(46a) Improving Efficiency and Operation of Heat and Mass Transfer Equipment

The integration of heat and mass transfer within one unit operation is an efficient way to operate a process. This approach leads to significant capital and energy savings. On the other hand, design and operation of such unit operations is not very well understood. In some cases these unit operations are designed under the assumption of a ?limiting factor? when either mass transfer or heat transfer alone is considered.

Two cases from our practical experience will be considered. In both cases neglecting simultaneous heat and mass transfer led to product losses and operating problems.

In the first case an absorber for a strongly non-ideal liquid was operated without taking into account mass transfer limitations. The operating efforts were concentrated around removing significant heat of absorption only. A model taking into the account simultaneous heat and mass transfer in the absorber was developed. This approach allowed us to improve operation of the absorber, prevent significant material losses and eliminate potential environmental liability.

In the second case extensive tray damage was observed during operation of a stripping column with a built-in condenser. A dynamic model for the column and the built-in condenser operation was developed. We identified a problem with the column start up procedure that did not take into account the built-in condenser dynamics. An improved start up procedure considering combined dynamics of the column and condenser was developed which resolved the problem.

These cases demonstrated that quite often the complex nature of the unit operations dealing with simultaneous heat and mass transfer can not be ignored.