JPH01208410A - Smelting reduction method for iron oxide raw material - Google Patents

Abstract

PURPOSE:To reduce unit consumption of slag making material and producing quantity of slag and also to strengthen reducing capacity by blowing gaseous carbonic material into molten metal in a smelting reduction furnace to reduce iron oxide raw material and conducting reaction heat into the molten metal. CONSTITUTION:The iron oxide raw material is supplied into the smelting reduction furnace together with the gaseous carbonic material of LNG, etc., and oxygen. Then, a part, desirably >=10% of the gaseous carbonic material is directly blown into the molten metal to execute heat decomposition, and the iron oxide is sufficiently reduced. The reaction heat at this time is conducted to the molten steel almost 100% to raise the molten temp. CO and H2 generated from the molten metal are secondarily burnt with oxygen or preheated air separately blown and these reaction heats are absorbed into the molten metal at high efficiency. By this method, the molten iron having low S content, etc., and high quality can be produced.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides a method for producing hot metal by supplying iron oxide raw materials such as iron ore to a smelting reduction furnace together with carbonaceous substances, oxygen-containing substances, and slag-forming agents. Regarding iron oxide, we have succeeded in significantly reducing the amount of slag-forming agent used and the amount of slag produced by using a gaseous carbonaceous material such as natural gas (hereinafter referred to as LNG) as the carbonaceous material. This invention relates to a method for melting and reducing raw materials.

[Prior art] The so-called smelting reduction method is attracting attention as a pig iron manufacturing technology other than blast furnace.
Many processes have been developed, such as the R method, the SC method, and the C0IN method.

The general process of the smelting reduction iron manufacturing process is to supply high-temperature gas mainly composed of Co generated in a smelting reduction furnace to a pre-reduction furnace as a heat source and reducing agent, and reduce some or, if necessary, most of the iron ore, to prepare a preliminary reduction. While producing reduced iron, carbonaceous material and oxygen-containing gas are blown into the smelting reduction furnace to supply a heat source and reducing gas. Pig iron is produced by reduction.

Known techniques for such smelting reduction iron manufacturing methods include, for example,
(1) Charge the pre-reduced iron obtained in the pre-reduction furnace to the smelting-reduction furnace, blow coal and oxygen into the iron bath formed in the smelting-reduction furnace, and burn part of the generated gas on the bath. (2) Preheating the iron ore (Japanese Patent Application Laid-open No. 59-222508), in which the iron ore is melted down while being subjected to post-compassion, and the gas extracted from this is reformed and introduced into a pre-reduction furnace. ,
Furthermore, after being pre-reduced in a pre-reduction furnace, it is supplied to a smelting-reduction furnace along with carbonaceous substances, oxygen, and a slag-forming agent, and a portion is further burned for secondary combustion, and the iron bath produced in the smelting-reduction furnace is heated and simultaneously A method of adjusting the degree of oxidation by recovering heat and decarboxylating the generated reducing gas, and introducing it into a preliminary reduction furnace to control the preliminary reduction rate (Japanese Patent Laid-Open No. 60-145307
(3) Although the principle is slightly different from the above two known techniques, (3) briquette and quicklime consisting of iron ore and carbon sources are placed in a converter (iron bath type smelting reduction furnace) without a preliminary reduction furnace. Examples include a method of obtaining pig iron by oxygen blowing while adding (Japanese Patent Publication No. 57-40883).

[Problem to be solved by the invention] In the operation of such an iron bath type smelting reduction furnace, it is necessary to use carbonaceous materials (particularly in these methods, since economic efficiency is emphasized, cheap fuels such as energy-poor low-grade coal) are used. A large amount of slag forming agent such as limestone or quicklime must be added for the purpose of removing the large amount of sulfur content brought in by the furnace, suppressing slag foaming, and protecting the furnace refractories. In other words, these slag-forming agents function as desulfurization agents and coolants to prevent slag foaming, and from the viewpoint of protecting refractories, it is required that the slag be highly basic. ,
The aspect of the slag-forming agent as a basicity regulator is also important.

