JP5617195B2 - Hot metal desulfurization method - Google Patents

Description

  The present invention relates to a hot metal desulfurization method using a mechanical stirring desulfurization apparatus, and more particularly to a method of efficiently desulfurizing hot metal by promoting a desulfurization reaction.

  The hot metal discharged from the blast furnace contains high concentrations of phosphorus (element symbol: P) and sulfur (element symbol: S), which adversely affect steel quality, and various technologies have been developed to remove them. Has been. In today's steel refining process, a method of previously removing phosphorus and sulfur contained in hot metal prior to decarburization refining in a converter, so-called “pretreatment of hot metal” is generally performed. Among these, the hot metal desulfurization treatment holds the hot metal in a refining vessel having a substantially circular horizontal cross section, adds a desulfurizing agent onto the hot metal, and is called an impeller (also referred to as “stirring blade” or “stirring blade”). A method (hereinafter referred to as “mechanical stirring type desulfurization method”) in which a rotor having blades is immersed in hot metal and rotated, and the hot metal and the desulfurizing agent are stirred and desulfurized is widely used. In this mechanical stirring desulfurization method, an inexpensive desulfurization agent mainly composed of CaO (lime) is used.

The desulfurization reaction of molten iron with CaO is generally represented by the following formula (1).
[S] + (CaO) = (CaS) + [O] (1)
Here, [S] represents sulfur in the molten iron, (CaO) represents calcium oxide in the slag, (CaS) represents calcium sulfide in the slag, and [O] represents oxygen in the molten iron. It can be seen that it is effective to reduce the oxygen potential in the molten iron to make a reducing atmosphere in order to promote the reaction of formula (1) to promote desulfurization.

  As a technique for realizing this, Patent Document 1 discloses a method of promoting desulfurization reaction by blowing hydrocarbon gas into hot metal through a stirrer and keeping the atmosphere reducible in hot metal desulfurization by mechanical stirring. ing. Patent Document 2 discloses a desulfurization method in which hot metal desulfurization by mechanical stirring is performed by adding a desulfurizing agent to a hot metal bath surface through a top blowing lance together with a reducing carrier gas such as hydrocarbons. ing. Furthermore, in Patent Document 3, in hot metal desulfurization by mechanical stirring, a gas containing hydrocarbon gas is blown onto the hot metal bath surface, or a substance that generates hydrocarbon gas is added to the hot metal bath surface, and the reaction interface is set. A method for promoting the desulfurization reaction by using a reducing atmosphere is disclosed.

JP 55-76005 A JP 2005-179690 A Japanese Patent Laid-Open No. 2001-20006

  However, the above prior art has the following problems.

  That is, as disclosed in Patent Document 1, when the hydrocarbon gas is blown into the molten iron through a stirring device, a special pipe or joint for supplying the gas is necessary, which increases the equipment cost. There is a point. Also, the hydrocarbon gas blown into the rotating hot metal tends to gather at the center of the rotation when the hot metal rises due to the density difference between the hot metal and the gas. This is not sufficient, and there is a problem that the effect of improving the desulfurization reaction efficiency cannot be obtained sufficiently.

  Patent Document 2 is excellent in that a powdery desulfurizing agent is efficiently added to hot metal, but there is a problem in that the oxygen potential of hot metal is lowered by a reducing gas such as hydrocarbon. That is, when a reducing gas such as hydrocarbon is sprayed on the hot metal bath surface together with a desulfurizing agent as a carrier gas, first, an inert gas and a hydrocarbon gas are mixed and used as a carrier gas. In this case, the hydrocarbon gas concentration may decrease, and the deoxidation effect of the hot metal due to the hydrocarbon may not be sufficiently obtained. Second, when only the hydrocarbon gas is used as the carrier gas However, since the gas flow rate increases too much, the exhaust gas temperature rises due to the combustion of hydrocarbons, and the heat load on the dust collection equipment increases.

  Patent Document 3 is excellent as a means for reducing the oxygen potential of hot metal to promote the desulfurization reaction. However, the hot metal in the processing vessel is stirred so as to be swirled by an impeller, and is directed downward toward the center of the vessel. The hot metal flow rate increases. According to the detailed investigation results of the present inventors, the desulfurization rate changes greatly by changing the spraying position of the gas containing hydrocarbon. That is, there is an optimum range for the spray position of the gas containing hydrocarbon. In this regard, Patent Document 3 does not disclose anything, and there is a problem that a highly efficient desulfurization reaction cannot be obtained stably.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to efficiently use a fine desulfurization agent having excellent reactivity when desulfurizing hot metal using a mechanical stirring desulfurization apparatus. At the same time, the oxygen potential of the hot metal is efficiently reduced to provide a method for stably and efficiently desulfurizing the hot metal.

