Liquefied Natural Gas Ship Research Articles

Optimizing Air Separation and LNG Cold Utilization: Energy Savings, Exergy Efficiency, and System Reliability

AbstractAir separation processes are time‐consuming and energy‐intensive. Most of the energy used in air separation unit (ASU) is used for air compression. During the air compression process, some energy is lost, which is converted into waste heat. This wasted energy is used to warm liquefied natural gas (LNG). At some point, LNG ships will dock at an LNG regasification facility. Here, LNG is converted back to gas and supplied to the distribution and transmission systems. During the regasification process, cryogenic LNG has a huge opportunity for cold energy recovery. An innovative air separation process that is integrated with the cold utilization of LNG is presented in this study along with a thorough conceptual design and analysis. The results of this study show that producing high‐purity oxygen and nitrogen, respectively, requires 0.28 kWh kg−1 and 0.06 kWh kg−1 of specific energies. Prior to integration with cold utilization of natural gas, 25 141.6 kW is needed for air compression. However, following integration, 10 554.6 kW of energy is needed, resulting in a 58.01 % energy savings. Exergy destruction as well as efficiency have been calculated for the primary components of the system. Sensitivity analysis is carried out to examine the effects of LNG streams on important parameters. In conclusion, a cryogenic ASU is integrated with an LNG‐direct expansion cycle‐organic Rankine cycle power cycle to supply the necessary power for operation and reduce extraneous power inputs. Overall, this integrated approach increases efficiency, lowers costs, benefits the environment, allows for flexibility and adaptability, and raises system dependability.

Tank-level robust control of LNG carrier based on hyperbolic tangent function nonlinear modification

Abstract The objective of this study was to achieve a better control effect of the controller on the liquid level of the liquefied natural gas (LNG) carrier and to achieve the goal of energy saving and carbon reduction. This paper took the loaded square tank of an S175 high-speed container ship as the research plant, combined with the closed-loop gain-shaping algorithm (CGSA) and nonlinear modification technology to further optimize the controller. We initially employed a third-order CGSA approach in formulating the foundation of our linear controller. Subsequently, we introduced a non-linear modification to this controller by harnessing the power of the hyperbolic tangent function, and the control effect is verified by the MATLAB simulation experiment. Based on the outcomes of MATLAB simulations, by integrating the third-order CGSA technique and introducing non-linear modification through the hyperbolic tangent function, we observed a significant enhancement in the controller's performance. Specifically, it outperformed the traditional PID controller by a substantial margin, demonstrating a remarkable 19% boost in control efficacy. Additionally, it provides better energy savings than the non-linear controller. The controller designed in this paper has a better control effect on the liquid tank-level control of LNG ships, the control process is more energy-saving and the purpose of carbon reduction is realized.

A Simulation Model of the Influence of LNG Ships on Traffic Efficiency at Tianjin Port

Tianjin Port is one of the largest ports in northern China. Liquefied natural gas (LNG) ships are one of the most special ship types, and their navigation safety and efficiency has become the top concern of the port authority. There are two LNG berths at the port, and the annual arrivals, which reach more than 100, increasingly influence other ships. The objective of this study is to evaluate the influence of LNG ships on other ships in a quantitative way. To realize this, a simulation system is established by analyzing the factors affecting waterway transit efficiency. The software Arena is adopted to simulate the arrival and departure of the ships at Tianjin Port and to simulate how the average waiting time and the average queue length in the port area are affected by the LNG ships. A traffic system for the two ship types is formulated, and the mutual influences between them are expressed by the inbound and outbound waterway states. The simulations are performed under both existing and new ship traffic regulations. Cases in which the number of LNG ships gradually increases are simulated comprehensively. The simulation model as well as the results can serve as a good reference for the local port authority in the formulation of traffic regulations.

Techno-economic analysis of natural gas distribution using a small-scale liquefied natural gas carrier

The design of the gas distribution for small-demand power plants located on remote islands is logistically challenging. The use of small-scale liquefied natural gas (LNG) vessels can be an option for these logistic problems. This paper aims to conduct a techno-economic analysis of using small-scale LNG vessels for gas distribution to the power plants that are spread across different islands. Route optimisation has been conducted using the capacitated vehicle routing problem method. The ship’s principal dimensions were determined using the aspect ratio from a linear regression of existing small-scale LNG vessels. As a case study, the gas demands for a gas power plant in eastern Indonesia were analysed into four distribution clusters. The results of the techno-economic analysis showed that the four distribution clusters have different characteristics regarding the LNG requirements, location characteristics and ship specifications. The capacity of small-scale LNG vessels feasible in terms of technical aspects varies from 2500, 5000, to > 10,000 m3 with variations in the ship speed depending on the location of the power plants. The amount of cargo requested and the shipping distance was affected to the cost of LNG transportation. The economic assessment proposes that the feasible investment by considering small-scale LNG cargo distribution, from the case study shows that with a ship capacity of 5000 m3 feasible margin rate is ≥ 3 USD/metric million British thermal units with an internal rate of return of 10% and estimated payback period is less than 15 years.

Numerical Investigation of Hydrodynamic Responses of a Moored Liquefied Natural Gas Ship under Multimodal Waves

Ocean waves typically consist of wind, sea, and swell trains. Conventionally, the treatment of multimodal waves has been to conceptualize them as a unified wave system and employ a single set of aggregate wave parameters for the representation of their collective characteristics. Nevertheless, a better understanding of multimodal waves is important when analyzing the interactions between waves and moored vessels, considering the pronounced sensitivity of a ship’s responses to wave periods and directions. Many spectral partitioning methodologies have been proposed to discern and segregate multimodal waves into two or more distinct wave systems, providing fundamental information for investigating moored ship responses to multimodal waves. Utilizing the wave spectra data acquired from a specific water region in South America, a comprehensive numerical study was undertaken by employing the specialized ocean engineering software ORCAFLEX 11.2e. The primary objective of this investigation is to analyze the dynamic response of a moored liquefied natural gas (LNG) vessel in ballast conditions subjected to waves defined by distinct wave identification methods (i.e., overall method and spectral partition method). Furthermore, the waves are categorized into two groups: beam waves and head waves. Results show that beam waves induce a substantial ship response, whereas head waves pose a comparatively lower risk to maritime vessels. Furthermore, the conventional overall wave approach tends to neglect the roll motion generated by multimodal waves when they propagate as head waves. Nevertheless, when the wave direction aligns with beam waves, the overall wave approach tends to produce the roll motion. These findings indicate the importance of considering multimodal waves in quay layout and mooring configuration design.

Advanced natural gas liquefaction and regasification processes: Liquefied natural gas supply chain with cryogenic carbon capture and storage

Natural gas combined cycle power plants generate substantial amounts of CO2. Also, since natural gas is produced in limited sites, the liquefied natural gas (LNG) supply chain consumes considerable energy in transporting natural gas overwide. Herein, advanced natural gas liquefaction and regasification processes using an LNG supply chain with cryogenic CO2 capture and storage (CCS) are proposed using Aspen Plus® V11. This solves three significant problems associated with conventional LNG supply chains. First, through the utilization of LNG cold energy, the cryogenic CCS process reduces the efficiency penalty of power generation from 14.34 to 4.45%. Second, solid CO2 from cryogenic CCS is used as an additional cold source in the natural gas liquefaction process by conveying it to the liquefaction site via the returning LNG ship. As a result, the power consumption in the refrigerant cycle is reduced by up to 67.17% than single mixed refrigerant (SMR) process. Finally, the LNG supply chain with cryogenic CCS minimizes the sustained energy waste between the natural gas liquefaction and regasification stages owing to the geographical separation. LNG cold energy from the regasification stage is utilized in the form of solid CO2 in the CCS and liquefaction stages. Consequently, the exergy efficiency in the overall LNG supply chain increases from 18.18 to 46.39%. The findings of this study can potentially provide environmentally friendly design guidelines for various LNG processes that use LNG cold energy in CCS and natural gas liquefaction.

Economic Analysis of Gas Supply System For Dual Fuel Engines With Life Cycle Cost

The regulations of the international maritime organization (IMO) on ship emission are becoming increasingly strict. Liquefied natural gas (LNG) is an ideal alternative fuel for vessels, considering its environmental and economic advantages. This paper compares the life cycle cost (LCC) of LNG ships low pressure gas supply system (FGSS). Comparative analysis of the three main pressurization modes for supplying LNG in the low pressure gas supply system, namely external gas source pressurization, self-pressurization and cryogenic pump boost. Through modeling in Aspen HYSYS software, system operation is simulated, life cycle costs are compared, and the implementation effects of the three system schemes are analyzed and evaluated. The application of life cycle economic analysis in ships mainly focuses on the overall energy saving and emission reduction of ships. Its application in low pressure gas supply systems for dual-fuel engines is rare. This study helps the gas supply system choose the most economical and applicable scheme in practical applications.

Analysis on the Development of LNG Clean Energy Technology for Inland Ships in China

Liquefied natural gas (LNG) is recognized as the most mature and feasible low-carbon clean alternative energy for ships in the world. Liquefied natural gas is widely favored by ship owners. This paper systematically summarizes the development status of promoting the application of LNG in ships at home and abroad. This paper deeply studies the key technologies of ship LNG power system, and focuses on the comparison of the characteristics of power technology at home and abroad. This paper comprehensively summarizes and analyzes the supporting system for the development of LNG powered ships in China. This paper explores the problems existing in the application of LNG in ships. The paper puts forward a power development path of LNG ships in China in the future. The proposed development path can provide strong support for China to achieve green shipping and dual carbon goals.

Propeller selection optimization on mini LNG ship based on engine propeller matching approach

Mini LNG Carrier Ship is specially designed for the purpose of distributing Liquefied Natural Gas (LNG) throughout Indonesia and supporting the national program of generating 35.00 MegaWatt (MW). Indonesia’s vast territory with long distances requires an efficient transportation, including Mini LNG Carrier Ship to reduce costs, especially fuel and emission levels that meet the EEDI criteria set by the International Maritime Organization (IMO). One of the efficiency factors of Mini LNG Ship Carrier is obtained by optimizing the design, especially to the propulsion system. The propulsion system consists of the main engine and propeller. This study focuses on the selection of ship propulsion propellers, especially the type and number of propeller blades. The good propeller will have an impact on the level of energy efficiency. The research method used is a computational simulation using the Engine Propeller Matching (EPM) method. The study tested the B-Series propeller with an alternative number of propeller blades are (z) = 3, 4, 5, 6, and. 7. Calculating simulation results show that the analysis of the EPM computational results at 10 knots service speed, shows that the B6.40 propeller has a better efficiency value than the other propeller types (z = 3, 4, 5, and 7). Propeller type B6.40 produces a good level of efficiency according to the planned 2 x 250 KW engine performance diagram.

Motion Responses of a Berthed Tank under Resonance Coupling Effect of Internal Sloshing and Gap Flow

The growth of global energy transportation has promoted the rapid increase of large-scale LNG (liquefied natural gas) carriers, and concerns around the safety of LNG ships has attracted significant attention. Such a floating structure is affected by the external wave excitation and internal liquid sloshing. The interaction between the structure’s motion and the internal sloshing under wave actions may lead to the ship experiencing an unexpected accident. In this research, a hydrodynamic experiment is conducted to investigate the motion responses of a floating tank mooring, both close to and away from a dock. The resonance coupling effect of the internal sloshing and gap flow on the tank’s motion is considered. Based on the measured motion trajectory of the floating tank, the stability and safety of the floating tank are estimated. The results show that the sloshing resonance and narrow gap resonance are beneficial to the stability of the ship. This is helpful for controlling the motion of a berthed ship under wave action with a reasonable selection of the gap distance and the liquid level.

Advanced design and analysis of BOG treatment process in LNG fueled ship combined with cold energy utilization from LNG gasification

The use of re-gasified liquefied natural gas (LNG) and boil-off gas (BOG) as a fuel in LNG fueled ships generally results in a waste of cold energy. Meanwhile, when the ship is docked, BOG should be re-liquefied to minimize the LNG loss using external energy. To efficiently utilize wasted cold energy, a novel BOG treatment concept combined with air liquefaction is proposed and a new process for recovering cold energy of BOG and fueled LNG is designed and analyzed in this paper. The system is divided into three sections: the BOG and LNG regasification into the fuel gas supply system (FGSS), liquid air energy storage and liquid air energy release. The proposed system is analyzed in three ways: energy analysis by the first law of thermodynamics, heat exchanging analysis by the heat flow, and exergy analysis by the second law of thermodynamics. The energy efficiency of the BOG and LNG gasification into the FGSS, air storage and air release sections are 34.2%, 93.4%, and 52.3%, respectively. The overall heat exchange efficiency is 42.28% and the exergy efficiency is 30.4%. The economic analysis of the system is investigated on the lifecycle of 20 years. This study not only combines the BOG treatment process and the FGSS of the LNG ship but also reduces the energy consumption of the system onboard.

Evaluation of Methane Emissions Originating from LNG Ships Based on the Measurements at a Remote Marine Station.

We analyzed pollution plumes originating from ships using liquefied natural gas (LNG) as a fuel. Measurements were performed at a station located on the Utö island in the Baltic Sea during 2015–2021 when vessels passed the station along an adjacent shipping lane and the wind direction allowed the measurements. The ratio of the measured concentration peaks ΔCH4/ΔCO2 ranged from 1% to 9% and from 0.1% to 0.5% for low and high pressure dual fuel engines, respectively. The ratio of the measured concentration peaks of ΔNOx/ΔCO2 varied between 0.5‰ and 8.7‰, which was not explained by engine type. The results were consistent with previously measured on-board or test-bed values for the corresponding ratios of emissions. While the methane emissions from high pressure dual fuel engines were found to fulfill the goal of reducing the climatic impacts of shipping, the emissions originating from low pressure dual fuel engines were found to be substantially high, with a potential for increased climatic impacts compared with using traditional marine fuels. Taking only the global warming potential into account, we can suggest a limit value for the methane emissions; the ratio of the emissions ΔCH4/ΔCO2 originating from LNG powered ships should not exceed 1.4%.

A new LNG wharf health assessment model considering structural weak areas

The structural health state of liquefied natural gas (LNG) wharf is important for the docking and operation of LNG ships. Based on the finite element modal analysis (FEMA) and evidential reasoning (ER) rule, a new health assessment model for the LNG wharf is proposed in this paper, where structural weak areas are considered. Firstly, combining the structural mechanism and FEMA, the LNG wharf is simulated and modeled. The weak areas of the wharf in common working modes are analyzed and obtained. Secondly, based on the analysis results, the sensor deployment is guided and the wharf health information is collected. Finally, based on the ER rule, the sensor monitoring information is fused to realize the health assessment of the wharf. This paper takes an LNG wharf in the Hainan Yangpu area of China as an example. The experimental results show that the proposed method can accurately and effectively assess the health state of the wharf.

Modelling liquefied natural gas ship traffic in port based on cellular automaton and multi-agent system

AbstractOver the past few decades, the number of liquefied natural gas (LNG) ships and terminals has been increasing, playing an important role in global clean energy transportation. However, the traffic capacity of LNG shipping in port areas is limited because of its high safety requirements. In view of this problem, a novel model is proposed to study the ship traffic in a port area by combining cellular automaton (CA) and multi-agent methods. Taking the CNOOC Tianjin LNG Terminal as an example, the ship traffic in Tianjin Port is simulated. Based on the simulation results, the LNG ship traffic capacity and its impact on the general shipping traffic flow under different special traffic rules are obtained. This model can provide theoretical support for optimising the port traffic organisation for LNG ships.

Numerical study of the boil-off gas (BOG) generation characteristics in a type C independent liquefied natural gas (LNG) tank under sloshing excitation

In this paper, a numerical model considering phase change and external heat leakage is established to study the thermodynamic and hydrodynamic of a type C LNG tank under sinusoidal sloshing excitation. The volume of fluid (VOF) method, coupled with the mesh motion treatment, is adopted to predict the movement of the vapor-liquid interface. The sinusoidal sloshing excitation is realized by a user-defined function (UDF). Compared with related fluid sloshing experiments, the feasibility of the numerical model is verified. The numerical results show that the sloshing excitation has great influences on the thermophysical process and the BOG generation of the LNG tank. The effects of different sloshing frequencies and amplitudes on the thermodynamic characteristics of the LNG tank are studied. In addition, the partial damage of the insulation system is also studied, and it is found that the sloshing has little effect on the critical superheat of the tank wall where the insulation layer is partial damaged, but it will delay the increase of the tank wall temperature. This study is significant to deeply understand the thermal behavior of the LNG sloshing and the characteristics of the BOG generation under sloshing condition during the actual marine transportation of LNG ships.

Performance and Regeneration of Methane Oxidation Catalyst for LNG Ships

Liquefied natural gas (LNG) use as marine fuel is increasing. Switching diesel to LNG in ships significantly reduces air pollutants but the methane slip from gas engines can in the worst case outweigh the CO2 decrease with an unintended effect on climate. In this study, a methane oxidation catalyst (MOC) is investigated with engine experiments in lean-burn conditions. Since the highly efficient catalyst needed to oxidize methane is very sensitive to sulfur poisoning a regeneration using stoichiometric conditions was studied to reactivate the catalyst. In addition, the effect of a special sulfur trap to protect the MOC and ensure long-term performance for methane oxidation was studied. MOC was found to decrease the methane emission up to 70–80% at the exhaust temperature of 550 degrees. This efficiency decreased within time, but the regeneration done once a day was found to recover the efficiency. Moreover, the sulfur trap studied with MOC was shown to protect the MOC against sulfur poisoning to some extent. These results give indication of the possible use of MOC in LNG ships to control methane slip emissions.

Liquefied natural gas supply chain using liquid air as a cold carrier: Novel method for energy recovery

A novel concept for energy integration across the liquefied natural gas (LNG) supply chain is proposed by using liquid air as a medium for recycling cold energy. This allows the natural gas liquefaction and LNG regasification stages to be integrated despite the long distance between the two sites. LNG carrier ship is used to convey liquid air on its return journey when it would otherwise be empty. On its return to the liquefaction site, the cold energy stored in the liquid air can then be harnessed to liquefy natural gas for transportation. At the regasification site, LNG cold energy is used to regenerate liquid air for the ship’s return journey. In this way, LNG cold energy, which is generally wasted, is used in the proposed LNG supply chain. As a result, the energy requirement for liquefying natural gas can be reduced significantly, and the waste LNG cold energy recovered. The proposed mixed refrigerant with liquid air (MRLA) process design has an energy requirement of 865.82–917.20 kJ/kg-LNG, which is 26.1–30.2% lower than that for a single mixed refrigerant (SMR) process. The proposed process exhibits even lower energy requirements with a much lower capital cost when compared to the propane precooled mixed refrigerant (C3MR) process (974.0–992.0 kJ/kg-LNG), known as one of the most efficient natural gas liquefaction processes. The results of exergy analysis for the proposed processes show that the cold energy supply from liquid air achieves a reduction in the energy requirement. Furthermore, a techno-economic study reveals that an 18.6–22.6% reduction in total costs for LNG liquefaction can be achieved and economically attractive to be implemented in commercial natural gas liquefaction plants, given the minimal infrastructural changes necessary. Overall using this novel approach, the liquefaction and regasification stages are integrated despite the physical separation of the individual processes over long distances. This significantly enhances the LNG supply chain by not only improving its energy performance but also contributes to the utilization of cold energy by using the empty LNG ship on the return journey.

Co-benefits of reducing CO2 and air pollutant emissions in the urban transport sector: A case of Guangzhou

The transport sector has become an important source of urban greenhouse gas (GHG) and air pollutant emissions, with the continuous growth of transportation demand. The co-benefits of reducing GHG and air pollutant emissions in the transport sector are receiving more and more attention. Taking Guangzhou as the case study city, this study quantitatively analyzed the co-benefits of reducing CO2 and air pollutant emissions under the sustainable scenario in the transport sector by developing a quantitative analysis model based on the Long-range Energy Alternatives Planning (LEAP) framework. The co-benefits quantitative parameter and the co-benefits radar chart analysis method are used to identify and evaluate the generated co-benefits, and then the co-benefits generated by implementing the sustainable measures are discussed. The results show that adjusting transport modes and increasing the application of electricity are the two most effective measures for achieving the co-benefits of reducing CO2 and air pollutant emissions in the Guangzhou transport sector. Thus, these two measures are highly preferential for mitigating CO2 and air pollutant emissions. In addition, increasing the application of biofuel and hydrogen energy also has good co-benefits. However, increasing the application of Liquefied Natural Gas (LNG) has poor co-benefits. Promoting the utilization of LNG intercity buses, trucks, and cargo ships will lead to emission increases of CO and HC compared to the current policy scenario, and small emission reductions of CO2 and other air pollutants. Therefore, to promote the utilization of LNG vehicles and ships, it is necessary to cooperate with the use of air pollutant end removal devices and high-pressure direct injection (HPDI) gas engines.

Optimization of the propulsion plant of a Liquefied Natural Gas transport ship

Stricter emission regulations and variability of fuel prices pose the focus on the optimization of steam turbine based propulsion plants of Liquefied Natural Gas (LNG) ships. The efficiency of such a propulsion plant has been improved in this work by studying the introduction of reheating and preheating stages in the onboard regenerative Rankine cycle. A thermodynamic model of the propulsion plant has been developed from the facility diagrams, being validated afterwards with available experimental data from actual ship operation. The predictions of different scenarios obtained by the model when introducing modifications in the power propulsion cycle showed promising results. It was found that a combination of preheating and reheating stages was found to increase the cycle efficiency up to 33.71%, reducing fuel consumption in around 20 t/day and CO2 emissions in more than 20,000 t per year. An exergy analysis of the impact of cycle modifications and an economic assessment of the proposed investment plan were performed. It was found that the boiler was the main contributor to exergy destruction, fact that justifies the cycle modifications performed. The economic analysis of the investment plan of implementing the selected alternative provided benefits even in a conservative scenario, with an Internal Rate of Return higher than 12% and a Pay-Back Period less than 9 years for all the studied scenarios. In summary, a practical industrial application of thermodynamic and exergy analysis to the propulsion plant of a LNG ship has been shown, allowing an efficiency, economic and environmental improvement.

Numerical simulation and experiment verification of the static boil-off rate and temperature field for a new independent type B liquefied natural gas ship mock up tank

In this paper, a new independent type B liquefied natural gas (LNG) ship mock up tank with the net capacity of 40 m3 and an insulation thickness of 400 mm was taken as the research target. After reasonable simplification, two-phase flow and phase change heat transfer of cryogenic fluid in the mock up tank was simulated by using unsteady three-dimensional CFD method. Volume of fluid (VOF) model was selected to track the vapour-liquid interface, Lee model was used as the phase change model, and the influence of the static pressure on the phase change model was considered. The temperature distribution and the static boil-off gas (BOG) generation rate of the mock up tank was calculated, and working conditions of the simulated tank under different liquid levels and partial insulation system damage were discussed. The pressurization characteristics of the mock up tank under closed conditions was also studied. Comparing the simulation with the experimental results, it showed that this model could effectively simulate the evaporation process of cryogenic liquids in the mock up tank under stationary conditions, which provides an important reference for the design and improvement of the new independent type B LNG ship.