Britt Halvorsen

Numerical simulation of particulate flow by the Eulerian¿Lagrangian and the Eulerian¿Eulerian approach with application to a fluidized bed

Abstract This work presents a computational study of the flow behavior of a lab-scale fluidized bed. The results obtained from a ‘discrete particle method’ (DPM) are qualitatively compared to the results obtained from a multi-fluid computational fluid dynamic (CFD) model. In the DEM, also referred as Eulerian–Lagrangian (EL) model, the two-dimensional motion of each individual spherical particle is directed calculated from the forces acting on them, accounting for the interaction between the particle and the gas-phase. The implemented collision model is based on the conservation laws for linear and angular momentum and requires, apart from geometrical factors, two empirical parameters: a restitution coefficient and a friction coefficient. The fluidynamic model of the gas is based on the volume-averaged Navier–Stokes equations. In the multi-fluid CFD model, also referred as Eulerian–Eulerian (EE), the gas and the solid phases are considered to be continuous and fully inter-penetrating. Both phases are described in terms of separate sets of conservation equations with appropriate interaction terms representing the coupling between the phases. Experiments results of a two-dimensional lab-scale bubbling fluidized bed are furthermore compared to the computational results obtained by the two approaches. A discussion about the obtained results and their discrepancies is presented.

Pressure drop, flow pattern and local water volume fraction measurements of oil–water flow in pipes

Oil–water flow in horizontal and slightly inclined pipes was investigated. The experimental activities were performed using the multiphase flow loop at Telemark University College, Porsgrunn, Norway. The experiments were conducted in a 15 m long, 56 mm diameter, inclinable steel pipe using Exxsol D60 oil (density of 790 kg m−3 and viscosity of 1.64 mPa s) and water (density of 996 kg m−3 and viscosity of 1.00 mPa s) as test fluids. The test pipe inclination was changed in the range from 5° upward to 5° downward. Mixture velocity and inlet water cut vary up to 1.50 m s−1 and 0.975, respectively. The time-averaged cross-sectional distributions of oil and water were measured with a single-beam gamma densitometer. The pressure drop along the test section of the pipe was also measured. The characterization of flow patterns and identification of their boundaries are achieved via visual observations and by analysis of local water volume fraction measurements. The observed flow patterns were presented in terms of flow pattern maps for different pipe inclinations. In inclined flows, dispersions appear at lower mixture velocities compared to the horizontal flows. Smoothly stratified flows observed in the horizontal pipe disappeared in upwardly inclined pipes and new flow patterns, plug flow and stratified wavy flow were observed. The water-in-oil dispersed flow regime slightly shrinks as the pipe inclination increases. In inclined flows, the dispersed oil-in-water flow regime extended to lower mixture velocities and lower inlet water cuts. The present experimental data were compared with the results of a flow-pattern-dependent prediction model, which uses the area-averaged steady-state two-fluid model for stratified flow and the homogeneous model for dispersed flow. The two-fluid model was able to predict the pressure drop and water hold-up for stratified flow. The homogeneous model was not able to predict the pressure profile of dispersed oil–water flow at higher water cuts. The two-fluid model and the homogeneous model over-predict the pressure drop for dual-continuous flow.

Smart Well With Autonomous Inflow Control Valve Technology

A smart well concept with autonomous inflow control valve (AICV) is presented. AICV utilized the best from smart wells (ICV) and inflow control devices (ICD). The technology is presented, discussed and compared against other conventional inflow control technologies, id est (i.e.) passive ICD. The flow characteristics are presented and implemented in reservoir model simulations. Significant increased production and recovery are shown for the application in a thin oil rim with gas cap and heterogeneous reservoir. The AICVs are autonomous, i.e. self-regulating and do not required any external control or force. This makes them simple and robust, and a large number of control valves can be mounted in the well, i.e. one in each screen. When water and/or gas breakthrough occur the valves in the breakthrough zone will autonomously shut-off. This provides the operator with a significantly more efficient production and increased recovery. The AICV technology also enables opportunities to drill longer wells and achieve maximum reservoir contact of each well. In addition, the AICV removes the risk, cost and requirement for separation, transportation and handling of unwanted fluid. Introduction Traditionally, oil reservoirs were accessed by drilling vertical wells. This is simple and straight-forward technique, but with limited reservoir contact per well. Therefore, in order to access more reservoir contact, techniques and devices have been developed to drill horizontal wells, i.e. turning the well from vertical to horizontal oriented [1]. Multi-lateral wells have been installed by several oil companies to maximize the reservoir contact. A major challenge in oil production is to maximize the oil recovery of the reservoir. Today, only a limited part of the oil in a given reservoir is actually recovered and produced before the field is shut down. There are strong incentives for developing new technology in order to increase oil production and recovery. Two factors are of particular importance in order to increase production and recovery from a reservoir: • Obtaining maximum reservoir contact • Preventing negative effects of gas and/or water breakthrough Good reservoir contact may be achieved by drilling long horizontal and/or multi-lateral wells. The pressure drop inside the well is caused by the fluid friction within the pipe, and is proportional to flow rate, fluid density, diameter and length of the well. Hence, longer wells give increased pressure drop, and increased pressure difference between the toe and heel section of the well. This creates non-uniform oil production along the well and results in an early breakthrough in the heel section, as indicated in Figure 1. Permeability differences or heterogeneities along the well may also result in early breakthrough [2] in some parts of the well. The negative effects of breakthrough may be delayed by ICD, [3]. Well completion with ICDs consists of a large number of ICDs disposed at regular intervals along its entire length. The ICDs causes a flow restriction of the fluid flowing from the reservoir and into the well, and will make the inflow profile more uniform. The ICDs are ports having a fixed flow area. The result is a significant increase in the recovery compared with wells without ICDs [3].

