Side-Stream Strippers Control

Side-stream strippers are common in refinery fractionators. The control system depends on whether the stripper feed is withdrawn from 

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Figure 19.11 Side-stream stripper control, (a) Total drawoff (6) partial drawoff. (Concept based on N. Lieberman, Chemical Engineering, September 12,1977.)...

A side-stream product drawn from a crude tower is only half fractionated. Refluxing below the drawoff tray controls the product end point. Front-end fractionation takes place in the side-stream stripper. 

I found that the instrument air tubing connection to the kerosene-draw control valve was loose. That valve controls the flow of kerosene from the crude tower to the side-stream stripper. The control valve simply wasn t getting enough air to open fully. I tightened the connection, and kerosene production rose to the normal rate. 

Compared to reactive distillation, the side reactor configuration has 1 extra manipulated variable, side stream flowrate Fss, in addition to two feedflows (Fe,oh and Fhac). two reboiler duties (<2r,rd and <2r,str). two condenser duties, one subcooling duty, aqueous and organic distillate flowrates, organic reflux flowrate and stripper bottoms flowrate. Similar to the control of the reactive distillation system, the alcohol feedflow is selected as the throughput manipulator. We are left with 11 manipulated variables. 

FIGURE 6i28 Magnified view of a (a) side stripper and (b) side rectifier with all stream definiticms and a mass balance around the dashed control volume. 

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