JPS5885091A - Method and device for preheating scrap - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method and apparatus for preheating scrap, and more specifically, when preheating scrap using sensible heat of exhaust gas from an electric furnace through a post-combustion device, the preheated exhaust gas is transferred to the electric furnace and the post-combustion device. The present invention relates to a method and device for preheating scrap that eliminates the risk of secondary pollution caused by returning the scrap to the device.

Electric furnaces are widely used for melting metals, but this type of electric furnace generates high-temperature exhaust gas due to the nature of melting raw materials using arc heat. This exhaust gas is then transferred to an after-combustion device (
It undergoes post-combustion by so-called self-combustion in a combustion tower (usually a combustion tower is used), and is generally rendered harmless through a cooler and dust collector before being released into the atmosphere. However, it is a significant waste of thermal energy to release the sensible heat of exhaust gas from such an electric furnace into the atmosphere without using it particularly effectively.

Therefore, the sensible heat of exhaust gas from such an electric furnace has been conventionally utilized for preheating raw material scrap. This conventional means involves preheating the scrap by introducing the stabilized exhaust gas from the electric furnace into the preheating device body, which is filled with scrap in advance, and then transferring the preheated exhaust gas to the Combustion tower--return and ultimately to a dust collector as described above.

However, this conventional means has the following drawbacks. In other words, when the preheated low-temperature exhaust gas 2 is returned to the combustion tower, the temperature inside the tower decreases by that amount. On the other hand, there are few problems when preheating high-grade scrap and scrap, but when preheating low-grade scrap, a large amount of white smoke and malodorous components are contained in the exhaust gas after preheating. Even when the exhaust gas is returned to the combustion tower, where the temperature inside the tower has decreased, the white smoke and malodorous components are not sufficiently post-combusted and end up being released into the atmosphere, causing serious secondary pollution. occurs.

The present invention provides an improved method for preheating scrap that overcomes these prior drawbacks and an apparatus for direct use in carrying out the method.

Hereinafter, the configuration of the present invention will be explained in detail based on the drawings.

FIG. 1 is a schematic process diagram of the method according to the present invention. Exhaust gas having a huge amount of sensible heat from the electric furnace 1 is supplied to a combustion tower 3, which is a post-combustion device, via a damper 2 according to an arrow A. The combustion tower 3 usually consists of a cavity whose outer periphery is water-cooled, and the exhaust gas supplied in the presence of air undergoes after-combustion by so-called self-combustion in the combustion tower 3-.
A part of it is controlled by a damper 4 and is made harmless through a dust collector 5 via a cooler (not shown) in accordance with the arrow B, and then released into the atmosphere, and the remaining part is controlled by a damper 6 and is released into the atmosphere as shown in the arrow B. C is introduced into the preheating device main body 7. The exhaust gas after preheating the scrap in the preheating device body 7 reaches the switching damper 8 in the direction of the arrow, and is further sent back between the electric furnace 1 and the combustion tower 2 in the direction of the arrow E via the fan 9. be.

Figure 2 shows a preheating device used between the initial loading of the electric furnace and the tapping of the steel, as a typical example where the exhaust gas from the electric furnace is after-combusted in a combustion tower and introduced into the main body of the preheating device filled with scrap. It is a temperature curve diagram showing the exhaust gas temperature at the main body inlet and the exhaust gas temperature at the preheating device main body outlet. According to the temperature curve a at the inlet of the preheating device main body, the exhaust gas temperature at the inlet, that is, the exhaust gas temperature approximately at the combustion tower outlet, is strongly influenced by the operating stage of the electric furnace, and the temperature curve a at the preheating device main body inlet related to the exhaust gas after scrap preheating is strongly influenced by the operating stage of the electric furnace. It is known from the temperature curve that the exhaust gas temperature after preheating is significantly lower. If the temperature curve a is inappropriate for preheating the scrap, the exhaust gas from the combustion tower is not introduced into the preheating device main body and is directly directed toward the dust collector, as shown by the cut section in the figure of the temperature curve a. Sending out, the damper described above 4.
6 can be controlled in such a case as well.

