Page 309 - Design of Simple and Robust Process Plants

8.3 Automation of Operation 295
A character trait of human beings is also their limited memory or even wrong
memories, phrased here as:

If you don't have to memorize, you can't forget it.
Automation solves this problem. The computerized systems can recall instructions
and procedures exactly over its lifetime. To accommodate this loss in memory,
operational software can easily be provided with status overview and progress in
operation sequences and terms and conditions to be fulfilled for transient opera-
tions.
Automation always triggers the question, ªHow far do we automate?º Quality and
economic requirements drive us to more consistent production with less variability,
while production is optimized. The operation of simple and robust plants will be
grouped more and more in one control room. The approach of simple and robust is
full automation, but there can be some economic constraints to this approach. It
should be noted that simple and robust might lead to some more process trips. Due
to full automation and fewer operational personnel, the process will trip more in
situations of failures or supposed failures, which in the past was how the process
was kept ªon airº by operators. The automation of all activities that require frequent
operational activities are beyond the discussion here. All batch operations are auto-
mated like batch reactors, batch extraction but also regeneration for adsorption and
de-sorption units, reactors. The start-up of a unit might also lead to a dangerous
situation if not automated like furnaces that require a burner management system
for start-up.
Also interlocking and process trips require automation as the operation crew is
not available nor consistent enough for manual operation. The debate starts about
the start-up of continuous processes which have very long production times without
interruptions. The latest world-scale ammonia plants have experienced uninter-
rupted production of 4 years, and clearly in such cases a complete automated start-
up might be costly. In those specific cases one might develop a start-up procedure
that should be loaded in the instrumentation system and tracks and verifies the
start-up by the system, in case a start-up team is required (Stassen et al., 1993; Wei
Zhi-Gang et al., 1998).

8.3.1
Instrumentation Selection (Analog In and Outputs and Digital In and Outputs)

The bases for the instrumentation are the operational and control strategies. The
instrumentation selection is performed from different viewpoints:
. Control, CVs and MVs (controlled and manipulated variables)
. Automation of operation (digital actions and operational trajectories)
. Safeguarding
. Observation, including performance measurement