CO2 Removal

[ElectricMech]

Hello,

I have a gas stream that has 12% CO2 in it. I need to knock it down to pipeline quality (2%). The recommended method based on the GPSA is to use Amine. However it has been requested that I try to use a physical solvent. I dont know if it is even possible to do so. Can anyone point me to a reference that would indicate the benefirs of one versus the other. I know that with a physical solvent you can sometimes lose some of the volume of the gas product and with and an amine unit is more costly than a simple scrubber. Also, I have heard that a Glycol-Amine process would be a great solution. I have to create a unit for dehy so if I could do both at once that would be better. Any references on that would be great.

Thanks in advance for the attention.

Gela

 

[JJPellin]

We have a hydrogen plant that uses Benfield solution to remove the CO2 from a stream of hydrogen. Benfield solution is selective enough at removal of C02 that we capture the (almost) pure C02 stream, liquefy it and sell it for food service uses. I am a machinery engineer so I have no idea how the chemistry of Benfield solution differs from the other options you mention (or if it really is different).

 

[dcasto]

There are several solutions to your treating problem, to find the most economical one requires understanding of all your choices. You have looked at the GPSA book and saw almost all of the typical solutions. Heres the data that you will need to gather before you look at any solution.

Volume of Gas
Presure of gas
Presence of other contaminates that need removed
Gas composition
Environmental regulations and permit requirements
Other adjacent process that could supply synergies


For example, we have facilities with some of your listed conditions,there are large volumes and the gas is medium pressure. A combination of membranes and formulated amines that act like physical solvents and reactive agents.

I will warn you, you will have some treating problems because of the high CO2. There will be a heat build up (temperature bulge) in most contacting situations that will need some consideration.

If you need some help, most chemical suppliers will be glad to discuss with you even before you engauge an engineering design firm.

 

[ElectricMech]

Thank you for your responses. I did speak to a couple of membrane unit suppliers and they all agree that there is too much CO2 to get out without taking Methane along with it. There must be less risk of losing methane with amine.

 

[dcasto]

The reason the membranes worked on the system I listed was: It was a multistage system and we could blend one stage into fuel into the compression and recycle another stage into compression. So the combined system worked. It was a real rare fit. Thats my point, lots of solutions. If the volume is small, keep it simple used a mixed amine.

Yes, the methane losses with amines and solvents are lower.

 

[djack77494]

With the large concentration and, I presume, large gas volumes, a continuous adsorption/regeneration process is likely the way to go. There are various amines as well as potassium carbonate/bicarbonate (Benfield) sorbents that have been used successfully in similar applications. I can't imagine any other approach unless my assumption about large volumes is not correct. If that were the case, a throw-away solid adsorbent might work.
Doug