JP5626072B2 - Operation method of vertical melting furnace - Google Patents

Description

  The present invention relates to a method for operating a vertical melting furnace for producing pig iron by melting or dissolving and reducing an iron source such as iron waste.

  Conventionally, using a vertical melting furnace, iron sources such as iron scrap, foundry scrap, pig iron and the like, which have a higher metallization rate than iron ore and do not require reduction, are manufactured. In recent years, vertical melting furnaces have begun to be used in integrated steelworks for the purpose of treating dust generated there.

  Simply mixing coke, iron scrap and the above steelmaking dust and putting them in a vertical melting furnace has a limit in the amount of use. For example, in Non-Patent Document 1, a hot air cupola with an air blowing temperature of 450 ° C. is used, but the amount of carbon-containing pellets used is only 5% by weight.

  Conventionally, it has been considered that a technical problem when using a large amount of an iron source that has a low metallization rate such as iron-making dust and needs to be reduced is the difficulty of thermal balance in the furnace. In other words, ironmaking dust contains a lot of iron oxide, and its metallization rate is lower than iron scrap, so when using an iron source containing ironmaking dust, (a) an iron source with a high metalization rate is used in the melting vertical furnace. In addition to the function of dissolving (b), (b) a function of reducing an iron source containing a large amount of oxide and having a low metalization rate is also required.

In order to allow melting and reduction to proceed simultaneously in the furnace, it is necessary to secure the amount of heat necessary for melting and to secure the reducing gas (CO) necessary for the reduction. However, the combustion reaction of oxygen in the air blowing (O ₂₎ and the furnace top charging coke _{(C) (C + O 2} → CO 2) is an exothermic reaction, solution loss reaction (CO of CO ₂ produced and coke (C) _{Since (2} + C → 2CO) is an endothermic reaction, if a large amount of reducing gas (CO) is generated in the furnace, the amount of heat for dissolving the iron source will be insufficient.

  A means for improving the heat balance in the furnace has already been proposed. The means described in Patent Document 1 performs heat compensation by increasing the heat insulation of the furnace body itself and reducing heat loss. Further, in Patent Documents 2 and 3, focusing on the raw material filling method, a method of changing the weight ratio of the iron source / solid fuel and the like for each charging charge, and an iron source with a low metallization rate, respectively. A method of mixing with a solid fuel and charging it to the periphery is disclosed.

JP 2009-79289 A JP 09-203584 A Japanese Patent Application Laid-Open No. 10-036906

Goksel et al .: Transactions of the American Foundryme's Society, Vol.85, AFSDes Plaines, 111, (1977), p327-332.

  Actually, in the operation of the vertical melting furnace using the methods of Patent Documents 1 to 3, when a large amount of carbonized iron-made dust pellets was used, up to 10% was possible, but more However, the air permeability in the furnace deteriorated and it was difficult to keep the operation stable.

  That is, since iron-making dusts (iron sources with a low metallization rate) have a small particle size, if a large amount of iron-making dusts are mixed with an iron source with a high metallization rate as it is, the air permeability in the furnace is inhibited. Therefore, it has been found that there is a limit to the mixing rate of the iron source having a low metallization rate from the viewpoint of ensuring air permeability in the furnace.

  Thus, when using a large amount of an iron source with a low metallization rate, it is necessary to solve not only a thermal problem but also a problem of air permeability in the furnace at the same time. Then, this invention provides the operating method of the vertical melting furnace which solves the said subject for the purpose of using effectively the iron-making dust which generate | occur | produces in large quantities in a steelworks exceeding the conventional use limit amount.

  The inventors of the present invention have found through the operation of various conditions of the vertical melting furnace that the cause of the aeration inhibition is pulverization of the iron-making dust pellets. And we studied earnestly to prevent it. As a result, as a requirement of the iron-making dust pellets, when the required amount of carbon material, particle size, and strength are mixed with iron scrap, the use ratio can be increased up to 30 without inhibiting the furnace air permeability. It was found that it can be increased to about%.

