JP2006249568A - Method for producing molten iron having low phosphorus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing molten iron having low phosphorus in which when producing the molten iron having low phosphorus, the improvement of an allowance of heat and the dephosphorizing treatment with high efficiency are achieved. <P>SOLUTION: Only in a fixed time at the first half of the whole blowing term, a secondary combustion ratio is raised to ≥10% and a slag basicity at that time, is restrained to ≤1.8. In this way, while performing the high efficient dephosphorization, the damage of a refractory for furnace body is restrained to the minimum and the heat-transmission to the molten iron can efficiently be performed and the allowance of heat in the molten iron effectively be improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a low phosphorus hot metal that can perform a highly efficient dephosphorization process while improving the thermal margin of the hot metal.

  In recent years, a steelmaking method has been developed in which dephosphorization treatment (preliminary dephosphorization treatment) is performed in advance in the hot metal stage, and phosphorus in the hot metal is removed to some extent and decarburization refining is performed in a converter. In the dephosphorization process, the lower the Si concentration in the hot metal, the lower the amount of generated slag and the more efficient dephosphorization can be carried out. Therefore, oxygen gas or A method has been adopted in which an oxygen source such as iron oxide is supplied to carry out a desiliconization process to lower the Si concentration in the hot metal before the dephosphorization process. However, since the hot metal is oxidized and refined with an oxygen source in the desiliconization process, a so-called decarburization reaction in which the carbon in the hot metal is oxidized and reduced occurs in parallel with the desiliconization reaction. Further, since the silicon removal treatment is performed, the Si concentration in the hot metal before the phosphorus removal treatment is naturally reduced. Therefore, since the thermal margin of the hot metal during the dephosphorization process is reduced, the amount of scrap melting is restricted, and it becomes difficult to ensure the upward elasticity of production.

In order to solve such a problem, various methods have been conventionally proposed. For example, in Patent Document 1, dephosphorization blowing is first performed in a converter, and after dephosphorization slag is discharged, decarburization blowing is subsequently performed, and the slag after decarburization blowing is left in the furnace. The method of starting the dephosphorization blowing of the next charge in the state is disclosed. Patent Document 2 discloses a method of increasing the thermal margin by setting the secondary combustion rate during the dephosphorization process to 12% or more.
Japanese Patent No. 2558292 JP 2002-167614 A

In the method of Patent Document 1, since dephosphorization and decarburization blowing are performed in one converter and decarburization slag is recycled hot, there is little heat loss at the time of processing, and the heat margin is improved. Can be achieved. However, it is difficult to completely remove the slag after the dephosphorization treatment, and there is a problem that dephosphorization from the dephosphorization slag occurs during decarburization blowing. Moreover, since dephosphorization is performed at a low basicity (1.0 to 2.0), it is difficult to perform efficient dephosphorization itself.
In addition, when the secondary combustion rate is increased for a long period of time as in the method of Patent Document 2, the influence on the furnace refractory is large, and the life of the refractory is shortened due to heat damage, which may lead to an increase in cost. .

  Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a method for producing a low phosphorus hot metal that can achieve both improvement in thermal margin and high-efficiency dephosphorization.

  The inventors of the present invention have repeatedly studied to find the dephosphorization treatment conditions that can solve the above-mentioned problems. As a result, the secondary combustion rate is increased only within a certain period of the first half of the total blowing period, and in that case, By suppressing the slag basicity to a predetermined level or less, it is possible to efficiently apply heat to the hot metal while minimizing damage to the furnace refractory while performing highly efficient dephosphorization. It has been found that the thermal margin of can be effectively improved. Further, in such hot metal dephosphorization treatment, (1) as a method of supplying a CaO source as a dephosphorizing agent, a method of spraying a powdered CaO source from the top blowing lance onto the hot metal bath surface, (2) treatment It has been found that dephosphorization can be performed more efficiently by increasing the slag basicity at the end to a predetermined level or more.

The present invention has been made on the basis of the above findings, and the gist thereof is as follows.
(1) When hot metal contained in a converter-type vessel is subjected to dephosphorization treatment by adding a CaO source and an oxygen source as dephosphorization agents, 50% of the first half of the total blowing period Within the period and within a period corresponding to 20% or more of the total blowing period, the secondary combustion rate defined by CO ₂ / (CO + CO ₂ ) is set to 10% or more, and slag base A method for producing low phosphorus hot metal, characterized in that the degree (CaO / SiO ₂ ) is 1.8 or less, and the secondary combustion rate is less than 10% in other periods.
(2) In the production method of (1), the phosphorus removal treatment is performed by spraying at least part of the oxygen gas or the oxygen-containing gas and the dephosphorizing agent onto the hot metal bath surface through an upper blowing lance. Hot metal manufacturing method.

