To those who live in the developed world, it may come as a surprise to learn that more than two billion people still cook and heat their homes with primitive stoves or open fires, burning wood, straw, dung, or coal.
These inefficient technologies emit air pollution that can harm respiratory and cardiac health and exacerbate global warming. People struggle to gather enough biomass fuels to meet their needs. And in many cases, the demand for wood accelerates deforestation.
For nearly two decades a small group of researchers and development advocates has worked to improve household biomass energy technologies. Now concerns over global warming have added a new reason to accelerate the transition to cleaner biomass energy use in the developing world. New stove technologies can produce both heat for cooking and biochar for carbon sequestration and soil building. Limited testing indicates that these stoves are much more efficient and emit less pollution
There are many challenges faced by stoves designers. These include:
Health: Biochar-producing stoves are potentially much cleaner, with lower emissions of carbon monoxide, hydrocarbons, and fine particles.
Climate: Biochar-producing stoves have lower greenhouse gas (carbon dioxide and methane) and black carbon emissions, create biochar that can be used to sequester carbon in soils, and reduce the use of fossil-fuel based fertilizers.
Deforestation: Biochar-producing stoves use less fuel, can use a wider variety of fuels, and can replace inefficient charcoal production technologies.
Soils: Biochar-producing stoves create biochar that sequesters carbon in soils, may in some cases reduce emissions of nitrous oxide (a powerful greenhouse gas) from soils, improves fertility, and increases productivity in degraded soils.
Income Generation: Biochar-producing stoves can accommodate many forms of agricultural residues—some without further treatment. Collecting this residue is another income generating opportunity not presently available for most other stoves since they cannot utilize that type of fuel.
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).
A number of researchers and programs world wide are devoted to producing efficient and cost-effective biochar-producing stoves, however, as yet there has been very little in the way of funding for these projects. Below is a description of some of the designs and programs that are in operation.
There are two basic types of stoves that can be used to produce charcoal and heat, the Top-Lit Updraft Gasifier (TLUD) and the Anila stove.
There are many variations on the TLUD, 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 (see diagram to the right, modified from Anderson & Reed, 2004). The charcoal can be retained if it is removed at the proper time and quenched.
The modern Anila stove was developed by U.N. Ravikumar, an environmentalist and engineer with the Director of the Centre for Appropriate Rural Technologies (CART) at India’s National Institute of Engineering. Anila-type stoves use two concentric cylinders of different diameters (see diagram). 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. (Anila diagram courtesy of Stephen Joseph).
A large variety of stoves, including some biochar-producing stoves are demonstrated and discussed on the website bioenergylists.org.
United Nations Ministerial Conference of the Least Developed Countries. 2007. Energizing the least developed countries to achieve the Millennium Development Goals: the challenges and opportunities of globalization. Issues Paper.
V. Ramanathan, et al. 2008. Atmospheric Brown Clouds: Regional assessment report with focus on Asia, Summary. United Nations Environment Program.
V. Ramanathan and G. Carmichael. 2008. Global and regional climate changes due to black carbon, Nature Geoscience 222.
N. MacCarty, et al and T. Bond, et al. 2008. A laboratory comparison of the global warming impact of five major types of biomass cooking stoves. Energy for Sustainable Development, Volume XII No. 2.
P. Anderson, Biomass Energy Foundation. 2009. CO and PM Emissions from TLUD Cookstoves. Presented at 2009 ETHOS Conference, 23-25 January 2009, Kirkland, WA, USA.
P. Anderson and T. B. Reed. 2004. Biomass gasification: clean residential stoves, commercial power generation, and global impacts, prepared for the LAMNET Project International Workshop on “Bioenergy for a Sustainable Development,” 8-10 Nov 2004, Viña del Mar, Chile.