10 results found
Vinnett L, Contreras F, Díaz F, et al., 2022, Estimating residence time distributions in industrial closed-circuit ball mills, Minerals, Vol: 12, Pages: 1-14, ISSN: 2075-163X
This paper compares two deconvolution methodologies used to estimate residence time distributions (RTD) in industrial closed-circuit ball mills. Parametric and non-parametric deconvolution techniques were evaluated. Both techniques allowed for direct RTD estimates from inlet and outlet tracer measurements in the mills, with no need for mass balances nor assumptions to correct the effect of the tracer recirculation in the grinding circuits. Measurements of inlet and outlet concentrations were conducted by radioactive solid tracers and on-stream detectors. The parametric deconvolution was applied assuming the N-perfectly-mixed-reactors-in-series model, whereas the non-parametric deconvolution consisted of a constrained least squares estimation subject to non-negativity. The shapes of the estimated RTDs were consistent between these methodologies, showing mound-shaped distributions in all cases. From the parametric approach, mixing regimes described by 2–4 perfect mixers in series were observed, which indicated significant differences regarding perfect mixing. The mean (τmean) and median (τ50) residence times were more consistent with the RTD shapes when applying the parametric deconvolution. The non-parametric approach was more sensitive to noise, a disadvantage leading to mean residence times significantly higher than the median, and less consistent with the RTD locations. From the comparisons, the estimation strategies proved to be applicable in industrial closed-circuit ball mills. The parametric deconvolution led to better overall performances for τ50 = 1.7–8.3 min, given a suitable model structure for the RTDs.
Vinnett L, Pino-Munoz CA, Yianatos J, et al., 2022, A sensitivity analysis of kinetic characterizations in continuous flotation circuits under moderate deviations with respect to perfect mixing, PHYSICOCHEMICAL PROBLEMS OF MINERAL PROCESSING, Vol: 58, ISSN: 1643-1049
Simon BA, Gayon-Lombardo A, Pino-Muñoz CA, et al., 2022, Combining electrochemical and imaging analyses to understand the effect of electrode microstructure and electrolyte properties on redox flow batteries, Applied Energy, Vol: 306, Pages: 1-22, ISSN: 0306-2619
Reducing the cost of redox flow batteries (RFBs) is critical to achieving broad commercial deployment of largescale energy storage systems. This can be addressed in a variety of ways, such as reducing component costs orimproving electrode design. The aim of this work is to better understand the relationship between electrodemicrostructure and performance. Four different commercially available carbon electrodes were examined – twocloths and two papers (from AvCarb® and Freudenberg Performance Materials) – and a comprehensive study ofthe different pore-scale and mass-transport processes is presented to elucidate their effect on the overall cellperformance. Electrochemical measurements were carried out in a non-aqueous organic flow-through RFB withthese different electrodes, using two supporting solvents (propylene carbonate and acetonitrile) and at a varietyof flow rates. Electrode samples were scanned using X-ray computed tomography, and a customised segmentation technique was employed to extract several microstructural parameters. A pore network model was used tocalculate the pressure drops and permeabilities, which were found to be within 1.26 × 10− 11 and 1.65 × 10− 11m2 for the papers and between 8.61 × 10− 11 and 10.6 × 10− 11 m2 for the cloths. A one-dimensional model wasdeveloped and fit to polarisation measurements to obtain mass-transfer coefficients, km, which were found to bebetween 1.01 × 10− 6 and 5.97 × 10− 4 m s− 1 with a subsequent discussion on Reynolds and Sherwood numbercorrelations. This work suggests that, for these fibrous materials, permeability correlates best with electrochemical cell performance. Consequently, the carbon cloths with the highest permeability and highest masstransfer coefficients, displayed better performances.
