A rolling heating furnace on-line monitoring control method based on near-zero residual oxygen combustion control mechanism

Abstract

The application discloses a kind of based on near zero residual oxygen combustion control mechanism's steel rolling heating furnace on-line monitoring control method, belong to heating furnace monitoring control field.The application dynamically detects and compares the CO content in each heating furnace hearth, judges the combustion deviation state;And according to whether the control temperature of each heating section is in the set range, comprehensively judges the air flow and the coal gas flow so that the CO content in the furnace hearth is in the set control range, and the combustion in the furnace is in the best combustion state.The application proposes a near zero residual oxygen combustion control method according to the process characteristics of the steel rolling heating furnace, meets the demand of accurate control on site, realizes energy saving and emission reduction, reduces burning loss, improves heating quality (prevents decarburization), improves the economic efficiency of flue gas purification treatment and the like effects.

Description

Technical Field

[0001] This invention belongs to the field of heating furnace monitoring and control, and more specifically, relates to an online monitoring and control method for steel rolling heating furnaces based on the near-zero residual oxygen combustion control mechanism. Background Technology

[0002] The heating furnace is a major energy-consuming and pollutant-emitting device in the steel rolling process. The goal of steel rolling heating furnace production is to reduce energy consumption, emissions, and oxidation loss while meeting rolling process requirements. Currently, the combustion control method for steel rolling heating furnaces mainly adopts a segmented approach, where the heating temperature of each combustion section is independently controlled according to the heating process requirements. The flue gas generated by combustion in the furnace is collected segment by segment in a counter-current manner with the heated material before being discharged externally.

[0003] Traditional air-fuel ratio control in heating furnaces primarily relies on excess air control, achieved through adjusting the excess air coefficient. This means that the required theoretical air volume for the fuel (when the flue gas produced by combustion contains no combustible components and the oxygen content is 0) is 1 Nm³. 3 The required amount of air for combustion is multiplied by an excess air coefficient (1.1–1.5) to ensure complete combustion, resulting in an oxygen content of approximately 5% in the flue gas. Since the ratio of oxygen to nitrogen in the combustion air is approximately 1:4, adding one extra unit volume of oxygen will simultaneously introduce four units of nitrogen. This excess nitrogen requires more combustion gas for heating to maintain the furnace temperature. This leads to the introduction of excess nitrogen, resulting in a larger volume of flue gas and a higher exhaust temperature.

[0004] A search revealed that patent application number 2017100040765 discloses a targeted CO-controlled combustion control system and method for a heating furnace. This system uses the optimal CO value as an indicator to find the optimal air / fuel ratio, measures the CO content in each cycle, and determines the control quantity for the current cycle based on the change and the output control quantity of the previous cycle. Patent application number 2020115933878 discloses a pure oxygen combustion control system and method for a steel rolling furnace. This system pre-sets control ranges for O2 and CO content in the flue gas of each heating section; it also detects and compares the O2 and CO content in the furnace to determine if combustion deviates from the optimal state; when O2 exceeds the set range, it is determined to be excessive air; when CO exceeds the set range, it is determined to be excessive gas; the temperature is controlled within the set range, and the flow rates of air, oxygen, and gas are adjusted according to temperature changes. In practice, the application effect of the above designs still has room for further improvement and optimization. Summary of the Invention

[0005] 1. The problem to be solved

[0006] To address the aforementioned shortcomings of traditional air-fuel ratio control methods in heating furnaces, this invention aims to provide an online monitoring and control method for steel rolling heating furnaces based on a near-zero residual oxygen combustion control mechanism. According to the process characteristics of steel rolling heating furnaces, a near-zero residual oxygen combustion control method is proposed to meet the requirements for precise on-site control, achieving effects such as energy saving and emission reduction, reduced burn-off, improved heating quality (preventing decarburization), and improved economic efficiency of flue gas purification treatment.

[0007] 2. Technical Solution

[0008] To solve the above problems, the present invention adopts the following technical solution.

