JP6648711B2 - Hot metal desulfurization method - Google Patents

Description

  The present invention relates to a hot metal desulfurization method using a mechanical stirring type desulfurization device.

  In recent years, the demand for higher purity of steel has become stronger than ever before, and accordingly, technology for removing impurities in steel has been actively developed. In today's steelmaking refining process, a method of removing phosphorus (P) and sulfur (S) contained in hot metal prior to decarburization refining in a converter, that is, pretreatment of hot metal is generally performed. I have. Among these, in the desulfurization treatment of hot metal, the hot metal is held in a refining vessel having a substantially circular horizontal cross section, a desulfurizing agent is added on the hot metal, and a stirring blade (also referred to as an "impeller") is provided. 2. Description of the Related Art A method of immersing a rotor in hot metal, rotating the hot metal, and agitating the hot metal and a desulfurizing agent to desulfurize the material (referred to as “mechanical stirring type desulfurization method”) is widely used. This desulfurization device is called "mechanical stirring type desulfurization device".

Examples of the desulfurizing agent at this time include a desulfurizing agent containing calcium oxide (hereinafter, also referred to as “CaO”) as a main component, calcium carbide (CaC ₂ ), and the like. Is widely used. This desulfurization reaction with calcium oxide proceeds based on the reaction formula shown in the following formula (3). In the formula (3), [S] represents sulfur in the hot metal, (CaS) represents calcium sulfide (CaS) in the slag, and [O] represents oxygen (O) in the hot metal.

[S] + CaO = (CaS) + [O] (3)
Calcium oxide has a melting point of about 2500 ° C, does not melt in the temperature range of 1250 to 1450 ° C, which is the temperature range for hot metal desulfurization, and the desulfurization reaction is a solid-liquid reaction between solid calcium oxide and liquid hot metal. The desulfurization reaction rate is extremely low.

Thus, as one of the methods for promoting the reaction of the above formula (3), a substance that reacts with calcium oxide to form a low melting point compound is added to promote the slagging of calcium oxide. For example, alumina _(Al 2 _{O 3)} and CaO-based desulfurizing agent obtained by mixing a calcium fluoride (CaF ₂₎ is used. However, alumina has a slag-promoting effect at a relatively high temperature of about 1400 ° C., but has little slag-promoting effect at a temperature of about 1300 ° C. Therefore, even at a low temperature of about 1300 ° C., the slag-forming property is good. Incidentally, CaO-based desulfurizing agents containing 3 to 5% by mass of calcium fluoride have been widely used. However, in recent years, the effect of fluorine on the environment has been regarded as a problem, and the development of a CaO-based desulfurizing agent in which fluorine is reduced and a CaO-based desulfurizing agent in which fluorine is not added are eagerly desired.

Even without adding alumina or calcium fluoride, the reaction of the above formula (3) is promoted by increasing the activity of the CaO-based desulfurizing agent. From this viewpoint, for example, Patent Literature 1 discloses a method of granulating calcium hydroxide powder or calcium carbonate powder as granules as a highly active CaO-based desulfurizing agent, subjecting the granulated body to a predetermined heat treatment and firing. A specific surface area of 5 m ² / g or more and a particle size of 1 mm or more produced by contacting with carbon dioxide in the latter stage of the calcination or by further treating the calcination in a carbon dioxide atmosphere until the carbonation ratio becomes at least 10%. A porous calcium oxide granular composite comprising highly active calcium oxide porous particles and a calcium carbonate coating layer formed on the surface thereof is disclosed.

  In order to increase the desulfurization reaction rate of the hot metal, it is effective to increase the reaction interface area between the hot metal and the desulfurizing agent. From this viewpoint, the smaller the particle size of the CaO-based desulfurizing agent used, the better. However, in the actual mechanical stirring type desulfurization apparatus, generally, a method of adding a CaO-based desulfurizing agent onto the bath surface of hot metal through a charging chute from above a refining vessel holding hot metal, and An exhaust duct connected to the dust collector is provided above the hot metal ladle, and gas and dust generated during the desulfurization process are configured to be discharged. In addition, the amount of the desulfurizing agent that reaches the hot metal due to the scattering decreases, and the yield of the desulfurizing agent added decreases. Therefore, there arises a problem that the desulfurization reaction efficiency is reduced. Furthermore, the interfacial tension between calcium oxide and hot metal is 1.75 N / m, and calcium oxide has a property that it is difficult to wet with hot metal. The calcium oxide inside remains unreacted, which causes a problem that the desulfurization reaction efficiency is reduced.

  From these facts, in order to promote the desulfurization reaction of hot metal, the size of calcium oxide is reduced, the aggregation of calcium oxide added as powder is suppressed, and the penetration of the desulfurizing agent into the hot metal bath is improved, It is effective to promote dispersion in the hot metal bath.

  As a technique for realizing this, Patent Literature 2 uses a stirring blade provided with a desulfurizing agent ejection port opened at the lower end of the rotating shaft of the stirring blade, and immerses and rotates the stirring blade to stir the hot metal. Meanwhile, a method has been proposed in which desulfurizing agent powder is blown into hot metal together with a carrier gas from the jet port to perform desulfurization. Further, Patent Document 3 proposes a method of desulfurizing by adding a desulfurizing agent powder to a bath surface of hot metal being stirred by stirring blades together with a carrier gas through a top blowing lance and blowing the powder upward. Further, Patent Document 4 discloses that a desulfurizing agent heated by a flame of a burner is placed on a hot metal bath surface stirred by a stirring blade in order to improve desulfurization efficiency by suppressing a decrease in temperature due to the addition of a desulfurizing agent. A desulfurization method in which top blowing is added has been proposed.

