Forced rapid cooling method and system for steam turbine

Abstract

The invention discloses a forced rapid cooling method and system for a steam turbine, and belongs to the field of steam turbine power generation. In order to solve the problems of high investment, complicated operation and thermal shock risk of the existing injection type cooling technology, efficient cooling is realized by utilizing original shaft seal system equipment of a steam turbine: for a double-split high-pressure cylinder structure, vacuum is damaged after shutdown, shaft seal steam supply is stopped, only operation of a shaft seal fan is maintained, and hot air in a cylinder is naturally pumped and exhausted through an end steam seal; for a high and medium pressure combined cylinder structure, a detachable exhaust branch pipe with a portable exhaust fan is additionally arranged on an original steam seal exhaust pipe of a gap bridge steam seal, and the exhaust fan is started during cooling to strengthen air flow in a gap bridge steam seal area. According to the method, a large air compression device is not needed, a double-split-flow machine type does not need additional equipment, a combined cylinder machine type only needs a low-cost portable assembly, the air exhaust flow is adjusted and controlled through a valve, mild heat exchange is achieved, and thermal shock is avoided. The method has the advantages of low investment, quick use, high safety and wide adaptability.

Description

Technical Field

[0001] The present invention belongs to the field of steam turbine power generation, and particularly relates to a method and system for realizing forced rapid cooling by using existing shaft sealing system equipment after the steam turbine stops, which is applicable to the rapid cooling processes of various steam turbines such as thermal power and nuclear power. Background Art

[0002] As a high-temperature operating device, high-temperature components such as the high-pressure cylinder and the high- and intermediate-pressure cylinder of a steam turbine bear significant thermal loads during operation. With the increase in unit power, the size and weight of high-temperature components increase sharply, resulting in a substantial increase in heat capacity. At the same time, in order to reduce heat dissipation losses, the application of high-quality thermal insulation materials and technologies has improved the heat insulation performance, but it has also formed a constraint factor for natural cooling after shutdown, making the cooling speed of the cylinder and the rotor slow.

[0003] In the overhaul process after the steam turbine stops, it is necessary to wait for the component temperature to drop to a safe range before stopping the turning gear and opening the cylinder for overhaul. The traditional natural cooling method takes too long, seriously affecting the overhaul period, thereby reducing the unit utilization rate and damaging the economic benefits of the power plant. This problem is particularly prominent in the nuclear power field, which is sensitive to the overhaul period.

[0004] The existing mainstream rapid cooling technology adopts an injection method, that is, compressed air that has been heated, filtered, and dehumidified is injected into the steam turbine through a compressed air device. However, this method has significant defects: firstly, it is necessary to equip large-scale equipment such as an air compressor and a heating device, with high initial investment costs, occupying a large amount of factory building space, and being difficult to arrange the equipment; secondly, each operation requires complex installation and connection with the steam turbine, which is time-consuming and laborious for installation and disassembly, and the equipment utilization rate is extremely low; thirdly, the externally injected compressed air may cause thermal shock to the steam turbine due to improper control of temperature and flow parameters, posing a risk of damage, and requiring cumbersome calculations and evaluations.

[0005] In view of the above problems, there is an urgent need for a steam turbine rapid cooling technology that does not require additional large-scale equipment, uses existing system components, and is safe and efficient, so as to solve the problems of high investment, complex operation, and low safety in the traditional method, and meet the urgent needs in actual engineering for shortening the overhaul period and improving the economy of the unit. Summary of the Invention

[0006] The present invention aims to overcome the above-mentioned disadvantages of the prior art and provides a method and system for forced rapid cooling of a steam turbine.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A method for forced rapid cooling of a steam turbine, comprising the following steps:

[0009] S1: After the steam turbine stops, maintain the operation of the turning gear to make the rotor continuously rotate at the turning speed;

[0010] S2: After the steam in the cylinder is basically exhausted, stop the shaft seal steam supply and break the unit vacuum;

[0011] S3: Keep the shaft seal fan running continuously, extract the air in the cylinder through the end steam seal body, form a continuous air flow cycle, and cool the cylinder and the rotor.

[0012] Further, "maintaining the operation of the turning gear" in step S1 runs through the entire cooling process until the cylinder temperature drops to the specified limit value.

