Exergy Evaluation on the Pellets Production and Direct Reduction Processes for the Fired and Nonfired Pellets
Tomohiro Akiyama, Reijiro Takahashi, Jun-ichiro Yagi
In order to make a clear evaluation of overall energy requirement for the production systems of directly reduced iron through pellets from iron ore powders, exergy analysis was applied to the two systems. The first one consists of pelletizing, firing and reduction processes, Fired pellets method, and the second one includes pellets curing process instead of firing process, Nonfired pellets method.
Being compared with enthalpy balance, exergy analysis has two advantages in that the exergy expresses the quality of energy and evaluates different kinds of energy like chemical, thermal, pressure and mixing energy by a unified measure.
As a result of exergy analysis, fired pellets lose less exergy than nonfired pellets in the shaft furnace. As the overall systems, however, exergy requirement in the nonfired pellets method is about 50% of that in the fired pellets method. This marked difference is caused by the large exergy loss in the firing process. Furthermore, exergy loss in the production of nonfired pellets will be decreased by decreasing the amount of cement added as binder.