JPH02141513A - Smelting reduction iron making method - Google Patents

Abstract

PURPOSE:To lower the concn. of Cr in formed molten iron and slag by discharging more than half the molten iron to lower the content of iron oxide when the content of the iron oxide in the molten slag in an iron bath type smelting reduction furnace lined with refractories contg. a Cr oxide is high and then discharging a part of the molten slag. CONSTITUTION:The molten iron in the above-mentioned iron bath type smelting reduction furnace is tapped by 50 to 90% of its amt. when the content of iron oxide content of the molten slag in the furnace is >=1.5wt.%. The finish reduction period is provided to sufficiently reduce the iron oxide in the molten slag and to adjust the iron oxide concn. in the molten slag to <=0.9wt.% after the above-mentioned tapping. The molten slag after the above-mentioned adjustment which is 5 to 100wt.% of the amt. of the molten iron existing in the furnace is discharged. As a result, the content of the Cr contained as the impurity element in the formed molten iron is lowered and the concn. of the Cr oxide of the slag to be discharged is simultaneously lowered as well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing hot metal using an iron bath type smelting reduction furnace lined with a refractory containing chromium oxide.

[Prior Art] FIG. 3 shows an example of an iron bath type melting reduction apparatus described in, for example, Japanese Patent Application No. 17236/1983. The iron bath type melting reduction furnace 1 is in the form of a converter lined with a refractory 7.

Reference numerals 4 and 5 indicate a side blowing tuyere and a bottom blowing tuyere for supplying oxygen, stirring gas, powder raw material, etc., which are provided as necessary.

6 is an oxygen top blowing lance.

In the iron bath smelting reduction method, the molten material in the iron bath smelting reduction furnace 1, which is made up of hot metal 2 and molten slag 3, is
While adding the iron oxide-containing raw material, carbonaceous material, and solvent, top-blown acid is applied using the oxygen top-blowing lance 6 to reduce the iron oxide to iron and increase the amount of hot metal. When a predetermined amount of hot metal is reached, the hot metal and Discharge the molten slag.

At this time, the hot metal and molten slag are not discharged in their entirety, but a portion remains in the furnace and is used as seed metal 2 and molten seed slag 3 for the next heat.

An iron bath type smelting reduction furnace sufficiently burns the CO gas generated by the molten material in the furnace to achieve a secondary combustion rate, that is, the rate of gas discharged outside the furnace ((CO, +H, 0)/( CO+CO2+H2
+u, o)) It is preferable from the thermoeconomic point of view to operate with a large value of x too (%).

In that case, the heat load on the refractory becomes large, so as a large resistant material for the iron bath type smelting reduction furnace, use a refractory containing chromium oxide, such as maguro brick (MgO: 70%).

It is said that a lining of 30% Cr2O3 is good.

However, according to the knowledge of the present inventors, if an iron bath type melting reduction furnace lined with maguro bricks is operated without special measures, the following problems will occur.

When the refractory is eroded, chromium oxide migrates into the slag. While the iron oxide concentration of the slag is high, the chromium is mainly distributed in the slab.

Therefore, if the slag is discharged in this state, it is not preferable because the slag contains chromium oxide.

On the other hand, when the iron oxide concentration in the slag decreases, chromium oxide is reduced and mainly distributed in the molten iron.

However, molten iron containing chromium as an impurity element is undesirable because, for example, when it is refined and further rolled to produce a thin steel plate, the cold workability of the thin steel plate is impaired, and its uses are limited.

FIG. 4 is a diagram showing an example of the change in iron oxide concentration of molten slag in iron bath smelting reduction. During the smelting reduction period 12, the concentration of iron oxide in the molten slag is high, but during the finishing reduction period 13
In this case, the iron oxide in the molten slab is reduced and the iron oxide concentration is reduced.

In the conventional iron bath type smelting reduction method, the final reduction period is not performed, or after the final reduction period, the tapping and slag of molten iron and molten slag are performed simultaneously or continuously at approximately the same time.

In this case, as described above, the problem of either the slag containing chromium oxide or the hot metal containing chromium could not be avoided.

[Problems to be Solved by the Invention] The present invention provides a smelting reduction ironmaking method that can lower the chromium content contained as an impurity element in the produced hot metal and simultaneously reduce the chromium oxide concentration in the discharged slag. This is what we provide.

