JPS6229485B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for preheating scrap, and more particularly to a method for preheating scrap with high thermal efficiency, which utilizes the heat of high-temperature exhaust gas from a steelmaking furnace. Traditionally, the heat contained in the exhaust gas discharged from a melting furnace such as an arc furnace is used to preheat the scrap, such as iron scraps, that is charged into the melting furnace to the highest possible temperature. , a method of obtaining high thermal efficiency is known. However, conventional preheating of scrap is generally performed outside the furnace body of the melting furnace, and in such cases, if the material to be melted contains low-grade scrap such as milling powder, it may be difficult to preheat the material. There is a problem in that the oil contained in the low-grade scrap burns and the scrap, which is the material to be melted, is melted outside the melting furnace. However, in order to avoid such problems, it would be better to suppress the preheating temperature of the material to be melted.
In this case, incomplete combustion of the oil contained in the low-grade scrap generates foul-smelling white smoke, deteriorating the working environment and making it impossible to obtain a sufficiently high thermal efficiency. On the other hand, the furnace body of the melting furnace is directly used as a scrap preheating container, and after charging a specified amount of scrap into the furnace body and heating it with high-temperature gas introduced therein, the preheated scrap is directly stored in the furnace body. A method has been devised in which the scrap is melted, and if this method is followed, the scrap preheating melter becomes the melting furnace, so even if the scrap melts during preheating, there is no inconvenience; Therefore, it can exhibit the great feature of imparting the maximum amount of heat from the introduced high-temperature gas to the scrap. However, in the method of using such a melting furnace body as a scrap preheating container, the quality of scrap preheating in the furnace is an important point. However, in order for the preheated scrap to melt more easily in the next melting step, and to melt more uniformly and quickly, the temperature of the preheated scrap should be adjusted to a level where the temperature of the preheated scrap is lower than the localized high temperature areas caused by local heating. This is because it is preferable that the entire scrap has a uniform preheating temperature with less variation than the average value obtained by averaging the low-temperature portions. Moreover, since the amount of heat added to the scrap by high-temperature gas is approximately constant, it is necessary to make the scrap absorb as much of that heat as possible in order to further improve thermal efficiency. However, when the scrap starts to melt due to the above-described local heating, the amount of heat from the high-temperature gas passing through the melted portion cannot be effectively absorbed, resulting in a decrease in thermal efficiency. In view of the above circumstances, the present inventors have investigated various ways of preheating scrap through cold model experiments, etc. in a method using a melting furnace body such as an arc furnace as a scrap preheating container, and based on the results obtained using fluid dynamics. As a result of a comprehensive analysis, it was found that depending on the introduction position of the high-temperature gas for scrap preheating and the point where it is taken out (exhausted) from the furnace body,
They found that the preheating patterns for scrap differ significantly. That is, the present invention was completed based on this knowledge, and its purpose is to heat the scrap charged into the furnace as uniformly as possible, thereby increasing its thermal efficiency. The object of the present invention is to provide a preheating method for obtaining scrap metal, and for this purpose, in the present invention, a furnace body of a melting furnace is used as a scrap preheating container, and a prescribed amount of scrap is charged into the furnace body and heated with high-temperature gas. In a method in which the preheated scrap is melted in the furnace body after heating, the high-temperature gas is melted.
