provide a heating method that can automatically identify the medium state and adjust the heating power in a closed loop to achieve a complete measurement method without throttling or increased pressure loss throughout the entire process.

[0005] Therefore, there is an urgent need for a method for measuring the pumping flow rate of condensing steam turbines that is suitable for the pumping system, has low flow resistance, and high precision. Summary of the Invention

[0006] In response to the shortcomings of the existing production technology, the applicant provides a method for measuring the extraction flow rate of a condensing steam turbine, which converts the extracted gas from the condenser of the condensing steam turbine from a two-phase mixture of steam and water into slightly superheated dry steam, and then uses a conventional flow meter for accurate measurement.

[0007] The technical solution adopted in this invention is as follows: A method for measuring the extraction flow rate of a condensing steam turbine includes the following working process: On the negative pressure extraction pipeline between the condenser extraction port of the condensing steam turbine and the inlet of the extraction equipment, a pipeline heating device and a low pressure loss gas flow meter are installed sequentially along the medium flow direction with the same inner diameter, no change in diameter, and no throttling. A first pressure sensor and a first temperature sensor are installed on the inlet pipe of the pipe heating device, and a second pressure sensor and a second temperature sensor are installed on the outlet pipe of the pipe heating device. Using the inlet pressure and inlet temperature parameters collected by the first pressure sensor and the first temperature sensor, it is determined whether the medium in the pipeline is saturated wet steam with entrained liquid water. If it is identified as saturated wet steam, the pipeline heating device is started to heat the steam-water mixture, so that all the liquid water in the condenser exhaust gas is heated and vaporized until the medium at the outlet of the pipeline heating device is slightly superheated dry steam. Using the outlet temperature and outlet pressure parameters collected by the second pressure sensor and the second temperature sensor, it is determined whether the medium in the pipeline is slightly superheated dry steam, and the heating power of the pipeline heating device is automatically adjusted in a closed loop until the outlet medium temperature reaches the local pressure steam saturation temperature +5℃ or more. After the outlet medium temperature reaches the local pressure steam saturation temperature +5℃, the pumping flow rate is measured by a low pressure loss gas flow meter. The pipeline heating device and the low-pressure-loss gas flow meter use equipment with the same inner diameter as the original extraction steam pipeline, without adding additional throttling elements or additional pressure loss in the extraction pipeline that affects the unit's vacuum.

[0008] The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 1 includes the step of automatically identifying the state of the medium in the pipeline: transmitting the inlet pressure and inlet temperature signals of the pipeline heating device to the frequency converter heating controller; the frequency converter heating controller automatically determines whether the inlet medium is wet steam or dry steam based on the saturated physical property parameters of the medium; if it is determined to be dry steam and the temperature reaches the local pressure steam saturation temperature +5°C or higher, then no heating is required, and the extraction flow rate is directly measured by the flow meter.

[0009] The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 1, wherein the step of automatically adjusting the heating power in a closed loop includes: connecting the outlet temperature and outlet pressure signals to the power adjustment module of the frequency converter heating controller to form a power closed-loop control loop; determining the state of the medium in the pipeline; when the outlet medium temperature is less than the local pressure steam saturation temperature +5°C, automatically increasing the output power of the pipeline heating device; when the outlet medium temperature is ≥ the local pressure steam saturation temperature +5°C, locking the current heating power unchanged.

[0010] The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 1 uses a vortex flow meter as the low-pressure-loss gas flow meter.

[0011] The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 1, wherein the pipeline heating device adopts a pipeline electromagnetic heating device, the specific structure of which includes a magnetically conductive seamless steel pipe, an electromagnetic heater, and an insulation shell, wherein the magnetically conductive seamless steel pipe is provided with connecting flanges at both ends, the inner diameter of the magnetically conductive seamless steel pipe is consistent with the inner diameter of the extraction pipe of the steam turbine condenser, and further includes an electromagnetic heating coil spirally wound on the outer wall of the seamless steel pipe and a frequency conversion heating controller; the insulation shell covers the outside of the electromagnetic heating coil; A low-pressure-loss gas flow meter is installed downstream of the pipeline heating device, with its inner diameter matching that of the magnetically conductive seamless steel pipe of the pipeline heating device. The first pressure sensor and the first temperature sensor are installed on the pipe on the inlet side of the pipe heating device. The second pressure sensor and the second temperature sensor are installed on the pipe on the outlet side of the pipe heating device. The signals measured by the first pressure sensor, the first temperature sensor, the second pressure sensor, and the second temperature sensor are all transmitted to the variable frequency heating controller.

