DE2737441A1 - METHOD AND DEVICE FOR CONTINUOUS HEATING OF A MELT OF IRON - Google Patents

Description

Sulzbach-Rosenberg, August 17, 1977

i>

"Method and device for continuous heating of an iron melt"

The invention relates to a method and a device for continuously heating an iron melt, which is preferably produced from scrap.

The melting of scrap for the production of steel nowadays usually takes place in the electric arc furnace or in the Sieniens-Martin furnace. Both furnace processes do not work optimally with regard to their degree of heating efficiency and the associated economic efficiency. In the SM process, only about 30 % of the heat energy supplied is used; in the electric furnace, expensive electrical energy is used.

Extensive attempts have also been made to scrap the scrap to melt directly through the burner. These scrap melting attempts, in which mostly the scrap from above with a Burner flame applied showed as insurmountable Disadvantage of a strong iron slagging. The formation of the iron oxide-rich slag had a particularly unfavorable effect heat transfer and continues to cause unusually high rates of wear on the refractory lining Melting vessels out.

The German patent specification 18 00 610 describes a method and a device for melting down scrap, in which in a cylindrical melting vessel in the lower part of this

909809/0274

a burner is arranged, which continuously melts the scrap. The melt flows steadily with a temperature close to the liquidus point from this melting vessel into a pan. The process according to this patent largely avoids the disadvantages the unfavorable energy balance and the high refractory wear rates. This method is particularly disadvantageous in that low temperature of the generated molten iron. Without additional measures to lower the melting point practically at liquidus temperature molten iron flowing out of the melting unit it cannot be fed to any downstream processing stage. Therefore, for example, describes the German Patent 23 26 721 a carburizing process for the generated Scrap melting according to the mentioned melting process.

Another known way of increasing the temperature of an iron melt is to use the so-called duplex process. With this method, the melt to be heated is e.g. charged into an electric furnace and heated there in a known manner to the desired tapping temperature. Additionally fresh and slag reactions can be carried out in order to achieve a desired final analysis.

The disadvantages of most duplex processes are generally in the transport and transferring of the molten iron, as well as in the use of relatively expensive electrical energy for heating also in the process for the production of duplex steel according to the German Offenlegungsschrift 25 49 967 is used.

The continuous steelmaking processes, e.g. B. the method for producing steel from pig iron according to the German Auslegeschrift 25 07 961, are also suitable with certain Modifications to heat up and finish freshening iron

909809/0274

-Jr-

melt from scrap. However, those that have become known are continuous Steel making process preferred to processing of conventional pig iron and the associated, relatively complex slag work eliminated. You turn out to be • accordingly, as costly to heat scrap generated Molten iron. In addition, the continuous steelmaking processes have not yet become operational practice the iron-making industry introduced, and there is therefore no experience of the operational sequence in their large-scale application.

Method, an iron bath below the bath surface carbon and / or supply substances containing hydrocarbons, also belong to the state of the art. The German Offenlegungsschrift 25 20 938 relates to a method and a Device for the production of a reducing gas for metallurgical applications, in which in a so-called iron bath reactor Carbon is fed into the iron bath to produce carbon monoxide from it. So this iron bath reactor is used coal gasification and is a closed vessel that allows overpressure operation. The iron melt is only called Aid used for converting fuel into reducing gas.

The present invention is now based on the object of developing a method and a device with which it is possible to use molten iron, which is preferably produced from scrap and has a temperature close to the liquidus point, Heat continuously without intermediate transport to another furnace unit and generate molten steel.

The invention solves this problem in that the iron melt in a, separate from the melting vessel, but thus in a direct Connecting, heating room flows and the iron

909809/0274

2737U1

melt in the heating chamber fuel, in particular solid carbon, and oxygen are supplied.

According to the invention, scrap and / or comparable materials are preferred, for example pre-reduced pellets or solid pig iron, as well as mixtures thereof, are melted in an essentially cylindrical melting vessel, e.g. a shaft furnace, and flow from the melting chamber, at a temperature close to the liquidus point, into a heating room. In the heating room, the melt is fed with fuel, i.e. exothermically oxidizable substances, and oxygen and / or gases containing oxygen.

