Dynamic Material Flow Analysis for Stainless Steels in Japan–Reductions Potential of CO2 Emissions by Promoting Closed Loop Recycling of Stainless Steels

Abstract

Stainless steels are corrosion resistant alloys that are widely used in consumer goods and industrial equipment. Stainless steels contain scarce and energy intensive elements such as Ni, Cr, Mo, which means that closed loop recycling is preferable for sustainable stainless steel production. However, some stainless steels are not separated from ordinary steel scraps in the recycling processes and cannot be recycled as “stainless steel”. The objective of this study is to analyze the dynamic substance flow of stainless steels in Japan and assess the potential for reducing CO2 emissions by promoting closed loop recycling of stainless steels in the future. First, the authors analyzed material balance of input elements, i.e. Fe, Ni and Cr, in the production of stainless steels in 2002 to determine which aspects associated with the material flow of stainless steel cannot be elucidated from available statistical data. The amount of post-consumer stainless steel that would enter into society in the future was estimated by employing a Population Balance Model (PBM). It was found that only 2% of post-consumer stainless steel containing Fe–Cr alloys was collected as stainless steel scraps while the remainder was collected as ordinary steel scrap. Conversely, approximately 95% of post-consumer stainless steel consisting of Fe–Ni–Cr alloys was collected as stainless steel scrap. A CO2 emission reduction potential for a 1% increase in the closed loop recycling of stainless steel scraps of Fe–Cr alloys was estimated at 75 000 t/year by Life Cycle Assessment (LCA).