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Mathematical Formulation and Numerical Modeling of Wax Deposition in Flow Lines Using SPH

Haddad, Mahdi | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40170 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Taghizade Manzari, Mehrdad; Kazemzade Hannani, Siamak
  7. Abstract:
  8. Phase change and deposition of solid particles in liquid flows are undesirable in industrial and natural processes and hazardous in some cases. Considering the intentions to petroleum exploration in deep waters such as Caspian Sea, the Gulf of Mexico and North Sea, precipitation and deposition of wax crystals in petroleum and gas pipelines is a real concern due to the fact that during production, oil is exposed to more intense temperature gradient (the dominant mechanism in wax deposition) and its heavier components change their phase to solid and deposit. Wax deposition in production lines starting at crude oil storage tanks is not accepted due to reduction in production rate and performance difficulties. Wax crystals increase viscosity and as a result, increase energy consumption to pump crude oil and decrease pumping capacity. Wax deposition increases pipeline roughness which increases pressure loss. Reduction in the pipeline effective cross section is the other consequence of wax deposition. Due to formation of wax porous solid layer inside the pipeline, SPH method (Smoothed Particle Hydrodynamics), as a numerical simulation method of fluid dynamics problems with moving boundary, has a high potential in simulation of wax deposition problems. In this work, based on SPH method, a numerical code is developed to simulate the laminar flow containing heavy hydrocarbons accompanied by wax deposition inside channel due to temperature gradient. Several former works have conducted on various aspects of wax deposition inside pipes. The mechanisms involving in these studies include the following: (1) Molecular diffusion, (2) Shear Dispersion, (3) Brownian Diffusion, and (4) Gravity settling. In this work, because of lower effect of the other mechanisms in wax deposition, molecular diffusion is considered solely. Wax deposition simulation in channel, includes the solution of continuity, momentum, heat transfer, species transfer, and phase equilibrium. In the current study, heat and species transfer equations are discretized in SPH form and solved. The results are examined and validated for simplified cases which have analytical solutions. Because of the considerable effect of viscous dissipation term in highly viscous flows with high flow rates which is common in waxy crude oil transfer, this term is imposed in heat transfer equation and a method for its SPH discretization is presented. An algorithm for solid-liquid phase equilibrium calculations is proposed and is evaluated by the comparison of WAT. In order to consider the hydrodynamic influences of wax porous solid layer inside channel, a source term is added to momentum equation according to Darcy equation. High-Reynolds flow simulation and under high pressures like several atmospheres in SPH has a lot of difficulties. In the concurrent work, some remedies are proposed and examined to solve them. The obtained results show that neglecting the viscous dissipation term overestimates the wax deposition, and the Peng-Robinson EOS leads to reliable solid-liquid phase equilibrium calculations despite its low calculation cost.

  9. Keywords:
  10. Molecular Diffusion ; Darcy’s Model ; Smoothed Particle Hydrodynamics (SPH) ; Waxy Crude Oil ; Solid-Liquid Phase Equilibrium ; Porous Solid Layer

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  • In the name of God
  • First Page
  • verification page
  • acknowledgement
  • acknowledgement2
  • Abstract
  • ListOfContents
  • ListOfTables
  • ListOfFigures
  • ListOfSymboles
  • Chapter One
  • Chapter Two
  • Chapter Three
  • Chapter Four
  • Chapter Five
  • Chapter Six
  • references
  • Attachment
  • HEFAT, Attachment No. 1
  • Journal, Attachment No. 2
  • AbstractEng
  • First Page Eng
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