According to the invention, the fuel and the oxygen can also be fed directly into the sump of a shaft furnace or into its Forehearth will be initiated.

The method according to the invention is particularly suitable for heating up iron melts from scrap which flow out of the melting vessel at liquidus temperature. For example it can be an almost cylindrical melting pot that is charged with scrap from above and in which the im Lower vessel section burners are arranged to melt the scrap continuously. A melting pot, same or similar to that described in German Patent 18 00 610 is suitable.

From this melting vessel, the molten iron flows continuously into a second vessel, which in this description is generally referred to as the heating chamber. In the heating room the iron melt, which is at about liquidus temperature when it flows in and therefore no longer has any heat reserves in the liquid state, fuel and oxygen with the aim fed to heat the melt.

909809/0274

A preferred method of adding fuel and oxygen is, according to the invention, both reactants by one or to blow several nozzles below the bath surface into the melt. It has been made for the addition of oxygen the nozzle known from the OBM process has been tried and tested. It essentially consists of two concentric tubes, with oxygen through the central tube, with or without a load of slag forming agents, and gaseous and / or liquid hydrocarbons are passed through the annular gap to the nozzle protection. The pulverized one Fuel, preferably coke dust, can be fed through a separate nozzle system or through the same nozzle as the oxygen Bath to be supplied. In this case, the oxygen introduction nozzle consists of three or more concentric tubes, wherein the carbon dust either through the zeniral tube or through one of the annular gaps is guided. The substances used to protect the nozzle can also be used as a carrier for the carbon will.

According to a further embodiment of the method according to the invention, the fuel, for example coke, is whole or partially passed from above into the heating chamber of the melt. It has been proven in practice to pass the coke through a suitable shaft that ends or directly above the bath immersed in this to feed the iron melt.

This veg of fuel addition is particularly suitable, when preheating the fuel. For example, according to the invention, the reaction gas from the heating chamber, which consists primarily of CO, is wholly or partially used to heat the Fuels used, i.e. passed through the coke shaft in order to give off its sensible heat to the fuel, or if necessary partially burned there with the aim of To further increase the heat supply. If that comes from the reaction

909809/0274

If gas originating in the room is to be passed into the scrap smelting room, the coke can also be burned by partial means Preheat oxygen-containing gases.

• There is an alternative embodiment for adding fuel in dipping the carbon as a shaped body, for example as a cylinder, similar to electrodes, in the molten iron. This can either be done from above, or in special cases it has been found to be expedient to use the electrode slowly pushing through the refractory masonry from below into the melt. The feed rate is approximate matched with the rate of dissolution of the carbon in the melt.

According to a further embodiment of the invention, the reaction gas escaping from the iron melt is fed to the melting vessel and burned there in one or more levels through the addition of oxygen and / or air. The CO gas from the heating room can be fed into the smelting shaft at the same level as the oxygen. A particularly good thermal efficiency is achieved, however, if the reaction gases from the heating space flow through the melting shaft from below, that is, starting from the melting zone. The exhaust gases then give off their sensible heat to the scrap in the lower area of the scrap melting shaft. They thus help to save fuel on the meltdown burners and also counteract the undesired oxidation of the iron melt in the meltdown space.

According to the invention, when adding fuel, preferably carbon and oxygen for heating the molten iron, a ratio of carbon to oxygen greater than 12:16. This way of working makes it

909809/0274

possible to lower the melting temperature of the iron bath at the same time by means of slow, controlled carburization in addition to the heating of the melt by the carbon combustion.

In the context of the invention, it is also to design the heating space so that it consists of two chambers below the Bath surface are connected to one another and have an overflow opening above the bath level. The heating room can take the form of a U-shaped vessel, as already described in connection with continuous steel production, e.g. in the German Auslegeschrift 25 07 961. However, in the present case, the molten iron from scrap is added from above and not, as in the patent application specified for the pig iron, below the bath surface, if the heating space is arranged below the 'melting space.

