D7.3 – Characterisation of biomass samples

This report presents the results of the analyses of five types of biomass selected for further research work in the BeBOP project, namely the recovery of valuable elements (WP7, Enabling technologies at lab-scale for SOEC characterisation and resource recovery, T7.2, Recovery elements from solid gasification residues via leaching, WP8, Technology validation: SOEC and gasification residues recovery - T8.2, Leaching conditions validation and T8.3, Assessment of the recovery of elements via innovative combinations of physio-chemical processes) and the pilot-scale tests of the entire gasification and bio/e-methanol synthesis chain in WP3, TRL6 testing of the integrated Biomass to MeOH system.

The investigated biomass types were:
• Clean, commercial grade wood pellets;
• Post-consumer, demolition wood chips;
• Miscanthus pellets, a blend of Miscanthus x Giganteus and seed-based hybrids, both grown on contaminated, post-industrial marginal land in Southern Poland;
• Hay pellets, commercial grade;
• Switchgrass (Panicum virgatum), grown on post-industrial marginal land in Greece.

The analyses performed on the samples of the abovementioned biomass types involved proximate (moisture content, ash content, volatile matter and fixed carbon) analysis as well as ultimate (elemental) analysis. The latter one included both the main constituents (carbon, hydrogen, sulphur, nitrogen and oxygen) and the inorganic (trace) elements.

Besides the biomass samples, also char samples were analysed for their composition, using the same techniques described above, extended by the XRD (crystalline structures) and BET (surface area) analyses, which were performed to get the information relevant from the leaching and recovery task point of view.
Char samples were obtained by pyrolyzing the raw biomass in a bench-scale, batch pyrolysis/gasification setup, by exposing batches of biomass to an inert atmosphere at the temperature of max. 550°C, until complete devolatilization. Such pyrolysis conditions allowed to preserve the maximum of the inorganic ash constituents in the char, which is relevant for the activities related to the recovery of elements via leaching.
The results obtained from the analyses described above in general were in agreement with the expected parameters of woody and herbaceous biomass, as found in the literature. Due to the high importance of the elemental composition of the inorganic fraction of the char samples, an additional focus was put on this aspect. Here, different results were obtained for the same sample if analysed at a different laboratory, but using the same technique (ICP-OES), and the differences sometimes reach up even to an order of the magnitude. It was concluded that these differences were caused by the different digestion methods applied by different analytical laboratories, as some of them were using microwave-assisted digestion in nitric acid and some digestion in aqua regia. Despite the provided information about the nature of the sample to be analysed, not all laboratories applied the most aggressive digestion method (nitric acid and microwaves), as suggested, e.g., by the US EPA method 3052. It has to be stressed, that the deviations among the samples were not caused by the inhomogeneous nature of the substrate, as the samples analysed in duplo yielded the results which differed significantly less than the analytical results of the same material delivered by different laboratories. Therefore, it is advisable to impose the digestion method to be applied when having the samples analysed by external laboratories.