Effect of particle size distribution on the behavior of alkali and alkaline earth metals in solid-recovered fuel combustion in a circulating fluidized bed

ABSTRACT

In this paper, the effect of the particle size distribution (PSD) of the bed material on alkali and alkaline earth metal behavior in circulating fluidized bed combustion of solid-recovered fuel was studied. The Sauter mean diameter, of the PSDs studied: Gaussian-, flat-, binary-, and narrow distributions, was 200 µm. The concentration of both alkali and alkaline earth metals was found to decrease with increasing particle size, both on the surface and the cross-section, except for the surface concentration for calcium (Ca) which showed the opposite trend for the Gaussian and flat PSDs, increasing from approximately 1.7%-w to above 3%-w. The total surface concentration varied from 2.1% for the binary PSD to 2.6% for the flat, while the cross-section concentration varied from 0.4% for the Gaussian PSD to 0.7% for the binary. Ca is less volatile than the other elements studied making it less prone to vaporize and leave the circulating fluidized beds with the flue gases and it was also the most abundant element in the fuel. The experimental results presented here indicate smaller variation in potassium, sodium, and magnesium behavior between the PSDs than for Ca and that particle size changing phenomena, such as attrition, influence it as well.

KEY WORDS:

• Circulating Fluidized Bed
• Waste Combustion
• Solid Recovered Fuel
• Alkali Metal Behavior
• Alkaline Earth Metal Behavior

Acknowledgments

We would like to thank the technical staff working on the CFB, Seppo Poimuvirta, Vadim Desyatnyk, and Petteri Kivivuori.We would also like to thank Linus Silvander at Åbo Akademi University for conducting the SEM-EDS analysis and Sakari Salonen at Lahti energia for providing the SRF. We would also like to thank Eeva-Leena Rautama at the Department of Chemistry and Materials Science at Aalto University for conducting the XRF analysis. Great help was provided by Timo Ylönen and Hans Orassaari regarding fuel preparation and by Janne Vuori regarding sieving. Thomas Kohl is acknowledged for giving valuable comments. Aalto University is acknowledged as the sole funder of this article.

Additional information

Funding

This work was supported by Aalto University.