I have to say that the senior process design class here at Lehigh was taught in much more detail compared to design class taught in other universities. I was able to learn a lot about Chemical Engineering process that I wouldn’t be able to learn as much had I joined a ChE undergraduate program at another school. One of a fundamental things about Chemical Engineering Plant Design that I learn from my senior design project here was distillation disturbances. The ability to handle disturbance is another very important aspect of a successful plant design. For our Ethylene Oxide plant, the distillation column should be able to handle flow and composition disturbance. For the flow disturbance, feed flow rates of 20% increase and decrease to the steady state flow rate were tested, assuming that the upstream unit does not generate more than 20% disturbance feeding into the distillation column.
I wanted to show you here a comparison of how a bad column scheme handled the disturbance poorly and a good column scheme where disturbance was handled much better.The above disturbance graph was generated as a result of a feed flow rate increases and decrease of 20% of its original steady state value. The objective of our plant involves meeting the specified product purity. The column scheme that generated this graph used a flow controller to fix reflux ratio by fixing the reflux and distillate flow rate. As you can see, the overhead impurity (top right graph) kept increasing as time goes on, eventually, it would fail out of the required purity value. The graphs below is a example where the overhead product purity was controlled.The overhead impurity eventually reached a new steady state. Although the response was as sharp as the Temperature, bottoms impurity, or reboiler duty (middle right, middle left, and bottom left), it was able to gradually reach new steady state values. One thing that we could work on was a figure out how to make the response quicker. Also, I probably should have plotted the reflux flow rate just to see how it works in correlation with the purities.