Hydrogen Liquefaction Process Research Articles

Design and optimization of a high-density cryogenic supercritical hydrogen storage system based on helium expansion cycle

Cryogenic supercritical hydrogen storage technology is a high-density physical hydrogen storage method, which is a highly promising hydrogen storage approach. However, existing research has mainly focused on the development of storage devices for cryogenic supercritical hydrogen, with limited research on the cooling process of supercritical hydrogen. Therefore, a novel cooling process for cryogenic supercritical hydrogen production based on helium expansion cycle with liquid nitrogen (LN2) pre-cooling is proposed in this paper. In this process, after being compressed and cooled in multiple stages, the feed hydrogen is pre-cooled by LN2. Then, cryogenic supercritical hydrogen (10 MPa, −235.15 °C, 63.36 g/L) is obtained by helium multi-stage expansion refrigeration. The process is simulated by Aspen HYSYS and optimized by genetic algorithm (GA) to obtain lower specific energy consumption (SEC). Thermodynamic analyses are conducted to evaluate the process. And compared with the conventional hydrogen liquefaction process, the results show that the proposed process is reasonable and superior. The SEC0, figure of merit (FOM), and the total exergy loss of the system are 5.432 kWh/kgH2, 43.88%, and 289.69 kW respectively. This study indicates that the proposed process has significant implications for the hydrogen industry and provides valuable information for cryogenic supercritical hydrogen storage systems.

Techno-economic-environmental assessment and AI-enhanced optimization of a gas turbine power plant with hydrogen liquefaction

Most of the power plants in the world are based on gas turbines and many researchers tried to improve their efficiencies. This goal can be attained by the optimum utilization of heat losses. The authors of the present study aim to design, model, and optimize a gas turbine-based multigeneration power plant that uses the maximum possible of input energy to boost the products capacity and improve the efficiency. To decline the hydrogen storage and transportation costs, a hydrogen liquefaction process is applied to liquified the produced hydrogen at the same time. Besides, the power plant stack containing a substantial amount of energy is employed to operate a multi-effect desalination unit. To solve the main functions of the model, a programming code is developed. Then, the objective functions of the model are optimized using a machine learning model coupled with a genetic algorithm. Sensitivity analysis reveals that the fuel mass flow rate plays a pivotal role on total cost rate and hydrogen production rate; however, does not affect the exergy efficiency. Applying such a design for heat recovery, leads to 3.27% improvement in exergy efficiency rather than similar studies. The optimization results indicates that the LCOE is declined by 8.16% and normalized emission of CO2 is mitigated by 5.82 kg/GJ.

Tapping the energy and exergy benefits of channeling liquid air energy system in the hydrogen liquefaction process

Hydrogen's low volumetric energy density challenges its role as an energy vector, especially from bulk storage and transportation viewpoint. Similar to natural gas, hydrogen liquefaction is considered the solution and way forward. The energy-intensive process typically uses liquid nitrogen as a refrigerant in the precooling cycle; however, alternative candidates have also been studied. Liquid air, which has already drawn attention as a standalone cryogenic energy-storage system, can also be a potential candidate. The discharge half-cycle of a liquid-air energy storage system is integrated as the refrigerant stream in the precooling section of the hydrogen liquefaction process. The studied scenario is part of a larger integral scheme involving multiple processes. Aspen HYSYS® v12.1 was used for the design and performance analysis of this unique concept. A process-knowledge-inspired approach was employed to optimize the design variables and realize the maximum potential benefits of the proposed integration. As a result, the total refrigerant requirement was reduced by approximately 46 % compared with the base process. Furthermore, the flexibility brought about by using equilibrium reactors helped optimize the cycle temperatures and pressures. Consequently, 42.1 % (7.88 kWh/kgLH2) less energy was consumed in the liquefaction process. The high exergy efficiency of 84.29 % indicated excellent integration and optimization. Cryogenic heat exchangers were identified as the primary sources of exergy destruction, and the coefficient of performance of the integrated process was 0.155. The concept presented and the approach adopted in this study are expected to have far-reaching outcomes and benefit the hydrogen energy network and hydrogen economy perspectives.

