Page 54 - Design of Simple and Robust Process Plants

38 Chapter 3 Design Philosophies
the accuracy of a dynamic model for control design, which does not require the
same level of accuracy.
Generic process simulators (e.g., from Aspen Technology, Simulation Science,
and Hyprotech) have physical property banks, unit models, economic sections and
optimization routines available. The availability of cost estimation data is still lim-
ited, and is to be seen as a short-coming. Currently an estimating package is avail-
able which can be connected to the simulators, but at present it is very detailed, the
initial approach being to use it for authorization estimates. This makes it far to de-
tailed for use in process evaluations and optimization during conceptual design,
where it is used on a comparison basis. The cost estimation section is a requirement
to find the most optimal design. Another current short-coming is that, for optimiza-
tion, the equipment costs should be described as a continuous function to avoid dis-
continuities.
The challenge is to benefit consistently from process knowledge encapsulated in the dif-
ferent models. Major software suppliers support this concept, and have as their objec-
tive the development of one modeling environment with a broad spectrum of mod-
els, as supported by the CEFIC vision.

3.3
Design Philosophies

The overall definition of the simple and robust process plant is:
1. An optimally designed safe and reliable plant that is operated hands-off
under the most economical conditions; this is also called a ªcompetitive pro-
cessº.
2. The ultimate objective of the chemical industry is to make long-term maxi-
mal profit; this objective emphasis two basic elements ± maximize profit and
long term.

3.3.1
Profit

The element of ªprofitº means that the industry must make a margin on capital.
The element capital should be minimized in comparison to the margin that should
be maximized. Historically, the trend was to maximize the margin through improve-
ments on capacity, and raw material and energy utilization, with less emphasis on
capital. In the design philosophies presented here, we address both aspects as equal
partners.