Method for reducing nitrogen oxide in blast furnace gas

Abstract

The invention belongs to the technical field of blast furnace smelting, relates to a method for reducing nitrogen oxides in blast furnace gas, and aims to solve the problems of poor adaptability and unstable effect when an existing NOx control method for a large blast furnace of more than 2000m is applied to a blast furnace of 1000m. According to the method, gas flow distribution is controlled by optimizing a charging system, and formation of a local high-temperature area is avoided; the theoretical combustion temperature is accurately controlled; optimizing the matching relation between the oxygen enrichment rate and the coal injection amount; performing fine desulfurization treatment on the blast furnace gas; a real-time monitoring and feedback control system is established, and corresponding treatment measures are made according to special working conditions. After the method is applied, NOx generation can be effectively controlled from the source, the NOx content in the blast furnace gas is greatly reduced, meanwhile, the gas utilization rate is increased, the fuel ratio is reduced, the enterprise operation cost is remarkably saved, and double benefits of economy and environmental protection are achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of blast furnace smelting, and relates to a method for reducing nitrogen oxides of blast furnace gas. BACKGROUND

[0002] In the steel metallurgical industry, nitrogen oxides (NOx) in blast furnace gas is one of the main pollutants, which is an important precursor of photochemical smog and fine particulate matter (PM2.5), harmful to the human respiratory system, and can cause acid rain and ozone layer destruction.

[0003] When the emission exceeds the standard, the enterprise must install expensive denitration devices for treatment, which not only requires a large initial investment, but also increases the continuous operation cost.

[0004] In the actual production process, 1000m³ blast furnace faces many technical problems, as follows: The furnace capacity is relatively small, and the gas flow distribution control is difficult, which is prone to excessive development of edge or center gas flow; The adjustment range of operating parameters is relatively narrow, and the control accuracy is higher; The monitoring point arrangement is limited, and the monitoring of gas flow distribution is not perfect; The regulation and control means under special working conditions are not fine enough.

[0005] Most of the existing NOx control methods are for large blast furnaces above 2000m³, and when directly applied to 1000m³ blast furnaces, there are problems such as poor adaptability and unstable effect. Therefore, it is of great significance to develop a method for reducing nitrogen oxides of blast furnace gas, which is specially applicable to 1000m³ blast furnaces and can control NOx generation from the source. SUMMARY

[0006] The purpose of the present application is to overcome the deficiencies in the prior art and provide a method for reducing nitrogen oxides of blast furnace gas.

[0007] The present application solves its technical problem by the following technical scheme: A method for reducing nitrogen oxides of blast furnace gas, characterized in that it comprises the following steps: Step 1: adopting the combination of central coke addition and edge gas flow control to realize uniform distribution of gas flow; Step 2: calculating the theoretical combustion temperature on the basis of uniform distribution of gas flow and controlling it at 2200-2400℃, while controlling the coal powder injection amount at 110-150kg / t and the hot air temperature at 1150-1210℃, which can be adjusted by injecting low-temperature medium or using flue gas recirculation technology; Step 3: Establish the correspondence between oxygen enrichment rate and pulverized coal injection rate. When the oxygen enrichment rate is 1.5%, the pulverized coal injection rate is 130-140 kg / t; when the oxygen enrichment rate is 2.0%, the pulverized coal injection rate is 145-150 kg / t; when the oxygen enrichment rate is 2.5%, the pulverized coal injection rate is 155-160 kg / t. Control the bituminous coal ratio to be 40-50%, the volatile matter content to be 18-22%, the pulverized coal fineness to be ≥70% passing through a 200-mesh pore, and the pulverized coal moisture content to be ≤2.5%. Step 4: A semi-dry desulfurization process is adopted, with sodium bicarbonate powder as the desulfurizing agent. The desulfurizing agent loading height is controlled at 2.5-3.0m, the empty tower gas velocity is 0.8-1.2m / s, the operating temperature is 20-40℃, and the operating pressure is atmospheric pressure. The hydrogen sulfide concentration of the outlet gas is monitored regularly. When the outlet concentration exceeds 15mg / m³, an early warning is issued. When it exceeds 20mg / m³, more desulfurizing agent is injected. Step 5: Install a monitoring system in the furnace body to monitor the gas flow data; Step 6: Based on the monitoring data from Step 5, develop specific handling measures for special operating conditions such as material shortage, material suspension, and air supply interruption to ensure that NOx emissions meet standards across all scenarios.

