Does anybody have any experience of using mixed amines, i.e. DEA+MDEA, for sweetening? I am interested in operational problems like foaming, sludging etc related to mixed amines treatment.
Answers
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18/10/2010
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Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
When swapping over from DEA to MDEA, some mixing can occur, but running a DEA/ MDEA blend in long term is not commonly done for several reasons. It's not so much issues with foaming or sludge that you are concerned about. DEA is typically running at up to 30% strength, and MDEA up to 50% strength. As MDEA is having the lower heat of reaction (lower reboiler duty), the problem comes with regeneration as MEA and MDEA will generally have different reboiler set points so that becomes difficult to manage. If set up for optimum MDEA regen, DEA won't be regenerated properly. Likewise, if reboiler run hotter to accommodate DEA regeneration, then MDEA thermal degradation could be expected to somewhat faster, plus of course it is not so energy efficient as more energy is being expended to regenerate the MDEA than is necessary. Bear in mind that typically 70% of amine plant running costs is energy usage and this is one of the main advantages of MDEA over MEA. plus the lower corrosiveness of MDEA which provides the ability to run at higher amine concentrations.
With respect to foaming issues; regardless of if it is DEA or MDEA or a blend, we'd recommend 2 things:
i) Clean amine doesn't form stable foam. So filter your amine loop properly with 10-20um absolute ratad filters (99.98% rated) at at least 15-20% or better still full flow amine filters. Rich side filtration tends to be better to do too. Don't employ bag filters , strainers, metallic or AC filters to try and clean amine loop. Pre-coat filters or backwash filters are not well suited to maintain TSS levels <5ppm either. Ideally TSS level should be <1 ppmw for stable amine plant operation.
ii) Keep liquid hydrocarbons out. Employ high efficiency SepraSol Liquid Gas coalescers on inlet to amine absorbers. KO pots / mesh pads, horizontal filter-seps are often not able to remove aerosol sized droplets of HC's effectively. Even small amounts of liquid HC carryover can cause foaming. It's even worse if the amine is dirty too as fine particulates in the amine stabilises foaming and the foaming event can be a lot more severe & prolonged. If there is multiple contactors, or HC ingress source is unknown, then PhaseSep Liquid Liquid coalescers can be used to remove liquid hydrocarbon from lean amine after the flash tank before the lean-rich exchanger.
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17/10/2010
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Egbert van Hoorn, Hocon B V, Egbertvh@hotmail.com
Likely there are quite a few people with this experience. Some may not know it.
In answering your question, it would be helpful if you can give us a brief background of the reason for the question. This helps to focus the answer.
Anyhow, these are a few things which may help (if you have a problem).
A mix of MDEA and DEA is mostly used for enhanced CO2 removal.
It is an old (outdated) technology, which works but has some drawbacks.
Degradation of the DEA is an important one.
For H2S removal in oil refinery service the mixture is just a sales talk.
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