JP4252684B2 - Reduced blast furnace operation method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a reduced scale operation when a blast furnace is closed during periodic inspections / repairs and the like.
[0002]
[Prior art]
The inner wall of the blast furnace lined with refractory is used in an environment where it is exposed to impact / friction of the charge and high-temperature gas. Therefore, refractories that have been worn out by long-term operation are regularly inspected and repaired if the wear is severe.
During inspections / repairs, etc., a scale-down operation that gradually lowers the level of the raw material charging layer is implemented. However, the distribution of charges in the furnace and the distribution of gas in the furnace change irregularly during the reduction process, and troubles such as slips and blowouts are likely to occur, and the reduction to the target level may not be possible.
[0003]
Troubles such as slips and blowouts are caused by the circumferential balance of the cohesive zone being lost during the reduction process, and when the inside of the furnace is viewed in a horizontal section, the fall of the charge and the gas flow in the furnace rise locally. There is. Therefore, a method of reducing the air volume while adjusting the air flow rate according to the level of the raw material charging layer has been conventionally employed. For example, a method of performing a reduction operation with a predetermined air flow below a predetermined amount according to the lowering of the charge raw material layer top surface (Japanese Patent Laid-Open No. 55-110710), from the top surface of the cohesive zone to the charge There is a method of taking an action of decreasing the air volume or increasing the furnace top pressure when the distance is abnormally close (Japanese Patent Laid-Open No. 56-116806).
[0004]
[Problems to be solved by the invention]
In the conventional scale-down operation, troubles such as slips and blowouts are mainly prevented by adjusting the air flow rate. However, when the blowing pressure fluctuates due to a sudden change in the gas flow in the furnace due to the change in the shape of the cohesive zone, the adjustment of the blowing amount cannot sufficiently prevent the occurrence of slips and blow-throughs, and it is still reduced to the target level. Operation may not be possible. Therefore, actions such as finger scale reduction and air flow rate reduction are taken while confirming that there is no fluctuation in the air flow rate. However, with this method, the amount of wind reduction increases, and the amount of production reduction increases accordingly.
The present invention has been devised to solve such a problem, and by switching the blowing condition control from the blowing amount designation to the blowing pressure designation in the reduction process, the maximum blowing amount is prevented while preventing slipping or blow-through. The purpose is to reduce the scale under stable furnace conditions.
[0005]
[Means for Solving the Problems]
In order to achieve the object, the present invention blows hot air into the furnace with an air volume adjusted according to the lowering of the level of the charged raw material layer during the reduced operation of lowering the charged raw material layer in the blast furnace to the vicinity of the furnace belly. The difference between the maximum value and the minimum value of the pressure in the circumferential direction measured by the pressure gauges provided in the upper, middle and lower stages of the shaft portion is 30 g / cm ² or less, and When the fluctuation range is stabilized within 20 g / cm ² , hot air is blown into the furnace by switching to the blowing pressure designation .
[0006]
[Action]
In the blast furnace scale-down operation, air blowing is continued without charging raw materials such as ore and coke, and the level of the charged raw material layer in the furnace is gradually lowered. The distance from the top of the furnace to the stock line is required to be lowered to the target position, and the reduction is required to reach the tuyere level. For this reason, the total amount of air blown according to the charged raw materials from the start of reduced scale operation to resting air becomes an important factor in maintaining the furnace condition stably.
[0007]
During the scale-down operation, the resistance to ventilation in the furnace decreases as the level of the charged raw material layer decreases. Therefore, if a constant air flow rate is maintained, slipping or blow-through tends to occur. The decrease in ventilation resistance is also greatly affected by the stopping of pulverized coal blowing. Therefore, the blower that blows hot air into the blast furnace is controlled so that the specified air volume corresponding to the level drop is obtained. Although the reduction operation specified by the air flow rate is easy to control, the action of lowering the finger scale and air flow rate is taken while confirming that there is no change in the air flow pressure. An action that significantly reduces the amount of air blown to suppress fluctuations is required. Moreover, even if fluctuations in the blowing pressure are suppressed, recovery of the blowing amount that induces fluctuations in the blowing pressure becomes difficult to execute, so the amount of wind reduction is further increased. Specifically, as shown in FIG. 1 which shows the actual value when the stock line is reduced by 15 m in a blast furnace having an internal volume of 1650 m ³ , 8 to 9 hours from the start of the reduction operation to the stop of air blowing. Take it. The increase in the amount of wind reduction causes the temperature in the furnace to drop more than necessary, and causes a longer time to start up the furnace after the stop of the wind.
