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Numerical Study of Gas Release, Diffusion and Explosion in the High Pressure Gas Pipeline

Adibi, Omid | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51294 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farhanieh, Bijan; Afshin, Hossein
  7. Abstract:
  8. With the advent and development of modern technologies, the need for energy in industrial societies has been dramatically increased. Currently, natural gas is considered as one of the most important energy sources in the world. High pressure transmission lines are widely used to transfer natural gas from wells and natural resources to industrial centers. High costs, limited results, and the potential risks of empirical experiments along with further need for problem simplification in analytical studies have led numerical methods to become the most practical tools for researchers in the safety field of high pressure gas transmission lines. Numerical simulations of explosive events require a deep understanding of the simultaneous phenomena of fluid-structure interaction, compressibility, shock waves, turbulent flow and chemical reactions. The present research is based on the knowledge and study of the above mentioned phenomena. In this study, to provide appropriate predictions of fluid and structural behavior in explosive events, the simulations have been conducted using near-realistic assumptions. Statistical analysis of the incidents having occurred in the world and Iran's gas transmission lines showed that 4 stages, i.e. 1) external explosive loading, 2) gas leakage, 3) gas mixing with ambient air, and 4) combustion and gas explosion, are the key mechanical parameters in these events. In this research, numerical studies such as grid independency and comparison of the results with benchmark experimental and analytical data for each of the 4 mentioned stages have been presented to successfully create a numerical model being capable of reproducing these events. Numerical results have shown that with an increase in the burial depth of the 56-inch pipeline, from 1.4 to 2.8 m, the pipeline's destruction rate will decrease by about 70%. Simulating the gas leakage from the reservoirs and damaged pipes indicate that expansion and compression shock waves are formed at the leakage zone. The Mach-disk area was created by combination of these waves. The fluid temperature drop up to 70 K was observed downstream of the Mach-disk area. Parametric simulation of natural gas and ambient air mixing in different atmospheric conditions shows that unstable weather conditions (high speed winds) limit the flammable areas to altitudes near the ground surface and produce a larger flammability radius than the stable atmospheric conditions. The fire caused by natural gas leakage was simulated by means of numerical simulation of combustion. The results of these simulations indicate that the minimum safe distance from the pipeline to the threshold health flux of 5 and 15 kW/m2 are 272 and 205 m, respectively. Ultimately, the detonation simulation of the premixed hydrogen-air mixture in large scales shows that the detonation pressure and velocity are 18.5 atm and 2009 m/s, respectively. The small difference between these results and the condition of Chapman–Jouguet confirms that the proposed method for reducing computational costs of combustion kinetic modeling is suitable and can be used to simulate large scale detonations (macroscopic viewpoints)
  9. Keywords:
  10. Numerical Simulation ; Shock Wave ; Gas Mixing ; Gas Releas ; Gas Explosion ; High Pressure Lines

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