Russian Federation
Adsorption-Based Hydrogen Storage in Activated Carbons and Model Carbon Structures
Jul 2021
Publication
The experimental data on hydrogen adsorption on five nanoporous activated carbons (ACs) of various origins measured over the temperature range of 303–363 K and pressures up to 20 MPa were compared with the predictions of hydrogen density in the slit-like pores of model carbon structures calculated by the Dubinin theory of volume filling of micropores. The highest amount of adsorbed hydrogen was found for the AC sample (ACS) prepared from a polymer mixture by KOH thermochemical activation characterized by a biporous structure: 11.0 mmol/g at 16 MPa and 303 K. The greatest volumetric capacity over the entire range of temperature and pressure was demonstrated by the densest carbon adsorbent prepared from silicon carbide. The calculations of hydrogen density in the slit-like model pores revealed that the optimal hydrogen storage depended on the pore size temperature and pressure. The hydrogen adsorption capacity of the model structures exceeded the US Department of Energy (DOE) target value of 6.5 wt.% starting from 200 K and 20 MPa whereas the most efficient carbon adsorbent ACS could achieve 7.5 wt.% only at extremely low temperatures. The initial differential molar isosteric heats of hydrogen adsorption in the studied activated carbons were in the range of 2.8–14 kJ/mol and varied during adsorption in a manner specific for each adsorbent.
Pd Catalysts Supported on Bamboo-Like Nitrogen-Doped Carbon Nanotubes for Hydrogen Production
Mar 2021
Publication
Bamboo-like nitrogen-doped carbon nanotubes (N-CNTs) were used to synthesize supported palladium catalysts (0.2–2 wt.%) for hydrogen production via gas phase formic acid decomposition. The beneficial role of nitrogen centers of N-CNTs in the formation of active isolated palladium ions and dispersed palladium nanoparticles was demonstrated. It was shown that although the surface layers of N-CNTs are enriched with graphitic nitrogen palladium first interacts with accessible pyridinic centers of N-CNTs to form stable isolated palladium ions. The activity of Pd/N-CNTs catalysts is determined by the ionic capacity of N-CNTs and dispersion of metallic nanoparticles stabilized on the nitrogen centers. The maximum activity was observed for the 0.2% Pd/N-CNTs catalyst consisting of isolated palladium ions. A ten-fold increase in the concentration of supported palladium increased the contribution of metallic nanoparticles with a mean size of 1.3 nm and decreased the reaction rate by only a factor of 1.4.
Complex Methods of Estimation Technological Strength of Welded Joints in Welding at Low Temperatures
Feb 2021
Publication
A comprehensive methodology for estimating the technological strength of welded joints are developed based on parameters reflecting the welding technology weldability hydrogen force and deformation conditions for welding and other informative parameters that correlate with the characteristics of the welded joint as well as improving existing methods for estimating the technological strength of welded joints connections through the introduction of modern equipment and non-destructive testing systems. It has been established that the proposed comprehensive estimation methodology will allow reaching a new qualitative level in assessing the technological strength of a welded joint using modern equipment and measuring instruments. According to the results of the experimental work it was found that when welding at low temperatures the increase in the probability of the formation and development of cold cracks is mainly determined by the critical content of diffusible hydrogen in the weld metal depending on the structural and force parameters of the welded joints.
A New Model For Hydrogen-Induced Crack (HIC) Growth in Metal Alloy Pipelines Under Extreme Pressure
Dec 2020
Publication
Pipeline failure caused by Hydrogen-Induced Cracking (HIC) also known as Hydrogen Embrittlement (HE) is a pressing issue for the oil and natural gas industry. Bursts in pipelines are devastating and extremely costly. The explosive force of a bursting pipe can inflict fatal injuries to workers while the combined loss of product and effort to repair are highly costly to producers. Further pipeline failures due to HIC have a long lasting impact on the surrounding environment. Safe use and operation of such pipelines depend on a good understanding of the underlying forces that cause HIC. Specifically a reliable way to predict the growth rate of hydrogen-induced cracks is needed to establish a safe duration of service for each length of pipeline. Pipes that have exceeded or are near the end of their service life can then be retired before the risk of HIC-related failures becomes too high. However little is known about the mechanisms that drive HIC. To date no model has been put forth that accurately predicts the growth rate of fractures due to HIC under extreme pressures such as in the context of natural gas and petroleum pipelines. Herein a mathematical model for the growth of fractures by HIC under extreme pressures is presented. This model is derived from first principles and the results are compared with other models. The implications of these findings are discussed and a description of future work based on these findings is presented.
