The compressive strength of the raw ball is generally only 1 to 2 kilograms per ball (9.80665 to 19.6133 cows per ball). After drying, the strength of the ball is improved, up to 8 to 10 kilograms per ball (78.4532~ 98.0665 cows / ball), but still can not meet the requirements of transportation and blast furnace smelting. Although there are many ways to increase the strength of pellets, more than 95% of the pellets are still consolidated by roasting.
The roasting consolidation of pellets is the most complex process in the production process, and many physical and chemical reactions are completed at this stage. And for the metallurgical properties of the pellets, such as strength, degree of porosity, and the like have a significant impact on reducing.
The equipment for roasting pellets includes three types: shaft furnace, belt type roaster and chain grate-rotary kiln. Regardless of which equipment is used, the roasting pellets should include five processes of drying, preheating, roasting, soaking and cooling. See the following figure for different raw materials, different roasting equipment, temperature level and duration of each process. And the atmosphere is different.
The temperature of the drying process is generally 200 to 400 ° C. The main reaction carried out here is to evaporate the water in the green ball, and part of the crystal water in the material can also be excluded.
The temperature level of the preheating process is 900 to 1000 °C. A small amount of water that has not been removed during the drying process is excluded here. The main reaction is the oxidation of magnet hematite ore, decomposition of carbonate minerals, sulfide oxidation and decomposition, and certain solid-phase reaction.
The temperature level of the calcined zone is generally from 1200 to 1300 °C. Unfinished reactions in the pre-tropical zone, such as decomposition, oxidation, sulfur removal, and solid phase reactions, are also carried out here. The main reactions here are the crystallization and recrystallization of iron oxides, grain growth, solid phase reaction and melting of low melting point compounds or eutectic produced therefrom, forming part of the liquid phase, volume shrinkage of the pellets and densification of the structure. .
The temperature level in the soaking stage should be slightly lower than the calcination temperature. At this stage, the main purpose is to make the crystal inside the pellets grow up, make it as complete as possible, homogenize the mineral composition, and eliminate some internal stress.
During the cooling phase, the pellet temperature should be cooled from above 1000 °C to the temperature that the conveyor belt can withstand. The cooling medium is air, and its oxygen potential is high. If there is still unoxidized magnetite inside the pellet, it can be fully oxidized here.
Plasma Products,Anti-Hbs,Safe Plasma,Safe Plasma Storage
Sichuan Yuanda Shuyang Pharmaceutical Co., Ltd. , https://www.syimmunoglobulin.com