JPH10298620A - Method for charging ore and the like into blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the lowering of a heat level at the lower part of a furnace while sufficiently executing the reduction of ore at the time of operating at high O/C and to reduce the producing cost of molten iron while continuing stable operation by injecting a large quantity of pulverized fine coal from a tuyere in a blast furnace and charging the roe having high reducibility from the furnace top. SOLUTION: The pulverized fine coal is injected at >=160 kg/t-p from the tuyere in the blast furnace and while alternately charging the ore and coke from the furnace top in layers, the high O/C operation is executed and the charging quantity of the coke is reduced. At this time, the ore kind having high reducibility to 1200 deg.C is charged on the upper layer in each ore layer, desirably charged at 20-50 mass % of each ore layer. By this method, the dripping temp. of the reduced ore is raised and the lowering of the heat level at the lower part of the furnace is prevented and the stable operation can be obtd. without remarkably increasing the fuel ratio. This reducibility is evaluated when the are can be reduced at >=60% with the gas of CO:N2 =3:7 while raising the temp. to 1200 deg.C at 7 deg.C/min after reducing to wustite with gaseous mixture of CO:CO2 =1:1 matching to the furnace condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for charging raw materials into a blast furnace.

[0002]

2. Description of the Related Art There have been many reports on ore charging methods for improving the reduction efficiency and reducing the fuel ratio in a blast furnace. Most of the prior art controls the ore / coke weight ratio (hereinafter, O / C) in the blast furnace radial direction by a movable armor or a swirling chute to improve the CO gas utilization rate.

This method is used when the O / C is low (4 or less).
However, when a large amount of pulverized coal is blown from the tuyere, the O / C of the charge increases (5.0 to 5.5). An extremely high O / C (7 or more) locally occurs from the radially intermediate portion to the peripheral portion. In this extremely high O / C portion, ore reduction is delayed due to a reduction in the gas reduction potential in the upper layer of the ore layer. Therefore, the ore in the upper layer in the region of 1200 ° C. or more corresponding to the cohesive zone in the blast furnace is generated. Are easily melted, leading to a lower heat level in the lower part of the furnace.

[0004]

In the prior art, high O /
During the C operation, ores are easily melted in a region of 1200 ° C. or more due to delay in reduction of ores. Therefore, the slag and the hot metal are dropped before being sufficiently heated, so that the heat level in the lower part of the furnace is reduced. In addition, since the reduction of ores at this time is incomplete, unreduced iron oxide (Fe
O) is contained in a large amount. These FeOs form a melt together with the gangue component and are dropped into the lower part of the blast furnace. These melts are dropped or in the pool of the hearth, and the following (1)
As shown in the formula, it reacts with carbon in coke and hot metal and is reduced.

Since the reaction of the formula (1) is an endothermic reaction, the more FeO in the slag, the lower the heat level in the lower part of the furnace. FeO + C = Fe + CO (1) Therefore, it is an issue to reduce the heat level in the lower part of the blast furnace by sufficiently reducing the ore during the high O / C operation.

[0006]

In order to solve the above-mentioned problems, the present invention does not reduce the reduction rate by charging ore having good reducibility up to 1200 ° C. in the upper layer of the ore layer, A method for realizing the dropping temperature of ore and maintaining FeO in slag and maintaining the heat level in the lower part of the blast furnace even during high O / C operation was found. That is, when pulverized coal is blown at 160 kg / tp or more from the blast furnace tuyere and the ore and coke are charged alternately in layers from the furnace top, ore having high reducibility up to 1200 ° C. is added to each ore layer. A method for charging ore into a blast furnace, wherein the ore is charged into an upper layer of the blast furnace.

[0007] 20 to 50 mas of each ore layer in the blast furnace
A method for charging ore into a blast furnace, wherein s% is a reducible high ore at 1200 ° C. CO and CO ₂ at a volume ratio of 1: 1,
After reduction to wustite at 0 ° C, 12 ° C at 7 ° C / min.
Ores with a reduction rate of 60% or more after reduction with a gas mixture of CO and N ₂ at a volume ratio of 3: 7 while raising the temperature to 00 ° C. are used as ores with high reducibility up to 1200 ° C. This is a method for charging ore into a blast furnace.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The pulverized coal injection amount is 160 kg /
Although the amount of coke charged can be reduced at the time of high O / C operation of at least t, since the coke layer plays a role of securing air permeability in the blast furnace, it must be charged at a certain amount or more (5000 m ^3). About 25t / charge in a high-grade blast furnace).
Therefore, the layer thickness of the ore increases with an increase in O / C, and the unreduced portion increases in the upper layer of the ore layer because the reduction potential of the reducing gas decreases. These under-reduced ores correspond to the cohesive zone in the blast furnace,
Melting becomes easy in the region of 0 ° C. or higher, which leads to a decrease in the heat level in the lower part of the furnace.

