Method and apparatus for producing metallic iron from iron oxide fines

Abstract

Method and apparatus for producing direct reduced iron (DRI) powder or molten iron from iron ore fines by mixing said iron ore fines with hydrogen and oxygen and igniting the mixture in a flame reactor with flame temperatures controlled to produce solid iron powder or molten iron.

Claims

1. A process for producing metallic iron from iron oxide fines, the process comprising: a) feeding iron oxide fines into the mixing chamber of an In-Flight reactor, b) creating an internal heat-generating gas comprising hydrogen and oxygen generated by the electrolysis of water in an electrolyzer, c) introducing a stream of an internal heat-generating gas into said mixing chamber, d) introducing a stream of a reducing gas into said mixing chamber, e) delivering the mixed iron oxide, reducing gas, and heat-generating gas into a reducing reaction flame through a burner nozzle, and f) forming hot metallic iron entrained in a hot exhaust gas.

2. The process according to claim 1 wherein said reducing gas and internal heat-generating gas are premixed prior to introduction into said mixing chamber.

3. The process according to claim 1 wherein the internal heat-generating gas is a stoichiometric mixture of oxygen and hydrogen produced in an electrolyzer.

4. The process according to claim 1 wherein the internal heat-generating gas may include a combination of oxygen and natural gas.

5. The process according to claim 1 wherein the internal heat-generating gas is a combination of oxygen and any carbon based fuel.

6. The process according to claim 1 wherein the reducing gas is hydrogen.

7. The process according to claim 1 wherein the reducing gas is natural gas.

8. The process according to claim 1 wherein the reducing gas is a combination of natural gas and hydrogen.

9. The process according to claim 1 wherein the reducing gas is a combination of any carbon based fuel and hydrogen.

10. The process according to claim 1 wherein the reducing gas is an industrial process exhaust gas with high reduction potential.

11. The process according to claim 1 wherein a fine solid biomass is entrained within the reducing gas.

12. The process according to claim 1 wherein the product is cooled to a temperature below the Curie point for iron and the solid iron product is recovered by magnetic separation.

13. The process according to claim 1 wherein the solid iron product is separated from the product gases by any conventional gas/solid separation equipment.

14. The process according to claim 1 wherein the product gases are fed into a condenser and the condensed water is recycled to the said electrolyzer.

15. The process according to claim 1 wherein the product gases are fed into a condenser and the hydrogen is recycled and combined with the feed hydrogen stream.

16. The process according to claim 1 wherein the flame temperature is controlled by the flow rate of the heat generating gas.

17. The process according to claim 1 wherein the temperature is controlled to a value below the melting point of iron to produce solid iron.

18. The process according to claim 1 wherein the temperature is controlled to a value above the melting point of iron to produce molten iron.

19. A process for producing metallic iron from iron oxide fines, the process comprising: a) feeding iron oxide fines into the mixing chamber of an In-Flight reactor, b) creating an internal heat-generating gas, c) introducing a stream of the internal heat-generating gas into said mixing chamber, d) introducing a stream of a reducing gas into said mixing chamber, e) delivering the mixed iron oxide, reducing gas, and heat-generating gas into a reducing reaction flame through a burner nozzle, and f) forming hot metallic iron entrained in a hot exhaust gas.

20. The process for producing metallic iron from iron oxide fines of claim 19 wherein the internal heat-generating gas comprises hydrogen and oxygen generated by the electrolysis of water in an electrolyzer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A detailed description of the invention is hereafter described with specific reference being made to the drawings in which:

(2) FIG. 1 is a schematic representation showing the basic functions of the In-Flight Reactor using hydrogen as the reducing gas,

(3) FIG. 2 is a schematic representation showing the basic functions of the In-Flight Reactor using natural gas as the reducing gas,

(4) FIG. 3 is a schematic diagram of a nozzle section and a multiple nozzle assembly with annular oxygen feed directly into the flame,

(5) FIG. 4 is a schematic diagram of the reaction column,

(6) FIG. 5 presents the basic In-Flight Reactor Configuration with Preheat and with hydrogen as the reducing gas,

