The developing role of gas in decarbonizing China's energy system:system analysis of technical, economic and environmental improvements of LNG and low carbon gas supply chains and infrastructure

The gas system in China is essential for an energy transition towards a low-carbon future. The optimization of gas supply chains and gas infrastructure deployment is crucial for energy-saving, cost-saving, and GHG emissions mitigation. In the short term, natural gas can act as a transition fuel by replacing oil and coal in especially power and transport sectors. In the long term, gradually replacing natural gas with low-carbon gas can secure the role of the gas infrastructure in a low carbon energy system. As China is undergoing an energy transition from a coal dominated energy system to a low-carbon energy system, the main objective of this thesis is to investigate how gaseous energy carriers and the NG infrastructure can be used in the most efficient way for a low-carbon energy system in China towards 2050. In this thesis, the potential role of LNG in the short term and low-carbon gases in the long term for a low-carbon energy system with infrastructure deployment pathway in China are investigated by assessing the energy efficiency, GHG emissions, and costs of the supply chains

Comprehensive review of current natural gas liquefaction processes on technical and economic performance

This paper provides a quantitative technical and economic overview of the status of natural-gas liquefaction (LNG) processes. Data is based on industrial practices in technical reports and optimization results in academic literature, which are harmonized to primary energy input and production cost. The LNG processes reviewed are classified into three categories: onshore large-scale, onshore small-scale and offshore. These categories each have a different optimization focus in academic literature. Besides minimizing energy consumption, the focus is also on: coproduction for large-scale; simplicity and ease of operation for small-scale; and low space requirement, safety and insensitivity to motion for offshore. The review on academic literature also indicated that optimization for lowest energy consumption may not lead to the lowest production cost. The review on technical reports shows that the mixed-refrigerant process dominates the LNG industry, but has competitions from the cascade process in large-scale applications and from the expander-based process in small-scale and offshore applications. This study also found that there is a potential improvement in adopting new optimization algorithms for efficiently solving complex optimization problems. The technical performance overview shows that the primary energy input for large-scale processes (0.031–0.102 GJ/GJ LNG) is lower than for small-scale processes (0.049–0.362 GJ/GJ LNG). However, the primary energy input for identical processes do not necessarily decrease with increasing capacity and the performance of major equipment shows low correlation with scale. The economic performance overview shows specific capital costs varying significantly from 124 to 2255 $/TPA LNG. The variation could be, among others, caused by the different complexities of the facility and different local circumstances. Production cost, excluding feed costs, varies between 0.69 and 4.10$/GJ LNG, with capital costs being the dominant contributor. The feed cost itself could be 1.51–4.01 $/GJ LNG, depending on the location. Lastly, the quantitative harmonization results on technical and economic performance in this study can function as a baseline for the purpose of comparison

Liquid air as an energy storage:A review

With the increasing demand for energy due to rapid industrialisation and the environmental concerns due to the usage of fossil fuels as the main energy source, there is a shift towards renewable energy. However, the intermittent nature of renewable energy requires energy produced during off-peak hours to be stored. This paper explores the use of liquefied air as an energy storage, the plausibility and the integration of liquefied air into existing framework, the role of liquefied air as an energy storage in addressing the Grand Challenges for Engineering as well as its employability in Malaysia

Risk-based design tools for process facilities

Process facilities include operations with different levels of risks. Risk-based design incorporates risk analysis into the design process and thus facilitates discovering design limitations and making improvements with respect to process safety. This work presents two risk-based design tools: (i) a hazard identification methodology and (ii) a risk-based layout optimization technique. The first tool developed and presented in this research is for dynamic hazard identification. In risk assessment, the first major step is hazard identification that helps to unveil what may go wrong during operation of a process. Traditional hazard identification tools have the limitations of being static in nature; changing circumstances are not considered in the existing tools. Therefore, the present work develops a new methodology which realizes hazard identification by tracing hazard evolutions. A generic model is proposed. The model is dynamic in making predictions for the most likely hazard in terms of different input evidences based on field observations. A risk-based design is to design for safety.Means of conducting risk-based design can be various. The second aspect of this thesis presents a risk-based design method that uses inherent safety metrics for layout optimization of floating liquefied natural gas (FLNG) facilities. Layout plays a paramount role in hazard evolution and thus affects the risk of an operation. Three topside layouts are proposed and evaluated using inherent safety indices. Finally, a layout is chosen as the most optimal one in terms of layout evaluation results. In this way, the layout becomes inherently safer and thus brings tremendous benefits to reducing risks as well as potential loss

지속 가능한 화학 공정 설계를 위한 리스크 기반의 배치 최적화에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2013. 8. 윤인섭.This thesis presents the method and applications of process layout optimization based on the quantitative assessment of the individual risk (IR) in order to limit the effect to humans from the accidents can occur in a chemical process. The process layout of chemical plants is usually designed in a compact configuration for economic efficiency, although most of the chemical process units operate under high pressure and temperature, and/or deal with hazardous materials which are flammable or toxic. The possibility of the accident such as fires, explosions, and toxic gas releases which can cause severe damage to humans and properties is always present, and the social concerns of the community for this are also accompanied. Therefore, a method to quantitatively evaluate the risks arise from the chemical process equipment/facilities is required so that the actual damage can be prevented. This study tries to achieve such goal by proper arrangement of the process layout. First, various former approaches for the process layout problem, their formulations, and the solution methods have been analyzed. In addition, the method of quantitative risk assessment (QRA) of chemical processes and the concept of risk indices are introduced. Subsequently, the formulation of the risk-based layout optimization problem for sustainable chemical process design is presented. The individual risks (IR) caused from the fire and explosion that can affect the workers in the process site and the surrounding public are calculated according to the distance from the equipment, and then converted into the safety distance. The risk zones around the process equipment are modeled by using the safety distance constraints and the former layout optimization problems. Then the costs of process layout including land, pipeline, equipment purchase and protective devices are minimized to determine the economically optimized process layout. The formulation of layout optimization problem uses the framework of mixed-integer linear programming (MILP), and the procedure of iterative search for the reduced problem is applied to tackle the problem with large scale. Process layout optimization based on individual risk (IR) through these procedures can provide the layout that secures the inherent safety as well as the economic feasibility. The proposed methodology is applied to three kinds of chemical processes for validation. First case is dimethyl ether (DME) filling stationan example of the fuel gas station which is the simplest process but can cause heavy damage to humans due to its typical location. Next application is an ethylene oxide (EO) plant, as an example of general chemical process plant. In that case, the selection among the options for site location with different surrounding land uses is considered. A liquefaction process of an LNG-FPSO (liquefied natural gas - floating production, storage and offloading) vessel is considered last for multi-floor and more space-restricted case. Through these case studies, it has been shown that the proposed method can enhance the sustainability of the process layout by ensuring the safety and support the decision making related to the process layout in the early stage of process design.Abstract i Table of Contents v 1 Introduction 1 1.1 Motivation 4 1.2 Research scope 5 1.3 Thesis outline 6 2 Backgrounds Theory 9 2.1 Process layout optimization 9 2.1.1 Heuristic models 9 2.1.2 Mathematical models 12 2.2 Quantitative risk assessment 16 2.2.1 Risk indices 16 2.2.2 Assessment of risks 21 3 Risk-based Process Layout Optimization 29 3.1 Individual risk assessment and safety distances 31 3.2 Mathematical formulation for layout problem 34 3.2.1 Objective function 35 3.2.2 Risk Zone constraints 37 3.2.3 Other constraints 47 3.3 Iterative search for efficient solution 47 4 Case Studies 51 4.1 Facility layout optimization of DME filling station 51 4.1.1 Problem statement 53 4.1.2 Risk calculation 59 4.1.3 Layout result and discussion 62 4.2 Optimal layout of ethylene oxide plant 80 4.2.1 Problem statement 81 4.2.2 Risk calculation 88 4.2.3 Layout result and discussion 90 4.3 Multi-floor layout optimization of liquefaction process of LNG FPSO 105 4.3.1 Problem statement 108 4.3.2 Formulation for multi-floor layout 112 4.3.3 Risk calculation 115 4.3.4 Layout result and discussion 119 5 Conclusion 127 Nomenclatures 131 References 135 초록Docto

