Cumulative exergy demand analysis of the primary aluminum produced in China and its natural resource-saving potential in transportation

The purposes of this study are to quantify the natural resource consumption of primary aluminum production in China and to determine the resource-saving potential of aluminum in the transportation sector relative to steel.

In this study, exergy, which expresses both the quantity and the quality of a resource, was adopted for natural resource accounting. The cumulative exergy demand (CExD) of primary aluminum was calculated by the process analysis method, which begins in the final link of the fabrication of the considered product and runs through the production of semifinished products. This method can provide detailed information about each process.

The CExD value of 1 t of primary aluminum produced in China is 246,778 MJ_ex, and the largest contributor to the CExD is electricity, which is mainly consumed in the electrolytic process. Compared with the CExD derived from the national average resource consumption data of alumina production (three techniques), if alumina was only produced by the Bayer process, the CExD of primary aluminum would decrease by 10 %. Taking wheel hubs as a case study, although aluminum wheel hubs have a lower natural resource consumption rate during the use phase relative to steel wheel hubs, no natural resource savings are obtained before a certain driving distance (breakeven distance) is reached because of higher resource consumption in the production phase. The total amount of natural resources that aluminum wheel hubs could save (relative to steel wheel hubs) over its lifetime driving distance is 3,652 MJ_ex. In contrast, the breakeven distance derived from the CML model is approximately 80 % lower than that derived from the CExD model.

A determination of the advantages of the Bayer process in terms of resource saving suggests that importing high-grade bauxite from abroad to promote the application of the Bayer process is an effective way to reduce primary aluminum’s CExD, i.e., resource intensity, in China. A comparison of the characterization results between the CML model (China’s own factors) and the CExD model shows that the CExD model assigns more weight to coal than to minerals, whereas the CML model assigns more weight to minerals.