Thank you Glenn for passing this email along. I work on this topic. Biochar, as char and most carbon-rich solids, is a reactive material prone to self-heating. If self-heating goes uncheck, it leads to fires. Some people refer to self-heating as "spontaneous combustion" referring to the spontaneous ignition of a reactive material that then start to burn with or without a flame (flaming or smouldering combustion).
As we speak, I am conducting experiments in my new fire lab on the reactivity of char and biochar. You can read a bit more here: http://www.scribd.com/doc/61065720/Very-long-term-sequestration-of-solid-carbon-Geo-Engineering-facilities-for-biochar-storage Cheers G. Dr Guillermo Rein Senior Lecturer in Mechanical Engineering, Imperial College London, SW7 2AZ http://www.imperial.ac.uk/people/g.rein "Knowing is not enough, we must apply. Willing is not enough, we must do" JW von Goethe From: Glenn Stracher [mailto:[email protected]] Sent: 25 February 2013 13:52 To: Paul Anderson; Discussion of biomass cooking stoves; Crispin Pemberton-Pigott; Harold Annegarn; James Robinson; Hugh McLaughlin; Bob Fairchild; [email protected]; Luke Iseman Cc: Rein, Guillermo; [email protected] Subject: RE: [Stoves] combustion of char -- spontaneous and dangerous Hello Everyone, I'll forward your chain of comments to Dr. Guillermo Rein, a Mechanical Engineer that specializes in spontaneous combustion experiments and Fire Safety Engineering. Here's the contact information for Guillermo: (1) Dr Guillermo Rein Senior Lecturer in Mechanical Engineering Imperial College London E-mail: [email protected]<mailto:[email protected]> http://www.eng.ed.ac.uk/~grein (2) Dr Guillermo Rein Lecturer in Mechanical Engineering Royal Academy of Engineering/Leverhulme Trust Senior Research Fellow BRE Centre for Fire Safety Engineering http://www.see.ed.ac.uk/~grein School of Engineering The University of Edinburgh Email: [email protected]<mailto:[email protected]> Tel: +44 (0) 131 650 7214 http://edinburghfireresearch.blogspot.com I'll also forward your comments to Dr. Mark Nelson, a mathematician that has done a lot of theoretical work with spontaneous combustion. (1) Dr. Mark Nelson School of Mathematics and Applied Statistics University of Wollongong Northfields Avenue, Wollongong, NSW 2522, Australia E-mail: [email protected] Phone: (02)-4221-4400 Fax: (02)-4221-4845 Regards, Glenn B. Stracher Glenn B. Stracher Professor of Geology and Physics East Georgia State College Swainsboro, Georgia 30401 USA Web Address: http://faculty.ega.edu/facweb/stracher/stracher.html Elsevier Coal and Peat Fires: Volumes 1 and 2 of the Four-Volume Book<http://faculty.ega.edu/facweb/stracher/V1%20and%202%20Coal%20&%20Peat%20Advertising.pdf> Elsevier Coal and Peat Fires: Microsite<http://www.elsevierdirect.com/brochures/coalpeatfires/index.html> Elsevier Coal and Peat Fires: Interactive Online World Map<http://www.elsevierdirect.com/brochures/coalpeatfires/onlinemap.html> Geological Society of America: Geology of Coal Fires<http://faculty.ega.edu/facweb/stracher/GSACoalFires.pdf> From: Paul Anderson [mailto:[email protected]] Sent: Saturday, February 23, 2013 1:42 PM To: Discussion of biomass cooking stoves Cc: Harold Annegarn; James Robinson; Glenn Stracher; Hugh McLaughlin; Bob Fairchild; [email protected]; Luke Iseman Subject: Re: [Stoves] combustion of char -- spontaneous and dangerous Dear Stovers AND to all who make biochar or TLUDs with char-saving. The two messages below are very important. And they lead to asking this question: When the quantities of char production are small, such as from a domestic-size TLUD stove, or from a biochar barrel (as with RE:Char), does this danger of spontaneous combustion pose a threat to households, etc? Because Frank's experience was with a small sample of char, I suspect that the danger to households could be very real!!! Therefore, what are the correct and incorrect ways of dealing with TLUD chars that are being saved and stored? It is interesting that no stories of spontaneous combustion in stored cookstove TLUD chars have reached us. How big is this danger? Paul Paul S. Anderson, PhD aka "Dr TLUD" Email: [email protected]<mailto:[email protected]> Skype: paultlud Phone: +1-309-452-7072 Website: www.drtlud.com<http://www.drtlud.com> On 2/23/2013 2:49 AM, Harold Annegarn wrote: Response from Harold Annegarn I make reference not to char, but to coal. Perhaps the same will apply to freshly prepared char surfaces. The following information arises from the phenomenon of spontaneous combustion in underground coal and in coal slag heaps. Exposure of freshly broken coal surfaces, or in situ coal that has been in water filled voids that is subsequently exposed to air (oxygen) (as occurs when previously mined areas by bord & pillar extraction is exposed by strip mining) results in a chemical reaction known as oxysorption ==> oxygen