Page 80 - Design of Simple and Robust Process Plants

64 Chapter 3 Design Philosophies
. Operation optimization
± Capacity constraint controller on feed.
. Just in time production
± Direct HC feeds, resulting in removal of HC feed tanks.
± Elimination of product storage.
. Design for total quality control
± Automation of plant to obtain consistent production.
± Elimination of lot tanks by improved feed forward control for consistent
product
The design philosophies represent an integrated effort and all take part in an overall
activity to obtain,

an optimal designed safe and reliable plant, operated hands-off at the most economical
conditions.

It should be mentioned that these philosophies can also be applied as stand-alone
philosophies, especially in an existing process. In Chapter 10, which refers to the
operation and continuous improvement of a quality plant, special attention is given
to the improvement of existing facilities ± which often form the basis for the design
of a new facility. Some aspects should be mentioned at this point. Hands-off opera-
tion can be developed for an existing process by tabulating what operators are doing;
a plan may then be developed to minimize theses activities by ongoing screening. A
similar situation exists for maintenance, as well as for just-in-time production,
whereby the operation is run at minimum stock so that storage is made available for
other applications. In addition, it is folly to install and maintain a spare compressor
when it could be removed and the operational unit made more reliable.
The ultimate savings for the design or upgrading of a process based on the design
philosophies are very large. In practice, a capital saving of 30±40% on capital cost
can be achieved, while savings on operational cost are in the order of 5±10%,
depending on the plant. Savings on maintenance should reduce in equivalence to
the capital reduction, but also be less than 1% of invested capital. The number of
operational personnel will also be reduced, their activities shifting from operation to
supervision, and focusing on low-cost operation.

References

Aelion, V., Powers, G.J. Synthesis and Biegler, L.T., Grossmann, I.E., Westerberg,
evaluation of operating and flowsheet A.W. Systematic Methods of Chemical Process
structures. Annual Meeting, AIChE, Design. Prentice-Hall PTR, 1997.
November 1991, paper 143h. ISBN 0-13-492422-3.
APME (Association of Plastic Manufacturers Brundtland,G.H. Our Common Future. WCED,
in Europe). Eco-profiles of the European Oxford University Press, 1987.
Plastic Industry. Report 9, September 1997.