JP2012237028A - Method for heating cast slab - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for heating a cast slab with which in order to improve the precision of a temperature control in the cast slab, an unnecessary heating in a heating furnace is restrained and economical temperature-rising can be obtained by setting a controlled temperature index for operating by applying a three-dimensional temperature calculation with multi-points continuous calculation to the temperature.SOLUTION: In the method for heating the cast slab, produced with a continuous casting machine, the relation of a temperature distribution between the length of the cast slab 10 and the cross-sectional temperature from the surface temperature of the cast slab 10 and casting condition, is obtained through from a charging side to an extracting side. Then, the thermal powers of each burners 18, 19 are controlled based on the center position of the cast slab 10, and the difference of the average temperatures between the one side and the other side in the longitudinal direction at the extracting position based on the center position, is made to be -15°C to +15°C, and the difference between the lowest temperature of the cross-sectional surface of the one side and the average temperature distribution of the other side, is controlled to be -10°C to +20°C.

Description

The present invention relates to a method for heating a slab having a temperature distribution (in particular, a slab immediately after continuous casting).

Conventionally, for example, in order to hot-roll a slab after continuous casting (an example of a slab) and adjust it to target thickness and width dimensions, the slab is heated in advance by a heating furnace or the like.
As this heating method, for example, in Patent Document 1, the slab temperature passing through the heating furnace is estimated, and the target temperature increase pattern of the slab is determined from the estimated value, the target temperature during extraction, and the heating time. And the method of setting the heating zone of a heating furnace and the atmospheric temperature of a soaking zone so that this slab follows a target temperature rising pattern is disclosed. Specifically, the current slab temperature is estimated using a distributed constant system temperature model, and the temperature rise pattern and set furnace temperature with the optimal fuel consumption rate are obtained using this model, and this slab temperature is estimated. , One cross section of the slab (or two cross sections including the skid cross section).

JP-A-9-209044

However, in continuous casting, for example, a temperature distribution occurs mainly in the longitudinal direction (casting direction) of the slab due to variations in the length of the slab to be manufactured and casting conditions. Furthermore, slabs produced by continuous casting are long, and partly due to temperature differences between the part where the continuous casting was performed first and the part immediately after continuous casting, or due to fluctuations in casting conditions. In many cases, temperature drop or temperature rise occurs. For this reason, like the above-mentioned heating method of the slab, when estimating the slab temperature only in one cross section (or two cross sections), the temperature distribution in the longitudinal direction of the slab is not reflected, Since the entire slab is heated in the heating furnace under the same conditions, a portion that is excessively heated is generated. Therefore, the above-described method is uneconomical due to the waste of energy costs required for heating.

Furthermore, the conventional method is a method of controlling the temperature in the furnace by estimating the temperature of a slab by one section of the slab by simple two-dimensional difference calculation based on one point calculation of the temperature at a certain position of the slab. Instead, in order to improve the accuracy of control, it is considered to control the temperature in the furnace by applying three-dimensional temperature calculation by multi-point continuous calculation in order to grasp the slab temperature more accurately. It is done. However, even considering the application of this three-dimensional temperature calculation, the length and casting conditions of the slabs to be produced are actually different, and in order to apply these to the slab, it is necessary to operate the three-dimensional temperature calculation. If you do not set various temperature indicators, you will not be able to get a sufficient energy saving effect.

The present invention has been made in view of such circumstances, and when controlling the temperature in the heating furnace by calculating the temperature distribution of the slab by performing a three-dimensional temperature calculation, unnecessary heating is suppressed in order to achieve an energy saving effect. It aims at providing the heating method of the slab which provides and manages a temperature parameter | index.

The method for heating a slab according to the first invention that meets the above-mentioned object is characterized in that a slab having a gradient temperature distribution that increases from one end to the other end is placed in a transverse direction in the longitudinal direction, and the width of the heating furnace above and below the slab. A method for heating a slab to be placed in a heating furnace provided with a plurality of burners arranged along a direction, wherein the length of the slab and the three-dimensional temperature calculation of the slab are calculated from the surface temperature and casting conditions of the slab. The relationship between the average cross-sectional temperature in the longitudinal direction corresponding to the above is obtained from the charging side to the extraction side, and the heating power of the burner is controlled with reference to the center position of the slab, and 1) the center position of the slab is determined. The difference between the average temperature on one side in the longitudinal direction at the extraction position and the average temperature on the other side is between −15 ° C. and + 15 ° C., and 2) the lowest temperature of the cross section on one side and the average temperature distribution on the other side Is controlled to −10 ° C. to + 20 ° C.
As a result, the temperature distribution of the slab is heated to be within a predetermined range by comparing a predetermined temperature index on one side and the other side in the longitudinal direction. Energy consumption can be reduced.

The method for heating a slab according to the second invention is the method for heating a slab according to the first invention, wherein the control of the burner is performed by dropping a part of the heating power of the burner provided on the other side in the width direction. Do.
As a result, by directly controlling the thermal power of the burner on the other side, quick temperature management can be performed and energy consumption of the heating furnace can be suppressed.

The method for heating a slab according to the third invention is the heating method for the slab according to the first invention or the second invention, wherein the heating method for the slab is a traveling direction in which the slab is loaded and extracted. Are divided into a plurality of furnace zones, and the group of the burners is divided into a plurality of groups for each of the plurality of furnace zones.
As a result, along with the direction in which the slab is charged and extracted, for example, by separately controlling the burner group divided into heating zone and soaking zone, fine temperature in time series from charging to extraction Management is possible and optimal temperature management is possible.

