7 replies to this topic

[Ravi2012]

We have an absorption column (valve trays) intended for H2S absorption using DEA amine which operates at high pressures 9000 kpag). Gas component mainly consists of >90% hydrogen along with H2S, NH3 and lighter hydrocarbons (gaseous effluent from hydrotreater). Recently we had experienced slight foaming/carryover in the column. Most of the times, the lean amine inlet to the column remains at 55 deg C and the temperature difference between lean amine and gas is maintained at 20 deg C. The gas outlet temperature is same as outlet gas. On analysing lab sample, it was found that amine conc is only 25% (against 30% required) and H2S conc is less tha 0.10 mol% in the treated gas. We are experiencing continuous amine carry over and hence are running the column at less than 70% of the designed amine circulation rate. Injection of the antifoam improves the satuation but do not resolve this issue. Lean amine foaming test was negative. When we reduce the lean amine flow by 40 m3/hr (tarhet is 240 m3/hr) no carryover occurs.

We made the amine strength back to 0.3 mol/mol and still having foaming/carryover issue.
Is the poor amine strength caused amine absorber plugging or some clodding in the tower which prevails the carryover?


Anyone earliest feedback will be appreciated.
Thanks.

[Dacs]

Do you strip your amine or do you send it outside for stripping?

Have you tried looking at heat stable salt formation in your amine?

[Bobby Strain]

Time to clean the solvent.

Bobby

[thorium90]

Is yours a trayed tower? How is the dP across the absorber like? Fluctuating wildly? When was the last time you opened the column and looked if the trays are still "where it should be". Does your system maintain positive water balance by injection of water on the top trays of the absorber? Foaming can be caused by particulates or tensides. Do you employ side stream filtration with carbon filter and micron filter? Could be important to check since your feed gas contains hydrocarbons. Does analysis of the solvent reveal presence of tensides? Can your pump leak lube oil into the system?

[Ravi2012]

Thanks for reply.
Dacs@ Yes we did strip amine in April 2012 and we had this carryover/foaming first time in Nov 2012. Heat stable salts were within the limit. FeS and Suspended solids were significantly high.

thorioum90@ Yes valve type trays. DP is not changing much only 10 kpa differential. Tower is never opened. First turnaround is coming April 2013. Wash water section never commitioned. We do have carbon filter (5 micron). No chance of getting lube oil in the system. No tensided test was done.

What is tensides?

Thanks

[thorium90]

High FeS and SS... Sure your micron filter is working? How often do you clean your filter and how is it done? 100mBar for dP does seem on the higher side but it could be normal since I dont know your liquid to gas ratio. High FeS is a sign of corrosion in the unit. Damaged trays can cause foaming and carryover to occur.
You have mentioned the following:
Reducing lean amine flow reduces carryover.
Anitifoam is no help.
Reached recommended amine strength but no help.
High FeS and SS.

I think the most likely reason is that corrosion has caused some damage to the trays evidenced by high FeS and SS and your symptoms seem to point in that direction too. Perhaps you better prepare for a good inspection in April. In the mean time, you might have to clean that filter more often. I would suggest using ultrasonic cleaner with degreaser.

I'm gonna assume you have both activated carbon filter and a micron particulate filter since you mentioned "carbon filter (5 micron)".

Tenside definition from the dictionary :
Agents that modify interfacial tension of water; usually substances that have one lipophilic and one hydrophilic group in the molecule; includes soaps, detergents, emulsifiers, dispersing and wetting agents, and several groups of antiseptics

Edited by thorium90, 25 January 2013 - 01:40 AM.

[Satyajit]

Hi Ravi,
I think your trays are partially plugged with thick layer of HSS. Some of the valves are not operable anymore.
You have to open up these trays, do cleaning by hydrojet. Do the trays elevation and leak test after reinstallation.
Replace solution partially by fresh solution during start up .
Do not forget to passivate your system during start up. Please also see my comments post on a simialr post"Benfield foaming Issue".
I would also recommend you to do a thorough lab analysis of your solution and attach the analysis in the forum.
Good Luck.
Kind regards,
Satyajit

[thorium90]

Heat stable salts were within the limit. FeS and Suspended solids were significantly high.

trays are partially plugged with thick layer of HSS.

That seemed an odd observation..