17 replies to this topic

[GASCO]

Hi all

We have sweetening unit consisting of MDEA
During quick shutdown "24 hour" we kept the amine pumps running on minimal flow recycle to the amine storage tank
We noticed the storage tank temperature gradually increasing from 65 to 95 degrees and the PV vent is opening to the atmosphere
so we stopped the pump

The amine storage tank normal operating pressure is 5 mbar and temperature of around 65 C degrees

My question is we all know that amine degradation temperature is around 133 C at around 1.2 bar
So what is the amine degradation temperature and viscosity and hydrocarbon absorption at high temperature (95 C) and low pressure( 5 mbar)?

[Art Montemayor]

GASCO:

You are going to get all kind of wild responses to your not-so-clear query. Please explain exactly what it is that you did and what you mean:

• You say you “kept the amine pumps running on minimal flow recycle to the amine storage tank”. What is it that you were pumping to? Were you pumping to the MDEA (hot, without using your MDEA cooler?) directly to the tank? Or were you just routing the minimu flow of the MDEA pump to the storage tank (hot)?
• Why do you have a minimum flow system on a closed circuit solution pump? In an Amine unit you want to circulate the design rate – so why would you have a “minimum” flow? Are you varying the amine solution flow rate so much that you have a “minimum flow?
• What is the temperature of the “minimum flow” solution? Your amine pump is supposed to pull suction after the amine heat exchangers (in the worse case), just before the amine cooler. This solution temperature is approximately 70 oC. How can you be pumping 100 oC solution?
• In order to understand what exactly you are (and have been) doing, please furnish a schematic flow diagram of your MDEA unit.
• You state you “all know that amine degradation temperature is around 133 C at around 1.2 bar”. Fine. So what is the problem in not knowing what is the amine degradation temperature at high temperature (95 C) and low pressure( 5 mbar)? Simply forget what interest you might have in the viscosity and hydrocarbon absorption. Common sense tells you that if you are close to degrading the solution, it won’t be good for anything except the trash can. Worry about pumping hot (instead of cool) solution to the storage tank.

Await your response to the above,.

[GASCO]

Dear Art Montemayor

Sorry for being not clear
anyway I attached drawing of our MDEA system
the pumps in red are the pumps that were running on minimum flow
these pumps are MDEA pump, the first one is booster pump with discharge around 5 bar, the second pump is the main circulating pump with discharge around 80 bar.
the green lines represent the minimum flow lines

"Or were you just routing the minimu flow of the MDEA pump to the storage tank (hot)?"
Yes excactly from the MDEA pumps back to amine storage tank, because the absorber was shutdown

"Why do you have a minimum flow system on a closed circuit solution pump? In an Amine unit you want to circulate the design rate – so why would you have a “minimum” flow? Are you varying the amine solution flow rate so much that you have a “minimum flow?"

I did not understand you fully,
but yeah we have to vary the amine solution flow rate depending on the feed otherwise it will create problem if we delivered lower or higher amine flow rate
generally all pumps with huge capacity of 800 m3/hr will have a minimum flow line


What is the temperature of the “minimum flow” solution? Your amine pump is supposed to pull suction after the amine heat exchangers (in the worse case), just before the amine cooler. This solution temperature is approximately 70 oC. How can you be pumping 100 oC solution?

Unfortunately we do not have temperature gauge or Temperature transmitter on the minimum flow line
the solution temperature is around 70 oC in normal operation but since we had shutdown the absorber was isolated and the regenerator was isolated so referring to attached diagram XV255 XV 256 & XV281 "yellow" were closed, as you notice from the digram that the fan cooler is upstream of XV 255 and XV256


In order to understand what exactly you are (and have been) doing, please furnish a schematic flow diagram of your MDEA unit.
attached

You state you “all know that amine degradation temperature is around 133 C at around 1.2 bar”. Fine. So what is the problem in not knowing what is the amine degradation temperature at high temperature (95 C) and low pressure( 5 mbar)? Simply forget what interest you might have in the viscosity and hydrocarbon absorption. Common sense tells you that if you are close to degrading the solution, it won’t be good for anything except the trash can. Worry about pumping hot (instead of cool) solution to the storage tank.

Maybe i was not clear on that i am saying if amine degradation temperature is 133 oC @ 1.2 bar
what is the degradation temperature @ 5mbar
because i am worried if i would degrad my amine @ 95 oC

and amine Viscocity and Hydrocarbon absorption tendency varying with the solution tempetaure


 MDEA.ppt   200.5KB   108 downloads

regards

[Zauberberg]

There is no way that thermal amine degradation can occur below 150 degC.

Read: http://www.bre.com/b...aspx?EntryID=75 and download the referenced material at: http://www.gastreati...y-June 1994.pdf

[GASCO]

Zauberberg

the second reference is very useful

thnx

[Propacket]

We noticed the storage tank temperature gradually increasing from 65 to 95 degrees and the PV vent is opening to the atmosphere
so we stopped the pump

GASCO,

Why temperature of amine was increasing in the storage tank? I understand that this temperature increase is associated with temperature rise due to pumping. You are pumping the amine in a closed loop and there is no way of removing energy from the system. That is why temperature of the tank increased from 65C to 95C. What do you say?

[Propacket]

There is no way that thermal amine degradation can occur below 150 degC.

