This work investigated systematically the effect of NaCl, Na2CO3 and Na2SO4 on the agglomeration of quartz particles and the bed defluidisation in a bubbling fluidised bed operating at high temperatures. Detailed chemical, mineralogical, morphological and cross-sectional characterisations on the bed particles and the agglomerates had been performed. With an interval feeding of NaCl or Na2CO3, bed defluidisation did not happen at 700 °C but occurred at 800–900 °C at NaCl(Na2CO3)/SiO2 ratios <1.32%, highlighting the role of Na and temperature in promoting particle agglomeration. This is respectively attributed to the NaCl melt and low melting point Na2SiO3 and Na2Si2O5 up to 155 μm for agglomeration initiation. As for Na2SO4, bed defluidisation did not occur at all the temperatures examined. In addition, pressure fluctuations of the bed as time were also analysed, with the release rate of these Na salts in 0.032–0.332 min−1 determined to comprehend the transitions behaviour of fluidisation.