A method for dynamically controlling air-fuel ratio of a hot blast stove

Abstract

The application provides a hot blast stove dynamic air-fuel ratio control method, comprising the following steps: dividing the hot blast stove combustion period into four stages based on different temperature rising speeds: a temperature rising period, a temperature equalizing period, a constant temperature period and a temperature maintaining period; controlling air, gas quantity and air-fuel ratio based on different combustion periods; the temperature rising period is a period for rapidly heating the hot blast stove dome to rapidly reach a predetermined temperature; the temperature equalizing period is a period for rapidly increasing the temperature of the high-temperature zone grid brick under the condition of ensuring the dome temperature unchanged; the constant temperature period is a period for rapidly heating the low-temperature zone grid brick; and the temperature maintaining period is a period for performing temperature maintaining operation with minimum gas consumption after the hot blast stove reaches the temperature requirement and before the stove is replaced. The application is aimed at the dominant heat transfer mechanism of the hot blast stove in different heating periods, and the air, gas quantity and air-fuel ratio are reasonably controlled to realize rapid stove heating, improve the heat exchange efficiency of the hot blast stove and further reduce the energy consumption of the hot blast stove.

Description

Technical Field

[0001] This invention relates to the field of energy-saving technology in the steel industry, and in particular to a method for controlling the dynamic air-fuel ratio of a hot blast stove. Background Technology

[0002] Ironmaking is the largest energy consumer in the steel industry, accounting for over 60% of total energy consumption. Reducing energy consumption in ironmaking is a crucial means of addressing the industry's energy problems. The main energy-consuming equipment in ironmaking is the blast furnace and hot blast stove. The blast furnace uses a reduction reaction to convert iron oxides into iron-carbon alloys, providing raw materials for subsequent steelmaking and rolling processes. The hot blast stove provides the blast furnace with hot air at a suitable temperature. Experience shows that for every 100°C increase in hot blast temperature, the blast furnace coke ratio decreases by 3%–7%. Simultaneously, the hot blast stove is also a major consumer of gaseous fuels in the blast furnace process, accounting for over 14% of its energy consumption. Therefore, how to increase hot blast temperature while reducing hot blast stove consumption is a pressing problem that needs to be solved in ironmaking.

[0003] The invention patent, a method for optimizing the air-fuel ratio control of a hot blast stove (CN201910496517.7), automatically sets an initial gas flow rate of 4000 cubic meters per hour based on the stove's combustion status. Every 80 seconds, the gas flow rate increases by 500 cubic meters per hour until the maximum set gas flow rate is reached, at which point combustion continues. When the exhaust gas temperature reaches the set management temperature (190-230℃), the gas flow rate automatically decreases by a calculated amount for every degree Celsius increase in exhaust gas temperature. When the exhaust gas temperature reaches its maximum (250℃), the gas flow rate remains at 4000 cubic meters per hour. These steps can be automatically completed by a PLC, thus achieving precise gas control through optimized program control. This patent operates the hot blast stove by designing an optimal air-fuel ratio and reasonable gas supply. However, the dominant heat transfer methods of the hot blast stove differ at different stages. Using the same air-fuel ratio will result in insufficient filling of the checker bricks with flue gas at the end of the combustion process, causing temperature imbalances.

[0004] The invention patent "Automatic Optimization Combustion Intelligent Control Method for Hot Blast Stove" (CN201010206032.9) provides an automatic optimization combustion intelligent control method for hot blast stoves. Based on total heat supply calculation, it sets target values ​​for combustion dome temperature and exhaust gas temperature. An air-fuel ratio fuzzy controller optimizes the optimal air-fuel ratio coefficient in real time during the combustion cycle, adjusting the combustion air flow and mixed gas flow in real time. The control of the combustion air flow is achieved by the exhaust gas temperature regulator, heat supply regulator, and combustion air regulator; the control of the mixed gas flow is achieved by the dome temperature regulator and the mixed gas regulator; and the air-fuel ratio control is achieved by the air-fuel ratio fuzzy controller. This invention improves the combustion control level of hot blast stoves, resulting in high combustion efficiency, full energy utilization, and strong heat storage capacity. However, this method uses fuzzy control for air-fuel ratio adjustment, aiming to maximize the temperature. This method is commonly used when a calorimeter (or residual oxygen meter) is unavailable, aiming to find the highest theoretical combustion temperature, but it cannot solve problems such as heat transfer efficiency at different times.