[0012] Its further technical solution lies in: The variable frequency heating controller has an automatic steam medium status determination function: based on the received signals from the first pressure sensor and the first temperature sensor, it determines whether the state of the inlet medium of the pipeline heating device is wet steam or dry steam; based on the received signals from the second pressure sensor and the second temperature sensor, it determines whether the state of the outlet medium of the pipeline heating device is wet steam or dry steam, and can determine how many degrees the temperature of the outlet medium of the heating device is higher than the steam saturation temperature under local pressure.

[0013] The variable frequency heating controller has the function of automatically adjusting and controlling the heating power of the pipeline electromagnetic heating device. Based on the received signals from the second pressure sensor and the second temperature sensor and the determined state of the outlet medium of the pipeline heating device, it automatically adjusts and controls the power of the pipeline electromagnetic heating device so that the state of the outlet medium of the pipeline heating device meets the requirements for accurate measurement of the air extraction flow.

[0014] The variable frequency heating controller rectifies, filters, and inverts the input power frequency to a high-frequency AC output of 5-40kHz and 300-600V. The high-frequency AC output from the variable frequency heating controller is connected to the electromagnetic heating coil. The alternating magnetic field of the electromagnetic heating coil causes eddy currents to be generated in the magnetically conductive seamless steel pipe, thereby heating the steam-water mixture flowing through the pipe heating device, so that all the liquid water in the condenser exhaust gas is heated and vaporized.

[0015] The magnetically conductive seamless steel pipe is coaxially connected to the upstream and downstream pipelines via flanges, forming a structure with no shrinkage or expansion of the entire pipeline diameter. After the overall installation, the pipeline does not incur additional resistance loss.

[0016] The insulation shell is made of high-temperature resistant heat-insulating material to prevent heat loss from the heating coil.

[0017] The beneficial effects of this invention are as follows: (i) This invention has no throttling, zero additional pressure loss, and does not disturb the vacuum of the machine unit: This invention involves arranging a pipeline heating device and a low-pressure-loss gas flow meter along the negative pressure extraction pipeline from the condenser extraction port to the inlet of the extraction equipment, ensuring a constant inner diameter without any change in diameter or throttling along the entire flow direction of the medium. A seamless, magnetically conductive metal pipe is coaxially connected to the preceding and following pipelines via flanges, forming a pipeline structure with no shrinkage or expansion throughout the entire flow path. The overall installation does not increase the pipeline's resistance loss. Compared to existing technologies using orifice flow meters, venturi tubes, or other throttling measurement devices, this invention does not generate any additional throttling elements and does not increase the power consumption of the extraction equipment (vacuum pump, water jet ejector, etc.), fundamentally avoiding disturbance to the condenser vacuum and ensuring the safe and stable operation of the turbine unit.

[0018] (II) This invention converts the two-phase steam and water mixture into a single-phase micro-superheated dry steam, enabling high-precision measurement: This invention utilizes a pipeline electromagnetic heating device to convert saturated wet steam containing liquid water within the extraction pipeline into single-phase slightly superheated dry steam (outlet temperature ≥ local pressure saturation temperature + 5℃), completely eliminating interference from liquid water droplets on the flow detection element. Combined with a low-pressure-loss vortex flow meter, it enables high-precision continuous measurement of the extraction flow rate of condensing turbine condensers, solving the problem of directly and accurately measuring the extraction flow rate of condensing turbine condensers. Simultaneously, the pipeline heating device uses the magnetically conductive seamless steel pipe itself as the heating element. When a 5-40kHz high-frequency alternating current is applied to the electromagnetic heating coil, the pipe wall is directly heated by eddy currents. Heat is directly transferred to the medium inside the pipe through the pipe wall, resulting in a fast thermal response, high thermal efficiency, and uniform heating without dead zones.

