Sulphur Spec with Molecular Sieves in NGL Plant

[CHML713]

NGL plant using DGA and Glycol Dehydration and Molecular Sieves. The Mole Sieve is being used primarily for mercaptan removal. Even when we can provide 10lbs/mcf water content gas to the mole sieves we cannot run for more than 4 hrs before we go over 200ppm on sulfur. Any suggestions on what could be our the problem?

There were a few Glycol Unit upsets due to foaming during operation of the mole sieve.

 

[phex]

How long should you be able to go? That is, how long is design cycle time?

what proe diameter does your molsieve have? is it possible that you are removing also other species than mercaptanes? Perhaps even non-sulfur species? Have you ever analysed the ladden adsorbent?

My guess would be that the capacity of your mole sieve is taken by other species than sulphur.

hth,
chris

 

[tickle]

I agree with Phex

Check the composition of the adsorbent inlets with the mol seive supplier.

Other alternatives may be:
You have channeling in part of the beds and the whole of the beds are not being used (check pressure drops). Or the regeneration is not working properly (check the required temperature and the acheived temperature during regen). The gas temperature is too high (the lower the temp the better the adsorption).

Glycol carry over will impact on the mol seive - check with the supplier.