57 research outputs found
An EOS-Based Dynamic Modelling for Depressurisation of Pressure Vessels Containing Hydrocarbons
No full text© 2016, Offshore Technology Conference Managing overpressure of a pressure vessel is critical to the safety of a hydrocarbon producing facility. As a result of rapid depressurisation called blowdown, temperature of the pressure vessel wall can be severely decreased. For these reasons, dynamic behavior of properties (e.g., temperature in pressure vessels) during depressurisation has to be analyzed for material selection and design process. In this work, a dynamic model for depressurisation was developed to simulate the low temperature phenomena inside a pressure vessel under depressurzation. Thermodynamic and transport property calculation theories were used to describe hydrocarbon systems. Heat tranfers between internal fluid and inner wall surface and between surroundings and outer vessel wall surfaces were considered. Temperature of each vessel wall surface was calculated using transient conduction temperature profile. The result showed good fitting to reported experimental data.N
Novel propane-free mixed refrigerant integrated with nitrogen expansion natural gas liquefaction process for offshore units
No full textThe presence of propane inventory in offshore liquefaction processes increases the concerns for platform safety. To address this, we propose a novel liquefaction process that integrates propane-free mixed refrigerant and nitrogen expander cycles (MR-N-2). The proposed design adopts the advantages of both nitrogen expander and single mixed refrigerant (SMR) processes. The process was rigorously simulated using Aspen HYSYS, and the specific energy consumption was optimized as an objective function using the genetic algorithm technique. Additionally, the MR-N-2 process was investigated using exergy and sensitivity analyses to compare the obtained results with those of the previous studies. The results verify that both liquefaction and exergy efficiencies are improved by 27.15% and 14.92%, respectively, in comparison with those of the base case. Moreover, the MR-N-2 process exhibits enhanced energy efficiency compared to that of the various existing nitrogen expander-based processes. The energy savings of the proposed method varies between 3.2% and 61.7%, and the cycle capacity is 22.43% better than that of the SMR process. (C) 2021 Elsevier Ltd. All rights reserved.N
Simulation methodology for hydrogen liquefaction process design considering hydrogen characteristics
No full text© 2022 Hydrogen Energy Publications LLCOne promising method to improve the storage capacity of hydrogen is to liquefy it, resulting in high energy density. However, liquefying hydrogen is a challenging task because hydrogen characteristics, such as a boiling point at a cryogenic temperature and changes in equilibrium compositions of spin isomers constituting hydrogen molecules, must be considered. For a design of a hydrogen liquefaction process, it is necessary to use an equation of state that can accurately calculate the properties of hydrogen, and to consider conversion reactions of the spin isomers. In this study, it is confirmed that the modified Benedict-Webb-Rubin equation is a suitable equation of state for simulating hydrogen liquefaction processes and that an equivalent model used in this study for the conversion reactions of the spin isomers shows reasonable results. Furthermore, the economic feasibility of the designed hydrogen liquefaction process is investigated based on energy optimization and economic analysis.N
Process design of onboard membrane carbon capture and liquefaction systems for LNG-fueled ships
No full textThis study proposes an onboard membrane carbon capture and liquefaction system for LNG-fueled ships to satisfy the IMO's 2050 greenhouse gas reduction targets. The exhaust gas from a natural gas ship has a low CO2 fraction (similar to 3%) and high O-2 fraction (similar to 16%) compared to the flue gas from power plants. Herein, considering the above distinguishing features, a membrane carbon capture and liquefaction system has been proposed that is energy efficient and compact for the application of ships. To ascertain the performance of the proposed membrane-based system, it is compared to an amine-based onboard system in terms of energy consumption and major equipment size. This work evaluates four process configurations by varying the number of membrane stages and associated liquefaction processes at different CO2/N-2 selectivity and CO2 permeance. The results show that energy consumption (3.98 GJ(e)/t(LCO2)) is higher than the amine-based system (3.07 GJ(e)/t(LCO2)) at the CO2/N-2 selectivity of 50, but it can be decreased to 3.14 and 2.82 (GJ(e)/t(LCO2)) with an improved selectivity of 100 and 150, respectively. The major equipment size decreases to 54%, 28%, and 20% of the amine-based system when the permeance is 1000, 2000, and 3000 GPU, respectively. The results indicate that the new onboard membrane carbon capture and liquefaction system can be a competitive solution for the IMO's greenhouse gas reduction targets for 2050.N
Performance Degradation of the Monoethylene Glycol Regeneration Process in the Presence of Electrolytes: Pilot-Scale Experiments and Dynamic Simulations
No full textSafe production of natural gas from offshore gas fields would rely on the injection and regeneration of mono-ethylene glycol (MEG) to inhibit hydrate formation as well as corrosion and scale issues in subsea flowlines. In this study, we investigated the solubilities of NaCl and the vapor pressure of aqueous MEG solutions experimentally with a laboratory-scale apparatus. A thermodynamic model adopting the electrolyte NRTL-RK was developed using newly obtained experimental data and by adjusting binary interaction parameters. Then, we constructed and operated the pilot-scale MEG regeneration plant with a feed flow rate capacity of 200 kg/h to investigate the concentration of MEG solution. We varied the reboiler temperature at the bottom of the packed distillation column and the concentration of NaCl in the feed stream. It was observed that the MEG concentration decreased with decreasing reboiler temperature but with increasing NaCl concentration. The enhanced electrolyte NRTL-RK model was verified using the operation data from the pilot-scale MEG regeneration system, which was in good agreement with both steady-state and dynamic operation data from the pilot-scale experiments. Based on the developed simulation model, case studies were carried out to manage the risk of NaCl precipitation in the MEG regeneration system while achieving the target lean MEG concentration. The safe operation window, avoiding the risk of NaCl precipitation, was developed using the relationship among the distillation temperature, MEG concentration, and amount of NaCl based on the developed model. When 50 wt % rich MEG solution was regenerated to 90 wt % lean MEG solution, no precipitation of NaCl was predicted by the enhanced model until the total dissolved salt (TDS) reached 100 g/L; however, the default model predicted the precipitation of NaCl at the bottom of the distillation column above the TDS of 85 g/L, which suggested that the inaccuracy model can overestimate the risk of NaCl precipitation.N
Life cycle cost analysis of CO2 compression processes coupled with a cryogenic distillation unit for purifying high-CO2 natural gas
No full textNovel compression processes coupled with a cryogenic distillation unit are designed in this study to puri fy high-CO2 natural gas or biogas before injection into the reservoir. Four different designs are evaluated to achieve the required injection pressure and minimize both the capital and operation costs. Depending on the pressure-temperature pathway for the compression of the top and bottom products of the distillation unit, the energy and equipment costs are quantified using process simulation models and economic analysis tools, which are integrated with the flow simulation model to determine the required injection pressure. This holistic approach of integrating the compression process and injection pipeline is efficient for optimizing the process design and operation variables. The results suggest that liquefying the top product followed by mixing with the bottom product is the most cost-effective method, as it eliminates costly compressors and simplifies the process configuration. In addition to the li f e cycle cost analysis of the process, the sudden release of CO2 from the vessel is also studied experimentally. The results show that releasing gaseous CO(2)through the valve induces the formation of solid CO2 inside the vessel before complete removal of CO2 from the vessel, thus requiring a controlled release strategy to avoid solid CO2 formation inside the vessel and through the valve.N
과냉각 재액화 시스템 적용에 따른 액화가스운반선의 효율 향상에 대한 해석적 연구
No full text학위논문(박사) -- 서울대학교대학원 : 공과대학 조선해양공학과, 2024. 2. Youngsub Lim.Advanced process design of subcooling re-liquefaction system for the liquefied gas carrier Jaejun Lee Dept. of Naval Architecture & Ocean Engineering The Graduate School Seoul National University By strengthening the International Maritime Organizations strategies for greenhouse gas (GHG) reduction to achieve net-zero emissions by 2050, the energy demands of natural gas (NG), which acts as a transitional energy source for the ways to net zero emission society, will peak in 2030. Additionally, the transportation of carbon dioxide (CO2) captured from the production process of carbon neutral fuels such as blue hydrogen or from exhaust gas generated after the combustion of fossil fuel is expected to increase marginally until 2050. To transport large amounts of natural gas and carbon dioxide to the various regions, the method of ship transportation in the liquid phase is evaluated as the most economical way. To maximize transportation capacity of a liquid cargo carrier, the re-liquefaction system must be considered. This study suggests a new LNG subcooling system combined with a mixed refrigerant cycle (MR-SLNG), which can significantly increase re-liquefaction performance. For the transportation of liquefied CO2 (LCO2), the optimized storage pressure condition of LCO2 is analyzed, and the subcooling system is proposed for the first time in an LCO2 re-liquefaction system. The results of LNG re-liquefaction system show that the coefficient of performance (COP) of the system is improved by 2.5 times compared to that of the conventional LNG subcooling system based on a reverse Brayton cycle (RBC-SLNG). The results of the LCO2 re-liquefaction system show that the suggested LCO2 subcooling system has lower specific energy consumption, which means it is more efficient than conventional LCO2 re-liquefaction systems, even with a simpler configuration. At 15 bar of storage pressure, the LCO2 subcooling system has a lower specific energy consumption of 176.91 kJ/kg, which is 18.2 % and 5.3 % lower than that of the Linde–Hampson cycle and vapor-compression refrigeration cycle using NH3 as a refrigerant, respectively. In addition to the re-liquefaction performance improvement, economic benefits can be obtained by applying a subcooling system. MR-SLNG can be designed more compactly because the volumetric flowrate of the refrigerant compressor is decreased to 10% of the conventional subcooling system (RBC-SLNG), which brings additional benefits to the ship design. For the LCO2 carrier, the boil-off CO2 (BOGCO2) compressor is not required and can be removed in an LCO2 subcooling system. By considering the CO2 re-liquefaction performance and the design constraints of the LCO2 cargo tanks, 15 bar LCO2 storage conditions with a subcooling system are considered the most economical LCO2 carrier design. Consequently, the subcooling system can be an attractive solution for industrial fields that store and utilize the low-temperature liquid cargo because of its improved performance and features that ensure the operational flexibility of the liquid cargo handling system.
Keyword: Subcooling system, Mixed refrigerant cycle, Re-liquefaction performance, Natural gas, Carbon dioxide
Student Number: 2021-355942050년까지의 온실가스 규제가 배출 제로의 단계로 강화됨에 따라 청정에너지시대로의 전환에너지로 평가받고 있는 천연가스의 수요는 2030년까지 증가될 예정이다. 또한 블루 수소와 같은 탄소중립 연료의 생산 및 화석연료의 연소를 통해 발생되는 배기가스에서 포집되는 이산화탄소의 운송량은 크게 증가할 예정이다. 천연가스와 이산화탄소를 다양한 지역에 효과적으로 운반하기 위해서는 액화 후 선박으로의 수송이 가장 경제적인 방법으로 평가되고 있다. 본 연구에서는 혼합 냉매 사이클을 적용한 과냉각 시스템을 제안하였으며, 이로 인해 재액화성능이 크게 개선되는 것을 확인하였다. 액화 이산화탄소 운반선의 경우, 최적 저장압력을 평가하고 이산화탄소 과냉각 시스템을 이산화탄소 재액화 시스템으로 최초 제안하였다. 액화천연가스 재액화 시스템의 분석결과 혼합 냉매 재액화 사이클을 과냉각 시스템에 적용함에 따라 기존 reverse Brayton 사이클 기반의 과냉각 시스템 성능 대비 약 2.5배 개선된 성능을 확인할 수 있었다. 액화 이산화탄소의 재액화 시스템 분석결과 과냉각 시스템이 더욱더 간단한 시스템 구성을 가짐에도 불구하고 더 개선된 재액화성능을 가지는 것을 확인하였다. 15 바 액화 이산화탄소 저장압력조건에서 이산화탄소 과냉각 시스템은 Linde–Hampson 재액화 사이클대비 18.2 %, 암모니아 독립 재액화 시스템 대비 5.3 % 개선된 재액화 성능을 가지는 것을 확인할 수 있었다. 재액화 성능 개선효과와 더불어 과냉각 시스템을 적용함에 따라 경제적인 효과도 얻을 수 있다. 혼합 냉매 과냉각 시스템의 경우 과냉각 시스템에 활용되는 압축기의 유량이 기존 대비 1/10로 줄어들기 때문에 공간활용도가 높게 설계될 수 있으며 이는 선박의 장비배치 관점에서 큰 장점을 가질 수 있다. 액화 이산화탄소 운반선의 경우 과냉각 시스템이 적용됨에 따라 증발가스 압축기가 제거될 수 있기 때문에 경제적인 설계가 가능하다. 이산화탄소 재액화 시스템의 성능과 액화 이산화탄소 저장탱크의 설계 기준을 고려하였을 때 15 바 저장압력조건에서 과냉각 시스템을 적용하는 것이 가장 경제적인 액화 이산화탄소 운반선의 설계임을 확인하였다. 결과적으로 과냉각 시스템은 개선된 시스템 성능과 액체화물의 관리 측면에서 운전 유연성을 보장하는 특징을 가지고 있으며, 이는 저온 액체 화물을 저장하고 운용하는 산업영역에서 매력적인 시스템으로 제안될 수 있다.
주요어: 과냉각 시스템, 혼합 냉매 사이클, 재액화 시스템, 천연 가스, 이산화탄소
학번: 2021-35594Abstract i
Table of Contents iii
List of Tables v
List of Figures vii
Chapter 1. Introduction 1
1.1. Future energy demands in the era of NZE 1
1.2. Re-liquefaction system in current LNG and LCO2 carrier 5
1.3. Re-liquefaction system performance by considering flash gas generation . 7
1.4. Purpose of Research 11
Chapter 2. Backgrounds 14
2.1. System configuration of LNG carrier and LNG re-liquefaction process 14
2.2. System configuration of LCO2 carrier and CO2 re-liquefaction process 21
2.3. Type of re-liquefaction system 29
2.4. Methods of process optimization 37
2.5. Design guideline of hazardous area for liquid gas carrier 41
Chapter 3. Modeling of re-liquefaction system 45
3.1. Boundary conditions 47
3.2. Process description 50
3.3. Design variables for system optimization 62
3.4. Evaluation of the re-liquefaction system efficiency 66
3.5. Methods of optimization 71
Chapter 4. Results and discussion 78
4.1. BOG re-liquefaction performance by considering flash gas generation in LNG re-liquefaction system 78
4.2. LNG subcooling system performance by applying a mixed refrigerant 82
4.3. Re-liquefaction performance of BOGCO2 re-liquefaction system depending on the LCO2 storage pressure and type of re-liquefaction system 94
4.4. Re-liquefaction performance considering SLCO2 96
Chapter 5. Conclusion 113
5.1. Performance analysis results for LNG re-liquefaction system 113
5.2. Performance analysis results for CO2 re-liquefaction system 115
Chapter 6. Future works 116
6.1. CO2 re-liquefaction system considering impurity of liquid CO2 116
6.2. Opportunities by applying subcooling system to other liquid cargo containment system 120
Nomenclature 123
Bibliography 125
Abstract in Korean 137박
Modeling and Simulation of CO2 Capture Process for Coal- based Power Plant Using Amine Solvent in South Korea
No full textAbstractThe interest in carbon capture technology is continuously rising since worldwide climate-change problems have intensified the concern regarding efficient removal of carbon dioxide. Amine-based capture technology is a conventional technology to remove carbon dioxide in natural gas processing, and also can be used for carbon dioxide removal from flue gas in coal-based power plants. In particular, monoethanolamine is a conventional commercial absorbent to remove carbon dioxide and considered as a standard amine absorbent. Due to the high non-ideality of amine, rate-based models have been suggested to describe absorption and desorption of amine absorbent. However, most suggested models were validated against large-scale pilot plant results, and there were few models to consider both absorber and stripper with rate-based model. In this study, we applied two rate-based models introduced by previous literature to the actual pilot plant operation data in 0.1MW-scale Boryeong pilot plant, South Korea and developed a modified model with increased accuracy. The developed model showed good agreements with pilot plant results for both absorber and stripper. However, under low liquid-to-vapor ratio operation with high rich loading value, all model showed worse estimations
Optimal Process Design of Onboard BOG Re-liquefaction System for LNG Carrier
No full textHigh-pressure gas injection engines (HPGI) took center stage in LNG carrier propulsion systems after their advent. The HPGI engine system can be easily modified to include a re-liquefaction system by adding several devices, which can significantly increase the economic feasibility of the total system. This paper suggests the optimal operating conditions and capacity for a re-liquefaction system for an LNG carrier, which can minimize increases in the total annualized cost. The installation of a re-liquefaction system can save 0.23 million USD per year when the cost of LNG is 5 USD/Mscf. A sensitivity analysis with different LNG costs showed that the re-liquefaction system is profitable when the LNG cost is higher than 3.5 USD/Mscf
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