JPH06287621A - Melting process for iron scrap with low consumption of energy - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] Energy consumption that covers most of iron source from iron scrap by using vertical furnace and converter or electric furnace in combination Provide a dissolution process. [Structure] Iron scrap and coke in a vertical furnace such as cupola
After charging carbon material such as coke and blowing air etc. to melt iron scrap to make hot metal, this hot metal and iron scrap etc. as an iron source are charged to a converter or electric furnace to decarburize. Impurity elements in the product during refining, especially Cu, N
Depending on the total allowable concentration of i, Cr, and Sn and the impurity elements contained in the hot metal, among them, the total concentration of Cu, Ni, Cr, and Sn is separately installed in the converter or electric furnace as an iron source. The total of the mixing ratio of the iron scrap and the like and the concentration of the impurity elements contained in the iron source is adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a melting process of iron scrap that consumes a small amount of energy. More specifically, most of the iron source is iron scrap by using a combination of a solid furnace and a steelmaking converter or an electric furnace. It is related to an economical melting and refining process that mixes and adjusts the iron source so that the impurity element concentration in the product falls within the allowable range.

[0002]

2. Description of the Related Art In recent years, with the increase in the amount of iron scrap generated, the recycling of iron scrap has been drawing attention from the viewpoint of environmental protection and cost reduction of steelmaking. Conventionally, as iron sources for steelmaking, in addition to hot metal obtained by smelting and reducing iron ore in a blast furnace or cold iron obtained by cooling and solidifying this, along with the processing of steel materials and the aging of buildings and machine products, etc. There is iron scrap, etc. that occurs. When using these iron sources in the steelmaking stage, iron ore is used as the base in the case of hot metal or cold pig iron, so the concentration of impurity elements contained is low and the product quality can be high-grade, while iron ore is used. Since a large amount of energy is required to melt and reduce the steel, there is also a problem that the amount of energy used in each of the processes of ironmaking and steelmaking increases, which is not economical. On the other hand, in general, the use of iron scrap has the advantage that the energy consumption can be reduced by the amount of reduction heat compared to iron ore, but on the other hand, the concentration of impurity elements contained is higher than that of blast furnace pig iron, so high-quality There was also a problem that it was not suitable for manufacturing products.

Conventionally, with respect to the recycling of iron scrap, a method of reusing it as a structural material through a melting and refining process mainly composed of an electric furnace is generally used. Also,
As another method, there is a case where iron scrap and molten pig iron obtained from a blast furnace are charged into a converter to melt and smelt the iron scrap and reused mainly in the form of a thin steel plate.

The difference between these two methods is that, in the case of the electric furnace method, electricity is used as the melting energy of the iron scrap, whereas in the converter method, the sensible heat of the hot metal and the carbonaceous material such as coke are used. This is the point of utilizing the oxidation heat of. In addition, due to the difference in the products manufactured, in the case of the electric furnace method, mainly waste waste is used as the brand of iron scrap, whereas in the case of the converter method, self-generated waste mainly containing few impurity elements is used. To do.

From the above differences, from the viewpoint of energy cost, electric power mainly burns fossil fuel and converts it into electric power via steam, and since this conversion efficiency is as low as 40% at most, fossil fuel It is more economical to use the converter method that directly uses On the other hand, from the perspective of expanding the amount of iron scrap used, it is difficult to increase the amount of used waste in the converter process because most of the iron scrap generated is waste and it is difficult to increase the amount of waste used in the converter process. The law is advantageous.

In this respect, according to the knowledge of the present inventors, it is possible to selectively use the iron scrap or to appropriately mix the blast furnace hot metal according to the impurity element concentration in the iron scrap in each process of the iron making and the steel making. It has become clear that it is possible to minimize the total energy consumption of the processes according to the required product quality.

That is, this is a method in which a vertical furnace and a converter or an electric furnace are used in combination in each step of iron making and steel making. Specifically, iron scrap is melted in a vertical furnace such as a cupola to produce hot metal. In addition to the cupola pig iron, one or both of iron scrap and blast furnace molten pig iron are charged into a converter or a metallurgical furnace of an electric furnace to melt and refine the iron scrap.

In the following, an example of using a cupola as a vertical furnace will be shown. However, other types of furnaces can be used as long as they can dissolve an iron scrap etc. by blowing an oxidizing gas. Things can also be used.

In this case, the combined use of the vertical furnace and the air-cooling furnace can significantly reduce the energy cost as compared with the case where only the electric furnace is used because the molten iron is mixed into the electric furnace. Therefore, it has been clarified by the study by the present inventors that the above-mentioned disadvantage due to the use of the electric furnace can be avoided.

