The refrigeration demands of the process are supplied by various levels of
cascaded propylene and ethylene refrigerant. These are further supplemented by refrigeration from
matched internal process streams. Lowest-level refrigerant is supplied from the turboexpander.
Propylene is condensed against cooling water. Refrigerant is supplied to the demethanizer chilling
train by a three-stage ethylene machine. The ethylene is condensed using propylene refrigerant.
Process-process heat integration is restricted to streams within a given system, thereby avoiding
potential operating instability within the plant.