JPH059517A - Method for operating blast furnace - Google Patents

Abstract

PURPOSE:To improve the combustibility of fine coal without executing oxygen enrichment in hot blast and to lower the operational cost, in the operation for blowing the fine coal. CONSTITUTION:The fine coal having >=100kg/pt is blown from a tuyere in the blast furnace together with hot blast having no oxygen enrichment and <=10g/Nm<3> moisture at >=1100 deg.C. By lowering the moisture in the hot blast, the combustibility of fine coal is improved. Increase in the cost accompanying dehumidification in the hot blast is cancelled by decrease in coke ratio. Hence, there is no possibility of causing unstable operation due to the shortage of hydrogen feed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blast furnace operating method by blowing pulverized coal.

[0002]

2. Description of the Related Art Blast furnace operation has shifted from heavy oil injection to all-course operation, and further has advanced to pulverized coal injection. For example, of the blast furnaces currently in operation in Japan, more than half are blowing pulverized coal, and the blowing amount is also increasing, and about 100 kg / pt is becoming the mainstream. These days, 150 to 20 as well as Europe
The target for the amount of pulverized coal blown at 0 kg / pt is increasing, and there are blast furnaces that actually blow pulverized coal at 150 kg / pt or more.

However, pulverized coal, which is a powder fuel, is
Compared with liquid fuels such as heavy oil and tar, it has inherently poor combustibility and has the drawback of containing unburned substances such as ash. Therefore, it is necessary to take various measures in order to prevent the deterioration of the combustibility when the pulverized coal is blown, especially when a large amount of it is blown. The deterioration of flammability when the amount of pulverized coal blown is large is explained as follows.

Pulverized coal is blown into the blast furnace from the tuyere of the blast furnace together with hot air. The pulverized coal blown from the tuyere of the blast furnace into the blast furnace is rapidly heated by the hot air flowing through the tuyere,
Volatile components such as hydrogen and carbon monoxide are volatilized, and these reach the ignition temperature to start combustion. At this time, if the amount of pulverized coal blown in is large, the start of volatilization of the volatile components in the pulverized coal is delayed, the volatilization rate becomes slower, and the time until the volatile gas reaches the ignition temperature also becomes longer. For these,
It takes a considerable time from blowing to ignition and combustion. As a result, the combustion rate of the pulverized coal when it leaves the raceway is reduced, and a large amount of unburned char is generated. A part of the unburned char that jumps out of the raceway is consumed in the blast furnace due to the solution loss reaction, but most of the remaining unburned char accumulates in the core coke or near the root of the cohesive zone, It causes inactivation. Therefore, the combustibility decreases as the amount of pulverized coal blown increases.

In order to improve the combustibility of pulverized coal,
In the operation of blowing pulverized coal of 80 kg / pt or more, the temperature of hot air is raised (1100 ° C or more) and its oxygen is enriched (+ 0.7 ~).
+ 2.0% by volume) is common. Although there is a special case where the hot air temperature is lowered (Japanese Patent Publication No. 1-29846), oxygen in the hot air is enriched by 23 vol% or more and +2.0 vol% or more.

[0006]

In such a measure for improving the combustibility of pulverized coal by enriching hot air with oxygen, a large amount of expensive oxygen is required, and therefore an increase in blast furnace operating cost cannot be avoided.

An object of the present invention is to provide a low-cost blast furnace operating method in which a large amount of pulverized coal of 100 kg / pt or more is blown and the combustibility of the pulverized coal is improved without enriching hot air with oxygen. .

[0008]

[Problems to be Solved by the Invention] Deterioration of combustibility of pulverized coal when a large amount of pulverized coal of 100 kg / pt or more is blown,
This is explained by an increase in unburned char due to a decrease in the oxygen excess coefficient in front of the tuyere and a decrease in the combustion temperature in front of the tuyere due to the heat of decomposition of a large amount of pulverized coal. For this deterioration of flammability,
Although the hot air temperature increase and the oxygen enrichment have been adopted, it has become clear from the investigation by the present inventors that dehumidification of the hot air can be an effective countermeasure.