The Microstructure Study of the Hydrogenated Titanium Specimens Tested at High Temperature Creep for Long-term Tensile Strength
Feb 2020
Publication
Experimental tests of flat titanium samples at a temperature of 450 °C stretched with a constant force up to destruction were carried out. Titanium samples were hydrogenated in the Moscow Aviation Institute laboratory to a hydrogen content of 0.1 % 0.3 % and 0.6 % by weight of the specimen and then tested in the laboratory of Lomonosov Moscow State University. From the experiments the time to failure the localization time of the deformations and the stress distribution along the longitudinal coordinate of the sample over time were obtained. A metallographic study was conducted and the phase composition was investigated in Moscow Aviation Institute. The effect of hydrogen on long-term strength mechanical characteristics and phase composition has been elucidated.
Sensitivity to Detonation and Detonation Cellular Structure of H2-O2-AIr-H2O2 Gas Mixtures
Sep 2005
Publication
Today it is not known – neither qualitatively not quantitatively - how large the impact can be of the promoters on sensitivity to hydrogen-air detonation in hypothetical accidents at hydrogen-containing installations transport or storage facilities. Report goal is to estimate theoretically an effect of hydrogen-peroxide (as representative promoter) on sensitivity to detonation of the stoichiometric hydrogen-oxygen gas mixtures. The classical H2-O2-Ar (2:1:7) gas mixture was chosen as reference system with the well established and unambiguously interpreted experimental data. In kinetic simulations it was found that the ignition delay time is sensitive to H2O2addition for small initial H2O2concentrations and is nearly constant for the large ones. Parametric reactive CFD studies of two dimensional cellular structure of 2H2-O2-7Ar-H2O2 detonations with variable hydrogen peroxide concentration (up to 10 vol.%) were also performed. Two un-expected results were obtained. First result: detonation cell size is practically independent upon variation of initial hydrogen peroxide concentration. For practical applications it means that presence of hydrogen-peroxide did not change drastically sensitivity of the stoichiometric hydrogen-oxygen gas mixtures. These theoretical speculations require an experimental verification. Second result: for large enough initial H2O2concentrations (> 1 vol.% at least) a new element of cellular structure of steady detonation wave was revealed. It is a system of multiple secondary longitudinal shock waves (SLSW) which propagates in the direction opposite to that of the leading shock wave. Detailed mechanism of SLSW formation is proposed.
Modelling of Lean Uniform and Non-Uniform Hydrogen-Air Mixture Explosions in a Closed Vessel
Sep 2009
Publication
Simulation of hydrogen-air mixture explosions in a closed large-scale vessel with uniform and nonuniform mixture compositions was performed by the group of partners within the EC funded project “Hydrogen Safety as an Energy Carrier” (HySafe). Several experiments were conducted previously by Whitehouse et al. in a 10.7 m3 vertically oriented (5.7-m high) cylindrical facility with different hydrogen-air mixture compositions. Two particular experiments were selected for simulation and comparison as a Standard Benchmark Exercise (SBEP) problem: combustion of uniform 12.8% (vol.) hydrogen-air mixture and combustion of non-uniform hydrogen-air mixture with average 12.6% (vol.) hydrogen concentration across the vessel (vertical stratification 27% vol. hydrogen at the top of the vessel 2.5% vol. hydrogen at the bottom of the vessel); both mixtures were ignited at the top of the vessel. The paper presents modelling approaches used by the partners comparison of simulation results against the experiment data and conclusions regarding the non-uniform mixture combustion modelling in real-life applications.
