JP2010242201A - Operation method for vertical type melting furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably produce high quality (high C content, low S content) pig iron by using blast furnace coke, in the operation of a vertical type melting furnace which produces pig iron by melting or melting and reducing an iron source including low carbon iron waste. <P>SOLUTION: There is provided an operation method for the vertical type melting furnace which uses solid fuel with blast furnace coke blended therein to produce pig iron by melting or melting and reducing an iron source including low-grade iron waste. The method: (x) keeping height H (mm) of a coke bed at a range of following expression (1): 1.10×h≤H(mm)≤1.20×h (wherein h denotes a standard height of the coke bed); (y) keeping basicity of slag (%CaO)/(%SiO<SB>2</SB>) at a range of following expression (2): 1.00≤(%CaO)/(SiO<SB>2</SB>)≤1.20 (wherein (%CaO) denotes a CaO content (mass%) in the slag and (%SiO<SB>2</SB>) denotes an SiO<SB>2</SB>content on the slag) by charging CaO-containing sub raw material; and (z) thus, producing high carbon and low-S high grade pig iron. <P>COPYRIGHT: (C)2011,JPO&INPIT

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.

In the blast furnace method in which pig iron is produced using an iron source mainly composed of iron ore and sintered ore, the iron source in the iron ore and sintered ore is lowered while the iron source charged from the top of the furnace descends in the furnace. Is produced by the reaction (C + O ₂ → CO ₂ , CO ₂ + C → 2CO) of oxygen (O ₂ ) and coke (C) in the hot air blown from the tuyere, and the hot reducing gas (CO ) Indirect reduction.

In the blast furnace method, in order to secure an indirect reduction rate of about 60% or more, the blast temperature is set to 1000 ° C. or more, and the blast speed is increased to form a raceway in front of the tuyere in the furnace. Gas utilization rate: Reducing gas (CO) is generated so that η _CO (= CO ₂ / (CO + CO ₂ )) becomes zero.

  On the other hand, the cupola method uses a vertical melting furnace with a smaller internal volume than the blast furnace method, and has a metallization rate higher than iron ore and sintered ore, mainly iron scrap, foundry scrap, pig iron, etc. Dissolve the source to produce pig iron. Thus, the cupola method uses an iron source with a high metallization rate that does not require reduction. Therefore, there is little need for reducing gas (CO) in the furnace, and the amount of heat that can sufficiently melt the iron source is reduced. It is necessary to secure.

In the operation of a vertical melting furnace in the cupola method, when a raceway is formed in front of the tuyere, as in the blast furnace method, the combustion reaction of oxygen (O ₂ ) and coke (C) in the blast (C + O ₂ → CO ₂ ) After the heat is generated, heat absorption by the solution loss reaction (CO ₂ + C → 2CO) of CO ₂ gas and coke (C) reduces the amount of heat in the furnace, making it difficult to sufficiently melt the iron source.

  Therefore, when melting an iron source with a high metallization rate by the cupola method, do not form a raceway in front of the tuyere from the tuyere of the vertical melting furnace with oxygen-enriched cold air or hot air of 600 ° C or less. In order to blow into the furnace at a low blowing speed and to further suppress the decrease in the amount of heat in the furnace, coke for casting is used as the solid fuel.

  The coke for casting has a larger particle size than the coke for blast furnace, so that it does not easily cause a solution loss reaction (endothermic reaction). Further, the casting coke has high strength and low ash content, so that the amount of pulverization and generation of slag in the furnace is small and contributes to the maintenance of air permeability in the furnace. Therefore, in the operation of the vertical melting furnace in the cupola method, casting coke is mainly used.

  However, coke for casting is more expensive than coke for blast furnace, which increases the production cost of pig iron. Therefore, in the operation of vertical melting furnaces in the cupola method, coke for blast furnace is often used. It is strongly desired to reduce the manufacturing cost of

  Also, in recent years, in the operation of vertical melting furnaces in the cupola method, there is a tendency to use a large amount of ironmaking dust generated in the ironmaking process as an iron source, but ironmaking dust contains a lot of iron oxide, Since the metallization rate is low, vertical melting furnaces are required to have a reducing function for reducing iron oxide in the iron source in addition to a melting function for melting the iron source.

  Against this background, in recent years, as an iron source, in addition to iron sources that do not require reduction of iron scraps, foundry scraps, pig iron, etc. generated in the sintering process (iron sources with a high metallization rate), dust What are the operating methods of vertical melting furnaces that use iron sources (iron sources with low metallization rate and need to be reduced) such as agglomerated or self-reducing ores (agglomerated minerals with high carbon content) Have been proposed (see Patent Documents 1 to 3).

  In the proposed operation method, in order to ensure the reduction function, small-diameter coke having a smaller particle size than that of casting coke is mixed with an iron source and charged into the furnace, and used as bed coke. The bed coke also has a carburizing function for hot metal and is consumed, so that the required bed height is necessary to maintain the C content in the hot metal at a desired level.

  However, when blast furnace coke is used as the small-diameter coke, S in the blast furnace coke enters the molten iron simultaneously with carburizing, and the S concentration increases. Since blast furnace coke contains a relatively large amount of S as compared with foundry coke, the penetration of S into the hot metal accompanying carburization lowers the quality of the hot metal.

  Moreover, when low-carbon iron wastes such as iron scraps generated at ironworks are used as the iron source, the amount of C in the hot metal does not reach a desired level. The shortage of C can be compensated by carburizing from the coke bed, but if the coke bed is constructed with blast furnace coke, S in the blast furnace coke penetrates into the hot metal along with carburizing, and the amount of S in the hot metal is reduced. To rise.

  That is, in the operation of a vertical melting furnace in the cupola method, when the blast furnace coke is used for a solid fuel and / or a coke bed, there is a quality problem that the amount of S in the hot metal is increased.

  However, blast furnace coke is inexpensive and the use of blast furnace coke is indispensable when producing low-cost pig iron using an iron source such as iron waste as a raw material. Therefore, in the operation of a vertical melting furnace in the cupola method, it is required to stably produce high quality (high C amount, low S amount) pig iron even if blast furnace coke is used instead of casting coke. It has been.

Japanese National Publication No. 01-501401 Japanese Patent Application Laid-Open No. 10-036906 JP 09-203584 A

  In view of the above request, the present inventors have used a blast furnace coke in the operation of a vertical melting furnace that dissolves or dissolves and reduces iron sources including low-carbon iron waste to produce pig iron. It is an object to stably manufacture quality (high C amount, low S amount) pig iron. And it aims at providing the operating method of the vertical melting furnace which solves the said subject.

  The present inventors diligently studied a method for operating a vertical melting furnace that can stably produce high-quality (high C content, low S content) pig iron using blast furnace coke.

As a result, the height of the (C) coke bed is made higher than the standard height, and a sufficient amount of C is replenished to the low C amount of hot metal, and (Y) slag basicity (% CaO) / (% SiO _2), to maintain the required range, when promoting furnace desulfurization, high-quality (high C content, the pig iron low S content) was found to be able to be stably manufactured.

  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 that uses solid fuel containing blast furnace coke and dissolves or dissolves and reduces iron sources including low carbon iron waste to produce pig iron.
(X) maintaining the height H (mm) of the coke bed within the range of the following formula (1), and
(Y) By charging the CaO-containing auxiliary material, the slag basicity (% CaO) / (% SiO ₂ ) is maintained in the range of the following formula (2),
(Z) A method for operating a vertical melting furnace characterized by producing high-quality pig iron with high C and low S.
1.10 · h ≦ H (mm) ≦ 1.20 · h (1)
h: Standard height of coke bed (mm)
1.00 ≦ (% CaO) / (% SiO ₂ ) ≦ 1.20 (2)
(% CaO): CaO amount (% by mass) in slag,
(% SiO ₂ ): SiO ₂ amount in slag (mass%)

  (2) The method for operating a vertical melting furnace as described in (1) above, wherein the solid fuel is a solid fuel containing 70 to 100% by mass of coke for blast furnace.

