These clean-burning stoves may help sustainably feed nations
March 29, 2017
According to the United Nations Refugee Agency (UNHCR), there are currently more than 65 million people around the world who have been displaced from their homes. That figure amounts to one in every 113 people and is the highest number in history.
About three million of those people are awaiting asylum in industrialized countries, but that leaves more than 60 million who live either in refugee camps abroad or in their own countries. In these places, cooking food can be a challenge even when it is readily available. Stoves are scarce and cooking fuel to power those stoves is even more so.
Cooking over a campfire can be an option, but campfires are inefficient, polluting the air and being potentially hazardous to health. Some non-governmental organizations (NGOs) are trying to raise money to bring more gas stoves and cooking fuel to refugees. Others are adapting the thousands of years-old technology of the campfire into a cleaner and greener stove.
Researchers from North Carolina State University and the Liverpool School of Tropical Medicine in the UK recently studied forced draft biomass cookstoves: a wood-burning stove that uses small fans to ensure the wood fuel completely burns and decreasing the amount of harmful smoke.
Their work showed that these stoves did a great job limiting the harmful chemicals and particles in the lab, but as with some tests, the results out in the real world were not as good. The results were published in the journal Environmental Science and Technology.
Before getting to the stoves' report, it's important to understand the chemistry behind their main component: fire. Fire is a chemical reaction in which carbon fuel and oxygen rapidly rearrange themselves into carbon dioxide and water. When a fire is short on oxygen, the reaction cannot go the full distance, so instead of carbon dioxide, you are left with poisonous carbon monoxide and small particles of unburnt carbon ash that fly away in the smoke. That process is called incomplete combustion and frequently breathing in the products of incomplete combustion can lead to asthma, pneumonia and other breathing issues.
Forced draft stoves help suck air into the fire to make sure the combustion completes. Andrew Grieshop, associate professor of civil, construction and environmental engineering at NC State and Roshan Wathore, a graduate student in Grieshop’s lab, tested two commercially available forced draft stoves against clay stoves and open fires. The forced draft stoves emitted 47 percent less carbon monoxide and 45 percent fewer fine ash particles than open fires, and since the stoves use less wood than open fires, the total reduction in particles was closer to 75 percent.
In a controlled laboratory setting, the forced draft stoves make a lot of sense. Beyond the environmental and health benefits, the fact that these stoves require less wood also helps to make the most out of what can quickly become a limited resource around refugee camps where many people stay in the same place for extended periods of time.
When Grieshop and Wathore took the stoves on the road, however, they did not fare as well. Even beyond refugee camps, hundreds of millions of people in rural, non-industrialized communities rely on open fires or clay stoves to cook, and the researchers took the forced draft stoves to one such community in rural Malawi. The researchers repeated their tests in 10 homes, and found that the forced draft stoves released more than eight times as many fine particles and had twice as much greenhouse impact as they did in the lab.
There were a few reasons for this steep drop-off in effectiveness. First, the type of biomass is different in every location, and the plant species and dryness of the wood can affect how it burns. Second and more importantly, however, is how the stoves were used in the field.
The stoves themselves have a small burning compartment that contains the fire in a space where the fans have maximum effect, and as a result the stoves operate best when the woody fuel is cut down into tiny pieces. The act of cutting branches and logs down to size requires tools, time and effort, any or all of which could be scarce in rural developing areas or refugee camps. In Malawi, many of the residents using the stoves ended up using larger pieces of wood than the stoves’ manufacturers recommend.
It would seem that the solution is simple: just cut the wood into smaller pieces, but having the time and energy to do that is not always realistic in the environments where these stoves are needed. Another solution could be to adapt the technology to use a larger burning chamber, or incorporate other improvements that make the stoves easier to use, the researchers say.
The ideal scenario, according to the researchers, would be a full switch to a cleaner burning fuel like natural gas. But until there is a good way to provide enough fuel to those who need it, improving these wood-burning stoves could be the best way to limit the emissions harmful to health and the environment.
Daniel Lane covers science, medicine, engineering and the environment in North Carolina.