Here, particularly important matters are the compounding ratio of the iron scrap charged into the converter or the electric furnace and Cu and N.
By adjusting the total concentration of the impurity elements such as i, Cr, and Sn according to the product allowable impurity element concentration and the impurity element concentration contained in the cupola pig, while satisfying the required product quality, each of the ironmaking and steelmaking can be performed. This is the point that the energy consumption of the total process can be minimized.

On the other hand, a method of using a vertical furnace such as a cupola in combination with a converter is disclosed in JP-B-57-61089 and JP-A-56-123310, in which a shaft furnace, a cupola and a converter are combined. A method is disclosed. This method uses reduced iron obtained by reducing iron ore from a shaft furnace as an iron source charged into a cupola, and does not positively use iron scrap. Rather, it is a technique for dealing with the shortage of iron scrap, and not only the method of the present invention but also the recent situation in which the amount of iron scrap is increasing as described above cannot be dealt with, and iron ore as an iron source This is an energy-poor method because it uses reduced iron by reduction as a base.

Further, JP-A-61-84309 discloses a method for producing steel from scrap iron by directly connecting a cupola and a converter stepwise and physically. In this method, the converter exhaust gas is introduced into the cupola by the direct connection of the cupola and the converter to not only promote the dissolution of scrap iron in the cupola by the sensible heat and combustion heat of the exhaust gas, but also with the hot metal obtained from the cupola. Separately, scrap iron is charged into the converter and melted and refined.

Therefore, this method is very advantageous in terms of energy because all the scrap iron is used as the iron source and the converter exhaust gas is effectively used as the heat source in the cupola.

However, the problem with this method is that the hot metal obtained from the cupola is continuously fed into the converter due to the physical connection between the cupola and the converter. Not only is it difficult to adjust the temperature components in the furnace, but since molten steel with varying temperature components is continuously discharged from the inside of the converter through the outlet, it also affects the temperature and components suitable after the converter. The temperature drop becomes large and stable operation cannot be realized.

Further, in this method, since all scrap iron is used as an iron source, in order to obtain the required product quality,
It is necessary to use expensive waste iron with a low impurity element concentration as a raw material, or to continuously adjust the impurity element concentration of the scrap iron charged into the cupola and the converter according to the product quality, which increases the cost of the main raw material. Problems such as increase in equipment cost due to the installation of many main raw material charging equipment,
It is difficult to realize economical operation.

[0016]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and more specifically, the molten iron obtained by melting iron scrap using a vertical furnace is installed in a converter or an electric furnace. When charging and decarburizing and refining, separately from the hot metal, by charging either or both of scrap and blast furnace hot metal into the converter depending on the product quality, the total energy-cost is reduced, Moreover, it is an object of the present invention to provide an economical iron scrap melting process that consumes less energy and maximizes the deterioration of product quality.

[0017]

According to the present invention, iron scrap and carbonaceous material are charged into a tight-fitting furnace, and an oxidizing gas such as air is blown from below the furnace body to generate iron scrap due to the oxidation heat of the carbonaceous material. After separating hot metal and slag obtained by heating and melting, this hot metal and either or both of iron scrap or blast furnace hot metal as an iron source are charged into a steelmaking converter or an electric furnace, and oxidizing gas is added. When melting and decarburizing refining the iron scrap by using the above, impurity elements in the product required, among them, the total of the allowable values of the concentrations of Cu, Ni, Cr and Sn and the impurity element contained in the hot metal Depending on the total concentration, adjust the mixture ratio of either one or both of iron scrap or blast furnace hot metal separately charged into the converter as an iron source, and the total concentration of impurity elements contained in the iron source. To It is an butterfly.

Before the molten pig iron obtained from the vertical furnace is charged into a steelmaking converter or an electric furnace, a desulfurization treatment can be performed by blowing a flux containing CaO and CaF ₂ as a main component into the molten pig iron. .

The structure and operation of the means of the present invention will be described in detail below.

The use of iron scrap as an iron source in the ironmaking process does not require reduction as compared with the method of using iron ore as in the blast furnace method or the like, so that it is sufficient to supply only the heat of melting, and the energy It is effective in the sense that it can be used in a small amount. In addition, the use of the vertical furnace in the pig iron making process makes it possible to use an inexpensive carbonaceous material such as coke as a heat source (energy source) and to lower the exhaust gas temperature due to the characteristics of the furnace. Therefore, the thermal efficiency can be improved, which is advantageous in terms of energy consumption and cost.

Further, when decarburizing and refining the hot metal to obtain molten steel, the use of the top-bottom blowing converter can sufficiently stir the iron bath with the bottom-blowing gas, so that the deoxidization efficiency of the iron bath is improved and the decarburization efficiency is improved. In addition to the above, it is possible to control the combustion rate of exhaust gas by adjusting the lance height and the acid transfer rate according to the mixing ratio of iron scrap to the converter in the acid transfer from the top blowing lance. It is effective in the sense that a relatively large amount of iron scrap can be compounded without adding a large amount of heat source such as gas.