  The technology proposed in Patent Document 4 in which a desulfurizing agent is heated with a burner flame and blown upward is added. Various proposals have been made not only for desulfurization treatment of hot metal but also for desulfurization of molten steel in a secondary refining process after decarburization refining. It has been done. For example, Patent Document 5 discloses a method of improving the desulfurization efficiency by melting a refining agent for desulfurization by a burner flame in a vacuum degassing apparatus. Further, in Patent Document 6, similarly, in a vacuum degassing apparatus, when a desulfurizing refining agent is melted by a burner flame, a reducing gas burner flame is formed by adjusting a combustion gas supply rate and a fuel supply rate. There is disclosed a method for suppressing a decrease in efficiency of a desulfurization reaction as a reduction reaction.

JP-A-6-9215 JP 2005-68506 A JP 2005-179690 A JP 2009-299126 A JP 2010-111940 A Japanese Patent No. 5382275

  However, the above prior art has the following problems.

  That is, in Patent Document 1, since many steps and processing times such as kneading of calcium hydroxide powder or calcium carbonate powder, heat treatment, and pulverization are required until a calcium oxide porous granular composite suitable for desulfurization treatment is obtained. However, the production cost is high, and it is not practical to use it as a desulfurizing agent.

  In Patent Literatures 2 and 3, there is a problem that the sensible heat of the hot metal is removed by the desulfurizing agent by adding the desulfurizing agent, and the temperature of the hot metal decreases, which is a disadvantageous condition for the desulfurization reaction. The desulfurization reaction, which is a reduction reaction, is more advantageous at higher temperatures. Further, as described above, since the interfacial tension between the desulfurizing agent and the hot metal is large, even when the methods of Patent Documents 2 and 3 are used, the effect of causing the desulfurizing agent to enter the hot metal and disperse it is limited. However, the effect of promoting the desulfurization reaction was not sufficient.

  In Patent Literature 4, the desulfurizing agent is heated by a burner in a mechanical stirring type desulfurization apparatus. Although the decrease in hot metal temperature, which was a problem in Patent Literature 2 and Patent Literature 3, can be solved, the combustion gas supply speed and fuel The appropriate range of supply speed is not clear. In addition, simply adjusting the combustion gas so as not to directly reach the hot metal bath surface, it is considered that the burner flame itself is oxidizing, so that a decrease in desulfurization efficiency is suspected. Patent Literature 4 aims at suppressing a drop in hot metal temperature, but does not mention at all the effect on desulfurization efficiency due to a property change of a desulfurizing agent due to a burner flame.

  In Patent Literature 5, the desulfurizing agent is melted by heating with a burner flame, and the required amount of fuel is large relative to the amount of the desulfurizing agent to be supplied. Patent Literature 6 discloses a method for obtaining a reducing flame. Although an appropriate range in a vacuum degassing apparatus is indicated, desulfurization treatment using a mechanical stirring type desulfurization apparatus performed under atmospheric pressure is disclosed. Does not mention the proper range at all.

  The present invention has been made in view of the above circumstances, and an object thereof is to suppress a decrease in hot metal temperature accompanying the addition of a CaO-based desulfurizing agent in desulfurizing hot metal using a mechanical stirring type desulfurizer. By generating a CaO-based desulfurizing agent that is less likely to coagulate by a low-cost and simple method and directly adding it to the hot metal bath surface, the dispersion of the desulfurizing agent in the hot metal is promoted, so that it is efficient in a short time. It is an object of the present invention to provide a hot metal desulfurization method which can be desulfurized.

The gist of the present invention for solving the above problems is as follows.
[1] In a method of desulfurizing hot metal using a mechanical stirring type desulfurization apparatus,
Using an upper blowing lance having a powdery refining agent supply passage, a fuel supply passage, and an oxygen-containing gas supply passage for fuel combustion, supplying fuel from the fuel supply passage and simultaneously supplying the oxygen-containing gas while supplying an oxygen-containing gas from the supply channel to form a flame at the tip below the lance on the, transport powder calcium hydroxide (Ca (OH) ₂₎ from the powdery refining agent supply passage And the calcium hydroxide is thermally decomposed by the heat of the flame, and the calcium oxide (CaO) generated by the pyrolysis is added by blowing upward onto the hot metal bath surface stirred by the stirring blade. In desulfurizing hot metal,
The supply rate of the calcium hydroxide is S (kg / min), the lower heating value of the fuel is Q (MJ / kg), the supply rate of the fuel is F (kg / min), and the oxygen-containing gas is contained. Assuming that the supply rate of the oxygen gas is G (Nm ³ / min), the supply rate S of the calcium hydroxide, the supply rate F of the fuel, and the supply rate F of the fuel satisfy the following equations (1) and (2). A method for desulfurizing hot metal, comprising adjusting one or more of the oxygen gas supply rates G.

Here, (G / F) is an oxygen fuel ratio (= oxygen gas supply speed / fuel supply speed), and (G / F) _st is a stoichiometric value of the oxygen fuel ratio at which the fuel is completely burned. .
[2] The bath of the hot metal so that aluminum dross containing metallic aluminum is in a ratio of 4% by mass to 35% by mass with respect to the amount of calcium oxide (CaO) generated by thermal decomposition of the calcium hydroxide. The hot metal desulfurization method according to the above [1], wherein the hot metal is added to the surface.

  According to the present invention, calcium hydroxide powder is appropriately heated with a burner flame to thermally decompose it into calcium oxide, and the generated calcium oxide is sprayed on the hot metal bath surface together with the reducing flame, which is accompanied by the addition of a desulfurizing agent. The decrease in the temperature of the hot metal is suppressed, and the desulfurization reaction is promoted, so that the desulfurization rate is improved, the desulfurization treatment time is shortened, and the desulfurizer unit consumption is reduced.

