China, People’s Republic
Formation Criterion of Hydrogen-Induced Cracking in Steel Based on Fracture Mechanics
Nov 2018
Publication
A new criterion for hydrogen-induced cracking (HIC) that includes both the embrittlement effect and the loading effect of hydrogen was obtained theoretically. The surface cohesive energy and plastic deformation energy are reduced by hydrogen atoms at the interface; thus the fracture toughness is reduced according to fracture mechanics theory. Both the pressure effect and the embrittlement effect mitigate the critical condition required for crack instability extension. During the crack instability expansion the hydrogen in the material can be divided into two categories: hydrogen atoms surrounding the crack and hydrogen molecules in the crack cavity. The loading effect of hydrogen was verified by experiments and the characterization methods for the stress intensity factor under hydrogen pressure in a linear elastic model and an elastoplastic model were analyzed using the finite-element simulation method. The hydrogen pressure due to the aggregation of hydrogen molecules inside the crack cavity regularly contributed to the stress intensity factor. The embrittlement of hydrogen was verified by electrolytic charging hydrogen experiments. According to the change in the atomic distribution during crack propagation in a molecular dynamics simulation the transition from ductile to brittle fracture and the reduction in the fracture toughness were due to the formation of crack tip dislocation regions suppressed by hydrogen. The HIC formation mechanism is both the driving force of crack propagation due to the hydrogen gas pressure and the resisting force reduced by hydrogen atoms.
Enhanced Hydrogen Generation from Hydrolysis of MgLi Doped with Expanded Graphite
Apr 2021
Publication
Hydrolysis of Mg-based materials is considered as a potential means of safe and convenient real-time control of H2 release enabling efficient loading discharge and utilization of hydrogen in portable electronic devices. At present work the hydrogen generation properties of MgLi-graphite composites were evaluated for the first time. The MgLi-graphite composites with different doping amounts of expanded graphite (abbreviated as EG hereinafter) were synthesized through ball milling and the hydrogen behaviors of the composites were investigated in chloride solutions. Among the above doping systems the 10 wt% EG-doped MgLi exhibited the best hydrogen performance in MgCl2 solutions. In particular the 22 h-milled MgLi-10 wt% EG composites possessed both desirable hydrogen conversion and rapid reaction kinetics delivering a hydrogen yield of 966 mL H2 g−1 within merely 2 min and a maximum hydrogen generation rate of 1147 mL H2 min−1 g−1 as opposed to the sluggish kinetics in the EG-free composites. Moreover the EG-doped MgLi showed superior air-stable ability even under a 75 RH% ambient atmosphere. For example the 22 h-milled MgLi-10 wt% EG composites held a fuel conversion of 89% after air exposure for 72 h rendering it an advantage for Mg-based materials to safely store and transfer in practical applications. The similar favorable hydrogen performance of MgLi-EG composites in (simulate) seawater may shed light on future development of hydrogen generation technologies.
Recent Advances in Carbon Dioxide Conversion: A Circular Bioeconomy Perspective
Jun 2021
Publication
Managing the concentration of atmospheric CO2 requires a multifaceted engineering strategy which remains a highly challenging task. Reducing atmospheric CO2 (CO2R) by converting it to value-added chemicals in a carbon neutral footprint manner must be the ultimate goal. The latest progress in CO2R through either abiotic (artificial catalysts) or biotic (natural enzymes) processes is reviewed herein. Abiotic CO2R can be conducted in the aqueous phase that usually leads to the formation of a mixture of CO formic acid and hydrogen. By contrast a wide spectrum of hydrocarbon species is often observed by abiotic CO2R in the gaseous phase. On the other hand biotic CO2R is often conducted in the aqueous phase and a wide spectrum of value-added chemicals are obtained. Key to the success of the abiotic process is understanding the surface chemistry of catalysts which significantly governs the reactivity and selectivity of CO2R. However in biotic CO2R operation conditions and reactor design are crucial to reaching a neutral carbon footprint. Future research needs to look toward neutral or even negative carbon footprint CO2R processes. Having a deep insight into the scientific and technological aspect of both abiotic and biotic CO2R would advance in designing efficient catalysts and microalgae farming systems. Integrating the abiotic and biotic CO2R such as microbial fuel cells further diversifies the spectrum of CO2R.
Molybdenum Carbide Microcrystals: Efficient and Stable Catalyst for Photocatalytic H2 Evolution From Water in The Presence Of Dye Sensitizer
Sep 2016
Publication
Rod-like molybdenum carbide (Mo2C) microcrystals were obtained from the pyrolysis of Mo-containing organic-inorganic hybrid composite. We investigated the photocatalytic H2 evolution activity of Mo2C by constructing a Mo2C-dye sensitizer photocatalyst system. A high quantum efficiency of 29.7% was obtained at 480 nm. Moreover Mo2C catalyst can be easily recycled by simple filtration.
Raw Biomass Electroreforming Coupled to Green Hydrogen Generation
Mar 2021
Publication
Despite the tremendous progress of coupling organic electrooxidation with hydrogen generation in a hybrid electrolysis electroreforming of raw biomass coupled to green hydrogen generation has not been reported yet due to the rigid polymeric structures of raw biomass. Herein we electrooxidize the most abundant natural amino biopolymer chitin to acetate with over 90% yield in hybrid electrolysis. The overall energy consumption of electrolysis can be reduced by 15% due to the thermodynamically and kinetically more favorable chitin oxidation over water oxidation. In obvious contrast to small organics as the anodic reactant the abundance of chitin endows the new oxidation reaction excellent scalability. A solar-driven electroreforming of chitin and chitin-containing shrimp shell waste is coupled to safe green hydrogen production thanks to the liquid anodic product and suppression of oxygen evolution. Our work thus demonstrates a scalable and safe process for resource upcycling and green hydrogen production for a sustainable energy future.
Life Cycle Assessment of Fuel Cell Vehicles Considering the Detailed Vehicle Components: Comparison and Scenario Analysis in China Based on Different Hydrogen Production Schemes
Aug 2019
Publication
Numerous studies concerning the life cycle assessment of fuel cell vehicles (FCVs) have been conducted. However little attention has been paid to the life cycle assessment of an FCV from the perspective of the detailed vehicle components. This work conducts the life cycle assessment of Toyota Mirai with all major components considered in a Chinese context. Both the vehicle cycle and the fuel cycle are included. Both comprehensive resources and energy consumption and comprehensive environmental emissions of the life cycles are investigated. Potential environmental impacts are further explored based on CML 2001 method. Then different hydrogen production schemes are compared to obtain the most favorable solution. To explore the potential of the electrolysis the scenario analysis of the power structure is conducted. The results show that the most mineral resources are consumed in the raw material acquisition stage the most fossil energy is consumed in the use stage and global warming potential (GWP) value is fairly high in all life cycle stages of Toyota Mirai using electrolyzed hydrogen. For hydrogen production schemes the scenario analysis indicates that simply by optimizing the power structure the environmental impact of the electrolysis remains higher than other schemes. When using the electricity from hydropower or wind power the best choice will be the electrolysis.
