JP4653689B2 - Continuous steel heating furnace and method of heating steel using the same - Google Patents

Description

  The present invention relates to an air ratio control device and control method for a continuous steel heating furnace for heating a steel material for continuous hot rolling provided with a regenerative switching combustion burner. In particular, in a continuous steel furnace with at least two combustion control zones equipped with a regenerative switching combustion burner, a combustion control zone equipped with a regenerative switching combustion burner is appropriate for energy saving, low NOx and steel material oxidation control. A continuous steel material heating furnace capable of burning at an air ratio and a method of heating a steel material using the same.

An outline of a conventional continuous steel heating furnace and heating method will be described with reference to FIG.
FIG. 5 shows one combustion control zone of the continuous steel heating furnace, which is provided with heat storage type switching combustion burners 1a, 1b, 1c, 1d, 1e, and 1f. These regenerative switching combustion burners 1 operate as a set of two units, but generally two adjacent units or two opposing units are selected as one set. Here, a case where two opposing units are used as a group will be described as an example. When the burner 1a is in the combustion state, the fuel gas switching valve 2a and the combustion air switching valve 3a are in the open state, and the induced exhaust gas switching valve 4a is in the closed state. On the other hand, the opposing burner 1d is in the exhaust gas attracting state, the fuel gas switching valve 2d and the combustion air switching valve 3d are in the closed state, and the induced exhaust gas switching valve 4d is in the open state. Also in the other burners, the valve open / close state similar to that of the burner 1a or 1d is taken depending on whether the burner is in a combustion state or an exhaust gas induction state.

  The induced exhaust gas passes from the combustion control zone through a regenerative switching combustion burner, for example, 1d, 1e, and 1f, through the induced exhaust gas header pipe 19 for the combustion control zone, through the induced exhaust gas main pipe 22, and through the exhaust gas induction fan 13 And is discharged into the atmospheric space through the chimney 14. At this time, the flow rate is controlled to a desired induced exhaust gas flow rate by the induced exhaust gas flow rate detector 9 and the induced exhaust gas flow rate control valve 10 installed in the induced exhaust gas header pipe 19. In general, the flow rate of the induced exhaust gas is controlled based on an instruction value of an exhaust gas thermometer (not shown) installed in the induced exhaust gas header pipe 19.

  The fuel gas passes through the fuel gas main pipe 20, passes through the fuel gas header pipe 17 for the combustion control zone, and is supplied to the burner, for example, 1a, 1b and 1c. At this time, the fuel gas flow rate detector 5 and the fuel gas flow rate control valve 6 installed in the fuel gas header pipe 17 are controlled to a desired fuel gas flow rate. In general, the fuel gas flow rate is controlled so as to satisfy the set furnace temperature of the combustion control zone or to be a set fuel gas flow rate.

  Combustion air is supplied from the combustion air blower 12, passes through the combustion air main pipe 21, passes through the combustion air header pipe 18 for the combustion control zone, and is supplied to the burner in the combustion state, for example, 1 a, 1 b and 1 c. At this time, the combustion air flow rate detector 7 and the combustion air flow rate control valve 8 installed in the combustion air header pipe 18 are controlled to a desired combustion air flow rate. The control device and control method of the combustion air flow rate according to the prior art are as follows.

  The air ratio control device includes a fuel gas flow rate detector 5, a combustion air flow rate detector 7, a combustion air flow rate control valve 8, and a combustion control device 16 having a calculation function. The combustion control device 16 receives the following three as inputs. That is, the set air ratio or oxygen concentration in the set exhaust gas from the heating furnace operator or the heating furnace control computer 23, the fuel gas flow rate supplied to the combustion control zone from the fuel gas flow rate detector 5 And the combustion air flow rate supplied to the combustion control zone from the combustion air flow rate detector 7. Then, the combustion control device 16 adjusts the combustion air flow rate to the set air ratio, or the set exhaust gas oxygen concentration or the equivalent exhaust gas oxygen concentration calculated from the set air ratio and the fuel type. Then, the combustion air flow rate control valve 8 is controlled.

  However, in an actual heating furnace, due to the influence of intruding air from the door or the bottom of the furnace or errors of various flow rate detectors, the furnace may not necessarily burn at the set air ratio. Therefore, there is a technique for controlling the air ratio by utilizing the fact that if the fuel gas component and the air ratio are determined, the oxygen concentration in the exhaust gas can be theoretically calculated.

