Advanced Process Control of a Propylene Refrigeration Compressor

At the NOVA Chemicals ethylene plant in Corunna, Ontario, the propylene refrigeration compressor is the second largest steam user on site.  The propylene refrigerant provides heating or chilling for more than 20 process streams throughout the cold side of the plant and changes in compressor operation affect a number of different unit operations.  As ambient conditions and olefins production rates vary, there are opportunities to reduce the amount of energy used by the compressor by adjusting key operating variables to reduce recycle streams and lower compressor throughput.  Because of the complexity of the system, this is difficult to accomplish without controls that will manage the interactions between the compressor and the process.  This paper describes the development and use of an APC application that drives the compressor to lower energy usage while maintaining stable process and compressor operation.  As well as reducing greenhouse gas emissions from the plant, the application simplifies operation of the compressor system.