Lyes Khezzar

Hydrocyclones for De-oiling Applications—A Review

Abstract The de-oiling hydrocyclone is a device for liquid–liquid separation and production water cleanup. Significant progress has been made in the development of such a device since its first introduction and use in the late 1970s. The present article is a literature review of development and research work performed so far on de-oiling hydrocyclones. It reviews the performance parameters affecting the de-oiling hydrocyclone operation; namely, the inlet oil concentration and drop size distribution, the turn-down ratio, the pressure drop ratio, the flow split, and the geometrical parameters. The article addresses work done to elucidate the internal flow structure and performance of de-oiling hydrocylones in both experimental and computational fluid dynamics areas. Challenges and remaining research issues are also identified.

Measurement of fluid velocity development in laminar pipe flow using laser Doppler velocimetry

In this paper we present a non-intrusive experimental approach for obtaining velocity gradient profiles in a transparent smooth pipe under laminar flow conditions (Re = 925) using a laser Doppler velocimeter (LDV). Measurements were taken within the entrance region of the pipe at l = 300 mm and l = 600 mm from the pipe inlet, in addition to measurements of the fully developed flow at l = 1800 mm. The obtained results show how the velocity profile from upstream of the pipe develops into a classical laminar profile downstream, which matches the theoretical profile well. Additionally, a brief summary of historical information about the development of flow measurement techniques, in particular LDV, is provided.

The impact and air entrainment process of liquid plunging jets

This article presents a three-dimensional unsteady numerical simulation of a turbulent liquid plunging jet impinging on a quiescent liquid pool. The focal point of the study is the initial impact, penetration, and the subsequent air entrainment process. The multiphase, volume of fluid model with the geo-reconstruct algorithm is used in combination with the Reynolds averaged k–ε turbulence model. The process of the initial impact of the jet on the free surface, the formation of an air cavity, and the subsequent break-down of the cavity into small bubbles are captured and analysed. These simulations show, clearly and in detail, the process of air carry under by the liquid jet. The air cavity caused by the initial jet impact deeply stretches under the pool surface until break-down due to the shear created by a toroidal vortex. The predicted maximum height of the developing air cavity shows very good agreement with existing semi-empirical correlations from the literature and experiments. The velocity of the front of the air cavity is found to be equal to about half the jet velocity at impact in agreement with previous studies, and the predicted penetration depth shows good agreement with previous correlations.

Large eddy simulation study of turbulent flow around smooth and rough domes

Large eddy simulation of turbulent flow around smooth and rough hemispherical domes was conducted. The roughness of the rough dome was generated by a special approach using quadrilateral solid blocks placed alternately on the dome surface. It was shown that this approach is capable of generating the roughness effect with a relative success. The subgrid-scale model based on the transport of the subgrid turbulent kinetic energy was used to account for the small scales effect not resolved by large eddy simulation. The turbulent flow was simulated at a subcritical Reynolds number based on the approach free stream velocity, air properties, and dome diameter of 1.4 × 105. Profiles of mean pressure coefficient, mean velocity, and its root mean square were predicted with good accuracy. The comparison between the two domes showed different flow behavior around them. A flattened horseshoe vortex was observed to develop around the rough dome at larger distance compared with the smooth dome. The separation phenomenon occurs before the apex of the rough dome while for the smooth dome it is shifted forward. The turbulence-affected region in the wake was larger for the rough dome.

Numerical Simulation of Solid-Phase Split at Junctions in Particle Laden Pipe Flow

The present study is a part of an industrial research project and consists in simulating a gas-particle flow through junctions under different geometrical and flow conditions. The purpose is to study the effects of the size of particles, the angles of the junction and the flow rate on the flow split. The particles are usually considered as products to transport, such as in pneumatic conveying, where phase split, if necessary, is done in symmetrical Y-junctions to avoid mal-distribution issues. Thus, asymmetrical junctions were, usually, avoided in transportation networks. However, it appeared that the particles can manifest within networks for transportation of gases as contaminants to be eliminated. A typical example is that of Black Powder in gas pipelines in the oil industry. In such piping networks, different types of junctions can be used and it is worth understanding the behavior of particles for unsymmetrical configurations as well. The numerical simulation combines the k-e and the Discrete Phase DPM turbulence and multiphase models, respectively. Relatively, good agreement in the results between the model and the experiments was obtained. The simulations were extended to Black Powder particles and the corresponding results showed interesting features for different Stokes numbers. The simulation results showed that, for Stokes numbers much smaller than unity (St≤0.2), the solids phase split can be considered to follow the air flow split closely. For intermediate Stokes numbers (St≈1), the particles gain some independence from the gaseous phase. For Stokes numbers slightly higher than unity (St≥5), the orientation plays an important role.Copyright