[0019] (III) This invention features closed-loop automatic control based on temperature and pressure parameters, enabling adaptive operation under all working conditions: This invention utilizes a first pressure sensor and a first temperature sensor to collect inlet parameters and automatically determine the medium state (wet steam or dry steam). It uses a second pressure sensor and a second temperature sensor to collect outlet temperature and pressure signals, which are then fed into the power regulation module of the variable frequency heating controller to form a power closed-loop control circuit. This circuit automatically determines the outlet medium state of the heating device and automatically adjusts and controls the heater's heating power. When the outlet temperature is less than the local saturation temperature at pressure + 5°C, the power is automatically increased; when it is greater than or equal to the saturation temperature at pressure + 5°C, the power is locked. This closed-loop control mechanism enables the invention to respond in real time to changes in the medium's moisture content and dynamically adjust the heating power under conditions such as unit start-up and shutdown, and variable load operation, always ensuring that the outlet medium is in a slightly superheated state. This achieves continuous and accurate flow measurement throughout all operating conditions and processes without manual intervention.

[0020] (iv) The present invention has a compact structure, requires minimal modification work, and is highly adaptable: The pipeline heating device of this invention uses seamless steel pipe as the heating base and connects it in series with the existing main exhaust pipeline, eliminating the need for bypasses or sampling branches and altering the original pipeline layout, resulting in minimal modification work. The variable frequency heating controller's input power is compatible with 220V / 50Hz or 380V / 50Hz industrial power frequency, adapting to various on-site power supply conditions. The insulated shell effectively reduces heat loss and improves heating efficiency. The entire device has a compact structure and small footprint, and can be easily adapted to various power levels of existing condensing steam turbine units, demonstrating good versatility and promotional value.

[0021] (v) This invention has a high degree of automation and is easy to maintain: This invention utilizes a variable frequency heating controller to automatically complete all control logic, including medium status identification, heating start / stop, and power adjustment, based on sensor signals. No manual intervention is required during operation, reducing the workload for operators. Furthermore, the device has no moving parts or additional throttling elements, making it less prone to clogging and wear. Daily maintenance is minimal, and it has a long service life, resulting in excellent economic efficiency.

[0022] In summary, this invention achieves high-precision, fully automatic, continuous and stable measurement of the pumping flow rate of a condensing steam turbine while maintaining the original vacuum conditions of the unit. It effectively solves the long-standing problem of two-phase flow measurement in this field and has significant technological advancements and industrial application value. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the pipe heating device of the present invention.

[0024] Figure 2 This is a partial structural schematic diagram of the pipeline heating device of the present invention.

[0025] Figure 3This is a cross-sectional view of the magnetically conductive seamless steel pipe of the present invention.

[0026] The components include: 1. First pressure sensor; 2. First temperature sensor; 3. Magnetic seamless steel pipe; 4. Electromagnetic heating coil; 5. Insulation shell; 6. Second pressure sensor; 7. Second temperature sensor; 8. Vortex flow meter; 9. Variable frequency heating controller. Detailed Implementation

