Method for controlling the combustion air ratio

Abstract

To improve the technology for controlling the combustion air ratio. [Solution] A method for controlling the combustion air ratio in a heating furnace for heating metals, in which fluctuations occur in the furnace atmosphere composition during continuous operation, comprising the steps of: acquiring an oxygen concentration value using a laser oxygen concentration analyzer; and adjusting the flow rates of air and fuel gas by performing feedback control of the combustion air ratio based on the oxygen concentration value.

Description

Technical Field

[0001] The present disclosure relates to an operation technique for a heating furnace that heats metal and performs multi-variety and small-lot production (hereinafter also referred to as a metal heating furnace), and more particularly to a method for controlling the combustion air ratio of a metal heating furnace.

Background Art

[0002] As for the combustion in a conventional metal heating furnace having a plurality of burners, feedback control is known in which an appropriate mixing ratio of air and fuel gas is calculated according to the actual oxygen concentration in the furnace measured using a zirconia analyzer and the flow rate is adjusted (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional zirconia analyzer, there was a time lag in the analysis of oxygen concentration measurement. Therefore, the actual fluctuations in oxygen concentration were not reflected in real time, and it was difficult to set an appropriate air-fuel ratio. This problem could cause incomplete combustion or combustion with too much or too little air, and particularly in a metal heating furnace that performs multi-variety and small-lot production, it was difficult to put feedback control into practical use. In multi-variety and small-lot production, it is necessary to adjust the extraction temperature for each product when changing the product size. Along with this, the flow rate of fuel gas such as LNG used for burner combustion in the furnace fluctuates greatly, and the oxygen concentration in the furnace changes significantly. This large fluctuation in oxygen concentration affects the accuracy of feedback control due to the time lag, and there is a problem of frequent occurrence of incomplete combustion. Thus, there was room for improvement in the technology related to the method for controlling the combustion air ratio.

[0005] In light of these circumstances, the purpose of this disclosure is to improve the technology for controlling the combustion air ratio. [Means for solving the problem]

[0006] (1) A method for controlling the combustion air ratio according to one embodiment of the present disclosure is: In a heating furnace for heating metals, where fluctuations in the atmosphere composition inside the furnace occur during continuous operation, the step of obtaining an oxygen concentration value using a laser-type oxygen concentration analyzer, The steps include: adjusting the flow rates of air and fuel gas by performing feedback control of the combustion air ratio based on the oxygen concentration value; Includes.

[0007] (2) A method for controlling the combustion air ratio according to one embodiment of the present disclosure is the method for controlling the combustion air ratio described in (1), further The step includes correcting the oxygen concentration value by multiplying it by a density correction value based on the actual furnace temperature, In the step of adjusting the flow rates of the air and fuel gas, feedback control of the combustion air ratio is performed based on the corrected oxygen concentration value.

[0008] (3) A method for controlling the combustion air ratio according to one embodiment of the present disclosure is the method for controlling the combustion air ratio described in (1) or (2), The aforementioned feedback control is a cross-limit control method for controlling the combustion air ratio, wherein the target air flow rate and the command fuel gas flow rate are determined based on the following formulas. (Target air flow rate) = (Actual fuel gas flow rate) × (Theoretical air ratio) × (Adjustment coefficient) × {(Target oxygen concentration) ÷ (Oxygen concentration value) × 0.5 + 0.5} (Fuel gas flow rate target value) = (Actual air flow rate) × {1 / (Theoretical air ratio) × 1 / (Adjustment coefficient) × 1 / {(Oxygen concentration target value) ÷ (Oxygen concentration value) × 0.5 + 0.5}

[0009] (4) A method for controlling the combustion air ratio according to one embodiment of the present disclosure is a method for controlling the combustion air ratio according to any one of (1) to (3), Cooling air is flowed through the light-emitting and light-receiving sections of the laser-type oxygen concentration analyzer, and the oxygen concentration value is corrected based on the cooling length and furnace width. [Effects of the Invention]

