Liquid Hydrogen Transportation Research Articles

Contact electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen transportation

The issue of electrostatic safety in liquid hydrogen systems has garnered increasing attention, especially concerning the potential threat of electrostatic explosions due to the collision-electrification phenomenon of solid oxygen particles formed after air leakage in liquid hydrogen pipelines. To delve into the contact electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen transportation, a mathematical model based on the computational fluid dynamics-discrete element method (CFD-DEM) two-phase flow dynamics has been developed. This model integrates the Hertz contact theory for describing particle collision processes and the condenser model for describing particle collision-electrification. The reliability of this model has been validated in existing literature through its ability to capture the flow characteristics of two-phase flow and the electrification characteristics of particle groups. Using density functional theory to compute the solid oxygen work function and considering the low-temperature properties of liquid hydrogen, a series of numerical studies on the flow sedimentation and electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen pipelines have been conducted. The results indicate that particles carry negative charges after colliding with stainless steel pipe walls, with single charge exchange magnitudes of approximately 10−12C for particle-wall continuous collision processes and 10−14C for particle-particle collision processes, resulting in particle charge-to-mass ratios on the order of tens of μC/kg at the outlet interface. The impact of electrostatic forces on particle motion is significant and cannot be overlooked. Furthermore, the effects of velocity, particle diameter, and pipe diameter on particle charge characteristics have been thoroughly analyzed. At low flow velocities, severe particle settlement occurs, leading to increased collision frequency between particles and walls and significant charge accumulation. Increasing flow velocity can mitigate particle settlement and reduce charge levels. Changes in particle and pipe diameters have a minor impact on particle settlement but can increase single charge amounts with larger particle diameters and intensify particle charging with reduced pipe diameters due to shortened radial travel distances, leading to increased collision frequency. Our study meticulously illustrates the charge characteristics of individual particles and particle groups, providing a theoretical basis for assessing the electrostatic safety of liquid hydrogen transportation systems under extreme conditions.

Changes in holding time depending liquid filling ratio, heat transfer parameters, and shape of the tank

This study simulates the self-pressurization of liquefied hydrogen using a three-element lumped model. We analyze the effects of liquid filling ratio, heat flux distribution, interface heat transfer parameters, and tank shape on pressure build-up, which can vary due to ship transportation conditions. Key findings are: lower liquid levels correlate with faster pressure build-up; the sensitivity of pressure build-up to changes in the heat flux ratio between vapor and liquid is higher during laden voyages compared to ballast voyages; The effect of heat absorption by vapor on pressure build-up is greater than that of BOG caused by heat transfer; and horizontal tanks exhibit the longest holding time. These findings enhance the understanding and prediction of pressure dynamics in liquid hydrogen transportation, aiding the design and optimization of systems for safe and efficient operation.

Solvent-free polyurethane adhesives with excellent adhesion performance at ultra-low temperature

Adhesives with excellent adhesion and high elongation at cryogenic temperatures are necessary for fields such as aerospace, transportation, superconductors, and medicine, but have difficult requirements. This study aimed to develop a solvent-free, two-component polyurethane (PU) adhesive with excellent adhesion and high elongation, especially in ultra-low temperature conditions. we incorporated bulky polydimethylsiloxane (PDMS) diol into the hard segment of the PU adhesive to enhance flexibility and improve physical cross-linking within the adhesive matrix. The resulting PDMS-based PU adhesive showed a tensile strength of 120 MPa at −170 °C and a high elongation of approximately 4 %. It showed a lap-shear strength of up to 13 MPa at −196 °C. Additionally, the adhesive was curable at 23 °C. In this study, the cryogenic applicability of the PU adhesive was evaluated at −170 °C (103 K, liquid natural gas) and −196 °C (77 K, liquid nitrogen). Future research on the polymer adhesive materials applicable to ultra-low temperatures, such as 20 K, may be necessary if storage and transportation of liquid hydrogen become feasible.

Study on a novel hydrogen liquification process applying mixed-refrigerant for pre-cooling and cryogenics

Reducing the energy consumption of hydrogen liquefaction process is an urgent issue to improve the economy of liquid hydrogen transportation. A novel large-scale hydrogen liquefaction system, with a capacity of 100 TPD, is proposed in this paper. The pre-cooling system is composed of a mixed-refrigerant (MR) refrigeration cycle and a CO2–NH3 cascade refrigeration cycle. Due to the auxiliary pre-cooling effect of the CO2–NH3 cascade cycle, temperature of the pre-cooled hydrogen can be as low as −200.9 °C. A modified MR Joule Brayton cycle with an additional compressor is used as the cryogenic system to cool the hydrogen from −200.9 °C to −252.2 °C. Besides, a four-stage ortho-to-para conversion (OPC) process is utilized. Performance of the novel system is investigated and optimized using the Aspen HYSYS software. According to the results, the lowest specific energy consumption (SEC) of the proposed process is 6.15 kWh/kgLH2 and the exergy efficiency is as high as 67.4%. Based on the energy analysis, the best system coefficient of performance is 0.1751 with a 96.3% of p-H2 in the liquid hydrogen. In addition, compared to the initial conceptual system, the proposed system exhibits significant performance enhancements, a 20% reduction in SEC and a 27.9% increase in exergy efficiency. A sensitivity analysis is conducted to assess the impact of refrigerant composition and hydrogen pressure on the system, resulting in the determination of the optimal proportions of refrigerant components and the optimal inlet pressure. Results of the study can provide theoretical reference for the further development of large-scale hydrogen liquefaction technology.

Numerical study on thermodynamic characteristics of large-scale liquid hydrogen tank with baffles under sloshing conditions

The control of the evaporation rate is essential to the long-distance transportation of liquid hydrogen (LH2). This paper conducts a numerical investigation of the thermodynamic characteristics in tanks with baffles under LH2 sloshing conditions by establishing a computational fluid dynamics (CFD) model. The pressurization rate and vapor-liquid interface sloshing behavior predicted by the numerical model is validated against experimental data. The effects of baffles, amplitude, frequency, and storage pressure on thermodynamic characteristics such as temperature, pressurization rate, and evaporation rate of the LH2 tank under sinusoidal sloshing are analyzed in detail. The simulation results suggest that adding baffles can effectively suppress the pressure fluctuation of LH2 under sloshing conditions, but baffles as a "thermal bridge" accelerate the pressurization rate in the tank. Adding baffles during smooth transportation accelerates the pressurization rate. The baffles gradually demonstrate the effect of suppressing the pressurization rate as the acceleration amplitude increases. Assuming that the LH2 evaporation rate is stable for a certain value, the daily evaporation rates in the LH2 tank account for 2.59 % and 5.13 % when the maximum acceleration is 5.92 m/s2 and 9.87 m/s2, respectively, which contradicts the long-term storage goal of LH2. The slower the sloshing frequency, the higher the maximum liquid phase level in the tank, and the faster the evaporation rate. The sloshing frequency has little effect on the LH2 pressurization and evaporation rates compared to the amplitude. The growth of pressure decreases from 139.9 Pa to 85.62 Pa for a period of 15 s when the storage pressure in the tank increases from 0.1 MPa to 0.6 MPa. This study provides guidlines for the in-depth investigation of the thermodynamic behavior in LH2 tanks during transportation.

CFD Modeling for Estimating Consequences of Liquid Hydrogen Release Transported by Road Tankers through Tunnels

Among the new energy carriers targeted at mitigating greenhouse gas emissions, the use of hydrogen is likely to experience substantial growth in the future. In this context, the transport of liquid hydrogen by means of road tankers might represent the most cost‐effective option for delivery over long distances in the short‐term perspective. Liquid hydrogen, however, entails non‐negligible risks, especially in confined spaces like road tunnels. An accidental release might form a flammable hydrogen cloud that might deflagrate or even detonate. Nevertheless, the consequences on users in the event of accidental leakage of liquid hydrogen from road tankers have not yet been sufficiently investigated. Therefore, this paper regards specific 3D computational fluid dynamics models to quantify the effects due to both liquid hydrogen release and potential deflagration and/or detonation within road tunnels. The proposed models were calibrated and subsequently validated with the findings of certain literature studies. Since the effects on tunnel users might be influenced, apart from tunnel geometry, by the type of ventilation and traffic flow, tunnel environmental conditions involving natural or mechanical ventilation, as well as off or peak traffic hours (i.e., night or day traffic) were more especially investigated. The results of simulations, in terms of overpressures generated from a potential hydrogen explosion, showed benefits due to mechanical ventilation and/or under lower traffic flows. By providing additional knowledge to the field of hydrogen safety, this study might help tunnel management agencies to make improved management and/or traffic control strategies (e.g., decisions on whether or not mechanical ventilation should be installed also in tunnels less than 1,000 m long and/or allowing the transit of road tankers transporting liquid hydrogen only at night rather than day).

Assessment of Commercially Available Hydrogen Supply Chains for Gas-Fired Boilers

Hydrogen energy is a clean and efficient secondary energy source, and hydrogen derived from renewable sources is regarded as the key to achieving a low-carbon clean energy supply. Currently, the hydrogen energy supply chain is still in its development stage and requires a comprehensive comparative analysis of various hydrogen production technologies as well as storage and transportation methods to ensure the optimal application route for hydrogen energy. In this study, GaBi 10 software is used to conduct a comparative and evaluative analysis of the potential environmental impact associated with hydrogen energy application. The life cycle assessment encompasses all stages of the hydrogen supply chain, including production, transportation and utilization. The results indicate that hydrogen production from wind power has the lowest global warming potential (GWP), acidification potential (AP), eutrophication potential (EP) and photochemical ozone creation potential (POCP). Due to the high energy consumption of the liquefaction process, liquid hydrogen transportation is currently associated with the largest carbon emissions among all modes of hydrogen transport. However, if renewable energy sources are utilized to power hydrogen liquefaction, significant reductions in carbon emissions can be achieved. An evaluation of the carbon footprint associated with the completed hydrogen supply chain indicates that hydrogen produced from renewable sources is cost-effective for use in gas-fired boilers from an environmental perspective.

Numerical approach to analyze fluid flow in a type C tank for liquefied hydrogen carrier (part 2: Thermal flow)

The present study aimed to analyze and compare vacuum insulation systems suitable for a type C liquid hydrogen storage tank. Multiphase thermal analysis was conducted via computational fluid dynamics, and experimental results for the boil-off rate (BOR) of a type C liquid nitrogen storage tank were obtained to verify the simulation technique. The simulation results showed a maximum error of 0.941 % compared to experimental results. Three insulation systems with superior thermal performance were selected and compared in a 3D system. The Vacuum+MLI Mylar-net insulation system showed the best thermal performance, with a result of 0.189 %/day. An analysis of the parts vulnerable to heat loss was conducted. These findings contribute to the development of high-performance insulation systems for the safe and economic transportation of liquid hydrogen. The study is an important resource for assessing insulation performance during the design phase and preventing local heat loss during operation.

Effect of unpaired electron number elements (Al, Cr, Mn) doping in Fe2O3 on ortho to para hydrogen conversion at 77 K

Para hydrogen (p-H2), as a low-energy spin isomer of hydrogen molecule, has an important significance in the storage and transportation of liquid hydrogen. The ortho hydrogen (o-H2) to p-H2 conversion catalyst accelerates the intrinsically slow o-H2 to p-H2 conversion and becomes an essential component of the hydrogen liquefaction process. In this paper, doped Fe2O3 with different hetero elements (X-FO, X = Al, Cr, Mn) are prepared by a simple co-precipitation method to explore the effect of different unpaired electron numbers in doping elements on catalytic performance. It is shown that the disorder in the internal crystal structure of X-FO caused by doping of hetero elements is the main reason for the increased performance of X-FO, as this leads directly to an increase in the internal magnetic disorder. The catalytic performance is enhanced with the increase in the number of unpaired electrons in doping elements. Mn-FO with high unpaired electron number exhibits optimal catalytic performance. When the hydrogen flow rate is 100 mL min−1, p-H2 content is 49.45 % after catalytic conversion at 77 K. In this paper, a simple method is adopted, which has advantages in terms of production process and cost, and provides experimental support for the large-scale production of catalysts.

