A combustion control method for regenerative heating furnace based on rolling line downtime length

Abstract

This invention relates to a combustion control method for a regenerative heating furnace based on the downtime of a rolling mill line, belonging to the field of steel rolling heating control technology. It solves the problem of adapting temperature and combustion strategies under dynamic downtime scenarios, addressing the difficulty in balancing energy saving and quality control. This method identifies the downtime level of the rolling mill line, implements graded cooling control, and precisely raises the temperature during rerolling according to the downtime level (at a rate of 5~15℃ / min), achieving gas savings and reduced oxidation loss. This invention has the advantages of requiring no modification to existing equipment, rapid implementation, annual gas savings of 1-2 million m³ per unit (200t heating furnace), and a reduction in oxidation loss rate of 0.1-0.3 percentage points. It combines energy saving, quality improvement, and high efficiency, and is applicable to multi-specification steel rolling production lines for φ50mm~φ180mm round bars.

Description

Technical Field

[0001] This invention relates to the field of combustion control technology for regenerative heating furnaces in steel rolling mills, specifically to an intelligent control method that dynamically adjusts the furnace temperature based on the downtime of the rolling line to achieve gas conservation and reduced oxidation loss. Background Technology

[0002] Regenerative heating furnaces are core energy-consuming equipment in the steel rolling process. Their conventional control mode is constant temperature and constant combustion, without linkage to the rolling line shutdown status. When the rolling line stops due to roll changing, maintenance, scheduling, or other reasons, the furnace continues to maintain high-load combustion at the initial rolling temperature, which has two major drawbacks: 1. Significant waste of gas: During shutdown, steel billets are not fed into the furnace, and continuous heating only results in heat loss, with extremely low energy utilization. 2. Increased oxidation loss: If the billet stays in a high-temperature environment (≥1100℃) for too long, the oxidation reaction rate increases exponentially, directly reducing the yield.

[0003] Existing technologies mostly focus on steady-state combustion optimization (such as precise air-fuel ratio control and flue gas waste heat recovery) or segmented heating for specific operating conditions. They have not solved the problem of temperature and combustion strategy adaptation in dynamic shutdown scenarios, making it difficult to balance energy saving and quality control. Summary of the Invention

[0004] This invention aims to provide a combustion control method for regenerative heating furnaces based on the downtime of rolling mill lines, which solves the problem of adapting temperature and combustion strategies in dynamic shutdown scenarios, and the difficulty in balancing energy saving and quality control.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a combustion control method for a regenerative heating furnace based on the downtime of a rolling mill, comprising the following steps: Step 1: Classify the downtime levels of the rolling mill, including short downtime, medium downtime, and long downtime; Step 2: Monitor the rolling line operation status in real time. When the rolling line stops, identify the shutdown level and dynamically adjust the temperature setpoint and combustion load inside the regenerative heating furnace. During a short shutdown, the billet temperature in the furnace is ≥1050℃, the combustion power is reduced by 30%~40%, and the temperature drop is ≤50℃. During the shutdown, the billet temperature in the furnace is 950℃~1050℃, the combustion power is reduced by 50%~60%, and the temperature drop is 50℃~150℃. During long shutdowns, the billet temperature in the furnace is 800℃~950℃, the combustion power is reduced by 70%~80%, and the temperature drop is 150℃~300℃. Intermittent combustion is used during long shutdowns. Step 3: When the rolling line resumes operation, implement precise temperature control based on the downtime and the current furnace temperature; During short stops, heat up at a rate of 5~8℃ / min, and control the heating time to 10~15min, until the rolling temperature is reached; During the interruption, the temperature is increased at a rate of 8~12℃ / min, and restored to the initial rolling temperature within 20~30 minutes; During long shutdowns, the temperature is increased at a rate of 12~15℃ / min and restored to the initial rolling temperature within 40~60 minutes. Step 4: During the resumption of operation of the rolling mill, monitor the furnace temperature and oxidation loss in real time, and dynamically adjust the heating rate and combustion load to ensure control accuracy of ±5℃.

