Patent Application
20180243756
The invention relates to an electromagnetic apparatus and system that sorts different electrically conductive substantially non-ferrous metals, including alloys, from each other and sorts different electrically conductive substantially non-ferrous metals from electrically non-conductive materials.
There are many occasions in scientific and industrial applications where materials need to be separated from one another. For example, in the mining industry, valuable metals need to be efficiently separated from other materials which are found in the ore. In the scrap metal industry, mixed metals (e.g, copper and aluminum) need to be separated into pure compositions. Even alloys (e.g., aluminum alloys) often need to be separated from other alloys.
In many industrial applications, separation of particles having different sizes and densities relies on the earth's gravity as well as some additional process, such as filtration. Arrangements which have been devised utilizing gravity to separate particles of different densities include various drawbacks. For example, such arrangements may require water as a carrier for the particles to be separated. After separation, the water needs to be removed from the particles. Moreover, in some mining and scrap metal operations, water is not readily available. Liquid separation methods also have additional costs with the chemicals involved and environmental concerns.
In order to provide efficient separation without water, various apparatus and techniques have been proposed which also utilize some electromagnetic properties of materials, rather than density alone, to separate materials. While the task of separating magnetic materials from nonmagnetic materials is relatively straightforward, the task of separating nonmagnetic materials from other nonmagnetic materials utilizing the magnetic properties of the materials has various challenges. The technology (systems, devices, and methods) described herein resolves many of the challenges of separating nonmagnetic materials from other nonmagnetic materials.
In one embodiment, the invention provides a variable frequency eddy current sorter technology that provides a means of sorting substantially non-ferrous metals from other non-ferrous. Unlike present eddy current sorters that use mechanical rotation to spin a collection of permanent magnets, the technology described herein utilizes a stationary magnet excited by an alternating electric current. The technology described herein is capable of sorting nonferrous particles with sizes as low as 1.0 mm, including such metals as copper (Cu), aluminum (Al), zinc (Zn), brass (Cu and Zn alloy), magnesium (Mg), and titanium (Ti). The technology is capable of separating many combinations of nonferrous metal from other nonferrous metal, for example copper from aluminum, copper from brass, or aluminum from titanium. Finally, the technology can even separate nonferrous metals by alloy, for example aluminum 5052 from aluminum 6061.
In an example, an electrodynamic sorting circuit includes a wire-wound, gapped core (WWGC) and a capacitor bank. The capacitor bank may be coupled in series with the electrical conductor of the WWGC and excited to resonance. The WWGC includes a magnetic material (e.g., the WWGC is a magnetic toroid) and has a gap where particles of material are fed for separation. A current in the electrical conductor generates a magnetic field in the magnetic core and the gap, which excites the particles for magnetic separation.
In another configuration, an eddy current sorter includes a wire-wound, gapped, core (WWGC) with windings concentrated primarily near the gap. Nonlinearities in the magnetic core material are thus circumvented for greater field strength in the gap.
In another configuration, an eddy current sorter includes a wire-wound, gapped, core (WWGC) having a multiple-cut gap. The multiple-cut gap provides a more precise, engineered force profile.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Numbers provided in flow charts and processes are provided for clarity in illustrating steps and operations and do not necessarily indicate a particular order or sequence.
Eddy current sorting provides an electrodynamic mechanism to sort non-ferrous metals, which can provide a light metal and alloy sorting technology for the recycling industry. An eddy current indicates the electrical currents that are induced on electrically conductive materials due to the presence of a time-varying magnetic field. Eddy current sorting, also called electrodynamic sorting, can employ an eddy current separator or electrodynamic separator that uses a powerful magnetic field to separate non-ferrous metals from each other. A ferrous material generally refers to a generic ferromagnitc/ferrimagnetic material (i.e., ferrites), and is not limited just to iron alloys. Eddy current separators are typically not designed to sort ferrous metals because the ferrous metals are easily sorted by other means and tend to overheat inside the eddy current field. For example, ferrous or ferromagnetic materials are strongly attracted by magnetic fields. Thus, separating ferrous or ferromagnetic materials is relatively straightforward because these ferrous or ferromagnetic materials can be pulled out of scrap material with a permanent magnetic field.
