Preventing Failures by Using No-Tube-in-the-Window (NTIW) Baffling in Feedwater Heater Design

High and intermediate pressure feedwater heaters increase the thermal efficiency of a power plant. During their lifetime they are subject to many different failure, mechanisms. Some of these failures are attributed to flow induced vibration resulting from operation at high overload conditions and load cycling. No-Tubes-in-the-Window (NTIW) baffle designs have been used for many years in the design of power plant and process plant heat exchangers. This baffle design is typically used in larger units which have high flows are susceptible to failures attributable to flow induced vibration. The NTIW design allows for the inclusion of intermediate supports between baffles that allows the design engineer to “tune” the tubes by increasing their natural frequency to levels above any possible flow condition. Utilizing a NTIW baffle design, several of these operational failure mechanisms can be directly addressed in the design and fabrication stage of a new or replacement feedwater heater. In particular, the NTIW can be designed to have extremely short unsupported spans and excellent vibration characteristics even at the highest predicted loads. The design also incorporates a larger minimum bend radii which minimizes high U-Bend stresses as a result of differential leg expansion. The NTIW design puts the exhaust steam into the steam dome without the wet/dry conditions in the condensing zone area just outside the desuperheating zone. The ability to place intermediate tube supports in the baffle space allows the design engineer to have the flexibility to keep zone pressure drops low, even in high load situations.