The UB JR 200 l Natural Draft TLUD Oven: This winter we have been working on improving the performance of some basic 200 l biochar ovens. We feel that good low tech units in this size range will prove to be the ‘work horse’ units for biochar production for programs that hope to utilize thinly distributed feedstock for biochar production in sustainable rural development, particularly for those such as the UBI concept which aim to leverage this development into significant and timely climate change mitigation.

The core fired 200 l retort oven reported on earlier has been improved, including external integral insulation. One line utilizes a simple ‘3 stone’ fire for bottom and core heating (with pyrolysis gases burned in the core pipe) while a second line is developing a simple stove arrangement for better air management and eventually side heating by separating the insulation from the barrel side and affixing it to the outside of a lightweight cowling with a gap between the barrel and cowling that will serve as a ‘chimney’ for the primary fire and as an secondary fire box. Both designs produce good biochar but require about as much fuel wood as feedstock as well as the attention of an attendant throughout the firing, though a single attendant could attend to 4 or 5 ovens at once.

However, the large amount of biomass consumed in the external heating of the retort oven lead us to begin thinking of the possibility of developing a 200 l TLUD with its efficient use of the generated breakdown products in producing the char. Fortuitously, John Rodgers’ TLUD highlights this type of system. We’ve added upgrades to the air control system, while still keeping it low-tech and simple to construct and use. See pictures and simple instructions below. For additional information and detailed pictures contact Karl Frogner.

Only a power drill and a power grinder are needed to construct this oven, although the student who was doing the metal work had access to a welder and used it to put the handles on the slip rings on the primary air & afterburner air, the male slip coupe for the chimney and the handle for the chimney flue. Easy workarounds could be used if welding is a problem.

We’ve run two trials so far, both with cow manure that was air dried after being shoveled out of the cowshed. Both runs were smokeless. The first, in which a full load of hand sized to 20-30 x 20-30 x 5-10 cm sized clumps of manure on down ‘burned’ down in 55 min, the second, a full load of fairly uniform 7-10 x 7-10 x 5-10 cm pieces together with the fines from chopping up the larger pieces, ‘burned’ down in 1 hr 40 min. There was no smoke throughout either run. The charing was complete throughout the charge in both runs, slightly oily on the ‘rub on the hand’ rub test.

Another run was made (I was absent) using birch branch & twigs segments (2 cm on down) about 10 cm long. The first time operators had smoke problems, probably caused by difficulties in finding the right air adjustment for keeping the afterburner lit in an exposed site on a windy day, but the char came out good I’m told. Devising a wind shield should not be much of a problem.

We are calling this machine the UB JR 200 l natural draft TLUD oven; or UB T-oven, the t-oven or even the Toven (toven) for short. But please, please, please – don’t call it a stove or a kiln.

I’m using the UB designation to recognize the part the local people in Ulaanbaatar have played in the creativity, work, and support in developing working 200 l biochar ovens, work that has been ongoing over the past several years – JR in recognition of John Rogers’ work in pioneering the low-tech, simple construction, 200 l (55 galon) ‘oil drom’ natural draft TLUD and his unselfish sharing of his work with the interested community. I use the designation ‘oven’ because the primary purpose here is to make serious weight biochar. That is, to bake appreciable amounts of feedstock into biochar, much as an oven bakes dough into bread. Of course there are technical names such as retort, kiln, gasifier, etc that can be used, but ‘oven’ gives a connection to the common man’s understanding. I feel that this latter distinction is important to distinguish these machines (ovens) from cook stoves and the framing that has grown up, that low tech biochar = cook stoves, as well as the more primitive and larger machines designated as ‘kiln’ by IBI. The oven designation is especially important for the recognition and understanding of programs such the UBI concept that are trying to get significant amounts of biochar in the ground in time to help in phase 1 climate change mitigation (see: Hansen, Woolf & Timelines for Biochar Potential: some thoughts. /regional/ubi).

From initial crude estimates we expect that a run should yield approximately 8 – 12 kg of biochar. A single operator using 5 ovens should be able to produce 100 kg in an 8 hr work day, while two operators working on a staggered shift using 7 ovens could produce 250 kg in a 8 hr work day. Such intensive usage would undoubtedly take a heavy toll on ordinary steel drums, but stainless steel barrels could be used for the feedstock chamber and the afterburner for greater longevity. Clearly, for use by most smallholders, biochar production with this type of oven will be feedstock limited, not equipment limited, quite the opposite from the normal situation for cook stoves.

We are very interested in developing these large TLUDs for getting serious amounts of biochar into the ground, leveraging smallholder benefits of biochar in sustainable rural development into timely climate change mitigation. UBI is initiating a sib-project based on a virtual community of people interested in low-tech biochar production, TLUD designers, and tinkers who would want to test, quantify and improve the design and or support this sort of work. Please let us know if you are interested.

Photos courtesy of Karl Frogner