Page 269 - Design of Simple and Robust Process Plants

7.4 Site Selection 255
Please note that one of the design philosophies for a process plant as discussed ear-
lier is, ªDesign for single reliable components unless justified economically or safety wiseº.
It will be clear that there is a difference between a process plant and an integrated
complex, which boils down to the acceptability of a certain financial risk.
The reason for the above-mentioned site design philosophies is to avoid a chain of
events, which may lead to a total or part site outage, as these involve a high cost. An
immediate plant outage which results in an emergency stop (as in case of a total
power failure) may cause different types of losses:
. Mechanical failures may occur due to the high temperature transients specif-
ic to this type of stop.
. Off-spec product(s) will be produced.
. Equipment may be blocked through polymerization or solidification.
Recovery from such stops can take considerable restart time (capacity loss) com-
pared to a controlled stop. The above situations can justify an emergency power pro-
vision for certain subsystems, such as cooling water or a heating system. This can
be considered as a third level of defense to name, in order of action: level of redun-
dancy/back-up, load shedding system, and emergency provision.

7.4
Site Selection

Before the optimization and vulnerability of a complex is discussed, it is important
to understand the technical aspects of site selection for the complex. It should be
clear that site optimization is only a suboptimization compared to the selection of
the site. In the past (and no doubt in the future), some sites have been totally phased
out as the logistic situation was not sufficiently competitive in the global or regional
markets.
The main aspects for site selection, although not all of equal importance, can
have a major impact on the development and or economical operation of the com-
plex. The selection aspects to be considered are:

. The process plants considered for the site are often part of a product chain(s),
and will have to be subject to careful evaluation. The alternative options with
(dis)advantages will largely be reflected in business studies and logistic stud-
ies (business studies are considered beyond the scope of this book). Any busi-
ness partners or co-owners of the complex need to be identified. The selec-
tion of the site needs to incorporate these aspects.
. Develop a site mass and energy balance showing all process and utility
streams between the plants and outside supplies. Such a balance will be sub-
ject to some iterations, but is necessary for a complete overview and to under-
stand all interactions. Plants will not all be built and started at the same time,
and therefore have to be scheduled in time. The balances have to be made
available for all steps during evolution of the site.