Page 41 - Design of Simple and Robust Process Plants

2.2 The Level of Complexity 25
elderly people can operate it. On the other hand, it is a very complex system to
design and manufacture. By contrast, the manifold is a very simple device to design,
but very complex to operate. It is essential that the conditions of all connecting ves-
sels are known for a correct operation, and it is difficult to analyze for error detec-
tion.
In the above text, ªsimpleºwas defined from an operational perspective (easy to
operate), but this does not have any relation with the complexity of the device/sys-
tem. It will be understood that the operation is simplified when less degrees of free-
dom (DOFs) are available for the operator. In practice, this is realized by the intro-
duction of automation, as a higher level of automation reduces the DOFs for the
operator.

NUMBER OF
INTERCONNECTIONS
AB C D E F G
42
A
20
BC D E
A
MINIMIZE THE NUMBER OF
12
BC D INTERCONNECTIONS TO AVOID
A • HUMAN ERRORS
• SOFTWARE ERRORS
6
• MECHANICAL FAILURES
BC
A
2
B
Fig. 2.3. Manifold with the number of flow interconnections
Table 2.1. The number of piping connections versus the number of flow interconnections.

No. of connections No. of flow interconnections

1 2
3 6
4 12
5 20
6 30
7 42
8 54

2.2
The Level of Complexity

The term ªcomplexityºis introduced when a total system is considered. It was Scur-
icini (1988) who defined the complexity of a system as: