CONTROL OBJECllVEs Process constraints
The process has 41 measurements and 12 manipulated
variables as listed in Tables 3-5. A prerequisite
for most studies on this problem is a process control
strategy for operating the plant. The control objectives
for this process are typical for a chemical process:
1.
2.
3.
4.
5.
Maintain process variables at desired values.
Keep process operating conditions within
equipment constraints.
Table 6 lists the specific operational constraints
that the control system should respect. These constraints
are primarily for equipment protection. The
high and low shutdown limits are part of the process
interlock strategy and are used to shutdown the
process in the event the process conditions get out of
hand.
Product variability
Minimize variability of product rate and
product quality during disturbances (stream 11).
Minimize movement of valves which affect
other processes (in this case the gas feeds as
described below).
Recover quickly and smoothly from disturbances,
production rate changes or product mix
changes.
The variability of the product stream is important
with regard to the downstream distillation system
which refines products G and H. Flowrate changes
of stream 11 greater than f 5% with significant
frequency content in the range &I6 h-’ are particularly
harmful. In addition, composition variability
greater than +5 mol% G with significant frequency
content in the range 6-10 h-l are equally harmful.