JP2012180560A - Method for melting ferrous scrap with complex arc-melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for manufacturing molten steel with which the high utilizing efficiency of energy and also, the decrease in manufacturing cost can be obtained.SOLUTION: The arc-melting furnace is composed of an arc-melting chamber and a shaft-type preheating chamber vertically arranged at the upper part of the arc-melting chamber and communicated with the arc-melting chamber. In the furnace, during dropping down the ferrous scraps charged and filled up in the preheating chamber, into the preheating chamber in order, these scraps are preheated by using high temperature waste gas, and when these scraps are successively introduced into the melting chamber and arc-melted, the ferrous scraps charged in the preheating chamber in the filling state are charged and melted so that the apparent bulk density (P) value may become 0.7 t/mor higher.

Description

  The present invention relates to a method for melting iron-based scrap by a combined arc melting furnace, and in particular, devise a method for charging and charging iron-based scrap into a shaft-shaped preheating chamber of the melting furnace, thereby efficiently melting molten steel. The method is proposed.

  In recent years, a new process has been developed in which molten steel is produced by melting iron-based scrap (hereinafter sometimes simply referred to as “iron scrap”) using an electric furnace (arc furnace). In this process, a part of the electric energy is replaced with an inexpensive fuel such as charcoal, and the iron scrap is preheated with high-temperature exhaust gas generated in the melting chamber (furnace). Reduction can be achieved.

  A typical example is a composite electric furnace (hereinafter referred to as “composite arc melting furnace”) as disclosed in Patent Documents 1 and 2. The composite arc melting furnace is mainly characterized by a melting chamber and a shaft type preheating chamber capable of attracting high-temperature exhaust gas generated in the melting chamber. That is, the composite arc melting furnace allows the iron-based scrap to be charged into the preheating chamber to be straddled across the preheating chamber and the melting chamber, and the iron-based scrap is transferred to the melting chamber from the preheating chamber. Preheated using high-temperature exhaust gas generated in the melting chamber, and those that have reached the melting chamber are heated and melted by arc heat, and when at least one heat of molten metal has accumulated in the melting chamber It is a furnace that takes out hot water as molten steel.

JP-A-3-505625 JP-A-10-292990

  As described above, the operation of the combined arc melting furnace is characterized in that the raw material (iron scrap) in the preheating chamber is preheated and heated using the high temperature exhaust gas generated in the melting chamber. However, if the filling state, which is governed by the type of iron scrap and the mixing ratio, is poor, the heat transfer efficiency between the iron scrap and the exhaust gas is reduced, and sometimes the exhaust gas energy cannot be used effectively (from the preheating chamber). In some cases, the temperature of the exhaust gas discharged has not decreased). In other words, it is originally desirable to operate the furnace with high energy efficiency by lowering the temperature of the generated exhaust gas, but in reality it is difficult to realize this.

  As described above, in the operation of the conventional combined arc melting furnace, improvement of energy efficiency and further labor saving are demanded from the viewpoint of global environmental problems. In particular, in the field of the steel industry that originally consumes a large amount of energy, there is a strong demand for solutions to these problems.

  Accordingly, an object of the present invention is to establish a technology capable of overcoming the above-described problems of conventional composite arc melting furnaces, and in particular, molten steel that has high energy utilization efficiency and can contribute to reduction of manufacturing costs. It is to propose a manufacturing technique.

  As a result of intensive investigations to solve the technical problem, the inventors of the present invention, in the case of a composite arc melting furnace, efficiently preheats the iron-based scrap charged and filled in the preheating chamber of the furnace. It is important to keep the iron-based scrap in a proper filling state, and in particular, it has been found that adjusting the apparent bulk density of the iron-based scrap in the preheating chamber to an appropriate range is particularly effective.

