Fly ash deposition onto convective heat exchangers during combustion of willow in a circulating fluidized bed boiler

The deposition of fly ash onto the convective back pass in the CFBC of Swedish willow (Salix) between two soot-blowing periods was found to be 56–64%. The deposition was mainly determined by the particle size. The particle composition had no effect on the deposition. The deposition increased rapidly with increasing particle size. For example, it was found to be about 5% for the 1 µm-sized particles and about 90% for the 10 µm-sized particles. The elements which were mainly in the coarse fly ash fraction, Si, Al, Ca and P, were deposited most efficiently, whereas the deposition was smaller than average for K, S and Cl. Large amounts of K, S and Cl were found to be released during the combustion and were therefore found in the fine fly ash particle fraction.