(3) A method for producing low phosphorus hot metal, characterized in that, in the production method of (1) or (2), the slag basicity (CaO / SiO ₂ ) at the end of dephosphorization treatment is 2.0 or more.
(4) In the manufacturing method according to any one of (1) to (3), the tip has a blowing gas supply nozzle that opens vertically downward or obliquely downward, than the blowing gas supply nozzle. A method for producing low-phosphorus hot metal, characterized by performing blowing using an upper blowing lance having an oxygen supply nozzle for secondary combustion opened horizontally or obliquely downward on a side surface at an upper position.

  According to the present invention, the secondary combustion rate is increased only within a certain period of the first half of the entire blowing period, and the slag is formed by suppressing the slag basicity at a predetermined level or less, thereby forming the secondary slag. The heat of combustion can be efficiently applied to the hot metal, heat can be effectively applied to the hot metal while minimizing damage to the furnace refractory, and the heat margin can be improved. Moreover, it is possible to achieve both the improvement of the thermal margin and the highly efficient dephosphorization treatment. As a result, it is possible to perform a highly efficient dephosphorization process while dissolving a large amount of scrap as compared with the conventional case, and it is possible to significantly increase the production amount of low phosphorus hot metal.

Using a converter-type vessel, adding a CaO source, which is a dephosphorization agent, and an oxygen source to the hot metal, and performing dephosphorization treatment under various conditions, it is possible to improve the thermal margin and achieve high-efficiency dephosphorization treatment. The results of investigating and examining optimum dephosphorization conditions are described below.
As described above, in order to advance the dephosphorization reaction with high efficiency in the hot metal dephosphorization process and reduce the amount of slag generated, it is necessary to reduce the Si concentration in the hot metal before the dephosphorization process. However, if the silicon removal treatment is performed in advance, the thermal margin of the hot metal is lowered, so that some thermal compensation is required to ensure the upward elasticity of the production amount. As a typical heat compensation, the addition of charcoal is considered, but the dephosphorization of hot metal is one of the important factors to maintain the slag oxygen potential high by increasing the (FeO) concentration in the slag. If carbonaceous material is added, the slag (FeO) may be reduced and the dephosphorization reaction may be hindered.

Accordingly, the present inventors have studied focusing on secondary combustion as means for increasing the thermal margin of the hot metal without inhibiting the dephosphorization reaction. As a result, the following facts were found.
First, the inventors conducted an experiment in which the secondary combustion rate was increased during the dephosphorization process. Here, the secondary combustion rate is a value defined by CO ₂ / (CO + CO ₂ ) (CO and CO ₂ are vol%). However, when the operation with the secondary combustion rate increased throughout the dephosphorization process, the furnace refractory was significantly damaged by heat, and the refractory was damaged (melting). It became clear that it was difficult to continue the operation in this state. Therefore, a method for increasing the secondary combustion rate only during a certain period in the early stage of blowing was studied. As a result, the secondary combustion rate is increased only within a certain period of the first half of the entire blowing operation, and the slag basicity at that time is suppressed to a predetermined level or less, thereby performing high-efficiency dephosphorization and the furnace. It was found that heat could be efficiently applied to the hot metal while minimizing damage to the body refractory, and the heat margin was greatly improved. Specifically, the secondary combustion rate is set to 10% or more only within the first 50% of the total blowing period and the length corresponding to 20% or more of the total blowing period. In addition, the slag basicity (CaO / SiO ₂ ) is set to 1.8 or less. Here, the slag basicity CaO, SiO ₂ is mass%.

