JP2000008115A - Dissolution method of cold iron source - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To obtain molten steel by melting a cold iron source such as iron scrap and reduced iron very efficiently. A method for melting a cold iron source (11) in a melting furnace (1) using both oxygen burner heating and arc heating,
First, the heating of the cold iron source is started only with the oxygen burner 7, and then, at least after the melting of the cold iron source, the heating is switched from the oxygen burner heating to the heating by the arc generated at the electrodes 5 and 6. Is heated and dissolved. At that time, a preheating tank directly connected to the melting furnace is provided, and the exhaust gas from the melting furnace is introduced into the preheating tank to preheat the cold iron source, thereby more efficiently heating and heating.
Can be dissolved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently melting a cold iron source such as iron scrap or reduced iron in a melting furnace by a combination of oxygen burner heating and arc heating.

[0002]

2. Description of the Related Art In recent years, due to resource saving and environmental problems, instead of an integrated iron making method using a blast furnace and a converter mainly made of iron ore,
Steel production by the steelmaking method of remelting high-yield iron scrap is increasing. As a furnace for melting the iron scrap, an arc furnace using electric energy as a heat source and a melting furnace using combustion heat of fossil fuel by an oxygen burner are generally known.

[0003] In an arc furnace, a cold iron source such as iron scrap is heated by arc heat generated from an electrode. However, since a large amount of power is consumed, for example, in order to save power consumption, for example,
As disclosed in JP-A-7-190629, a method of preheating a cold iron source by introducing high-temperature exhaust gas generated in an arc furnace into a preheating tank provided with a cold iron source is disclosed. 7
As disclosed in Japanese Patent No. 26318, a method is used in which inexpensive carbon-containing fuel and oxygen-containing gas are blown into a furnace from an auxiliary burner during arc heating to utilize the heat of combustion of the carbon-containing fuel.

[0004] Heavy oil,
A fossil fuel such as kerosene, pulverized coal, propane gas, or natural gas is burned to heat a cold iron source. In order to use combustion heat efficiently, for example, as disclosed in JP-A-56-161478. A method of preheating a cold iron source with a high-temperature combustion gas is provided by directly connecting a preheating tank of a cold iron source above a melting furnace provided with an oxygen burner. Note that the oxygen burner has advantages in that the amount of combustion gas is smaller than that of a burner using air, so that the amount of heat taken out of the combustion gas discharged outside the furnace is small and the amount of heat transferred to the furnace is high.

[0005]

Although the above method reduces the electric power consumption in the arc furnace, it is still about 400 kW / t at present, which is one of the main causes of the increase in the production cost.

In a melting furnace using oxygen burner heating,
When the cold iron source is in a solid state in the early stage of melting, the contact area between the combustion gas and the cold iron source is large, so that it can be heated more efficiently than arc heating.・ Liquid coexisting or dissolving into a liquid state, heat transfer efficiency is poor because the transfer of combustion heat of fossil fuel is performed only on the iron bath surface, and as a result, the manufacturing cost is not much different from the case of melting with an arc furnace, From the viewpoint of effective use of heat, it is still not enough.

[0007] The present invention has been made in view of the above circumstances,
An object of the present invention is to provide a method for obtaining molten steel by extremely efficiently melting a cold iron source such as iron scrap and reduced iron in a melting furnace.

[0008]

A method for melting a cold iron source according to the first invention is a method for melting a cold iron source in a melting furnace using both oxygen burner heating and arc heating. Start heating the cold iron source, and then switch the oxygen burner heating to arc heating at least after the cold iron source burns out, heat and melt the remaining cold iron source, and raise the temperature of the iron bath to a predetermined temperature. It is characterized by hot water.

A method for melting a cold iron source according to a second aspect of the present invention is the method according to the first aspect, wherein a preheating tank directly connected to the melting furnace is provided, and the exhaust gas of the melting furnace is introduced into the preheating tank to preheat the cold iron source. It is characterized by the following.

In the present invention, a melting furnace capable of performing both oxygen burner heating and arc heating is used, and heating is performed only by the oxygen burner during a period in which a solid state cold iron source is mainly used in the initial stage of melting. Since the temperature of the cold iron source in the initial stage of melting is relatively low and the main body is in a solid state, the contact area of the oxygen burner with the combustion gas is large, and the combustion gas freely passes between the cold iron sources. As a result, the heat of combustion of fossil fuels is transferred to the cold iron source very efficiently, and can be heated more efficiently than arc heating.

