Amine Gas Sweetening HP

[alex.gutu]

Dear all

Everybody of you knows amine treating unit and their operation parameters. As I have seen, in the the most of Amine Sweetening Units the regeneration column for amine operates at very low pressure, I mean somewhere about 0.5-1 barg because of the problem of amine degradation.
As far as I know, the amine degradation temperature is somewhere about 125-130C depending on concentration. having a look through the internet, I could find out that basically the bottom temperature of the regeneration column is about 133C, maximum 135C, depending on the pressure and concentration. So...it's perfect, but I have a question regarding regeneration column of amine.
I started to simulate (in Aspen HYSYS) a simulation for amine sweetening plant. Feed stream is natural gas with 30% content of CO2, and I want remove it up to 3 %. So at the low pressure (0.5-1 barg) everything works fain, but I have a restriction in the top of the column, more exactly 3 barg for acid gas CO2. So, to get in top 3 barg, I have to get in the bottom somewhere about the 3.2-3.3 barg, and in this case the boiling temperature of the amine solution is about 148-150C. Now, I'm asking you what about with amine solution, the degradation temperature of amine solution seems to be exceeded and I'm aware of the amine degradation.
Could anybody tell me, or suggest me how could get a regenerated amine solution at a working pressure of 3 barg in the column.

Maybe should I use another philosophy for remove CO2 from sour Gas?
What kind of methods are used to remove CO2 and H2S from natural gas at pressure higher than 1 barg. Are there used another solutions beside amine solutions?

Sincerely,
A.G.

[aseptman]

Dear Alex,
You mean you have first a absorber which you want to operate at 3 kgcm2(g) . In there you use amine to absorn CO2. Amine there must be at lower temeprature right. Now in next the regneration column you have a distillation unit which can be operated near atm pressure say less than 0.5 bar (g). Then the regerated amine would be at lower pressure from Column-2. Your question is how to get it to column -1 ?
Ist this right?

[mobek]

MDEA can be used at 5 bar without having any problems during the regen. However, MDEA is very good and selective to H2S but poor amine when it comes to CO2 absorption. In the chem. industry, you always have to compromise. Is it OK for you or your client to use a mix of amines? If so then you could do a good job.

[aseptman]

mobek,
Any experience with use of MEDA in Biogas H2S removal?
MEDA from BAIF/shell is supposed to be better?

[alex.gutu]

Dear ASEPTMAN,

First of all I want to thank you for your time and interest.

Sorry for this confused description of the plant. So...the unit has 2 columns. The first one which is the absorber of CO2 from Natural Gas works at 34.5 - 35 barg. The content of CO2 in NG is about 30% mole, and I have to reduce it up to 3 % mole of CO2. After 1st column (absorber) follows a flash drum where the pressure is reduced up to about 4 barg. Next, the feed with the most amount of CO2 absorbed from NG (let call it Riich Amine) passes through a heat exchanger (for preheating) and in the last, preheated Rich Amine enters in the 2nd column. The 2 column is the column where is removed CO2 from amine solution and finally we get a fresh amine solution for recirculation. So...here in the 2nd column (let call it amine regenerator) I have to get 3.1-3.3 barg for CO2 in the top of the column. It means that in the bottom I have to have about 3.4 - 3.5 barg, and at this working pressure, the boiling temperature for amine solution is about 148 - 150 C which exceeds 125 C. Because of that I'm afraid of amine degradation solution because as far as I know, the maximum working temperature for amine solution is about 131-133 C.
So mrs ASPETMAN this is a short description of the process.
Now my question is how can I regenerate amine solution so that to avoid degradation of amine solution. Also I'm not mandatory on the amine solution I'm going to use. I also can use any amine solution (MEA, TEA, MDEA), not mandatory DEA, but as far as I know the maximum working temperature for the most amine solution is somewhere about 133-135 C.

Another thing, when I say amine solution I mean a mixture between DEA and water. I want to specify that I haven't used another type of amine mixture so far.

[alex.gutu]

Dear MOBEK,

have you any experience in amine treating unit using MDEA. Amine in simulation if amine units using MDEA. What is the degradation temperature for MDEA and which are the recommendations for MDEA about the working temperature.
Is there possibility that working to 3.5 barg to get a degradated amine solution because of high temperature.
I understood from you that MDEA is very selective for H2S, but unfortunately I didn't understand what is your opinion of MDEA solution regarding CO2. Could I reduce the content of CO2 from 30% mole up to max. 3 % mole using MDEA? What is your opinion?

