13 replies to this topic

[SANDEEPCH]

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!

[Nikolay_]

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?

[SANDEEPCH]

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. 

[Nikolay_]

Did you analyze your solvent?

 

Regards,

Nikolai

Attached Files

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

[Lavi]

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

[SANDEEPCH]

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

[Technical Bard]

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.

[Nikolay_]

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

[Nikolay_]

Hello Sandeep,

 

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

 

Regards,

Nikolai

[SANDEEPCH]

@ 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

[Nikolay_]

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.

[Pronab]

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.

[SANDEEPCH]

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.

[Nikolay_]

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.