1 is a schematic side view illustrating an example of an embodiment of a desulfurization treatment according to the present invention. FIG. 2 is a schematic enlarged sectional view of an upper blowing lance shown in FIG. 1. The figure which shows the relationship between the desulfurization rate in each test in Example 1 which used methane gas as a fuel, and the value of S / [G * Q * (G / F) / (G / F) _st ] of Formula (1). It is. The relationship between the desulfurization rate in each test in Example 2 using propane gas as a fuel and the value of S / [G × Q × (G / F) / (G / F) _st ] in equation (1) is shown. FIG. FIG. 9 is a view showing the relationship between the addition ratio of aluminum dross and the desulfurization rate in each test of Example 3.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic side view showing an example of the embodiment of the desulfurization treatment according to the present invention, and FIG. 2 is a schematic enlarged sectional view of the upper blowing lance shown in FIG.

  Hot metal 3 from a blast furnace is received by a hot metal pot 2 or a torpedo car (not shown) mounted on a bogie 1 and the received hot metal 3 is transported to a mechanical stirring type desulfurizer. When the pig iron is received by a torpedo car, it is transferred to a ladle-type processing vessel such as a hot metal ladle 2 prior to the desulfurization treatment. FIG. 1 shows an example in which a hot metal pot 2 is used as a processing vessel. In the present invention, the hot metal 3 to be subjected to the desulfurization treatment may be any component, for example, may be subjected to a desiliconization treatment or a dephosphorization treatment in advance. The desiliconization process is a process of adding an oxygen source such as oxygen gas or iron ore to the hot metal 3 to remove mainly silicon in the hot metal before the dephosphorization process in order to efficiently perform the dephosphorization process, The dephosphorization process is a process of adding an oxygen source such as oxygen gas or iron ore and a CaO-based solvent to the hot metal 3 to mainly remove phosphorus in the hot metal.

  The mechanical stirring type desulfurization device is provided with a refractory stirring blade 4 for immersing in the hot metal 3 accommodated in the hot metal pot 2, rotating and stirring the hot metal 3, and the stirring blade 4 is a lifting device. (Not shown), it moves up and down in a substantially vertical direction, and rotates about a shaft 4a as a rotation axis by a rotating device (not shown).

The mechanical stirring type desulfurization apparatus is provided with an upper blowing lance 5 and a hopper 10, and the upper blowing lance 5 and the hopper 10 are connected by a desulfurizing agent supply pipe 6, and the powder stored in the hopper 10 Calcium hydroxide (Ca (OH) ₂ ) 12 is supplied to the upper blowing lance 5 together with the carrier gas through a desulfurizing agent supply pipe 6 using a non-oxidizing gas such as an argon gas or a nitrogen gas as a carrier gas. Then, it is blown from the tip of the upper blowing lance 5 toward the hot metal 3 stored in the hot metal pot 2. A rotary feeder 11 is disposed in the hopper 10, and the supply amount of calcium hydroxide 12 as a desulfurizing agent is controlled by the rotary feeder 11. The desulfurizing agent supply pipe 6 is provided with a flow control valve (not shown) for controlling the flow rate of the carrier gas.

  Further, the upper blowing lance 5 includes a hydrocarbon gas fuel such as butane gas, propane gas, methane gas, and natural gas, a gas fuel containing CO gas such as coke oven gas, and a hydrocarbon liquid such as heavy oil and kerosene. A fuel supply pipe 7 for supplying at least one of a fuel, a carbon-based solid fuel such as coke and coal, and an oxygen-containing pipe for supplying an oxygen-containing gas such as oxygen gas, oxygen-enriched air and air. A gas supply pipe 8 and a cooling water supply / drain pipe 9 for supplying / discharging cooling water for cooling the upper blowing lance 5 are connected. Each of the fuel supply pipe 7 and the oxygen-containing gas supply pipe 8 is provided with a flow rate control valve (not shown) for controlling the flow rate of each.

  As shown in FIG. 2, the upper blowing lance 5 includes a cylindrical lance main body 13 and a copper lance tip 14 connected to a lower end of the lance main body 13 by welding or the like. , The outermost pipe 15, the outer pipe 16, the middle pipe 17, the inner pipe 18, and the innermost pipe 19, that is, five kinds of concentric steel pipes, that is, a five-ply pipe. The desulfurizing agent supply pipe 6 communicates with the innermost pipe 19, the fuel supply pipe 7 communicates with the gap between the inner pipe 18 and the innermost pipe 19, and the oxygen-containing gas supply pipe 8 communicates with the middle pipe 17 and the inner pipe. The cooling water supply / drain pipe 9 communicates with the gap between the outermost pipe 15 and the outer pipe 16 and the gap between the outer pipe 16 and the middle pipe 17.

  In other words, the inside of the innermost pipe 19 is a powdery refining agent supply flow path, and the powdered calcium hydroxide 12 passes through the innermost pipe 19 together with the carrier gas, and communicates with the inner pipe 18. The gap with the pipe 19 is a fuel supply flow path, and the fuel passes through the gap between the inner pipe 18 and the innermost pipe 19, and the gap between the middle pipe 17 and the inner pipe 18 supplies the oxygen-containing gas for fuel combustion. It is a flow path, and the oxygen-containing gas passes through the gap between the middle pipe 17 and the inner pipe 18. The gap between the outermost pipe 15 and the outer pipe 16 and the gap between the outer pipe 16 and the middle pipe 17 serve as a water supply channel and a drainage channel for the cooling water.

  The inside of the innermost tube 19 is connected to a center hole 20 arranged at a substantially central position of the lance tip 14, and a gap between the inner tube 18 and the innermost tube 19 is formed by a fuel injection hole provided around the center hole 20. The gap between the middle pipe 17 and the inner pipe 18 is connected to an oxygen-containing gas injection hole 22 arranged side by side near the fuel injection hole 21. The fuel injection holes 21 and the oxygen-containing gas injection holes 22 are, for example, arranged in a plurality and the same number. The center hole 20 is a nozzle for blowing the powdered calcium hydroxide 12, the fuel injection hole 21 is a nozzle for blowing the fuel, and the oxygen-containing gas injection hole 22 is a nozzle for blowing the oxygen-containing fuel. This is a nozzle for blowing gas, and is configured so that one fuel injection hole 21 and one oxygen-containing gas injection hole 22 form one burner. That is, the fuel injected from the fuel injection holes 21 is burned by the oxygen gas in the oxygen-containing gas injected from the oxygen-containing gas injection holes 22, and a burner flame is formed at the tip of the upper blowing lance 5. Have been.

  As shown in FIG. 2, the center hole 20 has a so-called Laval nozzle shape which is formed by two conical bodies having a section whose section is reduced and a section which is enlarged, but has a straight shape. Is also good. Further, the fuel supply passage and the oxygen-containing gas supply passage may be replaced. Further, in FIG. 2, the fuel injection holes 21 and the oxygen-containing gas injection holes 22 form separate flow paths to the tip of the lance tip 14, but the two are mixed in a nozzle in the middle of the lance tip 14. You may do so.

  A mechanical churning type desulfurizer has an input chute (not shown) for adding an auxiliary material such as a massive or powdery deoxidizing agent (metal aluminum, aluminum dross, etc.) onto the bath surface of the hot metal 3 and adding it. In addition, an exhaust duct port (not shown) connected to a dust collector (not shown) is provided at a position above the hot metal ladle 2, so that gas and dust generated during the desulfurization process are discharged. Is configured. The desulfurization reaction of the hot metal 3 is a reduction reaction. By adding a deoxidizing agent such as aluminum dross containing metallic aluminum onto the hot metal bath surface, the oxygen potential is reduced and the desulfurization reaction is accelerated. In the present invention, as described later, powdery calcium hydroxide 12 is added by blowing upward while heating with a burner flame, so that desulfurization can be sufficiently performed without using a fluorine source.

  The size of the powdered calcium hydroxide 12 to be blown can be selected from the optimum particle size according to the size of the top blow lance 5 and the size of the hot metal pot 2 to be used. For quick heating, fine-grained calcium hydroxide is preferably used. For example, the particle size is preferably 200 μm or less, more preferably 100 μm or less. Further, as the calcium hydroxide 12, commercially available special hydrated lime or No. 1 hydrated lime used for industrial purposes may be used, or a hydrated product of commercially available calcium oxide (quick lime) may be used.

  The position of the bogie 1 on which the hot metal pot 2 is mounted is adjusted so that the position of the stirring blade 4 is substantially at the center of the hot metal pot 2, and then the stirring blade 4 is lowered and immersed in the hot metal 3. When the stirring blade 4 is immersed in the hot metal 3, the rotation of the stirring blade 4 is started, and the speed is increased to a predetermined rotation speed. When the rotation speed of the stirring blades 4 reaches a predetermined rotation speed, the rotary feeder 11 is started, and the powdered calcium hydroxide 12 stored in the hopper 10 is transferred to the bath surface of the hot metal 3 together with the carrier gas. Spray and add. Since the desulfurization reaction is accelerated as the speed of spraying onto the surface of the hot metal 3 is increased, the flow rate of the carrier gas and the upward blowing are set so that the flow velocity of the carrier gas colliding with the bath surface of the hot metal 3 becomes 10 m / s or more. It is preferable to adjust the height of the lance 5.

  Before the start of the top-blowing addition of the powdered calcium hydroxide 12, a hydrocarbon-based or CO-gas-based gas fuel, a hydrocarbon-based liquid fuel, or a carbon-based solid fuel is supplied from the fuel injection hole 21 in advance. And at the same time, supply oxygen-containing gas such as oxygen gas or air from the oxygen-containing gas injection holes 22 to ignite fuel at the outlet side of the fuel injection holes 21 as necessary. A flame is formed at the tip of the blowing lance 5. In this case, it is preferable to dispose the fuel injection holes 21 and the oxygen-containing gas injection holes 22 such that a flame is formed around a jet containing the powdered calcium hydroxide 12 ejected from the center hole 20.

When supplying the powdered calcium hydroxide 12, the supply rate of the powdered calcium hydroxide 12 is S (kg / min), the lower heating value of the fuel is Q (MJ / kg), and the supply rate of the fuel is When F (kg / min) and the supply rate of the oxygen gas contained in the oxygen-containing gas are G (Nm ³ / min), water is set so that the following equations (1) and (2) are simultaneously satisfied. One or more of the calcium oxide powder supply speed S, the fuel supply speed F, and the oxygen gas supply speed G are adjusted. The term "lower heating value" means that when a fuel containing hydrogen or moisture is burned, a part of the heating value is stored in the combustion gas as latent heat of moisture evaporation, but this latent heat is not generally available. Therefore, a value obtained by subtracting these latent heats from the total calorific value is referred to as “lower calorific value”.

Here, (G / F) is the oxy-fuel ratio (= oxygen gas supply rate (Nm ³ / min) / fuel supply rate (kg / min)), and (G / F) _st indicates that the fuel is completely burned. Is the stoichiometric value of the oxy-fuel ratio. (G / F) _st is, for example, 2.80 (Nm ³ / kg) when the fuel is methane gas, and 2.55 (Nm ³ / kg) when the fuel is propane gas.

By adjusting any one or more of the supply rate S of the powdered calcium hydroxide 12, the supply rate F of the fuel, and the supply rate G of the oxygen gas so as to satisfy the expression (1). The powdered calcium hydroxide 12 to be blown up is heated by the flame formed at the tip of the top blow lance 5, causing a thermal decomposition reaction shown in the following formula (4) in the flame, The particles of calcium oxide that are decomposed into body-like calcium oxide (CaO) and water vapor (H ₂ O gas) and generated by a thermal decomposition reaction are sprayed on the bath surface of the hot metal 3.

