Title of Invention

A PROCESS FOR SMELTING FINE-GRAINED ,DIRECT-REDUCED IRON

Abstract

A process for smelting fine—grained, direct—reduced iron (DRI) which consists to at least 80% by weight of a grain size of at most 3 mm, in an electric are furnace which contains a bath of malten iron and a foamed s1ag 1ayer on the molten iron, wherein the DRI during operation of the furnace is passed through at least one lance which passes through the roof of the furnace, from above through the aperture of the lance into the foamed slag layer and on to the molten iron, wherein the DRI falls through the lance or lances on to the iron bath solely through the force of gravity and without using a conveying gas, characterised in that each lance aperture is located in the foamed slag layer, and that the proportion of the DRI fed through the lance or lances to the iron bath relative to the total amount of iron material charged is 85 to 100% by weight.

Full Text

Process of Melting Granular, Directly Reduced Iron in an Electric Arc Furnace Description This invention relates to a process for smelting fine-grained, direct-reduced iron. further This invention /relates to a process of melting granular, directly reduced iron (sponge iron), which for at least 80 wt-% has a grain size of not more than 3 mm, in an electric arc furnace containing a bath of liquid iron, where during the operation of the furnace a foamy slag layer is formed on the bath. Among experts, directly reduced iron is also referred to as sponge iron or DRI (directly reduced iron). The U.S.-Patent 5,433,767 describes the direct reduction of fine-grained iron ore in at least two fluidized beds, where hot reduction gas is also used as fluidizing gas. There is produced fine-grained sponge iron, which is subsequently liquefied in a melting reactor at temperatures of 1500 to 1700°C and is further reduced. The production of fine-grained sponge iron is also described in the U.S.-Patent 5,603,748. It is the object underlying the invention to supply the granular, directly reduced iron also in the hot condition largely free of loss to the iron bath during the operation of the furnace. In accordance with the invention this is -2 — achieved in the above-mentioned process in that during the operation of the furnace the directly reduced iron is passed through at least one movable lance from the top through the aperture of the lance into the slag layer. Apart from the directly reduced iron other granular or lumpy iron may also be added to the iron bath, e.g. scrap. During the operation of the furnace gases are constantly ascending from the iron bath, which are discharged to the top and sucked off from the furnace. The introduced, directly reduced iron first of all enters the more or less foamy slag layer, where it is either directly molten on or sinks into the iron bath due to its weight. The foamy slag layer prevents that fine-grained reduced iron introduced via the lance is entrained by the ascending gases and discharged from the furnace, which would lead to increased losses of iron. Entrained iron may also deposit as caking in the upper portion of the furnace or in the waste gas line and thus lead to interruptions. The electric arc furnace may be operated in the known manner with direct current or alternating current. It is also known to design the electrodes introduced through the furnace roof as vertically movable electrodes and gradually raise the same during the operation of the furnace, so that their distance from the bath surface remains more or less constant during the batch operation. The fine-grained, directly reduced iron is supplied onto the iron bath from the top through one or several lances, where it is expediently prevented that the aperture of the lance or lances gets in contact with the liquid iron of the iron bath. Therefore, the aperture of each lance is vertically movable, where for instance the lance like the electrode is pulled upwards with rising level of the iron bath. Expediently, the distance of the aperture of each lance from the surface of -3 — the iron bath is 3 to 100 cm, and mostly 5 to 50 cm. It is expedient to ensure that the lance aperture is always kept inside the foamy slag layer, so that no sponge iron is entrained to the top by ascending gases. The directly reduced iron can be moved through the lance towards the bath merely by means of gravity, but it may also be blown through the lance into the foamy slag by means of a gaseous accelerator, e.g. nitrogen. By adding carbon and oxygen it can be ensured in a manner known per se that a stable foamy slag layer is formed on the iron bath and is maintained there during the operation of the furnace. This layer constitutes a reaction zone, which