JPS6038636B2 - Preheating and supply method of scrap used in electric furnace for steelmaking - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of heating scrap used as a raw material for an electric furnace for steelmaking with high-temperature exhaust gas from the electric furnace and supplying the scrap to the electric furnace.

In an electric furnace for steelmaking that uses scrap as the main raw material,
Power consumption per ton of steel ingot produced is approximately 500Kw
H, and about 25% of it is lost as thermal energy of 50,000 to 120,000 high-temperature exhaust gases. Therefore, in order to save power consumption by recovering the thermal energy of this high-temperature exhaust gas, devices have been developed and used to subheat raw material scrap with high-temperature exhaust gas. An example of a conventionally used scrap preheating device will be explained with reference to FIG.

In FIG. 1, reference numeral 1 indicates an electric furnace. This electric furnace 1
The exhaust system is first provided with a combustion chamber 2 at its upstream portion, where the unused gas contained in the high-temperature exhaust gas is combusted. A scrap preheating device 3 is provided downstream of the combustion chamber 2. This child heating device 3 is called a batch type, and includes two removable buckets 4a,
4b. These two buckets 4a and 4b are alternately filled with scrap and heated, and alternately supplied with heated scrap to the electric furnace 1.
When preheating the scrap in the first bucket 4a, the valves 6a, 6d, and 6e are opened and the valves 6b, 6c, and 6f are closed to guide high-temperature exhaust gas into the second bucket 4b. After the child heating is completed, the bucket 4a or 4b is removed from the installed position and moved to the position of the electric furnace 1, and scrap is charged from the upper opening □ of the electric furnace 1 with the furnace lid la opened. A cooler 7 and a fan 8 are provided downstream of the preheater 3, and the exhaust gas drawn by the fan 8 is cooled by the cooler 7 and sent to a dust collector. FIG. 3 shows the time schedule of the conventional batch type preheating device.

Since it is difficult to charge the entire amount of scrap at once due to the internal volume of the electric furnace 1 and the high specific gravity of the scrap, it is charged in parts. Generally, as shown in Figure 3, in one charge, 50% of the total charge is initially charged, and the remaining 50% is charged.
% is divided into at least two batches, for example, 25% each is added to the bag. To explain the scrap charging in more detail, in the n-th charge, the scrap in the first bucket 4a that was preheated in the previous charge is charged first, and after a predetermined time (25 minutes) has elapsed, the scrap in the second bucket 4a is charged. Bucket 4b
Additional preheated scrap is charged, and the preheated scrap is further charged for a specified period of time (
After 18 minutes have elapsed, additional heated scrap is added to the first bucket 4a. In addition, in the n11th charge, the heated scrap in the second bucket 4b is first charged. In this way, the pre-heated scraps in the two buckets 4a and 4b are charged alternately, and each bucket 4
Bucket 4a is also used for filling and preheating scraps in buckets a and 4b.
, 4b.o However, such a conventional child heating device has the following drawbacks.

River: In one charge, open the electric furnace lid at least three times: at the initial charging time and two additional charging times.

In particular, since the two additional charges are performed during the melting process in which the inside of the electric furnace reaches a high temperature, heat dissipation is large, and as a result, the scarlet heat recovery effect due to scrap child heat is offset. {o
- During at least two additional scrap charges,
When the electric furnace lid is opened, significant smoke is emitted and the working environment deteriorates.

However, in order to heat the entire amount of scrap to be charged into the electric furnace, complete and complicated schedule management of the two preheating buckets is required.

8 This is related to the above-mentioned drawback, but since there is no flexibility in the time schedule for scrap preheating, the scrap for the initial charging, which is the largest amount, is mainly used in the final process of the previous charging. Scrap is forced to be heated by the exhaust gas from certain oxidation, reduction, and steel processes, but the temperature of the exhaust gas during this process is relatively low, and the heating temperature of scrap only reaches about 200 to 250oO.

