Figure 14.16 Results for 20% step decrease in reactants in feed.
A step change of + 20% is made in the setpoint of the feedflow controller at 0.1 h in Figure 14.13. The production rate of TAME (stream B1) increases by 20% over a 1.5-h period. More fresh feed of methanol (FFmeoh stream) is brought into the system. The composition of the TAME product (xB1) remains close to its specification. The composition controller in the reactive column increases the feed of methanol to that column (C1MeOH stream). The increased amount of inert C5s in the feed produce an increase in organic stream D2 and the aqueous stream from C2. The flowrates of the methanol recycle and the makeup water also increase. The purity of the methanol recycle xD3 is maintained.
In Figure 14.14 the disturbance is a 20% step decrease in feedflow. The responses are essentially the reverse of those seen for the increase. These results demonstrate that the control structure handles throughput disturbances quite well.
Feed composition disturbances are made by changing the molar flowrates of reactants 2M1B and 2M2B while decreasing the molar flowrate of the isopentane by the same amount so that the total feed flowrate remains constant. The feed composition disturbance used in Figure 14.15 is a 20% increase in the reactants (2M1B increases from 85.6 to 102.7 kmol/h and 2M2B increases from 165 to 198 kmol/h). The corresponding decrease in iC5
is from 501 to 451 kmol/h. More TAME is produced (B1 stream), more fresh methanol is brought into the plant (FFmeoh stream), and less inert C5 has to be removed (D2 stream). The purities of the TAME and recycle methanol are maintained close to the desired values. The responses to a 20% decrease in the reactants are given in Figure 14.16. The results are essentially the inverse of those found for the increase.
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