  (3) The method for operating a vertical melting furnace according to (1) or (2), wherein the coke bed is constructed of blast furnace coke.

  (4) The method for operating a vertical melting furnace as described in (1) or (2) above, wherein the coke bed is constructed of blast furnace coke and casting coke.

  (5) The method for operating a vertical melting furnace according to any one of (1) to (4), wherein h is 1000 to 1300 mm.

As (6) the CaO-containing auxiliary raw material, limestone, serpentinite, dolomite, and was charged with one or more of the converter slag, slag basicity (% CaO) / (% SiO _2), the The method for operating a vertical melting furnace according to any one of the above (1) to (5), characterized in that it is maintained within the range of the formula (2).

  (7) C type | mold of the said high C and low S high quality pig iron is 4.0-4.8 mass%, The saddle type in any one of said (1)-(6) characterized by the above-mentioned. How to operate the melting furnace.

  (8) The saddle mold according to any one of (1) to (7) above, wherein the amount of S of the high-quality pig iron of high C and low S is 0.3 to 0.7 mass%. How to operate the melting furnace.

  According to the present invention, in the operation of a vertical melting furnace that dissolves or dissolves and reduces an iron source containing low carbon iron waste to produce pig iron, high quality (high C content) is obtained using blast furnace coke. , Low S amount) pig iron can be stably produced.

It is a figure which shows the one aspect | mode of the vertical melting furnace which implements this invention. It is a figure which shows the aspect of the coke bed in the furnace bottom part of the vertical melting furnace which implements this invention.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an embodiment of a vertical melting furnace for carrying out the present invention.

  The vertical melting furnace 1 is basically provided with a tuyere 6 provided at the lower part of the furnace body 2, a gas suction part 4 provided at the upper part of the furnace body 2, and the gas suction part 4 so as to penetrate therethrough. And a furnace top 3.

  The tuyere 6 basically has two upper tuyere 6a and lower tuyere 6b in the height direction of the furnace. The upper tuyere 6a is provided at a height position directly above the surface of the coke bed 8 constructed in the lower part of the furnace, and the lower tuyere 6b is provided at a height position in the coke bed 8.

  The tuyere diameter is set so that the air blowing speed is lower than that of the blast furnace so as not to make a raceway at the tuyere. Note that the implementation of the present invention is not limited to a two-stage tuyere vertical melting furnace, and may be performed in a single-stage tuyere vertical melting furnace depending on the blowing conditions.

When blowing from the upper tuyere 6a and the lower tuyere 6b, air at room temperature or 600 ° C. or less is blown from the lower tuyere 6b, mainly coke is burned, and air at room temperature is blown from the upper tuyere 6a. The CO gas produced by the solution loss reaction (endothermic reaction) between part of the combustion gas (CO ₂ ) and coke (C) is combusted to compensate for the decrease in the heat of fusion caused by the solution loss reaction.

  When the air is blown from the first tuyere, the lower tuyere 6b is provided at the same height as the lower tuyere 6b to promote the combustion of coke and increase the heat of fusion of the iron source. Therefore, it is necessary to enrich oxygen in the air blown from room temperature or in air of 600 ° C. or lower to increase the oxygen concentration.

  On the other hand, when the air is blown from the two-stage tuyere shown in FIG. 1, the amount of heat can be compensated by the air blown from the upper tuyere 6a. It is not always necessary to do.

