Thermodynamic analysis of a new double-pressure condensation power generation system recovering LNG cold energy for hydrogen production

Cold energy during the LNG regasification process is usually applied for power generation, but the electricity demand varies with the time. Therefore, a thought that transforming electrical energy into hydrogen energy by PEM electrolyzer is put forward to adjust the adaptability of power output to electricity demand. This paper proposes a new double-pressure condensation Rankine cycle integrated with PEM electrolyzer for hydrogen production. In this system, seawater is used as the heat source, and binary mixed working fluids are applied. Meanwhile, multi-stream heat exchanger is introduced to improve the irreversibility of heat transfer between LNG and working fluid. The key system parameters, including seawater temperature, the first-stage condensation temperature, the second-stage condensation temperature, and outlet temperature of LNG, are studied to clarify their effects on net power generation, hydrogen production rate and energy efficiency. Furthermore, the hydrogen production rate is as the objective function, these parameters are optimized by genetic algorithm. Results show that seawater temperature has positive impact on the net power output and hydrogen production rate. The first-stage condensation temperature, the second-stage condensation temperature, and outlet temperature of LNG have diverse effects on the system performance. Under the optimal working conditions, when the LNG regasification pressure are 600, 2500, 3000 and 7000 kPa, the increasing rate for optimized net power output, hydrogen production rate and energy efficiency are more than 11.68%, 11.67% and 8.88%, respectively. The cost of hydrogen production with the proposed system varies from 1.93 $/kg H2 to 2.88 $/kg H2 when LNG regasification pressure changes from 600 kPa to 7000 kPa.     

Thermodynamic analysis and assessment of an integrated hydrogen fuel cell system for ships

In this thermodynamic investigation, an integrated energy system based on hydrogen fuel is developed and studied energetically and exergetically. The liquefied hydrogen fueled solid oxide fuel cell (SOFC) based system is then integrated with a steam producing cycle to supply electricity and potable water to ships. The first heat recovery system, after the fuel cells provide thrust for the ship, is by means of a turbine while the second heat recovery system drives the ship's refrigeration cycle. This study includes energy and exergy performance evaluations of SOFC, refrigeration cycle and ship thrust engine systems. Furthermore, the effectiveness of SOFCs and a hydrogen fueled engine in reducing greenhouse gas emissions are assessed parametrically through a case study. The main propulsion, power generation from the solid oxide fuel cells, absorption chiller, and steam bottoming cycle systems together have the overall energy and exergy efficiencies of 41.53% and 37.13%, respectively.     

Research on low-temperature heat exchange performance of hydrogen preheating system for PEMFC engine

The durability of membrane electrodes, which are the core components of the Proton Exchange Membrane fuel cell (PEMFC), seriously affects the service life of the stack. Under the action of long-term low temperature, the gas diffusion layer at the entrance will be aged and its micro-porous layer structure will be destroyed, which will hinder the removal of liquid water and gas transport, so it is necessary to preheat the anode hydrogen. In the present study, the influence of different pitch ratio and diameter ratio on heat transfer of corrugated tube heat exchanger is simulated by means of thermal-fluid coupled numerical simulation and periodic unit model, the effects of coolant flow rate and temperature on the overall heat transfer performance were also studied. The validity of the simulation results is verified by experiments, and the effect of hydrogen preheating on the stack performance is also tested. The simulation results show that the corrugated joint will disturb the flow of hydrogen, which increases the temperature gradient along the radial direction of the main flow and enhances the heat transfer. When Re is lower than 4000, the friction factor decreases quickly and then gradually flattens out. Compared with 0.5 for bellows with a pitch ratio of 1, the friction factor increases by 17%. With the increase of Re, the j values of different pitch ratios differ greatly and decrease linearly. For every 5 cm increase in the length of the corrugated tube, the total heat exchange capacity is increased by about 20%,and the total heat transfer increases about 100 W with the increase of the coolant flow 0.04 kg/s.     

