Abstract: The heat recovery efficiency of different BF slag waste heat recovery systems were analyzed by using enthalpyexergy diagram. Enthalpy and exergy efficiency were calculated and compared by physical recovery method to produce hot water or steam and chemical recovery method by endothermic reactions of decomposition of limestone， coal gasification， methane reforming. The results showed that the heat efficiency of applying the waste heat of BF slag to produce hot water is 769%， equal to that of producing steam. While the enthalpy efficiency of the two is different， the former is 144%， and the later is 342%. The heat efficiency of chemical reaction with BF slag is as high as 922%， while the enthalpy efficiency is 627%. Both are higher than those of physical heat recovery method. Applying the coal gasification to recover the waste heat of BF slag can absorb 165 kg per tone of slag， which attribute to realize the goal of energy conservation and slow down the greenhouse effect.

Key words: BF slag waste heat, enthalpyexergy diagram, thermodynamic analysis, endothermic chemical reaction, recovery system