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5.2 Avoidance or Elimination of Process Functions 145
It should be realized that the cost of non-existent equipment emphasizes the follow-
ing terms: capital, interest, operational cost (operational people, energy nitrogen),
maintenance, insurance, land, overheads (emergency, guards, management) ± and
of course you have to make a profit! Although many engineers try to focus on incre-
mental cost, this is the wrong approach.
It is a challenge for the design of simple and robust processes to overcome
these conservative attitudes and to be receptive to simplification/intensification
technology.

5.2
Avoidance or Elimination of Process Functions
There are a many functions in a process design which might be challenged as to
whether their inclusion is really necessary. The identification of these functions,
using a function analysis technique, will be discussed in Chapter 10, but at this
point only the technical opportunities will be discussed.

5.2.1
Tanks and Vessels

In the illustration of a tank farm in Chapter 1 (Figure 1.3), it can be seen that six
tanks are replaced by two. Initially, check tanks (which might also be check silos) are
only required if it is assumed that the production process is not operating at specifi-
cation. This assumption is challenged. Instrument technology and control technol-
ogy are of such a level that, by using an appropriate predictive model-based control
design, the quality at the product stream can meet its specification. This requires
some in-process provisions (e.g., internal recycle lines) to cope with any extraordin-
ary disturbances.
Lot tanks/silos are often used to smooth the quality of different batches or cam-
paigns of the same product through blending. These storage mixing facilities can be
fully eliminated if the process has an appropriate and reliable instrument and con-
trol system and consistent operation practices (automation). The differences in prod-
uct quality of batch plants are mostly caused by inaccurate measurements of feed
quantities. One of the most frequent causes is that flows are metered on volume,
rather than mass.
Mixed feed tanks are regularly used in batch plants for feed preparation. These
facilities are not justifiable if an adequate direct feed system is designed, or if feeds
are delivered in containers at the required composition by the supplier. These mix
tanks have a low mixing efficiency, large volumes (which are not to be preferred
from a safety perspective), and require a high investment.
Storage facilities such as tanks, silos or warehouses might be reduced in number,
or even eliminated. In the example, four tanks are reduced to two. Elimination can
be realized by: