Liquefaction Cycle Research Articles

EXERGY ANALYSIS OF LIQUID AIR ENERGY STORAGE SYSTEM BASED ON LINDE CYCLE

The paper presents a theoretical analysis from an energetic and exergetic point of view for a liquid air energy storage system (LAES). This paper identifies upper bounds on the energy and exergetic efficiency for this system. The system uses the simple Linde-Hampson liquefaction cycle for the liquefaction subsystem and the direct expansion method without heating above ambient temperature, for the power generation subsystem. It is known that as the temperature decreases, the destruction of mechanical work input increases due to the irreversibility of working processes. As a result, any irreversible process is very important to observe in cryogenic processes. The purpose of this paper is to develop an exergetic analysis which is then used in a procedure to optimize the Linde installation within the liquid air energy storage system when some functional parameters are changed. The analysis aims to find the functional parameters for which the exergetic efficiency of the installation is maximum. For each subsystem of the simple Linde installation an exergetic product and a fuel were defined and, based on their definition, the coefficient of performance of each functional area was calculated as well as the exergy destructions. Finally, the analysis of system components is presented in order to identify the components that have the greatest impact on energy and exergetic efficiency in an ideal environment. The analytical approach presented in this paper can be applied to other LAES configurations to identify the optimal operating points in terms of energy and exergetic efficiency.

Techno-economic and multi objective optimization of zero carbon emission biomass based supercritical carbon dioxide oxy combustion system integrated with carbon dioxide liquefaction system and solid oxide electrolyzer

Consumption of fossil fuels and their scarcity of resources as a global challenge has posed a major problem for the energy sector. To this end, four sub-systems including oxy-fuel production and combustion, hydrogen production, power generation and liquefaction and storage of carbon dioxide were integrated to obtain a new power generation system. The proposed system was evaluated based on techno-economic analyses and multi-objective optimization. Syngas was used as a fuel where syngas was obtained through biomass gasification. Linde-Hampson liquefaction system was used to facilitate storage and transport of carbon dioxide. Solid Oxide Electrolyzer was employed to save the extra energy of system efficiently and supercritical carbon dioxide cycle was used because it is environmentally friendly. The results showed that the obtained values of the levelized cost of electricity are 0.6019 $/kWh, 0.7117 $/kWh, 0.5059 $/kWh, and 0.42114 $/kWh, respectively, for the configurations of power generation, power + hydrogen production, power + hydrogen + liquid carbon dioxide production cycle, and power + liquid carbon dioxide production cycle. Integration of carbon dioxide liquefaction cycle into the system is a desirable factor so that causes 30% and 29% reduction in the levelized cost of electricity when it is integrated with power generation, power + hydrogen production. If the cash flow of the system and the levelized cost of electricity are selected as the objective functions in system optimization, the cost of electricity and cash flow will be 0.36 $/kWh and $ 3.8 million at the selected optimal point, respectively.

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.

Maximum Liquefaction of Gases Revisited

Joule-Thomson liquefiers are the commonest machines to liquefy gases. Over the years, countless number of articles have been published on the subject. Dozens of 1st and 2nd law analyses were carried out on Joule-Thomson liquefaction cycles. And yet an aspect of purely theoretical interest seems to have passed unnoticed, namely: for a given volume of gas, what conditions should be fulfilled to achieve maximum liquefaction without considering engineering details of design equipment and the highly irreversible character of work-consuming devices, heat exchangers, heat leaks and the throttling process. This work addressed this issue by applying the 1st law analysis and elementary calculus prescriptions to a simple Linde-Hampson liquefying process. The same approach could be applied to other liquefying cycles. As is well-known, for a given mass flow rate of a gas, maximum fraction liquefied occurs when the pre-cooling temperature, Ti , and initial pressure, Pi , lie on the inversion curve. It has been proved that this is only true if an additional condition is fulfilled. Expressions for it were derived for the van der Waals, RKS and PR equations of state.