Comparison of three different solar collectors integrated with geothermal source for electricity and hydrogen production

In this study, an integrated system is proposed for mainly electricity and hydrogen production. Energy and exergy analyses of the system are also examined by using Engineering Equation Solver (EES, version 2019) under solar radiation during day time on 1st July. The proposed system consists of a middle-temperature geothermal source with fluid temperature 93 °C, three solar collectors (SCs of 300 m²) namely parabolic trough solar collectors (PTSCs), evacuated tube solar collectors (ETSCs), flat plate solar collectors (FPSCs), an organic Rankine cycle (ORC), proton exchange membrane (PEM), a compressor, hot water storage tank and a mushroom cultivation room. The temperature of the geothermal fluid is upgraded via solar collectors by harvesting solar radiation to operate the ORC. Thus the generated electricity is used in the PEM electrolysis system for producing hydrogen. When the PTSCs, ETSCs, and FPSCs are integrated with the geothermal source separately, it is found that 2758.69 g, 1585.27 g, and 634.42 g of hydrogen can be produced, respectively for a day. The highest overall energetic and exergetic performance of the system is calculated as to be 5.67% and 7.49%, respectively.     

Analysis of a novel concentrated solar power and magnetohydrodynamic liquid metal units integrated system with hydrogen production

The engineers are very interested in concentrated solar power (CSP) due to its renewable energy source nature. However, for this technology to grow, it is crucial to integrate efficient, cost-effective subsystems. On the other hand, since liquid metal magnetohydrodynamic (LMMHD) power generation systems can operate at high temperatures of 600 °C–3000 °C, they are ideal for use as a subsystem of a CSP-based plant to improve efficiency. The use of waste heat recovery units is another method of increasing efficiency and preventing exergy losses. Taking these points into consideration, the proposed trigeneration system includes an LMMHD, a CSP, and humidification-dehumidification and proton exchange membrane units to produce power, freshwater, as well as hydrogen, respectively. Performance evaluation of the presented system includes thermodynamic and thermoeconomic considerations. The results show that the presented system produces 11.87 kW of power, 6.1 m³/h of hydrogen, and 860.2 L/h of freshwater with an energy utilization factor of 45.81%, a total exergy efficiency of 4.63%, and a unit cost of 19.57 $/kWh. The receiver is the most destructive component of the system, with 256.9 kW of exergy destruction. Further, the parametric study indicates that it is possible to maximize the energy efficiency of the system by changing the concentration ratio of the receiver.     

Assessment of system variations for hydrogen transport by liquid organic hydrogen carriers

One option to transport hydrogen over longer distances in the future is via Liquid Organic Hydrogen Carriers (LOHC). They can store 6.2 wt% hydrogen by hydrogenation. The most promising LOHCs are toluene and dibenzyltoluene. However, for the dehydrogenation of the LOHCs – to release the hydrogen again – temperatures above 300 °C are needed, leading to a high energy demand. Therefore, a Life Cycle Assessment (LCA) and Life Cycle Costing are conducted. Both assessments concentrate on the whole life cycle rather than just direct emissions and investments. In total five different systems are analysed with the major comparison between conventional transport of hydrogen in a liquefied state of matter and LOHCs. Variations include electricity supply for liquefaction, heat supply for dehydrogenation and the actual LOHC compound. The results show that from an economic point of view transport via LOHCs is favourable while from an environmental point of view transport of liquid hydrogen is favourable.     

Performance analysis of vapor-cooled shield insulation integrated with para-ortho hydrogen conversion for liquid hydrogen tanks

A composite thermal insulation system consisting of variable-density multi-layer insulation (VDMLI) and vapor-cooled shields (VCS) integrated with para-ortho hydrogen (P-O) conversion is proposed for long-term storage of liquid hydrogen. High-performance thermal insulation is realized by minimizing the thermal losses via the VDMLI design and fully recovering the cold energy released from the sensible heat and P-O conversion of the vented gas. Effects of different design considerations on the thermal insulation performance are studied. The results show that the maximum reduction of the heat leak with multiple VCSs can reach 79.9% compared to that without VCS. The heat leak with one VCS is reduced by 61.1%, and further reduced by 11.6% after adding catalysts. It is found that the deterioration of the insulation performance has an almost linear relationship with catalytic efficiency. A unified criterion with relative optimization efficiency is finally proposed to evaluate the improvement of the VCS number.     

