JPS5810673B2 - Scrap preheating method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for preheating scrap, and more particularly to a method for preheating scrap using exhaust gas from an electric arc furnace when the scrap is melted in an electric arc furnace.

Conventionally, the exhaust gas from an electric arc furnace has a high temperature and contains CO, so outside air is introduced into the furnace or outside air is introduced at the smoke elbow exit to lower the exhaust gas temperature, and then it is combusted in a combustion tower. It was released into the atmosphere through a cooling tower and back filter.

Therefore, a method has been proposed in which the heat of the exhaust gas is used to preheat scrap to be fed into an electric arc furnace.

This method involves putting the scrap into metal baskets and preheating each basket with exhaust gas.

In this case, the preheating temperature is limited by the material of the basket.

Therefore, exhaust gas having an average temperature of 1000° C. is cooled with dilution air, then combusted in a combustion tower, and then cooled with water to serve as a preheating source, which is uneconomical because the sensible heat of the exhaust gas is not fully utilized.

In addition, since the scraps are preheated together with the basket, it is very difficult to create a seal to prevent outside air from entering the preheating chamber, uneven preheating occurs due to cold air entering, and the preheating temperature is difficult to control.

Furthermore, with this method, the loss of the exhaust gas coming out of the furnace is large, the effective amount of heat in the furnace is small, the basic unit of heat input into the furnace is high, and the heat utilization of the exhaust gas is insufficient.
Complete combustion control of O was not possible.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional art, and during preheating, it prevents cold air from entering the electric arc furnace, and also suppresses the exhaust gas released from the electric arc furnace as much as possible. The CO or 02 inside is controlled and used for preheating, and the heat value of the exhaust gas is fully utilized, and the preheating device is provided with an opening and closing port for inputting and removing materials so that only the scrap is preheated.
It is an object of the present invention to provide a method and apparatus for preheating scrap that can reliably prevent air from entering.

Next, the present invention will be explained according to the drawings which are examples.

FIG. 1 is a flow sheet showing a preheating method according to the present invention, in which exhaust gas of about 1200C from an electric arc furnace 1 is supplied from an exhaust gas duct 2 to a mixing section 6 of a preheating device 3, which will be described in detail below, and the lid 4 The scrap that is introduced through the opening is sufficiently heated by the exhaust gas temperature and the combustion of CO.

At this time, the air added to the mixing section 6 is controlled depending on the CO or CO2 concentration in the exhaust gas, and the scrap is preheated with high-temperature gas.

Note that an auxiliary fuel burner may be provided depending on the case.

When the scrap is sufficiently heated, the lower lid 5 is opened and the preheated scrap is put into the metal basket 8 mounted on the cart 1, and then the scrap is melted in the electric arc furnace 1.

In addition, at least C
An O or 02 concentration detector 10 and a flow meter 11 are provided, and signals from these are compared by a comparator 12 and a flow valve 13 is provided.
The amount of combustion air supplied from the blower 14 is adjusted to the optimum level, thereby ensuring that the residual CO concentration in the exhaust gas in the exhaust gas duct 9 is below the explosion limit value.

As mentioned above, the exhaust gas that has contributed to the heating of the scrap in the preheating device 3 is cooled in the cooling tower 15, then removed by the bag filter 16, and released into the atmosphere from the chimney 17.

Note that another example of the preheating method is shown in FIG.

In this example, the furnace pressure of the electric arc furnace is measured by the furnace pressure detector 42 in order to stabilize the operation of the electric arc furnace, prevent cold air from entering the electric arc furnace, and suppress exhaust gas emission from the electric arc furnace as much as possible. , operate the damper 43 so that the furnace pressure of the electric arc furnace is always at a predetermined pressure.

Further, the temperature of the exhaust gas is measured by a thermometer 44 at the entrance of the preheating furnace, and the amount of air supplied is adjusted in accordance with the CO concentration and temperature in the exhaust gas.

Furthermore, in order to lower the exhaust gas temperature to a safe temperature allowed by the bank filter 16 in the combustion tower 19, air may be mixed in or water cooling may be performed.

By appropriately providing the auxiliary fuel burner 18, it becomes possible to use it for alleviating fluctuations in exhaust gas temperature or increasing preheating capacity.

In the present invention, the exhaust gas may be sent sequentially to the sliding pipe 60, the combustion tower 19, and the preheating device 3 without introducing cold air into the duct 2 system. Of course, the names and names are not limited to those shown in the drawings.

Next, the preheating device 3 will be explained with reference to FIG. 3 and subsequent figures.

The preheating device 3 is a fixed preheating furnace 20 made of a fireproof structure.
The preheating furnace 20 consists of an upper lid 4 and a lower lid 5, and is installed on a base 22 by side columns 21.

A column 23 is provided on the side of the preheating device 3, and the arm 2
5 and 7 are rotatably mounted by a drive motor 24.

The upper lid 4 is suspended from a chain 27 that is hoisted up and down by a hydraulic cylinder 26 attached to an arm 25.
It is attached to and detached from the upper surface of the preheating furnace 20 by the drive motor 24 and hydraulic cylinder 26 .

Note that 28 is a seal. On the other hand, the lower lid 5 is attached to the base 22
two lids 31a attached to a rotating shaft 30 rotatably supported by bearings 29a, 29b provided on both sides;
31b, and each lid body 31a, 31b opens and closes the lower opening of the preheating furnace 20 by the operation of the hydraulic cylinders 32, 32.

The bearing 29a in one lid 31a is provided on a slider 33, and the slider 33 is attached to a lever 36 projecting downward from both ends of a rotating shaft 35 supported by a bearing 34 provided on the base 22. 37.

Further, a lever is provided at the center of the rotating shaft 35 as described above, and is connected to a rod 39 of a hydraulic cylinder 38 attached to the base 22.

