JPH09227919A - Smelting reduction method of chromium ore - Google Patents

Abstract

PROBLEM TO BE SOLVED: To promote reduction reaction and, at the same time, to reduce the erosion of refractory of a reaction vessel by specifying a Hardgrove index and volatile matter content of carbonaceous material simultaneously added with an ore, at the time of executing smelting reduction of chromium ore in a metallurgical reaction vessel of a converter, etc. SOLUTION: The carbonaceous material added together with the chromium ore into molten iron in the converter, uses a coal having >=45 Hardgrove index(HGI) and <=10% volatile matter(VM). Further, at least 90% of this coal have >=3mm grain diameter and the secondary combustion ratio in the furnace is regulated to >=30%. By this method, the reduction of the chromium ore in slag is promoted and reduction efficiency is improved, and further, the erosion of the refractory can be reduced. Then, an Mg-C brick having 8-25% C content is preferably used for at least a part of the wall part being in contact with the slag in the furnace.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for smelting and reducing chromium ore, and more particularly to an attempt to effectively produce a chromium-containing molten metal, which is a mother molten metal of stainless steel, by directly using inexpensive chromium ore. .

[0002]

2. Description of the Related Art In recent years, in a smelting reduction furnace such as a converter, a so-called smelting reduction technology has been developed in which a chromium-containing molten metal is obtained by directly using an inexpensive chromium ore instead of using expensive alloy iron. In this smelting reduction, most of the chromium ore used is a sandy ore with a small particle size, so it is important to put such a sandy chromium ore into the converter without scattering. . Moreover, since chromium ore is extremely hard, it is also an important technique to reduce the wear of the supply pipe.

In view of such circumstances, the inventors have conducted researches on a solution to the above problem, and as a result, not only can the powdery chromium ore be supplied without the wear of the pipe, but also at a high yield. Then, a method for charging the material into the furnace was found and disclosed in Japanese Patent Publication No. 7-33536. In this method, in the top-bottom blowing converter, an ore charging lance that can be operated independently of the top-blowing lance has a radius of 2 /
By setting the height of the lance to a predetermined level in relation to the top blowing lance, the ore is supplied at a low speed without wear of the pipes, and the addition yield is high. It is possible to put in the furnace.

[0004]

By the above method, it becomes possible to stably charge chromium ore with a high yield, but still the following problems remain. That is, chrome ore is iron oxide
It is an ore containing metal oxides such as chromium oxide, and the smelting reduction process reduces such metal oxides with carbonaceous materials such as coke in molten slag. Here, as the furnace wall refractory, so-called MgO-based refractory, in particular, MgO-C brick having excellent oxidation resistance is often used. In this way, the metal oxide is reduced by the carbonaceous material in the slag, but since the metal oxide also reacts with the carbon in the refractory, carbon is consumed from the MgO-C brick, and as a result, the brick is consumed. Will be melted. As a result, there is a problem that the refractory life is significantly shorter than in the case of using a normal converter.

As a technique for preventing the refractory melting loss in the smelting reduction furnace, the technique of adding a MgO source is particularly advantageous from the viewpoint of preventing the elution of MgO from the MgO-C structure. Although proposed in Kaihei No. 7-11319 and No. 7-11321, such a technique has not yet achieved satisfactory results.

Further, in the smelting reduction furnace, the heat supply controls the supply of chromium ore, and it is effective to increase the secondary combustion in order to increase the heat supply capacity. However, when the secondary combustion rate is increased, It has the disadvantage of shortening the refractory life.

The present invention advantageously solves the above-mentioned problems, and promotes the reaction between the metal oxide in the ore and the carbonaceous material and the reaction with the carbon in the refractory during the smelting reduction of the chromium ore. It is an object of the present invention to propose a smelting reduction method for chromium ore, which can improve the chromium reduction efficiency and reduce the wear of refractory and thus extend the life of the converter by suppressing the above.

[0008]

[Means for Solving the Problems] As a result of many studies to achieve the above object, the inventors have found that the carbonaceous materials supplied as a heat source and a reducing agent are not limited to the reduction of chromium ore, It was newly found that it also has a great influence on the refractory life of the converter. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. 1. In the molten iron housed in a metallurgical reaction vessel such as a converter, carbon material and chromium ore are added, in a so-called melting reduction smelting method of melting a chromium-containing molten metal by supplying oxygen gas, as the carbon material , Hard Globe Index (HGI)
A method for smelting and reducing chromium ore, which comprises using a coal having a volatile component amount (VM) in carbonaceous material of 45 or less and 10% or less.

