JPH09143522A - Method for melting iron scrap at high speed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a melting method of iron scrap which improves the utilizing efficiency of combustion heat of carbonaceous material by using inexpensive carbonaceous material to improve the secondary combustion ratio and causes small erosion of a refractory and small scattering loss of slag and dust to the outside of a furnace even if gaseous oxygen supplying speed per unit vol. in the furnace is same as or quicker than that of the ordinary converter method. SOLUTION: At the time of melting the iron scrap and reducing iron oxides by charging the iron scrap containing the iron oxides, the iron path 10 and molten slag layer 11 on the iron bath are formed in a melting furnace and the carbonaceous material and gaseous oxygen are supplied on the molten slag layer 11 to burn the carbonaceous material. Further, in the iron content in the charged iron raw material, wt. ratio of the iron content in the iron oxide is adjusted in the range of 0.02-0.3 and atmospheric pressure P (10<2> kPa) in the melting furnace is adjusted in the range as the following inequality. 0.005(F/ V)+1.0<=P<0.01(F/V)+3.0. Wherein, F is the supplying speed of gaseous oxygen (Nm<3> /h) and V is the inner vol. of melting furnace (m<3> ).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for melting iron scrap (hereinafter simply referred to as "scrap") by heat of combustion of carbonaceous material at a high thermal efficiency and at high speed without using electric power.

[0002]

2. Description of the Related Art Scrap is usually melted in an electric furnace, but it is generally uneconomical in Japan due to the high power cost. In particular, due to the balance of supply and demand of electric power, in many cases the unit price of electricity during the day is set to be much higher than the unit price of electricity at night, and there are many cases where the electric furnace is operated only at night. There is a problem of low productivity and insufficient productivity.

In Japan in recent years, the amount of scraps generated has increased remarkably, and the ratio of those made from scraps in steel production has increased, and it is desired to develop a more economical and highly productive melting method. There is.

As a method of melting scrap without using electric energy, for example, by using a reactor type reactor vessel, carbonaceous material and oxygen gas are supplied to the inside or the upper part of the iron bath in the vessel to generate oxygen gas. Attempts have been made to dissolve scraps by the heat of combustion of carbonaceous materials. In this melting method, scrap is sequentially supplied to a small amount of iron bath in the reaction vessel from above to melt, and the molten iron is tapped after the iron bath reaches a predetermined amount. In many cases, a so-called residual hot water system is used in which the liquid is left inside.

In the combustion of solid carbon in carbonaceous material by oxygen gas, the combustion heat up to CO ₂ is much larger than the combustion heat up to CO, so that ((% CO ₂ ) / ( (% CO)
A major issue is how to raise the ratio of (+ (% CO ₂ )) × 100 (%) (hereinafter referred to as the secondary combustion rate). However, it is already well known that the combustion loss from CO to CO ₂ is mainly performed in the upper space of the melting furnace, so that the melting loss of the furnace wall refractory increases when the secondary combustion rate is increased. By the way.

On the other hand, in order to improve the productivity of the melting furnace, it is necessary to increase the amount of heat generated in the furnace and to increase the supply rates of oxygen gas and carbonaceous material. As seen in the example of a steelmaking converter, if the oxygen gas supply rate is increased, the oxygen jet will blow up the contents of the furnace and dust will be scattered outside the furnace, making stable operation difficult. . Increasing the inner volume of the furnace in order to avoid this not only increases the amount of refractory used, but also increases the size of various incidental equipment, which is not economical.

Therefore, it is necessary to increase the value of the supply rate F / V of oxygen gas per unit inner volume, with the inner volume of the furnace being V (m ³ ) and the supply rate of oxygen gas being F (Nm ³ / h). There is. In the current steelmaking converter, the value of V changes due to the melting loss of the refractory, so it is difficult to accurately calculate the value of F / V, but it is estimated to be in the range of about 100 to 500. Steelmaking converters are required to have high productivity, and various efforts have been made to increase the F / V value, but no technique has been proposed for stable operation even when the F / V value is larger.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and the purpose of the present invention is to reduce the energy consumption during melting of iron scrap. An object of the present invention is to provide a method for melting iron scrap, which uses a low cost carbonaceous material and has high productivity. In particular, even if the secondary combustion rate is increased to improve the utilization efficiency of the combustion energy of the carbonaceous material, and the oxygen gas is supplied at the F / V value equal to or higher than that of the existing converter method, the refractory material can be supplied. An object of the present invention is to provide a method for melting iron scrap, which is capable of stable operation with less melting loss and scattering loss of slag and dust outside the furnace.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted various studies on the means for solving the above-mentioned problems, and as a result, have found that the iron bath in the converter-type reaction vessel has an appropriate state in the upper part. It was found that the molten loss of refractory can be reduced even if the secondary combustion rate is increased by forming a molten slag layer that has been formed and burning the carbonaceous material therein with oxygen gas. Also,
It has been found that controlling the atmospheric pressure in the furnace is the most effective because the formed molten slag is easily scattered outside the furnace which increases the supply rate of oxygen gas.

