Liquefied Natural Gas Regasification Research Articles

Numerical Modeling and Experimental Validation of Icing Phenomena on the External Surface of a U-Bend Tube

The regasification of liquefied natural gas (LNG) is a crucial process that involves certain challenges created by the low temperature of LNG and the risk of ice formation on the external surfaces of the tubes of heat exchangers, which can hinder heat transfer and increase flow resistance. This study presents a numerical model for ice formation on the external surface of the U-bend tube of shell-and-tube heat exchangers. The numerical model has been further enhanced by applying a custom user-defined function. The numerical results were validated using experimental data and demonstrated excellent predictive capability, particularly for the surface temperature of the tubes and the thickness of the ice layer. Hence, this model can reliably capture the overall behavior of the ice formation on the external surfaces of the tubes of shell-and-tube heat exchangers. By highlighting the importance of maintaining stable heat transfer conditions to prevent freezing, this study offers valuable insights that can guide the optimization of heat exchanger designs for LNG regasification.

Integration of the single-effect mixed refrigerant cycle with liquified air energy storage and cold energy of LNG regasification: Energy, exergy, and efficiency prospectives

The escalating global energy demand has prompted increased focus on the industry of liquefied natural gas (LNG), emphasizing the need for optimizing liquefaction processes to minimize capital costs. Thus, the integration between liquified natural gas LNG regasification and liquid air energy storage (LAES) to produce electricity and utilize the cold energy of LNG regasification has several interests to maximize the benefits of the process to generate power and face the challenges such as energy saving and reducing the total operations costs … etc. Fortunately, this study introduces a novel approach that combines a single-effect mixed refrigerant (SMR) cycle with air liquefaction, incorporating regenerative Rankine cycles for enhanced efficiency. The effectiveness of the LNG-SMR-LAES process was evaluated using comprehensive energy, exergy, and economic analyses to ascertain its viability. The results showed a notable improvement in the overall net power energy by 6 % and an increase in exergy efficiency by 11.7 % compared to the base case. Energy savings of 31.6 % (470.10 kW) contributed to the process's environmental and economic feasibility. The net present value was estimated at 11,230.4 US dollars, affirming the industrial-feasible design and economic viability of the LNG-SMR-LAES process.

Impact and Technical Solutions of Hydrodynamic and Thermodynamic Processes in Liquefied Natural Gas Regasification Process

Transporting natural gas in liquid form increases opportunities for storage and export worldwide, thus making transportation more sustainable. However, liquefied natural gas (LNG) is in an unsteady state, leading to LNG conversion to the gas state occurring throughout the storage, loading, unloading, and transportation processes. To observe the transition of LNG to natural gas, mathematical models are developed to monitor technical parameters. This research analyses a floating storage and regasification unit for and adopts a mathematical model of the LNG regasification system, aiming for improved observation of hydrodynamic, dynamic, and thermo-physical properties. The complex mathematical model of the system was implemented using the Fortran programming language and MATLAB R28a. From the investigation of the total LNG regasification system, it could be concluded that increasing the outlet pressure of the system results in a decrease in the velocity of LNG. It was found that the total hydraulic energy losses of the total LNG regasification system were approximately 41.3 kW (with outlet pressure of 2 MPa), 12.75 kW (with outlet pressure of 5 MPa), and 4.24 kW (with outlet pressure of 7 MPa).

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.

Co-benefits of the liquid hydrogen economy and LNG economy: Advances in LNG integrating LH2 production processes

Against the global energy transition towards decarbonization and zero-carbon targets, hydrogen (H2) has emerged as a promising medium for energy storage and transportation in large-scale systems. Simultaneously, liquefied natural gas (LNG), serves as a transitional resource in moving towards cleaner energy sources. Consequently, the integration of LNG into liquid hydrogen (LH2) has garnered significant attention in recent years. This paper comprehensively reviews current research on LH2 production processes by integrating the energy mass of LNG. These processes, which include pre-cooling H2 utilizing the cold energy released from LNG regasification, producing blue H2 from natural gas (NG) derived from LNG regasification, synergistic liquefaction of NG and H2, and simultaneous production of LNG and LH2 from industrial by-products, can markedly increase the thermodynamic efficiency. Furthermore, this study explores potential future developments that could benefit both aspects of the LH2-LNG economy, thereby expanding the scope of related research. The integration of LNG into the LH2 production process through an energy mass approach, aimed at creating a mutually beneficial LH2-LNG economy, is an effective strategy for fostering energy transition. Finally, a brief discussion is presented on the constraints and challenges that may affect the future growth of the global LH2-LNG economy.

Sensitivity and sustainability analysis of combined cycle plant with integrated LNG pressure energy recovery

Although combined cycle power plants (CCPPs) and liquefied natural gas (LNG) have arisen as solutions to the intermittent nature of renewable energy sources, they still need creative methods for performance enhancement and sustainability of the energy systems. Moreover, the energy efficiency of CCPPs is negatively impacted by environmental conditions, higher specific fuel consumption and a large quantity of waste heat released into the ambient. On the other hand, using seawater as a heating medium in LNG regasification circuits has a detrimental effect on the marine ecosystem. In this context, the LNG pressure energy recovery system through a direct expansion cycle (DEC) integrated with CCPP is proposed to improve sustainability, enhance exergetic performance and to reduce the heat recovery steam generator (HRSG) exhaust loss. To improve the cycle performance, low grade heat harnessed from CCPP is used as the heat source in the DEC rather than seawater. The system performance is analyzed by the energy and exergy method through a mathematical model. Moreover, the sensitivity analysis of the combined system is accomplished to examine the influence of LNG flow rate and ambient temperature on various performance indicators of the total system. It is observed that the integration of DEC boosts the HRSG performance by reducing the stack exergy loss and the efficiency is sensitive to LNG flow rate. The total integrated system energy efficiency ηtot, enhanced to 1.55% compared to the base case. Whereas, for ambient temperature in range of 15 – 45 °C, the system minimum and maximum exergetic efficiency ηex,tot is found to be 54.52 % and 55.94 %. Furthermore, the comparison of exergetic sustainability indicators is calculated and presented for three different simulation cases. The results demonstrate that increase in ηex,tot, affects the environment impact factor, ref and the sustainability index, θsi and improved 2.09 % compared to base case combined cycle.

A novel designation of LNG solid oxide fuel cells combined system for marine application

This paper presents a pioneering multigeneration system for marine vessel applications, involving the integration of solid oxide fuel cells (SOFCs) fueled by liquefied natural gas (LNG), coupled with LNG cold energy utilization cycles and exhaust gas heat recovery systems. The system comprises a tandem arrangement of organic Rankine cycle (ORC) and trans-critical carbon dioxide cycle (TCO2), specifically engineered to harness the cold energy released during LNG regasification process. The elevated temperature exhaust gases emanating from the SOFC are efficiently recuperated through a series of components including a gas turbine (GT), regenerative, steam Rankine cycle (SRC), and waste heat boiler (WHB). The proton exchange membrane fuel cells (PEMFC) is designed to enhance the overall operational flexibility and responsiveness of the multigeneration system. The Aspen Hysys V12.1 is used to simulate the propose system and numerical method is employed to parameter optimize of system. The first and second laws of thermodynamics are applied to establish the thermodynamics equations and calculated the system performances. The described system is estimated to obtain energy efficiency of 69.32 % and exergy efficiency of 33.85 %. The high-temperature exhaust gas harvesting integrated systems are sufficiently generated 2091.24 kW which accounted 35.49 % of entire power generate. Furthermore, the parametric researches are implemented to examine the influence of current density, β values to the performance indicators of systems. The WHB is designed to generate 1081 kg/h of superheated vapor at 170 °C and 405 kPa for various purposes of seafarers and equipment's onboard ship. The economic feasibility is performed to view the possibility of investment, maintenance cost and payback period for the described system.

Оптимизация перевозок термочувствительных грузов в рефрижераторных контейнерах с применением альтернативных источников энергии

Purpose: to consider the main problems of transportation of temperature-sensitive cargoes in refrigerated containers (refcontainers). To show the possibilities of transportation optimization through the introduction of alternative energy sources. Methods: comparison of technical and economic indicators of diesel, hydrogen and hydrogen plants is carried out. The exergetic method of estimating the effect of replacing diesel fuel with LNG was applied. Results: the article defines the peculiarities of cargo transportation in containers with built-in refrigeration units — autonomous refcontainers. Classification of existing energy units for power supply of refcontainers is given. The design of an autonomous installation for power supply of refcontainers is described. Environmentally safe alternatives for providing autonomous power supply of refrigerating units of refrigeration containers are proposed. The advantages of autonomous power supply based on high-temperature fuel cells are presented. An autonomous power unit with liquefied natural gas (LNG) as fuel is described. The feasibility of utilization of cold from LNG regasification is analyzed in order to ensure the stability of refcontainer operation. The estimation of the expected effect from the use of alternative fuels for autonomous power supply is made. Practical significance: the obtained results can be used for modernization of low-capacity power plants used in refrigerated and other types of transport.

Assessment of a sustainable multigeneration system integrating supercritical CO2 Brayton cycle and LNG regasification: Thermodynamic and exergoeconomic evaluation

This study proposes a cost-effective multigeneration system that integrates a supercritical carbon dioxide (sCO2) power cycle with a liquefied natural gas (LNG) regasification process. The system aims to deliver electricity, cooling, heating, and hydrogen simultaneously. Utilizing the temperature difference between the sCO2 cycle and the LNG thermal sink, an ammonia-water-based absorption refrigeration cycle (ARC) recovers waste heat from the sCO2 power cycle, producing cooling. The elevated ammonia concentration at the ARC's condenser outlet is leveraged by a heat pump system for heating production. Concurrently, cold energy from LNG is used to recover latent heat from the condenser and heat rejected from the sCO2 power cycle, providing inputs for additional electrical power through an NG turbine. The system incorporates a PEM electrolyzer (PEME) for hydrogen production. A comprehensive examination, including energy, exergy, and exergoeconomic analyses, evaluates system performance. A sensitivity analysis illustrates the impacts of key parameters. In the baseline scenario, the system achieves energy and exergy efficiencies of 62.79% and 54.89%, with a low product unit cost of 11.35 ($/GJ). The system demonstrates substantial net power output (259.184 MW), cooling capacity (88.938 MW), heating capacity (2.839 MW), and hydrogen production (391.68 kg/h). This robust performance, coupled with cost-effectiveness, positions the proposed system as a versatile and impactful solution for sustainable and environmentally friendly energy applications.

LNG AND CLIMATE CHANGE: EVALUATING ITS CARBON FOOTPRINT IN COMPARISON TO OTHER FOSSIL FUELS

The increasing global demand for energy, coupled with growing concerns about climate change, has prompted a critical examination of the environmental impact of various energy sources. Liquefied Natural Gas (LNG) has emerged as a significant player in the energy landscape, touted for its potential as a cleaner alternative to traditional fossil fuels. This review provides a concise overview of a comprehensive evaluation that assesses the carbon footprint of LNG in comparison to other fossil fuels. The research delves into the lifecycle analysis of LNG, scrutinizing its carbon emissions from extraction and production to transportation and combustion. This holistic approach seeks to unravel the nuanced environmental implications associated with LNG utilization. Comparative analyses with conventional fossil fuels such as coal and oil are conducted, aiming to offer a comprehensive understanding of LNG's relative environmental performance. Key aspects covered include the environmental considerations throughout the LNG supply chain, encompassing extraction, liquefaction, shipping, regasification, and combustion. Special attention is given to technological advancements and innovations that influence the carbon intensity of LNG operations. The assessment incorporates recent data and insights, providing an up-to-date perspective on the evolving landscape of LNG's carbon footprint. The review highlights the significance of evaluating the entire spectrum of emissions associated with different fossil fuels, acknowledging the varying impacts on global warming potential. Additionally, the research considers regional and geopolitical factors influencing the sourcing and consumption of LNG, contributing to a nuanced understanding of its carbon profile in diverse contexts. As the world navigates the transition towards a more sustainable energy future, this research aims to contribute valuable insights into the role of LNG in mitigating climate change. The findings have implications for policymakers, industry stakeholders, and environmental advocates, offering a basis for informed decision-making and strategic planning in the pursuit of a low-carbon energy paradigm.
 Keywords: LNG, Climate, Carbon, Footprint, Fossil Fuels.

The Application of Cryogenic Carbon Capture Technology on the Dual-Fuel Ship through the Utilisation of LNG Cold Potential

The International Maritime Organization (IMO) has set targets to reduce carbon emissions from shipping by 40% by 2030 (IMO2030) and 70% by 2040 (IMO2050). Within the framework of decarbonising the shipping industry, liquefied natural gas (LNG) fuel and carbon capture technologies are envisioned as a transitional option toward a pathway for clean energy fuels. The aim of the complex experimental and computational studies performed was to evaluate the CO2 capture potential through the utilisation of LNG cold potential on the FSR-type vessel within a dual-fuel propulsion system. Based on the experimental studies focused on actual FSRU-type vessel performance, the energy efficiency indicators of the heat exchanging machinery were determined to fluctuate at a 0.78–0.99 ratio. The data obtained were used to perform an algorithm-based systematic comparison of energy balances between LNG regasification and fuel combustion cycles on an FSRU-type vessel. In the due course of research, it was determined that LNG fuel combustion requires 18,254 kJ/kg energy to separate and capture CO2 in the liquid phase to form exhaust gas; meanwhile, low sulfur marine diesel oil (LSMDO) requires 13,889 kJ/kg of energy. According to the performed calculations, the regasification of 1 kg LNG requires 1018 kJ/kg energy, achieving a cryogenic carbon capture ratio of 5–6% using LNG as a fuel and 7–8% using LSMDO as a fuel. The field of carbon capture in the maritime industry is currently in its pioneering stage, and the results achieved through research establish an informative foundation that is crucial for the constructive development and practical implementation of cryogenic carbon capture technology on dual-fuel ships.

Thermo-economic-environmental evaluation of an innovative solar-powered system integrated with LNG regasification process for large-scale hydrogen production and liquefaction

In order to achieve a sustainable energy future, it is of utmost importance to harness solar energy for the production of liquid hydrogen. This undertaking is justified by the significant role that liquid hydrogen plays as a clean and highly efficient fuel source, effectively addressing the pressing concerns regarding greenhouse gas emissions and reducing reliance on conventional fossil fuels. An additional advantage lies in the easy storage and transportation capabilities of liquid hydrogen, making it a viable solution for energy storage across diverse sectors. In this regard, the current research presents a novel solar-powered setup consisting of parabolic trough solar collectors (PTSCs), a sequential organic Rankine cycle (ORC), a liquefied natural gas (LNG) regasification unit, and a module dedicated to the production and subsequent liquefaction of hydrogen. A meticulously crafted MATLAB code is utilized to replicate the operations of the proposed system, facilitating a thorough examination of its energy, exergy, environmental, and economic performance. The proposed system exhibits a net output power of 1.13 MW and possesses the capacity to produce hydrogen at a rate of 34.92 kg/h, featuring a levelized cost of hydrogen (LCOH) of 3.59 $/kg. Additionally, the system encompasses a cooling capability of 192 kW. From an environmental perspective, this configuration contributes to a decrease in carbon dioxide emissions by 255.96 kg/h. After conducting a dynamic analysis with meteorological data, it was determined that the system has the potential to generate an annual hydrogen output of 536.84 tons in San Francisco.

An innovative renewable energy–based tri-generation system for electricity, LNG regasification and hydrogen production

Waste incineration is a potent technique, that deals with the waste generated in a sustainable way to properly manage and reduce the generated waste and produce useful energy simultaneously. However, the waste-to-electrical efficiency of incineration plants is less (20–22) % because of the high moisture content of waste and flue gas heat losses. In the present study, a tri-generation system consisting of a solar parabolic trough collector integrated with a waste-to-energy plant, a liquefied natural gas (LNG), and a hydrogen production system is proposed and thermodynamically investigated. Parabolic trough collectors serve as a secondary heating source to the steam coming out of the incineration boiler. The useful heat collected by the parabolic trough solar field is provided to the fluid exiting the incineration boiler and entering into the steam turbine to improve the steam condition, while LNG is vaporized by the energy of exhaust flue gas and produces power for the PEM electrolyzer. Waste-to-energy incineration facility is capable of operating with a feed rate of 350 tons/day, producing 6.3 MW of power at an inlet temperature of 400 °C of the turbine. However, the net power produced is increased to 7.72 MW with increase in turbine inlet temperature to 515 °C. Results of the study conclude that the energetic and the exergetic efficiencies of the incineration plant are found to be 27.93 % and 26.51 %, respectively. In addition, both the first and second law efficiencies are observed as 21.51 % and 25.74 %, respectively, while the rate of hydrogen production is 7.72 kg/h. The cumulative exergy destruction rate of the system is 29.3 MW and the WtE boiler shares the maximum portion (58.14 %) of the exergy destruction.

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.

Conceptual design of floating storage and regasification unit (FSRU) for Eastern Part Indonesia

Liquefied Natural Gas (LNG) can be used as an alternative fuel with environmentally friendly solutions. In general, the domestic distribution of natural gas in LNG is more cost-effective than transporting gas through underwater pipelines considering Indonesia as archipelagic country. According to Indonesia’s Minister of Energy and Mineral Resources Regulation Number 13 of 2020, the government supports converting 52 power plants to LNG. However, the current challenge in the LNG industry is the lack of supporting facilities. Storage and regasification facilities are among the infrastructure that requires optimization. Floating Storage and Regasification Unit (FSRU) are viable options for energy distribution that offer opportunities and competitiveness compared to onshore terminals. Small and medium-scale FSRU can serve as an alternative solution due to their relatively fast, flexible, and affordable development process. Therefore, this research will develop a small-medium FSRU design with a capacity of 60 MW − 70 MW in Eastern Indonesia. FSRU design should consist of four segments including location considerations and environmental conditions, powerplants gas requirements, LNG storage tank sizing and LNG regasification process. Calculations for various supporting FSRU components, seakeeping analysis, loading-offloading processes, 3D modelling and the integration of solar panels were discussed. The results obtained include the principal dimension, technical aspects of FSRU design, and the technology for LNG regasification processes used.

Gas turbine-based system taking advantage of LNG regasification process for multigeneration purposes; Techno-economic-environmental analysis and machine learning optimization

It is viable for engineers to determine how thermodynamic systems can benefit from heat recovery in order to improve efficiency, reduce costs, and lower carbon dioxide emissions. The authors of the study propose a new energy system that incorporates various cycles and units, including gas turbines, Rankine and two organic Rankine cycles, an absorption refrigeration unit, a proton exchange membrane (PEM) electrolyzer, and a liquefied natural gas (LNG) unit. The hydrogen produced is stored and transferred for use as fuel. The system was modeled and optimized using MATLAB programming software, with a parametric study and sensitivity analysis conducted before employing a genetic algorithm optimization to find the most suitable performance conditions. Modifying the compressor's pressure ratio within the range of 6–18 caused a shift in the cooling load, ranging from 45 to 36 MW. Nonetheless, these adjustments in pressure ratio yielded a reduction of 0.4 Cent/kWh in levelized cost of electricity (LCOE) and 0.15 $/kg in levelized cost of hydrogen (LCOH). In the base design mode, the total cost rate is 5715.3 $/h, the exergy efficiency is 39.03%, and the normalized CO2 emissions are 335.89 kg/GJ. However, the optimization results showed a reduced total cost rate of 1884.50 $/h, along with an improved exergy efficiency from 39.03% to 40.32% and a decrease in annual CO2 emissions from 211,000 metric tons to 175,000 metric tons. The implementation of artificial neural networks (ANN) has significantly decreased the time required for optimization from 47 h to just 16 min.

Cold energy recovery from liquefied natural gas regasification process for data centre cooling and power generation

This process simulation study investigates the utilisation of cold energy from Liquefied Natural Gas (LNG) regasification for meeting the cooling and electrical demands of a data centre with 5000 racks. The study proposes a cogeneration system based on an organic Rankine cycle (ORC) to generate power and chilled water at 5 °C by using the cold energy released from a 5 MMTPA LNG regasification plant. The simulation results demonstrate that a double-stage ORC system, which has ethane and propane as working fluids, can fully satisfy the data centre's cooling requirement of 34.6 MW. Additionally, it produces 15.8 MW of power that can serve 46% of the data centre's electrical demand. The maximum energy and exergy efficiencies are 58% and 33%, respectively, when the system is optimised for the maximum work output. Economic analysis reveals a levelized cost of electricity of 0.04 US$/kWh and an internal rate of return (IRR) of 29%. Moreover, the cogeneration system leads to an annual reduction of 210 kilotons of CO2 emissions, which makes it a promising and environmentally-friendly alternative.