Investigating the influence of fines in fluidized bed reactors using 3D ECT images

Electrical Capacitance Tomography (ECT) has become a useful measurement tool in process technology applications, especially in fluidized bed research. The ECT system is neither intrusive nor invasive which make the system practically viable for monitoring the internal flow behaviour in a fluidized bed. The sensor is placed on the outside of the non-conductive experimental reactor thus making implementation very convenient. ECT also presents user friendly equipment that is safe and easy to use compared to some of the other tomographic modalities currently available. There hasbeen postulatedthatthe insertionoffines into a powderwill give more uniform flow behaviour in a fluidized bed. Smaller and more evenly distributed bubbles are observed. These conditions lead to better mixing of gas and solids in a fluidized bed and thus improving the reactions in the reactor. These phenomena have been investigated in the present study using ECT and a reconstruction program developed in the present study. This reconstruction program created three dimensional images of the fluidized bed reactor under consideration. The reconstructions allow the user to get a three dimensional visual image of the flow behaviour inside the experimental reactor without disturbing the flow. Bubbleand bed characteristics of several powders with different percentages of fines were investigated. The volume, location and shape of individual bubbles were studied and thus the average bubble size, volume and frequency of a particular experimental set up was calculated. These quantities are of great importance for numerous industrial applications. Applications of these results are in almost all fields involving fluidization. The research is part of ongoing global research in optimizing and understanding fluidized beds better.

Circulating fluidized bed combustion reactor: Computational Particle Fluid Dynamic model validation and gas feed position optimization

Abstract A 3D Computational Particle Fluid Dynamic (CPFD) model is validated against experimental measurements in a lab-scale cold flow model of a Circulating Fluidized Bed (CFB). The model prediction of pressure along the riser, downcomer and siphon as well as bed material circulation rates agree well with experimental measurements. Primary and secondary air feed positions were simulated by varying the positions along the height of the reactor to get optimum bed material circulation rate. The optimal ratio of the height of primary and secondary air feed positions to the total height of the riser are 0.125 and 0.375 respectively. The model is simulated for high-temperature conditions and for reacting flow including combustion reactions. At the high temperature and reaction conditions, the bed material circulation rate is decreased with the corresponding decrease in pressure drop throughout the CFB for the given air feed rate.

Computational study on non-asymptotic behavior of developing turbulent pipe flow

In general, developing turbulent pipe flow is a transition from a boundary layer type flow at the entrance to a fully developed flow downstream. The boundary layer thickness grows as the distance from the pipe inlet increases. An accurate description of the velocity and pressure distribution within the entrance region is very important to calculate the pressure drop for hydrodynamic inlets. More important perhaps, the velocity distribution is needed for an analysis of forced convection and mass transfer in a tube entrance. In the current study, we report the results of a detailed and systematic numerical investigation of developing turbulent pipe flow. Two-dimensional, axisymmetric computational scheme has been devised for determining the flow development in the entrance region of a circular pipe at different Reynolds numbers. The simulations are performed using commercial CFD software ANSYS FLUENT 12.0. Non-asymptotic behavior observed in developing turbulent pipe flow is discussed in detail. The predicted results are also compared with literature data.

Velocity and turbulence measurements of oil-water flow in horizontal and slightly inclined pipes using PIV

Oil-water flows in horizontal and slightly inclined pipes are investigated using Particle Image Velocimetry (PIV). PIV offers a powerful non-invasive tool to study such flow fields. The experiments are conducted in a 15 m long, 56 mm diameter, inclinable steel pipe using Exxsol D60 oil (viscosity 1.64 mPa s, density 790 kg/m 3 ) and water (viscosity 1.0 mPa s, density 996 kg/m 3 ) as test fluids. The test pipe inclination is changed in the range from 5° upward to 5° downward. The experiments are performed at mixture velocity 0.25 m/s and inlet water volume fraction 0.25. The instantaneous local velocities are measured using PIV, and based on the instantaneous local velocities mean velocities and turbulence profiles (U-rms, V-rms and Reynolds stresses) are calculated. The time averaged cross sectional distributions of oil and water phases are measured with a traversable gamma densitometer. The flow regimes are determined based on visual observations. The measured flow regimes, water hold-up, slip ratio and velocity and turbulence profiles show a strong dependency with pipe inclination.

Extension Of A Model For The Distribution Of Voidage Around Bubbles In A Fluidized Bed

Up to date most models predicting the voidage around bubbles in fluidized beds assume a simple two-phase flow model. A classic example of a model using this basic assumption is the Davidson and Harrison bubble model. In more recent experimental studies it has been shown that there exists a shell of lower voidage around a bubble in a fluidized bed. Better understanding of these phenomena might play a significant role in understanding other very important effects associated with bubbles in fluidized beds. An example of this might be better understanding the wake of a bubble rising in a fluidized bed and also to better predict mixing in a fluidized bed. The amount of contact between the gas and the solids in a gas-solid fluidized bed is paramount for designing an effective fluidized bed reactor. In the present study a model describing the voidage distribution in front and behind a bubble in a fluidized bed was reexamined and extended. The model proposed by Buyevich et al. used some basic assumptions and previously derived models to compose the model. In the present study the model is extended to two dimensions to give a non-uniform particle distribution around the bubble. Thus voidage distributions all around the bubble could be determined. This new distribution of the voidage could be used to determine a new form of the bubble surface and thus a new boundary condition for the fluidized bubble. The results from the model are compared with simulations carried out at the TUC in Porsgrunn, Norway. The results are discussed and evaluated.