Simulation on a proposed large-scale liquid hydrogen plant using a multi-component refrigerant refrigeration system

A proposed liquid hydrogen plant using a multi-component refrigerant (MR) refrigeration system is explained in this paper. A cycle that is capable of producing 100 tons of liquid hydrogen per day is simulated. The MR system can be used to cool feed normal hydrogen gas from 25 °C to the equilibrium temperature of −193 °C with a high efficiency. In addition, for the transition from the equilibrium temperature of the hydrogen gas from −193 °C to −253 °C, the new proposed four H₂ Joule–Brayton cascade refrigeration system is recommended. The overall power consumption of the proposed plant is 5.35 kWh/kg_LH2, with an ideal minimum of 2.89 kWh/kg_LH2. The current plant in Ingolstadt is used as a reference, which has an energy consumption of 13.58 kWh/kg_LH2 and an efficiency of 21.28%: the efficiency of the proposed system is 54.02% or more, where this depends on the assumed efficiency values for the compressors and expanders. Moreover, the proposed system has some smaller-size heat exchangers, much smaller compressor motors, and smaller crankcase compressors. Thus, it could represent a plant with the lowest construction cost with respect to the amount of liquid hydrogen produced in comparison to today’s plants, e.g., in Ingolstadt and Leuna. Therefore, the proposed system has many improvements that serve as an example for future hydrogen liquefaction plants.     

Conventional and enhanced exergy analysis of a hydrogen liquefaction system

In the present work, conventional and enhanced exergy analyses were applied to the cryogenic liquefaction process of hydrogen gas. The hydrogen liquefaction unit consists of a multi-stage compressor, booster compressor-turbine pair, and heat exchanger block. Convectional exergy analysis cannot identify parts of exergy inefficiencies. In addition, by convectional exergy analysis, it cannot determine inevitable exergy losses that occur due to technological limits. For this reason, enhanced exergy analysis should be applied to the system. The exergy destruction affecting the exergy efficiency of the hydrogen liquefaction unit was investigated in detail. This study suggests an enhanced exergy analysis of a cryogenic liquefaction system. According to the results of the convectional exergy analysis, exergy efficiency of the whole liquefaction process are 32.22%. Also, the highest and lowest endogenous exergy destruction among whole components is calculated as 9563 kW and 92.83 kW in the turbine and CM-1, respectively. With these calculated results, the potential for improvement in the turbine in the liquefaction system was found to be high.     

A novel hydrogen liquefaction process configuration with combined mixed refrigerant systems

A novel large-scale plant for hydrogen liquefying is proposed and analyzed. The liquid hydrogen production rate of the proposed plant is 100 tons per day to provide the required LH₂ for a large urban area with 100,000–200,000 hydrogen vehicles supply. In the pre-cooling section of the process, a new mixed refrigerant (MR) refrigeration cycle, combined with a Joule–Brayton refrigeration cycle, precool gaseous hydrogen feed from 25 °C to the temperature ?198.2 °C. A new refrigeration system with six simple Linde–Hampson cascade cycles cools low-temperature gaseous hydrogen from ?198.2 °C to temperature ?252.2 °C. The process specific energy consumption (SEC) is $7.69{\text{kWh/kg}}_{L{H}_2}$ which minimum value is $2.89{\text{kWh/kg}}_{L{H}_2}$ in ideal conditions. The exergy efficiency of the system is 39.5%, which is considerably higher than the existing hydrogen liquefier plants around the world. However, assuming more efficiency values for the equipment can improve it. The energy analysis specifies that coefficient of performance (COP) of the process is 0.1710 which is a high quantity of its kind between other similar processes. Effect of various refrigerant components concentration, discharge pressure of the high pressure compressors of the pre-cooling section, and hydrogen feed pressure on the process COP, exergy efficiency, and SEC are investigated. After that, a new MR will be offered for the cryogenic section of the plant. The system improvements are considerable comparing to current hydrogen liquefying plants, therefore, the proposed conceptual system can be used for future hydrogen liquefaction plants design.     

