DE1800131B1 - Multi-zone melting process and multi-zone melting furnace for the continuous production of steel - Google Patents

Description

The invention relates to a multi-zone melting process for continuous Manufacture of steel by electrothermal reduction of oxide ores, smelting and refining them so that the finished steel can be poured into solid forms can. The invention also relates to a multi-zone melting furnace for continuous Manufacture of steel with an electro-reduction chamber and an inflation freshness chamber to carry out the proposed method.

There are known multi-zone melting furnaces in which the metal to be melted Entered into a melting chamber batchwise or continuously and the melt is refined in a fresh chamber connected to the melting chamber. slag and steel are tapped directly from the fresh chamber, i.e. H. from a proportionate restless zone, so that the slag has a relatively high Fe content (U.S. Patent 3,353,807 and French Patent 1,929, respectively).

It is also known in a single chamber smelting furnace to be continuous to put preheated crushed ore into the treatment chamber where it is melted and is freshened. Here, too, the slag and the finished steel are immediate tapped from the fresh zone, which is why there is no high Fe content in the slag should be avoided (U.S. Patent 1,819239).

It is also known to use pre-reduced ores in a multi-chamber furnace to melt and separate the melt consisting of pig iron from the slag and fresh in a separate oven. To get as much iron out of the slag as possible to deposit, a second melting chamber is provided in which the slag is treated again before the final parting, but the parting takes place the slag produced during melting in a relatively restless zone (British Patent 961,408).

On the other hand, it is known to enter ores before continuously preheat and preheat in an electric smelting furnace (U.S. Patent 1 987 952). In the case of electric melting furnaces, it is also known in principle, the melt to stir inductively.

Around the slag in a relatively quiet zone after refining to separate from the melt, a fresh furnace has already been proposed, the one Having fresh chamber with metal tapping into which the molten pig iron is entered and to which a separate slag separation chamber in the form of a branch connected. There is at least partially a countercurrent between slag and melt takes place, so that some of the slag is still deposited before it is tapped Iron can return to the bulk of the melt (USA.Patent 3,326,672). In another embodiment of a refining furnace, in a chamber Refined to form an emulsion of slag and metal and in another Chamber calms this emulsion so that the slag settles and tapped can be (Austrian patent specification 261 645). After all, it is also known to carry out freshening in several interconnected chambers (Belgian Patent 537 844). In these three cases, however, the ores must be stored in a separate Furnace must be melted beforehand.

All of these known steelmaking processes have the disadvantage in common that a relatively large amount of equipment is necessary, with the slag has a relatively high Fe content.

The object of the invention is to provide steel with relatively to produce little capital investment, whereby the slag tapped off an extremely has a low Fe content.

To solve this problem, a multi-zone melting process for the continuous production of steel by electrothermal reduction of oxidic ores, smelting and refining suggested that by combining the following known measures are characterized: a) continuous introduction of preheated and prereduced, agglomerated or crushed oxidic Ores in the arc melt zone; b) inductive stirring of the melt in the arc melting zone; c) continuous forwarding of the melt from the arc melting zone into the Fresh zone in which the melt is placed in several consecutive locations is refined with oxygen-containing gas, and d) continuous countercurrent between Slag and melt for the slag separation zone and for separate metal tapping.

According to the invention, the melting and refining takes place in different, however, interconnecting zones take place, and it is also a special slag settling and separation zone provided in one and the same furnace.

The liquid metal in the melting zone becomes turbulent and circulation is added and kept in this state, the melt being continuous flows from the melting zone into the fresh zone and the slag flows into the slag separation zone got. This allows you to continuously work in a single furnace with relatively Melting ores and processing them into steel with little energy.

In a preferred embodiment of the invention, the ore at a temperature between 400 and 12000 C, preferably between 850 and 11000 C, entered into the arc melting zone of the electric furnace, by a half steel with a carbon content between 0.5 and 4 O / o and a silicon content of not more than 1 O / o to be produced, whereupon this melt by blowing in a oxygen-containing gas and a basic flux in the fresh zone to steel is freshened.

