Category: Reboiler

Kettle Reboilers

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Reboilers are sometimes inserted into the bottom of a tower. These are called “stab-in” reboilers. It is not a terribly good idea, because it makes it more difficult to fix a leaking or fouled reboiler without opening the tower itself. However, the “kettle” reboiler, shown in Fig. 7.7, has essentially the same process performance characteristics …

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Forced-Circulation Reboilers

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Figure 7.6 shows a once-through forced-circulation reboiler. Such a reboiler differs from a thermosyphon reboiler in that it has a pump to force circulation, rather than relying on natural or thermosyphon circulation. This extra pump seems rather wasteful—and it is. The great advantage of forced circulation is that careful calculation of the pressure drop through …

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Excessive Thermosyphon Circulation

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In a once-through reboiler, the liquid flow coming out of the reboiler is limited to the bottoms product. In a circulating reboiler, the liquid flow coming out of the reboiler can be extremely high. If the reboiler return nozzle is located too close to the bottom tray of the tower, the greater volume of liquid …

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Circulating vs. Once-Through Thermosyphon Reboilers

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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 circulating reboiler. But if this is bad, then the once-through reboiler must be better than …

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Circulating Thermosyphon Reboilers

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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 liquid from the reboiler outlet will always recirculate back into the reboiler feed. • Some …

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Loss of Once-Through Thermosyphon Circulation

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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. • Bottoms product too light. • Reboiler outlet temperature hotter than the tower-bottom temperature. • Opening …

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Once-Through Thermosyphon Reboilers

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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 liquid in the reboiler feed line is 0.600. • The height of liquid above the …

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How Reboilers Work

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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 the type of reboiler used, the following statement is correct: Almost as many towers flood …

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