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Intergal Reflux Condensor 1

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dcasto

Chemical
Jul 7, 2001
3,570
I first came across some old (circa 1950's) distillation columns that had the water exchangers on top of the column. Water was pumped up to them and the condensed (iso-pentanes) just gravity flowed back to the column.

I then came across a similar deethanizer column with a intergal chiller. The tower was in a yard laying down. The attached drawing deplicts how I decided it must be installed.

The chiller bundle was a u-tube type. Propane (flashed) liquid enters one side and vaporized C3 vapors the other. The tube bundle was bolted to a top flange on the tower. The tower had a ID od 24 inches and the bundle had a 23" OD.

My theory is that by setting the pressure of the propane to be 30 psia, i knew that at a 10 degreeF product overhead temp, all the propane would be heated above its dew point of -20F.

I didn't show the reboiler or dump system on the propane outlet seperator in the diagram. I had the level controler set to override the Pressure Controller an close the valve that allowed C3 to enter the chiller.

AM I way off base? Has anyone else run this type tower?
 
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I built a number of these back in the early 80's. I used a couple of them on deethanizers and a couple on amine strippers using a water/glycol mix. The ones on the deeth were on flashing propane similar to the ones you described however, we used to bolt the NEN exchanger to the top of the tower so that the tower overheads went through the tubes and the boiling propane on the shellside. Then the condensed liquids just dribbled down the tubes and dripped back into the tower. We used to set the propane temp at the same as the main gas chiller - alternately you can use a pressure valve to let it down if you reflux too much.

Your arrangement should work fine but you will have to be careful not to flood the chiller if the overhead temp controller calls for more cooling.

Depending on your temps, you could use a TX valve to allow for a slight amount of superheat on the propane vapour leaving the top of the chiller. Also, if you do this, I don't think you'll need the extra scrubber as it would be useless.

The other consideration is that the overhead chiller was maybe supposed to be a subcooler for the liquid propane and you can leave it flooded. This has also been done a few times to allow for some preheat on deeth overheads and a bit of propane subcooling on the way to the real chiller. Let me know if you need more on this - I can probably dig up some old drawings.
 
Thanks.

We have an application for a real small application for a 20" to 24" column and the latest rules for emissions make operating little reflux pumps a real pain. I've looked at mag drives as a solution to the pumps.

The HX exchanger rateing is giving warnings about flood on the propane. So I'm reviewing different tube sizes.

Finally, I remeber now that some of the first attemps to build Ortlofts GSP process called for the type of exchangers you described, that could be a nice route too. Thanks.
 
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