On the other hand, in the present invention, in the period (the shortest period and 50% of the total blowing period) other than the period for increasing the secondary combustion rate (hereinafter referred to as “high secondary combustion rate period”) as described above, The combustion rate is less than 10%. No particular limitation is imposed on the slag basicity in the high post combustion ratio period other than the period (CaO / SiO _2), preferably in the conditions as described below.
Here, the high secondary combustion rate period is defined as the first half of the total blowing period because heat transfer to the scrap metal is promoted by applying heat from the initial stage of the blowing period to a large amount of scrap. On the other hand, the reason why it is limited to 50% of the total blowing period is that if the period exceeds 50%, damage to the furnace refractory due to heat becomes remarkable. The reason why the high secondary combustion rate period is set to 20% or more of the total blowing period is that heat application to the molten iron cannot be sufficiently performed in a period of less than 20%. The high secondary combustion rate period may be within the range of the first half 50% of the entire blowing period, and therefore the period may not be from the start of blowing.
The secondary combustion rate in the high secondary combustion rate period is 10% or more. As a result, heat is applied to the hot metal, and a sufficient heat margin can be secured. However, if the secondary combustion rate is too high, the refractory damage due to heat is large, and there is a concern of operability deterioration. Therefore, it is desirable to suppress the secondary combustion rate to 30% or less.

In addition, by setting the slag basicity (CaO / SiO ₂ ) to 1.8 or less during the high secondary combustion rate period, the efficiency of heat application of the secondary combustion heat to the hot metal is improved. This is considered to be because slag forms by lowering slag basicity. The secondary combustion is a reaction in which CO gas generated from the bath surface by the decarburization reaction is combined with unreacted oxygen gas or oxygen in the air entrained in the furnace to become CO ₂ gas. It is considered that there is a combustion region at a relatively upper position, at least above the slag surface. In the hot metal dephosphorization reaction, the amount of generated slag is originally small, but if there is such a small amount of slag, there is nothing that can be a heat receiving medium in the combustion region, so the combustion heat does not reach the hot metal and is taken away into the exhaust gas. It will be. On the other hand, if slag exists in the combustion region due to slag forming, the combustion heat is applied to the slag, and the slag becomes a heat transfer medium and is applied to the molten iron. When the slag basicity exceeds 1.8, it becomes difficult to form the slag, the effect of improving the heat receiving property as described above cannot be obtained, and as a result, the heat application to the molten iron cannot be performed effectively. That is, in the high secondary combustion rate period, heat application to the hot metal can be effectively performed only by combining the control of the secondary combustion rate and the slag basicity as described above.

In addition, in the area | region where slag basicity is less than 1.0, since the ejection of slag from a furnace port may generate | occur | produce, the slag basicity in the period of a high secondary combustion rate shall be the range of 1.0-1.8. It is desirable.
The slag basicity (CaO / SiO ₂ ) may be obtained from the amount of generated SiO ₂ calculated from the Si concentration in the hot metal and the amount of CaO to be added, or may be obtained by actual measurement by collecting slag.
As described above, by increasing the secondary combustion rate during the high secondary combustion rate period and controlling the slag basicity to increase the heat receiving property of the secondary combustion heat, it is possible to efficiently apply heat to the hot metal. As a result, heat transfer to the scrap is dramatically promoted, and the scrap can be rapidly melted. As a result, a large amount of scrap can be melted. In addition, since the secondary combustion rate is increased only within a limited period of the first half of the blowing period, damage to the furnace refractory can be minimized, and stable operation can be continued.

  On the other hand, with regard to the dephosphorization reaction, it is generally known that the phosphorus concentration can be reduced as the slag basicity is increased. In this regard, in the present invention, since the slag basicity is lowered during the high secondary combustion rate period in the first half of the blowing, phosphoric acid cannot be fixed in the slag, and the dephosphorization reaction is deteriorated due to the dephosphorization reaction. There was concern. However, the dephosphorization efficiency in the present invention was slightly higher than the conventional level. This is thought to be because the dephosphorization reaction was promoted by increasing the secondary combustion rate in the first half of blowing and increasing the slag temperature and promoting slag hatching.

In order to further improve the dephosphorization efficiency and further reduce the phosphorus concentration, oxygen gas or oxygen-containing gas and at least a part of powdered dephosphorization agent (CaO source) are sprayed on the hot metal bath surface through an upper blowing lance. Thus, it has been found preferable to perform the dephosphorization treatment. The powdered dephosphorizing agent has a higher melting rate than the bulk dephosphorizing agent, and can promote the dephosphorization reaction in combination with the effect of increasing the slag temperature and promoting the hatching by the secondary combustion heat. As oxygen gas or oxygen-containing gas blown from the top blowing lance, pure oxygen, air, oxygen-enriched air, etc. can be used, but in view of thermal efficiency and dephosphorization rate, industrial pure oxygen is generally used. Is done.
Furthermore, by adjusting the rate of addition of the dephosphorization agent and gradually increasing the slag basicity after the end of the high secondary combustion rate period, it is possible to suppress the recovery and reduce the phosphorus concentration in the same time as before. It was. At this time, it was found that if the slag basicity after the treatment is 2.0 or more, phosphorus can be reduced to a sufficiently low concentration. Therefore, the slag basicity (CaO / SiO ₂ ) at the end of the dephosphorization treatment is preferably 2.0 or more. On the other hand, if the slag basicity becomes too high, the hatchability of the slag may be deteriorated, so the slag basicity is preferably about 3.5 or less.

