22 replies to this topic

[rosa]

hi,

I work in the gas refinary that MDEA is used as a selective solvent to remove H2S from feed gas.there are 8 stages as feed amine tray.I mean the amine could enter from 1st tray or 8th tray inaccording the process need.
I'd like to know if the amine can enter to absorber from 2 feed tray simeltanously?

I am eagerly waiting for the answer.

[Profe]

Hi Rosa


First of all you must review the process flow diagram or P&ID of this unit. And get yourself the correct answer.

But in absortion column like amine absorber. The contact betwen gas and liquid is conterflow.
Liquid stream (MDEA solution) in over the upper tray, and gas to sweetening below the last tray. If the column is pcked, the same fashion Liquid over pack, gas below package.
In liquid - liquid absorber, like MDEA solution and LPG or Gasoline is the same less density fluid below last tray or package.

I hope to be useful to you.

[Pronab]

MDEA used as a selective removal of acid gases.
Feed tray location ( 1st, 2nd ..) depends on your product quality, how much CO2 in product you need.
Because with MDEA, H2S will remove all (of course you have to maintain operating parameters), but CO2 will depends on residence time aswell.
Why you want to feed amine simultaneously two feed tray? Even if you put two trays most of amine will flow through the bottom feed tray, due to the nature of liquid gravity.

Pronab.

[rosa]

hi friends,

I want to know that if we have more felexibility in controling or adjusting the main parameter is gas sweetening units in this case or not?

Thanks for your replies.

Rosa.

[Pronab]

Rosa
I am totally confused, what you are asking.
You can adjust your controlling parameters as your
product specifications. More specifically you can change
amine temperature, Concentration of MDEA, feed location.
Exactly wht you are looking for in an amine plant?
Regards.
Pronab.

[rosa]

Pronab

Thank you for your following.As you said before if the amine enter frome 2 amine feed trays due to gravity.I also think most of amine enter from lower trays.

Do you heard that entering amine from both trays has any advantages?thats it.

Thanks in advance.

Goodluck.

[Profe]

Hi Rosa

Normally the solution of MDea enters by the 1 tray, if there is possibility of entering by an inferior tray, this is advised in cases in that loss Mdea by foam formation or high gas flow can be produced that can also promote entraiment and loss of MDea.

[hamadi]

Hello

In my LNG plant the MDEA have 2 feed location, the top and the the middle one. This to achieve maximum absorption in the absorber.

[Pronab]

To Rosa
To be honest, I never seen, two feeding tray at a time.
Hamadi
Are you usin both tray at a time in your plant?

[rosa]

it is just an idea.

[Art Montemayor]

Rosa:

It is rare, in my experience in operating and designing Amine Absorbers, to have two distinct heights to feed your lean Amine in order to absorb the H₂S. I would position my Lean solution inlet as high as I possibly could in order to absorb the maximum H₂S. Profe and Pronab are telling approximately the same thing by questioning your intent. It is not considered common sense to reduce the H₂S removal capacity unless you have strict and direct intentions to do so (which you do not indicate). The strictest quality control on natural gas is the H₂S content and this should be as low as you can justify - always lower than your lowest regulated specifications given you.

Therefore, it isn't "smart" to consider increasing the H₂S content. The CO₂ content is something totally different. The CO₂ content only affects your heating value and I've tolerated up to 40% CO₂. I would highly recommend you discard your idea of using a lower Lean Amine feed nozzle to the absorber. I can't explain why you have a lower nozzle, but then you haven't given much basic data or explanation of what it is that you are trying to do. The outlet content of the CO₂ is not controlled by switching feed trays. That much I can clearly state.

I strongly recommend also that you go to the BR&E webpage (use Google) and download all the valuable and useful technical articles they give you regarding the design and operation of MDEA gas sweeterning plants. You will find a lot of valuable information there for you.

Perhaps if you explain your scope of work clearly, we can be of further help.

[hamadi]

Hi

About the 2 feed locations:

I dont know really why they use two feed location, but what I know that the top feed enters in lower temperature than the middle feed.

[Profe]

Hi again Rosa

About the valve below the last tray, sometimes de absorber is the vessel that acumulates the total inventory of MDEA, and when you replace the inventory partialy without disturbing the main flow by trays, you can send the new MDEA to the bottoms directly for make inventory and mantain operaiting the absorber.

