Cooling and Heating Considerations

The following are some of the important considerations for column cooling and heating  

Columns containing hot, condensable materials must be cooled slowly at shutdown. Rapid cooling may cause excessive condensation, with identical ill effects to those described in guidelines 1 to 4 in Sec. 11.7. In vacuum services, this excessive condensation may also burst the bursting disk and/or induce excessive air leak- 

Condenser wind-down is the key to the column cooling rate at shutdown. The condenser cooling should be cut back so that column pressure is kept on control for as long as possible. The cutback may raise the condenser outlet cooling water temperature this temperatime must be kept below the boiling point, even if it means losing column pressure. 

An inert or process gas can often be admitted into the column to keep pressure up and prevent vacuum while the column is cooled. 

As much liquid as possible should be drained out of a hot column prior to and during the initial cooling period. This is particularly important if the liquid solidifies or becomes highly viscous as it cools. The author experienced a case where overlooking this guideline caused a hard, solid mass to form at the bottom sump. The mass was extremely difficult to break up. 

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