When the melting proceeds and an iron bath is formed in the melting furnace, the remaining solid-state cold iron source settles down in the iron bath due to a difference in specific gravity. It will be buried inside and will be in a solid / liquid state. The point at which all of this cold iron source is buried in the iron bath is called burn-through. When the cold iron source begins to be buried in the iron bath, the area of contact between the cold iron source and the combustion gas of the oxygen burner gradually decreases, reducing the heat transfer efficiency. After the burn-through buried in the fossil fuel, the combustion heat of the fossil fuel is transmitted only on the surface of the iron bath, so that the heat transfer efficiency becomes extremely poor. Therefore, at least after burn-through, heating is switched from oxygen burner heating to arc heating. The present inventors have confirmed that when the cold iron source is melted down, arc heating has higher heat transfer efficiency than oxygen burner heating.

As described above, in the present invention, the cold iron source is melted by a heating method having a high heat transfer efficiency in accordance with the melting time, so that a state having a good heat transfer efficiency can be maintained from the beginning to the end of the melting. Energy required for heating and melting can be greatly reduced.

Furthermore, a preheating tank for a cold iron source is provided directly connected to the melting furnace, and the cold iron source is preheated in the preheating tank by the exhaust gas of the melting furnace, so that the combustion heat of the fossil fuel is effectively supplied to the cold iron source. It is possible to further improve energy efficiency.

The oxygen burner used in the present invention is a method of burning high-temperature flames by burning fossil fuels such as heavy oil, kerosene, pulverized coal, propane gas and natural gas using oxygen or oxygen-enriched air. Things.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of a melting facility showing one example of an embodiment of the present invention.

In FIG. 1, a furnace wall 3 having a water-cooled structure is disposed on an upper part of a furnace main body 2 having a furnace bottom electrode 5 provided at the bottom and having an inner opening made of a refractory. It is covered with a furnace lid 4 having a free water cooling structure. The melting furnace 1 is provided with an oxygen burner 7 penetrating through the furnace wall 3 and a graphite upper electrode 6 penetrating through the furnace lid 4 and vertically movable into the furnace main body 2. Although only one oxygen burner 7 is shown in the figure, a plurality of oxygen burners 7 are provided in the circumferential direction of the melting furnace 1, and oxygen or oxygen-enriched fossil fuels such as heavy oil, kerosene, pulverized coal, propane gas, and natural gas are provided. Furnace body 2 by air
Burn in. The bottom electrode 5 and the top electrode 6 are connected to a DC power supply (not shown) to generate an arc between the bottom electrode 5 and the top electrode 6.

An oxygen blowing lance 9 and a carbon material blowing lance 10 are provided which penetrate through the furnace wall 3 and can move obliquely up and down in the furnace body 2, and oxygen is introduced into the furnace body 2 from the oxygen blowing lance 9. Then, carbon materials such as coke, char, coal, and charcoal are blown into the furnace body 2 from the carbon material blowing lance 10 using air, nitrogen gas or the like as a carrier gas. Further, the projecting portion 2a of the furnace body 2 has a furnace bottom, the exit side of which is pressed by a door 15 and filled with a mud agent on the inside thereof, and the exit side by a door 17 on the side wall thereof. Slag outlet 1 which is pressed down and filled with mud inside
6 is provided, and the furnace lid 4 is provided with a duct 18 connected to a dust collector (not shown).

In the operation of the melting furnace 1, first, the furnace lid 4 is opened, and a cold iron source 11 such as iron scrap, direct reduced iron, and pig iron is charged into the furnace body 2, and the furnace lid 4 is closed. Next, the fossil fuel is burned by the oxygen burner 7 and the cold iron source 1 is burned.
Heat 1 The cold iron source 11 near the oxygen burner 7
It is directly heated and melted by the flame 7a of the oxygen burner 7,
In addition, the cold iron source 11 located away from the oxygen burner 7 is efficiently heated by the combustion gas flowing toward the duct 18 in the melting furnace 1. During heating by the oxygen burner 7, the upper electrode 6 is blown with oxygen to expand the furnace space of the melting furnace 1 to facilitate heating of the cold iron source 11 and to prevent damage to the equipment. It is preferable that the lance 9 and the carbon material blowing lance 10 are kept on standby outside the furnace main body 2.