Enhanced Hydrogen Storage Properties of Mg by the Synergistic Effect of Grain Refinement and NiTiO 3 Nanoparticles
May 2021
Publication
As a promising hydrogen storage material the practical application of magnesium is obstructed by the stable thermodynamics and sluggish kinetics. In this paper three kinds of NiTiO3 catalysts with different mole ratio of Ni to Ti were successfully synthesized and doped into nanocrystalline Mg to improve its hydrogen storage properties. Experimental results indicated that all the Mg-NiTiO3 composites showed prominent hydrogen storage performance. Especially the Mg-NiTiO3/TiO2 composite could take up hydrogen at room temperature and the apparent activation energy for hydrogen absorption was dramatically decreased from 69.8 ± 1.2 (nanocrystalline Mg) kJ/mol to 34.2 ± 0.2 kJ/mol. In addition the hydrogenated sample began to release hydrogen at about 193.2 °C and eventually desorbed 6.6 wt% H2. The desorption enthalpy of the hydrogenated Mg-NiTiO3 -C was estimated to be 78.6 ± 0.8 kJ/mol 5.3 kJ/mol lower compared to 83.9 ± 0.7 kJ/mol of nanocrystalline Mg. Besides the sample revealed splendid cyclic stability during 20 cycles. No obvious recession occurred in the absorption and desorption kinetics and only 0.3 wt% hydrogen capacity degradation was observed. Further structural analysis demonstrates that nanosizing and catalyst doping led to a synergistic effect on the enhanced hydrogen storage performance of Mg-NiTiO3 -C composite which might serve as a reference for future design of highly effective hydrogen storage materials.
Hydrogen Safety Prediction and Analysis of Hydrogen Refueling Station Leakage Accidents and Process Using Multi-Relevance Machine Learning
Oct 2021
Publication
Hydrogen energy vehicles are being increasingly widely used. To ensure the safety of hydrogenation stations research into the detection of hydrogen leaks is required. Offline analysis using data machine learning is achieved using Spark SQL and Spark MLlib technology. In this study to determine the safety status of a hydrogen refueling station we used multiple algorithm models to perform calculation and analysis: a multi-source data association prediction algorithm a random gradient descent algorithm a deep neural network optimization algorithm and other algorithm models. We successfully analyzed the data including the potential relationships internal relationships and operation laws between the data to detect the safety statuses of hydrogen refueling stations.
Modeling of Fixed Bed Reactor for Coal Tar Hydrogenation via the Kinetic Lumping Approach
Nov 2018
Publication
Hydrogenation technology is an indispensable chemical upgrading process for converting the heavy feedstock into favorable lighter products. In this work a new kinetic model containing four hydrocarbon lumps (feedstock diesel gasoline cracking gas) was developed to describe the coal tar hydrogenation process the Levenberg–Marquardt’s optimization algorithm was used to determine the kinetic parameters by minimizing the sum of square errors between experimental and calculated data the predictions from model validation showed a good agreement with experimental values. Subsequently an adiabatic reactor model based on proposed lumped kinetic model was constructed to further investigate the performance of hydrogenation fixed-bed units the mass balance and energy balance within the phases in the reactor were taken into accounts in the form of ordinary differential equation. An application of the reactor model was performed for simulating the actual bench-scale plant of coal tar hydrogenation the simulated results on the products yields and temperatures distribution along with the reactor are shown to be good consistent with the experimental data.
Influence of Synthesis Gas Components on Hydrogen Storage Properties of Sodium Aluminium Hexahydride
Feb 2021
Publication
A systematic study of different ratios of CO CO2 N2 gas components on the hydrogen storage properties of the Na3AlH6 complex hydride with 4 mol% TiCl3 8 mol% aluminum and 8 mol% activated carbon is presented in this paper. The different concentrations of CO and CO2in H2 and CO CO2 N2 in H2 mixture were investigated. Both CO and CO2gas react with the complex hydride forming Al oxy-compounds NaOH and Na2CO3 that consequently cause serious decline in hydrogen storage capacity. These reactions lead to irreversible damage of complex hydride under the current experimental condition. Thus after 10 cycles with 0.1 vol % CO + 99.9 vol %H2 and 1 vol % CO + 99 vol %H2 the dehydrogenation storage capacity of the composite material decreased by 17.2% and 57.3% respectively. In the case of investigation of 10 cycles with 1 vol % CO2 + 99 vol % H2 gas mixture the capacity degradation was 53.5%. After 2 cycles with 10 vol % CO +90 vol % H2 full degradation was observed whereas after 6 cycles with 10 vol % CO2+ 90 vol % H2 degradation of 86.8% was measured. While testing with the gas mixture of 1.5 vol % CO + 10 vol % CO2+ 27 vol % H2 + 61.5 vol % N2 the degradation of 94% after 6 cycles was shown. According to these results it must be concluded that complex aluminum hydrides cannot be used for the absorption of hydrogen from syngas mixtures without thorough purification.
Hydrogen-Assisted Crack Growth in the Heat-Affected Zone of X80 Steels during in Situ Hydrogen Charging
Aug 2019
Publication
Herein the hydrogen embrittlement of a heat-affected zone (HAZ) was examined using slow strain rate tension in situ hydrogen charging. The influence of hydrogen on the crack path of the HAZ sample surfaces was determined using electron back scatter diffraction analysis. The hydrogen embrittlement susceptibility of the base metal and the HAZ samples increased with increasing current density. The HAZ samples have lower resistance to hydrogen embrittlement than the base metal samples in the same current density. Brittle circumferential cracks located at the HAZ sample surfaces were perpendicular to the loading direction and the crack propagation path indicated that five or more cracks may join together to form a longer crack. The fracture morphologies were found to be a mixture of intergranular and transgranular fractures. Hydrogen blisters were observed on the HAZ sample surfaces after conducting tensile tests at a current density of 40 mA/cm2 leading to a fracture in the elastic deformation stage.
Direct Ammonia Low-temperature Symmetrical Solid Oxide Fuel Cells with Composite Semiconductor Electrolyte
Jan 2022
Publication
In this work a low-temperature symmetrical solid oxide fuel cell with Ni-NCAL|SDC/NCAL|Ni-NCAL (70 SDC:30 NCAL) configuration was successfully constructed by a simple dry press method. At 500 and 550 ◦C the peak power densities of the cell in ammonia were 501 and 755 mW cm− 2 and in hydrogen were 670 and 895 mW cm− 2 respectively. EIS data showed that the Rp values of the cell in ammonia and hydrogen at 550 ◦C were 0.250 and 0.246 Ω cm− 2 respectively indicating the excellent catalytic activity of the Ni-NCAL electrode toward ammonia decomposition and hydrogen oxidation. The different cell output can be ascribed to additional ammonia decomposition steps compared to hydrogen. The noticeable reaction product on the surface of the Ni foam was detrimental to ammonia decomposition. In summary a symmetrical cell with SDC/NCAL semi-conductor electrolyte and Ni-NCAL electrodes exhibited higher electrochemical performance at low temperature than the results reported to date. Therefore higher electrochemical performance can be expected from this cell configuration with more efficient ammonia decomposition catalysts.
Efficient Hydrogen Production Through the Chemical Looping Redox Cycle of YSZ Supported Iron Oxides
Jul 2020
Publication
The chemical looping process where an oxygen carrier is reduced and oxidized in a cyclic manner offers a promising option for hydrogen production through splitting water because of the much higher water splitting efficiency than solar electrocatalytic and photocatalytic process. A typical oxygen carrier has to comprise a significant amount of inert support to maintain stability in multiple redox cycles thereby resulting in a trade-off between the reaction reactivity and stability. Herein we proposed the use of ion-conductive yttria-stabilized zirconia (YSZ) support Fe2O3 to prepare oxygen carriers materials. The obtained Fe2O3/YSZ composites showed high reactivity and stability. Particularly Fe2O3/YSZ-20 (oxygen storage capacity 24.13%) exhibited high hydrogen yield of ∼10.30 mmol·g-1 and hydrogen production rate of ∼0.66 mmol·g-1·min-1 which was twice as high as that of Fe2O3/Al2O3. Further the transient pulse test indicated that active oxygen diffusion was the rate-limiting step during the redox process. The electrochemical impedance spectroscopy (EIS) measurement revealed that the YSZ support addition facilitated oxygen diffusion of materials which contributed to the improved hydrogen production performance. The support effect obtained in this work provides a potentially efficient route for the modification of oxygen carrier materials.