  The hot metal desulfurization method according to the first aspect of the present invention for solving the above-mentioned problem is a hot metal desulfurization method using a mechanical stirring desulfurization apparatus, wherein the hot metal desulfurization method is conveyed from a top blowing lance onto a hot metal bath surface being stirred by an impeller. A desulfurizing agent is added together with the working gas, and a desulfurization treatment is performed by spraying a gas containing hydrocarbons from a top blowing lance different from the top blowing lance onto the bath surface of the hot metal. It is.

In the hot metal desulfurization method according to the second invention, in the first invention, when the gas containing the hydrocarbon is blown onto the hot metal bath surface, the inner wall radius of the processing container containing the hot metal is D, the center of the processing container The horizontal distance (A) is within a range satisfying the relationship of the following expression (2) with respect to the inner wall radius (D), where A is the horizontal distance from the gas to the gas blowing position. Then, a gas containing hydrocarbon is blown.
0 ≦ A ≦ (2/3) × D (2)

  In the hot metal desulfurization method according to the third invention, in the first or second invention, the position at which the hydrocarbon-containing gas is blown onto the hot metal bath surface is more circular than the position at which the desulfurizing agent is blown up. It is the center side in the circumferential direction.

  According to the present invention, since the fine desulfurization agent having excellent reactivity is added together with the carrier gas, the scattering during the addition is reduced, the addition yield of the desulfurization agent is improved, and the fine desulfurization agent is added. Has a large reaction interfacial area, which promotes the desulfurization reaction and at the same time allows the gas containing hydrocarbons to be blown at the optimum position, so that the oxygen potential of the hot metal is efficiently reduced, and the The desulfurization reaction is accelerated, and the desired desulfurization treatment can be performed with a small amount of desulfurization agent. As a result, a reduction in the desulfurization agent basic unit and a reduction in the amount of generated slag associated therewith are achieved, and an industrially beneficial effect is brought about.

It is a schematic diagram which shows the flow direction in the bath surface vicinity at the time of stirring calculated | required in the water model experiment apparatus. It is the schematic of the experimental apparatus which simulated the mechanical stirring desulfurization apparatus. It is a figure which shows the relationship between the installation position of the upper blowing lance for gas spraying, and a desulfurization rate. It is a figure which shows the desulfurization rate when the installation position of the upper blowing lance for gas spraying is changed in the circumference direction with respect to the installation position of the upper blowing lance for powder spraying. 1 is a schematic side view of a mechanical stirring desulfurization apparatus embodying the present invention.

  Hereinafter, the present invention will be specifically described. First, the background to the present invention will be described.

  In the desulfurization treatment of hot metal using a mechanical stirring desulfurization apparatus, the present inventors can add a fine-grain desulfurization agent to the hot metal with a high yield, so that desulfurization from the top blowing lance disclosed in Patent Document 2 is performed. Based on the premise that the additive top blowing is used, various means for reducing the oxygen potential of the hot metal were studied in order to desulfurize the hot metal even more efficiently.

  As a result, it has been found that the method of spraying and adding a hydrocarbon-containing gas disclosed in Patent Document 3 onto the hot metal bath surface significantly improves the desulfurization rate. That is, it has been found that it is optimal to blow hydrocarbon-containing gas onto the hot metal bath surface from an upper blowing lance different from the upper blowing lance to which the desulfurizing agent is added. This is because an arbitrary amount of hydrocarbon can be supplied to an arbitrary position, and the atmosphere can be easily adjusted.

  However, even if the gas containing hydrocarbons is blown from the top blowing lance different from the top blowing lance that blows up the desulfurizing agent from the test results in the actual machine, the desulfurization rate depends on the blowing position of the gas containing hydrocarbons. Has been found to change significantly. Therefore, as a result of various investigations of this cause, it came to the idea that the effect of reducing the oxygen potential of hot metal is small unless the gas containing hydrocarbons is efficiently involved in the bath, and in the stirring bath stirred by the impeller Focused on flow.

  Therefore, first, the water flow in the bath at the time of mechanical stirring was quantitatively determined using a water model experimental apparatus of a mechanical stirring type desulfurization apparatus. The inner wall radius of the container of the water model experimental apparatus used is 150 mm. As a result of measuring the flow in the vertical direction and the flow velocity value during mechanical stirring by the impeller, as shown in FIG. 1, in the vicinity of the surface of the bath, the position is 100 mm from the container center, that is, the radius of the inner wall of the container is 2 It was found that the flow changed from downward to upward at the position of / 3. That is, in the range from the container center of the rotating bath surface to the position of 100 mm, the substance added to the bath surface is immediately involved in the bath, whereas in the range of the outer peripheral portion beyond the position of 100 mm from the container center, the bath is added. It was found that the substance added to the surface was difficult to get caught in the bath. From this result, the present inventors have come to the idea that the behavior of the hydrocarbon-containing gas sprayed onto the hot metal bath surface entering the bath is greatly influenced by the flow state of the bath, that is, the flow direction. It was.

  Therefore, using an experimental apparatus simulating a mechanical stirring type desulfurization apparatus, the blowing position of the gas containing hydrocarbon was changed, and the desulfurization rate when the blowing position was changed was investigated. Here, the desulfurization rate is the difference between the sulfur concentration (mass%) in hot metal before desulfurization and the sulfur concentration (mass%) in hot metal after desulfurization. It is shown as a percentage. FIG. 2 shows a schematic diagram of an experimental apparatus simulating a mechanical stirring desulfurization apparatus.

  The experimental apparatus includes a high-frequency heating coil 16. The impeller 14 is immersed in the molten iron 3 held in the crucible container 11 having an inner wall radius of 200 mm, which is heated and melted by the high-frequency heating coil 16, and the impeller 14 is rotated by the electric motor 15. The molten iron 3 was stirred. After stirring of the hot metal 3 reaches a steady state, a desulfurizing agent mainly composed of CaO is used as the hot metal with a nitrogen gas as a carrier gas through an upper blowing lance 12 for spraying powder disposed above the bath surface of the hot metal 3. Top spray was added to the bath surface. The installation position of the powder blowing upper lance 12 was fixed at a position where the horizontal distance from the center position of the crucible container 11 was 150 mm. At the same time, desulfurization was performed while a hydrocarbon-containing gas was sprayed on the bath surface of the hot metal 3 from a gas spraying upper lance 13 different from the powder spraying upper lance 12. The upper blowing lance 13 for gas blowing has a vertical direction at least at the front end where the gas is injected, and the installation position is a horizontal distance from the center position of the crucible container 11 when the inner wall radius of the crucible container 11 is D. The position was changed to 0-D. In addition, the temperature and sulfur content of the hot metal before the desulfurization treatment, and the addition amount of the desulfurizing agent were constant in each test.

FIG. 3 shows the desulfurization rate when the desulfurization treatment is performed by changing the installation position of the gas blowing upper lance 13. The horizontal axis in FIG. 3 is the radial distance from the center position of the crucible container 11 to the spraying position of the gas containing hydrocarbon. As shown in FIG. 3, the desulfurization rate changes according to the installation position of the gas blowing upper lance 13, and the installation position of the gas blowing upper lance 13 has a horizontal distance of 133 mm from the center position of the crucible container 11. It was found that a high desulfurization rate can be obtained when the range is up to (= (2/3) × D), that is, when the range satisfies the relationship of the following expression (2).
0 ≦ A ≦ (2/3) × D (2)
However, in the formula (2), A is the distance (m) from the center of the crucible container 11 as a processing container to the installation position of the gas blowing upper lance 13, and D is the inner wall of the crucible container 11 as a processing container Radius (m).

  Furthermore, in the experimental apparatus, the desulfurization treatment was performed by variously changing the spray position of the gas containing hydrocarbon and the top spray addition position of the desulfurizing agent. FIG. 4 is a diagram showing a part of the result of the desulfurization test. The installation position of the powder blowing upper lance 12 is constant at a position where the horizontal distance from the center position of the crucible container 11 is D / 2. And the desulfurization rate when the installation position of the gas blowing upper lance 13 is changed to the center side and the outer side in the circumferential direction of the powder blowing upper lance 12 for desulfurization. The horizontal axis in FIG. 4 is the radial distance from the center position of the crucible container 11 to the spray position of the gas containing hydrocarbons.

  As shown in FIG. 4, the crucible container 11 has a blowing position of the gas blowing upper lance 13 for blowing the gas containing hydrocarbons more than the blowing position of the powder blowing upper lance 12 for adding the desulfurizing agent. It was found that the desulfurization rate was improved when it was present at the center in the circumferential direction. This is because the powder blowing upper lance 12 for supplying the desulfurizing agent is provided in the case where the blowing position of the gas containing hydrocarbon is present on the outer side in the circumferential direction from the upper blowing addition position of the desulfurizing agent. This is because the transfer gas hinders the entrainment of hydrocarbon gas into the hot metal in the central portion of the processing vessel, and lowers the oxygen potential of the hot metal 3 to reduce the effect of reducing atmosphere. When located, this phenomenon does not occur.

  The present invention is based on these test results, and in the hot metal desulfurization method using a mechanical stirring desulfurization apparatus, the desulfurization agent together with the conveying gas from the top blowing lance on the bath surface of the hot metal being stirred by the impeller And a desulfurization treatment is performed by spraying a gas containing hydrocarbons onto the hot metal bath surface from an upper blow lance different from the upper blow lance. In that case, it is preferable that the position where the hydrocarbon-containing gas is sprayed satisfies the above-mentioned expression (2), and the position where the hydrocarbon-containing gas is sprayed onto the hot metal bath surface blows up the desulfurizing agent. It is preferable that it is the center side in the circumferential direction of the processing container rather than the position.

  Next, the hot metal desulfurization method according to the present invention will be described with reference to the drawings.

  FIG. 5 is a schematic side view of a mechanical stirring desulfurization apparatus embodying the present invention, and FIG. 5 shows an example in which a pan-type hot metal ladle having a circular horizontal cross section is used as a processing vessel for containing hot metal. Yes. Regarding the shape of the processing vessel, since the desulfurization treatment is performed by a mechanical stirring type desulfurization apparatus, a processing vessel having a circular horizontal cross section as shown in FIG. 5 is optimal.

  In FIG. 5, a hot metal ladle 2 containing hot metal 3 discharged from a blast furnace is mounted on a carriage 1 and carried into a mechanical stirring desulfurization apparatus. The mechanical stirring type desulfurization apparatus is equipped with a refractory impeller 4 that is immersed and buried in a hot metal 3 accommodated in a hot metal ladle 2 and swirls to stir the hot metal 3. The impeller 4 is an elevator device. (Not shown) is moved up and down in a substantially vertical direction, and is rotated 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 for blowing a desulfurizing agent for adding the desulfurizing agent 7 by blowing it upward toward the hot metal 3 accommodated in the hot metal ladle 2. The top blowing lance 5 for spraying the desulfurizing agent is connected to a supply device including a dispenser 8 for storing the powdery desulfurizing agent 7 and a cutting device 9 for quantitatively cutting out from the dispenser 8. From the lance 5, it has the structure which can supply the powdery desulfurization agent 7 with arbitrary timing with conveyance gas. As the carrier gas, a reducing gas, an inert gas or a non-oxidizing gas is used. Examples of the reducing gas include hydrocarbons, examples of the inert gas include argon gas, and examples of the non-oxidizing gas include nitrogen gas.

  Further, a gas blowing upper blow lance 6 is provided for blowing and supplying a gas containing hydrocarbons onto the bath surface of the hot metal 3 accommodated in the hot metal pan 2. As the gas containing hydrocarbons, hydrocarbon gas itself, or a mixed gas of hydrocarbon gas and inert gas or non-oxidizing gas can be used. Furthermore, a dust collection hood 10 that covers the hot metal ladle 2 is provided above the hot metal ladle 2, and exhaust gas and dust being processed are exhausted through an exhaust duct (not shown) attached to the dust collection hood 10. It is sucked by a dust collector (not shown). In this case, the shaft 4 a of the impeller 4, the upper blowing lance 5 for blowing the desulfurizing agent, and the upper blowing lance 6 for blowing gas are installed so as to penetrate the dust collection hood 10 and move up and down.

  The position of the carriage 1 on which the hot metal ladle 2 is mounted is adjusted so that the position of the impeller 4 is substantially at the center of the hot metal ladle 2, and then the impeller 4 is lowered and immersed in the hot metal 3. If the impeller 4 is immersed in the hot metal 3, the impeller 4 starts to turn and the speed is increased to a predetermined rotational speed. At the same time, a gas containing hydrocarbons is supplied to the hot metal bath surface from an upper blowing lance 6 for gas blowing. A gas containing a hydrocarbon is supplied from the top blowing lance 6 for gas blowing until the desulfurization treatment is completed. When the rotational speed of the impeller 4 reaches a predetermined rotational speed, the cutting device 9 is activated to spray the desulfurizing agent 7 accommodated in the dispenser 8 toward the bath surface of the hot metal 3 together with the conveying gas. Spray from top blow lance 5 and add.

  In this case, it is preferable that the position where the hydrocarbon-containing gas is sprayed satisfies the above-mentioned formula (2), and the position where the hydrocarbon-containing gas is sprayed onto the hot metal bath surface is to blow the desulfurizing agent 7 upward. It is preferable to set it as the center side of the circumferential direction with respect to the center of the hot metal ladle 2 rather than the position to perform.

