Apparatus and method for controlling steam turbine operating conditions during starting and loading

摘要

A steam turbine-generator system includes a reheater bypass valve which cooperates with both a high- and low-pressure bypass valve in the early stages of turbine loading to divert steam in a bypass flow from a high-pressure turbine to the input of a reheat turbine without passing the steam through a reheat portion of the boiler. The pressure and temperature drops in the high-pressure turbine are controlled by the setting of the pressure threshold of the low-pressure bypass valve. A check valve prevents steam flow into the reheat portion of the boiler until a desired operating condition is attained. The steam flowing to the reheat turbine directly from the high-pressure turbine is at a sufficiently low temperature to avoid temperature insult to the rotor of the reheat turbine. Once the turbine is partially loaded, the reheater bypass, high-pressure bypass and low-pressure bypass valves are closed to establish a conventional reheat turbine configuration. During a cold start, the main stop valve is employed to throttle steam to the high-pressure turbine to additionally decrease the temperature of the steam exiting the high-pressure turbine.