A method and system for controlling NOx in the flue gas of a steel rolling heating furnace

Abstract

The application provides a method for controlling NOx in flue gas of a rolling steel heating furnace, comprising the following steps: extracting flue gas at the root, middle and top of the outer flame of a target burner of the heating furnace respectively; cooling the flue gas at the root, middle and top of the outer flame to a target temperature respectively; analyzing target components in the flue gas at the root, middle and top of the outer flame to obtain target component data of the flue gas at the root, middle and top of the outer flame respectively; calculating the average value of the target component data of the flue gas at the root, middle and top of the outer flame, and then comparing the average value with a predetermined threshold value, and adjusting the air-fuel ratio of the target burner according to the comparison result. The application also provides a system for controlling NOx in flue gas of a rolling steel heating furnace. The application can accurately and continuously detect NOx generated by each burner, and can ensure that NOx meets the emission standard.

Description

Technical Field

[0001] This invention relates to the field of energy conservation and environmental protection in steel rolling, specifically to a method for controlling NOx in the flue gas of steel rolling heating furnaces, and also to a system for controlling NOx in the flue gas of steel rolling heating furnaces. Background Technology

[0002] When fuel and air burn at high temperatures, nitrogen oxides are released, mainly including nitric oxide, nitrous oxide, and nitrogen dioxide. Nitric oxide accounts for about 95%, while nitrogen dioxide accounts for only 5%. More than 95% of the NOx produced by fuel combustion originates from thermal NOx under high-temperature conditions, which is formed by intense atomic collisions between N2 and O2 at high temperatures. This reaction temperature is 1500℃, and the amount of NOx produced increases exponentially with increasing temperature (see...). Figure 1 In existing technologies, there are several ways to control NOx generation in industry: controlling O2 content and combustion temperature at the source, and using absorption and conversion measures at the end.

[0003] As a major energy consumer in steel rolling mills, the heating furnace accounts for approximately 90% of the mill's energy consumption. The furnace gas temperature during combustion reaches as high as 1300℃, while the flame temperature reaches 1800-2500℃. Under such high combustion temperature conditions, [the following text appears unrelated and likely refers to a separate issue:] ... Figure 1 It is known that if the O2 content is too high, a large amount of NOx will be generated. Therefore, accurate detection of NOx generated by the burner of the heating furnace is the key to its control.

[0004] Current technology for NOx detection involves fixing a sampling tube at a specific location within the furnace or flue of a heating furnace. By collecting NOx levels in the furnace or flue, the air-fuel ratio of each burner in the entire heating furnace is adjusted indiscriminately. However, heating furnaces contain numerous burners; for example, a large steel rolling furnace may have 6-18 controllable burners, with hourly flue gas emissions reaching 100,000 cubic meters. Therefore, simply installing a single NOx detector at a specific location in the furnace to adjust the air-fuel ratio of each burner is clearly insufficient for precise control and has numerous inherent limitations.

[0005] In addition, existing technologies also detect NOx by installing NOx detectors on the flue gas emission system of the heating furnace. Since the NOx produced by the flue gas is collected from many burners, this detection method is more crude and it is more difficult to adjust the air-fuel ratio of the burners.

[0006] In addition, sometimes due to damage or poor sealing, there may be air leaks in the furnace door, furnace bottom, and furnace walls. The O2 that seeps into the furnace will further aggravate the production of NOx. If you simply adjust the burners of the whole furnace to control NOx, it is obviously not accurate enough. At this time, neither tail-end detection nor fixed detection inside the furnace can play a role, and may even be misleading. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for controlling NOx in the flue gas of a steel rolling furnace, and also to provide a system for controlling NOx in the flue gas of a steel rolling furnace.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for controlling NOx in flue gas from a steel rolling furnace, comprising the following steps:

[0010] (1) Extract the flue gas from the root, middle and top of the outer flame of the target burner of the heating furnace respectively;

[0011] (2) Cool the smoke from the root, middle and top of the outer flame of the flame extracted in step (1) to the target temperature respectively.

[0012] (3) Analyze the target components in the flue gas at the root, middle and top of the outer flame in step (2) to obtain the target component data of the flue gas at the root, middle and top of the outer flame respectively.

[0013] (4) Calculate the average value of the target composition data of the flue gas at the root, middle and top of the outer flame of the flame, and then compare the average value with the predetermined threshold. Adjust the air-fuel ratio of the target burner according to the comparison result.

[0014] Furthermore, if the target component NOx 平均值 ≥50mg / m 3 This reduces the air-fuel ratio of the target burner.

[0015] Furthermore, if the target component O 2平均值 If the air-fuel ratio is ≥2.5% vol, then the air-fuel ratio of the target burner should be reduced.

