Top And Bottom Level Control Combinations

Considerable controversy has existed on the question of whether to have the condensate receiver level adjust the reflux flow or the top-product flow. One well-known author argues strongly for the former. Controversy also exists as to whether it is better to have column-base level control bottom-product flow or the reboiler heating medium, usually steam. Another expert recommends the second. It is probably apparent that we cannot follow both recommendations; at least one of the two levels must control a drawoff flow.

There are many columns operating today with condensate receiver level controlling reflux and base level controlling bottom-product flow. There are other columns in which condensate receiver level adjusts top-product flow while base level manipulates steam flow. How do we choose between them, assuming that we cannot, for some reason, have both levels adjust drawoff flows?

It seems to us that it is largely a matter of convenience. In a superfractionator, for example, the reflux flow may be ten or more times greater than the top-product flow. Inventory in the receiver may be regulated a little more readily by manipulation of the large flow than of the small one. This does not mean that level control via the small flow is either impossible or impractical. It does

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