Compact Separator Research Articles

Hydrodynamics of countercurrent two‐phase flow in a centrifugal field

AbstractCentrifugal adsorption technology (CAT) is a new method for continuous adsorption and ion exchange involving countercurrent flow of liquid and micrometer‐range adsorbent particles under the influence of a centrifugal force. Due to the fast adsorption kinetics associated with very small particles, CAT leads to extremely compact separation equipment with high capacities and excellent mass‐transfer efficiencies. Experimental results on the hydrodynamics of countercurrent flow of solids and liquid in a centrifugal field are discussed in terms of flooding conditions, pressure drops and holdup of the adsorbent particles in the contactor. A model developed based on the relations for homogeneous fluidization under gravity correctly describes countercurrent flow under gravity, but does not correctly describe countercurrent flow in a centrifugal field. In general, observed capacities of this model are higher than estimated. Although the centrifugal force magnifies the apparent density difference between the two phases, the two‐phase flow did not seem to exhibit heterogeneous behavior, such as observed in gas‐fluidized beds.

Computational Fluid Dynamics (CFD) Study of Bubble Carry-Under in Gas-Liquid Cylindrical Cyclone Separators

Summary The gas-liquid cylindrical cyclone (GLCC©) separator is an attractive compact separator alternative to the conventional vessel-type separator. Thus, it is important to develop predictive tools for design and to be able to improve the technology of the GLCC. Previous studies on the GLCC have focused on mechanistic models capable of predicting the operational envelope for liquid carryover and on the understanding of the flow field in the GLCC. The main objective of this work was to investigate the behavior of small gas bubbles in the lower part of the GLCC, below the inlet, and the related gas carry-under phenomena. This investigation was performed by flow visualization and by using a commercially available computational fluid dynamics (CFD) code. Simulations of single-phase and two-phase flows were carried out and bubble trajectories were obtained in an axisymmetric geometry that represents the GLCC configuration. Bubble trajectory analysis was used to quantify the effects of the important parameters on bubble carry-under. These include bubble size, ratio of the GLCC length below the inlet to diameter, viscosity, Reynolds number, and inlet tangential velocity.

Liquid Carry-Over in Gas/Liquid Cylindrical Cyclone Compact Separators

Summary The liquid carry-over phenomenon in gas-liquid cylindrical cyclone (GLCC©**) compact separators has been studied experimentally and theoretically. Experimental data have been acquired including the operational envelope for liquid carry-over and percent liquid carry-over beyond the operational envelope. The data show that at low gas and high liquid flow rates, under churn flow conditions in the upper part of the cylindrical cyclone, a large amount of liquid can be carried over relatively easily. On the other hand, at high gas and low liquid flow rates, under annular flow conditions, one should exceed the operational envelope significantly in order to have large amount of liquid carry-over. A mechanistic model has been developed for the prediction of the percent liquid carry-over beyond the operational envelope for churn flow conditions. An existing model for the prediction of the operational envelope for liquid carry-over has been extended to high-pressure conditions, including improved models for zero-net liquid flow holdup, droplet region and blowout and critical velocities. Comparisons between the new mechanistic model predictions for percent liquid carry-over with the experimental data, under churn flow conditions, show good agreement. Also, considering the lack of experimental data, the predictions of the operational envelope for liquid carry-over at high-pressure conditions show reasonable trends.

The effects of geometry, fluid properties and pressure on the hydrodynamics of gas–liquid cylindrical cyclone separators

The hydrodynamic flow behavior in a Gas–Liquid Cylindrical Cyclone (GLCC) compact separator is studied experimentally and theoretically. New experimental data are acquired utilizing a 7.62 cm I.D, 2.18 m high, GLCC separator for a wide range of operating conditions. Investigated parameters include three different inlet geometries (5.08 cm I.D single, 7.62 cm I.D single and 7.62 cm I.D dual inlets), four different liquid viscosities (1, 2.5, 5 and 10 cps), three system pressures (101.3, 273.6 and 487.2 kPa), and the effect of surfactant. The measured data comprise of equilibrium liquid level, zero-net liquid flow holdup and the operational envelope for liquid carry-over. The data are utilized to verify and refine an existing GLCC mechanistic model. Comparison between the modified model predictions and the experimental data show a very good agreement.

Designing Tomorrow's Compact Separation Train

This article is a synopsis of paper SPE 56644, "Designing Tomorrow's Compact Separation Train," by K.E. Arnold, SPE, and P.L. Ferguson, Paragon Engineering Services Inc., originally presented at the 1999 SPE Annual Technical Conference and Exhibition, Houston, 3-6 October.