[0027] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0028] like Figures 1-3 As shown, the method for measuring the extraction flow rate of a condensing steam turbine in this embodiment includes the following working process: On the negative pressure extraction pipeline between the condenser extraction port of the condensing steam turbine and the inlet of the extraction equipment, a pipeline heating device and a low pressure loss gas flow meter are installed sequentially along the medium flow direction with the same inner diameter, no change in diameter, and no throttling. A first pressure sensor 1 and a first temperature sensor 2 are installed on the inlet pipe of the pipe heating device, and a second pressure sensor 6 and a second temperature sensor 7 are installed on the outlet pipe of the pipe heating device. Using the inlet pressure and inlet temperature parameters collected by the first pressure sensor 1 and the first temperature sensor 2, it is determined whether the medium in the pipeline is saturated wet steam with entrained liquid water. If it is identified as saturated wet steam, the pipeline heating device is started to heat the steam-water mixture, so that all the liquid water in the condenser exhaust gas is heated and vaporized until the medium at the outlet of the pipeline heating device is slightly superheated dry steam. Using the outlet temperature and outlet pressure parameters collected by the second pressure sensor 6 and the second temperature sensor 7, it is determined whether the medium in the pipeline is slightly superheated dry steam, and the heating power of the pipeline heating device is automatically adjusted in a closed loop until the outlet medium temperature reaches the local pressure steam saturation temperature +5℃ or more. After the outlet medium temperature reaches the local pressure steam saturation temperature +5℃, the pumping flow rate is measured by a low pressure loss gas flow meter. The pipeline heating device and the low-pressure-loss gas flow meter use equipment with the same inner diameter as the original extraction steam pipeline, without adding additional throttling elements or additional pressure loss in the extraction pipeline that affects the unit's vacuum.

[0029] The steps for automatically identifying the state of the medium in the pipeline include: transmitting the inlet pressure and inlet temperature signals of the pipeline heating device to the frequency converter heating controller 9; the frequency converter heating controller 9 automatically determines whether the inlet medium is wet steam or dry steam based on the saturated physical property parameters of the medium; if it is determined to be dry steam and the temperature reaches the local pressure steam saturation temperature +5℃ or more, then no heating is required, and the pumping flow rate is directly measured by the flow meter.

[0030] The steps for closed-loop automatic adjustment of heating power include: connecting the outlet temperature and outlet pressure signals to the power adjustment module of the variable frequency heating controller 9 to form a power closed-loop control loop; determining the state of the medium in the pipeline; when the outlet medium temperature is less than the local pressure steam saturation temperature +5℃, automatically increasing the output power of the pipeline heating device; when the outlet medium temperature is ≥ the local pressure steam saturation temperature +5℃, the controller locks the current heating power unchanged.

[0031] The low-pressure-loss gas flow meter is a vortex flow meter 8.

[0032] The pipeline heating device adopts a pipeline electromagnetic heating device, the specific structure of which includes a magnetic seamless steel pipe 3, an electromagnetic heater and an insulation shell 5. The magnetic seamless steel pipe 3 is provided with connecting flanges at both ends. The inner diameter of the magnetic seamless steel pipe 3 is consistent with the inner diameter of the turbine condenser extraction pipe. It also includes an electromagnetic heating coil 4 spirally wound on the outer wall of the seamless steel pipe and a frequency conversion heating controller 9. The insulation shell 5 covers the outside of the electromagnetic heating coil 4. A low-pressure-loss gas flow meter is installed downstream of the pipeline heating device, and its inner diameter is the same as that of the magnetic metal seamless steel pipe 3 of the pipeline heating device. The first pressure sensor 1 and the first temperature sensor 2 are installed on the pipe on the inlet side of the pipe heating device; The second pressure sensor 6 and the second temperature sensor 7 are installed on the pipe on the outlet side of the pipe heating device. The signals measured by the first pressure sensor 1, the first temperature sensor 2, the second pressure sensor 6, and the second temperature sensor 7 are all transmitted to the variable frequency heating controller 9.

[0033] The variable frequency heating controller 9 has an automatic steam medium status determination function: based on the received signals from the first pressure sensor 1 and the first temperature sensor 2, it determines whether the state of the inlet medium of the pipeline heating device is wet steam or dry steam; based on the received signals from the second pressure sensor 6 and the second temperature sensor 7, it determines whether the state of the outlet medium of the pipeline heating device is wet steam or dry steam, and can determine how many degrees the temperature of the outlet medium of the heating device is higher than the steam saturation temperature under local pressure.

