JPH0941017A - Method for melting ferrous scrap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a secondary combustion rate and to improve scrap melting efficiency by providing an oxygen blowing lance with cooling gas ejection holes above the ejection holes of the lance and blowing gases, such as N2 and CO2 , from these holes at the time of melting the ferrous scrap by using a top blown converter type melting furnace. SOLUTION: The top blowing lance 1 is provided with the cooling gas ejection holes 3 separately from the oxygen-contg. gas ejection holes. The cooling gas ejection holes 3 are disposed in at least one piece, more preferably 4 to 20 pieces on the peripheral surface of the range where the distance H2 from the bottom end face of the lance 1 to the center of the ejection holes attains 0.2H1 <=0.8H1 with respect to the distance H1 from the bottom end face of the top blowing lance 1 under operation to the throat of the converter. As a result, the cooling gases consisting of one kind or >=2 kinds of N2 , Ar, Co and CO2 are blown at a rate corresponding to 5 to 30% of the supplying rate (Nm<3> /h) of the oxygen-contg. gas. One or >=2 kinds of Mg, CO3 , CaCO3 or coal powder contg. >=20wt.% volatile content or >=5wt.% moisture are blown together with the cooling gases.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for melting iron-based scrap.

[0002]

2. Description of the Related Art In recent years, it has become a technical subject to efficiently produce molten metal by recycling solid metal raw materials such as scrap due to resource and environmental problems. Conventionally, almost all electric furnaces have been used for melting scrap, but in the case of electric furnaces, a large amount of electric power is consumed for melting and refining scrap, so in countries such as Japan where electricity prices are extremely high. It is not preferable because it increases the cost. Therefore, as a method of economically melting and refining scrap without relying on an electric furnace, it is possible to melt scrap using inexpensive carbonaceous materials by utilizing the surplus production capacity of a converter with a high acid transfer capacity.
Refining methods have come to be considered.

Under such circumstances, generally, the existing upper-bottom-blown composite blowing converter is used to suppress the increase in equipment and to ignite the seeds charged in the furnace together with scrap. After that, a method of melting and refining while charging carbonaceous material as a heat source from above the furnace at the time of top-bottom blowing is proposed.

On the other hand, in Japanese Patent Laid-Open No. 2-141511, a reaction vessel capable of gas stirring the melt is used.
The amount of free fixed carbon present in the reaction vessel was set at 17 kg per ton of molten slag by using the molten slag in an amount of 350 kg or more per ton of molten iron and the sulfur content of 0.4% or more.
It discloses a method for melting steel scrap, which is kept above kg and sprayed with acid.

In this technique, the carbonaceous material existing in the molten slag phase is oxidatively burned (= exothermic reaction) with top-blown oxygen,
The slag phase is strongly stirred and the generated heat is transferred to the molten metal phase to dissolve the scrap, but the CO ₂ produced by the reaction of the carbonaceous material and oxygen is scattered outside the slag phase. It is easy to cause the so-called solution loss reaction (the following formula) in which the carbon material is brought into contact with the carbonaceous material again to be reduced to CO. CO ₂ + C = 2CO-Q (Endothermic reaction) ………… Formula Q: Calorie (J / mol)

The means for minimizing the amount of energy required for melting a unit weight of scrap and reducing the manufacturing cost (= the means for maximizing the melting energy efficiency) are CO in exhaust gas.
_It is preferable to increase the _two- quantity ratio (= CO ₂ % / [CO + CO ₂ %]), that is, the so-called secondary combustion rate. For that purpose, it is necessary to re-oxidize CO gas regenerated by the solution loss reaction to CO ₂ by O _{2 in} the upper space.

