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Selection of controlled variables and robust setpoints
 Ind. Eng. Chem. Res
, 2005
"... Optimal operation of chemical plants is usually accomplished by rst nding the optimal steadystate using the present (nominal) set of disturbances. This is usually implemented by sending constant setpoints for selected variables to the control system. The setpoints are then the nominally optimal va ..."
Abstract

Cited by 7 (5 self)
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Optimal operation of chemical plants is usually accomplished by rst nding the optimal steadystate using the present (nominal) set of disturbances. This is usually implemented by sending constant setpoints for selected variables to the control system. The setpoints are then the nominally optimal values. However, because of disturbances this may result in feasibility problems, which we here try to avoid by adjusting the setpoints ("backo"). First, we need to avoid infeasibility in the active constraints ("constraint backo") [1]. Second, we need to adjust the setpoints of the unconstrained controlled variables. This may be done by oine computation of robust setpoints ("optimal backo") or by online feasibility correction ("exible backo"). As a case study we consider a reactorseparatorrecycle process. For this process the control structures based on Luybens rule (x a ow in every recycle loop) are infeasible if we use the nominal setpoints, but are feasible with reasonable loss if we use robust setpoints. 1
Interaction of Design and Control: Optimization with Dynamic Models
, 1997
"... Process design is usually approached by considering the steadystate performance of the process based on an economic objective. Only after the process design is determined are the operability aspects of the process considered. This sequential treatment of the process design problem neglects the fact ..."
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Process design is usually approached by considering the steadystate performance of the process based on an economic objective. Only after the process design is determined are the operability aspects of the process considered. This sequential treatment of the process design problem neglects the fact that the dynamic controllability of the process is an inherent property of its design. This work considers a systematic approach where the interaction between the steadystate design and the dynamic controllability is analyzed by simultaneously considering both economic and controllability criteria. This method follows a process synthesis approach where a process superstructure is used to represent the set of structural alternatives. This superstructure is modeled mathematically by a set of differential and algebraic equations which contains both continuous and integer variables. Two objectives representing the steadystate design and dynamic controllability of the process are considered. T...