Dynamic simulation of the cool down process of double-pressure helium liquefaction cycle

A double-pressure helium liquefaction cycle, which consists of two compressors, six heat exchangers, two expanders and several valves, was proposed in this paper. The thermodynamic parameters of the process were calculated and analyzed. The mathematical models of the above-mentioned key equipment are established, and the cool down process of the helium refrigerator is dynamically simulated. By adjusting the parameters of each valve in the process, the working process of the compressor was simulated, and the cool-down process of heat exchangers and the expanders was obtained and analyzed. Finally the stable refrigeration capacity was obtained. The simulation of the dynamic process has a great guiding role for the actual experimental process afterwards.

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.

Thermodynamic assessment of a geothermal power and cooling cogeneration system with cryogenic energy storage

Geothermal energy is one of the main renewable energy sources for power generation and district cooling, and liquid air energy storage is an emerging technology suitable for both power and cold storages. Accordingly, a combined power and cooling cogeneration system with cryogenic energy storage is proposed in this paper, which is powered by geothermal energy and connected with the grid. The system is formed by integrating a turbine ejector cogeneration cycle with an air liquefaction cycle, a liquid air direct expansion cycle and a cryogenic organic Rankine cycle. In normal operation mode, only the turbine ejector cogeneration cycle works in the system based on the cooling load requirement. In charging operation mode, all the power produced in the system is used to liquefy air in the air liquefaction cycle owing to cheap electricity tariff. In discharging operation mode, the additional electricity is provided to meet peak time energy requirement by the direct expansion cycle and cryogenic organic Rankine cycle. A geothermal source at 180 °C with a flow rate of 100 kg/s is used as the heat source in this study, the cogeneration system has the ability to produce 15,470 kW of power and supply 4800 kW of cooling simultaneously, the system round trip efficiency is 41.07%, and the exergy efficiency of cryogenic energy storage is 60.43%. Also, the effects of geothermal energy temperature, system size, turbine mass split ratio and normalized mass flow rate on the system performance are clarified.

Experimental investigation and new correlation for the bubble departure diameter of methane and ethane binary mixtures during nucleate pool boiling

Methane and ethane are the main components of liquefied natural gas (LNG) and mixed-refrigerant liquefaction cycles. The pool boiling characteristics and bubble dynamic parameters of methane/ethane mixtures are important for the design and optimization of LNG systems. In this study, visual experiments were carried out to investigate the pool boiling of methane, ethane and their mixtures on a horizontal flat surface. Heat transfer characteristics and bubble departure diameters were acquired at 0.3 MPa for different concentrations of the mixtures. The bubble departure diameter increases with the increase in superheat temperature and dimensionless Jacob number for all concentrations of the mixture. The non-linear variation with concentrations of the bubble departure diameter can be observed due to the effects of mixtures. The bubble departure diameters for mixtures were predicted by twelve existing correlations, with Cole's correlation having the lowest mean absolute relative deviation (MARD) of 46.28%, with only 38.78% points within ±30% deviation. Therefore, a new model for mixtures was developed based on force equilibrium analysis in this study. Marangoni force is taken into account in the proposed model, as well as the effects of mass transfer on the bubble growth rate in mixtures. The MARD of the new model is 18.78%, which is better than all the twelve existing correlations.

A new biomass gasification driven hybrid system for power and liquid hydrogen cogeneration: Parametric study and multi-objective evolutionary optimization

The purpose of this paper is focused on introducing a new layout of an electricity and liquid hydrogen cogeneration power plant and evaluating its performance from the exergo-economic and environmental stand points. The system is based on the combination of a biomass gasification gas turbine cycle, a Rankine cycle, an electrolyzer unit, and a hydrogen liquefaction cycle. A parametric model is firstly developed to study the sensitivity of the system performance on the main design parameters (including biomass flow rate ṁbiomass, gas turbine inlet temperature TGT, compressor pressure ratio PR, and steam turbine inlet pressure PSRCT). Afterward, the optimal operation of system is selected using by a multi-objective optimization approach. The observations revealed that m˙biomass is the most effective design parameter. The optimal design parameters are obtained as ṁbiomass = 1.94 kg/s, TGT = 1421 K, PR = 5.52, and PSRCT = 3886 kPa, which results in the maximum electricity and hydrogen production of 3377 kW and 14.8 kg/h together with minimum total cost rate of 86.61 $/h. At this condition, the optimal environmental index is 1.09 kgCO₂/kWh.

