GB2056498A - Method and Apparatus for Producing Molten Iron from Iron Oxide with Coal and Oxygen - Google Patents

Abstract

Particulate molten iron is reduced in a shaft furnace 10 by gaseous reduction to form hot metallised iron particulates, and these are melted in a melter-gasifier vessel 30 into which solid fuel e.g. coal and oxygen are injected (inlet 40). The hot off-gases in the vessel 30 are recirculated to the shaft furnace 10, via 60, 69, to reduce the particular iron oxide therein. The hot off-gases may be cooled, by use of liquid water sprayed in at 55, to a temperature suitable for use in reduction. <IMAGE>

Description

SPECIFICATION Method and Apparatus for Producing Molten Iron from Iron Oxide with Coal and Oxygen The direct reduction of iron oxide to metallic iron has become a world-wide reality, and direct reduced iron is a commercially accepted feed material in steelmaking.

Direct reduced iron, or sponge iron, is particularly well suited for electric arc furnace technology.

It is not well suited as the principal feed material for other steel making furnaces, such as the bottom blown oxygen process, which require hot metal or molten metal, as feed material. At present, such hot metal is produced commercially only by means of blast furnaces which are inherently economically restricted to the availability of coking coal and to integrated steel making installations. It is, therefore, desirable to produce molten iron by direct reduction means which are economically suitable for small steelmaking plants and are independent of the use of coking coal.

The present invention accomplishes this end by (a) producing hot particulate direct reduced iron from particulate iron oxide in an efficient counterflow shaft furnace, (b) discharging the hot particulate iron into a melter containing a bath of molten iron, (c) injecting coal and oxygen into the melter to supply heat to melt the particulate iron and gasify the coal, and (d) introducing the hot melter off gases into the shaft furnace to reduce the iron oxide. The process is simple, efficient, non-polluting, economical for small steelmaking installations, and suitable for use with non-coking coals which are available woridwide.

According to the present invention there is provided a method for reducing particulate iron oxide and producing molten iron, comprising: a) chemically reducing particulate iron oxide to solid particulate metallised iron product in a shafttype reduction furnace by reaction with a hot reducing gas consisting principally of carbon monoxide and hydrogen; b) discharging the hot particulate metallised iron product into a melting chamber containing a pool of molten metal; c) injecting fossil fuel and oxygen into said chamber to melt the iron and to gasify the fossil fuel to form a hot off-gas within the chamber; dY cooling and humidifying the hot off-gas within the chamber to form a hot reducing gas;; e) removing said hot reducing gas from the chamber, and introducing said hot reducing gas to the shaft furnace as reductant to react with the particulate iron oxide to reduce it to particulate iron product; and f) drawing off the molten iron product from said chamber.

The present invention as particularly disclosed and illustrated herein provides a method for directly reducing particulate iron oxide to molten iron wherein solid fuel is utilised as the reductant source. Moreover it provides an energy efficient method for converting particulate iron oxide to molten iron in counterflow heat exchange by reaction with gaseous reductants produced from solid fuel and oxygen. Furthermore, it provides a method for producing molten iron from particulate iron oxide in a simple ance-through process without one being obliged to remove carbon dioxide and sulphur constituents from the reductant gases. In addition it provides a method for simultaneously producing molten iron and a clean gaseous fuel of high heating value.

The present invention will be more readily understood by referring to the examples described in the following detailed description and shown in the appended drawings in which: Figure 1 is a schematic drawing of a shaft furnace melting vessel and related equipment including solid fuel and oxygen injection into the melting vessel.

Figure 2 is a schematic drawing of equipment similar to that of Figure 1 in which solid fuel and oxygen are injected beneath the surface of the bath in the melting vessel.

Figure 3 is a schematic drawing of a shaft furnace coupled to a melting vessel and including related equipment in which the melting vessel is provided with an impact bed hearth.

Referring now to Figure 1, a shaft furnace 10 having a steel shell 11 is lined with refractory 12. A feed hopper 14 is mounted at the top of the furnace 10 for charging of particulate solids feed material 1 5 therein. The feed material consists of iron oxide in the form of pellets or lumps. The feed material descends by gravity through one or more feed pipes 1 6 to form a packed bed or burden 18 of particulate solids feed material in the furnace 10. Reduced particulate material 21 is withdrawn from furnace 10 through furnace discharge pipe 22 into sealing chamber 23, then through discharge pipe 25 into conveyor chamber 26 by means of a discharge conveyor 28, the speed of which controls the rate of descent of the burden through furnace 10.Discharge conveyor 28 is the primary iron-bearing solids metering device for the process.

Reduced particulate material 21 falls freely from discharge conveyor 28 through radiation shield pipe 29 into melter-gasifier vessel 30 having a steel shell 32 and being lined with refractory 34.

Radiation shield pipe 29 serves to minimize heat radiation from the interior of melter-gasifier vessel 30, the temperature of which is about 1 2000C, to discharge conveyor chamber in which the temperature is about 8000C. This prevents reduced particulate material from overheating and becoming sticky and non-free-flowing.

Reduced particulate material 21 falls into molten bath 35 and is melted. Reduced molten product is removed from melting vessel 30 through iron notch 37. Removal of the molten product from vessel 30 is intermittent or continuous but co-ordinated to the discharge of reduced particulate material 21 from furnace 10, which is normally continuous, to maintain a liquid level 38 in vessel 30 beneath coal and oxygen injection pipes 40 (only one of which is shown) and well below water injection pipes 42 (only one of which is shown).

As described, all iron bearing materials descend in gravitational flow from the feed hopper 1 4 to iron notch 37. All non-iron-bearing materials ascend through the melter-gasifier 30 and the shaft furnace 10 in a counterflow relationship to the descending iron bearing materials. This allows the most efficient use of energy for producing molten iron from coal and oxygen by a simple method.

Each injection pipe 40 is a dual passageway pipe having a central fossil fuel passageway communicating with a source of fossil fuel 44 by pipe 45 and an annular oxygen passageway communicating with a source of oxygen 47 through pipe 48. Pulverized coal or other carbonaceous material is pneumatically conveyed through pipe 45 to the injection pipe 40, which extends through opening 50 in the side wall of melter-gasifier 30, by a small stream of compressed gas from pipe 51.

Preferably, process gas is compressed by compressor 52 and used as the conveying media. The conveyed powdered coal is injected through the center pipe of injection pipe 40 and onto the surface of molten bath 35 at a point slightly above the elevation of liquid level 38. It is desirable to maintain the liquid level elevation slightly below pipe 40 so that the stream of coal and oxygen impinge on the surface of the molten product which insures good heat transfer and stable combustion of coal. Oxygen from source 47 is compressed to a suitable pressure and injected through the annular pipe of injection pipe 40 so that the streams of oxygen and powdered coal meet at the exits of their respective pipes at the discharge of injection pipe 40. Coal is combusted with oxygen on and above the surface 38 of molten bath 35.The combustion of coal and oxygen is exothermic, and sufficient heat is released to melt the hot particulate material 21 in vessel 30. The ratio of coal to oxygen is controlled to cause combustion to occur at a theoretical adiabatic flame temperature of about 1 9500 C. The quantity of coal combusted is controlled according to the quantity of reduced particulate material as measured by means of discharge conveyor 28. The ratio of coal to reduced particulate material is adjusted to maintain the proper quantity of melter-gasifier off-gas to reduce all iron oxide to metallic iron in furnace 10.

Hot, reductant-rich-off-gas 54 leaves the surface 38 of molten iron bath 35 at a temperature of about 14000C. The quality (ratio of reductants to oxidants) and temperature of the gas are both higher than desirable for use in the shaft furnace. Therefore, liquid water from source 55 is injected through water nozzles 42 to reduce the off-gas temperature to about 12000C and humidify the hot off-gas to obtain the desired quality of gas for reduction purposes. The humidified off-gas leaves the top of the melter-gasifier 30 through outlet pipe 56. Hot solids are separated from the humidified off-gas in a cyclone separator 57. The separated solids may be recycled to the melter-gasifier by injecting them through pipe 58 into pipe 45 with the pulverized coal.

Humidified off-gas leaving the cyclone separator 57 via pipe 60 is further cooled to obtain the desired temperature of gas for reduction purposes. Hot gas passes through a restrictive orifice 62 which allows only a controlled quantity of gas to pass therethrough. The remainder, also a controlled quantity of gas is diverted through pipe 64 then passes through a water cooled heat exchanger 66 wherein the gas is cooled. A portion of the cooled gas is diverted to pipe 51 to provide compressed gas for coal injection line 45. The remainder of the cooled gas passes through pipe 68 and is recombined with the stream of hot gas in pipe 69. The temperature of the reducing gas in pipe 69 is controlled by automatically adjusting the flow of cold by-passed gas from pipe 68. Heat exchanger 66 may be of the direct or indirect type.No steam is required for the process; however, if it is desirable to generate steam for use elsewhere, a waste heat boiler may be used. If steam generation is not desired, a simple direct water cooler may be used for heat exchanger 66.