Conceptual Design of Pyrolytic Oil Upgrading Process Enhanced by Membrane-Integrated Hydrogen Production System
May 2019
Publication
Hydrotreatment is an efficient method for pyrolytic oil upgrading; however the trade-off between the operational cost on hydrogen consumption and process profit remains the major challenge for the process designs. In this study an integrated process of steam methane reforming and pyrolytic oil hydrotreating with gas separation system was proposed conceptually. The integrated process utilized steam methane reformer to produce raw syngas without further water–gas-shifting; with the aid of a membrane unit the hydrogen concentration in the syngas was adjusted which substituted the water–gas-shift reactor and improved the performance of hydrotreater on both conversion and hydrogen consumption. A simulation framework for unit operations was developed for process designs through which the dissipated flow in the packed-bed reactor along with membrane gas separation unit were modelled and calculated in the commercial process simulator. The evaluation results showed that the proposed process could achieve 63.7% conversion with 2.0 wt% hydrogen consumption; the evaluations of economics showed that the proposed process could achieve 70% higher net profit compared to the conventional plant indicating the potentials of the integrated pyrolytic oil upgrading process.
Economic Viability and Environmental Efficiency Analysis of Hydrogen Production Processes for the Decarbonization of Energy Systems
Aug 2019
Publication
The widespread penetration of hydrogen in mainstream energy systems requires hydrogen production processes to be economically competent and environmentally efficient. Hydrogen if produced efficiently can play a pivotal role in decarbonizing the global energy systems. Therefore this study develops a framework which evaluates hydrogen production processes and quantifies deficiencies for improvement. The framework integrates slack-based data envelopment analysis (DEA) with fuzzy analytical hierarchy process (FAHP) and fuzzy technique for order of preference by similarity to ideal solution (FTOPSIS). The proposed framework is applied to prioritize the most efficient and sustainable hydrogen production in Pakistan. Eleven hydrogen production alternatives were analyzed under five criteria including capital cost feedstock cost O&M cost hydrogen production and CO2 emission. FAHP obtained the initial weights of criteria while FTOPSIS determined the ultimate weights of criteria for each alternative. Finally slack-based DEA computed the efficiency of alternatives. Among the 11 three alternatives (wind electrolysis PV electrolysis and biomass gasification) were found to be fully efficient and therefore can be considered as sustainable options for hydrogen production in Pakistan. The rest of the eight alternatives achieved poor efficiency scores and thus are not recommended.
An Intelligent Site Selection Model for Hydrogen Refueling Stations Based on Fuzzy Comprehensive Evaluation and Artificial Neural Network—A Case Study of Shanghai
Feb 2022
Publication
With the gradual popularization of hydrogen fuel cell vehicles (HFCVs) the construction and planning of hydrogen refueling stations (HRSs) are increasingly important. Taking operational HRSs in China’s coastal and major cities as examples we consider the main factors affecting the site selection of HRSs in China from the three aspects of economy technology and society to establish a site selection evaluation system for hydrogen refueling stations and determine the weight of each index through the analytic hierarchy process (AHP). Then combined with fuzzy comprehensive evaluation (FCE) method and artificial neural network model (ANN) FCE method is used to evaluate HRS in operation in China's coastal areas and major cities and we used the resulting data obtained from the comprehensive evaluation as the training data to train the neural network. So an intelligent site selection model for HRSs based on fuzzy comprehensive evaluation and artificial neural network model (FCE-ANN) is proposed. The planned HRSs in Shanghai are evaluated and an optimal site selection of the HRS is obtained. The results show that the optimal HRSs site selected by the FCE-ANN model is consistent with the site selection obtained by the FCE method and the accuracy of the FCE-ANN model is verified. The findings of this study may provide some guidelines for policy makers in planning the hydrogen refueling stations
Integrated Ni-P-S Nanosheets Array as Superior Electrocatalysts for Hydrogen Generation
Jan 2017
Publication
Searching for efficient and robust non-noble electrocatalysts for hydrogen generation is extremely desirable for future green energy systems. Here we present the synthesis of integrated Ni-P-S nanosheets array including Ni2P and NiS on nickel foam by a simple simultaneous phosphorization and sulfurization strategy. The resultant sample with optimal composition exhibits superior electrocatalytic performance for hydrogen evolution reaction (HER) in a wide pH range. In alkaline media it can generate current densities of 10 20 and 100 mA cm−2 at low overpotentials of only −101.9 −142.0 and −207.8 mV with robust durability. It still exhibits high electrocatalytic activities even in acid or neutral media. Such superior electrocatalytic performances can be mainly attributed to the synergistic enhancement of the hybrid Ni-P-S nanosheets array with integration microstructure. The kind of catalyst gives a new insight on achieving efficient and robust hydrogen generation.
The Path to Carbon Neutrality in China: A Paradigm Shift in Fossil Resource Utilization
Jan 2022
Publication
The Paris Agreement has set the goal of carbon neutrality to cope with global climate change. China has pledged to achieve carbon neutrality by 2060 which will strategically change everything in our society. As the main source of carbon emissions the consumption of fossil energy is the most profoundly affected by carbon neutrality. This work presents an analysis of how China can achieve its goal of carbon neutrality based on its status of fossil energy utilization. The significance of transforming fossils from energy to resource utilization in the future is addressed while the development direction and key technologies are discussed.
Electronic Structure and d-Band Center Control Engineering over Ni-Doped CoP3 Nanowall Arrays for Boosting Hydrogen Production
Jun 2021
Publication
To address the challenge of highly efficient water splitting into H2 successful fabrication of novel porous three-dimensional Ni-doped CoP3 nanowall arrays on carbon cloth was realized resulting in an effective self-supported electrode for the electrocatalytic hydrogen-evolution reaction. The synthesized samples exhibit rough curly and porous structures which are beneficial for gaseous transfer and diffusion during the electrocatalytic process. As expected the obtained Ni-doped CoP3 nanowall arrays with a doping concentration of 7% exhibit the promoted electrocatalytic activity. The achieved overpotentials of 176 mV for the hydrogen-evolution reaction afford a current density of 100 mA cm−2 which indicates that electrocatalytic performance can be dramatically enhanced via Ni doping. The Ni-doped CoP3 electrocatalysts with increasing catalytic activity should have significant potential in the field of water splitting into H2. This study also opens an avenue for further enhancement of electrocatalytic performance through tuning of electronic structure and d-band center by doping.