A Critical Analysis of Natural Gas Liquefaction Technology

Liquefied natural gas (LNG) is an important energy source and occupies an important proportion in natural gas consumption, therefore, the selection of appropriate liquefaction processes and related optimization should be seen as subjects of great importance. Accordingly, in the present review, we provide a comparative and critical analysis of the current status of natural gas liquefaction technology through examination of the advantages and disadvantages associated with three natural gas liquefaction processes (namely, the cascade liquefaction cycle, the expander-based cycle and the mixed refrigerant cycle). It is shown that the energy consumption related to the cascade refrigeration cycle is the lowest. Compared with it, the mixed refrigerant cycle has the advantages of being a simpler process, with less units, low investment cost and low requirements in terms of refrigerant purity. The expander-based cycle can be started and stopped quickly and simply, but the power consumption is relatively high.

Comparative Study between precooled Claude Liquefaction Cycle and an Active Magnetic Regeneration Cycle applied to Hydrogen Liquefaction

The present work aims at performing a comparative study between precooled Claude cycle and an Active Magnetic Regeneration Cycle (AMR cycle) applied to hydrogen liquefaction. It deals with a comparison between performances and energy consumption evaluated for the two systems at similar operating conditions. For Claude system, energy and material balances have been performed by using Aspen Hysys simulator. Thus, liquefaction power, energy consumption and coefficient of performance (COP) have been calculated. While, the AMR system considered is constituted of 6 stages operating in cascade. Each stage contains two regenerator beds, composed of a typical magnetic material, through which a carrier fluid is forced to follow alternatively between two heat reservoirs. Thermal analysis and evaluation of performances have been performed at once by a numerical model, developed on the basis of energy equations for fluid and solid within the regenerator bed, and Aspen Hysys simulator. Using the following magnetic materials (Gd, Dy, Tb and Ho), the COP found for the AMR system is 0.096. This value is higher than Claude cycle efficiency for which a COP of 0.094 was found. In terms of energy consumption, the value found for the AMR cycle is 0.053 kW which can be neglected compared to the Claude cycle consumption (14.5 kW).

A comprehensive evaluation of a novel integrated system consisting of hydrogen boil-off gas reliquifying process and polymer exchange membrane fuel cell using exergoeconomic and Markov analyses

The price of constructing hydrogen generation units is very high and sometimes it is not possible to build them in the desired location, so the transfer of hydrogen from the hydrogen generation system to the units that need it is justified. Since the storage of hydrogen gas needs a large volume and its transportation is very complex, so if hydrogen is stored in liquid form, this problem can be resolved. In transporting liquid hydrogen (LH2) over long distances, owing to heat transfer to the environment, the LH2 vaporizes, forming boil-off gas (BOG). Herein, in lieu of only reliquifying the BOG, this study proposes and assesses a system employing the BOG partially as feed for a novel liquefaction process, and also the remaining utilized in a proton exchange membrane fuel cell (PEMFC) to generate power. Using the cold energy of the onsite liquid oxygen utility of the LH2 cargo vessel, the mixed refrigerant liquefaction cycle is further cooled down. In this regard, by using 130 kg/h BOG as input, 60.37 kg/h of liquid hydrogen is produced and the rest enters PEMFC with 552.7 kg/h oxygen to produce 1592 kW of power. The total thermal efficiency of the integrated system and electrical efficiency of the PEMFC is 83.18% and 68.76%, respectively. Regarding the liquefaction cycle, its specific power consumption (SPC) and coefficient of performance (COP) were achieved at 3.203 kWh/kgLH 2 and 0.1876, respectively. The results of exergy analysis show that the exergy destruction of the whole system is 937.4 kW and also its exergy efficiency is calculated to be 58.38%. Exergoeconomic and Markov analyses have also been applied to the integrated system. Also, by changing the important parameters of PEMFC, its optimal performance has been extracted.