  As a method for increasing the secondary combustion rate, a method of increasing the distance between the upper blowing lance and the hot metal bath surface is known, but it is provided on the side surface at a predetermined distance from the lance tip of the upper blowing lance. It was found that the secondary combustion rate in the converter vessel can be easily increased by providing a nozzle in the horizontal or diagonally downward direction and supplying oxygen gas for secondary combustion therefrom. That is, it has a blowing gas supply nozzle that opens vertically or obliquely downward at the tip, and opens horizontally or obliquely downward on the side surface at a predetermined distance from this blowing gas supply nozzle. A desired secondary combustion rate can be easily obtained by supplying an oxygen gas from the secondary combustion oxygen supply nozzle during a high secondary combustion rate period using an upper blow lance having a secondary combustion oxygen supply nozzle. Can do.

Hereinafter, the details of the present invention will be described more specifically based on the drawings.
FIG. 1 shows an embodiment of a converter-type refining facility used for carrying out the method of the present invention. This converter-type refining equipment 1 has an outer shell composed of an iron shell 2 and a furnace body 4 in which a refractory 3 is arranged inside the iron shell 2, and is inserted into the furnace body 4 to move up and down. It is equipped with an upper blow lance 5 made of steel. At the upper part of the furnace body 4, a hot water outlet 7 for pouring out the molten iron 6 accommodated is provided, and at the bottom of the furnace body 4, a bottom blowing tuyere 8 for injecting stirring gas is provided. A gas introduction pipe 9 is connected to the bottom blowing tuyere 8. An oxygen gas pipe 10 is connected to the upper blow lance 5, and an oxygen gas or an oxygen-containing gas (hereinafter referred to as “oxygen gas” for convenience) as a gaseous oxygen source can be freely passed through the oxygen gas pipe 10. It is supplied into the furnace body 4 from the top blowing lance 5 at a flow rate.

  An oxygen gas pipe 10A branched from the oxygen gas pipe 10 is connected to a dispenser 12 containing a dephosphorization agent 11 as a CaO source. On the other hand, between the oxygen gas pipe 10 leading to the dispenser 12 and the upper blowing lance 5 A dephosphorizing agent transfer pipe 13 is connected to. Therefore, the oxygen gas supplied into the dispenser 12 can be used as a carrier gas for the dephosphorizing agent 11 in the dispenser 12, and the dephosphorizing agent 11 in the dispenser 12 is blown up via the dephosphorizing agent transfer pipe 13. It can be supplied by being transferred to the lance 5 and sprayed onto the hot metal bath surface in the furnace body 4 from its tip.

The oxygen gas pipes 10 and 10A are provided with flow rate adjustment valves 14 and 15 so that the oxygen gas can be arbitrarily adjusted to be blown directly from the top blowing lance 5 or through the dispenser 12. It has become.
When carrying out the method of the present invention, the upper blowing lance 5 does not have to serve as a supply flow path for the dephosphorizing agent 11, and a lance for supplying the dephosphorizing agent 11 may be provided separately from the upper blowing lance 5. . However, since the equipment arrangement in the upper part of the furnace body 4 becomes complicated, in order to prevent this, it is preferable that the top blowing lance 5 also serves as a supply path for the dephosphorization agent 11. Further, the carrier gas of the dephosphorizing agent 11 does not need to be an oxygen gas, and for example, an inert gas such as a nitrogen gas may be used. In that case, a separate piping is necessary.
Further, an addition device 17 for introducing various other refining agents 16 into the furnace body 4 is installed above the furnace body 4. As the addition device 17, for example, a conventional raw material supply device including a hopper, a chute, a weighing machine, a cutting device, and the like can be used, and the refining agent 11 may be supplied from the addition device 17.

