Metal Hydride Tank Research Articles

Effect of silicone oil additive on swelling stress alleviation in the metal hydride reactor

Considerable swelling stress associated with hydrogen absorption process caused by metal hydride expansion is extensively observed in a metal hydride tank which is usually designed for hydrogen storage application. Such swelling stress being applied to tank wall may cause potential safety issue such as tank failure. In the present investigation, silicone oil is selected as an additive incorporating into MlNi 4.5 Cr 0.45 Mn 0.05 alloy in an attempt to alleviate the swelling stress. The results obtained by a self-built direct swelling stress testing apparatus show that the addition of silicone oil can significantly reduce alloy particle swelling stress. The addition of 3 wt% silicone oil is appropriate to acquire efficient swelling stress alleviation. During cycling the maximum swelling stress increases with charging pressure. The formation of silicone oil thin film on the surface of alloy particles, acting as a “cushion” among alloy particles, would reduce particle agglomeration and enhance particle movement during hydrogen absorption and desorption cycling. This is the reason for the observed swelling stress alleviation by silicone oil. • Swelling stress was reduced by addition of silicone oil. • The maximum swelling stress increased with charging pressure. • The swelling stress alleviation was ascribed to oil thin film on particle surface.

Thermal integration of PEM Fuel Cells and metal hydrides storage system for Zero Emission Ultimate Ship (ZEUS)

The ZEUS (Zero Emission Ultimate Ship), developed in the framework of the national research project TecBia conducted by Fincantieri and co-founded by Italian Ministry of Economic Development, is a 25m length vessel characterized by a zero-emissions propulsion system. The on-board power generation is provided by 4 PEM Fuel Cell modules (140 kW power installation) fed by hydrogen stored into 48 Metal Hydride tanks (MH). PEMFC and MH thermal systems are coupled to recover the heat produced by PEMFC and to feed the endothermic dissociation reactions of hydrogen from MHs. This paper provides a Matlab-Simulink model to simulate the dynamic behaviour of the PEMFC power generation system and the thermal coupling with MH racks installed onboard. Three typical operative profiles are simulated to verify the thermal management control system and the impact of transient conditions on the propulsion plant. Furthermore, the effects of the major exogenous parameters are investigated. Results verify that thermal coupling between the two systems is guaranteed; however, an excessive load increase can lead the stacks to operate under non-optimal conditions for significant periods of time. The effect of exogenous parameters has been verified to be negligible and does not significantly affect the control system.

Development of a plug-in fuel cell electric scooter with thermally integrated storage system based on hydrogen in metal hydrides and battery pack

The thermal management of lithium-ion batteries in hybrid electric vehicles is a key issue, since operating temperatures can greatly affect their performance and life. A hybrid energy storage system, composed by the integration of a battery pack with a metal hydride-based hydrogen storage system, might be a promising solution, since it allows to efficiently exploit the endothermic desorption process of hydrogen in metal hydrides to perform the thermal management of the battery pack. In this work, starting from a battery electric scooter, a new fuel cell/battery hybrid powertrain is designed, based on the simulation results of a vehicle dynamic model that evaluates power and energy requirements on a standard driving cycle. Thus, the design of an original hybrid energy storage system for a plug-in fuel cell electric scooter is proposed, and its prototype development is presented. To this aim, the battery pack thermal power profile is retrieved from vehicle simulation, and the integrated metal hydride tank is sized in such a way to ensure a suitable thermal management. The conceived storage solution replaces the conventional battery pack of the vehicle. This leads to a significant enhancement of the on-board gravimetric and volumetric energy densities, with clear advantages on the achievable driving range. The working principle of the novel storage system and its integration within the powertrain of the vehicle are also discussed.

