Rapid cooling method for steam turbine cylinder

Abstract

The invention discloses a rapid cooling method for a steam turbine cylinder. The rapid cooling method specifically comprises the following steps: a unit chemical maintenance and sliding pressure preparation stage: ensuring that main steam temperature corresponding to main steam pressure after switching has a superheat degree of more than 100 DEG C; in the steam temperature adjusting stage, the main steam pressure continues to be reduced through the high side and the low side after brake opening, and meanwhile shaft seal steam supply is kept uninterrupted; continuously performing uniform-speed sliding pressure by adjusting high and low until the main steam temperature is 35 DEG C lower than the temperature after the adjusting stage; in the gas temperature adjusting stage, when the pressure of the boiler enters 0.5 MPa, the boiler discharges water to execute a waste heat drying scheme, the water feeding pump stops running, and the deaerator stops heating; when the pressure of the steam pocket is as low as 0.2 MPa, opening a manual valve for completely discharging air of a steam-water system of the boiler; and a superheated steam evacuation valve is opened, the number of vacuum pumps is gradually increased, and other steam trap valves except the steam extraction steam trap valve are closed. According to the cooling method, an original system does not need to be changed, the operation process is simple, the temperature control gradient is smooth, the rotating machine equipment temperature control surface is uniform, and the cooling effect is remarkable.

Description

Technical Field

[0001] The invention belongs to the technical field of cylinder temperature rate control, and in particular relates to a method for rapid cooling of a turbine cylinder. Background Art

[0002] During the operation and maintenance of steam turbines, the cooling of the cylinder has always been a concern. After the steam turbine stops running, due to its large size and complex structure, the heat dissipation in the cylinder is relatively slow. If the cylinder cannot be cooled in time and effectively, the maintenance time of the equipment will be extended, the availability of the equipment will be reduced, and the production cost will be increased. Usually, after the turbine of a subcritical steam turbine generator unit is shut down normally, the cylinder wall temperature of the high-pressure cylinder is about 360°C. The high-pressure cylinder needs to be naturally cooled to the high-pressure inner cylinder wall temperature of 150°C before shutting down the turning gear. The period takes a long time, generally about 10 to 12 days. If the cylinder temperature of the high-pressure cylinder is higher during the emergency shutdown of the unit, the waiting time for cooling will also be longer, generally about 12 to 15 days. Traditional methods of cooling the cylinder of steam turbines often have problems such as slow cooling speed and low efficiency. Some conventional cooling methods, such as water cooling, can speed up the cooling speed to a certain extent, but there are also risks such as cylinder corrosion and uneven thermal stress. Summary of the invention

[0003] The purpose of the present invention is to provide a method for rapidly cooling a steam turbine cylinder, which can effectively regulate the cylinder temperature rate and shorten the cooling time of the steam turbine.

[0004] The technical solution adopted by the present invention is a method for rapid cooling of a steam turbine cylinder, which is specifically implemented according to the following steps: Step 1, unit chemical maintenance and sliding pressure preparation stage: ensure that the main steam temperature after the gate is opened has a superheat of more than 100℃ corresponding to the main steam pressure; re-confirm that the steam traps of the high and medium pressure cylinders are open after the gate is opened; Step 2, steam temperature adjustment stage: after the gate is opened, continue to reduce the main steam pressure through the high and low bypass, while maintaining uninterrupted steam supply to the shaft seal; ensure that all safety equipment of the generator set starts normally; adjust the high and low bypass to continue to slide the pressure at a uniform speed until the main steam temperature is 35℃ lower than the temperature after the adjustment stage, and ensure that the superheat is greater than 100℃; Step 3, gas temperature adjustment stage: when the boiler pressure reaches 0.5MPa and the main steam temperature is 260℃, the boiler is drained to implement the waste heat drying plan, the feed water pump is stopped, and the deaerator stops heating; when the drum pressure drops to 0.2MPa, open all the manual air venting valves in the boiler steam-water system; open the superheated steam exhaust valve to the air, gradually increase the number of vacuum pumps according to the speed, and close all steam traps except the first stage extraction steam trap.

[0005] The present invention is also characterized in that: In step 1, the main steam pressure is not greater than 4MPa; the superheat of the main reheat steam is maintained at >120℃, and the regulating stage temperature is not less than 360℃; the turbine regulating valve is a single valve control method.

