JP2009256737A - Method for controlling furnace-top gas temperature in blast furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simplified and economical method for controlling a furnace-top gas temperature in a blast furnace by which the furnace-top gas temperature can be controlled in a wider range, without obstructing the stable operation of the blast furnace. <P>SOLUTION: The method for controlling the temperature of gas exhausted from the furnace-top of the blast furnace, is provided for controlling the above gas temperature to an adequate temperature range by blending water-containing pellets as iron raw material to be charged. In the method, at least 10% or more of a yard-pellet which is stored in a raw material yard and subjected to water spray treatment after granulated and fired is blended as the iron raw material to be charged according to the moisture content of the pellet. Since the yard-pellet contains a large quantity of water in comparison with a direct-feeding pellet, the heat of vaporization of the contained water in the pellet in the furnace is large, a sensible heat is small and also an angle of repose becomes large together with an increase in the water content, consequently the iron raw material is easily deposited on the inner wall side of the furnace and the charging density of the iron raw material in the center part of the furnace becomes low, hence the gas permeability in the furnace is not obstructed resulting in the simplified and effective lowering of furnace-top gas temperature without incurring trouble in the operation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for controlling the blast furnace top gas temperature that lowers the furnace top gas temperature by adjusting the moisture content and blending ratio of the pellet raw material charged into the furnace of the blast furnace.

  In recent years, in blast furnace operation, pulverized coal blowing operation using pulverized coal as an inexpensive auxiliary fuel has been performed in order to reduce hot metal costs. When performing pulverized coal injection operation, it is necessary to reduce the amount of coke charged from the top of the furnace in order to maintain the fuel ratio (= coke ratio + pulverized coal (auxiliary fuel) ratio). Since the charging amount of the solid from the top of the furnace decreases, the heat flow ratio [= (heat capacity of solid) / (heat capacity of gas)] decreases, and the gas temperature at the top of the furnace rises. This rise in the furnace top gas temperature is one of the causes of damage to furnace top equipment such as raw material charging equipment. Usually, in order to lower the furnace top gas temperature, water is sprayed from a nozzle installed at the top of the furnace into the blast furnace. However, this method of lowering the furnace top gas temperature by sprinkling water is not preferable when a dry dust collector is used as a dust collector for the furnace top gas, because it causes harmful effects such as condensation in the dust collector.

In order to lower the furnace top gas temperature without such harmful effects, for example, in Patent Document 1, in operation with charging dry coke and wet coke in a blast furnace equipped with a dry dust collector, A wet coke charging method is disclosed in which the furnace top gas temperature is within a preset temperature range by adjusting the charging position and charging ratio of the wet coke in the furnace radial direction. Moreover, in patent document 2, in the operation method of a blast furnace with a heat flow ratio of 0.80 or less, high-crystal water lump ore with a crystal water content of 3.5 wt% or more is used as a main raw material in the furnace. When the crystal water is separated, even if the ore collapses, select a particle size composition and blending ratio that will not impair air permeability, and insert it directly into the furnace so as to lower the average temperature of the top gas A method of operating a blast furnace is disclosed.
JP 2001-158905 A JP 2000-144219 A

  However, in the wet coke charging method disclosed in Patent Document 1, there is a possibility that the powder brought in by wet coke may deteriorate the air permeability in the blast furnace, and the blast furnace cannot be operated stably and economically. Further, in the blast furnace operating method disclosed in Patent Document 2, the procurement of iron ore raw materials is restricted, and the degree of freedom of the blending ratio of the high crystal water block ore is small, so the control range of the furnace top gas temperature is narrow. There is a problem.

  Accordingly, an object of the present invention is to provide a simple and economical method for controlling the blast furnace top gas temperature that can control the furnace top gas temperature in a wider range without impeding stable operation of the blast furnace.

  In order to solve the above problems, the present invention employs the following configuration.

  The blast furnace top gas temperature control method according to claim 1 is a blast furnace in which the temperature of gas discharged from the blast furnace top is controlled to an appropriate temperature range by blending pellets containing moisture as a charged iron raw material. A method for controlling the temperature of a furnace top gas, wherein the pellets are stored in a raw material yard after granulation and firing, and are sprinkled yard pellets. The yard pellets are charged iron according to the moisture content. It is characterized by blending at least 10% or more as a raw material.

