The importance of aluminosilicates in coal ash as protective
compounds against chlorine deposition, as demonstrated in this
study, is in agreement with results of our earlier studies with
coal and MBM mixtures [16]. Alkalis in chlorides can be
trapped by aluminosilicates present in the coal ash at fluidized
bed temperatures. Most of the available aluminosilicates for
NaCl and KCl sequestration are present in coal ash as kaolinite,
and their concentrations can be measured within acceptable
error limits. Fig. 11 shows the correlation between Cl
concentration in the deposits and kaolinite in coal/Cl in fuel
molar ratio in the coal blends. Chlorine deposition was
negligible in both CFBs when kaolinite in coal/Cl in fuel
was >3. Decrease in the molar ratio below value 3 strengthened
Cl deposition.
The above findings also make clear that high S/Cl molar
ratio in the fuel (related to sulfation) does not alone guarantee
combustion without risk of superheater corrosion. We have
measured strong Cl deposition even during high (>4) S/Cl
ratios whereas chlorine deposition during combustion of
80PC20RDF and SAC/RDF blends with S/Cl molar ratio