Dean cc list Thanks for bringing up this issue of optimizing the geometry between the stove and the cookpot. Are you aware of anyone who has theoretically and/or experimentally determined an optimum spacing? Presumably the optimum is around 1 or 2 cm - and depends on the ratio of pot and flame diameters?
Same for optimum stove top shape. Presumably here we are returning to the issue of radiative heat transfer - trying to avoid sending rays off radially that you would prefer to hit the pot. You have done a nice job with convective skirts. Have you seen any skirt that had an outer insulating layer? Any way to optimize the geometry (separation distance from the pot, height, etc)? Ron ----- Original Message ----- From: "Dean Still" <[email protected]> To: "Discussion of biomass cooking stoves" <[email protected]> Sent: Saturday, November 10, 2012 3:38:43 PM Subject: Re: [Stoves] Cost of stoves Dear All, Let's take a moment and consider that the heat transfer side of cooking can be just as important as the combustion side (in any kind of stove). Great heat transfer means that the food cooks faster using less fuel. Great combustion efficiency means we produce less smoke, gases, etc. It takes both to make a great stove, right? For example. if the pot is 4" above the heat source the water probably won't boil, etc. Usually great heat transfer costs less money because lower grade refractory materials can be used and we're just changing the shape of the stove top/pot bottom interface. If we can expose the side of the pot to the hot gases using appropriately sized channel gaps, that's great too. And system efficiency (how much fuel is used to cook) is usually more improved by great heat transfer than great combustion efficiency. Best, Dean On Sat, Nov 10, 2012 at 10:03 AM, Paul Anderson < [email protected] > wrote: Dear Crispin and Paal and Dean and all, (Also to be posted at www.drtlud.com ) The discussion (below by Paal and Crispin) has pointed out the difference between the "combustion device" and the "stove structure", and that they can be addressed separately. TINY devices do this, such as a "Steno" can or alcohol burner (note that neither says "stove"). The heat generation unit is separate from the stove body. In general, the combustor or burner is too small to support a reasonable pot. Tiny tincanium TLUDs can be in this category. When the cooking device gets larger, the heat making aspects are generally incorporated into the stove structure, as seen in most of the Rocket stoves and charcoal burners and simple ICS. For the most part, the "stick wood" burner (combustion device such as a ceramic/brick chamber or a heavy steel box) is built into the pot-holding stove structure. For this reason, there has been little thought to having the combustion device separate from the pot holding. It is VERY common for people to see a simple TLUD making heat and then asking "where do you put the pot" or declaring "that is not a stove." Well, the pot goes above the flame, and how the pot is supported makes little difference to the making of the heat. Also, TLUDs (because they are batch operated) need to be re-filled (or exchanged) regularly, which favors having sheet metal construction because of lighter weight and not being subject to cracking like clay/ceramic constructions. Yes, there is something not appealing about moving around containers of flaming fuel or hot charcoal, but even that problem has been resolved in the TChar variations of TLUDs. (You do not know what is TChar??? Are you kidding me?? Check it out at www.drtlud.com and let me know what you think.) Anyway, Wendlebo and Reed and other early TLUD developers have been well aware that the separation of the combustion device and the stove structure has numerous advantages, of which one is related to the cost of the stove (stove = combustion device AND the stove structure). NOTE: Sometimes combustion device and pot support are intertwined such as when a chimney is important to combustion and to the stove structure, but we are not focused on that case here. Comment about TLUDs with pots on top of them: Some of the Peko Pe units, Reed's campstoves, the Mwoto Classic and Mwoto Quad, etc have small pot supports on the tops. Three legs on the ground also serve as 3 pot supports on some PP units. Three tiny pieces of metal on Mwoto stoves are the only additional "stove structure" to turn a TLUD combustion device into a complete stove. Less expensive than 3 little supports is unlikely on such stoves. But it does imply that the combustion device is large enough to support the pot on the top. Much smaller TLUDs do not support the pots well. And for institutional cookers, because the pots are so large that they are not easily lifted off of the TLUDs that need refueling, the pots need to be supported separately from the combustion device. And that is the point being made by Paal and supported by Crispin: The cost of stoves can sometimes be separated between the cost of the combustion device and the cost of the stove structure (pot support), especially in the case of TLUD stoves. Consider the example of the Champion TLUD manufactured by Servals in India. The reactor (fuel unit where gas-making occurs) can be moved from under the tripod that supports the pot and the coupling device. The same reactor could be used under other stove structures, and the tripod could be used above other reactors (fuel units). In many cases, the vast majority of the expense of a stove is in the stove structure. It is often quite visible and people want it to look pretty. Beautiful decorative tiles and useful attached working surfaces all add to the cost. Our discussion is about LOW cost stoves. Under US$10 for a complete "stove" with both a combustion device and a stove structure. A. Stove structure: make it from locally available materials, including some possible "scrap." Use some adobe or other bricks to make two sidewalls (and maybe a backside) to an appropriate height, and then horizontally place 2 pieces of rebar to support the pot. In Haiti, use rebar from some of the crumbled walls of buildings. Or weld together a small "H-shaped" grate with 2 cross pieces to become like " # ". One dollar? maybe $2? Before long, the household might plaster (use dung and clay or cement?) the sides, and even whitewash it. Voila', stove structure that is inexpensive, and quite sturdy. B. Combustion devices: 1. The Mwoto TLUD gasifiers in Uganda are already sold at only US$14 with pot supports (and no subsidies). And that is for a full size unit with about 7 inch diameter fuel chamber. And the Awamu Biomass Energy company (GACC Partner in Uganda) is fully engaged on making it for less than $10 by using concepts such as the Mwoto Quad design, smaller sizes, TChar versions, and less metal (which is the major cost). (Full transparency: Awamu is owned by Nolbert Muhumuza and Paul Anderson, and they are looking for others to join them. Awamu means "together" in the Lugandan language.) 