The function of high exhaust and fast exhaust check valves (check valves)

The function of high exhaust and fast exhaust check valves (check valves)
The high-pressure cylinder exhaust check valve is installed on the horizontal pipeline of the reheated cold section of the steam turbine to prevent water and steam from flowing back into the high-pressure cylinder, thereby affecting the safety of the steam turbine.
The extraction check valve is designed to provide great protection for the extraction of steam from the turbine. They ensure that high-energy water or steam in the heater or thermal pipeline can be quickly isolated from the turbine by quickly and tightly closing when the generator trips or the main steam valve is closed, thereby protecting the turbine. The important design principle of the extraction check valve is that it must have high reliability as a protective device.
High exhaust application pressure range: reheater inlet pressure
High exhaust application temperature range: ≤ 420 ℃
Application pressure range for each section of steam extraction: vacuum~10MPa
Temperature range for each section of extraction: 200~510 ℃
The steam turbine of a certain 600MW unit is equipped with eight sections of non adjustable extraction steam.
The fourth stage of steam extraction is led from the exhaust of the intermediate pressure cylinder, and after 14 stages of the whole machine, it is supplied to the deaerator, feedwater pump turbine, and auxiliary steam system;
The fifth to eighth stages of steam extraction are all led from low-pressure cylinder A and low-pressure cylinder B. The fifth stage of steam extraction is led from the 16th stage of the entire machine and supplied to the 5th low-pressure heater;
The sixth section of the extraction steam is drawn from the 17th stage of the entire machine and supplied to the 6th low-pressure heater;
The seventh stage of steam extraction is from the 18th stage of the entire machine, and the steam extraction from low-pressure cylinder A is supplied to low-pressure heater 7A, while the steam extraction from low-pressure cylinder B is supplied to low-pressure heater 7B;
The eighth section of the extraction steam is introduced from the 19th stage of the entire machine, and the extraction steam from low-pressure cylinder A is supplied to No. 8A, while the extraction steam from low-pressure cylinder B is supplied to No. 8B low-pressure heater.
Except for the seventh and eighth sections of steam extraction, each extraction pipeline is equipped with pneumatic check valves and electric shut-off valves. The former serves as a protection against turbine overspeed and also as an auxiliary protection measure against water ingress into the turbine; The latter is used as an isolation measure to prevent water from entering the turbine. Due to the connection of the four pumps to the auxiliary steam header, deaerator, and feedwater pump turbine, there are many users and a large pipeline volume, so two check valves are installed on the pipeline. A pneumatic check valve and an electric shut-off valve are also installed on the pipelines of each steam consumption point in the four stage extraction.
Control and Chain
Automatic shutdown: 1. Steam turbine trip; 2. The water level of the heating equipment corresponding to each level of extraction steam pipeline is high high.
After the above conditions are restored to normal, it will automatically turn on.
Valve body pressure rating: standard range
ASME B16.34 1996–150 Class
ASME B16.34 1996–300 Class
ASME B16.34 1996–400 Class
ASME B16.34 1996–600 Class
Valve body material: cast steel
ASTM A216-WCB
ASTM A217-WC6/WC9 (1 # and 3 # extraction)
Sealing surface material:
For carbon steel valves (body A216-WCB)
Valve seat -13% Cr. Directly welded onto the valve body material
Valve Plate - Dewrance: Smart? Gr. 21 (or equivalent)
Directly weld onto the valve plate material.
For alloy steel valves (body A217-WC9)
Valve Seat - Dewrance: Smart? Gr. 21 (or equivalent)
Directly weld onto the valve body material
Valve Plate - Dewrance: Smart? Gr. 21 (or equivalent)
Directly weld on the valve plate material
Classification of extraction check valves:
1. Self closing type
Self weight closing type (closed): a check valve design that relies on the self weight or counterweight of the valve core to achieve valve closure.
Self weight closing type (open): relying on medium pressure to overcome the valve core and counterweight, the valve core is pushed up and maintained in the valve open position.
2. Power assisted closing type: The actuator provides a pulse point action, allowing the valve core to overcome the initial inertia caused by the medium or external factors in the closed position for a long time and complete the remaining stroke on its own, closing the valve.
3. Power off type: During the closing process, the actuator provides power from start to finish to complete the entire stroke of the valve core and close the valve.
Drive form of extraction check valve
Large units are mostly driven by pneumatic means, while small and medium-sized units are mostly driven by hydraulic means. At present, there are two main types of pneumatic systems: swing and lift. In terms of rotary type, cylinders are also divided into two categories: air supply valve opening and air supply valve closing. Currently, in large units, air supply valve opening is more common. Hydraulics generally use condensed water as power, and valves are mostly in the form of lifting valves.