[0010] 2. In the above 1, in the reaction vessel, the C content is 8 to 25% in at least a part of the portion contacting the slag
1. A method for smelting reduction of chromium ore, which is a converter using MgO-C bricks. 3. 1. The method for smelting reduction of chromium ore according to 1 or 2, wherein the secondary combustion rate in the reactor furnace is 30% or less. 4. In the above 1, 2 or 3, a method for smelting reduction of chromium ore, characterized in that coal containing at least 90% of particles having a particle size of 3 mm or more is used.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The clarification process of the present invention will be described below. By the way, the inventors first investigated the reduction state of slag and the melting mechanism / speed of refractory when a chrome ore was charged, using a small test converter. Generally, when chromium ore is charged from the chromium charging lance, as shown in FIG. 1, the ore does not form particles one by one, but becomes a group of particles and falls straight without being affected by the upward flow and falls into the slag. It is considered that the chromium ore that has entered and reached the slag is reduced by the carbonaceous material in the slag while melting in the slag.

However, according to the result of the actual test converter, as shown in FIG. 2, a part of the ore reaches the refractory wall without being melted, and the oxide in the ore, especially the iron oxide, is present. Has been found to react with the carbon in the refractory and promote the melting damage of the MgO-C brick. It was also clarified that the peroxide state of such slag becomes extremely large under the condition that the secondary combustion rate of the top blowing lance is high. In FIGS. 1 and 2, numeral 1 is a converter, 2 is an upper blowing lance,
3 is a chrome charging lance.

Therefore, the present inventors believe that promoting the reduction of chromium ore in the slag is effective not only for improving the reduction efficiency but also for reducing the melting loss of the refractory material. The same experiment was carried out by changing the kind of the above. Generally, coke is often used as a carbonaceous material used for the smelting reduction of chromium ores.
Examples are shown in Japanese Patent Laid-Open No. 55-91913 and Japanese Patent Laid-Open No. 55-91913. In the smelting reduction of iron ore, so-called general coal (volatile matter VM: about 25 to 40%), which is cheaper than coke, is used, and lump coal is directly sprayed from the top of the furnace and pulverized coal is directly sprayed from a nozzle provided on the shoulder of the furnace. Are disclosed in JP-A-3-177513. Further, recently, a method of using anthracite containing water in advance in the smelting reduction of chromium ore is disclosed in JP-A-7-41872.

The results of smelting reduction experiments of chrome ores using various carbon materials including the above-mentioned carbon materials show that the reduction rate of chrome ores and the refractory life are dramatically improved when a specific coal is used. Turned out to be. Therefore, when the properties of the coal for which dramatic improvement results were obtained were investigated, it was found that the carbonaceous material had a Hard Globe Index (HGI) of 45 or less and a volatile component content in the carbonaceous material. It has been determined that those satisfying (VM) of 10% or less are effective for improving the reduction rate of chrome ore and the life of refractory. Here, HGI is defined in JIS M 8801 and is a predetermined sample (powder having a particle size of about 1 mm: about 50 g).
Is crushed by a hard glove tester, sieved with a predetermined sieve (74 μm), and the mass (W) under the sieve is substituted into the following equation to obtain an index of crushability. HGI = 13 + 6.93 W

Next, in order to find out the reason why these coals have a dramatic improvement effect, as shown in FIG. 2, coal 4 is charged from the hopper on the furnace, and immediately after the addition, the furnace is blasted immediately after the addition. Sampling was performed during the slag. The results are shown in FIGS. 3 (a) and 3 (b) for comparison with the results of examining the particle size distribution of the carbonaceous material recovered from the slag before and after the addition. As is clear from the figure, it was found that the carbonaceous material satisfying the above-mentioned conditions was rapidly atomized in the furnace after being charged. Also, in the 5 ton test converter experiment, the same experiment was carried out on the coke, which had a low reduction rate, and the carbonaceous material with HGI of more than 45, and the particle size was only slightly decreased before and after the introduction, and thermal collapse was observed. There wasn't.

