Abstract
After 15 year development, it is still hard to find any real application of the self-optimizing control (SOC) strategy, although it can achieve optimal or near optimal operation in industrial processes without repetitive real-time optimization. This is partially because of the misunderstanding that the SOC requires to completely reconfigure the entire control system, which is generally unacceptable for most process plants in operation, even though the current one may not be optimal. To alleviate this situation, this paper proposes a retrofit SOC methodology aiming to improve the optimality of operation without change of existing control systems. In the new retrofitted SOC systems, the controlled variables (CVs) selected are kept at constant by adjusting setpoints of existing control loops, which therefore constitutes a two-layer control architecture. CVs made from measurement combinations are determined to minimize the global average losses. A subset measurement selection problem for the global SOC is solved though a branch and bound algorithm. The standard testbed Tennessee Eastman process is studied with the proposed retrofit SOC methodology. The optimality of the new retrofit SOC architecture is validated by comparing two state of art control systems by Ricker and Larsson et al., through steady-state analysis as well as dynamic simulations.
Highlights
O PTIMAL operation is the ultimate goal of all industrial plants
In order to work with the existing control system in operation, the retrofit self-optimizing control (SOC) provides a cascade solution to adjust setpoints of certain existing control loops such that self-optimizing controlled variables (CVs) constructed from measurement combinations are maintained at zero
The proposed retrofit SOC methodology aims to improve the economic performance of control systems that have been in usage for chemical plants
Summary
O PTIMAL operation is the ultimate goal of all industrial plants. achieving optimality is challenging due to inevitable uncertainties involved in any real plant operation. This is generally unacceptable for any real process in operation even though such an operation may not be optimal at all To alleviate this situation, this paper proposes a retrofit SOC methodology to show SOC can be implemented without reconfiguring existing control loops, but by updating the setpoint of these loops. Preliminary works on the retrofit SOC method and measurement subset selection for gSOC problem for the Tennessee Eastman process (TEP) have been recently reported in two conferences [13], [14], respectively This paper consolidates both with enhancements by, elaborating a systematic four-step procedure, which is easy to follow and potentially applicable to practical industrial processes, presenting a theoretical derivation to link the gSOC subset selection problem with the existing PB3 algorithm, and updating the case study with improved results.
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