Jiann-Tang HWANG -- Microwave steel manufacture

Inventor: HWANG JIANN-YANG [US] ; HUANG XIAODI

A method and apparatus for reducing iron oxides using microwave heating in a furnace chamber which is sealed against the entrance of air reduces the energy required and produces a low temperature reduction and allows the recovery of combustible synthetic gas as a byproduct of the process. Avoidance of the reduction of sulfur, phorphorus and silica is also insured, as is the need to reduce the silica content of the feed material prior to reducing the ore. A continuous rotary hearth furnace, a rotary kiln, a linear conveyor and vertical shaft furnace chamber configurations are described. A secondary heating zone can also be included to process the reduced iron into iron nuggets or liquid metallic iron.

Description

BACKGROUND OF THE INVENTION

[0002] Currently steel is produced by two types of operations: integrated mills and minimills. In the integrated mill, sintered iron ore pellets, coke and lime are charged into a blast furnace (BF). Air is blown in at high speed to combust the coke to generate carbon monoxide and heat. Sintered iron ore pellets are reduced to hot metal by the carbon monoxide and melted to form liquid iron. The liquid iron is then sent to a basic oxygen furnace (BOF) where pure oxygen is blown into the liquid iron to remove excessive carbon and convert iron into steel. The fundamental problems associated with this production route are the needs for coke and intense high temperature combustion. Coke making is one of the most polluting of industrial processes and high temperature combustion generates a great amount of dust and wastes energy in the exhaust gases.

[0003] Minimills employ electric arc furnaces (EAF) to melt steel scrap with or without DRI (Direct Reduced Iron) and produce generally lower quality steel. Minimills traditionally enjoyed an abundant supply of steel scrap, however, the recent strong demand for scrap internationally has doubled the price. DRI prices have also significantly increased due to high cost of reformed natural gas, causing many DRI plant closings.

[0004] A revolutionary steelmaking technology has been developed by the present inventors based on the use of microwave energy (U.S. Pat. No. 6,277,168). This technology can produce DRI, iron or steel from a mixture, consisting of iron oxide fines, powdered carbon and fluxing agents. This technology is projected to eliminate many current intermediate steelmaking steps, such as coking, sintering, BF ironmaking, and BOF steelmaking.

[0005] This technology has the potential to save up to 50% of the energy consumed by conventional steelmaking; dramatically reduce the emission of CO2, SO2, NOx, VOCs, fine particulates, and air toxics; substantially reduce waste and emission control costs; greatly lower capital cost; and considerably reduce steel production costs.

[0006] Microwave heating technology has the advantage over blast ovens relying on combustion in being faster to heat the iron oxide feed materials since it does not rely on conducting heat into the material through air or other gases but rather it generates heat internally directly by absorbing the microwave radiation. Furthermore, microwave heating is selective, i.e., it only heats components of the material that needs to be heated, i.e., to reduce the hematite or magnetite and does not heat the silica, phosphorus, sulfur or other non ferrous components of the feed material directly, so that the energy is much more efficiently used and the maximum temperature reached can be much lower. The feed material does not need to be electrically conductive to be heated with microwave radiation in being reduced.

[0007] Another problem with iron and steel making has been the retention of sulfur and phosphorus in the iron which may reduce the quality of the iron or steel produced. This problem results from the much higher temperatures typically reached in conventional reducing of iron oxide by combustion of natural gas or coal. These higher temperatures result since the outside of the pellets or green balls or other feed material is raised to a temperature much higher than needed to carry out reduction because of the need to achieve proper heating throughout the entire pellet or ball and to reduce the time required to raise the entire mass to the level required for reducing the iron oxide. At these higher temperatures, phosphorus and sulfur are also reduced and this results in elemental phosphorus and sulfur being retained in the iron or steel. This problem is exacerbated if coal is used to reduce the ore or other feedstock since coal sometimes contains sulfur, and this would further increase the level of sulfur in the iron.

[0008] A further problem resulting from the high temperatures required in conventional reduction processes is that expensive refractory material must be employed in the furnace increasing the capital costs. Also, any silica present may also be reduced, which will also contaminate the iron and have a deleterious effect on its quality in many cases.

[0009] Another problem encountered concerns excess silica being present in the feed material either from the mining operations or in the ore deposits. Silica content varies in iron ore from different deposits. While silica will be eliminated by being part of the slag forming on molten metal, if excessive slag forms this will block attempts to inject a gas into the molten metal and thus interfere with the process. Thus, in instances where excessive silica is present in the ore or the pellets, the silica content must first be removed or at least minimized. This has heretofore required grinding of the ore into a very fine powder in order to mechanically separate the silica from the ore, a quite costly process representing a major expense item and energy consumer in processing such ore. In fact, too high levels of silica can render some ores commercially worthless.

[0010] Another disadvantage a rises from the air injection of conventional practice and blast heating to reduce iron ore as this generally results in combustion of all the carbon associated with the feed material into carbon dioxide. This represents a waste of potentially useful carbon combustibles and adds to the carbon "footprint" of the process.

[0011] It is the object of the present invention to provide apparatus and methods for the production of metals and in particular iron and steel which utilize microwave heating in such a way to realize the potential benefits of using microwave heating in iron and steel production.

[0012] It is yet another object of the present invention to recover carbon combustibles involved in the reduction process in a useful form.

[0013] It is a further object of the present invention to avoid contamination of iron during production with phosphorus, sulfur or silica using a minimum energy and at a lower cost.

[0014] It is still a further object of the invention to separate silica from the ore at a minimum consumption of energy.

SUMMARY OF THE INVENTION

[0015] The above recited objects and other objects which will be understood upon a reading of the following specification and claims are accomplished by carrying out the reduction phase of iron oxide at a relatively moderate temperature by the use of microwave radiation while excluding air. The microwave radiation heats only the iron containing constituents of the feed material for maximum efficiency in the use of energy and the moderate temperatures avoid reduction of phosphorus, sulfur or silica present to minimize contamination of the iron with those elements.