Variable Frequency Eddy Current Sorter
A variable frequency eddy current separator (or sorter) is a type of eddy current separator that provides greater granularity and functionality in the types of materials that can be sorted.
The vibratory feeder 210 includes a hopper 212, a track 214, a vibrator 216, and a non-conductive feeder extension (e.g., polymeric feeder extension 218). The hopper 212 receives, holds, and funnels material (e.g., electrically conductive metals or particles) to the track 214, which provides a narrow flow or stream of material to an opening or gap in the WWGC 220. The track can also be referred to as a pan, skirt, or skirt taper. A vibrator 216 vibrates the track so the materials separate from each other, funnels the material even further, and/or moves the material towards the gap in the WWGC 220. The track 214 or the vibrator 216 supporting the track 214 can be angled at a decline from the hopper entry (input) end to the exit (output) end so the force of gravity helps to move the material to the WWGC 220.
The vibratory feeder 210B includes a hopper 212B, a track 214B, a vibrator 216,B and a conveyer 219. Similar to above, the hopper 212B receives, holds, and funnels material (e.g., electrically conductive metals or particles) to the track 214B, which provides a narrow flow or stream of material to an opening or gap in the WWGC 220 via the conveyer 219.
The shown WWGC 220 in
Although a gapped magnetic core used in the WWGC is shown in the various examples with toroid 222A, other volumes and geometries can also be used, such as an elliptic cylinder with an elliptic hole, an elliptic torus, a rectangular cuboid with a rectangular hole (e.g., a square cuboid with a square hole), or a rectangular prism with a rectangular hole. The gap can be placed at other locations in the magnetic core.
Referring back to
The signal generator 230 generates a signal with a specified frequency for the WWGC 220. The power amplifier 232 amplifies the current and/or voltage of the signal from the signal generator 230 and drives the amplified signal to the capacitor array 240 and the WWGC 220. A capacitance of the capacitor array 240 is adjusted based on an inductance of the magnetic toroid 222A and specified frequency for sorting. The capacitance (C) and inductance (L) forms a resonant circuit (LC circuit or RLC circuit) with a resonant frequency given by f=1/(2π√{square root over (LC)}). The current monitor 238 is used to monitor the current in the electrical conductor of the WWGC 220. In some constructions, a square wave voltage source, for example, with a power inverter can be used to generate the amplified signal to the capacitor array. The RLC circuit provides a natural band-pass filter that will only allow the fundamental harmonic to pass, thus resonating at the desired frequency.
In some configurations and operational conditions, the WWGC 220 generates excess heat that can degrade performance of the WWGC 220. A cooling tank 252 can surround the WWGC 220 and house cooling fluid/gas or coolant circulated by the cooling system 250. The warmer coolant of the cooling tank 252 is exchanged for the cooler coolant from the cooling system 250. In some configurations, the cooling tank 252 can be constructed of materials that provide magnetic shielding, so the magnetic fields and magnetic flux generated from the WWGC 220 is reduced in the space outside the cooling tank 252. In other configurations, the cooling tank 252 can be constructed of non-conductive materials (e.g., non-metallic materials).
Using non-conductive materials and components (that are not used in the WWGC) in the vicinity or close proximity (e.g., within 20 centimeters (cm)) of the WWGC 220 can reduce the interference and/or damping of the magnetic fields of the WWGC 220. In addition, the non-conductive materials in the vicinity or close proximity of the WWGC 220 will not generate eddy currents and heat associated with those eddy currents. Conductive material in close proximity to an operating WWGC 220 can generate its own eddy currents, which in turn generates additional heat and expends additional energy, which can be undesirable.
The collection bins can include containers, receptacles, or rectangular boxes with one side being open for collecting sorted or deflected material. The collection bins can be manufactured from steel, other metals, or non-conductive structural materials, such as polymers and plastics.
Variable Frequency Eddy Current Sorter Circuit
The signal generated by the signal generator can have different waveforms, such as a sinusoidal wave (or sine wave), a square wave, a triangle wave, or sawtooth wave. While a sinusoidal wave is considered simple and ideal, it can also potentially require costly, high-fidelity amplifiers to generate. In contrast, switched-mode square-wave generators can be more cost effective. In either case, the resulting current waveform is always a sinusoid, as any higher-order harmonics of the voltage waveform are filtered by the bandpass nature of the RLC circuit.
At the resonant frequency, the current 364 (in A) spikes in the variable frequency eddy current sorter circuit. The tuning capacitor 242 includes at least one high voltage capacitor (e.g., rated for greater than kilovolt (kV)), which can be used to generate resonance in the magnetic toroid 222A (e.g., resonance coil 360) at the specified frequency (f) 362 in hertz (Hz). In other examples, at least one high voltage capacitor is rated for at least 5 kV or 10 kV. The tuning capacitor can be a capacitor array (240 of
Electrical resonance occurs in an electric circuit at a particular resonance frequency when the imaginary parts of impedances or admittances (i.e., the inverse of impedance) of circuit elements cancel each other. Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied. Impedance includes the real part of complex impedance called resistance and the imagery part of complex impedance called reactance. Both the magnetic toroid 222A and the tuning capacitor 242 have reactance. The induction of voltages in conductors self-induced by the magnetic fields of currents (e.g., in the magnetic toroid 222A) is referred to as inductance, and the electrostatic storage of charge induced by voltages between conductors (e.g., in the tuning capacitor 242) is referred to as capacitance. Reactance applies only to AC circuits (i.e., a circuit with alternating, or time-varying, current or voltage applied).
The WWGC can be driven by voltage source 352 (or current source) using the series RLC circuit schematically represented in
The VFECS circuit creates a tuned RLC circuit (or band pass filter). The inclusion of the series capacitor helps lead to resonance for the circuit. The series capacitor is a tunable capacitor bank or array 242 (
Deflection for the Eddy Current Sorter
The physical principle of electrodynamic sorting can best be explained by applying appropriate assumptions into Maxwell's equations and mathematically computing the results. One can begin by assuming a sinusoidal steady state solution wherein all vector quantities are expressed as phasors. This allows us to replace all time derivatives with
where j=√{square root over (−1)} is the imaginary unit and ω=2πf is the angular frequency of excitation. One may then express Faraday's law of electromagnetic induction as
∇×E=−jωB, Eq. 1
where E is the electric field intensity and B is the magnetic field intensity. Likewise, Ampere's law in phasor form is expressed as
∇×B=μ0J+−jωμ0∈0E, Eq. 2
where μ0 is the permeability of free space, ∈0 is the permittivity of free space, and J is the electrical current density.
