My First Encounter with Super-Fractionation

In 1969,1 was working for Amoco Oil as a process design engineer. One of my earliest designs for Amoco was a gasoline debutanizer, the bottom portion of which is shown in Fig. 49.3. Note that this tower is 

All of the liquid from the bottom tray flows to the reboiler. 

But valve A was not closed. 1 had opened the valve myself during the initial tower start-up. Opening valve A is a necessary part of the tower start-up procedure. This allows liquid to gravitate out of the bottom of the tower and into the reboiler, the objective being to establish 

I rechecked my computer model for the tower. With an assumed 80 percent tray efficiency, which is normal for this service at the observed reflux ratio, a 1 percent butane in the gasoline would be expected. To force my computer model to match the observed 4 percent 

My boss organized a meeting with the plant manager. I reported that the bottom eight trays must have been damaged on start-up as indicated by their low tray efficiency of 40 percent, as compared to their design tray efficiency of 80 percent. 

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Once-through thermosyphon reboiler is also a su per-fractionation stage. 

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