Energy cost minimization in grate/kiln induration

A mathematical model of the grate/kiln process for the induration of iron ore pellets, verified for an operating plant, has been used to investigate the effects of process variables on fuel and power consumption, and on certain key temperatures and flowrates. The variables investigated include temperatures reached by pellets at the bottom of the preheated bed and in the kiln, feed diameter and temperature, height and void fraction of the grate furnace bed, kiln speed and flame dimensions, recuperation air temperature, and relative air rates for the two stages of cooling. Simulations in which variables were investigated individually provide an improved understanding of the complex interactions within the process, and show how energy consumption might be reduced. From these simulations, cases involving simultaneous changes to a number of variables were developed. One of these has been optimized by stepwise variation of the first stage cooling air rate and the temperature attained by pellets at the bottom of the grate furnace bed. Calculated fuel savings of 8 to 9 pct demonstrate the value of process models for energy minimization.