Modeling and Control of a Wet-Gas Centrifugal Compressor

Abstract

The development and production of small gas condensate discoveries require cost-efficient boosting technologies for profitable production. Subsea wet-gas compression is a new boosting technology, capable of boosting gas condensates containing up to 5% liquid per volume, removing the need for preseparation of the gas condensate, and resulting in lower investment and maintenance cost. Wet gas significantly changes the compressor performance compared with dry gas, including changing process gain and the normal operating region, creating a challenging modeling and control problem. A wet-gas compression model with an empirical approximation of the pressure rise, including a complex backstepping controller, was recently proposed to solve these challenges. However, the model did not correctly model negative mass flows and the empirical polynomial provided limited insight into wet-gas compression. Therefore, in this article, we extend these dynamics to correctly model negative mass flows (deep surge) and, inspired by previous work on first-principle dry-gas compression modeling, we replace the empirical approximation with a first-principle wet-gas compressor characteristic. A nonlinear controller is designed via the Lyapunov analysis, and the local asymptotic stability is proven.