  When the addition of a predetermined amount of the desulfurizing agent 7 is completed and stirring is performed for a predetermined time, the rotational speed of the impeller 4 is decreased and stopped. If the turning of the impeller 4 is stopped, the impeller 4 is raised and waited above the hot metal ladle 2. The generated slag floats to cover the hot metal surface, and the desulfurization process of the hot metal 3 is completed in a stationary state. After the desulfurization treatment, the generated slag is discharged from the hot metal ladle 2 and conveyed to the next refining process.

  As described above, according to the present invention, the fine desulfurization agent 7 having excellent reactivity is added together with the carrier gas, so that scattering during the addition is reduced and the addition yield of the desulfurization agent 7 is improved. The fine-grain desulfurization agent 7 has a large reaction interface area, which promotes the desulfurization reaction and at the same time allows the gas containing hydrocarbons to be sprayed at the optimum position. As a result, the desulfurization reaction is further promoted and the desired desulfurization treatment can be performed with a small amount of the desulfurization agent 7.

  The result of having performed the desulfurization process of hot metal using the mechanical stirring type desulfurization apparatus shown in FIG. 5 and using CaO powder as a desulfurization agent is shown.

  Nitrogen gas was used as the desulfurization agent conveying gas. The impeller used has four blades and the blades are not inclined. The chemical components of the hot metal used were C: 3.5 to 5.0 mass%, Si: 0.1 to 0.3 mass%, P: 0.05 to 0.15 mass%, S: 0.04 to At 0.05 mass%, the hot metal temperature was in the range of 1250 to 1350 ° C. In the desulfurization treatment, a hot metal ladle having an inner wall radius of 2000 mm, which can treat 200 to 500 tons of hot metal, was used as a treatment container. As the gas containing hydrocarbon, propane gas was used alone. The position of the top blowing lance for blowing the desulfurizing agent is 1333 mm from the center of the hot metal ladle (= 2/3 position of the inner wall radius of the hot metal ladle), and the position of the upper blowing lance for gas blowing is the center position of the hot metal ladle (example of the present invention). 1), 4 levels of 500 mm position from the center of the hot metal ladle (Example 2 of the present invention), 1333 mm position from the center of the hot metal ladle (Invention example 3), and 1500 mm position from the center of the hot metal ladle (Invention example 4).

  Sampling was performed from the hot metal before and after the desulfurization treatment, and the desulfurization rate was investigated from the sulfur content of the hot metal. The desulfurization rate is 96% in Invention Example 1, 91% in Invention Example 2, 90% in Invention Example 3, and 80% in Invention Example 4, and the propane gas spraying position is outside the processing vessel. In this case, the desulfurization rate is about 80%, but the propane gas spraying position is in the range from the hot metal ladle center to two-thirds of the inner wall radius and at the center in the circumferential direction from the desulfurizing agent blowing position. In some cases, a high desulfurization rate of 90% or higher was obtained.

DESCRIPTION OF SYMBOLS 1 Bogie 2 Hot metal ladle 3 Hot metal 4 Impeller 5 Upper blowing lance for spraying desulfurizing agent 6 Upper blowing lance for gas blowing 7 Desulfurizing agent 8 Dispenser 9 Cutting device 10 Dust collecting hood 11 Crucible container 12 Upper blowing lance for powder blowing 13 Gas spraying Top blow lance 14 Impeller 15 Electric motor 16 High frequency heating coil

Claims (1)

In the hot metal desulfurization method using the mechanical stirring desulfurization apparatus, the hot metal in the processing vessel rotates in the circumferential direction in the processing vessel, and the vertical flow of the hot metal in the vicinity of the hot metal bath surface is the processing vessel. The desulfurizing agent is added to the bath surface of the hot metal being stirred by the impeller so that the desulfurizing agent is blown up together with the carrier gas from the top blowing lance so that the surface is downward at the radial center side and upward at the outer side. When the desulfurization treatment is performed by spraying a gas containing hydrocarbons on the bath surface of the molten iron from an upper blowing lance different from the blowing lance, the inner wall radius of the treatment vessel containing the molten iron is D, from the center of the treatment vessel When the horizontal distance to the spraying position of the gas containing hydrocarbon is A, the horizontal distance (A) is a position that satisfies the relationship of the following expression (2) with respect to the inner wall radius (D). There At a position where the vertical direction of the flow of molten iron in the molten iron bath near the surface facing downward, and, at a position where the circumferential-direction center side of the process vessel from the position for blowing on the desulfurizing agent, containing said hydrocarbon The hot metal desulfurization method is characterized by spraying a gas to be applied onto the hot metal bath surface.
0 ≦ A ≦ (2/3) × D (2)

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