• Energy Research

<div class="section abstract"><div class="htmlview paragraph">Hydrogen technologies are among the main candidates to reduce carbon emissions in the automotive transport sector. Among the innovative solutions, Electric Vehicles (EVs) featuring hybrid powertrains, combining battery packs and hydrogen Fuel Cell (FC) stacks, are gaining prominence in our pursuit of sustainability objectives.</div><div class="htmlview paragraph">Nonetheless, realizing the full potential of these hybrid vehicles hinges on the implementation of efficient Energy Management Strategies (EMS). In this study, we present an integrated EMS approach to achieve extended driving ranges and reduced energy consumption. This is achieved primarily by operating the FC within its high-efficiency range, while ensuring that the battery packs operate in a charge-sustaining mode. The EMS is crafted through an adaptive algorithm that takes into account various driving conditions to establish the most suitable sub-optimal control strategy.</div><div class="htmlview paragraph">An integrated offline algorithm is developed: starting from an extensive sample of driving cycles, it is able to generate a set of sub-optimal fuzzy controllers, to be directly implemented onboard. These controllers are thoughtfully designed to replicate the optimal choices obtained through Dynamic Programming applied to the most representative driving cycles, as identified by the K-Means clustering algorithm.</div><div class="htmlview paragraph">Subsequently, a Driving Pattern Recognition (DPR) technique has been implemented on the vehicle model. This technique empowers real-time detection of the current driving conditions and facilitates seamless adaptive switching between the appropriate controllers.</div><div class="htmlview paragraph">Analysis has been performed for a microcar application, including an FC stack validated by experimental tests. The results have been evaluated for hydrogen fully discharge random missions and ambient temperature of 25 ° C, covering about 100km, with an increase of up to 9% compared to a range extender strategy. The improved performance (about 7% greater driving range) with respect to the range extender strategy has also been conserved for a more demanding driving cycle where additional security features have been added to the developed EMS to preserve the SOC to drop below 68%. Furthermore, the effectiveness of the proposed strategy is demonstrated by the increase in the mean efficiency of the fuel cell stack compared to the range extender strategy, approximately 10%.</div></div>

Abstract The thermochemical conversion of biomass can be effective for flexible and programmable production of electric and thermal power. Only a few models have been developed so far in the literature to describe the behavior of a screw reactor system designed for biomass fast pyrolysis. The temperature profile plays a crucial role in particular for fast pyrolysis purposes. Hence, a complete heat transfer model is required to that aim. This paper is focused on numerical modeling of a shaftless screw pyrolyzer with special focus on the kinetic framework, as well as the description of heat and mass transfer phenomena. A steady-state model with constant wall temperature has been developed to generate temperature profile and conversion patterns along the reactor. Residence time distribution input has been considered to take into account non-perfect mass conveying characteristics. The model, including all the different heat flux mechanisms such as conduction, convection and radiation, is based on a four parallel Distributed Activation Energy Model. The structure includes the three major biomass pseudo-component occurring in the biomass thermal degradation, and namely cellulose hemicellulose and lignin, along with the moisture evaporation process. Numerical results have been compared with experimental data of spruce wood pellet fast pyrolysis obtained in a lab-scale screw reactor. Numerical temperature profiles for both gas and solid phase, are in good agreement with experimental data. The results obtained allow for demonstrating that the selected framework gives realistic conversion rates for all the fast pyrolysis products namely bio-oil, char, and syngas. The maximum bio-oil production from ground spruce wood has been observed at 500 °C, with yield in the range of 64%. Moreover, the results show a strong dependence on wall temperature, gas-solid heating rate, and screw geometry.

