DIRECT PROCESSING OF METALLIC ORE CONCENTRATES INTO FERROALLOYS

Abstract

A method for producing liquid ferroalloy by direct processing of manganese and chromium bearing iron compounds, by the steps: of mixing carbonaceous reductant, fluxing agent, and a binder with materials such as iron sands, metallic oxides, manganese-iron ore concentrates and/or chromium-iron ore concentrates and silica sands, to form a mixture; forming agglomerates from the mixture; feeding the agglomerates to a melting furnace with other materials; melting the feed materials at a temperature of from 1500 to 1760 C and forming a slag and hot metal; removing the slag; and tapping the hot metal as liquid ferroalloy.

Description

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for direct processing of manganese, chromite and silica bearing compounds (Mn—Fe and Cr—Fe ores, and silica) to produce a liquid ferroalloy and iron, employing the concept of combined cycle power generation using a gas combustion turbine.

SUMMARY OF THE INVENTION

Mn—Fe ores, Cr—Fe ores, and silica are cold briquetted to form compact agglomerates containing a carbonaceous material such as coal, petcoke, char, etc., iron oxide (either already contained in the ore or added separately as iron ore fines, mill scale, metalized iron fines, etc., to the mix), fluxes such as lime, silica, spar, etc., and binder. An excess amount of carbon is present in the agglomerate not only to react with the manganese, chromium, and silica compounds, but also to reduce the iron oxide, manganese oxide, etc., so that the atmosphere within the melter is predominantly CO with some liberated H₂ from the volatilization of the carbonaceous material such as coal. Sulfur in the system is free to combine with the flux additions (CaO, CaF₂, MgO, etc.), to form a sulfur-containing liquid slag.

OBJECTS OF THE INVENTION

The principal object of the present invention is to provide a method of producing silicamanganese, ferromanganese or ferrosilicon ferroalloy from ordinary ore materials.

Another object of the invention is to provide a method of recovering manganese, chromium, vanadium, and titanium as oxides from ores.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects will become more readily apparent by referring to the following detailed description and the appended drawings in which:

FIG. 1 is a schematic flowsheet of the process, wherein the reference numerals refer to the items as indicated below.

FIG. 2 is a schematic flowsheet for handling of off-gases.

FIG. 3 is a schematic flowsheet for treating hot metal to form vanadium and titanium oxides.

FIG. 4 is a schematic depiction of recovering hot metal in pig form.

FIG. 5 is a schematic depiction of slag treatment to recover vanadium and titanium oxides or to recover concentrated slag for recycle.

FIG. 6 is a schematic flowsheet showing an alternative method for producing a liquid ferroalloy in which the feed materials are preheated with or without agglomeration, and then fed to the melting furnace.

In the figures, reference numerals refer to:

• 10—Mn—Fe, Cr—Fe, SiO2, or concentrates—100% passing 10 mesh Tyler Standard (1.70 mm), preferably 100% passing 100 mesh Tyler Standard (150 microns)
• 12—metallic iron fines, and iron oxide fines—100% minus 25 mm, preferably 100% passing 10 mesh
• 14—prepared reductant, such as coal, petroleum coke, char, etc., 100% passing 25 mm, preferably 100% passing 100 mesh Tyler Standard (150 microns)
• 16—fluxing agents—CaO, MgO, CaF₂, SiO₂, Al₂O₃, etc—100% minus 25 mm
• 18—binder such as cellulose, bentonite, molasses, starch—either organic or inorganic
• 20—recycled fines
• 22—mixer
• 24—briquetter/agglomerator (size 8 to 100 cc)
• 26—water addition (spray)
• 28—pelletizer—drum or disc type
• 30—screens—dry or roller type
• 32—greenball dryer (dries pellets to 1% moisture or less)
• 34—agglomerate (briquette) curing/storage hoppers, or preheaters
• 36—feed loss in weight system
• 38—electric melter, operating temperature >1500 C
• 40—ladles A and B for liquid ferroalloy
• 42—slag addition for desulfurization
• 44—pig iron caster
• 46—slag ladle (C)
• 48—slag disposal/quench bunker
• 50—recycle slag
• 52—offgas cooling scrubber/bag filter
• 54—fan
• 56—stack with combustion to convert CO & H₂ to CO₂ & H₂O
• 58—high pressure compressor (100-350 psig)
• 60—optional gas stream, sulfur removal system, such as Selexol
• 62—high pressure gas accumulator tank
• 64—gas turbine (exit gas temp 600-700 C)
• 66—generator
• 68—waste heat boiler exchanger
• 70—high pressure steam turbine
• 72—generator
• 74—boiler closed circuit water conduit
• 76—pump
• 78—optional chiller upstream of gas sulfur removal system
• 80—pressure sealed chamber
• 82—quenching and grinding and electrostatic separation
• 84—heater, direct or indirect rotary kiln type

DETAILED DESCRIPTION

As seen in FIG. 1, feed materials are introduced to mixer 22, the input materials consisting of: metallic iron fines, iron oxides, manganese-iron ore concentrates and/or chromium-iron ore concentrates 10, 100% passing 10 mesh Tyler Standard (1.70 mm), preferably 100% passing 100 mesh Tyler Standard (150 microns); prepared reductant 14, such as coal, petroleum coke, char, or other carbonaceous material, 100% passing 25 mm, preferably 100% passing 100 mesh Tyler Standard (150 microns); slag formers or fluxing agents 16, such as MgO, CaO, Al₂O₃, CaF₂ (fluorspar) and SiO₂, 100% of which are minus 25 mm; an organic or inorganic binder 18, such as cellulose, bentonite, molasses, or starch; recycled fines 20, and water 26 as needed.

These materials are mixed in mixer 22, then formed into agglomerates in briquetter/agglomerator 24, or in pelletizer 28 (such as a drum or disc type pelletizer), the agglomerates being in the form of uniformly sized briquettes or pellets. The agglomerates are screened by sizer 30, the undersized material being returned to the agglomerator 24 or to the pelletizer 28.

Alternatively, material D1 exiting mixer 22 can be fed to a heater 84 for the purpose of preheating the mixture to about 500 to 120° C., devolatizing the reductant, and producing a preheated charge to electric furnace melter 38. Pre-reduction of the iron oxide will occur to levels ranging from about 0 to 90%. Agglomerated material D2 can also be preheated, if desired, prior to feeding the material to the melter through the pressure seal 37. The heater 84 can be an indirectly heated rotary kiln, or a direct fired kiln, as shown, with off-gases being recycled. The heater 84 can be refractory lined, or it can be unlined, as desired.

Screened pellets from pelletizer 28 are dried in a greenball dryer 32 to 1% or less moisture content. The agglomerates are cured and/or stored in hoppers 34, then fed into an electric melter, or melting furnace 38 through a pressure-sealed feed system 36. Feed to the melter is through a pressure-sealed chamber 80, a conventional feed leg as is used with a shaft furnace, or through lock valves. The melter off-gas is treated, cooled and scrubbed in cooler-scrubber 52, compressed in compressor 54 and delivered to stack 56 which includes combustion means for converting carbon monoxide and hydrogen to carbon dioxide and water vapor. The melter 38 operates normally under a slight positive pressure. Tapping of the hot metal and slag is done on an intermittent basis.

