Magnetic field separation of ferromagnetic materials from granular technological mixtures

Transcription

1 Doctorate Thesis Summary Magnetic field separation of ferromagnetic materials from granular technological mixtures eng. BÎNĂ Dan Dumitru Coordinator: Prof.dr.eng. MORAR Roman The doctorate thesis started from a real problem of the Romanian economy, that of plastic waste recycling, but proposes to approach the wider theme of separating the ferromagnetic component from plastic granular mixtures. At the same time with the growth of industrial production, the volume of industrial waste grew also, as a result of semi-fabricates and finite products wear. From the variety of recyclable waste, plastic waste allows reuse through re-injection. In order to reuse granular waste we have to purify them by eliminating any metallic impurities. Ferromagnetic impurities can most efficiently be eliminated using magnetic separators. Electrostatic, electrochemical or mechanical separators can be used to eliminate non-ferromagnetic impurities. The essence of the magnetic separation process resides in the different action of the magnetic forces over the components of a mixture, depending on their ferromagnetic properties. In order to build efficient industrial magnetic separation installations it is necessary to identify, in theory and experimentally, the factors that influence the magnetic separation process. The quality of the process also depends on these factors. The capitalization of the industrial residue with high technological and economic efficiency rates leads to the reduction of the waste production, by using recycled waste as a primary source of raw materials. In this doctorate thesis, the author made an exhaustive analysis of the constructive variants for magnetic separators, in order to choose the optimal variant for recycling granular plastic waste. Another main point in the paper is identifying the main factors that influence technological efficiency and the quality of the separation, but especially the quantitative determination of the optimal values for these technological parameters. In the technological process of recycling plastic waste, a stage of separation for the ferromagnetic impurities from the granular plastic waste is necessary to be introduced between the mincing and injection stages. For the study of the magnetic separation of ferromagnetic impurities from a granular mixture of paramagnetic material, we built an experimental laboratory stand in the Electro-technologies Laboratory of the Engineering Faculty from Sibiu. The laboratory magnetic separator can simulate the magnetic separation regimes for different types of waste and can highlight the factors that influence the quality and the productivity of the separation. Such an installation served as experimental support for the scientific research of the characteristics of the main factors and parameters that influence technological efficiency and the quality of the separation. The main support for the magnetic separation process is the different action over the components of a mixture, of the magnetic forces in competition with other types of forces. All the forces determined by the presence of magnetic fields are considered to be magnetic forces. These forces depend (as value and orientation) on a series of physical characteristics of the bodies, which gives a selective character to the competing action. The competing forces of the magnetic forces are: hydrodynamic drive forces, when the dimensions of the bodies are small and weight, inertia and friction when we deal with large bodies.

