WO1998012358A1

WO1998012358A1 - Producing liquid iron having a low sulfur content

Info

Publication number: WO1998012358A1
Application number: PCT/US1997/016852
Authority: WO
Inventors: Richard B. Greenwalt
Original assignee: Bechtel Group, Inc.
Priority date: 1996-09-20
Filing date: 1997-09-19
Publication date: 1998-03-26
Also published as: AU4586997A

Abstract

A method of liquid iron production with high sulfur fuels such that the level of sulfur in the iron is maintained below 0.1 % sulfur by saturating the liquid iron with carbon and, preferably, silicon.

Description

PRODUCING LIQUID IRON HAVING A LOW SULFUR CONTENT

CROSS REFERENCE TO RELATED APPLICATIONS Provisional application number 60/026,460 is a continuation-in-part of Serial No. 08/167,268, filed December 15, 1993, now U.S. Patent No. 5,558,696, issued September 24, 1996, which is related to the following U.S. patents by the same inventor and assigned to the same assignee: No. 5,259,864, issued November 9, 1993; No. 5,354,356, issued November 11, 1994; No. 5,259,865, issued November 9, 1993; No. 5,320,676, issued June 14, 1994; No. 5,397,376, issued March 14, 1995; and No. 5,413,622, issued May 9, 1995. These patents and the above-noted application are incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

In the smelting and production of liquid iron, the liquid iron is commonly accompanied by a low melting temperature lime-silicate slag for removal of the gangue elements in the iron ore and coke charge materials. Under certain conditions, this 1.0 to 1.2 lime-silicate slag is efficacious in reducing the sulfur in the liquid iron-slag- reducing gas system by absorbing the sulfur in the slag in the form of a solid solution of calcium sulfide in solution. The amount of sulfur that can be absorbed into the slag as calcium sulfide is a function of the sulfur-to-oxygen (H₂S to 0₂ as C0₂ or H₂0) concentration in the supernatant reducing gases. The higher the sulfur concentration and reaction temperature, the higher the sulfur absorption capacity of the calcium- silicate slag. Testwork has shown that at high sulfur concentrations and ironmaking process temperatures of 1,500°C, it is possible to make a slag with a sulfur content of 6% sulfur or more.

The problem is that at these temperatures the gaseous sulfur in the system is highly soluble in the liquid iron. At ironmaking temperatures of 1,500°C, up to 23% of sulfur by weight is soluble in the liquid iron. Such a high level of sulfur destroys the malleable metallic properties of the iron for normal utilization. In fact, sulfur content of as little as 0.1% in the liquid iron ruins the iron for subsequent refining, casting and steelmaking. With high sulfur concentrations in the liquid iron-slag-reducing gas system, the sulfur content of the iron can exceed the 0.1% sulfur limit. Sulfur contents in excess of 0.1% and up to 1.0% in the liquid iron are unacceptable for subsequent iron and steelmaking. Without controlling the liquid iron-slag- reducing gas system, high concentrations of sulfur in the reducing gases cannot be tolerated, limiting the ironmaking process to low sulfur iron ores and low sulfur fuels.

SUMMARY OF THE INVENTION In accordance with the invention, it has been found in practice that by adhering to specific smelting parameters, the sulfur in the liquid iron can be controlled and a low sulfur liquid iron (< 0.1% S) can be produced even when there are high sulfur concentrations in the reducing gases. The invention provides for preventing contamination of the liquid iron by maintaining a liquid iron highly saturated in carbon and silicon (> 4.0% C + > 0.3% Si) in the presence of the high sulfur gases in the fusion zone. The high carbon and silicon levels in the iron prevent absorption of the sulfur in the iron and maintain a low level of sulfur (< 0.1% S) even in the presence of sulfur rich reducing gases. Unless otherwise stated herein the percentages of elements are by weight of the liquid iron.

The method of sulfur control in iron includes maintaining an adequate carbon content and fusion zone in the reactor and a slightly basic slag (1.0 to 1.2:1) such that the liquid iron is maintained at a saturation or near saturation level with carbon (> 4.0% C and preferably > 4.5%) and silicon (> 0.3% and preferably > 0.5%). The combined carbon and silicon levels in the liquid iron should be at least >4.3% and preferably >5.0% to maintain a sulfur level in the liquid iron below 0.1%. Saturation of other metals, such as manganese, in the liquid iron also assists in maintaining low sulfur content in the liquid iron. In instances where no or reduced amounts of silicon are present manganese is useful to substitute or add to the silicon to maintain a >0.3% concentration.

