Liquefied Natural Gas Liquefaction Research Articles

Operation optimization of propane pre-cooled mixed refrigerant LNG Process: A novel integration of knowledge-based and constrained Bayesian optimization approaches

Liquefied natural gas (LNG) technology, particularly the propane precooled mixed refrigerant (C3MR) process, has demonstrated efficiency and emerged as a distinctive dual-refrigerant technology widely used in LNG production. However, the liquefaction process is the highest energy-intensive stage within its supply chain as it consumes about 8 % of the LNG energy content. Thus, for the first time, this study proposes systematic knowledge-based and constrained Bayesian optimization approaches to identify the optimal operation of the C3MR process. These approaches optimize both the operational parameters (pressures and flow rates) and the composition of the mixed refrigerant with practical equipment specifications and rigorous constraints. The results show that the specific energy consumption (SEC) is reduced to 0.264 kWh/kgLNG, which is 14.6 %, and 26 % lower than the basic C3MR process (unoptimized case) and typical industrial C3MR processes, respectively. In addition, the optimized SEC in this study is 14.5 % to 38.6 % lower than those reported in the literature. At large-scale LNG production (10,000 tons per day), the reduction in the SEC is translated into an 18 MW decrease in compression power, saving approximately 4.7 million $ per year for each C3MR train. Moreover, the coefficient of performance (COP) of the C3MR process was improved by about 15 %, and the CO2 emissions were reduced by 17 % (7 tons per year) compared to the basic C3MR process, indicating potential advancements in large-scale LNG liquefaction processes.

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.

Risks and Safety Measures Associated with the Storage and Transport of Liquefied Natural Gas (LNG)

In recent years, there has been an exponential increase in LNG liquefaction and regasification capacity of many countries. The factors underlying this growth are the use of LNG to produce electricity, a reduction in costs due to technological advances and the current environmental concerns. In Italy, natural gas is transported into pipelines and LNG mainly by road, starting from coastal storage facilities, or from docks. But together with the development of these activities there is also a need to assess and counter the related risks. The handling of tanks offers dispersion scenarios connected to collision or impact, or to leaks during LNG transfer operations. So, there may be a need for emergency LNG transferring, managing the risks of the scenario. Some emergency procedures and safety measures for LNG storage and transport have been studied by the Italian Firefighters. This work offers a brief overview of the risks and safety measures associated with LNG storage and road transport in Italy and Europe.

Performance improvement potential of harnessing LNG regasification for hydrogen liquefaction process: Energy and exergy perspectives

Hydrogen serves as an energy vector; however, its storage and bulk transport are challenging because of its low energy content per unit volume. Similar to liquefied natural gas (LNG), pure hydrogen is liquefied prior to transportation—particularly for transportation over long distances. Liquid nitrogen is widely used as a refrigerant in the precooling phase of the liquefaction; however, considering the scale of the predicted hydrogen energy network, alternative sources must be considered. LNG is a promising candidate because the cold energy obtained during the regasification process of LNG is conventionally released in seawater. In the present study, a simple integrated scheme is proposed, wherein LNG cold energy is used to facilitate hydrogen liquefaction by eliminating the precooling refrigeration cycle. The proposed integrated process was designed and analyzed using the well-known commercial simulator Aspen Hysys® v10. The design of the proposed process was optimized via the modified coordinate descent methodology. The results indicated that the overall refrigerant quantity was reduced by approximately 50%, which resulted in a reduction of approximately 40% in the specific energy consumption, i.e., it was reduced to 7.64 kWh/kgLH2. The exergy efficiency of the proposed process was 42.25%, which is significantly higher than that reported for commercial plants (21%). The coefficient of performance of the proposed process was 40.2% higher than those of previously reported processes. The figure of merit of the proposed process was 0.422. The proposed process is expected to change the value chain dynamics of LNG and hydrogen liquefaction, promoting a shift toward a hydrogen economy.

Design and optimization of energy-efficient single mixed refrigerant LNG liquefaction process

The optimal design of single mixed refrigerant (SMR) natural gas liquefaction process is decisive for upgrading the liquefied natural gas (LNG) value chain and can be achieved using process simulators and derivative-free optimization techniques in simulation–optimization frameworks. The process work consumption can be reduced by modifying process flowsheet and manipulating refrigeration cycle thermodynamic conditions and refrigerant composition. The goal of this paper is the design of energy-efficient SMR liquefaction process for LNG production using simulation–optimization approach, in Aspen HYSYS® and MATLAB®, that considers more decision variables to be optimized with a Nelder–Mead simplex algorithm and small flowsheet modifications, such as hydraulic turbines and flash separators in between compression stages. The present approach resulted in liquefaction process with network duty of 750.2 kJ per kg of natural gas, which is considerably smaller than those reported in the literature.

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.

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.

Spot sale of uncommitted LNG from Middle East: Japan or the UK?

The importance of liquefied natural gas (LNG) is rising as demand for it grows rapidly and steadily due to growth in energy demand, the transition to a low carbon economy and the longer distances over which natural gas is now traded. Given its importance, this work proposes an optimization model that assists to decide on when and where LNG should be delivered by coordinating tanker type, assignment and routing, inventory management, contract obligations, arbitrage and uncommitted LNG. The model maximizes the profit mainly by taking advantage of price differences between different markets.The contributions of this work are twofold. First, following the analysis of expenses and revenues, a new mixed integer programming model for LNG liquefaction and shipping is proposed from a corporate finance perspective. Furthermore, a solution approach for it is implemented and tested. Second, the model is used to derive a short term trade policy for the Middle Eastern LNG producers regarding the spot sale of their uncommitted product to Japan or to the UK, namely to: dispatch to whichever market has the higher current spot price, regardless of the variability of the transport expenses.

Development of an optimal multifloor layout model for the generic liquefied natural gas liquefaction process

Liquefied natural gas (LNG) is attracting significant interest as a clean energy alternative to other fossil fuels, mainly for its ease of transport and low carbon dioxide emission. As worldwide demand for LNG consumption has increased, liquefied natural gas floating, production, storage, and offloading (LNG-FPSO) operations have been studied for offshore applications. In particular, the LNG-FPSO topside process systems are located in limited areas. Therefore, the process plant layout of the LNG-FPSO topside systems will be optimized to reduce the area cost occupied by the topside equipment, and this process plant layout will be designed as a multifloor concept. We describe an optimal layout for a generic offshore LNG liquefaction process operated by the dual mixed refrigerant (DMR) cycle. To optimize the multifloor layout for the DMR liquefaction cycle process, an optimization was performed by dividing it into first and the second cycles. A mathematical model of the multifloor layout problem based on these two cycles was formulated, and an optimal multifloor layout was determined by mixed integer linear programming. The mathematical model of the first cycle consists of 725 continuous variables, 198 equality constraints, and 1,107 inequality constraints. The mathematical model of the second cycle consists of 1,291 continuous variables, 286 equality constraints, and 2,327 inequality constraints. The minimization of the total layout cost was defined as an objective function. The proposed model was applied to DMR liquefaction cycle process to determine the optimal multifloor layout.

Toward a Fluid Global Market: A Guide to Understanding the Changing State of U.S. Liquefied Natural Gas Exports, Regulatory Procedures, and Stakeholder Interests

The close of 2014 ended a lively and prodigious year for energy. This follows $1.6 trillion in energy investments “to provide the world’s consumers with energy” in 2013 — a year in which energy production and consumption levels reached “record levels for every fuel type except nuclear power.” While the 2014 statistics had yet to be released at the time this article was completed, those in the energy field and observers alike undoubtedly saw 2014 as yet another instance of energy bolstering its status as one of the preeminent global issues of the 21st century.The natural gas sector — and liquefied natural gas (LNG) particularly — saw significant movement in 2014. In fact, long-term global growth is expected on the order of up to $500 billion in LNG development by 2025. The United States is seeing a considerable portion of this development due to massive underground natural gas reserves that have been unlocked through multi-directional drilling and hydraulic fracturing, which has opened the door to natural gas exports when, only a few years earlier, the United States was projected to be a growing natural gas importer. The year 2014 was, in a way, the visible beginning of a U.S. LNG export transformation — visible in the sense that approvals were granted for, and construction started on, a number of facilities seeking to export LNG produced in the United States. The United States Department of Energy (DOE) and the Federal Energy Regulatory Commission (FERC) authorized four LNG liquefaction and export terminals (at least conditionally) to site, construct, expand, and operate those facilities and export up to several billion cubic feet per day globally. These approvals mark one of the most recent shifts in the U.S. LNG market over the last 50 years, though another wrinkle came to the forefront in the fourth quarter of 2014: oil prices slid to nearly half of their opening value at the beginning of 2014, and in the process, at least partially quelled U.S. LNG export enthusiasm.This article is a guide to exploring the U.S. LNG liquefaction and export sectors, and specifically, how these sectors progressed over 2014. Part I of this article summarizes the natural gas lifecycle from underground wells to end-users on the opposite side of the globe. Part II then provides a brief history of U.S. LNG imports and exports. Part III outlines the processes necessary to obtain authorizations from the DOE and FERC, which differ depending on where the natural gas originated and its destination. Part IV provides information and statistics regarding four U.S. LNG liquefaction and export projects that received federal approvals in 2014 to site, construct, expand, and operate LNG terminals and export LNG to Free Trade Agreement (FTA) and non-FTA nations. Part V highlights some of the environmental, security, and community concerns that are being considered by stakeholders.

A potential auto-cascade absorption refrigeration system for pre-cooling of LNG liquefaction

Low temperature cooling is required during production or recovery processes of the liquefied natural gas (LNG). An absorption refrigeration system for pre-cooling of LNG production or recovery, which can be powered by low-grade thermal energy and produce low temperature cooling, could provide great potential of energy saving by recovering waste heat. An auto-cascade absorption refrigeration (ACAR) system is investigated for potential pre-cooling of LNG liquefaction in this context. Under the actuating heat with a temperature of 122.5 °C, a minimum refrigeration temperature of −52.9 °C is obtained by the ACAR system. An experimental COPr value of the ACAR system reaches 0.011 with a refrigeration temperature of −52.9 °C. For an absorption refrigeration system, used for re-liquefaction of a LNG bulk gas carrier by utilizing exhaust engine heat with a temperature of 145 °C, the required minimum value of COPr is about 0.05 with a refrigeration temperature of −30 °C. However, under the actuating heat with a temperature of 120 °C, the minimum value becomes about 0.023 with a refrigeration temperature of −53 °C. Therefore, performance of the experimental ACAR prototype is approaching the basic requirements for re-liquefaction of a LNG bulk gas carrier, which could utilize exhaust engine heat. Based on the theoretical COPr values of the ACAR system, it is found that its energy saving could be equivalent to that of an ammonia/water absorption refrigeration system for pre-cooling of LNG liquefaction. Moreover, the ACAR system could show good performance in broader operational conditions. Besides, it overcomes some drawbacks on the manufactured materials and operational maintenance of an ammonia/water absorption refrigeration system. In summary, an ACAR system could provide pre-cooling at lower temperatures for LNG liquefaction by utilizing waste heat and show comprehensive advantages over an ammonia/water absorption refrigeration system. Hence, it shows good potential for pre-cooling of LNG liquefaction, especially for re-liquefaction of a LNG bulk gas carrier.

Thermodynamic Processes Involving Liquefied Natural Gas at the LNG Receiving Terminals / Procesy termodynamiczne z wykorzystaniem skroplonego gazu ziemnego w terminalach odbiorczych LNG

The increase in demand for natural gas in the world, cause that the production of liquefied natural gas (LNG) and in consequences its regasification becoming more common process related to its transportation. Liquefied gas is transported in the tanks at a temperature of about 111K at atmospheric pressure. The process required to convert LNG from a liquid to a gas phase for further pipeline transport, allows the use of exergy of LNG to various applications, including for electricity generation. Exergy analysis is a well known technique for analyzing irreversible losses in a separate process. It allows to specify the distribution, the source and size of the irreversible losses in energy systems, and thus provide guidelines for energy efficiency. Because both the LNG regasification and liquefaction of natural gas are energy intensive, exergy analysis process is essential for designing highly efficient cryogenic installations.

The Second Unconventional Gas Wave

Guest editorial Gas exploration activity in North America looks like it is in the doldrums. In the past 12 months, gas-directed North American rig counts have fallen by almost half. This is easy to understand. Since the beginning of 2010, front-month gas futures prices have fallen from USD 5.60/MMBtu to their current level of USD 3.60/MMBtu. I have a bullish view on the long-term future of natural gas. When accounting for all of the upside influences—environmental imperatives, relentless demand growth in the developing world, the potential of the domestic power sector, revitalization of the US industrial base, and downstream innovations such as gas to liquids (GTLs)—the picture looks positive. At the same time, I have a firm belief that continuing innovation will drive efficiency, making gas an even more attractive alternative and leading to more exploration and development. These indicators lead me to believe a second wave in the development of the North American gas business is on the way. The first wave has been quite a ride. Only a few years ago, gas industry pundits assumed that new gas demand could only be met with imports. An entire subindustry was developed around the regasification, storage, and transport to market of imported liquefied natural gas (LNG). Today, LNG regasification facilities are largely idle. Instead of increasing, gas imports have fallen dramatically—from 12.6 Bcf/D in 2007 to less than 9 Bcf/D in the most recent 12 months. Although gas production has increased dramatically, from just under 55 Bcf/D in 2007 to a current rate of 69 Bcf/D, the increases in production have been absorbed incrementally, without long-term structural adjustments in the US energy economy or significant investments in infrastructure. Existing gas plants displacing coal in the power sector and reductions in imports have absorbed more than 70% of the increase in gas production. The United States is still a net gas importer, but the industry is now focused on developing export markets. Those markets are there. Demand growth in China is almost certain for a generation. If Japan follows up on its commitment to step away from nuclear power, new supplies will need to be found there. Exporting gas will require us to adopt workable regulations, develop infrastructure, and change a mind-set. The United States is accustomed to thinking as an energy importer. As new sources are developed, we tend to guard them jealously and reserve them for domestic use. The Federal Energy Regulatory Commission approves the construction of LNG liquefaction facilities and the Department of Energy grants export licenses based on a “public interest” standard.

