Diverter damper offers bypass for gas turbines in combined cycles

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Boldrocchi has completed in-house testing at its facility near Milan, Italy, of functional testing for a new large 7m × 7m (23' × 23') diverter damper for a GT, one of three such units to be delivered shortly. Customers from GE Power, Ansaldo Energia, Saipem, Edison and Nooter Eriksen were on hand to witness the success of the test.

The diverter damper has a three-way valve that discharges exhaust gas from the GT, either into the atmosphere via a by-pass stack or into a Heat Recovery Steam Generator (HRSG). As well as high capacity, it surpasses the norm in terms of geometrical sealing, sealing pressure and closing time, while reducing maintenance and easing transportation and assembly. This new diverter also allows for a rapid transition from single cycle to combined cycle systems.


This large diverter damper is designed to withstand temperatures of up to 700 °C (1,300 °F), vibrations and gas turbulence, as well as elevated wear of components. The geometrical seal around the perimeter is more than 99.95 % effective. The sum of all residual gaps in the free air passage section is less than 0.05% (less than 0.01% for this specific application). This percentage is the measure of the residual leakage areas between the blade and the landing bar, along the entire blade perimeter. The diverter is equipped with an air-sealing system which allows the sealing degree on exhaust gases to equal 100 % (full tightness). The air-sealing pressure is > + 500 mm wc, whereas OEMs only require +50 mm wc. Boldrocchi’s diverter is equipped with hydraulic actuators, giving it a normal operation time of less than 60 seconds and an emergency closing time of less than 20 seconds.

However, the diverter has been engineered and manufactured to obtain even shorter actuation times. The sealing lamellas (the strength point) have, on some applications, lifetimes of up to 10 years. Additional benefits include self-lubricated, high temperature, maintenance-free internal bearings as well as a solution for internal thermal-acoustic insulation. The diverter is pre-assembled in a few pieces or can be delivered fully assembled (in one single part). It is engineered for easy installation under single cycle exhaust stacks, instead of existing bend ducts.