  This invention was made | formed based on the said knowledge, and the summary is as follows.

(1) In a method for operating a vertical melting furnace, using coke for blast furnace as fuel, and producing pig iron using iron agglomerates as an iron source together with an iron source having a high metallization rate,
(x) the iron dust agglomerate has a carbonaceous material content of 5 to 12% by mass, a cold strength of 30 kg / cm ² or more, a diameter of 8 to 30 mm, and
(y) A method for operating a vertical melting furnace, wherein the use ratio of the iron-made dust agglomerates is 5 to 25% with respect to the total iron source.

(2) Coke and iron dust agglomerates are mixed in advance, and this mixture and an iron source having a high metallization rate are alternately charged into a melting furnace, and the vertical melting as described in (1 ) above How to operate the furnace.

  According to the present invention, an iron source having a low metallization rate, for example, iron-making dust generated in large quantities at a steel mill, can be effectively used as an iron source for a vertical melting furnace, exceeding the conventional limit of use. it can.

It is a figure which shows the range of a particle size and intensity | strength when operation in a vertical melting furnace in which the particle size and intensity | strength of iron-making dust were changed variously reached the furnace pressure limit and it became impossible to continue operation. It is a figure which shows the charging and deposition structure of the iron source for adjusting the mixing rate of the iron source with a low metallization rate. It is a figure which shows another charging and deposition structure of the iron source for adjusting the mixing rate of the iron source with a low metalization rate.

  The present invention will be described in detail. In the present invention, ironmaking dust is iron oxide-based dusts generated in steelworks such as blast furnace dust, sintered dust, converter dust, and other dusts containing iron oxide, and the metallization rate. A low iron source. An iron source having a high metallization rate refers to a raw material in which 90% or more of iron contained such as iron scrap (scrap), casting scrap, pig iron and the like is in a metal state.

  In the operation of the vertical melting furnace, the iron source with a high metallization rate is the main iron source, but in recent years, it has been practiced to mix it with iron-making dust. Steelmaking dust is usually granulated into pellets. At the time of use, it is mixed at a predetermined ratio together with coke and an iron source having a high metallization rate and put into a vertical furnace.

  When trying to effectively use iron dust agglomerates as an iron source, increasing the mixing rate deteriorates the air permeability in the furnace, and the air pressure from the tuyere gradually increases. A new challenge was encountered in that the equipment upper limit of pressure was reached and the mixing ratio could no longer be increased.

(First invention)
The present inventors have found that this increase in ventilation resistance is closely related to the strength and particle size requirements of iron dust agglomerates, and the improvement can make the use ratio of iron dust agglomerates markedly improved. It was. The gist of the first invention is to specifically define the strength and particle size requirements of this iron-making dust agglomerate.

  The carbonaceous material content of the iron-made dust agglomerates was set to 5% by mass or more and 12% by mass or less. This requirement does not directly relate to the strength of the agglomerate, but is a requirement for sufficiently proceeding reduction when a raw material with a low metallization rate such as iron-making dust is melted together with scrap in a melting furnace.

  That is, when the amount is less than 5% by mass, the charged iron-making dust agglomerate is discharged as slag without being sufficiently reduced. Moreover, in order to reduce | restore iron-making dust, it is not necessary to make it contain exceeding 12 mass%. Excessive carbon blending only leads to a reduction in the strength of the agglomerate.

  The cold strength of the iron-made dust agglomerates was defined as a range of 30 kg / cm 2 or more and a diameter of 8 mm or more and 30 mm or less. The lower limit of the strength and the particle size is a requirement resulting from the operation results shown in the examples described later. Within this range, it was possible to use up to 25% dust agglomerates.

  On the other hand, an iron agglomerate that does not satisfy this requirement has been forced to operate at a blending rate of about 5%, which is the same as in the past. The upper limit of the particle size is associated with restrictions on the progress of reduction, and if this is exceeded, the reduction of dust does not proceed sufficiently. Moreover, the minimum of a particle size is prescribed | regulated from a breathable viewpoint.

