Method for servicing a steam turbine

Abstract

The present disclosure relates to a steam turbine shutdown maintenance method, which comprises: before the steam turbine is shut down, exiting the condensate polishing operation, increasing the ammonia content of the condensate and feed water, so that the PH value of the feed water at the inlet of the economizer is within a first range; after the steam turbine is shut down, running the vacuum pump, maintaining the operation of the shaft seal system of the steam turbine, and controlling the vacuum degree of the steam turbine to be within a second range until the boiler is pressure drained; after the vacuum pump is operated for a first duration, the steam turbine is shut down, the quick cooling device of the steam turbine is started, and compressed air is introduced into the steam turbine to dry the steam turbine. The steam turbine shutdown maintenance method realizes the corrosion prevention effect of the steam turbine, and can effectively avoid oxygen corrosion of the steam turbine.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of steam turbines, in particular, to a steam turbine shutdown maintenance method. BACKGROUND

[0002] If effective protection measures are not taken, the metal inner surface of the water vapor system of a thermal power equipment will be seriously corroded by oxygen when the thermal power equipment is shut down, which is called shutdown corrosion. Shutdown corrosion occurs because when the thermal power equipment (such as a steam turbine) is shut down, the residual steam in the cylinder condenses (or leaks in) and adheres to a thin layer of water film on the surface of the moving blade and the static blade of the steam turbine. When the outside air enters the cylinder, the oxygen in the air dissolves in the water film, making the water film saturated with dissolved oxygen and causing oxygen corrosion of the metal. The maintenance method in the related art cannot effectively prevent oxygen corrosion of the steam turbine. SUMMARY

[0003] The purpose of the present disclosure is to provide a steam turbine shutdown maintenance method that can effectively solve the technical problems existing in the related art.

[0004] To achieve the above purpose, the present disclosure provides a steam turbine shutdown maintenance method, which comprises:

[0005] Before the steam turbine is shut down, the condensate water polishing treatment operation is exited, and the ammonia amount of the condensate water and the feed water is increased, so that the PH value of the feed water at the inlet of the economizer is within a first range;

[0006] After the steam turbine is shut down, a vacuum pump is operated to maintain the operation of the shaft seal system of the steam turbine, and the vacuum degree of the steam turbine is controlled to be within a second range until the boiler is pressurized and the water is discharged;

[0007] The vacuum pump is stopped after being operated for a first duration, a quick cooling device of the steam turbine is started, and compressed air is introduced into the steam turbine to dry the steam turbine.

[0008] Optionally, before the vacuum pump is operated, it is judged whether all the drain valves of the steam turbine are opened, and the steam turbine is vacuumized when all the drain valves of the steam turbine are opened.

[0009] Optionally, after the steam turbine is vacuumized;

[0010] The drain valves of the main steam pipeline on the machine side are closed;

[0011] After the reheat steam pipeline is extracted to zero, the drain valves of the reheat steam pipeline on the machine side are closed.

[0012] Optionally, after the drain valves of the reheat steam pipeline on the machine side are closed;

[0013] Maintain the vacuum state of the steam turbine, and wait for the boiler to drain under pressure, and after the pressure is reduced to zero;

[0014] Close the respective drain valves and respective evacuation valves of the boiler superheater, reheater, open the respective drain valves of the machine side main steam pipeline and the reheated steam pipeline, open the partial high bypass valve and low bypass valve, and make the vacuum degree of the separator greater than 50 kPa and maintain for a second time length.

[0015] Optionally, after the vacuum degree of the separator is greater than 50 kPa and maintains for a second time length, the evacuation valves of the economizer, the separator and the reheater are opened and maintained for a third time length.

[0016] Optionally, after the evacuation valves of the economizer, the separator and the reheater are opened and maintained for a third time length, the evacuation valves are closed, and vacuuming is continued for a fourth time length until the relative humidity of air in the steam turbine is reduced to 60% or equal to the ambient relative humidity.