[0010] According to one embodiment of the present disclosure, the technology for controlling the combustion air ratio is improved. [Brief explanation of the drawing]

[0011] [Figure 1] This block diagram shows a schematic configuration of a system according to one embodiment of the present disclosure. [Figure 2] This is a block diagram illustrating the schematic configuration of the control device. [Figure 3] This is a flowchart showing the operation of the control device. [Figure 4] This is a schematic diagram showing the system configuration according to the embodiment. [Figure 5] This graph shows the analysis results of oxygen concentration in this example and the comparative example. [Modes for carrying out the invention]

[0012] The embodiments of this disclosure will be described below.

[0013] (Summary of the embodiment)

[0014] Referring to Figure 1, the overview and configuration of System 1 according to this embodiment will be described. System 1 comprises a metal heating furnace 10, a laser oxygen concentration analyzer 20, a control device 30, and an air / fuel gas flow control valve 40. The laser oxygen concentration analyzer 20 and the control device 30 are connected via a communication interface such as wired or wireless.

[0015] First, the outline of this embodiment will be described, and the details will be described later. In the metal heating furnace 10 where the furnace atmosphere composition fluctuates during continuous operation, the laser oxygen concentration analyzer 20 is used to obtain the oxygen concentration value in the metal heating furnace 10. Further, the control device 30 of the system 1 performs feedback control of the combustion air ratio based on the oxygen concentration value, and adjusts the flow rates of the air and fuel gas supplied into the metal heating furnace 10 by the air / fuel gas flow rate adjustment valve 40.

[0016] Thus, the combustion air ratio control method according to this embodiment is a method that performs real-time feedback control by applying a laser oxygen concentration analyzer instead of a zirconia analyzer. In the prior art, it was mainstream to perform analysis with a zirconia analyzer that takes about 1 to 3 minutes from sampling to concentration analysis, but the laser oxygen concentration analyzer can complete measurement in 2 seconds, and although the analysis accuracy is inferior to the conventional one, it can significantly eliminate the time lag.

[0017] (Configuration of the control device) Next, the configuration of the control device 30 will be described in detail. As shown in FIG. 2, the control device 30 includes a control unit 31, a storage unit 32, an input unit 33, an output unit 34, and a communication unit 35.

[0018] The control unit 31 includes at least one processor, at least one dedicated circuit, or a combination thereof. The processor is a general-purpose processor such as a CPU (central processing unit) or a GPU (graphics processing unit), or a dedicated processor specialized for specific processing. The dedicated circuit is, for example, an FPGA (field-programmable gate array) or an ASIC (application specific integrated circuit). The control unit 31 executes processes related to the operation of the control device 30 while controlling each part of the control device 30.

[0019] The storage unit 32 includes at least one semiconductor memory, at least one magnetic memory, at least one optical memory, or at least two combinations thereof. The semiconductor memory is, for example, RAM (random access memory) or ROM (read-only memory). The RAM is, for example, SRAM (static random access memory) or DRAM (dynamic random access memory). The ROM is, for example, EEPROM (electrically erasable programmable read-only memory). The storage unit 32 functions, for example, as a main memory, auxiliary memory, or cache memory. The storage unit 32 stores data used for the operation of the control device 30 and data obtained by the operation of the control device 30.

[0020] The input unit 33 includes at least one input interface. The input interface may be, for example, a physical key, a capacitive key, a pointing device, or a touchscreen integrated with a display. Alternatively, the input interface may be, for example, a sound sensor that accepts voice input, or a camera that accepts gesture input. The input unit 33 accepts operations to input data used for the operation of the control device 30. Instead of being integrated into the control device 30, the input unit 33 may be connected to the control device 30 as an external input device. Any connection method can be used, for example, USB (Universal Serial Bus), HDMI (registered trademark) (High-Definition Multimedia Interface), or Bluetooth (registered trademark).