Development and Operation Modes of Hydrogen Fuel Cell Generation System for Remote Consumers’ Power Supply
Aug 2021
Publication
At the present stage of electric power industry development special attention is being paid to the development and research of new efficient energy sources. The use of hydrogen fuel cells is promising for remote autonomous power supply systems. The authors of the paper have developed the structure and determined the optimal composition of a hybrid generation system based on hydrogen fuel cells and battery storage and have conducted studies of its operating modes and for remote consumers’ power supply efficiency. A simulation of the electromagnetic processes was carried out to check the operability of the proposed hybrid generation system structure. The simulation results confirmed the operability of the structure under consideration the calculation of its parameters reliability and the high quality of the output voltage. The electricity cost of a hybrid generation system was estimated according to the LCOE (levelized cost of energy) indicator its value being 1.17 USD/kWh. The factors influencing the electricity cost of a hydrogen generation system have been determined and ways for reducing its cost identified.
Fundamentals and Principles of Solid-State Electrochemical Sensors for High Temperature Gas Detection
Dec 2021
Publication
The rapid development of science technology and engineering in the 21st century has offered a remarkable rise in our living standards. However at the same time serious environmental issues have emerged such as acid rain and the greenhouse effect which are associated with the ever-increasing need for energy consumption 85% of which comes from fossil fuels combustion. From this combustion process except for energy the main greenhouse gases-carbon dioxide and steam-are produced. Moreover during industrial processes many hazardous gases are emitted. For this reason gas-detecting devices such as electrochemical gas sensors able to analyze the composition of a target atmosphere in real time are important for further improving our living quality. Such devices can help address environmental issues and inform us about the presence of dangerous gases. Furthermore as non-renewable energy sources run out there is a need for energy saving. By analyzing the composition of combustion emissions of automobiles or industries combustion processes can be optimized. This review deals with electrochemical gas sensors based on solid oxide electrolytes which are employed for the detection of hazardous gasses at high temperatures and aggressive environments. The fundamentals the principle of operation and the configuration of potentiometric amperometric combined (amperometric-potentiometric) and mixed-potential gas sensors are presented. Moreover the results of previous studies on carbon oxides (COx) nitrogen oxides (NOx) hydrogen (H2 ) oxygen (O2 ) ammonia (NH3 ) and humidity (steam) electrochemical sensors are reported and discussed. Emphasis is given to sensors based on oxygen ion and proton-conducting electrolytes.
Critical Morphological Phenomena During Ultra-lean Hydrogen-air Combustion in Closed Horizontal Hele-Shaw Cell
Sep 2021
Publication
Free quasi-two-dimensional outward propagation of the ultra-lean hydrogen-air flames was studied in a horizontal closed flat channel in order to minimize the influences of gravity and natural convection. Experiments were carried out with a sequential change of initial hydrogen concentration in the premixed gaseous hydrogen-air mixtures in the range from 3 to 12 vol. % H2 under normal pressure and temperature conditions. Two types of critical (in term of concentration threshold behavior) morphological phenomena were observed - formation of a pre-flame kernel and primary bifurcation of the pre-flame kernel and the higher order (secondary tertiary etc.) bifurcations of the individual locally spherical and restricted in space flame fronts. For the given initial ambient conditions (channel thickness initial gas mixture pressure and temperature) variation of initial mixture stoichiometry results in a few substantial changes in overall flame shape. These changes were recorded at the specific concentration limits which delineate three characteristic macroscopic morphological forms (morphotypes) of the ultra-lean hydrogen-air flame's ""trails"" - ""ray-like"" ""dendritic"" and ""quasi-uniform"". Transitions between the revealed basic flame morphotypes took place in different ways. The ""pre-flame kernel-to- rays"" and ""rays-to-dendrites"" transitions were abrupt and resembled the first order transitions in physics. -to-quasi-uniform morphology"" were significantly blurred and can be regarded as analogue to the second order transitions.
Metallurgical Model of Diffusible Hydrogen and Non-Metallic Slag Inclusions in Underwater Wet Welding of High-Strength Steel
Nov 2020
Publication
High susceptibility to cold cracking induced by diffusible hydrogen and hydrogen embrittlement are major obstacles to greater utilization of underwater wet welding for high-strength steels. The aim of the research was to develop gas–slag systems for flux-cored wires that have high metallurgical activity in removal of hydrogen and hydroxyl groups. Thermodynamic modeling and experimental research confirmed that a decrease in the concentration of diffusible hydrogen can be achieved by reducing the partial pressure of hydrogen and water vapor in the vapor–gas bubble and by increasing the hydroxyl capacity of the slag system in metallurgical reactions leading to hydrogen fluoride formation and ionic dissolution of hydroxyl groups in the basic fluorine-containing slag of a TiO2–CaF2–Na3AlF6 system.
