JP5061624B2 - Method for estimating flow rate of molten steel in RH vacuum degassing apparatus and gas blowing method for recirculation - Google Patents

Description

  The present invention relates to a method for estimating a flow rate of a molten steel in an RH vacuum degassing apparatus that performs vacuum degassing refining on molten steel, and a method for blowing a circulating gas in the RH vacuum degassing apparatus.

  In recent years, steel grades that require vacuum degassing and refining have been increasing along with the upgrading of steel and the expansion of applications, and it is strongly desired to shorten the processing time from the viewpoint of increasing the throughput. It is in. A typical facility for carrying out this vacuum degassing refining is an RH vacuum degassing apparatus, and most of the molten steel excluding special products is subjected to vacuum degassing refining by the RH vacuum degassing apparatus.

  The RH vacuum degassing apparatus includes a vacuum tank and two dip pipes (an ascending side dip pipe and a descending side dip pipe) provided at the lower part thereof, and refines molten steel using the RH vacuum degassing apparatus. In this case, two dip tubes are immersed in the molten steel contained in the ladle, the inside of the vacuum chamber is decompressed, the molten steel is pulled up into the dip tube, and the recirculation gas provided in the rising side dip tube. An inert gas such as Ar gas is blown as a recirculation gas from the blowing nozzle, and the molten steel is raised and fed into the vacuum chamber according to the principle of the gas lift pump, vacuum processing is performed in the vacuum chamber, and the ladle from the descending dip tube It is back in. Thus, vacuum refining is performed continuously by circulating the molten steel between the ladle and the vacuum chamber. Therefore, in order to increase the processing capacity and the processing efficiency in the RH vacuum degassing apparatus, it is necessary to increase the amount of molten steel passing through the vacuum tank per unit time, that is, the ring flow rate per unit time.

  It has been empirically known that the flow rate of molten steel per unit time depends on the inner diameter of the dip tube, the flow rate of the recirculation gas, the pressure difference between the vacuum chamber and the atmosphere, etc. The circulation flow rate has been increased by increasing the circulation gas flow rate. However, the expansion of the inner diameter of the dip tube is accompanied by a significant modification of the equipment, resulting in an increase in equipment costs, and even if it is enlarged, there are limits to the size of the vacuum tank and ladle. On the other hand, although an increase in the recirculation gas flow rate is effective, if the recirculation gas flow rate is increased beyond a certain limit, the recirculation gas blow-through occurs, and conversely, the molten steel ring flow rate decreases.

In order to solve these problems, Patent Documents 1 and 2 have been proposed. Patent Document 1 proposes a method in which the circulating gas blowing nozzle is divided into two systems of a first system and a second system, and the blowing pressure of the second system is set higher than that of the first system. . By blowing the reflux gas in this way, the dip tube is filled with bubbles of the reflux gas, and the flow rate of the molten steel is increased. On the other hand, in Patent Document 2, while adjusting the inner diameter of the dip tube, the number of circulating gas blowing nozzles, the inner diameter of the circulating gas blowing nozzle, and the circulating gas flow rate so as to satisfy a predetermined relationship. A method of blowing in the reflux gas, that is, a method of blowing in the reflux gas under the optimum conditions considering not only the inner diameter of the dip tube and the flow rate of the reflux gas but also the inner diameter and the number of the installed nozzles of the reflux gas has been proposed. Yes. It is said that the molten steel can be efficiently recirculated by blowing the recirculation gas in this way.
Japanese Unexamined Patent Publication No. 64-79317 JP 2002-363636 A

  By the above conventional method, the molten steel can be efficiently circulated, and as a result, shortening of the refining time, reduction of components to be removed, reduction of the amount of gas used for recirculation, extension of the life of the dip tube, etc. to some extent However, the influence of the number of circulating gas blowing nozzles on the circulation flow rate or the influence of the inner diameter of the circulating gas blowing nozzles has not yet been fully confirmed and is not necessarily optimal. It's hard to say that it is operating in a recirculating condition.