Development of a new CO2 liquefaction system using the Linde–Hampson process, Kalina power generation unit, and flat plate solar collectors with Al2O3/H2O nanofluid

AbstractGreenhouse gas emissions into the atmosphere have had devastating environmental effects, including ozone depletion and global warming. Carbon dioxide (CO2) is widely used in oil and gas plants, the food industry, and as a working fluid in the power industry. Carbon dioxide is liquefied for long‐term storage, to be transported to remote areas, and is used for peak shaving in the power plants. Solar flat plate collectors and wasted heat from the CO2 liquefaction system can be used in power plant systems. Also, the use of nanoparticles in the collectors improves the thermal properties of the working fluid and increases the efficiency of solar collectors. This study has developed a new hybrid system for CO2 liquefaction using Linde–Hampson system, Kalina power generation unit, and flat plate solar collectors. The Linde–Hampson system's dissipated heat and solar collectors are used to supplying part of the power of the CO2 liquefaction system. The combined system produces 9416 kmol/h of liquid CO2 by absorbing 35.97 MW of power. The Kalina power generation unit provides 9.546 MW of power by absorbing 76.98 MW of the CO2 liquefaction cycle's dissipated heat and 91.18 MW from flat plate collectors. Based on the output of exergy assessment, exergy efficiency and exergy degradation of the developed integrated structure are 44.16% and 118.3 MW, respectively. Moreover, significant portions of exergy destruction in the combined process belong to solar collectors (74.68%), heat exchangers (12.47%), and compressors (7.157%), respectively. The use of Al2O3 nanoparticles in pure water has been investigated for heat transfer in flat panel solar collectors. According to the sensitivity analysis results, as the volume ratio of particles in nanofluid increases to 6%, the production capacity of the Kalina cycle and exergy efficiency improves to 9.56 MW and 9.522%, respectively. Also, as the pressure of the pumped fluid in the Kalina cycle increases from 800 to 1600 kPa, the exergy yield of the Kalina cycle and the exergy yield of the whole combined system increase to 36.34% and 44.26%, respectively.

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.

Exergy, economic and pinch analyses of a novel integrated structure for cryogenic energy storage and freshwater production using ejector refrigeration cycle, desalination unit, and natural gas combustion plant

This study aims to investigate an innovative hybrid structure of electricity storage at off-peak hours and its application at on-peak hours. In this paper, a novel hybrid system for energy storage and freshwater production using air compression and liquefaction system, ejector refrigeration cycle (ERC), thermal multi-effect desalination (MED) system, and natural gas combustion unit (GCU) is developed. The wasted heat of the liquefaction cycle is stored at off-peak hours to provide heat to the ERC and thermal desalination system and preheat the inlet streams to the turbines at on-peak hours. Also, wasted refrigeration of liquid air stream and refrigeration resulting from liquefied natural gas (LNG) regasification operations are stored at on-peak hours and are utilized in compressed air liquefaction at off-peak hours. This integrated structure produces 83.12 kg/s liquid air and 38.91 kg/s freshwater at off-peak hours with 58.24 MW power consumption. During on-peak hours, the liquid air along with 2.681 kg/s LNG enters the turbines after preheating and combustion and generated 122.6 MW power. Round-trip and storage efficiencies are obtained as 64.91% and 75.96%, respectively. Also, the exergy efficiencies of the energy storage system at off-peak hours, energy production system at on-peak hours and the whole system are estimated as 78.13%, 75.85%, and 65.92%, respectively. The results of the exergy study illustrate the reactors (43.37%), heat exchangers (26.76%), and throttle valves (10.58%) have the highest contribution to exergy destruction in the proposed combined structure, respectively. This study provides the refrigeration cycle integration with process core as hot and cold composite curves and pinch analysis. Pinch investigation is conducted on the system multi-stream exchangers and the heat exchanger networks are extracted. The economic analysis illustrates that the investment return period, the levelized cost of the product, and net annual benefit in the hybridized system are 4.877 years, 0.0919 US$/kWh, 78.38 MMUS$/year, respectively. The results of sensitivity analysis indicate the round-trip efficiency increases up to 65.32% by raising the pressure of the on-peak power generation cycle.

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.

