Implementation of one-layer gradient-based MPC+RTO of a propylene/propane splitter using dynamic simulation

Abstract

Here, the implementation of the gradient-based Economic MPC (Model Predictive Control) in an industrial distillation system is studied. The approach is an alternative to overcome the conflict between MPC and RTO (Real Time Optimization) layers in the conventional control structure. The study is based on the rigorous dynamic simulation software (SimSci Dynsim®) that reproduces the real system very closely and is able to communicate with Matlab where the control/optimization algorithm is implemented. The gradient of the economic function, which is required to the on-line execution of the extended control strategy, is obtained through the sensitivity tool of the real-time optimization package (SimSci ROMeo®). It is shown that the proposed integration approach leads to convergence and stability to the closed-loop system. In order to study the pros and cons of the new strategy, a propylene distillation system is simulated with both, the proposed approach (one-layer MPC+RTO) and the conventional two-layers hierarchical structure of control and optimization. The results show that, from the performance, stability and disturbance rejection viewpoint, the proposed gradientbased extended control method for this particular system is equivalent or better than the conventional approach.

One-layer gradient-based MPC + RTO of a propylene/propane splitter

“…In this section, simulation tests are presented to evaluate the performance of the proposed one-layer gradient-based approach when compared with the two-layer conventional structure presented in (Hinojosa and Odloak, 2013;Hinojosa, 2015) considering the dynamic simulation as a virtual plant.…”

“…To build up the dynamic simulation, a number of details is required for each of the equipment involved in the simulation, such as valve coefficients, heat transfer coefficients, compressor performance curves, equipment dimensions and PID tuning parameters. These details can be found in (Hinojosa, 2015).…”

“…The approach is implemented in a propylene/propane splitter and compared to the conventional multi-layer approach. The approach will be tested on the rigorous dynamic simulation software (Dynsim) that reproduces the system as a virtual plant and is able to communicate with the MPC algorithms (developed in Matlab) through an OLE for Process Control (OPC) interface (Hinojosa andOdloak, 2014, 2013). The gradient of the economic function, which is necessary to on-line execute the controller, is obtained through the use of the sensitivity tool of the real-time optimization package (ROMeo).…”