The cold iron source 11 is heated and melted, and the iron bath 12 is melted.
Is formed and the amount of the cold iron source 11 in the melting furnace 1 decreases, the furnace lid 4 is opened again, the cold iron source 11 is additionally charged, the furnace lid 4 is closed, and heating by the oxygen burner 7 is restarted. . This additional charging is repeated several times, and a predetermined amount of the cold iron source 11 is charged into the melting furnace 1. However, when the capacity of the melting furnace 1 is large and a predetermined amount of the cold iron source 11 is possible in the first charging, no additional charging is necessary. The predetermined amount of the cold iron source 11 is
This is the amount of the cold iron source 11 corresponding to the amount of the iron bath 12 for one heat or a plurality of heats.

A predetermined amount of the cold iron source 11 is charged into the melting furnace 1, and the heating by the oxygen burner 7 is further continued. Eventually, the iron bath 12 increases, and all the cold iron sources 11 are buried in the iron bath 12 due to the difference in specific gravity and melted down. When the amount of the cold iron source 11 in the free space in the furnace is reduced, the upper electrode 6 is previously inserted into the furnace main body 2, and a DC current is applied to the furnace bottom electrode 5 and the upper electrode 6 at least after burn-through. Power supply and upper electrode 6
An arc is generated between the iron bath 12 and
Dissolve the cold iron source 11 remaining therein. Oxygen burner heating is stopped with this arc heating. Before the melting of the cold iron source 11, the cold iron source 11 in the free space in the melting furnace 1 was used.
When the heat transfer efficiency of the combustion heat of the oxygen burner 7 is reduced and the arc heating is more advantageous, if the oxygen burner heating is switched to the arc heating, the cold iron source 11 can be more efficiently heated and heated. Can be dissolved. In addition, cold iron source 1
Although arc heating is a principle after burn through 1, it is difficult to strictly classify in actual operation, and it is acceptable that oxygen burner heating is allowed for several minutes after burn through.

In the furnace body 2, a flux such as quicklime or fluorite is charged in advance together with the cold iron source 11 and melted by heating with an oxygen burner to form a molten slag 13 on the iron bath 12. The oxidation of the iron bath 12 is prevented and the temperature of the iron bath 12 is maintained. If the amount of the molten slag 13 is too large, it can be discharged from the slag port 16 even during operation.

If the amount of the cold iron source 11 remaining in the free space in the furnace is reduced and the oxygen blowing lance 9 and the carbon material blowing lance 10 can be immersed in the molten slag 13, the oxygen blowing lance 9 and the carbon material blowing It is preferable that the lance 10 is inserted into the furnace main body 2 and its tip is immersed in the molten slag, and oxygen and carbon material are blown into the molten slag 13. The carbon material suspended in the molten slag 13 reacts with the blown oxygen to generate heat of combustion, thereby acting as an auxiliary heat source. In addition, the reaction product CO forms the molten slag 13, so that arc heating is performed. In this case, the generated arc is wrapped in the molten slag 13 and the heat transfer efficiency of the arc increases. The amount of carbon material to be blown is determined according to the amount of oxygen to be blown. That is, a carbon material is added in an amount equivalent to the chemical equivalent of the oxygen to be blown. If the amount of carbon material is smaller than the amount of oxygen to be blown, the iron bath 12 is excessively oxidized, which is not preferable.

By the arc heating, all the cold iron source 11 remaining in the iron bath 12 is melted, and then the iron bath 12 is refined to obtain a molten steel having a desired composition, and a predetermined temperature convenient for tapping. Heat up to Thereafter, the melting furnace 1 is tilted, and molten steel is discharged from the tapping port 14 into a holding vessel (not shown).
After tapping, the cold iron source 11 is charged into the furnace body 2 again, and the oxygen burner heating and the arc heating are performed as described above.
To continue operations.

By dissolving the cold iron source 11 in this manner, a state of good heat transfer efficiency can be always maintained from the beginning to the end of melting, and the energy required for heating and melting can be greatly reduced. it can.