About a mix of amine solution there is no problem to use it. I'm not mandatory on using specified amine solution.
Thank you mr. MOBEK for you attention

Kindly,
A.G.

[Andi]

Dear Alex,

Until recently, bulk removing CO2 and H2S (acid gas) using amine solution is best for economic reason, and the consideration of working temperature of amine in the bottom of amine regenerator/stripper is set to prevent degradation, since degradation amine could form and built corrosive material that make corrosion, foaming and other difficulties in system.
so the maximum operating temperature of amine solution is about 133 to 135 degree C (right as you've mention before).
You are right to set the flash drum as low as possible ( range 4 to 6 barg) that acid gas could flash decreasing the load CO2 in rich amine solution, also, rich amine still could reach flowing across into Regenerator Column above without additional pump.
If you use 133 - 135 C as operating solution temperature, so the top of column pressure could be about 0.5 to 1.8 barg ( less than 3.1 barg you supossed).
If you have a unit with downstream pressure requirement 3.1 or above, this we need additional small compressor or blower to slight increase the acid gas pressure of outlet regenerator (after gas-condensed/liq separator).

[alex.gutu]

Dear Andi,

Let me thank you for your remarks. I 100 % agree with you, but exactly this part I want to avoid, I mean to use a compressor to increase the pressure of CO2 after the regeneration column. You are right, this is a possibility and I took it in account, but from my point of view it is not feasible using a compressor to increase pressure of CO2 let say only for 1.5-2 barg. Because of that, I want to use a solution (not mandatory amine solution) to remove CO2 from NG up to 3 % mole and in the same time to get at least 3-3.3 barg in the top of regeneration column and whiout any problem of degradation of amine solution.

I just want to ask what other types of solution I could use so that I could regenerate the solution at a boiling temperature of 3 barg without problem of degradation.

Thank you all.

Kindly,
A.G.

P.S. Andi, I didn't understand your approach regarding "also, rich amine still could reach flowing across into Regenerator Column above without additional pump". Could you explain more exactly what do you mean (using another words), please.

[Andi]

Dear Alex,

Regarding "also, rich amine still could reach flowing across into Regenerator Column above without additional pump",
I mean : rich amine from absorber with high pressure is flashed in flash drum column to release some acid gas and hydrocarbon gas by lower pressure. The setting pressure of flash drum is made such that the rich amine flash drum out to overcome obstacles in the piping, lean rich exchanger, valve and against the head so as adequate to enter into the feed nozzle regenerator column as its should be.

[mobek]

No; but, i designed MEDA systems for a more complex applications than biogas.

mobek,
Any experience with use of MEDA in Biogas H2S removal?
MEDA from BAIF/shell is supposed to be better?

[mobek]

one of the units i designed using MDEA the regen tower bottom temp. was 128 C. @1.3 barg. The BP of MDEA is ~247 C.

Again, MDEA is the best amine for removing H2S but the worst for removing CO2. Why don't you consider a mix of amines or two treating stages?

Dear MOBEK,

have you any experience in amine treating unit using MDEA. Amine in simulation if amine units using MDEA. What is the degradation temperature for MDEA and which are the recommendations for MDEA about the working temperature.
Is there possibility that working to 3.5 barg to get a degradated amine solution because of high temperature.
I understood from you that MDEA is very selective for H2S, but unfortunately I didn't understand what is your opinion of MDEA solution regarding CO2. Could I reduce the content of CO2 from 30% mole up to max. 3 % mole using MDEA? What is your opinion?

About a mix of amine solution there is no problem to use it. I'm not mandatory on using specified amine solution.
Thank you mr. MOBEK for you attention

Kindly,
A.G.

[alex.gutu]

one of the units i designed using MDEA the regen tower bottom temp. was 128 C. @1.3 barg. The BP of MDEA is ~247 C.

Again, MDEA is the best amine for removing H2S but the worst for removing CO2. Why don't you consider a mix of amines or two treating stages?

Dear Sir Mobek,

Could you tell me please what type amine mixture would you recommend to me? I'll appreciate it very much and I'll try to use it in simulation to see what can I get using amine mixture.
If you don't mind you could recommend more than just one amine mix, in case I can't get what I expect with 1st amine mix.

Thank you Mobek.
Kindly,
A.G.