JP6763227B2 - Manufacturing method of reduced iron and manufacturing method of molten steel - Google Patents

Description

The present invention relates to a manufacturing method and a molten steel producing method of the reduced iron, particularly, for producing reduced iron or molten steel in combination with blast furnace, a shaft furnace or a fluidized bed reduction furnace using coke oven gas as a reducing agent about the.

In the large-scale blast furnace method based on a large-scale blast furnace, hot metal is produced by charging the sintered ore obtained by firing iron ore in a sintering furnace and coke produced by steaming coking coal in a coke oven into the blast furnace. , Iron ore is smelted with oxygen in a converter to produce molten steel. At that time, the coke oven gas (COG) generated in the coke oven and the blast furnace gas (BFG) generated in the blast furnace have conventionally been used as fuel for a heating furnace in a lower process such as hot spreading or for private power generation.

However, in the large-scale blast furnace process, the operation becomes unstable unless a certain proportion or more of high-quality iron ore and high-quality coking coal are mixed. Therefore, when faced with the deterioration of raw materials predicted in the near future, the operating specifications There is a concern that the operation will worsen or the operation will become difficult. For example, from the viewpoint of ensuring the strength of sinter, there is a limit to the mixing ratio of powder ore. Therefore, considering the deterioration of raw materials such as iron ore and coking coal that can be obtained in Japan in the near future, the high-efficiency iron-making method using large-scale blast furnaces and high-quality raw materials, which are currently the mainstream, will continue in the future. The possibility is small, and it is considered necessary to use a process such as a shaft furnace that can use inferior raw materials together.

Further, COG is a strongly reducing gas containing about 50 to 55% of hydrogen and having an ability to reduce iron oxide by itself, and the value of COG cannot be fully utilized only by burning it as fuel. In other words, the current blast furnace method leaves room for optimization as a steelmaking process.

In Patent Document 1, the heat of the exhaust gas of the coal gasification process is recovered by a waste heat boiler to generate steam, the steam is directly heated by the exhaust gas of the iron making process, and the superheated steam is used as an oxidizing agent in a coal gasification furnace. It describes how to supply and how to directly supply the produced gas generated by coal gasification to the heating and reducing furnace of the iron making process as fuel.

In Patent Document 2, oxygen is blown into a solid carbon substance in a vertical gasification furnace with a lance to gasify it, and the gas and iron ore are heated to 600 ° C. or higher to have a metallization rate of 0.4 or higher. A method for producing a pre-reduced agglomerated product is disclosed in which a pre-reduced product of 8.8 or less is produced, the pre-reduced product is classified into coarse particles and fine particles, and the fine particles are agglomerated.

Patent Document 3 discloses a direct reduction shaft furnace that reduces iron oxide to metallic iron using COG. Patent Document 4 discloses a direct reduction shaft furnace that reduces iron oxide to metallic iron using coke oven gas (COG) and basic oxygen steelmaking furnace gas (BOFG), and removes carbon dioxide from a mixture of BOFG. It is stated that.

Patent Document 5 discloses, as a method of reducing iron ore by using a direct reduction method, a method of adding a reducing gas to exhaust gas and then reheating it with electricity to reuse it as a reducing gas.

Patent Document 6 discloses a method for producing reduced iron, which supplies a reduced iron containing a by-product gas containing at least one of H ₂ and CO generated in the iron-making process to the reduced iron production apparatus as a part. However, it is described that it contains by-product gas generated from the coke oven.

Japanese Patent No. 4712082 Japanese Patent No. 5598423 Japanese Patent No. 5731709 Japanese Patent No. 5813214 Special Table 2015-532948 International Publication 2011/09970

However, Patent Document 1 describes the exhaust gas of coal gasification to generate steam through a boiler and heat exchange, and does not relate to the effective use of COG, which is a reducing gas discharged from the iron making process. Also, although the exhaust gas from the rotary hearth furnace (RHF) is used to superheat the steam, it does not necessarily have to be a direct reduction process.

Patent Document 2 reduces iron ore in a shaft furnace or the like using a reducing gas derived from coal, but it is necessary to newly use a solid carbon substance in order to generate a reducing gas.

Further, Patent Documents 3 and 4 relate to the shaft furnace and its peripheral equipment, and do not relate to effectively utilizing the COG produced as a by-product from the blast furnace in the shaft furnace. Patent Document 5 also does not relate to the effective use of COG produced as a by-product from equipment equipped with a blast furnace.

Patent Document 6 describes that in addition to by-product gas such as COG, natural gas and gasified gas of steam coal are reformed as a reducing gas, and by-product from equipment equipped with a blast furnace. It is not related to the effective utilization of the amount of COG produced in the shaft furnace in just proportion.

An object of the present invention is to effectively utilize COG, which is a reducing gas emitted from a steelmaking process equipped with a blast furnace, as a reducing agent to optimize energy utilization in a steelworks and to deteriorate the quality of raw materials in the future. Is also to be able to respond.

To solve the above problems, the present invention provides a blast of tapping capability P P _(t / Yr), determine the amount of coke that required for supplying to the blast furnace, then when producing the amount of coke in the by-product is coke oven gas generation amount F _COG ^(Nm 3 / t) determined by a shaft furnace or a fluidized bed reduction furnace having sought plant capacity _P D (t / Yr) by the following equation, the coke Provided is a method for producing reduced iron, which comprises producing reduced iron using furnace gas as a reducing material .
_{P D = P P × F COG} × ((C CO + C H2 + 3 × C CH4) ÷ 100) × (η ÷ 100) ÷ F O ÷ 22.4 × 16.0 ··· (1)
here,
P _P : Blast furnace tapping capacity (t / Yr)
F _COG : COG generation amount per 1 ton of hot metal in a blast furnace (Nm ³ / t)
C _CO : CO content in COG (volume%)
C _{H2: H 2} content in the COG (vol%)
C _CH4: CH ₄ content in the COG (vol%)
η: COG utilization efficiency (%) in a shaft furnace or a fluidized bed reduction furnace
F _O: In a shaft furnace or a fluidized bed reduction furnace, the reduced iron mass of oxygen that must be removed when 1t produced (kg-O 2 / _t)

Further, the present invention is characterized in that the reduced iron produced by the method for producing reduced iron and the hot metal produced in the blast furnace are mixed and put into a smelting furnace to perform finish reduction and smelting. Provide a manufacturing method.

Further, the reduced iron produced by the method for producing reduced iron is hot-molded to obtain HBI, and the hot metal produced in the blast furnace is charged into the smelting furnace using the HBI as a raw material for the blast furnace to perform finish reduction and refining. Provided is a method for producing molten iron, which is characterized by the above.

Further, the reduced iron produced by the method for producing reduced iron is hot-molded to obtain HBI, the HBI is sieved, the upper part of the sieve is used as a raw material for the blast furnace, and the lower part of the sieve is used as a hot metal produced in the blast furnace. Provided is a method for producing molten steel, which comprises mixing and putting into a smelting furnace to perform finish reduction and refining.

According to the present invention, in a steel mill equipped with a blast furnace, by providing a shaft furnace or a fluidized layer type reduction furnace according to the tapping capacity of the blast furnace, COG produced as a by-product in the coke oven can be used as a reducing material in just proportion. It can be used effectively. Therefore, it is possible to optimize the energy use of steelworks and to cope with the deterioration of raw materials in the future.

It is a block diagram which shows the structure and process of the steel mill which concerns on 1st Embodiment of this invention. It is a graph which shows the relationship between the blast furnace tapping capacity and the vertical shaft furnace equipment capacity in the 1st Embodiment. It is a block diagram which shows the structure and process of the steel mill which concerns on 2nd Embodiment of this invention. It is a graph which shows the relationship between the blast furnace tapping capacity and the vertical shaft furnace equipment capacity in the second embodiment. It is a block diagram which shows the structure and process of the steel mill which concerns on 3rd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and the drawings, elements having substantially the same functional configuration are designated by the same reference numerals to omit duplicate description. In the following embodiment, an example of a vertical shaft furnace is described as a furnace using COG as a reducing agent, but the same can be applied to a fluidized bed type reducing furnace.

<1. First Embodiment>
FIG. 1 shows an outline of the structure and process of a steel mill according to the first embodiment of the present invention.