The next important assumption is the quasi-static approximation, which says that the frequency of excitation is a very small value (e.g., f<100 kHz). Under such a condition, the displacement current term in Ampere's law is negligible and allows us to simply write
∇×B=μ0J. Eq. 3
As a final assumption, one can express the total magnetic field B as a superposition of two primary fields of interest, given as
B=B
i
+B
e. Eq. 4
The Bi term is called the impressed magnetic field and represents any given fields that are imposed onto a system of interest by external agents. All electrical currents that gave rise to Bi are assumed to lie well beyond the region of interest, thus setting the curl of this field to zero. The Be term is then called the induced field, or the eddy field, and represents any fields created by the presence of unknown electrical currents contained within J. One may therefore rewrite Ampere's law to reflect this distinction such that
∇×Be=μ0J. Eq. 5
One can then next invoke the point form of Ohm's law which relates the electric field to the conduction current density via
J=σE, Eq. 6
where σ denotes the electrical conductivity within some given material of interest. Plugging back into Ampere's law then gives
∇×Be=μ0σE, Eq. 7
We now take the curl of this expression to find
∇×∇×Be=μ0σ(∇×E). Eq. 8
The curl of a curl is a well-known vector formula that simplifies into
∇×∇×Be=−∇2Be+∇(∇·Be). Eq. 9
From Gauss's law, one also knows that ∇·Be=0 everywhere, leaving one only with
−∇2Be=μ0σ(∇×E). Eq. 10
Substituting from Faraday's law then results in
−∇V2Be=−jωμ0σ(Be+Bi). Eq. 11
Rearranging and simplifying finally leads one to
∇2Be+k2Be=−k2Bi, Eq. 12
where k=√{square root over (−jωμ0σ)} is the wavenumber of the eddy field. The above expression is the well-known Helmholtz equation and can readily be solved under a wide variety of useful geometries. What it tells us is that an impressed magnetic field Bi acting on a conductive object will act as a source term for the induced eddy fields in Be. Once Be has been derived, one may then calculate the eddy current density J by applying
∇×Be=μ0J. Eq. 13
After the eddy current density is finally calculated, we may then calculate the net force acting on a metal particle by applying the classical magnetic force law
F=∫∫∫r×JdV, Eq. 14
where r denotes a position vector in space and V denotes the spatial region occupied by the eddy currents within a conducting particle. If we then recall Newton's third law of motion,
one can at last solve for the net acceleration a experienced by a metal particle of mass m as it enters a time-varying magnetic field. The result is a distinct kinematic trajectory that varies heavily with such factors as electrical conductivity, frequency of excitation, and mass density. Thus, if the disparity between metal particles is significant, it becomes possible to sort them by placing a mechanical barrier between their trajectories.
To illustrate, the electrical conductivity of copper is roughly twice that of aluminum (60 MS/m versus 35 MS/m), but the mass density is over three times greater (8.96 g/cm3 versus 2.71 g/cm3). Consequently, even if the force on a copper particle were twice as great, the net acceleration in would still be significantly less than that of aluminum. Similar disparities likewise exist between other popular mixtures of scrap metal particles, including copper and brass, aluminum and titanium, or even wrought aluminum alloys and cast aluminum alloys.
In one sorting process (i.e., stage 1 sorting process) illustrated by
The splitter/collection bin for the WWGC tuned for the stage 1 sorting process shown in
The alloys with conductivities ≤26 MS/m can be further sorted in a second sorting process (i.e., stage 2 sorting process) illustrated by
The splitter/collection bin for the WWGC tuned for the stage 2 sorting process shown in
The alloys with conductivities <20 MS/m can be further sorted in a third sorting process (i.e., stage 3 sorting process) illustrated by
The splitter/collection bin for the WWGC tuned for the stage 3 sorting process shown in
The materials sorted by the processes shown in
In other configurations, other types of aluminum alloys can be sorted from other types of metal alloys (e.g., copper alloys, such as brass and bronze [Cu and tin (Sn) alloy]). For example, the initial mixture of material may consist of copper and aluminum scrap, typically mixed together by shredding, but with the nonconductive materials removed. Particle sizes on the range of 1.0-3.0 cm are fairly common and may not be easily separated with traditional, rotary-based eddy current sorters.
To sort aluminum from copper in this size range, excitation frequency generally needs to be much higher, reaching upwards of 8-10 kHz or more. With an initial magnetic field intensity of 40-60 mT, aluminum particles tend to deflect much further than copper when passing through a gapped magnetic core. Starting at a height of 0.5 m, the divider between separation bins may rest between 10-20 cm, with aluminum deflecting into the furthest bin and copper dropping directly into the near bin. Specific values may generally vary, depending on specific parameters within a practical configuration.