The method for heating a slab according to the fourth invention is the method for heating a slab according to any one of the first to third inventions, wherein the temperature distribution on the extraction side of the slab is one side in the longitudinal direction. This is a swell shape in which a mountain is formed in the vicinity of the central portion and a valley is formed in the vicinity of the central portion on the other side.
As a result, since it is easy to understand intuitively as an energy saving index by controlling paying attention to the temperature distribution of the waviness shape on the slab extraction side, it is possible to easily manage the energy consumption of the heating furnace.

The method for heating a slab according to the present invention finely detects the position of a high-temperature region where the temperature is higher than other locations by obtaining the temperature distribution of the slab three-dimensionally. The total temperature energy required for heating the slab by heating the slab while suppressing heating in the high temperature region by providing a temperature index for the set temperature of the heating furnace based on the three-dimensional temperature calculation and performing burner control Reduction (energy saving).

1 is a system diagram of a heating furnace in which a method for heating a slab according to an embodiment of the present invention is used. (A), (B) shows arrangement | positioning of the burner of the same heating furnace, and is explanatory drawing which planarly viewed the sectional side view of a heating furnace, and a heating furnace, respectively. (A) is explanatory drawing which shows the thermometer arrangement | positioning of the heating furnace, (B) is explanatory drawing which shows the flame emission direction of a burner. It is explanatory drawing which shows the calculation method of the temperature measurement of the slab heated in the same heating furnace. (A), (B) shows the temperature measurement method of a slab, and is explanatory drawing which shows the two-dimensional temperature measurement of a prior art, respectively, and explanatory drawing which shows three-dimensional temperature measurement. (A)-(C) show the temperature change of a slab notionally, respectively, the temperature change at the time of performing the heating of a prior art, the temperature change anticipated prior to employ | adopting a three-dimensional temperature measurement, a tertiary It is explanatory drawing which shows the actual temperature change at the time of heating using original temperature measurement. (A) is explanatory drawing of the temperature change of C cross-section average temperature between skids of a slab, (B) is explanatory drawing of the temperature distribution in a heating furnace. (A) is explanatory drawing of the temperature change of C cross-section average temperature between skids of a slab, (B) is explanatory drawing of the temperature distribution in a heating furnace. (A), (B) shows the temperature change of a slab, and is an explanatory view showing the concept of the “indentation temperature rise” state and the “swell-like temperature rise” state, respectively. (A), (B) shows the operation index of a heating furnace, and is an explanatory view showing a “indentation temperature rise” state and a “swell-like temperature rise” state, respectively. It is a bar graph which shows the ratio which a "swelling temperature rise" state generate | occur | produces. It is a bar graph which shows the frequency which the "medium dent temperature rising" state and the "swell-like temperature rising" state generate | occur | produce. It is explanatory drawing which shows a fuel basic unit reduction result.

Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIGS. 1 and 2, the method for heating a slab according to an embodiment of the present invention includes a plurality of upper burners 18 and lower burners 19 provided in the heating furnace 13. This is a method of heating the piece 10.
The slab 10 is manufactured by a continuous casting machine (not shown), continuously extracted, cut into a predetermined length by the CC cutter 11, and then loaded into the heating furnace 13 by the transfer table 12 (hereinafter, referred to as the slab 10). , Also called the entrance). The slab 10 cut into a predetermined length has a gradient temperature distribution that increases from one end to the other along the longitudinal direction. This is because time has elapsed since one end of the slab 10 exited the continuous casting machine compared to the other end.
The slab 10 conveyed to the entrance of the heating furnace 13 is charged into the heating furnace 13 with its longitudinal direction being transverse, and is heated and extracted in the heating furnace 13. The slab 10 heated to an appropriate temperature is rolled and sized.

In the present embodiment, the heating furnace 13 has a furnace width of 30 m and a furnace length of 18 m. The slab 10 has a thickness of 100 to 400 mm, a width of 650 to 3000 mm, and a length of 3 to 30 m. The size of the heating furnace and the slab is not limited to this size. For example, the size of the slab is determined according to the specifications of a product manufactured based on the slab.

The heating furnace 13 is divided into a plurality of furnace zones, that is, a heating zone 14 and a soaking zone 15 along an outlet from which the slab 10 is extracted from an inlet into which the slab 10 is charged. In the soaking zone 15, the amount of heat given to the slab 10 is smaller than in the heating zone 14, and the temperature rise of the slab 10 passing through the soaking zone 15 becomes more gradual than when passing through the heating zone 14. .
Moreover, the heating furnace 13 is divided into two areas in the width direction of the heating furnace 13, and in this embodiment, one of the two areas is an east side area 16 and the other is a west side area 17.
In the heating zone 14 (the same applies to the soaking zone 15), a plurality of upper burners 18 and a plurality of lower burners 19 are arranged above and below the slab 10 traveling in the heating zone 14, respectively. The upper burner 18 is provided on the ceiling 23 of the heating furnace 13 in the heating zone 14 and the soaking zone 15. Further, the slab 10 moves in the heating zone 14 with one half on the east side area 16 and the other half on the west area 17 with respect to the longitudinal center position.
The plurality of upper burners 18 (the same applies to the plurality of lower burners 19) are arranged side by side along the width direction of the heating furnace 13, and the slab 10 in progress in the heating furnace 13 is heated to a predetermined temperature. . In the present embodiment, in the heating furnace 13, the temperature of the cast slab 10 at the time of charging is increased by 180 ° C. on average, and the slab 10 is extracted at a temperature of about 1080 ° C.

FIG. 2 shows the burner arrangement of the heating furnace 13.
FIG. 2A is a cross-sectional view of the heating furnace 13.
The heating zone 14 of the heating furnace 13 and the ceiling 23 of the soaking zone 15 described with reference to FIG. 1 are each formed in a trapezoidal cross section, and the heating zone 14 and soaking zone 15 have respective heating zones from the ceiling 23 at the boundary. 14 and a plurality of upper burners 18 are provided in the longitudinal direction (width direction) of the heating furnace 13 so as to heat toward the center of the soaking zone 15. A plurality of lower burners 19 for heating the slab 10 being charged and extracted from the lower surface side are also provided in the width direction in the same manner as described above. The slab 10 moving from the inlet to the outlet is heated by the upper and lower burners 18 and 19.

The ceiling 23 of the heating furnace 13 protrudes in the furnace width direction in each of the heating zone 14 and the soaking zone 15, as shown in FIGS. 1, 2A, and 2B.
When viewed from the side of the heating furnace 13, each upper burner 18 arranged in the heating zone 14 is attached to the ceiling 23 so as to emit flame toward the center of the heating zone 14 and is arranged in the soaking zone 15. Each upper burner 18 is attached to the ceiling 23 so as to emit flame toward the center of the soaking zone 15.
Then, as viewed from the side of the heating furnace 13, each lower burner 19 provided in the heating zone 14 is disposed so as to emit flame toward the center of the heating zone 14, and each lower burner 19 provided in the soaking zone 15. Is arranged so as to emit flame toward the center of the soaking zone 15.
The slab 10 moving in the heating furnace 13 is heated from above and below by the upper burner 18 and the lower burner 19.

One row of upper burners 18 (hereinafter also referred to as “group of upper burners 18”) arranged in the heating furnace 13 along the width direction of the heating furnace 13 is provided in each of the heating zone 14 and the soaking zone 15. Similarly, one row of lower burners 19 (hereinafter also referred to as “group of lower burners 19”) arranged along the width direction of the heating furnace 13 is provided in the heating zone 14 and the soaking zone 15 respectively. Yes.
The heating furnace 13 is provided with a fuel pipe 20, and COG fuel and combustion air are supplied to the groups of the upper burners 18 and the groups of the lower burners 19 through the fuel pipes 20. Each upper burner 18 and each lower burner 19 is provided with a heating power adjusting valve, and by controlling this valve, the heating power of a part of each upper burner 18 group and each lower burner 19 group is controlled. Control the furnace temperature.
Since the upper burner 18 and the lower burner 19 at the same position in a plan view heat the upper and lower sides of the slab 10, basically the same heating power adjustment is performed. Further, for example, all the upper burners 18 and the lower burners 19 in the heating zone 14 are controlled to have the same heating power, or depending on the place where the upper burner 18 and the lower burner 19 in the heating zone 14 are arranged. Can be controlled.
The above is an example in which two furnace zones are provided along the direction of slab travel, and one group of upper burner 18 and one group of lower burner 19 are provided for each furnace zone.

FIG. 3 shows the thermometer arrangement of the heating furnace 13, FIG. 3A is a plan view of the inside of the heating furnace 13, and FIG. 3B is a cross-sectional view of the heating furnace 13.
As shown in FIG. 3A, a plurality of thermometers 21 are arranged on the heating zone 14 of the heating furnace 13 and the ceiling 23 of the soaking zone 15, respectively, to manage the furnace temperature. In the present embodiment, in FIG. 3 (A), the thermometer 21 is arranged at a place where numerals 1 to 9 are entered in the symbol ◯. Hereinafter, the thermometer 21 is distinguished and described by the numbers in the circles.
The heating furnace 13 is roughly divided into four areas. There are four areas: an east area 16 of the heating zone 14, a west area 17 of the heating zone 14, an east area 16 of the soaking zone 15, and a west area 17 of the soaking zone 15. In each area, thermometers 21 from No. 1 to No. 5 are arranged at different positions in the furnace width direction of the heating furnace 13. The thermometers 21 from No. 1 to No. 5 are arranged such that when adjacent thermometers 21 are connected by a straight line, a zigzag line is formed in plan view by the plurality of straight lines.
The first and second thermometers 21 are arranged with an interval of about 0.6 m to 1 m, and the third, fourth, and fifth thermometers 21 are also arranged with an interval of about 0.6 m to 1 m. It is arranged with a gap.

Next, the thermometers 21 from No. 6 to No. 9 of the thermometer 21 are arranged at predetermined intervals from the entrance (loading side) to the exit (extraction side) in both the east area 16 and the west area 17. Yes.
In contrast, conventionally, the first and second thermometers were used as control thermometers, and the furnace temperature was controlled only by this. Precisely, the temperature inside the furnace is measured by the first or second thermometer 21 in each of the heating zone 14 and the soaking zone 15 to calculate the cross-sectional temperature at a specific position of the slab 10, and this calculated slab 10 The temperature in the heating furnace 13 was adjusted by temperature estimation based on two-dimensional temperature calculation for estimating the temperature in the longitudinal direction of the slab 10 based on the temperature of. In addition, the third, fourth, and fifth thermometers 21 were already installed, but were used only for monitoring.