OBJECTS OF THE INVENTION

It is a principal object of the present invention to provide a method of liquid iron production wherein high-sulfur fuels may be used while maintaining the sulfur content of the liquid iron below 0.1% by saturating the liquid iron with carbon and, preferably, silicon. Other objects and advantages of the present invention will become apparent in view of the following detailed description and the accompanying drawings which are made a part of this specification.

DRAWINGS Fig. 1 is a graph showing percent by weight of carbon %C in the liquid iron versus percent by weight of sulfur in the liquid iron[S] .

Fig. 2 is a graph showing percent by weight carbon

%C in the liquid iron versus percent by weight of sulfur in the slag(S) over percent by weight of sulfur in the liquid ironfS] (partition ratio) .

Fig. 3 is a graph showing percent by weight carbon plus silicon (%C + %Si) in the liquid iron versus percent by weight sulfur in the liquid iron[S]. Fig. 4 is a graph showing percent by weight carbon plus silicon (%C + %Si) in the liquid iron versus percent by weight of sulfur in the slag(S) over the percent of sulfur[S] in the liquid iron[S] (partition ratio) .

Fig. 5 is a graph showing percent by weight carbon plus silicon plus hot metal temperature divided by 1,000 (%C +

%Si + HMT/1000) versus percent by weight of sulfur in the liquid iron[S] .

Fig. 6 is a graph showing percent by weight carbon plus percent silicon plus hot metal temperature divided by 1,000 (%C + %Si + HMT/1000) versus percent by weight sulfur in slag(S) over percent by weight of sulfur in the liquid iron[S] .

Fig. 7 is a graph showing percent carbon plus percent silicon plus percent manganese (%C + %Si + %Mn) versus percent sulfur in the liquid iron[S].

Fig. 8 is a graph showing percent by weight carbon plus percent silicon plus percent manganese versus percent by weight sulfur in the slag(S) over the percent by weight of sulfur in the liquid iron[S] (partition ratio) . Fig. 9 is a graph showing percent by weight carbon plus percent silicon plus percent manganese plus hot metal temperature divided by 1,000 (%C + %si + %Mn + HMT/1000) versus percent sulfur in the liquid ironfS] .

Fig. 10 is a graph showing percent by weight carbon plus percent silicon plus percent manganese plus hot metal temperature divided by 1000 (%C + %Si + %Mn + HMT/1000) versus percent by weight sulfur in the slag(S) over percent sulfur in the liquid iron[S] (partition ratio) .

Fig. 11 is a schematic flow sheet illustrating a melter gasifier ironmaking process in which the method of the invention is particularly useful.

Fig. 12 is a schematic vertical section of a melter gasifier useful in accordance with the present invention.

DESCRIPTION OF THE INVENTION The method of the present invention is useful with known commercial ironmaking practices and systems as well as the Corex® ironmaking system. These practices include the conventional blast furnace, the submerged arc furnace and the cupola furnace. The present sulfur in metal control technique is also applicable to ironmaking by emerging technologies that are adaptations of open hearth, converter, cupola and horizontal vessel (QSL) technology. The control of the sulfur in the liquid iron enables utilization of high sulfur low-cost solid fuels as the source of the smelter reductant. Residual high sulfur concentration in effluent gases can be controlled by standard modifications to the furnace off gas systems for gaseous sulfur elimination. The liquid iron in the fusion zone is saturated with carbon (>4.0% C) and silicon (>0.3% Si). It is desirable to control the depth or height of the fusion zone from about 0.15 to 3 meters. The height/depth of the fusion zone is maintained by an excess carbon contamination and by a coarse carbon particle bed or carbon within a foamy fluid slag fusion zone. The coarse carbon particles which emanate from the devolatilized solid fuel charge are embedded in a plastic semi-molten matrix of slag and metallic iron or in a foamy liquid slag and metal structure. The carbon or coke particles can range from 0.01 inch (0.25 mm) to substantially larger than 0.25 inch (6 mm) in size.

The sulfur concentration in the offgases of the method of the invention are handled by the standard sulfur removal techniques previously referenced. These techniques include sulfur removal devices to control the sulfur concentration in the furnace offgases released to the atmosphere. These standard sulfur removal devices can be arranged such that the high sulfur sludge from the offgas scrubbers is recycled to the smelter furnace and the H₂S and COS gases in the offgas are stripped as elemental sulfur for marketing, storage or disposal.

The invention provides a method of producing liquid iron in a fusion zone of a smelting process having a low sulfur content when using carbonaceous fuel containing substantial sulfur which, when combusted, form gases having a high sulfur content. In accordance with the invention the liquid iron is maintained, saturated with at least 4% of carbon by weight of the liquid iron and preferably at least

0.3% silicon by weight of the liquid iron during formation of the liquid iron in the fusion zone during the smelting process. The temperature of the liquid iron in the fusion zone is maintained in excess of l,450°C. For best results, the temperature of the liquid iron in the fusion zone is maintained between about 1,450°C and 1,550°C. Most preferably, the temperature of the liquid iron in the fusion zone is about 1,490°C. In a preferred embodiment, the smelting process is carried out in a melter gasifier having a fusion zone of about from 0.15 to 3 meters. The temperature of the liquid iron in the fusion zone is maintained in excess of 1,450°C. Generally the fusion zone temperature is between about 1,470°C and

1,550°C. In the preferred embodiment, the temperature of the liquid iron in the fusion zone is about l,490°C.

The following tables contain data relating to the method of the present invention. The data was used to plote the curves of Figs. 1-10. The left portion of Table l shows %C, %Si, %Mn, %S by weight in the liquid iron. The temperature for each tap is also shown. The righthand portion of Table 1 shows the % by weight of the various oxides as well as sulfur in the slag from each tap. Table 2 shows calculated data used in plotting certain of the curves of Figs. 1-10. In this regard THM used in the table refers to tons of hot metal; and HMT refers to hot metal temperature. (S)/[S] is the partition ratio; that is the sulfur in the slag(s) divided by the sulfur in the ironfsj. The term THM used in the tables refers to tons of hot metal; and HMT refers to hot metal temperature.

TABLE I

Metal Wt

TAP NO %c %SΪ %Mn %S Temp H %SiO_j %CaO

940263 4335 0315 0575 0023 1526 126400 3300 3300 2 940264 4605 0.285 0520 0025 1493 110750 3290 3360 2 940265 4345 0245 0470 0046 1506 140300 3300 3320 2 940266 4235 0455 0550 0029 1490 133200 3280 3320 1 940267 4335 0425 0500 0031 1465 134800 3240 3300 1 940268 4385 0435 0480 0040 1500 138900 3270 3310 940269 4465 0755 0555 0018 1471 117900 3310 3300 1 940270 4430 0430 0475 0038 1501 137200 3340 3290

TABLE 2

CaO+MeO CaO+MeO)

TAP NO CaO/SiO_j SiO, S

(Si0₂+A]A) (S)/[S] %C + %Si %C + %Mn %Si + %Mn

940263 1.00 1.63 1.21 90 4.650 4.910 0.890 5

940264 1.02 1.65 1.22 81 4.890 5.125 0.805 5

940265 1.01 1.63 1.21 42 4.590 4.815 0.715 5.

940266 1.01 1.61 1.20 64 4.690 4.785 1.005 5.

940267 1.02 1.61 1.19 63 4.760 4.835 0.925 5.

940268 1.01 1.62 1.20 51 4.820 4.865 0.915 5.

940269 0.99 1.60 1.18 1 17 5.220 5.020 1.310 5.

940270 0.99 1.59 1.18 51 4.860 4.905 0.905 5.

The test results shown in the figures and set out in the tables were obtained with a mixture of coal and petroleum coke in a COREX® 1000 ironmaking unit. These units and their operation are described in U.S. Patent Nos. 5,259,864; 5,259,865; 5,320,676; 5,397,376 and 5,413,622, which were incorporated by reference herein for all purposes.

