> My understanding of their > pressure cooking method is that it is possible to produce anthracite. > Surely this is not possible via pyrolysis or torrifaction? Not even > bitumin?
If you cook or just plain heat longer or hotter, as a general rule you'll get a solid product that is richer in C and poorer in O. That can nicely be plotted on the van Krevelen diagram, eg (see slide 6 of 10) and results in the same trend as for peat/bituminous coal/ anthracite: http://www.thermalnet.co.uk/docs/ECN_%20Torrefaction%20of%20Biomass%20as%20pretreatmentLille.pdf As for their product being exactly like coal otherwise, they say: http://www.mpg.de/english//illustrationsDocumentation/multimedia/mpResearch/2007/heft/pdf23.pdf "The product is brown or black, feels exactly like coal and has the same calorific value and many of the same chemical properties as fossilized coal. There are, however, some characteristic differences. For example, the nature of the carbon bonds is more aliphatic and there are only a few aromatic moieties. Furthermore, vegetable carbon is more chemically reactive and has an open, porous structure. ... If the bound carbon were to be considered for use as a means of improving the soil in the natural environment, the lack of biodegradability is obviously something that would need to be quantified." > I doubt that it is more expensive to produce in > quantity than biochar or torrified wood. Also as a general rule the longer and hotter you cook or heat, the more expensive it gets, and the less energy remains in the solid product. ECN don't just do torrefaction (heating to around 250C in the absence of oxygen), but also something called torwash (heating to around 200C in water under pressure). The latter is clearly more costly (due to the requirement for pressure vessels) and is intended for difficult feedstocks with a lot of ash and plenty of moisture to start off with. Residence time has a very direct impact on cost, having to heat something for 12 hours rather than 12 minutes means the same equipment will handle 60 times less material (or respectively you need to build something 60 times as big to handle the same throughput of biomass)! For cheap equipment that's not a problem, but for pressure vessels that need to be built to stand a potential thermal runaway and consequent explosion ... > With regard to natural coal persisting due to an anerobic environment, > I now do not think that is a requirement. I know of a site with > anthracite only a few centimeters under the soil. Paleoamericans used > the anthracite for heat, leading to a very wrong radiocarbon date! This sounds like a good argument for why charcoal (form forest fires and the like) is more biodegradable than anthracite. I must say that I've only got educated guesses for the issue of very long term biodegradability in soils. For torrefied biomass we are interested in whether it'll biodegrade when stored outside in large heaps for a few months or years and that sort of thing. This is a very different question from intimate soil contact for thousands of years. I would guess that fine distribution might matter, because bacteria living in anthracite might have to live from anthracite alone, while a bit of charcoal in soil would allow bacteria to crunch on the carbon as a little extra. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/globalchange -~----------~----~----~----~------~----~------~--~---