[0017] Optionally, after the relative humidity of air in the steam turbine is reduced to 60% or equal to the ambient relative humidity, the vacuum pump is stopped, and the shaft seal system is stopped.

[0018] Optionally, after the shaft seal system is stopped, the fast cooling device of the steam turbine is enabled, the exhaust relative humidity is measured every fifth time length, and when the relative humidity is less than 50%, the fast cooling device of the steam turbine is stopped.

[0019] Optionally, the second time length is 1 hour.

[0020] Optionally, the first range is between 9.6 and 10.5.

[0021] In the above technical solution, by increasing the condensate and the ammonia content of the feed water, the PH value of the feed water at the inlet of the economizer is within the first range, so as to realize the ammonia water alkalization treatment, that is, during the shutdown stage, the steam turbine is pre-maintained; after the steam turbine is blocked, the unit vacuum is maintained until the boiler is drained under pressure, the boiler negative pressure waste heat is dried, the steam turbine ammonia water is alkalized and dried, and the water accumulation in the steam turbine is avoided, and the unit vacuum does not need to be maintained for a long time, so as to effectively reduce the energy consumption; in addition, after the steam turbine fast cooling device is put into operation, the humidity in the steam turbine is effectively reduced, the anticorrosion effect of the steam turbine is realized, and the oxygen corrosion of the steam turbine is effectively avoided. Other features and advantages of the present disclosure will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0022] The accompanying drawings are included to provide a further understanding of the present disclosure and constitute a part of the specification, and together with the following specific embodiments, serve to explain the present disclosure, but do not constitute a limitation on the present disclosure. In the drawings:

[0023] Figure 1 is a flowchart of a steam turbine outage maintenance method according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0024] The specific embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0025] Referring to Figure 1 The present disclosure provides a steam turbine outage maintenance method, which comprises:

[0026] S101, before the steam turbine is shut down, the condensate polishing is exited, the ammonia amount of the condensate and the feed water is increased, so that the PH value of the feed water at the inlet of the economizer is within a first range;

[0027] S102, after the steam turbine is stopped by braking, the vacuum pump is operated, the shaft seal system of the steam turbine is maintained to operate, and the vacuum degree of the steam turbine is controlled to be within a second range until the boiler is drained under pressure;

[0028] S103, after the vacuum pump is operated for a first time length, the steam turbine is stopped, the quick cooling device of the steam turbine is started, and compressed air is introduced into the steam turbine, so that the steam turbine is dried.

[0029] In the above technical solution, by increasing the ammonia amount of the condensate and the feed water, the PH value of the feed water at the inlet of the economizer is within a first range, so that ammonia water alkalization treatment is realized, that is, the steam turbine outage is pre-maintained during the shutdown stage; after the steam turbine is stopped by braking, the unit vacuum is maintained until the boiler is drained under pressure, the boiler negative pressure waste heat is dried, the steam turbine ammonia water alkalization is dried, and the water accumulation in the steam turbine is avoided without the need to maintain the unit vacuum for a long time, so that the energy consumption is effectively reduced; in addition, after the steam turbine quick cooling device is put into operation, the humidity in the steam turbine is effectively reduced, the corrosion prevention effect of the steam turbine is realized, and the oxygen corrosion of the steam turbine is effectively avoided.

[0030] In an alternative embodiment, before the vacuum pump is operated, it is judged whether all the drain valves of the steam turbine are opened, and the steam turbine is vacuumed under the condition that all the drain valves of the steam turbine are opened. Thus, the effectiveness and safety of vacuuming are ensured. The specific judgment method can be judged by manual inspection or automatically detected by sensors, and the present disclosure does not limit this.

[0031] In other embodiments, after the steam turbine is vacuumed; all the drain valves of the main steam pipeline on the machine side are closed; after the reheat steam pipeline is extracted to zero, all the drain valves of the reheat steam pipeline on the machine side are closed. Thus, the sealing performance of the main steam pipeline on the machine side and the reheat steam pipeline on the machine side is ensured.

