JP4020453B2 - Operating method of bell-type annealing furnace using heat storage regenerative combustion system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for operating a bell-type annealing furnace using a heat storage regenerative combustion apparatus.
[0002]
[Prior art]
Conventionally, when annealing a metal strip coil (hereinafter referred to as a coil material), a bell-type annealing furnace that indirectly heats a coil material accommodated in an inner cover with a burner attached to an outer cover has been widely used. On the other hand, as a combustion device with excellent thermal efficiency from the viewpoint of energy saving, a heat storage regenerative combustion device that alternately repeats combustion and waste heat recovery is attracting attention, and the inventors have been developing bell-type annealing using a heat storage regenerative combustion device. I filed the furnace first. The annealing process using this bell-type annealing furnace is performed in each operation period of heating to raise the temperature in the furnace to a set temperature (annealing temperature), soaking to keep the temperature in the furnace at this set temperature, and cooling including slow cooling. (Hereinafter, each operation period is called a heating period, a soaking period, and a cooling period). Here, since it is necessary to raise the furnace temperature to the set temperature in a short time during the heating period, the burner needs to continue combustion in a state of 100% load.
[0003]
However, the soaking period gives the amount of heat necessary to maintain the furnace temperature at the set temperature (annealing temperature). As shown in FIG. 6, combustion and non-combustion are alternately performed while detecting the furnace temperature. A method is employed in which intermittent combustion is repeated repeatedly and the burner is operated at 100% load during combustion to gradually increase the non-combustion time.
[0004]
[Problems to be solved by the invention]
However, according to this operation method, the inner cover and the coil material in the vicinity of the burner are locally heated to generate a high temperature region and a low temperature region. This local heating state cannot be resolved even if the swirling airflow is formed in the cylindrical space between the outer cover and the inner cover and heat is diffused. Further, since the burner repeats combustion and non-combustion in a state of 100% load, it not only further promotes the local heating state, but also greatly increases the temperature fluctuation in the furnace and shortens the durable life of the inner cover.
[0005]
Then, this invention aims at providing the soaking | uniform-heating operation method which can keep the above-mentioned local heating and the temperature fluctuation in a furnace to the minimum, making use of the energy-saving advantage which a thermal storage regeneration combustion apparatus has. .
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a pair of heat storage regenerations in which a metal strip coil placed on a hearth is covered with an inner cover and an outer cover, and a space between the inner cover and the outer cover is provided on the outer cover. A bell-type annealing furnace for annealing a metal strip coil placed in the inner cover by forming a vertical flat flame from a combustion-type combustion device in a tangential direction of the outer cover, the bell-type annealing furnace When the metal strip coil is annealed by the above, during the soaking operation period of the bell-type annealing furnace, combustion is performed while continuously controlling the required combustion capacity at the soaking operation up to the combustion lower limit capacity of the heat storage regeneration combustion device. When the required combustion capacity reaches the combustion lower limit capacity, the combustion is intermittently performed in the state of the combustion lower limit capacity thereafter.
[0007]
【The invention's effect】
According to this operation method, the heat storage regenerative combustion apparatus gives the amount of heat necessary for the soaking operation without extinguishing the flame up to near the combustion lower limit capacity. Therefore, the temperature fluctuation in the furnace is reduced as compared with the case where the regenerative combustion apparatus is continuously burned intermittently in a state of 100% load.
[0008]
Next, when the operation of reducing the combustion capacity of the heat storage regenerative combustion device is performed, the flow rate of fuel and air injected from the heat storage regenerative combustion device is reduced, the straightness of the flame is reduced and the outer cover and the inner cover are reduced. A flame rises in the annular space, and local heating of the coil material and the inner cover is reduced, and the loaded coil material can be heated evenly.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In FIG. 1, a bell-type annealing furnace 1 using a regenerative combustion apparatus includes a hearth 2, an inner cover 3, and an outer cover 4. The coil material W, which is a treatment material, is stacked on the hearth 2 and is covered and annealed with the inner cover 3 and the outer cover 4.
[0010]
The outer cover 4 includes a pair of slit-type heat storage regenerative combustion devices (hereinafter referred to as “combustion devices”) 7a and 7b and a vent hole 8 in the ceiling portion 4a at a 180 ° symmetrical position of the lower circumferential circle. The combustion devices 7a and 7b are attached to the outer cover 4 in a tangential direction (see FIG. 2), and the fuel is jetted in a planar shape from the vertically long header pipes 8a and 8b, and the inner cover 3 and the outer cover 4 A vertical flat flame (see FIG. 3) is formed in the space 6 between the two. The vent hole 8 is preferably provided with a backflow prevention mechanism (for example, a check valve) for preventing outside air from flowing into the space 6.
