Develop pine biomass pellets to prevent fires

A research team from the University of Huelva has developed residual pine biomass pellets to prevent fires and increase the profitability of this plant material . This is the first study that analyzes the physical and chemical characteristics of stone pine waste to produce a solid biofuel that is used to generate heat in boilers and stoves.

Although pellets from different tree species were already produced, the researchers' proposal evaluates for the first time the density, moisture content, calorific value and mechanical resistance of the residual biomass of stone pine . With these data, they conclude that the final product has great energy potential in relation to its size , is efficient in combustion, emits a very low volume of polluting gases compared to fossil fuels and its production is sustainable.

The experts explain in their article 'Quality of the Pellets Obtained with Wood and Cutting Residues of Stone Pine' published in Forests, that stone pine biomass transformed into pellets has qualities such as its low moisture content, its bioavailability - it is a resource abundant in nature - and a high density, that is, it contains a large amount of useful material in a relatively small volume. This facilitates storage and reduces transportation costs, since more use is made of the available space.

Advantages
Thus, the development of these pellets implies two advantages: one environmental and the other economic . Firstly, collecting biomass from forests and mountains helps prevent forest fires, since potentially combustible material is reduced. On the other hand, obtaining and selling stone pine pellets could cover up to 80% of the costs of production and transportation of biomass. “Almost 1,000 kilograms of forest biomass per hectare per year could be sustainably obtained in the pine forests of Huelva alone. With three hectares, the energy needs of a home could be covered for a year,” explains Manuel Fernández, a researcher at the University of Huelva, .

To prevent forest fires from occurring or getting worse , public institutions usually remove large amounts of biomass from the areas most prone to fires. However, traditional methods have several disadvantages, such as the costs of collection and transportation, the low energy density of biomass - that is, it contains a small amount of energy compared to its volume - and the quality and particularities of the material. For example, there are tree remains that contain more water than useful material. This makes transportation more expensive, since a lot of volume is transported, but little effective biomass to generate energy or develop the pellets. Furthermore, mixing different types of biomass can make processing, energy efficiency and subsequent use difficult. “For these reasons, moving biomass more than 100 kilometers around is not profitable economically, environmentally, or energetically. The pellets that we propose try to solve these three problems ,” adds Manuel Fernández.

High density
To develop these cylindrical granules, scientists collected samples of bark, trunk, branches and leaves of stone pine in the vicinity of Doñana . Then, using traditional physical and chemical methods, they analyzed the density, moisture content, calorific value and mechanical resistance of the pellets made from each part of the tree.

In this way, they concluded that the trunk without bark and the thickest branches are the best 'ingredients' to create high-quality pellets , while the small, thin branches and leaves have worse physical qualities and when burned they emit a greater amount of nitrogen, sulfur and chlorine, gases with an impact on air pollution and human health. “Normally, biomass remains are crushed in the bush. We recommend transporting the trunks and thick branches whole, to take advantage of more material. However, we do suggest crushing the smallest branches and leaves in situ and spreading them over the forest floor to prevent them from becoming fuel and increasing the risk of forest fires,” says Manuel Fernández.

After establishing which were the most useful parts of the tree, the experts took the biomass to a pelletization plant, where they ground the barkless trunk and branches into sawdust and then densified them . This means that they extracted all the air and water possible and compressed the material to obtain the pellets, in the shape of elongated, cylindrical granules measuring between 1 and 2 centimeters. The scientists add that the sale of these pellets could cover between 30% and 80% of the costs of fire prevention work in the province of Huelva.

Meeting energy needs
The next step for the Natural Environment Analysis and Planning research team will be to evaluate how a mixture between these stone pine pellets and other tree species works. “If all forest and scrub biomass were used sustainably, we could avoid the incidence of fires and, at the same time, satisfy all the annual electrical and thermal energy needs of 60% of Andalusian homes,” explains Manuel Fernández.