JPH0469204B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for melting and reducing iron, and more specifically, the present invention relates to a method for melting and reducing iron. The present invention relates to a method for melting and reducing iron raw materials in an iron bath while performing secondary combustion in the iron bath and transferring heat generated by the secondary combustion to the iron bath with high efficiency.

[Conventional technology]

Oxygen for decarburization is blown into the iron bath from the lower end of a lance inserted from the top of the smelting furnace into the bottom of the slag layer above the iron bath in the smelting furnace, while being stirred by a stirring gas.
A method of melting and reducing iron is known in which iron raw material is melted and reduced in an iron bath while blowing oxygen for secondary combustion into a slag layer from a plurality of blowing nozzles on the lower side wall of a lance.

In this smelting reduction method, carbon monoxide produced by a decarburization reaction during stirring is secondary combusted in a slag layer above the iron bath to generate a large amount of heat, which is then transferred to the iron bath through the slag layer. Heat is applied to the bath to provide heat for the melting and reduction reaction of the iron raw material in the iron bath.

[Problem that the invention seeks to solve]

However, the conventional method has the following problems.

In other words, in order to increase the secondary combustion rate of carbon monoxide in the slag layer, if the amount of oxygen blown for secondary combustion is increased, the secondary combustion rate will increase as shown in Figure 4. The amount increases until a certain amount is blown, but it decreases when the amount is exceeded. This is because when the amount of secondary combustion oxygen blown increases, the granulated iron splashed from the iron bath comes into contact with the hot water surface of the iron bath.
This is thought to be because the amount of carbon monoxide generated increases as a result of the increased amount of decarburized carbon. In any case, the secondary combustion rate is about 50% at most.

Furthermore, although the heat transfer efficiency decreases as the secondary combustion rate increases, in laboratory scale smelting reduction using a small smelting furnace, the heat transfer efficiency can still be about 90% up to a secondary combustion rate of about 30%. There are conditions that apply. However, in actual-scale smelting reduction using a large refining furnace equivalent to a converter, a secondary combustion rate of 30% and a desorption efficiency of only about 70% are achieved.

From the above, it is possible to reduce the secondary combustion of carbon monoxide in the slag layer and the heat transfer of the heat generated by the secondary combustion to the iron bath by, for example, higher than 50% and higher than 90%, respectively. What is desired is a method for melting and reducing iron that is efficient and involves melting and reducing iron raw materials in an iron bath. Therefore, an object of the present invention is to provide such a method for melting and reducing iron.

[Means for solving problems]

This invention relates to blowing oxygen for secondary combustion into a slag layer in a smelting furnace from a plurality of blowing nozzles provided on the lower side wall of a lance in a method for melting and reducing iron. , (2) and (3).

P>1.9Kg/cm ² abs ...(1) L>0.0037v _g ^-0.028 θ ^1.7 (d√2) ^0.6 ρ _s ^-0.46 ...
…(2) D＞30.16v _g ^-0.012 θ ^-0.16 (d√2) ^0.52 ρ _s ^-0.47
...(3) However, the nozzle pressure of oxygen for secondary combustion at the injection nozzle is P [Kg/cm ² abs], and the injection angle of oxygen for secondary combustion from the injection nozzle is measured downward from the horizontal line. θ [degrees], the nozzle diameter of the blowing nozzle d [mm], the bulk density of the slag layer ρ _s [Kg/m ³ ], the superficial velocity of the gas generated in the smelting furnace v _g [Nm/S], The vertical distance between the blowing nozzle and the hot water surface of the iron bath is L [m], and the inner diameter of the refining furnace is D [m].

The method of this invention will be explained in detail below.

In an iron smelting reduction method, the present inventors have determined that, for example, the secondary combustion of carbon monoxide in the slag layer in the smelting furnace and the heat transfer of the heat generated by the secondary combustion to the iron bath are Regarding the injection of secondary combustion oxygen into the slag layer from multiple injection nozzles provided on the lower side wall of the lance, in order to enable high efficiency of greater than % and greater than 90%. , conducted extensive research. As a result, it was found that the following steps should be taken.

