CS7-R Structure

The final effects of increasing vapor boilup are decreases in both manipulated variables (feed flowrates) and product streams. Because the two temperamre controllers in the CS7-R structure have opposite actions, the initial responses of the two controllers are different. An increase in vapor boilup produces an increase in the temperature on both control trays (trays 4 and 13). The tray 4 temperature controller has direct action, so it increases the Fqa feed flowrate. However, the tray 13 temperature controller has reverse action, so it decreases the OB feed flowrate. Not enough reactant B is added in a timely enough maimer to prevent light reactant A from going to the upper section of the column. Once this breakthrough occurs, the column moves to a different operating condition in which the impurity of A in the distillate stream increases and product purities are lower. 

We can conclude that the CS7-R control structure provides good dynamically stable control, but it does not maintain conversion and product purities. 

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Because the dynamics of the 5/10/5 and 5/13/5 designs are similar, only the results of the case with 10 reactive trays will be discussed. We found that adding more reactive trays did not solve the problem of a drop in product purities for the CS7-R structure. Thus, we consider only the CS7-RR stmcture. 

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