(7) FIG. 6 shows three preheating options,

(8) FIG. 7 is a schematic representation of an electrolyzer,

(9) FIG. 8 shows an Open Circuit Flow Diagram and Mass Balance with hydrogen as the reducing gas,

(10) FIG. 9 is a Closed Circuit flow diagram and mass balance with preheat of Fe.sub.3O.sub.4 and hydrogen,

(11) FIG. 10 is a schematic representation of the flow of materials with recycle of hydrogen and oxygen,

(12) FIG. 11 shows the Flowsheet and Mass Balance for the IFDR components in an integrated IFDR/Pellet Plant installation, and

(13) FIG. 12 is a schematic representation showing granulation of molten iron.

DETAILED DESCRIPTION OF THE INVENTION

(14) The In-Flight reactor relies on conventional burner design. FIG. 1 is a schematic representation of an In-Flight reactor 11 with hydrogen as the reducing gas. Hydrogen 10, iron oxide fines 12 and oxygen 13 are fed into the pre-mx zone 14 prior to passage into the burner nozzle section 15 and then into the reaction flame 16.

(15) FIG. 2 is a schematic representation of an In-Flight reactor 11 with natural gas as the reducing gas. Natural gas 20, iron oxide fines 12 and heating gas 23 are fed into the pre-mix zone 14 prior to passage into the burner nozzle section 15 and then into the reaction flame 16. If desired the feed materials can be pre-mixed externally.

(16) The nozzle 30 can be a single large diameter nozzle or an assembly of several small diameter orifices as shown in FIG. 3. A cross section of a single annular nozzle 30 shows the annulus 32 for oxygen and the central feed tube 33 for the iron oxide/reducing gas mixture. A cross section of a multiple nozzle head 34 shows the iron oxide/reducing gas feed 36 into the multiple nozzle head and the oxygen feed 35 into the oxygen plenum 38. The multiple head nozzle shown in section in FIG. 3 has one central nozzle surrounded by six nozzles in a circle. If larger throughputs are needed, nozzles can be added in circles of increasing diameter.

(17) FIG. 4 shows a schematic representation of the reactor column assembly 42 with the In-Flight reactor 40 mounted at the top. The reducing flame 43 is created at the top of the reaction column 44 that has refractory insulation 45. The hot product gases and entrained iron 46 exit the bottom of the reaction column.

(18) If the process is operated at lower temperatures to produce a solid metallic iron product the solids are removed by high temperature gas filtration, by any other conventional solid/gas separation equipment or by magnetic separation if the solid iron product temperature is below the Curie point. The solid iron product is briquetted for transportation to steelmaking facilities as shown in FIG. 8.

(19) If the process is operated at a higher temperature and the iron product is molten then the molten iron is separated in a high temperature cyclone, or any other high temperature solid/liquid separation equipment and can be collected in a molten bath or fed directly into an electric arc furnace. If a granular product is required for transportation purposes, FIG. 12 shows a schematic representation of the high temperature cyclone 63 with plan view 65 showing the tangential feed 62. The separated gas stream 60, exits axially at the top. The cyclone is operated with a spray underflow discharge 68 into a cooling column 69 for solidification. Cooling gas 72 is introduced at the bottom of the cooling column with tangential inlet shown in the plan view 70 and discharges, also tangentially, at the top 66. The granulated iron 74 collects at the bottom of the cooling column for periodic discharge 76. Any other conventional granular metal process may be employed for producing the granular product.

(20) The speed of reaction is a function of particle size and the reduction reactions proceed faster as particle size decreases. Feed solids would be typically less than 3 mm but treatment of coarser feed solids may be practical if the reduction characteristics are favorable. Reaction times are typically of the order of 10 seconds or less.

(21) An open circuit mass balance is shown in FIG. 8, in which hydrogen is used both for reduction and for heat generation. For the production of 1000 kg of iron the hydrogen feed requirement is 224 kg and the temperature of the solid metallic iron product is 1044 C. Higher temperatures can be achieved, if desired, simply by increasing the hydrogen and oxygen heating gas input.