[0006] Furthermore, in step two, the residual oxygen content in the furnace during the short shutdown is ≤6%.

[0007] Furthermore, in step two, the air-fuel ratio during the mid-stop is 0.8 to 0.9.

[0008] Furthermore, in step two, the intermittent combustion involves short-term heating for 1-2 minutes every 30 minutes to maintain the furnace temperature at or above the critical reheating temperature of the steel billet.

[0009] Furthermore, in step three, the intermediate stop adopts a segmented heating method, wherein the segmented heating is first raised to 1050℃, and then raised to the rolling start temperature.

[0010] Furthermore, in step three, the long stop is achieved by heating to the rolling temperature using two methods: heating in a high-temperature section and heating in a low-temperature section with a gradient.

[0011] Furthermore, the short stop duration T < 30 min; the medium stop duration 30 min ≤ T ≤ 120 min; and the long stop duration T > 120 min.

[0012] Furthermore, the rolling temperature is 1100℃~1250℃.

[0013] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: The present invention provides an intelligent combustion control method for a regenerative heating furnace based on the downtime of a rolling mill line. This method is compatible with various downtime scenarios, including short, medium, and long downtimes, and requires no additional equipment modifications. It can be quickly implemented on rolling mill production lines with φ50mm~φ180 round steel specifications. It achieves fully automated control of the "downtime-re-rolling" process, reduces manual intervention, and improves the intelligence level of the heating furnace operation. During downtime, gas consumption is reduced by 30% to 60%. Based on an annual downtime of 200 hours, a single 200t regenerative heating furnace can save approximately 1 to 2 million cubic meters of gas per year, resulting in significant economic benefits. In addition, the high-temperature residence time of steel billets is shortened by 40% to 70%, the oxidation loss rate is reduced by 0.1 to 0.3 percentage points, and the yield per ton of steel is increased by 0.05% to 0.15%. Detailed Implementation

[0014] The technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0015] This invention provides a combustion control method for a regenerative heating furnace based on the downtime of a rolling mill line. This method is applicable to rolling mill production lines with round steel specifications ranging from φ50mm to φ180mm. The rolling mill production line includes a data acquisition layer, a control decision layer, and an execution layer. The data acquisition layer includes rolling mill line operation status sensors, furnace temperature thermocouples, billet infrared thermometers, and flue gas oxygen content analyzers. The control decision layer includes a PLC / DCS controller with a built-in downtime-temperature matching model and an MES system interface. The execution layer includes regenerative burners, reversing valves, and flow regulating valves.

[0016] Specifically, the combustion control method for regenerative heating furnaces based on rolling mill downtime includes the following steps: Step 1: Classify the downtime levels of the rolling mill. Downtime levels include short downtime, medium downtime, and long downtime. Among them, short downtime T < 30 min is a short interruption such as temporary equipment failure or roll changing; medium downtime 30 min ≤ T ≤ 120 min is a medium-duration downtime such as planned maintenance or furnace changing; long downtime T > 120 min is a long-duration downtime such as major maintenance or process adjustment.

[0017] Step 2: The system acquires the rolling line operation signal through the MES / PLC interface. When the rolling line stops, it identifies the shutdown level and dynamically adjusts the temperature setpoint and combustion load inside the regenerative heating furnace. During a short shutdown, the billet temperature in the furnace is ≥1050℃, the combustion power is reduced by 30%~40%, the temperature drop is ≤50℃, and the residual oxygen content in the furnace is ≤6% during the short shutdown. During the shutdown, the billet temperature in the furnace is 950℃~1050℃, the combustion power is reduced by 50%~60%, the temperature drop is 50℃~150℃, and the air-fuel ratio is 0.8~0.9 during the shutdown. During long shutdowns, the billet temperature in the furnace is 800℃~950℃, the combustion power is reduced by 70%~80%, and the temperature drop is 150℃~300℃. During long shutdowns, intermittent combustion is adopted, which involves short-term heating for 1~2 minutes every 30 minutes to maintain the furnace temperature not lower than the critical reheating temperature of the billet.

