On the Design of Chemical Processes With Improved Controllability Characteristics

Traditionally, process design and control system design are carried out sequentially. The premise underlying this sequential approach is that the decisions made in the process design phase do not limit the control design. However, it is generally known that incongruent designs can occur quite easily. In the literature two different classes of approaches are being described that consider the control performance of the design alternatives from the earliest design stages: (i) Anticipating sequential approaches where process design and control system design are still carried out sequentially, but in anticipation of the control design the controllability properties of the process are taken into account during the process design phase. (ii) Simultaneous approaches. In the simultaneous approach the process design and the control system design are carried out simultaneously. This work is focused on the first approach. Tools and methods are presented that can assist the process designer in designing processes that are well controllable. The control system design still needs to be carried out afterwards, but the process designer has already anticipated on it. The methods and tools presented in this thesis are aimed at the different stages of the conceptual process design phase: formulation, synthesis, analysis and evaluation. Primarily the synthesis and the analysis phases will be addressed to overcome some of the limitation of the anticipating sequential approaches. Since most industrially scale processes operate in a steady state this mode of operation has been the reference for this research. However as dynamic modes of operation are becoming more important, an exploration was made of the potential of periodic operation of Fischer Tropsch synthesis. This has led to the following methods and tools for steady-state operation.