Refer now to Fig. 11 which is a schematic flow sheet of a melter gasifier ironmaking process of the type in which the method of the invention is particularly useful. Further, the data for the tables were collected from a COREX® process substantially identical to the process illustrated in Fig. 1. The COREX® process utilizes a melter gasifier substantially similar to the melter gasifier of Fig. 12 and generally indicated in Fig. 11 by the numeral 100. The COREX® process is designed to operate under elevated gas pressures up to five bar gauge. The process pressure is supplied from the integral oxygen production facility which supplies oxygen through the tuyeres 119 on the COREX® melter gasifier 100 and operates the primary direct reduction furnace 126 for iron ore reduction to sponge iron.

Charging of petroleum coke and/or coal to the melter gasifier 100 is accomplished through a pressurized lock hopper 128. The iron ore is supplied to the reduction furnace 126 through a similar lock hopper 121 in a manner well known to those skilled in the art. The petroleum coke and/or coal is stored in a pressurized bin and charged into the melter gasifier by suitable means such as speed controlled feed screw 134.

Upon entering the dome of the melter gasifier 100, at entry port 101, some of residual hydrocarbons contained in the fuel are flashed off at l,100°C and cracked in the reducing atmosphere to CO and H₂. The calcined coke particles are rapidly heated to 1,100°C and descend with the hot reduced sponge iron particles from the reduction furnace 126 to the dynamic fluidized bed above the fusion zone.

The sponge iron is melted in the fusion zone generally indicated as bed 116 and drops to a molten liquid iron pool 111 accumulated below the oxygen tuyeres 119 on the melter gasifier hearth 114. The liquid iron is periodically tapped and removed through a taphole 110 from the melter gasifier hearth. These are the types of taps from which the data in Tables 1 and 2 are derived. A minor amount of sulfur freed from combustion of the petroleum coke is carried over with the molten iron as iron sulfide and removed from the melter gasifier. The iron sulfide is desirably removed from the iron by injecting and mixing calcium carbide and lime into the molten iron in a system external to the gasifier. The lime and calcium carbide form calcium sulfide from the residual sulfur in the molten iron. The calcium sulfide rises to the surface of the molten iron and is mechanically removed by skimming or by bottom tapping. The calcined coke (essentially all carbon) is gasified into CO which rises to the gasifier gas outlet 119. The combined reducing gases rise to the gasifier gas outlet main 119 at 1,100°C where they are tempered with a side stream from the cooling gas scrubber 109 and cooling gas blower 140 via line 103 to 850^βC before passing to the hot cyclone 115 and the reduction furnace 126. If necessary, a standard scrubber device is installed to remove H₂S from the cooling gas bleed, prior to be discharged as export gas 131 at 40°C. The gasifier gas cooling is essential to avoid sintering and to maintain discrete free flowing particles in the column of the reduction shaft furnace 126. Over-heating will cause clusters or clinkers to form inside the shaft furnace with disruption of the furnace solids and gas flow.

After being cooled in the cooling gas scrubber 109 and cleaned of dust in the hot cyclone 115, the gasifier gas is passed upward in the reduction furnace 126 through the descending bed of iron ore converting it to metallic sponge iron and carburizing the reduced iron to a level of three to five percent prior to hot discharge to the melter gasifier 100. The gasifier gases are partially consumed by the reaction in the reduction furnace and discharged at 127 as furnace top gas at 140°C. The top gases are cleaned in the top gas wet scrubber 129, removing water vapor formed during iron ore reduction. The scrubbed export gas is low in particulates and sulfur and has a heating value of 220 Btu/scf while containing 30% of C0₂.

Fig. 12 schematically illustrates a melter gasifier, generally indicated by the numeral 1 has side walls 2 which are refractory lined on the inner sides. The dome 3 of the melter gasifier 1 has three openings 4, 5 and 6. The opening 4 is adapted for charging petroleum coke and/or coal 7 of various grain sizes into the interior of the melter gasifier. The most useful carbon or coke particles range in size from 1/4 inch (6 mm) to as large as one inch (25 mm) and larger. The amount of carbon that should be added to the melter gasifier in accordance with the invention is determined by the amount of fixed carbon in the coal/coke needed for combustion in the process, residual FeO reduction, maintaining the temperature of the fusion zone, and an additional amount needed to saturate the liquid iron with at least 4.3% carbon by weight.

Particulate ferrous material 8 is charged into the melter gasifier through the opening 5, preferably iron sponge. It is suitable to supply the iron sponge at an elevated temperature. To carry away the reduction gas which is formed during the reaction in the melter gasifier, a conduit 9 is provided extending out of opening 6. The reduction gas carried away may be used in many processes to pre-reduce or reduce oxidic iron ore. When using petroleum coke and/or coal having a high sulfur content, i.e., in excess of 2-3%, it may be desirable to provide a scrubbing process for removing HS from the reduction cooling gas to maintain a low sulfur level when the reduction top gas is combined for export. An iron chelate process which provides elemental sulfur is useful in this instance.

In general, the melter gasifier comprises a lower section A, a central section B, an intermediate fusion section C between sections A and B, and an upper section D above the central section B, whose cross-section is widened and which serves as an expansion zone. In the bottom region of the lower section A of the melter gasifier 1, which serves to collect molten metal, a tapping opening 10 for the melt 11 is provided in the wall 2. Further up the wall there is an opening 12 for the slag tap which includes sulfur residue from the combustion of petroleum coke and/or coal in the lower section A. In the lower region of the central section B of the melter gasifier 1, a nozzle pipe is inserted through an opening 13 in the wall 2 for recirculating reduction gas cyclone dust. Oxygen-containing carrier gas may be injected into the melter gasifier through nozzle pipe 14. If desired, carbon carriers can be introduced into the melter gasifier 1 in a first horizontal blow-in plane 15. Preferably, a plurality of openings 13 with nozzle pipes 14 are present at this location spaced around the melter gasifier.

In the central section B, a first fluidized bed zone 16 may be formed by coke and/or coal particles from combusted petroleum coke and/or coal. The intermediate fusion section C, which, in the embodiment illustrated, is cylindrically designed, is provided to accommodate a second zone 17 of a fluidized bed formed by coke particles from combustion of the petroleum coke. Generally, the coke particles in the fusion section C fluidized bed of the melter gasifier will have less motion than those in section B. Through the wall of the intermediate section C, a gas supply means, in the present case, multiple nozzle pipes or tuyeres 19, are inserted. The tuyeres are positioned to direct the gases toward the central axis 18 of the melter gasifier. The tuyeres are adapted for injecting oxygen-containing gas, steam, carbon dioxide, and carbon carriers into the melter gasifier. They project into the second zone 17 of coke particles, ending closely above the slag layer 20. Just one nozzle pipe 19 has been illustrated in Fig. 12. Depending on the size of the melter gasifier, 10 to 40, preferably 20 to 30, nozzle pipes 19 may be provided, and located substantially in a second horizontal blow-in plane 21. The nozzle pipes 19 are arranged so as to be vertically pivotable in the direction of the double arrow 22. Also, the nozzle pipes 14, through which the carrier gas and additional fuel flow into the first fluidized-bed zone 16, are designed to be vertically pivotable with the embodiment of the invention i1lustrate .

The ferrous material 8, introduced through the opening 5, at first reaches the first fluidized-bed zone 16 after having fallen through the upper section D of the melter gasifier which serves as an expansion zone in which the ferrous material is slowed and heated. Smaller particles melt, drop through the second fusion zone 17 of coke particles and descend into the lower section A. Larger particles at first remain lying on the second zone 17 or are held fast in the uppermost layer of this zone, until they are also melted upon the action of the high temperature prevailing in the region of the first blow-in plane 15. In the second zone, the downwardly dropping metal melt is super-heated and, if desired, may be treated by the reaction of fine particle fluxes which are introduced through the nozzle pipes 19. The metal melt 11, tapped through the opening in 10, is sufficiently hot in order to be subjected to further metallurgical after treatments. Since there is no ash in the petroleum coke, no slag is formed from petroleum coke. The petroleum coke particles, during operation of the melter gasifier, must be continuously supplemented through the opening 4 with larger pieces, which are preferably used to build up the second zone 17, after falling through the first zone 16. The melter gasifier shown in Fig. 12 and the prior art operation using coal or coke produced from coal are described in U.S. Patent No. 4,588,437. From the foregoing, it is apparent that the present invention provides a method of producing liquid iron having a low sulfur content in a fusion zone of a melting or smelting process when using carbonaceous fuel containing substantial sulfur which, when combusted, forms gases having a high sulfur content. In accordance with the invention, the liquid iron is maintained saturated with at least 4% of carbon (and preferably at least 4.3% to 4.5%) by weight of the liquid iron and preferably at least 0.3% silicon by weight of the liquid iron during formation of the liquid iron in the fusion zone during the melting or smelting process. The temperature of the liquid iron in the fusion zone is maintained in excess of 1,450°C. For best results, the temperature of the liquid iron in the fusion zone is maintained between about 1,450°C and 1,550°C. Most preferably, the temperature of the liquid iron in the fusion zone is about 1,490°C. In a preferred embodiment, the melting or smelting process is carried out in a melter gasifier having a fusion zone of about from 2 to 3 meters in depth. The temperature of the liquid iron in the fusion zone is maintained in excess of 1,450°C. Generally, the liquid iron temperature on the fusion zone is between about 1,470°C and 1,550°C. In the preferred embodiment, the temperature of the liquid iron in the fusion zone is about 1,490°C.