Multi-objective thermo-economic optimization of Collins cycle

Many large scientific projects are emerging worldwide with the development of high energy physics nowadays. The indispensable subsystem, helium cryo-plants for such projects require extremely high energy consumption and total annual cost (TAC). In order to reduce energy consumption and TAC, multi-objective thermo-economic optimization that adopted non-dominated sorting genetic algorithm-II (NSGA-II) for helium cryo-plants is proposed in this work. As a typical helium liquefaction cycle, Collins cycle is selected as the optimization object. Both the exergetic efficiency (ηEx) and the TAC are set as objective parameters. The decision parameters, which include discharge pressure of compressor, flow fraction of expanders and effectiveness of heat exchangers, are optimized simultaneously. Linear programming technology of multidimensional analysis preference (LINMAP) is utilized as an example to select the optimal solution from the multi-objective optimization results. Compared to the maximum ηEx result, the LINMAP result reduces the TAC by 23.95% at the cost of 9.03% reduction in ηEx. In the proposed approach, eight decision parameters can be optimized simultaneously and the designed cryo-plant considers both economic and thermodynamic criteria, which is feasible for practical engineering project. Besides, alternative solution under limited investment situation is provided.

A novel integrated structure of hydrogen purification and liquefaction using natural gas steam reforming, organic Rankine cycle and photovoltaic panels

Nowadays, with the depletion of underground resources and the increase in carbon dioxide, humans are obliged to use renewable energy. Liquid hydrogen production as one of the clean energy carriers with proper storage capability and transport to distant places has attracted a lot of attention. One of the main problems of hydrogen liquefaction cycles is the high power consumption for purification and liquefaction. In this paper, a novel integrated structure of hydrogen purification and liquefaction is developed using natural gas steam reforming, organic Rankine cycle, and photovoltaic panels. This integrated structure produces 1020 kmol/h liquid hydrogen and 3321 kmol/h fuel gas. The energy and exergy efficiencies of the integrated structure are 74.15% and 72.41%, respectively. The specific power consumption of the pre-cooling and purification, liquefaction, and total hydrogen purification-liquefaction cycles are 5.909, 2.725, and 8.592 kWh/ kgLH₂, respectively. The exergy analysis of the integrated structure exhibits that the highest exergy destruction occurs in heat exchangers (44.51%) and reactors (17.59%). The impact of different parameters on the performance of the integrated structure is studied. The sensitivity analysis demonstrates that the power energy consumption decreases up to 7.881 kWh/ kgLH2 and exergy efficiency increases up to 0.801 when the methane content in inlet natural gas flow increases from 82 to 92 mol%. The thermal efficiency and productivity of the liquid hydrogen increase up to 0.7851 and 1084 kmol/h, respectively with the increase of reformer temperature from 550 °C to 650 °C.

A comparative investigation of thermodynamic performance and flow field structure of a modified Collins cycle-based helium turboexpander system

The optimum design of radial expansion turbine and nozzle (turboexpander) have a remarkable effect on the thermophysical performance of gas liquefaction cycles. The present study proposes a new mean-line design, sensitivity analysis, and optimization method to develop three turboexpander systems for a modified Collins cycle-based helium liquefaction system. The proposed method deals with the real gas equation of state to determine the turboexpander configurations and their performance at off-design conditions. The mean-line design approach integrated with different loss correlations has been performed using an in-house code in Matlab® environment. Furthermore, sensitivity analysis and artificial neural network-based optimization process of thirteen design coefficients and non-dimensional variables has been carried out which improves the off-design performance of the turboexpander up to 4.43%, 12.57%, and 16.36% for total-to-static efficiency, total losses, and power output respectively. Applying the aforementioned procedure, three turboexpanders have been designed. After that, a three-dimensional transient blade-row turbulent flow simulations have been carried out to stimulate the rotor-stator interaction at different operating conditions (25 bar & 80 K, 7 bar & 50 K, and 25 bar & 30 K) and rotational speeds (2.84 × 105, 1.61 × 105, and 2.75 × 105 rpm) using k-ω shear stress transport turbulence model. The commercial Navier-Stokes finite volume solver ANSYS CFX® has been used to study a comparative thermodynamic performance and flow field structures at different streamwise and spanwise directions of the entire flow passage. Additionally, the present numerical results have been validated with available experimental and computational data in the open literature. The present design, optimization, and numerical procedure presented herein will be advantageous for the future development of efficient small-scale turboexpander systems subjected to wide operating ranges.