The present invention has been made on the basis of these findings. The gist of the invention is to charge an iron scrap containing iron oxide into a melting furnace to dissolve the iron scrap and reduce the iron oxide. At that time, an iron bath in the melting furnace and a molten slag layer are formed on the iron bath, and the carbon material and oxygen gas are supplied to the molten slag layer to burn the carbon material, and the iron content in the charged iron raw material is increased. The weight ratio of iron in iron oxide is 0.02
To 0.3, and the atmospheric pressure in the melting furnace is adjusted to the range of the following formula.

0.005 (F / V) + 1.0 ≦ P <0.01 (F / V) +3.0 P: Atmospheric pressure in the melting furnace (10 ² kPa) F: Oxygen gas supply rate (Nm ³ / h) V: Internal volume of melting furnace (m ³ )

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a melting apparatus for carrying out the method for melting iron scrap of the present invention. The melting furnace body 1 is lined with a refractory 1a, and is connected to a scrap supply device 7 via a furnace opening seal device 5 and an exhaust gas duct 6. The damper (not shown) provided in the exhaust gas duct downstream of the scrap supply device 7 controls the pressure in the melting furnace and the scrap supply device 7.

An iron bath 10 and a molten slag layer 11 are provided in the melting furnace.
Are formed, and scrap is supplied from the scrap supply device 7 into the furnace at a predetermined supply rate. The carbonaceous material is supplied to the molten slag layer from the carbonaceous material supply device 8 in the upper part of the furnace. Oxygen gas is blown from the upper blowing lance 2 to the molten slag layer and the iron bath to burn carbonaceous material suspended in the molten slag layer and carbon in the iron bath.

In order to effectively use this combustion heat for melting scrap, gas is blown into the iron bath 10 from the bottom blowing tuyere 3 to stir the melt in the furnace to accelerate heat transfer. It is also possible to blow carbonaceous material, oxygen gas, or both at the same time into the molten slag layer from the side blowing tuyere 4 provided on the side wall of the furnace body.
It is effective in promoting heat generation and heat transfer.

As the oxygen gas in the present invention,
In addition to pure oxygen gas, it is possible to use crude oxygen gas containing a small amount of nitrogen or the like, or oxygen gas containing a non-combustible gas such as a part of air, but the concentration of oxygen is 70% or more. desirable.

Iron oxide is supplied from the iron oxide supply device 9 at the top of the furnace.
Alternatively, it is mixed with scrap, charged into a furnace, and melted to become iron oxide in molten slag. The iron oxide in the molten slag reacts with the carbonaceous material to generate fine CO gas bubbles, and the molten slag layer becomes a so-called forming state.

When the melting of a predetermined amount of raw material scrap is completed, the stored molten iron is discharged to the outside of the furnace. Molten iron is preferably discharged by opening a tap hole at the bottom of the furnace. The molten iron produced in the present invention includes molten pig iron and molten steel.

The first object of the present invention is to increase the secondary combustion rate to improve the utilization efficiency of the combustion energy of the carbonaceous material, but if the secondary combustion rate is increased, the exhaust gas temperature rises,
This overheats the furnace wall refractory and significantly increases the refractory wear rate.

Generally, the rate of refractory wear increases as the refractory is overheated and the concentration of iron oxide in the molten slag increases. In order to prevent overheating of the refractory material, it is extremely effective to form a stable forming slag layer having a sufficient height. The reason is that the exhaust gas heat-exchanges with the forming slag to lower the temperature, and the refractory itself is washed by the forming slag to lower the temperature.

FIG. 2 shows the weight ratio of iron in iron oxide (hereinafter referred to as the ratio of iron oxide charged) and the concentration of iron oxide in the molten slag (hereinafter simply referred to as iron oxide concentration) among the iron in the charged iron raw material. It is a figure which shows a relationship. Since the iron oxide concentration varies depending on the oxygen gas supply rate and the atmospheric pressure in the furnace, the iron oxide concentration when the charged iron oxide content ratio is 0.1 is 1 in FIG.
Is shown as an index.

When the charged iron oxide content ratio is 0.02 to 0.05 or less, the iron oxide concentration increases as the charged iron oxide content ratio increases, but the charged iron oxide content ratio is 0.07 to 0.15.
In the range, the iron oxide concentration does not increase so much even if the charged iron oxide content ratio increases.

