JP2552899B2 - Smelting reduction method for iron ore - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an iron bath by blowing iron ore or powder containing iron ore together with an oxygen-containing gas into the iron bath while controlling the carbon concentration in the iron bath. The present invention relates to a method for producing molten iron by stirring iron and reducing iron oxide in iron ore by carbon in the iron bath.

[Conventional technology and its problems]

The blast furnace method is generally used as a method for obtaining molten iron from iron ore, but it requires high equipment costs, lacks the degree of freedom of production fluctuations, requires pretreatment of iron ore such as pelletizing or sintering, and uses it at high temperatures. It has drawbacks such as high strength coke and lack of freedom in carbon source.

Recently, several smelting reduction methods have been proposed as alternatives to the blast furnace method. For example, in the method called the iron bath type, a carbon source, a flux, and iron ore are charged from the upper part of the converter and heated by blowing oxygen upward to melt the iron ore and remove carbon and slag in the slag. This is a method of obtaining molten iron by reducing iron oxide in iron ore with carbon in the iron bath.

In this case, oxygen is blown with the cooling gas from the bottom of the converter using a double-tube tuyere used in general converter steelmaking, and is also used in combination with top blowing, and the carbon source is an inert gas. At the same time, a method of bottom blowing is also proposed. (JP-A-62-4810, JP-A-62-185811, JP-A-62-185811
62-224610, etc.) In the smelting reduction with these iron baths, the stirring operation of the bath is an essential requirement. Therefore, the conventional method is the so-called double tube tuyere, or the single tube or slit method.
This is a method of blowing an inert gas such as N ₂ or Ar. Disadvantages of these methods are that the life of the nozzle and the refractory around the nozzle is short, and that the hydrocarbon gas for cooling and Ar are expensive, which is problematic in terms of economic efficiency and operational stability.

In addition, all of these smelting reduction methods using an iron bath method are methods in which iron ore is once slagged and reduced, and the iron oxide concentration in the slag is extremely high, which causes significant wear of the refractory and combustion of the carbon source. It has a drawback that the heat transfer efficiency of heat to the iron bath is low.

In addition, oxygen is also blown in at the bottom with an expensive cooling gas, and this cooling gas not only contributes to the reaction at all, but also cools the iron bath, resulting in an increase in the amount of carbon source and oxygen used. Will bring.

A method of pre-reducing iron ore outside the furnace in order to compensate for the increase in carbon source and oxygen usage due to this low heat deposition efficiency has also been proposed, but it is clear that the basic drawbacks have not been improved at all. Is. Therefore, these iron bath type smelting reduction methods have not yet been put to practical use.

A method using a shaft furnace has also been proposed as another method, but there is a restriction on the carbon source, and if powdered iron ore is charged from above, it will be scattered by the gas in the shaft furnace. Although it is blown from the mouth, it has not been put to practical use due to the problem that the improvement of thermal efficiency due to the preliminary effect of the charge by the gas in the furnace, which is the greatest advantage of the shaft furnace, cannot be achieved.

As described above, in the iron ore smelting reduction method, the life of the blowing nozzle for stirring the bath is short, the carbon source is limited, the thermal efficiency is poor, the iron oxide concentration in the slag is high, and the fire resistance is high. It is strongly desired to improve the problems of the prior art, such as heavy wear of the material, pretreatment of powdered iron ore, and difficulty in adjusting the production amount.

(Knowledge regarding solution of problems) In the smelting reduction method of iron ore, the problem of the present invention is that the life of a blowing nozzle for bath agitation is short, there is a restriction of a carbon source, thermal efficiency is poor, and slag It is to improve the problems of the prior art, such as high iron oxide concentration, severe wear of refractory, pretreatment of powdered iron ore, and difficulty in adjusting production. Regarding the solution to these problems, in a method of smelting and reducing iron ore while adding iron ore, a carbon source, flux and oxygen while controlling the carbon concentration in the bath to obtain an iron bath, iron ore or iron ore is blown from a blowing nozzle. Basically, a powder containing stones is blown into a bath together with an oxygen-containing gas, and a single tube made of ceramics is used for the blowing nozzle or a top blow of gaseous oxygen is used in combination to slag the dissolution of iron ore. The iron oxide in the iron ore is reduced by the carbon in the iron bath before reaching the slag layer above the iron bath, and the heat of reaction between the gaseous oxygen and the carbon in the iron bath causes the iron ore. It was found that the temperature decrease of the iron bath due to the reduction thermal reaction of stones can be offset, and the iron bath temperature can be controlled, and the smelting reduction can be efficiently performed, thus improving the above-mentioned problems of the prior art.

