EP0117928A1 - Process for production of steel by the melt-down of iron-sponge in an electric-arc-furnace - Google Patents

Abstract

Iron sponge produced by direct reduction is melted down in the arc furnace using the so-called swamp mode of operation. For a sufficient availability of liquid, carbon-containing iron for the sump and at the same time for the greatest possible economy of the process, the sponge iron is reacted on a bath of liquid, carbon-containing iron in an electric arc furnace, the liquid, carbon-containing iron (hot metal) also made of sponge iron or reduced Ore is generated in an electric reduction furnace, which is regulated in dependence on the electrical load fluctuations caused by the electric arc furnace in such a way that a practically constant load on the electrical network results.

Description

The invention relates to a method for producing steel by melting sponge iron in an electric arc furnace, the sponge iron being produced by direct reduction.

As is well known, difficulties arise when an electric arc furnace is only loaded with sponge iron. This is due to the low density and poor conductivity of the sponge iron. Nevertheless, the aim is to use mainly sponge iron in the arc furnace. Here it is advantageous to use the so-called swamp mode of operation, which consists in charging the sponge iron onto liquid, carbon-containing iron (hot metal) already in the furnace, the further supply of energy taking place essentially via the liquid bath.

In the swamp mode of operation, however, the arc furnace must still be completely emptied every two to three batches in order to repair the delivery. In this way, uninterrupted furnace operation with sump is not possible; rather, a sump must be generated again after each emptying, so that the advantages of this mode of operation can only be used incompletely if no liquid iron from another Source, preferably the blast furnace, is available. However, it is precisely this that is not available in a sponge processing company.

The arc furnace operation is also inevitably associated with strongly fluctuating energy consumption due to its characteristic and, moreover, discontinuous mode of operation. These fluctuations extend both to the chronological sequence and to the absolute amount of the decrease in energy. To connect an arc furnace, an electrical network is required which is so strong that the reaction - due to the furnace operation - does not exceed the maximum permissible limit values.

. The object of the invention is to provide a method which allows the advantageous operation of the arc furnace with sump by ensuring that there is sufficient availability of so-called "hot metal" and at the same time that the process sequence is as economical as possible.

This object is achieved by the sponge iron being implemented on a bath of liquid, carbon-containing iron in an electric arc furnace, the liquid, carbon-containing iron (hot metal) also being produced from sponge iron or pre-reduced ore in an electroreduction furnace, which is a function of the is regulated by the electric arc furnace-induced load fluctuations so that a practically constant load on the electrical network results.

The process according to the invention thus achieves by combining a process step in which the carbon-containing iron required for the sump in the arc furnace is obtained - and preferably from the same starting material as is used in the arc furnace - with the melting the sponge iron in an electric arc furnace, a total effect that inzelvorgänge goes beyond the sum of the processes occurring in the process sections _E, because the load on the electrical network is largely evened out in a surprisingly simple manner simultaneously with the improvement of the melting process.

The term "arc furnace" is to be understood as directly heated arc furnaces in which the heating is carried out by means of electrical arcs burning between the electrodes and the metallic insert or steel bath (direct arc furnace). The term "electroreduction furnace" is to be understood as furnaces in which the electrodes are either immersed in an open slag bath or in a standing Möller column and in which the energy conversion takes place preferably by resistance heating (submerged arc furnace). These ovens are eduktionsarbeit for _R, even with an open slag bath, suitable. They generate from sponge iron and added Kohlenstoffträ- ^g ren carbonaceous iron, which is used in the arc furnace as bottom. The electric reduction furnaces can be operated with variable power consumption.

'In an advantageous further development of the invention it is proposed that in the direct reduction in the exhaust gas waste heat and the composite arc furnace / or lektroreduktionsofen- in the direct reduction and for the _D irektreduktion accumulating energy sources for generating electrical energy to meet the energy needs of the _E and be used. Energy sources can be excess solid, carbon-containing materials or combustible gases which occur in the direct reduction or excess, combustible gases or solid, carbon-containing materials which arise in the production of the reducing medium for the direct reduction.

_E : ne advantageous embodiment is that the amount and analysis of the arc furnace used as a sump ten carbon-containing iron is chosen so that the total carbon balance is balanced during the charging of sponge iron in the arc furnace, the active power of the arc furnace being regulated so that the arc furnace is in the thermal equilibrium necessary for melting sponge iron. Thermal equilibrium means that there is no overheating and no freezing.

A further advantageous embodiment consists in the fact that sponge iron with a lower metallization size is mainly used for the production of liquid, carbon-containing iron (hot metal) in the electric reduction furnace.

