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Multi-Scale Design and Optimization of A High-Nitrogen-Content Natural Gas Processing Plant

Mostafavi, Mahdi | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56730 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Farhadi, Fathollah; Eini, Saeed
  7. Abstract:
  8. Given the environmental benefits of natural gas (NG) in comparison to other fossil fuels and its potential contribution to the shift towards renewable energy, there is an anticipated rise in the demand for NG as an energy source in the coming years. This surge in demand has sparked a growing interest in the exploration and development of unconventional gas fields with low hydrocarbon content, which were previously considered economically unviable. Among these fields, those rich in nitrogen have garnered significant attention. However, the presence of high nitrogen content in NG poses notable challenges, including a decrease in calorific value and increased costs associated with transportation and processing. While high-nitrogen-content NG can be utilized in certain applications like power plants, its presence is generally deemed unacceptable in many consumer sectors, particularly within the petrochemical industry. Consequently, the implementation of nitrogen rejection processes becomes necessary to meet industry standards and requirements. Therefore, the extent of nitrogen removal at the process scale depends on the desired quality within the NG supply chain, presenting a complex multi-scale problem. These processes primarily aim to purify NG and enhance its calorific value, while the rejected nitrogen can either be used in an enhanced oil recovery (EOR) process or vented into the atmosphere. Various technologies have been suggested to remove nitrogen from NG, including cryogenic distillation, absorption, adsorption, and membrane separation. This study focuses on the simulation and optimization of two specific cryogenic process configurations, namely the single-column and double-column, to handle feed gas obtained from a gas reservoir containing approximately 64.33 mol% nitrogen. In the process scale, the objective is to analyze the economic factors and compare the performance of these configurations within the framework of the aforementioned scenarios for rejected nitrogen. The results suggest that the double-column configuration is more economically favorable in all instances. The total annual cost for the single-column and double-column process schemes (7 MMSCMD feed gas capacity), in the scenario of nitrogen discharge into the atmosphere, is estimated to be roughly 32.8 and 11.5 million dollars, respectively. Similarly, in the nitrogen injection scenario into an oil field, the total annual cost for the single-column and double-column process schemes is calculated to be roughly 80.0 and 71.5 million dollars, respectively. The primary objective at the supply chain level is to determine the optimal configurations for a supply chain network in various scenarios, with the ultimate goal of supplying different consumers through the utilization of high-nitrogen-content NG reservoirs. The supply chain problem involves making different decisions, including the selection of the most suitable high-nitrogen gas reservoirs from a set of five reservoirs, the identification of suitable nitrogen process schemes, the selection of diverse consumers of NG such as power plants, petrochemical complexes, and exports, the strategic determination of gas processing unit location considering consumer locations, and devising a distribution plan for processed NG flow that meets the unique quality requirements of each consumer. The results show that by considering a unit including a train with a capacity of 7 MMSCMD, the total annual costs and profits of the optimized supply chain network in base case amount to approximately 491.02 million dollars and 663.38 million dollars, respectively. Additionally, this research provides optimal solutions for various scenarios that may arise within the supply chain network, allowing for effective decision-making in different circumstances
  9. Keywords:
  10. Cryogenic Distillation Process ; Optimization ; Supply Chain ; Natural Gas Processing Plant Design ; High Nitrogen Content Natural Gas ; MultiScale Optimization

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