Safe Storage of Compressed Hydrogen at Ambient and Cryogenic Temperatures in Flexible Glass Capillaries
Sep 2013
Publication
We have demonstrated that the strength of produced flexible quartz capillaries can be high enough to withstand the internal hydrogen pressure up to 233 MPa at normal and cryogenic temperature. According to the experimental results the cryo-compressed storage of hydrogen in the capillaries at moderate pressure can enable one to reach DOE 2015 aims for the gravimetric and volumetric capacities of vessels for the safe mobile hydrogen storage. Furthermore flexible capillaries in a bundle can probably serve as a high-pressure pipes for the transportation of gases over long distances. The developed technology of hydrogen storage can be applied to methane and hythane (H₂ - CH₄ mixture) which bridge the gap between conventional fossil fuels and the clean future of a hydrogen economy. It can be also applied to other gases i.e. air oxygen and helium-oxygen mixtures widely used in autonomic breathing devices.
An Extended Flamelet-based Presumed Probability Density Function for Predicting Mean Concentrations of Various Species in Premixed Turbulent Flames
Sep 2020
Publication
Direct Numerical Simulation (DNS) data obtained by Dave and Chaudhuri (2020) from a lean complex-chemistry hydrogen-air flame associated with the thin-reaction-zone regime of premixed turbulent burning are analyzed to perform a priori assessment of predictive capabilities of the flamelet approach for evaluating mean species concentrations. For this purpose dependencies of mole fractions and rates of production of various species on a combustion progress variable c obtained from the laminar flame are averaged adopting either the actual Probability Density Function (PDF) P (c) extracted from the DNS data or a common presumed β-function PDF. On the one hand the results quantitatively validate the flamelet approach for the mean mole fractions of all species including radicals but only if the actual PDF P (c) is adopted. The use of the β-function PDF yields substantially worse results for the radicals’ concentrations. These findings put modeling the PDF P (c) on the forefront of the research agenda. On the other hand the mean rate of product creation and turbulent burning velocity are poorly predicted even adopting the actual PDF. These results imply that in order to evaluate the mean species concentrations the flamelet approach could be coupled with another model that predicts the mean rate and turbulent burning velocity better. Accordingly the flamelet approach could be implemented as post-processing of numerical data yielded by that model. Based on the aforementioned findings and implications a new approach to building a presumed PDF is developed. The key features of the approach consist in (i) adopting a re-normalized flamelet PDF for intermediate values of c and (ii) directly using the mean rate of product creation to calibrate the presumed PDF. Capabilities of the newly developed PDF for predicting mean species concentrations are quantitively validated for all species including radicals.
Mathematical Modeling and Simulation of Hydrogen-fueled Solid Oxide Fuel Cell System for Micro-grid Applications - Effect of Failure and Degradation on Transient Performance
May 2020
Publication
We use a detailed solid oxide fuel cell (SOFC) model for micro-grid applications to analyze the effect of failure and degradation on system performance. Design and operational constraints on a component and system level are presented. A degrees of freedom analysis identifies controlled and manipulated system variables which are important for control. Experimental data are included to model complex degradation phenomena of the SOFC unit. Rather than using a constant value a spatially distributed degradation rate as function of temperature and current density is used that allows to study trajectory based performance deterioration. The SOFC unit is assumed to consist of multiple stacks. The failure scenario studied is the loss of one individual SOFC stack e.g. due to breakage of sealing or a series of fuel cells. Simulations reveal that degradation leads to significant drifts from the design operating point. Moreover failure of individual stacks may bring the still operating power generation unit into a regime where further failures and accelerated degradation is more likely. It is shown that system design dimensioning operation and control are strongly linked. Apart from specific quantitative results perhaps the main practical contribution are the collected constraints and the degrees of freedom analysis.