Renewable Hydrogen Production from the Organic Fraction of Municipal Solid Waste through a Novel Carbon-negative Process Concept
Apr 2022
Publication
Bioenergy with carbon capture and storage (BECCS) is one of the prevailing negative carbon emission technologies. Ensuring a hydrogen economy is essential to achieving the carbon-neutral goal. In this regard the present study contributed by proposing a carbon negative process for producing high purity hydrogen from the organic fraction of municipal solid waste (OFMSW). This integrated process comprises anaerobic digestion pyrolysis catalytic reforming water-gas shift and pressure swing adsorption technologies. By focusing on Sweden the proposed process was developed and evaluated through sensitivity analysis mass and energy balance calculations techno-economic assessment and practical feasibility analysis. By employing the optimum operating conditions from the sensitivity analysis 72.2 kg H2 and 701.47 kg negative CO2 equivalent emissions were obtained by treating 1 ton of dry OFMSW. To achieve these results 6621.4 MJ electricity and 325 kg of steam were utilized during this process. Based on this techno-economic assessment of implementing the proposed process in Stockholm when the negative CO2 equivalent emissions are recognized as income the internal rate of return and the discounted payback period can be obtained as 26% and 4.3 years respectively. Otherwise these values will be 13% and 7.2 years.
Anionic Structural Effect in Liquid–liquid Separation of Phenol from Model Oil by Choline Carboxylate Ionic Liquid
Feb 2019
Publication
The synthesis of low-cost and highly active electrodes for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is very important for water splitting. In this work the novel amorphous iron-nickel phosphide (FeP-Ni) nanocone arrays as efficient bifunctional electrodes for overall water splitting have been in-situ assembled on conductive three-dimensional (3D) Ni foam via a facile and mild liquid deposition process. It is found that the FeP-Ni electrode demonstrates highly efficient electrocatalytic performance toward overall water splitting. In 1 M KOH electrolyte the optimal FeP-Ni electrode drives a current density of 10 mA/cm2 at an overpotential of 218 mV for the OER and 120 mV for the HER and can attain such current density for 25 h without performance regression. Moreover a two-electrode electrolyzer comprising the FeP-Ni electrodes can afford 10 mA/cm2 electrolysis current at a low cell voltage of 1.62 V and maintain long-term stability as well as superior to that of the coupled RuO2/NF‖Pt/C/NF cell. Detailed characterizations confirm that the excellent electrocatalytic performances for water splitting are attributed to the unique 3D morphology of nanocone arrays which could expose more surface active sites facilitate electrolyte diffusion benefit charge transfer and also favorable bubble detachment behavior. Our work presents a facile and cost-effective pathway to design and develop active self-supported electrodes with novel 3D morphology for water electrolysis.
A Multi‐input and Single‐output Voltage Control for a Polymer Electrolyte Fuel Cell System Using Model Predictive Control Method
Mar 2021
Publication
Efficient and robust control strategies can greatly contribute to the reliability of fuel cell systems and a stable output voltage is a key criterion for evaluating a fuel cell system's reliability as a power source. In this study a polymer electrolyte fuel cell (PEFC) system model is developed and its performances under different operating conditions are studied. Then two different novel controllers—a proportional integral derivative (PID) controller and a model predictive control (MPC) controller—are proposed and applied in the PEFC system to control its output voltage at a desired value by regulating the hydrogen and air flow rates at the same time which features a multi‐input and single‐output control problem. Simulation results demonstrate that the developed PEFC system model is qualified to capture the system's behaviour. And both the developed PID and MPC controllers are effective at controlling the PEFC system's output voltage. While the MPC controller presents superior performance with faster response and smaller overshoot. The proposed MPC controller can be easily employed in various control applications for fuel cell systems.
Hydrogen Production as a Clean Energy Carrier through Heterojunction Semiconductors for Environmental Remediation
Apr 2022
Publication
Today as a result of the advancement of technology and increasing environmental problems the need for clean energy has considerably increased. In this regard hydrogen which is a clean and sustainable energy carrier with high energy density is among the well-regarded and effective means to deliver and store energy and can also be used for environmental remediation purposes. Renewable hydrogen energy carriers can successfully substitute fossil fuels and decrease carbon dioxide (CO2 ) emissions and reduce the rate of global warming. Hydrogen generation from sustainable solar energy and water sources is an environmentally friendly resolution for growing global energy demands. Among various solar hydrogen production routes semiconductor-based photocatalysis seems a promising scheme that is mainly performed using two kinds of homogeneous and heterogeneous methods of which the latter is more advantageous. During semiconductor-based heterogeneous photocatalysis a solid material is stimulated by exposure to light and generates an electron–hole pair that subsequently takes part in redox reactions leading to hydrogen production. This review paper tries to thoroughly introduce and discuss various semiconductor-based photocatalysis processes for environmental remediation with a specific focus on heterojunction semiconductors with the hope that it will pave the way for new designs with higher performance to protect the environment.
Comparison of Two-layer Model for High Pressure Hydrogen Jets with Notional Nozzle Model Predictions and Experimental Data
Oct 2015
Publication
A two-layer reduced order model of high pressure hydrogen jets was developed which includes partitioning of the flow between the central core jet region leading to the Mach disk and the supersonic slip region around the core. The flow after the Mach disk is subsonic while the flow around the Mach disk is supersonic with a significant amount of entrained air. This flow structure significantly affects the hydrogen concentration profiles downstream. The predictions of this model are compared to previous experimental data for high pressure hydrogen jets up to 20 MPa and to notional nozzle models and CFD models for pressures up to 35 MPa using ideal gas properties. The results show that this reduced order model gives better predictions of the mole fraction distributions than previous models for highly underexpanded jets. The predicted locations of the 4% lower flammability limit also show that the two-layer model much more accurately predicts the measured locations than the notional nozzle models. The comparisons also show that the CFD model always underpredicts the measured mole fraction concentrations.
Smart Designs of Mo Based Electrocatalysts for Hydrogen Evolution Reaction
Dec 2021
Publication
As a sustainable and clean energy source hydrogen can be generated by electrolytic water splitting (i.e. a hydrogen evolution reaction HER). Compared with conventional noble metal catalysts (e.g. Pt) Mo based materials have been deemed as a promising alternative with a relatively low cost and comparable catalytic performances. In this review we demonstrate a comprehensive summary of various Mo based materials such as MoO2 MoS2 and Mo2C. Moreover state of the art designs of the catalyst structures are presented to improve the activity and stability for hydrogen evolution including Mo based carbon composites heteroatom doping and heterostructure construction. The structure–performance relationships relating to the number of active sites electron/ion conductivity H/H2O binding and activation energy as well as hydrophilicity are discussed in depth. Finally conclusive remarks and future works are proposed.
Development of a Gaseous and Solid-state Hybrid System for Stationary Hydrogen Energy Storage
Jun 2020
Publication
Hydrogen can serve as a carrier to store renewable energy in large scale. However hydrogen storage still remains a challenge in the current stage. It is difficult to meet the technical requirements applying the conventional storage of compressed gaseous hydrogen in high-pressure tanks or the solid-state storage of hydrogen in suitable materials. In the present work a gaseous and solid-state (G-S) hybrid hydrogen storage system with a low working pressure below 5 MPa for a 10 kW hydrogen energy storage experiment platform is developed and validated. A Ti−Mn type hydrogen storage alloy with an effective hydrogen capacity of 1.7 wt% was prepared for the G-S hybrid hydrogen storage system. The G-S hybrid hydrogen storage tank has a high volumetric hydrogen storage density of 40.07 kg H2 m−3 and stores hydrogen under pressure below 5 MPa. It can readily release enough hydrogen at a temperature as low as −15 °C when the FC system is not fully activated and hot water is not available. The energy storage efficiency of this G-S hybrid hydrogen storage system is calculated to be 86.4%−95.9% when it is combined with a FC system. This work provides a method on how to design a G-S hydrogen storage system based on practical demands and demonstrates that the G-S hybrid hydrogen storage is a promising method for stationary hydrogen storage application.
Co-CoOx Supported onto TiO2 Coated with Carbon as a Catalyst for Efficient and Stable Hydrogen Generation from Ammonia Borane
Apr 2020
Publication
Ammonia borane (AB) can be catalytically hydrolyzed to provide hydrogen at room temperature due to its high potentaial for hydrogen storage. Non-precious metal heterogeneous catalysts have broad application in the field of energy catalysis. In this article catalysts precursor is obtained from Co-Ti-resorcinol-formaldehyde resin by sol–gel method. Co/TiO2@N-C (CTC) catalyst is prepared by calcining the precursor under high temperature conditions in nitrogen atmosphere. Co-CoOx/TiO2@N-C (COTC) is generated by the controllable oxidation reaction of CTC. The catalyst can effectively promote the release of hydrogen during the hydrolytic dehydrogenation of AB. High hydrogen generation at a specific rate of 5905 mL min−1 gCo−1 is achieved at room temperature. The catalyst retains its 85% initial catalytic activity even for its fifth time use in AB hydrolysis. The synergistic effect among Co Co3O4 and TiO2 promotes the rate limiting step with dissociation and activation of water molecules by reducing its activation energy. The applied method in this study promotes the development of non-precious metals in catalysis for utilization in clean energy sources.
Validation of Two-Layer Model for Underexpanded Hydrogen Jets
Sep 2019
Publication
Previous studies have shown that the two-layer model more accurately predicts hydrogen dispersion than the conventional notional nozzle models without significantly increasing the computational expense. However the model was only validated for predicting the concentration distribution and has not been adequately validated for predicting the velocity distributions. In the present study particle imaging velocimetry (PIV) was used to measure the velocity field of an underexpanded hydrogen jet released at 10 bar from a 1.5 mm diameter orifice. The two-layer model was the used to calculate the inlet conditions for a two-dimensional axisymmetric CFD model to simulate the hydrogen jet downstream of the Mach disk. The predicted velocity spreading and centerline decay rates agreed well with the PIV measurements. The predicted concentration distribution was consistent with data from previous planar Rayleigh scattering measurements used to verify the concentration distribution predictions in an earlier study. The jet spreading was also simulated using several widely used notional nozzle models combined with the integral plume model for comparison. These results show that the velocity and concentration distributions are both better predicted by the two-layer model than the notional nozzle models to complement previous studies verifying only the predicted concentration profiles. Thus this study shows that the two-layer model can accurately predict the jet velocity distributions as well as the concentration distributions as verified earlier. Though more validation studies are needed to improve confidence in the model and increase the range of validity the present work indicates that the two-layer model is a promising tool for fast accurate predictions of the flow fields of underexpanded hydrogen jets.
Consequence-based Safety Distances and Mitigation Measures for Gaseous Hydrogen Refueling Stations
Oct 2010
Publication
With the rapid development of hydrogen vehicle technology and large scale fuel cell vehicle (FCV) demonstration project worldwide more hydrogen refueling stations need to be built. Safety distances of hydrogen refueling stations have always been a public concern and have become a critical issue to further implementation of hydrogen station. In this paper safety distances for 35MPa and 70MPa gaseous hydrogen refueling station are evaluated on the basis of the maximum consequences likely to occur. Four typical consequences of hydrogen release are considered in modeling: physical explosion jet fire flash fire and confined vapor cloud explosion. Results show that physical explosion and the worst case of confined vapor cloud explosion produce the longest harm effect distances for instantaneous and continuous release respectively indicating that they may be considered as leading consequences for the determination of safety distances. For both 35MPa station and 70MPa station safety measures must be implemented because the calculated safety distances of most hydrogen facilities can not meet the criteria in national code if without sufficient mitigation measures. In order to reduce the safety distances to meet the national code some mitigation measures are investigated including elevation of hydrogen facilities using smaller vessel and pipe work and setting enclosure around compressors. Results show that these measures are effective to improve safety but each has different effectiveness on safety distance reduction. The combination of these safety measures may effectively eliminate the hazard of 35MPa station however may be not enough for 70MPa station. Further improvements need to be studied for compressors inside 70MPa station.
Ammonia for Power
Sep 2018
Publication
A potential enabler of a low carbon economy is the energy vector hydrogen. However issues associated with hydrogen storage and distribution are currently a barrier for its implementation. Hence other indirect storage media such as ammonia and methanol are currently being considered. Of these ammonia is a carbon free carrier which offers high energy density; higher than compressed air. Hence it is proposed that ammonia with its established transportation network and high flexibility could provide a practical next generation system for energy transportation storage and use for power generation. Therefore this review highlights previous influential studies and ongoing research to use this chemical as a viable energy vector for power applications emphasizing the challenges that each of the reviewed technologies faces before implementation and commercial deployment is achieved at a larger scale. The review covers technologies such as ammonia in cycles either for power or CO2 removal fuel cells reciprocating engines gas turbines and propulsion technologies with emphasis on the challenges of using the molecule and current understanding of the fundamental combustion patterns of ammonia blends.
Significantly Enhanced Electrocatalytic Activity of Copper for Hydrogen Evolution Reaction Through Femtosecond Laser Blackening
Jan 2021
Publication
In this work we report on the creation of a black copper via femtosecond laser processing and its application as a novel electrode material. We show that the black copper exhibits an excellent electrocatalytic activity for hydrogen evolution reaction (HER) in alkaline solution. The laser processing results in a unique microstructure: microparticles covered by finer nanoparticles on top. Electrochemical measurements demonstrate that the kinetics of the HER is significantly accelerated after bare copper is treated and turned black. At −0.325 V (v.s. RHE) in 1 M KOH aqueous solution the calculated area-specific charge transfer resistance of the electrode decreases sharply from 159 Ω cm2 for the untreated copper to 1 Ω cm2 for the black copper. The electrochemical surface area of the black copper is measured to be only 2.4 times that of the untreated copper and therefore the significantly enhanced electrocatalytic activity of the black copper for HER is mostly a result of its unique microstructure that favors the formation and enrichment of protons on the surface of copper. This work provides a new strategy for developing high-efficient electrodes for hydrogen generation.
Catalytic Effect of MoS2 on Hydrogen Storage Thermodynamics and Kinetics of an As-milled YMg11Ni Alloy
Jul 2017
Publication
In this study YMg11Ni and YMg11Ni + 5 wt% MoS2 (named YMg11Ni–MoS2) alloys were prepared by mechanical milling to examine the effect of adding MoS2 on the hydrogen storage performance of a Y–Mg–Ni-based alloy. The as-cast and milled alloys were tested to identify their structures by X-ray diffraction and transmission electron microscopy. The isothermal hydrogen storage thermodynamics and dynamics were identified through an automatic Sieverts apparatus and the non-isothermal dehydrogenation performance was investigated by thermogravimetry and differential scanning calorimetry. The dehydrogenation activation energy was calculated by both Arrhenius and Kissinger methods. Results revealed that adding MoS2produces a very slight effect on hydrogen storage thermodynamics but causes an obvious reduction in the hydrogen sorption and desorption capacities because of the deadweight of MoS2. The addition of MoS2significantly enhances the dehydrogenation performance of the alloy such as lowering dehydrogenation temperature and enhancing dehydrogenation rate. Specifically the initial desorption temperature of the alloy hydride lowers from 549.8 K to 525.8 K. The time required to desorb hydrogen at 3 wt% H2 is 1106 456 363 and 180 s corresponding to hydrogen desorption temperatures at 593 613 633 and 653 K for the YMg11Ni alloy and 507 208 125 and 86 s at identical conditions for the YMg11Ni–5MoS2 alloy. The dehydrogenation activation energy (Ea) values with and without added MoS2are 85.32 and 98.01 kJ mol−1. Thus a decrease in Ea value by 12.69 kJ mol−1 occurs and is responsible for the amelioration of the hydrogen desorption dynamics by adding a MoS2 catalyst.