When the heating room is divided into two chambers, fuel and oxygen are used to heat up the iron melt in the first chamber, i.e. the space downstream of the melting chamber, and the melt is in the second chamber refined to the desired steel quality. The steel can be fed continuously or in portions from the second chamber subtracted from.

E. A variant of the method according to the invention consists in introducing the oxygen into the molten iron not exclusively below the bath surface, but in some of it or to blow completely on the melt in the heating room. The known, water-cooled lances can be used here come, or the nozzles described from two concentric pipes are in the brickwork of the heating room above arranged on the bath surface. The addition of oxygen above the bath surface has proven particularly useful in cases where intensive, rapid heating is required

909809/0274

Jr-

the iron melt arrives. By the oxygen inflation comes This is because in the heating room there is partial afterburning of the reaction gas from the melt (CO to CO2), and thus it becomes the heat supply in the heating-up room is considerably increased. As a disadvantage of this method of operation one accepts that there is less CO Combustion in the smelting shaft is available.

According to the present invention, carbon is preferably used as fuel. Of course, carbon can be used come in any commercially available form, for example as coke, coal, graphite, are used. It has also stood out from the rest of the world On a case-by-case basis, some of the carbon is found to be advantageous through liquid and / or gaseous hydrocarbons to replace. Mainly by rapidly varying the amount of hydrocarbons, for example as an additional amount to the Nozzle protection medium, the temperature of the iron melt and the composition precisely adjust the gas produced here.

It is accordingly within the meaning of the invention, a certain basic amount of fuel in the form of solid carbon of the iron melt to be added continuously and the exact temperature setting by means of additional gaseous and / or liquid hydrocarbons to be carried out in varying amounts. Of course, the fuel content can be in the form of hydrocarbons can also be increased as desired and then not only serves to fine-tune the bath temperature.

According to a further embodiment of the invention are with a cylindrical melting vessel coupled several heating rooms. The heating rooms can be uniform or different be designed as one or two-chamber vessels. For example, a melting pot has proven itself in practice for scrap with two heating rooms in one and two-chamber

909809/0274

^2737U1

to couple execution. The molten iron from scrap at about liquidus temperature flows continuously into both heating rooms. In the two-chamber heating room, steel is continuously produced in the manner described. In the second Auftjeizraum, which consists of only one chamber, the inflowing molten iron is carbonized to its saturation value of about 3 to 4 % carbon and this synthetically produced pig iron is drawn off in pans in order to use it as feed material for the usual converter steel production use.

In the case described, it becomes a 60 t OBM converter loaded. Of course, in an alternative embodiment, several melting vessels can also be combined with one heating space. This embodiment offers advantages especially when the melting capacity of the melting vessels is too low. This occurs, for example, when using inferior types of scrap, such as melting down Garbage scrap, before.

The invention is based on drawings, the only preferred embodiments of devices for implementation of the process according to the invention, and explained in more detail using non-limiting examples.

The drawings show:

FIG. 1 shows the longitudinal section through a melting vessel in combination with a single-chamber heating room

FIG. 2 shows the section through a melting vessel

a two-chamber heating room for steelmaking.

909809/0274

A shaft furnace [1] with a chimney [2] is charged with a mixture [3] of scrap and about 50 kg coke / t scrap. The charge mixture is continuously fed to the melting vessel [1] through a closable opening (not shown). The scrap is heated up by the burners [5] until it liquefies. The molten iron that is being formed flows continuously from the melting vessel [1] into the heating room [7] via the opening [6J], where it forms the bath [β]. Through one or more nozzle systems [9] below the bath surface in the heating room [7], fuel, oxygen and, to protect the nozzle system, hydrocarbons are fed to the melt [β]. The reaction gas that forms, essentially CO, flows out of the heating space [7] through the opening [δ] into the shaft furnace [l]. There the gas first gives off part of its sensible heat to the melting scrap and is _{burned by supplying air through the nozzles [a} io]. The ring line [ll] serves to supply the nozzles [ίο] the burner [5] and the reaction gas combustion in the nozzle level [ίο] are coordinated so that the scrap melts continuously, but the melt that is formed is not overheated and is inevitably heavily oxidized.

