JPH01252710A - Method for operating iron bath type smelting reduction furnace - Google Patents

Abstract

PURPOSE:To improve reducing speed of iron ore and also secondary combustion ratio by specifying molten slag quantity in a furnace, remaining carbon quantity in the furnace and pressure of oxygen jet from to blowing lance at the time of reduction-refining molten pig by charging the iron ore and coal as reducing agent and blowing oxygen from top blowing lance into a iron bath type reduction furnace. CONSTITUTION:Under condition of remaining the molten pig 4 and the molten slag 5 in the converter type refining furnace 1 providing bottom blowing tuyeres 2 and the oxygen top blowing lance 3, the iron ore and the coal as the reducing agent are charged from the furnace top part and oxygen gas is blown from the top blowing lance 3 and inert gas, oxygen gas, etc., are blown from the bottom blowing tuyeres 2 and iron ore is reduced, to produce the molten pig. In this case, >=50% of the whole quantity of oxygen for blowing is blown from the top blowing lance 3 and the balance is blown from the bottom blowing tuyeres 2. Further, the refining furnace is operated under condition that the quantity of the molten slag 5 in the refining furnace is made to >=500kg/m<2> of cross section area of the furnace and the remaining carbon quantity in the furnace is made to >=5wt.% of the molten slag and also cavity depth Ls of the molten slag by oxygen jet of the top blowing lance 3 is made to <=0.7 of thickness Hs of the molten slag.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing molten iron using an iron bath type smelting reduction furnace.

[Prior Art] JP-A No. 61-213310 is an invention related to operating conditions regarding slag amount conditions, bottom blowing gas conditions, and slag components in producing molten iron-based alloys. The conditions for the amount of molten slag and the amount of residual carbon material required from the perspective of promoting the reduction reaction are not specified, and as will be explained later, from the perspective of secondary combustion, the conditions for the cavity of molten slag by oxygen jet are not specified. is not specified.

Furthermore, in Japanese Patent Application No. 181358/1982, the melting reduction furnace is pressurized to 2 atmospheres or more, and the coke/slag ratio is specified in the range of O01 to 0.3, but this invention pressurizes the melting reduction furnace. The purpose of this invention is to suppress slag forming, which is different from the present invention both in purpose and means.

In addition, Japanese Patent Application No. 1988-088662 describes the firing point area of an oxygen jet and the solid carbon/solid carbon content when melting iron-based metals and reducing oxides by burning solid carbon suspended in slag.
Although it specifies the ratio of slag amounts, it is aimed at slag foaming and only uses the concept of soft blowing using an oxygen jet acid blowing method, and does not include the idea of a slag cavity.

The present invention is a method for achieving both a high reduction rate and a high secondary combustion rate in iron bath smelting reduction in a converter-type reaction vessel, and as an operating method that reduces the amount of molten slag.

It stipulates the amount of carbonaceous material remaining in the furnace and the method of blowing the oxygen jet in the upper blowing acid.

[Lesson 9 that the invention attempts to solve! i] The present invention provides iron bath smelting reduction in a converter reaction vessel,
High reduction rate (reduction rate: 0.04 k+5ol-02
/T.

The present invention discloses an operating method for achieving both a high secondary combustion rate (secondary combustion rate of 40% or higher) and a high secondary combustion rate (secondary combustion rate of 40% or higher).

However, the secondary combustion rate here is a value defined by equation (4).

[ii. Means and operation for solving the problem] The present invention has the following features:
At least 50% of the total oxygen is blown into the molten material consisting of molten iron and molten slag from the upper lance in a converter-type reaction vessel capable of top-bottom blowing. , and the amount of residual carbonaceous material dispersed and floating in the molten slag is always in relation to the amount of molten slag (kg), (2)
Under the conditions of the equation, the depth Ls of the cavity formed in the molten slag is always (3) in relation to the thickness of the molten slag layer.
This is an operating method characterized by setting the conditions of Eq.

Molten slag amount ≧500kg/m”・・・・・・・・・
・・・・・・・・・・・・(1) However, the amount of molten slag is the value obtained by dividing the amount of molten slag in the furnace (kg) by the toilet area (m2) Amount of residual carbon in the furnace (kg) > Amount of molten slag (kg) x
o, os・・・・・・・・・・・・・・・(2)
However, Ls) and (Hs) are (am). FIG. 1 is a diagram showing an example of an iron bath type melting reduction furnace in which the present invention is implemented. The reaction vessel 1 is, for example, a converter-type vessel lined with an MgO-based refractory, and is equipped with a bottom blowing tuyere 2 at the bottom, through which oxygen gas or inert gas can be blown. The upper part is equipped with a lance 3 for blowing acid, and a lance 3 for blowing acid.
and molten slag 5 is blown with an oxygen jet.

In general, in iron bath smelting reduction, the reduction reaction occurs at a) the interface between the ore and molten iron during ore injection, b) the interface between molten slag and molten iron, and C) the molten slag and dispersed carbonaceous material in the molten slag. d) Occurs at the interface between molten slag and granulated iron in molten slag. In the case of ore injection, the reduction rate is high.

The generated gas inevitably increases the agitation of the molten iron, resulting in a decrease in the secondary combustion rate. Therefore, in order to achieve both a high reduction rate and a high secondary combustion rate, raw materials such as ore and carbonaceous materials are introduced into the furnace from above. The reduction reaction at this time is b
) to d).