[0016] Furthermore, if one or more of the target components CO, H2, and CH4 are present, the air-fuel ratio of the target burner is increased.

[0017] Furthermore, in step (2), the target temperature is 150℃-180℃.

[0018] Furthermore, the following steps are included before step (1):

[0019] An air intake hole is made on the outer wall of the target burner inlet to extract flue gas from the root, middle and top of the outer flame.

[0020] The present invention also provides a system for controlling NOx in flue gas from a steel rolling heating furnace, the system comprising:

[0021] The exhaust pipe is used to extract flue gas from the root, middle and top of the outer flame of the target burner in the heating furnace, respectively.

[0022] Cooling device, which is used to cool the flue gas at the root, middle and top of the extracted outer flame to the target temperature respectively;

[0023] The high-temperature flue gas analyzer is used to analyze the target components in the flue gas at the root, middle and top of the cooled outer flame, and obtain the target component data of the flue gas at the root, middle and top of the outer flame respectively.

[0024] The control device is used to calculate and obtain the average value of the target composition data of the flue gas at the root, middle and top of the outer flame, compare the average value with a predetermined threshold, and adjust the air-fuel ratio of the target burner according to the comparison result.

[0025] Furthermore, an air intake hole is opened on the outer wall of the target burner inlet, and the exhaust pipe draws the flue gas from the root, middle and top of the outer flame through the air intake hole.

[0026] Furthermore, the air intake hole is located 300-800mm from the center of the target burner, and the diameter of the air intake hole is 15-35mm.

[0027] Furthermore, it also includes thermocouples for detecting the temperature of the flue gas after it has been cooled by the cooling device.

[0028] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0029] This invention studies the shape and temperature of the flame during the combustion process of a burner, as well as the location of NOx generation. By extracting flue gas from the root, middle, and top of the outer flame of each target burner in the heating furnace, and analyzing the target components in the flue gas, the air-fuel ratio of each burner is determined based on the comparison of the average value of the target component data with a predetermined threshold. The method of this invention can accurately and continuously detect the NOx generated by each burner, thereby directing precise control of on-site operations and forming air-fuel ratio operation rules for each burner, achieving guided and precise NOx control. Furthermore, while solving the NOx control problem of the burner, the presence of CO, H2, and CH4 is also detected, and the air-fuel ratio is adjusted based on the detection results, thus achieving efficient combustion, reducing fuel consumption, and the method of this invention is simple and highly adaptable. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram showing the curves of thermal NOx, fuel NOx, and rapid NOx as a function of temperature.

[0032] Figure 2 This is a schematic flowchart of the method for controlling NOx in the flue gas of a steel rolling heating furnace according to the present invention.

[0033] Figure 3 This is a schematic diagram of the layout of the system for controlling NOx in the flue gas of a steel rolling heating furnace according to the present invention.

[0034] Figure 4 This is a schematic diagram of the flame of the burner in the steel rolling heating furnace of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0036] like Figure 2 As shown, the present invention provides a method for controlling NOx in the flue gas of a steel rolling heating furnace, comprising the following steps:

[0037] (1) Extract the flue gas from the root, middle and top of the outer flame of the target burner of the heating furnace respectively.

[0038] (2) Cool the flue gas at the root, middle and top of the outer flame extracted in step (1) to the target temperature. In a preferred embodiment, the target temperature is 150℃-180℃ to match the operating temperature range of the high-temperature flue gas analyzer.

[0039] (3) Analyze the target components in the flue gas at the root, middle and top of the outer flame in step (2) to obtain the target component data of the flue gas at the root, middle and top of the outer flame.

[0040] (4) Calculate the average value of the target composition data of the flue gas at the root, middle and top of the outer flame of the flame, and then compare the average value with the predetermined threshold. Adjust the air-fuel ratio of the target burner according to the comparison result.

[0041] When adjusting the excess air coefficient within the range of 1.0-1.5, the root, middle, and top of the outer flame (see...) Figure 4 The NOx content in the outer flame region increases exponentially, while almost no NOx is produced inside the flame. Therefore, only the flue gas from the root, middle and top of the outer flame is extracted to determine the target components in the flue gas.

[0042] The concentrations of the target component NOx at the root, middle, and top of the outer flame were obtained, and then the average NOx concentrations at these three locations were calculated. 平均值 If the target component NOx 平均值 ≥50mg / m 3 This indicates that NOx levels are too high. In this case, it is necessary to appropriately reduce the air-fuel ratio of the target burner. In a preferred embodiment, the current air-fuel ratio can be reduced by 3%-5%.

