JP4980175B2 - Lance for molten iron refining and molten iron refining method - Google Patents

Description

  The present invention relates to a method for blowing oxygen gas in molten iron refining using an upper blowing lance.

  Taking a steelmaking converter as an example, the refining reaction in the top blowing and top bottom blowing converter proceeds by supplying oxygen gas from the top blowing lance and burning impurities such as carbon, silicon, and phosphorus. To do. In top blowing converters before the development of top bottom blowing converters, oxygen gas is supplied and top blown oxygen gas is used to enhance iron bath agitation and promote metallurgical reactions such as decarburization and dephosphorization. Has been aimed at so-called hard blow, which causes a strong jet to collide with the bath surface. For this reason, single-hole or multi-hole medium and narrow wide nozzles (Laval nozzles) are generally employed for the purpose of converting oxygen gas pressure at the lance nozzle inlet side into kinetic energy of the jet with high efficiency (non-patent literature) 1). At this time, the oxygen pressure at the nozzle inlet side is set so that a rectified supersonic jet with less turbulence and attenuation is formed by making the pressure of the oxygen gas ejected from the Laval nozzle almost equal to the atmospheric pressure. The oxygen blowing method to be adjusted is generally used. The condition in which this rectified supersonic jet is an appropriate expansion jet and the pressure at the nozzle outlet is almost equal to the atmospheric pressure is called an appropriate expansion condition.

  However, deep cavities are formed on the bath surface by hard blow, and along with this, the amount of spitting and dust generation in which granular iron scatters increases. For this reason, the yield of molten steel is lowered, and spitting causes operational troubles such as with a furnace mouth metal. In particular, since the refining reaction rate is controlled by the oxygen supply rate from the initial to the middle stage of converter refining, it is necessary to supply a large amount of oxygen gas in a short time. As a result, the amount of spitting and dust generation increases. Therefore, in the current top-bottom blow converter in which stirring of the steel bath is ensured by the bottom-blown gas, the soft blow that weakens the jet strength as much as possible while maintaining the high oxygen gas flow rate is performed in the stage from the beginning of refining to the middle stage. desirable.

  On the other hand, the decarburization reaction at the end of refining is rate-controlled by the mass transfer of carbon in molten iron near the fire point. Therefore, at the end of refining, when the carbon concentration decreases and the amount of carbon supplied to the fire point decreases, excessive oxygen supply leads to iron peroxidation and chromium peroxidation in the case of stainless steel refining, and iron and chromium Therefore, it is desirable to reduce the oxygen flow rate in accordance with the amount of carbon supplied, because the oxygen concentration in the steel also increases and the deoxidation cost after steel is increased. Further, in order to promote the mass transfer of carbon at the hot spot and improve the decarburization reaction efficiency, it is better to use a hard blow to strengthen the stirring of the hot spot portion. In addition, if too much soft blow is used, secondary combustion of CO gas occurs in the furnace, and oxygen gas jets collide with the furnace wall, resulting in decreased oxygen gas reaction efficiency and increased refractory wear. This causes problems. From the above, in the final stage of refining, a hard blow that increases the jet strength as much as possible while reducing the oxygen gas flow rate is desirable, but in the conventional general oxygen blowing method, the soft blow becomes as the oxygen flow rate decreases, The problem as described above is likely to occur.

  As a means for reducing spitting and dust generation, it is effective to make a lance porous, which can disperse the collision energy of the jet against the bath surface, and a porous lance is widely used in current steelmaking converters. Porous lances are nozzles with a fixed inclination angle on the same circumference. The larger the number of holes, the greater the effect of dispersing the collision energy of the jet. Is a problem. That is, in the portion where the jets overlap to form one jet, the energy dispersed by the porosity is added again, so that hard blow occurs and a deep cavity is formed.

  As one means for solving this problem, a method of increasing the inclination angle of the porous lance and reducing the overlap of the cavities (Patent Document 1) has been proposed. In order to reduce the overlap of the cavities more effectively, a method (Patent Document 2) in which two types of nozzles having different inclination angles are alternately arranged has been proposed. Furthermore, a method (Patent Document 3) has also been proposed in which the nozzle diameter of the smaller tilt angle, which has a great influence on the increase in spitting, is made smaller so that the strength is weaker than the jet ejected from the other nozzle.

As a means for preventing peroxidation by strengthening the stirring force when the oxygen gas flow rate is reduced at the end of refining, for example, a spindle is provided in the oxygen pipe, and the pipe is moved up and down by moving the spindle up and down. A converter steelmaking lance has been proposed in which the cross-sectional area of the throat portion is made variable and the oxygen flow rate is reduced while maintaining the flow velocity at the outlet of the oxygen gas jet (Patent Document 4).
In addition, for the purpose of suppressing chromium oxidation at the end of stainless steel refining, a method of mixing a non-oxidizing diluent gas such as nitrogen with the top blowing gas (for example, Patent Document 5 and Patent Document 6) has also been proposed.