[0011]
In order to achieve these functions, the combustion devices 7a and 7b have a function of injecting and burning fuel and air, and a function of sucking exhaust gas in the space 6 and recovering waste heat during non-combustion. The heat accumulators 9a and 9b made of a heat storage medium are provided.
[0012]
The header pipes 8a and 8b of the combustion devices 7a and 7b are connected to the fuel supply device 14 by fuel branch pipes 12a and 12b passing through the regenerators 9a and 9b and the fuel main pipe 13, and are connected to the fuel branch pipes 12a and 12b. A fuel control valve 16 is provided in the on-off valves 15 a and 15 b and the fuel main pipe 13.
[0013]
Supply / exhaust pipes 17a and 17b are connected to the main bodies of the combustion devices 7a and 7b, respectively. The supply / exhaust pipes 17a and 17b are branched into air supply pipes 18a and 18b and exhaust gas pipes 23a and 23b. The air supply pipes 18 a and 18 b are connected to the combustion air supply blower 20 through the air supply main pipe 19, and the exhaust gas pipes 23 a and 23 b are connected to the exhaust blower 25 through the exhaust gas main pipe 24. The air supply pipes 18a and 18b are provided with on-off valves 21a and 21b, and the air supply main pipe 19 is provided with an air control valve 22. Similarly, the exhaust gas pipes 23a and 23b are provided with on-off valves 26a and 26b, and the exhaust gas main pipe 24 is provided with an exhaust gas control valve 27, respectively. The fuel control valve 16, the air control valve 22, and the exhaust gas control valve 27 are adjusted in opening by an air-fuel ratio control device 28.
[0014]
The operation of the bell-type annealing furnace 1 using the heat storage regenerative combustion apparatus will be described. As described above, the annealing process of the annealing furnace 1 includes a heating period, a soaking period, and a cooling period. In the heating period, combustion is alternately repeated in the combustion devices 7a and 7b, and the coil material W is heated to a predetermined temperature while exhaust gas is sucked and exhausted from the combustion device 7a or 7b in a non-combustion state and the waste heat is recovered. .
[0015]
Specifically, the combustion operation and the waste heat recovery operation will be described. It is assumed that combustion is performed by one combustion device 7a and waste heat is recovered by the other combustion device 7b. In this case, in the fuel piping system, the on-off valve 15a is opened and fuel is supplied from the fuel supply device 14 to the header pipe 8a of the combustion device 7a. On the other hand, the fuel switching valve 15b is closed to shut off the fuel supply to the combustion device 7b.
[0016]
In the air piping system, the on-off valve 21a is opened to supply combustion air to the combustion device 7a. On the other hand, the on-off valve 21b is closed to cut off the supply to the fuel device 7b. The fuel supplied to the header pipe 8a of the combustion device 7a is mixed with the air that has passed through the heat accumulator 9a and burned to form a vertical flat flame.
[0017]
In the exhaust gas piping system, the on-off valve 26b is opened and the other on-off valve 26a is closed. Incidentally, by adjusting the opening degree of the exhaust gas control valve 27, about 80% of the exhaust gas is sucked into the combustion device 7b, the waste heat is recovered by the heat accumulator 9b, and then exhausted by the exhaust gas blower 25. The remaining about 20% of the exhaust gas is exhausted to the outside through the vent hole 8.
[0018]
After the above operation is continued for a predetermined time, the combustion device 7b then performs combustion, and the other combustion device 7a moves to an operation of recovering waste heat. In this case, in the fuel piping system, the on-off valve 15a is closed to shut off the fuel supply to the combustion device 7a, and the on-off valve 15b is opened to supply fuel from the fuel supply device 14 to the header pipe 8b of the combustion device 7b. On the other hand, in the air piping system, the on-off valve 21a is closed to shut off the air supply to the combustion device 7a, and the on-off valve 21b is opened to supply air to the combustion device 7b. The fuel supplied to the header pipe 8b of the combustion device 7b is mixed with the preheated air that has passed through the heat accumulator 9b and burned to form a vertical flat flame.
[0019]
In the exhaust gas piping system, the on-off valve 26a is opened and the other on-off valve 26b is closed. Similarly, about 80% of the exhaust gas is sucked into the combustion device 7a, the waste heat is recovered by the heat accumulator 9a, and then exhausted by the exhaust blower 25. The remaining 20% of the exhaust gas is naturally exhausted from the vent hole 8 to the outside. In this manner, in the combustion devices 7a and 7b, the combustion operation and the waste heat recovery operation are alternately performed every predetermined time, and the furnace temperature is raised to the set temperature.