The recombined reducing gas having the desired temperature, quality, and quantity for reduction, enters the shaft furnace 1 0 through a bustle and tuyere system 70. The reducing gas flows inward and upwards through the descending burden 18 to heat the particulate iron oxide and reduce it to metallic iron. In the reaction of reducing iron oxide to iron, the reducing gas becomes partially oxidized and cooled. The partially oxidized and cooled gas leaves the reduction shaft furnace 10 through furnace offgas outlet pipe 72 into water-cooled scrubber 73 wherein it is cooled and scrubbed free of dust. Cool, clean furnace off-gas removed by pipe 75 contains CO and H2 and has a heating value of about 1 900 Kcal/Nm3. This is a valuable gaseous fuel for use throughout the steel mill, or elsewhere.

Oxygen and coal are introduced into the melter gasifier 30 at sufficiently high pressure to overcome the pressure drop created by the flow of gases through the melter-gasifier and shaft furnace systems, and to deliver off-gas fuel at a usable pressure. The gas pressure in gasifier-melter 30 is higher than in shaft furnace 10; therefore, a quantity of cold inert gas is introduced through inlet pipe 77 into plenum chamber 23 between furnace discharge pipe 22 and seal chamber discharge pipe 25.

The pressure in chamber 23 is maintained slightly higher than the pressure in the bottom of shaft furnace 10 and in discharge conveyor chamber 26 so that some cold inert seal gas flows upwards into shaft furnace 10 and downwards into discharge conveyor chamber 26. This prevents 1 2000C gases from the meiter-gasifier 30 from flowing directly upwards into the bottom of the shaft furnace.

The present invention employes a totally counterflow continuous process to most efficiently use non-coking solid fuels to produce molten iron from particulate iron oxide and, at the same time, produce valuable gaseous fuel.

To demonstrate the practicability of the invented process we have developed a process analysis which is summarized in Tables 1,2 and 3. The analysis is based on use of a typical Western U.S.A. subbituminous coal as the carbonaceous material.

Reducing gas quality is defined as the ratio of reductants (CO plus H2) to oxidants (CO2 plus H20) in the gas mixture. In order to take full advantage of the inherent chemical efficiency of a counterflow shaft reduction furnace, the quality of the hot reducing gas should be at least about 8.

Operation temperatures in a shaft furnace vary between 760 and 9000 C, and depend on the specific particulate iron oxide material being reduced. A practical operating temperature for most materials is 81 50C.

Table 1 Gas Flows and Temperatures Reference Flow in Gas Gas Item Numeral Nm3 * Quality Temperature OC Oxygen - 576 - 50 Melter-Gasifier Gas 54 1869 16.9 1400 Humidified Melter-Gasifier Gas 56 2014 8.0 1200 By-Passed Gas 64 741 8.0 60 Reducing Gas 69 1983 8.0 815 Furnace Off Gas 72 1983 1.4 Clean Off Gas Fuel 75 1850 - 60 *Nm3 - normal cubic meters.

Table 2 Feed and Energy Requirements Reference Item Numeral Nm3 kg Gcal Coal 45 - 1055 6.71 (HHV) Oxygen 48 576 - 1.01* Oxide 15 - 1420 Humidifying water 55 117 Off Gas Fuel 75 1850 - (3.47) Net Energy Required - - - 4.25 *Energy (HHV) of coal required to produce 576 Nm302 at 30% efficiency.

Because of the chemical thermodynamics involved in the reduction of iron oxide to metallic iron, only a portion of the initial reductants (CO plus H2) can be reacted before the oxidants (CO2 plus H20) which are formed cause the reduction reactions to cease. This thermodynamic situation results in the spent reducing gas leaving the shaft furnace through outlet 72 having a quality of about 1.5 for an efficiently operating furnace. Therefore, reducing gas with a quality of 8 is oxidized to a quality of 1.5 in the reduction process. The amount of CO plus H2 thus consumed determines the quantity of reducing gas required. A reducing gas quantity of 1800 to 2100 Nm3/t of reduced iron product is practical for efficient operation.

Each ton of molten iron product discharged from the melter-gasifier 30 requires that 1.035 tons of direct reduced particulate material be charged into the melter-gasifier. Typical metallization of direct reduced material is 92%. Material is delivered to the melter-gasifier at 7000C. Molten iron product is discharged at 1 3500C. Therefore, sufficient heat must be generated in the melter-gasifier to heat the 7000C incoming direct reduced material to 13500C, reduce residual FeO to iron, reduce SiO2, MnO, P205, etc., increase carbon, heat slag materials to 1 3500C, and satisfy heat losses from the system.