  The raw fuel 10 containing the low carbon iron waste and the solid fuel is cut out from each raw material hopper, weighed by a weigher, and then accommodated in the bucket 7 of the charging device. The raw fuel 10 containing low carbon iron waste and solid fuel is passed through the bucket 7 from the top 3 of the vertical melting furnace 1 to the low carbon on the coke bed 8 constructed in the lower part of the vertical melting furnace 1. The iron source including the iron waste and the solid fuel are charged so as to be deposited in a layered or mixed state.

  The coke bed 8 can be constructed of blast furnace coke. Moreover, blast furnace coke can be used as the solid fuel charged into the furnace together with the iron source.

  The in-furnace deposition height (stock level) of the raw fuel 10 is adjusted to an upper height position in the furnace top 3, and the raw fuel 10 is filled in the furnace above the gas suction part 4 in the furnace top 3. In this state, the top (opening) of the top of the furnace is sealed (this is called a material seal).

  As a matter of course, during operation, the stock level of the raw fuel 10 decreases as the raw fuel drops due to melting of the raw fuel 10. For this reason, a level meter (not shown) is attached to the inside of the furnace top 3 in order to perform stable melting or melting and reduction of the raw fuel while sealing the furnace top 3, and the stock of the raw fuel 10. The level is measured, and the charging timing of the raw fuel 10 is controlled so as to maintain the stock level at a predetermined level.

  The iron source in the raw fuel 10 charged from the top of the vertical melting furnace 1 is melted by the reaction heat of oxygen and coke (C) blown from the tuyere 6 while descending the furnace. At the same time, iron oxide partially contained in the iron source is reduced with reducing gas (CO), solid carbon (C), and carbon in hot metal ([C]). The molten iron produced by melting and reduction descends the coke bed 8 and is stored in the bottom of the furnace.

  On the top surface of the bottom of the bottom of the furnace, a connecting pipe 11 communicating with the storage part 12 provided outside the furnace is provided, and the hot metal accumulated in the bottom of the furnace passes through the connecting pipe 11. It flows out to the storage unit 12. The hot metal is separated into a hot metal (slag) in the upper layer part and a hot metal in the lower part, and after the separation, the hot metal in the lower part is taken out from the spout 9.

  The smelting reduction region where the iron source is melted and partially reduced is mainly from the surface of the coke bed 8 in the upper range of about 1 to 2.5 m (volume, the original housed in the bucket 7. Equivalent to about 1 to 2.5 charges of fuel).

  In the present invention, a solid fuel containing 70 to 100% by mass of blast furnace coke is used as the solid fuel. Blast furnace coke is cheaper than foundry coke and is manufactured by an iron making process, so that a predetermined amount can be stably obtained.

  When solid fuel containing 70 mass% or more of blast furnace coke is used, pig iron cost can be greatly reduced. Therefore, the mixing ratio of blast furnace coke is preferably 70 mass% or more.

  Blast furnace coke has a smaller particle size, more ash, and lower strength than ordinary cast coke. Usually, the casting coke has a maximum particle size of 300 mm or less, an average particle size of 80 mm or more, and an ash content of 9% by mass or less. In the present invention, it is preferable to use blast furnace coke having a maximum particle size of 72 mm or less, an average particle size of 60 mm or less, and an ash content of more than 9% by mass.

  In the present invention, the iron source to be dissolved or dissolved and reduced is an iron source containing low-carbon iron waste.

  Examples of the iron source include iron scrap, pig iron, foundry scrap, hot briquette iron (MBI), and direct reduced iron (DRI) that have a metallization rate of 95% or more and need only be dissolved (reduction is not required). In addition, there are dust agglomerates with a metallization rate of less than 95% and self-reducing ores that require reduction (agglomerated ores with a high carbonaceous material content), and these can be used by appropriately blending them. However, the present invention exhibits a remarkable effect when the amount of C in the iron source is small.

  Usually, when the amount of C in the iron source is small, the amount of C in the molten iron produced by melting or melting and reduction also decreases, and the melting temperature of the molten iron rises. An increase in the melting temperature of the hot metal will increase the thermal load on the vertical melting furnace, so if the amount of C in the hot metal is small, the shortage of C will be supplied in the coke bed.