In other words, since the iron-based scrap charged in the composite arc melting furnace differs in shape, thickness, size, etc., depending on what kind of scrap is charged and filled, what kind of scrap is charged in the preheating chamber. It was found that the apparent bulk density of the iron-based scrap charged was greatly different. And it discovered that the heat transfer efficiency to the iron-based scrap (iron source) by the high-temperature gas in the composite arc melting furnace greatly varies depending on the apparent bulk density of the iron-based scrap.
In the present invention, the apparent bulk density (P) is (P) = Σ (weight i) / Σ (volume i)
= Σ (weight i) / Σ (weight i / density i).

  For example, if the apparent bulk density of the iron-based scrap charged and filled in the preheating chamber is small, the temperature of the exhaust gas at the exhaust gas outlet of the preheating chamber becomes high. That is, it has been found that the sensible heat of the gas is not efficiently transferred to the iron-based scrap, resulting in insufficient heat exchange. This is because if the apparent bulk density is small, the proportion of iron-based scrap in the space of the preheating chamber is small, so that the sensible heat of the generated exhaust gas is not sufficiently transmitted to the iron-based scrap, and the exhaust gas It is thought that this is because the air blows through at a high temperature and reaches the exhaust gas outlet.

  Moreover, the high exhaust gas temperature at the exhaust gas outlet in the upper part of the preheating chamber means that there is a loss of gas sensible heat, which not only increases the power consumption rate but also increases the gas flow rate. This will increase the amount of dust produced and cause a heavy load on the exhaust gas treatment facility in the next process, which will hinder stable operation of the melting furnace.

  On the other hand, when the apparent bulk density is large, the effective reaction interface area between the exhaust gas and the iron scrap increases, so that the sensible heat of the gas is sufficiently transmitted to the iron scrap and the exhaust gas temperature at the outlet (exhaust dust) is also high. It becomes low temperature.

The present invention has been developed based on such knowledge, and has the following gist configuration. That is, the present invention relates to an iron-based scrap charged and filled in an arc melting chamber and a shaft-type preheating chamber standing on the top and communicating with the arc melting chamber. In the method of preheating using the high-temperature exhaust gas generated in the melting chamber while descending sequentially in the preheating chamber, and subsequently guiding to the melting chamber and arc melting,
A composite arc characterized in that iron scrap charged in a preheating chamber is charged and melted so that a filling state thereof becomes an apparent bulk density (P) value of 0.7 t / m ³ or more. This is a method for melting iron scrap in a melting furnace.

In the present invention, specifically,
(1) When charging iron-based scrap, adjusting by changing the type and amount of scrap so that the apparent bulk density P is 0.7 t / m ³ or more,
(2) The iron scrap to be blended is either a small or large, two or more types selected from heavy, press, shredder, new cutting, steel dairy powder, and waste iron in the “Iron Scrap Inspection Standard” Using a combination of scraps,
However, this is a more preferable solution.

According to the present invention having such a configuration, the filling type of the iron-based scrap in the preheating chamber is adjusted by adjusting the mixing type and amount of the iron-based scrap, and the apparent bulk density (P) value is 0.7 t / m ³ or more. By doing so, the molten steel can be melted by the composite arc melting furnace which has high energy use efficiency and is effective in reducing the cost.

It is a figure which shows the outline of the composite arc melting furnace explaining the embodiment of the method of this invention.

As described above, the present invention provides various shapes such that the apparent bulk density (P) indicating the filling state of the iron-based scrap charged in the preheating chamber is 0.7 t / m ³ or more. It is characterized by combining and blending various types of iron-based scrap having a size (as defined in the “Iron Scrap Inspection Standards” of the Japan Iron Source Association).

When the above apparent bulk density is less than 0.7 t / m ³ , the heat transfer efficiency between the melting chamber generated exhaust gas and the iron-based scrap filled in the preheating chamber is deteriorated, and heat is generated at the upper outlet of the shaft type preheating chamber. The high-temperature exhaust gas that is not exchanged is discharged, and the object of the present invention cannot be achieved.