That is, when the dehumidified hot air is blown into the blast furnace together with the pulverized coal from the tuyere of the blast furnace, even if the hot air is not oxygen-enriched, a combustibility improving effect almost equal to that of oxygen-enriched is obtained. Be done. Even if the amount of pulverized coal blown further increases from about 100 kg / pt, if the moisture content of the hot air is reduced corresponding to the increased amount, excellent combustibility can be ensured. Dehumidification of hot air requires a cost, but the increased cost is offset by the merit of reducing the coke ratio accompanying dehumidification. Therefore, the operation cost of the blast furnace is reduced because oxygen is not enriched. Also, the amount of hydrogen in the hot air decreases due to dehumidification of the hot air, but since hydrogen is supplied by pulverized coal, unstable operation due to insufficient hydrogen input, such as when the hot air was dehumidified in the old all-coke operation There is no danger of becoming

The blast furnace operating method of the present invention secures the combustibility when a large amount of pulverized coal is blown in by dehumidifying the hot air. ℃ or more and moisture content is 10g / N
It is characterized in that it is blown together with hot air of not more than m ^{3 and} not enriched with oxygen.

[0011]

The reason why the combustibility of pulverized coal is improved by reducing the moisture content of hot air is explained as follows.

Moisture in hot air, that is, H ₂ O, is C + H ₂ O → CO + H in the raceway formed at the tuyere.
The _second endothermic reaction, the cause of decomposition of H _2. At that time, the focal point temperature of combustion is lowered by the endothermic reaction, but in the operation of blowing pulverized coal, the combustion temperature is also lowered by the decomposition reaction of a large amount of pulverized coal, so that the focal point temperature is significantly lowered. Therefore, the char generated by removing the volatile components from the pulverized coal becomes difficult to burn in the raceway where the temperature becomes low, and lowers the burning rate. Here, when the moisture content in the hot air is reduced, the focal temperature of combustion in the raceway becomes
It rises by the decomposition heat of dehumidified H ₂ O. Therefore, the combustibility of the pulverized coal is improved by reducing the moisture content of the hot air.

When the blowing amount of pulverized coal is 100 kg / pt or more and the moisture content in the hot air exceeds 10 g / Nm ³ , the combustibility of the pulverized coal is not sufficiently improved under the condition that oxygen is not enriched. . Therefore, the moisture content in hot air should be 10 g / N
It was set to m ³ or less. This moisture content should be reduced as the amount of pulverized coal injected increases, and is preferably 5 g / Nm ³ or less at 150 kg / pt or more. By the way, the moisture content in hot air that is not dehumidified above 1100 ° C is 25 g / Nm.
It is about ³ . There is no problem with the lower limit of the moisture content even if it is 1 g / Nm ³ or less from the viewpoint of flammability. However, in a general blower dehumidifying equipment, the dehumidifying capacity is at most ³ to 4 g / Nm ³ . Therefore, in reality, the lower limit is about 3 g / Nm ³ .

The temperature of the hot air is 100 kg / pt
In the above pulverized coal blowing operation, for stable operation, 11
The temperature is required to be 00 ° C or higher, and the upper limit is preferably 1200 ° C or higher.

The reason why the coke ratio is reduced by reducing the moisture content of the hot air is explained as follows.

As described above, the moisture in the hot air is decomposed into free H ₂ by the reaction of H ₂ O + C → H ₂ + CO in the raceway. Since this reaction is an endothermic reaction, it causes an increase in the coke ratio in terms of heat balance.
When the moisture content in the hot air is reduced, the endothermic reaction is suppressed and the coke ratio is reduced accordingly.

Further, the reason why the unstable operation due to the shortage of hydrogen input can be avoided despite the reduction of the moisture content in the hot air is as follows.

In the all coke operation, hot air was dehumidified in many blast furnaces for the purpose of avoiding endothermic reaction due to moisture and preventing heat fluctuation in the furnace due to humidity fluctuation. However, in the all coke operation where there is no coolant in front of the tuyere (for example, pulverized coal, heavy oil, auxiliary fuel such as tar, steam, water spray, etc.),
On the contrary, due to the lack of H ₂ supply from the tuyere and the overheating of the combustion temperature in the raceway, the furnace condition became unstable,
Dehumidification of hot air has been abolished. However, in the pulverized coal blowing operation, H ₂ is supplied from the pulverized coal, and the combustion temperature is rather lowered to the lower limit due to the decomposition of the pulverized coal. Therefore, even if the H ₂ in the hot air decreases due to dehumidification of the hot air and the combustion temperature rises, the problem of unstable furnace conditions does not occur.