  In addition, as a means to achieve both spitting from the early stages of refining and reduction of dust generation and peroxidation suppression at the end of the process, a method of using an inappropriate expansion state in which the oxygen jet is intentionally removed from the appropriate expansion conditions Has been proposed. In other words, a soft blow is used as an improper expansion state from the beginning to the middle of refining, and a hard blow that keeps the jet flow velocity substantially constant even when the oxygen flow rate is reduced by approaching the appropriate expansion state at the end of refining (patented) Document 7 and Patent Document 8). Note that Non-Patent Document 2 describes the results of investigating improper expansion behavior in particular regarding the jet flow behavior of a converter top blowing lance using a Laval nozzle.

JP-A-60-165313 Japanese Patent No. 2848010 Japanese Patent No. 3424534 Japanese Patent Publication No.47-4770 JP 58-130216 A Japanese Examined Patent Publication No. 1-54409 Japanese Patent No. 3565662 JP-A-10-219332 3rd edition “Steel Handbook”, Volume II, Japan Iron and Steel Institute, 1982, p. 468 K.Naito et.al., “Characteristics of Jets from Top-blown Lance in Converter”, ISIJ International, Vol.40, No.1, pp.23-30

  In the method of increasing the inclination angle of the porous lance and reducing the overlap of the cavities, since the inclination angles of the nozzles are all equal, it is necessary to increase the inclination angle sufficiently to obtain the effect. There was a problem that the wear of refractory increased significantly due to collision.

  In the method of alternately arranging two types of nozzles with different inclination angles, spitting suppression is insufficient when the oxygen gas flow rate is significantly increased, and soft blow occurs when the oxygen gas flow rate is reduced at the end of refining. There were problems such as. In addition, by reducing the nozzle diameter of the smaller tilt angle and reducing the strength compared to the jet ejected from the other nozzle, the oxygen gas from the smaller tilt angle nozzle contributes greatly to the stirring of the hot spot. Since the flow rate was small, there was a problem that hard blow could not be maintained enough to enhance the stirring of the hot spot when the oxygen gas flow rate was reduced at the end of refining.

  In the method of moving the spindle provided in the pipe up and down, the spindle driving mechanism becomes complicated, requiring a large equipment cost, and spitting increases due to the merged jet.

  In stainless steel refining, the method of mixing non-oxidizing diluent gas increases the cost of gas when argon gas is used, causes nitrogen pick-up when nitrogen gas is used, and lowers the temperature of molten iron There was a problem such as.

  The method using the improper expansion state uses the characteristics of a single oxygen jet ejected from each nozzle, and the control range of the jet strength is narrow, reducing the amount of spitting and dust generation and the end of refining There was a problem that the peroxidation inhibitory effect of can not be sufficiently compatible.

  The present invention increases the control range of the jet strength when the oxygen gas flow rate is changed, stably reduces spitting and dust generation at the time of high oxygen gas flow rate from the initial stage of refining to the middle stage, and at the end of the refining stage. It is an object of the present invention to provide a method for stably suppressing the oxidation amount of iron or chromium at the time when the oxygen gas flow rate is reduced.

In order to solve this problem, the gist of the present invention is as follows.
(1) A molten iron refining lance 1 used for refining molten iron while supplying oxygen gas, wherein the angle between the longitudinal direction of the lance and the nozzle ejection direction is an inclination angle θ, and three or more nozzles having a small inclination angle 21 and three or more nozzles 22 having a large inclination angle, the total number of nozzles of the nozzle 21 and the large nozzle 22 having a small inclination angle is an even number, and the inclination angle θ1 of the nozzle having a small inclination angle and the inclination of the large nozzle The angle θ2 is different within a range of 5 degrees or more and 15 degrees or less, and the nozzles 21 having a small inclination angle and the nozzles 22 having a large inclination angle are alternately arranged in the circumferential direction, and the proper expansion absolute pressure P _0P1 and the inclination angle of the nozzle 21 having a small inclination angle. the proper inflation absolute pressure P _0P2 of the large nozzle 22, the maximum value P _0max of nozzle inlet side absolute pressure P ₀ in the refining, that is limited to a range of the following formula (1) and (2) Lance for molten iron refining and butterflies.
P _0max /2.0≦P _0P1 ≦ P _0max /1.3 (1)
P _0max /1.3 <P _0P2 ≦ P _0max /0.8 (2)
(2) When refining molten iron while supplying oxygen gas, the angle between the longitudinal direction of the lance and the nozzle ejection direction is the inclination angle θ, and the nozzles 21 having three or more small inclination angles and three or more inclination angles are used. The total nozzle number of the nozzle 21 having the large nozzle 22 and the small tilt angle 21 and the large nozzle 22 is an even number, and the tilt angle θ1 of the small tilt angle and the tilt angle θ2 of the large nozzle are different within a range of 15 degrees or less. Using the molten iron refining lance in which the nozzles 21 with the small inclination angle and the nozzles 22 with the large inclination are alternately arranged in the circumferential direction, the absolute pressure P ₀ at the nozzle inlet side during refining is set to the proper expansion absolute of the nozzle with the small inclination angle. _{Refinement of} molten iron, characterized by adjusting the flow rate of the top blown oxygen within the range of the following formulas (3) to (5) with respect to the pressure P _0P1 and the appropriate expansion absolute pressure P _{0P2 of the} nozzle having a large inclination angle Method.
0.8 × P _0P1 ≦ P ₀ ≦ 2.0 × P _0P1 (3)
0 <P ₀ <1.3 × P _0P2 (4)
P _0P1 <P _0P2 (5)
(3) the maximum value P _0max of nozzle inlet side absolute pressure P ₀ during refining in the following ranges (6) and (7), the minimum value P _0min nozzle inlet side absolute pressure P ₀ is the following (8 The method for refining molten iron according to claim 2, wherein the flow rate of the top blowing oxygen is changed within the range of the formula.
1.3 × P _0P1 ≦ P _0max ≦ 2.0 × P _0P1 (6)
0.8 × P _0P2 ≦ P _0max <1.3 × P _0P2 (7)
_{0.8 × P 0P1 ≦ P 0min <} 0.8 × P 0P2 (8)

  According to the present invention, when refining molten iron by supplying oxygen gas to produce general steel or stainless steel, the amount of spitting and dust generation at the time of high oxygen gas flow rate from the beginning to the middle of refining is stabilized. At the same time, it became possible to stably suppress the oxidation amount of iron and chromium when the oxygen gas flow rate decreased at the end of refining. As a result, the yield of iron and chromium was greatly improved, and the manufacturing cost was greatly reduced.

In the oxygen jet with Laval nozzle, oxygen flow rate F to be ejected is determined by the nozzle inlet side of the absolute pressure P ₀ and the throat opening sectional area S _t of the nozzle. Conversely, if the definite oxygen flow F injected from the opening cross-sectional area S _t and the nozzle throat section of the nozzle, it is possible to determine the absolute pressure P ₀ of nozzle inlet side by the following equation (10). The absolute pressure P ₀ on the nozzle inlet side is the total pressure of oxygen gas on the nozzle inlet side.
P ₀ = 0.169 · F / S _t (10)
P ₀ : Absolute pressure (MPa) on the nozzle inlet side
F: Oxygen flow rate ejected from the nozzle (Nm ³ / h)
_St : Open sectional area of nozzle throat (mm ² )

The Laval nozzle has a divergent nozzle from the throat to the outlet to make the jet flow supersonic. From the throat to the outlet, the gas flow rate increases in the supersonic region while the pressure decreases. When the pressure at the nozzle outlet is equal to the atmospheric pressure on the nozzle outlet side, this is called proper expansion. In proper inflation, absolute pressure (proper inflation absolute pressure P _0P) of the nozzle inlet side, an atmosphere absolute pressure P _e of the nozzle outlet, opening cross-sectional area S _t of the throat portion of the nozzle, between the opening cross-sectional area S _e of the nozzle outlet Is expressed by the following equation (11). Furthermore, the discharge Mach number M _0P at the time of proper expansion is calculated from the following equation (12).
_{S e / S t = 0.259 ·} (P e / P 0P) -5/7 · {1- (P e / P 0P) 2/7} -1/2 (11)
M _0P = [5 · {(P _0P / P _e ) ^2/7 −1}] ^1/2 (12)
S _e : Nozzle outlet opening cross-sectional area (mm ² )
P _e : Nozzle outlet side atmosphere absolute pressure (MPa)
(0.1013 in case of atmospheric pressure refining)
P _0P : Proper expansion absolute pressure (MPa) of lance nozzle

By the way, as described above, in adjusting the oxygen flow rate from the top blowing lance, the gas pressure on the nozzle inlet side is adjusted. When the oxygen flow rate is high, the absolute pressure P ₀ on the nozzle inlet side is higher than the proper expansion absolute pressure P _0P , and when the oxygen flow rate is low, the absolute pressure P ₀ on the nozzle inlet side is higher than the proper expansion absolute pressure P _0P . Also lower. In either case, oxygen is ejected from the nozzle in an inappropriate expansion state, and the former state is generally called underexpansion and the latter state is generally called overexpansion. In the case of underexpansion, the pressure at the nozzle outlet side is higher than the atmospheric pressure, and an expansion wave is generated immediately after the gas is ejected from the nozzle. To lose. Conversely, in the case of overexpansion, the pressure at the nozzle outlet side is lower than the atmospheric pressure, a shock wave is generated immediately after the gas is ejected from the nozzle, and the jet flow is turbulent while repeating the generation of the expansion wave and shock wave. To lose. Only under conditions close to proper expansion, a smooth supersonic jet with little disturbance is formed. In order to accurately grasp the jet flow behavior of the top blowing lance, it is important to grasp the inappropriate expansion behavior.

Non-Patent Document 2 describes the result of investigating improper expansion behavior in particular regarding the jet flow behavior of a converter top blowing lance using a Laval nozzle. The ratio of P ₀ / P _0P is changed between 0.4 and 5.0, and the jet core length H _C of the jet is actually measured. Here, regarding the jet core length H _CP at P ₀ / P _0P = 1,
H _CP = M _0P · (4.2 + 1.1M _0P ² ) · d _t × 1.4
d _t : Diameter (mm) of the throat portion of the lance nozzle
It is known that Thus, when the experimental results are plotted with H ₀ / P _{0P on} the horizontal axis and H _C / H _CP based on the measured H _C on the vertical axis, the results shown in the plot in FIG. 1 are obtained. Based on this result, polynomial approximation was performed in the range of 0.7 <P ₀ / P _0P ≦ 2.1 and 0.4 <P ₀ / P _0P ≦ 0.7, respectively, and f (X) = The following formula was obtained with 1.4 × H _C / H _CP and X = P ₀ / P _0P . The results calculated from this equation are shown as curves in FIG.
f (X) = − 2.709X ⁴ + 17.71X ³ −40.99X ² + 40.29X−12.90
(0.7 <X)
f (X) = 0.7994X−0.0602
(X ≦ 0.7)

  The jet core length is the distance in the supersonic jet region until the flow velocity on the central axis of the jet reaches the sonic velocity. Thereafter, the flow velocity on the central axis of the jet attenuates in inverse proportion to the distance. Therefore, the jet core length represents the strength of the jet at the same distance from the lance tip. However, this is a case where the jets ejected from the individual nozzles are separated without interfering with each other. When the jets interfere with each other and merge, the kinetic energy is added and the jet flow velocity, that is, the jet strength is increased. In addition, the jet flow does not spread so much in the jet core region, but after that, it becomes easy to entrain surrounding gases and spread easily. For this reason, interference with adjacent jets is likely to occur.

  In the present invention, as shown in FIG. 3, the angle between the longitudinal direction of the lance and the nozzle ejection direction is defined as an inclination angle θ, and two types of nozzles each having a total of three or more different even inclination angles are arranged in the circumferential direction. Alternating upper blown oxygen lances (having three or more nozzles 21 with a small inclination angle and three or more nozzles 22 with a large inclination angle, and the total number of nozzles 21 with a small inclination angle and a nozzle 22 with a large inclination angle) Is an even number, the inclination angle θ1 of the nozzle having a small inclination angle is different from the inclination angle θ2 of the large nozzle, and the top blowing oxygen lance 1 in which the nozzles 21 and 22 having a small inclination angle are alternately arranged in the circumferential direction 1) Is used. Due to the different inclination angles, the oxygen jets ejected from the individual nozzles are easily separated efficiently. In addition, the nozzle of the inclination angle 0 degree installed in the center of a lance for the prevention of adhesion of a metal to the lance etc. is not included in the above two types of nozzles.

  If you want to decarburize and refine at high speed from the beginning to the middle of refining, increase the oxygen supply amount, that is, oxygen that reduces spitting and dust generation as much as possible soft blow under high oxygen flow rate A blowing method is desirable. On the other hand, at the end of refining, the oxygen supply amount is reduced, that is, as a hard blow as low as possible under a low oxygen flow rate, iron peroxidation and peroxidation such as chromium in the case of stainless steel refining are suppressed. An oxygen blowing method that reduces the oxygen concentration is desirable. Therefore, in the present invention, for the oxygen jet jetted from the nozzle 21 having a small inclination angle that greatly contributes to the stirring of the hot spot, the control of the jet strength using the inappropriate expansion behavior on the insufficient expansion side is used.

As is apparent from FIG. 1, the jet core length H _C representing the jet strength is almost unchanged and constant in the range of P ₀ / P _0P of 0.8 to 2.0. It is clear from the above equation (10) that the oxygen flow rate F changes when P ₀ is changed. That is, in the present invention, P ₀ / P which can change the oxygen flow rate F greatly while maintaining the jet strength of oxygen ejected from the nozzle 21 (appropriate expansion absolute pressure: P _0P1 ) having a small inclination angle. _0P1 alters P ₀ in a range of 0.8 to 2. As the control range of P ₀ / P _0P1 in the nozzle 21 with a small inclination angle, the upper limit side 1.3 or more of the P ₀ / P _0P1 control range 0.8 to 2 in the refining initial stage to the middle stage where the oxygen flow rate should be increased 2 The lower expansion side of the P ₀ / P _0P1 control range of 0.8 to 2 is close to the appropriate expansion of 0.8 or more and less than 1.3 in the final stage of refining where the oxygen flow rate should be lowered using an underexpansion region of less than 0.0. Is a more desirable embodiment. This control makes it possible to perform oxygen blowing from the initial stage of the refining to the middle stage without increasing the jet strength even at a high oxygen flow rate and without reducing the jet flow strength even if the oxygen flow rate is reduced at the final stage of the refining.

