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Possible control strategies for multiple parallel distillation columns or column sections.

IP.com Disclosure Number: IPCOM000032045D
Publication Date: 2004-Oct-20
Document File: 1 page(s) / 11K

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Possible control strategies for multiple parallel distillation columns or column sections.

When distillation columns (for example in an air separation plant) become very large, it may be desirable to install multiple parallel columns or column sections to reduce the diameter of the individual columns, for example to stay within shipping constraints.

Various levels of control may be applied to such parallel columns.

The simplest and most desirable control strategy is to rely on hydraulics to feed each column with the correct split of vapour and liquid, so that there is no active control or liquid or vapour split during normal operation.  This is like manifolding multiple heat exchangers together.  Flashing liquid streams could be separated outside the columns with the liquid and vapour fed symmetrically to each column.

A slightly more complex possibility is to control only the liquid flow split actively during normal operation and to allow the vapour split to be determined hydraulically.  In most circumstances this will prove the best strategy because it provides the ability to compensate continuously for natural imbalances in flow for the relatively minor cost of small liquid-phase valves.

The most undesirable possibility is to control actively both liquid and vapour flows to each of the columns.  This introduces valves and additional pressure drop into at least one of the vapour flows and therefore increases the capital cost and energy consumption over the other two opt...