[0021] The output unit 34 includes at least one output interface. The output interface is, for example, a display that outputs information as video, or a speaker that outputs information as sound. The display is, for example, an LCD (liquid crystal display) or an organic EL (electroluminescence) display. The output unit 34 displays and outputs data obtained by the operation of the control device 30. Instead of being provided in the control device 30, the output unit 34 may be connected to the control device 30 as an external output device. Any connection method can be used, for example, USB, HDMI (registered trademark), or Bluetooth (registered trademark).

[0022] The communication unit 35 includes at least one external communication interface. The communication interface may be either a wired or wireless communication interface. In the case of wired communication, the communication interface may be, for example, a LAN (Local Area Network) interface or a USB (Universal Serial Bus) interface. In the case of wireless communication, the communication interface may be, for example, an interface compatible with mobile communication standards such as LTE (Long Term Evolution), 4G (4th generation), or 5G (5th generation), or an interface compatible with short-range wireless communication such as Bluetooth (registered trademark). The communication unit 35 receives data used for the operation of the control device 30 and transmits data obtained by the operation of the control device 30.

[0023] The functions of the control device 30 are realized by executing the program according to this embodiment on a processor corresponding to the control device 30. In other words, the functions of the control device 30 are realized by software. The program causes the computer to perform the operations of the control device 30, thereby causing the computer to function as the control device 30. That is, the computer functions as the control device 30 by performing the operations of the control device 30 according to the program.

[0024] In this embodiment, the program can be recorded on a computer-readable recording medium. The computer-readable recording medium includes non-temporary computer-readable media, such as magnetic recording devices, optical discs, magneto-optical recording media, or semiconductor memory. The program can be distributed, for example, by selling, transferring, or lending portable recording media such as DVDs (digital versatile discs) or CD-ROMs (compact disc read-only memory) on which the program is recorded. Alternatively, the program may be distributed by storing it on the storage of an external server and transmitting it from the external server to other computers. The program may also be provided as a program product.

[0025] Some or all of the functions of the control device 30 may be implemented by a dedicated circuit corresponding to the control unit 31. In other words, some or all of the functions of the control device 30 may be implemented by hardware.

[0026] (Operation of the control device) The operation of the control device 30 according to this embodiment will be described with reference to Figure 3.

[0027] Step S10: The control unit 31 of the control device 30 acquires the oxygen concentration value using the laser oxygen concentration analyzer 20. The control unit 31 acquires the oxygen concentration value inside the metal heating furnace 10 measured by the laser oxygen concentration analyzer 20 from the laser oxygen concentration analyzer 20 via the communication unit 35.

[0028] Step S20: The control unit 31 performs feedback control of the combustion air ratio based on the oxygen concentration value and adjusts the flow rates of air and fuel gas using the air / fuel gas flow rate adjustment valve 40.

[0029] As explained above, the combustion air ratio control method according to this embodiment is a system that uses a laser oxygen concentration analyzer instead of a zirconia analyzer to perform real-time feedback control. In conventional technology, analysis was mainly performed using a zirconia analyzer, which takes about 1 to 3 minutes from sampling to concentration analysis, but a laser oxygen concentration analyzer can complete the measurement in 2 seconds, significantly reducing the time lag.

[0030] (Examples) The following describes an embodiment employing System 1 according to the present disclosure. Figure 4 shows the system configuration of System 1a according to the embodiment of the present disclosure. System 1a comprises a metal heating furnace 10, a laser oxygen concentration analyzer 20, a control device 30, and an air / fuel gas flow rate control valve 40. The laser light-emitting unit 21 and light-receiving unit 22 of the laser oxygen concentration analyzer 20 are installed in the furnace width direction relative to the burner 11 inside the metal heating furnace 10. Infrared spectral analysis is performed in the light-receiving unit 22, and the analysis data is transmitted to the control device 30. In this embodiment, the light-emitting unit 21 and light-receiving unit 22 are installed by drilling holes in the furnace wall. Therefore, in this embodiment, cooling pipes 23 and 24 are provided, respectively, to prevent thermal damage to the light-emitting unit 21 and the light-receiving unit 22, and cooling air is flowed at a rate of 80 to 100 L / min.

