Aluminum Industry Based On Life Cycle Assessment Of Environmental Load

Life cycle assessment is a powerful tool in the evaluation of the environmental impact of manufacturing processes and environmental management. However, there hasn't been a methodology that can be widely accepted. On the basis of the life cycle approach in combination with aluminum processes, the purpose of the study and the system boundaries are defined, resource consumptions and environmental conditions in the aluminum industry have been discussed in detail. As a large amount of natural resources and energy are consumed in aluminum production stand out. It is also pointed out that it is necessary to reduce the quantity of waste generation and emission by improving the raw material and energy structure, and reinforcing the waste control and management. Furthermore, the total emissions of waste gas, wastewater and waste solid are forecast during the next decade.Based on the characteristics of the aluminum processes in China, Integrated relative environmental index (IREI) is defined and a new accumulative comparative model for life cycle assessment is established. In addition, the concepts of dynamic correlated weighting and statistical correlated weighting are defined. The shared principle on multi-products environmental load has been explanted.With the economic benefits as optimal goal and environmental impact as constraints, optimal programming for structure of aluminum products is performed. Based on combining the environmental impact assessment with integrated economic benefits, it helps to apply the results of environmental impact assessment to the practical use.According to the characteristic of process industry, the mathematical model for calculating the product's environmental load of process industry was developed. Based on the data of Zhen Zhou alumina plant in 2004, the environmental load of alumina manufacturing process with Bayer, sinter and Bayer-sinter combination method were calculated and compared. The result shows that the environmental load of Bayer method with indirectly heated digestion is the lowest, the environmental load of sinter method is the highest and that of Bayer-sinter combination method is within these two methods. The per-ton-alumina environmental discharges of each unit process with different method were calculated. The main unit processes and reasons which lead to environmental load were analyzed in detail, and the definite measures to decrease each environmental discharge were put forward.It is shown from above part that in order to decrease the environmental load of aluminum, the following measures should be taken: (1) optimize the structure of alumina manufacturing process. For Bayer method, direct heated caldron digestion should be replaced by indirect heated digestion; For sinter method, direct heated desilication should be replace by indirect heated desilication; For Bayer-sinter combination method, the proportion of Bayer method and purified sinter liquor for carbonate precipitation should be increased, the proportion of sinter method should be decreased. (2) adjust the structure of raw material and fuel. The alumina to silica ratio of bauxite should be increased to 11-20 by efficient ore dressing technology and some high grade gibbsite should be imported from other countries. The cleaner fuel should be used in some enterprises. (3) promote the progress of technology. The advanced process, equipment as well as waste utilization technology should be used. (4)for aluminum electrolysis catering, should develop new technology, reduces the energy consumption, enhances each technical index.