2 replies to this topic

[nachop]

Hi !

 

I have some trouble with a PSV in glycol contactor. 

 

The vendors (fabricators) have a practice to throw in a 1" x 2" PSV with a 'D' orifice on most glycol contactors and say it’s sufficient for the fire case.  It may be correct, the PSV may never pop in the next 15 years.  Then comes upgrading and modifications to the plant and engineering maybe asked to find out if the PSV is adequate.

 

What is the latent heat of triethylene glycol which is about 60% pure, 30% water and the 10% C5+ at the relieving conditions?  ( Set pressure 80 kg/cm²g).  I look for it in Hysys but the mass heat of vaporization results too low. API 521 gives a minimum value of 115 Kj/kg for a HC mixture.  Is that correct?

 

What happens to the contactor in a fire case?

 

Thank you in advance
 

Edited by Art Montemayor, 07 June 2014 - 12:42 AM.
Readability, grammar

[fallah]

nachop,

 

If the only credible scenario for the glycol contactor is fire case; fabricator practice to consider a small PSV on such contactor could be right and he/she considers the PSV mostly for code compliance because in most cases a PSV cannot protect a pressure vessel from failure in fire case.

[ColinR33]

What really happens is you will boil off what little bit of water there is absorbed in the TEG plus any condensed HC, a very small load.  The TEG itself will not vaporize at those pressures, it will "cook" (thermally degrade into sludge) and not contribute any significant amount to the relief load.  There will be some gas expansion effects as well, but this is a very smal relief area requirement.  A 1D2 PSV provides more than enough relief area for these scenarios.  If you want to be VERY conservative you could calculate the fire vaporization relief load assuming the liquid is the tower is completely water or HC liquid.  The water will have a higher heat of vaporization but lower MW, while the HC will have a lowe heat of vaporization but a higher MW, so check both, but this is really not necessary.

 

The only other real relief load possibility is if you have a pressure letdown valve immediately upstream of the contactor and the PSV has to be sized for gas blowthrough in the event of a control failure.