Enhancement of Hydrogen Storage Process Using Heat Pipe

Heat transfer from/to the metal hydride bed is a critical factor affecting the performance of metal hydride storage tanks (MHSTs for short). This study examined the effect of heat pipe on the metal hydride tank by means of heat management. The experimental study explains the use of heat pipe for enhancement the heat transfer in MHSTs, which built using LaNi4.75Al0.25 as the storage media and under various hydrogen pressure supply in the range of 2 to10 bar. This study also presents comparisons between the two different MHSTs which are designed with and without heat pipe. Two configurations of metal hydride tanks are considered and consisted of tubular cylindrical tanks with same base dimensions. The first one is a closed cylinder that exchanges heat through its lateral and base surfaces by means cool with natural convection. Heat pipe is made of copper–methanol combination and situated along the axis of the second reactor. Results show that the usage of heat pipe can be a good choice to increase hydrogen storing performance. The absorption time at 10 bar hydrogen inlet pressure was reduced more than 30%, and the mass of hydrogen storage increased by approximately 10% - 15%.

Potential Feature of Combined AB5-Type Metal Hydride Tank and PEMFC as a Safer System for Hydrogen Fueling in Bangladesh

Metal hydrides are very much reported as a potential safe option for high-density hydrogen storage materials. A combined system of proton-exchange membrane hydrogen fuel cell (PEMFC) and metal hydride (MH) tanks is designed to investigate their characteristics and performances as hydrogen storage and stable power supply system. An AB5-type (LaCe)Ni5 material containing three MH tanks is selected for investigation. Endothermic dehydrogenation of metal hydride controls the hydrogen evolution rates during a discharging period, which reduces the risk of accidents. The MH tank charged at a 20°C water bath sustains and supplies hydrogen for a longer time of 240 min. The performances of the MH tank at a water bath of 20°C and 10-bar conditions correspond to the optimum condition of hydrogen storage at the MH tank of Pragma Industries. The performances of the combined system were investigated in different working conditions. The system sustains and supplies hydrogen to PEMFC for 240, 160, 130, and 110 min for the working loads of 250, 500, 1,000, and 2,000 W, accordingly. It is concluded that hydrogen consumption frequency increases for higher load demand.

Design and calculation of heat transfer of the passive cooling modules for low-pressure hydrogen vessels

This paper deals with the issue of improving the temperature management of a metal hydride tank to reduce the energy intensity of cooling. The problem of absorption and adsorption of hydrogen gas in metals, cooling of metal hydride tanks in the process of hydrogen absorption while protecting the current level of development of science and research for this area is analysed. The work also deals with numerical and experimental verification of a prototype metal hydride tank with passive cooling.

Design of internal heat transport intensifier for metal hydride storage tank

The present article deals with potential improvement of heat removal from the centre of a metal hydride tank towards the tank’s periphery while using passive heat transfer modules. Passive cooling elements are used in order to improve heat removal from the centre of a tank towards its peripheral parts. This increases the homogeneity of the thermal field in a tank’s cross-section, which is perpendicular to the longitudinal axis. Moreover, the use of such elements improves the kinetics of hydrogen absorption into an alloy, in particular by prolonging the time to an equilibrium temperature of the alloy for a particular equilibrium pressure, which may shorten the time to a tank being 100% filled with hydrogen. The article describes four different designs of internal heat transfer intensifiers, which are aimed at improving the thermal field distribution inside the tank and their theoretical impact on the thermal field, which was examined using Ansys CFX software.

Refuelling scenarios of a light urban fuel cell vehicle with metal hydride hydrogen storage. Comparison with compressed hydrogen storage counterpart

The high price of hydrogen fuel in the fuel cell vehicle refuelling market is highly dependent on the one hand from the production costs of hydrogen and on the other from the capital cost of a hydrogen refuelling station's components to support a safe and adequate refuelling process of contemporary fuel cell vehicles. The hydrogen storage technology dominated in the vehicle sector is currently based on high-pressure compressed hydrogen tanks to extend as much as possible the driving range of the vehicles. However, this technology mandates the use of large hydrogen compression and cooling systems as part of the refuelling infrastructure that consequently increase the final cost of the fuel. This study investigated the prospects of lowering the refuelling cost of small urban hydrogen vehicles through the utilisation of metal hydride hydrogen storage. The results showed that for low compression hydrogen storage, metal hydride storage is in favour in terms of the dispensed hydrogen fuel price, while its weight is highly comparable to the one of a compressed hydrogen tank. The final refuelling cost from the consumer's perspective however was found to be higher than the compressed gas due to the increased hydrogen quantity required to be stored in fully empty metal hydride tanks to meet the same demand.

