Page 30 - Design of Simple and Robust Process Plants

1.5 Process Simplification and Intensification Techniques 13
1.3.10
Environmentally Sound Design

Nowadays, although the chemical industry operates increasingly on a global scale,
the environmental criteria applied in different countries vary widely. Many global
criteria and trends are introduced first in the Western world, but in time become
readily accepted throughout the rest of the world. A relatively new term in that
respect is ªsustainabilityº, and this needs to be addressed adequately during the
design. For a new facility, this means that the design should increasingly meet glo-
bal criteria, rather than local criteria.

1.4
Process Synthesis and Design Optimization

These are the most important stages during the design as they determine the flow-
sheet and its sizing, and therefore set the bases for the economics of the process
(see Chapter 4). In the past, different hierarchical structures have been developed,
such as the well-known ªonion modelº. The drawback of the proposed schemes is
that the level of interaction is unsatisfactorily addressed. Therefore, another hier-
archical structure for conceptual process design is presented, and this is referred to
as the ªinteractive onion modelº. The design starts from a feasible flowsheet(s) with
alternatives, and concludes step-wise to one frozen mass and energy balance, with
all major equipment sized. The steps are described, and in particular the interaction
with process integration and controllability are include in the structure. Guidelines
are included to avoid complex integration and to de-couple interactions through
hardware or software solutions.
Specific attention is given to the optimization effort ± a staged approach ± which
is applied during the process synthesis methodology, starting from the evaluation of
a large number alternatives for the different sections against variable cost. Finally,
the ultimately selected flowsheet is fully optimized with regard to conditions and
equipment sizing at NPV (net present value). It is considered to be an advantage
that the designer can follow the gradual development of the flowsheet, simulta-
neously monitoring the different optimization stages while increasing the modeling
details.

1.5
Process Simplification and Intensification Techniques

The emphasis in Chapter 5 is placed on technical aspects of process simplification
and intensification. Process intensification is driven by the same objectives as sim-
plification and cost reduction, and therefore both are discussed. The difference is in
the approach, with intensification being focused primarily on the decrease in unit