2 Depending on the value and orientation of the resultant for this group of forces, the components of a mixture are collected and deviated differentially, thus fractionating it. Independent of the action of the competing forces, previously enumerated, interaction forces are exerted between the components of the mixture. Most often these forces have a negative effect on the magnetic separation process. After the study of the magnetic action, the magnetic separation processes can be divided in two classes: Processes of separation in which the main role is that of the magnetic action exerted directly over the components of a mixture. Magnetic materials are separated using these processes, in accordance with their magnetic susceptibilities, and good conductor materials in accordance to their electric conductibility. Processes of separation in which the main role is played by the magnetic action, which manifests indirectly through the environment in which the components of the mixture are immersed. Using these processes we separate the non-magnetic materials (with negligible magnetic susceptibility) and those which are not electric conductors (with negligible electric conductibility). The separation is made according to the material densities, the materials being immersed either in liquids that can be magnetized, or in good electric conductor liquids. In the work space of the separator, the magnetic field must not only be very intense in order to completely extract the magnetic particles in the magnetic fraction, but also selective enough to avoid the mixing of the magnetic particles with the non-magnetic ones (because of the drive of the fluid, and especially because of the particle interaction forces). The condition for obtaining a magnetic fraction as pure as possible is to obtain a resultant of the contrary forces that are exerted on the particles, as big as possible. In order to obtain this it is necessary to achieve a superior degree of material release and centrifuge or vibrating forces to ensure the fragmenting of the material into pieces as small as possible. The efficiency of the magnetic separation and the quality of the products obtained can be conveyed through a series of quality indexes. They are: recuperation, degree, extraction, efficiency and selectivity of the separation, indexes which depend on the forces that act upon the particles and on many other factors (most of them being correlated between each other). The indexes used most frequently to characterize the quality of the magnetic separation we mention the degree of separation, selectivity, total extraction, separation coefficient and efficiency. These parameters were used in the paper to evaluate the quality of the separation, the economic efficiency and to compare the proposed method with the ones used on a large scale and present in the specialty literature. The paper presents the main technical applications of magnetic separation in the use of waste, magnetic purification of water, magnetic separation of ores, including the enrichment of iron, nickel, cobalt, manganese and chrome ore. Also it presents the applications from the food industry, chemistry and medicine. A magnetic separator is generally a complex installation made of several elements that can be divided based on their importance for the separation process, into two groups: main components and auxiliary components. The thesis presents the main types of magnetic separators, of class I and II, including the functioning principles and the areas of applicability. From the analysis of the construction solutions currently present on an international level, the author chose the most advantageous variant for separating the granular plastic waste, variant that is to be constructively adapted and optimized. The author opted for a board separator, supplied through a vibrating table, with electromagnets and permanent magnets. For designing the magnetic separator it is necessary to determine the magnetic induction from the active separation zone, and based on that, the magnetic force that is exerted on the ferric particles from the granular mixture.

3 Based on the analysis of the main characteristics of the calculating methods for the magnetic field, the author chose the finite differences method because of the advantages it presents over the other methods. FDM was applied to the magnetic potential, vector A, as being the most advantageous for the studied field problem. The predimensioning of the magentic circuit for the separator was done based on some semiempirical relations, or on the calculation of the equivalent reluctances of the magnetic circuit. In order to calculate the magnetic field using FDM, we start from the magnetic field law ( written for the vector A magnetic potential), considering the non-liniarity of the ferromagnetic environment, but neglecting the remnant magnetic induction and the Faucault currents. The finite difference equations were done by considering a rectangular network with the passes h x after i, h y after j si h z after k., and approximating the laplacean by the five point formula. For the calculation of the magnetic field (in the active zone of the separator) by using FDM applied to the vector A magnetic potential, we conceived a program that starts from the equations of the magnetic field rewritten in finite differences, for equal passes after the three axes. The program is called PSM and consists of two parts. The first part is made of a program made in AutoLisp under AutoCad, called NG (network generation) and the second part is made of a C++ program called FC (force calculation). The PSM program was done in C++., and is based on the Seidel method, allowing the calculation of the axe projection of the vector A magnetic potential, and that of the magnetic induction B in every knot. The magnetization curve was given under the form of a string of pairs (μ, B), and through the program a value μ (i,k,j) was allocated to each point, for each step of the iteration. This value was obtained by interpolation with first degree Lagrange polynomials. The FC program contains an interface with the LISP (NG) program, which reads the data from the folders created in LISP, containing the characteristics of the network, generates the system of equations, and solves the system through the Seidel method. The iterative process continues until the required precision is achieved. The program gives as solutions the data: A x, A y, A z, B x, B y, B z, in each knot, B, F and L. The presented program was tested, verifying its convergence and stability. Because the folders containing the results are very large, the results were graphically presented, in a suggestive way (molded net type). Knowing the maximum mass of the ferromagnetic material granules we can appreciate if the magnetic field obtained in the active zone of the magnetic separator is sufficient, or if it is necessary to modify the ampere-turns of the electromagnet or their position. In conclusion, based on the calculation by FDM of the magnetic field we can constructively finalize the magnetic separator. Based on the method for the calculation of the magnetic field and of the force previously presented, a method for assisted design of magnetic separators was created, consisting of the following stages: - preliminary design (classic), - the stage of numeric modeling of the magnetic field, which allows the estimation of the technological performances of the installation even from the project phase. In this way we reduce the time, and the experimentation and design costs, and we benefit from an assisted and optimized design after different criteria, for industrial installations of this type.

