Simple mass transfer simulation using a single-particle heterogeneous reaction approach in rice husk combustion and rice husk ash extraction

Abstract

Rice husk conversion to silica is usually carried out through combustion to produce ash and then continued with ash extraction to obtain silica. There is a model to simulate the single-particle combustion, which abandoned the simplification. However, the model is complex and seems complicated for early beginners. This study, hence, aims to discuss the simple mass transfer simulation using a single-particle heterogeneous reaction approach. The shrinking core model was targeted for rice husk combustion time prediction, whereas mass transfer effectiveness analysis was used in rice husk ash extraction simulation. According to this study, a shorter combustion time is reached under smaller particle diameter, more spherical particle, and higher oxygen concentration. The result showed that a combustion time of 133 minutes is obtained for oxygen diffusion to rice husk with diameter 5.8 mm, sphericity 0.5, and oxygen concentration 21%-vol. Besides, in order to improve the rice husk ash extraction overall mass transfer effectiveness from 0.01 to 0.1, extraction should be done under particle diameter of 0.2 mm, sphericity of 0.8, and agitator tip velocity of 5 cm/s. All of the parameters lessen the mass transfer limitation due to diffusion, and in consequence, intrinsic kinetic becomes a major factor.