Saturday, July 31, 2010

My TLUD's Bigger 'n Yours

The kiln load (Gmelina mill scrap) must get up to around 280C before it will produce enough combustible gas to "kick over" into pyrolysis mode, then gases will burn in the kiln's fire chamber and generate sufficient heat to sustain pyrolysis until the entire load has been carbonized. Our kiln was designed to have combustible gas from a different source injected into the fire chamber to "prime" the kiln until it could produce enough combustible gas to sustain the reaction on its own.

We opted for a biomass gasifier for this purpose. Nik Foidl designed a beast for us––a TLUD (top-lit updraft) sawdust gasifier a meter in diameter, capable of generating 200-350kW. That's a lot of hot! A blower injects air into a space in the base of the unit, and the perforated floor of the basket allows air to migrate upward through the sawdust. Squirt a bit of kerosene onto the surface of the sawdust and ignite to get it started. Then put down the hood and turn on the blower.

The flame front migrates downward, toward its oxygen source, producing a mess of smoke (mix of combustible gases). A pair of air ports in the hood of the TLUD introduce more air, causing the smoke to burst into flames, and the hot exhaust gases are injected into the kiln. The TLUD is powered by a single large blower regulated by butterfly valves. The primary butterfly controls the total air introduced into the system. A "Y" and pair of butterfly valves control the relative amount of primary air, which is injected into the base and blows through the sawdust; and secondary air, which is injected into the hood to ignite the gases.

Hot, hot hot!

Know of a bigger TLUD? We'd love to hear about it!


  1. Dear Rob,
    That is a nice machine. Do you have some drawings and calculations? I would like to built one in my neighborhood, I hate to see the farmers burning the rice stems for fertilizer (Actually all they do is releasing tons of C0 and C02 and all they get is ash). For each kilo of biomass we can get 250 grams of bio char, that can be used as a valuable fertilizer and the gas cleaned and can be burned in ovens or further cleaned for as duel fuel in gen sets.
    Thanks, Robert

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  4. Love the scale of this..
    I need to build one to heat a 2500 ltr retort..
    Any chance of getting more photos or some drawings and calculations?

    Thanks very BIG in advance..
    smokenfire @ mac . com