In the present embodiment, the sixth to ninth thermometers 21 are newly attached to the ceiling 23. The sixth thermometer 21 is provided on the ceiling 23 near the entrance of the heating furnace 13, and measures the temperature at the highest temperature among the sixth to ninth thermometers 21.
The eighth thermometer 21 is provided in the nose portion 22 that is the boundary between the heating zone 14 and the soaking zone 15, and measures the temperature at the lowest temperature among the sixth to ninth thermometers 21. The seventh thermometer 21 measures the temperature in the heating furnace 13 on the exit side of the heating zone 14 and the ninth thermometer 21 on the entry side of the soaking zone 15.
The temperature in the heating furnace 13 increases from the entrance of the heating furnace 13 to the arrangement position of the sixth thermometer 21 in the traveling direction of the slab 10, and the eighth thermometer from the arrangement position of the sixth thermometer 21. It becomes low over the arrangement position of 21 and increases from the arrangement position of the eighth thermometer 21 to the arrangement position of the ninth thermometer 21.

Based on each temperature measured by the 1st to 9th thermometers 21, a three-dimensional temperature calculation is performed to calculate the temperature of the slab 10, and the east side area 16 and the west side area 17 (each top and bottom) of the heating zone 14 and the average The temperature is controlled by controlling the COG gas flow rate and the combustion air amount of the upper burner 18 and the lower burner 19 for all eight bands of the east side area 16 and the west side area 17 (upper and lower) of the tropics 15.
Since the thermometer 21 measures the temperature in the furnace, a thermocouple is generally used.

FIG. 4 is a diagram showing a three-dimensional temperature calculation model of the slab 10, in which the slab 10 is divided into lattices as a model.
And it is a three-dimensional temperature calculation model of the full length full width full thickness of the slab 10 which is moving the heating furnace 13, This is what is called a 3D online model (model which produces slab online using a three-dimensional temperature calculation model). As a real machine.

In the present embodiment, the model of the slab 10 is divided into 151 divisions (maximum) in the longitudinal direction of the slab 10, 12 divisions in the width direction and 7 divisions in the thickness direction, and is divided into 12684 division pieces. . The division pitch is, for example, about 200 mm in the longitudinal direction of the slab 10.
Then, a plurality (84 pieces) of the divided pieces at the same position in the longitudinal direction of the slab 10 are measured from one end to the other end in the longitudinal direction, and temperature measurement is performed on all 12684 divided pieces.

Thereby, since the temperature distribution about the both end surfaces of the longitudinal direction of the slab 10 and the cross section of a different position is obtained, the temperature distribution of the longitudinal direction, the width direction, and the thickness direction of the slab 10 is continuously three-dimensionally. Can be estimated.
Therefore, by controlling the output of the upper burner 18 and the lower burner 19 based on the estimated temperature distribution, the ambient temperature in each region in the heating furnace 13 is adjusted, and the longitudinal direction and width of the slab 10 are adjusted. The temperature distribution in the direction and the thickness direction is adjusted to the target temperature distribution.
In addition, the temperature difference generated in the longitudinal direction of the slab differs depending on the length of the slab 10 to be manufactured and the casting conditions. When the slab 10 is long, the temperature difference in the longitudinal direction becomes large. Become prominent.

That is, for the slab 10, a conventional method in which a cross-section is cut at a specific position in the longitudinal direction and two-dimensional temperature calculation is performed on the cross-section is performed at a plurality of (151) positions in the longitudinal direction. The three-dimensional temperature calculation is performed by measuring the temperature, and the fact that the accuracy of the temperature distribution by the temperature simulation is greatly improved contributes.

Further, the temperature distribution of the slab 10 is calculated using a conventionally known arithmetic unit (that is, a computer) having a RAM, a CPU, a ROM, an I / O, and a bus for connecting these elements. It is not limited to.

FIG. 5A is a diagram showing a two-dimensional differential temperature model of the prior art.
In the prior art, a temperature simulation calculation was performed on a cross section at a position 5 m from one end in the longitudinal direction of a slab moving in a heating furnace, and the entire cross section was represented. Note that the slab is at a low temperature because one end side in the longitudinal direction has elapsed from the continuous casting step compared to the other end side. And the point which performed temperature simulation calculation is a position near one end from the longitudinal direction other end of a slab.
Since the overall temperature of the slab 10 is estimated based on this result, the accuracy of the temperature distribution is rough. Since the other end side in the longitudinal direction of the slab is far from the temperature-simulated position, the furnace temperature in the region close to the other end side in the longitudinal direction of the slab cannot be controlled finely and energy cannot be saved.

FIG. 5B is a diagram showing a three-dimensional temperature calculation model of the present invention.
As shown in FIG. 5 (B), the slab 10 is subjected to temperature calculation for a cross section cut at different positions in the longitudinal direction in the entire longitudinal direction, and is heated and controlled. As a result, finer heating control is possible, and in the prior art, the slabs that can be monitored were four slabs in the heating furnace, but a maximum of 28 slabs could be monitored. In addition, it has become possible to save energy by optimally controlling the temperature of all slabs in the heating furnace.