  Since the coke bed is consumed by replenishing hot metal with C, the height of the coke bed is increased in the present invention to increase the volume of the coke bed. FIG. 2 shows a coke bed mode. As shown in the figure, in the present invention, the coke bed height H is made higher than the standard coke bed height h to increase the coke bed volume.

  The present inventors investigated the relationship between the amount of C in the iron source and the consumption rate of the coke bed. The consumption rate of the coke bed was calculated from the reduction rate by estimating the height H (mm) of the coke bed.

  As a result, it has been found that the height H (mm) of the coke bed needs to be maintained in the range of the following formula (1). This is the first feature of the present invention.

1.10 · h ≦ H (mm) ≦ 1.20 · h (1)
h: Standard height of coke bed (mm)
The standard height h (mm) of the coke bed is the height of the coke bed when performing standard operation of the vertical melting furnace by the cupola method using an iron source containing 30 to 50% of carbon-containing scrap. Although h is 1000-1300 mm normally, when implementing this invention, 1200-1500 mm is preferable.

  If the height H (mm) of the coke bed at the time of operation is less than 1.10 · h, the amount of C supplied from the coke bed to the hot metal will be insufficient and the hot metal quality will deteriorate. The lower limit is 1.10 · h.

If the height H (mm) of the coke bed during operation exceeds 1.20 · h, the endothermic reaction of the solution loss reaction (CO ₂ + C → 2CO) becomes significant, increasing the coke ratio and increasing the heat in the furnace Since the shortage is caused, the upper limit of H (mm) is set to 1.20 · h. A preferable range of H (mm) is 1.13 · h or more and 1.17 · h or less.

  However, blast furnace coke has a higher ash content than cast coke and contains more than 9% by mass of ash, so S in the ash enters the hot metal in the coke bed, increasing the amount of S in the hot metal. To do. Since S adversely affects the material of pig iron, it is preferable to reduce it as much as possible.

The present inventors investigated the relationship between the amount of S in hot metal and slag basicity by reducing the amount of S in hot metal by adjusting the slag basicity (% CaO) / (% SiO ₂ ). did. The slag basicity was adjusted by charging limestone or silica stone into the furnace together with the iron source.

As a result, it was found that when the slag basicity (% CaO) / (% SiO ₂ ) is maintained in the range of the following formula (2) and the in-furnace desulfurization is promoted, the amount of S in the hot metal can be suppressed. This is the second feature of the present invention.
1.00 ≦ (% CaO) / (% SiO ₂ ) ≦ 1.20 (2)
(% CaO): CaO amount (% by mass) in slag,
(% SiO ₂ ): SiO ₂ amount in slag (mass%)

In the standard operation of the vertical melting furnace in the cupola method, since solid fuel mainly composed of casting coke with less ash content than blast furnace coke is used, slag basicity (% CaO) / (% SiO ₂ ) Operate under conditions of less than 1.00.

  In the present invention, since the blast furnace coke uses a solid fuel containing 70 to 100% by mass, it is difficult to suppress the penetration of S into the hot metal when the slag basicity is less than 1.00. The lower limit of basicity is 1.00.

  On the other hand, if the slag basicity is more than 1.20, the S suppression effect is saturated and a large amount of CaO-containing auxiliary materials such as limestone and quicklime are used, leading to an increase in production cost. .20. The preferable range of slag basicity is 1.05-1.15.

In order to maintain the slag basicity within the range of (% CaO) / (% SiO ₂ ) of the above formula (2), a CaO-containing auxiliary material is charged together with an iron source containing low-carbon iron waste. . As the CaO-containing auxiliary material, one or more of limestone, serpentine, dolomite, and converter slag are used.

  And if a vertical melting furnace is operated under the conditions satisfying the above formulas (1) and (2), an iron source containing low-carbon iron waste is dissolved or dissolved and reduced, and a high C · High quality pig iron with low S can be produced.

