Compressor Systems with Recycle Loops; Modeling and Control

A common loop from gas processing is studied from a modeling and control perspective with an emphasis on the simplicity and control-orientation of the model components which comprise the model: pipes, branches, compressor, valves, tanks etc. The process is to take recent component model classes and to lift them to be more realistic and representative of a practical compressor operational area, notably taking into account compressor operation curves. The control objective is to improve transient response of the overall system by developing two-input controllers to manage fluctuations in either compressor suction pressure or discharge pressure in response to supply and delivery changes. The control mechanism is the use of a recycle loop capable of transporting gas from the discharge side to the suction side – this is the faster manipulated variable – together with the slower dynamics of the compressor speed, which regulates overall flow. The return of the recycle valve to closed during steady-state operation is included into the design.