  For example, in Patent Document 1, an oxygen concentration detector 15 is provided in the exhaust gas induction system in order to detect a stable oxygen concentration, and a feedback circuit is assembled so that the detected oxygen concentration converges to a target value. A method is described in which the combustion air flow rate control valve 8 is controlled so that the substantial air ratio is as intended.

  Patent Document 2 discloses a technique for measuring an oxygen concentration by directly inserting detection ends of an oxygen concentration detector at a plurality of locations in a heating furnace.

JP-A-7-103461 JP 55-35837 A

  Although the continuous heating furnace includes a plurality of combustion control zones, the amount of fuel gas supplied to these combustion control zones is generally different for each combustion control zone. For example, in a general continuous heating furnace having 3 to 4 combustion control zones, the amount of fuel gas supplied to the combustion control zone closest to the charging side is supplied to the combustion control zone closest to the extraction side. Usually, it is about 5 to 20 times larger than the amount of fuel gas. For this reason, the influence of the air ratio in the combustion control zone where the fuel gas flow rate is relatively small is buried in the state of the combustion control zone where the fuel gas amount is relatively large, and is adjusted to an appropriate air ratio for each combustion control zone. It was difficult to do.

  In the extraction-side combustion control zone, where the supply of fuel gas is relatively small, the temperature of the steel material is generally high, and this is a temperature condition where the steel material is likely to oxidize. From the viewpoint of preventing surface quality deterioration due to field oxidation, the accuracy of air ratio control is important. Furthermore, the fact that the intrusion of air into the furnace is unavoidable every time the extraction door is opened and closed in the most extraction side belt increases the importance of the air ratio control accuracy of these extraction side combustion control zones.

  In order to realize energy saving, low NOx, and steel material oxidation suppression, it is necessary to burn at a low air ratio as close to 1 as possible without causing unburned. In the state where unburned has occurred, it means that the amount of combustion heat of the fuel cannot be used effectively, and there is a problem in terms of energy saving. When the supply amount of combustion air is equivalent, mixing may not be performed completely. Therefore, in an ordinary heating furnace, the air ratio is set higher than 1. On the other hand, if the air ratio exceeds 1, it means that excess oxygen is generated, and the oxygen reacts with nitrogen and steel in the combustion air, leading to NOx generation and steel oxidation. Therefore, it is desirable that the excess oxygen is as small as possible.

  For this reason, it is common to set the air ratio to 1.2 or less in a heating furnace, and it is desirable to lower it to about 1.05. However, it is difficult to set an air ratio suitable for each combustion control zone in the conventional technology such as Patent Document 1 in which the air ratio of a plurality of combustion control zones having significantly different amounts of fuel gas is determined from the exhaust gas oxygen concentration of the entire heating furnace. There is a limit to promoting energy saving and NOx reduction based on this.

  Further, in the conventional technique such as Patent Document 2 in which the oxygen concentration is measured by directly inserting the detection end into the heating furnace, a gas containing unburned components is sampled due to the slow combustion that is a feature of the regenerative switching combustion burner. Therefore, there is a problem that an appropriate oxygen concentration cannot be detected. Therefore, effective air ratio control cannot be realized. In addition, since the clogging is unavoidable when the sampling tube is inserted into the furnace, the conventional technology also causes inconvenience in maintenance of the instrumentation equipment.

  The present invention is a continuous steel furnace having a regenerative switching combustion burner in at least two combustion control zones, and can continuously control with high accuracy to an appropriate air ratio even if combustion control zones having greatly different fuel gas flow rates are mixed. A steel material heating furnace and a method for heating a steel material using the same, and an object of the present invention is to provide a technique that is superior in energy saving and low NOx emission than before, and that can simultaneously reduce iron loss due to steel material oxidation.

  The present invention provides a steel material for continuous hot rolling comprising a regenerative switching combustion burner in at least two combustion control zones, and a detector for detecting an oxygen concentration in the exhaust gas in an exhaust gas induction system of the combustion control zone. A continuous steel heating furnace using a continuous multi-band type walking beam that is heated to a predetermined temperature, wherein the oxygen concentration is detected in an induced exhaust gas header pipe for each combustion control zone having the regenerative switching combustion burner A continuous steel heating furnace comprising a detector and a control means for controlling an air ratio in the furnace based on a detection value of the detector.