Abstract The integration of different conversion technologies can strongly contribute to the biomass potential exploitation. To this aim, the use of intermediate pyrolysis biochar is analyzed in this paper as an alternative co-substrate in anaerobic digestion. The specie Ampelodesmos mauritanicus has been specifically chosen in this case for its capacity to tolerate, accumulate and, in some cases, degrade organic and inorganic pollutants. The biochar, produced under intermediate pyrolysis conditions at 450 °C, 500 °C and 550 °C, has been here considered for a biomethane potential assessment. The intermediate pyrolysis process improves the herbaceous bioavailability and promotes the microbial activity by reducing the digestion lag phase. Three reactors, namely B450, B500 and B550, have been considered in this study. Acclimatized cow manure from food wastes digestion has been used as inoculum with 5 g of biochar. The reactors have been continuously monitored for 15 days keeping the temperature fixed at 37 °C. Excluding the inoculum contribution, an accumulated methane production of 465–540.4 ml CH4/g-VS has been measured with an LHV evaluated in the range 25.8–26.9 MJ/kg. The modified Gompertz equation has been then used to describe the influence of biochar production temperature on methane conversion. A lag phase of 1.8, 2.2 and 3.8 days respectively for B450, B500 and B550, has been estimated showing an inverse proportionality to the biochar production temperature. The biomass to biogas energy conversion analysis reveals a reduction in the efficiency with the biochar production temperature increase. This fact is attributed to the steep reduction in volatile solids occurring by increasing the pyrolysis process severity. As a whole, the paper present a novel approach to possibly combine phytoremediation and production of renewable energy by using Ampelodesmos mauritanicus.

The last Intergovernmental Panel on Climate Change (IPPC) assessment report highlighted how actions to reduce CO2 emissions have not been effective so far to achieve the 1.5 C limit and that radical measures are required. Solutions such as the upgrading of waste biomass, the power-to-X paradigm, and an innovative energy carrier such as hydrogen can make an effective contribution to the transition toward a low-carbon energy system. In this context, the aim of this study is to improve the hydrogen production process from wet residual biomass by examining the advantages of an innovative integration of anaerobic digestion with thermochemical transformation processes. Furthermore, this solution is integrated into a hybrid power supply composed of an electric grid and a photovoltaic plant (PV), supported by a thermal energy storage (TES) system. Both the performance of the plant and its input energy demand—splitting the power request between the photovoltaic system and the national grid—are carefully assessed by a Simulink/Simscape model. The preliminary evaluation shows that the plant has good performance in terms of hydrogen yields, reaching 5.37% kgH2/kgbiomass, which is significantly higher than the typical value of a single process (approximately 3%). This finding demonstrates a good synergy between the biological and thermochemical biomass valorization routes. Moreover, thermal energy storage significantly improves the conversion plant’s independence, almost halving the energy demand from the grid.

The transition towards a low-emission economy requires advanced carbon-based materials for multiple applications. This study aimed to correlate the temperature of intermediate pyrolysis with surface morphology and the electrochemical performances of biochar from hazelnut shells (HZS) and spent coffee grounds (SCG), obtained as by-products in bio-oil production. For this process, the biochar from HZS and SCG were produced using a labscale screw-type reactor designed in-house and operated in a semi-continuous regime, under two pyrolysis temperatures (450 degrees C and 550 degrees C) and thermal post-treatment (TT) durations of 10 and 60 minutes, respectively. Physical-chemical characterization through Scanning Electron Microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) revealed distinct structural and electrochemical differences, unrevealing the fundamental importance of the feedstock selection. SEM analysis highlighted a more homogenous and open structure of HZS than SCG-based biochars. Electrochemical testing of biochar-modified screen-printed electrodes (BC-SPEs) demonstrated enhanced electron-transfer efficiency and diffusivity for HZS produced at 550 degrees C, with the HZS_550 variant yielding a 1.5-fold increase in the heterogeneous electron transfer rate constant (k0) and a 2-fold increase in diffusion coefficient (D0) compared to SCG-SPEs. Notably, HZS_550-SPEs showed enhanced sensitivity for both reversible and non-reversible redox probes, achieving a limit of detection (LOD) in the micromolar (mu M) range, halving the LOD of unmodified SPEs. These findings underscore that biochar's electron-transfer efficiency and texture are key factors driving its sensing performance. Crucially, these properties are governed by the formation of graphite-like sheet structures (GSSs), along with crystallinity and aromaticity, which develop from the condensation of amorphous carbon sheets during primary pyrolysis and are largely unaffected by TT.