Aspect Ratio Modeling and Design Procedure for GLCC Compact Separators

The petroleum industry has recently shown interest in the development of innovative alternatives to the conventional vessel-type separator. One such alternative is the gas-liquid cylindrical cyclone (GLCC) separator, which is simple, compact, and low weight, and has low capital and operational costs. A new mechanistic model is proposed, for the first time, to predict the aspect ratio of the GLCC, based on its complex hydrodynamic multiphase flow behavior. This model incorporates an analytical solution for the gas-liquid vortex interface shape, and a unified particle trajectory model for bubbles and droplets. A simplified GLCC design methodology, based on the foregoing mechanistic model, is developed and specific design criteria are proposed as user guidelines for GLCC design. A summary of four actual field application designs is provided to demonstrate the capability of the aspect ratio modeling and the impact the GLCC technology may have on the petroleum industry.

State of the Art of Gas/Liquid Cylindrical-Cyclone Compact-Separator Technology

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Summary The petroleum industry has relied mainly on conventional, vessel-type separators to process wellhead production of oil/water/gas flow. However, economic and operational pressures continue to force the industry to seek less expensive and more efficient separation alternatives in the form of compact separators, especially for offshore applications. Compared with vessel-type separators, compact separators, such as the gas/liquid cylindrical cyclone(GLCC), are simple, low-cost, low-weight separators that require little maintenance and are easy to install and operate. However, the inability to predict GLCC performance adequately has inhibited its widespread deployment. Current R&D is aimed at creating the necessary performance-prediction tools for proper design and operation of GLCC separators. This paper presents the status of the development of the GLCC, the state of the art with respect to its simulation and design, and current successful and potential applications. Introduction The GLCC (Fig. 1) consists of a vertical pipe with a tangential inclined inlet and outlets for gas and liquid. The tangential flow from the inlet to the body of the GLCC creates a swirl that produces centrifugal and buoyancy forces on the fluids that are an order of magnitude higher than the force of gravity. The combination of gravitational, centrifugal, and buoyancy forces separates the gas and liquid. The liquid is pushed radially outward and downward toward the liquid exit, while the gas is driven inward and upward toward the gasoutlet. The low-cost, low-weight, compact GLCC separator offers an attractive alternative to the conventional vessel-type separator. A size comparison between the GLCC and conventional vessel-type vertical and horizontal separators has been conducted recently for a typical field application with oil and gas flow rates of 100,000 B/D and 70,000 Mscf/D, respectively, at 100 psig. For this case, the required GLCC inner diameter and height are 5 and 20 ft, respectively. These dimensions are approximately one-half of the corresponding dimensions of the required conventional vertical separator (9 x 35 ft) and about one-quarter of the dimensions of a conventional horizontal separator (19x 75 ft).

Field Evaluation of a Multiphase Meter in Well-Testing Operation

Summary This paper describes the evaluation results on the measurement accuracy and long-term operation of a multiphase meter used for well testing. The test was conducted by Chevron at its Lost Hills field in California. After many years of development work, several multiphase meter manufacturers have begun to offer their meters commercially for production operation. In this paper, commercial multiphase meters are first briefly reviewed based on the methods that those meters use to handle the fluid flow. The multiphase meter selected for this application was manufactured by Accuflow Inc. It uses the compact separation approach in handling the oil/gas/water flowstream by first separating the gas from the liquid stream and then measuring the gas and oil/water separately. The Accuflow system was installed at a gauge station in January 1996. It was designed to test wells that have productions ranging approximately from 100 to 400 bbl of fluid per day, with a high water cut (40 to 90%), and up to 200 Mcf/D of gas. For accuracy testing, the multiphase meter was piped in series with a test separator at the gauge station. Production from selected wells, covering a wide range of flow rates, water cuts, and gas volume fractions, flowed through the multiphase meter first and then through the test separator, which enabled comparison of the new meter's performance and accuracy with an existing reference. Additional tests also were conducted to compare results with a test tank at the site. The paper also discusses other operational aspects of the multiphase meter such as equipment maintenance and sand accumulation. Overall, satisfactory performance of this multiphase meter was observed, and additional units have been installed at the Lost Hills field.

Control of civilian plutonium inventories using burning in a non-fertile fuel

The increasing inventories of plutonium generated by commercial nuclear power production represent a potential source for proliferation of nuclear weapons. To address this threat we propose separating the plutonium from the other constituents of commercial reactor spent fuel and burning it in a non-fertile fuel based on a zirconium dioxide matrix. The separation can be performed by the Purex process currently in use, but we recommend development of a more compact separation technology that would produce less secondary waste than currently used technology and would allow for more stringent accounting of plutonium inventories. The non-fertile fuel is designed for use in conventional light water power reactors and does not require development of new reactor technology.

