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The usage of biomass can reduce vast amounts of fossil resource dependence. Rice husk is attractive due to its calorific value and high silica content in ash. In order to produce amorphous silica in ash, rice husk was combusted with temperatures below 700°C and this can be realized in a suitable furnace type, i.e. suspension furnace. This study began with rice husk ignition test in a fixed bed furnace. The ignition temperature was observed above (428 ± 8)oC. Combustion was then performed in a suspension furnace. Rice husk was semi-continuously fed when it attained the ignition temperature with total air to biomass ratio of 8.5. The mass flowrates of rice husk were set at 9.27, 20.23, 25.20, 31.36, and 42.51 kg/h. The feeding was stopped until it reached 2500 g for the first 4 variations and 500 g for the last variation. From this study, the flaming combustion lasted for 15–30 min and then continued with glowing combustion which plays an important role in the successful conversion to ash. The highest temperatures of combustion were 552–560°C. Besides, the yield of produced ash was 18.94–23.68%-wt with silica content therein of 88.29–89.15%-wt. Ash was acquired in the amorphous silica phase with unburnt carbon content of 5.11–23.27%-wt.

An acrylic suspension furnace was used to study the flow structure of air and rice husk. The standard k–ε model with standard wall function was employed in the simulation study while the cold test experiment, for results validation, utilized onionskin (thin oil paper) and rice husk itself. From the simulation, both air and rice husk flows are in swirling mode due to the tangential air. The cold test experiment strengthened that swirl flow of air is indicated by the onionskin movement upward and downward forming a curve and circular directions. On the other hand, swirl flow of rice husk is visualized by the sinusoidal peaks and valleys. In addition, the contribution of secondary air generates recirculation flow at the bottom area of the furnace. Also, there are backflow phenomena that occur, and yet, the revalidation study revealed that modification of tangential air pipes angle with a longer burner length can overcome the problem. Finally, this model can predict the flow structure in a good compliment to the cold test experiment results. Moreover, the less-intensive computation load with a shorter computation time makes it in demand for the design purpose and performance evaluation of process equipment.