Therefore, according to the experimental results of the present inventors regarding the reduction reaction, the reduction reaction rate is influenced by the amount of molten slag and the amount of carbon material dispersed and suspended in the molten slag.

The results shown in Figure 2 were obtained.

Based on these results, the conditions for increasing the reduction reaction in the slag and causing an overall efficient reduction reaction are (1)
The conditions for equation and equation (2) were obtained.

Next, regarding secondary combustion, since the dissolved carbon contained in molten iron has good reactivity with oxygen jet, at temperatures such as iron bath smelting reduction (1300℃ or higher), - oxidation It only burns up to carbon.

This is because when the top-blown oxygen jet directly contacts molten iron and burns with carbon in the molten iron, carbon monoxide in the combustion gas increases and the secondary combustion rate decreases. Therefore, by interposing molten slag between the oxygen jet that blows oxygen from the top and the molten iron to provide a shielding effect, direct combustion of carbon in the molten iron by the oxygen jet is inhibited, and the carbonaceous materials in the molten slag are combusted. As a result, a high secondary combustion rate of 40% or more can be obtained.

Regarding this shielding effect, in experiments conducted by the inventors, the secondary combustion rate was determined by the ratio of the depth Ls of the cavity of the molten slag generated by the top-blown oxygen jet to the thickness Hs of the slab layer, as shown in Figure 3. I got different results.

From these results, it is possible to obtain a high secondary combustion rate of 40% or more under the conditions of equation (3).

[Example] Top-bottom blowing converter melting reduction furnace with rated molten metal capacity of 120 tons (4 bottom blowing tuyeres, double pipe, outer pipe: inner diameter 24+*m, LP for cooling)
molten iron (C: 4.2%, Si: 0.3%) was added to the inner tube: inner diameter 20 mm + oxygen gas injection)
0 tons was charged.

Iron ore and coal were charged into the furnace from the upper hopper.

The nozzle of the top blowing lance is a 7-hole nozzle (hole diameter 60 mm x 7) with a radiation angle of 15 degrees for soft blowing, and the slag cavity depth Ls is calculated using equation (5), and the ratio with the slag thickness Hs is determined as follows. The lance height was adjusted to the value of . The ratio of the amount of carbonaceous material in the slag (weight f&)/the amount of slag (weight) will be within a predetermined range based on the measurement results of the secondary combustion rate and the mass balance calculation from the values of the carbonaceous material supply rate and the oxygen supply rate. I adjusted it as follows.

n: Number of holes in the lance, d: Diameter of the holes in the lance (m+n)FO,
:Top blow MJi (Nm'/hr), 1g Nislag-
Distance of lance tip (mm), ρII: Specific gravity of molten iron, ρS
: Specific gravity of molten slag As shown in Table 1, five different conditions (A, B, C, D , E) were operated steadily for about 12 hours, and the average values of the secondary combustion rate and the T and Fe values in the slab were obtained.

We also investigated the presence or absence of slag foaming, which often occurs when the reduction rate is insufficient. The main operating conditions and the above ;**a data are shown in Table 1.

In addition, the amount of oxygen delivered in each case was approximately 30,000 N m'
/hr, ore (unreduced) supply amount is 600 ~! 000k
The operation was carried out at a temperature of molten iron of 1450 to 1520° C. and a basicity of slag (Cab/Sin) of 1.0 to 1.5.

In addition, a portion of the molten iron and molten slag in the furnace was discharged every 1.5 to 2 hours.

As shown in Table 1, only in the case of A, which satisfies all the conditions of the present invention, the secondary combustion rate is high, the (T, Fe) in the slag is low even if the ore supply rate is high, and the forming In the case of B with a large slag cavity, the reduction rate was quite high and (T, Fe) in the slag only increased slightly, but the secondary combustion rate was not high. When the carbonaceous ratio in the slag is less than 0.03, the reduction rate is extremely slow;
As a result, forming was induced.

In addition, when the amount of slag is relatively small, such as about 400 kg/m'', the reduction rate is generally low, so the (
T, Fe) remained high, and the ore supply rate had to be lowered.

[Effects of the Invention] The present invention enables operation that achieves both a high reduction rate and a high secondary combustion rate in iron bath smelting reduction.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of an iron bath type smelting reduction furnace in which the present invention is implemented. FIG. Figure 3 shows Ls/Hs
It is a figure which shows the relationship between and secondary combustion rate. Patent applicant Nippon Steel Corporation

Claims (1)

[Claims] When 50% or more of the total oxygen is blown into the molten material consisting of molten iron and molten slag in a converter-type reaction vessel capable of top-bottom blowing from an upper lance, the amount of molten slag is constantly controlled. (1), and the amount of residual carbonaceous materials dispersed and floating in the molten slag is always in relation to the amount of molten slag (kg), and the condition of (2) is satisfied, and the amount of residual carbonaceous material dispersed and suspended in the molten slag is A method for operating an iron bath smelting reduction furnace, characterized in that the depth L_s of the produced cavity always satisfies the condition of equation (3) in relation to the thickness of the molten slag layer. Amount of molten slag ≧500kg/m^2...(1) However, the amount of molten slag is calculated by dividing the amount of molten slag in the furnace (kg) by the cross-sectional area of the furnace (m^2).The amount of residual carbon in the furnace (kg) )>Amount of molten slag (kg) x 0.
05...(2) Molten slag cavity (L_s) <0.7...(3) Molten slag thickness (H_s) However, (L_s) and (H_s) are (mm)