4 Figura 1. Magnetic induction B in the active zone 230x430 mm δ = 6 mm, J = 2,16 A/mm 2, Bmax = [T]. In this way we reduce the time, and the experimentation and design costs, and we benefit from an assisted and optimized design after different criteria, for industrial installations of this type. For the experimental study of magnetic separation of granular plastic waste, the author built a laboratory magnetic separator, board-type chosen from the variants presented in the thesis. The laboratory magnetic separator has the following facilities: - The adjustment of the magnetic field on the board. - Supply with variable debit for the separation zone. - Modifying the position of the permanent magnets. - Modifying the position of the electromagnets. - Supplying with variable voltage for the electromagnets. - Modifying the inclination angle for the spout. - Verifying the stretching of the transporting belt. The mechanical design of the separator was done in Pro/Engineer. The mechanic design of the stand was done through a process of pre-dimensioning the markers, based on the estimation of the mechanical solicitation they are subjected to. The markers have been designed: the adjustment screw, the adjustment screw nut, the belt stretcher, the rods with the drive wheels, the device for the elimination of ferric impurities and the ensemble design for the magnetic separator. An electromagnetic vibrator was designed for maneuvering the vibrating table. The working regime of the vibrating table was simulated even from the design stage in order to verify its working parameters, by using the Matlab-Simulink program.

5 Figura 2. Laboratory magnetic separator For the power supply of the active separation zone we used a commutation source that complies with the demands imposed by the designed magnetic separator. The chosen scheme uses the NE555 integrated circuit. The commutation source was designed in OrCad based on the catalogue data. In order to estimate (even from the design stage) the working behavior and the parameters that can be obtained using this source, a simulation of the working source was made in PSPICE. Having in mind the reduction of the experimentation expenses and the improvement of the technological parameters of the laboratory magnetic separator, the command of the laboratory stand was made through a negative reaction loop, commanded by a Hall magnetic induction transducer. The author used a Hall IC TLE4990 transducer, satisfying the need for versatility and accuracy in the measurement of the magnetic intensity. With the help of this transducer we built a negative reaction loop, giving the possibility to build an automated magnetic separator. The analysis of the cinematic characteristics for the vibrating table is necessary to a correct supply of the active separation zone. Using a piezoelectric transducer we have realized measurements of speed, acceleration and maximum amplitude for the vibrating table. The experimental results certify the fact that the adjustment of the granule flow must be done in accordance with the uniformity of the granulation and granulometry, by modifying the supply voltage and by adjusting the inclination angle of the vibrating table. The following technological parameters were studied, in view of their influence over the quality of the magnetic separation and efficiency of the magnetic separator: - the amplitude of the oscillations of the vibrating table on the material flow, both in a dry and wet environment; - granulometry and the angle of the vibrating table over the material debit; - granulometry, the inclination of the vibrating table and the debit of material on the quality of the separation, in the presence and in the absence of mechanical vibration, in a dry and then moist environment; - granulation on the magnetic separation;

6 - granulation, intensity of the magnetic field and the material flow on the quality of the separation, in a dry and moist environment; - humidity, granulation and the angle of the vibrating table on the quality of the separation; - the inclination angle of the vibrating table on the quality of the separation. The way these factors influence the quality and technological efficiency of the separation was suggestively represented in a graphic form. Figure 3. The influence of granulometry d[mm], intensity of the magnetic field and material flow D[g/min] on the quality of the separation, in a dry environment Figure 4. The influence of granulometry d[mm], intensity of the magnetic field (supply voltage of the electromagnet, U) and the material flow D[g/min] on the quality of the separation, in a moist environment

