Abstract
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.
Highlights
The use of biomass as an energy source currently presents itself as an alternative to fossil fuels in the generation of different forms of energy, namely in the generation of electrical and thermal energy [1,2,3]
The carbon content rose in all samples, with gains between 8% for rice husk and 60% for pine woodchips
The values obtained were in line with those presented in previous studies, namely by Kalderis et al (2014) for rice husk [67], Demirbas (2002) for almond husk [68], Torreiro et al (2020) for kiwi pruning [69], San José et al (2013) for vine pruning [70], Nunes et al (2020) for olive pomace [71], and Nunes et al (2019) for pine chips [72]
Summary
The use of biomass as an energy source currently presents itself as an alternative to fossil fuels in the generation of different forms of energy, namely in the generation of electrical and thermal energy [1,2,3]. Among this group of residues or by-products, it is possible to identify a wide range of materials that, if properly framed and processed, can be presented as alternatives to traditional forms of biomass, both for the characteristics they present and the quantities available [8] The fact these by-products exist in abundance is problematic in some situations, mainly from an environmental perspective, since the volume generated from some waste is significant enough that, if an alternative is not found for its use and recovery, simple placement and landfilling does not appear to be a viable solution [9]. This group of residual biomass forms includes those from the agroforestry industry, and Portugal has a number of examples that can be introduced into the supply chain of units dedicated to the production of energy from biomass [11]
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