[0032] Optionally, after closing the respective drain valves of the machine-side reheating steam pipeline; maintaining the vacuum state of the steam turbine, waiting for the boiler to discharge water under pressure, and depressurize to zero; closing the respective drain valves and respective evacuation valves of the boiler superheater and reheater, opening the respective drain valves of the machine-side main steam pipeline and reheating steam pipeline, and opening part of the high bypass valve and low bypass valve, the vacuum degree of the separator is greater than 50 kPa and maintained for a second time length. To achieve good drying maintenance effect, and the present disclosure does not limit the second time length.

[0033] In another optional embodiment, after the vacuum degree of the separator is greater than 50 kPa and maintained for a second time length, the evacuation valves of the economizer, separator and reheater are opened and maintained for a third time length. The present disclosure also does not limit the third time length.

[0034] After opening the evacuation valves of the economizer, separator and reheater and maintaining for a third time length, the evacuation valves are closed, and vacuuming is continued for a fourth time length until the relative humidity of the air in the steam turbine is reduced to 60% or equal to the ambient relative humidity, thereby achieving good drying effect, and the present disclosure also does not limit the fourth time length.

[0035] In addition, after the relative humidity of the air in the steam turbine is reduced to 60% or equal to the ambient relative humidity, the vacuum pump is stopped, and the shaft seal system is stopped. At this point, the steps of boiler negative pressure waste heat drying and steam turbine ammonia alkalization drying are completed.

[0036] Optionally, after stopping the shaft seal system, the quick cooling device of the steam turbine is started, the exhaust relative humidity is measured every fifth time length, and when the relative humidity is less than 50%, the quick cooling device of the steam turbine is stopped. The steam turbine quick cooling device can not only reduce the temperature of the cylinder, but also dry and maintain the cylinder.

[0037] Optionally, the second time length described above can be 1 hour, but the present disclosure does not limit the specific time of the second time length, which can be set according to the drying effect.

[0038] Optionally, the first range described above is between 9.6 and 10.5, and the present disclosure also does not limit this.

[0039] In general, the specific steps of an embodiment of the steam turbine shutdown maintenance method described above can be as follows:

[0040] First stage, ammonia alkalization treatment. 4 hours before shutdown, exit the condensate polishing treatment operation, increase the ammonia amount of condensate and feedwater, and increase the pH value of the feedwater at the inlet of the economizer to 9.6 to 10.5, and then stop the unit.

[0041] Second stage, boiler negative pressure waste heat drying and steam turbine ammonia alkalization drying.

[0042] (1) After the unit is tripped, maintain the vacuum pump running, maintain the unit shaft seal system running, control the unit vacuum to be within the normal range. Check that all the drains of the turbine body are open. Vacuum the turbine body.

[0043] (2) Close the drains of the main steam pipe on the turbine side, and check that the main steam pressure does not abnormally decrease.

[0044] (3) After the reheated steam pipe is evacuated to zero, close the drains of the reheated steam pipe on the turbine side.

[0045] (4) Maintain the unit vacuum, and after the boiler is drained under pressure and depressurized to zero, close the drains and emptying doors of the boiler superheater and reheater. Open the drains of the main steam pipe and the reheated steam pipe on the turbine side, open 20% of the high bypass and low bypass, so that the vacuum degree of the separator is greater than 50 kPa, and maintain for 1 hour.

[0046] (5) Open the air heater, separator, and reheater emptying doors, and maintain for 2 hours. Replace the residual moisture in the boiler with air, and close the air door.

[0047] (6) Continue to evacuate for 2 hours, until the relative humidity of the air in the boiler is reduced to 60% or equal to the ambient relative humidity.

[0048] (7) Stop the vacuum pump, and stop the shaft seal system when the vacuum is zero.

[0049] The third stage is turbine drying maintenance.

[0050] (1) Turn on the turbine quick cooling device, which dries and maintains the turbine while reducing the temperature of the cylinder.

