JP6669024B2 - Method of estimating hot metal flow velocity in blast furnace and operating method of blast furnace - Google Patents

Description

  The present invention relates to a method for estimating the flow velocity of hot metal near a portion of a blast furnace where erosion of a bottom brick is most advanced, and a method of operating a blast furnace for suppressing the extension of erosion of the bottom brick.

  Furnace bottom bricks of a blast furnace are exposed to the flow of molten pig iron (hereinafter referred to as “hot metal”), and are gradually eroded during a long-term operation. On the other hand, once the operation of the hearth of the blast furnace is started by burning, it is technically difficult to repair such as transshipment during the subsequent operation period. Therefore, in order to extend the life of the hearth of the blast furnace, only a method of performing an operation capable of suppressing the extension of erosion of the hearth brick is limited. On the other hand, with respect to the furnace wall of a blast furnace, wear of the furnace wall no longer determines the life of the blast furnace due to the development of a cooling technique using a stave or the like and a repair technique for reducing the scale during operation.

  In recent years, the life (operating period) of a blast furnace has been over 20 years. In order to achieve a longer service life, it has become more important to extend the life of the furnace bottom of the blast furnace by one step. Specifically, it is to accurately estimate the erosion line and to implement an operation method capable of effectively suppressing the extension of erosion based on the estimation result.

  Conventionally, as one method of estimating the amount of wear of a hearth brick, for example, in Patent Document 1, based on the measured temperature of a thermocouple embedded at two points in a refractory brick, the temperature and distance between two points and A method of calculating a heat flux from the thermal conductivity of the brick and estimating the remaining thickness of the brick by assuming the temperature of the operating surface in the furnace as the temperature at which the hot metal solidifies is disclosed.

  As another method for estimating the amount of wear of the hearth brick, Patent Literature 2 proposes a method of measuring the remaining thickness of the blast furnace hearth brick using cosmic ray muons.

  Further, Patent Literature 3 proposes a method of accurately predicting an equilibrium wear line of a hearth brick based on a calculation of a hearth flow, and appropriately designing a structure of the hearth brick.

JP-A-2002-266011 JP-A-08-261741 JP 2011-236474 A

"3D Mathematical Model of Liquid Flow in Blast Furnace Hearth", Iron and Steel, Japan Iron and Steel Association, 2006, Vol. 92, No. 12, p. 967-975

  However, in any of the method for estimating the inside of a blast furnace using a thermocouple described in Patent Document 1 and the method for measuring the thickness of blast furnace refractories by muon measurement described in Patent Document 2, the residual thickness of the brick is Although it can be estimated, there is no description of an operating method that can effectively suppress the extension of brick erosion. Further, in the method of accurately predicting the equilibrium wear line of the hearth brick described in Patent Document 3 and appropriately designing the structure of the hearth brick, the furnace capable of long-term operation under given operating conditions is used. The purpose of the present invention is to design a bottom brick structure, and it does not provide an operation method capable of effectively suppressing the extension of refractory erosion in a blast furnace already in operation.

  The present invention has been made in view of such a viewpoint, and an object of the present invention is to effectively suppress the erosion of hearth bricks from being extended to an operating blast furnace.

  In order to solve the above problems, the present invention is a method of estimating the flow velocity of hot metal at a site where erosion is progressing most, of a hearth brick lined at the hearth of a blast furnace, which is lined at the hearth of the blast furnace. A calculation grid is generated from the structure of the hearth brick, and two thermocouples are embedded in the hearth brick in a pair. Based on the measured temperature of the two thermocouples, a calculation grid is formed between the two points. Calculate the heat flux from the temperature and distance and the thermal conductivity of the hearth brick, calculate the remaining thickness of the hearth brick assuming the temperature of the operating surface of the hearth brick, and calculate the plurality of sets of thermoelectric Perform the pair to determine the shape of the operating surface of the hearth brick, set the current operating conditions, the lower end level and shape of the core coke in the furnace, mechanically from the operating conditions and the wear situation of the hearth brick Calculate based on the balance and determine the flow resistance in the furnace. The temperature of the hot metal, slag, and coke packed bed at the bottom of the furnace based on the material balance, momentum balance, and energy balance formulas when there is a packed bed of molten metal, slag, and coke in the furnace. Distribution, and calculating the flow velocity distribution of the hot metal and slag, from the flow velocity distribution of the hot metal, characterized by estimating the flow velocity of the hot metal in the vicinity of the site where the erosion of the hearth brick is most advanced, the hot metal in the blast furnace A method for estimating flow velocity is provided.

