Modelling and control of hydrogen and energy flows in a network of green hydrogen refuelling stations powered by mixed renewable energy systems

The planning of a hydrogen infrastructure with production facilities, distribution chains, and refuelling stations is a hard task. Difficulties may rise essentially in the choice of the optimal configurations. An innovative design of hydrogen network has been proposed in this paper. It consists of a network of green hydrogen refuelling stations (GHRSs) and several production nodes. The proposed model has been formulated as a mathematical programming, where the main decisions are the selection of GHRSs that are powered by the production nodes based on distance and population density criteria, as well the energy and hydrogen flows exchanged among the system components from the production nodes to the demand points. The approaches and methodologies developed can be taken as a support to decision makers, stakeholders and local authorities in the implementation of new hydrogen infrastructures. Optimal configurations have been reported taking into account the presence of an additional hydrogen industrial market demand and a connection with the electrical network. The main challenge that has been treated within the paper is the technical feasibility of the hydrogen supply chain, that is mainly driven by uncertain, but clean solar and wind energy resources. Using a Northern Italian case study, the clean hydrogen produced can be technically considered feasible to supply a network of hydrogen refuelling stations. Results show that the demands are satisfied for each time period and for the market penetration scenarios adopted.     

太阳能氢能系统

随着社会经济的发展,已有的能源和资源正在以越来越快的速度消耗,特别是包括石油、煤、天燃气等在内的矿物质能源,不仅将在未来的一、二百年内耗尽,而且每年正在以千万吨计的 CO2、 NOx和 SOx向大气排放。节约能源资源,保护环境已成为人类可持续发展的必要条件。现在,人们的注意力已逐步转向可再生能源的利用开发,它包括太阳能、风能、水能、生物质能、地热能、海洋能等等。近十年来,这些新的可再生能源的利用技术已有长足的进步,在常规能源中所占的份额正在不断上升,其中有的能源,如太阳能光发电,已成为全球发展速度最快…     

Characterization of liquid flows in microfluidic systems

The microfluidic devices have recently attracted tremendous interest due to their potential of bringing novel applications into reality in many areas including biomedical industry. However, the challenges in the design of microfluidic devices still remain since all aspects of fluid flow in microchannels have not been yet fully understood. This paper presents major findings in the literature on fundamentals of flow physics in microchannels. The review is intended to provide an extensive overview on the available knowledge base as well as the areas that require intensive investigation. It includes studies on both pressure-driven and electro-osmotic flows in microchannels.     

Safety aspects of hydrogen combustion in hydrogen energy systems

Safety aspects will become essential for the introduction and acceptance of gaseous and liquid hydrogen as an energy carrier and fuel in energy supply systems. Prevention and control of accidental formation and ignition of large volumes of fuel-air mixtures are of primary importance when safety aspects of released gaseous hydrogen are discussed. Detailed knowledge of the overpressure in an accidental situation is essential for the protection of the public as well as for the corresponding plants and safety installations. Considerable progress has been made in the last few years concerning the understanding of the complex phenomena involved in combustion processes of gaseous mixtures. This holds in particular for flame acceleration and maximum turbulent flame speeds in unconfined and confined geometries. Fast turbulent deflagrations often transit spontaneously to detonations if flame speeds are high enough, depending on the combustible and boundary conditions. This paper discusses the potential hazards of hydrogen in the energy market as compared with other and already familiar energy carriers like natural gas and propane.     

Benzyltoluene/dibenzyltoluene-based mixtures as suitable liquid organic hydrogen carrier systems for low temperature applications

In this contribution we propose mixtures of the two LOHC systems benzyltoluene (H0-BT)/perhydro benzyltoluene (H12-BT) and dibenzyltoluene (H0-DBT)/perhydro dibenzyltoluene (H18-DBT) as promising hydrogen storage media for technical applications at temperatures below ambient. The mixing of the two LOHC systems provides the advantage of a reduced viscosity of the hydrogen-rich system, for example a 20 wt% addition of H12-BT to H18-DBT reduces the viscosity at 10 °C by 80%. Interestingly, it is also found that the dehydrogenation of such mixture provides a hydrogen release productivity that is 12–16% higher compared to pure H18-DBT dehydrogenation under otherwise identical conditions. This enhanced rate is attributed to a combination of reduced hydrogen partial pressure in the reactor (due to the higher H12-BT vapor pressure), preferred H12-BT dehydrogenation (due to faster H12-BT diffusion) and effective transfer hydrogenation between the two LOHC systems.     

Ultrasonic flow rate measurement of low speed non-isothermal flows

In this study, a performance evaluation of a non-intrusive ultrasonic flowmeter is carried out for slow, non-isothermal flows. The purpose of the study is to investigate the adequacy of the above meter for flow rate measurements in thermal convection loops. The flowmeter is found to be useful only for part of the range of interest.     

