High Liquid Holdup Research Articles

Experimental investigation on long hydrodynamic slugs in offshore pipeline

In the process of liquid-dominated offshore oil and gas transportation, long hydrodynamic slugs are likely to occur in subsea pipelines at high liquid holdup. A large number of long hydrodynamic slug data at high liquid velocity and low gas velocity were obtained by using visual images in a 46 mm ID, 1657 m long pipeline. The flow pattern map close to the industrial parameters is plotted, and slug flow can take place at a lower superficial gas velocity (VSG = 0.045 m/s) in the long pipeline. The maximum slug length is 2.5 times the average slug length, and the longest liquid slug is 969 D near the transition boundary of slug flow. When VSG < 1.00 m/s, slug length increases rapidly and slug frequency decreases significantly with the decrease of superficial gas velocity at the same superficial liquid velocity. The prediction correlations of slug velocity, length, and frequency are developed for long-distance offshore pipelines at high liquid velocity and low gas velocity, and the maximum error is less than 25%.

Economic comparison of reactive distillation (RD) to a benchmark conventional flowsheet: Regions of RD applicability and trends in column design

A novel methodology for the techno-economic assessment of Reactive Distillation (RD) is presented. The developed methodology benchmarks reactive distillation (RD) to a conventional reactor + distillation train flowsheet (R+D) on a cost-optimized basis, with the optimization being performed on the process unit level (reactor sizing, number of stages, feed point(s)) and the internals level (reactive tray design). This methodology is applied to the ideal quaternary system A+B↔C+D with the conventional boiling point order of TC < TA < TB < TD (αAD = 4, αBD = 2, αCD = 8). From this pool of data, a regime map of RD vs. R+D is established in which the attractive regions of either flowsheet option are identified in terms of the chemical reaction rate and chemical equilibrium. It is found that RD can arise as the cost optimal option for a large range of residence time requirements by virtue of overcoming the external recycle requirements of R+D. This is achieved through optimized reactive tray design. Contrary to conventional distillation design practices, it was found that the preferred use of bubble-cap trays over sieve trays to allow elevated weir heights and designing the column diameter below 80% of flooding become relevant design choices when accommodating high liquid holdup.

Experiments and simulations on a cold-flow blast furnace hearth model

The blast furnace hearth plays an important role in the operational stability and lifetime of the reactor. The quasi-stagnant bed of coke particles termed the deadman undergoes complex interaction with the flowing hot metal, and remains largely ill-understood. In this work, a cold model blast furnace hearth is presented, and studied using both numerical and experimental techniques. Magnetic Particle Tracking (MPT) is used to investigate the individual particle behaviour within the cylindrical, opaque bed. At high liquid holdup, the particle bed was found to alternate between floating and sitting states, following the liquid level during the tapping and filling cycle. This bed motion was found to induce a migration of particles, thereby slowly renewing the deadman. The rate of horizontal migration increases with the vertical bed amplitude, and the renewal of particles is concentrated around the opening of the tap hole. No direct influence of the coke-free space on the tapping rate was found in these experiments. Instead, the disturbance of the packing in front of the tap hole was observed to lead to a higher tapping rate. Additionally, a coupled numerical framework is presented, in which Computational Fluid Dynamics (CFD), the Volume of Fluid (VOF) method and the Discrete Element Method (DEM) are combined. A simulation set-up is presented which closely replicates the experimental conditions. The position and movement of the floating bed are found to be well-predicted by the VOF/CFD-DEM model. Particle trajectories are presented, and migration of particles within the deadman is observed. Alongside the particle motion, the liquid flow pattern during draining of the vessel is visualised. It is concluded that a coke-free space underneath the deadman significantly impacts the shape of the liquid flow pattern, which affects the erosion processes within the blast furnace hearth.

Combining a robust thermophilic methanogen and packing material with high liquid hold-up to optimize biological methanation in trickle-bed reactors

The hydrogen gas-to-liquid mass transfer is the limiting factor in biological methanation. In trickle-bed reactors, mass transfer can be increased by high flow velocities in the liquid phase, by adding a packing material with high liquid hold-up or by using methanogenic archaea with a high methane productivity.This study developed a polyphasic approach to address all methods at once. Various methanogenic strains and packings were investigated from a microbial and hydrodynamic perspective. Analyzing the ability to produce high-quality methane and to form biofilms, pure cultures of Methanothermobacter performed better than those of the genus Methanothermococcus. Liquid and static hold-up of a packing material and its capability to facilitate attachment was not attributable to a single property. Consequently, it is recommended to carefully match organism and packing for optimized performance of trickle-bed reactors. The ideal combination for the ORBIT-system was identified as Methanothermobacter thermoautotrophicus IM5 and DuraTop®.