In addition, the use of an electric furnace allows not only a large reduction in energy cost by blending a small amount of hot metal, but also a relatively large weight of iron compared with the case of using the above-mentioned converter. It is effective in that it can be efficiently dissolved even when scrap is mixed.

The technique, which is the essence of the present invention, not only enjoys the above advantages by simply combining the vertical furnace and the converter or the electric furnace, but also provides most of the iron sources in the respective steps of ironmaking and steelmaking. If it is possible to supply from iron scrap, separately from the hot metal obtained from cupola, that is, the cupola hot metal and the iron scrap and / or the blast furnace hot metal as an iron source, are separately charged. Either one or both of iron scrap or blast furnace hot metal charged into the converter or electric furnace as an iron source, and the total mixing ratio, and the impurity element concentration contained in the iron source,
That is, the total concentration of Cu, Ni, Cr, and Sn is adjusted to be equal to or less than the product allowable impurity element concentration.

More specifically, it is difficult to adjust the concentration of the impurity element contained in the cupola pig iron for each charging of the converter or the electric furnace for the same reason as in the above-mentioned prior application, and therefore it is contained in the cupola pig iron. In addition to satisfying the required product quality by adjusting the mixing ratio of the iron source and the impurity element concentration contained in the iron source to below the product allowable impurity element concentration in consideration of the impurity element concentration, This is effective in that it can expand the iron source selection range in each process of pig iron and steel making depending on the quality, and can minimize the main raw material cost and energy consumption of the total process. In addition, it is important to expand the range of iron source selection so that it is possible to manufacture from general steel materials having a relatively high allowable impurity element concentration to materials having a low allowable impurity element concentration and a high added value in the same process.

Further, by desulfurizing the hot metal obtained from the cupola and then charging it in a converter or an electric furnace, the desulfurization load in the converter or the electric furnace can be greatly reduced, and thus the basic raw material unit can be reduced. It is effective in the sense that it can.

[0026]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing a flow of a melting and refining process of iron scrap in an embodiment of the present invention.
The respective devices shown in the schematic view of FIG. 1 are (a) melting, (b) desulfurization, (c) charging, (d) melting and refining and (e)
It consists of each process of tapping.

In FIG. 1, iron scrap 1a as a charging raw material
And coke as carbonaceous material 1b, and limestone (not shown) are charged into a vertical furnace 1 such as a cupola, and oxygen enriched air (as an oxidizing gas) is supplied from a tuyere 2 provided below the furnace body. (Not shown) is blown, and the charged raw material is melted to continuously produce the hot metal 3a. The obtained hot metal 3a is tapped from the taphole 3 and is stored in a transport container 4 such as a pot or a mixing pig car, and if necessary, desulfurization treatment is performed in the desulfurization step (b) using the immersion lance 5. After desulfurization, remove the residue.

Next, a desulfurized hot metal 3 is placed in a steelmaking converter, such as an upper-bottom blowing converter 6, into which iron scrap 6a has been charged in advance.
In the converter 6, the bottom blowing tuyere 7 and the lance 8 are charged.
Dissolve and refine while blowing with oxygen.
When decarburization is complete, the converter 6 goes through the ladle 9 and melts 6
b is tapped, and the process proceeds to the next step of secondary refining or continuous casting.

According to the schematic diagram of the process flow shown in FIG. 1, a cupola and a cupola 5 having a capacity of 5 t / h as a vertical furnace are used.
Iron scrap was melted and decarburized and refined using a t / ch top-bottom blowing converter. In this case, since the hot metal S concentration was low, the de-S treatment was not performed.

The iron scrap used in the cupola is shredder scrap having a size of 25 to 200 mm, and the impurity concentration, that is, the sum of Cu, Ni, Cr and Sn is 0.4.
5 wt%. The size of the heat source is 2
A 5-75 mm blast furnace coke was used.

As scraps to be charged into the converter, trimming scraps of hot-rolled steel plate and cut pieces of slabs are used. Impurity concentration in scraps in this case, namely Cu, Ni, Cr,
The total Sn content was 0.06 wt%.

As the operating conditions, the mixing ratio of the cupola pig and the converter charging scrap was variously changed so that the converter charging scrap ratio was in the range of 0% to 80%.

Further, as shown in FIG. 2, an electric furnace 10 of 5 t / ch is used instead of the converter 6, and in the electric furnace 10, the electrode 11 is used for arc heating and the lance 12 is used for blowing oxygen. Was done. In this method, the iron scrap 1a was melted and decarburized and refined according to the same procedure and operating conditions as the above-mentioned operation.