Thermodynamic analysis and assessment of a novel integrated geothermal energy-based system for hydrogen production and storage

In this paper, thermodynamic analysis and assessment of a novel geothermal energy based integrated system for power, hydrogen, oxygen, cooling, heat and hot water production are performed. This integrated process consists of (a) geothermal subsystem, (b) Kalina cycle, (c) single effect absorption cooling subsystem and (d) hydrogen generation and storage subsystems. The impacts of some design parameters, such as absorption chiller evaporator temperature, geothermal source temperature, turbine input pressure and pinch point temperature on the integrated system performance are investigated to achieve more efficient and more effective. Also, the impacts of reference temperature and geothermal water temperature on the integrated system performance are studied in detail. The energetic and exergetic efficiencies of the integrated system are then calculated as 42.59% and 48.24%, respectively.     

Thermodynamic analysis of high‐temperature helium heated fuel reforming for hydrogen production

In order to take full advantage of the heat from high temperature gas cooled reactor, thermodynamic analysis of high‐temperature helium heated methane, ethanol and methanol steam reforming for hydrogen production based on the Gibbs principle of minimum free energy has been carried out using the software of Aspen Plus. Effects of the reaction temperature, pressure and water/carbon molar ratio on the process are evaluated. Results show that the effect of the pressure on methane reforming is small when the reaction temperature is over 900 °C. Methane/CO conversion and hydrogen production rate increase with the water/carbon molar ratio. However the thermal efficiency increases first to the maximum value of 61% and then decreases gradually. As to ethanol and methanol steam reforming, thermal efficiency is higher at lower reaction pressures. With an increase in water–carbon molar ratio, hydrogen production rate increases, but thermal efficiency decreases. Both of them increase with the reaction temperature first to the highest values and then decrease slowly. At optimum operation conditions, the conversion of both ethanol and methanol approaches 100%. For the ethanol and methanol reforming, their highest hydrogen production rate reaches, respectively, 88.69% and 99.39%, and their highest thermal efficiency approaches, respectively, 58.58% and 89.17%. With the gradient utilization of the high temperature helium heat, the overall heat efficiency of the system can reach 70.85% which is the highest in all existing system designs. Copyright © 2014 John Wiley & Sons, Ltd.     

Performance evaluation of an integrated hydrogen production system with LNG cold energy utilization

This study aims to develop a novel integrated geothermal based system by the application of different thermodynamic cycles such as Kalina, liquefied natural gas (LNG), Stirling and proton exchange membrane electrolyzer (PEME) to produce cooling, hydrogen, and electricity. Energy and exergy analyses of the system are performed to evaluate the performance of the system. Additionally, the effects of five different input variables are investigated to determine their impacts on the corresponding values of net power and cooling, exergy efficiency, hydrogen production, and sustainability index. In a defined condition, the exergy efficiency of the suggested system is computed around 43%. The cycle net generated power is 10.69 MW, which is the generated power by the Stirling, LNG, and Kalina turbines each by 8.07 MW, 1.13 MW, and 1.49 MW, respectively. The produced cooling load by the cooling unit of the LNG stream is also 6.09 MW, while the rate of hydrogen production in the electrolyzer is 204.77 kg/h by consuming all the generated power. Additionally, a sensitivity analysis is performed to study the effects of each design parameters on the system performance.     

Thermodynamic analysis and optimization of an integrated solar thermochemical hydrogen production system

In this study, thermodynamic analysis of solar-based hydrogen production via copper-chlorine (Cu–Cl) thermochemical water splitting cycle is presented. The integrated system utilizes air as the heat transfer fluid of a cavity-pressurized solar power tower to supply heat to the Cu–Cl cycle reactors and heat exchangers. To achieve continuous operation of the system, phase change material based on eutectic fluoride salt is used as the thermal energy storage medium. A heat recovery system is also proposed to use the potential waste heat of the Cu–Cl cycle to produce electricity and steam. The system components are investigated thoroughly and system hotspots, exergy destructions and overall system performance are evaluated. The effects of varying major input parameters on the overall system performance are also investigated. For the baseline, the integrated system produces 343.01 kg/h of hydrogen, 41.68 MW of electricity and 11.39 kg/s of steam. Overall system energy and exergy efficiencies are 45.07% and 49.04%, respectively. Using Genetic Algorithm (GA), an optimization is performed to evaluate the maximum amount of produced hydrogen. The optimization results show that by selecting appropriate input parameters, hydrogen production rate of 491.26 kg/h is achieved.     