Exergy destruction improvement of hydrogen liquefaction process considering variations in cooling water temperature

Exergy destruction improvement of hydrogen liquefaction process considering variations in cooling water temperature

Integrated hydrogen liquefaction process with a dual-pressure organic Rankine cycle-assisted LNG regasification system: Design, comparison, and analysis

Improving the efficiency and reducing the cost of hydrogen liquefaction systems have become a subject of importance nowadays. Through the comparison and analysis of existing processes, a hydrogen liquefaction system that can enhance the utilization efficiency of liquefied natural gas (LNG) cold energy is developed. The system includes a dual-pressure organic Rankine cycle (DORC)-assisted LNG regasification process and improved cascade Joule-Brayton refrigeration cycles. To assess the performance of the proposed process, two forms of ORC and three Brayton refrigeration cycles are compared, respectively. The genetic algorithm is applied to optimize the proposed process. The coefficient of performance, exergy efficiency, and specific energy consumption of the proposed process is 0.20, 46.9%, and 6.61 kWh/kgLH2, respectively. Owing to the efficient utilization of LNG cold energy, the power output of the DORC is 16.2% higher than that of a regular ORC. Furthermore, the improved cryo-cooling process exhibits a significant performance enhancement. Compared to two existing processes, the UA value of the heat exchangers in the proposed cryo-cooling process is reduced by 47.6% and 8.3%, respectively, and the required mass flow rate of helium is reduced by 45.3% and 8.6%, respectively. Moreover, the exergy analysis performed on the system indicates that the exergy utilization rate of the hydrogen pre-cooling process is 80.2%, while that of the cryo-cooling process is only 48.7%.

Investigation and development of a novel solar-biomass integrated energy system for clean electricity and liquid hydrogen production

In the present work, an innovative power generation system based on solar and biomass energy resources is proposed. Energy and exergy methods are applied to analyze and model the system. Also, to evaluate the system's performance during the year, the values of solar radiation and ambient temperature as a transient are studied for a case study in Khuzestan province. The system consists of a biomass unit, a solar unit, a waste heat recovery unit, and a hydrogen liquefaction unit. The power is generated by two gas turbines and two Rankine cycles. Furthermore, the system produces liquid hydrogen with a Linde-Hampson hydrogen liquefaction process and a proton exchange membrane electrolyzer, and hot water with a water heater. A gasifier is utilized to convert biomass to syngas, and a heliostat field is employed to harness solar energy. For solar energy storage, molten salt is used. The system’s power output is 7967 kW, while the exergy efficiency is 11.06%. Also, the production rates of liquid hydrogen and hot water are found to be 10.74 kg/h and 7 kg/s, respectively. To gain a deeper understanding of the impact of using solar energy, a comparison of biomass, solar-biomass, and solar-biomass with waste-heat recovery is made. The results show that solar energy with waste-heat recovery reduces CO2 emissions by 30.5% while increasing the system's electrical power output by 44% as compared to scenario 1 in which only biomass fuel was used. In addition, the highest component cost rate is attributed to the solar power system, accounting for 51% of the capital investment cost.

Optimization and Analysis of an Integrated Liquefaction Process for Hydrogen and Natural Gas Utilizing Mixed Refrigerant Pre-Cooling

Liquefying hydrogen is an efficient way to store and transport hydrogen. However, the hydrogen liquefaction process is energy intensive. Therefore, an integrated liquefaction process of hydrogen and natural gas utilizing the mixed refrigerant cycle and the hydrogen Claude cycle is proposed. The process not only couples a steam methane reforming process to produce hydrogen and a carbon dioxide refrigeration cycle to assist in pre-cooling, but also employs a solar energy absorption refrigeration system to enhance energy efficiency. The proposed process is simulated and optimized using HYSYS and the particle swarm optimization algorithm, and energy, exergy, and economic analyses are performed. The energy analysis shows that the specific energy consumption of the proposed process is 5.2201 kWh/kg, a reduction of 10.67% compared to the base case. The exergy loss and exergy efficiency are 64,904 kW and 62.21%, which are 13.63% and 6.63% lower than the base case, respectively. The economic analysis shows that the total annualized cost of the process is USD 28.6 million per year. The proposed integrated liquefaction process not only realizes the high efficiency of energy utilization but also follows the development trend of integrated energy systems.

