Leaks/leakage exchanger-tube

Tube leaks may occur in the reboiler, condenser, preheater, precooler, or any other heat exchanger linked with the column. Several experiences where leakage caused poor performance have been reported (71, 238, 239). The effect of a leaking heat exchanger tube depends on the magnitude, the direction, and the location of the leak. 

The reason illustrates the true nature of the shell-and-tube heat exchanger. It is a compromise between an ideal heat-transfer configuration and practical mechanical limitations. In this case, the difficulty is preventing leakage around the longitudinal baffle. Such leaks permit the shell-side fluid to short-circuit the tube bundle that is, a percentage of the inlet flow, may flow directly to the outlet nozzle. In extremely serious cases, I have seen the bell head (shown in Fig. 19.8) 100°F colder than the shell-side outlet temperature. 

Shell Fluid Bypassing. Various clearances are required for the construction of a plate-baffled shell-and-tube exchanger. The shell fluid leaks or bypasses through these clearances with or without flowing past the tubes. Three clearances associated with a plate baffle are tube-to-baffle hole clearance, bundle-to-shell clearance, and baffle-to-shell clearance. Various leakage streams associated with these clearances are identified elsewhere. 

Leak prevention. A major problem in the HRE-1 was to maintain absolute leaktightness in all components. The radioactivity of the solution during operation was about 30 curies/cc. Twenty-four hours after shutdown the activity was about 3 curies/cc. With these high activities, the total leakage from the system had to be kept below 1 cc per day. A much better performance than this was attained through the use of canned-rotor pumps, double tube-sheet exchangers, and bellows-sealed valves. 

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