[0005] The invention patent "A Control Method for a Large Blast Furnace Hot Blast Stove" (CN201410160908.9) analyzes actual field data, combustion and heat storage mechanisms, and structural materials of the hot blast stove to determine the target value of the hot blast stove's dome temperature, thereby obtaining the stove's start-up and braking capabilities. Discrete state equations are obtained through subspace identification. Based on these discrete state equations, the actual field data is optimized to form optimized data. The average combustion data of the hot blast stove is compared with the optimized data. The dome temperature and exhaust gas temperature of the blast furnace hot blast stove are used as input signals to the response function, respectively, forming a subspace-identified state equation response output diagram. Control values ​​are obtained using the discrete state equations and a defined evaluation function. The hot blast stove is then controlled based on these control values. This invention can help engineers design predictive steps based on engineering experience to achieve nonlinear process control of hot blast stove combustion. However, the control method based on empirical models has low accuracy and, relying on field experience, can produce erroneous control methods under certain conditions.

[0006] Comparative analysis of documents reveals that the advanced operation of hot blast stoves primarily involves ensuring complete combustion of fuel within the furnace by providing a reasonable air-fuel ratio. Simultaneously, controlling the gas flow rate regulates the dome temperature and flue gas temperature, enabling heat storage and release in the checker bricks, thereby achieving cold air heating. However, in actual operation, the heat transfer mechanisms of hot blast stoves are not entirely consistent across different combustion phases. Even within the same combustion phase, heat transfer varies at different locations within the checker bricks. Generally, high-temperature zones are dominated by radiative heat transfer, while low-temperature zones rely on convective heat transfer. Therefore, new heating methods are needed to improve the heat transfer efficiency of the hot blast stove and reduce its fuel consumption. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a dynamic air-fuel ratio control method for hot blast stoves. By controlling the air-fuel ratio at different combustion stages, this invention improves the combustion efficiency of the hot blast stove and reduces its fuel consumption while ensuring the dome temperature and exhaust gas temperature. The technical means employed in this invention are as follows:

[0008] A method for dynamic air-fuel ratio control of a hot blast stove includes the following steps:

[0009] Based on different heating rates, the combustion period of the hot blast stove is divided into four stages: heating period, soaking period, constant temperature period, and holding period. The air and gas quantities and air-fuel ratio are controlled according to the different combustion periods.

[0010] The heating period is the period during which the hot air furnace dome is rapidly heated so that the temperature of the hot air furnace dome quickly reaches the predetermined temperature.

[0011] The solubility period is the period during which the temperature of the checker bricks in the high-temperature zone is rapidly increased while ensuring that the temperature of the arch remains constant.

[0012] The constant temperature period is the period during which the checker bricks in the low-temperature zone are heated rapidly;

[0013] The heat preservation period is the period during which heat preservation operations are carried out with minimal gas consumption after the hot blast stove reaches the required temperature and before the stove is replaced.

[0014] Furthermore, the heating period operation method includes the following steps:

[0015] The hot air furnace is ignited and combustion begins to enter the heating period. The operation method is to open the air and gas valves, and the air-fuel ratio is calculated according to formula (1), where the excess air coefficient α = 1.05~1.2. The arch heating rate is 10~15℃ / min to rapidly heat up until the arch temperature is 50℃~100℃ higher than the target hot air temperature, and the heat equalization period begins.

[0016]

[0017] Where: a is the air-fuel ratio; α is the excess air coefficient; Q d The lower heating value of coal gas is expressed in kJ / Nm³. 3 .

