Reboilers circulating thermosyphon

This last statement requires some clarification. But to understand our explanation, an understanding of the important differences between a once-through thermosyphon reboiler, and a circulating thermosyphon reboiler, is critical. Figure 5.4 shows a circulating reboiler. In this reboiler... 

For a circulating thermosyphon reboiler, the rate of circulation can be increased by... 

Because the liquid from the bottom tray of a tower with a circulating thermosyphon reboiler is of a composition similar to that of the bottoms product, we can say that the circulating thermosyphon reboiler... 

Figure 6.4 shows a distillation tower served by a circulating thermosyphon reboiler. To some unknown extent, some foam will always be found in the bottom of such vessels. Not sometimes, but always. Why ... 

For most once-through and many circulating thermosyphon reboilers (see Figs. 18-1 and 18-2), a high liquid level covering the reboiler vapor return nozzle will retard thermosyphon circulation and cause a precipitous loss in reboiler duty, instead of tower flooding. 

One helpful suggestion is to avoid the use of kettle reboilers or once-through thermosyphon reboilers, in favor of circulating thermosyphon reboilers. That is, feed the reboiler directly from the bottom of the stripper and design for about a 10% to 20% vaporization rate (see Fig. 47.3). This will reduce, but unfortunately not eliminate, the reboiler tube failures by maintaining more liquid flow across the tubes. 

Referring to Fig. 47.3, for many refinery operations, the circulating thermosyphon reboiler shown can be eliminated and replaced with the same quantity of stripping steam, thus further simplifying the design of your waste water stripper installation. 

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