Optionally one or more additional feed materials may be introduced through a pressure seal to the melter 38, including metallic iron fines and iron oxide fines 12, 100% of which are minus 25 mm; prepared reductant 14, such as coal, petroleum coke, char, or other carbonaceous material, 100% passing 25 mm, preferably 50% passing 10 mesh; slag formers or fluxing agents 16, such as MgO, CaO, Al₂O₃, CaF₂ (fluorspar) and SiO₂, 100% of which are minus 25 mm; and recycled slag 50. The feed materials are melted in the melting furnace 38 at a temperature of from 1500 to 1760 C to form a liquid ferroalloy with a slag thereon;

Liquid ferroalloy is removed from the melter into ladles 40 and may be cast into ferroalloy pigs at pig caster 44, as shown. Additional fluxing agents 14 may be added to the hot ferroalloy as it is discharged into ladles 40 (A and B). A desulfurizing slag addition 42 is introduced into a hot metal ladle shown as B, the addition being CaO, MgO, Ca/Mg wire, or a mixture thereof. The hot metal from either ladle A or B can be cast into pigs.

The slag from ladle C may contain unreduced oxidized species of Mn, Cr, V and Ti due to partitioning effects between the liquid ferroalloy and slag. The slag can then be treated as shown in FIG. 5 by a quenching and grinding and electrostatic separation 82 to recover MnO, Cr₂O₅, V₂O₅ and TiO₂. This concentrated slag 50 may then be recycled to the melter, if desired, in order to increase the desired material concentration of slag, and improve the efficiency of recovery.

Recovery of oxidized species, MnO, Cr₂O₅, V₂O₅ and TiO₂, from the concentrated slag can also be obtained by solvent extraction techniques.

The operating parameters of the invented process are as follows:

	Normal Range	Maximum
	Ferroalloy	1500-1600 C.	1700-1760 C.
	Melter Temp.
	Melter Off-Gas	500-1500 C.	1200-1650 C.
	Melter Off-Gas	0-0.2″ H2O gauge	<15″ H2O gauge
	Pressure
	Gas Accumulator	100-350 psig
	Off-Gas Pressure
	Gas Turbine	750-900 C.	<1000 C.
	Combined Product
	Exit Temp.

Off-gas exiting the melting furnace 36 is cleaned in cooler-scrubber 52. Optionally, the off-gas may be moved by fan 54 through high pressure compressor 58, which operates in the range of about 100 to 350 psig, and the cleaned, compressed off-gas is used as combustion fuel in gas turbine 64, or used for preheating agglomerates in hopper/preheaters 34 prior to their introduction to the electric melting furnace 36. Gas turbine 64 drives generator 66 to produce electricity, and sensible heat contained in offgas exiting the gas turbine is recovered in a waste heat recovery boiler system 68. The waste heat boiler system 68 steam cycle could be a “Kalina” cycle based on using 70% ammonia and 30% water for better range processing and heat recovery efficiency at lower gas temperatures. Ammonia/water boiling occurs over a range of temperatures rather that at a specific temperature and pressure. Steam produced by the waste heat boiler system 68 is then used to drive a steam turbine 70 and associated generator 72 to produce additional electricity. A secondary objective of the invention is to supplement or produce all the required electricity to accommodate the process and operate the plant so as to be electricity self sufficient. If sufficient fuel gas is not produced by the melter, then additional fuel gas, such as natural gas, can be used to supplement the fuel gas feed to the gas turbine.

Gas from the compressor 54 can be treated for sulfur removal in an optional sulfur removal system 60, which may require an optional chiller 78 upstream of the sulfur gas removal system.

The agglomerate curing or storage hoppers 34 can be preheaters, such as a shaft or vessel preheater, as desired. When used as preheaters, off-gas from the electric furnace or melter 38 can be utilized as shown in FIG. 1. The off-gas is returned to the gas handling system at cooler-scrubber 52.

SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION

From the foregoing, it is readily apparent that I have invented an improved method of producing liquid ferroalloy (ferrosilicon, ferromanganese, and silicomanganese) from ordinary ore materials, as well as a method of recovering metallic oxides contained in the slag, such as manganese oxide, chromium oxide, vanadium oxide and titanium oxide.

It is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof, and that various modifications and additions may be made to the apparatus by those skilled in the art, without departing from the spirit and scope of this invention.

