Hydrogen Liquefaction Processes Research Articles

Energy optimization of hydrogen liquefaction process via process knowledge combined with multivariate Coggin's algorithm

Sustainable and cost-effective transportation of hydrogen is one of the major challenges to futuristic hydrogen value chain. Hydrogen, in its produced form, exhibits low energy density and large volume, rendering it highly unsuitable for transportation, particularly over extended distances. Liquefaction is one of the promising approaches to improve hydrogen's energy density and to make it more compact. However, liquefaction is an energy intensive process, raising the cost of transportation. In this study, the specific energy consumption of the hydrogen liquefaction process is aimed to reduce through knowledge-based optimization followed by optimization using the multivariate Coggin's algorithm to improve energy and economic profiles of the process. Design variables, composite curve, exergy, and economic analyses are performed to evaluate and compare the thermodynamic, economic, and environmental feasibility of the optimized process. The results depict a significant reduction (14.3%) in specific energy consumption to 9.40 kW/kgLH2 without increasing process complexity. Further key improvements include a massive drop in refrigerant flowrates (9.2%), annualized cost (m$ 0.15), and annual CO2 emissions (1008.45 tCO2/annum). The largest exergy destruction is observed in CHX-201, reflecting further room for improvement. These results underscore the potential for optimizing hydrogen liquefaction processes to enhance energy efficiency, process economics and environmental impact, providing valuable insights for researchers and industry professionals seeking to advance hydrogen liquefaction technologies. However, challenges remain in the comprehensive evaluation of chemical exergy for ortho- and para-hydrogen and in conducting advanced exergy analyses to further optimize hydrogen liquefaction processes without adding complexity.

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.

Artificial intelligence-based surrogate modeling for computational cost-effective optimization of hydrogen liquefaction process

The chemical processes are inherently complex, and obtaining desired product quality and high energy efficiency by optimizing the design variables is challenging. The progress in computing technologies can be a blessing since machine learning models can process the information and data for learning purposes and eventually help ease the simulation and optimization efforts. Against this backdrop, an artificial neural network-based surrogate model is developed in the present study and applied to the challenging process of hydrogen liquefaction. Optimization of hydrogen liquefaction processes is still an open challenge because of convergence issues and many design variables; only a handful of algorithms are considered successful. One of those algorithms, particle swarm optimization (PSO), is used here to compare computational effort and results accuracy. The percentage error of prediction of the ANN-based surrogate model compared to PSO was 4% for the minimum internal approach temperature, which is usually considered as a constraint, and 0.04% for specific energy consumption considered as the objective function. The optimization of the proposed model significantly reduced the time needed for PSO optimization of the existing model by more than 99.99%. As an extension of the current work, the ‘shallow' neural network model, with one hidden layer used in the present study, can be used to analyze the whole liquefaction process.

Design and optimization of high-density cryogenic supercritical hydrogen storage systems integrating with dual mixed refrigerant cycles

To address the low density of high-pressure gaseous hydrogen and evaporation issues associated with liquid hydrogen storage, cryogenic supercritical hydrogen storage method is presented in this paper. Based on a dual parallel mixed refrigerant cycle (DPMR) and a dual cascade mixed refrigerant cycle (DCMR), the density of supercritical hydrogen product is 70.74 kg/m3, closely approaching liquid hydrogen. The processes are simulated in Aspen HYSYS, optimized by genetic algorithm for lower specific energy consumption (SEC). Thermodynamic analysis is conducted to compare with hydrogen liquefaction processes, demonstrating the feasibility and superiority of proposed process. The results show that the DPMR process has an SEC of 6.422 kWh/kgH2 and exergy efficiency of 52.66%, while DCMR is 6.872 kWh/kgH2 and 49.24%. Additionally, the inclusion of ortho-para convertors in DPMR process is investigated to further analyze the impact of heat release for ortho-para conversion. Furthermore, a techno-economic analysis is conducted on three processes, validating the economic feasibility. The study indicates that cryogenic supercritical hydrogen storage system is of great significance to the development of high-density hydrogen storage technology. The DPMR and DCMR presented in this paper can significantly improve the energy efficiency and provide valuable information for the design of high-density hydrogen storage system.

