Baghouses alone don’t automatically stop aerosols reaching amine capture plants

This article is not intended to be a full review of aerosol issues for amine post-combustion capture (PCC) plants but just a quick heads-up that simply having a baghouse alone won’t automatically avoid aerosol issues.? Other measures that are associated with baghouses, Powdered Activated Carbon (PAC) injection for mercury control and hydrated lime injection for SOx control, are probably also important.? A new PCC plant on any fuel with the potential for SO3 or other aerosol formation that has, or is considering using, a baghouse and hasn’t already included PAC and hydrated lime injection may wish to consider at least providing the potential to do add these.? And apologies to any egg-sucking grandmothers who are on top of this problem and being told the obvious, please stop reading (also please make some constructive and corrective comments if you are free to do so)!

Fine aerosols in flue gases going to amine capture units can lead to very high amine carryover.? As flue gases going up the absorber pass the warmest point and start to get cooled by the incoming lean solvent at the top of the absorber they become super-saturated and any aerosol particles present will provide nuclei for small droplets to form.? Very small droplets of water and amine are not easily stopped in a water or acid wash because they follow the streamlines of the gas and don’t contact any surfaces.? So, if an amine ‘fog’ is produced, amine emissions from the absorber can be very high, perhaps several orders of magnitude or more higher than would be achieved with only amine vapour present and well-operated water and acid washes.

There are a number of absorber exit countermeasures proposed for amine aerosols but discussing these, and their merits, is beyond the scope of this article.? The alternative, with which this article is concerned, is stopping aerosols getting to the PCC plant in significant quantities in the first place.? Technology Centre Mongstad in Norway installed a Brownian filter that successfully removed aerosols after seeing problems with cat cracker flue gases, but this is a specialised unit with a relatively high pressure drop. ??The National Carbon Capture Centre in Alabama USA did not use?a specialised unit but found that their aerosol issues went away when a baghouse was added to Plant Gaston that supplies their coal flue gas slipstream.? This led to the assumption in the field that ‘baghouses stop aerosols’.

This simple link is, however, challenged by Toshiba’s recent experience with a large PCC pilot on the Mikawa biomass plant in Japan.? Despite there being a baghouse in the flue gas path this PCC unit also needs to use, apparently successfully, significant additional absorber exit washing measures to remove an amine aerosol .? Obviously fuels differ from the NCCC coal application above and the aerosols may be different (e.g. they may include condensed biomass ash species) and full details of the baghouse and its operation are not published.

Nonetheless, at least circumstantial evidence is there that some combination of additional upstream interventions, possibly providing PAC or hydrated lime particles for SO3 to condense on as the flue gas goes through the acid dew point, and the nature of the filter cake in the baghouse, with PAC, lime and coal fly ash all present, may be what is required to successfully remove aerosols when using a baghouse in combination with an amine PCC unit.? Hence the suggestion that, if they are not already there, provision to add these additional features to a baghouse installation be considered in case they are found to be necessary when the PCC plant is operated.