From FIG. 1, when P ₀ / P _0P is less than 0.8, the jet core length H _C is remarkably reduced. _Therefore , when the oxygen flow rate is reduced at the end of refining, P ₀ is more than 0.8 times P _0P. is necessary. In addition, when P ₀ / P _0P is 2 or more, the jet core length H _C is 1.5 times or more of the core length H _CP at the time of proper expansion, and sufficient spitting and dust generation amount is obtained from the initial stage of refining to the middle stage. Reduction effect cannot be obtained.

In addition, as a result of various measurements of the strength of the oxygen jet ejected from the lance, the present inventors have made the oxygen jet ejected from the nozzle 21 with a small inclination angle using the improper expansion behavior to have a high oxygen flow rate. In this case, if the oxygen jet 32 ejected from the nozzle 22 having a large inclination angle is not in a region close to proper expansion when the soft blow is performed, the turbulence of the jet due to the pressure difference from the atmospheric pressure described above occurs. It has been found that the fire point cannot be dispersed due to the interference and coalescence of the jets. Conversely, when the oxygen flow rate is reduced at the end of the refining, the jet flow 32 from the nozzle 22 having a large inclination angle is used as an overexpansion condition to increase the turbulence of the jet and reduce the jet core length H _C2 . It was also found that the degree of overlap of fire points can be increased by promoting interference and coalescence, resulting in a jet strength that is significantly greater than that of a single jet.

In the present invention, the oxygen jet 32 ejected from the nozzle 22 having a large inclination angle (appropriate expansion absolute pressure: P _0P2 ) is also used for controlling the jet strength using the improper expansion behavior. P ₀ / P _0P2 is 1.3 so that the jet core length can be significantly reduced when the oxygen flow rate is reduced at the end of refining in order to control the interference and coalescence of oxygen jets ejected from two types of nozzles with different angles. P ₀ is changed in the range of less than. As a control range of P ₀ / P _0P2 in the nozzle 22 with a large inclination angle, a range close to an appropriate expansion in which P ₀ / P _0P2 is 0.8 or more and less than 1.3 is used from the initial stage to the middle stage of the refining to increase the oxygen flow rate. It is a more desirable embodiment to use an _{overexpansion} range where P ₀ / P _0P2 is less than 0.8 at the end of refining in which the oxygen flow rate should be reduced. The behavior of the top blown oxygen jet in the preferred embodiment is schematically shown in FIG. By the control of P ₀ / P _0P of the present invention, at the time of a high oxygen flow rate shown in FIG. 2A, the jet core length H _C2 of the oxygen jet 32 ejected from the nozzle having a large inclination angle extends, and the nozzle having a small inclination angle. The hot spot is efficiently dispersed without causing interference with the oxygen jet 31 ejected from the nozzle, and the amount of spitting and dust generated is reduced. On the other hand, at the time of the low oxygen flow rate shown in FIG. 2B, the jet core length H _C2 of the oxygen jet 32 ejected from the nozzle having the large inclination angle is shortened, and united with the oxygen jet 31 ejected from the nozzle having the small inclination angle. Since the hot spots overlap, the stirring of the hot spot portion is strengthened to suppress iron or chromium peroxidation.

As described above, in the present invention, the oxygen jet 31 ejected from the nozzle 21 having the small inclination angle (appropriate expansion absolute pressure: P _0P1 ) has an approximate P ₀ / P _0P1 of 0.8-2. Using the underexpanded region from the region, the oxygen jet 32 ejected from the nozzle 22 (appropriate expansion absolute pressure: P _0P2 ) having a large inclination angle is properly expanded from the _overexpanded region where P ₀ / P _0P2 is less than 1.3. In order to use the region close to, the proper expansion absolute pressure P _0P1 of the nozzle 21 having a small inclination angle is not effective unless it is smaller than the proper expansion absolute pressure P _{0P2 of the} nozzle 22 having a large inclination angle.

  When the difference between the inclination angle θ1 of the nozzle 21 having a small inclination angle and the inclination angle θ2 of the nozzle 22 having a large inclination angle is more than 15 degrees, the oxygen concentration is reduced even when the jet core length in the overexpansion region is small. The phenomenon that the jets interfere and merge is not recognized, and the present invention cannot be applied. Further, if the difference in inclination angle is less than 5 degrees, the fire point dispersion effect due to the difference in inclination angle cannot be obtained sufficiently, so that it cannot be applied to the present invention.

  The nozzle on the center axis of the lance for preventing the adhesion of the metal to the lance may be installed as appropriate, and is not included in the above two types of nozzles having different inclination angles.

Next, regarding the molten iron refining lance of the present invention used when refining molten iron while supplying oxygen gas, the proper expansion absolute pressure P _{0P1 of the} nozzle 21 with a small inclination angle and the appropriate expansion absolute pressure of the nozzle 22 with a large inclination angle are used. _Consider the preferred range of each of P _0P2 .

