Answers to Daily Question (September 6) released

On large-diameter pipes, a branch pipe is connected before and after the main valve; this branch pipe is called a bypass pipe. The reheat unit bypass system is actually a (regulation) and (protection) system for the reheat unit during the (start-up), (shutting down), or (emergency) conditions of the unit. Reduce the opening force of large-diameter gate valves. Warm the pipe. At low load and low flow rates, the bypass valve can be opened while the main valve is closed.

This post was last edited by djjt on 2009-9-6 04:51. What is the main function of the bypass system in a boiler intermediate reheating unit? The main functions are: 1: To ensure the evaporation rate at the boiler’s minimum load. 2: Ensure that the reheater achieves the necessary cooling evaporation rate to prevent overheating. 3: The bypass system is used to meet the requirements for warming up the main steam and reheat steam pipelines, as well as to regulate the steam temperature, thereby enhancing the safety of the unit’s operation. 4: During accidents and emergency shutdowns, the steam inside the furnace is vented to prevent the safety valves from activating due to overpressure. 5: Recycle the working fluid and some heat, while reducing exhaust noise. 6: Establish a steam-water cleaning system before starting the turbine; steam can be introduced into the turbine only after its quality meets the specified standards, in order to prevent erosion of the turbine.

This post was last edited by hzliangke on 2009-9-6 10:05. When the turbine loses load or the unit starts and stops, the reheater may be damaged due to a lack of steam for cooling. It is equipped with a high-pressure bypass, which directs the superheated steam to the reheater through a rapid temperature and pressure reduction device on the bypass, thereby protecting the reheater.

The bypass system can operate in both constant-pressure and variable-pressure modes; it has a regulating function that prevents the boiler safety valve from activating, reduces noise, recovers working fluid, and sends excess steam to the condenser. It can also protect the reheater, and is used in cases of unit tripping, load shedding, grid failures, and shutdowns without shutting down the furnace.

1. Ensure the evaporation rate at the boiler’s minimum load, so that the boiler and turbine can operate independently； 2 When the turbine starts, stops, or loses load, protect the reheater to prevent it from overheating ； 3. Maintain the main and reheat steam parameters at the prescribed levels before starting the turbine, in order to meet the requirements of various startup methods ； 4 After the boiler is ignited, a bypass can be used to recover the working fluid and some of the heat during the process of increasing steam parameters, thereby reducing the noise generated by the exhaust steam ； 5 Ensure that in the event of an emergency shutdown due to an accident, the steam inside the furnace can be discharged through a bypass, thereby preventing the operation of the boiler safety valves ； 6 Establish a steam-water circulation cleaning system before starting the turbine, so that the steam quality can reach the required standards as soon as possible ； 7 During startup or load shedding, the bypass system can be used as an auxiliary steam source for the deaerator and shaft seal steam supply.

I. Improve the startup performance of the unit. When the unit is started under various operating conditions (cold, warm, hot, and extremely hot), it enables the steam temperature to match the metal temperature of the turbine cylinder more quickly, thereby reducing startup time and minimizing steam leakage into the atmosphere. This helps to reduce wear on the turbine cycle and improves economic efficiency. II. Meet the requirements of the unit’s startup mode. Adjust the steam inlet parameters and flow rate of the medium-pressure cylinder to accommodate scenarios such as simultaneous startup of the high-pressure and medium-pressure cylinders, or startup of only the medium-pressure cylinder. Three-stage protection reheater. During startup and load shedding, it is necessary to ensure that sufficient steam flows through the reheater during startup, so as to protect the reheater located in areas with high flue gas temperatures from being damaged due to dry burning. IV. Reduce the restrictions on fuel input during the startup phase. Since the reheater is protected by a bypass system, the amount and rate of fuel feed can be reduced, thereby accelerating the startup speed. V. A bypass system is employed to allow small solid particles in the steam to enter the condenser via this bypass, thereby preventing erosion of the turbine’s throttle valves, nozzles, and blades by hard particles. VI. Meeting the special requirements of the power grid for various loads. When the turbine load is below the boiler’s minimum oil-free stable combustion load, the unit can be allowed to operate stably at a low load level through the regulation of the bypass device. VII. Implement the unit shutdown without shutting down the furnace and the FCB function. When a turbine fails, an operation mode of shutting down the turbine without shutting down the boiler can be adopted ； Or in the event of a power grid failure, the unit can operate using plant electricity, which helps to restore power supply as quickly as possible and limit the scope of the incident. VIII. It has a function for overpressure safety protection. When the boiler experiences overpressure, the high-pressure bypass is activated to reduce the activation of the PCV valve and safety valves; it also adjusts automatically according to the main steam pressure of the unit until normal levels are restored. 9. During startup, the 100% capacity high-pressure bypass three-way valve system equipped with safety functions enables shortening the startup time while ensuring the turbine’s service life, and it can also take over the function of the boiler safety valve when the turbine is rapidly reduced in load. X. Recover the working fluid to reduce noise. Recycle the working fluid during startup or load shedding to reduce noise from exhaust steam.