JPH0611883B2 - Smelting reduction furnace - Google Patents

Description

The present invention relates to a smelting reduction furnace for producing pig iron by smelting reduction of iron ore using a rotary furnace.

[Prior Art] In recent years, a technology for smelting and reducing iron ore by, for example, a converter-type rotary furnace has been developed.

As the manufacturing process, for example, a method in which seed hot water is charged in advance and iron ore is charged in a furnace together with coke which is a reducing agent, anthracite, coal which is a slag-forming agent, and oxygen is blown to perform reduction is generally used. Known to be.

As already known, this process is based on the converter steelmaking method by blowing from the top and bottom, and as the refractory lining for the smelting reduction furnace, Mg0-C and Mg0-CaO-, which have a good track record of use in conventional converters, are used.
Carbon-bonded graphite-containing basic refractories such as C, MgO-MgCO ₃ and CaCO ₃ -C are often used. These refractories have excellent corrosion resistance against slag having a relatively wide range of basicity (CaO / SiO ₂ ), and the amount of erosion loss can be further reduced by enriching MgO in the slag. or,
It has excellent thermal shock resistance and high durability in converters. However, it is hard to say that it is sufficiently suitable as a refractory material for a smelting reduction furnace.

[Problems to be Solved by the Invention] As described above, the carbon-bonded graphite-containing basic refractory material exhibits significantly excellent characteristics in a converter having a relatively high basicity and capable of MgO-rich operation. The smelting reduction furnace has the following problems.

To describe the reduction of iron ore in detail, iron ore forms a mixed layer with coke, anthracite, and a slag-forming agent on the surface of the seed melt, and is preheated and melted by the combustion heat of coke and anthracite by top-blown oxygen. Is further reduced by the reaction of Fe ₂ O ₃ + 3C2 [Fe] + 3CO by the coke in the mixed layer. The generated CO is 2CO + O2 due to the reaction with top-blown oxygen.
An exothermic reaction of 2CO ₂ occurs in the furnace mouth furnace. Therefore, the upper part of the slag bath surface has a high temperature and an oxidizing atmosphere.

The slag composition of the slag bath is adjusted to slag basicity (CaO / SiO ₂ ) 1.0 to 1.3 to increase the reduction rate, and Al ₂ O ₃ and MgO concentrations differ slightly depending on the iron ore and carbonaceous materials, Two
It is around 0% and 5%.

Under these conditions, when lining a conventional carbon-bonded graphite-containing basic refractory such as MgO-C, the slag bath and the lining brick at the bottom of the slag bath surface have low basicity, high Al ₂ O _{3 and} low MgO slag. To contact.

In general, basic bricks containing MgO as a main component produce low-melting minerals such as Monticellite (CaO / MgO / SiO ₂ ) and erode low basicity slag.

Incidentally, amount of dissolution into the slag MgO in brick CaO-SiO ₂ -
It is governed by the MgO saturated solution concentration of the four components of Al ₂ O ₃ -MgO.
That is, when the basicity (CaO / SiO ₂ ) is kept constant, the dissolved concentration of MgO increases and the elution of MgO in bricks increases as the Al ₂ O ₃ concentration increases. In order to reduce the MgO elution concentration in the slag, there is also a method of suppressing the elution amount by enriching the MgO source such as dolomite into the slag, but when the slag is granulated and used, MgO is used. Increasing the amount is not desirable (MgO hydration reaction has a very low reaction rate compared to CaO hydration reaction, the concrete structure is likely to break within a few years after construction, and MgO is severely restricted. Therefore, the generation of high MgO slag becomes a problem in resource utilization.) In the current blast furnace method, which is the current ironmaking process, the slag produced is mainly effectively used as a roadbed material and a cement raw material. .

The smelting reduction method aims to replace the blast furnace as an ironmaking method, and if the generated slag contains a large amount of MgO, the following two problems occur.

(B) If the content of MgO is close to the saturated amount, it tends to be digested, which is not preferable as a roadbed material.

(B) If the content of MgO is 7% or more, it becomes unsuitable as a raw material for cement. Therefore, in order to effectively utilize the produced slag in the route of the current blast furnace method, the MgO content of the slag cannot be increased. Therefore, under the circumstances where the enriched operation of MgO in the slag is impossible for this reason,
76% of MgO and 17% of C, which show high durability in the conventional converter
In the case of lining MgO-C bricks, the elution of MgO in the bricks limits the rate of erosion.

During blast furnace operation, the rate of erosion at the relevant part is 0.04 mm / blowing acid time (min), and the amount of erosion is as large as 1 heat 4.8 mm. When the lining layer thickness is 600 mm, the furnace stops at 120 heat and melts. The loss rate is about 4 times larger than 0.01 mm in the conventional converter / blown acid time (min).

