Page 154 - Design of Simple and Robust Process Plants

4.2 The Methodology of Process Synthesis 139
. the reliability, size and frequency of the supply system;
. the reliability and unplanned availability of the process; and
. the reliability, size and frequency of the delivery system.
The sizing must be based on a supply chain, including its transportation systems.
Details about storage optimization are discussed in Chapter 7.

4.2.6.4 Integration of a complex
This is a factor that is exploited to reduce the operational cost of a complex. There is
no doubt that an integrated energy system and other process stream integration can
generate high savings. The integration however also might result in vulnerability of
a complex. The design of a complex was historically based on design strategies ± an
approach that was developed on scenarios and has led to over-design in redundancy
provisions. Nowadays, the integration receives more emphasis, and to achieve a low-
cost design a quantified approach must be applied to optimize both the design and
the provisions for back-up. With regard to design optimization, sufficient tech-
niques are available to establish a good design. With regard to quantification of the
vulnerability, reliability engineering techniques are available and provisions can be
judged on their economic contribution.
These techniques need to be applied in order to achieve an optimally designed,
safe and reliable complex. The optimization of storage and site integration are dis-
cussed in more detail in Chapter 7.

Summary
A process mostly fits in an environment of several processes at a site (complex).
Simple and robust designs of a complex require careful design of facilities in order
to benefit from integration and avoid excess investment and operational costs in
redundancy. The example of the evolution of a batch process demonstrated the
move from a process designed to do everything within itself, to a design that is large-
ly based on external provisions/services.

. Additives are handled under specified conditions in dedicated containers to
be used as feed tanks at the consumer plant; this avoids feed preparation and
handling.
. Services are bought externally; these range from (traditionally) power and
water up to steam, cooling water, refrigeration, fuel-gas and on-line raw mate-
rials. The services need to be designed, based on availability and reliability
calculations, to cover the total supply line from supplier to customer in order
to avoid any over-design that would result in higher costs.
. The direct supply of raw materials with pipelines is practiced more to reduce
inventory, handling, and transportation cost while minimizing safety risk. As
a consequence, chemical plants are increasingly built in clustered locations,
and this also leads to increased integration between complexes and plants.