The direction of heat transfer obtained by this oxidation reaction is
Since it is in the same direction as the moving direction of the exhaust gas (= from the slag phase or the molten metal phase to the top of the melting furnace), it is difficult to transfer heat to the slag phase. Therefore, the heat transfer efficiency represented by the following formula is poor,
At the same time as raising the temperature of the exhaust gas in the upper space,
The temperature of the wall surface of the refractory furnace was raised, causing considerable wear. Heat transfer efficiency = (1-sensible heat amount corresponding to temperature difference between exhaust gas and molten metal phase / heat generation amount due to combustion from CO to CO ₂ ) × 100

As a countermeasure against the wear of the refractory furnace wall,
In JP-A-61-67708, molten iron, agglomerates of pre-reduced ore, carbonaceous material and oxygen are supplied to a reaction vessel capable of blowing an oxygen-containing gas into the molten metal at the top and bottom to reduce oxides.
In the smelting reduction process of melting, the method of cooling the furnace wall part above the slag level or its vicinity, and the cooling of the furnace wall part above the slag level or its vicinity are determined by the oxygen content in the upper blowing lance (composite lance). By injecting one or more of CO ₂ , N ₂ , hydrocarbon-containing fluid, powdered carbonaceous material, water mist and water vapor into the furnace wall portion from a system independent of the gas supply system, and / or the furnace. A method of water-cooling the iron shell of the wall portion and a method of ejecting from the wall surface of the furnace wall portion through a pipe or a porous refractory material are disclosed. This is not a method of melting iron-based scrap but a method of smelting reduction of ore, but it can be applied as a measure against wear of refractory furnace walls.

[0009]

However, Japanese Patent Laid-Open No. 61-6.
When the cooling gas or the coolant is sprayed onto a part of the refractory furnace wall as in the method described in Japanese Patent No. 7708, the part is excessively cooled to a temperature higher than necessary or below the temperature of the molten metal phase. Non-uniformity of temperature occurs locally. In particular, in the method of ejecting the coolant from the lance, heating / cooling is repeated when tapping or slag or when the lance height is changed. On the other hand, the method of ejecting the coolant from the tuyere fixed to the refractory furnace wall cannot deal with the fluctuation of the slag level due to the increase or decrease of the amount of slag or molten metal during the operation.

The degree of wear of the furnace wall is mainly proportional to the time of exposure to a high temperature, but if the above-mentioned local temperature nonuniformity or repeated heating / cooling occurs, stress / strain is generated. Amplify wear and tear. Therefore, the method of cooling by cooling a specific part of the refractory furnace wall is to increase the amount of slag and molten metal in the furnace, such as scrap melting, or to change the lance height. On the other hand, it is not a fundamental solution. The present invention solves such a problem,
An object of the present invention is to provide a method for melting iron-based scrap that can reliably extend the life of the refractory wall surface by uniformly cooling the temperature of the refractory material furnace wall and without locally repeating heating / cooling.

[0011]

DISCLOSURE OF THE INVENTION The inventor of the present invention does not directly spray a cooling agent to a specific portion of a refractory furnace wall, but rather blows a cooling agent into the upper space to exhaust the entire exhaust gas existing in the upper space. As a method that enables uniform cooling of the furnace wall, avoids repeated heating / cooling, and significantly suppresses wear of the refractory furnace wall, the coolant from the upper blowing lance is used under the following conditions. We have found that the blowing method is the most effective. The present invention is based on this finding. The summary is as follows.

(1) In a method of melting iron-based scrap in a melting furnace of a top-bottom blowing converter type by utilizing the heat of oxidation of carbonaceous material by oxygen, a top-blowing lance for supplying an oxygen-containing gas is used, A cooling gas ejection hole separate from the oxygen-containing gas ejection hole is provided such that the distance (H ₂ ) from the lower end surface of the lance to the center of the cooling gas ejection hole is the lower end surface of the upper blowing lance in operation and the cross section of the converter furnace opening. 0.2H ₁ ≦ H _{2 with} respect to the distance (H ₁ ) from
At least one cooling gas is provided in a range of ≦ 0.8H ₁ , and one or more cooling gases of N ₂ , Ar, CO, and CO ₂ are blown into the melting furnace through the cooling gas ejection holes. A characteristic method for melting iron-based scrap.

