2 replies to this topic

[siretb]

Hello,
I would like to know to what extent, oxidation is going to be a problem with amine scrubbing (and recovery) with the following system
flowrate: 100000-200000 Nm3/hr (t ref=0°c Pref=101 kPa)
composition O2 9%, CO2 9%, H2O 14% N2: 68% (mole %)
In fact I am wondering whether, with such composition, it would make sense to attempt to recover CO2.
The choice of amine candidate is not made (MEA, MDEA, .....).

Could anyone provide an educated guess as to the amine losses, due to oxidation? I have found figures in the range of 1.5 to 3 kilos/ton CO2, but I think it's only relevant for O2-lean mixtures. Thank you.

[Art Montemayor]

siretb:

You are basically correct in following your engineering logic and sense. I achieved an average of 1 kg MEA consumed/ton of Liq. CO2 produced in one of my Lima, Peru CO2 plants in 1966. That was a record and it was thanks to having an outstanding and meticulous plant supervisor. This happened within the company I worked for at the time - Liquid Carbonic - and I never heard of anyone coming close to matching that consumption figure in the remaining years till now. I designed my MEA absorber to employ cool Stripper condensate as a water wash on the top, exit stream. We analyzed before and after and saw the difference.

Your analysis seems to be the flue exhaust from a power plant or a turbine exhaust. I wouldn't apply any Amine to this gas stream. Maybe Hot Carbonate would do it - but if evaluated on an economic level, that's another totally different thing. I'm presuming that you are debating recovering the CO2 on a competitive, economic basis. If that's the case, you've got a rough row to hoe. The 9% Oxygen content is going to eat your absorbing solution's lunch if you use an Amine.

I've made various studies and participated in several projects to recover CO2 from many sources. Power plant flues was one "attractive" application. The costs, even from a purely conceptual level, were very high and not competitive. However, this was mainly due to the cost of steam requirements on the solution's reboiler load as well as the compression and refrigeration loads. This is bad enough on its own without having to put up with solution degradation and consumption due to oxidation effects. In my experience, you shouldn't apply any amine to a gas stream with an excess of 0.75% O2. There are other absorbing solutions besides the Amines - however, they start to cost in licensing fees and other factors.

With a source potential of 25 tons/hr of CO2 you've got to be very careful - as you are doing - in selecting a viable absorbing solution and regeneration system.

I wouldn't take an educated guess on your Amine losses in a 9% O2 gas stream; I know they would be astronomical, but more importantly your solution would have a very, very short life - as well as that of your related equipment - unless you construct using special Stainless steel alloys. And even then, your stainless alloy may fail under the degraded, acidic amine solution in your heat exchangers and in the Stripper reboiler. It would be a real mess! Recovering CO2 from other sources - such as chemical process, ammonia plants, and fermentation plants is much easier and more benign to design and operate - economically.

I hope my experience is of some aid to you, albeit the message is not a happy one.

Art

[siretb]

Thank you,
I am going to have a deeper look at the carbonate or carbonate/piperazine. I fear that the overall mass transfer coefficient will be much lower and that the towers will be too high, at least without piperazine. And piperrazine will also suffer from degradation.
Your post was helpful, and you confirm another worry of mine: corrosion. Have a nice day.