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The analysis of a two-phase slug flow is of immense importance due to its vast applications in many industrial problems. A number of experimental and analytical studies have been carried out to study this complex and unwanted phenomenon. Mostly, these studies were limited to the liquid phase and to the statistical parameters and formation mechanism. So far, no attempt has been made to study the phase interaction and coupling effects of both phases simultaneously, which is more important in understanding this complex flow behavior. This kind of study requires the instantaneous velocity fields of both phases simultaneously. Therefore, in this study a PIV–LIF technique has been applied to study two-phase (liquid–gas) slug flow in a laboratory facility. Water and gas were considered as working fluids, and slug flow was generated in a nearly horizontal pipe with an inclination of 1.16° to consider the terrain slugging mechanism. Liquid and gas phases were seeded simultaneously with fluorescent and titanium dioxide tracer particles, respectively. Two CCD cameras installed with low pass and band pass filters were used to capture images for separate phases. Instantaneous velocity field for both liquid and gas phases was measured simultaneously. To extract the coherent structures and for the analysis of turbulence in liquid and gas phase, the proper orthogonal decomposition (POD) analysis technique was applied to the velocity fields. Large energy containing modes were successfully revealed by POD. The energy distribution of spatial modes for both phases was also measured and compared.

IBM (Immersed boundary method) and DEM (Discrete element method) coupling method were used to simulate the flow of cylinder-shaped particles in a fluidized bed. The greatest advantage of IBM-DEM is that it can reveal the microscopic characteristics of dense-phase gas-particle flow in Cartesian grids. Large cylinder-shaped particles are very difficult to fluidize, and slugging flow can be observed even if the static bed height is low. The gas flow field around the particle in fluidized bed is analyzed, and the formation and development of vortex behind the particle is affected obviously by the neighboring particles. Particle trajectory is obtained, and the effect of gas phase on particle rotation becomes active as particle size increases. Compared with the experimental results, the gas-solid force in simulation results is higher. This calculation error may be reduced by decreasing the grid size.

Transport Disengaging Height (TDH), defined as the freeboard height whereby the entrainment rate does not change appreciably [1–6], is an important parameter in the design of gas–solid fluidized bed systems to minimize particle loss. Unfortunately, despite the initiation and subsequent development of TDH correlations since 1958 [4], poor agreement between predicted and experimental values persists [1] due to the reliance on empirical data-fitting in the absence of a fundamental understanding of the TDH phenomenon. Accordingly, this work aims to provide a comprehensive review of the available TDH correlations. TDH values predicted by 25 correlations were evaluated over a range of superficial gas velocities, particle sizes, particle size distributions, and column diameters. Four observations are worth highlighting: (i) Discrepancies of up to five orders of magnitude were found among TDH values predicted by the various correlations, (ii) Unphysical phenomena predicted include negative TDH values, (iii) Geldart Group B correlations perform better for Geldart Group B particles than Geldart Group A correlations for Geldart Group A particles, and (iv) Prediction often fails in the transition from the freely bubbling to the slugging regime. The ad hoc inclusion and/or exclusion of parameters, and the use of empirical constants to improve empirical data-fitting in the generation of empirical TDH correlations are not useful in either improving predictions of TDH values or advancing the understanding of the TDH phenomenon. Correlations empirically derived do not perform well beyond the narrow scope of experimental condition tested, while semi-empirical or theoretical models available fall short. The lack of predictive capability of the available TDH correlations appears to stem from a deficiency in an understanding of the impact of inter-particle (e.g., cohesion or clustering effects) and inter-species interactions (e.g., collisional momentum transfer effects).

Modeling two-phase pipe flow commonly involves gas and liquid fields which can differ greatly in density and compressibility. The physical scales governing the dynamics are divided amongst the phases in a way where the numerical grid requirements of one phase may be poorly suited for the other. Adopting a phase discriminating multigrid strategy is therefore an attractive approach, though little is known about how the phase coupled dynamics will respond to separate, non-equivalent numerical grids. The purpose of this article is to explore the resolution sensitivity of the two-fluid model for each phase individually, and examine how the dynamic coupling between phases is maintained across phase-individual grids of unequal coarseness. A dual-grid scheme is proposed and applied to S-riser terrain slugging and roll wave capturing simulations. Resolution sensitivity is checked. It is found that the resolution requirements in both cases are liquid dominated; we are able to reduce the spatial resolution of the ga...

Numerous studies on unconventional shale well production data have shown that downhole pressure fluctuations can exceed 300 psig during a slugging period. Such pressure fluctuation will result in very high drawdown and could lead to near-wellbore formation damage when the rock failure criterion was met. An engineering workflow was developed to investigate the impact of multiphase slugging events on cemented casing plug and perforation (CCPP)and open hole sliding sleeves (OHSS) completions. Based on transient pressure analysis and geomechanical evaluation, safety operational envelope was generated to minimize the risk of formation damage due to slugging behavior.In this study, a dynamic multiphase flow simulator was used to predict the pressure amplitude and frequency during the slugging events in both a CCPP and OHSS completion configuration. The results from the simulation were then incorporated into a geomechanical model to analyze and identify potential hydraulic fracture closure and formation damage concerns, which can compromise well performance.The results from this study show that OHSS completion is more vulnerable to damage during the downhole slugging period than a CCPP completion. However, severe formation and fracture damage could occur during downhole slugging for CCPP well if the well is operated outside the safety operational envelope. Results from the two case studies led to the conclusion that it is crucial to consider the effect of downhole slugging on near-wellbore fracture and formation integrity to avoid permanent and irreversible damage.

