Layer formation mechanism of K-feldspar in bubbling fluidized bed combustion of phosphorus-lean and phosphorus-rich residual biomass

• Published in: Applied energy Vol. 248; pp. 545 - 554
• Main Authors: Wagner, Katharina, Häggström, Gustav, Skoglund, Nils, Priscak, Juraj, Kuba, Matthias, Öhman, Marcus, Hofbauer, Hermann
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.08.2019
• Subjects: Agglomeration; Energiteknik; Energy Engineering; Fluidized bed; K-feldspar; Layer formation; Phosphorus; Phosphorus; Agglomeration; Layer formation; K-feldspar; Fluidized bed
• ISSN: 0306-2619; 1872-9118; 1872-9118
• DOI: 10.1016/j.apenergy.2019.04.112

•Phosphorus-rich fuels shift the ash chemistry to the formation of phosphates.•The admixture of chicken manure to straw increases the time until defluidization.•The fuel ash content is not a fitting parameter to predict bed defluidization.•K-feldspar is less susceptible to layer formation compared to quartz. The use of phosphorus-rich fuels in fluidized bed combustion is one probable way to support both heat and power production and phosphorus recovery. Ash is accumulated in the bed during combustion and interacts with the bed material to form layers and/or agglomerates, possibly removing phosphorus from the bed ash fraction. To further deepen the knowledge about the difference in the mechanisms behind the ash chemistry of phosphorus-lean and phosphorus-rich fuels, experiments in a 5 kW bench-scale-fluidized bed test-rig with K-feldspar as the bed material were conducted with bark, wheat straw, chicken manure, and chicken manure admixtures to bark and straw. Bed material samples were collected and studied for layer formation and agglomeration phenomena by scanning electron microscopy combined with energy dispersive X-ray spectrometry. The admixture of phosphorus-rich chicken manure to bark changed the layer formation mechanism, shifting the chemistry to the formation of phosphates rather than silicates. The admixture of chicken manure to straw reduced the ash melting and agglomeration risk, making it possible to increase the time until defluidization of the fluidized bed occurred. The results also highlight that an increased ash content does not necessarily lead to more ash melting related problems if the ash melting temperature is high enough.