Thermodynamic analysis on molten slag waste heat cascade recovery method (MS-WHCR)

thermal energy recovery of pyrometallurgy slags is a worldwide problem that is widely concerned for decades. as chemical recovery method, molten slag cascade recovery method (ms-whcr) is proposed in this work. as typical endothermic chemical reactions, pyrolysis, gasification, calcination and reforming reactions are applied in this method. gasification–pyrolysis system, calcination–pyrolysis system, enhanced pyrolysis system (r-sep) and fixed carbon gasification and sorption-enhanced pyrolysis system (cg–sep) systems of ms-whcr method are designed. based on the first law of thermodynamics and second law of thermodynamics, enthalpy–exergy compass analysis method is applied to analyze the exergy efficiency, consumption of reactants and products of designed ms-whcr method, compared with traditional water quenched (wq) method and gravity bed waste heat recovery (gwhr) method. as calculation example, 1000kg copper slag is used in this paper. the results showed that the exergy efficiency and exergy loss of wq method are 20.7% and −947 mj respectively. by wq method, energy quality of molten copper slag is discounted. copper slag particles should be fast cooled during granulation process. thus, lots of air is blown in to make enough heat transfer with copper slag particles, which generate some exergy loss. and exergy efficiency of gwhr method is 76.9%. using chemical endothermic reactions, ms-whcr method improves the exergy efficiency of molten slag waste heat recovery. there is a slight fluctuation of exergy efficiency by ms-whcr method for four kinds of systems from 66.6 to 70.1%. fixed carbon and combustible syngas are acquired by ms-whcr. and enhanced pyrolysis process in proposed r-sep and cg–sep systems improves hydrogen contents in syngas.