  The mixing ratio of the iron-making dust was 5% by mass or more and 25% by mass or less. When the mixing ratio is less than 5% by mass, the problem of the present invention that efficiently treats iron-making dusts generated in large quantities at steelworks cannot be solved. Moreover, when it exceeded 25 mass%, even if it had this invention as mentioned above, operation became difficult by the raise of ventilation pressure. That is, it means the application limit of the present invention.

  When iron dust agglomerates are blended, it is necessary to adjust the amount of coke and the amount of blown air according to the blending amount in order to continue the operation of the vertical furnace. The specific method is as already disclosed in Patent Document 3 (Japanese Patent Laid-Open No. 10-36906).

(Second invention)
In cupolas that only use scrap melting, it is common to have a facility configuration in which coke and scrap are weighed and mixed in advance when the raw materials are charged. Therefore, when dusts are used in such a vertical melting furnace, coke, scrap and dust agglomerates are weighed and mixed in advance and then put into the melting furnace.

  On the other hand, it is preferable to mix coke and iron dust agglomerates in advance and alternately charge the mixture and an iron source having a high metallization rate as shown in FIG. This is because the porosity of the packed bed is increased and the air permeability in the furnace is improved when the raw materials having different shapes are mixed and filled separately.

  In addition, the iron dust agglomerate and coke are mixed in advance in order to facilitate reduction of the iron dust.

  Specifically, it is carried out as follows. As shown in FIG. 2, the vertical melting furnace is provided with a furnace main body 1 having a lower tuyere 10 and an upper tuyere 11, and a gas suction port 5 on a furnace bottom portion 2 having a tap outlet 3 and a lower furnace wall 14. The gas suction unit 4 is composed of a furnace top 6 that seals the furnace top with a housed iron source, and an inlet 7 that charges the iron source 8 into the furnace.

  A coke bed 9 is constructed at the lower part of the furnace body 1. Usually, an upper tuyere 11 is provided at a height position directly above the surface of the coke bed 9, and a lower tuyere 10 is provided in the coke bed 9. Provided at the height position. When the iron source 8a having a high metallization rate such as scrap and the mixture 8b of granulated iron source and solid fuel are alternately charged from the charging port 7, the mixture and the metallization are brought into the furnace. A layered structure in which high-rate iron sources are alternately deposited in layers is realized.

  Inside the furnace, air at room temperature or 600 ° C. or less is fed from the lower tuyere 10 to mainly burn solid fuel (coke), and the iron source is dissolved by this combustion heat. From the upper tuyere 11, cool air or air of 100 ° C. or less is sent to compensate for the decrease in the amount of heat in the furnace caused by the solution loss reaction, ensuring the amount of heat necessary for melting the iron source having a high metallization rate, Reducing gas necessary for reduction of iron source with low metalization rate is secured.

(Third invention)
Further, when a granulated iron source and solid fuel mixture and a high metalization iron source are alternately charged to form a layered structure in the furnace, the mixture is In particular, the furnace may be charged and deposited more in the furnace periphery than in the center. The state of deposition is shown in FIG.

  The granulated iron source and solid fuel mixture 8b 'having a low metallization rate is charged and deposited in the furnace periphery. By carrying out like this, reduction | restoration of a low metalization rate iron source can be further accelerated | stimulated, and furnace operation can be stabilized.

(Fourth invention)
In the operation of a vertical melting furnace, a high amount of reducing gas (CO) is required if the low metallization rate iron source mixing rate is increased. If a large amount of reducing gas (CO) is generated in the solution loss reaction (CO ₂ + C → 2CO) (endothermic reaction), the amount of heat for dissolving the iron source becomes insufficient. In the first invention, this is adjusted by the coke ratio or the like, but an increase in the amount of coke used may not be preferable in terms of manufacturing cost.