FIG. 2 is a schematic sectional view of a melting facility showing another embodiment of the present invention. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted. In the present embodiment, the preheating tank 8 is disposed directly connected to the furnace lid 4, and the melting furnace 1 and the preheating tank 8 are directly connected. A duct 18 is provided at the upper end of the preheating tank 8, and the duct 18 is connected to a dust collector (not shown). High-temperature exhaust gas generated in the melting furnace 1 is sucked through the preheating tank 8 and the duct 18 in this order. The cold iron source 11 inserted into the preheating tank 8 is preheated through an openable / closable cold iron source inlet 19 provided at the uppermost part of the preheating tank 8. The oxygen burner 7, the oxygen blowing lance 9, and the carbon material blowing lance 10 penetrate the furnace lid 4.

In the operation of the melting furnace 1 having the preheating tank 8, first, the cold iron source 11 is charged into the preheating tank 8 from the cold iron source supply port 19. Cold iron source 11 charged in preheating tank 8
Is also charged into the melting furnace 1. Thus, the preheating tank 8 is filled with the cold iron source 11. In order to uniformly load the cold iron source 11 into the melting furnace 1, the furnace lid 4 may be opened and the cold iron source 11 may be charged into the melting furnace 1 on the opposite side of the preheating tank 8. Then, heating by the oxygen burner 7 is started. Since the combustion gas of the oxygen burner 7 passes through the preheating tank 8, not only the heating of the cold iron source 11 in the melting furnace 1 but also the preheating of the cold iron source 11 in the preheating tank 8 are performed at the same time.

When the cold iron source 11 is heated and melted, the cold iron source 11 in the preheating tank 8 falls freely into the melting furnace 1 according to the amount melted in the melting furnace 1 and decreases. In order to compensate for this decrease, the cold iron source 11 is supplied to the preheating tank 8.
The supply of the cold iron source 11 into the preheating tank 8 is performed continuously or intermittently so that the state where the cold iron source 11 exists continuously in the melting furnace 1 and the preheating tank 8 is maintained. Cold iron source 11 to preheating tank 8
It is not necessary to stop the heating of the oxygen burner 7 even when the additional gas is charged, and the oxygen burner 7 is continuously heated. Thus, a predetermined amount of the cold iron source 11 is charged into the preheating tank 8. However, if the capacity of the preheating tank 8 is large and a predetermined amount of the cold iron source 11 is possible in the first charging, no additional charging is necessary.

A predetermined amount of the cold iron source 11 is charged into the preheating tank 8 and heating by the oxygen burner 7 is continued. Thereafter, the operation of the melting furnace 1 having no preheating tank 8 is started. The operation will be performed according to the description, and the description will be omitted.

By dissolving the cold iron source 11 in this manner, the state of good heat transfer efficiency can be maintained at all times from the beginning to the end of melting, and the cold iron source 11 can be preheated. Energy required for melting can be further reduced.

In the above description, arc heating using a DC power supply has been described. However, the present invention can be applied to arc heating using an AC power supply without any problem. Although the preheating tank 8 has been described as being connected to the melting furnace 1 without boundaries, a plurality of openable and closable iron grids are provided in the preheating tank 8, and the cold iron source 11 is preheated on the iron grid, and the preheated cold iron is heated. Even if the preheating tank is of a type in which the source 11 is sequentially dropped on the lower iron grate and the cold iron source 11 that is finally preheated to the melting furnace 1 is charged, as long as the preheating tank is directly connected to the melting furnace. The present invention can be applied without hindrance. Further, it is needless to say that a difference in the number of the upper electrodes 6, the structure of the furnace bottom electrode 5 and the like, a difference in a charging method of the cold iron source, and the like do not hinder the present invention.

[0031]

[Embodiment 1] An embodiment of the melting equipment shown in FIG. 1 will be described. 30 tons of iron scrap was charged into a melting furnace having an inner diameter of 3.3 m and a height of 2.8 m, and heating was started with four oxygen burners using heavy oil as fuel and a fuel oil combustion amount of 700 l / Hr to form an iron bath. Accordingly, iron scrap was additionally charged once and a total of 50 tons was charged. After confirming the burn-through of the iron scrap, the heating was switched from oxygen burner heating to arc heating. The arc heating was performed using a graphite electrode having a diameter of 24 inches and a DC power supply of 400 V and 60 KA.
Immediately after switching to arc heating, 30 Nm ³ / min of oxygen was blown into the molten slag from the oxygen blowing lance, and 30 kg / min of coke was blown from the carbon material blowing lance.
Then, the temperature was raised to 1620 ° C., and the carbon concentration was 0.12 wt.
% Molten steel. In about 60 minutes, 50 tons of molten steel were obtained.

