Production of amorphous rice husk ash in a 500 kW fluidized bed combustor

• Rice husk is burnt in a 500 kW fluidized bed combustor.
• 660–720 °C and fluidization velocity of 1.0–1.2 m s−1 appear to be the optimal.
• Ash with amorphous SiO2 is over 93.8 wt.% and unburnt carbon less than 5%.
• Combustion efficiency is ∼90% in all test runs.

A 500 kW rice husk-firing fluidized bed combustor was designed for obtaining low carbon and high silicon ash in the amorphous form. The influence of operating condition (temperature, fluidizing velocity) on combustion efficiency and rice husk ash quality was experimentally investigated. Furthermore, the quality of rice husk ash collected from inner bed, two-stage cyclones and bag-house was analyzed using XRD, TEM and SEM instruments, in terms of amorphous silicon dioxide and unburnt carbon content. Comparative study was carried out between the rice husk ash produced in an electronic oven and that produced in the above-mentioned fluidized bed combustor. The results show that quality of ash from the industrial-scale fluidized bed is even better than that from electronic oven. Temperature of 660–720 °C and fluidization velocity of 1.0–1.2 m s−1 appear to be the favoring parameters for producing high quality rice husk ash with amorphous structure of silicon dioxide content over 93.8 wt.% and unburnt carbon context less than 4.5 wt.%. The fluidized bed combustor also assures combustion efficiency ∼90% in all test runs. This research indicates amorphous structure of silicon dioxide may be economically promisingly produced from the self-designed rice husk combustor.