[Means for Solving the Problems] The present invention is carried out using an iron bath type melting reduction furnace lined with a refractory containing chromium oxide. Compared to the blast furnace method, the iron bath smelting reduction method can use powdered raw materials as they are, so the raw material pretreatment step of molding the powdered raw materials into a lump can be omitted.
It also has the advantage of being able to use low-grade carbonaceous materials. In the present invention, a refractory containing chromium oxide is used as the lining material of the iron bath type smelting reduction furnace, and the refractory containing chromium oxide has excellent high heat resistance and corrosion resistance for slabs. . As refractories containing chromium oxide,
Chromatic refractories (e.g. Cr2O3: 45%, MgO
: 35%), maguro refractories (MgO: 40%H
Cr 203 :35%), etc., but the present invention can be applied to all refractories containing chromium oxide.

In the present invention, the iron oxide content of the molten slag is 1.5% by weight.
Under the above conditions, 50 to 90% of the amount of hot metal is tapped. In the present invention, slag is not tapped during tapping, but it is difficult to separate hot metal and molten slag, and this does not prevent a small amount of molten slag from being discharged from the furnace mixed with the hot metal. In the present invention, tapping is performed in a state where the iron oxide content of the molten slab is 1.5% by weight or more.

The present inventors investigated the concentration of chromium in the molten slag (Cr) and the concentration [Cr] in the hot metal in an iron bath type smelting reduction furnace, and grasped the behavior of the chromium distribution ratio [Crl/(Cr). As a result, the present invention was completed. FIG. 1 is a diagram showing an example. As shown in Figure 1, the molten slag contains 1.5 iron oxides.
When the content is more than % heavy starvation, [Cr]/(Cr) is sufficiently small, and almost all of the chromium from the lining refractory is distributed to the molten slab, and almost no chromium is contained in the hot metal. Therefore,
If the pig iron is tapped during this period, the hot metal obtained by tapping will contain almost no chromium.

In the present invention, 50 to 90% of the amount of hot metal in the furnace is tapped.

If the tapped iron amount is less than 50%, productivity per furnace volume decreases, which is not preferable. If the tapped iron amount is over 90%, the amount of seed metal remaining in the furnace for the next charge is too small.
The smooth operation of the next charge will be impaired.

In the present invention, a final reduction period is provided after tapping, and the iron oxide in the molten slag is sufficiently reduced so that the iron oxide concentration in the molten slag is 0.7% or less. This reduction converts the iron oxide in the molten slag to the carbonaceous material excessively contained in the molten slag and the carbon in the remaining molten iron, FeO+ C→Fe+CO
This can be achieved by reacting as follows.

In the present invention, the content of iron oxide in the molten slag is 0.7% by weight.
Under the following conditions, only molten slag is tapped without tapping hot metal. However, it is difficult to separate the hot metal and molten slag, and this does not prevent a small amount of hot metal from being mixed with the molten slag and being discharged from the furnace.

In Figure 1, when the iron oxide content in the molten slag is 0.7% or less, [Cr] / (Cr) is large, and the [Crl concentration of the hot metal remaining in the furnace is high; Ma\
Then the iron will not be tapped. This hot metal becomes the seed water for the next charge, but as already mentioned, if the iron oxide content of the molten slag is 1.5% by weight or more in the next charge, the hot metal [ CRL is also kept low.

If the amount of slag is too large, the amount of molten seed slag in the next charge will be too small, impairing the smooth operation of the next charge.

In addition, if the amount of slag produced is small and too much molten slag is left in the furnace, the productivity per unit volume of the furnace decreases, which is a problem. Therefore, in the present invention, 50 to 100 of the amount of hot metal in the furnace is
% by weight of the molten slag remains in the furnace and the remaining molten slag is slaged.

[Function] FIG. 2 is an explanatory diagram showing the relationship between the tapping period, the slag tapping period, and the oxygen concentration of molten slag according to the present invention.

In the present invention, iron is tapped during the oxidation period when [Cr]/(Cr) is low. Therefore, the [Cr] of the tapped hot metal is low.

After tapping, a small amount of molten pig iron and the entire amount of molten slag remain in the furnace, which will be used as the next seed hot water.

