Hydrogen Liquefier Research Articles

Energy‐Efficient Hydrogen Liquefaction Process with Ortho‐Para Conversion and Boil‐Off Gas Recovery

AbstractHydrogen liquefaction is essential for the efficient storage and transportation of hydrogen. In the liquefaction process, catalytic ortho‐para conversion is crucial to achieve a product with at least 95 % para‐hydrogen to reduce boil‐off losses. The proposed hydrogen liquefaction process using a catalyst‐filled heat exchanger for continuous ortho‐para conversion is modeled through steady‐state thermal simulations in Aspen HYSYS. Additionally, an ejector is integrated to reliquefy boil‐off gas. The proposed design achieves a specific energy consumption (SEC) of 10.50 kWh ()−1 and an exergy efficiency (EXE) of 30.1 %, which is 18 % lower in SEC compared to processes with separate converters. The integrated approach enhances energy utilization and offers references for future hydrogen liquefiers.

Thermoeconomic analysis of novel hydrogen liquefaction assisted by absorption refrigeration utilizing heat from Brayton cycle

Abstract Current research presents a novel method for reducing the energy consumption of hydrogen liquefaction through heat recovery of hydrogen liquefier. An ammonia absorption refrigeration cycle on the hydrogen precooling utilizes the heat generated by the compressor intercooler and aftercooler of the reverse Brayton cycle of hydrogen liquefier to precool hydrogen feedstock. The system is analyzed from exergy, energy, and economic perspective. The results are compared with the reference case without a heat recovery system. The proposed system can reduce SEC (specific energy consumption) from 7.37 kWh/kgLH2 to 6.23 kWh/kgLH2 and exergy efficiency improvement from 55.2% to 60.90%. The economic analysis shows that the levelized cost of energy to produce 5.07 tons/day of liquid hydrogen for the reference and novel case is 5.88 USD/kgLH2 and 5.03 USD/kgLH2, respectively. The results imply that the proposed method can be a reference for designing an integrated hydrogen liquefaction system to minimize energy consumption.

Helium screw compressor for 5tpd large-scale hydrogen liquefier

Liquid hydrogen has promising applications in various industries. As an important heart role, compressors are essential for efficient hydrogen liquefaction. This study introduced a novel profile screw compressor employed in large-scale hydrogen liquefaction processes. The development addressed the challenges associated with large-scale rotors, high pressure differences, and demanding capacity or torque requirements. By utilizing a 5/7-lobe combination of male to female rotors, this technology effectively tackled issues related to rotor dynamics, such as heavy-load rotor stiffness and dynamic balance. The profile design followed hydrodynamics principles, reducing viscosity loss and oil–gas flow loss at high speeds, large flow rates, and significant pressure differences. The profile curve’s curvature and geometric configuration were tailored to the specific pressure state during compression. In high-pressure areas, the profile remained relatively flat to maintain machining accuracy. While in low-pressure areas, the curvature was increased, and the meshing clearance was reduced to minimize helium leakage. Experimental tests conducted under conditions similar to actual hydrogen liquefaction processes have successfully validated the theoretical profile design and the newly developed multi-point oil injection cooling technologies. These advancements have led to an impressive isothermal efficiency of 58.1 % for the entire screw set. Furthermore, the stability and reliability of the compressor were verified through noise and vibration signal testing. The results demonstrated that the compressor operated with noise levels below 96 dB (A) and vibration levels below 7 mm/s, further ensured its suitability for large-scale cryogenic applications. These compressors have successfully run stably on the 5.17 tpd (ton per day) hydrogen liquefier. Overall, this research would significantly contribute to the advancement of screw compressors and large-scale cryogenic technology.

