A case study of hydraulic transformation from pneumatic bypass

Project Name: Xinjiang Zhun Aluminum Thermal Power Plant Steam Turbine High and Low Side Valves Pneumatic to Hydraulic

Reason for renovation:

The original bypass system was designed with integrated blocks, solenoid valve groups, and hydraulic motors installed centrally on the valves. Due to the high temperature here, and the vibration of the valves and pipelines inevitably affecting the fatigue strength of the bolted components of the integrated blocks and solenoid valve groups and the sealing performance of the sealing components, hydraulic oil leakage is prone to occur, resulting in fire accidents;

The flow rate of the proportional valve is too small, and the initial torque when opening the valve is not enough to overcome the resistance of the valve core, resulting in the proportional valve not acting;

The ambient temperature of the main valve is relatively high, which is not suitable for the working temperature of the built-in amplifier module of the proportional valve, causing the proportional valve to refuse to move due to no driving current output;

At present, the control strategy involves sending DCS commands to the local PLC, which drives the on-site equipment to operate. The internal logic of the PLC cannot be accessed, and the control status cannot be monitored online;

Renovation plan:

1. Divide the hydraulic actuator and control module into two parts, and the hydraulic actuator will continue to be fixed on the top of the valve. The control module will be separated from the hydraulic actuator and moved to a separate control platform. The control platform will be away from the high-temperature components of the valve and covered with a dust cover for protection. The hydraulic motor is connected to the control module using stainless steel pipes, ensuring that the control principle remains unchanged;

2. Replace the piston rod oil seal of the hydraulic servomotor with high-temperature resistant fluororubber, and use a stainless steel seal for the piston rod seal. The sealing level has been increased from level 2 to level 3, further reducing the possibility of leakage;

Replace the proportional valve with a large flow rate and a supporting external amplifier, and add a vibration signal to enable the proportional valve to respond quickly and prevent valve rejection;

4. By laying cables, each measuring point of the oil station will be introduced into the DCS control system, and the DCS logic diagram will be constructed according to the bypass oil station and valve control principles to achieve the functions of DCS system monitoring, control, alarm, interlocking, etc;