3 replies to this topic

[AColling]

All,

 

Recently, we installed a new condensate pot on a debutanizer thermosiphon reboiler. This reboiler uses 95# steam as the heat source for the tower (tube side). An interesting design feature of this reboiler, is that the vapor outlet has been equipped with a vapor belt or an "annular distributor" as some may call it. 

 

I was curious to see if anyone has encountered this throughout their work, what the purpose was, or if there were any particular performance issues of note to comment on?

 

These vapor belts have been known to exist on condenser inlets, but we have yet to come across one on a reboiler outlet.

 

Thanks in advance,

AC

 

PS - I've attached a 3D drawing (compliments of HTRI) that shows the reboiler (TEMA Type: AJ21U)

 

Purpose of query - We are having performance issues where our steam flow oscillates dramatically and our reboiler cannot achieve the necessary duty. Originally, it was thought that a larger condensate pot would resolve the issue, but unfortunately that has not been the case.

Attached Files

•  Thermosiphon Reboiler AJ21U.png   18.51KB   19 downloads

[Bobby Strain]

You didn't tell us very much. Start from the beginning. Process data is essential.  Like, when did the problem start? Give a sketch of the system including relative elevations and locations. And what is used to control steam to the reboiler? Etc.

 

Bobby

[AColling]

I appreciate your suggestion. But I was more curious to know if this is as uncommon a design as I believe it to be (At a high level). I've since learned that typical design considerations demand that the outlet line not exceed 1/2 of the exchanger diameter. In this case, my outlet line was 24 inches in diameter and my reboiler was 36 inches in diameter. Structurally this would not be acceptable, so an annular distributor was used for mechancial purposes (Increasing the shell diamter to 48 inches). The question now becomes, why was a 24 inch return line desired? I'll have to keep digging to figure that out.

 

Although, since you asked, I've included a spreadsheet that has some more details. Of course, I'm limited to how much information I can disclose, but I've tried to give plenty to at least provide a view of the situation. Steam is controlled by tray 6 temperature (6th from bottom). Tower has never run properly, dating back to 1999.

 

The main problem right now is that when we try to run with the condensate in level control, we see large swings in our steam rate (Varies by about 10,000 lb/hr every 5 minutes).

Attached Files

•  Debutanizer Thermosiphon Sketch.xlsx   20.54KB   44 downloads

[Bobby Strain]

Well, this helps. The liquid piping is poorly arranged, but it should still work. My suggestion is that you first connect tray 6 temperature controller directly to the condensate outlet valve from the pot. And tune it properly. You will never get the temperature control to work by trying to adjust the level in the condensate pot. If you could tell me who the designer of this system was, I might have a better insight. I have fixed a number of installations like this. And, it's likely that the designer didn't know on which tray to locate the thermocouple to achieve the best control either. You can use private communication if you wish.

 

Bobby