Ca (OH) ₂ = CaO + H ₂ O (g) (4)
Powdered calcium oxide generated by thermal decomposition of calcium hydroxide 12 in a flame under appropriate heating conditions has a large specific surface area, a BET specific surface area of 4 to ²⁰ m ² / g, and is in a porous form. It is thought that it is. According to the test results of the present inventors, it has been confirmed that when such a calcium oxide having a large specific surface area is used as a desulfurizing agent, the desulfurization reaction rate is significantly improved. However, when calcium hydroxide is held at a high temperature around the hot metal temperature as described later, since the above-described effect of increasing the specific surface area and promoting the desulfurization reaction does not occur, the porous structure as described above is used. It is considered that at high temperatures around the temperature of the hot metal, it is hardened and disappears in a short time.

  For this reason, it is doubtful whether the above-mentioned effect of promoting the desulfurization reaction is a phenomenon that can be simply explained by an increase in the reaction interface area due to an increase in the specific surface area, and another mechanism may be involved. It is not clear what mechanism this is due to, but since the specific surface area has been significantly increased, the physical or chemical state of the surface of the generated calcium oxide particles has changed from that of conventional calcined quicklime. It may be significantly different from pulverized calcium oxide particles, which may have affected the conditions under which the calcium oxide particles generated in the flame enter the hot metal .

  In other words, the calcium oxide particles supplied to the hot metal either enter the hot metal or remain at the gas-liquid interface or the gas phase without being able to enter the hot metal. If the efficiency of infiltration into the hot metal increases, the calcium oxide particles once dispersed in the hot metal easily associate and do not agglomerate, so even if the specific surface area of the individual calcium oxide particles entrained in the hot metal decreases, In addition, the reaction interface area of desulfurization can be increased as compared with the case where the conventional quick lime powder is used. On the other hand, calcium oxide particles tend to stay at a high density at the gas-liquid interface or gas phase, so that calcium oxide particles tend to agglomerate with each other. Is difficult to efficiently increase.

  In addition, in the calcium oxide particles having an increased specific surface area, the direct contact area between adjacent particles is reduced, so that it is possible that the calcium oxide particles are hardly aggregated even after being supplied onto the hot metal. In this case, it is considered that the size of the pseudo particles when subsequently entrained in the hot metal becomes smaller than in the case where the conventional quick lime powder is used, and it becomes possible to increase the reaction interface area of desulfurization.

In order to maximize the desulfurization efficiency, as the heating condition, the value of S / [G × Q × (G / F) / (G / F) _st ] in equation (1) is close to 0.28. It is preferable that the specific surface area is more easily increased. When the value of S / [G × Q × (G / F) / (G / F) _st ] in the expression (1) is less than 0.20, the specific surface area is increased due to baking of the generated powdery calcium oxide. And it becomes difficult to obtain the desulfurization accelerating effect by the mechanism described above. For example, it is considered that since the contact area between the particles increases, the particles are aggregated after being supplied onto the hot metal, and the desulfurization efficiency is reduced. On the other hand, when the value of S / [G × Q × (G / F) / (G / F) _st ] in equation (1) exceeds 0.28, the calcium hydroxide 12 is sufficiently heated in the flame. However, the entire amount cannot be thermally decomposed, and the thermal decomposition of calcium hydroxide that has not yet decomposed into the hot metal increases the oxygen potential in the atmosphere and decreases the desulfurization efficiency.

Further, when the supply rate G of the oxygen gas contained in the oxygen-containing gas and the supply rate F of the fuel satisfy the formula (2), the reducibility of the burner flame is secured, and a decrease in the desulfurization efficiency can be suppressed. . When the value of (G / F) / (G / F) _st is smaller than 0.4, no flame is formed and calcium hydroxide is not thermally decomposed. On the other hand, when the value of (G / F) / (G / F) _st exceeds 0.8, the flame becomes oxidizing, and the desulfurization reaction as a reduction reaction is inhibited. The closer the value of (G / F) / (G / F) _st is to 0.4, the higher the reducibility of the flame is. However, in order to suppress the fuel cost, the value of (G / F) / (G / F) _st is more preferably close to 0.8.

As (G / F) / (G / F) _st is smaller, the amount of oxygen gas with respect to the fuel is reduced, the combustion state is incomplete, and the flame temperature is also reduced, so that the calcium hydroxide 12 is appropriately pyrolyzed. , It is necessary to reduce the supply speed S of the calcium hydroxide 12.

  Calcium oxide generated by being thermally decomposed through the reducing flame is sprayed on the bath surface of the hot metal 3 and is caught in the hot metal 3 being stirred by the stirring blades 4. The sulfur (S) contained in the hot metal 3 reacts with the calcium oxide entrained in the hot metal 3 according to the above-mentioned equation (3), and the desulfurization of the hot metal 3 proceeds.

  In addition, in order to promote the desulfurization reaction, in parallel with or before the top-blown addition of the powdered calcium hydroxide 12, or during the entire period of the desulfurization treatment period, metal aluminum is contained. It is preferable to add a deoxidizing agent such as aluminum dross onto the hot metal 3 from a charging chute (not shown). When the calcium oxide particles are likely to aggregate, the deoxidizing agent may not fully exhibit the deoxidizing effect due to aggregation with the calcium oxide particles. When added together with hard calcium oxide particles, aggregation of the deoxidizing agent is also suppressed, so that a more remarkable deoxidizing effect is exhibited, and desulfurization efficiency is improved.

  When aluminum dross containing 10-30% by mass of metallic aluminum is added as a deoxidizing agent, the ratio of aluminum dross is 4% by mass to 35% by mass with respect to the amount of calcium oxide generated by thermal decomposition of calcium hydroxide to be added. It is preferable to add them so that If it is less than 4% by mass, the amount of the deoxidizing agent is small, and the desulfurization efficiency is not sufficiently improved. On the other hand, when it exceeds 35% by mass, the calcium oxide component is diluted, and the desulfurization efficiency is reduced. The ratio (% by mass) of aluminum dross to the amount of calcium oxide generated by thermal decomposition is determined by the following equation (5).