By the way, when high-grade scrap is preheated as a raw material, there are fewer problems described below, so the exhaust gas after preheating can be directly sent toward the dust collector. The switching damper 8 described above is used in such a case,
In this case, the exhaust gas after preheating will flow as shown by the dashed arrow in Figure 1. However, when preheating low-grade scrap as raw material, such switching is not possible. When low-grade scrap consisting of iron scraps is preheated, the exhaust gas after preheating contains a large amount of white smoke and malodorous components. This white smoke is a liquid mist containing oil vapor, and the malodorous components are typically hydrogen sulfide, acetaldehyde, and styrene. When the exhaust gas after preheating is returned to the combustion tower as in the past, the temperature inside the combustion tower is originally strongly influenced by the operation stage of the electric furnace, as is known from Fig. 2 above. As shown in Figure 2, as a result of the introduction of low-temperature exhaust gas (temperature curve b in the figure), the internal temperature of the column decreases, and in some cases, its original function may be impaired. In a combustion tower under such conditions, white smoke with a suitable combustion temperature of 430 to 450°C and an ignition temperature of 37°C are produced.
It is not possible to sufficiently post-combust the preheated exhaust gas containing large amounts of hydrogen sulfide, acetaldehyde, styrene, etc. at temperatures of 3°C, 400°C, and 650°C to render it harmless, and therefore these white smoke and malodorous components remain as they are. It is released into the atmosphere through dust collectors, etc., causing serious secondary pollution.

As explained in FIG. 1, the method according to the present invention is based on returning the preheated exhaust gas between the electric furnace and the after-combustion device (in the case of the drawing, the combustion tower). In other words, high-temperature exhaust gas from an electric furnace inevitably gets cooled by mixing with low-temperature air while reaching the combustion tower.
When the preheated exhaust gas is returned to the combustion tower in the post-cooling stage as in the past, the temperature inside the tower further decreases, and this does not allow for sufficient post-combustion while thermally decomposing white smoke and malodorous components. However, as mentioned above, serious pollution is caused. However, as in the method according to the present invention, if the preheated exhaust gas is returned between the electric furnace and the combustion tower, which are in a relatively high temperature atmosphere before or during cooling,
White smoke and malodorous components are immediately thermally decomposed at this stage, and are subjected to sufficient post-combustion in the combustion tower, which is the post-process, until they are completely rendered harmless. However, from the viewpoint of thermally decomposing the preheated exhaust gas in a high-temperature atmosphere, it is also possible to directly return the exhaust gas to the electric furnace. However, the method according to the present invention also prevents the possibility of adverse metallurgical effects on the exhaust gas after preheating. Next, a scrap preheating device that is directly used in the method described above will be described.

FIG. 3 is an enlarged side view of a main part illustrating a conventional and general interlocking relationship between an electric furnace and a combustion tower. Since the electric furnace 1 is operated for loading raw materials, tapping products, etc.,
The duct on the electric furnace 1 side is a movable duct 10. On the other hand, since the combustion tower 3 is not movable in this way, the duct on the combustion tower 3 side is a fixed duct 11.

, and the retaining portion 12 of both ducts has 7 lunges 1.
3.14 is formed on each of the retaining portions 12, and is configured to prevent excessive mixing of low-temperature air from the retaining portion 12, but this level of flange formation is extremely insufficient.
．． be. Therefore, recently, one of the 7 flange is made into a sliding flange with the assistance of a driving means such as an air cylinder, so that both 7 langes are in sliding contact as much as possible, but this still prevents excessive mixing of low-temperature air. FIG. 4 is an enlarged sectional view of a main part showing an embodiment of the device according to the present invention. The high-temperature exhaust gas having a huge amount of sensible heat from the electric furnace 1 reaches the combustion tower 3 via the engaging part 12 of the movable duct 1o and the fixed duct 11, and after the necessary part is introduced into the preheating device main body 7, The preheated exhaust gas is returned to the engaging portion 12 between the electric furnace 1 and the combustion tower 3. When returning the gas, the exhaust gas duct 15 from the preheating device main body 7 is connected to surround the end of the fixed duct 11 at the engaging part 12, and in the case of this embodiment, the exhaust gas duct 15 from the preheating device main body 7 is A ring-shaped nozzle 16 is formed on the outer circumferential surface of the fixed duct 11 at the end thereof so that the preheated exhaust gas is directed toward the central axes of both ducts.