[0008] Furthermore, the method for achieving uniform gas flow distribution by combining central coking with edge airflow control is as follows: The charging sequence is as follows: first, load a batch of central coke, then load a batch of ore, then load a small amount of coke, and finally load the remaining ore to form a stable central airflow channel while ensuring stable edge airflow. Material layer parameter control: control the coke layer thickness to be 400-500mm, the ore layer thickness to be 1200-1500mm, the material line depth to be 1.3-1.6m, and the ore-to-coke ratio to be 3.8-4.2:1; Dynamic adjustment of the throat device: The throat baffle angle is 28-35°, the edge airflow velocity is 2.5-3.5m / s, and the throat baffle angle is adjusted every 2 hours, with each adjustment not exceeding 2°, to adapt to changes in coal and gas flow in real time and maintain a uniform distribution.

[0009] Furthermore, the method for calculating the theoretical combustion temperature is achieved through the following formula: T 理 =1550+0.8t 风 -4.0W 喷 +60O2% Among them, T 理 The theoretical combustion temperature is expressed in °C; t 风 Hot air temperature, in °C; W 喷 _t represents the amount of pulverized coal injected, in kg / t; O2 represents the oxygen enrichment rate, in _t_.

[0010] Moreover, the method of setting up a monitoring system in the furnace body to monitor the data of the gas flow is as follows: 6 temperature measuring points are arranged on each of the four planes of the furnace body, and 8 pressure measuring points are arranged on each of the two planes. The data acquisition frequency is once per minute, the data of the most recent 30 days is saved, an alarm is set when the temperature deviation exceeds ±50℃, and the response time of the control system is less than 30 seconds. Moreover, the four planes of the furnace body are as follows: the first plane is the lower part of the furnace body, the second plane is the middle part of the furnace body, the third plane is the upper part of the furnace body, and the fourth plane is the furnace throat.

[0011] Furthermore, based on the monitoring data from step 5, the specific handling measures formulated for special operating conditions such as material shortage, material suspension, and interrupted air supply are as follows: When the material is insufficient, the air volume should be reduced by 10-15%, and the air volume reduction rate should not exceed 50m³ / min. After the material line returns to normal, the air volume should be gradually restored. When the material is suspended, the sudden material-sitting method should be used. The material-sitting depth should not exceed 500mm, and the material should not be sagged again within 30 minutes after staking. During the off-peak air supply operation, the top pressure fluctuation should not exceed 8 kPa, the air volume recovery rate should be 80-100 m³ / min, and the recovery time should be controlled within 2-3 hours.

[0012] The advantages and beneficial effects of this invention are as follows: This method, designed to reduce nitrogen oxide emissions from blast furnace gas, effectively controls NOx formation at its source through a series of measures, including optimizing the charging system, controlling combustion temperature, and adjusting operating parameters. Under normal smelting conditions, NOx levels in blast furnace top gas can be controlled at low levels, far below the national standard of 200 mg / m³, and even meeting the ultra-low emission requirements of below 50 mg / m³ in some regions. This reduces air pollution and lowers the emission control requirements for downstream gas users. Specific treatment measures are developed for special operating conditions to ensure that NOx emissions meet standards under all circumstances.

