Bowl Centrifuge Research Articles

Resolved Simulation for the Prediction of Classification in Decanter Centrifuges

Solid–liquid separation plays a decisive role in various industrial applications particularly in the treatment and purification of suspensions. Solid bowl centrifuges, such as the decanter centrifuge, are commonly employed in these processes as they operate continuously and enable high throughputs with short processing times. However, predicting the separation performance of solid bowl centrifuges proves to be challenging due to dynamic phenomena within the apparatus, such as particle settling, sediment build-up, consolidation and sediment transport. In practice, design considerations and the dimensioning of the apparatus rely on analytical models and the manufacturer’s expertise. Computational Fluid Dynamics (CFD) offers a way to deepen our understanding of these devices by allowing detailed examination of flow phenomena and their influence on the separation processes. This study utilizes the open-source software OpenFOAM to simulate multiphase flow in a laboratory-scale decanter centrifuge, solving individual transport equations for each particle size class. The basis is the characterization of the material through targeted laboratory experiments to derive material functions that describe the hindered settling and the sediment consolidation. Furthermore, experiments on a laboratory decanter served as validation. The results demonstrate the solver’s capability to replicate clarification and classification within the apparatus. Furthermore, the solver supports the definition of geometries tailored to specific separation tasks. This research demonstrates the potential of CFD for a better understanding of complex centrifuge processes and for optimizing their design to improve performance.

About Modeling and Optimization of Solid Bowl Centrifuges

About Modeling and Optimization of Solid Bowl Centrifuges

Model‐based Scale Up of Solid Bowl Centrifuges Using Experimentally Determined Material Functions

AbstractThe scale up of solid bowl centrifuges is a major challenge as the process and material behavior are complex and difficult to describe. A common approach to forecast the process behavior is to use analytical models and transfer the experience gained from the lab to the industrial scale. In this context, time‐consuming and cost‐intensive pilot scale experiments are necessary. This paper presents a methodology to improve the scale up process and make it more sustainable by using a numerical model that allows the real‐time tracking of the process and a more reliable scale up process. For this approach, the material behavior is derived from laboratory experiments whereby the scalability is given. Here, the determination of material functions allows an accurate representation of the material behavior for solid bowl centrifuges of different scales. The focus of this paper is the detailed explanation of material related functions for the scale up of decanter centrifuges.

A Resolved Simulation Approach to Investigate the Separation Behavior in Solid Bowl Centrifuges Using Material Functions

The separation of finely dispersed particles from liquids is a basic operation in mechanical process engineering. On an industrial scale, continuously operating decanter centrifuges are often used, whose separation principle is based on the density difference between the solid and the liquid phase due to high g-forces acting on both phases. The design of centrifuges is based on the experience on the individual manufacturer or simplified black box models, which only consider a stationary state. Neither the physical behavior of the separation process nor the sediment formation and its transport is considered. In this work, a computationally-efficient approach is proposed to simulate the separation process in decanter centrifuges. Thereby, the open-source computation software OpenFOAM was used to simulate the multiphase flow within the centrifuge. Sedimentation, consolidation of the sediment, and its transport are described by material functions which are derived from experiments. The interactions between the particles and the fluid are considered by locally defined viscosity functions. This work shows that the simulation method is suitable for describing the solid-liquid separation in a simplified test geometry of a decanter centrifuge. In addition, the influence of the rheological behavior on the flow in the test geometry can be observed for the first time.

Study of the operation of a centrifuge to obtain apiary wax from wax raw materials

The article is devoted to the issue of reducing the loss of beeswax during the processing of wax raw materials in the apiary. To do this, the author proposes the use of a complex of installations, including a wood-fueled steam generator, a frame wax melter and a centrifuge for squeezing wax from the waste of wax melting. The article examines the technological parameters of the centrifuge and describes its design. The results of a multifactorial study of the operating parameters of the centrifuge, including the speed of the centrifuge bowl, the duration of rotation and the temperature of the steam, are presented. The rational operating parameters of the centrifuge when squeezing wax from wax waste are within the following limits: rotational speed n=1000 min-1, steam temperature t=100 °C, centrifuge operation time T=15 min. The noted parameters make it possible to obtain the largest amount of wax in the centrifuge, the mass of which was M=1127 grams with the initial mass of the pressed raw material m0 =3000±10 grams. The conducted studies show that the use of a centrifuge when squeezing wax from the remelting waste of dark bee honeycombs can increase the wax yield by 37.5% and increase the profitability of the apiary.