Magnetic Cores
The magnetic core can have toroidal geometry. A toroid 222A is a doughnut-shaped object or ring-shaped object with a region bounded by two concentric circles (i.e., an inner concentric circle 402 and an outer concentric circle 404), as shown in
The toroid 222A also includes a gap or void for the conductive particle to pass. The gap can be a parallel gap 410 between substantially parallel planes or be an angled gap 420 forming an arc-like void between two non-parallel planes with a defined radius and angle. In one example, the gap of the magnetic core forms a wedged frustum-like shaped void. A frustum (plural: frusta or frustums) is the portion of a solid (e.g., cone, pyramid, or wedge) that lies between two parallel planes cutting the solid.
The relation between the magnetizing field H and the magnetic field B can be expressed as the magnetic permeability μ=B/H or the relative permeability μr=μ0, where μ0 is the vacuum permeability or permeability constant. Magnetic permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. Hence, permeability is the degree of magnetization that a material obtains in response to an applied magnetic field. The reciprocal of magnetic permeability is magnetic reluctivity. The permeability constant (μ0), also known as the magnetic constant or the permeability of free space. The magnetic constant has defined value μ0=4π×10−7 H·m−1≈1.2566370614 . . . ×10 −6 H·m−1 or N·A−2). A good magnetic core material should have high permeability (e.g., μr>100).
The permeability of ferromagnetic materials is not constant, but depends on H. In materials, the relative permeability increases with H to a maximum (i.e., saturation knee or μmax), then as the magnetization curve approaches saturation the relative permeability inverts and decreases toward one.
The magnetic core 320 (e.g., toroid 222A) includes ferromagnetic and ferrimagnetic materials. Inherent to ferromagnetic materials and ferroelectric materials is a characteristic or effect referred to as hysteresis. Hysteresis is the time-based dependence of a system's output on current and past inputs. The dependence arises because the history affects the value of an internal state. To predict the system's (e.g., magnetic cores) future outputs, either the system's internal state or the system's history needs to be known. Hysteresis occurs in the flux density B of ferromagnetic materials and ferroelectric materials in response to a varying magnetizing force H.
The hysteresis of a material strongly affects the material's suitability for a particular application.
Different materials have different saturation levels. For example, high permeability iron alloys used in transformers reach magnetic saturation at 1.6-2.2 Teslas (T), whereas many popular ferrites tend to saturate between 0.2-0.5 T.
Magnetic Core Materials
The magnetic cores 320 can include various materials, such as solid metal core (e.g., a silicon steel core), a powdered metal core (e.g., carbonyl iron core), and ferrite or ceramic cores. The solid metal cores can include “soft” (annealed) iron, “hard” iron, laminated silicon steel, special alloys (specialized alloys for magnetic core applications, such as mu-metal, permalloy, and supermalloy), and vitreous metals (e.g., amorphous metal alloys [e.g. Metglas] that are non-crystalline or glassy).
Laminated silicon steel is specialty steel tailored to produce certain magnetic properties, such as a small hysteresis area (i.e., small energy dissipation per cycle or low core loss) and high permeability. Two techniques commonly used together to increase the resistance of iron, and thus reduce the eddy currents, is lamination and alloying of the iron with silicon.
Among the two types of silicon steel, grain-oriented (GO) and grain non-oriented (GNO), GO is more desirable for magnetic cores. Grain-oriented silicon steel (GOSS) core or a cold-rolled grain-oriented (CRGO) silicon steel is anisotropic, offering better magnetic properties than GNO in one direction. As the magnetic field in inductor and cores is along the same direction, it is an advantage to use grain oriented steel in the preferred orientation. Rotating machines, where the direction of the magnetic field can change, gain no benefit from grain-oriented steel, thus GNO silicon steel can be used.