Pino-Munoz C, 2020, MATHEMATICAL MODELLING OF VANADIUM-BASED REDOX FLOW BATTERIESw batteries
Pino-Muñoz CA, Chakrabarti BK, Yufit V, et al., 2019, Characterization of a regenerative hydrogen-vanadium fuel cell using an experimentally validated unit cell model, Journal of the Electrochemical Society, Vol: 166, Pages: A3511-A3524, ISSN: 0013-4651
A hydrogen-vanadium electrochemical system was characterized using extensive experimental tests at different current densities and flow rates of vanadium electrolyte. The maximum peak power density achieved was 2840 W m−2 along with a limiting current density of over 4200 A m−2. The cycling performance presented a stable coulombic efficiency over 51 cycles with a mean value of 99.8%, while the voltage efficiency decreased slowly over time from a value of 90.3% to 87.0%. The capacity loss was of 5.6 A s per cycle, which could be related to crossover of ionic species and liquid water. A unit cell model, previously proposed by the authors, was modified to include the effect of species crossover and used to predict the cell potential. Reasonable agreement between the model simulations and the experimental charge-discharge data was observed, with Normalized Root-Mean-Square Errors (NRMSEs) within the range of 0.8–5.3% and 2.9–19.0% for charge and discharge, respectively. Also, a good degree of accuracy was observed in the simulated trend of the polarization and power density, with NRMSEs of 3.1% and 1.0%, and 1.1% and 1.9%, for the operation at a flow rate of vanadium electrolyte of 100 and 50 mL min−1, respectively, while the voltage efficiency during the cycling test were estimated within a Root-Mean-Square Error (RMSE) of 1.9%. A study of the effect of the component properties on the cell potential was carried out by means of a model sensitivity analysis. The cell potential was sensitive to the cathodic transfer coefficient and the cathode porosity, which are directly related to the cathodic overpotential through the Butler-Volmer equation and the cathodic ohmic overpotential. It was recognized that a kinetic study for the cathodic reaction is needed to obtain more reliable kinetic parameters at practical vanadium concentrations, as well as reliable microstructural parameters of carbon electrodes.
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Muñoz CAP, Dewage HH, Yufit V, et al., 2017, Unit cell model of a regenerative hydrogen-vanadium fuel cell, Journal of the Electrochemical Society, Vol: 164, Pages: F1717-F1732, ISSN: 0013-4651
In this study, a time dependent model for a regenerative hydrogen-vanadium fuel cell is introduced. This lumped isothermal model is based on mass conservation and electrochemical kinetics, and it simulates the cell working potential considering the major ohmic resistances, a complete Butler-Volmer kinetics for the cathode overpotential and a Tafel-Volmer kinetics near mass-transport free conditions for the anode overpotential. Comparison of model simulations against experimental data was performed by using a 25 cm2 lab scale prototype operated in galvanostatic mode at different current density values (50 - 600Am-2). A complete Nernst equation derived from thermodynamic principles was fitted to open circuit potential data, enabling a global activity coefficient to be estimated. The model prediction of the cell potential of one single charge-discharge cycle at a current density of 400Am-2). Was used to calibrate the model and a model validation was carried out against six additional data sets, which showed a reasonably good agreement between the model simulation of the cell potential and the experimental data with a Root Mean Square Error (RMSE) in the range of 0.3-6.1% and 1.3-8.8% for charge and discharge, respectively. The results for the evolution of species concentrations in the cathode and anode are presented for one data set. The proposed model permits study of the key factors that limit the performance of the system and is capable of converging to a meaningful solution relatively fast (s-min).
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- Citations: 10
Bergh L, Yianatos J, Pino C, 2013, Advances in developing supervisory control strategies for flotation plants, Pages: 110-115, ISSN: 1474-6670
The wide plant control integration of mineral processes poses many challenges Flotation plants consist of complex interacting circuits where minerals are processed in different stages with recycling Today, a common arrange are the RCS circuits, where a rougher circuit is combined with a cleaning circuit and a scavenger circuit The global objectives of a flotation plant are to maximize the value metal recovery while the grade of the final concentrate is kept inside a narrow band To achieve this, for any time variant feed attributes (flow rate, solid percent, grade, particle size distribution, pH, and chemicals), a capability of modifying the operation of each circuit, in order to achieve some local objectives, is demanded To advance in this study, a family of simulators can be of great help Recently, an algorithm to set the froth level profile in a rougher circuit, have been proposed The simulator used was based on phenomenological models with parameters estimated from industrial data, collected under designed experiments In this work, a simulator for the cleaning and scavenger circuits, including a regrinding stage is presented This simulator is based on phenomenological models, with parameters estimated from industrial data The simulators are used to provide insight on how the available resources in each circuit can be administrated, to obtain some local objectives which are harmonized in a global control strategy Copyright © 2013 IFAC.
