Multi-scale simulation of solid oxide fuel cell power units

A multi-scale physically-based model is presented in this study in order to quantitatively assess the effect of geometrical modifications and working conditions in an existing SOFC small power unit. The model, validated in different operating conditions, describes transport and reaction phenomena within the electrodes and the feeding channels through conservation equations, while the electrode microstructural properties are evaluated through the particle-based three-dimensional reconstruction of the microstructure. The model is able to capture the main chemical and physical phenomena occurring from the microscale to the macroscale, thus predicting the power output from the knowledge of the same input parameters available in reality, such as powder characteristics and operating conditions. The presented simulations rationalize how the power unit behaves upon a variation in flow configuration, operating temperature and cell geometry, thus providing a tool to predict how to optimize and control the operation of an SOFC system

Effective transport properties in random packings of spheres and agglomerates

A modelling framework for the prediction of effective properties in random packings of particles is presented. Random packings of spheres and agglomerates of spheres are numerically generated by using packing algorithms. Effective properties of both the types of packings are evaluated through a Monte-Carlo random-walk (a.k.a. mean square displacement) method, which allows the calculation of both geometrical parameters (e.g., pore size distribution, specific surface area) and transport properties (e.g., effective gas diffusivity, permeability). The results are reported as a function of porosity in dimensionless form, in order to obtain scale-independent information. The effective properties obtained for random packings of spheres are compared with independent experimental data showing a satisfactory agreement. Effective properties of packings of agglomerates are also evaluated, showing that particle agglomeration significantly increases the mean pore size while reducing the effective gas diffusivity and the specific surface area. The results show that agglomerates can not be generally assimilated to spheres with an equivalent diameter. The modelling approach presented in this study may improve the quantitative characterization of porous media composed by aggregates of particles

Engineered electrode microstructure for optimization of solid oxide fuel cells

This paper presents a mathematical model for the description of transport and reaction phenomena in porous composite electrodes for solid oxide fuel cell (SOFC) applications. The model is based on charge and mass balances, describing transport of charged and gas species along with the electrochemical reaction occurring at the solid/gas phase interface. Effective properties of the porous media are evaluated on numerically reconstructed microstructures. The correlation between electrode microstructure and electrochemical performance is investigated. In particular, the study focuses on how a distribution of particle size within the thickness may improve the air-electrode efficiency. The results show that distributing smaller particles at the electrolyte interface reduces the sensitivity of the cathode efficiency to the electrode thickness, with clear advantages from the manufactory point of view. However, the conditions for which this advantage is relevant, that is, particle size smaller than 0.10 μm and porosity in the order of 15 %, are not technically achievable at the presen

Thermal hazard analysis of organic peroxides by adiabatic calorimetry

Organic peroxides are widely used in the chemical industry as initiators or curing agents for polymerization reactions. However, the use of peroxides presents an intrinsic hazard due to the presence of the highly unstable peroxy group which causes peroxides readily decompose. In present study, the thermal hazards of a selected organic peroxide, the benzoyl peroxide (BPO), were experimentally investigated by using adiabatic calorimetry. On the basis of experimental results, the thermal hazard parameters under adiabatic conditions were estimated. Preliminary data with respect to decomposition onset temperatures and decomposition heat were obtained by simultaneous TG-DSC-FTIR analysis. A Phi-Tec II adiabatic calorimeter was used to study the thermal decomposition of the selected peroxide. The experimental data obtained allowed the assessment of thermokinetic parameters. Decomposition products formed during the experimental runs were sampled and characterized by FTIR and gas chromatographic techniques. The results obtained in the present investigation could be useful for the adoption of inherently safer design in the manufacturing, handling, storage, and disposal of organic peroxides

Hazards and safety issues associated to the residual solid content in crude edible oil processing

The present work focuses on the hazards connected with edible oil refining during process and maintenance operations. A specific experimental protocol was set up in order to verify the possibility of having fire hazards connected with the unwanted residual solids which might accumulate on the bottom of storage tanks, due to sedimentation, or in process equipment, due to progressive fouling. The analysis of residual solid samples taken from an actual edible oil refinery allowed evaluating the possible formation of flammable mixtures or products during maintenance operations. Specific hazard indexes were defined in order to analyse two case studies which provided indications for the safety enhancement of process and maintenance operations

Recycling of Lithium-Ion Batteries: Overview of Existing Processes, Analysis and Performance