  The present invention has been made in view of such circumstances. The object of the present invention is to influence the number of circulating gas blowing nozzles on the flow rate of the molten steel ring in the RH vacuum degassing apparatus and the number of circulating gas blowing nozzles. Providing a method of estimating the flow rate of the molten steel by clarifying the influence of the inner diameter, and a method of injecting a circulating gas that can adjust the flow rate of the molten steel to the maximum and perform efficient refining It is to be.

In order to solve the above problems, the molten steel ring flow rate estimation method of the RH vacuum degassing apparatus according to the present invention blows a reflux gas from a dip pipe in which a plurality of reflux gas blow nozzles are arranged, and enters the inside of the dip pipe. An RH vacuum degassing apparatus that forms a plurality of bubbles in existing molten steel and circulates the molten steel between a ladle and a vacuum chamber, and the reflux gas is used so that the plurality of bubbles do not overlap each other. When estimating the flow rate of the molten steel with the RH vacuum degassing apparatus to be blown, the flow rate of the molten steel is calculated using the following (1) using the flow rate of the recirculation gas, the number of the recirculation gas blow nozzles and the inner diameter of the recirculation gas blow nozzle. ) Is calculated by the equation.

However, in (1), W is the molten steel ring flow (kg / sec), N is the ring diverted gas injectors installed number of the nozzle, the bubble diameter of d _b the ring diverted gas (m), Q _g the ring diverted gas flow rate (M ³ (standard state) / sec), and d _b is expressed by the following equation (2).

In equation (2), σ is the surface tension of molten steel (dyn / cm), d ₀ is the inner diameter (m) of the circulating gas blowing nozzle, ρ _l is the molten steel density (kg / m ³ ), and g is the acceleration of gravity. (M / sec ² ), Q _g is the circulating gas flow rate (m ³ (standard state) / sec), and N is the number of circulating gas blowing nozzles.

In addition, in order to solve the above problems, the reflux gas blowing method of the RH vacuum degassing apparatus according to the present invention blows a reflux gas from a dip tube in which a plurality of reflux gas blow nozzles are arranged , An RH vacuum degassing device that forms a plurality of bubbles in molten steel existing inside and circulates the molten steel between a ladle and a vacuum tank, and is used for reflux so that the plurality of bubbles do not overlap each other. a ring diverted gas blowing method of RH vacuum degassing apparatus for blowing gas, the recirculation flow of the molten steel, the ring diverted gas flow rate, installation number and ring diverted gas ring diverted gas blowing nozzle blowing with an inner diameter of the nozzle below (1) Calculated by the formula, and so that the calculated molten steel ring flow rate becomes the target molten steel ring flow rate, the circulating gas flow rate, the number of circulating gas blowing nozzles installed, the inner diameter of the circulating gas blowing nozzle It is characterized in that for adjusting at least one or more out.

However, in (1), W is the molten steel ring flow (kg / sec), N is the ring diverted gas injectors installed number of the nozzle, the bubble diameter of d _b the ring diverted gas (m), Q _g the ring diverted gas flow rate (M ³ (standard state) / sec), and d _b is expressed by the following equation (2).

In equation (2), σ is the surface tension of molten steel (dyn / cm), d ₀ is the inner diameter (m) of the circulating gas blowing nozzle, ρ _l is the molten steel density (kg / m ³ ), and g is the acceleration of gravity. (M / sec ² ), Q _g is the circulating gas flow rate (m ³ (standard state) / sec), and N is the number of circulating gas blowing nozzles.

  According to the present invention, it is possible to accurately grasp the molten steel ring flow rate that has been vague in the past from the recirculation gas flow rate, the number of installed recirculation gas blowing nozzles, and the inner diameter of the recirculation gas blowing nozzle. Also, by accurately grasping the molten steel ring flow rate, it is possible to adjust the molten steel ring flow rate by adjusting at least one of the circulating gas flow rate, the number of circulating gas blowing nozzles installed, and the inner diameter of the circulating gas blowing nozzle. As a result, it is possible to carry out the prescribed RH vacuum degassing refining under any conditions, and as a result, it is possible to perform stable RH vacuum degassing without any component detachment. It becomes.