protects the fine-grained iron from reoxidation. At the same time, it provides for the immersion of the elec-trode(s), to protect them from oxidation and improve the heat transfer from the arc flare to the melt. Carbon-containing media and O2-containing gas are supplied to the iron bath through submerged tuyeres. The carbon-containing media may be powdery, liquid or gaseous, and as O2-containing gas there is commonly used technically pure oxygen. The submerged tuyeres may be arranged as desired, e.g. in the bottom of the furnace or in the side walls. Expediently, the gas space above the foamy slag also comprises one or several tuyeres, for instance for introducing O2-containing gas, so as to effect a partial afterburning of CO. The iron bath of the furnace usually consists of at least 90 wt-% liquid iron. The furnace may be used for producing liquid pig iron or steel. The liquid metal is withdrawn from the furnace at temperatures in the range from 1300 to 1700°C and preferably at a temperature of at least 1350°C in the case of pig iron and at least 1550°C in the case of steel. Embodiments of the process will be explained with reference to the accompanying drawing, wherein: - 4 - Fig. 1 shows a vertical section along line I-I of Fig. 2 through a DC electric arc furnace in a schematic representation, Fig. 2 shows a horizontal section along line II-II of Fig. 1, Fig. 3 shows an AC electric arc furnace in a representation analogous to Fig. 1, in a section along line III-III of Fig. 4, and Fig. 4 shows a horizontal section along line IV-IV of Fig. 3. The electric arc furnace 1 of Fig. 1 and 2 comprises a brick-lined crucible 2 and a removable roof 3. The crucible is provided with at least one bottom electrode 4. Having been introduced through apertures in the roof 3, an upper electrode 5 and three lances 6 protrude from the top into the interior of the furnace, of which lances only two are shown in Fig. 1. The number of the upper electrodes 5 and the lances 6 may also be chosen different from that in the drawing. The lances 6 are provided with a water cooling, which is not represented in the drawing. During the operation, the furnace 1 contains an iron bath 8, which reaches up to the bath level 8a. During the operation of the furnace, a layer 9 of foamy slag is formed above the bath level 8a, which is desired. Through submerged tuyeres 10 and 11 carbon-containing media and/or O2-containing gas is introduced into the iron bath 8. Through a double lance 12 -see Fig. 2 - oxygen and carbon-containing media can be blown through the opened furnace door 13 into the slag layer 9, thereby promoting the foam formation in a manner known per se. By means of lateral tuyeres 14 disposed at an angle above the bath, oxygen can be blown onto the bath in a manner known - 5 - per se. Horizontal tuyeres 15 are used in a likewise known manner for supplying oxygen, so as to afterburn CO. The upper electrode 5 can, as is likewise known, be adjusted vertically, so that its distance from the bath level 8a is kept constant with rising liquid level of the iron bath. Through the lances 6 the fine-grained, directly reduced iron is introduced from a not represented reservoir into the furnace 1, so that it is absorbed by the iron bath 8 without any remarkable losses. For this purpose, the apertures 6a of the lances 6 are disposed at a relatively short distance above the bath level 8a and preferably in the foamy slag layer 9. Like the upper electrode 5, the lances 6 can also be moved vertically upwards, so that the desired distance of the apertures 6a of the lances 6 from the bath level 8a is maintained. This distance usually lies in the range from 3 to 100 cm, and preferably 5 to 50 cm. The sponge iron can also be introduced hot into the furnace through the lances 6, e.g. at temperatures of 300 to 1000°C. The furnace 1 is operated batchwise, and at the end of a melting phase liquid pig iron or liquid steel are withdrawn through the sealable taphole 16, see Fig. 2. The AC electric arc furnace la shown in Fig. 3 and 4 comprises three upper electrodes 5, of which only one is shown in Fig. 3. Moreover, the reference numerals have the meaning already explained in conjunction with Fig. 1 and 2. Example: There is employed an electric arc furnace operated with three-phase alternating current, as it is represented in Fig. 3 and 4. The furnace is capable of being tilted. The crucible 2 has a capacity of 150 t liquid iron, the current is supplied by a transformer with a power of 100 MVA. The three - 6 - electrodes 5 consist of graphite, their distance from the ir-ron bath is kept constant at 50 mm. Before the first directly reduced iron is charged into the furnace after an extended downtime, there