Thermal Analysis and Exergy Analysis of Evaporation Process in Alumina Refinery

To reduce the energy consumption of evaporation process in alumina refinery, thermal and exergy analysis were applied to the four-effect evaporators and three-stage flashes evaporation system. Result indicates that the thermal efficiency of the evaporation system is only 15.22%. The thermal efficiencies of all links are high except that of the evaporator of effect IV, which is only 6.91%. The heat losses in the evaporators of effect IV, III and I are large, which are mainly in the form of condensed water and exhausted vapor output. The exergy efficiency of the evaporation system is only 19.33%and those of the four-effect evaporators are relative low. The exergy destruction ratios of the evaporators of effect IV, III and I are 37.42%, 34.64% and 19.41%, respectively, which are the key links for the improvement of the exergy efficiency of the evaporation system. The total intrinsic exergy destruction is slightly larger than the total extrinsic one. Thus recovery and utilization of waste heat and of condensed water and exhausted vapor should be enhanced, the operating parameters in evaporators and the way of using preheaters should be optimized or improved.