Evaluation of Separation Efficiency in a Tubular Bowl Centrifuge

AbstractCentrifugal sedimentation, a well‐known solid‐liquid separation process, is typically used for the separation of solids from low concentration feeds because of its high separation efficiency due to high settling velocities. The performance of the tubular bowl centrifuge (TBC) can be studied by using the sigma theory, which assumes plug flow and rigid body motion inside the rotating bowl wall. The separation efficiency of the system is evaluated by determining the effective fluid layer thickness from the experimental data. A method suitable for evaluating the separation efficiency at different parameters for a given TBC is explained along with experimental validation. By using this method, different case studies are performed which depict the influence of each parameter on the separation efficiency. Also, it is demonstrated that the same higher separation efficiency (98 %) at 20 000 rpm could be achieved at higher bowl capacities.

Modelling solid-liquid separation and particle size classification in decanter centrifuges

Decanter centrifuges or solid bowl centrifuges (SBCs) are widely used in separation applications ranging from solid-liquid separation to the classification of ultrafine particles. Several models have been developed by others to describe the solid-liquid separation process in the SBC and to predict the separation efficiency (solids recovery). These models cannot, however, provide detailed information on particle size classification in the SBC, mainly resulting from the neglect of the liquid backflow (in the direction away from effluent discharge point) near the sediments within the SBC and the disregard for different drag regimes. The present work addresses these issues. A physical model without any adjustable parameters was developed to predict solid-liquid separation and particle size classification in the SBC. The model predictions are in good agreement with published experimental data.

Cell saver physics – a review

Cell salvage, cell saver, cell processor or autologous blood transfusion is the process of collecting a patient’s blood from the surgical field, washing, filtering and transfusing it back to the same patient. There are six basic steps involved in cell salvage. Step one involves the collection of shed blood into a reservoir with an anticoagulant-saline mixture. Step two is the filtration of debris and clots. In step three, the red blood cells (RBCs) are separated from the nonerythrocyte components. This process may be likened to clothes in the washing machine. Washing with saline removes contaminants in step four and the RBCs are resuspended in saline and transferred to the reinfusion bag. Waste products are transferred into the waste bag in step five. In step six, the resuspended, washed RBCs are collected in a bag at room temperature which can be reinfused. The functioning of the cell saver is based on Newton’s First and Second Laws of Motion, where centripetal forces are generated to separate the blood components depending on their density. The denser RBCs are driven to the outer wall of the centrifuge bowl with the plasma collecting on the inside. A typical yield will retrieve 50–95.8% RBCs with a final haematocrit of 50–70%. Cell savers are used in procedures with a large volume of anticipated blood loss, high risk of bleeding, low preoperative haemoglobin, in patients with rare blood groups or multiple antibodies and in some Jehovah’s Witness patients.

Effective size separation of laser-generated, surfactant-free nanoparticles by continuous centrifugation

High-power, nanosecond, pulsed-laser ablation in liquids enables the continuous synthesis of highly pure colloidal nanoparticles (NPs) at an application-relevant scale. The gained mass-weighted particle size distribution is however often reported to be broad, requiring post treatment like centrifugation to remove undesired particle size fractions. To date, available centrifugation techniques are generally discontinuous, limiting the throughput and hindering economic upscaling. Hence, throughout this paper, a scalable, continuously operating centrifugation of laser-generated platinum NPs in a tubular bowl centrifuge is reported for the first time. To that end, using a 121 W ns-laser, the continuous production of a colloidal suspension of NPs, yet with broad particle size distribution has been employed, yielding productivities of 1–2 g h−1 for gold, silver, and platinum. The power-specific productivities (Au: 18 mg h−1 W−1, Pt: 13 mg h−1 W−1, Ag: 8 mg h−1 W−1, Ni: 6 mg h−1 W−1) are far higher than reported before. Subsequent downstream integration of a continuously operating tubular bowl centrifuge was successfully achieved for Pt NPs allowing the removal of undesired particle size with high throughput. By means of a systematic study of relevant centrifugation parameters involved, effective size optimization and respective size sharpness parameters for a maximum Pt NP diameter of 10 nm are reported. The results of the experimental centrifugation of laser-generated Pt NPs were in excellent agreement with the theoretically calculated cut-off diameter. After centrifugation with optimized parameters (residence time of 5 min; g-force of 38,454 g), the polydispersity indices of the Pt NPs size distributions were reduced by a factor of six, and high monodispersity was observed.