[0013] (2) the feed rate of the cooling gas blown from an oxygen-containing gas blown onto a feed lance (Nm ³ / h), and 5-30% equivalent feed rate of oxygen-containing gas (Nm ³ / h) (1) The method for melting iron-based scrap as described above. (3) The iron-based scrap according to (1) or (2), characterized in that 4 to 20 cooling gas ejection holes are provided on the upper blowing lance for supplying the oxygen-containing gas, on the peripheral surface of the upper blowing lance. Dissolution method.

(4) The angle of the cooling gas ejection hole provided in the upper blowing lance for supplying the oxygen-containing gas is such that the angle formed by the central axis of the ejection hole and the horizontal plane is from 45 degrees upward to 45 degrees downward. The method for melting iron-based scrap according to any one of (1) to (3), characterized in that it is present. (5) One or more of magnesium carbonate, calcium carbonate, or coal powder containing 20 wt% or more of volatile matter or 5 wt% or more of water is blown together with the cooling gas from the cooling gas ejection holes. The method for melting iron-based scrap according to any one of (1) to (4), which is characterized.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. 1 and 2 which are schematic views showing an embodiment of the present invention.
The first condition is the blowing position and amount of the cooling gas. That is, the cooling gas ejection hole 3 is provided at a position 0.2H ₁ ≤H ₂ ≤0.8H ₁ from the lower surface of the lance tip with respect to the distance H ₁ between the lower surface of the lance tip and the cross section of the converter throat. Is good. 1 indicates lance.

The reason for this will be explained with reference to FIG. 2 showing the "relationship between exhaust gas temperature and gas injection position" obtained by experiments. That is, at a position lower than 0.2H ₁ from the tip of the lance, part of the blown cooling gas is caught in the oxygen jet blown from the lance main hole 2 and hits the slag phase or the molten metal phase. Therefore, not only the exhaust gas but also the slag phase and the molten metal phase are cooled, which causes an essential problem that the amount of scrap melted per unit time is reduced.

Further, the temperature of the portion formed by the jet of the oxygen-containing gas colliding with the molten metal phase (hereinafter referred to as the fire point) is also cooled, the molten iron is easily oxidized, and the yield of iron is increased. There is also the problem of lowering.

On the other hand, in the case of a position higher than 0.8H ₁ , most of the cooling gas is dissipated from the melting furnace due to the flow of the exhaust gas moving from the fire point to the furnace opening of the melting furnace at high speed. Therefore, since the exhaust gas is sucked together with the exhaust gas by the exhaust gas treatment facility at the upper part of the furnace, the effect of cooling the upper space gas is significantly reduced.

The amount of the cooling gas is 5 to 3 of the oxygen supply rate.
0% is appropriate. When the cooling gas is not blown, the exhaust gas space temperature in the melting furnace is, for example, 1700 to 2300 ° C.
However, the temperature of the molten metal phase is, for example, 1600 ° C., and there is a difference of 100 to 700 ° C.

On the other hand, in an experiment investigating the wear of refractory materials, it has been confirmed that the wear rapidly increases from 1620 ° C. in a magnesia-carbon system, for example, and it is necessary to lower the temperature to 1620 ° C. or less by blowing cooling gas. . For that purpose, the minimum cooling gas flow rate is 1700 ° C. × 0.05 = 85 ° C. 1700 ° C.-85 ° C. = 1615 ° C. at a volume ratio of 5% of the exhaust gas amount (= oxygen supply rate).

If it is less than 5%, the amount of sensible heat taken away by the cooling gas is small, and the exhaust gas temperature cannot be lowered sufficiently. On the other hand, the maximum is 2300 ° C. × 0.30 = 690 ° C. 2300 ° C.−660 ° C. = 1610 ° C., which requires a flow rate of about 30%.

When it is more than 30%, not only the temperature of the exhaust gas but also the temperatures of the molten metal phase and the slag phase are lowered, and the essential amount of scrap melted per unit time is lowered. Come on. The gas species may be non-oxidizing with respect to CO in the exhaust gas, but from the gas cost perspective, one or two of N ₂ , Ar, CO, and CO ₂ may be used.
A mixed gas of at least one kind is preferable.

