The analysis of chemical composition of the deposits accumulated
on the surface of the P91 steel tube samples during the residence
in the CFB boiler are shown in Table 7. The results are quite
similar for all types of the tested fuels and indicate strong effect of
the location area on the tube samples on the composition of the
accumulated solids. The sodium, potassium and chlorine compounds
were found at both front and rear side thus probably
indicating that they were, to large extend, condensed from the gas
phase. Contrary to the above, the calcium and sulfur compounds
were mainly found in the front area, probably as a result of fine
solid sorbent particle impacts with the tube surface. The iron (Fe)
was found in both front and rear areas, while Mn and Cr were
mainly found in the rear section. Those elements might enter the
boiler system with fuel ash (e.g. with coal), or be formed due to
attrition of steel elements in some previous section of the boiler
(e.g. in the combustion chamber).