CA1049792A

CA1049792A - Process and apparatus for producing molten iron

Info

Publication number: CA1049792A
Application number: CA241,177A
Authority: CA
Inventors: Paul Metz; Adolphe Faber
Original assignee: Arbed SA
Current assignee: Arcelor Luxembourg SA
Priority date: 1974-12-06
Filing date: 1975-12-05
Publication date: 1979-03-06
Also published as: SE7513508L; IN155530B; NO142312C; GB1474357A; AR208103A1; PL100437B1; SU603349A3; IT1052536B; FR2293494A1; ZA757537B; BR7507962A; NO142312B; AU8720875A; AT350087B; FR2293494B1; ATA854175A; AU499951B2; ES443235A1; RO69533A; BE836278A

Abstract

ABSTRACT OF THE DISCLOSURE
Molten crude iron is made with simultaneous recovery of flue gases adapted for use in the prereduction of the ore from which the iron is obtained by following these steps a carbon precursor is introduced together with a gaseous reactive medium into a first zone of a main reaction chamber, the introduction being effected beneath the surface of a bath formed by the molten ore or iron so as to cause the carbon to combine with the iron and to supersaturate the melt with carbon; oxygen is simultaneously blown into an adjoining second zone, acting as combustion zone, of the main reaction cham-ber and below the surface of the bath while the bath is continuous-ly agitated so as to convert the excess carbon introduced in the first zone to carbon monoxide, the ore continuing to be melted by the thus produced exothermic reaction in the second zone; the flue gases generated in the main reaction chamber are recycled into a reduction chamber so as to subject the ore to an at least partial prereduction; the ore is passed from said prereduction chamber in-to the second zone of the main reaction chamber at a point close to the point where the oxygen is blown into the bath, and the form-ed molten crude iron is withdrawn from the bath.

Description

~04979Z
The present invention relates to a process of making molt-en iron while simultaneously obtaining a gas mixture which can be used for the prereduction of the employed iron ore.
Undertakings have been going on for quite some time to re-place the blast furnace process and the ore dressing processes, i.e.
coking and subsequent refining as required in a blast furnace pro-cess, by other direct procedures. Within the framework of these efforts many suggestions have been made of which however only vari-ous direct reduction processes have been used in the actual practice.
All propositions to make liquid steel of a desired composition in a single process step from iron ore by means of the so-called melt re-duetion proeesses have so far not had a satisfactory and industrial-ly useful result.
One of the prior art proposals has been to obtain molten steel in a single process step by reacting iron ore in a reduction chamber with a reducing gas and melting the product of the reduction in an adjoining chamber which acts as the melting and gas generating part of the installation. The reduction gas in this process is pro-dueed in the gas generating part of the apparatus by introducing a suitable fuel such as coal or a liquid or gaseous hydrocarbon through a nozzle together with technically pure oxygen. By ad]usting the fuel and oxygen supply passing into the nozzle the composition of the reduction gas could be controlled so as to cause it to have a redueing aetion on the iron ore. The heat neeessary for the melt-ing of the preredueed produet was usually obtained from a separate heating installation at the reaetion ehamber.
The earbon earrier passed into the burner accordingly is used essentially for generating the reduetion gas by an ineomplete oxidation with oxygen. Under the aspeet of the desired direet steel manufaeture it has however not been possible to eontrol the eomposi--

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- ~ , tion of the bath resulting from the molten prereduced material to the extent necessary. Particularly the possibility to cause the fuel to act on the composition of the melt could not be fully ex-ploited.
It is therefore an object of the present invention in the melting of a prereduced material, upon simultaneous recovery of a reduction gas for the ore and upon employment of low priced fuels, to control the reaction process taking place in the bath in a manner that a crude iron melt of desired carbon contents is obtained.
This object is met by (a) introducing a carbon precursor together with a reactive medium adapted to dissociate in the course of the reaction into a first zone, acting as carburization zone, of a main reaction chamber, the introduction being effeeted beneath the surface of a bath formed by the molten ore or iron so as to eause the earbon of a bath formed by the molten ore or iron so as to eause the earbon to eombine with the iron and to supersaturate the melt with earbon;
(b) blowing oxygen into an adjoining seeond zone, acting as eombustion zone, of the main reaction chamber and below the sur-faee of the bath while eontinuously agitating the bath so as to con-vert the excess carbon introdueed into said first zone to carbonmonoxide, the ore continuing to be melted by the thus produced ex-othermic reaetion in said second zone;
(e) recycling the flue gases generated in the melt cham-ber into a reduetion chamber so as to subject the ore to an at least partial prereduetion;
(d) passing the ore from said prereduction chamber into the second zone of the main reaction chamber at a point close to the point where the oxygen is blown into the bath, and (e) withdrawing the formed molten crude iron from the bath.

