JP2001123208A - Operating method of blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the pick-up of Si in a blast furnace operation, in which the tapping quantity of molten iron is extremely lowered. SOLUTION: By operating under condition of regulating the heat flow rate shown with (heat capacity of charging material/heat capacity of gas) <=0.7 and the blasting temperature to <=500 deg.C, the Si content in the molten iron is made to <=0.45%, at the tapping rate <=1.1 t/dm3.

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 for suppressing an increase in the Si concentration in hot metal, even when operating at a low tapping ratio.

[0002]

2. Description of the Related Art In a blast furnace, ore and coke are charged into the furnace from the furnace top, deposited in layers to form a packed bed, and high-temperature air is blown into the furnace from tuyeres installed at the lower part of the furnace. The ore in the packed bed is reduced and melted by using the heat of combustion and the generated reducing gas such as carbon monoxide. At this time, a coke combustion zone called a raceway is formed in front of the tuyere, and the high-temperature carbon monoxide gas and the like generated here rises in the furnace. This gas transmits heat to the ore and coke deposited in the upper part of the furnace, and contributes to the heating, reduction, and melting of the ore.
In the operation of the blast furnace, the amount of coke used for the reduction and melting of the ore can be changed by changing the ratio of the ore and the coke. Here, the amount of coke per ton of hot metal produced is called a coke ratio, and the amount of ore per ton of hot metal is also called an ore ratio. If the coke ratio is reduced, the fuel cost for producing hot metal can be reduced, but on the other hand, it is necessary to take care that the amount of heat required for reduction and melting is not insufficient. If the calorific value is insufficient, the temperature of the hot metal or slag generated in the furnace decreases and the viscosity increases, making it difficult to discharge from the taphole,
This is because unreduced FeO increases in the slag, and the iron yield decreases. For this reason, in the operation management of the blast furnace, generally, while monitoring the temperature of the hot metal, the amount of FeO contained in the slag generated together with the hot metal, and the like, an effort is made to lower the coke ratio as much as possible without hindrance.

On the other hand, the amount of hot metal produced in the blast furnace (the amount of hot metal)
Is determined by the amount of hot air blown from the tuyere (blowing amount). That is, if the blowing amount is increased, the amount of coke burned per unit time increases, thereby promoting the reduction and melting of the ore. The tapping ratio (unit: t / t) is calculated by dividing the daily output of the blast furnace by the furnace volume.
dm ³ ), which is between 1.6 and 2.4 t in normal operation.
/ Dm ³ .

[0004] In a normal blast furnace operation, it is desirable to increase the tapping ratio and increase the production in order to reduce the production cost of pig iron. However, if the demand for hot metal changes, it is also necessary to continue operations while maintaining a low tapping ratio, taking into account various conditions such as the energy situation, production efficiency, and economic efficiency in the steelworks. It becomes. For example, in an ironworks in which two blast furnaces are operated at the same time, one of the blast furnaces is set to have a high tapping ratio, and the other blast furnace is operated while keeping the tapping ratio as low as possible.

In such a case, in order to reduce the tapping ratio, a method reverse to the above-mentioned method is generally used, that is, the amount of coke burned per unit time is reduced by reducing the amount of air blow, and the amount of molten ore is reduced. The method is taken. According to this method, although the effect of lowering the tapping ratio is effective, the amount of heat released from the furnace body per unit time is almost constant depending on the scale of the furnace body. However, it is necessary to increase the amount of heat input into the furnace. To increase the heat input, it is necessary to increase the blowing temperature or coke ratio.
This leads to an increase in the amount of Si. An increase in the amount of Si in the hot metal is not preferable because an adverse effect such as an increase in the amount of used flux occurs in the steelmaking process of refining the hot metal.

[0006]

As described above, in the conventional low tapping ratio operation, the lower the tapping ratio, the more the heat input needs to be compensated, and this heat compensation is performed by increasing the blast temperature. In any case, when increasing the coke ratio due to the limitation of the equipment capacity of the hot blast stove, the increase in the amount of Si in the hot metal could not be avoided. Therefore, an object of the present invention is to propose a blast furnace operating method capable of suppressing an increase in Si in a blast furnace operation at a low tapping ratio in which production is extremely reduced. In addition, the present invention has a tapping ratio of
It is an object of the present invention to propose a blast furnace operation method capable of suppressing Si in hot metal to 0.45% or less even at a low tapping ratio of 1.4 t / dm ³ or less, particularly 1.1 t / dm ³ or less.