[0013] The method of this invention eliminates the need for expensive end-of-pipe denitrification devices, avoiding the initial investment of tens or even hundreds of millions of yuan for denitrification systems, as well as annual operating costs in the millions of yuan range (including catalyst replacement, reducing agent consumption, and electricity consumption). Only minor adjustments and optimizations to the existing system are required, resulting in low investment and quick returns. Simultaneously, it improves gas utilization and reduces the fuel ratio, further saving production costs for enterprises. For example, after applying this method to the 1000m³ blast furnace at Tianjin Steel Pipe, annual operating costs were reduced by approximately 4 million yuan, demonstrating significant economic benefits and contributing to enhancing the market competitiveness of steel enterprises. Detailed Implementation

[0014] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0015] A method for reducing nitrogen oxides in blast furnace gas includes optimizing the charging system, controlling the combustion temperature, optimizing operating parameters, fine desulfurization treatment of the gas, constructing a monitoring system, and handling steps for special operating conditions.

[0016] Optimization of loading system Given the characteristics of a 1000m³ blast furnace, precise control of the gas flow distribution is the primary measure to reduce NOx formation in the blast furnace gas. By coordinating a reasonable charging and blasting system, it is ensured that the gas flow is evenly distributed across the blast furnace cross-section, avoiding localized high-temperature zones caused by excessive gas flow at the edges or center. Specific operations are as follows: Optimization of the charging sequence: A batch of coke is charged first (center coke addition), followed by a batch of ore, then a small amount of coke again, and finally the remaining ore. This charging method creates a suitable central airflow channel while ensuring the stability of the edge airflow. Adjusting the probe depth, changing the ore-to-coke ratio, and using adjustable throat baffles can also make the gas flow distribution more regular. Optimizing the charging sequence is crucial for gas flow distribution. By adopting different charging methods such as staged charging, forward charging, or reverse charging, the pile angle and porosity distribution of the burden can be changed, thus affecting the gas flow path. For example, increasing the coke layer thickness can improve the permeability of the burden column, making the gas distribution more uniform; while appropriately reducing the ore layer height helps reduce edge airflow resistance and avoid excessive local airflow concentration. These measures can effectively prevent localized high-temperature zones at the furnace top and reduce the formation of thermal NOx.

[0017] Material layer parameter control: control the coke layer thickness to be 400-500mm, the ore layer thickness to be 1200-1500mm, the material line depth to be 1.3-1.6m, and the ore-coke ratio to be 3.8-4.2:1.

[0018] Operation of the furnace throat adjustment device: The angle of the furnace throat baffle is controlled at 28-35°, the edge airflow velocity is controlled at 2.5-3.5m / s, the baffle adjustment frequency is once every 2 hours, and the angle of each adjustment does not exceed 2°.

[0019] Combustion temperature control Theoretical combustion temperature (T) 理 Controlling nitrogen oxides (NOx) is the most effective way to reduce thermal NOx formation. Studies have shown that when T... 理 Below 2000℃, the rate of thermal NOx formation is relatively slow; while when T 理Above 2100℃, the NOx formation rate increases exponentially. Therefore, controlling the theoretical combustion temperature within the range of 2200-2400℃ can ensure complete combustion of pulverized coal while effectively suppressing NOx formation.

[0020] Theoretical combustion temperature calculation and control: The theoretical combustion temperature is calculated using a formula and controlled within the target range of 2200-2400℃.

[0021] T 理 =1550+0.8t 风 -4.0W 喷 +60O2% Among them, T 理 The theoretical combustion temperature is expressed in °C; t 风 Hot air temperature, in °C; W 喷 _t represents the amount of pulverized coal injected, in kg / t; O2 represents the oxygen enrichment rate, in _t_.

[0022] Temperature control methods: Control the pulverized coal injection rate to 110-150 kg / t and the hot blast temperature to 1150-1210℃. Lowering the blast temperature is a direct method to control the combustion temperature, but it may affect smelting efficiency. A more preferable method is to inject a low-temperature medium, such as steam or bituminous coal volatiles. Steam absorbs a large amount of heat during gasification, which can effectively reduce the peak temperature of the combustion zone. Data shows that injecting an appropriate amount of steam (5-10 g / m³) can reduce the theoretical combustion temperature by 50-100℃ and reduce NOx formation by 15-25%. In addition, flue gas recirculation technology is also an effective method. Part of the hot blast stove exhaust gas is mixed into the combustion air, utilizing the CO2 and H2O in the exhaust gas to reduce the oxygen concentration and increase the heat capacity, thereby inhibiting the rise in combustion temperature. A steel plant's practice shows that after adopting 20% ​​flue gas recirculation, the NOx emission concentration of the hot blast stove decreased from 385 mg / m³ to 246 mg / m³, a reduction of 36%.

