show the composition control scheme, and identify the output ,manipulated an disturbance variables. Draw a complete block diagram of the closed loop system with transfer function of each block indicated. What ahould be the failsafe position of the control valve used for the composition control?

QUESTION 6 Consider the typical control system for the double effect evaporator shown in Figure 5. Manipulating the steam in the first effect controls the composition of the product out of the last effect (control loop not shown). Step testing carried out on the double effect evaporator gives the relationship between the concentrated solution's composition and the steam flow rate as: 9p 5.Os +1 while the relationship between the concentrated solution's composition and the feed density is given as: 17.5e-2.755 12.8e-1.65 9a 2.5s +1 The sensor/transmitter has a dynamics expressed by: 0.12 0.008s + 1 Valve dynamics can be assumed negligible. Vapour Vapour Steam M M Feed Consecrated Solution Condunsane Condenrete Figure 5 Double Effect Evaporator