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Large Eddy Simulation and Design of the Three phase Immiscible Oil/Water/Solid Particles flow Separation System based on Vortices Generation

Akrami, Ehsan | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48489 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Roshandel, Ramin; Ashjari, Mohammad Ali
  7. Abstract:
  8. In the process of extraction and refining of crude oil, a considerable amount of waste water are produced and if they are not removed, they would become one of the most hazardous environmental factors. Furthermore, purification and separation of such wastewaters are extremely costly, which with an increase in separation efficiency can lead to a decrease in valuable product loss. On the other hand, in the extraction process from oil reservoirs, because of porous and permeable nature of them, solid particles may be added to the extracted crude oil, which can result in an obstruction in pipelines and transport equipment.The most conventional method for separating a mixture of water, oil, and suspended solid particles is the gravity methods. The main drawbacks of this method are high variations in flow rate and concentrations of the wastewater, intense pressure drop, using heavy equipment, and influence of ocean motions to its performance. In recent years, a new system has been developed in which,by producing combined vortex in straight pipes, multi-phase flows can be separated based on the density differences and each phase can be extracted by concentric cylinders at the end of the pipe.These systems have been named linear separator and their advantages are little pressure drop, small volume equipment, and being robust in ocean wave motions and their disturbance. In order to develop these separator systems, the numerical simulation can play a major role. An accurate understanding of flow regime, design and prediction of separator systems in various operation condition with much fewer costs in comparison to experimental studies are the advantages of numerical simulation of these systems. In this field of research lack of numerical simulation with acceptable accuracy exists because of implementing inappropriate turbulence models.In this study, numerical modeling of the systems has been done using Large Eddy Simulation Turbulence Modeling. Firstly, in order to gain a correct understanding of the flow behavior, the system with single water phase was simulated and the error between tangential velocity and axial velocity was calculated. In order to evaluate the effect of the main factors of the flow, a sensitivity analysis on mass flow rate, the ratio of flow and the diameter of light pickup tube was done. The most important obtained result from analysis of single flow is an increase in centrifugal acceleration with respect to the increase in the ratio of flow and the diameter of light pickup tube.Secondly, the system in the two-phase flow mode, water, and oil, with an Eulerian- Eulerian approach was simulated. After obtaining the separation efficiency, it was shown that the separation efficiency error achieved by the Reynolds stress model, which was equaled to 53% in single phase flow, decreased to 15%. In this part, the important factors in the system are also analyzed by a sensitivity analysis. It was shown that an increase in droplets' diameter and the aspect ratio of the flow, and a decrease in diameters of separating tubes and volume fraction of oil lead to an improvement in the separation efficiency. The highest separation efficiency in this part can be achieved up to 75% for an inflow with 10% volume fraction of oil part.In order to add the capability of the model to simulate the three-phase flow of water, oil, and suspended solid particles, the geometry of the two-phase part was redesigned and by using an Eulerian- Eulerian approach and kinetic theory of granular flow was remodeled. For this part, a sensitivity analysis was done for all important factors in the flow again and an increase in the separation efficiency was shown with respect to an increase in the aspect ratio of the suspended solid particles phase in the outflow, the concentration of the solid phase, and the diameter of solid particles. At the end, a novel design to address drawbacks of the designed structure was proposed. By taking these three steps, a profound insight into the behavior of linear separators was achieved so that by developing this technology and an appropriate purification of waste water of crude oils, losses of these energy carriers will reduce and the environment will be protected
  9. Keywords:
  10. Large Eddy Simulation (LES) ; Computational Fluid Dynamics (CFD) ; Numerical Solution ; Swirling Flow ; Suspended Solid

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