A leak detection method for a vacuum system of a water-cooling unit in a thermal power plant

Abstract

The present invention relates to a method for detecting leakage of a vacuum system of a water-cooled unit in a thermal power plant, comprising the following steps: (1) isolating a system connected to a condenser from a positive pressure part in operation; (2) heating a deaerator to heat condensate of the unit, so that the temperature of the condensate rises to 50°C; (3) normally putting a steam turbine and a steam seal of a feedwater pump steam turbine into operation; (4) introducing steam into a condenser drain expansion tank; and (5) after the pressure of the condenser reaches 8-12 kPa, detecting leakage points by checking the on-site steam and water leakage points. The method can quickly and accurately detect leakage points, detect leakage of the condenser, and detect leakage of transformer areas such as a low-pressure cylinder, a safety membrane, a shaft seal sleeve, a cylinder joint surface, a small steam turbine of a feedwater pump, and a low-pressure heater of the steam turbine, thereby expanding the scope of leakage detection.

Description

Technical Field

[0001] The invention belongs to the technical field of leakage detection of thermal power plant equipment, and in particular relates to a leakage detection and inspection method for a vacuum system of a water-cooling unit in a thermal power plant. Background Art

[0002] Large thermal power plants use condensers to cool the steam output by the turbine to form condensate, which is then returned to the boiler through a condensate pump and a feed water pump for recycling.

[0003] The working principle of the condenser Figure 1 The main functions of the condenser are to establish and maintain a high vacuum at the exhaust port of the steam turbine, and to use the water condensed from the exhaust steam of the steam turbine as boiler feed water to form a complete cycle. The condensing equipment plays the role of a cold source in the thermal cycle of the steam turbine device. Reducing the exhaust temperature and exhaust pressure of the steam turbine can improve the efficiency of the thermal cycle. The condenser is a heat exchanger that condenses the exhaust steam of the steam turbine into water, also known as a rehydrator. Condensers are mainly used in steam turbine power plants and are divided into water-cooled condensers and air-cooled condensers.

[0004] At present, the leakage inspection of the vacuum system of the water-cooled unit of the thermal power plant after shutdown is generally carried out by injecting water to a high level on the steam side of the condenser, and the leakage point is found by checking the leakage point on site.

[0005] In the prior art, a Chinese patent with application number 202010228574.X discloses a method for water injection and leak detection in the vacuum system of an air-to-condenser in a thermal power plant, which specifically includes the following steps: 1) After the air-to-condenser reaches the maintenance condition, close the condensate return isolation door of each column of the air-to-condenser; 2) The condensate in the condensate system of the unit is transported to all equipment in the vacuum system of the air-to-condenser in sequence through a newly added water injection pipe and the air extraction pipes of each column, so that the heat exchange tube bundle, the condensate header, and the condensate return pipe are filled with water, and the water level is controlled to submerge the weld on the upper edge of the groove at the bottom of the top steam distribution pipe; 3) After the water level reaches the required height, start searching for leaks in the air-to-condenser filled with water, and each leak is a leak in the vacuum system.

[0006] The Chinese patent application number is 201910771613.8, which discloses a condenser and a method for inspecting and leaking the condenser. During the inspection and leak detection, the condensate and cooling water of the condenser are discharged, and after a vacuum is formed in the heat exchange chamber and the heat exchange tube, the first control valve, the second control valve, the cooling water outlet, the cooling water inlet and all the inlets and outlets of the condenser are closed. Cooling water is introduced from the steam inlet tank to fill the entire shell and the steam inlet chamber. After staying for 15-30 hours, the shell wall, the heat exchange tube wall and all accessory equipment are checked. If water seepage is found, the position of the seepage water is marked. If no water seepage occurs, there is no leakage, and the inspection and leak detection is completed.

[0007] The existing water injection leak detection method is affected by factors such as the support force at the bottom of the condenser and the layout of the turbine. Water can only be pressed to the throat, and the leak points of equipment above this level are difficult to find. As the position increases, the water pressure decreases and the leak point is more difficult to be found. Summary of the invention

[0008] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for detecting leakage of a vacuum system of a water-cooling unit in a thermal power plant, which can quickly and accurately find leakage points.