Thermodynamic assessment of a novel multigenerational power system for liquid hydrogen production

A Brayton plant-based multigenerational system is proposed and investigated thermodynamically through energetic and exergetic approaches in this study. Liquid hydrogen, electrical energy, heating-cooling and fresh water are the useful outputs produced by the combined plant. For this purpose, the Brayton cycle, organic Rankine cycle, multi-effect distillation plant, single-effect absorption cooling plant, hydrogen generation and liquefaction unit are used in the multigeneration system design. The study targets are to design a novel multigeneration system design, develop the related software codes, analyze the system thermodynamically, and evaluate the effects of plant design indicators. Thermodynamic assessment results indicate that the energy efficiency of the multigeneration system ranges between 63.64% and 74.31%, the exergy efficiency value ranges from 55.67% to 67.35%. Parametric analyses performed in this study indicate that the most influential parameter is the fuel mass flow rate. Also, it should be stated that an increase in the dead state temperature, combustion chamber temperature, and fuel mass flow rate positively affects the plant effectiveness.     

Development and thermodynamic assessment of a novel solar and biomass energy based integrated plant for liquid hydrogen production

In this paper, a combined power plant based on the dish collector and biomass gasifier has been designed to produce liquefied hydrogen and beneficial outputs. The proposed solar and biomass energy based combined power system consists of seven different subplants, such as solar power process, biomass gasification plant, gas turbine cycle, hydrogen generation and liquefaction system, Kalina cycle, organic Rankine cycle, and single-effect absorption plant with ejector. The main useful outputs from the combined plant include power, liquid hydrogen, heating-cooling, and hot water. To evaluate the efficiency of integrated solar energy plant, energetic and exergetic effectiveness of both the whole plant and the sub-plants are performed. For this solar and biomass gasification based combined plant, the generation rates for useful outputs covering the total electricity, cooling, heating and hydrogen, and hot water are obtained as nearly 3.9 MW, 6584 kW, 4206 kW, and 0.087 kg/s in the base design situations. The energy and exergy performances of the whole system are calculated as 51.93% and 47.14%. Also, the functional exergy of the whole system is calculated as 9.18% for the base working parameters. In addition to calculating thermodynamic efficiencies, a parametric plant is conducted to examine the impacts of reference temperature, solar radiation intensity, gasifier temperature, combustion temperature, compression ratio of Brayton cycle, inlet temperature of separator 2, organic Rankine cycle turbine and pump input temperature, and gas turbine input temperature on the combined plant performance.     

Thermodynamic analysis of novel hybrid liquid air energy storage system combined with ORC

为了进一步提高液态空气储能（LAES）的系统效率,提出了一种利用有机朗肯循环（ORC）回收利用LAES放电过程中余冷和余热的新型LAES系统。采用Aspen HYSYS V8.4流程模拟方法研究了系统中不同设备性能参数对LAES系统热力特性的影响。结果表明：低温泵等熵效率和换热器夹点温度对LAES系统效率的影响较小;透平等熵效率和燃烧室出口温度对LAES系统效率的影响非常显著,LAES系统效率随透平等熵效率和燃烧室出口温度的增加而显著增加;LAES系统效率随低温泵出口压力的升高而增加,但增加幅度会逐渐减小。该研究结果可为LAES系统的工程应用和效率提升提供重要参考和依据。     

Effect of compression on liquid water transport and microstructure of PEMFC gas diffusion layers

This work explores how the degradation of the gas diffusion layer (GDL) under compression contributes to the formation of preferential pathways for water transport. Fluorescence microscopy is used to provide ex situ visualization of liquid water transport through the GDL placed beneath an optically transparent clamping plate. Transient image data obtained with a CCD camera indicates that areas of compression in the GDL coincide with preferential pathways for water transport and break-through. Preferential flow of water through the smaller pores resulting from GDL compression is contrary to the expected behaviour in a hydrophobic medium, and this suggests a loss of hydrophobicity. Scanning electron microscopy (SEM) is used to investigate the effect of compression on the morphology of the GDL. These SEM images show that compressing the GDL causes the breakup of fibers and, indeed, deterioration of the hydrophobic coating.     

