Hydrogen Liquefaction Process Research Articles

Optimization of hydrogen liquefaction process based on parallel genetic algorithm

The optimization process of hydrogen liquefaction process is complex and time-consuming. In order to solve the above problems and improve the solving efficiency of the optimization process, this paper proposed the method of using parallel genetic algorithm combined with simulation software for optimization. Parallel genetic algorithm effectively overcomes the premature convergence of standard genetic algorithm and has strong global search ability. The parallel processing accelerates the optimization process by 2.01 times, and saves 50.22% of the time compared with the serial calculation. It not only improves the solving speed, but also improves the solving quality and the calculation performance. After optimization, the specific energy consumption of the system is reduced by 52.26%, the exergy loss is reduced by 49.81%, the heat exchange efficiency is improved, and the process performance of the system is improved. This work has reference significance for hydrogen liquefaction process optimization using parallel genetic algorithm.

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.

Conceptual design and performance evaluation of a novel cryogenic integrated process for extraction of neon and production of liquid hydrogen

Novel integration of a hydrogen liquefaction process and cryogenic rectification of air is presented. The thermodynamics analysis including the 2nd Law and sensitivity analysis regarding this process are conducted. The proposed cryogenic process can produce 111.3 kg/s of nitrogen and 42 kg/s of oxygen with argon. In addition, this process produces more than 132 × 103 tons of liquid hydrogen and 751 tons of crude neon per year. Moreover, as the number of the used compressor is very fewer than of the conventional process, the required power consumption of the proposed cryogenic plant is almost low. Based on the exergy analysis, using expanders, providing the requested refrigeration condition by solar heat exchangers and proper streams, and integrating two processes with the similar operating condition, the exergetic efficiency of the cycle is more than 70 %. The sensitivity analysis of operating parameters such as pressure, temperature, reflux ratio, and the number of stages of column presents their the importance of them on the recovered neon, oxygen, and nitrogen. Moreover, the production of cryogenic liquids is more sensitive to operating pressure and temperature than the reflux ratio and the number of stages.

Model for analyzing the energy efficiency of hydrogen liquefaction process considering the variation of hydrogen liquefaction ratio and precooling temperature

The energy efficiency of the hydrogen liquefaction process is studied, and a general model of the hydrogen liquefaction process is built for analyzing the energy efficiency and the influence of multiple parameters. Energy and exergy analysis models of the typical single-pass cycle and multiple-pass cycle are developed. The specific relationships among the parameters and energy efficiency of the total liquefaction system are deduced. A hydrogen liquefaction process with precooling nitrogen and cryogenic helium cycles is studied. For the precooling and cryogenic cycles, the SEC and net power consumption of the cryogenic helium cycle have different variation trends along with the precooling temperature and hydrogen liquefaction ratio. Their optimal values are identified to be −194 °C and 0.9453, and the corresponding SEC, exergy efficiency, total capital expense, and total annual cost are 3.619 kWh/kgLH2, 33.44%, 82.58%, 8.263 M$, and 531.62 M$/yr, respectively. The proposed model can be used in the design and operation stages to analyze the variation of energy efficiency along with multiple parameters of the hydrogen liquefaction process.

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.

Comparative analysis and multi-objective optimization of hydrogen liquefaction process using either organic Rankine or absorption power cycles driven by dual-source biomass fuel and geothermal energy

The present work presents a novel approach of employing two renewable energy sources for power and liquefied hydrogen cogeneration. Meanwhile, the main scheme comprises a biomass-fed (municipal solid waste) Brayton cycle using a digester, a geothermal-based flash binary cycle, and a Claude cycle for hydrogen liquefaction; the heat recovery is also performed through either an organic Rankine cycle (case A) or a Kalina cycle (case B) joint to the main scheme having two different configurations. Regarding the waste-to-energy framework designed for high performance, the system is comprehensively studied and optimized from the energy, exergy, and economic aspects. In this regard, thermodynamic- and economic-based sensitivity analysis, net present value method, and multi-objective grey wolf optimization are implemented; the multi-criteria optimization is performed in three scenarios containing exergy efficiency-NPV, exergy efficiency-liquefied hydrogen's unit cost, and NPV-liquefied hydrogen cost. According to the results, the first scenario offers higher exergetic efficiency; the third scenario also provides a better hydrogen cost. As a result, the better optimum exergetic efficiency and liquefied hydrogen cost are equal to 10.95% and 3.84 $/kg for case A, and 10.38% and 3.74 $/kg for case B.

