Method for guiding the situation of the air entering the heating furnace

Abstract

To provide a method that provides guidance on the state of intrusion air into a furnace, wherein: the volume of intrusion air into the furnace is quantified in real time; an air ratio in a burner is monitored; the times at which the intrusion air increases are properly determined and presented; and this enables prompt repair of the furnace areas affected by the intrusion air.SOLUTION: A method monitors the state of a furnace 1 that heats a cast material to a predetermined temperature using a burner 5 and gives guidance to an operator. Taking into account the intrusion air entering the furnace 1 through means other than the standard supply route, the air ratio of the burner 5 is controlled. Based on time-dependent changes of the burner air ratio in the burner 5, the times at which the burner air ratio falls to or below a threshold are predicted, and the predicted times are presented to the operator.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for controlling a heating furnace, which monitors the situation of the infiltrating air in the heating furnace and guides the operator about the situation.

Background Art

[0002] In the hot rolling process, steel materials (cast slabs) such as slabs, billets, and blooms manufactured in the steelmaking process are heated in a heating furnace and sent to a rolling mill (rough rolling mill, finishing rolling mill) on the downstream side, and rolled continuously to manufacture rolled materials. When heating steel materials in a heating furnace, the steel materials are charged into the heating furnace and heated up to a temperature suitable for rolling. The heating of the furnace atmosphere is carried out by burners provided in the furnace. In the heating furnace, control is performed to keep the air ratio (burner air ratio) of the burner constant.

[0003] Note that the burner air ratio is the ratio of the air actually supplied to the theoretical air amount, where the theoretical air amount is the minimum amount of air required for complete combustion theoretically. When controlling the furnace temperature using the burner air ratio, infiltrating air may enter the heating furnace from outside the normal supply path, and it is necessary to monitor the situation in the heating furnace in consideration of this.

[0004] As a technique for monitoring the situation in the heating furnace, for example, it is disclosed in Patent Documents 1 and 2. Patent Document 1 aims to determine an abnormality of an oxygen concentration meter, detect the oxygen concentration in the exhaust gas, calculate the difference in the oxygen concentration calculated from the combustion conditions, and correlate the response delay time of the detected oxygen concentration, and determine so that the air ratio does not respond excessively. Patent Document 2 aims to clarify the deterioration factors of the fuel unit based on the investigation items in the heat settlement on a daily basis. In this Patent Document 2, the difference between the oxygen concentration in the exhaust gas and the oxygen concentration calculated from the combustion conditions is determined as the influence of infiltrating air and specified as a deterioration factor of the fuel unit.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Now, the burner air ratio of the heating furnace is set to a constant value in order to prevent the generation of unburned gas and NOx in the furnace. However, with the aging deterioration of the heating furnace, external air enters the furnace from locations other than the predetermined ones, resulting in the generation of intrusion air. It has been confirmed that due to the influence of the intrusion air, the air ratio in the furnace increases and the oxygen concentration in the furnace becomes high. Therefore, in order to keep the air ratio in the furnace constant, for example, control is sometimes performed to keep the oxygen concentration in the furnace constant by reducing the burner air ratio.

[0007] However, the amount of scale generated on the surface of the slab in the heating furnace is greatly affected by the oxygen concentration of the furnace gas. Therefore, it is necessary to repair the location of the intrusion air at an early stage and review the combustion conditions of the burner, etc., to prevent an increase in the amount of intrusion air into the heating furnace. In Patent Document 1, since the intrusion air is not directly considered, the oxygen concentration meter determines that there is no abnormality with respect to the oxygen concentration fluctuation caused by the influence of the intrusion air. Therefore, the factor causing the oxygen concentration to fluctuate cannot be identified. That is, this technology overlooks the influence of the intrusion air. As a result, there is a risk that the identification of the location of the intrusion air and the determination of the timing for performing the repair work of the heating furnace will be delayed.

[0008] In Patent Document 2, based on heat settlement on a daily basis, the influence of infiltrating air is specified as a factor deteriorating the unit consumption from the difference between the oxygen concentration in the exhaust gas and the oxygen concentration calculated from the combustion conditions. However, in addition to the fact that the heating zone where infiltrating air is generated cannot be specified, it is a technology that further cannot monitor the influence of infiltrating air in real time. Therefore, there is a major problem that the combustion conditions of the burner considering the amount of infiltrating air cannot be reviewed. There is a major problem such that the combustion conditions of the burner considering the amount of infiltrating air cannot be reviewed.