For this reason, scarlet heat recovery cannot be said to be sufficient. Especially
Due to the drawbacks mentioned in A' and S1, the current situation is that the power consumption savings can only be achieved with a steel ingot of 30 to 4 arc wH/ton.

The present invention has been made based on the above-mentioned circumstances, and its purpose is to eliminate the above-mentioned conventional drawbacks, to significantly reduce power consumption, and to improve work efficiency and work environment. The purpose is to provide a preheating and supply method.

In order to achieve the above object, the gist of the present invention is to include a rotary drum in the high-temperature gas exhaust system of an electric furnace, and a rotary drum connected to the lid of the electric furnace through a charging chute. 1 preheating device, and '. } A second preheating device that is disposed downstream of the first preheating device and has a removable bucket; The large scrap scraps are preheated by guiding the chute and then stored in the bucket and preheated by the high temperature exhaust gas from the rotary drum, and only before the melting process begins, the preheated large scrap scraps in the bucket are transferred to the furnace lid. When the scrap is melted with the lid opened and the furnace lid closed, the small pieces of scrap in the rotary drum are continuously charged into the electric furnace little by little through the bagging chute. The present invention provides a method for supplying scrap heat to an electric furnace for steelmaking, which is characterized by: Preferably, the scrap fragments preheated by the first preheating device have a diameter of less than 500 ribs.

For example, there are shredders, reduced iron, pig iron, Onidarai, etc. A shredder is scrap obtained by cutting a scrapped car or a thin plate object using a shredding machine so that each side has, for example, 25 ribs or less. In addition, in this specification, reduced iron and pig iron shall also be interpreted as a type of scrap. The large pieces of scrap that are heated by the second heating device include Koyama scrap, various types of presses, dry powder, return shoulders, etc.

It is preferable that the proportion of small scrap scrap in the total amount of scrap to be charged into the electric furnace is 5% by weight or more.

However, even if the proportion of small scrap pieces is less than 50%, for example about 30%, the effects of the present invention can be obtained. If the proportion of small-piece scrap is small, the small-piece scrap may be obtained by the shredding machine described above. next,
An embodiment of the scrap preheating pupil for carrying out the method of the present invention will be described with reference to FIG.

In FIG. 2, reference numeral 11 indicates an electric furnace, and 11a is a furnace lid for opening and closing the electric furnace 11. As shown in FIG. A first heating element 13 is connected to the furnace lid 11a via a charging chute 12. The charging chute 12 has a sliding structure and is extendable and retractable, and a portion (not shown) is bendable so as not to interfere with the movement of the electric furnace 11. The first child heating device 13 has a rotary drum 14 . This rotary drum 14 is lined with a refractory material, is equipped with a delivery blade 15, and has a conveyance function. On the other hand, scrap fragments are loaded into a receiving hopper 17 by a lifting magnet crane 16, continuously weighed by a weighing machine 18, and further stored in 201 hoppers by a comparer 19. A feeder 21 is inserted into the lower part of this hopper 20. This feeder 21
uses a screw system to prevent external air from being sucked in, maintaining airtightness. As the feeder 21 rotates, the scrap scraps stored in the hopper 20 are continuously fed into the rotary drum 14 described above. High-temperature exhaust gas from the electric furnace 11 is introduced into the rotary drum 14 . Further, within this rotary drum 14, unburned gas in the high temperature exhaust gas is combusted.
The temperature of the exhaust gas inside this rotary drum 14 is about 800~
It is 120,000. The small pieces of scrap fed into the rotary drum 14 are rotated by the rotation of the rotary drum 14 (approximately 0.1 to 15 rpm) to the sending blade 15.
Under the feeding action of the chicks, the chicks are gradually transported toward the electric furnace 11 while being held, and are continuously inserted into the electric furnace 11. When the small pieces of scrap are retained in this rotary drum 14, the time is approximately 2 hours.
Approximately 500 to 600 oo after contacting the above high temperature exhaust gas for 0 minutes
preheated to a high temperature. The preheating capacity of the rotary drum 14 is determined by the diameter and length of the drum, scrap charging capacity, conveyance capacity based on the delivery blade and rotation speed, etc., but it has approximately twice the melting capacity of the electric furnace 11. In order to stabilize the operation of the electric furnace 11 and to maximize its performance, it is desirable that the Note that the entrance side end of the rotary drum 14 and the lower end of the hopper 20 are connected to the dust hopper 2.
The scrap shoulders collected in the dust hopper 22 are returned to the conveyor 19 again. Next, reference numeral 30 in the figure indicates a second preheating device 30. This second preheating device 30 is arranged downstream of the first ripening device 13 in the exhaust system. The second heating element 20 is of a batch type like the slave, and has a detachable bucket 31. This bucket 31
is removed from its installed position and moved to the position shown in phantom where it can be filled with large piece scrap by lifting magnet crane 32.
This bucket 31 heats the large pieces of scrap with the high temperature exhaust gas from the first heating device 13 at the set pupil position. The temperature of the exhaust gas from the first preheating device 13 is lower than the outlet temperature of the electric furnace 11 because it is after preheating the small pieces of scrap, but the temperature of the exhaust gas from the first preheating device 13 is lower than the exit temperature of the electric furnace 11. Due to the heat generation, the temperature drop is relatively small, about 800-1000 oo, so that the large scrap scrap is heated at extremely high temperatures. After this preheating, the bucket 31 is removed again and moved to the electric furnace 11 in a closed state, and the large pieces of scrap are poured into the electric furnace 11. Reference numeral 33 indicates a turning device, and this turning device 33 allows the bucket 31 to be
The lid 31a is opened and closed. In the case of child heating, the valves 34a and 34b (valves whose opening degree can be adjusted, the same applies hereinafter) are opened and the valves 34c and 34d are closed to guide the high-temperature exhaust gas from the first preheating device 13 into the bucket 31.
It is designed to heat the large pieces of scrap stored inside. Furthermore, when removing the bucket 31 and filling it with scrap, or when charging preheated scrap into the electric furnace 11, the valves 34a, 34b, and 34d are closed.
4c is opened to guide the high-temperature exhaust gas to the bypass pipe 36 without passing through the second preheating device 31. Exhaust gas from the second heating element 30 or the bypass pipe 36 is sent to a dust collector (not shown) by a fan 35. In addition, the above-mentioned charging shoe
Exhaust gas from the second heating element 30 or external air is sent to the upper part of the rotary drum 12 by a fan 37, thereby making it possible to adjust the temperature inside the rotary drum 14.

That is, when the valve 34d is opened, exhaust gas from the second heating element 30 enters the rotary drum 14, and when the valve 34e is opened, cold air from the outside enters the rotary drum 14. Next, the operation of the above-mentioned child heating device will be explained with reference to the time schedule shown in FIG.

In the n-th charge shown in FIG. 4, the proportion of each scrap to the total charge is approximately ideal: 50% small pieces and 50% large pieces. 50% of the large pieces of scrap have been preheated by the bucket 31 in the previous charge, and are initially charged into the electric furnace 11 in a batch in this n-th charge. Immediately after this, electric furnace 111
Electricity is applied to start melting the scrap. and,
10 minutes after the start of melting, the rotary drums 14 to 5
Started continuous charging of 0% grade/fragment scrap. This continuous bagging is carried out in small quantities for 48 minutes. During this continuous charging, the small pieces of scrap are placed in the rotary drum 14 for approximately 1 hour.
It is placed in a bag in the electric furnace 11 in a state where it is heated to about 60,000 ℃ by contact with exhaust gas of 20,000 ℃. Since the initial charging of large pieces of scrap is carried out when the temperature inside the furnace is low immediately after preparations for furnace repair etc. are completed, heat loss is small even if the furnace lid 11a of the electric furnace 11 is opened. Since the furnace lid 11a is not opened during the melting process where the temperature inside the furnace is high, large heat loss can be eliminated, and deterioration of the working environment due to smoke generation can be prevented. In addition, in this n-time charging, after the initial charging, the bucket 31 is again filled with large pieces of scrap and preheated, but since this large pieces of scrap are not additionally charged, the melting period when high-temperature exhaust gas is discharged is delayed. It is preheated for a long time, about 3 minutes during the redox period, and about 2 minutes during the redox period, and can reach an extremely high temperature of about 500 oo. In this way, the ripening temperature of large scrap scraps is 50,000, and the ripening temperature of small scrap scraps is 60,000, and the average temperature is 55,000.
This can be extremely high compared to the 200 to 250 qo of the conventional method, and in other words, the thermal energy in the exhaust gas can be efficiently recovered, reducing the power consumption by 11 qo.
The plates wH/ton can be made of steel ingots and significant savings can be achieved. Note that the present invention is not limited to the embodiments described above, and various embodiments are possible.

