Co-product Allocation in Life Cycle Assessment: A Case Study

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Courtesy of Trinity Consultants

As the interest toward industrial sustainable practice grows; companies are increasingly turning to life cycle assessments (LCA) as a metric to measure sustainability impacts by analyzing the environmental and energy burden of their products and services. LCA is a method of measuring these impacts through the raw material procurement, production, usage and disposal stages of a products life cycle.1 LCA for example can be used to measure a products carbon foot print or determine the viability of alternative fuels. The outcome of LCA’s can vary greatly depending on the assumptions made in the assessment; specifically for processes which produce multiple products. Allocation is a method of distributing the production energy consumption and environmental impacts between products and co-products through the determination of a coproduct credit. This credit is utilized in and can have a significant impact on the overall LCA result.

LCA standards call for avoiding allocation when possible by including within the boundary of the assessment production processes for materials that are replaced by co-products.2 A common approach in LCA and net energy analysis, known as the “system expansion' method (also know as the “substitution”, “displacement”, or “replacement” allocation method), credits input energy to co-products associated with the products displaced in the market. This method uses the life cycle energy required to produce the material that is displaced by the co-product, attributing this energy to the co-product in subsequent stages of an energy and environmental analysis.3 The U.S.EPA has stated that the displacement method is the preferred allocation method for life-cycle energy and GHG analyses in its analysis of the Renewable Fuel Standard Program.

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