Economic optimal plantwide control
Project members: A.E.M. Huesman
The objective of plantwide control (the control of a complete chemical
plant) can be formulated as:
 support (not guarantee) safety,
 realize the required conversion,
 minimize the operating costs.
It should be noted that the three aspects of the objective are
mentioned in the order of economic importance. The support of
safety is essential to avoid (economic) loss, the required conversion
is a necessary condition to make profit and minimizing the operating
costs leads to maximum profit.
There are at least two approaches to realize this objective. The first
approach is traditional. This approach focuses on the required
conversion and tries to realize this by control. If necessary
or possible the support of safety and the minimization of the
operating costs is also handled by control. An advantage of this
approach is that it leads to control problems that can be solved
easily realtime. A disadvantage is that it does not minimize
the operating cost to the lowest possible level, so potential profit
is lost. Another disadvantage is that the traditional approach only
works well for continuous processes.
The second approach uses the objective to formulate a dynamic
optimization problem:
DOF stands for Degrees Of Freedom (valve positions etc.), s.t. for
subjected to. The optimization approach is attractive since it leads
to economic optimal plantwide control. Furthermore it can not
only handle continuous processes but also batch processes.
However the typical size of the optimization problems involved is
considerable (the number of variables and equations is
). And the effect of disturbances can only be taken into account
by repeating the optimization realtime. The current research
concentrates on the question how to solve large optimization problems
realtime (in a plantwide control context).
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