[0009] Therefore, in view of the above problems, the present invention provides a method for guiding the situation of infiltrating air into a heating furnace, which can quantify the amount of infiltrating air into the heating furnace in real time, monitor the burner air ratio, appropriately judge and present the timing of an increase in infiltrating air, and thus enable early response to the repair of the heating furnace caused by infiltrating air.

Means for Solving the Problems

[0010] To achieve the above object, the present invention takes the following technical means. A method for guiding the situation of infiltrating air into a heating furnace according to the present invention is a method for monitoring the situation of a heating furnace that heats a slab to a predetermined temperature using a burner and guiding an operator, in which air ratio control of the burner is performed while considering infiltrating air that infiltrates into the heating furnace from other than a regular supply path, and from the change over time of the burner air ratio in the burner, the timing when the burner air ratio becomes equal to or lower than a threshold value is predicted, and the predicted timing is presented to the operator.

[0011] Preferably, the heating furnace is provided with one or a plurality of heating zones for heating the slab, and in each heating zone, the timing when the burner air ratio becomes equal to or lower than a threshold value is predicted from the change over time of the burner air ratio, and the predicted timing is presented to the operator. Preferably, based on the result of predicting the timing when the burner air ratio becomes equal to or lower than a threshold value, the inspection location and repair timing of the infiltrating air are presented to the operator.

[0012] Preferably, when the cumulative frequency below the threshold value within a predetermined period regarding the burner air ratio becomes a certain value or more, the situation may be presented to the operator. Preferably, the threshold value of the burner air ratio may be determined based on the boundary value at which the concentration of unburned components in the heating furnace reaches the explosion range.

Advantages of the Invention

[0013] According to the present invention, after quantifying the amount of infiltrating air in the heating furnace in real time, the burner air ratio is monitored, and the timing of the increase in infiltrating air is appropriately determined and presented, so that it is possible to respond early to the repair of the heating furnace caused by infiltrating air.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of a method for guiding the situation of infiltrating air into the heating furnace according to the present invention will be described with reference to the drawings. It should be noted that the embodiments described below are examples embodying the present invention, and do not limit the configuration of the present invention with those specific examples. A method for guiding the situation of the infiltrating air into the heating furnace 1 according to the present invention is a method for controlling the heating furnace 1. In order to keep the oxygen concentration in the heating furnace 1 constant, when controlling the ratio of the air supplied into the furnace (air ratio) to be the target air ratio, a threshold value of the controllable burner air ratio (the ratio of the air supplied to the burner 5) is set in advance. The comparison between the burner air ratio in actual operation and the threshold value is carried out in real time (for example, at short intervals such as every 5 seconds or every 10 seconds). When the obtained burner air ratio is lower than the threshold value, it is determined that the infiltrating air in the heating furnace 1 has increased, and the situation of the infiltrating air in the heating furnace 1 is guided (presented) to the operator.

[0016] Note that the air ratio is the ratio of the actual air supplied to the theoretical air quantity, where the theoretical air quantity is the minimum amount of air required for complete combustion theoretically. That is, it is the ratio of the actual air supplied to this theoretical air quantity. First, the configuration of the heating furnace 1 to which the present invention is applied will be described. Fig. 6 schematically shows the configuration of the heating furnace 1. Regarding the gas flow in the heating furnace 1, as shown in Fig. 6, it is in the direction from the left side to the right side of the paper. That is, the gas flows from the soaking zone 4 (upstream) → the heating zone 3 → the preheating zone 2 (downstream). However, although not shown in the figure, the conveying direction of the slab is in the direction from the right side to the left side of the paper.

[0017] The heating furnace 1 has a furnace body for heating the slab, a burner 5 (burner) for raising the ambient temperature in the furnace body, and a flue (exhaust gas path) for discharging the exhaust gas generated in the furnace body to the outside. The furnace body is a housing with a hollow interior, and is provided with a carry-in port for carrying the slab into the interior and a carry-out port for carrying out the steel material heated to a predetermined temperature to the outside of the furnace. In addition, inside the furnace body, a walking beam (steel material conveying device) for conveying the slab little by little over a certain period of time (about 1 to 2 hours) is provided. The slab is continuously conveyed from the carry-in port into the furnace body (from the right side to the left side of the paper in Fig. 6) by the walking beam while being heated and its temperature is raised, and is carried out from the carry-out port.

