Case Study of an Alternative Solution to a High-Energy Drain Problem in a Surface Condenser

During the startup of an early vintage steam turbine-generator unit (prior to engineered steam bypass systems), warming of the steam piping is commonly achieved through numerous small-bore steam line drains that “dump” into the main surface condenser. And in some cases, it is not unusual for these drains to be open till well beyond the point at which full throttle pressure and temperature are achieved at the turbine resulting in high-energy superheated steam flowing at sonic velocities. And most condensers built earlier than 1980 were ill equipped to handle these high-energy drains without damage. Midwest Generation’s Collins Station, like many others, was built before the EPRI guidelines for high-energy drains were written. Consequently, the initial condenser, provided by Southwestern Engineering, did not adequately address these drains. But unlike most other stations, Collins was operated from the beginning as a cycling station, i.e. 50–100 startups per year. Consequently, their condensers have had a significant portion of their operating lives devoted to startup situations with these drains in operation. As a result, the condensers began exhibiting wall distortion and thermal fatigue cracks less than a year into their service life. The station spent the next 25 years repairing, patching, and trying modifications, all without lasting success. In the Fall of 2002, they asked Raymond Professional Group to study the situation and formulate a cost-effective permanent repair.