Ring Formation in the Smelting of Saprolite Ni-ore in a Rotary Kiln for Production of Ferro-nickel Alloy: Examination of the Mechanism

The mechanism of SR (Slag-Ring) formation in the actual rotary kiln that proposed in the previous paper has been examined by the firing experiment of the anthracite and limestone composite Ni-ore briquettes using the batch type experimental kiln. The rapid increases in the degree of reduction and CO gas content and the sticking begin to take place at about the same time. The temperature of raw materials apparently begin to decrease from around 1200°C owing to the sticking of raw materials to the tips of alumina (SSA-S) protecting tube with an inserted thermocouple, entering the depression region. Therefore, from above mentioned the mechanism of SR formation is confirmed. A large amount of charge of powdery materials and the increase in the gas velocity at the top of SR causes SR to shrink and fall into the vicious circle, which allows the serious difficulty in the operation of the kiln. The sintering of briquettes provides the suppression of powder generation coming from the fracture of that, which allows no occurrence of sticking. The mechanism of MR (Metal-Ring) formation is extremely involved in the behavior of fine particles as well as SR. A large amount of fine reduced metal with high C content without the growth transports toward the discharge end, allowing that to melt and be precipitated on the wall by Ostwald ripening.