[0016] Volatile gases from coal and carbon combustibles are produced and can be recovered for use as a fuel or as a reducing gas.

[0017] Continuous processing at moderate temperatures becomes practical due to the speed of microwave heating of the material to reach reduction temperatures. According, to the invention, feed materials may be reduced in a rotary hearth furnace , a linear conveyor furnace, a rotary kiln, or in vertical shaft furnaces which each enable multiple microwave wave guide mountings to readily achieve the necessary heating capacity for a given application. The DRI produced can be discharged into a collecting container or directly into an electric arc furnace for producing steel. The microwave heating reduction may be combined with a secondary heating of the reduced ore (DRI) to obtain iron nuggets. An induction melting furnace to produce liquid iron can also be used to receive the DRI.

[0018] The rotary kiln (and all of the other furnaces can utilize a combination of microwave and combustion heating to produce DRI or solely by multiple microwave sources.

[0019] A linear conveyor associated with a conveyor can produce either DRI or iron nuggets with secondary heating after the reduction phase which may also be accomplished with microwave heating or by burner heating, radio frequency radiation, etc.

[0020] A vertical shaft furnace can also be used in which the ore pellets or other feed material is introduced at the top of a refractory lined cylinder. Microwave heating is carried out as the material descends down the furnace. An induction heater may be provided at the bottom which receives DRI and produces melted iron discharged therefrom and is slag drawn off from the melted iron. Alternatively, injection of natural gas or other reducing gas can be done to produce DRI in the shaft furnace without carbon material in the feed.

[0021] The use of microwave energy to reduce the feed materials allows reduction to be carried out at lower a temperature since the entire mass is heated at once such that overheating of any portion is not necessary.

[0022] If the phosphorus and sulfur remain as oxides in the feed material, they form part of the slag when the reduced feed material is melted and are thereby eliminated from the metal with the slag.

[0023] Continuous processing is rendered easier by using microwave energy to reduce the feedstock while avoiding any problem with retention of sulfur and or phosphorus.

[0024] By microwave heating at lower temperatures, reduction of silica is minimized. However, the major benefit of the approach is that gas injection is not required such that a reduction of silica in the slag by a mechanical removal of the silica prior to processing is not required. Even relatively large quantities of silica can be removed in the slag and need not be removed by costly fine grinding and mechanical separation as practiced conventionally to reduce silica content prior to reduction of the ore.

DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a diagrammatic sectional view through a rotary hearth furnace and related components according to the present invention.

[0026] FIG. 1A is an enlarged view of a section taken through one side of the rotary hearth furnace showing constructional details.

[0027] FIG. 2 is a diagrammatic plan view of the rotary hearth furnace shown in FIG. 1.

[0028] FIG. 3 is a view of a vertical section through the rotating base of the rotary hearth furnace of FIGS. 1 and 2.

[0029] FIG. 4 is a plan view of the rotating base shown in FIG. 5.

[0030] FIG. 5 is an enlarged view of a section taken through one side of the rotary furnace shown in FIG. 1 showing a DRI discharge and microwave guide.

[0031] FIG. 6 is a vertical section through an electric arc furnace alternatively receiving the DRI for melting.

[0032] FIG. 7 is a diagrammatic view of a vertical section through an induction melting furnace arranged to receive the DRI discharge.

[0033] FIG. 8 is a diagrammatic plan view of an alternate form of rotary hearth furnace according to the invention and showing components for recovery for synthetic gas.

[0034] FIG. 9 is a diagrammatic section view of a rotary kiln version of a microwave heated reduction furnace according to the invention.

[0035] FIG. 10 is a diagram of a conveyor or traveling grate embodiment of a furnace chamber according to the present invention with secondary heating.

[0036] FIG. 11 is a diagram of a vertical shaft furnace chamber according to the present invention.

[0037] FIG. 12 is a diagram of an alternate form of vertical shaft furnace chamber according to the
present invention.

[0038] FIG. 13 is a diagrammatic depiction of an overall installation according to the present invention.

DETAILED DESCRIPTION

[0039] In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims.

[0040] Referring to the drawings and particularly FIGS. 1-5, a rotary hearth furnace 10 according to the present invention is depicted. This comprises a stationary annular upper chamber 12 having outer walls 14 of a refractory insulating material and an inner skin 16 of stainless steel attached to embedded anchors 17 in the refractory walls 14. A rotating base assembly 18 supports a ring shaped hearth 20 which is rotated beneath the stationary annular chamber 12 by a motor-right angle drive 24 and chain 26. A series of main rollers 27 are mounted on a base plate 21 and beneath a support plate 23 rotatable about a pivot 25. A series of inside and outside secondary rollers 29 attached to brackets 29A transfer the weight of the upper chamber 12 onto bracket flanges 31 on the base assembly 18.

[0041] A refractory material hearth base 22 holds a hearth layer of such material such as silica, limestone etc. dispensed from a feed opening 28. Feedstock material is dispensed onto the hearth layer through a dispenser 30. Such feed material may include iron ore pellets admixed with ground coal or other carbonaceous material to supply carbon for reduction of the ore, and other components to form "green" balls in the well known manner, creating a bed of feed material on the hearth base 22. Flux, binders and other components are used to create such feed material. Cross pipes 15 can be included to reinforce the chamber 22 particularly during shipping.

[0042] Refractory divider walls 32, 34 of refractory material define a furnace reduction subchamber 36 within the annular chamber 12 wherein the reduction of the iron oxide feed material takes place.

[0043] A refractory rope air seal 38 resting on bracket flange 31 encircles the rotating hearth structure 20 to prevent air from entering the chamber 12 and a metal rope microwave seal 40 prevents the escape of microwaves during operation. Similar seals are provided at the material charge and discharge ports for air and microwave sealing.

[0044] Microwaves from a generator 46 are introduced into the annular chamber 12 through a pair of waveguides 42, 44 which are preferably oriented at 90[deg.] to each other to create homogeneous microwave distribution in chamber 12.

[0045] A microwave "stirrer" blade (not shown) can also be included for even greater homogeneousness of the microwave irradiation.