  Hereinafter, the present invention will be specifically described with reference to the drawings.

  FIG. 1 is a schematic longitudinal sectional view of an RH vacuum degassing apparatus. As shown in FIG. 1, the RH vacuum degassing apparatus 1 includes a vacuum tank 5 composed of an upper tank 6 and a lower tank 7, and an ascending-side dip pipe 8 and a descending-side dip pipe 9 provided below the lower tank 7. The upper tank 6 is provided with a duct 11 connected to an exhaust device (not shown), and a raw material charging port 12 for charging a component adjusting alloy iron and the like. A recirculation gas blowing nozzle 10 for blowing recirculation gas is provided. From the reflux gas blowing nozzle 10, Ar gas is blown into the rising side dip tube 8 as the reflux gas. Although only one recirculation gas blowing nozzle 10 is shown in FIG. 1, a plurality (N) of recirculation gas blowing branches from one supply pipe in the circumferential direction of the ascending-side dip pipe 8. The nozzle 10 is installed with the discharge direction as a horizontal direction toward the center of the ascending-side dip tube 8. From the viewpoint of raising the molten steel 3 uniformly in the circumferential direction of the ascending side dip tube 8, it is desirable that the reflux gas blowing nozzles 10 be installed at equal intervals in the circumferential direction of the ascending side dip tube 8, if possible. In FIG. 1, the discharge direction of the recirculation gas blowing nozzle 10 is the horizontal direction toward the center of the ascending-side dip tube 8, but it is upward or downward, or inclined from the direction toward the center to the horizontal direction. It is good also as a direction.

  In the RH vacuum degassing apparatus 1 having such a configuration, the ladle 2 containing the molten steel 3 refined in a converter or an electric furnace is transported directly under the vacuum tank 5 and is taken up by a lifting device (not shown). 2 is raised, and the ascending side dip tube 8 and the descending side dip tube 9 are dipped in the molten steel 3 accommodated in the pan 2. The ladle 2 is partially mixed with slag 4 generated by refining in a converter or an electric furnace, and covers the molten steel 3 surface. Then, Ar gas is blown into the ascending-side dip tube 8 from the circulating gas blowing nozzle 10. Before and after the blowing of Ar gas, the inside of the vacuum chamber 5 is evacuated by the exhaust device through the duct 11 to decompress the inside of the vacuum chamber 5. When the inside of the vacuum chamber 5 is depressurized, the molten steel 3 accommodated in the ladle 2 ascends the rising side dip tube 8 together with the Ar gas bubbles 13 blown from the recirculation gas blowing nozzle 10 to the vacuum chamber 5. After flowing in, a flow returning to the ladle 2 through the descending side dip pipe 9 is formed, so-called recirculation, and RH vacuum degassing is performed.

  In this case, even if the circulating gas flow rate is the same, if the number of circulating gas blowing nozzles 10 is too small, the circulating gas flow rate per one circulating gas blowing nozzle 10 increases excessively. When the bubble 13 becomes large and the circulating gas blows through and inhibits the circulating flow of the molten steel 3. On the other hand, when the number of the circulating gas blowing nozzles 10 is too large, the nozzle 1 of the circulating gas blowing nozzle 10. The flow rate of the circulating gas per book decreases too much, the discharge flow rate of the circulating gas from the circulating gas blowing nozzle 10 becomes slow, and the blown Ar gas rises along the inner wall of the ascending-side dip tube 8, Not only is there no effect on the recirculation of the molten steel 3, but it also promotes melting of the inner wall of the dip tube. Similarly, the inner diameter of the circulating gas blowing nozzle 10 influences the discharge flow rate of the circulating gas from the circulating gas blowing nozzle 10 and has an important influence on the molten steel ring flow rate.

  Therefore, the effect of the number of the circulating gas blowing nozzles 10 and the inner diameter of the circulating gas blowing nozzle 10 on the molten steel ring flow rate were investigated by water model experiments.

