Page 271 - Design of Simple and Robust Process Plants

7.5 The Optimization of an Integrated Complex 257
7.5
The Optimization of an Integrated Complex

The optimization of an integrated site is a balanced activity. On one hand, process
plants can be designed totally independently of any integration, while on the other
hand the site can be totally integrated and the system made totally dependent. The
integration aspects are discussed where the right economic balance is the target for
this activity. The discussion will be divided into:

. Site flowsheet with the corresponding mass balances and its variability.
. Site utility integration.
The integration will take place within the design philosophies, as discussed pre-
viously. Storage optimization and site vulnerability evaluation is discussed in the fol-
lowing sections.

7.5.1
The Site Flowsheet

7.5.1.1 Logistic considerations
The overall site flowsheet should be prepared to reflect the different processing
plants. A plant is considered as a partially independent entity, characterized by a raw
material storage up front and a product storage after the plant. These storage facil-
ities might be shared by other consumers or producers, and often have loading and
unloading facilities for import and export. A plant can have an intermediate storage
tank in process for operational reasons; in that case the tank normally has only one
supplier and one user and no (un)loading facilities. The site flowsheet must be com-
pleted with a site mass-balance. The individual plants can be subject to variations
not only capacity-wise (as determined by the business), but also technically as cata-
lyst aging or fouling might also have an impact. These last variations are however
small compared to fluctuations as a result of market conditions. During operation, a
difference in the site supply and demand balance will have to be solved by (un)load-
ing facilities for the different (intermediate) products or provisions for external pipe-
lines connections. The overall capacity for these provisions depends on the esti-
mated imbalance by the businesses. Optimization of the storage facilities depends
on the failure rates of the plant, the transportation volume, and frequency; reliability
will be discussed in Section 7.6.
Of special consideration are the gas streams such as hydrogen, carbon dioxide,
and fuel-gas as feed streams. In a similar way, this also applies to the utilities such
as power steam, nitrogen, and air. These streams are, in general, all characterized by
no storage facilities (very expensive), and can force a plant to an immediate stop as a
result of a supplier outage. Different situations for direct supplies without any stor-
age can be applicable: