• Energy Research

The process of electrostatic precipitation that depends on the migration of particles toward the grounded collecting plates and, therefore, on their associated drift velocity, is investigated using a laboratory-scaled electrostatic precipitator (ESP). The migration of the charged particles due to the electric force exerted by the field is affected by the turbulent gas flow. Estimating the particles drift velocity requires controlling the electric conditions inside the ESP (electric field of collection, particles charge) as well as knowing the flow field. A two-stage-like electrostatic precipitator was designed. In the first zone of the filter, "barbed" ionizing electrodes were used, leading to charging of the particles and also to some dust precipitation. The collection of precharged fine particles is studied in the second section where the electric field is uniform. Using some models of electrostatic precipitation, the drift velocity of particles is derived from measurements of collection efficiency in the second section of the precipitator for different values of the turbulent diffusivity. Finally, the influence of gas flow turbulence is discussed.

Metallic and complex hydrides may act as anode and solid electrolytes in next generation of lithium batteries. Based on the conversion reaction with lithium to form LiH, Mg- and Ti-based anode materials have been tested in half-cell configuration with solid electrolytes derived from the hexagonal high temperature modification of the complex hydride LiBH 4 . These anode materials show large first discharge capacities demonstrating their ability to react with lithium. Reversibility remains more challenging though possible for a few dozen cycles. The work has been extended to full-cell configuration by coupling metallic lithium with positive electrodes such as sulfur or titanium disulfide through complex hydride solid electrolytes. Beside pure LiBH 4 which works only above 120 °C, various strategies like substitution, nanoconfinement and sulfide addition have allowed to lower the working temperature around 50 °C. In addition, use of lithium closo-boranes has been attempted. These results break new research ground in the field of solid-state lithium batteries. Finally, operando and in-situ neutron scattering methods applied to full-cells are presented as powerful tools to investigate and understand the reaction mechanisms taking place in working batteries.

Abstract Thermochemical heat storage is expected to play an important role in the ongoing transformation of the European energy system. The efficiency of thermochemical heat storage systems largely depends on that of the reactor, since it limits the amount of the heat stored per unit volume as well as the rate of the heat recovery. Thus, the optimization of the reactor design is of great importance and can be achieved via local numerical modelling, where intrinsic parameters of the materials are utilized. In the present study, we developed a procedure for the determination of the intrinsic kinetic parameters of ammonia sorption on metal halides and applied it to strontium chloride SrCl2 – ammonia NH3 working pair. A distinctive feature of the procedure is that the kinetic measurements were performed on a Sieverts type apparatus at constant temperature, which allowed resolving the common problem of heat-up time. Besides, the kinetic measurements were carried out using the optimal mass of SrCl2 – expanded natural graphite composite material (70 mg of SrCl2), ensuring that the chemical reaction rate is not constrained by the heat and mass transfer limitations. As a result, the intrinsic kinetic equations of NH3 sorption on SrCl2 ammines were derived for the first time and were demonstrated to predict the experimental data, from which they had been computed, over a wide pressure–temperature range. In addition, the obtained intrinsic kinetics, as well as the ones found in literature, were implemented in a three-dimensional numerical model computing the local temperature, pressure, and reaction advancement through the coupled equations of the heat transfer, fluid dynamics, and chemical reaction rate. The numerical results were compared with experimental data obtained on 466 mg of SrCl2 powder at various pressure–temperature conditions. In contrast to the literature kinetics, the simulation results with the intrinsic kinetic equations were found to be in a good agreement with the experimental data, demonstrating the importance of using intrinsic parameters in the local modelling of sorption reactions.

On the basis of the occurrence of a geometrical pattern for the dust layer deposited in an electrostatic precipitator, the physical phenomena leading to such a deposit are characterized. The measurement of the current-density distribution on the collecting plate shows that the dust layer pattern is strongly correlated with this distribution, leading to two kinds of deposition: zones of dense packing and zones of dendritic packing. Some explanations about the observed pattern are proposed. The size distribution of the collected powder is determined for the two zones of collection and as a function of the distance downstream from the precipitator entrance. This analysis reveals the existence of a clear difference in the size distributions of deposited powder in the two collection zones. A Deutsch-like model fairly well accounts for the observed decrease of mean diameter of the collected particles as a function of the distance downstream from the precipitator entrance. In the light of some considerations on re-entrainment and electrohydrodynamic secondary flows, possible mechanisms leading to such phenomena are briefly discussed.

Abstract Strontium chloride octaammine Sr(NH3)8Cl2 offers high volumetric and gravimetric NH3 densities and can store and release heat upon exo-/endothermal absorption and desorption of NH3. Thus, it is a promising material for thermochemical heat storage (THS) applications. In the present work, in-situ neutron imaging was applied to analyze spatio-temporal development of Sr(NH3)8Cl2 powder in a thermochemical heat storage prototype reactor during NH3 absorption and desorption processes. The powder was embedded in a stainless steel honeycomb for the efficient heat transfer during the NH3 desorption process. 2D radiography images were obtained during NH3 ab-/desorption cycles at selected temperatures. The swelling and formation of the porous structure in SrCl2 is monitored during the first cycles. A powder bed expansion of up to 10% upon NH3 absorption was observed. Neutron tomography experiment were also performed to acquire 3D information which revealed the deformation of the honeycomb. This neutron imaging experiment brought crucial information for optimizing the design of efficient and safe THS systems.

This paper describes the synthesis, crystal structure, and NH3 sorption properties of Mg1-xMnx(NH3)6Cl2 (x = 0–1) mixed metal halide ammines, with reversible NH3 storage capacity in the temperature range 20–350 °C. The stoichiometry (x) dependent NH3 desorption temperatures were monitored using in situ synchrotron radiation powder X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. The thermal analyses reveal that the NH3 release temperatures decrease in the mixed metal halide ammines in comparison to pure Mg(NH3)6Cl2, approaching the values of Mn(NH3)6Cl2. Desorption occurs in three steps of four, one and one NH3 moles, with the corresponding activation energies of 54.8 kJ⋅mol-1, 73.2 kJ⋅mol-1 and 91.0 kJ⋅mol-1 in Mg0.5Mn0.5(NH3)6Cl2, which is significantly lower than the NH3 release activation energies of Mg(NH3)6Cl2 (Ea = 60.8 kJ⋅mol-1, 74.8 kJ⋅mol-1 and 91.8 kJ⋅mol-1). This work shows that Mg1-xMnx(NH3)yCl2 (x = 0 to 1, y = 0 to 6) is stable within the investigated temperature range (20–350 °C) and also upon NH3 cycling.

Magnesium hydride owns the largest share of publications on solid materials for hydrogen storage. The Magnesium group of international experts contributing to IEA Task 32 Hydrogen Based Energy Storage recently published two review papers presenting the activities of the group focused on magnesium hydride based materials and on Mg based compounds for hydrogen and energy storage. This review article not only overviews the latest activities on both fundamental aspects of Mg-based hydrides and their applications, but also presents a historic overview on the topic and outlines projected future developments. Particular attention is paid to the theoretical and experimental studies of Mg-H system at extreme pressures, kinetics and thermodynamics of the systems based on MgH2,nanostructuring, new Mg-based compounds and novel composites, and catalysis in the Mg based H storage systems. Finally, thermal energy storage and upscaled H storage systems accommodating MgH2 are presented.