FIG. 2 is a conceptual diagram schematically showing the state of the inside of the ascending side dip tube 8, and N circulating gas blowing nozzles 10 are arranged at equal intervals on the same horizontal plane in the circumferential direction of the ascending side dip tube 8. This is an example of arrangement. In FIG. 2, D _P is the inner diameter (m 2) of the ascending-side dip tube 8, d ₀ is the inner diameter (m 2) of the circulating gas blowing nozzle 10, d _b ′ is the bubble diameter (m 2) after temperature correction, and d _b max Is the maximum bubble diameter (m 2) where the bubbles do not overlap, L _b is the horizontal reach distance of the bubble 13, θ _N is the circumferential angle (rad) sandwiched between the adjacent circulating gas blowing nozzles 10, θ _N Is 2π / N.

Ar gas blown into the ascending-side dip tube 8 from the reflux gas blowing nozzle 10 forms bubbles 13 and raises the molten steel 3 by the principle of a gas lift pump. At this time, if the diameter of the bubble 13 formed at the outlet of the circulating gas blowing nozzle 10 is d _b (m), this bubble diameter (d _b ) is expressed by the following equation (2) in Document 1. (Reference 1: Sano et al., Iron and steel, vol.14, p.2308). Where σ is the molten steel surface tension (dyn / cm), ρ _l is the molten steel density (kg / m ³ ), g is the gravitational acceleration (m / sec ² ), and Q _g is the reflux gas flow rate. (M ³ (standard state) / sec).

Since the molten steel 3 exists inside the ascending-side dip tube 8, the bubbles 13 formed at the outlet of the circulating gas blowing nozzle 10 are affected by the molten steel temperature and expand. If the temperature of the molten steel 3 is T _m (K) and the temperature of Ar gas at the outlet of the circulating gas blowing nozzle 10 is T _g (K), the bubble diameter after thermal expansion, that is, the bubble diameter after temperature correction (d _b ′) is expressed by the following equation (3).

As is clear from the equation (3), the bubbles 13 receive the heat of the molten steel 3 and become 1.5 to 1.8 times larger. If the bubbles 13 overlap and coalesce, the effect of the gas lift pump is greatly reduced. Therefore, it is necessary to blow in Ar gas for reflux so that the bubbles 13 do not overlap. Maximum bubble size bubbles together do not overlap (d _b max) is geometrically from the positional relationship shown in FIG. 2, obtained by the following equation (4).

Here, the horizontal direction reachable distance (L _b ) of the bubbles 13 is proposed in Document 2 to be expressed by the following formula (5) (Document 2: Ishibashi et al., Iron and Steel, 1979, A133). . In equation (5), ρ _g is the density of Ar gas for reflux (kg / m ³ ), V _g is the gas flow velocity (m / sec) at the outlet of the reflux gas injection nozzle, and g is the acceleration of gravity (m / sec). ² ).

Here, the gas flow velocity (V _g ) at the outlet of the recirculation gas blowing nozzle can be obtained by the following equation (6).

That is, as the bubble size after temperature correction (d _b ') is smaller than the maximum bubble diameter (d _b max), the inside diameter of the installation number (N), the ring diverted gas blowing nozzle 10 of the ring diverted gas blowing nozzle 10 (D ₀ ) and the recirculation gas flow rate (Q _g ) are set. This can be achieved as follows. That is, any one of these three elements is determined, and the other two elements are set accordingly, and any two of these three elements are determined, One other element may be set accordingly.

A water model experiment was conducted with this condition satisfied, and the influence of bubble size and bubble generation frequency on the ring flow rate was investigated. In this test, the bubble size is evaluated by the horizontal bubble projection area (Sb, unit: m ² ) shown in the following equation (7), and the bubble generation frequency (F _b , unit: 1 / sec). ) Was evaluated by a numerical value calculated by the following equation (8) from the reflux gas flow rate (Q _g ) and the bubble diameter (d _b ).

