JPS5814845B2 - Direct reduction steelmaking operation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a direct steelmaking operation method, in particular, to introduce high-temperature reduction scum into iron oxide pellets charged into a shaft furnace or fixed bed retort, thereby reducing raw material granules produced when producing sponge iron. This article relates to an operating method for efficiently and smoothly manufacturing sponge iron by preventing troubles such as the occurrence of shelving due to mutual fusion and the inability to cut out the sponge iron after reduction outside the furnace.

In the direct steelmaking method, iron oxide raw materials are charged into a furnace such as a shaft furnace, and CO and H are mainly extracted through tuyeres installed at the bottom of the furnace.
This method injects high-temperature reducing gas consisting of 2 into the furnace, and promotes heat conduction and reduction reaction between the reducing gas rising in the furnace and the raw materials falling.This method has high efficiency in reducing gas usage and reduces energy consumption. Recently, many commercial-scale shaft processes (for example, Midrex method, Armc
o method, Puroter method, etc.) and fixed bed retort methods (for example, Hyl method, etc.) have come into operation.

The raw materials used in these direct iron manufacturing methods are generally formed into pellets, taking into account the subsequent steel manufacturing process that requires high-quality raw materials and the convenience of transportation to reduced iron manufacturing plants. used in

Therefore, in shaft furnace operation, increasing the temperature of the reducing gas injected into the tuyere increases the reduction reaction rate between the reducing gas and the iron oxide raw material in the furnace, which only contributes to improving productivity. It is also advantageous for preventing re-oxidation of finished products (reduced iron).

However, when the temperature of the reducing gas is increased, a so-called clustering phenomenon occurs in which the charges are fused to each other in the lower part of the reduction zone in the furnace.

This clustering is particularly likely to occur when the pellets are used as a raw material.

Once clusters begin to form in the shaft furnace, the raw materials in other parts are compressed, further accelerating clustering, and in severe cases, smooth unloading and flow of reducing gas are hindered, resulting in shelving or It becomes impossible to cut the finished product outside the furnace, causing serious problems such as having to stop operations.

Therefore, the reducing gas temperature cannot be raised sufficiently,
There are certain strong restrictions that must be imposed on improving the quality of life.

The present inventors have been conducting research for some time to elucidate the details of the cluster generation mechanism in order to overcome the above-mentioned problems in the direct reduction ironmaking process and establish an efficient and smooth operating method.

FIG. 1 shows an apparatus for investigating the production process of Krasku in a shaft furnace. A raw material (pellet) 3 is put into a reaction tube 2 inserted into an electric furnace 1, and a pressure means 4 is placed on top of the reaction tube 2. A pressure commensurate with the load inside the shaft furnace is applied to the raw material.

This pressure is exerted by a weight 7 applied to a bar 6 supported at a fulcrum 5.
can be adjusted freely.

Reducing gas is supplied from an inlet 8 at the bottom of the reaction tube 2, and waste residue after the reaction is discharged from an outlet 9.

The atmospheric pressure inside the reaction tube is measured and controlled by a manometer 10, and the temperature of the reaction zone is measured and controlled by a thermocouple 11.

Furthermore, 12 is a measuring device for measuring the amount of shrinkage that occurs when the raw material is heated and reduced, and is continuously recorded by vertical displacement of a pen 13 that is directly connected to the rod of the pressing means 4.

In the above-mentioned apparatus, when reducing gas is maintained at a predetermined temperature while flowing, metallic iron is produced as the reduction time progresses, and the pellet layer contracts at the same time.

In this way, when the reduction rate of the raw material iron oxide reaches approximately 95%, it is taken out of the furnace.
It is recognized that the larger the load and the higher the reduction temperature, the higher the shrinkage rate and the easier it is to form stronger clusters.

It is desirable that the clusters thus formed have mutual adhesion strength below a certain level and are easily peelable.