[0034] The variable frequency heating controller 9 has the function of automatically adjusting and controlling the heating power of the pipeline electromagnetic heating device. Based on the received signals from the second pressure sensor 6 and the second temperature sensor 7 and the determined state of the outlet medium of the pipeline heating device, it automatically adjusts and controls the power of the pipeline electromagnetic heating device so that the state of the outlet medium of the pipeline heating device meets the requirements for accurate measurement of the air extraction flow.

[0035] The variable frequency heating controller 9 rectifies, filters, and inverts the input power frequency to a high-frequency AC output of 5-40kHz and 300-600V. The high-frequency AC output of the variable frequency heating controller 9 is connected to the electromagnetic heating coil 4. The alternating magnetic field of the electromagnetic heating coil 4 causes eddy currents to be generated in the magnetically conductive seamless steel pipe 3, thereby heating the steam-water mixture flowing through the pipe heating device, so that all the liquid water in the condenser exhaust gas is heated and vaporized.

[0036] The magnetically conductive seamless steel pipe 3 is coaxially connected to the front and rear pipelines through flanges, forming a structure with no shrinkage or expansion of the entire pipeline diameter. After the overall installation, the pipeline does not increase the resistance loss.

[0037] The heat insulation shell 5 is made of high-temperature resistant heat insulation material to prevent the heat from the heating coil from dissipating outward.

[0038] Example 1: A 50MW condensing steam turbine unit has a condenser extraction header pipe diameter of DN200, and the extraction equipment is a vacuum pump. The absolute pressure range inside the extraction pipeline is 10kPa to 30kPa.

[0039] Implement according to the following steps: Step 1: Cut a DN200 magnetic seamless steel pipe of the same specification as the heating base, with a length of 800mm. Fit flanges of the same specification at both ends and connect it directly in series with the straight pipe section between the condenser exhaust port and the vacuum pump to ensure that the pipe diameter is consistent throughout the entire process.

[0040] Step 2: A spiral electromagnetic heating coil (40 turns, 10mm pitch) is wound tightly around the outer wall of a seamless steel pipe. An external frequency converter heating controller (9) is connected to the coil, powered by a 380V / 50Hz industrial power supply. The coil is fully encased in a 50mm thick aluminum silicate insulation shell to reduce heat dissipation.

[0041] Step 3: Install a first pressure transmitter (range 0-100kPa absolute pressure) and a first temperature thermocouple (Pt100) on the inlet side pipeline of the heating device; install a second pressure transmitter and a second temperature thermocouple on the outlet side pipeline of the heating device. All pressure and temperature signals are connected to the frequency converter heating controller 9.

[0042] Step 4: Install a low-pressure-loss vortex flow meter 8 (DN200, pressure loss ≤80Pa) 500mm downstream of the heating device (straight pipe section), and transmit the flow meter measurement signal to the unit DCS.

[0043] Step 5: During normal operation of the unit, the first sensor measures a wet steam pressure of 12 kPa (absolute pressure), corresponding to a saturation temperature of 49.4℃; the actual measured temperature is 48.5℃. The controller determines that the medium is wet steam containing liquid water and starts heating. The controller outputs a 20kHz, 400V high-frequency alternating current, and the medium inside the steel pipe is heated by eddy current heating.

[0044] Step Six: The second sensor collects the outlet steam temperature and pressure in real time. When the outlet pressure is 12 kPa, the saturation temperature is 49.4℃, and the controller is set to a target temperature ≥ 54.4℃. The initial heating power is 3kW, and the measured outlet temperature is 52℃ (< 54.4℃). The controller automatically increases the power to 14kW; after the outlet temperature stabilizes at 55℃, the power is locked. At this time, the vortex flow meter 8 stably collects the pumping flow rate, and the displayed value is 220 kg / h.

[0045] Step 7: The unit load drops from 50MW to 40MW, the moisture content of the extracted gas increases, and the outlet temperature drops to 52℃. The controller automatically increases the power to 16kW to restore the outlet temperature to 55℃, continuously ensuring a slightly overheated state, and the flow meter continuously outputs an accurate flow signal.

