Implementable MPC-based surge avoidance nonlinear control strategies for non-ideally modeled natural gas compression systems

The surge avoidance control plays a pivotal role in a centrifugal compression process to maintain safety and high efficiency. In the literature, MPC-like schemes have shown promise for use in such tasks given that they can systematically deal with several process constraints. However, to obtain a good performance in the compression process with a significant deviation of gas ideality, the model used in MPC formulations has to be able to predict the process behavior correctly. This paper proposes surge avoidance feasible optimization based MPC schemes for non-ideally modeled natural gas compression systems. Its pivotal contributions are: (i) extension of the isothermal and ideal gas thermodynamic behaviors commonly adopted in models of surge prevention MPC schemes to a non-isothermal flow and non-ideally behaved gas-like more realistic compression system; (ii) formulation of a proposed nonlinear model-based MPC control law with surge protection being managed by slacked nonlinear constraints; (iii) synthesis of an adaptive infinite horizon MPCbased surge avoidance scheme that relies upon the successive linearization of the proposed rigorous model for the compression system. From simulations carried out with a plant-model mismatch oriented by distinct equations of state, results obtained from the proposed rigorous model-based surge avoidance NMPC strategy are favorably compared to those obtained with the simplified model widely used in the literature. Finally, the proposed adaptive MPC-based surge prevention scheme showed convergence towards the corresponding NMPC with a drastically reduced computational cost.