Therefore, when the rod 39 of the hydraulic cylinder 38 is extended, the rotating shaft 35 rotates clockwise in FIG.
1b, the two lids 31a and 31b can be easily opened by the hydraulic cylinder 32, and the preheated scrap can be thrown into the basket 8.

On the other hand, when closing, conversely, the two lid bodies 31a, 3
1b is rotated upward, the lid body 31a is moved to the right by the hydraulic cylinder 38, the two differential bodies 31a and 31b are brought into a butt state, and after a complete seal is formed between the two, the scrap is newly preheated. It is put into the furnace 20.

Note that 40 is a stopper when the lids 31a and 31b are closed, and 41 is a heat shield plate.

FIGS. 6 to 8 show other embodiments of the preheating device, in which an upper lid 4 is provided at the upper input port of the preheating furnace 20 and rotates around a shaft 45 to open and close the input port.

A lower lid 5 is provided at the scrap outlet on the side of the preheating furnace, and is rotated about a shaft 30 by a drive device such as a hydraulic cylinder 46 to open and close the outlet.

The hearth 47 is tilted by a hydraulic cylinder 48 so that the scrap in the preheating furnace 20 can be taken out quickly.

Note that 49 is a seal. In this device, the upper lid 4 is opened by the operation of a chain or a hydraulic cylinder (not shown), the scrap is put into a preheating furnace 20, and the upper lid 4 is opened.
Close and seal completely, then pass exhaust gas through to preheat.

After the preheating is completed, the lower lid 5 of the extraction port is opened by operating the hydraulic cylinder 46, and at the same time, the hydraulic cylinder 48 is operated to tilt the hearth 47 and quickly take out the preheated scraps into the metal basket 8.

As described above, the preheating method of the present invention
The O or 02 concentration is measured, and the amount of combustion air supplied is optimally controlled according to this concentration.

In addition, in addition to preventing excess cold air from entering, high-temperature exhaust gas is used to preheat the scrap, so the heat retained in the exhaust gas can be effectively used, and the exhaust gas is safe and harmless. I can do it.

Furthermore, since the inside of the electric arc furnace is controlled to a predetermined pressure, it is possible to prevent cold air from entering the electric arc furnace and to suppress exhaust gas released from the electric arc furnace as much as possible, reducing the amount of heat lost in the electric arc furnace. Moreover, exhaust gas can be used effectively.

In addition, the preheating device of the present invention has a scrap inlet and a scrap outlet equipped with a lid with an opening/closing mechanism in the preheating furnace so that only the scraps can be preheated in the preheating furnace. The high-temperature exhaust gas from the electric arc furnace can be directly introduced into the furnace without any heating, and the scrap can be preheated at a high temperature in a short time by combustion of CO in the exhaust gas, radiation, convection, etc.

In addition, since the lid is simply crimped onto the preheating furnace, its sealing mechanism is complete and prevents cold air from entering.
No uneven preheating occurs.

Furthermore, when burning exhaust gas, the CO concentration is always detected and controlled to be below a standard value, so there is no risk of explosion.

In the figure, 60 is a sliding pipe, and 19 is a combustion tower. Conventionally, the exhaust gas from the electric arc furnace 1 was cooled by introducing dilution air through the sliding pipe 60, and was further cooled in the combustion tower 19. It was later burned and released into the atmosphere through the cooling tower 15 and bag filter 16.

In the present invention, the sliding pipe 60 in the exhaust gas duct 2 and the combustion tower 19 are sealed to prevent cooling air from entering.

[Brief explanation of the drawing]

1 and 2 are flow sheets showing the operating method of the scrap preheating device according to the present invention, FIG. 3 is a partially sectional front view of the preheating device, and FIG. 4 is a sectional view taken along the line ■-■ in FIG. 3. , 5th
The figure is a partial plan view of FIG. 3. FIG. 6 is a plan view of a preheating device of another embodiment, and FIG.
FIG. 8 is a cross-sectional view taken along the line ■--■ in FIG. 6. 1... Electric arc furnace, 2, 9... Exhaust gas duct, 3... Preheating device, 4... Lid, 5.
...Lid, 6...Mixing section, 8...
Basket, 10...CO or 02 detector, 13...Flow rate valve, 18...Auxiliary burner, 20...Preheating furnace, 22...・・Base,
23... Strut, 24... Drive motor,
25... Arm, 26... Cylinder,
27...Chain, 29a, 29b...
・Bearing, 30...Rotating shaft, 31a, 31b...
...Lid body, 32, 46...Hydraulic cylinder.

Claims (1)

[Scope of Claims] 1. When preheating scrap using electric arc furnace exhaust gas, the scrap is preheated using the gas while detecting and controlling CO or 02 concentration or both in the electric arc furnace exhaust gas. A method for preheating scrap using electric arc furnace exhaust gas. 2. When preheating scrap using electric arc furnace exhaust gas, the furnace internal pressure of the electric arc furnace is controlled to a predetermined pressure, and the CO or 02 concentration or both in the electric arc furnace exhaust gas is detected and controlled. 1. A method for preheating scrap using electric arc furnace exhaust gas according to the patent scope item 1, which is characterized in that the scrap is preheated. 3. A preheating furnace lined with refractory material that is connected to the electric arc furnace exhaust gas duct and has a mixing part for exhaust gas and combustion air, a scrap inlet, and an outlet for taking out the preheated scrap, and a packet for transporting the preheated scrap. and a CO or 02 concentration detector for regulating the combustion air supplied to the mixing section, and the scrap is characterized in that the input port and the removal port are each provided with a lid having an opening/closing mechanism. Preheating device. 4. The scrap preheating device according to claim 3, wherein the preheating device is provided with an auxiliary fuel burner device.