Inculding Prices in Control Structure Design - Applied on a Subsea Separation System
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The selection of controlled variables and measurements is an important aspect ofthe control structure design. Using the self-optimizing control framework makesit possible to select controlled variables as combinations of measurements whichminimizes the steady state loss. However, in a broader perspective, one is notonly interested in the steady state loss, but also in the chemical plant s economy.This work has combined the steady state loss with prices of measurements using aMixed Integer Quadratic Programming (MIQP)-formulation, so that the optimalsubset of measurements also results in the overall best economics for the processplant. In this way the control structure design could be implemented as part of theprocess design phase, to make the plant as profitable as possible. This work alsoutilized the power of the MIQP-formulations to include wider selection criteria,which made it possible to select different measurement devices with a variety ofprices and uncertainty. From this it was possible to calculate the best trade-offbetween prices and losses due to measurement uncertainty when different measuringdevices are available to a project. Normal process plants also handles constraints,which also need to be controlled. The constraints also have a corresponding loss -also called back-off (due to measurement uncertainty) related them. This has alsobeen included in the total cost calculation, and evaluated both within an activeconstraint region and an unconstrained region. The developed methods have beentested and evaluated on a Dummy problem and a Subsea separation system.