JP2016185552A - Management method of molten steel ladle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a management method of a molten steel ladle capable of efficiently managing the molten steel ladle by accurately predicting wearing.SOLUTION: The wearing speed V[m/s] of a slag line refractory 3c is predicted from equation (1): V=KρΔ(wt%A)/100ρ(1) and equation (2): K=eV(2) using numerical value coefficients such as a [-] and e [ms] (where, K [m/s] is a mass transfer coefficient; ρ[kg/m] is slag density; ρ[kg/m] is the density of the slag line refractory 3c; A is the component of the slag line refractory 3c eluting into slag during refining treatment; Δ(wt%A) [%] is difference between the saturation concentration to the slag of the component A and the concentration of the component A in the slag; and V[m/s] is the flow rate of the slag in a tangential direction in the vicinity of the operation surface of the slag line refractory 3c).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for managing a molten steel pan used for refining in which molten steel is stirred with gas.

  Molten steel ladle charged with molten steel is used at various points from a converter to a secondary refining device (molten steel processing facility) to a continuous casting device. Each time this molten steel pan is used, wear of the refractory provided in the molten steel pan proceeds. In particular, when secondary refining treatment is performed, it is known that wear of the refractory progresses in the slag line portion where the slag contacts. In particular, it is known that the refractory wears out in the LF treatment in which an inert gas or the like is blown into the molten steel while being energized and heated. If the wear of the refractory progresses, it will lead to leakage steel, so it is very important to monitor the wear state of the refractory, that is, grasp the thickness of the refractory in the molten steel pan.

  As a method of monitoring the remaining thickness of the refractory, a method of measuring and managing the remaining thickness each time using a remaining thickness measuring device can be considered. However, there is a problem that sufficient measurement accuracy cannot be obtained due to adhesion of the metal to the refractory and local wear. Moreover, it is technically difficult to improve the accuracy, and it takes a lot of time for countermeasures. In addition, measuring the remaining thickness of the refractory for each treatment takes time and effort, which adversely affects productivity. Therefore, there is a demand for a method for estimating and managing the wear state of the refractory without measuring the remaining thickness of the refractory.

  In Patent Document 1, during refining, the temperature of the iron skin corresponding to the slag line portion of the iron skin of the ladle is measured, the temperature of the iron skin is compared with a predetermined threshold, and the temperature of the iron skin is predetermined. The use method of the ladle which interrupts refining when the threshold value of this is exceeded is disclosed. By concentrating and managing the slag line, which is the most susceptible to erosion in refining, refining can be continued to the maximum.

  Further, Patent Document 2 selects from the ash input amount, input power, main ash / fly ash mixing ratio, slag temperature, cooling water amount and cooling water temperature, refractory temperature, furnace temperature, current, and voltage of the ash melting furnace. An operation method of an ash melting furnace that predicts the remaining amount of refractory based on one or more of the operation data is disclosed. By obtaining appropriate operating conditions from the remaining amount of refractory, the life of the refractory can be extended.

  Moreover, in patent document 3, management of the molten steel pan which calculates the estimated remaining thickness of a slag line refractory using the erosion rate of the slag line refractory obtained based on the basic unit of the electric power at the time of electrode heating A method is disclosed. By monitoring the remaining thickness of the slag line refractory, the number of times the molten steel pan is used can be improved.

JP 2010-17756 A JP 2006-145122 A JP 2012-223776 A

  However, each of Patent Documents 1 to 3 is a method of concentrating and managing places that are easily worn out. Therefore, it is impossible to predict the wear state of the refractory over the entire circumference of the molten steel pan. In addition, when the refining conditions (stirring conditions) are changed, the location to be managed again must be specified. Further, in some cases, there is a possibility that a portion where the wear is noticeable cannot be detected.

  The objective of this invention is providing the management method of the molten steel pan which can manage a molten steel pan efficiently by predicting wear accurately.