In order to solve such a problem at the time of high O / C operation, it is necessary to increase the reduction rate up to 1200 ° C.
At present, the reducibility at 900 ° C is specified by JIS.
Although the index is -RI, there is no unified method for evaluating the reduction rate up to 1200 ° C. The reduction rate up to 1200 ° C. depends on the softening of the ore which becomes significant at temperatures above 1100 ° C. That is, JIS at 900 ° C
In -RI, since pore closure due to softening of ores does not occur, it is difficult to accurately reflect the reduction behavior of ores in an actual furnace.

The reason why the sample is equilibrated at 1000 ° C. with a CO—CO ₂ mixed gas (mixing ratio: 1: 1 vol%) is to match the test conditions with the reduction rate of ores in an actual furnace.
1000 in actual furnace by sampling with vertical sonde
It is known that the reduction rate becomes about 30% wustite at ℃, and the same reduction rate can be obtained under the above-mentioned reduction conditions (2 to 3 hours until equilibrium is reached). After adjusting the reduction rate at 1000 ° C., the reducing gas was changed to a CO—N ₂ mixed gas (mixing ratio 3: 7 vol%, 5 [liter / min]), and the temperature was raised to 1200 ° C. while increasing the temperature at 7 ° C./min. Is measured.

The reason for the measurement up to 1200 ° C. is that the temperature on the surface of the cohesive zone in the blast furnace is almost 1200 ° C. This is because the amount of FeO is substantially determined. 7 ℃ /
The reason why the temperature is raised at a minimum is that the temperature is raised at a rate of 5 to 10 ° C./min in the case of an actual furnace by the measurement using the above-described vertical sonde.

The CO-N ₂ mixed gas is used for the following reasons. The composition of the blast furnace that performs high-temperature reduction is
_{Usually, CO: 35~40vol%, N 2} : 50~55v
ol%, H ₂ : _{2 to} 5 vol%, CO ₂ : _{2 to} 5 vol
%, And the main components are CO and N ₂ . H ₂ and CO ₂ are also gases that affect the reduction, but there is no problem in the evaluation of ores as long as the proportion in the Bosch gas is small and a gas of the same composition is always used.

According to the above-mentioned test method, charging an ore having a reduction rate of not less than 60% at 1200 ° C. into each upper layer of a plurality of ore layers charged inside the blast furnace increases the reduction rate. Is preferred. As a method of charging the ore layer into the upper layer, the ore having a normal reduction rate (about 55 to 60%) is charged in the first batch and then 1200 is cut out from another ore storage.
There is a method in which ores having a reduction rate at 60 ° C. of 60% or more are charged in the second batch.

Here, the reason why the reduction rate at 1200 ° C. is 60% or more is that the ore whose reduction rate at 1200 ° C. is 60% or more is further reduced before dropping to a higher temperature part. Temperature of 1450 ℃ or more, FeO in slag
Is 30 mass% or less, and it was confirmed that the heat level in the lower part of the blast furnace was not reduced.

The amount of the ore having a reduction rate of not less than 60% up to 1200 ° C. is preferably 20 to 50 mass% of the ore. Here, if it is less than 20 mass%, the effect of improving the reducibility of the upper layer of the ore layer is small, and it is difficult to maintain the heat level in the lower part of the furnace. This is because the production cost is relatively high, and the advantages of pulverized coal injection cannot be sufficiently enjoyed.

Here, the ores are iron ore, sintered ore, and pallets, and the lower part of the blast furnace is a drip zone, a furnace core, and a water pool below the morning glory.

[0017]

Embodiments of the present invention will be described below. As a measuring method of the present invention, in order to simplify the test, a sample weight was set to 20 g, and a CO-CO ₂ mixed gas (mixing ratio 1: 1).
And reduced to wustite at 1000 ° C. with CO—N ₂
The flow rate of the mixed gas (mixing ratio 3: 7) was 5 [liter / mi].
n] at a rate of 7 ° C./min to 1200 ° C. to measure the reduction rate. If economics are not taken into consideration, the flow rate of the CO—N ₂ mixed gas may be changed in proportion to the sample weight. The reduction rate of ores was calculated by the following equation.