[0031] In this embodiment, cross-limit control was used as feedback control of the combustion air ratio based on the oxygen concentration value. Cross-limit control is a control method that adjusts the air flow rate and fuel gas flow rate by alternately repeating a control pattern that makes the actual value of the air flow rate follow the target air flow rate (hereinafter also referred to as pattern A) and a control pattern that makes the actual value of the fuel gas flow rate follow the target fuel gas flow rate (hereinafter also referred to as pattern B). When pattern A control is being executed, the fuel gas flow rate is a fixed value. On the other hand, when pattern B control is being executed, the air flow rate is a fixed value.

[0032] Specifically, in the feedback control according to this embodiment, the target air flow rate and the target fuel gas flow rate are determined based on the following equations (1) and (2), respectively. (Target air flow rate) = (Actual fuel gas flow rate) × (Theoretical air ratio) × (Adjustment coefficient) × {(Target oxygen concentration) ÷ (Oxygen concentration value) × 0.5 + 0.5}·····(1) (Fuel gas flow rate target value) = (Actual air flow rate) × {1 / (Theoretical air ratio) × 1 / (Adjustment coefficient) × 1 / {(Oxygen concentration target value) ÷ (Oxygen concentration value) × 0.5 + 0.5}·····(2)

[0033] Here, the theoretical air ratio in equations (1) and (2) is the ratio of air required when it is assumed that 100% of the fuel gas at a unit flow rate reacts, and is a fixed value. For example, the theoretical air ratio may be 10. The adjustment coefficient is a coefficient for adjusting the theoretical air ratio. Depending on the incomplete combustion or NOx generation situation in the metal heating furnace 10, the adjustment coefficient is between 0.5 and 1.5. The oxygen concentration target value is the target value of the oxygen concentration in the metal heating furnace 10, and is a fixed value. For example, the oxygen concentration target value is 2%. The oxygen concentration value is the oxygen concentration value in the metal heating furnace 10 measured by the laser oxygen concentration analyzer 20.

[0034] The control unit 31 of the control device 30 sends a command signal to the air / fuel gas flow control valve 40 so that the actual value of the air flow rate follows the target value of the air flow rate in equation (1). This executes pattern A described above. After executing pattern A and the actual value of the air flow rate generally follows the target value of the air flow rate, the control unit 31 executes pattern B described above. That is, the control unit 31 sends a command signal to the air / fuel gas flow control valve 40 so that the actual value of the fuel gas flow rate follows the target value of the fuel gas flow rate in equation (2). In this way, the control unit 31 controls both the actual value of the air flow rate and the actual value of the fuel gas flow rate so that they follow the target value of the air flow rate and the target value of the fuel gas flow rate. As a result, opening commands are sent to each air flow valve and fuel gas flow valve at the automatically adjusted air ratio, and combustion is possible in the burner at the appropriate air ratio.

[0035] Figure 5 is a graph showing the analysis results of oxygen concentration in this embodiment and the comparative example. In the comparative example, oxygen concentration was analyzed using a zirconia analyzer. As test conditions, changes in fuel gas flow rate and air flow rate were measured every second. From the analysis results of this embodiment, it was confirmed that the actual value followed the theoretical value of oxygen concentration in response to changes in fuel gas flow rate. On the other hand, from the analysis results of the comparative example, it was confirmed that there was a time lag of more than one minute after the change in fuel gas flow rate occurred, and that the measured value was reflected after time had been required for fuel gas suction and cleaning analysis. From Figure 5, it can be seen that, according to the analysis of this embodiment, the actual value is reflected more than 100 seconds faster than in the comparative example.