FIG. 2 is a longitudinal sectional view showing an upper blowing lance suitable for carrying out the present invention.
The upper blow lance 5 is composed of a cylindrical lance main body 21 and a copper lance nozzle 22 connected to the lower end of the lance main body 21 by welding or the like. The middle tube 24, the inner tube 25, and the innermost tube 26 have a quadruple tube structure in which concentric circles are arranged. The carrier gas pipe is connected to the innermost pipe 26, and the oxygen gas pipe is connected to the inner pipe 25. Therefore, when the dephosphorizing agent as the CaO source is blown from the top blowing lance, the dephosphorizing agent is used as the carrier gas. At the same time, the gas is supplied to the inside of the innermost pipe 26, and oxygen gas is supplied to the flow path (gap) between the innermost pipe 26 and the inner pipe 25. Further, the gap between the inner pipe 25 and the middle pipe 24 and the gap between the middle pipe 24 and the outer pipe 23 serve as a cooling water supply / drain passage.

  The innermost tube 26 communicates with a center hole 28 disposed at substantially the center position of the lance nozzle 22, and a plurality of flow paths between the innermost tube 26 and the inner tube 25 are provided around the center hole 28. It communicates with the peripheral hole 29. The central hole 28 and the peripheral hole 29 are blowing gas supply nozzles that are opened vertically downward or obliquely downward, and the nozzles are so-called so-called two cones having a section that is reduced and an area that is enlarged. The shape of a Laval nozzle may be sufficient, or a straight shape may be sufficient. Further, a secondary combustion oxygen nozzle 27 for supplying secondary combustion oxygen is provided on a side surface at a position above the lance tip at a predetermined interval. It communicates with the oxygen gas flow path. In the embodiment of FIG. 2, the secondary combustion oxygen nozzle 27 is opened obliquely downward, but may be opened horizontally.

An embodiment of the method of the present invention using the above converter type refining equipment will be described. In FIG. 1, 6 is hot metal, 20 is slag, and 18 is scrap.
First, the scrap 18 is charged from the scrap chute 19 into the furnace body 4, and then the hot metal 6 is charged. The hot metal 6 may be subjected to desulfurization treatment or desiliconization treatment in advance. A desulfurization process is a process which mainly adds sulfur to hot metal, and removes sulfur. The desiliconization process is a process in which oxygen gas or iron oxide is added to the hot metal to mainly remove silicon in the hot metal. The chemical components of the hot metal before dephosphorization are generally C: 3.8 to 5.0 mass%, Si: 0.2 mass% or less, S: 0.05 mass% or less, P: 0.08 to 0.2 mass. %. As described above, when the amount of slag in the furnace body 4 increases during the dephosphorization process, the dephosphorization efficiency decreases. Therefore, in order to increase the dephosphorization efficiency by reducing the amount of slag in the furnace, a desiliconization process or the like is performed in advance. It is preferable to reduce the silicon concentration in the hot metal to 0.1 mass% or less. Moreover, if the hot metal temperature is in the range of 1200 to 1350 ° C., dephosphorization can be performed without any problem.

In the dephosphorization treatment, a dephosphorizing agent is added to the hot metal 6 and a non-oxidizing gas such as nitrogen gas or a rare gas such as Ar gas is blown into the hot metal 6 from the bottom blowing tuyere 8 as a stirring gas. Oxygen gas is supplied from the top blowing lance 5. As the dephosphorizing agent, bulk CaO can be added on top through an addition device 17 installed on the furnace, but the powdered dephosphorizing agent 11 is sprayed onto the bath surface of the hot metal 6 through the upper blowing lance 5. Is preferred.
Of the total blowing period, the oxygen from the top blowing lance 5 is within the period of the first 50% and within a period corresponding to 20% or more of the total blowing period (high secondary combustion rate period). By controlling the gas supply speed, the lance height, etc., the secondary combustion rate is set to 10% or more, and the dephosphorization agent 11 is added according to the Si concentration in the hot metal to reduce the slag basicity to 1.8 or less. Apply heat to the hot metal. Then, after such a high secondary combustion rate period, the secondary combustion rate is set to less than 10%, and the dephosphorization agent 11 is added to increase the slag basicity, and the slag basicity after the completion of the dephosphorization is 2. Blowing is performed so that it becomes 0 or more.