The magnetic core can utilize CRGO silicon steel or GOSS for aluminum alloy sorting due to high possible field strengths with silicon steel at low operating frequencies. In one example, CRGO has a relative permeability (μr) as high as 100,000 and a saturation magnetic flux density B (BS, BSat or BSaturation) of 2.1 T. Electrical conductivity, however, can also reach the order of 1.0 MS/m and above. Even with laminated layers to squelch eddy currents, the internal heat dissipation of a single, small-sized core might exceed 1.0 kW at frequencies above 5.0 kHz. At lower frequencies (say, <2.0 kHz), the heat dissipation is much lower and thus far more manageable through proper heat-sinking techniques.
Ferrites are another type of ferrimagnetic magnetic material that can be used for the magnetic core 320. The ferrite is both electrically nonconductive and ferrimagnetic, meaning that the ferrite can be magnetized or attracted to a magnet. Ferrites are usually non-conductive ferrimagnetic ceramic compounds derived from iron oxides such as hematite (Fe2O3) or magnetite (Fe3O4) as well as oxides of other metals.
Ferrite cores can be used for sorting mixed metals such as copper and brass from aluminum, or titanium from aluminum at moderate field strength for high operating frequencies. Ferrite cores can also be suitable for sorting aluminum alloys at low frequencies as well. Alloys require high field strengths to be generated by the magnetic cores to have the most specificity between highly similar alloys (e.g. where there is a very small difference in conductivity between materials, differences on the order of 2-5 MS/m). The conductivity/density ratio and particle size can be used determine the optimal sorting frequency. Where alloys are concerned, the densities can be nearly identical and therefore conductivity, particle size, and B field strength become the master variables in establishing the optimal sorting frequency.
Typical frequencies used for sorting metals, alloys, and various particle sizes likely to be encountered in a real world situation is 500 Hz to 50 kHz. Due to the relatively high internal resistance of silicon steel at high frequencies, silicon steel cores (e.g., GOSS or CRGO silicon steel cores) can be useful for metal and alloy sorting at low frequencies (e.g., 100 Hz-2 kHz). Ferrites tend to have much higher resistivity and thus dissipate far less heat at higher frequencies (e.g., 2-50 kHz). However, ferrites also tend to have much lower saturation fields (<0.5 T), thus imposing certain design trade-offs.
Although silicon steel and ferrites have been discussed specifically, other core materials with high flux densities (e.g., >300 mT) at both low and high frequencies may also be used for the magnetic core of an electrodynamic sorting system. Magnetic core materials can be selected based on magnet saturation characteristics (e.g., saturation flux density, BS, or Bsat) and power dissipation per unit volume.
Magnetic Core Geometry and Gap
As mentioned, the magnetic core can have various geometries or shapes. The magnetic core also includes a gap (or core gap). The gap is a break or void of core material in a loop forming the magnetic core, as illustrated in
As shown and described with reference to
The core gap geometry can be variable and tunable according to the material sizes being sorted, the core material, and a desired field gradient. The core gap geometry along with the electrodynamic sorting circuit can be used to control the magnetic field profile (e.g., a cross sectional distribution of magnetic field intensity) as well as ensure the maximum gradient, which imparts a direction and magnitude to a particle encountering the magnetic field.
The gradient can be tunable according to the gap angle and/or flare angle (and the core material). Models can be developed to maximize the field strength with a distribution where some particles will fall through the gap while maintaining the gradient required to direct and deflect the particle in the desired direction.
In another example shown in
As previously discussed, in some configurations, the magnetic core also includes a flare.
The shape and dimensions of the plane geometrical figure and/or gap face can affect the magnetic gradient of the magnetic core, force generated by the magnetic core, trajectory of the particles from the magnetic core, and/or efficiency of the magnetic core.
Additional Gap Designs
Begin by considering the simple gapped core depicted in
As the figure shows, most of the force is packed tightly towards the rear of the gap and then decays rapidly in position away from the apex. This kind of profile is generally undesirable, in some constructions, as random perturbations in the particle insertion can potentially lead to drastic variations in deflected trajectories. It also creates large regions of relatively weak forces, such that a particle is more likely to just fall directly through the gap rather than exhibit any significant deflection.