An advantageous embodiment consists in that the separated from the effluent of direct reduction with fixed kohlenstoffhiltigen reducing agents excess carbonaceous material is at least partly combusted in a combustion unit with the addition of oxygen-containing gases, the hot combustion gases and the exhaust gas of the _D irektreduktion used for generating electrical energy , the amount of electrical energy generated being regulated so that it corresponds at least to the maximum energy requirement of the electric arc furnace plus the minimum energy requirement of the _electric reduction furnace, and that the energy not required by the electric arc furnace is converted in the _electric reduction furnace. The excess carbonaceous material is completely burned if its quality is not suitable for use in the electric reduction furnace or if an addition is not required there. Good quality means that the ash and sulfur content is relatively low and the ash is basic. It is also possible to process the separated carbonaceous material and then to insert the good quality fraction into the _electric reduction furnace and the poor quality fraction into the combustion. The minimum energy requirement of the electric reduction furnace is the holding power.

The sensible heat of the hot combustion gases and the exhaust gases from the direct reduction are used to generate steam, and the steam drives a generator to generate electricity via steam turbines. The hot combustion gases and the exhaust gases from the direct reduction are expediently conducted separately into separate steam generators and the steam flows into separate turbines. This allows the turbine for the vapor of the exhaust gas. Direct reduction can always be operated in the optimal range, and better utilization and control is possible. The amount of electrical energy generated must correspond to the maximum energy requirement of the electric arc furnace plus the minimum energy requirement of the electrical reduction furnace. More electrical energy can also be generated for other purposes of one's own operation, but this additional generation is then not included in the regulation of the current distribution. The electrical energy is distributed in such a way that the energy requirements of the arc furnace are always met, i.e. if it has high energy requirements, the electric reduction furnace receives less electrical energy, and if the arc furnace is switched off, the electric reduction furnace receives more energy.

The sponge iron is divided in such a way that the amount of carbon-containing iron (hot metal) required for steel production in the electric arc furnace is obtained in the electric reduction furnace.

After hot sieving, the sponge iron can be used hot in the melting furnace. The combustion of the excess carbonaceous material can take place in fluidized bed apparatuses or dust furnaces, e.g. Cyclone firing.

A preferred embodiment is that the exhaust gas from the direct reduction is afterburned before use in electrical power generation. On the one hand, this will also the latent heat content of the exhaust gas is utilized and, on the other hand, an uncontrolled combustion is avoided, especially with higher contents of combustible gaseous and solid components.

A preferred embodiment is that further combustible material is charged into the combustion unit. As a result, self-sufficient operation can be carried out even if the heat in the exhaust gas and the hot combustion gases of the excess carbon-containing material is too low.

A preferred embodiment is that the combustion unit is a circulating fluidized bed. The circulating fluidized bed works without a jump in the material density between the dense phase and the dust space above. The solids concentration decreases continuously from bottom to top.

bzw.

wobei

und

sind.

• u die relative Gasgeschwindigkeit in m/sec.
• Ar die Archimedes-Zahl
• Fr die Froude-Zahl
• 
  g die Dichte des Gases in kg/m
• 
  k die Dichte des Feststoffteilchens in kg/m³
• d_k den Durchmesser des kugelförmigen Teilchens in m
• die kinematische Zähigkeit in m²/sec.
• g die Gravitationskonstante in m/sec.²

When defining the operating conditions using the key figures from _F roude and Archimedes, the following areas result:

respectively.

in which

and

are.

• u the relative gas velocity in m / sec.
• Ar is the Archimedes number
• For the Froude number
• 
  g is the density of the gas in kg / m
• 
  k is the density of the solid particle in kg / m ³
• d _{k is} the diameter of the spherical particle in m
• the kinematic toughness in m ² / sec.
• g is the gravitational constant in m / sec. ^2nd

Such methods, which are particularly suitable for the combustion of the excess carbon-containing material are described in the _E-AS 25 39 546, US-PS 41 65 717, DE-OS 26 24 302 US-PS 4,111,158.

A preferred feature is that a combustible gas is supplied through separate carbonization and / or partial gasification of solid carbonaceous material produced, the combustible gas is used for generating electrical energy and irektreduktion the geschwelte solid, carbonaceous material in the _D and / or Electric reduction furnace and / or the combustion unit is used. Direct reduction is relieved by the use of carbon-containing material on the exhaust side and its throughput is increased. _Since the exhaust gases from the direct reduction contain less combustible gaseous constituents, less electrical energy is generated by the exhaust gas, ie the non-controllable base load becomes smaller and the possibility of regulating the electrical energy generated by the combustion increases. A portion of the geschwelten, carbonaceous material or optionally can all be directed into the combustion unit, so that the extent is also flexible in the _D irektreduktion stock charged amount. The generation of the electrical energy from the flammable gases is very flexible. Some of the flammable gas can also be used for other purposes in your own company.