This small amount of hot metal and the entire amount of molten slag are left in the furnace to reduce the molten slag. When this reduction progresses and the iron oxide concentration in the molten slag becomes 0.7 or less, as shown in Figure 1,
Although Crl/(Cr) increases, in the present invention, slag is produced in this state, that is, in a state where the chromium oxide concentration in the slag is low.

As the above operations are repeated, the amount of chromium remaining in the furnace gradually increases. As a result, there is an effect that the melting loss of the refractory containing chromium oxide is suppressed in an equilibrium manner.

In addition, if the amount of chromium accumulated in the furnace exceeds the limit value, finish reduction should be carried out by selecting an opportunity to melt a steel type that is desirable to contain chromium or a steel type that can contain chromium. After that, the hot metal containing chromium is discharged and used.

In this way, it is possible to prevent the spread of chromium contamination of hot metal and slag when using a refractory containing chromium oxide.

[Example] Iron ore, coke, and limestone were charged into a converter-like melting reduction furnace with an internal volume of 180 m3 and lined with maguro bricks, while oxygen was blown at the top (3000 ON m'/h) and nitrogen gas was blown at the bottom. (120ONm3/h), and a "finish reduction period" in which iron ore input was stopped and only blowing and coke supply were carried out. The temperature of the molten material in the furnace during operation is 1
It is within the range of 450 to 1520°C.

The amount of hot metal in the seed bath and the amount of seed slag were varied to various levels as shown in Table 1, but at the end of the ``smelting reduction period'', 30 tons of hot metal, which was increased from the amount of hot metal in the seed hot metal, was discharged, and then ``finish reduction'' was carried out. After carrying out the "period", 9 tons of slag, which was increased from the seed slag, was discharged.

Chromium content of discharged hot metal when various combinations of seed molten pig iron amount: A and seed slag amount: B are changed: [%C
r], Cr-11 content of discharged slag: (%Cr
) are shown in cases 1 to 3 of Table 3. In either case, the iron oxide concentration in the slab during the "smelting reduction stage" is in the range of 3 to 6%, while the iron oxide concentration in the slag during the "finish reduction stage" is 0.4 to 0.8%. % range. For comparison, unlike the case of the present invention, there are cases in which hot metal and slag are discharged only during the "smelting reduction period" (Case 4), and cases in which hot metal and slag are discharged after the "finish reduction period" (Case 4). Case 5
) are also shown.

In all cases 1 to 3, the effect of reducing [%Crl and (%Cr) was observed compared to the conventional method (cases 4 and 5). However, particularly in case 3, which satisfies the conditions of the present invention, remarkable effects were observed.

In case 3, once every 20 taps, the discharge of hot metal after the "melting reduction period" is stopped, and after the "finish reduction period" is completed, the hot metal and slag are discharged, and [Cr] is 0.5 to 2.6. % of hot metal was obtained and used for the production of steel grades in which chromium is an active ingredient.

The components of the obtained hot metal other than chromium are in the following ranges in each case.

C=4.5-4.7%, 5i=0.09% or less, S=
0.03% or less, P=0.04% or less.

Table 1 It is possible to solve the problem of chromium contamination of the produced hot metal and slag, which is a problem when using a lined iron bath type smelting reduction furnace.

[Brief explanation of the drawing]

Figure 1 shows the oxygen concentration in molten slag and the chromium distribution ratio [C
r]/(Cr), Figure 2 is an explanatory diagram showing the relationship between the tapping period, the slag tapping period, and the oxygen concentration in molten slag according to the present invention, and Figure 3 is an iron bath type smelting reduction diagram. A diagram showing an example of the device,
FIG. 4 is an explanatory diagram of the conventional iron bath smelting reduction method. 1: Iron bath type smelting reduction furnace, 2: Hot metal, 3: Molten slag, 4: Side blowing tuyere, 5: Bottom blowing tuyere, 6: Oxygen top blowing lance, 7: Refractory. Patent applicant Nippon Steel Corporation

Claims (1)

[Claims] Using an iron bath-type smelting reduction furnace lined with a refractory containing chromium oxide, 50 to 90% of the molten iron in the furnace is discharged when the iron oxide content of the molten slag is 1.5% by weight or more, and then A treatment is performed to reduce the iron oxide concentration of the molten slag to 0.
After reducing the amount to 9% by weight or less, 50% of the amount of hot metal present in the furnace
A smelting reduction ironmaking method characterized by leaving ~100% by weight of molten slag in the furnace and discharging the remaining molten slag.