The maximum value of the nozzle inlet side absolute pressure P ₀ in the refining P _0max, the minimum value of the nozzle inlet side absolute pressure P ₀ and P _0min.

The maximum value P _0max of P ₀ is 2.0 × P _0P1 or less so that P ₀ ≦ 2.0 × P _{0P1 on} the right side of the equation (3). Therefore,
P _0max /2.0≦ P _0P1 (1-1)
Is obtained. Similarly, from the right side of equation (4), P _0max /1.3 <P _0P2 (2-1)
Is obtained.

On the other hand, when P _0max is smaller than 1.3 × P _0P1 , when P ₀ is changed within the range of P _0max or less, nozzles with a small inclination angle have P ₀ / P _0P1 of 0.8-2. It becomes difficult to use in the underexpanded region from the region close to the appropriate expansion. Therefore,
P _0P1 ≦ P _0max /1.3 (1-2)
Is necessary. In addition, when P _0max is smaller than 0.8 × P _0P2 , the jet flow from the nozzle with a large inclination angle is in an _overexpanded range, interference with the jet flow from the nozzle with a small inclination angle, and coalescence progress, and the fire point becomes Since it becomes impossible to disperse, the dust reduction effect from the refining initial stage to the middle stage cannot be obtained. Therefore,
P _0P2 ≦ P _0max /0.8 (2-2)
Is necessary.

From the formulas (1-1), (1-2), (2-1), and (2-2),
P _0max /2.0≦P _0P1 ≦ P _0max /1.3 (1)
P _0max /1.3 <P _0P2 ≦ P _0max /0.8 (2)
Is guided.

As described above, in the molten iron refining lance 1 of the present invention used when refining molten iron while supplying oxygen gas, as shown in FIG. 3, the angle between the lance longitudinal direction and the nozzle ejection direction is set to be an inclination angle, The nozzle 21 having the small inclination angle and the three or more nozzles 22 having the large inclination angle are provided, and the total number of nozzles of the nozzle 21 and the large nozzle 22 having the small inclination angle is an even number. The angle θ1 and the inclination angle θ2 of the nozzle having a large inclination angle are different in a range of 5 degrees or more and 15 degrees or less, and the nozzles 21 having a small inclination angle and the nozzles 22 having a large inclination angle are alternately arranged in the circumferential direction, and the nozzle having a small inclination angle. the proper inflation absolute pressure P _0P1 of 21 proper inflation absolute pressure P _0P2 of the inclination angle of the large nozzle 22, the maximum value P _0max of nozzle inlet side absolute pressure P ₀ in the refining, the ( It is limited to the range of the formulas (1) and (2), and by using this molten iron refining lance, the flow rate of the top blown oxygen is adjusted in the range of the above formulas (3) to (5). It becomes possible to carry out the refining method.

Similarly, from the equations (1-1) (1-2) (2-1) (2-2),
1.3 × P _0P1 ≦ P _0max ≦ 2.0 × P _0P1 (6)
0.8 × P _0P2 ≦ P _0max <1.3 × P _0P2 (7)
Is guided.

Further, the equation (3) left on as phrase 0.8 × P _0P1 ≦ P ₀ of the minimum value P _0min of P ₀ is 0.8 × P _0P1 above. Therefore,
_{0.8 × P 0P1 ≦ P 0min (} 8-1)
Is obtained. Further, when P _0min is greater than equal to or this and 0.8 × P _0P2 is, P ₀ / P _0P2 in refining end to reduce the flow rate of oxygen can not be used hyperinflation range of less than 0.8. Therefore,
_{P 0min <0.8 × P 0P2 (} 8-2)
Is necessary.

(8-1) From the equations (8-2),
_{0.8 × P 0P1 ≦ P 0min <} 0.8 × P 0P2 (8)
Is guided.

In the molten iron refining method of the present invention, the maximum value P _0max of the nozzle inlet side absolute pressure P ₀ during refining is within the range of the above formulas (6) and (7), and the minimum value of the nozzle inlet side absolute pressure P ₀ . By changing the top blowing oxygen flow rate within the range of the above formula (8), P _0min can be preferably carried out.

Example 1
The converter was used to decarburize ordinary steel, and about 350 tons of molten steel was produced. After charging the hot metal into the converter, decarburization and refining was carried out while blowing oxygen at a flow rate of 80000 Nm ³ / h from the top blowing lance, and oxygen from the time when the C concentration in the molten steel became 0.3 to 0.4 mass%. The flow rate was reduced to 50000 Nm ³ / h. The total oxygen content was adjusted so that the C concentration in the molten steel after decarburization would be constant at about 0.04% by mass. Six types of lances shown in Table 1 were used for the top blow lance, and 10-charge decarburization operation was carried out. The lance gap was 3.5 m. Table 2 shows the operation conditions and refining results of Examples and Comparative Examples. P ₀ described in Table 2 as the refining initial stage to middle stage (total oxygen flow rate of 80000 Nm ³ / h) is P _0max .

