Page 31 - Design of Simple and Robust Process Plants

14 Chapter 1 Introduction
size by application of improved techniques, while simplification benefits from exist-
ing techniques.
Design techniques to achieve low-cost processes may be divided into different
categories:
. Elimination of functions
. Combination of functions in the same unit/equipment
. Integration of equipment
. Intensification of process functions
. Overall process simplification
The opportunities need to be recognized during the conceptual design stage. The
details of the different categories will be presented and illustrated with examples in
Chapter 5.
In order to make simplification and intensification more easily approachable,
opportunities are presented for the most common process units, including that of
piping design. The examples will clearly illustrate what can be achieved by applica-
tion of this method. The chapter concludes with a debate on any contradiction
between simplification and further process integration.

1.6
Design Based on Reliability

Reliability engineering is one of the pillars of simplification, and is based on the
philosophy, ªDesign for single robust components unless ¼º.
The technique of reliability engineering is discussed in Chapter 6, together with
its application in the design of process plants. The text provides a quantitative basis
for any design decisions around the installation of more parallel units (provisions)
as back-up, or the installation of more reliable units. The same technique can also
be applied to evaluate instrumental safe guarding, and to estimate nuisance trips
due to instrument failure. Although the mechanical reliability of process units is
improving, the number of nuisance trips is increasing as a result of instrument fail-
ure. This is also due to the tendency to add more and more instruments to the pro-
cess. Reliability engineering also provides a quantitative base for risk analysis with
regard to the likelihood of an event. It should be realized, however, that all predic-
tions on the probability of failures are based on historic data, and this is not a guar-
antee that newly designed components will always meet these criteria. For example,
the motor industry suffers from this phenomenon if certain components are
replaced by new alternatives.