Dear Clem >Question: What does preheated air do to an already burning charcoal mass? Clem
Good question. When burning a high carbon fuel like charcoal it is important to keep the temperature of the gases coming off the fuel as hot as possible in order to burn as much of the CO as possible. CO is difficult to light if it is below 850 degrees. The concentrating ring or cone used in many stove designs tries to bring any available flame together with all smoke (which includes CO) do one lights the other. This is easier to accomplish if the general environment is hot. It is important that, if adding secondary air, it be preheated. What matters is that the resulting mix have a minimum temperature, not that the heat come from a particular source. Preheating primary can badly affect some fuels unless the air supply is restricted. It tends to over-produce gases from light biomass briquettes unless it is very restricted. High carbon and dense fuels benefit from having the primary air preheated because it harder to get them to make combustible gases. Choked, hot high carbon fuels make rich CO and burn very cleanly if the combustion region is kept hot. The worst case is to make a good high CO gas which is vented into a heat exchanger which never gets hot. That pretty much guarantees high CO in the final mix. Many stoves that appear to be burning with low smoke have too small a region above the primary combustion for the flame to finish burning properly. It is typically the chilling of the half-finished burn that looks clean but is high in CO. If the gas flame from charcoal of a gasifier does not have at least 50mm (usually 100 is needed) for flame space, it will not complete the burn and have high CO. By flame space I mean the distance from the beginning of the flame and the bottom of the pot or heat exchanger. If you see flames running along the bottom of a pot, or exiting into the air, you will know it has high CO. Regards Crispin _______________________________________________ The Stoves list has moved to [email protected] - please update your email contacts to reflect the change. Please visit BioEnergy Discussion Lists http://info.bioenergylists.org/ Thank you, Stoves Administrator http://stoves.bioenergylists.org http://info.bioenergylists.org UNSUBSCRIBE HERE; http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