Modeling and Simulation of Solid‐Bowl Centrifuges as an Aspect of the Advancing Digitization in Solid‐Liquid Separation

AbstractAs a part of the Industry 4.0 initiative, the level of digitization in the process industry is increasing. Through a close link between analytics and dynamic modeling, digitization enables the optimization of processes and the model predictive control. In the field of solid‐liquid separation using centrifuges, the advancing digitization forces the development of methods for computational fluid dynamics (CFD) and short‐cut models to deepen process understanding and process intensification. CFD should be seen as support for experiments to develop suitable short‐cut models for the process simulation. Based on the prerequisites, this article describes the development of dynamic models and their application using the example of solid bowl centrifuges. Therefore, the particulate level is first addressed by discussing critical material properties. Afterwards, the developed numerical algorithms to investigate centrifuges on different time and length scales will be presented. Finally, the mathematical modeling on the process level by using short‐cut models is shown and discussed for decanter and tubular centrifuges.

Performance evaluation of a tubular bowl centrifuge by using laser obscuration method as an online measurement tool

ABSTRACT In the nuclear reprocessing plant, after the dissolution of spent fuel, high-speed tubular bowl sedimentation centrifuge is being used to remove the solid particles from the solvent. The performance of the system and extent of clarification of the solvent is ascertained in the chemical laboratory by drawing the sample. A noninvasive methodology, the laser obscuration, is studied for its adaptability as an online measurement tool for determination of clarification status. This would help to manipulate the operation of the centrifuge to achieve desired separation efficiency with minimum time and without interruption. In this context, the performance evaluation of a uniquely designed high-speed tubular centrifuge for reprocessing of fast reactor fuel has been carried out by using laser obscuration method. The light scattering technique has been widely used for the determination of concentration of clarification liquid. In addition, the size distribution is also ascertained in our study, which is useful to determine the grade efficiency of centrifuge system. Two different particulate liquid suspensions namely ferric oxide (Fe2O3) and zirconium molybdate suspended in de-ionized water are used. The tubular bowl centrifuge is tested at the high-speed rotation of the inner bowl (14000–20000 rpm), various throughput of clarifier liquid (30–470 lph) and in half-loaded bowl condition. The laser obscuration method is found to be useful for ascertaining the performance of the centrifuge system and it is recommended as an online tool for monitoring and maintaining separation efficiency by adjusting rotational speed, throughput and to monitor the bowl-loading condition.

Effects of inner angle of bowl, flow rate and speed on the efficiency of glycerol separation from the raw biodiesel using cylindrical bowl centrifuge

The centrifugal technique has been widely used for separation of fluids with moderately high viscosities because it provides an efficient separation in short residence times. In this work, the cylindrical bowl centrifuge was selected for separation of raw biodiesel and glycerol. In addition, the inner angle of bowl, flow rate and speed were investigated on their effects on the efficiency of separation. The experimental results showed that the inner angle of bowl and the flow rate affected the efficiency of separation significantly. The increase of inner angle of bowl (from 90 to 135 degree) and flow rate (from 50 to 200 ml/min) provided the increase of separation efficiency. In term of speed, the efficiency of separation was increased when increasing the speed from 1,800 rpm to 2,100 rpm. On the other hand, the efficiency of separation was decreased when increasing the speed from 2,100 rpm to 2,400 rpm. The efficiency of cylindrical bowl centrifuge was in the ranges of 29.17-39.83%, 52.83-61.83% and 84.6-91.4% for bowl inner angles of 90, 120 and 135 degree, respectively. The bowl inner angles of 135 degree, flow rate of 200 ml/min and speed of 2,100 rpm were appropriate conditions for glycerol separation from the raw biodiesel using cylindrical bowl centrifuge.

Limit Moisture Content of Coal Concentrate Produced with Industrial Drainers

The process of coal suspension dewatering in centrifuges and pneumatic drainage in vacuum filters and filter presses is theoretically studied. From the condition of equal centrifugal forces and surface tension applied to liquid in a granular layer of the working element of the centrifuge bowl, the analytical relation is obtained to calculate residual concentration of liquid in the treated layer. It is shown that calculation results obtained using the relation, rated data and specifications of industrial drainers agree well. With regard to the equality between the kinetic energy applied by filtration flow in the granular layer to the liquid film in the granules and the work to overcome surface tension forces that keep the film on the surface of the granules, the analytical relation is obtained to calculate residual concentration of a liquid in the layer under pneumatic drainage. The estimates prove realistic nature of the results obtained with the latter relation as well as their agreement with the test and rated data of industrial vacuum filters and filter presses.