The scrap charged into the furnace body is introduced into the scrap from above and discharged from a plurality of exhaust ports provided on the side of the furnace body, thereby circulating the scrap inside the furnace body. The reason is that it is preheated. As described above, according to the present invention, the high-temperature gas is introduced from the top of the scrap and extracted from multiple locations on the side of the furnace body, so that the introduced high-temperature gas can effectively circulate through the scrap gap. This did not cause any significant imbalance in the flow of the high-temperature gas, and the heat of the high-temperature gas could be effectively imparted to the charged scrap, resulting in high thermal efficiency. Further, as the scraps are heated uniformly, the scraps are easily melted in the melting operation in the next step, and thus the scraps can be melted more uniformly and quickly. Incidentally, the cold model experiment conducted by the present inventors is as follows. First, as shown in FIG. 1, scrap 4 is placed in a transparent model container 2 with two entrances and exits 3 and 5 on the top and side, and parasol benzene is added to a predetermined position inside the scrap 4. The gas flow velocity distribution within the transparent model container 2 was determined by arranging the spheres 6 and measuring the sublimation rate of the parasol benzene spheres 6. The flow direction of the gas is method A when it is introduced from the top 3 and discharged in two horizontal directions 5, method B is when it is introduced from the top 3 and discharged in one horizontal direction 5, or method B is used when it is introduced from the top 3 and discharged in one horizontal direction 5. 3 is closed, gas is introduced from one side entrance 5, and gas is discharged from the other side entrance 5. The case of discharge was assumed to be Method D, and each case was examined. Figure 2 shows the relationship between the sky Reynolds (Re) number and the flow velocity in the vessel for each gas flow direction.
In addition, the relationship between the Re number of the empty tower and the variation in the flow velocity in the container is shown in FIG. 3. As is clear from FIG. The average flow velocity in the container is small, so it is difficult to apply sufficient heat to the scrap.In order to increase thermal efficiency, it is necessary to use A, B, It is understood that method C is better. Also, from the results in Fig. 3, we can see that the gas is introduced from the upper part 3 and discharged to the two sides 5, 5, which is surrounded by a broken line.
It is understood that in the case of this method, the variation in gas flow rate is smaller than in other methods, and is therefore the most preferable. Further, FIGS. 4 to 7 schematically show the gas flow velocity distribution (v/) and gas flow in the container when a 1/14 scale cold model is used. Note that the gas flow conditions in each gas flow direction and the correspondence relationship between the symbols and the flow velocity distribution are as shown in the table below.

[Table] According to these results, A shown in Figure 4
The method of introducing gas into the scrap in the container from the top and discharging it from two sides is a good method with less variation in gas flow velocity and can obtain a uniform gas flow velocity distribution. It has become clear that the average flow velocity between scraps can also be increased, thereby improving thermal efficiency. On the other hand, in method B, as shown in Fig. 5, the gas flow is extremely uneven, and it became clear that uniform scrap heating could not be expected with this method, and as shown in Fig. 6. In method C, the scrap located at the gas inlet and outlet tends to be extremely heated, and as with method B, there is large variation in the gas flow rate, making it difficult to uniformly heat the entire scrap. ,
Furthermore, method D shown in FIG. 7, in which gas is introduced from two horizontal directions and exhausted to the top, is considered to have the same effect as the present invention in terms of flow velocity variation within the container. However, the average flow velocity within the gas container becomes extremely low, and the gas flow also tends to be uneven, which poses a problem in absorbing enough heat from the introduced gas and improving thermal efficiency. That's obvious. Based on these results, in the present invention, by adopting method A, in which gas is introduced from the top and discharged from the side, it is possible to uniformly heat the scrap and further improve thermal efficiency. It was achieved. In addition, in the present invention, a set of two melting furnaces is used, and high-temperature CO-containing exhaust gas generated during scrap melting operation in one of the furnace bodies is used as the high-temperature gas. The CO-containing exhaust gas is combusted by introducing the CO-containing exhaust gas into another furnace body into which the scrap to be preheated is charged, and blowing oxygen-containing gas into the other furnace body. It is recommended to contribute to the preheating of the scrap in one of the other furnace bodies, and in this way the scrap before melting will be effectively preheated in the other furnace body. Therefore, the preheating temperature of the scrap can be increased.
Also, the CO generated in one of the reactor bodies
Since the scrap is preheated by burning gas in the other furnace body,
There is an advantage that the heat generated in the one furnace body is used extremely effectively for preheating, and high thermal efficiency can be obtained.