This requires 403,000 Kcal per ton of molten iron product. The heat required is furnished by the exothermic reaction of coal and oxygen within the melter-gasifier and cooling the products of combustion to 1 4000C.

Table 3 shows gas analyses at the indicated positions in the process.

Table 3 Gas Analyses Throughout Process Reference Item Numeral % CO % CO2 % H2 % H20 % N2 Melter-Gasifier Gas 54 66.9 2.3 26.2 3.2 1.4 Reducing Gas 69 63.0 2.2 24.7 8.8 1.3 Furnace OffGas 72 36.6 28.1 21.7 12.3 1.3 Clean Off Gas Fuel 75 38.8 29.8 23.0 6.0 2.4 Although the preferable fossil fuel to be injected through Line 45 is non-coking coal or lignite, the process can also be operated with coking coal, char or coke. The injected solid fossil fuel must be pulverized to a particle size finer than one quarter inch. Alternatively, the process can be operated with a liquid petroleum derived fossil fuel or a gaseous fossil fuel such as natural gas.

In an alternative embodiment of the invention shown in Figure 2, coal and oxygen are injected into vessel 30 beneath the surface 38 of bath 35. Molten iron and slag are intermittently removed from vessel 30 to maintain a liquid level 38 above the discharge end of coal and oxygen injection pipes 80 (only one of which is shown) and below water injection pipes 42 (only one of which is shown). The elevation of liquid level 38 is not critical but only dependent upon the design of vessel 30 and the vertical distance between the elevation of pipes 80 and 42. It is desirable to minimize the liquid level elevation above the outlet of pipe 80 in order to keep the pressures at which coal and d oxygen must be compressed for injection as low as possible.The powdered coal is injected through a center pipe of injection pipes 80 and into molten bath 35 at a point below the elevation of liquid level 38. Oxygen from source 47 is compressed to a suitable pressure then injected through an annular pipe 82 surrounding injection pipe 80 so that oxygen and powdered coal streams meet at the exits of their respective pipes at the discharge of injection pipes 80 and 82. Coal is combusted with oxygen within molten bath 35. The combustion of coal and oxygen is exothermic, and sufficient heat is released to melt the hot particulate material 21 within the bath. The ratio of coal to oxygen is controlled to cause combustion to occur at a theoretical adiabatic flame temperature of about 1 9500C.The quantity of coal combusted is controlled according to the quantity of reduced particulate material as measured by means of discharge conveyor 28, A second alternative embodiment is shown in Figure 3. A gasifier-melter chamber 110 having a steel shell is lined with firebrick type refractory 11 2 in the upper region and carbon brick type refractory 114 in the lower region. The chamber 110 preferably has a generally circular cross-section. An elevated melting hearth 11 6 may be provided in the bottom region of the chamber. This hearth is situated within the chamber to form a molten iron and slag reservoir 11 8 for accumulating molten iron 11 9 and slag 120.An iron and slag notch 37 is provided for periodically withdrawing hot liquid from the reservoir 11 8. The hearth 11 6 is preferably a centrally situated upstanding pedestal surrounded by an annular molten metal pool 11 8. Alternatively, the hearth may be formed by a pile of pellets or other material on the furnace bottom.

A plurality of water cooled tuyeres 123 are positioned in a wall of the chamber and are inclined downwardly toward the upper region of melting hearth 11 6. The upper region of the chamber is provided with a water atomizing nozzle 42 arranged to spray water into the chamber. A gas outlet pipe 56 and a hot reduced iron pellet inlet opening 128 are situated at the top of the chamber.

A shaft-type direct reduction furnace 10 is coupled to the upper region of gasifier-melter chamber 110.

Hot reduced iron pellets are withdrawn from furnace discharge pipe 22 at a controlled rate by a discharge feeder 130 to establish gravity descent of furnace burden 1 8. The discharge feeder 1 30 can be any conventional type hot discharge feeder such as a heat resisting alloy reciprocating wiper bar or apron feeder. The hot reduced iron pellets discharged by feeder 1 30 fall by gravity onto hearth 11 6 where a natural angle of repose pile 132 is formed. A small amount of lump coke may be added to the oxide pellet feed in charge hopper 14to provide a sacrificial source of fixed carbon intermixed with the hot direct reduced iron melted on the impact bed hearth. The coke will travel through the reduction furnace 10 without reacting.When it impinges upon the bottom of the furnace which need not be an elevated pedestal in this case, it will form an upstanding impact bed hearth along with the iron pellets: The coke will insure a carbon-rich environment at the location where melting occurs.