The slag flows in at least part of the refreshment bowl compulsorily in countercurrent to the melt and reaches a relatively calm slag separation zone, from which the slag is tapped after it has settled sufficiently.

Because of the immediate continuous addition of preheated Ore in the arc melting zone, the melting process is extremely fast and taking economic energy utilization carried out. The circular motion of the melt in the continuously operating arc melting zone can be used as a stirrer Electric induction coils are generated under the arc melting chamber sit. However, other precautions can also be taken to reduce the stirring movement or to generate rotary motion of the liquid metal. In any case, the The composition of the melt leaving the melt zone should be as homogeneous as possible.

It has been found that it is advantageous if the in the arc melting zone entered pre-reduced iron ore agglomerates have a residual carbon content of 2.5 to 6%. This residual carbon content supports the melting reactions, reduces the heat and energy requirements of the procedure and helps to achieve an optimal Maintain carbon content in the melt for desulfurization during refining. If the prereduced ore chunks or ore agglomerates are not inherently carbon Contained in the desired amount, carbon is made out in the form of tiny bits Bone charcoal, coal, coke or graphite are added along with the ore.

For example, the melt or the half-steel has in the melt zone a carbon content between 1.5 and 2.5 O / o and a silicon content between 0.1 and 0.5 o / o. However, other compositions may be used in special circumstances the melt or the semi-steel be possible.

One possibility that always the correct ones in the arc melting zone Amounts of carbon and silicon are present in this zone either directly or through a slag separation zone connected to it constantly introduce molten pig iron, using this in the usual manner a hot blast cupola from scrap or melted using scrap will. Such a metal normally contains 3 to 4.5% carbon and 1 to 2 O / o silicon.

Preferably the temperature is in the arc melting zone held metal in the range of 1420 to 15000 C, but can also Temperatures outside this range apply if the same suitable for special operating conditions or special materials or purposes appear.

The melt flows from the arc melting zone into the fresh zone over, the flow velocity and the overflowing amount being a function the amount of prereduced ores added and the melting rate that in turn depends on the energy consumption of the melting zone. These conditions can be easily monitored and controlled.

The slag is continuously removed from the furnace via one or more Hearth-like slag separation chambers removed, the bottom of which is inclined towards the melting zone runs. In this way, from the relatively quiet slag separation zone slowly moving slag granular or other metal are deposited and migrates back into the bulk of the melt under the influence of gravity. this is a feature of the invention which contributes to the fact that the discharged with the slag Iron losses are reduced compared to known methods.

Another feature of the invention, which is used to reduce the through the slag contributes to iron losses, is that the slag in the fresh zone at least partially in the opposite direction flows to the melt. If the Slag over hot metal with a carbon content of 1.5 o / o and more and If it has to flow back with a low silicon content, it becomes part of that in it dissolved iron deposited by the following reaction: (FeO) in the slag + [C] in the metal Fe + CO. In one embodiment of the invention, the slag is not only over a larger part of the length of the elongated fresh zone, but also passed through the arc melting chamber itself and finally from a Slag separation zone or chamber cut off from the fresh zone or fresh chamber is separated, d. H. at another point like the fresh chamber to the arc melting zone or chamber connects.

The reduction in the FeO content of the slag can be further increased when molten pig iron enters the arc melting chamber via an at the same connected slag separation chamber is introduced in such a way that that it flows essentially in the opposite direction to the outflowing slag. The above given reaction is a typical reaction between in the inflowing pig iron the carbon and the FeO content of the outflowing slag. Additionally Part of the silicon in the molten pig iron becomes as follows Equation react: [Si] in pig iron + (2FeO) in the slag + 2Fe + SiO2 Die The resulting silica immediately turns into slag.

