Energy Recovery of Shrub Species as a Path to Reduce the Risk of Occurrence of Rural Fires: A Case Study in Serra da Estrela Natural Park (Portugal)

Leonel Nunes,Carlos Gomes,Mauro Raposo,Catarina Meireles,Nuno Ribeiro

doi:10.3390/fire4030033

Leonel Nunes, Carlos Gomes + Show 3 more

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https://doi.org/10.3390/fire4030033

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Abstract

The accumulation of biomass fuels resulting from the growth of heliophilous shrubs and small tree species at the edge of forests and on scrub and pasture lands contributes to the increased risk of rural fires in Mediterranean climate regions. This situation has been managed with a set of legislative measures launched with the objective of promoting cleaning and the control of these species. Areas of scrub and pasture already constitute the largest part of the annually burnt area in Portugal, resulting in high-intensity fires. In the present study, shrubs and small tree species were characterized in the laboratory. Thermogravimetric, chemical and calorimetric analyses for the evaluation of the potential for the energy recovery of the selected species were carried out. It was observed that energetic valorization (i.e., to enhance the value by planned actions) of these species is difficult because they present high levels of ash and metals, becoming prone to the occurrence of fouling and slagging phenomena. Thus, the creation of value chains that justify the incorporation of these materials becomes very difficult, except if used in non-certified, small-scale and locally based processes. The possibility of recovery through thermochemical conversion processes, such as torrefaction, pyrolysis or gasification, must be studied so that more efficient and feasible recovery alternatives can be found, allowing for the creation of value chains for these residual materials to promote their sustainable management and, thus, mitigate the risk of rural fires occurring.

Highlights

Humanity is currently facing one of its greatest challenges with the occurrence of severe anomalous phenomena caused by climate change [1]
From the parameters normally analyzed in thermogravimetry, especially when the materials are used for energy recovery, ash appears to be a determining factor, since an excessive amount of ash can greatly affect the use of the material as a fuel
Exploratory works involving the characterization of the biomass types analyzed in the present work have been presented from the perspective of energy recovery, such as the work presented by Marques et al (2011), where the possibility of pellet production from species belonging to the genera Cytisus and Cistus is analyzed [30], or the work presented by Marques et al (2019), where the characterization of charcoals produced with blends of Cytisus with cork residues, Cistus with Eucalyptus and Cytisus with Cistus is presented [31]

Summary

Introduction

Humanity is currently facing one of its greatest challenges with the occurrence of severe anomalous phenomena caused by climate change [1]. One way to reduce CO2 content is through the substitution of fossil origin energy by renewable energy, since this substitution avoids the return of carbon captured in past geological times to the actual atmosphere [4]. Biomass is an alternative, since, its use is not exempt from CO2 emissions, its release is considered neutral [6] In other words, this CO2 released, for example, by the combustion of firewood, is equivalent to what the biomass sequestered during its lifetime, which certainly occurred during the current carbon cycle [7]

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