Thermal Strength of Cold-Pressed Pellets

Performance Aspects · Dimensional and Shape Stability: Pellets can maintain their original size and shape under high temperatures without significant expansion, contraction, deformation, or fragmentation due to thermal stress and other factors. For example, in the blast furnace ironmaking process, if pellets have poor thermal stability, they may break into small pieces or powder in the high-temperature zones of the furnace, affecting the permeability of the furnace burden column and the smooth operation of the furnace. · Strength Stability: Pellets can maintain a certain mechanical strength in high-temperature environments without experiencing a sharp decline in strength. Sufficient strength is necessary to withstand the pressure from the upper burden in the blast furnace and the forces from rising gas, preventing pellets from breaking due to collision and compression during transportation, charging, and smelting. · Chemical Stability: The chemical composition of pellets remains stable under high temperatures, without excessive oxidation, reduction, decomposition, or other chemical reactions, to avoid affecting pellet performance and subsequent ironmaking processes. For instance, iron oxides in certain pellets should undergo reduction according to the expected reaction pathway at high temperatures, rather than abnormal reactions that alter pellet properties. Importance · Ensuring Blast Furnace Permeability: Pellets with good thermal stability can remain intact in the blast furnace, maintaining reasonable gaps between the burden materials, allowing gas to pass through the burden column evenly and smoothly. This facilitates good gas-solid mass and heat transfer processes, improving blast furnace production efficiency and gas utilization. · Maintaining Blast Furnace Operational Stability: Stable pellets enable more uniform burden flow and temperature distribution within the blast furnace, reducing fluctuations in furnace conditions caused by pellet breakage and pulverization. This lowers the probability of abnormal situations such as furnace wall erosion and channeling, ensuring stable blast furnace operation and extending its service life. · Improving Ironmaking Quality and Output: Good thermal stability of pellets ensures that reduction and other reactions proceed according to the predetermined mechanisms in the blast furnace, making the iron reduction process smoother and more efficient. This helps improve the quality and output of molten iron while reducing energy consumption and production costs. Influencing Factors · Raw Material Characteristics: The type, particle size distribution, and chemical composition of the ore powder can affect the thermal stability of pellets. For example, impurities and moisture content in the ore powder, if too high, may have adverse effects during heating. · Binder Usage: The type, dosage, and performance of binders are crucial for pellet thermal stability. Suitable binders can form strong bonds between pellet particles, enhancing thermal stability; conversely, improper binder selection or insufficient dosage can lead to issues such as pellet breakage under high temperatures. · Production Processes: These include pelletizing, drying, and roasting processes. For instance, improper control of roasting temperature and time may result in insufficient or excessive roasting, affecting the crystal structure and strength of pellets, thereby reducing thermal stability.