15 replies to this topic

[J_Leo]

Dear there,

 

We have an Amine Sweeting Unit in a LNG project. BASF activated solvent is used. They gave us the design already, using 40 wt% MDEA/Activator, with 60wt% water.

How to check if their design is optimized? We cannot just take their design without any confidence in it.

Based on the molecular weight of lean amine, I guessed PZ concentration, assuming the solvent is MDEA + Piperazine + water

I am trying to use promax to simulate the process. How many theoretical stages should I use for the absorber and stripper? How can I get HETP value for the towers?

 

Thank you

 

Best regards,

Leo

[Bobby Strain]

I don't think you have the data, experience, or skills to verify BASF design. You paid them good money for their knowledge. Use it.

 

Bobby

[J_Leo]

Thank you Bobby. I have been assigned the job to do it.

 

 Anyone had the experience to veryfy BASF design? Was it successful?

 

Regards,

Leo

[RockDock]

Hi Leo,

 

Yes, this is doable. You need to look out for your interests. BASF's job is to sell you solvent and meet their performance guarantee. They would like to do that the easiest and most profitable way possible. I see many plants that have been oversold on their amine units because they either do not have the ability to check it, or are unwilling to. I recommend modeling it. BRE will be able to help you do it. They will find the right concentration of piperazine and verify the design.

 

As Bobby mentioned, you don't have the expertise to do it. Find another independent source to do it, such as BRE. They may even do it for free if you use their software. They have helped me with similar work, all for free because our company uses their software.

[Bobby Strain]

I have licensed many such systems for LNG plants from BASF. They do give you a reliable design. Just make sure you see the details.

 

Bobby

[J_Leo]

Dock,

 

How close can the BRE guy get?  I have been doing it fow a few weeks now.  It seems impossible to match both the composition and temperature profile.

[RockDock]

Leo,

 

I've seen them get pretty close. I think they must have a database of these solvents, or something. It can't hurt to ask them. I've gone to them with both BASF and Dow solvents before. Been happy each time. From what I understand, DEA and piperazine may both be used as activators. They may even use phosphoric acid.

 

There was one LNG plant in particular that BRE matched exactly with a mixture of MDEA and piperazine. I can't say I remember if it matched the temperature profile in the absorber (can't remember), but the sweet gas composition, solvent circulation and reboiler duty all matched.

 

Good luck!

[J_Leo]

Dock,

 

Thank you very much for the info. I have another question, for BASF solvent you used, is there anything else beside MDEA, PZ and water?

 

Thanks

[RockDock]

Leo,

 

For the LNG plant I mentioned above, it was just MDEA, piperazine and water. However, that does not mean DEA is not in your solvent. Your case may be different.

[J_Leo]

Dock,

 

Thank you. It was said aMDEA. The lean amine molecular weight they provided was aounrd 27.6.  If based on 60 wt% water, the biggest possible MW of the solvent is 27.28 when PZ is 0 wt% and MDEA 40 wt%, with MW = 119.17 for MDEA,  MW = 86.14 for PZ. MW for DEA is smaller (105.14), so there has to be something heavier than MDEA if water is truely  60wt% to make a lean solvent with MW 27.58.

 

Or water is less than 60 wt% in the mixture.

[J_Leo]

Dock,

 

I have sent you a private message. Would you please check your message?

 

Thank you!

[RockDock]

Water  wt% will be less than 60% until additional water is made up. Where is the makeup water being added? The Water wt% is less than 60% upstream of the makeup water.

 

It is a good point about the molecular wt. 

[J_Leo]

Dock,

 

I added water to the top of the absorber (1 st stg). I used one theoretical stage for the actual three water wash trays. It is easy to make one case match because I can easily add or delete ideal stages to meet the target CO2 in the sweet gas. It is diffcult to make all cases match by keeping the tower internals fixed.

[Bobby Strain]

It is like looking for the lost coin in the light.

 

Bobby

[RockDock]

You are right that you need to fix your tray numbers. I can take a look at your model, if you like. Feel free to send it to me.

[J_Leo]

Dock,

 

Thank you very much for your kindness. Check your private message