Page 223 - Design of Simple and Robust Process Plants

208 Chapter 5 Process Simplification and Intensification Techniques
all unnecessary connections and lines. Based on the new design, he was able to
design software for the storage area.
The objective for piping is minimize, as this makes the operation surveyable. This
is especially important in remote-operated plants, where the demand for rapid diag-
nosis of a process upset is high. Next to surveyability, minimization of piping also
improves safety, as fewer lines can lead to fewer operational errors. The way that
lines are tied together should also be limited, the greater the number of connections,
the greater the risk of an inter-reactivity problem.
During the discussion about complexity in Chapter 2, the following terms were
mentioned with regard to unit complexity:

In formula form; C unit = f (M) (N) (O) (P) (Q) (R) (2)
The level of complexity C of a unit in a chemical process was defined as a function
of:

. M, the number of equipment accessible by the operator.
. N, the number of DOFs, including manual/actuated valves/switches and set
points of control loops.
. O, the number of measurement readings.
. P, the number of input and output streams, including energy streams.
. Q, the interaction in the unit requiring an operator intervention.
. R, the number of external disturbances (for the unit) asking for action from
an operator.
For piping, this can be transformed in a similar form:

Complexity of piping is; C = f (M) ( N) ( O) (Q) (3)
where M is number of lines, including bypasses, jump-overs;
N is the number of automatic valves as well as manual, including bypass, drain
and vent valves;
O is the number of piping items others than valves, such as check valves, reverse
and excess flow valves, safety relieve devices, bellows, excluding reducers (these last
are seen as part of the fixed pipe); and
Q is the number of flow interconnections that it is possible to make (see Table 2.1
in Chapter 2) if no special provisions are made to avoid any reverse flow.
These terms clearly show how, as the complexity of piping grows, the number of
flow interconnections expands exponentially. The solution is clear ± the number of
piping items shown in Eq. (3) needs to be reduced.

5.7.3.1 How do we minimize the piping?
There are several ways to reduce the piping, some being equivalent to minimization
of equipment:
. Avoidance of equipment.
. Combination of functions.
. Combination of equipment.