Environmentally friendly utilization of LNG regasification process and geothermal-based dual-loop power cycle for desalinated water and hydrogen production

The global scarcity of fresh water has prompted the development of innovative strategies for establishing affordable and efficient desalination systems that utilize waste heat from industrial processes. This study presents a novel combination of a geothermal-driven dual-loop organic Rankine cycle and liquefied natural gas (LNG) regasification process intended for electricity, desalinated water, and hydrogen production. The integration of diverse energy sources holds the capability to reduce dependence on traditional fossil fuels and promote a more sustainable and diversified energy portfolio, conducive to ecological well-being. In the suggested approach, a thermoelectric generator (TEG) is employed to harness the thermal contrast present between the residual heat of the geothermal process and the cold LNG stream, which reduces irreversibility and increases the system's power output. After examining the effect of key parameters on the system's performance, a data-driven approach is adopted in which the system's performance is predicted based on artificial neural networks (ANNs). According to the results, the primary generated power, desalinated water production rate, total cost rate, and cooling load are 5.15 MW, 127.31 m3/h, 188.22 $/h, and 2.92 MW, respectively. Also, the findings of the financial investigation demonstrate that the electrolysis unit, with an hourly cost rate of 85.2 $, constitutes more than 45 % of the total cost rate. In addition, the optimization of the system is performed in three distinct cases, wherein each case pertains to a different objective. In optimal conditions, the amount of produced desalinated water and the total cost rate are 153.89 m3/h and 153.58 $/h, respectively.

Optimal design of direct expansion systems for electricity production by LNG cold energy recovery

The aim of this paper is the investigation of cold energy recovery of liquefied natural gas (LNG) in regasification terminals achievable through direct expansion techniques. After an overview of the state of the art related to the LNG system and the technologies proposed for power recovery, multi-pressure direct expansion solutions with internal heat recovery (multi-pressure DE) are analysed. The purpose is to identify the highest level of recoverable energy and the optimal design parameters, considering technological constraints such as pressure and minimum end-expansion temperature. The multi-pressure DE solutions prove to be innovative power recovery methods because, with a relatively low use of seawater, it is possible to save regasified LNG and generate electrical power, valorising the energy invested in liquefaction. An estimate of recoverable power in operating terminals is carried out. Configurations with cryogenic or non-cryogenic turboexpanders are discussed. Using the proposed solution with non-cryogenic turboexpander and distribution pressure of 3.5 MPa, 56 kJ for each kg of LNG can be produced, which can become more than 150 kJ/kg with cryogenic turboexpanders. For long-distance distribution, cryogenic multi-pressure DE cycles can recover around 100–120 kJ per kg of LNG. The presented techniques can allow recovery of up to and over 30% of the maximum specific work available in LNG regasification.

Integrated hydrogen liquefaction process with a dual-pressure organic Rankine cycle-assisted LNG regasification system: Design, comparison, and analysis

Improving the efficiency and reducing the cost of hydrogen liquefaction systems have become a subject of importance nowadays. Through the comparison and analysis of existing processes, a hydrogen liquefaction system that can enhance the utilization efficiency of liquefied natural gas (LNG) cold energy is developed. The system includes a dual-pressure organic Rankine cycle (DORC)-assisted LNG regasification process and improved cascade Joule-Brayton refrigeration cycles. To assess the performance of the proposed process, two forms of ORC and three Brayton refrigeration cycles are compared, respectively. The genetic algorithm is applied to optimize the proposed process. The coefficient of performance, exergy efficiency, and specific energy consumption of the proposed process is 0.20, 46.9%, and 6.61 kWh/kgLH2, respectively. Owing to the efficient utilization of LNG cold energy, the power output of the DORC is 16.2% higher than that of a regular ORC. Furthermore, the improved cryo-cooling process exhibits a significant performance enhancement. Compared to two existing processes, the UA value of the heat exchangers in the proposed cryo-cooling process is reduced by 47.6% and 8.3%, respectively, and the required mass flow rate of helium is reduced by 45.3% and 8.6%, respectively. Moreover, the exergy analysis performed on the system indicates that the exergy utilization rate of the hydrogen pre-cooling process is 80.2%, while that of the cryo-cooling process is only 48.7%.