[0018] As shown in Fig. 6, the heating furnace 1 is provided with a plurality of heating zones (heating regions). The heating furnace 1 of the present embodiment is provided with three heating zones. In order from the loading port to the unloading port, there is a preheating zone 2 (preheating zone) for preheating the slab carried in at normal temperature, a heating zone 3 (heating zone) for further heating the slab preheated in the preheating zone 2 to approximately 1000°C, and a soaking zone 4 (soaking zone) for further heating to eliminate the temperature unevenness of the slab heated in the heating zone 3.

[0019] Note that, regarding the heating furnace 1, the number of heating zones is not limited to three. For example, it may be provided with four such as a preheating zone, heating zone (1), heating zone (2), and soaking zone. As long as the functions of the heating furnace 1 are provided, the number of heating zones may be one or more. In each of the preheating zone 2, the heating zone 3, and the soaking zone 4, a plurality of burners 5 are provided along the conveying direction (line direction) of the slab. A pipe 6 for supplying fuel and air is connected to the burner 5. Note that the burner may be installed in the direction of the conveying direction of the slab as shown in Fig. 6, or may be installed in a direction orthogonal to the conveying direction. The installation location of the burner is on the side wall or the ceiling surface, and usually, a plurality of burners are provided.

[0020] As shown in Fig. 6, the supply pipe 6 has an air line 6a for supplying air and a fuel line 6f for supplying fuel, and is respectively connected to the burner 5. For example, in the air line 6a of the preheating zone 2, there is a valve for controlling the supply of air and an air flow meter Q a for measuring the flow rate of the air. In the fuel line 6f of the preheating zone 2, there is a valve for controlling the supply of fuel and a fuel flow meter Q f for measuring the flow rate of the fuel. Also, in the preheating zone 2, a furnace temperature gauge T and a furnace oxygen concentration gauge O are provided.

[0021] For example, the temperature inside the preheating zone 2 is measured by the in-furnace thermometer T provided in the preheating zone 2, and the measured temperature data is taken into a programmable controller (ProCon), a programmable logic controller (PLC), or the like. Also, the oxygen concentration inside the preheating zone 2 is measured by the in-furnace oxygen concentration meter O provided in the preheating zone 2, and the measured oxygen concentration data is taken into a ProCon, a PLC, or the like. The ProCon, the PLC, or the like also takes in the value of the air flow meter Q in the air line 6a provided in the preheating zone 2 a and the value of the fuel flow meter Q in the fuel line 6f f and so on. Based on the values taken in in this way, the valves of the respective lines 6a and 6f are adjusted. Note that similar measuring means and data intake means are also provided in the heating zone 3 and the soaking zone 4, enabling control for each of the preheating zone 2, the heating zone 3, and the soaking zone 4

[0022] The gas inside the heating furnace 1 can move in the order of the preheating zone 2 → the heating zone 3 → the soaking zone 4. From this, if the gas composition of the preheating zone 2 is known, the gas composition of the heating zone 3 can be calculated, and if the gas composition of the heating zone 3 is known, the gas composition of the soaking zone 4 can be calculated, so it becomes possible to grasp the overall situation of the heating furnace 1 A method for guiding the situation of the air entering the heating furnace 1 of the present invention (an air intrusion guidance alarm in the heating furnace 1) will be described in detail

[0023] Control of the burner air ratio considering the intrusion air is carried out for each heating zone (in this embodiment, the preheating zone 2, the heating zone 3, and the soaking zone 4) partitioned inside the heating furnace 1. That is, the air ratio control of the burner 5 is carried out while considering the intrusion air that enters the heating furnace 1 from outside the normal supply path. For the control of the burner air ratio considering the intrusion air, for example, refer to Japanese Patent Application Laid-Open No. 2020-139698

[0024] In each heating zone (preheating zone 2, heating zone 3, soaking zone 4), based on the change over time of the burner air ratio in the burner 5 during actual operation, predict the time when the actual value of the burner air ratio during operation will fall below the threshold in the future, and present the predicted time to the operator. For example, present an alarm indicating the repair time of the heating furnace 1 and an alarm prompting inspection of the location of the infiltrating air in the heating furnace 1 on a monitor or the like to convey it to the operator.