Ratio of aluminum dross (mass%) = aluminum dross supply amount (kg / t) × 100 / [(calcium hydroxide addition amount (kg / t)) × (56/74)] (5)
When the addition of a predetermined amount of powdered calcium hydroxide 12 is completed and the stirring is performed for a predetermined time, the rotation speed of the stirring blade 4 is reduced and stopped. The supply of the fuel from the fuel injection holes 21 and the supply of the oxygen-containing gas from the oxygen-containing gas injection holes 22 are completed when the addition of the powdered calcium hydroxide 12 is completed. When the rotation of the stirring blades 4 is stopped, the stirring blades 4 are raised and made to stand by above the hot metal pot 2. The generated slag floats and covers the surface of the hot metal, and the desulfurization process of the hot metal 3 ends in a stationary state. After the desulfurization treatment, the generated slag is discharged from the hot metal pot 2, and the hot metal pot 2 is transported to the next refining process.

  By subjecting the hot metal 3 to the desulfurization treatment in this manner, even when the fine-grained powdered calcium hydroxide 12 is added, the scattering at the time of addition is small, and the calcium oxide particles heated and generated in the reducing flame And the calcium oxide particles produced by heating have a large specific surface area and have an effect of accelerating the desulfurization reaction. In addition, the addition of the heat-generated calcium oxide particles suppresses the temperature drop of the hot metal 3, promotes the desulfurization reaction, remarkably improves the desulfurization rate, shortens the desulfurization treatment time, and reduces the desulfurizer unit consumption. You.

  Note that the present invention is not limited to the above description range, and various modifications can be made. For example, a plurality of burners may be arranged around the upper blowing lance 5, and the burner may be used to heat the powdered calcium hydroxide 12 blown from the upper blowing lance 5. Further, in addition to the powdered calcium hydroxide 12, as a part of the desulfurizing agent, it does not prevent the conventional quick lime powder from being blown up or thrown in and used together.

In the mechanical stirring type desulfurization apparatus shown in FIG. 1 described above, the stirring blade is immersed in about 300 tons of hot metal accommodated in the hot metal pot for transferring hot metal and rotated, and 6.5 kg of calcium hydroxide (Ca (OH) ₂₎ powder (commercial product, Japanese Patent slaked lime, the average particle diameter of 100 [mu] m), blown added above at a feed rate S of 130~270kg / min while heating with a burner flame by various conditions, the stirring blade Was rotated at a rotation speed of 140 rpm, and a test was performed in which the calcium hydroxide powder and the hot metal which were heated by the burner and added by blowing upward were stirred for 20 minutes to perform desulfurization treatment.

  Each of the hot metal components before the desulfurization treatment had a carbon concentration of 4.4% by mass, a silicon concentration of 0.3% by mass, a phosphorus concentration of 0.1% by mass, and a sulfur concentration of 0.04% by mass. Methane gas (lower heating value Q = 57.8 MJ / kg) was used as fuel supplied from the upper blowing lance, and pure oxygen gas (industrial pure oxygen gas) was used as the oxygen-containing gas.

  Table 1 shows treatment conditions and desulfurization rates in each test (test numbers 1 to 48). Table 2 also shows, as a comparison, a test (test in which calcium oxide (CaO) powder (commercial product, average particle size 100 μm) was heated in a burner flame and top-blown, and similarly desulfurized. Nos. 49 to 56) are shown. In Test Nos. 49 to 56, the amount of calcium oxide added was adjusted to be equal to the mass of calcium oxide generated by thermal decomposition of calcium hydroxide in Test Nos. 1 to 48. The desulfurization rates (%) shown in Tables 1 and 2 are shown as the ratio (percentage) of the decrease in the sulfur concentration due to the desulfurization treatment to the sulfur concentration in the hot metal before the desulfurization treatment (0.04 mass%).

Test Nos. 1 to 8 show the results of desulfurization treatment in which calcium hydroxide was blown up without heating with a burner, and the desulfurization rate was 77.5% for all, and Test Nos. It was lower than the desulfurization rate of 90% in the test in which the calcium oxide powder was heated with a burner and top-blown. This is considered to be because in Test Nos. 1 to 8, the oxidizing atmosphere due to water vapor (H ₂ O) generated by the calcium hydroxide powder reaching the hot metal surface and being thermally decomposed inhibited the desulfurization reaction, which is a reduction reaction. .

In Test Nos. 9 to 16, there is a tendency that the desulfurization rate changes according to the value of S / [G × Q × (G / F) / (G / F) _st ] in equation (1). The desulfurization rate is low. This is because the oxygen gas supply rate G is too high with respect to the fuel supply rate F, so that the steam generated by the thermal decomposition of the calcium hydroxide powder can be used even under the condition of stoichiometrically reducing flame. It is considered that the oxygen potential of the atmosphere increased due to the influence of the above, and the desulfurization reaction, which is a reduction reaction, was inhibited. For this reason, in Test Nos. 9 to 16, the desulfurization rate in the test for adding the calcium oxide powder to the burner by heating top blowing (Test Nos. 49 to 56) could not be exceeded.

  In Test Nos. 17 to 21 and Test Nos. 25 and 26, the adverse effect of the oxidizing atmosphere was gradually reduced by increasing the fuel supply rate F with respect to the oxygen gas supply rate G. There was a tendency for the rate to improve. However, the amount of calcium hydroxide powder that is heated against the combustion heat of the fuel is small, and as the powder becomes hot, the porous calcium oxide particles are sintered by the time they reach the hot metal bath surface, resulting in a specific surface area. This is considered to be due to the decrease to the same level as the conventional calcium oxide powder (quick lime powder). For this reason, the effect of accelerating the desulfurization reaction cannot be obtained, and as a result, the desulfurization reaction is slower than the test (test numbers 49 to 56) of the addition of the calcium oxide powder to the burner by heating, due to the influence of the oxidizing atmosphere described above. It is thought that it became.