The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. The embodiments are to be construed as illustrative rather than restrictive. Variations and changes may be made by others without departing from the spirit of the present invention. Accordingly, all such variations and changes which fall within the spirit and scope of the present invention is defined in the following claims are expressly intended to be embraced thereby.

Claims

CLAIMSI claim:

1. A method of producing liquid iron in a fusion zone of a smelting process having a low sulfur content when using carbonaceous fuel containing substantial sulfur which, when combusted, form gases having a high sulfur content comprising maintaining the liquid iron saturated with at least 4% of carbon by weight of the liquid iron during formation of the liquid iron in the fusion zone during the smelting process.

2. A method of producing liquid iron in a fusion zone of a smelting process having a low sulfur content when using carbonaceous fuel containing substantial sulfur which, when combusted, form gases having a high sulfur content comprising maintaining the liquid iron saturated with at least 4% of carbon by weight of the liquid iron and at least 0.3% silicon by weight of the liquid iron during formation of the liquid iron in the fusion zone during the smelting process.

3. The method of claim 2 further characterized in that the temperature of the liquid iron in the fusion zone is maintained in excess of 1,450°C.

4. The method of claim 3 further characterizing that the temperature of the liquid iron in the fusion zone is between about 1,450°C and 1,550°C.

5. The method of claim 4 further characterized in that the temperature of the liquid iron in the fusion zone is about 1,490°C.

6. The method of claim 2 further characterized in that the concentration of manganese is maintained at at least 0.35% by weight.

7. The method of claim 2 where the smelting process is carried out in a melter gasifier having a fusion zone of about from 0.15 to 3 meters and that the temperature of the liquid iron in the fusion zone is maintained in excess of 1,450°C.

8. The method of claim 7 further characterized in that the temperature of the liquid iron in the fusion zone is between about 1,470°C and 1,550°C.

9. The method of claim 8 further characterized in that the temperature of the liquid iron in the fusion zone is about 1,490°C.

10. A method of producing liquid iron in a fusion zone of a smelting process having a low sulfur content when using carbonaceous fuel having a substantial sulfur content which, when combusted, form gases having high sulfur content, said fuel supplying heat to the smelting process and forming a slag when combusted, maintaining the liquid iron saturated with at least 4% of carbon by weight of the liquid iron and at least 0.3% silicon by weight of the liquid iron during formation of the liquid iron in the fusion zone during the smelting process to cause sulfur fro the carbonaceous fuel to be preferentially dissolved into the slag.

11. The method of claim 10 further characterized in that the temperature of the liquid iron in the fusion zone is maintained in excess of 1,450°C.

12. The method of claim 11 further characterized in that the temperature of the liquid iron in the fusion zone is between about 1,450°C and 1,550°C.

13. The method of claim 12 further characterized in that the temperature of the liquid iron in the fusion zone is about 1,490°C.

14. The method of claim 10 further characterized in that the concentration of manganese is maintained at at least 0.35% by weight.

15. The method of claim 10 where the smelting process is carried out in a reactor having a fusion zone depth of from about 0.15 to 3 meters and that the temperature of the liquid iron in the fusion zone is maintained in excess of l,450°C.

16. The method of claim 15 further characterized in that the temperature of the liquid iron in the fusion zone is between about 1,470°C and 1,550°C.

17. The method of claim 15 where the reactor is a melter gasifier.

18. The method of claim 16 further characterized in that the temperature of the liquid iron in the fusion zone is about 1,490°C.