  The pellets (yard pellets) stored in the raw material yard after granulation and firing are sprinkled with a frequency of about once every two hours, for example, from the viewpoint of dust prevention. As a raw material charged to the blast furnace, pellets granulated and fired by adding auxiliary materials such as a binder to fine ore obtained by pulverizing raw iron ore contain pores of about 25% in porosity. In the normal raw material yard storage, the water content reaches several percent, and after granulation and firing, the direct feed pellets and sintered ore that are not stored in the raw material yard and charged into the blast furnace are used. In addition, it contains a larger amount of moisture than other charged iron raw materials having a moisture content of less than 2%. Yard pellets have less sensible heat than direct pellets. Furthermore, the angle of repose of the iron raw material in which yard pellets are blended at a certain ratio or more increases as the moisture content of the pellets increases, as will be described later. Therefore, the weak point of the pellet shape that it is easy to roll when water is included is alleviated. For this reason, the iron raw material charged in the blast furnace and blended with a certain proportion or more of the yard pellet is likely to be deposited on the periphery of the furnace, that is, on the inner wall side, thereby charging the iron raw material in the furnace center. Since the density is low, the air permeability in the center of the furnace is not hindered and can contribute to stable and economical operation of the blast furnace. From these facts, when iron raw materials containing yard pellets at a certain ratio or more, that is, at least 10% or more, are charged into the furnace, the heat of vaporization of the moisture contained in the pellets is large, the sensible heat of the yard pellets is small, and the furnace Since the inside air permeability is not hindered, the temperature of the furnace top gas can be easily and effectively lowered without causing any adverse effects on operation. In addition, the range of 120 degreeC-200 degreeC can be set as an appropriate temperature range of furnace top gas temperature. If the furnace top gas temperature exceeds 200 ° C, as mentioned above, it will be one of the causes of damage to the furnace top equipment such as raw material charging equipment, and if it is less than 120 ° C, it will cause harmful effects such as condensation in the dry dust collector. This is because neither is preferable. In addition to the watering treatment in the raw material yard, the yard pellets are also watered to remove the powder component on the outer surface of the pellets before entering the storage tank for blast furnace charging. . For this reason, the moisture content of the yard pellet is not affected by the weather while being stored in the raw material yard, and is mainly determined by the porosity and the pore diameter of the pellet. Therefore, the moisture content of the yard pellets manufactured with a stable process capability falls within a narrow range of 5 to 7%, for example, as will be described later. However, the magnitude of the water content itself varies depending on the manufacturing process of the pellet.

FIG. 1 shows the relationship between the blending ratio Pd of yard pellets in the charged iron raw material and the furnace top gas temperature, measured in an actual blast furnace operating at a tapping ratio of about 2.2 t / day. That is, it is stored in the raw material yard after granulation and firing to an average particle size of 10 to 13 mm, and the flow density is about 0.02 m ³ / h / m ² at a frequency of about once every 2 hours and about 1 minute per time. The raw material containing 5% to 7% of yard pellets with a water content of 5% to 7% and the required auxiliary materials such as coke and pulverized coal were charged, and hot air was blown from the tuyere for operation. The results obtained by actually measuring the furnace top gas temperature Tg with a thermometer installed at the top of the furnace are plotted against the blending ratio Pd of yard pellets. The furnace top gas temperature Tg tends to decrease with an increase in the blending ratio Pd of the yard pellets, and it can be seen that when the blending ratio is 10% or more, the furnace top gas temperature can be suppressed to an upper limit value of 200 ° C. or less. Moreover, if the regression equation shown in the figure is used, the upper limit of the yard pellet mixing ratio for setting the furnace top gas temperature to the lower limit of 120 ° C. or higher can be calculated to be about 70%. On the other hand, FIG. 2 shows the result of measuring the angle of repose θr when the moisture content of the yard pellet, that is, the moisture content Pw was changed, when 37 mass% of the diamond pellet was blended as the charged iron raw material. . It is clearly recognized that the angle of repose θr increases as the water content Pw increases. This indicates that, as described above, the pellet is an iron raw material that is easy to roll in shape, but its weakness is reduced as the moisture content Pw increases.

  The blast furnace top gas temperature control method according to claim 2 is characterized in that the average particle size of the yard pellet is in the range of 10 mm to 15 mm and the moisture content thereof is in the range of 2% to 7%. .

