Sample Preparation of Refused Derived Fuels – (ir)relevant for Determining Their Climate Impact?

SUMMARY: The paper presents investigations on the effect of sample preparation on the result of the adapted balance method (aBM). The aBM is deployed to determine the biomass content in defined waste mixtures. " Waste " mixtures are generated out of defined mass fractions of biogenic (paper, cardboard) and fossil (plastics) materials. Different mills are used to comminute the mixtures down to a grain size of < 200 µm. Finally the mixtures are analyzed using a combustion elemental analyzer (CHNSO). The water-and-ash-free composition is derived which serves as input for the aBM. The results of the aBM demonstrate a good agreement between calculated mass fractions (biogenic, fossil) and theoretical data of the defined mixtures (deviation of below 3 %rel). However, a significant effect of the sample preparation on the result is observed comparing samples comminuted with different mills (ultracentrifugal mill, cryogenic mixer mill). Combining both mills reveals smaller variances. We conclude that plastics as well as cellulose fibers are crushed sufficiently when both mills are applied at the final milling step.