Exergy and energy analysis of a hybrid natural Gas/Hydrogen liquefaction cycle combined with methanol production plant

This paper presents an innovative renewable multi-generation system designed to simultaneously produce various fuels, including biomass-based methanol, liquid hydrogen, and liquid natural gas. This system is part of a broader strategy aimed at streamlining different processes within a comprehensive plant, enabling the simultaneous production of multiple biomass-based fuels at a single location. The implementation of this system in regions where natural gas liquefaction plants coexist with abundant forest resources allows for the efficient production of all required fuels. In this process, a new configuration leverages to regenerate the waste heat of methanol synthesis process in the diffusion absorption refrigeration cycle integrated to the natural gas liquefaction process to maximize energy and exergy efficiencies. Additionally, three hydrogen liquefaction processes are evaluated to identify the most suitable option based on performance, efficiency, and power consumption. The investigations reveal that the combined mixed refrigerant cycle (CMRC) emerges as the ideal choice for hydrogen liquefaction process, characterized by lower power consumption and a higher coefficient of performance. The energy and exergy efficiencies of biomass gasification and methanol synthesis processes are 87.54% and 80.41%. The energetic coefficient of performance of the natural gas liquefaction process and CMRC is 0.9 and 0.2209. The specific power consumption of natural gas liquefaction process is 0.225 kWh/kgLNG, and the specific power consumption of CMRC is 5.462 kWh/kgLH2. The natural gas liquefaction process is responsible for the highest portion of the total exergy destruction, with 32%.

An energy-saving hydrogen liquefaction process with efficient utilization of liquefied natural gas cold energy

Storage and transportation of hydrogen in liquid form offers considerable advantages, but the high energy consumption of hydrogen liquefaction processes needs to be addressed. In this study, a novel hydrogen liquefaction process integrated with a dual-pressure organic Rankine cycle (DORC) is proposed. It offers significant energy-saving by efficiently utilizing the cold energy of liquefied natural gas (LNG). The key parameters in the proposed process are investigated, and the results are combined with an improved genetic algorithm for efficient optimization of the process. The optimal exergy efficiency of the proposed process is 48.7%, and the minimal energy consumption is 6.29 kWh/kgLH2. Thanks to the power output (381.3 kW) of the DORC and the energy saved by the cryogenic compression of nitrogen (586.6 kW), energy consumption of the proposed process is reduced by approximately 3.1% compared to that of the process without a DORC. Moreover, an improved helium Brayton refrigeration cycle for hydrogen cryo-cooling is simpler, but less the refrigerant usage and energy consumption compared to the previously proposed cycles. The proposed process demonstrates excellent performance in terms of energy saving and efficiency improvement, providing a low-cost scheme to produce liquid hydrogen.

Conceptual design of two novel hydrogen liquefaction processes using a multistage active magnetic refrigeration system

Hydrogen is a promising clean energy carrier. However, its transportation in liquid form faces many challenges because the conventional liquefaction processes for hydrogen are highly inefficient and expensive. Moreover, due to the rising environmental concerns and low energy efficiency of compressor refrigeration technologies, active magnetic regenerator refrigeration technique (AMR) can be used as an alternative. This study presents a novel conceptual design for two hydrogen liquefaction (LH2) processes where the precooling section consists of AMR instead of the traditional compressors technology. The aim is to reduce the specific energy consumption and increase the exergy efficiency of the process while utilizing an AMR pre-cooling section for better environmental safety. Although, the process is considered small scale for LH2 production, it is infact the highest reported capacity for AMR processes. Hence, a comprehensive economic analysis is performed to analyze the costs involved within the processes. The results indicate that the proposed AMR processes provide ∼5.9–15.4% energy savings (SEC 4.15 kWh/kg for process 1 and 8.73 kWh/kg for process 2) as compared to the mixed refrigerants (MR) pre-cooling based processes (SEC 4.41 kWh/kgLH2 for conventional process 1 and 10.32 kWh/kgLH2 for conventional process 2). The Coefficient of performance (COP) of the proposed processes has values of 0.191 and 0.143, which are ∼6.3% and 18.2% more than the conventional processes 1 and 2. Compared to conventional MR processes 1 and 2, the exergy efficiency of process 1 increases by 10.55%, while that of process 2 increases by 18.2%. The economic analysis shows that LH2 can be produced with a competent levelized cost of product (LCOP) ranging between 1.31 and 1.75 US$/kg LH2.