Figure 2 shows a device for measuring the adhesion force between clusters, which consists of a steel barrel 14 (120mmφ x 700mm) and a drive source 16 that rotates this around a shaft 15. After the particles are placed in a container and rotated at a constant rotational speed for a certain period of time, the amount of clusters that remain without being peeled off is measured, and the adhesion strength is compared based on the amount.

Considering the conditions in the shaft furnace, the present inventors peeled the clusters under the conditions of a parel rotation speed of 30 R/M and a rotation time of 5 minutes, and calculated the value (CS) obtained by the following formula into the cluster. Defined as strength.

CS=100-(A-B)/A [However, A: cluster weight before one rotation test, B: remaining cluster weight after sieving through a sieve with a mesh size corresponding to the raw material pellet particle size after the rotation test.

] Using the above-mentioned apparatus, calcined pellets containing 68.4% iron (average particle size 12III/I.φ) were reduced by varying the temperature and pressure load, and the relationship between the final shrinkage rate and cluster strength was investigated. When investigated, the results shown in Figure 3 were obtained.

In other words, as long as the shrinkage rate does not exceed 15%, the clusters will peel off in the rotation test described above, and clusters with strong adhesion (that are difficult to peel off) will not be formed, but when the shrinkage rate exceeds about 15%, the cluster strength will suddenly decrease. indicates that the value will rise.

In addition, when the cluster strength of the clustered products produced in an actual shaft furnace was measured by the above-mentioned rotation test, it was generally about 20 to 30%. Considering this, if the cluster strength is about 15% or less, clustering is not possible. It is judged that this can be substantially prevented.

From the above experimental results, it has become clear that by knowing the shrinkage rate of the raw material, it is possible to estimate the cluster strength, which is an indicator of whether the clusters are easily peeled off or firmly adhered.

On the other hand, when considering the cluster generation mechanism, the temperature employed in a shaft furnace is generally about 700 to 900°C.
Since the temperature at which γ iron with a C content of about 1% forms a liquid phase is about 1350°C (even considering the presence of a solid solution of iron oxide and silicic acid, its melting point is about 1190°C), Liquid phase sintering cannot be considered for cluster formation, and therefore it is appropriate to treat it as solid-state mutual diffusion sintering.

Figure 4 is a diagram explaining the fusion of pellet grains. The pellets before reduction (a in the figure) are in point contact, and the area around the contact point is moved in the direction of filling the concave area around it due to the action of surface tension. Movement of atoms occurs.

This movement creates vacancies in the contact area, and by repeating the process of filling the lattice points with the movement of atoms from inside the pellet or from the surface, the contact area gradually increases (Figure b), and sintering takes place. .

In this case, it is clear from Fick's law of diffusion that the better the reduction temperature is, the more active the movement of atoms is, and the higher the applied pressure, the more this phenomenon is accelerated.

According to the results of measuring the clustering characteristics of various raw materials by the present inventors, it has been found that, in general, pellets are easier to form clusters than lump ores.

FIG. 5 is a diagram schematically showing the transmission of load between pellets to explain why pellets tend to form clusters. Since the contact between pellets that are close to spherical is close to point contact, It is thought that the pressure at the contact point due to this load (arrow) becomes extremely high, promoting clustering.

If clustering of pellets can be explained as the phenomenon described above, it is possible to prevent cluster formation by dispersing the concentrated load on the pellets, which is considered to be a major factor in cluster formation, and by equalizing the pressure distribution within the layer. It is thought that this can be a powerful means.

As a result of further experiments from this point of view, the present inventors found that
It has been found that clustering can be effectively prevented by interposing iron oxide solids such as pellet fragments and ore fragments into the voids formed between spherical solids (pellets).

Figure 6 is a diagram schematically showing the pressure distribution within this pellet layer, and shows that the load from above is not concentrated on the contact area of the pellets, but is appropriately dispersed by the solid matter interposed between the pellets. It is thought that there are.

