Patent Application
20220032314
Refractory materials are used as a lining material for ovens, processing equipment, melting furnaces, investment casting molds, 3D printing of refractory shapes, and other high temperature processes. Currently, about 40 million tons of refractory products are used each year, and 28 million tons of refractory waste are generated. About 7% of refractory waste material is currently recycled. Because most recycled refractory materials remain contaminated with binder materials and low-grade components, most are only suitable for use in low value applications such as roadbed foundations or slag conditioners. Furthermore, refractory waste is largely inert. Therefore, landfilling has been industry's lowest cost disposal option.
Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
Refractory materials are vital to industry and national security. Examples of industries depending on large quantities of refractories include steel, iron, aluminum, cement, glass, and ceramics. The chemistry of the refractory for a specific application is dependent upon the environment in which it is used. Three composition classes of refractories can include acid, neutral, and basic. Furthermore, there are several refractory installation methods. Each installation requires a specific recipe of refractory aggregates, typically a cement or resin binder, and water. In a brick installation, refractories are mixed, pressed into a shape, and fired prior to installation. In a monolithic installation, the refractory recipe is mixed off site and remains in powder form until installation by mixing with water or other chemicals on site and then applied by ramming, gunning, pouring, vibrating, etc.
Due to the rising cost of raw materials, supply concerns, political concerns, environmental considerations, and the increasing costs for landfilling, refractory recycling is desirable. Existing refractory recycling efforts have targeted the “basic” MgO refractories and have been unsuccessful at producing a consistent quality product that can be used as an alternative high value raw material in new refractory production. Existing processes for recycling of refractories can include sorting the materials, crushing, and screening. The reasons for failure can include:
Inconsistent Supply: Spent refractories are being procured from many different companies in small batch quantities.
Sorting of Raw Material: The different classes of refractories cannot be mixed. Often, consumers “zone” their furnaces with different classes of refractories. Several methods of sorting have been investigated but they can be either too expensive, or unreliable.
Contamination: Lime, soda, pot ash, and other materials used in metals production are detrimental to the recycling effort. Likewise, the binders used in making the original refractories and mixed refractory classes within a certain refractory class, contaminates the raw material of the recycling process.
To summarize, the fundamental failure of previous attempts to produce a high value recycled refractory material can be seen as the inability to remove contamination. Therefore, the resulting product is only useful in low value applications. A simple sorting, crushing, and screening process crushes the larger, pure aggregate as well. The resulting aggregate particles still have cement and other unwanted contaminants adhered to them rendering them unsuitable for use in new, high value, refractory production. For refractory recycling to be successful, a new recycling method is required. Various embodiments of the present disclosure allow for the recycling and refining of spent (used) refractory materials, reduce landfill costs, reduce energy consumption, and can produce products which can be used as a high value replacement of the virgin raw material currently used in the production of new refractory materials. In the following discussion, a general description of the system and its components is provided, followed by a discussion of the operation of the same.
With reference to
The initial cleaning process may involve subjecting the aggregate material through a quick preparation process to remove residual dirt or debris. For example, the aggregate material may include refractory brick, which is usually composed of clays that include alumina and silica. The refractory brick may be cleaned with hot water, a degreaser, pressure washing, or even placed in a rotary device that uses the aggregate material to clean itself while tumbling.
At step 106, a maximum aggregate size of an individual refractory component of the network of refractory aggregates is determined. The maximum aggregate size may be determined based on the properties of the raw material to be refined, such as hardness, density, etc. For example, the composition of refractory brick can include 80% alumina, silica (SiO2) aggregates, mullites, and magnesia (Mgo) aggregates, and an object may be to extract alumina without the other compounds. Since alumina has the highest concentration and density in the compound, the maximum aggregate size should be of sufficient size so that individual particles, after a crushing and screening process, can withstand impact at high velocities. If the maximum aggregate size is too small, the desired refractory component may fracture as well when subjected to impact at high velocities. In some embodiments that use an automatic crusher, the maximum aggregate size to crush raw material may be manually set in the crushing machine.
