• Energy Research

Agroforestry waste stores a considerable amount of energy that can be used. Portugal has great potential to produce bioenergy. The waste generated during agricultural production and forestry operation processes can be used for energy generation, and it can be used either in the form in which it is collected, or it can be processed using thermochemical conversion technologies, such as torrefaction. This work aimed to characterize the properties of a set of residues from agroforestry activities, namely rice husk, almond husk, kiwi pruning, vine pruning, olive pomace, and pine woodchips. To characterize the different materials, both as-collected and after being subjected to a torrefaction process at 300 °C, thermogravimetric analyses were carried out to determine the moisture content, ash content, fixed carbon content, and the content of volatile substances; elementary analyses were performed to determine the levels of carbon, nitrogen, hydrogen, and oxygen, and the high and low heating values were determined. With these assumptions, it was observed that each form of residual biomass had different characteristics, which are important to know when adapting to conversion technology, and they also had different degrees of efficiency, that is, the amount of energy generated and potentially used when analyzing all factors.

The use of biomass as energy source becomes considered again as a possibility, after a period in which practically felt in disuse, especially in industrial environments. Nowadays it is again an important alternative, mainly due to the increasing prices of fossil fuels, especially oil and natural gas, as well as by the growing environmental and sustainability concerns, since the biomass fuel is considered neutral in terms of CO2 emissions. The use of biomass as solid fuel poses several logistic difficulties that do not allow their straightforward dissemination in all industrial units, which intend to change its fuel source. In this paper, a case study of integration of renewable energy sources provides results obtained based on an experimental setup using biomass technology, posing a major advantage for the Portuguese textile industry, in particular the dyeing textile industry, over the traditional use of fossil fuels.

Evaluating Global Warming Potential (GWP) in waste management scenarios is crucial, especially in light of the escalating global concern for climate change and the pivotal role that waste management plays in mitigating this crisis. This research examines the GWP of three distinct waste management scenarios, each with a unique approach: (1) open burning, a method involving direct combustion with a GWP of 1600.1 kg·CO2eq, chiefly attributed to direct emissions without any mitigation tactics; (2) energy recovery, which capitalizes on converting waste into energy, yielding a GWP of 1255.4 kg·CO2eq, the reduction resulting primarily from avoided heat production; and (3) pyrolysis, an advanced thermal decomposition process that remarkably registers a negative GWP of −1595.1 kg·CO2eq, mainly credited to the carbon sequestration capacity of biochar production and optimal energy conversion efficiency. These outcomes emphasize the ecological merits of waste management approaches that produce lower, or even better, negative GWP values. In particular, pyrolysis emerges as a powerful way of transforming waste management into a potential carbon sink, proving crucial for climate change counteraction. Nevertheless, for effective real-world deployment, the study highlights the importance of addressing technical, economic, and societal challenges, underscoring the need for holistic, interdisciplinary research.

Citizens’ attitudes and beliefs towards climate change are decisive in the adoption of mitigating measures. Limiting the use of energy in the context of climate change can be one of the mitigation measures, and therefore, understanding the position of the citizens towards it is important. With this aim, we used data from the 10th European Social Survey to relate the European citizens’ beliefs and attitudes on limiting the use of energy to tackle climate change. We have used variables related to demography and individuals’ perception of society and its policies. Statistical models were successfully fitted to data. Individuals with higher levels of trust in scientists have a higher degree of satisfaction with the national economies, are more worried about climate change and are more capable of assuming self-responsibility in climate change mitigation. These individuals have higher probabilities of believing that climate change mitigation could be achieved by limiting the use of energy. The EU citizens are, however, very skeptical in relation to the probability of many other citizens adopting measures to limit the use of energy.

This review summarizes the intricate relationship between climate change and forest ecosystems in the Northwest Iberian Peninsula, outlining both their resilience and vulnerabilities. The study asserts the significant impact of climate change on these ecosystems, reinforcing earlier theories about their responsive behavior to global climatic alterations. However, the impacts are highly localized, contingent upon specific forest compositions, topography, and interaction with other environmental stressors. The temperate forests of the Northwest Iberian Peninsula manifest a delicate balance of resilience and vulnerability in the face of these phenomena. Notably, the study underscores that this region’s forest ecosystems remain a relatively uncharted research territory, promising fruitful prospects for future exploration. Although existing studies offer vital insights into the climate change impacts, there is a stark need for further research to gain a deeper understanding of, and formulate appropriate responses to, the challenges that these specific ecosystems confront in the wake of climate change.

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.

Abstract The need to generate thermal and electrical energy, global warming caused by increased emissions of greenhouse gases, rising fossil fuel prices and demand for energy independence, have created a new industry focused on energy production through the use of renewable sources. Among the different options, biomass is the third most important source for obtaining electricity, and is the main source for the production of thermal energy. However, problems related to the low density of the different types of biomass, and the difficulty of transportation and storage, have led to the need to find solid fuels with higher density and greater hardness, known as pellets and briquettes. This paper seeks to develop an analysis of the current situation of the production of pellets, mainly with mixed biomass types, and the possible uses they have, with the main emphasis on the review of different combustion processes.

The growing search for alternative energy sources is not only due to the present shortage of non-renewable energy sources, but also due to their negative environmental impacts. Therefore, a lot of attention is drawn to the use of biomass as a renewable energy source. However, using biomass in its natural state has not proven to be an efficient technique, giving rise to a wide range of processing treatments that enhance the properties of biomass as an energy source. Torrefaction is a thermal process that enhances the properties of biomass through its thermal decomposition at temperatures between 200 and 300 °C. The torrefaction process is defined by several parameters, which also have impacts on the final quality of the torrefied biomass. The final quality is measured by considering parameters, such as humidity, heating value (HV), and grindability. Studies have focused on maximizing the torrefied biomass’ quality using the best possible combination for the different parameters. The main objective of this article is to present new information regarding the conventional torrefaction process, as well as study the innovative techniques that have been in development for the improvement of the torrefied biomass qualities. With this study, conclusions were made regarding the importance of torrefaction in the energy field, after considering the economic status of this renewable resource. The importance of the torrefaction parameters on the final properties of torrefied biomass was also highly considered, as well as the importance of the reactor scales for the definition of ideal protocols.