variables are: Problem 1. The temperature in tray # 18 of a distillation column is regulated by the flow ON NOTES 75 MINUTES EXAM rate of the reflux to the tray just below it. The typical steady state values of these Temp.zo = Tss = 370F lb Reflux Flow rate =Rss = 10000 h The results of a step change test carried out on this column is presented below: Time R T tray 18 h Ib/h t0 10000 370 0.0 12500 370 0.5 12500 370.9 1.0 12500 373.1 1.5 12500 376.1 2.0 12500 377.8 2.5 12500 379.1 3.0 12500 381.2 3.5 12500 381.7 4.0 12500 382.4 4.5 12500 383.0 5.0 12500 383.4 6.0 12500 384.0 7,0 12500 384.4 8.0 12500 384.7 9.0 12500 384.8 10,0 12500 384.9 11.0 12500 385.0 12.0 12500 384.9 13.0 12500 385.1 14.0 12500 385.0 This process can be modeled with a FOPTD model with transfer function y(s)_Kpe-tas G(s) = f(s) Tps +1 a) (40 points) Use the data from the above test to determine Kp , Tp and ta (please include the appropriate units). b) (10 points) Using the Cohen and Coon method, determine the parameters for a PI controller to control the temperature of tray # 18 by manipulating the reflux flow rate to the tray below