The lances A, B, and C are the lances of the present invention as shown in FIG. 3, and as can be seen from Tables 1 and 2, the proper expansion absolute pressure P _{0P1 of the} nozzle 21 with a small inclination angle and the nozzle with a large inclination angle. The appropriate expansion absolute pressure P _{0P2 of} 22 is P _0max /2.0≦P _0P1 ≦ P _0max / 1 with respect to the maximum value P _{0max of} the nozzle inlet side absolute pressure P ₀ corresponding to the total oxygen flow rate of 80000 Nm ³ / h. .3 and P _0max /1.3<P _0P2 ≦ P _0max /0.8. D, E, and F are lances of the comparative example, D is an appropriate expansion absolute pressure P _0P2 for a nozzle having a large inclination angle, and E is an appropriate expansion absolute pressure P _0P1 for a nozzle having a small inclination angle. Yes. In F, the difference in inclination angle between the nozzle having a small inclination angle and the nozzle having a large inclination angle is more than 15 degrees.

Inventive examples 1, 2, and 3 in Table 2 show examples in which lances A, B, and C are used. The jet flow ejected from the nozzle having a small inclination angle is set to an underexpansion region of 1.3 ≦ P ₀ / P _0P1 ≦ 2.0 from the beginning to the middle of the refining, and 0.8 ≦ P ₀ / P at the end of the refining. _{As the} region close to the appropriate expansion of _0P1 <1.3, the stirring of the hot spot portion is maintained, and the jet flow ejected from the nozzle having a large inclination angle is set to 0.8 ≦ P ₀ / P _0P1 from the initial stage of refining to the middle stage The range close to the appropriate expansion was used, and at the end of the refining, the _{overexpansion} region of P ₀ / P _0P2 <0.8 was promoted to interfere and merge with each other. As a result, the hot spots were dispersed from the beginning to the middle of the refining, and the degree of overlap of the hot spots was increased at the end of the refining. The [O] concentration (ppm) in Fe (mass%) and molten steel can be remarkably reduced, and iron peroxidation is suppressed.

On the other hand, Comparative Example 1 shows the case where the lance D is used, but the jet flow ejected from the nozzle having a large inclination angle from the refining initial stage to the middle stage is a region where the degree of insufficient expansion of 1.3 ≦ P ₀ / P _0P2 is strong. Therefore, the amount of dust generated is slightly increased. Further, at the end of refining, the jet flow ejected from the nozzle having a large inclination angle is in a region close to the appropriate expansion of 0.8 ≦ P ₀ / P _0P2 <1.3, so the jets do not interfere with each other, and iron In the slag. Fe concentration and [O] concentration in molten steel are increasing. Comparative Example 2 is a case where the lance E is used, but the jet flow ejected from the nozzle having a small inclination angle at the end of refining is an _{overexpansion} region where P ₀ / P _0P1 <0.8, Stirring power is significantly reduced and iron peroxidation is greatly advanced. The Fe concentration and the [O] concentration in the molten steel are greatly increased. Comparative Example 3 shows a case where a lance F is used. The jet flow ejected from the nozzle with a large inclination angle at the end of refining is an _{overexpansion} region of P ₀ / P _0P2 <0.8, but the angle difference with the nozzle with a small inclination angle is more than 15 degrees. The jets do not interfere with each other, and iron peroxidation proceeds. Fe concentration and [O] concentration in molten steel are increasing.

(Example 2)
Using a converter having the same size as in Example 1, a stainless steel decarburization operation was performed. After the ordinary hot metal was charged into the converter, ferrochrome was used as a chromium raw material and an appropriate amount of carbon was used as a heat source, and a molten stainless steel having a chromium concentration of about 17% was melted. After charging the hot metal into the converter, decarburization and refining was performed while blowing oxygen at a flow rate of 80000 Nm ³ / h from the top blowing lance, and when the C concentration in the molten steel reached about 1 mass%, the oxygen flow rate was changed to 50000 Nm ³ / lowered to h. The total oxygen content was adjusted so that the C concentration in the molten steel after decarburization would be constant at about 0.5 mass%. Six types of lances shown in Table 1 were used for the top blow lance, and 10-charge decarburization operation was carried out. The lance gap was 2.5 m. Table 3 shows the operating conditions and refining results for the examples and comparative examples.

Invention Example 4 in Table 3 shows an example in which Lance A is used. The amount of dust generated can be reduced even at high oxygen flow rates by making the jet flow ejected from a nozzle with a small inclination angle from the early stage of refining to an underexpanded region of 1.3 ≦ P ₀ / P _0P1 ≦ 2.0. Yes. Inventive Examples 5 and 6 show examples where lances B and C are used. A jet flow ejected from a nozzle with a small inclination angle from the initial stage of refining to an underexpanded region of 1.3 ≦ P ₀ / P _0P1 ≦ 2.0, and further, 0.8 ≦ P ₀ / P _0P1 < As the region close to the proper expansion of 1.3, stirring of the hot spot portion is maintained, and the jet flow ejected from the nozzle having a large inclination angle is defined as an _{overexpansion} region of P ₀ / P _0P2 <0.8, and the jets interfere with each other. Since the coalescence was promoted, the oxidation amount of chromium was remarkably reduced.

