Flash drum control configurations

In Example 23.1 we identified the controlled and manipulated variables for the flash drum. But how are these interconnected to form the control loops Table 23.1 shows the 24(= 4 ) possible loop configurations... 

To eliminate conflict (a) we can delete the feedforward flow control loop in the coolant system. To erase conflict (b) we delete the flow control loop in the flash drum. Thus the final control configuration for the overall process is shown in Figure 23.6b. It has no conflicts among the loops and the process is exactly specified. 

Figure 23.1 (a) Flash drum unit (b) best configuration of control loops. 

To select the most promising control configuration for the flash drum we employed qualitative arguments. In subsequent sections we will study quantitative techniques for selecting the optimal coupling between controlled and manipulated variables. 

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