JPH08200957A - Two-drum type arc furnace - Google Patents

Abstract

PURPOSE: To prevent scrap from collecting in a duct and so enhance an energy recovery rate by providing an exhaust duct at an exhaust port of a preheat gas on a side of a preheat furnace and connecting an introduction duct and an exhaust duct, respectively, to a combustion tower through a bypass duct. CONSTITUTION: A high temperature exhaust gas containing much of unburned CO gas generated in an operating furnace 1 enters a preheat furnace 2 through an introduction duct 3 to preheat scrap having been beforehand charged in the preheat furnace 2. Thereafter, the exhaust gas leaving an exhaust port 5 provided on the preheat furnace 2 enters a combustion tower 4 through an exhaust duct 6 and a bypass duct 7b to be drawn into a dust collector via a stationary duct 27. At this time, a lightweight scrap charged near the exhaust port 5 collects at inflection points or the like in the stationary duct 27 to present an increased resistance to a flow of the exhaust gas. Thus a gas flow passage in the combustion tower 4 has an area several times cross-sectional areas of the bypass duct 7b and the stationary duct 27, so that a gas flow velocity decreases to permit scrap, dust or the like to be settled by gravity to be removed optionally.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to two arc furnaces used for melting metal materials, refining molten metal, and the like, and is a two-tank type in which melting and preheating are alternately repeated to effectively utilize the heat quantity of exhaust gas. Regarding the arc furnace.

[0002]

2. Description of the Related Art An arc furnace used for melting a metal material, refining a molten metal, etc. mainly uses electric energy. 150% of the energy was input, and 30 to 50% was discharged without being utilized. Most of these are the sensible heat of the exhaust gas discharged from the arc furnace, and the success or failure of the effective use of this sensible heat of the exhaust gas was an important issue for the operation of the arc furnace.

Therefore, as a means for effectively utilizing the sensible heat of the exhaust gas, as described in Japanese Patent Publication No. 59-52359, a preheating tank provided separately from the arc furnace is provided to preheat the scrap with the exhaust gas. A scrap preheating system has been proposed. This system enabled the recovery of the sensible heat of the exhaust gas, but the length of the duct leading the exhaust gas to the preheating tank became longer, and the duct was water-cooled to maintain its strength. The reality is that the temperature drops and sufficient sensible heat of exhaust gas cannot be recovered. In addition, 800 scraps with oil etc.
When preheated with exhaust gas below ℃, odor and white smoke are generated, and when the scrap is put into the furnace, it is carried on the work floor, which causes a phenomenon that foul odors and white smoke are scattered on the work floor, which is not preferable in terms of pollution control. It was

In order to solve these problems and problems, the scrap is preheated with high-temperature exhaust gas to completely decompose the odor and white smoke generated by the oil adhering to the scrap into two tanks (Twin Vessel type arc furnaces are known. This is a system in which two arc furnaces are operated by alternately repeating melting and preheating, and high-temperature exhaust gas from the arc furnace during the melting operation is introduced into the other arc furnace to preheat scrap at high temperature.

As a technique related to this method, Japanese Patent Application No.
An improved technique is proposed in 146800. In Japanese Patent Application No. 05-146800, a part of the scrap filled in the preheating furnace is sucked and accumulated in the discharge duct to prevent the cross-sectional area of the duct from being reduced. A scrap catcher for collecting the sucked scrap is provided in the connecting exhaust duct to secure a stable exhaust gas flow and improve the preheating efficiency. Also,
In such a two-tank arc furnace, a combustion tower is usually installed between the exhaust gas ducts that connect two arc furnaces so that it can be operated with only one furnace without preheating. Bypass ducts that are directly connected to the dust collector without being installed are used to adjust the gas flow by opening and closing dampers in the ducts in the front and rear of the combustion tower.

[0006]

However, in the improvement technique of such a two-tank type arc furnace, the scrap catcher is provided in the exhaust duct connected to the exhaust port of the preheating gas of the preheating furnace, so that the facility cost is low. With the increase, there arises a problem that an extra installation space is required. Further, a combustion tower is provided between exhaust gas ducts connecting the two arc furnaces, and high-temperature exhaust gas containing a large amount of unburned CO gas emitted from the operating furnace passes through the combustion tower. Due to this, heat is removed and a large amount of secondary combustion occurs, and the gas temperature at the time of entering the preheating furnace drops slightly.