[0006] In step 1, the cylinder expansion change rate is controlled to be less than 0.5mm / h, and the expansion difference is greater than -3mm; the temperature difference between the main and reheat steam is less than 20℃ throughout the whole process; the temperature difference between the main steam temperature and the temperature after the regulating stage is greater than 45℃; the temperature difference between the middle of the flange bolt and the regulating stage is greater than 100℃.

[0007] In step 2, during the steam temperature adjustment stage, the drum maintains a high water level, the deaerator maintains 0.5MPa water supply to the drum, and ensures that the temperature difference between the upper and lower walls of the drum is not greater than 10°C; when the main steam pressure drops to 0.2MPa, observe that the temperature is not lower than 200°C. If the parameters are stable, set the turbine speed to 1200rpm.

[0008] In step 2, the temperature difference between the inner and outer walls of the high and medium pressure outer cylinder flanges is controlled to be less than 80°C; the temperature difference between the inner and outer walls of the high and medium pressure outer cylinders and the high pressure inner cylinder is controlled to be less than 50°C; and the cylinder metal temperature drop rate is greater than 1°C / min.

[0009] In step 3, during the boiler draining process, the turbine continues to maintain the original cooling mode until the speed can no longer maintain 1200rpm; when the temperature of the middle part of the flange bolt drops below 140℃, close the main and re-steam valves to stop the vacuum pump, destroy the vacuum, and stop the steam supply to the shaft seal.

[0010] The beneficial effects of the present invention are: the method for rapid cooling of the turbine cylinder of the present invention has a simple control method, a simple operation process, and extremely low operation risk, and does not require the investment of unnecessary manpower costs, and does not require the change of the original system, does not require the investment of external media, the temperature control gradient is smooth, the temperature control surface of the rotary equipment is uniform, there is no technical blind spot, and the cooling effect is significant. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The present invention is a flow chart of the method for rapid cooling of a steam turbine cylinder. DETAILED DESCRIPTION

[0012] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0013] Example 1 The method for rapid cooling of a steam turbine cylinder of the present invention is specifically implemented according to the following steps: Step 1, unit chemical maintenance and sliding pressure preparation stage; This stage provides protection and maintenance for the main engine maintenance and emergency repairs; at the same time, it lays a good foundation for the second stage of steam temperature adjustment to prevent steam from carrying water; Ensure that the main steam temperature has a superheat of more than 100°C corresponding to the main steam pressure after the gate is opened; after the gate is opened, reconfirm that the drain valves of the high and medium pressure cylinders are open, and the high-pressure cylinder ventilation valve ensures that the high and medium pressure cylinders and the exhaust device are unobstructed.

[0014] The main steam pressure is not more than 4MPa; the superheat of the main reheat steam is maintained at >120℃, and the regulating stage temperature is not less than 360℃; the turbine regulating valve is a single valve control mode; Control the cylinder expansion rate to be less than 0.5mm / h, and the expansion difference to be greater than -3mm (pay special attention to the sufficient shaft seal pressure); the temperature difference between the main and reheat steam is less than 20℃ throughout the whole process; the temperature difference between the main steam temperature and the temperature after the regulating stage is greater than 45℃; the temperature difference between the middle of the flange bolt and the regulating stage is greater than 100℃; Step 2, gas temperature adjustment stage; After the gate is opened, the main steam pressure continues to be reduced through the high and low bypasses, while maintaining uninterrupted steam supply to the shaft seal; ensure that all safety equipment of the generator set starts normally; adjust the high and low bypasses to continue uniform sliding pressure until the main steam temperature is 35°C lower than the temperature after the regulating stage, and ensure that the superheat is greater than 100°C; at the same time, increase the back pressure to facilitate the control of the turbine speed, the turbine speed is 2100rpm.

[0015] During the steam temperature adjustment stage, the water level of the drum is kept high, the deaerator supplies water to the drum at 0.5MPa, and ensures that the temperature difference between the upper and lower walls of the drum is no more than 10°C; When the main steam pressure drops to 0.2MPa, observe that the temperature is not lower than 200℃. If the parameters are stable, the turbine speed can be set to 1200rpm.

[0016] Control the temperature difference between the inner and outer walls of the high and medium pressure outer cylinder flange to be less than 80℃; the temperature difference between the inner and outer walls of the high and medium pressure outer cylinder and the high pressure inner cylinder to be less than 50℃; the cylinder metal temperature drop rate is greater than 1℃ / min.

