ecoinvent Forum Archive

Hi

I am moddeling a product with a main content of wood. When using the CML-method my end result comes out negative, due to the large uptake of Co2 in the production phase. I isolated the issue to the balance of carbon uptake/release for wood in the system. 

For production I use the EcoInvent 3.2 dataset "Sawnwood, lath, softwood, dried (u=10%), planed - CH

For disposal the wood is incinerated, and I use the dataset "treatment of waste wood, untreated, municipal incineration with fly ash extraction - CH"

Using the CML method I get resulting impacts on climate change of 1m3 wood:

Production: -1298kgCO2eq

Incinerarion: 650kgCO2eq

Why is this not in balance, so the carbon uptake in production phase is again released when the wood is incinerated so the system is neutral (or more likely positive due to additional processing and transport). Am I missing something cruicial or is there a more appropiate dataset for the disposal phase I should use? 

Kind regards

Kathrine

Dear Kathrine, 

The imbalance you observe is due to economic allocation.  Wood-related activities often have many by-products, and the impact is allocated according to the price of each products and by-products.  This creates a distortion of the mass balance in the allocated datasets, and this in turn causes imbalance when you look at the whole system.  To be more specific: the mass of the sawnwood, divided by the mass of the sawnwood and the mass of all other byproducts, this ratio is lower than the ratio of the revenu of the sawnwood divided by the revenue of the sawnwood and the revenu of all other byproducts.  This means that the sawnwood gets allocated a larger portion of the grown wood.  Indirectly, this attributes a larger uptake of CO2 than it really contains.  So when it is incinerated, it emits less CO2 than what has been absorbed at the other end of the life cycle.  

Version 2 of ecoinvent contained "allocation correction" to circumvent this problem.  This feature has not been implemented yet on version 3.  

The problem you describe is not specific to CML, and also occurs for metals, when they are mined through operations that extract more than one metal.  This will also be taked care of in the allocation correction algorithm that is under planning.  Datasets will be carefully documented, and correction exchanges will have comment, and some separate document will be published on our website for the users to be able to understand how the calculation occurs.  

I hope this answers your question.  

Kind regards, 

Guillaume Bourgault, Project Manager, ecoinvent

Dear Guillaume Bourgault,

Thank you for your elaboration on the issue, this made it a lot clearer for me.

Since the allocation correction is not incooperated yet, is there any way I can manually circumvent this problem in my system so I can opbtain the balance?

Kind regards

Kathrine

Dear Guillaume Bourgault,

do you know if the allocation correction is implemented yet (ecoinvent verrsion 3.6) ? At least when looking at carbon uptake in the "sawing, softwood" dataset it seems to me its not and I could not find a report that declares its implementation.

Or maybe it needs to be activated ? I am using openLCA and could not find such an option yet.

Greetings, Christian