The present invention is a method for managing a molten steel pan used for refining in which molten steel is stirred with gas, and in which a slag line refractory is applied to a slag line portion in contact with the slag, and the mass transfer coefficient is K [m / s]. , The density of the slag is ρ _b [kg / m ³ ], the density of the slag line refractory is ρ _r [kg / m ³ ], and the components of the slag line refractory eluted to the slag during the refining process are A Δ (wt% A) [%] representing the difference between the saturated concentration of the component A with respect to the slag and the concentration of the component A in the slag in terms of mass percent concentration, and the working surface of the slag line refractory When the tangential flow velocity of the slag in the vicinity is V _s [m / s], the wear rate V _w [m / s] of the slag line refractory is expressed by numerical coefficients a [−] and e [m ^{−a + 1} · s ^a-1 ], the following formula (1), formula ( It is characterized by predicting from 2).
V _w = Kρ _b Δ (wt% A) / 100ρ _r Formula (1)
K = eV _sa ^a formula (2)

  According to the present invention, the wear rate of the slag line refractory is predicted from the equations (1) and (2) which are relational expressions between the tangential flow velocity of the slag and the wear rate of the slag line refractory. The flow behavior (slag flow velocity) of slag when stirring with gas greatly affects the wear of the slag line refractory. Therefore, the wear rate of the slag line refractory can be accurately predicted by considering the tangential flow velocity of the slag. And by determining the amount of wear of the slag line refractory from the wear rate of the slag line refractory, the wear of the slag line refractory can be accurately predicted. Furthermore, the wear state of the slag line refractory can be predicted over the entire circumference of the molten steel pan by using the tangential flow velocity distribution in the circumferential direction of the molten steel pan. Thereby, since it is possible to specify the most easily worn portion, the molten steel pan can be managed efficiently.

It is sectional drawing of a molten steel pan. It is a top view of a molten steel pan. It is a figure which shows distribution of the absolute value of the flow velocity of the tangential direction of slag. It is a figure which shows distribution of the mass transfer coefficient in a slag line part. It is a figure which shows distribution of the maximum wear rate of a slag line refractory.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(Composition of molten steel pan)
The management method of the molten steel pan by embodiment of this invention manages the molten steel pan used for the refining which stirs molten steel with gas.

  As shown in FIG. 1, which is a cross-sectional view, the molten steel pan 1 has an iron shell 2 that forms an outer shell, and a refractory 3 that is constructed inside the iron shell 2. The refractory 3 includes an amorphous refractory 3a provided on the operating surface side (contact side with molten steel) on the bottom side (laying portion 4 side) of the iron skin 2, and the operating surface side on the body portion 5 of the iron shell 2. And the fixed refractory 3c provided on the working surface side (contact side with the slag) in the slag line portion 6 on the upper part of the iron shell 2. The amorphous refractory 3a and the amorphous refractory 3b are castable (alumina amorphous refractory) or the like. The regular refractory 3c is magnesia, MgO-C, or the like. The slag line portion 6 is a portion where the slag, which is an oxide, is in direct contact, and is the portion that is most easily melted. Hereinafter, the refractory provided in the slag line portion 6 is referred to as a slag line refractory 3c.

  Moreover, the molten steel pan 1 has a pair of trunnions 8 for pivotally supporting the molten steel pan 1 as shown in FIG. 2 which is a top view. A removal port 9 for discharging slag is formed at the upper end of the molten steel pan 1.

The refractory 3 provided in the molten steel pan 1 melts particularly when the secondary refining treatment is performed. In the present embodiment, among the secondary refining processes, LF refining is particularly targeted. The LF refining is an operation aimed at removing impurities from the molten steel in the molten steel pan 1 or adjusting alloy components. In order to achieve this purpose, in the LF refining, an inert gas such as Ar gas is blown into the molten steel in the molten steel pan 1 to vigorously circulate and agitate the molten steel, and the molten steel is floated on the molten steel. For example, sulfur in the molten steel is adsorbed by the slag by reacting with, for example, CaO—SiO ₂ —Al ₂ O ₃ slag. In LF refining, electrode heating is performed in which the molten steel surface or the slag floating on the molten steel is directly heated by arc discharge using an electrode.

  The inert gas is blown from a refractory lance immersed in the molten steel, or a fine gas-blown refractory formed on the bottom of the molten steel pan 1 (so-called porous plug, slit plug, nozzle, etc.) ) And so on. In general, the blowing of the inert gas is performed by slightly removing the center of the molten steel pan 1 in a plan view in order to form a solid unidirectional stirring flow in the molten steel in the molten steel pan 1.