  FIG. 1 is a view showing an example of a combined arc melting furnace used in carrying out the method of the present invention. As shown in this figure, the composite arc melting furnace 1 used in the present invention comprises a melting chamber 2 and a shaft-type preheating chamber 3 standing upward from a part of the upper portion thereof, and the inside thereof is lined with a refractory. Has been. The melting chamber 2 has a furnace bottom electrode 6 at the bottom, and has the shaft-shaped preheating chamber 3 and the water-cooled furnace wall 4 communicating with the melting chamber 2 at the top. A furnace lid 5 is provided so as to cover the opening. The furnace lid 5 has a water cooling structure that can be opened and closed, and is provided with a graphite upper electrode 7 that moves up and down toward the melting chamber 2. The upper electrode 7 and the furnace bottom electrode 6 are energized by a DC / AC power source (not shown) through the iron-based scrap in the furnace, thereby generating an arc therebetween. It is like that.

Further, an oxygen blowing lance 8 and a carbonaceous material blowing lance 9 are attached to the furnace lid 5. The oxygen blowing lance 8 is supplied with oxygen for assisting the melting of the iron scrap 13, and the carbonaceous material. Auxiliary heat sources such as coke, char, coal, charcoal, graphite, biomass charcoal powder, or a carbon material made of a mixture thereof are blown from the blowing lance 9 through air or nitrogen. As a result, the generated exhaust gas always contains unburned components (CO gas), carbon dioxide (CO ₂ ), and the like.

  Above the preheating chamber 3, a bottom-opening type supply bucket 11 is provided. From the supply bucket 11, an iron-based supply bucket 11 is provided via an openable / closable supply port provided in the upper portion of the preheating chamber 3. Scrap 13 or the like can be charged into the preheating chamber 3.

  In the composite arc melting furnace configured as described above, the iron scrap 13 charged in the preheating chamber 3 is preheated while descending sequentially with time, and eventually reaches the melting chamber 2 and then the upper part. It is melted by the arc heat generated from the electrode 7. When the iron scrap 13 is melted, high-temperature exhaust gas is generated in the melting chamber 2. The exhaust gas is sucked into the duct 12 through the preheating chamber 3 by a blower or a dust collector provided upstream of the duct 12 provided above the preheating chamber 3, and in the process, iron-based scrap in the preheating chamber 3 is sucked. 13 is preheated by the heat of the high temperature exhaust gas. Note that the preheated iron-based scrap 13 in the preheating chamber 3 sequentially or intermittently moves into the melting chamber 2 in accordance with the speed of melting in the melting chamber 2.

  In the present invention, when the iron scrap 13 is melted in the melting chamber 2 by the heat of the arc as described above, the carbon material is supplied into the melting chamber 2 through the carbon material blowing lance 9 and burned. Thus, in the process of melting the iron-based scrap 13 in the melting chamber 2 and the high-temperature exhaust gas generated in the melting chamber 2 being sucked into the duct 12 through the preheating chamber 3, the inside of the preheating chamber 3 is The iron scrap 13 is preheated by the rising high temperature exhaust gas (about 400 to 1000 ° C.).

Hereinafter, the melting procedure of the iron-based scrap 13 in the DC arc melting furnace 1 will be described.
First, iron scrap 13 is charged into the preheating chamber 3 from the supply bucket 11. The charged iron-based scrap 13 is charged through the preheating chamber 3 until reaching the melting chamber 2, and then gradually filled into the preheating chamber 3. In order to uniformly charge the iron scrap 13 into the melting chamber 2, the iron scrap 13 is placed in the melting chamber 2 on the side opposite to the side directly connected to the preheating chamber 3 with the furnace lid 5 opened. It can also be charged. Moreover, hot metal may be charged into the melting chamber 2 when the iron-based scrap 13 is charged. According to this, the amount of electric power used can be significantly reduced by the heat of the hot metal.

