From trees to electricity, the physics beyond the LCA

Institut Jean Lamour, Labex DAMAS, CNRS, Université de Lorraine, Nancy, France
olivier.mirgaux@univ-lorraine.fr

Received: 21 September 2015
Accepted: 10 February 2016

Abstract

A critical issue in life cycle assessment (LCA) often lies in the accuracy of the data collected during the inventory process. Moreover when processes involved are linked to breakthrough or uncommon technologies, or when the data are deeply connected to local parameters, collection for the inventory relies on many assumptions that cannot be handled properly with standard commercial databases. To avoid this common and well-known drawback of LCA, Institut Jean Lamour has been developing for some years a hybrid LCA methodology based on process modeling. To generate the inventory, all the main processes of the chain are modeled using a process flowsheeting software, which ensures rigorous mass and energy balances. This methodology offers the possibility to assess different configurations of the processes involved. In this paper we illustrate this methodology through a recent study focused on the use of biomass for combined heat and power (CHP) production. We conducted a comparative LCA in which two options were modeled and assessed to produce CHP: a standard combustion process and an alternative innovative gasification process. All the main steps, from forest growth to heat and electricity distribution were considered and modeled. An application to the local context of the city of Nancy in France, in which heat was assumed used for local district heating and electricity delivered to the grid, is presented. Modeling the whole chain of processes made it possible to assess and compare several scenarios including different options of forest harvesting. Globally the study showed that both combustion and gasification of biomass exhibit lower impacts than conventional fossil systems. Influence of harvesting options was found to be weak regarding global results. However, improvement in the characterization of soil depletion due to forest exploitation could be made to refine the results. Eventually, a strong influence of the electricity grid mix was found.