Detailed working principle of steam turbine control valve

The detailed working principle of steam turbine regulating valves is that in a certain load range, the control mode of "single valve" can be adopted, and its essence is throttling regulation. Several regulating valves are opened and closed at the same time, and steam is evenly introduced to the surrounding area to adjust power. For large steam turbines with nozzle adjustment, there are two inherent adjustment methods, namely "single valve" and "sequential valve". Because the steam inlet partition of the regulating stage is divided into several steam inlet arc sections according to the nozzle, there are always some arc sections without steam inlet, so the steam turbine with nozzle regulation always has a "partial steam inlet degree".

The regulating system is mainly composed of speed sensing mechanism, intermediate amplification mechanism, oil motor, steam distribution mechanism, synchronizer and starting device, which converts the speed signal of the rotor into a first-order control signal, which can be divided into three categories according to the working principle: mechanical, hydraulic and electronic. The intermediate amplifier amplifies the power of the main control signal, performs control operation according to the adjustment target, and generates the control signal of the oil motor.

According to the control signal of the intermediate amplifier, the driving force is generated to drive the steam distribution mechanism to move and reach the predetermined opening position. The steam distribution mechanism converts the stroke of the oil motor into the opening of each regulating valve. Through the nonlinear transmission characteristics of the steam distribution mechanism, the relationship between the steam intake of the steam turbine and the stroke of the oil motor is modified to be approximately linear.

The synchronizer acts on the intermediate amplifier, generates control signals, controls the stroke of the oil motor, and changes the rotating speed of the steam turbine when the single machine is running and the power of the unit when it is connected to the grid. The starting device is used for rushing when the unit is started, and the rotating speed rises to the synchronizer rotating speed.

Extended data

The tasks of steam turbine governing system:

(1) When the external load is compatible with the unit power, keep the turbine running stably.

(2) When the external load changes or the unit load changes, the regulating system of the steam turbine can change the power of the steam turbine accordingly, make it adapt to the external load or the unit load, establish a new balance, and keep the working speed of the steam turbine within the specified range.

(3) For the extraction steam turbine, when the working conditions change, adjust the extraction pressure within the specified range. The regulating system of steam turbine should not only receive the signal of speed change of steam turbine, but also receive the signal of driven machinery, that is, it has double pulse regulating device.

The signal is amplified, and finally the opening of the regulating valve is controlled to change the amount of steam entering the steam turbine to adapt to the change of external load or steam state, so as to keep the speed of the steam turbine within a certain range. When the unit speed rises, the throttle valve should be closed quickly; When the speed of the unit decreases, the throttle valve should be opened quickly to establish a new balance.

The regulating system should also meet the requirements of the process system to ensure the constant speed operation and variable speed operation of the unit. Industrial steam turbines in petrochemical plants rely on regulating systems to accomplish this task automatically.