On the other hand, the above-mentioned reduction product gas is above the slag bath surface.
Due to CO ₂ and O ₂ gas blown into the top, a high-temperature oxidizing atmosphere was created, and the preferential oxidation of graphite caused a marked decrease in strength on the operating surface of MgO-C bricks, and the melting rate was as large as 0.2 mm / propoxylic acid time (min). Become. As a countermeasure against this, an attempt was made to improve the oxidation resistance by adding metals such as Al and Si and preferentially oxidizing them, but the improvement was not radical.

The present invention has been made to provide a smelting reduction furnace having a lining structure that is highly suitable for smelting reduction of iron ore.

[Means for Solving the Problems] The present invention relates to a method in which iron ore is introduced into a furnace together with a reducing agent and a slag-forming agent.
Provided and blown oxygen into the furnace to smelt and reduce the iron ore, and in the smelting and reduction furnace that produces pig iron, the furnace wall located below the slag bath surface in the operating state and the lining of the furnace bottom contain carbon bond graphite. A smelting reduction furnace characterized in that it is made of neutral bricks, and the lining of the side wall portion located above the slag bath surface in the operating state is made of a ceramic-bonded basic brick having a high melting point.

The present inventors first conducted an elucidation experiment of the in-furnace conditions for the refractory for high-temperature oxidizing atmosphere above the slag bath surface, and as a result, the conventional carbon-bonded graphite-containing basic refractory
It was confirmed that the oxide-based refractory of the ceramic bond has high durability. Specifically, the Al ₂ O ₃ —SiO ₂ refractory material is stable against oxidation because it softens at a high temperature in the relevant part, but has low corrosion resistance.

Basic refractories that form direct bond ceramic bonds such as MgO-Cr ₂ O ₃ and MgO-MgO.Al ₂ O ₃ showed high durability. In the fixed type smelting reduction furnace, the upper part of the slag bath surface is not constantly immersed in molten slag or molten metal,
Since slag or molten metal does not permeate through the pores in the brick, only the splash adheres to the brick surface, so a dense altered layer is not formed on the operating surface side, and ceramic bond basic fire resistance There is almost no occurrence of structural spall which is a defect of the product.

On the other hand, damage due to thermal shock can be dealt with by strengthening heat retention in order to minimize temperature fluctuation between operations, and graphite such as that generated in carbon-bonded graphite-containing basic bricks can be used. There is no tissue deterioration due to the oxidation of
High durability at the upper part of the slag bath surface.

Also, for the refractory in the lower basicity and high Al ₂ O ₃ low MgO slag bath, the MgO
Based on Al ₂ O ₃ aggregate, which has a smaller diffusion rate than that, contains graphite that prevents slag infiltration and improves thermal shock resistance, and further contains Al or Si alone or in combination with two types to oxidize graphite. It was confirmed that the application of carbon-bonded graphite-containing neutral bricks, which was designed to prevent this, significantly reduced the elution of aggregates and demonstrated high durability. Although it has a lower melting point than Al ₂ O ₃ ,
Since the solubility of the site is about 1500 ° C at most, there is no adverse effect due to the softening of the aggregate.

Therefore, in the smelting reduction furnace of the present invention, the bricks forming the inner lining below the slag bath surface and the bricks forming the upper lining above the slag bath surface have different brick suitability as bricks of different properties. It was done.

As the graphite-containing neutral refractory of this carbon bond,
Al ₂ O ₃ -C type and Al ₂ O ₃ -SiC-C type are suitable. In the case of Al ₂ O ₃ -C type, Al ₂ O ₃ contains 75 to 90% by weight and C 7 to 22% by weight. , 1% to 5% of Al, Si, etc. as graphite oxidation inhibitors
When contained, it is suitable for ensuring slag resistance, oxidation resistance, thermal shock resistance, and in the case of Al ₂ O ₃ -SiC-C system, Al ₂ O _{3 is} 75 to 90% by weight. C5-20%, SiC5-15%
In addition, 1 to 5% of a metal such as Al and Si as a graphite oxidation inhibitor is suitable for ensuring slag resistance, oxidation resistance and thermal shock resistance.

Incidentally, SiC in this case is vitrified under operating conditions, coats the brick surface, particularly suppresses oxidation of graphite,
Functions to improve spall resistance.

Further, it is preferable to use Al ₂ O ₃ , SiC, C and the like having a purity of 96% or more in order to suppress the reaction with slag.
When an Al alloy such as Mg-Al or Cal-Al is used as the Al source from the economical viewpoint, Hg and Ca are contained in about 2%, but Mg,
Since Ca has many negative factors, it is preferable to make it 2% or less as much as possible.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG.

The smelting reduction furnace in this example is a converter type smelting reduction furnace having a furnace capacity of 170 ton / ch.