Lithium-ion batteries (LIBs) have become a widespread technology for electrochemical energy storage in the current era of digitalization and transport electrification, being used as electric stationary storage as well as for powering electric vehicles, e-bikes and portable electronic devices such as smartphones and laptops. However, LIBs contain valuable materials, such as cobalt, nickel, lithium and graphite, whose supply has become critical to meet the increasing demand of batteries. Therefore, proper recycling processes are required in order to recover these materials from spent batteries and re-use them to produce new batteries in a sustainable cycle. This contribution provides an extensive survey of the main recycling routes available today, focusing specifically on pyrometallurgical and hydrometallurgical processes based in Europe, North America and Asia. Attention is also devoted to the recycling behaviour of individuals and companies and to the possible ways to increase their recycling rate. The comparison of different processes allows for the ranking of best practices as well as the drawbacks of different process units, with identification of which materials can be recovered, their recovery rate, and an assessment of the overall recycling efficiency of the process for different battery sizes (small and large, for portable electronics and electric vehicles, respectively). The analysis reveals that pyrometallurgical processes can flexibly treat different LIB chemistries but, since the electrolyte and graphite are burnt in the process, the global recycling efficiency cannot compete with hydrometallurgical processes, especially for small format batteries. Nevertheless, hydrometallurgical processes typically require preliminary mechanical separation treatments to separate the black mass, which contains valuable electrodic materials, as well as complex precipitation steps, which eventually reduce the material recovery rate and the applicability to diverse LIB chemistries. Finally, the study reports an analysis of the electrochemical performance of a battery made with recycled materials, showing that even if recycled cathodic materials had a lower gravimetric capacity and solid-state diffusivity, the performance of a recycled battery could be compensated by simple minor changes to the cell design which would ultimately decrease the specific energy density by a few percent compared to a LIB made with virgin materials

Development of phenol-enriched olive oil with phenolic compounds extracted from wastewater produced by physical refining

While in the last few years the use of olive cake and mill wastewater as natural sources of phenolic compounds has been widely considered and several studies have focused on the development of new extraction methods and on the production of functional foods enriched with natural antioxidants, no data has been available on the production of a phenol-enriched refined olive oil with its own phenolic compounds extracted from wastewater produced during physical refining. In this study; we aimed to: (i) verify the effectiveness of a multi-step extraction process to recover the high-added-value phenolic compounds contained in wastewater derived from the preliminary washing degumming step of the physical refining of vegetal oils; (ii) evaluate their potential application for the stabilization of olive oil obtained with refined olive oils; and (iii) evaluate their antioxidant activity in an in vitro model of endothelial cells. The results obtained demonstrate the potential of using the refining wastewater as a source of bioactive compounds to improve the nutraceutical value as well as the antioxidant capacity of commercial olive oils. In the conditions adopted, the phenolic content significantly increased in the prototypes of phenol-enriched olive oils when compared with the control oil

Common inconsistencies in modeling gas transport in porous electrodes: The dusty-gas model and the Fick law

The paper shows as two assumptions typically made in modeling gas transport in solid oxide fuel cell electrodes, i.e., a) uniform pressure in the dusty-gas model, and b) validity of the Bosanquet formula in the Fick model, may lead to serious inconsistencies (such as molar fractions that do not sum up to one or fluxes that do not obey reaction stoichiometry), thus nullifying the efforts of the mechanistic modeling of transport phenomena. The nature of the inconsistent use of the models is explained with clear examples, then the correct implementation of the gas transport models is discussed. The study aims to promote a coherent physically-based modeling of gas transport phenomena in porous electrodes in order to assist their rational design

Mathematical modeling of monolith reactors for photocatalytic oxidation of air contaminants

A distributed parameter model for photocatalytic oxidation of air contaminants in monolith reactors is presented. Heat and mass balance equations for monolith structure are combined with a model of irradiation from a light source and a kinetic model for photon adsorption and chemical reaction to describe the processes of heat, mass and photon transfer within the system and the heterogeneous chemistry at the catalyst surface. The model accounts for interaction between light and matter at the catalyst surface, convective and interphase gas-solid heat and mass transfer, reaction at the catalyst surface and heat conduction within the solid structure. Together with detailed axial profile of temperature and conversion in the gas phase and at the catalyst surface under different operating conditions (inlet gas temperature, composition and flow rate, light source power, monolith geometry), the model provides the distribution of photon flux along the channels and allows the discrimination between thermal and pure photonic effect on the overall rate of conversion. (C) 1998 Elsevier Science S.A. All rights reserved