Display omitted
•Effect of different M: S ratios in magnetic roller design have studied using FEMM.•Prediction analysis of FEMM data using ANN modelling technique.•Fabrication of optimized magnetic ...roller and development of new lab-scale PRMS.•Design calculations of newly developed/fabricated lab-scale PRMS.•Separation tests using fabricated PRMS indicates the better Fe grade and recovery %.
In the present work, an attempt has been made to develop a PRMS in a cost effective and environmental friendly way through FEMM analysis of magnetic roller (active part of PRMS). The FEMM analysis indicates that, the optimized magnetic roller having magnet-to-steel disk thickness ratio of 5 mm: 2.5 mm was proved to be gainful in beneficiating paramagnetic minerals due to the best magnetic field value from the roller surface that is, 0.89 to 2.59 T. Prediction analysis was performed on FEMM data using artificial neural network (ANN) modelling technique. Further, the design calculations of lab scale PRMS in terms of power requirements and belt tensions were addressed. The fabricated PRMS was tested on paramagnetic mineral (hematite ore) assayed 51.24% of Fe, 10.20% of SiO2, and 2.98% of Al2O3 for different roller speeds and the belt thickness. The result showed that, at 0.5 mm belt thickness with 180 rpm roller speed the fabricated lab scale PRMS works well in terms of improvement in the Fe content up to 59.5% at the concentrate along with the Fe recovery of 71.41%. The obtained results suggest that, the FEMM analysis is more suitable to optimize the effective magnetic roller for the PRMS.
Display omitted
•A magnetic roller with axial arrangement for eddy current separation is designed.•The generation mechanism of axial eddy current force is clarified.•Axial eddy current force can make ...particles be thrown away further.•The optimized magnetic roller greatly reduces the consumption of permanent magnets.
Non-ferrous metal recovery is of great significance to the sustainable development of resources. Small-sized nonferrous metal particles account for a large proportion of nonferrous metals in solid waste, but the recovery efficiency is low. Eddy current separation is an important technology for physical recovery of non-ferrous metals. Optimizing its magnetic roller is extremely important for improving the recovery efficiency and economy of small-sized non-ferrous metals. In this study, COMSOL Multiphysics is used to establish a three-dimensional transient simulation model of the vertical rotary-drum ECS. On the basis of the two-dimensional Halbach array magnetic roll, the magnetic system of the magnetic roll is designed in the axial direction, so that the particles are subjected to the axial eddy current force opposite to the direction of gravity for the first time. This force can slow down the falling velocity of particles, increase the difference in falling trajectory and repulsion distance, improve recovery efficiency. In addition, due to the generation of axial eddy current force, the interlayer dislocation type magnetic roller can achieve the same recovery effect by only using 1/3 of the length of the basic type magnetic roller. Based on the electromagnetic theory and particle dynamics, by comparing the axial magnetic density distribution of different magnetic rollers, the axial eddy current force and the trajectory of non-ferrous metal particles, the generation mechanism of the axial eddy current force and the magnetic system structure that can generate the axial eddy current force are clarified.
•The influences of different factors on separation efficiency are analyzed.•The separation effects of the vertical and horizontal separators are compared.•The optimal application conditions and ...reasons for separators have been revealed.•The magnetic roller for separating small-sized non-ferrous metal is optimized.
The eddy current separator is the key equipment used for the separation and enrichment of non-ferrous metals from the solid waste. The customization and universality requirements for eddy current separators have been improved with the increasingly strict environmental protection requirements in various industries and the pursuit of higher economic benefits by enterprises. The low separation efficiency of the small-sized non-ferrous metals and the difficulty in separating between non-ferrous metals are two urgent problems that limit the development of the eddy current separation. The separator structures design, the factors regulation and the core component magnetic roller optimization are the keys to solve problems. Vertical and horizontal eddy current separators are the two main types of permanent magnet eddy current separators in practical applications and reported studies. However, the study and production cost of the eddy current separator are high, and there are few reports on the separator structures in existing studies. There is also a lack of comparative analysis of different applicable conditions for eddy current separators and optimization design of the magnetic roller. This study compared and analyzed the effects of different factors on the vertical and horizontal eddy current separation efficiency, and clarified the advantages and prospects of the vertical eddy current separator in optimizing the separation efficiency between non-ferrous metals. The comparison and multi-objective optimization were conducted on the magnetic rollers to expand the particle size range that can be separated. The separation performance and the economy of the magnetic roller have been improved significantly, and the performance indicators are better than those of existing equipment with the same specifications. The magnetic roller with specific structural parameters has increased eddy current force and magnetic efficiency density by 75.0% and 63.5%, respectively. It is expected to further expand the applicable materials for the eddy current separator.