  In Test Nos. 31 and 32 and Test Nos. 35 to 40, the desulfurization rate increases to some extent but does not reach 90%. This is because the amount of calcium hydroxide powder to be heated with respect to the heat of combustion of the fuel is too large, and the powder has a low temperature, so the thermal decomposition of calcium hydroxide is not completed before it reaches the hot metal bath surface, As in Test Nos. 1 to 7, rapid thermal decomposition on the hot metal bath surface does not allow a high specific surface area to be obtained, and in addition, a reducing atmosphere is not locally secured by the steam generated by decomposition, and the desulfurization reaction proceeds. It is considered to have been inhibited.

  In Test Nos. 41 to 48, the burner flame was not formed and the calcium hydroxide powder was not heated because the fuel supply speed F was too large with respect to the oxygen gas supply speed G. It is considered that the desulfurization rate was low for the reason described above.

  In Test Nos. 22 to 24, Test Nos. 27 to 30, and Test Nos. 33 and 34, the thermal decomposition of the calcium hydroxide powder was performed because the supply speed S of the calcium hydroxide powder to the combustion heat of the fuel was appropriate. After the completion, the generated calcium oxide particles were able to maintain a large specific surface area without burning, and the fuel supply rate F with respect to the oxygen gas supply rate G was appropriate. , And a decrease in desulfurization efficiency was suppressed, so that a high desulfurization rate could be obtained.

FIG. 3 shows that among the test numbers 1 to 48 in Example 1, the value of S / [G × Q × (G / F) / (G / F) _st ] in the expression (1) is 0.06 to 0. 4 shows the relationship between the desulfurization rate in the test within the range of 0.34 and the value of S / [G × Q × (G / F) / (G / F) _st ] in equation (1).

In the mechanical stirring type desulfurization apparatus shown in FIG. 1 described above, the stirring blade is immersed in about 300 tons of hot metal accommodated in the hot metal pot for transferring hot metal and rotated, and 6.5 kg of calcium hydroxide (Ca (OH) ₂ ) powder (commercially available product, special name slaked lime, average particle diameter 100 μm) was added by blowing upward at a supply rate S of 145 to 295 kg / min while heating with a burner flame under various conditions, and stirring blades were added. Was rotated at a rotation speed of 140 rpm, and a test was performed in which the calcium hydroxide powder and the hot metal which were heated by the burner and added by blowing upward were stirred for 20 minutes to perform desulfurization treatment.

  Each of the hot metal components before the desulfurization treatment had a carbon concentration of 4.4% by mass, a silicon concentration of 0.3% by mass, a phosphorus concentration of 0.1% by mass, and a sulfur concentration of 0.04% by mass. Propane gas (lower heating value Q = 46.4 MJ / kg) was used as fuel supplied from the upper blowing lance, and pure oxygen gas (industrial pure oxygen gas) was used as oxygen-containing gas.

  Table 3 shows processing conditions and desulfurization rates in each test (test numbers 61 to 100). As in Example 1, the desulfurization rate (%) is shown as a ratio (percentage) of the sulfur concentration decrease by the desulfurization treatment to the sulfur concentration in the hot metal before the desulfurization treatment (0.04% by mass).

  In Example 2, propane gas was used as fuel, but the same behavior as in Example 1 using methane gas as fuel was confirmed.

In Test No. 61 to 68, (1) the S / [G × Q × ( G / F) / (G / F) st] Although desulfurization rate in accordance with the values tend to vary seen, the entire The desulfurization rate is low. This is because the oxygen gas supply rate G is too high with respect to the fuel supply rate F, so that the steam generated by the thermal decomposition of the calcium hydroxide powder even under the condition where the combustion becomes almost complete stoichiometrically. It is considered that the oxidizing atmosphere caused by the influence of CO ₂ gas and water vapor generated by the combustion of the fuel inhibited the desulfurization reaction as the reduction reaction. For this reason, in Test Nos. 61 to 68, the desulfurization rate in the test of addition of the calcium oxide powder to the burner by heating top blowing (Test Nos. 49 to 56 in Example 1) could not be exceeded.

  In Test Nos. 69 to 72 and Test Nos. 77 to 79, as the fuel supply rate F was increased with respect to the oxygen gas supply rate G, the atmosphere was gradually reduced and the desulfurization efficiency was improved. Is low. This is because the amount of calcium hydroxide powder heated against the combustion heat of the fuel is small, and the calcium oxide particles are sintered by the time the powder reaches a hot metal surface before reaching the hot metal bath surface. This is considered to be due to the decrease to the same level as calcium oxide powder (quick lime powder). For this reason, the effect of accelerating the desulfurization reaction was not obtained, and as a result, it is considered that the desulfurization reaction was slower than the test of adding the calcium oxide powder onto the burner with heating (Test Nos. 49 to 56 in Example 1).

  In Test No. 84 and Test Nos. 88-92, the desulfurization rate is somewhat high, but does not reach 90%. This is because the amount of calcium hydroxide powder to be heated with respect to the heat of combustion of the fuel is too large, and the powder has a low temperature, so the thermal decomposition of calcium hydroxide is not completed before it reaches the hot metal bath surface, It is considered that the rapid thermal decomposition on the hot metal bath surface did not allow a high specific surface area to be obtained, and that the reducing atmosphere was not locally secured by the steam generated by the decomposition, thereby inhibiting the desulfurization reaction.

  In Test Nos. 93 to 100, the burner flame was not formed and the calcium hydroxide powder was not heated because the fuel supply speed F was too large with respect to the oxygen gas supply speed G. It is considered that the desulfurization efficiency was low for the same reason as in Nos. 1 to 7.