As the dephosphorization agent 11 that is a source of CaO, quick lime is generally used. Alumina or the like may be added to the quicklime as a solvent, but in the present invention, the slag temperature is increased by secondary combustion and the hatchability is improved, so that even quicklime alone is sufficiently hatched. It is possible to sufficiently remove phosphorous without using a solvent such as a solvent. In particular, from the viewpoint of protecting the environment by suppressing the amount of fluorine eluted from the slag 20, it is preferable not to use a fluorine-containing substance such as fluorite as a slagging agent.
If only oxygen gas is used as the oxygen source during the dephosphorization process, the hot metal temperature will rise too much and the dephosphorization reaction may be inhibited. Therefore, mill scale or iron ore can be added as a solid oxygen source as necessary. May be. The ratio between the addition amount of the gaseous oxygen source and the addition amount of the solid oxygen source may be appropriately selected according to the silicon concentration, phosphorus concentration, carbon concentration, etc. in the molten iron 6. The amount of the dephosphorization agent 11 is selected according to the silicon concentration and the phosphorus concentration in the hot metal 6, but about 40 kg per ton of hot metal is sufficient.

According to the method of the present invention as described above, the slag is formed by increasing the secondary combustion rate only within a certain period of the first half of the total blowing period and suppressing the slag basicity at a predetermined level or less. By doing so, the secondary combustion heat can be efficiently applied to the hot metal, heat can be effectively applied to the hot metal while minimizing damage to the furnace refractory, and the heat margin can be improved. As a result, the dissolution rate of scrap can be increased and the amount added can be increased, and the production amount can be increased without extending the processing time.
It is desirable to measure the secondary combustion rate by sampling exhaust gas from the secondary combustion area in the furnace, but if it is difficult to measure due to the high temperature field, analyze the gas near the top of the furnace. Alternatively, the secondary combustion rate may be calculated by correcting the nitrogen content and oxygen content in the entrained air.

Using a converter-type refining facility (furnace capacity 300 tons) as shown in FIG. 1, scrap was introduced into the furnace together with hot metal, and the hot metal was dephosphorized. In this hot metal dephosphorization, oxygen gas is blown from the top blowing lance, (1) Placement: a method of adding a bulk dephosphorization agent (CaO) from the furnace hopper, (2) Projection: using carrier gas The dephosphorizing agent is added by any one of a method of spraying a powdered dephosphorizing agent (CaO) from the top blowing lance to the hot metal bath surface, and at the same time, nitrogen gas is added from the bottom blowing tuyere to 0.05 to 0.15 Nm. ^The hot metal was stirred by blowing at a supply rate of ³ / min · t-pig. The oxygen gas supply rate is in the range of 1.0 to 2.0 Nm ³ / min · t-pig, and the dephosphorization agent (CaO) supply rate is in the range of 0.3 to 1.5 kg / min · t-pig. And controlled each. The hot metal temperature before and after the treatment was adjusted to a range of 1270 to 1360 ° C. During the treatment, the secondary combustion rate in the furnace was measured with an exhaust gas analyzer. Moreover, the forming height of the slag was measured using a microwave.

Moreover, the heat receiving efficiency was calculated by the following formula.
[Heat absorption efficiency] = ([Unknown heat calculated from heat balance] / [Secondary combustion heat calculated from secondary combustion rate by exhaust gas measurement]) × 100
In addition, the numerator of the above formula is [Unknown heat component calculated from heat balance] in the input calorie shown in FIG. 12, and the value of the denominator was obtained by the following equation.
[Secondary combustion heat calculated from secondary combustion rate by exhaust gas measurement] = ([Secondary combustion rate by exhaust gas measurement (%)] / 100) × [ΔC (kg / t-pig)] × 5.63
In this equation, ΔC is the amount of decarburized hot metal, and “5.63” is the calorific value (Mcal / kg-C) when CO → CO ₂ .

  Tables 1 to 4 show the operation conditions and operation results in Examples 1 to 14 of the present invention and Comparative Examples 1 to 13. In Tables 2 and 4, the “lance side hole” is a secondary combustion oxygen supply nozzle provided on the side surface at a position higher than the blowing oxygen supply nozzle of the top blowing lance. A case where an upper blow lance equipped with a secondary combustion oxygen supply nozzle was used was “present”, and a case where an upper blow lance without a secondary combustion oxygen supply nozzle was used was designated “none”. In addition, regarding the “refractory status”, “X” indicates that the refractory in the furnace is severely worn, and “◯” indicates that no wear is confirmed. Moreover, the secondary combustion rate, slag basicity, and slag height show average values.

