7.5. Fouling and corrosion
A possible negative impact of co-combustion of agricultural
residues in coal power plants is the expected increase
in fouling and corrosion due to the presence of compounds
with low melting point in the ash. Trebbi et al. [38] investigated
the fireside fouling tendency during co-firing of coal
with straw (20.58% K2O) in the 80 MWth CFB boiler at
Grenaa, and in another test with straw (18.57% K2O) in a
125 MWe pulverized coal boiler at Esbjerg, both in
Denmark. They observed increased deposition rates during
co-firing the coal/straw mixture. In the CFBC, the deposits
remained non-sticky even when the straw ratio was
increased to 60% of the total heat input. Analysis indicated
a major presence of potassium chloride in the deposit.
However, Hansen et al. [76], later reported a severe superheater
corrosion in the convective path of the 80 MWth CFB
boiler. High concentrations of potassium and chloride in the
straw, insufficient control of the combustion temperatures in
the upper part of the combustion chamber and in the
cyclones caused a severe fouling in the cyclones and in
the convective path and several unscheduled shut downs
in order to clean the plant. Eighteen months after commissioning,
the final superheater located in the convective