JP4100361B2 - Reduced blast furnace operation method - Google Patents

Description

  The present invention relates to a reduced operation method of a blast furnace, and in particular, suppresses a flame generated from the raw material in the furnace when the wind is off so as not to hinder the work such as repair, and at the time of restarting the operation after the wind The present invention relates to a reduced-scale operation method that does not cause a furnace condition failure.

  The operation of blast furnaces for iron making may be stopped for repairs. At that time, the operation of stopping the charging of the raw material into the furnace, resting the air, and gradually lowering the charge remaining in the furnace downward is performed. This is called blow-off or scale-down operation.

  During the scale-down operation, in order to prevent explosion and to make CO gas harmless, the combustible gas generated from the surface of the raw material in the furnace is ignited and burned. This is called furnace top ignition. However, if the flame after ignition is too strong, the work in the furnace or at the top of the furnace will be hindered. Therefore, incombustible materials are introduced and distributed in an appropriate range of the surface layer of the raw material to suppress the flame.

  As the incombustible material, it is common to use blast furnace slag (slowly cooled slag, also referred to as ballast) that is available in an ironworks and easy to handle (see, for example, Patent Document 1).

JP, 2000-239716, A The incombustible material thrown in for a fire suppression finally turns into slag in a furnace. In order to continue the operation of the blast furnace, the hot metal and hot metal generated in the furnace must be discharged from the outlet. If the composition of the slag is inappropriate and its melting point is high, or if the viscosity is too high, or if the furnace heat is too low to sufficiently dissolve the slag, it will cause a decrease in unloading and smooth air flow recovery. Be disturbed. In the worst case, the slag can no longer be discharged and the blast furnace operation cannot be continued.

  In view of the above circumstances, what is put into the furnace and becomes slag is desirably melted at a low temperature. In addition, since heat is required for melting, especially in operation in a state where the furnace heat after resting is low, there is little slag generated in the furnace, in other words, the amount of input that becomes slag is It is desirable to have as few as possible.

  The blast furnace slag exemplified in Patent Document 1 has a relatively high melting point. Therefore, when this is introduced as an incombustible material, when the air flow is resumed after the furnace heat has been lowered due to long periods of off-air, the introduced incombustible material (blast furnace slag) cannot be sufficiently dissolved, and the air volume due to worsening of unloading Problems such as a delay in return and a decrease in air permeability due to the deterioration of exhaustability will cause a malfunction of the furnace.

  An object of the present invention is to provide a scaled-down operation method capable of suppressing a flame during scale-down operation of a blast furnace and preventing a malfunction of the furnace state after restarting the operation due to an incombustible material to be introduced.

The gist of the present invention is the following reduced scale operation method (1) and (2) .

(1) As non-combustible material to be introduced to reduce the flame at the top of the furnace when performing scaled off-air, the solid phase deposition temperature is 1430 ° C or less, CaO / SiO ₂ is 0.13 to 1.15, Al ₂ O ₃ is 10.0 to 15.0%, MgO is 13.3% or _{less, CaO, SiO 2, Al 2} O 3 , and reducing scale operation method of the blast furnace, characterized in that the sum of MgO uses incombustible material 95% or more. However, said% is the mass%.

(2) The reduced operation method for a blast furnace according to the above (1), wherein after incineration of the top of the furnace, a part of the incombustible material is selectively introduced into a position where the flame is strong.

1. About solid phase deposition temperature of incombustible material to be introduced FIG. 1 is a diagram showing a relationship between a resting time and a hot metal temperature at the first time after resumption of operation (resumption of air blowing). The area A in FIG. 6 is an area where the rest time is short and the temperature drop in the furnace is relatively small. At this time, even if ordinary blast furnace slag is introduced as an incombustible material, there is no problem in operation after resuming ventilation. On the other hand, the region B is a region where a long wind break exceeding 50 hours has been performed, and in that case, the hot metal temperature of the first brewing after the restart of operation is remarkably lowered. This means that the temperature in the furnace is greatly reduced. If blast furnace slag is introduced as an incombustible material, the unloading and unloading after the resumption of air blowing become difficult, leading to a malfunction of the furnace.

  As described above, the incombustible material to be introduced for suppressing the flame becomes slag, but if the melting is insufficient, various troubles occur in the continuous operation of the blast furnace. Accordingly, it is required that the incombustible material to be introduced can be melted even in the furnace temperature lowered by the resting wind. In the present invention, first, the goal is to lower the melting temperature of the incombustible material to be charged.

