Distillation. Absorption - Control and regulation

In the 1950s, it was possible to run a multi-column distillation plant without any regulation. Today, this is virtually impossible, for the following reasons:

• improvements in phase contact devices have led to a reduction in column diameter and, consequently, in product residence time;

• improvements in calculation methods and the accumulation of experimental results have led to a reduction in safety coefficients, both in terms of hydrodynamics and efficiency;

• energy savings have resulted in more complex schematics and more intertwined circuits for the various columns.

This article deals with the control and regulation of columns from the point of view of the chemical engineer. It is aimed at non-specialists who need to :

• operate production plants with one or more distillation or absorption columns;

• design a distillation unit ;

• understand a supplier's control and regulation options.

It is drafted with continuous operations in mind, but most of its content also applies to discontinuous operations, with the last chapter of the article focusing more specifically on the special nature of the latter.

This article does not deal with measuring instruments, data transmission, control devices or control systems. All these subjects are covered in the Measurement and Control treatise, in particular in the Automation section, and we invite the reader to refer to it. A comparison between the three competing control systems (programmable logic controllers, digital control systems and personal computers) can be found in the bibliographic reference [1] .