The exhaust gas from the smelting shaft furnace [IJ escapes via the Kanin [2] and flows through a recuperator, not shown, with which the air for the nozzles [10] is preheated.

The ratio of the amount of carbon supplied to the molten iron to oxygen is kept greater than 12: 16, which is one part of the carbon remains in the iron bath and lowers the melting point.

The heated iron melt [β] is transferred from the heating room [7] withdrawn continuously or in portions via the outlet [12].

909809/0274

According to Figure 2 is directly below the melting vessel [15] for the scrap is arranged in a heating room consisting of two chambers [16, 17]. The scrap column [18j is essentially through the burner [I9] melted as far as the sensible heat and the heat of combustion of the gas escaping from the heating rooms is not sufficient.

Since the first chamber [16] of the heating-up area extends to below the Scrap smelting shaft [15], scrap scrap pieces that have not been melted may extend into the melt [20J dissolve the chamber [16].

The supply of fuel, in the illustrated case of lumpy coke [21], takes place in the chamber [17] through the shaft [22], which ends above or below the bath surface. The coke column [21] is preheated by the hot reaction gases from the heating room [16, 17]. Part of the reaction gases, essentially CO, flows through the openings [23] into the shaft [22], there give the major part of their sensible heat to the coke column. [2l] and get out of the shaft [22] through the Inflow opening [24] into the scrap melting vessel [15]. Above the supply of oxygen or air through the nozzles [25], which are connected to the ring line [26], the CO in the scrap column [18] burned. The combustion takes place in the upper area of the scrap smelting shaft and is controlled in such a way that that despite the high combustion temperature from CO to C0 "through the offered amount of scrap can only be reached at preheating temperatures of around 100 ° C. Up to this temperature the oxidation losses of the scrap are low. ,

In the coke preheating shaft [22] there are also nozzles [27] for introducing oxygen. At a desired high preheating temperature of the coke is achieved through the nozzles [27]

909809/0274

Oxygen or air is introduced to the reaction gas from the heating room partially burn to CO2. The heat transferred to the coke in this way is transferred to the melt in chamber [17] directly benefits and contributes to a shorter heating time or higher heating temperature.

The chamber [16j in the heating room has oxygen inlet nozzles [28] below the bath surface. The nozzles [28J exist Essentially consisting of two concentric tubes, through the inner tube of which oxygen and through the annular gap gaseous and / or liquid hydrocarbons flow as nozzle protection medium. The nozzles [28] can be installed at an angle in order to use the entry impulse of the media to the melt in the chamber [16] to inject a rotational movement. The bath movement of the melt in the chamber [16J in turn contributes to good heat transfer on scrap pieces that have not yet melted and for temperature equalization.

The nozzles are located in the chamber [I7J of the preheating room [30]. In principle, these nozzles [30] have a similar structure to the nozzles [28] · Oxygen is supplied to the iron bath via the nozzles [30] added with or without loading of slag forming agents. Of course, the nozzles [30J also have a Protective medium coating with gaseous and / or liquid hydrocarbons. The protective medium causes a uniform- ^ ges Burning back of the nozzles with the walling of the chamber [17].

In the chamber [17] the steel is refined and the necessary slag work is carried out. The finished steel melt is withdrawn continuously or in portions through the tap opening [31] from the chamber [17]. It has been found to be functional proved to design the tapping opening [31] like a siphon.

909809/0274

The opening [32J is used to remove the slag from the chamber [l7j · Furthermore, as a closure for the tap opening [31] the usual stopper or slide closures have proven their worth.

It is also within the meaning of the invention, from the chamber [17J Schlakke and, if necessary, flow back steel via the overflow [33] into the chamber [16J to let, for example, to reduce FeO from the slag in the chamber [16]. To this end, the Chamber decrees [l6] via a slag discharge opening

By the overflow of steel from the chamber [17] into the chamber [16J can the heat balance of the iron melt in chamber [16J can be improved and controlled to a certain extent. It is accordingly possible to start a partial cycle of molten metal .Maintain chamber [17] via overflow [33] and inflow opening [29]. The chamber [16] also has a tap opening [35] which is used in the event that the entire system is shut down is used to draw off the melt.

