EP4653552A1

EP4653552A1 - Blast furnace operation method

Info

Publication number: EP4653552A1
Application number: EP23922845.5A
Authority: EP
Inventors: Taisuke Yotsuya; Yuki Kawashiri
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2023-02-14
Filing date: 2023-10-10
Publication date: 2025-11-26
Also published as: TWI889106B; KR20250134667A; JPWO2024171511A1; WO2024171511A1; CN120584201A; TW202432841A; JP7827130B2

Abstract

Provided is a blast furnace operation method capable of lowering a reducing agent rate by using a coke with an appropriate reactivity. The blast furnace operation method includes: charging a ferrous raw material and coke in layers from a furnace top of a blast furnace; and blowing an oxygen-containing gas and a reducing agent containing a hydrocarbon-based gas into the blast furnace from a tuyere of the blast furnace, wherein when the oxygen-containing gas has an oxygen concentration of 80 vol% or more, operation is carried out using a coke with a reaction index CRI of 35 or less. The hydrocarbon-based gas is preferably a hydrogen gas and/or a gas of a hydrogen-containing compound.

Description

Technical Field

The present invention relates to a blast furnace operation method capable of lowering a reducing agent rate in blast furnace operation.

Background Art

Generally, in a blast furnace, operation is performed in such a manner where a ferrous raw material and coke are charged in layers from the furnace top, and hot blast (hot air) and a reducing auxiliary agent such as pulverized coal are blown from tuyeres located at the lower portion of the furnace. In this way, the ferrous raw material descending in the furnace is reduced by a reducing gas ascending from the lower part of the furnace, thus producing pig iron.
As mentioned above, in blast furnace operation, reducing agents such as coke and pulverized coal are used to reduce the iron source in the furnace. The total weight of reducing agents required for producing 1 t of pig iron is called reducing agent rate. If reducing agent rate can be lowered, it is possible to reduce CO₂ emission from the blast furnace and production cost of pig iron; lowering reducing agent rate is a major issue in blast furnace operation, and there have been a number of technical developments in this regard.
For example, as disclosed in Patent Literature 1 and Patent Literature 2, there is a technique of lowering reducing agent rate by using a highly reactive coke. If employing a coke with a high reactivity, the coke gasification reaction expressed by C+CO₂=2CO starts from a low temperature. Since gasification reaction is also a significant endothermic reaction, a gasification reaction starting from a low temperature results in a decreased thermal reserve zone temperature in the blast furnace. Thus, the reduction equilibrium point of FeO-Fe shifts toward the lower side of a reducing gas concentration. As a result, indirect reduction is promoted as the difference between the reducing gas concentration in the furnace and the reducing gas concentration at the reduction equilibrium point widens, thereby leading to a reduced smelting reduction (reaction formula: FeO+C=Fe+CO) amount, thus yielding a lowered reducing agent rate.
Ferro coke is well known as a typical highly reactive coke. Ferro coke is a coke produced by mixing an iron ore powder into coal and performing carbonization; the reactivity of ferro coke is improved as Fe contained therein acts as a catalyst for the coke gasification reaction. In Patent Literature 3 and Patent Literature 4, and Non-Patent Literature 1, there are descriptions that reducing agent rate can be lowered by using ferro coke.
Here, in recent years, technical developments aimed at massively reducing CO₂ emissions are underway in the entire steel industry for the purpose of realizing a carbon-neutral society. Blast furnaces emitting large amounts of CO₂ are no exception; for example, as disclosed in Patent Literature 5, consideration is being given to a type of blast furnace operated by blowing, from tuyeres, an oxygen-containing gas with an oxygen concentration close to 100% as a blast gas, and methane as a reducing agent. This type of blast furnace differs from a conventional and general blast furnace in that a high-concentration oxygen-containing gas is blown from the tuyeres instead of hot air, and that a large amount of methane is blown from the tuyeres as a reducing agent instead of pulverized coal, which requires a set of significantly modified operational conditions.