  The C content of the high-quality low-S high-quality pig iron is preferably 4.0 to 4.8% by mass, and the S content is preferably 0.3 to 0.7% by mass.

  Next, examples of the present invention will be described. The conditions of the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. Is not to be done. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

(Example)
Raw fuels with the blending ratios shown in Table 1 were charged into the vertical melting furnace shown in FIG. 1, and were melted and dissolved and reduced under the operating conditions shown in Table 2. C amount and S amount of the manufactured pig iron were measured. The results are also shown in Table 2.

  The pig iron manufactured by operating under the conditions satisfying the formulas (1) and (2) of the present invention has a larger amount of C and a smaller amount of S than pig iron produced by operating under other conditions. I understand.

  The amount of hot metal can be calculated from the amount of iron source by the following formula.

Hot metal production per ton of iron source (kg / t)
= 1 (t) x Σ (mixing ratio of each iron source x [T.Fe%] in each iron source) / ([T.Fe%] in hot metal)
[T.Fe%] in hot metal: A value calculated from the remainder of [C%] and [S%] in hot metal.

  As described above, according to the present invention, in the operation of a vertical melting furnace for producing pig iron by melting or dissolving and reducing an iron source containing low-carbon iron waste, using blast furnace coke, High quality (high C content, low S content) pig iron can be produced stably. Therefore, the present invention has great applicability in the steel industry.

DESCRIPTION OF SYMBOLS 1 Vertical melting furnace 2 Furnace main body 3 Furnace top part 4 Gas suction part 5 Gas suction port 6a Upper tuyere 6b Lower tuyere 7 Bucket 8 Coke bed 9 Outlet 10 Raw fuel (iron source, solid fuel)
11 Communication pipe 12 Storage section

Claims (8)

In a method for operating a vertical melting furnace that uses solid fuel blended with coke for blast furnace and melts or dissolves and reduces iron sources including low-carbon iron waste to produce pig iron,
(X) maintaining the height H (mm) of the coke bed within the range of the following formula (1), and
(Y) By charging the CaO-containing auxiliary material, the slag basicity (% CaO) / (% SiO ₂ ) is maintained in the range of the following formula (2),
(Z) A method for operating a vertical melting furnace characterized by producing high-quality pig iron with high C and low S.
1.10 · h ≦ H (mm) ≦ 1.20 · h (1)
h: Standard height of coke bed (mm)
1.00 ≦ (% CaO) / (% SiO ₂ ) ≦ 1.20 (2)
(% CaO): CaO amount (% by mass) in slag,
(% SiO ₂ ): SiO ₂ amount in slag (mass%)   The method for operating a vertical melting furnace according to claim 1, wherein the solid fuel is a solid fuel containing 70 to 100% by mass of coke for blast furnace.   The method of operating a vertical melting furnace according to claim 1 or 2, wherein the coke bed is constructed of blast furnace coke.   The method for operating a vertical melting furnace according to claim 1 or 2, wherein the coke bed is constructed of coke for blast furnace and coke for casting.   The said h is 1000-1300 mm, The operating method of the vertical melting furnace of any one of Claims 1-4 characterized by the above-mentioned. As the CaO-containing auxiliary material, one or more of limestone, serpentine, dolomite, and converter slag are charged, and the slag basicity (% CaO) / (% SiO ₂ ) is expressed by the above formula (2 The vertical melting furnace operating method according to any one of claims 1 to 5, wherein the operating method is maintained in a range of).   The operation of the vertical melting furnace according to any one of claims 1 to 6, wherein the amount of C of the high-quality low-S high-quality pig iron is 4.0 to 4.8 mass%. Method.   The operation of the vertical melting furnace according to any one of claims 1 to 7, wherein the amount of S of the high-quality low-S high-quality pig iron is 0.3 to 0.7 mass%. Method.

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