The test was carried out under various conditions, and the influence of the bubble projection area (S _b ) and bubble generation frequency (F _b ) on the ring flow rate was analyzed by a dimensional analysis method. As a result, the following formula (9) was obtained. That is, when the ring flow rate of the molten steel 3 is W, the molten steel ring flow rate (W) is proportional to the 0.643th power of the bubble projection area (S _b ) and the bubble generation frequency (F _b ) power of 0.881 power. It was found to be proportional to

Substituting the equations (7) and (8) into the equation (9) and further converting the bubble diameter (d _b ′) into the bubble diameter (d _b ) using the equation (3), the following (1) The formula is obtained.

That is, molten steel ring flow (W) is proportional to -0.238 square of installation number of rings diverted gas blowing nozzle 10 (N), proportional to -1.357 square of the cell diameter of the ring diverted gas (d _b) And proportional to the 0.881 power of the reflux gas flow rate (Q _g ). That is, from the above equation (1), the molten steel ring flow rate (W _g ) is _{calculated from the} recirculation gas flow rate (Q _g ), the number of installed recirculation gas injection nozzles (N), and the inner diameter (d ₀ ) of the recirculation gas injection nozzle 10. ) Can be calculated accurately. Further, when the obtained molten steel ring flow rate (W) is different from the target molten steel ring flow rate, the circulating gas flow rate (Q _g ), by adjusting at least one of the number of circulating gas blowing nozzles (N) and the inner diameter (d ₀ ) of the circulating gas blowing nozzle, the target molten steel ring flow rate can be obtained.

Furthermore, the molten steel ring flow rate (W) at a certain predetermined recirculation gas flow rate (Q _g ) according to the specifications of the RH vacuum degassing apparatus 1 is set to the number of installed recirculation gas blowing nozzles 10 (N) and The number of installed recirculation gas blowing nozzles 10 under the condition that the inner diameter (d ₀ ) of the recirculation gas blowing nozzle 10 is changed and calculated by the above equation (1) and the calculated molten steel ring flow rate (W) is maximized. If (N) and the inner diameter (d ₀ ) of the circulating gas blowing nozzle 10 are employed, the ring flow rate of the molten steel 3 becomes maximum, and RH vacuum degassing can be performed efficiently. In this case, when the number (N) of the circulating gas blowing nozzles 10 and the inner diameter (d ₀ ) of the circulating gas blowing nozzles 10 are already determined in terms of equipment, various circulating gas flow rates (Q _g ) are used. The equation (1) is calculated by changing the flow rate, and the circulating gas flow rate (Q _g ) under the condition that the calculated molten steel ring flow rate (W) is maximized may be adopted.

In calculating these equations, the surface tension (σ) of the molten steel 3 is 1540 dyn / cm, the density of Ar gas for reflux (ρ _g ) is 1.786 kg / m ³ , and the density (ρ _l ) of the molten steel 3 is It may be set to 7000 kg / m ³ . The maximum value of the inner diameter (d ₀ ) of the circulating gas blowing nozzle 10 may be considered to be about 10 mm.

In addition, before adopting the calculated conditions, the circulating gas flow rate (Q _g ) to be adopted, the number of installed circulating gas blowing nozzles (N), and the inner diameter (d ₀ ) of the circulating gas blowing nozzle 10 using 'calculates and maximum bubble size (d _b max), bubble diameter after temperature correction (d _b bubble size after temperature correction (d _b)') than the maximum bubble diameter (d _b max) It is preferable to confirm that it becomes smaller. Bubble diameter after temperature correction (d _b ') if is greater than the maximum bubble diameter (d _b max) is to such redo the calculation again, the bubble diameter of the temperature-corrected (d _b') up to it is desirable that newly obtaining the smaller becomes conditions than bubble diameter (d _b max).

Thus, in the present invention, while considering the inner diameter (D _P ) of the ascending-side dip tube 8, the circulating gas flow rate (Q _g ), the number of installed circulating gas blowing nozzles (N), the circulating gas Since the Ar gas for recirculation is blown with the inner diameter (d ₀ ) of the blow nozzle 10 as the optimum condition, the molten steel 3 can be recirculated extremely efficiently, and as a result, the refining time is shortened, the components to be removed are reduced, and the recirculation is used. It becomes possible to reduce the amount of Ar gas used, extend the life of the dip tube, and the like.

