What is a Biochar Stove?

Throughout the undeveloped world, more than two billion people cook and heat their homes with inefficient stoves or open fires, burning wood, straw, dung, or coal. These technologies, though essential emit air pollution that can harm respiratory and cardiac health of the individuals (typically women who are doing the household work) and exacerbate global warming. (Though the big perps here are the definitely the industrialized US and rapidly expanding China.) People struggle to gather enough biomass fuels to meet their needs, and in many cases, the demand for wood and other bio-matter accelerates deforestation, leading to more environmental damage.

Biochar Stove

Biochar stoves, you guessed it make biochar! They can be made in a variety of styles for easy cooking.

A biochar stove, even if mass produced overseas, can still help. This stove can boil water, making it safe to drink. What makes it unique is that the fuel, such as wood or dried sticks is burned, and turns into a biproduct of charcoal.

Most stoves are designed specifically to produce a clean flame suitable for cooking and not necessarily to maximize biochar production. A biochar stove produce between 25 and 30% biochar weight from the initial feedstock weight. In stoves which produce biochar, pyrolysis and gasification will occur resulting in biochar production, if incineration is allowed to follow, the biochar will turn into ash. However, if at this point the stove is extinguished, the biochar can be kept for other purposes (for example as a soil amendment) or as a fuel later.

Basically as you burn, your fuel is turning into yet another purpose, more fuel or ash, which can be used to help replenish the soil for growing food.

There are two popular basic types of biochar stoves that can be used to produce charcoal and heat, the Top-Lit Updraft Gasifier (TLUD) and the Anila stove. TLUD stoves have many variations but the biggest distinction is between natural draft TLUDs and fan-forced TLUDs. The TLUD operates as a gasifier by creating a stratified pyrolysis/combustion regime with four basic zones: raw biomass, flaming pyrolysis, gas combustion and charcoal combustion.

The Anila-type stoves use two concentric cylinders of different diameters. Biomass fuel is placed between the two cylinders and a fire is ignited in the center. Heat from the central fire pyrolyzes the concentric ring of fuel. The gasses escape to the center where they add to the cooking flame as the ring of biomass turns to char. The center combustion chamber can be configured as either a rocket stove design (with a side opening door) or as a TLUD with primary combustion air entering from the bottom.

Biochar stove technologies can produce both heat for cooking and biochar for carbon sequestration and soil building. These biochar cook stoves provide benefits which typically include increasing efficiency and reducing smoke production. Gasification stoves in addition to these benefits also produce biochar which can increase food production (where biochar is used as a soil amendment) and can thus reduce hunger.

Biochar-producing stoves are not yet a mature technology, and indeed, the emissions from the few designs that have been developed have not yet been systematically tested. However, there are good reasons to believe that they will be as clean as or cleaner than other gasifier stoves that do not retain the biochar but combust it.

A biochar stove doesn’t reach super high temperatures like a rocket stove can. But it is likely that it will suit your basic cooking and heating needs. -Annabel Schoeman

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