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Amine Gas Sweetening Unit Turndown Problems

amine unit gas sweetening turndown capacity

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#1 wafasaleem

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Posted 19 February 2017 - 04:15 AM

Hi friends,

 

I am an intern in a natural gas processing plant. The plant was initially designed for 40 mmscfd feed gas and has declined now to 11 mmscfd. This is causing some operational problems in the amine unit (MDEA). How can we change the amine parameters to increase the turndown ratio of the unit?  What are further changes to be made during this process?

 

kind regards,

wafa



#2 Bobby Strain

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Posted 19 February 2017 - 02:02 PM

You are more likely to get help by providing complete information. "causing some operational problems" won't get you much.

 

Bobby



#3 wafasaleem

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Posted 20 February 2017 - 12:28 AM

sorry, but there is no problems in the contactor so far, but we are intending to increase the percentage CO2 in the sales gas to increase the sales gas amount and bring down the CV to the specified amount. what could be the changes that can be brought about the amine unit for this? can we make any changes to the concentration? the amine flow rate is around its minimum possible for the circulation pump.



#4 RockDock

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Posted 28 February 2017 - 12:04 PM

You can likely change the solvent concentration, but you really need to provide a complete picture of the plant. This seems like a pretty standard study you can do with a process simulator.



#5 wafasaleem

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Posted 04 March 2017 - 11:48 PM

You can likely change the solvent concentration, but you really need to provide a complete picture of the plant. This seems like a pretty standard study you can do with a process simulator.

 

Here we are removing the H2s and CO2 from the feed gas by amine treatment. The solution used is 50% MDEA, which is the normal standard. Amine is regenerated using steam and recirculated back. Currently, the sweet gas H2S conc. after treatment is 1.6 ppm which according to spec. can go upto 15 ppm and CO2 conc is 1.7% which can go upto 4%. We are trying to increase the CO2 conc to 2-2.5%. What could be the ways? Does conc change helps? What could be the problems due to this? I have no knowledge about HYSYS or any other simulation software. Please help me.



#6 Pilesar

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Posted 08 March 2017 - 12:02 AM

If the turndown is permanent, you may need to modify equipment. Install a smaller impeller in the pump or blank portions of the column trays possibly. You may also need to change the column internal distributor design. The minimum flow on the pump can be handled by a properly sized dedicated recirculation line for minimum flow. Reducing circulation flow is what I would try first. 



#7 wafasaleem

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Posted 09 March 2017 - 12:47 AM

But changing the flowrate is practically not possible. Is there any other options for CO2 slipping? Like, can we change the concentration of amine?



#8 pronab

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Posted 09 March 2017 - 03:57 AM

To understand better your process, provide a PFD. Amine feed to the contactor should different trays to adjust CO2 in sweet gas. To increase CO2 you should put amine to the lower tray of the amine Contactor. Inctrease lean amine temperature and possibly reduce lean amine flow to Contactor.



#9 wafasaleem

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Posted 12 March 2017 - 12:30 AM

PFD attached below.

 

We have only one inlet valve for lean amine which is at the top, as the capacity is quiet small. How does increasing lean amine temp increase co2 slip? its low temp that actually favors the selectivity process right? Could you please explain the mechanism?

 

Thanks

Attached Files



#10 PRO_ING

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Posted 13 March 2017 - 04:54 AM

hi 

is there any bypass for this unit, so you can trait only a small amont and when mixed you will get your required value. 

or maybe you can change MDEA with DEA.



#11 wafasaleem

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Posted 14 March 2017 - 12:28 AM

There is no bypass currently and the inlet gas H2S content is 97 ppm which should come down to less than 4, so I don't think it will be possible. And DEA is not as selective as MDEA right?

 

 



#12 ColinR33

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Posted 14 March 2017 - 12:18 PM

If you want to slip more CO2 into the sales gas, reduce the amount of contact in the amine contactor.  This is usually done by adding additional feed points at say trays 3 & 5.  If the tower already has multiple feed points you are set, just close off the top feed and take the next lowest.  You will see the CO2 slip rise.  If you want to slip more, change the feed to the next nozzle down, and if slip is too high, then go back up the tower.  If you don't have multiple amine feed nozzles this means vessel and piping mods which are ugly.  Alternatively you can open up the tower and reduce the weir height on the trays to reduce tray residence time and allow more slip.  3rd option, talk to your amine supplier and see what they recommend!



#13 wafasaleem

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Posted 16 March 2017 - 01:26 AM

Thanks Colin






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