[0046] Additional waveguides 48 can be employed if greater power is required for a particular application.

[0047] A viewing window 49 is also provided.

[0048] The power level is set to raise the temperatures to that at which reduction will occur i.e., approximately 600-1200[deg.] C., which as discussed above is much lower than the temperatures in excess of 1600[deg.] C. reached in conventional combustion reducing processes.

[0049] It will be understood by those skilled in the art that one or more pyrometers 45 and gas probes 47 will be used to monitor the process conditions for control and safety reasons.

[0050] The speed of microwave heating is much greater than combustion heaters since the microwave radiation heats the material from the inside and only heats the iron bearing material (not the silica). Thus, a continuous process operated at relatively low temperatures is made practical.

[0051] The feed material is reduced to direct reduced iron (DRI) by this heating in the present of carbon and then moved to a discharge port and chute 50 (FIG. 5). A steel plow (or screw) 52 causes the DRI to be discharged through the port so where it is collected in a container 54 for further processing.

[0052] A refractory guide block 56 may be used to adjust the width and depth of feed material on the hearth 22.

[0053] As shown in FIG. 6, the DRI may alternatively be directly discharged into an electric arc furnace 58 for the production of steel from the DRI.

[0054] As another alternative shown in FIG. 7, the DRI may be discharged into an induction melting furnace 60 with discharge ports for liquid metal and slag (not shown). A liquid bath must first be formed using iron prior to initiating the process using DRI.

[0055] FIG. 8 shows an alternative embodiment in which a secondary heating source 64 is provided in order to increase the DRI temperature about 200[deg.] C. in a secondary heating zone 68 within the chamber furnace. This temperature increase along with a proper recipe of the feed material and the hearth layer material can produce iron nuggets as the end product.

[0056] The secondary heating source could include microwave radiation but microwave absorbing material such as carbon must be added, as the DRI material does not absorb microwave energy. Other heating means could be employed. As discussed above, since the furnace chamber 12 is sealed, preventing air from entering, volatile components of coal (primarily methane) gassed off and the carbon monoxide generated from the carbon reducing the iron oxides by the lower temperature reduction process can be collected via a discharge duct 62 (FIG. 8) for use elsewhere. That gas can be used to fuel a burner (not shown) comprising the secondary heat source after removal of dust by a cleaning system such as a bag house 68.

[0057] The dust can contain byproducts such as zinc or zinc oxide which may be recovered as indicated.

[0058] FIG. 9 shows a rotary kiln 70 embodiment of the invention in which a cylindrical housing 72 is rotatably mounted and driven with its axis inclined shallowly from the horizontal.

[0059] The feed material (iron ore pellets with coal) is loaded via a charging port 74 into the furnace chamber 76 defined in the housing 72. Microwave radiation from a generator 78 is introduced via a longitudinally aligned waveguide 80. Mating flanges at 77, 79 have interposed microwave and air seals 81, 83. Additional waveguides can be provided on the side via microwave transparent windows 82 (which can be constructed of a refractory material). A burner 84 can augment the heat of the microwaves to produce DRI discharged at discharge port 86.

[0060] An auger device 77 may also be provided to assist movement of the feed material.

[0061] FIG. 10 shows a linear conveyor furnace 88 in which a furnace chamber defining structure 90 has an endless conveyor 92 (which can be comprised of a traveling grate) with an upper run 94 extending beneath it supported on a support structure 96. Feed material is loaded at one end and carried into a furnace chamber 98.

[0062] Furnace chamber 98 has a primary zone 98A irradiated by microwaves radiation from a generator 100 introduced via wave guides 102.

[0063] In a secondary zone 98B further heating of the reduced iron is carried out, as by radio frequency radiation, burners, etc., which can optionally be provided to produce iron nuggets. The DRI or iron nuggets are off loaded at the other end of the conveyor 92.

[0064] Microwave seals 104 are comprised of an array of steel bars or rods, spaced apart in a pattern which will block microwave leakage through the end openings by well known techniques.

[0065] Furnace gas can be collected through duct 106.

[0066] A screw conveyor 105 may be employed to assist in advance of the feed material.

[0067] FIG. 11 shows a vertical shaft embodiment of the invention, in which a tubular housing 108 defines a furnace chamber 110. The housing 108 can be constructed of a steel grille cover with a refractory shell, allowing penetration of microwaves from generators 112 directed through an outer enclosure 114.

[0068] Feed material such as pellets or a mixture as described is fed into a charging port 116.

[0069] An induction heater 118 at the lower end of furnace chamber 108 receives the DRI produced by the microwave heating in the upper region of the chamber 100 and heats it sufficiently to produce molten iron discharged at port 120. Slag is discharged at the top through port 122.

[0070] The synthetic gas produced is discharged at the top through port 124.

[0071] FIG. 12 shows a variation in which DRI is discharged via a bottom opening 126.

[0072] The DRI can be produced without carbon in the feed material by injecting natural or other reducing gas into bottom ports 128.

[0073] FIG. 13 illustrates an integrated apparatus for concurrent production of steel and syngas. Coal is used as both reducing agent and gasification material.

[0074] Ore from a source A is loaded into a first dispenser 130 positioned over a conveyor 132, coal from a source B into a second dispenser 134, (via a pulverizer 135) additives such as flux from source C into a third dispenser 136 (via a pulverizer 137), and binder from source D in a fourth dispenser 138. The conveyor discharges all of these materials into a mixer which discharges the mixed ingredients into a pulverizer 142 which in turn charges a dispenser 144. Carbon particles are also deposited in a layer onto a conveyor 148 by a second dispenser 146.

[0075] A rotary conveyor or traveling grate 148 is disposed in a sealed housing 150 (the conveyor perimeter shown in FIG. 13 is developed into a straight line).

[0076] The pellets are dispensed to form a bed 152 on top of a carbon particle bed 155 on the conveyor 148 via a charging port 154. The carbon particles are deposited onto the conveyor 148 via a charging port 156.

[0077] An organic binder is used to agglomerate iron ore concentrate, pulverized coal and fluxing agent into pellets. The feed material is dispensed onto the conveyor 148 in a layer leveled by the lower end of the dispenser 154 and is transported from the entrance to the exit of the furnace chamber 168. Microwave radiation from generators 160 is introduced into the furnace through waveguides 158 to heat the feed material to reduce the iron oxide.

[0078] Iron oxides and many carbon bearing materials are excellent microwave absorbers and can be readily heated by microwave irradiation. Upon microwave heating, volatiles, primarily methane in the coal, are released into the off-gasses to form a portion of the syngas.

[0079] Continuous heating will cause the following reactions:
C+O2-CO2
CO2+C-2CO
3Fe2O3+CO-2Fe3O4+CO2
FeO+CO-Fe+CO2
H2O+C-CO+H2
CO2+CH4Fe->2CO+2H2
H2O+CH4Fe->CO+3H2

[0080] Thus, iron ore is reduced into metallic iron or DRI in the reduction zone 168. At the elevated temperature and carbon rich environment which are required for fast and complete iron ore reduction, most of the water and carbon dioxide are reacted with carbon to form hydrogen and carbon monoxide. The process is a continuous operation.

[0081] The produced DRI also function as a catalyst to promote the transformation of methane into hydrogen and carbon monoxide. The off-gases eventually reach a steady composition, a mixture of volatiles and iron ore reduction spent gas. Due to no oxygen or air required for combustion as in a ordinary gasifier or a combustion furnace, the off-gas composition can be readily controlled and a high quality syngas can be produced and collected.

[0082] The coal volatile content and the equilibrium phase diagram or iron oxides, iron, CO, and CO2 vs. temperature can be used as references for controlling the off-gas composition. The exhaust port 166 can be located either near the feed material charging port or the product discharging port to form a countercurrent or concurrent flow. The countercurrent flow transfers gas heat better to the feed material and the concurrent flow generates a higher quality syngas.

[0083] After DRI is formed, the feed material becomes a poor microwave absorber due to formation of networked metallic iron. Therefore, the underling carbon layer or coating, preferably made of pyrolyzed carbon particles such as coke, graphite, activated carbon, or fly ash carbon in dry or slurry form, is layered or applied before charging iron ore agglomerates into the furnace by the dispenser 156. The carbon layer 155 or coating becomes the major microwave receptor/susceptor to be heated by microwave and to transfer heat to the above disposed DRI in the smelting zone.

[0084] The smelting zone 170 is separated from the reduction zone by refractory dividers 152 to reduce interference between the two zones. As an alternative, such carbon microwave receptor material can be applied over the agglomerates/DRI at an appropriate location. The carbon material is heated by microwave and transfers heat to the underneath agglomerates/DRI. A powdered poor microwave absorbing material also can be used to cover the agglomerates/DRI to reduce convection and radiation heat loss. The DRI's temperature continues to rise and the DRI reacts with the remaining internal carbon and the underlying or covering carbon to form molten iron nuggets and associated slag. The eutectic iron and carbon composition (4.26% C) helps to lower the melting point of the iron to 1154[deg.] C. The associated slag has a composition suitable for desulphurization and dephosphorization with lower melting point, lower viscosity, proper plasticity, and easy separation of iron nuggets from slag after cooling.

[0085] The remaining underlying carbon layer also functions as an isolator between the molten nuggets/slag and the refractory base to prevent erosion of the molten nuggets/slag to the refractory and facilitates discharging the produced nuggets/slag from the refractory base. If necessary, another refractory coating made of oxides, borides, carbides and/or nitrides can be applied between the carbon layer and the refractory base.

[0086] The produced iron nuggets can be used as a feed material for steelmaking by EAF or a feed material for ferrous foundries.

[0087] Because of no major combustion heating, the off-gas is of lower temperature and contains less particulate. The off-gas is passed through a cleaning system 164 to further cool down, remove and collect particulates in a container 172, recover and collect sulfur in a container 172, and separate H2O and CO2 if any and necessary, becoming a syngas. Because of no steam and combustion requirements, the syngas production has fewer problems of H2O separation and NOx formation. The syngas can be used as a fuel for ordinary heating, a raw material for production of chemicals and liquid fuels, a hydrogen source after separation, a fuel to drive a power plant, or a reducing gas for iron ore reduction. Various heat exchangers can be installed along the line to utilize waste heat.

Inventor: HUANG XIAODI [US] ; HWANG JIANN-YANG

A method for the direct preparation of metal from metal-containing material comprising providing metal-containing material and a reducing agent, mixing the metal-containing material with the reducing agent to form a mixture charging the mixure by an appropriate method except flowing a stream of small particles into a container, heating the mixture with minimal contamination by applying microwave energy to the mixture until molten metal is released from the metal-containing material, accumulating the molten metal by gravity at the bottom of the container, and discharging the metal from the container.

Background of the Invention

The present invention relates to a direct metal making method that utilizes microwave energy as the primary or secondary energy to reduce and melt metal-containing material, and separate molten metals from slag.

Description of the Related Art

Current processes for the extraction of metals from their respective ores are characterized by extensive energy consumption and by the release of environmentally undesirable by-products, including large quantities of fine particulate, SO2, CO2, and NO2.

Prior to the instant invention, steel making has been practiced using an indirect method whereby iron is first produced from ore or scrap metal. The iron so produced is then converted to steel. In a typical iron smelting process, iron ore is ground to 500 mesh to liberate iron oxides from other minerals. The resultant material then goes through a separation process such as magnetic separation and/or froth flotation to concentrate iron oxides. The resulting fine particles are normally pelletized with limestone and bentonite.

The pellets are sintered to make them strong, and charged, along with coke, into a furnace in which the raw materials are subjected to a blast of very hot air. In the furnace, the iron oxide is reduced and melted. During the melting, the iron picks up carbon and sulfur from the coke charged into the furnace with the pellets.

