Improving the quality of pellets for metallization by controlling the size of the bottom and side bed

It was noted that the improvement of the gas dynamic processes occurring in the layer of pellets is a significant reserve for the improvement of the processes of thermal strengthening of the pellets and the latest works devoted to this direction were analyzed. The experience of foreign enterprises has confirmed that the use of pellets of a slightly larger size for the formation of the bottom and side beds improves the metallurgical characteristics of the finished products. An improvement of the overall gas-dynamic picture of the process due to the optimization of the bed size was noted. The closest technological solution to the separation of the bottom and side beds was analyzed, in which the fired pellets, the average diameter of which exceeds the average diameter of the raw pellets by 1.08-1.75 times, are isolated. The found drawback of this technology is that when using this method at a minimum factor of 1.08, the average bed pellet size will be 12.96 mm. Thus, about 57% (from their maximum size of 15 mm) of fired pellets of the bottom and side bed, which have undergone repeated high-temperature heating and have a decrystallized iron-silicate bond of ore grains, will be included in the finished products. The technology was developed, the essence of which is that only pellets with a diameter of 1-3 mm larger than the maximum diameter of the suitable fraction of fired pellets are used as bottom and side bedding. Laboratory studies have been carried out to develop the proposed technology. From the prepared charge, raw pellets were made with a grain size that ensured the production of fired pellets of fraction 9-15 mm and the separation of bottom and side bed +15 mm from them. The degree of pellet shrinkage and their final size were taken into account for the conditions of further metallization. Experimental sintering was performed in a firing bowl with a cross-sectional diameter of 300 mm and a layer height of 400 mm. The research results showed that the specific productivity of the firing unit during heat hardening of raw pellets according to the developed technology practically does not differ from that adopted in industry, however, the impact and abrasion resistance when recovering the fired pellets obtained using the proposed technology in a suitable fraction is significantly better than the existing ones. It has been proven that improving the strength characteristics of fired pellets in the process of their recovery in a mine furnace for metallization is quite possible without costly reconstructions and significant capital investmen