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Residual H2S Loading In Lean Amine

amine regeneration unit lean amine h2s loading amine treatment unit reflux rate in aru

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#1 SANDEEPCH

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Posted 02 February 2018 - 01:11 PM

In our FCCU unit there is facility of amine treatment of fuel gas and LPG. We also have an amine regenerator column which strips out H2S from rich amine. Our unit went for long M&I approximately for 2 month. Before shut down we regenerated the whole Amine and stored in a tank with N2 blanketing. During start-up we took back our amine from the tank. Some amine got loss in process upset. So we had to take fresh MDEA (AROUND 10-20% OF TOTAL AMINE). After start-up we are facing residual H2S loading in Lean Amine.

Here are details.

Amine used- MDEA (25% strength)

Amine solution circulation rate 25m3/hr for fuel gas and 12m3/hr for LPG.

Reflux in amine regenerator column- 0.5 m3/hr

Amine regenerator top temp- 110 oC

Amine regenerator bottom temp -129.5 oC

 

Before shutdown we were maintaining amine regenerator top temp 106 oC and reflux rate 0.35 m3/hr and were getting 0.05 wt% H2S in Lean amine. We have increased top temp from 106 oC to 110 oC and reflux rate 0.5 m3/hr. But still we are getting Lean amine H2S around 2wt%. What could be the probable reason? How we can troubleshoot this problem. Please enlighten me from your expertise.

 

Thanks & Regards!



#2 Nikolai T

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Posted 04 February 2018 - 09:17 PM

Hello,

 

The amine strength seems too low. The 40-50 wt% is acceptable value for MDEA. If I were you I woud review old trends (concentrations, temperatures, pressures, flow rates) since first run if possible. What is design value of concentration?



#3 SANDEEPCH

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Posted 10 February 2018 - 10:54 PM

Earlier concentration was also 25-27%. Circulation rate, bottom temperature were same. Top temperature used to be 106 oC (now 110 oC ). Unit was designed for DEA. But solution has been changed for so many years and it was working fine before shutdown. 



#4 Nikolai T

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Posted 18 February 2018 - 07:54 PM

Did you analyze your solvent?

 

Regards,

Nikolai

Attached Files


Edited by Nikolai T, 18 February 2018 - 07:57 PM.


#5 Lavi

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Posted 19 February 2018 - 02:47 AM

You have added fresh amine to your system. And this is causing the lean loading to increase. It is normal.

The system will get back to regular amine lean loading after a certain period of time (when you have stable salts formed).

If you urgently want to decrease the loading try the below

1. Decrease the amine flowrate giving more time for amine to stay inside the column for more stripping
2. Increase column top temperature

#6 SANDEEPCH

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Posted 26 February 2018 - 08:21 AM

Sir,

I have also read one or two article regarding effect of HSS on Lean Amine H2S loadings. But we have not changed all the MDEA used in the system. We have changed hardly 20%. It has been more than 1.5 months but still we are getting 1.4 wt% H2S in Lean Amine. (Yes, It is decreasing but at very slow pace)

 

Thanks & Regards !

Sandeep



#7 Technical Bard

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Posted 27 February 2018 - 10:14 PM

Do you have a simulation using ProMax, OGT, VMG, Unisim or HYSYS that matched the process conditions before this problem?  

 

I suspect you are not sufficiently reboiling the regeneration column.  That is the usual reason lean loadings are too high.



#8 Nikolai T

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Posted 06 March 2018 - 03:26 AM

It may not be HSS. It can be products of degradation, typical for FCC MDEA.
Can you continue increase reflux?

#9 Nikolai T

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Posted 19 March 2018 - 01:50 AM

Hello Sandeep,

 

I hope you are doing well. Which parameters do you have at this time?

 

Regards,

Nikolai



#10 SANDEEPCH

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Posted 03 May 2018 - 08:18 PM

@ Nikolai T

Our lean amine loading has been constant around 1.3 wt% since 1 month. It is not decreasing further. We have tried with high reflux also but no benefit observed so we revert back to normal reflux rate.

 

Regards!

Sandeep



#11 Nikolai T

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Posted 03 May 2018 - 09:46 PM

Hello,

 

Please compare CO2, H2S concentration data of sour FCC gas and LPG before and after start-up (if possible). What amount of steam is used for regeneration? Is total circulation rate 37m3/hr? What NH3 concentration of regenerator reflux do you have?

 

Regards,

Nikolai


Edited by Nikolai T, 06 May 2018 - 11:55 PM.


#12 pronab

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Posted 28 May 2018 - 02:05 AM

0.5 m3/hr reflux is very low. It shows that very poor vapor traffic across the regenarator column. I beleive regenarator column operating pressure aprrox.1.0 barg. Compare the reboiler duty with before and after shut down. How much is the feed to the unit. You can try to reduce regenarator pressure if down stream there is no other issue.

I want to know the updates from you.



#13 SANDEEPCH

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Posted 06 June 2018 - 05:38 AM

Sorry for late reply.

Earlier column operating pressure was 1.1 and now 1.0 kg/cm2g. Reboiler duty is more or less same. Feed to amine re-generator is around 40 m3/hr. Steam consumption in reboiler is 1700 kg/hr.



#14 Nikolai T

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Posted 13 June 2018 - 09:10 PM

Hello,

 

Steam flow rate seems low. I've calculated 282 BTU/gal or 0,75 Mkcal/h. More steam flow will produce more reflux. Practical range for MDEA is 800...900 BTU/gal. It is possible MDEA solution was contaminated before unit shut down.

 

Regards,

Nikolai


Edited by Nikolai T, 13 June 2018 - 09:15 PM.





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