The individual refractory component may correspond to the material to be recycled from the aggregate materials. For example, the material that is desired to be recycled from the refractory brick may be alumina (Al2O3). Therefore, an object according to one example embodiment of the flowchart shown in
At step 109, the network of refractory aggregates is subjected to a crushing process. The crushing process may be manual or automatic. For example, automatic crushers may include gyratory crushers, jaw crushers, cone crushers, and impact crushers. Examples of automatic crushers that may be used include Screen Machine's 5256T Rock Crusher, 4043T Rock Crusher, 4043TR Recirculating Rock Crusher, JXT Jaw Rock Crusher, Superior™ primary gyratory crushers, Nordberg® C Series™ jaw crushers, and other crushers. Manual crushers may involve hand operated crushers such as a stone crusher that can be hand spun. According to the example embodiment, it may be beneficial that the crushed particles of the network of refractory aggregates be sized slightly larger than the maximum aggregate size that was determined in step 106. Crushing to a size slightly larger than the maximum aggregate size can minimize loss of individual aggregate particles being fractured during the crushing and/or refining process.
At step 112, any metal fragments or pieces may be removed from the network of refractory aggregates by exposing the aggregate material to a magnet. For example, a magnetic separator may be used to remove iron impurities from the refractory aggregate material. A magnetic field gradient may be applied to the refractory aggregates causing the iron impurities to move in the direction of the applied magnetic field. Examples of magnetic separators that may be used include cross belt magnets and pulley magnets. Cross belt separation magnets may include magnets such as the SEMO241 and SEMO722, which may generate a range of 1652-14500 watts. In addition, metal detectors may be used in conjunction with the magnetic separators to detect and remove tramp metal such as Bunting's TN77 series conveyor belt metal detector. Implementation of metallic detectors and magnetic separators may be beneficial in preventing damage to crushers, screens, and conveyors.
At step 115, the crushed network of refractory aggregates may be filtered by one or more screens to obtain consistently sized particles to deposit into a refiner machine. In an example embodiment, the screen used may be a RO-TAP® sieve shaker, Powerscreen® Chieftain 400, Powerscreen® Chieftain 600, Powerscreen® Chieftain 2100X, and other screens. Screen types may include freely vibrating screens, circular motion screens, linear motion screens, elliptic motion screens, brute force screens, resonance screens, sizers, banana screens, special screens, and other screen types. A screen may have a mesh size, such as a U.S. Mesh Size, that is defined as the number of openings in one square inch of a screen. According to one embodiment of the present disclosure, the mesh size may be equal to or slightly greater than the maximum aggregate size determined in step 106. That is, if the maximum aggregate size determined is ⅜ inch2, each opening of the screen may be ⅜ inch2.
In another embodiment, the mesh size may be smaller than the maximum aggregate size determined. Ultimately, the mesh size may be selected based on individual preference and/or the maximum aggregate size of the individual refractory component to be extracted from the network of refractory aggregates. Selecting such mesh sizing can allow consistently sized particles of crushed aggregate refractory material to be obtained. Once the crushed network of refractory aggregates is filtered through the screen, particles of a sufficient size are retained on the screen, while smaller particles may fall through the screen.
At step 118, the retained particles discussed in step 115 may be deposited into a refiner machine 600 for the refining and fragmentation process. According to one embodiment of the present disclosure, the refiner machine 600, as shown in
To deposit the retained particles discussed in step 115 into the refiner machine 600, the retained particles discussed in step 115 may first be deposited through the feed hopper 609. The feed hopper 609 is connected to the magnetic feeder 633, which can control flow of the retained particles into the blast chamber 603. In an example embodiment, the magnetic feeder 633 can include a Syntron® magnetic feeder with a control unit. The magnetic feeder 633 can include a vibrating feeder that can vary the flow of material through the feeder by adjusting the amplitude of the feeder pan. In one embodiment, the magnetic feeder 633 can be configured to process 4-15 tons of material per hour. In other embodiments, the magnetic feeder 633 may have a feed rate of up to 30 tons of material per hour depending on the size of the feed hopper 609.
In one embodiment, the feed hopper 609 may be designed to support a mass flow or a funnel flow of material. In mass flow, an entire bed of solids is in motion when material is discharged from the outlet, which eliminates the formation of stagnant regions in the vessel, and affords a “first-in, first-out” flow sequence, which provides a more uniform velocity profile during operation. A uniform velocity profile may also help to reduce the effects of sifting segregation. By contrast, in funnel flow, an active flow channel forms above the outlet, but stagnant material remains (called ratholes) at the periphery of the vessel. Funnel flow can cause erratic flow, exacerbate segregation, reduce the live capacity of a vessel, and allow particle degradation in stagnant region. In one embodiment, the feed hopper 609 includes a cylindrical shape that tapers down to a cone like shape toward the exit of the feed hopper 609.
Once passed through the magnetic feeder 633, the retained particles from the first screening process can be deposited into the blast chamber 603. The retained particles (aggregate raw material) may be passed into the blast chamber 603 through a funnel that is connected to the magnetic feeder 633.
The inner lining of material 706 surrounds the inner circumference of the outer wall 703. As an example embodiment,
Shown in
When determining the velocity and the RPM to be applied to the wheel 803, specific properties of individual refractory components within a network of refractory aggregates should be considered to separate the refractory network into purified aggregates. For example, the specific properties that should be considered can include density, compressive strength, fracture toughness, and hardness. Applying impact dynamics derived from Newton's 2nd and 3rd law of motion, the mechanism for separating the refractory network into purified aggregates are described below:
Newton's 2nd law: Force=mass*acceleration
Newton's 3rd law: For every action, there is an equal and opposite reaction
Applying impact dynamics, the kinetic energy just prior to impact=work done after impact:
KE=0.5 mv2 (1)
W=Fd (2)
Approximation of the forces experienced on impact are expressed:
where Favg is the average force experienced over a deformation distance d, in an impact scenario, and
is also the average force experienced over a deformation time t, in an impact scenario. Therefore, it can be said that:
F
max=2Favg (4)
where Fmax is equal to the maximum impact force over a deformation distance d, or over a deformation time t.
In addition, refractory materials are some of the hardest materials known, and while they are tough, they have little elasticity. Therefore, in an example embodiment of the present disclosure, the distance d or the time t in the above equations may be miniscule in an impact scenario. Accordingly, a piece of refractory material propelled into a stationary object, impacting at a force which exceeds the crushing strength of the material, can fracture the material. Using the mechanical properties of the individual materials, the “critical” velocity (fracture velocity) required to fracture each individual material within the refractory matrix, for a given particle size, can be estimated. However, other influences like friction, air resistance, and particle shape can impact the estimation of the critical velocity. Considering a system of millions of particles, and the fact that each material has its own hardness, the particles will be cleaned during the rebound action and the scrubbing action, both of which occur below the fracture velocity.
With reference to
According to various embodiment of the present disclosure, refractory brick, castable, or dry vibrateable refractory products include a matrix of smaller aggregate particles and cement filling the voids between larger aggregate particles. The present embodiments are based upon the concept of returning a spent refractory material, as close as possible, to their original aggregate state.
For example, consider an 80% alumina refractory brick. Each material within the refractory brick has its own unique physical and mechanical properties. Considering the refractory mix within the brick, the Al2O3 aggregate, typically has the largest aggregate, has the highest density, the highest crushing strength, the highest fracture toughness, and the highest hardness of any of the materials within the brick. The other components are typically SiO2 aggregate, mullite clays, and cement. These have lower mechanical properties and are usually smaller sized aggregates.