(Management method of molten steel pan)
The management method of the molten steel pan of this embodiment estimates the wear rate _Vw [m / s] of the slag line refractory 3c using the following formulas (1) and (2).
V _w = Kρ _b Δ (wt% A) / 100ρ _r Formula (1)
K = eV _sa ^a formula (2)
Here, K [m / s] is a mass transfer coefficient, ρ _b [kg / m ³ ] is the density of slag, and ρ _r [kg / m ³ ] is the density of the slag line refractory 3c. A is a component of the slag line refractory material that elutes into the slag during the refining process, and Δ (wt% A) [%] is the mass percent difference between the saturated concentration of the component A with respect to the slag and the concentration of the component A in the slag. V _s [m / s] expressed by the concentration is the tangential flow velocity of the slag near the working surface of the slag line refractory 3c. Further, a [−] and e [m ^{−a + 1} · s ^a−1 ] are fitting parameters (numerical coefficients). In addition, the density | concentration of the component A in slag is an average density | concentration of the component A contained in the whole slag (bulk slag) actually used for the molten steel pan 1. FIG.

  Here, as a result of sincerity studies by the inventors, the flow rate of the slag near the working surface of the slag line refractory 3c, or the location where the oscillation of the slag line as the slag layer is large during gas agitation during secondary refining It was found that wear of the slag line refractory 3c appears remarkably at large locations.

Therefore, the slag flow behavior during secondary refining such as LF treatment with gas stirring is predicted, and an estimation formula representing the relationship between the tangential flow velocity V _s of the slag and the wear rate V _w of the slag line refractory 3c. (Equation (1), Equation (2)) is obtained as follows. Furthermore, the distribution of the wear rate V _w of the slag line refractory 3c is predicted, and the remaining thickness of the slag line refractory 3c after the LF treatment is estimated.

In the secondary refining process that performs electrode heating and gas stirring such as LF process, the components of the slag line refractory 3c (mainly MgO, Al ₂ O ₃ , SiO ₂ , CaO, etc.) are eluted into the slag. Wear progresses. Moreover, in the location where the flow rate of slag is large, the elution of the component is promoted, and the wear is accelerated. The above phenomenon can be expressed by the following equation (3) using Fick's first law based on the mass transport theory.
V _w = −dLr / dt = Kρ _b Δ (wt% MgO) / 100ρ _r Formula (3)
Here, Lr [m] is the thickness of the slag line refractory 3c, and t [s] is time. MgO is a component of the slag line refractory 3c that elutes into the slag during the refining treatment, and Δ (wt% MgO) [%] is the difference between the saturation concentration of the component MgO with respect to the slag and the concentration of the component MgO in the slag. It is expressed in percent concentration.

If various dimensionless numbers related to the movement phenomenon are used, a dimensionless correlation equation such as the following equation (4) can be obtained.
Sh = cRe ^a Sc ^b Formula (4)
Here, Sh is the Sherwood number, Re is the Reynolds number, and Sc is the Schmitt number. Further, a, b, and c [-] are fitting parameters according to the phenomenon.

The Sherwood number, Reynolds number, and Schmidt number are expressed as follows.
Sh = K · L / D (5)
Re = V _s · L · ρ _b / η _s (6)
Sc = η _s / (ρ _b · D) (7)
Here, L [m] is the representative length, D [m ² / s] is the diffusion coefficient, and η _s [Pa · s] is the slag viscosity.

When formulas (5) to (7) are arranged, the mass transfer coefficient K and the flow velocity V _{s in} the tangential direction of the slag have a relationship as shown in the following formula (8).
K = eV _sa ^a formula (8)
Here, e [m ^{−a + 1} · s ^a−1 ] is a fitting parameter.

By substituting equation (8) into equation (3), a prediction equation for the wear rate of the slag line refractory 3c in consideration of the slag flow velocity is obtained as the following equation (9).
_{V w = -dLr / dt = eV} s a ρ b Δ (wt% MgO) / 100ρ r ··· formula (9)

Regarding the V _s distribution (absolute value of the tangential velocity) flow rate of the slag in the working face near the slag line refractory 3c in secondary refining, it can be determined from the flow simulation that corresponds to the refining process of interest .