Claims

1. A method for producing liquid ferroalloy by direct processing of manganese and chromium bearing compounds (Mn—Fe and Cr—Fe ores), comprising the steps of: (a) mixing: i. materials selected from the group comprising: iron sands, metallic oxides, manganese-iron ore concentrates and/or chromium-iron ore concentrates, silica sands, and mixtures thereof;ii. carbonaceous reductant;iii. fluxing agent; andiv. a binder to form a mixture;(b) forming agglomerates from said mixture(c) introducing said agglomerates to a melting furnace;(d) maintaining a positive pressure within the melting furnace:(e) melting the feed materials at a temperature of from 1500 to 1760 C and forming a slag thereon;(f) removing the slag; and(g) tapping the hot metal as hot liquid ferroalloy.

2. A process according to claim 1, further comprising maintaining a reducing atmosphere within said melting furnace.

3. A process according to claim 1, further comprising preventing substantially all air ingress to the melting furnace by providing a pressure seal.

4. A process according to claim 1, further comprising preheating the mixture, the agglomerates, or both, prior to introducing them to the melting furnace.

5. A process according to claim 1, wherein: 100% of the iron sands, metallic oxides, manganese-iron ore concentrates and/or chromium-iron ore concentrates and silica sands pass 10 mesh Tyler Standard (1.70 mm);100% of the carbonaceous reductant is minus 25 mm; and100% of the fluxing agent is minus 25 mm.

6. A process according to claim 1 wherein the carbonaceous reductant is selected from the group comprising coal, coke, petroleum coke, and char.

7. A process according to claim 1, wherein the fluxing agent is selected from the group comprising CaO, MgO, CaF2, SiO2, Al2O3, and mixtures thereof.

8. A process according to claim 1, further comprising forming a liquid iron-iron sulfide mixture in the melting furnace; removing the liquid iron-iron sulfide mixture from the melting furnace, desulfurizing the iron, and solidifying the resulting iron for further use.

9. A process according to claim 1, further comprising forming off-gases in the melting furnace, cleaning and cooling the off-gases, and utilizing the cleaned off-gases as combustion fuel to drive a turbine and to generate electricity.

10. A process according to claim 9, further comprising producing off-gases in the turbine, recovering the off-gases from the turbine and recovering the sensible heat contained therein as steam in a waste heat boiler recovery system.

11. A process according to claim 10, further comprising utilizing the steam to drive a steam turbine and an associated generator to produce additional electricity, thereby accommodating substantially all the electrical requirements of the process.

12. A method for producing liquid ferroalloy by direct processing of manganese and chromium bearing compounds (Mn—Fe and Cr—Fe ores), comprising the steps of: (a) mixing: i. materials selected from the group comprising: iron sands, metallic oxides, manganese-iron ore concentrates and/or chromium-iron ore concentrates and silica sands;ii. carbonaceous reductant;iii. fluxing agent; andiv. a binder to form a mixture;(b) preheating at least a portion of said mixture in a heater to a temperature of 500 to 120° C.;(c) introducing said preheated mixture to a melting furnace;(d) melting the feed materials at a temperature of from 1500 to 1760 C and forming a slag thereon;(e) maintaining a positive pressure within the melting furnace:(f) removing the slag; and(g) tapping the hot metal as hot liquid ferroalloy.

13. A process according to claim 12 wherein: 100% of the iron sands, metallic oxides, manganese-iron ore concentrates and/or chromium-iron ore concentrates and silica sands pass 10 mesh Tyler Standard (1.70 mm);100% of the carbonaceous reductant is minus 25 mm; and100% of the fluxing agent is minus 25 mm.

14. A process according to claim 12, wherein the carbonaceous reductant is selected from the group comprising coal, coke, petroleum coke, and char.

15. A process according to claim 12, wherein the fluxing agent is selected from the group comprising CaO, MgO, CaF2, SiO2, Al2O3, and mixtures thereof.

16. A process according to claim 12, wherein the binder is selected from the group comprising cellulose, bentonite, molasses, starch or mixtures thereof.