Page 259 - Chemical engineering design
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PIPING AND INSTRUMENTATION
(e) 235
Figure 5.22. (e) Batch distillation, reflux flow cascaded with temperature to maintain constant top composition
Figure 5.23. A typical stirred tank reactor control scheme, temperature: cascade control, and reagent:
flow control
5.9. ALARMS AND SAFETY TRIPS, AND INTERLOCKS
Alarms are used to alert operators of serious, and potentially hazardous, deviations in
process conditions. Key instruments are fitted with switches and relays to operate audible
and visual alarms on the control panels and annunciator panels. Where delay, or lack
of response, by the operator is likely to lead to the rapid development of a hazardous
situation, the instrument would be fitted with a trip system to take action automatically
to avert the hazard; such as shutting down pumps, closing valves, operating emergency
systems.