(Structure of the invention) The above-mentioned object is a method of obtaining molten iron by adding iron ore, a carbon source, flux and oxygen to melt-reduce the iron ore while controlling the carbon concentration in the iron bath to obtain molten iron. Alternatively, the iron ore or the powder containing iron ore is supplied with oxygen-containing gas in an upward or obliquely downward direction from a blowing nozzle consisting of a ceramic single tube installed on the side of the iron bath on the side wall of the reaction vessel and below the iron bath surface. It is achieved by a method of smelting reduction of iron ore, characterized in that it is blown into an iron bath.

The iron ore used in this method need only be in powder form, can be of any brand, and does not require preliminary treatment. Powdered sinter or pretreated iron ore such as pre-reduced iron ore may be used. The carbon source is also free, in the form of lumps, powder,
Any material such as coal, graphite or coke may be used. As a method for adding a carbon source, any method conventionally proposed may be used.

The oxygen-containing gas may be gaseous oxygen itself, but may be appropriately diluted with nitrogen or another inert gas.

As the flux, lime-based, dolomite-based, fluorite-based, etc. are used, but they may be blown into the iron bath together with the iron ore and the oxygen-containing gas, or may be simply added to the upper part of the iron bath. The former may be more effective depending on the properties of the iron ore.

The method of blowing iron ore or powder containing iron ore requires blowing into an iron bath. Desirably, the gas is blown upward from a nozzle installed at the bottom of the reaction container or obliquely downward from a nozzle installed on the side of the side wall of the reaction container and below the bath surface.

The blowing nozzle is a refractory single tube nozzle. Desirably, Si ₃ N has excellent wear resistance, thermal shock resistance, and heat resistance.
Ceramic nozzles such as _{4 and} Sialon are good.

Controlling the carbon concentration and temperature of the iron bath is achieved by controlling the amounts of carbon source, gaseous oxygen, and iron ore added. The CO gas generated at this time may be used as an auxiliary means for increasing the temperature of the iron bath by introducing an oxygen source into the upper portion of the reaction vessel and burning it, or may be recovered and used for other fuel or the like. Further, the sensible heat may be used to preheat the iron ore used in this method.

Although not a direct object of the present invention, the present invention can also perform smelting reduction as well as melting of scrap iron. In this case, preheating the scrap iron by the sensible heat of the exhaust gas is also an efficient means.

The present invention uses powdery iron ore without any preliminary treatment, and blows an oxygen-containing gas into an iron bath as a carrier gas to reduce iron oxide in the iron ore with carbon in the iron bath. However, the basic method is to control the temperature of the iron bath by offsetting the temperature drop of the iron bath due to the reduction endothermic reaction of the iron ore by the heat of reaction between the gaseous oxygen and the carbon in the iron bath.

In principle, the iron ore is melted in the iron bath rather than in the slag and reduced by the carbon in the iron bath before reaching the slag layer above the iron bath. Therefore, there is no transfer of iron oxide in the iron ore to the slag layer, and the iron oxide concentration in the slag can be maintained at a low level. Furthermore, the gaseous oxygen blown at the same time reacts with the iron in the iron bath to form FeO near the blowing nozzle, which locally raises the temperature and F
eO promotes the dissolution of iron ore. This FeO is reduced by carbon in the iron bath in the process of levitating in the iron bath. That is, the reaction of Fe + 1/20 ₂ = FeO and the reaction of FeO + C = Fe + CO are carried out in the iron bath, so that the reaction heat of C + O = CO is transferred to the iron bath.

Unlike the conventional method, heat is directly transferred without passing through slag, so that the thermal efficiency is extremely excellent. Further, the gaseous oxygen also causes a reaction of C + 1/20 ₂ = CO to proceed at the same time, and the reaction heat is also transferred to the iron bath.

