Page 201 - Design of Simple and Robust Process Plants

186 Chapter 5 Process Simplification and Intensification Techniques

Bayonet
Shell and Tube Hairpin Bayonet
tube
Fig. 5.34. Heat exchangers with increasing flexibility for
temperature excursions from left to right.

Mechanical construction might be limited by the furnaces available for heat treat-
ment, such as glass-lined. During the past few decades the size of glass-lined vessels
3
3
has increased from 20 m to over 60 m , and this might increase further still in
future. Shop versus field fabrication, which often depends on transportation restric-
tions, may also have an impact on size.
Flow distribution and mixing is a factor that is considered to be one of the most
difficult points for scale-up. In the meantime, wide application of computational
fluid dynamics (CFD), which also has the capability of including reaction kinetics,
has greatly reduced the risks associated with scale-up.
Process design constraints might also appear, an example being the STR that is
constrained by a jacket cooling a solution, and which might be a refluxing condenser
(Figure 4.11 in Chapter 4). Combinations of mechanical and process constraints
might also become apparent. One solution to this was found by modifying a nitra-
tion reactor system of CSTRs in series (which is completely glass-lined) by using an
adiabatic plug flow reactor system (Figure 4.8 in Chapter 4).
Although many systems might be considered as being constrained, careful study
of these constraints might lead to solutions of the problems involved. The accompa-
nying savings in costs are extensive, and clearly worth the effort.

5.6.3
Strategy Around Supplies and Storage

Flowsheets of the evolution of batch processes (Figures 1.4±1.7 in Chapter 1) show
that, by the second millenium, the latest generation of systems were using additives
prepared by suppliers and delivered in containers, rather than prepare additives on-
site. This avoids the handling and storage of large amounts of chemicals, and hence
the process is made much safer and cheaper to operate. For some utility systems,