JPS6146751B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for preheating steelmaking scrap (hereinafter simply referred to as scrap). BACKGROUND ART As part of the utilization of scrap provided during steel rolling processing, etc., the scrap is melted in a melting furnace such as an electric furnace, and then manufactured into products such as special steel. Before melting scrap using this melting furnace, it is preferable to preheat the scrap using a preheating device in advance, since the thermal energy consumed in the melting furnace is also small, which is preferable from the perspective of energy saving. Not only that, but the time required for its dissolution is also reduced. In addition, as a preheating method at this time, from the viewpoint of effectively utilizing the amount of heat of the exhaust gas discharged from the melting furnace,
Scrap is also preheated by introducing the exhaust gas generated in the melting furnace into a preheating device. Here, a conventional method of preheating scrap using exhaust gas will be explained with reference to a system diagram of a scrap preheating apparatus shown in FIG. In FIG. 1, reference numeral 1 is a melting furnace for melting scrap. The high-temperature exhaust gas generated in the melting furnace is introduced via the combustion tower 4 and ducts 5 and 6 into a preheating device 7 loaded with scrap to preheat the scrap. Note that reference numerals 8 and 9 in FIG. 1 are ducts, which are passages for guiding the exhaust gas used for preheating to the next process. The preheated scrap is moved from the preheating device and placed in the melting furnace, where it is subjected to the melting process. In such a scrap preheating (process), increasing the scrap preheating temperature even slightly will greatly contribute to reducing power consumption in the scrap melting process. For example, the temperature of the scrap itself can be increased by about 10 degrees Celsius. The melting time can be shortened even with a temperature increase of 500 mL, and power consumption can be significantly reduced. In order to raise the temperature of this preheating scrap, it is necessary to enhance the preheating effect within the preheating device and raise the temperature of the exhaust gas atmosphere within the device. However, according to the conventional method, the temperature of the exhaust gas atmosphere inside the preheating device remains at about 600 to 650°C,
The temperature of the momentum scrap itself was also low. Although the method of preheating scrap using exhaust gas is an effective method as described above, there are limits to the method of directly introducing the exhaust gas into the preheating device. Therefore, in order to further increase the preheating temperature of scrap, scrap preheating devices that use gaseous fuel such as propane gas or liquid fuel such as heavy oil have been considered, but all of these require the installation of a burner or other combustion device. However, in addition to high equipment costs, these fuels themselves are also expensive, making them uneconomical. The present invention provides a method for preheating scrap using exhaust gas that eliminates the drawbacks of the conventional method described above. , adding solid fuel to the scrap,
The present invention resides in a scrap preheating method characterized by preheating the solid fuel by burning it with exhaust gas. The present invention is an extremely economical scrap preheating method that does not require any special equipment modification and can significantly improve the preheating effect by simply charging an inexpensive solid fuel into a conventional scrap preheating device. be. The solid fuel used in the present invention includes wood chips (sawdust, etc.) exemplified by Ogalite (trade name).
Examples include fuel obtained by compressing and solidifying charcoal, coke, charcoal, coal, wood, paper, tires, etc., but an appropriate one is selected depending on the temperature of the exhaust gas used for preheating, the preheating time, the amount of scrap, etc. When performing scrap preheating, it is desirable to maximize the preheating effect within a limited time. However, a fuel that satisfies these conditions must have a high combustion heat and a high combustion rate. Products that satisfy these conditions include those made by compressing fine particles such as ogalite and charcoal,
Alternatively, it has been demonstrated that something porous and with a large burning surface area, such as charcoal, is better. Furthermore, the ignition temperature of the fuel needs to be low, and in this respect, ogalite, charcoal, pea charcoal, etc. are superior to coal and coke. Furthermore, it has been found that flammable fuel is desirable as an element to enhance the preheating effect of scrap. That is, ogalite, wood, etc. can produce a powerful flame that heats the entire scrap inside the clamshell. Table 1 below compares the combustion heat amount, ignition temperature, and combustion speed of the solid fuels exemplified above.

