In-situ quantification of alkali metals from biomass combustion by optical emission spectroscopy

Abstract

In this study, an in-situ method was developed to quantify the alkali metal emissions and its speciation from the combustion of biomass in a 150 kWth furnace. An optical emission spectrometer was used to detect the spontaneous atomic emissions of the potassium and sodium in the flame. A calibration is performed to obtain the radiation intensities of potassium and sodium, which are precursive values needed to quantify each alkali metals’ relative ground state number densities. The results show that the spontaneous emissions of the alkali metals appear as doublet lines in the spectra. The calibrated radiation intensities for sodium were converted to relative values via Lorentzian fitting. The relative excited state number densities for sodium and potassium were within the range of 0.536 to 0.791 cm−3 and 23.468 and 30.320 cm−3 respectively. This shows that potassium vapours and its compounds were higher compared to sodium. These number densities will be compared to the sodium and content in the ash for further discussion and validation.