Crude Distillation column with two stage cooling system

[ispengg]

Greetings,

In a Crude column overhead section with two stage cooling system i.e. First stage operated hot and dry with condensed Hydrocarbon refluxed back to the column. In second cold stage water + hydrocarbon is condensed. In such system which location is ideal for Neutralizing Amine Injection to avoid corrosion??

 

[NBrink]

So, IF this is actually the way it runs, and you don't condense any water in the first stage, the ideal location would be after the first stage separator. This way you avoid refluxing amines back into the column. I've never heard of one that didn't actually condense a bit of water in the first stage though. Just enough to cause problems...



Nathan Brink

 

[ispengg]

NBrink,

I agree that though first stage is called Dry & Hot, there is a always presence of smaller quantity of water due to shock condensation... Even then will you prefer inject amine in the first stage??

 

[NBrink]

It's kind of a lousy situation. It's not the water that causes problems, it's the HCl that's dropping out in those first few drops. You'll tear up your condensers from the HCl, unless you metal WAY up. Unfortunately that tiny amount of water that's dropping out won't necessarily separate out in the first stage accumulator (if you even have a water boot on it, I know a lot of those two stage systems do not, since they're "dry"), so you'll be refluxing back any chlorides and amines (either from a neutralizer injection, stripping steam to the column, or from H2S scavengers in the crude) back to the top of the column. This can cause massive corrosion, fouling, and all sorts of other problems in the top section of the tower.

The two stage overhead was a really great sounding idea that never really panned out.

Solution tends to either be:
~ Run so hot that you DON'T condense water or drop amine salts in the first stage and inject neutralizer after the first stage accumulator
Or:
~ Inject neutralizer before the first stage and redesign to force the dewpoint well within the first stage (perhaps with a very large water injection before), and size the accumulator appropriately to get good separation. Forget all about the energy benefit to a hotter reflux.

Nathan Brink

 

[0707]

On top line of the destillation column, where the dew point takes place, normally up stream of the first top condensers.

good luck

luis