Design and analysis of an efficient hydrogen liquefaction process based on helium reverse Brayton cycle integrating with steam methane reforming and liquefied natural gas cold energy utilization

In order to solve the high energy consumption of the hydrogen liquefaction process, the conceptual design of an integrated hydrogen liquefaction system is proposed and performed by integrating the steam methane reforming (SMR) process and the utilization of liquefied natural gas (LNG) cold energy. Before LNG enters the SMR process, its cooling energy is utilized in the pre-cooling section, which can reduce the use of liquid nitrogen (LN2) and improve performance. The inert gas helium is relatively safe as a refrigerant in the cooling and cryogenic section and performs well in small and medium-sized hydrogen liquefaction systems. The proposed design which produces 5 t/d of liquid hydrogen (LH2) is compared to a based case only using LN2 for pre-cooling to verify its effectiveness and feasibility. Comprehensive comparative analysis reveals that the specific energy consumption (SEC) of the proposed process is reduced from 10.78 kWh/kg LH2 to 7.948 kWh/kg LH2, and the COP is improved from 0.1205 to 0.1634. The use of LNG cold energy makes the fuel cost of the proposed system only account for 73.7% of the base case, which makes it perform better in terms of recurring investment. In conclusion, the present method and results can provide a reference for the design of integrated hydrogen production and liquefaction system by reducing energy consumption, taking into account the recovery of the cold energy of LNG.

Conceptual design and optimization of a novel hydrogen liquefaction process based on helium expansion cycle integrating with mixed refrigerant pre-cooling

Due to the safety of operation and the development of high-efficiency helium refrigerators, the development of helium refrigeration cycles in hydrogen liquefaction is continuously promoted. To reduce the energy consumption and exergy loss of this energy-intensive process, a novel hydrogen liquefaction process integrating with mixed refrigerant (MR) pre-cooling is simulated by Aspen HYSYS and optimized by genetic algorithm (GA) to improve performance under the premise of safe production and multi-faceted analyzed based on the helium expansion refrigeration cycle. A new MR with reasonable composition and ratio is used in the pre-cooling cycle to improve the matching of heat transfer curves. Energy, exergy and economic analyses are applied to evaluate the liquefaction process, and horizontal comparison is also used to evaluate the rationality and superiority of the process design. The output of 5 t/d of liquid hydrogen (21.7 K, 1.5 bar) can be achieved and the overall specific energy consumption (SEC), exergy efficiency (EXE) and coefficient of performance (COP) are 9.703 kWh/kg LH2, 39.1%, and 0.1333, respectively. Compared with similar processes, the proposed process shows better performance and potential development prospects.

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.

Thermodynamic and exergy evaluation of an innovative hydrogen liquefaction structure based on ejector-compression refrigeration unit, cascade multi-component refrigerant system, and Kalina power plant

Considerable recent ecological and energy concerns have aroused the exploitation of sustainable resources and cost-effective production of green energy carriers such as liquid hydrogen. Despite the remarkable merits of the multi-component refrigerant cycle in enhancing the hydrogen liquefaction process efficiency, it contributes to problematic controllability, increasing investment costs. Moreover, it is not easily possible to keep the composition share of refrigerants in case of leakage. This paper develops an innovative integrated structure for liquid hydrogen production, which benefits from the compression-ejector unit and six cascade multi-component refrigerant cycles in the pre-cooling and liquefaction stages. The Kalina power generation uses wasted heat in the integrated system. A power of 595.6 MW is necessary to produce 22.34 kg/s liquid hydrogen, resulting in specific energy consumption (SEC) of 7.405 kWh/kg LH2 and a coefficient of performance (COP) of 0.103. Besides, the COP of the compression-ejector refrigeration cycle is 0.8682, and the thermal efficiency of the Kalina cycle is 0.1228. The exergy efficiencies of the proposed structure and the ejector-compression refrigeration cycles are 0.2359 and 0.6462, respectively. Heat exchangers take the lion's share of exergy destruction with 39.55%, followed by gas turbines (27.92%) and compressors (21.81%). Based on sensitivity analysis, with the pressure increase in the secondary stream of Ejector1, the SEC increases by 7.435 kWh/kgLH2, and the COP of the ejector-compression refrigeration cycle decreases by 0.8242. As the pressure rises in the Kalina cycle, the SEC declines to a low of 7.4135 kWh/kg LH2 at 26 bar, then increases with pressure.

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.

Energy, exergy, and economic analyses of an innovative hydrogen liquefaction process utilising liquefied natural gas regasification system

Energy, exergy, and economic analyses of an innovative hydrogen liquefaction process utilising liquefied natural gas regasification system

Energy, exergy, and economic analyses of an innovative hydrogen liquefaction process utilising liquefied natural gas regasification system

Energy, exergy, and economic analyses of an innovative hydrogen liquefaction process utilising liquefied natural gas regasification system

Proposal and investigation of a novel hybrid hydrogen production and liquefaction process using solid oxide electrolyzer, solar energy, and thermoelectric generator

In this research, an integrated system of large-scale hydrogen production and liquefaction has been introduced. Conceptual configurations for the hydrogen liquefaction cycle are designed, modeled, simulated, optimized, and analyzed for energy, and the most appropriate ones are selected for use in system. A combination of several units is provided together to produce and then liquefy hydrogen utilizing solar energy. The designed system uses linear Fresnel collectors in combination with a solid oxide electrolyzer set, thermoelectric generator, and Rankine cycle to form the hydrogen production section. The proposed system has a production capacity of 6400 kg of liquid hydrogen each hour. The specific energy consumption and coefficient of performance of the proposed refrigeration cycle were calculated for mass flows rates of 1 kg/s, 1.5 kg/s, and 1.77 kg/s. These values at best were 5.72Kwh/KgLH2 and 0.1804, respectively. Declared values are significantly better than the corresponding values of similar and reference liquefaction cycles. The energy efficiencies of the electrolyzer, LFR, Rankine cycle, and thermoelectric generator were calculated as 71.18%, 21.42%, 46.64%, and 12.4% respectively. Also, the effect of operational parameters of each subsystem, including temperature and pressure of the input current to the electrolyzer and the total area of the solar reflector on the overall proficiency of the system was researched and the results are presented. The energy efficiency of the hydrogen production sector was 15.98% and the system's total solar fraction was 0.86.

Study on continuous cooling process coupled with ortho-para hydrogen conversion in plate-fin heat exchanger filled with catalyst

A mathematical model of the plate-fin heat exchanger filled with catalyst (CFPFHX) is established to investigate the continuous cooling process coupled with ortho-para hydrogen conversion at 42–70 K. The flow and heat transfer performance and the efficiency of ortho-para hydrogen conversion in the CFPFHX are quantitatively evaluated, and the effects of the structural parameters on the flow and heat transfer coupled with ortho-para hydrogen conversion are analyzed. The results show that the Elovich model is the best existing kinetic models of ortho-para hydrogen conversion with an average relative deviation of 1.8%. The Colburn heat transfer factor (j factor) of the hot side of the CFPFHX is 4.3 times that of the plate-fin heat exchanger (PFHX), and the thermal enhancement factor (TEF) of the hot side is 37.7% of that of the PFHX. Meanwhile, for the CFPFHX, the j factor and the TEF of the hot side under different structural parameters are always about 8–10 times and 68%–93% of that of the cold side respectively. Therefore, the CFPFHX can ensure the flow and heat transfer performance and realize the ortho-para hydrogen continuous conversion. And a fin with the larger flow area (high fin height, wide fin spacing and small fin thickness) has a better flow and heat transfer performance and ortho-para hydrogen conversion. The outlet para-hydrogen ratio youtp-H2 and the mass space velocity vm in the CFPFHX have an approximate linear trend. When mass space velocity vm ≤ 0.6589 kg/(m3·s), the outlet para-hydrogen ratio youtp-H2 can meet the requirement at 42–70 K. Above all, the mechanism of flow and heat transfer coupled with ortho-para hydrogen conversion is revealed for the first time in this study, which can provide a theoretical guidance for the application of the integrated technology in large scale hydrogen liquefaction process.