[0018] Furthermore, the homogenization period operation method includes the following steps:

[0019] The target temperature for the arch crown is set, and ±1% to ±5% of the target temperature is used as the upper and lower limits for temperature control. The arch crown temperature is kept within the upper and lower limits by controlling the gas supply, while also adjusting the excess air coefficient α. 均热 =1.1~1.5, adjust the air-fuel ratio to achieve a flue gas temperature rise rate of 0.1~20℃ / min, and after reaching the minimum allowable flue gas temperature, enter the constant temperature period.

[0020] Furthermore, the minimum allowable exhaust temperature is 240℃~300℃.

[0021] Furthermore, the isothermal operation method includes the following steps:

[0022] Heating is performed using a high air-fuel ratio mode to ensure the dome temperature operates above the lower limit, reducing the gas volume by 5%–10%, and using the excess air coefficient α. 恒温 =1.2~2.5, adjust the air-fuel ratio to ensure the exhaust gas temperature rise rate is 0.1~10℃ / min, and when the exhaust gas temperature reaches the target exhaust gas temperature, enter the heat preservation period.

[0023] Furthermore, the target temperature for the exhaust gas is 350℃~400℃.

[0024] Furthermore, the insulation period operation method includes the following steps:

[0025] Using normal air-fuel ratio mode, the excess air coefficient α 保温 =1.05~1.2, reduce the gas supply, specifically, with the arch temperature as the target, make it higher than the set minimum temperature, and control the gas supply. Ensure that the arch temperature is above the lower limit, and at the same time monitor the flue gas temperature to reach the maximum allowable flue gas temperature, and carry out furnace replacement or furnace shutdown operations pending replacement.

[0026] Furthermore, the maximum permissible exhaust temperature is no more than 400°C.

[0027] The reasons for the specific strategy adopted in this invention are as follows:

[0028] Heating period: The hot blast stove dome is rapidly heated to quickly reach the predetermined temperature. A weak oxidizing atmosphere (excess air coefficient 1.05-1.20) is required for combustion to ensure the highest theoretical combustion temperature and achieve rapid heating.

[0029] The heating period is as follows: Under the condition of keeping the arch temperature constant, the temperature of the checker bricks is rapidly increased. By changing the air-fuel ratio to adjust the amount of flue gas generated (excess air coefficient 1.1 to 1.5), the radiative heat transfer and convective heat transfer play a dominant role in the heating process under different working conditions, so as to achieve rapid heating of the checker bricks under the premise of controlling the arch temperature.

[0030] The goal of the constant temperature period is to quickly heat the checker bricks in the low temperature zone. Since the heat transfer in this process is mainly convective heat transfer between the flue gas and the checker bricks, while taking into account the uniform distribution of flue gas inside the checker bricks, the air-fuel ratio (excess air coefficient 1.2 to 2.5) is greatly increased to ensure that the flue gas fills each checker brick hole and to increase the flow rate of the flue gas to enhance convective heat transfer.

[0031] The purpose of the heat preservation period is to maintain the heat with minimal gas consumption during the period after the hot blast stove reaches the required temperature, without replacing the stove. This involves adjusting the air-fuel ratio to achieve weak oxidation (excess air coefficient 1.05-1.20) and ensuring a balance between the supplied heat and the heat loss.

[0032] The hot blast stove referred to in this article is the ironmaking hot blast stove in the steel industry. It is an intermittent regenerative hot blast stove and is applicable to internal combustion, external combustion, and top combustion hot blast stoves. This invention targets the dominant heat transfer mechanism of hot blast stoves in different heating periods. By reasonably controlling the air-gas volume and air-fuel ratio, it can achieve rapid furnace firing of hot blast stoves and improve the heat exchange efficiency of hot blast stoves, thereby reducing the energy consumption of hot blast stoves. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] A certain factory 2580m 3 The blast furnace has three hot blast stoves, which are internal combustion type, using a two-burner-one-feed combustion method. The original furnace operation was a conventional method with fuel quantity control. The furnace gas was blast furnace gas with a low calorific value of 800 kcal / Nm³. 3 The real-time flow rate is 100,000 Nm. 3 / h, furnace firing time 120min, air supply time 90min, air supply volume 5000Nm 3 The gas consumption is 1858 kJ / Nm³, operating in constant air-fuel ratio mode with an air-fuel ratio of 0.8, a supply air temperature of 1200℃, a maximum exhaust gas temperature of 370℃, and a gas consumption of 1858 kJ / Nm³. 3 热风 .

