On Sat, 25 Feb 2012 09:19:55 -0800, Tom Miles wrote: > >about 285 C which is supposed to be the magic temperature for torrefaction. >When you modify the cellulose and hemicellulose the plastic flow of the >lignin is not as complete so you do not get thorough bonding. I suspect that >producers will find a slightly lower temperature that will provide the >pellet quality but still be more than over-dried wood.
Tom do you know if lignin is thermoplastic or sort of thermosetting? I ask because we were told that when steaming wood to bend it and keep the set bend would only work once. Also lignin is a large polymerised macro molecule, could the higher temperature rupture some bonds. It certainly makes sense to bring all the sawdust up to a plastic state before the die to save mechanical energy in crushing the cells. Pellets leaving the die with cold sawdust often are charred on the outside so with a higher temperature as a starting point how black do they emerge? Is the die taper different to allow for the less effort needed? Presumably the compression the wood particles undergo remain the same. With work being force times distance and the distance remaining the same the lower force needed for pre plasticised wood would be evident in lower power requirement. Has any work been done on the temperature distribution across the cross section of a pellet as it is extruded? Difficult to see how but it would be interesting to know how much heat was either generated in the middle by the crushing or conducted in from the friction of the die surface. Not really relevant for cook stoves because of the high price demanded for pellets, in UK they are about 4 times the cost of cordwood on a dry weight comparison. AJH _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org for more Biomass Cooking Stoves, News and Information see our web site: http://www.bioenergylists.org/
