(a 12.1 Consider the distillation column shown in Fig. 12.2. It would be reasonable to control the liquid level in the reflux drum, hp, by manipulating either reflux flow rate, R, or distil- late flow rate, D. How would the nominal value of the reflux ratio (R/D) influence your choice? As a specific example, as- sume that R/D = 4. 12.2 A stirred-tank blending system with a bypass stream is shown in Fig. E12.2. The control objective is to control the composition of a key component in the exit stream, x4. The chief disturbance variables are the mass fractions of the key component in the inlet streams, x, and x2. Using the following information, discuss which flow rate should be selected as the manipulated variable: (i) inlet flow rate w2, (ii) the bypass fraction f, or (ii) exit flow rate, wa. Your choice should reflect both steady-state and dynamic considerations. (1-f)wi - X1 X2 W 2. y ful X3 W4 W3 Figure E12.2