Chemical process networks: Stability and control

The main focus of this research is to formalize the links between process control and thermodynamics for large scale chemical processes. The idea is that all process systems obey the laws of thermodynamics, and by using physical insight from thermodynamics improvements can be made in the control of process systems. Passivity based analysis is used to determine if a system is stable, and if not is used to design a stabilizing distributed control system. This theory is applied to interconnected networks consisting of parallel and recycle streams. Analysis is done using a thermodynamic based storage function that is similar to exergy or available work. The theory requires the modeling of process systems from two different view points. The hydrodynamics of the system are described from a fixed frame of reference or Eulerian view point and the energy and component flows are described from a moving frame of reference or Lagrangian view point. The analysis is performed in each view point where stability can be determined and a control configuration designed.; The ideas introduced above are applied to individual unit operations, mixing, flash reaction, and heat exchange. An important result from the analysis is that a large class of chemical process systems are asymptotically stable with an exception being non-dissipative reactive elements. With the introduction of the correct control these elements can be stabilized. The theory also shows that when the mass flow network is controlled for any stable process networks, the temperatures and compositions are asymptotically stable. Optimal setpoints can be implemented and the theory can guarantee asymptotic convergence of the entire process to the optimal operating point.; The most recent work has focused on the stability of distillation. No theory has been able to show the stability for a general multicomponent distillation column. The results show that as long as the resistance to liquid flow is equal or decreases down the column the system is asymptotically stable. This result contradicts previous published simulations results and the differences can be explained by additional details introduced by the thermodynamically driven flows.