In FIG. 1, A is a smelting reduction furnace, and the inside of the furnace is a molten metal bath M.
And iron ore, coke, slag, mixed bath area S, and further upper atmosphere area B.

The furnace wall in the upper atmosphere area B is lined with a direct bond brick 1 of MgO-Cr ₂ O ₃ which is a ceramic bond basic brick, and in addition, carbon bond graphite containing Al ₂ O ₃ -SiC-C is included. Sex brick 2 was lined. In the drawing, L is an upper blowing lance N is a lower blowing nozzle.

Here, the results of laboratory tests of the composition properties of each of the bricks used are shown together with those of the conventional MgO-C system.
Shown in 1.

The characteristic is that the erosion property against slag equivalent to smelting reduction of basicity 1.0, Al ₂ O ₃ 20%, MgO 5% is Al ₂ O ₃ -C = Al ₂ O ₃
-SiC-C> is in the order of MgO = Cr ₂ O ₃ Direct _{Bond> MgO-C, Al 2 O} 3 system when low dissolution rate into the slag in the oxidation wear of the graphite-containing bricks under high-temperature oxidizing atmosphere Is remarkable.

Table 2 shows the erosion rate when the smelting reduction reaction of one charge was completed in about 2 hours in a converter type smelting reduction furnace with a furnace capacity of 170 ton / ch as compared with the conventional lining structure. .
Compared with the conventional method, the melting rate of the furnace wall above the slag bath surface is 1 /
In addition, the area below the slag bath surface can be reduced to 1 / 2.4, and the life of the lining is greatly reduced, which greatly reduces the unit consumption of furnace material, improves productivity, and greatly reduces manufacturing costs.

Although an example of Al ₂ O ₃ -C bricks was not described in detail, the same corrosion loss rate as Al ₂ O ₃ -SiC-C in Table 1 can be obtained. Incidentally, Al ₂ O ₃ -C, added to Al ₂ O ₃ -SiC-C. Al, Si and metal in the case of C and for example, Al in the brick, generates Al ₄ C _3,
It is effective in suppressing the oxidation of graphite and developing the strength of the graphite matrix part.

In the present invention, in order to prevent spalls caused by rapid cooling of the lining bricks due to heat radiation from the furnace opening between the operations, the heat retention was strengthened compared to the case where the conventional MgO-C bricks were lined.

[Advantages of the Invention] In the smelting reduction furnace of the present invention, the lining structure is lined with a ceramic bond basic refractory in the high temperature oxidizing atmosphere above the slag bath surface, and the carbon bond graphite-containing neutral in the other parts. By lining the brick, the loss rate of the lining of the entire furnace becomes uniform, and the furnace life can be greatly extended, and the cost of the furnace material can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional explanatory view showing an embodiment of the smelting reduction furnace of the present invention. 1 ... Ceramic bond basic brick, 2 ... Carbon bond graphite-containing neutral brick, B ... Atmosphere region, L ... Top blowing lance, M ... Molten metal bath, N ... Bottom blowing nozzle, S ... Iron ore, coke, anthracite, Slag bath for slag pipe.

Front page continuation (72) Atsushi Nakao Atsushi Nakao 1-1-1, Emitsu Hachimanto-ku, Kitakyushu, Fukuoka Prefecture Inside the Engineering Department, Nippon Steel Co., Ltd. ―1-1 ― Inside Nippon Steel Co., Ltd. 3rd Technical Research Laboratory (72) Inventor Katsuhiko Sakamoto No. 1 Tsukiko Hachiman-cho, Sakai City, Osaka Prefecture Inside Nippon Steel Co., Ltd. Sakai Steel

Claims (3)

[Claims] 1. A slag in a smelting reduction furnace in which iron ore is supplied into a furnace together with a reducing agent and a slag-forming agent, and oxygen is blown into the furnace to melt-reduce the iron ore to produce pig iron. The inner wall of the furnace wall located below the molten surface is made of carbon-bonded graphite-containing neutral bricks, and the inner wall of the furnace wall located above the slag bath surface in operation is made of ceramic-bonded basic bricks. Smelting reduction furnace 2. The furnace wall lining located below the slag bath surface in an operating state is 75 to 95% by weight of Al ₂ O ₃ and C = 7 to 22.
Containing chemical components within the range of%, Al, Si type 1 or 2
The smelting reduction furnace according to claim 1, wherein the smelting reduction furnace is formed of a carbon-bonded graphite-containing neutral brick containing 1 to 5% of seeds. 3. A furnace wall lining located below the surface of the slag bath under operating conditions contains 75 to 90% by weight of Al ₂ O ₃ and C = 7 to 2
2%, SiC has a chemical component within the range of 5 to 15%, and is formed of a carbon-bonded graphite-containing neutral brick containing 1 to 5% of one or two of Al and Si. The smelting reduction furnace according to claim 1, wherein