(22) Significant improvement in energy efficiency can be achieved by preheating the feed materials by heat exchange with the hot reactor products. FIG. 5 is a schematic diagram of a heat exchanger in which the iron oxide fines and hydrogen mix 50 are heated by the hot IFDR product 52 which then exits as cooled product 54. The preheated feed 55 enters the reactor 56 and combines with oxygen input 58 to generate the reducing flame 59.

(23) Preheat can be carried out preferably by entraining the iron oxide fines in the feed reduction gas stream and preheating the solids/gas mix. Alternatively the iron oxide fines and the reducing gas stream may be preheated independently, prior to mixing. The feed oxygen may also be preheated. Some preheat options are shown in FIG. 6.

(24) The hydrogen and oxygen are produced on site in an electrolyzer 70 represented diagrammatically in FIG. 7.

(25) The reaction flame is a hot reducing gas and the iron oxide is rapidly converted into metallic iron in a hot gas stream containing the excess reducing gas and steam.

(26) If hydrogen is the reducing gas the remaining gas, after removal of the metallic iron, contains only hydrogen and steam. This is fed into a condenser and liquid water is removed for recycling to the electrolyzer. The remaining hydrogen is recycled into the feed hydrogen stream. The hydrogen and oxygen produced by electrolysis are recycled to the IFDR unit. The final products are metallic iron and oxygen. FIG. 9 shows the flowsheet and mass balance for closed circuit operation with preheat and recycling of hydrogen and oxygen. Note that the hydrogen demand for the production of 1000 kg of iron has decreased from 224 H2 in the open circuit case shown in FIG. 8 to 182 H2, an 18% reduction. However this hydrogen is obtained from the condensed water by electrolysis and consequently there is no net consumption of hydrogen.

(27) FIG. 11 is a different representation of closed circuit operation focusing on the material flows. The feed hydrogen is divided into three components: H.sub.R for reduction, H.sub.E for excess and H.sub.H for heat generation. O.sub.R is the oxygen contained in the iron oxide and O.sub.H the oxygen required for generating heat. The four process units are A: IFDR, B: Solid Separation, C: Condensation and E: Electrolysis.

(28) If the IFDR plant is adjacent to a pellet or sinter plant, any excess oxygen can be used to produce enriched air for the pellet or sinter plant furnaces.

(29) If natural gas is used for the reducing gas the reactor products are metallic iron entrained in a hot gas stream containing carbon monoxide, carbon dioxide, hydrogen and steam plus a small quantity of residual methane. In most cases IFDR plants using natural gas as the reducing gas would be located next to a pellet or sinter plant where fine iron oxide feed materials are readily available. The hot combustible off gas can be used directly as a supplemental fuel for the pellet or sinter plant furnaces as illustrated in FIG. 11.

(30) In-Flight Iron (IFI) is produced in a combustion reactor fed by fine iron oxide, a reducing gas and an internal heat generating gas. Typical iron ore fines are predominantly either magnetite (Fe.sub.3O.sub.4) or hematite (Fe.sub.2O.sub.3). Other iron ore mineral fines or fine biomass, or industrial waste products with high enough iron content may be used as feed materials or combined with high-grade ores.

(31) The combined mixture of gas streams and entrained solids is ignited and forms a reducing flame. Depending on selected operating conditions, the metallic iron product can be either solid or liquid.

(32) The process can be operated at elevated pressures. However, the design pressure will vary depending on the balance between reduced capital costs and increased operating costs.

(33) The Following mass balances were obtained using the NASA CEARUN thermodynamic program. The IFDR product composition depends on a) the proportion of excess reducing gas and b) the flow rate of internal heating gas. The mass balances were calculated with the objective of finding product temperatures achieving high recovery of metallic iron while minimizing both excess reducing gas and internal heating gas requirements. Excess Ratio is the ratio of excess reducing gas to gas required for reduction. The basis for all calculations was 1000 Kg metallic iron product.

(34) If natural gas is used as the reducing gas a hot combustible gas remains after the metallic iron is removed. This can be profitably used as a valuable fuel supplement in adjacent pellet plant or sinter plant furnaces. This approach is expected to be more cost effective than cleaning by conventional methods to yield pure syngas, but could be possible in favorable circumstances.