Performance optimization of the magnetic roller of eddy current separator is an issue of great significance in the recycling industry. In this study, the Halbach array is proposed for the first time ...to be used in the eddy current separator. And the new concepts of area field intensity and magnet efficiency density are proposed to quantitatively evaluate the magnetic field intensity around the magnetic roller surface and the utilization efficiency of the magnet respectively. Then the effects of various structural parameters of the Halbach magnetic roller on the area field intensity and magnet efficiency density were systematically investigated by employing finite element analysis and response surface methodology. The results showed that the regression models of the area field intensity (R2=0.9846, Pred.R2=0.9420) and magnet efficiency density (R2=0.9946, Pred.R2=0.9782) are extremely significant and have good prediction capability. The magnetic roller can form a stronger magnetic field by selecting a larger magnetic block, and the utilization efficiency of the magnet is higher when the magnetic block’s shape tends to be flat or has larger curvature. Furthermore, a multi-objective optimization model with the area field intensity, magnet efficiency density, and magnetic pole number is established, and a multi-objective genetic algorithm is applied to get the optimal combinations of various structural parameters. It was found that the points of the Pareto-optimal solution are concentrated on a spatial surface, which reflects the trade-off relationship among the three objectives. It also shows that the performance parameters of many Pareto-optimal solutions are superior to that of previous studies and the eddy current separators found in the vicinity. The proposed method framework and the results are useful for the design and optimization of the magnetic roller, which will improve the separation efficiency of eddy current separation.
•Halbach array was proposed for the first time to be used in eddy current separator.•Evaluation indicators for the performance of magnetic roller were established.•A multi-objective optimization model was used for the design of magnetic roller.•Relationship between the structure and performance of magnetic roller was obtained.•Pareto frontier reveals a trade-off relationship among the performance indicators.
The separation process of eddy current separator is effected by the structure parameters of magnetic roller, the working parameters of the separator and some parameters of the scrap metal, such as ...the material, the shape, the size and so on. This is a complex process of electric field and magnetic field coupling. During this process, the sorting function of separator is powered by the existence of the eddy current power in waste particles, and the separation effect is directly determined by the flying distance of the scrap metal in the separation process. This paper armed for studying the eddy current power and the flying distance of the waste particles in separation to realize the simulation of the separation process. The eddy current force was obtained by the finite element analysis of the magnetic roller based on COMSOL, and the flying distance was got by the joint simulation of COMSOL and MATLAB.
Display omitted
•Novel fixation methods for green tea process were investigated and novel fixation used electromagnetic energy were discussed.•Volatile compounds in green tea under different fixation ...methods were compared.•Multivariate analyses and odor activity values were combined with sensory evaluations.•Roller-hot air–steam and roller-hot air fixation facilitate a chestnut-like odor.•Six compounds for differentiating chestnut and non-chestnut odor teas were identified.
Fixation is the key process to ensure green tea quality; however, the effect of various fixation methods on the formation of green tea with a chestnut-like aroma and the evolution of key volatile compounds has not been assessed to date. In this study, we compared four types of fixation methods for green tea: roller-hot air–steam, roller-hot air, roller-steam, and single roller. Infrared-assisted headspace solid-phase microextraction and gas chromatography-tandem dual mass spectrometry technology were used to detect the volatile compounds of green tea samples during processing. Partial least-squares discriminant analysis (PLS-DA), multiple experiment viewer (MEV), odor activity value (OAV), and least-significant difference analyzes were then applied to clarify the best fixation method for forming a chestnut-like aroma and associated compounds, and to explore the change law of key volatile compounds using different green tea fixation processes. One hundred and eighty-four volatile compounds were detected in the processed samples, with roller-hot air fixation found as the optimal method for generating an intense and long-lasting chestnut-like aroma and floral taste, based on sensory evaluation. The PLS-DA model clearly distinguished the four kinds of fixation samples and obtained 32 differential volatile compounds. Combining OAVs with screening by MEV analysis, 2,6,10,10-tetramethyl-1-oxaspiro 4.5 dec-6-ene, linalool, cedrol, 3-methyl-butanal, trans-β-ionone, and τ-cadinol emerged as key differential volatile compounds between green teas with and without a chestnut-like aroma. The evolution of these six differential volatile compounds throughout the tea-making process confirmed that rolling-hot air coupling treatment is most conducive to produce a chestnut-like aroma, which is beneficial to form and transform 2,6,10,10-tetramethyl-1-oxaspiro4.5 dec-6-ene, 3-methyl-butanal, and τ-cadinol with baking aromas and fruity substances. These results provide a theoretical basis and technical guidance for the precise and directional processing of high-quality green tea with a chestnut-like aroma.
PDF