Features of the Hydrogen-Assisted Cracking Mechanism in the Low-Carbon Steel at Ex- and In-situ Hydrogen Charging
Dec 2018
Publication
Hydrogen embrittlement has been intensively studied in the past. However its governing mechanism is still under debate. Particularly the details of the formation of specific cleavage-like or quasi-cleavage fracture surfaces related to hydrogen embrittled steels are unclear yet. Recently it has been found that the fracture surface of the hydrogen charged and tensile tested low-carbon steel exhibits quasi-cleavage facets having specific smoothly curved surface which is completely different from common flat cleavage facets. In the present contribution we endeavor to shed light on the origin of such facets. For this purpose the notched flat specimens of the commercial low carbon steel were tensile tested using ex- and in-situ hydrogen charging. It is found that in the ex-situ hydrogen charged specimens the cracks originate primarily inside the specimen bulk and expand radially form the origin to the specimen surface. This process results in formation of “fisheyes” – the round-shape areas with the surface composed of curved quasi-cleavage facets. In contrast during tensile testing with in-situ hydrogen charging the cracks initiate from the surface and propagate to the bulk. This process results in the formation of the completely brittle fracture surface with the quasi-cleavage morphology - the same as that in fisheyes. The examination of the side surface of the in-situ hydrogen charged specimens revealed the straight and S-shaped sharp cracks which path is visually independent of the microstructure and crystallography but is strongly affected by the local stress fields. Nano-voids are readily found at the tips of these cracks. It is concluded that the growth of such cracks occurs by the nano-void coalescence mechanism and is responsible for the formation of fisheyes and smoothly curved quasi-cleavage facets in hydrogen charged low-carbon steel.
Progress in Catalytic Hydrogen Production from Formic Acid over Supported Metal Complexes
Mar 2021
Publication
Formic acid is a liquid organic hydrogen carrier giving hydrogen on demand using catalysts. Metal complexes are known to be used as efficient catalysts for the hydrogen production from formic acid decomposition. Their performance could be better than those of supported catalysts with metal nanoparticles. However difficulties to separate metal complexes from the reaction mixture limit their industrial applications. This problem can be resolved by supporting metal complexes on the surface of different supports which may additionally provide some surface sites for the formic acid activation. The review analyzes the literature on the application of supported metal complexes in the hydrogen production from formic acid. It shows that the catalytic activity of some stable Ru and Ir supported metal complexes may exceed the activity of homogeneous metal complexes used for deposition. Non-noble metal-based complexes containing Fe demonstrated sufficiently high performance in the reaction; however they can be poisoned by water present in formic acid. The proposed review could be useful for development of novel catalysts for the hydrogen production.
Research of Nanomaterials as Electrodes for Electrochemical Energy Storage
Jan 2022
Publication
This paper has experimentally proved that hydrogen accumulates in large quantities in metal-ceramic and pocket electrodes of alkaline batteries during their operation. Hydrogen accumulates in the electrodes in an atomic form. After the release of hydrogen from the electrodes a powerful exothermic reaction of atomic hydrogen recombination with a large energy release occurs. This exothermic reaction is the cause of thermal runaway in alkaline batteries. For the KSL-15 battery the gravimetric capacity of sintered nickel matrix of the oxide-nickel electrode as hydrogen storage is 20.2 wt% and cadmium electrode is 11.5 wt%. The stored energy density in the metal-ceramic matrix of the oxide-nickel electrode of the battery KSL-15 is 44 kJ/g and in the cadmium electrode it is 25 kJ/g. The similar values for the KPL-14 battery are as follows. The gravimetric capacity of the active substance of the pocket oxide-nickel electrode as a hydrogen storage is 22 wt% and the cadmium electrode is 16.9 wt%. The density of the stored energy in the active substance oxide-nickel electrode is 48 kJ/g and in the active substance of the cadmium electrode it is 36.8 kJ/g. The obtained results of the accumulation of hydrogen energy in the electrodes by the electrochemical method are three times higher than any previously obtained results using the traditional thermochemical method.