CFD Simulation of Three-Phase Separator: Effects of Size Distribution

The gas/oil/water separation in a three-phase horizontal separator, employed by the ADCO company in Abu Dhabi, was studied previously using the Eulerian-Eulerian with the k-e model assuming mono-dispersed secondary phases (oil and water). The separator was equipped with new internals due to the increasing amounts of water and Gas-to-Oil Ratio GOR from the field. The approach allowed the description of several features of the internal flow but the prediction of the overall efficiency was largely overestimated compared to the measured value from the field. The source of the discrepancy could be traced back to the assumption of mono-dispersed secondary phases and possibly to the unknown structure of the size distribution at the inlet of the separator preventing thus a correct modeling of drag between the phases and, hence, influencing momentum and secondary phases (oil and water) dispersion. Investigations, using the Population Balance Model, for size distribution, were conducted. Normal and Skewed distributions were employed to represent, only, the secondary water phase due to the limitation of the population model used to only one secondary phase. The paper presents, in addition to the separation efficiency, the internal multiphase flow behavior in terms of overall and local phase distributions. The simulations with PBM model showed a clear improvement of the results in terms of separation efficiency compared with field tests although no experimental data related to the size distribution were available.Copyright

Study of the Pressure Drop and Flow Field in Standard Gas Cyclone Models Using the Granular Model

A particle-laden flow inside solid gas cyclones has been studied using computational fluid dynamics (CFD). The effects of high temperatures and different particle loadings have been investigated. The Reynolds stress (RSM) model-predicted results, in the case of pure gas, are within engineering accuracy even at high temperatures. Using the granular mixture model for the cases of particle-laden flow, discrepancies occurred at relatively high loadings (up to 0.5 kg/m3). Since the pressure drop is strongly related to the friction inside the cyclone body, the concept of entropy generation has been employed to detect regions of high frictional effects. Friction has been observed to be important at the vortex finder wall, the bottom of the conical-part wall, and the interface separating the outer and the core streams. The discrepancies between the present numerical simulation and the experimental results taken from the existing literature, which are caused by the mixture and turbulence models simplifying assumptions, are discussed in this paper.

CFD Simulation of Liquid-Liquid Hydrocyclone: Oil/Water Application

In the present work, the oil-water separation occurring inside a de-oiling hydrocyclone is investigated numerically using the RSM [1] and the RNG k-e [2] turbulence models combined with the multiphase mixture model of Manninen et al. [3] implemented in the commercial code FLUENT. Interesting results are obtained concerning the effects of the inlet oil concentration, the oil droplet size, and the flow rate on the separation efficiency. The results are in agreement with the experimental measurements of Colman et al., [4]. The separation efficiency is known to be unaffected for a large range of inlet oil concentrations (Colman et al. [4], Gomez et al. [5]) and this is confirmed in the present study. In addition to the overall performance parameters, remarkable results describing the flow field behavior are obtained. The radial profiles of the axial and tangential velocity components are discussed. The flow reversal on the axis and the swirling behavior are shown. Results concerning the pressure drops, the friction coefficient and the turbulent Reynolds stresses are also presented. Since detailed results on the flow field for de-oiling hydrocyclones are scarce, the present study might be useful for future studies aiming to improve liquid-liquid separation efficiency depending strongly on the inside flow field behavior.© 2009 ASME

Large Eddy Simulation of Multiple Round Impinging Jets

Large eddy simulation of flow and heat transfer of multiple turbulent round jets in an in-line array impinging on a flat plate is conducted. The full geometry is used in the simulation of the 9 jets. To capture the interactions between the jets the full geometry is meshed in this work. The Reynolds number based on the nozzle diameter of 13 mm, jet initial average velocity of 23.88 m/s and properties of air at room temperature was equal to 20,000. The computations of the mean vertical and horizontal component of the velocity vector in selected planes show very good agreement with experiments. The flow behavior of the jets agrees with experimental findings in terms of vortices surrounding the jets and the appearance of the asymmetry on and close to the flat impingement plane. The predicted mean surface Nusselt number on the flat heated plate shows also excellent agreement with experiments and a relative maximum between the jets in the region of the upwash fountain flow where the wall jets collide, not seen in the experiments, is captured by the numerics.Copyright

Natural Convection in Inclined Two Dimensional Rectangular Cavities

Steady two-dimensional natural convection in fluid filled cavities is numerically investigated. The channel is heated from below and cooled from the top with insulated side walls and the inclination angle is varied. The field equations for a Newtonian Boussinesq fluid are solved numerically for three cavity height based Rayleigh numbers, Ra = 104, 105 and 106, and several aspect ratios. The calculations are in excellent agreement with previously published benchmark results. The effect of the inclination of the cavity to the horizontal with the angle varying from 0° to 180° and the effect of the startup conditions on the flow pattern, temperature distribution and the heat transfer rates have been investigated. Flow admits different configurations at different angles as the angle of inclination is increased depending on the initial conditions. Regardless of the initial conditions Nusselt number Nu exhibits discontinuities triggered by gradual transition from multiple cell to a single cell configuration. The critical angle of inclination at which the discontinuity occurs is strongly influenced by the assumed startup field. The hysteresis effect previously reported is not always present when the calculations are reversed from 90° to 0°. A comprehensive study of the flow structure, the Nu variation with varying angle of inclination, the effect of the initial conditions and the hysteresis effect are presented.