Potential risk of vapour cloud explosion in FLNG liquefaction modules

Floating Production Storage and Offloading vessels have been in operation for four decades and there are now well over 250 vessels in existence, but their gas equivalent floating liquid natural gas plants kwon as FLNGs are still very new. Consequently designs and arrangement of top-side process units are still evolving and their safety has yet to be fully and objectively evaluated. This paper explores the probability of occurrence of accidents leading to vapour cloud explosion at one of the topside liquefaction modules of an FLNG. The worst possible scenario with the maximum tolerable probability is identified and the impact of the corresponding vapour cloud explosion is estimated. The strength of the structures supporting the neighbouring modules was examined using finite element analysis to determine if the accident has a potential of escalating to neighbouring modules. It is found that the current levels of safety gaps between the liquefaction modules may be insufficient for the structural arrangement in place. It is thought that a new structural design using circular pipes as the structural elements instead of the I-beams may enhance the integrity of the top-side supporting structures against the impact of potential vapour cloud explosion. The effectiveness of the new structure is demonstrated by comparing it to the conventional supporting structure using I-beam members. This also implies that, by using pipe elements, the safety gaps can be reduced, thus making it possible to optimise the topside arrangement more easily

천연가스 액화 및 재기화 공정의 모형 및 최적 설계

학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2014. 8. 한종훈.Natural gas is the worlds fastest-growing fossil fuel, favored for electric power and industrial sectors because of its low carbon intensity and reduced emissions. International natural gas trade is expected to double from 1 trillion cubic meter (tcm) in 2010 to 2 tcm in 2030. Liquefied natural gas (LNG) accounts for a growing share of world natural gas. The core of LNG value chain is the phase change of natural gas that makes it feasible for ship transportation to remote regions. This thesis addresses modeling and optimal design for LNG value chain and it contains two main processes: one is the liquefaction process in the production plant and the other is the regasification process in LNG receiving terminal. These two processes occupy the main parts in the whole in LNG value chain and are worth to be studied in depth. This thesis has five main parts. First, modeling and simulation of a liquefaction plant is conducted. Second part proposes a simulation-based optimization methodology, taking full advantage of commercial simulator in process design step. The methodology is applied to a case study of double-expander process optimization to prove its performance. A novel process design of natural gas liquefaction using nonflammable refrigerants is developed in the third part. Safety issue for floating LNG drives interest in minimization of hydrocarbon refrigerants. A new N2O-N2O-N2 cascade liquefaction process with nitrous oxide for the pre-cooling and condensation section and nitrogen gas for the sub-cooling section is proposed. Lastly, retrofit design scheme is introduced for boil-off gas handling process in LNG receiving terminal.Abstract i CHAPTER 1 : Introduction １ 1.1. Research motivation １ 1.2. Research objectives ３ 1.3. Outline of the thesis ４ CHAPTER 2 : Modeling and Simulation of Liquefaction Cycles [4] ５ 2.1. Introduction to LNG processing ５ 2.1.1. LNG value chain ５ 2.1.2. State of LNG industry ７ 2.1.3. Floating LNG ８ 2.2. Liquefaction Cycles ９ 2.2.1. Vapor compression refrigeration ９ 2.2.2. Gas refrigeration system １１ 2.2.3. Natural gas liquefaction processes １２ 2.3. Modeling and simulation １４ 2.3.1. Mathematical modeling １５ 2.3.2. Modeling and simulation using Aspen HYSYS® ２１ 2.3.3. Degree of freedom analysis ２４ CHAPTER 3 : Simulation-based optimization methodology for process design with case study of turbine-based liquefaction process ２８ 3.1. Introduction ２８ 3.2. Simulation-based optimization framework ３０ 3.3. Case study of natural gas liquefaction process ３５ 3.3.1. STEP 1: Base case design ３５ 3.3.2. STEP 2: Specifying the design variables ３５ 3.3.3. STEP 3: Optimization formulation ３５ 3.3.4. STEP 4: Providing additional constraints in the simulator ３８ 3.3.5. STEP 5: Determining the design space ３８ 3.3.6. STEP 6: Comprehensive simulation of the design space ４０ 3.3.7. STEP 7: Process mapping of the design space using empirical modeling ４０ 3.3.8. STEP 8: Empirical modeling validation ４１ 3.3.9. STEP 9: Optimization ４３ 3.4. Comparison with response surface methodology ４７ CHAPTER 4 : Natural gas liquefaction process design with nonflammable refrigerants for offshore application ５２ 4.1. Introduction ５２ 4.2. Thermodynamic analysis of carbon dioxide and nitrous oxide ５４ 4.3. Design of N2O-N2O-N2 cascade process ５７ 4.3.1. Pre-cooling section ５９ 4.3.2. Condensation section ６１ 4.3.3. Sub-cooling section ６３ 4.4. Results and discussion ６５ 4.5. Case study with a leaner feed gas ６９ CHAPTER 5 : Retrofit design of liquefied natural gas regasification process [79] ７２ 5.1. Introduction ７２ 5.2. Methodology ７７ 5.3. Case study ８０ 5.3.1. Base case design definition ８０ 5.3.2. Thermodynamic analysis of the base case design ８７ 5.3.3. Proposal of the retrofitting design for energy saving ８９ 5.3.4. Optimization of design variables ９５ 5.3.5. Design variables ９７ 5.4. Results and discussion １０３ 5.4.1. Comparison with the base design １０３ 5.4.2. Sensitivity analysis １０８ 5.4.3. Profitability of the proposed design １１５ CHAPTER 6 : Conclusion and Future Works １１７ 6.1. Conclusion １１７ 6.2. Future Works １１９ Literature Cited １２０ Abstract in Korean (요약) １３２Docto

Green vs fossil-based energy vectors: A comparative techno-economic analysis of green ammonia and LNG value chains

This study conducts a comparative techno-economic assessment on the value chains of ammonia, as a green energy vector, and Liquefied Natural Gas (LNG), representing the benchmark energy vector, for long-distance energy transportation from Middle East to Europe. The value chain involves production from resources, conversion to an energy vector, storage and transport and reconversion of the energy vector to a suitable fuel. For comparison purposes, an electric power output of 400 MW is assumed to be produced by a power plant that utilizes either green or fossil fuels delivered to it. The adopted parameter for this comparison is the Levelized Cost of Energy (LCoE). Greenhouse gas emissions are economically penalized through the Social Cost of Carbon (SCC). Considering a SCC of 0.100 euro/kg, the LCoE of the LNG value chain is 59.19 euro/MWh, while that of ammonia is 231.71 euro/MWh. Since the cost of producing green hydrogen and purified natural gas strongly affects the results, a sensitivity analysis is performed to assess the impact of the assumed values. The SCC required to break even the LCoE of the two value chains is: 0.183 euro/MWh when considering the most favorable scenario for the green energy vector (low green hydrogen and high purified natural gas production costs) and 1.731 euro/kg when considering the most unfavorable one. This study highlights the cost-effectiveness of LNG in the current economic and regulatory landscape. However, the break-even range for the SCC indicates the potential for green ammonia to gain economic viability under higher carbon pricing scenarios

Gas flaring reduction in nigeria in context of carbon dioxide (CO₂) reduction and utilisation requirements.

The growing demand for energy due to a rise in global population and an improved standard of living has resulted in the production, refining and consumption of hydrocarbon fuel. A consequence of this has been an increase in the global rate of natural gas flaring. While natural gas flaring is accepted as a waste of energy and natural resources, as well as a contravention of Nigeria’s current energy policy for sustainable development through natural gas conservation, natural gas flaring is still considered the most cost efficient and effective Associated Natural Gas (ANG) flaring management option in developing countries such as Nigeria. The need to further consolidate routine gas flaring reduction or management techniques has never been greater with the 2030 zero routine flaring initiative by the World Bank fast approaching. While there are several studies on natural gas utilisation techniques, they rarely consider the shortage of practical tools that integrate economic, technical, and regulatory factors into a gas flaring management framework; and also, the intricacies of the existing tools, which often comes at the expense of simplicity, to obtain real-time information output. Thus, the aim of this study was to develop a systematic framework and ANG management tool to aid the reduction of routine natural gas flaring in Nigeria. This research developed a systematic management framework (using a flowchart decision tree technique) and models to further develop a simple, relatively quick, flexible, and user-friendly ANG flaring management tool (using a MATLAB graphical user interface). This was integrated with techno-economic models for the Liquefied Natural Gas, Gas to Methanol and Gas to Wire ANG utilisation options using the ASPEN HYSYS computer software. The tool was then tested with data obtained from three fields A, B and C in the Niger Delta region of Nigeria. Field A is an offshore field in Bayelsa State in the South-West Niger Delta. Field B is an offshore field in Rivers State in the South-South Niger Delta while Field C is an onshore field in Delta State in the South-West Niger Delta. Results obtained showed the choice of Gas to Methanol option as the most optimal for Field A due to its preference for large gas volumes and cost effectiveness, Liquefied Natural Gas for Field B because of its proximity to the Liquefied Natural Gas pipeline infrastructure and Gas to Wire utilisation option for Field C due to its proximity to the electrical grid and high electricity requirements of that area when both economic and technical considerations were taken into account. The addition of further regional profiles within West Africa, as well as the consideration of more ANG utilisation options were among suggested areas for further research.Simms, Nigel J. (Associate)PhD in Energy and Powe