[0007]

Means for Solving the Problems In order to solve the above problems, the present inventors consider the process of transferring from the SiO ₂ contained in the charged raw material into Si in the hot metal, and consider the transition process and operating factors. The relationship was investigated and examined in detail. As a result, it has been concluded that the problem can be solved by limiting the heat flow ratio and the blowing temperature to special ranges which have not been experienced before, and the present invention has been completed. That is, in the present invention, when performing the blast furnace operation with a low tapping ratio, the heat flow ratio in the shaft portion of the blast furnace is set to 0.7 or less, and the blast furnace is operated under the condition that the blowing temperature is set to 500 ° C. or less. This is a method for operating a blast furnace, which is characterized by suppressing the rise of the blast furnace. Further, the present invention is effectively applied to a blast furnace operation with a tapping ratio of 1.1 t / dm ³ or less. According to the present invention, the Si content in the hot metal can be suppressed to 0.45% or less. The heat flow ratio in the shaft portion of the blast furnace is defined as B (kJ / kg · m ² · h) where the heat capacity of the raw material falling per unit time at a certain level in the shaft portion is the furnace heat rising per unit time. When the heat capacity of the internal gas is G (kJ / kg · m ² · h), it is a numerical value represented by B / G.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In a blast furnace, Si is considered to migrate into hot metal by the following mechanism. That is, Step 1: In the high-temperature portion in front of the tuyere, SiO ₂ in coke ash or ore is reduced by carbon by the reaction of the formula (1) to form SiO gas. SiO ₂ + C → SiO + CO (1) Step 2: This SiO gas is reduced by the reaction of the formula (2) by the carbon in the hot metal dripped while ascending in the furnace, and is dissolved as Si in the hot metal. SiO + C → Si + CO (2) According to the above reaction process, it is necessary to suppress the reaction in Step 1 or Step 2 in order to reduce the amount of Si in the hot metal. As a basic means, for the suppression of the reaction in step 1, the air blowing temperature is lowered to lower the temperature in front of the tuyere, while for the suppression of the reaction in step 2, molten iron and SiO 2 are used. It is possible to reduce the chance of contact with gas.

FIG. 1 shows a state inside the blast furnace in a cross section passing through the furnace central axis (only half of the furnace cross section is shown because it is symmetrical about the furnace central axis). The hatched portion in the figure is a semi-solid zone of ore called a cohesive zone. The ore charged at the furnace top is heated and reduced by the gas rising in the furnace while descending in the furnace, but at this time, the ore softens near the melting temperature of the ore and is further heated. Melts completely. At the center of the furnace, the ore temperature rises quickly due to the strong rising gas flow inside the furnace, and the ore softens relatively at the top of the furnace. On the other hand, since the rising gas flow in the furnace is relatively small in the furnace wall slightly inside, the temperature rise of the ore is delayed, and the ore softens near the lower part of the furnace. Accordingly, the cohesive zone has a chevron shape, as shown in FIG. 1, which is high at the center of the furnace and low near the furnace wall. Below the cohesive zone, the ore and the metal and slag generated by the reduction of the ore are dropped and flow. The area below the fusion zone is referred to as a dripping zone. The longer the length of the drip zone from the tuyere level (the distance corresponding to Ha and Hb in Fig. 1, hereinafter referred to as the height of the cohesive zone), the longer the furnace is generated in front of the tuyere and accompanies the gas flow. The contact time between the rising SiO gas and the hot metal is prolonged, and the reaction in step 2 is further promoted, so that the amount of Si in the hot metal increases. That is, there is a relationship that the higher the height of the cohesive zone, the higher the amount of Si in the hot metal. In the conventional low tapping ratio operation, generally, the shortage of heat input has been covered by a mere increase in coke ratio. Therefore, as shown in FIG. The length of the dropping zone was increased), and the reaction in Step 2 was accelerated, and Si in the hot metal increased.

The present inventors have focused on the reaction of step 2 and investigated the phenomenon that the SiO gas is absorbed as hot metal Si, and also examined the degree of the effect of steps 1 and 2 on the amount of Si in the hot metal. Investigations were conducted to investigate the operation method to control the amount of Si in the hot metal under the low tapping ratio operation.
Hereinafter, this will be described.