Comparison of mean-line methods for hydrogen turbo-expanders in hydrogen liquefiers

The energy consumption of a large-scale industrial hydrogen liquefaction system is primarily determined by the hydrogen turbo-expanders. To estimate the performance of the expander quickly, a one-dimensional preliminary design is conducted. This paper aims to identify dependable one-dimensional design codes for hydrogen turbo-expanders by employing three mean-line design approaches. The precision of the loss models is validated through hydrogen experiments, revealing a maximum deviation of less than 10 %. This study presents a summary of the optimal design parameter ranges for achieving high-efficiency hydrogen turbo-expanders. One common factor among the three methods is the characteristic ratio, which exhibits an optimal value range of 0.67–0.71. Furthermore, the three methods are applied to design hydrogen turbo-expanders of three different sizes, and the compositions of losses are thoroughly analyzed. The PR method exhibits the highest losses related to geometry sizes, while the VC method shows the greatest losses associated with velocities. The SS-CR method with moderate parameters is recommended for hydrogen turbo-expander design due to its superior maximum efficiency design limit and convenience. The two initial design parameters (specific speed and characteristic ratio) of this method play crucial roles in determining the scalability and efficiency of the hydrogen turbo-expander design.

Design and performance comparison of large-scale hydrogen liquefaction processes based on mixed refrigerant cycle

Liquid hydrogen (LH2) is an efficient carrier for storage and transportation of hydrogen energy. To investigate the effect of mixed refrigerant cycle (MRC) on the performance of large-scale hydrogen liquefiers, three processes with a capacity of 50 TPD LH2 are designed in a relatively achievable way. Process I utilizes a dual-pressure hydrogen Claude cycle with nitrogen precooling as a reference. Process II incorporates a five-component mixed refrigerant cycle in place of the nitrogen cycle. Process III advances further by replacing the hydrogen cycle in Process II with an additional MRC composed of Ne, He and H2. Sensitivity analysis is applied to optimize the parameters of the three processes prior to the comparison of their heat exchangers performance and the energy and exergy analyses. Due to the synergistic effect of smaller temperature difference and higher refrigeration temperature, the employment of MRC for precooling yields a SEC of 1.350 kWh/kg LH2, 57.1% and 66.3% lower than those of nitrogen cycle and liquid nitrogen, respectively. The sensible heat of the Ne/He/H2 mixture shows a better temperature matching than the latent heat of the refrigerant hydrogen when cooling the product hydrogen, reducing energy consumption by 28.4%. The utilization of MRC for precooling generates more exergy loss in the separators, mixers and throttle valves, but the absence of nitrogen expanders and much lower flow rate of refrigerant save more exergy in total. The essential reason for the progressiveness of Process III is that the integrated heat exchanger in the cryostat achieves the logarithmic mean temperature difference (LMTD) of 2.11 K, effectively reducing the exergy loss of the refrigerant compressors, thereby diminishing the thermodynamic irreversibility.

Mobile hydrogen liquefaction and storage system

A mobile hydrogen liquefaction and storage unit has been developed to demonstrate the liquid hydrogen (LH2) value chain including hydrogen production, liquefaction, storage, transfer, and recovery. This unique LH2 technology demonstrator, or LS20 mobile system, is one of the primary systems for a multipurpose LH2 test platform that evaluates liquefaction, controlled storage, and zero-loss transfer (ZLT) methodologies. The LS20 system has been designed, fabricated, and tested at GenH2. The primary subsystems include an electrolyzer option, gas precooler, Ortho-Para hydrogen converter, cryocooler-based hydrogen liquefier, portable LH2 storage tank, ultralight LH2 vehicle tank for aviation application, safety devices and sensors, automated venting system, associated sensors, instrumentation, and control system. The system was successfully demonstrated by continuous hydrogen liquefaction according to the design specification with the help of an automated control system to maintain the liquid at a desired level without boiloff loss. In addition to liquefaction and controlled storage, the functions of zero-loss transfer, boiloff gas recovery, and re-liquefaction were also demonstrated. The results provide proof-of-concept data for future LH2 infrastructure design as well as the critical LH2 refilling and servicing methodology for many hydrogen mobility applications. The system design, fabrication, operational methodology, and test performance results are discussed.