[0025] Fig. 1 shows an example when determining the threshold of the burner air ratio. As shown in Fig. 1, when the flow rates of gas and air increase, the combustion amount becomes large, and the relationship between the unburned component concentration [%] and the air ratio [-] becomes like the one-dot chain line (thick line). On the other hand, when the fuel flow rate decreases, the flow velocities of the fuel and air decrease, so the mixing property of the fuel and air deteriorates, and combustion failure, that is, unburned is likely to occur. In order to prevent combustion failure, control to increase the air ratio may be adopted in the region where the combustion amount is small. Here, the relationship between the unburned component concentration [%] and the air ratio [-] when the combustion amount is minimum becomes like the solid line (thick line).

[0026] As shown in Fig. 1, the threshold of the burner air ratio for each of the preheating zone 2, heating zone 3, and soaking zone 4 is set to the value of the burner air ratio just before the unburned component concentration generated in the operating combustion amount range for the burner 5 used in the preheating zone 2, heating zone 3, and soaking zone 4 enters the explosion range. That is, the threshold of the burner air ratio is determined based on the boundary value at which the unburned component concentration in the heating furnace 1 becomes the explosion range that occurs in actual operation.

[0027] However, the range in which the unburned component concentration in the heating furnace 1 becomes the concentration at which a combustion reaction occurs at a location other than the predetermined location of the heating furnace 1 (for example, a flue, etc.) is defined as the "explosion range". Preferably, since problems occur when an unburned component causes a combustion reaction (abnormal combustion) at a location other than the predetermined location of the heating furnace 1, the threshold is determined in consideration of a safety factor or the like based on the boundary value of the unburned component concentration. That is, the threshold is a value for determining abnormal combustion in the heating furnace 1.

[0028] When the burner air ratio has elapsed for a predetermined period, if the duration (cumulative frequency) of the situation where the actual value of the burner air ratio is equal to or less than the threshold value is equal to or greater than a certain value, it is determined that the infiltrating air is increasing, and an abnormality is displayed in real time on a monitor or the like and the situation is presented to the operator. That is, based on the result of predicting the time when the burner air ratio becomes equal to or less than the threshold value, the inspection location and repair time of the infiltrating air location are presented to the operator.

[0029] FIG. 2 shows the inspection of the generation location of the infiltrating air that infiltrates into the heating furnace 1 and the prediction of the repair time of the heating furnace 1. FIG. 3 shows the change in the burner air ratio due to the increase in the infiltrating air. Furthermore, as shown in FIG. 2, based on the change over time of the burner air ratio, the time when the actual value of the burner air ratio falls below the threshold value, that is, the next inspection and repair time of the heating furnace 1 is predicted. As shown in the left diagram of FIG. 3, in actual operation, when the burner air ratio of the heating furnace 1 is controlled to be constant, as the amount of infiltrating air into the heating furnace 1 increases, the net (overall in the furnace) air ratio increases, leading to an increase in the oxygen concentration in the furnace.

[0030] Therefore, as shown in the right diagram of FIG. 3, when the amount of infiltrating air into the heating furnace 1 increases, in order to control the net air ratio to be constant, the burner air ratio is decreased in consideration of the infiltrating air. That is, the burner air ratio is made variable according to the situation so that the inside of the heating furnace 1 becomes the target air ratio. By adjusting this burner air ratio, it becomes possible to control the oxygen concentration in the furnace of the heating furnace 1 to be constant. However, if the burner air ratio is decreased too much, it becomes difficult to maintain the ideal flame shape of the burner 5 and combustion failure occurs, allowing the generation of unburned components.

[0031] Therefore, the comparison between the actual value of the burner air ratio during operation and the threshold value is performed in real time (for example, at very short intervals such as every 5 seconds or every 10 seconds). When the actual value of the burner air ratio falls below the threshold value, an alarm regarding the inspection of the heating furnace 1 is displayed in real time on a monitor or the like and transmitted to the operator to identify the location of the infiltrating air. The alarms displayed include, for example, checking the location of invading air, repairing heating furnace 1, and The alarms are not limited to the above examples, but can be changed as appropriate depending on the operating conditions of the heating furnace 1, etc.