The reaction in step 2 depends on the height of the cohesive zone as described above. The fusion of the ore occurs as a result of the temperature rise by the gas, but more specifically, the raw material such as the ore and coke to be heated is heated by the heat from the rising gas in the furnace as the heating medium. As a result, the ore reaches a predetermined temperature and softens and fuses. Therefore,
The heat capacity of the raw material when the raw material falls to a certain area of the shaft portion in the furnace (referred to as the heat capacity flow rate of the raw material), and the heat capacity of the gas that rises in the furnace to that area and comes into contact with the raw material (heat capacity of the gas) Flow rate) and heat flow ratio
Considering (heat capacity flow rate of raw material / heat capacity flow rate of gas), the larger the heat flow ratio, the larger the amount of fall of the raw material, which is the object to be heated, and the smaller the flow rate of the furnace gas, which is the heating medium, so that Since the fusion of the raw materials does not occur until the temperature rise is delayed and the raw materials drop to a low level in the furnace, the height of the fusion zone is reduced. On the other hand, if the heat flow ratio is small, the temperature rise of the raw material proceeds quickly, and the height of the cohesive zone increases. The heat flow ratio is given by the formula
It can be calculated by (3). (Heat capacity of charge) / (Heat capacity of gas) = (0.21 × Ore ratio + 0.35 × Coke ratio) / (0.33 × (Blast unit unit−O ₂ enrichment unit unit) × 79 / N in furnace top gas ₂ %) ... (3) As long as the blast furnace is operated under the proper heat balance,
The heat flow ratio given by equation (3) falls within a certain range. Within that range, the unit heat output increases by increasing the coke ratio, so that the heat flow output ratio expressed by equation (3) decreases.

FIG. 2 shows the relationship between the SiO gas absorption rate and the heat flow ratio. Here, the SiO gas absorption rate is defined by the following equation. SiO gas absorptivity = 100 x (amount of Si absorbed into metal) / (amount of SiO generated before tuyere) ... (4) The molecule of the above formula is converted into metal by the reaction of the above formula (2).
It is the amount of Si absorption, and the denominator is
It is the amount generated. As can be seen from FIG. 2, when the heat flow ratio is decreased, the SiO gas absorption rate increases.
It saturates to 100% and no further increase in absorption occurs. As described above, when the heat flow ratio is reduced, the level of the cohesive zone is increased, and as a result, the chance of contact with the dropping hot metal and the SiO gas in the rising furnace gas is increased, and the heat flow ratio is 0.7 or less. So the reaction in step 2 is almost 100%
Will progress. That is, at a heat flow ratio of 0.7 or less,
Since the reaction of Step 2 itself proceeds almost 100%,
Almost all of the SiO gas generated in front of the tuyere will be dissolved as Si in the hot metal.

Here, a general measure taken to reduce the heat flow ratio in actual operation is to increase the coke ratio. In other words, an increase in the coke ratio necessarily entails an increase in the unit air intensity, and at this time, the increase in the denominator is larger than the increase in the numerator in equation (3). Will decrease.

The inventors pay attention to the results shown in FIG.
The optimization of operating conditions of the blast furnace was studied. That is,
The saturation region of the SiO gas absorption rate in FIG.
Therefore, when the heat flow ratio is in the range of 0.7 or less, it is considered that even if the heat flow ratio is decreased (the coke ratio is increased), the Si content in the hot metal does not further increase. On the other hand, in the range of the heat flow ratio of 0.7 or less, since the heat input compensation by the decrease of the heat flow ratio, in other words, the increase of the coke ratio, is sufficient, the blowing temperature is reduced by the heat component corresponding to the excess heat input compensation. It should be possible. That is,
Even in a situation where the reaction in step 2 proceeds almost 100%, if the amount of generated SiO gas is suppressed by lowering the tuyere temperature, the transfer of Si into the hot metal can be suppressed accordingly. it is conceivable that. By adopting such an operation policy, it seems that it is possible to operate at a low tapping ratio without increasing the amount of Si in the hot metal.