Read: http://www.bre.com/b...aspx?EntryID=75 and download the referenced material at: http://www.gastreati...y-June 1994.pdf

Zauberberg,

Is 150C the skin temperature or bulk amine temperature? Both references recommend bulk amine temperature of 260F (126.6F).

[henri paradowski]

Hi

From my experience no degradation of MDEA at these conditions.
Possibly degradation of the antifoam agent if any. Resulting is polymethylsiloxane (silicon) oil.

Absorption of Hydrocarbons limited except aromatics. Amine circulation can be kept during gas shut down but some cooling has to remove the heat that is put in the system by the pumps.

Henri

[Zauberberg]

PEngr:

... a reboiler operation with an amine bulk temperature below 260°F (126 degC).

The rule of thumb is to maintain amine skin temperatures between 300°F and 325°F (148-162 degC), and not exceed 350°F (176 degC).

[GASCO]

Zauberberg
The rule of thumb is to maintain amine skin temperatures between 300°F and 325°F (148-162 degC), and not exceed 350°F (176 degC).

what kind of amine you are talking about cuz we have MDEA and the vender recommend maximum bottom temperature is 133 oC

henri paradowski
Possibly degradation of the antifoam agent if any. Resulting is polymethylsiloxane (silicon) oil .
how come antifoam agent degradation temperature is lower than amine degradation ?
to be honest with u i dnt know wat is the chemical compound of our antifoam agent ?



P.Engr
I understand that this temperature increase is associated with temperature rise due to pumping

yes exactly

Regards

[Zauberberg]

Gasco,

If you have the exact degradation temperature specified by the vendor, why do you bother at all to explore so many different figures and temperatures (bulk, wall, etc.) for various amines? There is no doubt in your case: as long as you are below 133 degC, no need to worry. And in reality you will not come even close to that figure - unless something really abnormal is going on.

[aanita]

Before shut down amine circulation pump,if rich amine solvent( mixture of acid gas + aMDEA) not fully regenerated, temperature may rise and I beleive what it happen to your case. 35 deg C (from 60 to 95 Deg C.)temperature rise due to pumping not possible and it is not matching with the HYSYS results. MDEA degradiation temperature is 155 and not 133 Deg C. When you cut off feed gas there is no chance to hydrocarbon absorption.

[GASCO]

Zauberberg

I was talking specifically about MDEA, amine for me is just MDEA
sry if i wasnt clear

as long as you are below 133 degC, no need to worry. And in reality you will not come even close to that figure

in reality we are working as close as 132.5 oC when the train is running with full capacity "Sour feed around 420,000 m3/hr and amine circulation of 800 m3/hr"

aanita
the bottom temperature of the regenerator recommended by the vender "UOP" to be 133 oC,

"MDEA degradiation temperature is 155 and not 133 Deg C"
do u have manual or data sheet of MDEA that show that, please attach it

thnx all

[Zauberberg]

In reality we are working as close as 132.5 oC when the train is running with full capacity "Sour feed around 420,000 m3/hr and amine circulation of 800 m3/hr"

This is a separate issue - now you are speaking about the reboiler outlet temperature, which is a completely different subject. Your original post was referring to the amine heating up through the pump when unit is in circulation mode.

Still, 132.5 degC shouldn't be that troublesome although it appears a bit high, in my experience. Essentially, this is the boiling point of water at the reboiler operating pressure. If you have exceeded the normal operating temperature of the reboiler, perhaps you can try to decrease the regenerator pressure - if there is a margin to avoid flooding at full rates. What is the normal (as designed) reboiler temperature?

[aanita]

There are thousands of literatures to get informations now a days.
For MDEA degradiation have a look :
http://www.bre.com/b...aspx?EntryID=75

Will be appreciate if you updates your findings.

So far I know GASCO is a corporate gas processing company, not a person,
and should you use this name?
Oviously last question is from persoanl querisity.
Regards.

[GASCO]

which is a completely different subject
yeah i agree
but i dnt know what dragged us to talk about it

Still, 132.5 degC shouldn't be that troublesome although it appears a bit high

why do u think its high? u worked with MDEA before or it was different kind of amine ?
r u worried about over consuming steam to the reboilers?

perhaps you can try to decrease the regenerator pressure - if there is a margin to avoid flooding at full rates.

i can not decrease the regenerator pressure alot because down stream of the regenerator we have acid gas compression unit so i have to maintain slighty higher differential pressure to the suction of the compressors
can u explain more about the flooding of the regenerator ?

What is the normal (as designed) reboiler temperature?

Desgin shell side is 162 oC
Desgin tube side is 195 oC
the operating temperature is 130 to 133 oC

Attached Files

•  130-GD-B-00116.pdf   95.2KB   47 downloads

[GASCO]

There are thousands of literatures to get informations now a days.
For MDEA degradiation have a look :
http://www.bre.com/b...aspx?EntryID=75

Will be appreciate if you updates your findings.

So far I know GASCO is a corporate gas processing company, not a person,
and should you use this name?
Oviously last question is from persoanl querisity.
Regards.

legally i dnt know
maybe i am not allowed to use it

[Propacket]

can u explain more about the flooding of the regenerator ?

When you decrease pressure of the regenerator, actual volume of rising vapors increases due to which velocity of the vapors also increases. This causes liquid on the tray to flood.