• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2022.06a
• /
• pp.213-213
• /
• 2022

본 논문은 슬로싱(Sloshing) 거동에 놓인 극저온 액체수소 화물창의 BOG 예측을 위한 CFD 해석 절차를 다루고 있다. 특히, 적재율(Filling Ratio)에 따라 달라지는 열 유입과 그에 따른 액체수소의 기화 경향을 파악하기 위한 목적으로 수행되었다. 액체수소와 기체수소의 혼재에 의한 다상 열유동(Multiphase-Thermal flow) 특성을 반영하고 유동에 따른 강제 대류 현상을 열유속에 반영하기 위한 CFD 해석을 수행하였다. 다상 유동 모델의 정확성을 검증하기 위하여 슬로싱 실험의 압력 계측 값과 해석의 압력 값 및 자유수면(Free surface) 형상을 비교하였다. 소형 C-Type 독립형 액화수소 탱크를 대상으로 슬로싱 유동과 BOG 발생을 수치적으로 예측하였다. 해석 과정에서 VOF(Volume of fraction) 모델과 Eulerian 모델을 모두 적용하여, 액체수소에 유입되는 열 유속(Heat flux)의 예측 정확성을 비교하였다. 슬로싱 유무에 따라 액체수소에 유입되는 열 유속을 비교하여 슬로싱 유동의 포함 여부에 따른 BOG 발생량의 변화를 제시하였으며, 최종적으로 액체수소의 충전율(Filling ratio) 별로 BOG 발생량의 경향성을 제시하였다.

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

• Journal of the Korean Institute of Gas
• /
• v.25 no.6
• /
• pp.106-110
• /
• 2021

The emergence of new hydrogen-related technologies and new businesses has expanded the need to reorganize systems in related fields such as manufacturing liquefied hydrogen (charging), and manufacturing liquefied hydrogen storage tanks and containers, and special applications continue to increase. Accordingly, we intend to establish and implement measures to strengthen safety management to share the status of designation of special hydrogen-related regulatory projects and secure minimum safety.

• Journal of Navigation and Port Research
• /
• v.44 no.4
• /
• pp.283-290
• /
• 2020

BOG (Boil Off Gas) generation is unavoidable in the liquefied hydrogen carrier, and proper measures are necessary to prevent pressure problems inside the cargo tank. The BOG can be used as propulsion fuel for ships, and the remaining parts used for propulsion must be effectively managed, such as in the form of reliquefying or burning. This study proposes an BOG reliquefaction system optimized for a 160,000 m3 liquefied hydrogen carrier with a hydrogen propulsion system. The system comprises a hydrogen compression and helium refrigerant section, and increases the efficiency by effectively using the cold energy of the BOG discharged from the cargo tank. In this study, the system was evaluated through the exergy efficiency and SEC (Specific Energy Consumption) analysis according to the rate of the reliquefaction of the BOG while the hydrogen BOG with a supply temperature of -220℃ entered the reliquefaction system. As a result, it showed SEC of 4.11 kWh/kgLH2 and exergy efficiency of 60.1% at the rate of reliquefaction of 20%. And the parametric study of the effects of varying the hydrogen compression pressure, inlet temperature of the hydrogen expander, and the feed hydrogen temperature was conducted.

• Transactions of the Korean hydrogen and new energy society
• /
• v.31 no.1
• /
• pp.41-48
• /
• 2020

The present study discussed the thermodynamic analysis of the hydrogen liquefaction process to build a hydrogen liquefaction pilot plant with a small capacity (0.5 ton/day). A 2-stage Brayton cycle utilizing LNG/LN2 cold energy was suggested to be built in Korea for the hydrogen liquefaction pilot plant with a small capacity. Thermodynamic analysis on the effect of various variables on the efficiency of hydrogen liquefaction process was performed. As a result, the CASE in which the ortho-para conversion catalyst was infiltrated inside the heat exchanger showed the best process efficiency. Finally, thermodynamic analysis was performed on the effect of turbo expander compression ratio on the hydrogen liquefaction process and it was confirmed that an optimal turbo expander compression ratio exists.

• Transactions of the Korean hydrogen and new energy society
• /
• v.31 no.1
• /
• pp.33-40
• /
• 2020

As hydrogen utilization becomes more active recently, a large amount of hydrogen should be supplied safely. Among the three supply methods, liquefied hydrogen, which is an optimal method of storage and transportation convenience and high safety, has a low temperature of -253℃, which is complicated by the liquefaction process and consumes a lot of electricity, resulting in high operating costs. In order to reduce the electrical energy required for liquefaction and to raise the efficiency, hydrogen is cooled by using a mixed refrigerant in a precooling step. The electricity required for the precooling process of the mixed refrigerant can be reduced by using the cold energy of LNG. Actually, LNG cold energy is used in refrigeration warehouse and air liquefaction separation process, and a lot of power reduction is achieved. The purpose of this study is to replace the electric power by using LNG cold energy instead of the electric air-cooler to lower the temperature of the hydrogen and refrigerant that are increased due to the compression in the hydrogen liquefaction process. The required energy was obtained by simulating mixed refrigerant (MR) hydrogen liquefaction system with LNG cold heat and electric system. In addition, the power replacement rate of the electric process were obtained with the pressure, the temperature of LNG, the rate of latent heat utilization, and the hydrogen liquefaction capacity, Therefore, optimization of the hydrogen liquefaction system using LNG cold energy was carried out.

• Journal of the Korean Institute of Gas
• /
• v.27 no.4
• /
• pp.116-122
• /
• 2023

In addition to analyzing the hydrogen economy trends of the international community (Korea, the United States, Europe, Japan, etc.), which is being promoted to realize a carbon-neutral society, this study compared and analyzed the differences between the gaseous hydrogen refueling station, which is a key hydrogen-using facility close to the people, and a liquefied hydrogen refueling station that is scheduled to be built in the future. In addition, SAFETI, a quantitative risk assessment program, was used to analyze the safety of liquefied hydrogen refueling stations and In consideration of the individual and societal risks and the ranking of risks by facility, which are conditional allowable areas, a plan to improve safety such as facility layout was proposed

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.9 no.3
• /
• pp.284-291
• /
• 1997

A hydrogen liquefaction equipment by direct cooling has been designed and built at KIST. Cool-down characteristics and liquefaction performance of the equipment have been investigated. The hydrogen liquefaction equipment consists of a GM refrigerator, a liquefaction velssel, a radiation shield and a cryostat. It is found that the hydrogen starts to be liquefied in the liquefaction vessel after 40~50 minutes of cool-down from the gas state of 270K. The effect of natural convection phenomena of charged gas in liquefaction vessel on the cool-down characteristics is evaluated by comparing with those in vacuum of liquefaction vessel. It is seen that the cool-down time of a liquefaction vessel is substantially increased in vacuum environment of liquefaction vessel. The experiments have been performed for 1~5 atm of hydrogen pressure to investigate the influence of hydrogen pressure on the liquefaction rate and figure of merit(FOM). It is found that both liquefaction rate and FOM are increased as the charged hydrogen pressure is increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.11 no.3
• /
• pp.349-358
• /
• 1999

Thermodynamic cycle analysis has been performed to maximize the liquid amount for various hydrogen liquefaction systems using GM(Gifford-McMahon) refrigerator. Since the present authors' previous experiments showed that the liquefaction rate was approximately 5.1mg/s in a direct contact with a commercial GM refrigerator, the purpose of this study is to predict how much the liquefaction rate can be increased in different configurations and with improved heat exchanger performance. The optimal operating conditions have been analytically sought with real properties of normal hydrogen for the single-stage GM precooled L-H(Linde-Hampson) system, the two-stage GM direct contact system, the two-stage GM precooled L-H system and the two-stage helium GM-JT (Joule-Thomson) system. The maximum liquefaction rate has been predicted to be only about 7 times greater than the previous experiment, when the two-stage precooling is employed and the effectiveness of heat exchangers approaches to 99.0%. It is concluded that the liquefaction rate is limited mainly by the cooling capacity of the current GM refrigerators and a larger scale of hydrogen liquefaction is possible with a greater capacity of cryocooler at 60-70 K range.

• Journal of Energy Engineering
• /
• v.9 no.3
• /
• pp.228-236
• /
• 2000

본 연구에서는 순간 고온식 tubing-bomb reactor를 사용하여 41$0^{\circ}C$에서 Alaska산 아역청탄, 폐타이어, 폴리프로필렌 혼합물의 공동액화 시 액화특성 및 상승효과를 연구하였다. 석탄, 폐타이어와, 폴리프로필렌의 조성을 변화시키고 수소공여용매인 tetralin의 양을 변화시켜가며 공동액화를 진행했을 경우 공동액화율을 살펴보면, 무촉매 반응의 경우 폴리프로필렌의 양이 많아지면 tetralin이 첨가되지 않았을 경우 액화율이 증가하였으나 tetralin이 첨가되었을 경우 공동액화율이 감소하였다. 촉매 반응의 경우에는 모든 반응조건에서 상승효과가 나타났으며 폴리프로필렌의 양이 증가할수록 공동액화율이 증가하여 석탄 : 폐타이어 : 폴리프로필렌의 조성이 1:1:3에서 tetralin 4$m\ell$, Co-naphthenate 촉매 사용하였을 때가 최적의 반응조건으로 83%의 공동액화율을 나타내었다.