Evaluation and Optimization of an X-ray Fluorescence Analyzer for Rapid Analysis of Chemical Elements in Solid Biofuels

To optimize wood-fired heat (and power) plants, it is essential to rapidly determine the chemical composition of solid biofuels on-site shortly before combustion. However, the standard procedures for chemical analysis [inductively coupled plasma-optical emission spectrometry (ICP-OES), inductively coupled plasma-mass spectrometry] are time-consuming, expensive and require highly trained personnel. Thus, they are unsuitable for online fuel analysis. Newly developed, rapid, on-site analysis methods might enhance analysis at the plant. Thereby, X-ray fluorescence (XRF) analysis is one of the most promising methods. So far, XRF has been evaluated in various fields like geology, coal, ash analysis, as well as biomass in general, but this method is still insufficiently investigated for the sector of solid biofuels. The aim of this work is to evaluate and optimize an XRF analyzer for the rapid determination of chemical elements in wood fuels. The XRF analyzer was calibrated using several wood chip samples. Measurements before and after calibration were compared with the reference method (ICP-OES). Results show that XRF can be recommended for analyzing the elements Mg, P, K, Ca, Si, Al, Cr, Mn, Fe, Zn and Pb, while S, Cl, Ti and Ni can potentially be determined with element-specific calibrations. Cu, As, and Cd could not be measured satisfactorily, as many measurements were below the limit of detection. Still, XRF might be used for threshold value monitoring (e.g., in the scope of the German Waste Wood Ordinance).