Compressor Station Recycle System Dynamics During Emergency Shutdown

Transient phenomena associated with gas recycling during compressor emergency shutdown (ESD) have been studied both experimentally and numerically. A scaled-down laboratory test rig has been constructed to study the influence of various underlying parameters on ESD operation. Three different configurations representing different design scenarios were tested. The first configuration has a long recycle system with a volume capacitance representing an air-cooled heat exchanger in the recycle loop, and the recycle valve located close to the discharge side. The second one is the same as the first except the recycle valve is placed close to the suction side. In the third configuration, the cooler capacitance was removed from the recycle loop and the piping capacitance on the discharge side was further reduced. Shutdown tests were carried out from different steady-state initial conditions varying the recycle valve opening time, and the synchronization time between the compressor ESD signal and valve opening signal. Numerical simulations based on the solution of the full one-dimensional conservation equations using the method of characteristics were also conducted for the above configurations. Good agreement was obtained between measurements and simulation results. Numerical simulations were used to analyze other cases, which were not investigated experimentally, to further investigate the interaction between equipment and flow parameters. Results indicate that the valve prestroke time is more crucial than the stroke time and that it should be made short to avoid surging the compressor during ESD. Locating the recycle valve as close as possible to the suction or discharge of the compressor helps reduce unit surge during shutdown.