Session: 10-08-01: Multiphase Flows and Applications

Paper Number: 145204

145204 - Numerical Study on the Flow Characteristics of Air-Water-Oil Mixture With Highly Viscous Oil in the Horizontal Separator Based on Various Internal Geometric Conditions 

Non-traditional oil is a resource produced through non-traditional methods. Although the non-conventional oil reserves occupy most of oil reserves around the world, they have not received much attention for a long time due to high production costs. However, as securing an energy resource supply chain becomes more important globally, various countries have begun making efforts to develop production technology for non-traditional oil and become internationally competitive.

A separator is a key facility that separates the inflowing multi-phase fluid into its individual phase fluids according to the intended purpose and then discharges them. Given that one of the key roles of the upstream sector of the oil industry is to process produced fluids from the well to a level that can be supplied to individual processes in the downstream sector, the separator is an important equipment.

Since the horizontal separator in the oil production process operates by exploiting the density differences between phases, its performance improves with sufficient separation time. In other words, the longer the separator, the more effective its separation performance. To determine the optimal size of the separator, previous studies have proposed a design method. The commonly used method is based on the fall of liquid droplets and the rise of gas bubbles, assuming their velocities are equal to their terminal velocities. These terminal velocities are determined by balancing gravity, buoyancy, and drag forces.

Meanwhile, the longest route that gas bubbles can take begins at the bottom of the separator’s inlet and ends at the normal liquid level at the separator’s outlet. Similarly, the longest route for water droplets starts at the top of the separator’s inlet and ends at the normal interface level at the separator’s outlet. By considering both the terminal velocity and the route of bubbles or droplets, the necessary size of the separator can be calculated. However, an unconditional increase in separation time results in higher volume, weight, and manufacturing costs for the equipment. Therefore, it is crucial to reduce the size of the separator while maintaining its performance.

This can be achieved by introducing structures inside the separator that accelerate the separation of each phase in the working fluid. These internal structures can change the flow momentum and help bubbles or droplets to coalesce. Many studies have investigated the influence of internal structures on separation and suggested the best designs among the examined structures. However, most of these studies have rarely succeeded in quantifying the effect of internal structures on separation performance. Moreover, the design methods proposed in several prior studies, which consider internal structures, may only be applicable to a certain range of flow conditions. Therefore, research aimed at quantifying the impact of internal structures on separation performance and deriving the correlation between them is essential to ensure appropriate separation performance.

This study performed three-dimensional computational fluid dynamics (CFD) to investigate the flow characteristics under various geometric conditions of the horizontal separator and verify the effect of geometric conditions on the separation performance. The gas-oil-water mixture flows into the separator inlet, and outlets for each phase exist downstream of the separator. The numerical analysis technique adopted in this study is validated by comparing the numerical results with with experimental results.

This study also discussed the effect of geometric conditions on the performance of the separator based on the results of numerical analysis. Separator performance is assessed by the separation efficiency which is expressed as the function of inlet fraction of each phase and the corresponding fraction at outlets. Two key internal structures were considered in this study: the inlet diverter and weir. The inlet diverter changes the momentum of the incoming fluid, suppresses the formation of liquid droplets that may generate when the incoming fluid collides with the fluid in the vessel, and mitigates the transfer of fluid turbulences to the downstream area of stratified fluids. Meanwhile, the weir that is positioned between the oil and water outlets divides sections for oil and water. Relatively low-density oil floats on the water and flows beyond the weir to the oil area and outlet, whereas high-density water is blocked by the weir and is discharged directly through the water outlet. Additionally, this study also investigated the effect of vessel’s slenderness ratio, defined as the ratio of the sim-to-sim length to the vessel diameter.

Presenting Author: Hyeon-Seok Seo KOREA INSTITUTE of CIVIL ENGINEERING and BUILDING TECHNOLOGY

Presenting Author Biography: Hyeon-Seok Seo received his Ph.D. degree in Mechanical Engineering from Sungkyunkwan University, Korea, in 2015. The title of dissertation is "A Study on the Flow Characteristics of Oil-Based Ferrofluid Using Electro-Magnetophoresis". He has investigated the thermal-flow characteristics of HVAC system, multi-phase flow in the conventional industry, and gas-liquid hydrogen system using CFD methods. His research interests include thermal fluid science with multi-physics and fluid machinery based on energy conversion system including hydrogen infra-structure.

Authors:

Hyeon-Seok Seo KOREA INSTITUTE of CIVIL ENGINEERING and BUILDING TECHNOLOGY
Hong-Cheol Shin KOREA INSTITUTE of CIVIL ENGINEERING and BUILDING TECHNOLOGY
In-Ju Hwang KOREA INSTITUTE of CIVIL ENGINEERING and BUILDING TECHNOLOGY