[0009] The technical solution adopted by the present invention is: it comprises the following steps:

[0010] (1) Drain the main reheat steam connected to the condenser, drain the turbine body, drain the low-pressure bypass system, the deaerator and condenser connecting pipes, the heater emergency drain, the heater normal drain, the heater drain, the ash hopper heating system, and drain the steam pipelines to the positive pressure part in operation and isolate them;

[0011] (2) Heat the deaerator to heat the condensate of the unit, raising the condensate temperature to 50°C;

[0012] (3) Put the steam turbine and feedwater pump steam turbine seal into operation;

[0013] (4) introducing steam into the condenser drain expansion tank;

[0014] (5) After the condenser pressure reaches 8-12 kPa, the leakage point is found by checking the steam and water leakage points on site.

[0015] Furthermore, in step (1), the exhaust butterfly valve of the feed pump turbine is kept open, the main and reheat steam drain valves on the turbine side are closed, the drain valves of the turbine body are closed, the steam extraction drain valves of each section are closed, the vacuum breaking valve is closed, and the water seal groove of the vacuum breaking valve is filled with water; and the pneumatic valves at the inlet of each vacuum pump are closed.

[0016] Furthermore, in step (1), the manual door for extracting air from the low-pressure heater and the manual door for extracting air from the deaerator are closed.

[0017] Furthermore, in step (2), the unit executes the normal operation mode to deliver steam seal, reduce the pressure of the steam seal mother pipe, and lower the negative pressure of the lubricating oil tank.

[0018] Furthermore, the steam seal mother pipe pressure was reduced to 0.02MPa and the negative pressure of the lubricating oil tank was reduced to 100Pa.

[0019] Furthermore, in step (3), the bypass door of the auxiliary steam header automatic steam trap, the bypass door of the auxiliary steam to deaerator heating automatic steam trap, the bypass door of the steam seal main pipe automatic steam trap, and the electric door from the steam seal overflow to the condenser are opened, and the steam seal overflow regulating valve is gradually opened depending on the change of the condenser pressure to allow steam to enter the condenser until the condenser pressure reaches 8-12 kPa.

[0020] Furthermore, in step (4), steam is introduced into the condenser drain expansion tank through the steam seal overflow regulating valve.

[0021] Furthermore, in step (5), during the inspection process, the condensate temperature does not exceed 65°C, the low-pressure cylinder exhaust temperature does not exceed 93°C, and the shutdown value is 107°C.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention can quickly check the leakage point of the condenser, and can detect the position that cannot be checked by the conventional water-cooling unit water pressure leak detection.

[0024] 2. Compared with the conventional water pressure leak detection measures, the present invention can efficiently find the leakage point. The micro-positive pressure leak detection process does not exceed 2 hours from the beginning to the end of pressure relief, which is greatly shortened compared with the conventional condenser water pressure leak detection time.

[0025] 3. Compared with conventional water pressure leak detection, it has a significant water-saving effect, saving about 300 tons of water per leak detection.

[0026] 4. The time node of micro-positive pressure leak detection is better controlled and can be achieved during each unit shutdown and startup process without increasing the auxiliary machine operation time. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the working principle of the condenser;

[0028] Figure 2 It is a system schematic diagram of the present invention.

[0029] Figure numerals: 1 condenser, 2 steam turbine, 3 feed water pump turbine, 4 deaerator, 5 vacuum pump, 6 drain pipeline, 7 deaerator drain pipe, 8 high and low heater and emergency drain pipes, 9 low bypass, 10 turbine shaft seal, 11 steam seal steam inlet pressure regulating door, 12 steam seal overflow valve, 13 steam seal overflow switching valve, 14 drain expansion tank, 15 deaerator air extraction pipe, 16 medium pressure cylinder. DETAILED DESCRIPTION

[0030] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0031] Example 1

[0032] In this embodiment, during the shutdown of the unit, the leakage point of the negative pressure system is found by using the leakage detection method of the condenser of the water-cooled unit of the thermal power plant of the present invention, and the leakage is handled in time.