The listed exemplary embodiments of the method according to the invention can be supplemented by many variants. One idea of the invention is the flexibility of the method to that effect to take advantage of adapting it to the operating conditions in the users' steelworks. The inventive method enables steelmaking from scrap with the advantage of collecting the reaction gases and their energy content to a large extent to use. The gas is preferably used in the system itself. Of course, it can also be used externally as a Find fuel gas use.

909809/0274

Claims (20)

Claims 1) A process for continuously heating an iron melt, which is preferably produced from scraps, characterized in that the iron melt separated in one of the melting vessel, but therewith in direct communication flows heating chamber and the melt in the heating compartment fuel, in particular solid carbon, and Oxygen can be supplied. 2) Method according to claim 1, characterized in that a cylindrical melting vessel, for example a shaft furnace, is used as the melting vessel for the scrap and / or comparable materials, such as pre-reduced pellets. 3) Process according to claims 1 and 2, characterized in that the solid, carbon-containing fuels, mainly coke, coal, graphite, and similar materials, dusty, lumpy and / or as molded bodies are entered into the melt. 4) Method according to one or more of claims 1 to 3t, characterized in that the fuel and the oxygen are added in the forehearth of a shaft furnace or directly in the metal sump. ' 5) Method according to one or more of claims 1 to 4, characterized in that the heating space is formed from two communicating chambers, for example as a U-shaped vessel, in order to continuously produce steel therein in a manner known per se. 6) Method according to one or more of claims 1 to 5i, characterized in that the fuel, preferably powdered coke, is blown through nozzles below the bath surface into the heating room. 7) Method according to one or more of claims 1 to 6, characterized in that the fuel is lumpy
or as a shaped body, for example as a conventional electrode}
is fed from above the melt. 8) The method according to one or more of claims 1 to 7 » characterized in that the fuel, preferably carbon, as a displaceable shaped body, for example as a pushable electrode, below the bath upper - surface gets into the melt. 9) Method according to one or more of claims 1 to 8, characterized in that the oxygen with a coating of gaseous and / or liquid hydrocarbons, through nozzles, below the bath surface in the refractory lining of the heating chamber, is blown into the melt. 10) Method according to one or more of claims 1 to 9, characterized in that the fuel is preheated. 11) Method according to one or more of claims 1 to 10, characterized in that the fuel by
the reaction gas from the iron melt is preheated. 909-09 / 0274 12) Method according to one or more of claims 1 to 11, characterized in that a quantitative ratio of carbon and oxygen is set greater than 12:16. 13) Method according to one or more of claims 1 to 12, characterized in that the solid carbon as fuel is partially replaced by gaseous and / or liquid hydrocarbons. 14) Method according to one or more of claims 1 to 13, characterized in that the reaction gas escaping from the melt is passed into the scrap melting vessel and is burned there with the addition of oxidizing gases in a temperature zone of the scrap column of about 1000 C. 15) Method according to one or more of claims 1 to l4, characterized in that the reaction gas is introduced from the heating chamber in the lower, hot part of the melting vessel and transfers its sensible heat to the scrap in the melting phase. 16) Method according to one or more of claims 1 to 15, characterized in that the oxygen is partially or exclusively blown from above onto the melt in the on heizra.um. 17) Device for carrying out the method according to claims 1 to l6, characterized in that a known, essentially cylindrical, scrap melting vessel [l, 15] is directly connected to a heating room [7 »l6, 17] and oxygen inlet nozzles in the heating room [9, 28, 30] below the bath surface and fuel supply devices [9, 22] are installed. 909809/0274 27374 * 1 18) Device according to claim 17, characterized in that the heating chamber [7, l6, 17J consists of one chamber [7] or two interconnected chambers [l6, 17J. 19) Device according to claims 17 and 18, characterized in that several heating chambers [7 »16, 17J are coupled to a cylindrical melting vessel [1, 15]. 20) Device according to claims 17 and 18, characterized in that several cylindrical melting vessels [l, I5J are connected to a heating space [7, 16, 17]. 909809/0274