Energy Consumption Analysis And Energy Saving Research For Alumina Manufacturing Process

The alumina production with mixed combination process of one branch of CHALCO as the research object has been studied by the exergy analysis method and the e-p method in this paper. The conclusions of the exergy analysis and the e-p analysis were compared which shows that the more significance of exergy analysis. The characteristics and advantages of the exergy analysis had been shown on identifing the major energy consuming production process and evaluating the energy saving potential of the production process according to comparison between the conclusions of the exergy analysis and the e-p analysis. The exergy balance was widely used for rational energy use and conservation in production, and become an important foundation of thermoeconomics. The gray box model of exergy analysis of alumina production process of bayer-sinter combination method was established, and the exergy flow diagram of alumina production process was drawn, and the exergy analysis conclusion and the e-p analysis results were compared. At last, the measures can be taken and the potential of alumina production energy-saving were studied and forecasted.Two factors determine energy consumption of alumina in e-p method, one is the product ratio of each unit process, another is the energy intensity of each unit process, so energy-saving is divided into direct and indirect energy-saving. The energy consumptions of several sub processes reduced, however, the related comprehensive energy consumptions increased after taking the product-ratios into account. The alumina production status of one branch CHALCO, from 2007 to the first half of 2008, was analyzed by the e-p method. Compared with the first half of 2007, the overall energy intensity of alumina was increased in the second half of 2007 and the first half of 2008,and evaporation process, clinker burning process, tube digestion process and high pressure digestion process were main increased energy consumption processes. The total of four processes of increased energy consumption amounting to the net increased overall energy intensity 88.87% or 99.58%,and the direct energy-saving is almost equal the indirect energy-saving. A/S lower is the root causes of the increased overall energy intensity.The exergy was consumed in clinker burning process account for the overall exergy intensity 43% or more, and the data of evaporation process was only 11%-12%.The conclusions is great difference with the results of e-p analysis. While the clinker burning process with high exergy consumption, exergy efficiency was very low, but only 7%, and the inevitable exergy loss is mainly about adiabatic combustion, heat transfer and so on. Inevitable energy loss and internal energy losses can not be reflected in e-p analysis or other energy balance analysis. So the exergy analysis as a more scientific method was proved on identifing the major energy consuming production process and evaluating the energy saving potential of the production process compared with the e-p analysis method.Finally, the relation between the overall energy intensity of alumina and A/S was studied, and the overall energy intensity of alumina was predicted by fitting function after improving A/S. The results showed that the overall energy intensity of alumina and the overall exergy intensity of alumina of the first half of 2008 can be decreased respectively 31.58% and 20.80% when A/S was improved to 10.0. This showes that it has great potential of energy saving through improving A/S.