Thus, the HGI is 45 or less, and the VM
If coal of 10% or less is used, first of all, the reaction interfacial area, which is most important for the reduction reaction, increases by refining the particles by thermal decay after addition in the furnace. As a result, it is considered that the reduction rate in the smelting reduction step is improved. Also, the second
A part of the collapsed carbonaceous material is formed by secondary combustion in the furnace
It reduces CO ₂ and lowers the gas temperature. Therefore, this C
It is considered that the melting temperature of the refractory is reduced by the reduction of the gas temperature due to the reduction of O ₂ and the rapid reduction of the metal oxide described above in the slag.

The HGI is 45 or less, but the VM is 30
When an experiment was also performed using about% steaming coal as the carbonaceous material, it was confirmed that the carbonization became fine after charging, but the following problems occurred in operation. First, the amount of C scattered into the dust was increased, the addition efficiency was extremely deteriorated, and as a result, the carbonaceous material remaining in the slag was decreased and the reduction rate of the ore was decreased. The reason for this is considered to be that when the VM is high, the reaction of volatile components immediately progresses when placed in the furnace, and the amount of exhaust gas generated sharply increases, so that the scattering of carbonaceous materials to the outside of the system increases. . Secondly, the life of the refractory was significantly deteriorated. It is considered that this is because the exhaust gas temperature rises when the VM is high, so that the temperature of the slag surface increases particularly as the secondary combustion rate increases.

Therefore, in the present invention, the carbonaceous material has a low volatile content (VM) of 10% or less, and when added to the furnace, it is instantly thermally decomposed and atomized in the gas in the furnace.
We decided to use coal that satisfies the following requirements. In addition, when coal with HGI of more than 45 was used, improvement of refractory life could not be expected. The reason for this is that the thermal cracking of the carbonaceous material did not occur in the sampling from the inside of the furnace, and therefore the above-mentioned coal did not undergo thermal collapse, so the reduction promoting effect and the temperature lowering effect of the exhaust gas could not be obtained. it is conceivable that.

By the way, as the MgO-C brick, a brick whose C content in the brick is usually used is C> 5%, but from the viewpoint of slag oxidation resistance, C> 8% is better. Increasing C is advantageous in terms of slag oxidation resistance and spalling. In the experiment, the upper limit of C could be used up to 25%, but when C was high, it was disadvantageous in terms of denseness, which is important in terms of abrasion resistance, and prevention of oxidation resistant gas.

FIG. 4 shows the result of investigation on the relationship between the C concentration in brick and the erosion rate of the slag line (see FIG. 2). As is clear from the figure, excellent effects are obtained when the C content is in the range of 8 to 25%, particularly 13 to 20%. However, as described above, spalling, oxidation resistant gas, etc. are also important depending on the site, so it is preferable to appropriately use bricks having different C concentrations depending on the site.

Further, as the secondary combustion rate increases, the erosion rate of the slag line increases. This is because, as already mentioned, when the secondary combustion rate increases, the thermal efficiency transmitted to molten steel decreases,
This is because the slag surface temperature and the exhaust gas temperature rise, and under such conditions, the oxidation of bricks by the oxides in the slag progresses. On the other hand, if coal with HGI of 45 or less is used, the reduction rate increases and the exhaust gas temperature decreases as described above, which is advantageous for preventing brick oxidation, but the secondary combustion rate is still high. Refractory protection is still disadvantageous under certain conditions.

FIG. 5 shows the results of an examination of the relationship between the secondary combustion rate and the erosion rate of the slag line (the interface between the slag and the gas phase). Here, as coal, Vietnam (HG
I = 35, VM = 5.8%) was used. Grain size is 6 to 50 mm is 80
% Or more. As is clear from the figure, when the secondary combustion rate exceeds 30%, the melting rate rapidly increases. Therefore,
It is preferable to operate at a secondary combustion rate of 30% or less. According to the survey results, the exhaust gas temperature rises sharply when the secondary combustion rate exceeds 30%, and it is estimated that the melting loss of the refractory has advanced due to the decrease in the heat efficiency of the secondary combustion rate.

