JP6540301B2 - Molten iron discharge work method - Google Patents

Description

The present invention is a converter or by using Tappuho Le utilized in the step of discharging the molten iron, such as manufactured molten iron or molten steel in a container such as a ladle in an electric furnace, adversely affect slag and quality in a subsequent step The molten iron discharge work method for realizing the shortening of the molten iron discharge time and the improvement of productivity etc. while suppressing the increase of the outflow amount of

  Conventionally, in order to discharge molten metal typified by molten steel from a smelting furnace such as a converter or an electric furnace to a container with good yield, a steel hole (hereinafter referred to as a tap hole) is provided on the inner wall of the converter or the electric furnace. It is provided. By discharging the molten metal from this tap hole, it is possible to efficiently tap steel while preventing simultaneous outflow of slag present on the molten metal in the furnace at the time of refining, and is generally used widely.

  In recent years, the blowing time at the time of decarburization processing has reached a level that can be implemented in 10 to 15 minutes in a converter of 300 t scale. However, it takes about 5 to 10 minutes to take out molten steel from the tap holes. Therefore, from the viewpoint of productivity improvement in the converter, the need to reduce the steel tapping time is very high.

  Therefore, in order to shorten the tapping time, it is conceivable to increase the tapping amount of the molten steel per unit time by enlarging the diameter of the tap hole. However, at the end of steel tapping, vortices are easily formed in the vicinity of the tap hole, and the slag is simultaneously discharged along with the formation of the vortex, so the simultaneous discharge amount of slag is accompanied by the increase in diameter of the tap hole. It will increase. If the amount of slag discharge increases, re-oxidation occurs due to the slag that has flowed into the ladle from the next process, or the inclusion of slag causes deterioration in cleanliness and removal of components due to reversion, etc. There is a serious problem that

  With respect to these problems, in order to reduce the amount of slag outflow due to the vortex, a technology has been proposed in which a slag ball having an intermediate specific gravity between slag and molten steel is introduced at the time of tapping. For example, Patent Document 1 proposes a highly efficient special shape as a slag ball. Moreover, in order to improve the efficiency which prevents a whirlpool, the method etc. of inserting the dart provided with the whirlpool prevention stick inside a tap hole are proposed like the method of patent documents 2, for example.

  Moreover, in order to suppress the simultaneous outflow of slag by generation | occurrence | production of a vortex, the control method which blows in gas in a tap hole which is described in patent document 3, and a tap which is described in patent document 4 There has also been proposed a device that mechanically drives a plug by detecting the outflow of slag from the change in impedance of an electromagnetic coil provided on the outer periphery of a hole.

  However, in order to carry out slag cutting using slag balls and darts, it is necessary to insert a slag outflow prevention tool into the furnace from the back of the furnace into the furnace port at high temperature during operation of the converter, and further, Since the slag outflow prevention device itself is an expensive consumable item, there are problems in workability and cost. Further, when a special tuyere structure is provided as described in Patent Documents 3 and 4, the workload on maintenance in continuous operation is large.

  Also, in continuous operation on the premise that high productivity is usually maintained, since the tap holes are melted and metal adheres to the tap holes, a sleeve as described in Patent Document 5 is used. By exchanging between charges, stable operation is carried out in a short time with low maintenance of work load. However, if a special tuyere structure is provided, the work load increases, which causes the productivity to deteriorate. Furthermore, although the example which applied the special sleeve which has a taper to an inner surface is reported to the nonpatent literature 1, as described in the nonpatent literature 1, the deterioration of the operability by the wear of the tapered portion is It is an invitation. In addition, there is a limitation in manufacturing the sleeve itself in which the inner wall is provided with a taper, which increases the cost.

Japanese Patent Application Laid-Open No. 11-209816 Unexamined-Japanese-Patent No. 2006-124737 JP 11-279620 A Japanese Patent Application Laid-Open No. 11-61225 Japanese Patent Application Laid-Open No. 6-184617

Michael M. Berger, Christian Rham: Iron Steel Technical Conf. Proc. (2007), p1111.

  As described above, in order to discharge the molten iron at high speed while suppressing the deterioration of the quality in the post process, there is a problem that the cost becomes high and the work load for maintenance increases.

The present invention overcomes this problem, by suppressing a and workload low cost, and to provide a soluble iron discharge working method for discharging the molten iron at a high speed while suppressing the outflow of slag.

The gist of the present invention for solving the above-mentioned subject is as follows.
(1) In the tap hole for discharging the molten iron from the refractory inner wall of the smelting container to the outside of the smelting container during the smelting charge or before the start of the molten iron discharge after the end of the smelting,
The diaphragm Ri part to be inscribed in the taphole provided at a position apart more than 400mm from the end of the refractory inner wall,
L ₂ / (L ₁ + L ₂ ) × 100 (%), which indicates the position of the narrowed portion, is 37.5% or less,
The minimum cross-sectional area A of the passage in the narrowed portion is 80% or less of the minimum cross-sectional area of the passage between the end on the inner wall side of the refractory and the narrowed portion,
And the said molten iron is discharged so that the following (2) Formula may be satisfied, The molten iron discharge working method characterized by the above- mentioned.
A 50 50 × W ············· (2)
Here, A indicates the minimum cross-sectional area (mm ² ) of the passage in the squeezed portion, W indicates the amount of molten iron (t) discharged in one heat, and L ₁ indicates the upper end of the squeezed portion from the end on the refractory inner wall side until the length (m), L ₂ represents the length (m) to the tip of the molten iron discharge passage from the upper end of the narrowed portion.
(2) The molten iron discharging work method according to the above (1), wherein the narrowed portion is provided at a position separated by 30 mm or more from the tip of the molten iron discharge passage.

  According to the present invention, tap holes used in the process of discharging molten iron such as molten iron and molten steel produced in a converter or electric furnace to a container such as a ladle, and by using the same, quality in the subsequent process It is possible to realize shortening of the molten iron discharge time and to realize productivity improvement etc. while suppressing the increase in the outflow amount of slag which adversely affects, and its industrial utility value is extremely high.

It is a figure for demonstrating a mode that steel tapping to a ladle from a converter is carried out. It is a figure for demonstrating the flow velocity distribution of molten iron.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG. The present invention is not limited to the embodiment shown in FIG. 1, and the above-described means can be appropriately implemented in other modes as well, for example, hot metal pretreatment using a converter-type refining facility. In the case of carrying out or leaving the scrap melting furnace, it can be suitably used, for example, in the case of discharging the molten iron from the inside of the furnace at the time of producing the molten iron using the electric furnace.

  FIG. 1A shows the end of tapping the molten steel 3 from the inside of the converter 1 into the ladle 2. Generally, at the end of tapping, slag existing on the molten steel flows out from the tap hole with a vortex, but in the present embodiment, it is an object to realize tapping at high speed while suppressing the outflow.

  FIG. 1B shows an example of a detailed structure around the tap hole 4. As shown in FIG. 1 (b), perm brick 7 is constructed on the inside of the iron shell 6 and wear brick 8 is further built on the inside thereof. A tuyere brick 9 is installed at the tap hole 4 and a tuyere sleeve 10 is inserted inside the tuyere brick 9. For maintenance of the tap hole 4, it is possible to remove the bare metal attached by oxygen cleaning during charging or the like, or to replace the tuyere sleeve 10 when a crack occurs.

  Moreover, in the example shown in FIG.1 (b), the aperture | diaphragm | squeeze part 11 is provided in the exit side by integral with the tuyere sleeve 10. As shown in FIG. The narrowed portion 11 does not necessarily have to be an integral structure with the tuyere sleeve 10, and a structure capable of fixing and replacing a ring-shaped refractory as the narrowed portion 11 at the tip of the cylindrical tuyere sleeve 10, an irregular shape Even by a method in which a refractory material is built up by thermal spraying or the like to form the constricted portion 11, the effect of the present invention works equally and can be appropriately selected for the practice of the invention.

In FIG. 1 (b), H _s represents the thickness of the slag 5 _(m), H m represents the molten steel depth up refractory inner wall surface of the (m). L ₁ denotes the length (m) from the inner wall surface of the refractory to the throttling portion 11 in the tuyere sleeve 10, and L ₂ denotes the length (m) from the upper end of the throttling portion 11 to the tip of the tap hole 4 Show. Further, in the example shown in FIG. 1 (b), the inner diameter of the drawn portion 11 is constant, and in this case, the flow velocity u (m / s) of the molten steel to be tapped is expressed by the Bernoulli equation by equation (3) Is represented.
_{u = ((ρ s × H} s + ρ m × (H m + L 1)) × g) 1/2 ······· (3)
Here, ρ _s represents the specific gravity of the slag (kg / m ³ ), ρ _m represents the specific gravity of the molten steel (kg / m ³ ), and g represents the gravitational acceleration (9.8 m / s ² ).