Optimization and analysis of a cascaded dual mixed refrigerant hydrogen liquefaction process considering the influence of pre-cooling stages

To reduce the energy consumption of the hydrogen liquefaction process, a hydrogen liquefaction process based on cascaded mixed refrigerant cycles is proposed in this paper. The two mixed refrigerant cycles are connected in series so that the cooling capacity of refrigerants can be fully utilized. Cascaded processes with different numbers of pre-cooling stages are compared. The processes are optimized using the particle swarm algorithm. And cascaded and non-cascaded processes are compared under the same conditions. The results show that the more the number of pre-cooling stages, the lower the SEC and the higher the exergy efficiency. And the cascaded process has higher energy efficiency than the non-cascaded process. The specific power consumption of the process is 5.664 kWh/kgLH2, the coefficient of performance is 0.2322, and the exergy efficiency is 52.77%. This research can provide valuable ideas and methods for the improvement of hydrogen liquefaction process design.

Thermodynamic analysis of a dual reverse Brayton cycle (dual-RBC) hydrogen liquefaction process precooled by mixed-refrigerant

In order to reduce hydrogen liquefaction power consumption, a dual reverse Brayton cycle (dual-RBC) process is proposed and analyzed in this paper, which consists of a mixed-refrigerant J-T cycle for precooling, a hydrogen RBC for hydrogen liquefaction, and a helium RBC for liquid hydrogen subcooling. Compared with typical dual-Claude processes, the two-phase low-pressure cycling hydrogen for liquid hydrogen product subcooling is replaced by an independent helium RBC, reducing the temperature difference and exergy loss in subcooling heat exchangers. Consequently, the specific power consumption (SPC) of dual-RBC process is 4.16% lower than dual-Claude process under the same conditions. The mixed-refrigerant J-T cycle (driven by single-stage oil-lubricated compressor, no liquid/two-phase expanders) could reduce precooling power consumption by >45% comparing with liquid nitrogen. The dual-RBC process could reach a SPC of 7.08 kWh kg−1 under typical conditions. While it is more realizable with mature technologies than novel processes.

Comparative study on thermodynamic performance of hydrogen liquefaction processes with various ortho-para hydrogen conversion methods

Catalytic conversion of ortho-para hydrogen is essential for hydrogen liquefaction. Among the three ortho-para hydrogen conversion methods, i.e., isothermal, adiabatic and continuous conversion, it has already been accepted that the continuous conversion is the most energy-efficient. However, studies on quantitative analyses and the underling mechanisms are still lacking. In this paper, the three conversion methods are evaluated based on a reference 5 t/d-scale hydrogen liquefaction process with a self-developed numerical model. Optimizations are conducted to identify the lowest specific energy consumption (SEC) of the hydrogen liquefaction process with different conversion methods. The three conversion methods are compared in terms of the temperature distribution along the process, the conversion-heat-associated exergy and SEC. The optimization results show that the continuous-conversion based process reaches the lowest SEC, i.e., 11.38 kWh/kgLH2, which is 21.8% and 28.7% lower than the adiabatic and isothermal ones. Exergy analyses indicate that the exergy consumption associated with dissipating the conversion heat is the lowest for the continuous conversion (139.54 kW), followed by the adiabatic conversion and then the isothermal conversion, i.e., 174.94 kW and 273.90 kW, respectively. This work demonstrates the differences quantitively and reveals its mechanism thermodynamically, which would be helpful for understanding, and designing hydrogen liquefaction processes.

A novel integrated system of hydrogen liquefaction process and liquid air energy storage (LAES): Energy, exergy, and economic analysis