A preferred feature is that the _S w _e - ment and / or carried partial gasification in a circulating fluidized bed. The circulating fluidized bed is very suitable and flexible to operate. A particularly suitable method is described in EP-A - 0 062 363. When the geschwelte carbonaceous material is used in the gasification stage in the _D irektreduktion, no charging takes place in the combustion stage.

A preferred embodiment consists of the fact that combustible gas is stored in a gas storage device and is removed when necessary to generate electrical energy. Through this storing a very good flexibility is achieved, and _R are created eserven also particularly for the start-up and shutdown.

A preferred feature is that the combustible _G is used as using a gas turbine for generating electrical energy. A very fast regulation of the amount of energy generated is possible with a gas turbine.

A preferred embodiment is that baking coals are used in the circulating fluidized bed. This makes it possible to use these coals without additional effort, which cannot be used directly in direct reduction.

An embodiment is daß..das from the effluent of the _D is used irektreduktion separated excess carbonaceous material in the electric reducing furnace, additional energy carriers are burnt in a combustion unit with the addition of oxygen-containing gases, the hot combustion gases and the waste gas of the direct reduction to produce corresponds furnace, and that the energy of each is not required by the electric arc furnace is converted in an electric reduction furnace - the amount of the generated electric energy is controlled so that these _ns at least the maximum power consumption of the arc furnace plus the minimum energy requirement of the Elektroreduktio be used by electrical energy. The separated excess carbon is completely added to the electric reduction furnace when this carbon is of good quality and is required in the electric reduction furnace.

A preferred embodiment is that the direct reduction is carried out in a rotary kiln. The coals used as reducing agents mostly contain higher levels of volatile components, e.g. Lignites, and have a high reactivity.

The invention is explained in more detail with the aid of figures.

As FIG. 1 shows, iron ore 2 is charged in the tube furnace 1 and reduced to sponge iron. The discharge material 3 is separated in a separation stage 4 into sponge iron 5 and excess carbon-containing material, part 6a of which is passed into the electric reduction furnace 7 and the other part 6b into the circulating fluidized bed 8 and is burned by air 9. The hot combustion gas 10 is fed into the steam generator 11. A generator 13 is driven with the steam 12. The electrical energy generated is fed via line 14 to the electric reduction furnace 7 and the arc furnace 16. The exhaust gas 17 from the rotary kiln 1 is afterburned in a post-combustion chamber 18 with the addition of air 19. The hot gas 20 is passed into the steam generator 21. A generator 23 is driven with the steam 22. The generated electric energy is an ^g e-fed into the line 14 via line 24th The iron sponge 5 becomes part 5a in the electric ^{reduction furnace 7} and part 5b in the light arc furnace 16 charged. The pig iron produced in the electric reduction furnace 7 is chärgiert in the arc furnace 16, from which the steel 25 is withdrawn. As much electrical energy as is required is always supplied to the arc furnace 16 via line 14a. The remaining electrical energy is fed into the electric reduction furnace 7 via line 14b.

The rotary kiln 1 can be operated with coal with a high proportion of volatile constituents, which are charged via 26 into the loading end and are partly blown into the discharge end by the blowing device 27. In this case, the exhaust gas 17 contains higher proportions of combustible gaseous components and the amount of electrical energy generated in 24 is correspondingly large.

In the circulating fluidized bed 28, coal 29 can additionally be smelted and partially burned with gases 30 containing oxygen. The combustible gas 31 is burned in a gas turbine 32 that drives a generator 33. The electrical energy generated is fed into line 14 via line 34. The smoldered carbonaceous material is charged from the fluidized bed 28 via line 35 into the rotary kiln 1. In this case, no coal with a high proportion of volatile components is charged into the rotary kiln and the exhaust gas 17 contains only small proportions of combustible, gaseous components. The amount of electrical energy generated in 24 is correspondingly less.

The generation of electrical energy can be increased by adding coal 36 to the fluidized bed 8. Part of the carbonized material from the fluidized bed 28 can be fed into the fluidized bed 8 via line 37.

Excess current which is constantly generated for other consumers of the company can be taken off via line 40.

Flammable gas is stored in the gas store 38 and removed if necessary. Flammable gas can be withdrawn for operation via line 39 if this amount is scheduled for generation.

Via line 41, ore and aggregates can be charged into the _electric reduction furnace 7.

When operating the arc furnace, the liquid, carbon-containing iron produced in the electric reduction furnace is adjusted in terms of quantity and analysis - mainly carbon - in such a way that the total carbon balance is balanced when the sponge iron is charged. If, e.g. due to an error in the production of sponges, sponges of less metallization, e.g. instead of 92% only 85%, this can still be processed. However, the spongy iron is only used to charge the electric reduction furnace. It is therefore possible to operate the process with spongy iron with different degrees of metallization.

