Effect of material flows on energy intensity in process industries
Introduction
Many process industries, such as alumina refining and steelmaking, are energy-intensive and have material flows, which have a strong effect on overall energy intensity of the final product (OEIF) [1], [2], [3]. This problem, however, has only been recognised qualitatively due to the lack of a comparative data and quantitative analysis. Recent efforts have mainly focused on developing calibrated models of energy and material consumption patterns in manufacturing processes [4] and applying them to the paper industry [5], [6], [7] and the steel industry [8]. The standard material flow diagram (SMFD) was specifically developed in the steel industry to quantitatively analyse the relationship between material flows and energy intensity of the final product [9], [10], [11], [12]. As in the steel industry, there are many process industries such as alumina refining where raw materials are transformed into a final product through a series of unit processes. The output product of one upstream unit process is the input material of the next downstream unit process, except obviously the last unit process, which produce the final product.
The focus of this paper is to extend the application of the SMFD in the steel industry to other process industries and present an in-depth quantitative analysis of the effect of material flows on the OEIF. The procedure developed to perform a quantitative analysis is presented in Section 2. Initially, a SMFD for any process industry was developed based on that used in the steel industry. Then, the material flows that deviate from the SMFD were quantified for the practical material flow diagram (PMFD), and their effects on product ratio and unit process energy intensity (UPEI) as well as OEIF were analysed. In Section 3, the effect of material flows on the overall energy intensity of alumina (OEIA) in the Chinese Zhenzhou alumina refinery plant was analysed as a case study.
Section snippets
SMFD of a process industry
As in the case of the SMFD of the steel industry [9], the SMFD of a process industry is a “closed one-way express highway”, that is:
- (1)
the only flow direction of raw materials which contain an element of final product is from each unit process to its next downstream unit process, and finally to the exit of the manufacturing process;
- (2)
there is no intermediate input, output or recycle of raw materials during the manufacturing process.
The SMFD developed for a typical process industry is based on 1 t of
Material flows diagram
Based on 1999 data of the Chinese Zhenzhou alumina refinery plant which uses the Bayer process [14], [15], a PMFD was constructed (Fig. 6). It consists of six unit processes, namely slurry preparation for high-pressure caldron digestion (SC), high-pressure caldron digestion (CD), slurry preparation for tube digestion (ST), tube digestion (TD), seed precipitation (PC), and aluminium trihydrate calcining (TC). The supplied fraction of high-pressure caldron digestion is 85.6% and the supplied
Conclusions
A detailed SMFD to analyse the effect on the energy intensity of material flows in process industries has been presented based on the concept of SMFD, which is used specifically in the steelmaking industry. Possible material flows which occur in a practical process industry were analysed by comparison with the SMFD. The effect of each material flow deviating from the SMFD on the OEIF was also quantitatively determined. The results show that the input of final product-containing materials from
Acknowledgements
The authors would like to thank the Chinese Scholarship Council for financial support. Guangdong University of Technology in China provided a PhD scholarship to Liru Liu, which is also appreciated. The authors would like to thank Dr Bob Fuller, International Technologies Centre (IDTC), The University of Melbourne for comments and editing the final manuscript. The secretarial support from the IDTC is also acknowledged.
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