  Further, the present invention is a blast furnace operating method for determining the operating conditions of the blast furnace using the flow rate estimation method of the hot metal in the blast furnace, wherein a plurality of different operating conditions are set, the same as the current operating conditions Calculate the flow velocity distribution of the hot metal in the procedure, among the plurality of different operating conditions, the one where the flow velocity of the hot metal in the vicinity of the site where the erosion of the hearth brick is progressing becomes the smallest, as a new operating condition. A method for operating a blast furnace is provided.

  In the operating method of the blast furnace, the plurality of different operating conditions, tap hole depth, lap time at the time of tapping, mud erosion rate, and the presence or absence of coke free space, any one alone, or two or more May be combined.

  According to the present invention, it is possible to estimate the flow velocity of the hot metal in the site where the most erosion of the brick is advanced, and by using the estimation result, by selecting an operation method capable of reducing the flow rate of the hot metal, the furnace bottom brick Erosion extension can be effectively suppressed.

5 is a flowchart illustrating a calculation procedure according to the embodiment of the present invention. It is a figure which shows the example of the calculation grid produced | generated based on the structure of the hearth brick. It is a top view which shows the example of arrangement | positioning of the thermocouple buried in a furnace bottom. It is a top view which shows the example of the residual thickness distribution of a hearth brick. It is a figure which shows the positional relationship between the furnace bottom brick working surface and the furnace core coke lower surface.

  The present inventors have repeatedly studied means for effectively stopping the erosion of the bottom brick of the blast furnace through various experiments and dismantling investigations of the blast furnace. As a result, it was found that, by reducing the flow velocity of the hot metal in the portion where the erosion of the brick is progressing most, the extension of the erosion of the hearth brick can be effectively suppressed in the operating blast furnace. The gist of the present invention is to determine the flow velocity of hot metal in a portion where erosion of brick is most advanced, and among various conceivable operating conditions, the flow speed of hot metal in a portion where erosion of brick is most advanced is the most. Adopt conditions to be reduced.

  Hereinafter, the calculation procedure of the operation method according to the embodiment of the present invention that effectively suppresses the extension of the erosion of the hearth brick will be described in detail with reference to the drawings. FIG. 1 is a flowchart of a calculation procedure according to the embodiment of the present invention.

  First, the flow velocity of the hot metal at the place where the brick erosion is most severe in the current blast furnace hearth is estimated by the following procedure.

Step S1
A computational grid is generated from the structure of the hearth brick lined at the bottom of the blast furnace. The size and the like of the calculation grid may be appropriately determined according to the desired accuracy, the capacity that can be calculated, and the like.

Step S2
Based on the measured temperature of two different thermocouples embedded in the hearth brick, the heat flux is calculated from the temperature difference and distance between the two points and the thermal conductivity of the hearth brick, and the temperature of the brick operating surface is calculated. Assuming (for example, 1150 ° C.), the remaining thickness of the hearth brick is calculated. The brick working surface is obtained by arranging thermocouples as a set of two points at appropriate positions in the radial direction and height direction, and calculating the remaining thickness of the hearth brick for a plurality of thermocouple units. Can be obtained. This calculation can be performed by a conventionally known method, for example, described in Patent Document 1, but the calculation method is not limited to this.

Step S3
Set the current operating conditions. Specifically, the operating conditions (blowing volume, blowing temperature, oxygen-enriched flow rate, blowing moisture, coke ratio, pulverized coal ratio, furnace The operating conditions (lap time, taphole depth, mud erosion rate, etc.) required to determine the flow velocity distribution of the hot metal and slag in the lower part of the furnace in step S5 are shown. Set.

Step S4
With respect to the blast furnace operating conditions (S3) and the structure of the hearth brick (S1), the sinking level and shape of the core coke are calculated and set as conditions for the resistance to liquid flow in the furnace bottom flow. This is, for example, a known model based on rigid-plastic mechanics (ISIJ
int. , 49 (2009), pp. 470) can be calculated as follows. Here, equations (1) to (4) show governing equations of a model based on rigid-plastic dynamics. Equation (1) is a continuous equation, equation (2) is a motion equation, equation (3) is a Drucker-Prager yield condition equation, and equation (4) is a constitutive equation.

here,
It is.

