Formation of potassium chloride reduces ash sintering temperature and causes fouling deposits in
biomass combustion applications. In the present work, the capacity of two mineral additives zeolite 24A
and kaolin to capture KCl were investigated. A series of thermogravimetric experiments were carried out
to measure fractions of KCl retained in the two additives as function of reaction temperature and heating
time. The residues from additive-KCl mixtures after heating treatment were analyzed by X-ray diffractometry
(XRD). When heated at 900 C for 1 h, the overall KCl capturing efficiencies of the two additives
were 60% and 45% for zeolite 24A and kaolin respectively, which slightly decreased to 50% and 43% as the
heating time increased to 12 h. At 1000 C, the fractions of KCl captured by zeolite 24A and kaolin
significantly decreased from 50% and 40% to 26% and 17%, as the KCl-additive mixtures were heated for 1
and 12 h, respectively. The decrease in of the overall KCl capturing efficiencies is mainly attributed to
reduction of surface areas and chemically active compounds of the two additives with increasing temperature
and heating time. The XRD analysis results showed that both zeolite 24A and kaolin can react
with KCl to form different potassium aluminium silicates. It indicates that chemical reactions play an
important role in the overall capturing process. The effects of zeolite 24A and kaolin on sintering
behaviors of the barley straw ash were also investigated. The residues from sintering tests were analyzed
by a combination of X-Ray diffractometry (XRD) and scanning electron microscopy equipped with energy
dispersive X-Ray analysis (SEM-EDX). The barley straw ash melted intensively at elevated temperatures.
Together with XRD analysis, the SEM-EDX analysis results revealed that severe melting of the barley
straw ash was due to formation and fusion of low temperature melting potassium silicates. Addition of
kaolin and zeolite 24A significantly reduced the sintering tendency of the barley straw ash. Upon additive
addition, high temperature melting potassium aluminium silicates formed in the barley straw ash as
revealed by XRD and SEM-EDX analyses. Formation and presence of the refractory potassium aluminium
silicates partly explain the improved sintering behaviors of the ash-additive mixtures.