As described above, in view of maintenance and cost, as the tuyere sleeve, one having a straight shape whose cross-sectional area is constant in the molten steel passing direction as shown in Patent Document 5 is generally adopted. However, the flow velocity u of the molten steel in this case is controlled by the sleeve inlet (refractory inner wall surface) where the nozzle cross-sectional area is minimum and the static pressure is the highest value. From this, the flow velocity u of the molten steel calculated using equation (3) is a value calculated as L ₁ = 0. In order to carry out steel tapping at such high-speed tap holes in a general-purpose tap hole, it is necessary to enlarge the diameter of the sleeve so that a large amount of molten steel can be discharged at the same flow velocity. However, in this case, the conditions under which the swirling of slag is started by the vortex are controlled by the tapping speed and the molten steel head (H _m ), so stopping the tapping while leaving a large amount of remaining hot water Operations with significant yield loss had to be carried out, and it was the biggest problem that it was not possible to extract steel at high speed by suppressing the discharge of slag.

Therefore, in the present invention, the squeeze portion is provided near the tip of the molten iron discharge passage (corresponding to the tuyere sleeve 10 in FIG. 1 (b)), which is the feature, and the molten steel amount in the furnace is compared under the same condition. Since the static pressure maximum position can be lowered, the head pressure can be increased to increase the flow rate of the steel extraction flow, and the steel extraction time can be efficiently shortened. That is, the molten steel head exerted on the height (depth) at which the outflow of slag starts is defined by (H _m + L ₁ ), and when the winding of the slag by the vortex is started, for example, the upper end of the tuyere sleeve is The residual water in the furnace can be reduced until it reaches the state filled with slag. Thereby, it is possible to suppress an increase in the outflow amount of slag when the steel tapping is performed at high speed, which becomes a problem in the operation using a general-purpose tap hole.

  In order to receive the above effects, the throttling portion in the molten iron discharge passage is provided to increase the static pressure serving as the outflow driving force, and as shown in FIG. 1B, the throttling portion is extended to the outlet tip It does not have to be provided. Providing the throttling portion in the passage as appropriate within a range that does not affect the construction or the operability does not hinder the realization of the effects of the present invention. In addition, in order to prevent the cross-sectional area of the throttling portion from being enlarged due to melting loss or the like during discharge of molten iron or during continuous charge operation, a plurality of throttlings can be performed within the range described later. You may install a department. Thereby, the load of maintenance work can be reduced.

According to the hydraulic examination by the present inventors and the operation investigation of the actual machine, the length (L ₁ + L ₂ ) of the molten steel discharge passage is approximately 600 mm even in consideration of the erosion effect of tuyere brick according to the number of converter operations. This is the above, and for the discharge by the tuyere sleeve of 100 to 200 mmφ, a stroke of 400 mm or more is provided from the end (refractory inner wall surface) on the refractory inner wall side to the narrowed portion. As described above, by lowering the maximum static pressure position, the flow velocity can be increased and the residual water in the furnace can be reduced, so in the present invention, the distance from the inner wall surface of the refractory to the throttling portion is specified as 400 mm or more. did.

  As described above, the throttling portion in the molten iron discharge passage provided in the present invention is qualitatively more effective as it approaches the tip of the molten iron discharge passage, but a throttling portion with a short stroke is installed only at the tip portion. In this case, the metal deposits in and around the tap holes due to the discharge of molten iron and the like, and there is a possibility that the metal may be damaged at the time of removing the deposited metal. Therefore, it is preferable to provide the throttling portion at a position 30 mm or more away from the tip of the molten iron discharge passage.

In addition, since the viscous fluid passes under high turbulence conditions where the molten iron, which is a viscous fluid, passes through the tap hole at a high speed on the order of several meters per second, the flow of molten iron is from the inner wall surface of the refractory to the throttling portion The influence of pressure loss can not be ruled out. When installing the throttling portion, it is not necessary to set a numerical value at the upper limit in the cross-sectional area of the passage as long as the minimum cross-sectional area in the molten iron discharge passage can be defined. It is known that when the viscous fluid is molten iron, the flow velocity distribution passing through the cylindrical tube in a turbulent flow condition follows the 1/7 power law shown in the following equation (4).
U = U _max (y / r) ^1/7 ........... (4)

Here, r represents the radius (m) of the cylindrical tube, and y represents the distance (m) from the inner wall of the cylindrical tube toward the center of the tube. Also, U _max represents the flow velocity (m / s) at the center of the cylindrical tube, and U represents the flow velocity (m / s) at the y position.

  FIG. 2 is a diagram for explaining the flow velocity distribution based on the equation (4). As shown in FIG. 2, when providing the throttling portion, if the inner diameter of the throttling portion is close to the inner diameter before the throttling portion (the inner diameter of the tuyere sleeve), the area near the inner wall of the molten iron discharge passage affected by viscosity. However, the pressure improvement effect can not be obtained. That is, the effect of providing the throttling portion appears only at the portion where the flow velocity is low, and the effect of increasing the head pressure is reduced. Therefore, according to the present invention, as shown in FIG. 2, the flow velocity in the pipe exceeds 70% of the maximum flow velocity in the pipe (tube central flow velocity) as y / r> 0.1 (as shown in FIG. 2). The cross-sectional area of the passage in the throttling portion numerically limits 80% or less of the cross-sectional area of the passage in front of the throttling portion as the throttling rate of the minimum cross-sectional area from the inner wall surface to the throttling portion. That is, the minimum cross-sectional area of the passage in the narrowed portion is 80% or less of the minimum cross-sectional area of the passage between the inner wall surface and the narrowed portion.

Furthermore, the size of the cross-sectional area itself of the tap hole is not particularly limited as long as the conditions of the above-described throttling portion are satisfied, but it substantially falls out for the converter blowing time of about 10 to 20 minutes. When the steel time exceeds 10 minutes, the effect of shortening the total cycle time of the converter according to the present invention is diminished. Therefore, the range in which the minimum cross-sectional area of the passage in the constriction part deviates from the condition of the following equation (5) is excluded from the present invention from the actual results of the furnace volume of the ordinary smelting furnace and the charged amount of molten iron.
A ≧ 50 × W (5)
Here, A indicates the minimum cross-sectional area (mm ² ) of the passage in the narrowed portion, and W indicates the amount (t) of molten iron discharged in one heat.

  In addition, in the refining process of molten iron for producing various steel types for each charge, it is possible to provide an efficient operation method by utilizing the effect of the above-described tap holes. As an example of the operation method according to the present invention, for example, in the case where a converter steelmaking process is usually operated using a conventional general-purpose straight type tap hole, especially when tapping a steel type for which high cleanliness is required, A removable inner ring between refining charges is provided as a squeezed portion at the above-described position of the molten iron discharge passage, and steel material of which high cleanliness is required in this state is steeled out to prevent cleaning after the secondary refining process. It is also possible to adopt an operation form that reduces the load efficiently. In addition, when the hatching failure at the end of the blowing process is recognized, or when the blow-off temperature is higher than the assumed temperature, the frequency at which the dephosphorization becomes insufficient becomes high. Therefore, in such a charge, the amount of slag outflow is reduced by carrying out tapping after installing the removable interior ring as described above after the end of refining and before the start of discharge of molten steel. It is possible to adopt an operation mode which reduces the amount of re-phosphorization in the ladle after deoxidation from the next refining to the continuous casting and prevents the upper limit of the P concentration on the product from being deviated.

  Next, the present invention will be further described based on examples, and the conditions in the examples are one example of conditions adopted to confirm the practicability and effects of the present invention, and the present invention The conditions are not limited to the example. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the scope of the present invention.

  In order to verify the effect of the present invention, a test was conducted to conduct blowing and tapping steel to a steel pan using an upper bottom blowing converter with a heat size of 350 t / ch. Hot metal before blowing was blown at a scrap blending ratio of 15% using the compositions and temperatures shown in Table 1 below. At this time, using a cylindrical sleeve with a stroke from the inner wall of the converter to the outlet of 800 mm and an inner diameter of 180 mm installed in the tap hole, the inner diameter 150 mm, length 200 mm, outer diameter 170 mm The refractory ring was inserted, and its periphery and the inner surface of the cylindrical sleeve were fixed with an irregular repair material. As a result, the reduction ratio of the minimum cross-sectional area of the narrowed portion was 69% (the minimum cross-sectional area of the passage in the narrowed portion was 69% of the minimum cross-sectional area of the passage between the inner wall surface and the narrowed portion).

