Thermodynamics analysis of carbothermal-chlorination reduction in aluminum production

Highlights: • Studying in thermodynamics the vacuum carbothermal-chlorination reduction for Al production. • Studying the reaction efficiency and exergy efficiency with the temperature. • The optimal reaction temperature region was obtained for carbothermal-chlorination reduction. • Heat recovery was key to improve the energy consumption and exergy efficiency. • Carbothermal-chlorination reduction performs better than electricity aluminum. - Abstract: Carbo-thermal reduction aluminum is regarded as the future aluminum production method for its low energy consumption. A thermodynamics analysis is performed, taking the Al–C two-step model as the objective. High temperature is beneficial to the reaction efficiency, but harmful to the exergy efficiency of the first reaction (Al₂O₃ + 3C + AlCl₃ = 3AlCl + 3CO, R1). The second reaction (3AlCl = AlCl₃ + 2Al, R2) presents an opposite pattern. An optimal reaction temperature window exists for the AlCl mediated carbon reduction method. The temperature of R1 is above 1520 K and that of R2 is 398–798 K in the optimal window. Heat recovery is significantly important in enhancing both exergy efficiency and energy consumption in actual processes. Energy consumption is reduced from 11,335 kW h/t(Al) to 8063 kW h/t(Al) when an ideal heat recovery is performed. Compared with electrolytic aluminum, carbothermol-chlorination reduction presents a significantly better performance in some condition. Energy consumption is 10,151 and 13,200 kW h/t(Al) in carbothermol-chlorination reduction and electrolytic aluminum, respectively. Moreover, 67% of the exergy efficiency of the carbothermol-chlorination reduction is greater by 1.7 times than that of the electrolytic aluminum.