[0023] Operating parameter optimization Synergistic optimization of oxygen enrichment and pulverized coal injection is crucial for controlling NOx formation. Oxygen enrichment improves combustion efficiency but increases flame temperature; pulverized coal injection supplements the fuel source, but the characteristics of the pulverized coal affect the combustion process. A precise match between the two is necessary to achieve efficient, low-NOx combustion.

[0024] Oxygen enrichment and pulverized coal injection ratio: Establish the corresponding relationship between oxygen enrichment rate and pulverized coal injection rate. When the oxygen enrichment rate is 1.5%, the pulverized coal injection rate is 130-140 kg / t; when the oxygen enrichment rate is 2.0%, the pulverized coal injection rate is 145-150 kg / t; when the oxygen enrichment rate is 2.5%, the pulverized coal injection rate is 155-160 kg / t.

[0025] Coal selection and blending: Optimizing coal selection and blending is a key measure to reduce fuel-type NOx. Different coal types have significantly different volatile matter and nitrogen content, and their impact on NOx formation also varies. Generally, anthracite has low volatile matter and produces less fuel-type NOx; bituminous coal has high volatile matter, burns more intensely, and tends to produce more NOx. Data shows that increasing the bituminous coal blending ratio from 0 to 50% increases NOx formation by 80%. Therefore, controlling the bituminous coal blending ratio to 40-50% and the volatile matter content to 18-22% balances combustion efficiency and emission control while ensuring the combustion performance of pulverized coal. Meanwhile, by controlling the coal powder fineness to have a 200-mesh passing rate of ≥70% and a coal powder moisture content of ≤2.5%, the uniformity of coal powder distribution and the stability of injection can be improved by finely adjusting the coal injection process parameters. The combustion atmosphere can also be changed by adjusting the carbon oxygen supply. Studies have shown that reducing the 1 mol carbon oxygen supply from 2.0 mol to 1.2 mol can significantly reduce NOx generation by 68%. Appropriately reducing the oxygen concentration and creating a weakly reducing combustion atmosphere can effectively inhibit the formation of NOx.

[0026] Coal gas desulfurization treatment While fine desulfurization of blast furnace gas does not directly reduce NOx formation, it can reduce total pollutant emissions and create more flexibility for blast furnace operation. Henan Province's 2019 non-power industry upgrading and pollution control plan explicitly requires that after fine desulfurization retrofitting of blast furnace gas, the hydrogen sulfide concentration in the gas should be less than 20 mg / m³. By reducing the sulfur content in the gas, SOx formation in downstream combustion equipment can be reduced, avoiding ammonium salt blockage problems during ammonia-based desulfurization and denitrification processes.

[0027] Desulfurization process selection: A semi-dry desulfurization process is adopted, with sodium bicarbonate powder as the desulfurizing agent. The desulfurizing agent loading height is controlled at 2.5-3.0m, the empty tower gas velocity is 0.8-1.2m / s, the operating temperature is 20-40℃, and the operating pressure is atmospheric pressure.

[0028] Desulfurization effect control: Regularly monitor the hydrogen sulfide concentration of the outlet gas. When the outlet concentration exceeds 15 mg / m³, an early warning is issued. When the outlet concentration exceeds 20 mg / m³, the amount of desulfurizing agent injected is increased to ensure the desulfurization effect, improve the gas quality, make combustion more stable, and reduce combustion instability and NOx generation fluctuations caused by gas composition fluctuations.

[0029] Construction of monitoring system Monitoring point layout: Monitoring points are arranged on four planes of the furnace body. Six temperature measuring points are arranged on each of the first plane (lower part of the furnace body), the second plane (middle part of the furnace body), the third plane (upper part of the furnace body), and the fourth plane (furnace throat). Eight pressure measuring points are arranged on each of the two planes to achieve comprehensive monitoring of temperature and pressure in different parts of the blast furnace.

[0030] Data Acquisition and Processing: Data is acquired once per minute, and data from the most recent 30 days is saved for subsequent analysis and traceability. An alarm is set when the temperature deviation exceeds ±50℃, and the control system response time is less than 30 seconds to ensure timely detection of anomalies and rapid adjustment of operating parameters.

[0031] Special working condition handling Under special operating conditions such as insufficient fuel, suspended fuel, or interrupted blast furnace operation, the reduction capacity inside the blast furnace decreases, and NOx reduction is insufficient, which may lead to an increase in NOx concentration in the furnace top gas. Therefore, special treatment measures need to be developed. Material shortage condition: Reduce air volume by 10-15%, and reduce the air volume rate by no more than 50 m³ / min. Gradually restore the air volume after the material line returns to normal to avoid abnormal gas flow distribution and temperature fluctuations caused by material shortage, and reduce NOx generation.

[0032] Suspended charge condition: The sudden charging method is adopted, and the charging depth does not exceed 500mm. The charging should not be repeated within 30 minutes after charging to prevent frequent charging from causing excessive impact on the working conditions inside the blast furnace, ensuring the stable operation of the blast furnace and reducing abnormal NOx generation.

[0033] During the shutdown and ventilation period: the top pressure fluctuation should not exceed 8 kPa, the air volume recovery rate should be 80-100 m³ / min, and the recovery time should be controlled within 2-3 hours to ensure a smooth transition of blast furnace operating conditions during the shutdown and ventilation period, and to avoid NOx emissions exceeding the standard due to drastic changes in operating conditions.

[0034] Example Taking the implementation of this method in Tianjin Steel Pipe's 1000m³ blast furnace (June 2025) as an example: Charging system: The charging sequence is as follows: first charge a batch of central coke, then charge a batch of ore, then charge a small amount of coke, and finally charge the remaining ore. The coke layer thickness is 450mm, the ore layer thickness is 1350mm, the material line depth is 1.5m, and the ore-coke ratio is 4.0:1. Temperature control: theoretical combustion temperature 2350℃, pulverized coal injection rate 130-140kg / t, hot air temperature 1200℃; Operating parameters: oxygen enrichment rate 2.0%, pulverized coal injection rate 130-140 kg / t, bituminous coal ratio 45%; Desulfurization system: desulfurizing agent loading height 2.8m, empty tower gas velocity 1.0m / s, outlet hydrogen sulfide concentration 12mg / m³ 3 .

[0035] Implementation results: NOx content in blast furnace gas decreased from 170 mg / Nm³ to 80 mg / Nm³; gas utilization rate increased from 42.5% to 46%, an increase of 3.5%; fuel ratio decreased from 559 kg / t to 550 kg / t, a decrease of 9 kg / t; annual operating costs were reduced by approximately 4 million yuan.

