50% and 43% of blended KCl were retained in the kaolin and zeolite
24A, respectively. At 1000 C, the fractions of KCl captured by
zeolite 24A and kaolin significantly decreased, to respectively 26%
and 17%, as the additive-KCl mixtures were heated for 12 h.
Reduction of overall KCl capturing efficiencies can be attributed to
changes of physical and chemical properties of the two additives at
elevated temperatures and/or extended reaction time. Adsorption
of KCl on additive surfaces was reduced due to loss of surface areas
and microporosity as of additive particles as they were heated at a
higher temperature or with a longer reaction time. In addition, the
content of chemical active compounds in the additive might
decrease as the additive is heated at elevated temperature. It hinders
chemical binding of KCl vapours by the additive and reduces
the overall KCl capturing efficiency consequently. Zeolite 24A has a
large specific surface area and a microstructure with channel pore
and intracrystalline voids. With such favorable microstructures,
higher levels of KCl retention in zeolite 24A were observed in
comparison of with kaolin. In the residues from the sintered
additive-KCl mixtures, a number of high temperature melting potassium
aluminum silicates were identified. It suggests that
chemical binding is one main route for an additive to capture the
KCl vapours.