The present work is an attempt to conserve energy in coal based sponge iron industry incorporating
certain design modifications without disturbing the process technology. A typical sponge iron plant has
been investigated to find out the potential areas where energy is being wasted. To recover heat from
these areas two design modifications, Case-1 and Case-2, are proposed. Case-1 accounts for preheating
of air using waste gas exiting from ESP. However, for Case-2 initially water is heated using hot sponge
iron exiting rotary kiln and further hot water is used to preheat air. To compute coal demand of modified
designs a model is developed based on heat of reactions, feed preheating, sensible and radiation losses,
etc. Preheating of air up to 170 ◦C for Case-1 reduces coal consumption by 8.7%. Consequently, waste gas
generation reduces by 16.7%. Thus, for Case-1 profit is Rs 9.6 million/year. However, for Case-2 preheating
of air to 80 ◦C before entering the kiln reduces coal and water consumption by 7.2% and 96.3%. Consequently,
cooling tower capacity is reduced by 37.2%. Due to 27.8% less profit for Case-1 in comparison to
Case-2 Case-1 offers higher payback period than that of Case-2. Thus, Case-2 is selected as best proposed
design.