Characteristics and quality of intra-operative cell salvage in paediatric scoliosis surgery

ObjectiveTo determine the hematological and microbiological characteristics of blood recovered by using a cell saver with a rigid centrifuge bowl (100ml) in pediatric scoliosis surgery and to determine whether it conforms to the standard expected in adult patients. Material and methodsA cross-sectional, descriptive cohort study was performed on 24 consecutive red blood cell (RBC) units recovered from the surgical field and processed by a Haemolite® 2+ (Haemonetics Corp., Braintree, MA, USA) cell saver. Data were collected regarding age, weight, surgical approach (anterior or posterior), processed shed volume and volume of autologous RBC recovered, full blood count, and blood culture obtained from the RBC concentrate, and incidence of fever after reinfusion. ResultsThe processed shed volume was very low (939±569ml) with high variability (coefficient of variation=0.6), unlike the recovered volume 129±50ml (coefficient of variation=0.38). A statistically significant correlation between the processed shed volume and recovered RBC concentrate haematocrit was found (Pearson, r=0.659, p=0.001). Hematological parameters in the recovered concentrate were: Hb 11±5.3gdl−1; haematocrit: 32.1±15.4% (lower than expected); white cells 5.34±4.22×103μl−1; platelets 37.88±23.5×103μl−1 (mean±SD). Blood culture was positive in the RBC concentrate recovered in 13 cases (54.2%) in which Staphylococcus coagulase (−) was isolated. ConclusionsCell salvage machines with rigid centrifuge bowls (including pediatric small volume) do not obtain the expected haematocrit if low volumes are processed, and therefore they are not the best choice in pediatric surgery.

Características y calidad de la sangre autóloga recuperada del campo quirúrgico durante cirugía de escoliosis en pediatría

ObjectiveTo determine the haematological and microbiological characteristics of blood recovered by using a cell saver with a rigid centrifuge bowl (100ml) in paediatric scoliosis surgery and to determine whether it conforms to the standard expected in adult patients. Material and methodsA cross-sectional, descriptive cohort study was performed on 24 consecutive red blood cell (RBC) units recovered from the surgical field and processed by a Haemolite® 2+ (Haemonetics Corp., Braintree, MA, EE. UU.) cell saver. Data were collected regarding age, weight, surgical approach (anterior or posterior), processed shed volume and volume of autologous RBC recovered, full blood count, and blood culture obtained from the RBC concentrate, and incidence of fever after reinfusion. ResultsThe processed shed volume was very low (939±569ml) with high variability (coefficient of variation=0.6), unlike the recovered volume 129±50ml (coefficient of variation=0.38). A statistically significant correlation between the processed shed volume and recovered RBC concentrate haematocrit was found (Pearson, r=.659, P=.001). Haematological parameters in the recovered concentrate were: Hb 11±5.3g dl−1; haematocrit: 32.1±15.4% (lower than expected); white cells 5.34±4.22×103 ul−1; platelets 37.88±23.5×103 ul−1 (mean±SD). Blood culture was positive in the RBC concentrate recovered in 13 cases (54.2%) in which Staphylococcus coagulase (−) was isolated. ConclusionsCell salvage machines with rigid centrifuge bowls (including paediatric small volume) do not obtain the expected haematocrit if low volumes are processed, and therefore they are not the best choice in paediatric surgery.

Process monitoring and control for constant separation conditions in centrifugal classification of fine particles

Due to their high centrifugal acceleration tubular bowl centrifuges enable the separation and classification of fine particles. However, this type of centrifuge which is operated in a semi-continuous mode has a major disadvantage: sediment buildup in the rotor leads to a successive degradation of separation conditions over process time. In this study, a light scattering sensor was used to monitor this mechanism online by measuring the solids concentration in the overflow. Polyvinylchloride (low micrometer range) and fumed silica particles (nanometer range) served as experimental products. By incorporating the sensor signal in a control loop with the speed of the centrifuge, the mentioned drawback was compensated. As a result, grade efficiency and product loss were kept constant up to a high filling level of the rotor. It is outlined how this technology can be used for very demanding classification tasks, especially in case of fine, low-density materials.

