Overrides For Column Overhead System

Let us assume we have a conventional column with the following normal controls:

—Condensate receiver level controls top-product drawofF.

—Base level controls bottom-product drawofF.

—Reflux is ratioed to feed.

—Steam is ratioed to feed.

As indicated by Figure 9.9, this column has a horizontal condenser and vertical, cylindrical condensate receiver or reflux drum. We will assume that the level controller is of the PI type with set point at midscale of the level transmitter span and that gain 2 auto overrides are employed. The level overrides then function as described in the following.

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