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104979;~
The invention also comprises an apparatus for carryingout the process wherein two lances extend into the reaction chamber, one lance having an internal channel into which the reactive mixture and, suspended therein, the carbon precursor may be passed below the surface of the intended bath and the second lance having an internal channel for introduction of the ore and another channel, preferably arranged coaxially around said first channel for introducing oxygen below the surface of the bath.
The single FIGURE of the drawing illustrates in diagramma-1- tic form an apparatus for practicing the invention.
The carbon precursor or carrier may be any kind of fossil fuel. Particularly solid fuels may be used such as coal which is not suited for coking, anthracite or lignite, and these materials can be used without expensive preliminary preparation, that is in their unmodified condition in bulk form.
In a preferred embodiment the fuel is blown into the bath in the form of a fine grained or dust-like state suspended in the -likewise introduced reactive medium which may be hydrogen, carbon dioxide or a fuel gas having a high contents of carbon dioxide or also a hydrocarbon material. This causes the carbon to pass into the bath and to combine with the iron to an extent that the carbon contents of the iron is at least 3~ while the volatile components of the carbon are dissociated and together with the dissociation-and reaction products of the reactive medium pass into the flow of the fuel gases.
~ Technical oxygen is then blown into the bath in a carbon ; combustion zone which adjoins the carburization zone with a flow en-ergy to cause at least the penetration of the slag layer on the iron.
This again causes a portion of the carbon, which is combined with the iron in an amount depending on the oxygen introduction, to be `

converted into carbon oxide. By adjusting the carbon and oxygen supply the carbon contents of the molten product can be controlled to obtain a preconceived value in lines with the values for crude or pig iron.
The gases formed in the reaction chamber predominatly are composed of the hydrogen formed in the carburization zone and of the carbon oxide formed in the zone where the oxygen is blown in.
These gases which are generated in the amounts necessary for the reduction of the ore are then passed on a path as direct as possible into an ore-direct reduction installation. It is preferred to con-tinuously check the composition of the reduction gases in order to maintain the desired C0/H2 ratio by adjusting the supply of carbon hydrogen and oxygen. This ratio preferably should not be larger than 3 expressed in volume percent.
The ore which is prereduced by the action of the still hot CO/H2 mixture is then in turn introduced into the melting and ;~
gas generating reaction chamber. This introduction is effected di-rectly into the zone where the ozygen is blown in or to the immed-iate neighborhood of such zone since in this zone excess heat for melting is available. The charge of the ore can for instance be effected by a lance which is provided with several coaxially ar-ranged inlet tubes and is subject to continuous cooling. Thus, through the same lance the oxygen can also be blown into the bath.
The iron oxide which is still present in the partially prereduced product and may also additionally be formed during the blowing in of the oxygen is then largely reduced in the agitated bath by the carbon dissolved in the bath. A sufficient intermixing of the melt can in amny cases be obtained by the mere kinetic ener-gy of the media which are blow into the bath through the lances arranged at an angle. Additional mixing devices such as an induc-, .. . . .

tion coil at the melt and gas generating vessel may be used particu-larly where nozzles are provided in the masonry of the reaction cham-ber for introducing the gaseous media.
The control of the carbon contents of the molten product is effected by adjustment of the fuel and oxygen supply so as to obtain the conventional amounts of carbon contents for pig iron.
For this reason it is possible to keep the temperature in the melt-ing chamber at a comparatively low level. Thus, no problems will arise regarding the durability of the refractory walls of the reac-tion chamber as this is the case in all processes for the directmanufacture of steel from ore or prereduced products.
Because of the vigorous mixing the molten carbon contain-ing crude iron is mixed in the bath with slag which may be separated in a separator vessel which may for instance have the form of a forehearth of the furnace. The crude iron that remains in the re-action chamber serves simultaneously as heat storage material, as `
heat transmission agent, and as reaction promoter.
A further advanctage of the invention is the possibilityto reduce the sulfur contents of the bath in case even of the use of inferior coal having a high sulfur contents. This can be affect-ed by adding finely ground slag forming constitutents for combining with the sulfur. The sulfur can thus be reduced to a point where the crude iron can be further processed into steel without any sub-sequent desulfurization. If fuels are used of a high ash contents, it is preferred however to effect a partial desulfurization in the i separator vessel in view of the volume of slag which will be present in the reaction chamber.
The process of the invention is particularly suited for continuous operation. The introduction of the raw materials as well as the tapping of the melt and of the slag or the emulsion thereof . .