According to a device having such a configuration, the problem of excessive mixing of low-temperature air, which has been difficult to overcome in the past, can be easily solved as described above. That is, according to the device according to the present invention, preheated exhaust gas is returned in place of most of the excessively mixed low-temperature air. As a result, the preheated exhaust gas (usually 300 tl) is hotter than the low-temperature air.
The temperature inside the duct in the engaging part 12 can be prevented from decreasing by the amount that is returned instead of the amount of 1: degree), and therefore the thermal decomposition of white smoke and malodorous components contained in the exhaust gas after preheating at this stage is improved. It is also possible to prevent a temperature drop in the combustion tower 3, which is a subsequent treatment step, by a similar amount, and therefore to continue introducing relatively high temperature exhaust gas from the combustion tower 3 into the preheating device main body 7. , the preheating effect of raw material scrap can also be improved. And furthermore,
According to the device according to the present invention, preheated exhaust gas is returned instead of the excessively mixed low-temperature air, so there is no need to install complicated devices such as conventional sliding flanges.
Furthermore, since the exhaust gas duct 15 is connected to the fixed duct 11 side, there is no inconvenience in the operation of the electric furnace 1, and the preheating device is inseparable from the electric furnace 1 and the combustion tower 2 due to the overall line configuration. This allows the main body 7 to be assembled in a highly desirable manner.

Table 1 shows the results of the first test using the apparatus illustrated in FIG. 4 above.
The specific effects of the test examples carried out according to the process chart shown in the figure are representatively illustrated using comparative examples using conventional means. Both are the results of preheating low-grade scrap for 40 minutes during the oxidation or reduction stage of an electric furnace, with other conditions not listed being relatively the same.Inspections for white smoke and bad odors were conducted by sampling exhaust gas at the combustion tower outlet and using a gas chromatograph. and sensuality.

Table 1 Calculated average value.

*1; The remaining 100 is mixed air. *2: The remaining 500 is mixed air)

[Brief explanation of the drawing]

Fig. 1 is a schematic process diagram of the method according to the present invention, Fig. 2 is a temperature curve of exhaust gas at the inlet and outlet of the preheater body as a typical example, and Fig. 3 is a diagram of the temperature curve of the exhaust gas at the inlet and outlet of the main body of the preheating device. FIG. 4 is an enlarged side view of a main part illustrating a conventional general engagement relationship, and FIG. 4 is an enlarged sectional view of a main part showing an embodiment of the device according to the present invention. 1...Electric furnace, 2.4.6...Danno (,3...
・Combustion tower, 5...dust collector, 7...preheating device body, 8...switching device (,9...
Fan, 10...Movable duct, 11...Visiting duct, 12...Engagement part, 13.14...7 lange, 15...Exhaust gas duct, 16...Ring-shaped nozzle , Patent applicant Daido Steel Co., Ltd. Representative Patent attorney Hiroshi Iriyama Figure 1 Figure 2

Claims (1)

[Claims] 1. A method in which sensible heat of exhaust gas from an electric furnace is used to preheat scrap through a post-combustion device, and the preheated exhaust gas is returned between the electric furnace and the after-combustion device. A scrap preheating method characterized by: 2. A device that uses sensible heat of exhaust gas from an electric furnace to preheat scrap through an after-combustion device, and an exhaust gas duct from a preheating device main body connected to the after-combustion device is connected to a movable duct on the electric furnace side and the above-mentioned A scrap preheating device connected so as to surround an end of the fixed duct at a position where the fixed duct on the after-combustion device side engages and relates the electric furnace and the after-combustion device.