Design and Stress Analysis of Metalhydride Pressure Vessel

The article describes the design and strength calculation of a low-pressure steel tank, which is used for storage of hydrogen in a metal alloy based on Ti and Zr. An external liquid heat exchanger is considered in the design of the metal hydride tank. Strength calculations were performed to verify the selected wall thickness of the vessel and the wall thickness of the selected bottom type according to STN EN 13322-2 standard for the implementation of a metal hydride tank in operating conditions.

Shrinking and receding horizon approaches for long-term operational planning of energy storage and supply systems

To efficiently solve long-term operational planning problems of energy storage and supply systems, a near-optimal solution method based on the shrinking and receding horizon approaches was developed. A lower bound of the original problem is first calculated by solving a simplified problem, in which the number of binary variables is reduced and the related constraints are simplified. Then, a short-term operational planning problem, with a shrunken planning horizon length, is solved by providing the simplified problem results as the terminal condition for stored energy. Within this problem, the original binary variables and constraints are considered. The short-term operational planning is updated using a receding horizon approach, in which the initial and terminal conditions are provided by the previous short-term operational planning results and simplified problem results, respectively. The solution, obtained by connecting the solutions in all the updating horizons, is regarded as a near-optimal solution of the original problem. The developed method was applied to solve a long-term operational planning problem for an energy storage and supply system, which includes a photovoltaic unit and a metal hydride tank with a water electrolyzer. The results showed that the developed method could find a better solution in a shorter computation time than the conventional methods.

Hydrogen release from a metal hydride tank with phase change material jacket and coiled-tube heat exchanger

Hydrogen fuel cells are received increasingly wide attention in order to develop green ships and reduce greenhouse gas emissions in the field of waterway transportation. Metal hydrides (MHs) can be used to store hydrogen for green ships due to their high volumetric storage capacity and safety. Various measures should be considered in the design and manufacture process of the MH reactor to strengthen its performance of heat and mass transfer and obtain an acceptable hydrogen storage capacity. In this work, LaNi5 hydride is used as the hydrogen storage material and packed in the reactor. A basic axisymmetric numerical model for the hydrogen storage system without a heat exchanger has been developed and proved to be effective through the comparison between its simulation results and the published data during dehydriding. A hybrid heat exchanger, which is consisted of a phase change material (PCM) jacket and a coiled-tube, has been applied into the hydrogen storage system to relieve the thermal effect of MH in the dehydriding process on system performance. Effects of the heat transfer coefficient between the circulating heating water in the coil-tube and the MH bed, the temperature of circulating heating water and the pressure at the outlet on the dehydriding performance have been investigated. Based on parametric study, the relationships among the average dehydriding rate, the heat transfer coefficient, the heating water temperature and the outlet pressure have been found and fitted as simple equations. These fitted equations can be considered as a reference, which provides an important method to effectively control the dehydriding rate in order to satisfy the fuel requirement of the power unit and ensure the safe navigation of green ships in the future.

Coupling a metal hydride tank with a PEMFC for vehicular applications: A simulations framework

This paper presents a thermal coupling topology of a proton exchange membrane fuel cell (PEMFC) with a metal hydride tank (MHT) based on FeTi metal hydride (MH) for vehicular applications. Usually, the heat produced by the PEMFC is evacuated to the ambient and MHT is heated by an external heat source, which negatively affects the efficiency of the PEMFC system as a whole. The idea is to reuse the heat generated by the PEMFC and re-inject it into the MHT to extract the usable hydrogen (H2) for PEMFC. Initially, a comprehensive model of a multiphysics system to manage the exchange of energy flux among the PEMFC and MHT is developed. Subsequently, two distinctive heat exchangers are integrated into the multiphysics system. The performance of the overall system depends on the effective regulation of both temperature and pressure associated with introduced exchanges. For that, two parallel controllers are devised to simultaneously regulate the H2 pressure and temperature of the PEMFC stack. The simulations of the system are established on MATLAB/Simulink software. It is shown by the simulation results that the proposed controller achieves the two requested objectives: maintaining the temperature and pressure of both the PEMFC stack and MHT for reliable operation.

A novel porous metal hydride tank for hydrogen energy storage and consumption assisted by PCM jackets and spiral tubes

Hydrogen energy storage through Metal Hydride (MH) reactors has various applications in concentrated solar powers and fuel cells for stationary applications in renewable energy systems. Hydrogen storage performance and consumption of these systems are strongly dependent on heat and mass transfer characteristics. Incorporating Phase Change Materials (PCMs) and spiral tube heat exchangers into metal hydride reactors improves storage performance significantly. The present paper includes a numerical investigation on the storage performance of a novel Porous Metal Hydride Tank (PMHT) integrated with PCM as a passive heat transfer system. Moreover, a heat exchanger with newly-offered Flat Spiral Tube Planes (FSTPs) is mounted into a reactor for heat transfer enhancement. The air as Heat Transfer Fluid (HTF) flows into the metal reactor through a spiral tube to enhance the heat and mass transfer. The effects of various spiral configurations, different shapes, and thicknesses of PCM jackets on the absorption/desorption process of hydrogen are investigated in detail. Also, various inlet temperatures are applied to the system to examine its impact on the absorption/desorption process. According to the results, increasing the number of FSTPs along the PMHT reduces the absorption duration by 8%. Moreover, compared with PMHT without PCM, the absorption and desorption performance of PCM-based PMHT is improved by 44% and 20%, respectively. Furthermore, increasing and decreasing the air inlet temperature leads to a 43% and 47% reduction in total desorption and absorption duration, respectively. Finally, conical-shaped PCM-jackets are found to be capable of demonstrating better absorption and desorption performances. They offer the advantage of less PCM usage to provide even a higher performance than annulus PCM-jackets. In this regard, the conical-shaped PCM provides the means for the PMHT to reach its maximum hydrogen absorption by only 85% usage of its PCM volume. In comparison, annulus-shaped PCM uses 98% of its PCM volume to help the PMHT reach its maximum hydrogen absorption capability.

Solar electricity storage through green hydrogen production: A case study

Electricity storage technologies appear as one of the solutions in most African country's national electrical grids issues. In this context, hydrogen production from renewable could be used to testing their ability for energy storage. It is possible to recover grid losses through hydrogen production and reinject it into the grid. This research aims at demonstrating numerically and experimentally how much renewable hydrogen can be produced in a sub-Saharan African context (Cotonou, Benin). Solar photovoltaic coupled to a proton exchange membrane (PEM) electrolyzer is built to demonstrate the hydrogen production followed by a model validation. The developed model accounting for all irradiation (not only the global horizontal) is simulated on MatLab-Simulink, and results fit the experimental data significantly. Results show 19% efficiency for solar hydrogen production of 115 L·day−1 knowing that lead-acid battery is included. Limits to the production rate are the storage pressure in the metal hydride tanks and the available electricity to be stored. Economic analysis through levelized cost of hydrogen (LCOH) shows that production of hydrogen from solar photovoltaic is about 1.09 €·m−3 under the present conditions. Storing renewable electricity through hydrogen might be cost-effective when disregarding certain constraints.

An innovative multi-zone configuration to enhance the charging process of magnesium based metal hydride hydrogen storage tank

High-temperature metal hydride (MH), such as magnesium hydride, is considered as one of the most promising technology to store hydrogen. However, there are two main bottlenecks, including the low rate of hydrogen absorption and low capacity of the MH reactor. In this regard, heat removal from the MH tank plays a crucial role in the hydrogen storage process. In the present study, to increase the hydrogen absorption performance, a novel configuration of the MH reactor is proposed and simulated using computational fluid dynamics (CFD). The study aims to assess the geometrical parameters of the proposed heat exchanger. Besides, a sensitivity analysis of the operating parameters of the reactor, including the Reynolds number and temperature of the air as well as hydrogen supply pressure is performed. The results indicate that the charging time drops significantly by increasing the number of air passages since the heat transfer rate improves dramatically. By raising the heat transfer fluid initial temperature, the charging time increases; however, as the heat transfer fluid Reynolds number and the inlet pressure of hydrogen increase, the absorption process accelerates. The recommended configuration is introduced by considering both charging time and manufacturing limitations. It is shown that the loading is approximately 30 minutes for the new multi-zone hydrogen energy storage using four passages for the air which provides a more applicable hydrogen fuel system.

