Question 4 An evaporator is used to concentrate a dilute solution of a single, nonvolatile solute in a volatile solvent by evaporating solvent using heat supplied by a steam coil. You as a control engineer, have proposed the control strategy as shown in Figure a 3 3. -D. LC San FFC contro Feed F. Ty Product B Figure 3: Evaporator with feedback and feedforward control strategy Based on the information of the evaporator, the transfer function models for the system are: , The transfer function models for the system are given below 2.5 1.5 H- F- 1.1s +1' 118+1 P 1.1s +1 P P 5 D+ D' 1.1 2s(1.9s +1) 1.95 + 1 +1 0.8 1.3 X- F B 53 +1 3.55 +1 0.165 +1 1 G1 G2 G= 0.43s +1 where HP and X'g are deviation in liquid height, pressure in the evaporator and product concentration at bottom, respectively. F. B. D'and Ps are deviation in feed, bottom, distillate flow rate and steam pressure, respectively. Gm.Gm3 and Gare the transfer function for level pressure and flow transmitters, respectively, Feedback control a) Tune the Pi controller for height of liquid in the evaporator using autotuning in Simulink for setpoint change and give justification based on the control performance and robustness [10 Marks] b) Determine the PID controller for the pressure in the evaporator using internal Model Control (IMC) method. Tune the design parameter for the best performance in Simulink. Note: compare at least three values of the design parameter. ) : . Give justification based on the control performance, [12 Marks! Determine the gain and phase margin for both controllers using Bode Dlagram. Evaluate whether the controllers will give a well-tuned controller. [10 Marks] Feedforward Control d) Design for a lead-lag compensator to control the product concentration is based on feedforward control strategy. The compensatoris given in Equation (5 G, (s)-K, ats +1 (5) where a phase-ad compensator has a 1. Determine the value of a to determine the type of the compensator required to obtain the best control 16 Marks) e) Using Simulink simulate the system for a unit step deviation in the feed flow rate Critically describe the dynamic responses for all control variables. 16 Marks ) A problem anisen in the pressure control loop for the evaporator. The pressure control loop had functioned in a satisfactory manner for a long period. However, the pressure is gradually increasing with time even though the pressure controller outpur has saturated. Furthermore, the distillate how rate is well above the nominal value, while the feed flow rate is at the nominal value, according to the recorded measurements from the two flow transmitters. The accuracy of the pressure transmitter measurement has been confirmed by comparison with the on-site pressure indicator. The two flow measurements are obtained via orifice plates and differential pressure transmitters. Suggest two possible causes for this problem and describe how you would troubleshoot this situation 16 Marks *Please submit the Simulink file together with the answer sheet for Question 4 (50 Marks)