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Design for Dynamic Performance

The design of a plant can have a significant impact on its ability to be satisfactorily controlled. A plant design which is optimal on the basis of steady-state considerations, but which has poor dynamic characteristics, may not be able to achieve the expected economic performance in practice. Moreover, the unfavorable dynamic characteristics could seriously affect the plant's ability to handle safety and environmental constraints effectively. Our research group has been involved in the development of optimization-based computational strategies, both for assessing plant operability and for incorporating operability requirements into optimal design calculations. A key contribution is the rigorous inclusion of actuator saturation effects through a complementarity constraint formulation which achieves significantly superior computational performance over an alternative mixed-integer programming formulation. This led to the development of an effective methodology for including the closed-loop effects of constrained model predictive control (MPC) within a dynamic optimization problem through replacement of the inner MPC optimization sub-problems by their equivalent first-order optimality conditions, and solving the resulting problem using an interior-point approach. A recent study utilized a dynamic optimization framework to identify design limitations to the responsiveness of a cryogenic air separation unit (ASU). ASUs are large consumers of electricity, and potentially significant benefits may accrue by rapid adjustment of ASU operation in response to electricity price changes. A first-principles based dynamic model of a nitrogen plant was developed, and incorporated within an optimization framework to identify design limitations to the dynamic response to demand and electricity price fluctuations. Current extensions include consideration of uncertainty, control system dynamics, and application to a multi-product air separation plant.

Dr. Chris L. E. Swartz
Professor and Director, MACC
Xiaoqiang Wang
Visiting PhD Student
Ian Washington
Research Engineer
Preemptive Dynamic Operation of Cryogenic Air Separation Units
Cao, Y., Flores-Cerrillo, J, Swartz, C. L. E.
AIChE J (2017)  -  [ Publisher Version ]
Dynamic Modeling and Collocation-Based Model Reduction of Cryogenic Air Separation Units
Cao, Y.Swartz, C. L. E., Flores-Cerrillo, J, Ma, J
AIChE J, 62 (5) 1602-1615 (2016)  -  [ Publisher Version ]
Optimization-Based Assessment of Design Limitations to Air Separation Agility in Demand Response Scenarios
Cao, Y.Swartz, C. L. E., Baldea, M, Blouin, S
J Process Control, 33 37-48 (2015)  -  [ Publisher Version | Open Access Version (free) ]
Design under uncertainty using parallel multi-period dynamic optimization
AIChE Journal (2014)  -  [ Publisher Version ]
Design for dynamic performance: Application to an air separation unit
Cao, Y.Swartz, C. L. E., Baldea, M.
Proc. American Control Conference, San Francisco. (2011)