【table】

[Table] Shown.
Although the ignition temperature is not shown for the tires in Table 1 above, tires melt and decompose at around 200℃ and become gasified, and the gas is mainly hydrocarbons, so the ignition temperature is around 500℃. It is estimated to be. Therefore, in view of the above-mentioned matters and the data in Table 1 above, the solid fuel of the present invention can be obtained by heating and compressing wood chips such as ogalite and charcoal with or without using a binder. It is preferable to use a solid fuel with a large surface area that has been solidified without any heat loss. Ogalite in particular ignites at a relatively low temperature (200
~300℃), and the temperature after ignition reaches 1000~1100℃ at the top of the clam shell of the preheating device, which is higher than the exhaust gas temperature of the combustion tower. In addition, even if it is difficult to preheat scrap, the preheating effect is enhanced to the point where it becomes red hot, and there is little white smoke. One or more of the above solid fuels may be used. When two or more types are used in combination, the preheating effect can be further enhanced. For example, to explain the combined use of ogalite and coal, ogalite ignites early during preheating, and the flame hits the coal.
Coal, which has a high combustion heat but is difficult to ignite, is ignited and burned. This allows for even more effective use of coal as preheating fuel. In the preheating method of the present invention, scrap is charged into a preheating device, solid fuel is added to the scrap, high temperature exhaust gas discharged from a melting furnace is introduced into the scrap, and the solid fuel is heated using the temperature of the exhaust gas. Preheat the scraps by burning them. According to this method of the present invention, the calorific value of the exhaust gas and the calorific value of the solid fuel combine to raise the gas atmosphere temperature in the preheating device and the scrap temperature more than expected. FIG. 2 shows an embodiment of the preheating method of the present invention and the preheating device used therein. 1 in Figure 2
0 is scrap, 11 is solid fuel, and 12 is clam shell. As shown in FIG. 2, in a preferred embodiment of the present invention, solid fuel is placed on the scrap in the preheating device in advance, and then high-temperature exhaust gas is introduced from the direction of the arrow in FIG. Preheat the scrap. However, when using something like small charcoal, it is better to disperse it in the scrap and charge it in order to enhance the preheating effect. Furthermore, when two or more types of solid fuel are used in combination, for example, when ogalite and coal are used together, it is preferable to place the ogalite on top of the coal with the coal facing down. An example of the scrap preheating and melting pattern in the preheating method of the present invention is shown in a process flow sheet in FIG. In FIG. 3, A is a melting pattern, and B is a scrap preheating pattern. Next, examples of the present invention will be shown. Example 1 First loading of 31 tons of scrap with the following composition
20 tons were put into the preheating device shown in Fig. 2, and 105 kg of Ogalite was placed on top of the scrap to preheat it. Scrap composition: NP [Steel plate punching scrap from new cutting press] 18 [Ton] Special grade 5 Crop 7 Others 1 Ogalite ignited quickly and burned rapidly.
Even though it was NP material, it was red hot. After ignition, the atmospheric temperature inside the clam shell rose to approximately 1050°C, which was higher than the exhaust gas temperature from the combustion tower. The atmospheric temperature in the clam shell, the exhaust gas temperature of the combustion tower, and the temperature measurement results at the input and outlet of the scrap preheater (SPH) are shown in FIG. 4B. In addition, the scrap temperature was as high as 380°C on average. After the above preheating, 11 tons of additional scrap with the same composition was charged into the same preheating device, preheated without solid fuel, and added to the melting furnace. Then, it was melted in a melting furnace to obtain 31 tons of SF steel (carbon steel) as a molten steel type. The power consumption unit (power required to melt 1 ton of scrap, kwt)
h/cht) was 95 when the case without solid fuel input was set to 100, and it was found that the power consumption was extremely low. Also, the time required for Tap-Tap could be reduced. Example 2 45 kg of Ogarite and NP as scrap
Scrap was preheated in the same manner as in Example 1, except that 31 tons (initial loading: 20 tons, additional loading: 11 tons) were used.
In addition, SF steel (carbon steel) of 31 tons was obtained as a steel type. The average scrap temperature was 360°. In addition, the electricity consumption rate is 98 when the case without solid fuel is set as 100, indicating that electricity consumption is low. The atmospheric temperature inside Clamsiel rose to approximately 950℃. The atmospheric temperature in the clam shell, the exhaust gas temperature of the combustion tower, and the temperature measurement results at the input and outlet of the preheater (SPH) are shown in FIG. 4A. Comparative Example 1 When preheating was carried out in the same manner as in Example 1 except that solid fuel was not used, the atmospheric temperature inside the clam shell remained at about 600°C, and the scrap temperature was 350°C on average. The atmospheric temperature inside the clamshell and the temperature measurement results of the SPH input are shown in Figure 5. Example 3 Preheating was carried out in the same manner as in Example 1 except that 100 kg of charcoal was used. Average scrap temperature is 360℃
It was hot. The electricity consumption rate was 98 when compared to the case without solid fuel [Comparative Example 1] as 100. Since the small charcoal is not flammable, it only raises the temperature of the scrap around the small charcoal, and does not raise the temperature of the whole atmosphere of the clam shell, especially the upper part. In addition, the charcoal was dispersed and charged into the scrap. Example 4 Preheating was carried out in the same manner as in Example 1, except that 105 kg of Ogarite and 100 kg of Onishi charcoal (produced in China) were used. The scrap temperature increased significantly to an average of 400℃. Also, the electricity consumption rate is based on the case without solid fuel [Comparative Example 1].
When set to 100, it decreased significantly to 93. The test results of Examples 1 to 4 above are summarized in Table 2 below.

[Table] Thus, according to the present invention, the ambient temperature of the exhaust gas in the preheating device and the temperature of the scrap itself can be significantly increased within a short time without requiring any special equipment, and moreover, it is possible to significantly increase the temperature of the exhaust gas in the preheating device and the temperature of the scrap itself. It has been possible to provide a method for preheating scrap that enables melting in a short time with even less power consumption.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention; FIG. 1 is a system diagram of a scrap preheating device in the preheating method of the present invention; FIG. 2 is a sectional view of essential parts for explaining the method of the present invention and the apparatus used therein; FIG. 3 is a process flow diagram of preheating and melting patterns in the method of the present invention, FIG. 4 is a graph showing the effects of the present invention, and FIG. 5 is a graph showing the exhaust gas atmosphere temperature according to the conventional method. 1... Melting furnace, 2... Electrode, 3... Duct, 1
0...Scrap, 11...Solid fuel.

Claims (1)

[Claims] 1 In a method for preheating steelmaking scrap that uses high-temperature exhaust gas discharged from a melting furnace, solid fuel is added to steelmaking scrap, and the solid fuel is combusted by the exhaust gas to preheat it. A method for preheating steelmaking scrap, characterized by performing the following steps.