Assessment of power and hydrogen production performance of an integrated system based on middle-grade geothermal source and solar energy

In this study, power and hydrogen production performance of an integrated system is investigated. The system consists of an organic Rankine cycle (ORC), parabolic trough solar collectors (PTSCs) having a surface area of 545 m², middle-grade geothermal source (MGGS), cooling tower and proton exchange membrane (PEM). The final product of this system is hydrogen that produced via PEM. For this purpose, the fluid temperature of the geothermal source is upgraded by the solar collectors to drive the ORC. To improve the electricity generation efficiency, four working fluids namely n-butane, n-pentane, n-hexane, and cyclohexane are tried in the ORC. The mass flow rate of each working fluid is set as 0.1, 0.2, 0.3, 0.4 kg/s and calculations are made for 16 different situations (four types of working fluids and four different mass flow rates for each). As a result, n-butane with a mass flow rate of 0.4 kg/s is found to be the best option. The average electricity generation is 66.02 kW between the hours of 11⁰⁰-13⁰⁰. The total hydrogen production is 9807.1 g for a day. The energy and exergy efficiency is calculated to be 5.85% and 8.27%, respectively.     

Thermodynamic assessment of modified Organic Rankine Cycle integrated with parabolic trough collector for hydrogen production

Hydrogen is one of the most clean energy carrier and the best alternative for fossil fuels. In this study, thermodynamic analysis of modified Organic Rankine Cycle (ORC) integrated with Parabolic Trough Collector (PTC) for hydrogen production is investigated. The integrated system investigated in this study consists of a parabolic trough collector, a modified ORC, a single effect absorption cooling system and a PEM electrolyzer. By using parabolic trough collector, solar energy is converted heat energy and then produced heat energy is used in modified ORC to produce electricity. Electricity is then used for hydrogen production. The outputs of this integrated system are electricity, cooling and hydrogen. By performing a parametric study, the effects of design parameters of PTC, modified ORC and PEM electrolyzer on hydrogen production is evaluated. According to the analysis results, solar radiation is one of the most important factor affecting system exergy efficiency and hydrogen production rate. As solar radiation increases from 400?W/m² to 1000?W/m², exergy efficiency of the system increases 58%–64% and hydrogen production rate increases from 0.1016?kg/h to 0.1028?kg/h.     

Thermodynamic assessments of a novel integrated process for producing liquid helium and hydrogen simultaneously

Liquid helium and hydrogen are two precious cryogens with advanced applications in various energy research fields. However, producing these cryogens generally come with high-cost processes. In this research, Liquid hydrogen is obtained in two stages with the aid of a mixed refrigeration subprocess and helium cryogen. Also, liquid helium is obtained in three stages with the aid of helium upgrader, pressure swing adsorption, and helium liquefier subprocesses. The liquid helium is produced at 19.42 K, 195 kPa, and 6161 kgmole/h. Also, the liquid hydrogen is produced at 3.69 K, 110.3 kPa, and 17,970 kgmole/h. The novelties of this research can be described as the production of liquid helium and hydrogen simultaneously, low SEC, novel configuration, and production of liquid helium and hydrogen at near ambient pressure. Thermodynamic analyses show that the specific energy consumption, coefficient of performance, and figure of merit are equal to 18.96 kW h/kg, 0.03, and 0.37, respectively. Also, the exergy analysis shows that the exergy efficiency and exergy destruction in the whole process are equal to 67% and 4471 MW, respectively. Also, sensitivity analysis shows that increasing the PSA process efficiency positively impacts all process parameters like SEC, COP, FOM, and exergy efficiency.     

Optimization and analysis of an integrated energy system based on wind power utilization and on-site hydrogen refueling station

An integrated energy system coupled with wind turbines and an on-site hydrogen refueling station is proposed to simulate the future scenario, which can meet the demands of cooling, heating, power and hydrogen. The system was modeled to calculate the capacity and annual operation of each equipment with the total annual cost as the optimization objective. This study evaluates the performance of the system based on the results. When the system is configured with 0–10 wind turbines, the economics, energy consumption and carbon emissions improve as the scale of wind turbines increases. Energy utilization and wind power utilization are above 66.79% and 99.73%, respectively. The on-off coefficient of the power generation unit can affect energy efficiency. When the system contains 5 turbines, 91% of the hydrogen can be self-produced with the minimum amount of energy redundancy.