• Transactions of the Korean hydrogen and new energy society
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• v.7 no.2
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• pp.121-128
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• 1996

A direct cooling equipment for hydrogen liquefaction has been developed and tested. A direct cooling equipment consists of a liquefaction vessel, a radiation shield, a cryostat and a GM refrigerator. The cool-down and warm-up characteristics of the liquefaction apparatus have been investigated in detail. It is found that the hydrogen starts to be liquefied in the liquefaction vessel after 45 minutes of cool-down. The cool-down and warm-up tests of helium gas are also performed. The cool-down and warm-up characteristics of helium gas are found to be very different from those of hydrogen gas, since helium is not liquefied under the present operating conditions. When the liquefaction vessel is evacuated, natural convection phenomena of charged gas in liquefaction vessel can be removed. It is seen that the cool-down time of liquefaction vessel is substantially increased in vacuum environment.

• Progress in Superconductivity and Cryogenics
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• v.25 no.3
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• pp.49-55
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• 2023

This paper presents the design of a re-liquefaction system as a BOG (boil-off gas) handling process in liquid hydrogen transport vessels. The total capacity of the re-liquefaction system was assumed to be 3 ton/day, with a BOR (boil-off rate) of 0.2 %/day inside the cargo. The re-liquefaction cycle was devised using the He-Brayton Cycle, incorporating considerations of BOG capacity and operational stability. The primary components of the system, such as compressors, expanders, and heat exchangers, were selected to meet domestically available specifications. Case studies were conducted based on the specifications of the components to determine the optimal design parameters for the re-liquefaction system. This encompassed variables such as helium mass flow rate, the number of compressors, compressor inlet pressure and compression ratio, as well as the quantity and composition of expanders. Additionally, an analysis of exergy destruction and exergy efficiency was carried out for the components within the system. Remarkably, while previous design studies of BOG re-liquefaction systems for liquid hydrogen vessels were confined to theoretical and analytical realms, this research distinguishes itself by accounting for practical implementation through equipment and system design.

• Applied Chemistry for Engineering
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• v.31 no.2
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• pp.153-163
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• 2020

Compared to gaeous hydrogen, liquid hydrogen has approximately 1/800 volume, 800 times higher volumetric energy density at the same pressure, and the advantage of lower explosion risk and easier transportation than gaseous hydrogen. However, hydrogen liquefaction requires larger scale facility investment than simple compression storage method. Therefore, the research on energy-saving hydrogen liquefaction processes is highly necessary. In this study, helium/neon (mole ratio 80 : 20) refrigeration cycle was investigated as the main refrigeration process for hydrogen liquefaction. Process simulation for less energy consumption were carried out using PRO/II with PROVISION V10.2 of AVEVA. For hydrogen liquefaction, energy consumption was compared in three cases: Using a helium/neon refrigerant cycle, a SMR+helium/neon refrigerant cycle, and a C3-MR+helium/neon refrigerant cycle. As a result, the total power consumptions of compressors required to liquefy 1 kg of hydrogen are 16.3, 7.03 and 6.64 kWh, respectively. Therefore, it can be deduced that energy usage is greatly reduced in the hydrogen liquefaction process when the pre-cooling is performed using the SMR process or the C3MR process, which have already been commercialized, rather than using only the helium/neon refrigeration cycle for the hydrogen liquefaction process.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.3
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• pp.180-188
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• 2021

This paper conducted a study on the ortho-para hydrogen conversion in the cryogenic heat exchanger filled with catalysts for hydrogen liquefaction by utilizing the numerical model of plate-fin heat exchanger considering catalytic reaction of ortho-para hydrogen conversion, heat and mass transfer phenomena and fluid dynamics in a porous medium. Various numerical analyzes were performed to investigate the characteristics of ortho-para hydrogen conversion, the effects of space velocity and activated catalyst performance.

• Transactions of the Korean hydrogen and new energy society
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• v.26 no.4
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• pp.301-307
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• 2015

We present a study of hydrogen liquefaction using the CFD (Computational Fluid Dynamics) program. Liquid hydrogen has been evaluated as the best storage method because of high energy per unit mass than gas hydrogen, but efficient hydrogen liquefaction and storage are needed in order to apply actual industrial. In this study, we use the CFD program that apply navier-stokes equation. A hydrogen is cooled by heat transfer with the while passing gas hydrogen through Cu tube. We change diameter and flow rate and observe a change of the temperature and flow rate of gas hydrogen passing through Cu tube. As a result of, less flow rate and larger diameter are confirmed that liquefaction is more well. Ultimately, When we simulate the hydrogen liquefaction by using CFD program, and find optimum results, it is expected to contribute to the more effective and economical aspects such as time and cost.

• Progress in Superconductivity and Cryogenics
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• v.22 no.3
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• pp.20-24
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• 2020

The purpose of this analytic study is to design and examine an efficient hydrogen liquefaction cycle by using a pre-cooler. The liquefaction cycle is primarily comprised of a pre-cooler and a refrigerator. The fed hydrogen gas is cooled down from ambient temperature (300 K) to the pre-cooling coolant temperature (either 77 K or 120 K approximately) through the pre-cooler. There are two pre-cooling methods: a single pre-coolant pre-cooler and a cascade pre-cooler which uses two levels of pre-coolants. After heat exchanging with the pre-cooler, the hydrogen gas is further cooled and finally liquefied through the refrigerator. The working fluids of the potential pre-cooling cycle are selected as liquid nitrogen and liquefied natural gas. A commercial software Aspen HYSYS is utilized to perform the numerical simulation of the proposed liquefaction cycle. Efficiency is compared with respect to the various conditions of the heat exchanging part of the pre-cooler. The analysis results show that the cascade method is more efficient, and the heat exchanging part of the pre-coolers should have specific UA ratios to maximize both spatial and energy efficiencies. This paper presents the quantitative performance of the pre-cooler in the hydrogen liquefaction cycle in detail, which shall be useful for designing an energy-efficient liquefaction system.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.6
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• pp.490-498
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• 2019

The intermittent electric power supply of renewable energy can have extremely negative effect on power grid, so long-term and large-scale storage for energy released from renewable energy source is required for ensuring a stable supply of electric power. Power to gas which can convert and store the surplus electric power as hydrogen through water electrolysis is being actively studied in response to increasing supply of renewable energy. In this paper, we proposed the novel concept of hydrogen liquefaction process combined with pre-cooling process using the liquid air. It is that hydrogen converted from surplus electric power of renewable energy was liquefied through the hydrogen liquefaction process and vaporization heat of liquid hydrogen was conversely recovered to liquid air from ambient air. Moreover, Comparisons of specific energy consumption (kWh/kg) saved for using the liquid air pre-cooling was quantitatively conducted through the performance analysis. Consequently, about 12% of specific energy consumption of hydrogen liquefaction process was reduced with introducing liquid air for pre-cooling and optimal design point of helium Brayton cycle was identified by sensitivity analysis on change of compression/expansion ratio.

• Journal of the Korean Institute of Gas
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• v.24 no.4
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• pp.56-61
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• 2020

For the hydrogen liquefaction, the large amount of energy is consumed, due to precooling, liquefaction and o-p conversion processes. The aim of this work is to improve the performance of hydrogen liquefaction process by introducing the new energy saving processes, that are the liquid nitrogen precooling process by using LNG cold energy, and the new design of cold box insulation using cold air circulation. The results show that the indirect use of LNG cold energy in precooling process enables not only to get energy saving, but to make safer operation of liquefaction plant. In new cold box, the energy loss of equipments could be reduced by nearly 35%~50% compared to the present perlite insulation, if insulation structure is organised as 3mm steel wall/20cm PUF/5cm air/20cm PUF/equipment. Additionally the equipments installed in cold box can get cooling effect, if the temperature is higher than the temperature of cold air. The application of this results can gives to increase the liquid yield of about 50% substantially in industrial hydrogen liquefaction plant.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.5
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• pp.534-540
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• 2022

Liquid hydrogen has the best storage capacity per unit mass and is economical among storage methods for using hydrogen as fuel. As the demand for hydrogen increases, the need to develop a storage and supply system of liquid hydrogen is emphasizing. In order to liquefy hydrogen, it is necessary to pre-cool it to a maximum inversion temperature of -253℃. The Gifford-McMahon (GM) refrigerator is the most reliable and commercialized refrigerator among small-capacity cryogenic refrigerators, which can extract high-efficiency hydrogen through liquefied hydrogen production and boil of gas re-liquefaction. Therefore, in this study, the optimal conditions for liquefying gas hydrogen were sought using the GM cryocooler. The process was simulated by PRO/II under various cooling capacities of the GM refrigerator. In addition, the flow rate of hydrogen was calculated by comparing with specific refrigerator capacity depending on the pressure and flow rate of a refrigerant medium, helium. Simulations were performed to investigate the optimal values of the liquefaction flow rate and compression pressure, which aim for the peak refrigeration effect. Based on this, a liquefaction system can be selected in consideration of the cycle configuration and the performance of the refrigerator.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.5
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• pp.430-438
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• 2008

Siberian spruce, found in the northern temperature and boreal regions of the earth, is usable biomass as fuels. In this study, parameters of thermochemical degradation by pyrolysis-liquefaction reaction of siberian spruce such as the effect of reaction temperature, reaction time and degradation products and energy yields were investigated. The liquid products from pyrolysis-liquefaction of siberian spruce contained various kinds of cyclicketones, cresols, dimethyl phenols and benzenediols. Combustion heating value of liquid products from pyrolysis-liquefaction conversion processes was in the range of $7,650{\sim}7,800cal/g$. The energy yield in pyrolysis-liquefaction of siberian spruce was as high as 69.5% after 40min of reaction at $400^{\circ}C$. The liquid products from the thermochemical conversion of siberian spruce could be used as high octane value fuels and fuel additives.