Estimation of the Emissions of CO 2 , SO x , and NO x of Steel Alloys
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Estimation of the emissions of CO2 , SOx , and NOx of steel alloys K. Halada, K. Ijima, and K. Yagi National Research Institute of Metals, 2-1, Sengen 1-chrome, Tsukuba, Ibaraki 305, Japan (Received 18 February 1997; accepted 4 January 1998)
The emissions of CO2 , SOx , and NOx of various steel alloys in the production stage were calculated by using the unit requirement of each subsystem of the steel-making process, in order to compare the superiority from the viewpoint of the environmental issue among various types of steel alloys. As steel production is a typical integrated system with multiproducts, allocation of emissions to each product, effect of the composition, and sharing the load by the by-product gases are considered. Calculated values of emission were arranged for fifteen kinds of finished steel products and for arbitrary contents of alloying elements.
I. INTRODUCTION
The quantitative analysis of an environmental load of metal and their data is very important for the sustainable development. In a previous paper,1 the emissions of CO2 , SOx , and NOx of nonferrous metallurgical processes are estimated. As alloying processes of nonferrous metals are mainly separated from the extractive process of metals, the procedure of bottom-up and summation is sufficient to calculate the final value of the environmental load of alloyed and worked nonferrous products. On the other hand, steel-making has various products with different compositions and with different shapes and finishings in the same factory. Furthermore, exhausted gases are used as a cascade to utilize the energy and elements thoroughly. This makes the allocation of environmental load to each product much more difficult. When the emission data are used in LCA (environmental life cycle assessment) of a product, the problem mentioned above becomes serious, because the environmental load data are required to reflect the selection and the history of the production system. Furthermore, from the viewpoint of a metallurgist, the data of environmental load are expected to be suitable parameters that give some guidelines to the material design or the process design that is mindful of the global environment. Figure 1 shows a typical example to indicate the direction of composition change into more suitable composition to the global environment.2 Figure 1 shows that the addition of Mn strengthens with less increase of the CO2 emission than Ni, Cr, or a higher temperature sintering process. This example was calculated because the subjected process was a powder metallurgical process in which the composition was adjusted by mixing each elemental powder additively. If we intend to apply the same method to steel alloy, we have to find the method to identify the history of processing and the difference of compositions. On that occasion, it is important that the data should be estimated 2514
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J. Mater. Res., Vol. 13, No. 9, Sep 1998
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