JPH06228623A - Steelmaking method having small energy consumption - Google Patents

Abstract

PURPOSE:To efficiently produce molten steel with a small quantity of energy, by using iron source of iron scrap, etc., as the main raw material. CONSTITUTION:At the time of obtaining the molten steel by the equipment combining a cupola 1, converter and scrap preheating device, combustion heat obtd. by burning CO generated in the cupola is given to the raw material of the iron scrap 7 in the furnace. Further, this heat is used for drying and preheating the charged raw material and also, the exhaust gas containing CO generated from the converter is recovered and supplied to a heat exchanger and the air for blasting into the cupola is made to be hot blast.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steelmaking method using a small amount of energy, more specifically, a steelmaking method for producing molten steel by using an iron source such as iron scrap as a main iron raw material and using a cupola and a converter. Pertain to.

[0002]

2. Description of the Related Art As a steelmaking method using iron scrap or the like as an iron source, a method using an arc electric furnace has been the mainstream.
In this method, a large current is passed through a thermal scrap through a graphite electrode, and the scrap is melted by the heat generated in the scrap. In addition to a conventional AC electric furnace that uses three graphite electrodes to pass three-phase AC, a DC electric furnace that passes DC between one graphite electrode and a steel electrode installed at the bottom of the furnace Has been actively used in recent years.

A process for producing molten steel using iron scrap as an iron source using only a converter has also been proposed. In this process, iron scrap is charged into a converter, fossil fuels such as pulverized coal and coke are burned with oxygen, and the heat of combustion melts the scrap. The method of obtaining molten steel by continuing oxygen blowing in the same converter, or the method of producing molten iron in one converter and decarburizing it with oxygen in another converter to obtain molten steel is adopted. There is.

Conventionally, as a facility for melting iron scrap to produce cast iron for casting, there is a solid type furnace such as a cupola, and a method for obtaining molten steel by combining the cupola with a converter has been proposed. For example, Japanese Patent Laid-Open No. 61-8430
According to the method described in Japanese Patent Publication No. 9, the cupola and the converter are connected to each other, the exhaust gas from the converter is introduced into the coke filling portion of the cupola, and the exhaust gas is burned by the exothermic reaction at the tuyere portion of the cupola, thereby producing the total energy for producing molten steel. -It is intended to reduce the intensity.

There is also a conventional method in which the cupola and the converter or the open hearth are operated simultaneously and independently, and the molten pig iron produced in the cupola is decarburized and refined in the converter or the open hearth. There was no idea to use the converter exhaust gas to reduce the coke intensity of cupola, and each process was operating independently.

[0006]

The inventors of the present invention compared the energy consumed by various steelmaking methods using iron scrap or the like as an iron source, and found that the conventional electric furnace steelmaking method was
Electric power generated from fossil fuel as primary energy is the main melting energy, and the energy conversion efficiency at this time is at most 40%, so the total energy intensity is large.

On the other hand, the converter method for melting an iron source such as iron scrap in the converter consumes more energy than the electric furnace steelmaking method. Certainly, the total energy intensity can be reduced by recovering and utilizing CO contained in the converter exhaust gas. But,
There is a limit to the recovery rate of converter exhaust gas, which is at most about 85%. Since this exhaust gas recovery equipment is complicated and expensive,
It cannot be said that it is an economical process unless it is a very large-scale steel mill using iron scrap as an iron source. Above all, this process is 300 kg / ton per ton of scrap.
Since n carbonaceous materials are used, a large amount of CO ₂ is generated, which is not preferable for global environment protection.

Further, the steelmaking method by combining a cupola suitable for melting scrap with a converter or open hearth is superior to the electric furnace steelmaking method and the converter method in terms of energy consumption. However, it cannot be said that the exhaust gas from the converter is being used efficiently. For example, in the method described in Japanese Patent Laid-Open No. 61-84309, the cupola and the converter are mechanically connected, and the exhaust gas containing CO from the converter is directly introduced into the cupola to reduce the energy consumption. Is proposed to reduce.

