4.4. Corrosion
Ash deposition from biomass fuels which contain certain
chemicals can also create corrosion and erosion of metals
[41]. Blander and Pelton [48] simulated the inorganic chemistry
of the combustion of wheat straw with the help of
equilibrium calculations including solid and liquid solutions
of salts and silicates. The two most abundant inorganic
elements in wheat straw are Si and K, which form silicates
with a low melting point. The combustion of the straw leads
to the condensation of molten silicates, which are likely to
cause fouling and corrosion in combustion systems. Metals
in combustion systems are exposed to chemical attack when
silicates are present because protective layers of oxides can
be relatively soluble and/or reactive in silicate slags. In
addition, the very high volatilities of alkali metals can
lead to unexpected corrosion by reactions such as
K2O
silicate 1 Fe $ FeO
silicate 1 K
g
5
for the case where potassium bearing gas phase is not
present at the interphase.
Petersen et al. [49] reported about corrosion in straw fired
boilers based on the questionnaires sent to all operators of
straw-fired district heating boilers in Denmark. The boilers
mostly consist of a firebox, three convection passes, an
economizer and a flue gas filter. The flue gas temperature
after the economizer was limited since the filter was of a bag
type. The temperature of the boiler water was mostly kept