  Conventional blast furnace slag has a solid phase deposition temperature (ie, the temperature at which everything becomes completely liquid) of about 1470 ° C. On the other hand, as shown in FIG. 1, the initial hot metal temperature is about 1370 ° C. at the lowest in the case of a resting wind of up to about 50 hours that is normally performed. However, the furnace temperature at the time of resumption of air blowing after resting is considered to be higher than the initial hot metal temperature. Absent. From this, it is considered that any incombustible material having a solid phase precipitation temperature that is 100 ° C. higher than the initial hot metal temperature can be used as an input for suppressing the flame.

According to FIG. 1, the lowest initial hot metal temperature is about 1330 ° C. even in a long-term wind break of about 100 hours. Therefore, it can be estimated that incombustible materials having a temperature higher than this temperature by 100 ° C., that is, a solid-phase precipitation temperature up to 1430 ° C., can be input even in a scaled operation premised on long-term resting. And this inventor confirmed that this estimation was correct in the test in a real furnace. Therefore, in the present invention , the incombustible material to be added has a solid phase deposition temperature of 1430 ° C. or lower.

  There are various non-combustible materials having a solid-phase deposition temperature of 1430 ° C. or lower. Since these are thrown into the blast furnace and eventually become slag, there are no particular restrictions on the type as long as they do not contain components that cause a large variation in the chemical composition of the hot metal. However, the following oxide-based materials are desirable.

2. About composition of incombustible material to be charged Blast furnace slag is mainly composed of CaO, SiO ₂ , Al ₂ O ₃ and MgO. Since the incombustible material to be added becomes slag as described above, it is desirable that the composition is mainly composed of these oxides. Among the above oxides, the viscosity of slag increases as the content of Al ₂ O ₃ increases. Therefore, the content of Al ₂ O ₃ is set to 15.0% or less so that the viscosity of the incombustible after dissolution does not become too large. On the other hand, if the amount of Al ₂ O ₃ is too small, the crystallization temperature will rise, so the lower limit was made 10.0%.

FIG. 2 is a CaO—SiO ₂ —MgO phase diagram when Al ₂ O ₃ is 15%. As is apparent from this figure, the composition which is completely liquid at 1430 ° C. is the composition of the region surrounded by the straight lines AA, BB and CC, that is, CaO / SiO ₂ is 0.13 to 1.15, MgO. Has a composition of 13.3% or less. The straight line AA is a line with CaO / SiO ₂ of 0.13, the straight line BB is a line with CaO / SiO ₂ of 1.15, and the straight line CC is a line with MgO of 13.3%.

FIG. 2 is a state diagram when Al ₂ O ₃ is 15%, but also when Al ₂ O ₃ is 10%, the composition of the region surrounded by the above-mentioned straight lines AA, BB and CC. Since the melting temperature of the product is 1430 ° C. or lower, the temperature at which the CaO—SiO ₂ —MgO composition is completely liquid when Al ₂ O ₃ is 15.0% may be used as a reference.

Next, the reason that the total of CaO, SiO ₂ , Al ₂ O ₃ and MgO is 95% or more is that even if oxides other than these, such as FeO and MnO, are mixed, the total amount thereof If it is less than 5%, the solid phase precipitation temperature is not substantially affected and the temperature is not increased.

3. Regarding the invention of (2) The flame becomes smaller as the amount of incombustible material introduced into the surface of the raw material in the furnace increases. Therefore, in order to suppress a strong flame, it is necessary to throw in a large amount of incombustible material. However, as described above, it is better that the amount of incombustible material introduced into the furnace is as small as possible. That is, it is desirable to suppress the flame with a minimum amount of incombustible material.

  The strength of the flame varies depending on the position of the raw material surface. The variation cannot be predicted until the actual flame condition is observed. Even if there is a part with strong flames, it will hinder the work, so far, assuming the strongest flame, a large amount of non-combustible material with the safety expected to cover the entire raw material surface has been introduced. It was. That is, an incombustible material has been introduced so that a strong flame can be generated at any position on the raw material surface. As a result, an excessively incombustible material is unnecessarily introduced in a portion where the flame is not strong, and this has caused the various furnace conditions described above.

  In general, incombustibles are charged before the wind breaks. This is because the bleeder valve at the top of the furnace is opened to discharge the gas in the furnace after the wind is off, and dust generated when the incombustible material is thrown in after the wind is off may come out.