[0017] Step 3: Gas temperature adjustment stage; When the boiler pressure reaches 0.5MPa and the main steam temperature approaches 260℃, the boiler is drained to implement the waste heat drying plan, the feed water pump is stopped, and the deaerator stops heating; during the draining period, the turbine continues to maintain 1200rpm; When the drum pressure drops to 0.2MPa, open the manual air release valve of the boiler steam-water system; when the drum pressure drops to 0.15MPa, reduce the back pressure and maintain the speed unchanged; When the drum wall temperature drops to 160°C, the temperature of the boiler heat exchanger decreases, and the boiler performs the waste heat drying maintenance method after draining the water. During the boiler draining process, the turbine continues to maintain the original cooling method until the speed can no longer maintain 1200rpm.

[0018] Open the superheated steam exhaust valve to air, gradually increase the number of vacuum pumps according to the rotation speed, close all steam traps except the first stage extraction steam trap (it is forbidden to open the air valve of the reheat steam pipeline), and adjust the number of vacuum pumps according to different seasons and the speed of main steam temperature drop.

[0019] When the temperature in the middle of the flange bolt drops to below 140℃, the main and re-steam valves can be closed to stop the vacuum pump, destroy the vacuum, and stop the steam supply to the shaft seal.

[0020] The biggest advantage of the above three temperature control stages is that they can accelerate the cooling of the turbine and reduce the temperature of the middle part of the flange bolt to less than 140°C within 72 hours after normal coasting; the cylinder expansion is reduced to 9mm, and the expansion difference is <-1.8mm.

[0021] Example 2 The method for rapidly cooling a steam turbine cylinder of the present invention is as follows: Figure 1 As shown, specifically: The first stage: chemical maintenance and sliding pressure preparation stage of the unit provides protective maintenance for main engine maintenance and emergency repairs; at the same time, it lays a good foundation for sliding pressure in the second stage of steam temperature control to prevent steam from carrying water.

[0022] The main parameters of turbine shutdown and generator disconnection are: load 10MW, main steam pressure 3.3Mpa, main steam temperature 396℃, resteam pressure 0.2Mpa, resteam temperature 378℃, high-pressure inner cylinder upper wall temperature 364℃, expansion difference -0.25 / 3.0mm.

[0023] The second stage: the steam temperature adjustment stage. After the gate is opened, the main steam pressure continues to be reduced through the high and low bypasses, while maintaining uninterrupted steam supply to the shaft seal; ensure that all safety equipment of the generator set starts normally; adjust the high and low bypasses to continue to slide the pressure at a uniform speed until the main steam temperature is 35°C lower than the temperature after the regulation stage, and ensure that the superheat is greater than 100°C; at the same time, increase the back pressure to facilitate the control of the turbine speed.

[0024] High-speed temperature control parameters: reduce the main steam pressure to 2.36Mpa, the main steam temperature to 335℃, the re-steam pressure to 0.05Mpa, the re-steam temperature to 358℃, the temperature of the upper inner wall of the high-pressure inner cylinder to 343℃, the expansion difference to 0.65 / 3.75mm, the vacuum to 8.1Kpa, the high-regulation valve opening to 10.4%, the medium-regulation valve opening to 29%; the turbine speed to 2100rpm.

[0025] During the steam temperature adjustment stage, to prevent the drum temperature difference from being greater than 10°C and the boiler waste heat from being lost prematurely, the drum should always maintain a high water level and maintain a 0.5MPa pressure in the deaerator to supply water to the drum. When the drum pressure drops to 0.5MPa and the drum upper wall temperature is less than 160°C, the boiler begins to release water under pressure. During the release process, the turbine continues to maintain the original cooling mode until the speed can no longer maintain 1200rpm.

[0026] The main steam pressure is 0.29Mpa, the main steam temperature is 266℃. In order to avoid the turbine staying in the critical speed for a long time, the turbine speed is reduced to 1200rpm: the resteam pressure is 0.01Mpa, the resteam temperature is 255℃, the temperature of the upper inner wall of the high-pressure inner cylinder is 304℃, the expansion difference is -0.41 / 3.89mm, the vacuum is 30Kpa, the high-control valve opening is 23%, and the medium-control valve opening is 98%.

[0027] The total time from the start of the steam temperature control stage to the adjustment of the turbine speed to 2100rpm was 90 minutes, and the cylinder temperature dropped by about 5.3℃ / h.