Novel dual-mixed refrigerant precooling process for high capacity hydrogen liquefaction plants with superior performance

Liquid hydrogen is a superior alternative for the current energy storage methods and energy carriers as it has higher energy density and cleanliness. However, hydrogen liquefaction is an energy-intensive process. In particular, the precooling process of hydrogen consumes a tremendous portion of about 30 % of the total compression power of the plant. Several previous studies introduced various pure-refrigerant and single mixed refrigerant (SMR) precooling processes, however, their specific energy consumption (SEC) still very high especially at large-scale capacities. Therefore, this study presents a novel, efficient, and large-scale dual-mixed refrigerant (DMR) process to precool the hydrogen from 25 °C to -192 °C at a pressure of 21 bar. New heavyweight-based mixed refrigerant MR1 and lightweight-based mixed refrigerant MR2 are developed for the DMR process using a new-proposed systematic approach. The proposed DMR process is capable of handling a wide range of hydrogen flow from 100 TPD to 1000 TPD with SEC of 0.862 kWh/kgH2Feed, which is 20.33 % lower than the most competitive SMR process available in the literature. Based on the sensitivity analysis, further optimization of the DMR operating parameters reduced the SEC to 0.833 kWh/kgH2Feed at an optimal capacity of 500 TPD. Furthermore, the COP of the new process is improved by 14.47 % and the total annualized cost is reduced by 12.24 %. Compared to five other technologies that use the pure-refrigerant and other SMR precooling processes, the DMR reduces the SEC by 39.0 % to 63.0 %. The novel precooling process presented herein has the potential to drive the development of large-scale hydrogen liquefaction processes.

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 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.

Thermodynamic analysis of low-temperature and high-pressure (cryo-compressed) hydrogen storage processes cooled by mixed-refrigerants

Cryo-compressed hydrogen (CcH2) is a promising hydrogen storage method with merits of high density with low power consumption. Thermodynamic analysis and comparison of several CcH2 processes are conducted in this paper, under hydrogen storage conditions of 10–100 MPa at 60–100 K. Mixed-refrigerant J-T (MRJT), nitrogen/neon reverse Brayton (RBC) and hydrogen expansion are employed for cooling hydrogen, respectively. Combined CcH2 processes such as MRJT + neon-RBC are proposed to reach higher CcH2 density at lower temperatures (<80 K). It was indicated that the specific power consumptions (SPC) of MRJT processes are obviously lower than those of nitrogen/neon-RBC or hydrogen expansion processes. For a typical storage condition of 50 MPa at 80 K, MRJT CcH2 process could achieve hydrogen density of 71.59 kg m−3, above liquid hydrogen. While its SPC of 6.42 kWh kg−1 is about 40% lower than current dual-pressure Claude hydrogen liquefaction processes (10.85 kWh kg−1).