The reason why such a difference occurs is considered as follows. That is, the charged iron oxide fraction is 0.02 to 0.
When it is less than 05, a stable forming slag layer is not formed, so the specific gravity of the molten slag is large, and the carbonaceous material is in a state of floating above the molten slag layer. Therefore, the contact interface area between the carbonaceous material and the molten slag is small, and the reduction rate of the molten iron oxide is small.

On the other hand, the iron oxide charge ratio is 0.07 to 0.1.
In the range of 5, a stable forming slag layer is formed, the apparent specific gravity of the molten slag is reduced, and the carbonaceous material is suspended inside the molten slag layer. for that reason,
The contact interface area between the carbonaceous material and the molten slag increases, the reduction rate of the molten iron oxide also increases, and the iron oxide concentration does not increase much even if the charged iron oxide content ratio increases.

Further, the iron oxide content ratio is 0.15 to 0.
When it exceeds 25, the iron oxide concentration gradually increases as the charged iron oxide content ratio increases again. It is considered that the reason is that the effect of increasing the contact interface area between the carbonaceous material and the molten slag cannot cover the required reduction rate. Further, it was found that when the charged iron oxide fraction exceeds 0.30, the iron oxide concentration increases to such an extent that the refractory wear rate is obviously affected.

Therefore, in carrying out the method for melting iron scrap of the present invention, the ratio of the iron oxide charged is 0.02.
It is necessary to adjust to the range of ~ 0.3. further,
Desirably, the iron oxide content ratio is in the range of 0.07 to 0.15.

Another object of the present invention is to increase the secondary combustion rate and to keep the (oxygen gas supply rate F) /
Even if oxygen gas is supplied at the value of (internal volume V of melting furnace), there is little melting loss of refractory and scattering loss of slag and dust outside the furnace, and a method of melting iron scrap that enables stable operation is provided. To provide.

As described above, when a stable foaming slag layer is formed, and a carbonaceous material is suspended in the layer and burned with top-blown oxygen gas, slag droplets and charcoal with a small particle size are generated by an oxygen jet. The material is blown up and is entrained in the rising exhaust gas flow, and easily blows out of the furnace as dust. Even if the F / V value is about the same as that of the existing steelmaking converter, there is a problem that the amount of dust is significantly increased.

Such dust emission not only lowers the yield of carbonaceous materials and slag-forming agents, but also adheres to exhaust gas ducts, scrap supply ports, etc., making stable operation difficult. The most effective way to prevent this is to increase the atmospheric pressure in the melting furnace to reduce the flow velocity of the oxygen jet and the rising exhaust gas flow.

FIG. 3 shows the relationship between the atmospheric pressure P in the melting furnace and the value of F / V, which enables stable operation. The amount of dust flying out increases as the F / V value increases, but in order to perform stable operation, P is 1.5 × 10 ² kPa (absolute when the F / V value is about 100). Pressure) or higher, F /
When the value of V is about 300, P is 2.5 × 10 ² kPa
Or more is needed.

Therefore, in order to carry out the melting method of the present invention, it is necessary to adjust the atmospheric pressure P (10 ² kPa) in the melting furnace within the range of the following formula, as indicated by the straight line A in FIG. . P ≧ 0.005 (F / V) +1.0 On the other hand, if the atmospheric pressure P in the melting furnace is too high,
The volume of CO gas bubbles in the forming slag layer becomes small, and the forming slag layer having a sufficient height cannot be formed.

Therefore, it has been recognized that when P exceeds a certain level, the melting loss of the furnace wall refractory increases when the secondary combustion rate is increased. Since the amount of CO gas bubbles generated increases as the value of F / V increases, the atmospheric pressure in the melting furnace at this limit depends on the value of F / V.

As shown by the straight line B in FIG. 3, when the F / V value is about 100, P is 4 × 10 ² kPa (absolute pressure) or more and the F / V value is about 200. If P is 5
When it is × 10 ² kPa or more, the melting loss of the furnace wall refractory becomes large.

Therefore, in order to carry out the melting method of the present invention, it is necessary to adjust the atmospheric pressure P in the melting furnace within the range of the following formula. P <0.01 (F / V) +3.0 In the melting method of the present invention, since the inside of the melting furnace is pressurized, the exhaust gas is introduced into a shaft furnace or other scrap preheating device to generate sensible heat of the exhaust gas. It is also easy to effectively utilize the scrap for preheating.

[0034]

EXAMPLE A test converter having an internal volume of about 7 m ³ was modified into a pressure type to test the scrap melting method of the present invention. The operation method in the test furnace is as follows. Prior to the charging of scrap, about 1.5 tons of hot metal was poured into the furnace as seed water, and while stirring with bottom-blown gas and top-blown oxygen blowing, a predetermined amount of slag-making agent was charged into the furnace. To form a molten slag layer. After that, the inside of the furnace is pressurized to start charging of carbonaceous material and full-scale oxygen blowing, and at the same time, start charging of scrap from the upper part of the furnace. As a carbonaceous material, the particle size is mainly 10
A 50 mm coke was used.

The raw material scrap is used after being cut to a size of about 10 cm or less. The raw material scrap is pre-stored in a pressurized bunker and cut out at a predetermined supply speed. Iron ore, dust pellets, etc. are used as the iron oxide source to be charged, and the iron oxide is charged from a bunker on the furnace. When the predetermined amount of raw material scrap is melted, the tap hole at the bottom of the furnace is opened to discharge the molten metal in the furnace. Part of the melt is left in the furnace and used as the seed melt for the next melt.

The range of major operating conditions in the test furnace is
It is as follows. Raw material scrap charge 4.5-5.5 ton / heat Iron oxide charge 0-1.8 ton / heat Slag slag charge 0.1-0.2 ton / heat Furnace atmosphere Pressure 1.0 to 5.0 × 10 ² kPa (absolute pressure) Oxidation amount 700 to 2100 Nm ³ / h Carbon material supply amount 500 to 1500 kg / h Bottom blow Ar gas flow rate 10 to ³⁰ Nm ³ / h Secondary combustion rate 45 ~ 90% Amount of molten slag in the furnace 1.0 to 2.0 tons.

In order to clarify the range in which the furnace wall refractory is less likely to melt and dust is small and stable operation is possible, the atmospheric pressure in the furnace, the F / V value and the iron oxide content ratio are changed. Table 1 shows the results of an investigation of the amount of dust generated and the melting damage of the furnace wall refractory.

Here, as the internal volume V of the melting furnace, the value at the time of furnace construction was used. The amount of dust generated is the total amount of carbonaceous material, granular slag, iron oxide dust, granular iron, etc. collected by a cyclone dust collector provided downstream of the exhaust gas duct. Further, the melting loss status of the furnace wall refractory is determined from the result of measuring the thickness of the refractory material at several parts of the furnace wall after the completion of melting for several heats, but here the degree of melting loss is large, Display in medium and small. In Table 1, the conditions within the range of the present invention are shown as Examples, and the conditions outside the range are shown as Comparative Examples.

[0039]

[Table 1]

From the results shown in Table 1, under the conditions within the range of the present invention, stable operation is possible with less melting loss of the furnace wall refractory and less dust generation, but outside the range of the present invention.
It was clarified that the amount of melting loss or dust generation of the furnace wall refractory increases.

[0041]

According to the present invention, it is possible to melt iron scrap at a high production rate using a carbon material having low energy cost. In particular, in a converter-type iron scrap melting furnace, the secondary combustion rate is increased to improve the utilization efficiency of the combustion energy of the carbonaceous material, and the F / V value is equal to or higher than that of the existing converter method. Even when oxygen gas was supplied, stable operation was possible with little melting loss of refractory and scattering loss of slag and dust outside the furnace.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a melting apparatus for carrying out the method for melting iron scrap of the present invention.

FIG. 2 is a diagram showing a relationship between a weight ratio of iron in iron oxide among iron in a charged iron raw material and an iron oxide concentration in molten slag.

FIG. 3 is a diagram showing a relationship between an atmospheric pressure P and a value of F / V in a melting furnace capable of stable operation.

[Explanation of symbols]

 1 Melting Furnace Furnace Body 1a Refractory 2 Top Blowing Oxygen Lance 3 Bottom Blowing Tuyer 4 Side Blowing Tuyer 5 Furnace Sealing Device 6 Exhaust Gas Duct 7 Scrap Supplying Device 8 Carbon Material Supplying Device 9 Iron Oxide Supplying Device 10 Iron Bath 11 Molten slag layer

Claims (1)

[Claims] 1. When an iron scrap containing iron oxide is charged into a melting furnace to melt the iron scrap and reduce the iron oxide, an iron bath and a molten slag layer are formed on the iron bath in the melting furnace. The carbonaceous material and the oxygen gas are supplied to the molten slag layer to burn the carbonaceous material, and the weight ratio of the iron content in the iron oxide to the iron content in the iron raw material is 0.02 to 0.3. A high-speed melting method for iron scrap, characterized by adjusting the pressure within the range and adjusting the atmospheric pressure in the melting furnace within the range given below. 0.005 (F / V) + 1.0 ≤ P <0.01 (F / V) + 3.0 P: Atmospheric pressure in the melting furnace (10 ² kPa) F: Oxygen gas supply rate (Nm ³ / h) V: Melting Inner volume of furnace (m ³ )