However, in the first place, the cupola is a melting facility for continuous operation, whereas the converter is originally a batch-type process. In the method described in JP-A-61-84309, in order to avoid this contradiction, the converter is operated continuously and a siphon type molten steel discharging device is installed. In this method, in order to continuously discharge molten steel, it is necessary to always decarburize and store the molten metal in the converter to a molten steel state, and it is necessary to store molten steel at least at 1600 ° C or higher. Therefore, it is unrealistic because the heat loss from the furnace body is large, the melting loss of the converter refractory is large, and it is not economical. Further, in order to intermittently discharge the molten steel, it is necessary to provide a complicated mechanism at the tapping hole portion, which is also not realistic.

Therefore, the cupola and the converter are connected (connected).
It is desirable to use a method in which each is operated independently and the energy used between them is minimized.

[0011]

The present invention relates to a process for solving the above-mentioned problems and efficiently melting scrap with a small amount of energy to obtain molten steel, which is an iron source such as iron scrap. Is melted in a cupola and the resulting molten metal is refined in a converter to obtain molten steel. In the cupola operation, CO generated from the cupola is burned to CO _{2 in the} furnace as much as possible, Is supplied to the iron source such as the raw material iron scrap in the furnace to lower the exhaust gas temperature, and the low temperature exhaust gas is used for drying and preheating the charged raw material, while in the converter refining operation, C generated from the converter
It is a steelmaking method with a small energy consumption, characterized in that exhaust gas containing O is recovered and the air to be blown to the cupola is supplied to a heat exchanger for making hot air.

The structure and operation of the means of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is an explanatory view showing the flow of iron and gas in each equipment used for carrying out the present invention, and FIG. 2 is a longitudinal sectional view showing the main part of the cupola of FIG. In the figure, reference numeral 1 is a cupola body, 2 is a hot air generating facility, 3 is a cupola exhaust gas treatment facility, 4 is a hot metal holding furnace, 5 is a converter, 6 is an unburned recovery device for converter exhaust gas, 7 is scrap, 8 Is
And 9 are scrap preheating drying equipment, 10 is a gas holder, 11 is a ventilation duct, and 12 is an exhaust gas duct.

In FIG. 1, the material for charging the cupola body 1 is an iron source of at least one of steel scrap, pig iron scrap, cold pig iron, reduced iron, and iron oxide, and coke, agglomerated coal, and fine powder. At least one of charcoal, fuel gas, and carbon-containing material is used as a heat source. As the cupola equipment, a normal cupola can be used, but in order to efficiently achieve the object of the present invention, for example, a multi-stage tuyere is provided, and oxidizing gas and coke blown from the tuyere at the bottom are used. CO, which is a reaction product gas with the carbonaceous material, is burned to CO ₂ by the oxidizing gas blown from the tuyere at the top. Furthermore, to increase efficiency,
The scrap filling height is made high so that heat exchange with high-temperature CO ₂ gas can be sufficiently achieved (at least 2 m). As shown in FIG. 2, carbonaceous material such as coke is in the middle of the scrap filling layer. It is best to use a special type of cupola as supplied by The reason for this is that if scrap and coke coexist, the high temperature CO ₂ gas reacts with the coke (solution loss reaction), and again becomes CO gas, which is easily discharged outside the furnace. This is because it does not meet the purpose of the invention.

The hot metal discharged from the cupola body 1 in FIG. 1 is temporarily stored in the hot metal holding furnace 4 and is intermittently discharged in conformity with the converter operation of the next process. Also,
In the hot metal holding furnace 4, the temperature and components are made uniform.

The hot metal discharged from the hot metal holding furnace 4 is charged into a converter 5 and decarburized and blown. When molten steel having a low sulfur concentration ([% S]) in the hot metal is required, hot metal desulfurization treatment is performed with a desulfurizing agent such as lime, soda ash, and calcium carbide before charging into the converter.