[0032] In addition to the above, based on the change over time in the burner air ratio, the time when the actual value of the burner air ratio will fall below the threshold value, i.e., the time when the next inspection and repair of the heating furnace 1 will be performed, is predicted. In this way, by applying the method of the present invention for guiding the status of air entering the heating furnace 1 (the method of monitoring the heating furnace 1 and presenting the status), the need for repair of the heating furnace 1 can be quickly grasped, and the specific operating conditions of the heating furnace 1 and the heating zone where the air is occurring (in this embodiment, any of the preheating zone 2, heating zone 3, and soaking zone 4) can be identified, which makes it possible to quickly review the combustion conditions of the burner 5, identify the location of the air entering the heating furnace 1, and adjust the maintenance schedule based on the maintenance cycle. That is, the present invention makes it possible to control the oxygen concentration inside the heating furnace 1 to a constant value by adjusting the burner air ratio according to the situation.

[0033] In this way, the method of providing guidance on the status of air entering the heating furnace 1 of the present invention quantifies the amount of air entering the heating furnace 1 in real time, monitors the air ratio of the burner 5, and appropriately determines and indicates the time when the amount of air entering the heating furnace 1 increases, making it possible to quickly respond to repairs to the heating furnace 1 caused by the air entering the heating furnace 1. [Example] An embodiment carried out in accordance with the method of the present invention for guiding the state of air entering the heating furnace 1 will be described below.

[0034] The heating furnace 1 is provided with one or more heating zones for heating the slab. In this embodiment, a preheating zone 2, a heating zone 3, and a soaking zone 4 are provided. In this embodiment, an explanation will be given focusing on the heating zone 3 and the soaking zone 4 upstream (upstream of the gas flow) of the heating zone 3 among the preheating zone 2, the heating zone 3, and the soaking zone 4. However, the gas flows from the soaking zone 4 → the heating zone 3 → the preheating zone 2. That is, the gas upstream side is the soaking zone 4, and the gas downstream side is the preheating zone 2.

[0035] First, in the heating zone 3 and the soaking zone 4, check the calculated values of the burner air ratio before and after the increase in the infiltrating air. To confirm the present invention, as an example, a situation is set where an increase in infiltrating air entering from below the hearth part due to equipment trouble (such as the trough seal box provided on the walking beam falling off in the hearth part of the heating furnace 1) is allowed in the heating zone 3, and countermeasures for improvement are taken.

[0036] Here, when checking the calculated values of the burner air ratio before and after the trouble occurred, it was found that due to the increase in infiltrating air, only in the heating zone 3, the output of the burner air ratio was in a decreasing trend. From this, by checking the change over time of the burner air ratio of each heating zone (preheating zone 2, heating zone 3, soaking zone 4), it is possible to predict the time when the burner air ratio becomes below the threshold value and the infiltrating air increases, and by presenting the predicted time to the operator, it becomes possible to identify the heating zone (preheating zone 2, heating zone 3, soaking zone 4) where the infiltrating air is increasing.

[0037] Fig. 4 shows the change in the air ratio before and after the increase in infiltrating air in the heating zone 3. As shown in Fig. 4, from the trend of the burner air ratio, it is shown that in the heating zone 3, there is an optimal threshold value above the boundary value of the unburned component concentration and between the actual values of the burner air ratio at the two calculated points (before and after the increase in infiltrating air). By setting this threshold value of the burner air ratio in advance, it becomes possible to predict the timing of inspection and repair of the heating furnace 1.

[0038] As described above, in this embodiment, it is possible to display the timing of inspection and repair of the heating furnace 1 due to the increase in the infiltrating air in the heating zone 3 in real time, and it was confirmed that it is possible to predict the timing when the actual value of the burner air ratio becomes equal to or lower than the threshold value. As another example, threshold values of the burner air ratio calculated from the fuel flow rate and the air flow rate supplied to the burner 5 are set at the upper and lower parts of the heating zone 3. The threshold value is a value for determining combustion abnormalities in the heating furnace 1 (for example, unburned components cause combustion reactions at locations other than the predetermined locations).