We use state-based stochastic greybox modeling - combining physics and statistics - to model the slugging phenomenon. We extend the model of DiMeglio et al. (2010) to include random components and variable flow coefficients, providing 30 seconds prediction intervals. Altogether six models, each comprising no more than ten equations, are fitted to off-shore riser training data and then cross-validated on new data sets. We use advanced statistical methods to 1) obtain optimal parameters of a given model fitted to measurements, 2) give model predictions with uncertainty intervals, and 3) quantitatively measure the relative goodness of the extended models. These features of our reductive method are general and can be applied to any data sets. For the slugging data, simpler models are preferable over the more complex ones (although the differences are minute for practical purposes in oil and gas industry) and a high statistical significance obtained on the training data does not imply improved long term prediction on independent data. Better physical (mechanistic) models to capture slugging oscillations are needed, ultimately to develop effective control strategies.

The most recent general reconstruction of the Block 6 of the Thermal Power Plant Tuzla resulted in dual effect on energy efficiency of the Block itself. This article deals with an analysis of modernization projects that has been done on coal boiler and steam turbine and possible consequences on boiler performances. The modern project solution, which has been implemented on the coal combustion system, has enabled the application of low emission concept of combustion and reduction of ash slugging on walls of combustion furnace. As those were the main goals of reconstruction, they have been successfully achieved. However, after reconstruction has been completed, the total heat load distribution on the surface of the boiler reheater is not able to provide enough heat to achieve the nominal temperature value of reheated steam at lower loads, particulary in exploitation conditions case which deviate from the calculated and guaranteed conditions. Accordingly, this article will provide a review of two possibilities of temperature increasement of reheated steam that leaves the boiler. That includes two situations: a. Increase the heating surface on the boiler reheater to the possible limits, b. The use of recirculated cold waste gas for regulation of the temperature of reheated steam.

Slug is one of the most avoided flows in the piping system network. The high pressure fluctuations can cause damage to the pipes. Therefore, prevention of the slug flow is very important. To understand the phenomenon, an experimental study to investigate the pattern of stratified to slug flow transition has been examined. The present work was conducted on a 26 mm diameter acrylic horizontal pipe with the length of 10 m. Air and water are used as working fluids. Visual image capture is done using Phantom Miro M310 High speed camera on L/D 180-210 from inlet. As a supporting visual observation result, CECM method is also used to measure liquid holdup of fluid flow. The onset of slugging mechanism due to change of both gas and liquid superficial velocity will be discussed. As a result, it is found that the slug formation from stratified flow is at least divided into two basic mechanisms. At low gas velocity, the slug stability condition is created by wave growth mechanism. The increase of JG resulted in the increase of aeration and the of the liquid slug length. When the gas velocity is above 3 m/s, wave coalescence and large disturbance waves initiated the onset of slugging. The Increase of JL on the high JG makes the roll waves higher to create a pseudo slug. In addition, it is found that the formation of high aeration slug is seen at JL = 0.3 m/s when JG is maintained at 3.77 m/s.

[object Object] Abstract A case of natural intermittent flow regime (slug/churn) of a CO2-enriched spring water is discussed as an example of trigger process for the collapse of sinkholes. The hydrodynamic regime of the spring, situated in the area of S. Vittorino alluvial plain (Rieti, Italy), was investigated by monitoring acoustic emission, carrying out geochemical analyses and installing a sedimentation trap during a long-lasting phase of slug flow regime followed by a churn flow phase. The slug and churn flows can erode and transport upward fine and medium size particles of sand, progressively removing them from some underground shallow sandy levels where the groundwater mixes with gas of deep crustal origin to form the intermittent flow that can be observed at the surface. The slug flow regime was characterized by a stable slugging frequency whose value is in agreement with the estimated superficial velocities of Taylor bubbles and liquid slugs. The transition from the slug to the churn flow regime, the latter characterized by an increase of gas flux and by more severe erosion, was also observed during our study. In a span of 15 years, the transport of sand upward could produce a collapse volume similar to those of the sinkholes that recently originated in the same area. The study of such multiphase flows prolonged over time could help to monitor and prevent the sinkhole formation process.

Slugging flow in offshore oil & gas multi-phase transportation pipelines cause big challenges as the flow regime induces flow and pressure oscillations in the multi-phase pipelines. The negative impacts of the most severe slugs are significant and thus the elimination of slugging flow in the pipelines is a highly investigated topic. To eliminate the slug in an online manner real-time slug detection methods are often required. Traditionally topside pressure transmitters upstream a 3-phase separator have been used as the controlled variable. In this paper Electrical Resistivity Tomography (ERT) has been examined as an alternative to the traditional pressure transmitters. A lab-scaled testing facility has been constructed in order to obtain test data from a ERT transmitter with 12 probes. Different flow regimes have been generated by a pump and a compressor where 2-phase flow can be tested. Based on the results the study concludes that the ERT is able to detect the slug very well when the oil and water is well mixed. Furthermore the traditional pressure transmitters have the limitation that pressure variations can be caused by other operating conditions than slug, such as change in the back pressure from control valves. The biggest limitation using ERT is the lack of ability to distinguish between gas and oil, and thus the ERT can only be used as an effective slug detect measurement when the oil-to-water ratio is low.

The problem of suppressing the slugging phenomenon is investigated. Industrial oil facilities such as gas-lifted wells and offshore production oil-risers are examples of systems where occurs such phenomenon. To study this problem, we consider that these systems are written as a set of 3 x 3 hyperbolic partial differential equations of balance laws, where the control variable appears at the boundary condition. By means of the characteristic coordinates approach, we deduce the stabilizing control law. The exponential stability of the equilibrium is proved by means of a Lyapunov stability analysis. Through simulation results, the method is shown effective in stabilizing the slugging phenomenon.