[0009] The present invention discloses an online monitoring and control method for a steel rolling heating furnace based on a near-zero residual oxygen combustion control mechanism. This method dynamically detects and compares the CO content in the furnace of each heating section to determine the combustion deviation state. Based on whether the controlled temperature of each heating section is within the set range, it comprehensively judges and adjusts the air flow and gas flow to ensure that the CO content in the furnace is within the set control range, and that the combustion in the furnace is in the optimal combustion state.

[0010] The specific process is as follows:

[0011] S1. Dynamically detect and compare the CO content in the furnace to determine the combustion deviation state: when CO is less than the set range, there is excessive air; when CO exceeds the set range, there is excessive gas.

[0012] S2. Control the temperature within the set range: When CO is less than the set range, reduce the air flow; when CO exceeds the set range, reduce the gas flow.

[0013] S3, Controlling the temperature above the set maximum value: Gradually reduce the gas flow and air flow, and then optimize the combustion state through the S1 and S2 processes;

[0014] S4. Control the temperature below the set minimum value: gradually increase the air flow and gas flow, and then optimize the combustion state through the S1 and S2 processes;

[0015] By using the S1-S4 principle to cyclically optimize and adjust the air flow and gas flow, the CO content in the furnace is kept within the set control range, and the combustion inside the furnace is in the optimal combustion state.

[0016] Furthermore, the combustion section of the heating furnace includes a preheating section, heating section 1, heating section 2, and a soaking section. The steel billet enters from the preheating section and exits from the soaking section, with the flue gas flow direction being opposite to that of the preheating section. Specifically, the CO control range in the flue gas of the preheating section is 0-500 ppm, the CO control range in the flue gas of heating section 1 is 500-1500 ppm, the CO control range in the flue gas of heating section 2 is 1000-2000 ppm, and the CO control range in the flue gas of the soaking section is 2000-3000 ppm.

[0017] "Near-zero residual oxygen" method for controlling flue gas characteristics in each combustion stage

[0018] The heating temperatures of each heating section and the CO control range in the flue gas of each section are shown in the table below:

[0019]

[0020] Furthermore, the temperature control range of the preheating section of the heating furnace is 900±25℃, the temperature control range of heating section 1 is 1100±25℃, the temperature control range of heating section 2 is 1220±25℃, and the temperature control range of the soaking section is 1200±25℃.

[0021] Specifically, the present invention uses an online flue gas monitoring system to collect data in real time. The monitoring system includes multiple sets of burners located on the side or top of the heating furnace body. Combustion air enters through the air main and is distributed to each burner in the corresponding section through the air branch pipes of each combustion section. Coal gas enters through the gas main and is distributed to each burner in the corresponding section through the coal gas branch pipes of each combustion section. Each air branch pipe and coal gas branch pipe is equipped with a flow meter and an electric regulating valve.

[0022] Each combustion section of the heating furnace is equipped with a gas sampling port. The flue gas to be tested is drawn into the flue gas analyzer through the sampling tube. The data acquisition and processing system is electrically connected to the flue gas analyzer, each flow meter, and the electric regulating valve. The data acquisition and processing system adjusts each flow meter and the electric regulating valve to meet the control requirements based on the changes in the monitoring data.

[0023] Furthermore, the flue gas analyzer uses infrared analysis for CO and electromagnetic oxygen analysis for O2, and the analysis results should meet the following correlation: when CO > 2000 ppm, O2 < 0.5%.

[0024] Furthermore, each air intake hole is located at the end of each heating section and the middle of the furnace top, with the opening vertically inserted into the furnace chamber.

[0025] Furthermore, each gas sampling port is connected to a corresponding set of flue gas analyzers via a sampling tube.

[0026] Furthermore, each combustion section of the heating furnace is independently controlled, with independent control of the heating temperature and air-gas flow ratio of each heating section.

[0027] Furthermore, the heating furnace is equipped with only one exhaust duct, and the furnace pressure is controlled at a slightly positive pressure.

[0028] 3. Beneficial effects

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) Suppress excessive air infiltration to achieve energy conservation and emission reduction effects;

[0031] (2) Inhibit metal oxidation at high temperatures, reduce burn-off, prevent decarburization, and improve product quality;

[0032] (3) Suppress the formation of thermal NOx and achieve emission standards.