reacts with carbon/carbonaceous matter at the surface of the coal in an exothermic reaction that results in the oxygen being absorbed into the chemical structure of the coal without necessarily being emitted as CO.. This oxysorption can occur at room temperatures and does not require elevated temperatures or a spark to start. Thereafter, basic physics applies: if thermal energy is released from a chemical reaction, that heat is either conducted, convected or radiated away. If the rate of production is faster than the rate of dissipation, then the temperature will rise in the zone where the oxysorption is taking place. The balance between conduction, convection and radiation may change as the local temperature increases; likewise the reaction rate will increase. There must be some convection possible, otherwise the available oxygen will be consumed and the process will stop, If the local convection is large, then the surface remains cool and the reaction proceeds without large temperature rise. If the convection is limited, local temperature will increase, and eventually may reach the point where volatile matter that is driven off reaches ignition point, i.e. spontaneous combustion has commenced. It is not a matter of whether spon com occurs, it is just a matter of when. For this reason, modern practise of stockpiling coal discards and fines requires continual compaction of the surface to limit air ingress, and final sealing of surfaces with a meter or more of soil. Although I I have not read anything about oxysorption on char, it is logical that similar processes are occurring, The char is a freshly prepared surface with high specific surface area due to the voids created by driving off volatile material, and with many dangling bonds at these surfaces. Not for nothing is this material also known as "activated charcoal" with good properties for absorbing ions e.g. from water for water purification. . To test this it would be possible to char wood in a dry nitrogen or helium stream, although this would result in a different surface chemistry than if the same material is passed through the same heating cycle in the presence of oxygen. If the material is then cooled, and placed on a balance with automatic recording, the the change of weight with time can be recorded. If this is done in a closed system, with dry air passed over, then one could isolate the effect of oxygen absorption from the absorption of H2O from the atmosphere if this was done in open laboratory air with variable relative humidity. In the case of the spontaneous combustion accident described by Frank Shields, it appears that the raising of the temperature to just over 100 degrees C assisted in creating a heat generation rate and oxygen supply to the char samples that allowed the oxysorption to proceed to the point at which full ignition commenced - yes, he is lucky to have a lab still! I have copied this message and thread to Glenn Stracher, an expert on spontaneous combustion on coal, who has a much deeper understanding of these matters than the qualitative handwaving that I have given above. Best regards Harold On 23 February 2013 03:43, Frank Shields <[email protected]<mailto:[email protected]>> wrote: Stovers, FYI After having about 30 compost samples in a drying oven go up in flame it looked like it started with a single char sample placed in the corner. I decided to do a little research by asking Hugh McLaughlin. Another question I had for him was why does some biochar samples gain weight in a drying oven set at 105c. So it seems soon after a char is produced it wants to take up oxygen. If bagged in a sealed container and sent to the lab soon after being made the dry sample will take up oxygen in the oven therefore gaining weight. If a sample is wetted soon after being made the water prevents oxygen from being taken up. Then if it becomes dry it wants oxygen, increases temperature and can catch fire under the right (wrong) conditions. Char is a great insulator so the heat can be trapped and build up. If there is organic materials around it can flame. So before storage better give it time to take up oxygen. Or if wetted do not let it dry out and keep bags of char in single layers. The forced air drying oven was left on overnight and it was in the morning we found all the burned up samples. It was placed against the wall so we are lucky we still have a lab! Regards Frank _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected]<mailto:[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/ -- Harold Annegarn Department of Geography Environmental Management and Energy Studies University of Johannesburg Mobile +27 (0)83 628 4210 Fax +27 11 559 2430 Office +27 11 559 3927 _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected]<mailto:[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/
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