[Pronab]

Let me differ with both Art and Profe.
Designing gas sweetening plant especially with MDEA which is selective absorption of CO2 need full understanding of down stream of the gas sweetening plant as well where sulfur is recovered from H2S by means of (mainly) Claus process. Processing acid gas (mainly CO2 and H2S) using once through Claus process need a minimum concentration (~ 40%) of H2S for stable flame in the reaction furnace. When H2S concentration becomes low (due to more CO2 in acid gas) flame is not stable and sulfur recovery plant design should be different (split flow or other types). With MDEA feed to higher tray (giving more residence time), CO2 absorption will be more which will lead to a lean acid gas (due to high CO2 in acid gas). Again feeding higher tray giving more CO2 for absorption will decrease PH of MDEA which will lead to lower absorption of H2S. Also when high CO2 will absorption, there will be less room for H2S absorption (for details please visit www.bre.com). So designing an amine contactor with feed tray as high as possible is not always desired or feasible. Multiple feed locations are chosen for CO2 in sweet gas. For lower CO2 in sweet gas need more residence time (higher location of the feed tray) and vice versa.
To Profe: I am not agree with you about your idea on total inventory.Because there is normally a storage tank where amine circulation pump is taken it suction flow.There are 3 or 4 feed tray at different location of amine contactor, normally one in service.
To Hamadi: is it you are using lean and semi-lean amine in your system, where lean amine is cooled before entering into the contactor. Otherwise whole temperature of amine should be same.
Finally there are lot of thechnical papers in the website if one is interested.
Regards.
Pronab.

[Luis]

Hola rosa!!
LA verdad 2 corrientes entrando en una misma torre no es viable debido a que su ubicación depende deque tanto H2S deseas remover mientras mas alto el plato mayor pureza en el gas pero esto acarrea un mayor gasto en solvente todo depende de los requerimientos de tu proceso.

Saludos

[Pronab]

Luis
Can you explain it in ENGLISH.
Pronab.

[you]

Hi

About the 2 feed locations:

I dont know really why they use two feed location, but what I know that the top feed enters in lower temperature than the middle feed.

Hi Brother,
I never seen a lean Mea or MDEA enter to an absorber in a two location but may be due to high concentration of H2S and CO2 in the feed gas, they divided the MDEA steam in two streams (resident time in absorber is short) to absorb maximum of acid gas but I don't think that the MDEA enters one under the other but may be between them four trays (exemple).
Just an Idea

[you]

Hi

About the 2 feed locations:

I dont know really why they use two feed location, but what I know that the top feed enters in lower temperature than the middle feed.

Hamadi can send me an email
y2005m@hotmail.com

[vicini]

Another reason to have two feed points is to cool the absober. The heat of absortion/reaction will build up in the column and the process will not meet specifications. In order to cool the tower, a semi rich stream can be added at mid tower. The semirich amine will absorb a lot of heat with very little additional heat requirements in the stripper.

[rosa]

Dear vicini
about 2 amine feed stream I should say that both of amine streams are lean amine not semirich amine.

Kind regards,
rosa

[M S Miglani]

Just to add a little bit. Two or three feeds to the column are provided for flexibility and at no point more than one feed tray is used .

[ravi.s]

Just to add a little more. I have came across with one unit, which uses multiple amine feed points to meet deep H2S removal & maximum CO2 slip (>80%). The Absorber has total 10 trays & amine is fed to 1, 3, 5 & 7 tray.

[thanigaivel]

hi,

I work in the gas refinary that MDEA is used as a selective solvent to remove H2S from feed gas.there are 8 stages as feed amine tray.I mean the amine could enter from 1st tray or 8th tray inaccording the process need.
I'd like to know if the amine can enter to absorber from 2 feed tray simeltanously?

I am eagerly waiting for the answer.

hi,

i m working in merox units, we are removing H2S by using same amine absorber with 8 trays. i would like to clarify one think H2S removal not only depends on amine quantity it depends on temp, H2S content in feed, feed flow. High amine flow leads to carry over, this will affect ur downstream process. You have to maintain Acid/Gas ratio such that maximum removal of H2S is possible.
i hope i m right.