[0043] The volume fractions of the target component O2 at the root, middle, and top of the outer flame were obtained, and then the average value of the three fractions was calculated. 2平均值 If the target component O 2平均值 A ≥2.5% vol indicates that there is too much excess air, which will produce a large amount of NOx. In this case, it is necessary to reduce the air-fuel ratio of the target burner. In a preferred embodiment, the current air-fuel ratio can be reduced by 3%-5%.

[0044] If one or more of the target components CO, H2, and CH4 appear at the root, middle, or top of the outer flame, it indicates that the fuel is not completely burned and the air-fuel ratio of the target burner is too low. In this case, it is necessary to increase the air-fuel ratio of the target burner. In a preferred embodiment, the current air-fuel ratio can be increased by 3%-5%.

[0045] In a preferred embodiment, before step (1), a step of opening a gas intake hole at the outer wall of the target burner inlet is included to extract flue gas from the root, middle, and top of the outer flame. Furthermore, if multiple burners are controlled from one side, i.e., several burners are controlled by the same valve, only one burner needs to be tested. If the upper and lower burners are controlled separately, then the upper and lower burners need to be tested separately.

[0046] like Figure 3 As shown, the present invention also provides a system for controlling NOx in the flue gas of a steel rolling furnace, including an extraction pipe, a cooling device, a high-temperature flue gas analyzer, and a control device.

[0047] The extraction pipe is used to extract flue gas from the root, middle, and top of the outer flame of the target burner in the heating furnace. Extraction detection and air-fuel ratio adjustment are performed continuously, with the extraction pipe's intake position adjusted via the insertion port. The extraction pipe is made of heat-resistant Co50 steel, 5-8 meters long, with an inner diameter of 5-10 mm. The outer wall is wrapped with heat-insulating refractory material (e.g., refractory asbestos felt) to prevent bending due to high furnace temperatures and gravity. The extraction pipe extracts flue gas from the root, middle, and top of the outer flame through intake holes located on the outer wall of the inlet of each target burner in the heating furnace. The intake holes have a diameter of 15-35 mm and are positioned 300-800 mm from the center of the target burner to facilitate angled observation and extraction. Furthermore, for precise control of the extraction position, a professional flame observation goggle is required for flame observation, typically using blue cobalt glass with a lens thickness of 1-3 mm.

[0048] The cooling device is used to cool the flue gas at the root, middle, and top of the extracted outer flame to the target temperature. The cooling device can be a water-cooled system: a 25 kg water tank containing a cooling coil, circulated by a small water pump at a rate of 1-3 liters per minute. Furthermore, thermocouples are used to measure the temperature of the cooled flue gas at the outlet. In a preferred embodiment, a type K thermocouple and a digital display instrument (Huayi PM6501) are used. The type K thermocouple is drilled and installed at the water-cooled flue gas outlet to control the circulating water supply.

[0049] The high-temperature flue gas analyzer is used to analyze target components in the flue gas at the root, middle, and top of the cooled outer flame, obtaining target component data for each location. The model of the high-temperature flue gas analyzer is Fodisch MCA14m, with a flue gas temperature ≤180℃, an indication deviation ≤0.1℃, and tests for target components including NOx, CO, H2, CH4, and O2.

[0050] The control device calculates and obtains the average value of the target component data of the flue gas at the root, middle, and top of the outer flame, compares this average value with a predetermined threshold, and adjusts the air-fuel ratio of the target burner based on the comparison result. If the target component is NOx... 平均值 ≥50mg / m 3 This indicates that NOx levels are too high, at which point the control device will reduce the air-fuel ratio of the target burner. If the target component is O... 2平均值 A concentration of ≥2.5% vol indicates excessive air volume, which will generate a large amount of NOx. In this case, the control device will reduce the air-fuel ratio of the target burner. If one or more of the target components CO, H2, and CH4 are present, it indicates incomplete combustion of the fuel and that the air-fuel ratio of the target burner is too low. In this case, the control device will increase the air-fuel ratio of the target burner.

[0051] Before determining the method for controlling NOx in the flue gas of a steel rolling mill heating furnace according to the present invention, simulation experiments were conducted in the laboratory, ultimately determining the technical solution of the present invention. In the laboratory, a high-temperature resistant glass tube was used as the combustion chamber of the furnace burner. The high-temperature resistant glass tube could withstand a maximum temperature of 1500℃, and its length was 2-3 meters. The high-temperature resistant glass tube was in an open configuration, allowing the hot flue gas to be directly discharged into the atmosphere. Three detection holes with a diameter of 10-20 mm were opened on the high-temperature resistant combustion chamber to facilitate the extraction of high-temperature flue gas. Aerospace heat-resistant steel Co50 was used as the extraction pipe, contacting the root, middle, and top of the outer flame. A common central direct-flow burner used in heating furnaces was employed in the laboratory for the mixed combustion of air and gas, where the gas was a high-coke mixed gas with a calorific value of 1500-1800 kcal. Mechanical water pumping was used to cool the flue gas in the sampling tube, and the temperature was controlled to 150-180℃ using digital thermocouples. Combustion parameters are adjusted by detecting the contents of NOx, CO, H2, CH4 and O2 in the flue gas using a high-temperature flue gas analyzer.

[0052] In cases of major overhaul of the heating furnace, large-scale adjustment of the heating furnace, changes in structural parameters, or changes in gas source parameters, the NOx emissions of the heating furnace can be calibrated using the method of this invention, thereby improving the process system to ensure that excessive NOx generation can be suppressed and NOx emissions meet standards during actual use of the heating furnace.

[0053] Example

[0054] According to the method for controlling NOx in the flue gas of a steel rolling mill heating furnace described above, a heating furnace with six burners was calibrated. The furnace was then put into operation, and the NOx content generated during actual use was measured (see Tables 1 and 2). Table 1 shows the NOx content and corresponding air-fuel ratio generated by burners 1-3. Table 2 shows the NOx content and corresponding air-fuel ratio generated by burners 4-6. The data from Tables 1 and 2 show that, in actual use, the NOx generated by each burner in the root, middle, and top of the outer flame of the heating furnace is less than 50 mg / m³. 3 Within a reasonable control range, NOx emissions can therefore meet standards.

[0055] Table 1. NOx content and corresponding air-fuel ratio produced by burners 1-3

[0056]

[0057] Table 2 NOx content and corresponding air-fuel ratio produced by burners 4-6

[0058]

[0059] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for controlling NOx in flue gas from a steel rolling mill heating furnace, characterized in that, Includes the following steps: (1) Extract the flue gas from the root, middle and top of the outer flame of the target burner of the heating furnace respectively. The gas extraction hole is opened on the outer wall of the inlet of each target burner of the heating furnace. The diameter of the gas extraction hole is 15-35mm and the distance between the gas extraction hole and the center of the target burner is 300-800mm. (2) Cool the smoke from the root, middle and top of the outer flame of the flame extracted in step (1) to the target temperature respectively; (3) Analyze the target components in the flue gas at the root, middle and top of the outer flame in step (2) to obtain the target component data of the flue gas at the root, middle and top of the outer flame respectively. (4) Calculate the average value of the target composition data of the flue gas at the root, middle and top of the outer flame of the flame, and then compare the average value with the predetermined threshold. Adjust the air-fuel ratio of the target burner according to the comparison result, wherein the excess air coefficient is adjusted in the range of 1.0-1.

5.

2. The method according to claim 1, characterized in that, If the target component is NOx 平均值 ≥50mg / m 3 This reduces the air-fuel ratio of the target burner.

3. The method according to claim 1, characterized in that, If the target component O 2平均值 If the air-fuel ratio is ≥2.5% vol, then the air-fuel ratio of the target burner should be reduced.

4. The method according to claim 1, characterized in that, If one or more of the target components CO, H2, and CH4 are present, the air-fuel ratio of the target burner should be increased.

5. The method according to claim 1, characterized in that, In step (2), the target temperature is 150℃-180℃.

6. A system for controlling NOx in flue gas from a steel rolling mill heating furnace, characterized in that, The system includes: A suction pipe is used to extract flue gas from the root, middle, and top of the outer flame of the target burner in the heating furnace. A gas intake hole is opened on the outer wall of the inlet of the target burner. The suction pipe extracts flue gas from the root, middle, and top of the outer flame through the gas intake hole. The gas intake hole is 300-800mm away from the center of the target burner, and the diameter of the gas intake hole is 15-35mm. Cooling device, which is used to cool the flue gas at the root, middle and top of the extracted outer flame to the target temperature respectively; The high-temperature flue gas analyzer is used to analyze the target components in the flue gas at the root, middle and top of the cooled outer flame, and obtain the target component data of the flue gas at the root, middle and top of the outer flame respectively. A control device is used to calculate and obtain the average value of the target composition data of the flue gas at the root, middle and top of the outer flame of the flame, and compare the average value with a predetermined threshold. Based on the comparison result, the air-fuel ratio of the target burner is adjusted, wherein the excess air coefficient is adjusted in the range of 1.0-1.

5.

7. The system according to claim 6, characterized in that, It also includes thermocouples, which are used to detect the temperature of the flue gas after it has been cooled by the cooling device.

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