Yianatos J, Pino C, Vinnett L, et al., 2012, Cleaning flotation and regrinding circuits characterization, Pages: 5922-5934
The cleaning circuit operation and its effect on the plant metallurgical performance, was characterized at Los Pelambres concentrator, Chile. Experimental data from columns, scavenger and regrinding stages was evaluated. Each stage was characterized by size fractions, and the interaction between stages (columns, scavenger, regrinding) as well as the effect that circulating loads had. The approach for describing the flotation equipment operation (cells and columns) considered the collection and froth zones separately. This methodology allows for the identification of the impact that particle size distribution has on the actual collection and froth transport processes, independently. In this way the effect of regrinding on flotation recovery and grade can be related to the corresponding operating variables, e.g. pulp flowrate, air flowrate, pulp level and pulp density, among others. The effect of gangue entrainment was considered using an empirical dimensionless correlation. The interaction between the circulating load and the overall performance of cleaning circuit was evaluated. The circulating load was defined as the ratio between the solid flowrate of scavenger concentrate over rougher concentrate. It was found that the overall cleaning flotation circuit (column-scavenger) can operate at a relatively high and constant recovery for a wide range of mineral treatment. This is possible when the scavenger has the capacity for compensating the decrease in column recovery at larger circulating loads. Under the condition of high overall cleaning recovery, the rougher stage closely represents the plant recovery. However, at large mineral treatment conditions, the design characteristics (e.g. concentrate transport channel capacity and transfer boxes) as well as instrumentation, control facilities and operation, became bottle-necked. A simulator was developed using empirical models for each stage (column, scavenger and regrinding) in order to evaluate proper operational stra
Yianatos J, Bergh L, Vinnett L, et al., 2012, Modelling of residence time distribution in regrinding vertimills, Pages: 5935-5946
The regrinding stage is necessary to achieve the particle size (liberation) for the final upgrade in the cleaning flotation process. At present, vertical mills (Vertimill) are employed at industrial scale, using small steel balls as grinding media. The regrinding process characterization requires mixing regime knowledge along with the mean residence time of the liquid and solid phases. The residence time distribution (RTD) and the actual mean residence time estimations from theoretical relationships are complex due to the presence of three components (solid mineral, balls and water), mass transport characteristics and segregation affecting solid holdup. Therefore, the experimental RTD determination is suitable for industrial mills. In this work, RTD measurements were performed in two different industrial flotation plants. Both plants operate with Vertimills of 1000-1500 HP in the regrinding process with different circuit arrangements according to the plant treatment capacity. The RTD was measured using the radioactive tracer technique. This technique allows for non-invasive tracer detection where the procedure consists of selecting a liquid (Br82 in aqueous solution) or solid (irradiated solid) tracer for RTD data acquisition in real time. The RTD was modelled by the Large and Small Tanks in Series (LSTS) model, which allowed the characterization of the different mixing regimes for both liquid and solids in the regrinding mills. Effective mean residence times in the range 2-11 min were obtained with RTD shapes similar to those obtained in tumbling ball mills. It was found that residence times of liquid and fine particles were similar, which is consistent with results observed in other mixing systems, e.g. mechanical flotation cells. Also, the mean residence times estimated from the RTD allowed the mass balance adjustment to be validated from metallurgical sampling data. RTD estimations are useful for better understanding the Vertimill behaviour and to identify the a
Yianatos J, Bergh L, Pino C, et al., 2012, Industrial evaluation of a new flotation mechanism for large flotation cells, Minerals Engineering, Vol: 36-38, Pages: 262-271, ISSN: 0892-6875
A new flotation mechanism was evaluated in the rougher flotation circuit at Collahuasi Concentrator Plant in Chile. For this purpose, the flotation mechanism FloatForce® was installed in one of three parallel rougher flotation lines, consisting of nine TankCell-160 (160 m3) cells, while the other two lines operate with a conventional OK-mechanism. The evaluation was carried out based on a hydrodynamic and metallurgical characterization of the flotation circuits. Three overall samplings and mass balance adjustments for kinetic flotation characterization were performed. The residence time distribution RTD, of liquid and solids (per size class) was measured in the rougher lines using radioactive tracers. Thus, the effective mean residence time as well as the mixing condition in single flotation cells and along the rougher lines were evaluated. Also, measurements of axial solids segregation (per size class), axial mineral grade profiles, local superficial gas rate, bubble size distribution, bubble load and top of froth grades were performed in cells provided with both flotation mechanisms. The comparison of the rougher flotation operation with the FloatForce® and the conventional OK-mechanism is presented and discussed in this work. © 2012 Elsevier Ltd. All rights reserved.
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