  In the above description, the circulating gas blowing nozzles 10 are arranged on the same horizontal plane. However, this is for ease of explanation, and there is no need to arrange them on the same horizontal plane. Further, although the circulating gas blowing nozzles 10 are arranged at equal intervals in the circumferential direction, there is no need to arrange them at equal intervals.

It is a schematic longitudinal cross-section of RH vacuum degassing apparatus. It is a conceptual diagram which shows typically the condition inside the ascending-side dip tube.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 RH vacuum degassing apparatus 2 Ladle 3 Molten steel 4 Slag 5 Vacuum tank 6 Upper tank 7 Lower tank 8 Rising side immersion pipe 9 Lowering side immersion pipe 10 Recirculation gas blowing nozzle 11 Duct 12 Raw material inlet 13 Bubble

Claims (2)

A gas for recirculation is blown from a dip tube in which a plurality of gas recirculation gas blowing nozzles are arranged to form a plurality of bubbles in the molten steel existing inside the dip tube, and the molten steel is circulated between the ladle and the vacuum chamber. The RH vacuum degassing apparatus is a RH vacuum degassing apparatus for estimating the flow rate of molten steel with an RH vacuum degassing apparatus that blows in a reflux gas so that each of the plurality of bubbles does not overlap. A molten steel ring flow rate estimation method for an RH vacuum degassing apparatus, which is calculated by the following equation (1) using the gas flow rate, the number of circulating gas blowing nozzles and the inner diameter of the circulating gas blowing nozzle.

However, in (1), W is the molten steel ring flow (kg / sec), N is the ring diverted gas injectors installed number of the nozzle, the bubble diameter of d _b the ring diverted gas (m), Q _g the ring diverted gas flow rate (M ³ (standard state) / sec), and d _b is expressed by the following equation (2).

In equation (2), σ is the surface tension of molten steel (dyn / cm), d ₀ is the inner diameter (m) of the circulating gas blowing nozzle, ρ _l is the molten steel density (kg / m ³ ), and g is the acceleration of gravity. (M / sec ² ), Q _g is the circulating gas flow rate (m ³ (standard state) / sec), and N is the number of circulating gas blowing nozzles. A gas for recirculation is blown from a dip tube in which a plurality of gas recirculation gas blowing nozzles are arranged to form a plurality of bubbles in the molten steel existing inside the dip tube, and the molten steel is circulated between the ladle and the vacuum chamber. a RH vacuum degassing apparatus causes the plurality of a ring diverted gas blowing method of RH vacuum degassing apparatus for blowing ring diverted gas so as not to overlap each bubble, the recirculation amount of the molten steel, the ring diverted Calculate by the following formula (1) using the gas flow rate, the number of circulating gas blowing nozzles installed and the inner diameter of the circulating gas blowing nozzle, so that the calculated molten steel ring flow rate becomes the target molten steel ring flow rate, At least one of the circulating gas flow rate, the number of circulating gas blowing nozzles installed, and the inner diameter of the circulating gas blowing nozzle is adjusted, and the circulating gas blowing of the RH vacuum degassing apparatus is characterized in that Only way.

However, in (1), W is the molten steel ring flow (kg / sec), N is the ring diverted gas injectors installed number of the nozzle, the bubble diameter of d _b the ring diverted gas (m), Q _g the ring diverted gas flow rate (M ³ (standard state) / sec), and d _b is expressed by the following equation (2).

In equation (2), σ is the surface tension of molten steel (dyn / cm), d ₀ is the inner diameter (m) of the circulating gas blowing nozzle, ρ _l is the molten steel density (kg / m ³ ), and g is the acceleration of gravity. (M / sec ² ), Q _g is the circulating gas flow rate (m ³ (standard state) / sec), and N is the number of circulating gas blowing nozzles.

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