Thermodynamic analysis of the effect of initial ortho-hydrogen concentration on thermal behaviors for liquid hydrogen tanks

Due to the extra evaporation loss caused by the ortho-para hydrogen conversion (OPHC) during the storage and transportation of liquid hydrogen (LH2), the initial concentration of ortho-hydrogen (o-H2) plays an important role in the large-scale safe operation and utilization of LH2. However, there are very limited studies focusing on clarifying the impact of the OPHC on thermal behaviors of LH2 tanks. In light of this, this paper establishes and develops an extended thermal multi-zone model that couples the OPHC process with the mass and energy conservation equations of the ullage and liquid for an LH2 tank. With the help of the model, a thermodynamic analysis of the pressurization rate is performed to obtain the dominant parameter that evaluates the effect of the initial o-H2 concentration on the pressure build-up process. The results indicate that the interfacial mass transfer rate caused by the OPHC is the dominant parameter accounting for more than 90% of the effect of all parameters on the pressurization rate during a 10-day process with an initial liquid fill ratio of 90% and a heat leakage of 40 W. Additionally, the effect of the initial o-H2 concentration on the optimal liquid fill ratio is discussed in this paper. The results indicate that when the initial o-H2 concentration changes from 0.2% to 10%, the optimal liquid fill ratio decreases from 82.5% to 74%. The present work provides theoretical support and guidance for controlling the o-H2 concentration to realize the long-term and high-efficiency storage of LH2.

Investigation on the Electrostatics Saturation of Flow Electrification in the Liquid Hydrogen Transportation

Research on the flow electrification characteristic is of paramount importance for ensuring the electrostatic safety of liquid hydrogen transportation systems. However, the discussion about electrostatic saturation in flow electrification has been lacking. To address this gap, a theoretical model governing the process of flow electrification is constructed which couples the charge conservation equation with the Navier-Stokes equations and applies the Neumann boundary conditions at the solid-liquid interface, and the application of this model is validated by existing experimental data with the simulation parameters of At and n being 9.08 × 1012 and 0.85 for liquid hydrogen. A comparison with benzene reveals that benzene almost reaches the electrostatic saturation state after flowing one meter, whereas the flow of liquid hydrogen remains in the linear growth stage. However, with an increase in pipe length, a gradual saturation trend emerges in the curves of streaming current versus flow distance when the flow distance exceeds 10 m. At the outlet, the corresponding streaming current and charge density are approximately 160 pA and 3 μC/m3, respectively, significantly higher than those observed at one-meter flow distance. Furthermore, the influences of pipe radius and flow velocity on the arrival of electrostatic saturation are analyzed, and the results show that increasing both the pipe radius and flow velocity leads to a delay in the arrival of electrostatic saturation and enhances the saturation value of the streaming current. In conclusion, this study thoroughly discusses the development of flow electrification along with the flow distance and the phenomenon of electrostatic saturation in the long-distance flow of liquid hydrogen, which is crucial for the safe transportation of liquid hydrogen over extended distances.

Multi-Objective Optimization of Variable Density Multi-Layer Insulation for Liquid Hydrogen Containers Based on Reduced-Order Surrogate Model

For liquid hydrogen transportation, thermal insulation materials that are lightweight, compact and exhibit high-performance have been pursued for several decades, and variable density multi-layer insulation (VD-MLI) has been regarded as a promising choice. The thermal insulation performance of the insulation materials is important, but is not at the top of the list; many constraints, such as the space and weight of the insulation structures, are imposed on the design of a VD-MLI. Consequently, this makes the optimization of VD-MLIs more complicated. The present authors conducted a multi-objective optimization of a VD-MLI stacked with specific insulation units. The number of repetitions of the basic insulation unit was regarded as the dimensionless design parameter of the VD-MLI. Based on the experimentally validated layer-by-layer (LBL) model for MLI design, the multi-objective optimization of VD-MLI for liquid hydrogen storage was conducted by the combination of proper orthogonal decomposition with a general regression neural network (POD-GRNN) surrogate model optimization framework. The results showed that the optimal solutions for VD-MLI configurations could be achieved under different constraints. The present optimization framework provides a new reference for the optimization of VD-MLI for cryogenic liquid storage.