[0036] Using the method of this invention, the gas volume is set to 120,000 Nm³ during the initial heating period of combustion. 3 The air-fuel ratio is set to 0.67, the excess air coefficient is 1.05, the combustion time is 10 minutes, and the heating rate is 15℃ / min. The dome temperature is rapidly heated from 1130℃ to 1280℃, reaching the minimum dome temperature requirement. At this point, the exhaust gas temperature rises from 240℃ to 260℃, entering the homogenization period. The gas flow rate is then reduced to 90,000 Nm³. 3The gas flow rate was set at 0.75, the air-fuel ratio at 0.75, and the excess air coefficient at 1.145. Fine-tuning the gas flow rate and air-fuel ratio caused the dome temperature to fluctuate between 1270℃ and 1290℃. After 46 minutes, the exhaust gas temperature reached 300℃, with a heating rate of 0.8℃ / min, entering a constant temperature period. The gas flow rate was then reduced to 80000 Nm³. 3 The gas flow rate was set at 1.2 / h, the air-fuel ratio at 1.2, and the excess air coefficient at 1.752. The gas flow rate and air-fuel ratio were controlled to maintain the dome temperature between 1270℃ and 1290℃. After 54 minutes, the exhaust gas temperature reached 360℃, with a heating rate of 1.12℃ / min. The system then entered the heat preservation period, and the gas flow rate was reduced to 50000 Nm³. 3 The gas flow rate was set at 0.67, the air-fuel ratio at 0.67, and the excess air coefficient at 1.05. The gas flow rate and air-fuel ratio were controlled to maintain the dome temperature between 1270℃ and 1290℃. After 10 minutes, the flue gas temperature reached 369℃, triggering a boiler change command. The forced draft temperature was set at 1206℃, the forced draft time at 82 minutes, and the forced draft volume at 5050 Nm³. 3 / min, with a single energy consumption of 1709kJ / Nm 3 热风 It reduces fuel consumption by 7.99%, resulting in significant energy savings.

[0037] Example 2

[0038] A factory 3200m 3 The blast furnace has four hot blast stoves, which are externally combusted hot blast stoves using a two-burner, two-feeder combustion method. The original furnace operation was conventional, with fuel quantity control and blast furnace gas as the combustion gas, with a calorific value of 850 kcal / Nm³. 3 The real-time flow rate is 120,000 Nm. 3 / h, furnace firing time 120min, air supply time 70min, air supply volume 6000Nm 3 The gas flow rate is [value missing] / min, using a constant air-fuel ratio mode, with an air-fuel ratio set at 0.78, a supply air temperature of 1200℃, a maximum exhaust gas temperature of 400℃, and a gas consumption of 2030 kJ / Nm³. 3 热风 .