Pulverized coal to be gasified in gasifier-melter chamber 110 is admitted to tuyeres 1 23 from a pulverized coal source 44 and oxygen for gasifying is admitted to tuyeres 123 from an oxygen source 47. The tuyeres are directed to impinge on the surface of the pile of h6t direct reduced iron pellets on hearth 11 6. This impingement serves not only to accelerate the gasification combustion but also to accelerate the melting of the pellets. As the pellets melt, superheated molten iron and slag continuously trickle over the edge of hearth 116 and down into the annular molten iron and slag reservoir 118. Molten iron and slag are periodically tapped through iron notch 37.As the pellets in pile 132 melt, causing the pile to shrink in size, a nuclear level sensing probe, not shown, serves to actuate the reduction furnace discharge feeder 130 to replace melted pellets with hot reduced iron pellets from reduction furnace 10.

To regulate the amount-of hot gas from pipe 60 which passes through by-pass cooler 66, a flow control valve 140, which is responsive to a gas temperature sensing element 142 by conventional control means not shown, is provided which serves to control the temperature of the gas entering inlet pipe 70.

To provide for a nominal molten slag fluidity and iron desulfurizer, such as is utilized in a conventional blast furnace, lump limestone or dolomite is preferably fed to the process along with iron oxide pellets into reduction furnace charge hopper 1 4. As an alternative method, pulverized limestone or dolomite could be injected through tuyeres 123.

From the above, it can readily be seen that there has been particularly described a counterflow continuous apparatus and process for the direct reduction of particulate iron oxide to molten iron which effectively uses non-coking solid fossil fuels as the principal source of reductant, and which simultaneously produces a valuable gaseous fuel for use wherever desired.

Claims (36)

Claims

1. A method for reducing particulate iron oxide and producing molten iron, comprising: a) chemically reducing particulate iron oxide to solid particulate metallised iron product in a shafttype reduction furnace by reaction with a hot reducing gas consisting principally of carbon monoxide and hydrogen; b) discharging the hot particulate metallised iron product into a melting chamber containing a pool of molten metal; c) injecting fossil fuel and oxygen into said chamber to melt the iron and to gasify the fossil fuel to form a hot off-gas within the chamber; d) cooling and humidifying the hot off-gas within the chamber to form a hot reducing gas; e) removing said hot reducing gas from the chamber, and introducing said hot reducing gas to the shaft furnace as reductant to react with the particulate iron oxide to reduce it to particulate iron product; and f) drawing off the molten iron product from said chamber.

2. A method according to claim 1 in which said fossil fuel and oxygen is directed onto the surface of the pool of molten metal.

3. A method according to claim 1 in which said fossil fuel and oxygen is injected into the pool of molten metal beneath its surface.

4. A method according to claim 1 in which a generally central upstanding impact bed hearth of particular iron product is formed, surrounded by a molten metal pool.

5. A method according to any of claims 1 through 4 characterized in that a reacted off gas is formed in said shaft furnace, removed from said shaft furnace, cleaned and cooled to produce a gaseous fuel.

6. A method according to any of claims 1 through 4, wherein said fossil fuel is in solid form.

7. A method according to claim 6 characterized in that said solid fuel is selected from the group consisting of coal, lignite, char and coke.

8. A method according to any of claims 1 through 4 characterized in that said fossil fuel is in the liquid or gaseous state.

9. A method according to any of claims 1 through 4 further comprising removing particulate matter from said hot gas upon removal from said chamber,

10. A method according to claim 9 characterized in that said removed particulate matter is returned to said chamber with said fossil fuel.

11. A method according to any of claims 1 through 4 characterized in that a portion of said hot reducing gas is used as a carrying medium for said fossil fuel.

12. A method according to claim 1 characterized in that the temperature of said hot gas in said chamber is reduced to about 1 2000C by introducing water to said chamber above the elevation of said fossil fuel injection and beneath the elevation of said hot gas removal.

13. A method according to claim 1 characterized in that reacted reducing gas is removed from said shaft furnace, cleaned and cooled to form a clean fuel gas.

1 4. Apparatus for reducing particulate iron oxide and producing molten iron characterized by: a) a generally vertical shaft furnace having a particle inlet for admitting particulate iron oxide material at the top thereof and an outlet for discharging particulate material from the bottom thereof, a gas inlet intermediate the ends of the furnace for introducing a hot reducing gas to the material therein and a gas outlet for withdrawing spent reducing gas from the top thereof;; b) a melter-gasifier vessel having a molten metal bath therein, a conduit communicating with the material outlet of said shaft furnace for admitting particulate shaft furnace product to the top of said vessel, means for melting said particulate materials in said vessel, and a tap hole for withdrawing molten product from said vessel, said vessel being in sealed relationship with the outlet of said shaft furnace; c) means for introducing oxygen and fossil fuel into said vessel; d) a water injection nozzle for introducing water to the interior of said vessel to humidify the hot gases therein; and e) a reducing gas conduit connected to said vessel and to the reducing gas inlet of said shaft furnace for introducing humidified off gas from said vessel to said shaft furnace as reducing gases.

1 5. Apparatus according to claim 14 characterized by a central impact bed hearth in the bottom of said vessel, surrounded by a molten metal pool.

16. Apparatus according to claim 14 characterized by said means for introducing oxygen and fossil fuel in such a manner that they are directed against the surface of the molten metal bath whereby said oxygen and fossil fuel will impinge on said surface.

1 7. Apparatus according to claim 14 characterized by said means for introducing oxygen and fossil fuel terminating beneath the surface of the bath.

1 8. Apparatus according to claim 14 characterized by said means for introducing oxygen and fossil fuel into said bath being a dual passageway pipe having a central fossil fuel passageway surrounded by an annular oxygen passageway.

1 9. Apparatus according to claim 14 characterized by a feed rate controller for controlling the rate of feed of reduced particulate material entering said vessel.

20. Apparatus according to claim 1 4 characterized by cooling means in said reducing gas conduit for cooling the gas in said reducing gas conduit.

21. Apparatus according to claim 14 characterized by a hot gas cyclone in said reducing gas conduit for removing solids from said reducing gas.

22. Apparatus according to claim 21 characterized by a solids return conduit connected to the cyclone and to the fossil fuel introducing means for injecting removed particulates into said fossil fueJ line to return removed particulates to said vessel.

23. Apparatus according to claim 14 characterized by a hot gas conduit connected to said reducing gas conduit and to said fossil fuel introducing means for introducing a portion of said reducing gas to said fossil fuel introducing means to assist in injecting fossil fuel into said vessel.

24. Apparatus according to claim 14 characterized by at least one water spray nozzle in the wall of said vessel above the molten metal bath for cooling and humidifying gases from said bath.

25. Apparatus according to claim 14 characterized by a sealing chamber connected to the discharge end of said shaft furnace and the top of said vessel including gas injection means for introducing an inert gas to said sealing chamber to prevent the flow of gases between said vessel and said shaft furnace through said sealing chamber.

26. Apparatus according to claim 25 characterized by means for maintaining the pressure in said sealing chamber greater than the pressure in either said furnace or said vessel.

27. Apparatus according to claim 1 5 characterized by said melting means being directed onto said impact bed hearth to melt metallic material on said hearth and to form a hot gas.

28. Apparatus according to claim 27 characterized by said heating means being a burner.

29. Apparatus according to claim 27 characterized by said heating means being a hot blast tuyere.

30. Apparatus according to claim 14 characterized by a restrictive gas flow orifice in said reducing gas conduit, a gas by-pass pipe connecting said reducing gas conduit on each side of said orifice, a by-pass cooler in said by-pass pipe, a gas temperature sensor in said reducing gas conduit adjacent the reducing gas inlet to said shaft furnace, and a flow control valve in said by-pass pipe connected to and responsive to said sensor, whereby the temperature of the reducing gas injected into said shaft furnace is controlled.

31. A method for producing molten iron substantially as herein described with reference to and as illustrated in Figure 1 of the accompanying drawings.

32. A method for producing molten iron substantially as herein described with reference to and as illustrated in Figure 2 of the accompanying drawings.

33. A method for producing molten iron substantially as herein described with reference to and as illustrated in Figure 3 of the accompanying drawings.

34. Apparatus for producing molten iron substantially as herein described with reference to and as illustrated in Figure 1 of the accompanying drawings.

35. Apparatus for producing molten iron substantially as herein described with reference to and as illustrated in Figure 2 of the accompanying drawings

36. Apparatus for producing molten iron substantially as herein described with reference to and as illustrated in Figure 3 of the accompanying drawings.