[0046] This embodiment demonstrates that the method and apparatus can accurately measure the extraction flow rate of a condensing steam turbine under all operating conditions, and without any perceptible additional impact on the unit vacuum (vacuum pump inlet pressure fluctuation is less than 0.1 kPa).

[0047] Example 2: The process is essentially the same as in Example 1, except that the extraction device is a water jet ejector, and the absolute pressure inside the extraction pipeline is 8 kPa. The variable frequency heating controller 9 is powered by 220V / 50Hz. The first sensor measures a pressure of 8 kPa, corresponding to a saturation temperature of 41.0℃. The actual measured inlet temperature is 40.2℃, indicating wet steam. Closed-loop control heats the outlet temperature to 46.5℃ (≥ saturation temperature + 5℃), and the vortex flow meter 8 (pressure loss ≤ 60Pa) measures a flow rate of 180 kg / h. The entire measurement process did not cause a drop in condenser vacuum.

[0048] Its pipelines are arranged with equal diameters and no local throttling structure, so they generate almost no additional pipeline pressure loss, do not increase the load on the air extraction equipment, and do not change the original vacuum conditions of the unit.

[0049] The medium in the extraction pipeline is transformed from a two-phase mixture of saturated steam and condensed liquid water into a single-phase slightly superheated steam. The extraction flow rate can be accurately measured using a general-purpose vortex flow meter 8. Based on the temperature and pressure values ​​at the inlet and outlet of the pipeline heating device, the medium state is automatically determined, and the heating power is automatically adjusted and controlled in a closed loop, enabling automated operation without manual adjustment. This device has a compact structure, requires minimal modification work, and is suitable for flow measurement of various types of condensing steam turbines currently in service.

[0050] The above description is an explanation of the present invention and not a limitation thereof. The scope of the present invention is defined by the claims. Within the scope of protection of the present invention, any form of modification may be made.

Claims

1. A method for measuring the extraction flow rate of a condensing steam turbine, characterized in that: The work process includes the following: On the negative pressure extraction pipeline between the condenser extraction port of the condensing steam turbine and the inlet of the extraction equipment, a pipeline heating device and a low pressure loss gas flow meter are installed sequentially along the medium flow direction with the same inner diameter, no change in diameter, and no throttling. A first pressure sensor (1) and a first temperature sensor (2) are installed on the inlet pipe of the pipe heating device, and a second pressure sensor (6) and a second temperature sensor (7) are installed on the outlet pipe of the pipe heating device. Using the inlet pressure and inlet temperature parameters collected by the first pressure sensor (1) and the first temperature sensor (2), it is determined whether the medium in the pipeline is saturated wet steam with liquid water entrained. If it is identified as saturated wet steam, the pipeline heating device is started to heat the steam-water mixture, so that all the liquid water in the condenser exhaust gas is heated and vaporized until the medium at the outlet of the pipeline heating device is slightly superheated dry steam. Using the outlet temperature and outlet pressure parameters collected by the second pressure sensor (6) and the second temperature sensor (7), it is determined whether the medium in the pipeline is slightly superheated dry steam, and the heating power of the pipeline heating device is automatically adjusted in a closed loop until the outlet medium temperature reaches the local pressure steam saturation temperature +5℃ or more. After the outlet medium temperature reaches the local pressure steam saturation temperature +5℃, the pumping flow rate is measured by a low pressure loss gas flow meter. The pipeline heating device and the low-pressure-loss gas flow meter use equipment with the same inner diameter as the original extraction steam pipeline, without adding additional throttling elements or additional pressure loss in the extraction pipeline that affects the unit's vacuum.

2. The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 1, characterized in that: The steps for automatically identifying the state of the medium in the pipeline include: transmitting the inlet pressure and inlet temperature signals of the pipeline heating device to the frequency converter heating controller (9). The frequency converter heating controller (9) automatically determines whether the inlet medium is wet steam or dry steam based on the saturated physical property parameters of the medium. If it is determined to be dry steam and the temperature reaches the local pressure steam saturation temperature +5℃ or more, then no heating is required, and the pumping flow rate is directly measured by the flow meter.