FIG. 6 shows the concept of “medium recess temperature rise”.
FIG. 6A is an explanatory diagram showing a temperature change in the prior art.
In the prior art, as shown in FIG. 6 (A), the entire slab was heated under the same conditions without considering the temperature distribution in the longitudinal direction of the slab. When the slab is extracted from the heating furnace, the required extraction temperature (the temperature of the slab required for rolling with a rolling mill) is greatly exceeded, and energy costs required for heating are wasted.

FIG. 6B is an explanatory diagram showing the temperature change of the slab assumed prior to the application of the present invention.
Based on the detection result of the temperature distribution of the slab described above, in order to heat the slab while suppressing the heating of the west region in the heating furnace, the burner (upper burner and lower burner) arranged in the west area in the heating furnace. ) Is lower than the output of the burners (upper burner and lower burner) arranged in the east area. As a result, the temperature of the slab when extracted from the heating furnace is equivalent to the portion disposed on the west side as the portion disposed on the east side. Thereby, the waste of the energy cost required for the heating of the part arrange | positioned at the west side of slab can be eliminated, and the energy-saving effect is acquired. Such a temperature change was initially assumed.

FIG. 6C is an explanatory diagram showing the actual temperature change of the slab when the present invention is applied.
When the three-dimensional temperature calculation is actually performed to calculate the temperature of the slab 10 and the temperature in the heating furnace 13 is adjusted, as shown in FIG. The temperature at one end in the longitudinal direction in the east side area 16 is the lowest and the temperature increases linearly as it approaches the other end in the west side area 17. Became closer to the longitudinal center.
The slab 10 at the time of extraction of the heating furnace 13 had the lowest temperature at the center in the longitudinal direction, and became higher as it approached both ends, and in particular, the temperature at the end in the west area 17 increased.
At the time of extraction of the heating furnace 13, a “middle depression temperature rise” in which the temperature drop at both ends in the longitudinal direction of the slab 10 is insufficient, that is, a so-called central portion is depressed.

FIG. 7 illustrates “indentation temperature rise”.
FIG. 7A is an explanatory diagram showing the temperature change of the C cross-section average temperature between skids. The relationship between the length of the slab 10 and the cross-section average temperature of the slab 10 is obtained from the charging side to the extraction side. Is shown.
The horizontal axis represents the length of the cast piece 10 (base material), and the vertical axis represents the inter-skid C cross-section average temperature (C is an abbreviation of the cross section: cross section) of the base material between the skids (cast piece 10). Here, detailed description of the skid etc. which support the slab 10 is abbreviate | omitted.
In FIG. 7 (A), numbers from 1 to 18 are written in the symbol O, which indicates the order of the intermediate portion where the influence of the skid supporting the slab 10 is small. A plurality of line segments in the figure is a temperature distribution in the longitudinal direction of the slab 10, and a line segment at the bottom in the vertical axis direction in the figure shows the slab 10 when charged in the heating furnace 13. . The plurality of line segments is the slab 10 that is closer to the exit side of the heating furnace 13 as it is higher in the vertical axis direction.

As shown in FIG. 7A, the “C cross-sectional average temperature” having a predetermined linear temperature gradient (gradient temperature distribution) at the time of charging is the east side (B side: B) during the heating process of the heating furnace 13. Means the bottom) and the west side (T side: T stands for the top) has a large temperature rise and a relatively small temperature rise near the center. It becomes a state. And the amount of temperature rising of the slab 10 from the time of charging the furnace 13 to the time of extraction is substantially the same value at the east side (one side) end and the west side (other side) end of the slab 10. In FIG. 7A, the temperature increase amount at the east end is indicated by T _B , and the temperature increase amount at the west end is indicated by T _T.

FIG. 7B is a furnace temperature distribution diagram in the width direction of the heating zone and the soaking zone.
The horizontal axis indicates the furnace width, and the vertical axis indicates the furnace temperature. FIG. 7B shows that the furnace temperature distribution in the furnace width direction is lower at the center than at both ends. And it is presumed that this causes “indentation temperature rise”.
Because both furnace zones of heating zone 14 and soaking zone 15 have a high furnace temperature at both ends, they show “middle depression temperature rise”. This is because the amount of COG gas is on the east side area 16 and the west side. This is because such a furnace temperature distribution is obtained when the area 17 is almost equal.
In the heating zone 14, the west side in the furnace width direction is higher than the east side.

FIG. 8 explains “swelling temperature rise”.
FIG. 8 (A) is an explanatory view showing the temperature change of the C cross-section average temperature between skids, and the relationship between the length of the slab 10 and the cross-section average temperature of the slab 10 is obtained from the charging side to the extraction side. Is shown.
7A, the horizontal axis indicates the length of the base material (slab 10), and the vertical axis indicates the inter-skid C cross-sectional average temperature of the base material (slab 10) between skids. A number from 1 to 18 is written in the symbol indicates the order of the intermediate portion with less influence of the skid supporting the slab 10.
A plurality of line segments in the figure is a temperature distribution in the longitudinal direction of the slab 10, and a line segment at the bottom in the vertical axis direction in the figure shows the slab 10 when charged in the heating furnace 13. . The plurality of line segments is the slab 10 that is closer to the exit side of the heating furnace 13 as it is higher in the vertical axis direction.

