ADVANCED STEAM TURBINE BYPASS VALVE DESIGN FOR FLEXIBLE POWER PLANTS

摘要

The authors company has had extensive experience providing steam turbines including auxiliary systems as a turn key contractor for more than 40 years. Bypass systems are an integrated part of modern Combined Cycle Power Plants (CCPP). Bypass systems contribute a major part for operational flexibility. They allow the shortest start-up times by minimising mismatches between boiler/HRSG and turbine. Bypass systems also lead to predictable and repeatable start-up times, as well as reducing solid particle erosion of component, to a great extent. The functional requirements for bypass valves are: 1. Control mode for an accurate control of the IP and LP bypass steam flow during the unit start-up and shutdown, as well as during normal operating transients. 2. Fast closing mode for bypass-trip (supported by spring force) when required for condenser protection. 3. Combined mode for fast reaction on pressure increase to a define set point and further action in control mode. In the past, a combined stop and control valve design, each with a separate stern, was common. The challenging objective for the bypass valve design was to integrate the control function and the trip function with a single stem design.