  Further, the present invention is for continuous hot rolling, comprising a regenerative switching combustion burner in at least two combustion control zones, and having a detector for detecting an oxygen concentration in the exhaust gas in the exhaust gas induction system of the combustion control zone. A continuous steel heating furnace using a continuous multi-band type walking beam that heats a steel material to a predetermined temperature, wherein the stored heat of the induced exhaust gas main in which the induced exhaust gas of the combustion control zone having a regenerative switching combustion burner collects The oxygen concentration detector that detects the oxygen concentration in at least two or more exhaust gas downstream of the merged portion with the induced exhaust gas header pipe for each combustion control zone having the type switching combustion burner, and the detection value of the detector It is a continuous steel heating furnace characterized by installing a control means for controlling the air ratio in the furnace based on the above.

Further, the present invention is a steel material heating method using the former continuous steel material heating furnace, wherein when the set value of the combustion control device is an oxygen concentration in the induced exhaust gas, the oxygen concentration detector detects the oxygen concentration of attraction in the exhaust gas of each of the combustion control zones, so that the oxygen concentration set, the combustion of the combustion air flow rate supplied to the control zone to adjust for each of the combustion control zone, the combustion control device When the set value is the air ratio of the combustion control zone, the oxygen concentration in the induced exhaust gas corresponding to the set air ratio is determined from the preset theoretical air amount and theoretical exhaust gas amount determined by the fuel gas type. The combustion control zone is calculated such that the oxygen concentration in the induced exhaust gas for each combustion control zone detected by the oxygen concentration detector is the oxygen concentration in the induced exhaust gas calculated by this computation. A steel heating method characterized by controlling the air ratio by adjusting the supply combustion air flow rate for each of the combustion control zone.
Further, the present invention is a steel material heating method using the latter continuous steel material heating furnace, and is joined with the induced exhaust gas header pipe upstream from the oxygen concentration detector on the most upstream side of the induced exhaust gas main pipe. All combustion control zones with a portion constitute one air ratio control target range, and all combustion control zones with a junction with the induced exhaust gas header pipe between the adjacent oxygen concentration detectors, A separate air ratio control target range is configured for each adjacent oxygen concentration detector, and when the set value of the combustion control device is the oxygen concentration in the induced exhaust gas, the oxygen concentration detector The combustion air flow supplied to the combustion control zone is adjusted for each combustion control zone so that the oxygen concentration in the induced exhaust gas for each detected air ratio control target range becomes the set oxygen concentration, and the combustion control is performed. The set value of the device is In the case of the air ratio of the combustion control zone, the oxygen concentration in the induced exhaust gas corresponding to the set air ratio is calculated by calculation from the preset theoretical air amount and theoretical exhaust gas amount determined by the fuel gas type. Combustion air supplied to the combustion control zone so that the oxygen concentration in the induced exhaust gas for each air ratio control target range detected by the oxygen concentration detector becomes the oxygen concentration in the induced exhaust gas calculated by this calculation. The steel material heating method is characterized in that the air ratio is controlled by adjusting the flow rate for each combustion control zone.

  According to the present invention, in a continuous steel heating furnace having a regenerative switching combustion burner in at least two combustion control zones, even if there is a mixture of combustion control zones in which the fuel gas flow rate is significantly unbalanced, higher energy saving and lower than conventional ones. NOx emission properties can be obtained, and iron loss due to steel material oxidation can be simultaneously reduced.

An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows an example of the first invention among the continuous steel heating furnaces according to the present invention. In the following, a continuous steel furnace having a combustion control zone having four regenerative switching combustion burners will be described as an example, but the application of the present invention is limited to four combustion control zones having a regenerative switching combustion burner. It is not a thing and any number of two or more may be used.

  The attraction exhaust gas from the combustion control zone having the regenerative switching combustion burner passes through the attraction exhaust gas header pipes 19-ad provided in the combustion control zone having the regenerative switching combustion burner one by one, and the attraction exhaust gas main pipe At 22, all the induced exhaust gases merge, pass through the exhaust gas induction fan 13, and are discharged from the chimney 14 to the atmosphere.

  The first invention of the present invention is constituted as follows. That is, the oxygen concentration detectors 15a to 15d installed in the induced exhaust gas header pipes 19a to 19d, the input signals from these oxygen concentration detectors 15a to 15d, and the input signal of the fuel gas flow rate detector 5 (not shown). A combustion control apparatus capable of transmitting an input signal from the combustion air flow rate detector 7 (not shown) and an output signal to the combustion air flow rate adjusting valve 8 (not shown) and having an arithmetic function thereof 16 is composed.

  The combustion control device 16 receives the set value of the air ratio or the set value of the oxygen concentration in the induced exhaust gas from the furnace operator or the heating furnace control computer. A different value may be set for each combustion control zone, or the same value may be set for all combustion control zones. The combustion controller 16 controls the combustion air flow rate control valve 8 in the same combustion control zone as the oxygen concentration detectors 15a to 15d so that the values of the oxygen concentration detectors 15a to 15d become the oxygen concentration in the induced exhaust gas thus set. Adjust. When the air ratio is set in the combustion control device 16, the oxygen concentration in the exhaust gas corresponding to the air ratio set based on the theoretical air amount and theoretical exhaust gas amount set in advance determined by the fuel gas type is calculated by calculation. Then, the flow rate control valve for the combustion air in the combustion control zone combined with the oxygen concentration detectors 15a to 15d so that the value of the oxygen concentration detectors 15a to 15d becomes the oxygen concentration in the induced exhaust gas calculated by this calculation. Adjust 10a-d.

  According to the first aspect of the present invention described above, the air ratio of the plurality of combustion control zones having the regenerative switching combustion burner can be individually controlled to a desired value. The air ratio control is facilitated when there is a mixture of combustion control zones in which the fuel gas flow rate is significantly unbalanced. Therefore, it is excellent in energy saving property and low NOx emission property, and at the same time, reduction of iron loss due to steel material oxidation can be achieved.

  Then, an example of the 2nd invention of the air ratio control apparatus in the continuous steel material heating furnace by this invention is shown using FIG. Hereinafter, an example in which a continuous steel heating furnace having a combustion control zone having four regenerative switching combustion burners and two oxygen concentration detectors 15a and 15b installed in the induced exhaust gas main pipe 22 will be described. The application of the second invention is not limited to four combustion control zones having a regenerative switching combustion burner, and any number of combustion control zones may be used as long as it is two or more. Also, the number of oxygen concentration detectors is not limited to two, and any number of oxygen concentration detectors may be used as long as there are two or more, and one oxygen concentration detector may be provided at the junction. However, the number of oxygen concentration detectors may be the same as the number of combustion control zones having the regenerative switching combustion burner, but it is not necessary to exceed that number.

  The induced exhaust gas from the combustion control zone having the regenerative switching combustion burner passes through the induced exhaust gas header pipes 19a, 19b, 19c, 19d provided one by one in the combustion control zone having the regenerative switching combustion burner, and the induced exhaust gas main pipe At 22, all the induced exhaust gases merge, pass through the exhaust gas induction fan 13, and are discharged from the chimney 14 to the atmosphere.

  The air ratio control device according to the present invention is constituted as follows. That is, the flow rate detectors 9a, 9b, 9c, 9d for induced exhaust gas installed in the induced exhaust gas header pipes 19a, 19b, 19c, 19d, respectively, and the oxygen concentration detectors 15a, 15b installed in the induced exhaust gas main pipe 22 in a plurality. In addition, input signals from the oxygen concentration detectors 15a and 15b, input signals from the fuel gas flow rate detector 5 (not shown), input signals from the combustion air flow rate detector 7 (not shown), and combustion air flow rate. The combustion control device 16 is configured to be able to transmit an output signal to the control valve 8 (not shown) and to have a calculation function thereof.

  In the continuous steel heating furnace according to the second aspect of the present invention, since the induced exhaust gas of the plurality of combustion control zones having the regenerative switching combustion burner is joined, the oxygen concentration in the induced exhaust gas is detected. Although the combustion control zone with the combustion switching burner cannot be individually controlled, the oxygen concentration is set so that the combustion control zone with the regenerative switching combustion burner in which the fuel gas flow rate level is balanced is within the same control target range. By disposing the detector, the air ratio control equivalent to the case where the oxygen concentration detectors are installed in all the induced exhaust gas headers in the combustion control zone having the regenerative switching combustion burner becomes possible.

