Table 9 contains the analysed elements recalculated from their corresponding oxides. The composition of the
ash varied widely. The silicon content in ash, calculated as oxides, varied between 15% in cattail to 22% in reed. The calcium content seemed to correlate with the silicon content in the ash in an inverse way (i.e., ash high in silicon were usually low in calcium). All the ash were rich in potassium, chlorine and sulphur, which could cause sintering problems in combustors, since alkali, sulphur and chlorine vaporise during combustion. Compounds such as KCl and K2SO4 can condense on heat exchanger surfaces or on the surface of bed material particles if the fluidised bed combustion technique is used.