According to a further embodiment of the invention is in two refined separate zones, being silicon and sulfur and a part of the phosphorus in the first refining zone, in which the slag is essentially flowing in the same direction as the half-steel, while in the second fresh zone, in which the slag flows in the opposite direction to the metal, the decarburization and the removal of phosphorus predominates. Thereby two different slags are generated, with a wall separating the two zones from each other separates. The conditions in the first zone, in which the carbon content of the Melt is still relatively high, d. H. is above 10 / o, and the influence of the Low in oxygen are beneficial for removing silicon and sulfur. In the second zone, in which the effectiveness of the oxygen both in the melt as well as increasing in the slag are the conditions for removing phosphorus and beneficial for further removing sulfur, especially if the slag flows in this zone in the opposite direction to the metal. In this embodiment of the invention are at least two locations for removing the slag from the fresh zone and a third site may be provided for removing slag from the arc melting zone be provided.

In yet another embodiment, two are separate from one another Fresh zones formed in the fresh chamber, but only one of the metal tapping separate slag removal takes place via a single slag separation chamber. These Embodiment of the invention uses that in U.S. Patent 3 326 672 described process for refining metals, metal alloys and of pig iron. In the first of the two fresh zones, in which the silicon is deposited and sulfur predominates, the slag flows essentially in the same direction like the melt, while the slag in the second zone, in which the deposition of carbon and phosphorus predominate, essentially in countercurrent to the melt to be led. There are deflection zones and / or rows of lances in the furnace, to support the slag flow.

In all embodiments of the invention, the freshening process follows for removing silicon, sulfur, carbon and phosphorus, preferably one continuous deoxidation and temperature regulation before the steel melt enters a casting device. This is useful in an extension of the Fresh chamber or carried out in a special chamber or a special container.

The liquid with the correct composition and temperature Steel leaves the furnace via a suitable overflow and either enters a Ladle or directly into the inlet of a continuous caster Continuously pouring the steel into solid forms while separating the slag is cut off and further processed in the usual way.

To further explain the invention are three in the drawing various embodiments of a trained and working according to the invention Multi-zone melting furnace for the continuous production of steel shown schematically, namely, FIG. 1 a horizontal section of a multi-zone melting furnace, in which the slag flows completely in countercurrent to the melt and from a Separation chamber is tapped, which is opposite the fresh chamber to the Melting chamber is connected, Fig. 2 is a vertical longitudinal section through the Multi-zone melting furnace from FIG. 1, FIG. 3 shows a section as in FIG. 1 through another Embodiment of a multi-zone melting furnace in which the slag is partially countercurrent and partially in the rectified current flows to the melt and from one to the Fresh chamber connected separation chamber is tapped, Fig 4 a vertical Longitudinal section of a further embodiment of a multi-zone melting furnace with two Slag separation chambers connected to the fresh chamber, each with a tap and FIG. 5 shows a horizontal section of the multi-zone melting furnace from FIG. 4th

In the embodiment of FIGS. 1 and 2, the multi-zone melting furnace has an arc melting chamber 6 with a substantially circular plan, which has a floor 7 and a roof 8 each made of refractory material.

Electrodes 9 protrude through the roof 8 into the melting chamber. By a line 11 located in the middle of the roof 8 can ore 10 in the vicinity of the Arc zone can be entered. At the bottom of the arc chamber 6 are formed by a plate 12 made of austenitic stainless steel separates with a lot Low frequency working induction stirrer 13 arranged, for example by the Swedish company A. S. E. A. Ltd. were developed.

On one side of the arc melting chamber 6 is an elongated one Fresh chamber 14 attached, while on the opposite side there is a slag separation chamber 15 is located. Oxygen-containing gas is blown into the fresh zone through lances 16, the lances 16 at an angle to the surface of the melt in the furnace are arranged in order to counter-flow the slag 18 with respect to the melt 17 support. Behind the lances 16 a pipe 16 'is arranged through which basic Flux material, for example powdered lime or fluorite, is entered. The flux is in the slag or the melt by the during the injection process strong turbulence generated.

The refined steel 19 is through a tap opening 20 from the Furnace tapped while the slag passed through the furnace at the other end of the same a tap opening 21 leaves. To achieve this, the freshness chamber is at the end 14 a slag bridge 22 is provided, which allows an outflow of slag together with the rejuvenated steel prevented.