Citation List

Patent Literature

Patent Literature 1: JP-A-2006-206982
Patent Literature 2: JP-A-2007-231326
Patent Literature 3: JP-A-2011-162845
Patent Literature 4: JP-A-2012-140691
Patent Literature 5: WO2021/106578
Patent Literature 6: JP-A-2022-149214

Non-Patent Literature

Non-Patent Literature 1: Tetsuya Yamamoto and seven others, "Reaction Behavior of Ferro Coke and Its Evaluation in Blast Furnace," Tetsu-to-Hagane, Volume 97 (2011), Issue 10, p.501-509
Non-Patent Literature 2: Takeshi Sato and others, KAWASAKI STEEL GIHO, Vol.29 (1997) No.1, P.30-36

Summary of Invention

Technical Problems

A blast furnace operation method in which reducing agent rate is lowered by using a highly reactive coke as typified by ferro coke is known to be effective with respect to a conventional and general blast furnace operated by blowing hot air and a reducing agent mainly composed of pulverized coal from tuyeres. Meanwhile, detailed examination has not yet been given to the type of blast furnace disclosed in Patent Literature 5, i.e., a blast furnace operated by blowing an oxygen-containing gas with an oxygen concentration close to 100% from the tuyeres as a blast gas, and blowing a hydrocarbon-based reducing agent containing a large amount of hydrogen from the tuyeres other than pulverized coal. Thus, if using a highly reactive coke in such blast furnace, it is not clear as to whether or not there can be achieved the level of reducing agent rate lowering effect observed with the conventional and general blast furnace, nor is it clear on a coke reactivity suitable for lowering reducing agent rate.
In this regard, for example, Patent Literature 6 discloses that when blowing a large amount of a hydrogen-containing gas that contains a hydrogen gas into a blast furnace, lowering coke reactivity is effective to suppress endotherm caused by the coke gasification reaction. However, Patent Literature 6 is targeted at a blast furnace operated by blowing a hot air with a high nitrogen gas concentration from the tuyeres. For this reason, there has been no knowledge on a coke reactivity suitable for lowering reducing agent rate in the case of a blast furnace operated by blowing an oxygen-containing gas with an oxygen concentration close to 100% from the tuyeres as a blast gas, and blowing a hydrocarbon-based reducing agent containing a large amount of hydrogen from the tuyeres other than pulverized coal.
It is an object of the present invention to solve the aforementioned problems by providing a blast furnace operation method that is capable of lowering reducing agent rate by employing a coke with an appropriate reactivity in a so-called oxygen blast furnace operated by blowing an oxygen-containing gas with an oxygen concentration of 80 vol% or more from the tuyeres as a blast gas.

Solution to Problem

The blast furnace operation method of the present invention was developed to solve the above problems. This method includes: charging a ferrous raw material and coke in layers from a furnace top of a blast furnace; and blowing an oxygen-containing gas and a reducing agent containing a hydrocarbon-based gas into the blast furnace from tuyeres of the blast furnace, wherein when the oxygen-containing gas has an oxygen concentration of 80 vol% or more, operation is carried out using a coke with a reaction index CRI of 35 or less.
Here, with regard to the blast furnace operation method of the present invention that is configured in the abovementioned manner, it is considered that more preferable solutions can be brought when:

(1) the hydrocarbon-based gas is a hydrogen gas and/or a gas of a hydrogen-containing compound.

Advantageous Effects of Invention

According to the blast furnace operation method of the present invention, when blowing an oxygen-containing gas with an oxygen concentration of 80 vol% or more from tuyeres as a blast gas, a blast furnace operation capable of lowering reducing agent rate can be realized by using a coke having an appropriate reactivity with its reaction index CRI being 35 or less.

Brief Description of Drawings

[FIG.1] is a graph showing a correlation between CRI and reducing agent rate in the case of a blast furnace of the present invention.
[FIG.2] is a graph showing a correlation between CRI and consumed C in terms of a smelting reduction amount and an amount of coke gasified in the case of the blast furnace of the present invention.