Flow electrification characteristics of liquid hydrogen in pipe flow

Flow electrification occurs when a dielectric liquid flows along the wall surface, and it may cause electrostatic hazards such as spark discharges. Flow electrification issues of liquid hydrogen should be carefully treated since its low electrical conductivity and dangerous flammability. In this study, flow electrification characteristics of liquid hydrogen in pipe flow are numerically investigated. A theoretical model coupling the electric field and the flow field is introduced to govern the behaviour and distribution of charges, and an interface discharge model is adopted to describe the charge transfer boundary condition. The theoretical model is validated by comparing the simulation with experiment data, and the results show a good agreement with the averaged related deviation below 10%. The result of a common case, with flow velocity u of 1 m/s, pipe radius a 0.01 m, and length L 1 m, shows that the charge density, streaming current, and the electric potential of liquid hydrogen flow are in the magnitude of 10−12 C·m−3, 10−16 A and 10−2 V, respectively. Flow parameters, including flow velocity and pipe size, have a certain effect on the flow electrification characteristics of liquid hydrogen flow. By dimensionless parameterization, it is found that Reynolds numbers (Re), r/a, and x/a are exactly three orthogonal parameters determining the charge density distribution. Furthermore, the effects of electrical conductivity on the distribution of charges and charge dissipation have also been discussed. Finally, the safety assessment of the liquid hydrogen transportation system has been discussed, with extra consideration of the impurities and gas-liquid two-phase flow regime. To sum up, this work presents an in-depth and comprehensive insight into the flow electrification of liquid hydrogen flow, which is of great significance to the transportation safety of liquid hydrogen.

Comparative study on ammonia and liquid hydrogen transportation costs in comparison to LNG

Since ammonia and liquid hydrogen are the optional future shipping cargo and fuels, the applicability was crucial using the current technologies and expectations. Existing studies for the economic feasibility of the energies had limitations: empirical evaluation with assumptions and insufficiency related to causality. A distorted estimation can result in failure of decision-making or policy in terms of future energy. The present study aimed to evaluate the transportation costs of future energy including ammonia and liquid hydrogen in comparison to LNG for overcoming the limitations. An integrated mathematical model was applied to the investigation for economic feasibility. The transportation costs of the chosen energies were evaluated for the given transportation plan considering key factors: ship speed, BOR, and transportation plan. The transportation costs at the design speed for LNG and liquid hydrogen were approximately 55% and 80% of that for ammonia without considering the social cost due to CO2 emission. Although ammonia was the most expensive energy for transportation, ammonia could be an effective alternative due to insensitivity to the transportation plan. If the social cost was taken into account, liquid hydrogen already gained competitiveness in comparison to LNG. The advantage of liquid hydrogen was maximized for higher speed where more BOG was injected into main engines.

Numerical simulation on the thermal dynamic behavior of liquid hydrogen in a storage tank for trailers

In the present study, a numerical model was established to investigate the thermal dynamic behavior of liquid hydrogen in a 40-foot ISO tank. The volume of fluids (VOF) method was applied to capture the liquid surface, and a phase change model was used to describe the evaporation phenomenon of hydrogen. The mesh independence analysis and the experimental validation have been made. Under different filling levels, motion statuses, and heat leakage conditions, the variations in pressure and temperature of the tank were investigated. The pressure of 90% filling level case was reduced by 12.09%, compared to the 50% case. Besides, the pressure of the sloshing condition has increased twofold, contrasted with the stationary one, and thermal stratification disappeared. Additionally, 16.67 min were taken for the ullage pressure to reach around 1 MPa in emergencies of being extremely heated. Some valuable conclusions and suggestions for the transportation of liquid hydrogen arrived. Those could be the references to predict the release time of boil-off hydrogen, and primarily support for gas-releasing control strategies.

Liquid Hydrogen Production, Transportation and Economic Analysis

With rapid development of hydrogen energy industry in China, liquid hydrogen transportation mode with high energy storage density has great advantages over the current high-pressure gaseous transportation mode, and will become an important and efficient carrier to realize the large-scale development of hydrogen energy. The high economic efficiency of liquid hydrogen can be better applied to civil market with cost sensitivity. This paper describes the current global liquid hydrogen production capacity and distribution, summarizes the liquefaction methods and transportation technical characteristics of liquid mode, and analyzes the economic cost composition of the liquid hydrogen technology route. It is concluded that liquid mode as hydrogen carrier of large-scale development of hydrogen energy will be suitable for the development route of civil hydrogen energy in China. Suggestions are also put forward for the future development of hydrogen energy in China.

