Dear folks, Very interesting proposals, and much appreciated. The question was prompted by the overall need to stop the heat in the firebox from reaching the foundation (made of clay) and burning it up. As we install the liners in kitchens that have been using three stone open fires we find that we have to dig a bit deeper to get below the burnt up soil in before building the foundation.
The option of a grate, whatever else it does, will definitely increase either the cost of the process or of the stove, so that is a no-go zone, for this particular stove. Also, since the installation process depends on the skills of diverse artisans scattered all over the country it means that any improvements must be 'transferable' and Vincent Okello From: Stoves [mailto:[email protected]] On Behalf Of Dr.-Ing. Dieter Seifert Sent: Thursday, January 23, 2014 3:21 PM To: Discussion of biomass cooking stoves Subject: Re: [Stoves] ash layer beneath fire Dear Crispin, Richard and Vincent, I should like to make some remarks regarding the practice in the use of a stove with a grate fuelled with thin sticks or appropriate pellets: The lighting is greatly simplified if one places igniting paper in the form of three or four rolls, crosswise to the steel bars. One can then ignite the paper rolls (with the kinlding on them) from the heating port, after having already inserted the pot. The smoke-phase is then short and heat loss is reduced. With experience one can ensure that the insertion of the sticks is stopped in time, so that the sticks burn completely and the pot contents are parboiled - but the cooking is finished in the thermos-container (haybox, haybasket) as mentioned earlier. The wood consumption may be 330 g (corresponding to 5 MJ of heat content) for cooking 6 kg of food (requiring theoretically about 1.9 MJ heat supply). Thereby a little ash (about 2 g) is produced. This method reduces the stress on the cook. A consumption of charcoal of more than 1.3 tons per year (more than 8000 kg chopped tree weight) by a household is reduced to about 600 kg of thin sticks, moreover with more comfort for all involved and less health burden. I believe that this technology is in the sense of E. F. Schumacher that is promoted exemplary through Practical Action. With kind regards Dieter Am 22.01.2014 23:51, schrieb Crispin Pemberton-Pigott: Dear Richard and Vincent Jambo. I see just about everyone found that adding a grate to a flat-bottomed stove improves the performance. RS>.I would advise use of round bars as Crispin but I would suggest you grind any round bars down to result in effectively a series of had cylinders along their length with the flat side up. I would advise the opposite and the metric to use in evaluating the difference is the mass fraction of charcoal produced by the fire. We found (for reasons that are not yet known) having a flat top definitely produces more char thus losing more heat. It may have something to do with the thermal contact the char piece makes with the metal, conducting the heat away. This lowers the temperature of the 'coal' and causes it to burn poorly or go out. There was a large mass difference for flat and round bars - more than double. The thermal contact between a coal and the round bar is much smaller. That is the only 'guess' I have so far. We will look into this further at YDD this year. The two things tried were round bars from mild steel (multiple welded pieces) and cast iron with a flat top (single piece). Cast iron conducts less heat than mild steel but it still consistently produced much more char. That is not useful as fuel in most homes and it is tossed with the ash. Indar reported the round bar grate produced virtually no char at all, finishing its burn at virtually the same time as the wood. That was amazing. You may need to restrict the air entry area to limit the air level below the combustion chamber. If it is 'right' you will see large flames wandering around in a low velocity environment below the pot - no flapping arms of flame. You should limit the pot gap (by shaping those tongues of clay) to about 7mm for all pot sizes. This means trimming the slanted ones and lowering the top ones (in most stoves). The combination gives you the right balance of primary and secondary air. Nzuri kuhusu Crispin _______________________________________________ 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://stoves.bioenergylists.org/ [http://bit.ly/10PEMC6]<http://www.practicalaction.org/> Practical Action uses technology to challenge poverty, working with poor women and men around the world.www.practicalaction.org<http://www.practicalaction.org/> [http://bit.ly/17osJ5h]<http://www.facebook.com/practicalaction> [http://bit.ly/12Eshft] <http://www.twitter.com/practicalaction> [http://bit.ly/17osOpB] <http://www.youtube.com/practicalaction> [http://bit.ly/Z5rh4c] <http://www.flickr.com/photos/practicalaction> [http://bit.ly/XpFdWm] <http://www.linkedin.com/groups/Practical-Action-2428887> [http://bit.ly/YestUa] <http://practicalaction.org/blogs> [http://bit.ly/XpFkRI] <http://practicalaction.org/get-our-e-newsletter> Support our work today [Donate online] <http://practicalaction.org/signature> Practical Action, The Schumacher Centre, Bourton on Dunsmore, Rugby, Warwickshire, UK, CV23 9QZ Practical Action is a charity registered in England and Wales, and a company limited by guarantee in England no. 871954 VAT Reg No. 880992476 | Reg Charity No. 247257. 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