Simulation of particles and sediment behaviour in centrifugal field by coupling CFD and DEM

Centrifugal separation systems, such as solid bowl centrifuges, are used to effectively separate fine particles from industrial fluids. Knowledge of the streams and sediment behaviour inside such solid bowl centrifuges is required to determine the geometry and the process parameters that lead to an optimal performance. The multiphase flow of water, air and particles is calculated numerically in a cylindrical solid bowl centrifuge using a Computational Fluid Dynamics (CFD) software coupled with a Discrete Element Method (DEM) software. The CFD software calculates the flow of water and air and transfers the hydrodynamic forces to the DEM software in order to calculate the particle positions adding the hydrodynamic effect to the contact forces. Afterwards, the influence of the particles on the flow is considered. Thus, an unsteady and coupled simulation calculates flow and particles alternatively. Different sediment forms and solid volume concentrations are obtained when varying the geometry, operating conditions, particle size and contact model parameters such as the friction coefficient.

A novel approach for determining the flow patterns in centrifuges by means of Laser-Doppler-Anemometry

The flow pattern in process machinery has a significant impact on the product quality, because it influences the residence time, the mixing of components and the stability of chemical reactions. Hence the determination of the residence time and the measurement of the flow patterns have been the emphasis of many studies. The work presented shows a novel approach for the determination of the tangential and axial velocity profiles in a tubular bowl centrifuge. For the first time, flow velocities inside a fast rotating centrifuge have been measured using Laser-Doppler-Anemometry. The rotor of the centrifuge is made of carbon fibre reinforced plastic with an inner diameter of 100 mm and a length of 200 mm. The maximum rotational speed is 20,000 rpm, creating the multiple of 22,400 times the earth gravitational force. No failure of the material was detected at any process parameters. The centrifuge is operated with two different setups. One setup employs an assembly of two coaxial cylinders, in which the void between them is entirely filled with water. In the second arrangement, only the outer rotor is assembled and the centrifuge is operated like an overflow centrifuge. The Laser-Doppler measurements of the axial fluid velocity are confirmed by determining the residence time distribution at various parameters. The results obtained show an effective tangential acceleration; the liquid exhibits a rigid body rotation for rotational speeds up to 8000 rpm for throughputs between 0.5 and 1.8 l/min. The axial flow pattern depend on the volume flux and the rotational speed. The cross-section through which the liquid flows was in most cases between 60% and 100% of the overall area. The influence of the inlet subsides towards the outlet with an inlet zone of 15% of the length of the rotor. No boundary layer flow was detected in the overflow setup, which is due to the plunged inlet and the effective tangential acceleration of the incoming liquid.

A Numerical Study of the Impact of Radial Baffles in Solid Bowl Centrifuges Using Computational Fluid Dynamics

Centrifugal separation equipment, such as solid bowl centrifuges, is used to carry out an effective separation of fine particles from industrial fluids. Knowledge of the streams and sedimentation behavior inside solid bowl centrifuges is necessary to determine the geometry and the process parameters that lead to an optimal performance. Regarding a given industrial centrifuge geometry, a grid was built to calculate numerically the multiphase flow of water, air, and particles with a computational fluid dynamics (CFD) software. The effect of internal radial baffles on the multiphase flow was investigated. The results show that the baffles are helpful for the acceleration of the fluid, but they disturb the axial boundary layer, making it irregular, and originate a secondary circulating flow which hinders the sedimentation of small particles.

Processing of dispersions containing fine particles or biological products in tubular bowl centrifuges

The demand for instruments that are suitable for the separation of fine particles and biological cells is steadily increasing. Various innovative particles have already implemented in bulk products and many others are close to commercial availability. Tubular bowl centrifuges offer high centrifugal forces at reasonable throughputs. There is a high potential for the optimisation of existing processes and in the design of new tubular centrifuges especially for the separation of nanoscale materials. The separation of fine particulates and biological cells in a semibatch tubular bowl centrifuge at high rotational speeds is described in this work. Furthermore, the influence of the sediment on the process outcome and possibilities to enhance the separation efficiency were investigated. A boundary layer flow was indirectly detected. Structures inside the rotor of the centrifuge cause defined liquid flow patterns, which influence the separation efficiency. A comparison of the separation behaviour with an unimpaired flow and the redirected flow yielded conclusions about the actual flow patterns.