FIG. 3 shows changes with time in the slag forming height, secondary combustion rate, and slag basicity in Comparative Example 1, and FIG. 4 shows changes with time in the slag forming height, secondary combustion rate, and slag basicity in Example 1 of the present invention. , Respectively. Comparative Example 1 does not have a high secondary combustion rate period and has a high slag basicity. On the other hand, in Example 1 of the present invention, the initial stage of blowing, which corresponds to 30% of the total blowing period, is a high secondary combustion rate period, and the slag basicity is 1.8 or less so that slag forming is easy in this high secondary combustion rate period. Is controlled. In addition, after the high secondary combustion rate period, the slag basicity is gradually increased.
Comparative Examples 2 and 3 are examples in which the secondary combustion rate was increased during the entire blowing period, but refractory wear was observed.

  For Comparative Examples 4 and 5 and Invention Examples 1 to 14, the secondary combustion rate in the high secondary combustion rate period in the first half of blowing (however, Comparative Examples 4 and 5 have no high secondary combustion rate period, FIG. 5 shows the relationship between the secondary combustion rate in the first 50% of the period and the amount of scrap added. Comparative Examples 4 and 5 and Invention Examples 1 to 14 are both high secondary combustion rate periods (however, Comparative Examples 4 and 5 have no high secondary combustion rate period, so the first 50% of the total blowing period) In Comparative Example 4 and 5, since the secondary combustion rate is less than 10%, the amount of scrap added is small.

About Comparative Examples 6-9 and this invention Examples 1-14, the relationship between the time ratio with respect to the whole blowing period of a high secondary combustion rate period and scrap addition amount is shown in FIG. In Comparative Examples 6 to 9, the secondary combustion rate during the high secondary combustion rate period is controlled to 10% or more, but in Comparative Examples 6 and 7, the time ratio during the high secondary combustion rate period is less than 20%. Therefore, the effect of increasing the heat margin cannot be obtained sufficiently, and therefore the amount of scrap added is small. On the other hand, in Comparative Examples 8 and 9, since the time ratio of the high secondary combustion rate period exceeds 50%, although the thermal margin is increased, the wear of the refractory is observed.
For Comparative Examples 10 to 13 and Invention Examples 1 to 14, the relationship between the slag forming height and the scrap addition amount during the high secondary combustion rate period is shown in FIG. In Comparative Examples 10 to 13, the time ratio of the high secondary combustion rate period is 20 to 50% and the secondary combustion rate is 10% or more. However, since the slag basicity exceeds 1.8, the slag forming height is high. Low scrap addition due to insufficient heat build-up.

  There is a correlation between the slag forming height and the heat receiving efficiency as shown in FIG. 8, and if the slag forming height is low, the slag cannot be a medium that heats the secondary combustion heat to the molten iron, so the heat receiving efficiency is lowered. It is considered a thing. Further, there is a relationship as shown in FIG. 9 between the slag basicity and the slag forming height. To increase the slag forming height, the slag basicity needs to be 1.8 or less. However, as described above, since the slag basicity is in the range of less than 1.0, there is a risk of slag ejection from the furnace port, so the slag basicity should be in the range of 1.0 to 1.8. More preferred.

  FIG. 10 shows the relationship between the slag basicity at the end of the dephosphorization treatment and the phosphorus concentration in the hot metal after the treatment for Invention Examples 1 to 14 and Comparative Examples 1 to 13. It can be seen that when the slag basicity at the end of the treatment is low, the phosphorus concentration in the hot metal after the treatment tends to be slightly high. In the comparative example, a bulk dephosphorization agent (CaO) was added on top, but “time ratio of high secondary combustion period: 20 to 50% of total blowing period, secondary combustion rate: 10% or more, slag Since the condition “basicity: 1.8 or less” is not satisfied, the phosphorus concentration is relatively high. On the other hand, in the present invention examples (invention examples 13 and 14) in which a bulk dephosphorizing agent (CaO) was added, the phosphorus concentration in the hot metal was lower than that in the comparative examples. Further, in the present invention example in which a powdered dephosphorizing agent was sprayed from the top blowing lance onto the hot metal bath surface (projection), the phosphorus concentration in the hot metal was further reduced. In addition, in some examples of the present invention in which the dephosphorizing agent was projected from the top blowing lance, there was a case where a bulk refining agent (CaO) was added on top, but the amount of massive CaO was not increased excessively. If there is, there is no problem even if used together. Moreover, it turns out that the phosphorus density | concentration in hot metal after a process can be reduced to 0.02 mass% or less by making the basicity after a process into 2.0 or more.

