Amine Contactor Harmonics Problem

[AggieCHEN04]

I work for an engeneering and construction company that has recently refurbished and is currently restarting an old Sulfinol plant. The plant was originally designed for processing 6 MMSCFD of high H2S gas with a 28 tray, 42" ID Contactor at 200 psig. Upon restarting it, we anticipate 2 MMSCFD of gas and have modified the contactor's treys to operate at 1/3 capacity.

The modifications include replacing the tray decks and adding channel baffles that effectively reduce the active area to a 16.5" wide by 20.75" long square. The new trays were designed for 110 gpm of solvent and 2 MMSCFD of gas but can operate at liquid rates as high as 250 gpm without creating liquid flooding or exceeding the maximum recommended downcomer velocity.

About 2 weeks ago we began circulating water through the system. We circulated water for approximately 2 days without incident. We then circulated the solvent, Sulfinol, without incident for a day or two until we noticed the tower swaying (by approximately 1 ft to 2 ft at the top) along the same direction as the liquid inlet nozzle and shut the system down. At this point we have not started flowing gas through the contactor.

Due to a lack of a minimum flow bypass we were pumping liquids in excess of 350 gpm initially but have recently added a bypass through the filter to maintain a flow rate of less than 200 gpm through the tower. Reducing the flow rate has not prevented the tower from swaying. We have tried heating the solvent and going back to circulating water but have not had success. We are currently installing an additional flow controlled bypass around the contactor to allow for as much as 100% turndown. After notifying the tray manufacturer of this problem, they confirmed that the trays and tower hydraulics should be able to handle up to 250 gpm of solvent. The tower has a 4" liquid inlet nozzle, which is considered to be on the small side for the 250 gpm, but the tower had originally operated at 275 gpm, fully loaded without swaying. We have performed an inspection of the tower and trays and have found no damage.

Please let us know if you have any insight into the root cause of this problem.

 

[pmover]

please clarify that the tower, itself, has movement of 1-2 feet inline with liquid inlet nozzle!
i've not ever heard of a tower swaying that much and still be standing.
is it possible that something else is moving 1-2 feet relative to the tower?
please clarify.

-pmover

 

[AggieCHEN04]

The one to two feet may not be accurate. This is based on observations made by the operators. One of our own personnel said that he saw it move about 3 inches on a separate occasion, but it is definitely visible. I haven't had a chance to witness it myself. As a point of reference the total height of the tower is about 80 - 90 ft at its highest elevation.

 

[AggieCHEN04]

Just to clarify: I didn't mean that it was moving that much on each side, but total movement. And again, this is third-hand information so I may be the one getting the facts confused, but it is very visable.

 

[sshep]

AggieCHEN04,

I wouldn't jump to the conclusion that your changes are the cause of this movement. About 2 years back we noticed one of our towers swinging. It was a large scary looking deflection which we had never noticed before (i.e. fine for years), but ultimately the cause was wind coming from a new direction and perhaps the influence of other large towers on the site. As your tower has not had attention for awhile, you should consider that the problem was pre-existing and has gone unnoticed until now.

As a side note, all towers have movement which can be felt, but which is difficult to observe from the ground due to lack of fixed reference. Last week when inspecting a tower over 100m tall and 5m diameter we could feel some good movement. The internals were specified to be leveled to 1.5mm over the 5m diameter, and I couldn't help but wonder at the difficulty of actually getting such a tight specification considering the movement of the tower.

best wishes,
sshep

 

[AggieCHEN04]

It should be noted that the tower is swaying perpendicular to the wind and doesn't have any new buildings or towers in front of the contactor that would block or divert the wind. If I remember correctly they had started circulating water in fairly windy conditions (approximately 20 mph) and hadn't noticed any swaying for the first few days. It has been less windy for the past week and a half when the problem started occuring. The tower is only swaying when liquid is flowing through it. Would loading the tower with liquid increase it's tendency to sway in the wind?