The carbon content of the iron must be reduced to make steel. This is commonly done in a basic oxygen furnace (BOF). Pure oxygen is blown, at supersonic velocity, into a molten mass, including liquid iron, contained in a bottle-shaped furnace. The oxygen reacts with the carbon in the molten iron to form CO and CO2. Sulphur, which is harmful to most steels, is removed by injecting a powdered material into the molten steel to form sulfides, which are collected as slag from the top of the molten mass.

This production route is very energy and material inefficient and causes serious environmental problems. Iron ore pelletizing and sintering are necessary to provide the required permeability for blast air and strength to support the heavy load in a blast furnace. The whole process is very dusty and noisy which poses health and environmental problems for workers and others in the area. Coke must be used to generate a temperature high enough for melting iron. Adding coke to the mixture, however, causes the introduction of carbon and sulfur into the iron. These elements must then be removed in subsequent processing. Also, the production of coke is an environmentally unfriendly process, and recently a shortage of coke has been a serious problem as well.

The production of other metals such as copper, nickel, lead, zinc and ferroalloys present similar problems. SO2 emission is an additional problem for ores containing sulfur.

Various methods have been used to supply the heat necessary to melt the metal and the material in which it is borne so that they may be separated. These included the burning of fossil fuels such as coal, coke, and oil, and the use of electric heaters.

Electric induction heating has been particularly useful because it introduces no additional contaminants into the metal being melted and produces no local emissions. One drawback of induction heating, however, is that it relies on the conduction of eddy currents within the material being heated. Induction heating is impossible if the material is not an electric conductor such as a metallic ore. Typically induction heating is only used where scrap metal is available in the initial charge to the furnace.

Electric arc heating is a popular method to produce metals from scraps.

Similar to the drawback of induction heating, the material to be heated must be an electric conductor. Metallic ores can't be heated directly by electric arc.

Microwave heating, as disclosed herewithin, transmits energy to non-electric conducting materials or small agglomerations of metallic material more efficiently than induction heating or electric arc heating. It thus provides an alternative to the burning of fossil fuel, and can do the initial heating that makes later use of induction heating or electric arc heating feasible.

Various processes have been developed utilizing microwave energy in the purification of metallic compounds. U. S. Patent No. 4,321,089 discloses a process for the recovery of molybdenum and rhenium from their sulfide ores. In the disclosed process, the sulfide ores are subjected to microwave energy in the presence of oxygen or chlorine to form chlorides respectively. In neither case is the metal reduced. These oxides or chloride intermediates are then subjected to additional processing under reducing conditions to produce metal. Both of these processes differ from the direct reduction processing disclosed herewithin, inasmuch as the microwave processing results only in an oxidized intermediate.

U. S. Patent No. 4,324,582 (the'582 patent), also to Kruesi et al., also discloses a process applying microwave energy to copper compounds to convert the compounds into other compounds, such as oxides and chlorides, from which copper is more readily recoverable. The claims of the'582 patent are restricted in scope to using microwave energy"to convert the sulfidic and oxidic compounds in the ores to compounds from which copper is more readily recoverable."

The specification of the'582 patent specifically teaches away from the ferrous metal processing disclosed herein, asserting that"the oxides of iron and chromium, which are transition metals, do not absorb microwaves,"and"the gangue of the ore does not appreciably absorb microwave radiation.

In contrast to the application of microwaves to the preparation of an intermediate material as disclosed above, the process of the present invention results in the direct preparation of a purified metal by the chemical reduction of oxide, sulfide, and other ores, and metal sources through the application of microwaves and appropriate reducing agents in combination with induction heating or electric arc heating.

U. S. Patent No. 5,131,941 to Lemelson issued July 21,1992, discloses a process for refining metal from ore, including flowing a stream of small particles of ore to a reaction zone.

It is thus clear that the above-mentioned examples from the prior art do not possess the novel attributes of the present invention, namely the clean direct production of metals and efficient use of materials for the metal industry. This invention presents a revolutionary method to produce metals directly from ores by utilizing microwave energy as the primary heating source. This process is dramatically different from any of the current metal making techniques. The foreseeable advantages of this new metal making method over the traditional metal making methods include reductions in energy consumption and combustion emissions, the elimination, or reduction, of coke with its related environment problems, lower capital investment, and lower production cost, and minimal contamination of the metal product.

Brief Summary of the Invention

The invention described herewithin includes a method for the direct preparation of metal from metal-containing material, such as metallic ore or scrap metal. To practice the invention one provides a metal-containing material and a reducing agent and mixes these either prior to or after introducing them into a container. The container should be of appropriate material to serve as, or use within, a microwave cavity, and should be able to tolerate high temperatures without substantial degradation, and could be able to apply induction or electric arc heating. Once the mixture of metal-containing material and reducing agent have been charged into the container in the form of pellets, cakes or other appropriate forms except flowing a stream of small particles, scattered microwaves are generated using a microwave source and applied to the contents of the container. It is preferable that the frequency of microwaves used selectively heats the metallic ores or metals of the metalcontaining material. The application of microwaves to the metal-containing material continues until the reducing agent breaks the bond between metal atom and other atoms in the metallic ore to release metal and the metal has absorbed enough energy to become molten.

Meanwhile, additional induction or electric arc energy could be directed into the system to assist heating after the mass of metal-containing material becomes an electric conductor, and allow time for the molten material to accumulate, under the action of gravity, at the bottom of the container.

Brief Description of the Several View of the Drawings

The invention is further described with reference to the several views of the drawings wherein, without limiting the scope of the claimed invention:

Figure 1A shows a vacuum pump;

Figure 1B shows a sulfur condenser;

Figure 1 C shows a crucible within a microwave cavity including valved inlet, valved outlet and a waveguide;

Figure 2 shows a high powered microwave furnace;

Figure 3 shows a further embodiment of a high powered microwave furnace, including apparatus for the introduction of metal containing materials and an induction coil;

Figure 4 shows another embodiment of a high powered microwave furnace, including apparatus for the introduction of metal containing materials and electric arc heating ; and

Figure 5 shows a furnace for continuous production, including a raw materials charging port, a separate molten metal discharge port, and a slag discharge port.