The current offshore oil & gas multi-phase production and transportation installations have big challenges related with the slugging flow: An unstable multi-phase flow regime where the flow rates, pressures and temperatures oscillate in the considered processes. Slug can be caused by different operating conditions and installation structures. The most severe slugs are often induced in long vertical risers or production wells, where liquid blocks gas at the riser/well base and correspondingly it causes the pressure to accumulate and hence originates the oscillating performance. There are many severe consequences to the production processes because of the slugging flow. This paper reviews some observed latest status and key challenges about slug detection, dynamical modeling and elimination of slugging flows. Mathematical modeling of slug has been used to investigate the slug mechanism and anti-slug control. Most of available models are based on mass-balance formulations, which often require sufficient data for reliable parameter tuning/identification. Slug elimination and control have been investigated for many years and there exist many solutions to eliminate the slug, but some of these methods can simultaneously reduce the oil & gas production, which is a very big concern as the production rate is the key evaluation parameter for offshore production. We conclude that the slugging flow is a well-defined phenomenon, even though this subject has been extensively investigated in the past decades, the cost-effective and optimal slug modeling and control are still open topics with many related challenges.

In this work the influences of solid viscosity and the way to scale-down traditional drag models on the predicted hydrodynamics of Geldart A particles in a lab-scale gas-solid bubbling fluidized bed are investigated. To evaluate the effects of drag models, the modified Gibilaro et al. drag model (constant correction factor) and the EMMS drag model (non-constant correction factor) are tested. And the influences of solid viscosity are assessed by considering the empirical model proposed by Gidaspow et al. (1997, Turbulence, Viscosity and Numerical Simulation of FCC Particles in CFB. Fluidization and Fluid-particle Systems, AIChE Annual Meeting, Los Angeles, 58–62) and the models based on kinetic theory of granular flow (KTGF) with or without frictional stress. The resulting hydrodynamics by incorporating the different combinations of the drag model and solid viscosity model into two-fluid model (TFM) simulations are compared with the experimental data of Zhu et al. (2008, Detailed Measurements of Flow Structure inside a Dense Gas-Solids Fluidized Bed.” Powder Technological 180:339–349). The simulation results show that the predicted hydrodynamics closely depends on the setting of solid viscosity. When solid viscosity is calculated from the empirical model of Gidaspow et al., both drag models can reasonably predict the radial solid concentration profiles and particle velocity profiles. When the KTGF viscosity model without frictional stress is adopted, the EMMS drag model significantly over-estimates the bed expansion, whereas the modified Gibilaro et al. drag model can still give acceptable radial solid concentration profiles but over-estimate particle upwards and downwards velocity. When KTGF viscosity model with frictional stress is chosen, both drag models predict the occurrence of slugging. At this time, the particle velocity profiles predicted by EMMS drag model are still in well agreement with the experimental data, but the bed expansion is under-estimated.

Slug flow is a flow assurance issue that staggers production and, in some cases, 'kills the flow' of the well. Severe slugging, a type of slugging which usually occurs at the base of the riser column, causes large amplitudes in the fluctuation of pressure within the riser column and consequently damages equipment placed topside. An adaptation of a novel concept to slug mitigation: the self-lifting model, is presented. This model presents variations to the internal diameter of the self-lift bypass to produce effective mitigation to severe slugging.

The continuous demand for oil and gas forces the petroleum industry to develop new and cost-efficient technologies in order to increase recovery and exploit existing fields. Subsea wet gas compression of the unprocessed well stream is a powerful tool in increasing production capacity and utilizing remote regions. Wet gas compressors are particularly useful for handling gas-dominated multiphase flows. Although a limited amount of research has been done on the field, previous studies have revealed that the liquid phase has considerable impact on the compressor performance, from both a fluid mechanical and a thermodynamic perspective. Being able to ensure stable and predictable compressor behavior in subsea installations is challenging. As the reservoir pressure drops during production, the compressor enters a region where it is far more susceptible to inlet slugging. Inlet slugging may lead to internal compressor damage, including damage to seals, bearings and compressor blades. It needs to be stressed that a slug in this context does not entail 100% liquid holdup upfront of the compressor, but a substantial increase of liquid content in a gas dominated multiphase flow. An experimental investigation has been carried out on an advanced wet gas test rig, consisting of a shrouded centrifugal impeller, a vaneless diffuser and a circular volute. The paper explores the possibilities of creating realistic inlet slugging scenarios and documents its impact on the compressor system. Slugging was introduced either by collection of liquid in a negatively sloped inlet pipe (i.e. terrain slug simulation) or by sudden opening of an inlet liquid valve upstream of a symmetrical injection manifold, so to create a more “homogenous” slug. The compressor ability to handle such slugs is analyzed. Furthermore, the drive capability to respond to sudden changes in torque requirement is documented. The experimental results form a basis for future dynamic simulation.

A quasi one-dimensional OpenFOAM-based transient solver is proposed to investigate slugging-induced pressure fluctuations for multi-phase flow in pipeline-riser systems. Following the two-fluid Eulerian approach, the governing equations of mass, momentum and energy are expressed for each phase of gas and liquid. The frictions and energy exchanges between the two phases are estimated by several empirical enclosure models. Gmsh is employed for geometrical models and one-dimensional mesh generations, while ParaView is used for data collection and necessary processing. By two of previously published experimental investigations, the newly proposed open source approach is validated and demonstrated capable of carrying out the study of transient multi-phase flow dynamics in pipeline-riser systems. Using the OpenFOAM-based one-dimensional way in the present work, the multi-phase slugging-related analysis for subsea product transportations in future deep ocean projects could be much more economical due to the approach natures of ‘open source’ and ‘one-dimensional’.