As shown in FIG. 8A, the “C cross-sectional average temperature” having a predetermined linear temperature gradient at the time of charging is from the east side (B side) to the west side (T side) in the process of raising the temperature of the heating furnace 13. The temperature distribution over the swell has a wavy shape. That is, a mountain is formed near the center of the east area 16 and a valley is formed near the center of the west area 17. As a result, compared with FIG. 7, the base material (slab 10) at the time of extraction of the heating furnace 13 has a smaller difference between the lowest temperature and the highest temperature in each part in the longitudinal direction. This is the “swell-like temperature increase”, which is an energy saving type temperature increase that successfully increases the temperature of the inclined charging. Here, T _T is in T _B value less than the temperature rise of the eastern end is a temperature rise in the western end of the slab 10. As a result, it is possible to control the slab temperature without dents with appropriate furnace temperature distribution control, and to save energy.

FIG. 8B is a furnace temperature distribution diagram in the width direction of the heating zone and the soaking zone.
As in FIG. 7, the horizontal axis indicates the furnace width, and the vertical axis indicates the temperature in each furnace. From FIG. 8B, in the furnace width direction, a flat furnace temperature distribution (particularly the heating zone 14) is obtained as a whole in comparison with FIG. 7, and in the soaking zone 15, due to a decrease in the furnace temperature particularly on the west side, It is estimated that the “swelling temperature rise” state is obtained.

FIG. 9 shows the concept of “medium dent temperature rise” and “swell-like temperature rise”.
FIG. 9A is an explanatory diagram showing “indentation temperature rise”.
9A, the horizontal axis indicates the length of the base material (slab 10), and the vertical axis indicates the C cross-sectional average temperature between skids of the base material (slab 10). 9A, the horizontal axis indicates the furnace width, and the vertical axis indicates the temperature in each furnace.
9A, as shown above, the “C cross-sectional average temperature” having a predetermined linear temperature gradient at the time of charging is changed to the east side (in the process of raising the temperature of the heating furnace 13). Since the temperature rise on the B side) and the west side (T side) is large and the temperature rise near the center is relatively small, the vicinity of the center in the longitudinal direction at the time of extraction is depressed.

In the upper diagram in FIG. 9A, the furnace temperature distribution in the furnace width direction appears in a “middle dent” state, and both ends thereof are at a high temperature (particularly on the west side). As a result, the base material has a larger temperature rise than when the west side (T side) portion has the same temperature rise as that of the center portion from the charging to the extraction at the time of extraction. Specifically, the temperature increase width of the west side portion of the base material is larger than the center portion by the amount indicated by the up arrow in the lower diagram in FIG. 9A.

FIG. 9B is an explanatory diagram showing “swelling temperature rise”.
9B, the horizontal axis indicates the length of the base material (slab 10), and the vertical axis indicates the C cross-sectional average temperature between skids of the base material (slab 10). 9B, the horizontal axis indicates the furnace width and the vertical axis indicates the temperature in each furnace. In the figure below, the temperature distribution from the east side (B side) to the west side (T side) of the “C cross-sectional average temperature” having a predetermined linear temperature gradient at the time of charging becomes high when the base material is extracted. It has a so-called swell shape that decreases and increases again.

9B is a state in which the furnace temperature distribution in the furnace width direction is substantially flat or the flat part on the west side (T side) is lower than the flat part on the east side (B side) by a predetermined temperature difference. . That is, the temperature distribution in the longitudinal direction of the slab 10 is within a certain range. As a result, the base material has a smaller temperature rise than the case where the west side (T side) portion has the same temperature rise as the center portion from the charging to the extraction at the time of extraction. Specifically, the temperature increase width of the west side portion of the base material is reduced by the amount indicated by the down arrow in the lower diagram in FIG. 9B.

FIGS. 10A and 10B are explanatory diagrams of operation indices of the heating furnace.
FIG. 10A shows an index of “medium dent temperature rise” and FIG. 10B shows an index of “swell-like temperature rise”.
10 (A) and 10 (B), the vertical axis represents the inter-skid C cross-section average temperature of the slab between skids, and the horizontal axis represents the position of the slab in the longitudinal direction of each part of the slab. From the east side to the west side, the straight line that rises to the right is the temperature gradient in the longitudinal direction of the slab at the charging position, and the curve that is above the straight line that rises to the right is the longitudinal length of the slab at the extraction position. It is the temperature distribution in the direction.

Further, in FIGS. 10A and 10B, there are two points each on the straight line and the curved line rising to the right, and the cross section of the part in the east area and the part in the west area of the slab The minimum temperature is shown.
10 (A) and 10 (B), four horizontal solid lines indicate the average temperatures of the part in the east side area and the part in the west area of the slab at the charging position and the extraction position, respectively. .

The curve shown in FIG. 10 (A) (indented curve) represents a state in which the temperature distribution in the longitudinal direction of the slab at the extraction position decreases at the center and increases as it approaches both ends. And the curve shown to FIG. 10 (B) forms the mountain | side where the temperature distribution of the longitudinal direction of the slab in the extraction position protruded upwards near the center part of the east side (one side), and the west side (other side) It represents a state in which a undulation is formed with a valley that is depressed downward near the center.
In addition, here, an index of the temperature of the west area 17 is represented with the temperature of the east area 16 as a reference. The evaluation index (A) indicates the difference between the lowest temperature of the part in the east area 16 and the lowest temperature of the part in the west area 17 of the slab 10. Next, the evaluation index (B) indicates the difference between the average temperature of the portion in the east side area 16 of the slab 10 and the average temperature of the portion in the west area 17. Furthermore, the evaluation index (C) represents the temperature difference between the lowest temperature of the portion in the east side area 16 of the slab 10 and the average temperature of the portion in the west area 17.

Here, the inventors initially set the evaluation index (A) as the operation index, and burned the burners (upper burner 18 and lower burner 19) in the west area 17 with a lower thermal power than the burner in the east area 16, and Although heating was performed, the effect of suppressing the energy consumed when heating the slab 10 was limited. Therefore, the temperature of the slab 10 is calculated using a three-dimensional temperature calculation model, and a part of the burner in the west area 17 is heated to another burner in the west area 17 and the burner in the east area 16. The slab 10 was dropped and the slab 10 was heated, and an experiment was conducted to investigate an operation index with a large energy saving effect.
Then, the inventors have newly found an evaluation index (B) and an evaluation index (C) as operation indexes that have a large energy saving effect. If the evaluation index (B) and the evaluation index (C) are within the predetermined ranges, the temperature distribution in the longitudinal direction of the slab 10 is within a certain range, and the energy saving effect is increased. Moreover, both the state of the curve of the indentation shown in FIG. 10 (A) and the state of the wavy shape shown in FIG. 10 (B) satisfy the condition of the temperature distribution of the slab required at the time of extraction in the heating furnace, Compared to conventional operations, it was confirmed that the amount of energy used when heating the slab was small.
Since the evaluation index (A), the evaluation index (B), and the evaluation index (C) are represented by numerical values, it is convenient for statistical management.

FIG. 11 is a diagram showing the generation ratio of “swell-like temperature rise”, and the ratio of the slab 10 in which “swell-like temperature rise” has occurred with respect to the total number of slabs 10 heated in the heating furnace 13. Show.
The horizontal axis indicates the month on the time axis, and the vertical axis indicates the occurrence rate of “swelling temperature rise”. The classification recognized here as “swell-shaped temperature rise” is a state in which the slab 10 is heated and the temperature distribution in the longitudinal direction of the slab 10 at the extraction position becomes a swell shape. In the pattern of the temperature distribution of the slab 10 as described above, shapes having predetermined characteristic portions are classified and determined for convenience. The classification certified as “swelling temperature rise” can be achieved by performing appropriate furnace temperature control using the evaluation index.

In the following, specific measures and results are shown in chronological order. The basic idea is to set the furnace temperature lower in the west area 17 based on the east area 16.
May: Operation is in progress using a three-dimensional temperature calculation model. As a result, “swelling temperature rise” of about 10% of the whole occurs.
June: In addition to the above, in order to reduce the furnace temperature of the west area 17, the furnace temperature setting of the heating zone 14 and the west area 17 of the soaking zone 15 is set to be 10 ° C. lower than the east area 16 by 15 ° C. It expanded (5 degreeC expansion). And only the west side area 17 of the heating zone 14 was further expanded to a state 20 ° C. lower than a state 15 ° C. lower (5 ° C. expansion). As a result, “swelling temperature rise” occurs at a rate of about 52%.

July: From the end, the furnace temperature setting in the west area 17 of the heating zone 14 is 25 ° C. lower than the east area 16 (expanded by 5 ° C.), and the furnace temperature setting in the west area 17 in the soaking zone 15 is 20 The operation was performed at a low temperature (expanded by 5 ° C). As a result, “swelling temperature rise” of about 61% occurs.
August: The furnace temperature setting in the west area 17 of the heating zone 14 was set to be 30 ° C. lower than the east area 16 (expanded by 5 ° C.). As a result, “swelling temperature rise” of about 63% occurs.
September: The furnace temperature setting in the west area 17 of the heating zone 14 was set to 40 ° C. lower than the east area 16 (expanded by 10 ° C.). As a result, “swelling temperature rise” of about 78% occurs.
October: Ultimately, the furnace temperature setting in the west area 17 of the heating zone 14 is 40 ° C. lower than the east area 16 and the furnace temperature setting in the west area 17 of the soaking zone 15 is 20 ° C. lower than the east area 16 And operated. As a result, “swelling temperature rise” of about 80% occurs.

In this way, it can be seen that the rate of occurrence of “swelling temperature rise” increases with each month, and the energy saving effect is improved.
Here, if the decrease width of the furnace temperature of the west side area 17 with respect to the east side area 16 is expanded more than the operation conditions at the time of October, a portion in the west side area 17 of the slab 10 that originally has a high temperature is obtained at the extraction position. It was confirmed that the temperature in the east side area 16 sometimes became too low.
Further, the relationship between the length of the slab 10 and the average cross-sectional temperature in the longitudinal direction corresponding to the three-dimensional temperature calculation of the slab 10 from the charging side to the extraction side can be obtained from the surface temperature of the slab 10 and the casting conditions. it can. The surface temperature of the slab is preferably measured with a known radiation thermometer.

Therefore, the heating power of the upper burner 18 and the lower burner 19 is adjusted based on the relationship between the obtained length of the slab 10 and the average cross-sectional temperature in the longitudinal direction corresponding to the three-dimensional temperature calculation of the slab 10, and an evaluation index ( The point of the present invention is to sequentially control B) to −15 ° C. to + 15 ° C. and the evaluation index (C) to −10 ° C. to + 20 ° C. And by this control, while suppressing energy consumption, the slab can be heated to a state having a temperature at which the slab is required at the extraction position.
The control for setting the evaluation index (B) to −15 ° C. to + 15 ° C. and the evaluation index (C) to −10 ° C. to + 20 ° C. is based on the center position of the slab 10 (the portion in the west area 17). A part of the burner (upper burner 18 and lower burner 19) is compared with other burners on the other side and burners on one side (the part in the east side area 16) to reduce the heating power.

FIG. 12 is a relational diagram showing the evaluation index in the three-dimensional temperature calculation model and the energy saving effect of “swelling temperature rise”.
FIG. 12 shows the results of the measures described with reference to FIG. 11 in May (before measures), June (after the primary measures), and September (after the secondary measures). For each month, the results when the evaluation index (A), the evaluation index (B), and the evaluation index (C) are employed as operation indexes are shown.
The bar graphs in each table represent the occurrence frequency of “indentation temperature rise” and the occurrence frequency of “undulation temperature rise” for each slab 10 to be heat-treated (heated). The horizontal axis indicates an evaluation value (unit: temperature) obtained by calculating the difference between the furnace temperature in the east area 16 and the furnace temperature in the west area 17. The numerical value X on the horizontal axis indicates that the evaluation range is “(X−5) to X”. For example, the “0” portion is “−5 to 0”, and the “10” portion is "5-10". Thus, it has a step width of 5 ° C.

That is, each bar in the table is the difference between the temperature of the slab 10 in the east side area 16 defined by each evaluation index and the temperature in the part in the west area 17 (evaluation index (A)) at the extraction position. The difference between the lowest temperature of the part in the east side area 16 of the slab 10 and the lowest temperature of the part in the west area 17) is in the range of (X-5) ° C to X ° C.
In addition, as a result of the operation using the three-dimensional temperature calculation model, the number of occurrences of “indentation temperature rise” and the number of occurrences of “undulation temperature rise” with respect to the total number are shown by bar graphs. As can be seen from this figure, when attention is paid to the evaluation indices (B) and (C) in which the ratio of the “swelling temperature rise” rises every month, the scale of −10 to +10 on the horizontal axis. It can be seen that the rate of “swelling temperature rise” has been increasing, especially with the month.
And based on the results shown in the table in FIG.
For the evaluation index (B), the difference between the (cross-section) average temperature on one side and the (cross-section) average temperature on the other side is between −15 ° C. and + 15 ° C.,
For the evaluation index (C), by managing the operation for controlling the difference between the lowest temperature on the one side (in the cross section) and the average temperature on the other side (in the cross section) to −10 ° C. to + 20 ° C. It can be seen that the ratio of “has increased and the energy saving effect has been achieved.

FIG. 13 is a diagram illustrating a result of fuel consumption reduction.
The abscissa indicates the month on the time axis, and the ordinate indicates the heating fuel consumption rate of the heating furnace 13 and is 100% before the countermeasure (SM: indicates a sizing mill). As shown in FIG. 13, the fuel consumption rate is reduced every month, and finally, a significant reduction of 9% is achieved in the actual performance in October, compared with the planned reduction of 2%. Thus, in relation to the generation of “medium dent temperature rise” and “swell-like temperature rise”, the effect of reducing the fuel consumption rate more than expected is exhibited.

As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the configuration described in the above embodiment, and the matters described in the scope of claims. Other embodiments and modifications conceivable within the scope include, for example, a slab having a temperature distribution such as a hot-slab slab to be rolled such as a hot-rolled steel plate or a thick plate.

10: slab, 11: CC cutter, 12: transfer table, 13: heating furnace, 14: heating zone, 15: soaking zone, 16: east area, 17: west area, 18: upper burner, 19: lower burner, 20: Fuel pipe, 21: Thermometer, 22: Nose part, 23: Ceiling

Claims (4)

A slab having a gradient temperature distribution that increases from one end to the other is placed in the heating furnace provided with a plurality of burners arranged in the longitudinal direction of the slab along the width direction of the heating furnace, with the longitudinal direction being transverse. A method for heating a slab,
From the surface temperature and casting conditions of the slab, find the relationship between the length of the slab and the average cross-sectional temperature in the longitudinal direction corresponding to the three-dimensional temperature calculation of the slab from the charging side to the extraction side,
The heating power of the burner is controlled with reference to the center position of the slab, and 1) the difference between the average temperature on one side in the longitudinal direction and the average temperature on the other side at the extraction position with reference to the center position of the slab. A method for heating a slab, characterized in that it is between −15 ° C. and + 15 ° C. and 2) the difference between the lowest temperature on one side and the average temperature on the other side is sequentially controlled to −10 ° C. to + 20 ° C. The slab heating method according to claim 1, wherein the burner is controlled by dropping a part of the thermal power of the burner provided on the other side in the width direction. The method for heating a slab according to claim 1 or 2, wherein the heating furnace is divided into a plurality of furnace zones along a traveling direction from the charging side to the extraction side of the slab, and the burner is provided for each furnace zone. A method for heating a slab, characterized in that a group is provided. The method for heating a slab according to any one of claims 1 to 3, wherein the temperature distribution on the extraction side of the slab has a peak near the central portion on one side in the longitudinal direction and a valley near the central portion on the other side. A method for heating a slab, wherein the slab has a swell shape.

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