[0039] When the cumulative frequency (continuous period) of the actual value of the burner air ratio in actual operation being equal to or lower than the threshold value continues for a certain period or longer, it is determined that there is a combustion abnormality in the burner 5 provided in the upper part or the lower part of the heating zone 3, and an abnormality signal for the heating zone 3 is sent out. Based on the abnormality signal, the warning reporting unit issues, for example, an alarm indicating an increase in infiltrating air and an alarm indicating the necessity of inspecting the heating furnace 1. Due to the alarm of the warning reporting unit, the control of the burner air ratio considering the infiltrating air is temporarily stopped.

[0040] Regardless of the presence or absence of infiltrating air (regardless of the presence or absence of infiltrating air in particular), the control of the heating zone 3 is individually performed by switching to the constant burner air ratio set value control. After confirming that the actual value of the switched burner air ratio becomes equal to or higher than the threshold value, the control returns to the constant burner air ratio set value control considering the infiltrating air, and the control of the heating zone 3 is performed. FIG. 5 shows a flowchart of a method for guiding the situation of infiltrating air into the heating furnace 1 according to the present invention.

[0041] As shown in FIG. 5, in step 1 (S1), the threshold value of the burner air ratio is set. The threshold value of the burner air ratio is set based on the boundary value of the unburned component concentration (the boundary value at which an unburned component combustion reaction (abnormal combustion) occurs at a location different from the predetermined location in the heating furnace 1), considering the safety factor, etc. In step 2 (S2), the control of the burner air ratio considering the infiltrating air is applied to the heating furnace 1.

[0042] In step 3 (S3), the actual value of the burner air ratio during operation is acquired and calculated in real time (for example, at short intervals such as every 5 seconds or every 10 seconds). Then, it proceeds to step 4 (S4) or step 6 (S6). In step 4 (S4), the inspection and repair timing of the heating furnace 1 (preheating zone 2, heating zone 3, soaking zone 4) is calculated. Then, in step 5 (S5), the predicted timing of inspection and repair of the heating furnace 1 (preheating zone 2, heating zone 3, soaking zone 4) is displayed.

[0043] In step 6 (S6), it is determined whether the actual value is less than or equal to the threshold value, that is, whether "burner air ratio (actual value) ≤ threshold value" is satisfied. If Yes, it proceeds to step 7 (S7). If No, it returns to step 2 (S2). In step 7 (S7), the duration during which the actual value of the burner air ratio during operation is less than or equal to the threshold value is measured.

[0044] In step 8 (S8), if any of the preheating zone 2, heating zone 3, and soaking zone 4 satisfies "duration ≥ threshold value" (Yes), it proceeds to step 9 (S9). If No, it returns to step 2 (S2). In step 9 (S9), the burner air ratio set value constant control is restored for all of the preheating zone 2, heating zone 3, and soaking zone 4. Then, it proceeds to step 10 (S10) or step 11 (S11).

[0045] In step 10 (S10), it is determined that the infiltration air has increased, and an abnormal signal for the corresponding heating zone (any one of the preheating zone 2, heating zone 3, and soaking zone 4) is sent out. In step 11 (S11), the actual value of the burner air ratio after switching is calculated. In step 12 (S12), it is determined whether the actual value is greater than or equal to the threshold value, that is, whether "burner air ratio (actual value) ≥ threshold value" is satisfied. If Yes, it proceeds to step 13 (S13). If No, it proceeds to step 9 (S9).

[0046] In step 13 (S13), the duration during which the actual value of the burner air ratio during operation is greater than or equal to the threshold value is measured. In step 14 (S14), when "duration ≥ threshold value" is satisfied in all zones of the preheating zone 2, heating zone 3, and soaking zone 4 (in the case of Yes), the process proceeds to step 2 (S2). In the case of No, the process proceeds to step 9 (S9).

[0047] Finally, summarizing the method for guiding the situation of the air entering the heating furnace 1 of the present invention, it is as follows. In a method for monitoring the situation of the heating furnace 1 that heats the slab to a predetermined temperature using the burner 5 and guiding the operator, the infiltrating air that enters the heating furnace 1 from outside the normal supply path While considering, the air ratio control of the burner 5 is carried out, and from the change over time of the burner air ratio in the burner 5, when the burner air ratio becomes equal to or less than the threshold value, the time (timing) when the infiltrating air increases is predicted, and the predicted time is presented to the operator.