[0033] Before the search, the steam turbine body, condenser, small machine exhaust pipe and other related auxiliary equipment of the present invention have not been inspected and maintained.

[0034] The turbine is cranked and put into operation for more than 4 hours.

[0035] Maintain the operation of the condensate system, shut down the circulating water system, and test whether the low-pressure cylinder water spray cooling system is normal.

[0036] Reference Figure 2 The research object of the present invention is the vacuum system of the water-cooled unit of a thermal power plant, which includes a condenser 1, a steam turbine 2, a feedwater pump steam turbine 3, a deaerator 4, a vacuum pump 5, an intermediate pressure cylinder 16, a drain expansion tank 14 and related pipelines. The drain pipeline 6 in the figure includes steam turbine drain, small steam turbine drain, ash hopper heating drain, heater drain, and exhaust steam recovery drain. The pipeline also involves a deaerator drain pipe 7, a high and low heater and accident drain pipe 8, a low bypass 9, a steam turbine shaft seal 10, a steam seal steam inlet pressure regulating door 11, a steam seal overflow valve 12, a steam seal overflow switching valve 13, a drain expansion tank 14 and a deaerator air extraction pipe 15.

[0037] The leak detection method of the present invention comprises the following steps:

[0038] (1) Isolate the system connected to the condenser to the positive pressure part in operation; specifically, drain the main reheat steam connected to the condenser, drain the turbine body, low-pressure bypass system, deaerator and condenser connecting pipes, heater emergency drain, heater normal drain, heater drain, ash hopper heating system, and steam pipelines to the positive pressure part in operation;

[0039] (2) Heat the deaerator to heat the condensate of the unit, raising the condensate temperature to 50°C;

[0040] (3) Start the steam turbine and feedwater pump steam turbine steam seal in normal operation;

[0041] (4) introducing steam into the condenser drain expansion tank;

[0042] (5) After the condenser pressure reaches 8-12 kPa, the leakage point is found by checking the steam and water leakage points on site.

[0043] Example 2

[0044] The process of this embodiment is the same as that of embodiment 1. More specifically, in step (1) of this embodiment, the exhaust butterfly valve of the feedwater pump turbine is kept open. Specifically, the exhaust butterfly valve of small turbine A and the exhaust butterfly valve of small turbine B are opened. The main and reheat steam drain valves on the turbine side are closed, the drain valves of the turbine body are closed, the steam extraction drain valves of each section are closed, the vacuum breaking valve is closed, and water is injected. The inlet doors of each vacuum pump are closed.

[0045] Close the low-pressure air extraction manual door and the deaerator air extraction manual door.

[0046] In step (2), the condensate of the unit is heated by heating the deaerator and opening the overflow valve from the deaerator to the condenser, thereby gradually increasing the condensate temperature to 50°C.

[0047] In step (3), the unit performs normal steam seal delivery and appropriately reduces the steam seal mother pipe pressure to about 0.02MPa. Appropriately lower the negative pressure of the lubricating oil tank to avoid water ingress into the oil.

[0048] Example 3

[0049] The process of this embodiment is the same as that of embodiment 2. More specifically, in step (5), according to the need for leak detection, the bypass door of the auxiliary steam header automatic steam trap, the bypass door of the auxiliary steam to deaerator heating automatic steam trap, the bypass door of the steam seal main pipe automatic steam trap, and the electric door from the steam seal overflow to the condenser are opened. Depending on the change in the condenser pressure, the steam seal overflow regulating valve is gradually opened to allow steam to enter the condenser until the pressure in the condenser reaches 8-12 kPa (gauge pressure).

[0050] When the pressure is too high, the pressure in the system is controlled by adjusting the test vacuum breaking door (manual door). If the pressure rises quickly, the vacuum breaking door (electric door) is immediately opened to release the pressure.

