Avoiding co-product allocation in the metals sector
Weidema B P, Norris G A (2004)
Pp. 81-87 in A Dubreuil: “Life Cycle Assessment and Metals: Issues and research directions.” Pensacola: SETAC. (Proceedings of the International Workshop on Life Cycle Assessment and Metals, Montreal, Canada, 2002.04.15-17). Note the error in the two formulas on p. 4: 1*11/14 –> 1*10/14 and 4*11/14 –> 4*1/14.
Co-production (the combined or joint production of two or more products from the same process or system) has been seen as presenting a problem to the system modelling in life cycle assessment, and the traditional solution has been co-product allocation (the partitioning and distribution of the environmental exchanges of the co-producing process or system over its multiple products according to a chosen allocation key) in parallel to cost allocation. Compared to this traditional solution, system expansion according to ISO 14041 provides a more realistic modelling of the actual consequences of product related management decisions. Through a number of examples, including recycling of steel and aluminium, it is demonstrated how co-product allocation can be avoided in practice. The example of platinum-group metals is used to illustrate how system expansion may sometimes be used as a justification for economic allocation.