At stage 1 they close inner cascade loops involving eight flows and two temperature. This
reduces the effect of the disturbances associated with these loops. At stage 3 they use a
simple mass balance of the plant. This gives some constraints for stage 2, for example, that either the C-feed or the product flow must be left for the third stage. At stage 2 decentralized loops are closed. They start with the level loops since they are the most important loops. There are three level loops; reactor, separator and stripper, and they consider four possible level configurations. Three of the configurations were ruled out based on controllability analysis. The alternative where the E-feed is used for reactor level control is analyzed in greater detail. They look at three 6*6....., eighteen 5*5., and fifteen 4*4 systems, where the controlled outputs seem to be rather randomly chosen. After an analysis involving RGA, Niederlinski index and linear valve saturation, only four alternatives are left. These are further screened on their steady-state behavior for a range of disturbances