[0013] Further, "breaking the unit vacuum" in step S2 is achieved by opening the vacuum breaker valve of the condenser.

[0014] Further, when the steam turbine has a combined high-pressure and intermediate-pressure cylinder structure, the following steps are also included: Add an extraction branch pipe to the original steam seal extraction pipe of the cross-over steam seal, and install a portable extraction fan on the extraction branch pipe; When the rapid cooling system is put into use, turn on the portable extraction fan to enhance the air flow in the cross-over steam seal area.

[0015] Further, the extraction branch pipe is connected to the original steam seal extraction pipe through a flange, and the interface is removed and blocked with a blind flange during normal operation of the unit.

[0016] Further, while "turning on the portable extraction fan", control the extraction flow rate at the cross-over steam seal by adjusting valve 1 on the original steam seal extraction pipe and valve 2 on the extraction branch pipe to meet the requirements of different cooling rates.

[0017] Further, a forced rapid cooling system for a steam turbine includes:

[0018] A shaft seal fan, connected to the end steam seal body of the steam turbine, for extracting the air in the cylinder;

[0019] A vacuum breaker valve, installed on the condenser, for breaking the unit vacuum;

[0020] A turning gear, for driving the rotor to rotate at the turning speed.

[0021] Further, it also includes an extraction branch pipe assembly, applicable to a steam turbine with a combined high-pressure and intermediate-pressure cylinder structure. The extraction branch pipe assembly includes:

[0022] An extraction branch pipe, one end is connected to the steam seal extraction pipe of the cross-over steam seal, and the other end is connected to a portable extraction fan;

[0023] Valve 1, set on the original steam seal extraction pipe, for cutting off the connection with the regenerative extraction pipeline;

[0024] Valve 2, set on the extraction branch pipe, for adjusting the extraction flow rate.

[0025] Further, the extraction branch pipe is a flexible pipe, and is detachably connected to the original steam seal extraction pipe through a flange.

[0026] Furthermore, the shaft seal fan is a standard equipment of the existing shaft seal system of the steam turbine, and there is no need to additionally configure a large air compression device.

[0027] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0028] By innovatively utilizing the original equipment of the shaft seal system of the steam turbine, the present invention significantly reduces the implementation cost and operation risk of the fast cooling technology:

[0029] Equipment reusability and economy: The double-flow high-pressure cylinder structure does not require any new equipment. For the combined high-pressure and intermediate-pressure cylinder, only a low-cost portable exhaust fan and a hose branch pipe need to be added, avoiding the problems of high investment and low utilization rate of large equipment such as air compressors and heating devices in the traditional injection method, and significantly reducing the initial investment and the occupation of plant space.

[0030] Convenient and efficient operation: Relying on the existing shaft seal fan and the detachable exhaust branch pipe design, the fast cooling system can be put into use without complex equipment installation and pipeline transformation. It can be achieved only by switching valves and connecting portable equipment, significantly shortening the cooling preparation time and meeting the urgent needs of the overhaul period.

[0031] Safety and reliability: Using the "exhaust type" cooling to replace the "injection type" forced air supply, the shaft seal fan slowly extracts the air in the cylinder, and the air outside the cylinder naturally replenishes the cylinder through the vacuum breaker valve, forming a mild heat exchange process, avoiding the risk of thermal shock caused by the direct injection of external high-pressure air flow, ensuring uniform cooling of the cylinder and the rotor, and improving the operation safety.

[0032] System compatibility and flexibility: The exhaust branch pipe adopts a detachable structure connected by flanges. During normal operation, it is isolated from the original system and does not affect the daily operation of the steam turbine; during the cooling process, the exhaust air flow can be accurately adjusted through valves to adapt to the cooling rate requirements of different models, with both universality and customization advantages, especially suitable for the overhaul scenario of nuclear power steam turbines sensitive to the construction period, effectively improving the unit utilization rate and the economic benefits of the power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is the overall structural schematic diagram of the steam turbine of the present invention when it is a double-flow high-pressure cylinder;

[0034] Figure 2 is the structural schematic diagram of the steam turbine of the present invention when it is a combined high-pressure and intermediate-pressure cylinder structure.