  In general, when the pellet particle diameter exceeds 15 mm, the specific surface area (surface area per unit weight) decreases, and the efficiency of the reduction reaction decreases. When the pellet particle diameter is less than 10 mm, the air permeability decreases. . Yard pellets are less susceptible to particle size reduction due to handling than yard sintered ore, and if the average particle size is formed (granulated and fired) to 10 mm or more, the air permeability in the furnace will be hindered. Absent. In addition, if the moisture content exceeds 7%, the furnace top gas temperature tends to fluctuate due to the change in the blending ratio of the yard pellet, and if the moisture content is less than 2%, the effect on the decrease in the furnace top gas temperature becomes small. Neither is preferred. The recommended range of moisture content is 5-7%. When blending yard pellets with a moisture content lower than the recommended range, increase the blending ratio of yard pellets based on the measured value of the furnace top gas temperature to bring the furnace top gas temperature within the appropriate range. It is possible to control.

  In this invention, since the temperature of the gas discharged from the top of the blast furnace is blended with yard pellets having a high moisture content and low sensible heat as a charged iron raw material and a large angle of repose, a certain ratio or more, When charged in the furnace, the heat of vaporization of the moisture contained in the yard pellets is large, and the air permeability in the furnace is not hindered, so the temperature of the furnace top gas can be adjusted without increasing the total energy consumption of steelmaking. It can be simply and effectively reduced. As a result, it is possible to reliably prevent adverse effects on the operation such as damage to the furnace top equipment and condensation in the dry dust collector.

  Embodiments of the present invention will be described below with examples.

  Yard pellets used in the present invention, that is, pellets once stored in a raw material yard and sprinkled, and then charged into a blast furnace as an iron raw material are general manufacturing processes, raw pellet granulation process, drying -It can manufacture by a preheating process, a baking process, and a cooling process. For example, in the granulation process of raw pellets, fine iron ore with an average particle size of about 50 μm by beneficiation and pulverization of raw iron ore, and limestone and dolomite finely pulverized to be equal to or less than this fine iron ore, etc. In order to increase the granulation efficiency, a binder such as bentonite or slaked lime is added and mixed, and then granulated water is added as necessary, and the particle size is 10 with a granulator such as a disk type pelletizer. A spherical raw pellet of about 15 mm is produced. Next, the raw pellets are stacked in layers at a required thickness on a traveling grating that moves endlessly, and a gas of about 180 to 250 ° C. is circulated through the moving pellet layer to granulate moisture from the raw pellets. Then, 250 to 400 ° C. gas is circulated to separate crystal water in the ore, and finally preheating is performed by circulating high-temperature gas of about 1000 to 1100 ° C. in the preheating step, so that the pellet strength is predetermined. Increase to level. And in a baking process, this preheating pellet is inserted into baking facilities, such as a rotary kiln, and it heats to the temperature range of 1250-1350 degreeC, and raises crushing strength. Subsequently, it cools by charging in cooling facilities, such as an air cooling, and the baking pellet as an iron raw material charged into a blast furnace is obtained. In addition, the yard pellet used for this invention is not necessarily limited to said manufacturing method.

Except for the direct feed pellets that are directly conveyed to the blast furnace after firing, the fired pellets are usually stacked in a cone shape and stored in the raw material yard according to the charging schedule to the blast furnace. During this storage period, for the environmental measures such as dust prevention, water spraying treatment with a flow density of about 0.02 m ³ / h / m ^{2 is} usually piled up at a frequency of about once every 2 hours. Applied to the dried or yard pellet. Since the yard pellet has pores of a certain ratio (usually about 25% porosity), the water content in the yard pellet is increased by the watering treatment as compared with the direct feed pellet. For example, when the porosity is about 25%, the moisture content is 2% or more. Particularly, the pellets produced by the great kiln method have a high water retention due to the dense surface, and increase to about 5-7%. Further, since the yard pellet is cooled by the watering treatment, the sensible heat is less than that of the direct feed pellet. Furthermore, as shown in FIG. 2, the angle of repose θr increases with an increase in the moisture content Pw. Therefore, when an iron raw material containing a certain percentage or more of yard pellets is charged into the blast furnace from the top of the furnace, Since it is easy to deposit on the peripheral part, that is, on the inner wall side, and the charging density of the iron raw material in the furnace center part becomes low, the air permeability of the furnace center part is not hindered. By blending the yard pellets having such characteristics as a raw material for charging with a certain ratio or more, as described above, the temperature of the furnace top gas can be simply and without increasing the total energy consumption of iron making. It can be effectively reduced.