[0036] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for reducing nitrogen oxides in blast furnace gas, characterized in that: Includes the following steps: Step 1: A combination of central coking and edge airflow control is used to achieve uniform distribution of coal gas flow. Step 2: Calculate the theoretical combustion temperature based on the uniform distribution of the gas flow and control it at 2200-2400℃. At the same time, control the pulverized coal injection rate to 110-150kg / t and the hot air temperature to 1150-1210℃. The temperature can be adjusted by injecting low-temperature medium or by using flue gas recirculation technology. Step 3: Establish the correspondence between oxygen enrichment rate and pulverized coal injection rate. When the oxygen enrichment rate is 1.5%, the pulverized coal injection rate is 130-140 kg / t; when the oxygen enrichment rate is 2.0%, the pulverized coal injection rate is 145-150 kg / t; when the oxygen enrichment rate is 2.5%, the pulverized coal injection rate is 155-160 kg / t. Control the bituminous coal ratio to be 40-50%, the volatile matter content to be 18-22%, the pulverized coal fineness to be ≥70% passing through a 200-mesh pore, and the pulverized coal moisture content to be ≤2.5%. Step 4: A semi-dry desulfurization process is adopted, with sodium bicarbonate powder as the desulfurizing agent. The desulfurizing agent loading height is controlled at 2.5-3.0m, the empty tower gas velocity is 0.8-1.2m / s, the operating temperature is 20-40℃, and the operating pressure is atmospheric pressure. The hydrogen sulfide concentration of the outlet gas is monitored regularly. When the outlet concentration exceeds 15mg / m³, an early warning is issued. When it exceeds 20mg / m³, more desulfurizing agent is injected. Step 5: Install a monitoring system in the furnace body to monitor the gas flow data; Step 6: Based on the monitoring data from Step 5, develop specific handling measures for special operating conditions such as material shortage, material suspension, and air supply interruption to ensure that NOx emissions meet standards across all scenarios.

2. The method for reducing nitrogen oxides in blast furnace gas according to claim 1, characterized in that: The method for achieving uniform gas flow distribution by combining center coking with edge airflow control is as follows: The charging sequence is as follows: first, load a batch of central coke, then load a batch of ore, then load a small amount of coke, and finally load the remaining ore to form a stable central airflow channel while ensuring stable edge airflow. Material layer parameter control: control the coke layer thickness to be 400-500mm, the ore layer thickness to be 1200-1500mm, the material line depth to be 1.3-1.6m, and the ore-to-coke ratio to be 3.8-4.2:1; Dynamic adjustment of the throat device: The throat baffle angle is 28-35°, the edge airflow velocity is 2.5-3.5m / s, and the throat baffle angle is adjusted every 2 hours, with each adjustment not exceeding 2°, to adapt to changes in coal and gas flow in real time and maintain a uniform distribution.

3. The method for reducing nitrogen oxides in blast furnace gas according to claim 1, characterized in that: The method for calculating the theoretical combustion temperature is achieved through the following formula: T 理 =1550+0.8t 风 -4.0W 喷 +60O2% Among them, T 理 The theoretical combustion temperature is expressed in °C; t 风 Hot air temperature, in °C; W 喷 _t represents the amount of pulverized coal injected, in kg / t; O2 represents the oxygen enrichment rate, in _t_.

4. A method for reducing nitrogen oxides in blast furnace gas according to claim 1, characterized in that: The method for monitoring the gas flow data by setting up a monitoring system on the furnace body is as follows: 6 temperature measuring points are arranged on each of the four planes of the furnace body, and 8 pressure measuring points are arranged on each of the two planes. The data acquisition frequency is once per minute, and the data of the most recent 30 days is saved. An alarm is triggered when the temperature deviation exceeds ±50℃, and the response time of the control system is less than 30 seconds.

5. A method for reducing nitrogen oxides in blast furnace gas according to claim 4, characterized in that: The four planes of the furnace body are as follows: the first plane is the lower part of the furnace body, the second plane is the middle part of the furnace body, the third plane is the upper part of the furnace body, and the fourth plane is the furnace throat.

6. A method for reducing nitrogen oxides in blast furnace gas according to claim 1, characterized in that: Based on the monitoring data from step 5, the specific handling measures formulated for special operating conditions such as material shortage, material suspension, and interrupted air supply are as follows: When the material is insufficient, the air volume should be reduced by 10-15%, and the air volume reduction rate should not exceed 50m³ / min. After the material line returns to normal, the air volume should be gradually restored. When the material is suspended, the sudden material-sitting method should be used. The material-sitting depth should not exceed 500mm, and the material should not be sagged again within 30 minutes after staking. During the off-peak air supply operation, the top pressure fluctuation should not exceed 8 kPa, the air volume recovery rate should be 80-100 m³ / min, and the recovery time should be controlled within 2-3 hours.