[0018] Step 3: When the rolling line resumes operation, calculate the heating rate and target temperature based on the shutdown level and the current furnace temperature to ensure that the billet reaches the starting rolling temperature in the shortest possible time. The starting rolling temperature is 1100℃~1250℃, while suppressing oxidation and burning loss. During short stops, heat up at a rate of 5~8℃ / min, and control the heating time to 10~15min, until the rolling temperature is reached; During the interruption, the temperature is raised in stages. The temperature is raised to 1050℃ first, and then to the rolling temperature. The temperature is raised at a rate of 8~12℃ / min throughout the process, and then restored to the rolling temperature within 20~30 minutes. During long shutdowns, the billet is heated to the initial rolling temperature using both high-temperature and low-temperature gradient heating methods to avoid thermal stress cracking. The overall heating rate is 12~15℃ / min, and the temperature is restored to the initial rolling temperature within 40~60 minutes.

[0019] Step 4: During the resumption of rolling mill operation, the furnace temperature and oxidation loss (i.e., the thickness of oxide scale on the billet surface) are monitored in real time, and the heating rate and combustion load are dynamically adjusted to ensure control accuracy of ±5℃. The oxidation loss rate is reduced by 0.1~0.3 percentage points compared to conventional control.

[0020] The following explanation, in conjunction with specific implementation methods, will provide further details: Example

[0021] Short-stop scenario (20-minute stop for roller change) 1. Stop identification: When the rolling mill roll change triggers a stop signal, the system determines it to be a short stop (T=20min<30min). 2. Temperature control: The furnace temperature is reduced from 1180℃ to 1130℃ (a decrease of 50℃), the combustion power is reduced to 60%, the air-fuel ratio is adjusted to 0.85, and the residual oxygen is controlled at 5%; 3. Re-rolling heating: After the rolling line recovers, the temperature is increased at a rate of 6℃ / min, and the initial rolling temperature of 1180℃ is reached after 12 minutes; 4. Effect verification: Gas consumption during downtime was reduced by 35%, and the oxidation loss rate of steel billets after re-rolling was 0.20%, which was 0.12 percentage points lower than the conventional control (0.32%). Example

[0022] Intermediate shutdown scenario (planned maintenance shutdown of 60 minutes) 1. Shutdown identification: The system determines it to be a medium-level shutdown (30min≤60min<120min); 2. Cooling control: The furnace temperature is reduced from 1180℃ to 1020℃ (a temperature drop of 160℃), the combustion power is reduced to 40%, and intermittent combustion is used (heating is provided for 1 minute every 30 minutes). 3. Re-rolling heating: Heat at a rate of 10℃ / min, and restore to 1180℃ after 26 minutes; 4. Effect verification: Gas consumption during shutdown periods was reduced by 55%, and the oxidation loss rate was 0.18%, which was 0.14 percentage points lower than conventional control. Example

[0023] Long-term shutdown scenario (major maintenance shutdown of 150 minutes) 1. Shutdown identification: The system determines it to be a long shutdown (T=150min≥120min); 2. Cooling control: The furnace temperature is reduced from 1180℃ to 880℃ (a temperature drop of 300℃), the combustion power is reduced to 25%, and short-term heating is provided for 2 minutes every 30 minutes; 3. Re-rolling heating: Heat at a rate of 13℃ / min, and then restore to 1180℃ after 50 minutes; 4. Effect verification: Gas consumption during shutdown periods was reduced by 65%, and the oxidation loss rate was 0.17%, which is 0.15 percentage points lower than conventional control.

