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August
2019
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HYDROCARBON
ENGINEERING
E
thylene plants rely on cracked-gas compressors (CGCs),
along with refrigeration compressors, for their
complete process to work properly. Damage caused to
a compressor, particularly from a surge event, costs
owners millions of dollars in both equipment and lost
production. Compressor operation must be fine-tuned to
maximise performance and reduce spurious trips that result in
downtime and unnecessary maintenance.
Thwarting an unplanned shutdown is in many ways like a
juggling act between compressor controls whose functions
are different yet must all be maintained at the same time.
Compressor control incudes monitoring and controlling a set
of dynamic variables to keep the compressor operating at its
optimum performance. The critical factors of flow,
temperature, and pressure of the discharge gas must be
considered when determining the compressor’s optimum
operating point. Maintaining the desired levels of these factors
is the job of multiple control functions that must all work well
together. These individual control tasks must be handled
differently while keeping all of them in motion and operating
correctly.
In addition to managing multiple controllers, ethylene
plants must contend with challenges that are unique to CGCs.
Cracked-gas compressors
CGCs, sometimes called process-gas or charged-gas
compressors, are high-power compressors that draw gas from
the cracking furnaces through various quench coolers and
Vinai Misra, Woodward, USA,
outlines
the important role that compressor
controllers play in the successful
operation of ethylene plants.