The steel mill 1 is provided with a blast furnace 2, a sintering furnace 3 for producing sinter by firing iron ore, and a coke furnace 4 for producing coke from coking coal. The sinter and coke are charged into the blast furnace 2, and hot metal is produced in the blast furnace 2. The hot metal is smelted in a smelting furnace 7 including a converter 5 or an electric furnace 6 to produce molten steel. The blast furnace gas produced as a by-product in the blast furnace 2 (hereinafter referred to as BFG) is used as fuel for the heating furnace 9 and the power plant 10 for private power generation.

In the present embodiment, a vertical shaft furnace 11 capable of reducing blast furnace 2 is provided in the same site as the blast furnace 2 or in the vicinity of the installation location of the blast furnace 2 in the steel mill 1 centered on the blast furnace 2. It is provided. Powdered ore, which is difficult to use in the blast furnace 2, is pretreated and put into the shaft furnace 11 by, for example, pelletization, and a reducing agent is added to produce reduced iron. By installing such a shaft furnace 11 in parallel, the range of raw material properties that can be used in the steel mill 1 can be expanded, and it is possible to cope with the deterioration of raw materials such as iron ore and coking coal.

As the reducing agent in the shaft furnace 11, coke oven gas (hereinafter referred to as COG) produced as a by-product in the coke oven 4 is used. The COG used as the reducing agent may be used as it is discharged from the coke oven 4 or after being modified. Further, a part of COG may be used as fuel for the coke oven 4 and the sintering furnace 3.

The installed capacity of the shaft furnace 11 shall be of a scale corresponding to the amount of COG generated in the steelworks 1. That is, first, the amount of coke required for supplying to the blast furnace 2 is obtained from the tapping capacity of the blast furnace 2. Next, the amount of COG produced as a by-product from the coke oven 4 when the amount of coke is produced is determined. Then, the shaft furnace 11 has an equipment capacity such that the amount of COG that can be supplied to the shaft furnace 11 is substantially equal to the amount of reducing material required for the amount of reducing iron that can be reduced by the shaft furnace 11. By determining the equipment capacity of the shaft furnace 11 in this way, the COG can be utilized most effectively without excess or deficiency.

Conventionally, in steelworks, COG is used as fuel for the heating furnace 9 and not as reducing gas. On the other hand, as the reducing agent of the shaft furnace 11, natural gas was used, or coal was gasified to synthesize a mixed gas of CO and H ₂ . In the present embodiment, inexpensive steaming coal is supplied as fuel to a heating furnace or a power plant that uses COG as fuel in a conventional steel mill. Further, the BFG produced as a by-product in the blast furnace 2 is used as fuel for the heating furnace 9 and the power plant 10 as in the conventional case. As a result, COG, which is a strongly reducing gas, is effectively used as the reducing gas in the shaft furnace 11.

The reduced iron produced in the shaft furnace 11 is smelted in a smelting furnace 7 including an electric furnace 6 or a converter 5. That is, the reduced iron is put into the electric furnace 6 as it is, or is compressed by hot heat to be briquette (HBI), and HBI is put into the converter 5 together with the hot metal produced in the blast furnace 2 and refined in the smelting furnace 7. To manufacture molten steel.

FIG. 2 shows the relationship between the tapping capacity of the blast furnace 2 and the installed capacity of the shaft furnace 11 in the present embodiment.

When the reduced iron produced in the shaft furnace 11 and the hot metal produced in the blast furnace 2 are mixed and refined in the smelting furnace 7 to produce molten steel, the tapping capacity of the blast furnace 2 and coke are supplied to the blast furnace 2. The relationship between the amount of COG generated from the coke oven 4 and the installed capacity of the vertical shaft furnace 11 estimated from the amount of reduced iron that can be reduced was obtained by simulation. In FIG. 2, the solid line is the case where the total amount of COG generated in the coke oven 4 is used as the reducing agent of the shaft furnace 11, and the dotted line is the case where the COG used in the coke oven 4 and the sintering furnace 3 is preferentially directed there. The case where it supplies and supplies the surplus COG to the shaft furnace 11 is shown. The alternate long and short dash line indicates the minimum capacity of the existing vertical shaft furnace as a commercial process.

Equipment capacity P _D of the shaft furnace or fluidized bed reduction furnace _(t / Yr) was determined by the following equation.
_{P D = P P × F COG} × ((C CO + C H2 + 3 × C CH4) ÷ 100) × (η ÷ 100) ÷ F O ÷ 22.4 × 16.0 ··· (1)
here,
P _P : Blast furnace tapping capacity (t / Yr)
F _COG : COG generation amount per 1 ton of hot metal in a blast furnace (Nm ³ / t)
C _CO : CO content in COG (volume%)
C _{H2: H 2} content in the COG (vol%)
C _CH4: CH ₄ content in the COG (vol%)
η: COG utilization efficiency (%) in a shaft furnace or a fluidized bed reduction furnace
_FO : Mass of oxygen (kg-O ₂ / t) that needs to be removed when producing 1 ton of reduced iron in a shaft furnace or a fluidized bed type reduction furnace.

When the total amount of COG generated in the coke oven 4 is used as the reducing agent for the shaft furnace 11 in carrying out the simulation, in the equation (1), F _COG = 158.3 (Nm ³ / t), C _CO = 6 _{.5%, C H2 = 55%} , C CH4 = 27%, η = 75%, and the _{F O = 434 (kg-O} 2 / t). Further, when the COG used in the coke oven 4 and the sintering furnace 3 is preferentially supplied to the coke oven 4 and the surplus COG is supplied to the shaft furnace 11, in the equation (1), F _COG = 130.6 ( Nm ³ / t), C _CO = 6.5%, C _H2 = 55%, C _{CH 4} = 27%, η = 75%, _FO = 434 (kg-O ₂ / t).

When the steel mill 1 is equipped with a blast furnace 2 having a certain tapping capacity or is newly installed, COG produced as a by-product from the coke oven 4 for producing coke to be supplied to the blast furnace 2 is used as a reducing agent in just proportion. The equipment capacity of the shaft furnace 11 that can be utilized is defined by the solid line shown in FIG. If a shaft furnace 11 larger than the solid line is installed, the COG produced as a by-product from the coke oven 4 will not be enough for the necessary reducing agent, so it is necessary to set up a separate coal gasification facility and natural gas supply base. Incurred, equipment costs skyrocket.

On the other hand, if the steel mill 1 cannot supply fuel gas other than COG to the coke oven 4 and the sintering furnace 3 due to piping equipment or the like, COG must be preferentially supplied to these processes. , The amount of COG that can be supplied to the shaft furnace 11 decreases. In that case, the maximum installed capacity of the shaft furnace 11 determined from the amount of COG decreases to the dotted line in FIG.

When the shaft furnace 11 smaller than the installed capacity shown by the solid line or the dotted line in FIG. 2 is installed, the COG becomes surplus in each case, but this surplus COG is used as the fuel gas for the heating furnace 9 and the like as before. Since it can be used, there are no major disadvantages. However, if the shaft furnace 11 having an equipment capacity of less than 0.3 (Mt-DRI / y) shown by the one-point chain line in FIG. 2 is installed, the ratio of the surface area of the furnace body to the furnace volume is large and the heat transfer efficiency is deteriorated. Not economical. Therefore, from the viewpoint of thermal economic rationality, the lower limit of the installed capacity of the newly installed shaft furnace 11 is preferably 0.3 (Mt-DRI / y) or more shown by the alternate long and short dash line in FIG. That is, depending on the tapping capacity of the existing or newly installed blast furnace 2, installing the shaft furnace 11 having the equipment capacity in the area between the solid line or the dotted line and the alternate long and short dash line in FIG. 2 is a by-product having a reducing capacity. It is preferable from the viewpoint of effective use of COG. The solid line and the dotted line change depending on the amount of coke used in the blast furnace 2, the composition of COG, and the reduction rate of the reduced iron produced in the shaft furnace 11.

<2. Second Embodiment>
FIG. 3 shows an outline of the structure and process of the steel mill showing the second embodiment of the present invention, and FIG. 4 shows the tapping capacity of the blast furnace 2 and the equipment of the shaft furnace 11 in the second embodiment. Show the relationship with ability.