The second condition is the number of ejection holes, which is 4 to 4 on the circumference of the horizontal cross section (= usually circular) of the upper blowing lance.
It is necessary to provide 20 pieces. In order to cool the exhaust gas in the space around the lance, if it is not branched and blown in at least four directions, the temperature of the exhaust gas becomes uneven, and the reaction in the furnace becomes uneven.

Also, the current lance diameter, for example, 100 to
Considering the ejection hole diameter of 300 mmφ that can be installed in 300 mmφ, considering the supply amount of cooling gas (= 5 to 30% of oxygen-containing gas supply rate 10000 to 30000 Nm ³ / h), it is more than 4 If the number is small, the initial velocity of the cooling gas ejected from one hole will be higher than the sonic velocity (= about 300 m / sec), leading to the facing refractory wall.
The refractory furnace wall is locally and excessively cooled.

On the other hand, when the number is more than 20, the gap between the adjacent ejection holes for the cooling gas becomes small when the lance diameter is constant, so that the adjacent gas jets coalesce with each other to form one large gas flow. Then, the gas flow in the melting furnace (=
Flow from the fire point to the melting furnace mouth) will be disturbed and
The refractory furnace wall is locally overcooled.

The third condition is the jetting angle of the cooling gas with respect to the horizontal plane. When the central axis of the jet flow is upward above 45 degrees with respect to the horizontal plane, it is entrained in the upward flow of the exhaust gas and taken out of the furnace in a short time, and the cooling effect is small. Further, in the case of downward from 45 degrees, a part of the cooling gas is caught in the oxygen jet blown from the lance main hole and hits the slag phase or the molten metal phase,
Even the slag phase and molten metal phase are cooled.

The gas ejection angle in the horizontal plane is
The direction of connecting the central axis of the lance body and the cooling gas ejection hole is basically used, but in order to secure the distance between the refractory furnace wall and the ejection hole as much as possible and to accelerate the damping of the gas ejection flow, It is preferable to have an angle at.

However, if the angle formed by the tangent line on the outer circumference of the lance at the central axis of the ejection hole and the radius of the outer circumference of the lance at the central axis of the ejection hole is less than 15 degrees or more than 165 degrees,
It is preferable to avoid cooling the outer surface of the lance to form temperature unevenness on the outer surface of the lance and shorten the life of the lance body.

Further, in order to efficiently cool the exhaust gas, magnesium carbonate, calcium carbonate, or volatile matter of 20 wt% or more or water content of 5 with the cooling gas.
It is advisable to blow one or more coal powders containing at least wt%.

According to this method, in addition to cooling the exhaust gas by sensible heat of the cooling gas, in the case of magnesium carbonate and calcium carbonate, endothermic heat of decomposition (decomposition heat), and in the case of coal, CO ₂ by coal Heat of reduction and evaporation of water,
The effect of removing heat corresponding to the heat of decomposition of volatiles from the exhaust gas is added. If the volatile content of coal is less than 20 wt% or the water content is less than 5 wt%, the heat of decomposition (= latent heat) of these is not large enough and the cooling effect of exhaust gas is small, so it should be avoided. is there.

[0031]

EXAMPLE An upper-bottom blown converter of molten iron 8 ton scale was used in the examples. As the bottom blowing gas, a mixed gas of oxygen and nitrogen gas for tuyere cooling was used, and a gas having an oxygen content concentration of 99% was supplied from a top blowing lance. The top blowing lance has the shape shown in FIG.
The position, number and angle of the cooling gas ejection holes were changed.

In the experiment, with about 3 tons of hot metal, about 1 ton of slag, and 200 kg of carbonaceous material initially added, the carbonaceous material was continuously added while the oxygen was blown upward to raise the temperature. 135
When the temperature reaches about 0 ° C, scrap is added, and
The carbonaceous material was continuously added while the oxygen was blown upward to melt the scrap. The carbonaceous material was added in excess of the amount burned by top-blown oxygen so that the carbonaceous material was always present in the slag.
Coke and anthracite were used as the carbonaceous material, the oxygen supply rate F was 1500 Nm ³ / h, and the distance H between the tip of the lance and the cross section of the converter furnace mouth was about 3 m. The exhaust gas temperature was measured with a two-color thermometer, and the state of wear of the converter refractory was evaluated by observing the inside of the furnace after the test.