[0036] While this disclosure has been described based on the drawings and embodiments, it should be noted that those skilled in the art may make various modifications and alterations based on this disclosure. Therefore, it should be noted that these modifications and alterations are within the scope of this disclosure. For example, the functions, etc., included in each component or step can be rearranged in a logically consistent manner, and multiple components or steps can be combined into one or divided into two.

[0037] The oxygen concentration value measured here by the laser oxygen concentration analyzer 20 may be corrected. The control device 30 may correct the oxygen concentration value by multiplying the measured oxygen concentration value by a density correction value based on the actual furnace temperature value. First, the calculated air density value ρPV is calculated based on the following equation (3).

[0038]

number

[0039] Here, T is the actual internal furnace temperature. Based on equation (3), the air density correction value β is calculated based on the following equation (4).

[0040]

number

[0041] The oxygen concentration value (hereinafter referred to as X) measured by the laser oxygen concentration analyzer 20 is corrected by the air density correction value β based on the following equation (5), and the corrected concentration measurement value Y is obtained.

[0042]

number

[0043] Cross-limit control may be performed based on equations (1) and (2) above using the corrected oxygen concentration value Y described above. Using the corrected oxygen concentration value Y can suppress the problem of measurement error.

[0044] Furthermore, when the light-emitting unit 21 and light-receiving unit 22 of the laser oxygen concentration analyzer are connected to cooling tubes 23 and 24, respectively, and cooling air is flowed through them, the oxygen concentration value may be corrected based on the furnace width length L1 and the cooling tube length L2+L3. In this case, the corrected oxygen concentration value Ya is determined by the following formula (6) based on the oxygen concentration value Xa before correction.

[0045]

number

[0046] For example, if the furnace width is 12m, the cooling tube length is 2m (1m on the light-emitting side and 1m on the light-receiving side, totaling 2m), and the atmospheric oxygen concentration is 21%, the corrected oxygen concentration value can be calculated using the following formula (7).

[0047]

number

[0048] When using cooling air, the measurement error caused by the cooling air can be reduced by using the corrected oxygen concentration related to equation (6). [Explanation of symbols]

[0049] 1 System 10 Metal heating furnace 20. Laser-type oxygen concentration analyzer 30 Control device 40 Air / Fuel Gas Flow Control Valve 11 burners 21 Light-emitting part 22 Light receiving part 23, 24 Cooling pipe

Claims

1. In a heating furnace for heating metals, where fluctuations in the atmosphere composition inside the furnace occur during continuous operation, the step of obtaining an oxygen concentration value using a laser-type oxygen concentration analyzer, The steps include: adjusting the flow rates of air and fuel gas by performing feedback control of the combustion air ratio based on the oxygen concentration value; A method for controlling the combustion air ratio, including the following.

2. A method for controlling the combustion air ratio according to claim 1, further The step includes correcting the oxygen concentration value by multiplying it by a density correction value based on the actual furnace temperature, A method for controlling the combustion air ratio, comprising the step of adjusting the flow rates of the air and fuel gas, wherein feedback control of the combustion air ratio is performed based on a corrected oxygen concentration value.

3. A method for controlling the combustion air ratio according to claim 1, The aforementioned feedback control is a cross-limit control method for controlling the combustion air ratio, wherein the target air flow rate and the command fuel gas flow rate are determined based on the following formulas. (Target air flow rate) = (Actual fuel gas flow rate) × (Theoretical air ratio) × (Adjustment coefficient) × {(Target oxygen concentration) ÷ (Oxygen concentration value) × 0.5 + 0.5} (Fuel gas flow rate target value) = (Actual air flow rate) × {1 / (Theoretical air ratio) × 1 / (Adjustment coefficient) × 1 / {(Oxygen concentration target value) ÷ (Oxygen concentration value) × 0.5 + 0.5}

4. A method for controlling the combustion air ratio according to claim 1, A method for controlling the combustion air ratio, comprising flowing cooling air through the light-emitting and light-receiving sections of the laser-type oxygen concentration analyzer, and correcting the oxygen concentration value based on the length of the cooling tube and the width of the furnace.

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