Liquid loading is the mechanism that is associated with increased liquid hold-up and liquid back flow at lower gas flow rates in gas production wells. In laboratory, most liquid loading experiments are performed at fixed gas and liquid rates (mass flow controlled). In the field, the well behavior is a coupled well-reservoir system in which the reservoir results in a pressure or mass flow controlled inflow, depending on the reservoir characteristics. In this paper results are presented which have been performed with a pressure controlled vessel attached to a vertical pipe. The pressure drop between the vessel was varied to represent reservoir characteristics from tight to prolific. The goal of the experiments was to evaluate the relation and the time ‘trajectory’ between the minimum in the pressure drop curve and the actual flooding point. From these experiments it was concluded that the stability is determined by the overall pressure drop curve. That is the pressure drop from vessel to separator and not the tubing pressure drop curve. This stability point can be at a higher or lower velocity than the actual loading/flooding point and therefore, loading is not the cause of the production decrease. That also means stable production is possible below the flooding point in slugging conditions. In future, the distinction between stable flow and loading/flooding must be made more strict.

Recently, with the ever-increasing development of offshore fields, the use of long risers fed by lateral flow lines has significantly increased. This type of configuration exposes the production system to severe slugging, particularly with decline in reservoir pressure and consequently flow rates. Severe slugging can cause huge pressure fluctuations and may result in decreased recovery and separator flooding. This study is an experimental and theoretical effort to analyze how the application of surfactants can suppress or eliminate severe slugging. The experimental study is performed in a 2-in ID facility, consisting of a 64-ft flow line with 1° downward inclination, followed by a 41-ft riser. Water and compressed air are the liquid and gas phases, and an anionic surfactant is applied continuously. First, effects of surfactant delivery location are investigated by injecting at three points, namely, riser base and flowline inlet without or with a static mixer, used as an external source of agitation. Pressure and holdup fluctuations with time, slugging frequency and surfactant efficiency are monitored. Moreover, a high-speed camera is used to monitor blowout stage and analyze gas front thickness and velocity. Pressure fluctuations and surfactant efficiency are experimentally investigated by changing the operating conditions. Tests include without and with surfactant at different liquid and gas flow rates. Firstly, the experiments are conducted with lowest superficial gas velocity (vSg) and highest superficial liquid velocity (vSL) values. At these conditions, severe slugging is partially eliminated only with high surfactant concentration and the use of static mixer. The use of surfactant in other locations results in elimination of slug production stage and reduced cycle duration, but negligible changes in pressure profile. Then, a new test matrix is designed to conduct tests at higher vSg and lower vSL values, moving towards the boundary of Bøe's criterion for severe slugging. Under these conditions, severe slugging cycle durations and pressure fluctuations reduce and elimination efficiency of surfactant increases significantly. In addition, severe slugging severity and elimination efficiency are correlated with Boe's criterion coefficient. This study is an attempt to characterize severe slugging magnitude based on operating conditions, and investigate surfactant efficiency for different delivery locations. Considering the limited number of studies on this subject, the results can provide an experimental and theoretical source to optimize surfactant application in production systems facing severe slugging.

Horizontal wells experience transient flow regimes throughout their long laterals. The average gas/liquid ratio (GLR) produced by a horizontal well may not overwhelm an ESP if the fluids travel in a steady stream. However, gas slugs commonly develop in the lateral section of a horizontal well, growing in size as they approach the heel of the well and move into the vertical section of the wellbore. A well with a pump intake pressure (PIP) of 500 psi at the ESP gauge may have plenty of fluid over the pump intake and still have problems with gas locking the pumps. Even with sophisticated gas handling pumps and gas lock-breaking control algorithms in the variable speed drive (VSD), the ESP still goes down with a gas locked pump. This paper covers a patent pending technology developed at EOG Resources' Production Technology Center that improves gas-liquid separation of fluids entering an ESP. The tool has been installed in wells with high GLRs, where ESP run times are lower than the field average, and has improved operational stability. This paper follows the development of the technology in the model wellbore at EOG's lab, the design and manufacturing of field trial separators, and the results of several field trials.

To solve the problem of a high pressure drop in an ordinary J-valve, this paper describes the design of a new type of J-valve, namely, the Jet J-valve. We contrast the ordinary J-valve with the Jet J-valve and analyse the material transport capacity and stability of pressure drops. The experimental results show that the pressure drop fluctuations of the riser, standpipe and J-valve are slightly greater in the states of dilute-phase and dense-phase transport for the Jet J-valve than for the ordinary J-valve. However, under the same operating conditions, the solids circulation rate is 41-84 kg·m–2·s–1 higher when the Jet J-valve is used. In addition, the pressure drop of the Jet J-valve is approximately 18% lower than that of the ordinary J-valve. When the steady state transitions to a slugging state, the solids circulation rate decreases by 76.5% and the pressure drop of the J-valve decreases by 23.3%, which is relatively small compared with that of the riser and the standpipe. [Received: December 30, 2017; Accepted: July 5, 2018]

Hydrodynamic slug fl ow is the commonest fl ow regime observed in high viscosity liquid–gas horizontal pipelines over a wide range of different fl ow conditions. Hydrodynamic slugging tends to generate large vibrations that may impose structural instability or even damage oil production pipelines. For that reason, there is a need to investigate high viscosity slug fl ow regime to understand its complex characteristics. This is pertinent when considering that existing slug fl ow models used in the petroleum industry to design production pipelines are not suitable for predicting the behaviour of high viscosity oil–gas fl ow. In this study, the effects of liquid viscosity and fl ow variables on slug fl ow regime were investigated experimentally through the analysis of two key parameters—slug frequency and slug body liquid holdup, both measured with a gamma densitometer. Comparison of the measured slug parameters to existing correlations revealed that slug body liquid holdup correlations were in close agreement with high viscosity experimental data. However, none of the existing slug frequency correlations used was able to produce accurate predictions. A new empirical correlation for slug frequency was proposed. Compared with existing correlations, the newly proposed correlation performed much better in predicting slug frequency of high viscosity liquid–gas fl ows.

