Biochar Technology

An estimated two billion people in the developing world cook and heat their homes with primitive stoves or open fires through the burning of wood, straw, dung, or coal. These inefficient stoves emit air pollution that can harm respiratory and cardiac health and exacerbate the climate crisis. Biochar producing stoves offer a solution. For decades, a small group of researchers and development advocates have worked to improve household biomass energy technologies. Newer stove designs can create heat for cooking while also producing biochar for carbon sequestration and soil building. Testing indicates that these stoves are much more efficient and emit less pollution, while the need for less wood can lead to decreased deforestation.

There are, however, many challenges that face biochar stove designers.

1. Ensuring that biomass consumption is lowered.
2. Producing an affordable, durable stove that is easy to operate and maintain.
3. Producing a stove whose efficiency doesn’t decrease over time.
4. Understanding the potential added burdens of producing and distributing
5. biochar—especially for women.
6. Understanding behavioral and sociological barriers to new technologies.

The UN Environment Program now recognizes that Atmospheric Brown Clouds (ABCs) are a major contributor to climate change (UNEP, 2008). ABCs are caused by particulate emissions from inefficient combustion of biomass and fossil fuels and they include both black particles (soot) that heat the atmosphere by absorbing sunlight, and white particles that reflect sunlight and contribute to cooling.

Black carbon has a significant effect on global warming, second only to carbon dioxide (CO2) (V. Ramanathan & G. Carmichael, 2008). However, the atmospheric residence time of black carbon is only a few weeks, while CO2 emissions stay in the atmosphere for more than a century. This means that we have an opportunity for immediate action to decrease climate forcing by reducing black carbon emissions.

While much of the black carbon is emitted by forest fires and diesel fuel used in industrialized nations, between 25 and 35 percent comes from household energy use in China and India (V. Ramanathan & G. Carmichael, 2008). Unfortunately, even some improved (non-biochar-making) cookstoves that are otherwise efficient users of wood still emit large amounts of black carbon. One study comparing improved cookstoves showed that a common design, the rocket stove, had black carbon emissions equal to those of an open fire (MacCarty & Bond, et al, 2008). The study found that gasifier stoves, both natural draft and fan-assisted, had very low black carbon emissions. These are the types of stoves that can be configured to produce biochar.

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 (P. Anderson, 2009).

Continuous feed pyrolyzers to improve energy efficiency and reduce pollution emissions associated with batch kilns. Exothermic operation without air infiltration to improve energy efficiency and biochar yields. Recovery of co-products to reduce pollution emissions and improve process economics. Control of operating conditions to improve biochar properties and allow changes in co-product yields. Feedstock flexibility allows both woody and herbaceous biomass (like crop residues or grasses) to be converted to biochar. Some technologies that hold promise for helping achieve these goals include drum pyrolyzers, rotary kilns, screw pyrolyzers, the flash carbonizer, fast pyrolysis reactors, gasifiers, hydrothermal processing reactors, and wood-gas stoves, all of which produce varying quantities of gas and liquids along with biochar.