  In Test Nos. 73 to 76, Test Nos. 80 to 83 and Test Nos. 85 to 87, the thermal decomposition of the calcium hydroxide powder was performed because the supply speed S of the calcium hydroxide powder to the combustion heat of the fuel was appropriate. After the completion, the generated calcium oxide particles were able to maintain a large specific surface area without burning, and the fuel supply rate F with respect to the oxygen gas supply rate G was appropriate. , And a decrease in desulfurization efficiency was suppressed, so that a high desulfurization rate could be obtained.

FIG. 4 shows that among the test numbers 61 to 100 in Example 2, the value of S / [G × Q × (G / F) / (G / F) _st ] in the expression (1) is 0.06 to 0. and the desulfurization rate at .34 in the range of the test (1) shows the relationship between the value of S / [G × Q × ( G / F) / (G / F) st] in the formula.

In the mechanical stirring type desulfurization apparatus shown in FIG. 1 described above, stirring blades are immersed in about 300 tons of hot metal accommodated in a hot metal ladle for transferring hot metal and rotated to rotate 6.5 kg of calcium hydroxide (Ca) per ton of hot metal. (OH) ₂ ) powder (commercially available product, special name slaked lime, average particle size 100 μm) was blown up at a supply speed S of 230 kg / min while heating the burner under various conditions, and the stirring blade was rotated at 140 rpm. A test was performed in which the powder was rotated at a speed, the burner was heated, and the calcium hydroxide powder and the hot metal that had been blown up were stirred for 20 minutes to desulfurize the powder. At the same time as the start of the desulfurization treatment, a predetermined amount of aluminum dross containing 15% by mass of metallic aluminum was added at once and added.

Each of the hot metal components before the desulfurization treatment had a carbon concentration of 4.4% by mass, a silicon concentration of 0.3% by mass, a phosphorus concentration of 0.1% by mass, and a sulfur concentration of 0.04% by mass. Methane gas (lower heating value Q = 57.8 MJ / kg) was used as fuel supplied from the upper blowing lance, and supplied at 10.7 kg / min. Pure oxygen gas (industrial pure oxygen gas) was used as the oxygen-containing gas, and was supplied at 24 Nm ³ / min.

  Table 4 shows treatment conditions and desulfurization rates in each test (test numbers 111 to 122). As in Example 1, the desulfurization rate (%) is shown as a ratio (percentage) of the sulfur concentration decrease by the desulfurization treatment to the sulfur concentration in the hot metal before the desulfurization treatment (0.04% by mass). The ratio of aluminum dross shown in Table 4 is a value calculated by the above-described equation (5).

  In Test Nos. 112 to 118, by adding an appropriate amount of aluminum dross, the desulfurization rate was further improved as compared with the inventive examples not using aluminum dross shown in Tables 1 and 3. This is because, in addition to the desulfurization accelerating effect of the calcium oxide particles having a large specific surface area generated by the thermal decomposition of the calcium hydroxide powder, the deoxidizing effect or the slag accelerating effect of the added aluminum dross is the above-mentioned calcium oxide particles. It is thought that it effectively contributed to the desulfurization reaction by

  In Test No. 111, the amount of aluminum dross added was small, and a sufficient deoxidizing effect was not obtained. Therefore, the desulfurization rate was almost the same as that of the inventive example not using aluminum dross. On the other hand, in Test Nos. 119 to 122, the amount of aluminum dross added was too large, and the calcium oxide was diluted to offset the deoxidizing effect, resulting in a desulfurization rate comparable to that of the present invention example using no aluminum dross. It is considered that

  FIG. 5 shows the relationship between the addition ratio of aluminum dross and the desulfurization rate in each test of Example 3.

Reference Signs List 1 cart 2 hot metal pot 3 hot metal 4 hot metal stirring blade 5 top blowing lance 6 desulfurizing agent supply pipe 7 fuel supply pipe 8 oxygen-containing gas supply pipe 9 cooling water supply / drain pipe 10 hopper 11 rotary feeder 12 calcium hydroxide 13 lance body 14 lance tip 15 Outer tube 16 Outer tube 17 Middle tube 18 Inner tube 19 Inner tube 20 Center hole 21 Fuel injection hole 22 Oxygen-containing gas injection hole

Claims (2)

In the desulfurization method of hot metal using a mechanical stirring type desulfurization device,
Using an upper blowing lance having a powdery refining agent supply passage, a fuel supply passage, and an oxygen-containing gas supply passage for fuel combustion, supplying fuel from the fuel supply passage and simultaneously supplying the oxygen-containing gas The powder of calcium hydroxide (Ca (OH) ₂ ) is conveyed from the powdery refining agent supply passage while supplying an oxygen-containing gas from the supply passage to form a flame below the tip of the upper blowing lance. And the calcium hydroxide is thermally decomposed by the heat of the flame, and the calcium oxide (CaO) generated by the pyrolysis is added by blowing upward onto the hot metal bath surface stirred by the stirring blade. In desulfurizing hot metal,
The supply rate of the calcium hydroxide is S (kg / min), the lower heating value of the fuel is Q (MJ / kg), the supply rate of the fuel is F (kg / min), and the fuel is contained in the oxygen-containing gas. the feed rate of oxygen gas as a G (Nm 3 / ^min), so as to satisfy the equation (1) and (2) below, the feed rate S of the calcium hydroxide, the feed rate F of the fuel, the oxygen A method for desulfurizing hot metal, comprising adjusting one or more of the gas supply rates G.

Here, (G / F) is the oxygen fuel ratio (= oxygen gas supply speed / fuel supply speed), and (G / F) _st is the stoichiometric value of the oxygen fuel ratio at which the fuel is completely burned. .   Aluminum dross containing metallic aluminum is placed on the bath surface of the hot metal so as to have a ratio of 4% by mass to 35% by mass with respect to the amount of calcium oxide (CaO) generated by thermal decomposition of the calcium hydroxide. The hot metal desulfurization method according to claim 1, wherein the hot metal is added.

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