[0028] The third stage: gas temperature adjustment stage; after the main steam pressure drops to 0.2MPa, observe that the main steam temperature is not lower than 200℃. If the parameters are stable, the speed can be appropriately increased to 1200rpm; check that the top shaft oil pump is operating normally; The total time from the start of the steam temperature adjustment stage to the adjustment of the turbine speed to 1200rpm was 170 minutes, and the cylinder temperature dropped by about 9.4℃ / h.

[0029] Open the superheated steam exhaust valve to air, gradually increase the number of vacuum pumps according to the speed, close all steam traps except the first stage extraction steam trap (manually adjust the opening of the air valve of the reheat steam pipeline), and maintain the regulated gas volume greater than 339kg / h (the temperature drop rate in autumn does not exceed 5.5℃ / h); the turbine speed drops back to 70rpm, and the number of vacuum pumps can be adjusted according to different seasons and the speed of main steam temperature drop.

[0030] The negative pressure system drives the turbine to exchange uniformly, and the main and re-regulating valves are fully opened: the temperature of the upper inner wall of the high-pressure inner cylinder is 211℃, the expansion difference is -2.6 / 4.1mm, the three vacuum pumps are all started, the vacuum degree is 45KPa, and the turbine speed is about 71rpm. After 45h: the main steam temperature is 48℃, the re-steam temperature is 72℃, the middle temperature of the flange at the highest point of the turbine temperature is <145℃, the expansion difference is -2.3 / 4.4mm, and the vacuum degree is 32Kpa.

[0031] The biggest advantage of the above three temperature control stages is that they can accelerate the cooling of the turbine and reduce the temperature of the middle part of the flange bolt to less than 140°C within 72 hours after normal coasting; the cylinder expansion is reduced to 9mm, and the expansion difference is <-1.8mm.

[0032] Example 3 The steam turbine of a power plant needs to be urgently repaired after running for a period of time. The rapid cooling method of the present invention is used to cool the steam turbine cylinder, specifically: Unit chemical maintenance and sliding pressure preparation stage: immediately after the gate is opened, confirm that the main steam temperature is 450℃, the corresponding main steam pressure is 3.8MPa, and the superheat is 105℃. After reopening the high and medium pressure cylinders' steam traps and high pressure cylinder ventilation valves, confirm that the high and medium pressure cylinders and the exhaust device are unobstructed. The regulating stage temperature is 365℃, and the turbine regulating valve is adjusted to the single valve control mode.

[0033] The monitoring cylinder expansion rate is 0.4mm / h, the expansion difference is -2.5mm, and the shaft seal pressure is maintained at 0.05MPa. The temperature difference between the main and reheat steam is 18℃, the temperature difference between the main steam temperature and the temperature after the regulating stage is 48℃, the middle temperature of the flange bolt is 270℃, and the temperature difference with the regulating stage is 95℃.

[0034] Steam temperature adjustment stage: After the brake is opened, the main steam pressure begins to be reduced through the high and low bypass, while maintaining the uninterrupted steam supply to the shaft seal. After the safety equipment is started normally, the pressure is uniformly reduced at a rate of 0.5MPa per hour. After a period of time, when the main steam temperature drops to 35℃ below the temperature after the adjustment stage, that is, when it reaches 330℃, the superheat is 110℃. At this time, the back pressure is increased and the turbine speed is controlled at 2100rpm.

[0035] The water level of the drum is maintained at 100mm (high water level), and the deaerator supplies water to the drum at a pressure of 0.5MPa. The temperature difference between the upper and lower walls of the drum is always controlled within 8℃. When the main steam pressure drops to 0.2MPa, the temperature is 205℃, and the turbine speed is set to 1200rpm. The temperature difference between the inner and outer walls of the high and medium pressure outer cylinder flange is 75℃, the temperature difference between the inner and outer walls of the high and medium pressure outer cylinder and the high pressure inner cylinder is 45℃, and the cylinder metal temperature drop rate is 1.2℃ / min.

[0036] Gas temperature adjustment stage: When the boiler pressure reaches 0.5MPa and the main steam temperature is 258℃, the boiler water discharge waste heat drying plan is implemented, the feed water pump is stopped, and the deaerator stops heating. During the water discharge, the turbine continues to maintain 1200rpm. When the drum pressure drops to 0.2MPa, open the manual valve for all air discharges in the boiler steam-water system. When the drum pressure drops to 0.15MPa, reduce the back pressure and maintain the speed unchanged. When the drum wall temperature drops to 158℃, the boiler heat exchanger temperature also drops accordingly. After the water is discharged, the boiler performs the waste heat drying maintenance method. During the whole process, the turbine continues to maintain the original cooling method until the speed can no longer maintain 1200rpm.