7 The paper sets the grounds for the optimization of the magnetic separation process, from an experimental point of view, and allows the validation or invalidation of the models and numeric simulations for this technological process. The findings of the experiment will be the basis for the design of industrial installations for magnetic separation of ferric waste from plastic waste mixtures, meant to solve the stringent problem of industrial waste. Based on the economic estimates it is expected to quickly compensate the investment made in such an installation ( ), in approximately 4 years, after which the benefits will not only be of ecological nature but also economic ones. We can conclude that the main original contrivbutions of the doctorate thesis are: - designing a magnetic separator that satisfies the imposed demands, with minimum costs and maximum versatility; - the theoretical determination of the forces that contribute to the magnetic separation process in dry granular environments; - the numeric calculation, using FDM, of the magnetic induction and the specific force in the active zone of separation, using an original program (in C++); - the elaboration of a design method for the stand, starting from the classic methods, but optimized by numeric modeling (even from the design phase) of the magnetic field; - the theoretical and experimental proof for the supply variant for the active separation zone, with vibrating table; - mechanical design in PRO/ENGINEER for the mechanic markers of the installation; - the design of the vibrating tale, including the elastic system; - the design of the supply source with variable voltage (in commutation), using the NE555 circuit, and a simulation of it functioning even from the the project phase (in PSPICE); - creating an automated magnetic separator (by the adjustment in a negative reaction loop), with the Hall IC TLE4990; - building the experimental installation for magnetic separation, meant for the empiric study of the magnetic separation phenomenon; - the experimental determination of the influence of granulometry, humidity and cinematic parameters on the technological efficiency and quality of the separation; - creating an optimal adjustment algorithm for the flow of granular mixture, depending on the homogeneity and granulometry of the granular mixture; - the study of the influence of permanent magnets, which has proven that their presence is not necessary in the case of mixtures poor in ferromagnetic particles; - the study of the influence of humidity on the separation process, which set the bsis for a necessary stage of drying in the recycling technology, or modifying the recycling strategy; The theoretical and experimental considerations from this thesis are an useful contribution to the solution of a stringent technical problem for the Romanian industry, forced to align itself to the standards of the EU in a relatively short period of time. When elaborating this thesis, the author used 306 bibliographical references and an exhaustive Internet documentation.

8 CURRICULUM VITAE 1. Personal data: Surname: BÎNĂ Name: DAN DUMITRU Date and place of birth: May 11 th, 1961, Nadrag, Timis County, Romania Civil Status: married, 2 minor sons. Address: Timişorii Str. nr.110 bl. 5A ap. 7, loc. Lugoj, Timiş County, code Tel/Fax: /359002, Dan_Bina@novar.com 2. Studies: Coriolan Brediceanu High school, Lugoj Traian Vuia Politechnical Institute, Timisoara, Faculty of Electrotechnics, Electronics and Communication Section, Specialty of industrial electronics since 2000 Doctorate studies at the Technical University of Cluj Napoca 3. Specialties: Maintenance of electrical devices, Ministry of Metallurgical Industry, Center for perfection for workers in the metallurgical industry, Bucharest, 1989 Initiation marketing and management, Human Resources Development Center, Bucharest, 1992 Training and perfection in the field of work protection, I.M.M. Consulting Association Romania & Work and Social Protection Ministry, Timisoara, 2000 Pedagogy Course, Department for training didactic personnel, West University, Timişoara, Professional activity: Ciocanul Plant, Nadrag, Probationary Engineer at the Calculating Office; IUPS Lugoj, system engineer and programming analyst within the Calculating Office; SC. Rosada S.A. Lugoj, Chief electronic and energetic engineer to present, SC Novar Electric Romania SRL Lugoj, electronic engineer, maintenance compartment; teacher at the Post-high school department of the Coriolan Bradisteanu High school, for the subjects of Operating systems and computer architectures, and Structural programming; Pascal language 5..Scientific activity: author of 8 published articles, 3 of which were published abroad participated at 4 scientific conferences (2 were held abroad) AGIR member 6. Competence Domains: Plastic waste processing; Automations and industrial measurements; Repairing and maintenance of electronic and electric devices; Exploiting, programming, maintenance and development of analogical and digital phone centers and networks; Computer operating and programming. 7. Foreign languages: English, French, German. Lugoj,