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[aanita]

Due to some recent operating parameters change in a MDEA based gas sweetening plant ( where regenerator top temperature reduced from 104 to 94 Deg. C) , reflux flow reduced a substantial amount. All others parameters are within the design limit. I want to know whether it( low reflux flow) will affects in the regenerator column internal in the corrosion point of view or other aspects. Any references or others plant operating parameters references are highly welcome.
Thanks in advance.

[Art Montemayor]

Aanita:

I have not used any reflux on an Amine CO2 Stripper whereever I could. I did this initially many years ago and it worked so well that I never went back to employing a reflux stream on the Stripper - as many Engineering & Construction companies design for. I did this based on practical, hands-on experience and also based on the theory of what is happening inside the top section of the Stripper.

A stripper is supposed to be designed to literally "flash" the majority of the non-condensable gases at the top plate (or section) of the Stripper. This is the main purpose of a Stripper --- that is why it is rightfully called a "stripper". It is meant to "strip" the incoming solution of its gases.

Therefore, I ask myself, why employ a distillation column technique - such as a reflux - to a stripper? What is the function of a reflux stream? A reflux stream is meant to ensure the purity of the overheads, condensable vapor that is emitted from the top of the column and into an overheads condenser. In an Amine Stripper, the overheads, condensable vapor that is emitted is nothing more than a mixture of primarily water vapor and acid gases --- plus a small quantity of amine vapor in equilibrium with the water. I have found in the field that any reflux sent back to the top of the Stripper did nothing to affect the quality of the acid gas - but did reduce slightly the amount of amine in the overheads.

My main purpose on analyzing the use of reflux was to find a much better use for the resulting high-water content of the condensate collected after the acid gas cooler. I mainly wanted to reduce amine losses --- especially Monoethanolamine (MEA) -- because this represents a goodly quantity of the operating costs and it polluted (or contaminated) the downsteam gas stream coming out of the amine absorber. I designed a packed bed on top of the main absorber beds to receive the condensate from the acid gas cooler and distributed this water-rich liquid over the packing. The result was an immediate reduction in amine consumption (or MEA make-up). There was not difference noted in the Stripper operation; everything in the Stripper-reboiler section went on as usual. The employment of the wash water on the exiting stream out of the absorber was not only a cost and process benefit, it also returned the water fluid back into the amine circulation system where it belonged. Since that time, I have found out that I am not the only one who challenged the use of Stripper reflux and won; others have done the same and some have written articles about it. I advocate this type of amine unit operation whereever it is possible. Now with the advent of possible "CO2 capture" processes in the planning, I highly recommend this type of design when using MEA. I know from personal field experience that the emission of absorber outlet gases into the atmosphere will result in a "fog" - in which will be found practically all the MEA consumption used in the unit. This fog is very, very difficult to break up and I know of no one who has eliminated it. The point here is that MEA content in this nitrogen-rich waste fluid is easily detected with the human nose and, therefore, will be a large environmental issue. Water-washing this waste stream with condenstate will reduce the MEA expelled and reduce contamination.

Anyone who has run an amine unit and can defend the use of Stripper reflux in the basic design is free to comment on this issue. I welcome any arguments for justifying its use in the Stripper rather than anywhere else.