In order to better control the force profile acting through the magnetic gap, one can either shape the field intensity B0, or the field slope dB/dx. However, the only mechanism to control these parameters is the gap spacing at some particular radius value. Narrower spacing tends to increase B0, while wider spacing tends to reduce it. Also the spacing needs to monotonically increase, or else the slope might suddenly change sign. This would have the effect of pulling the particle back into the gap rather than eject it. Consequently, if one wishes to shape the force profile more efficiently, our only option is to control the rate at which the gap widens. Greater are angles have the effect of increasing dB/dx, thus producing a much greater force than would have been otherwise.
Now consider the gap geometry in
Looking closely at
Further refinements are also possible along extra dimensions for better feed behavior. For example, one problem that has been experienced is the particles bouncing off the top of the gap without really entering the main field. This tends to introduce significant variability in the trajectories that needs to be mitigated. One contemplated solution is to open the gap along the Y-axis, thereby reducing the repulsive forces on particles falling in.
Voltage Reduction in Magnetic Cores for Electrodynamic Sorting
In practice, it is common to drive the magnetic core by using a series RLC circuit.
This creates a resonant circuit wherein large electrical currents can be achieved through a relatively small drive voltage V. However, no matter how the circuit is arranged, V=L dI/dt always holds true across the terminals of the magnetic core. Depending on the specific parameters of the system, this has the potential to create large voltages across the core wiring.
As an example, consider a typical ferrite core with a total inductance of 80 mH. When driven at a current amplitude of 4.0 A and a frequency of 6.5 kHz, the peak voltage across the windings is found to be over 12 kV. Voltage levels of this magnitude are not preferred, as most copper wiring is only rated to carry perhaps 10 kV or less.
One solution to the problem is to cut the winding into two segments. If the two segments are then driven with equal current magnitude, the net current density around the core remains unchanged, and thus does not perturb the magnetic field within the gap. However, the original series inductor now behaves as two separate inductors connected in parallel. If one assumes that the two coils are perfectly split into equally inductive components at half the original value, then the net inductance across the coil has effectively dropped by a factor of 4. Thus, if one increases the net input current by a factor of 2 (to maintain a consistent B-field), the final voltage across the coils will be reduced by a net factor of 2.
For example,
Speaking generally, segmentation of the windings invokes the trade-offs between voltage and current. One may generalize this result by stating that for n divisions of the wire into equal segments, the voltage across the coils will drop by a factor of n as well. However, this drop is made up for by a proportionate rise in the total current by a factor of n, since each new segment should be fed with the same current in order to maintain a consistent magnetic field. Due to the separate segments of wire around the coil, embodiments now have the option of sharing the current among multiple amplifiers (an option that was not available with a single, series wire under fewer turns). Thus, as long as an embodiment maintains phase consistency among the segments, the embodiment will deliver consistent magnetic field to a scrap particle with less voltage
One challenge to segmentation is making sure that impedances are balanced across each coil. Otherwise, the coil with the lowest impedance will tend to draw a disproportionate amount of current from the other coils. While this does not immediately affect the final magnetic field within the gap, it does place a potential burden on the wiring itself, which must now support a greater current than the neighboring coils. Proper load balancing helps ensure a greater peak value in total current that can be driven through the coils.
Winding Configurations for Electrodynamic Sorting
The primary component of electrodynamic sorting is a core of magnetically permeable material, ideally with a relative permeability μr between 1000-2000. One exemplary core is typically shaped as a rectangular toroid, wrapped up with several dozen turns of copper wiring. A gap then cut away from one end so that scrap particles can be inserted and sorted accordingly. To magnetize the gap, an electrical current is driven through the copper wiring, which then fills the gap with the desired magnetic field. Since the force of repulsion experienced by a particle is directly proportional to the field intensity within the gap, it is preferred, in some embodiments, to generate as much field intensity as possible for maximum separation distance.