As described above, as the carbonaceous material, the VM is 10
% And coal with an HGI of 45 or less is most effective, and the result is
The life of converter refractory using MgO-C brick for slag line is dramatically improved. However, when this carbonaceous material was used, the C scattering rate to dust was increased as compared with the normal lump coke. When the particle size of scattered C in the dust was examined, it was 99% for 2 mm or less and 0.5 mm or less for 85%. Based on the above findings, it is considered that fine carbonaceous materials are disadvantageous in terms of dust loss, and in order to investigate the effect of charged carbonaceous material grain size on dust loss, tests were conducted by sieving anthracite by various methods. It was A carbonaceous material having a particle size distribution shown in Table 1 was sieved to obtain a carbonaceous material having a particle size distribution shown in Table 2. In the table, symbol a to
e is intended mainly for cutting particles having a particle size of 3 mm or less, and f is intended for mainly cutting particles having a particle size of 1.2 mm or less.

[0024]

[Table 1]

[0025]

[Table 2]

FIG. 6 shows the results of the operation using the sieving anthracite charcoal as compared with the case without sieving and the case with coke. As is clear from the figure, dust loss could be reduced when cutting mainly those with a grain size of 3 mm or less, but surprisingly 1.
When the particles with a grain size of 2 mm or less were mainly cut, the effect of reducing dust loss was hardly seen. Moreover, in terms of operation, when sieved at 1.2 mm, there was a disadvantage that the sieve was frequently clogged. From the above findings, it has been found that it is effective to suppress the ratio of pulverized coal having a diameter of 3 mm or less to substantially 10% or less, preferably 5% or less, in order to reduce the dust loss of the carbonaceous material.

In the present invention, the metallurgical reaction vessel is not particularly limited, and any of a top-blowing furnace, a bottom-blowing furnace and a side-blowing furnace can be used, but an upper-bottom blowing converter is particularly preferable. Is.

[0028]

EXAMPLES Experiments were conducted using a 150 ton scale top-bottom blown smelting reduction furnace. 130 tons of hot metal that had been desiliconized and dephosphorized in advance was transported by a truck truck, 30 tons of scrap was loaded in advance, and then charged into a smelting reduction furnace. The lance for charging the chromium ore and the top blowing lance for supplying oxygen were arranged as shown in FIG. MgO—C bricks having a carbon content of 13 to 20% were used for the portion that became the slag line.

The height of the upper blowing lance 2 is from the stationary molten steel surface.
4.2m, and the height of the input lance is 5.2m from the stationary molten steel surface.
Was blown, and blowing was carried out under the conditions of top-blowing oxygen amount: 400-800 Nm ³ / min, bottom-blowing oxygen flow rate: 80 Nm ³ / min, bottom-blowing nitrogen: 40 Nm ³ / min. Various types of coal (A brand (Vietnamese): HGI = 3 from 1550 ℃ to 1600 ℃
5, VM = 5.8%, B brand (Russia): HGI = 38,
VM = 3.7%, C brand (made in China): HGI = 42, VM =
9%) was supplied as a carbonaceous material at a ratio of 1.60 kg / Nm ³ -O ₂ .
The carbonaceous material was sieved by using an inclined vibrating screen called a jumping screen with a horizontally long mesh of about 3 to 4 mm × 17 mm. Therefore, the carbonaceous material after sieving had the particle size shown in d in Table 2, and the ratio of 3 mm or more was 96% or more.

When the hot metal temperature reached a predetermined temperature, chromium ore was supplied. Supply amount of chrome ore: 1.35
The ratio was kg / Nm ³ -O ₂ and carbon material: 1.25 to 1.4 kg / Nm ³ -O ₂ . The blowing slag was periodically sampled and the temperature was measured to maintain the temperature in the range of 1570 ° C to 1600 ° C. The chromium concentration in the slag varied in the range of about 2-4%. After the lapse of a predetermined time (about 70 to 80 minutes), the lance was raised to stop the supply of chromium ore, and further, the blowing for supplying only oxygen was carried out for about 5 to 7 minutes. The secondary combustion rate was around 25%. Immediately after the completion of blowing, colemanite was charged into the furnace to improve the slag after the treatment. This operation was continuously performed for about 100 charges, and the melting point of each refractory was measured with a laser profiler. The obtained result is
Table 3 shows the summary. As is clear from the table, when the carbonaceous material according to the present invention is used, the wear rate of the refractory can be reduced to 1.2 mm / ch or less under the high chromium reduction rate of 89% or more. It was

[0031]

[Table 3]

Further, as Comparative Examples 1 and 2, the secondary combustion rate is
The operation was carried out in the same manner as in the example except that it was increased to 35% and 45%. In this case, although the chromium reduction rate was improved, the refractory melting loss of the slag line was significantly deteriorated.