Table 1 shows examples (No.1, No.2, No.4.No.5, No.6) and comparative examples (No.1, No.1, No.2, No.5, No.6) in blast furnace operation (output ratio 2.17t / day to 2.34t / day). The operational data (specifications) of 3) is shown. In each of Examples No. 1, No. 2 and Comparative Example No. 3, the pellet ratio in the charged iron raw material is about 30%, but yard pellets (average particle size: 10 to 13 mm, moisture content: 5 to 7) %) Was 23.2% in Example No. 1 (6.8% direct feed pellets), and in Example No. 2, all were 30% of yard pellets (0% direct feed pellets). In No. 3, it is 5% (direct feed pellet 25%). First, operation data (furnace top gas temperature and pressure in the furnace) was collected at a yard pellet mixing ratio of 5% in Comparative Example No. 3, and then direct feed pellets in the mixing ratio of 25% in Comparative Example No. 3 were sequentially yarded. Transfer to pellets, collect the operation data of Example No. 1 at a yard pellet mixing rate of 23.2%, increase the transfer amount to yard pellets, and increase the transfer rate to 30% (total amount transfer) of Example No. .2 operational data was collected. In the process of transferring the direct pellets to yard pellets, the furnace top gas temperature began to drop, and as shown in Table 1, the furnace top gas temperature was changed to a blending ratio of Example No. 1 of 23.2%. At that time, it dropped from 201 ° C. in Comparative Example No. 3 with a blending rate of 5% to 192 ° C., and further down to 181 ° C. when the blending rate was changed to 30% (total amount) in Example No. 2. is doing. Thus, it was confirmed that increasing the blending ratio of the yard pellets is effective for lowering the furnace top gas temperature. On the other hand, for the furnace pressure loss, from 2.00 kg / cm ² of Comparative Example No.3, Example No.1 In 1.99kg / cm ^2, Example No. No. 2 showed a tendency to be improved to 1.98 kg / cm ^2, and it was confirmed that increasing the blending ratio of the yard pellets does not hinder the air permeability in the furnace. Note that 1 kg / cm ² = 980665 Pa.

Further, in Examples No. 4, No. 5, and No. 6, the pellet content in the charged iron raw material was 31%, but the yard pellet content in Example No. 4 was 24. 0% (direct feed pellets 7%), all in Example 5 are 31% of yard pellets (direct feed pellets 0%), and in Example No. 6, it is 16.5% (direct feed pellets 14.5%) . Operation data (furnace top gas temperature and pressure in the furnace) were first collected at a yard pellet mixing ratio of 14.5% in Example No. 6, and then at a mixing ratio of 14.5% in Example No. 6. Transfer direct pellets to yard pellets sequentially, collect the operation data of Example 3 at a compounding rate of 24.0%, and increase the amount of transfer to yard pellets, and implement at a compounding rate of 31% (total amount transfer) No.5 operation data was collected. In the process of transferring the direct pellets to yard pellets, the furnace top gas temperature began to drop, and as shown in Table 1, the furnace top gas temperature was changed to the blending ratio of Example No. 4 to 24.0%. At that time, it decreased from 200 ° C. of Example No. 6 with a blending ratio of 16.5% to 180 ° C., and further to 31% (total amount), it decreased to 169 ° C. Even in different operations, it was confirmed that increasing the blending ratio of yard pellets was effective in lowering the furnace top gas temperature. On the other hand, for the furnace pressure loss, tends to be improved from 1.88 kg / cm ² of Comparative Example 2, Example No.4 With 1.83 kg / cm ^2, and 1.79 kg / cm ² in Example No.5 In the case of Example No. 4, No. 5 and Example No. 6, it was confirmed that increasing the blending ratio of the yard pellet does not hinder the air permeability in the furnace. The pressure loss inside the furnace is a value calculated from the blowing pressure (pressure before entering the blast furnace) −the gas pressure at the top of the furnace.

It is explanatory drawing which shows the relationship between the blending ratio Pd of the yard pellet in an actual machine blast furnace, and the furnace top gas temperature Tg. It is explanatory drawing which shows the relationship between the water | moisture content (water content) Pw of a pellet, and the angle of repose θr.

Claims (2)

  Blast furnace top gas temperature control method for controlling the temperature of the gas discharged from the top of the blast furnace to an appropriate temperature range by blending moisture-containing pellets as the charged iron raw material, the pellets, Blast furnace which is stored in a raw material yard after granulation and firing and is sprinkled, and the yard pellet is blended with at least 10% as a charged iron raw material according to its moisture content. Control method of top gas temperature.   The blast furnace top gas temperature control method according to claim 1, wherein an average particle diameter of the yard pellet is in a range of 10 mm to 15 mm and a moisture content thereof is in a range of 2% to 7%.

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