  When the temperature was measured with a sublance after the completion of blasting and further sampling was performed, the composition of the molten steel was [C]: 0.04-0.08 mass%, [Si] <0.05 mass%, [P] It was: 0.013-0.017 mass%, [Mn] <0.03 mass%, [S]: 0.01-0.015 mass%, and the temperature was in the range of 1630 ° C. to 1660 ° C. After that, the tilting of the furnace body was started, and from the time when the outflow of molten steel from the tap hole was started, the time until the effluent from the tap hole disappeared by tilting return was measured, and the steel tapping time was measured. In addition, after completion of steel tapping, a metal rod for slag thickness measurement was immersed, and the slag thickness on the pan was measured for each charge, and used as an index of the slag outflow amount. Table 2 below shows the results of the test run.

Example 1 is an experimental result by the tap hole which matched the refractory ring as a squeeze part with the lower end of the sleeve and was constructed. The position of the narrowed portion described in Table 2 corresponds to L ₂ / (L ₁ + L ₂ ) × 100 (%) shown in FIG. 1 (b), and the length L ₁ from the refractory inner wall surface to the narrowed portion is It is 600 mm. The steel tapping time at this time was 4 minutes or more, and steel tapping was possible in the same time as Comparative Example 1 in which the refractory ring was not used. In addition, it was possible to complete steel extraction with a small amount of slag thickness equivalent to Comparative Example 2 using a small diameter cylindrical sleeve having the same size as the inner diameter of the refractory ring without using the refractory ring.

Further, Example 2 is an example of changing a position different from the working position of the refractory ring as in Example 1, from refractory inner wall surface in _{L 2 / (L 1 + L} 2) × 100 = 37.5% the length L ₁ to the diaphragm portion is 500 mm. Also in the case of Example 2, good results almost equivalent to Example 1 were obtained.

On the other hand, although the test result by the tap hole (straight sleeve) which is a prior art is shown as a comparative example, in comparative example 1 which is not equipped with a refractory ring, a large amount of slag flows out compared with Examples 1 and 2. The load of the refining process performed in the post process to maintain the quality was increased. Further, in Comparative Example 2 using the cylindrical sleeve having the same inner diameter as the refractory ring, L ₁ = 0 is considered in the Bernoulli's formula described above, and the flow velocity u of the molten steel is smaller than those of Examples 1 and 2; The time was longer than that of Examples 1 and 2 by 2 minutes or more, and the operation was difficult to maintain high productivity.

  According to the present invention, tap holes used in the process of discharging molten iron such as molten iron and molten steel produced in a converter or electric furnace to a container such as a ladle, and by using the same, quality in the subsequent process It is possible to realize shortening of the molten iron discharge time and to realize productivity improvement etc. while suppressing the increase in the outflow amount of slag which adversely affects, and its industrial utility value is extremely high.

1 converter 2 ladle 3 molten steel 4 tap hole 5 slag 6 iron skin 7 permanent brick 8 wear brick 9 tuyere brick 10 tuyere sleeve 11 drawing part

Claims (2)

In the tap hole for discharging the molten iron from the refractory inner wall of the smelting vessel to the outside of the smelting vessel during the smelting charge or after the end of the smelting and before the start of the molten iron discharge,
The diaphragm Ri part to be inscribed in the taphole provided at a position apart more than 400mm from the end of the refractory inner wall,
L ₂ / (L ₁ + L ₂ ) × 100 (%), which indicates the position of the narrowed portion, is 37.5% or less,
The minimum cross-sectional area A of the passage in the narrowed portion is 80% or less of the minimum cross-sectional area of the passage between the end on the inner wall side of the refractory and the narrowed portion,
And the said molten iron is discharged so that the following (2) Formula may be satisfied, The molten iron discharge working method characterized by the above- mentioned.
A 50 50 × W ············· (2)
Here, A indicates the minimum cross-sectional area (mm ² ) of the passage in the squeezed portion, W indicates the amount of molten iron (t) discharged in one heat, and L ₁ indicates the upper end of the squeezed portion from the end on the refractory inner wall side until the length (m), L ₂ represents the length (m) to the tip of the molten iron discharge passage from the upper end of the narrowed portion. The molten iron discharging work method according to claim 1, wherein the narrowed portion is provided at a position separated by 30 mm or more from a tip of the molten iron discharge passage.