Identification of Robust Thermophilic Methanogenic Archaea and Packing Material for High Liquid Hold-Up at Low Volumetric Gas Flow Rates for Use in Trickle-Bed Reactors for Biological Methanation

Identification of Robust Thermophilic Methanogenic Archaea and Packing Material for High Liquid Hold-Up at Low Volumetric Gas Flow Rates for Use in Trickle-Bed Reactors for Biological Methanation

Experimental evaluation and modeling of the hydrodynamics in structured packing operated with viscous waste oils

The purpose of this work was to study the hydrodynamic behavior of two viscous waste oils (a transformer oil and a lubricant characterized by viscosities of 19 mPa s and 79 mPa s at 25°C, respectively) and a silicone oil (20 mPa s at 25°C) in a laboratory-scale packed column (Dcol = 0.12 m). The column was filled with structured packing made of corrugated sheets (Flexipac® 500Z HC) and was operated at counter-current. Thus, the gas superficial velocities at the loading point were in the range from 0.40 to 0.65 m s−1 for liquid loads between 1 and 24 m3 m−2 h−1, and, at the flooding point from 0.56 to 1.07 m s−1 for liquid loads between 6 and 36 m3 m−2 h−1. Both loading and flooding points were particularly influenced by the solvent viscosity, leading to a narrow loading zone for the most viscous solvent (lubricant). The pressure drop values remained reasonable, lower than 450 Pa m−1 in the loading zone, even for the lubricant. Billet-Schultes correlations were used for the prediction of the loading and flooding velocities and of the pressure drop. The specific constants of the model were determined. These correlations enable accurate predictions of the loading and flooding points, with an average relative error around 7–8%, and of the pressure drop in the loading zone, with an average relative error of 15%. Simulations were performed with the Billet-Schultes correlations and showed that high liquid holdup and interfacial area would be obtained with these viscous solvents in the selected packing. Scale-up calculations proved that it would be possible to implement the transformer oil at industrial scale in a packed column filled with the studied structured packing.

Review on gas–liquid–liquid three–phase flow patterns, pressure drop, and liquid holdup in pipelines

Gas–liquid–liquid three–phase co-current flow commonly occurs in the oil & gas production pipelines. The dynamics of three-phase flow are more complex than single and two-phase flow. High pressure drop and liquid holdup are common flow assurance problems in the upstream oil and gas production pipelines. These problems increase the energy consumption of the flow system, especially in the process of enhanced oil recovery (EOR). Three-phase flow behavior is highly dependent on the flow patterns. For an economical and energy-efficient production process, the flow pattern with less pressure drop and liquid holdup needs to be identified. In this article, three-phase flow patterns’ classification and structures are critically reviewed and discussed in detail. Flow regime transition with the change in volumetric fractions and superficial velocities of phases are also elaborated. The prediction models for flow regime transition and stability, pressure drop, liquid holdup, and three-phase flow characteristics are presented.

Removal of trace hexavalent chromium from aqueous solutions by ion foam fractionation.

Ion foam fractionation is a green and cost-effective technology where separation of molecules exploits the difference in surface affinity. In this work, a batch ion foam fractionation system was designed and optimized for the separation of trace hexavalent chromium (Cr(VI)) from aqueous solutions. The effect of surfactant head groups (collectors) on the adsorption dynamics was analyzed. Cetyl trimethyl ammonium bromide (CTAB), a cationic surfactant showed high efficiency for the removal of Cr(VI) from aqueous solutions. An experimental investigation of the effect of different operational parameters on the separation characteristics is presented. The recovery of Cr(VI) increased with the increase in CTAB/Cr(VI) molar ratio and reached a maximum of 92.5% at optimum operating conditions. However, with CTAB concentrations close to the critical micelle concentration (CMC) wet foams were produced resulting in high liquid hold-up and poor enrichment ratio. The presence of Cr(VI) at the gas-liquid interface significantly improved the drainage characteristics of the foam decreasing the liquid hold-up. Further, a three-stage ion foam fractionation unit was developed with Cr(VI) removal efficiency of more than 99%. The concentration of Cr(VI) in the residue after the three-stage operation was less than 0.02 mg/L which is below the USEPA recommended standards for drinking water.