  Therefore, this can be dealt with by using a vertical melting furnace provided with two tuyeres at the upper and lower stages (hereinafter sometimes referred to as “two-stage tuyere”). That is, it is because an endothermic component due to the solution loss reaction can be compensated by blowing an oxygen-containing gas (air) from the upper tuyere and burning a part of the generated CO.

  The following examples were conducted using a vertical melting furnace having the specifications shown in Table 1. Table 2 shows the composition of iron-making dust pellets used as raw materials. As scrap, shredded H2-H4 scrap and thick plate scrap were used, and coke used was blast furnace coke having an average particle diameter of 50 mm.

Example 1
The operation test was performed using pellet samples having various strengths and particle sizes prepared by sieving the dust pellets with different cement blending amounts and curing periods and different strengths so as to be in a predetermined particle size range. . The result is shown in FIG.

  In the figure, a circle indicates a case in which the dust mixing ratio can be increased to 25%, and the operation can be performed without any problem of ventilation, and a mark X indicates a case where the dust mixing ratio is less than 25% and the operation is hindered due to deterioration of the ventilation in the furnace. Show.

As shown in FIG. 1, if the strength> 30 kg / cm ² and the lower limit particle size> 8 mm, an iron source with a low metallization rate is mixed with an iron source with a high metallization rate up to about 25% by mass, Pig iron can be manufactured stably and continuously.

(Example 2)
Steelmaking dust pellets having a particle size of 10 to 30 mm and coke were mixed in advance. This mixture and scrap (iron scrap, casting scrap, pig iron) were charged into a vertical melting furnace whose specifications are shown in Table 1 under the charging conditions shown in Table 3, and the charged iron source was dissolved and reduced. The operation results are also shown in Table 3.

In the case of mixing 20% dust pellets with the scrap before charging (comparative example), the air pressure is 25000 Nm ³ / h, the furnace pressure is near the upper limit of control (ventilation limit), and the output is 36 t / h. However, when dust pellets were alternately charged with scrap (Invention Example 1), the air flow rate could be increased to 26000 Nm ³ / h within the ventilation limit, and the output amount increased to 38 t / h. .

Furthermore, when dust pellets are periodically charged in the periphery of the furnace using a device that can be charged in the periphery, and charged so as to accumulate a large amount in the periphery (Invention Example 2), ventilation is further improved. The air flow rate could be increased up to 27000 Nm ³ / h within the ventilation limit, and the output amount increased to 40 t / h.

  As described above, according to the present invention, an iron source having a low metallization rate, for example, a large amount of iron-making dust generated at a steel mill is used as an iron source for a vertical melting furnace, exceeding the conventional limit of use. It can be used effectively. Therefore, the present invention has great applicability in the pig iron manufacturing industry.

DESCRIPTION OF SYMBOLS 1 Furnace body 2 Furnace bottom part 3 Outlet 4 Gas suction part 5 Gas suction part 6 Furnace top part 7 Inlet 8 Iron source 8a Iron source with high metallization rate 8b, 8b ' Solid fuel mixture 9 Coke bed 10 Lower tuyere 11 Upper tuyere 12 Hot metal 13 Hot water reservoir 14 Furnace wall

Claims (2)

In the operation method of a vertical melting furnace, using coke for blast furnace as fuel and producing pig iron using iron dust agglomerates as an iron source together with an iron source having a high metallization rate,
(x) the iron dust agglomerate has a carbonaceous material content of 5 to 12% by mass, a cold strength of 30 kg / cm ² or more, a diameter of 8 to 30 mm, and
(y) A method for operating a vertical melting furnace, wherein the use ratio of the iron-made dust agglomerates is 5 to 25% with respect to the total iron source. The method for operating a vertical melting furnace according to claim 1, wherein coke and iron dust agglomerates are mixed in advance, and the mixture and an iron source having a high metallization rate are alternately charged into the melting furnace. .

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