LNG for Petroleum Engineers

Summary While remote parts of the world are awash with hundreds of trillions of cubic feet (Tcf) of natural gas, the industrialized West and emerging economies of the East cannot get enough of the clean-burning, environmentally friendly fuel. The problem is transporting this compressible fluid long distances and across major bodies of water. For markets more than 1,500 miles distant, liquefied natural gas (LNG) has proved to be the most economic option. By refrigerating natural gas (primarily methane) to–260°F (–162°C), thereby shrinking its volume by 600:1, natural gas in the form of LNG can be transported in large insulated cryogenic tankers at a reasonable cost. Natural-gas liquefaction is a series of refrigeration systems similar to home air-conditioning (AC) systems, consisting of a compressor, condenser, and evaporator to chill and condense the gas. The difference is in the scale and magnitude of the refrigeration. A typical single-train LNG plant may cost USD 1.5 billion and consume 6 to 8% of the inlet gas as fuel. Because many of the impurities (e.g., water vapor, carbon dioxide, hydrogen sulfide) and heavier hydrocarbon compounds in natural gas would freeze at LNG temperatures, they must first be removed and disposed of or marketed as separate products. This paper will provide an overview of LNG liquefaction facilities, from inlet gas receiving to LNG storage and loading. However, the focus is on the liquefaction process and equipment. Differences among the commercially available liquefaction processes (e.g., cascade, single mixed refrigerant, propane precooled mixed refrigerant, double-mixed refrigerant, nitrogen) will be discussed. The aim is to provide SPE members with a clear understanding of the technologies, equipment, and process choices required for a successful LNG project.

Safety design approach for onshore modularized LNG liquefaction plant

A safety design approach for onshore modularized Liquefied Natural Gas (LNG) liquefaction plant is discussed in this paper. As onshore modularized LNG liquefaction plants have both onshore and offshore plants features, and the safety in design for the plant can only be achieved when the project environment and specific design features are properly understood, this paper identifies specific safety design features of each plant (onshore and offshore) and compares the typical “onshore” and “offshore” safety design approaches. Based on this comparison and consideration for modularization features, a safety design approach for onshore modularized LNG liquefaction plant is proposed.

A Transcritical CO2 Rankine Cycle With LNG Cold Energy Utilization and Liquefaction of CO2 in Gas Turbine Exhaust

A novel transcritical Rankine cycle is presented in this paper. This cycle adopts CO2 as its working fluid with exhaust from a gas turbine as its heat source and liquefied natural gas (LNG) as its cold sink. With CO2 working transcritically, large temperature difference for the Rankine cycle is realized. Moreover, the CO2 in the gas turbine exhaust is further cooled and liquefied by LNG after transferring heat to the Rankine cycle. In this way, not only is the cold energy utilized but also a large part of the CO2 is recovered from burning of the vaporized LNG. In this paper, the system performance of this transcritical cycle is calculated. The influences of the highest cycle temperature and pressure to system specific work, exergy efficiency, and liquefied CO2 mass flow rate are analyzed. The exergy loss in each of the heat exchangers is also discussed. It turns out that this kind of CO2 cycle is energy-conservative and environment-friendly.

Future evolution of the liberalised European gas market: Simulation results with a dynamic model

Abstract Strategic behaviour by gas producers is likely to affect future gas prices and investments in the European Union (EU). To analyse this issue, a computational game theoretic model is presented that is based on a recursive-dynamic formulation. This model addresses interactions among demand, supply, pipeline and liquefied natural gas (LNG) transport, storage and investments in the natural gas market over the period 2005–2030. Three market scenarios are formulated to study the impact of producer market power. In addition, tradeoffs among investments in pipelines, LNG liquefaction and regasification facilities, and storage are explored. The model runs indicate that LNG can effectively compete with pipelines in the near future. Further, significant decreases in Cournot prices between 2005 and 2010 indicate that near-term investments in EU gas transport capacity are likely to diminish market power by making markets more accessible.