JP3031877B2 - Preheating method of steel scrap - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention can be widely used in the steel making or iron making process for melting steel scrap, and contributes to the reduction of the melting energy required at that time.

[0002]

2. Description of the Related Art Preheating of steel scrap is a technique that greatly contributes to reduction of melting energy, and is still being actively implemented. However, in the preheating of steel scrap by the most commonly used bucket method, the preheating temperature is at most 3 due to the heat resistance of the bucket body.
00 ° C is the limit.

[0003] Further, since the preheating of the steel scrap in the shaft type furnace or the vertical type filling furnace is a countercurrent type preheating in which the heat flow and the movement of the scrap face each other, high thermal efficiency can be expected. However, when the preheating temperature is increased, heat generation and fusion accompanying the oxidation reaction of steel scrap become remarkable. For this reason, it causes troubles of ventilation and unloading due to the fusion of the steel scrap, and the preheating temperature is again from 800 ° C. to 9%.
00 ° C is the limit. It is presumed that the influence of the preheating gas atmosphere and the preheating temperature is large on the fusion phenomenon of steel scrap, but sufficient information has not been obtained so far. For this reason, in the conventional technology, it was impossible to preheat to a high temperature of 900 ° C. or more while avoiding the oxidative fusion of the steel scrap as described above.

[0004]

SUMMARY OF THE INVENTION In the present invention, a method for preheating steel scrap at a high temperature in which a problem of airflow and unloading due to fusion of the steel scrap which occurs during preheating at 900 to 1200 ° C. is prevented. Is provided.

[0005]

According to the present invention, when preheating steel scrap, the limit oxygen concentration (%) representing the oxygen concentration in the heating atmosphere is -37.94 × (T / 1000) ³ +5.
3.58 × (T / 1000) ² −29.59 × (T / 1
000) +25.89 or less, and the preheating temperature T is 90
This is a method of preheating steel scrap in which oxidation fusion between steel scraps is prevented by heating the steel scrap within a range of 0 to 1200 ° C.

The present inventors have devised an experimental apparatus (see FIG. 1 to be described later) which can simulate the preheating state of steel scrap in a shaft type or vertical type filling furnace in a laboratory, and determine the atmosphere and temperature of the preheating gas. Various changes were made to analyze the presence or absence of fusion. As a result of investigating the relationship between various types of steel scrap and the atmosphere, it was possible to find out the conditions under which fusion of the steel scrap did not occur.

FIG. 1 shows a conceptual diagram of an experimental apparatus used in this experiment. The steel scrap 5 is charged into the sample container 1 and heated to an arbitrary temperature by the electric furnace 2. The sample container 1 is hermetically sealed in the reaction tube 3 and has an atmosphere gas inlet 6.
An arbitrary atmosphere is maintained by the atmosphere gas 6 flowing from -1. Here, the alumina balls 10 are filled in the atmosphere gas inflow path in the sample container supporting refractory 8 in order to uniformly preheat the temperature of the atmosphere gas 6, and the temperature of the steel scrap is set to the thermoelectric temperature for sample temperature measurement. The temperature is measured in pairs 12.
If necessary, the steel scrap 5 in the sample container 1 may be used.
The pressurizing cylinder 9 applies an arbitrary load between the load-bearing refractory 7 and the sample container supporting refractory 8. The steel scrap 5 in the sample container kept at a predetermined temperature and atmosphere was oxidized and fused to confirm the situation.
It is lowered to the sample outlet 11 at the lower part of the electric furnace by the elevating gantry 14, and is taken out after cooling to room temperature.

FIG. 2 is an enlarged view of the steel scrap preheating section of FIG. The sample container 1 is divided into an inner cylinder 1-1 and an outer cylinder 1-2, and a dummy plate 15 and a lower plate 16 are inserted above and below the steel scrap. Other symbols indicate the same parts as those in FIG.

[0009] By the configuration and operation of these experimental devices, the steel scrap can be heated to an arbitrary preheating temperature in an arbitrary gas atmosphere while being sealed with the atmosphere.

FIG. 3 shows an example of an actual furnace for carrying out the present invention obtained by the experimental apparatus of FIG. FIG. 3A shows the preheating state of the steel scrap in the vertical filling furnace.
Steel scrap 5 is 900-
Preheating can be performed within the range of 1200 ° C., and the molten iron 19 and the like are discharged from the hearth. In the figure, 17 is a furnace wall, and 18 is a grate.
Although the distribution of high-temperature atmosphere gas such as locally detailed temperature distribution and oxygen concentration distribution in the vertical filling furnace and the fusion behavior corresponding thereto are not clear, the macro temperature distribution in the furnace is shown in FIG. As shown in FIG. 3), the temperature is higher at the lower part of the furnace into which the hot air is blown, and the temperature decreases as the furnace height increases. The oxygen concentration distribution in the furnace has distributions such as a to d as shown in FIG. It can be considered. Therefore, in the experiment of the present invention, the fusion behavior in an arbitrary temperature and oxygen concentration or a CO-CO ₂ -N ₂ mixed gas is performed by the above-described experimental apparatus in consideration of various situations in such a vertical filling furnace. Was simulated.

FIG. 4 shows the appearance of the fused steel scrap and the microstructure of the welded portion. The upper row shows the results of the actual furnace, and the lower row shows the results of simulating the actual furnace with the above experimental apparatus. Since the oxygen concentration is equal to or higher than the limit oxygen concentration, granular iron, which seems to have once melted and solidified the steel as the base material, is observed in the fused portion.

Next, with respect to various steel scraps, the presence or absence of fusion of the steel scraps in an arbitrary preheating gas atmosphere and temperature was evaluated. FIG. 5 shows the test material corresponding to heavy waste scrap, FIG. 6 shows the test material corresponding to shredder scrap, and FIG. 7 shows the preheating temperature at which fusion of steel scrap occurred in each preheating gas atmosphere of the test material corresponding to Dalai powder scrap.
This shows a quantitative relationship between the oxygen concentration at which fusion of various steel scraps occurs and the preheating temperature. In each of the figures, the symbol x indicates that fusion of steel scrap occurred, and the symbol ○ indicates that fusion of steel scrap did not occur. The composition (wt%) of A gas and B gas is as follows:
%, CO ₂ 50 wt%, B gas is CO ₂ 50 wt%, N ₂ 5
0 wt%. In the A gas and B gas atmospheres, fusion of steel scrap does not occur at any preheating temperature.

The results of these experiments were subjected to thermodynamic studies. From the thermodynamic data, a typical calorific value of oxidation by the oxidizing gas is: Fe + 1 / 2O ₂ → FeO... 1132 kcal / kg-Fe Fe + CO ₂ → FeO + CO... -80 kcal / kg-Fe Fe + H ₂ O → FeO + H ₂ . / Kg-Fe. From these, it is understood that a large amount of heat is generated by oxidation with oxygen. This calorific value is about 3.7 times the calorific value for melting iron at room temperature, about 305 kcal / kg-Fe, and it is calculated that if about 27% of the steel scrap is oxidized, the calorific value for melting all the steel scrap is obtained. Will be.

On the other hand, it is understood that the oxidation of iron by CO ₂ or H ₂ O is an endothermic reaction, and its absolute value is small. Therefore, in the case of the CO—CO ₂ —N ₂ mixed gas, oxidative fusion does not actually occur under any conditions. Thus, the factor governing the fusion of steel scrap is oxidation by oxygen, which generates a large heat of oxidation.
It was found that other oxidizing gases did not contribute to the fusion of steel scrap.

From these experimental results, in order to find the limit of the occurrence of fusion of steel scrap under the most severe conditions for oxidation fusion, data on steel scrap oxidized and fused at the lowest temperature at each oxygen concentration in the atmosphere was obtained. Was summarized by a multi-order regression equation. FIG. 8 shows the result. From the curve shown in FIG. 8, the oxygen concentration in the atmosphere gas to be controlled to avoid the oxidative fusion, that is, the limit oxygen concentration defined by the following equation (1), for the preheating temperature of 900 ° C. to 1200 ° C. Recognize.

The limiting oxygen concentration (%) = − 37.94 × (T / 1000) ³ + 53.58 × (T / 1000) ² −29.59 × (T / 1000) +25.89 (1) ( However, T is a preheating temperature in the range of 900 to 1200 ° C.) By controlling the oxygen concentration in the atmosphere to be equal to or lower than the limit oxygen concentration in preheating the steel scrap,
It has been found that steel scrap can be preheated at a high temperature from 900 ° C. to 1200 ° C. while avoiding oxidation fusion of the steel scrap.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples.

In the test, 150 g of a test material equivalent to a heavy scrap, a test material equivalent to a shredder scrap, and a test material equivalent to a Dalai powder scrap each having the same composition as the actual steel scrap 5 were tested by the experimental apparatus shown in FIG.
The operation was carried out by charging 450 g in total weight.

Table 1 shows the results of preheating the steel scrap from 900 ° C. to 1200 ° C. by the method for controlling the oxygen concentration in the atmosphere according to the present invention and the method for controlling the oxygen concentration in the atmosphere as a comparative example. As is clear from the results, according to the present invention, when the oxygen concentration in the atmosphere gas was controlled based on the formula (1) by each preheating temperature, no fusion of the steel scrap occurred in any case. . On the other hand, in the comparative example, fusion of steel scrap occurred at any preheating temperature.

[0020]

[Table 1]

As described above, according to the method for preheating steel scrap of the present invention, a test material equivalent to heavy scrap, a test material equivalent to shredder scrap, and a test material equivalent to Dalai powder scrap, which have the same composition as actual steel scrap. Also in the material, it was found that it was possible to avoid oxidation fusion of steel scrap and to perform preheating from 900 ° C to 1200 ° C.

[0022]

According to the present invention, when pre-heating steel scrap, the oxygen concentration in the heating atmosphere is controlled to a limit oxygen concentration or less, so that even when the steel scrap is heated at a high temperature of 900 to 1200 ° C., the oxidative fusion between the steel scraps is performed. Can be prevented.
Therefore, since the preheating temperature of the steel scrap can be increased to a high temperature, a remarkably excellent effect can be brought about in reducing the melting energy cost of the steel making or pig making process in the steel making process.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an experimental apparatus for preheating steel scrap in the present invention.

FIG. 2 is an enlarged view of a steel scrap preheating section in the experimental apparatus of FIG.

3 (a) is a conceptual diagram showing a structure of a preheating section of steel scrap in a vertical filling furnace, FIG. 3 (b) is a graph showing a temperature distribution in the furnace, and FIG. 3 (c) is a graph showing an oxygen concentration distribution in the furnace. It is a graph.

FIG. 4 is a micrograph showing the appearance and microstructure of a steel scrap fusion product of an actual furnace and an experimental apparatus according to the present invention.

FIG. 5 is a graph showing the relationship between the occurrence of fusion in a test material equivalent to heavy waste scrap and each preheating gas atmosphere and preheating temperature.

FIG. 6 is a graph showing the relationship between the occurrence of fusion in a test material equivalent to a shredder scrap and each preheating gas atmosphere and preheating temperature.

FIG. 7 is a graph showing the relationship between the occurrence of fusion in a test material equivalent to Dalai powder scrap and each preheating gas atmosphere and preheating temperature.

FIG. 8 is a graph showing a fusion occurrence limit curve of steel scrap in the present invention.

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Claims (2)

(57) [Claims] In the preheating of steel scrap, heating is performed within a range of 900 to 1200 ° C. while controlling the oxygen concentration in the heating atmosphere to a limit oxygen concentration defined by the following formula (1). Steel scrap preheating method. Limit oxygen concentration (%) = − 37.94 × (T / 1000) ³ + 53.58 × (T / 1000) ² −29.59 × (T / 1000) +25.89 (1) (However, T Is the preheating temperature in the range of 900 to 1200 ° C.) 2. The method for preheating steel scrap according to claim 1, wherein the oxygen fusion between the steel scraps is prevented by controlling the oxygen concentration to be equal to or lower than the critical oxygen concentration.