is first of all produced an iron bath of 1560°C through partial melting of 40 t iron scrap. Through three water-cooled lances 6 directly-reduced iron with an upper grain size limit of 1.2 mm is charged into this bath, which iron comes from a fine-ore reduction plant and has a temperature of 650°C. The directly reduced iron contains 7 wt-% FeO, 4 wt-% SiO2, 2 wt-% A12O3 and 1 wt-% C apart from metallic iron. The apertures 6a of the lances 6 have a distance of 80 mm from the bath level 8a, which is controlled and kept constant over the entire melting phase. The feed rate of directly reduced iron is 1.2 t/min per lance. Through the submerged tuyeres 11, 5 Nm3 /min technically pure oxygen and 25 kg/min carbon in the form of heating oil are introduced into the furnace, and in addition lime is supplied at a rate of 300 kg/min. Moreover, through the double lance 12, which is adjustable in a manner known per se and is immersed in the foamy slag layer 9, minor amounts of oxygen and carbon are blown in, so as to support the formation of a stable foamy slag layer. There is produced a steel melt of 1630°C, which is withdrawn from the furnace after an operating time of one hour. At a temperature of 1630°C, the amounts of directly reduced iron, carbon, oxygen and lime supplied to the furnace provide a steel quantity of 150 t with a carbon content of 0.1 wt-%. The slag formed has a basicity (weight ratio CaO/SiO2) of 2.5. Upon tapping, 30 t of the steel remain in the furnace, so that with the next batch the supply of directly reduced iron can immediately be started without having to melt on scrap. - 7 -We Claim: 1. A process for smelting fine-grained, direct—reduced iron (DRI) which consists to at least 80% by weight of a grain size of at most 3 mm, in an electric arc furnace which contains a bath of molten iron and a foamed slag layer on the molten iron, wherein the DRI during operation of the furnace is passed through at least one lance which passes through the roof of the furnace, from above through the aperture of the lance into the foamed slag layer and on to the molten iron, wherein the DRI falls through the lance or lances on to the iron bath solely through the force of gravity and without using a conveying gas, characterised in that each lance aperture is located in the foamed slag layer, and that the proportion of the DRI fed through the lance or lances to the iron bath relative to the total amount of iron material charged is 85 to 100% by weight. 2. A process as claimed in claim 1, wherein each lance is vertically adjustable and its aperture is held at an approximately constant distance of 3 to 100 cm above the surface of the iron bath during furnace operation. 3. A process as claimed in claim 1, wherein the furnace has nozzles for introducing carbon—containing material and 0 — 2 containing gas. 4. A process as claimed in claim 1, wherein the DRI is passed o into the furnace at temperatures in the range of 300 to 1000 C. - 8 - 5. A process as claimed in claim 1, wherein the iron bath has the quality of pig iron or steel. A process for smelting fine—grained, direct—reduced iron (DRI) which consists to at least 80% by weight of a grain size of at most 3 mm, in an electric are furnace which contains a bath of malten iron and a foamed s1ag 1ayer on the molten iron, wherein the DRI during operation of the furnace is passed through at least one lance which passes through the roof of the furnace, from above through the aperture of the lance into the foamed slag layer and on to the molten iron, wherein the DRI falls through the lance or lances on to the iron bath solely through the force of gravity and without using a conveying gas, characterised in that each lance aperture is located in the foamed slag layer, and that the proportion of the DRI fed through the lance or lances to the iron bath relative to the total amount of iron material charged is 85 to 100% by weight.

Documents:

01218-cal-1998-abstract.pdf

01218-cal-1998-claims.pdf

01218-cal-1998-correspondence.pdf

01218-cal-1998-description(complete).pdf

01218-cal-1998-drawings.pdf

01218-cal-1998-form-1.pdf

01218-cal-1998-form-2.pdf

01218-cal-1998-form-3.pdf

01218-cal-1998-form-5.pdf

01218-cal-1998-letters patent.pdf

01218-cal-1998-p.a.pdf

01218-cal-1998-priority document others.pdf

01218-cal-1998-priority document.pdf

1218-CAL-1998-CORRESPONDENCE 1.1.pdf

1218-CAL-1998-FORM 15.pdf

1218-cal-1998-granted-abstract.pdf

1218-cal-1998-granted-claims.pdf

1218-cal-1998-granted-description (complete).pdf

1218-cal-1998-granted-drawings.pdf

1218-cal-1998-granted-form 2.pdf

1218-cal-1998-granted-specification.pdf

1218-cal-1998-priority document.pdf

1218-cal-1998-translated copy of priority document.pdf