(38a) Control and Optimization of Refrigeration Compressors Using Process Model Based Control

Optimal control of refrigeration compressors is important during each phase of ethylene operations; startup, steady state, and shutdown. At steady state, optimal control of the refrigeration compressors can help maximize production rates and minimize horsepower.  During startup and shutdown, optimal control can relieve the operator of having to manage refrigeration compressors right when his attention is needed elsewhere.  Typical compressor surge control designs are dependent on stage discharge conditions which is problematic in general and particularly challenging with refrigeration compressors. These designs can be difficult to tune, are unforgiving at surge, and are susceptible to disturbances.  The result is suboptimal control during all phases of operation.

Our Process Model Based Control design uses compressor impeller geometry and gas physical properties to maintain the desired distance from surge without dependence on stage discharge conditions.  The result is a stable design that is easily tuned, forgiving at surge, and able to handle disturbances. 

An additional benefit of our approach is the ability to optimize compressor speed against the current refrigeration load.