Tables 1 to 5 show the test results when nitrogen was used as the cooling gas and the powder was not blown. Here, the blowing angle is displayed as "0" when horizontal, "+" when upward, and "-" when downward.

In the experiments based on the present invention shown in test Nos. 1 to 11, as compared with the comparative examples shown in test Nos. 12 to 15, only the exhaust gas temperature was efficiently reduced without affecting the scrap melting amount. Wear of refractories can be suppressed to a low level.
Test numbers 16 to 19 are cases in which the number and angle of the gas ejection holes are not appropriate, but there are some problems compared with test numbers 1 to 5 to 11, but they are at a level that can be practically used sufficiently. .

Test Nos. 20 to 24 are those in which the kind of gas was changed under the same conditions as Test No. 1, but nitrogen, Ar,
No significant difference is observed with one or more gases of CO and CO ₂ . Test Nos. 25 to 27 are those in which nitrogen gas was mixed with magnesium carbonate and calcium carbonate under the same conditions as in Test No. 1, but the exhaust gas temperature was further lowered. Test Nos. 28 to 31 are obtained by mixing coal with nitrogen gas under the same conditions as Test No. 1, but in the case of coal powder containing 20% or more of volatile matter or 5% or more of moisture, from Test No. 1 A further decrease in exhaust gas temperature is seen.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

[0041]

EFFECTS OF THE INVENTION The present invention enables efficient scrap melting without the problem of causing significant wear of refractories.

[Brief description of drawings]

FIG. 1 is an explanatory view of a top blowing lance of the present invention.

FIG. 2 is a chart of experimental results showing a relationship between exhaust gas temperature and positions of cooling gas supply holes.

[Explanation of symbols]

 1: Lance 2: Main hole for oxygen supply 3: Cooling gas supply hole H: Distance between tip of lance and cross section of converter throat

Claims (5)

[Claims] 1. A method of melting iron-based scrap in a melting furnace of a top-bottom blowing converter type by utilizing the heat of oxidation of carbonaceous material by oxygen, wherein oxygen is added to a top-blowing lance for supplying an oxygen-containing gas to be used. The distance (H ₂ ) from the lower end surface of the lance to the center of the cooling gas ejection hole is different from that of the upper blowing lance during operation and the cross section of the converter furnace opening. With respect to the distance (H ₁ ) of 0.2H ₁ ≦ H ₂ ≦
At least one cooling gas is provided in a range of 0.8H ₁ , and one or more cooling gases of N ₂ , Ar, CO, and CO ₂ are blown into the melting furnace through the cooling gas ejection holes. Method for melting iron-based scrap. The feed rate of 2. A cooling gas blown from an oxygen-containing blown on gas supply lance (Nm ³ / h), be 5-30% equivalent feed rate of oxygen-containing gas (Nm ³ / h) The method for melting iron-based scrap according to claim 1, wherein: 3. A cooling gas ejection hole provided in an upper blowing lance for supplying an oxygen-containing gas is provided with 4 to 2 on a peripheral surface of the upper blowing lance.
The method for melting iron-based scrap according to claim 1 or 2, characterized in that zero pieces are provided. 4. The angle of the ejection hole of the cooling gas ejection hole provided in the upper blowing lance for supplying oxygen-containing gas is such that the angle between the ejection hole central axis and the horizontal plane is in the range of 45 degrees upward to 45 degrees downward. The method for melting iron-based scrap according to any one of claims 1 to 3, characterized in that: 5. Magnesium carbonate, calcium carbonate, or one or more kinds of coal powder containing volatile matter of 20 wt% or more or water content of 5 wt% or more is blown together with the cooling gas from the cooling gas ejection hole. The method for melting iron-based scrap according to any one of claims 1 to 4, wherein: