Modeling and optimal design of natural gas liquefaction and regasification processes

다국어 초록 (Multilingual Abstract)

Natural gas is the world’s 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.

목차 (Table of Contents)

• 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) １３２