  In order to obtain the MgO concentration difference Δ (wt% MgO) that becomes the driving force for elution, it is first necessary to obtain the saturation concentration of MgO with respect to the bulk slag. In this regard, a thermodynamic study (estimated from thermodynamic equilibrium calculation or equilibrium state diagram) based on the material composition of the target slag line refractory 3c, the composition of the slag used during refining, and the refining treatment temperature. It can be obtained by doing. The difference between the saturation concentration of MgO with respect to the bulk slag and the concentration of MgO in the slag to be used (bulk slag) is Δ (wt% MgO).

With respect to the fitting parameters e and a, the wear rate based on the actual measured residual thickness value of the slag line refractory 3c (measured when the pan is repaired) and the wear of the slag line refractory 3c predicted by equation (3) It is obtained by comparing the speed. Note that the wear rate V _w of the slag line refractory 3c is obtained by dividing the refractory wear amount [m] by the target processing time [s] of secondary refining.

  If the component of the slag line refractory 3c that elutes into the slag during the refining process is MgO, the wear rate of the slag line refractory 3c can be accurately predicted from the equation (9). Then, the amount of wear of the slag line refractory 3c after the refining process can be calculated by integrating Equation (9) with the integration time of the refining process. By subtracting this amount of wear from the thickness of the slag line refractory 3c before use, the remaining thickness of the slag line refractory 3c is obtained. By determining that the molten steel pan 1 has reached the use limit when the remaining thickness reaches a predetermined value, it is possible to avoid accidents such as leakage steel caused by wear of the slag line refractory 3c.

  Moreover, if it generalizes as a component A including MgO, the wear rate of the slag line refractory 3c can be estimated more accurately from the equations (1) and (2).

(Flow simulation)
About the above-mentioned molten steel pan 1, the flow simulation based on typical operation conditions was implemented for LF process. First, the slag tangential flow velocity (absolute value) in the vicinity of the operating surface of the slag line refractory 3c was calculated. Specifically, the distribution of the absolute value of the flow rate in the tangential direction of the slag at a position 10 to 20 mm away from the operating surface of the slag line refractory 3 c was extracted over the entire circumference of the molten steel pan 1. The result is shown in FIG. Here, as shown in FIG. 2, the angle θ was set to 0 to 360 ° clockwise with an imaginary line L passing through the trunnion 8 on the left side of the drawing from the center of the molten steel pan 1 as 0 °.

  Next, a thermodynamic study was performed based on information on the material composition of the slag line refractory 3c, the composition of the slag used in the LF treatment, and the treatment temperature. In the case examined this time, MgO was the target, and Δ (wt% MgO) = 20 to 30%. Therefore, an intermediate value is taken as Δ (wt% MgO) = 25%. And the distribution of the mass transfer coefficient in the slag line part 6 was computed using distribution of the flow velocity of the tangential direction of slag shown in FIG. 3, and Formula (8). The result is shown in FIG.

Next, the distribution of the maximum wear rate of the slag line refractory 3c was estimated using Equation (9). The result is shown in FIG. Here, calculation was performed using ρ _r = 2840 [kg / m ³ ] and ρ _b = 2730 [kg / m ³ ], which are general representative values. Further, as shown by a broken line in FIG. 5, the two fittings are made so that the distribution of the predicted maximum wear rate and the maximum wear rates in the actual furnaces (pan A, pan B, pan C) based on the actual measurement are approximately the same. As a result of fitting the values of the parameters a and e, in this case, the values of the fitting parameters are e = 3 × 10 ⁻⁵ and a = 0.35.

  In FIG. 5, the wear rates at the measurement point (1), the measurement point (2), the measurement point (3), and the measurement point (4) are the wear rates actually obtained by measuring the remaining thickness of the slag line refractory 3c. Almost matched. Here, the measurement point (1), the measurement point (2), the measurement point (3), and the measurement point (4) are set at the positions shown in FIG. That is, the measurement point (1) is set in the vicinity of the trunnion 8 on the left side in the drawing, the measurement point (2) is set in the center of the removal port 9, and the measurement point (3) is set in the removal port 9. The measurement point (4) is set between the trunnion 8 and the removal port 9 on the right side in the figure. FIG. 5 shows that the wear rate can be predicted even at a location where the remaining thickness of the slag line refractory 3c is not actually measured.

