Page 415 - Design of Simple and Robust Process Plants

402 Chapter 9 Operation Optimization
optimization exercises provide a good insight into the robustness of the
model for optimization. Any problem in this area often requires model
updating.
. Implementation of CLO is the last operational step, and concludes the whole
sequence of OO, from data analysis to implementation of set-points.
. Evaluate and maintain the project. Specifically, the maintenance of the sys-
tem is not a trivial effort, and an ongoing maintenance system needs to be
set up to maintain the operation and quality of CLO.
. Other types of optimization are discussed briefly, such as off-line optimiza-
tion, mixed integer optimization, and dynamic optimization.

9.7
Pragmatic Approach to Operation Optimization

Most applications of OO take place in existing processes. Therefore, it is a legitimate
question to ask whether the approach taken as described above is the best. If the
process is well-known, not only from a reactor kinetics standpoint but also from a
process modeling perspective, the size is of a world-scale plant, and the process is
subject to frequently changing economic environment, it most likely is. In many
plants, the process knowledge is only available to a limited extent and the plant capa-
cities are limited. The approach taken in those situations might be more step-wise.
The question will be, ªWhat will be the preferred step plan?º. In the first place, the
steps planned need to have a value contribution and be sufficient to recover the
investment required in knowledge (software)and hardware. The order of steps to be
considered are:

. Reactor modeling
. Performance meter
. Process modeling, off-line optimization
. Quality of control, to achieve process stability, including self-optimizing
control
. Constraint control
. Process optimization (closed loop)
It is not likely that all these steps have to be taken, and ultimately only one, two or
more steps will be required. The order of development is not necessarily as tabulated
above, although the logic is in agreement with the order of implementation for total
OO. The following qualitative approach is proposed for the selection of implementa-
tion steps. The different steps are listed, and are given an effort (investment)in
knowledge and potential added value level. Both levels have four categories: High
(H), Medium (M), Low (L), and Not Applicable (NA).