Detailed Description of the Invention

In the practice of the instant invention, ore is crushed, ground and concentrated by a separation process. The separation process can be a flotation, gravity, magnetic, electrostatic, or other physical separation processes. The concentrated fine particles of ore are mixed with a reducing agent, an internal combustion auxiliary fuel, and a fluxing agent, in a certain ratio. It is preferable that the reducing agent, the internal combustion auxiliary fuel and the fluxing agent are introduced as powdered solids or pellets or cakes. Gases or liquids may also be used, however. The preferred reducing agents include materials containing carbon, hydrogen, hydrocarbons, Al, Si Mn, Mg, Ti, Cr Na, Li, Ca Y and Zr. The preferred internal combustion auxiliary fuels include coal, coke, carbon, wood, oil, and hydrocarbon wastes. The preferred fluxing agents include lime, limestone, CaF2, and Na2O. The preferred ratio is determined according to the composition of the concentrated ore, the reducing agent, the internal combustion auxiliary fuel, and the fluxing agent, as well as the desired percentage of energy provided by the internal combustion auxiliary fuel.

Generally the reducing agent, internal combustion auxiliary fuel and fluxing agent comprise 5-40%, 1-20%, and 1-15% by weight respectively of the contents of the container.

By-products or metal-containing wastes such as smelter dust, roll scale and plating sludge also can be used as the metal-containing material. Consequently, the metals in these by-products or wastes can be partially or entirely recovered through the use of this invention. The by-products or wastes should preferably be powders or agglomerates of powders. Metal scraps and other recyclable metals also can be added into the concentrated ores, by-products, or wastes.

In some cases a metal-containing material may be incapable of efficiently absorbing microwave radiation of an available frequency. In such cases a microwave absorber material may be blended with the ore or metal-containing material to increase its microwave absorption. The microwave absorber material can be selected from the group of materials containing anthracite, argentite, arsenopyrite, bismuth, bonite, braunite, chalcocite, chalcopyrite, chrysotile, cobaltite, covellite, enargite, galena, graphite, hematite, ilmenite, magnetite, manganite, marcasite, molybdenite, proustite, pyrargyrite, pyrite, pyrolusite, pyrrhotite, smaltite, tetrahedrite, zincite, and hydrocarbon. The microwave absorber materials are used in powder form or in a solution of 0.1-20% concentration. As an alternative, the metal-containing material may be preheated by a gas, oil, coal or electric furnace to a critical temperature, over which the metal-containing material becomes a good microwave absorber. The metal-containing material is then charged into a microwave furnace to continue metal making.

As shown in Figure 1C, after mixing, the raw material 101 is charged into a crucible 102 in the form of pellets, cakes or other appropriate forms except flowing a stream of small particles. It is preferred to use a crucible made of a material which absorbs relatively less microwave energy than the mixed raw material does. The crucible also should have a softening temperature higher than the melting point of the mixed raw material. Appropriate crucible materials include fireclay, mullite, Si02, Al203, SiC, MgO, zircon, and chromite.

After charging, the crucible is moved into a special high power microwave furnace 103 with a single mode or multi-mode cavity 103A. Scattered microwaves 104 are introduced into the cavity through a waveguide 105. The high power microwave furnace can deliver intensive microwave energy in a small space. For example, the microwave power can reach over lOW/cm3. The microwave frequency is 0.915 Ghz, 2.45 Ghz, or other frequency, or continuously adjustable. An inlet 106 and an outlet 107 with valves may be constructed on the microwave cavity to introduce a gas and to release exhaust gas for controlling the atmosphere of the microwave cavity.

To produce a metal, microwave power is turned on and the mixed raw material starts to absorb microwave energy and increase in temperature. The ore reacts directly or indirectly with the reducing agent to become a metal. In the case of indirect reaction, the reducing agent reacts first with air to form a reducing gas. The ore subsequently reacts with the reducing gas to form a metal. Alternately, the ore decomposes first to form a compound and the compound thus formed reacts with the reducing agent to form a metal.

When the mixture within the crucible reaches an appropriate temperature, the internal combustion auxiliary fuel ignites to generate heat 108 and to further increase temperature. The ore starts to melt and form molten metal droplets 109 and a molten slag 110. Due to the specific density differences between the metal and the slag, the molten metal droplets descend by gravity and form a molten pool 111 at the bottom of the crucible and the slag 110 floats on the top of the molten metal. The fluxing agent melts and reacts with the slag to reduce the viscosity of the slag. The result is better separation of the molten metal and the molten slag.

After molten metal forms, the slag and the crucible material continue to absorb microwave energy and maintain an elevated temperature. After the separation of the molten metal and slag, the microwave generator is turned off, and the crucible is moved out of the microwave furnace and allowed to cool. This cooling results in the formation of a solid metal ingot. The solidified slag is broken from the ingot using a mechanical impact. Alternately, the slag may be stripped off while still molten after the crucible is moved out the microwave furnace. The molten metal can then be poured into molds to solidify and form ingots.

If the ore contains a great amount of sulphur such as Cu2S, N2S3, PbS and ZnS, a sulphur condenser 112 or an SO2 scrubber should be connected to the outlet 107 of the furnace to condense the sulphur vapor and capture SO2 released from the mixture during heating.

Some ores are poor microwave absorbers at ambient temperature but absorb microwaves much more efficiently at higher temperatures. To process these materials, the mixture of ore, reducing agent and fluxing agent may be preheated in a conventional electrical, gas or oil furnace to a certain temperature and then transferred into the microwave furnace, where the reduction and melting process are continued under the influence of applied microwave energy.

The use of a gaseous reducing agent may be efficacious in some circumstances. In such a case a reducing gas may be continuously introduced into the cavity of the microwave furnace during microwave heating. The reducing gas reacts with the metalcontaining material therein to good effect. CO, H2 and hydrocarbon gases can be used as the reducing gas. If a reducing agent contains carbon, COZ emission, HZ or a hydrogen based reducing agent such as ammonia is preferred.