Simulation methodology for hydrogen liquefaction process design considering hydrogen characteristics

One promising method to improve the storage capacity of hydrogen is to liquefy it, resulting in high energy density. However, liquefying hydrogen is a challenging task because hydrogen characteristics, such as a boiling point at a cryogenic temperature and changes in equilibrium compositions of spin isomers constituting hydrogen molecules, must be considered. For a design of a hydrogen liquefaction process, it is necessary to use an equation of state that can accurately calculate the properties of hydrogen, and to consider conversion reactions of the spin isomers. In this study, it is confirmed that the modified Benedict-Webb-Rubin equation is a suitable equation of state for simulating hydrogen liquefaction processes and that an equivalent model used in this study for the conversion reactions of the spin isomers shows reasonable results. Furthermore, the economic feasibility of the designed hydrogen liquefaction process is investigated based on energy optimization and economic analysis.

Efficient Heat Exchange Configuration for Sub-Cooling Cycle of Hydrogen Liquefaction Process

The hydrogen liquefaction process is highly energy-intensive owing to its cryogenic characteristics, and a large proportion of the total energy is consumed in the subcooling cycle. This study aimed to develop an efficient configuration for the subcooling cycle in the hydrogen liquefaction process. The He-Ne Brayton cycle is one of the most energy-efficient cycles of the various proposed hydrogen liquefaction processes, and it was selected as the base case configuration. To improve its efficiency and economic potential, two different process configurations were proposed: (configuration 1) a dual-pressure cycle that simplified the process configuration, and (configuration 2) a split triple-pressure cycle that decreased the flow rate of the medium- and high-pressure compressors. The ortho–para conversion heat of hydrogen is considered by using heat capacity data of equilibrium hydrogen. Genetic algorithm-based optimization was also conducted to minimize the energy consumption of each configuration, and the optimization results showed that the performance of configuration 1 was worse than that of the base case configuration. In this respect, although less equipment was used, the compression load on each compressor was very intensive, which increased the energy requirements and costs. Configuration 2 provided the best results with a specific energy consumption of 5.69 kWh/kg (3.2% lower than the base case configuration). The total expense of configuration 2 shows the lowest value which is USD 720 million. The process performance improvements were analyzed based on the association between the refrigerant composition and the heat exchange efficiency. The analysis demonstrated that energy efficiency and costs were both improved by dividing the pressure levels and splitting the refrigerant flow rate in configuration 2.

Comparative design, thermodynamic and techno‐economic analysis of utilizing liquefied natural gas cold energy for hydrogen liquefaction processes

This study mainly focuses on determining the optimal configuration that efficiently utilizes liquefied natural gas (LNG) cold energy in hydrogen precooling for liquid hydrogen production. To achieve this goal, two different configurations are designed: (a) adding LNG cold energy to the existing hydrogen precooling cycle and (b) replacing the existing hydrogen precooling cycle with LNG cold energy. An equilibrium hydrogen model is developed to reflect the thermodynamic property of ortho-para conversion of hydrogen. Bayesian optimization is performed to determine the optimal operating conditions which minimize the specific energy consumption for all configurations. The specific energy consumption of the configuration involving hydrogen precooling with only LNG is 5.613 kWh/kg-LH2, and it is reduced by 8.13% and 3.19% from the base case design and the configuration involving hydrogen precooling with both LNG and a mixed refrigerant cycle, respectively. In addition, a techno-economic analysis is conducted. Compare to the base case design, the capital cost and operating cost of the design replacing hydrogen precooling with LNG are reduced by 31.76% and 11.55%, respectively. This study shows that the proposed design of replacing the hydrogen precooling cycle with an LNG stream can save energy consumption, moreover, it is highly effective for capital investment saving due to its simple configuration.