In some structures, significant field strength can be added to the magnetic gap by rewiring the core with a specific winding geometry. The basis for this discovery has been the realization that the magnetic field profile within the gap is relatively insensitive to where exactly the windings are placed. For example, ten windings wrapped together at a single location will tend to produce just as much magnetic flux as ten windings distributed uniformly around the core. However, since the magnetic core is comprised of a nonlinear material, the arrangement of wires does have an impact on where the flux is generated and how much headroom exists before saturation occurs. Thus, by placing the wires more efficiently, it is possible to direct a much greater flux into the magnetic gap without prematurely saturating the core inside.
To begin, consider the magnetic core depicted in
In
To measure this headroom, it is useful to compare the saturation profiles shown in
Next, the effect of swath angle on the magnetic field intensity inserted within the gap is considered. First begin by driving the current up to 10 A, which is well-beyond the saturation threshold for the core. That way, any improvement in the saturation headroom will manifest as a greater field intensity inserted into the gap. The swath angle is then varied from 5 degrees to 165 degrees, representing a transition from the highly packed configuration toward the uniform distribution. The result is plotted in
Feeding Mechanism Design
In embodiments, it is may be desirable to feed the materials being sorted in such a manner that irregular shapes are limited from interlocking and clumping. This helps keep the core gap free of obstruction but also maximizes throughput where is a single-file continuous feed. The more uniform the materials being sorted, the higher the throughput as well as higher recovery and grade. It is therefore preferred, in some embodiments, to screen the materials being sorted to ensure uniformity to maximize sorting efficiencies. A second pass of the product can refine grade if initial feed has a wide standard deviation in particle size.
In some embodiments, a feeding mechanism, such as a conveyor or vibratory feeder, has a plastic extension of at least 15 cm or more to minimize field perturbation and loss in close proximity to the magnet.
The feeding system can include a vibratory feeder, a feed chute, and a feed funnel. The feed chute is typically made of non-metallic material is attached to the discharge end of the vibratory feeder. The shown chute has a flat bottom and a 30 degree angled side wall. It is open on the top side and assists in the disentanglement of the material. Also, the nonmetallic material does not conduct eddy current generated by the magnet to the vibratory feeder.
Next, the feed funnel is coupled to the discharge end of the feed chute. The feed funnel can be a square shaped funnel at the top. This design disentangles the scrap feed, helps guide the material into the gap, and overcomes the upward force exerted by the magnet.
In certain embodiments, the feeder is shaped such that the material flows into the attachment that narrows the material into a smaller cross-sectional area to be delivered into the gap.
In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of teachings.
The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
Moreover in this document, relational terms such as first and second and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Directional references, such as upper, lower, downward, upward, rearward, bottom, front, rear, etc., may be made herein in describing the drawings, these references are made relative to the drawings (as normally viewed) for convenience. These directions are not intended to be taken literally. The terms “comprises,” “comprising,” “has”, “having,” “includes”, “including,” “contains”, “containing” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially”, “essentially”, “approximately”, “about” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1% and in another embodiment within 0.5%. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed.
It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or “processing devices”) such as microprocessors, digital signal processors, customized processors and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the method and/or apparatus described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used.
Moreover, an embodiment can be implemented as a computer-readable storage medium having computer readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory) and a Flash memory. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.
This application claims the benefit of U.S. Patent Application No. 62/217,005, filed on Sep. 10, 2015, and U.S. Patent Application No. 62/300,429, filed on Feb. 26, 2016, the contents of both of which are incorporated herein by reference.
This invention was made with government support under Grant DE-AR0000411 awarded by the Department of Energy. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2016/051124 | 9/9/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62300429 | Feb 2016 | US | |
| 62217005 | Sep 2015 | US |
