Combined production is a production process in which the relative amounts of co-products can be varied independently. This distinguishes it from joint production, where the proportions of product outputs are technically or physically fixed by the nature of the production process itself.
In combined production, the producer can adjust the output ratios between different products according to market demand, technical preferences, or economic conditions. This flexibility means that the production volumes of individual co-products can respond independently to changes in their respective demands. For example, a refinery might adjust its operations to produce more diesel and less petrol, or vice versa, depending on market conditions, even though both products come from the same crude oil input.
This distinction matters for Life Cycle Assessment because it influences how the system should be modelled. According to ISO 14040 clause 3.10, co-products are "any of two or more products coming from the same unit process or product system". When dealing with combined production, the ability to vary output proportions independently suggests that changes in demand for one product may not necessarily affect the production of the other co-products in fixed ratios.
Knowing whether a production process involves combined or joint production helps practitioners make more accurate modelling choices regarding co-product allocation and system expansion approaches.
As Chief Operating Officer, Iris leads our organisational development and oversees day-to-day operations. Before joining 2-0, she worked in the biotechnology sector. As an LCA consultant, Iris has devoted her expertise primarily to the domains of sustainable agriculture and food production. She is dedicated to teaching LCA and is responsible for our educational efforts. Iris holds an M.Sc. in Biology – Biotechnology from the University of Copenhagen.
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Glossary terms are clearer once you have seen them applied. Our guide to what LCA is and how it works walks through the complete methodology: goal and scope, inventory modelling, impact assessment, and interpretation.
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