A high-precision experimental measurement system and method for the parahydrogen concentration and the Ortho-Para hydrogen catalyst's catalytic performance

An experimental system that combines the measurement of parahydrogen concentration with the assessment of ortho-para hydrogen catalyst's catalytic performance was created for this investigation. The concentration of parahydrogen was detected by a thermal conductivity detector integrated into the gas chromatograph. The catalyst sample and the generator of standard gas were integrated into one experimental setup for easier operation. Meanwhile, a new method for catalytic performance evaluation of ortho-para hydrogen catalyst was developed based on this system. This method can decrease test time and yield more valuable test results than the conventional way. Throughout the experiments, the system's dependability was increased by optimizing the utilization of the carrier gas. The deviation analysis and repeatability verification of the relevant test data showed that the relative standard deviation was less than 0.35% and the mean value of the variation coefficient was less than 0.20%, which demonstrated the method had high accuracy, stability, and reliability. Further studies have shown that the catalysts should be densely packed inside the converter and kept out of the air to maximize their catalytic activity. These pertinent findings regarding the application of ortho-parahydrogen catalysts in this study can guide the design of the ortho-parahydrogen converter in actual hydrogen liquefiers. Moreover, the method and the procedure proposed in this study may contribute to the optimization of the ortho-parahydrogen catalyst production process as well as the calibration of the parahydrogen concentration in liquid hydrogen products.

Analysis of vortex characteristics and energy losses in a cryogenic hydrogen turbo-expander for a 5 t/d hydrogen liquefier

The cryogenic hydrogen turbo-expander (CHTB) is the most core component which determines the dependability and efficiency of hydrogen liquefiers. In present study, CFD method are adopted to simulate the internal flow field inside a CHTB for a 5 t/d hydrogen liquefier. The Ω method and entropy generation method are implemented to identify vortex structures and calculate energy losses. The results show tip leakage vortex is the primary vortex and causes energy losses through strong fluid shear but not rotation effect. The turbulent dissipation is the main energy dissipation. The total entropy generation of CHTB impeller is significantly higher than nozzle because of tip clearances. As tip clearances increase from 0% to 1.6%, total entropy generation increases by 83%, and output shaft power and isentropic efficiency reduce by 9% and 6% respectively. Working conditions mainly affect the inlet angle of attack and significantly impact vortex characteristics and energy losses in the CHTB.

Study of activation methods for Ortho-para hydrogen catalysts in a small isothermal converter based on gas chromatography at LN2 temperature

The efficiency of the O–P catalyst activation directly affects how long liquid hydrogen may be kept. The ideal O–P catalyst activation condition must therefore be investigated. In this study, the effects of activation temperature, activation duration, and activation methods on the catalytic efficiency of a commercial O–P catalyst were thoroughly evaluated experimentally. We assessed the O–P catalysts' catalytic performance under richer activation conditions compared with previous studies. We also employed multiple linear regression to analyze the effects of the aforementioned experimental factors based on our experimental data. Results suggest that O–P catalyst for industrial applications should be activated at 160 °C for 8–12 h while being constantly vacuumed. We also found that the activation temperature had the largest influence on the catalytic performance of O–P catalyst. The pertinent experimental findings from this investigation provide a reference for the development and use of Ortho-Para hydrogen converters in hydrogen liquefiers.

Development of a condensing-type hydrogen liquefaction system for improving cooling efficiency and long-term storage

In this study, the experimental investigations for production of liquid hydrogen were conducted using a manufactured condensing-type hydrogen liquefaction device. A direct-cooling type hydrogen liquefier was designed, fabricated, and tested using a commercially available cryo-coolers, heat pipe, ortho-para converter, LN2 shield, and LN2 pre-cooler. In order to effectively carry out the experimental investigations in the presence of two cryo-coolers and LN2 shield in addition to the small-scale liquefaction system, this study introduced the new experimental system based on the cryogenic techniques. The production of liquid hydrogen could be achieved just by controlling the temperature and pressure inside the storage vessel. The cooling time of the vessel was reduced by approximately 100 min using new experimental system. The total time required to produce the same amount of liquid hydrogen, around 20L, was reduced by approximately 200 min. The experiments successfully demonstrated the liquefaction of hydrogen gas in the vessel at a rate of approximately 3.5L/h, corresponding to a level meter reading of 14.5 cm (6.95 % of the vessel's height). Therefore, the cooling time of the vessel and the total time required for liquid hydrogen production were found to be significantly influenced by the gas used to cool the initial container and the presence of LN2 shield.

CFD Thermo-Hydraulic Evaluation of a Liquid Hydrogen Storage Tank with Different Insulation Thickness in a Small-Scale Hydrogen Liquefier

Accurate evaluation of thermo-fluid dynamic characteristics in tanks is critically important for designing liquid hydrogen tanks for small-scale hydrogen liquefiers to minimize heat leakage into the liquid and ullage. Due to the high costs, most future liquid hydrogen storage tank designs will have to rely on predictive computational models for minimizing pressurization and heat leakage. Therefore, in this study, to improve the storage efficiency of a small-scale hydrogen liquefier, a three-dimensional CFD model that can predict the boil-off rate and the thermo-fluid characteristics due to heat penetration has been developed. The prediction performance and accuracy of the CFD model was validated based on comparisons between its results and previous experimental data, and a good agreement was obtained. To evaluate the insulation performance of polyurethane foam with three different insulation thicknesses, the pressure changes and thermo-fluid characteristics in a partially liquid hydrogen tank, subject to fixed ambient temperature and wind velocity, were investigated numerically. It was confirmed that the numerical simulation results well describe not only the temporal variations in the thermal gradient due to coupling between the buoyance and convection, but also the buoyancy-driven turbulent flow characteristics inside liquid hydrogen storage tanks with different insulation thicknesses. In the future, the numerical model developed in this study will be used for optimizing the insulation systems of storage tanks for small-scale hydrogen liquefiers, which is a cost-effective and highly efficient approach.

Development of Advanced Hydrogen Liquefaction System by using Magnetic Refrigeration Technology for JST-MIRAI Large-scale Project

For the supply chain of hydrogen, as the liquefaction cost may occupy 1/3 of the total supply price, developing a highly efficient hydrogen liquefier is one of the most important technology issues for hydrogen society. Magnetic refrigeration using the magnetocaloric effect has the potential to realize liquefaction efficiency higher than 50 %, and also to be environmentally friendly and cost effective. A hybrid refrigeration cycle consisting of the precooling cycle and magnetic active regenerator cycle has been proposed and is estimated to achieve a liquefaction capacity of >100 kg/day with liquefaction efficiency of >50 %.

Study on Performance Comparison of Two Hydrogen Liquefaction Processes Based on the Claude Cycle and the Brayton Refrigeration Cycle

Hydrogen liquefaction is an essential section for efficient storage and transportation of hydrogen energy. Both the Claude cycle and Brayton refrigeration cycle are available for large-scale hydrogen liquefaction systems. Two large-scale hydrogen liquefiers with the liquefaction capacity of 120 t/d based on the Brayton refrigeration cycle and the Claude cycle, respectively, are analyzed and compared in this study. Sensitivity analysis is used to optimize the parameters of two liquefaction systems in HYSYS. According to the results, the exergy loss and specific energy consumption of the Claude liquefier are 18.98 MW and 5.62 kWh/kgLH, which are 6.6% and 4.4% less than those of the Brayton liquefier, respectively. Exergy analysis reveals the exergy loss of compression and expansion systems in the Claude liquefier is less than that of the Brayton liquefier, while the exergy loss of the throttle valve in the Claude liquefier is more notable. In addition, the molar flow rate of hydrogen used as refrigerant in the Claude liquefier is 10.6% less than that of refrigerant in the Brayton liquefier. Owing to the smaller size requirements of equipment and the lower specific energy consumption, the Claude cycle is more suitable for large-scale hydrogen liquefaction processes.