[0019]

[Examples] In a blast furnace operation by blowing pulverized coal, the following experiment was conducted in order to investigate the influence of the moisture content of hot air on the combustibility of pulverized coal. The experimental apparatus is shown in FIG.

Inner size lined with refractory is 1500L × 10
Particle size 25-30 in the combustion furnace 1 of 00D x 2500Hmm
mm coke 2 was charged, and pulverized coal was blown into the combustion furnace 1 from the tuyere 3 together with hot air. The hot air is air that is not enriched with oxygen at 1100 ° C. (oxygen concentration is constant at 21% by volume, moisture content is adjusted variously), and the blowing rate is 600 m ³ / H
And Pulverized coal has a volatile content of about 33% and an ash content of about 12%, and the blowing rate is 50 kg / pt, 100 kg.
/ Pt and 150 kg / pt.

Exhaust gas generated by the combustion of coke 2 and pulverized coal is discharged from the furnace top of the combustion furnace 1, and the coke consumed by the combustion is supplemented by the charging of coke from the furnace top, and the height of the coke packed bed is increased. Was kept constant.
For the combustibility of pulverized coal, combustion gas is sampled at various distances from the tuyere 3 by the probe 4 inserted into the combustion furnace 1 from the opposite side of the tuyere 3 to analyze unburned dust in the sampling gas. It evaluated by doing. Probe 4
Were installed in two stages at the tuyere level and 700 mm above it. The experimental results are shown in FIG.

When the pulverized coal blowing rate is 50 kg / pt, even under the condition of hot air humidity of 25 g / Nm ³ (non-dehumidified),
The combustion rate of pulverized coal exceeds 95% at the tip of the raceway, and is almost 100% at a point 1000 mm from the tuyere. Increasing the pulverized coal injection rate to 100 kg / pt while the hot air humidity remains 25 g / Nm ³ , the combustion rate of pulverized coal is over 70% at the tip of the raceway and 1000 m from the tuyere.
It drops to about 90% at the point of m. However, when the hot air humidity is reduced to 8 g / Nm ³ , the combustion rate of pulverized coal is significantly improved, and it is almost 100 at a point 1000 mm from the tuyere.
%.

When the blowing amount of pulverized coal was increased to 150 kg / pt, the burning rate of pulverized coal was extremely reduced with the hot air humidity remaining at 25 g / Nm ³ , and the wing was less than 60% at the tip of the raceway. Only about 80% at a point 1000 mm from the mouth. However, when the hot air humidity was reduced to 10 g / Nm ³ , the combustion rate of pulverized coal was improved to about 95% at the point 100 mm from the tuyere, and when the hot air moisture was further reduced to 5 g / Nm ^3. Is almost 100% at a point 1000 mm from the tuyere.

By the way, when the hot air humidity is kept at 25 g / Nm ³ and an attempt is made to secure a similar burning rate by enriching oxygen, the following will occur. Pulverized coal injection amount is 10
Oxygen enrichment of about + 2.0% by volume is required in order to obtain the same burning rate as when hot air humidity is 8 g / Nm ³ at 0 kg / pt. To obtain a burn rate of 5 g / Nm ³ at 150 kg / pt, an oxygen enrichment of about +2.5 vol% is required.

[0024]

As is apparent from the above description, the blast furnace operating method of the present invention ensures excellent combustibility despite blowing a large amount of pulverized coal of 100 kg / pt or more. Moreover, oxygen is not used to secure combustibility, hot air is dehumidified, and the increase in cost due to dehumidification is offset by the reduction in coke ratio. Therefore, the blast furnace operating cost can be significantly reduced as compared with the case where oxygen enrichment is performed. Further, unstable operation due to dehumidification of hot air can be avoided. Therefore, it has a great effect on the promotion of the pulverized coal blowing operation.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an experimental device for investigating the effect of implementing the present invention.

FIG. 2 is a chart showing the results of an investigation of the effects of implementing the present invention.

[Explanation of symbols]

 1 combustion furnace 2 coke 3 tuyeres

Claims (1)

Claims: 1. A pulverized coal of 100 kg / pt or more from a tuyere of a blast furnace at a temperature of 1100 ° C. or more and a moisture content of 10 g / N.
A method for operating a blast furnace, which comprises blowing with hot air of m ³ or less that is not oxygen-enriched.