Page 49 - Design of Simple and Robust Process Plants

2.5 Summary 33
dition. Recovery might be applicable if a standby unit/provision must be
started for automatic kick-in. The process actions are planned to be taken
before any safety device is activated.
A strategy for the design of operational software needs to be available, and followed,
see Chapter 8. This to ensure consistency in the automation of all units and pro-
cesses, particularly if they are under the control of a single operator.
The instrumentation of the process is a major contributor to control and opera-
tional robustness, and in the field of measurements major shortcomings are a fre-
quent problem, including:
. measurement selection;
. type selection;
. operating range selection;
. installation; and
. calibration.
The above points are independent of mechanical robustness, and address the instru-
ment robustness as a function of the process. An example worth mentioning here is
the selection of a flow meter. Often, a volumetric flow meter is selected even though
the intention is to measure mass flow. The mass meters are automatically corrected
for any density differences, which includes the effect of concentration, temperature
or pressure changes. They measure what we want ± so why don't we select them as
a standard?
Instruments are the eyes, ears and hands of the process plant, and are vital to the
process. Therefore, an experienced instrument engineer should be present on a pro-
ject team from the process design phase until full operation to cover all facets of the
instrumentation.
Although the design of the facilities needs to be considered from the perspective
of robustness, this is a reasonably undefined area and hence can lead to pitfalls for
those who prefer to save on capital but may lose on profit. The challenge is to recog-
nize the likely mishaps and select the adequate component design.

2.5
Summary

The challenges for the chemical industry are to design facilities much more simply,
hence making them much cheaper and easier to operate. Simplicity in design can
be understood from developments in domestic equipment, and must meet require-
ments for ease of operation.
The level of complexity is a measure of the simplicity of a facility. A formula has
been derived to quantify the level of complexity, and this can be applied on different
plant designs to compare their complexity. The terms that define complexity also
provide a means for its reduction.