Elaborated models, such as those used for simulation purposes [e.g., in the OLGA simulator (Bendiksen et al. 1991)], cannot be used for model-based control design because these models use too many state variables and the model equations are not usually available for the user. The focus of this paper is on deriving simple, dynamical models with few state variables that capture the essential dynamic behavior for control. We propose a new simplified dynamic model for severe-slugging flow in pipeline/riser systems. The proposed model, together with five other simplified models found in the literature, are compared with results from the OLGA simulator. The new model can be extended to other cases, and we consider also a well/pipeline/riser system. The proposed simple models are able to represent the main dynamics of severe-slugging flow and compare well with experiments and OLGA simulations.

This paper presents the development and results of a simplified multiphase model for terrain-induced slugging analysis considering the viscosity effect of the liquid phase in the conservation equations. The phenomenon has been successfully modelled with numerical models (Fabre et al. 1990, Sarica et al 1991) that neglect the liquid viscosity effect. The objective of the present study is to clarify its importance in the numerical prediction of the characteristics of severe slugging. The results of the model where compared with experimental data reported in the literature showing a maximum percentage difference of 6% which represents a 7% improvement with respect to the prediction of existing models. The liquid viscosity has an effect on the duration of the severe slugging cycle. The cycle will reduce while the viscosity increases. Additionally, the effect of the riser inclination angle is analyzed showing a mitigation of the severe slugging phenomenon while decreasing the angle

The flow patterns and transitions in a gas–liquid–solid three phase spouted bed were investigated. Experiments were carried out in a cylindrical and a semi-cylindrical spouted bed with conical base. Glass beads and water were used as the solid phase and liquid phase, respectively. The changes in pressure drop and photographs were used to determine the flow patterns. Five distinct flow patterns were identified and described, i.e. fix bed (FB), grain spouting (GS), cluster spouting with slugging (CS-S), solid fixed with gas–liquid bubbling (SF-GLB), and slurry agitated bed (SA). Flow pattern maps of a three phase spouted bed (d = 2.6 mm, H0/Dt = 1.86) under different liquid saturations were plotted. It was found that the flow pattern transition with the spouting gas velocity increasing at different liquid saturations (S) could be divided into three stages, i.e. transition from FB to GS when S 0.5. Increase in liquid saturation (S) always leads to increasing of the amplitude of pressure fluctuations. Besides, in stage I (GS), the minimum spouting velocity increases initially and then decreases apparently with increasing S. The range of stage I region becomes wider with lower initial bed height and particle diameter.

Vacuum fluidised beds have a distinct advantage of being operated with reduced mass consumption of the fluidising media. However, a low quality of fluidisation reduces the opportunity to utilise the bubbling regime in vacuum fluidised beds. Fluidisation maps are often used to depict the interface between the quiescent, bubbling and slugging regimes inside a fluidised bed. Such maps have been obtained by visual observations of the fluidisation interface in transparent fluidised beds. For beds which are visually inaccessible fluidisation maps are difficult to obtain. The present work therefore attempts to model the interface travel in a vacuum fluidised bed. The pressure gradient due to the bed weight has been determined to be a main contributor for fluidisation/defluidisation under vacuum. A simple analytical model based on the pressure gradient (PG model) is developed to predict the interface location in a vacuum fluidised bed. For a segregated bed, the Gibilaro–Rowe (GR) model is modified and used to predict the jetsam layer growth along with the fluidisation interface. The predictions are compared with the experimental data for minimally and highly segregated particles and it is seen that for non-segregated powders the predictions are quite accurate. Lack of sufficient knowledge of bubble characteristics, however, impeded accurate prediction of the jetsam growth especially at high flow rates. However, an approximate complete fluidisation interface is successfully predicted using the GR–PG model.

We suggested an adjusted OPS and weighted adjusted OPS as indices to explain run productivity of teams using the slugging average and adjusted OBP from Korean professional baseball. First, we defined adjusted OBP by modifying currently used OBP. Next, we defined adjusted OPS as the sum of adjusted OBP and slugging average. We also defined weighted adjusted OPS as the weighted average of adjusted OBP and slugging average. Analysis of the data from all games in the regular seasons from 1982~2013 shows that adjusted OPS better explains runs than OPS. For 25 seasons out of 32 seasons, adjusted OPS explains runs better than OPS. Further, weighted adjusted OPS consisting of adjusted OBP (with weight 60%) and slugging average (with weight 40%) gives the best explanation of run productivity. Weighted adjusted OPS has been found to explain run productivity better than weighted OPS proposed in Kim (2012).

The periodic slugging behavior of Geldart D particles in a vibrated gas-fluidized bed (VFB) is favorable for some applications involving the processes of particles stratification, especially for fine coal beneficiation in a VFB. It is of great significance to conduct systematic studies on slug formation, slug coalescence and growth, slug rising velocity, and slugging frequency in a VFB of Geldart D particles. The slug formation model is proposed based on theoretical analysis and indicates that the vibration amplitude, the vibration frequency, and the superficial air velocity all have significant effects on the slugging behavior. Also, the comparison of predicted values and measured values of the slug height at its initial formation verifies that the slug formation model has high prediction accuracy. The dynamic of the coalescence of bubbles into an adjacent slug is qualitatively studied and the correlations of the slug height and the slug rising velocity are established, respectively. The results show tha...

