Page 205 - Design of Simple and Robust Process Plants

190 Chapter 5 Process Simplification and Intensification Techniques
. Heat exchange
. Fluid transport
. Piping
. Instruments
The objective of this section is to create a list of increasing complexity for several of
the most common units operations. Piping and instrumentation are also discussed
to illustrate how problems of complexity can be approached for these items. The
selected unit operations will be ranked in order of their increasing complexity. It is
not the intention here to develop a design methodology for these items, but to use it
as a reference of what is ªsimpleº, and what effect increases in complexity can have
on the design. The priority ranking is based on industrial experience but it always
has to be judged in the context of the specific situation. Often, designs are initially
too complicated because they are based on the engineer's personal experiences.
Design engineers must realize that there are simple ways of doing things, and that
the priority ranking applied to the different items is intended to promote simple
thought processes. The innovative techniques are not included in the listing, neither
is it the intention to list items that have a multiple function. However, these are
included in the ranking as they might be used for a mono function as well as multi-
ple functions. In this respect, it should be understood that a mono function such as
reaction and absorption includes the inherent heat transfer system to remove reac-
tion or absorption heat, as is applied in multi-tubular reactors. However, reactor
feed effluent heat exchange in a reverse-flow reactor and reactive separations as reac-
tive distillation are considered as being multi-functional.
Piping and instruments have been included as these have a considerable impact on
complexity, specifically for operations. The terms contributing to complexity as pre-
sented in Section 2.2 in Chapter 2 come within the context of piping and instru-
ments, and are re-discussed in this section.

5.7.1
Reactors

Reactors are the most important part of a process as they are the place where the
products are formed and the selectivities are determined. Reactors are where the
energy ªhouseholdº requires adequate design and control, and where safety aspects
must be respected. In this section, the discussion will be restricted to continuous
reactors, (Krishna and Sie, 1994; de Hooge and de Nobel, 1998) which can be
divided into the following categories:
1. Homogeneous reaction, G and L
2. Heterogeneous, L/L
3. Heterogeneous reaction, G/S and L/S
4. Heterogeneous reaction, G/L
5. Heterogeneous reaction, G/L/S