[0039] Using the method of this invention, the gas volume is set to 140,000 Nm³ during the initial heating period of combustion. 3 The gas flow rate is set at 12 min / h, air-fuel ratio of 0.75, excess air coefficient of 1.055, combustion time of 12 min, and heating rate of 10℃ / min. The dome temperature is rapidly heated from 1150℃ to 1270℃, reaching the minimum dome temperature requirement. At this point, the exhaust gas temperature rises from 220℃ to 240℃, entering the homogenization period. The gas flow rate is then reduced to 120000 Nm³. 3The gas flow rate was set at 0.86, the air-fuel ratio at 0.86, and the excess air coefficient at 1.206. Fine-tuning the gas flow rate and air-fuel ratio caused the dome temperature to fluctuate between 1260℃ and 1280℃. After 52 minutes, the exhaust gas temperature reached 310℃, with a heating rate of 1.3℃ / min, entering a constant temperature period. The gas flow rate was then reduced to 100,000 Nm³. 3 The gas flow rate was set at 1.2 / h, the air-fuel ratio at 1.2, and the excess air coefficient at 2.089. The gas flow rate and air-fuel ratio were controlled to maintain the dome temperature between 1270℃ and 1290℃. After 44 minutes, the exhaust gas temperature reached 380℃, with a heating rate of 1.59℃ / min. The system then entered the heat preservation period, and the gas flow rate was reduced to 80000 Nm³. 3 The gas flow rate was controlled at 0.75, the air-fuel ratio was set at 0.75, and the excess air coefficient was 1.055. The gas flow rate and air-fuel ratio were controlled to keep the dome temperature fluctuating between 1270℃ and 1290℃. After 14 minutes, the flue gas temperature reached 400℃, and the furnace was shut down for heat preservation without receiving a furnace replacement command. The air supply temperature was 1212℃, the air supply time was 72 minutes, and the air supply volume was 5890 Nm³. 3 / min, with a single energy consumption of 1828kJ / Nm 3 热风 It reduces fuel consumption by 9.96%, resulting in significant energy savings.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for dynamic air-fuel ratio control in a hot blast stove, characterized in that, Includes the following steps: Based on different heating rates, the combustion period of the hot blast stove is divided into four stages: heating period, soaking period, constant temperature period, and holding period. The air and gas quantities and air-fuel ratio are controlled according to the different combustion periods. The heating period is the period of rapid heating of the hot air furnace dome, so that the temperature of the hot air furnace dome reaches the predetermined temperature quickly, with a rapid heating rate of 10~15℃ / min. The solubility period is the period during which the temperature of the checker bricks in the high-temperature zone is rapidly increased while ensuring that the temperature of the arch remains constant. The rate of increase in flue gas temperature is 0.1~20℃ / min. The constant temperature period is the period during which the checker bricks in the low temperature zone are heated rapidly, and the flue gas temperature rise rate is 0.1~10℃ / min; The heat preservation period is the period during which heat preservation operations are carried out with minimal gas consumption after the hot blast stove reaches the required temperature and before the stove is replaced. The operation method during the warming period includes the following steps: The hot air furnace is ignited and combustion begins to enter the heating period. The operation method is to open the air and gas valves, and the air-fuel ratio is calculated according to formula (1), where the excess air coefficient α = 1.05~1.2, until the arch temperature is 50℃~100℃ higher than the target hot air temperature, and enter the heat equalization period. （1） Where: a is the air-fuel ratio; α is the excess air coefficient; Q d The lower heating value of coal gas is expressed in kJ / Nm³. 3 ; The homogenization period operation method includes the following steps: The target temperature for the arch crown is set, and ±1% to ±5% of the target temperature is used as the upper and lower limits for temperature control. The arch crown temperature is kept within the upper and lower limits by controlling the gas supply, while also adjusting the excess air coefficient α. 均热 =1.1~1.5, adjust the air-fuel ratio, and after reaching the minimum allowable exhaust temperature, enter the constant temperature period; The constant temperature period operation method includes the following steps: Heating is performed using a high air-fuel ratio mode to ensure the dome temperature operates above the lower limit, reducing the gas volume by 5% to 10%, and using an excess air coefficient α. 恒温 =1.2~2.5, adjust the air-fuel ratio, and when the exhaust temperature reaches the target exhaust temperature, enter the heat preservation period; The insulation period operation method includes the following steps: Using normal air-fuel ratio mode, the excess air coefficient α 保温 =1.05~1.2, reduce the gas supply, ensure the dome temperature is above the lower limit, and at the same time monitor the flue gas temperature to reach the maximum allowable flue gas temperature, and carry out furnace replacement or furnace shutdown operation in preparation for furnace replacement. The minimum allowable exhaust temperature is 240℃~300℃; The target temperature for exhaust gas is 350℃~400℃; The maximum permissible exhaust temperature is no more than 400℃.

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