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Tower Internal Manways

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 … Continue reading

30. April 2011 by Jack
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Tower Final Inspection

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 … Continue reading

30. April 2011 by Jack
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Shear Clips

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. … Continue reading

30. April 2011 by Jack
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Seal Pans Downcomer

The downcomer from the bottom tray is submerged in a seal pan (see Fig. 8.3), to preserve its downcomer seal. I always set the horizontal dimension between the over-flow lip of the seal pan, (dimension y) the downcomer at four … Continue reading

30. April 2011 by Jack
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Inlet Weirs

Most trays have outlet weirs devoted to maintaining the downcomer seal. But some trays have inlet weirs too, or inlet weirs, but no outlet weirs. A sketch of an inlet weir is shown in Fig. 8.2. Note the horizontal distance … Continue reading

29. March 2011 by Jack
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Improper Downcomer Clearance

The bottom edge of the downcomer from the tray above should be 0.25 to 0.5 in below the top edge of the weir of the tray below. This is called a positive downcomer seal. Without a positive downcomer seal, vapor … Continue reading

29. March 2011 by Jack
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Loss of Downcomer Seal Due to Leaks

The vertical edges to the downcomers are bolted to bars welded to the vessel wall. These are called, “downcomer bolting bars.” Gaskets are often used to tightly seal the edge of the tray downcomer to these bars. If the bolts … Continue reading

29. March 2011 by Jack
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Tray Deck Levelness

For smaller diameter towers a visual check of tray deck levelness is sufficient. For two-pass trays, a small diameter tower is less than 8 ft. For single-pass trays, a diameter of less than 6 ft is small.For towers of 10 … Continue reading

29. March 2011 by Jack
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Kettle Reboilers

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. … Continue reading

29. March 2011 by Jack
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Forced-Circulation Reboilers

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. … Continue reading

29. March 2011 by Jack
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