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.

Thermodynamic and economic analysis of a novel hydrogen liquefaction process with LNG precooling and dual-pressure Brayton cycle

Liquid hydrogen with high energy density and cleanliness is a superior alternative to current energy carriers. However, high costs and low efficiency are barriers to liquefy hydrogen. To reduce the energy consumption and investment costs of hydrogen liquefaction, a hydrogen liquefaction process that utilizes a direct expansion cycle of liquefied natural gas for hydrogen precooling and a dual-pressure Brayton cascaded cycle for hydrogen cryo-cooling is proposed. The hydrogen liquefaction performance and economic benefits of the proposed process are assessed by comparing it with two reference processes with different cryo-cooling cycles. The results reveal the advantageous operating costs and capital costs of the proposed process, especially in terms of the costs of helium and heat exchangers. Moreover, the specific energy consumption of the proposed process is 6.60 kWh/kgH2, which is 4.0% and 4.5% lower than those of the reference processes. The exergy losses and exergy efficiency of the proposed process are 12.36 MW and 47.0%, respectively, and the exergy losses are mainly caused by the compressors and expanders. The energy consumption of the proposed process decreases at first and subsequently increases with the increasing pre-compression pressure of helium.

A novel hydrogen liquefaction process based on LNG cold energy and mixed refrigerant cycle

• A novel hydrogen liquefaction cycle using LNG cold energy and mixed refrigerant cycle is proposed. • Energy, exergy, and economic analyses are performed. • Take advantage of using LNG cold energy of the regasification system in the hydrogen liquefaction cycle. • The proposed cycle is compared and analyzed with other cycles. • COP, SEC, and FOM are investigated for the proposed hydrogen liquefaction cycle. A novel hydrogen liquefaction cycle with a capacity of 369 tons per day has been proposed. Given the fact that the process integration and appropriate design can reduce the power consumption of the light gas liquefaction cycle, wasted cold energy of a natural gas regasification system is integrated into the pre-cooling part of the liquid hydrogen production. In this study, after being evaporated in the pre-cooling part of the hydrogen liquefaction cycle, the liquefied natural gas (LNG) enters the steam methane reforming (SMR) to feed the hydrogen liquefaction process by hydrogen gas. Energy, exergy, and economic analyses are carried out to investigate the process. The mixed refrigerant method is implemented in the proposed model. The specific energy consumption (SEC) of the proposed process is 19.90% less than that of the similar cycles mentioned in the literature. The economic analysis results illustrate that the total annual cost of the proposed model is 13.43% less than that of the base model. A comparison between the proposed and other hydrogen liquefaction cycles is made to verify feasibility and efficiency. The minimum selling price of the liquid hydrogen is $ 2.07 k g − 1 in a payback time of three years, making it economically viable.

Optimization and analysis of a novel hydrogen liquefaction process for circulating hydrogen refrigeration

In industrial engineering, hydrogen is usually transported and stored after being liquefied, which is an energy-intensive process. Aiming to liquefy hydrogen with high efficiency and low consumption, a novel hydrogen liquefaction process based on dual-path hydrogen refrigeration is proposed innovatively and simulated by Aspen HYSYS to determine the key parameters. Taking the specific energy consumption (SEC) as the objective function for the optimization by genetic algorithm (GA), optimum parameters could be obtained. Meanwhile, the single variable method is conducted to analyze the impact of key parameters on process characteristics. Under the premise of complete liquefaction, the SEC, coefficient of performance (COP) and exergy efficiencies (EXE) of the proposed system are 7.041 kWh/kg LH2, 0.1834, 0.5413, respectively. Compared with the other three hydrogen liquefaction systems simulated under the same conditions, they are decreased by 22.16% and increased by 33.58% and 42.37%, respectively. The results show that the proposed system shows better performance under lower consumption.