Page 373 - Design of Simple and Robust Process Plants

360 Chapter 9 Operation Optimization
9.5
Closed Loop Steady-state Optimization

In this section we will discuss different OO techniques and the basic modules for
the execution of an optimization cycle for continuous (steady-state)and dynamic
operations (Krist et al., 1994; van Wijk et al., 1992; Marlin and Hrymak, 1997; US
Patent 5,486,995; US Patent 6,038,540). During this discussion we will illuminate
the different technical aspects around process optimization. Off-line optimization is
not discussed separately, but most of the elements discussed are also applicable in
that specific situation.

9.5.1
Optimization Techniques

Three different operation optimization techniques can be recognized for a continu-
ous process plant, and these are discussed prior to the modules of the optimization
cycle:
1. Self-optimizing control/optimized unit control
2. Empirical optimization
3. Fundamental model-based optimization

9.5.1.1 Self-optimizing control or optimized unit control
Self-optimizing control is a technique developed at the University of Trondheim,
Norway (Halvorsen and Skogestad, 1997, 1999; Skogestad, 1999, 2000; Skogestad et
al., 1998, 1999).

COOLING COOLING

PRODUCT A PRODUCT A
3
FEED Main column 14
PRODUCT B FEED PRODUCT B
Pre-fractionator
25
STEAM
STEAM
6

PRODUCT C
PRODUCT C

Petlyuk column Divided wall column

Fig. 9.6. Petlyukcolumn and divided wall column both capable
to separate a three component mixture at required specification.