[0051] The maintenance personnel shall conduct on-site leak detection and mark the leak points found. During the negative pressure system charging and leak detection, the condensate temperature shall not exceed 65°C. The operating personnel shall pay attention to monitoring the metal temperature of the steam turbine and the exhaust temperature of the low-pressure cylinder shall not exceed the limit (not exceeding 93°C, the shutdown value is 107°C, and the shutdown temperature exceeds this temperature during operation. The 93°C alarm is a safety control measure). Otherwise, the steam seal steam inlet and condensate pressure shall be adjusted in time, and the water spray volume of the low-pressure cylinder shall be increased. After all inspections are completed, the maintenance personnel contact the operating duty officer to complete the leak detection work. Close the bypass door of the auxiliary steam header automatic steam trap, the bypass door of the auxiliary steam to deaerator heating automatic steam trap, and the bypass door of the steam seal mother pipe automatic steam trap, and stop the steam supply to the condenser.

[0052] Perform condensate water exchange to lower the condensate temperature. When the exhaust cylinder temperature is less than 50°C, start the circulating water pump and vacuum pump. After the negative pressure system is depressurized to 0, open the steam turbine body drain valves and each section steam extraction drain valve to fully drain for 15 minutes. Maintain the vacuum system for 120 minutes (fully extract the steam accumulated in the negative pressure system), destroy the steam turbine vacuum, and shut down the steam seal.

[0053] It should be noted that the thermal workers of the maintenance department installed positive pressure gauges (0-20kPa pressure gauges, which were calibrated and qualified in advance) at the low-pressure cylinder exhaust and vacuum pump inlet.

[0054] Before leak detection begins, professional steam turbine personnel in the maintenance department will take protective measures by installing explosion-proof membranes on the main engine's low-pressure cylinder and small unit's exhaust pipe, and open the manhole door on the circulating water side. When the condenser is pressurized, the flanges of the condenser body and various pipeline connectors will be regularly temperature-checked. The temperature on the condenser shell side will not exceed 90 degrees, and the temperature on the tube side, including the water chamber seal, will be kept below 50 degrees. On-site personnel will regularly perform temperature checks on the condenser shell and tube sides.

[0055] The present invention can detect leaks in condensers, and can also detect leaks in transformer areas such as low-pressure cylinders, safety membranes, shaft seal sleeves, cylinder joint surfaces, feedwater pump turbines, and low-pressure heaters of steam turbines, thereby expanding the scope of leak detection.

[0056] The present invention can quickly check the leakage points of the condenser, and can realize the locations that cannot be checked by the conventional water-cooled unit pressure water leak detection, mainly including: 1) The steam system of the small steam turbine that shares the condenser with the main engine: because the twenty-five countermeasures clearly prohibit the water inlet of the steam turbine, the usual practice during the conventional pressure water leak detection is to close the small machine exhaust butterfly valve to achieve isolation from the condenser, and the leakage points of the small machine system are difficult to find; 2) Equipment above the throat of the steam turbine, such as: low-pressure cylinder, safety film, shaft seal sleeve, cylinder joint surface, this part of the leakage points is limited by the conventional pressure water height and cannot be found, and weak parts such as the connecting pipe expansion joint lack supervision; 3) Negative pressure drain pipes that are far away from the condenser or at a higher position: such as the deaerator overflow pipe, the deaerator water discharge pipe, the drain pipes of various high-level steam pipes, the low-pressure heater and other pressure-changing areas, the furnace side (heater drain pipe, ash hopper heating drain pipe, exhaust steam recovery drain pipe, etc.) long-distance drain pipes, etc.

[0057] Effect example

[0058] A certain power plant unit uses the leak detection method of the present invention to detect leaks.

[0059] Through positive pressure leak detection, it was found that the exhaust cylinder joint surface of the small steam turbine A in the power plant's #1 unit was not tight, the low-pressure shaft seal sleeve of the small steam turbine B was leaking vacuum, the low-pressure cylinder shaft seal joint surface of the steam turbine was leaking vacuum, and the pipe behind the drain valve behind the heating steam extraction electric door was leaking vacuum.

[0060] By applying glue to the joint surface of the low-pressure cylinder shaft seal of the steam turbine, tightening and applying glue to the joint surface of the exhaust cylinder of the small steam turbine A, and applying glue to the low-pressure shaft seal sleeve of the small steam turbine B, the vacuum leakage rate was reduced from 620Pa / min to 146Pa / min after the pipeline after the drain valve and the electric door of the heating and exhaust was repaired and welded, the vacuum was increased by 0.7kPa, and the coal consumption per kilowatt-hour was reduced by 0.21g / kWh. It is better than the standards of two types of enterprises.

[0061] The low-pressure cylinder shaft seal of the A\B small steam turbine of the power plant's #4 unit leaked vacuum, the low-pressure cylinder shaft seal on the generator side leaked vacuum, and the manual door bolts of the small steam turbine drain main pipe leaked vacuum.

[0062] By applying glue to the joint surface of the low-pressure cylinder shaft seal of the steam turbine, tightening and applying glue to the joint surface of the exhaust cylinder of the A small steam turbine, opening the cylinder of the B small steam turbine for inspection and replacement of the shaft seal, and dismantling and overhauling the manual door of the small steam turbine drain main pipe, the vacuum leakage rate was reduced from 820Pa / min to 140Pa / min. It is better than the standards of the two types of enterprises.

[0063] At present, the technical solution of the present invention has been put into pilot production, that is, a small-scale experiment before the large-scale mass production of the product. After the pilot production was completed, a user survey was conducted on a small scale, and the survey results showed that user satisfaction was high. Now, preparations have been started for the formal production and industrialization of the product (including intellectual property risk warning survey).

[0064] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for leak detection of a vacuum system of a water-cooling unit in a thermal power plant, characterized in that: The method comprises the following steps: (1) draining the main reheat steam connected to the condenser, draining the turbine body, the low-pressure bypass system, the deaerator and condenser connecting pipes, the heater emergency drain, the heater normal drain, the heater drain, the ash hopper heating system, and draining each steam pipeline to the operating positive pressure part and isolating; (2) Heat the deaerator to heat the condensate of the unit, raising the condensate temperature to 50°C; (3) Put the steam turbine and feedwater pump steam turbine seal into operation; (4) introducing steam into the condenser drain expansion tank; (5) After the condenser pressure reaches 8-12 kPa, the leakage point is found by checking the steam and water leakage points on site; In step (1), keep the exhaust butterfly valve of the feedwater pump steam turbine open, close the main and reheat steam drain valves on the turbine side, close the drain valves of the turbine body, close the steam extraction drain valves of each section, close the vacuum breaking valve, and fill the water seal groove of the vacuum breaking valve with water; close the pneumatic valves at the inlet of each vacuum pump; In step (1), close the manual air extraction door for low-pressure heater and the manual air extraction door for deaerator.

2. A method for leak detection of a vacuum system of a water-cooling unit in a thermal power plant according to claim 1, characterized in that: In step (2), the unit executes the normal operation mode to deliver steam seal, reduce the pressure of the steam seal mother pipe, and lower the negative pressure of the lubricating oil tank.

3. A method for leak detection of a vacuum system of a water-cooling unit in a thermal power plant according to claim 2, characterized in that: The steam seal mother pipe pressure dropped to 0.02MPa and the negative pressure of the lubricating oil tank dropped to 100Pa.

4. A method for leak detection of a vacuum system of a water-cooling unit in a thermal power plant according to claim 1, characterized in that: In step (3), open the bypass door of the auxiliary steam header automatic steam trap, the bypass door of the auxiliary steam to deaerator heating automatic steam trap, the bypass door of the steam seal main pipe automatic steam trap, and the electric door from the steam seal overflow to the condenser. Depending on the change in the condenser pressure, gradually open the steam seal overflow regulating valve to allow steam to enter the condenser until the condenser pressure reaches 8-12 kPa.

5. A method for leak detection of a vacuum system of a water-cooling unit in a thermal power plant according to claim 1, characterized in that: In step (4), steam is introduced into the condenser drain expansion tank through the steam seal overflow regulating valve.

6. A method for leak detection of a vacuum system of a water-cooling unit in a thermal power plant according to claim 1, characterized in that: In step (5), during the inspection process, the condensate temperature does not exceed 65°C, the low-pressure cylinder exhaust temperature does not exceed 93°C, and the shutdown value is 107°C.

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