Reduction rate [%] = (reduced oxygen amount) /
(The amount of oxygen combined with FeO) × 100 (the amount of reduced oxygen) can be calculated from the composition change of the exhaust gas and the reducing gas, and the (amount of oxygen combined with FeO) is obtained by chemical analysis of the sample. Can be measured. Table 1 shows the operation results.

[0019]

[Table 1]

In a blast furnace having an inner volume of 4000 m ³ , ores having a reduction ratio of 60% or more according to the measurement method of the present invention are not used during normal operation. Ores are usually broken down by sinter ore 88mas
s% and lump ore 12 mass%. The reduction rate of ordinary ores in the measurement method of the present invention was 55.0%, and the dropping start temperature was 1380 ° C. When quantifying the dropping start temperature, a large dropping test apparatus different from the present invention was used (the same applies to the following examples). When only ordinary ores were used, the pulverized coal ratio was 140 kg / t. -P, fuel ratio 490 kg /
tp, the hot metal temperature was operating at 1515 ° C.

Example 1 shows that 50% of the ore layer of highly reducible ores having a reduction rate of 60.1% by the measuring method of the present invention was placed on the upper layer.
This is an example in which mass% is charged. Ores other than highly reducible ores are usually the same as ores. At this time, since the reduction rate of the ore was improved, the dropping start temperature was 1460 ° C., and the heat level in the lower part of the blast furnace could be easily maintained. Therefore, pulverized coal injection of 200 kg / tp could be performed without increasing the fuel ratio.

In Example 2, the reduction rate was 6 in the measurement method of the present invention.
20m above the ore layer of 2.3% high reducible ore
This is an example in which ass% is charged. At this time, the dropping start temperature of the ore is 1450 ° C., as in the case of Example 1,
200 kg / tp pulverized coal injection was possible without increasing the fuel ratio.

Comparative Example 1 has a reduction ratio of 6 in the measurement method of the present invention.
2.3% of highly reducible ore is placed 10m above the ore layer
This is an example in which ass% is charged. At this time, since the compounding ratio of the highly reducible ores is low, the reduction ratio of the ores is slightly improved, but the effect is small. The dropping start temperature is 1400 ° C., and it is difficult to maintain the heat level in the lower part of the blast furnace. there were. Therefore, the fuel ratio must be increased to maintain the hot metal temperature, and the fuel ratio is 507 kg / tp and the pulverized coal ratio is also 180.
It could only blow up to kg / tp.

Comparative Example 2 has a reduction rate of 5 in the measurement method of the present invention.
This is an example in which 8.9% ore was charged at 50 mass% in the upper layer of the ore layer. At this time, since the reduction rate of the ore charged in the upper layer part was insufficient, the reduction rate of the ore was slightly improved, but the effect was small, and the dropping start temperature was 1390 ° C. It was difficult to maintain. Therefore, the fuel ratio was forced to increase in order to maintain the hot metal temperature, and the fuel ratio could be blown only up to 505 kg / tp and the pulverized coal ratio up to 175 kg / tp.

[0025]

According to the present invention, a large amount of inexpensive pulverized coal can be blown while continuing stable operation without greatly increasing the fuel ratio, and the cost of hot metal production can be reduced.

Claims (3)

[Claims] 1. Pulverized coal from a blast furnace tuyere at 160 kg / t-
When the ore and the coke are charged alternately in layers from the furnace top by injecting p or more, ore with high reducibility up to 1200 ° C is charged into the upper layer of each ore layer. Ore loading method. 2. 20 to 50 mas of each ore layer in the blast furnace
2. The method for charging ore into a blast furnace according to claim 1, wherein the s% is an ore having a high reducibility at 1200 ° C. Wherein CO, CO ₂ volume ratio of 1: After reduction to wustite at 1000 ° C. in a mixed gas by 1, 7 ° C. /
While reducing the temperature to 1200 ° C. in min. with a gas obtained by mixing CO and N ₂ at a volume ratio of 3: 7, the reduction rate after reduction was 60%.
3. The method for charging ores into a blast furnace according to claim 1 or 2, wherein the ores having a percentage of not less than 1% are used as ores having high reducibility up to 1200 ° C.