Compressor Speed Decay During Emergency Shutdowns

The emergency shutdown of a compressor train is a necessary safety feature. In this event, the power supply (either from a gas turbine or an electric motor) is cut off. The compressor train will continue to spin due to its inertia, but the speed will reduce fast. To avoid damage of the equipment during a shutdown event, compressor surge must to be avoided. In many instances, the dynamic behavior of the compression system is simulated to ensure that the necessary recycle valves are sized, and arranged properly. One of the key problems of dynamic simulation, and a major source of uncertainty in the results, is the correct treatment of the speed decay of the compressor train. The present study provides the background to evaluate the speed decay, and includes data from actual rundown situations. The evaluation shows general trends, that can be used to reduce the simulation uncertainties in dynamic simulations.