Innovative method to estimate state of charge of the hydride hydrogen tank: application of fuel cell electric vehicles

ABSTRACT Significant attention has been paid to metal hydrides (MH) as an environmentally friendly and safe way to store hydrogen. This technology has considerable potential for the application of embedded hydrogen storage in fuel cell electric vehicles, but its widespread application faces a major problem in terms of estimating the remaining hydrogen amount in the tank. In this work, a new method is proposed for estimating the state of charge (SoC) of the hydrogen hydride tank (HHT) by application of piezoelectric material. The idea is to cover the entire inner wall of the metal-hydride tank with a layer of piezoelectric material. During the process of hydrogen absorption, the pressure inside the tank increases, resulting in an increase in the mechanical stress applied to the piezoelectric layer, thus generating a voltage. This effect can therefore be used as an effective means of estimating the amount of hydrogen absorbed. The COMSOL Multiphysics software was used to implement the model and solve the differential equation of energy, mass, and moment. The simulation results showed that the voltage evolution as a function of hydrogen concentration follows the same behavior as the variation of the Pressure Concentration Isotherm (PCI).

Optimal design of a metal hydride hydrogen storage bed using a helical coil heat exchanger along with a central return tube during the absorption process

Metal-hydride (MH) reactors are one of the most promising approaches for hydrogen storage because of their low operating pressure, high storage volumetric density and high security. However, the heat transfer performance of the MH reactor for high hydrogenation rate is inferior. In this study, the heat transfer and hydrogen absorption process of metal hydride tank performance in Mg2Ni bed is analyzed numerically using commercial ANSYS-FLUENT software. The MH reactor is considered a cylindrical bed including a helical tube along with a central straight return tube for the cooling fluid. The effects of geometrical parameters including the tube diameter, the pitch size and the coil diameter as well as operational parameters on the heat exchanged and hydrogen absorption reactive time are evaluated comprehensively. The results showed that the helical heat exchanger along with central return tube could effectively improve heat exchanged between the cooling fluid and the metal alloy and reduce the temperature of the bed results in a higher rate of hydrogen absorption. For a proper configuration and geometry of the helical coil heat exchanger with a central return tube, the absorption reaction time is reduced by 24% to reach 90% of the storage capacity. After the optimization study of the geometrical parameters, a system with the heat exchanger tube diameter of 5 mm, coil diameter of 18 mm and the coil pitch value of 10 mm is recommended to have lower hydrogen absorption time and higher hydrogen storage capacity. The presented MH reactor can be applied for improvement of heat exchange and absorption process in industrial MH reactors.

Droop based control strategy for balancing the level of hydrogen storage in direct current microgrid application

An adaptive droop control method based on level of stored hydrogen (LSH) is proposed in order to balance the LSH of each metal hydride (MH) hydrogen storage unit for DC microgrid application. In this methodology, the droop coefficient is inversely proportional to the nth order of the LSH in charging mode, whereas it is proportional to nth order of the LSH in discharging mode. The droop coefficient is modified according to the LSH of MH tanks and controls the power sharing between the FC generators using DC-DC converters. Simulation results confirm the effectiveness of the proposed control strategy. It is found that using the adaptive droop control method, fuel cell (in discharging mode) with higher LSH of MH tank delivers more power using DC-DC converter, while other fuel cell with lower LSH of MH tank provides less power. Load sharing speed between the fuel cell units can be adjusted by modifying the exponent n of LSH in droop control. This control strategy is very useful for the decentralized control of hydrogen storage based microgrid.

