Energy Of Liquefied Natural Gas Research Articles

A Thermodynamics Model for the Assessment and Optimisation of Onboard Natural Gas Reforming and Carbon Capture

The paper examines pre-combustion carbon capture technology (PreCCS) for liquefied natural gas (LNG) propelled shipping from thermodynamics and energy efficiency perspectives. Various types of LNG reformers and CCS units are considered. The steam methane reformer (SMR) was found to be 20% more energy efficient than autothermal (ATR) and methane pyrolysis (MPR) reactors. Pressure swing adsorption (PSA) had a lower energy requirement than membrane separation (MEM), cryogenic separation (CS), and amine absorption (AA) in pre-combustion carbon capture, with PSA needing 0.18 kWh/kg CO2. An integrated system combining SMR and PSA was proposed using waste heat recovery (WHR) from the engine, assuming similar efficiency for LNG and H2 operation, and cooling and liquefying of the CO2 by the LNG. The SMR-PSA system without WHR had an overall efficiency of 33.4% (defined as work at the propeller divided by the total LNG energy consumption). This was improved to 41.7% with WHR and gave a 65% CO2 emission reduction. For a higher CO2 reduction, CCS from the SMR heater could additionally be employed, giving a maximum CO2 removal rate of 86.2% with 39% overall energy efficiency. By comparison, an amine-based post-engine CCS system without reforming could reach similar CO2 removal rates but with 36.6% overall efficiency. The advantages and disadvantages and technology readiness level of PreCCS for onboard operation are discussed. This study offers evidence that pre-combustion CCS can be a serious contender for maritime propulsion decarbonization.Graphical

Techno-economic-environmental study and artificial intelligence-assisted optimization of a multigeneration power plant based on a gas turbine cycle along with a hydrogen liquefaction unit

According to the literature, there is a research gap concerning the practical heat recovery in solar-driven systems that have the capability to produce liquid hydrogen. In this study, an innovative combination of dual-loop solar-driven organic Rankine cycle and liquefied natural gas (LNG) heat recovery is designed to produce and liquefy hydrogen. The proposed system includes parabolic trough solar collectors (PTSCs), a Rankine cycle, a dual-loop organic Rankine cycle, LNG regasification process, proton exchange membrane (PEM) electrolyzer, and Claude hydrogen liquefaction cycle. A data-driven method is developed to analyze the system from techno-economic and environmental perspectives. The results show that LNG energy recovery improves the liquefaction work by as much as 7.96 kWh/kgH2. It is also concluded that the optimum compaction pressure range for the liquefaction cycle is 4.67 MPa, which is associated with better results. In these conditions, liquefaction work, liquefaction Coefficient of Performance (COP), and liquefaction exergy efficiency are 164.6 kJ/kg, 0.157 and 17.05%, respectively. To find optimum operating conditions, a supervised learning approach is applied to the developed code and the trained network is optimized using the genetic algorithm (GA). The optimization results reveal that a 10.98 $/h increase in total cost rate causes an 18% improvement in hydrogen production rate.

Development and modification of large-scale hydrogen liquefaction process empowered by LNG cold energy: A feasibility study

Hydrogen (H2) is considered a promising fuel and an energy carrier for carbon neutrality, but H2 has an issue in transportation and storage due to its low volumetric density. H2 liquefaction is an important technology in H2 supply that can overcome the low density issues, but the system has a serious challenge of high energy consumption. Thus, an improved energy efficient 50 ton day−1 of H2 liquefaction system comprising 4 mixed refrigeration cycles is proposed in this study. Especially, liquefied natural gas (LNG) was mainly used in the replacement of the precooling cycle, and the energy was saved by using the cold energy of LNG and generating electricity through vaporization. The specific energy consumption (SEC) of the proposed system was obtained as 3.996 kWh kg−1, however, particle swarm optimization (PSO) was implemented to increase energy efficiency of proposed process. As a result, the SEC of the optimized process was reduced to 2.917 kWh kg−1 where the LNG-cold energy control during the optimization was crucial to improve the energy efficiency. In addition, the economic and environmental feasibility were investigated. For the optimized process, the cost of the liquefied H2 (LH2) model was calculated as 1.37 $ kg-1, and 1.14 kgCO2 kg−1LH2 emissions were recorded as a result of environmental assessment. Moreover, the uncertainty analysis was implemented to assess the degree of the cost variance and the possibility of H2 production from water electrolysis was quantified. Unfortunately, electrolysis-based LH2 was hard to be economically better than steam methane reforming-based H2, however, alkaline water electrolysis-based LH2 showed the potential to overcome that of steam methane reforming in the future through technological advancement and reduction in production cost. The proposed H2 liquefaction process has a highly improved energy consumption rate, and this process can contribute to developing the H2 economy and become the potential candidate to overcome storage and transportation issues.

Exhaust emissions reduction and fuel consumption from the LNG energy system depending on the ship operating modes

In today’s environment of increasing pressure to reduce fuel consumption and emissions of carbon dioxide (CO2) and nitrogen oxides (NOx), the LNG (Liquefied Natural Gas) transportation industry is growing in size and influence. In this context, further efforts are needed to improve the energy efficiency of LNG marine energy power plant. The LNG vessels and their equipment considered in this study have different power consumption requirements depending on the vessel’s mode of operation (loading/unloading, maneuvering, anchoring, at sea, etc.). For each ship mode, where the power plant requirements are the same, the specific fuel consumption (SFOC) and exhaust emissions, NOx and CO2, are compared with a different number of engines in the network to find the optimal number of engines in the network, considering both the safety aspect and the port requirements. An analysis was performed showing the efficiency of the on-board power management system (PMS) in terms of manual load sharing between engines. A comprehensive analysis of the data and its comparison led to the conclusion that the manual distribution of power among the engines is the slightly better solution. The obtained results show that further analysis of the number of engines for a given load with minimum fuel consumption and CO2 and NOx emissions is required.

Design and optimization of LNG-powered ship cold energy and waste heat integrated utilization system based on novel intermediate fluid vaporizer

Based on a novel integrated intermediate fluid vaporizer with liquefied natural gas (LNG) cold energy utilization proposed by the author's team, a full-power generation integrated system is constructed in this study. It is a two-stage cascade Rankine cycle with two-stage condensation and coupled with a trans-critical CO2 Rankine cycle. This study regards a river–sea direct transportation type of 25,000-ton LNG fuel-powered chemical ship as the application object and considers combined utilization of the medium-temperature waste heat of flue gas from the exhaust turbine power generation cycle outlet and the vaporization cold energy of LNG. Through the simulation and analysis of the scheme, circulating working fluid optimization and operation parameter optimization based on a genetic algorithm are conducted. The overall exergy efficiency of the optimized system reaches 45.1%, while the power generation of the system reaches 72.66 kW. Furthermore, economic analysis shows that the net annual income of the optimized system can reach 280,700 yuan, and the recovery cycle of initial investment cost is expected to be 6.11 years.

Theoretical analysis of liquefied natural gas cold energy recovery using thermoelectric generators

This paper presents a complex thermo-electric analysis of liquefied natural gas (LNG) cold energy recovery system using thermoelectric generators (TEG). The modeling uses the concept of effective thermal conductivity. In addition, it includes not only heat transfer and electric phenomena in TEG module but also all other secondary heat transfer processes: boiling of liquefied natural gas, conduction through walls, thermal contacts at both side of TEG and convection at the water side. Analysis is firstly made for commercial TEGs which are designed for operation at different temperatures. Next part of the analysis aims to optimize the geometry of TEG to temperature specific for liquefied natural gas. It is shown that the optimization of TEGs geometry for LNG conditions can lead to 50% increase of electric power generation. Moreover, for assumed filling factor of between 0.4 to 0.6, the length of TEG module should be between 0.4 mm to 0.7 mm. The conducted analysis provides important information on the possibility of recovering the cold energy of LNG using TEG modules.

Design and analysis of an efficient hydrogen liquefaction process based on helium reverse Brayton cycle integrating with steam methane reforming and liquefied natural gas cold energy utilization

In order to solve the high energy consumption of the hydrogen liquefaction process, the conceptual design of an integrated hydrogen liquefaction system is proposed and performed by integrating the steam methane reforming (SMR) process and the utilization of liquefied natural gas (LNG) cold energy. Before LNG enters the SMR process, its cooling energy is utilized in the pre-cooling section, which can reduce the use of liquid nitrogen (LN2) and improve performance. The inert gas helium is relatively safe as a refrigerant in the cooling and cryogenic section and performs well in small and medium-sized hydrogen liquefaction systems. The proposed design which produces 5 t/d of liquid hydrogen (LH2) is compared to a based case only using LN2 for pre-cooling to verify its effectiveness and feasibility. Comprehensive comparative analysis reveals that the specific energy consumption (SEC) of the proposed process is reduced from 10.78 kWh/kg LH2 to 7.948 kWh/kg LH2, and the COP is improved from 0.1205 to 0.1634. The use of LNG cold energy makes the fuel cost of the proposed system only account for 73.7% of the base case, which makes it perform better in terms of recurring investment. In conclusion, the present method and results can provide a reference for the design of integrated hydrogen production and liquefaction system by reducing energy consumption, taking into account the recovery of the cold energy of LNG.

Advanced exergy and exergo-economic analyses of a novel combined power system using the cold energy of liquefied natural gas

In this study, a new combined power system using the cold energy of liquefied natural gas (LNG) is designed. Conventional and advanced exergy and exergo-economic analyses of the system were made. According to the research in the literature, for the first time, advanced exergo-economic analysis was applied to a combined power system using the cold energy of LNG with the Modified Productive Structure Analysis (MOPSA) method. 23% of the exergy destruction and exergy destruction cost rate of the combined system is avoidable. In both conventional and advanced exergy analysis, the highest exergy destruction and cost rate were found in the parabolic solar collector. In addition, as a result of the analyses, it has been seen that the most effective main system components with the potential to improve the performance of the combined system are the parabolic solar collector, the turbine in direct expansion cycle and the turbine in the Organic Rankine cycle, respectively. The study revealed that there is potential to improve the performance of the proposed combined power system.

Heat and mass transfer analysis and optimization of freeze desalination utilizing cold energy of LNG leaving a power generation cycle

Freeze desalination (FD) works upon the separation of impurities from pure water during ice crystals formation. The required cold source could be supplied by the cold energy of liquefied natural gas (LNG). In the current study, freeze desalination of seawater is explored by directly exploiting the cold energy of LNG within an appropriate range of temperature after producing work in a power generation cycle. A detailed discussion has been given on the inlet temperature of LNG to the FD unit for the first time. The direct utilization has the privilege of eliminating the addition of a secondary refrigerant and its refrigeration cycle to the FD process. A multi-objective optimization is conducted to specify the optimal conditions to acquire the highest ice mass with lowest salinity. Results show that decreasing LNG inlet temperature from −10 to −60 °C improves the ice mass production from 60.9 to 977.6 g, whereas diminishing its quality by 90%. Also, increasing Reynolds number of LNG from 4000 to 32,000 leads to the production of 492 g more ice and increment of ice salinity from 1.22 to 1.56%. Finally, conducting multi-stage freezing reveals that for Reynolds numbers below 16,000, potable water is achievable after three-stage desalination.

Thermodynamic Investigation of a Trigeneration ORC Based System Driven by Condensing Boiler Hot Water Heat Source Using Different Working Fluids

This study conducts thermodynamic analysis on three trigeneration cycles including Organic Rankine Cycle (ORC), Liquefied Natural Gas (LNG) cold energy, and absorption refrigeration cycle in order to select appropriate working fluids. Different types of ORC cycles including simple ORC, regenerative, and ORC with Internal Heat Exchange (IHE) were investigated. For those types, the operation of six working fluids with different thermodynamic behaviors (R141b, R124, R236fa, R245fa, R600, and R123) was evaluated. In power plants, a low-grade heat source was provided by condensing boiler hot water energy while the thermal sink was prepared by cold energy of LNG. The effect of boiler temperature variation on energy and exergy efficiencies was investigated. According to the derived results, regenerative ORC-based systems possessed maximum energy and exergy efficiencies, while simple ORC and ORC with internal heat exchanger exhibited approximately the same quantities. Also, among these analyzed working fluids, R141b had the maximum energetic and exergetic efficiencies, while R124 and R236fa had minimum performance.

Analysis and efficiency enhancement for energy-saving re-liquefaction processes of boil-off gas without external refrigeration cycle on LNG carriers

Re-liquefaction of boil-off gas (BOG) that is inevitably generated owing to heat leaks in liquefied natural gas (LNG) carriers can result in energy savings and protection of the environment. Because the direct re-liquefaction process without an external refrigeration cycle requires lower power and smaller size of the system than existing re-liquefiers, two novel direct re-liquefaction processes are proposed: (1) a dual-pressure Claude re-liquefaction process (DCRP) with BOG as the refrigerant, which adopts an improved BOG cycle structure and reasonable initial parameters; (2) a re-liquefaction process based on the LNG direct expansion refrigeration cycle (LERP), which, for the first time, completes the re-liquefaction of BOG using the cold energy of LNG directly. The two processes are simulated and analyzed using Aspen HYSYS. The results reveal that the specific energy consumption (SEC) and exergy efficiency (EXE) of the DCRP are 0.6338 kWh/kgLNG and 45.7%, respectively, while those of the LERP are 0.7012 kWh/kgLNG and 37.63%, respectively. The exergy losses of the two re-liquefaction processes are 1089.54 kW and 1325.60 kW, respectively. Compared with the indirect re-liquefaction processes, the direct re-liquefaction processes offer better performance and exhibit simpler structures and are thus more attractive re-liquefaction systems on LNG carriers.

Energy, exergy and economic analysis of offshore regasification systems

Energy, exergy and economic analysis are proposed herein to evaluate regasification systems in Floating Storage Regasification Units (FSRUs). Three regasification systems typical in these types of vessels are considered: seawater system, open loop propane system and closed loop water-glycol system. The energy and exergy analyses were performed using the Engineering Equation Solver (EES), while Suite AspenONE programmes were used for the economic assessment. The exergy analysis provides a better understanding of the components of physical exergy (thermal and mechanical exergy) in order to define an exergy efficiency applicable to any liquefied natural gas (LNG) regasification system or FSRU. The results obtained prove the seawater regasification system to be most efficient from an energy and exergy standpoint. The specific energy consumption and exergy efficiency for this system are 227.33 kJ/kg and 50.00%, respectively. On the other hand, the open loop propane regasification system is most cost-effective for an LNG price between 1.32 and 11 USD/MMBtu. The vast amounts of destroyed exergy in the regasification process of current systems was also demonstrated and hence the need to develop new, more efficient configurations that could exploit the cold energy of LNG.

Heat recovery in an actual LNG supply chain: Retrofitting of designed heat exchange networks (HENs) for potential fuel saving

The demand for liquefied natural gas (LNG) is steadily increasing and projected to become an important component of global energy demand. Although LNG processing requires high-energy to convert the gas into liquid, it is still the most preferable method of supply due to technical, economic, safety, and political reasons. Energy integration strategies and process optimization between units have been emphasized as ways to reduce energy demand. In this study, a rigorous simulation for proposed heat exchanger networks (HENs) between sulfur recovery units (SRU) and gas sweetening units (GSU) that exhibit heat sources and sinks was conducted. The HENs were designed using pinch analysis tools in Aspen Energy Analyzer (AEA) and were used to determine the maximum energy recovery and potential fuel savings after retrofitting within LNG supply chain. The feasibility of retrofitting the HENs into LNG plant without affecting process conditions or product quality was also determined. Although universal HEN reduces energy consumption of the existing plant by 68%, the network complexity limits its practical application. Simplified HENs between the sub-units reduced energy demand by 50% and achieved fuel saving of 34%. Retrofitting HENs improved existing LNG energy integration, enhanced process economy, reduced fossil fuel burning and protected the environment.

Backtracking and prospect on LNG supply chain safety

The safety issues of Liquefied Natural Gas (LNG) in production, storage, loading/unloading, transportation/shipping, and re-gasification have became a major concern, since an accident in the LNG industry would be very costly. Understanding the threat of LNG not only contributes to the process safety and reliability in the research and development (R&D) system, but improves the efficiency of loss prevention, fire protection and emergency responses. As of April 2019, in order to obtain the present status and trend of LNG safety research, basing 1122 documents of the Web of Science database about safety research of LNG as a data source, CiteSpace and VOS viewer were used for network knowledge map analysis. A comprehensive knowledge map of LNG safety field was obtained from several research aspects including scientific research power, research hot spots and trends, research knowledge base and frontier. According to the study results, the development of LNG safety research was divided into four stages from 1970s to 2019, China and South Korea made a lot of contributions, and the United States is the most influential. Among them, the research from 2005 to 2019 was the most representative. Current research results indicate that a combination of Formal Safety Assessment (FSA) methodology and Dynamic Procedure for Atypical Scenarios Identification (DyPASI) will fully identify risks; The PHAST and TerEx programs quickly define safety zones. Computational Fluid Dynamics (CFD) software package can provide accurate quantitative data for the study of LNG safety. Research on quantitative risk assessment (QRA) and LNG evaporated gas (BOG) has been a hot topic and trend in this field. The application of expansion foam in LNG accident mitigation covers most of the research content in this field, and the optimization of LNG liquefaction process has a great influence on this industry. As the international demand for LNG energy output increases, floating liquefied natural gas (FLNG) will have considerable development, and increasingly researchers attach vital importance to the safety of LNG offshore production integrated unit.

Investigation of measurement uncertainties in LNG density and energy for custody transfer

In the custody transfer of fuels such as liquefied natural gas (LNG), energy measurement accuracy is critical. The important elements in calculating transferred energy are the volume, the density and the superior calorific value (SCV). In this paper we have used a new approach to carefully study the various uncertainty factors contributing to two of these elements: the density and the SCV. For density, six methods were evaluated, namely the method of extended corresponding states, the Hiza method, the revised Klosek–McKinley method, the Groupe Européen de Recherche Gazière (GERG-2004) method, the GERG-2008 method, and the equation of state–LNG method, to estimate the modelling error in the density calculation. Other factors affecting LNG density estimation (LNG composition, reference densimeter, temperature and pressure) have also been investigated to derive the total uncertainty in LNG density estimation. For the SCV, the uncertainty has been analysed with consideration given to uncertainties in the composition and the SCV of LNG components. The expanded uncertainty in LNG energy during custody transfer is estimated to be 0.58% (k = 2) after considering the uncertainties due to the membrane-type tank’s unloaded LNG volume, SCV, density and their correlation effect.

Thermodynamic investigation and optimization of two novel combined power-refrigeration cycles using cryogenic LNG energy

• Develop two novel combined cycles into optimal usage of LNG cryogenic energy. • Thermodynamic analysis and optimization of two novel proposed cycles. • uncertainty analysis of two novel combined cycles. • Increasing the cold energy utilized by novel cycles compared to direct LNG evaporation. • Reducing the exergy destruction of the heat transfer process using the novel cycles. The present study aimed to introduce two novel combined power-refrigeration cycles into optimal usage of liquefied natural gas (LNG) cryogenic energy and reduce exergy destruction due to high-temperature difference in the heat transfer process. The combined cycles include a compression-ejector refrigeration cycle and two low and high-pressure Rankine cycles in which the power required to drive the compression-ejector refrigeration cycle compressor is provided by the power generated by the two low and high-pressure Rankine cycle turbines. Increasing the utilizable cooling energy of LNG is considered as the benefits of the new combined cycles compared to direct LNG evaporation. A comprehensive thermodynamic analysis, along with optimizing both novel combined power-refrigeration cycles, was performed through the first and second thermodynamics laws and the constant area model assumption for the ejector. Analyzing the design parameters demonstrated that the maximum energy efficiency, exergy efficiency, and the highest refrigeration increasing ratio (RIR) increase in both novel combined power-refrigeration cycles as increasing the pump discharge pressure and decreasing turbine outlet pressure of the low-pressure Rankine cycle. The maximum thermal efficiency and exergy efficiency were 77.3% and 23.7% in cycle І and 87.5% and 23.9% in cycle ІІ, respectively, through performing optimization in the boundary set for the design parameters. Finally, the highest obtainable cooling energy to direct the evaporation of LNG ratio in the two cycles І and ІІ was 62.6% and 73.9%, respectively.

Hydrogen liquefaction process with Brayton refrigeration cycle to utilize the cold energy of LNG

A thermodynamic process is investigated and designed for hydrogen liquefaction system to utilize the cold energy of liquefied natural gas (LNG). This study is an initial effort of newly launched five-year governmental project in Korea, aiming at efficient hydrogen liquefiers. Since Korea is a major LNG import country, the cold energy is abundantly available and could be useful in reducing the liquefaction cost. Hydrogen gas at ambient temperature is pre-cooled by LNG and then fed into a closed-cycle Brayton refrigerator. Rigorous thermodynamic analysis is carried out on the process with standard or modified Brayton cycles for the optimal condition to minimize the power consumption. It is revealed that LNG at atmospheric pressure is much more effective in pre-cooling than pressurized LNG (for pipeline distribution), because of the temperature pinch problem in heat exchanger. By taking into consideration the efficiency and other factors such as safety, compactness, and simplicity of operation, 2-stage expansion cycle with LNG pre-cooling is identified as most suitable for the pilot system with a capacity of 0.5 ton/day. Full details of liquefaction process are presented with the optional use of catalysts for ortho-para conversion.

Design and simulation optimization of cold storage and air conditioning system in LNG powered carrier by using cold energy of LNG based on HYSYS

In order to solve the problem that the LNG (Liquefied Natural Gas) cold energy in LNG powered carrier is not used sufficiently, a set of system is designed. This cold storage and air conditioning system is used in LNG powered carrier. At the same time, the refrigerant required by the system is selected and simulate the process of the system by HYSYS. This paper describes the specific process and gives the simulation parameters of each node. The simulation results meet the expected requirements and accord with the actual situation. The main purpose of this system is to reduce energy consumption by using LNG cold energy as a cold source of cold storage and room air conditioning.

Thermodynamic Performance Study of the SOFC–GT–RC System Fueled by LNG With CO2 Recovery

Abstract Distributed energy technology is an important developing direction of the future energy technology. This paper puts forward a distributed energy system named SOFC–GT–RC (solid oxide fuel cell–gas turbine–recovering carbon dioxide) with liquefied natural gas (LNG) as fuel and recovering carbon dioxide. In the system, the cold energy of LNG can not only cool the compressor inlet air to reduce the consumption of compressor work, but also to supply cold energy and to recover CO2. Based on the mathematical model of each part, the thermodynamic calculation model of the whole system is built by fortran, which is embedded in aspen plus. The results of calculation indicate the thermal efficiency and total power efficiency are 74.5% and 56.7% while the exergy efficiency is 61.8%. In addition, some operating parameters such as fuel utilization factor and fuel flow rate are selected. Based on these operating parameters, the new system thermodynamic performance is studied. The results point that this SOFC–GT–RC system fueled by LNG increases the total power and decreases waste of cold energy and the pollution of the environment, which would be an effective utilization style of energy in China's LNG satellite stations.

Energy analysis and multi-objective optimization of waste heat and cold energy recovery process in LNG-fueled vessels based on a triple organic Rankine cycle

Due to the high level of pollutant emissions from traditional marine diesel engines, Liquefied Natural Gas (LNG) as clean energy is becoming a better choice for main engines to replace the traditional fuels. Meanwhile, in order to improve the energy efficiency of the marine power system, the Organic Rankine Cycle (ORC) has been regarded as the most suitable solution to recover the waste heat for the power generation of vessels. In this paper, both the waste heat of the main engine and the cold energy of LNG have been fully considered, and a novel triple ORC process has been proposed for the waste heat and cold energy recovery of LNG-fueled vessels. It adopts the exhaust gas of the main engine and the cooling water from the engine jacket as heat sources, and uses the cold energy of LNG and the sea water as cold sources. Based on the 15 optional working fluid conditions, the heat source utilization rate, system exergy efficiency, net output power, and system cost are, respectively, combined as two objectives, and the multi-objective adaptive firefly algorithm is used to optimize the thermodynamic performance of the system. The optimization results of different heat and cold sources as well as the design parameters have been discussed. Finally, the system's exergy loss has been analyzed to make suggestions for further improvement. The results show that this novel ORC system can better meet the energy recovery requirements of LNG-fueled vessels, with higher net output power, lower cost, and greater energy recovery efficiency. The largest exergy loss of the system exists in the condensers of the stages 2 and 3, and the expanders in the various stages. Therefore, subsequent cooling energy recovery and the use of Stirling engines can be considered to further improve the system efficiency.