Development of large-scale hydrogen liquefaction processes from 1898 to 2009

This paper presents a review of the development of large-scale hydrogen liquefaction processes throughout the world from 1898 to 2009. First, there is a concise literature review including numerous past, present, and future designs given such as the first hydrogen liquefaction device, long time ago simple theoretical processes, today's actual plants with efficiencies 20–30%, a list of the capacity and location of every hydrogen liquefaction plant in the world, and some modern more efficient proposed conceptual plants with efficiencies 40–50%. After that, further information about the development and improvement potential of future large-scale liquid hydrogen liquefaction plants is given. It is found that every current plant is based on the pre-cooled Claude system, which is still the same as was 50 years ago with little improvement. Methods to resolve the challenges of the future plants include proposing completely new configurations and efficient systems coupled with improved efficiencies of the main system components such as compressors, expanders, and heat exchangers. Finally, a summary and comparison of the process efficiencies are described, including a newly proposed Multi-component Refrigerant (MR) system being developed by NTNU and SINTEF Energy Research AS.     

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/kg_LH2, 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.     

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.     

Exergy analysis of solar assisted double effect absorption refrigeration system

Exergy or the available energy is based on the second law of thermodynamics and goes back to Maxwell and Gibbs. It is the exergy content and not the energy content, that truly represents the potential of the substance to cause change. Exergy is the only rational basis for evaluating the system performance. The aim of this project is to study in detail the exergy variation in the solar assisted absorption system. The influence of the cycle parameters are analysed on the basis of first law and second law effectiveness and the results indicated various ways of improving system performance by better design. Also a better quality of the evaporator has more effect on the system performance than the better quality of other components. It was shown that second law analysis quantitatively visualizes losses within a system and gives clear trends for optimization.     

The performance assessment of a combined organic Rankine-vapor compression refrigeration cycle aided hydrogen liquefaction

In this study, the performance of the combined cooling cycle with the Organic Rankine power cycle, which provides cooling of the hydrogen at the compressor inlet which compresses the constant temperature in the Claude cycle used for hydrogen liquefaction, on the system is examined. The Organic Rankine combined cooling cycle was considered to be using a geothermal source with a flow rate of 120 kg/s at a temperature of 200 °C. The first and second law performance evaluations of the whole system were made depending on the heat energy at different levels taken from the geothermal source. The thermodynamic analysis of the equipment making up the system has been done in detail. The temperature values at which the hydrogen can be effectively cooled were determined in the presented combined system. The efficiency coefficient of the total system was calculated based on varying pre-cooling values. As a result of the study, it was determined that cold entry of hydrogen into the Claude cycle reduced the energy consumption required for liquefaction. Amount of hydrogen cooled to specified temperature increase by increase in mass flow of geothermal water and its temperature. Liquefaction cost is calculated to be 0.995 $/kg H₂ and electricity produced by itself is calculated to be 0.025 $/kWh by the new model of liquefaction system. Cost of the liquefaction in the proposed system is about 39.7% lower than direct value of hydrogen liquefaction of 1.650 $/kg given in the literature.     

Analysis and assessment of an advanced hydrogen liquefaction system

In the present work, an advanced hydrogen liquefaction system with catalyst infused heat exchangers is proposed, analyzed and assessed energetically and exergetically. The analysis starts with exergetic considerations on hydrogen liquefaction using different alternatives of pre-cooling including the conversion from normal to parahydrogen. It further explains the fundamentals of a proposed liquefaction process. The goal is then to assess the proposed system, make modifications and improve the system. The present system covers all of these portions of a hydrogen liquefaction system with an ultimate goal of achieving a sustainable and environmentally harmless system. The proposed hydrogen liquefaction system is simulated in the Aspen Plus and the performance of the system is measured through energy and exergy efficiencies. The resulting energy efficiency of the system is calculated to be 15.4%, and the exergy efficiency of the system is found to be 11.5%.     

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.     

Performance analysis and optimization of a hydrogen liquefaction system assisted by geothermal absorption precooling refrigeration cycle

The present paper deals with the hydrogen liquefaction with absorption precooling cycle assisted by geothermal water is modeled and analyzed. Uses geothermal heat in an absorption refrigeration process to precool the hydrogen gas is liquefied in a liquefaction cycle. High-temperature geothermal water using the absorption refrigeration cycle is used to decrease electricity work consumption in the gas liquefaction cycle. The thermoeconomic optimization procedure is applied using the genetic algorithm method to the hydrogen liquefaction system. The objective is to minimize the unit cost of hydrogen liquefaction of the composed system. Based on optimization calculations, hydrogen gas can be cooled down to ?30 °C in the precooling cycle. This allows the exergetic cost of hydrogen gas to be reduced to be 20.16 $/GJ (2.42 $/kg LH₂). The optimized exergetic cost of liquefied hydrogen is 4.905 $/GJ (1.349 $/kg LH₂), respectively.     

Energetic and exergetic assessments of a novel solar power tower based multigeneration system with hydrogen production and liquefaction

In this article, a thermodynamic investigation of solar power tower assisted multigeneration system with hydrogen production and liquefaction is presented for more environmentally-benign multigenerational outputs. The proposed multigeneration system is consisted of mainly eight sub-systems, such as a solar power tower, a high temperature solid oxide steam electrolyzer, a steam Rankine cycle with two turbines, a hydrogen generation and liquefaction cycle, a quadruple effect absorption cooling process, a drying process, a membrane distillation unit and a domestic hot water tank to supply hydrogen, electrical power, heating, cooling, dry products, fresh and hot water generation for a community. The energetic and exergetic efficiencies for the performance of the present multigeneration system are found as 65.17% and 62.35%, respectively. Also, numerous operating conditions and parameters of the systems and their effects on the respective energy and exergy efficiencies are investigated, evaluated and discussed in this study. A parametric study is carried out to analyze the impact of various system design indicators on the sub-systems, exergy destruction rates and exergetic efficiencies and COPs. In addition, the impacts of varying the ambient temperature and solar radiation intensity on the irreversibility and exergetic performance for the present multigeneration system and its components are investigated and evaluated comparatively. According to the modeling results, the solar irradiation intensity is found to be the most influential parameter among other conditions and factors on system performance.     

Analysis and assessment of a novel hydrogen liquefaction process

In the present study, a novel supercritical hydrogen liquefaction process based on helium cooled hydrogen liquefaction cycles to produce liquid hydrogen is thermodynamically analyzed and assessed. The exergy analysis approach is used to study the exergy destruction rates in each component and the process efficiency. The energy and exergy efficiencies of liquefaction process are found to be 70.12% and 57.13%, respectively. In addition, to investigate the process efficiency more comprehensively to see how it is affected by varying process parameters and operating conditions, some parametric studies are undertaken to examine the impacts of different design variables on the energy efficiency, exergy efficiency and exergy destruction rates of the hydrogen liquefaction process. The results show that the increases in the cycle pressure of hydrogen and helium result in increasing hydrogen liquefaction process exergy efficiency and providing a smaller pinch point temperature difference of catalyst beds related with the heat transfer surface area and more efficiently process.     

An exergy analysis of small-scale liquefied natural gas (LNG) liquefaction processes

Four processes for small-scale liquefied natural gas (LNG) production are evaluated. These include a single-stage mixed refrigerant (SMR), a two-stage expander nitrogen refrigerant and two open-loop expander processes. Steady-state simulations were undertaken to ensure that each process was compared on an identical basis, was fully optimised and was in agreement with published results. Composite curves for the feed and recycle streams and the refrigerant or cold recycle stream showed the degree of optimisation available within each process. The full exergy analysis showed the relative contributions to the total shaft work requirements, with the lowest being the SMR process. The lower efficiency of the expander-driven compressors is the main difference between processes. A more general comparison suggested that the nitrogen refrigerant process and the New LNG open-loop process are the leading candidates for offshore compact LNG production.     

Exergy analysis of a hybrid solar hydrogen system with activated carbon storage

A proposed hybrid solar hydrogen system with activated carbon storage for residential power generation is assessed using exergy analysis. Energy and exergy balances are applied to determine exergy flows and efficiencies for individual devices and the overall system. A ‘base case’ analysis considers the proposed system without modification, while a ‘modified case’ extends the base case by considering the possibility of multiple product outputs. It is determined that solar photovoltaic-based sub-systems have the lowest exergy efficiencies (14-18%) and offer the most potential for improvement. A comparison of these two scenarios shows that the additional outputs raise the exergy efficiency of the modified case (11%) relative to the base case (4.0%). An investigation of the energy and exergy efficiencies of separate devices illustrates how energy analyses can be misleading. The hybrid system is expected to have several environmental benefits, which may offset to some degree economic barriers to implementation.     

Experimental study on small-scale hydrogen liquefaction of 0.5 L/h

A small-scale hydrogen liquefaction device based on two-stage G-M refrigerator was designed and manufactured. Many practical operation processes on the liquefaction device were conducted in the open-air test base. The experimental results shown that 1) The direct liquefaction scheme of micro-positive pressure with normal temperature hydrogen realized by two-stage pressure reducing valve was feasible and effective; 2) Design of four-stage heat exchanger for G-M refrigerator cold head was reasonable and reliable; 3) The liquefaction rate in pure hydrogen was 0.47 L/h, and liquefaction pressure can maintain the range of about 120 kPa～160 kPa; 4) After venting hydrogen-helium mixture, the liquefaction rate of hydrogen was 0.439 L/h again. In other words, the previously filled helium in the liquid hydrogen Dewar could be discharged through multiple venting method. The residue helium had little effect on the hydrogen liquefaction rate; 5) The scheme of simultaneous liquefaction and transmission was proved to be feasible; 6) Operation process experience and safety precautions on the hydrogen liquefaction were summarized. The testing results provided a technical support for design and operation of small-scale hydrogen liquefactions.     

Exergetic analysis of the refrigeration system in ethylene and propylene production process

The exergetic analysis is a tool that has been used successfully in many studies aiming a more rational energy use reducing the cost of the processes. With this analysis it is possible to perform an evaluation of the overall process, locating and quantifying the degradation of exergy. In this context, the present work aimed the exergetic analysis of the refrigeration cycles in ethylene and propylene production process, calculating the loss of exergy, in order to propose changes in the operational variables of the cycles used, trying to reduce the rate of destroyed exergy in the process. The commercial simulator Hysys^© (version 3.2) was used to obtain thermodynamic properties of the process streams and to perform mass and energy balances. The application of new operational conditions in these cycles resulted in a reduction of about 13% of the losses of exergy for the refrigeration system of the process.     

Exergy analysis of a simulation of the sulfuric acid decomposition process of the SI cycle for nuclear hydrogen production

This article details comprehensive energy and exergy analyses of the sulfuric acid decomposition process of the sulfur–iodine (SI) thermochemical cycle for hydrogen production. Energy and exergy efficiencies of the proposed process were evaluated over a variety of reaction temperatures and pressures. At an atmospheric temperature of 25 °C, the calculated values of exergy destruction of the H₂SO₄ decomposer ranged between 157 kJ/mol and 360 kJ/mol over reaction temperatures of 800–1000 °C and pressures between 1 and 50 atm. It was shown that the exergy efficiency of the H₂SO₄ decomposer improved with an increase in reaction temperature, while reaction pressure had a negative effect on exergy efficiency.