  The air ratio control target range is defined as follows. All combustion control zones in which the joining portion with the attraction exhaust gas header pipe is upstream of the oxygen concentration detector on the most upstream side of the attraction exhaust gas main pipe 22 constitutes one air ratio control target range. In addition, all combustion control zones that have a junction with the induced exhaust gas header pipe between the oxygen concentration detector on the most upstream side and the oxygen concentration detector on the second most upstream side are separate air ratio control targets. Configure the range. All combustion control zones with a junction with the induced exhaust gas header pipe between the second oxygen concentration detector from the uppermost stream side and the third oxygen concentration detector from the uppermost stream side are still another one air The ratio control target range is configured, and so on. In FIG. 2, the air ratio control target range is two, and the combustion control zone connected to the induced exhaust gas header pipes 19a and 19b constitutes one air ratio control target range, and the induced exhaust gas header pipes 19c and 19d. The combustion control zone connected to the other part constitutes another air ratio control target range.

  The combustion control device 16 receives the set value of the air ratio or the set value of the oxygen concentration in the induced exhaust gas from the furnace operator or the heating furnace control computer. A different value may be set for each air ratio control target range, or the same value may be set for all air ratio control target ranges. The combustion control device 16 adjusts the combustion air flow control valve 8 so that the values of the oxygen concentration detectors 15a and 15b become the target values of the oxygen concentration detectors calculated from the set oxygen concentrations in the induced exhaust gas. To do. When the air ratio is set in the combustion control device 16, the oxygen concentration in the exhaust gas corresponding to the air ratio set based on the theoretical air amount and theoretical exhaust gas amount set in advance determined by the fuel gas type is calculated by calculation. Then, the combustion air flow rate control valve 8 is adjusted so that the values of the oxygen concentration detectors 15a and 15b become the oxygen concentration in the induced exhaust gas calculated by this calculation.

  Below, the calculation method of the target value in each oxygen concentration detector is demonstrated. In the explanation, the following symbols are defined. The induced exhaust gas flow rates detected by the induced exhaust gas flow rate detectors 9a, 9b, 9c, and 9d are Va, Vb, Vc, and Vd, respectively, and the detected values at the oxygen concentration detectors 15a and 15b are O2a and O2b, respectively. The target oxygen concentration values at the detectors 15a and 15b are O2a ′ and O2b ′, the target oxygen concentration value of the combustion control zone connected to the induced exhaust gas header pipes 19a and 19b is O2a ″, and the induced exhaust gas header pipes 19c and 19d. The target oxygen concentration value of the combustion control zone connected to is O2b ″.

First, the target oxygen concentration value O2a ′ of the oxygen concentration detector 15a on the most upstream side of the induced exhaust gas main pipe 22 is:
O2a ′ = O2a ″ (1)
It becomes. Since the induced exhaust gas in the air ratio control target range is merged with the most upstream side of the induced exhaust main 22, the oxygen concentration detector 15 a does not attract the induced exhaust gas in the other air ratio control target range. Therefore, the combustion air flow rate adjustment valve 8 in the air ratio control target range may be controlled so that the target value O2a ′ approaches the target oxygen concentration value O2a ″ itself of the combustion control zone.

Next, the target oxygen concentration value O2b ′ of the second oxygen concentration detector 15b from the most upstream side of the induced exhaust gas main pipe 22 is
O2b ′ = ((Va + Vb) × O2a + (Vc + Vd) × O2b ″)
/ (Va + Vb + Vc + Vd) (2)
It becomes. Since the induced exhaust gas in the air ratio control target range merges in the middle part of the induced exhaust gas main pipe 22, the oxygen concentration detector 15 b causes the induced exhaust gas to be mixed with the induced exhaust gas in the other air ratio control target range. In order to control the oxygen concentration of the induced exhaust gas in the air ratio control target range, the target value in consideration of the oxygen concentration of the induced exhaust gas in the upstream air ratio control target range is detected. Setting is required.

  The calculation method of the target oxygen concentration value in each oxygen concentration detector when three or more oxygen concentration detectors 15 are installed in the induced exhaust gas main pipe 22 can be calculated in the same manner as Equation (2). That is, the air ratio control that is the object of control is the product of the flow rate of the induced exhaust gas passing through one upstream oxygen concentration detector and the oxygen concentration in the induced exhaust gas passing through one upstream oxygen concentration detector. The value obtained by adding the product of the target exhaust gas flow rate in the target range and the target value of the oxygen concentration in the target exhaust gas in the target air ratio control range, which is the control target, and dividing the product by the total amount of the exhaust gas that passes through the oxygen concentration detector. Is the target value.