Emission control efficiency and limited fuel consumption penalty and are the main design factors driving the development of engine-after-treatment exhaust systems according to both ACEA/DOE targets and continental regulations. The particulate-filter is certainly a critical technology to this aim as usually presents very high pm reduction efficiencies (even more than 90% on a mass basis depending on soot loading) leading however to a back pressure increase and eventually to an appreciable fuel consumption penalty. Nevertheless, it is in general discussion that health hazard related to particulate depends primarily on total number of emitted particles rather than on mass. The partial-flow-filter has been recently developed presenting lower reduction efficiencies on a mass basis but also a reduced penalty on fuel consumption. As a selective capability of this filter in capturing the smaller particles has also been experimentally observed, technological and scientific interest in the development of design and analysis tools dedicated to this technology has developed. However, traditional 1D and 2D models cannot be directly applied to study this technology, as the coupling between fluid-dynamics and filtration must be properly taken into account by exactly modeling single channel geometry as it is. Thus, in order to represent filtration effects by varying diameter class in partial-flow-filters, a 3D model has been coupled to a phenomenological filtration submodel taking into account Brownian diffusion and interception phenomena within an Eulerian transport framework for different particle classes depending on diameter. Results have been compared to experimental data and state that the model is able to represent the main occurring fluid-dynamic and filtration phenomena by varying mass flow rate and particle diameter.

Abstract Water management in cathode gas diffusion layers and catalyst layers of PEFCs (Polymer Electrolyte Fuel Cells) plays an important role toward the obtainment of optimal performance. Flooding may indeed occur under different operating conditions, in these components, requiring special attention both in the development and in the design processes. Simulation is a reliable tool to support the design of PEFCs, and thus provide designers with a better interpretation of experimental data. Flooding within porous media is still a critical issue for multiphase flow fuel cell modeling, representing a challenge in terms of model reliability. This paper aims at extending the validity of a literature available 1D GDL multiphase model presented in Ref. [24] . Special attention has been devoted to the analysis of the difference between multiphase and non-multiphase (multispecies) approaches, and to the 3D aspects of cell design related to flooding issues. Results indicate that flooding must be treated as a 3D phenomenon, as it has a different impact on the different active area regions. In fact, although the land is the most affected zone, current is mainly limited in the channel zone close to the gas inlet section.

Spent coffee grounds (SCG) are a valuable biogenic waste diffused on a global scale, containing a significant amount of extractives. The aim of this study is to characterize the pyrolysis oil fractions, under various process conditions, targeting their potential applications as biofuels and source of valuable chemicals. Pyrolysis tests were carried out in the range of 400-550 degrees C with a laboratory-scale screw reactor and a two-step solvent extraction process, was conducted for the aqueous bio-oil phase. The results showed that heavy organic bio-oil resulted in a carbon rich biofuel, with a carbon content of up to 63 % (w/w) and HHV up to 34.8 MJ/kg. Chloroform was selective in extracting xantines (68-74 % of the peak area), furans, phenols, and fatty acids from the aqueous phase, while the ethyl acetate extract was abundant in p-benzoquinone (70-83 % of the peak area), a key-player chemical for the petrochemical industry. The residual unextracted water phase is very rich in organic acids i.e. acetic, propionic, and formic-whose concentration is in the range 47 g/L and 87.9 g/L. The results of this study outline how solvent extraction is a promising technique for extracting valuable chemicals to improve the economic potential of spent coffee grounds pyrolysis-based biorefinery.