Low pressure Amine plant design 1

[Jency]

Hi,

I am just working on an sour gas treating project.The problem is the inlet sour gas is under very low pressure situation (65psig @120F)and the composition of the gas is also light ( the heavist component is C3).I am not confident for this simulation, Although I can run it using Hysis. Did anyone have worked on similer cases before? Is it realistic to run under such low pressure and high temperature condition if the flowrate is just 25000Sm3/day? I need some idea about it and some reference. Thanks for your advice .

 

[Montemayor]

Jency:

As a ChemE, you've got to be specific. What do you mean by "sour gas"? Are you dealing with removing both H2S and CO2 at the same time with the same absorbing solution (presumably an amine - MEA?)?

To answer your general question: Yes, it is more than possible to remove acid (CO2) gas and sour (H2S) gas from a hydrocarbon gas stream. It's been done many, many times using MEA, DEA, DGA, etc. Depending on the ratios of the composition and the total components, it has been successful. On other applications, the H2S consumes the MEA irreversibily. The literature (especially Hydrocarbon Processing) and text books are full of specifics on the application. During the 1940's, 1950's, and 1960's the Girbotol Process was a mainstay in doing this at 35 psig to 100 psig and 100 - 110 oF. I personally have designed, built, and operated CO2 removal units using 12% MEA in absorbers with 14% CO2 in the inlet gas at 100 oF and 24" W. C. pressure - essentially flue gas (and I did it with hand calculations - no computer simulation programs). That's how low the pressure can go and still successfully remove the acid gas. The same can apply to the sour gas component -- except if you are dealing with Carbonyl Sulfide (COS). That will kill the Amine.

The process is easy. The experience is hard to get nowadays and this is probably what will determine the complexity of the application. The Materials of construction, the corrosion control, the instrument controls, the solution regeneration, the solution concentration, the solution purification (redistillation), etc. will be the key elements in applying the technology - not the computer simulation program. As you will (or already have) find out, neither Hysis, Aspen, SimSci, or any other simulation program will tell you or guide you on how to REALLY design the process - especially the mechanical components. All these simulations do is tell you the theoretical heat and material balance with an approximation on the diameter and height of the towers as well as an estimation of the heat transfer surfaces. No one in his right mind would invest money and build a process under the sole direction of a simulator. You need an experienced and proven process/mechanical engineer who has done it and operated such a unit.

I hope these comments are of some help.

Art Montemayor
Spring, TX

 

[Jency]

Montemayor,

Thanks for your comments. I do need to get rid of H2S and CO2 at same time. But the main issue is 4000ppm H2S.I got just 2.5%CO2 in the stream.

For this small amount gas (5000Sm3/day-25000Sm3/day). Is the amine plant an economical way to sweeten it? I am thinking a altinative process to get gas specs down to less then 60ppm. Do you have some advice?

Thanks

Jency