This embodiment has the same configuration as that of the above-described embodiment shown in FIG. 2 and the structure of the steel mill 1, but as shown in FIG. 3, the reduced iron produced in the shaft furnace 11 is hot-compressed and HBI. The density and strength are increased, and HBI is put into the blast furnace 2 as a raw material for the blast furnace. Then, the hot metal produced in the blast furnace 2 is oxygen-refined in a smelting furnace 7 including a converter 5 or an electric furnace 6 to produce molten steel.

FIG. 4 shows the shaft furnace 11 in which the tapping capacity of the blast furnace 2 and the amount of COG generated from the coke furnace 4 for supplying coke to the blast furnace 2 are estimated from the amount of reduced iron that can be reduced in the present embodiment. The relationship with the equipment capacity was obtained by simulation. The meanings of the solid line, the dotted line, and the alternate long and short dash line are the same as those in FIG.

When the total amount of COG generated in the coke oven 4 is used as the reducing agent for the shaft furnace 11 in carrying out the simulation, in the equation (1), F _COG = 134.8 (Nm ³ / t), C _CO = 6 _{.5%, C H2 = 55%} , C CH4 = 27%, η = 75%, and the _{F O = 434 (kg-O} 2 / t). Further, when the COG used in the coke oven 4 and the sintering furnace 3 is preferentially supplied to the coke oven 4 and the surplus COG is supplied to the shaft furnace 11, F _COG = 112.2 (1) in the formula (1). Nm ³ / t), C _CO = 6.5%, C _H2 = 55%, C _{CH 4} = 27%, η = 75%, _FO = 434 (kg-O ₂ / t).

Also in the case of the present embodiment, a shaft furnace 11 having an equipment capacity in the region between the solid line or the dotted line and the alternate long and short dash line in FIG. 4 can be installed according to the tapping capacity of the existing or newly installed blast furnace 2. preferable. In FIG. 4, the equipment capacity of the maximum shaft furnace that can be installed in a blast furnace having the same tapping capacity is smaller than that in FIG. This is because HBI, which consumes less reducing agent, is put into the blast furnace 2, so that the amount of reducing agent (coke) required in the blast furnace 2 is reduced even with the same amount of tapping, and as a result, by-products This is because the amount of COG produced is reduced.

In the case of the present embodiment, there is an advantage that the operation of the smelting furnace 7 is more stable than that of the first embodiment described above. That is, since the reduced iron produced in the shaft furnace 11 is charged into the blast furnace 2 as HBI, only the hot metal ejected from the blast furnace 2 is supplied to the smelting furnace 7. Therefore, since it is not necessary to mix hot metal and reduced iron in the smelting furnace 7 or to carry out a finishing reduction reaction of the reduced iron, not only the smelting time is stable, but also the supply of iron oxide into the smelting furnace 7 is possible. It can be minimized and the melting damage of fireproof materials can be suppressed. Also in this embodiment, the solid line and the dotted line in FIG. 4 change depending on the amount of coke used in the blast furnace 2, the composition of COG, and the reduction rate of the reduced iron produced in the shaft furnace 11.

<3. Third Embodiment>
FIG. 5 shows an outline of the structure and process of a steel mill showing a third embodiment of the present invention.

Conventionally, when reducing iron is produced in the shaft furnace 11, it is generally mixed with hot metal in a smelting furnace 7 such as a converter 5 or an electric furnace 6 and smelted to obtain molten steel as in the first embodiment. Is the target. However, when the input ratio of reduced iron in the smelting furnace 7 increases, the operation of the smelting furnace 7 becomes unstable when the reduction rate of reduced iron fluctuates due to the operation fluctuation of the shaft furnace 11, and the input amount of reduced iron becomes unstable. There will be an upper limit. Further, if a high reduction rate is aimed at in order to stabilize the operation of the smelting furnace 7, there is a concern that the productivity of the shaft furnace 11 may decrease.