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accordingly are preferably carried out without interruption as a continuous process.
From this description it will be understood that the in-vention creates optimum reaction conditions by employing different reaction zones and by the temporary formation of a carbon excess in the bath. Thus, it is on one hand possible to obtain a valuable re-ducing gas in spite of the employment of inexpensive and inferior fuels and gas forming materials. On the other hand an iron melt is formed with a preconceived carbon contents because of the immediate passing or for further processing of the gases obtained by the re-duction of the ore by the reaction gas. The working temperature can be maintained at a low level compared with melt redcution pro-cesses and this will keep the wear on the refractory all materials of the furnace within reasonable limits.
With particular reference to the drawing which illustrates an apparatus for carrying out the process of the invention it will be noted that 1 indicates a melt furnace which is connected with a eonventional direct reduction installation. The refractory wall 2 of the smelting furnace 1 surrounds a hearth 3 for receiving the melt product and a cover which is connected with a gas outlet 5.
The starting products are introduced for instance through lanees into the reaetion ehamber.
A frist water-eooled lance 70 penetrates the lateral wall of the hearth 2 and extends directly below the surface of the bath.
This lance is arranged at a slant in order to cause the introduced materials to have a motion component which is directed towards the overflow tap hole 6. The height of the lance ban be adapted to the variations of the bath level by changing the depth of immersion of the lance.
In the exterior annular channel 71 cooling water for the lance circulates. In addition this lance serves to introduce the carbon containing material and the reactive medium which preferably consists of a flue gas mixture composed of carbon monoxide, carbon dioxide and hydrogen. The finely divided coal is obtained from a storage bin 73 and is passed across a bucket wheel 74 into the cen-tral portion 72 of the lance. The bucket wheel is adjustable by a variable adjustment device in regards to its performance. The re-active medium in the preferred form of a flue gas is introduced through an extension 75 of the central channel 72. The flue gas will entrain the carbon particles and cause both components to pene- --trate the bath at a sufficient depth.
A second lance 80 which is also water-cooled passes through the cover 4 of the furnace and extends into the bath in an area be-tween the lance 70 and the tapping hole 6.
The prereduced material is introduced through a drop pipe 83 provided in the lance 80. The pipe is adapted to the granulomet-ery of the prereduced material (Fe/FeO). The drop pipe is provided directly or via a separate storage with the hot ore material. An intermediate annular channel or jacket 82 is provided between the central pipe 83 and the outer cooling jacket 81. The oxygen is pass-ed through this intermeidate channel at a sufficiently great force into the bath to penetrate below its surface.
It is also possible to add for instance lime from a stor-age funnel 84 to combine with the coal ash and the sulfur or also to add an ore concentrate in order to modify the temperatureO All this can be done in a continuous or discontinuous operation.
Both lances 70 and 80 are adjustable as to their height and preferably are sealed against the wall portion of the furnace by gas seals.
The portion of the melt which flows from the carbon in-troduction or carburization area into the area where the oxygen is blown in is subject in that second area to the action of the oxygen and thus the excess portion of dissolved carbon will be converted to carbon monoxide which can then escape in gaseous form.
The introduced prereduced material melts in the zone where the oxygen is blown in because of the excess heat present in that zone and the melt then mixes with the remainder of the bath.
Any unreduced iron oxide that may still be present in the charge passes into the bath and is exposed to the contact with the carbon dissolved in the bath and will thus be subject to direct re-duction.
The carbon containing iron is discharged from the lower portion of the melt through an overflow drain 6. This discharge is effected to the extent that new melt forms so that the volume will continuously remain constant. As required by the fuel employ-ed and the developing reaction the iron may also be subjected to a desulfurization in a forehearth or mixer~type vessel. It can there also be completely separated from the slag. The slag may then be immediately granulated while the pig iron is continuously or period-; 20 ically passed for further processing.
The gas which forms in the reaction chamber will predomin-antly consist of a CO/H2 mixture. It is passed via an outlet 5 di-rectly into a direct reduction installation which is not further shown in the drawing. If desired there may be a compensatory con-trol in the gas outlet of the volume of gas and temperature.
The flue gases formed in the prereduction or obtained from any other suitable operation can be recycled into the main reaction chamber where the melting and gas generation takes place. If de-sired there may be a CO2 and/or H2O scrubbing device interposed.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The process of making molten crude iron with simultane-ous recovery of flue gases adapted for use in the prereduction of the ore from which the iron is obtained, the said process comprising (a) introducing a carbon precursor together with a reactive medium adapted to dissociate in the course of the reaction into a first zone, acting as carburization zone, of a main reaction cham-ber, the introduction being effected beneath the surface of a bath formed by the molten ore or iron so as to cause the carbon to com-bine with the iron and to supersaturate the melt with carbon;
(b) blowing oxygen into an adjoining second zone, acting as combustion zone, of the main reaction chamber and below the sur-face of the bath while continuously agitating the bath so as to con-vert the excess carbon introduced into said first zone to carbon monoxide, the ore continuing to be melted by the thus produced ex-othermic reaction in said second zone;
(c) recycling the flue gases generated in the melt cham-ber into a reduction chamber so as to subject the ore to an at least partial prereduction;
(d) passing the ore from said prereduction chamber into the second zone of the main reaction chamber at a point close to the point where the oxygen is blown into the bath; and (e) withdrawing the formed molten crude iron from the bath.

