[논문]Effectiveness analysis of pre-cooling methods on hydrogen liquefaction process

Yang, Yejun; Park, Taejin; Kwon, Dohoon; Jin, Lingxue; Jeong, Sangkwon

doi:10.9714/psac.2020.22.3.020

Effectiveness analysis of pre-cooling methods on hydrogen liquefaction process 원문보기

Progress in superconductivity and cryogenics : PSAC, v.22 no.3, 2020년, pp.20 - 24

Yang, Yejun (Cryogenic Engineering Laboratory, Korea Advanced Institute of Science and Technology) , Park, Taejin (Cryogenic Engineering Laboratory, Korea Advanced Institute of Science and Technology) , Kwon, Dohoon (Cryogenic Engineering Laboratory, Korea Advanced Institute of Science and Technology) , Jin, Lingxue (Cryogenic Engineering Laboratory, Korea Advanced Institute of Science and Technology) , Jeong, Sangkwon (Cryogenic Engineering Laboratory, Korea Advanced Institute of Science and Technology)

Abstract ▼ AI-Helper

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.

주제어

표/그림 (7)

그림 Fig. 1. Schematics of pre-cooler which reutilizes the cold exergy of boil-off pre-coolant (left) and equivalent schematic composed of heat exchangers (right).
그림 Fig. 2. Three types of pre-cooling method.
그림 Fig. 3. Variation of required amount of the pre-coolant and UA according to $T_2$. (All the values are obtained for 1 kg-$H_2$/s.)
$Fig. 4. Variation of total required liquefaction work according to <TEX>${UA}_{vapor}$</TEX> ratio. (UAvapor ratio is the ratio of the UA of the vapor heat exchanging part to the total UA; All the values are obtained for 1 kg-<TEX>$H_2$</TEX>/s.)$ 그림 Fig. 4. Variation of total required liquefaction work according to ${UA}_{vapor}$ ratio. (UAvapor ratio is the ratio of the UA of the vapor heat exchanging part to the total UA; All the values are obtained for 1 kg-$H_2$/s.)
그림 Fig. 5. The required work according to UA ratio of each heat exchanging part in cascade pre-cooling method (All the values are obtained for 1 kg-$H_2$/s.)
그림 Fig. 6. Minimum required work for each pre-cooling method (All the values are obtained for 1 kg-$H_2$/s.)
그림 Fig. 7. The minimum required work for hydrogen liquefaction according to FOM for pre-coolant production when total UA is 70 kW/K. (All the values are obtained for1 kg-$H_2$/s.)

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문제 정의

In this study, we aim to find an effective pre-cooling method on hydrogen liquefaction process. Required works for liquefying the hydrogen are numerically calculated under various conditions of the pre-cooler and the results are discussed.

가설 설정

This assumption may result in the overestimation of the required work of the liquefying refrigerator because as shown in Eq. (2), the COP of the refrigerator is proportional to the cold end temperature. In practical application of the refrigerators, the cold end temperature is set to close to the temperature of the cooling target because big temperature difference between them will lead to large entropy generation as a result.
2. The pre-cooling cycle using each pre-coolant and the cascade pre-cooling cycle using both pre-coolants were compared. In addition, the efficiency changes of the entire cycle according to the UA ratio in the pre-cooler were analyzed.
3. When the total UA was fixed, there was a specific UA ratio that maximizes efficiency. Thus, it was important that selecting the optimum portion of the vapor heat exchanging part in the pre-cooler when the total UA of the pre-cooler is limited.

제안 방법

This configuration is considered just for realistic manufacturability. Based on this illustration, the numerical analysis is conducted to confirm the effect of reutilizing the cold exergy of boil-off pre-coolant.
In this study, the efficiency changes of hydrogen liquefaction cycle according to the pre-cooling method and the level of cold exergy reutilization are analyzed. The detailed process analysis is conducted by a commercial analyzer, Aspen HYSYS.
The methodology in this study can be adapted to design the hydrogen liquefaction cycle especially for finding the proper pre-cooling method and the optimum UA ratio inside the pre-cooler.

대상 데이터

per second, where U is the overall heat transfer coefficient, and A is the area of the heat exchanger. The analysis is conducted using two different pre-coolants, LNG (CH4) and LN₂.

데이터처리

In this study, the efficiency changes of hydrogen liquefaction cycle according to the pre-cooling method and the level of cold exergy reutilization are analyzed. The detailed process analysis is conducted by a commercial analyzer, Aspen HYSYS. The physical properties of fluids are calculated by Peng-Robinson equation of state.

이론/모형

The detailed process analysis is conducted by a commercial analyzer, Aspen HYSYS. The physical properties of fluids are calculated by Peng-Robinson equation of state. The properties of methane (CH4) are utilized to simulate LNG for simplicity.

성능/효과

The results of this study quantitatively show that the efficiency of the hydrogen liquefaction sensitively depends on the pre-cooling conditions and the UA ratio of heat exchanging parts. Therefore, to design the hydrogen liquefaction cycle, the optimum pre-cooling method and UA ratio should be carefully determined according to the conditions, such as the type of pre-coolant and the FOM for pre-coolant production.

참고문헌 (8)

H. Chang, K. Ryu, J. Baik, "Thermodynamic design of hydrogen liquefaction systems with helium or neon Brayton refrigerator," Cryogenics, vol. 91, pp. 68-76, 2018.

상세보기
C. Lee, J. Lee, S. Jeong, "Design of closed-loop nitrogen Joule-Thomson refrigeration cycle for 67 K with sub-atmospheric device," Journal of the Korea Institute of Applied Superconductivity and Cryogenics, vol. 15, pp. 45-50, 2013

원문보기 상세보기
D. O. Berstad, J. H. Stang, P. Neksa, "Large-scale hydrogen liquefier utilising mixed-refrigerant pre-cooling," International Journal of Hydrogen Energy, vol. 35, Issue 10, pp 4512-4523, 2010.

상세보기
A. Kuendig, K. Loehlein, G. J. Kramer, J. Huijsmans, "Large scale hydrogen liquefaction in combination with LNG re-gasification," In Proceedings of the 16th world hydrogen energy conference, pp. 3326-3333, 2006.
R. F. Barron, Cryogenic Systems, Oxford University Press, 1985.
S. Jeong, L. Jin, "Thermodynamic performance comparison of a two-stage cryocooler and cascade cryocoolers with thermal anchoring for precooling purpose", Cryogenics, vol. 99, pp 32-38, 2019.

상세보기
H. Chang, "A thermodynamic review of cryogenic refrigeration cycles for liquefaction of natural gas," Cryogenics, vol. 72, Part 2, pp. 127-147, 2015.

상세보기
V.S. Bisht, Thermodynamic Analysis of Kapitza Cycle based on Nitrogen Liquefaction. IOSR Journal of Engineering (IOSRJEN), vol. 4, Issue 5: V6, pp 38-44, 2014.

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