Optimization of a hydrogen liquefaction process utilizing mixed refrigeration considering stages of ortho-para hydrogen conversion

The ortho-to-para hydrogen conversion (OPC) is an integral part of the hydrogen liquefaction process. The optimal stages and conversion temperatures of OPC are important to reduce the specific energy consumption (SEC) of the process. However, a limited number of studies directly discuss this aspect of the effect of the OPC stages on the SEC. Therefore, based on an efficient refrigeration liquefaction cycle, this paper analyzes the effect of different OPC stages on the SEC of the efficient refrigeration cycle. Additionally, the impact of different combinations of conversion temperatures for the same OPC stages on the SEC is investigated. Results are obtained using a process model developed in HYSYS V10 and the particle swarm optimization algorithm in MATLAB. The results show the impact of OPC stages on the SEC, and that the increase in the stages of OPC can reduce the SEC, but the reduction tends to be slow. The SEC of the five-stage OPC process decreases by 16.39% compared to the SEC of the one-stage. Furthermore, the reduction of SEC for the process with the same stages of OPC can be achieved by setting the optimal combinations of conversion temperatures, which can reduce the SEC by up to 10.63%. The results of this study demonstrate that optimizing the OPC stages is important to reduce the SEC and will provide valuable information for the design of OPC for hydrogen liquefaction processes.

Performance enhancement of hydrogen liquefaction process via absorption refrigeration and organic Rankine cycle-assisted liquid air energy system

This study focuses on the design and analysis of a liquid hydrogen production process integrated with an absorption refrigeration system, a liquid air energy storage system, and an organic Rankine cycle for designing an energy-efficient integrated process. The absorption refrigeration system and liquid air energy storage system facilitate hydrogen pre-cooling, whereas the organic Rankine cycle helps to recover the waste heat generated after air combustion. An ammonia/water-based absorption refrigeration system accompanied by liquid air precools the hydrogen to −180 °C, and the vapor compression refrigeration system liquifies the hydrogen. In this study, an energy-efficient process integration scheme was designed to reduce the overall energy consumption and recover waste heat. The net specific energy consumption of the process was 6.71 kWh/kg. The design variables and composite curve analyses indicate that the most energy-intensive part of the process is the liquefaction section. Moreover, exergy analysis indicates that multi-stream heat exchangers primarily contribute towards exergy destruction. The exergy efficiency of the process was 35.7%. Environmental analysis shows that the refrigeration cycles mainly contribute towards carbon dioxide emissions. Furthermore, according to the economic analysis, compressors and multi-stream heat exchangers accounted for 88.5% of the total capital investment. Overall, these analyses report energy efficient integration and indicate the potential for further improvements, particularly in the refrigeration cycle. This study is expected to provide insights into the design of energy-efficient integrated hydrogen liquefaction processes that exploit the benefits of the absorption refrigeration system, liquid air energy storage system, and organic Rankine cycle.

Carbon-dioxide-precooled hydrogen liquefaction process: An innovative approach for performance enhancement–Energy, exergy, and economic perspectives

Hydrogen is an important clean energy carrier that can facilitate and promote clean energy production and mitigate greenhouse gas emissions. However, long-term storage and long-distance transportation of hydrogen are challenging owing to its low energy density, which can be effectively enhanced via liquefaction, an energy- and cost-intensive process. Commercial hydrogen liquefaction processes exhibit specific energy consumptions in the range of 12.0–15.5 kWh/kg with an exergy efficiency of 19.0%–23.6%. This study presents an energy-efficient and cost-effective process configuration for producing liquid hydrogen through stepwise cooling and subsequent ortho–para conversion. The energy intensive precooling cycle is divided into two sub-cycles employing carbon dioxide as a refrigerant. This process exploits the benefits of carbon dioxide in a simple yet efficient configuration. A specific energy consumption of 7.63 kWh/kg was achieved, along with an exergy efficiency of 31.4%. The coefficient of performance and figure of merit of this study was 0.16 and 0.31, respectively. Economic evaluation yielded total equipment and total annualized costs of $12.3 million and $24.2 million/year, respectively. The proposed process can assist in achieving a sustainable and green energy economy by enhancing the overall hydrogen value chain through competitive and efficient hydrogen storage and transportation.