  Next, while feeding a direct current between the furnace bottom electrode 6 and the upper electrode 7 in the melting chamber 2, the upper electrode 7 was moved up and down, and was inserted between the furnace bottom electrode 6 and the upper electrode 7 or charged. An arc is generated between the iron-based scrap 13 and the upper electrode 7, and the iron-based scrap 13 is melted by the heat of the arc. At this time, the molten slag may be generated by melting the flux. This is because the molten metal produced by the molten slag can be kept warm.

  When the oxygen blowing lance 8 and the carbonaceous material blowing lance 9 can be inserted into the melting chamber 2 after energization of the furnace bottom electrode 6 and the upper electrode 7, oxygen is supplied from the oxygen blowing lance 8 and iron scrap 13 To help dissolve. On the other hand, from the carbon material blowing lance 9, carbon material is blown into the molten slag as an auxiliary heat source in order to reduce the electric power intensity.

  In the operation of the composite arc melting furnace, since the iron scrap 13 is intermittently charged into the preheating chamber 3 from the bucket 11 in accordance with the melting amount of the iron scrap, the sensible heat of the exhaust gas is changed to iron. It can be used continuously for preheating scrap. When a predetermined amount of iron-based scrap is melted and stays in the melting chamber 2, the furnace is tilted and the molten steel is taken out into the ladle 10 through a nozzle embedded in the furnace bottom.

An example in which iron-based scrap is melted using the DC type composite arc melting furnace shown in FIG. 1 will be described below. The composite arc melting furnace used has a melting chamber having a furnace diameter of 6 m, a height of 3 m, a preheating chamber having a width of 3 m, a depth of 4 m, a height of 5 m, a furnace capacity of 150 t / ch, and a transformer capacity of 100 MVA. 150 tons of the following iron-based scraps were charged in the melting chamber and the prechamber, and an arc was generated by the upper graphite electrode to melt the iron-based scrap. Further, oxygen was fed from the oxygen blowing lance at 5000 Nm ³ / h, and 70 kg / min coke was blown from the carbonaceous material blowing lance. As the iron-based scrap melts in the melting chamber and is charged into the preheating chamber and the iron-based scrap descends in sequence, additional iron-based scrap is supplied from the scrap charging bucket above the preheating chamber, and the preheating chamber The height of the iron-based scrap was kept constant.

  In this way, the melting is progressed in a state where iron-based scrap is continuously present in the melting chamber and the preheating chamber, and when 150 tons of molten steel is generated in the melting chamber, 50 tons are left in the furnace. 100 tons of charged steel was discharged from the outlet to the ladle. The temperature of the molten steel at the time of steel output was 1600 ° C., and the C concentration in the molten steel was operated to be 0.1 mass%.

Even after 100 tons of steel has been delivered, the iron-based scrap is continuously melted while feeding acid and coke, and once again, when the amount of molten steel in the melting chamber reaches 150 tons, 100 tons of steel is repeatedly produced. A molten steel of 100 tons was obtained with an oxygen amount of 25 Nm ³ / t and a coke amount of 21 kg / t for 30 minutes.

  During this operation, the composition of the iron-based scrap charged from the bucket into the preheating chamber was changed, the temperature on the exhaust gas outlet side was measured, and the influence of the scrap composition on the exhaust gas outlet temperature was investigated. Note that the blending of the scraps was performed while keeping the blending constant for a time sufficient to replace the preheating chamber with the predetermined blending according to the capacity of the preheating chamber.

The results of this dissolution experiment are shown in Table 1. As shown in this table, in the case of a melting method suitable for the method of the present invention, the apparent bulk density (P) is 0.7 t / m ³ or more, the exhaust gas temperature at the outlet is lower than 500 ° C., and the electric power unit of the electric furnace is It became smaller than the target 300 kWh / t, and it was found that the sensible heat energy of the exhaust gas can be efficiently recovered.
In addition, the apparent bulk density (P) when a plurality of raw materials are mixed and charged is (P) = Σ (weight i) / Σ (volume i) = Σ (weight i) / Σ (weight i / density i) Calculated from

