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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Loss of Once-Through Thermosyphon Circulation

There are several common causes of loss of circulation. The common symptoms of this problem are • Inability to achieve normal reboiler duty. • Low reflux drum level, accompanied by low tower pressure, even at a low reflux rate. • … 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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Internal Reflux Evaporation

The tray temperatures in our preflash tower, shown in Fig. 6.4, drop as the gas flows up the tower. Most of the reduced sensible-heat content of the flowing gas is converted to latent heat of evaporation of the downflowing reflux. … Continue reading

24. January 2011 by Jack
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Conversion of Sensible Heat to Latent Heat

When we raise the top reflux rate to our preflash tower, the tower-top temperature goes down. This is a sign that we are washing out from the upflowing vapors more of the heavier or higher-molecular-weight components in the overhead product. … 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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Heat-Balance Calculations

If you have read this far, and understood what you have read, you will readily understand the following calculation. It is simply a repetition, with numbers, of the discussion previously presented. However, you will require the following values to perform … 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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