Modelling of variable speed centrifugal compressors for anti-surge control
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A mathematical model for simulation of gas compressor systems is developed. The model is designed for anti-surge control validation, and models a continuous flow gas compressor. The model also includes a cooler for gas cooling, a scrubber for liquid draining, and a recycle line with a control valve for anti-surge control. The system outlet has a check valve to prevent reversed flows. The model is one-dimensional and models pressure, temperature and mass flow for all system components, and also compressor shaft speed. It is modular and derived using mass, momentum and energy balance. Compressor characteristics maps from compressor manufacturer are used to determine compressor pressure ratio, efficiency and shaft power. The model also includes upstream and downstream systems, which are modelled as large vessels with very slow dynamics. In addition, a model structure for gas turbine, which can be used as compressor governor, has been proposed.The mathematical model has been implemented in Simulink\textregistered\ and verified against experimental data from an oil and gas installation. The simulations give good fit with the dataset. Simulations also show that the dynamics at the compressor inlet and outlet is dominated by the large volumes, mainly the upstream and downstream vessel, while the faster dynamics are damped out.