Energy, exergy, economic, and environmental analysis of RC-DPORC system for waste heat utilization from slag dry centrifugal granulation

Aiming at shortcomings in existing dry centrifugal granulation technology, such as insufficient waste heat cascade utilization and a lack of system coupling research, this study proposes a Rankine cycle-dual pressure organic Rankine cycle (RC-DPORC) coupling system. Through a three-level energy recovery strategy, multi-grade waste heat is collaboratively utilized. A comprehensive evaluation model integrating slag thermophysical properties, energy/exergy analysis, economic cost, and environmental impact is established to analyze the effects of droplet diameter (d), granulation chamber discharge slag temperature (Tslag,out1), and fluidized bed discharge slag temperature (Tslag,out2) on system performance. The non-dominated sorting genetic algorithm II (NSGA-II) and the technique for order preference by similarity to an ideal solution (TOPSIS) are used to obtain optimal solutions for different objective functions, providing diverse feasible schemes for engineering applications. The results indicate that, within the investigated parameter range, smaller d, Tslag,out1, and Tslag,out2 enhance the performance of the RC-DPORC system by improving radiant heat transfer. Under optimal efficiency conditions (ηt = 33.42%, ηr = 96.81%, ηex = 41.54%), the payback period (PBP) ranges from 5.02 to 5.34 years with AER of 2.81–2.92 × 109 kg, the crucial optimization parameters include d = 1.97–2.26 mm and Tslag,out1 = 1073–1082 K. While these results are obtained under modeling conditions and require practical validation, the proposed methodology is extendable to other metallurgical slags for waste heat recovery analysis.