[0033] This invention proposes an online monitoring and control method for near-zero residual oxygen combustion control mechanism. This method maintains the main combustion sections of the heating furnace in a low-oxygen-deficient combustion state and the preheating section near the final emission stage in a low-oxidation state. This ensures that the emitted flue gas can be fully combusted with a low oxygen content, while suppressing the introduction of excess nitrogen. This results in a smaller flue gas volume and a lower exhaust temperature, which can improve the operational economy of the flue gas after-treatment system. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the distribution of the furnace combustion monitoring system in this invention;

[0035] In the picture:

[0036] 1. Heating furnace; 2. Steel billet; 3. Burner; 4. Flow meter; 5. Electric regulating valve; 6. Air main pipe; 7. Gas main pipe; 8. Air branch pipe; 9. Gas branch pipe; 10. Flue gas analyzer; 11. Sampling tube; 12. Data acquisition and processing system; 13. Gas sampling port; 14. Data cable. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example

[0039] First, combine Figure 1 As shown, the monitoring system used for online monitoring and control in this embodiment is described, including a heating furnace 1. The combustion section of the heating furnace includes a preheating section, a heating section 1, a heating section 2, and a soaking section. The steel billet enters from the preheating section and exits from the soaking section. The flue gas flow direction is opposite, that is, from the soaking section to the preheating section. Multiple sets of burners 3 are provided on the side or top of the heating furnace 1, that is, multiple sets of burners 3 are provided for each combustion section. Combustion air at a certain pressure enters the area of ​​the heating furnace 1 through the air main pipe 6 and is distributed to each burner 3 of the corresponding section through the air branch pipes 8 of each combustion section. Each air branch pipe 8 is equipped with an electric regulating valve 5 and a flow meter 4. Coal gas at a certain pressure enters the area of ​​the heating furnace 1 through the gas main pipe 7 and is distributed to each burner 3 of the corresponding section through the coal gas branch pipes 9 of each combustion section. Each coal gas branch pipe 9 is equipped with a flow meter 4 and an electric regulating valve 5.

[0040] Each combustion section of the heating furnace 1 is equipped with a gas sampling port 13. The flue gas to be tested is drawn into the flue gas analyzer 10 through the sampling tube 11. The data acquisition and processing system 12 is electrically connected to the flue gas analyzer 10, each flow meter 4, and the electric regulating valve 5 through data cables 14. The data acquisition and processing system 12 adjusts each flow meter 4 and the electric regulating valve 5 to meet the control requirements according to the changes in the monitored data. Specifically, along the flue gas flow direction, each gas sampling port 13 is set at the end of each heating section and the middle of the furnace top, with the opening vertically inserted into the furnace chamber; and each gas sampling port 13 is connected to a corresponding set of flue gas analyzers 10 through the sampling tube 11.

[0041] The following table provides a table listing the names and functions of each component of the monitoring system:

[0042]

[0043]

[0044] In this embodiment, the purpose of the heating furnace 1 is to use air gas to heat the steel billet during the conveying process to the process temperature required for rolling, thus meeting the needs of the next rolling step. In practice, to ensure the realization of segmented combustion control, each combustion section of the heating furnace 1 is independently controlled, that is, the heating temperature and air gas flow ratio of each heating section can be independently controlled; secondly, a side-fired heating method is adopted, with burners 3 arranged on both sides of the furnace body; at the same time, the heating furnace 1 is equipped with only one flue gas passage, and the furnace pressure is controlled at a slightly positive pressure state of 0 to +20 Pa to fully ensure the uniformity and representativeness of the flue gas composition.

[0045] The online flue gas monitoring system in this embodiment is used to monitor parameters such as CO and O2 in the flue gas generated by combustion in each combustion section online, and guides the optimization of combustion control in each combustion section based on corresponding constraints. Specifically, an extraction-type cold-drying method is adopted. That is, flue gas is directly extracted online through an opening, and after cooling purification, transportation, steam-water separation, cooling drying, extraction pressurization, desulfurization, dust removal, and flow stabilization, it enters the flue gas analyzer 10 for analysis. The flue gas analyzer 10 uses infrared analysis for CO and electromagnetic oxygen analysis for O2, and the analysis results should meet the following correlation: when CO > 2000 ppm, O2 < 0.5%. The data acquisition and processing system 12 collects the data transmitted online and guides the optimization of combustion control based on the changes in control temperature and thermal parameters such as O2 and CO in each section.

[0046] Based on the above system, this embodiment presents an online monitoring and control method for a steel rolling heating furnace based on a near-zero residual oxygen combustion control mechanism. This method dynamically detects and compares the CO content in the furnace of each heating section to determine the combustion deviation state. Furthermore, based on whether the controlled temperature of each heating section is within the set range, it comprehensively judges and adjusts the air flow and gas flow to ensure that the CO content in the furnace is within the set control range, and that the combustion in the furnace is in the optimal combustion state.

[0047] The specific process is as follows:

[0048] S1. Dynamically detect and compare the CO content in the furnace to determine the combustion deviation state: when CO is less than the set range, there is excessive air; when CO exceeds the set range, there is excessive gas.

[0049] S2. Control the temperature within the set range: When CO is less than the set range, reduce the air flow rate and reduce the excess air coefficient; when CO exceeds the set range, reduce the gas flow rate and increase the excess air coefficient.

[0050] S3, Controlling the temperature above the set maximum value: Gradually reduce the gas flow and air flow, and then optimize the combustion state through the S1 and S2 processes;

[0051] S4. Control the temperature below the set minimum value: gradually increase the air flow and gas flow, and then optimize the combustion state through the S1 and S2 processes;

[0052] By using the S1-S4 principle to cyclically optimize and adjust the air flow and gas flow, the CO content in the furnace is kept within the set control range, and the combustion inside the furnace is in the optimal combustion state.

[0053] Specifically, the CO control range in the flue gas of the preheating section is 0-500 ppm, the CO control range in the flue gas of heating section 1 is 500-1500 ppm, the CO control range in the flue gas of heating section 2 is 1000-2000 ppm, and the CO control range in the flue gas of the soaking section is 2000-3000 ppm. In terms of flue gas volume, it is a process of gradual accumulation across sections; that is, the flue gas volume in the preheating section is the sum of the flue gas produced by combustion in the soaking section, heating section 2, heating section 1, and the preheating section. Therefore, the CO control range in each heating section gradually decreases. Correspondingly, the temperature control range of the preheating section is 900±25℃, the temperature control range of heating section 1 is 1100±25℃, the temperature control range of heating section 2 is 1220±25℃, and the temperature control range of the soaking section is 1200±25℃.

[0054] This embodiment proposes a near-zero residual oxygen combustion control mechanism, which is mainly based on the process characteristics of steel rolling heating furnaces:

[0055] a. Segmented heating method, that is, each combustion section is independently temperature controlled according to the heating process requirements, and the heating temperature is controlled by the amount of gas;

[0056] b. The flue gas generated by combustion in the furnace is collected in stages and discharged in a counter-current manner with the heated material, and the upstream flue gas participates in the next stage of combustion reaction;

[0057] c. Current industry standard air-fuel ratio control primarily employs the excess oxygen control method: this involves multiplying the theoretical air volume required for the fuel by an excess air coefficient (1.1–1.5) to ensure complete combustion, with residual oxygen in the flue gas around 5%. The main problem with the excess oxygen control method is that if one extra unit volume of oxygen is added, four units of nitrogen will be introduced simultaneously. These extra four units of nitrogen require additional coal gas for heating to maintain the furnace temperature.

[0058] The near-zero residual oxygen combustion control mechanism of this embodiment is as follows: the main combustion sections of the heating furnace 1 are kept in a low-oxygen-deficient combustion state, and the preheating section near the final emission is kept in a low-oxidation state to ensure that the exhaust gas can be fully combusted and has a low oxygen content. At the same time, the introduction of excess nitrogen is suppressed, resulting in less exhaust gas volume and lower exhaust temperature. For the flue gas post-treatment system, this can improve the operating economy.

[0059] The examples described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention.

