Methods for the determination of biomass content in solid recovered fuels

Central analytical laboratory - testing laboratory (CAL-TL) in ÚJV Řež a.s. has been performing an accredited determination of biomass carbon content since 2009. The method is based on the determination of ¹⁴C content in CO₂ from combusted solid recovered fuel (SRF) sample using liquid scintillation counter (LSC). The tube furnace consists of the 1st zone where 2 g of sample is placed and the 2nd zone where the CuO catalyst is located, which ensures complete oxidation of the flue gases. The temperature in the area with the catalyst is constant at 800°C, while in the 1st zone the temperature gradually increases up to 1000°C. A mixture of O₂ and N₂ gases flow through the whole system. The O₂ content raises with increasing temperature up to 100 % oxygen atmosphere. The flue gases are then purged in several bubblers and the CO₂ is trapped into ice-cooled amines-based trapping solution. The trapping solution is then weighted into a measuring plastic vial and mixed with scintillation cocktail in ratio 1:1. A coal sample is combusted together with each set of samples, which represents a pure fossil source and therefore zero value of biomass carbon. On the other hand, 100% biomass carbon content is represented by the oxalic acid standard, which is also combusted with each set of samples. The samples prepared in this way are then measured by low background LSC for 24 hours each.