Description of Embodiments

An embodiment of the present invention is described in detail hereunder. Here, the following embodiment is a set of examples of a device and/or method embodying the technical concept of the present invention and is not to limit the configuration of the present invention to those shown below. That is, various modifications can be made to the technical concept of the present invention within the technical scope described in the claims.
In the beginning, a blast furnace operation method of the present embodiment is described. In the blast furnace operation method of the present embodiment, a ferrous raw material and coke are charged in layers from the furnace top of a blast furnace, an oxygen-containing gas with an oxygen concentration of 80 vol% or more is blown from the tuyere(s) of the blast furnace as a blast gas, and a reducing agent containing a hydrocarbon-based gas is blown from the tuyeres.
Here, the blast furnace operation method of the present invention uses the oxygen-containing gas as a blast gas, instead of hot blast. If using hot blast (air heated to about 1200°C) as a blast gas, since the combustion gas contains about 50 vol% of nitrogen that does not contribute to combustion reaction, it is difficult for the flames in the raceway to reach a high temperature. Thus, if blowing into the blast furnace a large amount of a reducing agent containing a hydrocarbon-based gas, the tuyere-outlet temperature will decrease, which will cause operational troubles.
In contrast, in the blast furnace operation method of the present invention, by using the oxygen-containing gas as a blast gas, nitrogen gas that does not contribute to combustion reaction can be restricted from being mixed thereinto, whereby the tuyere-outlet temperature can be raised to a sufficient temperature. That is, the temperature of the flames in the raceway is higher than if using hot blast.
The oxygen concentration of the oxygen-containing gas is 80 vol% or more. A low oxygen concentration of the oxygen-containing gas may cause operational troubles as a sufficient tuyere-outlet temperature cannot be secured when blowing a large amount of a hydrocarbon-based gas. For this reason, the oxygen concentration of the oxygen-containing gas needs to be 80 vol% or more, preferably 90 vol% or more, more preferably 95 vol% or more. The oxygen concentration may even be 100 vol%. Here, as the remaining gas other than oxygen in the oxygen-containing gas, there may be contained, for example, nitrogen, carbon dioxide, argon, water vapor and the like. Since water vapor decreases the tuyere-outlet temperature, it is preferably contained at a low concentration in the oxygen-containing gas; water vapor is preferably contained at a concentration of 10 g/Nm³ or less, more preferably 5 g/Nm³ or less, per 1 Nm³ of the oxygen-containing gas.
The hydrocarbon-based gas is preferably a hydrogen gas and/or a gas that contains a hydrogen-containing compound. For example, the hydrocarbon-based gas may be methane, ethane, propane, ethylene, propylene, methanol, ethanol and the like. Further, the hydrocarbon-based gas may be a gas composed by containing even part of these gases, such as a natural gas, city gas, and coke oven gas that are supplied from outside. Furthermore, the hydrocarbon-based gas may also be a regenerated gas generated utilizing the blast furnace gas. For example, the hydrocarbon-based gas may be a regenerated methane gas obtained by reacting hydrogen with carbon monoxide and/or carbon dioxide contained in the blast furnace gas, via the method described in Patent Literature 5. By utilizing a regenerated gas as the hydrocarbon-based gas, CO₂ emission can be reduced significantly.
Further, other blowing reducing agents including, for example, pulverized coal, waste plastics, and/or a reducing gas such as a carbon monoxide gas may be used together with the hydrocarbon-based gas. Here, it is preferred that the amount of such other blowing reducing agents blown into the blast furnace be 20 wt% or less with respect to the total amount of all the blowing reducing agents including the hydrocarbon-based gas. Here, a unit "kg/t" indicates the amount of the other blowing reducing agents that are blown into the blast furnace when producing 1 t of hot metal. If using the other blowing reducing agents, these other blowing reducing agents may also be together introduced into a hydrocarbon-based gas supply part. Further, if using pulverized coal and/or waste plastics as the other blowing reducing agents, it is preferred that there be provided a separate reducing agent supply part (passage) that is separate from the hydrocarbon-based gas supply part and is configured to pass pulverized coal and/or waste plastics therethrough.
Using the two-dimensional blast furnace mathematical model illustrated in Non-Patent Literature 2, which was developed by taking reaction, heat transfer, and substance flow into consideration, the inventors used cokes with different reactivities to study changes in the reducing agent rate when operating the blast furnace in such a manner that the hot metal temperature and tapping quantity were constant.
The reactivity of coke was studied by employing CRI (Coke Reaction Index) that is also used as the actual operation control index. CRI is determined as follows. That is, 200 g of a coke adjusted to a size of 20±1 mm (grain size) is reacted under conditions of: gas composition CO₂ (100 mol%); reaction temperature 1100°C; and reaction time 2 hours. Next, the mass of the reacted sample is measured to calculate (mass before reaction - mass after reaction)/mass before reaction×100. This is defined as CRI.
Methane was used as a hydrocarbon-based reducing agent, and study was conducted at a methane rate of 148 kg/t.
According to a result calculated by the above blast furnace mathematical model, in the case of a blast furnace operated by blowing an oxygen-containing gas with a concentration of 100 vol% as a blast gas and methane from the tuyeres, the reducing agent rate decreased as CRI decreased (see FIG.1). Thus, a high-reactive coke which is considered as favorable for use in a conventional and general blast furnace is disadvantageous in lowering the reducing agent rate with regard to the blast furnace of the present invention. In contrast, a low-reactive coke is advantageous in lowering the reducing agent rate. Here, in the graph shown in FIG.1, the slope of a part of the graph that corresponds to reducing agent rates of 485 kg/t or less is steeper than the slope of a part of the graph that corresponds to reducing agent rates of 487 kg/t or more. In this regard, in the present invention, the goal is set to a reducing agent rate of 485 kg/t or less.
This is attributed to the following reasons. The hydrogen concentration in the furnace increases as a result of blowing, from the tuyeres, an oxygen-containing gas with a concentration of 100 vol% as a blast gas, and a large amount of a hydrocarbon-based reducing agent containing a large quantity of hydrogen. Further, the reducing gas concentration will be relatively high if performing blasting in a nitrogen-less condition. In this way, a smelting reduction amount decreases as reduction efficiency improves, whereby a decreased coke reactivity will cause the amount of coke gasified to decrease to an extent equal to or greater than an increase in the smelting reduction amount, thus lowering the reducing agent rate (see FIG.2). Smelting reduction and coke gasification are both significant endothermic reactions, which leads to an increased reducing agent rate.
As such, in the case of a blast furnace operated by blowing an oxygen-containing gas with a concentration of 80 vol% or more from the tuyeres as a blast gas, and blowing a reducing agent containing a hydrocarbon-based gas from the tuyeres, a coke reactivity as low as possible is preferred from the perspective of lowering the reducing agent rate, and it is required that CRI be of a certain value or less in order to achieve the reducing agent rate of a given value or less in blast furnace operation.