As a comparison, the melting equipment shown in FIG. 1 was used, and the heating conditions were changed to a case of only oxygen burner heating (Comparative Example 1) and a case of only arc heating (Comparative Example 2). The conditions were the same as in Example 1, and 50 tons of molten steel were manufactured. Table 1 shows a comparison of various basic units, unit prices, and manufacturing costs of Example 1 and Comparative Examples 1 and 2 according to the present invention.

[0033]

[Table 1]

As shown in Table 1, in Example 1, it can be dissolved at a power consumption rate of 95 kWh / t, an oxygen consumption rate of 70 Nm ³ / t, a heavy oil consumption rate of 38 l / t, and the production cost is 324.
The cost was 5 yen / t, and the production cost was significantly reduced as compared with Comparative Example 1 and Comparative Example 2. [Embodiment 2] An embodiment in the melting facility shown in Fig. 2 will be described. 90 tons of iron scraps are collectively charged into a preheating tank 2.5 m wide, 4.5 m long and 6 m high directly connected to a melting furnace with an inner diameter of 6.2 m and a height of 3.5 m, and heavy oil burning using heavy oil as fuel Heating was started with eight oxygen burners having a volume of 700 l / Hr. At the time when a small amount of iron scrap remained in the free space in the furnace immediately before the iron scrap burned down, the heating was switched from oxygen burner heating to arc heating. The arc heating was performed using a graphite electrode having a diameter of 28 inches and a DC power supply of 500 V and 90 KA. Immediately after switching to arc heating, oxygen was injected from the oxygen blowing lance at 60 Nm ³ / min,
60 kg / min of coke was blown into the molten slag from a carbon material blowing lance. Then, the temperature was raised to 1620 ° C., and molten steel having a carbon concentration of 0.12 wt% was poured. About 60
In 90 minutes, 90 tons of molten steel were obtained.

As a comparison, the melting equipment shown in FIG. 2 was used, and the heating conditions were changed to those using only oxygen burner heating (Comparative Example 3) and those using only arc heating (Comparative Example 4). Produced 90 tons of molten steel in the same manner as in Example 2. Table 2 shows a comparison of various basic units, unit prices, and manufacturing costs of Example 2 and Comparative Examples 3 and 4 according to the present invention.

[0036]

[Table 2]

As shown in Table 2, in Example 2, 90 kWh / t of electric power consumption, 65 Nm ³ / t of oxygen consumption, and 35 l / t of heavy oil consumption can be dissolved, and the production cost is 304.
The cost was 5 yen / t, and the manufacturing cost was significantly reduced as compared with Comparative Examples 3 and 4.

[0038]

According to the present invention, since the cold iron source can be melted while maintaining good heat transfer efficiency from the beginning to the end of melting, the energy required for heating and melting is greatly reduced. And the manufacturing cost can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a melting facility showing one example of an embodiment of the present invention.

FIG. 2 is a schematic sectional view of a melting facility showing another example of the embodiment of the present invention.

[Description of Signs] 1 Melting furnace 2 Furnace body 3 Furnace wall 4 Furnace lid 5 Furnace bottom electrode 6 Upper electrode 7 Oxygen burner 8 Preheating tank 9 Oxygen blowing lance 10 Carbon material blowing lance 11 Cold iron source 12 Iron bath 13 Melting slag

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ryuji Yamaguchi 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term in Nihon Kokan Co., Ltd. (Reference) 4K014 CB01 CB07 CC01 CC05 CD01 4K063 AA04 BA02 CA01 CA06 GA02 GA09

Claims (2)

[Claims] 1. A method for melting a cold iron source in a melting furnace using a combination of oxygen burner heating and arc heating, wherein heating of the cold iron source is started only by oxygen burner heating, and then at least melting of the cold iron source is performed. A method for dissolving a cold iron source, comprising: switching the oxygen burner heating to arc heating after dropping, heating and melting the remaining cold iron source, and raising the temperature of the iron bath to a predetermined temperature to discharge hot water. 2. The method for melting a cold iron source according to claim 1, wherein a preheating tank directly connected to the melting furnace is provided, and exhaust gas from the melting furnace is introduced into the preheating tank to preheat the cold iron source. .