Effect of liquid filling level on sloshing hydrodynamic characteristic under the first natural frequency

Hydrogen energy is a promising renewable alternative energy and hydrogen storage obtains more interest all over the world. During the transportation of liquid hydrogen, fluid sloshing is inevitable due to low kinetic viscosity. As fluid sloshing has obvious negative effects, the corresponding safety issues should be given detailed considerations. This work aims to study fluid sloshing hydrodynamic performance in a cryogenic fuel storage tank by utilizing volume of fluid (VOF) method. The numerical model validation is conducted by compared with related experimental results. The first natural frequency of the storage tank is selected as external excitation, and influence of initial liquid filling level on fluid sloshing is researched and analyzed. Different fluid sloshing hydrodynamic parameters, including sloshing force, fluid pressure, interface area ratio and interface fluctuation, are simulated. It is found that the initial liquid filling level causes evident influences on fluid sloshing hydrodynamic characteristics. The sloshing hydrodynamic parameters increase with the liquid filling level. The free interface experiences obvious fluctuations subjected to the first natural frequency. Moreover, the interface monitor close to tank wall has large amplitude displacement fluctuations. Generally, the displacement fluctuation increases with the initial liquid filling level. The present work is of significance to understand fluid sloshing hydrodynamics under the natural frequency, and may supply some references to weaken and inhibit large amplitude fluid sloshing.

Large-Scale Maritime Transport of Hydrogen: Economic Comparison of Liquid Hydrogen and Methanol

For the first time, a comparative economic study between liquid hydrogen and methanol as hydrogen vectors for the bulk transport of hydrogen at sea has been performed. The objective of this study is to gain insight on whether it is cost-effective to produce green hydrogen locally or, instead, import it from another location overseas featuring lower costs of renewable energy. In addition, this study aims to determine the break-even point at which the hydrogen transport alternatives, covered in this study, become more inexpensive. The alternatives covered include the seaborne transport of liquid hydrogen or methanol with the reconversion to hydrogen at the destination through methanol electrolysis or a steam-reforming process. Three different production mass flow rates of hydrogen at the origin are explored, 100 kt/y, 1 Mt/y, and 10 Mt/y, in regard to three representative routes: Brazil–Spain, Brazil–The Netherlands, and Australia–Japan. The findings of this study suggest that for the production of hydrogen at 1 Mt/y with an electricity cost of 40 USD/MWh, liquid hydrogen is the cheapest alternative with a levelized cost of hydrogen at the destination of approximately 2 USD/kg for all of the explored routes. If the synthesized e-methanol reaching the import destination is directly used as an energy vector, the levelized cost of energy contained in this e-methanol practically coincides with that of liquid hydrogen at a mass flow rate of 10 Mt/y at the origin.

Hydrofluoroolefin-based mixed refrigerant for enhanced performance of hydrogen liquefaction process

Hydrogen has the highest gravimetric energy density of all fuels; however, it has a low volumetric energy density, unfavorable for storage and transportation. Hydrogen is usually liquefied to meet the bulk transportation needs. The exothermic interconversion of its spin isomers is an additional activity to an already energy-intensive process. The most significant temperature drop occurs in the precooling cycle (between −150 °C and up to −180 °C) and consumes more than 50% of the required energy. To reduce the energy consumption and improve the exergy efficiency of the hydrogen liquefaction process, a new high-boiling component, Hydrofluoroolefin (HFO-1234yf), is added to the precooled mixed refrigerant. As a result, the specific energy consumption of precooling cycle reduces by 41.8%, from 10.15 kWh/kgLH2 to 5.90 kWh/kgLH2, for the overall process. The exergy efficiency of the proposed case increases by 43.7%; however, the total equipment cost is also the highest. The inflated cost is primarily due to the added ortho-to-para hydrogen conversion reactor, boosting the para-hydrogen concentration. From the perspective of bulk storage and transportation of liquid hydrogen, the simplicity of design and low energy consumption build a convincing case for considering the commercialization of the process.

Installation for experimental research of thermal and hydraulic processes of hybrid power systems of high power transmission

An installation for experimental research of thermal and hydraulic processes in hybrid high-power energy transmission systems is considered, in which an increase in power transmission and energy flux density is achieved by the simultaneous transportation of liquid hydrogen or LNG (liquefied natural gas) and in electrical form - using a superconducting cable.