[0035] Markings in the figure:

[0036] 1 - shaft seal fan, 2 - steam turbine, 3 - valve 1, 4 - valve 2, 5 - gland steam extraction pipe, 6 - extraction branch pipe, 7 - shaft seal steam supply, 8 - end gland, 9 - cross-over gland, 10 - portable extraction fan. Detailed implementation mode

[0037] The present invention will be described in detail below with reference to the accompanying drawings.

[0038] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] Embodiment 1

[0040] In this embodiment, as Figure 1 shown, a method for forced rapid cooling of a steam turbine includes the following steps:

[0041] S1: After the steam turbine is shut down, maintain the operation of the turning gear so that the rotor rotates continuously at the turning speed.

[0042] S2: After the steam in the cylinder is basically exhausted, stop the shaft seal steam supply and break the vacuum of the unit.

[0043] S3: Keep the shaft seal fan running continuously, extract the air in the cylinder through the end gland body, form a continuous air flow cycle, and cool the cylinder and the rotor.

[0044] Further, "maintaining the operation of the turning gear" in step S1 runs through the entire cooling process until the temperature of the cylinder drops to the specified limit value.

[0045] Further, "breaking the vacuum of the unit" in step S2 is achieved by opening the vacuum breaker valve of the condenser.

[0046] The steam turbine is equipped with a turning gear, which can drive the rotor to rotate at the turning speed; this can prevent the rotor from bending and deforming due to gravity or temperature difference.

[0047] The shaft seal fan is an existing equipment of the shaft seal system, and is connected to the end gland bodies at both ends of the steam turbine through pipelines.

[0048] The vacuum breaker valve of the condenser is installed at the throat of the condenser, and the condenser is connected to the exhaust port of the steam turbine.

[0049] Turning gear maintenance: Start the turning gear immediately after shutdown, and the rotor rotates continuously.

[0050] Steam extraction and discharge: First, maintain the shaft seal steam supply and vacuum, and extract the residual steam in the cylinder.

[0051] Vacuum destruction and shaft seal steam supply shutdown: After the steam is exhausted, open the vacuum destruction valve to destroy the condenser vacuum; at the same time, close the shaft seal steam supply valve to cut off external steam input.

[0052] Continuous exhaust cooling: Keep the shaft seal fan running to extract the air in the cylinder through the gap of the end steam seal body (air flow path: vacuum breaker valve → condenser → cylinder → end steam seal → shaft seal fan pipeline → exhaust atmosphere). The shaft seal fan will also extract some normal temperature air outside the end steam seal.

[0053] Beneficial effect: The existing shaft seal fan is utilized without the need for new equipment; the continuous rotation of the turning wheel ensures uniform cooling of the rotor to avoid thermal deformation.

[0054] Embodiment 2

[0055] like Figure 2 As shown, when the steam turbine is a high and medium pressure combined cylinder structure,

[0056] The bridge steam seal is located between two cylinders, and its nearby components (such as the steam seal body and partition) are in direct contact with high-temperature steam, resulting in concentrated heat load. However, the original steam seal extraction pipe is only connected to the heat recovery extraction pipe. After shutdown, the natural air extraction capacity is limited, and it is difficult to form effective air flow, resulting in slow heat dissipation in this area, which becomes a cooling bottleneck. The shaft seal fan mainly extracts air from both ends of the cylinder through the end steam seal, and cannot cover the "suction blind area" of the hot air in the middle bridge steam seal area. By adding an exhaust branch with a portable exhaust fan, the hot air in the bridge steam seal area can be actively extracted (airflow path: bridge steam seal gap → exhaust branch → exhaust fan → exhaust atmosphere), forcing local air flow to quickly take away the accumulated heat. This branch works in conjunction with the original shaft seal fan to fill the cooling gap in the middle area, achieve balanced cooling of the entire cylinder (including high-pressure cylinder, medium-pressure cylinder and bridge connection components), and accelerate the cooling speed.

[0057] The method comprises the following steps: adding an exhaust branch pipe to the original steam seal exhaust pipe of the bridge steam seal, and installing a portable exhaust fan on the exhaust branch pipe; when the rapid cooling system is put into use, turning on the portable exhaust fan to enhance the air flow in the bridge steam seal area.

