Modelling and nonlinear control of a wet gas centrifugal compressor
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Production of gas condensate from small and remote gas condensate fields require cost-efficient boosting technology for maintaining an economically satisfactory throughput. Wet gas compressors are a new boosting technology enabling boosting of gases containing up to 5% liquid per volume, removing the need for pre/bulk separation, resulting in lower investment and maintenance costs. However, introduction of liquid significantly changes the compression performance from that of dry gas compression, including the process gain and the normal operating region, resulting in a challenging modelling and control problem. Therefore, in this paper, we extend the commonly applied dynamic model of Greitzer for dry gas compression with one additional state and extended polynomial approximation of the compressor characteristic. A nonlinear process control algorithm, using the angular velocity as input, is derived by applying backstepping, and local asymptotic stability proven via Lyapunov analysis. The control performance is studied in different simulations with and without saturation on the control input. The steady-state performance of the dynamic model is quantitatively validated against experimental data.