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Integrated and Multi-Scale Design of the Value Chain of Liquefied Natural Gas (Lng) Production from Associated Gas Considering Economic, Safety, and Environmental Objectives

Eini, Saeed | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53109 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Davood Rashtchian; Mahdi Sharifzadeh
  7. Abstract:
  8. Natural gas liquefaction is an enabling technology which could make natural gas resources globally accessible. Nonetheless, the design and operation of LNG processes is highly complex, and is subject to multiple criteria including energetic, environmental and safety performance. Moreover, such processes must be flexible enough to operate under different feed conditions. The present research applies integrated process and product design framework to enhance simultaneously energy efficiency, environmental benignness, and inherent safety of a small-scale LNG process. The challenge is that the current group contribution methods applied for the estimation of the thermophysical properties, suffer from prediction errors, rendering their solutions unrealistic. To manage this issue, a multi-stage framework based on pure component property validation was proposed in this study, that maintains the model fidelity while eliminating suboptimal solutions. In this framework the physical properties of the designed pure refrigerants are validated at an intermediate stage. Then, the integrated process and mixture design is conducted using the validated pure refrigerant properties. For the sake of comparison, the process was optimized first, considering a conventional mixed-refrigerant (i.e., a mixture of nitrogen and light hydrocarbons) as the baseline. Then, the process was optimized using the proposed decomposition and validation-based framework. In comparison to the baseline design, the optimal solution of the integrated process and mixed-refrigerant design problem has 10% less power consumption (with the same heat exchanger area), 14% less refrigerant flow rate, 41% lower compressor discharge pressure, and the optimal mixture shows improved environmental and safety metrics. As a post-optimization step, flexibility analysis was performed to investigate the ability of optimal designs in overcoming gas flow fluctuations. The results showed that with respect to the design constraints, the process resulted from integrated process and refrigerant design framework is more flexible in conmparison to the baseline design. Therefore, this optimal solution not only has a higher energy efficiency, but also it is more compact, more environmentally friendly, inherently safer, and more flexible
  9. Keywords:
  10. Process Optimization ; Flexibility ; Multiobjective Optimization ; Equation-Oriented Optimization ; Liquefaction Process ; Integrated Process and Refrigerant Design

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