[0058] Furthermore, the exhaust branch pipe is connected to the original steam seal exhaust pipe through a flange, which is removed during normal operation of the unit and the interface is sealed with a blind flange.

[0059] Furthermore, while "turning on the portable exhaust fan", the exhaust flow at the bridge steam seal is controlled by adjusting valve 1 on the original steam seal exhaust pipe and valve 2 on the exhaust branch pipe to meet different cooling rate requirements.

[0060] The bridge steam seal is located between the high-pressure cylinder and the medium-pressure cylinder, and its steam seal extraction pipe is originally connected to the heat recovery steam extraction pipe;

[0061] Air extraction branch pipe assembly: Valve 1 (gate valve) is installed on the original steam seal air extraction pipe to cut off the original regenerative air extraction pipeline;

[0062] The air extraction branch pipe is a flexible pipe. One end is connected to the original steam seal air extraction pipe downstream of Valve 1 through a flange, and the other end is connected to a portable air extractor (with adjustable air volume). Valve 2 (throttle valve) is provided on the branch pipe.

[0063] Installation of the branch pipe: Close Valve 1, remove the blind flange, and connect the air extraction branch pipe;

[0064] Open Valve 2 and start the portable air extractor. The air extractor extracts air from the cross-over steam seal area (air flow path: cross-over steam seal gap → original steam seal air extraction pipe → air extraction branch pipe → air extractor → atmosphere);

[0065] By adjusting Valve 1 (partially opening to introduce a small amount of high-pressure cylinder air flow) and Valve 2 (adjusting the opening of the branch pipe), control the air extraction flow rate at the cross-over steam seal (enhance the air flow on the steam inlet side of the high-pressure cylinder and the steam inlet side of the intermediate-pressure cylinder near the cross-over steam seal).

[0066] Beneficial effects: Only add a low-cost portable air extractor and a flexible pipe branch, with small investment; the detachable flange connection does not affect normal operation and can be put into use quickly; specifically cool the high-temperature components of the cross-over steam seal to avoid local overheating.

[0067] Furthermore, a forced rapid cooling system for a steam turbine includes:

[0068] A shaft seal fan, connected to the steam turbine end steam seal body, for extracting air from the cylinder;

[0069] A vacuum breaker valve, installed on the condenser, for breaking the unit vacuum;

[0070] A turning gear, for driving the rotor to rotate at the turning gear speed.

[0071] Furthermore, it also includes an air extraction branch pipe assembly, applicable to a steam turbine with a combined high-pressure and intermediate-pressure cylinder structure. The air extraction branch pipe assembly includes:

[0072] An air extraction branch pipe, with one end connected to the air extraction pipe of the cross-over steam seal and the other end connected to a portable air extractor;

[0073] Valve 1, provided on the original steam seal air extraction pipe, for cutting off the connection with the regenerative air extraction pipeline;

[0074] Valve 2, provided on the air extraction branch pipe, for adjusting the air extraction flow rate.

[0075] Furthermore, the air extraction branch pipe is a flexible pipe, and is detachably connected to the original steam seal air extraction pipe through a flange.

[0076] Furthermore, the shaft seal fan is a standard equipment for the existing shaft seal system of the steam turbine, and there is no need to additionally configure a large air compression device.

[0077] Shaft seal fan: It is directly connected to the air extraction port of the end steam seal body, and the pipeline diameter matches the original shaft seal system (utilizing the existing design parameters without modification).

[0078] Air extraction branch pipe assembly: The main body of the pipeline is a flexible hose with flanges at both ends, and it is connected to the original steam seal air extraction pipe through standard flange bolts, with a detachable structure.

[0079] Valve 1 and Valve 2: Valve 1 is located in the horizontal section of the original pipeline for easy operation; Valve 2 is close to the inlet of the extraction fan for fine adjustment of the flow rate (by controlling the two valves, the extraction air volume can be dynamically adjusted during the cooling process to avoid excessive temperature difference caused by too fast cooling).

[0080] Double-flow high-pressure cylinder: Only relying on the air extraction of the shaft seal fan to evenly remove the heat of the cylinder (without adding new components, the process is optimized).

[0081] High-pressure and intermediate-pressure combined cylinder: On the above basis, "directional air extraction" is carried out on the cross-over steam seal area through the air extraction branch pipe to make up for the air flow dead angle caused by the combined cylinder structure in this area and achieve the balanced cooling of the overall cylinder.