Integrating hydrogen liquefaction with steam methane reforming and CO2 liquefaction processes using techno-economic perspectives

The increasing demand for liquid hydrogen as an environmentally friendly energy source necessitates developing an effective hydrogen liquefaction process. In this study, hydrogen production (steam methane reforming), hydrogen liquefaction, and CO2 liquefaction processes were successfully integrated by conducting several parametric studies involving three small-scale models and six scaled-up models. The enhanced liquefaction process included a modified Claude cycle that reduced the specific energy consumption to 6.15 kWh/kgLH2, 47% lower than that of a reference process. Three different refrigerants (nitrogen, liquified natural gas, and hydrogen) were utilized in the integrated process, and an interactive genetic algorithm-based multi-objective optimization model was developed using the MATLAB–Aspen HYSYS interface to minimize the energy consumption and CO2 generation. In addition, a hybrid non-isothermal ortho–para hydrogen cooling heat exchanger was designed by performing an H2 specific heat correction to enhance the robustness of the developed model. Techno-economic analysis of the designed process indicated that the integrated system considerably improved the main economic indicators (Levelized cost of hydrogen) and environmental friendliness of the hydrogen production process by approximately 51% and 95%, respectively. Moreover, CO2 liquefaction was performed most efficiently at a pressure of 120 bar with a reduced overall process cost. In addition, the LOCH (Levelized cost of hydrogen) of all the design integrated processes is less than $3/kg in market accessibility compared to the reference process. The sensitivity analysis results conducted by varying the costs of refrigerants, power (electricity), the selling price of liquid hydrogen, and carbon price revealed that the proposed integrated process had a higher application potential than other commonly used processes. In particular, under conditions of 45 tonne/day or more of carbon prices, the integrated process is environmentally and economically advantageous over the CO2 emission process with a reduced PBP of at least 10%.

Integrated hydrogen liquefaction processes with LNG production by two-stage helium reverse Brayton cycles taking industrial by-products as feedstock gas

Hydrogen-rich industrial by-products, such as coke oven gas (COG) and synthetic ammonia exhaust tail gas, are often simply utilized as fuel gas, or even not utilized at all in many cases. An innovative and efficient utilization method is proposed and investigated in this paper. Aiming to coproduce liquid hydrogen and liquefied natural gas (LNG), three helium reverse Brayton cycles are constructed, optimized, analyzed and compared. The LN-He-1 process is constructed with reference to conventional industrial hydrogen liquefaction processes, but with different feedstock gas. The LN-He-2 and N–He processes, which are an improvement on the basis of LN-He-1. A combination of distillation and flash is utilized to reduce the separation load. Analysis of load variation, power consumption, exergy, heat transfer and turbomachinery efficiencies are carried out. For different feedstock gas compositions, the specific power consumptions of LN-He-1, LN-He-2 and N–He processes are within 26.45–54.78 kWh/kmol (feedstock gas), 26.32–53.78 kWh/kmol (feedstock gas) and 21.94–50.42 kWh/kmol (feedstock gas), respectively. The exergy efficiencies are between 13.0% and 66.5%.

Review on the design and optimization of hydrogen liquefaction processes

The key technologies of liquefied hydrogen have been developing rapidly due to its prospective energy exchange effectiveness, zero emissions, and long distance and economic transportation. However, hydrogen liquefaction is one of the most energy-intensive industrial processes. A small reduction in energy consumption and an improvement in efficiency may decrease the operating cost of the entire process. In this paper, the detailed progress of design and optimization for hydrogen liquefaction in recent years are summarized. Then, based on the refrigeration cycles, the hydrogen liquefaction processes are divided into two parts, namely precooled liquefaction process and cascade liquefaction process. Among the existing technologies, the SEC of most hydrogen liquefaction processes is limited in the range of 5–8kWh/kgLH2 (LH2: liquid hydrogen). The exergy efficiencies of processes are around 40% to 60%. Finally, several future improvements for hydrogen liquefaction process design and optimization are proposed. The mixed refrigerants (MRs) as the working fluids of the process and the combination of the traditional hydrogen liquefaction process with the renewable energy technology will be the great prospects for development in near future.