Centrifugal Compressors During Fast Transients

Transient studies for compressor systems allow the prediction of the compressor system behavior during fast transients such as they occur during emergency shutdowns. For the system simulations, the compressor behavior is assumed to be quasi steady state. This means in particular that the steady state compressor flow-head-efficiency-speed map remains valid. During well instrumented emergency shutdown tests conducted on a centrifugal compressor system under realistic operating conditions, data showing the head-flow-speed relationship of the rapidly decelerating compressor was taken. This data is compared to steady state head-flow relationships taken at a number of speeds. This allows to determine the relative deviation between the transient and steady state head-flow-relationships, and thus answers the question of the validity of steady state assumptions during rapid transients. The impact of the fast transients on efficiency and consumed power, which can be derived from the speed decay of the system, as well as the impact of non-stationary heat transfer are also evaluated and reported.