Small-Scaled Production of Blue Hydrogen with Reduced Carbon Footprint
Aug 2021
Publication
This article reviews a method of hydrogen production based on partial non-catalytic oxidation of natural gas in an original synthesis gas generator. The working principles of the unit are similar to those of liquid-propellant rocket engines. This paper presents a description of the operation and technical characteristics of the synthesis gas generator. Its application in the creation of small-scaled plants with a capacity of up to 5–7 thousand m3/h of hydrogen is justified. Hydrogen production in the developed installation requires a two-stage method and includes a technological unit for producing a hydrogen-containing gas. Typical balance compositions of hydrogen-containing gas at the synthesis gas generator’s outlet are given. To increase the hydrogen concentration it is proposed to carry out a two-stage steam catalytic conversion of carbon monoxide contained in the hydrogen-containing gas at the synthesis gas generator’s outlet using a single Cu–Zn–cementcontaining composition. Based on thermodynamic calculations quasi-optimal modes of natural gas partial oxidation with oxygen are formulated and the results of material balance calculation for the installation are presented. In order to produce “blue” hydrogen the scheme of carbon dioxide separation and liquefaction is developed. The conclusion section of the paper contains the test results of a pilot demonstration unit and the recommendations for improving the technology and preventing soot formation.
Flare Gas Monetization and Greener Hydrogen Production via Combination with Crypto Currency Mining and Carbon Dioxide Capture
Jan 2022
Publication
In view of the continuous debates on the environmental impact of blockchain technologies in particular crypto currency mining accompanied by severe carbon dioxide emissions a technical solution has been considered assuming direct monetization of associated petroleum gas currently being flared. The proposed approach is based on the technology of low-temperature steam reforming of hydrocarbons which allows flare gas conditioning towards the requirements for fuel for gas piston and gas turbine power plants. The generation of electricity directly at the oil field and its use for on-site crypto currency mining transforms the process of wasteful flaring of valuable hydrocarbons into an economically attractive integrated processing of natural resources. The process is not carbon neutral and is not intended to compete zero-emission technologies but its combination with technologies for carbon dioxide capture and re-injection into the oil reservoir can both enhance the oil recovery and reduce carbon dioxide emissions into the atmosphere. The produced gas can be used for local transport needs while the generated heat and electricity can be utilized for on-site food production and biological carbon dioxide capture in vertical greenhouse farms. The suggested approach allows significant decrease in the carbon dioxide emissions at oil fields and although it may seem paradoxically on-site cryptocurrency mining actually may lead to a decrease in the carbon footprint. The amount of captured CO2 could be transformed into CO2 emission quotas which can be spent for the production of virtually “blue” hydrogen by steam reforming of natural gas in locations where the CO2 capture is technically impossible and/or unprofitable.
Hydrogen Storage: Thermodynamic Analysis of Alkyl-Quinolines and Alkyl-Pyridines as Potential Liquid Organic Hydrogen Carriers (LOHC)
Dec 2021
Publication
The liquid organic hydrogen carriers (LOHC) are aromatic molecules which can be considered as an attractive option for the storage and transport of hydrogen. A considerable amount of hydrogen up to 7–8% wt. can be loaded and unloaded with a reversible chemical reaction. Substituted quinolines and pyridines are available from petroleum coal processing and wood preservation or they can be synthesized from aniline. Quinolines and pyridines can be considered as potential LOHC systems provided they have favorable thermodynamic properties which were the focus of this current study. The absolute vapor pressures of methyl-quinolines were measured using the transpiration method. The standard molar enthalpies of vaporization of alkyl-substituted quinolines and pyridines were derived from the vapor pressure temperature dependencies. Thermodynamic data on vaporization and formation enthalpies available in the literature were collected evaluated and combined with our own experimental results. The theoretical standard molar gas-phase enthalpies of formation of quinolines and pyridines calculated using the quantum-chemical G4 methods agreed well with the evaluated experimental data. Reliable standard molar enthalpies of formation in the liquid phase were derived by combining high-level quantum chemistry values of gas-phase enthalpies of formation with experimentally determined enthalpies of vaporization. The liquid-phase hydrogenation/dehydrogenation reaction enthalpies of alkyl-substituted pyridines and quinolines were calculated and compared with the data for other potential liquid organic hydrogen carriers. The comparatively low enthalpies of reaction make these heteroaromatics a seminal LOHC system.
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