  According to the present invention described above, since the air ratio of the plurality of combustion control zones having the regenerative switching combustion burner can be controlled to a desired value for each air ratio control target range, the fuel gas flow rate is the same level. By configuring one air ratio control target range by the combustion control zone, it becomes easy to control the air ratio when there is a mixture of combustion control zones in which the fuel gas flow rate is extremely unbalanced, which was difficult in the prior art. Therefore, it is excellent in energy saving property and low NOx emission property, and at the same time, reduction of iron loss due to steel material oxidation can be achieved.

  Hereinafter, the present invention will be described using Example 1 as the first invention, Example 2 as the second invention, and Comparative Examples 1 and 2, and these implementation conditions and evaluation results are shown in Tables 1 to 3. Shown in comparison.

Example 1
In Example 1, a continuous multi-zone walking beam heating furnace having a pre-tropical zone, a first heating zone, a second heating zone, and a soaking zone was used as the continuous steel heating furnace in accordance with the first invention. The combustion burners are all regenerative switching combustion burners and are arranged on the side walls of the heating furnace. Coke oven gas was used as the fuel gas.

  The steel material to be heated is a slab group having a length of 5.5 to 12 m, a width of 0.8 to 2.0 m, and a thickness of 220 to 250 mm. The range of the heating temperature during extraction was 1150 ° C to 1220 ° C. Moreover, the heating time of these slab groups was in the range of 120 minutes to 180 minutes.

  Zirconia-type oxygen concentration detectors 15a to 15d are respectively attached to the induced exhaust gas headers from the combustion control zones on the downstream side of the flow control valves for the induced exhaust gas, and output signals thereof are input to the combustion control device 16. Has been. In addition to this, the combustion control device 16 outputs an output signal from a fuel gas flow detector attached to a fuel gas header that supplies fuel gas to each combustion control zone, and combustion air that supplies combustion air to each combustion control zone. The output signal from the flow detector for fuel air attached to the header and the output signal from the flow detector for induced exhaust gas that is attached to the header for induced exhaust gas that exhausts the induced exhaust gas from each combustion control zone are input. ing. Further, the combustion control device 16 receives the set values of the air ratio and the furnace temperature for each combustion control zone, and for the fuel gas attached to the fuel gas header that supplies the fuel gas based on these inputs and the input signal. Adjust the flow rate control valve to set the furnace temperature to the set value, and adjust the fuel air flow rate control valve attached to the combustion air header that supplies the combustion air to set the air ratio to the set value To control. For this control, general PID control with parameter adjustment was used.

  The set air ratio of each combustion control zone was set to 1.05, and the heating operation in which the air ratio control was performed using the above-described air ratio control apparatus was carried out for about 50 hours to heat 250 steel materials. The actual air ratio of each combustion control zone was controlled in the range of 1.03 to 1.08, and it was possible to heat at a set air ratio. The amount of fuel gas supplied to each combustion control zone at that time was as shown in FIG. The ratio of the fuel gas flow rate between the pre-tropical zone and the soaking zone was about 12 times. The fuel consumption rate during this period was 0.921 MJ / kg. The thickness of the oxide scale layer of the steel material was 580 μm in terms of iron, and no defects on the surface quality occurred. Moreover, as a result of measuring NOx density | concentration in a chimney part during this, it was 45 ppm (oxygen concentration 11% conversion value) on the average.

(Example 2)
The continuous steel heating furnace includes a continuous multi-zone walking beam heating furnace having a pre-tropical zone, a first heating zone, a second heating zone, and a soaking zone above and below the same steel material conveyance line as in Example 1. Using. The combustion burners are all regenerative switching combustion burners and are arranged on the side walls of the heating furnace. Coke oven gas was used as the fuel gas.

  The steel material to be heated is a slab group having a length of 5.5 to 12 m, a width of 0.8 to 2.0 m, and a thickness of 220 to 250 mm. The range of the heating temperature during extraction was 1150 ° C to 1220 ° C. Moreover, the heating time of these slab groups was in the range of 120 minutes to 180 minutes.

  Two zirconia-type oxygen concentration detectors are attached to the induced exhaust gas main. FIG. 4 shows the positional relationship between the invitation exhaust gas header from each combustion control zone, the junction of the induction exhaust gas main, and the oxygen concentration detector. That is, there are two air ratio control target ranges in this embodiment, the pre-tropical zone and the first heating zone constitute one air ratio control target range, and the second heating zone and the soaking zone are another air. The ratio control target range is configured.

