Field Tests for Minimum Acceptable Throughput

Minimum acceptable throughput tests are often conducted when the column is anticipated to operate at low throughput for lengthy periods. The tests supply information on whether column internals should be modified or replaced to improve performance (e.g., reduce energy consumption) during low-rate operation. 

Minimum throughput tests are usually carried out by reducing the feed rate to the column while at the same time reducing reflux and reboil rates in proportion until the separation falls off sharply or until an instability is observed. The procedure for reducing the reflux and reboil rates should take the control system into account, and should be carried out in a manner similar to that used for flood testing (see Sec. 14.1.4). 

Consideration must be given to the thermal state of the feed this state should either be kept constant or be adjusted in the manner anticipated under low-rate operation conditions. Often, spare capacity is available in a preheater or a precooler when the column operates at low rates, and this can be utilized. 

For best results in a minimum throughput test, it has been recommended (2) to carry out a series of tests at diminishing feed rates (and reflux and reboil in proportion). An efficiency versus throughput curve can then be plotted from which the minimum throughput for acceptable separation can be determined. 

---