LIQUID HOLDUP MANAGEMENT BY PREDICTING STEADY STATE TURNDOWN RATE IN WET GAS PIPELINE NETWORK

Now days, one of the greatest challenges in gas development is transport the fluid especially multiphase fluid to long distances and multiphase pipeline to sell point. Yet, a challenge to transport multiphase fluid is how to operate the systemsin operating a long distance, large diameter, and multiphase pipeline.The operating system include how to manage high liquid holdup, mainly built during low production rate (turn down rate) periods especially during transient operations such as restart and ramp-up, so that liquid surge arriving onshore will not exceed the liquid handling capacity of the slug catcher. The objective of this research is to predict liquid trapped in pipeline network by analysis turn down rate in order to determine minimal gas production rate for stable operation. This research was carried out by two steps: Simulation Approach and Optimization Techniques. Simulation approach include define fluid composition and built pipeline network configuration while optimization technique include conduct scenario for turn down rate. The fluid composition from wellhead to manifold is wet gas. First scenario and Second scenario of turndown rate yield minimum gas rate for stable operation. The pipeline has to be operated above 600 MMSCFD from peak gas production rate is 1200 MMSCFD (A-Manifold Mainline) and 60 MMSCFD from peak gas production rate is 150 MMSCFD for D-Manifold Mainline.

Solid Foam Packings for Multiphase Reactors: Modelling of Liquid Holdup and Mass Transfer

In this paper, experimental and modeling results are presented of the liquid holdup and gas–liquid mass transfer characteristics of solid foam packings. Experiments were done in a semi-2D transparent bubble column with solid foam packings of aluminum in the range of 5–40 pores per inch (ppi). The relative permeability model described by Saez and Carbonell (1985) is used to describe the liquid holdup data for solid foam packings of 5, 20 and 40 ppi. The investigated system variables are the superficial gas and liquid velocities, using counter-current flow with maximum gas velocities and liquid velocities of 0.8 m s−1 and 0.03 m s−1, respectively. The relative permeability model is able to describe the liquid holdup in the low liquid holdup or trickle flow regime as well as in the high liquid holdup regime, which resembles flow in a packed bubble column. Gas-to-liquid mass transfer is modelled using the penetration theory. Mass transfer coefficients up to 6 s−1 are predicted; these high values are largely due to the high specific surface area of the solid foam packings.

Hydrodynamics of gas–liquid counter-current flow in solid foam packings

Solid foam materials combine high voidage and high surface area. These two properties are advantageous for use in chemical reactors due to the low frictional pressure drop and relatively high surface area that may be used for catalyst deposition. Hydrodynamic parameters such as liquid holdup, pressure drop, and flow regimes similar to those for packed beds, have been obtained for the gas and liquid flows through these solid foam packings. The open-celled solid foam packings used were in the range of 5–40 pores per linear inch (ppi). The regimes studied are two high liquid holdup regimes and a low liquid holdup regime (trickle flow regime). Also the flooding points for counter-current flow have been determined.

Combining Distillation and Heterogeneous Catalytic Reactors

The hardware design of reactive distillation (RD) columns pose severe challenges with respect to the choice and design of the hardware; the requirements of reaction (i.e. high liquid or catalyst holdup) are not in consonance with the requirement of separation (high interfacial area). In this paper we examine an alternative to the RD concept, namely a distillation column networked with a single side (external) reactor, which we call the SR concept. For the case study of tertiary-amyl ether (TAME) production by reaction of isoamylene (IA) with methanol, we show that employing the SR concept it is possible to meet the design targets of IA conversion, TAME purity in bottom product and TAME impurity in top product using just one side reactor. From detailed hardware designs, we see that the RD column is significantly taller than the distillation column in the SR configuration; this is due to the placement of the catalyst load with in the RD column. We conclude that the SR concept will be competitive with the RD column configuration provided the IA conversion targets are not too stringent.

