Dynamical Properties of Product Life Cycles: Implications to the Design and Operation of Industrial Processes

Life cycle assessment (LCA) offers a systematic approach in identifying the potential in reducing the environmental burden throughout the product life cycle. Generally, it deals with the steady-state aspect of material and/or energy balances under the recycle structure. In this work, the dynamic behavior of the product life cycles is studied. First, the well-known block diagram analysis is incorporated in the LCA, and the implications of recycling to process dynamics are explored. The result indicates that, as a result of the positive feedback from material recycling, the overall production dynamics becomes much slower. This implies a lack of flexibility as more and more recycled materials are utilized in product manufacturing, and this cannot be foreseen without incorporation of dynamics in the life cycles. To meet the market demand, increased inventories for the raw and recycled materials are needed to compensate the slow recycle dynamics and a larger turndown ratio is necessary for the raw material processing plants. The missing inventory, due to slow dynamics, can be expressed analytically in terms of the recycle ratio and the recycle time constant. It can be used for legislating new recycle policies which can alleviate the increased inventory and large turndown ratio problems for the future processing plants. The results indicate that the dynamic analysis provides a better assessment of product life cycles and, moreover, only the recycle ratio and recycle time constant are needed to complete the analysis.