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… Read More »
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… Read More »
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… Read More »
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… Read More »
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… Read More »
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… Read More »
Figure 3.1 shows a typical modern gas well, with the wellhead, gas?liquid separator, instrument shed, and condensate tank. Figure 3.2 shows the electronic flow meter, along with the solar collector that powers electronic transmission of the data. The wellhead is in the background. Most companies use electronic metering. However, some wellheads still have circular chart… Read More »
Contract maintenance workers often will not replace the tray manways unless the tray manway is adjacent to a tower external manway. They reason that once the tray manways that are visible from the tower manway are closed, there is no way for someone to inspect the other trays. This problem is not just common—it is… Read More »
At a Gulf Coast refinery, the reboiler thermosyphon circulation could not be reestablished after a turnaround. The tower was reopened and a lessthan-alive contract employee was found stuck in the reboiler draw-off nozzle. At the Good Hope Refinery (when I was the technical manager), we once left a complete scaffold (poles, boards, everything) in the… Read More »
If a tower has a history of tray deck damage due to pressure surge or high liquid level, the mechanical integrity of the trays should be upgraded. This is done by the use of shear clips, as shown in Fig. 8.4. The use of shear clips is not the best way to improve the mechanical… Read More »