FIG. 1 is an explanatory diagram of the method of the present invention. In FIG. 1, 1 is a smelting furnace, 2 is a lance inserted in the lower part of a slag layer 4 above an iron bath 3 in the smelting furnace 1,
5 is a bottom blowing nozzle provided on the bottom wall of the refining furnace 1. Oxygen for decarburization is blown into the iron bath 3 from the lower end of the lance 2 while being stirred by the stirring gas from the bottom blowing nozzle 5, and into the slag layer 4 from the plurality of blowing nozzles on the lower side wall of the lance 2. Oxygen for secondary combustion is blown in.

First, the amount of oxygen blown for secondary combustion per blow nozzle on the lower side wall of the lance 2 and the heat generated by the secondary combustion of carbon monoxide in the slag layer 4 to the iron bath 3 are determined. The relationship between heat transfer efficiency and heat transfer efficiency was investigated. The results are shown in FIG.

As is clear from Figure 2, the nozzle diameter is 3 mmφ,
For both 6mmφ and 10mmφ, the injection amount of secondary combustion oxygen from the injection nozzle is such that the injection jet of secondary combustion oxygen from the injection nozzle can obtain the sonic velocity (indicated by ▽ in the figure). Below that, the heat transfer efficiency rapidly decreases from almost its maximum value. Therefore, in order to obtain a high heat transfer efficiency from the viewpoint of the blowing amount for each nozzle diameter, it is sufficient to ensure a blowing amount that is greater than the blowing amount that can obtain the sonic velocity, that is, an injection velocity that is greater than the sonic velocity. To obtain an injection speed higher than the speed of sound, the nozzle pressure must be at least 1.893Kg/cm ² abs, with a margin of 1.9Kg/cm ²
Just make it larger than abs.

Therefore, in this invention, first, the nozzle pressure P of oxygen for secondary combustion in the blowing nozzle is set to 1.9Kg/cm ²
It is larger than abs. That is, as shown in equation (1) below.

P＞1.9Kg/cm ² abs ...(1) Next, we experimented with the relationship between the amount of oxygen blown into the secondary combustion and the secondary combustion rate by changing the oxygen supply conditions for the secondary combustion. I asked for it. As a result, it was found that the conditions under which almost 100% of the blown oxygen for secondary combustion is used for secondary combustion of carbon monoxide can be expressed by the following equation (2).

L＞0.0037v _g ^-0.028 θ ^1.7 (d√2) ^0.6 ρ _s ^-0.46 …
...(2) Here, L is the vertical distance [m] between the blowing nozzle and the hot water level of the iron bath 3 (the hot water level when it is stationary), and v _g is the distance of the gas generated in the smelting furnace 1. Sky velocity [N
m/S], θ is the injection angle [degrees] measured downward from the horizontal line of secondary combustion oxygen from the injection nozzle,
d is the nozzle diameter [mm] of the blowing nozzle, and ρ _s is the bulk density [Kg/m ³ ] of the slag layer 4.

When the condition expressed by equation (2) above is satisfied, almost 100% of the injected oxygen for secondary combustion is used for the secondary combustion of carbon monoxide, so a secondary combustion rate corresponding to the amount of injected oxygen can be obtained. It will be done. Therefore, by setting the injection amount, it is possible to obtain a high secondary combustion rate exceeding 50%.

Therefore, in the present invention, the equation (2) is satisfied as well as the equation (1).

Next, the relationship between the heat transfer efficiency of the heat generated by secondary combustion to the iron bath 3 and the distance between the blowing nozzle and the furnace wall was investigated. The results are shown in FIG. As is clear from Figure 3, when the distance between the blowing nozzle and the furnace wall is about 1.1 m or more, the heat transfer efficiency shows a constant high value of over 90%, but when the distance is shorter than 1.1 m, the heat transfer efficiency remains high. Thermal efficiency decreases rapidly.