(35) TABLE-US-00001 Case 1: Iron Oxide: Hematite Flowsheet: Open Circuit Reducing Gas: Methane Excess Ratio: 3.1 Iron Phase: Solid Product Temperature: 781 C. Feed: Fe.sub.2O.sub.3 CH.sub.4 H.sub.2 O.sub.2 Total Kg 1,430 440 80 640 2590 O = 2070 F = 520 O/F = 3.9808 Product: Fe CH.sub.4 H.sub.2 CO CO.sub.2 H.sub.2O Total Kg 1000.4 1.7 129.83 497.02 421.32 539.73 2590 Gas wt % 2.5 8.5 28.4 31.6 29.0

(36) The hot gas stream contains 36.9% by mass of a hydrogen rich syngas with molar H.sub.2/CO ratio of 4.19. The remaining gases are steam, 29.0%, CO.sub.2, 31.6% and methane 2.5%.

(37) TABLE-US-00002 Case 2: Iron Oxide: Magnetite Flowsheet: Open Circuit Reducing Gas: Methane Excess Ratio: 3.0 Iron Phase: Solid Product Temperature: 910 C. Feed: Fe.sub.3O.sub.4 CH.sub.4 H.sub.2 O.sub.2 Total Kg 1,382 382 77.6 620.75 2462.35 O = 2002.75 F = 459.6 O/F = 4.3576 Product: Fe CH.sub.4 H.sub.2 CO CO.sub.2 H.sub.2O Kg 1000.3 0.06 110 462.3 321.2 568.9 2462.46 Gas wt % 0.00 7.5 31.6 22.0 38.9 100

(38) The hot gas stream contains 39.1% by mass of a hydrogen rich syngas with molar H.sub.2/CO ratio of 3.32. The remaining gases are steam, 38.9%, CO.sub.2, 21.96% and a trace of methane.

(39) TABLE-US-00003 Case 3: Iron Oxide: Magnetite Flowsheet: Closed Circuit Preheat Temperature: 627 C. Reducing Gas: Methane Excess Ratio: 2.5 Iron Phase: Solid Product Temperature: 833 C. Feed: Fe.sub.2O.sub.3 CH.sub.4 H.sub.2 O.sub.2 Total Kg 1383 334 49 394 2160 O = 1777 F = 383 O/F = 4.64 Product: Fe CH.sub.4 H.sub.2 CO CO.sub.2 H.sub.2O Kg 1000 0.4 90.0 400.4 286.1 382.7 2159.6 Gas wt % 0.01 7.76 34.53 24.67 33.0

(40) The hot gas stream contains 42.29% by mass of a hydrogen rich syngas with molar H.sub.2/CO ratio of 3.15. The remaining gases are 24.67% CO.sub.2 and 33% steam.

(41) TABLE-US-00004 Case 4: FIG. 8 Iron Oxide: Magnetite Flowsheet: Open Circuit Reducing Gas: Hydrogen Excess Ratio: 3.7 Iron Phase: Solid. Product Temperature: 1185 C. Feed: Fe.sub.3O.sub.4 H.sub.2 O.sub.2 Total kg 1382 224 406 2012 O = 1788 F = 224 O/F = 7.9821 Product: Fe H.sub.2 H.sub.2O Total kg 1000 125 887 2012 Gas wt % 12.4 83.6 H.sub.2 used 99 (44.2%)

(42) The hot gas stream contains 12.4% by mass of hydrogen and 83.6% steam.

(43) TABLE-US-00005 Case 5: FIG. 9 Iron Oxide: Magnetite Flowsheet: Closed Circuit Preheat Temperature: 627 C. Reducing Gas: Hydrogen Excess Ratio: 2.8 Iron Phase: Solid Product Temperature: 833 C. Feed: Fe.sub.3O.sub.4 H.sub.2 O.sub.2 Total kg 1382 182.6 95.5 1660.1 O = 1477.5 F = 182.8 O/F = 8.0915 Product: Fe H.sub.2 H.sub.2O Total kg 1000 122.4 538.1 1660.1 Gas wt % 12.4 83.6 H.sub.2 used 60.2 (33.0% Note: The excess hydrogen is directly recycled from the condenser and the hydrogen contained in the water is recovered by electrolysis and recycled. Consequently there is no net consumption of hydrogen and the only off gas is 382 kg of oxygen.