[0008]
Therefore, in the present invention, the period from the start of the reduced operation to the stop of the blowing is shortened by suppressing the increase in the reduced amount of wind by switching from the blowing amount designation to the blowing pressure designation during the reduction operation. The timing for switching from the blowing amount designation to the blowing pressure designation is set after confirming that the pressure fluctuation in the vertical direction of the blast furnace shaft portion is stabilized at a low level. The pressure fluctuation is detected from the time change of the measured value by measuring the pressure in the furnace in multiple stages with a pressure gauge inserted in the furnace wall in the vertical direction of the blast furnace shaft portion.
[0009]
Specifically, as shown in FIG. 2, four pressure gauges are embedded at equal intervals in the circumferential direction in the upper, middle and lower stages of the blast furnace shaft, and the fluctuation parts and fluctuations of the charging material and gas flow in the blast furnace are embedded. Know the size. In a blast furnace operating in a reduced scale, if the pressure value detected by the upper pressure gauge approaches the furnace top pressure as the charge level decreases, the pressure value of each stage will vary if there is a deviation in the charge level. Fluctuation range occurs. Therefore, it is possible to determine the stability of the furnace condition and the quality of the reduced scale operation from the transition of the pressure in the furnace and the fluctuation range of the pressure value in the circumferential direction of each stage, and in the present invention, from the air flow rate designation based on this determination result The timing to switch to blow pressure specification is set.
[0010]
The timing of switching is the pressure of each part in the furnace and the blowing pressure measured by four pressure gauges arranged at equal intervals in the circumferential direction at the upper, middle and lower stages of the shaft part and the pressure gauge provided at the tuyere It is decided according to.
When the fluctuation range of the pressure value obtained by each pressure gauge is 20 g / cm ² or less, a stable furnace condition without slipping or blow-through is maintained. On the other hand, if the pressure fluctuation exceeds 20 g / cm ² , there is a high possibility that partial slip or blow-through has occurred, and switching to wind pressure designation at this stage will make the furnace condition more unstable. In addition, a pressure fluctuation is shown by the result in the past about 5 minutes of the value measured every minute with all 13 pressure gauges. Further, when the fluctuation range in the circumferential direction of the furnace body obtained as the maximum value-minimum value of the pressure detected by the pressure gauge at each stage is 30 g / cm ² or less, the furnace condition is stably maintained. . On the other hand, the fluctuation range exceeding 30 g / cm ² is a manifestation of a difference in the raw material descending speed such as a decrease in the charged raw material layer in the circumferential direction. The air volume is concentrated on the reduced part, and it becomes easy to induce blow-through.
[0011]
In addition, since the blown air volume is reduced as the level of the charged raw material layer is gradually reduced in the scale operation, the reduction in the gas flow rate passing through the blast furnace reduces the possibility of blow-through. Therefore, the operation specified by the blowing pressure can be performed. However, a decrease in the gas flow rate is likely to cause a deviation in the charged raw material layer due to a shortage of the central flow accompanying a decrease in the tuyere wind speed or a local peripheral flow. Therefore, shortening the operation time with a low air flow rate in order to reduce the operating time with a low air flow rate in order to stabilize the furnace conditions before and after the off-air flow, while reducing the target raw material layer level in the furnace conditions where slips and blow-offs do not occur. It is important for conversion.
[0012]
At the stage where the reduction operation shifts to the blowing pressure designation, the furnace pressure loss (= blowing pressure−furnace top pressure) is controlled according to the finger scale level. From the results of investigations and researches by the present inventors, it is possible to prevent the occurrence of troubles such as slips and blowouts when maintaining the pressure loss in the furnace in the blowout prevention area below the straight line in FIG. 3 in relation to the finger scale level. I understood. The relationship shown in FIG. 3 indicates that the pressure at the top of the furnace can be kept constant and the decompression operation can be performed at a specified blowing pressure.
Since the pressure at the top of the furnace is kept constant, the finger pressure level and the pressure loss in the furnace are always known during the operation of the blast furnace, so that the blowing pressure can be specified prior to the reduction of the finger level. In addition, the maximum air volume is ensured under furnace conditions where slip and blow-out do not occur. Therefore, a reduced charging operation with a reduced reduction time as shown in FIG. 1 is possible, and a reduction in production due to reduction and resting wind can be kept low.
[0013]
【Example】
When the blast furnace with an internal volume of 1650 m ³ was rested, the air volume was lowered as shown in FIG. During the reduction operation, the furnace pressure in the vertical direction of the shaft part is constantly measured, and the fluctuation range of the furnace pressure is within 20 g / cm ² , and the maximum and minimum pressure values measured by the pressure gauge at each stage When the difference from the above reached 30 g / cm ² or less, the blowing condition was switched from the blowing amount designation to the blowing pressure designation. This switching time corresponds to approximately 70% of the specified air volume during normal operation before reduced operation. In the scaled operation specified by the blowing pressure, hot air was blown into the furnace with the blowing pressure adjusted to the blowout prevention area (Fig. 3) determined from the relationship between the stock line and the pressure loss in the furnace.
[0014]
It took 8 hours from the start of the scale-down operation until the level of the raw material layer in the furnace interior reached the vicinity of the furnace belly, but no slip or blow-through was detected during this time. Next, after repairing and inspecting the inside of the furnace, the furnace condition was started and the operation was shifted to normal operation. The period until the transition to normal operation was as short as 11 hours. This is because the decrease in the amount of wind reduction during the reduced scale operation was suppressed.
For comparison, using the same blast furnace, the level of the raw material layer in the furnace interior was lowered to the vicinity of the furnace belly by the reduced operation specified by the blast amount. In this case, it took 9 hours longer than the example of the present invention. For this reason, the amount of wind reduction during the reduced scale operation increased, and it took 15 hours and a long time for the blast furnace to recover to the normal furnace condition after the wind break.
[0015]
【The invention's effect】
As described above, in the present invention, when the blast furnace is closed, hot air having an air volume adjusted according to the level of the charged raw material layer was blown into the furnace, and it was detected that the pressure in the furnace was stabilized at a low level. At the stage, the blowing condition is switched from the blowing amount designation to the blowing pressure designation. By this switching, the level of the charged raw material layer can be lowered to the vicinity of the furnace bellows in a relatively short time, and the increase in the amount of wind reduction and the duration of wind reduction accompanying the reduced operation / rest wind is suppressed. For this reason, the blast furnace after the resting of the wind recovers to the normal furnace condition in a short time, and the reduced scale operation with the reduced production amount becomes possible.
[Brief description of the drawings]
[Fig. 1] A graph showing the change in operation specifications of reduced scale operation that switches from air flow rate designation to air flow pressure designation in contrast to air flow rate designation reduced operation [Fig. 2] Switch from air flow rate designation to air pressure designation Blast furnace with shaft part with multiple pressure gauges embedded in the vertical direction to detect timing [Figure 3] Graph showing the effect of the relationship between stock line and pressure loss in the furnace on the blow-through

Claims (1)

During scale-down operation in which the charged material layer in the blast furnace is lowered to the vicinity of the furnace, hot air is blown into the furnace with an air flow adjusted according to the lowering of the charged material layer level, and is provided in the upper, middle and lower stages of the shaft section. The difference between the maximum value and the minimum value in the circumferential direction measured by each pressure gauge was 30 g / cm ² or less, and the fluctuation range of the pressure and blowing pressure of each stage was stabilized within 20 g / cm ² . A reduced-scale operation method for a blast furnace, characterized in that hot air is blown into the furnace by switching to a specified blowing pressure at a stage.

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