On the other hand, Fe ₂ O _{3 in} iron ore is carbon in the iron bath and Fe ₂ O ₃ + 3C =
It is melted and reduced by the reaction of 2Fe + 3CO. The decrease in temperature of the iron bath due to this endothermic reaction is compensated by the heat of CO formation described above, and prevents the decrease in iron bath temperature. It is obvious from the above description that it is easy to raise or lower the temperature of the iron bath by changing the use ratio of iron ore and gaseous oxygen. The CO gas generated here becomes exhaust gas, but it has a large amount of latent heat. This recovery may be collected as raw gas and used as fuel, or may be used for raising the temperature of the iron bath by supplying oxygen from the upper portion and burning in the present method.

Although these reactions consume carbon in the iron bath, this supplementation can be accomplished by conventional techniques. That is, it may be added from above the iron bath onto the iron bath, or may be blown into the iron bath using a nozzle. Even in this case, in the present invention in which iron ore and gaseous oxygen, which will be described later, are simultaneously blown into the iron bath, the stirring force is strong and it is an advantageous condition for transferring the carbon source to the iron bath. Is better. Therefore, coal, graphite or coke can be freely selected as the carbon source.

As described above, in the present invention, it is essential to blow oxygen and iron ore into the iron bath at the same time. Blowing oxygen into the iron bath without the use of any cooling gas or oil was not achieved in the prior art. When oxygen is blown in, the temperature near the nozzle rises significantly, and as described above,
This is because FeO is also generated, which causes the nozzle to wear significantly. In the present invention, by blowing iron ore together with the oxygen-containing gas, the temperature rise near the nozzle is prevented, and the deposits that have aggregated at the tip of the nozzle are generated to achieve protection of the nozzle. Although this method can be operated economically enough, there is also a phenomenon in which the nozzle is physically worn when a hard solid such as iron ore is blown. As a countermeasure, we have confirmed that using a refractory material such as Sialon or Si ₃ N ₄ that has excellent wear resistance and excellent fire resistance and thermal shock resistance can dramatically improve the nozzle life. The position of the nozzle is
If you are in an iron bath, you can use bottom blowing or diagonal downward blowing.

Furthermore, a mixed powder of iron ore and flux can be blown together with the oxygen-containing gas. This is an effective means especially in the case of iron ore, which is hardly soluble. As the iron ore used in the present invention, any iron ore that is normally used can be used as long as it is a powder, and since the reaction efficiency is excellent, no pretreatment is required.

Unlike the blast furnace, the method of the present invention does not have to be continuously operated for a long period of time and can be operated in accordance with production demands, and can be used when a large amount of molten iron is required or a small amount is required.

(Specific Disclosure of the Invention) The present invention will be specifically described below with reference to Examples.

Example 1 200 kg of hot metal (temperature 1530 ° C., composition C: 4.9%, Si: tr, Mn: 0.
30%, P: 0.011%, S: 0.025%, balance Fe), bottom injection of iron ore (carol lake), quick lime, and gas O ₂ was performed with a sialon nozzle with an inner diameter of 3.5 mmφ installed at the bottom of the furnace. , Smelting reduction of iron ore. Blow rate is iron ore 760 g / min, quick lime 40 g / min, gas O ₂ 70 Nl / min, N ₂ 10 Nl /
It was a minute. In addition, coke as carbonaceous material
It was added continuously at 0 g / min. The temperature drop accompanying the reaction was compensated by induction heating with a high frequency coil attached to the furnace. This treatment was carried out for 60 minutes. (% Of the obtained slag
T, Fe) was 1.8%, and the reduction of iron ore proceeded efficiently. In addition, the blowing nozzle was completely sound, slag-like deposits were formed on the upper surface of the nozzle, and no melt loss of the nozzle was observed.

