The operating time and batch size may be controlled by economics or other factors. For instance, it is not uncommon for the entire batch including startup and shutdown to be done in one eight-hour shift. If the same apparatus is used for several different chemicals, the batch sizes may vary. Also the time to change over from one chemical to another may be quite long, since a rigorous cleaning procedure may be required.
The total batch time, tbatch, is
The down time, tdown, includes dumping the bottoms, cleanup, loading the next batch, and heating the next batch until reflux starts to appear. This time can be estimated ...