Dynamic Simulation and Operability Study on Parallel Compressor Strings for LNG Application

New train configurations have been developed to satisfy new requirements in LNG industry in terms of availability of liquefaction plants. GE Oil&Gas has recently designed a new refrigerant train configuration composed by two identical strings each of them capable of 2x50% LNG production for APCI^® C3-MR™ liquefaction process.

The peculiarity of this configuration requires dedicated studies to analyze critical transient scenarios such as trains start up, train trip in parallel configuration, malfunctions, etc. GE Oil&Gas performs dynamic simulations at two different levels.

The first level focuses on the emergency shutdown and start-up scenarios. The emergency shutdown analysis aims at evaluating additional protection (i.e. hot/cold gas bypass valves) for compressor surge/reverse rotation prevention. The start-up analysis is performed to evaluate driver capability. Further verifications are carried out to design and size process valves, validate check valves locations.

The second level addresses the entire compression train dynamic behavior by linking the compression system model to the actual compressor control system. This enhanced simulation environment, where also the interaction with liquefaction process is taken into account, allows to detect and solve in advance potential operability issues of parallel strings operation. In addition, start-up/ shutdown procedures are optimized and the actual control software can be tested, validated and pre-tuned before commission activities.

The present paper covers dynamic simulation activities on the most critical transient scenarios for two APCI^® C3-MR™ projects.