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Design and Performance Improvement of Distillation Column of Helium Purification Cycle

Bayat, Mohammad | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49849 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Afshin, Hossein
  7. Abstract:
  8. Due to its unique properties, helium has extensive applications in various fields such as medicine, life sciences, electronic industries, welding, meteorology, and the industries which require low-temperature cooling. Also, designing the cryogenic distillation columns is one of the complex aspects of these plants. In the present study, the distillation column of a helium extraction plant from natural gas has been simulated by means of theta method of convergence. The required thermodynamic properties were determined from the Enhanced Predictive Peng-Robinson (E-PPR 78) equation of state, which has high accuracy in predicting the thermodynamic properties of natural gas componens. The aforementioned computer code has been validated with those of previous studies. Furthermore, although the constant molar overflow assumption simplified the calculations and reduced the solution intricacies, the energy equation had to be used for the highly accurate simulation of the studied column, as performed in the present study. In order to reduce energy consumption and level of hydrocarbons in the top products, especially methane, the molar fraction of methane was decreased from 66.14% in the normal state to 13.75% in the improved state by the simultaneous optimization of reflux ratio, column operational pressure, and feed plate location. Moreover, the simultaneous optimization of these three parameters decreased energy consumption in the reboiler and condenser by 54% compared to the single-parameter optimization of the reflux coefficient. Further in this work, it has been demonstrated that in the optimum operational state, by simultaneous optimization of feed liquid fraction along with distillate rate, not only it is possible to decrease the methane liquid mole fraction to 1.774%, but also the total energy consumption can be decreased to less than 50% and 25% in comparison to single-parameter optimization and improved states. Besides, in this study a novel extractive scheme for complete separation of heavy and light components has been introduced. In this scheme by inserting a proper fraction of distillate products to 4th stage of the column, it is possible to reach below 1% and 97.28% liquid mole fractions for methane and nitrogen respectively in the top products
  9. Keywords:
  10. Distillation Column ; Optimization ; Vapor-Liquid Equilibrium (VLE) ; Extractive Distillation Method ; Cryogenic Distillation Process ; Theta Convergence Method ; Thermodynamic Relationships ; Fugacity

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