As the converter 5, a decarburizing blowing converter used in a normal steelmaking process can be used. In particular, when iron scrap is also mixed as an iron source in this converter, or when improvement in the yield of blowing is expected, it is desirable to use a generally used top-bottom blowing converter.

The exhaust gas recovery equipment 6 is preferably a so-called unburned gas recovery equipment 6 (for example, OG equipment) having a structure in which exhaust gas containing CO generated from the converter 5 is not easily combusted with air above the furnace. The exhaust gas collected from the converter 5 is stored in the exhaust gas holder and used for various purposes. In the case of the present invention, the recovered CO gas is guided to the hot-air generation facility 2 for cupolas, the converter exhaust gas containing CO gas as a main component is burned with air as air, and the oxidizing gas is blown to the cupola body 1. , Generally heating air or oxygen-enriched air.

Exhaust gas from the cupola body 1 is dust-removed by the cupola exhaust gas treatment equipment 3, but in the case of the present invention, it is a gas containing CO ₂ and N ₂ as a main component at a low temperature, so that it is used as a fuel gas. Is not very useful. However, since a small amount of CO gas can be burned to be used for drying or preheating the scrap 7 which is a charging raw material, or even for low-temperature exhaust gas, it can be used for drying or preheating scrap as well. Lead to the scrap preheat drying equipment 9.

As shown here, the coke used in the cupola body 1 is burned to CO ₂ in the cupola as much as possible and sufficiently exchanged heat in the furnace until the exhaust gas temperature becomes low. It is possible to remarkably reduce the carbon source unit of the heat source as described below. In a large cupola, the exhaust gas from the cupola usually contains 10% or more of CO, and this gas is guided to a combustion facility to be burned and heat exchanged with the air for blowing to heat the air blown to the cupola body 1. This method is a good means of reducing the carbonaceous material consumption rate when producing cast iron from cupola alone. However, the molten steel manufacturing process in combination with the converter, which is the object of the present invention, is disadvantageous in terms of energy because the exhaust gas from the converter cannot be used.

Further, in the method of directly introducing the converter exhaust gas to the cupola as shown in the prior art, the operation matching between the cupola and the converter cannot be obtained as described above, and the actual operation cannot be established. Also, in order to force matching, the converter must be operated continuously, which is an unrealistic process.

As described above, in the case of the present invention in which the material flow and the energy flow of the raw material, fuel and exhaust gas have been thoroughly examined, the basic unit of the carbonaceous material used is greatly reduced, and therefore the iron scrap 1 The energy required to dissolve tonnes is minimized and the CO ₂ gas produced can be significantly reduced compared to other processes.

[0023]

EXAMPLE An example of the operation according to the present invention, which is carried out by combining the respective equipments of the cupola body 1, the converter 5, and the scrap preheating drying equipment 9 shown in FIG. 1, will be described. The raw material used was steel scrap and was charged at a rate of 15 ton / hr. At the same time, 100 kg of coke was first mixed with 1 ton of steel scrap and the operation was started. After about 2 hours, 27 tons of hot metal as the component of "cupola hot metal" shown in Table 1 was stored in the hot metal holding furnace 4, and the hot metal was discharged into a ladle. At the time of discharging, 57 kg of soda ash was placed in front of the ladle for desulfurization to obtain the components of "charged hot metal" in Table 1.

Oxygen top blowing, inert gas bottom blowing 3
4 ton of iron scrap was charged in advance to the 0 ton top-bottom blowing converter, 27 ton of the hot metal was charged therein, and the converter decarburization blowing was started. During the blowing, the exhaust gas was recovered in an unburned state, and CO gas corresponding to 1130 Nm ³ was recovered in the gas holder-10. Simultaneously with the start of recovery, the CO gas in the gas holder 10 was introduced into the hot air generating facility 2 of the cupola body 1 and burned to obtain hot air having a blowing temperature of 600 ° C. Table 1 also shows the blow-stop components of the converter.

