JPS61153210A - Low-silicon operation method in blast furnace - Google Patents

Abstract

PURPOSE:To lower exactly the Si content in pig iron when ore and coke are alternately charged into a blast furnace in a prescribed ratio in layers to carry out operation, by forming ore-coke mixed layers contg. coke by a specified amount of the amount of coke charged as the ore layers. CONSTITUTION:Ore and coke are alternately charged into a blast furnace in a prescribed ratio in layers, the ore is preheated, reduced, softened and melted, and the resulting pig iron is discharged. At this time, ore-coke mixed layers contg. coke by 5-50% of the amount of coke charged are formed as the ore layers. Pig iron having <=0.15% Si content can be obtd.

Description

Detailed Description of the Invention Object of the Invention The present invention relates to a low-silicon operation method in a blast furnace, which reduces the amount of & in pig iron tapped from a blast furnace to 0.15% or less. However, the aim is to provide an operating method that does not adversely affect the furnace condition or the amount of pig iron tapped.

Industrial applications Operation for obtaining low-silicon pig iron using blast furnaces (1)
RiC.

Conventional technology The ability to completely reduce the St content during tapping from a blast furnace has been extensively studied in the past. Omit or simplify special processes such as desulfurization treatment.

However, the following two cases can be considered as the mechanism by which & is transferred into the pig iron in the blast furnace.

■ SL O2 in the slag is reduced by C in the pig iron as shown in the following equation, and St is contained in the hot metal.

StO
The StOt gas is reduced by C in the pig iron and enters into the pig iron.

5t02 (t, !+)+C(s)→, StO
(f)+co (f)840 (f) 10-+,!
j0CO(t) However, in the region below the tuyere, the above ■■ is the opposite, SL+ 2 Fn O→St Oz +2 Pm5L+
2 Mn O-+840! + 2 S like Mn
t is oxidized and the & in the pig iron decreases, but the & in the pig iron is determined by the balance of these reactions.

Therefore, in order to reduce St in the pig iron, it is necessary to increase the blending ratio of sintered ore in the charge, increase the basicity of the sintered ore, and add more MgO to the charge. Improving the properties of the tuyere, reducing the temperature at the tuyere tip by adding moisture to zero air blast, lowering the air temperature, increasing θ slag basicity, decreasing O hot metal temperature, ■ blowing oxides such as mill scale from the tuyere tip. Some suggestions have been made, including:

Problems to be Solved by the Invention However, the above-mentioned conventional techniques have their own problems and cannot be considered as a preferred method. In other words, (2) increases the cost even if it fails, and it is clear that there is an upper limit to increasing basicity in sintered ore, so it cannot be done as an economical and accurate method, and (0) increases the total fuel ratio. Either this increases the cost, or there are restrictions in terms of equipment, resulting in the same disadvantages as in (2). Of course O
is naturally limited because it affects the viscosity of the slag,
The O method is also limited in terms of tapping and slag collapse, so it is difficult to obtain the desired low & low temperature. This is not a preferred method. In either case, there is a tendency to have a certain influence on the furnace condition or the amount of iron tapped.

"Structure of the Invention" Means for Solving the Problems A blast furnace is charged with ore and coke in predetermined ratios in alternating layers, and the ore is preheated, reduced, softened,
A low-silicon operation method in a blast furnace characterized by forming a mixed layer of ore and coke in an amount of 5 to 50% of the amount of coke charged in the ore layer during melting and tapping.

By creating a mixed layer of ore and coke with coke mixed in the working ore layer, the load on the molten metal in the softened cohesive zone of the ore layer (coke mixture) is reduced, and the metal and coke are tightly compressed by the load. Reducing and eliminating the cause of intense inflammation caused by contact with the condition, such as this ^
Limiting the rate of coal application to metal in temperate zones, thus reducing SL migration in the pig iron caused by the coal removal.

If the ratio of coke mixed into the magnet layer in the total amount of coke charged is less than 5%, the desired reduction effect cannot be obtained, and if it exceeds 50%, the original coke layer thickness will decrease. Alternatively, if the coke layer thickness is constant, the mixed layer thickness of ore and coke becomes too thick, and carburization obtained from the coke layers above and below the ore layer cannot be stably performed in the blast furnace bosch section.

EXAMPLE To further explain the present invention described above, the inventors of the present invention have repeatedly conducted detailed research on reducing the St of tapping from a blast furnace. In either case, it can be said that the reaction does not proceed unless the C content in the pig iron exceeds a certain level.

However, inside the furnace, the ore and coke charged from the top of the furnace gradually descend, and the ore is preheated, reduced, softened, and melted to be tapped. Therefore, it is presumed that if the coaling speed is controlled, it is possible to control the amount of iron in the pig iron.

As a result of repeated studies on controlling the speed at which coal is coated into the metal, we found that the ore layer between the coke layers shrinks by about 70 to 80%, softens and fuses, and then the metal and coke are compressed by the load. It has been experimentally confirmed that dense flames occur when brought into close contact.

Therefore, it is estimated that by not applying the load that is the cause of such 8 coals and eliminating the cause of close contact between metal and coke, it is possible to avoid dense flames and, in turn, to lower the temperature of the coke. .

That is, as a result of studying methods for not applying load to the ore layer in the softened cohesive zone, we came up with the idea of mixing an appropriate amount of coke into the ore layer as described above, and we If the load from the upper charge is supported by the upper charge and close contact between the metal and coke under high temperature conditions is avoided, special additives are not required, and coal production into metal can be performed using simple operations. It can be said that this can be avoided or delayed, and the accompanying migration of St to the metal can be prevented.

The first study shows the appearance of coke mixed in the ore layer in the blast furnace in comparison with that produced by the conventional method.
In the figure, in the softening layer in the blast furnace 10, the coke layer 1 and the metal layer 2 are formed in a substantially orderly divided state in the conventional method, whereas the coke layer charged in the ore layer is It is natural that coke 11 will be distributed throughout the charging layer, and the thickness of the original coke snow 1 will be reduced to a certain extent, and that there will be a large amount of coke in that area. Since the coke mixed in the layer is in the molten metal and supports the upper load, it is obvious that it reduces the load on the metal, and therefore the effect of promoting carburization due to the load is weakened, and the soft weld zone is also shown. It will decrease as follows.

It goes without saying that a certain amount of coke is required to be mixed into the ore layer in order to bring about the above effects, and generally it should be 5 to 50% of the total amount of coke to be charged. be. In other words, this relationship is shown separately in Figure 2. In the conventional method in which the coke mixing ratio in the ore layer is O, the coke mixing ratio in the pig iron is about 0.4%, but this coke mixing ratio As the amount increases, the & in the tapping rapidly decreases, and at a coke mixing ratio of 5%, the & in the tapping becomes approximately 0.25%. At a coke mixing ratio of 20%, St.
can be set to 0.15%. However, if this coke mixing ratio is too large and exceeds 50%, the original thickness of coke r-1 will decrease, or the mixed layer of ore and coke will become too thick, causing the ore layer to form in the blast furnace bosch section. (Coke Mixing) Since the carburization of the upper and lower coke mixtures will not be performed stably, this level should be the upper limit. There are no particular restrictions on the amount of ore and coke, and a conventional particle size distribution is sufficient.

A specific example of operation according to the present invention will be described below.

The total amount of coke as charging raw material was 500.3Kf/T.
The blast furnace was operated at a constant ore-to-coke ratio (0/C) of 1,625 Kf/T, Pig, and a constant output of 6,500 t/daf) in a blast furnace with an effective internal volume of 2,900 m'. , the coke mixing ratio in the ore layer was increased every 10 days to negative 5i, 10%, 15π, and 20%.
The following table shows the average values of the air flow rate, wind pressure, and stg during tapping when carried out over a period of 20 years, together with those values before implementation of the method of the present invention. 0.22-0.12% from about 0.3% before implementation
was able to reduce it to.

"Effects of the Invention" According to the present invention as explained above, the amount of St in pig iron can be accurately reduced in this type of blast furnace operation, and st: 0.
．． We are able to obtain low SL pig iron of 15% or less, which cannot be obtained with conventional technology, and without any special additives or operational complexity.
Moreover, since the purpose can be effectively achieved without reducing the amount of pig iron tapped, the invention is industrially highly effective.

[Brief explanation of drawings]

The drawings are intended to illustrate the technical content of the present invention. Figure 1 is an explanatory diagram showing the softening zone in the blast furnace according to the method of the present invention and the conventional method, and Figure 2 is an explanatory diagram showing the entire coke charged. It is a chart showing the relationship between the mixing ratio of coke in ore and the amount of iron tapping. In FIG. 1, 1 is a coke layer, 2 is a metal layer, 10 is a blast furnace, and 11 is coke.

Claims (1)

[Claims] Ore and coke, each in a predetermined ratio, are charged to a blast furnace in alternating layers, and the ore is preheated, reduced, softened,
A low-silicon operation method in a blast furnace characterized by forming a mixed layer of ore and coke in an amount of 5 to 50% of the amount of coke charged in the ore layer during melting and tapping.