The Hydrogen Storage Properties of MgH2–Fe7S8 Composites
Nov 2020
Publication
Nanostructured Fe7S8 was successfully synthesized and its catalytic effect on hydrogen absorption/desorption performance of MgH22 is systemically discussed. The MgH2 + 16.7 wt% Fe7S8 composite prepared by ball-milling method offers a striking catalytic activity for hydrogenation kinetics and also reduces the initial decomposition temperature for MgH22. The composite of MgH2–Fe7S8 can absorb 4.000 wt% of hydrogen within 1800 s at 473 K which is about twice that of pristine MgH2 (1.847 wt%) under the same conditions. The onset hydrogen release temperature of Fe7S8-modified MgH2 is 420 K which is 290 K lower than that of additive-free MgH2 (710 K). Meanwhile the doped sample could release 4.403 wt% of hydrogen within 1800 s at 623 K as compared to 2.479 wt% of hydrogen by MgH2. The activation energy for MgH2–Fe7S8 is about 130.0 kJ mol−1 approximately 36 kJ mol−1 lower than that of MgH2. The hydriding process of MgH2 + 16.7 wt% Fe7S8 follows the nucleation and growth mechanism. The prominent hydrogen storage performances are related to the reactions between MgH2 and Fe7S8. The newly formed MgS and Fe in the ball-milling process present a co-catalytic effect on the hydrogen storage performance of MgH22.
The Impact of Disruptive Powertrain Technologies on Energy Consumption and Carbon Dioxide Emissions from Heavy-duty Vehicles
Jan 2020
Publication
Minimising tailpipe emissions and the decarbonisation of transport in a cost effective way remains a major objective for policymakers and vehicle manufacturers. Current trends are rapidly evolving but appear to be moving towards solutions in which vehicles which are increasingly electrified. As a result we will see a greater linkage between the wider energy system and the transportation sector resulting in a more complex and mutual dependency. At the same time major investments into technological innovation across both sectors are yielding rapid advancements into on-board energy storage and more compact/lightweight on-board electricity generators. In the absence of sufficient technical data on such technology holistic evaluations of the future transportation sector and its energy sources have not considered the impact of a new generation of innovation in propulsion technologies. In this paper the potential impact of a number of novel powertrain technologies are evaluated and presented. The analysis considers heavy duty vehicles with conventional reciprocating engines powered by diesel and hydrogen hybrid and battery electric vehicles and vehicles powered by hydrogen fuel cells and freepiston engine generators (FPEGs). The benefits are compared for each technology to meet the expectations of representative medium and heavy-duty vehicle drivers. Analysis is presented in terms of vehicle type vehicle duty cycle fuel economy greenhouse gas (GHG) emissions impact on the vehicle etc.. The work shows that the underpinning energy vector and its primary energy source are the most significant factor for reducing primary energy consumption and net CO2 emissions. Indeed while an HGV with a BEV powertrain offers no direct tailpipe emissions it produces significantly worse lifecycle CO2 emissions than a conventional diesel powertrain. Even with a de-carbonised electricity system (100 g CO2/kWh) CO2 emissions are similar to a conventional Diesel fuelled HGV. For the HGV sector range is key to operator acceptability of new powertrain technologies. This analysis has shown that cumulative benefits of improved electrical powertrains on-board storage efficiency improvements and vehicle design in 2025 and 2035 mean that hydrogen and electric fuelled vehicles can be competitive on gravimetric and volumetric density. Overall the work demonstrates that presently there is no common powertrain solution appropriate for all vehicle types but how subtle improvements at a vehicle component level can have significant impact on the design choices for the wider energy system.
Hydrogen Diffusion Mechanism around a Crack Tip in Type 304L Austenite Stainless Steel Considering the Influence of the Volume Expansion of Strain-Induced Martensite Transformation
Sep 2019
Publication
Strain-induced martensite transformation (SIMT) commonly exists around a crack tip of metastable austenite stainless steels. The influence of the volume expansion of the SIMT on the hydrogen diffusion was investigated by hydrogen diffusion modelling around a crack tip in type 304L austenite stainless steel. The volume expansion changed the tensile stress state into pressure stress state at the crack tip resulting in a large stress gradient along the crack propagation direction. Compared to the analysis without considering the volume expansion effect this volume expansion further accelerated the hydrogen transport from the inner surface to a critical region ahead of the crack tip and further increased the maximum value of the hydrogen concentration at the critical position where the strain-induced martensite fraction approximates to 0.1 indicating that the volume expansion of the SIMT further increased the hydrogen embrittlement susceptibility.
Experimental Investigation of the Effect of Hydrogen on Fracture Toughness of 2.25Cr-1Mo-0.25V Steel and Welds after Annealing
Mar 2018
Publication
Hydrogen embrittlement (HE) is a critical issue that hinders the reliability of hydrogenation reactors. Hence it is of great significance to investigate the effect of hydrogen on fracture toughness of 2.25Cr-1Mo-0.25V steel and weld. In this work the fracture behavior of 2.25Cr-1Mo-0.25V steel and welds was studied by three-point bending tests under hydrogen-free and hydrogen-charged conditions. The immersion charging method was employed to pre-charge hydrogen inside specimen and the fracture toughness of these joints was evaluated quantitatively. The microstructure and grain size of the specimens were observed by scanning electron microscopy (SEM) and by metallurgical microscopy to investigate the HE mechanisms. It was found that fracture toughness for both the base metal (BM) and the weld zone (WZ) significantly decreased under hydrogen-charged conditions due to the coexistence of the hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP) mechanisms. Moreover the formation and growth of primary voids were observed in the BM leading to a superior fracture toughness. In addition the BM compared to the WZ shows superior resistance to HE because the finer grain size in the BM leads to a larger grain boundary area thus distributing more of the diffusive hydrogen trapped in the grain boundary and reducing the hydrogen content.
Location-dependent Effect of Nickel on Hydrogen Dissociation and Diffusion on Mg (0001) Surface: Insights into Hydrogen Storage Material Design
Apr 2021
Publication
Density functional theory (DFT) calculations have been performed to investigate the hydrogen dissociation and diffusion on Mg (0001) surface with Ni incorporating at various locations. The results show that Ni atom is preferentially located inside Mg matrix rather than in/over the topmost surface. Further calculations reveal that Ni atom locating in/over the topmost Mg (0001) surface exhibits excellent catalytic effect on hydrogen dissociation with an energy barrier of less than 0.05 eV. In these cases the rate-limiting step has been converted from hydrogen dissociation to surface diffusion. In contrast Ni doping inside Mg bulk not only does little help to hydrogen dissociation but also exhibits detrimental effect on hydrogen diffusion. Therefore it is crucial to stabilize the Ni atom on the surface or in the topmost layer of Mg (0001) surface to maintain its catalytic effect. For all the case of Ni-incorporated Mg (0001) surfaces the hydrogen atom prefers firstly immigrate along the surface and then penetrate into the bulk. It is expected that the theoretical findings in the present study could offer fundamental guidance to future designing on efficient Mg-based hydrogen storage materials.
Production of High-purity Hydrogen from Paper Recycling Black Liquor via Sorption Enhanced Steam Reforming
Jul 2020
Publication
Environmentally friendly and energy saving treatment of black liquor (BL) a massively produced waste in Kraft papermaking process still remains a big challenge. Here by adopting a Ni-CaO-Ca12Al14O33 bifunctional catalyst derived from hydrotalcite-like materials we demonstrate the feasibility of producing high-purity H2 (∼96%) with 0.9 mol H2 mol-1 C yield via the sorption enhanced steam reforming (SESR) of BL. The SESRBL performance in terms of H2 production maintained stable for 5 cycles but declined from the 6th cycle. XRD Raman spectroscopy elemental analysis and energy dispersive techniques were employed to rationalize the deactivation of the catalyst. It was revealed that gradual sintering and agglomeration of Ni and CaO and associated coking played important roles in catalyst deactivation and performance degradation of SESRBL while deposition of Na and K from the BL might also be responsible for the declined performance. On the other hand it was demonstrated that the SESRBL process could effectively reduce the emission of sulfur species by storing it as CaSO3. Our results highlight a promising alternative for BL treatment and H2 production thereby being beneficial for pollution control and environment governance in the context of mitigation of climate change.
Analysis of Hydrogen Production Potential from Waste Plastics by Pyrolysis and In Line Oxidative Steam Reforming
Oct 2021
Publication
A study was carried out on the valorization of different waste plastics (HDPE PP PS and PE) their mixtures and biomass/HDPE mixtures by means of pyrolysis and in line oxidative steam reforming. A thermodynamic equilibrium simulation was used for determining steam reforming data whereas previous experimental results were considered for setting the pyrolysis volatile stream composition. The adequacy of this simulation tool was validated using experimental results obtained in the pyrolysis and in line steam reforming of different plastics. The effect the most relevant process conditions i.e. temperature steam/plastic ratio and equivalence ratio have on H2 production and reaction enthalpy was evaluated. Moreover the most suitable conditions for the oxidative steam reforming of plastics of different nature and their mixtures were determined. The results obtained are evidence of the potential interest of this novel valorization route as H2 productions of up to 25 wt% were obtained operating under autothermal conditions.
An Optimal Fuzzy Logic-Based Energy Management Strategy for a Fuel Cell/Battery Hybrid Power Unmanned Aerial Vehicle
Feb 2022
Publication
With the development of high-altitude and long-endurance unmanned aerial vehicles (UAVs) optimization of the coordinated energy dispatch of UAVs’ energy management systems has become a key target in the research of electric UAVs. Several different energy management strategies are proposed herein for improving the overall efficiency and fuel economy of fuel cell/battery hybrid electric power systems (HEPS) of UAVs. A rule-based (RB) energy management strategy is designed as a baseline for comparison with other strategies. An energy management strategy (EMS) based on fuzzy logic (FL) for HEPS is presented. Compared with classical rule-based strategies the fuzzy logic control has better robustness to power fluctuations in the UAV. However the proposed FL strategy has an inherent defect: the optimization performances will be determined by the heuristic method and the past experiences of designers to a great extent rather than a specific cost function of the algorithm itself. Thus the paper puts forward an improved fuzzy logic-based strategy that uses particle swarm optimization (PSO) to track the optimal thresholds of membership functions and the equivalent hydrogen consumption minimization is considered as the objective function. Using a typical 30 min UAV mission profile all the proposed EMS were verified by simulations and rapid controller prototype (RCP) experiments. Comprehensive comparisons and analysis are presented by evaluating hydrogen consumption system efficiency and voltage bus stability. The results show that the PSO-FL algorithm can further improve fuel economy and achieve superior overall dynamic performance when controlling a UAV’s fuel-cell powertrain.
Molecular Dynamics Studies of Hydrogen Effect on Intergranular Fracture in α-Iron
Nov 2020
Publication
In the current study the effect of hydrogen atoms on the intergranular failure of α-iron is examined by a molecular dynamics (MD) simulation. The effect of hydrogen embrittlement on the grain boundary (GB) is investigated by diffusing hydrogen atoms into the grain boundaries using a bicrystal body-centered cubic (BCC) model and then deforming the model with a uniaxial tension. The Debye Waller factors are applied to illustrate the volume change of GBs and the simulation results suggest that the trapped hydrogen atoms in GBs can therefore increase the excess volume of GBs thus enhancing intergranular failure. When a constant displacement loading is applied to the bicrystal model the increased strain energy can barely be released via dislocation emission when H is present. The hydrogen pinning effect occurs in the current dislocation slip system <111>{112}. The hydrogen atoms facilitate cracking via a decrease of the free surface energy and enhance the phase transition via an increase in the local pressure. Hence the failure mechanism is prone to intergranular failure so as to release excessive pressure and energy near GBs. This study provides a mechanistic framework of intergranular failure and a theoretical model is then developed to predict the intergranular cracking rate
Vented Hydrogen-air Explosion in a Small Obstructed Rectangular Container- effect of the Blockage Ratio
Sep 2019
Publication
The explosion venting is an effective way to reduce hydrogen-air explosion hazards but the explosion venting has been hardly touched in an obstructed container. Current experiments focused on the effects of different blockage ratios on the explosion venting in a small obstructed rectangular container. Experimental results show that three overpressure peaks are formed in the case with the obstacle while only two can be observed in the case of no obstacle. The obstacle blockage ratio has a significant influence on the peak overpressure induced by the obstacle-acoustic interactions but it has an ignorable effect on the peak overpressure caused by the rupture of the vent film. The obstacle-induced overpressure peak first increases and then decreases with the increase of the blockage ratio. In addition all overpressure peaks inside the container decreases with the increase of the vent area and its appearance time is relatively earlier for larger vent area.
Simulation Analysis on the Risk of Hydrogen Releases and Combustion in Subsea Tunnels
Oct 2015
Publication
Hydrogen is considered to be a very promising potential energy carrier due to its excellent characteristics such as abundant resources high fuel value clean and renewable. Its safety features greatly influence the potential use. Several safety problems need to be analyzed before using in transportation industry. With the development of the tunnel transportation technology the safe use of hydrogen in tunnels will receive a lot of research attentions. In this article the risk associated with hydrogen release from onboard high-pressure vessels and the induced combustion in tunnels was analyzed using the Partially Averaged Navier–Stokes (PANS) turbulence model. The influences of the tunnel ventilation facilities on the hydrogen flow characteristics and the flammable hydrogen cloud sizes were studied. The tunnel layouts were designed according to the subsea tunnel. And a range of longitudinal ventilation conditions had been considered to investigate the hydrogen releases and the sizes of the flammable hydrogen cloud. Then the hydrogen combustion simulation was carried out after the fixed leaking time. The overpressures induced after the ignition of leaking hydrogen were studied. The influences of ventilation and ignition delay time on the overpressure were also investigated. The main aim was to research the phenomena of hydrogen releases and combustion risk inside subsea tunnels and to lay the foundation of risk assessment methodology developed for hydrogen energy applications on transportation.