[0082] Beneficial effects: Portable design and flange connection, convenient for installation and disassembly, without occupying fixed space; no large-flow air injection, the air is slowly heated in the cylinder to avoid thermal shock.

[0083] In summary

[0084] Method steps and device coordination: Maintain the rotation of the rotor through turning gear → Extract air with the shaft seal fan after vacuum breakdown → Strengthen local cooling by adding a branch pipe to the special structure.

[0085] The above are only the preferred embodiments of the invention, and they are not intended to limit the invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the invention shall be included in the protection scope of the invention.

Claims

1. A method for forced rapid cooling of a steam turbine, characterized in that, It includes the following steps: S1: After the steam turbine stops, maintain the operation of the turning gear to make the rotor rotate continuously at the turning speed. S2: After the steam in the cylinder is basically exhausted, stop the shaft seal steam supply and break the vacuum of the unit. S3: Keep the shaft seal fan running continuously, extract the air in the cylinder through the end steam seal body to form a continuous air flow cycle, and cool the cylinder and the rotor.

2. The forced rapid cooling method of a steam turbine according to claim 1, wherein In step S1, "maintaining the operation of the turning gear" runs through the entire cooling process until the cylinder temperature drops to the specified limit value.

3. A forced rapid cooling method for a steam turbine according to claim 1, characterized in that, In step S2, "breaking the vacuum of the unit" is achieved by opening the vacuum breaker valve of the condenser.

4. A forced rapid cooling method for a steam turbine according to claim 1, characterized in that When the steam turbine has a combined high-pressure and intermediate-pressure cylinder structure, it further includes the following steps: add an extraction branch pipe to the original steam seal extraction pipe of the cross-over steam seal, and install a portable extraction fan on the extraction branch pipe; when the rapid cooling system is put into use, open the portable extraction fan to enhance the air flow in the cross-over steam seal area.

5. A forced rapid cooling method for a steam turbine according to claim 4, characterized in that The extraction branch pipe is connected to the original steam seal extraction pipe through a flange, and the interface is removed and blocked with a blind flange during normal operation of the unit.

6. A forced rapid cooling method for a steam turbine according to claim 4, characterized in that When the "portable extraction fan is opened", control the extraction flow rate at the cross-over steam seal by adjusting valve 1 on the original steam seal extraction pipe and valve 2 on the extraction branch pipe to meet the requirements of different cooling rates.

7. A forced rapid cooling system for a steam turbine, characterized in that, It includes: Steam turbine: End steam seals are provided at both ends of the steam turbine, and the end steam seals are connected to the shaft seal steam supply for supplying steam into the steam turbine. A condenser is provided at the exhaust port of the steam turbine. Shaft seal fan, connected to the end steam seal of the steam turbine, for extracting the air in the cylinder. Vacuum breaker valve, installed on the condenser, for breaking the vacuum of the unit. Turning gear, connected to the steam turbine, for driving the rotor to rotate at the turning speed.

8. A forced rapid cooling system for a steam turbine according to claim 7, characterized in that, It further includes an extraction branch pipe assembly, applicable to a steam turbine with a combined high-pressure and intermediate-pressure cylinder structure. A cross-over steam seal is provided in the middle of the steam turbine with a combined high-pressure and intermediate-pressure cylinder structure, and a steam seal extraction pipe is provided on the cross-over steam seal. The extraction branch pipe assembly includes: Extraction branch pipe, one end is connected to the steam seal extraction pipe of the cross-over steam seal, and the other end is connected to a portable extraction fan. Valve 1, provided on the original steam seal extraction pipe, for cutting off the connection with the regenerative extraction pipeline; valve 2, provided on the extraction branch pipe, for adjusting the extraction flow rate.

9. A forced rapid cooling system for a steam turbine according to claim 8, characterized in that, The extraction branch pipe is a flexible pipe and is detachably connected to the original steam seal extraction pipe through a flange.

10. A forced rapid cooling system for a steam turbine according to claim 7, characterized in that, The shaft seal fan is a standard equipment of the existing shaft seal system of the steam turbine, and there is no need to additionally configure a large air compression device.

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