Distillation column with reactive pump arounds: an alternative to reactive distillation

The hardware design of reactive distillation (RD) columns pose severe challenges with respect to the choice and design of the hardware; the requirements of reaction (i.e. high liquid or catalyst holdup) is not in consonance with the requirement of separation (high interfacial area). In this paper, we examine an alternative to the RD concept, namely a distillation column networked with a number of side (external) reactors. If each distillation stage is linked to a side reactor, the performance of the RD column is matched exactly. From a practical point of view, it is desirable to reduce the number of side reactors to below, say, six. The precise location of the chosen number of side reactors and the manner in which the liquid draw-offs and reactor effluent re-entry to the distillation column needs to be chosen carefully. We have developed an algorithm to determine an optimum configuration of the side-reactor concept in order to maximise conversion. For the case study of methyl acetate production, we see that it is possible to match the conversion level of an RD column by appropriate choice of the number of side reactors and the pump around ratio. The higher the conversion target the larger the number of side reactors and pump around ratios. For modest conversion levels, say <90%, even a 3-side-reactor configuration will be able to match the performance of the RD column. The study presented here reveals the potential, and limitations, of the side-reactor concept for use as an alternative to RD technology.

Distillation column with reactive pump arounds: an alternative to reactive distillation

The hardware design of reactive distillation (RD) columns pose severe challenges with respect to the choice and design of the hardware; the requirements of reaction (i.e. high liquid or catalyst holdup) is not in consonance with the requirement of separation (high interfacial area). In this paper we examine an alternative to the RD concept, viz. a distillation column networked with a number of side (external) reactors. If each distillation stage is linked to a side reactor, the performance of the RD column is matched exactly. From a practical point of view it is desirable to reduce the number of side reactors to say 3–6. The precise location of the chosen number of side reactors and the manner in which the liquid draw-offs and reactor effluent re-entry to the distillation column needs to be chosen carefully. We have developed an algorithm to determine the optimum configuration of the side reactor concept in order to maximize conversion. For the case study of methylacetate (MeOAc) production, we see that it is possible to match the conversion level of an RD column by appropriate choice of the number of side reactors and the pump around ratio. The higher the conversion target the larger the number of side reactors and pump around ratios. For modest conversion levels, say <90%, even a three-side reactor configuration will be able to match the performance of the RD column. The study presented here reveals the potential, and limitations, of the side reactor concept for use as an alternative to RD technology.

The induction of pulses in trickle-bed reactors by cycling the liquid feed

The operation of a trickle-bed reactor in the pulsing flow regime is well known for its advantages in terms of an increase in mass and heat transfer rates. However, fairly high gas and liquid flow rates necessitate the operation in the pulsing flow regime, resulting in relatively short contact times between the phases. By means of the periodic operation of a trickle-bed reactor it is possible to obtain pulsing flow at average throughputs of liquid usually associated with trickle flow during steady-state operation. This feed strategy to force pulse initiation is termed liquid-induced pulsing flow. The advantages associated with pulsing flow may then be utilized to improve reactor performance in terms of an increase in capacity and the elimination of hot spots, while interfacial contact times are comparable to trickle flow. An additional advantage of liquid-induced pulsing flow is the possibility to tune the pulse frequency and therefore the time constant of the pulses. During the periodic operation of a trickle bed, continuity shock waves are initiated in the column due to the step-change in liquid flow rate. This results in the division of the column into a region of high liquid holdup and a region of low liquid holdup. At high enough gas flow rates, the inception of pulses takes place in the liquid-rich region. Analysis of the performed experiments indicates that besides gas and liquid flow rates, an additional criterion for pulse inception is the available length for disturbances to grow into pulses. For self-generated pulsing flow this results in the upward movement of the position of the point of pulse inception with increasing gas flow rate. With liquid-induced pulsing flow this means that higher gas flow rates are necessary to induce pulses as the length of the liquid-rich region decreases. For both self-generated and liquid-induced pulsing flow this relationship between the gas flow rate and the available length for pulse formation is identical.

High liquid holdup airlift tower loop reactor: II. Downcomer hydrodynamic modeling

Hydrodynamics in the downcomer of a high liquid holdup airlift tower loop reactor, whose riser has been previously studied, is presented. A visual procedure with colorimetric tracers injected into the top part of the riser and monitored by means of a video camera system, for subsequent treatment of the obtained images, was used. The tracer front advance curves have suggested a compartmental model of three parameters to be used for physical transport processes. © 2000 Society of Chemical Industry

High liquid holdup airlift tower loop reactor: I. Riser hydrodynamic characteristics

The hydrodynamics of high liquid holdup airlift reactors have not been widely studied. In this work we study the riser of a reactor of this type, focussing on the influence of the gas flow rate and the submergence ratio on various hydrodynamic parameters: liquid circulation velocity, gas holdup, and gas residence time in the liquid. A notable difference in reactor behavior is observed with a submergence ratio equal to unity and with a ratio lower than unity. Correlations for the parameters studied in different conditions, as several submergence ratios, are proposed, these are extrapolations of other equations proposed in the literature for airlift reactors. The reactor studied in this work can be thought of as an element of a great pool formed by multiple elements of similar flux type. The studied parameters are shown to be very important for subsequent hydrodynamic and mass transfer modeling of the reactor.

High liquid holdup airlift tower loop reactor: II. Downcomer hydrodynamic modeling

Hydrodynamics in the downcomer of a high liquid holdup airlift tower loop reactor, whose riser has been previously studied, is presented. A visual procedure with colorimetric tracers injected into the top part of the riser and monitored by means of a video camera system, for subsequent treatment of the obtained images, was used. The tracer front advance curves have suggested a compartmental model of three parameters to be used for physical transport processes. © 2000 Society of Chemical Industry

Model Studies of Liquid Flow in the Blast Furnace Lower Zone.

The non-wetting flow of liquid iron in the blast furnace lower zone is simulated experimentally using a two dimensional raceway model with water, air and 4.1 mm diameter polyethylene beads to represent liquid iron, blast furnace gas and the coke bed respectively. An X-ray technique is used to visualise liquid flow in the packed bed and the distribution of liquid from the bottom of the bed is measured. The liquid percoates through the packed bed as series of rivulets which are continuously breaking up and rejoining. The direction and magnitude of the percolation velocity is determined by the balance between three forces acting on the liquid-gravity, gas drag and bed resistance. The gas drag has a very strong effect on the liquid distribution, forcing the liquid away from the raceway region. This effect increases with increasing gas flow rate. At high gas flow rate, the liquid flow rate and distribution at the top of the bed do not effect the liquid distribution leaving the bed. Near the raceway, the packed bed is dry. The size of the dry region increases with increasing gas flow rate. Above the raceway, beyond the dry packed bed, is a region of high liquid holdup. Liquid dripping into this region has a high residence time compared to liquid falling through the deadman zone. A mathematical model for liquid fow is outline which gives good agreement with experimentally observed liquid flow patterns in the cold raceway model and could be suitable for predicting the liquid flow pattern under real blast furnace conditions. This study confirms that the effect of gas drag on the flow of liquid iron through the blast furnace lower zone is important and should not be neglected.

An immobilized cell reactor with simultaneous product separation. II. Experimental reactor performance

The simultaneous separation of volatile fermentation products from product-inhibited fermentations can greatly increase the productivity of a bioreactor by reducing the product concentration in the bioreactor, as well as concentrating the product in an output stream free of cells, substrate, or other feed impurities. The Immobilized Cell Reactor-Separator (ICRS) consists of two column reactors: a cocurrent gas-liquid "enricher" followed by a countercurrent "stripper" The columns are four-phase tubular reactors consisting of (1) an inert gas phase, (2) the liquid fermentation broth, (3) the solid column internal packing, and (4) the immobilized biological catalyst or cells. The application of the ICRS to the ethanol-from-whey-lactose fermentation system has been investigated. Operation in the liquid continuous or bubble flow regime allows a high liquid holdup in the reactor and consequent long and controllable liquid residence time but results in a high gas phase pressure drop over the length of the reactor and low gas flow rates. Operation in the gas continuous regime gives high gas flow rates and low pressure drop but also results in short liquid residence time and incomplete column wetting at low liquid loading rates using conventional gas-liquid column packings. Using cells absorbed to conventional ceramic column packing (0.25-in. Intalox saddles), it was found that a good reaction could be obtained in the liquid continuous mode, but little separation, while in the gas continuous mode there was little reaction but good separation. Using cells sorbed to an absorbant matrix allowed operation in the gas continuous regime with a liquid holdup of up to 30% of the total reactor volume. Good reaction rates and product separation were obtained using this matrix. High reaction rates were obtained due to high density cell loading in the reactor. A dry cell density of up to 92 g/L reactor was obtained in the enricher. The enricher ethanol productivity ranged from 50 to 160 g/L h while the stripper productivity varied from 0 to 32 g/L h at different feed rates and concentrations. A separation efficiency of as high as 98% was obtained from the system.