Some ores can be reduced under vacuum at high temperature without a reducing agent. In such circumstances no reducing agent need be used and the general consequence is the elimination of unwanted C02 emissions. The ore and fluxing agent are blended together and pelletized. The pellets are charged into a crucible and placed into the cavity 103A as shown in Figure 1C. A vacuum pump 113 is connected with the outlet 107 and inlet 106 is closed. The pump evacuates the cavity 103A to less than about 200 um.

Microwave energy heats the pellets under vacuum and the pellets reduce and melt to form molten metal and slag. A quartz window 114 is installed to hermetically seal the waveguide 105 but permit passage of microwaves 104.

In an alternative method, as shown in Figure 2, a high power microwave furnace can be constructed with a water cooled metal vessel 201 and a removable water cooled metal cover 202. Both the vessel and the cover are lined with a refractory material 203. An inlet 205 and an outlet 204 may be included in the cover 202. Gases may be introduced through the inlet 205 and exhaust gases may be released via the outlet 204, thus controlling the atmosphere within the furnace. To produce a metal, the cover 202 is moved away and the mixed raw material containing ore and reducing agent in the form of pellets, cakes, or other appropriate forms except flowing a stream of small particle, is charged into the microwave cavity 206. The cover 202 is then moved back to close the vessel.

Microwave is introduced through the waveguide port 207 into the cavity 206 and scattered in the entire cavity. Thereafter the mixed raw materials starts to absorb the microwave energy and increase in temperature. When the temperature is high enough, any auxiliary fuel introduced with the mixed raw material ignites to generate more heat 208 and further increase the temperature within the vessel. The reducing agent by direct contact with ore breaks the bond between metal atom and other atoms in the ore. The ore starts to melt and form molten metal droplets 209 and a molten slag 210. Due to the specific density differences, the molten metal droplets descend to form a molten pool 211 at the bottom of the vessel and the slag 210 floats on the top of the molten metal. The fluxing agent melts and reacts with the slag to form a lower viscosity slag for better separation of the molten meal and the molten slag. The slag are the refractory material continue to absorb microwave energy and maintain an elevated temperature while metal and slag separate. After the separation of the molten metal and slag, the microwave generator is turned off, and the molten mass is allowed to cool. This cooling results in the formation of a solid metal ingot and slag. The solidified slag is broken from the ingot using a mechanical impact. Alternately, the molten slag may be stripped off after the microwave power is turned off. The cover 202 is moved away. The vessel is tilted to pour the molten slag through a discharging port 212 into a slag container. Subsequently, the molten metal is poured into molds to form ingots, or into a caster to produce a continuous cast. The molten metal also can be poured into a ladle and transferred into another smelter for refining.

As another alternative method, a furnace with both microwave heating and induction heating capabilities can be constructed as shown in Figure 3. The furnace comprises a water cooled metal vessel 301 and a removable water cooled metal cover 302, both lined with a refractory material 303. The refractory material may be selected from materials having poor microwave absorption characteristics, such as quartz. A portion of the metal vessel 301 is a coil made of copper tubing which serves as an induction coil 304. The apparatus is arranged to allow the flow of cold water inside the tubing to cool the coil. The gaps between the turns of the coil are small to prevent microwave leakage. The metal vessel 301, the cover 302, and the induction coil 304 form the microwave cavity 305. An inlet 306 and an outlet 307 may be included in the cover 302 to allow introduction of process gases and the release of exhaust gases. Thus, the atmosphere within the furnace may be controlled.

To produce a metal, the cover 302 is moved away and a mixture 307A of metal-containing material, reducing agent, and other process-enhancing chemicals as appropriate to the particular circumstances, is charged into the cavity 305 in the forms of pellets, cakes or other appropriate forms except flowing stream of small particles. The cover 302 is then moved back to close the vessel. Microwave energy is introduced through the waveguide 308 and the mixture 307A of raw materials starts to absorb the microwaves, with a resulting increase in temperature. The ore reacts with the reducing agent in the mixture, or with the reducing gas introduced via the inlet 306, to release a metal. Once metal begins to appear and the mass of raw material becomes electrically conductive, the induction heating power is turned on. Current flows through the induction coil 304 and the metal is further heated by the action of induced current. This additional heat input further raises the temperature of the mixture within the vessel. As the temperature rises, droplets of molten metal 309 accumulate and a molten slag 310 forms. Due to the difference in specific density between the molten metal and slag, the molten metal droplets descend to the bottom by gravity and form a molten pool 311 and the slag 310 floats to the top of the molten metal.

The fluxing agent, which melts along with the rest of the mixture, lowers the viscosity of the slag and thus allows between separation of the molten metal and molten slag. The slag continues to absorb microwave energy and the molten metal continues to be heated by the induction current. After a short period of time for molten metal and slag to separate, the microwave and the induction heating powers are turned off. The vessel is tilted to pour the molten slag through a discharging port 312 into a slag container. The vessel is then tilted further to pour the molten metal into molds to form ingots, or into a caster to produce continuous casting. The molten metal also can be poured into a ladle and transferred into another smelter for refining.

It is also possible to use the instant furnace for refining. After the slag is poured into a slag container, the vessel is restored to the upright position, and the cover 302 is replaced. The induction heating power is turned on again. Powdered materials such as CaO and NaC03 may be blown into the cavity 305 through a hole 313 at the bottom of the vessel 301, or a movable pipe 314 which can be immersed into the molten metal to remove S and P.

Scrap metals and alloys can be added into the molten metal to adjust the composition to meet particular specifications. During this portion of the process, induction heating is used to control the temperature.

As another alternative method, a furnace with both microwave heating and electric arc heating capabilities can be constructed as shown in Figure 4. The furnace comprises a water cooled vessel 401 and a removable water cooled metal cover 402, both lined with a refractory material 403. Three graphite electrodes of greater than 50 mm in diameter are introduced through the metal cover 402 into the furnace chamber 404. A port 405 is opened on the cover 402 to introduce microwave 406 into the chamber 404 through a connecting waveguide 407.