The refined steel flows in the exemplary embodiment according to FIG. 1 and 2 through the tap opening 21 into a separate deoxidation chamber 23, into which Deoxidizing agent can be entered through a funnel 24. If as a result of the Small amounts of slag are formed in the deoxidation chamber 23, this slag is then tapped through an auxiliary tap opening 23 '. The deoxidation chamber 23 can also be in the form of a degassing apparatus, which is shown, for example, in Australian Patent 279,591.

The deoxidation can also be carried out in an easily removable bell jar or a fixed gas bell, in both cases the Melt is stirred inductively during degassing or deoxidation.

The multi-zone melting furnace from FIG. 1 and 2 has two gas outlet lines 25 and 26, the one gas outlet line 25 being at the end of the slag separation chamber 15 and the other gas outlet line 26 at the entrance to the fresh chamber 14 near the Arc melting chamber 6 is located.

Scrap from the same plant, for example, can be put into the furnace has arisen, can be entered in two forms, namely a) in crushed form through openings at suitable points in the side wall of the furnace to prevent erosion of the refractory furnace lining, or b) as a stream of molten pig iron or half steel, which is through a channel 27, for example near the connection point between the slag separation chamber 15 and the arc melting chamber 6 in the Furnace arrives, in such a direction that it has the desired flow conditions supported in the melt.

The bottom slopes and depths of the hearth sections of the oven are off F i g. 2 to be recognized, whereby the bottom of the hearth-shaped slag separation chamber 15 inclines downward from the tap opening 21, so that the in the Slag separation chamber 15 from the slag separated metal back into the arc melting chamber 6 wanders back.

An auxiliary tap opening 28 is also provided around the furnace to be able to completely empty it at the end of a trip. This auxiliary tapping opening is located for example on the side of the arc melting chamber 6, as shown in FIG. 1 shows.

In the embodiment of the multi-zone melting furnace shown in FIG is a slag separation chamber 29 with the fresh chamber 14 near the connection of the the latter is connected to the arc melting chamber 6. A lance 16 a is inclined arranged that gas flowing out of the same causes a flow of the slag in the same Direction as the melt is supported while another lance 16 b is arranged is that the gas flowing out of this is a countercurrent of the slag to the melt supports. The gases flowing out of both lances move the slag by and large and all in the direction of the slag separation chamber 29.

In this embodiment, the deoxidation chamber 23 is with the fresh chamber 14 made in one piece. An outflow of slag with the melt from the fresh chamber 14 in the deoxidation chamber 23 is through a liquid-cooled slag bridge 30 prevents. There is only one gas outlet 31 on or provided near the end of the slag separation chamber 29.

In the case of the multi-zone melting furnace from FIG. 4 and 5 is the fresh zone in two chambers 32 and 33 divided, in each of which there is a countercurrent between slag and melt is present. Each of these fresh zones or fresh chambers has one own slag separation chamber 34 and 35, each with a tapping opening 36 and 37, respectively. In addition, there are liquid-cooled partitions 38, 39 and 40 and liquid-cooled weirs 41 provided to separate the different zones from one another to separate.

Example The considerable metallurgical advantages of the invention were shown in a series of experiments in a small pilot plant in Cockle Creek, New South Wales, Australia, this pilot plant having a furnace, which is essentially the same as in FIG. 3 corresponds to the furnace shown schematically.

The slag separation chamber 29 is close to the fresh chamber 14 Connection point of the latter connected to the arc melting chamber 6 The arc melting chamber and the fresh chamber of the furnace were made of magnesia bricks high quality, while the slag separation chamber is lined with basic pulped or lubricated material, which was also lined with a high magnesium oxide content exhibited.

To avoid erosion of the basic bricks or lining stones in the case of long Reducing the furnace's continuous melting-fresh travel was an air-cooled one Channel in the furnace housing at the line around the entire melting chamber and also the entire fresh room. In addition, there was slag erosion in the melting chamber reduced by periodic addition of cold crushed steel scrap, the one Mixture of lumpy charcoal or the like and ferro-silicon was added, with this addition of the scrap mixture on the side walls of the melting chamber and in particular took place where the heat radiation of the arcs was greatest.

In the melting zone were mainly in a rotating shaft furnace produced incandescent metallized pellets via a chute through the central inlet port 11 entered directly into the hot arc zone. The pellets got as hot as possible and usually with a temperature in the range of 1000 bis 11000 C, which saves a lot of electrical energy that would otherwise be required to get the heat required for the melting process from the arcs to transfer the material. The energy saving achieved in this way was in Range from 200/0.

A wide variety of metallized pellets have been used, most of which were based on two substantial raw materials, the average composition of which is as follows: Fine-grain palabora Hamersley Hematite Magnetft Material concentrates Total Fe,%. 67.5 67.2 Mn,% ... . Lanes 0.15 SiO2,% ... 2.1 0.3 Al2O3,%. 1.0 0.7 TiO2,% .......... Lanes 0.6 Bound H2O,% .. 0.3 traces S,%. . 0.02 0.03 P,% ..... 0.03 0.02 CaO,%. . Lanes 1.0 MgO,% ... ... .. traces 2,3 unidentifiable Materials . . rest Most pellets were made from a mixture of ore, coal and CaO in a ratio of 79: 17: 4. The assembled wet pellets were allowed to air carburize and dry for a period of at least 30 hours before being placed in the furnace for metallizing.

The bone char used was made from a low ash, low sulfur lignite from Yallourn, Victoria, Australia and had the following average composition on a dry solids basis: Solid carbon ... . 94.20 / 0 volatile components. 1.0% ash ... 4.1% sulfur ....................... 0.3% non-determinable materials. 0.4% The metallized pellets produced from the two ore base mixes had the following analytical composition: Hamersley Pellets 1 Palabora Pellets Total Fe, ° / 0. @ 82 to 88.5 80.5 to 88.0 Metallic Fe,% .. ........ 75 to 83 73 to 82.5 Carbon, ° / o. @ @ .. 3.5 to 4.1 3.2 to 4.5 Sulfur,% ... 0.04 to 0.06 0.05 to 0.07 Phosphorus,% .. ...... .......... ..... ... 0.02 to 0.04 0.02 to 0.03 Other materials (oxygen + ore rock + Lime),% ........ . . 12 to 7.0 13.2 to 6.8 Base / acid ratio, approx. @ 1.0 about 1.5 Since the small experimental furnace did not have an induction stirrer, circulation of the melt in the melting zone was achieved by tangentially blowing in a dense coal-air or bone-coal-air mixture through two liquid-cooled lances that were just below the slag metal level near the periphery of the circular melting chamber.

This blowing process was not only used to create a circulation of the Maintaining melt in a horizontal plane, but also supported that Maintaining the desired carbon content in that in the melting chamber located metal, so that it was always in the half-steel area. Typical Analyzes of the half-steel in the melting chamber were in the following areas: C, O / o. ...... 2.3 to 2.6 Si, O / o .... 0.3 to 0.5 Mn,% ... ....... 0.02 to 0.1 Ti,%. . ..... traces up to 0.03 S,% 0.04 to 0.06 P,%. . ..... 0.03 to 0.06 Fe, ° / o. . . Remainder The temperature of the melt in the melting chamber was kept as far as possible in the range between 1475 and 15100 C, whereby as Result of the reaction of the carbon in the melt and the residual content on FeO of the added pellets and in the slag a slight boiling took place. This reaction can be represented by the following equation: (FeO) + [C] # Fe + CO The semi-steel produced flows continuously from the melting chamber into the Fresh chamber, where it was gradually refined to steel with oxygen. The oxygen (02) was blown into the slowly flowing stream of metal through four to six lances, the greater number of lances being used when a low carbon steel should be established. The lances were at an angle of about 600 to the horizontal and were directed into the freshness chamber in such a way that they countercurrent to that of freshness supported the resulting slag in relation to the melt.

The fresh slag was by adding a mixture of 90% lightly burnt lime and 10% fluorite by a near the last oxygen lance Horizontal auxiliary lance made of alloyed steel.

This slag was practically "infinitely" basic where it originated and thus had a high freshness for sulfur and phosphorus. At the Stream in the opposite direction over the molten metal, the slag gradually took these elements and later also silicic acid and finally united with that in it Direction as the metal flowing slag and got along with the same into the slag separation chamber. There was no possibility of sulfur and remove phosphorus from the hot slag and return to the hot steel, like that of other known methods of continuously making steel the case is.

The goal with most of the trials was to get a slag in the end in which the ratio of CaO + MgO: SiO2 + Al202 between 2 and 2.5, but, as already stated above, the basicity of the slag was in the fresh zone over the greater part of its length is many times higher and approached the value "infinite" towards the point of addition of lime.

The iron losses in the slag were low.

The total content of Fe in the slag, so far on average is between 10 and 12 percent by weight of the steel produced, was at the Try between 3 and 7 0 / o. The FeO content could be brought to very low values which come close to those of the slag from blast furnaces by adding bone char or poorly volatile coal in the slag at the beginning of its way through the slag collecting and slag separation zone were injected or entered. That through the reaction (FeO) precipitated iron formed in the slag + C # Fe + CO sat on the inclined hearth floor of the slag separation chamber and wandered due to the Gravity from the slag separation chamber into those in the fresh zone Main stream of the melt back.

Due to the working method explained, depending on the steel is blown into the melt flowing through the fresh zone can be produced with any desired carbon content. The others, as pollution Notable elements such as sulfur and phosphorus were only present in small quantities. A typical analysis of a low carbon steel was: C. . ...... .. 0.11% Si ... ...... 0.01% Mn. ..... 0.01% Ti ............... traces also on steel, made from Ti-containing Palabora pellets S ....... ........ 0.0120 / 0 P ................ 0.004% In particular, low-grade steel was needed a deoxidation and degassing in a special chamber 23 before being potted could be. In economic and practical operation, this is achieved through Addition of commercially available deoxidation alloys or, for example, by a continuous one Vacuum treatment.

Claims: 1. Multi-zone melting process for continuous Manufacture of steel by electrothermal reduction of oxide ores.

Melting down and freshening, g e k e n n n z e i c h -net through the combination the following known measures: a) continuous introduction of preheated and pre-reduced, agglomerated or crushed oxide ores into the arc melting zone (6); b) inductive stirring a of the melt in the light arc melting zone (6); c) continuous Forwarding the melt from the arc melting zone (6) into the fresh zone (14), in which the melt at several successively arranged points with oxygen-containing Gas is refined; d) continuous countercurrent between slag and melt to the slag separation zone (15, 29) and to the metal tapping (23) separated therefrom.

Claims (1)

2. The method according to claim 1, characterized in that the ore entered into the arc melting zone at a temperature between 400 and 12500 C is used to produce a half steel with a carbon content between 0.5 and 4 ovo and with a silicon content of not more than 10%. 3. The method according to claim 2, characterized in that the ore is entered with a temperature between 850 and 1100 C. 4. The method according to one or more of claims 1 to 3, characterized characterized in that in the arc melting zone aggiomeriefles pre-reduced iron ore with a residual carbon content of 2.5 to 6 0 / o entered as the starting material will. 5. The method according to one or more of claims 1 to 4, characterized characterized in that the half-steel located in the melting zone has a carbon content between 1.5 and 2.5% and a silicon content between 0.1 and 0.5%. 6. The method according to one or more of claims 1 to 5, characterized characterized in that the temperature of the metal in the arc melt zone is in the range is kept between 1420 and 15000 C. 7. The method according to one or more of claims 1 zs 6. thereby characterized in that refining is carried out in two separate zones, silicon and sulfur and part of the phosphorus in the first fresh zone in which the Slag is removed in substantially the same direction as the half-steel flows will. while in the second fresh zone, in which the slag is opposite to the Metal flows decarburizing and removing phosphorus predominates. 8. Multi-zone melting furnace for the continuous production of steel with an electro-reduction chamber and an inflation freshening chamber, according to the process from one of the preceding claims, characterized in that additionally one per se known slag separation chamber (15, 29) with a separate from the metal tap (23) Slag tapping is provided