Accordingly, the velocity required in propelling a particle against a stationary object, to cause fracturing or explosion of the particle, can be calculated based at least in part on the physical and mechanical properties of individual particles. Since Al2O3 aggregate has a higher density (weight/volume), a higher compression strength, and a higher fracture toughness than those of magnesia (MgO) aggregates, silica (SiO2) aggregates, etc., equally sized particles of Al2O3, SiO2, mullite, etc., propelled at a velocity slightly under the “fracture velocity” of the Al2O3, can fracture everything but the Al2O3 aggregate. In addition, Al2O3 has a higher hardness than those of magnesia (MgO) aggregates, silica (SiO2) aggregates, mullites, etc. Therefore, the abrasive action created during the process will aid the cleaning of the Al2O3 aggregate. Coupled to a screening system, and velocity control system, the Al2O3 particles of different sizes can be refined and extracted.
Referring to
The contaminants or “fractured” material are relatively fine particles. Due to the nature of the centrifugal force created and the positive and negative air pressure effect created by the spinning wheel 803, the contaminants, which can include fugitive dust, and alumina (Al2O3) aggregate fall to the compartment 606 after hitting the inner lining of material 706.
For example, the wheel 803 spinning at high speeds without the dust collection chamber 1304 and the anti-vortex blades 1307 can cause the desired refractory aggregate to get picked up by the dust collection valves 618a and 618b. However, with the implementation of the dust collection chamber 1304 and anti-vortex blades, which has an opening at an end portion of the body of the dust collection chamber 1304 that is opposite the end connected to the dust collection valves 618a and 618b (
In other embodiments, in lieu of the anti-vortex blades 1307, an air curtain mechanism may be implemented within the refiner machine 600. For example, air curtains, also known as an air door, is a machine that blows a controlled stream of air across an opening to the other side to create an air seal. The seal separates different environments while allowing a smooth, uninterrupted flow of air traffic. Air curtains that may be used include air curtain velocities that can range from 1500-300 feet per minute (fpm).
In one embodiment, the dust collection system 1603 can incorporate butterfly valves 1606 for flow regulation. Similar to a ball valve, butterfly valves can be used for flow regulation where a rod passes through a disc to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow. In operation, the valve may be fully open or closed when the disc is rotated a quarter turn. The butterfly valve 1606 can operate to start or halt airflow for the dust collection system 1603.
Referring back to
In an example embodiment, refractory material that remained after crushing an example brick, depositing the brick into the refiner machine, and extracting the contaminant particles were tested for refractory content.
At step 124, the volume or mass of contaminants accumulated in the dust collection system 1603 is assessed. For instance, the drum may be connected to an industrial weighing system such as floor scales, hanging scales, bench scales, etc. In some embodiments, the volume or mass of contaminants may be measured through use of a load cell. When a certain mass or volume of contaminants is reached, the refining machine 600 can be shut down since the target contaminant volume or mass can be estimated based on how much initial refractory material is deposited into the refining machine. If the dust collection system 1603 target is not met, desired refractory material that has accumulated at a lower portion of the compartment 606 can be transferred back to the feed hopper 609 for a second pass. In some embodiments, it may be necessary to run the processed material again for a third pass to obtain a purer refractory aggregate material.
At step 127, the refining machine 600 can be stopped, and the desired refractory material in the compartment 606 can be transported to the harvest hopper 615. For example,
Other than the compressed air system approach to move refined aggregate material as discussed in step 127, other approaches may be implemented in some embodiments. For example, a conveyor belt system may be used to move the refined aggregate material. Different types of conveyor belt systems that can be used include beam trolley systems, belt conveyors, chain conveyors, inverted conveyors, live or motorized roller conveyors, overhead conveyors, over-under conveyors, slat conveyors, and other types of conveyors.
Although the flowchart of
It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt % to about 5 wt %, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. The term “about” can include traditional rounding according to significant figures of numerical values. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.
Disjunctive language, such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is to be understood with the context as used in general to present that an item, term, etc., can be either X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to be each present.
It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications can be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.
This application claims priority to, and the benefit of, U.S. Provisional Patent Application No. 63/058,027, entitled “RECYCLING WASTE REFRACTORY MATERIAL,” filed on Jul. 29, 2020, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63058027 | Jul 2020 | US |
