JP2014224291A - Method of charging object to be charged into blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To catch a sign of instability of a blast furnace and prevent the instability in advance before an operation of the blast furnace becomes unstable.SOLUTION: A method of charging an object to be charged into the blast furnace, which method is used in such the bell-less blast furnace that a coke batch (C) and an ore batch (O) are charged into the blast furnace as one charge and in which method another coke batch (Cc) is charged in a center part of the blast furnace before the coke batch (C) is charged, is characterized in that when a difference between the inside pressure of a middle part of a shaft of the blast furnace and that of a furnace throat part becomes 1.5 times or larger of the difference at the steady-state time, the coke batch (Cc) of 5-20 mass% of the total coke amount (Cc+C) of one charge is charged into the center part of the blast furnace by 1-10 charges.

Description

  The present invention relates to a charging method for charging a blast furnace. In particular, the present invention relates to a method of charging a blast furnace to prevent instability of blast furnace operation.

  The blast furnace is in the upper process of the steel plant, and it is important to stably produce pig iron. However, the blast furnace may not be able to maintain stable operation due to various reasons. If the stable operation of the blast furnace is impaired, it will not be possible to supply raw materials to the next and subsequent processes, which will hinder the production of the entire steelworks.

  There are various reasons why blast furnace operation may be sluggish. For example, there are cases where the properties of the incoming raw material deteriorate and the quality of the raw material charged in the blast furnace deteriorates, or the furnace wall of the blast furnace is damaged and the flow of the gas in the furnace is modulated. If the economy is in good condition, the production must be increased. If the economy deteriorates and demand declines, the production must be reduced. The production elasticity of a blast furnace is not always good, and in particular, it may be extremely difficult to reduce the production of a blast furnace.

The blast furnace may be forced to stop air blowing for a certain period of time for equipment maintenance. If the wind is rested for a long time, the combustion of coke in the blast furnace stops during the rest period, so the charge and the semi-molten material in the blast furnace lose their retained heat. Therefore, it is important that the rising of the air blow after a long period of off-air is applied to the blast furnace with furnace heat and returned to the normal blast furnace operation at an early stage.
As mentioned above, the blast furnace operation method that recovers early from an unstable operation state may occur due to a deterioration in raw material quality or other causes, as described above, not only during the start of rest wind but also during steady operation. Is desired.

The in-furnace situation in the blast furnace is explained by the shape of the cohesive zone in the furnace. FIG. 1A shows the profile A of the cohesive zone 1 during stable operation of the blast furnace. Coke and ore, which are blast furnace charges, are charged in layers from the top of the furnace into the furnace. The ore layer is heated by the in-furnace gas generated by the combustion of coke in front of the tuyere 4 and rising in the furnace, starts softening at about 1000 ° C., and forms the cohesive zone 1. The fusion zone 1 includes a fusion layer 2 and a coke slit 3 interposed therebetween. When the temperature of the fusion layer 2 rises and the reduction of the ore proceeds, the temperature of the fusion layer 2 reaches 1200 to 1300 ° C., the ore melts, and the lower surface of the fusion layer 2 melts down. Inside the fusion layer 2, voids between the ores are reduced due to softening and melting of the ores, and it is difficult for the gas in the furnace to pass through. As a result, the in-furnace gas is limited to the coke slit 3 between the fusion layer 2 and the fusion layer 2, and the ventilation resistance increases rapidly. As described above, the profile of the fusion zone 1 formed from the fusion layer 2 and the coke slit 3 affects the ventilation resistance in the blast furnace.
The shape of the fusion zone 1 during stable operation is such that the position of the top of the fusion layer 2 in the center of the furnace is at a certain height, and the width of the top of the fusion layer 2 is around the furnace. It is smaller than the width of a certain fusion layer 2. As a result, the ventilation resistance in the furnace center is smaller than that in the furnace periphery, and the gas flow in the furnace in the furnace center increases. The entire profile of the fusion zone 1 is slim, and the width of the individual fusion layers 2 is narrow. Therefore, the overall ventilation resistance is small, and stable operation is possible.

