Design and Troubleshooting of Compressor Systems by using Dynamic Process Simulation
The use of dynamic process simulation has been established in the last few years as a reliable and effective tool to analyse the behaviour of processing equipment and systems during transient events.
Centrifugal compressors systems show performance characteristics that mainly depend on the operating point imposed on them by the process units and the connection piping around the compressor.
Often, large compression systems have several compressors operating in parallel, with some of them in standby. Therefore, even in normal operation there are frequent start-up and shutdown operations while switching between compressors, e.g. to accommodate throughput changes. The transient analysis of these operations is critical to evaluate the dynamic behaviour of the compressor system and of its associated control and safety systems.
Frequently, the most important analysis to be carried out for compressor systems is to understand if the compressor system could enter into surge due to changes in the operating conditions, or due to shut down/start-up of other compressors in the system. Surge situations can be overcome by varying the number of compressors in use and/or changing the recycle rate, therefore moving the operating point in the performance map away from the surge line. This is accomplished by an integrated anti-surge control system. Surge controllers are designed to prevent surge, and (for complex systems) the surge control strategy can be validated by dynamic modelling. Another aspect of the complexity of large compressor systems is the overlay of dynamic behaviour of the different compressors in the system with the dynamic behaviour of their respective drivers and the dynamic performance of the process connected to the compressor. Again, dynamic process simulation is the adequate tool to assess the influence of these transient effects on the compressor operation.