With the global positive response to environmental issues, cleaner energy will attract widespread attention. To improve the flexible consumption capacity of renewable energy and consider the urgent need to optimize the energy consumption and cost of the hydrogen liquefaction process, a novel system integrating the hydrogen liquefaction process and liquid air energy storage (HLP–LAES) is proposed. The operating strategy of the system ensures that it can produce liquid hydrogen and has the function of energy storage and power generation. A 3E study (energy, exergy, and economics) is carried out to evaluate the techno-economic performance of the proposed energy-intensive process. After optimization of key parameters, when the daily output of liquid hydrogen is 50 tons, the maximum daily power generation can reach 131.3 MWh, accounting for 1.21% of the daily electricity consumption of urban and rural residents in Qinghai Province, China. The round-trip efficiency of the proposed process is 58.9%, the specific energy consumption of liquid hydrogen is 7.25 kWh/kgLH2, and the total exergy efficiency is 53.2%. The payback period will be reduced to 1.7 years when the liquid hydrogen is sold at 7.0 $/kgLH2. If the proposed process is retrofitted from a stand-alone hydrogen liquefaction plant, the shortest retrofitting payback period is 9.2 years. The charging and discharging processes of the LAES are innovatively redesigned to better match the hydrogen liquefaction process, while achieving deep coupling and good synergy between the systems. This work aims to provide a reference for the efficient consumption of renewable energy, grid load balancing, and commercialization of the combination of liquid air energy storage and hydrogen liquefaction plants.

A novel integrated hydrogen and natural gas liquefaction process utilizing a modified double mixed refrigerant process pre-cooling system

The hydrogen liquefaction process is energy-intensive due to the lower liquefaction temperature. To improve the energy efficiency of the hydrogen liquefaction process, a novel integrated liquefaction process employing a modified double mixed refrigerant process pre-cooling is proposed and analyzed. The three-stage adiabatic ortho–para hydrogen conversion makes the process compact. Furthermore, the particle swarm optimization algorithm is utilized to find the optimal decision variables. The result reveals that the total specific energy consumption (SEC) of the process is 6.5921 kWh/kgLH2-LNG, which is 15.83% lower than the base case. The SECs for the production of LNG and LH2 are 0.2445 kWh/kgLNG and 6.3476 kWh/kgLH2. Moreover, the exergy analysis and thermodynamic evaluation reveal that the exergy efficiency, coefficient of performance, and figure of merit of the process are 49.26%, 0.2306, and 0.49, exhibiting high thermodynamic performance. Finally, the sensitivity analysis indicates that the evaporation pressure of the sub-cooling refrigerant has the greatest impact on the performance of the process. The proposed process has an important reference value in the design of the combined production of LH2 and LNG from industrial by-products and the H2 liquefaction process.

Optimization and analysis of a hydrogen liquefaction process integrated with the liquefied natural gas gasification and organic Rankine cycle

Combination of the hydrogen pre-cooling and liquefied natural gas gasification processes is forward-looking in the hydrogen liquefaction industry. To enhance the cold energy utilization, a hydrogen liquefaction process integrated in conjunction with a liquefied natural gas gasification process assisted by an organic Rankine cycle is designed. Furthermore, a simplified refrigeration system incorporating a dual-pressure Joule-Brayton cycle is developed to provide efficient cryo-cooling for the hydrogen. A binary mixture consisting of ethylene and propane is preferred as the working fluid for the organic Rankine cycle when liquefied natural gas gasification pressure is 30 bar, which results in 2.2% and 15.5% improvement in the liquefied natural gas cold energy utilization compared to the organic Rankine cycle with the pure refrigeration as the working fluid and the hydrogen pre-cooling process without the organic Rankine cycle, respectively. In the proposed cryo-cooling process using two Joule-Brayton cascade cycles, the utilization rate of the input exergy reaches 48.84%. The exergy loss generated in the compressors and coolers accounts for approximately 66.2% of the total exergy loss. Therefore, they are regarded as the priority targets for improving the hydrogen liquefaction system. After the optimization of the proposed process using the genetic algorithm, optimal results are obtained with a specific energy consumption of 6.59 kWh/kgH2 and an exergy efficiency of 47.0%.

