Recovery and utilisation of waste heat for sponge iron process through combined preheating and power generation

This paper deals with an option accounted for total waste gas heat recovered through combined preheating as well as power generation of feed material, kiln air, as well as slinger coal when it reaches 250 °C from 994 °C. The heat recovery is obtained through GCC Profile is plotted using HINT software. The power produced is 2.757 MW with an optimal condition having a temperature of 280 °C saturated, 600 °C superheated, as well as superheated pressure of 350 bar. The heat required around the superheater, boiler and preheater is 5066.9 kW, 12,669.93 kW and 6873.6 kW. The air requirement for this option is 52.588 t/h after iteration. Also, the iterative waste gas flow rate is 22.31 kg/s. Three new heat exchangers are required to achieve possible heat recovery by designing HEN through Pinch Analysis. The water requirement around EC is 14.88 t/h and 7.8 t/h as in the case of actual and modified HEN. The calculated pressure drops of different ducts having lengths 25 m and pressure 0.034 atm, 80 and 105 m are obtained pressure as 0.034, 0.12 and 0.16 atm. 3 FD fans are required for maintenance of required pressures in the duct. The TAC is INR 8068.8/y; payback period is 2.62 y. •Combined approach of preheating and power generation option (Option-3) has been proposed.•Utilisation of waste gas heat for energy conservation using Pinch Technology (PI) Principles.•Total annual cost is found as INR 8086.8 lakh/y; and payback period is 2.62 y.