[0051] (2) After the quick cooling device is running, measure the exhaust relative humidity every 6 hours (at the low-pressure cylinder manhole). When the relative humidity is less than 50%, the drying and maintenance is complete, and the quick cooling device is stopped.

[0052] The present disclosure uses two methods of reducing humidity and using corrosion inhibitors to prevent rust and corrosion of the turbine from the preparation of the turbine for shutdown to the end of the turbine quick cooling. In the shutdown stage, the turbine is pre-maintained by ammonia alkalization treatment. After the turbine is tripped, the unit vacuum is maintained until the boiler is drained under pressure, which avoids the accumulation of water in the turbine and does not need to maintain the unit vacuum for a long time, thereby reducing energy consumption. After the turbine quick cooling device is turned on, the humidity in the turbine is effectively reduced.

[0053] The preferred embodiments of the present disclosure are described in detail above with reference to the drawings, but the present disclosure is not limited to the specific details in the above-described embodiments. Various simple modifications can be made to the technical solutions of the present disclosure within the technical concept of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0054] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations are not described again in the present disclosure.

[0055] In addition, various different embodiments of the present disclosure can also be combined in any appropriate manner, as long as they do not deviate from the idea of the present disclosure, and they should also be considered as disclosed in the present disclosure.

Claims

1. A method for shutting down and maintaining a steam turbine, characterized in that, The turbine shutdown and maintenance method includes: Before shutting down the steam turbine, stop the condensate polishing operation and increase the ammonia addition to the condensate and feedwater to ensure that the pH value of the feedwater at the economizer inlet is within the first range. After the steam turbine is tripped and shut down, the vacuum pump is run to maintain the operation of the steam turbine's shaft sealing system and control the steam turbine's vacuum level within the second range until the boiler finishes its pressurized water discharge. After the vacuum pump has been running for a first period of time, it is stopped. The rapid cooling device of the steam turbine is then activated and compressed air is introduced into the steam turbine to dry it. Before running the vacuum pump, it is determined whether all the drain valves of the steam turbine are open, and the steam turbine is evacuated when all the drain valves of the steam turbine are open. After the turbine is evacuated; Close all drain valves on the main steam pipeline on the machine side; After the reheat steam pipeline is evacuated to zero, close all drain valves on the reheat steam pipeline on the machine side; After closing all the drain valves in the reheat steam pipeline on the machine side; Maintain the vacuum state of the steam turbine until the boiler discharges water under pressure and the pressure is reduced to zero; Close all drain valves and vent valves of the boiler superheater and reheater, open all drain valves of the main steam pipeline and reheat steam pipeline on the machine side, open some high-pressure bypass valves and low-pressure bypass valves, and maintain the separator vacuum degree greater than 50 kPa for the second duration.

2. The turbine shutdown and maintenance method according to claim 1, characterized in that, After the separator vacuum degree is greater than 50 kPa and maintained for a second time, the vent valves of the economizer, the separator, and the reheater are opened and maintained for a third time.

3. The turbine shutdown and maintenance method according to claim 2, characterized in that, After opening the vent valves of the economizer, the separator, and the reheater and maintaining this for a third time, the vent valves are closed, and the vacuum process continues for a fourth time until the relative humidity of the air inside the turbine drops to 60% or equal to the ambient relative humidity.

4. The turbine shutdown and maintenance method according to claim 3, characterized in that, After the relative humidity of the air inside the turbine drops to 60% or equal to the ambient relative humidity, the vacuum pump is shut down, and the shaft sealing system is shut down when the vacuum reaches zero.

5. The turbine shutdown and maintenance method according to claim 4, characterized in that, After shutting down the shaft sealing system, the rapid cooling device of the steam turbine is activated. The relative humidity of the exhaust gas is measured every five hours. When the relative humidity is <50%, the rapid cooling device of the steam turbine is shut down.

6. The turbine shutdown and maintenance method according to claim 1, characterized in that, The second duration is 1 hour.

7. The turbine shutdown and maintenance method according to claim 1, characterized in that, The first range is between 9.6 and 10.5.

Images