Page 392 - Design of Simple and Robust Process Plants

9.6 Project Methodology for Operation Optimization 379
9.6.1
Feasibility Study: Step 0

The elements of a feasibility study are discussed below, after provision of an over-
view of the elements to be addressed. The elements of a feasibility study include:
1. Objective of the study
2. Modeling background
3. DOFs for optimization and model-based control
4. Sensitivity of DOFs on process performance
5. Constraints identification
6. Parameters
7. Control performance
8. Performance measurement
9. Projected cost and time planning and manpower resources
10. Project savings and evaluation

9.6.1.1 Objective ofthe study
During the feasibility study, the different options for optimization should be
explored and result in an estimated cost versus benefits analysis. The different
options to be studied depend to a large extent on the type of process:
± For batch processes, scheduling and constraints control on the feeds must be
considered to obtain shorter batch times.
± Continuous processes with consistent feed sources and pure products, effi-
ciency improvement and capacity increase are target objectives.
± Continuous processes with different feed stock options, an improvement of
the efficiency of operation at the different feed stocks is quite achievable. An
OO project might include as a spin-off a feed stock evaluation tool which can
generate considerable savings.
± Continuous processes with many transient operations for different product
grades: scheduling, increasing capacity and reducing off-grade are subject to
evaluation (this is particularly applicable to polymer processes).

The basic factor behind an OO project is the economic benefit achievable by ongoing
adapting the process conditions at changing circumstances.
Variability An overview must be made of the variation in circumstances, and the
frequency of occurrence which have an impact on the economic performance. This
should provide input for the answer to the question of off-line versus on-line optimi-
zation. Variations might include feedstock and product variations, product distribu-
tion, price sets but also environmental effects. The benefits are to be found in more
efficient operation including capacity increase. The capacity of a facility is only
important if the business has a market for an increased production. On the other
hand, an optimization can provide a cheaper capacity increment.