Development of a simple and rapid test method for potassium (RAPPOD) to ensure fuel quality of woody biomass fuels

Elevated contents of potassium in low quality residues from forestry and agriculture are recognized as main reason for high particulate matter emissions and an increased slagging risk in the bottom ash during utilization of these assortments. Determination of potassium content with reliable rapid and simple test methods could contribute to an appropriate selection and optimum use of biomass for combustion, gasification, and pyrolysis. A cheap soil analysis test kit with investment costs below 1000 € was used to determine potassium contents in different wood assortments. Sample preparation (e.g. particle size) as well as the analysis procedure (e.g. dilution rates, solution agents, and analysis time) were adapted to the requirements for the analysis of the biomass matrix. Activated carbon had to be added to the reagent to improve the precision of the analysis method. The rapid test method is most suitable for potassium contents between 500 and 2000 mg·kg−¹ d.b. Potassium contents higher than 2000 mg·kg−¹ d.b. can be well detected though with a higher variance. Reliable results were achieved within 10 min analysis time and low cost of about 5 € per sample (consumables). Measurement accuracy was evaluated using ICP-OES analysis of the fuels after digestion with hydrofluoric acid and reveals an overall underestimation of the potassium content though on a comparable level over the whole analysis range.