Refrigeration Compressor Recycle Quench Control

Many olefins plant refrigeration compressors use a spray quench of liquid refrigerant to cool the hot recycle gas stream. Typically, the recycle flow is managed by an anti-surge control system while the recycle cooling is managed by the DCS. The interactions of these two control systems can lead to flow swings at the compressor inlet and side streams.

 A coordinated control of both the vapor recycle and liquid recycle flows will ensure the proper amount of cooling is applied without excessive liquid flow that could lead to suction drum level problems. The vapor-liquid equilibrium properties of the refrigerant are used to calculate the split between vapor recycle and liquid recycle to maintain stable recycle flow and proper cooling. A dynamic simulation is used to show the conventional control solution and the coordinated control solution.