Individual experiments have been performed on the process in Figure Q6.3. The fo
ID: 518464 • Letter: I
Question
Individual experiments have been performed on the process in Figure Q6.3. The following transfer function models were determined from these experiments: T_3(s)/T_2(s) = 0.55e^-0.5s/2s + 1 T_4(s)/T_3(s) = 3.4e^-2.1s/2.7s + 1 (a) What are the units of the gains and do they make sense? Is the reaction exothermic or endothermic? (b) Determine an approximate first-order-with-dead-time transfer function model for T_4(s)/T_2(s). (c) With better planning, could the model requested in (b) have been determined directly from the experimental data used to determine the models given in the problem statement? (a) The chemical reactor system in Figure Q6.3 is to be modeled. The relationship between the steam valve on the preheat exchanger and the outlet concentration is to be determined. Develop a complete experimental plan for a process reaction curve experiment. Include in your plan all actions, variables to be recorded or monitored, and any a priori information required from the plant operating personnel. (b) Repeat the discussion for the experiment to model the effect of the flow of the reboiler heating medium on the distillate composition for the distillation tower in Figure 5.18.Explanation / Answer
(1)
gain is dimensionless.It is dimensionless proportional band, PB.
(2)
T4(s)/T2(s)=T4(s)/T3(s)*(T3(s)/T2(s))=(1.87e-2.6s)/(5.4s2+4.7s+1)=1.87 e-2.6s/(5.4s2+4.7s+1)
so approximately
T4(s)/T2(s)=0.38 e-2.6s/4.7s+1
So K=1.87
dead time constant Td=-2.6
time constant t=4.7