Evaluation of Compressor Anti-Surge Control During Unexpected Shutdown

Abstract

Compressors play significant roles in the oil and gas industries. Compressors’ operating points shift to the surge line during startup or emergency shutdown as the flow decreases. Surge causes a compressor to lose the ability to maintain peak head, causes the system to overheat, reduces discharge pressure, damages thrust bearing, and make the entire system unstable. This study aims to evaluate compressor anti-surge control in emergence shutdown using Aspen HYSYS. Aspen HYSYS Dynamics extends models into dynamic model enabling process verification control scheme, design, safety studies, relief valve sizing and rating, failure analysis, development of a startup, shutdown, and operational model changes. Extensive numerical and graphical results generated from dynamic models in Aspen HYSYS allow for in-depth analysis for each completed simulation. The study used dynamic simulation to confirm the recycling valve’s performance and computing surge control scaling of a boil-off gas compressor. The study investigated further if the anti-surge valve would open during operation, keeping the compressor from surging and testing compressor procedure during startup and shutdown. Simulation results show that when the inlet gas flow decreases, compressor speed increases and all anti-surge valves opened to keep the compressor away from a surge. Finally, the paper reveals compressor performance, such as efficiency, surge control line, compressor duty, control tuning parameters, and valve flow coefficient can be predicted using Aspen HYSYS. Thus, the use of Dynamic simulation is a great and efficient design tool for the centrifugal compressors system, and it is highly recommended. For the simulation result to reflect what happens in the plant, it is recommended to select an appropriate thermodynamic method. Improper selection of the thermodynamic model and plant data inconsistent will produce an absurd result. For oil and gas applications, it is advised to use the Peng-Robinson equation of state. It provides accurate results, an extensive applicability range in terms of temperature and pressure, and has a comprehensive binary interaction parameter database.