When the reason for this was further investigated, it was found that the heat transfer efficiency decreases under conditions where the injection jet of secondary combustion oxygen from the injection nozzle collides with the furnace wall. From this, we can reduce the heat transfer efficiency to, for example, 90%.
In order to achieve a higher value, it is necessary that the secondary combustion oxygen injection jet does not collide with the furnace wall, and when we experimentally investigated the conditions to prevent collision, we found the following.
It was found that it is sufficient to satisfy equation (3).

D＞30.16v _g ^-0.012 θ ^-0.16 (d√2) ^0.52 ρ _s ^-0.47
...(3) Here, D is the inner diameter [m] of the refining furnace 1.

Therefore, in the present invention, formula (3) is satisfied as well as formulas (1) and (2).

Therefore, in the present invention, the slag layer 4 is discharged from the plurality of blowing nozzles provided on the lower side wall of the lance 2.
Regarding blowing oxygen for secondary combustion into the
It is operated to satisfy equations (1), (2), and (3). According to this, the secondary combustion of carbon monoxide in the slag layer 4 in the smelting furnace and the transfer of heat generated by the secondary combustion to the iron bath 3 can be reduced by, for example, more than 50% and The iron raw material can be melted and reduced in the iron bath 3 while performing the process with high efficiency of more than 90%.

〔Effect of the invention〕

As explained above, according to the smelting reduction method of the present invention, the secondary combustion of carbon monoxide in the slag layer in the smelting furnace and the transfer of heat generated by the secondary combustion to the iron bath can be reduced. for example greater than 50% and
It is possible to melt and reduce iron raw materials in an iron bath while performing the process with high efficiency of more than 90%.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the method of melting and reducing iron according to the present invention, and Fig. 2 shows the amount of oxygen blown into each injection nozzle for secondary combustion and the heat generated in the secondary combustion in the iron bath. Figure 3 is a graph showing the relationship between heat transfer efficiency and the distance between the blowing nozzle and the furnace wall, and Figure 4 is a graph showing the relationship between heat transfer efficiency and the distance between the blowing nozzle and the furnace wall. It is a graph which shows the relationship between the injection amount of oxygen for secondary combustion, and a secondary combustion rate in . In the drawings, 1... Refining furnace, 2... Lance,
3... Iron bath, 4... Slag layer, 5... Bottom blowing nozzle.

Claims (1)

[Claims] 1. While stirring the iron bath by blowing stirring gas into the iron bath in the refining furnace from a bottom blowing nozzle provided on the bottom wall of the refining furnace, from the top of the refining furnace. Oxygen for decarburization is blown into the iron bath from the lower end of a lance inserted into the lower part of the slag layer on the iron bath, and the slag is In a method for melting and reducing iron, which consists of blowing oxygen for secondary combustion into a layer, the nozzle pressure of the oxygen for secondary combustion at the blowing nozzle is P [Kg/cm ² abs], and the blowing nozzle The injection angle of the secondary combustion oxygen measured downward from the horizontal line is θ [degrees], the nozzle diameter of the injection nozzle is d [mm], and the bulk density of the slag layer is ρ _s [Kg/
m ³ ], the superficial velocity of the gas generated in the refining furnace is v _g [N
m/S], the vertical distance between the blowing nozzle and the hot water surface of the iron bath is L [m], and the inner diameter of the refining furnace is D [m], the following (1) formula,
A method for melting and reducing iron, characterized by operating so as to satisfy equations (2) and (3). P>1.9Kg/cm ² abs ...(1) L>0.0037v _g ^-0.028 θ ^1.7 (d√2) ^0.6 ρ _s ^-0.46 ...
…(2) D＞30.16v _g ^-0.012 θ ^-0.16 (d√2) ^0.52 ρ _s ^-0.47
...(3)