In the method (2) of the present invention, the amount of the incombustible material before the wind break is assumed to be an amount that assumes the average flame strength, and the necessary amount of the incombustible material is selectively applied to the strong flame portion after ignition. Is added. In this way, it is not necessary to input an excessive incombustible material over the entire surface of the raw material, and the input amount can be greatly reduced as shown in the examples described later.

  The intensity of the flame that requires additional incombustibles can be determined by observing the level of radiant heat and hot air from the actual work site. Which part of the flame is strong can be judged by visual observation from the top manhole.

  There are no particular restrictions on the form of incombustible material. For example, it is possible to adopt a method in which powdered or lump-shaped products are filled in a bag. After ignition at the top of the furnace, it may be selectively added to a position where the flame is strong. After ignition, it is possible to open the manhole at the top of the furnace. Therefore, the input after ignition may be performed in small portions so as not to generate dust.

The conventional method (case 1) and the method of the present invention (cases 2 and 3) were carried out in a blast furnace with an internal volume of 2700 m ³ . Implementation conditions are shown in Table 1.

  In case 1, a general blast furnace slag was used as an incombustible material, and the wind was stopped. The input amount was 40 tons, and everything was input before the wind break. The solid phase precipitation temperature of the blast furnace slag that was input is 1470 ℃. This is 125 ° C higher than the initial hot metal temperature (temperature of the hot metal first produced after resumption of air blowing) of 1345 ° C. For this reason, the output rate is poor and the unloading failure occurs, so the air volume return time (the time to return to the air volume before resting) is 56 hours. The output rate is defined as “output time ÷ output time x 100”. The small value means that there are too many non-combustibles and the temperature inside the furnace is not sufficient, or the temperature inside the furnace. This means that the incombustibles etc. are not sufficiently dissolved in

In Case 2, an incombustible material having a low Al ₂ O ₃ content and a small CaO / SiO ₂ content was added. The solid phase deposition temperature of this incombustible material is 1420 ° C. The input amount was the same as in Case 1, and everything was input before the break. In this case, the initial output rate improved to 83.7%, and the air flow return time was shortened to 30 hours. This is due to the fact that the solid phase deposition temperature of the incombustible material is low, so that it is easy to melt in the furnace, and the viscosity of the molten slag is small.

  In Case 3, the amount of incombustible material input before the wind break was 20 tons. Due to the small amount of input and the surface condition of the raw material in the furnace was not uniform, a strong flame portion was formed on a part of the raw material surface. That part was confirmed from the furnace top manhole, and additional incombustible material packed in a sandbag bag was added there. The amount is 0.7 tons. As a result, the flame was suppressed to such an extent that the work was not hindered. In the end, the total input was 20.7 tons.

  As shown in Table 1, in case 3 as well, the initial output rate improved to 81.4%, and the air flow return time was 29 hours, which is significantly improved over case 1. Moreover, the amount of incombustible material input is about half that of Case 2.

  According to the operation method of the present invention, not only the flame can be suppressed during the reduced scale operation, but also the fluidity of the hot metal produced can be improved, and the resumption of air blowing after a pause can be realized smoothly, and the subsequent furnace condition is prevented. it can. Moreover, according to the selective injection | pouring of the incombustible material to the position where a flame is strong, the quantity of slag to produce | generate can be reduced. A decrease in the amount of slag means a decrease in the heat of melting of the slag, and the furnace heat recovery is accelerated accordingly. It also has the effect of preventing the risk of inoperability due to a decrease in furnace heat after long periods of off-air.

  While there is a demand for extending the life of blast furnaces, the frequency of repair work due to reduced wind breaks increases, but the present invention is extremely useful in dealing with such situations.

It is a figure which shows the relationship between a rest time and the hot metal temperature of the first extraction after ventilation resumption. Al ₂ O ₃ is CaO-SiO ₂ -MgO system phase diagram when 15%.

Claims (2)

As non-combustible material to be introduced to reduce the furnace top flame when performing scaled off-air, the solid phase deposition temperature is 1430 ° C or less , CaO / SiO ₂ is 0.13-1.15, Al ₂ O ₃ is 10.0-15.0%, MgO is 13.3% or _{less, CaO, SiO 2, Al 2} O 3 , and reducing scale operation method of the blast furnace, characterized in that the sum of MgO uses incombustible material 95% or more. However, said% is the mass% . 2. The reduced operation method of a blast furnace according to claim 1, wherein a part of the incombustible material is selectively put into a strong flame position after the top ignition of the furnace .

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