Burning Smoke: Gasification


Let’s play with fire — and learn from it!

Gasification is central to understanding the efforts to produce smokeless and safe stoves for cooking with biomass fuels as well as making biochar. In layman’s terms, it means using heat to drive off the components of biomass that are not carbon and heating them in an air rich environment so that they burn and leave the carbon behind. So you are literally burning smoke and generating lots of heat. A primary supply of heat to drive out the volatile materials of the wood as smoke and a secondary supply to ignite the smoke.

Dirk-Jan built a gasifier to evaluate the grass pellets he produces and to assess how much slag and ash they produce.  It was kludged together with scrap parts he had lying around his shop and is certainly not a production model but it does illustrate how to burn smoke.


We have been taught to light fires from the bottom of the wood pile but in this video the fuel was lit by from the top while the hot air came from below. This gives the stove the name Top Lit Up Draft, TLUD.

When the fuel is lit from below it completely burns the fuel above it rather than just creating smoke. That leaves ash instead of the carbon in the form of charcoal, the desirable biochar. Pronounced “B-LUD”. The fuel is ignited from the bottom and up until a certain point generates a lot of smoke.

The TLUD has the advantage of producing biochar while it is being used as a cooking stove. TLUD has the advantage of producing biochar while it is being used as a cooking stove.

Here is a diagram to help with the terminology of the TLUD.

As I wanted to make a video that would illustrate how gasification actually burns “smoke” in order to produce heat, we ignited the fuel through a port at the bottom of the stove to generate lots of smoke and then lots of heat. If we had lit the fuel from the top, it would have been smokeless. This same stove works in two different ways: as a TLUD and as a BLUD. Pronounced “T-LUD”. The fuel is ignited from the top and is essentially smokeless.

A diagram by Paul Anderson of the TLUD gasifier stove.

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