3. The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 1, characterized in that: The steps of the closed-loop automatic adjustment of heating power include: connecting the outlet temperature and outlet pressure signals to the power adjustment module of the variable frequency heating controller (9) to form a power closed-loop control loop; determining the state of the medium in the pipeline; when the outlet medium temperature is less than the local pressure steam saturation temperature +5℃, automatically increasing the output power of the pipeline heating device; when the outlet medium temperature is ≥ the local pressure steam saturation temperature +5℃, the controller locks the current heating power unchanged.

4. The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 1, characterized in that: The low pressure loss gas flow meter is a vortex flow meter (8).

5. The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 1, characterized in that: The pipeline heating device adopts a pipeline electromagnetic heating device, the specific structure of which includes a magnetic metal seamless steel pipe (3), an electromagnetic heater and a heat insulation shell (5). The magnetic metal seamless steel pipe (3) is provided with connecting flanges at both ends. The inner diameter of the magnetic metal seamless steel pipe (3) is consistent with the inner diameter of the steam turbine condenser extraction pipe. It also includes an electromagnetic heating coil (4) spirally wound on the outer wall of the seamless steel pipe and a frequency conversion heating controller (9). The heat insulation shell (5) covers the outside of the electromagnetic heating coil (4). A low-pressure-loss gas flow meter is installed downstream of the pipeline heating device, and its inner diameter is consistent with the inner diameter of the magnetic metal seamless steel pipe (3) of the pipeline heating device. The first pressure sensor (1) and the first temperature sensor (2) are installed on the pipe on the inlet side of the pipe heating device; The second pressure sensor (6) and the second temperature sensor (7) are installed on the pipe on the outlet side of the pipe heating device; The signals measured by the first pressure sensor (1), the first temperature sensor (2), the second pressure sensor (6), and the second temperature sensor (7) are all transmitted to the frequency converter heating controller (9).

6. The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 5, characterized in that: The variable frequency heating controller (9) has an automatic steam medium status determination function: based on the received signals from the first pressure sensor (1) and the first temperature sensor (2), it determines whether the state of the inlet medium of the pipeline heating device is wet steam or dry steam; based on the received signals from the second pressure sensor (6) and the second temperature sensor (7), it determines whether the state of the outlet medium of the pipeline heating device is wet steam or dry steam, and can determine how many degrees the temperature of the outlet medium of the heating device is higher than the steam saturation temperature under local pressure.

7. The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 5, characterized in that: The variable frequency heating controller (9) has the function of automatically adjusting and controlling the heating power of the pipeline electromagnetic heating device. Based on the received signals from the second pressure sensor (6) and the second temperature sensor (7) and the determined outlet medium state of the pipeline heating device, it automatically adjusts and controls the power of the pipeline electromagnetic heating device so that the outlet medium state of the pipeline heating device meets the requirements for accurate measurement of the air extraction flow rate.

8. The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 5, characterized in that: The variable frequency heating controller (9) rectifies, filters, and inverts the input power frequency power into a high frequency AC output of 5-40kHz and 300-600V. The high frequency AC output of the variable frequency heating controller (9) is connected to the electromagnetic heating coil (4). The alternating magnetic field of the electromagnetic heating coil (4) causes eddy currents to be generated in the magnetic metal seamless steel pipe (3) to generate heat, thereby heating the steam-water mixture flowing through the pipe heating device, so that all the liquid water in the condenser exhaust gas is heated and vaporized.

9. The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 5, characterized in that: The magnetic metal seamless steel pipe (3) is coaxially connected to the front and rear pipelines through flanges to form a structure with no shrinkage and no expansion of the entire pipeline diameter. After the overall installation, the pipeline does not increase the resistance loss.

10. The method for measuring the extraction flow rate of a condensing steam turbine as described in claim 1, characterized in that: The heat insulation shell (5) is made of high temperature resistant heat insulation material to isolate the heat of the heating coil from being lost to the outside.

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