In ironmaking production, maintaining the stability of blast furnace operations is crucial. Key parameters influencing this stability include furnace temperature, ore batch weight, slag alkalinity, charge ratio, wind pressure and temperature, and top pressure.
Furnace temperature
Maintaining stable furnace temperature helps keep the drop zone height proper, stabilize the differential pressure of the feed column, enhance the slag’s desulfurization capacity, and improve slag mobility. It is beneficial to maintain a slightly higher material column and the center temperature of the furnace hearth, aiding in the elimination of dead zones within the material column.
Ore batch
With good fuel conditions, selecting an appropriate ore batch weight and adjusting it according to furnace conditions and airflow distribution is crucial. This helps maintain a balanced airflow distribution, higher gas utilization, smelting intensity, and blast furnace efficiency. The ore batch size significantly affects the differential pressure of the material column. The optimal batch size should ensure 7 to 9 material batches per hour, tailored to the smelting characteristics and pig iron varieties.
Slag alkalinity
Stable slag alkalinity is essential for several reasons:
- Soft Melt Zone Stability: It stabilizes the soft melt zone of the material column, ensuring consistent permeability and a stable rate of charge descent.
- Slag Fluidity and Viscosity: Stable alkalinity helps maintain the fluidity and viscosity of the slag. The slag adheres to the furnace wall to form a protective slag skin, which prolongs the life of the furnace lining.
- Desulfurization Capacity: It stabilizes the slag’s desulfurization capacity, preventing high sulfur content in pig iron and avoiding the emergence of excess iron.
- Pig Iron Quality: Consistent slag alkalinity helps adjust the composition of pig iron, improving its overall quality.
Proportioning
Proportioning involves not only balancing acidic and alkaline ores but also the proportion of flux, scrap, and coke. A stable ratio is essential for determining the quantities of various materials in the blast furnace, selecting production technology indices and process parameters, and analyzing the smelting process and energy use comprehensively and quantitatively.
Furnace load
Large blast furnaces, with their significant heat capacity due to a larger hearth cross-sectional area, have higher thermal inertia. Adjusting the comprehensive load requires precise calculations. Under fixed full air temperature and volume, adjusting the hourly coal injection according to material speed and furnace temperature changes stabilizes the comprehensive load, thus maintaining furnace temperature.
Fine-tuning coal injection based on material speed ensures the integrated load (fuel ratio) remains within a reasonable range, ensuring stable furnace temperature, gas generation, airflow distribution, and furnace conditions.
Wind pressure & temperature
Blast furnace operation should maintain a stable air supply with full air volume to promote a reasonable furnace type and uniform gas flow distribution. The effects of increased wind temperature include:
- Reduced Gas Production per Unit of Pig Iron: This lowers the furnace top gas temperature and reduces heat loss, leading to a decreased coke ratio.
- Downward Shift of the High-Temperature Zone: This expands the indirect reduction zone, reducing the degree of direct reduction.
- Improved Coal Injection Efficiency: Higher wind temperature provides the necessary thermal compensation for coal injection, enhancing the injection and blowing effect.
- Influence on Pressure Difference, Fuel Consumption, and Gas Amount: Wind temperature affects the pressure difference, iron fuel consumption, and the overall gas amount produced.
Top pressure
High-pressure operation enhances the material column’s permeability, reduces gas flow rate in the furnace, increases output, and reduces coke ratio, contributing to furnace condition stability. It decreases pressure difference, reducing charge falling resistance. Maintaining unchanged differential pressure allows for increased wind volume, improving smelting intensity.
Pressure difference
Pressure difference, the difference between wind pressure and furnace top pressure, reflects changes in blast furnace air permeability. Under fixed top pressure operation, the pressure difference can more accurately judge changes in the air permeability of the material column, especially during recovery from collapse, suspension, or other furnace conditions. Stabilizing the pressure difference ensures stable furnace operations. In a high coal ratio state, the coke load significantly increases, reducing the material column skeleton and coke layer thickness, and prolonging the retention time of coke in the furnace, leading to an increased pressure difference. With general coke quality, it is crucial to stabilize the pressure difference to prevent burden suspension.