Hilbert-Huang transformation was used to investigate the nonlinear characteristics of two-component (biomass particles and quartz sand) mixing flow by analyzing the pressure fluctuation signals in fluidized bed. Based on empirical mode decomposition (EMD), the Hilbert-Huang spectra in bubbling and slugging flow patterns were obtained and analyzed. In bubbling flow pattern, compared with one-component (quartz sand) flow, the energy of two-component mixing flow is lower in 0-5 Hz and higher in 40–50 Hz. In slugging flow pattern, the energy in pressure fluctuation mainly lies in 0–5 Hz. and the effect of biomass particles on the Hilbert-Huang spectrum is not very obvious. Compared with traditional power spectral density (PSD), HHT is much more suitable for investigating pressure fluctuation signals in fluidized beds.

It is important to understand the flow hydrodynamics behavior of a circulating fluidized bed (CFB) reactor for efficient operation. The objective of this research is to identify and characterize the flow regimes in a fluidized bed with different riser diameters. For this purpose, electrical capacitance tomography (ECT) combined with pressure measurement has been used to investigate the flow characteristics and flow regime transitions. Experiment was carried out in a cold gas-solids fluidized bed to investigate the flow regimes and the transition velocities. Three risers of different diameter, 10, 12 and 15cm, are designed and used for comparison. A twin-plane ECT sensor and a differential pressure transducer are used to obtain the solids volume fraction and differential pressure in the bottom region. Different flow regimes including bubbling, slugging and turbulent flow regime were formed with two distinct transition velocities. The flow characteristics are investigated in terms of solids volume fraction, bubble diameter and bubble rising velocity. The transition velocities are compared based on the ratio of the static bed height to bed diameter (Hst/D) and the measured position (i.e. the axial position and radial position). ?? 2014 Elsevier Ltd. cited By (since 1996)0

Circulating fluidized bed system consists of SEWGS reactor - lower loop seal - regeneration reactor - riser - cyclone - upper loop seal has been used for solid circulation between the SEWGS reactor and the regeneration reactor in a SEWGS system for pre-combustion capture. A vertical type lower loop seal has been used in current system but this lower loop seal requires high gas flow rate through the lower loop seal for fluidization and smooth solid circulation, and consequently, causes slugging behavior sometimes. To overcome these disadvantages, inclined type lower loop seal was proposed by this study. Solid circulation characteristics with change of lower loop seal geometry were measured and compared in a bubbling - bubbling - riser type circulating fluidized bed using absorbent (P-78) as bed material at ambient temperature and pressure. We could conclude that the inclined lower loop seal is better than the vertical type lower loop seal from the viewpoints of minimum flow rate requirement for stable solid circulation and solid height change during solid circulation.

Numerical simulations are carried out for gas-solid fluidized bed of cork particles, using discrete element method. Results exhibit the existence of a so-called anti core-annular porosity profile with lower porosity in the core and higher porosity near the wall for non-slugging fluidization. The tendency to form this unfamiliar anti core-annular porosity profile is stronger when the solid flux is higher. There exist multiple inflection points in the simulated axial solid volume fraction profile for non-slugging fluidization. Results also show that the familiar core-annular porosity profile still appears for slugging fluidization. In addition, the classical choking phenomenon can be captured at the superficial gas velocity slightly lower than the correlated transport velocity.

Summary Severe slugging is a transient multiphase-flow phenomenon that can occur in pipeline-riser systems, particularly in offshore production of oil and gas. It is characterized by large pressure fluctuations at the base of the riser and is accompanied by fluctuations in fluid delivery from the top of the riser. This unstable phenomenon is undesirable because production and equipment are affected adversely by the large pressure and flow-rate fluctuations. In this study, air-/water-flow experiments have been carried out at the S-shaped-riser facility in the multiphase-flow laboratory of the Norwegian University of Science and Technology (NTNU) and have been compared with results from a flow simulator (OLGA). The results obtained in the work show that stability maps, pressure amplitudes, and slug frequencies are in acceptable agreement with each other; however, some deviations are seen regarding the slug frequencies at low flow rates.

Due to the special structure of offshore multiphase pipes, it is easy for severe slugging to occur in the riser at low gas-liquid velocity. Violent pressure fluctuations and dramatic changes of flow rate are the main characteristics of severe slugging, leading to the risk of serious damage. In this paper, the separator control is adopted to accurately control the separator liquid level and pressure under severe slugging flow conditions. This indicates that the separator liquid level control alone does not have a significant impact on the upstream flow, but it is beneficial for normal operation and pressure control of the separator. As the separator pressure increases, the peak pressure in the riser apparently diminishes, and the amplitude of pressure fluctuation gradually decreases, which means that severe slugging is inhibited. During the slug blowing out, the gas/liquid slipping in the riser intensifies. The long gas plug quickly flows through the riser, and then tends to morph into short and slowly flowing gas bubbles. The elimination effect of the pressure control strategy on severe slugging is related to the relative rate of the superficial gas/liquid flow.

Multi-phase flow is experienced in many instances of the oil and gas industry. There is multi-phase flow in the sea lines, transferring the production from the South Pars offshore platforms to the receiving onshore facilities. By pigging at frequent intervals, liquid inventory buildup in a sea pipeline and the maximum slug size can be reduced. Uncontrolled speed of a pig can cause to large liquid slugging formation and bursting of pipeline due to pig stuck. In June 2008 the slug catcher levels increased unexpectedly to 100–105%. The main objective of this study is composed of calculation for liquid holdup, pig velocity, amount of slug during pigging operation and the influence of the production flow rate during the pigging of South Pars sea lines that is located in south of Iran. Besides the slug catcher liquid level, some parameters such as liquid bottle level were measured during pigging time process. The comparison between the actual and simulated sea line glycol holdup, travel time for the pig, sea line inlet pressure and the liquid slug volume has been done in this work. The difference between the actual and simulated travel time for the pig was 0.7 and 1.3 h for 600 and 300 million standard cubic feet per day (MMSCFD) of the gas flow rate. The absolute average relative errors of condensate and water slug volume are 5.6% and 9.1% respectively, which are very satisfactory. The results showed that the optimum gas flow should be around 500 MMSCFD to handle the slug volume and running the pigs is most effective at a near constant speed.

