Boil-off Gas Research Articles

Analysis of discharging characteristics of the storage system by adsorption for boil off gas (BOG) from onboard LNG

Analysis of discharging characteristics of the storage system by adsorption for boil off gas (BOG) from onboard LNG

A cryogenic CO2 capture system coupled with boil-off gas re-liquefaction for LNG carriers

A cryogenic CO2 capture system coupled with boil-off gas re-liquefaction for LNG carriers

Optimizing LNG efficiency by implementing reliquefaction technology to reduce boil-off gas and enhance profitability

Run an analysis of this abstract, focusing on its relevance, format, flow, and coherence. Technological advancements compel companies to enhance the efficiency of their business operations, including those in the oil and gas sector. Natural gas, particularly Liquefied Natural Gas (LNG), is a vital commodity in significant demand. A primary challenge within the LNG supply chain is minimizing the losses caused by gas evaporation (boil-off gas) during distribution and reception. This study proposes the implementation of a reliquefaction plant on a 170,000 m³ Floating Storage and Regasification Unit (FSRU). Through this innovative approach, this study aims to optimize the utilization of Boil-off Gas (BOG) and augment the company's revenue. The results indicate that the liquefaction plant can reduce BOG by 77 percent, significantly outperforming conventional methods. The economic feasibility analysis revealed a Net Present Value (NPV) of $82,892,970 and an Internal Rate of Return (IRR) of 25 percent, suggesting substantial profit potential. Furthermore, the reliquefaction of 1,777.6 MMBtu BOG per day could potentially increase the company's revenue by IDR 94,078,421,500 annually, surpassing initial estimates. This study contributes significantly to the advancement of more efficient LNG management technologies, providing concrete solutions to minimize energy waste and enhance profitability within the LNG industry. These findings facilitate the implementation of similar technologies at other LNG facilities, potentially transforming industry-wide practices.

Design and optimization of large-scale natural gas liquefaction process based on triple refrigeration cycles

In large-scale natural gas liquefaction, minimizing specific energy consumption has consistently been a primary objective. This study aims to develop a large-scale natural gas liquefaction process that balances energy efficiency and cost-effectiveness, presenting a viable option for industrial production. By employing a refrigerant strategy of “propane + mixed refrigerant + mixed refrigerant”, a novel large-scale natural gas liquefaction process based on triple refrigeration cycles (TRC) is proposed. To address the challenge of boil-off gas (BOG) re-liquefaction, the TRC process is further refined to integrate BOG re-liquefaction (TRC-BR). Thermodynamic models are built for the proposed TRC and TRC-BR processes, as well as the propane pre-cooled mixed refrigerant (C3MR) and AP-X processes as baseline cases. Global optimization is conducted using the Particle Swarm Optimization (PSO) algorithm, with the specific power consumption (SPC) serves as the objective function. The results reveal that the SPC of the TRC and TRC-BR processes are 0.2726 and 0.2704 kWh/kg-LNG respectively. Compared with the C3MR and AP-X processes, the SPC of the TRC decrease by 1.54% and 4.84%, respectively. The total investments for the TRC and TRC-BR processes are estimated at a similar level compared to the baseline cases, demonstrating their significant potential for industrial application.

Thermo-economic analysis of green hydrogen production onboard LNG carriers through solid oxide electrolysis powered by organic Rankine cycles

LNG carriers play a crucial role in the shipping industry meeting the global demand for natural gas (NG). However, the energy losses resulting from the propulsion system and the excess boil-off gas (BOG) cannot be overlooked. The present article investigates the H2 production on board LNG carriers employing both the engine's waste heat (WH) and the excess BOG. Conventional (ORC) and dual-pressure (2P-ORC) organic Rankine cycles coupled separately with a solid oxide electrolysis (SOEC) have been simulated and compared. The hydrogen (H2) produced is then compressed at 150 bar for subsequent use as required. According to the results, the 2P-ORC generates 14.79 % more power compared to ORC, allowing for an increased energy supply to the SOEC; hence, producing more H2 (34.47 kg/h compared to 31.14 kg/h). Including the 2P-ORC in the H2 production plant results in a cheaper H2 cost by 0.04 $/kgH2 compared to ORC, a 1.13 %LHV higher system efficiency when leveraging all the available waste heat. The plant including 2P-ORC exploits more than 86 % of the of the available waste compared to 70 % when using ORC. Excluding the compression system decreases the capital cost by almost the half regardless of the WH recovery system used, yet it plays in favour of the plant with ORC making the cost of H2 cheaper by 0.29 $/kgH2 in this case. Onboard H2 production is a versatile process independent from the propulsion system ensuring the ship's safety and availability throughout a sea journey.

Stable heterometallic metal-organic frameworks and pellet composites for low-temperature natural gas storage

Liquefied natural gas coupled with adsorbed natural gas charging (LNG-ANG) offers an efficient solution for recycling boil-off gas, providing a promising strategy for the competent storage and transportation of natural gas. The key challenge in LNG-ANG coupling systems is identifying adsorbents that exhibit superior methane adsorption performance and excellent stability under cryogenic conditions (∼159 K). In this work, we systematically investigated the methane adsorption performance of a stable metal–organic framework, PCN-250-Fe2Ni, under LNG-ANG related conditions. The results demonstrated that PCN-250-Fe2Ni exhibited a high methane capacity of 286 cm3 (standard temperature and pressure, STP) cm−3 (0.227 g g−1) at 6 bar/159 K. Furthermore, the pellet composite of PCN-250-Fe2Ni and polyvinyl butyral also displayed a high methane adsorption capacity with excellent cycling stability. Combined with grand canonical Monte Carlo simulations, our findings revealed that the cage-type pores serve as initial methane adsorption sites, followed by the channel-type pores, both of which contribute to the framework’s high low-temperature methane storage performance at saturation.

Analytical comparison of the boil-off gas recondensation process’s energy consumption and carbon emissions

With 28 operational liquefied natural gas receiving terminals in China by 2023, totaling a receiving capacity of 1.2 × 108 t/a, managing carbon emissions and boil-off gas has attracted increased attention. This study presents the optimization of 8 boil-off gas (BOG) recondensation processes, considering energy consumption and carbon emissions as assessment criteria, along with two types of vaporizers. The method involves analyzing how process parameters affect system performance using Hydraulic System Simulation Software, followed by optimizing system parameters with a genetic algorithm. It explores the impact of compressor output pressure, after-cooler inlet material ratio, and pre-cooler inlet material ratio on system energy consumption and carbon emissions. Results show that increased recondensing, compression, and cooling measures slightly elevate energy consumption but significantly reduce carbon emissions. Moreover, a higher BOG content enhances the carbon reduction effect. This study represents the first optimization of BOG recondensation processes focusing on carbon emissions, offering fresh theoretical insights and significant potential for enhancing energy efficiency and reducing carbon emissions.

Coupled CFD modeling and thermal analysis of multi-layered insulation structures in liquid hydrogen storage tanks for various vapor-cooled shields

The present study aims to propose a coupled numerical model for analyzing the influence of the configuration of the vapor-cooled shield tubes on insulation performance. The numerical model is developed to calculate the effective thermal conductivity of multi-layer insulation (MLI) and rigorously evaluated. Specifically, the tank evaporation simulation software BoilFAST is manually coupled with the CFD commercial software of ANSYS FLUENT (2020 R2) to accurately determine the mass flow rate and temperature of boil-off gas in a tank, which is then used as inputs for the CFD simulations. This coupling methodology can be used for reliable calculations of boil-off losses for liquid hydrogen and heat transfer inside the MLI structures. Results demonstrate that the estimated effective thermal conductivity agrees with the earlier published data and that increasing the diameter and number of tubes enhances heat exchange between the VCS tubes and MLI structures. Also, the heat flux into the tank is relatively reduced by 32.04 % by increasing the diameter of the tube and 49.14 % by adding the number of tubes. Moreover, the maximum temperature difference of the VCS is estimated to be less than 1 K, indicating nearly uniform distributions of the VCS.

Optimization of BOG Reliquefaction Process of Carbon Dioxide Considering Nitrogen Content

<i>As the importance of carbon capture and storage (CCS) technology increases for greenhouse gas reduction, CO<sub>2</sub> transportation technology is also becoming crucial. Efficiently handling boil-off gas (BOG) generated during voyages is particularly important. This paper proposes a process incorporating two-stage separation and mixed refrigerants to reliquefy CO<sub>2</sub> BOG containing nitrogen efficiently. This process was optimized based on specific power consumption (SPC) criteria and compared with the conventional single-stage separation using an ammonia refrigerant. The two-stage separation allows the removal of non-condensable gases, such as nitrogen, before expansion, and the use of mixed refrigerants enables more efficient heat exchange than ammonia refrigerants, improving the reliquefaction rate. As a result, the proposed process reduced SPC by up to 8.8 % with a nitrogen content of 5 mol% and up to 74.7 % with a nitrogen content of 15 mol%. In addition, the proposed process achieved a reliquefaction rate of over 74.2 % across all nitrogen content ranges of 5–15 mol%.</i>

Thermodynamic Modeling and Analysis of Boil-off Gas Generation and Self-Pressurization in Liquefied Carbon Dioxide Tanks

The importance of the safe transport of liquefied carbon dioxide (LCO2) is increasing owing to environmental issues. When transporting a low-temperature liquid, boil-off gas generation and self-pressurization occur due to heat ingress, affecting the holding time of a low-temperature liquid tank. This study developed and compared three thermodynamic self-pressurization models to estimate the holding time of LCO2: Thermal homogeneous model (THM), Thermal two-zone model (TTZM), and Thermal multi-zone model (TMZM). Thermodynamic differential equations were solved for THM, and software was used for TTZM. For TMZM, the parameters were optimized using experimental data to determine the heat ratio parameter f and heat transfer parameters K1 and K2. THM and TTZM estimated an unreasonably long holding time, approximately 42 days. The TMZM, however, showed a satisfactory holding time of 12–13 days. These results can help predict the self-pressurization in the storage tanks of LCO2 and be applied to actual LCO2 carrier cargo handling systems, with the modeling results indicating that the 12–13 days of LCO2 self-pressurization based on the TMZM appears to be the most suitable.

Responding to low-carbon shipping via a novel BOG-ORC-CCS system onboard LNG carrier: 4E analyses and optimization

As the international LNG trade market is booming, the LNG carrier fleet has expanded year after year. How to reduce energy consumption in boil-off gas (BOG) re-liquefaction process and CO2 generated during transportation has become a hot topic. This paper obtains ideas from the LNG cold energy contained in LNG carriers, and proposes a novel BOG-ORC-CCS system for direct BOG re-liquefaction, Organic Rankine cycle (ORC) and carbon capture and storage (CCS). The BOG-ORC-CCS system recycles waste heat from the ship while realizing the LNG cold energy gradient utilization. The reference ship (Q-Flex) is specified under the framework of Energy Efficiency Design Index (EEDI) phase Ⅲ requirement and the BOG-ORC-CCS system is simulated by Aspen HYSYS software. A comprehensive evaluation of the system performance is carried out under the guidance of energy, exergy, economic and environment (4E) modeling. The results of the 4E analyses show that the proposed BOG-ORC-CCS system has the advantage of low energy consumption and good economic performance. Finally, a multi-objective optimization of the system performance in 4E aspects: system energy and exergy efficiency (ηen,sys×ηex,sys), payback period (PBP) and primary energy saved (PES) are carried out by the third-generation non-dominated sorting genetic algorithm (NSGA-Ⅲ). As a result, the optimal solutions are as follows: ηen,sys is 50.91%, ηex,sys is 54.00%, PBP is 1.55 years and PES is 1.32 MWh, while Load of 75%, TL5 is −136.01 °C, pB5 is 1.82 MPa and ScrL2 is 99.88%. Additionally, SEC is 0.20 kWh/kg, which is much lower than that of conventional indirect re-liquefaction. This demonstrates the feasibility of the BOG-ORC-CCS system on LNG carriers.

Modeling and experimental testing of a UAV liquid hydrogen propulsion set

In this paper, an analytical model of an Unmanned Aerial Vehicle (UAV) propulsion system using liquid hydrogen to supply a fuel cell is presented. The article also describes experimental tests of the performance of a liquid hydrogen (LH2) tank at different ambient temperatures and ground tests of the UAV propulsion system using LH2. These tests were used to validate and calibrate the analytical model. The model is of reduced order and is based on the literature. Despite the simplicity of the model, the tank Boil-Off Gas (BOG) rate and pressure drop, the time for complete evaporation of LH2, the fuel cell performance, and the coolest temperature that the hydrogen can reach, were predicted with deviations not exceeding 0.3%, 0.5%, 2.2%, 0.6%, and 0.5% respectively. The final proposed model allows the incorporation of different conditions, materials, and geometries to suit each mission, all at low operational cost.

Feasibility Study on Production of Slush Hydrogen Based on Liquid and Solid Phase for Long Term Storage

To achieve net-zero objectives, the expansion of renewable energy sources is anticipated to be accompanied by an increased use of carbon-free fuels, such as hydrogen. Internationally, there are proposals for transporting hydrogen by synthesizing it into carriers like ammonia or Liquid Organic Hydrogen Carriers (LOHCs). However, considering the energy consumption required for hydrogenation and dehydrogenation processes and the need for high-purity hydrogen production, the development of liquid hydrogen transportation technologies is becoming increasingly important. Liquid hydrogen, with a density approximately one-sixth that of liquid natural gas and a boiling point roughly 90 K lower, poses significant challenges in suppressing and managing boil-off gas during transportation. Slush hydrogen, a mixture of liquid and solid phases, offers potential benefits. with an approximate 15% increase in density and an 18% increase in thermal capacity compared to liquid hydrogen. The latent heat of fusion of solid hydrogen effectively suppresses boil-off gas (BOG), and the increased density can reduce transportation costs. This study experimentally validated the long-duration storage and transportation concept of slush hydrogen by adapting NASA’s (National Aeronautics and Space Administration) proposed IRAS (Integrated Refrigeration and Storage) technology for compact and mobile tanks. Slush hydrogen was successfully produced by reaching the triple point of hydrogen, resulting in a composition of 47% solid and 53% liquid, with a density of approximately 80.9 kg/m3. Most importantly, methodologies were presented to observe and measure whether the hydrogen was indeed in the slush state and to determine its density. Additionally, CFD (Computational Fluid Dynamics) analysis was performed using solid hydrogen properties, and the results were compared with experimental values. Notably, this analytical technique can be utilized in designing large-capacity tanks for storing slush hydrogen.

Estimation of Boil-Off Gas Generation by using Phase-Field Model for Liquid Hydrogen Vacuum-Jacketed Valve

Estimation of Boil-Off Gas Generation by using Phase-Field Model for Liquid Hydrogen Vacuum-Jacketed Valve

Revisiting the cost analysis of importing liquefied green hydrogen

Hydrogen emerges as a promising energy carrier in achieving carbon neutrality, especially in countries such as South Korea and Japan, where renewable energy resources are scarce. Consequently, economically importing hydrogen from overseas is paramount to a stable supply. However, previous studies have often oversimplified the estimation of hydrogen import costs with optimistic assumptions, raising doubts about their reliability. This study comprehensively assesses costs incurred from green hydrogen production to liquefaction and transportation. The cost analysis includes detailed design considerations for hydrogen liquefaction and re-conditioning plants, alongside thermodynamic simulations to estimate the boil-off gas rate of liquid hydrogen during transport. Focusing on a case study of importing liquefied green hydrogen from Australia to South Korea, our findings reveal that the levelized cost of hydrogen is approximately 30.2 USD/kgH2 as of 2023. Projections suggest a decrease to around 18.3 USD/kgH2 by 2050, assuming technological advancements, significantly exceeding values reported in the existing literature. Sensitivity analysis highlights the renewable electricity price in Australia and the boil-off rate during shipping as key factors that significantly influence the levelized cost of hydrogen.

Thermo-Economic Comparison between Three Different Electrolysis Technologies Powered by a Conventional Organic Rankine Cycle for the Green Hydrogen Production Onboard Liquefied Natural Gas Carriers

The high demand for natural gas (NG) worldwide has led to an increase in the size of the LNG carrier fleet. However, the heat losses from this type of ship’s engines are not properly managed, nor is the excess boil-off gas (BOG) effectively utilised when generation exceeds the ship’s power demand, resulting in significant energy losses dissipated into the environment. This article suggests storing the lost energy into green H2 for subsequent use. This work compares three different electrolysis technologies: solid oxide (SOEC), proton exchange membrane (PEME), and alkaline (AE). The energy required by the electrolysis processes is supplied by both the LNG’s excess BOG and engine waste heat through an organic Rankine cycle (ORC). The results show that the SOEC consumes (743.53 kW) less energy while producing more gH2 (21.94 kg/h) compared to PEME (796.25 kW, 13.96 kg/h) and AE (797.69 kW, 10.74 kg/h). In addition, both the overall system and SOEC stack efficiencies are greater than those of PEME and AE, respectively. Although the investment cost required for AE (with and without H2 compression consideration) is cheaper than SOEC and PEME in both scenarios, the cost of the H2 produced by the SOEC is cheaper by more than 2 USD/kgH2 compared to both other technologies.

THERMODYNAMIC CONSIDERATIONS FOR THE APPLICATION OF LIQUEFIED NATURAL GAS AS TRANSPORTATION FUEL

This study aims to analyze the thermodynamic considerations for the application of liquefied natural gas (LNG) as a transportation fuel. It is designed to solve transport fuel problems and tackle public health issues associated with vehicular engine emission, and vehicle fuel shortages. It considers the economic and technical viability of applying low-temperature fluid as fuel in an LNG-fuel Spark Ignition Engine through computer simulation. Process design configuration was achieved using the User Define Function (UDF) in fluid simulation software (ANSYS Fluent), Finite Element Analysis and Aspen Hysys. 12 kg capacity volume cryogenic tank design was done through Autodesk inventor with an initial temperature of -162 0C and pressure of 1 bar and ambient temperature application ranges of 20 0C to 40 0C. The ANSYS simulation result showed a thermodynamic effect of heat and mass transfer rate range of 1.6% to 7% W/m 2k concerning the time taken by the tank to absorb heat through temperature ranges of -155 0C to 250 0C. Also, 0.04kg/s was the total volume of boil-off gas (BOG) produced, while the maximum exhaust gas emissions recorded was 0.254kg/s. The advantage of this technology was the minimal volume of greenhouse gases released during combustion relative to gasoline and diesel, signifying less pollution, and buttressing the applicability and adoption of LNG-Fuel as a transport fuel.

An efficient high cooling capacity Stirling cryocooler and its application for capturing boil-off methane from liquefied natural gas

Natural gas is a cost-effective energy supply for the development of low-carbon economy and environmental protection worldwide. Despite the environmentally friendly properties of natural gas, methane is a potent greenhouse gas. Therefore, efficiently recovering the boil-off methane gas (BOG) generated from liquefied natural gas (LNG) devices is becoming a pressing problem involving both the economy and the environment. The Stirling cryocooler is a promising technology in dealing with BOG. This technology has superior characteristics, including large cooling capacity, high efficiency, compact configuration, and flexible operating characteristics. In the study, a high cooling capacity Stirling cryocooler was developed. The influences of the regenerator on the cryocooler were studied. The refrigeration performance and the operating characteristics were systematically analyzed. A cooling power of 1050 W at 77 K with a relative Carnot efficiency of 33.28 % was achieved. Accordingly, the cryocooler outperforms the reported Stirling-type cryocoolers in terms of overall performance. A BOG liquefaction system based on the cryocooler was installed in an LNG refueling station. On-site test results demonstrated that the system can produce 27.3 L/h LNG with a power consumption of 14.5 kW. The present research lays a good foundation for future optimizations and applications of the cryocooler in liquefying BOG.

Development of Strength Evaluation Methodology for Independent IMO TYPE C Tank with LH2 Carriers

Given the inadequate regulatory framework for liquefied hydrogen gas storage tanks on ships and the limitations of the IGC Code, designed for liquefied natural gas, this study introduces a critical assessment procedure to ensure the safety and suitability of such tank designs. This study performed a heat transfer analysis for boil-off gas (BOG) calculations and established separate design load cases to evaluate the yielding and buckling strength. In addition, the study assessed methodologies for both high-cycle and low-cycle fatigue assessments, complemented by comprehensive structural integrity evaluations using finite element analysis. A comprehensive approach was developed to assess the structural integrity of Type C tanks by conducting crack propagation analysis and comparing these results with the IGC Code criteria. The practicality and efficacy of these methods were validated through their application on a 23K-class liquefied hydrogen carrier at the concept design stage. These findings may have important implications for enhancing safety standards and regulatory policies.

Boil-Off Gas Generation in Vacuum-Jacketed Valve Used in Liquid Hydrogen Storage Tank

The boiling point of liquid hydrogen is very low, at −253 °C under atmospheric pressure, which causes boil-off gas (BOG) to occur during storage and transport due to heat penetration. Because the BOG must be removed through processes such as re-liquefaction, venting to the atmosphere, or incineration, related studies are required to estimate the heat transfer of storage and transport devices and to improve insulation to reduce BOG generation. In this study, a vaporization analysis was performed on a vacuum-jacketed valve used in liquid hydrogen storage and transport devices to calculate the amount of BOG generation considering the flow characteristics at the vena contracta and the saturation temperature. At a pressure of 1 bar in the liquid hydrogen storage tank, the maximum fluid flow velocity and minimum static pressure occurred at the vena contracta, with values of 62.9 m/s and −0.4 bar, respectively, and the BOG generation rate was estimated as 0.132 m3/h, where the saturation temperature was minimized at 19.3 K. Furthermore, through case studies, when the pressure in the liquid hydrogen storage tank increased to 1.5 and 2 bar, the static pressure and saturation temperature decreased, and the BOG generation rate increased to 0.221 and 0.283 m3/h, respectively.