For example, the second heating element may have multiple buckets. As explained above, the present invention can have the following effects.

Before the melting process, when the temperature inside the electric furnace is at its lowest, the lid of the electric furnace is opened and large pieces of scrap are fed into the electric furnace.
In the melting process, small pieces of scrap are fed with the furnace lid closed, and the furnace lid is not opened during the melting period.
The problems of large heat loss and smoke generation caused by this opening can be solved.

The operation time schedule is simple and efficient scrap heating can be carried out over a long period of time.

During the melting stage, small pieces of scrap are continuously fed in small quantities by a rotary drum, and stable operation can be performed without the scrap melting temperature significantly or locally decreasing.

Small scrap scraps are heated upstream of the exhaust system compared to large scrap scraps, so they can be reliably heated to a high temperature, and from this point of view, the melting temperature in the electric furnace can be significantly and locally increased during continuous supply. can be prevented from decreasing. The rotary drum is connected to the lid of the electric furnace via a charging chute.
The above-mentioned small pieces of scrap and electric furnace exhaust gas are introduced, and the exhaust gas near the furnace lid, which has the highest temperature in the space inside the electric furnace, can be introduced, and the small pieces of scrap can be heated at a high temperature.

From this point of view as well, it is possible to prevent the melting temperature in the furnace from significantly and locally decreasing when small pieces are supplied. The upstream side of one exhaust system in which the first child heat device and the second child heat device are connected,
Since it is placed on the downstream side, the configuration of the arrangement system is also relatively simple.

Since the small and large fragments are heated in a rotary kiln and bucket, a large amount of heat can be generated over a long period of time, and the thermal energy of the exhaust gas can be efficiently recovered.

[Brief explanation of drawings]

FIG. 1 shows a conventional scrap heating device, and FIG. 2 is a schematic diagram showing an embodiment of the scrap preheating device of the present invention.
FIG. 3 shows a time schedule for operation using a conventional scrap preheating device, and FIG. 4 shows an example of a time schedule for operation using the device of the present invention. 11...Electric furnace, 11a...Furnace lid, 12...
...Charging chute, 13...First child heating device, 14...Rotary drum, 30...Second preheating device, 31...Bucket. Figure 1 Figure 2 Figure 4 Figure 3

Claims (1)

[Claims] 1 A continuous high-temperature gas exhaust system derived from the electric furnace,
(b) a first preheating device having a rotary drum having a conveyance function and connected to the lid of the electric furnace via a charging chute;
a second preheating device disposed downstream of the preheating device and having a removable bucket, the small pieces of scrap are stored in the rotary drum, and the high temperature exhaust gas of the electric furnace is guided through the charging chute. The large pieces of scrap are stored in the bucket and preheated by the high-temperature exhaust gas from the rotary drum, and only before the melting process begins, the preheated large pieces of scrap in the bucket are heated by opening the oven lid and applying electricity. For steelmaking, the small pieces of scrap in the rotary drum are continuously charged little by little through the charging chute when the scrap is charged into the furnace and melted with the furnace lid closed. Method for preheating and supplying scrap used in electric furnaces.