Process knowledge inspired opportunistic approach for thermodynamically feasible and efficient design of hydrogen liquefaction process

Hydrogen (H2) liquefaction process is one of the complex processes because of the highly non-linear interaction between design variables and objective function. Finding a feasible design for such a complex process is challenging. Knowledge of refrigerant selection, composition, cycle temperatures, and compression ratio is essential in finding this feasible design. This study presents a simple, yet efficient approach inspired by process knowledge, known as knowledge-based optimization (KBO), to selecting an optimal mixed refrigerant (MR) composition and studying the effect of each refrigerant on the performance of the H2 liquefaction process. The infeasible design shows approach temperature (i.e., MITA) values as −33.5 °C, −4.0 °C, and −11.65 °C. The design variables' values are adjusted based on the KBO approach to keep the MITA value in the range of 1–2 °C. The share of each MR component in optimal case is 17% C1, 5% C2, 70% C3, 8% N2 in precooling, 9% C1, 80% N2, 11% H2 in cooling and 85% H2, 15% He in liquefaction cycle. Further, the KBO approach guides in selecting the lower and upper limit of each refrigerant based on their impact inside heat exchangers. Additionally, the heat flow behavior of H2 streams is analyzed for adiabatic and isothermal ortho-to-para reactors. This study will help process engineers and engineering practitioners to develop an energy-efficient and cost-effective initial design for the H2 liquefaction process.

Multi-objective optimization of an innovative integrated system for production and storage of hydrogen with net-zero carbon emissions

Global energy consumption has been exponentially increasing, leading to the depletion of conventional energy sources and a considerable increase in greenhouse gas emissions. The exploitation of sustainable energy sources and the development of innovative methods for mitigation of CO2 emissions is necessary. Hydrogen (H2) as a versatile and green fuel can be produced and stored in liquid form using sustainable energy sources through innovative methods. In this paper, a novel optimal hybrid structure is proposed for hydrogen production and storage with net-zero CO2 emissions. A high-temperature fuel cell is utilized to reduce CO2 emissions and supply the heat and power needed to produce and liquefy hydrogen. The hybrid configuration employs an electro-thermochemical unit for hydrogen production, molten carbonate fuel cells, a hydrogen liquefaction process, and a biogas upgrading by water scrubbing. A robust combination of meta-heuristic algorithms and artificial intelligence is developed to optimize the investment return period and energy/exergy efficiencies. The fuzzy Bellman-Zadeh, LINMAP, and TOPSIS techniques are also used to make decisions in multi-objective optimization. This innovative configuration generates 108 kmol/h liquid hydrogen, 18.88 MW power, 54 kmol/h oxygen, and 3258 kmol/h hot water. Pinch, sensitivity, exergy, and economic assessments are implemented to evaluate the performance of the hybrid structure. The thermal and exergy efficiencies of the proposed configuration are obtained to be 78.21 % and 64.83 %, respectively. The greatest portions of destructed exergy are resulted from the fuel cells-gas turbine hybrid system (63.63 %), electro-thermochemical unit (25.96 %), and biogas upgrading technology (6.23 %). The returns period on investment, the prime price of electricity, and the net benefit are computed as 4.854 years, 0.0420 US$/kWh, and 15.73 million US$/years, respectively, based on the energy potentials of Newfoundland and Labrador, Canada.

An efficient hydrogen liquefaction process integrated with a solar power tower and absorption precooling system

An efficient hydrogen liquefaction process integrated with a solar power tower and absorption precooling system

Significance of ortho-para hydrogen conversion in the performance of hydrogen liquefaction process

Hydrogen is an energy vector and is produced just like electricity. In order to overcome the shortcomings associated with its low molecular weight and energy density per unit volume, hydrogen is liquefied for storage and transportation purposes. The liquefaction of hydrogen differs from that of other substances as it involves the reactive transformation of its isomeric states. At 25 °C, molecular hydrogen consists of 75% orthohydrogen and 25% of parahydrogen. As the normal boiling point, hydrogen essentially exists in the para-state, which is preferred because of its lower boil-off gas rate. However, the conversion of ortho-to-para hydrogen is an exothermic reaction, and this enthalpy of conversion enhances the total reversible work by about 15%. Little work has been done regarding ortho-to-para hydrogen conversion from the process systems point of view. Therefore, parametric analysis of this vital conversion reaction was studied with potential impact on the performance of cryogenic heat exchangers, reactors configuration and mode of operation, and probable impact on the energy efficiency of the liquefaction process. An alternate approach to simulate the reaction is also proposed. The results show that the current approaches to process design need to be changed. The study opens avenues for more in-depth analysis and optimization approaches to present a holistic framework for future integrated energy systems.