  By using the above equations (1) to (4) and calculating the in-furnace stress distribution by FEM (finite element method), the settlement level and shape of the furnace core coke can be calculated. According to the above method, it is possible to greatly reduce the calculation load as compared with the case where the DEM (discrete element method) is used.

Step S5
Using the shape of the operating surface of the hearth brick determined in S2, the operating conditions set in S3, and the distribution of resistance to liquid flow in the lower part of the furnace set based on the sinking level of the core coke determined in S4, hot metal is introduced into the blast furnace. The temperature distribution of the coke packed bed, the hot metal and the slag, and the flow velocity distribution of the hot metal and the slag in the lower part of the blast furnace are calculated based on the mass balance formula, the momentum balance formula and the energy balance formula when the slag is contained. In S5, it is desirable to obtain the coke packed bed in the lower part of the blast furnace, the temperature distribution of the hot metal and slag, and the flow rate distribution of the hot metal and slag. In the present invention, it is most preferable to obtain the flow rate of the hot metal near the brick working surface. Since it is important, it is not always necessary to calculate the slag flow velocity distribution and the furnace bottom temperature distribution.

  This step S5 can be performed using, for example, a known model or the like described in Non-Patent Document 1. That is, the furnace bottom of the blast furnace is assumed to be composed of a brick as a structure and a molten iron, slag and coke packed bed as contents. The material balance equation (8), the momentum balance equation (9), and the energy balance equation (10) for hot metal and slag are as follows.

here,
It is.

The energy balance equation (14) for coke is as follows.

However, in the above equations (8) to (14),
U: velocity vector, ρ: density, S: generation amount (dropping amount), p: pressure, μ: viscosity, β: volume expansion coefficient, g: gravitational acceleration, Cp: specific heat, T: temperature, T ₀ : reference temperature , T _coke : temperature of coke, T _liq : temperature of hot metal and / or slag, λ: thermal conductivity, ε: porosity, φ: particle shape factor, dp: particle diameter, F: liquid flow resistance, ε: void Rate, h: convective heat transfer coefficient, A: specific surface area of the coke packed bed.

  If the above equations (8) to (14) are simultaneously solved, it is possible to obtain the time transition of the flow and temperature of the hot metal and slag.

Step S6
From the flow velocity distribution of the hot metal obtained in S5, the flow velocity of the hot metal near the portion where the erosion of the brick is most advanced is obtained. Here, the “nearby” is most preferably a mesh including the most eroded portion. Further, the mesh may be within a range of a half of an interval (21d in FIG. 2) between adjacent thermocouple units from the mesh.

  The erosion of the lower furnace brick proceeds mainly due to a rise in the temperature of the brick working surface. The temperature rise of the brick is mainly caused by convective heat transfer from the hot metal to the brick. It is a known fact that the amount of heat supplied from the hot metal to the brick by convective heat transfer decreases as the flow velocity of the hot metal near the brick decreases. Therefore, it is not necessary to determine the erosion behavior of the brick by the unsteady calculation in order to determine the operating condition that can suppress the erosion of the brick most, and it is necessary to determine the operating condition that minimizes the flow velocity of the hot metal near the brick at the predetermined position. Is enough.

  In the case where the unsteady calculation is performed in S5, the flow velocity of the hot metal in the vicinity of the part where the erosion of the brick is most advanced may be given, for example, as an average velocity in a time corresponding to one cycle of the tapping schedule.

  From the above, the flow velocity of the hot metal at the location where the brick erosion is most severe at the current blast furnace bottom is estimated.

  Next, a procedure for determining an operation method that can effectively suppress the extension of the erosion of the brick at a location where the erosion of the brick is most severe using this estimation method will be described.

Step S7
When a plurality of possible countermeasures (operating conditions) are considered to reduce the flow velocity of the hot metal at the predetermined position, the flow velocity of the hot metal in the vicinity of the site where the erosion of the brick is most advanced is determined by the above-described steps S3 to S6. Calculate with the procedure. That is, when the calculation of all the operating conditions assumed in advance is not completed, the process returns to S3, and after the operating conditions are changed, the processes of S4 to S6 are performed under the operating conditions, and the calculation is repeated for each operating condition. Then, the flow velocity of the hot metal in the vicinity of the portion where the erosion of the brick is most advanced under the respective operating conditions is estimated.

