New biofuel raw materials for energy pellet production
are now
being studied as potential energy sources for the heating market.
Because of the complexity of the chemical and physical properties
of novel fuels, such as some agricultural residues and energy crops,
the study of their ash-related aspects is crucial for the sustainable
development of this potential energy sector. Ash fractions formed
during fixed-bed combustion of different pelletized novel crops; i.e.,
two Mediterranean crops (one herbaceous, brassica, and one woody species,
poplar) and three Chinese cassava stems (cassava species from three
different Chinese regions), and three Chinese cassava stems (cassava
species from three different Chinese regions), were characterized,
and their formation paths assessed in this study. Special emphasis
was placed on elucidating the role of major ash-forming elements in
the fractionation and transformation behavior, leading to the formation
of bottom ash, deposits, and particulate emissions (fine and coarse
ash particle fractions) on the basis of experimental data. In the
Mediterranean fuels, the predominant ash fraction obtained was bottom
ash, mainly characterized by silicates. Phosphates were found to be
the main crystalline phases in the Chinese fuels. The slagging tendency
was low for all of the fuels, although more significant for the cassava
species under the studied conditions. Further, combustion of the studied
Chinese energy crops resulted in a considerably finer particle fraction
compared to the Mediterranean fuels. Deposits and particulate matter
were dominated by K-sulfates as well as K-chloride in all fuels (except
poplar), with the occurrence of K-phosphates for cassava pellets.
Overall, this study showed fundamental differences in ash transformation
behavior during combustion of P-rich fuels (i.e., cassava mixtures)
compared to Si-rich fuels (i.e., poplar and brassica mixtures). Of
major importance is the experimental verification of the higher thermodynamic
stability of phosphates in relation to silicates. Furthermore, in
P-rich fuels at high (K + Na)/(Ca + Mg) ratios, a significant degree
of alkali metal volatilization occurs, which forms larger amounts
of particulate matter, whereas this ratio has no/low effect in Si-rich
fuels at high alkali metal ratios.
A promising route to attain a reliable impact reduction of supply chain materials is based on considering circular economy approaches, such as material recycling strategies. This work aimed to evaluate potential benefits of recycling scenarios for steel, copper, aluminium and plastic materials to the battery manufacturing stage. Focused on this aim, the life cycle assessment (LCA) and the environmental externalities methodologies were applied to two battery study cases: lithium manganese oxide and vanadium redox flow (VRFB) batteries, based on a cradle-to-gate LCA approach. In general, the results provided an insight into the raw material handling route. Environmental impacts were diminished by more than 20% in almost all the indicators, due to the lower consumption of virgin materials related to the implemented recyclability route. Particularly, VRFB exhibited better recyclability ratio than the Li-ion battery. For the former, the key components were the periphery ones attaining around 70% of impact reduction by recycling steel. Components of the power subsystem were also relevant, reaching around 40% of environmental impact reduction by recycling plastic. The results also foresaw opportunities for membranes, key components of VRFB materials. Based on findings, recycling strategies may improve the total circularity performance and economic viability of the studied systems.
Electricity from the combination of photovoltaic panels and wind turbines exhibits potential benefits towards the sustainable cities transition. Nevertheless, the highly fluctuating and intermittent character limits an extended applicability in the energy market. Particularly, batteries represent a challenging approach to overcome the existing constraints and to achieve sustainable urban energy development. On the basis of the market roll-out and level of technological maturity, five commercially available battery technologies are assessed in this work, namely, lead–acid, lithium manganese oxide, nickel–cadmium, nickel–metal hydride, and vanadium redox flow. When considering sustainable development, environmental assessments provide valuable information. In this vein, an environmental analysis of the technologies is conducted using a life cycle assessment methodology from a cradle-to-gate perspective. A comparison of the environmental burden of battery components identified vanadium redox flow battery as the lowest environmental damage battery. In terms of components, electrodes; the electrolyte; and the set of pumps, motors, racks, and bolts exhibited the greatest environmental impact related to manufacturing. In terms of materials, copper, steel, sulphuric acid, and vanadium were identified as the main contributors to the midpoint impact categories. The results have highlighted that challenging materials 4.0 are still needed in battery manufacturing to provide sustainable technology designs required to the future urban planning based on circular economy demands.
Agricultural residual biomass presents a high potential for energy use around the world, often not utilized to a large extent due to its significant differences with respect to other biomass types, such as the one of forest origin. These differences are mainly related to the characteristics of its ashes (quantity and composition) which increase certain problematic phenomena during combustion, among them bottom ash sintering and fly ash deposition. The main goal of this paper is the experimental study of these issues for four different agropellets made of residual agricultural biomass (one woody and three blended with an herbaceous component) and a forest wood pellet (used as a reference), evaluated under different operating conditions in a laboratory fixed bed reactor. The influence of inlet air flow and temperature on the sintering degree and deposition ratio has been analyzed in a systematic way. For the five biofuels, under tested conditions, a clear relation inversely proportional between air excess ratio and deposition ratio has been determined. Deposition was more substantial for the four agropellets; meanwhile the sintering degree was more important for the three with an herbaceous component. The information obtained in this research work is intended to help researchers and technologists to make choices regarding the design and operation of conversion systems adapted for agricultural residual biomass, enhancing its market penetration.
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