On the other hand, Comparative Example 4 shows a case where the lance D is used, but the jet flow ejected from the nozzle having a large inclination angle from the early refining stage to the middle stage is a region where the degree of insufficient expansion of 1.3 ≦ P ₀ / P _0P is strong. Therefore, the amount of dust generated is slightly increased. Further, at the end of the refining, the jet flow ejected from the nozzle having a large inclination angle is a region close to the appropriate expansion of 0.8 ≦ P ₀ / P _0P <1.3, so that the jets do not interfere with each other, and chromium Peroxidation is progressing. In Comparative Example 5, the lance E was used, but the jet flow ejected from the nozzle with a small inclination angle at the end of refining was an _overexpanded region of P ₀ / P _0P <0.8, The stirring power is remarkably reduced, and chromium peroxidation is greatly advanced. Comparative Example 6 shows the case where the lance F is used. The jet flow ejected from the nozzle having a large inclination angle at the end of refining is an _{overexpansion} region of P ₀ / P _0P <0.8, but the angle difference from the nozzle having a small inclination angle is more than 15 degrees. The jets do not interfere with each other, iron peroxidation proceeds, and the amount of chromium oxidation increases.

A lance nozzle inlet side of the absolute pressure ratio P ₀ / P _0P, a diagram showing the relationship between the jet core length ratio H _C / H _CP. It is a figure which shows typically the change of the behavior of the top blowing oxygen jet in desirable embodiment of this invention, (a) is the figure at the time of high oxygen flow, (b) is the figure which shows at the time of low oxygen flow. It is a figure which shows the lance tip for molten iron refining of this invention, (a) is AA arrow sectional drawing, (b) is the figure seen from the bottom.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lance for molten iron refinement 2 Nozzle 21 Nozzle with a small inclination angle 22 Nozzle with a large inclination angle 3 Oxygen jet 31 Oxygen jet with a small inclination angle 32 Oxygen jet with a large inclination angle 4 Molten steel

Claims (3)

A molten iron refining lance used for refining molten iron while supplying oxygen gas, wherein the angle between the longitudinal direction of the lance and the nozzle ejection direction is an inclination angle, three or more nozzles having a small inclination angle, and three or more The total number of nozzles of the nozzle with a small inclination angle and the nozzle with a large inclination angle is an even number, and the inclination angle of the nozzle with a small inclination angle and the nozzle with a large inclination angle is different from 5 degrees to 15 degrees, Nozzle with a small inclination angle and nozzle with a large inclination are alternately arranged in the circumferential direction, and the appropriate expansion absolute pressure P _{0P1 for a} nozzle with a small inclination angle and the appropriate expansion absolute pressure P _0P2 for a nozzle with a large inclination angle are _supplied to the nozzle inlet. The lance for molten iron refining characterized by being limited to the range of the following formulas (1) and (2) with respect to the maximum value P _0max of the side absolute pressure P ₀ .
P _0max /2.0≦P _0P1 ≦ P _0max /1.3 (1)
P _0max /1.3 <P _0P2 ≦ P _0max /0.8 (2) In refining molten iron while supplying oxygen gas, the angle between the lance longitudinal direction and the nozzle ejection direction is the inclination angle, and there are three or more nozzles with a small inclination angle and three or more nozzles with a large inclination angle. The total number of nozzles of the small and large nozzles is an even number, the inclination angle of the small and large nozzles is different in the range of 15 degrees or less, and the small and large nozzles are in the circumferential direction. Using the molten iron refining lances arranged alternately, the nozzle inlet-side absolute pressure P ₀ during refining is set to the appropriate expansion absolute pressure P _{0P1 for the} nozzle having a small inclination angle and the appropriate expansion absolute pressure P for the nozzle having a large inclination angle. _A method for refining molten iron, wherein the flow rate of top blowing oxygen is adjusted within the range of the following formulas (3) to (5) with respect to _0P2 .
0.8 × P _0P1 ≦ P ₀ ≦ 2.0 × P _0P1 (3)
0 <P ₀ <1.3 × P _0P2 (4)
P _0P1 <P _0P2 (5) Maximum value P _0max of nozzle inlet side absolute pressure P ₀ during refining in the following ranges (6) and (7), the minimum value P _0min nozzle inlet side absolute pressure P ₀ is the following equation (8) 3. The method for refining molten iron according to claim 2, wherein the flow rate of the top blowing oxygen is changed within the range.
1.3 × P _0P1 ≦ P _0max ≦ 2.0 × P _0P1 (6)
0.8 × P _0P2 ≦ P _0max <1.3 × P _0P2 (7)
_{0.8 × P 0P1 ≦ P 0min <} 0.8 × P 0P2 (8)

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