Optimization and analysis of a hydrogen liquefaction process: Energy, exergy, economic, and uncertainty quantification analysis

To reduce the specific energy consumption (SEC) of the hydrogen liquefaction process, a conceptual design of a hydrogen liquefaction process that integrates a modified natural gas single mixed refrigerant process and a hydrogen expansion cycle. The energy efficiency of the process is improved by operating each refrigeration cycle at different pressures. The process is optimized using a particle swarm optimization algorithm. Furthermore, the uncertainty levels of the SEC and the minimum internal temperature approach of the heat exchanger with varying parameters are investigated by applying uncertainty quantification (UQ). The results indicate SEC is 5.963 kWh/kg with 52.61% exergy efficiency. The thermodynamic evaluation shows that the coefficient of performance and figure of merit are 0.2218 and 0.526. The UQ analysis reveals that the SEC is strongly influenced by changing the flow rate and pressure of the sub-cooling refrigerant, with a distribution of SEC between 5.479 and 6.451 kWh/kg. Finally, the economic evaluation yields a total annualized cost of $25.42 million/y. This study is expected to provide an insight into designing an energy-efficient hydrogen liquefaction process by introducing a natural gas mixed refrigerant process.

A molecular dynamics study on the mechanism of heterogeneous bubble nucleation of mixed liquid

The nucleate boiling of mixed boiling is widely utilized in natural gas, hydrogen liquefaction process, and other fields. In this paper, the molecular dynamics study of heterogeneous bubble nucleation of pure argon liquid and the argon‑krypton mixed liquid on the platinum surface was conducted. The nucleate boiling characteristics were presented and the variations of the density, temperature, nucleation embryo volume, and heat flux were analyzed. The difference in the nucleation mechanism of pure liquid and mixed liquid was explained based on the competition of atomic potential energy and atomic kinetic energy. The effect of the component mole fraction on the bubble nucleation of mixed fluid was also discussed. The results showed that the onset superheat of boiling of argon‑krypton mixed liquid is higher than that of pure argon. The higher the mole fraction of the component with a lower saturation temperature, the lower the onset superheat of the liquid nucleate boiling. When x < 0.5, the growth rate of the nucleation embryo is dominated by the x value, when x > 0.5, the growth rate is dominated by wall temperature. Moreover, the difference in diffusion coefficients of each component is one of the direct causes of determining the growth rate of nucleation embryos. The findings provide insights into the mechanisms of differences in boiling nucleation between mixed liquid and pure liquid, as well as guide the reasonable utilization of mixed liquid.

Mixed refrigerant–based simplified hydrogen liquefaction process: Energy, exergy, economic, and environmental analysis

In current study, process of hydrogen liquefaction was proposed to overcome the transportation and storage issues associated with hydrogen. The proposed model is consisted of three refrigeration cycles which are coupled to liquefy hydrogen. Unique selection of mixed refrigerants was adopted in each refrigeration cycle to reduce the energy consumption of the process. The precooling cycle based on mixed refrigerant stream reduces the H2 temperature from 25 to −160 °C. Whereas, cooling and liquefaction cycles reduce the hydrogen temperature up to −251 °C which then is further expanded in an expander to approach the liquefaction temperature (−252.1 °C) at 1.3 bar. As of authors' knowledge, this is the first study which demonstrates the 4 E's analysis (Energy, exergy, economic, and environmental) of hydrogen liquefaction process. Result of proposed study reveals that the specific energy consumption of proposed process was calculated as 9.477 kWh kg−1 LH2 which is less than any commercial scale process. As a result, the exergy efficiency of the proposed process was increased by 34%. In addition, the estimated unit production cost was recorded as 5.54 $ kg−1 of LH2 at the capacity of 1TPD. Cost estimation of proposed model was evaluated at higher capacities 1 to 50 TPD with cost reduction of up to 3.2 $ kg−1 LH2. Life cycle assessment of proposed process revealed that the 67.85 kg of CO2eq emissions were observed against unit production of liquefied hydrogen for new plant at day 1 while 0.253 kg of CO2eq emissions at day 2. The simplicity and less energy consumption of proposed model built a basis for its development to commercial scale adoption.