  Using the estimated maximum wear rate shown in FIG. 5, the maximum wear amount (time integral value) based on the accumulated refining treatment time is calculated, and the maximum wear amount is subtracted from the initial value of the thickness of the slag line refractory 3c. When the remaining thickness reaches a predetermined value, it can be determined that the molten steel pan 1 has reached the use limit. In addition, since the wear rate of the slag line refractory 3c can be predicted over the entire circumference of the molten steel pan 1, a place where the wear rate is maximized can be traced without setting a specific management place. . Therefore, it becomes possible to predict the wear rate with higher accuracy than in the conventional technology.

(effect)
As described above, according to the method for managing a molten steel pan according to the present embodiment, equations (1) and (2) which are relational expressions between the tangential flow rate of the slag and the wear rate of the slag line refractory 3c. ) To predict the wear rate of the slag line refractory 3c. The slag flow behavior (slag flow velocity) when stirring with gas greatly affects the wear of the slag line refractory 3c. Therefore, the wear rate of the slag line refractory 3c can be accurately predicted by considering the tangential flow velocity of the slag. And the wear of the slag line refractory 3c can be accurately predicted by obtaining the wear amount of the slag line refractory 3c from the wear speed of the slag line refractory 3c. Furthermore, the wear situation of the slag line refractory 3 c can be predicted over the entire circumference of the molten steel pan 1 by using the distribution of the tangential flow velocity of the slag in the circumferential direction of the molten steel pan 1. Thereby, since the location which is most likely to be worn can be specified, the molten steel pan 1 can be managed efficiently.

  Moreover, when the remaining thickness of the slag line refractory 3c reaches a predetermined value, it is determined that the molten steel pan 1 has reached the use limit, thereby preventing accidents such as leakage steel caused by wear of the slag line refractory 3c. can do.

  The embodiment of the present invention has been described above, but only specific examples are illustrated, and the present invention is not particularly limited, and the specific configuration and the like can be appropriately changed in design. Further, the actions and effects described in the embodiments of the invention only list the most preferable actions and effects resulting from the present invention, and the actions and effects according to the present invention are described in the embodiments of the present invention. It is not limited to what was done.

DESCRIPTION OF SYMBOLS 1 Molten steel pan 2 Iron skin 3 Refractory 3a, 3b Unshaped refractory 3c Slag line refractory 4 Laying part 5 Body 6 Slag line part 8 Trunnion 9 Removal port

Claims (2)

It is used for refining to stir molten steel with gas, and is a method of managing a molten steel pan in which a slag line refractory is applied to the slag line part where the slag contacts,
The mass transfer coefficient is K [m / s], the density of the slag is ρ _b [kg / m ³ ], the density of the slag line refractory is ρ _r [kg / m ³ ], and it elutes into the slag during the refining process The component of the slag line refractory is A, and the difference between the saturated concentration of the component A with respect to the slag and the concentration of the component A in the slag is expressed in mass percent concentration as Δ (wt% A) [% ], Where the flow rate in the tangential direction of the slag near the working surface of the slag line refractory is V _s [m / s], the wear rate V _w [m / s] of the slag line refractory is expressed by a numerical coefficient a A method for managing a molten steel pan, which is predicted from the following formulas (1) and (2) using [-] and e [m ^{-a + 1} · s ^a-1 ].
V _w = Kρ _b Δ (wt% A) / 100ρ _r Formula (1)
K = eV _sa ^a formula (2) By integrating the wear rate V _w of the slag line refractory over time with the integrated value of the refining treatment time, the maximum wear amount of the slag line refractory is calculated, and the maximum value is calculated from the initial value of the thickness of the slag line refractory. 2. The method of managing a molten steel pan according to claim 1, wherein when the remaining thickness obtained by subtracting the amount of wear reaches a predetermined value, it is determined that the molten steel pan has reached a use limit.