2. The process of claim 1 which is carried out as a con-tinuous operation.

3. The process of claim 1 wherein the carbon carrier is introduced in solid, finely granulated form into the path of an endothermically reacting medium and is passed into the bath while suspended in said medium.

4. The process of claim 1 wherein the reactive medium predominantly consists of a carbon monoxide-carbon dioxide mixture.

5. The process of claim 1 wherein the oxygen is blown in-to the second area of the reaction chamber in an amount related to the carbon excess in the bath and at a flow speed so that it pene-trates the layer of slag formed on said bath.

6. The process of claim 1 wherein the gas mixture generat-ed in said reaction chamber predominantly consists of carbon monoxide and hydrogen.

7. The process of claim 6 wherein the total volume of said flue gases generated in said two zones of the reaction chamber and the ratio of carbon monoxide to hydrogen in said flue gases are adjusted to a preconceived relation to the amounts of carbon carrier and reactive medium introduced into the bath.

8. The process of claim 6 wherein the ratio of CO/H is maintained below 3.

9. The process of claim 1 wherein the carbon carrier and reactive medium are forced into the bath with a high flow speed and at an angle relative to the surface of the bath so as to cause the melt to move away from the point of entry of the carbon carrier and reactive medium.

10. The process of claim 9 wherein the carbon carrier and reactive medium are caused to move toward the area where the oxygen and ore enters the bath.

11. The process of claim 1 wherein the flue gases generat-ed in the two zones of the reaction chamber are directly passed in-to the reduction chamber while still in hot condition.

12. The process of claim 1 wherein the prereduced ore is passed into the bath at about the center of the area where the blown-in oxygen enters the bath.

13. The process of claim 1 wherein the oxygen and the prereduced ore pass into the bath in contiguous areas.

14. The process of claim 1 wherein slag forming and sul-fur absorbing additives are added to the bath.

15. The process of claim 1 wherein the withdrawal of the molten crude iron is effected by an overflow from the lower portion of the bath.

16. The process of claim 1 wherein the slag is separated from the melt outside said reaction chamber.

17. An apparatus for carrying out the process of claim 1, the said apparatus comprising (a) a reaction chamber for receiving of a bath of molten iron, the said reaction chamber forming part of a melt furnace;
(b) a first lance extending through the walls of said re-action chamber below the intended surface of said bath;
(e) a duet provided in said first lance for passing a gas-eous medium therethrough;
(d) an inlet channel for a solid carbon carrier merging into said duet prior to its inner end;
(e) a second lance extending through the walls of said re-action chamber below the intended surface of said bath, its inner end being disposed close to the point where said first lance enters the bath;

(f) two separate inlet channels provided in said second lance, one for receiving the oxygen and one for receiving the ore;
(g) an outlet for the flue gases generated in said reac-tion chamber, the said outlet being connected with a prereduction chamber for said ore; and (h) an outlet from below the intended surface of said bath for discharge of the molten crude iron.

18. The apparatus of claim 17 wherein the two inlet channels in said second lance are coaxially arranged.

19. The apparatus of claim 17 wherein the outlet for the discharge of the iron is an overflow outlet.

20. The apparatus of claim 17 which includes an inlet channel for introducing slag forming substituents, the said inlet channel merging into said channel for introducing the ore.