Naturally, even if the material to be melted contains low-grade scrap, the high preheating temperature ensures that the oil contained in the low-grade scrap is completely combusted, and the working environment will not deteriorate. It is. Furthermore, since carbon is preferably burned to generate CO gas in one of the furnace bodies during melting, the heat of combustion can also be used for melting, thereby significantly reducing the use of expensive electricity. There are also benefits that can be saved. Further, FIG. 8 shows an example in which the method of the present invention is applied to an arc furnace melting apparatus that melts scrap, which is a material to be melted, by alternately using a pair of arc furnace furnace bodies. In FIG. 8, a pair of arc furnace furnace bodies 10
In one of the furnaces a and 10b, an arc is generated by supplying electric power to an electrode 12 inserted through the furnace lid, thereby melting the already preheated scrap and depositing molten steel 14 in the lower part. The melting operation is allowed to proceed to produce a slag 16 on top. During this melting, carbon is generally mixed with the scrap, and during the melting operation, carbon, oxygen, or an oxygen-containing gas such as air is blown into the furnace body 10a from a carbon injection nozzle or an oxygen injection nozzle (not shown). The injected carbon is combusted by oxygen, and high-temperature exhaust gas containing CO is formed within the furnace body 10a. On the other hand, in the other furnace body 10b, scrap 18 to be preheated is charged,
Further, a duct 20 for guiding high temperature exhaust gas from the one furnace body 10a is connected to the top of the furnace lid. In addition, at a lower position on the side of this furnace body 10b (a position higher than the surface of the molten steel to be formed),
A plurality of exhaust ports 22 are provided, and the high-temperature exhaust gas generated in the one furnace body 10a is transferred to the duct 20.
After being introduced into the upper space of the furnace body 10b for preheating through the scrap 18, the scrap 18 is introduced into the inside from the upper part of the scrap 18, and is then discharged from a plurality of exhaust ports 22, 22 provided at the lower side of the furnace body 10b. It is becoming. Incidentally, the furnace body 10b is provided with a carbon injection nozzle and an oxygen injection nozzle like the other furnace body 10a, and during scrap preheating, oxygen-containing gas such as oxygen or air is injected from the oxygen injection nozzle. It is designed to be introduced into the furnace body 10b. Therefore, in a melting apparatus using a pair of furnace bodies 10a and 10b, one furnace body 10a performs the scrap melting operation, while the other furnace body 10b melts the scrap charged there. 1
8, the high-temperature exhaust gas generated in one furnace body 10a is made to flow into the inside of the scrap 18 from the upper part thereof through a duct 20, and is discharged from a plurality of exhaust ports 22, 22 provided on the side of the furnace body. As a result, the scrap charged into the furnace body 10b can be preheated uniformly and while enjoying high thermal efficiency as described above. Moreover, in the high-temperature exhaust gas generated in one furnace body 10a, carbon blown into the furnace body 10a and carbon mixed with scrap are combusted by oxygen or oxygen in an oxygen-containing gas such as air. If the exhaust gas contains CO generated by
When the furnace body 1 is combusted by oxygen-containing gas blown into the upper space of
The scrap 18 in 0b will be preheated to an extremely high temperature by combustion of CO. and,
The scrap 18, which is the material to be melted, is transferred to the furnace body 10b.
Since the scrap 18 is preheated while being charged in the furnace, the scrap 18 can be preheated to a high temperature without worrying about melting, and the furnace body 10 during melting can be preheated.
Since the heat in the furnace body 10b is effectively used for preheating the other furnace body 10b, high thermal efficiency can be obtained. Moreover, since the scrap 18 is preheated at a high temperature, the oil content of the lower grade scrap contained in the scrap 18 is completely combusted, so that the working environment will not be deteriorated at all. Also, the scrap 1 charged into the furnace body 10b
Since a space is formed above the scrap 8, the high-temperature exhaust gas guided through the duct 20 spreads over the entire upper surface of the scrap 18 and is then guided into the scrap 18, so that the flow of the high-temperature exhaust gas is biased. This has the advantage of effectively suppressing such problems, and furthermore, if CO is present in the exhaust gas introduced through the duct 20, such a space can also be used as a combustion space for CO. Therefore, the combustion heat generated by the combustion of CO can be applied to the entire scrap 18, resulting in a great advantage. When the melting in the furnace body 10a is completed, the preheated scrap in the furnace body 10b is similarly melted, and the furnace body 10a is also melted.