Development of a methodology to optimize the air bleed in PEMFC systems operating with low quality hydrogen

The use of hydrogen with lower quality than that specified in current regulation is an attractive option for stationary PEMFC power production. In this paper, the effect of CO is mitigated using air bleed levels up to 2% in an H₂ PEMFC fed with CO concentrations below 20 ppm. A methodology to optimize the air bleed levels is developed using a novel arrangement of cells coupled to a gas chromatograph. The methodology relies on evaluating the distributed performance of the cell and on determining the CO and CO₂ molar flow rates at the anode outlet. Furthermore, the amount of CO adsorbed onto the catalyst and the fraction of catalytic sites covered by CO are estimated. The results show that different parameters, such as the H₂ volumetric flow rate, CO concentration and air bleed level, influence both the steady state and dynamics of PEMFCs operated with low quality hydrogen.     

Mathematical modelling of hydrogen storage systems

A detailed mathematical model of a hydride bed has been developed to describe its behaviour under both hydriding and dehydriding conditions. In contrast to other hydride bed models previously reported in the literature, this model simulates an actual, commercially available containment vessel, rather than that of an abstract ideal situation. Thus the model provides a convenient means of predicting the time taken to release or absorb given amounts of hydrogen. These are calculated from the heat transfer characteristics and diffusion properties of particular metal alloys. Comparisons are given between the actual operating characteristics and those simulated by the model. A brief discussion of the reaction kinetics of hydriding certain metal alloys is also included.     

Sustainability assessment of hydrogen energy systems

This paper gives an overview of the potential on multi-criteria assessment of hydrogen systems. With respective selection of the criteria comprising performance, environment, market and social indicators the assessment procedure is adapted for the assessment of the selected options of the hydrogen energy systems and their comparison with new and renewable energy systems.The single parameter assessment for each indicator is demonstrated as the traditional approach in the evaluation of the option under consideration which reflects a biased result depending on the selected indicator. In order to apply the multi-criteria approach to the hydrogen systems, it was necessary to use the multi-criteria procedure based on the sustainability index rating composed of linear aggregative functions of all indicators with respective weighting function.The example under consideration are hydrogen fuel cell systems with three options including natural gas turbine, photovoltaic and wind energy systems representing different renewable power plant option. These options are evaluated with the multi-criteria method comprising the following indicators: performance indicator, market indicator, environment indicator and social indicator. The indicators are composed of a number of sub-indicators agglomerated in respective indicators. The evaluation of options under consideration was performed under constraint expressing non-numeric relation among the indicators. The group comprises cases when priority is given to a single indicator and other indicators have the same value.     

Simulation of solar hydrogen energy systems

Solar hydrogen is a promising long-term global energy option for the post-fossil fuel era. On the other hand, solar hydrogen may have already found an early commercial application in the form of seasonal energy storage for remote stand-alone photovoltaic (PV) applications. In a stand-alone solar hydrogen energy system, the photovoltaic array is coupled with an electrolyser to produce H₂ which is stored to be later converted back to electricity in a fuel cell. The system setup comprises several subsystems which have to be controlled in an optimal way. Numerical simulations are used to get a closer insight into the transient response behavior of these elegant, but rather complicated systems during variable insolation conditions and to estimate the overall system performance accurately over extensive periods of time. The simulations are performed with the H2PHOTO program which has been successfully used for the design of a solar hydrogen pilot plant. It has also shown good accuracy against experimental data.     

Suppression of hydrogen absorption into 304L austenitic stainless steel by surface low temperature gas carburizing treatment

Effect of low temperature gas carburizing (LTGC) on hydrogen absorption and hydrogen embrittlement (HE) susceptibility of 304L metastable austenitic stainless steel was investigated. The LTGC treatment imparted carburized layer on the steel surface with supersaturated solute carbon atoms (namely expanded austenite or S-phase) and more than 1 GPa surface compressive stress. Carburized layer thickness, carbon concentration level, residual compressive stress and hardness increased but hydrogen absorption decreased with increasing LTGC treatment time. Carburized surface layers had much higher austenite stability. The HE susceptibility of carburized steel was reduced due to the reduction of hydrogen absorption and the increment of austenite stability. The specimens whose residual compressive stresses were eliminated by tensile plastic straining also exhibited low hydrogen absorption during hydrogen charging, indicating that, besides the residual compressive stress, the supersaturated solute carbon atoms also have the ability to reduce hydrogen absorption. In addition, the results indicate that the supersaturated solute carbon atoms in the LTGC case can suppress hydrogen solubility without affecting diffusivity.     

