Forever wood

From the domestication of fire in prehistoric times to the pellet stoves now flourishing in our living rooms, wood remains an essential source of energy. An energy with a bright future, thanks in particular to research aimed at optimizing its use to better preserve resources and the environment.

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A third of the world's population, or 2.4 billion people worldwide, use wood as their primary source of energy, whether for cooking, heating or even generating electricity. " Wood is the main energy resource in developing countries", explains Bruno Clair, CNRS researcher at the Montpellier Laboratory of Mechanics and Civil Engineering(LMGC)* and co-director of the Master's degree in Wood Sciences.

But its use is widespread in both hemispheres, as evidenced by the 88.5 million people who use wood fuels as their main source of heating, mainly in North America and Europe. "In fact, the University of Montpellier itself uses a wood-fired boiler," notes the researcher.

Tight market

And wood is on a roll everywhere: "It's the leading source of renewable energy in France, ahead of solar and wind power. And in a market under pressure, with gas and oil prices soaring, more and more people want to heat with wood", Bruno Clair points out.

How can we preserve wood resources in the face of ever-increasing demand? " In essence, wood is a renewable energy source, because when you cut down a tree, another one grows if the forest is managed sustainably," explains the researcher. Moreover, in France, the forest area is expanding, from 9 million hectares in 1840 to 14 million in 1985 and 17 million hectares in 2021.

The situation is even more worrying on a global scale: according to the United Nations Food and Agriculture Organization, the world has lost an estimated 420 million hectares of forest since 1990. "But this deforestation has little to do with the use of wood as a source of energy or material! For the most part, these trees are cut down to create new agricultural land", explains Bruno Clair. "It's important to remember that a significant proportion of the population in Africa grow crops to produce their own food, and as these food crops are more productive on plots of land that have just been deforested, this is still the most widespread practice today," adds François Pinta, researcher at the BioWooEB laboratory (Biomass, Wood, Energy and Bioproducts)**.

Best option

For the LMGC researcher, heating with wood is often the best option. "There's a balance between the CO 2 emissions generated by wood combustion and the quantities of CO 2 absorbed during tree growth, but you also have to take into account the energy required to harvest and transport it. For wood energy to be virtuous, it has to be an end-of-pipe recovery after the noblest woods have been recovered for uses where the carbon will be stored over a long period of time, such as construction", Bruno Clair qualifies.

A very good carbon footprint does not mean, however, that heating with wood is not synonymous with pollution. " When combustion is carried out properly, wood can be considered to emit virtually no greenhouse gases, but for that to happen, the combustion processes must be carried out under the right conditions," explain François Pinta and Kevin Candelier, who also teach at the Sciences du Bois master's program.

Cleaning up smoke

Optimizing these processes is just one of the avenues being explored by the two researchers and their colleagues in the BioWooEB laboratory. Some wood-energy processes, such as wood pyrolysis, release a wide variety of gaseous molecules, not only carbon dioxide, but also carbon monoxide, fine particles and other volatile compounds, such as acetic acid for example," explains Kevin Candelier. We are analyzing the composition of these fumes produced under different conditions to gain a better understanding of them and seek to add value to them."

Because a fraction of the chemical compounds emitted can be highly polluting for the environment and toxic for human health. " Our research is aimed at reducing pollution linked to the use of wood energy, in particular by cleaning up the fumes from the charcoal production process," explains François Pinta.

And while optimizing wood-energy utilization processes helps to protect the environment and health, the virtues of this research go far beyond that. " If the fuel is well used, we reduce the need for wood, which in turn reduces costs and the pressure on natural resources. Research offers a real virtuous circle of improvement," concludes François Pinta.

A healthy gas

When it comes to generating energy from biomass, the BioWooEB researchers are firing on all cylinders. Biomass can be transformed in a variety of ways: combustion, carbonization, torrefaction, carbonization, flash pyrolysis and even gasification. " Gasification is a thermochemical transformation involving the thermal decomposition of a solid carbonaceous fuel in the presence of a gaseous reagent," explains François Pinta. The result is a gas that can be used as a fuel. What's it called? Syngas for synthetic gas. Once purified, it can be used to power an internal combustion engine to generate electricity, or in an industrial burner to produce heat. In both cases, it can be used to replace fossil gas and drastically reduce greenhouse gas emissions. "Syngas is very interesting when you need to obtain controlled heat, for example to fire clay bricks at very high temperatures. Our team is currently monitoring new applications set up in companies in France and the Occitanie region", explains the researcher.

**BioWooEB (Cirad)

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