Comparative analysis of energy losses in hydrogen and helium turbo-expanders for hydrogen liquefiers

Liquid hydrogen plays an essential role in the large-scale hydrogen energy development. Claude cycle is the baseline process for most industrial hydrogen liquefactions. The hydrogen turbo-expander is the crucial component, determining the system efficiency and reliability. In this paper, a hydrogen turbo-expander is designed by using a mean-line method with loss models which have been validated against experimental data of helium turbo-expanders. Geometrical and velocity field similarity can be achieved between a hydrogen turbo-expander and a helium turbo-expander by selecting the same specific speed and the characteristic ratio. CFD simulations are performed to illustrate the internal flow field and loss mechanisms in helium and hydrogen turbo-expanders. The CFD predictions of passage efficiencies agree well with that by the loss models, demonstrating the mean-line design method and loss models can be used to guide the preliminary design of hydrogen turbo-expanders. The CFD simulation results show that the passage efficiency of hydrogen turbo-expander is 1.88% higher than that of helium expander. Due to a higher sound speed and a lower viscosity, the hydrogen turbo-expander has smaller nozzle loss, incidence loss and impeller passage compared with the helium turbo-expander. The lower viscosity of hydrogen results in a higher tip leakage flow, and the tip leakage accounts for 1.09% and 1.23% of total mass flow in helium and hydrogen turbo-expanders, respectively. Since the cross flow over the blade tips can increase the vortices and secondary flow losses in impeller passages, it is necessary to reduce tip clearance in the design of hydrogen turbo-expanders.

Microporous Materials for Hydrogen Liquefiers and Storage Vessels

Microporous Composite Materials, made of metal oxide ionic fragments inserted in carbonaceous substrates, might be used as intermediates in hydrogen phase transitions, allowing progressive switch between their gas and liquid states. When crossed by an hydrogen flow these composite materials combine adsorbing, magnetic, catalytic and thermal properties efficient in hydrogen devices, liquefiers or storage vessels. Liquefaction and storage are complementary processes in practice, although inverse in principle. Plate-fin devices filled with composite materials can conjugate many thermal functions, heat exchangers, catalytic converters and pressure expanders that are necessary stages in large-scale liquefiers. Break-even storage times permit operation of the liquefaction unit at optimum ortho-para conversion thus yielding minimum practical work to be furnished. A barrage-system of successive porous plugs inserted in Hydrogen vessels would regulate the flow rate by J-T expansions, convert part of the environmental heat in rotational energy and confer stability to the system by damping the fluctuations. Consequently storage vessels of short dormancy period might be manufactured to be of low weight and low cost. After a short review of existing devices, a logical scheme interconnecting physical, economic and technologic challenges suggests that activated carbon materials of cage-like porous structures would promote and accelerate the development of storage vessels in hydrogen transport vehicles and facilitate the liquid hydrogen production by regulating the hydrogen streams in the industrial liquefiers.

Influence of drive chamber discharging process on non-linear displacer dynamics and thermodynamic processes of a fluidic-driven Gifford-McMahon cryocooler

Abstract Continuous effort is made on Gifford-McMahon cryocoolers (GMC) to amplify its refrigeration power, so they can be used to cool the cryopumps, high Tc magnets and development of efficient small-scale hydrogen liquefiers, etc. The fluidic-driven GMC is considered to be more reliable and prominent candidate than the mechanically-driven GMC due to its structural simplicity and reliability. Nonetheless, cooling mechanism of the fluidic-driven GMC is complicated, as the displacer motion inside the displacer cylinder is simultaneously controlled by the pressure difference between drive chamber and compression/expansion chamber. Different paths of displacer can be traced inside the displacer cylinder for different drive-chamber discharging process, hence, pressure–volume power of compression and expansion chambers, and refrigeration power changes. A theoretical study is conducted in present paper to visualize the influence of drive-chamber discharging process on the thermodynamic characteristics of fluidic-driven GMC for the first time. Thermodynamic cycles are drawn at the expansion chamber of the fluidic-driven GMC for different values of drive-chamber discharging process for two types of valve timing arrangements. Energy and work loss behaviors in different components of the GMC are also analysed. Adequate experimental investigations have also been carried out on a fluidic-driven displacer type GMC to verify the simulation results.

