TUBE FAILURE DURING STARTUP IN ASTEAM SURFACE CONDENSER INSTALLED IN ACOMBINED CYCLE PLANT OPERATING IN COLD CLIMATE

摘要

Combined cycle plants in cold climates experience low circulating water inlet temperaturesduring winter months. During winter startups, low circulating water inlet temperatures combinedwith partial bypass steam flow to the condenser results in extremely low condenser pressures andhigh steam velocities. Improper design, control & operation of desuperheating valve andimproper drainage of bypass header lines can lead to pockets of moisture in the bypass steam.High steam velocities combined with moisture pockets of varying quality can cause flowinducedvibration and tube failures. This paper examines the performance of a condenser inbypass mode for varying condenser pressures, bypass steam flow rates, support plate spacing,and moisture pockets with varying quality. Actual and critical steam velocities are calculated.Condenser operating points prone to flow-induced vibration and associated tube failures arepredicted. Recommendations on safeguards to eliminate flow induced vibration and resultingtube failures are discussed.