An object of the present invention is to collect scraps sucked in an exhaust duct connected to an exhaust port for preheating gas in a combustion tower located on the exhaust gas outlet side of a normal arc furnace, so that a conventional two tank With the same equipment cost and installation space as the electric arc furnace, it prevents scrap accumulation in the duct, secures a stable gas flow, eliminates the need to remove scrap accumulated in the duct, and at the same time preheats it. Sometimes the exhaust gas emitted from the operating furnace is directly introduced into the preheating furnace without passing through the combustion tower, thereby eliminating heat removal in the combustion tower and introducing the exhaust gas containing a large amount of unburned CO gas into the preheating furnace to preheat it. (EN) A two-tank arc furnace in which scrap is preheated with a gas having a temperature higher than ever before by secondary combustion in the furnace to improve the energy recovery rate.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a two-tank type arc furnace in which two arc furnaces are alternately used for melting and preheating scraps. Exhaust gas generated from the melting furnace side is connected by an introduction duct for introducing it to the preheating furnace side as a preheating gas, and the preheating gas discharge port on the melting furnace side blocks the outside air from entering the furnace during melting. A lid or a valve is provided, a discharge duct for connecting the discharge port and a dust collector is provided at the preheating gas discharge port on the preheating furnace side, and a bypass duct connecting the introduction duct and the discharge duct to the combustion tower is provided. It is characterized by having.

[0009]

In the two-vessel arc furnace of the present invention, the scrap sucked into the exhaust duct connected to the exhaust port for the preheating gas has a gas flow path area enlarged and gravity is reduced in the combustion tower. Either it will settle down, or it will collide with and fall into the baffle plate provided in the combustion tower and be collected, so that the required cross-sectional area of the duct will always be secured without the accumulation of scrap in the discharge duct. There is no increase in resistance to gas flow and sufficient preheating gas can be introduced to the preheating furnace. Further, by guiding the exhaust gas containing a large amount of unburned CO gas from the operating furnace into the preheating tower without passing through the combustion tower, heat removal due to water cooling in the combustion tower is reduced, and at the same time,
Exhaust gas can be introduced into the preheating furnace without secondary combustion in the combustion tower and secondary combustion can be performed in the preheating furnace, preheating with high-temperature exhaust gas is possible, and preheating effect can be improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an exhaust gas flow diagram of the two-vessel arc furnace of the present invention, and FIG. 2 is a vertical sectional view. In FIG. 1, A and B are a pair of two arc furnaces, and FIG.
The state of B furnace preheating is shown, and FIG. 1 (b) shows the state of A furnace operation and B furnace preheating.

In FIG. 1 (a), the high-temperature exhaust gas containing a large amount of unburned CO gas generated in the operating furnace 1 (A furnace) does not pass through the introduction duct 3 and the combustion tower 4 and goes through the preheating furnace 2 (B
Furnace, and preheats the scrap that has been charged into the preheating furnace 2 in advance. After that, the exhaust gas from the exhaust port 5 provided in the preheating furnace 2 enters the combustion tower 4 through the exhaust duct 6 and the bypass duct 7b, and is further drawn through the fixed duct 27 to a dust collector (not shown). It is preferable that the position of the furnace lid of the connected introduction duct 3 and the position of the discharge port 5 provided at the lower part of the furnace body are symmetrical so that they are located as far as possible from the preheating efficiency of scrap. Valves 8a, 8b, 11 having an opening / closing mechanism at the discharge port 5 part
a, 11b are provided, the valve on the preheating furnace side is opened when used as a preheating furnace, and the outside air from the companion flanges 28a and 28b to the furnace bodies 1 and 2 and the combustion tower 4 is used when used as a melting furnace. The valve on the melting furnace side is closed to block the intrusion.

Although the fixed exhaust duct 6 is installed and the exhaust port 5 is closed by the valves 8a and 8b in the example, a movable duct and an opening / closing lid may be used instead of the fixed duct and the valve. Small scraps / light weight scraps or lightweight dusts filled in the vicinity of the discharge port 5 may be sucked together with the exhaust gas from the discharge duct 5. For example, if the size is large, it is plate-shaped 500.
mm × 500 mm and weight is about 10 kg.
The sucked scraps are accumulated in a portion of the fixed duct 27 where stagnation occurs in the exhaust gas flow, such as a bending point and a confluence point, and the duct cross-sectional area decreases as the operation is repeated, which increases the resistance to the exhaust gas flow and hinders the operation. Will cause

In order to prevent this, two arc furnaces 1,
A discharge duct 6 connected to the second discharge port 5 is connected to the combustion tower 4 via a bypass duct 7b. The gas passage in the combustion tower 4 is connected to the front and rear of the bypass duct 7
b, it has an area several times larger than the cross-sectional area of the fixed duct 27, and scrap or dust settles down by gravity due to the decrease in gas flow velocity, or the inside of the combustion tower 4 is obstructed as shown in FIG. It is also effective to provide the plate 25 to collide and drop scraps and dust to collect them. Further, by providing an openable / closable gate 26 as shown in FIG. 2 in the lower part of the combustion tower 4, scrap and dust collected in the combustion tower 4 can be removed from the outside at any time.

FIG. 1 shows the flow of electric wiring and exhaust gas from the electric chamber 19 to the arc furnace according to the present invention. The furnace A is in the state of being electrically melted and the furnace B is being preheated. The wiring 21 extending from the furnace transformer 20 is used by a power source switch 22 to supply electricity to the furnace A or furnace B or to control the stoppage of electricity. It is connected to the upper movable electrode 17 via the power source switching device 22 and the wirings 23 and 24. Further, the wiring similar to that of the movable electrode 17 on the upper side is made between the furnace bottom electrode 16 and the furnace transformer 20. In addition, the valve 9 installed in the introduction duct 3
The a and 9b are not used in the normal operation and are always in the open state, and the purpose of installation will be described later.

The valve 10 is normally closed, and when it is necessary to operate only one of the arc furnaces for some reason, the valve 10 is operated to open so that the single furnace operation can be performed without any problem. For example, as shown in FIG.
When only the furnace is operated, the valves 9a and 10 are opened and the valves 9b, 8a, 8b, 11a and 11b are closed. At this time, the exhaust gas from the operating furnace passes through the introduction duct 3 and the bypass duct 7a and enters the combustion tower 4,
Then, the unburned CO gas is secondarily burned, and further drawn through a fixed duct 27 to a dust collector (not shown). Combustion tower 4
The former introduction duct 3 and bypass duct 7a are arranged to prevent dust in the exhaust gas from accumulating in the duct.
It is preferable to have a structure in which the dust is collected in the combustion tower 4 as in the case of preheating, the angle being equal to or greater than an angle.

In FIG. 2, A and B are a pair of two arc furnaces, the furnace body 12 is lined with a refractory material 13 and a water cooling panel 14, and scrap is charged into the furnace at the upper part of the furnace body 12. An openable / closable furnace lid 15 is arranged for this purpose. Further, a furnace bottom electrode 16 is arranged in the furnace bottom portion, and an arc 18 is generated between the furnace bottom electrode 16 and the movable electrode 17 above. In addition,
Although the introduction duct 3 is connected to the furnace lid 15 in the example, it may be connected to the furnace body 12.

Although the example of the embodiment shows a DC arc furnace as an example, it goes without saying that the present invention is also applied to an AC arc furnace, and one furnace transformer is used for each load side. The figure shows an arc furnace having a power source switching device capable of feeding or stopping electricity to the furnace body, which has two furnace lids and upper movable electrodes independently, but shows two furnace lids and upper movable electrodes. Needless to say, the present invention is also applied to an arc furnace in which each furnace body having a separate furnace transformer has a dedicated furnace transformer. It goes without saying that the present invention is also applied to an arc furnace having a shared furnace lid movable between the base furnace bodies and a movable electrode on the upper part.

[0018]

The present invention has the following effects. (1) Since the accumulation of scrap in the connecting duct can be prevented, a stable exhaust gas flow can be secured at all times without increasing the resistance to the exhaust gas flow for preheating, and it is more efficient and stable than the conventional technology. Pre-heating of scraps can be performed. (2) Since the scrap sucked into the introduction duct and the discharge duct can be collected by the combustion tower, it is not necessary to collect scraps accumulated in the duct. (3) High-temperature preheating can be performed by introducing high-temperature exhaust gas containing a large amount of unburned CO gas emitted from the operating furnace into the preheating furnace and causing secondary combustion in the preheating furnace. (4) High-temperature preheating can be performed by introducing the high-temperature exhaust gas discharged from the operating furnace into the preheating furnace without removing heat from the combustion tower. (5) Since stable scrap preheating can be performed by high-temperature exhaust gas as described above, highly efficient exhaust gas energy can be recovered, productivity can be improved by shortening melting time, and power consumption can be reduced by energy saving. Productivity costs can be reduced by reducing the electrode unit consumption.

[Brief description of drawings]

FIG. 1 is an exhaust gas flow diagram of a two-tank arc furnace of the present invention.

FIG. 2 is a vertical sectional view of the present invention.

[Explanation of symbols]

 1 A furnace main body 2 B furnace main body 3 introduction duct 4 combustion tower 5 discharge port 6 discharge duct 7a, 7b bypass duct 8a, 8b valve 9a, 9b valve 10 valve 11a, 11b valve 12 furnace body 13 refractory 14 water cooling panel 15 furnace Lid 16 Furnace bottom electrode 17 Movable electrode 18 Arc 19 Electric chamber 20 Furnace transformer 21,23,24 Wiring 22 Power switch 25 Baffle plate 26 Gate 27 Fixed duct 28a, 28b Companion flange

Claims (1)

[Claims] 1. In a two-tank type arc furnace in which two arc furnaces are alternately used for melting and preheating scrap, the exhaust gas generated from the melting furnace side of the two arc furnaces is used as a preheating gas to the preheating furnace side. It is connected by an introduction duct for introduction, and a preheating gas outlet on the smelting furnace side is provided with a lid or valve that shuts in the outside air from entering the furnace during melting, and a preheating gas outlet on the preheating furnace side. A two-tank arc furnace, characterized in that an exhaust duct connecting the exhaust port and the dust collector is provided in the chamber, and a bypass duct connecting the introduction duct and the exhaust duct to the combustion tower.