Claims

1. A method for online monitoring and control of a steel rolling heating furnace based on a near-zero residual oxygen combustion control mechanism, characterized in that: Dynamically detect and compare the CO content in the furnace of each heating section, judge the combustion deviation state based on the CO content, and comprehensively judge and adjust the air flow and gas flow based on whether the temperature control of each heating section is within the set range to ensure that the CO content in the furnace is within the set control range and the combustion in the furnace is in the optimal combustion state. The specific process is as follows: S1. Dynamically detect and compare the CO content in the furnace, and judge the combustion deviation state based on the CO content: when the CO is less than the set range, there is excessive air; when the CO exceeds the set range, there is excessive gas. S2. Control the temperature within the set range: When CO is less than the set range, reduce the air flow. When CO exceeds the set range, reduce the gas flow rate; S3, Controlling the temperature above the set maximum value: Gradually reduce the gas flow and air flow, and then optimize the combustion state through the S1 and S2 processes; S4. Control the temperature below the set minimum value: gradually increase the air flow and gas flow, and then optimize the combustion state through the S1 and S2 processes; By using the S1-S4 principle to cyclically optimize and adjust the air flow and gas flow, the CO content in the furnace is kept within the set control range, and the combustion in the furnace is in the optimal combustion state. The combustion section of the heating furnace includes a preheating section, heating section 1, heating section 2, and a soaking section. The steel billet enters from the preheating section and exits from the soaking section, with the flue gas flow direction opposite to that of the preheating section. Specifically, the CO concentration in the flue gas is controlled within the range of 0-500 ppm in the preheating section, 500-1500 ppm in heating section 1, 1000-2000 ppm in heating section 2, and 2000-3000 ppm in the soaking section. This ensures that the steel billet is in a weakly oxidizing atmosphere in the preheating section and a weakly reducing atmosphere in heating sections 1, 2, and the soaking section. The flue gas generated during combustion in the furnace is collected section by section in a counter-current manner with the heated material before being discharged, with upstream flue gas participating in the next stage of combustion reaction. The temperature control range of the preheating section of the heating furnace is 900±25℃, the temperature control range of heating section 1 is 1100±25℃, the temperature control range of heating section 2 is 1220±25℃, and the temperature control range of the soaking section is 1200±25℃. Each combustion section of the heating furnace (1) is independently controlled, and the heating temperature and air-gas flow ratio of each heating section are independently controlled to keep the main combustion sections of the heating furnace in a low oxygen-deficient combustion state, and the preheating section near the final discharge is kept in a low oxidation state; the heating furnace (1) is only equipped with one flue gas passage, and the furnace pressure is controlled in a slightly positive pressure state of 0~+20Pa. The method uses an online flue gas monitoring system to collect data in real time. The monitoring system includes multiple sets of burners (3) located on the side or top of the furnace body of the heating furnace (1). Combustion air enters through the air main pipe (6) and is distributed to each burner (3) in the corresponding section through the air branch pipes (8) of each combustion section. Coal gas enters through the coal gas main pipe (7) and is distributed to each burner (3) in the corresponding section through the coal gas branch pipes (9) of each combustion section. Each air branch pipe (8) and coal gas branch pipe (9) is equipped with a flow meter (4) and an electric regulating valve (5). Each combustion section of the heating furnace (1) is provided with a gas sampling hole (13). The flue gas to be tested is drawn into the flue gas analyzer (10) through the sampling tube (11). The data acquisition and processing system (12) is electrically connected to the flue gas analyzer (10), each flow meter (4) and the electric regulating valve (5) respectively. The data acquisition and processing system (12) adjusts each flow meter (4) and the electric regulating valve (5) according to the changes in the monitoring data to meet the control requirements. The flue gas analyzer (10) uses infrared analysis principle for CO and electromagnetic oxygen analysis principle for O2. The analysis results should meet the following correlation: when CO>2000ppm, O2<0.5%.

2. The online monitoring and control method for a steel rolling heating furnace based on a near-zero residual oxygen combustion control mechanism according to claim 1, characterized in that: Each air intake hole (13) is located at the end of each heating section and the middle of the furnace top, with the opening vertically inserted into the furnace chamber.

3. The online monitoring and control method for a steel rolling heating furnace based on a near-zero residual oxygen combustion control mechanism according to claim 1, characterized in that: Each gas sampling port (13) is connected to a set of flue gas analyzers (10) via a sampling tube (11).

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