The steam generated in the steam generator 11 can also be passed via line 12 to the generator 23.

Fig. 2 shows a typical load diagram for three arc furnaces and two electric reduction furnaces, which work in the compound operation. The time in minutes is plotted on the x-axis and the active power in megawatts on the y-axis. The dotted curve shows the total active power of the electric furnace, the dashed curve shows the total active power of the arc furnace and the solid curve shows the total active power of all furnaces. The diagram shows the sequence of typical work cycles. In particular, sicb reveals that the total active power of all melting furnaces is relatively constant, although the arc furnaces have very large fluctuations in power consumption.

The advantages of the invention are that the entire smelting process can be carried out independently of the performance of the public supply network available, that the operation takes place with minimal energy consumption per ton of steel, that the waste heat of the direct reduction producing the sponge iron is optimally used and that the excess carbon-containing material is used Material of the discharge of the direct reduction and possibly additionally used coal can be burned in an environmentally friendly manner by adding limestone with the accumulation of a landfillable CaSO ₄ -containing residue.

Claims (15)

1. A process for the production of steel by melting sponge iron in an electric arc furnace, the sponge iron is produced by _D irektreduktion, characterized in that the sponge iron is reacted in a bath of liquid carbon-lenstoffhalti ^g em iron in the arc furnace, wherein the liquid carbon containing iron (hot metal) is also produced from sponge iron or pre-reduced ore in an electric reduction furnace, which is regulated in dependence on the electrical load fluctuations caused by the electric arc furnace so that a practically constant load on the electrical network results. 2. The method according to claim 1, characterized in that the waste heat generated in the direct reduction in the exhaust gas as well as in the direct reduction and / or for the direct reduction energy sources used to generate electrical energy to cover the energy requirements of the electric reduction furnace and electric arc furnace combination . 3. The method according to claim 1 or 2, characterized in that the amount and analysis of the iron in the arc furnace as sump. Carbon-containing iron is selected such that the total carbon balance is balanced during the charging of sponge iron in the arc furnace, the active power of the Arc furnace is regulated so that the arc furnace is in the thermal equilibrium necessary for melting iron sponge. 4. The method according to any one of claims 1 to 3, characterized in that sponge iron with a lower degree of metallization is mainly used for the production of liquid, carbon-containing iron (hot metal) in the electric reduction furnace. 5. The method according to any one of claims 2 to 4, characterized in that the excess carbon-containing material separated from the discharge of the direct reduction with solid carbon-containing reducing agents is at least partially burned in a combustion unit with the addition of oxygen-containing gases, the hot combustion gases and the exhaust gas of the direct reduction be used to generate electrical energy, the amount of electrical energy generated being regulated so that it corresponds at least to the maximum energy requirement of the electric arc furnace plus the minimum energy requirement of the _electric reduction furnace, and that the energy not required by the electric arc furnace in the _electric reduction furnace is implemented. 6. The method according to claim 5, characterized in that the exhaust gas of the direct reduction is afterburned before use in electrical power generation. 7. The method according to claim 5 or 6, characterized in that further combustible material is fed into the combustion unit. 8. The method according to any one of claims 5 to 7, characterized in that the combustion unit is a circulating fluidized bed. 9. The method according to any one of claims 5 to 8, characterized in that a separate carbonization and / or partial gasification of solid carbonaceous material combustible gas is generated, combustible gas is used for generating electrical energy and irektreduktion geschwelte the solid carbonaceous material into the _D and / or the electric reducing furnace and / or the combustion unit is used. 10. The method according to claim 9, characterized in that the _S chwelung and / or partial gasification takes place in a circulating fluidized bed. 11. The method according to claim 9 or 10, characterized in that combustible gas is stored in a gas storage and is removed if necessary for generating electrical energy. 12. The method according to any one of claims 5 to 11, characterized in that the combustible gas is used to generate electrical energy using a gas turbine. 13. The method according to claim 10, characterized in that baking coals are used in the circulating fluidized bed. 14. The method according to claim 2 or 3, characterized in that the excess carbon-containing material separated from the discharge of the direct reduction is used in the electric reduction furnace, additional energy sources are burned in a combustion unit with the addition of oxygen-containing gases, the hot combustion gases and the exhaust gas of the direct reduction be used to generate electrical energy, the amount of electrical energy generated being regulated so that it is at least the maximum energy consumption of the arc furnace plus the minimum energy requirement of the electrore corresponds to the production furnace, and that the energy not required by the arc furnace is converted in the electric reduction furnace. 15. The method according to any one of claims 1 to 14, characterized in that the direct reduction is carried out in a rotary kiln.

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