Improvement of blast furnace pellet quality through an integrated analysis of the production chain and process modelling

By different grinding methods, hematite and magnetite were ground to pelletizing fineness for balling and induration testwork. The specific energy consumption for ball mill and roller press grinding were recorded and the difference in particle size distribution and shape were evaluated. The pellets produced after roller press grinding resulted in improvement of the tumble abrasion and disintegration. The same is not noticed for magnetite due to non-satisfactory oxidation during preheating. In order to understand the mechanisms in pelletizing more fundamentally, new techniqes have been developed, like PaRMAC for sizing of the material. Thermogravimetric (TGA) methods and Raman microprobe have successfully been used to study the dependence of particle size, surface reactivity and mineral phases on pellet quality. The relationship between green pellet properties, induration, cold compression strength (CCS) and metallurgical quality has been established. There are today two mathematical models at LKAB and CORUS, describing the induration process. They have, whithin this project, been improved and validated against plant data and pot furnace tests. An on-line dynamic model for LKABs pellet plants has been developed by CISA. The evaluation shows that it generates useful non-measurable information in real time, including cold compression strength, oxidation rates and temperature profiled thoughout the process.