2. Paal Wendelbo and his associates have Peko Pe models (mainly in Zambia, I believe) that also could probably be reduced to under the $10 price. 3. Prof. M. Nurhuda in Indonesia is making excellent progress with his low cost TLUD stoves. So, the target of very clean stoves for under $10 can be met. But the nay-sayers will quickly point out that people want better looking stoves, or have fuel preparation problems, or do not want to change out the TLUD batch. (Conveniently forgetting that the fire has run UNattended - but not out of sight - for 10 or 20 or 40 or more minutes, depending on the fuel types. TLUDs do not need the 3 to 5 minute attendance cycle that Crispin so correctly pointed out as a major problem with the vast majority of stick-burning Rocket and simple ICS stoves.) In conclusion, if you are not into the TLUD stoves yet, please reconsider. We welcome your participation. Paul Paul S. Anderson, PhD aka "Dr TLUD" Email: [email protected] Skype: paultlud Phone: +1-309-452-7072 Website: www.drtlud.com On 11/10/2012 5:03 AM, Crispin Pemberton-Pigott wrote: <blockquote> Dear Paal and All This idea of making a replaceable combustor has additional benefits. The idea is already in use though it may not at first be obvious to a casual observer. ++++++++++Paal Wendelbo wrote: Dean and Paul are right if they also adopt the original idea with the TLUD-ND from the 1980ties and see the TLUD as a kind of a wrapping for the fuel; a unit loaded with energy to be put into a stove. Then you will have a lot of more possibilities. ++++++++++Crispin continues: I will post a photo of a stove I have recently seen in Cambodia which has a very substantial built-in brick and cement three-pot layout. There is a single chimney against the wall and three pot-holes. There is a wood fire space under or in front of each pot with a horizontal channel to the chimney behind it. This theme is used in Indonesia as well. I saw the exact same system used in urban Jogjakarta and a multi-pot single-fire version in rural Java. In all cases the hole is shaped so that it can take large woks and flat bottomed pots of different sizes from about 230mm to 900mm in diameter. The smaller pots are accommodated using reduction rings that fit the open hole and the pots. The point is the holes are substantial and the fires variable. When there is a desire to cook for a long time the ring(s) are removed and a taper-bodied stove that looks a lot like a tall JIKO is placed into the hole. This is a 'burner insert' or 'combustor' just as described by Paal. I have a photo of such a stove in operation. It has a charcoal burning stove dropped into the larger stove body. This can be done with all three holes if desired depending on what is cooking. As the concept is already well established, all that remains is to create other combustors that will either fit into the existing holes or stove body-combustor combinations that will accept appropriate pots. Further in our favour is that there is in Indonesia a (regionally?) established precedent for having an ash cleaning hole that is built into the floor below a clay grate. This satisfies the requirement to have a low overall height (about 300 mm) for the stove body. It means the combustor can be taller than 300 mm and still fit into the stove body. All the drop-in burners (which are stand-alone stoves if you take them out) can be improved as they stand so the new system performance should be much better than the baseline. Paal, in order to be able to get the PP or similar burners accepted in the same communities they will have to be 1) power controllable and 2) refuellable or the equivalent of refuellable such as a convenient swappable insert that can be managed easily. There is a stove in Mongolia that is copied from a Japanese brand 'Royal' which has two TLUD combustors connected by a Y-shaped channel to a common chimney. It is able toi cook constantly while swapping back and forth between two fires which can be run sequentially or in parallel. If one is started say, 1 hour before the other, the heat is continuous and the cook can re-charge the used one while the second burns. The big mis-match at the moment is the almost unchanging power output of the simple TLUD and the need for long term variable cooking for various foods, tea, palm sugar making, sea salt making, boiling chips and sterilising or heating water. People exercise quite a bit of control over the firepower during a burn cycle. For everyone's interest the most /hated/ aspect we could determine about stoves was the time interval between needing attention. At present it is about 5 minutes for domestic stoves. Although this will be investigated in the near future in detail, the people I interviewed rated a longer time away from the stove (perhaps 10-20 minutes) more valuable than fuel saving, smoke, ignition time, cost or fuel preparation (though objection to preparation of fuel was strong). The biggest opportunity I see at the moment with basically no change for the TLUD's is the load, fire and forget water steriliser. Lanny, don't forget. It can be a stand alone or a drop-in unit. Regards Crispin in Carrying Place, Ontario (is there really such a place??) This was the message from Paal Wendelbo: <blockquote> Stovers Dean and Paul are right if they also adopt the original idea with the TLUD-ND from the 1980ties and see the TLUD as a kind of a wrapping for the fuel; a unit loaded with energy to be put into a stove. Then you will have a lot of more possibilities. You will cover the whole specter of energy needed for household and institutional cooking, bakery and heating, with a lot of warranties of types of fuel, and easy to adjust to local needs and local resources. The technology itself is so simple that a child with a nail, a hammer and a tin can make a perfect clean burning unit. And the most important it will create jobs near connected to the marked philosophy, cheap and short time lasting. Paal W </blockquote> <blockquote> _______________________________________________ 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/ </blockquote> _______________________________________________ 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/ </blockquote> _______________________________________________ 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/
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