[0020]
When entering the soaking period, as shown in FIG. 4, the combustion capacity of the combustion apparatuses 7a and 7b operated at a 100% load in the heating period can be used to form a flame in a steady manner with these combustion apparatuses 7a and 7b. The alternate combustion described above is continued while continuously controlling the required combustion capacity during the soaking operation to near the lower limit capacity (for example, about 20%). When the combustion capacity of the combustion devices 7a and 7b reaches near the combustion lower limit capacity, the above-described alternate combustion is intermittently performed near the combustion lower limit capacity.
[0021]
The required combustion capacity in the soaking period and the combustion time and non-combustion time in the vicinity of the lower combustion limit capacity are detected by detecting the temperature in the furnace with a plurality of temperature detection devices (not shown) arranged inside the inner cover 3. Control is performed so that the internal temperature and the temperature of the coil material W are maintained at substantially constant values.
[0022]
As described above, when the combustion capacity of the combustion devices 7a and 7b is continuously controlled to the required combustion capacity in the soaking period, the combustion capacity is substantially reduced, and therefore from the combustion device during the combustion operation. As the flow rate of the injected fuel and air decreases, the swirling airflow formed in the annular space between the outer cover and the inner cover causes the flame to rise. As a result, local heating of the inner cover 3 is prevented and the durability life thereof is extended, and the plurality of loaded coil members W are evenly heated.
[0023]
In addition, as described above, the regenerative combustion apparatus heats the combustion air using the heat of the exhaust gas in the furnace, so the flame temperature is high and the amount of heat transfer is proportional to the fourth power of the flame temperature. The laminated coil material W is efficiently heated evenly by the amount of radiant heat transfer using the rise of the flame caused by.
[0024]
For example, when the coils W are stacked in four stages in the furnace, and the combustion devices 7a and 7b are arranged facing the coil material W in the lowermost stage and the upper stage, the coil material W in the second stage from the top is sufficiently heated. However, according to the present invention, the coil material W at each stage is substantially evenly distributed by the high-temperature radiant heat. The annealing time is shortened as compared with the prior art.
[0025]
The operation method of the present invention and the operation method (comparative example) shown in FIG. 6 are carried out, and the temperature difference between the highest temperature point (hot point) and the lowest temperature point (cold point) inside the coil material is determined for each. It was measured. As a result, as shown in FIG. 5, according to the operation method of the present invention, it was confirmed that the temperature difference could be reduced by about 5 ° compared to the comparative example. Further, it was confirmed that the annealing time until the temperature difference was settled within a range of ± 10 ° (20 ° in the graph) or less was about 2 hours earlier than the comparative example in the present invention, and the entire annealing time could be shortened by this time. .
[0026]
When the soaking operation is completed, the cooling operation is started.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a bell-type annealing furnace using a regenerative combustion apparatus according to the present invention and a piping system diagram thereof.
FIG. 2 is a cross-sectional view of the annealing furnace shown in FIG.
FIG. 3 is a perspective view showing a flame state near the annealing lower limit capacity.
FIG. 4 is a graph showing the operation method according to the present invention (the horizontal axis represents time, and the vertical axis represents the combustion capacity of the combustion apparatus).
FIG. 5 shows a material temperature difference (temperature difference between a hot point and a cold point in a coil material) when the operation method of the present invention and the operation method (comparative example) shown in FIG. 7 are used.
FIG. 6 is a graph showing an operation method of a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Bell type annealing furnace using heat storage regenerative combustion apparatus, 3 ... Inner cover, 4 ... Outer cover, W ... Coil material (processing material), 6 ... Space, 7a, 7b ... Slit type heat storage regenerative combustion apparatus, 8 ... Vent hole.

Claims (1)

A metal strip coil placed on the hearth is covered with an inner cover and an outer cover, and a pair of heat storage regenerative combustion devices provided on the outer cover in a space between the inner cover and the outer cover toward a tangential direction of the outer cover. A bell-type annealing furnace operating method for annealing a metal strip coil placed in the inner cover by forming a vertical flat flame,
When annealing the metal strip coil with the bell-type annealing furnace, continuously control the required combustion capacity during the soaking operation up to the lower limit combustion capacity of the regenerative combustion apparatus during the soaking operation of the bell-type annealing furnace. and while the combustion, the when required combustion capacity reaches the lower flammable limit capacity then performs intermittently the combustion state of the combustion limit capacity, operating method of the bell furnace using a regenerative regenerative combustion apparatus.

Images