[0037] Open the superheated steam exhaust valve to the air, and gradually increase the number of vacuum pumps according to the speed. When the speed is 1000rpm, add a vacuum pump. When the main steam temperature drops by 20℃ per hour, add another vacuum pump. Close all steam traps except the first stage steam extraction steam trap, and do not open the air valve of the reheat steam pipeline.

[0038] According to this rapid cooling method, the entire cooling process is about 70% shorter than the traditional natural cooling method. After inspecting the steam turbine, no damage or safety hazards caused by improper cooling were found. The equipment maintenance measures also effectively protected the equipment and extended its service life. At the same time, due to the shortened cooling time, production can be resumed faster, which improves production efficiency and brings significant economic benefits to the enterprise.

Claims

1. A method for rapid cooling of a steam turbine cylinder, characterized in that: Follow the steps below to implement it: Step 1, unit chemical maintenance and sliding pressure preparation stage: ensure that the main steam temperature after the gate is opened has a superheat of more than 100℃ corresponding to the main steam pressure; re-confirm that the steam traps of the high and medium pressure cylinders are open after the gate is opened; Step 2, steam temperature adjustment stage: after the gate is opened, continue to reduce the main steam pressure through the high and low bypass, while maintaining uninterrupted steam supply to the shaft seal; ensure that all safety equipment of the generator set starts normally; adjust the high and low bypass to continue to slide the pressure at a uniform speed until the main steam temperature is 35℃ lower than the temperature after the adjustment stage, and ensure that the superheat is greater than 100℃; Step 3, gas temperature adjustment stage: when the boiler pressure reaches 0.5MPa and the main steam temperature is 260℃, the boiler is drained to implement the waste heat drying plan, the feed water pump is stopped, and the deaerator stops heating; when the drum pressure drops to 0.2MPa, open all the manual air venting valves in the boiler steam-water system; open the superheated steam exhaust valve to the air, gradually increase the number of vacuum pumps according to the speed, and close all steam traps except the first stage extraction steam trap.

2. The method for rapid cooling of a steam turbine cylinder according to claim 1, characterized in that: In step 1, the main steam pressure is not greater than 4 MPa; the superheat of the main reheat steam is maintained at >120°C, and the regulating stage temperature is not less than 360°C; the turbine regulating valve is a single valve control mode.

3. The method for rapid cooling of a steam turbine cylinder according to claim 2, characterized in that: In step 1, the cylinder expansion change rate is controlled to be less than 0.5mm / h, and the expansion difference is greater than -3mm; the temperature difference between the main and reheat steam is less than 20°C throughout the whole process; the temperature difference between the main steam temperature and the temperature after the regulating stage is greater than 45°C; the temperature difference between the middle of the flange bolt and the regulating stage is greater than 100°C.

4. The method for rapid cooling of a steam turbine cylinder according to claim 3, characterized in that: In step 2, during the steam temperature adjustment stage, the drum maintains a high water level, the deaerator maintains 0.5MPa to supply water to the drum, and ensures that the temperature difference between the upper and lower walls of the drum is not greater than 10°C; when the main steam pressure drops to 0.2MPa, the temperature is observed to be no less than 200°C, and if the parameters are stable, the turbine speed is set to 1200rpm.

5. The method for rapid cooling of a steam turbine cylinder according to claim 4, characterized in that: In step 2, the temperature difference between the inner and outer walls of the high and medium pressure outer cylinder flange is controlled to be less than 80°C; the temperature difference between the inner and outer walls of the high and medium pressure outer cylinder and the high pressure inner cylinder is controlled to be less than 50°C; and the cylinder metal temperature drop rate is greater than 1°C / min.

6. The method for rapid cooling of a steam turbine cylinder according to claim 5, characterized in that: In step 3, during the boiler draining process, the turbine continues to maintain the original cooling mode until the speed can no longer maintain 1200 rpm; when the temperature of the middle part of the flange bolt drops below 140° C., the main and re-steam valves are closed to stop the vacuum pump, destroy the vacuum, and stop the steam supply to the shaft seal.

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