(PW056) Consistent Modeling of Wood and Wood Processing Based on Multi-Output Unit Processes.
Althaus, H1, Werner, F2, 1 Technology & Society Laboratory, EMPA, Duebendorf, Switzerland2 Environment & Development, Zurich, Switzerland
ABSTRACT- The consistent modeling of wood in LCA poses many specific difficulties because of its biogenic nature and of its two-fold usage as material and fuel. First of all, important wood properties such as density or heating value of wood vary in wide ranges in dependency of its water content. Thus the functional unit has to be chosen carefully and the product has to be described correctly, stating also its water content. Second, the processing of wood commonly generates large quantities of co-products such as sidings, bark, sawdust, etc. with different potential uses and economic values. Thus, many production steps in the wood chain have to be modeled as multi-output processes, which have to be dealt with consistently as co-product allocation. Third, the co-products of some of these multi-output processes are to be regarded as waste from an economic point of view. Since this waste-wood might be used as fuel in other processes, it is important that the carbon and energy content are modeled correctly to comply with the mass and energy balance, which means a modeling independent of the co-product allocation procedure chosen for this unit-process. The definition of special unit processes can be necessary to correct the inappropriate allocation of these flows within the whole system. In this presentation a consistent modeling of the wood chain based on multi-output unit processes is presented and selected results are compared to a model applying cut off for products of no economic value.
Key words: biomass, wood, co-production, Allocation