FIG. 3 shows the operation results in the above examples. In FIG. 3, the horizontal axis is the total energy-intensity unit, the vertical axis is the concentration of impurity elements in the product, among which Cu, Ni, C
It is the total concentration of r and Sn, and is a relative value standardized to 1 when 100% of blast furnace hot metal is used as an iron source in the blast furnace, converter method or electric furnace method.

As is clear from FIG. 3, the total energy consumption rate decreases as the mixing ratio of the cupola pig iron increases, that is, the mixing ratio of the iron or iron scrap scraped in the converter or the electric furnace decreases. On the other hand, the impurity element concentration increases. Therefore, by adjusting the mixing ratio of cupola pig iron and the concentration of impurity elements in converter or electric furnace charging scrap according to the required product quality, the minimum energy required while ensuring product quality
It became clear that steel can be produced with the amount used.

Further, in the case of using the electric furnace in FIG. 3, the impurity element concentrations of the products obtained under the same raw material mixing conditions are almost the same as in the case of using the converter, and the energy-units are also almost the same. The result is that there is.

Further, in addition to the top-bottom blowing converter, equivalent results were obtained by using a top-blowing or bottom-blowing converter instead of this.

[0039]

As described in detail above, according to the present invention, a solid-type furnace is charged with iron scrap and carbonaceous material such as coke, and an oxidizing gas such as air is blown from the tuyere below the furnace body. After separating the hot metal and slag obtained by heating and melting the iron scrap by the oxidation heat of the carbonaceous material such as coke, this hot metal and the iron scrap and / or the blast furnace hot metal as a separate iron source are used to make steel. In the case of charging into an electric converter or an electric furnace and decarburizing and refining with an oxidizing gas, the allowable value of the impurity element concentration in the required product is the sum of the concentrations of Cu, Ni, Cr, Sn and the hot metal. Depending on the total impurity element concentration contained, either one or both of iron scrap or blast furnace hot metal charged separately into the converter or electric furnace as an iron source, or the total mixing ratio, and the impurity element concentration contained in the iron source. Adjust the sum of That the dissolution of iron scrap,
It has been clarified that not only the total energy required for refining can be lowered, but also the concentration of the impurity element in the product can be made equal to or lower than the allowable value.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a flow of an iron scrap melting and refining process in one embodiment of the present invention.

FIG. 2 is a schematic diagram showing a flow of an iron scrap melting and refining process according to another embodiment of the present invention.

FIG. 3 is a graph showing a comparison of the results of carrying out a melting and refining process of iron scrap based on the flow shown in FIGS. 1 and 2.

[Explanation of symbols]

 1 Vertical furnace 2 Blower tuyeres 3 Tap holes 4 Conveyor container 5 Immersion lance 6 Top-bottom blowing converter 7 Bottom-blowing tuyeres 8 Top-blowing lance 9 Ladle 10 Electric furnace 11 Electrode 12 Lance

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenichi Sorimachi, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Technical Research Division, Kawasaki Steel Co., Ltd. (72) Tetsuya Fujii 1, Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Corporation Technical Research Division

Claims (5)

[Claims] 1. A vertical furnace is charged with iron scrap and carbonaceous material,
An oxidizing gas is blown from the tuyere below the furnace body, the iron scrap is heated and melted by the heat of oxidation of this carbon material, and this molten pig iron is separated from the slag, and the iron scrap or the blast furnace molten pig iron prepared separately as an iron source. Either or both of them are charged into a steelmaking furnace such as a converter or an electric furnace, and in this steelmaking furnace, when the iron scrap is melted by using an oxidizing gas and the hot metal is decarburized and refined, Depending on the total amount of the impurity element concentration in the product and the impurity element concentration contained in the hot metal obtained from the vertical furnace, either iron scrap as an iron source or blast furnace hot metal Alternatively, a melting process of iron scrap with a small energy consumption, characterized in that the total amount of both the compounding ratio and the concentration of the impurity element contained in the iron source is adjusted. 2. The energy according to claim 1, wherein the allowable amount of impurity element concentration in the required product is the total amount of Cu, Ni, Cr and Sn concentrations.
Melting process of iron scrap with low usage. 3. The melting process of iron scrap with low energy consumption according to claim 1 or 2, wherein the vertical furnace is a cupola. 4. The melting process of iron scrap with low energy consumption according to claim 1, 2 or 3, wherein the steelmaking furnace is an upper-bottom blowing converter. 5. The energy consumption according to claim 1, wherein the hot metal melted in the vertical furnace is desulfurized prior to charging it into the steelmaking furnace. Low iron scrap melting process.