(44) TABLE-US-00006 Case 6: Iron Oxide: Magnetite Flowsheet: Open Circuit Reducing Gas: Hydrogen Excess Ratio: 7.9 Iron Phase: Liquid Product Temperature: 1589 C. Feed: Fe.sub.3O.sub.4 H.sub.2 O.sub.2 Total Kg 1,382 405.9 907.2 2695.1 Product: Fe H.sub.2 H.sub.2O Kg 997.8 243.5 1450 2691.3* Gas wt % 14.38 85.62 100 2.2% Fe loss to minor iron species.
The hot gas stream contains 18.5% by mass of hydrogen and 81.5% steam. With pre-heating and recycling hydrogen demand is reduced by 18%.

(45) TABLE-US-00007 Case 7: FIG. 11. Off gas to Pellet Plant Iron Oxide: Magnetite Flowsheet: Closed Circuit Preheat Temperature: 627 C. Reducing Gas: Methane Excess Ratio: 2.1 Iron Phase: Solid Product Temperature: 833 C. Feed: Fe.sub.3O.sub.4 CH.sub.4 H.sub.2 O.sub.2 Total Kg 1383 334 49 394 2160 O = 1777 F = 383 O/F = 4.64 Product: Fe CH.sub.4 H.sub.2 CO CO.sub.2 H.sub.2O Kg 1000 0.4 90.0 400.4 286.1 382.7 2159.6 Gas wt % 0.01 7.76 34.53 24.67 33.0

(46) The hot gas stream contains 42.29% by mass of a hydrogen rich syngas with molar H.sub.2/CO ratio of 3.15. The remaining gases are 24.67% CO.sub.2 and 33% steam.

(47) Cost Estimates

(48) With current interest focused on the reduction of atmospheric carbon dioxide and the long term goal of a hydrogen economy, future costs for hydrogen and electric power are projected to decrease significantly. There is also interesting research into novel power generation technology that could become commercial in the medium term future. One example is the use of nano pulse technology as reported by Dharmaraj and Kumar (IJEE vol 3, 1, 2012 pp 129-136) They report experimental results of 0.58 W for the production of 0.58 ml/s of hydrogen, that is 1 kWh per 3600 L. A more conservative value of 1 kWh for 3000 L is used below.

(49) The amount of hydrogen required for the production of 1000 kg of metallic iron varies greatly with plant configuration as shown in the following table:

(50) TABLE-US-00008 Flowsheet Kg H.sub.2 Kg CH.sub.4 Case 4 FIG. 8 224 0 Case 5 FIG. 9 182* 0 Case 7 FIG. 11 49 334 *Recycled so no net demand.

(51) In the case of hydrogen as the reducing gas, the products are metallic iron and oxygen only. If the IFDR plant is adjacent to a pellet plant or sinter plant, the oxygen can be used to enrich the combustion air. However without corresponding cost benefit data, the following cost estimates do not include any oxygen credits. A recent NEL estimate of the cost of hydrogen produced by electrolysis and wind power in Minnesota gave figures in the range $3.15 to $3.25 per kg of hydrogen. An average of $3.20/kg is used in the following IFDR estimates:

(52) TABLE-US-00009 Case 5: Hydrogen. Closed circuit with pre-heat No credit for excess oxygen Units Cost $ Total $ Taconite Concentrate Metric tons 1.5 45.00 67.50 Water 750 gal 0.3 2.00 0.60 Hydrogen by electrolysis Kg 60 3.20 192.0 Labor Man Hours 0.5 35.00 17.50 Maintenance & Other $/t 15 1.00 15.00 Briquetting $/t 1 10.00 10.00 Total Cost 302.6 Iron Concentration 97%

(53) TABLE-US-00010 Case 7: Natural gas and off-gas going to pellet plant Units Cost $ Total $ Taconite Concentrate Metric tons 1.5 45.00 67.50 Water 750 gal 0.3 2.00 0.60 Natural Gas Kg 334 0.20 66.80 Hydrogen Kg 49 3.20 156.80 Labor Man Hours 0.5 35.00 17.50 Maintenance & Other $/t 15 1.00 15.00 Briquetting $/t 1 10.00 10.00 Total Cost 334.2 Iron Concentration 97%

(54) Future Projection:

(55) With a nano pulse power supply for electrolysis Case 5 hydrogen requirements are 60 kg or 672,000 L=224 kWhr

(56) At $0.07/kWh the cost for power is $47.73 per metric ton of iron.

(57) TABLE-US-00011 Units Cost $ Total $ Taconite Concentrate Metric tons 1.5 45.00 67.50 Water 750 gal 0.3 2.00 0.60 Electricity kWh 224 0.07 15.68 Labor Man Hours 0.5 35.00 17.50 Maintenance & Other $/t 15 1.00 15.00 Briquetting $/t 1 10.00 10.00 Total Cost 126.28 Iron Concentration 97%
UBS estimates for Shaft Furnace DRI and Mesabi Nuggets are given below for comparison. Case 5 and case 7 above are comparable Whereas the future estimate indicates the substantial cost benefits achievable with low electrolysis costs.

(58) TABLE-US-00012 DRI Shaft Cost Assumptions Source: Energiron, Midrex, UBS estimates Units Cost $ Iron Ore Tons 1.45 170 $246.5 Natural Gas mmbtu 8.9 3.75 $33.5 Electricity kwh 95 0.07 $6.7 Labor Man Hours 0.14 $35 $4.9 Maintenance and Other $/t 15 $1 $15.0 Total Cost $306.5 Iron Concentration 92.0% Assuming ore cost is the same adjusted cost is $

(59) TABLE-US-00013 DRI Rotary Hearth Furnace Cost Assumptions Source: Midrex, UBS estimates Units Cost $ Iron Ore Tons 1.6 155.0 $248.0 Thermal Coal Tons 0.5 65 32.5 Natural Gas mmbtu 4.4 3.75 16.3 Electricity kwh 200 0.07 14.0 Labor Man Hours 0.2 35 7.0 Maintenance and Other $/t 30 1 30.0 Total Cost $347.8 Iron Concentration 96.5% Note: See NUCOR estimate below for DRI costs of $369.
Molten Iron

(60) For the production of 1000 kg of molten iron from magnetite using a nano pulse power supply for electrolysis 3,482,000 L of hydrogen is required. The power needed is 3,482,000/3000=1,160 kWh. At $0.07/kWh the cost for power is $81.26 per metric ton of iron.

(61) TABLE-US-00014 Units Cost $ Total $ Taconite Concentrate Metric tons 1.5 45.00 67.50 Water 750 gal 0.7 2.00 1.40 Electricity kWh 1,160 0.07 81.26 Labor Man Hours 0.5 35.00 17.50 Maintenance & Other $/t 15 1.00 15.00 Briquetting $/t 1 10.00 10.00 Total Cost. 192.66 Iron Concentration 99% Note: See NUCOR estimate below for Adjusted pig iron cost of $436

(62) TABLE-US-00015 DRI and PIG IRON COSTS (extract from NUCOR PRESENTATION March 2014) DRI VERSUS PIG IRON COST COMPARISON (using estimated long-term prices) $/ton Iron Ore (62% FE, FOB Brazil) $125 $125 Pellet Premium $40 $40 Iron Premium (BF = 65% Fe & DRI = 68% Fe) $7 $13 Freight $25 $15 Iron Ore Consumption (BF = 1.6 ton & DRI = 1.5 ton) $315 $290 Cash Conversion Costs $70 $35 BF Reductant (100% coke) $107 DRI Reduction (11 mmbtus @$4) $44 Iron Unit Cost $492 $369 BF with sinter plant cost savings $30 BF Cost Savings by Substituting 40% coke $11 Usage with PCI & natural gas BF Higher Value-In-Use Benefit $15 Adjusted BF Iron Unit Cost $436

(63) While this invention may be embodied in many different forms, there are shown in the drawings and described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.

(64) This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.