Development and Testing of a Compact Liquid-Gas Auger Partial Separator for Downhole or Surface Applications

Summary In some applications, complete separation of liquid and gas is not required and removing only a portion of the gas is sufficient. One application that was developed fully is separation of gas from one well for raw gas lift of other wells. This can be done either on the surface or downhole. The auger separator is a new, patented device that was initially developed to fit inside production tubing and, thus, is an ultra-compact separator design. It differs from other separators in that it requires no complex controls or power to operate and, for most applications, has a diameter of only a few inches. The multiphase fluid enters an auger section where the pitch of the stationary auger blade causes the flow to rotate. Centrifugal forces created by this rotation cause the liquid to flow along the outer wall with the gas flowing in the center. A portion of the gas is ported through a crossover to the annulus in downhole applications or to a gas line in surface applications. The downhole separator can be placed by wireline in the tubing. The surface version is placed as a spool piece in the production line. Equations were developed to predict performance and were incorporated into a spreadsheet for ease of design. Laboratory tests were performed to validate the predictions and to explore various design details. Following successful lab testing, the prototype separator, which was 3½ in. in diameter, was placed downhole inside 4½-in. tubing. The separated gas was ported to the annulus through a gas-lift mandrel. This test showed that the equipment could be placed in the well with wireline, that downhole separation was feasible, and that the theoretical pressure-drop calculations were accurate. Following this test, an 8-in.-diameter auger separator was designed for separation of gas on the surface as a full-scale pilot test. This was placed in the production line from a well, and the separated gas was used to provide raw lift gas for other wells on the drillsite. These two field tests showed that partial separation was feasible with this device, and that the equations used for design were reasonable. The surface auger separator was left in place after the test and continues to provide lift gas. This paper presents the concept, design equations, laboratory test results, and field-test results of both a downhole and a surface application. Although raw gas lift is an application that has been fully developed, other potential uses also are discussed.

Simultaneous Optimization Model for Multicomponent Separation

This paper describes the general optimization model for the simultaneous synthesis of heat integrated separation sequences and their heat exchanger networks (HEN). The model enables an optimal selection of the separation sequence, type of separation units, heat matches, operating conditions and design parameters. The synthesis of the separation sequence can be either homogeneous (the same type of separators) or heterogeneous (different types of separators) allowing sharp and/or nonsharp separations. The synthesis can be carried out either for a separation problem only or for a separation system together with its flowsheet. The model is formulated as a mixed-integer nonlinear problem (MINLP). The approach is illustrated by two examples: one of them presents the homogeneous synthesis of a sharp distillation sequence using a network separation superstructure and a more compact superstructure. The second example presents the application of the general optimization model in the synthesis of the heterogeneous separation system together with its flowsheet when the compact separation superstructure is used.

MODELING OF THE FLUID FLOW AND HEAT TRANSFER AT THE EDGE OF A FIXED BED

As a preliminary study of the nature of heat transfer between a packed bed and a bounding wall, a first-order model is considered where the bed is taken to be a row of rectangular compacts. Results are obtained numerically for the fluid flow and heat transfer in the voids between compacts and to the wall. Different gap sizes and compact-plane separations, with Prandtl numbers of 0.72 and 7 and Reynolds numbers ranging from 0 to 100, are considered. As the compact separation and the Reynolds number increase, the heat transfer from the void increases and the maximum temperature decreases. Increasing the Prandtl number improves the heat transfer from the void, and when the compact-bounding plane separation increases, the fluid flow and heat transfer settle down to essentially a stationary value, independent of the Reynolds number.

Laboratory Experience with Long-Term Bearing Lubrication

This paper presents the results of laboratory testing of several types of size-204 ball bearings. Three of these bearings had lubricant compact ball separators; three other types of conventional bearings were operated without applied lubrication in the form of oils, greases, or dry powders. Bearing performance was judged from friction and wear life results. Bearings with lubricant compact separators have operated for periods as long as 38,000 hours without failure in a vacuum environment of less than 3 × 10−6 torr. The test conditions included 1,790-r pm rotational speeds, no applied heat, and a nominal axial load of seven pounds. Based on rate of weight loss, predictions were made on the expected wear lives of the bearings. Conventional bearings, using three different ball separator designs, were subjected to the same test conditions (in vacuum) as the lubricant compact separator bearings, as well as to similar conditions in an air environment. Average wear lives are reported for the three types of bearings operating in air and for two of these operating in vacuum. The third type of bearing continues to operate in vacuum and a life prediction is made based upon the wear rate of another specimen.