Blending Ammonia into Hydrogen to Enhance Safety through Reduced Burning Velocity
Sep 2019
Publication
Laminar burning velocities (SL) of hydrogen/ammonia mixtures in air at atmospheric pressure were studied experimentally and numerically. The blending of hydrogen with ammonia two fuels that have been proposed as promising carriers for renewable energy causes the laminar flame speed of the mixture SL to decrease significantly. However details of this have not previously available. Systematic measurements were therefore performed for a series of hydrogen/ammonia mixtures with wide ranges of mole fractions of blended ammonia (XNH3) and equivalence ratio using a heat flux method based on heat flux of a flat flame transferred to the burner surface. It was found that the mixture of XNH3 = 40% has a value of SL close to that of methane which is the dominant component of natural gas. Using three chemical kinetic mechanisms available in the literature i.e. the well-known GRI-Mech 3.0 mechanism and two mechanisms recently released SL were also modelled for the cases studied. However the discrepancies between the experimental and numerical results can exceed 50% with the GRI-Mech 3.0 mechanism. Discrepancies were also found between the numerical results obtained with different mechanisms. These results can contribute to an increase in both the safety and efficiency of the coutilization of these two types of emerging renewable fuel and to guiding the development of better kinetic models.
Application of DFT Simulation to the Investigation of Hydrogen Embrittlement Mechanism and Design of High Strength Low Alloy Steel
Dec 2022
Publication
In this work first-principles methods were performed to simulate interactions between hydrogen and common alloying elements of high strength low alloy (HSLA) steel. The world has been convinced that hydrogen could be one of the future clean energy sources. HSLA steel with a balance of strength toughness and hydrogen embrittlement susceptibility is expected for application in large-scale hydrogen storage and transportation. To evaluate the property deterioration under a hydrogen atmosphere hydrogen embrittlement (HE) of HSLA steel attracts attention. However due to the small size of hydrogen atoms the mechanism of HE is challenging to observe directly by current experimental methods. To understand the HE mechanism at an atomic level DFT methods were applied to simulate the effects of alloying elements doping in bcc-Fe bulk structure and grain boundary structure. Furthermore the potential application of DFT to provide theoretical advice for HSLA steel design is discussed.
To Adopt CCU Technology or Not? An Evolutionary Game between Local Governments and Coal-Fired Power Plants
Apr 2022
Publication
Carbon dioxide capture and utilization (CCU) technology is a significant means by which China can achieve its ambitious carbon neutrality goal. It is necessary to explore the behavioral strategies of relevant companies in adopting CCU technology. In this paper an evolutionary game model is established in order to analyze the interaction process and evolution direction of local governments and coal-fired power plants. We develop a replicator dynamic system and analyze the stability of the system under different conditions. Based on numerical simulation we analyze the impact of key parameters on the strategies of stakeholders. The simulation results show that the unit prices of hydrogen and carbon dioxide derivatives have the most significant impact: when the unit price of hydrogen decreases to 15.9 RMB/kg or the unit price of carbon dioxide derivatives increases to 3.4 RMB/kg the evolutionary stabilization strategy of the system changes and power plants shift to adopt CCU technology. The results of this paper suggest that local governments should provide relevant support policies and incentives for CCU technology deployment as well as focusing on the synergistic development of CCU technology and renewable energy hydrogen production technology
Heat Transfer Analysis for Fast Filling of On-board Hydrogen Tank
Mar 2019
Publication
The heat transfer analysis in the filling process of compressed on-board hydrogen storage tank has been the focus of hydrogen storage research. The initial conditions mass flow rate and heat transfer coefficient have certain influence on the hydrogen filling performance. In this paper the effects of mass flow rate and heat transfer coefficient on hydrogen filling performance are mainly studied. A thermodynamic model of the compressed hydrogen storage tank was established by Matlab/Simulink. This 0D model is utilized to predict the hydrogen temperature hydrogen pressure tank wall temperature and SOC (State of Charge) during filling process. Comparing the simulated results with the experimental data the practicability of the model can be verified. The simulated results have certain meaning for improving the hydrogenation parameters in real filling process. And the model has a great significance to the study of hydrogen filling and purification.
Predicting Radiative Characteristics of Hydrogen and Hythane Jet Fires Using Firefoam
Sep 2013
Publication
A possible consequence of pressurized hydrogen release is an under-expanded jet fire. Knowledge of the flame length radiative heat flux and fraction as well as the effects of variations in ground reflectance is important for safety assessment. The present study applies an open source CFD code FireFOAM to study the radiation characteristics of hydrogen and hydrogen/methane jet fires. For combustion the eddy dissipation concept for multi-component fuels recently developed by the authors in the large eddy simulation (LES) framework is used. The radiative heat is computed with the finite volume discrete ordinates model in conjunction with the weighted-sum-of-gray-gases model for the absorption/emission coefficient. The pseudo-diameter approach is used in which the corresponding parameters are calculated using the correlations of Birch et al. [22]. The predicted flame length and radiant fraction are in good agreement with the measurements of Schefer et al. [2] Studer et al. [3] and Ekoto et al. [6]. In order to account for the effects of variation in ground surface reflectance the emissivity of hydrogen flames was modified following Ekoto et al. [6]. Four cases with different ground reflectance are computed. The predictions show that the ground surface reflectance only has minor effect on the surface emissive power of the hydrogen jet fire. The radiant fractions fluctuate from 0.168 to 0.176 close to the suggested value of 0.16 by Ekoto et al.[6] based on the analysis of their measurements.
RBD-fast Based Sensitivity and Uncertainty Analysis on a Computational Hydrogen Recombiner Test Case
Sep 2017
Publication
Deflagration-to-Detonation Transition Ratio (DDTR) is an important parameter in measuring the hazard of hydrogen detonation at given thermodynamic conditions. It’s among the major tasks to evaluate DDTR in the study of hydrogen safety in a nuclear containment. With CFD tools detailed distribution of thermodynamic parameters at each instant can be simulated with considerable reliability. Then DDTR can be estimated using related CFD output. Forstochastic or epistemic reasons uncertainty always exists in input parameters during computations. This lack of accuracy can finally be reflected in the uncertainty of computation results e.g. DDTR in our consideration. The analysis of the influence of the input uncertainty is therefore a key step to understand the model’s response on the output and possibly to improve the accuracy. The increase of computational power makes it possible to perform statistics-based sensitivity and uncertainty (SU) analysis on CFD simulations. This paper aims at presenting some ideas on the procedure in safety analysis on hydrogen in nuclear containment. A hydrogen recombiner case is constructed and simulated with CFD method. DDTR at each instant is computed using a semi-empirical method. RBD-FAST based SU analysis is performed on the result.
A Study on the Influential Factors of Stress Corrosion Cracking in C110 Casing Pipe
Jan 2022
Publication
In this paper we analyze the potential factors affecting the hydrogen sulfide type of stress corrosion cracking in C110 casing pipes. In order to further study these cracking factors the methods of material property testing scanning electron microscopy XRD TEM and 3D ultra-depth-of-field were applied in the experiments. Besides that an HTHP autoclave was independently designed by the laboratory to simulate the actual corrosion environment and the potential factors affecting the stress corrosion cracking of C110 casing pipes were determined. The test results showed that the chemical composition metallographic structure hardness and non-metallic inclusions of the two types of C110 casing pipes were all qualified. In fact there remains a risk of stress corrosion cracking when the two kinds of C110 casing pipes serve under long-term field-working conditions. It is considered in this paper that the precipitates on the material surface stress damage and pitting corrosion are all critical factors affecting the stress corrosion cracking of casing pipes.
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