Bottom ashAndersson, S., Karltun,E. et al. Wood ash - properties and ecological consequences of recycling to forest.
Bottom ash consists of solid residues remaining at the bottom of the incineration compartment. This type of ash may contain a lot of sand and stones that are brought in with the fuel, especially if bark is used. It can also contain sand from the incineration bed, especially in CFB furnaces. Because of this, the bottom ash is a course material, which pieces vary in size and shape.
It can also be seen that the chemical composition of bottom ash often varies compared to that of fly ash. This may be explained by the fact that the combustion temperature is a very significant parameter for determining the ash properties.
For example, sulphate is less commonly present in bottom ash than in fly ash since S is volatilised during combustion. Other volatile elements are chromium (Cr), cadmium (Cd), lead (Pb) and zinc (Zn) and these usually have lower concentrations in bottom ash compared to fly ash.