[0048] The heating furnace 1 is provided with one or more heating zones for heating the slab (in this embodiment, the preheating zone 2, heating zone 3, and soaking zone 4). In each heating zone (preheating zone 2, heating zone 3, soaking zone 4), from the change over time of the burner air ratio, the time when the burner air ratio becomes equal to or less than the threshold value is predicted, and the predicted time is presented to the operator. For example, when the burner air ratio in the heating zone 3 becomes equal to or less than the threshold value, it is determined that the infiltrating air entering the heating zone 3 has increased.

[0049] Based on the result of predicting the time when the burner air ratio becomes equal to or less than the threshold value, the operator is presented with the inspection and repair time of the location of the infiltrating air. Regarding the burner air ratio, when the cumulative frequency (duration) below the threshold value in a predetermined period is equal to or more than a certain value, it is determined that the infiltrating air is increasing, and the situation is presented to the operator. The threshold value of the burner air ratio is determined based on the boundary value at which the unburned component concentration in the heating furnace 1 becomes the explosion range (the range where abnormal combustion occurs).

[0050] According to the method for guiding the situation of the infiltrating air into the heating furnace 1 of the present invention (the method for monitoring the situation of the heating furnace 1), after quantifying the amount of infiltrating air in each heating zone (preheating zone 2, heating zone 3, soaking zone 4) of the heating furnace 1 in real time, by monitoring the burner air ratio which is a control factor, it is possible to appropriately determine the timing of the increase in infiltrating air, and by presenting the location where the infiltrating air occurs, the repair time of the heating furnace 1 due to the infiltrating air (maintenance information), and the combustion conditions of the burner 5 when the infiltrating air occurs, etc., it becomes possible to grasp and respond to the situation of the heating furnace 1 at an early stage, and it becomes possible to reduce the scale loss by the oxygen concentration management in the heating furnace 1 of the hot rolling process.

[0051] Further, by adjusting the burner air ratio according to the situation of the heating furnace 1 and controlling the oxygen concentration in the furnace to be constant, it becomes possible to maintain the overall air ratio in the heating furnace 1 at the target value. It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. In particular, in the embodiments disclosed this time, matters not explicitly stated, for example, operating conditions, operation conditions, various parameters, dimensions, weights, volumes of components, etc., do not deviate from the scope usually implemented by those skilled in the art, and those skilled in the art usually adopt values that can be easily assumed.

Explanation of Signs

[0052] 1 Heating furnace 2 Preheating zone 3 Heating zone 4 Soaking zone 5 Burner

Claims

1. In a method for monitoring the situation of a reheating furnace that heats a slab to a predetermined temperature using a burner and guiding an operator, while taking into account the intrusion air that enters the reheating furnace from outside the normal supply path, the air ratio control of the burner is carried out, from the change over time of the burner air ratio in the burner, the time when the burner air ratio becomes equal to or less than a threshold value is predicted, and the predicted time is presented to the operator A method for guiding the situation of the intrusion air into the reheating furnace, characterized in that.

2. The reheating furnace is provided with one or more heating zones for heating the slab, in each heating zone, from the change over time of the burner air ratio, the time when the burner air ratio becomes equal to or less than a threshold value is predicted, and the predicted time is presented to the operator A method for guiding the situation of the intrusion air into the reheating furnace according to claim 1, characterized in that.

3. Based on the result of predicting the time when the burner air ratio becomes equal to or less than a threshold value, the inspection location and repair time of the intrusion air are presented to the operator A method for guiding the situation of the intrusion air into the reheating furnace according to claim 1 or 2, characterized in that.

4. Regarding the burner air ratio, when the cumulative frequency below the threshold value in a predetermined period becomes a certain value or more, the situation is presented to the operator A method for guiding the situation of the intrusion air into the reheating furnace according to claim 1 or 2, characterized in that.

5. The threshold value of the burner air ratio is determined based on the boundary value at which the unburned component concentration in the reheating furnace is in the explosion range A method for guiding the situation of the intrusion air into the reheating furnace according to claim 1 or 2, characterized in that.

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