Combustion and co-combustion experiments with four kinds of straw, specially selected for
their different alkali, Cl, and Si contents, and Columbian black coal were carried out in a
circulating fluidized bed (CFB) reactor at Delft University of Technology. The influence of
operating conditions and fuel composition on the release of the alkali compounds to the gas phase
was investigated. The amount of the total gas-phase sodium and potassium compounds in the
flue gases was measured with excimer laser induced fluorescence (ELIF). The results show that
the release of gaseous alkali species depends on fuel composition, in particular the K/Cl and
K/Si ratios in the fuel. The fuels with high K and Cl values show higher concentrations of the
gaseous alkalis. A synergetic effect of the co-combustion with coal was observed, which led to a
strong decrease in gaseous alkali concentrations. Together with experiments, chemical equilibrium
modeling was performed to help in interpreting the experimental data. The calculations confirmed
that the equilibrium is very strongly influenced by the composition of the fuel blend. Moreover,
the simulations provided more information on sequestering of alkali species.
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