Efficiency control of the cooling-down process of a cryogenic helium turbo-expander for a 2 t/d hydrogen liquefier

Efficient liquefaction of hydrogen is a crucial part for the large-scale storage and long-distance transportation of hydrogen. Helium Brayton cycle based on high-speed turbo-expanders has been widely employed in small and medium hydrogen liquefiers. In present study, a coupled model is proposed to predict the performance and cooling-down process of helium turbo-expanders with brake blower, and validation experiments were performed on a helium turbo-expander of a 2 t/d hydrogen liquefier. Experimental results indicated that the characteristic ratio of expander varied significantly during the cooling-down process which led to a large deviation from the optimal efficiency. The impact of brake pressure on the characteristic ratio and efficiency of the helium turbo-expander is studied, and a variable pressure control method is proposed for the efficient operation of turbo-expanders during the cooling-down process of a hydrogen liquefier. Compared with the constant brake pressure control method, the variable pressure control method can increase the expander efficiency by 5%–10% during the cooling-down process in the high temperature zone.

Design, construction, and commissioning of a deployable liquid hydrogen production and fueling system for unmanned aerial systems

Liquid hydrogen has historically been limited in proximity to baseload liquefiers and research laboratories. This accessibility barrier is a primary limitation to the development of advanced aircraft and is exacerbated by recent trends in unmanned aerial systems to convert to electric propulsion systems. This article describes the design, construction, and commissioning of a self-contained, automated, and deployable liquid hydrogen production and fueling system. Housed within a mil-spec shipping container, the system utilizes a water purifier, proton exchange membrane electrolyzer, cryogenic refrigerator, and custom liquid hydrogen dewar. The system requires only water, electricity, and periodic helium purge gas input for continuous operation. Overall system performance specifications are provided. The system demonstrates the capability of field deployable hydrogen liquefiers and fueling systems.

Entropy optimization of an additively manufactured heat exchanger with a dual stage Gifford-McMahon cryogenic refrigerator for hydrogen liquefaction

Small-scale hydrogen liquefaction has emerged as an approach to fuel small aircraft powered by fuel cells. However, limited research on the design and optimization of small-scale hydrogen liquefiers, specifically the heat exchangers, is available. This paper describes a minimum entropy design for a heat exchanger mounted on a dual stage Gifford-McMahon cryogenic refrigerator. To minimize entropy generation the heat exchanger utilizes a bifurcating flow structure with varying wall thickness. Numerical optimization indicates that the heat exchanger will generate half of the entropy of a single coiled tube, significantly reducing the required heat exchanger length by 91.4% and the thermal mass by 43.8%. The heat exchanger was 3D printed with an aluminum alloy and the interior coated with a ruthenium-based catalyst for ortho-parahydrogen conversion. Hydrogen entering the heat exchanger near 293 K and 653 kPa is cooled to 28.1 K and full ortho-parahydrogen conversion is assumed before entering the storage dewar. The resulting experimental tests indicate a potential to increase heat exchanger efficiency in a more compact form factor, as well as a promising future for additively manufactured components in cryogenics.

Comparative Analysis on Energy Losses in Hydrogen and Helium Turbo-Expanders for Hydrogen Liquefiers

Comparative Analysis on Energy Losses in Hydrogen and Helium Turbo-Expanders for Hydrogen Liquefiers