In this way, when iron oxide solids are interposed between pellets, if the small particles are too small, the contact area with the pellet surface increases, which has the opposite effect of making sintering easier, so it is important to prevent clustering. Therefore, it is thought that there is a certain appropriate range for the small particle mixing ratio.Also, taking into account that shaft furnace operation is accompanied by an increase in pressure drop in the furnace or an increase in dust loss, the particle size and mixing ratio of solids should be adjusted accordingly. Must be set appropriately.

As a result of repeated detailed experiments, we found a quantitative relationship between the particle size and mixing ratio of the small particles to be mixed into the raw material and the shrinkage rate and cluster strength during reduction treatment.

The present invention was completed based on the above series of research results.

That is, the present invention provides a method for producing sponge iron by charging iron oxide pellets, which are easily clustered, into a shaft furnace or fixed bed retort as a raw material and using high-temperature reducing gas. By mixing the solid materials and charging them into the furnace, it is possible to effectively prevent clustering of the charged raw materials and maintain smooth and efficient operation.

The present invention will be explained in detail below.

According to the method of the present invention, when iron oxide pellets as a raw material are charged into a shaft furnace or a fixed bed retort, iron oxide solids having a particle size finer than the raw material particle size are mixed with the raw material and filled.

As the iron oxide solids, small pieces thereof, which are produced as a by-product during the production of the raw material pellets 1 or during the particle size adjustment of the iron oxide ore, are preferably used.

The shape of these oxide solids may be spherical or any other shape.

Figure 7 shows Beresotho calcined in a rotary kiln as iron oxide pellets at a particle size of about 10
, 13 mm as a raw material, and the same pellets were further adjusted to approximately 34 to 4.8 mm and mixed in various proportions and charged into the apparatus shown in Fig. 1 (charging amount). 5
00g), reduction temperature 910℃, load 2 Ky/crl
Reduced scum (H2: 55%, CO35%, C
It is a graph showing the influence of the mixing ratio of solids on the raw material shrinkage rate when reduction treatment is performed using 4% H4%, CO25%).

In the same figure, ■, ■, ■ and ■ are respectively a mixture rate of 20%,
This is a curve showing cases of 40%, 50% and 0% (all weight %).

As can be seen from the figure, when iron oxide solids are not mixed (in the figure, 〕)
, the shrinkage rate at 40% (same figure, [■]) is very small, and even at 50% (same figure, [■]) the shrinkage rate is about 10%.
It is recognized that the following can be suppressed.

As shown in Fig. 3, the cluster strength is almost zero in a range where the shrinkage rate does not exceed about 15%, so the mixing ratio of iron oxide solids should be in the range of about 2 to 50%. desirable.

Next, we will discuss the influence of the solid particle size on the shrinkage rate and cluster strength when iron oxide solids having various particle sizes are blended into the raw material pellets at a mixing ratio of 20%.

・ Figure 8 shows iron oxide pellets with a particle size of 10 to 13 mm and iron oxide solids with various particle sizes ((a) 0.4
2~0.59wIt (average particle size 0.5 7K111
), (b) 1. 0 to 1. ．． ．． 1 97/IJ
l (average particle size),. l g ), (c) 3. 4
~4. 8 7tl;Ill (average particle size 4, 1M
) and (d) 4.7 to 5.6 6 rtrta (average particle size 5.27#!)], each was blended at a mixing ratio of 20% and treated under the same reducing conditions as above. The shrinkage rate ((1) in the same figure) and the cluster strength ([■] in the same figure) in the case of this are shown.

As is clear from the figure, when the average particle size of the iron oxide solid particles to be mixed is in the range of about 1 to 5 wIl, the shrinkage rate is about 15% or less, and the cluster strength is also very small, which is a suitable state. It is recognized that the

The reason why the shrinkage rate and cluster strength increase when the diameter of the solid particles exceeds 5'IIgIl is thought to be because the concentrated load distribution function of the contact points between the raw materials (pellets) decreases rapidly.