  The combustion control device receives the output signals from the two oxygen concentration detectors and the output signals from the fuel gas flow rate detectors attached to the fuel gas header that supplies the fuel gas to each combustion control zone. And for the induced exhaust gas that receives the output signal from the flow detector for fuel air that is attached to the header for combustion air that supplies the combustion air to each combustion control zone, and exhausts the induced exhaust gas from each combustion control zone An output signal is input from the flow rate detector for attracting exhaust gas attached to the header. Further, the combustion control device is inputted with set values of the air ratio and the furnace temperature for each air ratio control target range, and based on these inputs and the input signal, the fuel gas attached to the fuel gas header for supplying the fuel gas Adjust the flow rate control valve to control the furnace temperature to the set value, and adjust the fuel air flow rate control valve attached to the combustion air header that supplies the combustion air to set the air ratio Control to become. For this control, general PID control in which parameters were adjusted as in the first embodiment was used.

  The set air ratio of each combustion control zone was set to 1.05, and the heating operation in which the air ratio control was performed using the above-described air ratio control apparatus was carried out for about 70 hours to heat 350 steel materials. The actual air ratio of each combustion control zone was controlled within the range of 1.03 to 1.07 for both oxygen concentration detectors, and it was possible to heat at a set air ratio. The amount of fuel gas supplied to each combustion control zone at that time was as shown in FIG. The ratio of the fuel gas flow rate within each air ratio control target range was about 6 times. During this time, the fuel consumption rate was 0.925 MJ / kg. The thickness of the oxide scale layer of the steel material was 590 μm in terms of iron, and no defects on the surface quality occurred. Moreover, as a result of measuring NOx density | concentration in a chimney during this period, it was 47 ppm (oxygen concentration 11% conversion value) on average.

(Comparative Example 1)
On the other hand, the combustion control method by a prior art was implemented in the same heating furnace on the same slab group conditions as the Example. In the air ratio control device according to the prior art, one oxygen concentration detector is provided downstream from the position where the induced exhaust gas header pipe of the combustion control zone is joined to the induced exhaust gas main pipe, and all the combustion control zones are made up of one air. The air ratio was controlled as the ratio control target range.

  When the air ratio control method according to the prior art was performed on 150 steel materials for about 30 hours with a set air ratio of 1.05, the actual air ratio of each combustion control zone was 1.03 to 1.15. There was a tendency for the air ratio to increase when the combustion load decreased. Even if there is a combustion control zone where there is surplus oxygen due to the influence of the intruding air and the air ratio increases, all of the control is performed with the oxygen concentration at one point after the induced exhaust gas in the combustion control zone joins, so the amount of gas is The air ratio of the relatively few second heating zones and the soaking zone could not be controlled properly. The fuel consumption rate was 0.984 MJ / kg. The oxide scale layer thickness of the steel was 670 μm in terms of iron. Immediately after heating and rolling, no defects in surface quality were observed, but thereafter, surface defects due to poor plating due to steel surface oxidation occurred. During this time, the measurement result of the NOx concentration at the chimney was 65 ppm (oxygen concentration 11% conversion value) on average. Although the emission standard was satisfied, the emission concentration increased compared to the present invention.

(Comparative Example 2)
In addition, one oxygen concentration meter was inserted into the furnace from the pretropical zone, the first heating zone, the second heating zone, and the soaking zone, and the air ratio control of each combustion zone was attempted. However, the unburned component and oxygen are both detected and the oxygen concentration fluctuates with time due to the slow combustion characteristic of the livestock heat switching combustion burner, so that the air ratio control cannot be achieved.

  As described above, according to the present invention, both the first invention and the second invention have obtained results superior in energy saving and low NOx emission than the conventional one, and the iron loss due to steel material oxidation is also reduced. Furthermore, surface defects due to steel material oxidation were avoided.

It is a figure which shows one form of the part of the air ratio control apparatus in the continuous steel material heating furnace of this invention. It is a figure which shows one form of the part of the air ratio control apparatus in the continuous steel material heating furnace of this invention. In the Example of this invention, it is a figure which shows the fuel gas flow volume supplied to each combustion control zone. It is a figure explaining the continuous steel material heating furnace which is an Example of this invention. It is a figure explaining the continuous steel material heating furnace by a prior art.

Explanation of symbols

1a, 1b, 1c, 1d, 1e, 1f Burner 2a, 2b, 2c, 2d, 2e, 2f Fuel gas switching valve 3a, 3b, 3c, 3d, 3e, 3f Combustion air switching valve 4a, 4b, 4c, 4d, 4e, 4f Induction exhaust gas switching valve 5 Fuel gas flow rate detector 6 Fuel gas flow rate adjustment valve 7 Combustion air flow rate detector 8 Combustion air flow rate adjustment valve 9, 9a, 9b, 9c, 9d For attraction exhaust gas Flow rate detector 10, 10a, 10b, 10c, 10d Flow control valve for induced exhaust gas 11 Kuseki valve 12 Combustion air blower 13 Exhaust gas induced fan 14 Chimney 15, 15a, 15b, 15c, 15d Oxygen concentration detector 16 Combustion control device 17 Fuel gas header pipe 18 Combustion air header pipe 19, 19a, 19b, 19c, 19d Attracted exhaust gas header pipe 20 Fuel gas main pipe 21 Combustion air main pipe 2 attractant exhaust gas main pipe 23 furnaces Programming Port

Claims (4)

  A steel material for continuous hot rolling at a predetermined temperature having a regenerative switching combustion burner in at least two combustion control zones, and having a detector for detecting oxygen concentration in the exhaust gas in the exhaust gas induction system of the combustion control zone. A continuous steel heating furnace using a continuous multi-band type walking beam for heating, the oxygen concentration detector for detecting an oxygen concentration in an induced exhaust gas header pipe for each combustion control zone having the regenerative switching combustion burner; A continuous steel heating furnace comprising a control means for controlling an air ratio in the furnace based on a detection value of the detector.   A steel material for continuous hot rolling at a predetermined temperature having a regenerative switching combustion burner in at least two combustion control zones, and having a detector for detecting oxygen concentration in the exhaust gas in the exhaust gas induction system of the combustion control zone. A continuous steel heating furnace using a continuous multi-band type walking beam to be heated, having the regenerative switching combustion burner of the induced exhaust gas main body where the induced exhaust gas of the combustion control zone having the regenerative switching combustion burner is gathered The oxygen concentration detector for detecting oxygen concentration in at least two or more exhaust gases on the downstream side of the merged portion with the induced exhaust gas header pipe for each combustion control zone, and the inside of the furnace based on the detection value of the detector A continuous steel heating furnace comprising a control means for controlling an air ratio. A steel material heating method using the continuous steel material heating furnace according to claim 1 ,
Wherein when the setting value of the combustion control device for an oxygen concentration in said attractant exhaust gas, so that the oxygen concentration of the attractant in the exhaust gas of the oxygen concentration detector by detecting said combustion control zone each becomes the oxygen concentration set, adjust the combustion air flow supplied to the combustion control zone for each of the combustion control zone,
When the set value of the combustion control device is the air ratio of the combustion control zone, the induced exhaust gas corresponding to the set air ratio from the values of the preset theoretical air amount and the theoretical exhaust gas amount determined by the fuel gas type The oxygen concentration in the induced exhaust gas for each combustion control zone detected by the oxygen concentration detector is calculated to be the oxygen concentration in the induced exhaust gas calculated by this calculation. A steel material heating method, wherein an air ratio is controlled by adjusting a flow rate of combustion air supplied to a combustion control zone for each combustion control zone . A steel material heating method using the continuous steel material heating furnace according to claim 2,
All combustion control zones that have a confluence with the induced exhaust gas header pipe upstream of the oxygen concentration detector on the most upstream side of the induced exhaust gas main pipe constitute one air ratio control target range and are adjacent to each other. All combustion control zones that have a confluence with the induced exhaust gas header pipe between the matching oxygen concentration detectors constitute a separate air ratio control range for each adjacent oxygen concentration detector And
When the set value of the combustion control device is the oxygen concentration in the induced exhaust gas, the oxygen concentration in the induced exhaust gas for each air ratio control target range detected by the oxygen concentration detector is set to the set oxygen concentration. And adjusting the flow rate of combustion air supplied to the combustion control zone for each combustion control zone,
When the set value of the combustion control device is the air ratio of the combustion control zone, the induced exhaust gas corresponding to the set air ratio from the values of the preset theoretical air amount and the theoretical exhaust gas amount determined by the fuel gas type The oxygen concentration in the induced exhaust gas for each air ratio control target range detected by the oxygen concentration detector is calculated to be the oxygen concentration in the induced exhaust gas calculated by this calculation. A steel material heating method, wherein an air ratio is controlled by adjusting a flow rate of combustion air supplied to the combustion control zone for each combustion control zone.

Images