Truly excellent observations about Bangladesh efforts.
Adding this thought: Thinking of a standard TLUD with metal fuel chamber, has anyone measured the temperature of the outside wall of that fuel chamber as the pyrolytic front moves to it, is at it, and then past that point of measurement?
This could be done even with a single wall TLUD (no outer cylinder) or with a large hole in the outer cylinder so that an infrared thermal sensor could read the temperature on the wall of the fuel chamber. [But the chamber wall should not be shiny reflective metal because that messes up the infrared readings — so use some high-temp-resistant paint.)
Who will do this first and then report the results? (please do not wait for me or others to do it.)
Paul
Hi All;Mahbubul Islam and I have tried TLUDs cast as a single concrete cylinder. You can see photo of a prototype here: http://www.biochar-bangladesh.org/ on the home page. The concrete is made using Portland cement, sawdust, sand, and ground biochar. It is not refractory quality, so the interior of the reactor is lined with clay, which can be replaced. In another design, there is a concrete ring above the concrete reactor with a space between the two created with 12-16 spacers.I have also done some experiments with burners, and you can see a video of that here: https://youtu.be/QmnUgj75TF0We haven’t done much work on this type of TLUD in over a year, because we have concentrated efforts on the metal reactor cylinder in the Akha Stove.What we really needed to develop concrete or ceramic reactors is research money to pay for gas analysis and materials. There are many design parameters to adjust, and without gas measurements, we can’t justify and explain our decisions. In the mean time, we have other things to work on.There are a couple of drawbacks in the designs illustrated above. They are vulnerable to ambient wind, we don’t preheat secondary air, and there are no pilot holes in the reactor walls. Pilot holes can be made, and protection from wind could be designed.The reactor bodies will be a heat sink. I am not sure how big an issue that would be, becaue gas flame is a the top of the stove, and heat in the center of the char above the ‘flaming pyrolysis’ moves predominantly upwards and not sideways, because air movement is upwards, and char is a poor conductor of heat sideways. (I have measured the horizontal profile of temperature in metal TLUD reactors, and the temperature only drops in the 1-2 cm near the reactor sidewalls.).For burning pieces of wood more than 1 cm thick, some holes in the sidewalls of the reactor would provide pilot lights to prevent accidental shut-down of the reaction. I belive this is important for thicker pieces of fuel than 5 mm pellets, because it takes longer to reach pyrolysis temperatures at the center of thick pieces of fuel. That means that when the reaction is turned down, char combustion on the surface of particles becomes important to keep the primary pyrolysis reaction going. If the char combustion goes out because of insufficient oxygen, then it is tough to get the reaction started again if a lot of the partially pyrolyzed wood has charred surfaces. Some holes in the side walls of the reactors keeps some embers glowing, so the gas flame stays lit, and maintains draft. The primary air can be turned-up if need be.We have to design these stoves with pilot lights so that it is not that easy for the gas flame to go out accidentally. If that happened in semi-enclosed cooking spaces, the air would fill with smoke, and the cook would get angry. We are going to sell stoves, we need happy cooks.I think it is important to work on ceramic and concrete reactors. I needs a research grant to do it properly.(Just a side comment. I have observed that the thicker the fuel the more primary air is required for the primary pyrolysis reaction. I believe that this is because of the time it takes for the center of thick pieces of wood to reach pyrolysis temperatures. Because the time it takes to completely char the wood, the heat from flaming pyrosysis is not sufficient, and heat from char combustion becomes important. Thus a higher flow rate of primary air is required for a TLUD loaded with chunks of wood than pellet fuel. As fuel thickness increases, the yield of biochar decreases.)Cheers,Julien.—
Julien Winter
Cobourg, ON, CANADA