A mathematical model and numerical simulations corresponding to severe slugging in air-water pipeline-riser systems are presented. The mathematical model considers continuity equations for liquid and gas phases, with a simplified momentum equation for the mixture. A drift-flux model, evaluated for the local conditions in the riser, is used as a closure law. In many models appearing in the literature, propagation of pressure waves is neglected both in the pipeline and in the riser. Besides, variations of void fraction in the stratified flow in the pipeline are also neglected and the void fraction obtained from the stationary state is used in the simulations. This paper shows an improvement in a model previously published by the author, including inertial effects. In the riser, inertial terms are taken into account by using the rigid water-hammer approximation. In the pipeline, the local acceleration of the water and gas phases are included in the momentum equations for stratified flow, allowing to calculate the instantaneous values of pressure drop and void fraction. The developed model predicts the location of the liquid accumulation front in the pipeline and the liquid level in the riser, so it is possible to determine which type of severe slugging occurs in the system. A comparison is made with experimental results published in literature including a choke valve and gas injection at the bottom of the riser, showing very good results for slugging cycle and stability maps. Simulations were also made assessing the effect of different strategies to mitigate severe slugging, such as choking, gas injection and increase in separation pressure, showing correct trends.

Oil and gas activities across the globe now take place deep offshore. To operate in this harsh environment, there are numerous challenges. These can be in the form of high cost of production, space constraints, operational and technological demands. The co-transportation of oil and gas in same pipeline is one of the operational and technological approaches adopted in the industry to meet the transportation of produced crude. This approach comes with its attendant flow assurance difficulties. Slugging is one of such problems which can constitute operational hitches resulting in production reduction and sometimes eventual plant shutdown. Existing attenuation techniques are limited in various ways. Therefore, seeking a reliable solution to this problem is highly desired.In this study, an experimental study of multiple techniques for slug attenuation was attempted. A passive device-the intermittent slug absorber, topside choking and topside separator were investigated. The results show that a combination of the methods proves to be more effective compared to individual techniques. A significant reduction in riser- base pressure of up to 39% was achieved. This is advantageous and translates to an increase in oil recovery. Thus, the proposed strategy helps to achieve system stability and improved production at a lower cost.

A comparison of the technologies of thermal utilization of solid chemical waste was carried out, the advantages and disadvantages of the thermal utilization technologies of WtE thermal power plants used in worldwide were given. A method of comparison and selection of the preferred technology of thermal utilization, depending on the specific conditions of the placement of TPPs at MSW, is proposed. Thermal utilization can be classified into three categories (combustion, gasification and pyrolysis), the difference between them lies in the amount of excessive air present in combustion chamber. The gasification technology that can be often in use in WtE can be divided into two main types – slugging gasification and plasma gasification.

This article describes a comprehensive experimental analysis that defines typical fluidization characteristic curve for Geldart's classification groups. Geldart defined four types of materials which differ by the cohesion forces between particles. An experimental apparatus containing fluidized beds of four pipe diameters and fully controlled by LabVIEW was used to perform the fluidization tests. All tests were performed automatically by gradually increasing the air velocity and measuring the pressure drop over the bed. For each test, the fluidization curve was recorded and the minimum fluidization, bubbling, and slugging velocities were defined. It was found that the fluidization curve of material define accurately the Geldart's group to which the material belongs. In addition, was reviewed the reason for those materials and under which conditions the pressure drop increases in the slugging state. Finally, the influence of height to bed diameter H/D ratio on the shape of characterization curve was found. ...

Slugging flow in the offshore oil & gas production attracts lot of attention due to it's limitation of production rate, periodic overload on processing facilities, and even direct cause of emergency shutdown. This work aims at two correlated objectives: (i) Preventing slugging flow; and meanwhile, (ii) maximizing the production rate at the riser of an offshore production platform, by manipulating a topside choke valve through a learning switching model-free PID controller. The results show good steady-state performance, though a long settling time due to the unknown reference for no slugging flow.

The hydrodynamics of a two-dimensional gas-solid fluidized bed with 0.03 m diameter and 0.3 m height were studied experimentally and computationally. The slugging fluidization of large particles was experimentally investigated and simulated using the Fluent 6.3 computational fluid dynamics (CFD) package. By a series of cold-model test, characterization of gas-solid fluidization with large particles was studied. These results can be used to research slugging characteristics. A multifluid Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the unsteady-state behavior and momentum exchange coefficients were calculated by using the Syamlal-OBrien drag functions. These results of the transfer of fluidization state, maximum bed expansion ratio and pressure fluctuation were systemically simulated in a gas-solid fluidized bed. The modeling predictions compared reasonably well with experimental data and qualitative slugging regime. The simulation results can better predict the slugging fluidization characterization of large particles.

Multiple fluidization regimes were studied using X-ray tomography. Geldart B sand particles were used in a 14 cm (ID) column with a dual cyclone return system. Cross sectional solids concentration (ϕ) was measured and the time averaged ϕ ( ϕ ¯ ) decreased with velocity and axial height except in the turbulent regime where ϕ ¯ remained constant. Radial profiles of ϕ ¯ decreased to the centre, while all turbulent regime velocities resulted in similar radial ϕ ¯ profiles. Results confirm the bubbling-turbulent transition velocity (Uc) determined from pressure fluctuations is a reliable quantification technique. The system exhibited slugging behaviour at higher bubbling regime velocities with voids taking on cylindrical shapes. Turbulent regime voids were characterised by elongated cylinders with diameters slightly less than the bubbling regime’s slugs or fast fluidization regime’s core annulus. Distribution curves of the ϕ signal indicated a distinct dense phase in the bubbling and turbulent regime with a velocity independent solid concentration. Void velocity analysis suggested that the bubble linking algorithm was unable to detect fast rising voids at higher velocities.

A series of experiments on air/water two-phase flow in a flowline riser have been performed. The riser has a free-standing form (7 m high) with the flowline of a 2° downward inclination toward the riser-base. Severe slugging flows are described in the free-standing riser (FSR). Then, experimental pressure comparison between the FSR and L-shaped riser is presented, and three differences are analyzed. Finally, the behavior of severe slugging flow in the FSR was simulated with OLGA software. In conclusion, it is difficult to do the theoretical simulation of severe slugging in a FSR.

In the offshore petroleum industry, it is important to recognize the severe slugging in multiphase flow patterns in oil and gas transportation through a pipeline–riser system. After analyzing the inadaptability of the existing methods, we proposed a simple and practical method of measuring the multiphase flow patterns based on pressure fluctuations. Our recognition was carried out in three steps. First, the outlet pressure signals were selected and processed because of their accessibility to practical applications in oil fields. Second, statistical and principal component analysis were performed on the sampled signals to obtain the clear interrelations between the signals and flow patterns and to extract useful features for forming flow pattern clusters for classification in the feature space. Finally, machine learning was applied to the clusters for constructing classifiers to predict the flow patterns automatically. The experimental results from a small-scale flow loop and an offshore petroleum field show that the proposed method is feasible and effective for recognizing the multiphase flow patterns in the pipeline–riser system.

In this work, experiments on flow patterns during air–water two-phase flow in a long pipeline–riser system has been carried out. The test loop with 50 mm i.d. consists of a horizontal pipeline with 114 m in length, followed by a 16 m downward inclined section, and ended at an S-shaped flexible riser. The inclination of the downward section varied from −2° to −5° from the horizontal. Liquid and gas superficial velocities ranged from 0.03 to 1.5 m/s, and 0.04 to 6.0 m/s, respectively. Based on the analysis of the pressure at the riser base and liquid holdup at the riser top, the flow regimes observed were classified into four categories. In contrast with severe slugging in a vertical or catenary riser where fluid blowout is initiated by gas penetration into the riser base, fluid blowout of severe slugging in an S-shaped riser is induced by gas intrusion into the upper limb of the riser. Flow pattern maps for each declination were generated based on the experimental data. The region of severe slugging was found to be sensitive to pipeline inclination. An existing model for the stability of steady state operation was modified. The modified model was tested against our experimental results. An excellent agreement between the experimental data and the predictions was obtained.

Dual-bed gasifier is a new gasifier system with separated combustion and gasification zones. The two-zone separation makes it possible to increase calorific value of the producer gas. In order to develop and improve the process operation, understanding of system dynamics and parameters that describe the in-depth hydrodynamics are essential. Computational fluid dynamics is a tool that can be used to explain the complex multiphase system behavior. The considered dual-bed gasifier had 3.00 m height and the maximum width diameters of riser and downcomer were 0.14 and 0.40 m, respectively. Conservation equations of mass, momentum, energy and species for each phase were solved coupling with the kinetic theory of granular flow using ANSYS FLUENT version 12.1. Here, two-dimensional simulation had been successfully determined the flow pattern and chemical reaction corresponding with actual experimental and theoretical data. The calculated results of the solid volume fraction in the riser section showed the bubbling and slugging flow patterns. The product gas composition and gas temperature inside dual-bed gasifer reflected the advantages for this type of reactor over the other conventional gasifiers. The system turbulences were firstly explored in dual-bed system which were normal Reynolds stresses and granular temperatures. For the effect of interphase exchange coefficient model, the pressure-loop using drag force model proposed by Gidaspow was in good agreement with the experiment than the ones proposed by Wen-Yu and Syamlal-O'Brien.

Severe slugging is a dynamic two-phase flow phenomenon with regular liquid accumulation and blow-out in flow-line riser geometries. This paper discusses the applicability of a slug tracking model on a case where hydrodynamic slug initiation in a horizontal part of the pipeline upstream the riser base affects the severe slugging cycle period. The given experimental case is from the Shell laboratories in Amsterdam: air–water flow in a 100 m long pipe (65 m horizontal and 35 m −2.54° downwards) followed by a 15 m long vertical riser. A Lagrangian slug and bubble tracking model is described. A two-fluid model is applied in the bubble region and the slug region is treated as incompressible flow, with an integral momentum equation. Slug initiation from unstable stratified flow can be captured directly by solving the two-fluid model on a fine grid (a hybrid capturing and tracking scheme). Alternatively, slug initiation can be made from sub grid models, allowing for larger grid sizes. The sub grid models are based on the two established flow regime transition criteria derived from the stability of stratified flow and from the limiting solution of the unit cell slug flow model. Sensitivity studies on hydrodynamic slug initiation models on the severe slugging characteristics are presented. No hydrodynamic slug initiation (e.g. large grid size in the capturing scheme) overestimates the severe slug period compared with the experiments. Slug capturing and sub grid initiation models both give good predictions for small grid sizes (provided the detailed inlet configuration is included in the capturing case). Good predictions are also shown for larger grid sizes (factor of 50) and sub grid initiation models. The numerical tests show that correct prediction of the severe slugging cycle is sensitive to the initiation of upstream hydrodynamic slugs, but less sensitive to the local structure of the slug flow (frequencies and lengths) in the upstream region.