  FIG. 11 shows the difference in the secondary combustion rate depending on the presence or absence of the side holes (secondary combustion oxygen gas supply nozzle) of the top blowing lance. The secondary combustion rate is the average of the examples. Although it is possible to control the secondary combustion rate to 10% or more without side holes, the use of a lance having side holes can easily increase the secondary combustion rate, so the thermal margin For improvement, it is preferable to use an upper blowing lance having a side hole.

Explanatory drawing which shows one Embodiment of the converter type refining equipment used for implementation of this invention method The longitudinal cross-sectional view which shows the top blowing lance suitable for implementation of this invention The graph which shows the time-dependent change of the slag forming height, the secondary combustion rate, and the slag basicity in the comparative example 1 of an Example. The graph which shows the time-dependent change of the slag forming height, secondary combustion rate, and slag basicity in the example 1 of this invention of an Example. The graph which shows the relationship between the secondary combustion rate and scrap addition amount in the high secondary combustion rate period in the first half of blowing for Comparative Examples 4 and 5 and Examples 1 to 14 of the Examples The graph which shows the relationship between the time ratio with respect to the total blowing period of a high secondary combustion rate period, and scrap addition amount about the comparative examples 6-9 of this Example, and the invention examples 1-14. The graph which shows the relationship between the slag forming height of a high secondary combustion rate period, and the amount of scrap addition about the comparative examples 10-13 of an Example, and the invention examples 1-14. Graph showing the correlation between slag forming height and heat receiving efficiency during the high secondary combustion rate period (first half of blowing) Graph showing the correlation between slag basicity and slag forming height during the high secondary combustion rate period (first half of blowing) About the invention examples 1-14 and comparative examples 1-13, the graph which shows the relationship between the slag basicity at the time of completion | finish of a dephosphorization process, and the phosphorus concentration in hot metal after a process The graph which shows the difference of the secondary combustion rate with the presence or absence of the side hole (the oxygen gas supply nozzle for secondary combustion) of the top blow lance Drawing showing the breakdown of Input calorific value and Output calorific value in dephosphorization process

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Converter type refining equipment 2 Iron skin 3 Refractory 4 Furnace main body 5 Top blowing lance 6 Hot metal 7 Hot water outlet 8 Bottom blowing tuyere 9 Gas introduction pipe 10, 10A Oxygen gas piping 11 Dephosphorization agent 12 Dispenser 13 Dephosphorization agent transfer Piping 14 Flow adjustment valve 15 Flow adjustment valve 16 Refining agent 17 Addition device 18 Scrap 19 Scrap chute 20 Slag 21 Lance body 22 Lance nozzle 23 Outer pipe 24 Middle pipe 25 Inner pipe 26 Innermost pipe 27 Oxygen supply nozzle for secondary combustion 28 Center hole 29 Perimeter hole

Claims (4)

When hot metal contained in a converter type vessel is subjected to dephosphorization treatment by adding a CaO source and an oxygen source as dephosphorization agents, within the first 50% of the total blowing period. In addition, within a period corresponding to 20% or more of the total blowing period, the secondary combustion rate defined by CO ₂ / (CO + CO ₂ ) is set to 10% or more, and slag basicity (CaO / SiO ₂ ) is set to 1.8 or less, and the secondary combustion rate is set to less than 10% in other periods, the method for producing low phosphorus hot metal.   2. The method for producing low phosphorus hot metal according to claim 1, wherein the dephosphorization treatment is performed by spraying at least a part of the oxygen gas or the oxygen-containing gas and the dephosphorizing agent onto the hot metal bath surface through an upper blowing lance. The method for producing a low phosphorus hot metal according to claim 1 or 2, wherein the slag basicity (CaO / SiO ₂ ) at the end of the dephosphorization treatment is 2.0 or more.   A secondary combustion oxygen supply nozzle having a blowing gas supply nozzle that opens vertically or obliquely downward at the tip, and that opens horizontally or obliquely downward on the side surface above the blowing gas supply nozzle. The method for producing a low phosphorus hot metal according to any one of claims 1 to 3, wherein the blown blasting is performed using an upper blowing lance having the following.

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