Ammonia Injection in CDU reflux drums

[consideritsolved]

Hi,
Why is Ammonia injected to the reflux from CDU? Any specific reasons.

Thanks

 

[Milutin]

Hi consideritsolved,

Possible reason is because somebody intended to neutralize HCl coming from furnace to column overhead. It doesn't looks to me as good idea, because ammonia in that way is returned back in column and can form ammonia chlorides salts on column trays,this salts can cause corrosion on column trays. For more details you can read thread483-197804.

Regards,

Milutin

 

[RogerH]

consideritsolved
As Mulitin points out the reason is to neutralise the HCl. In the "old" days and on some site still today this is used. Many have moved to the use of performance amines, neutralising and corrosion inhibiting ones. These is to be better adapted in so far they condense before HCl condeses. The intial condensation of HCl nomrally occurs before the water and at this point there can be some substantial corrosion. The newer amines are geared to counteract this corrosion.
As Miluting points out there are some drawbacks with NH3. In some crude units NH3 condensate effluent can also be a problem due to restricted sour water stripping capacity.

 

[Milutin]

Hi RogerH,

I was pointing out especially on adding anything (amines or ammonia) in CDU reflux. This can cause (depending on ions concentration) salt deposition on column trays. Salt deposits will eat trays rapidly due underdeposit corrosion.

Regards,

Milutin

 

[0707]

CONSIDERITSOLVED

Contact Nalco or Baker Hughes THEY HAVE GOOD "KNOW HOW" ON THIS SUBJECT. The other posters have pointed some good reasons to avoid the use of Ammonia


luis marques

 

[EmmanuelTop]

Ammonia is injected in the top pumparound flow, only in the case when pumparound return temperature is below calculated water dew point, by taking into account tower operating conditions (pressure and H2O vapor concentration). This is ADU column design option in which you achieve higher thermodynamic efficiency of top P/A exchangers at the expens of having higher corrosion rates in the pumparound loop. Otherwise, there is no reason to inject ammonia or amine compounds, because HCL vapors are not corrosive; they become aggresive only when liquid water is present in the system.

Overhead reflux should not be used on a continuous basis, whichever design you choose, because this stream is rich in liquid H2O - acting as a "spider net" for acid gases absorption inside the column. If overhead reflux flow is required on a continuous basis (in order to maintain column heat balance), then another option has to be found instead of injecting neutralizer in reflux line - for example, this can be solved by addition of another pumparound loop etc. Or, if you can operate the tower with observed corrosion rates, then there is no need for additional concerns.

http://antwrp.gsfc.nasa.gov/apod/astropix.html