[0024] In summary, the regenerative heating furnace combustion control method based on rolling line downtime proposed in this application offers the following advantages in steel rolling production lines: 1. Significant energy saving: Gas consumption is reduced by 30% to 60% during downtime. Based on 200 hours of downtime per year, a single 200t regenerative heating furnace can save approximately 1 million to 2 million m³ of gas per year, resulting in significant economic benefits. 2. Reduced losses and improved quality: The high-temperature residence time of steel billets is shortened by 40% to 70%, the oxidation loss rate is reduced by 0.1 to 0.3 percentage points, and the yield per ton of steel is increased by 0.05% to 0.15%; 3. Strong adaptability: It is compatible with various downtime scenarios of short, medium and long durations, without the need for additional equipment modification, and can be quickly implemented on rolling production lines of multiple specifications such as φ50~φ180 round steel. 4. Intelligent and efficient: It realizes full-process automatic control of "shutdown-re-rolling", reduces manual intervention, and improves the level of intelligence of heating furnace operation.

[0025] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A combustion control method for a regenerative heating furnace based on the downtime of a rolling mill line, characterized in that, Includes the following steps: Step 1: Classify the downtime levels of the rolling mill, including short downtime, medium downtime, and long downtime; Step 2: Monitor the rolling line operation status in real time. When the rolling line stops, identify the shutdown level and dynamically adjust the temperature setpoint and combustion load inside the regenerative heating furnace. During a short shutdown, the billet temperature in the furnace is ≥1050℃, the combustion power is reduced by 30%~40%, and the temperature drop is ≤50℃. During the shutdown, the billet temperature in the furnace is 950℃~1050℃, the combustion power is reduced by 50%~60%, and the temperature drop is 50℃~150℃. During long shutdowns, the billet temperature in the furnace is 800℃~950℃, the combustion power is reduced by 70%~80%, and the temperature drop is 150℃~300℃. Intermittent combustion is used during long shutdowns. Step 3: When the rolling line resumes operation, implement precise temperature control based on the downtime and the current furnace temperature; During short stops, heat up at a rate of 5~8℃ / min, and control the heating time to 10~15min, until the rolling temperature is reached; During the interruption, the temperature is increased at a rate of 8~12℃ / min, and restored to the initial rolling temperature within 20~30 minutes; During long shutdowns, the temperature is increased at a rate of 12~15℃ / min and restored to the initial rolling temperature within 40~60 minutes. Step 4: During the resumption of operation of the rolling mill, monitor the furnace temperature and oxidation loss in real time, and dynamically adjust the heating rate and combustion load to ensure control accuracy of ±5℃.

2. The combustion control method for a regenerative heating furnace based on the downtime of a rolling mill as described in claim 1, characterized in that, In step two, the residual oxygen content in the furnace during the short shutdown is ≤6%.

3. The combustion control method for a regenerative heating furnace based on the downtime of a rolling mill, as described in claim 1 or 2, is characterized in that... In step two, the air-fuel ratio during the intermittent shutdown is 0.8 to 0.

9.

4. The combustion control method for a regenerative heating furnace based on the downtime of a rolling mill as described in claim 3, characterized in that, In step two, the intermittent combustion involves short-term heating for 1-2 minutes every 30 minutes to maintain the furnace temperature at or above the critical reheating temperature of the steel billet.

5. The combustion control method for a regenerative heating furnace based on the downtime of a rolling mill, as described in claim 1 or 4, is characterized in that... In step three, the intermediate stop adopts segmented heating, which involves first heating to 1050℃ and then heating to the rolling start temperature.

6. The combustion control method for a regenerative heating furnace based on the downtime of a rolling mill as described in claim 5, characterized in that, In step three, the long stop is achieved by heating to the rolling temperature using two methods: heating in a high-temperature section and heating in a low-temperature section with a gradient.

7. The combustion control method for a regenerative heating furnace based on the downtime of a rolling mill as described in claim 6, characterized in that, The short stop duration T < 30 min; the medium stop duration 30 min ≤ T ≤ 120 min; the long stop duration T > 120 min.

8. The combustion control method for a regenerative heating furnace based on the downtime of a rolling mill as described in claim 7, characterized in that, The rolling temperature is 1100℃~1250℃.