Dynamic Analysis of Compressor Trips in the Sno̸hvit LNG Refrigerant Circuits

Compressors are key components in the refrigerant circuits of the Sno̸hvit LNG plant and contain large amounts of mechanical energy. Thus it is imperative that the control system is able to keep the compressor out of surge in case of driver trip. A dynamic process simulator describing the total LNG plant has been developed by Kongsberg Process Simulation and the simulator has been applied in the engineering phase for the design and process verification. The simulator has also been used to verify the robustness of the closed loop refrigerant circuits and to verify that the refrigerant compressors are sufficiently protected after a driver trip. The presented work demonstrates the value of dynamic simulations for verification of compressor protection systems. In addition it shows the importance of using correct data for polar inertia of the rotating equipment, as well as the opening and dead times of the anti-surge valves. It is recommended to include a sensitivity analysis of these parameters as part of plant verification studies.