Therefore, in the present embodiment, the reduced iron produced in the shaft furnace 11 is hot-molded into HBI, and further sieved using a sieve 21 having a size of about 40 to 50 mm, which is equivalent to that of sinter. Then, the sieve component (product HBI) is used as a raw material for the blast furnace together with the sinter, and is charged into the blast furnace 2. Since the product HBI is sufficiently reduced, it is not necessary to reduce it again in the blast furnace 2, and as a result, the amount of tapped iron output from the blast furnace 2 can be increased while maintaining stable blast furnace operation. On the other hand, since the subsieving portion (powder HBI) of the sieve 21 is unreduced and has low strength, it cannot be reused as a raw material for a blast furnace. Therefore, this powder HBI is put into the smelting furnace 7, finished and reduced, and then dissolved. If HBI having a low reduction rate is put into the smelting furnace 7, there is a concern that the operation of the smelting furnace 7 may become unstable, but if only the subsieving portion is used, the amount is small and the influence can be minimized. Further, the operation may be performed by adjusting the presence or absence of the powder HBI input according to the operating state of the smelting furnace 7. In the present embodiment, the configuration of the steelworks 1 other than the sieving process is the same as that of the above-described embodiments shown in FIGS. 1 and 3.

As described above, according to the present invention, by utilizing the by-product gas generated in the iron-making process by the blast furnace 2 in just proportion, another iron-making process by the shaft furnace 11 can be efficiently operated, and the energy of the steelworks 1 is used. Can be optimized. Further, by using the blast furnace 2 and the shaft furnace 11 together in the steelworks 1, it is possible to manufacture molten steel from raw materials of a quality that cannot be handled by the blast furnace 2 in one steelworks 1, and it is possible to handle various raw materials. Will be.

When COG is not produced as a by-product due to maintenance of the blast furnace 2, natural gas or synthetic gas generated from coal, which has been conventionally used as a reducing agent, may be used as the reducing agent of the shaft furnace 11.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the technical idea described in the claims, and of course, the technical scope of the present invention also includes them. It is understood that it belongs to.

For example, in the above embodiment, an example of the vertical shaft furnace 11 is described as a furnace using COG as a reducing agent, but the same can be applied to the fluidized bed type reducing furnace 12.

The present invention is suitable for a steel mill having a blast furnace and a shaft furnace or a fluidized bed reduction furnace for producing reduced iron by reducing gas.

1 Steelworks 2 Blast furnace 3 Sintered furnace 4 Coke furnace 5 Converter 6 Electric furnace 7 Refining furnace 11 Shaft furnace 12 Flow layer type reduction furnace 21 Sieve

Claims (4)

From blast furnace tapping capability _P P _(t / Yr), determine the amount of coke that is required to be supplied to the blast furnace,
Next, the coke oven gas generation amount _FCOG (Nm ³ / t) produced as a by-product during the production of the coke amount was determined.
The shaft furnace or a fluidized bed reduction furnace having the production capacity obtained by the formula P _{D (t} / Yr), characterized by producing reduced iron the coke oven gas as a reducing agent, the production of reduced iron Method.
_{P D = P P × F COG} × ((C CO + C H2 + 3 × C CH4) ÷ 100) × (η ÷ 100) ÷ F O ÷ 22.4 × 16.0 ··· (1)
here,
P _P : Blast furnace tapping capacity (t / Yr)
F _COG : COG generation amount per 1 ton of hot metal in a blast furnace (Nm ³ / t)
C _CO : CO content in COG (volume%)
C _{H2: H 2} content in the COG (vol%)
C _CH4: CH ₄ content in the COG (vol%)
η: COG utilization efficiency (%) in a shaft furnace or a fluidized bed reduction furnace
_FO : Mass of oxygen (kg-O ₂ / t) that needs to be removed when producing 1 ton of reduced iron in a shaft furnace or a fluidized bed type reduction furnace. Manufacture of molten steel, which comprises mixing the reduced iron produced by the method for producing reduced iron according to claim 1 and the hot metal produced in the blast furnace and putting them into a smelting furnace for finish reduction and refining. Method. The reduced iron produced by the method for producing reduced iron according to claim 1 is hot-molded to obtain HBI, and the hot metal produced in the blast furnace is charged into the smelting furnace using the HBI as a raw material for the blast furnace for finish reduction and refining. A method for producing molten iron, which comprises performing. The reduced iron produced by the method for producing reduced iron according to claim 1 is hot-molded to obtain HBI, the HBI is sieved, the upper part of the sieve is used as a raw material for the blast furnace, and the lower part of the sieve is produced in the blast furnace. A method for producing molten steel, which comprises mixing with hot metal and putting it into a smelting furnace for finish reduction and refining .

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