JPS5950723B2 - How to operate a blast furnace using iron ore pellets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates in particular to a method for operating a blast furnace using iron ore pellets.

Conventionally, iron ore calcined pellets (including iron ore containing powdered iron oxide-containing materials such as dust, in addition to iron ore) are charged as the iron raw material into a blast furnace, typically a blast furnace, for smelting. Since the pellets are generally spherical, it is possible to densely pack them into the blast furnace, allowing for a large pellet charge/furnace volume, which is expected to increase productivity. However, compared to sintered ore, the softening start temperature is generally lower, and there are drawbacks to so-called high-temperature reduction properties, such as the formation of a thick softened cohesive layer during the reduction period.As a result, the blowing pressure in the furnace fluctuates greatly, and molten iron It also had disadvantages such as variations in quality, low productivity, and increased coke ratio.

The purpose of the present invention is to improve the difficult properties of such pellets by strictly controlling them using specific factors, and to stably improve the production efficiency of blast furnaces through the synergistic effect of adding the unique advantages of pellets. There is something to do.

In order to solve the above-mentioned disadvantages in operational use, the inventors of the present invention have repeatedly researched and operated seeds, and found that if the hot shrinkage rate of the pellet itself is adjusted and maintained within a certain range, its high-temperature reduction properties are advantageous. The present invention was completed based on the knowledge that a highly productive blast furnace operation with less fluctuation in blowing pressure and a low coke ratio can be established.

The shrinkage rate of pellets referred to here is measured using the apparatus shown in Fig. 5, in which the pellets to be tested are placed in the electric furnace 2 in the reduction apparatus under load.
2 to pellet 1, which is heated by load 3.
A load of kg/cm2 is applied, and reducing gas 4 is fed from the bottom of the pellet 1.

In this case, reducing gas and N2 are used, the reducing gas temperature is increased at 800°C/lhr, and from 800°C to 1100°C, the increase is 100°C per hour, and the gas amount (N270
%, CO30%) is 151/min.

After the test is completed, the specimen is cooled to room temperature in a N2 atmosphere.

Assuming that the initial height of the test pellet 1 is A, and the height of the pellet when heated and loaded is B, the shrinkage rate is expressed by the following formula.

Therefore, the present inventors focused on this shrinkage rate, and distributed dolomite, which has a strong correlation with this, into the pellet raw material by changing the amount added, granulated and fired, and produced a large number of pellets with different shrinkage rates. The coke ratio (kg/l, pig iron), pressure loss in the furnace, amount of fluctuation in the furnace pressure (g/cm□, fluctuation value of the furnace pressure measured every minute) in the blast furnace operation using these products. When we investigated the average value over 1 hour) and the load reduction rate (%) of pellets, we found that
The results shown in the figure were obtained.

As is clear from this, when the shrinkage rate exceeds 20%, the pressure loss in the furnace increases and the amount of pressure fluctuation in the furnace increases.
Slips and shelf hangings increase, making it impossible to ensure smooth unloading, resulting in poor gas return in the furnace, resulting in a decrease in gas utilization rate as shown in the figure, and an increase in coke ratio.

On the other hand, when the shrinkage rate is less than 5%, the load reduction rate of the pellets decreases, the reduction rate of the pellets themselves decreases, the gas utilization rate decreases, and as a result, the coke ratio increases significantly, and furthermore, the shrinkage rate decreases to 5%. If the reduction rate is less than
eO remains, which becomes a slag component and becomes CaO9A1
203. Together with SiO□, the internal melting point is lowered, and as a result, the softening and melting time of the pellet is accelerated, and a phenomenon occurs in which these particles seep from the inside of the pellet to the surface, causing the pellets to stick to each other and agglomerate, causing the raw materials in the furnace to melt. This obstructs the ventilation of the furnace and makes the furnace condition unstable.

That is, the fuel ratio increases as shown in FIG.

As mentioned above, it is optimal to operate the pellet shrinkage rate in the range of 5 to 20%, and it was decided to limit the operation to this range.

Now, as a means to maintain and adjust the shrinkage rate within the above range, it is very effective and preferable to add MgO-containing minerals such as dolomite and serpentine to the pellet raw material, but other methods such as adding MgO-containing minerals such as dolomite and serpentine to the pellet raw material It also makes no difference whether it is carried out depending on the particle size or firing temperature.

In particular, regarding the addition of dolomite, which was specifically adopted by the inventors, the amount of dolomite added is required to maintain the shrinkage rate within the range of 5 to 20%, as shown in Figure 4, which shows the relationship between the shrinkage rate and the amount added. may be selected within the range of 4 to 11%.

As described above, according to the present invention, by selectively using pellets that have a shrinkage rate within a certain range and have improved reducing properties, blast furnace operation with a low coke ratio and stable furnace conditions and high productivity can be achieved. This provides the excellent effect of being able to continue.

[Brief explanation of drawings]

Figures 1 to 3 are graphs showing the relationship between coke ratio, pressure loss in the furnace, blast furnace pressure fluctuation, pellet load reduction rate, and pellet shrinkage rate, respectively. Figure 4 is the amount of dolomite added to the pellet raw material and shrinkage rate. A graph showing the relationship in FIG. 5 is a test device for measuring the shrinkage rate of pellets. 1... Pellet, 2... Electric furnace, 3.
...Load, 4...Reducing gas, 5...
...Shrinkage detector.

Claims (1)

[Claims] 1. A method of operating a blast furnace using iron ore pellets as the iron raw material charged into the blast furnace, characterized in that the iron ore pellets have a hot shrinkage rate of 5 to 20%.