[0025]

[Table 1]

In the operation by the cupola shown in FIG. 2, when the blowing of hot air from the blowing duct 11 is started, the exhaust gas duct 12 is burned to CO ₂ and has a low temperature due to heat exchange.
Are discharged from the cupola body 1. It is possible to gradually reduce the coke rate by adjusting the blowing temperature and amount. At 4 hours after the start of the operation of the cupola body 1, even if the coke ratio was reduced to 65 kg per ton of steel scrap, the molten iron having an average temperature of 1520 ° C was stably fed for 15 t.
It could be obtained at a rate of on / hr.

At this point, the CO concentration in the cupola exhaust gas was 2 to 5%, and the average temperature was 152 ° C. This exhaust gas was mixed with air and burned under a pilot burner to obtain a preheating gas of about 300 ° C. This preheating gas was introduced to the scrap preheating drying facility 9 and used for drying and preheating the charging raw material scrap. With this equipment, the iron scrap just before charging was heated to about 170 ° C. on average.

The above process is one cupola of cupola.
It continues until two months after the end of the session, 1500
Molten steel of 0 ton was obtained. The amount of coke used per ton of steel scrap is 67 kg when averaging this campaign.
Met.

It has been confirmed that the amount of coke used is less than that of the above-mentioned conventional technique (Japanese Patent Laid-Open No. 61-84309), and the process is economical and produces a small amount of CO ₂ . In addition, the primary energy
Converted energy per 1 ton of molten steel is about 8
It could be reduced to 0%.

[0030]

As described above in detail, according to the present invention, when the iron source such as iron scrap is melted in the cupola and the obtained molten metal is refined in the converter to obtain the molten steel, the cupola is operated in the cupola operation. As much as possible, the CO generated from the furnace is burned up to CO ₂ in the furnace, the combustion heat is given to the iron source such as raw material iron scrap in the furnace to lower the exhaust gas temperature, and the low temperature exhaust gas is charged as the charging raw material. In the converter refining operation, the exhaust gas containing CO generated from the converter is collected and supplied to a heat exchanger for converting the air blown to the cupola into hot air.

In the present invention, a cupola, a converter, and a scrap preheating drying equipment are combined so that the material flow and the heat flow are optimized, that is, the converter exhaust gas is used as the fuel for the hot-blast stove of the cupola, and the cupola is used. Since the maximum heat exchange was performed and the exhaust gas from the cupola was used to preheat the charging raw material, it was possible to establish a steelmaking method with a very low coke consumption rate.

Further, since the present invention directly utilizes the combustion heat of the carbonaceous material, the primary energy
It is an excellent process as a steelmaking method with low unit consumption and low CO ₂ generation.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the flow of iron and gas in each facility used when carrying out the present invention.

FIG. 2 is a vertical sectional view showing a main part of the cupola of FIG.

[Explanation of symbols]

 1 Cupola main body 2 Hot air generating equipment 3 Cupola exhaust gas treatment equipment 4 Hot metal holding furnace 5 Converter 6 Converter unburned gas recovery equipment 7 scrap 8 coke 9 scrap preheat drying equipment 10 gas holder 11 air duct 12 exhaust gas duct

Claims (1)

[Claims] 1. When melting an iron source such as iron scrap in a cupola and refining the resulting molten metal in a converter to obtain molten steel, in the cupola operation, CO generated from the cupola is kept in the furnace as much as possible. together by burning up CO ₂ giving the combustion heat in the furnace iron source such as the raw material iron scrap to lower the exhaust gas temperature at the drying-in charging the raw material of this low temperature exhaust gas
While utilizing for preheating, in the converter refining operation, the exhaust gas containing CO generated from the converter is recovered and supplied to a heat exchanger for converting the air blown to the cupola into hot air. Less steelmaking method.