Examples

Blast furnace operation was carried out under the various operational conditions shown in the following Table 1, where a pulverized coal ratio was set to 0 kg/t, the methane rate was set to 148 kg/t, an oxygen-containing gas unit consumption was set to 316 to 318 Nm³/t, the oxygen concentration in the oxygen-containing gas was set to 100%, the temperature of the oxygen-containing gas was set to 25°C, and the moisture of the oxygen-containing gas was set to 0 g/Nm³, provided that cokes with various CRIs were used. Here, the various operational conditions were determined based on the result shown in FIG.1. Coke rates were adjusted (331 to 342 kg/t) such that a productivity of 2.2 t/day/m³ and a hot metal temperature of 1510°C were achieved.

[Table 1]

	Item	Unit	Invention Example 1-1	Invention Example 1-2	Invention Example 1-3	Comparative Example 1-1	Comparative Example 1-2	Comparative Example 1-3
Operational Condition	Productivity	t/day/m³	2.2	2.2	2.2	2.2	2.2	2.2
	Hot Metal Temperature	°C	1510	1510	1510	1510	1510	1510
	Coke Rate	kg/t	331	333	335	339	341	342
	Pulverized Coal Rate	kg/t	0	0	0	0	0	0
	Methane Rate	kg/t	148	148	148	148	148	148
	Oxygen-containing Gas Unit Consumption	Nm³/t	316	316	316	317	318	318
	Oxygen Concentration in Oxygen-containing Gas	%	100	100	100	100	100	100
	Temperature of Oxygen-containing Gas	°C	25	25	25	25	25	25
	Water Content of Oxygen-containing Gas	g/Nm³	0	0	0	0	0	0
	CRI	-	13	19	31	43	55	61

The following was made clear from the results shown in Table 1. At first, in Table 1 showing the results of a blast furnace operation where the concentration of the oxygen blown from the tuyeres was 100 vol%, and methane as a hydrocarbon-based gas was blown from the tuyeres, focus was placed on the reducing agent rate (coke rate + pulverized coal rate + methane rate). As a result, of the examples shown in Table 1, the invention example 1-1 (reducing agent rate 479 kg/t), the invention example 1-2 (reducing agent rate 481 kg/t), and the invention example 1-3 (reducing agent rate 483 kg/t) were found to meet the goal of a reducing agent rate of 485 kg/t or less. In contrast, it became clear that the comparative example 1-1 (reducing agent rate 487 kg/t), the comparative example 1-2 (reducing agent rate 489 kg/t), and the comparative example 1-3 (reducing agent rate 490 kg/t) failed to meet the goal of a reducing agent rate of 485 kg/t or less. As is clear from FIG.1 and the above results, in the present invention, CRI needs to be 35 or less.

Claims

A blast furnace operation method comprising:
charging a ferrous raw material and coke in layers from a furnace top of a blast furnace; and

blowing an oxygen-containing gas and a reducing agent containing a hydrocarbon-based gas into the blast furnace from a tuyere of the blast furnace,

characterized in that when the oxygen-containing gas has an oxygen concentration of 80 vol% or more, operation is carried out using a coke with a reaction index CRI of 35 or less.
The blast furnace operation method according to claim 1, wherein
the hydrocarbon-based gas is a hydrogen gas and/or a gas of a hydrogen-containing compound.