After the molten steel 14 is taken out, new scrap is charged and the scrap is preheated in the same manner as the scrap preheating in the furnace body 10b as described above. At this time, the high temperature gas is transferred from the furnace body 10b where the melting operation is being carried out to the duct 2.
0 to the furnace body 10a side. By repeating the preheating melting operation in the furnace bodies 10a and 10b alternately in this manner, molten steel can be manufactured with high productivity and thermal efficiency. In addition, according to the present invention, the scrap preheated in the furnace body is uniformly preheated because high-temperature gas is made to flow from the top to the plurality of exhaust ports on the side, and therefore, the scrap is significantly heated in the subsequent melting operation. Since it becomes easier to dissolve, more uniformly, and furthermore, it dissolves further, the dissolution operation can be carried out very efficiently and quickly. Although specific examples of the present invention have been described above, such specific examples are merely examples of the method of the present invention, and are by no means limited to these, and the present invention can be applied without departing from the spirit of the present invention. It goes without saying that various changes, modifications, improvements, etc. can be made to the invention. For example, an exhaust port 22 provided on the side of the furnace body
may be provided not only in the two cases illustrated, but also in three or more numbers,
Generally, it is desirable that a plurality of such exhaust ports 22 be provided at approximately equal intervals in the circumferential direction of the furnace body, and such exhaust ports are related to the arrangement position of the electrode 12 arranged for the melting operation. Therefore, it is desirable to arrange it in a place where cold spots are likely to occur in the furnace body. In addition, the combustible gases used for effective heating of scrap in one furnace body include not only the CO-containing exhaust gas generated during scrap melting operations in the other furnace body, but also other suitable combustion gases. There is no problem even if it is a gas that can be
In addition to burning the CO-containing exhaust gas in the one furnace body, the CO-containing exhaust gas is combusted and then introduced into the one furnace body, and the combustion heat is used to preheat the scrap. is also possible.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the model used in the cold model experiment, Figure 2 is a graph showing the relationship between the sky Reynolds number and the flow velocity in the vessel, and Figure 3 is a graph showing the relationship between the sky Reynolds number and the flow velocity in the vessel. It is a graph showing a relationship. Figures 4 to 7 are explanatory diagrams showing models of the gas flow velocity distribution in the container in various gas flow directions, respectively, and Figure 8 is a diagram showing a method of melting scrap by alternately using a pair of arc furnace bodies. 1 is a schematic diagram showing an example in which the present invention is applied to an arc furnace melting device. 2: Transparent model container, 3, 5: Gas inlet/outlet, 4:
Scrap, 6: Parasol benzene sphere, 10
a, 10b: Furnace body, 12: Electrode, 14: Molten steel, 1
6: Slag, 18: Scrap, 20: Duct,
22: Exhaust port.

Claims (1)

[Scope of Claims] 1. A furnace body of a melting furnace is used as a scrap preheating container, and a prescribed amount of scrap is charged into the furnace body and heated with high-temperature gas, and then the preheated scrap is melted in the furnace body. In this method, the high-temperature gas is introduced into the scrap from above the scrap charged into the furnace, and is discharged from a plurality of exhaust ports provided on the side of the furnace. A scrap preheating method characterized in that the scrap is preheated by flowing through the scrap. 2. The method according to claim 1, wherein a space is provided above the scrap charged into the furnace body, and the flammable gas is combusted in the space. 3. CO-containing exhaust gas generated during the scrap melting operation in the other furnace body is used as the high-temperature gas, and the amount of heat generated by burning this CO-containing exhaust gas is transferred to the gas charged into one furnace body. The method according to claim 1, wherein the method is used for preheating scrap. 4. CO-containing exhaust gas generated during the scrap melting operation in the other furnace body is used as the high-temperature gas, and this CO-containing exhaust gas is introduced into one furnace body into which the scrap to be preheated is charged, while Claim 1 or 2, wherein the CO-containing exhaust gas is combusted by blowing oxygen-containing gas into one of the furnace bodies, thereby contributing to the preheating of scrap in the one furnace body. the method of.