FIG. 1C shows an example of the profile C of the cohesive zone 1 in an unstable operation state. If there is the above-mentioned blast furnace destabilization factor, the gas flow in the furnace at the center of the furnace during stable operation is suppressed, and the center flow cannot be secured. As a result, the heating of the charge in the furnace center by the furnace gas is delayed, and the top position of the fusion layer 2 in the furnace center is lowered. Due to the suppression of the in-furnace gas flow in the center of the furnace, the gas flows to the middle part of the furnace and the periphery of the furnace where the ventilation resistance is large, and the in-furnace gas flow becomes unstable. Due to destabilization of the gas flow, heating of the charge in the intermediate part and the furnace peripheral part is delayed, and the position of the fusion zone 1 in the furnace intermediate part and the furnace peripheral part is also lowered. On the other hand, the length of the fusion zone 1 in the width direction becomes longer due to the lower position of the top portion of the fusion layer 2 in the center of the furnace. As a result, the ventilation resistance of the coke slit 3 between the fusion layers also increases, and the gas flow becomes unstable. Heating of the fusion layer 2 by the gas passing through the coke slit 3 is also delayed, and the ore melting and dropping are delayed. As a result, the positions of the middle and peripheral portions of the fusion zone 1 are also lowered.
The position of the top of the fusion layer 2 in the center of the furnace is low, and the width of the fusion layer 2 is long. The entire profile of the cohesive zone 1 is a stubby type, and the portion of the lowermost cohesive zone 1 that contacts the furnace wall (hereinafter referred to as the root of the cohesive zone) is thick and long. When the furnace heat of the blast furnace decreases, the melting rate of the ore on the lower surface of the cohesive zone 1 is slower than the upper surface softening rate of the cohesive zone 1, and the cohesive zone 1 is enlarged, and the middle part of the furnace and the periphery of the furnace The ventilation resistance of the in-furnace gas increases.

  As a blast furnace operation method when the blast furnace operation becomes unstable and the cohesive zone 1 becomes a profile C, there is a central coke charging method in which a large amount of coke is charged in the center of the furnace (Patent Document 1).

  As the blast furnace operation method when the blast furnace operation becomes unstable and the cohesive zone 1 becomes the profile C, the mass ratio of the coke layer to the ore layer (hereinafter referred to as O / C) until the blast furnace operation is stabilized. There is a method for continuously lowering. This method is a method in which when the operation of the blast furnace becomes unstable and the furnace heat decreases, the furnace heat is recovered by increasing the coke charging amount, and the cohesive zone 1 is returned from the profile C to the profile A. This is a conventionally used method (hereinafter referred to as a conventional method).

JP-A-7-268212

  In the invention described in Patent Document 1, the gas in the furnace is centrally flowed, the air permeability of the blast furnace is ensured, and the furnace zone cohesive zone 1 crushed by the profile C by raising the furnace heat in the furnace center. Can be lifted high. However, it does not improve the root of the cohesive zone 1 enlarged by the profile C, and there is a problem that blast furnace operation takes time.

  According to the conventional method described above, when the operation of the blast furnace is unstable, the furnace heat is recovered by reducing the O / C, and the cohesive zone profile is improved, but the low O / C charge reaches the tuyere. Until then, the low O / C charge is continuously charged, so the heat in the furnace becomes excessive and the heat balance is lost. As a result, there is a problem that it takes time to adjust the heat balance.

  If blast furnace operation becomes unstable and the shape of the cohesive zone 1 becomes Profile C, a significant increase in fuel ratio and a long recovery period are required for its recovery, but before the blast furnace operation becomes unstable, If the signs of stabilization can be caught and instability of the blast furnace can be prevented, it can greatly contribute to stabilization of blast furnace operation.

It is an object of the present invention to catch signs of destabilization and prevent instability of the blast furnace before the blast furnace operation becomes unstable.
An object of the present invention is to provide a method for charging a blast furnace to prevent instability of blast furnace operation.

  The present inventor catches a sign of instability of the blast furnace due to the difference in the furnace pressure between the center of the shaft of the blast furnace and the furnace mouth, and when the differential pressure exceeds a predetermined value, a predetermined coke is placed in the center of the blast furnace. It was found that the destabilization of blast furnace operation can be prevented by charging the blast furnace. The present invention is based on such knowledge, and the gist thereof is as follows.

(1) In a bell-less blast furnace in which a coke batch (C) and an ore batch (O) are charged into the furnace as one charge, the coke batch (Cc) is placed in the center of the blast furnace before the coke batch (C) is charged. A method of charging a charge into a blast furnace for charging
When the difference between the furnace pressure at the middle of the shaft of the blast furnace and the furnace pressure at the furnace mouth becomes 1.5 times or more of the steady state, it is 5% by mass with respect to the total coke amount of one charge (Cc + C). A method of charging a charge into a blast furnace, characterized in that the coke (Cc) of 20% by mass or less is charged into the center of the blast furnace for 1 to 10 charges.
However, the furnace pressure at the middle of the shaft of the blast furnace means the furnace pressure at a portion of 48 to 55% from the tuyere to the height from the tuyere to the stock line. The pressure in the furnace is 70-80% of the height from the tuyere to the stock line.

  It is possible to provide a charging method for charging a blast furnace to prevent instability of blast furnace operation.

The cohesive zone profile is shown. (A) is a stable operation cohesive zone profile. (B) is a cohesive zone profile in which the position of the top of the fused layer is lowered. (C) is a cohesive zone profile of unstable operation. The figure which shows the detection position of the in-furnace pressure in a real furnace. The figure which shows a 1/3 scale model experiment apparatus. The figure which shows the method to throw in the coke and the ore in a 1/3 scale experimental apparatus. The figure which shows the deposit accumulation condition at the time of center LC insertion by 1/3 scale model experiment. The figure which shows the layer thickness ratio of the charge at the time of center LC insertion by 1/3 scale model experiment. The figure which shows the blast furnace operation at the time of center LC implementation in a real furnace. The figure which shows the detection information of the gas flow in a furnace at the time of center LC implementation in a real furnace. The figure which shows upper sonde (eta) _CO (%) distribution at the time of center LC implementation in a real furnace.

The blast furnace destabilizes because the amount of central gas in the furnace is suppressed and the top of the cohesive zone is lowered.
The present invention catches a decrease in the top of the cohesive zone due to the difference between the furnace pressure at the center of the shaft of the blast furnace and the furnace pressure at the furnace port, and a small amount is placed in the center of the blast furnace when the differential pressure exceeds a predetermined value. It is characterized by preventing instability of blast furnace operation by charging the coke (light charge, hereinafter referred to as the center LC).
Hereinafter, (1) destabilization of the blast furnace due to the lowering of the cohesive zone top, (2) catching of the lowering of the cohesive zone top due to the difference in the pressure inside the shaft of the blast furnace and the furnace port, and (3) due to the center LC The prevention of destabilization of blast furnace operation is described.

(Blast furnace destabilization due to lowering of the top of the cohesive zone)
As described above, FIG. 1 (A) is the profile A of the cohesive zone 1 during stable operation of the blast furnace, and FIG. 1 (C) is the profile C of the cohesive zone 1 in an unstable state of the blast furnace. . FIG. 1 (B) is a cohesive zone profile in which the position of the top of the cohesive zone 1 is lowered with respect to the stable operation of the blast furnace. When shifting from FIG. 1 (A) to FIG. 1 (C), first, the central gas in the furnace is suppressed, and due to the decrease in the amount of central gas, the heating of the charge in the central portion is delayed, and the top of the cohesive zone decreases. To do. If it can catch early that the profile of the cohesive zone 1 is as shown in FIG. 1 (B), stable operation of the blast furnace will be maintained without shifting the cohesive zone 1 to the profile C. It is considered possible.

(Catch of lowering of the cohesive zone top due to the difference in furnace pressure between the shaft center of the blast furnace and the furnace port)
The present inventor has studied a method for catching a decrease in the cohesive zone top at an early stage in the operation of a blast furnace. FIG. 2 shows the detection end position for measuring the pressure in the furnace. The ratio from the tuyere to the interval from the tuyere to the stock line (SL) is shown. As another detection end, there is a rib thermometer embedded in the rib of the stave cooler. The skin flow temperature is a thermometer installed through the stave cooler in the furnace opening.

In operation of the blast furnace, the present inventor, when the top of the cohesive zone is lowered, among the various detection ends, the cohesive zone is the earliest due to the pressure difference of the pressure gauge in the furnace installed in the central part of the shaft and the furnace port part. We have found that we can catch signs of a drop in the top. If the top of the cohesive zone starts to decrease, the gas flow in the furnace changes, and the pressure in the furnace between the middle part of the shaft and the furnace port part fluctuates, which is considered to cause a change in the pressure difference.
Here, the in-furnace pressure in the middle part of the shaft of the blast furnace refers to the in-furnace pressure of 48 to 55% from the tuyere to the height from the tuyere to the stock line. A change in the difference between the furnace pressure at the center of the shaft and the furnace pressure at the furnace port is detected. This is because the pressure in the furnace within this range varies sensitively to the decrease in the top of the cohesive zone shown in FIG.

(Preventing instability of blast furnace operation due to central LC)
Conventionally, when the cohesive zone 1 becomes a profile C and the blast furnace becomes unstable, the ratio of the ore layer to the coke layer (hereinafter referred to as O / C) is, for example, O / C = 5. From 0, it was drastically lowered to about O / C = 3.0, and further, low O / C was continued for a long time until recovery, and recovery to profile A was attempted. As a result, it was already mentioned that the blast furnace heat balance was lost and it took a long time to recover. On the other hand, since this invention respond | corresponds when the sign of the fall of a cohesive zone top appears, the fall of O / C may be small.
Table 1 shows an example of the center LC in a large furnace of 5000 m ³ class. In Table 1, the center C (hereinafter referred to as Cc) represents the mass of coke charged in the center, and the Cc ratio in the base condition was 8.3 mass% with respect to the total coke amount (Cc + C) of one charge. is there. On the other hand, in the central LC operation, 17.9 mass% × 5 ch + 13.4 mass% × 5 ch is charged with respect to the total coke amount (Cc + C) of one charge. The center LC according to the present invention is charged in the center of the blast furnace at a center coke ratio (Cc ratio) of 5% by mass to 20% by mass with respect to the amount of coke of one charge (Cc + C).
In Table 1, the base 3 dump is a system in which 1 charge is charged with 3 dumps of Cc, C, and O, and the Cc ratio is calculated as Cc / (Cc + C) × 100. The ratio of Cc.

(Regarding the charge accumulation at the time of blast furnace charging by the central LC)
The state of charge accumulation during blast furnace charging by the central LC was investigated using a 1/3 scale model experimental device.
Fig. 3 shows a 1/3 scale model experimental apparatus for a 5000m class ³ blast furnace. The surge hopper 11, the charging conveyor 12, the furnace top hopper 13, the turning chute 14, and the furnace body shaft portion 15 are targeted. Moreover, the dropping in the furnace is taken into account by the cutting device 16 at the lower part of the apparatus, and the gas flow distribution is taken into consideration by the blowing from the lower part of the apparatus.

  FIG. 4 shows a charging method in a 1/3 scale experimental apparatus. The swivel chute 14 can change the elevation angle, and while changing the raw material fall position from the furnace wall position to the furnace center position and turning around the furnace axis, the raw material is ring-shaped from the furnace wall position to the furnace center position. Is inserted (forward tilt).

FIG. 5 shows the deposit accumulation measured by the 1/3 scale model experimental apparatus under the charging conditions shown in Table 1. The horizontal axis is the relative position when the furnace center is 0 and the furnace wall position is 1.0, and the vertical axis is the relative position when the position 1800 mm below the stock line (SL) is 1.0. Is shown. In the base 3 dump, 8.3% by mass of _CC is present in the center, which contributes to securing the central flow. When the central LC is charged, Cc is 17.9% by mass. When the top of the cohesive zone is lowered as shown in FIG. 1B, it is considered that the deposition amount of the central portion Cc is increased, and the top of the cohesive zone contributes to the rise of the decline.
FIG. 6 shows the layer thickness ratio of the charge measured by the 1/3 scale model experimental apparatus under the charge condition shown in Table 1. Lo represents the thickness of the ore layer, and Lc represents the thickness of the coke layer. When the center LC is charged, the low layer thickness ratio region is expanded to the range from the center to the 0.22 position, and the coke single layer region is expanded. The range from 0.22 to 0.50 from the center is thought to be the result of the increase in the layer thickness ratio relative to the base, and the inflow of ore was blocked by Cc. From 0.55 to the edge of the wall, the center LC was a single increase in coke to the center, so the deposition shape and layer thickness ratio distribution were almost the same as the base.

Next, examples of the present invention will be described, but the present invention is not limited thereto.
Internal volume in a large blast furnace ^tertiary 5000 m, embodying the present invention. 7 and 8 show the results of preventing instability of blast furnace operation due to the central LC charging. The horizontal axis shows the passage of time.

7 and 8, until the time T, the air flow rate (Nm ³ / min), the K value (−) in FIG. 7, the rib temperature (° C.), the skin flow temperature (° C.) in FIG. The differential pressure (hPa) at the mouth was substantially stable. The rib temperature is a temperature of a thermometer embedded in the rib of the stave cooler at positions of 25% and 35% from the tuyere to the height from the tuyere to the stock line. The skin flow temperature is a thermometer installed through the stave cooler at the furnace port.
Moreover, K value is what evaluates air permeability and was computed by the following formula.
For the height from the tuyere to the stock line, K = (P1 ² −P2 ² ) / G ^1.7
However, P1: ventilation pressure (MPa)
P2: Pressure at the top of the blast furnace (MPa)
G: Bosch gas amount in blast furnace (Nm ³ / min)
Until the time T, the other detection end information was stable, but at the time T, the difference between the pressure in the shaft middle part (P ₂ ) and the pressure in the furnace port part (P ₃ ) is about 1.6 h from about 150 hPa. Of about 240 hPa. Based on this information, Step 1 of the center LC shown in Table 1 was performed. Step 1 is for charging 5ch of a base that has been operated at a Cc ratio of 8.3% by mass, and then increased to a Cc ratio of 17.9% by mass. Note that the pressure gauges at the center of the shaft and the furnace port are installed at four locations in the circumferential direction of the furnace body, but even if the differential pressure between the center of the shaft and the furnace port varies. Judging that there was a sign of a decrease in the top of the bandage, the center LC was performed to prevent the decrease in the bandage.
Then, after Step 1, as Step 2, the amount increased to 13.4% by mass of Cc was charged into 5ch, and the level was gradually returned to the base level.
By performing Step 1 and Step 2 of the center LC as described above, after the time T + 24 hours, the above-mentioned detection end information indicating the gas flow in the blast furnace is stabilized, and instability of the blast furnace operation is prevented in advance. I was able to.

FIG. 9 shows the upper sonde η _CO (%) distribution at the base time, immediately before the center LC charging and after the center LC charging. The upper sonde η _CO (%) distribution immediately before the central LC is charged is a gas flow distribution in which the central portion η _CO (%) is higher than the base time and the central flow is suppressed. This is probably because the top of the cohesive zone has been lowered. After the center LC was charged, the center η _CO (%) decreased, and the blast furnace operation could be prevented from becoming unstable.
Here, the upper sonde η _CO (%) distribution is obtained by inserting a sonde into the furnace directly above the charge surface and measuring the gas utilization rate in the furnace radial direction. The distribution is evaluated.

  From the above, catching information on the differential pressure (hPa) between the shaft center and the furnace port, grasping the decrease in the cohesive zone top at an early stage, and carrying out central LC charging, destabilizing blast furnace operation It was found that it can be prevented beforehand.

  Before blast furnace operation becomes unstable, it can be used to catch signs of instability and to prevent instability of the blast furnace.

  DESCRIPTION OF SYMBOLS 1 ... Fusion zone, 2 ... Fusion layer, 3 ... Coke slit, 4 ... Feather, 5 ... Stave cooler, 11 ... Surge hopper, 12 ... Loading conveyor, 13 ... Furnace top hopper, 14 ... Turning chute, 15 ... furnace body shaft part, 16 ... cutting device at the lower part of the apparatus.

Claims (1)

In the bell-less blast furnace where the coke batch (C) and the ore batch (O) are charged into the furnace as one charge, the coke batch (Cc) is charged at the center of the blast furnace before the coke batch (C) is charged. A charging method for charging the blast furnace,
When the difference between the furnace pressure at the middle of the shaft of the blast furnace and the furnace pressure at the furnace mouth becomes 1.5 times or more of the steady state, it is 5% by mass with respect to the total coke amount of one charge (Cc + C). A method of charging a charge into a blast furnace, characterized in that the coke (Cc) of 20% by mass or less is charged into the center of the blast furnace for 1 to 10 charges.
However, the furnace pressure at the middle of the shaft of the blast furnace means the furnace pressure at a portion of 48 to 55% from the tuyere to the height from the tuyere to the stock line. The pressure in the furnace is 70-80% of the height from the tuyere to the stock line.