Rational optimization of metal hydride tank with LaNi4.25Al0.75 as hydrogen storage medium

Metal hydride tank (MHT) is a key device in a fusion reactor to absorb and desorb hydrogen isotopes at target rates. However, the rational optimization of MHT to achieve the target rates is difficult because hydrogen reaction and transport in MHT are highly complex. Here, we address this problem by parameterizing, experimentally validating and employing the model that we developed previously to accurately simulate the absorption and desorption processes in a double-layered annulus metal hydride tank (DAMHT) with LaNi4.25Al0.75 as the storage medium. The rate equations for the hydrogen absorption and desorption reactions, including their parameters, were firstly determined through experiments. The model and its parametrization were then validated against further experimental data for hydrogen absorption and desorption processes. The hydrogen absorption performance was found to be enhanced by increasing initial porosity ε0, as well as decreasing initial particle radius rp,0, temperature T0 and hydrogen concentration H/M0, and the order of their impacts was rp,0 > T0 > H/M0 > ε0. The hydrogen desorption performance was found to be mainly enhanced by increasing H/M0, and not sensitive to rp,0, ε0, or T0. Finally, optimal initial conditions were determined— rp,0 = 8.9 μm, ε0 = 0.6, T0 = 298/383 K, H/M0 = 0.5/2.9 to give a design of DAMHT that could meet the rate targets set for a single MHT. This physical model based and numerical simulation guided strategy is of general value for the design of MHT in hydrogen related applications.

Thermal Management of Edge-Cooled 1 kW Portable Proton Exchange Membrane Fuel Cell Stack

Air-cooled proton exchange membrane (PEM) fuel cell stacks are gaining momentum as power sources for portable applications such as electric bikes, unmanned aerial vehicles (UAVs), forklifts, etc. Usually the power of portable stacks (PS) is up to several kW [1,2]. Most of the heat generated during PS operation is dissipated into the surrounding atmosphere via forced air convection along the cooling channels or edge-cooling fins, while the higher power stacks require liquid cooling. The emphasis during the design phase of PS is primarily directed towards determining the most suitable material for bipolar plates and the accompanying thermal management. Some of the thermal management objectives are: (i) ensuring the appropriate heat transfer from the stack during startup, i.e. accurately determining the required convection flow rate, to achieve sufficiently high operating temperature from startup at ambient temperature, thus preventing flooding (occurring if the flow rate is high and temperature of the stack is low) or membrane dehydration (occurring if the flow rate is low and temperature inside the stack is high); (ii) ensuring sufficiently high heat removal rates via forced air convection during the operation characterized by stable temperature of the stack, i.e. loosely termed steady-state operation; (iii) ensuring as low as possible temperature difference between the inside and outside portions of the stack by choosing the materials with favorable thermal properties; (iv) properly design the stack and edge-cooling fins to ensure sufficiently high heat removal rates; (v) design the frame for the stack which will ensure that the cooling air is directed to uniformly flow along the edge-cooling fins. In previous studies [3,4] it was shown that the operating temperature inside PEM fuel cell is highly non-uniform and it is not accurate to represent the operating temperature with just one parameter, while at the same time if the temperature profile is controlled it can be exploited to result in high performance of the cell by manipulating the water vapor saturation profile, i.e. relative humidity profile inside the cell. The main contributions of this work to the research field are evident in outlining that the commonly used lumped models can be misleading for dynamic analysis of PEM fuel cell performance due to inability to accurately calculate the maximal temperature inside the stack and this work also outlines under which circumstances the lumped models can be used. This work also presents a novel transient CFD model for analysis of thermal management of PS which gives insight in mass and heat transfer both inside and outside of the cell (internal heat and mass transfer and forced air convection edge-cooling), while other works focus on only one aspect and simplify the other to a significant extent.In order to study thermal management influence on the performance od 1kW edge-cooled proton exchange membrane fuel cell stack without external humidification comprehensive numerical analyses are conducted. Two numerical approaches are considered and compared for a prescribed load profile: (i) lumped model and novel (ii) real-time transient computational fluid dynamics model incorporating realistic modeling of forced air convection on the edge-cooling of the stack. The developed computational fluid dynamics model is used to study the influence of (i) bipolar plate materials (ii) operating delta pressure along the flow field and (iii) different cooling fin configurations on the water and heat balance inside the stack. The results indicate that (i) maximal and average temperatures of the stack are almost linearly correlated to the thermal conductivity of bipolar plate materials and maximal temperatures can be significantly higher (ii) the operating delta pressure can be manipulated to increase the performance of the stack and (iii) the cooling fin redesign has major influence on the overall temperature uniformity across the stack. Additionally, the heat transfer between the stack and metal hydride tank is studied.