In the above Examples, the following iron scraps used in the blending examples shown in Table 1 were used.
(B) “Heavy” is sized by guillotine shear, gas cutting, heavy machinery, etc., and is classified by thickness, size, and unit weight. HS: thickness 6 mm or more, width or height 500 mm or less × A combination of length 700 mm or less, H4: thickness less than 1 mm, width or height 500 mm or less × length 1200 mm or less was used.
(B) “Press” is a rectangular parallelepiped that is mainly compression-molded with a press machine using a steel plate processed product as a base material, and is classified by the base material. A: Total of 3 sides is 1800 mm or less, maximum Sides of 800 mm or less, C: Same as above, upper limit dimensions are the same, and the lower limit is a combination of three sides totaling 600 mm or less.
(C) “Shredder” is iron-based scrap that is mainly crushed by a shredder machine using a steel plate processed product as a base material and then sorted by a magnetic sorter. “Dalai powder” is cutting scraps and chips generated when manufacturing screws, machine parts, etc., which are classified according to shape and degree of oxidation (total of three sides of press is 1800 mm or less, maximum side is 800 mm or less). Using.
(D) “Spent iron” was a block-shaped product obtained by finely pulverizing a used casting product, and one having an A1 side of 1200 mm or less divided by a base material was used.

  In the above-described embodiment, a DC type is exemplified as the arc melting furnace, but an AC type arc furnace can also be applied. Moreover, as a carbon material blown from a carbon material blowing lance, a biomass raw material can be used in addition to the exemplified coke powder. In this case, since biomass is carbon neutral, there is an effect in that the amount of carbon dioxide emission, which is one of the causes of global warming, can be reduced.

  Moreover, as a method for adding the carbonaceous material, as in the example described above, a lance blowing method may be used, or a method of injecting into the bath from the top of the melting chamber may be used, and a dedicated nozzle is embedded in the furnace bottom, Bottom blowing injection may be used. It is only necessary to implement with the optimal equipment according to the balance between capital investment and efficiency.

  Further, as the iron-based scrap, in addition to the scrap stipulated in the above-mentioned “Iron Scrap Inspection Standard” by the Japan Iron Source Association, iron-based scraps such as directly reduced iron and cold iron may be used as a main component. In addition, what contains a lot of iron oxides takes extra energy to reduce iron oxide, but may be used in consideration of operating costs.

  The technique according to the present invention is not limited to the exemplified composite arc melting furnace, and can be applied to other melting furnaces as a method for preheating iron-based scrap using the melting chamber-generated exhaust gas.

1 Arc melting furnace 2 Melting chamber 3 Preheating chamber 4 Furnace wall 5 Furnace lid 6 Furnace electrode 7 Upper electrode 8 Oxygen blowing lance 9 Carbon material blowing lance 10 Ladle 11 Bucket 12 Duct 13 Iron scrap

Claims (3)

The iron-based scrap charged and charged in the preheating chamber is sequentially placed in the preheating chamber by an arc melting furnace comprising an arc melting chamber and a shaft-type preheating chamber that stands upright and communicates with the arc melting chamber. In the method of preheating using the high-temperature exhaust gas generated in the melting chamber while descending to the arc, and subsequently guiding to the melting chamber and arc melting,
A composite arc characterized in that iron scrap charged in a preheating chamber is charged and melted so that a filling state thereof becomes an apparent bulk density (P) value of 0.7 t / m ³ or more. A method for melting iron scrap in a melting furnace. 2. The composite arc according to claim 1, wherein when charging iron-based scrap, the apparent bulk density P is adjusted by changing the kind and blending amount of the scrap so as to be 0.7 t / m ³ or more. A method for melting iron scrap in a melting furnace.   The iron scraps to be blended are small and large scraps of at least two types selected from heavy iron, press, shredder, new cutting, steel dairy powder, and waste iron in the “Iron Scrap Inspection Standard” The method for melting iron-based scrap by the composite arc melting furnace according to claim 1, wherein the methods are used in combination.

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