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

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.