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!