Monthly Archives for January 2011

Circulating vs. Once-Through Thermosyphon Reboilers

We said before that it was wrong to return the effluent from a oncethrough reboiler with a vertical baffle to the cold side of the tower’s bottom. Doing so would actually make the once-through thermosyphon reboiler work more like a … Continue reading

24. January 2011 by Jack
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Circulating Thermosyphon Reboilers

The important differences between a once-through thermosyphon reboiler and a circulating thermosyphon reboiler is critical. Figure 7.4 shows a circulating reboiler. In this reboiler • The reboiler outlet temperature is always higher than the tower-bottom temperature. • Some of the … Continue reading

24. January 2011 by Jack
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Once-Through Thermosyphon Reboilers

Figure 7.2 shows a once-through thermosyphon reboiler. The driving force to promote flow through this reboiler is the density difference between the reboiler feed line and the froth filled reboiler return line. For example: • The specific gravity of the … Continue reading

24. January 2011 by Jack
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How Reboilers Work

Four types of reboilers are : • Once-through thermosyphon reboilers • Circulating thermosyphon reboilers • Forced-circulation reboilers • Kettle or gravity-fed reboilers There are dozens of other types of reboilers, but these four represent the majority of applications. Regardless of … Continue reading

24. January 2011 by Jack
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Effect of Feed Preheat

Up to this point, we have suggested that the weight flow of vapor up the tower is a function of the reboiler duty only. Certainly, this cannot be completely true. If we look at Fig. 6.2, it certainly seems that … Continue reading

24. January 2011 by Jack
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The Reboiler

All machines have drivers. A distillation column is also a machine, driven by a reboiler. It is the heat duty of the reboiler, supplemented by the heat content (enthalpy) of the feed, that provides the energy to make a split … Continue reading

24. January 2011 by Jack
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Incipient Flood Point

As an operator reduces the tower pressure, three effects occur simultaneously: • Relative volatility increases. • Tray deck leakage decreases. • Entrainment, or spray height, increases. The first two factors help make fractionation better, the last factor makes fractionation worse. … Continue reading

24. January 2011 by Jack
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Selecting an Optimum Tower Pressure

The process design engineer selects the tower design operating pressure as follows: 1. Determines the maximum cooling water or ambient air temperature that is typically expected on a hot summer day in the locale where the plant is to be … Continue reading

24. January 2011 by Jack
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Optimizing Tower Operating Pressure

Why are distillation towers designed with controls that fix the tower pressure? Naturally, we do not want to overpressure the tower and pop open the safety relief valve. Alternatively, if the tower pressure gets too low, we could not condense … Continue reading

24. January 2011 by Jack
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High Capacity Trays

All vendors now market a high capacity tray. These trays have a 5 to 15 percent capacity advantage over conventional trays. Basically, the idea behind these high capacity trays is the same. The area underneath the downcomer is converted to … Continue reading

24. January 2011 by Jack
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