Abstract
High-density biomass plantations have played a key role in the national energy landscape in Italy since the 1990s but, to date, an inversion of tendency and a significant reduction of cultivated areas has been noted. Despite this, the existing plantations have seen their coppicing rotation become significantly lengthened, resulting in large quantities of biomass per hectare. This study aimed to identify the best raw material suitable for pellet production using whole trees or stems without branches from poplar plantations at the end of the third, sixth and ninth year of age. All types of pellets made reach the requirements of class A1 for diameter, length, moisture content, ash melting point, lower heating value, as well as nitrogen (N), sulfur (S), and heavy metals. None of the theses satisfied the bulk density parameters while for ashes and mechanical durability, a great variability was observed according to the different raw materials used. An improvement in terms of heating value was observed by transforming the poplar wood chips refined into pellets. The pelletizing process using high density poplar plantation as a raw material highlights the possibility of obtaining a product that meets many of the quality standards required on the market. These aspects are closely related to the innovation carried out in the agro-forestry sector for effective energetic sustainability.
Highlights
IntroductionThe critical issues related to the decreasing availability of energy sources of fossil origin, as well as their geographical distribution in politically unstable areas, together with huge environmental problems at a global scale, have led to an increased focus on the search for alternative energy sources.The use of renewable energy has increased steadily over time due to the need to mitigate climate change by reducing the use of fossil fuels [1,2], which are responsible for the constant increase in the concentration of greenhouse gases (GHG) in the atmosphere [3].The European Commission, through the 2020 climate and energy package, has drafted a set of binding rules to ensure that the EU achieves its climate and energy targets by 2020, providing for the cutting of 20% of greenhouse gas emissions (compared to the levels of 1990), 20% of energy requirements needing to be derived from renewable sources, and a 20% improvement in energy efficiency [4]. biomass has been a subject of great interest in terms of power generation, its use at the industrial level has attracted less attention; the various factors to explain this lack of attention are mainly the low mass and energy density, the dispersion of the raw material and its availability in less convenient forms, and the high transport costs [5].Energies 2019, 12, 2973; doi:10.3390/en12152973 www.mdpi.com/journal/energiesOne way to overcome the limitations resulting from the low bulk density and high transport costs is to use densification processes (pelletization and/or briquetting) before using this material for energy purposes, in order to exploit a homogeneous and easy-to-use solid biofuel, which is characterized by a higher energy density [6,7].For these reasons the pellet sector, unlike biomasses from Short Rotation Woody Crops (SRWC), has seen important developments both in terms of production and in terms of the number of installed transformation plants, with a market price exceeding €300/tons in 2018 [8]
By analyzing the data related to the heavy metals content we identified the types of pellets characterized by their lower concentration: As, Ni and Cr in the pellet obtained from the poplar of 6 years without branches, Pb and Cu in the pellet of 6 years with branches, Zn in the pellet of 3 years without branches, Cd in the poplar of 9 years without branches
The performed research and the analysis of the results reveals that it is possible to produce a good quality pellet starting from wood chips obtained from Short Rotation Coppice of poplar and thereby converting a material with a low commercial value into superior merchandise material, in terms of quality, cost and energy
Summary
The critical issues related to the decreasing availability of energy sources of fossil origin, as well as their geographical distribution in politically unstable areas, together with huge environmental problems at a global scale, have led to an increased focus on the search for alternative energy sources.The use of renewable energy has increased steadily over time due to the need to mitigate climate change by reducing the use of fossil fuels [1,2], which are responsible for the constant increase in the concentration of greenhouse gases (GHG) in the atmosphere [3].The European Commission, through the 2020 climate and energy package, has drafted a set of binding rules to ensure that the EU achieves its climate and energy targets by 2020, providing for the cutting of 20% of greenhouse gas emissions (compared to the levels of 1990), 20% of energy requirements needing to be derived from renewable sources, and a 20% improvement in energy efficiency [4]. biomass has been a subject of great interest in terms of power generation, its use at the industrial level has attracted less attention; the various factors to explain this lack of attention are mainly the low mass and energy density, the dispersion of the raw material and its availability in less convenient forms, and the high transport costs [5].Energies 2019, 12, 2973; doi:10.3390/en12152973 www.mdpi.com/journal/energiesOne way to overcome the limitations resulting from the low bulk density and high transport costs is to use densification processes (pelletization and/or briquetting) before using this material for energy purposes, in order to exploit a homogeneous and easy-to-use solid biofuel, which is characterized by a higher energy density [6,7].For these reasons the pellet sector, unlike biomasses from Short Rotation Woody Crops (SRWC), has seen important developments both in terms of production and in terms of the number of installed transformation plants, with a market price exceeding €300/tons in 2018 [8]. One way to overcome the limitations resulting from the low bulk density and high transport costs is to use densification processes (pelletization and/or briquetting) before using this material for energy purposes, in order to exploit a homogeneous and easy-to-use solid biofuel, which is characterized by a higher energy density [6,7]. For these reasons the pellet sector, unlike biomasses from Short Rotation Woody Crops (SRWC), has seen important developments both in terms of production and in terms of the number of installed transformation plants, with a market price exceeding €300/tons in 2018 [8]
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