From the point of view of cluster strength, it seems that the lower limit of the particle size of the solid can be tolerated up to approximately l'IIgIl, but from the point of view of the pressure drop of the reducing gas in the furnace, which will be described next, the lower limit of the particle size is It should be approximately 2 mm.

FIG. 9 is a graph showing the pressure loss of the reducing gas in the furnace in the reduction treatment described with reference to FIG. 8 above,
In the figure, I is the initial pressure drop, and ■ is the pressure drop at the final stage of treatment (
All of them are 澈Aq).

When the particle size of the oxide solid is fine, less than about 2 wIl, it is recognized that the solid flows down through the gaps between the raw materials (pellets) and induces a significant increase in pressure drop.

This means that during in-furnace reduction, a certain amount of reducing gas that should be blown in from the tuyere is prevented from rising, leading to a significant reduction in reduction efficiency.

In FIG. 8, when fine particles of less than about 2 wIl are used, the cluster strength is low and appears to be good at first glance, but this is thought to be due to insufficient reduction.

On the other hand, the particle size is about 27#! In the above, it is recognized that a significant increase in pressure loss can be avoided.

That is, by using solids in the range of about 2 to 5 wIl, strong clustering of raw material pellets can be effectively prevented as shown in FIG. 8, and the pressure loss in the furnace can be increased as shown in FIG. It is possible to ensure smooth and stable operations without causing problems.

Next, the present invention will be specifically explained with reference to Examples.

Example Particle size 1 containing about 70% Fe fired in a rotary kiln
Pellets sized to 0 to 13 mm are used as raw materials, charged into a shaft furnace, and reduced scum (H255%, CO35%, CH44%, CO25%) at approximately 900°C is passed through the tuyeres.
When we introduced and started operation, troubles such as hanging on shelves and difficulty in cutting outside the furnace occurred four times during 24-hour operation.
The operation was suspended due to circumstances.

On the other hand, the same fired pellets as above were used as raw materials, and 2 to 5 wIl of pellet fragments generated during sizing of the fired pellets were collected.
The particles are sized to form small agglomerates, mixed at a ratio of about 25% to the raw material, charged into the furnace, and operated using reducing gas at about 950°C (composition is the same as above). During the 48 hours of operation, there were no accidents such as hanging shelves, and the operation was smooth despite the temperature increase of the reducing gas.

Moreover, the production efficiency was also improved by about 35% compared to the production amount per net actual operating time excluding the interruption time in the operation.

As described above, according to the present invention, it is possible to reliably prevent operational troubles associated with clustering phenomena in shaft furnaces, etc., maintain smooth operation, relax the upper limit of the ζ reducing gas temperature, and further improve reduction efficiency. be able to.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional schematic diagram of a device for measuring the amount of shrinkage of raw materials during the reduction process, Fig. 2 is an external perspective view showing the cluster strength measuring device, and Fig. 3 shows the relationship between shrinkage rate of raw materials and cluster strength. Figures 4a and 4b are explanatory diagrams of the state of fusion of particles, Figures 5 and 6 are explanatory diagrams schematically showing the load distribution between aggregated particles, and Figure 7 is an explanatory diagram of the fusion state of particles. A graph showing the influence of the mixing ratio of solids on the raw material shrinkage rate. Figure 8 is a graph showing the relationship between the average particle size of iron oxide solids and the final shrinkage rate and cluster strength of the raw material. Figure 9 is a graph showing the in-furnace pressure drop. It is a graph which shows the relationship between and the average particle diameter of iron oxide solids. 1: Electric furnace, 2: Reaction tube, 3: Original needle, 4: Pressure means, 8
: reducing gas inlet, 9: outlet, 12: shrinkage measuring device, 14: barrel.

Claims (1)

[Claims] 1. In a method of producing sponge iron using iron oxide pellets as a raw material, charging them into a shaft furnace or fixed bed retort, and using high-temperature reducing gas, iron oxide solids with an average particle size of 2 to 51 are mixed. A direct steelmaking operation method characterized by charging the steel into the furnace.