  As a plurality of countermeasures, for example, tap hole depth, tapping lap time, mud erosion rate, presence or absence of coke free space, and the like can be considered, all of which can be used alone or in combination, or can be realized. Calculate for one of the measures. The taphole depth refers to the total length of the taphole including the furnace wall portion including the brick and the mud portion made of an irregular refractory provided inside the furnace of the taphole. The lap time refers to the overlapping time of tapping from a plurality of tap holes.

Step S8
When the calculation is completed for all the operating conditions assumed in advance, from the estimated values of the flow velocity of the hot metal in the vicinity of the site where the brick erosion is progressing, the flow velocity of the hot metal at Choose a countermeasure that will be smaller. Thereby, it is possible to determine a method of operating the blast furnace that can most effectively suppress the extension of erosion of the hearth brick.

  As described above, by combining the three techniques of the method of estimating the furnace bottom brick surface, the method of estimating the position and shape of the lower surface of the core coke, and the method of estimating hot metal and slag flow at the furnace bottom, It is possible to estimate the hot metal flow velocity at the site where the erosion of the hot metal is progressing. Then, by adopting an operating condition that minimizes the flow rate of the hot metal from among various countermeasure plans, it is possible to effectively suppress the erosion of the hearth brick without stopping the operation of the blast furnace. Conventionally, in order to suppress the erosion of refractories, measures such as controlling cooling water for cooling the furnace bottom have been taken. However, according to the present invention, an apparatus for controlling such cooling water, etc. It is not necessary to provide.

  Hereinafter, embodiments of the present invention will be described.

The present invention was applied to a blast furnace having a furnace volume of 1850 m ³ , and an operation method capable of most effectively suppressing the extension of erosion of a bottom brick was studied.

  First, a calculation grid was generated based on the hearth structure of the blast furnace. FIG. 2 shows a furnace bottom of the blast furnace 11 studied in the present embodiment, and is an example of a calculation grid in a cross section passing through two tap holes 12a and 12b. The furnace bottom of the blast furnace 11 has a brick 13 which is a structure, and hot metal 14 and slag 15 are deposited inside.

  FIG. 3 shows an example of a planar arrangement of thermocouples 21 embedded in a furnace bottom. In the present embodiment, tap holes 12a, 12b, and 12c are provided in three directions at the bottom of the blast furnace 11, and radial distances 1P, 2P, and 3P from the center of the furnace toward the outer periphery, directions NE, SE, and SW. , NW are each provided with a thermocouple 21. These thermocouples 21 are installed at three levels in the height direction, respectively (see FIG. 2).

  FIG. 4 shows the result of obtaining the residual thickness distribution of the hearth brick (middle buried brick) based on the temperature measured by the thermocouples arranged in the upper and middle tiers and the physical properties of the brick. The numbers in the figure indicate the remaining thickness (mm) of the brick. As shown in FIG. 4, the remaining thickness of the brick at the radial position: 2P (see FIG. 3) and the orientation: NE is the smallest, and the remaining thickness is eroded to about 100 mm.

  Next, based on the latest operating conditions, the settlement level and shape of the furnace core coke were calculated by a known model based on rigid plasticity mechanics (see ISIJ int., 49 (2009), p. 470). The solid line in FIG. 5 shows the lower surface of the core coke obtained from the calculation result. Further, the calculation result of the brick thickness at the hearth (brick operating surface) is indicated by a broken line. From FIG. 5, it can be seen that most of the first stage of the embedded brick has already disappeared, and the erosion of the brick has reached the second stage of the embedded brick.

  Since the area above the core coke lower surface is the area where the coke packed layer exists, the flow resistance F of the equation (9) was set by the above equations (11) to (13). The area sandwiched between the lower surface of the furnace core coke and the operating surface of the embedded brick is a coke free space, and there is no packed bed. Therefore, the flow resistance in equation (9) is set to F = 0.

  In the current operating state, the taphole depth, lap time, mud erosion rate, and sinking level of the furnace core (with or without coke free space) for the hot metal flow velocity near 2P-NE with the smallest brick thickness Table 1 shows the results of calculating the rate of decrease in the flow velocity of the hot metal near 2P-NE when the four types of operating conditions were changed alone or in combination.