Further, in Comparative Examples 3 to 7, D brand (made in China, HGI = 49, VM = 9.9%), E brand (Russian coal,
HGI = 75, VM = 18%), F brand (Australian coal, HGI =
68, VM = 20%), G brand (Australian coal, HGI = 70, VM
= 25%) and blast furnace coke were used. The operating conditions are the same as in the example. However, although the input coefficient was the same as that of the above-mentioned coal for coke, Russian coal and Australian coal were operated at 1.8 kg / Nm ³ -O ₂ during the heating period and 1.6 kg / Nm ³ -O ₂ during the smelting reduction period. Otherwise, operation was difficult from the viewpoint of sloping and temperature maintenance. Further steam coal (HGI = 40, VM = 30
%) Was attempted, but it was practically impossible to operate because of the large scattering to the above-mentioned dust.

In Comparative Examples 3 to 7 as well, about 80 charges were continuously carried out, and the erosion site of each refractory was measured by a laser profiler. There was a locally large amount of melting damage, and repairs were unavoidable. Further, the reduction rate of chromium was also deteriorated.

[0035]

As described above, according to the present invention, not only the reduction rate of chromium ore can be improved, but also the melting loss of refractory material in the smelting reduction furnace, which has been a problem in the past, in particular the local melting loss, can be markedly reduced, and the fire resistance can be improved. Since the product life can be greatly extended, it is possible to achieve improvement in productivity and reduction in refractory cost in the smelting reduction of chromium ore.

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which a chromium ore is dropped when a chromium ore is charged from a chromium charging lance.

FIG. 2 is a diagram showing a melt-damaged state of a furnace wall refractory when chromium ore is added by the above method.

FIG. 3 is a graph showing a particle size distribution of carbonaceous material before and after charging into a furnace.

FIG. 4 is a graph showing the relationship between the C concentration in brick and the erosion rate of the slag line.

FIG. 5 is a graph showing the relationship between the secondary combustion rate and the slag line melting rate.

FIG. 6 is a graph showing the influence of the type and size of carbonaceous material on C scattering to dust.

[Explanation of symbols]

 1 Converter 2 Top blowing lance 3 Chromium input lance 4 Coal

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Fumio Sato Inventor 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Yoshihisa Kitano 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Kyoichi Kameyama 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Terahata Chimichi, Kawasaki-cho, Chuo-ku, Chiba City 1 Address: Kawasaki Steel Co., Ltd., Chiba Steel Works (72) Inventor, Koji Aida, Kawasaki-machi, Chuo-ku, Chiba-shi, Chiba, No. 1 Inside Technical Research Institute, Kawasaki Steel Co., Ltd. (72) Shuji Takeuchi, Kawasaki-cho, Chuo-ku, Chiba, Chiba Address Inside Kawasaki Steel Corporation Technical Research Center

Claims (4)

[Claims] 1. A so-called smelting reduction smelting method for melting a chromium-containing molten metal by adding carbonaceous material and chromium ore and supplying oxygen gas to the molten iron contained in a metallurgical reaction vessel such as a converter. A method for smelting reduction of chromium ore, characterized in that as the carbonaceous material, coal having a hard globe index (HGI) of 45 or less and a volatile component amount (VM) in the carbonaceous material of 10% or less is used. 2. The reaction container according to claim 1, wherein the content of C is 8 to 25% in at least a part of the portion in contact with the slag.
1. A method for smelting reduction of chromium ore, which is a converter using MgO-C bricks. 3. The method for smelting reduction of chromium ore according to claim 1, wherein the secondary combustion rate in the reactor furnace is 30% or less. 4. The particle size according to claim 1, 2 or 3, wherein:
A method for smelting reduction of chromium ore, characterized in that coal containing at least 90% of 3 mm or more is used.