To produce a metal, the cover 402 is moved, away and a mixture 408 of metalcontaining material, reducing agent, and other process-enhancing chemicals as appropriate to the particular circumstances, is charged into the cavity 404. The cover 402 is then moved back to close the vessel. Microwave energy is introduced through the waveguide 407 and the mixture 408 of raw materials starts to absorb the microwaves, with a resulting increase in temperature. When the temperature is high enough, any auxiliary fuel introduced with the mixed raw material ignites to generate more heat 408 and further increase the temperature within the vessel. At an elevated temperature, the ore starts to react with the reducing agent in the mixture to become a directly reduced metal. Once metal begins to appear and the mass of raw material becomes electrically conductive, the powered electrodes 410 descend to form electric arcs between the electrode tip-s and the metal, and the metal is further heated by the action of arcing. This additional heat input further raises the temperature of the mixture within the vessel. As the temperature rises, droplets of molten metal 411 accumulate and a molten slag 412 forms. Due to the difference in specific density between the molten metal and slag, the molten metal droplets descend to the bottom by gravity and form a molten pool 413 and slag 412 floats to the top of the molten metal. The fluxing agent, which melts along with the rest of the mixture, lowers the viscosity of the slag and thus allows better separation of the molten meal and molten slag. After a short period of time for molten metal and slag to separate, the microwave and the electric arc powers are turned off. The vessel is tilted to pour the molten slag through a discharging port 414 into a slag container. The vessel is then tilted further to pour the molten metal into molds to form ingots, or into a caster to produce continuous casting. The molten metal also can be poured into a ladle and transferred into another smelter as refining.

As an alternative method aiming at continuous production, a continuous microwave/induction heating furnace can be constructed as shown in Figure 5. It mainly comprises a water cooled metal shell 501, a water cooled induction heating coil 502, a raw materials charging port 503, a waveguide port 504, a slag discharge port 505 and a molten metal discharge port 506. The metal shell 501 and the induction coil 502 are lined with a refractory material 507 that absorbs microwaves poorly. To start the process, the mixed raw material 508 in the form of pellets, cakes or other appropriate forms except flowing a stream of small particles is charged through the charging port 503 into the furnace. The microwave power is turned on and microwave is introduced through the waveguide 504 into the furnace chamber 509 and scattered in the chamber. The mixed raw material starts to absorb microwave energy and increase in temperature. As the temperature rises, the internal combustion auxiliary fuel ignites to generator heat 510 and further increase temperature. The ore reacts directly or indirectly with the reducing agent in the raw material to become a metal.

After the mass of raw material becomes electrically conductive, the induction heating power is turned on to heat the metal. The metal starts to melt and form molten metal droplets 511 and a molten slag 512. Due to specific density differences, the molten metal droplets descend to the bottom by gravity and form a molten pool 513, and the slag 512 floats on the top of the molten metal. The fluxing agent also melts and reacts with the slag to form a lower viscosity slag for better separation of the molten metal and the molten slag. After the molten metal forms and sinks to the bottom, the induction heating power continues to heat and maintain the temperature of the molten metal. The slag continues to absorb microwave energy. After accumulating enough molten slag or molten metal, the slag and metal are separately discharged through discharge holes 505 and 506 respectively. Holes 505 and 506 were blocked with fireclay before they were broken using a steel rod. The molten metal can be cast into ingots or a continuous casting, or transferred into a refining furnace to remove impurities, adjust composition, and control temperature to produce high quality alloys. As the molten slag and metal are discharged, more raw material is charged into the furnace through the charging port 503. The heating, ore reduction, melting, discharging and recharging continue to cycle.

Example 1. A sample was prepared comprising an iron ore concentrate containing 65% Fe mixed with 15% carbon black as the reducing agent, 1% lime as the fluxing agent, and 5% pulverized coal as an auxiliary fuel. The mixture was charged into a fireclay crucible and inserted into a microwave processing system MCR 200, which was manufactured by Wavemat, Inc. This unit includes a 2.45 Ghz microwave generator with 300 to 3,000 watts of power. This microwave system can be operated with a tunable, single mode or controlled multi-mode microwave cavity. The cavity can be evacuated or continuously purged with an inert gas or a reducing gas. The sample was heated to 1200 C in ten minutes using a single mode with 1 kw power. The temperature was measured using a pyrometer on the outer surface of the crucible. The crucible inside temperature was not measured but it is believed to have been higher than 1200 C. The pulverized coal burned and flame appeared during the heating. The sample temperature was maintained at about 1200 C for two minutes and then the power was shut off. The examination of this sample after is cooled to room temperature showed that metal and slag formed. The metal accumulated at the bottom and the slag at the top of the crucible. Chemical composition analyses shows that the metal contained 1.53% Si, 97.72% Fe, 0., 42% Al, 0.13% S, and 0.2% C and the slag contained 53.58% SiO2, 15.48%, FeO, 0,48% CaO, 1.56% MgO, 15.40% A1203, 0.53% K2O, 0.39% MnO, and 12.59% TiO2.

Example 2. A sample was prepared comprising Cu2S powder mixed with a stoichiometric amount of carbon black, i. e., 7.5% as a reducing agent. The mixture was charged into a fireclay crucible covered with a fireclay disk and placed into the microwave processing system MCR 200. The microwave cavity was continuously purged with N2 and the exhaust port of the cavity was connected to a scrubber. The scrubber consisted of a glass flask with a side tube and a rubber stopper to seal its mouth. The flask was half filled with an alkaline 10% NaOH solution. A tube passed through the rubber stopper and one end of the tube was submerged in the alkaline solution. The other end of the tube was connected to the exhaust port of the microwave cavity with a hose. During heating, a lot of smoke came out of the sample and was introduced into the NaOH solution. The sample was heated to 1100 C in 5 minutes using a single mode. The temperature was measured using a pyrometer on the outer surface of the crucible. The temperature was maintained at about 1100 C for two minutes and the power was then turned off. It was found that copper accumulated the bottom and a slag formed on the top of the crucible. An analysis indicted that the scrubber solution contained sulphur.