Photoproduction of hydrogen by dye-sensitized systems

Visible light-induced production of hydrogen has been investigated in five different systems. These are: safranine O/EDTA, safranine T/EDTA, proflavine/EDTA, acridine orange/EDTA, and acridine yellow/EDTA, with and without added K₂PtCl₆. In the two safranine systems photoproduction of hydrogen was observed even in the absence of a Pt catalyst. Also, the addition of an electron mediator such as methyl viologen was found not necessary. Acridine yellow/EDTA/K₂PtCl₆ has been shown to be the best system examined, which upon addition of Triton X-100, showed further enhancement of the rate of hydrogen evolution.     

Pressurized hydrogen from charged liquid organic hydrogen carrier systems by electrochemical hydrogen compression

We demonstrate that the combination of hydrogen release from a Liquid Organic Hydrogen Carrier (LOHC) system with electrochemical hydrogen compression (EHC) provides three decisive advantages over the state-of-the-art hydrogen provision from such storage system: a) The EHC device produces reduced hydrogen pressure on its suction side connected to the LOHC dehydrogenation unit, thus shifting the thermodynamic equilibrium towards dehydrogenation and accelerating the hydrogen release; b) the EHC device compresses the hydrogen released from the carrier system thus producing high value compressed hydrogen; c) the EHC process is selective for proton transport and thus the process purifies hydrogen from impurities, such as traces of methane. We demonstrate this combination for the production of compressed hydrogen (absolute pressure of 6 bar) from perhydro dibenzyltoluene at dehydrogenation temperatures down to 240 °C in a quality suitable for fuel cell operation, e.g. in a fuel cell vehicle. The presented technology may be highly attractive for providing compressed hydrogen at future hydrogen filling stations that receive and store hydrogen in a LOHC-bound manner.     

Computation of low Mach thermical flows with implicit upwind methods

In order to apply a Godunov method to steady and unsteady thermical flows, we first present a truncation error analysis which proves that the Turkel preconditioned Roe splitting is applicable to flows modelized by the classical low Mach number model, including thermics. The impact of the Turkel preconditioning on the first-order/second-order pseudo-Newton algorithm (referred in the literature as the defect-correction iteration) is also analysed. Implicit methods for steady flow resolution and for accurate unsteady time advancing are proposed and studied. Numerical illustrations involve the natural convection in a square box and a flow around a perforated wall inspired by helicopter engine applications.     

Efficiency of low-temperature adsorptive hydrogen storage systems

This study presents a thermodynamic analysis of adsorptive hydrogen storage systems at cryogenic temperatures, focusing mainly on the efficiency of the storage system. Four different operation modes, differing in the process used to release the hydrogen and the availability of cooling during storage time, are examined. A sensitivity analysis was performed to determine the dependency of the efficiency on several input parameters including storage time, enthalpy of adsorption, energy required for cooling, and system size. It can be concluded that the energetic efficiency of the hydrogen storage system not considering production and usage steps ranges from 65 to 81% for short storage times, depending on the energy effort and hydrogen losses of the applied operation mode. The storage time has the most noticeable impact on efficiency and cryo-adsorptive hydrogen storage is not suitable for long storage times due to the increasing cooling effort or hydrogen losses. For short storage times e.g. hours, cooling during storage time may be omitted due to the low hydrogen losses.     

Modeling of adsorbent based hydrogen storage systems

A numerical model was developed for the evaluation of adsorbent based hydrogen storage systems. The model utilizes commercial software and simultaneously solves the conservation equations for heat, mass and momentum together with the equations for the adsorbent thermodynamics. Conservation equations were derived for a general adsorbent bed-storage vessel configuration and the adsorbent thermodynamics were a modified form of the Dubinin–Astakhov model. The solver was the Comsol^™ Multiphysics software. Real gas thermodynamic properties for hydrogen were used in the calculations. Model predictions were compared to data for charging an activated carbon based system. Applications of the model were made for charging of MOF-5^™ and MaxSorb^™ based systems that employ flow-through cooling as a means for controlling the adsorbent temperature during charging. In addition, the model was used to evaluate the contribution of pressure work to the total energy released during charging. It was found that flow-through cooling has the potential to be an effective means for heat removal and that the contribution of pressure work can be significant, depending on the type of adsorbent and the charging procedure.     

Energy life cycle analysis of hydrogen systems

In any overall balance of hydrogen energy systems it is the way in which this energy is generated and the primary energy required to produce the equipment that are of decisive importance. Excerpts from the results of a study entitled “Process Chain Analysis for a Hydrogen Energy System”, commissioned by the Bavarian State Ministry of Economics, Transportation and Technology are presented and commented on.     

环境低负荷制氢技术及集成制氢系统

讨论了各种环境低负荷的制氢技术。SPE电解水制氢技术成熟,将成为未来主要制氢方法之一。生物化学制氢和半导体光解水制氢仅以太阳能为能源,前景广阔。生物质制氢清洁、节能,值得推广。环境低负荷集成制氢系统综合多种技术,是制氢技术发展的一个趋势。