Under such a policy, operation is further performed in a blast furnace having an inner volume of 2584 m ³ by changing the heat flow ratio and the blast temperature in various ranges.
The relationship with the amount of Si was investigated. The results are shown in FIGS.
Shown in FIG. 3 shows the relationship between the blowing temperature and the amount of Si in the hot metal. From FIG. 3, as the blast temperature decreases,
It can be seen that the value of Si in the hot metal decreases because the reaction of equation (1) hardly proceeds to the right. When the tapping ratio of the present invention is 1.1 or less, it can be said that maintaining the blowing temperature at 500 ° C. or less is effective. The heat flow ratio in the operation with a tapping ratio of 1.1 t / dm ³ or less in FIG. 3 was in the range of 0.65 to 0.7. FIG. 4 shows the relationship between the heat flow ratio and the amount of Si in the hot metal. From Fig. 4, it can be seen that in the operation where the heat flow ratio exceeds 0.7,
Although the amount of Si tends to increase, the amount of Si in the hot metal hardly increases when the heat flow ratio is less than 0.7. In addition, the blast temperature in the operation with a tapping ratio of 1.1 t / dm ³ or less in FIG. 4 was in the range of 400 to 500 ° C. The inventors have further studied the operating conditions in detail, and as a result, in the operating method of the present invention, by setting the heat flow ratio to 0.7 or less and the blowing temperature to 500 ° C. or less, the desired desired effect is obtained. Was confirmed.

In order to concretely carry out the method of the present invention, the ratio of ore to coke in the charged raw material is changed to increase the coke ratio, and at the same time, to increase the air flow. This makes hot metal 1
The excess heat input per t is reduced by lowering the blast temperature. By operating under such conditions, it is possible to reduce the amount of hot metal produced per unit time and at the same time to reduce the amount of Si. In the present invention, the level of the cohesive zone is increased by increasing the coke ratio,
According to equation (2), the absorption rate of Si from the SiO gas to the hot metal is almost 100.
%, But by lowering the blast temperature,
The amount of generation of the SiO gas in the above equation (1) can be reduced, and as a result, the Si content in the hot metal can be reduced. In this case, the lower limit of the blowing temperature is naturally determined by the range in which the blast furnace can be operated in a heat-balanced manner.

[0017]

EXAMPLES In blast furnace having an inner volume of 2584m ^3, 1.1t
/ Dm ³ of low tapping ratio operation. Heat flow ratio 0.75 (coke ratio 500 kg / t, air flow 2700 Nm)
³ / t), in the operation with a blowing temperature of 700 ° C, the amount of Si in the hot metal
It was in the range of 0.5-0.6%. On the other hand, the heat flow ratio
0.7 (coke ratio 600 kg / t, air volume 3300 Nm ³ /
t) When operated by the method of the present invention in which the blowing temperature was 450 ° C., a low value of 0.4 to 0.45% was obtained for the amount of Si in the hot metal. Such good results were obtained by implementing the method of the present invention, because the temperature before the tuyere was reduced to 1750 ° C due to the decrease in the blowing temperature, and the generation of SiO was suppressed. Seems to have greatly contributed.

[0018]

As described above, according to the method of operating a blast furnace with a low iron output ratio in the method of the present invention, the tuyere is maintained while heat input is compensated by setting the conditions of the heat flow ratio and the blast temperature to special ranges. It is possible to suppress the formation of SiO before and suppress the rise of Si in the hot metal.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a difference in cohesive zone level in operations with different heat flow ratios.

FIG. 2 is a graph showing the relationship between the absorptivity of SiO gas to hot metal and the heat flow ratio.

FIG. 3 is a graph showing the effect of blowing temperature on the amount of Si in hot metal.

FIG. 4 is a graph showing the effect of the heat flow ratio on the amount of Si in the hot metal.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hirofumi Nishimura 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Works Chiba Works (72) Inventor Takeshi Ken Sato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki (72) Inventor Mikiharu Takeda 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture F-term (reference) 4K012 BD01 BD03

Claims (2)

[Claims] Claims: 1. In operating a blast furnace with a reduced tapping ratio, a heat flow ratio in a shaft portion is set to 0.7 or less,
A method for operating a blast furnace, wherein an increase in the Si content in hot metal is suppressed by operating at a blowing temperature of 500 ° C. or lower. 2. The blast furnace operating method according to claim 1, wherein the blast furnace is operated at a tapping ratio of 1.1 t / dm ³ or less.