However, 3 to 15% of iron oxide raw materials such as iron ore
The gangue content and the 5 to 15% ash content contained in carbonaceous materials vary slightly depending on the brand, but most of it is composed of silica, which is an acidic component, and there is only a very small amount of basic components. It is. Therefore, slag tends to be biased toward the acidic side, and in order to offset this tendency and form basic slag, it is necessary to immerse a large amount of basic slag, and as a result, the amount of slag increases and melts. This results in a significant increase in the load on the reduction furnace operation.

Figure 8 is a graph showing the relationship between the secondary combustion rate, coal consumption rate, lime consumption rate, and slag amount in a certain iron bath type smelting reduction furnace. This is the value when the basicity is adjusted so that the [5] concentration in hot metal can be maintained at 0.15% or less. As is clear from the figure, as the secondary combustion rate increases, the coal consumption rate decreases, and as the input S and ash content also decrease, the lime consumption rate and slag amount also decrease. However, as can be seen in the curve marked * (slag, f, = 70) in the same figure, the operating load of the smelting reduction furnace is relatively high, with a metallization rate of pre-reduced iron of 70% and a secondary combustion rate of 25%. Even under conditions of low slag, the amount of slag reached 200 kg/T, which is significantly higher than that in normal converter operation.

Furthermore, in many examples of the above-mentioned smelting reduction furnaces, a large amount of coal powder is injected into the iron bath, but for this purpose, the steps of drying the lump coal, crushing, and adjusting the particle size are essential. The maintenance load on bottom blowing-related equipment such as bottom blowing tuyeres, piping, and refractories around the tuyeres is also extremely large.

On the other hand, most of the smelting reduction furnace operations are performed in combination with a pre-reduction step, and if the pre-reduction step can be omitted, it would be advantageous to reduce equipment costs and ultimately production costs. There were no proposals for a process using only a smelting reduction furnace. The reason is that if you try to melt the iron oxide raw material and reduce it sufficiently in the smelting reduction furnace alone,
This can be said to be because an excessive load is placed on the melting furnace, and no means have been developed to significantly increase the reducing power. Therefore, numerically, a method has been adopted in which the iron oxide raw material is reduced to some extent in a preliminary reduction furnace, preheated, and then introduced into a smelting reduction furnace. It can be considered that the lack of reducing ability in the smelting reduction furnace is largely due to the characteristics of the carbonaceous material used.

The present invention has been made with attention to these circumstances, and it significantly reduces the slag forming agent consumption rate and the amount of slag produced in the operation of a smelting reduction furnace, thereby reducing operating costs.
The aim is to economically produce hot metal by strengthening the reducing capacity in a smelting reduction furnace and establishing a method that can melt and reduce iron oxide raw materials all at once without preliminary reduction.

[Means for Solving the Problems] The method of the present invention, which has achieved the above object, supplies an iron oxide raw material such as iron ore to a smelting reduction furnace together with a gaseous carbonaceous material and an oxygen-containing material, and The main point is that some of the carbonaceous material is blown into the molten metal to reduce the iron oxide raw material, and the heat of combustion of the gaseous carbonaceous material or its thermal decomposition product is transferred to the molten metal to produce pig iron. It is something that you have.

[Operation] Figure 1 is a graph showing the relationship between the C concentration in molten iron and the FeO concentration in slag.The FeO concentration in slag increases as the C concentration in molten iron decreases, and when C becomes 2% or less Fe
O concentration increases rapidly. It is desirable that the FeO concentration in the molten iron be low from the viewpoint of improving iron yield and preventing slag foaming. On the other hand, in order to obtain high reduction efficiency and secondary combustion rate in the smelting reduction furnace, the C concentration in the molten iron should be high. desirable. However, from the viewpoint of protecting refractories, a relatively low operating temperature is desired, so it is not preferable to increase the Cm degree in the molten iron too much. In order to meet these requirements, it is desirable to control the C concentration in molten iron to approximately 2 to 5%, but in the case of the powdered carbonaceous material used conventionally, the carburization rate into molten iron is slow. Even if the injection method was adopted, it was difficult to control the Cta degree in hot metal to the above level.

In contrast, in the present invention, a gaseous substance such as LNG is used as the carbonaceous substance, and a part of the gaseous substance (preferably 10% or more and may be 100%) is directly blown into the molten metal. is adopted. In other words, gaseous carbonaceous substances such as LNG are immediately thermally decomposed when blown into the molten metal.
In order for the generated C to quickly carburize into the molten metal, C in the molten iron is
The concentration can be quickly controlled, and as a result, the FeO concentration in the slag can be kept to a low value.

Furthermore, since a sufficient amount of C is ensured in the molten iron, the iron oxide raw material can be sufficiently reduced in the smelting reduction furnace, producing CO and reaction heat. If oxygen-containing substances such as pure oxygen or air are simultaneously blown into the smelting reduction furnace, C in the molten iron will
reacts with oxygen in the oxygen-containing substance to form co, and almost 100% of the heat of reaction at this time is transferred to the molten metal, so it is extremely effective in raising the temperature of the molten metal. The CO and H2 generated from the molten metal are subjected to secondary combustion by oxygen and preheated air that are separately blown onto the surface of the molten metal, and this reaction heat is absorbed into the molten metal with high efficiency. Therefore, by continuously or semi-continuously immersing iron oxide raw materials in an amount corresponding to the heat of combustion, these can be rapidly melted, and as mentioned above, by sufficiently increasing the C concentration in the molten iron, the molten iron can be reduced. can do.

On the other hand, unlike conventional solid carbonaceous substances, gaseous carbonaceous substances that function as described above have a low content of 30% and ash, so calcium carbonate, quicklime, etc., which also function as desulfurization agents and basicity regulators, are used. The amount of sludge forming agent used can be reduced, and the amount of slag produced can also be reduced.

That is, at the same time as supplying the gaseous carbonaceous substance and oxygen-containing substance, for the purpose of protecting refractories, preventing slag foaming, maintaining optimal slag properties in consideration of slag drainage, etc.
In addition, by adding an appropriate amount of slag forming agent for the purpose of maintaining the slag basicity at 0.8 to 2, high quality hot metal with low S content etc. can be obtained economically.

Incidentally, one of the most significant advantages of using gaseous carbonaceous substances such as natural gas is improved pig iron quality. That is, if coal is used, 100
Hot metal S is 0 even in operations with lime consumption of kg/T or more.
．． However, in the method of the present invention, as an extreme example of 8i, it is possible to achieve molten CaS of less than 0.15% even when the CaO basic unit is 0. However, since it is also important to protect the furnace refractories and maintain appropriate slag properties, as a practical matter, it is unavoidable to add CaO for basicity adjustment. For example, in Example 1 described below where the slag basicity is 1.4, the lime consumption rate is 42 kg/T, and the slag amount is 96 kg/T.
kg/T operation, the hot metal S content is only 0.016%, and the P concentration is also 0.036%, making it possible to obtain extremely high purity pig iron. Furthermore, in operations with a basicity of 1.8, S is changed to Q, 012%.
Hereinafter, it is possible to reduce the P content to 0.02% or less, and this is an effective manufacturing method for high-P ores. Because high-purity pig iron can be obtained in this way, hot metal reserve F! It is also possible to produce steel by directly proceeding to carbon-free refining in the same container without conducting slag.

The basic configuration of the present invention is as described above, and smelting reduction of iron oxide raw materials is achieved only in a smelting reduction furnace without a preliminary reduction step, and the amount of slag-forming agent used and operational load at this time can be reduced. However, the present invention does not exclude the combined use of a preheating furnace or a prereduction furnace, and the main purpose of the present invention is to ensure excellent melting and reduction performance in the melting and reduction furnace. Therefore, it does not deviate from the present invention to construct a more efficient melting reduction system by combining it with a preheating furnace or a prereduction furnace. In fact, high-temperature exhaust gas is emitted from a smelting reduction furnace, so it is natural to make effective use of this from an energy-saving perspective. Needless to say, it can be used for preheating LNG, etc. by introducing it into a recuperator. In addition, a preheating furnace may be installed separately and used to preheat the iron oxide raw material, or the exhaust gas may be cooled and reformed by acting on a gaseous carbonaceous material such as LNG, and then introduced into a pre-reduction furnace to produce iron oxide. It can also be used for preheating and preliminary reduction of raw materials.

In addition, in the present invention, when the reduction in the smelting reduction furnace is completed, the furnace is normally tilted to tap the iron and slag, but without performing these operations, the gas blown into the smelting reduction furnace is replaced with gaseous carbonaceous material. Molten steel can also be produced by switching the substance to oxygen and subsequently carrying out decarbonization refining. In this case, preheating of the furnace body can be omitted, and heat radiation during standby can also be avoided, which is advantageous in terms of thermoeconomics.

In addition, when implementing the present invention, when LNG or the like is injected into the molten metal from the bottom of the smelting reduction furnace, since the thermal decomposition reaction of LNG is an endothermic reaction, a pine mushroom is formed at the tip of the injection nozzle, but how is the formation of the pine mushroom? Depending on the situation, the ventilation holes may become clogged and blowing may be inhibited. To avoid these inconveniences, it is recommended to use a ring-shaped gas injection nozzle with a core made of refractory material in the center, which stabilizes the injection of gaseous carbonaceous substances over a long period of time. It can be implemented by

[Example] Embodiments of the present invention will be described below with reference to the drawings.

The composition of the iron ore used in this example is shown in Table 1. Further, the gas composition and gas temperature at each main point in the flow sheets of Examples and Comparative Examples are summarized in Table 2.

Table 2 Note) SRV: Smelting reduction furnace, DRF: Preliminary reduction furnace Example 1 FIG. 2 shows a flow sheet of the example. The smelting reduction furnace uses natural gas (523kg/T), high temperature (1200℃) preheated air (289Nm3/T), and lime (42kg/T).
is charged to produce pig iron. The amount of slag produced at that time was 98 kg/T.

The smelting reduction furnace exhaust gas is led to a preheating furnace after being cooled, and the iron ore (1596 kg/T, 700° C.) preheated with the exhaust gas is charged into the smelting reduction furnace. The entire amount of natural gas was assumed to be bottom blown.

Example 2 FIG. 3 is a flow sheet showing another example. The melting reduction furnace is equipped with natural gas (519 kg/T) and oxygen (611 kg/T).
Nm'/T) and lime (42 kg/T) are charged to produce pig iron. The amount of slag produced at that time was 96 kg/T. The exhaust gas from the smelting reduction furnace is led to the preheating furnace after being cooled, and the iron ore (1559 kg/T, 700℃) is preheated by the exhaust gas.
) is charged into a smelting reduction furnace. The entire amount of natural gas was assumed to be bottom blown.

Embodiment 3 FIG. 4 is a flow sheet showing an embodiment of the one-through method. Natural gas (717kg/T) is used in the melting reduction furnace.
, high temperature (1200℃) preheated air (3493Nm3/
T), lime (43 kg/T) is charged to produce pig iron. The amount of slag produced at that time was 104 kg/T. The exhaust gas from the smelting reduction furnace is used to preheat natural gas, and after being cooled to a temperature suitable for preliminary reduction, it is led to the preliminary reduction furnace, where the reduced iron [f, (preliminary Reduction rate) =0.505, 1303kg/T, 70
0° C.] is charged into a melting reduction furnace. A part of the exhaust gas (2160 Nm3/T) discharged from the pre-reducing furnace is led to a hot stove and used for preheating the air. The entire amount of natural gas was assumed to be bottom blown.

FIG. 5 shows a flow sheet of a comparative example using coal.

Coal (994 kg/T) and lime (180 kg/T) are used in the smelting reduction furnace.
kg/T) and high-temperature preheated air (3052Nm3/T) to produce I Ton pig iron.

The amount of slag at this time was as high as 334 kg/T. As in Example 3, the smelting reduction furnace exhaust gas is led to the preliminary reduction furnace after being cooled, and reduced iron (fI11=0) is partially reduced with the reducing gas.
．． 241.1376 kg/T, 700°C) is charged into the melting reduction furnace.

Example 4 FIG. 6 shows a flow sheet of an example in which the secondary combustion rate in the smelting reduction furnace was increased to 55% and the preliminary reduction was limited to the wustite composition using a one-single method. The melting reduction furnace uses natural gas (366 kg/T) and high temperature (1200°C).
Preheated air (2037Nm3/T), lime (zkg/T)
is charged to produce pig iron. In addition, 80% of the natural gas was bottom blown. The amount of slag produced at that time was 100 kg/T. After cooling the smelting reduction furnace exhaust gas and preheating the natural gas, it is led to the pre-reduction furnace, where the reduced iron (f, = 0.0.1397 kg/T, 700°C) is extremely slightly reduced with the exhaust gas.
is charged into a smelting reduction furnace. A part of the exhaust gas (26,788 m3/T) discharged from the preliminary reduction furnace is led to a hot stove and used to preheat the air. The surplus gas energy was 0.1746 cal/T, which is extremely low compared to Example 1, and is an example of a self-contained process.

Embodiment 5 FIG. 7 shows an embodiment flow sheet of a one-through re-former. Natural gas (365 kg/
T), high temperature (1200℃) preheated air (18288m'
/T), lime (38kg/T) is charged to produce pig iron. In addition, 80% of the natural gas was bottom blown. The amount of slag produced at that time was 98 kg/T. After being cooled (1659°C-1100°C) with methane (145Nm'/T) in the melting reduction furnace exhaust gas beam former and reformed (degree of oxidation of reducing gas 0.252-0.119'), it is led to the pre-reduction furnace. , reduced iron (f, = 0.9
0.1121 kg/T, 700°C) is charged into the melting reduction furnace. Part of the exhaust gas discharged from the preliminary reduction furnace (1
02ONm'/T) is led to a hot stove and used to preheat the air. - By effectively utilizing the smelting reduction furnace exhaust gas, it becomes possible to operate with a lower natural gas consumption rate than in Example 3.

[Effects of the Invention] The present invention is configured as described above, and can obtain the effects summarized below.

(1) By using a gaseous carbonaceous material with a lower ash content than a solid carbonaceous material, it is possible to significantly reduce the unit consumption of slag-forming agent charged into the smelting reduction furnace and the amount of slag produced. It is possible to significantly reduce the operational load of the smelting reduction furnace and the problems of slag treatment.

(2) By blowing a gaseous carbonaceous substance into the molten metal, C? ! 4 degrees can be efficiently and quickly increased, and the reduction performance in the melting reduction furnace can be dramatically improved. As a result, the iron oxide raw material can be melted and reduced without going through a preliminary reduction process, and the production cost can be significantly reduced by simplifying the process.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between CtIA degree in molten iron and FeO concentration in slag, Figures 2 to 7 are flow diagrams showing examples, and Figure 8 is a graph showing the relationship between the secondary combustion rate and coal raw material in an iron bath type smelting reduction furnace. It is a graph showing the relationship between unit 1 limestone wheel position and slag amount. Figure 1 0 / 2 3 Hiro Dashi Registration Sun Cj

Claims (1)

[Claims] An iron oxide raw material such as iron ore is supplied to a smelting reduction furnace together with a gaseous carbonaceous substance and an oxygen-containing substance, and a part of the gaseous carbonaceous substance is blown into the molten metal to reduce the iron oxide raw material and at the same time A method for melting and reducing iron oxide raw materials, characterized in that pig iron is produced by applying combustion heat of a gaseous carbonaceous material or its thermal decomposition product to a molten metal.