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Published online by Cambridge University Press: 26 July 2016
Much recent effort has been focused on the development of monitoring methods to calculate the percentage of biomass in the fuel used for energy generation in power plants. One possible method is based on measurements of radiocarbon concentration in combustion gases by liquid scintillation (LS) spectrometry. Fossil fuels contain no 14C due to their age. Therefore, after the combustion of such fuels, the resulting CO2 contains no 14C as well. The only source of 14C comes from the admixture of biomass containing modern carbon. 14C is a beta-emitting radionuclide with a maximum beta energy of 156 keV. There is no emission of gamma rays during decay; therefore, no possibility of gamma spectrometry exists. A difficult task thus is to validate the method and to calibrate it in agreement with the known amount of biomass in the fuel. For this purpose, a set of samples was prepared that were mixtures of hard coal and biomass with a known percentage of carbon. The oxycombustion method was applied for sample preparation in which the combustion of the fuel is done in pure oxygen; therefore, the combustion gas contains mostly CO2 and steam. The CO2 from the gas sample is then adsorbed by 3-methoxypropylamine. A known amount of this absorbent was mixed with a scintillation cocktail and measured in the LS spectrometer. In this way, a calibration curve has been obtained, allowing quantitative measurements of biomass content in the fuel.