Example 2 An experiment was conducted under substantially the same conditions as in Example 1, using the top blowing of gas O ₂ together. That is, iron ore, quicklime,
Gas O ₂ and N ₂ respectively 760 g / min, 40 g / min, 70 Nl / min,
Bottom injection was performed at a blowing rate of 10 Nl / min, and top blowing of gas O ₂ was performed at 210 Nl / min. Also coke
It was charged from the upper part of the furnace at an addition rate of 245 g / min. In this experiment, high frequency power was not applied, but an increase in bath temperature was observed. (Approx. 10.5 ℃ / min) 15kg every 10 minutes
When added, the bath temperature became almost constant at 1530 ° C. In the treatment for 60 minutes, 45 kg of iron ore was smelt-reduced, and 75 kg of scrap could be melted. (% T, Fe) of treated slag is 2.1
%Met. Moreover, in this experiment, although a ceramic nozzle of ZrO ₂ —CaO system was used, no melt loss was observed.

Example 3 Coke powder was blown from the bottom while smelting ore was blown obliquely downward to carry out smelting reduction. Blowing speed is ore 1500
g / min, quick lime 80 g / min, oxygen 80 Nl / min, nitrogen 10 Nl / min. The coke was bottom blown at 400 g / min with 30 Nl / min nitrogen gas. Also, oxygen was top-blown at 400 Nl / min with a water-cooled copper lance. The temperature during the treatment was about 1530 ° C, and it was possible to carry out the experiment while keeping it almost constant. The amount of molten metal is 200 kg, and the composition is C: 4.5%, Si: tr, Mn: 0.25%, P: 0.015%, S:
0.015%, balance Fe.

The above experiment was carried out for 30 minutes. Of treated slag (% T, F
e) was 1.5%. In this experiment, in which no melting loss of the blowing nozzle was observed, 45 kg of iron ore could be efficiently smelt-reduced. In addition, CO from top-blown oxygen
The bath temperature could be kept almost constant by burning the gas.

(Effects of the Invention) As described above, the present invention solves the problem that the life of the blowing nozzle used for stirring the bath is short in the iron bath type smelting reduction furnace. Compared to the tuyere method, it has a great economic effect in that it enables inexpensive and stable stirring technology. Furthermore, by directly injecting iron ore into a powder form, a highly efficient reduction rate can be obtained, and the ore can be reduced simultaneously with the stirring of the bath, which is a great economic effect. Further, by using the top blowing of the gas O ₂ together, the hot metal can be manufactured in a scrap ratio in a high range, and an elastic smelting reduction technology suitable for the scrap market can be provided.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the smelting reduction furnace used in Example 1, FIG. 2 is an enlarged vertical cross-sectional view of a blowing nozzle portion (a portion surrounded by a circle) in FIG. 1, and FIG. FIG. 4 is a vertical cross-sectional view showing the smelting reduction furnace used in Example 2, and FIG. 4 is a vertical cross-sectional view showing the smelting reduction furnace used in Example 3. 1 ... Refractory, 2 ... Induction coil, 3 ... Molten metal, 4 ...
Slag, 5 ... Blowing nozzle, 6 ... Ceramic blowing nozzle, 7 ... Refractory (castable), 8 ...
… Furnace bottom refractory, 9 …… O ₂ top blowing lance, 10… diagonal bottom blowing lance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsunori Fukui 11-1 Showa-cho, Kure City, Hiroshima Prefecture Kure Research Institute, Nisshin Steel Co., Ltd. (56) References JP-A-63-33511 (JP, A) JP-A 1-252709 (JP, A)

Claims (2)

(57) [Claims] 1. In a smelting reduction method of iron ore for obtaining molten iron by adding iron ore, a carbon source, flux and oxygen to an iron bath in a reaction vessel, a ceramic single piece installed at the bottom or side of the reaction vessel. A method for smelting reduction of iron ore, which comprises blowing iron ore or powder containing iron ore into an iron bath using an oxygen-containing gas from a tube nozzle. 2. In a smelting reduction method of iron ore for obtaining molten iron by adding iron ore, a carbon source, a flux and oxygen to an iron bath in a reaction vessel, an oxygen-containing gas is top-blown using a top-blown lance. However, smelting reduction of iron ore characterized by blowing iron ore or powder containing iron ore into an iron bath using an oxygen-containing gas from a ceramic single-tube nozzle installed at the bottom or side of the reaction vessel Law.