  Case 1 is in the current operating state, the taphole depth is 2 m, and the taphole lap time is 0. Case 2 is the case where the tapping depth d was changed to 3 m by increasing the thickness of the mud 22, and the flow velocity of the hot metal in the vicinity of 2P-NE was reduced by 5.6% as compared with Case 1. Case 3 is a case in which lapping is performed with a lapping time of simultaneously opening two tapholes 12a and 12b being 30 minutes, and it has been found that the flow velocity of the hot metal near 2P-NE decreases by 15%. . Furthermore, Case 4 in which lapping was performed with a lap time of 30 minutes and the taphole depth d was changed to 3 m, the flow velocity of the hot metal near 2P-NE was reduced by 20%, and as a result, The extension of erosion could be suppressed.

  On the other hand, in the case 5 in which the melting loss rate was reduced by improving the mud 22, the reduction effect of the molten iron flow velocity near 2P-NE was 5.6%, and the time and cost required for the development of the mud material were reduced. In consideration of the effect and the effect, it was found that the change of the lap time alone or the change of the lap time and the taphole depth d can reduce the flow rate of the hot metal more efficiently. Further, in case 6 in which the taphole depth d was changed from 2 m to 3 m, and the core was completely landed on the bottom of the furnace to eliminate the coke free space, the flow velocity of the hot metal near 2P-NE was reduced to about 60. %, And the greatest effect was obtained. In case 6, the coke free space was eliminated by increasing the coke ratio from 320 kg / t (case 1) to 350 kg / t. The means for eliminating the coke free space is not limited to this, and for example, the air permeability and the gas composition may be adjusted.

  Based on the above results, in the target blast furnace, the tap hole depth d was changed from 2 m to 3 m, and the coke ratio was increased to secure air permeability in the furnace and completely attach the core to the furnace bottom. I let it floor. Thereby, the erosion of the brick in 2P-NE was suppressed, and the stable blast furnace operation was able to be performed.

  Conventionally, based on past experience, all means considered to suppress erosion of hearth bricks were implemented, but according to the present invention, the most effective means for erosion of hearth bricks is efficiently used. Now you can do it.

  INDUSTRIAL APPLICABILITY The present invention can be applied as a method for suppressing the extension of erosion of bricks in a furnace bottom of a blast furnace.

11 Blast furnace 12a, 12b, 12c Tap hole 13 Brick 14 Hot metal 15 Slag 21 Thermocouple (unit)
22 Mad

Claims (3)

A method of estimating the flow velocity of hot metal at a site where erosion is progressing most, in a hearth brick lined at the hearth of a blast furnace,
From the structure of the hearth brick lined at the bottom of the blast furnace, a calculation grid was generated,
In the hearth brick, two thermocouples are embedded in one set, and based on the measured temperature of the two thermocouples, the heat flow is determined from the temperature and distance between the two points and the thermal conductivity of the hearth brick. Calculate the bundle, calculate the remaining thickness of the hearth brick assuming the temperature of the operating surface of the hearth brick, calculate the shape of the operating surface of the hearth brick by performing this calculation for a plurality of sets of thermocouples ,
Set the current operating conditions,
The lower end level and the shape of the core coke in the furnace are calculated based on the mechanical balance from the wear conditions of the operating conditions and the hearth brick, and reflected as the flow resistance in the furnace,
The temperature distribution of the hot metal, slag, coke packed bed at the bottom of the furnace, and the hot metal and Calculate the slag flow velocity distribution,
A method for estimating the flow velocity of hot metal in a blast furnace, comprising estimating the flow velocity of hot metal near a portion where erosion of the hearth brick is most advanced from the flow distribution of the hot metal. A method for operating a blast furnace, which determines operating conditions for a blast furnace using the method for estimating flow velocity of hot metal in a blast furnace according to claim 1,
Set a plurality of different operating conditions, calculate the flow velocity distribution of the hot metal in the same procedure as the current operating conditions,
A method for operating a blast furnace, wherein a condition in which the flow velocity of hot metal in the vicinity of a portion where the erosion of the hearth brick is most advanced is the smallest among the plurality of different operating conditions is a new operating condition. The plurality of different operating conditions are tap hole depth, tapping lap time, mud erosion rate, and the presence or absence of coke free space, either alone or in combination of two or more. The method for operating a blast furnace according to claim 2, characterized in that: